In-line coated decorative wood-based boards

Abstract

The present invention relates to a process for manufacturing a decorative wood-based board, to a decorative wood-based board, to the use of at least one dry or liquid coating composition comprising at least one inorganic particulate filler material and at least one binder for in-line coating of decorative wood-based boards, and to the use of at least one dry or liquid coating composition comprising at least one inorganic particulate filler material and at least one binder for improving the mechanical properties of a decorative wood-based board. Furthermore, it relates to the use of a decorative wood-based board in flooring applications, furniture, walls, roof panels, display cabinets, storage units, loudspeakers and shop-fittings.

Claims

1. Process for manufacturing a decorative wood-based board, the process comprising the steps of: a) providing wood particles and/or fibres, in dry form or in form of an aqueous suspension, b) providing at least one dry or liquid coating composition comprising at least one inorganic particulate filler material and at least one binder, wherein the at least one inorganic particulate filler material comprises at least one inorganic particulate calcium carbonate-containing material having a median particle size d.sub.50 of 0.1 μm to 150.0 μm and/or a specific surface area of 0.5 to 200.0 m.sup.2/g, as measured by the BET nitrogen method; c) forming a wood-based mat having a first side and a reverse side from the wood particles and/or fibres provided in step a), d) pre-pressing the wood-based mat of step c) into a pre-pressed wood-based mat, e) applying at least one layer of the at least one dry or liquid coating composition of step b) on the first and/or reverse side of the pre-pressed wood-based mat obtained in step d), f) hot pressing the pre-pressed wood-based mat obtained in step e) into a solid wood-based board, and g) applying at least one decorative finishing on the first and/or reverse side of the wood-based board obtained in step f) by a step consisting of at least one of inkjet-printing, rotogravure-printing, and/or applying a decorative paper, a decorative foil or a liquid coating; wherein the at least one dry or liquid coating composition of step b) comprises the at least one inorganic particulate filler material in an amount from 80 to 98 wt.-%, and the at least one binder in an amount from 2 to 20 wt.-% based on the total dry weight of the at least one coating composition.

2. The process according to claim 1, wherein the wood particles and/or fibres of step a) are combined simultaneously or separately in any order with at least one base binder and/or at least one additive, preferably the at least one base binder is selected from the group comprising phenol-formaldehyde resin (PF), urea-formaldehyde resin (UF), melamine-formaldehyde resin (MF), melamine-urea-formaldehyde resin (MUF), urea-melamine-formaldehyde resin (UMF), urea-melamine-phenol-formaldehyde resin (UMPF), epoxy resin, methylene diphenyl diisocyanate resin (MDI), polyurethane resin (PU), resorcinol resin, starch or carboxymethylcellulose and mixtures thereof, and/or the at least one additive is selected from the group comprising waxes, colourants, filler, dispersants, biocides, hardener, flame retardants and mixtures thereof.

3. The process according to claim 1, wherein the wood particles of step a) are wood chips.

4. The process according to claim 1, wherein the at least one inorganic particulate calcium carbonate-containing material of step b) is selected from the group consisting of dolomite, ground calcium carbonate (GCC), preferably ground calcium carbonate (GCC) selected from the group comprising marble, chalk, limestone and mixtures thereof, precipitated calcium carbonate (PCC), preferably precipitated calcium carbonate (PCC) selected from the group comprising one or more of the aragonitic, vateritic and calcitic mineralogical crystal forms, modified calcium carbonate (MCC), gypsum, calcine clay, non-calcined (hydrous) clay, bentonite, inorganic pigments and mixtures thereof.

5. The process according to claim 1, wherein the at least one inorganic particulate calcium carbonate-containing material of step b) has a median particle size d.sub.50 from 0.3 μm to 50.0 μm and/or a specific surface area of from 0.5 to 75.0 m.sup.2/g as measured by the BET nitrogen method.

6. The process according to claim 1, wherein the at least one binder of step b) is selected from the group consisting of alkyd resin, epoxy resin, epoxy ester resin, poly(vinyl alcohol), poly(vinyl pyrrolidone), poly(vinyl acetate), poly(oxazolines), poly(vinylacetamides), partially hydrolyzed poly(vinyl acetate/vinyl alcohol), poly((meth)acrylic acid), poly((meth)acrylamide), poly(alkylene oxide), polyether, saturated polyester, sulfonated or phosphated polyesters and polystyrenes, poly(styrene-co-(meth)acrylate), poly(styrene-co-butadiene), polyurethane latex, poly(n-butyl (meth)acrylate), poly(2-ethylhexyl (meth)acrylate), copolymers of (meth)acrylates, such as n-butyl(meth)acrylate and ethyl(meth)acrylate, copolymers of vinylacetate and n-butyl(meth)acrylate casein, copolymers of polyvinylchloride, gelatin, cellulose ethers, zein, albumin, chitin, chitosan, dextran, pectin, collagen derivatives, collodian, agar-agar, arrowroot, guar, carrageenan, starch, tragacanth, xanthan, or rhamsan and mixtures thereof.

7. The process according to claim 1, wherein a single or multi-layer wood-based mat is formed in step c).

8. The process according to claim 1, wherein pre-pressing step d) is carried out at ambient temperature, e.g. from 10 to 60° C., more preferably from 15 to 30° C., and/or a pressure ranging from 5 to 40 bar, preferably from 8 to 35 bar.

9. The process according to claim 1, wherein coating step e) is carried out by metering size press, curtain coating, spray coating or roller coating.

10. The process according to claim 1, wherein coating step e) is carried out on the first and reverse side of the pre-pressed wood-based mat to manufacture a decorative wood-based board being coated on the first and the reverse side, and/or coating step e) is carried out a second time using a different or the same liquid coating composition of step b).

11. The process according to claim 1, wherein hot pressing step f) is carried out at a temperature ranging from 130 to 260° C., more preferably from 160 to 240° C.

12. The process according to claim 1, wherein the decorative wood-based board is a fibre board product, preferably a high-density fibre (HDF) board, medium-density fibre (MDF) board, low-density fibre (LDF) board, a particle board, an oriented strandboard (OSB), a hardboard, or an insulation board.

13. The process according to claim 1, wherein in step g) the at least one decorative finishing is applied as a liquid coating being a lacquer layer.

14. The process according to claim 1, wherein the process comprises the further steps of h) applying at least one protective layer on the at least one decorative finishing obtained in step g), and/or i) in case that the at least one decorative finishing is only present on one side, applying at least one backing layer on the side of the decorative wood-based board opposite to the at least one decorative finishing, preferably in form of a paper.

15. A decorative wood-based board, obtained according to the process of claim 1, comprising a) the solid wood-based board, b) the at least one coating layer on the first and/or reverse side of the solid wood-based board, wherein the coating comprises i) the at least one inorganic particulate filler material, having a ratio of particle size d.sub.80 to particle size d.sub.20 from 0.5 to 1.0, and ii) the at least one binder, and c) the at least one decorative finishing on the first and/or reverse side of the wood-based board.

16. The decorative wood-based board according to claim 15, wherein the at least one decorative finishing is present on the at least one coating layer on the first and/or reverse side of the wood-based board.

17. The decorative wood-based board according to claim 15, wherein the at least one decorative finishing is present on one side of the wood-based board and the at least one coating layer is present on the opposite side of the wood-based board and represents a backing layer or is part of a backing layer.

18. The decorative wood-based board according to claim 15, wherein the at least one inorganic particulate filler material has i) a particle size d.sub.98 of <500 μm, ii) a particle size d.sub.80 of 0.1 to 250 μm, iii) a median particle size d.sub.50 of 0.1 to 150 μm, and iv) a particle size d.sub.20 of 0.1 to 50 μm.

19. The decorative wood-based board according to claim 15, wherein the surface of the coated side of the decorative wood-based board has i) a brightness from 50 to 100%, according ISO R457 (Tappi452) and DIN 6167, ii) a yellowness from 2 to 70%, according ISO R457 (Tappi452) and DIN 6167, iii) L* from 50 to 100, according to DIN EN ISO 11664-4:2012, iv) a* from −5 to 10, according to DIN EN ISO 11664-4:2012, and v) b* from 0 to 30, according to DIN EN ISO 11664-4:2012.

20. The decorative wood-based board according to claim 15, wherein the at least one coated surface of the decorative wood-based board has i) a maximum roughness amplitude S.sub.z from 20 to 800 μm, ii) an arithmetic mean roughness S.sub.a from 2 to 80 μm, and iii) a root mean square roughness Sq from 2 to 20 μm.

21. The decorative wood-based board according to claim 15, wherein the at least one inorganic particulate filler material has i) a particle size d.sub.98 of <500 μm, ii) a particle size d.sub.80 of 0.1 to 250 μm, iii) a median particle size d.sub.50 of 0.1 to 150 μm, and iv) a particle size d.sub.20 of 0.1 to 50 μm, and the surface of the coated side of the decorative wood-based board has i) a brightness from 50 to 100%, according ISO R457 (Tappi452) and DIN 6167, ii) a yellowness from 2 to 70%, according ISO R457 (Tappi452) and DIN 6167, iii) L* from 50 to 100, according to DIN EN ISO 11664-4:2012, iv) a* from −5 to 10, according to DIN EN ISO 11664-4:2012, and v) b* from 0 to 30, according to DIN EN ISO 11664-4:2012, and i) a maximum roughness amplitude S.sub.z from 20 to 800 μm, ii) an arithmetic mean roughness S.sub.a from 2 to 80 μm, and iii) a root mean square roughness Sq from 2 to 20 μm.

22. The decorative wood-based board according to claim 15, wherein the decorative wood-based board is a fibre board product, preferably a high-density fibre (HDF) board, medium-density fibre (MDF) board, low-density fibre (LDF) board, a particle board, an oriented strandboard (OSB), a hardboard, or an insulation board.

23. The decorative wood-based board according to claim 15, wherein the decorative wood-based board has a bending strength of ≥5 N/mm.sup.2, preferably from 10 to 50 N/mm.sup.2 and most preferably from 15 to 45 N/mm.sup.2; and/or a modulus of elasticity of ≥500 N/mm.sup.2, preferably from 1 000 to 4 500 N/mm.sup.2 and most preferably from 1 500 to 3 500 N/mm.sup.2; and/or an internal bond strength of ≥0.10 N/mm.sup.2, more preferably from 0.2 to 1.4 N/mm.sup.2 and most preferably from 0.4 to 1.2 N/mm.sup.2; and/or a thickness swelling after 24 h water storage of ≤20%, more preferably from 2.0 to 15.0% and most preferably from 4.0 to 10%; and/or a brightness of at least 50%, more preferably of at least 65%, even more preferably of at least 75% and most preferably of at least 80%.

24. The decorative wood-based board according to claim 15, wherein the at least one coated side of the decorative wood-based board has a surface density ranging from 900 to 2 500 kg/m.sup.3, preferably from 1 200 to 2 400 kg/m.sup.3 and most preferably from 1 600 to 2 300 kg/m.sup.3.

25. The decorative wood-based board according to claim 15, wherein the decorative wood-based board further comprises d) at least one protective layer on the at least one decorative finishing and/or e) in case that the at least one decorative finishing is only present on one side, at least one backing layer on the side of the decorative wood-based board opposite to the at least one decorative finishing, preferably in form of a paper.

26. The decorative wood-based board according to claim 25, wherein the at least one protective layer comprises a transparent non-thermoplastic resin, preferably selected from the group consisting of urea-formaldehyde resins, melamine-resins, epoxy-resins and mixtures thereof.

27. The decorative wood-based board according to claim 15, wherein the at least one dry or liquid coating composition is used to improve the mechanical properties of the decorative wood-based board, the mechanical properties being selected from bending strength, modulus of elasticity, internal bond strength and/or thickness swelling.

28. Flooring applications, furniture, walls, wall panels, roof panels, display cabinets, storage units, loudspeakers, loudspeaker boxes and shop-fittings comprising the decorative wood-based board according to claim 16.

Description

DESCRIPTION OF FIGURES

(1) FIG. 1: Brightness CIE L* of the surface of medium density fibre boards coated according to the inventive process.

(2) FIG. 2: Contact angle after a wetting time of six seconds between water and the surface of medium density fibre boards coated according to the inventive process.

(3) FIG. 3: Change of the contact angle over a period of six seconds between water and the surface of medium density fibre boards coated according to the inventive process.

(4) FIG. 4: Raw density profiles of medium density fibre boards coated according to the inventive process.

(5) FIG. 5: Overall raw density of medium density fibre boards coated according to the inventive process.

(6) FIG. 6: Brightness CIE L* of the coated surface of medium density fibre boards finished with a 50 g/m.sup.2 white decorative paper according to the inventive process.

