EP3754109B1 - Pre-impregnate with improved flatness - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to prepregs for coating purposes and decorative papers or decorative coating materials obtainable therefrom.

BACKGROUND OF THE INVENTION

Decorative coating materials, so-called decorative papers or decorative foils, are preferably used for surface coating in the manufacture of furniture and in interior design, in particular laminate floors. Decorative paper/decorative film is synthetic resin-impregnated or synthetic resin-impregnated and surface-treated, printed or unprinted paper. Decor papers/decor foils are glued or glued to a carrier board.

Depending on the type of impregnation process, a distinction is made between decorative papers/decorative films with a paper core impregnated with a thermosetting resin and so-called pre-impregnated materials, in which the paper is only partially or almost completely impregnated with resin dispersions and water-soluble polymers online or offline in the paper machine.

Urea glues or polyvinyl acetate (PVAC) glues are usually used to glue the decorative foils to wood-based materials such as chipboard or MDF boards.

In the case of the laminates made from prepregs, the decorative film, an optionally printed prepreg with a lacquer layer, is used of the glue with a substrate, such as a chipboard, pressed using pressure at elevated temperature. This can be done, for example, with a short-cycle press or with a laminating calender.

In the processing industry, high demands are placed on the ability to bond and the adhesion of the applied decorative film. The adhesion must be good immediately after the gluing process in order to avoid damage to the freshly laminated board during further handling. The panels are often further processed by sawing, milling and drilling just a few minutes to hours after the decorative foil has been applied. Furthermore, the finished surfaces are often packaged for further transport using adhesive tapes which are also applied directly to the finished decorative surface. These adhesive tapes must have sufficient adhesive strength; it must be possible to remove them without leaving any residue after transport, without damaging or detaching the glued decorative foil. The decorative foil must therefore have a high splitting strength perpendicular to the decorative surface even after bonding.

The decorative foil used with the above-mentioned coating materials is white or colored with or without additional printing.

With regard to the application properties, the so-called decorative base papers used as starting materials must meet certain requirements. These include high opacity for better coverage of the substrate, uniform formation and grammage of the sheet for uniform resin absorption, high lightfastness, high purity and uniformity of the color for good reproducibility of the pattern to be printed, high wet strength for a smooth impregnation process, appropriate absorbency to obtain the required resin saturation level, dry strength, which is important in paper machine rewinding operations and printing press printing.

To create a decorative surface, the decorative prepregs can be printed. First and foremost, the so-called rotogravure printing process is used, in which the printed image is transferred to the paper with the help of several gravure rollers. The individual pressure points should be transferred completely and as intensively as possible to the paper surface. But especially in gravure printing, only a small part of the halftone dots on the gravure roller are transferred to the paper surface. This results in so-called missing dots, i.e. imperfections. The ink often penetrates too deeply into the paper structure, which reduces the color intensity. Prerequisites for a good print image with few defects and high color intensity are a surface topography that is as smooth and homogeneous as possible and a coordinated ink trapping behavior of the paper surface. Even with digital printing processes, such as inkjet printing, which are becoming more and more popular today, a surface topography that is as smooth and homogeneous as possible and a coordinated ink trapping behavior of the paper surface are crucial for a good print image.

For this reason, the base papers used for prepregs are usually calendered with so-called soft calenders, sometimes also with so-called Janus calenders. This treatment can cause the paper surface to be crushed and thus compacted, which has a negative effect on the resin absorption capacity.

The print and/or the coating are applied to one side of the prepreg and cause the prepreg to be fixed to the printed and/or coated side, which is also referred to as the decorative side or the visible side. If the side of the pre-impregnation opposite the decor side comes into contact with moisture, as is the case during further processing when gluing, the one-sided stretching and fixing on the opposite side leads to curling (rolling up) or bowling of the pre-impregnation, depending on the impregnation resin used. The pre-impregnation is not flat.

This effect is particularly disadvantageous when processing in multi-platen presses, short-cycle presses and in other non-continuous processes, since bonding with aqueous urea glues (UF glues) or polyvinyl acetate glues (PVAC glues) is impaired.

The decorative film to be bonded, an optionally printed pre-impregnated material provided with a layer of lacquer, is pressed onto a base, for example chipboard, using pressure at elevated temperature. If the edges curl (roll up) before pressing due to the poor flatness of the pre-impregnated material, it is no longer possible to press the decorative film without making mistakes.

