JPH093429A - Adhesive for air-permeable adherend - Google Patents

Abstract

PURPOSE: To obtain an adhesive comprising a filler and a compound which has or more NCO groups and is liquid at ambient temperature, useful for adhering to air-permeable adherends containing water, such as wood, long in pot life, and excellent in storage stability, curability and adhesive strength. CONSTITUTION: This adhesive comprises (A) 100 pts.wt. of a compound which has at least two isocyanate groups and is liquid at ambient temperature [preferably a polymeric MDI comprising various diphenylmethane diisocyanate (MDI) isomers and several kinds of their polymers], and (B) 50-200 pts.wt. of filler (preferably calcium carbonate). The water content of the adhered is preferably 2-20%. When the water content of the adherend is fine or when the effective curing of the applied adhesive is desired, water is preferably added to the adhesive in an amount of 1-5 pts.wt. per 100 pts.wt. of the component A, before the adhesive is coated. When adherends are bonded with the adhesive, the adhrends are preferably heated and pressed with a heating press, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adhesive which is mainly composed of an isocyanate compound and which is cured by heating and moisture. More specifically, the present invention relates to a breathable adhesive for an adherend for adhering an adherend made of wood, a lignocellulosic material, an inorganic material or the like, which is breathable and has moisture.

[0002]

2. Description of the Related Art As an adhesive for adhering adherends of wood or lignocellulosic materials, an aqueous solution of urea resin adhesive, melamine resin adhesive, phenol resin adhesive, polyvinyl acetate resin, etc. There is known an adhesive composed of an aqueous emulsion liquid such as a polyacrylic ester resin. These adhesives are easy to manufacture and advantageous in terms of cost, but their adhesive properties, particularly water resistance, are poor, and they have problems such as formaldehyde odor, so that their applications are limited.

Isocyanate adhesives do not use formalin and show excellent adhesive performance by reacting with a component having a hydroxyl group contained in wood and the like, and generally, water resistance, heat resistance, durability and impact resistance. Due to its excellent properties, the amount used has been gradually increasing in recent years. Examples of this type of isocyanate adhesive include, for example, Japanese Examined Patent Publication No. 51-30577.
JP-A-57-229959 and JP-B-58-29826 describe adhesives having an aqueous emulsion as a main component and having excellent water resistance. These adhesives are prepared by mixing an isocyanate compound with an aqueous emulsion containing an aqueous solution such as polyvinyl alcohol, or by reacting it with a small amount of a polyol in advance so that it is easily emulsified in water. % Water suspension. Further, since these adhesives are water-based and contain almost no organic solvent, they are advantageous in that they contain few volatile substances harmful to the human body and do not pose a risk to fire.

However, the isocyanate-based adhesive has a relatively short usable time (hereinafter referred to as a pot life), and since the adhesive contains a large amount of water, it has poor drying property and a sufficient curing time. It was necessary to take a long time, so there was a problem in workability. In addition, the adherend such as wood, lignocellulosic material, and inorganic material also contains water.If the water content is high, the adhesive may penetrate and the water contained may evaporate due to heating. However, the air layer generated by this may flatten due to the applied pressure, resulting in defective adhesion.
In particular, wood-based materials have problems such as warping and cracks on the surface of the adherend due to expansion and contraction due to moisture.

In order to solve these problems, a one-component moisture-curable polyurethane adhesive is disclosed in, for example, Japanese Patent Laid-Open No. 2-1.
A two-component curing type polyurethane adhesive described in JP-A No. 792, 792, for example, JP-A-3-244687, JP-A-4-298593, JP-A-5-170858.
It is described in each publication. Since the polyurethane adhesives of 1 and 2 contain almost no water or organic solvent, they solve both the problems in the working environment and the problems of adhesion failure due to water.

[0006]

However, since the above-mentioned polyurethane adhesive is a moisture-curable type composed of a prepolymer of an isocyanate compound, it generally has a slow curing rate and usually takes several days to be completely cured. , There was a problem in workability. Further, shortening the curing time lowers the storage stability and the pot life, so it is difficult to satisfy all of the curing time, the storage stability and the pot life.
Since the above polyurethane adhesive is a two-component curing type consisting of a prepolymer of an isocyanate compound, it can be cured at a low temperature or for a short time, but it uses a highly hygroscopic polyol or a high molecular weight and highly viscous polyol as a raw material. Therefore, the adhesive performance, particularly the water resistance, is deteriorated, and the resin itself, which occupies most of the adhesive, is expensive, so that the application is limited in terms of cost. Further, these prepolymers are likely to penetrate into the adherend, resulting in a thin adhesive layer with unstable adhesive performance and the need for clamping with high pressure.

[0007] Further, in order to reduce the apparent cost as an adhesive to the above polyurethane adhesive,
When a filler such as clay, calcium carbonate or wood powder is added, or when grain flour such as wheat flour is added as a filler, the moisture contained in the filler or filler may react with the isocyanate compound. However, there are problems such as deterioration in storage stability, low molecular weight of the polyurethane resin, and decrease in adhesive strength due to foaming during curing. In order to avoid a decrease in the adhesive strength due to foaming during curing, among the above, the polyurethane adhesives described in JP-A-4-298593 and JP-A-5-170858 are calcium oxide in the filler. , Magnesium oxide, and barium oxide are added to prevent foaming during curing. Other methods for preventing foaming include heating and drying the filler and adding zeolite having a limited component and structure to the uncured composition (Japanese Patent Publication No. 48-37).
No. 331), and a method of limiting the isocyanate compound and the polyol compound to be used (JP-A-54-12629).
No. 7) is known. However, these foaming prevention methods are insufficient, the adhesive component is limited, or the cost of the adhesive is increased.

The object of the present invention is to bond an adherend made of wood, a lignocellulosic material, an inorganic material, etc., which is breathable and has moisture content, has good storage stability, and has a usable life of An object is to provide an adhesive for air-permeable adherends that is long, has excellent curability, and has high adhesive strength. Another object of the present invention is to provide an adhesive agent for air-permeable adherends, which does not require dehydration treatment and whose adhesive strength does not decrease due to the foaming action during curing.

[0009]

Means for Solving the Problems The present inventors have found that even when an isocyanate compound foams by reacting with water,
We have found that an adherend that is breathable and has water content does not lower the adhesive strength by absorbing it, and arrived at the present invention. That is, the present invention is a one-part curable adhesive for adhering an adherend that is breathable and has moisture, and a compound that is liquid at room temperature and has at least two isocyanate groups in its molecule. 50 to 100 parts by weight of compound
˜200 parts by weight of filler.

Hereinafter, the present invention will be described in detail. (a) adherend The adherend adhered with the breathable adherend adhesive of the present invention,
It is made of wood, a lignocellulosic material, an inorganic material, etc. that is breathable and has moisture. It is effective for the adhesive surface or inside of the adherend to contain about 2 to 20% of water to accelerate the curing of the adhesive. More preferable adherends satisfying these conditions include high-stalk stalks, corn stalks, sugar cane stalks, plant stems such as bamboo, pulverized products thereof, and wood chips. The high stalk is
Although it is difficult to adhere the conventional adhesive due to the wax component of the epidermis, the adherend of the present invention is most preferable because it satisfies all the above conditions. If one of the two adherends satisfies the above conditions, the other adherend is a metal such as an aluminum plate that is not breathable or has no moisture, or melamine or polyester. It is possible to select a synthetic resin film such as.
In the present specification, the state of the adherend having air permeability and water refers to the state of the adherend before applying the adhesive, and refers to the state of the adherend after the adhesive is cured. is not. Further, the air-permeable state means a state in which the adherend has pores to the extent that the adhesive does not remain in a foamed state between the adhering surfaces of the adherends which are adhered and pressed after applying the adhesive.

(B) Room-temperature liquid compound having at least two isocyanate groups in the molecule Examples of the room-temperature liquid compound having an isocyanate group used in the present invention include tolylene diisocyanate and diphenylmethane diisocyanate (hereinafter referred to as MDI). , Xylene diisocyanate, hexamethylene
Compounds having at least two isocyanate groups of the same type in the molecule such as diisocyanate, naphthalene / diisocyanate, etc., and retaining a liquid state at room temperature (including various isomers of monomeric and polymeric), or selected from these compounds Mixtures containing one or more compounds selected from the above.

The viscosity of these compounds or mixtures is 0.5
It is preferably in the range of -20 poise. The viscosity is 0.
If it is lower than 5 poise, the adhesive permeates into the adherend so strongly that the adhesive performance becomes unstable. When the viscosity exceeds 20 poise, it becomes difficult to add a necessary amount of the filler or the extender, and the pot life of the adhesive is significantly shortened. Among the above compounds, a polymeric MDI composed of various MDI isomers and a polynuclear mixture of several kinds of multimers thereof is particularly preferable from the viewpoint of viscosity characteristics and adhesive strength. Prepolymers of isocyanate compounds obtained by reacting these isocyanate compounds with various polyols and the like are generally unfavorable because they have a high viscosity, require adjustment of viscosity by addition of a solvent, and decrease storage stability.

(C) Filler The filler used in the present invention includes a) clay, bentonite, carbonates such as calcium and magnesium, and b)
Calcium compounds such as calcium sulfate and calcium silicate, c) metal oxides or hydroxides such as aluminum, zinc, magnesium and iron, d) carbon, glass,
Inorganic powder or fibrous material such as mica, e) Wood powder, coconut shell powder, chaff, mosquito) Stem powder such as jade corn, high rye, Ki) Walnut, seed shell powder such as peach, Ku) Wheat flour, Proteins such as rice flour, potato starch, defatted soybean flour, blood meal, and casein, and starch quality can be mentioned. In addition, a flame retardant, a color pigment, a thickener, a lubricant and the like can be added if necessary.

The filler used in the present invention does not need to be previously dried by heating or dehydrated as long as it has a natural water content. The compounding amount thereof is preferably 50 to 200 parts by weight with respect to 100 parts by weight of the isocyanate liquid compound within a usable viscosity range. If the compounding amount of the filler is less than 50 parts by weight, the isocyanate compound easily penetrates into the adherend and the adhesive performance becomes unstable. On the other hand, if the amount is more than 200 parts by weight, the fluidity of the composition will be deteriorated, uniform coating on the surface of the adherend will not be possible, and the adhesiveness will be unstable. As the filler, one kind can be blended or a plurality of kinds can be mixed. Mixing fillers having different particle sizes is effective in preventing the settling of the filler. Among the above-mentioned fillers, calcium carbonate is suitable as the filler of the present invention because it is inexpensive, relatively easily available, contains a suitable amount of water, and has good reactivity with isocyanate.

(D) Water Present at the Time of Adhesion Although the adhesive of the present invention is sufficiently hardened only by the water held by the adherend, if the amount of water is very small, or in order to make the hardening more efficient, It is also possible to add a small amount of water to the adhesive before coating for the purpose of adjusting the viscosity. Normal,
When water is added to the isocyanate compound, the isocyanate compound and water are separated, so that it is difficult to uniformly disperse them regardless of the addition amount. However, in the adhesive of the present invention, the inclusion of the filler makes it possible to disperse water in the isocyanate compound relatively easily. The addition of water shortens the pot life, but it can improve workability and adhesion to the adherend by adjusting the viscosity to an optimum value according to the coating method and the type of adherend. it can. Also, the addition of a small amount of water accelerates the curing of the adhesive. The amount added is usually 100 parts by weight of the isocyanate compound,
It is 20 parts by weight or less, preferably 10 parts by weight or less, more preferably 1 to 5 parts by weight. When water is added in an amount of more than 20 parts by weight, the viscosity rises rapidly and the pot life becomes extremely short.

[0016]

When the adhesive of the present invention is prepared by mixing the isocyanate compound and the filler, a part of the isocyanate compound reacts with the water contained in the filler, so that the viscosity is slightly increased. However, the reaction rate with moisture in the air is extremely slow, and it can be stored for a long time in a sealed state. The adhesive of the present invention has a slight foaming property due to the reaction between an isocyanate compound and water, and the foamed adhesive fills the air holes of the adherend and cures to give an adhesive cured product. It is moored to the inside of the to obtain a large adhesive strength. The air holes of the adherend are also useful for discharging the gas generated at the time of curing the adhesive to the outside or for allowing moisture in the air to reach the adhesive layer. When the adherend having water content is adhered by the adhesive of the present invention, or when the adherend is adhered in the presence of water when the water content is small, the curing of the adhesive is accelerated.

