WOOD PARTICLE BOARDS

Abstract

The present invention relates to a multi layer particle board comprising at least one core layer and two surface layers, the core layer particles being bonded by a resin binder other than a carbohydrate based binder resin, and the surface layer particles being bonded by a carbohydrate based resin, and to a process for making same.

Claims

1. A multi-layer particle board comprising at least one core layer and a surface layer, the surface layer particles being bonded by a binder comprising carbohydrate based reaction products and the core layer particles being bonded by a binder other than the carbohydrate based binder resin used in the surface layer, wherein the binder comprising carbohydrate based reaction product comprises: reaction products of a reducing sugar and a nitrogen source.

2. The multi-layer particle board of claim 1 wherein the core layer binder is selected from a binders comprising: phenol formaldehyde resin; urea formaldehyde resin; and isocyanate based binder resin, such as methylene diphenyl diisocyanate.

3. The multi-layer particle board of claim 1 characterized by one or more of the following features: wherein the nitrogen source comprises an amine component, preferably a primary amine component wherein the nitrogen source comprises an amine component, preferably a primary amine component and wherein the ratio of carbonyl groups in the reducing sugar to reactive amino groups in the amine components of the surface layer binder is in the range of 5:1 to 1:2, preferably in the range of 5:1 to 1:1.8, 5:1 to 1:1.5, 5:1 to 1:1.2, 5:1 to 1:1, 5:1 to 1:0.8 and 5:1 to 1:0.5, 4:1 to 1:2, 3.5:1 to 1:2, 3:1 to 1:2, 2.5:1 to 1:2, 2:1 to 1:2 and 1.5:1 to 1:2.

4. The multi-layer particle board of claim 1 wherein the reducing sugar is selected from the group consisting of monosaccharides, disaccharides, and polysaccharides or a reaction product thereof.

5. The multi-layer particle board of claim 1 wherein the nitrogen source is selected from: NH3; an inorganic amine; an organic amine comprising at least one primary amine group; a polyamine; an organic or inorganic salt, notably an ammonium salts, of any of the aforementioned.

6. The multi-layer particle board of claim 5 wherein the nitrogen source comprises a polyamine having the structure H.sub.2N-Q-NH.sub.2, wherein Q is: an alkanediyl, notably an alkanediyl group selected from —C.sub.2-C.sub.24—; an alkanediyl group selected from —C.sub.2-C.sub.9—; or an alkanediyl group selected from C.sub.3-C.sub.7—; preferably Q is a C.sub.6 alkanediyl, cycloalkanediyl, such as cyclohexanediyl, cyclopentanediyl or cyclobutanediyl, heteroalkanediyl, or cycloheteroalkanediyl, each of which may be optionally substituted; or a divalent benzyl radical.

7. The multi-layer particle board of claim 6 wherein the polyamine is selected from 1,6-diaminohexane (hexamethylenediamine, HMDA) and 1,5-diamino-2-methylpentane (2-methyl-pentamethylenediamine).

8. The multi-layer particle board of claim 5 wherein the polyamine is selected from polyether-polyamine and polymeric polyamine.

9. (canceled)

10. The multi-layer particle board according to claim 1 characterized by one or more of the following features: wherein the surface layer binder comprises: a non-carbohydrate polyhydroxy component, notably selected from glycerol, a polyalkylene glycol, polyethylene glycol, polypropylene glycol, trimethylolpropane, pentaerythritol, polyvinyl alcohol, partially hydrolyzed polyvinyl acetate, fully hydrolyzed polyvinyl acetate, and mixtures thereof; and/or reaction products of a non-carbohydrate polyhydroxy component, notably selected from the aforementioned; wherein the multi-layer particle board further comprises at least one surface covering sheet or laminate.

