JP6737988B2 - Water-based pressure-sensitive adhesive, pressure-sensitive adhesive sheet, and method for producing water-based pressure-sensitive adhesive - Google Patents

Description

The present invention relates to water-based pressure sensitive adhesives containing a mixture of at least two emulsions.

In recent years, the shift from solvent-based adhesives to water-based adhesives has been remarkable even in pressure-sensitive adhesives in consideration of safety and hygiene and environmental issues. However, in the water-based pressure-sensitive adhesive, the emulsion particles are fused to form a dry coating film in the drying step after coating, and thus the coating film lacks the denseness as compared with the solvent-based pressure-sensitive adhesive. It had the drawback of being inferior in sticking to curved surfaces.

The curved surface sticking property is a term indicating suitability for sticking a pressure-sensitive adhesive coating product on a curved adherend. Unlike pasting on a flat surface, when pasting on a curved surface, stress that causes the base material of the coated object to restore from a curved surface state to a flat state occurs, so the coated object It acts so as to peel off from itself.
Therefore, if the adhesive strength of the adhesive layer applied to the coated article is not sufficient, the adhesive layer will spontaneously peel off from the adherend after a certain amount of time has elapsed after the application.
Moreover, if the cohesive force of the pressure-sensitive adhesive is too low, even if the pressure-sensitive adhesive has a sufficiently high adhesive force, a phenomenon called "cohesive failure" is usually caused, and the base material becomes flat. In some cases, the adhesive layer itself is broken in the middle of the layer without overcoming the stress of returning and the coated article is peeled off from the adherend. In this case, the adhesive is peeled off while the adhesive remains on both the adherend side and the base material side.
Therefore, in order to improve the sticking property to the curved surface, the two physical properties of the pressure-sensitive adhesive, namely the adhesive force and the cohesive force, must be satisfied without being significantly biased to either one.

Further, as the use of the water-based pressure-sensitive adhesive expands, the above-mentioned curved surface adhesiveness is good, and the cohesive force in a high temperature environment and a wide range of adherends including olefin low-polarity adherends such as polyethylene It is required to have both high adhesive strength to.

To improve these drawbacks, for example, an aqueous dispersion of a copolymer having a high glass transition temperature, an aqueous dispersion (B) of a copolymer having a low glass transition temperature, a tackifier, and a crosslinking agent are contained. A water-based pressure sensitive adhesive is proposed. (Patent Document 1)

Further, a pressure-sensitive adhesive that solves the above-mentioned problems has been proposed by using a low Tg acrylic emulsion in a specific temperature range and a high Tg acrylic emulsion in a specific temperature range (Patent Document 2).

Further, as an attempt to achieve both good adhesiveness and holding power, an oil-soluble component composed of an ethylenically unsaturated monomer (A) containing a (meth)acrylic acid alkyl ester as a main component and a tackifier (B) In the presence of a resin emulsion obtained by polymerizing an emulsion obtained by emulsifying an oil-soluble component so that the average particle size of the oil-soluble component is 1.0 μm or less in a medium, further, an alkyl (meth)acrylate is used. An aqueous pressure-sensitive adhesive composition characterized by being formed by polymerizing an ethylenically unsaturated monomer (E) containing an ester as a main component has been proposed (Patent Document 3).

An aqueous pressure-sensitive adhesive composition containing at least a low Tg acrylic pressure-sensitive adhesive emulsion and a high-Tg copolymer emulsion emulsion-polymerized in the presence of a tackifying resin as a low-viscosity pressure-sensitive adhesive having higher tackiness and tack. Has been proposed (Patent Document 4)

Japanese Patent Publication No. 2006-0165176 JP, 2010-95609, A JP, 2003-96420, A Japanese Patent No. 6183821

However, even with the above-mentioned means, it has not been possible to achieve a good curved surface sticking property, and further it is not possible to achieve an adhesive force to various adherends and a cohesive force in a high temperature environment.

An object of the present invention is to provide a water-based pressure-sensitive adhesive that has both excellent adherence to various adherends, excellent adherence to curved surfaces, and high cohesive strength/adhesive strength in a high temperature environment, and a method for producing the same. is there.
Among them, an adhesive sheet that can be used in a wide range of applications, such as adherends such as olefins that are generally considered to be difficult to adhere to, good adhesion to curved surfaces, and no deviation even under high temperature conditions are provided. That is.

As a result of intensive studies to solve the above problems, the inventors of the present invention can solve the above problems by using at least two types of water-based pressure-sensitive adhesives containing a specific acrylic emulsion. The present invention has been made based on this finding by discovering that it is possible.

That is, the water-based pressure-sensitive adhesive of the present invention is an aqueous pressure-sensitive adhesive containing the acrylic emulsion (A1) in an amount of 65 to 95 mass% and the acrylic emulsion (A2).
The acrylic emulsion (A1) is an emulsion of an acrylic copolymer (a1) having a glass transition temperature (Tg) of −70 to −40° C.,
The acrylic emulsion (A2) is obtained by emulsion-polymerizing the ethylenically unsaturated monomer mixture (a'2) in the presence of an emulsifier and a tackifying resin, and has a glass transition temperature (Tg) of 60 to 120°C. Is an emulsion of the acrylic copolymer (a2), and the content of the tackifying resin is 10 to 60 parts by mass with respect to 100 parts by mass of the ethylenically unsaturated monomer mixture (a'2). It is characterized by

The pressure-sensitive adhesive of the present invention can satisfy good curved surface adhesiveness, adhesive strength to various adherends, and cohesive strength under high temperature environment. Therefore, the pressure-sensitive adhesive sheet including the pressure-sensitive adhesive layer formed from the water-based pressure-sensitive adhesive of the present invention can suppress deviation in a high temperature environment after being attached. Therefore, there is an excellent effect that the adherend having a curved surface shape and an adherend such as an olefin which is difficult to be adhered have good adhesiveness.

