CN1240906C - method of coating the substrate - Google Patents

Abstract

The present invention relates to a method for coating a wooden, wood-like, and/or cellulose-containing substrate, comprising the steps of: a) applying a pressure coating to the substrate; b) applying heat and pressure to the coated substrate to cure the pressure coating to obtain a substrate having a smooth coating film, wherein the pressure is such that the substrate is not significantly compressed; c) applying a topcoat to the substrate after the pressure coating has cured; and d) curing the topcoat. As a result of the method, the amount of unreacted double bonds in the coated substrate is low.

Description

method of coating the substrate

technical field

The present invention relates to a method for coating wooden, wood-like and/or cellulose-containing substrates such as solid wood, wooden plywood, impregnated paper or reconstituted wooden substrates.

Background technique

Reconstituted wood substrates are substrates made from small pieces of wood, fibers, shavings or wood chips, such as hardboard, medium density fiberboard, oriented strand board (also known as veneer board), particle board, particle board and particle board. Such reconstituted wood substrates are typically manufactured from chips, fibers, wood shavings or wood chips under heat and pressure. Reconstructed wood substrates are typically produced by treating chips, shavings, chips or fibers with a binder and then arranging these treated chips, shavings, chips or fibers in a mat form under dry or wet conditions. Production. The mat is then compressed by the application of heat and pressure into a dense substrate, typically in sheet form. During this compression step, the mat is compressed to less than 10% of its original thickness, ie more than 90% of the thickness of the substrate is compressed. In the wet process, water is squeezed out of the mat during this compression step; in the dry process, the individual particles are tightly packed together. The binder binds the chips, wood shavings, wood chips or fibers together, enhancing the structural strength and integrity of the reconstituted wood substrate as well as its water resistance. If desired, the reconstituted wood substrate can be molded into a desired shape or provided with a textured surface such as a woodgrain texture. Typical examples of reconstituted wood substrates are hardboard, medium density fiberboard (MDF), high density fiberboard (HDF) and particle board.

For example, JP 57-113051 discloses a method for producing fiberboard. This document describes the cooking of wood chips into a fibrous material followed by the addition of a binder resin. Subsequently, the mixture is hot pressed into a fiberboard. Generally, this mixture is compressed significantly during the hot pressing. After pressing, the fiberboard was removed from the heat press. Next, the fiberboard is coated with an aqueous solution of an ester compound by a coater, a flow coater, or by spraying. The disadvantage of this method is that a relatively large amount of aqueous solution will penetrate into the fibreboard.

A problem encountered with coating woody, wood-like and/or cellulose-containing substrates is that relatively large amounts of lacquer are absorbed into the substrate. This will increase paint consumption for these substrates compared to low or non-absorbent substrates. Also, the larger amount of lacquer necessary to coat the substrate results in a longer overall drying time and a larger amount of solvent that must evaporate from the coating.

Additional problems are encountered when applying radiation-curable coating compositions to woody, wood-like and/or cellulose-containing substrates. Such a method is described, for example, in US 4,675,234. This document describes the application of thin layers of radiation curable coatings to various substrates such as wood or paper. In order to obtain thin coatings on these substrates, relatively large amounts of paint must be applied. The disadvantage of this method is that the coating cannot be obtained by irradiation, because the part of the coating that penetrates the substrate does not cure during the irradiation process. Uncured material can create health, safety and environmental concerns.

Today, a primary concern in the coatings industry is the need to reduce emissions of solvents, especially volatile hydrocarbons, to the air. The issue of radiation curable substances that are not fully cured is equally important.

Contents of the invention

The invention relates to a method for coating wooden, wood-like and/or cellulose-containing substrates with low paint consumption. In order to achieve this object, the inventive method comprises the following steps:

a) Applying a press coating to the substrate;

b) applying heat and pressure to the coated substrate, wherein the pressure is such that the substrate is not significantly compressed to cure the coating of the pressure coating to obtain a smooth coating film;

c) applying a topcoat to the substrate after the coating of pressure paint has cured; and

d) Curing the topcoat.