The aforementioned properties are essentially influenced by the impregnation of the decor base paper, i.e. by the type of impregnation agent used. If, for example, the usual formaldehyde-containing resins are used as the impregnating resin, the prepregs produced have good flatness properties, whereas the use of formaldehyde-free impregnating resins leads to poor flatness properties in the prepregs produced therewith.

The impregnating resin solutions usually used in the production of classic decorative papers for impregnating the decorative base papers are resins based on urea, melamine or phenolic resins. These lead to brittle products with poor tear resistance and printability. It is becoming increasingly important to ensure that the impregnating resin solutions used to impregnate decorative base paper are free of substances that are harmful to health, in particular free of formaldehyde. Furthermore, the components used should come from renewable raw materials as much as possible.

In the DE 197 28 250 A1 is the use of formaldehyde-free resins based on a styrene/acrylic acid ester copolymer for the production of non-yellowing prepregs described. The disadvantage of this material is that it leads to a product with insufficient adhesion after bonding.

Formaldehyde-free impregnating resin solutions for impregnating decorative base paper are also in the EP 0 648 248 A1 and EP 0 739 435 A1 described. These preferably consist of a styrene-acrylic acid ester copolymer and polyvinyl alcohol. However, the paper impregnated with such an impregnating resin solution can still be improved in terms of adhesion after bonding.

In the WO 2001/11139 A1 a formaldehyde-free composition of a binder, an aqueous polymer dispersion and glyoxal is proposed, which enables the production of split-resistant decorative papers. However, the paper impregnated with this composition does not bond well.

In the WO 2009/000769 A1 describes a formaldehyde-free composition of a styrene-acrylic acid ester copolymer and a starch with a specific molecular weight distribution for impregnation.

the EP 2 537 682 B1 describes a formaldehyde-free composition of a styrene-acrylic acid ester copolymer with hydroxyalkyl (meth)acrylate monomer fractions and a starch with a specific molecular weight distribution for impregnation. This improves the splitting strength and the adhesion of the prepreg after bonding. However, in particular in the process steps of printing, painting and gluing, such prepregs can have an insufficient flatness and undulate in a disruptive manner.

In the WO 2010/089086 A1 the application of aliphatic, polycarbonate-containing anionic polyurethane dispersions is also proposed on the reverse side of impregnated decorative papers intended for bonding in order to reduce the problem of insufficient flatness during further processing. However, comparatively high amounts of 5 g/m ² and more are applied to the back required, and the improvement in flatness only occurs if the front side is coated at the same time with the same polyurethane dispersion. In addition, the properties when gluing the pre-impregnated deteriorate significantly with increasing application quantity.

None of the prepregs known to date, which contain formaldehyde-containing duroplastic resins or formaldehyde-free acrylic resin dispersions, meet all the requirements placed on them, such as health and ecological safety, good flatness during further processing steps such as printing, painting and final gluing and good adhesion after gluing on a wood-based panel.

Either formaldehyde-containing resins are used, which have good flatness properties but whose use is undesirable for ecological and health reasons, or the prepregs based on formaldehyde-free resins have poor flatness properties and/or poor adhesion properties.

SUMMARY OF THE INVENTION

The invention is therefore based on the object of providing a formaldehyde-free prepreg with good flatness that does not have the disadvantages mentioned above and, in particular, after printing and/or painting, through good flatness during gluing and through simultaneous good adhesion after gluing and lamination a permanent carrier, for example a wood-based panel.

This object is achieved by a pre-impregnated material made from a decorative base paper impregnated with a formaldehyde-free impregnating resin solution, with a hydrophobic layer being arranged on at least one side of the pre-impregnated material, wherein the hydrophobic layer is arranged on the side opposite the decorative side of the prepreg.

Surprisingly, it was found that the use of a hydrophobic layer on at least one side of the prepreg, namely the side opposite the decorative side of the prepreg, leads to improved flatness or less bulging of the sheet edges or curling of the prepreg during further processing and at the same time good adhesion Bonding to a wood-based panel with the usual aqueous glues is retained.

The subject matter of the invention is also a decorative film or a decorative coating material containing the prepreg according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the invention, the hydrophobic layer (coating) is present on at least one side of prepregs which contain a decorative base paper impregnated with a formaldehyde-free impregnating resin, the hydrophobic layer being arranged on the side opposite the decorative side of the prepreg.