Hereinafter, the details of the present invention will be described. The ethylenically unsaturated monomer is a general term for radically polymerizable vinyl group-containing compounds including a (meth)acrylic acid alkyl ester monomer and the like. Sometimes referred to simply as "monomer".
The glass transition temperature is represented by Tg. Tg is a value theoretically obtained by the FOX equation based on the numerical value of the glass transition temperature of a homopolymer formed from each ethylenically unsaturated monomer to be supplied to an acrylic emulsion, and each ethylene With regard to the glass transition temperature of the homopolymer of a polyunsaturated monomer, known values described in various manuals, documents and the like can be used.
In the present specification, “parts” and “%” represent “parts by mass” and “mass %” unless otherwise specified.

<<Water-based pressure sensitive adhesive>>
The water-based pressure-sensitive adhesive of the present invention is a mixture of at least two kinds of emulsions containing an acrylic emulsion (A1) as a main component, and the acrylic emulsion (A1) in the water-based pressure-sensitive adhesive (100% by mass). In addition, 65-95 mass% and an acrylic emulsion (A2) are included.
The content of the acrylic emulsion (A1) is preferably 70 to 90% by mass, more preferably 75 to 87% by mass. Within this range, the adhesiveness to curved surfaces and the adhesion to olefins can be made excellent.
The content of the acrylic emulsion (A2) is preferably 5 to 35% by mass, more preferably 10 to 20% by mass. Within this range, it is possible to achieve excellent compatibility between the adhesiveness to curved surfaces and the holding power at high temperatures.

<Acrylic emulsion (A1)>
The water-based pressure-sensitive adhesive of the present invention contains an acrylic emulsion (A1). The acrylic emulsion (A1) has a glass transition temperature (Tg) of −70 to −40° C., which is obtained by emulsion-polymerizing an ethylenically unsaturated monomer mixture (a′1) containing an ethylenically unsaturated monomer. Which is an emulsion of the acrylic copolymer (a1), which is the main component of the water-based pressure-sensitive adhesive in the present invention, and contributes to the expression of basic adhesive performance. Further, the acrylic emulsion (A1) may be composed of a single emulsion or may be used as a mixture of two or more kinds.

[Acrylic copolymer (a1)]
The acrylic copolymer (a1) is an acrylic copolymer obtained by emulsion-polymerizing an ethylenically unsaturated monomer mixture (a'1) containing at least an ethylenically unsaturated monomer in the presence of an emulsifier. And the glass transition temperature (Tg) is −70 to −40° C.

Therefore, it is important to appropriately select the ethylenically unsaturated monomer such that the Tg of the acrylic copolymer (a1) made of the ethylenically unsaturated monomer is −70° C. to −40° C. When the glass transition temperature (Tg) of the acrylic copolymer (a1) is lower than -70°C, not only the adhesive strength to the adherend, particularly to the olefin, but also the curved surface sticking property becomes insufficient. On the other hand, when the temperature exceeds -40°C, the tackiness is lowered and the adhesiveness is lowered. The temperature is more preferably −65° C. to −50° C., further preferably −60° C. to −45° C.

As the ethylenically unsaturated monomer, a (meth)acrylic acid alkyl ester, which is an ester of a linear or branched alcohol and (meth)acrylic acid, an ethylenically unsaturated monomer having a carboxyl group, and a hydroxyl group Examples thereof include an ethylenically unsaturated monomer, an ethylenically unsaturated monomer having an amide bond, a styrene unsaturated monomer, and a vinyl compound.

The acrylic copolymer (a1) of the present invention may contain 2 to 10% by mass of an ethylenically unsaturated monomer having a hydroxyl group in 100% by mass of the ethylenically unsaturated monomer mixture (a'1). It is more preferable that the content of 3% by mass or more and less than 6% by mass allows the pressure-sensitive adhesive to have further improved adherence to a curved surface.
The acrylic copolymer (a1) is obtained by polymerizing a mixture containing 2 to 10% by mass of an ethylenically unsaturated monomer having a hydroxyl group in 100% by mass of such an ethylenically unsaturated monomer mixture. When the acrylic emulsion (A1x) is contained, the content of the acrylic emulsion (A1x) is 5 to 100 mass in the acrylic emulsion (A1) (100 mass %) from the viewpoint of the curved surface sticking property of the pressure-sensitive adhesive. %, and more preferably 10 to 100% by mass.

In addition, the content of the ethylenically unsaturated monomer having a carboxyl group is preferably 0.5 to 5 mass% in the total 100 mass% of the ethylenically unsaturated monomer mixture (a′1). .. When the amount used is within the range, generation of aggregates during synthesis is suppressed, and an emulsion having good handling after neutralization is easily obtained.

The content of monomers other than the ethylenically unsaturated monomer having a hydroxyl group and the ethylenically unsaturated monomer having a carboxyl group is preferably 95.0 to 99.5 mass%, and above all, When the content of butyl acrylate is 40.0 to 98.0% by mass, good curved surface sticking properties and adhesive strength can both be achieved, which is preferable.

"(Meth)acrylic acid alkyl ester"
Examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, n-octyl (meth)acrylate, 2 -Ethylhexyl (meth)acrylate, lauryl (meth)acrylate, myristyl (meth)acrylate, stearyl acrylate, etc. are mentioned.
These can be used alone or in combination of two or more.
Among them, as the (meth)acrylic acid alkyl ester, it is preferable to use a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms in order to improve tackiness and adhesive strength of the pressure-sensitive adhesive.