To adhere an adherend with the adhesive of the present invention, after applying the adhesive of the present invention, it is heated and pressed using a hot press or the like. In this case, it is necessary to adjust the press pressure so that the adherend has some voids. When using a hot press, inserting a spacer between hot plates
It is effective for this purpose. The preferred pressing pressure is
When the adherend is plant stem, wood chips, etc., the product specific gravity is
It is preferable to adjust it to be 0.5 or less. Generally, as the press pressure decreases, the adhesive strength slightly decreases, but below a certain pressure, the adhesive strength extremely decreases,
It may cause poor adhesion. In the case of these adherends, the limit is usually about 0.2 in terms of product specific gravity. The clamping time is
Although it depends on the temperature of the hot plate and the thermal conductivity of the material, it is usually possible to release the pressure within a few minutes after the temperature of the adhesive layer reaches 100 ° C. or higher. When hot-pressing and adhering, pressurizing steam is blown at the same time to accelerate heating of the adherend, and moisture accelerates the curing of the isocyanate compound. You can

[0018]

As described above, the adhesive for breathable adherends of the present invention has an extremely long storage stability and a long pot life, and after the adhesive is applied, it is left at room temperature for 1 to 3 days. However, almost no deterioration of the adhesive performance due to dry adhesion is observed. Therefore, the adhesive can be collectively applied to the adherend in advance, which significantly contributes to the reduction of the defective rate and the efficiency of the bonding work. Further, since the air-permeable adhesive for an adherend of the present invention effectively acts with both the moisture of the filler contained in the adhesive and the moisture of the adherend, the adhesive is filled like a conventional polyurethane resin-based adhesive. It is not necessary to dehydrate the agent or adherend in advance. Further, it is possible to adhere an adherend having a high water content and to perform pressing for a short time by a steam injection method.

[0019]

Next, examples of the present invention will be described together with comparative examples. <Example 1> With respect to 100 parts by weight of MDI (manufactured by Nippon Polyurethane Co., Ltd., trade name: MR-400), 60 parts by weight of calcium carbonate powder as a filler and 40 parts of corn starch.
An adhesive paste solution was prepared by mixing 5 parts by weight of water and 5 parts by weight of water. This adhesive was left standing in a room at 24 ° C. for 3 hours while rotating the roll on a roll spreader, but there was no change in the paste liquid state. Next, this adhesive was applied on both sides of a radiata pine veneer having a thickness of 1.8 mm and a water content of 18% at a rate of 180 g / m ² per adhesive layer, and then radiata pine veneer of the same thickness was overlaid to form 3 Ply plywood was made. Adhesive condition at that time is pressure 10k
Adhesion was performed by temporarily pressing at g / cm ² for 30 minutes and then hot pressing at a temperature of 130 ° C. and a pressure of 8 kg / cm ² for 3 minutes. Comparative Example 1 Commercially available melamine-urea co-condensation resin adhesive (manufactured by Honen Corporation, trade name: ML-0)
44) 20 parts flour as a filler for 100 parts by weight
An adhesive paste solution was prepared by blending 5 parts by weight, 5 parts by weight of water and 0.5 parts by weight of ammonium chloride powder. This adhesive paste solution was left in a room at 24 ° C. for 3 hours while rotating the roll on a roll spreader. After that, as a result of measuring the viscosity of the paste solution, the viscosity was 2.6 times higher than the initial viscosity.
Then, this adhesive was applied to both sides of the same radiatapine single plate as in Example 1 at a rate of 180 g / m ² per adhesive layer,
Further, a single plate of radiatapine having the same thickness was overlaid and bonded under the same conditions as in Example 1 to produce a 3-ply plywood. The obtained plywoods of Example 1 and Comparative Example 1 were each subjected to an adhesive strength test specified in the JAS ordinary plywood type 1 standard. Table 1 shows the results.

[0020]

[Table 1]

As is clear from Table 1, the adhesive strength of Example 1 was about 2.5 times that of Comparative Example 1. Further, from the value of the wood breaking rate, it was found that Comparative Example 1 was broken on the adhesive coated surface, whereas in Example 1, 92% of the broken pieces were broken on the single plate portion and firmly adhered.