Detailed description of the invention

For the purposes of this application, the pressure at which the substrate is not significantly compressed is the pressure at which the average thickness of the substrate is reduced by less than 10% of its original value.

Methods wherein the substrate is not significantly compressed include any method wherein the substrate is locally compressed by more than 10%, but the average thickness of the substrate is reduced by less than 10% of its original value. This localized compression occurs when a specific pattern is applied to the substrate during the step of applying heat and pressure to the substrate.

In the method of the present invention, pressure coating is used to seal the surface of the substrate and reduce its absorption of lacquer. Generally, pressure coatings are applied as aqueous colloidal dispersions, also known as polymer latexes. Such pressure coatings comprise polymer particles of ethylenically unsaturated monomers and filler and/or pigment particles, wherein the polymer has a _Tg of 10-100°C.

Polymerized latex suitable for obtaining a smooth hard coat on the surface or edge of a substrate comprising 10-60% by weight, based on emulsion solids, of polymer particles of an ethylenically unsaturated monomer and 40-60% by weight, based on emulsion solids, of a pigment and/or filler particles, wherein the polymer has a _Tg of 10-100°C.

Pressure coatings generally provide not only a smooth coating over the surface and/or edges of a substrate, but also a layer that provides improved adhesion between the substrate and any other coatings applied to the substrate.

The latex can be applied to the substrate by conventional equipment such as curtain coaters, spray nozzles, roll coaters, flow coaters or by extrusion, and is particularly useful for coating the edges of the substrate. The latex layer may be applied over one side of the substrate, such as the front and back sides, or along the sides of a substantially planar substrate or on the surface of a contoured substrate such as a molding or a molded door panel .

Optionally, to accelerate the evaporation of water from the latex, the substrate is preheated at 30-80°C, preferably 40-60°C, within 10 seconds to 5 minutes before applying the latex.

The latex layer dries to a hardened layer by reducing its moisture content. Generally, the latex layer is dried to a moisture content of 0-20% by weight of the solids content of the layer. Applicable drying temperatures and drying times are adjusted to suit the polymerized latex used and the thickness of the applied layer. The applicable drying temperature is generally room temperature to 120°C, preferably 50-80°C. The drying time is correspondingly shortened for higher applicable drying temperatures, and correspondingly extended for lower applicable drying temperatures. Suitable drying devices are conventional drying devices such as convection air drying ovens or conveyor belts passing through channels heated by infrared light.

Then, the dry layer is pressed for a period of time under a pressure of 0.1-3.5 N/mm ² , preferably 0.14-2.0 N/mm ² . The coating may be heated during the pressing. The temperature and time are adjusted to prevent thermal decomposition of the resulting coating or substrate or sticking of the coating to the platens of the press. The applicable temperature is generally 20-300°C.

After or concurrently with the pressing step, the latex layer is cured for an applicable curing time at an applicable curing temperature suitable for the polymerized latex used. Curing time and temperature are adjusted to prevent thermal decomposition of the resulting coating or substrate. The applicable curing temperature is generally 20-300°C, preferably 170-235°C; the applicable curing time is 120 minutes to 1-5 seconds, preferably 30-1 minute.

The curing step is preferably carried out simultaneously at an applicable curing pressure suitable for the polymerized latex used. The applicable curing pressure is 0.1-3.5 N/mm ² , preferably 0.14-2.0 N/mm ² . The applicable curing temperature is 50-250°C, preferably 150-200°C. Applicable curing times are from 0.1 seconds to 5 minutes. Conventional hot pressing equipment such as molding presses with pneumatic or hydraulic heating plates are suitable for batch operation, conventional hot pressing equipment such as a pair of heated calender rolls, a series of heated calender rolls, a pair of heated conveyor belts arranged in parallel, or UV curing Lamps can be used for continuous operation by extruding the substrate through them. Calendering at elevated temperature is the preferred method for simultaneous pressing and curing of pressure coatings.

