2. Description of the Prior Art Frosting articles, particularly those made of glass or plastic, for aesthetic reasons, have long been known and used in many diverse industries. These industries include architecture/construction, packaging, display systems and furniture making. Conventional frosting of these substrates is achieved either chemically by an etching liquid such as an acid solution, or mechanically by abrading such as by sandblasting.

Another method known in the prior art which is utilized to provide a textured surface on glass and plastic articles, comprises the steps of applying animal hide glue to the surface of the glass which has been sandblasted, and then heating the glue and allowing it to dry. This causes the glue to pull chips from the surface, thereby producing a random frosting pattern with an overabundance of fern-like surface patterns. For these reasons, the conventional glue chip process does not yield an ice crystal formation which closely simulates a natural pattern. Such a process is discussed transparent, although translucent and opaque substrates can be used. The ice crystal formation produced by the present process closely resembles ice crystal formations found in nature by substantially reducing the fern-like surface patterns associated with the prior art methods discussed. In accordance with the present invention in its broadest aspect, the process for producing an article having a three dimensional optical effect pattern comprises the steps of: a. applying a screen pattern of the ice crystal formation onto a substrate; b. screen printing a polymer coating composition on the substrate; and c. curing the polymer coating composition to provide a three dimensional translucent simulated ice crystal formation having from 0 to 50 percent of the surface area within said formation containing a fern-like surface pattern; The polymer coating composition is selected from synthetic thermoplastic or thermosetting polymers, which can be cured by thermally initiated polymerization or by photo-initiated polymerization or by a combination of these processes.

The process yields an article of manufacture which possess high standards of quality control regarding the reproducibility. of the ice crystal formation.

It is therefore a primary object of this invention to provide a simulated ice crystal formation which has a three dimensional appearance on a substrate, such as a glass or a plastic material. reference to the appended drawings in which: FIG. 1 is a door unit of a refrigerated display case having a transparent glass carrying a translucent discontinuous pattern on the surface simulating the appearance of a natural ice crystal formation.

FIG. 2 is a door unit of a refrigerated display case having a translucent continuous pattern of a simulated natural ice crystal formation according to the invention.

FIG. 3 is a drinking glass having a translucent continuous pattern of a simulated natural ice crystal formation according to the invention.

FIG. 4 is a magnified close-up of the fern-like pattern formed within the ice crystal formations.

FIG. 5 is a schematic view of the process according to the invention.

Detailed Description of the Preferred Embodiments In accordance with the present invention, a glass or plastic article is produced having a translucent three-dimensional simulated ice crystal formation controlling the amount and configuration of the fern-like patterns. Referring to the drawings in detail wherein the applied reference numerals indicate parts that are similarly identified. FIG. 1 shows an optically transparent door panel unit 10 of a refrigerated display case comprising a transparent glass 16 carrying a translucent discontinuous pattern on the surface of the glass simulating the appearance of a natural ice crystal formulation 18 within door frame 14 and attached on support frame 12. FIG. 2 basically is the same construction as described in FIG. 1 except that the ice crystal formation is shown as a continuous pattern. FIG. 3 shows a drinking glass 30 having a three-dimensional translucent simulated ice crystal formation 36 on glass surface 34. This example illustrates only one application of the present invention.

In FIG. 5 a simplified flow diagram is presented showing the major steps in the process of the invention. In one preferred embodiment, flat glass panels supported on a conveyor are moved through a series of operations. First the glass sheets are moved through a WASHER where detergent solutions and rotating brushes may be used to remove any dirt from the surface of the glass sheets, which are then dried with compressed air.

If desired, a solution of an adhesion promoter or primer may on be applied to the exposed surface areas to be coated of the substrate before the silk screening operation. Suitable adhesion promoters or primers include reaction products of epoxy resin- silanes and a polysulfide-silane system as disclosed in U. S. Pat.

No. 4,059,469 to Mattimoe, et al.

Next, the glass sheet is conveyed to a SCREEN PRINTING station where an ice crystal formation pattern is placed on the areas to be coated. A polymer coating composition is applied by screen printing on to the surface of the glass. Upon completion of the printing step, the glass sheet is then moved through a CURING OVEN where the polymer coating composition is cured either thermally or by photo curing to produce translucent simulated ice crystal formations on the substrate. After exiting the CURING OVEN, the sheet is transferred to a COOLING AND CLEANING station where after cooling, the surface is cleaned. Optionally, a hard coat to prevent scratch, abrasion or other damage may be applied by spraying or brushing at an AFTERTREATMENT station. Suitable coats which have optical clarity are silicone or polypolysiloxane compounds such as described in U. S. Pat. Nos. 4,027,073 and 4,942,083, which are herein incorporated by reference.

The substrates which may be used in the present invention may be of any size or shape, limited only by the capacity of the machinery available. Preferably plates or sheets of commercial plate, float or sheet glass composition are used. Thermoset polymers are also employed as substrates in the process. Suitable thermosetting resins include acrylic resins, amino resins, polyester resins, polycarbonate resins, polyurethane resins and ionomer resins.

It is preferred when the ultimate utility involves doors and windows that the sheet is optically transparent, however, either the substrate or the coatings may be tinted if desired with colorants such as with dyes or pigments. For other uses such as in drinking glasses and mugs, bottles, inter alia, opaque or translucent substrates may be employed.

Forming the simulated ice crystal formation on a silk screen pattern involves either computer generated imaging or hand drawing the formation pattern on paper or vellum in black and white.

Photographing the black and white image to develop a full-size film positive of the ice crystal formation image that is properly sized for the substrate. Finally using the photograph to develop a silk screen for applying the polymer coating on the substrates, in the same pattern as the desired ice pattern effect.

The polymer coating compositions which may be applied by screen printing in the practice of this invention are based on thermoplastic and thermosetting resins, which may be cured by thermal or photo initiation or by combinations thereof. The thickness of the polymer coating compositions in forming the ice crystal formation ranges from about 0.020 to about 0.125 inch.

Various conventional photocurable resins include acrylate resins and modified acrylate resins such as a urethane-modified polymethacrylate, a butadiene-modified polymethacrylate, a <BR> <BR> <BR> <BR> polyether-modified monomethacrylate and polyene-polythiol polymers.

Such photocurable resins are described in U. S. Pat. No. 5,461,086 to Kato, et al., the disclosure of which is incorporated by reference. Photoinitiated curing can be accomplished directly or with a photochemical initiator, such as acetophenone and derivatives thereof, benzophenone and derivatives thereof, Michler's ketone, benzyl, benzoin, benzoin alkyl ethers, benzyl alkyl ketals, thioxanthone and derivatives thereof, tetramethyl thiurammonosulfide, 1-hydroxycyclohexyl phenyl ketone, 2-methyl. l- [4-(methylthio) phenyl]-2-morpholino-propene-1 and the like alpha- amino ketone compounds, etc., alone or as a mixture thereof. Among them, benzoyl alkyl ethers, thioxanthone derivatives, 2-methyl-1- [4-(methylthio)-phenyl]-2-morpholino-propene-landthe like a-amino ketone compounds are preferable for more rapid curing. Further, 2- methyl-l- (4- (methylthio) phenyl] 2-morpholino-propene-1 is more preferable due to rapid curing as well as good storage stability.

It is possible to use together an amine compound for sensitizing the action of photopolymerization initiator.

Photopolymerization initiators decompose into free radicals by ultraviolet light in 3600 angstrom range. Convenient sources of ultraviolet light are available in the form of mercury-arc lamps or fluorescent lamps with special phosphors.

Thermally cured thermosetting resins useful as polymer coatings to be applied by a screen printing process include epoxy resins, polyurethane, polyvinyl butyryl resins, polyesters, ionomer resins, phenolic resins. For example, the preferred resins are epoxy resins, particularly epoxy resins which have at least two epoxy groups per molecule. Examples of the epoxy resin are polyglycidyl ethers or polyglycidyl esters obtained by reacting a polyhydric phenol such as bisphenol A, halogenated bisphenol A, catechol, resorcinol, etc., or a polyhydric alcohol such as glycerin with epichlorohydrin in the presence of a basic catalyst; epoxy novolaks obtained by condensing a novolak type phenol resin and epichlorohydrin; epoxidized polyolefines obtained by epoxidizing by a peroxide method; epoxidized polybutadienes; oxides derived from dicyclopentadiene; and epoxidized vegetable oils.

These epoxy resins can be used alone or as a mixture thereof.

When the thermosetting resin is an epoxy resin about 2 to 30 parts by weight of the curing agent for 100 parts by weight of the epoxy resin is used. Preferably the ratio is about 5 to 15 parts by weight of the curing agent to 100 parts by weight of the resin.

As curing agents for epoxy resins, there can be used actual curing agents which are insoluble in epoxy resins at a resin drying temperature of 176 degrees F. and dissolve at high temperatures to begin curing.

Examples of the curing agent are aromatic polyamines and hydroxyethylated derivatives thereof such as metaphenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 4,4' diaminodiphenyl oxide, 4,4'-diaminodiphenylimine, biphenylenediamine, etc; dicyandizmide; imidazole compounds such as 1-methylimidazole, 2-methylimidazole, 1,2-dimethylimidazole, 2- ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1-benzyl-2-methylimidazole, 2-phenylimidazole, 1- (2-carbamyl)-2- ethyl-4-methylimidazole, 1-cyanoethyl-2-phenyl-4; 5- di (cyanoethoxymethyl) imidazole, 2-methylimidazole isocyanuric acid adduct, l-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4- methylimidazole, 1-azinethyl-2-ethyl-4-imadiazole, 2-methyl-4- ethyl-imidazole trimesic acid adduct, etc.; BF3 amine complex compounds; acid anhydrides such as phthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, pyromellitic anhydride, chlorendic anhydride, benzophenonetetracarboxylic anhydride, trimellitic anhydride, polyazelaic anhydride, polysebacic anhydride, etc.; organic acid hydrazides such as adipic dihydrazide, etc; diaminomaleonitrile and It is also possible to use a diaminotriazine modified imidazole compound of the formula: wherein R is a residue of imidazole compound. Examples of such a compound are 2,4-diamino-6 {2'-methylimidazole-(l')) ethyl-s- triazine, 2,4-diamino-6 {2'-undecylimidazole- (1')}-ethyl-s-triazine, 2,4-diamino-6 {2'-methylimidazole (1')} ethyl-s-triazine, and isocyanuric acid adducts thereof.

Among these curing agents, a combination of diaminotriazine modified imidazole and dicyandiamide is particular preferable from the viewpoint of adhesiveness to form ice crystal patterns.

Additionally a compound capable of reacting with an epoxy resin and improving adhesiveness to the surface of the substrate when the epoxy resin coating composition is cured by ultraviolet light exposure may be added.

Examples of such a compound are thiazolines such as 2- mercaptothiazoline, thiazoline, L-thiazoline-4-carboxylic acid, 2,4-thiazolinedione, 2-methylthiazoline, etc.; thiazoles such as thiazole, 4-ethylthiazole, etc.; thiadiazoles such as 2-amino--5- mercapto-1,3,4-thiadiazole, etc.; imidazoles such as 2-mercaptobenzoimidazole, 2-mercapto-1 -methylimidazole, etc.; imidazolines such as 2-mercaptoimidazoline, etc., 1-H-1,2,4-triazole-3-thiol, etc. Among them, 2- mercaptothiazoline, 2-mercaptoimidazoline, thiazoline, 2-amino-5- mercapto-l, 3,4-thidiazole, and 1-H-1,2,4-triazole-3-thiol are more effective for improving the adhesiveness between the polymer coating and the glass or plastic substrate.

As mentioned earlier in this disclosure, the frosting pattern produced by the glue chip process produces an undesirable fern-like surface texture. FIG. 4 shows a magnified close-up of such fern- like surface structures 44 within the ice crystal formation pattern on the glass substrate of the perimeter portion of a door panel 40.

An overabundance of these fern-like structures or textures is undesirable, since they diminishe the natural effect desired in simulated ice crystal formation patterns. Further, the random configuration of the spine 42 and branches 46 in the fern leaf has a deleterious effect in reproducing a natural ice crystal formation. The process of this invention not only produces a more natural ice crystal formation by controlling the number of fern- like structures, and by controlling the configuration of the spines and branches, but the results are reproducible even in high volume production. The final product may contain as much as fifty percent of the surface area of the ice crystal formation, or may : be completely devoid of a fern-like pattern but preferably less than twenty percent and most preferably contains less than ten percent.

The present invention will be more fully understood from the descriptions of specific examples which follow: photoinitiator 4,4'-bis (N<N-diethylamino benzophenone in a parts by weight ratio of 62: 1 (resin/photoinitiator). About 1 part by weight of titanium dioxide pigment was added. Sufficient solvent, such as butyl Cellosolve was added to aid in dispersing the coating for screen printing.

SINGLE COATING PROCESS-PHOTOCURE A continuous silk screen pattern of simulated ice crystal formation is positioned on a previously cleaned optically transparent glass sheet. The epoxy coating composition as prepared above is screen printed onto the glass sheet. The coated glass sheet is transferred to a curing station. The resin composition was selectively photo cured by exposure to ultraviolet light using a 300 W high pressure mercury lamp for a period of 2 to 4 minutes.

After exiting the curing process station, the coated glass sheet is then cleaned and transferred for storage and shipping or for further processing or fabrication.

The processes as shown in Examples 1 and 2 produce simulated ice crystal formations which are devoid of fern-like patterns.

Example 3 shows a process where the fern-like pattern is added.

EXAMPLE 3 MULTIPLE COATINGS-DIFFERENT CURING MECHANISMS A discontinuous silk screen pattern of a simulated ice crystal formation is positioned on a previously cleaned optically transparent glass. sheet. The thermoset zing epoxy coating composition as described in Example 1 was screen printed onto the glass sheet. Upon completion of the printing operation, the coated sheet is passed into the curing oven station and thermally cured at about 310 to 340 degrees F. for about 5 minutes. These conditions provide an undercure in order to prevent delamination during subsequent curing operations. After cooling, the first coated glass sheet is transferred to a station where a silk screen having about ten percent surface area of a fern like pattern is applied to the surface. A photocurable resin coating composition as described in Example 2 but further including about 0.5 part of a blue pigment is deposited on the glass substrate. Following the second coating, the coated sheet is passed to the curing station and the coating is cured by exposure to ultraviolet light using a 300 W high pressure mercury lamp for about 2 to 5 minutes to completely cure both coatings. After cooling and cleaning, the coated sheet is transferred to an aftertreatment station where a silicone or poliysiloxane coating composition was sprayed on the cured ice crystal formation and then cured at about 100 degrees to 300 degrees F. to impart a hard transparent abrasion resistant coating.

The screen printing process and the subsequent curing steps may be repeated if more colors or passes are needed to yield the desired effect. Other patterns may be screen printed on or around the ice crystal formation such as snowflakes or even fern-like patterns. The important aspect is that the amount of fern-like patterns can be specifically controlled. However, in these cases, the abrasion resistant coating application and cure is the last step before storage or further fabrication.

There is no criticality in the manner the multi-pass processes are conducted. Example 3 shows a polymer coating which is thermally cured followed by a polymer coating system which is photo cured. The various coating systems are compatible and the