JPH1046117A - Heat-sensitive self-adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-sensitive self-adhesive sheet which is nonsticky or scarcely sticky at normal temp., develops stickiness when heated and/or pressurized to become effectively usable as a self-adhesive sheet, does not require any peeling treatment, and is excellent in water resistance. SOLUTION: This self-adhesive sheet has a self-adhesive power of 10g/25mm or lower at 25 deg.C according to the 180 deg. peeling method specified in JIS Z 0237 and comprises a substrate and a self-adhesive layer formed thereon from a water-base polymer emulsion obtd. by the emulsion polymn. of a free-radical- polymerizable monomer in the presence of a water-soluble or -dispersible copolymer. The monomer mainly comprises an alkyl (meth)acrylate and gives, when polymerized alone, a polymer having a glass transition temperature of -10 deg.C or lower. The copolymer is prepd. by partly or totally neutralizing carboxyl groups of a copolymer mainly comprising α,β-ethylenically unsatd. carboxylic acid units and hydrophobic free-radicalpolymerizable monomer units with a base having a b.p. of 110 deg.C or lower and has a glass transition temperature of 20 deg.C or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adhesive sheet.
More specifically, the present invention is unique in that it is non-tacky at room temperature or extremely low in tackiness and does not exhibit tackiness, while it exhibits tackiness when heated and also exhibits tackiness when pressed. And a heat-sensitive adhesive sheet having extremely excellent water resistance and moisture resistance.

[0002]

2. Description of the Related Art Generally, pressure-sensitive adhesive sheets are coated with a release paper (release paper) on the pressure-sensitive adhesive surface, and are stored, distributed, sold, and the like. In a roll-up type product such as an adhesive tape, a base material having a back surface subjected to a release treatment is used so that the product can be rewound during use. The release paper becomes unnecessary after the pressure-sensitive adhesive sheet is attached to the article, and a pressure-sensitive adhesive sheet that does not require a release paper is required from the viewpoint of resource saving and cost reduction. Furthermore, if the backing of the pressure-sensitive adhesive tape is not subjected to a release treatment, the manufacturing process of the pressure-sensitive adhesive tape substrate can be simplified, and the cost can be reduced.

As a pressure-sensitive adhesive sheet which does not require a release paper, a heat-sensitive pressure-sensitive adhesive sheet coated with a delayed tack type pressure-sensitive adhesive (Japanese Patent Publication No. 62-21835 and Japanese Patent Application Laid-Open No. 6-10084) is known. Discloses, as a delayed tack type adhesive, an adhesive obtained by mixing a solid plasticizer such as dicyclohexyl phthalate or the like with its surface coated with a colloid, and a thermoplastic resin such as an ethylene-vinyl acetate copolymer. I have. These prior documents describe that the pressure-sensitive adhesive is non-tacky at room temperature, and that the plasticizer is melted by heating to develop adhesive force.

However, the conventional delayed tack-type pressure-sensitive adhesive containing a solid plasticizer has various problems as described in the following (a) to (d), and is limited to limited special uses. Currently, it cannot be used. (B) After the crystallization of the solid plasticizer has progressed, the adhesive strength is lost, so once peeled from the adherend, it cannot be adhered to the adherend again. The heating temperature cannot be freely set because the temperature depends on the melting point of the solid plasticizer; (c) After the crystallization has progressed, the pressure-sensitive adhesive becomes hard and loses its flexibility, so the pressure-sensitive adhesive sheet is attached to the adherend. When the adherend is bent or vibrated after the adherence, the pressure-sensitive adhesive layer cannot follow the adherend, and there is a danger of peeling; and (d) the base material used for the adhesive sheet is a high-quality paper. In such a case, the plasticizer easily oozes out on the sheet surface when the pressure-sensitive adhesive sheet is heated.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a non-adhesive or extremely low-adhesive material at room temperature, and therefore, an adhesive layer such as a release paper or a release treatment of the back surface of a substrate. Provide a heat-sensitive adhesive sheet that can be handled as a product without peeling treatment, while exhibiting adhesiveness when heated or pressurized and can be effectively used as an adhesive sheet or adhesive tape. It is to be. An object of the present invention is to provide a high-quality heat-sensitive adhesive sheet that does not have the above-mentioned problems (a) to (d) in the conventional delayed tack-type adhesive. Further, an object of the present invention is to provide a heat-sensitive adhesive sheet having more excellent water resistance and moisture-heat resistance.

[0006]

Means for Solving the Problems The present inventors have intensively studied to solve the above problems. As a result, in the presence of a specific water-soluble or water-dispersible copolymer having a carboxyl group neutralized with a specific base, a specific radical polymerizable monomer having alkyl (meth) acrylate as a main component When an aqueous polymer emulsion obtained by emulsion polymerization of the polymer is coated on a substrate to form a pressure-sensitive adhesive layer, the pressure-sensitive adhesive sheet obtained thereby has no or no tack at room temperature. It was not shown, and it was found that when heated or pressurized, it exhibited adhesiveness and could be effectively used as an adhesive sheet.

Further, the present inventors have found that the pressure-sensitive adhesive sheet obtained as described above has a high degree of freedom in setting the heating temperature for developing the tackiness, and that the time has passed after the pressure-sensitive adhesive sheet was adhered to the adherend. Even after a certain period of time, the pressure-sensitive adhesive layer does not become hard, and the components in the pressure-sensitive adhesive layer bleed into the substrate even when heated. Not found.

Further, the present inventors have obtained an aqueous emulsion comprising an alkyl (meth) acrylate polymer having a glass transition temperature of -10 ° C. or lower and an aqueous polymer having a Tg of 20 ° C. or higher. We have already filed a patent application by finding that the pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the composition has the above-mentioned heat-sensitive adhesive property of exhibiting adhesiveness upon heating. Emulsion polymerization of a radical polymerizable monomer containing alkyl (meth) acrylate as a main component in the presence of a specific water-soluble or water-dispersible copolymer having a carboxyl group neutralized with a base It has been found that a heat-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the obtained aqueous polymer emulsion has even better water resistance. The present inventors have completed the present invention based on the various findings described above.

That is, the present invention provides a radical polymerizable polymer having a glass transition temperature of -10 ° C. or lower containing alkyl (meth) acrylate as a main component in the presence of the following copolymer (a): A heat-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from an aqueous polymer emulsion, obtained by emulsion polymerization of a monomer, on a substrate, comprising: JIS Z
Temperature 2 by 180 degree peeling method specified in 0237
A heat-sensitive adhesive sheet characterized in that the adhesive strength at 5 ° C. is 10 g / 25 mm or less. Copolymer (a): α, β-ethylenically unsaturated carboxylic acid unit and hydrophobic radical polymerizable Some or all of the carboxyl groups in the copolymer having a monomer unit as a main constituent unit are neutralized with a base having a boiling point of 110 ° C. or lower.
A water-soluble or water-dispersible copolymer having a glass transition temperature of 20 ° C or higher.

The above-mentioned heat-sensitive adhesive sheet of the present invention can be used without performing a release treatment on the pressure-sensitive adhesive layer (that is, without using a release paper or a release treatment on the back surface of the base material). If desired, it can be used even after it has been subjected to a release treatment. In addition, the glass transition temperature of the polymer in the present invention (hereinafter may be abbreviated as “Tg”) is
It means the value obtained from the following formula.

[0011]

1 / Tg = {W (a) / Tg (a)} + {W (b) / Tg (b)} + {W (c) / Tg (c)} +... Tg = Tg of polymer W (a) = weight fraction of structural unit consisting of monomer (a) in polymer W (b) = weight fraction of structural unit consisting of monomer (b) in polymer Ratio W (c) = weight fraction of structural unit consisting of monomer (c) in polymer Tg (a) = glass transition temperature of homopolymer of monomer (a) Tg (b) = monomer Glass transition temperature of homopolymer of (b) Tg (c) = glass transition temperature of homopolymer of monomer (c)

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. First, the "heat-sensitive adhesive sheet" in the present invention is:
Using an aqueous polymer emulsion obtained by emulsion-polymerizing a radical polymerizable monomer having an alkyl (meth) acrylate as a main component in the presence of the water-soluble or water-dispersible copolymer (a). Refers to those having a pressure-sensitive adhesive layer formed on a substrate, the shape of the substrate in the heat-sensitive adhesive sheet,
The size, form, material, and the like are not particularly limited, and may be any. Therefore, the "heat-sensitive adhesive sheet" of the present invention refers to a heat-sensitive adhesive sheet in which the base material is in a sheet shape, a heat-sensitive adhesive tape in which the base material is in a tape shape, a material in which the base material is in a plate shape, a base material other than those described above. Means a general term for those of the shape and form. Further, the heat-sensitive adhesive sheet of the present invention may have a pressure-sensitive adhesive layer only on one side of the substrate, or may have a pressure-sensitive adhesive layer on both sides of the substrate, or When the substrate has a certain thickness, the surface of the substrate and / or
Alternatively, an adhesive layer may be provided on another surface other than the back surface.

In the pressure-sensitive adhesive layer of the heat-sensitive pressure-sensitive adhesive sheet of the present invention, the copolymer (a) used for producing the above-mentioned aqueous polymer emulsion has a Tg of 20 ° C. or higher. When the Tg of the copolymer (a) is less than 20 ° C., a radical polymerizable monomer containing an alkyl (meth) acrylate as a main component is emulsion-polymerized in the presence of the copolymer (a). The adhesive layer formed from the obtained aqueous polymer emulsion does not become non-adhesive or low-adhesive at room temperature, that is, the adhesive strength at a temperature of 25 ° C. by a 180 ° peeling method specified in JIS Z 0237 is 10 g / It does not become less than 25 mm, and it becomes tacky even at room temperature, so that the object of the present invention cannot be achieved. Further, when the Tg of the copolymer (a) is extremely high, the heating temperature for developing the adhesiveness becomes high, and the workability and thermal efficiency at the time of sticking the adhesive sheet are reduced, and the heating at the time of heating is also reduced. The base material of the heat-sensitive adhesive sheet is easily deteriorated by high temperature. Therefore, from these points, the preferable Tg of the copolymer (a) is preferably from 30 to 200 ° C, more preferably from 70 to 150 ° C.

As the α, β-ethylenically unsaturated carboxylic acid used for producing the copolymer (a) (copolymer before neutralization), for example, acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, Examples thereof include itaconic acid, citraconic acid, and maleic anhydride, and one or more of these monomers can be used. The preferred amount of the α, β-ethylenically unsaturated carboxylic acid used is a copolymer obtained by copolymerizing the unsaturated carboxylic acid and another copolymerizable monomer before neutralization with a base (medium). Acid value of the copolymer before neutralization is from 30 to 260 per 1 g of the copolymer before neutralization.
It is the amount to become mgKOH. The acid value of the copolymer before neutralization is
If the amount is less than 30 mg KOH per 1 g of the copolymer before neutralization, it becomes difficult to obtain a copolymer which can be well dissolved or dispersed in water even if the copolymer is neutralized with a base.
If it exceeds KOH / g, the water resistance will be poor. The amount of the α, β-ethylenically unsaturated carboxylic acid used to give the acid value varies depending on the type of the unsaturated carboxylic acid used, but is based on the total weight of all the monomers used in the production of the copolymer before neutralization. On the basis of this, it is usually preferred to be about 3 to 40% by weight.

As the hydrophobic radical polymerizable monomer used together with the α, β-ethylenically unsaturated carboxylic acid for producing the copolymer (a) (copolymer before neutralization), 100 g of water is used. The solubility in water is preferably 2 g or less. For example, methyl methacrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, (meth)
N-propyl acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth) acrylic acid n-octyl, isooctyl (meth) acrylate,
Examples include alkyl (meth) acrylates such as n-nonyl (meth) acrylate and isononyl (meth) acrylate; and vinyl aromatic monomers such as styrene, α-methylstyrene, and vinyltoluene. The use amount of the above-mentioned hydrophobic monomer is preferably 30 to 80% by weight based on the total amount of all the monomers used for synthesizing the copolymer (a).

