JPH023432B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure-sensitive adhesive having excellent adhesive strength and moisture resistance to objects to be adhered, such as films and molded articles, made of polyolefins such as polyethylene, polypropylene, and polybutadiene. Pressure-sensitive adhesives are used for tapes, labels, stickers, stickers, etc., and the materials to which they are adhered include plastic, metal, glass, paper, and ceramics. In particular, plastic products are on the rise. In particular, the proportion of polyolefins in plastic products is gradually increasing due to safety and hygiene considerations. For example, polybutadiene film has recently been developed and marketed as a packaging film for tableware, containers, toys, packaging bags, etc., and has been attracting attention. On the other hand, the composition of pressure-sensitive adhesives has traditionally been natural rubber, synthetic rubber, polyvinyl alkyl ether,
It consists of polyacrylic acid ester as the main component and additives such as tackifiers, plasticizers, etc. as auxiliary components. Conventionally, pressure-sensitive adhesives have been so-called solution-type pressure-sensitive adhesives that use organic solvents such as aromatics, esters, and ketones, which have excellent adhesive properties, coating suitability, drying properties, and water resistance. Adhesives used to be the mainstay, but in recent years water-based dispersion type pressure-sensitive adhesives have attracted attention due to their resource saving, non-pollution, safety and hygiene aspects. Pressure adhesives are being actively researched, and the results are showing that the field is expanding. However, these water-based dispersion-type pressure-sensitive adhesives have disadvantages in terms of water resistance, adhesion, drying properties, stability, etc. compared to solution-type pressure-sensitive adhesives, and in particular, moisture resistance due to lack of water resistance. There has been a demand for improvements in holding power and adhesion, particularly in adhesion strength to objects such as molded articles made of polyolefin. The present invention eliminates the adhesion defects of conventional water-based dispersion type pressure-sensitive adhesives mainly composed of acrylic ester copolymers, and
The present invention provides a pressure-sensitive adhesive that has excellent adhesive strength and moisture resistance to films, molded articles, etc. made of polyolefins such as polypropylene and polybutadiene. The pressure-sensitive adhesive obtained by the present invention can be said to be an extremely promising pressure-sensitive adhesive in view of resource saving, non-pollution, safety, hygiene, and the current situation where the number of adhered objects made of polyolefins is increasing. . The present invention was developed in view of these current circumstances and demands, and was completed as a result of intensive research. That is, the present invention provides one or more acrylic acid alkyl esters having an alkyl group having 4 to 12 carbon atoms (a) 60 to 90 parts by weight, α, β-unsaturated carboxylic acid, acrylic acid having a hydroxyl group; or methacrylic acid alkyl ester, and one or more acrylamide or methacrylamide or derivatives thereof (b) 1 to 7 parts by weight, and one or two other vinyl-based or vinylidene-based copolymerizable monomers. More than 0 species
~40 parts by weight of the polyisocyanate compound (B) is added to 100 parts by weight (solid content) of an aqueous dispersion (A) obtained by emulsion polymerization using an emulsifier having a functional group that can react with isocyanate groups, and 0.1 to 1.0 parts by weight of the polyisocyanate compound (B). This invention relates to a pressure-sensitive adhesive prepared by adding parts by weight of a water-immiscible organic solvent solution and reacting at a reaction temperature and time sufficient to make residual isocyanate groups undetectable. Why does the pressure-sensitive adhesive of the present invention have excellent adhesion and overcome the biggest drawback of water-based dispersion-type pressure-sensitive adhesives, which is poor water resistance and therefore insufficient moisture-retention ability? The reason for this is still not explained theoretically. However, we believe that this is because the emulsifier, which is thought to have the most negative effect on water resistance, reacts selectively with the polyisocyanate at the interface of the water-immiscible organic solvent solution, causing the emulsifier to partially become hydrophobic. It will be done. Examples of the acrylic ester (a) having an alkyl group having 4 to 12 carbon atoms used in the present invention include linear butyl acrylate, hexyl acrylate, octyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, etc. Alternatively, acrylic acid esters of branched aliphatic alcohols can be mentioned, and two or more types can be used in combination. These monomers are effective in an amount of 60 to 99 parts by weight, preferably 80 to 95 parts by weight based on the total amount of monomers. In addition, monomers in group (b) include acrylic acid, methacrylic acid, and α- and β-unsaturated carboxylic acids.
Examples include crotonic acid, itaconic acid, maleic acid, and fumaric acid. Examples of acrylic esters or methacrylic esters containing a hydroxyl group include β-hydroxyethyl acrylate, β-hydroxypropyl acrylate, and β-methacrylic acid.