11. (canceled)

12. A method of manufacturing multi-layer particle boards comprising at least one core layer and a surface layer, comprising provision of core layer wood particles suitable for the core layer and contacting the core layer wood particles with a core layer binder composition to provide resinated core layer wood particles, provision of surface layer wood particles and contacting the surface layer wood particles with a surface layer binder composition to provide resinated surface layer wood particles, arrangement of layers of the resinated particles to form a layered mat of loosely arranged particles comprising in sequence or reverse sequence a first surface layer comprising resinated surface layer particles and at least one core layer comprising resinated core layer particles, and possibly a second surface layer comprising resinated surface layer particles, and subjecting the layered mat of resinated particles to pressure and curing, wherein the surface layer binder composition is selected from binder compositions comprising i) a reducing sugar and ii) a nitrogen source and/or reaction products of (i) and (ii) and the core layer binder composition is a binder compositions other than the surface layer binder composition.

13. The method of claim 12 wherein the core layer binder composition is selected from: phenol formaldehyde based binder compositions; urea formaldehyde based binder compositions; and isocyanate based binder compositions notably methylene diphenyl diisocyanate.

14. The method of claim 12 wherein the nitrogen source is an amine component, preferably a primary amine component.

15. The method of claim 14, wherein, the surface layer binder composition comprises a ratio of carbonyl groups in the reducing sugar to reactive amino groups in the nitrogen source in the range of 5:1 to 1:2.

16. The method of claim 12, wherein the surface layer binder composition comprises: (a) reducing sugar reactant(s) and a nitrogen source; and/or (b) curable reaction product(s) of reducing sugar reactant(s) and a nitrogen source; and wherein the combined weight of (a) and (b) makes up at least 30%, preferably at least 50%, more preferably at least 70% by dry weight of the surface layer binder composition.

17. The method of claim 12 characterized by one of the following features: wherein the surface layer binder composition comprises 50 to 90% by dry weight of reducing sugar(s) and 10 to 50% by dry weight of nitrogen source component(s), based on the combined dry weight of the reducing sugar and nitrogen source components; or wherein the surface layer binder composition comprises at least 70% by dry weight of reducing sugar(s) and less than 30% by dry weight of nitrogen source component(s), based on the dry weight of the surface layer binder composition.

18. The method of claim 12 wherein the surface layer binder composition further comprises 0.1-25% by dry weight of non-carbohydrate polyhydroxy component(s), preferably selected from glycerol, polyethylene glycol, polypropylene glycol, trimethylolpropane, pentaerythritol, polyvinyl alcohol, partially hydrolyzed polyvinyl acetate, fully hydrolyzed polyvinyl acetate, and mixtures thereof, preferably 2-18% by dry weight glycerol.

19. The method of claim 12 wherein the surface layer binder composition is at least partly pre-reacted.

20. The method of claim 12 wherein a post-curing is applied, notably by application of energy to the particle boards subsequent to release from a curing press.

21. A multi-layer particle board comprising at least one core layer and a surface layer, in which the surface layer comprises surface layer wood particles held together by a binder obtained by curing a carbohydrate based surface layer binder composition, wherein the surface layer binder composition comprises i) a reducing sugar and ii) a nitrogen source and/or reaction products of (i) and (ii); and the core layer comprises core layer wood particles held together by curing a core layer binder composition, the core layer binder composition being a binder composition which is different from the surface layer binder composition, preferably a non-carbohydrate based binder composition.

22. A process for the manufacture of multi-layer particle boards comprising at least one core layer and two surface layers, comprising provision of core layer wood particles suitable for the core layer and contacting the core layer wood particles with a core layer binder composition selected from phenol formaldehyde based binder compositions; melamine-urea-formaldehyde based binder compositions; urea formaldehyde based binder compositions; and isocyanate based binder compositions, notably methylene diphenyl diisocyanate, to provide resinated core layer wood particles, provision of surface layer wood particles and contacting the surface layer wood particles with a surface layer binder composition to provide resinated surface layer wood particles, arrangement of layers of the resinated particles to form a layered mat of loosely arranged particles comprising in sequence or reverse sequence a first surface layer comprising resinated surface layer particles and at least one core layer comprising resinated core layer particles, and a second surface layer comprising resinated surface layer particles, and subjecting the layered mat of resinated particles to pressure and curing, wherein the surface layer binder composition is selected from binder compositions comprising i) a reducing sugar and ii) a primary amine component and/or reaction products of (i) and (ii), wherein the surface layer binder composition comprises a ratio of carbonyl groups in the reducing sugar to reactive amino groups in the primary amine component in the range of 5:1 to 1:2, wherein the surface layer binder composition comprises: (a) reducing sugar and a primary amine component and/or (b) curable reaction product(s) of reducing sugar and primary amine component and the combined weight of (a) and (b) makes up at least 50% by dry weight of the surface layer binder composition, wherein the surface layer binder composition may further comprise 2-18% by dry weight glycerol.