<Example 2> MDI (Japan Polyurethane
Co., Ltd., trade name: MR-400) 70 parts by weight, xylidene diisocyanate (Takeda Chemical Industries Co., Ltd., trade name: Takenate 500) 30 parts by weight are uniformly mixed, and the mixture is carbonated as a filler. An adhesive paste solution was prepared by uniformly mixing 50 parts by weight of calcium powder, 50 parts by weight of wheat flour, and 5 parts by weight of water. This adhesive was left in a room at 18 ° C. for 3 hours while rotating the roll on a roll spreader, but there was no change in the paste liquid state. Next, this adhesive was previously mixed with a phenol resin in a solid content ratio of about 20.
% A number of 45 cm long impregnated stalks are arranged in parallel and are tied with a cord in the shape of a blind. Both sides of the sheet are applied at a rate of 150 g / m ² , and then the stalks are placed on top of each other. Stem sheets coated with an adhesive by the same method were stacked so as to be orthogonal to each other, and a radialatapine single plate having a thickness of 1.8 mm and a water content of 5% was further stacked on the front and back surfaces thereof. In this state, insert into a hot press maintained at 150 ° C,
The thickness is 25 m after thermocompression bonding for 20 minutes at a pressure of kg / cm ^2.
m thick plate was obtained.

<Example 3> MDI (Japan Polyurethane
An adhesive paste solution was prepared by uniformly mixing 100 parts by weight of clay powder as a filler with 100 parts by weight of a product name: MR-400 manufactured by Co., Ltd. This adhesive has a water content of 5
7% by weight of solid content on chips of plywood that have been dried to 6%
It was applied uniformly by spraying so that it would be%. Next, after the waste chips of plywood are made to have a uniform thickness, they are inserted into a hot press maintained at 180 ° C., a pressure of 20 kg / cm ² is applied, and they are pressed for 3 minutes, and further a pressure of 10 kg / cm ² for 3 minutes. It was pressed to form a thick plate having a thickness of 20 mm.

Example 4 100 parts by weight of MDI (Sumitomo Bayer Urethane Co., Ltd., trade name: Sumidule 44V) was added to 140 parts by weight of clay powder and 5 parts of water as a filler.
An adhesive paste solution was prepared by uniformly blending with parts by weight. This adhesive was left standing in a room at 21 ° C. for 3 hours while rotating the roll on a roll spreader, but there was no change in the paste liquid state. Next, apply this adhesive to a length of 45c
A large number of m high stalks were arranged in parallel and were applied at a rate of 150 g / m ² on each side of a sheet that was tied in a blind shape with threads, and then left at room temperature for 2 days. Then, make the stem sheet 5 so that the stems coated with the adhesive are orthogonal to each other.
The layers were laminated, and the front and back surfaces were laminated with a 1.8 mm thick radiatapine single plate having a water content of 15%. Insert into hot pressing steam injection system which was maintained at 0.99 ° C. In this state, immediately after pressing at a pressure of 8 kg / cm ^2, the pressurized steam to 5 kg / cm ² 30
Sprayed for seconds. Next, the plate was continuously clamped at the same temperature for 2.5 minutes, depressurized for another 3 minutes to remove water, and then taken out from the press to form a thick plate having a thickness of 40 mm.

Example 5 An adhesive paste solution was prepared by uniformly mixing 140 parts by weight of clay powder as a filler with 100 parts by weight of MDI (trade name: AP manufactured by Koyo Sangyo Co., Ltd.). . This adhesive was left for 3 hours in a room at 21 ° C. while rotating the roll on a roll spreader.
There was no change in the paste state. Next, this adhesive is placed on both sides of a sheet in which a large number of 45 cm long high-stalks are arranged in parallel and tied in the shape of a blind with 150 g / m 2 respectively.
After applying at a ratio of ² , the stem sheets coated with an adhesive in the same manner so that the stems are orthogonal to each other are laminated in 5 layers, and the front and back surfaces each have a thickness of 1.8 mm and a water content of 15%.
Layered radiata pine veneer. 15 in this state
0 Insert into hot pressing steam injection system held in ° C., immediately after pressing at a pressure of 8 kg / cm ^2, was injected water vapor pressurized to 5 kg / cm ² 3 minutes. Next, the plate was continuously clamped at the same temperature for 3 minutes, depressurized for 4 minutes to remove water, and then taken out from the press to form a thick plate having a thickness of 30 mm.

