JP2008195863A - Adhesive composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an adhesive composition that maintains essential characteristics of natural rubber as the polymer base of an adhesive composition, enhances cohesive power thereof and has an excellent adhesion. <P>SOLUTION: The adhesive composition comprises a modified natural rubber obtained by graft polymerization of a polar group-containing monomer. The polar group-containing monomer is a hydroxyalkyl carboxylic acid ester and/or a dialkylaminoethyl carboxylic acid ester. The graft amount is preferably 0.01-15 wt.% based on the natural rubber. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pressure-sensitive adhesive composition containing natural rubber, and more particularly, to a pressure-sensitive adhesive composition having improved pressure-sensitive adhesive properties by graft polymerization of a polar group-containing monomer on natural rubber.

  The pressure-sensitive adhesive composition is generally composed of a polymer base, a softener component, and a resin component (tackifier). Among these, the polymer base is required to have an affinity with an adherend as a required characteristic, mainly having a function of maintaining the strength of the entire composition. In contrast, the function of the softener component is to improve the adhesion to the adherend by adjusting the hardness of the entire adhesive, and the function of the resin component is the cohesive force (adhesiveness) of the adhesive composition. Is to improve the adhesive strength itself of the pressure-sensitive adhesive composition.

  Therefore, in order to improve the adhesive strength of the pressure-sensitive adhesive composition, it is generally considered that a large amount of a resin component is blended in order to supplement the cohesive strength of the polymer base. However, a large amount of the resin component leads to an increase in the glass transition temperature (Tg) of the composition, and as a result, there is a problem that the dependence of the adhesive property on the temperature becomes very large.

  As another method of improving the cohesive force, there is a method of using an acrylic polymer material having more excellent cohesive force in place of natural rubber which has been conventionally used as a polymer base. Acrylic polymer materials are characterized by good properties that themselves have cohesive strength by having ester groups with high polarity in the molecule. However, although such an acrylic polymer material is excellent in cohesive force, there is a problem that the strength of the material itself is inferior to that of natural rubber due to lack of stretch crystallinity. That is, it can be said that natural rubber is an excellent material in terms of the absolute value of adhesive strength.

  Therefore, in order to improve the pressure-sensitive adhesive properties of the pressure-sensitive adhesive composition, the excellent adhesive strength of the natural rubber was maintained by introducing a polar group into the natural rubber as the polymer base of the pressure-sensitive adhesive composition. It is possible to improve the cohesion of natural rubber. Specifically, by graft polymerizing a polar group-containing monomer to natural rubber, the cohesive force is increased by the hydrogen bonding effect derived from the polar group, and the adhesive performance of the adhesive composition is improved. This method can be said to be an excellent method for improving the adhesive performance of the pressure-sensitive adhesive composition as a whole without increasing the Tg of the composition.

Conventionally, as a pressure-sensitive adhesive composition in which a polar group is introduced into a natural rubber as a polymer base, JP-A-9-25468 proposes using a modified natural rubber obtained by graft polymerization of methyl methacrylate. .
Japanese Patent Laid-Open No. 9-25468

  However, even if methyl methacrylate is graft-polymerized with natural rubber, the effect of improving the cohesive force cannot be said to be sufficiently satisfactory, and further improvement is desired.

  The present invention solves the above-described conventional problems, and maintains an original characteristic of natural rubber as a polymer base of the pressure-sensitive adhesive composition, and further increases the cohesive force and provides a pressure-sensitive adhesive composition with excellent pressure-sensitive adhesive performance. The purpose is to provide.

As a result of repeated researches, the present inventor has improved the cohesive strength by graft polymerization of a specific polar group-containing monomer on natural rubber. It was found that the pressure-sensitive adhesive composition significantly improves the pressure-sensitive adhesive properties.
The present invention is based on such knowledge, and is summarized as follows.

[1] A pressure-sensitive adhesive composition containing a modified natural rubber obtained by graft polymerization of a polar group-containing monomer on natural rubber, wherein the polar group-containing monomer is a hydroxyalkylcarboxylic acid ester and / or dialkylaminoethylcarboxylic acid An adhesive composition, which is an ester.

[2] The pressure-sensitive adhesive composition according to [1], wherein a graft amount of the polar group-containing monomer is 0.01 to 15% by weight with respect to natural rubber.

[3] The pressure-sensitive adhesive composition according to [1] or [2], wherein the modified natural rubber is obtained by emulsion polymerization of the polar group-containing monomer in natural rubber latex, coagulation, and drying. .

[4] In any one of [1] to [3], the polar group-containing monomer is a hydroxyalkyl (meth) acrylate and / or a dialkylaminoethyl (meth) acrylate. Adhesive composition.

[5] The pressure-sensitive adhesive composition according to any one of [1] to [4], comprising the modified natural rubber, a softener, and a tackifier.