Examples of acrylamide or methacrylamide or acrylamide derivatives include N-methylolacrylamide, N-
Examples include butoxymethylacrylamide, N-butoxymethacrylamide, and the like. These monomers (b) are effective in amounts of 1 to 7 parts by weight. Other vinyl-based or vinylidene-based copolymerizable monomers (c) include acrylic acid alkyl esters having an alkyl group having 3 or less carbon atoms, such as methyl acrylate, ethyl acrylate, propyl acrylate, etc. There are 1 to 12 methacrylic acid esters, such as methyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, etc., and vinyl acetate, styrene, vinyltoluene, acrylonitrile, etc. Body (c) can be copolymerized if necessary. In the present invention, functional groups that can react with isocyanate groups include hydroxyl groups, carboxyl groups, amino groups, imino groups, and ammonium salts of sulfonic acid groups. Examples of emulsifiers having such functional groups include alkylbenzene sulfonates. Anionic emulsifiers such as ammonium salts of alkyl diphenyl ether disulfonates, ammonium salts of polyoxyethylene alkyl phenyl sulfates, ammonium salts of higher alcohol sulfates, polyoxyethylene alkyl ethers, polyoxy Ethylene alkyl phenyl ether, polyoxyethylene alkylamine, sorbitan laurate, sorbitan palmitate, sorbitan stearate,
Nonionic emulsifiers such as sorbitan oleate, polyoxyethylene sorbitan laurate, and polyoxyethylene sorbitan palmitate. The above emulsifiers can also be used in combination, and are used in an amount of 0.5 to 10% by weight based on the solid content of the aqueous dispersion. In addition, the above emulsifier is an essential component, and other emulsifiers such as
Sodium salt of alkylbenzene sulfonate,
Sodium salt of dialkyl sulfosuccinate,
Emulsifiers such as sodium salts of oxyalkyl phenyl ether sulfates can also be used to the extent that the effects of the present invention are not prevented. As polymerization initiators, persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate, persulfuric acid or hydrogen peroxide, and peroxides such as cumene hydroperoxide are used. Polymerization can also be carried out by redox reaction using a reducing agent such as sodium thiosulfate, ethylsorbic acid, or ferrous ammonium sulfate. Examples of the polyisocyanate compound (B) used in the present invention include aromatic diisocyanate compounds such as tolylene diisocyanate, xylene diisocyanate, and methylene bisdiphenyl isocyanate, and aliphatic or alicyclic diisocyanate compounds such as hexamethylene diisocyanate and isophorone diisocyanate. , and adducts of compounds having hydroxyl groups such as trimethylolpropane with diisocyanate compounds.These polyisocyanate compounds (B)
The appropriate amount to be used is 0.1 to 1.0 parts by weight per 100 parts by weight (solid content) of the aqueous dispersion (A) obtained as described above. If it is less than 0.1 part by weight, no improvement in moisture resistance can be expected, and if it is more than 1.0 part by weight, no significant improvement in moisture resistance can be expected, and at the same time, lumps will form in the aqueous dispersion, which may cause pressure-sensitive adhesives to deteriorate. This has the disadvantage of significantly impairing workability in the filtration process that is carried out after preparing the agent. Examples of water-immiscible organic solvents include aliphatic solvents such as ethyl acetate, methyl ethyl ketone, and methyl isobutyl ketone, and aromatic solvents such as benzene, xylene, and toluene. ie, 1 to 99% by weight, preferably 25 to 75% by weight, based on the polyisocyanate compound (B). When the polyisocyanate compound (B) is added alone to the aqueous dispersion (A), the polyisocyanate compound
(B) is consumed first by reaction with water,
As a result, lumps occur or the desired moisture resistance cannot be obtained. Therefore, in the present invention, since the polyisocyanate compound (B) is added as a solution in a water-immiscible organic solvent, the polyisocyanate compound (B) is selectively reacted with an emulsifier having a functional group that reacts with an isocyanate group at the interface thereof, thereby forming a pressure-sensitive adhesive. It is thought that it exhibits excellent properties as a drug. The reaction conditions for the aqueous dispersion (A) and the polyisocyanate compound (B) are 5°C or higher and 100°C or lower,
At temperatures below 5°C, the reaction is extremely slow and takes a long time. Further, at a temperature around 100° C., foaming is significant, the reaction is non-uniform, and coarse particles are formed, which is not a preferable condition. Particularly preferred reaction temperature is 10-75
It is ℃. There is no limit to the reaction time, but it is usually 1 minute to 3 minutes.
The time, particularly at a preferred temperature, is about 5 minutes to 2 hours. Pigments, plasticizers, tackifiers, protective colloids, thickeners, emulsifiers, antifoaming agents, preservatives, antifungal agents, PH regulators, and the like can be added to the pressure-sensitive adhesive of the present invention. In particular, when applying an aqueous dispersion type pressure sensitive adhesive, it is necessary to increase the viscosity to about 6,000 to 20,000 cps. In this case, useful thickeners include polyacrylates, celluloses, polyvinyl alcohol, and the like. Supports to which the pressure-sensitive adhesive of the present invention is applied include papers such as wood-free paper, art paper, coated paper, foil paper, and kraft paper, films such as polyester, acetate, and polyvinyl chloride, or composite laminates thereof. can be mentioned. As described above, the adhesive strength of the present invention has been greatly improved, especially in terms of moisture resistance, and since it is a so-called one-component type in which isocyanate groups have been completely consumed, it is easy to use and, of course, has extremely excellent storage stability. and there is little variation. This will be explained in more detail below using Examples and Comparative Examples. In the examples, "parts" and "%" are parts by weight, respectively.
