EP0022153A1 - Process for producing a decorative finished effect sheet - Google Patents

Abstract

1. Process for the manufacture of a decorative finished-effect film based on carrier webs made of paper, which contain, in the paper, condensation resins and additionally, if appropriate, polymerisation resins, uniformly distributed and in an amount adequate for achieving delamination resistance, these carrier webs being coated or printed with an acrylate resin, which may or may not be curable, and the coated carrier webs then being heated until they reach a Darr value of =< 6 % by weight, characterized in that the carrier webs thus obtained are printed by means of metered roller application, with 2 to 10 g (expressed as solid resin)/m**2 of a solution of a finishing lacquer consisting of nitrocellulose lacquer or of an acid-curing nitrocellulose-containing lacquer.

Description

The invention relates to a process for the production of a decorative finished effect film based on paper backing sheets which contain condensation resins and, if appropriate, additionally polymerization resins in a uniform distribution in the paper in an amount sufficient to achieve the splitting strength, and coating or printing these backing sheets with an optionally curable acrylate resin and then heating the coated carrier webs until a drying value of <6% by weight is reached.

Ready-made effect films are synthetic resin coatings that have been cured without pressure during manufacture and are glued by the processor to the surface of wood-based panels in veneer presses with a pressure of 0.3 to 1.5 N / cm ² . It is possible to overpaint the glued finished effect films.

Ready-made effect films usually have a paper backing which is interspersed with a condensation resin to achieve splitting resistance. Urea or melamine formaldehyde resins are used as condensation resins. In the form of their solution, these can be added to the paper during its manufacture, s _c inside. Mostly, however, the finished paper webs are soaked with the aqueous solutions of the condensation resins.

Polymerization resins, in particular acrylate resins, can optionally be added to the condensation resins. These acrylic resins can be thermosetting or thermoplastic. If curable acrylate resins are used, they contain reactive groups, e.g. Glycidyl ester groups, N-methylol methacrylamide groups or carboxyl groups. The acrylate polymers can react by reacting these groups with one another or with the reactive groups of the urea or melamine formaldehyde resins. Those acrylic resins which have glass transition temperatures <10 ° C. are preferably used.

The condensation resins and, if appropriate, carrier webs containing polymerization resins are then coated with dispersions or solutions of acrylate resins. It is preferred to use curable acrylic resins with glass transition temperatures of> 20 ° C., since these result in mechanically and thermally more resilient surface layers. The carrier web, which is interspersed with condensation resin and optionally polymerization resin and coated with acrylate resin, is then dried in a drying tunnel with circulation of circulating air until its volatile content, the so-called Darr value, has dropped to <6% by weight. This ensures that the amounts of liquid introduced by the impregnation and coating have evaporated and the condensation or polymerization of the curable resins has been brought to the desired value. During the subsequent gluing onto the wood-based panel to be tempered, there is practically no further curing of the finished effect films. Impregnation and coating of carrier webs is more common as in devices in which the carrier webs are drawn through the solution or dispersion of the impregnating or coating resin present in a soaking tub or float on the surface of such a solution while absorbing the resin solution. Then the resin application is leveled by rollers or doctor devices and, if necessary, an excess is wiped off. The coating can be applied in one or more layers. If relatively thin layers are sufficient, the acrylic resins can also be printed on the carrier webs.

Recently, production methods from printing technology have been used to apply resin to carrier webs. This way of working was not obvious, since the impregnation or coating of paper for the surface treatment of wood-based panels and the printing of paper belong to different technological areas. The specialist familiar with the impregnation and coating of paper usually has no experience with printing on paper and vice versa, the printing specialist hardly knows any impregnation and coating processes. By combining these two different technologies, however, advantageous effects can be achieved.

It was initially believed that only light-weight papers, so-called thin papers, with a low resin content could be provided with additional resin layers on a printing press. For example, DE-AS 27 27 312 describes a process for the production of gap-resistant coating webs on the decor side that have hardened synthetic resin on the basis of thin papers, with the solution or dispersion of a curable impregnating resin first being found on the side of the thin paper intended for decor printing Amounts are applied that the resin is not up penetrates to the back of the paper, then decoratively printed after drying of the impregnated thin paper and optionally coated with the solution or dispersion of a curable resin after application of an intermediate layer, then the film obtained dries and cures. This method is characterized in that the impregnating resin is applied to a thin paper with a basis weight <60 g / m ² in an amount of at least 8% (based on paper weight), but not so much that the resin breaks through, by means of the printing unit of a printing press becomes.

This method offered the use of a printing machine for two reasons: on the one hand, only a relatively small amount of impregnation resin had to be applied to the thin paper, and on the other hand, the basis weight of the paper was at most 60 g / m, so that despite the applied and contained in the paper Resin the flexibility of the paper was ensured to such an extent that printing in the printing unit of a printing machine appeared possible.

The present invention is based on the object of also providing those finished effect films which are impregnated and coated in the customary manner with a surface layer in order to avoid the known disadvantages of such finished effect films. A particular disadvantage of the conventional ready-made effect films is that they often tend to stick together when the warm wood-based panels glued with ready-made effect films are removed from the heating presses and stored in stacks. If, on the other hand, sufficient freedom from blockage is guaranteed, problems often arise in the subsequent painting of the surfaces due to insufficient adhesion of the covering. The surfaces are also mechanically vulnerable. By applying A top coat should both remove the tendency to stick and at the same time form a hard, mechanically stressable surface.

In contrast to the teaching of DE-AS 27 27 312, the topcoat is to be applied to finished effect films in which the hardened condensation and, if appropriate, polymerization resin is contained uniformly over the entire cross section of the carrier webs and in such an amount that the paper is resistant to splitting . While according to the teaching of DE-AS 27 27 312 the impregnating resin is applied only in such an amount that it does not penetrate to the rear, finished effect films are to be treated according to the invention in which the impregnating resin has penetrated to the rear and in which there is no limitation for this Paper weight is provided. This is particularly necessary in the case of finished effect films which contain paper backing sheets with a basis weight of 80 to 120 g / m ² ; at basis weights> 60 g / m ² , the splitting strength achieved according to DE-AS 27 27 312 is not sufficient to meet all technical requirements.

The object of the invention is achieved in that the carrier webs obtained in this way are printed with metered roller application with, based on solid resin, 2 to 10 g / m ^{2 of} a solution of a topcoat composed of nitrocellulose lacquer or acid-curing, nitrocellulose-containing lacquer.

The carrier webs are preferably printed with 2 to 6 g / m ^{2 of} a solution of the topcoat.

Printing with metered roller application is to be understood as a process in which one roller dips into a tub with the solution of the topcoat, is moistened with the solution and transfers it to a second roller, which acts as a printing roller. The paper is over this second roller performed, which is pressed against this by a third roller.

It is hardly possible using conventional coating technology to apply such small amounts of a topcoat evenly to the surface of a finished effect film. From DE-AS 27 27 312 it was known to use the printing unit of a printing press for applying small amounts of resin, but this interpretation also conveys the prejudice that conventional finished effect films are not fed to a printing process, since it was believed that finished effect films were too brittle for this be. The teaching of the present invention goes far beyond that of DE-AS 27 27 312: According to the teaching of DE-AS 27 27 312, thin papers are used which have only been partially and carefully treated with the impregnating resin, care being taken had that the resin did not penetrate to the back of the paper. This ensured that the papers had a high degree of flexibility. In the method according to the invention, carrier webs of any paper weight are used in which the impregnating resin is contained uniformly, i.e. up to the back of the carrier web. Even thin papers with a high resin content can be printed with the desired amount of top coat.

If necessary, the brittleness of an impregnated and coated film web can be reduced by preheating the film web to a temperature above room temperature of about 40 to 50 ° C. before printing.