[6] The pressure-sensitive adhesive composition according to [5], comprising 20 to 100 parts by weight of a softening agent and 10 to 100 parts by weight of a tackifier with respect to 100 parts by weight of the modified natural rubber.

  The pressure-sensitive adhesive composition of the present invention has an increased cohesive force without impairing the original properties of natural rubber as a polymer base, and is excellent in adhesive force and holding force (cohesive force). And since Tg of a composition is not raised, the temperature dependence of adhesive force is also small, and it can apply to the use in a wide temperature.

  In the present invention, the graft amount of the polar group-containing monomer is preferably 0.01 to 15% by weight based on the natural rubber (claim 2). The modified natural rubber is preferably obtained by emulsion polymerization of a polar group-containing monomer in natural rubber latex, coagulation, and drying (claim 3).

  In the present invention, the polar group-containing monomer is preferably a hydroxyalkyl (meth) acrylate and / or a dialkylaminoethyl (meth) acrylate. In the present specification, “(meth) acrylic acid” means “acrylic acid and / or methacrylic acid”. The same applies to “(meth) acrylate” described later.

  The pressure-sensitive adhesive composition of the present invention preferably contains a modified natural rubber, a softening agent and a tackifier (Claim 5), and more preferably, the softening agent 20 to 100 per 100 parts by weight of the modified natural rubber. And 10 to 100 parts by weight of a tackifier (claim 6).

  Hereinafter, embodiments of the pressure-sensitive adhesive composition of the present invention will be described in detail.

The pressure-sensitive adhesive composition of the present invention uses a modified natural rubber obtained by graft polymerization of a specific polar group-containing monomer as a natural rubber as a polymer base.
This modified natural rubber can be produced, for example, by emulsion polymerizing a polar group-containing monomer in natural rubber latex, coagulating and drying.

  The natural rubber latex used here can be any of field latex, ammonia-treated latex, centrifugal concentrated latex, deproteinized latex treated with a surfactant or enzyme, and combinations thereof, and the preferred rubber concentration of latex. Is 20 to 60% by weight.

  In the present invention, the polar group-containing monomer to be graft polymerized with natural rubber is a hydroxyalkyl carboxylic acid ester and / or a dialkylaminoethyl carboxylic acid ester.

  Examples of hydroxyalkyl carboxylic acid esters include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and 3-hydroxybutyl (meth) ) And hydroxyalkyl esters of acrylic acid or methacrylic acid such as acrylate and 4-hydroxybutyl (meth) acrylate. Among these, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and the like are preferable.

  Examples of the dialkylaminoethyl carboxylic acid ester include N, N-dimethylaminomethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N , N-dimethylaminobutyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate, N, N-diethylaminobutyl (meth) acrylate, N-methyl-N- Ethylaminoethyl (meth) acrylate, N, N-dipropylaminoethyl (meth) acrylate, N, N-dibutylaminoethyl (meth) acrylate, N, N-dibutylaminopropyl (meth) acrylate, N, N-dibutyl Aminobutyl (meth) a Cyclic acrylic acid having two alkyl groups having 1 to 8 carbon atoms, such as relate, N, N-dihexylaminoethyl (meth) acrylate, N, N-dioctylaminoethyl (meth) acrylate, acryloylmorpholine Or the dialkylamino ethyl ester of methacrylic acid is mentioned. Among these, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dipropylaminoethyl (meth) acrylate, N, N-dioctylaminoethyl (meth) Preferred are acrylate, N-methyl-N-ethylaminoethyl (meth) acrylate, and the like.

  The hydroxyalkyl carboxylic acid ester and dialkylaminoethyl carboxylic acid ester may be used alone or in combination of two or more. Moreover, you may use together 1 type (s) or 2 or more types of hydroxyalkylcarboxylic acid ester, and 1 type (s) or 2 or more types of dialkylamino ethyl carboxylic acid ester.

  The polymerization initiator for graft polymerization is not particularly limited, and various initiators, for example, an initiator for emulsion polymerization can be used, and the addition method is not particularly limited. Examples of commonly used polymerization initiators include benzoyl peroxide, hydrogen peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, 2,2-azobisisobutyronitrile, 2,2-azobis (2-diaminopropane) hydrochloride, 2,2-azobis (2-diaminopropane) dihydrochloride, 2,2-azobis (2,4-dimethylvaleronitrile), potassium persulfate, persulfate Examples thereof include sodium and ammonium persulfate. In order to lower the polymerization temperature, it is preferable to use a redox polymerization initiator. Examples of the reducing agent to be combined with the peroxide used in the redox polymerization initiator include tetraethylenepentamine, mercaptans, acidic sodium sulfite, reducing metal ions, ascorbic acid and the like. Particularly preferred examples of the combination as a redox polymerization initiator include tert-butyl hydroperoxide and tetraethylenepentamine. These polymerization initiators may be used alone or in combination of two or more.

  The graft polymerization according to the present invention is advantageously performed by general emulsion polymerization in which a polar group-containing monomer is added to natural rubber latex and polymerized while stirring at a predetermined temperature. In this case, water and an emulsifier may be added to the polar group-containing monomer in advance and sufficiently emulsified, and the natural group latex may be added directly to the natural rubber latex. An emulsifier may be added before or after the addition of the monomer, if necessary. The emulsifier is not particularly limited, and examples thereof include nonionic surfactants such as polyoxyethylene lauryl ether.

  In consideration of sufficiently improving the cohesion of natural rubber without degrading processability by modification with polar group-containing monomers, it is possible to introduce a small amount of polar groups uniformly into the natural rubber molecules. Since it is important, the addition amount of the polymerization initiator is preferably 1 to 100 mol%, more preferably 10 to 100 mol% with respect to 100 mol of the polar group-containing monomer.

  In order to graft polymerize a polar group-containing monomer to natural rubber latex, the above-mentioned components are charged into a reaction vessel and reacted at 30 to 80 ° C. for 10 minutes to 7 hours. Thereby, a modified natural rubber latex modified with a polar group-containing monomer is obtained. Polarized group-containing modified natural rubber can be obtained by coagulating and washing the resulting modified natural rubber latex, followed by drying using a normal dryer such as a vacuum dryer, air dryer, drum dryer or the like.

  The graft amount of the polar group-containing monomer of the modified natural rubber according to the present invention is preferably 0.01 to 15% by weight, more preferably 0.01 to 1.0% by weight, based on the natural rubber. If the amount of grafting is less than 0.01% by weight, the effect of improving the cohesive strength of natural rubber is not sufficient, and if it exceeds 15% by weight, the original properties of natural rubber are impaired and the physical properties of natural rubber are utilized. The application method may be difficult to apply, and processability and handleability may be deteriorated.

  The pressure-sensitive adhesive composition of the present invention is usually prepared by blending a softening agent and a tackifier in the modified natural rubber as described above.

As the softener, any general softener for rubber can be used. For example, polybutene softener, petroleum softener such as naphthene oil, aroma oil, spindle oil, Liq-polyisoprene, etc. Low molecular weight polymers and vegetable oils such as rapeseed oil can be used.
These softeners may be used alone or in combination of two or more.
The blending amount of the softening agent is preferably about 20 to 100 parts by weight, particularly about 30 to 80 parts by weight with respect to 100 parts by weight of the modified natural rubber.

Examples of the tackifier include rosin resins such as rosin ester, hydrogenated rosin ester, disproportionated rosin ester and polymerized rosin ester, coumarone indene resin, hydrogenated coumarone indene resin, phenol-modified coumarone indene resin and epoxy. Coumarone indene resin such as modified coumarone indene resin, terpene resin such as polyterpene resin, styrene modified terpene resin, phenol modified terpene resin, aliphatic petroleum resin, aromatic petroleum resin, aromatic modified aliphatic petroleum Appropriate ones such as petroleum resins such as resins and aromatic pure monomer resins can be used. These tackifiers may be used alone or in combination of two or more.
The compounding amount of the tackifier is generally 10 to 200 parts by weight, particularly 50 to 150 parts by weight per 100 parts by weight of the modified natural rubber, but is not limited thereto. In the present invention, the blending amount of the tackifier is less than the usual blending amount due to the cohesive force improving effect of the modified natural rubber obtained by modifying natural rubber with a specific polar group-containing monomer. As 100 to 100 parts by weight per 100 parts by weight, there is an advantage that an increase in the Tg can be suppressed.

  Various additives other than the modified natural rubber, the softener, and the tackifier may be added to the pressure-sensitive adhesive composition of the present invention as necessary. Examples of the additive include plasticizers, inorganic or organic fillers, thickeners, pigments, dyes, and the like, which are appropriately blended as necessary.

  Such a pressure-sensitive adhesive composition of the present invention is dissolved, for example, in a solvent such as toluene, cyclohexane, hexane, xylene, ligroin, petroleum benzine or the like at a concentration of about 5 to 30% by weight, and this pressure-sensitive adhesive solution is used as a base. It is used for applications such as forming an adhesive layer by applying and drying.

  EXAMPLES Next, although this invention is demonstrated based on an Example, this invention is not limited by a following example, unless the summary is exceeded.