Description

EXAMPLE

[0062] Several three layer particle board samples of 300×300 mm.sup.2 having a total thickness of 16 mm with approximately 5 mm thick surface layers and a target density of 650 kg/m.sup.3 were prepared according to a standard procedure. For the core layer, wood particles having particle dimensions between 1.25 mm and 4 mm and having a residual moisture content of about 7 wt. % (based on oven dried wood weight) were sprayed with binder composition having the composition and solid content as described below, such as to reach the binder loading described below, and with potential additives as described below, and were tumbled for uniform coating. Similarly, for the surface layer, surface layer particles having particle dimensions of about 1.25 mm or less and moisture content of about 3% were sprayed with relevant binder compositions at relevant loadings, and with potential additives and were tumbled for uniform coating.

[0063] The core layers of each of the samples was the same and comprised wood particles (1.25-4 mm) having a residual moisture content of approximately 7 wt. % and a urea-formaldehyde binder at a loading of 7.5 wt. % (binder solids by weight of resinated wood particles). The wood particles were treated with 0.60 wt. % SP45 wax. The urea-formaldehyde resin comprised 4.5 wt. % (of total binder) of an ammonium nitrate catalyst.

[0064] The different particle board samples had different surface layers as shown in Table 1 below. The loading of surface layer binder was 10 wt. % for all samples. For samples B1-B9, a carbohydrate based binder as defined below was used; for samples B10-B12, the same urea-formaldehyde binder as in the core layer was used, but at the said loading of 10 wt. %.

[0065] The carbohydrate based surface layer binder compositions used in this example comprise an aqueous mixture of dextrose monohydrate (“DMH”) and fructose and hexamethylene diamine (“HMDA”) as shown in Table 1 below:

TABLE-US-00001 TABLE 1 Binder composition of surface layers prior to reaction DMH Fructose HMDA (parts by (parts by (parts by Solids Board dry dry dry content Glycerol number weight) weight) weight) % addition B1, B2, B3 43.5 43.5 13 61%  5:95 B4, B5 43.5 43.5 13 61% 10:90 B6, B7 43.5 43.5 13 61% 0 B8, B9 43.5 43.5 13 69% 0 B10, B11, Comparative examples using UF based B12 surface layer binder composition

[0066] The solid content in Table 1 is the solid content (% wt) of the aqueous binder compositions prior to any addition of glycerol. For examples B1, B2 and B3 an initial aqueous binder solution was made by combining the DMH, fructose and water; 5 parts by weight glycerol were then added to 95 parts by weight of this initial aqueous binder solution to provide the aqueous binder composition. Similarly, for examples B4 and B4 10 parts by weight glycerol were added to 90 parts by weight of the initial aqueous binder solution to provide the aqueous binder composition.

[0067] Boards B10, B11 and B12 include a UF based surface binder containing wood particles (<1.25 mm) having a residual moisture content of approximately 10 wt. % and a urea-formaldehyde binder at a loading of 10 wt. % (binder solids by weight of resinated wood particles). The wood particles were treated with 0.5 wt. % SP45 wax. The urea-formaldehyde resin composition comprised 0.5 wt. % (of total binder, on a dry basis) of an ammonium nitrate catalyst.

