JP2005232335A - Aqueous emulsion type adhesive and adhesive sheet using the same adhesive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an adhesive not enlarging retaining force (cohesive force) before and after long-period storage and not lowering adhesive force even when using an acid-free paper sheet as a surface substrate of an adhesive sheet. <P>SOLUTION: The aqueous emulsion type adhesive comprises an aqueous dispersion of a resin composition containing (A) a copolymer formed of a polymerizable monomer (a) containing an aqueous medium and a (meth)acrylic acid alkyl ester having a 1-13C alkyl chain as essential components and not containing a polymerizable unsaturated carboxylic acid and (B) a copolymer formed of (b) a polymerizable monomer containing a (meth)acrylic acid alkyl ester having a 1-13C alkyl chain and 5-25 wt.% polymerizable unsaturated carboxylic acid as essential components in a weight ratio (A)/(B) of (7/3) to (9/1). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is a copolymer formed from a polymerizable monomer containing no polymerizable unsaturated carboxylic acid, a copolymer formed from a polymerizable monomer having a polymerizable unsaturated carboxylic acid as an essential component, And an aqueous emulsion-type pressure-sensitive adhesive containing a resin aqueous dispersion containing an aqueous medium, a pressure-sensitive adhesive sheet using the aqueous emulsion-type pressure-sensitive adhesive, and a method for producing the same.

As an adhesive sheet, the structure by which the adhesive layer was pinched | interposed between the surface base material and the peelable sheet is generally known. As the surface base material, plastic film, synthetic paper, paper, metal foil or the like is used. Adhesive sheets that use paper substrates, which are the mainstream, are widely used for food and product distribution management labels, delivery address labeling labels, copy forms and other forms printing materials, and adhesive tapes. .
In addition, if the adhesive sheet said to this invention is an above-described structure, it includes both the thing which wound the elongate thing in the roll shape, and the thing of a single wafer state.

Conventionally, the paper used for the base material of the pressure-sensitive adhesive sheet has been mainly paper made by acidic paper making using aluminum sulfate for fixing the solvent-type rosin sizing agent (hereinafter referred to as acidic paper). However, since aluminum sulfate shows weak acidity, there is a problem that the paper, which is the main component of the fiber, is hydrolyzed and the paper deteriorates over time.
Therefore, recently, papers made using neutral sizing agents such as AKD (alkyl ketene dimer) and ASA (alkenyl succinic anhydride) (hereinafter referred to as neutral paper) have been widely used in consideration of storage stability. ing.
By the way, calcium carbonate is easy to control the particle size, particle size distribution, and particle shape, has high whiteness and opacity, and is low in cost. However, since it dissolves under acidic conditions, it has not been used in conventional acidic paper. In the case of neutral paper, such calcium carbonate can be used as a filler.

In addition, recycled paper containing recycled paper as a raw material has been widely distributed as printing paper and copying paper to increase awareness of environmental issues and protect forest resources. When making these recycled papers, the waste paper raw material contains a very large amount of neutral paper containing calcium carbonate.
However, as described above, since calcium carbonate dissolves under acidic conditions, acidic papermaking cannot be performed. Accordingly, papermaking of recycled paper is inevitably neutral papermaking, and the proportion of neutral paper in the entire paper is increasing.

  Even in the pressure-sensitive adhesive sheet, conversion from acidic paper to neutral paper is unavoidable as the surface base material, and in particular, recycled paper = neutral paper can be used as the base material of the surface base material or the release sheet. It is necessary.

However, when the neutral paper containing calcium carbonate is used as the base material of the surface base material or the peelable sheet for the acrylic pressure-sensitive adhesive containing a carboxyl group, the pressure-sensitive adhesive sheet before being attached to the adherend During the storage, and after sticking to the adherend, the cohesive force of the pressure-sensitive adhesive layer increases over time, and the adhesive strength is greatly reduced compared to the case of using acid paper. . It is considered that the cause is that the pressure-sensitive adhesive polymer is crosslinked by the reaction of the carboxyl group in the acrylic pressure-sensitive adhesive and the calcium ion of calcium carbonate.
Such an adverse effect on the adhesive properties (hereinafter also referred to as neutral paper deterioration) due to the neutral paper is noticeable when a laminate of the neutral paper / adhesive layer is stored under high temperature and high humidity.
There are two types of releasable sheets, one based on paper and the other based on a plastic sheet, each having a hard-to-adhere peelable layer on at least one surface. That is, the pressure-sensitive adhesive sheet is basically composed of a base material / peelable layer / pressure-sensitive adhesive layer / surface base material of a peelable sheet. Even if neutral paper is used as the base material of the peelable sheet, the pressure-sensitive adhesive layer does not directly contact the neutral paper of the base material of the peelable sheet. However, the conventional pressure-sensitive adhesive having a carboxyl group gradually reacts with calcium in the neutral paper through the peelable layer.

