EP0115038A2 - Process for the production of coloured decorative paper with a three-dimensional surface structure - Google Patents

Abstract

1. A process for the production of colored decorative sheet-form paper having a three-dimensional surface structure by printing the paper sheets with a pattern using an aqueous printing ink, drying the printed sheet, lacquering the printed sheet with an aqueous lacquer and hardening the lacquered sheet, the printing ink applied in those areas where the lacquer film is thinner than in the other areas containing a lacquer repellent, characterized in that the printed sheet is coated with an aqueous lacquer having a viscosity of 15 to 40 sec. in an AK4 cup essentially containing as binder a mixture of A) a mixture of a urea and/or melamine resin dissolved in water an an aqueous acid as hardener, which hardens in less than 100 seconds at > 100 degrees C after mixing of the aqueous resin solution with the acid, B) a binder selected from the group consisting of a) water-dilutable polyester resin, b) acrylate resin c) ethoxylated glycerine derivative, binder B) containing 10 to 250 parts by weight solids to 100 parts by weight solids in binder A), and the lacquered sheet is hardened in the absence of pressure by exposure to air heated to beyond 100 degrees C.

Description

The invention relates to a process for the production of colored decorative paper foils with a 3-dimensional surface structure by printing the paper foils with a pattern and overpainting, the printing ink being printed on the areas where the lacquer layer is thinner than on the other areas contains paint repellent.

A method of the type described above includes in US-A-3811915. A major disadvantage of this method is that the printed paper must be coated within 20 hours at the latest, since otherwise a 3-dimensional pattern can no longer be obtained (see column 3, lines 59-61). However, there is a need to first print on the paper foils and to varnish them as required in a separate operation. One of the reasons for this is in that the printing of paper foils is often carried out in factories other than the impregnation or lacquering with solutions containing synthetic resin binders. The printed papers can then be stored and shipped and varnished at any time to produce the decorative paper films with a 3-dimensional surface structure.

Another process for producing decorative paper films of this type is described in DE-A 3024391. According to this method, the paper foils are printed by successively applying a plurality of primary colors, whereby the last base color contains a paint-repellent agent, and the paper is then optionally impregnated and then varnished. However, no information is given on suitable paints to be used.

The invention is based on the task of finding a simple method which is easy to carry out on an industrial scale for producing the decorative paper foils described at the outset and which reliably leads to a 3-dimensional surface structure.

The object is achieved in accordance with the method of claim 1. The paper foils are printed with a pattern as in the prior art. If only a two-color pattern is desired, it is sufficient if the paper film having a desired color is printed with a pattern with a different color. However, multi-colored decorative paper foils can also be produced by printing the paper foils in succession with several colors in order to achieve the desired pattern. In any case, the last printing ink must be printed on the areas where the lacquer layer of the finished film is thinner than on the other areas. In order for this to be achieved, this last printed ink must contain a paint-repellent. As described in the abovementioned literature references, polysiloxanes based on silicone resins and oils can be used as paint repellants. Specific examples are lower alkyl silicones such as dimethyl and diethyl silicone. Examples of such commercial products are Dri-Film 1040 from General Electric and silicone fluid 1107 from Dow Corning (registered trademarks). Lower alkyl silicones, which contain a certain proportion of phenyl groups, or ester waxes (waxes based on crude montan wax) can also be used.

The content of such paint-repelling agents in the last-printed printing ink ensures that when painting in the appropriate manner described, the paint is repelled at the points printed with this printing ink and is therefore thinner than in the other areas. In this way, a clearly 3-dimensional surface structure, such as that which has a wooden surface (veneer), is achieved on a decorative paper film having a smooth surface. The decorative paper foils according to the invention, when printed with a wood pattern, are practically indistinguishable from an artificial wood veneer.

