GB2250955A - Printing polymeric sheet material - Google Patents

Abstract

The polymeric sheet, e.g. rigid PVC and incompatible lithographic ink or electrographic toner have a primer layer interposed between them or the ink layer is encapsulated between two primer layers. The primer may be solvent or aqueous based, and preferably includes a benzene derivative, ketone, acetate or nitroparaffin solvent or film former. If aqueous based, the primer includes an organic solvent or film former. Preferred solvents include methyl isobutyl ketone, methyl ethyl ketone, n-propyl acetate, isopropyl acetate, and N-methyl-2-pyrrolidone. To deter dot distortion of the ink, the primer has a glass transition temperature (Tg) of at least 60 DEG C, and preferably at least 100 DEG C. Examples are given of sheets applied to limestone-filled tile material to make floor tiles.

Description

"SHEET MATERIAL" 225o955 This invention relates to a polymeric sheet

having an'incompatible ink thereon, and more especially to a floor covering having a lithographic ink or electrographic toner bonded thereto.

The term "incompatible" refers to the inability of the ink system to bond directly and permanently to a polymeric sheet only through4solvent or carrier evaporation. In contrast, an example of a compatible system is a typical rotogravure vinyl ink system when printed onto a rigid polyvinyl chloride (PVC) film.

To create a high quality colored (nearly photographic quality) decorative design on surfaces of tile products, the rotogravure printing technique is the state of the art technique most often selected. While this printing technique is relatively easy to operate, it has some drawbacks. It is capital intensive, in that new designs require new printing cylinders prior to printing. It requires long lead times to prepare the cylinders for printing. In addition, this technique is geared to high volume printing and usually on relatively thin webs, i.e., 0.04 to 0.25 mm in thickness. Clean up of the printing cylinders is more time consuming than most of the actual print run, resulting in potentially high labor costs associated with the actual job, and a natural tendency to make the runs longer than are necessary.

In order to provide a lower cost, short run, and faster turnaround printing system, departure from the current rotogravure printing system was attempted. Two high quality four color printing techniques, lithographic and electrographic printing, offered these opportunities. However, it has been found that the conventional ink systems used in these techniques do not adhere permanently to, i.e., in the terminology of the present specification, are hot compatible with, the polymeric films used in the manufacture of polymeric sheet products.

In the lithographic process, which can be a sheetfed printing process, the inks cure by oxidation. After printing on rigid PVC film, the ink will still be soft after drying. The image will readily smudge and result in an unacceptable print. This actually occurs to some extent in normal conventional lithographic printing of paper as is apparent on close examination of a four color process-printed page in a magazine or on an advertising poster. It has been found that when a conventional lithographic printed PVC film is bonded conventionally to a floor tile base, the ink layer will not impart the proper adhesion requirements after lamination for an adequately performing product.

The same is true of the electrographic printing system where the colored images are formed on the film using both liquid and dry toners. Even when the electrographic printing (e.g., from a color copying machine) is done on specially treated paper and films, the ink layer which is actually to act as the adhesive layer between the clear protective film and base or substrate after lamination is not strong enough to prevent delamination in use.

The present invention provides a polymeric sheet having an imcompatible ink permanently bonded thereto, the ink being bonded to the polymeric sheet by a first primer layer interposed between the polymeric sheet and the ink, the primer being compatible with the polymeric sheet. When the primer is applied, it comprises an organic solvent, advantageously one selected from the group consisting of benzene derivatives, especially alkyl benzenes, ketones, acetates, nitroparaffins, pyrrolidones, piperidones and acetamides. The primer may be an organic solvent based or an aqueous based primer.

In an organic solvent based primer system, the solvent system preferably includes toluene, methyl isobutyl ketone, methyl ethyl ketone, propyl acetate or isopropyl acetate. The binding materials of such a system may include resin such, for example, as a polyvinyl resin, acrylic resin, polyurethane resin or polyester resin, and optionally a pigment. To reduce smudging of the ink, the primer advantageously has a glass transition temperature (Tg) of at least 600C, and preferably of at least 1000C.