The smooth coating film thus obtained on the substrate is then used to apply the next coating, for example a topcoat. In principle, there is no restriction on the coating composition that can be used as a topcoat, as long as the topcoat adheres well to the coating film on the substrate. Both pigmented and unpigmented coating compositions can be used for the topcoat. In view of reducing the amount of solvent released during the drying and curing of the topcoat, it is preferable to use a high-solids solvent-based coating, water-based coating or hot-melt coating. Since the industrial-scale production of coated substrates according to the invention preferably takes place in a short time, the curing and drying times of the topcoat should be as short as possible. Curing and drying of the topcoat can be accelerated by heating the substrate, but due to its heat sensitive nature this is not always possible. Therefore, it is preferred to use a radiation curable topcoat which can be cured in a reasonably short time without having to heat the substrate too much.

In general, the use of radiation-curable coating compositions for coating woody, wood-like and/or cellulose-containing substrates is not recommended, as the coating composition will penetrate into the pores of the substrate and since the radiation does not reach these area, which results in uncured coating. This can create health, safety and environmental concerns, for example when cutting or grinding substrates. These problems can occur even years after the paint has been applied. However, in the method of the present invention, the pressure coating is applied to the substrate prior to the application of the radiation curable coating composition. Such pressure coatings effectively prevent penetration of the radiation curable coating composition into the substrate.

Within the framework of the present invention, a radiation-curable coating composition is a coating composition which is cured with electromagnetic radiation or electron beam radiation having a wavelength λ≦500 nm. An example of electromagnetic radiation with a wavelength λ≦500 nm is eg UV radiation.

In principle, any radiation-curable resin or resin mixture can be used in the topcoat used in the method of the invention. These resins are used in amounts of 20-100% by weight of the composition. Preferably the resin is used in an amount of 30-90 wt%, more preferably 40-90 wt%.

Polyester acrylate resins have been found to be very suitable for use in topcoat compositions. Examples of suitable commercially available polyester acrylate resins are: Crodamer UVP-215, Crodamer UVP-220 (both from Croda), Genomer 3302, Genomer 3316 (both from Rahn), Laromer PE 44F (both from BASF), Ebecryl 800, Ebecryl 810 (both from UCB), Viaktin 5979, Viaktin VTE 5969 and Viaktin 6164 (100%) (all from Vianova).

Epoxy acrylate resins can also be used in topcoat compositions. Examples of commercially available epoxy acrylate resins are: Crodamer UVE-107 (100%), Crodamer UVE-130 (both from Croda), Genomer 2254, Genomer 2258, Genomer 2260, Genomer 2263 (all from Rahn), CN 104 (from Cray Valley) and Ebecryl 3500 (from UCB).

Polyether acrylate resins can also be used in topcoat compositions. Examples of commercially available polyether acrylate resins are: Genomer 3456 (ex Rahn), Laromer PO33F (ex BASF), Viaktin 5968, Viaktin 5978 and Viaktin VTE6154 (all ex Vianova).

Urethane acrylate resins can also be used in topcoat compositions. Examples of commercially available urethane acrylate resins are: CN 934, CN 976, CN 981 (all from Cray Valley), Ebecryl 210, Ebecryl 2000, Ebecryl 8800 (all from UCB), Genomer 4258, Genomer 4652 and Genomer 4675 (all from Rahn).

Examples of other radiation curable resins that can be used in the topcoat composition used in the method of the invention are cationic UV curable resins such as cycloaliphatic epoxy resins (Uvacure 1500, Uvacure 1501, Uvacure 1502, Uvacure 1530, Uvacure 1531, Uvacure 1532, Uvacure 1533, Uvacure 1534, Cyracure UVR-6100, Cyracure UVR-6105, Cyracure UVR-6110 and Cyracure UVR-6128, all from UCB Chemicals), SarCat K126 (from Sartomer), acrylate-modified lipid Cyclic epoxides, caprolactone-based resins (SR 495 (=caprolactone acrylate from Sartomer), Tone 0201 (=caprolactone triols), Tone 0301, Tone 0305, Tone0310 (all caprolactone triols Both from Union Carbide), aliphatic urethane divinyl ether, aromatic vinyl ether oligomers, bismaleimide, bisphenol A diglycidyl ether or neopentyl glycol, hydroxyl Functionalized acrylic monomers, hydroxyl-functionalized epoxy resins, epoxidized linseed oil, epoxidized polybutadiene, glycidyl esters or partially acrylated bisphenol A epoxy resins.