A nitrocellulose lacquer, to which an acid-curing lacquer can optionally be added, is used as the topcoat. A partially or completely etherified aminoplast resin is used in particular as the acid-curing lacquer.

If mixtures of nitrocellulose lacquer and acid-curing lacquer are used, mixtures in a weight ratio of 20: 1 to 1: 2 have proven particularly useful.

Suitable solvents for the top coats are the solvents known for such lacquers, such as, for example: aromatic hydrocarbons, aliphatic esters, ketones, lower alcohols and mixtures thereof, in particular ethyl or butyl acetate, acetone, methyl ethyl ketone, ethanol or mixtures of these solvents.

It has proven to be expedient to use solutions whose viscosity, measured according to DIN 53 211 (4 mm nozzle, 20 ° _C. ), is 10 to 40 seconds. The viscosity is preferably 15 to 25 seconds.

It is particularly advantageous to print the top coat on the carrier webs using an anilox roller. In particular, a gravure printing device is used. The top coat in the depressions of the printing roller is applied to the material to be printed, i.e. the finished effect film.

This printing process does not produce a coherent film, but rather a dot-like, grid-like printed surface. It was therefore surprising that it is nevertheless achieved that the finished effect films thus obtained no longer stick to one another after gluing and after removal from the heating press, when they are stored in stacks. At the same time, a hard, mechanically stressable surface is supplied that can be easily overlaid. No disruptive optical phenomena form at the interface with the acrylic resin.

The process according to the invention is explained in more detail with reference to the following examples.

example 1

A smooth, filled paper with a decorative print with a basis weight of 80 g / m ² , a density of 0, .82 g / cm ³ , an air passage of 400 ml / min, an ash content of 18% and a resin absorption of 103% , is impregnated with the 50% solution of a urea-formaldehyde resin in water with 0.2 parts by weight of ammonium chloride.

After the water has evaporated, the basis weight is 120 g / m ² ; the volatile content is 9.5%.

The film web thus obtained is coated on the top side with the aqueous 50% dispersion of a crosslinkable acrylate copolymer with a minimum film-forming temperature of 23 ° C. using a wire knife. After drying, a film with a basis weight of 144 g / m ^{2 is} obtained; the volatile content is 2.5%.

On the top of this film web with a screen roller with 50 lines / cm in a printing unit, a coating using an 18% solution of a mixture of 10 parts by weight of nitrocellulose and 1 part by weight of a partially etherified urea-formaldehyde resin in a mixture of 1 part by weight of acetone and 3 parts by weight of ethyl acetate with a viscosity of 17 sec in an amount of 4 g / cm ² (based on solids). The process product obtained in this way is dried at 170 ^° C. for 20 seconds. The film now has a total weight of 147 g / m ² ; the volatile content is 1.8%.

Using a urea-formaldehyde resin as an adhesive, the film is at a temperature of 130 ° C and a pressure of 0.5 N / cm ² glued to a particle board for 30 sec.

The surface coating layer proves to be resistant to splitting and adhesion and shows an even, deep shine. Chipboard coated with this film and stacked for storage does not block even at temperatures of 80 ° C. The surface is scratch-resistant and, in the event of damage due to scratches, can be overpainted with paints that are usually used for this purpose with satisfactory adhesion. The properties of the surface meet the requirements of DIN 68 861 (requirements for furniture surfaces) according to stress group C.

Example 2

A decorative, smooth, filled paper with a basis weight of 106 g / m ² , a density of 0.90 g / cm, an air passage of 450 ml / min, an ash content of 21% and a resin absorption of 87% the mixture of 85 parts by weight of the 50% solution of a urea-formaldehyde resin in water with 0.2 parts by weight of ammonium chloride and 15 parts by weight of a 50% aqueous dispersion of a self-crosslinking, fine-particle acrylate copolymer with a minimum film formation temperature of 0 ° C.