Patent Document 1 (Japanese Patent Laid-Open No. 2002-338909) discloses a pressure-sensitive adhesive sheet obtained by sequentially laminating a surface base material containing a calcium component in a paper layer, a pressure-sensitive adhesive layer mainly composed of an acrylic copolymer, and a release sheet. Describes a pressure-sensitive adhesive sheet in which the calcium component in the surface substrate and the carboxylic acid component of the acrylic copolymer in the pressure-sensitive adhesive layer are suppressed from being ionized. And as an ionization suppression means, the means shown in following (1)-(3) etc. are specifically disclosed.
(1) The number of carboxyl groups that cause crosslinking is reduced as much as possible.
(2) The pressure-sensitive adhesive contains potassium sulfate, potassium pyrophosphate, and the like as a source of potassium ions that have a greater ionization tendency than calcium ions and are more likely to react with carboxylic acid than calcium ions.
(3) A chelating agent such as an ammonium salt of EDTA (ethylenediaminetetraacetic acid) is contained in the adhesive.

  The method (1) is the most direct and effective method. However, in both solvent-type and aqueous pressure-sensitive adhesives, the carboxyl group is an indispensable functional group for ensuring the holding power (cohesive force) of the pressure-sensitive adhesive layer. In particular, when an aqueous dispersion of a polymer obtained by emulsion polymerization of a (meth) acrylic monomer in an aqueous medium is used as a main component, emulsion polymerization is attempted without using any monomer having a carboxyl group. Stability is extremely poor, and a lot of bumps are generated. Even if the irregularities are separated, the viscosity of the pressure-sensitive adhesive changes greatly with time. Furthermore, the performance as an adhesive is extremely insufficient.

That is, it can be obtained by controlling the amount of the polymerization initiator, the amount of the chain transfer agent, etc. in the case where no monomer having a carboxyl group is used or only a very small amount of at most about 1% by weight or less is used. When the molecular weight of the polymer is reduced, the pressure-sensitive adhesive layer has a small holding force (cohesive force) and is in a solid state without so-called stiffness.
Such an adhesive sheet with an adhesive layer apparently exhibits a certain level of adhesive strength (adhesive strength), but adheres to the adherend when the adhesive sheet is peeled off from the adherend due to its low holding power (cohesive strength). The so-called “glue residue” phenomenon, in which the agent layer remains, becomes prominent. That is, the basic performance required for the pressure-sensitive adhesive is not satisfied.

  In addition, in the case where only a very small amount of a monomer having a carboxyl group is used at most of about 1% by weight or less, by controlling the amount of the polymerization initiator, the amount of the chain transfer agent, etc., the molecular weight of the polymer is increased, It is possible to increase the holding force (cohesive force) and suppress the adhesive residue phenomenon to some extent. However, in this case, it is extremely difficult to suppress the adverse effect of the neutral paper on the adhesive properties. That is, when neutral paper is used as the surface base material, the retention strength (cohesive force) is significantly increased after storage under high temperature and high humidity compared to after storage in a normal state, while the adhesive strength (adhesive strength) is increased. descend.

  Further, potassium is more easily ionized than calcium, and the generated potassium ion does not form a crosslinked structure with a carboxyl group, unlike calcium ion. Moreover, since the calcium ions form a hardly soluble salt with the carboxyl group, the crosslinking reaction is irreversible. Therefore, even if potassium sulfate, potassium pyrophosphate, or the like is contained in the pressure-sensitive adhesive as in the method (2) above, crosslinking of calcium ions will eventually occur.

The method (3) is effective as a countermeasure against deterioration of neutral paper, but on the other hand, when a metal ion sequestering agent is added to the pressure-sensitive adhesive, the viscosity of the pressure-sensitive adhesive is lowered and the coating property is ensured. It becomes difficult.
JP 2002-338909 A

  The present invention solves the problems of the prior art, and even when neutral paper is used as a surface base material, the pressure-sensitive adhesive sheet does not decrease in adhesive strength (adhesive strength) and holding strength (cohesive strength) over time. It aims at providing the adhesive which can form.

The present invention comprises an aqueous medium and a polymerizable monomer (a) containing an alkyl chain alkyl ester having 1 to 13 carbon atoms as an essential component and not containing a polymerizable unsaturated carboxylic acid. Polymerizable monomer comprising copolymer (A) to be formed, alkyl chain (meth) acrylic acid alkyl ester having 1 to 13 carbon atoms and 5 to 25% by weight of polymerizable unsaturated carboxylic acid as essential components Containing the copolymer (B) formed from (b) and containing the copolymers (A) and (B) in a weight ratio of (A) / (B) = 7/3 to 9/1. An aqueous emulsion-type pressure-sensitive adhesive containing an aqueous dispersion of a resin composition,
Furthermore, this invention relates to the water-based emulsion type adhesive as described in the said invention whose glass transition temperature of a copolymer (A) is -80--20 degreeC.

Moreover, this invention is from the polymerizable monomer (b) which contains the C1-C13 (meth) acrylic-acid alkylester of an alkyl chain, and 5-25 weight% of polymerizable unsaturated carboxylic acid as an essential component. In the presence of the copolymer (B) to be formed, a polymerizable monomer containing an alkyl chain (meth) acrylic acid alkyl ester having 1 to 13 carbon atoms as an essential component and not containing a polymerizable unsaturated carboxylic acid. An aqueous emulsion-type pressure-sensitive adhesive containing an aqueous dispersion of a resin composition obtained by polymerizing a monomer (a) in a weight ratio of (a) / (B) = 7/3 to 9/1;
Furthermore, this invention can be formed from the polymerizable monomer (a) which contains the C1-C13 (meth) acrylic-acid alkylester of an alkyl chain as an essential component, and does not contain polymerizable unsaturated carboxylic acid. It is related with the water-based emulsion type adhesive as described in the said invention whose glass transition temperature of a copolymer is -80--20 degreeC.

