JPH043721B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing plywood. [Prior art] Normally, the fiber direction of the first layer of plywood is parallel to the longitudinal direction of the plywood, the second layer is orthogonal to the first layer, and the third layer is orthogonal to the second layer. The fourth layer is configured to be perpendicular to the third layer (parallel to the second layer), and the adjacent veneers are configured to be perpendicular to each other. 1st layer,
For odd-numbered layers such as the 3rd layer, 5th layer, etc., the length in the fiber direction is long, so high-quality long logs are used.
Since it is expensive, it is used by stripping it as thinly as possible. On the other hand, for even-numbered veneers, low-quality material is peeled thickly so that the even-numbered veneers account for as much of the plywood thickness as possible. Therefore, when drying veneers in a dryer, the odd-numbered veneers are thin and easy to dry, but the even-layered veneers are thick, so naturally the dryer operating speed must be significantly reduced, and the entire factory is having a negative impact on productivity. Enlarging the size of the dryer, which is the most expensive piece of factory equipment, is not an easy task as it requires a large expense and necessarily increases the capacity of the boiler, increases the size of the chimney, and increases the size of pollution prevention equipment such as flue gas desulfurization and dust control. In terms of cost, the weight of raw wood in the plywood cost is not constant as it depends on the price of raw wood, the price of oil, etc., but in recent years it has accounted for around 70%, so it is important to consider how to improve the yield from raw wood to plywood. That is the biggest point. As a means of achieving this, we have introduced high-performance rotary laces to improve the rate of veneerization of raw wood (stripping until the core becomes thin), intensive use of narrow veneers, and reduced dryness of veneers. This reduces thermal energy costs, improves dryer operation rate, reduces drying shrinkage, reduces cracks, chips, and looseness caused by drying, and significantly improves the conversion rate from veneer to plywood. Conceivable. In this way, if high moisture content veneer could be used effectively, it would bring extremely great benefits, but at present, the pollution, punctures, etc. that occur when the moisture content of veneer is increased are
Since the problem of surface cracking has not been solved, it is usually used at a moisture content of 18% or less, preferably 12% or less. For example, if the veneer that makes up plywood has a moisture content of 20% or more, urea type, melamine type, urea/melamine type, urea/phenol type, melamine/urea type, etc.
When plywood is produced using amino-based resin adhesives such as phenol-based, melamine/phenol-based, etc., moisture in the adhesive layer does not transfer to the veneer, so the adhesive does not become concentrated and the curing reaction is significantly delayed. ,
When the press was opened and closed, the adhesive force between the veneers was insufficient, causing punctures in all areas where the adhesive force was less than the pressure of water vapor, and the adhesive was washed away by the high temperature water in the adhesive, causing a wide range of non-stick areas. Satisfactory adhesion cannot be obtained as each layer of veneer falls apart. Because the first layer of veneer on the front and back sides contains a lot of moisture and comes into direct contact with the hot press steel heating plate,
The tannin-iron reaction causes the entire plywood surface to turn black, significantly reducing the commercial value of the plywood. When taken out from the hot press, numerous cracks appeared on the surface of the first layer veneer on both the front and back sides due to heat shrinkage and dehydration shrinkage, making secondary processing such as painting, printing paper pasting, veneer pasting impossible. Reduces surface quality. If moisture curing or wet bonding adhesives such as urethane or epoxy adhesives are used, the above problems will not occur, but they are extremely expensive (more than 4 to 5 times the adhesive price), and the above problems cannot be avoided. Curing during hot pressing is significantly slower than that of amino resin adhesives. If a urethane-based or epoxy-based adhesive is used and bonded at room temperature, the above-mentioned problem will not occur, but curing will take an extremely long time, resulting in a fatal decline in productivity. For example, when manufacturing 3 mm 3-ply plywood, hot pressing at 110° C. for 60 seconds is sufficient when using an amino adhesive, but room temperature pressing using a urethane or epoxy adhesive requires 3 to 12 hours. [Object of the Invention] The present inventors have discovered that all of the above problems can be solved by using a large amount of an isocyanate compound in an amino resin adhesive and by using a dry veneer for the first layer on the front and back sides. , we have completed the present invention. [Structure of the Invention] The present invention provides a method for producing plywood using an amino-based resin adhesive, in which a veneer with a moisture content of 18% or less is used as the first layer veneer on each of the front and back sides; Use a moisture content of 20% or more as the even-numbered veneer from the front and back, and use a compound containing 8 parts or more of an isocyanate compound per 100 parts of aqueous amino resin adhesive as an adhesive. This is a method for manufacturing plywood characterized by the following. Next, the present invention will be explained in more detail. As the veneer dries in a dryer, its moisture content decreases, but it does not shrink until it reaches the fiber saturation point, and begins to shrink below this point. Not only does the yield decrease with shrinkage, but the veneer becomes more and more brittle, cracks and chips suddenly begin to increase, and the number of dents around the veneer also increases. Therefore, producing plywood using veneers with even a slightly higher moisture content greatly contributes to improving yields and reducing costs, but it causes many problems as described above. Therefore, at present it is unavoidable that veneers are used at an average moisture content of 18% or less overall. The method of the present invention allows the first layer veneer on the front and back sides to have a moisture content of 18% or less, but thick even-numbered veneers can be used with a moisture content of 20% or more, which greatly improves yield. It was something to look forward to.
Furthermore, odd-numbered veneers other than the first layer on the front and back sides may have a moisture content of 18% or less, but if favorable conditions are found, all veneers other than the first layer on the front and back sides can be used with a moisture content of 20% or more. This provides an extremely useful method. In the present invention, the aqueous amino resin connecting agent refers to compounds reactive with formaldehyde, including amino compounds such as urea, melamine, urea melamine, urea phenol, melamine urea phenol, and melamine phenol. This is an aqueous adhesive consisting of a condensate obtained by a reaction with The isocyanate compounds referred to in the present invention are TDI,
Refers to compounds with two or more isocyanate groups in the molecule, such as MDI and crude MDI. TDI, MDI,
Products with a high proportion of isocyanate groups relative to their molecular weight, such as crude MDI, are effective when added in relatively small amounts, but various prepolymers, such as GA
−704 (manufactured by Sumitomo Bakelite, ethylene oxide, propylene oxide polyether and
In the case of a prepolymer (prepolymer having isocyanate groups at both ends obtained by reaction with MDI), it is preferable to add a relatively large amount. Crude MDI is most preferred in terms of cost, ease of availability, storage stability, etc.
The amount of isocyanate compound added is generally 1 to 5% for crosslinking water-based adhesives, but in the case of the present invention, it is 8% or more, preferably 15 to 30%, and if it is less than 8%, there is no noticeable effect. . [Effects of the Invention] The present invention avoids surface contamination by setting the moisture content of the front and back first layer veneers to 18% or less, and uses a formulation in which 8% or more of an isocyanate compound is added to an inexpensive water-based amino resin adhesive. This enables temporary adhesion and adhesion of high moisture content veneers, and even-layered veneers.
This is an industrially useful plywood production method that greatly improves the yield, productivity, and economic efficiency of plywood by increasing the moisture content to 20% or more. In addition, when using urea-based or melamine-based adhesives, materials such as Kluin, Katya, Apitone, Nyato, Ramin, Kempas, Elima, China, and Elm are considered to be difficult to adhere to and often do not exhibit sufficient adhesive strength. It has been found that the use of an amino adhesive containing the isocyanate compound of the present invention exhibits good adhesive strength similar to that of lauan. [Example] Next, an example will be described. Example 1 For 1.4 mm and 4.0 mm thick lauan veneers, the moisture content was adjusted according to the plywood numbers in Table 1, and plywood materials were prepared. Next is the urea adhesive Vigetalime.
UA-126 (manufactured by Sumitomo Bakelite, commercially available type: 50
% resin aqueous solution) and melamine adhesive Vigetalime MA-204 (commercially available product manufactured by Sumitomo Bakelite:
A 53% resin aqueous solution) was blended as shown in A and C in Table 2, and crude MDI equivalent to 15% of UA and MA was blended as shown in B and D. Apply the compounded adhesive shown in Table 2 to plywood materials with various moisture contents shown in Table 1 at a rate of 200 g/m ² per glue line on the front and back sides of the veneer (4.0 mm veneer) for the front second layer and the back second layer. After cold pressing for 15 minutes, hot pressing was carried out at 110° C. for 180 seconds under a pressure of 10 kg/cm ² to produce 12 mm plywood. Plywood using combinations A and B was tested according to the JAS Type 2 standard.
Plywood using C and D was subjected to an adhesion test according to the JAS Type 1 standard, and as shown in Table 3, the results were passed (○ mark), retested (△ mark), failed (x mark), etc. Indicated. A comparison of A and B and C and D shows that the addition of an isocyanate compound enables adhesion of high moisture content veneers. However, since the moisture content of the first layer of plywood No. 7 and 8 was high, the front and back veneers were colored black regardless of whether they were bonded or not, resulting in significantly inferior commercial value. In addition, in the case of formulations A and C, high moisture content veneers do not reach temporary adhesion during cold pressing,
The automatic insertion equipment of the hot press could not be used. This indicates a major problem in factory production. It can be seen that B and D exhibit perfect temporary adhesion and are extremely good in practical use.

【table】

【table】

[Table] ○: Pass △: Retest ×: Fail Example 2 The veneer composition and moisture content are the same as plywood No. 4 in Table 1, and the veneer types are 6 types of difficult-to-adhesive materials, adhesives Plywood was made in the same manner as in Example 1 using the compositions A, B, C, and D in Table 2, and the adhesion test was conducted according to the JAS Type 2 and Type 1 standards as in Example 1, and the results are shown in Table 4. I got it. This indicates that the isocyanate compound-containing adhesive of the present invention is effective even for materials that are difficult to bond with amino-based resin adhesives such as urea-based and melamine-based adhesives.

[Table] ○: Pass ×: Fail

Claims (1)

[Claims] 1. In the method of producing plywood using amino resin adhesive, use a veneer with a moisture content of 18% or less as the first layer of veneer on each of the front and back sides,
Use a moisture content of 20% or more as the even-numbered veneer from the front and back, and use a compound containing 8 parts or more of an isocyanate compound per 100 parts of aqueous amino resin adhesive as an adhesive. A method for manufacturing plywood, characterized by: