EP1186708A1 - Process for making an abrasion-resistant overlay paper - Google Patents

Abstract

Production of an abrasion-resistant paper comprises uniformly spreading a composition containing hard particles and a binder to the surface of the paper by means of a screen printing drum.

Description

The present invention relates to a method for producing abrasion-resistant hard material particles coated overlay papers using the screen printing process, the overlay papers and the laminates produced with it.

Overlay paper is usually used to protect a paper surface, that of mechanical stress due to friction, scratching or the like is exposed. These are e.g. Decorative surfaces from e.g. Table and Cupboards, kitchen worktops, and laminate floors and decorative designed everyday objects such as Trays. overlay papers usually consist of α-cellulose impregnated with a melamine resin and then pressed with the base to be protected become. During this pressing, overlay papers become transparent, so that the decorative layer underneath optically through the overlay paper is not affected. Offer the overlay papers so applied the underlying paper has increased abrasion resistance, which internationally recognized measurement methods can be recorded (e.g. the Taber Abraser test). The initial abrasion of one covered with overlay paper Decorative paper, for example, increases to approximately 150 to 250 Revolutions (measured with the standardized "Taber Abraser" device). The abrasion protection can be improved even more by using the overlay paper abrasion-resistant hard material particles are applied. Usually For this purpose, overlay papers are made that contain such hard material particles included, or coated with these. Also described are processes that directly apply hard particles allow on the decorative layers to be protected.

Various materials are used as hard material particles are characterized by good abrasion resistance. The most common The materials used here are primarily aluminum oxide (in particular Corundum), but also silicon dioxide, silicon carbide and other hard Minerals. Corundum has the advantage that its refractive index is very close that of cellulose is so that when using this material there is no clouding of the overlay paper. The particle sizes used are usually in a range from 10 to 80 μm, preferred at 30 - 60 µm. When using smaller particles, the abrasion resistance not enough, larger particles give the surface a rough structure that adversely affects use, as well affects the optical properties.

Such an overlay paper with incorporated corundum is from DE-A 2 107 091 known. A paper is described therein, during which Manufacturing process corundum is introduced, so that the corundum after Finishing the paper inside, that is, between the cellulose fibers, is firmly integrated. The disadvantage of this type of overlay paper lies primarily in the moderate abrasion resistance of the top ones Layer of paper that consists only of cellulose fibers during the Corundum is embedded in the middle of the paper. This leads to stress to an uneven surface appearance. Because the corundum in this process already during the production of the paper in the Pulp used in papermaking is included, all equipment used here not only due to the filler particles contaminated, but also heavily used due to the friction.

European patent EP-B 329 154 describes a method for Applying hard material particles to a paper web (e.g. during production of overlay paper), the particles here with With the help of a metering roller on a paper web drawn under the roller be sprinkled. The paper web enters as the top layer thermosetting melamine resin that picks up the scattered particles. However, the corundum layer applied by this method is not perfectly even on the paper surface and in the resin layer distributed, because of the scattering process irregularities in the area distribution occur. Thus, the wear is uneven What to expect from the surface - especially with high-gloss overlay surfaces - as a qualitative disadvantage of a paper made in this way noticeable. In addition, smoothness of the surface can often occur cannot be achieved to the desired extent because the particles on the resin sprinkled just before drying and not necessarily evenly penetrate the resin.

DE-A 196 04 907 relates to a method for producing an overlay paper, in which a paste containing corundum and possibly a binder using the web on the paper machine at the wet end a slot coating head is applied.

Methods are known from DE-PS 195 08 797, DE-PS 28 58 182 and EP-A 186 257 known, according to which decor papers directly with an abrasion-resistant layer be covered without applying an overlay paper. In the described The process uses a relatively small proportion of corundum Cellulose fibers or microcrystalline cellulose mixed and either together with the melamine resin or in two successive steps (first coating, then impregnation) on the decor sheets applied. The mixture is applied by means of a Wire doctor blade, a reverse coating system or an anilox roller. The Decorative sheets produced according to these processes are therefore immediately effective an abrasion-resistant corundum layer, which is characterized in that relative little corundum is contained and this does not adhere to the fibers of the decorative paper is bound, but to that in the order layer Cellulose. The disadvantage of this method is that either relatively thick layer of resin is necessary to prevent excessive corundum loss avoid, or the bond of the corundum layer to the decorative paper designed very difficult, and thus with an increased loss of corundum is to be expected. However, a thicker resin layer is not as flexible and becomes more fragile, which makes processing the decorative sheets more difficult.

