JPH0114870B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for efficiently manufacturing a thick veneer laminate in a short time using a thermosetting adhesive.

Evaluation of the water-resistant adhesion of this type of laminated veneer material is conducted in Japan according to the Japanese Agricultural Standards, and laminated materials used mainly outdoors are required to have a high degree of water resistance and durability. Therefore, the above standards require special class or class 1 adhesive strength. Therefore, thermosetting synthetic resin adhesives such as thermosetting phenolic resin adhesives and melamine urea cocondensation adhesives, which have excellent water resistance, are often used for such laminated materials.

By the way, although it depends on the type of resin used for the above-mentioned thermosetting adhesive, the bonding conditions are generally such that each adhesive layer has a temperature of 100°C or higher during hot pressing, preferably 100°C or higher.
It is necessary to heat press until it is heated to a high temperature of around 120℃, and usually the hot press platen temperature is 140℃.
It is manufactured by keeping it at a high temperature and pressurizing it. However, wood veneer has poor thermal conductivity, so if the total thickness of the laminate exceeds 60 mm,
It takes time for the heat from the heating plate to conduct to the center layer, and it takes time for the adhesive to harden.If heating continues for a long time, the adhesive near the front and back layers will dry out before the center adhesive layer hardens. becomes overheated and carbonizes, resulting in problems such as a decrease in adhesive strength, and as a result, the thickness decreases.
It has been difficult to manufacture thick laminates exceeding 60 mm by a single heat-pressure treatment.

Therefore, in the past, for products with a thickness exceeding 60 mm, it was done in two steps, such as forming a film with a thickness of about 30 mm and then bonding it again with a room-temperature curing adhesive. , which required time and effort and had low productivity.

On the other hand, dielectric heating by applying high frequency waves is known as a method for efficiently heating internal parts in a short time.This heating method uses an electrode body with adhesive layers of laminated materials arranged in parallel to generate an electric field. When it acts,
Because heat dissipates on the front and back sides, the temperature rise only inside becomes large and the adhesive in the center hardens first, and by the time the temperature of the front and back layers reaches the curing temperature of the adhesive, the temperature in the center increases. There is a problem in that the adhesive layer is overheated and carbonized, and this tendency increases particularly as the thickness increases, making it impossible to expect uniform adhesive strength.

Another method is to place an electrode body orthogonally to the adhesive layer and apply an electric field to selectively heat the adhesive layer, which has a higher dielectric loss than wood. It is said to be advantageous because the adhesive can be cured in a short period of time. However, according to this method, when a resin with a high dielectric constant such as a phenolic resin adhesive is used, an electric field acts along the resin layer, causing a discharge phenomenon and causing local carbonization and combustion. There were problems, such as limitations on the adhesives that could be used.

The present invention has been made in view of the drawbacks and problems of hot platen heating and dielectric heating, and provides a method for using both heating means together while keeping the thickness of the veneer laminate within a specified range. This was done based on the discovery that the heating defects due to the heating plate described above and the heating defects due to high frequency dielectrics complement each other and it is possible to uniformly heat the laminated material. The objective is to produce thick veneer laminated materials that can be widely used as building materials such as timber and joist materials, as well as materials for vehicles, containers, ships, etc., in a relatively short pressing time and without causing adhesion failure. It is something to do.

In order to achieve this objective, the present invention has a structure in which a large number of wood veneers are laminated with a thermosetting adhesive to a total thickness of 60 to 200 mm to form a veneer laminate. The veneer laminate is inserted between the upper and lower hot plates of a hot press with the electrodes of the high-frequency generator arranged parallel to the adhesive layer of the veneer on the upper and lower surfaces of the veneer laminate, and the veneer laminate is placed between the hot plates. The temperature of the adhesive layer at the position divided by about 1/3 of the thickness of the laminate is 100℃ by simultaneously applying heat conduction heating from the laminate and dielectric heating using high frequency.
Each adhesive layer is cured by heating as described above. As a result, the heating of the adhesive in the surface layer from the upper and lower surfaces of the veneer laminate to the 1/3 dividing position is mainly caused by heating from the heating plate, and becomes insufficient as it approaches the 1/3 dividing position. The amount of heat generated is supplemented by dielectric heating using high frequency waves, while the heating of the adhesive in the inner layer inside the 1/3 division position of the laminated veneer material is mainly done by increasing the temperature using dielectric heating using high frequency waves, By supplementing the amount of heat that decreases as the adhesive is separated by heating from the heating plate, the entire adhesive layer from the surface layer to the inner layer can be heated almost uniformly in a short time and cured uniformly. This is what I did.

Hereinafter, the present invention will be explained in detail based on the drawings.

As shown in Fig. 1, first, a large number of wood veneers 1, 1, etc. made of rotary veneers, each having a predetermined thickness, are bonded with a thermosetting adhesive so that the total thickness is 60 to 200 mm. The veneer laminate 2 is obtained by laminating the veneer panels so as to have the same shape.

In this case, the thermosetting adhesive may be, for example, a phenol resin type, a phenol formaldehyde resin type, a urea resin type, a melamine resin type adhesive, etc., and one having a property of curing at approximately 100° C. or higher is used.

In addition, if the thickness of the veneer laminate 2 is less than 60 mm,
By heating only with a conventional hot press, the adhesive can be sufficiently cured to the inner layer of the laminate 2 (approximately 100℃ or higher).
On the other hand, if the temperature exceeds 200 mm, the dielectric heating due to the high frequency will be biased towards the center of the laminate 2, and the heat transfer from the heating plate will be limited to the surface layer only. 1/3 of the thickness of the laminate even if both are used together.
The temperature rise at the split position is small, resulting in poor curing, and no mutual effect can be obtained from both types of heating. Therefore, in the method of the present invention, the thickness of the laminate is set between 60 and 200 mm so that the temperature increase due to the heating plate and the temperature increase due to the high frequency complement each other at the 1/3 dividing position of the laminate and reach 100°C or more. In the range, preferably 80-150mm
Set to range.

Next, the plate-shaped electrodes 3a, 3a of the high frequency generator 3 are placed on the upper and lower surfaces of this veneer laminate 2, respectively, so as to be parallel to the adhesive layer 2a between the veneers 1, 1, and in this state. The veneer laminate 2 is placed on the upper and lower hot plates 4 of a hot press 4 together with the electrodes 3a, 3a.
Insert between a and 4a.

After that, the upper and lower heating plates 4a, 4 of the hot press 4 are
Pressurize the veneer laminate 2 at step a, and press the upper and lower heating plates 4.
The heating plates 4a, 4a are placed on the veneer laminate 2 under the conditions that the temperature of both a and 4a is kept at 120 to 160°C, the frequency of the high frequency generated by the high frequency generator 3 is kept at 1 to 100 MHz, and the output is kept at 5 to 80 kw. The temperature of the adhesive layer 2a at the position A where the entire thickness of the veneer laminate 2 is divided by approximately 1/3 is increased by simultaneously applying thermal conduction heating from the thermosetting adhesive and dielectric heating using the high frequency. Heat for 30 to 80 minutes to reach the curing temperature of 100°C or higher. As a result, each adhesive layer 2a in the veneer laminate 2 is cured, and a thick veneer laminate 5 as shown in FIG. 2 is produced.

