LAPPALAINEN, Esa (Niemenpääntie 26, Neuvoton, FI-49490, FI)
JAKORINNE, Hannu (Niemenkatu 16, Lahti, FI-15140, FI)
MIKKOLA, Olavi (Rutellinkatu 7 B, Lahti, FI-15140, FI)
LAPPALAINEN, Esa (Niemenpääntie 26, Neuvoton, FI-49490, FI)
JAKORINNE, Hannu (Niemenkatu 16, Lahti, FI-15140, FI)
CLAIMS
1. A method for manufacturing a wood board wherein the wood board of multiple veneer layers is formed from a number of veneers in such manner that the veneer layers are stacked one on top of the other and combined by glue, c h a r a c t e r i z e d in that air is added to the glue and the glue is foamed to form foam glue, and the foam glue is applied evenly on at least one surface of the veneer by spray application. 2. The method according the claim 1, c h a r a c t e r i z e d in that amount of the air that is added to the glue is adjusted so as to have the density of the foam glue between 0.2 and 0.8g/cm 3 .
3. The method according to claim 1 or 2, c h a r a c t e r i z e d in that amount of the air that is added to the glue is adjusted so as to have the density of the foam glue between 0.3 and 0.6g/cm 3 .
4. The method according to any one of claims 1 to 3, c h a r a c t e r i z e d in that the glue is sprayed by air diffusion, high pressure diffusion and/or ultrasound diffusion.
5. The method according to any one of claims 1 to 4, c h a r a c t e r i z e d in that the glue is sprayed by atomization and/or fan air. 6. The method according to any one of claims
I to 5, c h a r a c t e r i z e d in that the glue is in the form of a dispersion, containing air.
7. The method according to any one of claims 1 to 6, c h a r a c t e r i z e d in that the glue is se- lected from the group of polyphenol dispersion, poly- urea dispersion, polymelamine dispersion and mixtures thereof.
8. The method according to any one of claims I to 7, c h a r a c t e r i z e d in that the spraying is performed at low pressure.
9. The method according to any one of claims 1 to 7, c h a r a c t e r i z e d in that the spraying is performed by air diffusion at low pressure.
10. The method according to any one of claims 1 to 7, c h a r a c t e r i z e d in that the spraying is performed at high pressure.
11. An apparatus for applying glue between veneer layers in connection with the manufacture of a wood board, wherein the wood board of multiple veneer layers is formed from a number of veneers in such manner that the veneer layers are stacked one on top of the other and combined by glue, c h a r a c t e r i z e d in that the apparatus (1) comprises glue supply means (2) for supplying foamed glue for spray application, and at least one spray application head (8) for applying the foamed glue by spray application on at least one surface of the veneer.
12. The apparatus according to claim 11, c h a r a c t e r i z e d in that the apparatus comprises atomization air supply means (4,7) .
13. The apparatus according to claim 11 or 12, c h a r a c t e r i z e d in that the apparatus comprises fan air supply means (4,7) .
14. The apparatus according to any one of claims 11 to 13, c h a r a c t e r i z e d in that the apparatus comprises pressure control means. |
METHOD AND APPARATUS FOR MANUFACTURING A WOOD BOARD
FIELD OF THE INVENTION
The invention relates to a method for manu- facturing a wood board as defined in the preamble of claim 1 and to an apparatus for applying glue in conjunction with the manufacture of a wood board as defined in the preamble of claim 11.
BACKGROUND OF THE INVENTION
Known from the prior art are various types of wood boards, such as plywood and the like, and methods for their manufacture.
Known from the prior art are various gluing methods for gluing the veneers in wood boards together. The known gluing methods include for example line application, curtain application, spray application and roll application. These methods typically make use of a glue mixture in fluid state wherein a binder polymer with additives and curing agents has been dispersed in an aqueous or solvent solution. One example is the glue mixture of phenol-formaldehyde resin, which typically has a density of about 1.2g/cm 3 and a viscosity of about 500 - 1000mPa*s. Currently used in line application is also solid non-flowing foamed glue mixture which contains air as the medium and has considerably lower density than dispersion glue, i.e. about 0.2g/cm 3 . Industrial use of the foamed glue mixture has previously been possible only in connection with line application.
