CA2112524A1 - Cube-corner retroreflective articles - Google Patents
Cube-corner retroreflective articlesInfo
- Publication number
- CA2112524A1 CA2112524A1 CA002112524A CA2112524A CA2112524A1 CA 2112524 A1 CA2112524 A1 CA 2112524A1 CA 002112524 A CA002112524 A CA 002112524A CA 2112524 A CA2112524 A CA 2112524A CA 2112524 A1 CA2112524 A1 CA 2112524A1
- Authority
- CA
- Canada
- Prior art keywords
- cube
- retroreflective
- sheeting
- pigment particles
- corner
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/12—Reflex reflectors
- G02B5/122—Reflex reflectors cube corner, trihedral or triple reflector type
- G02B5/124—Reflex reflectors cube corner, trihedral or triple reflector type plural reflecting elements forming part of a unitary plate or sheet
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/14—Layer or component removable to expose adhesive
- Y10T428/1405—Capsule or particulate matter containing [e.g., sphere, flake, microballoon, etc.]
Abstract
Abstract of the Invention CUBE-CORNER RETROREFLECTIVE ARTICLES
A retroreflective article (30, 50) has opaque pigment particles (38, 58) dispersed in a retroreflective region (33, 53) of a front portion (35, 55) of a sheeting (32, 52) that includes a body portion (34, 54) and a multitude of cube comer elements (36, 56). The opaque pigment particles (38, 58) scatter white, yellow, or light brown light to allow the retroreflective article to demonstrate improved lightness and, if colored fluorescent, improved fluorescence. The improvement in lightness and fluorescence makes the retroreflective articles more conspicuous to persons during the daytime.
A retroreflective article (30, 50) has opaque pigment particles (38, 58) dispersed in a retroreflective region (33, 53) of a front portion (35, 55) of a sheeting (32, 52) that includes a body portion (34, 54) and a multitude of cube comer elements (36, 56). The opaque pigment particles (38, 58) scatter white, yellow, or light brown light to allow the retroreflective article to demonstrate improved lightness and, if colored fluorescent, improved fluorescence. The improvement in lightness and fluorescence makes the retroreflective articles more conspicuous to persons during the daytime.
Description
21 12~2~
CllB~CORNER RETROREFLECTIVE ARTICLES
FlELD OF THE INVENTION
S This invention pertains to (i) a cube-corner retroreflective article that provides a superior daytime lightness and (ii) a method of making the same.
BACKGROU~ OF IHE INV~NTION
Retroreflective ar~icles have the ability to return incident light back in the direction from which the light originated. This unique ability has led to the widespread use of retroreflective articles on a traffic signs. At nighttime,light from motor vehicle headlights is retroreflected by the articles to displayinformation on the sign to motor vehicle dri ~ers. Dunng daylight hours, if the retroreflective articles have a sufficient daytime lightness to make the sign readily noticeable to passing motorists, daytime motor vehicle drivers may become privy to the same information. An ongoing goal in the retroreflective art, therefore, has been to provide retroreflective articles that demonstrate good nighttime retroreflectivity and sufficient daytime lightness to make the articles readily noticeable to passing motorists at any time of the day.
An example of a commonly used and good pe~forming retroreflective article is a cube-corner retroreflective sheeting. A cube-corner retroreflectivesheeting employs a multitude of cube-corner or prismatic elements to retroreflect the incoming light. Each cube-corner element has three planar faces that meet at an apex. At the base of each element is a sheet-like body portion (also known as a ~land~) which unites the cube-corner elements in the form of a sheeting. Light which is retroreflected typica11y enters the sheeting through a cover layer, passes through the body portion to stril.~e the cube surfaces, and is reflected back in the direction from which the light entered the sheeting. A color is often provided to a cube-corner sheeting by incorporating a dye or transparent pigment into the body portion or cube-corner elements.
A fairly common cube-corner retroreflective sheeting has a metallic coating applied to the backside of the cube-corner elements to promote retroreflection; see for example, U.S. Patent 3,684,348. While it is known that the metallic coating can improve the sheeting's retroreflective performance, it is also known that the metallic coating can have a detrimental effect on daytime lightness. The metallic coating, which is often aluminum, 2~2~
:
imparts an undesirable grayish daytime color to the sheeting, making information on the sign more difficult to read. This drawback makes metallic coated cube-corner sheetings much less likely to be used on signs that require good daytime lightness.
S To improve the daytime lightness of metallic coated, cube-corner sheetings, the inventors of U.S. Patent 4,801,193 developed a method of removing a predominant portion of the metallic coating from the back side of the cube~orner elements. This removal is accomplished by superimposing a second coating material over a minor portion of the metallic coating in a grid-like pattern and then exposing the coated cube-corner elements to a solvent to ~move the metallic coating from the non-superimposed areas. A metallic coating in the form of a grid results. A backing element is then adhered to the backside of the cube-corner sheeting along the grid lines but is spaced apart from the cube-corner elements over the areas where the metallic coating has been removed. The patent discloses that upon observation of the sheeting in ambient light, a grayish grid pattern may be seen, which represents the residual metal on the backside of the cube-corner elements. Lighter areas between the grid lines are displayed which are characteristic of the areas where the metallic coating has been removed.
Another known approach for improving daytime lightness in a cube- ~;
comer sheeting involves placing opaque pigment particles that scatter white light in a base layer of the cube-corner sheeting. This approach does not rely on a metallic coating to promote retroreflection but instead employs a pluralityof hennetically-sealed air chambers, which allow air to interface with the back side of the cube corner elements without interference from moisture, dirt, and the like. A retroreflective article having this construction is shown in FIG.
1 where numeral 10 designates the retroreflective article.
Retroreflective article 10 includes a cube-corner sheeting 12 that has cube-corner elements 14 and a body portion 16. The body portion 16 has a smooth surface 18 through which light (such as from an automobile headlamp) passes in the direction of arrows 20 and 21. The incident light 20 strikes surfaces of cube-corner elements 14 and is reflected back in the direction 21 from which it originated. Air in hermetically-sealed air chambers 22 interfaces with the back side 27 of cube-corner elements 14 to promote the retroreflection of the incident light. Sealed chambers 22 are enclosed by a base layer 26 that is secured to sheeting 12 at bonding regions 24. ~ ~ -2112 ~ 2 ~
.
Retroreflective article 10 exhibits good daytime lightness by having opaque, white pigment particles 28 dispersed in the base layer 26. In the base layer's bonding region 24, the pigment particles 28 scatter the incident light to display a relatively light daytime color to the viewer. The cube-corner S element/air interface also assists in improving lightness of the article 10. An article having this kind of construction has been sold for many years by 3M
as Scotch2ite~ Diamond Grade Reflective Sheeting.
SUA~MARY OF THE~ JNY~NTION
In accordance with the present invention, a new cube-corner retroreflective ar~cle is provided that exhibits an extraordinarily good daytimelightness. The retroreflective article of this invention comprises:
a sheeting having a front portion that includes a retroreflective region that has a body portion and a plurality of cube-corner elements which project away from the body portion; and opaque pigment particles that have lightness improving properties, the opaque pigment particles being dispersed in the retroreflective region of the front portion of the sheeting.
In another aspect, the present invention provides a method of making a retroreflective ar~cle, which comprises:
dispersing opaque pigment particles in at least a retroreflective region of a front portion of a sheeting that contains a plurality of cube-corner elements, wherein the dispersed opaque pigment particles possess lightness improving properties.
As the terms are used herein, "front portion" means the portion of a retroreflective article through which incident light passes, and "retroreflective region" means those part(s) of the front portion of a cube-corner sheeting where the incident light is capable of being retroreflected. In the reboreflection region(s) of front portion of the retroreflective article, the opaque pigment particles may be located, for example, in the body portion or cube-corner elements or in an overlay film that is located on top of the cube-corner sheeting or in a combination of these parts of the front portion. The term "lightness improving properties" means possessing the ability to improve the lightness of the sheeting in which the opaque pigment particles are dispersed.
It was discovered in this invention that by dispersing opaque pigment particles that have lightness improving properties in the retroreflective -- 2 ~ 1 2 ~ 2 ~ ~
region(s) of the front portion of a retroreflective article, daytime lightness can , be increased substantially without destroying nighttime retroreflectivity.
Opaque pigment particles that have lightness improving properties are known to scatter incident light in a diffuse manner, and therefore it was expected that 5 the particles would seAous1y compromise retroreflectivity by causing the incident light to be scattered randomly. Instead, however, it was surprisingly discovered that good retroreflection is obtained by the cube-comer retroreflective articles of this invention -- in spite of the presence of the opaque pigment particles.
In addition to improving lightness while retaining retroreflectivity, it also was su~prisingly discovered that a significant increase in fluorescence canbe achieved by the dispersement of the opaque pigment particles in the front portion of a fluorescent-colored, cube corner sheeting. An improvement in fluorescence makes a fluorescent retroreflective article more conspicuous to 15 viewers during the daytime. Thus, a fluorescent article of this invention canhave extraordinary conspicuity by providing contemporaneous improvement in both lightness and fluorescence.
The above and other advantages and aspects of the invention are more fully illustrated in the detailed description of this invention and drawings, 20 where like reference numerals are used to represent similar parts. It is to be understood, however, that the description and drawings are for the purposes of illustration only and should not be read in a manner that would unduly limit the scope of this invention.
BRIEF DESCNPI'ION OF THE DR~4WINGS
FIG.lis a cross-sectional view of a prior art retroreflective sheeting 10.
FIG. 2 is a cross-sectional view of a retroreflective article 30 in accordance with the present invention.
FIG. 3 is a cross-sectional view of another embodiment of a retroreflective article S0 in accordance with the present invention.
FIG.4is a bottom view of the backside of cube~orner elements 66 in a retroreflective sheeting.
DliTAnED DESCN~ION OF THE PREFERRED EMBODIMENTS
In describing the preferred embodiments of the invention, specific terminology will be used for the sake o1 clarity. The invention, however, is i 2~ 2,2~
not intended to be limited to the specific terms so selected, and it is to be understood that each term so selected includes all the technical equivalen~s that opeMte similarly.