After the water has evaporated, the weight per unit area is 155 g / m ² ; the volatile content is 10.2%.

The film web thus obtained is coated on the top with the aqueous, 50% dispersion of a crosslinkable acrylate copolymer with a minimum film-forming temperature of 27 ° C. coated with a wire doctor. After drying, a film with a basis weight of 176 g / m ^{2 is} obtained; the volatile content is 2.4%.

On the top of this film web, an anilox roller with 50 lines / cm is used in a printing unit to apply a coating using an 18% strength solution of nitrocellulose in a mixture of 1 part by weight of acetone and 3 parts by weight of ethyl acetate with a viscosity of 20 seconds in a quantity of 4 g / m ² (based on solids) applied. The process product obtained in this way is dried at 170 ° C. for 20 seconds.

The film now has a total weight of 180 g / m ² ; _G e-halt of volatile components is 1.8%. The film is processed as in Example 1, the application properties of the film surface are the same except for improved adhesion compared to the paints used for the aftertreatment. The properties of the surface meet the requirements of DIN 68 861 (requirements for furniture surfaces) according to stress group C.

Example 3

A smooth paper provided with a decorative print, which was made gap-proof in the paper machine by adding aminoplast resin and acrylate resin to the paper pulp, with a basis weight of 59 g / m ² , a density of 0.93 g / cm ³ , an air passage of 120 ml / min, an ash content of 12% and a resin absorption of 19%, is printed twice with intermediate drying with a curable acrylate dispersion with a glass transition temperature of 27 ° C, resulting in a basis weight of 70.5 g / m ² after drying; the volatile content is 5%.

On the top of this film web, an anilox roller with 50 lines / cm is used in a printing unit to apply a coating using an 18% strength solution of nitrocellulose in a mixture of 1 part by weight of acetone and 3 parts by weight of ethyl acetate with a viscosity of 20 seconds in a quantity of 4 g / m ² (based on solids) applied. The process product obtained in this way is dried at 160 ° C. for 25 seconds.

The film now has a total weight of 73.8 g / m ² ; the volatile content is 4.0%.

Using a urea-formaldehyde resin as an adhesive, the film is glued to a chipboard at a temperature of 130 ° C. and a pressure of 1.5 N / cm ² against a structured phenolic resin laminate.

The surface coating layer proves to be gap and adhesive and shows a uniform, deep shine. Chipboard coated with this film and stacked for storage does not block even at temperatures of 80 ° C. The surface is scratch-resistant and, in the event of damage from scratches, can be overpainted with paints that are usually used for this purpose with good adhesion. The properties of the surface meet the requirements of DIN 68 861 (requirements for furniture surfaces) according to stress group C.

Claims (5)

1. A process for the production of a decorative finished effect film based on paper backing sheets which contain condensation resins and, if appropriate, additional polymerization resins in a uniform distribution in the paper in an amount sufficient to achieve the splitting strength, and coating or printing these backing sheets with an optionally curable acrylic resin and subsequent Heating the coated carrier webs until a drying value of <6% by weight is reached, characterized in that the carrier webs thus obtained are metered by roller application with, based on solid resin, 2 to 10 g / m ^{2 of} a solution of a topcoat made of nitrocellulose varnish or acid-curing, Nitrocellulose-containing varnish printed. 2. The method according to claim 1, characterized in that the carrier webs are printed with 3 to 6 g of a solution of a topcoat. 3. The method according to claim 1 or 2, characterized in that the carrier webs are printed with the top coat by means of an anilox roller. 4. The method according to one or more of the preceding claims 1 to 3, characterized in that the carrier webs are printed with the top coat by means of a gravure printing device. 5. The method according to one or more of the preceding claims, characterized in that the carrier webs with the solution of a top coat having a viscosity of 10 to 40 sec, measured according to DIN 53 211 at 20 ° C with a 4 mm nozzle, printed.