JPH0226570B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing plywood using an improved bonding technique for veneer veneer. Conventionally, in the bonding technology of veneer veneers (hereinafter referred to as veneers) in the plywood manufacturing process, the biggest cause of bond failures such as punctures or insufficient adhesive strength is the dry state of the veneer, that is, the moisture content of the veneer. It is well known that this is caused by However, it is currently impossible to make the moisture content of all veneers uniform after drying, and there are variations in size.
In particular, the deterioration of the raw wood situation in recent years has resulted in a significant mix of tree species that are difficult to dry and those that are easy to dry. If the temperature is lowered, various problems such as poor adhesion due to semi-drying will become apparent at production sites. Therefore, it is impossible to deal with these current situations and the future without developing practical adhesive technology that is not affected at all or is not easily affected by variations in moisture content. To fundamentally solve the problem, there has been a desire for a technology that enables bonding of so-called green veneers with a high moisture content as required, as in the present invention described below. By the way, regarding adhesive technology for veneers with high moisture content, for example,
No. 2 (title of invention: Method for manufacturing plywood) exists. According to the publication, this adhesive technology involves applying a known general-purpose adhesive to a veneer with a moisture content of 15% or more, drying the applied adhesive to the point where gelation occurs, and then applying it to a veneer with a low moisture content. The gist is to overlap the plates and heat press them. However, although all of the disclosed results show good results, the following problems are inherent in this technique. In other words, even if you install a drying device and set drying conditions consisting of a predetermined temperature and time in an attempt to dry the applied adhesive to the above-mentioned point, in the case of veneers with a low moisture content, it will be faster than that. Drying, or conversely in the case of high veneers, may be insufficient and not only will it not be possible to dry all the veneers to the desired extent, i.e. at or before the point at which the adhesive gels, but also Accordingly, the adhesive strength after hot pressing also varies significantly and becomes extremely unstable. This is clear from the fact that the drying conditions in the disclosed examples are variously set depending on the moisture content of the target veneer, and the higher the moisture content, the greater the drying conditions. This is due to the phenomenon that the degree of drying of the applied adhesive is not simply determined by the set drying conditions, but is largely influenced by the moisture content of the veneer. Basically, the higher the moisture content of the veneer, the more moisture in the applied adhesive needs to be removed, so under suitable drying conditions, the mixed veneer with a low moisture content will Naturally, the point at which gelation occurs is greatly exceeded. For example, even if you touch it strongly with your fingertips, it will not be sticky at all. In this case,
The dry adhesive lacks permeability to the veneers on the stacked side, leading to many adhesive failures in the plywood after hot pressing. Therefore, even in a single log, the difference in moisture content between the sapwood and the core wood is, for example, 30 to 120%, or even in a single veneer, there is usually a significant difference depending on the location. As is well known, considering the current state of manufacturing plywood of stable quality using various logs, the drawbacks of this type of technology cannot be overcome in the practice of plywood manufacturing that operates in a mass production format. It was difficult and still considered low-ranking. The present invention solves the problems described above by improving the adhesive technology that has the drawbacks described above, making it easily practical in production sites, and creating an adhesive technology that is less affected by the moisture content of veneers. The details are as follows. That is, as disclosed in the above-mentioned publication, the method of the present invention is aimed at actively drying and removing moisture in the applied adhesive to enable bonding of veneers with high moisture content. Although this is the same, as a pretreatment before applying the adhesive, the surface layer of the adhesive surface is dried by appropriately heating the veneer, and then the difference in moisture content between the surface layer and the inside (inside of the veneer) is Apply the adhesive while holding the adhesive, and dry the applied adhesive until it is dry to the touch (a term commonly used in adhesive technology, and is dry when it is no longer sticky when pressed lightly with your fingertips). is even drier,
Furthermore, in order to allow the adhesive to penetrate into the veneers to be stacked, a small amount of adhesive is applied to at least one of the dried adhesive layer or the adhesive surface of the veneers to be stacked, and then the veneers are stacked. The basic gist of this method is to heat-press the material. To explain in detail, first, heat treatment is performed to dry the adhesive surface of the veneer. The extent of this will depend on the initial moisture content, but as a guideline, the moisture content should be approximately 10 to 100%, until the veneer is dried to a so-called semi-dry state. The equipment for drying in this way is
Various conventional hot air circulation drying devices can also be used, but
Preferably, a hot plate drying device such as a hot press is used in which a heated hot plate is brought into direct contact with the veneer.
For example, Utility Model Application Publication No. 56-14994 by the applicant,
As in the drying equipment described in JP-A-56-16079, JP-A-56-30572, and JP-A-56-2323, the veneer is directly heated to a temperature of 110 to 300°C while being conveyed. A suitable product is one that intensively dries the surface layer of the adhesive surface by contacting the adhesive. In any case, even if the average moisture content of a veneer that has dried to the extent described is semi-dry as mentioned above, immediately after drying or within a certain period of time, the surface layer of the adhesive surface will have a lower moisture content than the inside. The temperature remains high until it is cooled to room temperature. In the present invention, this phenomenon is organically combined with the subsequent adhesive application process. That is, the adhesive is applied to the adhesive surface while there is a difference in moisture content between the surface layer and the inside, or the adhesive is cooled to room temperature while there is a difference in moisture content between the surface layer and the inside. The adhesive may be applied to the adhesive surface while it is in a high temperature state before it is applied, or if necessary, the adhesive may be applied to the adhesive surface while there is a difference in moisture content between the surface layer and the inside, and before it is cooled to room temperature. The adhesive is applied to the adhesive surface while the surface layer is temporarily cooled by a forced cooling means such as a cooling roll during the high temperature state. One example from many heat treatment experiments is illustrated in Figure 3. The moisture content distribution changes from 18 to 19 in the middle, and as is clear from the figure, semi-drying can be achieved with the moisture content of the surface layer significantly lower than that of the inside near the center. The state tends to equilibrate with the passage of time, and the difference in water content decreases, but
The basic principle of the present invention is to apply the adhesive as described above while there is a difference in moisture content between at least the surface layer and the inside, regardless of temperature conditions. By doing so, even if the veneer has a large and small variation in moisture content, and even if there is a large variation in moisture content within a single veneer, the surface layer of the adhesive surface to which the adhesive is applied can be improved. The variation in moisture content has become significantly smaller, and the relationship between the applied adhesive and the applied veneer, specifically the permeability of the adhesive into the veneer, is as if the entire surface had been sufficiently dried. It has been stabilized and improved in the same way as the original, and the amount of adhesive applied has also been made more uniform. On the other hand, the adhesive to be applied is, for example, a known plywood adhesive mainly composed of urea resin, melamine resin, phenol resin, water-based vinyl urethane resin, or co-condensed resin or mixed resin of these. This type of adhesive is water-soluble, and is formulated by adding water and, if necessary, fillers, extenders, plasticizers, hardeners, etc., and then liquefied and applied by spraying, curtain coater, spreader, etc. do. The amount of coating depends on the thickness of the veneer and the composition of the adhesive, but it is somewhat less than with conventional technology, and is approximately 8 to 20 g/square meter per adhesive surface, and other known water-based thermosetting adhesives. Agents or known special formulations other than the basic formulations may be applied as appropriate. Next, the adhesive applied in the above step is dried. Drying means include various conveyors and trays equipped with air blowing equipment as necessary, heating chambers, hot air drying equipment for those that involve heating, heated hot plates, heated rolls, or a combination of these for those that act directly. use To determine the degree of dryness, touch it lightly with your fingertips, and it should be almost non-sticky or even dryer to the touch. The drying conditions for drying in this way depend on the amount of adhesive applied, the composition, the moisture content of the veneer, etc., but for example, when using a heating chamber, the drying conditions are approximately 20 to 200℃, 1 to 1
About 30 minutes is enough. As a more specific guideline, it is desirable to set the product of the temperature and time to about 2000 [°C x minutes] or less. In general, if drying under high-temperature heating is used, the applied adhesive will not only evaporate water but also be cured by the condensation reaction of the resin that proceeds in parallel. On the other hand, at low temperatures, the condensation reaction is suppressed and dried. Although any method can be adopted, the temperature is preferably 100° C. or lower, more preferably about 50 to 60° C. or lower, and a so-called hot air drying device that sends heated hot air is used. In that case, it is more advantageous to increase the flow rate and flow rate of hot air and process within a short time, preferably within about 15 minutes. In addition, the veneer is heated as described above just before the adhesive is applied, and as a result, not only does the surface layer of the adhesive surface have a lower moisture content than the inside, but if it is still in a high temperature state, the adhesive After application, the heat retained in the veneer contributes to the drying of the applied adhesive, so that an adhesive drying device can be omitted or significantly simplified, or at least the drying time can be shortened. However, generally, applying adhesive to a veneer under high temperature conditions involves certain practical difficulties.
