CA1263264A - Transparent retroreflective sheets containing directional images and method for forming the same - Google Patents
Transparent retroreflective sheets containing directional images and method for forming the sameInfo
- Publication number
- CA1263264A CA1263264A CA000506782A CA506782A CA1263264A CA 1263264 A CA1263264 A CA 1263264A CA 000506782 A CA000506782 A CA 000506782A CA 506782 A CA506782 A CA 506782A CA 1263264 A CA1263264 A CA 1263264A
- Authority
- CA
- Canada
- Prior art keywords
- sheet
- sheeting
- microlenses
- retroreflective
- image
- 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.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/12—Reflex reflectors
- G02B5/126—Reflex reflectors including curved refracting surface
- G02B5/128—Reflex reflectors including curved refracting surface transparent spheres being embedded in matrix
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
- G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
- G06K19/08—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code using markings of different kinds or more than one marking of the same kind in the same record carrier, e.g. one marking being sensed by optical and the other by magnetic means
- G06K19/10—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code using markings of different kinds or more than one marking of the same kind in the same record carrier, e.g. one marking being sensed by optical and the other by magnetic means at least one kind of marking being used for authentication, e.g. of credit or identity cards
- G06K19/14—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code using markings of different kinds or more than one marking of the same kind in the same record carrier, e.g. one marking being sensed by optical and the other by magnetic means at least one kind of marking being used for authentication, e.g. of credit or identity cards the marking being sensed by radiation
Abstract
Abstract A directional image is created in substantially transparent retroreflective sheeting comprising a monolayer of microlenses and a partially light transmissive mirror disposed at the rear surfaces of at least some of said microlenses. The image is created by irradiation of the sheeting with a laser beam to form axial markings associated with at least some of the micro lenses. The image may be formed in sheeting which has been applied to a document as an overlay.
Description
~26:~Z/~;~
TRANSPARENT RETROREFLECTIVE SHEETS CONTAINING
_ . _ DIRECTIONAL IMAGES AND METHOD
FOR FORMING THE SAME
. _ _ Field of Invention _ This invention primarily concerns a substantially transparent sheet which includes a partially light transmissive mirror to make the sheeting retroreflective under retroreflective viewing conditions, and which further contains a directional imaye, i.e., an image that is viewable only within a restricted conical field of view of predetermined angular width and central axis.
This invention also concerns a method for forming such sheets.
Background Art Sheeting in which an image of a pattern or legend is built has found a number of important uses, particularly as distinctive labels useful to authenticate an article or document. Such sheeting has found use as validation stickers for vehicle license plates and as security films for driver's licenses, government documents, phonograph records, tape cassettes, and the like, as taught in U.S. Pat. Nos. 3,154,872; 3,801,183 4,082,426; and 4,099,838. In each of the patents, the built-in images must be incorporated into the sheeting while the sheeting is being constructed.
Sevelin et al., U.S. Pat. No. 3,801,183, discloses a substantially transparent sheeting to be used as an overlay on a document such as a credit card, a pass, ~a license or phonograph~label to serve as an identifying ~- or~authenticating means. The sheet is retroreflective over its entire surface~area and contains a retroreflecting pattern or legend which lS obscure in that it is invisible or only faintly visible to the naked eye under diffuse light and does not obstruct any underlying visual information.
Nordgren, U.S. Pat. No. 3,154,872, and Brown, .
;
U.S. Pat. No. 4,082,426, teach other retroreflective sheets containing images that may be obscure, which sheets can be adhesively bonded to documents to make counterfeiting more difficult. The imaged sheets disclosed in those patents are not transparent, however, and so would obstruct information over which they were applied.
Other methods have been developed which use laser irradiation of a sheet material to form directional images therein. These methods rely on opaque masking layers to focus the laser light to a damage locus within a monolayer of microlenses, or to themselves absorb radiation and develop deformations which are viewable as a directional image. If a transparent sheet containing a directional image is desired the opaque masking must be removed after formation of the visible deformations.
Galanos, U.S. Pat. No. 4,200,875, discloses a method of forming directional images in opaque retroreflective sheeting which comprises a specular reflecting layer disposed behind a monolayer of glass microspheres. In that method, laser irradiation of the retroreflective sheeting in an imagewise fashion causes visible structural alterations or modifications in the sheet which are viewable as directional images. Because the Galanos sheeting is opaque, it would obstruct underlying information if adhered to a document as an overlay.
~ ockert et al., Jap. Appln. No. 19824/84, filed February 6, 1984, Kokai No. 148004/84, laid open August 24, 1984, forms a directional image in sheeting which comprises a monolayer of microlenses, a masking layer disposed behind the monolayer of microlenses, and a transparent spacing layer located between those ; ~ two layers. Laser irradiation of the sheeting forms openings in the masking layer which are visible as a directional image. By coloring the transparent spacer layer through the openings and then removing the masking layer, such as with a chemical etch, one can obtain a transparent sheet containing a directional image.
... ~, ,. ~
_3_ The sheet may then be adhered to a document as an overlay which provides a secure means of authenticating the document without interfering with the normal use of the information contained thereon~
y__f_Invention This invention provides a method whereby directional images may be directly formed in transparent sheeting comprising a monolayer of microlenses and that, in most embodiments of the invention, comprises a partially light transmissive mirror, and further provides novel sheets made according to the new method.
By the present invention, directional images may even be formed in a piece of such sheeting that has already been applied as an overlay on a document such as a driver's license or passport.
The images formed according to this method are viewable both under diffuse light and under retroreflective conditions.
More particularly, according to one aspect, the invention provides a substantially transparent sheet comprising a monolayer of microlenses and a partially light transmissive mirror disposed behind the rear surfaces of at least some of said microlenses such that under retroreflective viewing conditions the sheet is brightly retroreflective in the areas occupied by the mirror, there being an axial marking in the rear portion of or on the rear surface of at least some of the microlenses, which markings together are viewable as an image across a predetermined coDicaI field in ordinary diffuse light conditions.
~: :
:~:
.~. ,....
~26326~
-3a-According to a second aspect, the invention provides a substantially transparent sheet comprising a monolayer of microlenses, there being an axial marking in the rear portion of or on the rear surface of at least some of the microlenses which markings together are viewable as an imaye from the front of the sheeting in ordinary diffuse light conditions, and under retroreflective conditions are viewable as a dark image across a predetermined conical field of view and are viewable as a bright image within a region annular to said conical field of view.
According to a third aspect, the invention provides a method of forming directional images in substantially trans-parent sheeting comprising a monolayer of closely spaced micro-lenses and a partially light transmissive mirror disposed at the rear surfaces of at least some of said microlenses, said method comprising directing a laser beam at a selected angle of incid-ence to the face of said sheeting, the wavelength of the laser being selected such that the beam is focused by the microlenses to form a marking in the rear portion of or on the rear surface of each microlens which said beam strikes.
A sheeting of the invention, with its combination of directional images and partially light transmissive mirror, offers unlque benefits as a secuxity film. Although the sheeting is ~transparent, the partially light transmlssive mirror makes the sheeting retroreflective when viewed under retroreflective view-ing conditions. As taught in Sevelin et al., U.S. Patent No.
:
~3~
-3b~
3,801,183, the mirror may be patterned, with some areas of the mirror having greater reflective efficiency than other areas, so that under retroreflective viewing conditions, a viewer discovers retroreflective images hidden within the sheeting.
Insofar as known, the combination in a transparent film of hidden retroreflective images and images tha-t are visible under ordinary diffuse lighting conditions only within a limited conical field of view, has never before been provided. This combination of features offers a unique set of criteria by which the authenticity of a document overlaid with the film can be judged.
3L2~i3~
Sheeting as described can be prepared by directing a suitable laser beam in an imagewise fashion at a selected angle of incidence to the face of the sheeting. The wavelength of the laser beam is selected such that it is focused by microlenses to form discrete rnarkings in the sheeting at the rear of each microlens which the beam strikes. Each microlens focuses the laser light incident upon it to a small spot -- having a diameter that is only a small fraction of the diameter of the microlens -- to create a localized marking, e.g., a cavity within an individual microlens, a cavity opening through the back of a microlens, an opening, charring, or other modifica-tion within the partially light transmissive mirror, or some combination among these various modifications. These markings may be termed "axial markings", in that the marking associated wi-th each microlens is centered on an axis that extends through the optical center of the microlens and is parallel to, or intersects at a common viewing point or line, the similar axes for -the other deformed microlenses in the image area. The resulting set of markings is visible as an image at the angle of incidence of the imaging laser beam.