(7) FIG. 7: Brightness CIE L* of the coated surface of medium density fibre boards finished with a 60 g/m.sup.2 white decorative paper according to the inventive process.

(8) FIG. 8: Brightness CIE L* of the coated surface of medium density fibre boards finished with a 66 g/m.sup.2 white decorative paper according to the inventive process.

(9) FIG. 9: Print gloss of cyan (C), magenta (M), yellow (Y) and black (K) colour printed by inkjet printing on the coated surface of medium density fibre boards according to the inventive process.

(10) FIG. 10: Ink density of cyan (C), magenta (M), yellow (Y) and black (K) colour printed by inkjet printing on the coated surface of medium density fibre boards according to the inventive process.

EXAMPLES

(11) Measurement Methods

(12) The following measurement methods are used to evaluate the parameters given in the examples and claims.

(13) Particle size distribution (weight % particles with a diameter <X) and weight median diameter (d.sub.50) of a particulate filler material having a particle size d.sub.50 of ≤45 μm

(14) Weight median grain diameter and grain diameter weight distribution of an inorganic particulate filler material such as calcium carbonate, were determined via the sedimentation method, i.e. an analysis of sedimentation behaviour in a gravimetric field. The measurement was made with a Sedigraph™ 5120.

(15) The method and instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurements are carried out in an aqueous solution of 0.1 wt.-% Na4P2O7. The samples were dispersed using a high speed mixer and ultrasound.

(16) BET Specific Surface Area of a Material

(17) Throughout the present document, the specific surface area (in m2/g) of the inorganic particulate filler material is determined using the BET method (using nitrogen as adsorbing gas), which is well known to the skilled man (ISO 9277:1995). The total surface area (in m2) of the inorganic particulate filler material is then obtained by multiplication of the specific surface area and the mass (in g) of the inorganic particulate filler material prior to treatment.

(18) Solids Content of an Aqueous Suspension

(19) The suspension solids content (also known as “dry weight”) was determined using a Moisture Analyser HR73 from the company Mettler-Toledo, Switzerland, with the following settings: temperature of 120° C., automatic switch off 3, standard drying, 5 to 20 g of suspension.

(20) pH of an Aqueous Suspension

(21) The pH of a suspension or solution was measured at 25° C. using a Mettler Toledo Seven Easy pH meter and a Mettler Toledo InLab® Expert Pro pH electrode. A three-point calibration (according to the segment method) of the instrument was first made using commercially available buffer solutions having pH values of 4, 7 and 10 at 20° C. (from Sigma-Aldrich Corp., USA). The reported pH values are the endpoint values detected by the instrument (the endpoint was when the measured signal differed by less than 0.1 mV from the average over the last 6 seconds).

(22) Brookfield Viscosity

(23) For the purpose of the present invention, the term “viscosity” or “Brookfield viscosity” refers to Brookfield viscosity. The Brookfield viscosity is for this purpose measured by a Brookfield DV-III Ultra viscometer at 24° C.±3° C. at 100 rpm using an appropriate spindle of the Brookfield RV-spindle set and is specified in mPa.Math.s. Once the spindle has been inserted into the sample, the measurement is started with a constant rotating speed of 100 rpm. The reported Brookfield viscosity values are the values displayed 60 seconds after the start of the measurement. Based on his technical knowledge, the skilled person will select a spindle from the Brookfield RV-spindle set which is suitable for the viscosity range to be measured. For example, for a viscosity range between 200 and 800 mPa.Math.s spindle number 3 may be used, for a viscosity range between 400 and 1600 mPa.Math.s spindle number 4 may be used, for a viscosity range between 800 and 3200 mPa.Math.s spindle number 5 may be used, for a viscosity range between 1000 and 2000000 mPa.Math.s spindle number 6 may be used, and for a viscosity range between 4000 and 8000000 mPa.Math.s spindle number 7 may be used.

(24) Size of Wood Fibres

(25) The size of the fibres was determined via fractioning by using sieve analysis. The measurement was made with an air jet sieve from Alpine e200 LS of HOSOKAWA ALPINE AG, Germany.