An aqueous based primer system preferably includes 4 - an aqueous colloidal dispersion of one of the abovelisted polymers. Also, the aqueous primers include a solvent or film former. The solvents or film foriners preferably comprise pyrrolidones, piperidones and acetamides.

If the polymeric sheet is to be used in a floor covering, performance of the floor covering and adhesion of the ink are improved by encapsulating the ink in the primer. The ink may be interposed between two layers of primer. In a preferred embodiment using a clear film which is backprinted, the first primer layer, interposed between the ink and polymeric sheet, is clear and the other primer layer is white or colored. Other options include any combination of clear and colored films and primers.

Floor coverings preferably include a polymeric wear layer such as clear polyvinyl, acrylic, polyurethane or polyester. In the present invention, the polymeric sheet may constitute all or part of the wear layer, or the wear layer may be in addition to the polymeric sheet of the invention. The wear layer may be crosslinked.

A primer containing certain resins and solvents, in either a solution or dispersion form (if water is the vehicle of preferred choice), is interposed between the polymeric sheet and incompatible ink or encapsulates the incompatible ink system and bonds it to the polymeric film. After solvent removal from the primer, permanent adhesion is achieved between the film and ink layer in the form of a scratch resistant image. Through additional post lamination steps the encapsulated ink layer can be directly bonded to other substrates to result in decorative products such as floor, wall, and ceiling tile products. This is advantageously achieved by conventional lamination with heat and pressure.

The primers used in this invention advantageouly consist at the time of application of an organic resin binder and an organic solvent or blend of solvents. In the vinyl polymer family, the organic resins may comprise polyvinyl chloride, polyvinyl acetate, carboxyl-modified vinyl chloride/vinyl acetate copolymers, hydroxy-modified vinyl chloride/vinyl acetate copolymers, vinyl chloride/vinyl acetatelmaleic acid terpolymers, or vinyl chloride/vinyl acetatelhydroxyalkyl acrylate terpolymers. other organic resins that may be employed include homopolymers and copolymers of acrylic and methacrylic acids and their esters, polyesters, polyurethanes, and poly(vinyl butyral).

The solvents used in this invention do not interact in any way chemically or physically with the ink system to cause adverse effects such as color bleed, image distortion, and milkiness in the polymeric film prior to or after lamination. Preferred solvents include methyl isobutyl ketone (MIBK), methyl ethyl ketone (MEK), isopropyl acetate, n-propyl acetate, propylene glycol monomethyl ether acetate, and 1-nitropropane. Single solvents may be used in the application of the encapsulating medium. However, multisolvent systems may be preferred in practice in order to achieve optimum balance between the application method of the primer, penetration of the material into the polymeric sheet and around the ink layers, and drying.

The primer in an aqueous based system preferably includes an aqueous colloidal dispersion of the polymer resins identified with respect to the organic solution primers above. Preferably the resins include acrylics, urethanes and polyvinyl acetates. Examples of the dispersion resins include S 575, a polyvinyl acetate dispersion (Armstrong World Industries); Tredfast 108, an acrylic dispersion (Tetrabond PLC); Permuthane UE-40-570, Permuthane UE-41-510 and Permuthane UE-41-512, urethane dispersions (Permuthane Coatings); Aquathane 60, a urethane dispersion (Peerless Emulsions); NeoRez XR-9409 and NeoRez XR-9679, urethane dispersions (ICI Resins); and combinations thereof. The dispersions as applied include an organic co-solvent or film former.

The preferred dispersion has about 30% to 45% solids and an organic solvent. The preferred solvents which may be used to improve the performance of the dispersed resins include 5% to 15t by weight of Nmethyl2-pyrrolidone solvent and 0.5% to 2.0% by weltght of N,Ndiethylethylamine. Other solvents include N-methyl piperidone and N,N-dimethyl acetamide.

The dispersion optionally comprises a surfactant, for example-an ethylene glycollethyl alcohol mixture such as.Permuthane KM-10-1610 (Permuthane Coatings). Such surfactants may conveniently be added up to 2% or as needed.

