JPH026604B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for bonding the end of a plate-like object such as plywood.

Conventionally, it has been known to form a long plywood by joining plywood together at their end faces. The method of joining these butt ends is to use a scarf,
After applying processing such as finger cutting and applying adhesive to the ends of the pieces, the ends were butted against each other and joined by heat pressing.

However, this method uses an external heating method that heats only the joint from outside.

By the way, as shown in Figure 1A, the temperature distribution in the case of external heating is such that the temperature transfer to the core of the plate is slow, so it takes time for the adhesive inside the joint to harden.
Bonding time becomes longer.

Furthermore, depending on the moisture content, specific gravity, and other conditions of the plate-shaped body, there is a difference in temperature transfer between the inside and outside of the joint, resulting in uncured portions of the adhesive. In order to prevent the occurrence of uncured portions of the adhesive, it is necessary to increase the curing time.

Further, since the adhesive is cured from both external sides, internal stress is generated due to volumetric contraction, and this internal stress causes natural peeling of the adhesive at the junction point where the adhesive is cured from both external sides.

Furthermore, even if the intermolecular attraction of the adhesive is strong and the above-mentioned natural peeling does not occur, due to the existence of internal stress, a relatively small external force will cause the adhesive to break, resulting in a weak joint. Become.

In order to solve these problems caused only by external heating, adhesive is applied to the butt ends of the joints, and after the butt ends are butted, high-frequency power is applied to the butted areas to harden the adhesive using only internal heating. Adhesion methods have also been tried.

By the way, this method using only internal heating
As shown in Figure B, the temperature rise on the outside side of the plate is slower, but as shown in Figure 1C, compared to the external heating method, the internal heating method enables bonding in a shorter time and improves work efficiency. improves.

However, in the external heating method, energy is consumed on the outside side to raise the temperature of the moisture in the adhesive and the moisture moved from the inside, which delays the temperature rise in that area and further slows down the curing of the adhesive.

In addition, poor adhesion occurs in the surface layer due to evaporation and release of moisture.

Furthermore, since it is an internal heating method, the curing of the adhesive starts from the inside, so internal stress is generated due to volumetric contraction during internal curing, and spontaneous peeling can occur on the outside side where intermolecular attraction is weak. be.

The present applicant filed an application in Japanese Patent Application No. 13051/1983 for a method of gluing the end of the joint in which the adhesive inside and outside the joint is uniformly cured by using both an external heating method and an internal heating method.

The present invention further improves the above application and uses a synthetic resin adhesive to which a latent curing agent is added as an adhesive, thereby further shortening the adhesive curing time and strengthening the adhesive strength.

Embodiments of the present invention illustrated in the drawings will be described below.

In Fig. 2, 1 is made by laminating and bonding veneers cut to an arbitrary thickness so that the fiber directions are perpendicular to each other.
3 ply 5m/m finished with a moisture content of 8-15%
It is made of thick plywood.

The front veneer 2 of the plywood 1 is placed on the end surface of the veneer 2 in the fiber direction.
A slope 3 having an arbitrary angle is formed in a direction perpendicular to the fiber direction of the fiber. The length L of the slope 3 portion is preferably formed at an angle that is 2 to 15 times the thickness a of the front veneer 2. If the length L of the slope 3 portion is less than twice the thickness of the veneer 2, the adhesive area will be small and the strength will be low.

On the other hand, if the length L is 15 times or more the thickness a of the veneer 2, cutting will be difficult and the strength of the joint surface will not improve much.

In addition, the slope 3 formed on the front veneer 2 also exists on the back veneer 4.
A slope 3' substantially parallel to the slope 3' is formed.

The length L' of the slope 3' section is the length L of the 3 section of the front veneer.
Do the same as.

Furthermore, the middle veneer 6 sandwiched between the front and back veneers 2 and 4
An abutting surface 7 that is nearly perpendicular to the slopes 3 and 3' is formed on the slopes 3 and 3', and the end surface of the plywood 1 is shaped into a Z-shaped end.

As shown in FIG. 2, the end surface of the plywood 1' to be joined is adhesively bonded to the Z-shaped end surface of the plywood 1 formed as described above. The end surface of the plywood 1' to be joined also has a slope 3a on the front veneer, a butt surface 7a on the middle veneer,
A slope 3a' is provided on the back veneer, and the direction of slope 3a, 3a' is opposite to that of slopes 3, 3', so
The Z-shaped end surfaces of the plywood boards 1 and 1' fit into each other.

As the adhesive for the end surface, a synthetic resin adhesive containing a latent hardener is used.

The joined parts of the fitted plywood boards 1 and 1' are pressed together from above and below using a heating plate that also serves as an electrode plate for applying high-frequency power, and external heating and internal heating are applied simultaneously.
Crimp and join.

External heating using a heating plate is performed at 150°C to 250°C for a short time.

By using both external heating and internal heating, the heating temperature distribution at the joint of the plate-like objects is averaged, and the moisture in the adhesive is instantly evaporated, and the pressure causes the wood fibers to evaporate. It is transferred into the tissue and is not released to the outside.

In addition, since a synthetic resin adhesive with a latent curing agent added is used as the adhesive, when the adhesive reaches a certain temperature by heating, the latent curing agent reacts with the resin and hardens. The heating temperature distribution is averaged, and when a certain temperature is reached, the adhesive is uniformly cured at the same time.

For example, when di-cyanate or di-amide is added to an epoxy resin as a latent curing agent, the curing agent is dissolved in the epoxy resin by heating and the epoxy resin is cured.

When bonding 12 m/m thick plywood, it took 30 seconds when only high-frequency power was applied, but it took 13 seconds when a heating plate was used.

In addition, when an epoxy resin with a latent curing agent added is used as an adhesive, the bonding is performed only by external heating using a hot plate (the former), and when external heating using a hot plate and internal heating using high-frequency power are used together (the latter).
I compared it with. As a result, it was confirmed that the bonding strength of the latter was 1.3 times higher than that of the former.

Effects of the present invention: (a) Since a synthetic resin adhesive containing a latent curing agent is used as the adhesive, the adhesive curing time is shortened and the adhesive strength is increased. This is because since the adhesion time is short, internal stress is less generated and natural peeling of the bonded portion does not occur.

(b) By using an adhesive containing a latent curing agent and using a combination of internal and external heating methods, the temperature distribution inside and outside during bonding is even, and the adhesive hardens uniformly inside and outside. At the same time, the addition of the latent curing agent allows the adhesive to harden quickly and uniformly inside and outside. Moreover, its adhesive strength is high.

[Brief explanation of drawings]

Figure 1 A: Temperature distribution diagram for external heating, Part 1
Figure B: Temperature distribution diagram for internal heating, Figure 1 C:
Comparison diagram of resin curing time in case of high frequency heating and external heating, Fig. 2: Cross-sectional view of plywood end joint surface, 1, 1': plywood, 2: front veneer, 3, 3', 3a,
3a': Slope, 4: Back veneer, 5: Convex part, 6: Middle veneer, 7, 7a: Butt surface, a: Thickness of veneer, L,
L': Length of slope 3, 3'.

Claims (1)

[Claims] 1. A method of applying an adhesive to the end surfaces of a plate-shaped body, and joining and bonding the end surfaces by butting each other, the joint portion being pressed from above and below with a heating plate, and then externally heated. At the same time, a method for adhering the end surface of a plate-like object is characterized in that, at the same time, high-frequency power is applied to the joint part to perform internal heating, and a synthetic resin adhesive to which a latent hardening agent is added is used as the adhesive. . 2 The shape of the butt surface of one of the plywood boards 1 to be joined is determined by the slope 3 forming the cutting part 5 of the front veneer 2, the butt surface 7 of the middle veneer 6, and the slope 3 forming the convex part 5' of the back veneer 4. 2. The bonding method according to claim 1, wherein the plywood 1' has a Z-shape, and the shape of the end surface of the plywood 1' to be joined thereto is shaped to fit into the shape of the end surface of the plywood 1.