In order to synthesize the copolymer (a),
A hydrophilic radically polymerizable monomer other than the above α, β-ethylenically unsaturated carboxylic acid can also be used as needed. Examples of such a hydrophilic radically polymerizable monomer include:
For example, methyl acrylate, vinyl acetate, acrylonitrile, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, (meth) Examples include acrylamide, N-methylolacrylamide, glycidyl methacrylate, styrenesulfonic acid and its sodium salt, and 2-acrylamido-2-methylpropanesulfonic acid and its sodium salt.

The types and proportions of the above-mentioned α, β-ethylenically unsaturated carboxylic acid, the hydrophobic radically polymerizable monomer, and the hydrophilic radically polymerizable monomer used as required are obtained. The polymer is selected based on the above formula so that the Tg of the polymer is 20 ° C.

As the polymerization method for obtaining the above-mentioned copolymer before neutralization, various polymerization methods can be adopted, and known methods such as a polymerization method by irradiation with radiation and a method using a radical polymerization initiator can be used. . Among them, a polymerization method using a radical polymerization initiator is preferable from the viewpoint of easiness of polymerization operation, easiness of controlling the molecular weight of the obtained copolymer before neutralization, and the like. Examples of the polymerization method include a solution polymerization method, a bulk polymerization method, a suspension polymerization method, an emulsion polymerization method, and a precipitation polymerization method. A solution polymerization method is preferable, and α, β-ethylenically unsaturated carboxylic acid and By dissolving another copolymerizable monomer in an organic solvent and performing polymerization using a suitable radical polymerization initiator, a copolymer before neutralization can be obtained smoothly.

In order to obtain a homogenous and stable copolymer (a) (copolymer before neutralization), the dropping rate of the monomer should be kept as constant as possible in the reaction system. It is desirable to control Specifically, a method in which a monomer having a low copolymerizability and a low reactivity is partially or entirely charged into a reactor at the beginning of polymerization, and a monomer having a high reaction rate is dropped in the middle of the reaction. , A part of the monomer having a slow reaction rate and a part of the monomer having a fast reaction rate are charged into a reactor, and the monomer having a slow reaction rate is adjusted to the consumption rate of the monomer having a fast reaction rate. Can be obtained in a reactor by employing a method of dropping the copolymer into a reactor.

Examples of the organic solvent preferably used for carrying out the above-mentioned solution polymerization include ketone solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone; acetate solvents such as ethyl acetate and butyl acetate;
Aromatic hydrocarbon solvents such as benzene, toluene and xylene; aliphatic hydrocarbon solvents such as cyclohexane, hexane and heptane; methanol, ethanol, isopropanol, methyl cellosolve, ethyl cellosolve, normal butyl cellosolve, ethylene glycol, propylene glycol, tri Alcohol solvents such as methylolpropane and glycerin; and tetrahydrofuran, dioxane, dimethylformamide, dimethylsulfoxide, hexamethylphosphamide and the like. These organic solvents can be used alone or in combination of two or more. You may.
Among them, methyl ethyl ketone and / or isopropyl alcohol are more preferably used as the organic solvent.

As the radical polymerization initiator used in the solution polymerization, any of those used in general radical polymerization can be used. For example, persulfate polymerization initiators such as potassium persulfate and ammonium persulfate can be used. Initiator: 2,2'-azobisisobutyronitrile, 2,2 '
Azo polymerization initiators such as azobis (2-methylbutyronitrile); organic peroxides such as benzoyl peroxide and lauroyl peroxide; cumene hydroperoxide, te
Rt-butyl hydroperoxide, redox-based polymerization initiators and the like by a combination of an oxidizing agent composed of an organic hydroperoxide such as diisopropylbenzene hydroperoxide and a reducing agent such as Rongalit, sodium bisulfite, and ascorbic acid. Can be. The preferred amount of the polymerization initiator to be used is 0.1 to 5% by weight based on the total amount of the monomers.

In the above solution polymerization, a chain transfer agent may be appropriately added to the polymerization system in order to adjust the molecular weight of the obtained copolymer before neutralization. , Mercaptoacetic acid, mercaptopropionic acid, 2-propanethiol, 1-butanethiol, 2-
Methyl-2-propanethiol, 2-mercaptoethanol, ethylmercaptoacetate, thiophenol,
Examples thereof include 2-naphthalene thiol, dodecyl mercaptan, and thioglycerol.

The polymerization temperature for obtaining the copolymer before neutralization is as follows:
It is preferably about 10 to 150 ° C, and 60 to 100 ° C.
C. is more preferred. The polymerization time is 1 to 10
0 hour is appropriate, and more preferably 3 to 10 hours.

The number average molecular weight of the copolymer before neutralization is preferably from 1,000 to 500,000.
When the number-average molecular weight of the copolymer before neutralization is less than 1,000, the water- and moisture-resistance of the pressure-sensitive adhesive layer in the heat-sensitive pressure-sensitive adhesive sheet is likely to be inferior. As a result, the production of the copolymer before neutralization itself becomes difficult.

Next, some or all of the carboxyl groups in the copolymer before neutralization obtained by the above polymerization are neutralized with a base having a boiling point of 110 ° C. or lower, and the copolymer (a) used in the present invention is used. ). When the boiling point of the base used for neutralization exceeds 110 ° C., the base remains in the pressure-sensitive adhesive layer after coating and drying, and the water- and moisture-resistance of the pressure-sensitive adhesive layer becomes poor. Specific examples of the base having a boiling point of 110 ° C. or lower used for neutralizing the carboxyl group of the copolymer before neutralization include ammonia, methylamine, ethylamine, propylamine, isopropylamine, butylamine, amylamine, dimethylamine, diethylamine, and diamine. Propylamine, diisopropylamine, trimethylamine, triethylamine and allylamine, and the like,
Among them, ammonia is preferably used.

The neutralization amount of the carboxyl group of the copolymer before neutralization is preferably at least 30 mol%, more preferably 50 mol%.
More preferably, it is the above. If the neutralization amount of the carboxyl group of the copolymer before neutralization is less than 50 mol%, the surface activity and water solubility of the copolymer (a) are liable to decrease.