  Furthermore, this invention relates to the water-based emulsion-type adhesive in any one of the said invention whose weight average molecular weights of a copolymer (B) are 1000-20000.

  Furthermore, this invention contains the copolymer (A) and the C1-C13 (meth) acrylic-acid alkylester of an alkyl chain as an essential component, and the polymerizable monomer which does not contain polymerizable unsaturated carboxylic acid The glass transition temperature of the copolymer (A) that can be formed from (a) is -80 to -20 ° C, and the glass transition temperature of the copolymer (B) is -10 to 30 ° C. 5. The aqueous emulsion-type pressure-sensitive adhesive according to any one of 5 above.

  Furthermore, the present invention is formed from a polymerizable monomer (b) containing, as essential components, an alkyl chain alkyl ester having 1 to 13 carbon atoms (meth) acrylic acid and 1 to 25% by weight of a polymerizable unsaturated carboxylic acid. In the presence of the copolymer (B), an alkyl chain (meth) acrylic acid alkyl ester having 1 to 13 carbon atoms as an essential component and no polymerizable unsaturated carboxylic acid is contained. Production of aqueous dispersion of resin composition for aqueous emulsion-type pressure-sensitive adhesive, wherein body (a) is polymerized in an aqueous medium at a weight ratio of (a) / (B) = 7/3 to 9/1 Regarding the method.

  Furthermore, the present invention relates to a pressure-sensitive adhesive sheet in which a peelable sheet, a pressure-sensitive adhesive layer formed from the water-based emulsion-type pressure-sensitive adhesive according to any one of the above inventions, and a paper containing a calcium salt are sequentially laminated.

Further, according to the present invention, the water-based emulsion-type pressure-sensitive adhesive according to any one of the above inventions is coated and dried on a peelable sheet to form a pressure-sensitive adhesive layer, and a paper containing a calcium salt is formed on the pressure-sensitive adhesive layer. It is a manufacturing method of the adhesive sheet laminated by applying a pressure of -100 (N / cm < ² >).

The aqueous emulsion-type pressure-sensitive adhesive of the present invention comprises a copolymer (A) formed from a polymerizable monomer not containing a polymerizable unsaturated carboxylic acid and a specific amount of a polymerizable unsaturated carboxylic acid as essential components. By containing the copolymer (B) formed from a polymerizable monomer in a specific ratio, the adhesive as a whole, although it contains a sufficient amount of carboxyl groups for expressing adhesive properties, Since the copolymer (A) as a component does not contain a carboxyl group that causes neutral deterioration, the adhesive property is not deteriorated due to crosslinking between calcium ions in the surface base material and carboxylic acid in the adhesive.
That is, according to the present invention, it is an adhesive having excellent stability during polymerization, excellent mechanical stability as an adhesive, and stable coating properties, and adhesive properties when using a neutral surface substrate. It is now possible to obtain a pressure-sensitive adhesive sheet that can suppress and prevent the change with time.

<Copolymer (A)>, <Copolymer (B)>
The copolymer (A) and the copolymer (B) are composed of alkyl chain (meth) acrylic acid alkyl ester having 1 to 13 carbon atoms in the alkyl chain, and the copolymer (A) is not polymerizable. The saturated carboxylic acid is not used as a constituent component, and the other copolymer (B) contains a polymerizable unsaturated carboxylic acid as a constituent component, and the copolymer (B) contains a polymerizable unsaturated carboxylic acid as 5 to 5%. It is formed from 100% by weight of the polymerizable monomer (b) containing 25% by weight.

The copolymer (A) is a main component of the aqueous dispersion of the resin composition that is the main component constituting the aqueous emulsion-type pressure-sensitive adhesive of the present invention, and is a polymerizable monomer (a) that does not contain a polymerizable unsaturated carboxylic acid. ) And is mainly responsible for adhesive properties. Therefore, the glass transition temperature (hereinafter referred to as Tg) is preferably from −80 to −20 ° C., more preferably from −60 to −40 ° C. from the viewpoint of developing adhesive strength (adhesive strength). Moreover, it is preferable that molecular weight is large compared with the copolymer (B) mentioned later from the point of ensuring retention strength (cohesion force).
In conventional aqueous emulsion-type pressure-sensitive adhesives, the component responsible for the pressure-sensitive adhesive property has a carboxyl group and has a large molecular weight. Therefore, when the carboxyl group and the calcium ion derived from neutral paper react and crosslink, the molecular weight of the pressure-sensitive adhesive increases, and as a result, the holding force (cohesive force) increases and the adhesive force (adhesive force) decreases. End up.
On the other hand, the copolymer (A) constituting the aqueous emulsion-type pressure-sensitive adhesive of the present invention does not have a carboxyl group even though it is a component responsible for the pressure-sensitive adhesive properties, so that it is crosslinked by calcium ions derived from neutral paper. The adhesive properties do not change over time.