Formaldehyde-free impregnating resins include, for example, starch and/or polyvinyl alcohol. The amount of formaldehyde-free impregnating resin in the prepreg can preferably be 10 to 35% by weight, but in particular 12 to 30% by weight, based on the weight per unit area of the decorative base paper.

Basically, pre-impregnates are decorative base papers impregnated with one or more impregnating resins, which are printed after impregnation. Traditionally, decor papers are first printed, for example with a wood pattern, and then impregnated. Pre-impregnated materials according to the invention are decorative base papers impregnated with formaldehyde-free impregnating resin.

The decorative base papers to be impregnated are papers that have undergone neither mass sizing nor surface sizing. They essentially consist of cellulose, pigments and fillers and the usual additives. Customary additives can be wet strength agents, retention aids and fixing agents. Decor base papers differ from conventional papers in that they have a much higher proportion of fillers or pigments and the absence of the internal or surface sizing that is usual with paper.

The hydrophobic layer on at least one side of the prepreg according to the invention, namely on the side opposite the decorative side of the prepreg, has the function of reducing the water vapor permeability without impairing the ability of the prepreg to bond to a substrate. It also reduces the penetration of moisture, for example the aqueous sizing agent.

The pre-impregnation usually has a decorative side and a side (rear side) opposite the decorative side. The decorative side is the visible side or pressure side of the prepreg that faces the observer of the finished decorative laminate. The side of the pre-impregnated material opposite the decorative side of the pre-impregnated material is referred to as the side of the pre-impregnated material that is opposite the side facing the observer of the finished decorative laminate and which, when the decorative laminate is bonded to a carrier material, faces the carrier material, e.g. the wood-based panel.

According to the invention, the hydrophobic layer is arranged on the side opposite the decorative side of the prepreg.

The coating liquid for obtaining the hydrophobic layer on at least one side of the prepreg can be in the form of a dispersion. This dispersion can be a suspension or an emulsion. Consequently, the waterproofing agent can be present in the dispersion as a solid or liquid (emulsified).

The weight of the hydrophobic layer applied can be 0.1 to 10 g/m ² atro (absolutely dry), preferably 0.3 to 5 g/m ² atro, particularly preferably 0.4 to 2.5 g/m ² atro, very particularly preferably 0.5 to 1.5 g/m ² atro, in each case based on the weight of the prepreg.

The hydrophobic layer according to the invention preferably contains an organic hydrophobing agent in an amount of 20 to 100% by weight, based on the total weight of the absolutely dry (atro) hydrophobic layer, in particular 40 to 90% by weight, particularly preferably 50 to 70% by weight. -%.

Waxes can be used as organic hydrophobing agents. Waxes according to the invention are, on the one hand, mixtures of esters of higher monohydric alcohols with higher fatty acids. On the other hand, according to the invention, this also includes mixtures of substances with a waxy consistency, which melt between 40° C. and 350° C. and which do not or only partially fit the chemical definition mentioned above. According to the invention, higher monohydric alcohols and higher fatty acids are those monohydric alcohols and fatty acids which have chains with 12 to 38 carbon atoms.

Animal, vegetable and synthetic waxes can be used as the wax. Chemically modified natural waxes, so-called semi-synthetic waxes, for example ester waxes (reaction products of long-chain wax acids and monohydric fatty or wax alcohols), amides of fatty and wax acids, such as disetarylethylenediamide or ethylene distearamide, stearic acid amide, behenic acid amide, erucic acid amide, oleic acid amide, acid waxes, lanette are preferred -Waxes, ketone waxes, ether waxes, soy wax, castor wax, rapeseed wax, and fully synthetic waxes, e.g. polyolefin waxes such as polyethylene waxes, high density polyethylene (HD-PE) waxes and polypropylene waxes, olefin copolymers- Waxes such as ethylene vinyl acetate (EVA) waxes, polyester waxes, and polyethylene glycol (PEG) waxes, as well as PTFE waxes and fluorowaxes and mixtures thereof. According to the invention, particular preference is given to polyethylene (PE) waxes, in particular high-density polyethylene (HDPE) waxes, paraffin waxes or mixtures thereof. The mixtures of waxes can be mixtures of two or more waxes of the same type or of different types. A mixture of waxes of the same type is understood to mean, for example, a mixture of two waxes, both of which can be assigned to PE waxes. A mixture of waxes of different types is understood to mean, for example, a mixture of a paraffin wax and a PE wax.