Furthermore, UV-curable aqueous resins can also be used in the topcoat composition used in the process of the invention, such as aliphatic polyurethane dispersions (Lux 101 VP from Alberdingk Boley), especially (meth)acryloyl-functional polyurethanes Dispersions. Very good results were obtained when the (meth)acryloyl-functional polyurethane resins contained alkylene oxide groups.

Other radiation-curable compounds suitable for use are, for example, vinyl ether-containing compounds, unsaturated polyester resins, acrylated polyether polyol compounds, (meth)acrylated epoxidized oils, (meth) ) acrylated hyperbranched polyesters, silicon-containing acrylates, maleimide-functional compounds, unsaturated imide resins, compounds suitable for light-induced cationic curing or mixtures thereof.

In order to obtain a suitable application viscosity of the topcoat, well-known UV-curable monomers can be added as viscosity reducers and reactive oligomers. Examples of these reactive oligomers are tripropylene glycol diacrylate (TPGDA), hexanediol diacrylate (HDDA) and 2-hydroxyethyl methacrylate (HEMA).

In addition, the composition may comprise a photoinitiator or a mixture of photoinitiators. Examples of suitable photoinitiators that can be used in the radiation curable composition of the present invention are benzoin, benzoin ethers, benzil ketals, α,α-dialkoxyacetophenones, α-hydroxy Alkylphenones, alpha-aminoalkylphenones, acylphosphine oxides, benzophenones, thioxanthones, 1,2-diketones and mixtures thereof. Copolymerizable bimolecular photoinitiators or maleimide functional compounds may also be used. Coinitiators such as amine-based coinitiators may also be present in the radiation curable coating composition. Sunlight curing photoinitiators can also be used.

Examples of suitable commercially available photoinitiators are: Esacure KIP 100F and Esacure KIP 150F (both ex Lamberti); Genocure BDK and Velsicure BTF (both ex Rahn); Speedcure EDB, Speedcure ITX, Speedcure BKL and Speedcure DETX (all from Lambson); Cyracure UVI-6990, Cyracure VUI-6974, Cyracure UVI-6976, and Cyracure UVI-6992 (all from Union Carbide); and CGI-901, Darocur 184, Darocur 500, Darocur 1000, and Darocur 1173 (all from Ciba Chemicals).

However, the presence of a photoinitiator is not necessary. In general, it is not necessary to add a photoinitiator when electron beam radiation is used to cure the composition. When UV radiation is used, a photoinitiator is generally added.

Although the total amount of photoinitiator in the composition is not critical, it should be sufficient to obtain an acceptable cure of the coating when it is irradiated. However, the amount used should not be so great that it affects the properties of the cured composition in an adverse manner. Generally speaking, when using electromagnetic radiation with a wavelength λ≤500nm to cure the coating, the composition should contain 0.1-10 wt% of a photoinitiator, calculated by the total weight of the composition.

The composition may also contain one or more fillers or additives. The filler may be any filler known to those skilled in the art, for example barium sulfate, calcium sulfate, calcium carbonate, silica or silicates such as talc, feldspar and china clay. Additives such as stabilizers, antioxidants, leveling agents, anti-settling agents, matting agents, rheology modifiers, surfactants, amine synergists, waxes or adhesion promoters may also be added. Generally, the coating composition of the present invention comprises 0-50 wt% of fillers and/or additives, calculated on the total weight of the coating composition.

The topcoat composition used in the method of the present invention may also contain one or more pigments. Pigments known to those skilled in the art can be used in the radiation-curable compositions of the invention. Care should be taken, however, that the pigment should not exhibit too high an absorption of the radiation used to cure the composition. Generally, the compositions of the present invention comprise 0 to 40 wt. % pigment, based on the total weight of the coating composition.

Topcoats can be applied to the substrate by conventional equipment such as curtain coaters, spray nozzles, roller coaters or flow coaters.

Optionally, one or more further coating layers, a so-called midcoat, are applied to the smooth coating film on the surface of the substrate before the topcoat is applied. This is done, for example, to obtain better adhesion of the topcoat or to obtain a topcoat with specific properties.

