CA2057117A1 - Polymeric sheet - Google Patents

Abstract

POLYMERIC SHEET

Abstract An adhesive system is suitable for use in adhering an incompatible ink system to a polymeric film; particularly, adhering a lithographic ink or electrographic toner bonded to a floor covering. The polymeric sheet and incompatible ink have a primer layer interposed between them or the ink layer is encapsulated between the two primer layers. The primer may be solvent based 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. The preferred solvent or film former includes methyl isobutyl ketone, methyl ethyl ketone, n-propyl acetate, isopropyl acetate, or N-methyl-2-pyrrolidone. To deter dot distortion of the ink, the primer should have a glass transition temperature (Tg) of at least 60°C, and preferably at least 100°C.

Description

2~71~ 7 POLYMERIC SHEET

This invention relates to a polymeric sheet having an inco~patible ink permanently bonded thereto. Specifically, the inver.tion includes a floor covering having a lithographic ink or electrographic toner bonded to a primer which is bonded to the floor covering.
The term incompatible refers to the inability of the ink system to directly and permanently ~ond to a polymeric sheet only through solvent or carrier evaporation. An example of a compatible system would be the case in a typical rotogravure vinyl ink system when it is printed onto a rigid polyvinyl chloride (PVC) film.
To create a high quality colored (nearly photographic) 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 2~57~17 associated wlth the actual ~ob, 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, a departure was made from the current rotogravure printing system. Two hi~h quallty four color printing techniques, lithographic and e'ectrographic printing, offered these opportunities.
However, it became obvious that the conventional ink systems used in these techniques were not compatible with the polymeric films that are used in the manufacture of polymeric sheet products.
In the lithographic process, which can be a sheet-fed printing process, the inks cure by oxidation. After printing on riqid polyvinyl chloride (PVC) film, the ink will still be soft after drying. The image will readily smud~e and result in an unacceptable print. This actually occurs to some extent in normal conventional lithographic printing of paper today if one were to examine 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 'ilm 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 electro~raphic printing systems 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 papers and films, the ink layer which is 2~57~17 actually to act 2S the adhesive layer between the clear protective ilm and base or substrate after lamination is not strong enough to prevent delamination in use.
The present invention provides 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 being compatible with the polymeric sheet, and wherein, during application of the primer, the primer comprises a solvent selected from the group consisting of benzene derivatives, ketones, acetates, nitroparaffins, pyrrolidones, piperidones and acetamides.
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 the same system may include resin such as a polyvinyl resin, acrylic resin, polyurethane resin or polyester resin, and optionally a pigment. To deter smudging of the ink, ths primer should have a glass transition temperature (Tg) of at least about 60C, and preferably at least about 100C.
An aqueous based primer system preferably includes an aqueous colloidal dispersion of one of the above-listed polymers. Also, the aqueous primers include a solvent or film former. The solvents or film formers preferably include pyrrolidones, piperidones and acetmides.
~ f the polymeric sheet is used in a floor covering, performance of the floor covering and adhesion of the ink is improved by encapsulating the ink in the primer. The ink 2~7~ ~7 may be interposed between two layers of primer. In a preferred embodiment using a clear film which is backprinted, the primer layer, interposed between the ink and pol~meric sheet, is clear and the other primer layer may be white or colored. Other options include any combination of clear and colo-ed films and primers.
The floor covering preferably includes a polymeric wear layer such as clear polyvinyl, acrylic, polyurethane or polyester. The wear layer may be crosslinked.
A p-imer 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 sneet and incompatible ink or encapsulates the ir.compatible 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, ard ceiling tile products. This i9 achieved by conventional lamination with heat and pressure.