The aqueous based primer also preferably includes a crosslinking catalyst to enhance smudge resistance. The catalysts include isocyanate, e.g., KM10-1880 (Permuthane Coatings); azodicarbonamide, e..g., KM-10-1869 (Permuthane Coatings); aziridine, e.g., KM-10-1703 (Permuthane Coatings); and hexamethoxylated melamine resins, e.g., Resimene R475 (Monsanto).

The sheet advantageously comprises a member of the polyvinyl, acrylic, polyester, and polyurethane families or copolymers thereof. The polymeric sheet is usually a clear film, which is backprinted in the product of the invention. Typically, for a decorative surface product for floors, walls and furniture, the sheet is a clear rigid PVC film which becomes the wear surface. Also, the film may consist of two layers in which one of the layers is crosslinked, advantageously the layer remote from the ink. For ceiling products, the film may, for example, be white, both primer layers clear, and the printed image encapsulated and permanently bonded to the white film. In such a case, the printed image will normally be on the free side of the film.

The primer resin should be compatible with the polymeric sheet. Typically polyvinyl, acrylic, polyurethane and polyester primer resins may be used with either PVC or acrylic sheets. Polyurethane and polyester primer resins may be used with polyurethane and polyester sheets.

While using primer resins of the same family as the polymeric sheet (e.g., a polyvinyl primer on a PVC sheet) will insure that the ptimer and sheet are compatible, as demonstrated by Examples 1 and 2, infra, the primer and sheet are not necessarily identical. The polymers may have different molecular weights, glass transition temperatures and moieties attached to the backbone. Further, the primers are dissolved or dispersed in a solvent, whereas the sheet is not.

The ink systems which are used in this invention and are incompatible with the polymeric film include lithographic inks (conventional drying and UV cure) and electrographic toners. They may be classified as either dry or wet in their imaging form, i.e., the printing process. Neither ink system without the use of this invention will adhere by itself to a rigid PVC film after evaporation of its respective carrier. In addition to providing an excellent color gamut, they are desirably heat and light stable as well as resistant to alkali.

The printed polymeric sheet may be applied to a base. The base may, for example, be another film,.a primed paper or board containing cellulosic and/or manmade fibers, a filled thermoplastic tile composition, or a tile composition containing a filled (white) latex topcoat.

The use of these two imaging systems in making decorative surface covering products requires that the colored pigment system adheres well to the protective wear layer and also to the base structure. In floor and wall products, the base structure often is composed of plasticized polyvinyl chloride resins and inorganic fillers (such as limestone and silica). The wear layer can be a clear polymeric film such as PVC, polyester, acrylic, polyurethane, or combinations thereof. When the inks of these imaging systems are printed directly onto these types of films, and subsequently laminated onto a PVC floor base structure using conventional flooring laminating conditions, the lamination is not successful. The adhesion of the pigment/resins used in both of these imaging systems between itself, the wear layer, and base, is unacceptable.

In order to guarantee the permanent adhesion required for performance, a primer is applied first to the polymeric film as described in detail above, and then to the back of the decorated image. Thus, the image becomes encapsulated between the primers on the polymeric film. It remains stable while it is either in a stack of films or wound up within a roll of film. It will not block in either case and can be reactivated at any time the correct lamination conditions are present.

Advantageously, the resin system used in the two primer layers will crosslink at temperatures typically at 800C to 1400C to further enhance smudge resistance, e.g., improve resistance to dot distortion. This is especially valuable during subsequent operations where heat and pressure may otherwise distort the image.

The invention also provides a method of permanently bonding an ink to the surface of a polymeric article, especially the sheet described above, the polymeric material and the ink being incompatible, which method comprises applying to the surface a primer that is compatible with the polymeric material, the primer containing a binder and an organic solvent, advantageously a benzene derivative, a ketone, an acetate, a nitroparaffin, a pyrrolidone, a piperidone, or an acetamide, the primer being applied in the form of an organic solution or in the form of an aqueous dispersion also containing the organic solvent, and applying the ink to the primer-carrying surface.

The following Examples illustrate the invention:

Example 1 - Lithographic printing system A 0.5 mm thick clear rigid PVC film in sheet form was gravure-coated with a clear primer made according to Formulation 1, below.