In neutralizing a carboxyl group in the copolymer before neutralization with a base, the copolymer before neutralization obtained by the above-described solution polymerization or the like is directly collected in the reaction medium without being recovered from the reaction medium. It is preferable to keep it in a state where it is present (particularly in a state of being dissolved in an organic solvent), and to add a base for neutralization thereto, since the operation is easy. In this case, it is more preferable to add a neutralizing base as an aqueous solution, since the neutralization of the carboxyl group is smoothly performed.

As described above, a copolymer (a) in which some or all of the carboxyl groups are neutralized can be obtained.
The copolymer (a) may be taken out of the reaction system after the neutralization treatment and used for emulsion polymerization of a radical polymerizable monomer mainly composed of an alkyl (meth) acrylate. However, a copolymer before neutralization is produced by solution polymerization, and an aqueous solution of a base for neutralization is added thereto to neutralize carboxyl groups in the copolymer before neutralization, and the copolymer ( After formation of a), the organic solvent present in the system is removed by a suitable method (eg, under reduced pressure) and the copolymer (a) is removed.
Is preferably in the form of an aqueous solution or an aqueous dispersion having a concentration of about 10 to 60% by weight, and a part or the whole thereof is taken out and used in the next step of producing an aqueous emulsion.

The aqueous polymer emulsion used in the present invention is a polymer containing a (meth) acrylic acid alkyl ester as a main component and having a glass transition temperature of -10 ° C. or lower in the presence of the copolymer (a). It is formed by emulsion polymerization of a radical polymerizable monomer that gives a coalescence. As the radical polymerizable monomer containing (meth) acrylic acid alkyl ester as a main component for forming the aqueous polymer emulsion, the (meth) acrylic acid alkyl ester as a main component is copolymerized with this, if necessary. A combination of a small amount (preferably 40% by weight or less) of another radically polymerizable monomer (hereinafter, this may be referred to as a “copolymerizable monomer”) is preferably used.

The alkyl (meth) acrylate used in the production of the aqueous polymer emulsion has the alkyl group having 1 to 12 carbon atoms (meth).
Alkyl acrylates are preferably used, for example, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate,
Isobutyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, (meth)
2-ethylhexyl acrylate, (meth) acrylic acid n
-Octyl, isooctyl (meth) acrylate, n-nonyl (meth) acrylate and isononyl (meth) acrylate, decyl (meth) acrylate, lauryl (meth) acrylate, and the like. )
One or more alkyl acrylates can be used. Particularly, in the present invention, in producing the aqueous polymer emulsion, one or more alkyl (meth) acrylates having an alkyl group having 4 to 9 carbon atoms are mainly used as the alkyl (meth) acrylate. It is preferably used as a component.

As described above, in the production of the aqueous polymer emulsion, other copolymerizable monomers may be used as a minor component together with the alkyl (meth) acrylate, but such a copolymerizable monomer may be used. Examples of the monomer include vinyl aromatic monomers such as styrene, α-methylstyrene, and vinyltoluene; and those such as (meth) acrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, and maleic acid. Saturated carboxylic acid; itaconic acid monoethyl ester,
Monoalkyl esters of unsaturated dicarboxylic acids such as monobutyl fumarate and monobutyl maleate; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, Hydroxyl-containing vinyl monomers such as polypropylene glycol mono (meth) acrylate; (meth) acrylonitrile, vinyl acetate,
Examples thereof include (meth) acrylamide, N-methylolacrylamide, glycidyl methacrylate, vinyl acetate, vinyl chloride, and vinylidene chloride. One or more of these copolymerizable monomers can be used.

When the above-mentioned other copolymerizable monomer is used, the use of the other copolymerizable monomer is based on the total weight of the radical polymerizable monomer used for producing the aqueous polymer emulsion. As described above, the proportion is preferably 40% by weight or less. When the use ratio of the other comonomer exceeds 40% by weight, the tackiness of the pressure-sensitive adhesive layer formed from the aqueous polymer emulsion tends to be insufficient, and the tackiness is increased even when the heat-sensitive pressure-sensitive adhesive sheet is heated. It is difficult to develop.

The method for producing the aqueous polymer emulsion is not particularly limited and can be carried out in the same manner as conventionally known emulsion polymerization. That is, in the presence of the copolymer (a), a radical polymerizable monomer containing an alkyl (meth) acrylate as a main component is uniformly dispersed in an aqueous medium, and emulsion polymerization is performed using a polymerization initiator. Thereby, an aqueous polymer emulsion can be obtained. In such emulsion polymerization, since the copolymer (a) functions as a surfactant (emulsifier), the use amount of the emulsifier such as a protective colloid or another surfactant during the emulsion polymerization is smaller than in the case of ordinary emulsion polymerization. It can be made in small amounts and, if desired, no other emulsifiers can be used. As a result, the heat-sensitive adhesive sheet of the present invention is more excellent in water resistance than an adhesive sheet in which an adhesive layer is formed using an aqueous emulsion obtained by ordinary emulsion polymerization.

As the polymerization initiator that can be used in the emulsion polymerization, any polymerization initiator generally used in emulsion polymerization can be used. For example, the polymerization initiator for obtaining the above-mentioned copolymer (a) can be used. The same organic peroxides, inorganic peroxides, or azo compounds as those exemplified as the radical polymerization initiator can be used. The preferred amount of the polymerization initiator to be used is from 0.1 to
5% by weight.

In the above-mentioned emulsion polymerization for producing the aqueous polymer emulsion, a chain transfer agent may be used for adjusting the molecular weight of the obtained polymer. As such a chain transfer agent, a copolymer ( Chain transfer agents having a mercapto group as described above for the preparation of a) are preferably used.

The polymerization temperature for producing the aqueous polymer emulsion is preferably about 0 to 150 ° C., and more preferably 20 to 90 ° C. Further, the polymerization time at that time is preferably about 1 to 24 hours,
More preferably, it is about 3 to 8 hours.

In the aqueous polymer emulsion, a copolymer portion (a) and a polymer portion produced from a radical polymerizable monomer containing alkyl (meth) acrylate as a main component [hereinafter referred to as “(meth) ) Alkyl acrylate-based polymer portion] is a core / shell structure, that is, a structure in which the alkyl (meth) acrylate-based polymer serves as a core and the copolymer (a) serves as a shell. It is presumed that it constitutes.

In the aqueous polymer emulsion, the weight ratio of the copolymer (a) portion to the alkyl (meth) acrylate-based polymer portion is represented by the weight ratio of the copolymer (a) Part / (meth) acrylic acid alkyl ester-based polymer part = 5/95 to 80/20, preferably 10/90 to 60/40. When the amount of the copolymer (a) is less than 5% by weight based on the solid content (total amount of the polymer) in the aqueous polymer emulsion, the resulting pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer at room temperature (25 ° C.). ) Exceeds 10 g / 25 mm, and such an adhesive sheet is not an object of the present invention, which is an adhesive sheet that does not require a release treatment (treatment with release paper or a release agent). On the other hand, when the proportion of the copolymer (a) in the aqueous polymer emulsion exceeds 80% by weight based on the solid content of the aqueous polymer emulsion, the Tg of the pressure-sensitive adhesive layer formed from the aqueous polymer emulsion is reduced. When the temperature is too high, the adhesive performance developed by heating or pressurization tends to be inferior.

The above-mentioned aqueous polymer emulsion used for the pressure-sensitive adhesive layer of the heat-sensitive pressure-sensitive adhesive sheet of the present invention may be, depending on its use, an antifoaming agent, a surfactant, and a fungicide, which are generally used in general pressure-sensitive adhesives. , Fragrance, neutralizer, tackifier, thickener, leveling regulator, antifreeze, foaming agent, antioxidant, ultraviolet absorber, reinforcing agent, filler, pigment, fluorescent brightener, antistatic agent , An anti-blocking agent, a flame retardant, a cross-linking agent, a plasticizer, a lubricant, an organic solvent or a colorant.

In the heat-sensitive adhesive sheet of the present invention, the type of the substrate is not particularly limited, and an appropriate material can be used according to the use of the heat-sensitive adhesive sheet.
Examples include films, sheets, plates, foamed plastic sheets, and the like made of paper, leather, wood, metal, glass, various plastics, and the like. In this case, examples of the base material made of the plastic described above include base materials made of polyester, polyamide, vinyl chloride polymer, polyethylene, polypropylene, polyurethane, and the like. In addition, the shape of the base material may be any of a long body, a shape cut into a predetermined size (for example, a shape cut in advance into a square, a circle, an ellipse, or another shape).

The heat-sensitive adhesive sheet of the present invention can be produced by applying the above-mentioned aqueous polymer emulsion to one or both surfaces of the above-mentioned substrate and drying it by an appropriate method. At that time, the method for applying the pressure-sensitive adhesive composition to the substrate is not particularly limited, and may be performed using any method such as roll coater coating, spray coating, casting coating, doctor plate coating, brush coating, and the like. Can be. In drying the pressure-sensitive adhesive composition applied on the substrate, it is necessary to heat the pressure-sensitive adhesive layer in the finally obtained pressure-sensitive adhesive sheet at a temperature such that the pressure-sensitive adhesive layer does not exhibit tackiness at normal temperature. It is dried at a temperature equal to or lower than the Tg of the copolymer (a) contained in the product. A more preferred drying temperature is a temperature that is 10 to 20 ° C. lower than the Tg of the copolymer (a).

In the heat-sensitive adhesive sheet of the present invention, the thickness of the pressure-sensitive adhesive layer can be appropriately adjusted according to the use and the like, but it is generally preferable to set the thickness to about 1 μm to 1 mm. When the sheet is heated and / or pressed to adhere to the adherend, the pressure-sensitive adhesive layer can exhibit good adhesiveness.

The heat-sensitive adhesive sheet according to the present invention is JIS Z
Temperature 2 by 180 degree peeling method specified in 0237
Since the adhesive strength at 5 ° C. is 10 g / 25 mm or less and does not exhibit adhesiveness at ordinary temperature or the adhesive strength at ordinary temperature is extremely small, the peeling treatment for the adhesive layer is different from the conventional general-purpose adhesive sheet. Can be stored, distributed and sold simply without packaging, or without packaging, as is the case with normal non-sticky products.
At that time, "not subjected to the peeling treatment" in the present invention means,
This means that the pressure-sensitive adhesive layer of the heat-sensitive pressure-sensitive adhesive sheet is not covered with a release paper, and that in the case of a wrap-around pressure-sensitive adhesive tape, no special release treatment is performed on the back surface of the substrate. Of course, if necessary, for example, the adhesive strength at 25 ° C. is 3 to 10 g / 25 mm.
In the case of the pressure-sensitive adhesive sheet, a peeling treatment may be applied depending on the use of the pressure-sensitive adhesive sheet.

In attaching the heat-sensitive adhesive sheet of the present invention to an adherend, the pressure-sensitive adhesive layer of the heat-sensitive adhesive sheet is heated, the side of the adherend is heated, or the heat-sensitive adhesive sheet is adhered to the heat-sensitive adhesive sheet. The heat-sensitive adhesive sheet can be adhered to the adherend by heating both of the adherends. The heating temperature for causing the pressure-sensitive adhesive layer to exhibit tackiness depends on the Tg of the copolymer (a) contained in the pressure-sensitive adhesive composition, and is usually at least 10 ° C., preferably 30 ° C. or more higher than the Tg. Is suitable. Further, when the pressure-sensitive adhesive layer of the heat-sensitive adhesive sheet of the present invention to exhibit adhesiveness by pressurizing, by applying a pressing force to the heat-sensitive adhesive sheet at a writing pressure of about the writing when using a ballpoint pen, the heat-sensitive adhesive sheet Can be attached to an adherend.

The pressure-sensitive adhesive sheet of the present invention once adhered to the adherend can be used even when the temperature returns to normal temperature or the pressing force is released.
Without losing its adhesiveness, it adheres well to the adherend,
It does not come off naturally. Then, when it is desired to peel the heat-sensitive adhesive sheet of the present invention from the adherend, it can be easily peeled off from the adherend by pulling it with a hand or the like, similarly to a general-purpose adhesive sheet. Because the layers are sticky,
It can be re-applied to the same adherend or another adherend.

The material and type of the adherend to which the heat-sensitive adhesive sheet of the present invention can be adhered are not particularly limited. For example, cloth, paper, leather, wood, metal, glass, concrete, ceramic,
It can be satisfactorily adhered to any of polyester, polyethylene, polypropylene, polyvinyl chloride, polyurethane, polycarbonate, polyamide, polyimide, styrene-based polymer, rubbers and the like.

[0047]

The present invention will be specifically described below with reference to Synthesis Examples, Examples and Comparative Examples, but the present invention is not limited thereto. In each of the following examples, “parts” and “%” indicate “parts by weight” and “% by weight”, respectively, unless otherwise specified. The adhesive strength, holding power, probe tack and water resistance of the adhesive sheet were measured or evaluated by the following methods.

(1) Adhesive force of pressure-sensitive adhesive sheet: A polyester film having a thickness of 50 μm has a coating film thickness of 20 after drying.
The pressure-sensitive adhesive composition is applied to a thickness of
Dry at 0 ° C for 5 minutes to make an adhesive sheet. The pressure-sensitive adhesive sheet was cut into a width of 25 mm and a length of about 250 mm to obtain a test piece. The test piece was left unheated (i) (2)
5 ° C), (ii) after heating to 100 ° C for 2 minutes, or (iii) after heating to 140 ° C for 2 minutes, affixed to a polished stainless steel plate as a test plate, and pressed and reciprocated with a 2 kg rubber roller. After 30 minutes, the adhesive strength at 180 ° C. peeling off from the test plate at a tensile speed of 300 mm / min was determined. It measured according to the adhesive strength of JISZ0237.

(2) Holding force of adhesive sheet: JIS Z
It was measured according to the holding power of 0237. That is, the same pressure-sensitive adhesive sheet as in the pressure-sensitive adhesive test was prepared, and the pressure-sensitive adhesive sheet was cut into a width of 25 mm and a length of about 150 mm to obtain a test piece. The test piece was left untreated (i) without heat treatment (25
° C), (ii) after heating to 100 ° C for 2 minutes, or (iii) after heating to 140 ° C for 2 minutes, so that the 25 mm x 25 mm area of the test piece is in contact with a stainless steel plate as a test plate, A 2 kg rubber roller was pressed back and forth once, and after 30 minutes, a load of 1 kg was applied at 40 ° C. to measure the time until the sample was peeled off. When held for 3 hours, the shifted distance was measured. In addition, when it peeled off immediately after applying a load, it was set to "0 minutes".

(3) Probe tack of adhesive sheet: JI
It was measured according to the probe tack test of SZ0237. That is, the same adhesive sheet as in the case of the adhesive strength test was prepared, and the adhesive sheet was cut into a width of about 20 mm and a length of about 20 mm to obtain a test piece. Using a test piece, after the same operation as (i) to (iii) in the above (2), a cylindrical probe having a diameter of 5 mm, a contact speed and a peeling speed of 0.2 / sec.
cm and a contact load of 0.98 ± 0.01 N / cm.

(4) Water resistance of the pressure-sensitive adhesive sheet: A pressure-sensitive adhesive sheet was prepared in the same manner as in the pressure-sensitive adhesive test, and was placed in water at 20 ° C.
After immersion for a time, the whitened state was observed with the naked eye, and the case where whitening did not occur was evaluated as 、, and the case where whitened was evaluated as ×.

<< Synthesis Example 1 >> [Preparation of Aqueous Solution of Copolymer (a ₁ )] (1) 20 parts of butyl methacrylate, 10 parts of methyl methacrylate, 35 parts of acrylonitrile, 2-methacrylic acid 2-
In a mixture of 10 parts of hydroxyethyl, 25 parts of methacrylic acid and 100 parts of methyl ethyl ketone, 0.5 part of 2,2′-azobisisobutyronitrile was dissolved, and a stirrer, a condenser, a thermometer, and a nitrogen inlet tube were provided. After charging in a flask and heating at 80 ° C. for 4 hours under a nitrogen atmosphere, 0.5 part of 2,2′-azobisisobutyronitrile was further charged, and the mixture was heated at the same temperature for 5 hours to give a solid content of 50%. % Of a copolymer before neutralization (acid value: 162.5 mg KOH / g copolymer) in methyl ethyl ketone was obtained. (2) 3.9% while stirring with 201 parts of a methyl ethyl ketone solution of the copolymer before neutralization obtained in the above (1).
100 parts of aqueous ammonia was gradually added to neutralize the carboxyl groups in the copolymer before neutralization, and the pH of the reaction solution was adjusted to 7
Then, methyl ethyl ketone was removed at a temperature of 50 ° C. under reduced pressure to obtain an aqueous solution (pH 7.7) of the copolymer (a) having a carboxyl group neutralized (solid content 54%). Hereinafter, this is referred to as “aqueous solution of copolymer (a ₁ )”].

<< Synthesis Examples 2 to 7 >> Solution polymerization was performed in the same manner as in Synthesis Example 1 using the monomers shown in Table 2 below to obtain a methyl ethyl ketone solution of the copolymer before neutralization. Ammonia water or an aqueous solution of triethanolamine was added in the same manner as in Synthesis Example 1 to neutralize the carboxyl groups in the copolymer before neutralization to adjust the pH of the reaction solution to about 7 to 8, and then methyl ethyl ketone under reduced pressure removal of the neutralized copolymer of a carboxyl group (a ₂₎ ~ copolymer (a ₃₎ solution and the copolymer (b ₁₎ ~ copolymer (b ₄₎ aqueous solution was prepared respectively.