In principle, there are no restrictions on the coating composition that can be used for the coating, as long as the coating adheres well to the coating film on the substrate. Both pigmented and unpigmented coating compositions can be used. In view of reducing the amount of solvent released during drying and curing of the coating composition, it is preferable to use a high solid solvent-based coating composition, an aqueous coating composition or a hot-melt coating composition. Since the industrial-scale preparation of coated substrates according to the invention is preferably carried out in a short time, the curing and drying times of the coating compositions should be as short as possible. Curing and drying of the coating composition can be accelerated by heating the substrate, but this is not always possible due to its heat sensitive nature. Therefore, preference is given to using radiation-curable coating compositions.

For the additional intermediate coat, although it is not necessary for the additional intermediate coat to have the same composition as the topcoat, in principle it is possible to use the same type of coating composition as the topcoat layer.

In order to obtain a suitable application viscosity of the intermediate layer, well-known UV-curable monomers can be added as viscosity reducers and reactive oligomers. Examples of these reactive oligomers are tripropylene glycol diacrylate (TPGDA), hexanediol diacrylate (HDDA) and 2-hydroxyethyl methacrylate (HEMA).

The intermediate coat can be applied to the substrate by conventional equipment such as curtain coaters, spray nozzles, roller coaters or flow coaters.

Optionally, printing is applied to the substrate prior to application of the topcoat. In doing so, substrates with specific surface structures, colors or textures can be obtained.

For the coating of woody, wood-like and/or cellulose-containing substrates in an industrial process, processes are preferred in which all coating and curing steps are carried out on a single production line. In this method, the substrate is placed on a conveyor belt that moves at a continuous rate. The substrate is then sequentially coated with a pressure coating, heated and pressed to dry and cure said pressure coating, optionally additional coatings are applied, heated or treated in another way to cure an optional current layer, Optionally provide a print, apply the topcoat and heat or treat in another way to cure the topcoat.

The method according to the invention, in which a woody, wood-like and/or cellulose-containing substrate is coated by first applying a pressure paint and then a further coating, has the following advantages over a method in which such a pressure paint is not used :

- a reduction in the total amount of paint required to obtain a substrate with the same performance and appearance;

- a reduction in the total amount of solvent required to obtain a substrate with the same performance and appearance;

- a reduction in the total energy required to obtain substrates with the same performance and appearance;

- Especially for substrates coated with UV-curable topcoats or midcoats, the amount of unreacted monomers is reduced. These monomers can create health, safety and environmental concerns, for example when cutting or grinding substrates. These problems can occur even many years after the paint has been applied.

- Improved heat resistance of the substrate.

The invention also relates to a woody, wood-like and/or cellulose-containing substrate coated with a pressure coating and at least one radiation-curable coating, wherein after curing of the radiation-curable coating, the The measured amount of unreacted double bonds in the substrate is less than 15%, preferably less than 10%, of the total amount of double bonds present in the uncured coating composition. This low amount of unreacted double bonds may be due to the effective sealing of the porous surface of the substrate by use of pressure coating. Due to this sealing, the penetration of the radiation curable coating into the substrate is reduced.

The term "IR chromatography" within the context of this application should be taken to mean chromatography followed by infrared spectroscopy, eg gas chromatography followed by infrared spectroscopy. If liquid chromatography is used, it should be noted that the IR spectrum of the mobile phase does not interfere with the IR spectrum of the sample.

The amount of extractables can be determined by taking a sample of ^5cm2 ×1-2mm from the surface of the substrate, the sample is extracted with dichloromethane, and the dichloromethane containing extractables is passed through GC/FID (gas chromatography/flame Ionization detection method) combined with GC/MS (gas chromatography/mass spectrometry) for analysis.

The invention will be illustrated with reference to the following examples. These examples will illustrate the invention and should not be considered in any way to limit its scope.

