JPH0735405B2 - Adhesive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an aqueous dispersion type pressure-sensitive adhesive used for the production of pressure-sensitive adhesive products such as pressure-sensitive adhesive paper, pressure-sensitive adhesive tape, and pressure-sensitive adhesive sheets.

[Problems to be Solved by Prior Art and Present Invention]

In recent years, adhesive products such as paper labels with adhesive layers, single-sided or double-sided adhesive tapes, and adhesive sheets with various designs have been widely used in various fields, and their application range will continue to expand. It seems to go. As the use of adhesive products expands, the demands on quality have become more sophisticated, and expectations for higher performance of adhesives are increasing. Although various natural or synthetic polymers are used as the pressure-sensitive adhesive, among them, acrylic polymers are preferred because they have good weather resistance and it is easy to design an appropriate resin according to the application. There is one. Acrylic polymers are often used in the form of organic solvent solutions or aqueous dispersions, and the organic solvent solution type may cause air pollution or fire, and there is a problem that the cost of the solvent is high, etc. The aqueous dispersion type is preferable in that these problems do not occur, but the aqueous dispersion type does not exhibit the adhesive performance inherent to the resin due to the effect of the emulsifier for emulsifying and dispersing the resin component in water, water resistance and moisture resistance. It had a performance defect such as poor performance. An object of the present invention is to develop an aqueous dispersion type pressure-sensitive adhesive that does not have the above-mentioned drawbacks.

[Means and Actions for Solving Problems]

The present inventors have an aqueous resin dispersion liquid obtained by emulsion-polymerizing a polymerizable monomer having a long-chain thioalkyl group at the terminal and using a polymer having a carboxyl group in the molecule as an emulsifier. The inventors have found that they can achieve the goal and completed the present invention.

That is, the present invention has an acid value of 20 obtained by polymerizing a polymerizable monomer component (A) containing an unsaturated carboxylic acid as an essential component in the presence of an alkylmercaptan (B) having 6 to 18 carbon atoms.
A polymer [I] having 0 or more water-soluble or water-dispersible terminal alkyl groups and / or a salt thereof is used as an emulsifier, and one or more kinds selected from the group consisting of an epoxy group, an aziridinyl group and an oxazolinyl group. A polymerizable monomer component (M) containing a polymerizable monomer having a functional group and / or an organic silicon monomer having a polymerizable unsaturated group and a hydrolyzable group directly bonded to a silicon atom in the molecule is prepared. The present invention relates to a pressure-sensitive adhesive containing an aqueous resin dispersion obtained by emulsion polymerization in an aqueous medium.

The polymer [I] used as the emulsifier in the present invention is obtained by the above-mentioned procedure, but it has an acid value of 200 or more in view of stability during emulsion polymerization and various physical properties of the resulting resin as an adhesive. There must be. The molecular weight is 300-700.
It is preferably 0, particularly in the range of 400 to 4000. If a polymer having a molecular weight outside this range is used, sufficient emulsion stability may not be obtained, or the performance such as water resistance, moisture resistance and tackiness may not be satisfactory.

The unsaturated carboxylic acid used in the synthesis of the polymer [I] has a functional group capable of introducing a carboxyl group into the polymer [I] to impart hydrophilicity and at the same time imparting curability to the resulting aqueous resin dispersion. It is used for that, and is not particularly limited as long as it has a carboxyl group and / or its salt and a polymerizable unsaturated group in the molecule, and examples thereof include (meth) acrylic acid, crotonic acid, maleic acid, Examples thereof include fumaric acid, itaconic acid, half esters thereof, salts thereof, and the like, and one kind or a mixture of two or more kinds thereof can be used.