"An ethylenically unsaturated monomer having a carboxyl group"
Examples of the ethylenically unsaturated monomer having a carboxyl group include (meth)acrylic acid, carboxyethyl (meth)acrylate, maleic acid, fumaric acid, and itaconic acid. Among them, it is preferable to use (meth)acrylic acid from the viewpoint of emulsion stability.
These can be used alone or in combination of two or more.

"Ethylene unsaturated monomer having hydroxyl group"
Examples of the ethylenically unsaturated monomer having a hydroxyl group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate and the like.
These can be used alone or in combination of two or more.

"An ethylenically unsaturated monomer having an amide bond"
Examples of the ethylenically unsaturated monomer having an amide bond include (meth)acrylamide and diacetone (meth)acrylamide.
These can be used alone or in combination of two or more.

"Other ethylenically unsaturated monomers"
In addition, other ethylenically unsaturated monomers can be used as long as the effects of the present invention are not impaired. Other ethylenically unsaturated monomers include methoxyethyl (meth)acrylate, acetoacetoxyethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, vinyl. Examples thereof include pyrrolidone, vinyl pyridine, vinyl acetate, vinyl propionate, styrene, (meth)acrylonitrile, butadiene, chloroprene and the like.
These can be used alone or in combination of two or more.

[emulsifier]
As the emulsifier used when obtaining the acrylic emulsion (A1), known emulsifiers such as reactive emulsifiers and non-reactive emulsifiers can be used.

The following compounds can be illustrated as a specific example of a reactive emulsifier.
Examples of anionic emulsifiers include long-chain alkyl skeletons manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. such as "ADEKA REASOAP SE-10N" manufactured by ADEKA with nonylphenyl skeleton, "AQUARON HS-10, HS-20" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. Examples thereof include "Aqualon KH-05, KH-10", "ADEKA REASOAP SR-10N" manufactured by ADEKA, and "KAYARAD" manufactured by Nippon Kayaku Co., which has a phosphoric acid ester skeleton. As the nonionic emulsifier, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, sorbitan higher fatty acid esters, glycerin higher fatty acid esters and the like have an unsaturated double bond at the molecular terminal or intermediate part, It is to be copolymerized with a polymer, and is made by ADEKA "Adekaria Soap NE-10", Dai-ichi Kogyo Seiyaku Co., Ltd. "Aqualon RN-10, RN-20, RN-50", Nippon Emulsifier "Antox". NA-16" etc. can be illustrated.

The following compounds can be illustrated as a non-reactive emulsifier.
As anionic emulsifiers, higher fatty acid salts such as sodium stearate, alkylaryl sulfonates such as sodium dodecylbenzene sulfonate, alkyl sulfate ester salts such as sodium lauryl sulfate, polyoxyethylene alkyl such as sodium polyoxyethylene lauryl ether sulfate. Examples thereof include ether sulfate ester salts and polyoxyethylene alkylaryl ether sulfate ester salts such as sodium polyoxyethylene nonylphenyl ether sulfate.
Nonionic emulsifiers include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene alkylphenyl ethers such as polyoxyethylene nonylphenyl ether, sorbitan higher fatty acid esters such as sorbitan monostearate, and oleic acid. Examples thereof include glycerin higher fatty acid esters such as monoglyceride.

These can be used alone or in combination of two or more.

[Polymerization initiator]
As a polymerization initiator used for obtaining the acrylic emulsion (A1), a water-soluble thermal decomposition type polymerization catalyst such as a persulfate such as potassium persulfate or ammonium persulfate or an azobis cation salt or a hydroxyl group-adding substance, or redox A system polymerization catalyst can be used. As the redox-based polymerization catalyst, a combination of an organic peroxide such as t-butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide and a reducing agent such as Rongalit or sodium metabisulfite, or potassium persulfate or ammonium persulfate is used. And Rongalit, sodium thiosulfate, etc., and a combination of hydrogen peroxide solution and ascorbic acid.

The acrylic emulsion (A1) is a thiol such as mercaptan-based, thioglycol-based, β-mercaptopropionic acid as a chain transfer agent for controlling the molecular weight and the molecular weight distribution when polymerizing an ethylenically unsaturated monomer. A system compound etc. can be used. The addition amount was 0.. with respect to a total of 100 parts by mass of the ethylenically unsaturated monomer mixture (a'1) constituting the acrylic emulsion (A1). It is preferably from 01 to 1.0 part by mass.

[Method for producing acrylic emulsion (A1)]
The method for producing the acrylic emulsion (A1) will be described.
The acrylic emulsion (A1) is obtained by emulsion-polymerizing an ethylenically unsaturated monomer mixture (a′1) containing an ethylenically unsaturated monomer, and has a glass transition temperature (Tg) of −70 to −40° C. It can be obtained by preparing an emulsion of the acrylic copolymer (a1). (Process 1)

Specifically, a mixture of ethylenically unsaturated monomers is polymerized in an aqueous medium using an emulsifier and a polymerization initiator to obtain an acrylic emulsion.
First, the ethylenically unsaturated monomer (a'1) is mixed to obtain a uniform mixed solution. This mixed solution may be subjected to the polymerization as it is, or may be subjected to the polymerization after adding a part or all of water and an emulsifier and stirring the mixture to obtain an emulsion.
After preparing these mixed solutions or emulsions, the polymerization is carried out in the presence of a polymerization initiator.As a method therefor, the whole amount of the mixed solution or emulsion may be charged into a reaction vessel to start the polymerization. After charging a part of the reaction vessel to start the polymerization, it may be divided and added in several divided portions, or a part of the reaction vessel may be charged to start the polymerization and then the rest may be continuously added dropwise, or water may be added beforehand. If necessary, a part or all of the emulsifier may be charged in a reaction vessel, and the whole amount may be continuously added dropwise. When polymerization is carried out using a mixed solution, it is preferable to previously charge the reaction vessel with the total amount of the emulsifier and a part or all of the water.
As a method for adding the polymerization initiator, the whole amount may be charged in advance in the reaction vessel, or the whole amount may be added after the temperature is raised. The reaction mixture may be dividedly added in portions, and a part of the mixture may be charged in a reaction vessel to start polymerization and then the rest may be continuously added dropwise, or the entire amount may be continuously added dropwise. When the polymerization initiator is dividedly added or continuously added dropwise, it may be separately added or continuously added dropwise into the reaction vessel, or may be added separately or continuously while being mixed with the mixed solution or the emulsion. good. After the polymerization initiator is added by these methods, the polymerization initiator may be additionally added once or twice or more for the purpose of increasing the reaction rate. Thus, the acrylic emulsion (A1) of the present invention can be obtained.