  The copolymer (B) is formed from a polymerizable monomer (b) containing 5 to 25% by weight of a polymerizable unsaturated carboxylic acid, and the copolymer (A) is converted into an aqueous medium. It is used to stably disperse in water, and has a kind of emulsifier function. Therefore, it is preferable that part or all of the carboxylic acid in the copolymer (B) is neutralized, and the amount of the basic substance used in the neutralization is preferably 30 to 120% of the theoretical equivalent.

Since the copolymer (B) has a carboxyl group, it can be crosslinked by calcium ions derived from neutral paper. Therefore, when there are many copolymers (B), the neutral paper deterioration suppression and prevention effect will become small. Moreover, since the copolymer (B) which has a carboxyl group is a component rich in hydrophilicity, when the carboxyl group derived from a copolymer (B) increases, the water resistance of an adhesive layer will fall. Furthermore, when the number of carboxyl groups derived from the copolymer (B) increases, problems such as excessive increase in the viscosity of the pressure-sensitive adhesive also occur. Therefore, it is important to make the copolymer (B) a relatively small amount relative to the copolymer (A) and to reduce the amount of carboxyl groups derived from the copolymer (B).
On the other hand, since the copolymer (B) plays a role as an emulsifier for the copolymer (A), if the amount of carboxyl groups derived from the copolymer (B) is too small, the copolymer (A) is stable in an aqueous medium. Can not be dispersed.
Therefore, it is important that the polymerizable unsaturated carboxylic acid constituting the copolymer (B) is 5 to 25% by weight, and preferably 15 to 20% by weight. Furthermore, it is important that the copolymer (A) and the copolymer (B) have a weight ratio of (A) / (B) = 7/3 to 9 // 1, and 7.5 / 2. It is preferable that it is 5-8.5 / 1.5.

Moreover, even if a copolymer (B) bridge | crosslinks with the calcium ion derived from neutral paper, in order to suppress the influence which acts on an adhesive characteristic, the one where the molecular weight of a copolymer (B) is not large is preferable. On the other hand, if the molecular weight of the copolymer (B) is too small, the adhesive properties may be adversely affected. Therefore, the weight average molecular weight (Mw) of the copolymer (B) is preferably 1000 to 20000, and more preferably 5000 to 15000.
By the way, as described in the section of the prior art, the pressure-sensitive adhesive sheet is generally in a state where a surface base material sheet, a pressure-sensitive adhesive layer, and a peelable sheet are laminated. The copolymer (B) contained in the pressure-sensitive adhesive has a lower molecular weight than that of the copolymer (A), specifically, the weight average molecular weight (Mw) is set to 1000 to 20000. It becomes easier for the polymer (B) to move closer to the surface base sheet than the copolymer (A). That is, by using the copolymer (B) having the molecular weight as described above, the copolymer (A) having a relatively large molecular weight and having a great influence on the adhesive property is placed in the vicinity of the surface base sheet (neutral paper). Before the transition, the copolymer (B) crosslinks with calcium ions in the vicinity of the interface between the surface base sheet (neutral paper) and the pressure-sensitive adhesive layer, thereby suppressing or preventing the copolymer (A) from being crosslinked. Also has the effect of.
Moreover, it is preferable that Tg of a copolymer (B) is -10-30 degreeC.
Compared to so-called solution polymerization in which the monomer and polymer are in a dissolved state, in the case of emulsion polymerization or the like in which the polymer is insoluble and forms a dispersoid, the molecular weight of the polymer formed is generally increased and the gel It is often difficult to determine the molecular weight by permutation (GPC). In the case of the present invention, it is preferable to polymerize the monomer (a) in the presence of the aqueous dispersion of the copolymer (B) to obtain an aqueous dispersion of the copolymers (A) and (B) as described later. It is difficult to specifically determine the molecular weight of the copolymer (A) formed later.

The alkyl chain (meth) acrylic acid alkyl ester having 1 to 13 carbon atoms of the alkyl chain used for forming the copolymer (A) and the copolymer (B) is a linear or branched aliphatic group having 1 to 13 carbon atoms. Acrylic esters of alcohol and the corresponding methacrylic esters, specifically, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, (meth) Examples include octyl acrylate, 2-ethylhexyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, and the like.
The (meth) acrylic acid alkyl ester is an abbreviation for acrylic acid alkyl ester or methacrylic acid alkyl ester.

  Examples of the polymerizable unsaturated carboxylic acid used for forming the copolymer (B) include acrylic acid, methacrylic acid, maleic anhydride, maleic acid, itaconic acid, and crotonic acid.

  Functional monomers that can be used to form the copolymer (A) or (B) include hydroxyl group, methylol group, amino group, amide group, glycidyl group, phosphoric acid group, sulfonic acid group, ethyleneimine And those having an isocyanate group and the like, specifically, 2-hydroxypropyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, polyethylene glycol acrylate, glycidyl acrylate Glycidyl methacrylate, mono- (2-hydroxyethyl-α-chloroacrylate) acid phosphate, vinyl isocyanate, N-methylol acrylamide, N-methylol methacrylamide, N -Methylaminoethyl acrylate, N-tributylaminoethyl acrylate, N, N-dimethylamino ester Ruacrylate, N, N-dimethylaminoethyl methacrylate, N, N-diethylaminoethyl methacrylate, acrylamide, methacrylamide, vinylpyrrolidone, acryloylmorpholine, N-vinylformamide, sulfoxyethylsodium methacrylate And vinyl sulfonic acid soda.

