JPH08218047A - Aqueous dispersion-type acrylic adhesive composition and production of adhesive product - Google Patents

Abstract

PURPOSE: To provide an aqueous dispersion-type acrylic adhesive composition excellent in high-speed coating performance, and to provide the production method of an adhesive product with high productivity. CONSTITUTION: This composition consists of an emulsion of an acrylic copolymer with a (meth)acrylic alkyl ester as the chief constituent, having the following characteristics: (a) solid content: >=50wt.%; (b) the average diameter of copolymer particles in the emulsion: >=0.2μm; and (c) the viscosity at a shear rate of 1.0×0<5> s<-1> : >=20cps. The other objective adhesive product is obtained by coating a substrate with this composition at a coating rate of 300-700m/min. This composition is suitable for high-speed coating operation, easily giving a coated surface of excellent smoothness by high-speed coating operation without developing cissings and/or contractions even in the case that the substrate to be used is a release paper subject to such phenomena. Using this composition, the other objective product can be obtained in markedly higher productivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-dispersible acrylic pressure-sensitive adhesive composition composed of an acrylic copolymer emulsion, which is suitable as a pressure-sensitive adhesive in pressure-sensitive adhesive products such as pressure-sensitive adhesive labels and pressure-sensitive adhesive tapes. The present invention relates to a method for producing a pressure-sensitive adhesive product, and particularly to a water-dispersible pressure-sensitive adhesive composition suitable for high-speed coating work and a method for producing a pressure-sensitive adhesive product with improved productivity.

[0002]

2. Description of the Related Art Currently, there are natural rubber-based, synthetic rubber-based and acrylic ester-based adhesives. These adhesives are applied to a base material and used in a wide variety of applications such as adhesive labels and adhesive tapes. Is used for. Among the above-mentioned pressure-sensitive adhesives, a water-based pressure-sensitive adhesive composition using an acrylic copolymer emulsion containing (meth) acrylic acid alkyl ester as a main component of a monomer is excellent in tackiness and weather resistance, By changing the body composition, a wide range of adhesive properties can be imparted, and the solid content and the average particle diameter of the copolymer particles can be varied over a wide range, depending on the application and coating equipment. Since it does not use an organic solvent, it has been widely used in many adhesive products in recent years.

A water-based pressure-sensitive adhesive composed of an acrylic copolymer emulsion is an excellent product as described above, but it has been conventionally applied to a substrate at a relatively low application speed. In order to improve the productivity of the adhesive product and reduce the manufacturing cost, the coating speed may be increased. However,
When the coating speed is increased, the shearing stress applied to the adhesive also increases, which causes a problem that a good coated surface cannot be obtained. For example, the problem that a good coating surface cannot be obtained due to the generation of aggregates of emulsion due to shear stress or the generation of bubbles in the coating bank,
In addition, the faster the coating speed, the more difficult it is to obtain a smooth coated surface, and the adhesive requires higher leveling properties.

In order to solve this problem, a shear rate of 0.5 × 10 ⁵ (1 / s) is applied to an aqueous pressure-sensitive adhesive composition.
It has been proposed that the viscosity in the above case be 75 cps or less (Japanese Patent Laid-Open No. 3-227387). If this condition is satisfied, the shearing stress applied to the adhesive during high-speed coating will be reduced, and the problem of aggregates and bubbles will be improved, but with regard to the leveling property, all that satisfy this condition are excellent. However, it has become clear that a smooth coated surface may not be obtained in some cases. Further, if the viscosity at the time of coating is too low, there is a problem that cissing or bleeding occurs on the coated surface. In particular, an adhesive product produced by applying a pressure-sensitive adhesive to a base material having a release material such as silicon on its surface is likely to cause cissing and bleeding. Further, if the viscosity is greatly reduced at a high shear rate, the leveling property is generally poor and a smooth coated surface cannot be obtained.

As another means for solving the problem caused by high shear stress at the time of high-speed coating, as for the problem of agglomerate generation, by adding an additive for improving the mechanical stability of the emulsion and generation of bubbles. Are solved by selecting a coating method such as using a slot die coater. However, even at the time of high speed coating, there is no cissing and blemishes, and a means for obtaining a smoother coated surface is not clear.

[0006]

DISCLOSURE OF THE INVENTION The present invention is suitable for high-speed coating in which a large shear stress is applied to the pressure-sensitive adhesive, and particularly in high-speed coating on a release-treated substrate which is apt to cause cissing and bleeding. Another object of the present invention is to provide a water-dispersed acrylic pressure-sensitive adhesive composition that is free from cissing and scratches and that provides a smooth coated surface, and a method for producing an adhesive product using the same.