Detailed Description Sheeting to be imaged according to the novel method comprises a monolayer of microlenses embedded in a layer of binder material. The binder material is typically a substantially transparent polymeric material, such as an alkyd resin, polyurethane, or ethylene vinyl acetate. The microlenses are preferably spherical because they may be imaged from virtually any angle of incidence.
Microlenses with different geometries may be restricted to narrower angles of effectiveness. An example of nonspherical microlenses is disclosed in de Montebello, U.S. Pat. 3,503,315. Glass microlenses are preferred because they tend to be more durable than microlenses ., .
~g~3~6f~
~5--formed from other materials.
Microspheres with a refractive index within a range of 1.5 to 2.7 are useful. Ho~ever, microspheres with refractive indices above 2.4 may introduce coloring, whereas colorless clarity is usually preferred so that the sheet may be as unobtrusive as possible when applied to a document as an authenticating means. Microspheres with a refractive index of approximately 1.8 to 1.9 are preferred, because when partially embedded in the support film and partially exposed above the support film, they will focus whi-te light at approximately the back surface of the microsphere.
The glass microspheres preferably have an average diameter of 10 to 100 micrometers, and are ideally of a uniform diameter of approximately 50-60 micrometers.
If the microspheres are much larger, the shee-ting tends to become thicker and more expensive to make, and images formed thereon will have less resolution. If the microspheres are much smaller, images formed on the sheeting will have greater resolution, but it is more difficult to uniformly distribute the microlenses when constructing the sheet, and the images formed thereon are less bright because of diffraction losses.
The set of axial markings is visible within a conical ~ield of view whose central axis is determined by the angle of incidence at which the imaging beam is directed to the sheeting. The angular width of the conical field of view is related to the size of the markings. Larger markings are visible as an image across a wider field of view than are smaller markings. The size of a marking is determined by the energy density of the irradiation applied to the sheeting which creates the marking. If a higher-energy-density beam is used to form the deformities, the image will have a wider conical field of view. Similarly, if a beam with a lower energy density is used, the image will have a narrower conical field of view.
~2 66~
Preferably the novel method of this invention employs a laser which has sufficient power to cause an axial marking associated with each of the microlenses which the laser beam strikes. Typically in the case of glass microlenses, a laser adjusted so as to provide a power density of approximately one megawatt per square centimeter at the sheeting's surface is useful. Suitable lasers include pulsed, ~4ff~-optically Q-switched Nd:~AG (Neodymium: Yttrium Aluminum Garnet) lasers, such as the Model 512Q laser available from Con-trol Laser Corporation of Orlando, Florida, which, equipped with a frequency doubler, emits a beam with a wavelength of 532 nanometers in pulses of approximately 200 to 400 nanoseconds in dura-tion.
When forming images on sheeting which comprises a monolayer of the preferred glass microspheres having a diameter of approximately 50-60 micrometers, the laser beam is preferably adjusted to form axial markings having diameters within a range from 1 to 20 micrometers. When the microlenses are substantially all about 50-60 micrometers in diameter and the average diameter of the markings is from 3 to 10 micrometers, each authentica-ting image is viewable under ordinary diffuse lighting conditions only across a cone of about 10 to 20 degrees. Images composed of larger markings are viewable within larger conical fields of view; however, there would seldom be any reason for a directional image to be visible across a cone exceeding 30 degrees. On the other hand, a directional image which was viewable only across a cone of less than six to eight degrees might be difficult to locate.
As previously indicated, most embodiments of sheeting of the invention include, in addition to a monolayer of microlenses, a semi-transparent, or partially light transmissive, dielectric mirror which reflects a portion of, and transmits another portion of, the light incident upon the microlenses. Such dielectric ~2~32~
mirrors are taught in Sevelin, wherein it is also taught to form such mirrors with at least two regions of different retroreflective efficiency, one a legend-defining area and the other a background-defining area, so as to form transparent sheeting containing legends which are obscure, i.e., invisible or only faintly visible to the naked eye, under diffuse light but are readily visible under retroreflective lighting conditions. The novel method may be performed on such sheeting to provide a sheet which contai~s both thè obscure or latent retroreflective legend disclosed by Sevelin and the directional images of this invention.
he partially light-transmissive mirror is typically coated directly on the rea~- ~ of the microlenses. In sheeting made with glass microspheres of 1.9 index of refraction partially embedded in, and partially exposed out of, the sheeting so as to have an air interface, white light is focused approximately at the rear of the microspheres. When such sheeting is irradiated with a laser beam of appropriate intensity, typically from 0.01 to 10 megawatts per square centimeter at~surface of the sheeting, and pulse duration, typically from 200 to 400 nanoseconds, cavities tend to be formed at the rear of the microspheres thereby leaving a distinctive marking in the sheeting.
The laser radiation may be directed to the sheet in a pattern, such as through a mask, to form markings at the rear of only a selected portion of the microlenses, or it may be applied uniformly over the whole surface of the sheeting. A sheet is regarded as "imaged" according to this invention whether it is prepared with selectively patterned or with whole-surface radiation, since in either case the sheet has a visibly distinctive appearance at certain angles of viewing and under certain lighting conditions.
A sheet bearing two directional images may be formed, if after directing a laser beam in an imagewise ~2~3%~
fashion at a sheet at a first selected angle of incidence, a laser beam is directed in imagewise fashion at the sheet at a different selected angle of incidence thereby forming two sets of markings. Further repetitions of the step may be performed to provide a sheet of the invention with more than two images. The angles of incidence selected may be spaced sufficiently far apart that the respective conical fields of view of the different images will not overlap or interfere with each other.
The novel method may also lead to other unique and unexpected visual effects. The set of markings formed in the sheeting by the laser beam are generally visible under ordinary diffuse lighting conditions within a conical field of view as a dark image. When viewed retroreflectively within that conical field of view, the set of markings is visible as an image which is darker than the surrounding retroreflecting background.
However, when viewed retroreflectively at an angle somewhat outside -that conical field of view, the set of markings can be visible as an image which is brighter than the surrounding retroreflecting background. This effect is seen within a region annular to the conical field of view, with the annular band typically being from 10 to 40 wide. When viewed at an angle outside this annular region of brighter retroreflectivity, the set of axial markings is indistinguishable from the surrounding background and no image is visible.
The precise cause of the annular region of bright retroreflectivity of the set of markings is not fully understood. One explanation is that the laser irradiation may cause separations between the microlenses and the underlying dielectric layer surrounding the primary deformations from which the dark image results.
This separation, if it exists, may provide another surface or optical spacing distance which increases the retroreflectivity of the markings when viewed within the region annular to the conical field of view of the ~2~32~
g dark image.
Another unexpected visual effect may be achieved with sheeting that comprises a monolayer of microlenses, but is free of a dielectric mirror. When irradiated with a laser beam according to the method of this invention, an i~age is formed which is nondirectional under diffuse light. The image is viewable across a wide angle, generally from any angle at which the sur~ace of the sheeting is visible. Under retroreflective conditions, the image exhibits directionality characteristics similar to those of images formed in sheetings which comprise a dielectric mirror disposed behind the monolayer of microlenses.
Because the sheets formed according to the novel method are transparent, they can easily be adapted to be adhesively bonded over the information areas of a document. Strong transparent adhesives are available which will form such a firm bond to a document that the overlying sheet cannot be removed without visibly damaging the document and sheet, thereby malcing such overlays a secure means for authenticating a document to which they might be attached. The sheets can be very thin and flimsy, essentially comprising only a layer of microlenses, a layer of binder material in which the microlenses are embedded, a partially light transmissive ~5 mirror, and optimally an additional adhesive layer.
In one embodiment, as an authenticating device for instance, the image may be made so as to be visible at an angle at which a document is not normally viewed so as not to interfere appreciably with the legibility of the underlying information such as written or printed matter or a photograph. When placed as an overlay directly on the in~ormation bearing portion of a document, a driver's license for instance, the sheet prevents tampering with the information and provides a secure form of 35 ~authentication that does not interfere with the normal use of the document. In another embodiment, the image may be made so as to be visible at an angle at which ~Z63Z~i~
a document is normally viewed to ensure that the imaye is brought to a reader's attention.
An advantage of this invention is that a transparent sheet which has already been adhered as an overlay may have a directional image formed therein.
This capability allows the information borne by an overlay to be updated and makes more convenient the formation of a limited number of sheets with a particular image contained therein. For instance, a driver's license which had been originally issued with a novel sheet of the invention applied as an overlay as a means of authentication might have a special message, such as a restriction to correc-tive lenses, incorporated therein at a later date. The restriction can be incorporated in the existing license, thereby avoiding the expense and delay of issuing a replacement. The newly added information will achieve the same degree of security as the images originally contained therein.