The contents of the copolymer (a ₁ ) to copolymer (a ₃ ) aqueous solution and the copolymer (b ₁ ) to copolymer (b ₄ ) aqueous solution obtained in the above Synthesis Examples 1 to 7 [ Table 2 below shows the monomer composition, Tg, and type of base for neutralization of the copolymer (copolymer before neutralization) contained in the aqueous solution. In Tables 2 and 3 below, the monomers are indicated by abbreviations, and the abbreviations and their contents are as shown in Table 1 below.

[0055]

[Table 1] Abbreviation: Type of monomer BMA: butyl methacrylate MMA: methyl methacrylate AN: acrylonitrile HEMA: 2-hydroxyethyl methacrylate MAA: methacrylic acid ST: styrene AA: acrylate AEH: 2-ethylhexyl acrylate BA: butyl acrylate EA: ethyl acrylate INA : Isononyl acrylate NMAM: N-methylolacrylamide

[0056]

[Table 2]

Example 1 (1) A monomer mixture was prepared by mixing 95 parts of 2-ethylhexyl acrylate and 5 parts of 2-hydroxyethyl methacrylate. (2) 100 parts of deionized water and Synthesis Example 1 were placed in a flask equipped with a stirrer, thermometer, condenser, and nitrogen inlet tube.
30 parts of the aqueous solution of the copolymer (a ₁ ) prepared in the above was added, and the temperature was raised to 60 ° C. in a nitrogen atmosphere. Then, 5 parts of an aqueous solution of t-butyl hydroperoxide, Rongalit (trade name: formaldehyde sodium sulfo 5 parts of a 10% aqueous solution of xylate dihydrate) and 100 parts of the monomer mixture prepared in the above (1) were separately added dropwise over 3 hours. After the dropwise addition, the reaction was continued at the same temperature for another 2 hours to terminate the polymerization, thereby obtaining an aqueous polymer emulsion having a solid content of about 49%. The contents of the obtained aqueous polymer emulsion were as shown in Table 3 below. (3) The aqueous polymer emulsion obtained in the above (2) was applied to a polyester film having a thickness of 50 μm by a bar coater so that the thickness of the pressure-sensitive adhesive layer after drying was 20 to 30 μm. The adhesive sheet was dried by drying at a drying temperature for 5 minutes. (4) When the pressure-sensitive adhesive strength, holding power, probe tack and water resistance of the pressure-sensitive adhesive sheet obtained in the above (3) were measured or evaluated by the above-mentioned methods, the results were as shown in Table 4 below.

Example 2 (1) 25 parts of butyl acrylate, 70 parts of 2-ethylhexyl acrylate, 4.9 parts of acrylonitrile and N
-A monomer mixture was prepared by mixing 0.1 part of methylolacrylamide. (2) Aqueous solution of copolymer (a ₂ ) 3 prepared in Synthesis Example 2
0 parts and 40 parts of deionized water were mixed with the monomer mixture prepared in the above (1), and emulsified by a three-one motor to prepare an aqueous emulsified dispersion. The contents of the obtained aqueous polymer emulsion were as shown in Table 3 below. (3) In a flask similar to that used in (2) of Example 1, 60 parts of deionized water and sodium carbonate (neutralizing agent)
0.2 parts were added, and while blowing nitrogen, the internal temperature of the flask was maintained at 70 ° C., and while stirring, an aqueous solution of ammonium persulfate (ammonium persulfate / deionized water = 0.3 part /
9.7 parts) 10 parts and 200 parts of the aqueous emulsified dispersion prepared in the above (2) were added dropwise over 3 hours, and the reaction was further continued for 2 hours to complete the polymerization, and the solid content concentration was reduced to about 49
% Aqueous polymer emulsion was prepared. The contents of the obtained aqueous polymer emulsion were as shown in Table 3 below. (4) Using the aqueous polymer emulsion obtained in (3) above, an adhesive sheet was prepared in the same manner as in (3) of Example 1, and the adhesive strength, holding power, probe tack and water resistance were described above. When measured or evaluated by the method, the results were as shown in Table 4 below.

Example 3 (1) 35 parts of ethyl acrylate, butyl acrylate 6
0 parts, 4.7 parts of methyl methacrylate and 0.3 part of N-methylolacrylamide were mixed to prepare a monomer mixture. (2) Synthesis example 3 during production of aqueous polymer emulsion
20 parts of the aqueous solution of the copolymer (a ₃ ) prepared in
An aqueous polymer emulsion was prepared by emulsion polymerization in the same manner as in (2) of Example 1 except that 100 parts of the monomer mixture prepared in Example 1 was used. An aqueous polymer emulsion as shown in Table 3 below was prepared. was gotten. (3) Using the aqueous polymer emulsion obtained in (3) above, an adhesive sheet was prepared in the same manner as in (3) of Example 1, and the adhesive strength, holding power, probe tack and water resistance were described above. When measured or evaluated by the method, the results were as shown in Table 4 below.

Example 4 (1) 95 parts of butyl acrylate, acrylonitrile 4
And 1 part of acrylic acid were mixed to prepare a monomer mixture. (2) Synthesis example 1 during production of aqueous polymer emulsion
30 parts of the aqueous solution of the copolymer (a ₁ ) prepared in
Using 100 parts of the monomer mixture prepared in the above, emulsion polymerization was carried out in the same manner as in Example 1, (2) to prepare an aqueous polymer emulsion. As a result, an aqueous polymer emulsion as shown in Table 3 below was obtained. Was done. (3) Using the aqueous polymer emulsion obtained in (3) above, an adhesive sheet was prepared in the same manner as in (3) of Example 1, and the adhesive strength, holding power, probe tack and water resistance were described above. When measured or evaluated by the method, the results were as shown in Table 4 below.

<< Comparative Examples 1-4 >> As a radical polymerizable monomer mixture containing an alkyl (meth) acrylate polymer as a main component, a monomer mixture 10 shown in Table 3 below was used.
Emulsion polymerization was carried out in the same manner as in Example 1 except that 0 parts by weight and 30 parts by weight of the aqueous copolymer solution shown in Table 3 below were used to prepare aqueous polymer emulsions. A pressure-sensitive adhesive sheet was prepared using the combined emulsion in the same manner as in Example 1, and the pressure-sensitive adhesive strength, holding power, probe tack, and water resistance were measured or evaluated by the above-described methods. The results were as shown in Table 4 below. there were.