Further, during the polymerization, a pH buffer may be used together for the purpose of adjusting the pH during the polymerization. When a monomer having a carboxyl group is used, a part or all of this may be ammonia, organic amine, potassium hydroxide. It may be neutralized with a basic compound such as sodium citrate or sodium hydroxide.

<Acrylic emulsion (A2)>
The water-based pressure-sensitive adhesive of the present invention contains an acrylic emulsion (A2). The acrylic emulsion (A2) has a glass transition temperature (Tg) of 60 to 120° C., which is obtained by emulsion-polymerizing the ethylenically unsaturated monomer mixture (a′2) in the presence of an emulsifier and a tackifying resin. The content of the tackifying resin is 10 to 60 parts by mass with respect to 100 parts by mass of the ethylenically unsaturated monomer mixture (a'2) which is an emulsion of a certain acrylic copolymer (a2).
As the ethylenically unsaturated monomer, the same ones as exemplified in the section of the acrylic copolymer (a1) can be used.

[Acrylic copolymer (a2)]
The acrylic copolymer (a2) is obtained by emulsion-polymerizing an ethylenically unsaturated monomer mixture (a'2) containing at least an ethylenically unsaturated monomer in the presence of an emulsifier and a tackifying resin. It is a copolymer and has a glass transition temperature (Tg) of 60°C to 120°C.
At this time, the content of the tackifying resin is 10 to 60 parts by mass with respect to 100 parts by mass of the ethylenically unsaturated monomer mixture (a′2).

Therefore, it is important to appropriately select the ethylenically unsaturated monomer such that the Tg of the acrylic copolymer (a2) made of the ethylenically unsaturated monomer is 60°C to 120°C. When the glass transition temperature (Tg) of the acrylic copolymer (a2) is within the above range, good adhesive strength, curved surface stickiness, and holding power can both be achieved, and more preferably 80°C to 115°C. It is preferably 90°C to 110°C.

As the ethylenically unsaturated monomer, those exemplified in the section of "acrylic emulsion (A1)" can be used.

The content of the ethylenically unsaturated monomer having a carboxyl group is preferably 0.5 to 5 mass% in the total 100 mass% of the ethylenically unsaturated monomer mixture (a′2). When the amount used is within the range, generation of aggregates during synthesis is suppressed, and an emulsion having good handling after neutralization is easily obtained.

The content of monomers other than the ethylenically unsaturated monomer having a carboxyl group is preferably 95.0 to 99.5% by mass, and the amount of use is within the range to provide good curved surface stickiness. Adhesive strength can be made compatible, and in particular, when the content of methyl methacrylate is 80% by mass or more, dissolution of the tackifying resin described later and improvement of curved surface stickiness are facilitated, which is preferable.

[Tackifying resin]
The tackifying resin used in the acrylic emulsion (A2) is not particularly limited as long as it can be dissolved or dispersed in a mixture of ethylenically unsaturated monomers, and conventionally known ones can be used. .. Examples of such tackifying resins include rosin-based resins, terpene-based resins, coumarone-indene resins, phenol resins, xylene resins, aliphatic hydrocarbon resins, aromatic hydrocarbon resins, and the like.
Also in the above, from the viewpoint of improving the stickiness of the curved surface, it is preferable to use a rosin resin, a terpene resin, an aromatic hydrocarbon resin, particularly preferably a rosin resin, and more preferably a polymerized rosin ester resin. Is preferably used.
Examples of the rosin-based 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 polyterpene resin include α-pinene resin, β-pinene resin, and terpene phenol resin. Examples of aromatic hydrocarbon resins include copolymers of styrene and α-methylstyrene.
These may be used alone or in combination of two or more.

Among the above-mentioned tackifying resins, those having a softening point of 100° C. or higher are preferable as the tackifying resin used in the present invention, more preferably 120° C. or higher, and further preferably 150° C. or higher. When the softening point is 100° C. or higher, the adhesive strength is high, and good curved surface applicability can be obtained.
Specific examples of the tackifying resin having a softening point within the above range include, for example, Pencel D-125 (manufactured by Arakawa Chemical Industry Co., Ltd.) which is a polymerized rosin ester having a softening point of 125° C. Pencel D-160 (manufactured by Arakawa Chemical Industry Co., Ltd.) which is a rosin ester, PINEREZ2410 (manufactured by LAWTER) which is a rosin ester having a softening point of 100° C., YS resin PX1150 (manufactured by Yasuhara Chemical Co., Ltd.) which is a terpene resin having a softening point of 115° C., Examples include YS Polystar T160 (manufactured by Yasuhara Chemical Co.), which is a terpene phenol resin having a softening point of 160°C.

Regarding the difference between the glass transition temperature (Tg) of the acrylic copolymer (a2) and the softening point of the tackifying resin, the temperature difference represented by the following formula (1) is preferably less than 100°C, and less than 80°C. Is more preferable. When the temperature is lower than 100°C, good curved surface sticking property/high adhesive strength and holding power can both be achieved.
If the absolute value of the temperature difference is within this range, the same effect can be exhibited regardless of which of the glass transition temperature (Tg) of the acrylic copolymer (a2) and the softening point of the tackifier resin is higher. it can. The softening point of the tackifier resin is preferably higher than the softening point of the acrylic resin, in which case good curved surface sticking properties and high adhesive strength and holding power can both be achieved.