Problems with the previously known gluing methods are e.g. slow line speed, application problems and staining /of the surrounding area at high application speeds as well as large consumption of the glue. In addition, when using a dispersion glue, breaking of
the glue joints in connection with hot-pressing, caused by vapour pressure due to a large amount of water, have proved problematic.
In addition, the need of many different types of glue for different gluing methods has been found problematic.
OBJECTIVE OF THE INVENTION
The objective of the invention is to elimi- nate the drawbacks referred to above and to disclose a new type of method and apparatus for manufacturing a wood board. One specific objective of the invention is to disclose the use of foamed glue in spray application.
SUMMARY OF THE INVENTION
The method and apparatus for manufacturing a wood board according to the invention are characterized by what has been presented in the claims. The invention is based on a method for manufacturing a wood board, in which method the wood board of multiple veneer layers is formed from a number of veneers in such manner that the veneer layers are stacked one on top of the other and connected by means of glue. According to the invention, air is added to the glue and the glue is foamed to form foam glue, and the foam glue is applied evenly between the veneer layers, on at least one surface of the veneer, by spray application. In this context, a wood board of multiple veneer layers refers to a wood board with two or more layers.
In addition, the invention is based on an apparatus for applying glue between veneer layers in connection with the manufacture of a wood board, wherein the wood board of multiple veneer layers is
formed from a number of veneers in such manner that the veneer layers are stacked one on top of the other and connected by means of glue. According to the invention, the apparatus comprises glue supply means for supplying foamed glue for spray application, and at least one spray application head for applying the foamed glue on at least one surface of the veneer.
In this context, a wood board refers to any wood board product, plywood product, composite product, beam, compressed board product or a corresponding layered product, formed from veneers and veneer layers and mainly from wood-based materials, in which the veneers are stacked one on top of the other and glued together. In this context, a veneer layer refers to any layer of material, typically a thin layer of material, used for forming a layered board. The layer of material may be formed from a wood-based material or other material applicable for the purpose.
In this context, glue refers to any type of glue or glue mixture known per se in the art that can be foamed to form foam glue and is typically used in different application methods. Foamed glue is more solid in mobility and has lower density than the traditional glue dispersion. In foamed glue, the water or solvent has been partly replaced by air, which reduces the risk of breaking due to vapour pressure in connection with curing, or of distortion of the board due to moisture .
In one embodiment of the invention, the em- ployed glue is in the form of a dispersion containing air, and the glue dispersion is foamed. In one embodiment, the glue contains a phenol-, resorcinol-, mela- mine- and/or urea-based resin or derivatives thereof and water or a solvent. In one embodiment of the inven- tion, the glue has been selected from the group of polyphenol dispersion, polyurea dispersion, polymelamine
dispersion and mixtures thereof. The glue may contain different additives, such as a curing agent, surface- active agent, stabilizer or the like. The additives may ¬ be added to the glue in any suitable stage. In one embodiment of the invention, the amount of air added to the glue is adjusted so as to have the density of the foam glue between 0.2 and 0.8g/cm 3 , more preferably between 0.3 and O.βg/cm 3 . In one embodiment, the density of the foam glue is arranged to be between about 0.4 and 0.5g/cm 3 . With these foam glue densities the homogeneity of the glue mixture is good. If the density rises considerably, the homogeneity and stability of the glue mixture normally drop.
In this invention, less air is added to the glue mixture compared e.g. with line application in which the density of the glue is very low and the glue therefore solidifies on the spot. The foamed glue according to the invention is more fluent and has higher density, so that it may be applied with spray applica- tion evenly and quickly. However, the density of the foam glue employed in the method according to the invention is not as high as with regular dispersion glue.
The glue or glue mixture may be foamed by commercial foaming devices known per se comprising air supply means and a homogenizer. In the commercial foaming devices the supply of glue mixture and air and the adjustment of temperature and pressure can be sufficiently controlled.
