WO1995006567A1

WO1995006567A1 - Method of fixing image to rigid substrate

Info

Publication number: WO1995006567A1
Application number: PCT/US1994/009104
Authority: WO
Inventors: Paul C. Adair
Original assignee: Brady Usa, Inc.
Priority date: 1993-09-03
Filing date: 1994-08-12
Publication date: 1995-03-09
Also published as: AU7484394A; US5871837A

Abstract

Rigid signs are prepared by a facile method of fixing an image to a rigid substrate coated with a thermally tackifiable coating. The image is readily produced through the use of a computer graphics program, and the image is printed onto a transfer film using a conventional computer printer. The image-bearing surface of the transfer film is then joined in pressing contact with the thermoplastic coating which has been warmed to a softened or tacky state. Upon cooling the thermoplastic coating to a hard, durable state, the transfer film is removed leaving the image securedly affixed to the rigid substrate.

Description

" METHOD OF FIXING IMAGE TO RIGID SUBSTRATE".

BACKGROUND OF THE INVENTION

This invention relates to signs. In one aspect, the invention relates to a method of producing a sign by fixing an image to a rigid substrate while in another aspect, the invention relates to a method in which the image is first printed by electrophotography onto a transfer film in an optically reversed manner and the rigid substrate is coated with a thermally tackifiable substance. In yet another aspect, the invention relates to a method for producing small batches of rigid signs in a facile, quick and inexpensive manner.

Rigid signs comprise an image carried on an inflexible substrate. Such signs are often used in an outdoor setting in which durability of the image is an important quality of the sign.

Rigid signs are typically produced in low volumes, e.g. less than 100 signs at a time, and are typically made by a silk screen printing process. While this process produces rigid signs with acceptable quality, silk screening is not cost effective for small production runs. Silk screening is time consuming and by its very nature, precludes quick order completion. At the moment, a good method does not exist for the rapid preparation of small volume production runs of surface-printed rigid signs. SUMMARY OF THE INVENTION According to this invention, surface-printed rigid signs bearing a durable image are produced by a method of fixing the image to a rigid substrate coated with a thermoplastic coating which is hard and durable under conditions of use such that the fixed image does not require an over-laminate for durability, the method comprising:

A. Providing an image comprising a transfer substance deposited upon a surface of a transfer film in an optically reversed manner;

B. Applying the image-bearing surface of the transfer film to the thermoplastic coating of the rigid substrate;

C. Joining the transfer film and the thermoplastic coating in pressing contact at an elevated temperature such that the image on the transfer film is transferred to the thermoplastic coating;

D. Cooling the thermoplastic coating; and

E. Removing the transfer film from the thermoplastic coating such that the transfer substance in the form of the image remains durably affixed to the thermoplastic coating.

In one embodiment of this invention, the image is constructed on a personal computer, laser printed in an optically reversed manner on a transfer film such as a sheet of polyethylene terephthalate, the film (image-side down) overlaid on an enameled aluminum sheet coated with a thermoplastic, the overlay passed through two heated pressure rollers and upon cooling, the transfer film removed from the aluminum sheet leaving a durable toner image affixed to the thermoplastic coating of the aluminum sheet. This method lends itself well to the production of small numbers of rigid signs in a short period of time.

BRIEF DESCRIPTION OF THE DRAWING The Figure is a flow diagram of one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The image can be affixed to the transfer film in any convenient manner. Typically, the image, i.e. any graphic such as one or more letters, numbers, symbols, pictures, and the like, is designed on a computer and then printed in an optically reversed manner with a conventional electrophotographic toner on the transfer film. "In an optically reversed manner" means that the image on the transfer film is inverted in such a manner that after transfer to the rigid substrate, it appears in right-reading form. Many computer programs, such as

Instant Artist™ by Autodesk, Paintbrush as supplied in Windows® Version 3.1 (Microsoft), and Cricket Paint Version 1.0 (Computer Associates) contain features that allow an image to be prepared in a right- reading form on a computer monitor which can then be optically reversed for printing purposes.

Any material that will form an image on a transfer film (otherwise known as a release or tight release film) , and will transfer from the film to a rigid substrate when the two are joined in pressing contact with one another at an elevated temperature, can be used in the practice of this invention. Typically and preferably, the transfer substance is any one of the commercially available dry powdered toners that are used in conventional computer printers, e.g. HP-Laser Jet 4, Xerox 4700, Canon CLC 500, QMS PS 2000. These dry powder toners can be any color, including black, white and any shade of gray, and these toners are used in their conventional manner. Representative toners include those used in the above printers, as well as those used in conventional electrographic copiers, such as the Canon CLC 300, Panasonic FP-C1, Minolta EP 410-Z, Minolta EP 4320.

The transfer film that is used in this invention is characterized by the ability of the toner to affix to it in a manner that will allow easy and near complete removal of the toner to a rigid substrate coated with a thermoplastic resin when the two are joined with one another in pressing contact at an elevated temperature. These films are constructed of a material that will not melt or otherwise deform under the conditions at which the image is imposed upon the film. Other physical and chemical characteristics of the film can vary to convenience, but typically the physical dimensions of the film are chosen to accommodate the procedure and equipment used to impose the image on the film. For example, in those applications in which a conventional laser printer is used to impose the image upon the film, the physical dimensions of the film are one of the paper sizes for which the printer is designed to accommodate, usually with a thickness between 3 and 6 mils. Representative of the transfer films that can be used in this invention are those constructed of polyester (e.g. polyethylene terephthalate (clear or pigmented) coated with a release agent or uncoated) , polyolefin coated paper (e.g. polyethylene coated paper) , paper coated with one or more release agents (typically silicone-based) , oriented polypropylene, and the like. Among the preferred release films are those containing titanium dioxide as a pigment.

The amount of toner that is releasably affixed to the tight release film can also vary to convenience, although it is typically an amount similar to that which is transferred by a conventional computer printer to a sheet of paper during a normal printing operation. Usually, essentially complete transfer of the transfer substance (e.g. toner) from the tight release film to the rigid substrate is desirable and as such, the maximum amount of toner deposited on the film does not exceed the maximum amount of toner that the rigid substrate can effectively receive during the transfer operation. Similarly, the minimum amount of toner deposited on the film is the minimum amount of toner required to impart the desired image on the rigid substrate. These amounts will vary with the nature of the transfer substance, tight release film, thermoplastic coating on the rigid substrate, and the transfer conditions (e.g. pressure, temperature, etc.) .

Any rigid substrate to which a thermoplastic coating will securely adhere, the thermoplastic coating exhibiting good durability under conditions of use and to which the transfer substance will securely affix, can be used in the practice of this invention. Preferred substrates are characterized not only by their rigidity, but by sufficient polar functionality that the thermoplastic coating will securely bond to it upon application and cure. Those rigid substrates that do not possess such polar functionality can be adapted to receiving a suitable thermoplastic coating by surface modification, e.g. chemical etching, plasma treatment, etc. , or by prior treatment with any suitable tie-layer, e.g. a primer. Preferred rigid substrates .include Lexan™ (a polycarbonate manufactured and sold by GE Plastics) , metal (e.g. aluminum, steel, brass, etc.), enamel-coated metal (e.g. enameled aluminum, etc.), polystyrene, any of the commercially available acrylic resins (i.e. thermoplastic polymers or copolymers of acrylic acid, methacrylic acid, esters of these acids, and acrylonitrile) , cellulose acetate butyrate, nylon, glass, wood, polyethylene-terephthalate-G, treated polyethylene and treated poly(vinyl)chloride (in which "treated" means that the surface to which the thermoplastic coating is applied has been modified by any suitable means to improve the adhesion between the substrate and the coating) , and the like.

The rigid substrate is coated with a thermoplastic resin that provides a hard, durable surface under conditions of use but when subjected to an elevated temperature, softens and becomes receptive to the transfer substance. Sufficient thermoplastic resin is applied to the substrate such that the coating will receive and firmly affix the transfer substance to the substrate. Typically, this coating is at least 0.5, and preferably at least 1.0, mil in thickness. Thicker coatings can be used with the only limitations on the maximum thickness being those of convenience and economy.

The composition of the coating, like that of the substrate, can vary widely, and includes both solvent and water-based resins and UV curable materials. For reasons of easy application, UV-curable resins of 100 percent solids are preferred. Representative water-based materials include such materials as RES 3103, RES 3016 and RES 6107 vinyl acrylic latexes; RES 202-AM and RES 6213 vinyl acetate homopolymer latexes and RES 6304, RES 6510 and RES 3112 acrylic latexes, all from Rohm and Haas Co. Representative solvent-based materials include acrylic resins, such as B-66 and B-67 acryloid resins (Rohm and Haas), or Elvacite resin (grade 2044 from E.I. Du Pont de Nemours Co.). The choice of resin for any given application is determined in large part by the performance characteristics required of the rigid sign, e.g. non-yellowing components are selected for clear coatings, acrylics for superior water and solvent resistance, and the like. The resins can be applied as a coating to the rigid substrate in any conventional manner, e.g. roll coating, spraying, brushing, screen printing, dip coating, curtain coating, etc.

The image on the transfer film is transferred to the thermoplastic resin coated rigid substrate by joining the film and substrate in a manner such that the image bearing surface of the film is joined in pressing contact with the thermoplastic resin coated surface of the substrate to form a laminate, heating the laminate to a temperature at which the thermoplastic resin coating softens or becomes tacky relative to the transfer film, cooling the laminate to a temperature at which the thermoplastic resin coating returns to a hard, durable state (i.e. non-tacky relative to the transfer film), and then removing or delaminating the transfer film from the substrate. During the pressing contact of the transfer film and thermoplastic resin coating at the elevated temperature, the transfer substance or toner affixes to the coating in such a manner that upon cooling, the substance or toner remains securely affixed to the hardened coating and releases from the film when the latter is removed from the former. Preferably, the transfer film and thermoplastic resin coating are brought into pressing contact with one another by means of heated press rollers such that the only area of the laminate that experiences both elevated temperature and pressure is that between the press rollers. Under these conditions, the elevated pressure and temperature experienced by the laminate is relatively short, e.g. less than a few seconds. The temperature and pressure of the transfer process will, of course, vary with the other method variables, particularly with the composition of the thermoplastic coating and transfer film.

The invention is further described by reference to the Figure which describes an embodiment in which a rigid sign with durable graphics is produced in a quick, facile manner. In this embodiment, the graphics for the rigid sign are first designed and produced on a computer through the use of a graphics program. The graphics (image) is optically reversed through the use of a feature of the program designed for such a purpose. The optically reversed graphic is then printed on a transfer film using a laser printer and a conventional dry powder toner.

Separately, a thermoplastic resin is prepared and then applied as a coating to a rigid substrate using any conventional technique, e.g. a draw down roller bar. The coating is then cured or dried in a manner consistent with its formulation, e.g. in an oven if it is solvent or water-based or is thermally curable, or in a UV curing unit if it contains a photoinitiator and photopolymerizable components. The graphics bearing surface of the transfer film is laid atop the coating bearing surface of the rigid substrate, and the resulting laminate is fed through two heated pressure rollers, and allowed to cool under ambient conditions to room temperature, and the tight release film removed from the coating-bearing surface of the rigid substrate. The resulting product is a rigid sign bearing the graphics in a right reading form, the graphics durably affixed to the thermoplastic coating of the rigid substrate.

The following examples are illustrative of specific embodiments of this invention. Unless indicated to the contrary, all parts and percentages are by weight.

SPECIFIC EMBODIMENTS

Example 1

Water-based coating. An aluminum sheet (6" by 10") with a white enamel coating was obtained from Alliance Company. This sheet was coated with a vinyl acrylic latex from Rohm and Haas (RES 3103 (TG=13 degrees)) using a #16 wire wound rod. The coating was dried under mild heat to a nontacky (to the human touch) film.

Sign graphics were designed and optically reversed using the drawing program supplied with Windows 3.1. The image was printed onto paper with the use of a Hewlett Packard LaserJet III printer. The resultant image was copied through the use of a Minolta EP 410-Z copier on to the release side of a silicone release-coated polyester sheet (8-1/2" by 11" by 3 mil) obtained from Custom Coatings and Laminating Corporation (C/l/S 6020) . Optionally, the graphics can be printed directly onto the film using the laser printer. The image-bearing film was placed, toner-side down, onto the coated side of the rigid substrate. The laminate was then run between two pressure rollers set at 50 pounds per square inch and heated to 100 C at a speed of 5 sec/in. Upon cooling to room temperature, the film was removed. The toner image remained securely affixed to the coating on the rigid substrate, thus producing a rigid sign. The image was not merely on the surface of the coating, but was integral to the coating.

Example 2

Water-based coating. The procedure of Example 1 was repeated except that an acrylic latex from Rohm and Haas (RES 3512 (Tg=26)) was substituted for the vinyl acrylic latex designated RES 3103. This coating produced results similar to those in Example 1, i.e. a rigid sign with a durably affixed graphic.

Example 3 UV-curable coating. The procedure of Example 1 was repeated with the exception that the coating on the rigid substrate was a UV-curable formulation, not a latex. The coating of this Example was prepared from Acryloid B-66 (55 g, an acrylic resin from Rohm and Haas) , SR 268 (110 g, tetraethylene glycol diacrylate from Sartomer) , and Irgacure 184 (4.13 g, a photoinitiator from Ciba-Giegy Corp.). This coating composition was applied to a white- enameled aluminum substrate with a number 8 wire wound rod, and the coating was allowed to level for a minute before curing with one medium pressure mercury lamp in a Fusion systems curing unit (3 passes at 30 ft/min) . After heat transferring the toner under the above conditions, the resultant rigid sign proved to be scratch resistant. Example 4

Solvent-based coating. An acrylic resin, B-66 (40g) from Rohm and Haas, was dissolved in toluene (lOOg) , and coated onto a white-enameled aluminum sheet (8" x 10" x 0.025") with a #24 wire-wound rod. The coating was air- dried for two hours.

An A-size sheet of clear, untreated polyester film (4.23 mil, Melinex Type 3285 from ICI United States Inc.) was printed in an optically-reversed fashion in a

Hewlett-packard Laser Jet 4 with an image designed on an IBM compatible 386 PC with the graphics program, Instant Artist™ (Autodesk) .

The film was placed, toner-side down, onto the dried acrylic coating of the rigid substrate and run between two heated (120 C) rubber pressure rollers at a speed of 8 sec/in. and a pressure of 50 psi. Upon cooling, the film was removed from the composite, yielding a finished sign with the graphics securedly affixed to the hard, durable acrylic coating.

Example 5

The following formulation was screen printed onto white-enameled aluminum with a 235 mesh screen:

Rohm & Haas Acryloid B-66 86.7g

Sartomer SR-268 acrylate monomer 186.Og

Sartomer SR-9015 acrylate monomer 62.lg

Ciba-Geigy Irgacure-184 9.3g

Dow-Corning DC-56 silicone surfactant 3.4g

Dow-Corning DC-11 silicone surfactant 3.4g The resultant UV-curable coating was then cured by two medium-pressure mercury bulbs at an exposure of 2060 mJ/cm2.

An optically-reversed graphics image was printed onto A-size white, untreated polyester (4 mil, Melinex Type 329 from ICI) . This sheet was coupled to the rigid sign and pressure/heat developed under the conditions described in Example 4. Upon removal of the film, a completed sign was obtained.

Example 6

A sheet of white polyester (Melinex Type 329) was printed with a color image in a Xerox 4700 color eletrophotographic printer/copier. This film was developed against a sheet of coated aluminum panel, prepared as in Example 5. Removal of the film yielded a completed color sign.

Example 7

The following formulation was coated onto various rigid substrates with a #8 wire wound rod and the resultant UV-curable coating cured at 2060 mJ/cm2 with two medium-pressure mercury lamps: Rohm and Haas B-66 acrylic resin 66.6g

Sartomer SR-268 acrylic monomer 100.Og

Sartomer SR-9015 acrylate monomer 33.4g

Ciba-Geigy Irgacure 184 5.0g

Substrate: a. 125 mil yellow acrylic b. 125 mil white acrylic c. 80 mil white polystyrene d. 15 mil polished brass e. 120 mil clear poly(carbonate) f. 110 mil clear cellulose acetate butyrate

Each of the resultant coated substrates were pressure/heat developed against a 4 mil PET transfer sheet which had been reverse-printed in a Hewlett Packard Laser Jet 4 printer. Upon cooling and removal of the film from the composite, a scratch-resistant rigid sign was obtained.

Although the invention has been described in considerable detail through the preceding examples, this detail is for the purpose of illustration only. Many variations and modifications can be made by one skilled in the art without departing from the spirit and scope of the invention as described in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A method of fixing an image to a rigid substrate coated with a thermoplastic coating, the coating hard and durable under conditions of use, such that the fixed image does not require any over laminate for durability, the method comprising:

C. Joining the transfer film and the thermoplastic coating in pressing contact at an elevated temperature such that the image on the release film is transferred to the thermoplastic coating;

D. Cooling the thermoplastic coating; and E. Removing the transfer film from the thermoplastic coating such that the transfer substance in the form of the

« image remains durably affixed to the 5 thermoplastic coating.

2. The method of Claim 1 in which the transfer substance is a dry powder toner.

10 3. The method of Claim 2 in which the toner is deposited upon the surface of the transfer film through the action of a laser printer.

4. The method of Claim 3 in which the transfer 15 film is selected from the group consisting of polyester film, polyolefin coated paper, paper coated with at least one release agent, and oriented polypropylene.

5. The method of Claim 4 in which the transfer 20 film contains titanium dioxide pigment.

6. The method of Claim 5 in which the transfer film is polyethylene terephthalate.

25 7. The method of Claim 5 in which the rigid substrate is selected from the group consisting of polycarbonate, metal, enameled metal, polystyrene, an acrylic resin, cellulose acetate butyrate, nylon, glass, wood, polyethylene terephthalate, treated polyethylene, and treated poly(vinyl)chloride.

8. The method of Claim 5 in which the rigid substrate is an enamel-coated metal.

9. The method of Claim 7 in which the thermoplastic coating is at least 0.5 mil in thickness.

10. The method of Claim 7 in which the thermoplastic coating is at least 1 mil in thickness.

11. The method of Claim 9 in which the thermoplastic coating is selected from the group consisting of vinyl acrylic latexes, vinyl acetate homopolymer latexes, and acrylic latexes.

12. The method of Claim 11 in which the thermoplastic coating is UV-curable.

13. The method of Claim 11 in which the transfer film and the thermoplastic coating are joined in pressing contact at an elevated temperature through the action of heated pressure rollers.

14. The method of Claim 13 in which the elevated temperature is at least about 100 C.

15. The method of Claim 13 in which the transfer film is removed from the thermoplastic coating at room temperature.

16. The method of Claim 1 in which the image is first prepared through the action of a computer program.

17. A rigid sign prepared by the method of Claim 1.