The primer described in this invention consists of an orqanic resin binder and an organic solvent or blend of solvents. In the vinyl polymer family, the organic resins can comprise polyvinyl chloride, polyvinyl acetate, carboxyl-modified vinyl chloride/vinyl acetate copolymers hydroxy-modified vinyl chloridetvinyl acetate copolymers, a blend of vinyl chloride/vinyl acetate/maleic acid, and vinyl chloride/vinyl acetate/hydroxy alkyl acrylate. In addition, 2 ~ J~ 7 orsanic resins that will work include polymers and copolymers of acrylic and methacrylic acids and their esters, polyes~ers, polyurethanes, and vinyl butyral.
The solvents of this invention do nGt 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. The solvents may include methyl isobutyl ketone (MIBK), methyl ethyl ketone (MEK), isopropyl acetate, n-propyl acetate, propylene glycol monome~hyl ether acetate, and 1-nitropropane. Singular solvents can be used in the application of the encapsulating medium. However, the solvent system sometimes needs to be modified in practice in order to achieve optimum balance between the application metnod of the primer, penetration of these materials into the film and zround the ink layers, and drying.
The film may come from the polyvinyl, acrylic, polyester, and polyurethane families or copolymers thereof.
The polymeric 'ilm is usually a clear film which is backprinted. ~ypically, for a decorative surface product fcr floors, walls and furniture, the film is a clear rigid PVC film which becomes the wear surface. Also, the film may consist o' two layers in which one of the layers is crosslinked. ~or ceiling products, the fiim may be white, both primer layers are clear, and the printed image would be encapsulated and permanently bonded to the white 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 2~5~3 7 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 primer and sheet are compatible, as demonstrated by Examples 1 and 2, infra, the primer and sheet are not identical. The polymers have different molecular wei~hts, 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 incompatibie with the po~ymeric film include lithographic inks (conventional drying and W cure) and electrographic toners. They may be classified as either dry or wet in their i~aging form, i.e., the printinq process.
Neither ink system without the use of this invention will adhere by itself to a rigid PVC film after evaporation of zheir respective carriers. In addition to providing an excellent color gamut, they must be heat and light stable as weli as resistant to alkali.
The base may be another film, a primed paper or board containing cellulosic and/or man-made fibers, a filled thermoplastic tile composition, a tile composition containing a filled (white) latex topcoat, and other base structures as well.
The use of these two imaqing systems in making decorative surface covering products necessarily requires that the colored pigment system adheres well to the - 2~7 3 17 protective wear layer as well as the base structure. In floor and wall products, the base structure often is composed of plasticlzed 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 cf these imaging systems are printed directly onto tAese 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 pisment/resins used in both of these imaging systems between itself, the wear layer, and base, is unacceptable.
Tn order to guarantee the permanent adhesion required for performance, a primer is applied first to the polymeric film 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.
In the second preferred embodiment, the resin sy~tem used in the two primer layers will crosslink at temperatures typically at 80C to 140C 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 primer in an aqueous based system preferably includes an aqueous colloidal dispersion of the polymer resins identified with respect to the organic solution 2~57~17 primers above. Pre~erably the resins lnclude 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 Ccatings); Aquathane 60, a urethane dispersion ~Peerless Emulsions); NeoRez XR-9409 and NeoRez XR-9679, urethane dispersions (ICI Resins); and combinations thereof.
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 about 5% to about 15% by weight of N-methyl-2-pyrrolidone solvent and about 0.5% to about 2.0% by weight of N,N-diethylethanamine. Other solvents include N-methyl piperidone and N,N-dimethyl acetamide.
Optional surfactants include an ethylene glycolJethyl alcohol mixture such as Permuthane KM-10-1610 (Permuthane Coatings). Such surfactants may 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., KM-10-1880 ~Permuthane Coatlngs); carbodimide, e.g., KM-10-1869 (Permuthane Coatings); aziridine, e.g., KM-10-1703 (Permuthane Coatings); and hexamethoxylated melamine resins, e.g., Resimene R475 (Monsanto).