<< Comparative Example 5 >> At the time of emulsion polymerization, the copolymer (a
₁ ) An aqueous polymer emulsion was prepared in exactly the same manner as in Example 1 except that 20 parts of a 25% aqueous solution of sodium dodecylbenzenesulfonate was used instead of 30 parts of the aqueous solution, and carried out using the aqueous polymer emulsion. A pressure-sensitive adhesive sheet was prepared in the same manner as in Example 1, and the pressure-sensitive adhesive strength, holding power, probe tack and water resistance were measured or evaluated by the above-mentioned methods. The results were as shown in Table 4 below.

[0063]

[Table 3]

[0064]

[Table 4]

From the results in Table 4 above, it is found that the copolymer obtained by copolymerizing a monomer mixture mainly composed of an α, β-ethylenically unsaturated carboxylic acid and a hydrophobic radically polymerizable monomer. (A ₁ ) having a glass transition temperature of 20 ° C. or higher in which part or all of the carboxyl groups in the copolymer is neutralized with a base having a boiling point of 110 ° C. or lower.
Example 1 having a pressure-sensitive adhesive layer formed from an aqueous polymer emulsion obtained by emulsion-polymerizing a radical polymerizable monomer mainly containing an alkyl (meth) acrylate in the presence of (a ₃ ) JIS Z
Adhesive strength at a temperature of 25 ° C. by a 180 ° peeling method specified in 0237 is 10 g / 25 mm or less, and does not exhibit adhesiveness at room temperature, while exhibiting good adhesiveness when heated, as a heat-sensitive adhesive sheet It turns out that it can be used effectively.

On the other hand, Comparative Examples 1 and 3 to
4, which is a copolymer obtained by copolymerizing a monomer mixture mainly composed of an α, β-ethylenically unsaturated carboxylic acid and a hydrophobic radical polymerizable monomer, Radical polymerizable monomer having alkyl (meth) acrylate as a main component in the presence of a copolymer whose part or whole amount is neutralized with a base but whose Tg is lower than 20 ° C. In the case of a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from an aqueous polymer emulsion obtained by emulsion polymerization of the above, it has high tackiness even at room temperature and has no heat-sensitive properties.

Further, from the results of Comparative Examples 2 and 4, it can be obtained by copolymerizing a monomer mixture mainly composed of an α, β-ethylenically unsaturated carboxylic acid and a hydrophobic radically polymerizable monomer. It is understood that the use of a copolymer whose carboxyl group is neutralized with a base having a boiling point higher than 110 ° C. results in poor water resistance of the pressure-sensitive adhesive sheet. From the results of Comparative Example 5, it was found that the copolymer (a) was used without using the above-described copolymer (a) and using a normal surfactant.
In an adhesive tape having an adhesive layer formed from an aqueous polymer emulsion obtained by emulsion polymerization of a radical polymerizable monomer having an alkyl acrylate as a main component,
The pressure-sensitive adhesive layer already shows tackiness even at room temperature, and the tackiness is basically unchanged before and after the heat treatment.

[0068]

Since the heat-sensitive adhesive sheet of the present invention exhibits no or little adhesiveness at room temperature, it can be used for an adhesive such as the use of release paper or the application of a release agent to the back surface of a substrate. There is no need to apply a peeling treatment to the layer, and it can be stored, distributed and / or sold, with or without packaging, as it is, in terms of resource saving, simplification of the process for manufacturing the adhesive sheet and cost. Very good. The heat-sensitive adhesive sheet of the present invention can exhibit various adhesive properties from high adhesiveness to medium adhesiveness and, in some cases, slightly lower adhesiveness by heating and / or pressurizing. By utilizing such properties, it can be effectively used for, for example, labels, tapes, seals for packages, wallpapers, markings, and other wide-ranging applications. Especially when used for wallpaper etc.
It is also possible to use a method in which positioning is performed using low tackiness, and thereafter, wallpaper is adhered and fixed by applying heat.

Further, the heat-sensitive adhesive sheet of the present invention exhibits adhesiveness by heating and / or pressurizing and adheres to an adherend, and even if the temperature returns to normal temperature, the adhesive force once developed does not exhibit the adhesive force. Since the adhesive sheet is maintained, the adhered pressure-sensitive adhesive sheet does not peel off from the adherend. And when it is desired to peel off the heat-sensitive adhesive sheet of the present invention stuck to the adherend, it can be easily peeled off simply by pulling with a hand or the like,
The peeled one can be attached again to the same adherend or another adherend if necessary. Furthermore, in the heat-sensitive adhesive sheet of the present invention, there is a degree of freedom in setting the heating temperature for developing the adhesiveness, and even if the adhesive layer is not hardened over time, even if the adhesive sheet is bent, There is no fear of peeling off from the adherend, and furthermore, there is no trouble that components in the pressure-sensitive adhesive layer seep into the base material. In the present invention, the aqueous polymer emulsion used to form the pressure-sensitive adhesive layer does not contain a low-molecular-weight surfactant, or the aqueous solution obtained by ordinary emulsion polymerization even when it is contained. Since the amount can be smaller than that contained in the polymer emulsion, a heat-sensitive adhesive sheet having excellent water resistance of the adhesive layer can be obtained.

Claims (1)

[Claims] 1. A radical polymerizable monomer having a glass transition temperature of −10 ° C. or lower containing alkyl (meth) acrylate as a main component in the presence of the following copolymer (a): A heat-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from an aqueous polymer emulsion on a substrate, which is obtained by emulsion polymerization, and is a heat-sensitive adhesive sheet specified in JIS Z 0237.
10g adhesive strength at 25 ° C by 0 degree peeling method
/ Comm (a): α, β-ethylenically unsaturated carboxylic acid unit and hydrophobic radical polymerizable monomer unit as main constituent units. Some or all of the carboxyl groups in the copolymer are neutralized with a base having a boiling point of 110 ° C. or lower,
A water-soluble or water-dispersible copolymer having a glass transition temperature of 20 ° C or higher.