Referring to FIG. 2, an example of a retroreflective article 30 is shown which includes a cube-corner sheeting 32 that has a retroreflective region 33 in a front portion 3S of the article 30. Front portion 3S includes a body portion 34 and a plurality of cube-corner elements 36 which project away from the body portion 34. Dispersed throughout the front portion 3S of cube-corner sheeting 32 are opaque pigment particles 38 which have lightness improving properties. As shown, opaque pigment particles 38 may be located in the body portion 34 and in the cube-corner elements 36 of sheeting 32. An overlay film 40 can be provided to protect the cube-corner sheeting 32 from ultra-violet rays and abrasion. Opaque pigment particles 38 which have lightness improving properties also can be incorporated into the overlay film 40. However, it is preferred that the opaque pigment particles be located in the cube-corner sheeting 32 because the light path through the sheeting 32 typically is significantly longer than the light path through the overlay film 40.
A longer light path allows a lower concentration of pigment particles 38 to be used in the retroreflective sheeting and provides more color uniformity. It is to be understood that the opaque pigment particles can be placed in a combination of the body portion 34, cube-corner elements 3C, and overlay film 40, or in other layers of a front portion of a retroreflective sheeting.
To promote retroreflectivity, the back side of cube-corner elements 3C
can interface with a reflective material (for example metal) or a material tllathas a significantly different refractive index from the polymeric material of the cube-corner elements (for example, air). A metallic coating 42 can be placed on the back side of polymeric cube-corner elements by vapor-depositing or chemically depositing a metal such as alun inum, silver, or nickel. A primer layer (not shown) may be applied to the cube-corner elements 36 to promote adherence of the meta11ic-coating 42. As shown, a backing material 44 can be placed in contact with the metallic coating 42, and an adhesive layer 46 can be applied to the backing 44, or alternatively, the adhesive layer 46 can be applied directly to the metallic coating 42. A release paper 48 can be provided to cover the adhesive 46 until the retroreflective article 30 is adhered to a substrate such as a panel for a sign (not shown).
FIG. 3 illustrates an embodiment of a retroreflective article 50 of this invention where the cube-comer elements interface with air. Like 21~ ~ ~ 2 i~
retroreflective article 30 shown in FIG. 2, article 50 has opaque pigment particles S8 which have lightness improving properties and which are dispersed in a front portion 55 of a retroreflective sheeting S2. Sheeting 52 includes a body portion 54 and cube-corner elements 56 projecting away from 5 ~e body portion S4. Article 50 differs from the embodiment of FIG. 2 by having the back side of the cube-corner elements S6 interface with air rather than with a metallic coating. The cube-corner/air interface is protected from moisture, dirt, and the like by providing hermetica11y-sealed air chambers S7.
Chambers S7 are defined by a base layer 59 that is secured to the retroreflec~ve sheeting 52 at bonding regions C0. The bonding regions 60 define a plurality of retroreflective regions S3 in the front portion 55 of article S0. Base layer S9 can be secured to the sheeting 52 using known methods such as disclosed in U.S. Patent 4,025,159, incorporated here by reference.
FIG. 4 illustrates an example of cube-corner elements CC that may bei lS used in a retroreflective sheeting of this invention. Each cube-corner element CC has three planar faces C7 that meet at an apex C8. The apex 68 of each cube-corner element CC may be vertically aligned with the center of the base of the cube-comer element, see, for example, U.S. Patent 3,684,348, or the apex may be canted to the center of the base as disclosed in U.S. Patent 4,588,258. Of the many cube-corner configurations, see also, for example, U.S. Patents 4,775,219, 4,243,618, 4,202,600, and 3,712,706, the cube-corner retroreflective elements described in U.S. Patent 4,588,258 is particularly preferred because they provide wide angle retroreflection among multiple viewing planes. The disclosures of each of these patents are incorporated hereby reference.
A retroreflective sheeting of this invention generally is about 75 micrometers (5 mils) to 600 micrometers (24 mils) thick. Each cube-comer element typically is about 60 micrometers (2.4 mils) to 200 micrometers (8 mils) high, and the body portion, typica11y, is about 25 micrometers (1 mil) to 250 micrometers (25 mils) thick. The body portion and the overlay film preferably interface at ? substantia11y smooth surface to prevent the dispersionof light. Overlay film, typically, is about 25 micrometers (l mil) to 125 micrometers (S mils) thick.
Opaque pigments useful in this invention generally have a refractive index greater than 1.8 and include those that are designated as opague or serni~paque by the National Association of Printing Ink Manufacturers in the NP~RI Raw Matenals Data Handbook, volume 4 (1983). Preferred opaque 2t ~ 2~2 ~
pigments have a refractive index greater than 2.2 and more preferably greater than 2.6 Examples of opaque pigments that have lightness improving properties are opaque pigments that diffusely reflect white light. The term "light" is used herein to mean electromagnetic radiation in the visible range, 4 X 10-7 meters to 7.7 X 10-7 meters approximately. Pigments that reflect ~, white light are designated as pigment whites in the Colour Ir~ (C.I.).
3 published by the Society of Dyers and Colourists. Examples of white opaque pigments that may be suitable for use in this invention include the following inorganic pigments: zinc-based pigments such as zinc oxide, zinc sulfide, and lithopone; zirconium oxide; alatimony oxide; and titanium dioxide. Titanium dioxide in its rutile form is t}le preferred opaque pigment. Examples of white, opaque pigments that may be employed to enhance sheeting lightness include the following identified by the Co~ur Index:
PigmentWhite 1 C.I. 77597 Basic CarbonateWhite Lead PigmentWhite 4 C.I. 77947 Zinc Oxide Pigment White 5 C.I. 77115 Lithopone Pigment White 6 C.I. 77891 Titanium Dioxide Pigment White 7 C.I. 77975 Zinc Sulfide Pigment White 11 C.I. 77052 Antimony Oxide Pigment White 12 C.I. 77990 Zirconium Oxide .
Other opaque pigments that have lightness improving properties and 25 may be suitable for use in this invention include the following pigments~
PigmentBrown 24 C.I. 77310 Titanium, Chrome and ~ . ~
Antimony Oxides - - -Pigment Yellow 34 C.I. 77603 Lead Sulfochromate -~ -Pigment Yellow 35 C.I. 77205 Zinc Sulfide Pigment Yellow 37 C.I. 77199 Cadmium Sulfide Pigment Yellow 53 C.I. 77788 Titanium, NickelandAntimony Oxides Pigment Yellow 161 C.I. 77895 Titanium, Nickel and Niobium Oxides Pigment Yellow 184 Bismuth Vanadate and Bismuth Molybdenate Combinations of the above pigments may a1so be used.
The pigment particles used in this invention preferably have a mean size ranging from about 0.1 to 5 micrometers, more preferably in the range of from about 0.5 to 2 micrometers. When titanium dioxide is used as the opaque pigment, its mean size typically ranges from about 0.2 to 0.3 micrometers. The quantity of pigment particles may vary depending on, for 2 1~ C~.~ 2 ~.
, A
example, the composition of the pigment particles, the size of the pigment particles, the size and geometry of the cube corner elements, the thickness of the front portion, the color of the sheeting, and the end usage of the retroreflective article. In genera1, however, the pigment particles are 5 dispersed in the front portion of the retroreflective sheeting in the range ofabout 0.0001 to 0.75 volume percent, and typically in the range of about 0.0002 to 0.075 volume percent and more typically in the range of 0.005 to 0.05 volume percent. The pigment particles are preferably evenly distributed throughout the front portion of the retroreflective sheeting so that uniform 10 color, lightness, and retroreflectivity are displayed by the retroreflective article.
The retroreflective article may be colored by incorporating a dye or a transparent pigment in the front portion of the sheeting. The dye or transparent pigment may be placed, for example, in the body portion, the 15 cube-corner elements, an overlay film, or a combination thereof. The retroreflective article also can be colored by applying an ink containing a dye or transparent pigment onto either side of an overlay film. The particular dye or transparent pigment selected depends, of course, on the desired color of the retroreflective article and on the polymeric composition of the cube-corner 20 sheeting. The selected dye or transparent pigment should not have a deleterious effect on the article's retroreflectivity, and it should not substantially compromise the daytime lightness of the article.
Examples of dyes that may be suitable for use in this invention include:
Violet: C.I. Solvent Violet, 13, 31, 32, 33, and 36;
Blue: C.I. Solvent Blue 94, 97, 101, and 121, and C.I. Disperse Blue 60 and 198;
Green: C.I. Solvent Green 3, 26, and 28;
Yellow: C.I. Solvent Yellow 93, 112, 113, 128, 129, 130, and 163, and C.I. Disperse Yellow 54, 64, and 160;
Orange: C.I. Solvent Orange 60, 68, 72, and 86, and C.I. Msperse Orange 47; and Red: C.I. Solvent Red 52, 111, 117, 135, 138, 139, 169, 195, and 207, and C.I. Disperse Red 5.
These dyes are available from one or more of the following companies: BASF
Corporation, Bayer AG, Color Chem International, and Mitsubishi Chemical Industries. Amaplast Violet PK from Color Chem International also may be useful, as well as fluorescent dyes such as a thioxanthene dye, a thioindigoid 40 dye, a benzoxazole coumarin dye, or a perylene imide dye. Retroreflective .
5 2 ~
articles containing these fluorescent dyes have been disclosed in European Patent Application 0,489,561 Al published June lO, 1992, the disclosure of which is incorporated here by reference. Combinations of the above dyes a1so may be employed, and/or transparent pigments may be employed to provide 5 color.
Examples of transparent pigments that may be suitable to color retroreflective articles of this invention include:
Violet: C.I. Violet, l9, 23, 27 Blue: C.I. Blue, lS
Green: C.I. Green, 7, lO, 36 Yellow: C.I. Yellow, 93, lO9, 128 Orange: C.I. Orange, 43, 46 Red: C.I. Red, lM, 179, 206 These transparent pigments are available from one or more of the following companies: Ciba-Giegy Corporation, BASF Corporation, Sandoz Chemicals, Sun Chemica1s, Hoechst Celanese and Miles Incorporated.
When the retroreflective article is colored, it is preferred that the 20 opaque pigment particles not be incorporated into the article in front of thecolored layer. Preferably, the opaque pigment particles are incorporated into the front portion of the retroreflective ar~cle in the same layer as the dye or transparent pigment, and more prefe~ably behind the colored layer (that is, closer to the back side of the cube-comer elements). The placement of the 25 pigment particles in front of the colored layer is not preferred because it would cause the color's saturation to become diluted.
