Self-adhesive material for wood board and wood board

Abstract

A self-adhesive material for a wood board is described. The self-adhesive material is formed of polyolefin film having a melt index is 4 g/10 min (measured at 190 C. and 2.16 kg), and the polyolefin film contains reactive groups with OH groups of the wood for forming self-adhesive properties. Further, a wood board in which the self-adhesive material is used as a coating and/or as a glue-line material is described.

Claims

1. A wood board, in which the wood board comprises wood-based veneers and the wood board is formed so that the veneers of the wood board are joined together, wherein the wood based veneers are bound together by a self-adhesive material formed of polyolefin film consisting of maleated polyolefin, and the maleated polyolefin contains maleic anhydride groups as reactive groups which react with OH groups of the wood for forming covalent bonds between the polyolefin film and OH groups of the wood-based veneers and the reactive groups of the polyolefin film have been activated at temperatures of more than 180 C. during the manufacturing of the polyolefin film, so that maleic acid has been converted to maleic anhydride and the polyolefin film contains maleic anhydride reactive groups, and the self-adhesive material is arranged as a glue-line material between the veneers for gluing the veneers together, and the polyolefin film is bonded directly to a wood surface without any priming and joining layers.

2. The wood board according to claim 1, wherein the polyolefin film comprises at least two layers which are a first layer and a second layer, and the first layer and the second layer contain the maleic anhydride groups which react with the OH groups of the veneers.

3. The wood board according to claim 1, wherein the polyolefin film comprises at least three layers, and the outer layers contain the maleic anhydride groups which react with the OH groups of the veneers.

4. The wood board according to claim 1, wherein the polyolefin film has a melt index of less than or equal to 4 g/10 min wherein the melt index is measured at 190 C. and 2.16 kg.

5. The wood board according to claim 1, wherein the polyolefin film is at least partially cross-linked.

6. The wood board according to claim 1, wherein the maleic anhydride groups of the polyolefin film are activated at a temperature of more than 180 C. for about 0.5-3 minutes during the manufacturing of the polyolefin film.

7. The wood board according to claim 1, wherein the maleic anhydride groups of the polyolefin film are activated at a temperature of more than 180 C. for at least 2 minutes by converting the maleic acid to maleic anhydride during the manufacturing of the polyolefin film.

8. The wood board according to claim 1, wherein the polyolefin film is formed by extrusion.

9. The wood board according to claim 8, wherein the maleic anhydride groups of the polyolefin film are activated during the extrusion by providing the polyolefin film in a melt for about 2-3 minutes during the extrusion.

10. The wood board according to claim 1, wherein the maleated polyolefin contains maleic acid in the amount of 0.3-15% by weight of the maleated polyolefin and maleic anhydride.

11. The wood board according to claim 1, wherein the self-adhesive material is heated and arranged between the veneers of the wood board by hot pressing at temperatures of 120-170 C. for joining the veneers together.

12. The wood board according to claim 1, wherein the wood board is selected from group consisting of plywood, particle board, fiber board, and paper board.

13. The wood board according to claim 1, wherein a catalyst is used in the manufacturing of the self-adhesive material.

14. A method for manufacturing a wood board, in which wood-based veneers are joined together to form the wood board, wherein the wood based veneers are bound together by a self-adhesive material formed of polyolefin film consisting of maleated polyolefin, and the maleated polyolefin contains maleic anhydride groups as reactive groups which react with OH groups of the wood for forming covalent bonds between the polyolefin film and OH groups of the wood-based veneers and the reactive groups of the polyolefin film have been activated at temperatures of more than 180 C. during the manufacturing of the polyolefin film, so that maleic acid has been converted to maleic anhydride and the polyolefin film contains maleic anhydride reactive groups, and the self-adhesive material is arranged as a glue-line material between the veneers for gluing the veneers together, and the polyolefin film is bonded directly to a wood surface without any priming and joining layers.

Description

LIST OF FIGURES

(1) In the following, the invention is described by means of detailed embodiment examples with reference to accompanying FIGS. 1 and 2, in which

(2) FIG. 1 shows a schematic diagram of the chemical reactions, and

(3) FIG. 2 shows a self-adhesive material structure according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) FIG. 1 discloses a schematic diagram of the chemical reactions in the manufacturing the self-adhesive material and the wood board, e.g. plywood. To make the plywood of the invention there are many steps. First is selection of the raw materials. Then is the conversion of the maleated material from maleic acid to maleic anhydride. The self-adhesive film is made it needs to be attached to the plywood where the active maleic anhydride groups react with the hydroxide groups of the wood.

