JPS62152802A - Manufacture of wood-plastic composite body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a method for producing a wood-plastic composite with excellent dimensional stability.

[Conventional technology]

In general, wood has the property of swelling and contracting when it absorbs and releases moisture, which causes warping and cracking, which ultimately leads to a decrease in strength. The reason for this is that when moisture moves in wood, the moisture near the surface of the wood evaporates first and causes drying shrinkage, but inside the wood the moisture content is high and does not shrink. It is thought that stress is generated at the boundary between dry shrinkage and non-shrinkage, and that warping and cracking occur when this stress is released. In particular, near the end of the wood, the movement of water in the direction of the fibers is significantly faster than the movement of water in the radial and tangential directions, so the end surface dries and shrinks quickly, creating tensile stress, which is thought to cause frequent wood cracks. It is considered.

Conventionally, methods to prevent these phenomena and improve the dimensional stability of wood include formal method, acetylation method,
Heating methods, cyanoethylation methods, alkyl ketene dimer treatments, ethylene oxide treatments, etc. are known, but these methods have drawbacks such as weakening of the wood, difficulty in implementation, and large cost increases, and none of them are practical. It has not yet become a reality.

On the other hand, in recent years, a swelling zone filling method and a monomer impregnation method have been proposed as wood treatment methods different from the above methods. Among these, the swelling region filling method is a method in which a suitable polymer is impregnated and filled into the voids of wood, and the monomer impregnation method is a method in which a polymerizable 7-mer is impregnated into the voids of wood and polymerized. It's a method. processed using these methods. All wood is a so-called wood-plastic composite consisting of wood and a polymer held within its voids, and physical properties such as hardness, tensile strength, bending strength, etc. of wood vary depending on the type of polymer. It has the characteristic that it can greatly improve the

[Problem that the invention seeks to solve]

However, in terms of improving the dimensional stability, which is the drawback of wood, the above two treatment methods cannot necessarily be said to be effective methods for the following reasons.

First, in the swelling region filling method described above, polyvinyl alcohol and polyethylene glycol are known to be applicable polymers, but among these, low molecular weight polyethylene glycol has relatively good dimensional stability. can get. However, because this polymer has a low molecular weight, it is liquid or semi-solid at room temperature, and therefore a wetting phenomenon appears on the surface of the treated wood or composite when administered orally.
Subsequent painting becomes difficult.

In addition, various monomers such as methyl methacrylate, styrene, 2-hydroxyethyl acrylate, and polyoxyalkylene glycol (meth)acrylate are known as monomers that can be applied to the monomer impregnation method. Even if you use selective monomers,
The dimensional stability of the wood cannot be sufficiently improved unless the polymer retention rate after impregnation polymerization is set to a high retention rate of 40 to 90%, and such a high polymer retention rate will significantly increase the production cost of the composite. becomes higher.

Therefore, in obtaining a wood-plastic composite that is effective in improving the physical properties of wood as typified by the above two treatment methods, the present invention is capable of producing a wood-plastic composite that is effective in improving the physical properties of wood, without causing the above-mentioned conventional problems. The above composite with highly improved dimensional stability can be produced without causing problems such as wetting phenomena on the body surface that makes subsequent painting difficult, or increased production costs due to polymer retention. The purpose is to obtain.

c. Means for Solving the Problems] As a result of intensive studies to achieve the above object, the inventors have developed a method that belongs to the monomer impregnation method among the above two treatment methods, and which is applicable to this method. It has been demonstrated that when using a specific monomer that has not been previously used as a polymerizable monomer, it is possible to produce a wood-plastic composite with highly improved dimensional stability without causing the problems described above. This led me to complete this invention.

That is, this invention provides wood with the following formula; % formula % (wherein R1 is hydrogen or a methyl group, R2 is
-30 alkyl or alkenyl groups) or this monomer and other monomers copolymerizable with it.
A wood-plastic composite (hereinafter referred to as wp) characterized by being impregnated with a mixed monomer consisting of
(abbreviated as c)).

As described above, in this invention, a specific (meth)acrylic acid ester monomer represented by the above formula is used as an essential component as a polymerizable monomer to be impregnated into wood. Since the molecule contains an alkyl group or alkenyl group with a carbon number of 1θ to 30, that is, a highly lipophilic group with a large number of carbon atoms, the polymer obtained by polymerizing this group is different from the conventional monomer content. The lipophilic property is much higher than that of the polymer formed by polymerizing monomers such as methyl methacrylate, which has been applied, and also compared to the polymer that has been applied to the conventional swelling region filling method.