Transparen-t sheets bearing directional images have many uses, most notably as authenticating images or overlays used to ensure that documents, products, or any articles to which they might be attached are genuine. Such sheets can be used by manufacturers or sellers of name brand products to prevent passing off of counterfeit products. The ability to make sheets bearing multiple images further increases this utili-ty.
An advantage of the sheets of this invention is the difficulty of removing or tampering with the image without destroying the structural integrity of the sheet. Further, duplicating or reproducing the images would be difficult without expensive and sophisticated equipment and know-how.
Possible uses for sheets imaged according to this invention include driver's licenses, passports, bank cards, credit cards, and identification cards.
Other applications wherein the sheets or method of this invention will be useful will be obvious to those skilled in the art.
, .. .
~;326~
Description O~ Drawings FIGU~ES 1-2 are schematic sections through fragments of sheets with different embodiments which are examples of some of the sheets which may be imaged according to this invention.
FIGURE 1 shows a substantially transparent retroreflective sheet comprising a monolayer of microlenses
TRANSPARENT RETROREFLECTIVE SHEETS CONTAINING
_ . _ DIRECTIONAL IMAGES AND METHOD
FOR FORMING THE SAME
. _ _ Field of Invention _ This invention primarily concerns a substantially transparent sheet which includes a partially light transmissive mirror to make the sheeting retroreflective under retroreflective viewing conditions, and which further contains a directional imaye, i.e., an image that is viewable only within a restricted conical field of view of predetermined angular width and central axis.
This invention also concerns a method for forming such sheets.
Background Art Sheeting in which an image of a pattern or legend is built has found a number of important uses, particularly as distinctive labels useful to authenticate an article or document. Such sheeting has found use as validation stickers for vehicle license plates and as security films for driver's licenses, government documents, phonograph records, tape cassettes, and the like, as taught in U.S. Pat. Nos. 3,154,872; 3,801,183 4,082,426; and 4,099,838. In each of the patents, the built-in images must be incorporated into the sheeting while the sheeting is being constructed.
Sevelin et al., U.S. Pat. No. 3,801,183, discloses a substantially transparent sheeting to be used as an overlay on a document such as a credit card, a pass, ~a license or phonograph~label to serve as an identifying ~- or~authenticating means. The sheet is retroreflective over its entire surface~area and contains a retroreflecting pattern or legend which lS obscure in that it is invisible or only faintly visible to the naked eye under diffuse light and does not obstruct any underlying visual information.
Nordgren, U.S. Pat. No. 3,154,872, and Brown, .
;
U.S. Pat. No. 4,082,426, teach other retroreflective sheets containing images that may be obscure, which sheets can be adhesively bonded to documents to make counterfeiting more difficult. The imaged sheets disclosed in those patents are not transparent, however, and so would obstruct information over which they were applied.
Other methods have been developed which use laser irradiation of a sheet material to form directional images therein. These methods rely on opaque masking layers to focus the laser light to a damage locus within a monolayer of microlenses, or to themselves absorb radiation and develop deformations which are viewable as a directional image. If a transparent sheet containing a directional image is desired the opaque masking must be removed after formation of the visible deformations.
Galanos, U.S. Pat. No. 4,200,875, discloses a method of forming directional images in opaque retroreflective sheeting which comprises a specular reflecting layer disposed behind a monolayer of glass microspheres. In that method, laser irradiation of the retroreflective sheeting in an imagewise fashion causes visible structural alterations or modifications in the sheet which are viewable as directional images. Because the Galanos sheeting is opaque, it would obstruct underlying information if adhered to a document as an overlay.
~ ockert et al., Jap. Appln. No. 19824/84, filed February 6, 1984, Kokai No. 148004/84, laid open August 24, 1984, forms a directional image in sheeting which comprises a monolayer of microlenses, a masking layer disposed behind the monolayer of microlenses, and a transparent spacing layer located between those ; ~ two layers. Laser irradiation of the sheeting forms openings in the masking layer which are visible as a directional image. By coloring the transparent spacer layer through the openings and then removing the masking layer, such as with a chemical etch, one can obtain a transparent sheet containing a directional image.
... ~, ,. ~
_3_ The sheet may then be adhered to a document as an overlay which provides a secure means of authenticating the document without interfering with the normal use of the information contained thereon~
y__f_Invention This invention provides a method whereby directional images may be directly formed in transparent sheeting comprising a monolayer of microlenses and that, in most embodiments of the invention, comprises a partially light transmissive mirror, and further provides novel sheets made according to the new method.
By the present invention, directional images may even be formed in a piece of such sheeting that has already been applied as an overlay on a document such as a driver's license or passport.
The images formed according to this method are viewable both under diffuse light and under retroreflective conditions.
More particularly, according to one aspect, the invention provides a substantially transparent sheet comprising a monolayer of microlenses and a partially light transmissive mirror disposed behind the rear surfaces of at least some of said microlenses such that under retroreflective viewing conditions the sheet is brightly retroreflective in the areas occupied by the mirror, there being an axial marking in the rear portion of or on the rear surface of at least some of the microlenses, which markings together are viewable as an image across a predetermined coDicaI field in ordinary diffuse light conditions.
~: :
:~:
.~. ,....
~26326~
-3a-According to a second aspect, the invention provides a substantially transparent sheet comprising a monolayer of microlenses, there being an axial marking in the rear portion of or on the rear surface of at least some of the microlenses which markings together are viewable as an imaye from the front of the sheeting in ordinary diffuse light conditions, and under retroreflective conditions are viewable as a dark image across a predetermined conical field of view and are viewable as a bright image within a region annular to said conical field of view.
According to a third aspect, the invention provides a method of forming directional images in substantially trans-parent sheeting comprising a monolayer of closely spaced micro-lenses and a partially light transmissive mirror disposed at the rear surfaces of at least some of said microlenses, said method comprising directing a laser beam at a selected angle of incid-ence to the face of said sheeting, the wavelength of the laser being selected such that the beam is focused by the microlenses to form a marking in the rear portion of or on the rear surface of each microlens which said beam strikes.
A sheeting of the invention, with its combination of directional images and partially light transmissive mirror, offers unlque benefits as a secuxity film. Although the sheeting is ~transparent, the partially light transmlssive mirror makes the sheeting retroreflective when viewed under retroreflective view-ing conditions. As taught in Sevelin et al., U.S. Patent No.
:
~3~
-3b~
3,801,183, the mirror may be patterned, with some areas of the mirror having greater reflective efficiency than other areas, so that under retroreflective viewing conditions, a viewer discovers retroreflective images hidden within the sheeting.
Insofar as known, the combination in a transparent film of hidden retroreflective images and images tha-t are visible under ordinary diffuse lighting conditions only within a limited conical field of view, has never before been provided. This combination of features offers a unique set of criteria by which the authenticity of a document overlaid with the film can be judged.
3L2~i3~
Sheeting as described can be prepared by directing a suitable laser beam in an imagewise fashion at a selected angle of incidence to the face of the sheeting. The wavelength of the laser beam is selected such that it is focused by microlenses to form discrete rnarkings in the sheeting at the rear of each microlens which the beam strikes. Each microlens focuses the laser light incident upon it to a small spot -- having a diameter that is only a small fraction of the diameter of the microlens -- to create a localized marking, e.g., a cavity within an individual microlens, a cavity opening through the back of a microlens, an opening, charring, or other modifica-tion within the partially light transmissive mirror, or some combination among these various modifications. These markings may be termed "axial markings", in that the marking associated wi-th each microlens is centered on an axis that extends through the optical center of the microlens and is parallel to, or intersects at a common viewing point or line, the similar axes for -the other deformed microlenses in the image area. The resulting set of markings is visible as an image at the angle of incidence of the imaging laser beam.
Detailed Description Sheeting to be imaged according to the novel method comprises a monolayer of microlenses embedded in a layer of binder material. The binder material is typically a substantially transparent polymeric material, such as an alkyd resin, polyurethane, or ethylene vinyl acetate. The microlenses are preferably spherical because they may be imaged from virtually any angle of incidence.
Microlenses with different geometries may be restricted to narrower angles of effectiveness. An example of nonspherical microlenses is disclosed in de Montebello, U.S. Pat. 3,503,315. Glass microlenses are preferred because they tend to be more durable than microlenses ., .
~g~3~6f~
~5--formed from other materials.
Microspheres with a refractive index within a range of 1.5 to 2.7 are useful. Ho~ever, microspheres with refractive indices above 2.4 may introduce coloring, whereas colorless clarity is usually preferred so that the sheet may be as unobtrusive as possible when applied to a document as an authenticating means. Microspheres with a refractive index of approximately 1.8 to 1.9 are preferred, because when partially embedded in the support film and partially exposed above the support film, they will focus whi-te light at approximately the back surface of the microsphere.