The cube-corner sheeting for a retroreflective article of this invention can have a polymeric composition. Polymers useful for forming a cube-corner sheeting include polymers that are transmissive to visible light and are 30 compatible with the pigment particles. If a dye is employed, the polymer should also be compatible with the selected dye. To be compatible, the polymer preferably does not allow the pigment (and dye) to nigrate or bloom out from the interior of the retroreflective article. Examples of polymers that may be used in retroreflective articles of this invention includepolycarbonates,35 polya1kylacrylates, polyalkylmetbacrylates such as polymethylmethacrylate, polyesters, vinyl polymers, polyurethanes, cellulose esters, fluoropolymers, polyolefins, ionomeric copolymers and copolymers of ethylene or propylene with acrylic acid, methacrylic acid, or vinyl acetate. Combinations of such polymers also may be employed. For example, the cube-corner sheeting may g ' ~
. ~
-~" 2~ 2-~J2~
be made from a blend of polymers, or the cube-corner elements and the body portion may be made from different polymers. Further, the body portion may comprise a plurality of layers of the same or different polymers.
Polycarbonates are preferred polymers for a cube-corner sheeting of this S invention because they possess tough, durable characteristics.
An overlay film for a retroreflec~ve sheeting may be made from polymers similar to those of the cube-corner sheeting; typical1y, types which are stable to ultra-violet (UV) light and have good abrasion resistance such as 3 acrylic polymers (e.g., polymethylmethacrylate) and copolymers. UV
stabilizers may also be added to the overlay film.
Cube-corner sheetings can be made according to known techniques such as disclosed in U.S. Patents 5,122,902, 4,938,563, 4,895,428, 4,703,9g9, 4,601,861, 4,576,850, 4,588,258, 4,025,159, 3,935,359, 3,811,983, and 3,810,804. The pigment particles may be dispersed in the front portion of the retroreflective article using known methods for incorporating pigments into polymers. For example, a twin-screw extruder can be employed to blend the pigmer,t particles with the polymer.
The retroreflective articles of tbis invention are particularly useful for placement on signs along roadways or on motorized vehicles or ~ailers, particularly large trucks and truck trailers. The improved daytime conspicuity makes the articles nicely suitable for such use.
Features and advantages of this invention are further illustrated in the following Examples. It is to be expressly understood, however, that while the F,xamples serve this purpose, the particu1ar ingredients and amounts used as well as other conditions and details are not to be construed in a manner that would unduly limit the scope of this invention.
EJY,4~PLES
Example3 C-l - C-2 and 1-14 Flat colored sheets were prepared for use in fabricating cube-corner retroreflective sheetings. The flat colored sheets were prepared by first mixing Type R-960 titanium dioxide pigment (E.I. DuPont De Nemours and Company, Wilmington, Delaware) with Makrolon 2407 polycarbonate pellets (Miles Inc., Pittsburgh, Pennsylvania) in a paint shaker. The amount of titanium dioxide pigment mixed with the polycarbonate resin ranged from zero volume percent to 0.048 volume percent (0.16 wt. %). The mixtures were then dried overnight in an oven overnight at 125 C (257 F) and were ' ' ~ ?; ,~
21~S~ J2~
`~
extruded into a sheet having two smooth sides, which was subsequently cut into pieces sized to about 30 centimeters (cm) by 30 cm. The melt temperature during the extrusion was about 250 C (483 F), and the die temperature was about 285 C (545 F). The extruded sheets are 1isted below 5 in Table I. The sheets produced had a thickness ranging from about Sl micrometers (2.0 mils) to approximately 122 micrometers (4.8 mils). A 3.18 cm (l 'h inch) KillionlY single screw extruder (Killion Extruders, Inc., Cedar Grove, New Jersey) coupled to a 30.5 cm (12 inch) flat sheet die was used to produce ~e sheets.
TABLE I
15 ~ ~
A 0.000 lO0.0000 102 B 0.0075 99.9925 53 . . . __ C 0.0012 99.9880 121 .
D 0 OlS0 99.9850 52 E 0.0240 99.9760 l l9 F 0 0300 99.9700 52 _ G 0.0300 99.9700 122 H 0.0480 99.9520 108 The cut sheets set forth in Table l were stacked and embossed to produce a cube corner retroreflective sheeting. Two sheets were used for each combination which will be referred to as a "blank stackn. Each blank 30 stack was embossed using a platen press to form cube-corner retroreflective elements on one side and a flat surface on the opposite side. The embossing operation involved about 5 minutes of preheating to a temperature of about 188 C (370 F), followed by about 20 seconds of embossing, which in tum was followed by about 8 minutes of cooling. The platen press had a pattern 35 which produced slightly canted, three-sided cube-comer elements in accordance with the teachings of U.S. Patent 4,588,258. The cube corner array had three sets of mutua11y intersecting V-shaped grooves where the base edges of the lateral faces of the cube-corner elements lied in a common base 2 ~ i r~ ~ 2 3 .
., plane. The cube-corner elements were arranged as matched pairs within this array, with paired elements rotated 180 degrees with respect to each other.
The optical axis of the cube-corner elements in each pair were rotated towards one another by 8.15 degrees. The distance from the peak of the cube-corner 5 elements to the base plane was approximately 0.0889 millimeters (mm).
In Examples 1-6, the blank stack was arranged such that the titanium dioxide containing sheet (sheets B-H) formed the cube-corner elemen~s and a minor part of the body portion, and the clear polycarbonate sheet (sheet A) formed the major part of the body portion of the cube-corner sheeting. In 10 Example 7, the blank stack had a reverse arrangement such that the titanium dioxide containing sheet formed the major part of the body portion and the , clear polyc~ubonate sheet formed the cube-corner elements and a minor part of the body portion. After the cube-corner retroreflective sheetings were produced, each sheeiting had a 90 nanometer (nm) thick layer of aluminum :~ 15 vapor coated on the back side of the coated cube-comer elements. The aluminum coatings were applied using a laboratory bell jar vapor coater with b~ a resistance type heat source.
The light path through the pigmented portion of the embosseid cube-corner sheeting was calculated by taking the total distance for which light 20 entering and exiting the pigmented cube-corner elements travels (2 times the cube element height) plus the length of the light path passing through the pigmented part of the body portion of the sheeting. For example, a sheeting that has a 88.9 micrometer high, cube-corner element having a 101.6 micrometer (4 mil) thick pigmented body portion, the light path length is 383 25 micrometers. The light path was multiplied by volume percent of pigment to give a parameter (Light Path x Vol. % TiO2) in units of micrometers (~m) This parameter was found to correspond to the increase in lightness.
Lightness of the cube comer sheeting was measured using a spectrocolorimeter according to standardized test ASTM E 1349-90.
30 Lightness is expressed by the parameter termed Luminance Factor Y (LFY), which is defined as the lightness of the test sample relative to a perfect diffusing reflector. Zero degree illumination and 45 degree circumferential viewing were employed in determining the LFY. LFY values range from 0 to 100, where a LFY value of 0 represents a perfect black color and a LFY
35 value of 100 represents a perfect white color. LFY values higher than S0 (and even higher than 70) have been demonstrated by cube-comer ~etroreflective articles of this invention. Using the LFY value of the clear, !~r ,'' . . ' ' ! . , ' ' , ~ :' . ` , , ' ~ , ` ~ ' ' ' ',' ~j':. ' '' ,. ' , , ' ' ' : ,;, ' ~ ' ', ''~ ' .,','. ' ' . .",.. '. . .
~112~
non-pigmented she ting of the Comparative Example (C-l and C-2) and the LFY value of the sheeting of the invention, the LFY Percent Gain was calculated. LFY Percent Gain for each Example is given in the Tables set forth below. Retroreflectivity of the sheetings expressed by the Coefficient S of Retroreflection, R,~, was determined using standardized test ASTM E 810-91. RA values are the ratio of the coefficlent of luminous intensity of a piane retroreflective surface to its area and are expressed in units of candelas per lux per square meter (cd. Ix~'m-2). RA values greater than 600 are readily obtainable by retroreflective articles of this invention which also exhibit LFY
10 values of 30 or better. Measurements of RA were made at a -4 entrance angle and a 0.2 degr~e observation angle. The RA values set forth in the following Tables are the average of one measurement taken at a æro degree rotational angle and one measurement taken at a 90 degree rotational angle.
TABLE II
C-l A, A 0.0000 0.00001476 0 : :
1 A, B 0.0075 0.01691158 446.6 .
2 A, D 0.0150 0.03341004 670.8 ~ -3 A, C 0.0120 0.0432 876 803.4 4 A, F 0.0300 0.0668 684 923.0 A, E 0.0240 0.0858 485 1068.9 6 A, G 0.0480 0.1739 163 1334.8 7 H, A 0.0480 0.1036 352 1213.7 ~: -' LE~Y % GaiD wa~ cdculated from a base LPY value of 3.2. The base LPY value : ~
was the LPY vdue of l~xampb C-l . : ~ ~ :
The data shown in Table II demonstrates that an increase in white pigment loading level dramatically increases the aluminum coated, cube-corner 7 ~
sheeting's LFY lightness value while still allowing the sheeting to be significantly retroreflective as expressed in the R" values.
Examples C-2 and 8-14 were prepared and tested as described a~ove, exeept the back sides of the cube-corner sheetings were vapor coated with a 5 120 nm thick layer of silver in place of the 90 nm thick layer of aluminum.
The data for these Examples is shown below in Table III.
TABLE m 10 ~ ~ ~'~a~'~
C-2 A, A 0.0000 0.0000 2175 0 8 A, B 0.0075 0.0169 1688 394.2 _ lS A, D 0.0150 0.0334 1434 627.1 A, C 0.0120 0.0432 1308 725.4 11 A, E 0.0300 0.0668 940 798.3 .-12 A, E 0.0240 0.0858 695 913.6 13 A, G 0.0480 0.1739 212 1157.6 20 14 H, A 0.0480 0.1036 553 1020.3 _ ' LFY X GdD was cdculated from a ba6e LFY value of 5.9. The base LFY ~Idue wa~ the LFY vdue of ~x~mple C-2. .
The data set forth in Table III demonstrates that an increase in white pigment loading dramatically increases the silver coated, cube-comer sheeting's LFY lightness value while still a11Owing the sheeting to be significantly retroreflective.