Formula (1)
Temperature difference (℃) =
|Glass transition temperature (Tg) of acrylic copolymer (a2)-softening point of tackifying resin|

[Method for producing acrylic emulsion (A2)]
A method for obtaining the acrylic emulsion (A2) will be described.
The acrylic emulsion (A2) is obtained by emulsion-polymerizing an ethylenically unsaturated monomer mixture (a'2) containing an ethylenically unsaturated monomer in the presence of an emulsifier and a tackifying resin to obtain a glass transition temperature (Tg). Is 60 to 120° C., which is an emulsion of the acrylic copolymer (a2). (Process 2)
At this time, the content of the tackifying resin is 10 to 60 parts by mass with respect to 100 parts by mass of the ethylenically unsaturated monomer mixture (a′2). The lower limit is more preferably 20 parts by mass or more, further preferably 30 parts by mass or more. The upper limit is more preferably 50 parts by mass or less. When the amount used is within the above range, good adhesive strength, adhesiveness to curved surface, and holding power can be achieved at the same time, and generation of aggregates during production can be suppressed.

Among them, a step of dissolving the tackifying resin in the ethylenically unsaturated monomer mixture (a′2),
A step of forcibly emulsifying the dissolved mixture (a′2) in the presence of an emulsifier and water to obtain an emulsion having an average particle size of 0.5 to 2 μ;
It is preferable to provide a step of emulsion-polymerizing the obtained emulsion in terms of suppressing the generation of aggregates during polymerization and not using an organic solvent for dissolving the tackifying resin during polymerization.

The acrylic emulsion (A2) is obtained by dissolving a tackifying resin in an ethylenically unsaturated monomer mixture, further adding water and an emulsifier, and emulsion-polymerizing the emulsified emulsion. As the emulsifier, the polymerization initiator and the chain transfer agent used at that time, the same ones as exemplified in the section of the acrylic emulsion (A1) can be used.

As the method of emulsion polymerization, the method exemplified in the paragraph of acrylic emulsion (A1) can be used, but by adjusting the average particle diameter (median diameter) of the emulsion of the monomer/tackifying resin during production. In addition, the performance of the water-based adhesive can be further improved.

The blending amount of the emulsifier (active ingredient) used in the production of the acrylic emulsion (A2) is 1. based on 100 parts by mass of the total amount of the ethylenically unsaturated monomer mixture (a′2) and the tackifying resin. It is preferably from 0 to 2.5 parts by mass. More preferably, it is 1.5 to 2.0 mass. When the compounding amount of the emulsifier is 1.0 part by weight or more, generation of aggregates during production can be suppressed, and when it is 2.5 parts by weight or less, the curved surface sticking property is further improved.

At this time, the average particle size of the emulsion may be any size as long as no aggregates are generated during synthesis or the stability in leaving when it is used as an aqueous pressure-sensitive adhesive is good. In order to obtain the acrylic emulsion (A2) that does not occur, the average particle size of the emulsion is preferably 0.5 to 2.0 μm. Further, it is more preferably 0.8 to 1.5 μm. Here, if it is less than 0.5 μm, the viscosity of the emulsion may become too high, and the energy and time required for forced emulsification may increase and the productivity may decrease. If it exceeds 2.0 μm, aggregates may be generated during synthesis.

The average particle diameter is the cumulative volume average diameter when the oil droplet diameter in water is measured by the dynamic light scattering method, and for example, the average particle diameter value (median measured by Nikkiso Microtrac UPA particle size distribution meter). Diameter D50).

As a method for obtaining an emulsion having an average particle diameter of 2.0 μm or less, a commercially available emulsifier can be used, and a rotary continuous emulsifier, a colloid mill emulsifier, a high pressure homogenizer emulsifier, and an ultrasonic treatment Although a forced emulsifying machine such as a mold type emulsifying machine can be used, among these, the rotor/stator type high speed rotating continuous emulsifying machine, which is a rotating type continuous emulsifying machine, produces an emulsion having a suitable average particle size. It is suitable for obtaining the product, and the amount of maintenance and the amount of treatment per unit time is large, which is preferable.

The water-based pressure-sensitive adhesive of the present invention contains the acrylic emulsion (A1) within the range of 65 to 95 mass% and the acrylic emulsion (A2) within the range of 5 to 35 mass %.

<Method for producing water-based pressure-sensitive adhesive>
As a method for producing the water-based pressure-sensitive adhesive, a known method can be used, and the acrylic emulsions (A1) and (A2) are neutralized with a known neutralizing agent, if necessary, and then a known method is used. A method of mixing (step 3) and further blending a leveling agent, a defoaming agent, and a viscosity modifier preservative is used. In order to adjust the adhesive strength, an appropriate amount of a tackifier such as rosin resin, phenol resin, polyterpene, acetylene resin, petroleum hydrocarbon resin, ethylene vinyl acetate copolymer, synthetic rubber, natural rubber, etc. is added. can do.
Further, a plasticizer, a filler, a coloring agent, a silane coupling agent, etc. may be added.
Furthermore, in order to cross-link the dispersed particles of each copolymer in the water-based pressure-sensitive adhesive of the present invention between particles, any cross-linking agent may be blended, for example, a hydroxyl group as an ethylenically unsaturated monomer component. When using a monomer having an isocyanate compound, an alkoxide compound such as titanium or zirconium can be used, and when using a monomer having a carbonyl group, an amine, a hydrazide compound or the like is used. I can do things. When a monomer having a carboxyl group is used, a metal compound such as a carbodiimide compound, an epoxy compound, an aziridine compound and zinc oxide can be used.

≪Pressure sensitive adhesive sheet≫
The pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer formed of an aqueous pressure-sensitive adhesive.
The pressure-sensitive adhesive layer can be formed by applying the water-based pressure-sensitive adhesive of the present invention to a substrate or a release liner and drying it.

Examples of the base material include polyolefin resins such as polyethylene, polypropylene and ethylene-propylene, polyester resins such as polyethylene terephthalate, vinyl acetate resins, polyimide resins, fluorine resins, polyvinyl chloride resins, cellophane resins and the like. Plastic film made of material; Rubber sheet made of natural rubber, butyl rubber, etc.; Foam sheet made by foaming polyurethane, polychloroprene rubber, polyethylene, etc.; Kraft paper, crepe paper, Japanese paper, etc.; Cotton cloth, soft cloth, etc. Cloths; non-woven fabrics such as cellulosic non-woven fabrics, polyester non-woven fabrics and vinylon non-woven fabrics; metal foils such as aluminum foils and copper foils; One or both surfaces of such a sheet-shaped substrate may be subjected to surface treatment such as application of an undercoating agent or corona discharge treatment. The thickness of the substrate can be appropriately selected according to the purpose, but is generally about 10 μm to 500 μm (typically 10 μm to 200 μm).

As the release liner (sometimes referred to as a separator), a conventionally known release liner can be used without particular limitation. For example, a suitable base material (eg glassine paper, kraft paper, clay coated paper, paper laminated with a resin film such as polyethylene, resin such as polyvinyl alcohol or acrylic polymer is coated with a release agent such as fluororesin or silicone resin. A release liner obtained by treating at least one surface of the prepared paper) can be preferably used.

The coating method may be a known method, such as a comma coater, a reverse coater, a slot die coater, a lip coater, a gravure chamber coater, a curtain coater, or other known coating apparatus, and a paper or plastic film substrate, Alternatively, the pressure-sensitive adhesive sheet of the present invention can be obtained by coating on a release liner and drying. Further, at that time, it is preferable to apply a water-based pressure-sensitive adhesive to a release liner or the like and then dry at 80°C to 120°C. If the drying temperature is 80° C. or lower, it is difficult to dry and it takes a long time to dry. On the other hand, if it is dried at a temperature higher than 120° C., the base material or the peelable sheet is thermally deteriorated, which is not preferable.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. In the examples, "parts" means "parts by mass" and "%" means "mass %" unless otherwise specified. In addition, except for water and solvent, the indicated blending amount is a nonvolatile content conversion value.

The method for measuring the average particle size of the emulsion and the method for calculating the glass transition temperature (Tg) of the acrylic copolymer are as follows.

[Average particle size of emulsion]
The average particle size of the emulsion was measured under the following conditions.
The cumulative volume average diameter when the oil droplet diameter in water was measured by the dynamic light scattering method was measured by using a Microtrac UPA particle size distribution analyzer manufactured by Nikkiso Co., Ltd., and an average particle diameter value (median diameter D50) was determined.

[Glass transition temperature (Tg) of acrylic copolymer]
The glass transition temperature (Tg) of the acrylic copolymer was calculated by the FOX equation.
The glass transition temperature of the homopolymer of each monomer used for the calculation is shown below.

2-ethylhexyl acrylate: -70°C
Butyl acrylate: -54°C
Methyl methacrylate: 105°C
Acrylic acid: 105°C
2-hydroxyethyl methacrylate: 71°C
Diacetone acrylamide: 65°C

The materials used in Table 2 are as follows.
[Tackifying resin]
Tackifying resin I: Pencel D-160 (Rosin-based resin: Arakawa Chemical Co., Ltd., polymerized rosin ester resin with a softening point of 160° C.)
Tackifying resin II: Pencel D-125 (Rosin-based resin: Arakawa Chemical Co., Ltd., polymerized rosin ester resin with a softening point of 125° C.)
Tackifying Resin III: Super Ester A-75 (Rosin Resin: Arakawa Chemical Industry's Disproportionated Rosin Ester Resin with a Softening Point of 75° C.)
Tackifying resin IV: YS Polystar T-160 (terpene resin: terpene phenol resin with a softening point of 160°C manufactured by Yasuhara Chemical)
Tackifying resin V: FTR-6100 (aromatic hydrocarbon resin: styrene-aliphatic monomer copolymer at 95°C manufactured by Mitsui Chemicals)

[Aqueous dispersion of tackifying resin]
Tackifying resin water dispersion I: Superester E-865 (manufactured by Arakawa Chemical Industries, water dispersion of polymerized rosin ester, solid content 50%,)

<Acrylic emulsion (A1)>
(Production of acrylic emulsion (A1-1))
2. Ethylhexyl acrylate 36.5 parts, butyl acrylate 62 parts, acrylic acid 1.5 parts, Newcol 707SF (polyoxyethylene polycyclic phenyl ether sulfate ester aqueous solution, active ingredient 30%, manufactured by Nippon Emulsifier) 3. 4 parts was dissolved in 10.9 parts of ion-exchanged water, then added and stirred to obtain an emulsion. This was placed in a dropping funnel.
24.4 parts of deionized water was charged into a four-necked flask equipped with a stirrer, a cooling tube, a thermometer and the dropping funnel, the air inside the flask was replaced with nitrogen gas, and the internal temperature was 76°C while stirring. The temperature was raised to 1.3 parts, and 1.3 parts of a 5% ammonium persulfate aqueous solution was added. After 5 minutes, the dropping of the emulsion was started from the dropping funnel, and in parallel with this, 3.8 parts of a 5% aqueous solution of ammonium persulfate was dropped from another dropping port over 3 hours.
While maintaining the internal temperature at 76° C., the mixture was further aged at 76° C. for 4 hours with stirring and then cooled, and neutralized with aqueous ammonia to obtain an acrylic emulsion (A1-1) having a solid content of 58%.
The glass transition temperature of the acrylic copolymer in the acrylic emulsion (A1-1) was -59°C.