Polymerizable monomer component (A) when synthesizing the polymer [I]
May be composed only of unsaturated carboxylic acid, but if necessary, a polymerizable monomer other than unsaturated carboxylic acid may be used in combination. The polymerizable monomer that can be used is not particularly limited as long as it is copolymerizable with an unsaturated carboxylic acid, and examples thereof include styrene, vinyltoluene, α-methylstyrene, chloromethylstyrene, styrenesulfonic acid and salts thereof. (Meth) acrylamides such as (meth) acrylamide, N-monomethyl (meth) acrylamide, N-monoethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide; (meth) acrylic acid (Meth) acrylic acid esters synthesized by esterification of (meth) acrylic acid such as methyl, ethyl (meth) acrylate, and butyl (meth) acrylate with C _{1 to} C ₁₈ alcohol; (meth) acrylic acid 2-hydroxyethyl, 2-hydroxypropyl (meth) acrylate, (meth) acrylic Hydroxyl group-containing (meth) acrylic acid ester such as monoester of acid with polypropylene glycol or polyethylene glycol; ethyl (meth) acrylate 2-sulfonate and its salt, vinyl sulfonic acid and its salt, vinyl acetate,
(Meth) acrylonitrile and the like can be mentioned, and one kind or a mixture of two or more kinds thereof can be used. Polymerizable monomer other than unsaturated carboxylic acid is a polymer [I] obtained.
It is used in an amount such that the acid value of is over 200. In addition, it is preferable to select the type and amount of the polymer [I] in consideration of the compatibility with the polymer component produced during emulsion polymerization.

Examples of the alkyl mercaptan (B) that can be used when synthesizing the polymer [I] include, for example, n-hexyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, cetyl mercaptan, stearyl mercaptan. And a mixture of one or more of these can be used. The alkyl mercaptan (B) is used for introducing an alkyl group at the terminal of the polymer [I] to impart surface activity, and the alkyl mercaptan having a carbon number of less than 6 has stability during emulsion polymerization and It cannot be used in terms of storage stability. The amount of the alkyl mercaptan (B) used is determined by the desired molecular weight of the polymer [I].
2 to 300 per 100 parts by weight of the polymerizable monomer component (A)
Used in the range of parts by weight.

The polymerization initiator used for the polymerization of the polymerizable monomer component (A) is
Well-known oil-soluble and water-soluble polymerization initiators can be used, but in order to efficiently produce the polymer [I] having a terminal alkyl group, the amount used is 1 mol or less per 1 mol of alkyl mercaptan (B). , And more preferably 0.1 mol or less.

The polymer [I] may be bulk-polymerized, solution-polymerized,
It can be produced by any method of suspension polymerization. The polymerization temperature is preferably 50 to 150 ° C, and the polymerization time is preferably 1 to 8 hours. As the solvent for the solution polymerization, any solvent can be used as long as it can dissolve the polymerizable monomer component (A), the alkyl mercaptan (B) and the radical polymerization initiator and does not inhibit the radical polymerization.

The polymer [I] has a sufficient surface-active ability by itself, but in order to obtain the desired aqueous resin dispersion having good stability during storage and storage stability when used in emulsion polymerization, It is preferable to neutralize a part or the whole amount and use it as a salt of the polymer [I].

As the neutralizing agent, usual ones can be used, for example, alkali metal compounds such as sodium hydroxide and potassium hydroxide; alkaline earth metal compounds such as calcium hydroxide and calcium carbonate; ammonia; monomethylamine, dimethyl Water-soluble organic amines such as amine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dimethylpropylamine, monoethanolamine, diethanolamine, triethanolamine, ethylenediamine and diethylenetriamine are listed, and selected from these groups 1 It can be used in one kind or a mixture of two or more kinds. When it is desired to further improve the water resistance of the cured film, it is preferable to use low boiling point amines such as ammonia, monomethylamine, dimethylamine and trimethylamine, which scatter at room temperature or upon heating.