In all of the methods described, the problem of even distribution of the abrasion-resistant particles on the paper sheets pointed. To ensure a uniform degree of wear across the entire To get a protective surface, the particles must be even in this Area to be distributed. However, the particles tend due to their density to sink in the application mix so that it easily becomes an uneven Spread over the surface of the paper comes up. This effect can on the one hand by stirring the mixture intensively during application, on the other hand can be counteracted by improved application methods.

The object of the invention presented here is a method for to provide a paper that is uniform across the entire Surface offers high protection for sensitive surfaces while at the same time good workability and low cost. This task is solved by a process for producing an abrasion-resistant paper, wherein a composition containing on a surface of the paper Hard material particles and a binder using a screen printing drum is applied as well as by one obtainable by this method abrasion resistant paper.

A mixture containing hard material particles is applied according to the invention one-sided using the rotary screen printing process. The rotary screen printing has the particular advantage that the applied Mixture during application by the rotation of the screen printing roller is constantly mixed, and thus the mixture is constantly in its original percentage composition is retained. This makes additional mixing organs just in front of the application organ, like them from the prior art e.g. DE-A 196 04 907 are known, superfluous and brings about a better homogeneity compared to this prior art the composition at the time they are on the paper web occurs. The application using a micro-perforated screen printing stencil also has the advantage of an extremely even distribution of the mixture on the paper web. So it differs the paper obtainable by the process according to the invention from the State of the art papers.

For the production of the overlay paper according to the invention, preference is given to using a high-quality paper which is distinguished by thermal resilience and high wet strength. This can be a paper made of cellulose, preferably α-cellulose, made from 100% softwood. A paper made of needle sulfate pulp with a proportion of up to 8% wet strength agent, based on the pulp, is particularly preferred. The basis weight of the paper can be 15-60 g / m ² , preferably 25-40 g / m ² , very particularly preferably at least 30 g / m ² . The bulk density of the paper is preferably 0.25-0.60 g / cm ³ , particularly preferably in a range of 0.32-0.45 g / cm ³ .

a) Hartstoffteilchen, vorzugsweise in einer Menge von 72 - 90 Gew.%,

b) Bindemittel, vorzugsweise in einer Menge von 9,5 - 25 Gew.-%,

c) Naßfestmittel, vorzugsweise in einer Menge von 0,5 - 3 Gew.-% und

d) Wasser.

In a preferred embodiment, the composition used to produce the overlay paper according to the invention contains:

a) hard material particles, preferably in an amount of 72-90% by weight,

b) binder, preferably in an amount of 9.5-25% by weight,

c) wet strength agent, preferably in an amount of 0.5-3% by weight and

d) water.

The composition particularly preferably contains wt.% 77-86 hard material particles, 13.5-21% by weight of binder and 0.5-2% by weight of wet strength agent. The percentages relate to the total weight the solids in the composition and the solids content is 30-60% by weight based on the total composition.

In the composition used in the method according to the invention the usual binders used in papermaking are used become. However, it has been found that the inventive Process on the use of melamine-formaldehyde resins as binders, which are usually used in the prior art during production of overlay paper can be used. This has considerable advantages in terms of occupational safety and health in compliance with environmental regulations.

Preferred binders are selected from branched or unbranched, short or long chain polysaccharides, polyurethanes, polyacrylates, Polyacetals, polyvinyl acetate, polyvinyl alcohol, polymers and Copolymers of styrene, acrylic esters, acrylic and methacrylic acid esters, Acrylonitrile, acrylates, acrylamide, gelatin, guar, viscose, or one Mixture of two or more of these substances. The polysaccharides are with regard to binding power for the hard material particles and desired transparency after lamination particularly advantageous and can be modified or unmodified starch or cellulose, also in crystalline and microcrystalline form, e.g. CMC include. A preferred binder for use in the present invention is starch, each in papermaking usable starch can be used. Is preferred a starch soluble in cold water is used, particularly preferably an acetylated one Starch of medium to high viscosity (viscosity from 1000 to 1800 BU; 25%, [HB], T = 30 ° C, according to Brabender). A particularly preferred one Binder is a cold soluble, substituted, weakly anionic Potato starch. The use of such a carrier has the Advantage that the hard material particles, especially corundum, adhere to it, and can be dispersed particularly well in the composition.