[0007]

Means for Solving the Problems The inventors of the present invention have made extensive studies as a solution to the above problems, and as a result, the solid content, the average particle diameter of polymer particles, and the viscosity at a high shear rate have specific values. It was found that the water-dispersible acrylic pressure-sensitive adhesive composition possessed had excellent coatability and could solve each problem, and completed the present invention.

That is, the first invention relating to this patent application consists of an emulsion of an acrylic copolymer containing (meth) acrylic acid alkyl ester as a main component,
(A) The solid content is 50% by weight or more, (b) the average particle diameter of the copolymer particles constituting the emulsion is 0.2 μm or more, and (c) the shear rate is 1.0 × 10 ⁵ (1 /
A water-dispersible acrylic pressure-sensitive adhesive composition having a flow characteristic that the viscosity in s) is 20 cps or more.

A second invention related to this patent application is the above specific water-dispersed acrylic pressure-sensitive adhesive composition.
A method for producing a pressure-sensitive adhesive product, which comprises coating the base material at a coating speed of 300 to 700 m / min.

The emulsion of the acrylic copolymer in the pressure-sensitive adhesive composition of the present invention is a radical emulsion polymerization of a monomer mixture containing an alkyl (meth) acrylate as a main component in an aqueous medium by a known method. By
Easy to manufacture. In the emulsion polymerization, a chain transfer agent or a plasticizer may be added if necessary. Examples of the (meth) acrylic acid alkyl ester which is the main component of the monomer in the above copolymer include methyl (meth) acrylate,
Ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate,
Hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate,
Examples include n-octyl (meth) acrylate, isooctyl (meth) acrylate, n-nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, and lauryl (meth) acrylate. ,
Among them, (meth) acrylic acid alkyl ester having an alkyl group having 4 to 9 carbon atoms is particularly preferable.

A typical example of the other monomer copolymerized with the (meth) acrylic acid alkyl ester is a vinyl monomer, and specific examples thereof include (meth) acrylonitrile and α.
-Vinyl monomers containing cyano group such as chloro (meth) acrylonitrile; vinyl aromatic monomers such as styrene, α-methylstyrene, vinyltoluene; (meth) acrylic acid, crotonic acid, cinnamic acid, itaconic acid Unsaturated carboxylic acids such as fumaric acid and maleic acid; monoalkyl esters of unsaturated dicarboxylic acids such as itaconic acid monoethyl ester, fumaric acid monobutyl ester, maleic acid monobutyl ester; (meth) acrylic acid 2-hydroxyethyl ester , 2-hydroxybutyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, glycerol (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol Mono (meta) acryl And hydroxyl group-containing vinyl monomers such as polyethylene glycol-polypropylene glycol mono (meth) acrylate; ethylenically unsaturated carboxylic acid amides such as acrylamide, methacrylamide, N-methylolacrylamide and N-substituted compounds thereof; There are saturated alcohols, and in addition, glycidyl (meth) acrylate, vinyl acetate, vinyl chloride, vinylidene chloride and the like can be used as the copolymerization monomer.

The above acrylic copolymer has a functional monomer unit having a functional group such as a carboxyl group, a hydroxyl group, an amide group or an epoxy group, based on the total amount of all monomer units. % Or less, more preferably 1 to 7% by weight
It is preferable to contain it in a ratio of. The presence of these functional groups in the acrylic copolymer is useful from the viewpoint of adhesive performance, and at the same time, the effect of improving the aggregation stability of the copolymer emulsion can be expected. When the proportion of the functional monomer unit is more than 10% by weight, the glass transition temperature of the obtained copolymer becomes high, and as a result, the tackiness of the pressure-sensitive adhesive composition tends to be lowered.

In order to improve the stability of the copolymer emulsion obtained by polymerization, alkali neutralization, for example, neutralization with aqueous ammonia can be performed according to a conventional method, and the desired water-dispersed acrylic type emulsion can be used. In order to impart the required physical properties and performance to the pressure-sensitive adhesive composition, a compounding agent of the type and amount used in the field of pressure-sensitive adhesives may be added, if necessary. Examples of the compounding agent that can be added include thickeners, mechanical stability imparting agents, tackifiers, leveling agents, cross-linking agents, preservatives, rust preventives, pigments, fillers, antifreezing agents, high-boiling solvents or deodorants. There are foaming agents.