There is no problem when using a non-contact coating device such as a sprayer or curtain coater, but with the currently commonly used veneer contact type spreader, the viscosity of the adhesive remaining on the surface of the coating roll changes, resulting in long-term During this process, there is a tendency to lose the uniformity of the coating amount. Therefore, in any case, in order to improve the results, the surface layer of the adhesive surface of the high-temperature veneer described above is temporarily forcedly cooled while applying the adhesive. For example, cooling water is passed through the doctor roll, applicator roll, etc. of a spreader to lower the temperature to room temperature to prevent the temperature of the applicator roll from rising, and the cooled applicator roll cools the surface layer of the adhesion surface while bonding. Alternatively, a veneer cooling roll may be installed in front of the spreader to apply forced cooling while applying the adhesive. Of course, the cooling here is not intended to bring the entire veneer to room temperature or lower, but rather to temporarily lower only the adhesive surface layer of the veneer to an appropriate temperature. do. By doing so, the difficulties associated with the coating device can be fundamentally resolved, and the applied adhesive can be dried much more easily by utilizing the heat possessed by the veneer. Next, a small amount of adhesive is applied to at least either the dried adhesive layer or the adhesive surface of the veneers to be stacked. In other words, the moisture in the previously applied adhesive is sufficiently removed by the drying process, and as a matter of course, the surface has dried the most compared to the inside, so it can be used as is for other adhesives. When veneers are stacked and heat-pressed, it lacks permeability and causes many of the problems described above.However, the adhesive applied this time, even in a small amount, moistens the surface and activates it. In addition, the adhesive significantly improves adhesion to the overlapping veneer. Also, it is most convenient to use the adhesive applied here with the same composition as the adhesive applied previously, but the composition may be changed if necessary, and preferably one with a low moisture content. Use. The appropriate amount of coating is about 0.5 to 10 g/square meter per adhesive surface, preferably about 1 to 5 g/square meter.
In addition, like the method of drying the adhesive that was applied to the previously dried adhesive layer and then applying it again, repeating the application and drying several times will dry the adhesive that has been applied more evenly. Even when aiming for this, the final drying process and the amount of adhesive to be applied can be done as described above. Therefore, as usual or in the past, veneers are stacked crosswise (regular plywood) or with the fiber directions parallel (parallel plywood), and if necessary cold pressed using a cold press and hot pressed to form plywood. The method for manufacturing the plywood of the present invention will be explained below based on specific examples. Note that "parts" means "parts by weight." Example 1 A lauan medium plate with a thickness of 3.4 mm and a size of 30 cm square,
Moisture content is 10%, 25%, 40%, 60%, 80%, 100%
Heat the adhesive surface layer between two heating plates at 150°C for 60 seconds while breathing drying, then heat the adhesive surface for 10 seconds.
After leaving it for a minute to bring it to room temperature, apply urea resin adhesive on both sides of each middle plate: 100 parts of S-Resin (product number SE-5) manufactured by Shoei Chemical Industry Co., Ltd., 22 parts of wheat flour, and 17 parts of water.
1 part of adhesive consisting of 0.4 parts of ammonium chloride.
The adhesive was applied at a rate of 13 g/square meter per adhesive surface using a spreader, and the adhesive was applied for 4 minutes with a hot air dryer at 70°C at a wind speed of 4 m/s. A small amount of the agent was applied to each adhesive surface using a spreader at a rate of 3 g/square meter, and lauan front and back plates with a thickness of 1.8 mm and a moisture content of 10% were stacked and cold-pressed at 8 kg/cm ² for 5 minutes, and then
Three-ply plywood was manufactured by heat pressing at 115° C. and 8 kg/cm ² for 3 minutes. Example 2 A lauan medium plate with a thickness of 3.4 mm and a size of 30 cm square,
Moisture content is 10%, 25%, 40%, 60%, 80%, 100%
After preparing and heat-treating under the same conditions as in Example 1, the same adhesive as in Example 1 was applied to both sides of each intermediate plate in the same amount, and the applied adhesive was dried under the same conditions. Then, a small amount of adhesive was applied instead of the middle plate to a thickness of 1.8 mm and moisture content to be overlapped.
Apply 10% lauan to the adhesive surfaces of the front and back plates at a rate of 3 g/square meter per adhesive surface using a spreader, then stack it on the middle plate, cold press for 5 minutes, and heat press as described above. A 3-ply plywood was manufactured. As described above, the type 2 plywood manufactured in Examples 1 and 2 was
An adhesion test was conducted based on the hot and cold water immersion test method stipulated by JAS, and the results are shown in a chart according to the moisture content of the middle plate as shown in Figure 2. Test results 20 are test results related to Example 2. Further, as a comparative experiment, the invention of Japanese Patent Publication No. 54-3929 was repeated as described below, and the test results were as indicated in 22. Comparative experiment example A lauan medium plate with a thickness of 3.4 mm and a size of 30 m/square, the moisture content of which was 10%, 25%, 40%, 60%, 80%,
Prepare a 100% adhesive, apply the same adhesive as in Example 1 to both sides of each middle plate at a rate of 16 g/square meter per adhesive surface using a spreader, and apply this.
Leave it in a heating room at 100℃ for 4 minutes to dry the adhesive.
Next, lauan front and back plates having a thickness of 1.8 mm and a moisture content of 10% were stacked together and cold-pressed and hot-pressed in the same manner as in Example 1 to produce 3-ply plywood. Therefore, evaluating the test results shown in FIG. 2, the example of the method of the present invention shows that, compared to the prior art according to the above-mentioned publication, the variation in moisture content of the veneer that is allowable under the set manufacturing conditions is It is clear that the area is extremely wide. If you want to shift the area to a higher moisture content or, conversely, to a lower moisture content, you can mainly change the drying conditions of the applied adhesive. The present invention is carried out under the above-mentioned characteristics, targeting veneers with a high moisture content, or, if the moisture content is small, veneers with a lower moisture content. However, in any case, the reality is that there is considerable variation in the moisture content of the veneer itself or the surface layer after heat treatment, so under the set manufacturing conditions, the applied adhesive may partially or It may be dried to a state below dry to the touch. However, even if such a situation occurs, it will not cause any particular problem because the amount of adhesive to be applied next is small, and in fact, from the point of view of production efficiency, it may be dry to the touch or even slightly dry. The drying conditions may be set based on the standard degree of dryness. As for increasing or decreasing the adhesive force itself, it is common practice to mainly change the composition of the adhesive, the amount of coating, etc., and manipulate it to a desired value to some extent. In this way, in the present invention, it is possible to manufacture plywood with a predetermined process focusing on an arbitrary veneer moisture content as needed, but it is possible to produce plywood with significantly better performance than in the prior art. For veneers that are
Use ~23%. In addition, if you dare to use a material with a content of about 35% or more, you should also apply the heat treatment described above to the veneer to reduce the moisture content of the surface layer of the adhesive surface before use, or you may also apply an adhesive. It is best to dry it before use. Also, regarding the quality of the manufactured plywood,
Considering the JAS standards, even when implementing the present invention, the surface layer of the adhesion surface is only slightly heated to a slightly lower moisture content, which is far beyond the standards for plywood with a high moisture content. Approximately 20% of the surface layer is
below, and the average moisture content of the entire veneer is approximately 25 ~
It is preferable to produce plywood with a lower moisture content, such as 60%, even if it is outside the standard. Of course, it is also possible to perform heat treatment in order to manufacture high quality plywood that meets the specifications. In addition, the adhesion strength of the finished plywood does not necessarily have to be within the JAS standards, and examples that achieve the desired quality are adopted. In this application, the initial adhesive application is basically carried out while there is a difference in moisture content between the inside of the veneer and the surface layer of the adhesive surface, but even when the applied adhesive dries, If the veneer heating step or subsequent steps are performed quickly in order to maintain such a state, a uniform degree of drying can be obtained under the specified drying conditions even in the adhesive drying step, regardless of variations in moisture content. This has a special effect and can also delay the rewetting of the adhesive by moisture from inside the veneer after drying, giving more time to subsequent steps. Of course, it is clear that it would be more effective to increase the processing speed of each process so that the state with a difference in moisture content is maintained even through cold pressing or hot pressing, and in general, processing can be done in a short time. It is essential. Regarding Tables 1 and 2,
The table shows embodiments of the present invention other than the above by number.

【table】

【table】

[Table] In the table, U in the resin section of the adhesive composition.
is a urea resin (specifically, S-Resin SE-5 manufactured by Shoei Chemical Industry Co., Ltd.), MU is a melamine urea cocondensation resin (specifically, S-Resin SA-30, manufactured by Shoei Chemical Industry Co., Ltd.), and P is a phenol resin (specifically, S-Resin SA-30, manufactured by Shoei Chemical Industry Co., Ltd.). S-Resin SP-100 manufactured by Shoei Chemical Industry Co., Ltd.)
