JP2005194448A - Acrylic copolymer emulsion for pressure-sensitive adhesive, method for producing the same and pressure-sensitive adhesive sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive material that is an aqueous emulsion-type pressure-sensitive adhesive and is hard to cause such a coating defect as wrinkles, cave-in, protrusion, etc., at an adhesive layer laminated on a plastic film, especially in a case of using a transparent plastic film as a base material. <P>SOLUTION: The acrylic copolymer emulsion for the pressure-sensitive adhesive is produced by copolymerization of a monomer emulsion (C1) in the presence of an initiator, the said monomer emulsion comprises an ethylenic unsaturated monomer (a), that contains a 0.1-20% carboxy group-containing monomer and a (meth)acrylate as main component, a calculated amount of a basic material for neutralizing a part of or all of the carboxy group contained in the monomer (a), water and emulsifier, and the emulsion type acrylic pressure-sensitive adhesive contains the emulsion. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an acrylic copolymer emulsion for pressure-sensitive adhesives, a method for producing the emulsion, and a pressure-sensitive adhesive sheet. More specifically, the present invention relates to an acrylic copolymer emulsion capable of providing an adhesive that hardly causes coating defects in an adhesive layer when a pressure-sensitive adhesive sheet based on a plastic film is obtained, a method for producing the emulsion, and the like.

Conventionally, solvent-type acrylic copolymers have been used in the field of pressure-sensitive adhesives. However, in recent years, water-based emulsion-type pressure-sensitive adhesives have been used as an alternative to solvent-based pressure-sensitive adhesives from the viewpoints of improving the global environment and work environment and effectively using resources. It is rapidly changing to a drug.
In general, an aqueous emulsion-type pressure-sensitive adhesive contains various additives such as a tackifier resin, an antiseptic, an antifoaming agent, a leveling agent, and a thickener in addition to the main agent.
By the way, when a plastic film, particularly a transparent plastic film, is used as a base material among pressure-sensitive adhesive sheets using a pressure-sensitive adhesive, a highly beautiful appearance is required as well as basic pressure-sensitive adhesive properties. When a conventional solvent-type pressure-sensitive adhesive was used, there was no particular problem. However, when an aqueous emulsion-type pressure-sensitive adhesive is used, abnormalities such as wrinkles, depressions, protrusions and the like having a diameter of about 200 to 500 μm as shown in FIG. 1 are observed in the pressure-sensitive adhesive layer. . Such a coating film abnormality (also referred to as coating defect) was a fatal problem as an appearance abnormality of the pressure-sensitive adhesive sheet.
Various studies have been made on such coating defects in terms of the main agent and other additives constituting the aqueous emulsion-type pressure-sensitive adhesive, but they have not yet been fully solved.

  The present invention is an aqueous emulsion-type pressure-sensitive adhesive, and when a plastic film, particularly a transparent plastic film is used as a base material, coating of wrinkles, depressions, protrusions, etc. on the pressure-sensitive adhesive layer laminated on the plastic film It aims at providing the adhesive which a defect does not produce easily.

In order to solve the above-mentioned problems, the present inventor has intensively studied to arrive at the present invention.
That is, the present invention relates to an ethylenically unsaturated monomer (a) containing 0.1 to 20% of a carboxyl group-containing monomer and a (meth) acrylic acid ester as a main component, the monomer (a). Acrylic system for pressure-sensitive adhesives obtained by copolymerizing a monomer emulsion (C1) containing a basic substance capable of neutralizing some or all of the carboxyl groups therein, water and an emulsifier in the presence of a polymerization initiator It relates to a copolymer emulsion.

  In addition, the second invention relates to one of the carboxyl groups in the ethylenically unsaturated monomer (a) containing 0.1 to 20% of a carboxyl group-containing monomer and (meth) acrylic acid ester as a main component. The pressure-sensitive adhesive according to the above invention, wherein a monomer emulsion (C1) obtained by neutralizing a part or all with a basic substance and then emulsified with water and an emulsifier is copolymerized in the presence of a polymerization initiator. The present invention relates to an acrylic copolymer emulsion.

  Further, the third invention relates to one of the carboxyl groups in the ethylenically unsaturated monomer (a) containing 0.1 to 20% of a carboxyl group-containing monomer and a (meth) acrylic acid ester as a main component. A part of or the whole is neutralized with a basic substance, and then a monomer emulsion (C1) emulsified with water and an emulsifier is copolymerized in the presence of a polymerization initiator. The present invention relates to a method for producing a copolymer emulsion.

  Moreover, 4th invention is related with the emulsion type acrylic adhesive containing the acrylic copolymer emulsion for adhesives in any one of the said invention, and tackifying resin (B).

  In addition, the fifth invention is an ethylenically unsaturated monomer (a) containing 0.1 to 20% of a carboxyl group-containing monomer and a (meth) acrylic acid ester as a main component, a tackifier resin (B ), A monomer emulsion (C2) containing a basic substance capable of neutralizing a part or all of the carboxyl groups in the carboxyl group-containing monomer, water and an emulsifier in the presence of a polymerization initiator. The present invention relates to an emulsion-type acrylic pressure-sensitive adhesive.

  Further, the sixth invention relates to an ethylenically unsaturated monomer (a) containing 0.1 to 20% of a carboxyl group-containing monomer and a (meth) acrylic acid ester as a main component and a tackifier resin (B And a monomer emulsion (C2) obtained by neutralizing a part or all of the carboxyl groups in the mixture with a basic substance and then emulsifying with water and an emulsifier in the presence of a polymerization initiator. It is related with the emulsion type acrylic adhesive as described in 5th invention made.

  The seventh invention relates to an ethylenically unsaturated monomer (a) containing 0.1 to 20% of a carboxyl group-containing monomer and a (meth) acrylic acid ester as a main component, a tackifier resin (B), After neutralizing part or all of the carboxyl groups in the mixture with a basic substance, the monomer emulsion (C2) emulsified with water and an emulsifier is copolymerized in the presence of a polymerization initiator. The present invention relates to a method for producing an emulsion-type acrylic adhesive.

  8th invention is related with the adhesive sheet obtained using the emulsion type acrylic adhesive in any one of 4th-6th invention.

  According to the present invention, an aqueous emulsion-type pressure-sensitive adhesive is formed, and when laminated on a plastic film as a base material, particularly a transparent plastic film, a pressure-sensitive adhesive layer is formed which is less prone to coating defects such as wrinkles, depressions and protrusions. It is now possible to provide a pressure sensitive adhesive.

The first to fourth inventions will be specifically described below.
As described above, the first to third inventions relate to the acrylic copolymer emulsion for pressure-sensitive adhesives, which is the main constituent of the emulsion-type acrylic pressure-sensitive adhesive, and a method for producing the same, and the fourth invention is obtained. The present invention relates to an emulsion-type acrylic pressure-sensitive adhesive containing an acrylic copolymer emulsion for pressure-sensitive adhesive and a tackifier resin (B).

  The ethylenically unsaturated monomer (a) used for forming the acrylic copolymer emulsion for pressure-sensitive adhesives of the first invention is a (meth) acrylic acid ester (a1) having 1 to 14 carbon atoms in the alkyl group. ), And the (meth) acrylic acid ester (a1) is methyl acrylate, ethyl acrylate, propyl acrylate, iso-propyl acrylate, butyl acrylate, iso-butyl acrylate, Acrylic esters of linear or branched aliphatic alcohols such as hexyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, dodecyl acrylate, and the corresponding methacrylic esters. Preferably, the (meth) acrylic acid ester to be used has an alkyl group having 4 to 12 carbon atoms and contains 60 to 99.8% by weight of the ethylenically unsaturated monomer (a). 1 type or 2 types or more are contained.