[Example 1]
(1) Modification reaction step of natural rubber latex The field latex was centrifuged at 7500 rpm using a latex separator (manufactured by Saito Centrifugal Co., Ltd.) to obtain a concentrated latex having a dry rubber concentration of 60% by weight. Separately, 10 ml of water and 1.5 g of emulsifier (Emulgen 1108 manufactured by Kao Corporation) were added to 60 g of diethylaminoethyl methacrylate to emulsify.
1000 g of the above concentrated latex was put into a stainless steel reaction vessel equipped with a stirrer and a temperature control jacket, diethylaminoethyl methacrylate emulsified in advance and 990 ml of water were added and stirred for 30 minutes while purging with nitrogen. Next, 2.0 g of tert-butyl hydroperoxide and 2.0 g of tetraethylenepentamine were added as polymerization initiators and reacted at 40 ° C. for 1 hour to obtain the desired modified natural rubber latex.

(2) Coagulation / Drying Step Next, formic acid was added to the modified natural rubber latex obtained in the step (1) to adjust the pH to 4.7 and coagulate. This solid matter was crumpled 5 times through a scraper and then shredded, and then dried at 110 ° C. for 210 minutes with a hot air dryer to obtain a modified natural rubber. From the weight of the resulting modified natural rubber, it was confirmed that the addition reaction rate of dimethylaminoethyl methacrylate was 100%. The modified natural rubber was extracted with petroleum ether and then extracted with a 2: 1 solvent mixture of acetone and methanol, but the homopolymer was detected by analyzing the extract. It was confirmed that 100% of the added diethylaminoethyl methacrylate was introduced into the natural rubber molecule. That is, the graft amount of diethylaminoethyl methacrylate is 10% by weight.

  Next, 60 parts by weight of a terpene-based tackifier resin, 30 parts by weight of a polybutene-based softener and 1 part by weight of an anti-aging agent are mixed with 100 parts by weight of the above modified natural rubber in a kneader-type kneading apparatus. I got a thing. Further, this pressure-sensitive adhesive composition was dissolved in 100 parts by weight of toluene to obtain a pressure-sensitive adhesive solution. The obtained adhesive solution was applied to a polyester film having a thickness of 30 μm and dried at 100 ° C. for 5 minutes to obtain an adhesive tape having an adhesive layer having a thickness of 40 μm.

[Comparative Example 1]
A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that natural rubber latex was used without being subjected to emulsion polymerization treatment, and a pressure-sensitive adhesive tape was similarly obtained.

[Comparative Example 2]
A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that the modifier was changed to methyl methacrylate, and a pressure-sensitive adhesive tape was similarly obtained.

<Evaluation test>
The following properties of the pressure-sensitive adhesive tapes obtained in Example 1 and Comparative Examples 1 and 2 were examined, and the results are shown in Table 1.
(Adhesive strength)
A stainless steel plate with a thickness of 2 mm, which has been surface-polished with No. 280 water-resistant abrasive paper, is bonded with a 20 mm wide adhesive tape by reciprocating a 2 kg rubber roller once, and after 30 minutes, the adhesive strength is pulled by 180 degrees. Speed 300 mm / min, 23 ° C., 65% R.D. H. It investigated in the conditions of.
(Holding power)
Under a temperature condition of 23 ° C., a pressure-sensitive adhesive tape that has been pressure-bonded to a baking plate in the same manner as described above with an area of width 5 mm × length 20 mm is suspended so that the plate surface is in the vertical direction, and the free end of the pressure-sensitive adhesive tape A uniform load of 500 g was applied to the sample, and the time until the pressure-sensitive adhesive tape was peeled off while being kept at 40 ° C. was measured with a creep tester.

  From Table 1, the pressure-sensitive adhesive composition of Example 1 is superior in adhesive strength and holding power (cohesiveness) compared to a conventional pressure-sensitive adhesive composition using natural rubber or natural rubber modified with methyl methacrylate. It turns out that it is excellent in practical use.

Claims (6)

In a pressure-sensitive adhesive composition containing a modified natural rubber obtained by graft polymerization of a polar group-containing monomer on natural rubber,
The pressure-sensitive adhesive composition, wherein the polar group-containing monomer is a hydroxyalkyl carboxylic acid ester and / or a dialkylaminoethyl carboxylic acid ester.   The pressure-sensitive adhesive composition according to claim 1, wherein the graft amount of the polar group-containing monomer is 0.01 to 15% by weight with respect to natural rubber.   3. The pressure-sensitive adhesive composition according to claim 1, wherein the modified natural rubber is obtained by emulsion polymerization of the polar group-containing monomer in natural rubber latex, coagulation, and drying.   4. The pressure-sensitive adhesive composition according to claim 1, wherein the polar group-containing monomer is a hydroxyalkyl (meth) acrylate and / or a dialkylaminoethyl (meth) acrylate. object.   The pressure-sensitive adhesive composition according to any one of claims 1 to 4, comprising the modified natural rubber, a softening agent, and a tackifier.   The pressure-sensitive adhesive composition according to claim 5, comprising 20 to 100 parts by weight of a softening agent and 10 to 100 parts by weight of a tackifier with respect to 100 parts by weight of the modified natural rubber.