Method for producing wood material panels, in particular OSB wood material panels, and wood material panel that can be produced in accordance with said method

Abstract

A method of producing wood-base panels, especially OSB wood-base panels is provided. The method including the steps of providing wood strands, applying at least one adhesive system to the wood strands having at least one polymer adhesive and at least one nanoparticle below 500 nm, and pressing the wood strands admixed with the adhesive system to form wood-base panels.

Claims

1. A method of producing an OSB wood-base panel, comprising the steps of: a) providing wood strands; b) applying at least one adhesive system to the wood strands, wherein the adhesive system comprises: solely a polyurethane adhesive, and nanoparticles below 500 nm, wherein at least one nanoparticle is modified with at least one compound of general formula (I)
R.sub.aSiX.sub.(4-a)(I), or of general formula (II)
O.sub.bX.sub.c(OH).sub.dR.sub.eSiO.sub.(4-b-c-d-e)/2(II), where X is H, OH or a hydrolyzable moiety selected from the group consisting of: halogen, alkoxy, carboxyl, amino, monoalkylamino or dialkylamino, aryloxy, acyloxy, alkylcarbonyl, R is a nonhydrolyzable organic moiety R selected from the group consisting of: substituted and unsubstituted alkyl, substituted and unsubstituted aryl, substituted and unsubstituted alkenyl, substituted and unsubstituted alkynyl, substituted and unsubstituted cycloalkyl, which may each be interrupted by O or NH, and wherein R may include at least one functional group Q selected from a group containing an epoxy, hydroxyl, ether, amino, monoalkylamino, dialkylamino, substituted and unsubstituted anilino, amide, carboxyl, acryloyl, acryloyloxy, methacryloyl, methacryloyloxy, mercapto, cyano, alkoxy, isocyano, aldehyde, alkylcarbonyl, acid anhydride and/or phosphoric acid group, a is =0, 1, 2, 3, b, c, d are=0 or 1, and e is =1, 2, 3; wherein the adhesive system is admixed to the wood strands in an amount between 1.0 and 2.5 wt % based on the wood strands, and c) pressing the wood strands admixed with the adhesive system to form the wood-base panel.

2. The method as claimed in claim 1, wherein the wood strands have a length between 50 to 200 mm, a width between 5 to 50 mm, and a thickness between 0.1 and 2 mm.

3. The method as claimed in claim 1, wherein the polyurethane adhesive is based on polydiphenylmethane diisocyanate (PMDI).

4. The method as claimed in claim 1, wherein X is selected from a group containing fluorine, chlorine, bromine, iodine, C.sub.1-6alkoxy, C.sub.6-10aryloxy, C.sub.2-7acyloxy, C.sub.2-7alkylcarbonyl, monoalkylamino or dialkylamino of C.sub.1 to C.sub.12.

5. The method as claimed in claim 1, wherein R is selected from a group consisting of: substituted and unsubstituted C.sub.1-30alkyl, substituted and unsubstituted C.sub.2-6alkenyl, substituted and unsubstituted C.sub.2-6alkynyl and substituted and unsubstituted C.sub.6-10aryl.

6. The method as claimed in claim 1, wherein R is selected from a group containing methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl, t-butyl, pentyl, hexyl, cyclohexyl, vinyl, 1-propenyl, 2-propenyl, butenyl, acetylenyl, propargyl, phenyl and naphthyl.

7. The method as claimed in claim 1, wherein the at least one functional group Q is selected from a group containing epoxy, hydroxyl, ether, acryloyl, acryloyloxy, methacryloyl, methacryloyloxy, alkoxy, cyano and/or isocyano groups.

8. The method as claimed in claim 1, wherein the at least one functional group Q is an epoxy group, an amine group or an isocyano group.

9. The method as claimed in claim 1, wherein the at least one nanoparticle has a size between 2 and 400 nm.

10. The method as claimed in claim 1, wherein the at least one nanoparticle comprises an oxidic, hydroxidic or oxyhydroxidic nanoparticle.

11. The method as claimed in claim 1, wherein the modified nanoparticles are used in an amount between 1 to 15 wt % based on the total amount of polyurethane adhesive.

12. The method as claimed in claim 1, wherein the modified nanoparticles are admixed to the polyurethane adhesive or are applied to the wood strands before resination thereof.

13. An OSB wood-base panel obtained by a method as claimed in claim 1, comprising an adhesive content between 1.0 and 2.5 wt % based on the total amount of the wood strands.

14. The method of claim 1, wherein a is =0 or 1.

15. The method of claim 1, wherein the adhesive system is admixed to the wood strands in an amount between 2.0 and 2.2 wt % based on the wood strands.

16. The method of claim 3, wherein the polyurethane adhesive based on PMDI is the sole polymer adhesive.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The invention will now be more particularly described with reference to several working examples.