  Furthermore, vinyl ester, vinyl pyridine, vinyl acetate, vinyl propionate, styrene, acrylonitrile, methacrylonitrile, butadiene, chloroprene, and the like can also be used in the formation of the copolymers (A) and (B).

A resin composition aqueous dispersion as a main component of the aqueous emulsion-type pressure-sensitive adhesive of the present invention is obtained by polymerizing the polymerizable monomers (a) and (b) in an aqueous medium, respectively, and an aqueous dispersion of both copolymers. Can be obtained by mixing the two, or the monomer (b) is polymerized, and the monomer (a) is copolymerized in an aqueous medium in the presence of the obtained copolymer (B). And the aqueous dispersion containing a copolymer (A) and a copolymer (B) can also be obtained, and the latter is preferable from the point of simplicity.
There are various methods for the latter. For example, after the monomer (b) is polymerized in an organic solvent, an aqueous dispersion of the copolymer (B) is obtained, and the monomer (a) is copolymerized in the presence of the aqueous dispersion. An aqueous dispersion containing the polymer (A) and the copolymer (B) can be obtained, or the polymerizable monomer (b) is polymerized in an aqueous medium, and in the presence of the aqueous dispersion. Monomer (a) can be copolymerized to obtain an aqueous dispersion containing copolymer (A) and copolymer (B), the latter being preferred.

  As the aqueous medium, water alone or water as a main component and a hydrophilic organic solvent can be used in combination.

  In initiating the polymerization reaction in an aqueous medium, a persulfate such as potassium persulfate or ammonium persulfate, or a water-soluble thermal decomposition initiator such as an azobis cation salt or a hydroxyl adduct can be used. An initiator can be used.

  Redox initiators include combinations of organic peroxides such as t-butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide and reducing agents such as Rongalite, sodium metabisulfite, or potassium persulfate, ammonium persulfate and A combination of Rongalite and sodium thiosulfate, a combination of hydrogen peroxide and ascorbic acid, and the like are used.

  In order to control the molecular weight of the copolymers (A) and (B), a thioglycolic acid ester compound, a thioglycolic acid ester compound having a methoxy group in the side chain or a mercaptopropionic acid ester compound, that is, octyl thioglycolate A chain transfer agent such as methoxybutyl thioglycolate or methoxybutyl β-mercaptopropionate is appropriately used.

In order to maintain the stability of the aqueous resin composition dispersion containing the copolymers (A) and (B) at the time of polymerization or over time, a surfactant may be added at the time of polymerization or after polymerization.
Examples of the surfactant that can be appropriately used in the present invention include anionic surfactants and nonionic surfactants.

Examples of the anionic surfactant include those having an alkylene oxide chain and a carboxyl group or a sulfate group at the terminal and neutralizing the acid at the terminal with ammonia or the like. Examples thereof include those obtained by neutralizing acid ends with ammonia, such as higher fatty acid salts, alkyl sulfate esters, polyoxyethylene alkyl ether sulfate esters, alkyl sulfosuccinate esters, and the like.
Specifically, “New Call SF Series” manufactured by Nippon Emulsifier Co., Ltd., “Adekaria Soap SE-10N” manufactured by Asahi Denka Kogyo Co., Ltd., “Adekaria Soap SR-10N” manufactured by Asahi Denka Kogyo Co., Ltd. Examples include “AQUALON HS series” manufactured by Ichiko Pharmaceutical Co., Ltd. Further, a phosphate ester type surfactant represented by “KAYARAD” manufactured by Nippon Kayaku Co., Ltd. may be used after neutralizing with ammonia.

Among the surfactants that can be used in the present invention, nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene phenyl ethers, sorbitan higher fatty acid esters, glycerin having a polymerizable functional group and an alkylene oxide chain. Examples include higher fatty acid esters.
Specific examples include “New Coal NS Series” manufactured by Nippon Emulsifier Co., Ltd. and “Aqualon RN Series” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

<Aqueous emulsion type adhesive>
The water-based emulsion-type pressure-sensitive adhesive of the present invention is mainly composed of a resin composition aqueous dispersion containing the copolymers (A) and (B), and further improves initial adhesive strength or applies to a specific substrate. For the purpose of improving adhesion, water dispersion of tackifiers such as rosin resin, terpene resin, phenol resin, polyterpene, acetylene resin, petroleum hydrocarbon resin, ethylene vinyl acetate copolymer, synthetic rubber, natural rubber May be blended.
Moreover, the water-based emulsion type adhesive of this invention can contain a various additive further as needed. For example, wetting agents (surfactant for preventing repellency, etc.), antifoaming agents, neutralizing agents, plasticizers, thickeners, fillers, colorants, preservatives, antifungal agents, solvents and the like can be mentioned.

  The aqueous emulsion-type pressure-sensitive adhesive of the present invention thus obtained preferably has a nonvolatile content of 40 to 70%, more preferably 50 to 65%. In this range, the viscosity when using a BL type viscometer 30 rpm and a # 4 rotor is preferably 100 to 4000 mPa · s, and more preferably 200 to 1000 mPa · s.

  The pH of the aqueous emulsion-type pressure-sensitive adhesive of the present invention is preferably 4.0 to 9.0, more preferably 7.0 to 8.5, from the viewpoint of storage stability over time and work environment.

<Adhesive sheet>
The pressure-sensitive adhesive sheet of the present invention is formed by sequentially laminating a peelable sheet, a pressure-sensitive adhesive layer formed from the above-described aqueous emulsion pressure-sensitive adhesive of the present invention, and paper containing a calcium salt.
Specifically, the above-mentioned aqueous emulsion-type pressure-sensitive adhesive of the present invention is applied to a peelable sheet with a comma coater, reverse coater, slot die coater, etc., and dried to form a pressure-sensitive adhesive layer. It is preferably obtained by laminating papers containing calcium salts. Pressure-sensitive adhesive layer to be formed, by dry weight is preferably 5 to 50 g / m ^2, and more preferably 10 to 25 g / m ^2. The film thickness at the time of drying is 8 to 25 μm.
Moreover, when laminating paper containing a calcium salt on the pressure-sensitive adhesive layer, it is preferable to apply a pressure of 5 to 100 (N / cm ² ). By laminating under such pressure, the copolymer (A) is responsible for the function of actively impregnating the relatively low molecular weight copolymer (B) into the paper, and mainly developing the performance as an adhesive. It is possible to effectively suppress and prevent the calcium crosslinking of the copolymer (A) by reacting with calcium ions that migrate from the paper earlier. When the pressure is small, the copolymer (B) is not so impregnated. When the pressure is too large, not only the copolymer (B) but also the copolymer (A) is easily impregnated, and the base materials are crushed. It tends to cause poor appearance such as twisting and tearing.
Examples of the peelable sheet used in the present invention include those based on paper and those based on plastic sheets, and imparting releasability by applying a conventionally known releasable coating agent. Can do.

  EXAMPLES Next, although an Example demonstrates this invention, this invention is not limited to these. In the examples, “part” means “part by weight” and “%” means “% by weight”.

[Example 1]
<Production example of copolymer (B)>
A dropping funnel was charged with 12 parts of methyl methacrylate, 70 parts of ethyl acrylate, 18 parts of methacrylic acid, and 4 parts of methoxybutyl thioglycolate.
A four-necked flask equipped with a nitrogen gas introduction tube, a thermometer, a reflux condenser and a stirring device was charged with 410 parts of ion exchange water, saturated with nitrogen gas and stirred, and the reaction system was heated to 83 ° C. A 5% ammonium persulfate aqueous solution was added in an amount of 0.0034 times the total amount of monomers in the solid content ratio. After 5 minutes, dropping of the composition of the dropping funnel was started and dropped over 40 minutes.
After completion of dropping, the mixture is aged for 10 minutes while maintaining the temperature. Thereafter, the temperature of the system was lowered to 78 ° C., and neutralized by adding 10% ammonia water having a theoretical neutralization equivalent while stirring. Furthermore, 0.2% of the total monomer was added to a 5% ammonium persulfate aqueous solution in a solid content ratio, and the mixture was aged for 20 minutes.
Theoretical Tg: An aqueous dispersion of a copolymer (B) having a Tg of 7 ° C., a weight average molecular weight of 8200, and a number average molecular weight of 5000 (molecular weight in terms of polystyrene by GPC (gel permeation chromatography) with tetrahydrofuran solution) was obtained. This aqueous resin dispersion had a surface tension of 37 mN / m and a solid content of about 20% by weight.

<Production Example of Resin Composition Aqueous Dispersion (1) Containing Copolymers (A) and (B)>
The dropping funnel was charged with 390 parts of 2-ethylhexyl acrylate, 396 parts of butyl acrylate, 29 parts of methyl methacrylate, and 0.57 parts of octyl thioglycolate to obtain a monomer mixture for dropping.
After adding 120 parts of water to 820 parts (164 parts of solid content) of the aqueous resin dispersion (B) of the copolymer (B) produced by the method of the above production example, ammonium persulfate was maintained at a temperature of 78 ° C. The aqueous solution was added in a solid content ratio of 0.0033 times the total amount of monomers. After 5 minutes, the monomer mixture was uniformly added dropwise over 4 hours.
After completion of dropping, an aqueous solution of perbutyl H (chemical name: tertiary butyl peroxide: manufactured by NOF Corporation) and an aqueous solution of Superlite C (chemical name: sodium formaldehyde sulfoxylate: manufactured by Mitsubishi Gas Chemical Co., Ltd.), each having a monomer ratio of 0 The .001 volume was added in 3 portions every 15 minutes. Further, the mixture was stirred at 78 ° C. for 2 hours to complete the polymerization, and then cooled to room temperature, to obtain a resin composition aqueous dispersion (1) having a solid content of about 55% by weight containing the copolymers (A) and (B). It was.
In addition, the theoretical Tg of the copolymer (A) calculated | required from the said composition of 2-ethylhexyl acrylate, butyl acrylate, and methyl methacrylate is -60 degreeC.

<Aqueous emulsion type adhesive>
After adding ammonia water suitably to 100 parts of resin composition aqueous dispersion (1) obtained above and adjusting pH to 7-8, antiseptic | preservative and tackifier resin (Arakawa Chemical Co., Ltd. superester E-786) 60) 7 parts were added, and the viscosity was adjusted using ion-exchanged water, a viscosity modifier, and aqueous ammonia to obtain an aqueous emulsion-type pressure-sensitive adhesive. The viscosity was 2000 mPa · s as measured with a BL type viscometer, # 2 rotor, 30 rpm. Moreover, it was 7.5 when pH was measured.