E:xamples C-3 and 15-17 The Examples were prepared as described above except transparent fluorescent polycarbonate blanks were used in place of the clear non-pigmented blanks. The transparent fluorescent sheeting was produced by placing 0.45 weight percent of Hostasol Red GG dye (available from Hoechst ~ . . ~ ., : ;,.":: . ., .. : , - :
~ ' -" 2:~i2~2-i~
Celanese Corporation, Somerville, New Jersey) in a polycarbonate resin (Makrolon Typei 2407). The dye-containing resin was extruded to produce a ~, flat sheet 127 rnicrometers thick. This sheet was cut into 30 cm by 30 cm pieces which were stacked upon a clear polycarbonate sheet (Example C-3~ or S upon a white pigmented polycarbonate sheet (Examples 15-17). Three differen~ levels of R-960 titanium dioxide pigment were used in Examples 15-17 to produce ~hree different white pigmented polycarbonate sheets (seei Table IV). One of each of the titanium dioxide pigmented sheets was combined with a fluorescent colored sheet, and they were embossed as described in the above Examples. In forming the cube-corner sheetings, the clear sheet (Example C-3) and the pigmented sheets (Examples 15-17) were placed against the pattemed platen, and the fluorescent colored sheets were placed against the i smooth platein. The light path through the pigmented portion of each of the sheetings was determined to be 347 micrometers. Following the embossing step, the cube-comer sheetings were vapor coated with a 90 nm thick layer of aluminum as described in Examples C-l and 1-7. In addition to measuring the R,~ and LFY, the maximum spectral reflectance factor (MSRF) in the 600 to 620 nanometer light range was measured using a Hunter Labscan 6000 zero -~
degree/45 degree spectrocolorimeter in accordance with standardized test ASTM E 991-90. The MSRF is the ratio of the sum of the spectral radiance reflected and emitted from the fluorescent specimen, to the spectral radiance reflected from the perfect reflecting diffuser, identically irradiated. The datapertuning to RA~ LFY and MSRF is shown below in Table IV.
:~
TABLE IV
C-3 .0000 780 00 47 16 0~40 279 57 81 -' LE~Y X Ga was calculab d from a bs~e LE~Y alue of 16. rhe base LFY value wa~ the LFY value of Example C-3.
:~
.
'. :.
The data set forth in Table IV shows that fluorescent colored cube-corner sheetings, which have white pigment particles incorporated into the front por~on of the sheeting and have an aluminum vapor-coated back side, 5 demons~ate substantially improved lightness, good retroreflectivity, and notable improvement in the MSRF. Part of the percent gain in MSRF can be attributed to the titanium dioxide pigment, which increased the lightness of thecolor. However, a portion of the gain in MSRF can be attributed to the increase in fluorescence. To show this, in accordance with ASTM E 1247-88, 10 a red PMMA film was inserted between the Lab Scan II light source and the sample specimens. This test was used to detect fluorescence by comparing the MSRP at specific light wavelengths with and without the red PMMA filter.
The we of the red filter in this test eliminated the excitation light wavelengths, and thus the fluorescent sheetings were rendered non-fluorescent.
15 The data per~uning to the LFY and MSRF with and without the red filter is shown in Table V. The MSRF differences were determined by subtracting the va1ues obtained with the red filter from the values obtained without the filter.
TABLE V
25 ~
C-3 19.54 S.83 13.71 59.779.93 49.84 24.80 11.83 12.97 80.6928.14 52.55 16 28.23 15.09 13.14 94.2137.68 56.53 17 31.42 18.15 13.27 103 81~5 59 58.22 The data set forth in Table V shows that while the difference in LFY
remained relatively constant (lightness did not increase), the difference in MSRF incre~ased significantly with increased amounts of opaque pigment for these aluminum vapor coated fluorescent sheetings. The MSR~ difference 35 increase shows that there was a significant increase in fluorescence. ASTM
~. . : ~ . , ... , . , ~, . . . .... . .
r- 2~2~2i~
E 1247-88 considers an increase in fluorescence to be significant if the MSR~
difference is greater than one percent.
Examples C~and 1~20 S These l~xarnples were prepared and tested as described in Examples C-3 and 15-17, except that the back side of the sheeting was coated with a 120 nm thick layer of silver.
TABLE VI -~ ~ ~ 1~
C-4 .0000 1188 00 72 ~ _ 19 .0240 399 68 129 ' LE;Y % Gain wa~ calculated from a base LFY ~/aluo of 22.2. The base LPY vdue w~ the Ll7Y ~alue of Exampb C4.
':~`
The data set forth in Table VI shows that fluorescent colored cube~
corner sheetings, which have white pigment particles incoIporated into the front portion of the sheeting and have a silver vapor-coated back side, demonstrate substantially improved lightness, good retroreflectivity, and good -fluorescence over a similar non-pigmented article. These sheetings were also tested in accordance with ASTM E 1247-88 to determine if fluorescence was -~improved. In this latter test, the differences in L~Y ranged from 17.39 to `~
18.95 and the MSR~ differences increased about 8 percent between ~xample C-4 and Example 20, thereby demonstrating a significant increase in fluorescence.
Examples C-5and21-23 These ~xamples were prepared and tested as described in E~amples C-4 and 18-20, respectively, except the back side of the cube-corner elements was not vapor coated with aluminum. Instead, a base layer of polyester (40.6 .
~:
~ 2112 ~ 2 ~
micrometer thick) having titanium dioxide pigment particles dispersed therein was thermally bonded to the cube-corner sheetings to form a multitude of hexagonally-shaped, hermetically-sealed air chambers of about 4 millimeters in size. The resulting cube-corner sheeting thus had in the front portion a S number of retroreflective regions encompassed by the bonding regions (see for example FIG. 3). The sheeting was ~sted as described above, and the data for R,~, LFY % Gain, and MSR~ is set forth below in Table VII.
TABLE VII
~¦a~
C-S .0000 441 00 120 ,.. __ . ....
LFY X Gaill was calculated from a baso LE~Y valuo of 34.3. The ba~o LE~Y vaho was the LE~Y value of l~xampb C-5.
The data set forth in Table VII shows that the fluorescent colored cube-corner sheetings (which have white pigment particles incorporated into the front portion of the sheeting and have a sealed base layer on the back side) 25 demonstrate improved lightness, good retroreflectivity, and good fluorescenceover a similar non-pigmented article. These sheetings were also tested in accordance with ASTM-1247-88 to determine if fluorescence was improved.
The differences in LFY ranged from 15.10 to 15.87, and the MSRF difference increased about 4 percent between Example C-5 and Example 23, thereby - 30 demonstrating a significant increase in fluorescence.
This invention may take on various modifications and alterations without departing from the spirit and scope thereof. Accordingly, it is to be understood that this invention is not to be limited to the above~escribed, but is to be controlled by the limitations set forth in the following claims and any35 equivalents the~eof. It is also to be understood that this invention may be : ~: , 2~
suitably practiced in the absence of any element not specifically disclosed herein.
- 19- : ~
CllB~CORNER RETROREFLECTIVE ARTICLES
FlELD OF THE INVENTION
S This invention pertains to (i) a cube-corner retroreflective article that provides a superior daytime lightness and (ii) a method of making the same.
BACKGROU~ OF IHE INV~NTION
Retroreflective ar~icles have the ability to return incident light back in the direction from which the light originated. This unique ability has led to the widespread use of retroreflective articles on a traffic signs. At nighttime,light from motor vehicle headlights is retroreflected by the articles to displayinformation on the sign to motor vehicle dri ~ers. Dunng daylight hours, if the retroreflective articles have a sufficient daytime lightness to make the sign readily noticeable to passing motorists, daytime motor vehicle drivers may become privy to the same information. An ongoing goal in the retroreflective art, therefore, has been to provide retroreflective articles that demonstrate good nighttime retroreflectivity and sufficient daytime lightness to make the articles readily noticeable to passing motorists at any time of the day.
An example of a commonly used and good pe~forming retroreflective article is a cube-corner retroreflective sheeting. A cube-corner retroreflectivesheeting employs a multitude of cube-corner or prismatic elements to retroreflect the incoming light. Each cube-corner element has three planar faces that meet at an apex. At the base of each element is a sheet-like body portion (also known as a ~land~) which unites the cube-corner elements in the form of a sheeting. Light which is retroreflected typica11y enters the sheeting through a cover layer, passes through the body portion to stril.~e the cube surfaces, and is reflected back in the direction from which the light entered the sheeting. A color is often provided to a cube-corner sheeting by incorporating a dye or transparent pigment into the body portion or cube-corner elements.
A fairly common cube-corner retroreflective sheeting has a metallic coating applied to the backside of the cube-corner elements to promote retroreflection; see for example, U.S. Patent 3,684,348. While it is known that the metallic coating can improve the sheeting's retroreflective performance, it is also known that the metallic coating can have a detrimental effect on daytime lightness. The metallic coating, which is often aluminum, 2~2~
:
imparts an undesirable grayish daytime color to the sheeting, making information on the sign more difficult to read. This drawback makes metallic coated cube-corner sheetings much less likely to be used on signs that require good daytime lightness.
S To improve the daytime lightness of metallic coated, cube-corner sheetings, the inventors of U.S. Patent 4,801,193 developed a method of removing a predominant portion of the metallic coating from the back side of the cube~orner elements. This removal is accomplished by superimposing a second coating material over a minor portion of the metallic coating in a grid-like pattern and then exposing the coated cube-corner elements to a solvent to ~move the metallic coating from the non-superimposed areas. A metallic coating in the form of a grid results. A backing element is then adhered to the backside of the cube-corner sheeting along the grid lines but is spaced apart from the cube-corner elements over the areas where the metallic coating has been removed. The patent discloses that upon observation of the sheeting in ambient light, a grayish grid pattern may be seen, which represents the residual metal on the backside of the cube-corner elements. Lighter areas between the grid lines are displayed which are characteristic of the areas where the metallic coating has been removed.
Another known approach for improving daytime lightness in a cube- ~;
comer sheeting involves placing opaque pigment particles that scatter white light in a base layer of the cube-corner sheeting. This approach does not rely on a metallic coating to promote retroreflection but instead employs a pluralityof hennetically-sealed air chambers, which allow air to interface with the back side of the cube corner elements without interference from moisture, dirt, and the like. A retroreflective article having this construction is shown in FIG.
1 where numeral 10 designates the retroreflective article.
Retroreflective article 10 includes a cube-corner sheeting 12 that has cube-corner elements 14 and a body portion 16. The body portion 16 has a smooth surface 18 through which light (such as from an automobile headlamp) passes in the direction of arrows 20 and 21. The incident light 20 strikes surfaces of cube-corner elements 14 and is reflected back in the direction 21 from which it originated. Air in hermetically-sealed air chambers 22 interfaces with the back side 27 of cube-corner elements 14 to promote the retroreflection of the incident light. Sealed chambers 22 are enclosed by a base layer 26 that is secured to sheeting 12 at bonding regions 24. ~ ~ -2112 ~ 2 ~
.