An essential feature of the method of the invention is that the paper film is printed with an aqueous gravure printing ink based on protein. The term "aqueous" means that the liquid phase consists essentially of water. Up to about 30% by volume, preferably up to 20% by volume, particularly preferably up to 10% by volume, based on the total amount of the liquid phase, of aliphatic monohydric or polyhydric alcohols can be contained in the printing ink as solubilizers. Examples of these are methanol, ethanol, ethyl glycol, propyl alcohols, glycerin, etc. Preferred are ethanol and ethyl glycol or a mixture thereof, the proportion of ethyl glycol in the mixture of ethanol and ethyl glycol expediently being about 10 to 40% by volume, preferably about 15 to Is 30% by volume.

The printing ink contains an organic binder. A preferred binder is casein. In addition, the printing ink naturally contains the desired coloring pigments as well as any aforementioned paint additives such as silicone resins or oils and special waxes.

Another essential feature of the method of the invention is that the printed decorative paper film is dried. It can last a long time, i.e. Can be stored for weeks, months or even years. The further processing can then take place at any place or at any time on a plant suitable for this. An aqueous paint according to the above definition is used for painting. The essential feature of the method of the invention in this regard is the use of an aqueous varnish. Here too, as already described in connection with the printing ink, the aqueous lacquer can contain small amounts, preferably up to 20% by volume, particularly preferably up to 10% by volume, of organic solvents as solubilizers. Suitable organic solvents for the varnish are ethanol, glycols, methoxybutanol.

It is important that the aqueous varnish have a processing viscosity in the range of 15 40 "AK 4/20 ° C, preferably 22-30". The viscosity in the AK-4 cup is determined according to DIN 53211.

• 1) Maprenal MF 900 = nichtplatifiziertes Hexamethoxymethylmelaminharz (Hoechst AG) (eingetragenes Warenzeichen)
• 2) Maprenal MF 920 = hochreaktives, nicht plastifiziertes Melaminharz (Hoechst AG) (eingetragenes Warenzeichen)
• 3) Methanolverätherte Aminoharze der Plastopal- und Luwipal-Reihe (BASF) (eingetragenes Warenzeichen).

An essential binder component is the urea and / or melamine resin defined under a). These are commercially available aqueous solutions of such resins. Examples of such commercial products are

• 1) Maprenal MF 900 = non-plated hexamethoxymethyl melamine resin (Hoechst AG) (registered trademark)
• 2) Maprenal MF 920 = highly reactive, non-plasticized melamine resin (Hoechst AG) (registered trademark)
• 3) Methanol etherified amino resins of the Plastopal and Luwipal series (BASF) (registered trademark).

Such urea and melamine resins are cured in a known manner with an aqueous acid, as is known to the person skilled in the art. Organic and inorganic acids can be used. Examples of organic acids are p-toluenesulfonic acid or blocked p-toluenesulfonic acid. Examples of suitable inorganic acids are phosphoric acid.

It is important that the mixture of urea and / or melamine resin and the hardener acid dissolved in water has a long pot life at room temperature (approx. 4 to 8 hours) and a short pot life at elevated temperature. The catalyzed lacquer mixture must therefore harden at a temperature> 100 ° C. in less than 100 seconds, expediently in less than 80 seconds and preferably in less than about 60 seconds.

In order to achieve a good 3-dimensional effect, it is necessary that the paint contains the component B described above in the amount specified above as a binder. At least about 10 parts by weight, preferably at least about 20 parts by weight, of binder B are preferably used per 100 parts by weight of solid-state binder A. On the other hand, the upper limit for the proportion of binder B is expediently 250 parts by weight, preferably 150 parts by weight.

The product (registered trademark) is an example of acrylic resins and glycerol derivatives.

Worleepol V 808 = water-dilutable, low-viscosity,. highly reactive polyester resin (Worlee-Chemie GmbH)

An example of a suitable acrylic resin is (registered trademark) Acronal 240 D = aqueous, plasticizer-free dispersion of a thermally crosslinkable copolymer based on an acrylic acid ester and styrene (BASF).