Therefore, when this monomer is impregnated into wood and polymerized, a high ID water property is imparted to the wood, and the hygroscopicity of the wood is significantly reduced. As a result, the moisture absorption and desorption properties that cause warping and cracking of the wood are reduced, and the generation of internal stress is suppressed, so that the resulting WPC exhibits extremely excellent dimensional stability.

And this dimensional stability is 1. Due to the above-mentioned characteristics of the monomer, the polymer retention rate after impregnating and polymerizing wood with this monomer is very small compared to the conventional monomer impregnation method or swelling region filling method. This results in good results in reducing the production cost of WPC. Moreover, since the polymer after polymerization essentially becomes a high molecular weight substance, a phenomenon of wetting appears on the surface of the composite orally, as seen in the conventional swelling region filling method, and subsequent painting is difficult. There is no particular risk of problems such as difficulty.

[Structure and operation of the invention]

Wood used in this invention includes softwood, hardwood,
Or there is no need to distinguish between domestic and foreign materials. Moreover, it can be applied to all forms of wood such as logs, logs, square columns, cylinders, and sawn boards.

The (meth)acrylic acid ester monomer represented by the above formula used in this invention needs to have an alkyl group or an alkenyl group having 10 to 30 carbon atoms. The reason for this is that when the number of carbon atoms is less than 10, the lipophilicity of the polymer after polymerization decreases;
This is because it is difficult to obtain products that exceed this amount, and there are problems such as poor impregnation properties when impregnating wood without using a solvent.

Specific examples of such (meth)acrylate monomers include lauryl (meth)acrylate, myristyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, and stearyl (meth)acrylate.
meth)7 acrylate, behenyl (meth)acrylate,
Oftacocil (meth)acrylate, oleyl (meth)
Examples include acrylate and palmitrail (meth)acrylate.

In this invention, one or more of the above (meth)acrylic acid ester monomers may be used,
A mixture of the above monomers and other monomers copolymerizable therewith may be used. In the latter mixed monomer, it is desirable that the (meth)acrylic acid ester monomer represented by the above formula generally accounts for 5% by weight or more, preferably 10% by weight or more of the total monomers. If this ratio is too small, sufficient dimensional stability cannot be obtained.

On the other hand, dimensional stability improves as the amount used increases, but equilibrium is generally reached at about 20 to 30% by weight.

Therefore, speaking only from the aspect of dimensional stability of WPC,
It is sufficient to use the above (meth)acrylic acid ester monomer in an amount within the above range among all monomers.

The other copolymerizable monomers include monofunctional monomers and polyfunctional monomers.

Monofunctional monomers are monomers that have one polymerizable carbon-carbon double bond in the molecule, and polyfunctional monomers are monomers that have two or more of the above double bonds in the molecule.
It is. These rain gear may be used alone or in combination.

Specific examples of monofunctional monomers include methyl (
(meth)acrylic acid ester monomers represented by 2 as above except that the number of carbon atoms in the alkyl group or alkenyl method such as meth)acrylate and ethyl (meth)acrylate is less than 10, and general acrylic polymers Styrene is often used as a modifying monomer in
(meth)acrylonitrile, vinyl acetate, etc., and 2-
Hydroxyl group-containing monomers such as hydroxy (meth)acrylate, polyethylene glycol mono (meth)acrylate, (meth)acrylic acid, maleic anhydride, etc.
Examples include B-containing monomers and epoxy group-containing monomers such as glycidyl (meth)acrylate.

Specific examples of the polyfunctional monomer include polyethylene glycol di(meth)acrylate, miglycerol tri(meth)acrylate, and pentaerythritol tri(meth)acrylate. These polyfunctional upper polymers improve the strength of the polymer after polymerization and the W
It is particularly desirable as a copolymerizable monomer because it provides good results on the strength of PC and also has an excellent effect on reliably preventing the phenomenon of wetting on the surface of WPC.

In this invention, when impregnating wood with a specific monomer as described above, this monomer may be impregnated alone, or the monomer may be dissolved in an appropriate organic solvent and impregnated. You may also do so.