Retroreflective article 10 exhibits good daytime lightness by having opaque, white pigment particles 28 dispersed in the base layer 26. In the base layer's bonding region 24, the pigment particles 28 scatter the incident light to display a relatively light daytime color to the viewer. The cube-corner S element/air interface also assists in improving lightness of the article 10. An article having this kind of construction has been sold for many years by 3M
as Scotch2ite~ Diamond Grade Reflective Sheeting.
SUA~MARY OF THE~ JNY~NTION
In accordance with the present invention, a new cube-corner retroreflective ar~cle is provided that exhibits an extraordinarily good daytimelightness. The retroreflective article of this invention comprises:
a sheeting having a front portion that includes a retroreflective region that has a body portion and a plurality of cube-corner elements which project away from the body portion; and opaque pigment particles that have lightness improving properties, the opaque pigment particles being dispersed in the retroreflective region of the front portion of the sheeting.
In another aspect, the present invention provides a method of making a retroreflective ar~cle, which comprises:
dispersing opaque pigment particles in at least a retroreflective region of a front portion of a sheeting that contains a plurality of cube-corner elements, wherein the dispersed opaque pigment particles possess lightness improving properties.
As the terms are used herein, "front portion" means the portion of a retroreflective article through which incident light passes, and "retroreflective region" means those part(s) of the front portion of a cube-corner sheeting where the incident light is capable of being retroreflected. In the reboreflection region(s) of front portion of the retroreflective article, the opaque pigment particles may be located, for example, in the body portion or cube-corner elements or in an overlay film that is located on top of the cube-corner sheeting or in a combination of these parts of the front portion. The term "lightness improving properties" means possessing the ability to improve the lightness of the sheeting in which the opaque pigment particles are dispersed.
It was discovered in this invention that by dispersing opaque pigment particles that have lightness improving properties in the retroreflective -- 2 ~ 1 2 ~ 2 ~ ~
region(s) of the front portion of a retroreflective article, daytime lightness can , be increased substantially without destroying nighttime retroreflectivity.
Opaque pigment particles that have lightness improving properties are known to scatter incident light in a diffuse manner, and therefore it was expected that 5 the particles would seAous1y compromise retroreflectivity by causing the incident light to be scattered randomly. Instead, however, it was surprisingly discovered that good retroreflection is obtained by the cube-comer retroreflective articles of this invention -- in spite of the presence of the opaque pigment particles.
In addition to improving lightness while retaining retroreflectivity, it also was su~prisingly discovered that a significant increase in fluorescence canbe achieved by the dispersement of the opaque pigment particles in the front portion of a fluorescent-colored, cube corner sheeting. An improvement in fluorescence makes a fluorescent retroreflective article more conspicuous to 15 viewers during the daytime. Thus, a fluorescent article of this invention canhave extraordinary conspicuity by providing contemporaneous improvement in both lightness and fluorescence.
The above and other advantages and aspects of the invention are more fully illustrated in the detailed description of this invention and drawings, 20 where like reference numerals are used to represent similar parts. It is to be understood, however, that the description and drawings are for the purposes of illustration only and should not be read in a manner that would unduly limit the scope of this invention.
BRIEF DESCNPI'ION OF THE DR~4WINGS
FIG.lis a cross-sectional view of a prior art retroreflective sheeting 10.
FIG. 2 is a cross-sectional view of a retroreflective article 30 in accordance with the present invention.
FIG. 3 is a cross-sectional view of another embodiment of a retroreflective article S0 in accordance with the present invention.
FIG.4is a bottom view of the backside of cube~orner elements 66 in a retroreflective sheeting.
DliTAnED DESCN~ION OF THE PREFERRED EMBODIMENTS
In describing the preferred embodiments of the invention, specific terminology will be used for the sake o1 clarity. The invention, however, is i 2~ 2,2~
not intended to be limited to the specific terms so selected, and it is to be understood that each term so selected includes all the technical equivalen~s that opeMte similarly.
Referring to FIG. 2, an example of a retroreflective article 30 is shown which includes a cube-corner sheeting 32 that has a retroreflective region 33 in a front portion 3S of the article 30. Front portion 3S includes a body portion 34 and a plurality of cube-corner elements 36 which project away from the body portion 34. Dispersed throughout the front portion 3S of cube-corner sheeting 32 are opaque pigment particles 38 which have lightness improving properties. As shown, opaque pigment particles 38 may be located in the body portion 34 and in the cube-corner elements 36 of sheeting 32. An overlay film 40 can be provided to protect the cube-corner sheeting 32 from ultra-violet rays and abrasion. Opaque pigment particles 38 which have lightness improving properties also can be incorporated into the overlay film 40. However, it is preferred that the opaque pigment particles be located in the cube-corner sheeting 32 because the light path through the sheeting 32 typically is significantly longer than the light path through the overlay film 40.
A longer light path allows a lower concentration of pigment particles 38 to be used in the retroreflective sheeting and provides more color uniformity. It is to be understood that the opaque pigment particles can be placed in a combination of the body portion 34, cube-corner elements 3C, and overlay film 40, or in other layers of a front portion of a retroreflective sheeting.
To promote retroreflectivity, the back side of cube-corner elements 3C
can interface with a reflective material (for example metal) or a material tllathas a significantly different refractive index from the polymeric material of the cube-corner elements (for example, air). A metallic coating 42 can be placed on the back side of polymeric cube-corner elements by vapor-depositing or chemically depositing a metal such as alun inum, silver, or nickel. A primer layer (not shown) may be applied to the cube-corner elements 36 to promote adherence of the meta11ic-coating 42. As shown, a backing material 44 can be placed in contact with the metallic coating 42, and an adhesive layer 46 can be applied to the backing 44, or alternatively, the adhesive layer 46 can be applied directly to the metallic coating 42. A release paper 48 can be provided to cover the adhesive 46 until the retroreflective article 30 is adhered to a substrate such as a panel for a sign (not shown).
FIG. 3 illustrates an embodiment of a retroreflective article 50 of this invention where the cube-comer elements interface with air. Like 21~ ~ ~ 2 i~
retroreflective article 30 shown in FIG. 2, article 50 has opaque pigment particles S8 which have lightness improving properties and which are dispersed in a front portion 55 of a retroreflective sheeting S2. Sheeting 52 includes a body portion 54 and cube-corner elements 56 projecting away from 5 ~e body portion S4. Article 50 differs from the embodiment of FIG. 2 by having the back side of the cube-corner elements S6 interface with air rather than with a metallic coating. The cube-corner/air interface is protected from moisture, dirt, and the like by providing hermetica11y-sealed air chambers S7.
Chambers S7 are defined by a base layer 59 that is secured to the retroreflec~ve sheeting 52 at bonding regions C0. The bonding regions 60 define a plurality of retroreflective regions S3 in the front portion 55 of article S0. Base layer S9 can be secured to the sheeting 52 using known methods such as disclosed in U.S. Patent 4,025,159, incorporated here by reference.
FIG. 4 illustrates an example of cube-corner elements CC that may bei lS used in a retroreflective sheeting of this invention. Each cube-corner element CC has three planar faces C7 that meet at an apex C8. The apex 68 of each cube-corner element CC may be vertically aligned with the center of the base of the cube-comer element, see, for example, U.S. Patent 3,684,348, or the apex may be canted to the center of the base as disclosed in U.S. Patent 4,588,258. Of the many cube-corner configurations, see also, for example, U.S. Patents 4,775,219, 4,243,618, 4,202,600, and 3,712,706, the cube-corner retroreflective elements described in U.S. Patent 4,588,258 is particularly preferred because they provide wide angle retroreflection among multiple viewing planes. The disclosures of each of these patents are incorporated hereby reference.
A retroreflective sheeting of this invention generally is about 75 micrometers (5 mils) to 600 micrometers (24 mils) thick. Each cube-comer element typically is about 60 micrometers (2.4 mils) to 200 micrometers (8 mils) high, and the body portion, typica11y, is about 25 micrometers (1 mil) to 250 micrometers (25 mils) thick. The body portion and the overlay film preferably interface at ? substantia11y smooth surface to prevent the dispersionof light. Overlay film, typically, is about 25 micrometers (l mil) to 125 micrometers (S mils) thick.
Opaque pigments useful in this invention generally have a refractive index greater than 1.8 and include those that are designated as opague or serni~paque by the National Association of Printing Ink Manufacturers in the NP~RI Raw Matenals Data Handbook, volume 4 (1983). Preferred opaque 2t ~ 2~2 ~
pigments have a refractive index greater than 2.2 and more preferably greater than 2.6 Examples of opaque pigments that have lightness improving properties are opaque pigments that diffusely reflect white light. The term "light" is used herein to mean electromagnetic radiation in the visible range, 4 X 10-7 meters to 7.7 X 10-7 meters approximately. Pigments that reflect ~, white light are designated as pigment whites in the Colour Ir~ (C.I.).
3 published by the Society of Dyers and Colourists. Examples of white opaque pigments that may be suitable for use in this invention include the following inorganic pigments: zinc-based pigments such as zinc oxide, zinc sulfide, and lithopone; zirconium oxide; alatimony oxide; and titanium dioxide. Titanium dioxide in its rutile form is t}le preferred opaque pigment. Examples of white, opaque pigments that may be employed to enhance sheeting lightness include the following identified by the Co~ur Index:
PigmentWhite 1 C.I. 77597 Basic CarbonateWhite Lead PigmentWhite 4 C.I. 77947 Zinc Oxide Pigment White 5 C.I. 77115 Lithopone Pigment White 6 C.I. 77891 Titanium Dioxide Pigment White 7 C.I. 77975 Zinc Sulfide Pigment White 11 C.I. 77052 Antimony Oxide Pigment White 12 C.I. 77990 Zirconium Oxide .
Other opaque pigments that have lightness improving properties and 25 may be suitable for use in this invention include the following pigments~
PigmentBrown 24 C.I. 77310 Titanium, Chrome and ~ . ~
Antimony Oxides - - -Pigment Yellow 34 C.I. 77603 Lead Sulfochromate -~ -Pigment Yellow 35 C.I. 77205 Zinc Sulfide Pigment Yellow 37 C.I. 77199 Cadmium Sulfide Pigment Yellow 53 C.I. 77788 Titanium, NickelandAntimony Oxides Pigment Yellow 161 C.I. 77895 Titanium, Nickel and Niobium Oxides Pigment Yellow 184 Bismuth Vanadate and Bismuth Molybdenate Combinations of the above pigments may a1so be used.
The pigment particles used in this invention preferably have a mean size ranging from about 0.1 to 5 micrometers, more preferably in the range of from about 0.5 to 2 micrometers. When titanium dioxide is used as the opaque pigment, its mean size typically ranges from about 0.2 to 0.3 micrometers. The quantity of pigment particles may vary depending on, for 2 1~ C~.~ 2 ~.
, A
example, the composition of the pigment particles, the size of the pigment particles, the size and geometry of the cube corner elements, the thickness of the front portion, the color of the sheeting, and the end usage of the retroreflective article. In genera1, however, the pigment particles are 5 dispersed in the front portion of the retroreflective sheeting in the range ofabout 0.0001 to 0.75 volume percent, and typically in the range of about 0.0002 to 0.075 volume percent and more typically in the range of 0.005 to 0.05 volume percent. The pigment particles are preferably evenly distributed throughout the front portion of the retroreflective sheeting so that uniform 10 color, lightness, and retroreflectivity are displayed by the retroreflective article.
The retroreflective article may be colored by incorporating a dye or a transparent pigment in the front portion of the sheeting. The dye or transparent pigment may be placed, for example, in the body portion, the 15 cube-corner elements, an overlay film, or a combination thereof. The retroreflective article also can be colored by applying an ink containing a dye or transparent pigment onto either side of an overlay film. The particular dye or transparent pigment selected depends, of course, on the desired color of the retroreflective article and on the polymeric composition of the cube-corner 20 sheeting. The selected dye or transparent pigment should not have a deleterious effect on the article's retroreflectivity, and it should not substantially compromise the daytime lightness of the article.
Examples of dyes that may be suitable for use in this invention include:
Violet: C.I. Solvent Violet, 13, 31, 32, 33, and 36;
Blue: C.I. Solvent Blue 94, 97, 101, and 121, and C.I. Disperse Blue 60 and 198;
Green: C.I. Solvent Green 3, 26, and 28;
Yellow: C.I. Solvent Yellow 93, 112, 113, 128, 129, 130, and 163, and C.I. Disperse Yellow 54, 64, and 160;
Orange: C.I. Solvent Orange 60, 68, 72, and 86, and C.I. Msperse Orange 47; and Red: C.I. Solvent Red 52, 111, 117, 135, 138, 139, 169, 195, and 207, and C.I. Disperse Red 5.
These dyes are available from one or more of the following companies: BASF
Corporation, Bayer AG, Color Chem International, and Mitsubishi Chemical Industries. Amaplast Violet PK from Color Chem International also may be useful, as well as fluorescent dyes such as a thioxanthene dye, a thioindigoid 40 dye, a benzoxazole coumarin dye, or a perylene imide dye. Retroreflective .
5 2 ~
articles containing these fluorescent dyes have been disclosed in European Patent Application 0,489,561 Al published June lO, 1992, the disclosure of which is incorporated here by reference. Combinations of the above dyes a1so may be employed, and/or transparent pigments may be employed to provide 5 color.
Examples of transparent pigments that may be suitable to color retroreflective articles of this invention include:
Violet: C.I. Violet, l9, 23, 27 Blue: C.I. Blue, lS
Green: C.I. Green, 7, lO, 36 Yellow: C.I. Yellow, 93, lO9, 128 Orange: C.I. Orange, 43, 46 Red: C.I. Red, lM, 179, 206 These transparent pigments are available from one or more of the following companies: Ciba-Giegy Corporation, BASF Corporation, Sandoz Chemicals, Sun Chemica1s, Hoechst Celanese and Miles Incorporated.
When the retroreflective article is colored, it is preferred that the 20 opaque pigment particles not be incorporated into the article in front of thecolored layer. Preferably, the opaque pigment particles are incorporated into the front portion of the retroreflective ar~cle in the same layer as the dye or transparent pigment, and more prefe~ably behind the colored layer (that is, closer to the back side of the cube-comer elements). The placement of the 25 pigment particles in front of the colored layer is not preferred because it would cause the color's saturation to become diluted.
The cube-corner sheeting for a retroreflective article of this invention can have a polymeric composition. Polymers useful for forming a cube-corner sheeting include polymers that are transmissive to visible light and are 30 compatible with the pigment particles. If a dye is employed, the polymer should also be compatible with the selected dye. To be compatible, the polymer preferably does not allow the pigment (and dye) to nigrate or bloom out from the interior of the retroreflective article. Examples of polymers that may be used in retroreflective articles of this invention includepolycarbonates,35 polya1kylacrylates, polyalkylmetbacrylates such as polymethylmethacrylate, polyesters, vinyl polymers, polyurethanes, cellulose esters, fluoropolymers, polyolefins, ionomeric copolymers and copolymers of ethylene or propylene with acrylic acid, methacrylic acid, or vinyl acetate. Combinations of such polymers also may be employed. For example, the cube-corner sheeting may g ' ~
. ~
-~" 2~ 2-~J2~
be made from a blend of polymers, or the cube-corner elements and the body portion may be made from different polymers. Further, the body portion may comprise a plurality of layers of the same or different polymers.
Polycarbonates are preferred polymers for a cube-corner sheeting of this S invention because they possess tough, durable characteristics.
An overlay film for a retroreflec~ve sheeting may be made from polymers similar to those of the cube-corner sheeting; typical1y, types which are stable to ultra-violet (UV) light and have good abrasion resistance such as 3 acrylic polymers (e.g., polymethylmethacrylate) and copolymers. UV
stabilizers may also be added to the overlay film.
Cube-corner sheetings can be made according to known techniques such as disclosed in U.S. Patents 5,122,902, 4,938,563, 4,895,428, 4,703,9g9, 4,601,861, 4,576,850, 4,588,258, 4,025,159, 3,935,359, 3,811,983, and 3,810,804. The pigment particles may be dispersed in the front portion of the retroreflective article using known methods for incorporating pigments into polymers. For example, a twin-screw extruder can be employed to blend the pigmer,t particles with the polymer.
The retroreflective articles of tbis invention are particularly useful for placement on signs along roadways or on motorized vehicles or ~ailers, particularly large trucks and truck trailers. The improved daytime conspicuity makes the articles nicely suitable for such use.
Features and advantages of this invention are further illustrated in the following Examples. It is to be expressly understood, however, that while the F,xamples serve this purpose, the particu1ar ingredients and amounts used as well as other conditions and details are not to be construed in a manner that would unduly limit the scope of this invention.
EJY,4~PLES
Example3 C-l - C-2 and 1-14 Flat colored sheets were prepared for use in fabricating cube-corner retroreflective sheetings. The flat colored sheets were prepared by first mixing Type R-960 titanium dioxide pigment (E.I. DuPont De Nemours and Company, Wilmington, Delaware) with Makrolon 2407 polycarbonate pellets (Miles Inc., Pittsburgh, Pennsylvania) in a paint shaker. The amount of titanium dioxide pigment mixed with the polycarbonate resin ranged from zero volume percent to 0.048 volume percent (0.16 wt. %). The mixtures were then dried overnight in an oven overnight at 125 C (257 F) and were ' ' ~ ?; ,~
21~S~ J2~
`~
extruded into a sheet having two smooth sides, which was subsequently cut into pieces sized to about 30 centimeters (cm) by 30 cm. The melt temperature during the extrusion was about 250 C (483 F), and the die temperature was about 285 C (545 F). The extruded sheets are 1isted below 5 in Table I. The sheets produced had a thickness ranging from about Sl micrometers (2.0 mils) to approximately 122 micrometers (4.8 mils). A 3.18 cm (l 'h inch) KillionlY single screw extruder (Killion Extruders, Inc., Cedar Grove, New Jersey) coupled to a 30.5 cm (12 inch) flat sheet die was used to produce ~e sheets.
TABLE I
15 ~ ~
A 0.000 lO0.0000 102 B 0.0075 99.9925 53 . . . __ C 0.0012 99.9880 121 .
D 0 OlS0 99.9850 52 E 0.0240 99.9760 l l9 F 0 0300 99.9700 52 _ G 0.0300 99.9700 122 H 0.0480 99.9520 108 The cut sheets set forth in Table l were stacked and embossed to produce a cube corner retroreflective sheeting. Two sheets were used for each combination which will be referred to as a "blank stackn. Each blank 30 stack was embossed using a platen press to form cube-corner retroreflective elements on one side and a flat surface on the opposite side. The embossing operation involved about 5 minutes of preheating to a temperature of about 188 C (370 F), followed by about 20 seconds of embossing, which in tum was followed by about 8 minutes of cooling. The platen press had a pattern 35 which produced slightly canted, three-sided cube-comer elements in accordance with the teachings of U.S. Patent 4,588,258. The cube corner array had three sets of mutua11y intersecting V-shaped grooves where the base edges of the lateral faces of the cube-corner elements lied in a common base 2 ~ i r~ ~ 2 3 .
., plane. The cube-corner elements were arranged as matched pairs within this array, with paired elements rotated 180 degrees with respect to each other.
The optical axis of the cube-corner elements in each pair were rotated towards one another by 8.15 degrees. The distance from the peak of the cube-corner 5 elements to the base plane was approximately 0.0889 millimeters (mm).
In Examples 1-6, the blank stack was arranged such that the titanium dioxide containing sheet (sheets B-H) formed the cube-corner elemen~s and a minor part of the body portion, and the clear polycarbonate sheet (sheet A) formed the major part of the body portion of the cube-corner sheeting. In 10 Example 7, the blank stack had a reverse arrangement such that the titanium dioxide containing sheet formed the major part of the body portion and the , clear polyc~ubonate sheet formed the cube-corner elements and a minor part of the body portion. After the cube-corner retroreflective sheetings were produced, each sheeiting had a 90 nanometer (nm) thick layer of aluminum :~ 15 vapor coated on the back side of the coated cube-comer elements. The aluminum coatings were applied using a laboratory bell jar vapor coater with b~ a resistance type heat source.