The polymerizable monomer component (M) used for obtaining the pressure-sensitive adhesive of the present invention is a polymerizable monomer having one or more functional groups selected from the group consisting of epoxy group, aziridinyl group and oxazolinyl group. Alternatively, it is necessary to include either or both of an organic silicon monomer having a polymerizable unsaturated group and a hydrolyzable group directly bonded to a silicon atom in the molecule. The epoxy group, aziridinyl group, and oxazolinyl group have reactivity with the carboxyl group in the polymer [I] used as an emulsifier. The polymerizable monomers having these functional groups are collectively referred to as "polymerizable monomers having a functional group capable of reacting with a carboxyl group" below. Examples of such a polymerizable monomer include epoxy group-containing polymerizable monomers such as glycidyl (meth) acrylate, 2-methylglycidyl (meth) acrylate, and allylglycidyl ether; (meth) acryloylaziridine, Aziridinyl group-containing polymerizable monomers such as 2-aziridinylethyl (meth) acrylate; Oxazolinyl group-containing polymerizable monomers such as 2-isopropenyl-2-oxazoline and 2-vinyl-2-oxazoline Is mentioned. Examples of the organic silicon monomer having a polymerizable unsaturated group and a hydrolyzable group directly bonded to a silicon atom in the molecule include vinyltrimethoxysilane, γ- (meth) acryloxypropyltrimethoxysilane and allyltriethoxysilane. , Trimethoxysilylpropylallylamine, and other organic silicon-containing polymerizable monomers. By using a polymerizable monomer having a functional group capable of reacting with the above-mentioned carboxyl group and / or an organic silicon monomer, the balance between adhesive strength and creep resistance, water resistance, moisture resistance, and adhesiveness at low temperature can be obtained. It can be further improved and properties such as removability can be imparted.

The polymerizable monomer component (M) other than the above-mentioned monomers is not particularly limited as long as it is a polymerizable one, but one of the following examples may be used depending on the purpose and application. Two or more kinds can be used in combination. For example, styrene derivatives such as styrene, vinyltoluene, α-methylstyrene, chloromethylstyrene, styrenesulfonic acid and salts thereof; (meth) acrylamide, N-
(Meth) acrylamide derivatives such as monomethyl (meth) acrylamide, N-monoethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide;
(Meth) acrylic acid esters synthesized by esterification of (meth) acrylic acid such as methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate with C _{1 to} C ₁₈ alcohol; Hydroxy group-containing (meth) acrylic acid esters such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and monoesters of (meth) acrylic acid with polypropylene glycol or polyethylene glycol; ) Basic polymerizable monomers such as dimethylaminoethyl acrylate, dimethylaminoethyl (meth) acrylamide, dimethylaminopropyl (meth) acrylamide, vinylpyridine, vinylimidazole, vinylpyrrolidone; (meth) acrylic acid and ethylene glycol , 1,3-butyre Polymerizable unsaturated groups in the molecule such as glycol, diethylene glycol, 1,6-hexane glycol, neopentyl glycol, polyethylene glycol, polypropylene glycol, trimethylolpropane, pentaerythritol, dipentaerythritol and other polyhydric alcohol esters. Polyfunctional (meth) acrylic acid esters having two or more; N-methylol (meth) acrylamide, N-butoxymethyl (meth)
(Meth) acrylamides such as acrylamide; and vinyl fluoride, vinylidene fluoride, vinyl chloride, vinylidene chloride, divinylbenzene, diallyl phthalate, ethyl (meth) acrylate 2-sulfonate and its salt, vinyl sulfonic acid and its salt , Vinyl acetate, vinyl propionate, (meth) acrylonitrile and the like.

As the emulsion polymerization method, any conventionally known emulsion polymerization method can be applied. For example, the aqueous resin dispersion of the present invention is prepared by a method in which a polymerization catalyst, water, the polymer [I] and the polymerizable monomer component (M) are mixed together for polymerization, or a method such as a so-called monomer dropping method or pre-emulsion method. The liquid can be synthesized. The polymerization temperature is 0 to 100 ° C, preferably 50 to 80 ° C, and the polymerization time is 1 to 10 hours. During emulsion polymerization, adding a hydrophilic solvent and other known emulsifiers,
Additives can be added within a range that does not adversely affect the physical properties of the pressure-sensitive adhesive. The amount of the polymer [I] used is not particularly limited, but is preferably 0.5 to 200 parts by weight, more preferably 1 to 15 parts by weight, based on 100 parts by weight of the polymerizable monomer component (M).