Working Example 1: Preparing a First Adhesive System

(2) An initial charge is provided in the form of a urethane matrix (PMDI) which still contains OH groups and/or unbound cyanato groups. SiO.sub.2 particles are stirred into the urethane matrix at a concentration of 0.1-10 wt % preferably 0.5-5 wt % preferably 1-2 wt %. This is followed by the admixture of an isocyanatopropyltriethoxysilane and possibly of a dibutylisotin dilaurate initiator in case an initiator is not already present in the polyurethane. This mixture is heated to 50? C. and maintained at 50? C. for about 30 minutes. After cooling down to room temperature, a glycidyloxypropyltriethoxysilane and an acid, for example phosphoric acid, as catalyst are admixed and stirred in for a further 60 minutes. The polyurethane-silane-SiO.sub.2 mixture thus obtained can then optionally be mixed with a melamine resin matrix.

Working Example 2: Preparing a Second Adhesive System

(3) An ethanol-water mixture is initially charged and admixed with a mixture of glycidyloxypropyltriethoxysilane and tetraethoxysilane. This is followed by the admixture of an aqueous silica sol solution, i.e., nanoscale SiO.sub.2 particles in water, and also the admixture of an acid, for example acetic acid or para-toluenesulfonic acid, as catalyst and stirring for 5 minutes. After a stirring time of 5 minutes, the PMDI adhesive is admixed. Thereafter the adhesive system is ready to use.

Working Example 3: Preparing a Third Adhesive System

(4) An ethanol-water mixture is initially charged and admixed with a mixture of 111.36 g of glycidyloxypropyltriethoxysilane (0.4 mol), 20.33 g of tetraethoxysilane (0.1 mol) and 17.8 g of methyltriethoxysilane. This is followed by the admixture of 114 g of an aqueous silica sol solution (Kieselsol A200/30), i.e., nanoscale SiO.sub.2 particles (particle size 12 nm) in water, and also the admixture of 4 g of para-toluenesulfonic acid, as catalyst and stirring for 5 minutes. After a stirring time of 5 minutes, the PMDI adhesive is admixed. Thereafter the adhesive system is ready to use.

Working Example 4: Preparing a Fourth Adhesive System

(5) An ethanol-water mixture is initially charged and admixed with a mixture of 111.36 g of glycidyloxypropyltriethoxysilane (0.4 mol), 20.33 g of tetraethoxysilane (0.1 mol) and 17.8 g of methyltriethoxysilane. This is followed by the admixture of 114 g of an aqueous silica sol solution (Kieselsol A200/30), i.e., nanoscale SiO.sub.2 particles (particle size 17 nm) in water, and also the admixture of 4 g of para-toluenesulfonic acid, as catalyst and stirring for 5 minutes. After a stirring time of 5 minutes, the PMDI adhesive is admixed. Thereafter the adhesive system is ready to use.

(6) Then, the third and fourth adhesive systems are applied to a flakeboard specimen and a flakeboard sample respectively. In each case 1 ml of the solution was applied to a cut area of the flakeboard sample and dried in a drying cabinet at 100? C. for 15 minutes. The depth of penetration of the solution was then determined by visual inspection. Five flakeboard specimens each were tested per experiment.

(7) Purely PMDI resin absorbs in this procedure (curing at 100? C. for 15 min) far into the flakeboard sample and thus disappears from the adhesive-adherend interface. In fact, the PMDI resin disappears so far into the flakeboard sample that this is discernible on the reverse side of the flakeboard sample as well as on the front side.

(8) By contrast, the admixture of 5 wt % of modified SiO.sub.2 particles as per the third and fourth working examples to the PMDI resin leads to a different result following curing at 100? C. for 15 min. On the front side and the reverse side, signs of penetration by the modified resin are barely discernible (working example 3) or completely absent (working example 4). On increasing the level of modified SiO.sub.2 particles to 20 wt % and curing at 100? C. for 15 min, the resin even remains completely on the surface and appears to foam up slightly.

(9) The results are unambiguous in showing that admixture of modified SiO.sub.2 nanoparticles to a PMDI foam is effective in preventing any absorption/diffusion of the PMDI resin into the wood fibers/strands, making it possible to reduce the binder quantity required in the manufacturing process of wood-base panels.

Working Example 5: Producing an OSB Panel

(10) An OSB line was used to manufacture OSB panels (18 mm) under standard conditions.

(11) PMDI resin was used in the outer layers and the central layer, the resin fraction amounting to 2.9 wt % based on strands (absolutely dry wood) (comparative panel).

(12) In a test, the silane described above under working example 2 was admixed, in an amount of 5 wt %, to the PMDI resin. The modified PMDI resin was used to manufacture OSB panels using a resin fraction based on the strands of 2.4 wt %. The transverse tensile strength of the panels was then determined. A value of 0.43 N/mm.sup.2 was found for the test panel. A value of 0.44 N/mm.sup.2 was determined for the comparative panel.

(13) This shows that a significant reduction in resin provides nearly the same technological values. The silanes coupled to nanoscale particles appear to be effective in at least partly preventing the absorption of the PMDI resin into the wood matrix.