EP3310498B1 - Coating of composite wood panels with aminoplast resin films fitted with an abrasion-resistant, easy-clean and hydrophobic surface - Google Patents

Description

The invention relates to the finishing of Aminoplastharzfilmen with an abrasion-resistant, easy clean and hydrophobic surface for the coating of wood-based panels, which are used for the production of floor panels or find application in furniture.

Aminoplast resin films are melamine, formaldehyde condensation resins or mixed resins of urea and melamine, which are finally condensed or spatially crosslinked under pressure and temperature.

Melamine resin films are used in the coating of HDF boards (High Density Fibreboards), which are then processed into floor panels. In this case, printed decor papers made of high-grade cellulose are impregnated with melamine resin, which are then precondensed in the drying zone of an impregnating channel. As a rule, the decorative papers are pressed together with impregnated overlay papers from 20 to 45 g / m2 in a hydraulic heating press. The overlay is used to compensate the decorative films and other highly stressed surfaces. It consists of high-quality, high-grade paper, which is impregnated with melamine resin and additionally contains defined amounts of mineral fillers, such as corundum.

Floor panels must be relatively resistant to abrasion, so their surfaces are reinforced with these fillers. Due to its hardness, transparency and inertness Al ₂ O ₃ in the form of electrocorundum, sintered corundum, single crystal corundum and / or calcined or sintered alumina products has proved to be suitable here as hard material.

The order of such hard materials is carried out in different ways according to the prior art. Thus, the melamine impregnating resin for the paper surface coating directly these hard materials can be mixed. In another case, the overlay paper was added directly to the papermaking a certain amount of corundum the raw paper mass, this eliminates the Korundbeimischung in resin impregnation.

In the EP 0732449 A1 For example, a process for producing decorative paper for use in the production of abrasion resistant laminates is described. Here, the resin is mixed with abrasion-resistant mineral components such as corundum.

The DE 195 29 987 A1 describes a process for the production of highly abrasion-resistant coating layers on a solid support material. This lacquer layer is produced by means of synthetic resin lacquers, such as acrylic resin, polyester resin or polyurethane resin lacquer, whereby a wear-inhibiting agent is scattered on the lacquer layers prior to hardening. In another document EP 1070688 A1 a surface-coated hard material with a certain hardness is described. This hard material is added as a wear-inhibiting agent in the paint layers.

The production of synthetic corundum is usually carried out in the electric arc furnace, wherein the starting material alumina or bauxite is melted at about 2000 ° C. In this process, the product is produced in blocks, which are comminuted after cooling and then processed into a granulation.

Due to its brittle fracture behavior, crushing of the corundum results in a strongly fissured surface with many step offsets, micro-edges and cracks.

These corundum particles cause considerable problems on the surfaces of the press plates used in the subsequent pressing process in the heating press.

The melamine resin films are pressed together with the overlay films in so-called hydraulic heating presses with corresponding press plates, which can be structured, matted or even shiny, under pressure and temperature. The melamine resin films are finally condensed and form irreversible, hard surfaces. The corundum particles are located after pressing on the surfaces of the coated wood-based panels.

The press plates used are usually made of hard chrome steels of provenance AISI 410, AISI 630 with a hardness of 38-42 HRC. However, it is also possible to use brass sheets MS 64 with a hardness of 130 HB. In order to improve the release properties of the metallic surfaces against the melamine resins and to protect the surfaces against scratches, the metal surfaces are provided with a chromium coating, which is carried out electrochemically in a chromic acid bath with Cr (VI) compounds. The chrome coatings should have functional properties, therefore, hard chromium layers are over 20 microns, sought.

Although the chromed sheet metal surfaces harden from 1000 to max. 1200 HV, nevertheless causes premature wear of the sheet surface, wherein the gloss level of the chromium layer is changed. This happens due to the large hardness differences, corundum has a hardness according to Vickers from 1800 to 2000 HV. During the pressing process, movements occur due to the sheet metal expansion after the heating plates have been closed. The press plates undergo a temperature jump because they get close contact with the hot plate. On the other hand, the progressive condensation of the melamine resins leads to a shrinkage of the surface, resulting in a high friction under the high pressure, which triggers the premature wear of the sheet surfaces. The sheet metal surfaces must therefore be reworked relatively quickly and re-chromed.

The invention has the object of providing aminoplast resin impregnated decor papers and overlays equip so that premature wear of chromed press plate surfaces prevented, the end-fused Aminoplastharzoberflächen are abrasion resistant and an additional easy clean and hydrophobic surface is formed.

This object is achieved according to the proposal of the invention in that the decorative and / or overlay papers obtained after impregnation with an aminoplast resin an additional sol-gel coating, which is enriched with nanostructured tungsten or molybdenum disulfide, wherein the nanostructures of the metal disulfides in Form of fullerene-like nanoparticles and nanotubes are formed.