In addition to the hydrophobing agent, the coating liquid can contain other auxiliaries, such as wetting agents, emulsifiers, binders and thickeners. In addition to the hydrophobing agent, the coating liquid particularly preferably contains binders based on acrylate or methacrylate polymers or based on copolymers, the (meth)acrylic acid esters as comonomer.

The hydrophobic layer can be applied to the back of a decorative base paper before or after impregnation of the decorative base paper. Application of the hydrophobic layer after impregnation of the decorative base paper is preferred.

The formaldehyde-free impregnating resin for the production of the prepreg is preferably a mixture of a water-soluble polymer and a polymer latex. The proportion of water-soluble polymer/polymer latex in the impregnating resin solution is preferably 80/20 to 20/80, but a proportion of 45/55 to 65/35 and in particular 50/50 to 60/40 is preferred, based in each case on the mass of the impregnating resin ( atro).

As a water-soluble polymer, for example, starch, starch derivatives or nanoscale starch particles, in particular starch dextrin, from renewable Raw materials can be produced used. According to a further embodiment of the invention, polyvinyl alcohol can also be used.

The polymer latex may preferably be a styrene copolymer such as a styrene-acrylic acid ester copolymer, a styrene-vinyl acetate copolymer, a styrene-butadiene or a styrene-maleic acid copolymer. However, mixtures of these copolymers can also be used.

In a particular embodiment of the invention, the formaldehyde-free impregnating resin used to produce the prepreg according to the invention contains a styrene-acrylic acid ester copolymer, preferably a styrene-butyl acrylate copolymer, as polymer latex.

The impregnating resin solution can contain pigments and/or fillers. The amount of pigment and/or filler can be 1 to 30% by weight, in particular 2 to 20% by weight. The stated quantity refers to the binder mass (atro). The term binder here means the mixture containing the polymer latex and the water-soluble polymer.

The impregnating resin solution used to produce the prepregs according to the invention can have a total solids content, based on the dry matter, of 9 to 40% by weight, preferably 20 to 35% by weight and particularly preferably 26 to 30% by weight.

The impregnated decorative paper coated according to the invention can contain a high proportion of a pigment or a filler. The proportion of filler in the decorative base paper can be up to 55% by weight, in particular 8 to 45% by weight, based on the weight per unit area. Suitable pigments and fillers are, for example, titanium dioxide, talc, zinc sulfide, kaolin, aluminum oxide, calcium carbonate, corundum, aluminum and magnesium silicates or mixtures thereof.

Softwood pulps (long-fiber pulps) and/or hardwood pulps (short-fiber pulps) can be used as pulps for the production of decorative base papers. It is also possible to use cotton fibers and mixtures thereof with the aforementioned types of pulp. For example, a mixture of softwood/hardwood pulps in a mass ratio of 10:90 to 90:10, in particular 20:80 to 80:20, is particularly preferred. However, the use of 100% by weight hardwood pulp has also proven advantageous. The amounts given relate to the mass of the cellulose (atro).

The pulp mixture can preferably contain a proportion of cationically modified pulp fibers of at least 5% by weight, based on the weight of the pulp mixture. A proportion of 10 to 50% by weight, in particular 10 to 20% by weight, of the cationically modified cellulose in the cellulose mixture has proven particularly advantageous. The cationic modification of the pulp fibers can be accomplished by reacting the fibers with an epichlorohydrin resin and a tertiary amine, or by reacting them with quaternary ammonium chlorides such as chlorohydroxypropyl trimethyl ammonium chloride or glycidyl trimethyl ammonium chloride. Cationically modified pulps and their production are, for example, from THE PAPER, Issue 12 (1980) p.575-579 known.

The decor base papers can be made on a Fourdrinier paper machine or a Yankee paper machine. For this purpose, the cellulose mixture can be ground at a consistency of 2 to 5% by weight to a degree of beating of 10 to 45°SR. Fillers such as titanium dioxide and talc and wet strength agents can be mixed in a mixing chest. added and mixed well with the pulp mixture. The high-viscosity stock obtained in this way can be diluted to a consistency of about 1% and, if necessary, other auxiliaries such as retention aids, defoamers, aluminum sulphate and other auxiliaries mentioned above can be added. This thin stock is fed to the wire section via the headbox of the paper machine. A non-woven fabric is formed and, after dewatering, the decorative base paper is obtained, which is then dried. The basis weights of the papers produced can be 15 to 300 g/m ² . However, decorative base papers with a basis weight of 40 to 100 g/m ² are particularly suitable.