Example

Example 1A

A medium density fiberboard (MDF) substrate is placed on a conveyor belt moving at a speed of 15 m/min, and a white pressure paint emulsion (pbw represents parts by weight) comprising the following components is applied:

26.7pbw of water;

20.7pbw acrylic polymer with a _Tg of 34°C;

16.8pbw of pigment;

31.5pbw of filler mix; and

4.3pbw additive blend

Apply to the MDF substrate in an amount of 15-20 g/m ² . The press paint was dried by passing the MDF substrate through an oven, pressed and cured by passing the substrate through a pair of calender rolls at a temperature of 150-200°C and a pressure of about 1 N/ ^mm2 .

On the coating film thus formed, a white solvent-based topcoat (Proff355NCS S- ^0502Y available from Akzo Nobel Wood Coatings AB Sweden, diluted to 50 wt. % solid content). The topcoat is cured by passing the substrate through a second oven.

The entire process takes place on a single line without removing the substrate from the conveyor belt.

Embodiment 1B (comparative example)

As a control, a coated MDF substrate was prepared using the same conditions, but without pressure coating. In the first step, a solventborne sealant coating (ProffSurf 150 available from Akzo Nobel Wood CoatingsAB Sweden) is applied; Apply in an amount of ² . In order to obtain a substrate with the same properties and appearance as in Example 1A, the sealant coating had to be applied in an amount of 100 g/m ² .

Contrast that with Example 1A, where 100% more solvent had to be used to obtain a coated MDF substrate with the same performance and appearance. Furthermore, the energy consumption of the entire process is higher in this comparative example due to the greater amount of solvent that has to be evaporated off.

Example 2A

A medium density fiberboard (MDF) substrate was placed on a conveyor belt moving at a rate of 15 m/min and the white colored pressure paint of Example 1A was applied to the MDF substrate in an ^amount of 15-20 g/m superior. The press paint was dried by passing the MDF substrate through an oven, pressed and cured by passing the substrate through a pair of calender rolls at a temperature of 150-200°C and a pressure of about 1 N/ ^mm2 .

On the coating film thus formed, a white finish paint (IC 102 Ikeawhite No. ⁵ , available from Akzo Nobel Wood Coatings AB Sweden, diluted to 35% by weight) was applied in an amount of 100 g/m by a curtain coater. solid content). The topcoat is cured by passing the substrate through a second oven.

The entire process takes place on a single line without removing the substrate from the conveyor belt.

Embodiment 2B (comparative example)

As a control, a coated MDF substrate was prepared using the same conditions, but without pressure coating. In the first step, a solvent-based sealant coating (Proff Surf 150 available from Akzo Nobel Wood CoatingsAB Sweden) is applied ^; amount applied. In order to obtain a substrate with the same properties and appearance as in Example 2A, the sealant coating had to be applied in an amount of 100 g/m ² .

Contrast that with Example 2A, where 100% more solvent had to be used to obtain a coated MDF substrate with the same performance and appearance. Furthermore, the energy consumption of the entire process is higher in this comparative example due to the greater amount of solvent that has to be evaporated off.

Example 3A

A medium density fiberboard (MDF) substrate was placed on a conveyor belt moving at a rate of 15 m/min and the white colored pressure paint of Example 1A was applied to the MDF substrate in an ^amount of 15-20 g/m superior. The press paint was dried by passing the MDF substrate through an oven, pressed and cured by passing the substrate through a pair of calender rolls at a temperature of 150-200°C and a pressure of about 1 N/ ^mm2 .

On the coating film thus formed, a white water-based topcoat (AquaTöck Line available from Akzo Nobel Wood Coatings AB Sweden) was applied in an amount of 100 g/m ² using a curtain coater. The topcoat is cured by passing the substrate through a second oven.

The entire process takes place on a single line without removing the substrate from the conveyor belt.

Embodiment 3B (comparative example)

As a control, a coated MDF substrate was prepared using the same conditions, but without pressure coating. In the first step, a water-based primer (Aqua Töck Line available from Akzo Nobel Wood Coatings ABSweden) is applied; Apply in an amount of ² . In order to obtain a substrate with the same properties and appearance as in Example 3A, the primer had to be applied in an amount of 100 g/m ² .

In contrast to Example 3A, the energy consumption of the overall process is higher in this comparative example due to the greater amount of water that has to be evaporated off.

