JPH0348237B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a water-resistant adhesive, and more particularly to an adhesive comprising a synthetic rubber latex as a main component and an isocyanate-based crosslinking agent, which can greatly expand the tolerance range of open and closed assembly times. More specifically, the present invention relates to an adhesive that does not contain formaldehyde (hereinafter referred to as "formalin") and is used for plywood and wood that requires particularly high water resistance, such as for secondary processing of plywood. Currently, adhesives for plywood or plywood secondary processing include urea resin, melamine-urea cocondensation resin,
Phenol resin etc. are mainly used. These adhesives are widely used because they are inexpensive and have relatively good water resistance, but recently the formalin that remains in these adhesives has worsened the environment for plywood manufacturing work, and the use of these adhesives has become increasingly difficult. Formalin is emitted from furniture and houses made of plywood, which has become a worldwide problem. Recently, various attempts have been made to reduce the release of formalin from urea resins, etc., and considerable results have been achieved. There is a high possibility that the curing of the adhesive will be incomplete due to variations in the temperature and heat and pressure conditions, and this is presumed to be the cause of formalin release from the product. On the other hand, there are adhesives for plywood that do not contain formalin at all, such as protein-based and vinyl acetate resin-based adhesives, but these are not generally used because of their poor water resistance. In addition, non-formalin based synthetic rubber latex (hereinafter referred to as latex) can be used as an adhesive for plywood.
Polyvinyl alcohol (hereinafter abbreviated as PVA)
An example of using isocyanate adhesive is
For example, they are disclosed in Japanese Patent Publication No. 55-18759, Japanese Patent Publication No. 50-69137, Japanese Patent Publication No. 50-69138, Japanese Patent Publication No. 50-69139, etc. However, when the above-mentioned water-based vinyl urethane adhesive is used as an adhesive for manufacturing plywood, the adhesive dries too quickly when applied to the adherend, resulting in poor adhesion. In addition, the heat-pressing method not only limits the bonding time but also has poor temporary adhesion (generally refers to the adhesion after being pressed at room temperature and left to decompress in the plywood manufacturing process). and the transition to the heat-pressing process is not smooth)
This has caused major problems in terms of plywood productivity, plywood quality, etc. in industrial implementation. In order to improve these drawbacks, there is a method of adding a water-soluble polymer compound such as methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, sodium polyacrylate, polyethylene glycol fatty acid diester, etc. in addition to a compound having water retention properties, such as polyvinyl alcohol. The use of nonionic surfactants, anionic surfactants, or a combination of these has been proposed. However, with the above method, not only does the product stability, flow characteristics, and size liquid stability as an adhesive product deteriorate, especially in conjunction with a decrease in water-resistant adhesive performance, but also the application with a roll etc. It has the disadvantage that it is difficult to maintain a constant coating amount. As a method to improve this, for example, as known in Japanese Patent Application Laid-Open No. 50-69140, a method has been proposed in which a highly hygroscopic compound is added to various emulsions to extend the open time of the adhesive. In particular, when synthetic rubber latex is used as an emulsion, it lacks product stability and adhesive stability, resulting in a particularly short pot life, which not only hinders workability, but also has the drawback of reducing adhesive performance. have The object of the present invention is to use a wood adhesive for plywood or secondary processing of plywood, which can have drying properties adjusted as desired.
Another object of the present invention is to provide a novel adhesive that has excellent product stability and size liquid stability as an adhesive, and is also excellent in water resistance. As a result of intensive research to achieve this, the present inventors discovered that the above-mentioned drawbacks could be eliminated by blending a deliquescent compound into a base of unmodified synthetic rubber latex, and completed the present invention. That is, the present invention provides a water-resistant adhesive characterized by comprising a main material consisting of unmodified synthetic rubber latex, polyvinyl alcohol, an extender, and a filler, a crosslinking agent of an isocyanate compound or an isocyanate polymer, and a deliquescent compound. be. The unmodified synthetic rubber latex used in the present invention is one whose main components are typified by open-chain aliphatic conjugated dienes, vinyl aromatics, and ethylenically unsaturated carboxylic acid esters. Specifically, the open chain aliphatic conjugated dienes include butadiene, isoprene, 2-
Examples include chlorobutadiene, but butadiene is particularly preferred. Usually this butadiene has 25% of the total monomer content.
Used in the range of ~60% by weight. In addition, examples of vinyl aromatic compounds include styrene,