(Production of acrylic emulsion (A1-2-4))
Emulsion polymerization is performed in the same manner as in the production of the acrylic emulsion (A1-1) except that the raw materials for producing the acrylic emulsion (A1-1) and the blending amount (parts by mass) thereof are changed as described in Table 1. Thus, an acrylic emulsion (A1-2-4) having a solid content of 58% was obtained.

<Acrylic emulsion (A2)>
(Production of acrylic emulsion (A2-1))
40 parts of tackifying resin I (Pencel D-160) as a tackifying resin was dissolved in 98 parts of methyl methacrylate and 2 parts of acrylic acid. Further, as an anionic emulsifier, 9.3 parts of Newcol 707SF (an aqueous solution of polyoxyethylene polycyclic phenyl ether sulfate ester salt, active ingredient 30%, manufactured by Nippon Emulsifier Co., Ltd.) and 29.0 parts of ion-exchanged water are added and stirred to emulsify. I got a thing. Further, emulsification was performed using a Cavitron CD1010 type (manufactured by Eurotech Co., Ltd.) in which a slit type unit was used for the rotor/stator to obtain an emulsion having an average particle (median) diameter of the oil-soluble component of 1.1 μm. , Which was placed in a dropping funnel.
21.8 parts of deionized water was charged into a four-necked flask equipped with a stirrer, a cooling tube, a thermometer and the dropping funnel, the inside of the flask was replaced with nitrogen gas, and the internal temperature was raised to 80°C while stirring. After warming, 1.1 parts of a 7.4% ammonium persulfate aqueous solution was added. After 5 minutes, the dropping of the emulsion was started from the dropping funnel, and in parallel with this, 2.7 parts of a 7.4% ammonium persulfate aqueous solution was dropped from another dropping port over 3 hours. While maintaining the internal temperature at 80° C., the mixture was further aged at 76° C. for 4 hours with stirring and then cooled and neutralized with aqueous ammonia to obtain an acrylic emulsion (A2-1) having a solid content of 60%.
The glass transition temperature of the acrylic copolymer in the acrylic emulsion (A2-1) was 105°C.

(Production of acrylic emulsion (A2-2-8))
Emulsion polymerization is performed in the same manner as in the production of the acrylic emulsion (A2-1), except that the raw materials for producing the acrylic emulsion (A2-1) and the blending amount (parts by mass) thereof are changed as shown in Table 2. Thus, acrylic emulsions (A2-2 to 8) each having a solid content of 60% were obtained.

(Production of acrylic emulsion (AC-1 to 6))
Emulsion polymerization is performed in the same manner as in the production of the acrylic emulsion (A2-1) except that the raw materials for producing the acrylic emulsion (A2-1) and the blending amount (parts by mass) thereof are changed as shown in Table 3. Thus, acrylic emulsions (AC-1 to 6) each having a solid content of 60% were obtained.

(Example 1)
<Preparation of water-based pressure sensitive adhesive>
After mixing 85 parts of the acrylic emulsion (A1-1) and 15 parts of the acrylic emulsion (A2-1), the pH was adjusted to 8.5 with ammonia water, and a defoaming agent, a leveling agent and a preservative were added. Was further added, and the viscosity was adjusted to 4000 mPa·s (BL type viscometer, #4 rotor used, measured at 60 rpm) with a viscosity modifier to obtain an aqueous pressure-sensitive adhesive.

(Examples 2-8, Comparative Examples 1-8)
An aqueous pressure-sensitive adhesive was produced in the same manner as in Example 1 except that the composition and the blending amount (parts by mass) of Example 1 were changed as shown in Tables 4 to 6.

<Production of pressure-sensitive adhesive sheet>
The resulting water-based pressure-sensitive adhesive was coated on a release paper with a comma coater so that the dry coating amount was 18 g/m ² , and dried in a drying oven at 105° C. for 40 seconds to obtain a high-quality paper (60 g/m ² ) Was laminated and wound up to obtain a water-based pressure-sensitive adhesive coated product, which was prepared into a sheet shape having a length of 100 mm and a width of 25 mm to obtain a pressure-sensitive adhesive sheet.
The evaluation items and evaluation methods of the obtained pressure-sensitive adhesive sheet are as follows. The results are shown in Tables 4 to 6.

<Adhesiveness;Adhesiveness>
The pressure-sensitive adhesive sheet was peeled off from the sample at 23° C. and 50% RH environment, and the exposed pressure-sensitive adhesive layer was attached to a polyethylene plate and pressure-bonded by reciprocating once with a 2 kg roll. Immediately after that, the adhesive force was measured and used as the adhesive force immediately after pressure bonding. The adhesive strength was measured according to JIS Z-0237 at a peeling speed of 300 mm/min and a peeling angle of 180°. The evaluation criteria are as follows.

Adhesive strength of 10 N/25 mm or more, excellent adhesive strength of 8 N/25 mm or more, less than 10 N/25 mm. Good adhesion is 6N/25mm or more and less than 8N/25mm. Practical use Adhesive strength less than 6N/25mm, not practical

<Attachability of curved surface>
The pressure-sensitive adhesive sheet was cut into a piece having a width of 20 mm and a length of 15 mm, the release paper was peeled off, and the sheet was attached around a polyethylene rod having a length of 30 cm and a diameter of 10 mm. The direction of attachment was such that the width direction (longitudinal direction) of the coated sample was parallel to the length direction of the polyethylene rod. After sticking, it was strongly pressure-bonded with a finger and left in an atmosphere of 23° C. for 7 days. After the lapse of a predetermined period, it was visually observed whether the sample was peeled off. The evaluation criteria are as follows.