Example 4A

A medium density fiberboard (MDF) substrate was placed on a conveyor belt moving at a speed of 15 m/min and the white colored pressure paint of Example 1A was applied to the MDF substrate in an ^amount of 15-20 g/m superior. The pressure paint was dried by passing the MDF substrate through an oven, pressed and cured by passing the substrate through a pair of calender rolls at a temperature of 150-200°C and a pressure of about 1 N/ ^mm2 .

On the coating film thus formed, the following coatings are applied:

- Apply a UV sealant (IS 401 UV sealant available from Akzo Nobel Wood Coatings AB Sweden) at 8 g/ ^m2 using a roller coater;

- Apply a white-pigmented UV base coat (UV base coat Br. Hvid available from Akzo NobelWood Coatings AB Sweden) with a roller coater in an amount of 8 g/ ^m2 ;

- applying a white-pigmented UV basecoat (UV basecoat Br. Hvid available from Akzo NobelWood Coatings AB Sweden) in an amount of 8 g/ ^m2 using a roller coater,

- Apply a white-pigmented topcoat (UV topcoat Ikea No. 5 available from Akzo Nobel Wood Coatings AB Sweden) at 23 g/ ^m2 using an Optiroller.

After application, dry and cure each coat before applying the next. Each coating was cured by passing the substrate under a UV lamp. Sand the substrate before applying the first coat of basecoat.

The entire process takes place on a single line without removing the substrate from the conveyor belt.

Embodiment 4B (comparative example)

As a control, a coated MDF substrate was prepared using the same conditions, but without pressure coating. In a first step, a UV putty (IF 401 UV light filler available from Akzo Nobel Wood Coatings AB Sweden) was applied in an amount of 20 g/m ² and cured.

On the cured putty, apply the following coats:

- Apply a UV sealant (IS 401 UV sealant available from Akzo Nobel Wood Coatings AB Sweden) in an amount of 8 g/ ^m2 using a roller coater;

- Apply a white-pigmented UV base coat (UV base coat Br. Hvid available from Akzo NobelWood Coatings AB Sweden) with a roller coater in an amount of 8 g/ ^m2 ;

- Apply a white-pigmented UV base coat (UV base coat Br. Hvid available from Akzo NobelWood Coatings AB Sweden) with a roller coater in an amount of 8 g/ ^m2 ;

- Apply a white-pigmented UV base coat (UV base coat Br. Hvid available from Akzo NobelWood Coatings AB Sweden) with a roller coater in an amount of 8 g/ ^m2 ;

- Apply a white-pigmented topcoat (UV topcoat Ikea No. 5 available from Akzo Nobel Wood Coatings AB Sweden) at 23 g/ ^m2 using an Optiroller.

After application, dry and cure each coat before applying the next. The coating was cured by passing the substrate under a UV lamp.

The entire process takes place on a single line without removing the substrate from the conveyor belt.

Contrast that with Example 4A, where more paint had to be used to obtain a substrate with the same performance and appearance, resulting in a higher overall cost price. Furthermore, in the coated substrate of Example 4B, about 20% of the double bonds in the coating composition were not converted, while in the coated substrate of Example 4A, only 3% of the double bonds in the coating composition were not converted . The conversion of the double bond was determined by IR chromatography.

The amount of unconverted double bonds in the coated substrate indicates that the material contains uncured monomeric species.

Example 5A

A medium density fiberboard (MDF) substrate was placed on a conveyor belt moving at a rate of 15 m/min and the white colored pressure paint of Example 1A was applied to the MDF substrate in an ^amount of 15-20 g/m superior. The press paint was dried by passing the MDF substrate through an oven, pressed and cured by passing the substrate through a pair of calender rolls at a temperature of 150-200°C and a pressure of about 1 N/ ^mm2 .

On the coating film thus formed, a whitening water-based primer (IP 610 water-based primer 2 available from Akzo Nobel Wood Coatings AB Sweden) was applied in an amount of 25 g/m ² using a roll coater. After the primer had dried and cured, a UV-curable topcoat (UV topcoat Ikea No. 5 available from Akzo Nobel Wood Coatings AB Sweden) was applied in an amount of 5 g/m ² using an Optiroller. The topcoat was cured by passing the substrate under a UV lamp.