The solid content in the water-dispersible acrylic pressure-sensitive adhesive composition of the present invention is controlled by controlling the quantitative ratio of the monomer and water used in the emulsion polymerization during the production of the acrylic copolymer emulsion. It is possible to freely change the composition by appropriately setting the type and amount of the compounding agent added to the emulsion after production. If the composition is the same, the lower the solid content, the lower the viscosity of the composition.

In order to facilitate the handling work of the pressure-sensitive adhesive composition, it is common practice to add a modified polyacrylate or a cellulose derivative to increase the viscosity at a low shear rate. However, even in such a case, if the solid content concentration itself is too low, the decrease in viscosity under a high shear rate becomes large. On the other hand, the pressure-sensitive adhesive composition, which has a large decrease in viscosity at a high shear rate as compared to a viscosity at a low shear rate, has poor leveling properties and a smooth coated surface cannot be obtained. Further, if the solid content is low, the energy required for drying also becomes large. Therefore, the lower the solid content, the more difficult the coating operation at high speed. For these reasons, the solid content in the water-dispersible acrylic pressure-sensitive adhesive composition of the present invention must be 50% by weight or more. The upper limit of the solid content is not specified, but about 80% by weight is the limit as an emulsion.

The average particle size of the copolymer particles constituting the acrylic copolymer emulsion can be freely changed by controlling the type of emulsifier in the emulsion polymerization, the amount used, the polymerization initiation conditions and the like. . Even if the emulsions have the same composition and the same viscosity at a low shear rate, the smaller the particle size, the greater the decrease in viscosity at a high shear rate, and the poorer the leveling property of the pressure-sensitive adhesive composition. Further, even with the same amount of emulsifier, the smaller the particle size, the worse the mechanical stability of the copolymer emulsion, and the more likely it is that aggregates will form during the application of the pressure-sensitive adhesive composition. Thus, if the average particle diameter of the copolymer particles is too small, it becomes difficult to obtain a good coated surface during high-speed coating, so the average particle diameter of the copolymer particles constituting the emulsion is At 0.2 μm or more.
The preferable upper limit of this average particle size is 2.0 μm, and if it exceeds this range, the copolymer particles may precipitate with time.

Further, in a water-dispersed PSA composition having a viscosity that is too low at a high shear rate, cissing and blemishes occur on the coated surface. In particular, for high-speed coating on a substrate treated with a release material, if the viscosity at the shear rate during coating is too low, cissing and bleeding will be large, and adhesive products that are practically required. Can't get Therefore, the water-dispersed acrylic pressure-sensitive adhesive composition of the present invention has a shear rate of 1.0 × 1.
It must have flow characteristics such that the viscosity at 0 ⁵ (1 / s) is 20 cps or more. The preferable upper limit of this viscosity is 200 cps from the viewpoint of coating performance and other practical uses.

In the method for producing a pressure-sensitive adhesive product according to the present invention, the coating operation of the pressure-sensitive adhesive composition can be easily performed by a coating machine such as a reverse roll coater or a slit die coater. According to the findings obtained by the present inventors,
The pressure-sensitive adhesive composition of the present invention is most suitable for high speed coating of 300 to 700 m / min. If the coating speed is lower than 300 m / min, the coating performance of the pressure-sensitive adhesive composition of the present invention cannot be fully utilized, while if the coating speed is higher than 700 m / min, the pressure-sensitive adhesive composition cannot be used. The emulsion constituting the composition is destroyed, which causes the disadvantage of forming aggregates. A more preferable coating speed is 450 to 550 m / min.

According to the present invention, a good coated surface can be easily obtained by high-speed coating, and even if the base material is treated with a release material, there is no cissing or blemishes and smoothness. Also, an excellent coated surface can be obtained.

