In-line coated wood-based boards

Abstract

The present invention relates to a process for manufacturing a wood-based board, a wood-based board as use of a liquid coating composition comprising at least one particulate filler material and at least one binder for in-line coating of wood-based boards.

Claims

1. A wood-based board comprising a) a base of wood particles and/or fibres, and b) a coating on the first and/or reverse side of the wood-based board, wherein the coating comprises i) at least one particulate filler material, having a ratio of particle size d.sub.80 to particle size d.sub.20 [d.sub.80/d.sub.20] from 0.5 to 1.0, and ii) at least one binder.

2. The wood-based board according to claim 1, wherein the coating is penetrated into the surface of the wood-based board.

3. The wood-based board according to claim 1, wherein the at least one particulate filler material has i) a particle size d.sub.98 of <500 m, ii) a particle size d.sub.80 of 0.1 to 250 m, iii) a median particle size d.sub.50 of 0.1 to 150 m, and iv) a particle size d.sub.20 of 0.1 to 50 m.

4. The wood-based board according to claim 1, wherein the surface of the coated side of the 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.

5. The wood-based board according to claim 1, wherein the surface of the coated side of the wood-based board has i) a maximum roughness amplitude Sz from 20 to 800 m, ii) an arithmetic mean roughness Sa from 2 to 80 m, and iii) a root mean square roughness Sq from 2 to 20 m.

6. The wood-based board according to claim 1, wherein the at least one particulate filler material has i) a particle size d.sub.98 of <500 m, ii) a particle size d.sub.80 of 0.1 to 250 m, iii) a median particle size d.sub.50 of 0.1 to 150 m, and iv) a particle size d.sub.20 of 0.1 to 50 m, and the surface of the coated side of the 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 Sz from 20 to 800 m, ii) an arithmetic mean roughness Sa from 2 to 80 m, and iii) a root mean square roughness Sq from 2 to 20 m.

7. The wood-based board according to claim 1, wherein the wood-based board further comprises a printing on the first and/or reverse side of the wood-based board on the coating of the wood-based board.

8. The wood-based board according to claim 1, wherein the wood-based board is a fibre board product comprising 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.

9. The wood-based board according to claim 1, wherein the wood-based board has a bending strength of >5 N/mm.sup.2.

10. The wood-based board according to claim 1, wherein the wood-based board has a bending strength of 10 to 50 N/mm.sup.2.

11. The wood-based board according to claim 1, wherein the wood-based board has a bending strength of 15 to 45 N/mm.sup.2.

12. The wood-based board according to claim 1, wherein the wood-based board has a modulus of elasticity of >500 N/mm.sup.2.

13. The wood-based board according to claim 1, wherein the wood-based board has a modulus of elasticity from 1 000 to 4 500 N/mm.sup.2.

14. The wood-based board according to claim 1, wherein the wood-based board has a modulus of elasticity from 1 500 to 3 500 N/mm.sup.2.

15. The wood-based board according to claim 1, wherein the wood-based board has an internal bond strength of >0.10 N/mm.sup.2.

16. The wood-based board according to claim 1, wherein the wood-based board has an internal bond strength of 0.2 to 1.4 N/mm.sup.2.

17. The wood-based board according to claim 1, wherein the wood-based board has an internal bond strength of 0.4 to 1.2 N/mm.sup.2.

18. The wood-based board according to claim 1, wherein the wood-based board has a thickness swelling after 24 h water storage of <20%.

19. The wood-based board according to claim 1, wherein the wood-based board has a thickness swelling after 24 h water storage from 2.0 to 15.0%.

20. The wood-based board according to claim 1, wherein the wood-based board has a thickness swelling after 24 h water storage from 4.0 to 10%.

21. The wood-based board according to claim 1, wherein the wood-based board has a brightness of at least 50%.

22. The wood-based board according to claim 1, wherein the wood-based board has a brightness of at least 65%.

23. The wood-based board according to claim 1, wherein the wood-based board has a brightness of at least 75%.

24. The wood-based board according to claim 1, wherein the wood-based board has a brightness of at least 80%.

Description

EXAMPLES

(1) Measurement Methods

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

(3) 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 m

(4) Weight median grain diameter and grain diameter weight distribution of a 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.

(5) The method and instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurements is carried out in an aqueous solution of 0.1 wt-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed mixer and ultrasound.

(6) Particle Size Distribution (Volume % Particles with a Diameter <X) and Volume Median Diameter (d.sub.50) of a Particulate Filler Material Having a Particle Size d.sub.50 of >45 m

(7) Volume median grain diameter and grain diameter volume distribution of a particulate filler material were determined via laser diffraction, i.e. the particle size is determined by measuring the intensity of light scattered as a laser beam passes through a dispersed particulate sample. The measurement was made with a Mastersizer 2000 or a Mastersizer 3000 of Malvern Instruments Ltd. (operating instrument software version 1.04). Alternatively, the measurement can be made with a HELOS particle-size-analyzer of Sympatec, Germany. The measurement may be considered equivalent to weight distribution assuming a constant density throughout the particle size distribution, and reference is made to the measurement technique.