In Table 1, "Adhesive application" refers to the first application, and in Table 2, "Adhesive application" refers to the working conditions for applying a small amount of adhesive. Number 1,
2, 3, and 4 relate to the production of 5-ply plywood, and the others relate to the production of 3-ply plywood. The apparatus for carrying out the method of the present invention is illustrated in FIG. 1 of the drawings, and will be explained below based on the apparatus. In the figure, A is the veneer heating device described in the above-mentioned publication, and the green veneer 1 is conveyed while being guided by linear bodies 9 and 10, and comes into contact with a number of heating rolls 11 to heat the surface layer of the adhesive surface. The semi-dried veneer 2 is discharged after reducing the moisture content and increasing the temperature. The next B is a veneer joining machine, and if the semi-dry veneer 2 is already a predetermined length,
Although it does not require installation, it has the function of simply cutting long strips to a regular length, and if it is an irregular narrow veneer, the unnecessary parts at the front and back are cut off and only the effective parts are joined. Then, it is made into a veneer 3 of a fixed length. C,
E is a spreader, especially E is for small amount application. D is an adhesive drying device installed to dry the adhesive applied to the veneer 3 of a predetermined length by the spreader C as described above. The veneers 4 are supported by needles 15 on each shelf and dried with hot air from a hot air fan 16, while the adhesive-dried veneers 5 are sequentially supplied to the spreader E. That is, at the entrance of the device, the adhesive-coated veneer 4 is pierced by needles 15 of each shelf by a conveyor 14 that moves up and down at appropriate times.
At the exit, the fixed conveyor 17 intersects with each shelf, so that the adhesive-dried veneer 5 is transferred to the needle 1.
5 and supplied to Spretzder E. Further, F is a veneer mechanism device, which assembles the second adhesive-applied veneer 6 and the overlapping veneer 8 in a predetermined manner, forming a so-called mechanism veneer 7, which is then cold pressed (not shown). supply Of course, it will obviously be connected to the hot press after that. With such a device, the present invention can be carried out efficiently and efficiently, and plywood of stable quality can be manufactured. ,1
It is important to appropriately set the speed and distance in step 3 to reach Spreader C in a state where there is a difference in moisture content between the adhesive surface surface layer and the inside of the veneer. Further, if necessary, it is possible to maintain this state even in subsequent steps, and furthermore, it is also possible to reach the spreader C in a high temperature state. If a cooling roll is provided as the forced cooling means described above, the end position of the conveyor 13 is suitable. As detailed above, the method of the present invention relates to adhesive technology in the plywood manufacturing process, and eliminates the problems of the conventional technology that could not be put into practical use using a new technical concept, thereby reducing the variation in moisture content. We have completed a practical adhesive technology that is not easily affected by moisture content, and have solved all of the above problems at once, including ease of moisture content management and yield loss factors such as shrinkage and cracking due to drying. It is also certain that it will make a significant contribution to future responses.

[Brief explanation of drawings]

FIG. 1 is a side view illustrating an example of an apparatus for implementing the present invention, and FIG. 2 is an adhesive force chart comparing the adhesive strength of plywood manufactured by the conventional method and the method of the present invention.
22 shows the results obtained by the conventional method, and 20 and 21 show the results obtained by the method of the present invention. Third
The figure is a moisture content distribution chart illustrating the moisture content distribution of a heat-treated veneer. In the figure, 1... Fresh veneer, 2... Semi-dried veneer, 4... Adhesive coated veneer, 5... Adhesive dried veneer, 8... Overlapping veneer, 9 and 10... Linear body, 11... Heating roll, 15... Needle, A... Veneer heating device, B... Veneer bonding machine, C and E... Spreader, D... Adhesive drying device, F... Mechanical device.

Claims (1)

[Claims] 1 Heat the plywood veneer to dry the adhesive surface layer,
An adhesive is applied to the adhesive surface while there is a difference in moisture content between the surface layer and the inside, and then the applied adhesive is dried to a touch-dry level or higher, and the dried adhesive layer or the overlapping layer is further dried to the touch or more. A method of manufacturing plywood, which involves applying a small amount of adhesive to the veneer veneers to be cut, and then stacking the veneer veneers together and heat-pressing them.