[0068] In order to fabricate the sample boards, a mass of coated wood particles adapted to achieve a target board density of 650 kg/m.sup.3 was transferred into a forming box in order to form three layered board samples of 300×300×16 mm, the larger particle sizes being used for the core layer and the smaller particle sizes being used for the surface layers. The quantity of resinated surface layer particles was adapted to form surface layers each having a thickness of approximately 3 mm. Board samples were pressed under 56 bar, to 16 mm thickness using metal stops, at a target platen temperature of 230° C. for a given time period to reach the press factors (seconds per mm thickness for a 16 mm thick board) indicated in Table 2.

[0069] The test samples were subjected to an internal bond strength test, such as per EN319, intended to evaluate the tensile strength perpendicular to the plane of the test piece and expressed in N/mm.sup.2.

[0070] The particle board samples were also tested for Surface Soundness. To that effect, a circular groove (inner diameter of 35.7 mm) is cut 0.3 mm deep into the test sample. A steel pad is glued onto the board surface, on the cut surface portion. After the adhesive has hardened a tensile force is applied at constant speed so that failure occurs, preferably within the surface layer; the force at failure is recorded and expressed in Newton per square millimetre. See for instance BS EN311.

TABLE-US-00002 TABLE 2 Average Surface Surface Surface board Soundness Soundness Board binder Glycerol: Press density IB bottom top number loading binder factors/mm kg/m.sup.3 N/mm.sup.2 N/mm.sup.2 N/mm.sup.2 B1 Carbo 10%  5:95 7 697.4 0.38 1.15 1.07 B2 Carbo 10%  5:95 6 645.4 0.35 0.97 0.90 B3 Carbo 10%  5:95 5.5 650.9 0.25 1.00 0.89 B4 Carbo 10% 10:90 6 640.1 0.29 1.02 0.97 B5 Carbo 10% 10:90 7 662.2 0.40 1.14 0.92 B6 Carbo 10% 0 6 644.1 0.33 0.89 0.92 B7 Carbo 10% 0 7 677.5 0.45 0.77 1.07 B8 Carbo 10% 6 626.2 0.32 0.80 0.89 B9 Carbo 10% 7 657.1 0.34 1.02 1.14 B10 UF 10% 5.5 623.8 0.18 0.70 0.58 B11 UF 10% 6 645.3 0.30 0.77 0.56 B12 UF 10% 7 669.1 0.40 0.86 0.74 Carbo: carbohydrate based binder as per Table 1 UF: urea-formaldehyde based binder IB: Internal bond strength

[0071] It was noticed that boards B10, B11 and B12 comprising UF-based binder (57% solids) bonded surface layer particles showed small surface defects on more than 60% of the panel bottom surface, and on approx. 25% of the panel top surface.

[0072] In contrast, boards B8 and B9 comprising carbohydrate based binder (69% solids) bonded surface layer particles show significantly fewer surface defects on the back side (about 40%) as well as on the top side (approx. 15%). Boards B6 and B7 comprising carbohydrate based binder (61% solids) bonded surface layer particles show even further reduced surface defects (about 5% and 15%, respectively, of both sides).

[0073] When adding 10 wt. % (on a dry basis) glycerol to the carbohydrate based binder composition for bonding the surface layer particles, see boards B4 and B5, the surfaces show further reduced defects: less than 5% on both sides of B4 and less than 10% on the backside with no defects on the top side of B5.

[0074] When adding 5 wt. % only of glycerol to the carbohydrate based binder composition, as in the case of boards B1, B2 and B3, the presence of surface defects varies between 40 and 50% of the back surface but falls to approx. 15% of the top side for B1 to no defect on the top side for B2 and B3.

[0075] The above-mentioned defects are small white spots which are an indicator of surface defects that become evident after melamining.

[0076] The surface soundness is significantly improved when comparing boards B1 to B9 and prior art type boards, represented by B10, B11 and B12. More particularly in the case of B7, the surface soundness of the back surface was such that the rupture occurred in the core layer. This shows that the surface layer was strongly bonded. In contrast thereto, in the case of the UF bonded boards B10 and B11, the rupture occurred in the top outside surface, and in the case of B12, the rupture occurred in the back outside surface.