(8) The method and the instruments are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurement is carried out in an aqueous solution of 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples are dispersed using a high speed stirrer and supersonics.

(9) BET Specific Surface Area of a Material

(10) Throughout the present document, the specific surface area (in m.sup.2/g) of the filler material is determined using the BET method (using nitrogen as adsorbing gas), which is well known to the skilled man (ISO 9277:2010). The total surface area (in m.sup.2) of the filler material is then obtained by multiplication of the specific surface area and the mass (in g) of the filler material prior to treatment.

(11) Solids Content of an Aqueous Suspension

(12) 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.

(13) pH of an Aqueous Suspension

(14) The pH of the aqueous slurry was measured using a standard pH-meter at room temperature, approximately 22 C.

(15) Pigment Volume Concentration (PVC)

(16) The PVC was calculated in accordance with the formula:

(17) $PVC=\frac{.Math.VP*.Math.VF}{.Math.VP+.Math.VF+.Math.VB}*100$
VP: Volume Pigment
VF: Volume Filler
VB: Volume Binder

(18) Whiteness and Yellowness

(19) Whiteness (or 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.

(20) Gloss

(21) Surface gloss was measured using Cotem CGL-3W device from Lehmann, according to EN ISO 8254-1:2003, TAPPI 75 (%).

(22) Evaluation of Surface Roughness

(23) 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

(24) Size of Wood Fibres

(25) The size or 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 20 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 25 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) Particle Size of Wood Particles

(28) Particle sizes of wood particles were determined by mechanical vibration sieves and calculation of grading curves. Sieves with differing sieve meshes were setup as a tower starting with the smallest sieve mesh on the bottom and the largest sieve mesh on the top. The wood particles were placed on the top sieve and the sieve tower was fixed in a vibrating machine. The wood particles are thus subjected to fractioning by continuous shaking of the sieve tower within a timer period of 5 min. The balance between the amount of wood particles before being placed on the top sieve and after fractioning was considered as the through fraction in gram. Thus, for each sieve mesh width the percentage of the total amount of wood particles which is fractionized can be calculated. The mesh widths of the sieves were chosen among the following mesh widths (in mm): 0.063-0.1-0.315-0.5-1.0-1.6-2.0-3.15-4.0-6.3-8-12.

(29) For each analysis at least seven mesh widths were chosen such that the size of the wood particles was sufficiently covered by the chosen mesh widths.

(30) The particle length and thickness of the wood particles were determined by electron microscopic analysis, such as transmission electron microscope (TEM) or scanning electron microscope (SEM).

(31) Wood Moisture Content

(32) 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 panel 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.

(33) Density

(34) Density (or raw density) measurements were made in accordance with DIN EN 323.

(35) Thickness Swelling

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

(37) Internal Bond Strength

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

(39) Bending Strength and Modulus of Elasticity Bending strength and modulus of elasticity were measured in accordance with DIN EN 310.

EXAMPLES

(40) Substrate 1: Medium Density Fibreboard. Production parameters are displayed in table 1 below:

(41) TABLE-US-00001 TABLE 1 Panel Structure Single layer Raw Material Pine Fibres Panel Thickness 17.5 mm Raw Density 700 kg/m3 Press Temperature 200 C. 2 C. Press Time Factor 12 s/mm Amount Of Binder 10% Type Of Binder K345, 68% BASF Hydrophobising agent 0.5% Hydrowax 140, Sasol Germany

(42) Substrate 2: Particle Board. Production parameters are displayed in table 2 below.

(43) TABLE-US-00002 TABLE 2 Panel Structure Three layer Raw Material Industrial Wood Particles Panel Thickness 17.5 mm Raw Density 680 kg/m.sup.3 Press Temperature 220 C. 2 C. Press Time Factor 15 s/mm Amount of Binder 12% (Surface layer); 8.5% (Middle Layer) Type of Binder K350, 66% BASF Hydrophobising Agent 0.5% Hydrowax 140, Sasol Germany