(5) FIG. 2 discloses a self-adhesive material structure of the invention.

(6) The self-adhesive material is formed of a film which comprises three layers: first (1), second (2) and additive (3) layers. The first layer is a bottom layer (1), second layer is a top layer (2) and additive layer (3) is arranged between the first and second layers.

(7) The top film layer (2) is formed of polyolefin, e.g. polyethylene or polypropylene, and maleated polyolefin, e.g. maleic anhydride polyethylene (MAPE) or maleic anhydride polypropylene (MAPP), including additives and fillers. The top film layer can be cross-linked.

(8) The bottom layer (1) is formed of MAPE or MAPP.

(9) The additive layer (3) is sandwiched between the top layer (2) and the bottom layer (1). The additive layer is formed of polyethylene or polypropylene including additives, like fire retardants and UV-stabilisers, and fillers.

(10) The self-adhesive material and the wood board used in the tests can be prepared following. At the first stage, the three-layer self-adhesive film is prepared of polyolefin, maleated polyolefin and additives and fillers by co-extruding. Maleated polyolefin contains maleic acid which is converted to maleic anhydride at temperatures of more than 190 C. during the manufacturing of the film. The top film layer can be cross-linked by electron beam radiation at this stage. The layers of the film are joined together for forming the film. At second stage, the formed film is cut to size and is arranged between the veneers of the wood board and/or onto the wood board as a coating. The veneers of the wood board are bound together and/or the coating is attached on the surface by hot pressing, cold pressing and/or high frequency pressing. The hot pressing is made at temperatures of about 120-140 C., at pressure of about 1.2-1.9 N/mm.sup.2 and by time of 2-8 minutes. The cold pressing can follow the hot pressing. The cold pressing is made until the temperature falls below 80-100 C., at pressure of about 1.2-1.7 N/mm and by time of 0.5-5 minutes. The high frequency pressing is made by frequency of 13.10 MHz and time of about 2-5 minutes. In an alternative embodiment, the self-adhesive material can be cross-linked by radiation or silane-moisture method at this stage.

(11) A wood board can be plywood, particle board, high or middle density fiberboard, or some other pressed and glued board containing wood or other plant fibers.

(12) When dissimilar polymers are co-extruded a compatibiliser material is required in the self-adhesive material to join the dissimilar materials.

(13) The maleated polyolefin contains normally 2-15% maleic acid of the amount of polyolefin. At extrusion at temperatures of more 180 C. the maleic acid is converted to maleic anhydride, partially or totally. The polymer film can also be cross-linkable if it in any case improves the use of the products.

Example 1

(14) In this example, a preparation of the polyethylene film was tested. The polyethylene film containing maleic acid was heated and activated so that maleic acid was converted to maleic anhydride during the preparation of the film. In table 1 is disclosed results of the test.

(15) TABLE-US-00001 TABLE 1 Treatment Treatment Maleic Maleic temperature time acid anhydride ( C.) (minutes) (%) (%) No treatment N/A 55 45 170 3 36 64 180 3 20 80 185 3 14 86 190 3 10 90 195 3 8 92

(16) It is clear from the results of Table 1 that the maleic acid is converted mostly to maleic anhydride at temperatures of more than 180 C. for 3 minutes and therefore it can be considered that during extrusion where the polymer is in the melt for about 2-3 minutes that an extrusion temperature of >180 C. is sufficient but preferably >190 C.

Example 2

(17) In this example, the self-adhesive material of FIG. 2 used in the tests was prepared. The tests are carried out as follows.

(18) Adhesion of the coating to the plywood was measured by three different methods peel test (ISO4578, SFS-EN204), the result was the separation force as a function of coating length (25 mm). The second test was the dolly test (EN311) and the third test was the shearing test. In the case of the shearing test and peeling test the measurements could be made after soaking and boiling in addition to the dry samples. However, the dolly test could only be performed on dry samples.

(19) Table 2 discloses birch plywood coating adhesive properties peeling (ISO 4578, SFS-EN204) and pull strength (dolly test, EN311). The melt index of the polyethylene is MI0.3 g/10 min (190 C./2.16 kg). The coupling agents are Fusabond MD-353D (MAPP) and Fusabond MB-226DE (MAPE). Pressing conditions are: Temp. 130-150 C., Pressure 1.8 N/mm.sup.2 and Time 8 minutes.

(20) TABLE-US-00002 TABLE 2 Pull strength N/mm.sup.2 Film Peel Wood thickness Coupling strength Strength fibre (mm) agent N/mm N/mm.sup.2 (%) 2% MAPE + 0.27 Fusabond 1.4 1.7 90 PE/PE/PE + MB-226DE 2% MAPE 2% MAPE + 0.1 Fusabond 0.8 2.2 95 PE/PE/PE MB-226DE 2% MAPP + 0.1 Fusabond 1 1.6 85 PP/PP/PP MD-353D Multi-Wall 0.28 2.1 2.2 100

(21) It is clear from Table 2 that the adhesive bond to plywood is to a similar level as WISA Multiwall which is glued with polyurethane glues. The bonding of this coating is WBP exterior bonded to EN314-2/Class 3.

(22) Table 3 discloses birch plywood coating adhesive properties peel strength measured for dry samples and after soaking and boiling. In all cases the melt index (MI) of the polyethylene is 0.3 (190 C./2.16 kg) except where specified as HDPE or MDPE and then MI0.2 g/10 min (190 C./2.16 kg) or MI0.7 g/10 min (190 C./2.16 kg) respectively is used. Hot pressing conditions are: Temp. 135-160 C., Pressure 1.7 N/mm.sup.2 and Time 3.5-8 minutes. The coupling agent used was Fusabond MB-226DE unless otherwise specified.

(23) TABLE-US-00003 TABLE 3 Film Peel strength thickness N/mm Film type (mm) dry soaked boiled 2% MAPE + 0.27 1 0.7 0.5 PE/PE/PE + 2% MAPE 2% MAPE + 0.27 1.8 0.9 0.7 PE/HDPE/PE + 2% MAPE 2% MAPE + 0.27 0.9 0.6 0.2 PE/MDPE/PE + 2% MAPE 2% MAPE + 0.27 0.6 0.5 0.4 PE/PE/PE + 2% MAPE (Fusabond 603) WISA Multi-Wall 0.28 2.1 1.3 1.2

(24) It is clear from the results in Table 3 that the peeling test is influenced by coating stiffness and is not totally a measure of adhesive strength to wood. It is also observed that the Fusabond 603 coupling agent is less affective. However, it is clear that the coating version with HDPE co-extruded in the middle layer is at a equivalent peeling strength as WISA Multiwall for dry and soaked conditions.

(25) Table 4 discloses birch plywood coating adhesion properties peeling (ISO 4578, SFS-EN204) and shear strength perpendicular to the surface (EN319) after different pretreatments (dry, soaking, boiling, EN204) for uncross-linked and cross-linked coated (0.27 mm) plywood. Hot-pressing: 7 minutes, 135 C. and 1.7 N/mm.sup.2. The coupling agent used was Fusabond MB-226DE unless otherwise stated.

(26) TABLE-US-00004 TABLE 4 Shearing Shearing strength strength (EN319) (EN319) Peel strength N/mm.sup.2 Dry N/mm.sup.2 Boiled (ISO 4578) Wood Wood N/mm Strength failure Strength failure Film dry boiled N/mm.sup.2 (%) N/mm.sup.2 (%) 2% MAPE 2 + 1.1 0.6 1.4 100 0.8 100 PE/PE/PE + % MAPE (uncrosslinked) 2% MAPE + 1 0.6 1.03 100 0.28 100 PE/PE/PE + % MAPE (cross-linked: 150 KGy) 2% MAPE + 0.6 0.4 1.2 100 0.7 80 PE/PE/PE + 2% MAPE (Fusabond 603) uncrosslinked 2% MAPE + 0.6 0.4 1.13 100 0.33 100 PE/PE/PE + 2% MAPE (Fusabond 603) (cross-linked: 150 KGy) 2% MAPE + 1 0.6 PE/HDPE/PE + % MAPE (uncrosslinked) 2% MAPE + 0.9 0.4 1.03 100 0.32 100 PE/HDPE/PE + % MAPE (cross-linked: 150 KGy) PE Mono 0.8 39 0.04 9 Uncross-linked

(27) The results in Table 4 show that cross-linking by E-beam radiation (100-200 KGy) after hot-pressing to the plywood does not damage the wood; however it does not improve the adhesive properties. In addition to this scratch resistance was not improved. In the case of the cross-linked coatings in Table 4 the coatings were cross-linked after adhesion to the plywood; however, the films were also cross-linked before adhesion to the plywood and in those cases it was found that the cross-linking made it difficult to hot-press the coating to the plywood this is because the radiation cross-linking rendered the whole coating more heat resistant.

(28) The mono film contained no MAPE it was just LDPE (MI0.3 g/10 min, 190 C./2.16 kg). The aim of using just polyethylene to coat the surface was to show the effect of having no coupling agent. The results were acceptable for dry conditions but after boiling the wood failure was 9%. Therefore failure was in the coating. This shows the importance of forming a chemical bond.

(29) Table 5 discloses birch plywood coating adhesive properties peel (ISO 4578 and SFS-EN204) and shear strength perpendicular to the surface (EN319) after different pretreatments (soaking, boiling, EN204) for low viscosity films (MI4 g/10 min (190 C./2.16 kg) in all layers). The films could not be extruded above 170 C.

(30) TABLE-US-00005 TABLE 5 Melt index (MI) Shear strength g/10 min Peel (EN319) N/mm.sup.2 Thickness (190 C./ strength Strength Wood Film (mm) 2.16 kg) N/mm N/mm.sup.2 failure 3% Mape + 0.1 4 Not 0.83 90 PE/3% MAPE + possible (soak) (soak) PE/PE + 2% MAPE 3% Mape + 0.1 4 Not 0.06 3 PE/3% MAPE + possible (boil) (boil) PE/PE + 2% MAPE

(31) It was not possible to measure the peel strength because the film coating with MI4 g/10 min (190 C./2.16 kg) polyethylene since it had penetrated into the wood so that the coating was too thin to measure. It is clear from the results in Table 5 that MI4 g/10 min (190 C./2.16 kg) provides deeper penetration into the wood; however, owing to the coupling agent not being converted sufficiently enough into maleic anhydride during extrusion there is poor chemical adhesion to the wood (hydrogen bonding) and therefore the shear strength properties after boiling are very poor with almost no wood fibre breakage. These results show the importance of forming a durable chemical bond.

(32) Table 6 discloses birch plywood coated with multi-layered dissimilar self-adhesive coating properties (scratch, boiling resistance and delamination of polypropylene or polyamide). Hot-pressing conditions are: Temp. 140, Pressure 1.7 N/mm.sup.2 and Time 8 min.

(33) TABLE-US-00006 TABLE 6 Hot- Delamination press of coating Film release Scratch layers thickness paper resistance during hot (mm) used N pressing 2% Mape + PE/PA 0.1 No 8-10 No Polyamide laminated 2% MAPE + PE/PE + 0.1 Yes 8-10 No mLLDPE + EVA/PP (co-extruded)

(34) The scratch test is performed using an Erichsen test pen (Model 318). The test was developed by Robert Boch GmBH. Samples 100100 mm are prepared and then the pen is applied which has forces (2-20 N). The surface is simply scratched using the pen the scratch force is increased from 2-20 N in steps of 2N. The first scratch that can be seen by the naked eye is the force that the coating can take and therefore the scratch resistance level.

(35) It is clear from Table 6 there is no delamination of the polyamide or polypropylene layers during hot-pressing and there is enough scratch resistance. The main advantage of the polyamide outer layer is that there is no need for any release paper during hot-pressing. Also cost of the coating is not increased considerably as this layer can be 12 m. Thicker polyamide layers may improve the scratch resistant properties slightly (thickness 12-20 m).

(36) Table 7 discloses birch plywood coating hardness (DIN 53505) and scratch resistance properties for different coatings compared with other coating materials for plywood. The different maleated polymers used are Fusabond MD-353D (MAPP), and Fusabond MB-226DE (MAPE).

(37) TABLE-US-00007 TABLE 7 Shore Scratch CaOH.sub.2 hardness resistance Boiling (DIN 53505) (N) test 2% MAPE + PE/PE/PE + 62 8-10 Pass 2% MAPE (0.27 mm) 2% MAPE + PE/PE/PE + 63 8-10 Coating worn 2% MAPE (0.03 mm) away 2% MAPP + 56 8-10 Pass PP/PP/PP (0.1 mm) Wisa multiwall 58 5-8 Pass (0.28 mm)

(38) It can be seen from Table 7 that the scratch resistance of the self-adhesive coatings is higher than for WISA Multiwall. This is important from the point of view of where the coated plywood is used. If it is used where it is easily or frequently touched or there are sharp objects then it is important that the coating on the plywood does not scratch easily. The CaOH.sub.2 boiling test results are also very important especially if the coatings are to be used in formwork for concrete applications.

(39) A self-adhesive material and a wood board according to the invention are suitable in its different embodiments for different types of applications.

(40) The embodiments of the invention are not limited to the examples presented rather many variations are possible within the scope of the accompanying claims.