The commercial product is an example of ethoxylated glycerine derivatives

Plasticizer 9 = oxyethylation product of glycerin (BASF).

The same applies here too. In addition to the binders, the paint contains suitable paint additives, such as plasticizers, matting agents, defoamers, and anti-settling agents, as is known to the person skilled in the art.

The paint contains about 40 to 60 weight percent solids in binder. It is expediently applied in an amount of 10 to 50 grams of lacquer solution per m ^{2 of} decorative paper film, preferably 25 to 35 grams per m ² .

Immediately after painting, the film is hardened by the action of air heated to more than 100 ° C. without the action of pressure. The upper temperature limit for the heated air is determined by the prevention of undesirable properties common in paint technology, such as blistering and paint flow.

It is expedient to dry in a hanging dryer, the temperature of the heated air rising to about 160 ° C. To produce a decorative paper film with particularly good mechanical properties, it is expedient that the process described in claim 2 is used.

Aqueous impregnating resins such as are state of the art can be used here as urea, melamine, polyester or acrylate resins.

To carry out this process step, the film impregnated with the resin solution can be passed over a co-rotating or counter-rotating water-carrying roller before it enters the drying zone. Then the wash water applied by the roller together with excess impregnation resin is removed from the (printed) top of the impregnated film e.g. smeared off with a squeegee. In order to avoid an accumulation of impregnating resin in the washing water that is fed to the roller, fresh water must be constantly added and the water containing impregnating resin must be removed. The film impregnated in this way and washed out on the top is then dried. The drying causes the impregnation resin to harden. It can be cured in the same way as described for the painting above. However, this impregnating resin is expediently cured at somewhat higher temperatures, i.e. the heated air suitably has a temperature of at least about 100 ° C, preferably at least about 140 ° C, and the upper limit for the heated air is suitably about 180 ° C, preferably 170 ° C.

A particularly pronounced effect with regard to the 3-dimensional surface can be achieved in that the coated film is passed directly after the coating application before heating with air with the unprinted side over a heated roller with a roller surface temperature of 60 ° C to 100 ° C.

The roller surface temperature is expediently at least about 80 ^° C. This process variant achieves a particularly strong formation of the pores.

A particular advantage of the process of the invention is that decorative paper films with excellent mechanical and chemical properties can be obtained from very thin paper films. According to the invention, paper foils with a square meter weight of 30 to 250 grams can be used. So-called laminate papers can be used which have not yet been impregnated with any synthetic resins.

Laminate papers which are smooth on one side and which are printed on the smooth side are particularly preferably used. The 3-dimensional surface structure appears particularly strongly on the smooth side. The rougher side, on the other hand, enables a better connection to the surface on which the decorative paper foils are applied.

The papers used for printing can also have a pre-impregnation, such as is already carried out in the paper mill in the manufacture of such papers to be printed. Such papers are commercially available under the name "special papers gap-proof".

In order to obtain a particularly smooth surface on the side to be printed, it is possible to pass the papers over so-called super calenders before printing with the side to be printed.

The invention is explained in the following examples. The stated amounts are parts by weight, unless stated otherwise.

Example of printing inks:

Examples of paint solutions can be mixtures of the following components:

Examples of impregnation solutions:

example 1

A commercially available paper with a weight of 60 gjm ² (commercial product special paper splitting-resistant 60 g / m ^{2 from} the company Holtzmann & Cie. AG) is printed using the ink A in the 1st inking unit with a wood grain pattern in direct gravure printing and dried. The film printed in this way is printed in the second inking unit with printing ink B, which contains a paint-repellent agent. Printing with this printing ink takes place only at the points at which pore formation is to be generated. This printing ink is colored darker than printing ink A. Printing ink B therefore basically has the same composition as printing ink A, only with the modifications described above.