2~57~ 1~

Example l - Lithoqraphic_printinq system A 0.5 mm thick clear rigid PVC film in sheet form was gravure-coated with a clear primer made according to Formula 1, below.
Formula 1 20% by weight VAGH, a hydroxy-modified polyvinyl chloride/vinyl 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 p_inted 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 overniqht drying, the white primer of Formula 2 below was applied over the dried lithographic inks at the dry weight rate of 7-9 grams/square meter and zir-dried.
Formula 2 20% by weight TiO2 pigment 80% by weight Formula l 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: 163C, 20 seconds, 100 psi for heating, and 38C, 20 seconds, 100 psi ~ 2~S7111.7 for cooling. By placing different texturing means against the unprinted side of the film, various textural surface fea~ures 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 as well as a more deeply embossed-in-register product where the depths were measured as much as 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 roSogravure inks are used as the ink layer.
Exam~le 2 - Electroaraphic Printin~ SYstem The same primer Formula 1 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 was applied colored llquid toners (Hilord Chemical Corporation). The toners that were applied seguentially were cyan, magenta, and yellow. The toners were applied using a modified electro~raphic imaging and developing system. The electrostatic imaging was provided by an ionographic deposition technique. After evaporation of toner carrier, another thickness of Formula 1 was applied and dried in the same manner. The post lamination and texturing steps of Example 1 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 adheslon between the protective film, toned image, and the tile base was permanent.

~- 2~a7:~7 Example 3 - Hi~her Tg 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 68C of Examples 1 and 2 to 105C by substituting a methyl methacrylate polymer, Acryloid A-21 (Rohm and Haas) for the VAGH of Formula 1 and a solvent comprising methyl ethyl ketone/isopropyl acetate/propyl acetate in a ratio of 1:1:1 for the MIBK of Formula 1.
ExamPle 4 - Aqueous Based Litho~raPhic Svstem 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 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. Adheslon between the O.S mm wear layer film and the floor tile base was excellent.
Though the inventors do not wish to be limited to the following explanation, they believe the improved adhesion 2~7~17 results from the solvents of the primer diffusing into the lithograp~,ic ink layers or electrographic toner layers carryin~ 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 sheat 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 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 (15)

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, and wherein, during application of the primer, the primer comprises a solvent selected from the group consisting of benzene derivatives, ketones, acetates, nitroparaffins, pyrrolidones, piperidones and acetamides.

2. The sheet of claim 1, wherein the ink is selected from the group consisting of a lithographic ink and an electrographic toner.

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

4. The sheet of claim 1 or 2, wherein, during application of the primer layer, the primer comprises an aqueous dispersion.

5. The sheet of claim 3 or 4, wherein the primer comprises a solvent selected from the group consisting of toluene, methyl isobutyl ketone, methyl ethyl ketone, isopropyl acetate, n-propyl acetate, propylene glycol monomethyl ether acetate, 1-nitropropane, N-methyl-2-pyrrolidone, N-methyl-piperidone and N,N-dimethyl-acetamide.

6. The sheet of any of claims 1 to 5, wherein the primer layer comprises a resin selected from the group consisting of polyvinyl, acrylic, polyurethane, polyester and copolymers thereof; preferably polyvinyl chloride, polyvinyl chloride/polyvinyl acetate copolymer, hydroxy modified polyvinyl chloride/vinyl acetate copolymer, carboxyl modified polyvinyl chloride/vinyl acetate copolymer, or methyl methacrylate polymer.

7. The sheet of any of claims 1 to 6, wherein the primer layer has a glass transition temperature of at least 60°C, preferably at least 100°C.

8. The sheet of any of claims 1 to 7, wherein the polymeric sheet is selected from the group consisting of polyvinyl, acrylic, polyurethane, polyester and copoylmers thereof.

9. The sheet of any of claims 1 to 8, further comprising a second primer layer and wherein the ink is encapsulated between the two primer layers.

10. The sheet of claim 9, wherein the first primer layer adjacent the polymeric sheet is clear and the second primer layer is white.

11. The polymeric sheet of any of claims 1 to 7, 9 or 10, wherein the polymeric sheet is a rigid PVC sheet.

12. A floor covering comprising the sheet, primer layer and ink of any of claims 1 to 8.

13. The floor covering of claim 12, wherein the ink is encapsulated between two layers of primer.

14. The floor covering of claim 12 or 13, wherein the polymeric sheet is a rigid PVC sheet.

15. The floor covering of any of claims 12 to 14, further comprising a crosslinked wear layer.