Formulation 1 20% by weight VAGH, a hydroxy-modified vinyl chloridelvinyl acetate copolymer (Union Carbide Corp.) 80% by weight methyl isobutyl ketone The coating was done with a 150 line overall knurl cylinder with two passes through the coater. The coating was air-dried to remove the carrier solvent. The amount of primer applied was 3-4 grams/square meter dry. The coating was printed with conventional air-dry lithographic inks (R. W. Rexford Company). The inks were printed onto the dry clear primer according to the following sequence: black, cyan, magenta, and yellow. The design was a four color process print representing a ceramic floor tile configuration. After overnight drying, the white primer of Formula 2 below was applied over the dried lithographic inks at a dry weight rate of 7-9 grams/square meter and air-dried. Formulation 2 20% by weight Ti02 pigment 80% by weight Formation 1 The back-printed 0.5 mm thick clear rigid PVC sheet was then post- laminated to a limestone-filled tile base formulation to make a floor tile product. The conditions of lamination in a two-stage press were as follows: 1630C, 20 seconds, 100 psi (about 6.8 bar) for heating, and 380C, 20 seconds, 100 psi for cooling. By placing different texturing means against the unprinted side of the film, various textural surface features were imparted to the face of the product during the lamination operation. A smooth and overall finely textured surface having depth of 0. 025 mm was produced. Also produced was a deeply embossed-in-register product, with the deepest depressions being of from 0.38 to 0.635 mm in depth. Adhesion between the 0.5 mm wear layer film and the floor tile base was excellent and found to be better than the adhesion when rotogravure inks are used as the ink layer.

Example 2 - Electrographic Printing System The same primer Formulation I was applied to a 0.075 mm clear rigid PVC film. In this case, the primer was applied by a knife blade coater and air-dried. The same application rate was applied as in Example 1.

To the dried surface were applied colored liquid toners (Hilord Chemical corporation). The toners that were applied sequentially were cyan, magenta, and yellow. The toners were applied using a modified electrographic imaging and developing system. The electrostatic imaging was provided by an ionographic deposition technique. After evaporation of toner carrier, another thickness of Formulation 1 was applied and dried in the same manner. The post lamination and texturing steps of Example I were used with a filled PVC tile base formulation to make a conventional floor tile product. The resulting PVC surface contained an embossing texture that was 0.15 to 0.25 mm deep and the adhesion between the protective film, toned image, and the tile base was permanent.

Example 3 - Higher Ta Primer While the above inks were permanently bonded to the polymeric sheet, they did have a tendency to distort in the post laminating and embossing steps. This tendency to distort was reduced by increasing the Tg of the primer resin from the 680C of Examples 1 and 2 to 1050C by substituting a methyl methacrylate polymer, Acryloid A-21 (Rohm and Haas), for the VAGH of Formulation 1 and a solvent comprising methyl ethyl ketone/isopropyl acetate/propyl acetate in a ratio of 1:1:1 for the MIBK of Formulation 1.

Example 4 - Aqueous Based Lithographic System A 0.5 mm thick clear rigid PVC film in sheet form was blade coated with a dispersion consisting of Permuthane UE-40-570 having a solids content of 33% by weight. The water based dispersion was applied at 0.001 inch (about 0.025 mm) wet thickness by hand drawdown to a thickness of 0.025 mm. The amount of coating applied was 3-4 grams/square meter dry.

The coating was then printed via a hand rubber roller with a conventional air dry lithographic ink (R.

W. Rexford Company). After drying overnight, the Permuthane UE-40-570 was applied over the dried lithographic inks at the dry weight rate of 3-4 grams/square meter and post-laminated to a limestone-filled tile base formulation to make a floor tile product using the same technique as described in Example 1. Adhesion between the 0.5 mm wear layer film and the floor tile base was excellent.

Though the applicants do not wish to be limited to the following explanation, it is believed that the improved adhesion results from the solvents of the primer diffusing into the lithographic ink layers or electrographic toner layers carrying the VAGH or A-21 resin with it. Then when the layers are laminated, the resins in the ink fuse with the resins in the primer and polymeric sheet.