The impregnating resin solution can be introduced into the decorative base paper (impregnation) in the paper machine or offline by spraying, impregnating, roller application or spreading (squeegee). Application via size presses or film presses is particularly preferred.

The impregnated papers are dried in the customary manner with the aid of IR dryers or drum dryers in a temperature range from 120 to 180° C. to a residual moisture content of 2 to 6%.

After drying, the impregnated papers (pre-impregnated papers) can also be printed and varnished and then laminated onto various substrates, for example chipboard or fiberboard, using conventional methods.

The hydrophobic layer can be applied to the back of the impregnated paper in the paper machine or offline using any of the application processes customary in the paper industry, such as spraying, soaking, roller application (e.g. kiss coater), brushing on (e.g. squeegee or blade) or cast coating (e.g. curtain coater). Application via a film press or anilox roller with a pressure chamber doctor blade is particularly preferred.

The impregnated and reverse-coated papers are dried in a conventional manner, for example using hot-air convection dryers, IR dryers or drum dryers, in a temperature range from 120 to 180° C. to a residual moisture content of 2 to 6%.

After drying, the prepregs coated in this way can also be printed and varnished and then laminated onto various substrates, for example chipboard or fiberboard, by conventional methods.

The following examples serve to further illustrate the invention. Percentages by weight are based on the weight of the pulp, unless otherwise stated. Quantity ratio means ratio of masses or weight ratio.

EXAMPLES Example V-1 (comparison)

A pulp suspension was prepared by grinding a pulp mixture of 80% by weight eucalyptus pulp and 20% by weight pine sulphate pulp at a consistency of 5% to a freeness of 33° SR (Schopper-Riegler). This was followed by the addition of 1.8% by weight of epichlorohydrin resin as a wet strength agent. This pulp suspension was adjusted to a pH of 6.5 with aluminum sulfate. A mixture of 30% by weight titanium dioxide and 5% by weight talcum, 0.11% by weight of a retention aid and 0.03% by weight of an antifoam was then added to the pulp suspension and a decorative base paper with a basis weight of 50 g / m ² and an ash content of 23 wt .-% manufactured. The weights relate to the weight of the pulp (atro).

This base paper was in a size press with an aqueous resin solution with a solids content of 30% by weight, containing starch dextrin (EMDEX ^® B1102, Emsland-Stärke, Emlichheim) and styrene-butyl acrylate copolymer latex (Revacryl ^® X4340 Synthomer, Marl) in a proportion of 55:45, impregnated on both sides. For this purpose, a 45% starch dextrin batch was first prepared and diluted with water to a concentration of 25% by weight. Then the corresponding amount of the 50% strength aqueous polymer dispersion was added and the polymer solution obtained was diluted with water to a solids content of 30% by weight and adjusted to pH 8.0 with sodium hydroxide solution.

The impregnated paper was then dried at a temperature of 120° C. to a residual moisture content of 2.5%. The applied amount of the impregnating resin solution after drying was 10 g/m ² .

The glass transition temperature T _g of the ^Revacryl® X4340 latex (copolymer) used is 28°C.

Example A-1 (Invention)

A wax-containing dispersion was applied to the back of the impregnated base paper produced as in Example V-1 using a rod doctor (100 μm groove depth). The solids content of the aqueous dispersion applied is 20% by weight after dilution. The waxy dispersion is commercially available under the brand name ^Wükoseal® KIT (solids content 40% by weight) from Munzing Chemie GmbH, Abstatt.

The paper coated on the back was then dried at a temperature of 120° C. to a residual moisture content of 2.5%. The applied amount of the coat after drying was 1.5 g/m ² , the applied amount of the wax contained in the dispersion was 0.5 g/m ²

Example A-2 (Invention)

The prepreg is coated as in Example A-1, but the solids content of the aqueous dispersion applied is 15% by weight after dilution.