The glass microspheres preferably have an average diameter of 10 to 100 micrometers, and are ideally of a uniform diameter of approximately 50-60 micrometers.
If the microspheres are much larger, the shee-ting tends to become thicker and more expensive to make, and images formed thereon will have less resolution. If the microspheres are much smaller, images formed on the sheeting will have greater resolution, but it is more difficult to uniformly distribute the microlenses when constructing the sheet, and the images formed thereon are less bright because of diffraction losses.
The set of axial markings is visible within a conical ~ield of view whose central axis is determined by the angle of incidence at which the imaging beam is directed to the sheeting. The angular width of the conical field of view is related to the size of the markings. Larger markings are visible as an image across a wider field of view than are smaller markings. The size of a marking is determined by the energy density of the irradiation applied to the sheeting which creates the marking. If a higher-energy-density beam is used to form the deformities, the image will have a wider conical field of view. Similarly, if a beam with a lower energy density is used, the image will have a narrower conical field of view.
~2 66~
Preferably the novel method of this invention employs a laser which has sufficient power to cause an axial marking associated with each of the microlenses which the laser beam strikes. Typically in the case of glass microlenses, a laser adjusted so as to provide a power density of approximately one megawatt per square centimeter at the sheeting's surface is useful. Suitable lasers include pulsed, ~4ff~-optically Q-switched Nd:~AG (Neodymium: Yttrium Aluminum Garnet) lasers, such as the Model 512Q laser available from Con-trol Laser Corporation of Orlando, Florida, which, equipped with a frequency doubler, emits a beam with a wavelength of 532 nanometers in pulses of approximately 200 to 400 nanoseconds in dura-tion.
When forming images on sheeting which comprises a monolayer of the preferred glass microspheres having a diameter of approximately 50-60 micrometers, the laser beam is preferably adjusted to form axial markings having diameters within a range from 1 to 20 micrometers. When the microlenses are substantially all about 50-60 micrometers in diameter and the average diameter of the markings is from 3 to 10 micrometers, each authentica-ting image is viewable under ordinary diffuse lighting conditions only across a cone of about 10 to 20 degrees. Images composed of larger markings are viewable within larger conical fields of view; however, there would seldom be any reason for a directional image to be visible across a cone exceeding 30 degrees. On the other hand, a directional image which was viewable only across a cone of less than six to eight degrees might be difficult to locate.
As previously indicated, most embodiments of sheeting of the invention include, in addition to a monolayer of microlenses, a semi-transparent, or partially light transmissive, dielectric mirror which reflects a portion of, and transmits another portion of, the light incident upon the microlenses. Such dielectric ~2~32~
mirrors are taught in Sevelin, wherein it is also taught to form such mirrors with at least two regions of different retroreflective efficiency, one a legend-defining area and the other a background-defining area, so as to form transparent sheeting containing legends which are obscure, i.e., invisible or only faintly visible to the naked eye, under diffuse light but are readily visible under retroreflective lighting conditions. The novel method may be performed on such sheeting to provide a sheet which contai~s both thè obscure or latent retroreflective legend disclosed by Sevelin and the directional images of this invention.
he partially light-transmissive mirror is typically coated directly on the rea~- ~ of the microlenses. In sheeting made with glass microspheres of 1.9 index of refraction partially embedded in, and partially exposed out of, the sheeting so as to have an air interface, white light is focused approximately at the rear of the microspheres. When such sheeting is irradiated with a laser beam of appropriate intensity, typically from 0.01 to 10 megawatts per square centimeter at~surface of the sheeting, and pulse duration, typically from 200 to 400 nanoseconds, cavities tend to be formed at the rear of the microspheres thereby leaving a distinctive marking in the sheeting.
The laser radiation may be directed to the sheet in a pattern, such as through a mask, to form markings at the rear of only a selected portion of the microlenses, or it may be applied uniformly over the whole surface of the sheeting. A sheet is regarded as "imaged" according to this invention whether it is prepared with selectively patterned or with whole-surface radiation, since in either case the sheet has a visibly distinctive appearance at certain angles of viewing and under certain lighting conditions.
A sheet bearing two directional images may be formed, if after directing a laser beam in an imagewise ~2~3%~
fashion at a sheet at a first selected angle of incidence, a laser beam is directed in imagewise fashion at the sheet at a different selected angle of incidence thereby forming two sets of markings. Further repetitions of the step may be performed to provide a sheet of the invention with more than two images. The angles of incidence selected may be spaced sufficiently far apart that the respective conical fields of view of the different images will not overlap or interfere with each other.
The novel method may also lead to other unique and unexpected visual effects. The set of markings formed in the sheeting by the laser beam are generally visible under ordinary diffuse lighting conditions within a conical field of view as a dark image. When viewed retroreflectively within that conical field of view, the set of markings is visible as an image which is darker than the surrounding retroreflecting background.
However, when viewed retroreflectively at an angle somewhat outside -that conical field of view, the set of markings can be visible as an image which is brighter than the surrounding retroreflecting background. This effect is seen within a region annular to the conical field of view, with the annular band typically being from 10 to 40 wide. When viewed at an angle outside this annular region of brighter retroreflectivity, the set of axial markings is indistinguishable from the surrounding background and no image is visible.
The precise cause of the annular region of bright retroreflectivity of the set of markings is not fully understood. One explanation is that the laser irradiation may cause separations between the microlenses and the underlying dielectric layer surrounding the primary deformations from which the dark image results.
This separation, if it exists, may provide another surface or optical spacing distance which increases the retroreflectivity of the markings when viewed within the region annular to the conical field of view of the ~2~32~
g dark image.
Another unexpected visual effect may be achieved with sheeting that comprises a monolayer of microlenses, but is free of a dielectric mirror. When irradiated with a laser beam according to the method of this invention, an i~age is formed which is nondirectional under diffuse light. The image is viewable across a wide angle, generally from any angle at which the sur~ace of the sheeting is visible. Under retroreflective conditions, the image exhibits directionality characteristics similar to those of images formed in sheetings which comprise a dielectric mirror disposed behind the monolayer of microlenses.
Because the sheets formed according to the novel method are transparent, they can easily be adapted to be adhesively bonded over the information areas of a document. Strong transparent adhesives are available which will form such a firm bond to a document that the overlying sheet cannot be removed without visibly damaging the document and sheet, thereby malcing such overlays a secure means for authenticating a document to which they might be attached. The sheets can be very thin and flimsy, essentially comprising only a layer of microlenses, a layer of binder material in which the microlenses are embedded, a partially light transmissive ~5 mirror, and optimally an additional adhesive layer.
In one embodiment, as an authenticating device for instance, the image may be made so as to be visible at an angle at which a document is not normally viewed so as not to interfere appreciably with the legibility of the underlying information such as written or printed matter or a photograph. When placed as an overlay directly on the in~ormation bearing portion of a document, a driver's license for instance, the sheet prevents tampering with the information and provides a secure form of 35 ~authentication that does not interfere with the normal use of the document. In another embodiment, the image may be made so as to be visible at an angle at which ~Z63Z~i~
a document is normally viewed to ensure that the imaye is brought to a reader's attention.
An advantage of this invention is that a transparent sheet which has already been adhered as an overlay may have a directional image formed therein.
This capability allows the information borne by an overlay to be updated and makes more convenient the formation of a limited number of sheets with a particular image contained therein. For instance, a driver's license which had been originally issued with a novel sheet of the invention applied as an overlay as a means of authentication might have a special message, such as a restriction to correc-tive lenses, incorporated therein at a later date. The restriction can be incorporated in the existing license, thereby avoiding the expense and delay of issuing a replacement. The newly added information will achieve the same degree of security as the images originally contained therein.
Transparen-t sheets bearing directional images have many uses, most notably as authenticating images or overlays used to ensure that documents, products, or any articles to which they might be attached are genuine. Such sheets can be used by manufacturers or sellers of name brand products to prevent passing off of counterfeit products. The ability to make sheets bearing multiple images further increases this utili-ty.
An advantage of the sheets of this invention is the difficulty of removing or tampering with the image without destroying the structural integrity of the sheet. Further, duplicating or reproducing the images would be difficult without expensive and sophisticated equipment and know-how.
Possible uses for sheets imaged according to this invention include driver's licenses, passports, bank cards, credit cards, and identification cards.
Other applications wherein the sheets or method of this invention will be useful will be obvious to those skilled in the art.
, .. .
~;326~
Description O~ Drawings FIGU~ES 1-2 are schematic sections through fragments of sheets with different embodiments which are examples of some of the sheets which may be imaged according to this invention.