The preferred application rate of the clear backcoated primer layer is three to four grams/square meter dry. However, the application rate could be as low as two grams/square meter dry and obtain adequate adhesion. The upper limit to the application rate depends merely on the cost of the applied primer.

For use in floor coverings, the preferred application rate of the white primer which is interposed between the base sheet and ink is seven to nine grams/square meter dry. However, the application rate could be as low as about six grams/square meter dry, particularly if - 15 there are open areas in the ink layer. The upper limit to the application rate depends merely on the cost of the applied primer.

Claims (25)

CLAIMS:

1. A polymeric sheet having an incompatible ink permanently bonded thereto, the ink being bonded to the polymeric sheet by a first primer layer, the primer layer being interposed between the polymeric sheet and the ink, the primer layer being compatible with the polymeric sheet.

2. The sheet of claim 1, wherein the ink is a lithographic ink or an electrographic toner.

3. The sheet of claim 1 or claim 2, wherein, during application of the primer layer, the primer is in the form of an organic solution.

4. The sheet of claim 1 or claim 2, wherein, during application of the primer layer, the primer is in the form of an aqueous dispersion, also comprising an organic solvent.

5. The sheet of any one of claims 1 to 4, wherein, during application, the primer comprises a solvent selected from benzene derivatives, ketones, acetates, nitroparaffins, pyrrolidones, piperidones and acetamides.

6. The sheet of any of claims 3 to 5, wherein the solvent is toluene, methyl isobutyl ketone, methyl ethyl ketone, isopropyl acetate, n-propyl acetate, propylene glycol monomethyl ether acetate, l-nitropropane, Nmethyl-2-pyrrolidone, N-methyl-piperidone or N,Ndimethylacetamide.

7. The sheet of any of claims 1 to 6, wherein the primer layer comprises a resin selected from vinyl, acrylic, urethane, or ester homopolymer or copolymer.

s. The sheet of claim 7, wherein the resin is polyvinyl chloride, vinyl chloride/vinyl acetate copolymer, hydroxy modified vinyl chloride/vinyl acetate copolymer, carboxy modified vinyl chloride/vinyl acetate copolymer, or methyl methacrylate polymer.

9. The sheet of any of claims 1 to 8, wherein the primer layer has a glass transition temperature (Tg) of at least 600C.

10. The sheet of claim 8, wherein the Tg is at least 1000C.

11. The sheet of any of claims 1 to 10, wherein the polymeric sheet is a vinyl, acrylic, urethane, or ester homopolymer or copolymer.

12. The sheet of any of claims 1 to 10, wherein the polymeric sheet is of rigid PVC.

13. The sheet of any of claims 1 to 12, further comprising a second primer layer, the ink being encapsulated between the two primer layers.

14. The sheet of claim 13, wherein the first primer layer adjacent to the polymeric sheet is clear and the second primer layer is white.

15. A floor covering comprising the sheet, primer layer and ink of any of claims 1 to 14.

16. The floor covering of claim 15, further comprising a crosslinked wear layer.

17. A polymeric sheet having an incompatible ink permanently bonded thereto, substantially as described in any of the Examples herein.

18. A method of permanently bonding to a polymeric surface an ink incompatible with the polymeric material, which comprises first applying to the surface a primer compatible with the polymeric material, the primer comprising a binder and an organic solvent, and subsequently applying the ink to the primer-carrying surface.

19. A method as claimed in claim!8, wherein the primer is applied in the form of an organic solution.

20. A method as claimed in claim 18, wherein the primer is applied in the form of an aqueous dispersion also comprising the organic solvent.

21. A method as claimed in any of claims 18 to 20, wherein the ink is a lithographic ink or an elect-rographic toner.

22. A method as claimed in any of claims 18 to 21, wherein the primer is as specified in any of claims 5 to 10, or the polymeric surface is of a sheet as specified in claim 11 or claim 12.

23. A method as claimed in any of claims 18 to 22, which also comprises applying a second primer layer over the inked and primed surface.

24. A method as claimed in claim 18, carried out substantially as described in any one of the examples herein.

25. Any new feature herein before described or any ne. w combination of hereinbefore described features.