The paper coated on the back was then dried at a temperature of 120° C. to a residual moisture content of 2.5%. The applied amount of the coat after drying was 1 g/m ² .

Example A-3 (Invention)

A wax-containing dispersion was applied to the back of the impregnated base paper produced as in Example V-1 using a rod doctor (300 μm groove depth). applied. The solids content of the aqueous dispersion applied is 25% by weight after dilution. The waxy dispersion is commercially available under the brand name ^Wükoseal® KIT from Münzing Chemie GmbH, Abstatt.

The paper coated on the back was then dried at a temperature of 120° C. to a residual moisture content of 2.5%. The applied amount of the coat after drying was 5 g/m ² .

Example A-4 (Invention)

A wax-containing dispersion was applied to the back of the impregnated base paper produced as in Example V-1 using a rod doctor (100 μm groove depth). The solids content of the aqueous dispersion applied is 20% by weight after dilution. The waxy dispersion is commercially available under the brand name Hydrowax 215 from Sasol, Hamburg.

The paper coated on the back was then dried at a temperature of 120° C. to a residual moisture content of 2.5%. The applied amount of the coat after drying was 1.5 g/m ² .

Example V-2 (comparison)

A suspension was applied to the reverse side of the impregnated base paper produced as in Example V-1 using a rod doctor (100 μm groove depth). The solids content of the aqueous suspension applied is 50% by weight after dilution. The silane-containing suspension is commercially available under the brand name Sitren 595 from Evonik Industries AG, Essen.

The paper coated on the back was then dried at a temperature of 120° C. to a residual moisture content of 2.5%. The applied amount of the coat after drying was 1.5 g/m ² .

example V-3 comparison)

A commercially available formaldehyde-containing prepreg 9327060 from Kämmerer Spezialpapiere GmbH, Osnabrück, is used as a comparison

The execution of the tests is explained below.

Flatness: tendency to curl according to Braun

A specimen measuring 10 cm x 7 cm is placed with its back on distilled water and a time measurement is started at the moment of placement. The water temperature is 20-22 °C. After 5 seconds the specimen is removed from the water surface. The test piece is pulled up on the narrow side (7 cm) with the tweezers and held down in a vertical position. The time measurement is stopped when the two long sides of the test piece touch each other.

The tendency to curl according to Braun is characterized by the time in seconds that elapses after the specimen has been removed from the water bath until the longitudinal sides of the specimen touch one another. The time read after stopping the time measurement must therefore be reduced by the 5 seconds that the examinee spent on the water surface. The result obtained is the Braun curl tendency.

Flatness: water value

A shallow bowl of DIN A3 format or larger is filled with distilled water. A DIN A4 format specimen is placed with its back on the water surface and a time measurement is started. The water temperature is 20-22 °C. The behavior of the edges of the specimen over time is observed. The time measurement is stopped as soon as the curl or the rolling up of the edges of the specimen has exceeded the maximum and the relaxation begins, ie the edges move towards the water surface again. The time thus obtained represents the water value.

Coating of the pre-impregnate

The prepreg samples are preheated at 160°C for 60 seconds. Thereafter, 10±1 g/m ² of the acid-curing paint system IV-49 from Plantagchemie, Detmold, is applied with a doctor blade. The samples are dried lying horizontally in the drying oven for 45 seconds at 160°C.

Lamination of the pre-impregnate

The lacquered pre-impregnate is applied to chipboard using a laboratory laminating calender. Standard chipboard (20 cm x 20 cm) is used. A urea resin glue solution (Kaurit Leim 122 from BASF, Ludwigshafen, powder dissolved in water with 50% solids content) is applied to one side of the chipboard with a doctor blade, the glue application (solids) is 35±5 g/m ² . The lacquered pre-impregnated sheet is placed on the chipboard surface provided with the glue, with the lacquered side of the pre-impregnated sheet pointing away from the chipboard and the sheet protruding about 2 cm over the chipboard on all sides. The chipboard provided with the prepreg is then pushed through the laminating calender, the contact pressure being 80 N/mm, the temperature of the pressure roller being 180° C. and the feed rate being 2 m/min.

adhesion strength

Adhesion testing begins immediately after lamination. For this purpose, the 2 cm wide strip of pre-impregnated material protruding laterally over the chipboard is cut perpendicularly to the edge of the board. The width of the strips and the distance between them is 12 mm.