The entire process takes place on a single line without removing the substrate from the conveyor belt.

Embodiment 5B (comparative example)

As a control, a coated MDF substrate was prepared using the same conditions, but without pressure coating. In the first step, a waterborne primer (IP 610 Waterborne Primer 2 available from Akzo Nobel Wood Coatings ABSweden) is applied; in the second step, a white UV-curable topcoat (available from Akzo Nobel Wood Coatings ABSweden) is applied. A UV topcoat (lkea No. 5) obtained from Nobel Wood Coatings AB Sweden was applied in an amount of 5 g/m ² . In order to obtain a substrate with the same properties and appearance as in Example 5A, the primer had to be applied 3 times in an amount of 35 g/m ² .

In contrast to Example 5A, the energy consumption of the overall process is higher in this comparative example due to the greater amount of water that has to be evaporated off. In addition, the lacquer consumption is also higher in the comparative process.

Example 6A

A medium density fiberboard (MDF) substrate was placed on a conveyor belt moving at a rate of 15 m/min and the white colored pressure paint of Example 1A was applied to the MDF substrate in an ^amount of 15-20 g/m superior. The press paint was dried by passing the MDF substrate through an oven, pressed and cured by passing the substrate through a pair of calender rolls at a temperature of 150-200°C and a pressure of about 1 N/ ^mm2 .

On the coating film thus formed, a UV curable putty (IF 401 UV light filler available from Akzo Nobel Wood Coatings AB Sweden) was applied in an amount of 5-15 g/m ² . The putty was cured by passing the substrate under a UV lamp. On the cured putty, a UV curable sealant coating (IS 483 WW UV sealant available from Akzo Nobel Wood Coatings ABSweden) was applied in an amount of 6-8 g/m ² . The sealant was cured by passing the substrate under a UV lamp. On top of the cured sealant coating a UV curable topcoat (UV topcoat lkea No. 5 available from Akzo Nobel Wood Coatings AB Sweden) was applied in an amount of 5 g/m ² . The topcoat was cured by passing the substrate under a UV lamp.

The entire process takes place on a single line without removing the substrate from the conveyor belt.

Embodiment 6B (comparative example)

As a control, a coated MDF substrate was prepared using the same conditions, but without pressure coating. In order to obtain a substrate with the same properties and appearance as in Example 6A, the UV-curable putty of Example 6A had to be applied in an amount of 15-40 g/m ² .

Contrast that with Example 6A, where more paint had to be used to obtain a substrate with the same performance and appearance, resulting in a higher overall cost price. Furthermore, in the coated substrate of Example 6B, about 25% of the double bonds in the coating composition were not converted, while in the coated substrate of Example 6A, only 7% of the double bonds in the coating composition were not converted . The conversion of the double bond was determined by IR chromatography. The amount of unconverted double bonds in the coated substrate indicates that the material contains uncured monomeric species.

Claims (6)

1. A method for coating and rebuilding wooden substrates, comprising the following steps: a) applying a pressure coating to the substrate as an aqueous colloidal dispersion; b) applying heat and pressure to the coated substrate, wherein the pressure is such that the substrate is not significantly compressed to cure the coating of the pressure coating to obtain a smooth coating film; c) applying a topcoat to the substrate after the coating of pressure paint has cured; and d) Curing the topcoat. 2. The method of claim 1, wherein in an additional step prior to applying the topcoat, a primer is applied and cured. 3. The method according to claim 1 or 2, characterized in that all process steps are carried out on a single production line. 4. The method according to claim 1 or 2, characterized in that the topcoat is a radiation curable topcoat and the radiation curable topcoat is cured with UV radiation. 5. A method as claimed in claim 1 or 2, characterized in that the print is applied to the substrate and the top coat is applied over the print before the top coat is applied. 6. The method according to claim 1 or 2, characterized in that the pressure coating is an aqueous colloidal dispersion comprising polymer particles of ethylenically unsaturated monomers and 40-60% by weight of fillers and/or pigments, Wherein the weight percentage is calculated according to the total weight of the emulsion solids.