Further, it is important that the ethylenically unsaturated monomer (a) contains 0.1 to 20% by weight of the carboxyl group-containing monomer (a2), and 0.5 to 10% by weight. preferable. Examples of the carboxyl group-containing monomer (a2) include acrylic acid, methacrylic acid, maleic anhydride, maleic acid, itaconic acid, and crotonic acid. If the carboxyl group-containing monomer (a2) is less than 0.1% by weight, the cohesive strength of the pressure-sensitive adhesive tends to decrease, and if it exceeds 20% by weight, the water resistance is remarkably deteriorated.
It is important that this carboxyl group-containing monomer (a2) is subjected to copolymerization after neutralizing at least a part of the carboxyl group with a basic substance, as will be described later.

Moreover, the ethylenically unsaturated monomer (a) can also contain the monomer (a3) which has crosslinkable functional groups other than a carboxyl group. Examples of the monomer (a3) having a crosslinkable functional group other than a carboxyl group include an alcoholic hydroxyl group-containing monomer (a3-1), a carbonyl group-containing monomer (a3-2), and an alkoxysilyl group-containing monomer. Body (a3-3) etc. are mentioned, 0.1-20 weight% is contained in total with the said carboxyl group-containing monomer (a2), and 1 type, or 2 or more types are contained.
Examples of the alcoholic hydroxyl group-containing monomer (a3-1) include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and the like.
Examples of the carbonyl group-containing monomer (a3-2) include acetoacetoxyethyl methacrylate and diacetone acrylamide.

  Further, the ethylenically unsaturated monomer (a) can contain a copolymerizable vinyl monomer (a4) other than the above. Examples of the copolymerizable vinyl monomer (a4) include polyethylene glycol acrylate, glycidyl acrylate, glycidyl methacrylate, mono- (2-hydroxyethyl-α-chloroacrylate) acid phosphate, phosphate group-containing vinyl monomer, vinyl block Isocyanate, etc., N-methylolacrylamide, N-methylolmethacrylamide, N-methylaminoethyl acrylate, N-tributylaminoethyl acrylate, N, N-dimethylaminoethyl acrylate, N, N-dimethylaminoethyl methacrylate, acrylamide, methacrylamide , Vinyl pyrrolidone, vinyl ester, vinyl pyridine, vinyl acetate, vinyl propionate, styrene, acrylonitrile, methacrylonitrile, butadiene, chloropropyl Emissions, and the like, are contained one or two or more are contained 0.1 to 20 wt%.

The emulsifier used in the present invention is not particularly limited, and a reactive (ionic or nonionic) surfactant, a nonreactive (ionic or nonionic) surfactant or the like may be used alone or in combination of several kinds. Used.
Examples of the reactive surface active agent include those that undergo a radical reaction with the ethylenically unsaturated monomer (a), and the following compounds can be exemplified.
As anionic, long chain alkyl such as “Adekaria soap SE-10N” manufactured by Asahi Denka Kogyo Co., Ltd., “Aqualon HS-10, HS-20” manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Skeletal Daiichi Kogyo Co., Ltd. “AQUALON KH-10, KH-20”, Asahi Denka Kogyo Co., Ltd. “ADEKA rear soap SR-10N”, etc. Nippon Kayaku Co., Ltd. “KAYARAD” Or the like.
Nonionic ones include polyoxyethylene alkyl ethers, polyoxyethylene phenyl ethers, sorbitan higher fatty acid esters, glycerin higher fatty acid esters, etc. "Adekaria Soap NE-10" manufactured by Asahi Denka Kogyo Co., Ltd. "AQUALON RN-10, RN-20, RN-50" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., "Antox NA-16" manufactured by Nippon Emulsifier Co., Ltd., and the like.
It is preferable that the compounding quantity of an emulsifier is 0.1-5 weight part with respect to 100 weight part of ethylenically unsaturated monomers (a), More preferably, it is 0.5-2.0 weight part. . The emulsifier may be used when emulsifying the monomer in advance, or a part thereof may be added in advance to the polymerization vessel.