Examples include α-methylstyrene and vinyltoluene, with styrene being particularly preferred. Typically, the vinyl aromatic compound is used in an amount ranging from 40 to 75% by weight of the total monomers. Furthermore, examples of ethylenically unsaturated carboxylic acids include methyl methacrylate and acrylonitrile methacrylate, with methyl methacrylate being particularly preferred. Usually, this ethylenically unsaturated carboxylic acid is used in an amount of 40 to 75% by weight of the total monomers. In particular, this monomer may be used in place of the open-chain aliphatic conjugated diene, or mixtures thereof may also be used. That is, in the present invention, in addition to functional monomers commonly used for modifying synthetic rubber latex, such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, and maleic acid containing carboxyl groups, amide groups are used. Those with hydroxyl groups include acrylamide, methacrylamide, etc., and those with hydroxyl groups include hydroxyethyl acrylate, hydroxymethyl acrylate,
Examples include hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, etc. Those having a glycidyl group include glycidyl acrylate, glycidyl methacrylate, acrylic glycidyl ether, etc. In addition, acrolein, parastyrene sulfonic acid, etc. are not used. The concentration of the unmodified synthetic rubber latex used in the present invention is usually
The concentration of the unmodified synthetic rubber latex is in the range of 5 to 30% by weight, preferably 10 to 20% by weight, based on the solid content in the base resin. The PVA used in the present invention refers to normal partially or completely saponified PVA or PVA derivatives, and the degree of polymerization and saponification are not particularly limited, but in particular, the degree of polymerization is 300 to 2,500, and the degree of saponification is not particularly limited. It is best to have a chemical degree of 80 to 100 mol%. Also, PVA
Although the concentration in the main agent is arbitrary, it is in the range of 1 to 15% by weight, preferably 3 to 8% by weight. The deliquescent compound used in the present invention refers to a compound in which the vapor pressure of a saturated aqueous solution of the compound is lower than the partial pressure of water vapor in the atmosphere, and specifically refers to, for example, chloride. Calcium, magnesium chloride or a mixture of magnesium chloride and sodium chloride are preferred, preferably compounds that exhibit neutrality when present in the adhesive system. The amount of the deliquescent compound added in the present invention depends on the properties of the synthetic rubber latex and the amounts of extenders, fillers, and crosslinking agents, but it is generally in the range of 0.5 to 5 parts by weight per 100 parts by weight of the base resin. Appropriate. If the amount added is less than 0.5 parts by weight, the anti-drying effect will be lacking, and if it is added more than 5 parts by weight, the latex, which is the base emulsion, will aggregate or foam, resulting in poor viscosity stability of the product. This is undesirable, and furthermore, it results in a decrease in adhesive performance. Furthermore, especially when an isocyanate compound as a crosslinking agent is blended, it is not preferable because the pot life becomes extremely short, the viscosity increases over time, and the adhesive performance is also affected. A preferred example of the case where a deliquescent compound is added and blended in the adhesive according to the present invention is as follows. Bulking agents, fillers, etc. are blended into a pre-prepared aqueous PVA solution at room temperature, then latex is added and blended, and after thorough stirring, a deliquescent compound is added and blended with thorough stirring. That is, it is a method of adding and blending it to the main ingredient side in advance. Alternatively, it may be added and blended immediately before use, that is, at the same time as the crosslinking agent is added and blended. The extender used in the present invention basically not only functions to increase the volume, but also reacts with other components of the adhesive, especially isocyanate compounds, and
It also has the effect of imparting water resistance and initial adhesiveness to the adhesive. In general, wheat flour, starch powder, defatted soybean flour, blood powder, etc. can be used, but among these, wheat flour and starch have water resistance due to isocyanate compounds, and furthermore, they do not gelatinize in cold water. It is particularly preferred because it becomes gelatinized and viscous when heated during bonding. As the filler, non-substrate fillers such as clay, kaolin, talc, and calcium carbonate are used, but organic fillers such as wood flour and walnut shell powder can also be used. The blending method and blending ratio of these extenders and fillers vary depending on the purpose of use of the adhesive.
Basically, the concentration in the main agent is 10 to 70% by weight, and especially for plywood adhesives, a range of 20 to 40% by weight is appropriate. Further, these extenders and fillers may be used alone or in combination, but it is preferable to use the extenders and fillers at the same time. On the other hand, the isocyanate compound or polymer thereof used in the present invention may be any compound as long as it yields polyurethane.
For example, tolylene diisocyanate (hereinafter abbreviated as TDI), hydrogenated TDI, trimethylolpropane (TMP)-TDI adduct, triphenylmethane triisocyanate (TTI), diphenylmethane diisocyanate (NDI), hydrogenated NDI, hexamethylene diisocyanate Examples include cyanate addition condensates. Furthermore, in mixing polyisocyanate and polyol, it is also possible to use a polyol such as polyester mixed with an excess amount of the above-mentioned isocyanate compound. It is also possible to use a prepolymer system, i.e., an NCO-terminated prepolymer prepolymerized with a polyol and an excess of polyisocyanate, or an OH-terminated prepolymer prepolymerized with an excess of polyol when using an excess of polyisocyanate as described above. It may be used by adding it to.