In order to increase the abrasion resistance of a surface, hard material particles have long been used in overlay paper production. Those hard material particles are preferred which do not appear to be disruptive when applied to a surface to be protected. Corundum (aluminum oxide, Al ₂ O ₃ ) has proven to be particularly suitable here, since this material becomes transparent when pressed with the surface to be protected, for example a decorative paper, when producing a laminate. However, any other material which has the desired properties can also be used, such as silicon carbide, tantalum carbide, tungsten carbide, silicon nitride, silicon dioxide, titanium nitride or boron nitride.

For the production of the overlay paper according to the invention is preferred Corundum with an average grain size of 10-80 µm used, preferably with a grain size of 20-70 microns. Especially preferred is a corundum with an average grain size of 35-55 µm.

The applied corundum can also contain traces of other minerals, such as SiO ₂ , Na ₂ O, TiO ₂ , FeO, CaO, SiO, K ₂ O, Fe ₂ O ₃ , MgO and the like, but preferably in a proportion of less 2%, particularly preferably less than 1%.

Particularly suitable wet strength agents for use in the process according to the invention are polyamidamine-epychlorohydrin resins, melamine-formaldehyde resins and epoxy resins. Melamine-formaldehyde resins are particularly preferred when high transparency of the overlay paper after it is pressed into a laminate is desired. Most preferred are modified melamine-formaldehyde resins, especially methyl etherified melamine-formaldehyde resins that are low in free formaldehyde.
Additional additives to the mixture according to the invention are all additives known in papermaking, in particular wetting agents, dispersants, retention agents, defoamers, dyes and surfactants.

The viscosity of the mixture according to the invention when applied preferably in a range of 250-600 mPa * s at 25 ° C, particularly preferred in a range of 300-500 mPa * s. The solids content in the mixture according to the invention is dependent on the application template used and speed set, but is preferably in a range of 30-60% based on the total weight of the mixture, particularly preferably between 38-46%.

The mixture according to the invention is produced with intensive stirring and by the rotation of the screen printing drum during the job constantly further mixed.

In screen printing, the recipe is made using a squeegee through a fine mesh Sieve (template) pressed. The order quantity is determined by the Mesh size of the template, the thickness of the template, thickness (diameter) of the squeegee and influenced by the recipe.

To ensure a defined and even application of hard material, the mixture to be applied and the screen printing template used optimized against each other.

Can be used to apply the mixture according to the invention described herein in particular the mesh size, the hole diameter and the thickness of the Stencil can be varied.

The preferred application amount of the mixture described above is 14-23 g / m ² , particularly preferably 15-21 g / m ² , based on solids. It is preferred here to select the composition of the mixture and also the total application amount of the mixture on the paper such that the amount of binder applied is 2.0-4.1 g / m ² , preferably 2.6-3.5 g / m ² , particularly preferably 2.8-3.2 g / m ² , the amount of hard material particles applied 12-18 g / m ² , preferably 13-17 g / m ² , particularly preferably 14-16 g / m ² and the amount of applied wet strength agent 0.12-0.5 g / m ² , preferably 0.12-0.3 g / m ² , particularly preferably 0.15-0.23 g / m ² , in order to achieve an optimal ratio of good transparency and to achieve good abrasion properties.

By applying the hard material composition according to the invention on the one hand, for the production of an abrasion-resistant paper extremely even distribution of the hard material over the surface, on the other hand a high degree of integration of the hard material particles is achieved. Because of that comes high abrasion resistance with extremely low loss of hard material particles. The one-sided hard material application also has a special one Advantage that in the further processing of the overlay paper, e.g. in laminate production, the equipment used in processing Protected against excessive wear from the hard material particles are.

The basis weight of the finished overlay paper is 20-100 g / m ^2, preferably 25-80 g / m ² .

Fig. 1 shows a schematic representation of a device with which the method according to the invention can be carried out.