When the (meth)acrylic acid ester monomer represented by the above formula is used alone as the impregnating monomer, it is preferable to use an organic solvent to facilitate impregnation.

Examples of the organic solvent include polar solvents such as methanol, ethanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, and dioxane, as well as nonpolar solvents such as toluene and xylene.

In addition, other additives, such as rust preventives and preservatives, which do not impede the purpose of the present invention may be added to the impregnating monomer or the solution obtained by dissolving it in an organic solvent, if necessary. It is also possible to add

In order to impregnate wood with such a monomer or monomer solution, the wood is first subjected to a drying process such as air drying, heat drying, or heat drying under reduced pressure to reduce the water content in the wood to 8 to 18% by weight. Adjust humidity to %wt% tube circumference. Next, this wood is sealed in a vacuum container, the pressure inside the container is reduced using a vacuum pump, etc. to remove the gas in the wood, and then monomer or monomer solution is poured into this container to return the inside of the container to atmospheric pressure. . As a result, the monomer or monomer solution is impregnated into the voids of the wood. In order to facilitate this impregnation, pressure impregnation may also be used. When an organic solvent is used, only the solvent is removed from the wood by performing a drying process depending on the type of monomer, such as natural drying, heat drying, or vacuum drying after the impregnation.

Next, the monomer impregnated into the wood as described above is polymerized. The polymerization method is not particularly limited, and for example, a method in which the above monomer-impregnated wood is heated and polymerized in a heating furnace in a state where oxygen is blocked, such as in nitrogen gas,
Co), etc., or by adding a peroxide such as benzoyl peroxide or methyl ethyl ketone peroxide to the impregnating monomer or its solution in advance, or a combination thereof with a reducing agent such as cobalt naphthenate or dimethylamine. A method can be employed in which a polymerization initiator consisting of the following is included and polymerization is performed using this initiator.

By the above polymerization, it is possible to obtain WPC in which wood is impregnated with a polymer made of a polymer of the specific monomer. The polymer retention rate of this WPC is generally 1~
The amount can be set to 35% by weight, particularly about 5 to 30% by weight, which is a much smaller amount than the conventional treatment method, and this provides good dimensional stability that can be applied to various uses.

Of course, depending on the purpose of use of WPC, in order to improve its physical properties and to achieve a higher degree of dimensional stability, the polymer retention rate may be higher than the above, for example, 50% by weight.
It is also possible to set the retention rate to a high level, even up to about 110% by weight.

In addition, in this specification, polymer retention rate refers to WP
It means the weight ratio of the polymer to the wood constituting C, that is, the value calculated by the following formula.

X: Absolute dry weight of WPC Y: Absolute dry weight of untreated wood [Effects of the invention] As described above, according to the method of this invention, the phenomenon of wetting appears on the surface of the composite over time and the subsequent We are developing WPC that exhibits excellent dimensional stability, which greatly suppresses the moisture absorption swelling and moisture release shrinkage characteristic of wood, without causing problems such as difficulty in painting or increased production costs due to polymer retention. It can be manufactured advantageously. For this reason, WPC obtained by this method is particularly suitable for use in external walls and flooring materials that are constantly exposed to humidity and dryness, wooden works of art, and other building materials that require a high degree of dimensional stability. It can also be used for various purposes.

[Examples] Next, examples of the present invention will be described in more detail.

Example 1 Tangential direction: 10 mm, radial direction: 70 mm, fiber direction: 130 mm
Straight-grained American cypress wood having a water content of 131 t% and measured to 1.0 mm was placed in a desiccator and the pressure was reduced to 10 mmHg. In this desiccator, 49.5% by weight of stearyl methacrylate, 49.5% by weight of polyethylene glycol dimethacrylate (average molecular weight 550), 0.99% by weight of benzoyl peroxide, and 0.9% by weight of ascorbic acid.
An impregnating solution consisting of 0.01 wt.

After wrapping this impregnated wood with aluminum foil, it was heated and polymerized in a hot press at 140°C for 4 hours, and the W
I got a PC. The polymer retention rate of this WPC is 16.2
% by weight. The polymer retention rate was calculated by drying the above WPC and untreated wood at 80° C. for 16 hours to determine their bone dry weights, and calculating from the bone dry weights of both wood by the method described above.