Particularly preferred among these isocyanate compounds and polymers are TMP-TDI adduct and MDI
It is. The blending ratio of the isocyanate compound or its polymer is 5 to 20 parts by weight per 100 parts by weight of the main ingredient.
is within the range of The adhesive of the present invention can be used for adhesives where at least one of the materials to be bonded is ordinary wood, as well as baseboards for plywood, precious wood for veneer plywood, single wood for parquet plywood, wood for overlay plywood, and the like. Other adherends that can be bonded to wood include paper, textile products, synthetic resins, inorganic boards, and metals. When using the adhesive of the present invention, it is possible to achieve sufficient adhesion with just room-temperature adhesion (cold press); however,
Furthermore, if a short-term rise in absolute adhesive performance is expected, thermopressure bonding is of course possible. The above-mentioned adhesive of the present invention is an adhesive of extremely high practical value as it prevents the adhesion failure caused by the dry adhesion described above, improves the tolerance of lamination and deposition time, and also improves temporary adhesion. Next, the present invention will be further explained by reference examples and examples, but the present invention is not limited thereto. In addition, in the following, parts and % unless otherwise specified.
is based on weight. Example 1 (1) Polyvinyl alcohol aqueous solution (Kuraray KK
Manufactured, product #217, adjusted to solid content 15.4%) 100
1 part, 60 parts of calcium carbonate (manufactured by Maruo Calcium, trade name: Super SS), 0.5 parts of sodium hexametaphosphate, 0.3 parts of dibutyl phthalate as an antifoaming agent.
The components were blended and stirred to obtain a blend for evaluating the physical properties of the water-resistant adhesive of the present invention. (below,
The viscosity of this masterbatch measured by a Bruckfield rotational viscometer (Model BH) at a temperature of 25° C. was 300 poise using a No. 6 rotor at 10 rpm. (2) Synthetic rubber latex (manufactured by Mitsui Toatsu Chemical KK,
50 parts of the product (trade name: Polylacx 501, solid content 50%) were blended and stirred to obtain a compound (hereinafter abbreviated as the main ingredient) consisting of the unmodified synthetic rubber Rolacx of the present invention, polyvinyl alcohol, filler, etc. . (3) Add 1 part, 2 parts, and 3 parts of calcium chloride dihydrate (CaCl ₂ 2H ₂ O) to 100 parts of the base material obtained in (2) above, stir and mix to deliquesce. A chemical compound was obtained. The viscosity change of the base agent thus obtained was monitored after 5 minutes, 7 days, and 30 days. In this case, if left unattended for 7 days and 30 days,
5 of each main ingredient containing calcium chloride
The sample was placed in a polyethylene bottle, capped, and left at a temperature of 40° C. for a predetermined period of time, and the viscosity was measured after returning to the above-mentioned conditions. The results are shown in Table-1. (4) Further, to 100 parts of each main ingredient of the calcium chloride addition blend system obtained in (3) above after 5 minutes, diphenylmethane-4,4'-diisocyanate compound (manufactured by Mitsui Nisso Urethane KK, trade name ,
15 parts of MDI-CR-200) were added and mixed by stirring to obtain a water-resistant adhesive of the present invention. Changes in viscosity of the obtained adhesive were monitored after 5 minutes and 60 minutes. The results are shown in Table-2. Furthermore, the open assembly time of the obtained adhesive was subjected to an adhesive production test under the following adhesive working conditions based on JIS-K-6802. (1) Bonding work conditions Material: Hemlock 200 x 80 x 15 m/m Coating amount: 300 g/m ² spatula coating Open assembly time: 10 minutes and 60 minutes
Closed assembly time: within 15 minutes Compressing pressure: 12.3Kg/ ^cm2 at room temperature with a press, tighten the clamp by hand after 5 minutes, and heat to 20℃ for 23 minutes.
I left it for a while. Curing: After the above-mentioned clamping, release the clamp and heat to 20℃.
The samples were cured at a temperature of 7 days. (2) Adhesive Performance Test (Compression Shear Adhesive Strength) As mentioned above, Γ normal state (abbreviated as T-) and Γ repeated boiling (abbreviated as T-) performance were evaluated based on JIS.K-6802. The above performance evaluation results are shown in Table 3. Reference Example 1 Using the same masterbatch obtained in Example 1-(1), a modified synthetic rubber latex (manufactured by Mitsui Toatsu Chemical KK) was prepared as a synthetic rubber latex with the same formulation as in Example 1-(2). The experiment was carried out using exactly the same procedure except that Polylac 750 (trade name: Polylac 750, solid content 50%) was used.
It was shown to. Table 2 also shows changes in viscosity of adhesives containing diphenylmethane-4,4' diisocyanate compounds. Furthermore, the adhesive performance evaluation results are also shown in Table 3.

【table】

【table】

[Table] 〓Note〓 % indicates the wood breakage rate.

Claims (1)

[Claims] 1 100 parts by weight of the main material consisting of unmodified synthetic rubber latex, polyvinyl alcohol, extender, and filler, 5 to 20 parts by weight of an isocyanate compound or isocyanate polymer, and 0.5 to 0.5 parts by weight of a deliquescent compound.
A water-resistant adhesive using 5 parts by weight.