The composition containing hard material particles according to the invention becomes continuously a screen printing drum 1 with a microperforated Screen printing stencil is supplied so that there is always a fabric swamp 2 is maintained within the screen printing drum 1. The Paper web 3 is between the rotating screen printing drum 1 and one also rotating carrier roller 4 passed. The hard material particles containing composition is supported by a doctor blade 5 through the openings of the screen printing drum 2 onto the paper web 3 applied. The application thickness of the composition according to the invention the paper web 3 can be in this method on the viscosity of the Composition, mesh size and thickness of the screen printing stencil used and regulate the diameter of the doctor rod 5 used.

Embodiment:

A corundum-containing mixture is made by combining: 19.5% by weight a commercially available cold water-soluble acetylated and oxidized potato starch as a binder, 79.5% by weight Corundum with an average particle size of 44.5 ± 2 µm and 1.0% by weight a commercially available wet strength agent based on an extremely formally low-dehydrated melamine-formaldehyde resin, where the percentages relate to the total weight of the solids of the composition,
and water in an amount such that a viscosity of 300-500 mPa * s at 25 ° C, with a total solids content of about 41% in the mixture is obtained.

The above-described corundum-containing mixture with an application weight of 15-18 is applied to a base paper made from 100% needle sulfate pulp with a proportion of 5% wet strength agent (polyamidamine-epychlorohydrin resin), based on the cellulose with a mass per unit area of approx. 30 g / m ² g / m ² , based on solids. For this purpose, the mixture, which was initially produced with vigorous stirring and adjusted to the desired viscosity, is filled into a screen printing drum which is equipped with a screen printing stencil which has a mesh width of 40, a hole diameter of 161 μm and a thickness of 100 μm, and according to FIG. 1 applied to the paper. An application speed of 40 - 60 m / min can be achieved

With such a template, the desired order quantity in one extremely uniform surface can be achieved. The so obtained Overlay paper is dried in a conventional dryer, in the usual Kind of wrapped up and then cut to size. According to an optical assessment, the corundum is on the produced overlay paper completely evenly distributed.

This corundum overlay paper comes with a quantity of approx. 200 % By weight of resin based on the weight of the paper coated with resin. This resin coated Overlay paper is placed over a decorative paper and with a MDF board pressed at 180 ° C and a pressure of 200 bar for 35 seconds. The product obtained in this way has abrasion values of class AC 3 (≥ 2500 Cycles Taber Abraser Test).

List of reference numerals:

1

Screen printing drum

2

fuel sump

3

paper web

4

king roll

5

roll doctor

Claims (12)

Process for producing an abrasion-resistant paper, wherein on a surface of the paper a composition containing hard material particles and a binder by means of a screen printing drum is applied. Method according to claim 1,
the composition being applied to the already formed paper web. Method according to one of the preceding claims,
the composition having a viscosity of 250-600 mPas at 25 ° C. Method according to one of the preceding claims,
the composition containing: a) hard material particles, b) binders, c) wet strength agent, and d) water. Method according to one of the preceding claims,
being the composition 72 - 90% by weight, hard material particles, 9.5-25% by weight of binder, 0.5 - 3% by weight wet strength agent, each contains based on the total weight of the solids in the composition and has a solids content of 30-60% by weight based on the total composition. Method according to one of the preceding claims,
wherein the binder is selected from branched or unbranched, short or long chain polysaccharides, polyurethanes, polyacrylates, polyacetals, polyvinyl acetate, polyvinyl alcohol, polymers and copolymers of styrene, acrylic esters, acrylic and methacrylic acid esters, acrylonitrile, acrylates, acrylamide, gelatin, guar, viscose , or a mixture of two or more of these substances. Method according to claim 6,
the binder being a starch, in particular a starch soluble in cold water. Method according to one of the preceding claims,
the hard material is selected from corundum, silicon carbide, tantalum carbide, tungsten carbide, silicon nitride, silicon dioxide, titanium nitride and boron nitride. Method according to one of the preceding claims,
the composition being applied in an amount corresponding to 14-23 g / m ² solids. Abrasion-resistant paper available according to one of claims 1-9. Abrasion resistant paper, where
the paper has a basis weight of 20-100 g / m ² . Laminate, which is an abrasion-resistant paper after a of claims 10 and 11 with an underlying decorative layer having.

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