Indicates weight %. Example 1 Two parts of ammonium salt of polyoxyethylene alkyl phenyl ether sulfate and polyoxyethylene alkyl phenyl ether were placed in a four-neck flask equipped with a reflux condenser, a thermometer, a nitrogen gas inlet, a dropping funnel, and a stirrer. After preparing a solution of 2 parts dissolved in 100 parts of ion-exchanged water and adding 3 parts of a 10% aqueous solution of ammonium persulfate, a solution consisting of 80 parts of 2-ethylhexyl acrylate, 17 parts of butyl acrylate, and 3 parts of acrylic acid was prepared. Initially 10 parts of the saturated monomer mixture were added dropwise under stirring and allowed to react at 70-80°C. Next, add the remaining 90 parts of the unsaturated monomer to
It was added dropwise for 180 minutes, and after the completion of the addition, stirring was continued for 120 minutes at 85°C to obtain an aqueous dispersion. Add 50% of hexamethylene diisocyanate to the aqueous dispersion obtained by the above method under stirring at 30 °C.
After dropping 1 part of toluene solution and reacting for 120 minutes,
Filtration was performed using a 120 mesh filter cloth to obtain a pressure-sensitive adhesive composition of the present invention. After applying this composition to paper and drying it, a test piece was prepared and the adhesion strength to a stainless steel plate was measured at 40℃ and relative humidity.
Adhesion retention at 65% and ball tack by J. Dow method were measured. The results are shown in Table 1. Example 2 5 parts of ammonium salt of dialkyl sulfosuccinate was used in place of the emulsifier used in Example 1, and 2 parts of acrylic acid was used as the unsaturated monomer mixture.
-Pressure-sensitive adhesive was prepared by the same procedure as in Example 1, except that 40 parts of ethylhexyl, 5 parts of vinyl acetate, and 5 parts of β-hydroxyethyl methacrylate were used, and methylene bisdiphenyl isocyanate was used instead of hexamethylene diisocyanate. A drug composition was obtained. Table 1 shows the measured values of test pieces prepared in the same manner as in Example 1. Comparative Example 1 A pressure-sensitive adhesive was prepared in the same manner as in Example 1, except that a 50% toluene solution of hexamethylene diisocyanate was added in twice the amount used in Example 1 to the aqueous dispersion obtained by the same operation as in Example 1. A composition was obtained. Table 1 shows the measured values of test pieces prepared in the same manner as in Example 1. Comparative Example 2 To the aqueous dispersion obtained by the same operation as in Example 2, 50% of methylene bisdiphenyl isocyanate was added.
A pressure-sensitive adhesive composition was obtained in the same manner as in Example 2, except that 1/10 the amount of the % toluene solution used in Example 1 was used. Table 1 shows the measured values of test pieces prepared in the same manner as in Example 1. Comparative Example 3 An aqueous dispersion obtained by the same procedure as in Example 1 was used as a pressure-sensitive adhesive without using an isocyanate compound. Table 1 shows the measured values of test pieces prepared in the same manner as in Example 1. Adhesion strength of the pressure-sensitive adhesives obtained in Examples 1 and 2 and Comparative Examples 1 to 3 to stainless steel plate, adhesive retention strength at 40°C and 65% relative humidity, J.
Ball tack was measured using the Dow method and the results are shown in Table 1. As is clear from Table 1, the pressure sensitive adhesive of the present invention has excellent performance in humidification retention and has a good balance between adhesive strength and adhesive strength. 【table】

Claims (1)

[Claims] 1 One or more acrylic acid alkyl esters having an alkyl group having 4 to 12 carbon atoms (a) 60
~90 parts by weight of an α,β-unsaturated carboxylic acid, an acrylic or methacrylic alkyl ester having a hydroxyl group, and one of acrylamide or methacrylamide or a derivative thereof
1 to 7 parts by weight of the species or two or more (b) and 0 to 40 parts by weight of one or more of the other vinyl-based or vinylidene-based copolymerizable monomers as functional groups capable of reacting with isocyanate groups. Aqueous dispersion (A) obtained by emulsion polymerization using an emulsifier having
To 100 parts by weight (solid content), 0.1 to 1.0 parts by weight of polyisocyanate compound (B) in a water-immiscible organic solvent is added, and the mixture is reacted under sufficient reaction conditions such that no residual isocyanate groups are detected. Pressure adhesive.