  Examples of the initiator used for initiating the polymerization reaction include water-soluble pyrolytic polymerization initiators such as persulfates such as potassium persulfate and ammonium persulfate, azobis cation salts, and hydroxyl adducts, and redox initiators. Can be used. Redox initiators include organic oxides such as t-butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide and combinations of reducing agents such as Rongalite and sodium metabisulfite, or sodium persulfate, ammonium persulfate and Rongalite. A combination of sodium thiosulfate, a combination of hydrogen peroxide and ascorbic acid, or the like can be used. The amount of the initiator used is usually 0.02 to 3 parts by weight, preferably 0.1 to 1 part by weight, based on 100 parts by weight of the ethylenically unsaturated monomer (a).

  In order to control the molecular weight and molecular weight distribution of the copolymer formed from the ethylenically unsaturated monomer (a), a mercaptan-based, thioglycol-based or β-mercaptopropionic acid-based alkyl ester is used as a chain transfer agent. can do. When used, the amount added is preferably 0.005 to 0.2 parts by weight per 100 parts by weight of the ethylenically unsaturated monomer (a).

In the first to third inventions, it is important that at least a part of the carboxyl groups in the carboxyl group-containing monomer (a2) is neutralized with a basic substance and then used for copolymerization. That is, as in the second and third inventions, a basic substance is added to the ethylenically unsaturated monomer (a), and after neutralizing at least a part of the carboxyl group with the basic substance, water and an emulsifier are added. The monomer emulsion (C1) can be obtained and the monomer emulsion (C1) can be subjected to polymerization. Alternatively, a basic substance capable of neutralizing at least a part of the carboxyl groups in the monomer (a), water and an emulsifier are added to the ethylenically unsaturated monomer (a), and the monomer emulsion (C1 And can be subjected to polymerization.
Further, in the former case, only the carboxyl group-containing monomer (a2) of the ethylenically unsaturated monomer (a) used for the polymerization is previously neutralized with a basic substance to X mol% of the carboxyl group, and the neutralization rate X mol% acid neutralized product (a ′) is obtained, and then the obtained acid neutralized product (a ′) and the remainder of the ethylenically unsaturated monomer (a) are mixed, and water and emulsifier are added. In addition, it can also emulsify and can obtain an emulsion (C1). In this case, it is preferable to dissolve water and an emulsifier in advance. Further, the acid neutralized product (a ′), water and an emulsifier may be mixed first, and this and the remainder of the ethylenically unsaturated monomer (a) may be mixed and emulsified.
Prior to polymerization, when at least a part of the carboxyl group in the carboxyl group-containing monomer (a2), which is a constituent component of the copolymer, is neutralized, there is a coating defect in the pressure-sensitive adhesive layer when obtaining a pressure-sensitive adhesive sheet. It becomes difficult to occur.

If the amount of carboxyl groups is 100, the neutralization rate may exceed 100%. Since the viscosity increases during polymerization, the neutralization rate is preferably 5 to 100%, and more preferably 40 to 100% from the viewpoint of suppressing the occurrence of coating defects.
The basic substance used for neutralization is not particularly limited, and an inorganic neutralizer or an organic neutralizer can be used alone or in combination.
An example of the inorganic neutralizing agent is sodium hydroxide.
An example of the organic neutralizing agent is triethylamine.

  In the first to third inventions, it is important to use the obtained emulsion (C1), and the polymerization method may be a general emulsion polymerization method, and is not limited thereto. An example is shown. Water (in some cases, emulsifier, part of emulsion (C1), other emulsion type resin composition, etc. may be charged) is put into the polymerization vessel, and part or all of emulsion (C1) is used as a polymerization initiator. The polymerization can be carried out dropwise in the presence.