The paper film printed in this way is coated after 2 months with the coating solution A on the printed surface with an application amount of 12 g / m ² on a conventional paper coating machine, the application amount being set by a circular doctor blade. The lacquered film is passed through a drying tunnel in which the air temperature rises from 100 ° C at the entrance to 150 ° C at the exit of the drying tunnel. The dwell time in the drying tunnel is about 40 seconds.

Example 2

A paper with a weight of ₇₀ g / m ^{2 is} used for printing, which is commercially available under the name: decor paper satin from PWA Dekor GmbH + Co. This paper is printed as described in Example 1.

The printed paper is impregnated with impregnation solution A in a conventional paper impregnation system. Excess impregnating agent is removed by squeezing rollers, so that the paper is provided with an amount of 4 ₅ g / m ² solid impregnating resin. Immediately afterwards, the paper sheet with the printed side is guided over a roller running in an ambient temperature water bath. As a result, the resin on the printed side that has not penetrated into the film is washed off. The wash water coating is wiped off using a circular doctor blade. The impregnated paper is then dried in a drying tunnel with an increasing ambient air temperature of 100 ° C to 175 ° C. This paper film can be stored and shipped.

This paper film is coated as described in Example 1. :

Example 3

A laminate paper with a weight of 220 g / m ^{2 is} used, as it is called smooth on one side by the company Holtzmann & Cie. AG is available.

This paper is equipped as 4-color printing. Finally, in the fourth printing unit, that is to say after the inks 1 to 3 have dried, the printing ink modified with ester wax is applied and dried.

After 2 months, the printed paper is subjected to an intensive core impregnation with impregnation solution B in a manner known per se, an impregnation of 70% by weight, based on the weight of the paper, being achieved before washing, as described in Example 2 ( calculated as solid impregnation resin). The impregnated paper is then passed over a water-carrying roller as described in Example 2 and dried.

The painting is done with paint C (matt paint).

The amount of paint applied is 15 grams of binder of the paint per m ^{2 of} the paper film. The film provided with the varnish is then immediately passed over a heating roller which has a surface temperature of 90 ° C. The film is then passed through a drying tunnel with an increasing temperature profile from 80 ° C to 170 ° C, the dwell time being 40 seconds.

Claims (3)

1. A process for producing colored decorative paper films with a three-dimensional surface structure by printing on the paper films with a pattern and overpainting, the printing ink which is printed on the regions where the lacquer layer is thinner than in the other regions containing a lacquer-repellent agent,
characterized in that 1. an aqueous printing ink is used, 2. the printed film is dried, 3. the printed film with an aqueous lacquer with a viscosity of 15 to 40 sec in the AK4 cup containing as a binder essentially a mixture of A) a mixture of a urea and / or melamine resin dissolved in water and an aqueous acid as hardener, which hardens in less than 100 seconds at> 100 ° C. after mixing the aqueous resin solution with the acid, B) a binder selected from the group a) water-dilutable polyester resin b) acrylic resin c) ethoxylated glycerol derivative, 10 to 250 parts by weight of solid binder B) per 100 parts by weight of solid binder A),
is painted, and 4. the lacquered film is hardened by the action of air heated to more than 100 ° C. without the action of pressure. 2. The method according to claim 1, characterized in that the printed film before painting with an aqueous impregnation solution with a viscosity of 15 to 30 sec in the AK4 cup containing a binder selected from the group i) urea resins ii) melamine resins iii) polyester resins iV) acrylic resins
impregnated and the impregnated film is passed immediately after impregnation with the printed side over a roller, the surface of which is coated with water, the wash water coating is wiped off the film, and the film by the action of air heated to more than 100 ° C without the action of Pressure is hardened. 3. The method according to claim 1 or 2, characterized in that the film impregnated according to claim 2 is passed immediately after the coating application before heating with air with the unprinted side over a heated roller with a roller surface temperature of 60 ° C to 100 ° C.