Here, to illustrate the temperature change in each part of the veneer laminate 2 when heat conduction heating from the hot platens 4a and dielectric heating by high frequency are applied to the veneer laminate 2 at the same time, for example, Overall thickness is 105mm
When the veneer laminate 2 is hot-pressed using only the hot platens 4a and 4a of the hot press 4 kept at a temperature of 155°C, as shown in Figure 3, even if the hot-pressing time is 80 minutes, the internal The temperature exceeds 100° C. within approximately 20 mm from the surface side, and the temperature beyond that cannot rise to the temperature required for curing the adhesive layer 2a. Furthermore, when the hot pressing time is 40 minutes, the heating effect only reaches a depth of about 10 mm. On the other hand, when the same veneer laminate 2 as described above is dielectrically heated only by high frequency with a frequency of 13.56 MHz and an output of 14 kW, as shown in Figs. 4 and 5, when the heating time is 40 minutes, the laminate The temperature at the center of the adhesive layer 2 rises to approximately 110°C, but the temperature below 30 mm of the surface layer falls below 90°C, and the adhesive layer 2a is not sufficiently cured. On the other hand, when heating by the heating plates 4a, 4a and heating by high frequency are used together, the temperature of the entire laminate 2 rises to approximately 110°C or more in a heating time of about 40 minutes, as shown in Fig. 6. Therefore, the adhesive layer 2 of each veneer 1, 1
a harden uniformly in a short time.

In that case, as is clear from Figure 6, the temperature distribution inside the laminate 2 is approximately 1/3 of the total thickness divided into three
The temperature at the dividing position A is the lowest and it is difficult for the temperature to rise, and as long as this 1/3 dividing position A rises to 100° C. or more, the other parts have also reached the curing temperature. Therefore, in order to efficiently raise the temperature of this 1/3 division position A to 100℃ or more, the thickness of the laminate should be set to 200 mm or less, and the temperature of the heating plate, the frequency and output of high frequency, and the heating time should be set as described above. is preferable. In other words, the hot platen temperature is
If the temperature is less than 120℃, it will take a long time to raise the above 1/3 division position A to 100℃ or more, and each adhesive layer 2 near the center will only be heated by the high frequency.
On the other hand, if the temperature exceeds 160°C, the carbonization of each adhesive layer 2a near the surface layer tends to progress, so the temperature is set in the range of 120 to 160°C. The temperature is preferably around 155°C.

Note that the frequency of the high frequency from the high frequency generator 3 may be within the range of 1 to 100 MHz, for example, the frequency band currently permitted for industrial use.
13.56MHz±6.78KHz, 27.12MHz±162.78KHz,
Either 40.68MHz±20.34KHz should be used. In addition, if the high frequency output is less than 5kw, the temperature rise due to high frequency heating will be slow and the balance with the temperature rise due to heating the heating plates 4a and 4a may be lost, and 80kw.
If the output exceeds 50kW, there is a risk that only the temperature increase due to high frequency heating will proceed and each adhesive layer 2a near the center will begin to carbonize before the combined effect is exerted. It is something to do.

Furthermore, the heating time is the time required for the above-mentioned 1/3 division position A to reach 100° or more when heating is performed by the heating plates 4a, 4a and high frequency, and it changes depending on the setting changes of the above-mentioned heating plate temperature, high frequency output, etc. However, if the heating time is less than 30 minutes, the effect of increasing the temperature by heating the heating plates 4a and 4a will be small, and sufficient heating cannot be expected; , each adhesive layer 2 near the surface layer
There is a risk that a may be carbonized by the heating of the hot plates 4a and 4a, and therefore the time is set to 30 to 80 minutes.

Although it is preferable that the high-frequency heating is carried out at the same time as the hot platen heating, the start of the heating may be slightly delayed from the start time of the hot platen heating, depending on the thickness of the laminate 2.
For example, when the thickness of the laminate 2 exceeds 150 mm, first, the laminate 2 is heated for about 10 minutes by keeping the temperature at approximately 120°C using only the heating plates 4a, 4a.
It is preferable to then add heating using high frequency waves to combine both heating methods, since a good heating balance can be maintained.

Therefore, the laminated material 5 manufactured in this manner has high strength without adhesion defects since each of the adhesive layers therein is uniformly cured. Also,
Since the heat-pressing time in the heat-pressing process is short and high productivity can be obtained, it can be provided at low cost.

Next, to explain specific examples, each
29 rotary veneers (thin veneers) with a thickness of 3.7 mm are laminated with a thermosetting phenolic resin adhesive to form a veneer laminate with a thickness of approximately 110 mm.
This veneer laminate was inserted between the upper and lower heating plates of a hot press heated to 127°C, with electrodes made of aluminum plates from a high-frequency generator arranged parallel to each adhesive layer on its upper and lower surfaces. , the veneer laminate was pressurized at 8 kg/cm ² using a heating plate and at the same time dielectrically heated using high frequency waves with a frequency of 13.56 MHz and an output of 5.5 kW.
A veneer laminate with a thickness of 110 mm was produced by performing the test for 1 minute. In the thus obtained laminated material, each adhesive layer was sufficiently cured, and no carbonization was observed, and the adhesive had good adhesive strength.

As explained above, according to the present invention, a veneer laminate with a thickness of 60 to 200 mm is formed by laminating a large number of wood veneers with a thermosetting adhesive, and high-frequency The application electrodes are placed parallel to each adhesive layer and inserted between the upper and lower heating plates, and the veneer laminate is simultaneously heated by the heating plate and high frequency until the laminate has a thickness of about 1. Since each adhesive layer is cured by heating so that the adhesive layer temperature at the /3 division position is higher than the curing temperature of the thermosetting adhesive, the temperature inside the laminate can be uniformly increased. Thick veneer laminates with a thickness of over 60mm can be produced in a short time and in a single heat-pressure treatment without causing poor curing or carbonization of the adhesive, and is therefore inexpensive. Moreover, it is possible to provide a high quality veneer laminate material.

In addition, the temperature of the upper and lower heating plates should be set to 120 to 160℃, the frequency of the high frequency should be set to 1 to 100MHz, and the output should be set to 5 to 80kw.
By heating the veneer laminate for 30 to 80 minutes while maintaining the temperature at Since the internal temperature rises uniformly, the surface does not become overly dry as in the case of only hot pressing, so there is less occurrence of deformation such as warping.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the heating state of a veneer laminate according to the present invention, Fig. 2 is a perspective view of a laminate manufactured according to the invention, and Fig. 3 is a laminate when heated only with a heating plate for a predetermined time. An explanatory diagram showing the temperature distribution in each part of the body, and Figures 4 and 5 are explanatory diagrams showing the temperature change over time in each part of the laminate and the temperature distribution in each part of the laminate when heated only by high-frequency dielectric heating, respectively. FIG. 6 is an explanatory diagram showing the temperature distribution of each part of the laminated body when heated for a predetermined period of time using both a heating plate and high-frequency induction heating. 1... Wood veneer, 2... Veneer laminate, 2a...
Adhesive layer, 3... High frequency generator, 3a... Electrode,
4... Hot press, 4a... Hot plate, 5... Thick veneer laminated material.

Claims (1)

[Claims] 1 A veneer laminate is formed by laminating a large number of wood veneers with a thermosetting adhesive so that the total thickness is 60 to 200 mm, and this veneer laminate is made into a veneer laminate. The electrodes of the high-frequency generator are placed on the upper and lower surfaces of the veneer so that they are parallel to the adhesive layer of the veneer, and the laminate is inserted between the upper and lower heating plates of the hot press, and the veneer laminate is heated by conduction from the heating plate. Thick material characterized by curing each adhesive layer by simultaneously applying dielectric heating using high frequency so that the adhesive layer temperature at approximately 1/3 of the thickness of the laminate reaches 100°C or higher. Method for manufacturing laminated veneer material. 2. A patent for heating a veneer laminate for 30 to 80 minutes under the conditions of maintaining the temperature of the upper and lower heating plates at 120 to 160℃, the frequency of high frequency generated by a high frequency generator to 1 to 100 MHz, and the output of 5 to 80 kW. Claim 1
A method for producing a thick veneer laminate material as described in .