The additional enrichment of the fullerene-like nanoparticles of z. As tungsten disulfide in the sol-gel mixture, surfaces with additional high release and sliding effect after curing of the films. This prevents abrasion on the press plate surfaces and improves the tribological properties of the composite layers. The resulting from the sol-gel process surface layers of, for example, Al ₂ O ₃ , TiO ₂ or SiO ₂ , the hardness of the surfaces of the later coated wood-based panels, creating plus an easy clean and hydrophobic surface.

The sol-gel process is a wet chemical process for producing ceramic and hybrid organic-inorganic materials. It is possible to produce thin layers but also small particles and fibers, aerogels and xerogels and also monolithic materials via the sol-gel process. Basically, the sol-gel process describes two typical stages that go through each product. First, a sol is prepared, which consists of finely dispersed colloidal particles of about 1 nm to 100 nm in size in a liquid or dispersed oligomers, which consist of branched macromolecules. For the production of the sol, a so-called precursor is used, which are metal alkoxides or metal salts dissolved in water or in another liquid. If, for example, the alkoxides of polyvalent metal ions (M = Ti, Si, or Al) which are hydrolyzable from an alcoholic solution are applied to a surface, a metal hydroxide is formed even in the presence of H ₂ O even during the evaporation of the solvent, even at low temperatures Network. This then contains numerous MOH groups and is therefore hydrophilic and antistatic.

As a result of the hydrolysis and condensation reactions, the particles grow and polymerize until finally a solid network has formed within the liquid phase, this is then called a gel. As a result of the evaporation of the solvent, the gel forms a xerogel, which changes into a solid and compact form as a result of further temperature supply. The H ₂ O cleavage leads to metal oxide groups and the surfaces become hard and scratch-resistant.

The deposition or application of thin layers on the impregnated decorative or overlay papers, also referred to as a substrate in the further description, can be carried out with the aid of a plurality of coating methods. Thus, the dip coating (dip-coating), spin coating is applicable, but has been suitable for the one-sided surface application, the coating by doctor blade or application with a Verreibewalze proved. Usually, the substrate is coated with the liquid sol. After the application, the solvent then evaporates, thereby greatly increasing the concentration of the particles, which now leads to the formation of a gel and thus to a solid, but still porous, layer due to the binding of the particles among one another. This layer, also called xerogel, still contains slight amounts of the solvent. Only by heat treatment, which takes place in the subsequent drying zone of the impregnation, already forms the solid phase of the metal oxide from the sol-gel process and in the further course of the final condensation of the impregnating resins in the press under pressure and temperature, the entire hard layer of metal oxides educated.

Depending on the desired surface hardness, the choice of metal oxides must be made. As suitable metal compounds, the metals aluminum, zirconium, titanium and silicon have been found. With the help of their oxidic compounds, very good sol-gel layers can be achieved. In the following, two sol-gel layers are described, those of Al ₂ O ₃ and SiO ₂ .

The starting material for the preparation of Al ₂ O ₃ may be, for example, a Yoldas sol. The first step of the process is the hydrolysis of aluminum alkoxide, it takes z. For example, aluminum tri-sec-butoxide Al (OCH (CH ₃ ) C ₂ H ₅ ) ₃ and hydrolyzed in a large excess of water at about 85 ° C. This results in an aluminum hydroxide slurry which is subsequently converted to a clear sol or colloidal solution by the addition of a small amount of nitric acid HNO ₃ .

If you want to work with the Yoldas process with a lower stoichiometric water content, so you mix z. For example, aluminum tri-sec-butoxide with absolute ethanol and acetic acid in a ratio of Al-tri-sec-butoxide: C ₂ H ₅ OH: H ₂ O (DI) = 1: 16: 0.6 and heated to about 65 ° C with constant stirring of about 50 minutes. The originally turbid mixture slowly becomes clear after the onset of hydrolysis. The clear sol mixture is cooled to room temperature. In the second step, a gel is produced by addition of methanol CH ₃ and H ₂ O, wherein the weight ratios can be approximately Sol: CH ₃ : H ₂ O = 1 g: 0.2 g: 0.003 g, this is still a small Supplied amount of acetic acid.

Another sol could be prepared from a boehmite powder which is commercially available.

Silica esters can be used in the preparation of SiO ₂ gels, for example a tetraethyl orthosilicate TEOS is used as precursor. The designation of such hybrid organic-inorganic layers of organically modified silica are also often referred to as ormosils. For the preparation of Ormosilschichten different materials can be applied, in particular one starts from different silanes. The subsequent mechanical behavior of the sol-gel layers depends on the chemical structure and its concentration in the sol. For example, one can use a silane of the formula (OC ₂ H ₅ ) ₃ Si (CH ₂ ) ₃ -CH (O) CH ₂ 3-glycidoxypropyltrimethoxysilane also known under the brand names Dynasylan® or GLYMO. If it is desired to increase the hardness of the layers, nanoparticles of SiO ₂ or Al ₂ O ₃ can additionally be introduced. On the surface of the colloidal, amorphous SiO ₂ particles located OH groups can react with the silane used and thus embed the particles in the layer matrix. It is also possible to prepare layers of organically modified SiO ₂ having a hydrophilic or hydrophobic or dirt-repellent action.

After the preparation of the sol, which is intended for the coating, the preparation for the inorganic fullerene-like tungsten disulphide particles then performs, both preparations are brought together.

Inorganic fullerene-like nanoparticles and nanotubes have particle diameters of 10 to 25 nm. Nanotubes have diameters of 10 to 25 nm and lengths from 200 to 300 nm. The first inorganic fullerene-like particles of tungsten or molybdenum disulfide were observed in thin layers formed by sulfidation of WO ₃ and MoO ₃ layers, respectively, under a reducing atmosphere. Inorganic fullerenes were first produced in Israel in 1990, and the materials used were tungsten disulfide (WS ₂ ) and molybdenum disulfide (MoS ₂ ). In the course of many other inorganic fullerene-like materials have been prepared, such as TiS ₂ , selenides, bromides and chlorides such as NiBr ₂ , NiCl ₂ , and various oxides such. B. V ₂ O ₅ and boron nitride. For the application according to the invention tungsten disulfide and also molybdenum disulfide was selected. Tungsten disulfide in the form of fullerene-like nanoparticles and nanotubes are excellent for various uses because of their physical properties and crystallographic morphology. In the sol-gel preparation, fullerene-like tungsten disulphide has proven to be excellent, thus avoiding abrasion on the coated wood-based panels during later use. Also, the abrasion on the press plates was prevented during the pressing process. The lubricating effect of tungsten disulfide and molybdenum disulfide in a tribological contact is mainly due to the formation of a thin film of WS ₂ or MoS ₂ , which forms in the contact zone on the surfaces of the grinding body. This so-called Tribofilm allows a frictionless sliding of the surfaces against each other and thus reduces the wear of the rubbing body. Therefore, this effect is quite positive, compared to the frictional forces acting on the chromed press plate surfaces, from.

Commercially, most inorganic fullerene-type tungsten disulfide particles are supplied as a dry powder. However, due to the production process, the particles are partially coalesced (aggregated) and agglomerated to form secondary particles several micrometers in diameter. If the powder thus formed is added directly to water and ethanol or to an aqueous sol, the tungsten disulfide precipitates directly due to the high mass. Therefore, the tungsten disulfide particles must be deagglomerated prior to preparation in the sol-gel process and stabilized as individual particles in the sol. The use of dispersants has proved to be advantageous. So is the WS ₂ powder with cetyltrimethylammonium bromide from the company Sigma-Aldrich or Pretoctol (BASF) dispersed by means of ultrasonic technology.

The proportion of fullerenartigem tungsten disulfide WS ₂ in the sol, depends on the desired surface finish of the coated wood-based panels and the release properties of the press plates used and can be from 1 to 50%, based on solids content.

The thus prepared sol-gel preparations with the dispersed WS2 particles are then applied to the surfaces of the resin-impregnated decorative or overlay papers used, as described above.

The sol-gel coating can be carried out in the known and state-of-the-art impregnation drying installations for thermoset resin impregnations. In this case, for example, the overlay paper is first impregnated with the corresponding liquid, aqueous aminoplast resin and dried in the heated drying zone to a certain moisture content at the same time takes place a precondensation. In a second application zone, the prepared sol is then applied with the fullerene-like WS ₂ particles and then transferred to the heated drying channel. The speed and channel temperature depend on the respective resin parameters that are set by the user beforehand.

Claims (6)

1. Finishing of aminoplast resin impregnated decorative and/or overlay papers which are used for coating composite wood panels and form an abrasion-resistant, easy clean and hydrophobic surface, characterized in that after resin impregnation, the impregnated papers are coated in a second application step with a sol-gel preparation comprising dissolved metal alkoxides and fullerene-like nanostructures and nanotubes made of metal disulfides of the metals molybdenum and/or tungsten and, after drying and final condensation, the surfaces are formed in a hydraulic heating press.
2. Finishing of aminoplast resin films according to claim 1, characterized in that the metal alkoxides are preferably of the metals aluminum, titanium, silicon or zirconium.
3. Finishing of aminoplast resin films according to claim 1, characterized in that the sol-gel preparation comprising the dissolved metal alkoxides is additionally dispersed with small quantities of nanoscale metal oxides (SiO₂, Al₂O₃, TiO₂, ZrO₂) in order to increase scratch resistance.
4. Finishing of aminoplast resin films according to claims 1 to 3, characterized in that the fullerene-like tungsten disulfide particles and/or molybdenum disulfide particles are dispersed with the cationic surfactants cetyltrimethylammonium bromide or Pretoctol KLC50.
5. Finishing of aminoplast resin films according to claims 1 to 4, characterized in that the sol preparation is an ormosil of formula 3-glycidoxypropytrimethoxysilane.
6. Finishing of aminoplast resin films according to claims 1 to 4, characterized in that the sol-gel preparation is a Yoldas sol of formula Al(OCH(CH₃)C₂H₅)₃.