[Create adhesive sheet]
The obtained water-based pressure-sensitive adhesive is applied to a commercially available release sheet so that the coating amount when dried is 20 g / m ² , dried at 100 ° C. electric open, and then commercially available neutral paper. (Weighing 80 g / m ² , containing about 15% calcium carbonate) was laminated with a laminating roll at a pressure of 30 N / cm ² to obtain an adhesive sheet.

[Evaluation of adhesive properties]
<Adhesive strength after normal storage>
Based on the measurement of the normal adhesive strength of JIS-Z-0237, the adhesive sheet was stored in an atmosphere of 23 ° C.-50% for 72 hours, and then the peelable sheet was peeled off and adhered to a stainless steel plate and a polyethylene plate, respectively. The adhesive strength (adhesive strength) was measured under an atmosphere of -50 ° C.
<Adhesive strength after storage at high temperature and high humidity>
After the pressure-sensitive adhesive sheet was stored in an atmosphere of 60 ° C.-95% for 72 hours, it was adhered to a stainless steel plate and a polyethylene plate in the same manner as in the normal state, and the adhesive strength (adhesive strength) was maintained in an atmosphere of 23 ° C.-50%. ) Was measured.

<Retention force (cohesive force)>
Peel off the peelable sheet, stick it to a stainless steel plate so that the sticking area is 25mm x 25mm, put a 1kg weight, store it under 40 ° C x 65% humidity, and wait until the weight falls (seconds) )

[Example 2]
A pressure-sensitive adhesive sheet was obtained in the same manner except that methacrylic acid used in the production example of the copolymer (B) of Example 1 was replaced with itaconic acid, and evaluated in the same manner.

[Example 3]
A pressure-sensitive adhesive sheet was obtained and evaluated in the same manner except that half of the ethyl acrylate used in the production example of the copolymer (B) of Example 1 was replaced with 2-ethylhexyl acrylate.

[Example 4]
The amount of the aqueous dispersion of the copolymer (B) used in obtaining the aqueous dispersion of the copolymers (A) and (B) in Example 1 was 660 parts (solid content: 132 parts). In the same manner as above, an adhesive sheet was obtained and evaluated in the same manner.

[Example 5]
In obtaining an aqueous dispersion of the copolymers (A) and (B) in Example 1, 820 parts of the aqueous dispersion of the copolymer (B) was added at the same time as the surfactant (C ₁₂ H ₂₅ —O The same procedure except that 10 parts of a 25% aqueous solution of — (CH ₂ CH ₂ O) ₆₀ —SO ₃ NH ₄ and C ₁₃ H ₂₇ —O— (CH ₂ CH ₂ O) ₆₀ —SO ₃ NH ₄ mixture) was added. Thus, an adhesive sheet was obtained and evaluated in the same manner.

[Comparative Example 1]
An aqueous dispersion of copolymer (B) having a solid content of 20% was prepared in the same manner except that the amount of methacrylic acid used in 18 parts in the production example of copolymer (B) in Example 1 was changed to 28 parts. As a result, the viscosity was increased during the reaction, and stirring became difficult, so the reaction was stopped.

[Comparative Example 2]
A copolymer (B) was produced in the same manner as in Example 1, except that the amount of methacrylic acid was 3 parts, the amount of methyl methacrylate was 17 parts, and the amount of ethyl acrylate was 80 parts. Using the obtained copolymer (B), an aqueous resin composition dispersion containing the copolymers (A) and (B) was obtained in the same manner as in Example 1 below. However, when the monomer mixture for copolymerization of the copolymer (A) was dropped from the dropping funnel, it was not emulsified and separated into an oil layer and an aqueous layer. The reaction was stopped.

[Comparative Example 3]
The amount of the aqueous dispersion of the copolymer (B) used in obtaining the aqueous dispersion of the copolymers (A) and (B) in Example 1 was 300 parts (solid content 60 parts). In the same manner, an aqueous dispersion containing the copolymers (A) and (B) was produced in the same manner. However, since a large amount of aggregates precipitated during the reaction, the subsequent reaction was stopped.

[Comparative Example 4]
The same procedure as in Example 1 was conducted except that the amount of the aqueous resin dispersion of the copolymer (B) produced in <Production example of copolymer (B)> in Example 1 was changed to 2100 parts (solid content 420 parts). Thus, an attempt was made to obtain a resin composition aqueous dispersion containing the copolymers (A) and (B). However, since the viscosity increased during the reaction and stirring became difficult, the subsequent reaction was stopped.

[Comparative Example 5]
390 parts of 2-ethylhexyl acrylate, 396 parts of butyl acrylate, 113 parts of ethyl acrylate, 49 parts of methyl methacrylate, 31 parts of methacrylic acid and 0.57 part of octyl thioglycolate were mixed and stirred there, and the interface used in Example 5 78 parts of a 25% aqueous solution of an activator and 300 parts of ion-exchanged water were added, emulsified, and charged into a dropping funnel.
In a polymerization tank equipped with a stirrer, a thermometer, a dropping funnel and a reflux condenser, 300 parts of ion exchange water is charged and saturated with nitrogen gas and stirred. The temperature of the reaction system is raised to 78 ° C., and a 5% ammonium persulfate aqueous solution is added. 0.00125 times the total amount of monomers was added at a solid content ratio. After 5 minutes, the emulsion of the dropping funnel previously emulsified was added dropwise to start the reaction, and in parallel with this, an ammonium persulfate aqueous solution was added dropwise over a period of 4 hours in an amount of 0.00375 times the total amount of monomers in a solid content ratio. did.
After completion of dropping, an aqueous solution of perbutyl H (chemical name: tertiary butyl peroxide: manufactured by NOF Corporation) and an aqueous solution of Superlite C (chemical name: sodium formaldehyde sulfoxylate: manufactured by Mitsubishi Gas Chemical Co., Ltd.), each having a monomer ratio of 0 The .001 volume was added in 3 portions every 15 minutes. The mixture was further stirred at 78 ° C. for 2 hours to complete the polymerization, and then cooled to room temperature to obtain an aqueous resin composition dispersion having a solid content of about 60% by weight. Thereafter, in the same manner as in Example 1, an aqueous emulsion-type pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were obtained, and pressure-sensitive physical properties were evaluated.
As a result, when the pressure-sensitive adhesive sheet was stored under high temperature and high humidity, the adhesive strength was significantly reduced as compared with normal storage.

Comparative Example 6
The experiment was performed in the same manner as in Comparative Example 6 except that 31 parts of methacrylic acid in Comparative Example 5 was changed to 2 parts of acrylic acid.
As a result, although there is almost no difference in adhesive strength between normal storage and storage under high temperature and high humidity, in any case, the peeling form becomes cohesive failure and the adhesive remains on the adherend, so-called `` glue residue '' As a result, practical problems occurred. In addition, the holding force was so low that it became a practical problem.

Claims (8)

A copolymer formed from an aqueous medium and a polymerizable monomer (a) containing an alkyl chain alkyl ester having 1 to 13 carbon atoms as an essential component and not containing a polymerizable unsaturated carboxylic acid. From the polymer (A) and a polymerizable monomer (b) having an alkyl chain (meth) acrylic acid alkyl ester having 1 to 13 carbon atoms and 5 to 25% by weight of a polymerizable unsaturated carboxylic acid as essential components The resin composition containing the copolymer (B) to be formed and containing the copolymers (A) and (B) in a weight ratio of (A) / (B) = 7/3 to 9/1 An aqueous emulsion-type pressure-sensitive adhesive containing an aqueous dispersion. The aqueous emulsion-type pressure-sensitive adhesive according to claim 1, wherein the copolymer (A) has a glass transition temperature of -80 to -20 ° C. A copolymer formed from a polymerizable monomer (b) containing an alkyl chain (meth) acrylic acid alkyl ester having 1 to 13 carbon atoms and 5 to 25% by weight of a polymerizable unsaturated carboxylic acid as essential components In the presence of (B), a polymerizable monomer (a) containing an alkyl chain (meth) acrylic acid alkyl ester having 1 to 13 carbon atoms as an essential component and not containing a polymerizable unsaturated carboxylic acid. (A) / (B) = Aqueous emulsion type pressure-sensitive adhesive containing a resin composition aqueous dispersion obtained by polymerization in an aqueous medium at a weight ratio of 7/3 to 9/1. Copolymer glass which can be formed from a polymerizable monomer (a) containing an alkyl chain alkyl ester having 1 to 13 carbon atoms (meth) acrylic acid as an essential component and not containing a polymerizable unsaturated carboxylic acid The aqueous emulsion-type pressure-sensitive adhesive according to claim 3, which has a transition temperature of -80 to -20 ° C. The aqueous emulsion pressure-sensitive adhesive according to any one of claims 1 to 4, wherein the copolymer (B) has a weight average molecular weight of 1,000 to 20,000. A copolymer formed from a polymerizable monomer (b) containing an alkyl chain (meth) acrylic acid alkyl ester having 1 to 13 carbon atoms and 1 to 25% by weight of a polymerizable unsaturated carboxylic acid as essential components In the presence of (B), a polymerizable monomer (a) containing an alkyl chain (meth) acrylic acid alkyl ester having 1 to 13 carbon atoms as an essential component and not containing a polymerizable unsaturated carboxylic acid. A method for producing an aqueous dispersion of an aqueous emulsion-type pressure-sensitive adhesive resin composition, wherein polymerization is performed in an aqueous medium at a weight ratio of (a) / (B) = 7/3 to 9/1. A pressure-sensitive adhesive sheet comprising a peelable sheet, a pressure-sensitive adhesive layer formed from the water-based emulsion-type pressure-sensitive adhesive according to any one of claims 1 to 5, and paper containing a calcium salt. The aqueous emulsion-type pressure-sensitive adhesive according to any one of claims 1 to 5 is coated and dried on a peelable sheet to form a pressure-sensitive adhesive layer, and a paper containing a calcium salt is formed on the pressure-sensitive adhesive layer in an amount of 5 to 100 (N / Cm ² ) A method for producing a pressure-sensitive adhesive sheet laminated by applying a pressure of