Example 2 The amount of stearyl methacrylate was 9.9% by weight, and the amount of polyethylene glycol dimethacrylate was 89.9% by weight.
WPC was obtained according to the method of Example 1, except that the content was changed to 1% by weight. The polymer retention rate of this WPC was 28% by weight.

Example 3 The amount of stearyl methacrylate was 19.8% by weight, and the amount of polyethylene glycol dimethacrylate was 79.2% by weight.
WPC was obtained according to the method of Example 1, except that the weight % was changed. The polymer retention rate of this wpC is 1
It was 9% by weight.

Example 4 The amount of stearyl methacrylate was 29.7% by weight, and the amount of polyethylene glycol dimethacrylate was 69.3% by weight.
WPC was obtained according to the method of Example 1, except that the weight % was changed. The polymer retention rate of this wpC is 2
It was 2% by weight.

Comparative Example 1 The method of Example 1 was followed except that 99.0% by weight of methyl methacrylate was used instead of 49.5% by weight of stearyl methacrylate and 49.5% by weight of polyethylene glycol dimethacrylate. and obtained WPC. The polymer retention rate of this WPC was 45% by weight.

Comparative Example 2 WPC was obtained according to the method of Example 1, except that 99.0% by weight of styrene was used instead of 49.5% by weight of stearyl methacrylate and 49.5% by weight of polyethylene glycol dimethacrylate.

The polymer retention rate of this WPC was 44% by weight.

Comparative Example 3 The method of Example 1 was followed except that 99.0% by weight of polyethylene glycol dimethacrylate having an average molecular weight of 550 was used instead of 49.5% by weight of stearyl methacrylate and 49.5% by weight of polyethylene glycol dimethacrylate. WPC was obtained accordingly. The polymer retention rate of this WPC was 27% by weight.

The water absorption rate and volume swelling rate of each WPC according to the above examples and comparative examples were measured, and from these measured values, each wp
The results of examining the anti-water absorption capacity (RWA) and anti-swelling capacity (ASE) of C were as shown in Table 1 below.

Note that the water absorption rate and volumetric swelling rate were measured by the following method.

Water absorption rate〉 WPC as an absolutely dry sample was left completely immersed in water at 20'C for a specified number of days, and the weight after being left (Xt) was
It was calculated using the following formula from the absolute dry weight (X) before standing.

Volume swelling rate〉 WPC as an absolutely dry sample was left completely immersed in water at 20°C for a predetermined number of days, and from the volume after standing (ML) and the volume before standing (M), the following 2 was calculated. Calculated by.

In addition, anti-water absorption capacity (RWA) and anti-swelling capacity (ASE) are determined by measuring the water absorption rate and volumetric swelling rate of untreated wood in the same manner as in the case of WPC above, and comparing this with the water absorption rate and volumetric swelling rate of WPC. It was calculated using the following formula.

Wc Wc Wc: Water absorption rate of untreated wood wt: Water absorption rate of WPC ■C: Volumetric swelling rate of untreated wood Vt: Volumetric swelling rate of WPC Note that the number of days left for measuring the water absorption rate and volumetric swelling rate was 4, respectively. 1 day and 7 days, but the water absorption rate and volume swelling rate calculated under the above measurement conditions are generally about 1
Equilibrium is reached after a week.

Table 1 As is clear from the results in Table 1 above, Examples 1 to 4
The WPC according to the present invention exhibits excellent dimensional stability even though the polymer retention is in the range of 15 to 30% by weight. However, the WPCs according to Comparative Examples 1 and 2 have high anti-water absorption ability (RWA) when the polymer retention rate is 41% by weight or more, but even in this case, high anti-swelling ability (ASE), which is an index of dimensional stability. It turns out that it has not been obtained. Also, comparative example 3
The WPC according to the above has a polymer retention rate of 30% by weight or less, but in this case, it is clear that both the anti-water absorption ability and the anti-swelling ability are low, and the dimensional stability is very poor.

Note that the WPCs according to Examples 1 to 4 above do not show any wetting phenomenon on the surface of the WPCs over time even if they are left at room temperature for a long period of time. Even when the surface was painted with normal paint, no problems occurred while painting became difficult.

Claims (1)

[Claims] (1) In the wood, there are the following formulas; 1. A method for producing a wood-plastic composite, which comprises impregnating a (meth)acrylic acid ester monomer or a mixed monomer consisting of this monomer and another monomer copolymerizable with the same, and then polymerizing the material.