The air may be added to the glue in connection with or before the foaming device.
In one embodiment of the invention, spraying is performed by air diffusion, high pressure diffusion and/or ultrasound diffusion.
In one embodiment of the invention, spraying is performed at low pressure, e.g. at a pressure of about 4 to 5 bar, preferably by air diffusion. In an
alternative embodiment., spraying is performed at high pressure, e.g. at a pressure of 15 to 20, bar.
In one embodiment of the invention, the glue is sprayed by atomization and/or fan air. Fan air provides formation of a fan and determines the shape of the fan when the glue is sprayed onto the surface of the veneer. Atomization air causes the foamed glue to be formed into droplets in connection with spraying. By the amount of air it is possible to adjust the droplet size in the glue during spraying while adjusting at the same time adhesion of the glue on the surface of the veneer.
In one embodiment, the volume of application of the glue has been arranged to be between 80 and 130g/m 2 . In one embodiment, the volume of application of the glue has been arranged to be between 90 and 100g/m 2 . By means of the invention, it is possible to reach lower application volumes as desired compared to the previously known solutions. Spray application and the application volume are governed by the speed of the conveyor line, glue supply pressure, density of the foamed glue, height of the spraying nozzles, orientation of the spraying nozzles and/or supply of the atomization and fan air. The glue may be sprayed from different heights, typically from a distance of 10 to 60cm. In one embodiment, the glue is sprayed onto the veneer surface from a height of less than 35cm, e.g. from a height of 20 to 30cm. The apparatus used in the manufacture of a wood board comprises conveying and stacking means for the veneers, supply means for the glue, a spray application device for arranging the glue between the veneers and a compression device for compressing the ve- neers to form a wood board. The spray application de-
vice according to the invention has been defined in the apparatus claims.
Preferably, the veneer layers are stacked one on top of the other and glue is arranged between the veneer layers. Preferably, the wood board is compressed under heat and pressure after stacking and gluing to form a wood board of a desired type. Preparation of the glue mixture, stacking of the veneers, gluing the veneers together and other typical steps in the manufac- ture of a wood board may be preferably performed in manners known per se in the art.
In one embodiment, the apparatus for manufacturing a wood board comprises a foaming device for the glue. Typically, the foaming device comprises a pump for supplying the glue, air supply means and a homoge- nizer in which the air is mixed with the glue. The glue may be foamed substantially in connection with the manufacture of the wood board or in a separate step.
In one embodiment of the invention, the spray application device comprises means for supplying atomi- zation air.
In one embodiment of the invention, the spray application device comprises means for supplying fan air. In one embodiment of the invention, the spray application device comprises pressure control means. In one embodiment, the device comprises at least one pressure balancing valve so that the supply pressure of the glue remains substantially steady at the spray application head. The pressure does not need to be constant .
Preferably, more than one nozzle have been arranged to the spray application head to apply the glue on the veneer surface. In one embodiment, the device comprises return means for the foamed glue for returning excess
glue, e.g. glue that has run through the glue pipe, back to use. In one embodiment, a centrifuge or a suchlike device is used as the return means, where the foam is separated and the liquid glue returns for use. The wood board according to the invention may comprise veneer layers of different thicknesses. The thickness of the veneer layers may vary. The veneer layers may be arranged in a desired position, i.e. transversely or longitudinally in a desired order. The method and the apparatus according to the invention for manufacturing a wood board may be used in different stacking processes.
Thanks to the invention, it is possible to use a foam glue mixture known per se in connection with spray application. The use of foam glue according to the invention in connection with spray application reduces gluing problems and in particular consumption of the glue considerably. By spraying, the glue can be applied very evenly and homogenously between the ve- neers. In addition, line speed during gluing may be raised e.g. to a level of 100 to 200m/min without problems e.g. in the application of the glue.
The invention provides the advantage that the foam glue contains less water or solvent than glue dispersion. Therefore, problems relating to vapour pressure in connection with hot-pressing are reduced. In addition, absorption of the glue into the veneers is reduced, and the gluing process allows higher mean moisture for the veneers. The invention allows the use of the same foamed glue in different glue application processes. A further advantage is the increased number of possible uses of the glue due to the foaming and the application method.
DETAILED DESCRIPTION OF THE INVENTION
In the following section, the invention will be described by presenting detailed examples of its embodiments and with reference to the accompanying Figure 1. Figure 1 presents a simplified schematic view of the spray application device for glue according to the invention.
Example 1
To examine spray application of foam glue, pilot test runs were first conducted to gain' more information for the actual test run. The pilot test runs comprised testing a spray application device with one nozzle and a spray application device with three noz- zles. These pilot test runs confirmed that foam glue can be successfully applied by spray application.
Example 2
In the actual test run, the spray application device 1 according to Figure 1 was used comprising glue supply means and a spray application head. Foamed glue mixture 5 was supplied into first horizontal glue pipe 2 in the spray application device. From the first pipe, the glue mixture was conducted to ten spray nozzles 8 in the application head (of which nozzles only part have been presented in the figure) , these nozzles being operated by air 4, 7, i.e. atomization and fan air. The spray nozzles 8 have been arranged at even intervals on the glue inlet pipe, i.e. the first pipe 2. The device comprises another pipe in parallel to the first pipe, namely a glue outlet pipe 3. Excess glue 6 was conducted out from the device through the second pipe 3. The first 2 and the second pipe 3 are arranged transversely or diagonally relative to the
conveyed veneer in the event where glue is being applied.
Arranged to the application head is an automatic pressure balancing valve (not shown in the fig- ure) , disposed to the second pipe 3, i.e. in connection with glue output. By the pressure balancing valve it is possible to balance the pressure at the spray application head to a desired level.
The spray nozzles 8 were arranged at a dis- tance of 20 to 30cm from the surface of the veneers.
The glue fans sprayed from the nozzles were arranged so that the fans which would hit the surface of the veneers overlapped each other.
In the tests it was found that the spray noz- zles were not blocked.
Example 3
The test of this example comprised manufac- turing plywood which was glued by foamed PF glue mixture and wherein the glue mixture was applied by spray- application on the surface of the veneers. The device according to Example 2 was used as the spray application device. The width of the veneers at the conveyor was about 2.6m. The speed of the conveyor line was about 30m/min.
A regular foam glue mixture suitable for birch and conifer plywood and containing about 59% of a commercial phenol-formaldehyde resin, about 13% of a curing agent, about 27.5% of water and about 0.5% of a surface-active agent was prepared.
The resin glue mixtures designed for birch and conifer plywood may differ in the amount and quality of the source materials. Essentially important factors for successful foaming of the glue dispersion are reduction of the surface tension and stabilization
of the foam so that the glue mixture would receive air and stabilize it for a sufficiently long period.
In preparing the foam glue mixture, air was added to the glue mixture using a commercial foamer, so that as it flowed through the foamer, a homogenous foam glue mixture was formed. The amount of air was adjusted so as to have the volume weight of the foam glue in the range of 0.2 to 0.8g/cm 3 . The optimum range was 0.3 to 0.6g/cm 3 . Sample plywood boards were manufactured from a 1.5mm birch veneer.
It was found that a lower than normal value, preferably between 80 and 130g/m 2 , was easily obtained as the volume of application of the glue. Furthermore, it was found that pressure variations in the glue pipe of the spraying device were controllable by the pressure balancing valve.
In addition, it was found that the optimum range of the foam glue volume weight was between 0.3 and 0.6g/cm 3 .
In summary of the tests, one can conclude that in the manufacture of plywood, a combination of foam glue and spray application can be successfully used in connection with the gluing of veneers, also in industrial application. The foam glue mixture was well applicable over the veneers and covered them evenly.
In addition, nozzles of the spray application head were not blocked.
The method and the apparatus according to the invention are suitable in different embodiments for different uses. The method according to the invention allows the manufacture of any types of wood boards in which a combination of foam glue and spray application can be used.
The embodiments of the invention are not limited merely to the examples, referred to above; instead many variations are possible within the scope of the accompanying claims.