<Example 6> The same adhesive as in Example 4 was used, in which a large number of 45 cm-long high stems were arranged in parallel and were tied in the shape of a blind with a sheet of 150 g / m ² on each side.
And then left for 2 days at room temperature. Then, the stem sheets were laminated in 5 layers in the same manner as in Example 4, and 1.8 mm thick radiatapine single plate having a water content of 15% was further laminated on the front and back surfaces thereof. This laminate was pressed with the same press as in Example 4 in the same manner to form a thick plate having a thickness of 40 mm.

Comparative Example 2 Polypropylene glycol (molecular weight 4000) against 50 parts by weight of MDI (Sumitomo Bayer Urethane Co., Ltd., trade name: Sumidule 44V)
An adhesive paste solution was prepared by uniformly mixing 50 parts by weight, 140 parts by weight of clay powder as a filler, and 5 parts by weight of water. This adhesive was left standing in a room at 21 ° C. for 3 hours while rotating the roll on a roll spreader, but there was no change in the paste liquid state. Then glue this adhesive to length 45
A large number of cm high stalks were arranged parallel to each other, and applied to both sides of a sheet which was tied in the shape of a cord with a thread at a rate of 150 g / m ² , and then left at room temperature for 2 days. Then, the stem sheets were laminated in 5 layers in the same manner as in Example 4, and 1.8 mm thick radiatapine single plate having a water content of 15% was further laminated on the front and back surfaces thereof. This laminate was pressed with the same press as in Example 4 in the same manner to form a thick plate having a thickness of 40 mm.

<Comparative Example 3> A commercially available moisture-curable polyurethane adhesive (manufactured by Nippon Polyurethane Co., Ltd., trade name: Woodlock) is arranged in parallel with a large number of 45 cm long high stems and tied in a blind shape with threads. 150 on each side
After coating at a ratio of g / m ² , the coating was left at room temperature for 2 days. Then, the stem sheets were laminated in 5 layers in the same manner as in Example 4, and 1.8 mm thick radiatapine single plate having a water content of 15% was further laminated on the front and back surfaces thereof. This laminate was pressed in the same press as in Example 4 to give a thickness of 40
mm thick plates were molded. However, this thick plate had insufficient adhesive strength, and each layer was easily peeled off by hand.

Each of the thick plates of Examples 2 to 6 and Comparative Example 2 was tested according to the test method specified in JIS A 5908 (particle board), and the specific gravity, average normal bending strength, and water content after boiling for 2 hours in boiling water were tested. The thickness swell rate was measured respectively. The results are shown in Table 2.

[0030]

[Table 2]

As is clear from Table 2, the thick plate of Comparative Example 2 was weak at a bending strength of 100 kgf / cm ² or less and the thickness swelling ratio exceeded 8%, while Examples 2 to 6 were used. Each of the thick plates had a bending strength of more than 120 kgf / cm ² , and had a thickness swelling ratio of less than 6.5%, and was excellent in performance as a thick plate.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Noriyuki Murakami, Inventor Koyo Sangyo Co., Ltd., 2-21-12 Umegaoka, Setagaya-ku, Tokyo

Claims (6)

[Claims] 1. An adhesive agent for adhering an adherend having air permeability and moisture, comprising: a compound which has at least two isocyanate groups in a molecule and is liquid at room temperature; and 100 parts by weight of this compound. On the other hand, the adhesive for breathable adherends, which contains 50 to 200 parts by weight of a filler. 2. The breathable adhesive for adherends according to claim 1, wherein the adherend has a water content of 2 to 20%. 3. Adhesion in the presence of water at the time of adhesion, and the amount of water present is 20 parts by weight or less based on 100 parts by weight of a compound having at least two isocyanate groups in the molecule and being liquid at room temperature. The air-permeable adhesive for an adherend according to claim 1 or 2. 4. The adhesive for breathable adherends according to claim 1, wherein the compound which is liquid at room temperature and has at least two isocyanate groups in the molecule contains diphenylmethane diisocyanate as a main component. 5. The air-permeable adhesive for adherends according to claim 1, wherein the filler is calcium carbonate or a mixture of calcium carbonate and another filler. 6. The adhesive for breathable adherends according to claim 1, wherein the filler has a water content of 1% or less.