To the acrylic copolymer emulsion for pressure-sensitive adhesive obtained as described above, a tackifier resin (B) can be further added as necessary to obtain the emulsion-type acrylic pressure-sensitive adhesive of the fourth invention. .
As the tackifier resin (B) used in the present invention, at least one kind of rosin resin, terpene resin, aromatic petroleum resin, aliphatic petroleum resin and the like can be used. Based resins are preferred.
Examples of the rosin resin include natural rosin, rosin ester, hydrogenated rosin, hydrogenated rosin ester, polymerized rosin, polymerized rosin ester, disproportionated rosin, and disproportionated rosin ester.
Examples of the terpene resin include α-pinene resin, β-pinene resin, and terpene phenol resin.
Aromatic petroleum resins include styrene oligomers and α-methylstyrene / styrene copolymers.
It is preferable that the usage-amount of tackifying resin (B) is 0.5-50 weight part% with respect to 100 weight part of copolymers (A) which consist of an ethylenically unsaturated monomer (a). When the amount is less than 0.5 part by weight, the adhesion to the nonpolar polymer tends to be lowered.

  The tackifier resin (B) can be added to the acrylic copolymer emulsion for the adhesive after polymerization as described in the fourth invention, or as described in the fifth to seventh inventions, The monomer emulsion (C2) is contained together with the ethylenically unsaturated monomer (a), the basic substance, water and an emulsifier, and the monomer emulsion (C2) is subjected to emulsion polymerization. You can also. In this case as well, it is important to neutralize at least a part of the carboxyl groups in the ethylenically unsaturated monomer (a) with a basic substance prior to polymerization.

  Several kinds of additives can be further added to the emulsion type acrylic pressure-sensitive adhesive of the present invention as required. Specifically, wetting agents (surfactant for preventing repellency, etc.), antifoaming agents, neutralizing agents, plasticizers, thickeners, crosslinking agents, fillers, colorants, antiseptics, rust inhibitors, solvents, etc. Is mentioned.

Next, an eighth invention will be described.
As described above, the eighth invention relates to a pressure-sensitive adhesive sheet using an emulsion-type pressure-sensitive adhesive containing a copolymer emulsion obtained by neutralizing at least a part of carboxyl groups in advance and then subjecting to polymerization. That is, an adhesive layer formed from an emulsion-type adhesive is laminated on at least one surface of a sheet-like substrate. A peelable sheet can be laminated on the other surface of the laminated pressure-sensitive adhesive layer.
Such a pressure-sensitive adhesive sheet can be obtained by applying an emulsion-type pressure-sensitive adhesive to a sheet-like substrate using various coating machines and drying, and laminating a peelable sheet on the formed pressure-sensitive adhesive layer. Alternatively, an emulsion-type pressure-sensitive adhesive can be applied to a peelable sheet, dried, and a sheet-like substrate can be laminated on the formed pressure-sensitive adhesive layer.

Examples of the sheet-like substrate used in the eighth invention include a plastic film and paper. A plastic film is preferable, and a plastic film excellent in transparency is particularly preferable.
Examples of the plastic film include a polyester film, a polyolefin film, and a vinyl chloride film. Examples of the polyester film include a polyethylene terephthalate film (hereinafter referred to as PET film), and examples of the polyolefin film include a polypropylene film.

Examples of the coating machine used include a comma coater, a reverse coater, a slot die coater, and a lip coater.
The obtained pressure-sensitive adhesive sheet is used as a pressure-sensitive adhesive sheet for film laminating, labeling, tape, building material, and packaging material, and is also useful as a general-purpose pressure-sensitive adhesive sheet that requires appearance and the like.

Examples of the present invention will be described. In the text, “part” means “part by weight”, and “%” means “% by weight”.

Example 1
2-ethylhexyl acrylate: 49 parts, butyl acrylate: 49 parts, acrylic acid: 1.6 parts, aqueous solution obtained by neutralizing acrylic acid 0.4 parts in advance with 100 mol% of ammonia water, reactive ammonia neutralizing anion As an emulsifier, KH-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd. is 2 parts in terms of solid content, New Coal 1860 manufactured by Nippon Emulsifier Co., Ltd. is 0.3 parts in terms of solid content, and deionized water is 76% in solid emulsion content. Thus, 33.3 parts were added, emulsified in advance, and placed in a dropping funnel. The neutralization rate of acrylic acid in the monomer emulsion placed in the dropping funnel is 20 mol%.

Using a reactor equipped with a polymerization vessel, a heating device, a stirrer, a reflux cooling device, a thermometer, a nitrogen introduction tube and a dropping funnel, the polymerization vessel contained 41 parts of deionized water and Aqualon KH-10 as a solid content. 1 part was charged, stirred under a nitrogen atmosphere and heated to an internal temperature of 80 ° C., and 0.15 part of 3% potassium persulfate solid content was added. After 5 minutes, the above pre-emulsified monomer emulsion was dropped from the dropping funnel, and in parallel, 0.4% part of 3% aqueous potassium persulfate solution was added to another dropping funnel over 3 hours. It was dripped from.
After completion of dropping, the temperature is kept at 80 ° C. for 30 minutes, then the internal temperature is set to 60 to 65 ° C. over 30 minutes, and 0.14 part of t-butyl hydroperoxide and 0.2 part of Rongalite are added three times every 30 minutes. Added in portions. Further, the mixture was aged for 1 hour with stirring and then cooled to room temperature, and the remaining carboxyl groups were neutralized with aqueous ammonia to obtain an acrylic copolymer emulsion.
The acrylic copolymer emulsion had a nonvolatile content of 51.5% and an average particle size of 180 nm. The nonvolatile content was measured by measuring the weight ratio after 20 minutes at 150 ° C. in an electric oven, and the average particle size was measured by Nikkiso Co., Ltd. Microtrac.

  Next, an antifoaming agent, a wetting agent, and a preservative are added to the acrylic copolymer emulsion obtained above, and the pH is adjusted to about 7.5 with aqueous ammonia, and the solid content of the acrylic copolymer emulsion is 100. 20 parts by weight of super ester E-720 manufactured by Arakawa Chemical Co., Ltd. was added as a rosin tackifying resin to parts by weight. Furthermore, the viscosity was increased to 2500 mPa · s (measured with a BL type viscometer, # 4 rotor / 60 rpm) with a thickener to obtain an emulsion type acrylic pressure-sensitive adhesive.

The pressure-sensitive adhesive was coated on a release paper with a comma coater to a dry film thickness of 20 g / m ² , passed through a drying oven at 90 ° C. for 40 seconds, laminated with a 50 μm PET film, wound up, and 23 ° C.-65 It was allowed to stand for 24 hours or more in a% RH atmosphere to obtain an adhesive sheet.
The number of coating defects within A4 size of the pressure-sensitive adhesive layer of the obtained pressure-sensitive adhesive sheet was visually confirmed. The results are shown in Table 1.

Examples 2-4
The neutralization rate of acrylic acid in the monomer emulsion which was 20 mol% in Example 1 was 40 mol% (Example 2), 60 mol% (Example 3), and 100 mol% (Example 4). The same experiment as in Example 1 was performed except for the above.

Example 5
2-ethylhexyl acrylate: 49 parts, butyl acrylate: 49 parts, acrylic acid: 1.6 parts, an aqueous solution obtained by neutralizing 100 parts by mole of ammonia in advance with 100% by mole of ammonia water, 100% by weight of acrylic monomer Parts, rosin tackifier resin Arakawa Chemical Co., Ltd. Superester A-100 5 parts by solid content, reactive ammonia neutralization type anionic emulsifier KOH-10 made by Daiichi Kogyo Seiyaku as solid content 2 parts, Nippon Emulsifier Co., Ltd. New Coal 1860 0.3 parts in terms of solid content, 33.3 parts deionized water so that the emulsion solid content is 76%, pre-emulsified and dripping funnel Put in. The neutralization rate of acrylic acid in the monomer emulsion placed in the dropping funnel is 20 mol%. Thereafter, the same experiment as in Example 1 was performed.

Comparative Example 1
The same experiment as in Example 1 was performed except that the neutralization rate of acrylic acid in the monomer emulsion, which was 20 mol% in Example 1, was 0 mol%.

Comparative Example 2
In Comparative Example 1, the same experiment as Comparative Example 1 was performed except that superester E-720 manufactured by Arakawa Chemical Co., Ltd. was not added.

Comparative Example 3
The same experiment as in Example 5 was performed, except that the neutralization rate in the emulsion in monomer that was 20 mol% in Example 5 was 0 mol%.

An example of an electron micrograph of coating defects in the adhesive layer

Claims (8)

An ethylenically unsaturated monomer (a) containing 0.1 to 20% of a carboxyl group-containing monomer and a (meth) acrylic acid ester as a main component, one of the carboxyl groups in the monomer (a) An acrylic copolymer emulsion for pressure-sensitive adhesives, which is obtained by copolymerizing a monomer emulsion (C1) containing a basic substance, water and an emulsifier capable of neutralizing part or all in the presence of a polymerization initiator. A part or all of the carboxyl groups in the ethylenically unsaturated monomer (a) containing 0.1 to 20% of a carboxyl group-containing monomer and a (meth) acrylic acid ester as a main component is a basic substance. The acrylic copolymer emulsion for pressure-sensitive adhesives according to claim 1, wherein the monomer emulsion (C1) emulsified with water and an emulsifier is copolymerized in the presence of a polymerization initiator after neutralization. A part or all of the carboxyl groups in the ethylenically unsaturated monomer (a) containing 0.1 to 20% of a carboxyl group-containing monomer and a (meth) acrylic acid ester as a main component is a basic substance. A method for producing an acrylic copolymer emulsion for pressure-sensitive adhesives, comprising neutralizing and then copolymerizing a monomer emulsion (C1) emulsified with water and an emulsifier in the presence of a polymerization initiator. . An emulsion-type acrylic pressure-sensitive adhesive containing the acrylic copolymer emulsion for pressure-sensitive adhesive according to claim 1 or 2 and a tackifying resin (B). Ethylenically unsaturated monomer (a) containing 0.1 to 20% of carboxyl group-containing monomer and (meth) acrylic acid ester as main components, tackifier resin (B), carboxyl group-containing monomer Emulsion type acrylic adhesive prepared by copolymerizing a monomer emulsion (C2) containing a basic substance capable of neutralizing a part or all of the carboxyl groups therein, water and an emulsifier in the presence of a polymerization initiator Agent. Carboxyl groups in a mixture of ethylenically unsaturated monomer (a) and tackifying resin (B) containing 0.1 to 20% of carboxyl group-containing monomer and (meth) acrylic acid ester as main components The monomer emulsion (C2) obtained by neutralizing a part or all of the above with a basic substance and then emulsified with water and an emulsifier is copolymerized in the presence of a polymerization initiator. Emulsion type acrylic adhesive. Carboxyl groups in a mixture of ethylenically unsaturated monomer (a) and tackifying resin (B) containing 0.1 to 20% of carboxyl group-containing monomer and (meth) acrylic acid ester as main components An emulsion type characterized by copolymerizing a monomer emulsion (C2) obtained by neutralizing a part or the whole with a basic substance and then emulsifying with water and an emulsifier in the presence of a polymerization initiator A method for producing an acrylic adhesive. A pressure-sensitive adhesive sheet obtained by using the emulsion-type acrylic pressure-sensitive adhesive according to claim 4.