Each protruding strip is jerked off by hand at an angle of 60° away from the chipboard using a triangular rod. It is peeled off after lamination. The area that is no longer or no longer completely covered by the prepreg after the stripping process is evaluated. The evaluation is based on grades (grade 1 = very good to grade 6 = unsatisfactory).

TESA test

The TESA test is based on the works standard IHD-W-463 of the Institute for Wood Technology Dresden. First, the laminated panels are stored for 24 hours. Then 15 cm long TESA film strips (TESA film type 4104) are applied to the laminated panel in and transverse to the running direction of the laminating calender and fixed without bubbles using a test roller (10 kg). After various times (immediately, 1 hour, 2 hours), the TESA film strip is torn off abruptly by hand at an angle of 30°. The area under the removed test strip is evaluated, ideally there is no splitting of the paper. The TESA strength is evaluated according to grades (grade 1 = very good to grade 6 = unsatisfactory)

The test results in Table 1 show that the application of a hydrophobic layer of 0.1 to 10 g/m ² dry on the back of a formaldehyde-free prepreg results in improved flatness (curl tendency according to Braun and water value) in conjunction with good adhesion bonding (adhesion strength and Tesa test). A further increase in the application quantity does not bring any further improvement in the flatness and can lead to a deterioration in the adhesive properties. Table 1: Composition of the impregnating resin solution and test results Hydrophobing agent of the hydrophobic layer Wükoseal ^® KIT Sitren ^® 595 Hydrowax 215 Formaldehyde free Flatness Curl according to Braun flat water adhesion strength TESA test 2h % by weight atro % by weight atro % by weight atro s s grade grade V-1 X 1 8th 2 3 V-2 1.5 X 54 66 6 4 V-3 31 34 2 2-3 A-1 1.5 X 14 12 2-3 2 A-2 1.0 X 13 11 2 2 A-3 5.0 X 19 15 3 2 A-4 1.5 X 10 11 3 3

Claims (14)

1. Pre-impregnate obtained from a decorative base paper impregnated with a formaldehyde-free impregnating resin, characterized in that a hydrophobic coating is applied onto at least one side of the pre-impregnate, the hydrophobic coating being arranged on the side opposite the decorative side of the pre-impregnate.
2. Pre-impregnate according to claim 1, characterized in that the grammage of the hydrophobic layer is 0.1 to 10 g (bd)/m².
3. Pre-impregnate according to one of claims 1 or 2, characterized in that the hydrophobic layer contains an organic hydrophobic agent, in an amount of 20 to 100% by weight, relative to the total weight of the bone dry hydrophobic layer.
4. Pre-impregnate according to one of claims 1 to 3, characterized in that the organic hydrophobic agent is a wax.
5. Pre-impregnate according to claim 4, characterized in that the wax is a chemically modified natural wax or a fully synthetic wax or mixtures thereof, in particular a polyethylene wax, a paraffin wax or mixtures thereof.
6. Pre-impregnate according to one of claims 1 to 5, characterized in that the content of the formaldehyde-free impregnating resin in the pre-impregnate is 10 to 35% by weight, based on the grammage of the decorative base paper.
7. Pre-impregnate according to one of claims 1 to 6, characterized in that the formaldehyde-free impregnating resin is a mixture of a water-soluble polymer and a polymer latex.
8. Pre-impregnate according to claim 7, characterized in that the water-soluble polymer is selected from starch, starch derivatives or nanoscale starch particles, in particular starch dextrin.
9. Pre-impregnate according to claim 7, characterized in that the aqueous polymer is polyvinyl alcohol.
10. Pre-impregnate according to one of claims 7 to 9, characterized in that the polymer latex is a styrene-acrylic acid ester copolymer, preferably a styrene-butyl acrylate copolymer.
11. Pre-impregnate according to one of claims 7 to 10, characterized in that the ratio of water-soluble polymer/polymer latex in the impregnating resin solution is 80/20 to 20/80 relative to the weight of the impregnating resin (bd).
12. Pre-impregnate according to any one of the preceding claims, characterized in that the pre-impregnate has a curl according to Braun of at least 10 seconds, preferably at least 13 seconds.
13. Pre-impregnate according to any one of the preceding claims, characterized in that the pre-impregnate has water values of at least 10 seconds.
14. Decorative film or decorative coating material containing the pre-impregnate according to any one of claims 1 to 13.