◎: No peeling. Excellent ◯: The end portions of the sample are peeled off (both ends less than 2 mm). Good Δ: The end portion of the sample is peeled off (either end is 2 mm or more). Practical possible ×: The entire surface is peeled off and the base material is flat. Impractical

<High temperature retention>
After peeling off the release paper of the pressure-sensitive adhesive sheet, it was attached to a test plate of stainless steel plate (SUS304) so that the attachment area was 25 mm × 25 mm, and a load of 1 kg was applied under the condition of 80°C × 50% RH. Then, the deviation (mm) of the coated product after 24 hours was measured according to the method for measuring the holding power of JIS Z 0237. In addition, in the case of falling, the number of falling seconds in which it completely slipped off was measured. The evaluation criteria are as follows.

The deviation is less than 1 mm, and the excellent deviation is 1 mm or more and less than 5 mm. Good deviation is 5 mm or more and less than 25 mm. Practical acceptable Drop due to 25 mm or more, not practical

Based on these results, the water-based pressure-sensitive adhesive containing two specific acrylic emulsions of the present invention was excellent in adhesive strength, curved surface stickiness, and high temperature holding power. Therefore, it has been confirmed that the adherend having a curved surface shape and the adherend such as olefin which is difficult to be adhered have good adhesiveness.
On the other hand, the water-based pressure-sensitive adhesives of Comparative Examples could not satisfy all of the adhesive force, the curved surface sticking property and the high temperature holding power.
INDUSTRIAL APPLICABILITY The water-based pressure-sensitive adhesive and the water-based pressure-sensitive adhesive sheet of the present invention exhibit excellent adhesive strength, adhesiveness to curved surfaces, and high-temperature holding power, and can be suitably used for pressure-sensitive adhesive applications such as labels.

Claims (8)

A water-based pressure-sensitive adhesive containing 65 to 95 mass% of an acrylic emulsion (A1) and an acrylic emulsion (A2),
The acrylic emulsion (A1) is obtained by emulsion-polymerizing an ethylenically unsaturated monomer mixture (a'1), and has an acrylic copolymer (a1) having a glass transition temperature (Tg) of -70 to -40°C. ) is an emulsion,
The content of the ethylenically unsaturated monomer having a hydroxyl group in 100% by mass of the ethylenically unsaturated monomer mixture (a′1) is 2 to 10% by mass,
The acrylic emulsion (A2) is obtained by emulsion-polymerizing the ethylenically unsaturated monomer mixture (a′2) in the presence of an emulsifier and a tackifying resin, and has a glass transition temperature (Tg) of 60 to 120° C. Which is an emulsion of the acrylic copolymer (a2)
Ethylenically unsaturated monomer mixture (a'2) amount of the tackifying resin against 100 parts by weight is 10 to 60 parts by weight, an aqueous pressure sensitive adhesive. The water-based pressure-sensitive adhesive according to claim 1, wherein the tackifying resin has a softening point of 100°C or higher. The water-based pressure-sensitive adhesive according to claim 1 or 2, wherein the tackifying resin is at least one selected from the group consisting of rosin-based resins, terpene-based resins, and aromatic hydrocarbon resins. The water-based pressure-sensitive adhesive according to any one of claims 1 to 3, wherein the temperature difference represented by the following formula (1) is less than 100°C.
Formula (1)
Temperature difference (℃) =
|Glass transition temperature (Tg) of acrylic copolymer (a2)-softening point of tackifying resin| Amount of the emulsifier, per 100 parts by weight of the ethylenically unsaturated monomer mixture (a'2) and the tackifying resin, 1.0 to 2.5 parts by weight, claim 1 4. The water-based pressure-sensitive adhesive according to any one of 4 above. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the water-based pressure-sensitive adhesive according to claim 1 . A method for producing a water-based pressure-sensitive adhesive containing an acrylic emulsion (A1) in an amount of 65 to 95 mass% and an acrylic emulsion (A2),
A method for producing a water-based pressure-sensitive adhesive comprising the following steps (1) to (3).
<Step (1)>
Of an acrylic copolymer (a1) having a glass transition temperature (Tg) of −70 to −40° C., which is obtained by emulsion polymerization of an ethylenically unsaturated monomer mixture (a′1) containing an ethylenically unsaturated monomer. A step of producing an acrylic emulsion (A1) which is an emulsion ,
Step in which the content of the ethylenically unsaturated monomer having a hydroxyl group in 100% by mass of the ethylenically unsaturated monomer mixture (a′1) is 2 to 10% by mass <Step (2)>
Emulsion polymerization of an ethylenically unsaturated monomer mixture (a'2) containing an ethylenically unsaturated monomer in the presence of an emulsifier and a tackifying resin, and an acrylic resin having a glass transition temperature (Tg) of 60 to 120°C. A step of producing an acrylic emulsion (A2) which is an emulsion of a copolymer (a2),
Ethylenically unsaturated monomer mixture (a'2) amount of the tackifying resin against 100 parts by weight is 10 to 60 parts by mass Step <Step (3)>
Step of mixing acrylic emulsion (A1) and acrylic emulsion (A2) Step (2) is
And obtaining the tackifying resin an ethylenically unsaturated monomer mixture (a'2) mixture was dissolved in a (a'2),
The resulting mixture (a'2), and forced emulsification in the presence of the emulsifier and water, a step of mean particle size of the oil soluble components to obtain an emulsion is 0.5 to 2 [mu] m,
The resulting said emulsion and a step of emulsion polymerization,
The method for producing the water-based pressure-sensitive adhesive according to claim 7 .