(26) The measurement was carried out by applying an air flow to the fibres being placed in a sieve by a rotating slit nozzle located underneath the sieve. The fibres are thus subjected to a fractioning by air dispersing and simultaneous suction of the fibres through the sieve over a time period of 5 min. The balance between the amount of fibre before being placed in the sieve and after fractioning was considered as the through fraction in gram. Depending on the number of the chosen sieve mesh widths, the fractioning is repeated starting with the smallest sieve mesh widths to the largest sieve mesh width. Thus, for each sieve mesh width the percentage of the total amount of the fibres which is fractionized can be calculated. The mesh widths of the sieves were chosen among the following mesh widths (in mm): 0.05-0.063-0.08-0.1-0.125-0.2-0.315-0.4-0.5-0.63-0.8-1.0-1.6-2.0-3.0-3.15-4.0-5.0. For each analysis, at least three sieve mesh widths were chosen such that the size of the fibres was sufficiently covered by the chosen mesh widths. Unless otherwise indicated the size of the fibres is measured at a sieve mesh width of 0.05 mm, 1.0 mm and 3.0 mm.

(27) Wood Moisture Content

(28) The wood moisture content is determined in accordance with DIN EN 322. The term “equilibrium moisture” has to be understood as moisture content of wood or wood-based board at which the wood neither gains nor loses moisture when surrounded by air at a given relative humidity and temperature (definition in “wood hand book”) The moisture content was determined after 7 days storage in a defined climate of: 65% relative humidity and 20° C. temperature.

(29) Evaluation of Surface Roughness

(30) Roughness was determined by topographical measurements using Nanoskop device from COTEM MESSSYSTEME. Measuring standard was for the x-axis: measuring length: 4.8 mm, resolution: 500 points and for the y-axis: measuring length 4.8 mm, resolution: 250 points, applying high-pass filter Gauss. Values: Sz=maximum roughness amplitude Sa=arithmetic mean roughness Sq=root mean square roughness
Brightness and Yellowness

(31) Brightness and yellowness were measured using an ELREPHO 450, Datacolor according ISO R457 (Tappi452) and DIN 6167. The CIELAB L*, a*, b* coordinates and brightness CIE were measured using Minolta-Spectrophotometer CM-3610d (OF 22) in accordance with DIN EN ISO 11664-4:2012.

(32) Print Gloss

(33) The gloss on the printed cyan (C), magenta (M), yellow (Y) and black (K) colours was determined according to EN ISO 8254-1:2003, TAPPI 75° (%) using a Schnettler Technologies STGL-3W measuring device. The average value of n=10 measurements (thereof n=5 in print direction and n=5 in cross direction) are compared.

(34) Ink Density

(35) The ink density of the printed cyan (C), magenta (M), yellow (Y) and black (K) colours on the wood-based boards was determined with Techkon SpectroDens Advanced Densitometer. The chosen mode was “automatic density measurement”.

(36) Contact Angle

(37) The contact angle was determined using the measuring device OCA 20 from DataPhysics, by analysing the contact angle of polar fluid (water) when in contact with a substrate. The number of measurements was n=12 per trial point. The contact angle was determined after a wetting time of six seconds.

(38) Thickness Swelling

(39) Thickness swelling measurements were made after 24 h water exposure in accordance with DIN EN 317.

(40) Internal Bond Strength

(41) Internal bond strength measurements were made in accordance with DIN EN 319.

(42) Bending Strength and Modulus of Elasticity

(43) Bending strength and modulus of elasticity were measured in accordance with DIN EN 310.

(44) Adhesiveness of Decorative Paper to in-Line Coated Wood-Based Boards

(45) The adhesiveness of a decorative paper applied onto the untreated or by in-line coating treated surface of the wood-based board was determined in accordance with the DIN EN ISO 2409:2013 (german version): Cross-cut test. A “1c” cutter with a rigid blade was used to cut six parallel cuts with a distance between the blades of 3 mm and six parallel cuts perpendicular to the first six cuts resulting in a lattice of squares. Loose particles, splitters or spalls were removed with a tape (Tesa 4331, 50 mm width). The classification of the cross-cut characteristic value was determined following the table below:

(46) TABLE-US-00001 TABLE 1 Description of cross-cut test values Classification Description 0 The edges of the cuts are completely smooth; none of the squares of the lattice is detached. 1 Detachment of small flakes of the coating at the intersection of the cuts. A cross-cut area not greater than 5% is affected. 2 The coating has flaked along the edges and/or at the intersections of the cuts. A cross-cut area greater than 5%, but not greater than 15%, is affected. 3 The coating has flaked along the edges of the cuts partly or wholly in large ribbons, and/or it has flaked partly or wholly on different parts of the squares. A cross-cut area greater than 15%, but not greater than 35%, is affected. 4 The coating has flaked along the edges of the cuts in large ribbons and/or squares have detached partly or wholly. A cross-cut area greater than 35%, but not greater than 65%, is affected 5 Any degree of flaking that cannot even be classified by classification 4.
Raw Density

(47) The raw density profile of the in-line coated wood-based boards was determined by using the lab device DAX 6000 from GreCon. The measurement system uses an X-ray tube which emits X-ray radiation through a sample of the respective wood-based board. Part of the X-ray radiation is absorbed, depending on the density of the material. The ionization chamber receives the non-absorbed X-ray radiation and transfers it into electrical signals. These signals are transformed into a raw density value. The raw density profile is visualized in a raw density profile curve.

(48) The measurements were conducted using the system settings displayed in Table 2:

(49) TABLE-US-00002 TABLE 2 Parameters for raw density measurements Parameter Unit Value Feed speed [mm/s] 0.5 incrementation parameter [μm] 20 Accuracy [%] ±0.5 Working voltage X-ray [kV] 40 Sample size [mm] 50 * 50
1) Production of in-Line Coated Wood-Based Boards

(50) Parameters for the production of in-line coated medium density fibre board are displayed in Table 3.

(51) TABLE-US-00003 TABLE 3 Production parameters Panel Structure Single layer Raw Material Pine fibres Panel Thickness 8.0 mm Raw Density 700 kg/m.sup.3 Press Temperature 200° C. Press Time Factor 12 s/mm Amount Of Binder 10% Type Of Binder K345, 68% BASF Hydrophobing Agent 1.0% Hydrowax 138, Sasol Germany Dry Coat Weight 100 g/m.sup.2 or 200 g/m.sup.2

(52) Production Set-Up [Step a) to f) of the Inventive Process]: 1) Resin (binder) application on wood fibres (for medium density fibre board) and addition of hydrophobing agent in blender (resin application of surface layer wood fibres and middle layer fibres was executed separately). 2) Resinated wood fibres were formed into a wood-based mat by manual spreading. 3) Wood-based mat was pre-pressed at ambient temperature, i.e. at a temperature of 23° C. 2° C. 4) Coating 1 or coating 2 (see Table 4 and 5) were applied on the one side of the pre-pressed wood fibre mat by air-pressure paint spray gun. Coat weight was 100 g/m.sup.2 or 200 g/m.sup.2 (dry), respectively. 5) A release paper commonly used in the art was applied between the coated side of the pre-pressed wood fibre mat and the press plate to provide easier release of the hot-pressed wood-based board from the hot press plate. 6) Pre-pressed and coated wood fibre was pressed to solid wood-based board in a hot press under the above defined conditions.

(53) TABLE-US-00004 TABLE 4 Composition of coating 1 Coating 1 Parts by Product weight Raw materials Calcium carbonate 1 Natural ground calcium 100.0 carbonate, commercially available from Omya International AG, Switzerland; d.sub.98: 7.0 μm; d.sub.50: 1.5 μm; BET: 6.9 g/m.sup.2; Brightness: 95.6%; yellowness index: 0.75; CIELAB L*: 98.5; CIELAB a*: −0.1; CIELAB b*: 0.4; 78% aqueous suspension, based on the total weight of the suspension Polyvinyl alcohol PVA BF-04, Chang Chun 8.0 Petrochemicals Starch C*Film 07311, Cargill 2.0 Total 110.0 Coating characteristics Solids [%]  65.8 pH  9.2 Viscosity [mPas] (RPM 100, 730 Spindle 3, Temp.: 32° C.)

(54) TABLE-US-00005 TABLE 5 Composition of coating 2 Coating 2 Parts by Product weight Raw materials Calcium carbonate 2 Modified calcium carbonate, 100.0 commercially available from Omya International AG, Switzerland; d.sub.98: 4.0 μm; d.sub.50: 0.975 μm; BET: 28.69 g/m.sup.2; brightness: 92.7%; yellowness index: 2.9; CIELAB L*: 97.9; CIELAB a*: 0.009; CIELAB b*: 1.57; 50% aqueous suspension, based on the total weight of the suspension Polyvinyl alcohol PVA BF-04, Chang Chun 8.0 Petrochemicals Starch C*Film 07311, Cargill 2.0 Total 110.0 Coating characteristics Solids [%]  45.8 pH  8.7 Viscosity [mPas] (RPM 100, 290 Spindle 3, temp.: 26° C.)

(55) The inventive board shows improved optical and physical properties after in-line coating, i.e. step f) of the inventive process, compared to a non-coated reference wood-based board (see FIGS. 1 to 5).

(56) Due to the in-line coating process, the brightness CIE L* values of the coated surface of all boards obtained after process step f) are increased compared to the uncoated reference board (see FIG. 1). For example, for a medium density fibre board coated with 200 g/m2 of coating 1 the brightness CIE L* value of the coated surface of the wood-based board increases by 39% compared to the reference.

(57) Furthermore, the contact angle of the coated surface of all wood-based boards obtained after step f) was reduced compared to the uncoated board (see FIG. 2). A low contact angle, respectively a high wettability with water, indicates an improved uptake of (water-based) inks, when direct printing, e.g. by ink-jet printing or rotogravure printing, is applied as decorative finishing in process step g). The dynamical contact angle development, i.e. the change of contact angle with time, also shows an improvement of the surface wettability of the inventive wood-based boards (see FIG. 3). The medium density fibre board with a surface comprising 200 g/m2 of coating 2 show the lowest contact angles.

(58) All in-line coated wood based boards show an increased raw density on the coated surface compared to the reference board. Highest local density values were achieved with coating 2 at a coat weight of 200 g/m2 and coating 1 at a coat weight of 200 g/m2 followed by coating 2 at a coat weight of 100 g/m2 and coating 1 at a coat weight of 100 g/m2 (see FIG. 4).

(59) The determined overall raw density of the in-line coated wood-based boards was slightly above the raw density of the reference board (see FIG. 5). All values lie within a range of max 5% difference.

(60) 2) Decorative Finishing of in-Line Coated Wood-Based Boards with Decorative Paper

(61) The coated medium density fibre boards obtained according to step f) (and the uncoated reference board) were further processed by applying a decorative paper according to step g) of the present invention, onto the coated (or raw) side of the surface of the wood-based boards.

(62) TABLE-US-00006 TABLE 6 Production parameters Decorative paper application Paper D1 white, filled, 50 g/m.sup.2, Kämmerer GmbH Paper D2 white, filled, 60 g/m.sup.2, Kämmerer GmbH Paper D3 white, filled, 66 g/m.sup.2, Kämmerer GmbH Press Type Short Cycle Press, Höfer Type of Binder Urea-formaldehyde, K285. 65.5% BASF Amount Of Binder 20 g/m.sup.2 decorative paper Type of Hardener Bonit 12830 Amount of Hardener 10% based on solids content of binder Press Temperature 150° C. Press Time 60 s Specific Pressing 33 bar Pressure

(63) Medium density fibre boards with a white decorative paper applied to the coated side of the board show improved optical parameters and adhesiveness compared to the uncoated board comprising a white decorative paper on the surface of one side (see FIGS. 6 to 8, and Table 7).

(64) The brightness CIE L* of the coated surface of the medium density fibre boards finished with a 50 g/m2, white decorative paper D1 was increased compared to the surface of the uncoated reference board also finished with a 50 g/m2, white decorative paper D1. In the best case (coating 1, 200 g/m2), the brightness CIE L* increases by 4.5% (see FIG. 6).

(65) The brightness CIE L* of the coated surface of the medium density fibre boards finished with a 60 g/m2, white decorative paper D2 was increased compared to the surface of the uncoated reference board also finished with a 60 g/m2, white decorative paper D2. In the best case (coating 1, 200 g/m2), the brightness increases 2.2% (see FIG. 7).

(66) The brightness CIE L* of the coated surface of the medium density fibre boards finished with a 66 g/m2, white decorative paper D3 was increased compared to the surface of the uncoated reference board also finished with a 66 g/m2, white decorative paper D3. In the best case (coating 1, 200 g/m2), the brightness increases 1.5% (see FIG. 8).

(67) TABLE-US-00007 TABLE 7 Adhesiveness Decorative Cross-cut Spalling Trial point paper classification predominantly in Reference D1 5 Substrate Reference D2 5 Substrate Reference D3 5 Substrate Coating 1, 100 g/m.sup.2 D1 5 In-line coating layer Coating 1, 100 g/m.sup.2 D2 5 In-line coating layer Coating 1, 100 g/m.sup.2 D3 5 In-line coating layer Coating 2, 100 g/m.sup.2 D1 4 In-line coating layer Coating 2, 100 g/m.sup.2 D2 1 — Coating 2, 100 g/m.sup.2 D3 3-4 In-line coating layer Coating 1, 200 g/m.sup.2 D1 5 In-line coating layer Coating 1, 200 g/m.sup.2 D2 3 In-line coating layer Coating 1, 200 g/m.sup.2 D3 4-5 In-line coating layer Coating 2, 200 g/m.sup.2 D1 5 Substrate Coating 2, 200 g/m.sup.2 D2 5 Substrate Coating 2, 200 g/m.sup.2 D3 5 Substrate

(68) The adhesiveness of the inventive wood-based board comprising an in-line coated surface and a decorative paper D1, D2 or D3 attached thereon is comparable with the adhesiveness of a wood-based board without an in-line coated surface but with a decorative paper D1, D2 or D3, or is even improved for trial point “coating 2, 100 g/m2, paper D1”, “coating 2, 100 g/m2, paper D2”, “coating 2, 100 g/m2, paper D3”, “coating 1, 200 g/m2, paper D2” and “coating 1, 200 g/m2, paper D3” (see Table 7).

(69) In case of a cross-cut classification of 3-5, the loose, spalled particles were visually inspected and it was evaluated where the cohesion fracture occurred. The cohesion fracture appeared for the reference board in the substrate, meaning that the adhesion of the decorative paper to the surface of the board is stronger than the bonding characteristics of the substrate itself. Comparable to this, the cohesion fracture of the inventive, i.e. surface coated and with decorative paper finished, wood-based boards occurred within the in-line coating layer, meaning that the adhesion of the decorative paper to the surface of the in-line coated wood-based board is strong, too.

(70) 3) Decorative Finishing of in-Line Coated Wood-Based Boards by Direct Printing

(71) A decorative finishing of the in-line coated medium density fibre boards obtained according to step f) was carried out by inkjet printing of the four colours cyan (C), magenta (M), yellow (Y) and black (K) with 100% tonal value on the coated side of the boards. An uncoated reference board was also printed for comparison. The printing and curing parameters are displayed in Table 8.

(72) TABLE-US-00008 TABLE 8 Printing and curing parameters Printing parameters Printer Hymmen Jupiter JPT-L Size of panels 250 * 250 mm Printing speed 25 m/min Ink type UV-curing Acrylate inks, Hymmen Ink amount Black 2.73 g/m.sup.2 Cyan/Magenta 4.17 g/m.sup.2 Yellow 3.19 g/m.sup.2 Curing parameters Printer UV HG (FE doped) 200 W/cm 100% UV LED 4x after printing head 100% Post-curing UV Channel HG/Ga 80 W/cm, 5 m/min, 1550 mj/cm.sup.2

(73) The following results were found by measuring the print gloss and ink density of the four printed colours cyan (C), magenta (M), yellow (Y) and black (K).

(74) Print Gloss:

(75) The results in FIG. 9 show, that print gloss can be improved by applying coating 1 with 100 g/m.sup.2, coating 2 with 100 g/m.sup.2 or 200 g/m.sup.2 in step e) of the inventive process. The comparison to the uncoated wood-based board shows that the print gloss could be increased from, for example, 4.7% for magenta colour on the reference board to 43.9% for magenta colour on the medium density fibre board with coating 1; 200 g/m.sup.2.

(76) Ink Density:

(77) The results in FIG. 10 show that the ink density of inkjet-printed colours cyan (C), magenta (M), yellow (Y) and black (K) is maintained or improved for the inventive wood-based boards compared to the values of the reference board. In the best case, the ink density was increased from 0.38 for yellow colour on the reference board to 1.01 for yellow colour on the medium density fibre board comprising coating 2, 200 g/m.sup.2. The ink-density of a printed colour is critical to its optical appearance. The higher the ink density of a printed colour is, the fuller or richer a colour appears to the human eye.