[0020]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below. Parts in each example are parts by weight,
Further,% means% by weight. Moreover, the amount of the emulsifier used is an amount calculated as pure content. Furthermore, each physical property value was measured by the following methods. 1 Solid content According to JIS-K6833, weighed after drying at 107 ° C. for 3 hours. (Unit:%) 2 Average particle diameter A laser diffraction / scattering particle size distribution measuring apparatus LA-910 manufactured by Horiba Ltd. is used to measure a volume-based median diameter. 3 Viscosity under high shear rate (unit: cps) Made by Rigaku Kumagai, HI-SHEAR VISCOMTER
HERCULESTYPE MODEL HR-80
Measured using 1C. Rotation speed 0-8800 rpm, measurement temperature 20 ° C

The monomers used in each example are represented by the following abbreviations. 2-ethylhexyl acrylate ... HA butyl acrylate ... BA methyl methacrylate ... MMA dodecyl mercaptan ... DM N-methylol acrylamide ... N-MAM acrylic acid ... AA methacrylic acid ...・ MAA

Example 1 80 parts HA, 20 parts MMA, 0.1 parts DM, N-MAM
A pre-emulsion was prepared by adding 1.5 parts of sodium polyoxyethylene alkylphenyl ether sulfate (using ReoNol WZ, trade name of Kao Corporation) and 27 parts of water to 0.1 part and 2.0 parts of AA. A reactor equipped with a reflux condenser, a thermometer, and a stirrer was charged with 33 parts of water, the inside of the reactor was replaced with nitrogen, the temperature was raised to 80 ° C., 0.5 part of ammonium persulfate was added, and then the above-mentioned pre-treatment was performed. Polymerization was initiated by adding 0.2% by weight of the total amount of the emulsion. After confirming the start of polymerization, the rest of the pre-emulsion (99.8 wt% of the total amount) was continuously added dropwise over 4 hours at a temperature of 79 to 81 ° C. After the continuous addition of the pre-emulsion was completed, 1.0 part of a 10 wt% ammonium persulfate aqueous solution was added, and the reaction was further maintained at 80 ° C. for 2 hours.

The acrylic copolymer emulsion obtained above was neutralized with 25% by weight aqueous ammonia, and an acrylic thickener (using B-300 manufactured by Toagosei Co., Ltd.) was added to give an adhesive composition. An agent composition was produced. In addition,
The amount of the thickener used is the B-type viscosity (JIS-
According to K6833, using a BM type rotational viscometer, rotor No. (Measured at 4 and 12 rpm) was 8000 cps. The nonvolatile content of this adhesive composition is 60.9.
%, Average particle size 1.02 μm, shear rate 1.0 × 1
The viscosity at 0 ⁵ [1 / s] was 55 cps. A release paper surface-treated with a silicone-based release material was coated with the above-mentioned pressure-sensitive adhesive composition at a speed of 500 m / min using a slot die coater, and the state of the obtained coated surface was observed. ,
There were no streaks, cissing, and streaks, and the smoothness of the coated surface was good.

Examples 2 to 3 and Comparative Examples 1 to 3 Example 1 except that the initial amount of water charged, the composition of the pre-emulsion and the amount of pre-emulsion used at the start of polymerization in Example 1 were changed as shown in Table 1. The same reaction operation and post-treatment were performed, and the obtained adhesive composition was evaluated for physical properties and coating performance in the same manner as in Example 1. The results are shown in Table 1 together with the results of Example 1. In addition, Emal 2F shown in Table 1 is a product of Kao Corporation, sodium lauryl sulfate, and viscosity [cps] is a value at a shear rate of 1.0 × 10 ⁵ [1 / s].

[0025]

[Table 1]

[0026]

The pressure-sensitive adhesive composition of the present invention is excellent in coating performance and suitable for high-speed coating, and does not cause streaks, cissing or streaks during high-speed coating, and has excellent smoothness. The work surface can be obtained. In particular, even when the surface is treated with a release material and the base material is a release paper that easily causes cissing and bleeding, high-speed coating can provide a good coated surface without cissing and bleeding. Further, according to the method for producing an adhesive product of the present invention, it is possible to easily produce an adhesive product having an adhesive performance equivalent to that of an adhesive product obtained at a conventional coating speed at a higher coating speed than before. Therefore, it is possible to significantly improve the productivity of the adhesive product.

Claims (2)

[Claims] 1. A copolymer particle comprising an acrylic copolymer emulsion containing (meth) acrylic acid alkyl ester as a main component, wherein (a) the solid content is 50% by weight or more, and (b) the copolymer particles constituting the emulsion. A water-dispersible acrylic pressure-sensitive adhesive composition having an average particle diameter of 0.2 μm or more, and (c) a flow characteristic that the viscosity at a shear rate of 1.0 × 10 ⁵ (1 / s) is 20 cps or more. Stuff. 2. The pressure-sensitive adhesive composition according to claim 1,
A method for producing an adhesive product, which comprises applying to a substrate at a coating speed of 700 m / min.