(44) Production Set-Up: 1. Resin (binder) application on wood fibres (for a medium density fibreboard (MDF)), substrate 1) or wood particles (for a particle board, substrate 2) and addition of hydrophobising agent was carried out in a blender (resin application of surface layer wood particles and middle layer particles for the particle board was executed separately). 2. Resinated wood fibres or wood particles were formed into a wood fibre mat or wood particle mat by manual spreading. 3. The wood fibre mat or wood particle mat was pre-pressed at ambient temperature, i.e. 23 C.2 C., and a pressure of 10 bar. 4. Coating 1 and Coating 2 (see tables 3 to 6 for composition and characteristics) were applied on one side of the pre-pressed wood fibre mat or wood particle mat by air-pressure paint spray gun. Coating 2 duplex was also applied on the second side of the pre-pressed and on one side coated wood fibre mat. Coat weight was for each trial point 100 g/m.sup.2 (dry). 5. Pre-pressed and coated wood fibre mat or wood particle mat was then hot pressed to a solid board in a hot press under the conditions disclosed in Tables 1 and 2. (Coating 2 duplex in the results means that the pre-pressed and on one side coated wood fibre mat was turned 180 and the second surface side was coated additionally).

(45) TABLE-US-00003 TABLE 3 Composition of coating 1 Parts by Raw Materials Product weight Calcium carbonate 1 Natural ground calcium 90.0 carbonate, commercially available from Omya International AG, Switzerland; d.sub.98: 7.0 m; d.sub.80: 3.3 m; d.sub.50: 1.5 m; d.sub.20: 0.5 m; BET: 6.9 m.sup.2/g; 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 Styrene butadiene latex 1 Styronal D628 10.0 Total 100.0

(46) TABLE-US-00004 TABLE 4 Coating characteristics of coating 1 Solids [%] 69.9 PVC [%] 77.5 pH 8.1 Viscosity [mPa .Math. s] 190 (RPM 100, Spindle 2)

(47) TABLE-US-00005 TABLE 5 Composition of coating 2 Parts by weight based on 100 parts Raw Materials Product host material Sodium polyphosphate Calgon N 0.1 Ammonium hydroxide Ammoniak, 25% 0.2 solution Modified Polymer Tego Dispers 750 W 1.5 Polyurethane system Tafigel PUR 45 0.8 Polyurethane system Tafigel PUR 41 0.4 Organic polymer Tego Foamex 830 0.4 Ester alcohol Texanol 0.5 Dipropylenglykol Dowanol DPnB 0.5 monomethylether Isothiazolinon Mergal 723K 0.1 Silicate Bentone LT 0.1 Titanium dioxide 1 TiONA 595 21.0 Calcium carbonate 2 Natural ground calcium 9.0 carbonate, commercially available from Omya International AG, Switzerland; d.sub.98: 10.3 m; d.sub.80: 4.9 m; d.sub.50: 2.6 m; d.sub.20: 1.1 m; BET: 3.6 m.sup.2/g; brightness: 93.1%; yellowness index: 1.7; CIELAB L*: 97.7; CIELAB a*: 0.03; CIELAB b*: 0.9. Clay 1 Burges No. 50 13.0 Water Tab Water 33.4 Styrene acrylate 1 Mowilith LDM 7451, 47% 19.0 Total 100.0

(48) TABLE-US-00006 TABLE 6 Coating characteristics of coating 2 Solids [%] 53.6 PVC [%] 62.3 pH 8.7 Viscosity [mPa .Math. s] 120 (RPM 100, Spindle 2)

(49) In general, it was possible to manufacture a wood-based board, i.e. a particle board, having a sandwich structure (with smooth transition between the layers, or interaction of the layers). It was also possible to manufacture a single-layer medium density fibreboard as wood-based board. The wood-based boards featured optimised board physical, mechanical and optical board parameters compared to a reference raw board. The reference boards were manufactured the same way as described for the inventive wood-based boards (table 1 and table 2), but without applying a coating between the pre-pressing and hot pressing step. In particular, it was possible to improve the bending strength and modulus of elasticity, the thickness swelling, the brightness CIE, the brightness R457, the yellowness, the gloss as well as the roughness Sa, Sz, Sq of the wood-based boards coated with coating 1 and coating 2 compared to the reference raw boards. The results are outlined in FIGS. 1 to 9 for substrate 1, i.e. the results for MDF boards coated with coating 1, coating 2. FIG. 1 and FIG. 2 also show the results of the MDF boards coated on both sides, i.e. coating 2 duplex.

(50) As regards substrate 2, it was possible to improve the brightness CIE, the brightness R457, the yellowness as well as the gloss compared to the reference raw board. The results are outlined in FIGS. 10 to 13 for substrate 2, i.e. the improved optical properties of the Particle Board surface by using coating 1 and coating 2.

(51) Table 7 outlines the theoretically achieved classifications of the boards coated with coating 1 or 2 following European standard DIN EN 622.

(52) TABLE-US-00007 TABLE 7 Classification Sample MBH MBH.H MBH.E MBH.LA 1 MBH.LA 2 MBH.HLS 1 MBH.HLS 2 Reference x x x x X Coating 1 x x X x x X x Coating 2 x x X x x X x