FIGURE 1 shows a substantially transparent retroreflective sheet comprising a monolayer of microlenses
2 which are partially embedded in a transparent polymeric binder 4, and a semi-transparent dielectric mirror 6 which reflects a portion of, and transmits another portion of, the light passing through the outer surface of the microlenses. A discontinuous spacing layer 8, such as a varnish layer, changes the retroreflective efficiency of the dielectric mirror 6 to form an obscure retroreflectively viewable image 10 as taugh-t in Sevelin.
The embodiment shown is adapted to be bonded as a transparent overlay to a document or article with a transparent adhesive 12. According to the method of this invention, a laser beam 14 is directed to the sheet in an imagewise fashion at an incident angle O. The laser beam incident upon a microlens is focused at location 16 thereby forming a marking associated with each microlens which the beam strikes. The set of markings thus formed is disposed such that it is visible as a directional image 18.
FIGURE 2 shows another embodiment of a substantially -transparent retroreflec-tive sheet imaged according to this invention in which the monolayer of microlenses 2 is embedded in a permanent transparent coverinq 20. The obscure retroreflectively viewable image 10 is provided by the different retroreflective efficiency of the continuous semi-transparent dielectric mirror 22 and discontinuous semi-transparent dielectric mirror 24. Such sheetings are also taught in Sevelin.
A directional image 18 may be formed in such a sheeting according to this invention by ~ laser irradiation at an incident angle O with a laser beam 14 of suitable ~3~
wavelength.
The schematic drawings are not literal section views, e.g. since each circle represents a full circumference as though the microspheres were of uniform diameter and arranged in uniform rows.
The invention will now be more specifically described by the following non-limiting examples. In each instance, the following equipment was used: a Model 512Q Nd:YAG Laser available from the Control I,asex Company of Orlando, Florida which, equipped with a frequency doubler, emits a beam with a wavelength of 532 nanometers in pulses of approxima-tely 200 to 400 nanoseconds in duration; a Model 5-8 Frequency Doubler (Second Harmonic Generator) available from the Inrad Company of Northvale, New Jersey; a Model 201 power meter available from Coherent, Inc. of Palo Alto, California; and a 2X upcollimator manufactured by the Quantrad Corporation of Torrance, California.
Example 1 A piece of exposed-lens sheeting comprising a monolayer of protruding glass microspheres with a partially light transmissive dielectric mirror disposed on the underside of the microspheres was irradiated from the exposed-lens side with the laser beam. The microspheres had a refractive index of approximately 1.9 and the dielectric mirror comprised vapor-deposi~ed zinc sulfide. Such sheeting is disclosed in Sevelin, U.S. Pat. No. 3,801,183. The laser, equipped with the frequency doubler, was adjusted to direct a beam approximately 1.0 millimeter in diameter with an average power of approximately 400 milliwatts at an incident angle of 0, i.e., normali to the surface of the sheeting.
The pulse rate of the beam was approximately 2.6 kilohertz.
The sheeting was scanned with the laser by manually drawing the sheeting across the path of the beam at approximately 1 centimeter per second.
After laser irradiation an image was visible ~3~
under diffuse light in the irradiated areas of the sheet as a dark image in a conical field of view. The conical field had as its central axis the incident angle of the laser irradiation and was approximately 10 to 20 wide~ The image was visible within approximately the same conical field of view under retroreflective conditions as a dark irnage. When viewed under retroreflective conditions in an annular region or band approxirnately 40 wide outside the conical field the imaye was briyhter than the surrounding background.
After the image was examined, an epoxy resin was cured in contact with the exposed microspheres and the polymeric binder material and dielectric mirror were removed to expose the back surfaces of the microlenses.
When viewed with a scanning electron microscope, the microspheres in the image areas were seen to have what appeared to be a small cavity opening through their rear surface on an axis normal to the face of the shee-t.
Example 2 . . .
A piece of sheeting similar to tha-t in Example 1 was first laminated as a substantially transparent overlay to a sample driver's license which contained printed information. It was then irradiated according to the procedure and conditions outlined in Example 1.
The resultant image had characteristics similar to that formed in Example 1. The underlying printed information remained viewable under ordinary diffuse lighting conditions.
Example 3 A piece of sheeting similar to that in Example 1 was irradiated using the same procedure and conditions as in Example 1 except the laser was adjusted to an average power of approximately 300 milliwatts and a motorized translation stage was used to provide a scanning ~L2~ ;4 speed of approximately 0.65 inch per second.
The resultant image had characteristics similar to that formed in Example l.
Example 4 A piece of sheeting similar to that in Example l was irradiated usiny the same procedure ar.d conditions as in Example 3 except the laser was adjusted to an average power of approximately 250 milliwatts.
The resultant image had characteristics similar to that ~ormed in Example 1 except that both the conical field o~ view and the annular region of brighter retroreflectivity were a few degrees (approximately 5) narrower than in Example l.
Example 5 A piece of sheeting similar to that in Example l was irradiated using the same procedure and conditions as in Example 4 except the laser was adjusted to an average power of approximately 230 milliwatts.
The resultant image had characteristics similar to that ~ormed in Example 4.
Example 6 A piece of sheeting similar to that in Example l except it comprised no partially light -transmissive, dielectric mirror was irradiated from the exposed bead side using the same procedure and conditions as in Example 5 except the laser was adjusted to an average power of approximately 250 milliwatts and a beam diameter of approximately 0.3 millimeter.
The resultant image was visible under ordinary diffuse light conditions as a dark image over a wide angIe, essentially any angle from which the front of the sheeting was visible. Under retroreflective viewing conditions the image had similar characteristics as in Example 1, i.e., visible as a dark image within a ~2~3~
conical field of view approximately 10 to 2n wide and visible as a bright image in a region annular to the conical field.
.
" ,
The embodiment shown is adapted to be bonded as a transparent overlay to a document or article with a transparent adhesive 12. According to the method of this invention, a laser beam 14 is directed to the sheet in an imagewise fashion at an incident angle O. The laser beam incident upon a microlens is focused at location 16 thereby forming a marking associated with each microlens which the beam strikes. The set of markings thus formed is disposed such that it is visible as a directional image 18.
FIGURE 2 shows another embodiment of a substantially -transparent retroreflec-tive sheet imaged according to this invention in which the monolayer of microlenses 2 is embedded in a permanent transparent coverinq 20. The obscure retroreflectively viewable image 10 is provided by the different retroreflective efficiency of the continuous semi-transparent dielectric mirror 22 and discontinuous semi-transparent dielectric mirror 24. Such sheetings are also taught in Sevelin.
A directional image 18 may be formed in such a sheeting according to this invention by ~ laser irradiation at an incident angle O with a laser beam 14 of suitable ~3~
wavelength.
The schematic drawings are not literal section views, e.g. since each circle represents a full circumference as though the microspheres were of uniform diameter and arranged in uniform rows.
The invention will now be more specifically described by the following non-limiting examples. In each instance, the following equipment was used: a Model 512Q Nd:YAG Laser available from the Control I,asex Company of Orlando, Florida which, equipped with a frequency doubler, emits a beam with a wavelength of 532 nanometers in pulses of approxima-tely 200 to 400 nanoseconds in duration; a Model 5-8 Frequency Doubler (Second Harmonic Generator) available from the Inrad Company of Northvale, New Jersey; a Model 201 power meter available from Coherent, Inc. of Palo Alto, California; and a 2X upcollimator manufactured by the Quantrad Corporation of Torrance, California.
Example 1 A piece of exposed-lens sheeting comprising a monolayer of protruding glass microspheres with a partially light transmissive dielectric mirror disposed on the underside of the microspheres was irradiated from the exposed-lens side with the laser beam. The microspheres had a refractive index of approximately 1.9 and the dielectric mirror comprised vapor-deposi~ed zinc sulfide. Such sheeting is disclosed in Sevelin, U.S. Pat. No. 3,801,183. The laser, equipped with the frequency doubler, was adjusted to direct a beam approximately 1.0 millimeter in diameter with an average power of approximately 400 milliwatts at an incident angle of 0, i.e., normali to the surface of the sheeting.
The pulse rate of the beam was approximately 2.6 kilohertz.
The sheeting was scanned with the laser by manually drawing the sheeting across the path of the beam at approximately 1 centimeter per second.
After laser irradiation an image was visible ~3~
under diffuse light in the irradiated areas of the sheet as a dark image in a conical field of view. The conical field had as its central axis the incident angle of the laser irradiation and was approximately 10 to 20 wide~ The image was visible within approximately the same conical field of view under retroreflective conditions as a dark irnage. When viewed under retroreflective conditions in an annular region or band approxirnately 40 wide outside the conical field the imaye was briyhter than the surrounding background.
After the image was examined, an epoxy resin was cured in contact with the exposed microspheres and the polymeric binder material and dielectric mirror were removed to expose the back surfaces of the microlenses.
When viewed with a scanning electron microscope, the microspheres in the image areas were seen to have what appeared to be a small cavity opening through their rear surface on an axis normal to the face of the shee-t.
Example 2 . . .
A piece of sheeting similar to tha-t in Example 1 was first laminated as a substantially transparent overlay to a sample driver's license which contained printed information. It was then irradiated according to the procedure and conditions outlined in Example 1.
The resultant image had characteristics similar to that formed in Example 1. The underlying printed information remained viewable under ordinary diffuse lighting conditions.
Example 3 A piece of sheeting similar to that in Example 1 was irradiated using the same procedure and conditions as in Example 1 except the laser was adjusted to an average power of approximately 300 milliwatts and a motorized translation stage was used to provide a scanning ~L2~ ;4 speed of approximately 0.65 inch per second.
The resultant image had characteristics similar to that formed in Example l.
Example 4 A piece of sheeting similar to that in Example l was irradiated usiny the same procedure ar.d conditions as in Example 3 except the laser was adjusted to an average power of approximately 250 milliwatts.
The resultant image had characteristics similar to that ~ormed in Example 1 except that both the conical field o~ view and the annular region of brighter retroreflectivity were a few degrees (approximately 5) narrower than in Example l.
Example 5 A piece of sheeting similar to that in Example l was irradiated using the same procedure and conditions as in Example 4 except the laser was adjusted to an average power of approximately 230 milliwatts.
The resultant image had characteristics similar to that ~ormed in Example 4.
Example 6 A piece of sheeting similar to that in Example l except it comprised no partially light -transmissive, dielectric mirror was irradiated from the exposed bead side using the same procedure and conditions as in Example 5 except the laser was adjusted to an average power of approximately 250 milliwatts and a beam diameter of approximately 0.3 millimeter.
The resultant image was visible under ordinary diffuse light conditions as a dark image over a wide angIe, essentially any angle from which the front of the sheeting was visible. Under retroreflective viewing conditions the image had similar characteristics as in Example 1, i.e., visible as a dark image within a ~2~3~
conical field of view approximately 10 to 2n wide and visible as a bright image in a region annular to the conical field.
.
" ,
Claims (17)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A substantially transparent sheet comprising a mono-layer of microlenses and a partially light transmissive mirror disposed behind the rear surfaces of at least some of said microlenses such that under retroreflective viewing conditions the sheet is brightly retroreflective in the areas occupied by the mirror, there being an axial marking in the rear portion of or on the rear surface of at least some of the microlenses, which markings together are viewable as an image across a predetermined conical field in ordinary diffuse light conditions.
2. A sheet as defined in claim 1, wherein the microlenses and associated partially light transmissive mirror in a first, legend defining area have a different retroreflective efficiency than the microlenses and associated partially light transmissive mirror in a second, background defining area such that said sheet has retroreflective legend areas and retroreflective background areas, which areas are substantially indistinguishable under ordinary diffuse light viewing conditions, but which are readily visually discernable from one another under retroreflective conditions.
3. A sheet as defined in claim 1, wherein the microlenses partially protrude from the front of the sheet.
4. A sheet as defined in claim 1, wherein said micro-lenses are microspheres.
5. A sheet as defined in claim 4, wherein said micro-spheres are glass.
6. A sheet as defined in claim 4, wherein said micro-spheres have a refractive index of about 1.9.
7. A sheet comprising a monolayer of microspheres which partially protrude from the front of said sheet, at least some of the microspheres having a marking in their embedded portion, which markings together are viewable across a predetermined conical field of view in ordinary diffuse light as an image, and a partially light transmissive mirror disposed behind the rear surfaces of some of the microspheres such that under retrore-flective viewing conditions the sheeting is brightly retrore-flective in the areas occupied by the mirror.
8. A sheet as defined in claim 7, wherein the micro-spheres and associated partially light transmissive mirror in a first, legend defining area have a different retroreflective efficiency than the microspheres and associated partially light transmissive mirror in a second, background defining area such that said sheet has retroreflective legend areas and retrore-flective background areas, which areas are substantially indistinguishable under ordinary diffuse light viewing con-ditions, but which are readily discernable from one another under retroreflective conditions.
9. A substantially transparent sheet comprising a mono-layer of microlenses, there being an axial marking in the rear portion of or on the rear surface of at least some of the micro-lenses which markings together are viewable as an image from the front of the sheeting in ordinary diffuse light conditions, and under retroreflective conditions are viewable as a dark image across a predetermined conical field of view and are viewable as a bright image within a region annular to said conical field of view.
10. A sheet as defined in claim 9, in which the markings are viewable as an image across a wide angle under ordinary diffuse light conditions.
11. A method of forming directional images in substantially transparent sheeting comprising a monolayer of closely spaced microlenses and a partially light transmissive mirror disposed at the rear surfaces of at least some of said microlenses, said method comprising directing a laser beam at a selected angle of incidence to the face of said sheeting, the wavelength of the laser being selected such that the beam is focused by the micro-lenses to form a marking in the rear portion of or on the rear surface of each microlens which said beam strikes.
12. A method as defined in claim 11, wherein said micro-lenses are microspheres.
13. A method as defined in claim 12, wherein said micro-spheres are glass.
14. A method as defined in claim 12, wherein said micro-spheres have a refractive index of about 1.9.
15. A method as defined in claim 11, further comprising adapting said sheeting to be adhesively bonded over the informat-ion area of a document without appreciably interfering with the legibility of that information.
16. A method as defined in claim 11, wherein said laser beam has a wavelength of approximately 532 nanometers, a pulse duration of from approximately 200 to 400 nanoseconds, a pulse frequency of from approximately 2 to 10 kilohertz, and a power intensity at the surface of said sheeting of approximately from 0.01 to 10.0 megawatts per square centimeter.
17. A method as defined in claim 11, wherein said sheeting has been adhesively bonded over the information area of a document without appreciably interfering with the legibility of that information before said laser beam has been directed at the face of said sheeting.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/733,067 US4688894A (en) | 1985-05-13 | 1985-05-13 | Transparent retroreflective sheets containing directional images and method for forming the same |
| US733,067 | 1985-05-13 | ||
| US06/733,066 US4691993A (en) | 1985-05-13 | 1985-05-13 | Transparent sheets containing directional images and method for forming the same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1263264A true CA1263264A (en) | 1989-11-28 |
Family
ID=27112518
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000506782A Expired CA1263264A (en) | 1985-05-13 | 1986-04-16 | Transparent retroreflective sheets containing directional images and method for forming the same |
| CA000508200A Expired CA1250952A (en) | 1985-05-13 | 1986-05-02 | Transparent sheets containing directional images and method for forming the same |
Family Applications After (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000508200A Expired CA1250952A (en) | 1985-05-13 | 1986-05-02 | Transparent sheets containing directional images and method for forming the same |
Country Status (8)
| Country | Link |
|---|---|
| US (2) | US4688894A (en) |
| EP (1) | EP0203752B1 (en) |
| JP (1) | JP2637952B2 (en) |
| KR (1) | KR940008669B1 (en) |
| AT (1) | ATE79182T1 (en) |
| AU (1) | AU589173B2 (en) |
| CA (2) | CA1263264A (en) |
| DE (1) | DE3686293T2 (en) |
Families Citing this family (90)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3905481C2 (en) * | 1988-02-23 | 2003-01-09 | Sony Corp | Method and device for optical data traffic |
| NL8802472A (en) * | 1988-10-10 | 1990-05-01 | Homer Hollandse Meet En Regels | DOCUMENT INCLUDING RANDOM INFORMATION, CARRIER OF THIS RANDOM INFORMATION AND METHOD AND DEVICE FOR READING THIS RANDOM INFORMATION. |
| JP2958964B2 (en) * | 1989-02-14 | 1999-10-06 | ソニー株式会社 | Retroreflective adhesive sheet |
| US4968063A (en) * | 1989-09-19 | 1990-11-06 | Minnesota Mining And Manufacturing Company | Transparent tamper-indicating document overlay |
| US5060981A (en) * | 1989-09-19 | 1991-10-29 | Minnesota Mining And Manufacturing Company | Transparent overlay for protecting a document from tampering |
| US5079644A (en) * | 1990-09-21 | 1992-01-07 | Elliott Richard C | Multi-layered reflective structure and method of making same |
| US5254390B1 (en) * | 1990-11-15 | 1999-05-18 | Minnesota Mining & Mfg | Plano-convex base sheet for retroreflective articles |
| US5420720A (en) * | 1992-06-25 | 1995-05-30 | Lockheed Missiles & Space Company, Inc. | Internally cooled large aperture microlens array with monolithically integrated microscanner |
| US5310623A (en) * | 1992-11-27 | 1994-05-10 | Lockheed Missiles & Space Company, Inc. | Method for fabricating microlenses |
| US5497269A (en) * | 1992-06-25 | 1996-03-05 | Lockheed Missiles And Space Company, Inc. | Dispersive microlens |
| US5444572A (en) * | 1992-11-27 | 1995-08-22 | Lockheed Missiles & Space Company, Inc. | Wavefront corrector for scanning microlens arrays |
| GB9309673D0 (en) * | 1993-05-11 | 1993-06-23 | De La Rue Holographics Ltd | Security device |
| AU3693395A (en) * | 1994-05-12 | 1995-12-05 | Minnesota Mining And Manufacturing Company | Retroreflective article and method of making same |
| US5591527A (en) * | 1994-11-02 | 1997-01-07 | Minnesota Mining And Manufacturing Company | Optical security articles and methods for making same |
| AU703068B2 (en) * | 1994-11-29 | 1999-03-11 | Minnesota Mining And Manufacturing Company | Transparent decorative article having an etched appearing/prismatic image thereon |
| US5638228A (en) * | 1995-02-14 | 1997-06-10 | Iomega Corporation | Retroreflective marker for data storage cartridge |
| US5986838A (en) * | 1995-02-14 | 1999-11-16 | Iomega Corporation | Thin retroreflective marker for data storage cartridge |
| AU6338096A (en) * | 1995-06-29 | 1997-01-30 | Minnesota Mining And Manufacturing Company | Rainbow sheeting having distinct color changes and/or hidden images |
| US5656360A (en) * | 1996-02-16 | 1997-08-12 | Minnesota Mining And Manufacturing Company | Article with holographic and retroreflective features |
| GB9604048D0 (en) * | 1996-02-26 | 1996-04-24 | Grossman Stanley I | Labelling device and label |
| US6086707A (en) * | 1996-02-29 | 2000-07-11 | Raytheon Company | Method for making an identification document |
| US5882771A (en) * | 1996-04-10 | 1999-03-16 | Minnesota Mining And Manufacturing Company | Conformable embossable retroreflective sheeting |
| JPH10170710A (en) * | 1996-12-12 | 1998-06-26 | Minnesota Mining & Mfg Co <3M> | Light retroreflective sheet |
| US6201662B1 (en) * | 1998-09-25 | 2001-03-13 | Iomega Corporation | Latent illuminance discrimination marker with reflective layer for data storage cartridges |
| US5940212A (en) * | 1997-10-30 | 1999-08-17 | 3M Innovative Properties Company | Cube corner article with altered inactive areas and method of making same |
| US6282026B1 (en) | 1998-02-05 | 2001-08-28 | 3M Innovative Properties Company | Retroreflectors having two optical surfaces and varying retroreflectivity |
| US6045230A (en) * | 1998-02-05 | 2000-04-04 | 3M Innovative Properties Company | Modulating retroreflective article |
| US6372341B1 (en) | 1998-04-27 | 2002-04-16 | 3M Innovative Properties Company | Tampa-indicating article for reusable substrates |
| EP0997750B1 (en) * | 1998-10-30 | 2005-05-04 | Avery Dennison Corporation | Retroreflective sheeting containing a validation image and methods of making the same |
| DE19907940A1 (en) * | 1999-02-24 | 2000-08-31 | Bundesdruckerei Gmbh | Process for the production of multi-layer security products and a security product produced by the process |
| GB9918617D0 (en) * | 1999-08-07 | 1999-10-13 | Epigem Limited | An optical display composite |
| US7336422B2 (en) * | 2000-02-22 | 2008-02-26 | 3M Innovative Properties Company | Sheeting with composite image that floats |
| US6288842B1 (en) | 2000-02-22 | 2001-09-11 | 3M Innovative Properties | Sheeting with composite image that floats |
| US7068434B2 (en) | 2000-02-22 | 2006-06-27 | 3M Innovative Properties Company | Sheeting with composite image that floats |
| US6500526B1 (en) | 2000-09-28 | 2002-12-31 | Avery Dennison Corporation | Retroreflective sheeting containing a validation image and methods of making the same |
| US20020045028A1 (en) | 2000-10-10 | 2002-04-18 | Takayuki Teshima | Microstructure array, mold for forming a microstructure array, and method of fabricating the same |
| US7255909B2 (en) * | 2002-02-19 | 2007-08-14 | 3M Innovative Properties Company | Security laminate |
| US20030184636A1 (en) * | 2002-02-19 | 2003-10-02 | Graham Paul D. | Image receptive material comprising cationically charged inorganic particles |
| US7036944B2 (en) * | 2002-04-11 | 2006-05-02 | 3M Innovative Properties Company | Retrochromic articles |
| US6978896B2 (en) * | 2002-04-11 | 2005-12-27 | 3M Innovative Properties Company | Method of making retrochromic beads and kit thereof |
| AU2003243471B2 (en) * | 2002-06-13 | 2007-10-11 | 3M Innovative Properties Company | System of controlled certificate production and management |
| US8867134B2 (en) * | 2003-11-21 | 2014-10-21 | Visual Physics, Llc | Optical system demonstrating improved resistance to optically degrading external effects |
| DE202004021714U1 (en) * | 2003-11-21 | 2010-09-23 | Visual Physics, Llc | Micro-optical security and image presentation system |
| US7648744B2 (en) * | 2004-08-06 | 2010-01-19 | 3M Innovative Properties Company | Tamper-indicating printable sheet for securing documents of value and methods of making the same |
| US7658980B2 (en) * | 2004-08-06 | 2010-02-09 | 3M Innovative Properties Company | Tamper-indicating printable sheet for securing documents of value and methods of making the same |
| US7616332B2 (en) | 2004-12-02 | 2009-11-10 | 3M Innovative Properties Company | System for reading and authenticating a composite image in a sheeting |
| MX2007014362A (en) * | 2005-05-18 | 2008-04-22 | Nanoventions Holdings Llc | Image presentation and micro-optic security system. |
| KR101293027B1 (en) * | 2005-06-16 | 2013-08-16 | 애버리 데니슨 코포레이션 | Retroreflective sheet structure |
| RU2422862C2 (en) * | 2005-09-26 | 2011-06-27 | Эвери Деннисон Копэрейшн | Retroreflective coating (versions) |
| US7981499B2 (en) * | 2005-10-11 | 2011-07-19 | 3M Innovative Properties Company | Methods of forming sheeting with a composite image that floats and sheeting with a composite image that floats |
| GB2433637A (en) * | 2005-12-21 | 2007-06-27 | 3M Innovative Properties Co | Semi-transparent retroreflective material |
| GB0602105D0 (en) * | 2006-02-02 | 2006-03-15 | 3M Innovative Properties Co | License plate assembly |
| US8284492B2 (en) * | 2006-05-12 | 2012-10-09 | Crane & Co., Inc. | Micro-optic film structure that alone or together with a security document or label projects images spatially coordinated with static images and/or other projected images |
| JP4614456B2 (en) * | 2006-07-07 | 2011-01-19 | 国立大学法人 東京大学 | Retroreflective material, projection device, aircraft, and aircraft simulator |
| US7586685B2 (en) * | 2006-07-28 | 2009-09-08 | Dunn Douglas S | Microlens sheeting with floating image using a shape memory material |
| US7951319B2 (en) * | 2006-07-28 | 2011-05-31 | 3M Innovative Properties Company | Methods for changing the shape of a surface of a shape memory polymer article |
| US20080027199A1 (en) | 2006-07-28 | 2008-01-31 | 3M Innovative Properties Company | Shape memory polymer articles with a microstructured surface |
| RU2422303C2 (en) | 2006-08-23 | 2011-06-27 | Ниппон Карбайд Когио Кабусики Кайся | Vehicle numberplate and retroreflecting sheet used for it |
| US20100028619A1 (en) * | 2006-09-11 | 2010-02-04 | 3M Innovative Properties Company | Card with a tearable security laminate |
| US7800825B2 (en) | 2006-12-04 | 2010-09-21 | 3M Innovative Properties Company | User interface including composite images that float |
| BRPI0811820A2 (en) | 2007-07-11 | 2014-11-04 | 3M Innovative Properties Co | "LAMINATED MATERIAL WITH FLOATING PICTURE IMAGE" |
| WO2009070434A1 (en) | 2007-11-27 | 2009-06-04 | 3M Innovative Properties Company | Methods for forming sheeting with a composite image that floats and a master tooling |
| US8111463B2 (en) | 2008-10-23 | 2012-02-07 | 3M Innovative Properties Company | Methods of forming sheeting with composite images that float and sheeting with composite images that float |
| US7995278B2 (en) | 2008-10-23 | 2011-08-09 | 3M Innovative Properties Company | Methods of forming sheeting with composite images that float and sheeting with composite images that float |
| US20120099200A1 (en) | 2009-07-17 | 2012-04-26 | Nippon Carbide Industries Co., Inc. | Retroreflective sheeting of micro glass sphere provided with image having visual direction |
| CA2769301C (en) * | 2009-08-12 | 2018-09-18 | Visual Physics, Llc | A tamper indicating optical security device |
| BR112012004113B1 (en) | 2009-08-25 | 2019-12-10 | Avery Dennison Corp | retro-reflective article with recorded image |
| JP5500548B2 (en) * | 2010-07-01 | 2014-05-21 | 独立行政法人 国立印刷局 | Latent image forming body |
| US8622555B2 (en) | 2010-08-31 | 2014-01-07 | 3M Innovative Properties Company | Security article having a switching feature |
| JP5558591B2 (en) | 2011-01-19 | 2014-07-23 | 日本カーバイド工業株式会社 | A micro glass sphere retroreflective sheet on which images with viewing directionality are installed |
| CA2825655C (en) | 2011-01-28 | 2019-04-30 | Crane & Co., Inc. | A laser marked device |
| GB2493369B (en) * | 2011-08-02 | 2013-09-25 | Rue De Int Ltd | Improvements in security devices |
| EP2745165B9 (en) | 2011-08-19 | 2018-07-18 | Visual Physics, LLC | Optionally transferable optical system with a reduced thickness |
| BR112014006707A2 (en) | 2011-09-23 | 2017-03-28 | 3M Innovative Properties Co | retroreflective articles that include a security mark |
| EP2758813B1 (en) | 2011-09-23 | 2018-06-06 | 3M Innovative Properties Company | Retroreflective articles including a security mark |
| CN102692660B (en) * | 2012-02-29 | 2014-10-15 | 3M中国有限公司 | Product capable of realizing 3D floating images and manufacturing method thereof |
| JP6053932B2 (en) | 2012-08-17 | 2016-12-27 | ビジュアル フィジクス エルエルシー | The process of transferring the microstructure to the final substrate |
| EP2969585B1 (en) | 2013-03-15 | 2019-04-24 | Visual Physics, LLC | Optical security device |
| US9873281B2 (en) | 2013-06-13 | 2018-01-23 | Visual Physics, Llc | Single layer image projection film |
| US10766292B2 (en) | 2014-03-27 | 2020-09-08 | Crane & Co., Inc. | Optical device that provides flicker-like optical effects |
| AU2015235889B2 (en) | 2014-03-27 | 2018-10-11 | Visual Physics, Llc | An optical device that produces flicker-like optical effects |
| EP3140684A1 (en) | 2014-05-09 | 2017-03-15 | 3M Innovative Properties Company | Colored retroreflective articles |
| EP3169531B1 (en) | 2014-07-17 | 2019-03-06 | Visual Physics, LLC | An improved polymeric sheet material for use in making polymeric security documents such as banknotes |
| KR102497982B1 (en) | 2014-09-16 | 2023-02-09 | 크레인 시큐리티 테크놀로지스, 인크. | Secure lens layer |
| KR20170110699A (en) | 2015-02-11 | 2017-10-11 | 크레인 앤 코, 인크 | Method for surface application of a security device to a substrate |
| DE102016106065A1 (en) | 2016-04-04 | 2017-10-05 | Erich Utsch Ag | A method of manufacturing a retroreflective license plate, retroreflective license plate and apparatus for carrying out the method |
| US11132554B2 (en) | 2016-05-13 | 2021-09-28 | 3M Innovative Properties Company | Counterfeit detection of an optically active article using security elements |
| CN110582412B (en) | 2017-02-10 | 2022-08-30 | 克瑞尼股份有限公司 | Machine readable optical security device |
| US11406473B2 (en) | 2018-08-29 | 2022-08-09 | Brainlab Ag | Engraved retro-reflective tracking marker |
| US20210097313A1 (en) * | 2020-11-27 | 2021-04-01 | Intel Corporation | Methods, systems, and devices for verifying road traffic signs |
Family Cites Families (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3154872A (en) * | 1963-02-13 | 1964-11-03 | Minnesota Mining & Mfg | Tamper-proof markings for reflecting structures |
| US3530779A (en) * | 1966-12-01 | 1970-09-29 | John W Alofs | Three-dimensional photography |
| US3503315A (en) * | 1966-12-12 | 1970-03-31 | Lucas Industries Ltd | Integral photography |
| US3573954A (en) * | 1967-07-05 | 1971-04-06 | Nihon Koken Co Ltd | Reflex-reflectors and method for the manufacture thereof |
| US3801183A (en) * | 1973-06-01 | 1974-04-02 | Minnesota Mining & Mfg | Retro-reflective film |
| US4099838A (en) * | 1976-06-07 | 1978-07-11 | Minnesota Mining And Manufacturing Company | Reflective sheet material |
| US4082426A (en) * | 1976-11-26 | 1978-04-04 | Minnesota Mining And Manufacturing Company | Retroreflective sheeting with retroreflective markings |
| US4200875A (en) * | 1978-07-31 | 1980-04-29 | The United States Of America As Represented By The Secretary Of The Air Force | Apparatus for, and method of, recording and viewing laser-made images on high gain retroreflective sheeting |
| JPS5941162A (en) * | 1982-08-30 | 1984-03-07 | Yaskawa Electric Mfg Co Ltd | Measuring device of resistance between bars of squirrel-cage type rotor |
| US4634220A (en) * | 1983-02-07 | 1987-01-06 | Minnesota Mining And Manufacturing Company | Directionally imaged sheeting |
| US4645301A (en) * | 1983-02-07 | 1987-02-24 | Minnesota Mining And Manufacturing Company | Transparent sheet containing authenticating image and method of making same |
| US4650283A (en) * | 1984-08-03 | 1987-03-17 | Minnesota Mining And Manufacturing Company | Directionally imaged retroreflective sheeting |
-
1985
- 1985-05-13 US US06/733,067 patent/US4688894A/en not_active Expired - Lifetime
- 1985-05-13 US US06/733,066 patent/US4691993A/en not_active Expired - Lifetime
-
1986
- 1986-04-16 CA CA000506782A patent/CA1263264A/en not_active Expired
- 1986-04-23 AU AU56545/86A patent/AU589173B2/en not_active Expired
- 1986-05-02 KR KR1019860003440A patent/KR940008669B1/en not_active IP Right Cessation
- 1986-05-02 CA CA000508200A patent/CA1250952A/en not_active Expired
- 1986-05-12 EP EP86303604A patent/EP0203752B1/en not_active Expired - Lifetime
- 1986-05-12 DE DE8686303604T patent/DE3686293T2/en not_active Expired - Lifetime
- 1986-05-12 AT AT86303604T patent/ATE79182T1/en active
- 1986-05-12 JP JP61108397A patent/JP2637952B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| DE3686293T2 (en) | 1993-01-28 |
| EP0203752A2 (en) | 1986-12-03 |
| DE3686293D1 (en) | 1992-09-10 |
| KR860009309A (en) | 1986-12-22 |
| EP0203752B1 (en) | 1992-08-05 |
| AU589173B2 (en) | 1989-10-05 |
| US4691993A (en) | 1987-09-08 |
| AU5654586A (en) | 1986-11-20 |
| CA1250952A (en) | 1989-03-07 |
| EP0203752A3 (en) | 1988-06-01 |
| ATE79182T1 (en) | 1992-08-15 |
| JP2637952B2 (en) | 1997-08-06 |
| JPS61261701A (en) | 1986-11-19 |
| KR940008669B1 (en) | 1994-09-24 |
| US4688894A (en) | 1987-08-25 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1263264A (en) | Transparent retroreflective sheets containing directional images and method for forming the same | |
| US4708920A (en) | Microlens sheet containing directional half-tone images and method for making the same | |
| CA1250609A (en) | Transparent sheet containing authenticating image and method of making same | |
| KR101369128B1 (en) | Methods of forming sheeting with a composite image that floats and sheeting with a composite image that floats | |
| US4650283A (en) | Directionally imaged retroreflective sheeting | |
| KR100749587B1 (en) | Sheeting with composite image that floats | |
| CA1242580A (en) | Directionally imaged sheeting | |
| US8057980B2 (en) | Sheeting with composite image that floats | |
| US4714656A (en) | Sheet containing contour-dependent directional image and method for forming the same | |
| US8006908B2 (en) | Data support with identifications written thereon by means of a laser beam and method for production thereof | |
| PL210068B1 (en) | Microlens sheeting with composite image that appears to float | |
| CA1273512A (en) | Sheet containing directional photographic images and method for making the same |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |