JPH0681682B2 - Method for producing modified wood - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing modified wood used for building materials, furniture and the like.

[Conventional technology]

BACKGROUND ART Conventionally, there has been known a method of injecting a non-aqueous polymerization type synthetic resin liquid such as polyester, acryl, styrene or the like into a wood material and curing it to make the wood material into a WPC.

In this method, since the cured resin is filled in the cell lumen, curing and transparency are improved, but the permeation of the synthetic resin solution into the wood cell wall is small, and sufficient water resistance and moisture resistance can be imparted. Can not.

Therefore, a water-soluble synthetic resin having a high permeability to the cell wall is injected.

[Problems to be Solved by the Invention]

However, when the wood material in which the water-soluble synthetic resin liquid is injected is heat-cured by a normal means, cracks may occur during heat-curing and drying, or the injected resin may flow out as water vapor evaporates, resulting in a small residual resin ratio. There is a tendency, especially in the case of thick wood such as sawn timber having a thickness of 10 mm or more.

Cracking during curing and drying causes a large water content gradient between the center of the material and the surface layer during heat curing due to the rapid movement of water in the material, causing cracks and irregularities due to the difference in shrinkage stress between the two. In addition, the injected synthetic resin liquid hardens before the central part on the surface of the material, preventing the residual water from trying to be discharged to the outside of the material. As a result, explosion occurs due to water vapor pressure in the central part.

Cracks during curing can be resolved by heating and curing while evaporating water under mild conditions below the curing temperature, but under such processing conditions, uncured and non-uniform reaction of the injected resin occurs and significant treatment occurs. It takes time and the production efficiency deteriorates, which is not suitable for practical use.

[Object of the Invention]

The present invention completely solves such problems, and is particularly effective for the modification treatment of thick wood materials such as lumber products, and can improve the performance such as dimensional stability by increasing the filling resin ratio. A method for producing modified wood is provided.

[Structure of Invention]

In order to achieve the above object, the method for producing a modified wood of the present invention comprises injecting an aqueous solution of a water-soluble dehydration-condensation resin into a wood material, and then performing dielectric heating at a temperature below the curing temperature of the synthetic resin under reduced pressure, It is characterized in that the reduced pressure is released and the synthetic resin is heated and cured.

[Action]

Since the water-soluble dehydration-condensation type synthetic resin liquid is injected into the wood material, the synthetic resin liquid can easily and satisfactorily penetrate into the wood cell wall. Thus, when the resin liquid permeating into the wood cell wall is dielectrically heated under reduced pressure. , The solvent injected below the hardness temperature of the resin gradually evaporates due to the boiling point drop of water, while the initial condensation reaction occurs as the dehydration progresses, and the resin content easily remains in the wall, so the resin outflow is reduced. Therefore, the resin residual rate becomes high.

Furthermore, since it is dielectric heating, the inside of the wood is evenly heated, and moisture is gradually transferred to the surface of the wood while dehydrating and condensing.
As a result, the inclination of water content in the material is reduced, cracks due to shrinkage stress are less likely to occur, and the variation in the curing reaction is lessened, the filling resin ratio is improved, and wrinkles are less likely to occur, resulting in natural grain Can be maintained.

Next, when the reduced pressure is released and the curing temperature is raised and heated, the synthetic resin is completely cured.

〔Example〕

Explaining the examples of the present invention in detail, first, an aqueous solution of dehydration condensation type synthetic resin is injected into a wood material by an appropriate means such as a dipping method, a reduced pressure heating method or a combination thereof.

As the wood material into which the resin liquid is injected, square wood and plate materials,
Thick lumber products such as hollow materials, laminated wood, molded materials with an irregular cross-sectional shape, and thick timber such as logs are used, but even thin plates such as veneers can of course be injected. is there.

Further, as the synthetic resin to be injected, a dehydration condensation type resin (thermosetting resin) which is water-soluble and easily penetrates into the cell wall of the wood material and reacts with the OH group in the wood component to be bonded, is used.
Examples of such synthetic resins include fibrin reactive resins (cyclic urea resins) such as glyoxal urea resins and ethylene urea resins.

Specifically, there are fibrin-reactive resins such as dimethylol ethylene urea, dimethylol propylene urea, dimethylol dihydroxy ethylene urea, dimethylol glyoxal monourein, dimethylol triazone, and dimethylol urone.

When such a fibrin-reactive resin is heated with a catalyst such as an acid catalyst or an acidic inorganic salt, it is chemically bonded to the OH group in the wood to impart dimensional stability.

Further, a formalin-based resin such as melamine or phenol which permeates a urea resin other than the above-mentioned fiber-based reaction type resin or a wood cell wall to form an insoluble or infusible substance in the cell wall structure, or the above-mentioned fibrin reaction type resin. Or may be injected into the wood material as a co-condensation resin liquid.

In particular, when an initial condensation product is used as the formalin-based resin, it easily penetrates into the cell wall, is less likely to be washed out of the material in the solvent volatilization step described later, and the fat content is improved, which is preferable.

The wood material injected with such a synthetic resin liquid is then placed in a decompression chamber and decompressed, and dielectric heating is performed by high frequency or microwave at a temperature not higher than the curing temperature of the injected resin liquid. ) Is volatilized and initial drying is performed.

The curing temperature is a temperature at which the high condensation reaction is promoted and the insoluble and infusible final product is produced at 70 ° C. or higher, preferably 10
It is 0 to 150 ° C.

In this case, the dielectric heating / decompression may be performed after the decompression at room temperature.

In this way, when the wood material is subjected to dielectric heating under reduced pressure, the injected solvent (water) is evaporated, the initial condensation reaction of the injected resin progresses as the dehydration progresses, and the resin component remains in the fine pores of the wood and flows out. Hard to do.

In addition, since it is a heat treatment under reduced pressure, the boiling point of water is unlikely to rise to a high temperature which is the curing temperature of the resin, but when it is volatilized to the resin component with vigorous evaporation of water vapor, Since it is not preferable in terms of rate and work environment, the dielectric heating should be adjusted by adjusting the power and turning it on and off as appropriate.

The solvent volatilization treatment by dielectric heating under reduced pressure is performed until the water content of the resin injection treatment material decreases to about 50 to 10%.

This is because as the drying of the wood material progresses to near the fiber saturation point, the dielectric energy is directed to increase the material temperature, and as the water content decreases, the dielectric loss coefficient decreases, making it difficult for the material temperature to rise. Temperature power is involved), so it is necessary to leave water to some extent.

Next, we move to the heat curing process of resin-injected wood,
In this step, the boiling point is raised by returning the inside of the decompression chamber to normal pressure while continuing the dielectric heating, and the material temperature is raised by the dielectric heating to cause the reaction of the injected resin.

At this time, since the heating power for dielectric heating is proportional to the amount of heat generated, the heating power is adjusted to control the temperature so that it is the curing temperature of the injected resin, and the heat treatment is performed for a predetermined time within the curing temperature range of the resin. To proceed with curing.

As the dielectric heating, as described above, a high frequency or a microwave is adopted. However, due to the frequency, the heating depth for the wood material, the appropriate material length per oscillator,
The dielectric heating method is appropriately selected depending on the size and shape of the material, such as the heating temperature.

Further, in the case of a log or a molding material, it is preferable to use a microwave having no restriction on the sectional shape.

Further, if necessary, after the dielectric heating, the finish drying or reaction may be adjusted by using steam or hot press.

As described above, in a state where the temperature of the material under reduced pressure is low, the water in the wood material is evaporated to remove volatile components, and then the reduced pressure is released and the temperature is raised to complete the reaction of the resin in a continuous process. is there.

At this time, if a decompression type high frequency heating device is used, the solvent volatilization in the wood material and the curing reaction of the injected resin can be continuously performed, and the productivity becomes good.

It should be noted that the resin liquid may be injected only in the vicinity of the surface layer without injecting it into the whole wood, and in this case as well, it is selectively heated by dielectric heating, so that the productivity is good.

Further, hot air or hot press may be used immediately after releasing the reduced pressure in the final heat curing temperature (100 ° C. or higher), the drying step, and the curing step.

Next, specific examples of the present invention will be shown.

Example 1 A fibrin-reactive resin aqueous solution (methylolglyoxymonourein resin 20% concentration) in which a magnesium chloride catalyst has been added to a Bitsuga lumber product (thickness 25 x width 100 x length 400 mm) is injected under reduced pressure. A treated material was obtained.

This injection-treated material was dried under reduced pressure (50 Torr, product temperature about 50 ° C) with a high-frequency vacuum dryer to a water content of about 30%, and then heated under normal pressure and heated at 120 ° C for 3 hours. To obtain modified wood.

The weight gain of the obtained modified wood was 22.2%. The results of this modified wood and the dimensional stability test (pressure-reduced pressure water absorption test) are shown below.

Anti-expansion rate (AE) 49.6% Anti-shrinkage rate (ASE) 50.9% Leach rate 1.7% As described above, the modified wood obtained had low leaching rate and excellent dimensional stability.

Example 2 Bitsuga lumber product (thickness 25 x width 100 x length 400 mm, a fibrin-reactive resin aqueous solution (methylolglyoxymonourein resin 10% concentration) and a phenolic resin aqueous solution (concentration 10%) Mixture with (mixing ratio 1: 1)
Was vacuum-injected under reduced pressure, and the obtained injection-treated material was pre-dried under reduced pressure (50 Torr, 50 ° C.) with a high-frequency vacuum dryer until the water content was 30%, and then returned to normal pressure as in Example 1. Then, the temperature was raised, and heat curing was performed at 120 ° C. for 3 hours.

The weight gain of the obtained modified wood was 35.8%.

The results of the dimensional stability test performed in the same manner as in Example 1 are shown below.

Anti-expansion rate (AE) 51.2% Anti-shrinkage rate (ASE) 52.6% Leaching rate 1.9% The obtained modified wood was superior in dimensional stability to the untreated wood.

Example 3 Instead of the fibrin-reactive resin used in Example 1, a phenol resin aqueous solution (concentration 10%) was used to perform pressure injection under reduced pressure in the same manner, and the obtained injection-treated material was hydrated with a high-frequency vacuum dryer. rate
After pre-drying to 10%, heat treatment was performed in the same manner as in Example 1.

The weight gain of the obtained modified wood was 18.6%.

As a result of the dimensional stability test as in Example 1, the anti-expansion rate (AE) was 50.6%, the anti-shrinkage rate (ASE) was 49.8%, and the leaching rate was 1.8%.

The obtained modified wood was superior in dimensional stability to the untreated wood.

(Comparative Example 1) After the same resin aqueous solution as in Example 1 was injected into the lumber product in Example 1, a hot air dryer was used instead of the high frequency vacuum dryer to perform heat treatment at 120 ° C for 3 hours. However, it was difficult to obtain satisfactory modified wood because of the large cracks.

(Comparative Example 2) The same resin aqueous solution as in Example 1 was injected into the lumber product in Example 1 and then the pressure was not reduced using a high-frequency vacuum dryer.
As a result of performing the dielectric heat treatment at 120 ° C. for 3 hours, cracks did not occur, but the weight increase rate of the lumber product was 10%, the resin yield was low, and some wrinkles were generated.

〔The invention's effect〕

As described above, according to the method for producing modified wood of the present invention, after injecting a water-soluble dehydration-condensation-type resin liquid into a wood material, dielectric heating is performed at a temperature below the curing temperature of the synthetic resin in a reduced pressure state, and then the reduced pressure Since the synthetic resin solution is released and heated and cured, the water-soluble dehydration condensation type synthetic resin solution is injected into the wood material, so that the swelling and permeation of the synthetic resin solution into the wood cell wall becomes easy and good, and the lumber Even thick wooden materials such as products can be injected into the inside of the resin as needed.In addition, the dielectric resin is hardened by dielectric heating under reduced pressure to reduce the outflow of injected resin and cause cracks and deformation. It can be done without.

Furthermore, since the resin liquid that has penetrated into the wood cell walls is dielectrically heated under reduced pressure, the solvent injected below the curing temperature of the resin is gradually evaporated due to the boiling point decrease, and the initial condensation reaction occurs as the dehydration progresses, and the resin Remains in the wall, and the resin residual ratio inside the cell increases, making it difficult for the wood cell wall to fall, and also to bond with wood components or generate insoluble and infusible substances in the cell wall structure. As a result, wood with a high filling resin ratio can be modified, and dimensional stabilization (bulking effect) can be achieved.

Moreover, the interior of the wood is heated evenly by the dielectric heating and the moisture moves to the surface side of the material, while in the curing process the moisture is generated by the dehydration condensation of the resin inside the material, resulting in a small water content gradient in the material. Is less likely to cause cracking due to shrinkage stress, and the variation in the curing reaction is less likely to cause wrinkles to occur, which makes it possible to maintain the natural grain and, as described above, the cured resin in the lumen of cells. Since it is present and a hardened product is formed in the cell wall, modified wood can be obtained which is expected to have antiseptic and insecticidal effects.

Claims (1)

[Claims] 1. A method of injecting a dehydration-condensation-type resin aqueous solution into a wood material, performing dielectric heating at a temperature below the curing temperature of the synthetic resin under reduced pressure, and then releasing the reduced pressure to heat and cure the synthetic resin. A method for producing modified wood.