The light path through the pigmented portion of the embosseid cube-corner sheeting was calculated by taking the total distance for which light 20 entering and exiting the pigmented cube-corner elements travels (2 times the cube element height) plus the length of the light path passing through the pigmented part of the body portion of the sheeting. For example, a sheeting that has a 88.9 micrometer high, cube-corner element having a 101.6 micrometer (4 mil) thick pigmented body portion, the light path length is 383 25 micrometers. The light path was multiplied by volume percent of pigment to give a parameter (Light Path x Vol. % TiO2) in units of micrometers (~m) This parameter was found to correspond to the increase in lightness.
Lightness of the cube comer sheeting was measured using a spectrocolorimeter according to standardized test ASTM E 1349-90.
30 Lightness is expressed by the parameter termed Luminance Factor Y (LFY), which is defined as the lightness of the test sample relative to a perfect diffusing reflector. Zero degree illumination and 45 degree circumferential viewing were employed in determining the LFY. LFY values range from 0 to 100, where a LFY value of 0 represents a perfect black color and a LFY
35 value of 100 represents a perfect white color. LFY values higher than S0 (and even higher than 70) have been demonstrated by cube-comer ~etroreflective articles of this invention. Using the LFY value of the clear, !~r ,'' . . ' ' ! . , ' ' , ~ :' . ` , , ' ~ , ` ~ ' ' ' ',' ~j':. ' '' ,. ' , , ' ' ' : ,;, ' ~ ' ', ''~ ' .,','. ' ' . .",.. '. . .
~112~
non-pigmented she ting of the Comparative Example (C-l and C-2) and the LFY value of the sheeting of the invention, the LFY Percent Gain was calculated. LFY Percent Gain for each Example is given in the Tables set forth below. Retroreflectivity of the sheetings expressed by the Coefficient S of Retroreflection, R,~, was determined using standardized test ASTM E 810-91. RA values are the ratio of the coefficlent of luminous intensity of a piane retroreflective surface to its area and are expressed in units of candelas per lux per square meter (cd. Ix~'m-2). RA values greater than 600 are readily obtainable by retroreflective articles of this invention which also exhibit LFY
10 values of 30 or better. Measurements of RA were made at a -4 entrance angle and a 0.2 degr~e observation angle. The RA values set forth in the following Tables are the average of one measurement taken at a æro degree rotational angle and one measurement taken at a 90 degree rotational angle.
TABLE II
C-l A, A 0.0000 0.00001476 0 : :
1 A, B 0.0075 0.01691158 446.6 .
2 A, D 0.0150 0.03341004 670.8 ~ -3 A, C 0.0120 0.0432 876 803.4 4 A, F 0.0300 0.0668 684 923.0 A, E 0.0240 0.0858 485 1068.9 6 A, G 0.0480 0.1739 163 1334.8 7 H, A 0.0480 0.1036 352 1213.7 ~: -' LE~Y % GaiD wa~ cdculated from a base LPY value of 3.2. The base LPY value : ~
was the LPY vdue of l~xampb C-l . : ~ ~ :
The data shown in Table II demonstrates that an increase in white pigment loading level dramatically increases the aluminum coated, cube-corner 7 ~
sheeting's LFY lightness value while still allowing the sheeting to be significantly retroreflective as expressed in the R" values.
Examples C-2 and 8-14 were prepared and tested as described a~ove, exeept the back sides of the cube-corner sheetings were vapor coated with a 5 120 nm thick layer of silver in place of the 90 nm thick layer of aluminum.
The data for these Examples is shown below in Table III.
TABLE m 10 ~ ~ ~'~a~'~
C-2 A, A 0.0000 0.0000 2175 0 8 A, B 0.0075 0.0169 1688 394.2 _ lS A, D 0.0150 0.0334 1434 627.1 A, C 0.0120 0.0432 1308 725.4 11 A, E 0.0300 0.0668 940 798.3 .-12 A, E 0.0240 0.0858 695 913.6 13 A, G 0.0480 0.1739 212 1157.6 20 14 H, A 0.0480 0.1036 553 1020.3 _ ' LFY X GdD was cdculated from a ba6e LFY value of 5.9. The base LFY ~Idue wa~ the LFY vdue of ~x~mple C-2. .
The data set forth in Table III demonstrates that an increase in white pigment loading dramatically increases the silver coated, cube-comer sheeting's LFY lightness value while still a11Owing the sheeting to be significantly retroreflective.
E:xamples C-3 and 15-17 The Examples were prepared as described above except transparent fluorescent polycarbonate blanks were used in place of the clear non-pigmented blanks. The transparent fluorescent sheeting was produced by placing 0.45 weight percent of Hostasol Red GG dye (available from Hoechst ~ . . ~ ., : ;,.":: . ., .. : , - :
~ ' -" 2:~i2~2-i~
Celanese Corporation, Somerville, New Jersey) in a polycarbonate resin (Makrolon Typei 2407). The dye-containing resin was extruded to produce a ~, flat sheet 127 rnicrometers thick. This sheet was cut into 30 cm by 30 cm pieces which were stacked upon a clear polycarbonate sheet (Example C-3~ or S upon a white pigmented polycarbonate sheet (Examples 15-17). Three differen~ levels of R-960 titanium dioxide pigment were used in Examples 15-17 to produce ~hree different white pigmented polycarbonate sheets (seei Table IV). One of each of the titanium dioxide pigmented sheets was combined with a fluorescent colored sheet, and they were embossed as described in the above Examples. In forming the cube-corner sheetings, the clear sheet (Example C-3) and the pigmented sheets (Examples 15-17) were placed against the pattemed platen, and the fluorescent colored sheets were placed against the i smooth platein. The light path through the pigmented portion of each of the sheetings was determined to be 347 micrometers. Following the embossing step, the cube-comer sheetings were vapor coated with a 90 nm thick layer of aluminum as described in Examples C-l and 1-7. In addition to measuring the R,~ and LFY, the maximum spectral reflectance factor (MSRF) in the 600 to 620 nanometer light range was measured using a Hunter Labscan 6000 zero -~
degree/45 degree spectrocolorimeter in accordance with standardized test ASTM E 991-90. The MSRF is the ratio of the sum of the spectral radiance reflected and emitted from the fluorescent specimen, to the spectral radiance reflected from the perfect reflecting diffuser, identically irradiated. The datapertuning to RA~ LFY and MSRF is shown below in Table IV.
:~
TABLE IV
C-3 .0000 780 00 47 16 0~40 279 57 81 -' LE~Y X Ga was calculab d from a bs~e LE~Y alue of 16. rhe base LFY value wa~ the LFY value of Example C-3.
:~
.
'. :.
The data set forth in Table IV shows that fluorescent colored cube-corner sheetings, which have white pigment particles incorporated into the front por~on of the sheeting and have an aluminum vapor-coated back side, 5 demons~ate substantially improved lightness, good retroreflectivity, and notable improvement in the MSRF. Part of the percent gain in MSRF can be attributed to the titanium dioxide pigment, which increased the lightness of thecolor. However, a portion of the gain in MSRF can be attributed to the increase in fluorescence. To show this, in accordance with ASTM E 1247-88, 10 a red PMMA film was inserted between the Lab Scan II light source and the sample specimens. This test was used to detect fluorescence by comparing the MSRP at specific light wavelengths with and without the red PMMA filter.
The we of the red filter in this test eliminated the excitation light wavelengths, and thus the fluorescent sheetings were rendered non-fluorescent.
15 The data per~uning to the LFY and MSRF with and without the red filter is shown in Table V. The MSRF differences were determined by subtracting the va1ues obtained with the red filter from the values obtained without the filter.
TABLE V
25 ~
C-3 19.54 S.83 13.71 59.779.93 49.84 24.80 11.83 12.97 80.6928.14 52.55 16 28.23 15.09 13.14 94.2137.68 56.53 17 31.42 18.15 13.27 103 81~5 59 58.22 The data set forth in Table V shows that while the difference in LFY
remained relatively constant (lightness did not increase), the difference in MSRF incre~ased significantly with increased amounts of opaque pigment for these aluminum vapor coated fluorescent sheetings. The MSR~ difference 35 increase shows that there was a significant increase in fluorescence. ASTM
~. . : ~ . , ... , . , ~, . . . .... . .
r- 2~2~2i~
E 1247-88 considers an increase in fluorescence to be significant if the MSR~
difference is greater than one percent.
Examples C~and 1~20 S These l~xarnples were prepared and tested as described in Examples C-3 and 15-17, except that the back side of the sheeting was coated with a 120 nm thick layer of silver.
TABLE VI -~ ~ ~ 1~
C-4 .0000 1188 00 72 ~ _ 19 .0240 399 68 129 ' LE;Y % Gain wa~ calculated from a base LFY ~/aluo of 22.2. The base LPY vdue w~ the Ll7Y ~alue of Exampb C4.
':~`
The data set forth in Table VI shows that fluorescent colored cube~
corner sheetings, which have white pigment particles incoIporated into the front portion of the sheeting and have a silver vapor-coated back side, demonstrate substantially improved lightness, good retroreflectivity, and good -fluorescence over a similar non-pigmented article. These sheetings were also tested in accordance with ASTM E 1247-88 to determine if fluorescence was -~improved. In this latter test, the differences in L~Y ranged from 17.39 to `~
18.95 and the MSR~ differences increased about 8 percent between ~xample C-4 and Example 20, thereby demonstrating a significant increase in fluorescence.
Examples C-5and21-23 These ~xamples were prepared and tested as described in E~amples C-4 and 18-20, respectively, except the back side of the cube-corner elements was not vapor coated with aluminum. Instead, a base layer of polyester (40.6 .
~:
~ 2112 ~ 2 ~
micrometer thick) having titanium dioxide pigment particles dispersed therein was thermally bonded to the cube-corner sheetings to form a multitude of hexagonally-shaped, hermetically-sealed air chambers of about 4 millimeters in size. The resulting cube-corner sheeting thus had in the front portion a S number of retroreflective regions encompassed by the bonding regions (see for example FIG. 3). The sheeting was ~sted as described above, and the data for R,~, LFY % Gain, and MSR~ is set forth below in Table VII.
TABLE VII
~¦a~
C-S .0000 441 00 120 ,.. __ . ....
LFY X Gaill was calculated from a baso LE~Y valuo of 34.3. The ba~o LE~Y vaho was the LE~Y value of l~xampb C-5.
The data set forth in Table VII shows that the fluorescent colored cube-corner sheetings (which have white pigment particles incorporated into the front portion of the sheeting and have a sealed base layer on the back side) 25 demonstrate improved lightness, good retroreflectivity, and good fluorescenceover a similar non-pigmented article. These sheetings were also tested in accordance with ASTM-1247-88 to determine if fluorescence was improved.