As the polymerization catalyst, any conventionally known catalyst can be used. However, in order to obtain an aqueous resin dispersion that gives a pressure-sensitive adhesive having even more excellent water resistance, hydrogen peroxide, di-t-butyl peroxide, peracetic acid, 2,2'-azobis (2-amidinopropane) diamine It is preferable to use one or a mixture of two or more polymerization catalysts that do not leave a sulfate group, such as hydrochloride and 4,4′-azobis (4-cyanopentanoic acid). Further, at least 1 in the polymerizable monomer component (M)
When the species has a functional group capable of reacting with a carboxyl group, 2,2′-containing an amidino group, a carboxyl group, or the like, which has high reactivity with those reactive groups, in the molecule
Azobis (2-amidinopropane) dihydrochloride, 4,4'-
It is more preferable to use azobis (4-cyanopentanoic acid) or the like. The amount of the polymerization catalyst used is usually in the range of 0.01 to 5 parts by weight with respect to 100 parts by weight of the polymerizable monomer component (M).

Further, the polymerizable monomer component (M) is divided into those containing a polymerizable monomer having a functional group capable of reacting with a carboxyl group and / or those not containing an organosilicon monomer, and these are multistage polymerized. By doing so, the tackiness, water resistance, moisture resistance and the like of the pressure-sensitive adhesive containing the obtained aqueous resin dispersion may be remarkably improved. At that time, each polymerizable monomer component may be emulsion-polymerized in any number of stages, and the order of polymerization is not particularly limited, but a functional group capable of reacting with a carboxyl group as a component to be polymerized in the final stage is particularly preferable. It is preferable to use a polymer which does not contain a polymerizable monomer having a group, because the storage stability of the resulting aqueous resin dispersion is dramatically improved.

The aqueous resin dispersion thus obtained can be effectively used as an adhesive by itself, but other known pH adjusting agents, viscosity adjusting agents, water repellents, ultraviolet absorbers,
A leveling agent, a cross-linking agent, a film forming aid, a penetrating agent, etc. may be added, and the composition may be used by adding a pigment or an aggregate. Further, it can be appropriately diluted.

〔The invention's effect〕

Since the pressure-sensitive adhesive of the present invention comprises an aqueous resin dispersion obtained by emulsion-polymerizing a polymerizable monomer using a polymer having a specific structure as an emulsifier, the pressure-sensitive adhesive in a normal state Not only does it have excellent water resistance and moisture resistance, so the adhesive layer does not whiten even when immersed in water, and the adhesiveness and creep resistance do not deteriorate even when placed in high humidity. It can be applied to fields requiring high performance, which could not be used with conventional adhesives. Furthermore, it has excellent adhesive strength at low temperatures, and since it is possible to impart removability,
It can be used for various applications in which these characteristics are required.

Therefore, the pressure-sensitive adhesive of the present invention is extremely useful as a pressure-sensitive adhesive for paper, cloth, plastic pressure-sensitive adhesive labels, pressure-sensitive adhesive tapes, and pressure-sensitive adhesive sheets.

〔Example〕

The present invention is described in detail below with reference to examples, but the scope of the present invention is not limited to these examples.
Unless otherwise specified,% means% by weight and part means part by weight.

Reference Example 1 180 parts of isopropyl alcohol was charged into a flask equipped with a stirrer, a reflux condenser, a nitrogen introduction tube, a thermometer, and a dropping funnel, the internal temperature was raised to 81 ° C. while blowing nitrogen, and isopropyl alcohol was refluxed for 10 minutes. Let Next, 1 part of a previously prepared polymerizable monomer mixture consisting of 174 parts of acrylic acid, 36 parts of n-dodecyl mercaptan, and 0.42 part of 2,2'-azobisisobutyronitrile (AIBN) was prepared.
The mixture was dropped and polymerized over time. After the dripping is completed, 1 at reflux condition
Aging was carried out for a time to obtain a solution of the polymer (1) having a solid content of 53.9%. The polymer (1) had a structure represented by the following general formula, and had an acid value of 645 and a number average molecular weight of 1200.

Reference Example 2 Isopropyl alcohol was placed in the same flask as in Reference Example 1.
180 parts were charged, the internal temperature was raised to 81 ° C. while blowing nitrogen, and isopropyl alcohol was refluxed for 10 minutes.
Then, a previously prepared polymerizable monomer mixture consisting of 86 parts of acrylic acid, 139 parts of 2-hydroxyethyl acrylate, 36 parts of n-dodecyl mercaptan, 30 parts of isopropyl alcohol and 0.30 part of AIBN was used for 1 hour. It was dropped and polymerized. After the dropping is completed, the mixture is aged under reflux for 1 hour to obtain a solid content of 5
A 5.4% solution of polymer (2) was obtained. The polymer (2) had a structure represented by the following general formula, had an acid value of 256 and a number average molecular weight of 1,500.

Reference Example 3 In the same flask as in Reference Example 1, add isopropyl alcohol.
180 parts were charged and heated to 80 ° C while blowing nitrogen. 148 parts of acrylic acid, 31 parts of itaconic acid, 18 parts of lauryl acrylate, 24 parts of n-octyl mercaptan and
A polymerizable monomer mixture consisting of 0.41 part of AIBN was added dropwise over 2.0 hours. After completion of the dropping, the mixture was agitated for 1 hour in a refluxed state and aged to obtain a solution of polymer (3) having a solid content of 54.2%. The polymer (3) had a structure represented by the following general formula, an acid value of 420 and a number average molecular weight of 2,000.

Comparative Reference Example 1 Isopropyl alcohol was placed in the same flask as in Reference Example 1.
180 parts were charged, the internal temperature was raised to 81 ° C. while blowing nitrogen, and isopropyl alcohol was refluxed for 10 minutes.
Subsequently, 86 parts of acrylic acid prepared in advance, 139 parts of 2-hydroxyethyl acrylate, 14 parts of thioglycol and A
A polymerizable monomer mixture consisting of 0.30 part of IBN was added dropwise over 1 hour to polymerize. After completion of the dropping, aging was carried out for 1 hour under reflux to obtain a comparative polymer (1) solution having a solid content of 56.9%.
The polymer for comparison (1) had an acid value of 280 and a number average molecular weight of 1400 having a structure represented by the following general formula.

Comparative Example 1 90 parts of ion-exchanged water was charged into a flask equipped with a dropping funnel, a stirrer, a nitrogen gas introduction tube, a thermometer and a reflux condenser, and heated to 65 ° C. while slowly blowing nitrogen gas. A polymerizable monomer mixture consisting of 190 parts of 2-ethylhexyl acrylate and 10 parts of vinyl acetate, 9.8 parts of a solution of the polymer (1) obtained in Reference Example 1, 3.9 parts of 28% ammonia water and 89.1 parts of ion-exchanged water. Stir well in advance and charge the completely emulsified pre-emulsion into the dropping funnel.
% Amount was dropped into the flask. Subsequently, 8 parts of a 5% aqueous solution of 2,2'-azobis (2-amidinopropane) dihydrochloride was injected. After 20 minutes, the dropping of the remaining pre-emulsion was started and the dropping was completed in 4 hours. After the dropping was completed, the dropping funnel was washed with 10 parts of ion-exchanged water so that the pre-emulsion did not remain, and the washing solution was added into the flask. The temperature was maintained at 65 to 70 ° C during the dropping, and after the dropping was completed, the mixture was stirred at the same temperature for 2 hours to terminate the polymerization, and the nonvolatile content was 49.8%, pH
A comparative aqueous resin dispersion [1] of 7.2 was obtained.

Examples 1 to 6 The same procedure as in Comparative Example 1 was repeated except that the composition of the polymerizable monomer mixture and the kind of the polymer used as the emulsifier in Comparative Example 1 were as shown in Table 1. Dispersions [1] to [6] and comparative aqueous resin dispersions [2] to
[3] was obtained.

Example 7 A flask similar to that of Comparative Example 1 was charged with 193.5 parts of ion-exchanged water, 11 parts of a solution of the polymer (1) and 1.6 parts of 28% ammonia water, and the temperature was raised to 65 ° C. while gently flowing nitrogen gas. 2,2'-azobis (2-amidinopropane)
After injecting 4 parts of a 5% aqueous solution of dihydrochloride, a first polymerizable monomer mixture consisting of 47 parts of butyl acrylate and 3 parts of glycidyl methacrylate, which had been prepared in advance, was added dropwise over 1 hour. did. After stirring for 30 minutes,
A second polymerizable monomer mixture consisting of 48 parts of butyl acrylate and 2 parts of methacryloyloxypropyltrimethoxysilane was added dropwise over 1 hour. After further stirring for 1 hour, the mixture was cooled to obtain an aqueous resin dispersion [7] having a nonvolatile content of 34.2% and a pH of 7.1.

Example 8 Aqueous resin dispersions [1] to [7] obtained in Examples 1 to 7
And the comparative aqueous resin dispersions [1] and [3] obtained in Comparative Examples 1 and 3 were coated on release paper so that the thickness after drying was 15 to 20 μm, and dried at 100 ° C. for 2 minutes. A paper label for testing was produced by pasting coated paper on the adhesive layer and transferring the adhesive layer from the release paper to the coated paper. Then, the physical properties of these test paper labels were evaluated by the test methods shown below. As a result, the aqueous resin dispersions [1] to [7] of the present invention were
It was found that the initial physical properties such as holding power were very excellent, and those physical properties did not deteriorate even after storage under high temperature and high humidity, and showed excellent moisture resistance. However, the comparative aqueous resin dispersion [1] was slightly inferior in tackiness, tackiness and holding power to those of the examples of the present invention, and in [3] the ball tackiness and tackiness after storage at high temperature and high humidity. The physical properties such as strength and holding power were remarkably deteriorated, and the moisture resistance was very poor. Detailed results are shown in Table 2.

Test Method Tack: Tack was measured by the ball rolling method specified in JIS Z-0237.

Adhesive force: 180 ° peeling adhesive force determined by JIS Z-0237 (adherent: stainless steel plate g / 25 mm) was measured. Also, the adhesive force when a polyethylene plate was used as an adherend was measured by the same method.

Holding power: In accordance with the method specified in JIS Z-0237, a sticking area of 20 mm × 20 mm and a load of 1 kg at 40 ° C. were applied, and a holding time or a deviation width after a fixed time was measured.

Example 9 Each aqueous resin dispersion liquid used in Example 8 was treated with OPP tape (1 cm ×
15cm) so that the dry film thickness becomes about 15μm, 105 ℃
And dried for 2 minutes to obtain an adhesive tape. This was attached to a stainless plate and immersed in tap water at 40 ° C for 5 days to evaluate the degree of whitening. The results are shown in Table 3.

Claims (1)

[Claims] 1. An acid value of 200 or more obtained by polymerizing a polymerizable monomer component (A) containing an unsaturated carboxylic acid as an essential component in the presence of an alkylmercaptan (B) having 6 to 18 carbon atoms. A polymer [I] having a water-soluble or water-dispersible terminal alkyl group and / or a salt thereof is used as an emulsifier to prepare one or more functional groups selected from the group consisting of an epoxy group, an aziridinyl group and an oxazolinyl group. A polymerizable monomer component (M) containing a polymerizable monomer and / or an organic silicon monomer having a polymerizable unsaturated group and a hydrolyzable group directly bonded to a silicon atom in a molecule is contained in an aqueous medium. A pressure-sensitive adhesive containing an aqueous resin dispersion obtained by emulsion polymerization according to 1.