The differences in LFY ranged from 15.10 to 15.87, and the MSRF difference increased about 4 percent between Example C-5 and Example 23, thereby - 30 demonstrating a significant increase in fluorescence.
This invention may take on various modifications and alterations without departing from the spirit and scope thereof. Accordingly, it is to be understood that this invention is not to be limited to the above~escribed, but is to be controlled by the limitations set forth in the following claims and any35 equivalents the~eof. It is also to be understood that this invention may be : ~: , 2~
suitably practiced in the absence of any element not specifically disclosed herein.
- 19- : ~
Claims (10)
1. A retroreflective article that comprises:
a sheeting having a front portion that includes a retroreflective region that has a body portion and a plurality of cube-corner elements which project away from the body portion; and opaque pigment particles that have lightness improving properties, the opaque pigment particles being dispersed in the retroreflective region of the front portion of the sheeting.
a sheeting having a front portion that includes a retroreflective region that has a body portion and a plurality of cube-corner elements which project away from the body portion; and opaque pigment particles that have lightness improving properties, the opaque pigment particles being dispersed in the retroreflective region of the front portion of the sheeting.
2. The retroreflective article of claim 1, wherein the opaque pigment particles are dispersed throughout the body portion or cube-corner elements of the front portion of the sheeting.
3. The retroreflective article of claims 1-2, wherein the back side of the cube-corner elements has an aluminum or silver metallic coating placed thereon.
4. The retroreflective article of claims 1-3, wherein the opaque pigment particles have a refractive index greater than 2.6.
5. The retroreflective article of claims 1-4, wherein the opaque pigment particles have a mean size ranging from 0.5 to 2 micrometers.
6. The retroreflective article of claims 1-5, wherein the opaque pigment particles are selected from the group consisting of Colour Index Pigment White 1, 4, 5, 6, 7, 11, 12, Pigment Brown 24, Pigment Yellow 34, 35, 37, 53, 161, 184, and combinations thereof.
7. The retroreflective article of claims 1-6, wherein the opaque pigment particles include rutile titanium dioxide pigment particles.
8. The retroreflective article of claims 1-8, wherein the opaque pigment particles are dispersed in the front portion of the sheeting in the range of 0.0002 to 0.075 volume percent.
9. The retroreflective article of claims 1-8, wherein retroreflective article displays a fluorescent daytime color.
10. A method of making a retroreflective article, which method comprises:
dispersing opaque pigment particles in at least a retroreflective region of a front portion of a sheeting that contains a plurality of cube-corner elements, wherein the dispersed opaque pigment particles possess lightness improving properties.
dispersing opaque pigment particles in at least a retroreflective region of a front portion of a sheeting that contains a plurality of cube-corner elements, wherein the dispersed opaque pigment particles possess lightness improving properties.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/014,334 US5272562A (en) | 1993-02-05 | 1993-02-05 | Cube-corner retroreflective articles |
| US08/014,334 | 1993-02-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2112524A1 true CA2112524A1 (en) | 1994-08-06 |
Family
ID=21764848
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002112524A Abandoned CA2112524A1 (en) | 1993-02-05 | 1993-12-29 | Cube-corner retroreflective articles |
Country Status (10)
| Country | Link |
|---|---|
| US (1) | US5272562A (en) |
| EP (1) | EP0609880B1 (en) |
| JP (1) | JPH06250006A (en) |
| KR (1) | KR100317834B1 (en) |
| CN (1) | CN1082670C (en) |
| AT (1) | ATE195376T1 (en) |
| AU (1) | AU661217B2 (en) |
| BR (1) | BR9400370A (en) |
| CA (1) | CA2112524A1 (en) |
| DE (1) | DE69425448T2 (en) |
Families Citing this family (83)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE69429924T2 (en) * | 1993-10-20 | 2002-08-22 | Minnesota Mining & Mfg | DIRECTLY MANUFACTURED STAGE-STRUCTURED RETRORE-REFLECTIVE CUBE-CORNER BODY AND PRODUCTION METHOD |
| EP0724738B1 (en) * | 1993-10-20 | 2000-05-10 | Minnesota Mining And Manufacturing Company | Asymetric cube corner article and method of manufacture |
| US5691846A (en) * | 1993-10-20 | 1997-11-25 | Minnesota Mining And Manufacturing Company | Ultra-flexible retroreflective cube corner composite sheetings and methods of manufacture |
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| US5700077A (en) * | 1995-03-23 | 1997-12-23 | Minnesota Mining And Manufacturing Company | Line light source including fluorescent colorant |
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| WO1996042024A1 (en) * | 1995-06-09 | 1996-12-27 | Minnesota Mining And Manufacturing Company | Retroreflective cube corner article having scalene base triangles |
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| US5672643A (en) * | 1995-09-29 | 1997-09-30 | Minnesota Mining And Manufacturing Company | Fluorescent dye blends |
| US20030170426A1 (en) * | 1995-12-01 | 2003-09-11 | W. Scott Thielman | Cellular retroreflective sheeting |
| USD383312S (en) * | 1996-01-19 | 1997-09-09 | Minnesota Mining And Manufacturing Company | Seal pattern on retroreflective sheeting |
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| WO1997037252A1 (en) * | 1996-04-01 | 1997-10-09 | Reflexite Corporation | A color-fast retroreflective structure |
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| CN102736150B (en) * | 2012-06-21 | 2014-09-17 | 绵阳龙华薄膜有限公司 | Improved microprism retroreflection material |
| WO2014098940A1 (en) * | 2012-12-21 | 2014-06-26 | 3M Innovative Properties Company | Signage overlay article |
| US20150354272A1 (en) * | 2014-06-10 | 2015-12-10 | Sergiy Vasylyev | Light-redirecting retractable window covering |
| US20160011346A1 (en) * | 2014-07-14 | 2016-01-14 | Sergiy Vasylyev | High incidence angle retroreflective sheeting |
| KR102497885B1 (en) * | 2015-04-21 | 2023-02-10 | 미래나노텍(주) | Retroreflective sheet |
| EP3451030B1 (en) * | 2016-04-28 | 2020-12-09 | Nippon Carbide Industries Co., Inc. | Retroreflective sheet |
| WO2018217519A1 (en) | 2017-05-25 | 2018-11-29 | 3M Innovative Properties Company | Cube corner retroreflective articles with tailored retroreflectivity and methods of making |
| JP7043211B2 (en) * | 2017-10-12 | 2022-03-29 | 日本カーバイド工業株式会社 | Retroreflective sheet |
| NL1042822B1 (en) | 2018-04-16 | 2019-10-23 | Own Greens Holding B V | Growing system comprising growing pots provided with a filling channel extending upwards from a bottom and / or side wall |
| US20200257024A1 (en) | 2019-02-11 | 2020-08-13 | Fiberlok Technologies | Light retroreflective graphic textile |
Family Cites Families (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3420597A (en) * | 1964-04-13 | 1969-01-07 | Minnesota Mining & Mfg | Retroreflective structure and method of making same |
| US3684348A (en) * | 1970-09-29 | 1972-08-15 | Rowland Dev Corp | Retroreflective material |
| US4025159A (en) * | 1976-02-17 | 1977-05-24 | Minnesota Mining And Manufacturing Company | Cellular retroreflective sheeting |
| US4055377A (en) * | 1976-08-03 | 1977-10-25 | Minnesota Mining And Manufacturing Company | Magnetically orientable retroreflectorization particles |
| US4123140A (en) * | 1977-06-30 | 1978-10-31 | Ferro Corporation | Reflecting sheeting having wide angle response |
| US4618518A (en) * | 1984-08-10 | 1986-10-21 | Amerace Corporation | Retroreflective sheeting and methods for making same |
| CA1279783C (en) * | 1985-11-21 | 1991-02-05 | Minnesota Mining And Manufacturing Company | Totally internally reflecting thin, flexible film |
| US4763985A (en) * | 1986-08-01 | 1988-08-16 | Minnesota Mining And Manufacturing Company | Retroreflective sheet with enhanced brightness |
| US4801193A (en) * | 1988-03-04 | 1989-01-31 | Reflexite Corporation | Retroreflective sheet material and method of making same |
| US5171624A (en) * | 1990-06-01 | 1992-12-15 | Reflexite Corporation | Retroreflective microprismatic material and method of making same |
| ZA918849B (en) * | 1990-12-06 | 1992-08-26 | Minnesota Mining & Mfg | Articles exhibiting durable fluorescence |
| IL104366A0 (en) * | 1992-01-16 | 1993-05-13 | Stimsonite Corp | Photoluminescent retroreflective sheeting |
-
1993
- 1993-02-05 US US08/014,334 patent/US5272562A/en not_active Expired - Lifetime
- 1993-12-29 CA CA002112524A patent/CA2112524A1/en not_active Abandoned
- 1993-12-31 AU AU52808/93A patent/AU661217B2/en not_active Ceased
-
1994
- 1994-01-18 KR KR1019940000823A patent/KR100317834B1/en not_active IP Right Cessation
- 1994-01-27 BR BR9400370A patent/BR9400370A/en not_active IP Right Cessation
- 1994-02-03 DE DE69425448T patent/DE69425448T2/en not_active Expired - Fee Related
- 1994-02-03 AT AT94101646T patent/ATE195376T1/en active
- 1994-02-03 CN CN94101191A patent/CN1082670C/en not_active Expired - Lifetime
- 1994-02-03 EP EP94101646A patent/EP0609880B1/en not_active Expired - Lifetime
- 1994-02-04 JP JP6012748A patent/JPH06250006A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| AU5280893A (en) | 1994-08-11 |
| ATE195376T1 (en) | 2000-08-15 |
| DE69425448T2 (en) | 2001-03-29 |
| AU661217B2 (en) | 1995-07-13 |
| JPH06250006A (en) | 1994-09-09 |
| US5272562A (en) | 1993-12-21 |
| EP0609880B1 (en) | 2000-08-09 |
| EP0609880A1 (en) | 1994-08-10 |
| BR9400370A (en) | 1994-08-23 |
| CN1082670C (en) | 2002-04-10 |
| KR940020130A (en) | 1994-09-15 |
| CN1099872A (en) | 1995-03-08 |
| KR100317834B1 (en) | 2002-05-30 |
| DE69425448D1 (en) | 2000-09-14 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |