JPH09249866A - Acrylic adhesive composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an acrylic adhesive composition capable of improving weatherability of the adhesive as well as a adhered material and having a highly balanced physical characteristics as the adhesive such as a peeling force, a retaining force, etc. SOLUTION: This acrylic adhesive composition contains a copolymer obtained by copolymerizing 70-99.9wt.% (meth)acrylic acid alkyl ester of the formula: CH2 =CR<1> COOR<2> (R<1> is H or methyl; R<2> is a 2-12C alkyl) with 0.1-30wt.% monomer having a benzotriazole group and a copolymerizable unsaturated double bond as indispensable component, as a main component.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an acrylic pressure-sensitive adhesive composition, and more particularly to an acrylic pressure-sensitive adhesive composition having excellent balance of physical properties and excellent weather resistance.

[0002]

2. Description of the Related Art Conventional acrylic pressure-sensitive adhesives contain a (meth) acrylic acid ester-based copolymer as a main component, and in order to balance high peel strength and high holding power, α, It has a constitution in which β-unsaturated carboxylic acid is copolymerized so as to occupy a ratio of several% to several tens% in the copolymer.

However, although conventional acrylic pressure-sensitive adhesives have a good balance of physical properties, they easily transmit ultraviolet rays, and when adhered to an adherend such as polyethylene having poor weather resistance, the adherend deteriorates. Was difficult to prevent.

On the other hand, in the case of a rubber-based pressure-sensitive adhesive, one or two kinds selected from natural rubber and synthetic rubber are used in order to improve weather resistance.
Anti-aging agents such as N, N'-di-β-naphthyl-P-phenylenediamine and 4-trimethyl-1,2-dihydroquinoline, and hydrogenated rosin and water-dispersed indene resin The above-mentioned tackifier has been proposed (JP-A-55-71769).

However, it has been difficult for this rubber-based pressure-sensitive adhesive to obtain pressure-sensitive adhesive properties and heat resistance similar to those of the above-mentioned acrylic pressure-sensitive adhesive in which high peel strength and high holding power are balanced.

[0006]

Although the conventional acrylic pressure-sensitive adhesives have excellent balance of pressure-sensitive adhesive properties as described above, they easily transmit ultraviolet rays. Therefore, there is a drawback that not only the weather resistance of the pressure sensitive adhesive itself is low, but also the weather resistance of the adherend is deteriorated. However, even in the case of acrylic pressure-sensitive adhesives, it has been attempted to increase the weather resistance of the pressure-sensitive adhesive itself or the adherend by incorporating a low-molecular weight ultraviolet absorber or antioxidant in the pressure-sensitive adhesive. However, even this type of acrylic pressure-sensitive adhesive has not been able to sufficiently satisfy both physical properties such as pressure-sensitive adhesive properties and heat resistance, and weather resistance.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide an acrylic pressure-sensitive adhesive composition which is further excellent in balance of physical properties such as pressure-sensitive adhesive properties and heat resistance and weather resistance.

[0008]

The present invention achieves the above-mentioned object and has the general formula CH ₂ = CR ¹ COOR.
70% to 99.9% by weight of at least one (meth) acrylic acid alkyl ester of the formula ( ² ) wherein R ¹ represents hydrogen or a methyl group, and R ² represents an alkyl group having 2 to 12 carbon atoms.
And 0.1 to 30% by weight of a monomer having a benzotriazole group and having a copolymerizable unsaturated double bond, as a main component, a copolymerized copolymer. The acrylic pressure-sensitive adhesive composition.

In the present invention, the number of carbon atoms of the alkyl group of the (meth) acrylic acid alkyl ester is preferably 2 to 12, and more preferably 4 to 9 in order to be tacky at room temperature. .

Examples of the (meth) acrylic acid alkyl ester include acrylic acid ethyl ester and acrylic acid n-
Propyl ester, acrylic acid isopropyl ester,
(Meth) acrylic acid n-butyl ester, acrylic acid s
ec-butyl ester, (meth) acrylic acid n-octyl ester, acrylic acid isooctyl ester, (meth) acrylic acid 2-ethylhexyl ester, acrylic acid isononyl ester, (meth) atalylic acid lauryl ester and the like can be mentioned. , Two or more of these may be used in combination.

The content of the (meth) acrylic acid ester is in the range of 70 to 99.9% by weight, preferably 80 to 97% by weight in the copolymer.
When the content of the (meth) acrylic acid alkyl ester is less than 70% by weight, the cohesive force of the acrylic pressure-sensitive adhesive composition becomes too high, and the unevenness followability deteriorates. On the other hand, 99.
If it exceeds 9% by weight, the cohesive force will be too low and the holding force will be low.

The monomer having a benzotriazole group and a copolymerizable unsaturated double bond is, for example, 2- (2'-hydroxy-5 '-(meth) acryloxyethylphenyl) 2H. Mention may be made of benzotriazole. This monomer not only fulfills the function of absorbing ultraviolet rays, but also acts as a cross-linking base point due to the OH group in the molecule. The blending ratio of the monomer having a benzotriazole skeleton is in the range of 0.1 to 30% by weight in the above copolymer, and when it is less than 0.1% by weight, the acrylic adhesive composition is used as an adhesive. When used as, the effect of increasing the weather resistance is not sufficient, and the holding power is also reduced. If it exceeds 30% by weight, the cohesive force becomes too high, and the conformability to unevenness is deteriorated.
Preferably, the proportion of the monomer having a benzotriazole skeleton is in the range of 0.2 to 15% by weight in the copolymer.

In the above-mentioned copolymer of the acrylic pressure-sensitive adhesive composition of the present invention, the above-mentioned (meth) acrylic acid alkyl ester and a monomer having a benzotriazole group and a copolymerizable unsaturated double bond are included. In addition to the body, if necessary, a carboxyl group-containing vinyl monomer such as (meth) acrylic acid, itaconic acid, maleic anhydride, (anhydrous) fumaric acid; (meth) acrylonitrile, N-vinylpyrrolidone, N-vinyl Vinyl monomers having high polar groups such as caprolactam, acryloylmorpholine, (meth) acrylamide, (meth) acrylic acid dimethylaminoethyl ester, (meth) acrylic acid diethylaminoethyl ester, dimethylaminopropylacrylamide; 2-hydroxyethyl (meth ) Acrylate and 4-hydroxybutene Le acrylate, have be used in combination of the monomer and copolymer vinyl monomer such as a hydroxyl group-containing monomers such as 2-hydroxypropyl (meth) acrylate.

The blending ratio of the vinyl monomer that can be used in the acrylic copolymer is preferably 30% by weight or less in the copolymer. If it exceeds 30% by weight, the cohesive force becomes too high and the adhesiveness to the uneven surface may not be sufficient.

In the acrylic copolymer of the present invention, a polymerization initiator may be added to the monomer composition containing the vinyl monomer, if necessary, to carry out solution polymerization, bulk polymerization, suspension polymerization,
It can be obtained by an appropriate polymerization method such as photopolymerization, but the heat of polymerization can be dispersed and the viscosity can be adjusted.
Solution polymerization is preferred because it facilitates uniform mixing of the tackifying resin.

Examples of the polymerization initiator that can be used in the above solution polymerization include azobisisobutyronitrile and benzoyl peroxide. The weight average molecular weight of the acrylic copolymer is preferably 200,000 to 1,500,000,
More preferably, it is 35 to 750,000. If the weight average molecular weight of the acrylic copolymer is less than 200,000, the necessary cohesive force may not be obtained, and if it exceeds 1.5 million, the viscosity becomes too high and the productivity in the coating process decreases. Because there are things.

In the acrylic pressure-sensitive adhesive composition of the present invention, it is preferable to use a cross-linking agent in order to enhance the holding power and the heat resistant adhesive strength. Examples of the cross-linking agent include polyfunctional isocyanate compounds, polyfunctional epoxy compounds, metal chelate compounds, and polyfunctional aziridine compounds.

Examples of the polyfunctional isocyanate compound include aromatic diisocyanate compounds such as tolylene diisocyanate (TDI), xylylene diisocyanate (XDI) and diphenylmethane diisocyanate (MDI); hexamethylene diisocyanate (HM).
DI), aliphatic or alicyclic diisocyanate compounds such as isophorone diisocyanate (IDI); tolylene diisocyanate trimer adducts of trimethylolpropane, and triisocyanate compounds such as triphenylmethane triisocyanate.

The amount of the polyfunctional isocyanate compound added is preferably 0.3 to 3 parts by weight based on 100 parts by weight of the acrylic copolymer. If the amount is less than 0.3 parts by weight, the effect due to the compounding of the polyfunctional isocyanate compound, that is, the effect of improving the cohesive strength may not be sufficient. If the amount exceeds 3 parts by weight, crosslinking of the adhesive may occur. The adhesive strength may be too high to obtain sufficient adhesive strength.

Examples of the polyfunctional epoxy compound include bisphenol A type or epichlorohydrin type epoxy resin, ethylene glycol diglycidyl ether, diglycidyl aniline, trimethylolpropane triglycidyl ether, N, N, N'N'-tetraglycidyl-
Examples thereof include m-xylenediamine.

Examples of the polyvalent metal chelate compound include compounds in which a polyvalent metal such as aluminum, iron, tin, zinc and titanium is coordinated with acetylacetone or acetoacetic acid ester.

Examples of the polyfunctional aziridine compound include:
N, N'-hexamethylene-1,6-bis- (1-aziridinecarboxamide), trimethylolpropane-
Examples thereof include tri-β-aziridinyl propionate.

The polyfunctional epoxy compound, polyvalent metal chelate compound or polyfunctional aziridine compound is preferably added in an amount of 0.01 to 100 parts by weight based on 100 parts by weight of the acrylic copolymer.
It is used in an amount of 1 part by weight, more preferably 0.05 to 0.5 part by weight. Two or more of these compounds may be used in combination, and in that case, it is preferable to add them in the above proportions in total. The compounding ratio of these compounds is 0.0
If the amount is less than 1 part by weight, the necessary cohesive force may not be obtained and the holding force may be lowered. If the amount is more than 3 parts by weight, the cohesive force may be too high and the peeling force may be lowered.

In the acrylic pressure-sensitive adhesive composition of the present invention, a rosin-based tackifying resin, a petroleum resin-based tackifying resin, or the like may be mixed as the tackifying resin in order to enhance the peel strength.

Examples of the rosin-based tackifying resin include rosin monomers, polymerized rosins, disproportionated rosins, hydrogenated rosins, and mixtures thereof. Esterified products of rosin-based compounds can also be used. An esterified product of a rosin-based compound and a polyhydric alcohol may be mentioned.

Examples of the polyhydric alcohol include diethylene glycol, glycerin, pentaerythritol and the like, and more preferably glycerin and pentaerythritol are used.

Examples of the petroleum resin-based tackifying resin include C
Examples include 5 (aliphatic) and C9 (aromatic) petroleum resins, and terpene resins, xylene resins, styrene resins, and modified phenol compounds thereof.

In the acrylic pressure-sensitive adhesive of the present invention, other additives such as a plasticizer, a softening agent, a filler, a pigment and a dye may be added, if necessary, within a range not impairing the object of the present invention. Good.

Action The acrylic pressure-sensitive adhesive composition according to the present invention is mainly composed of an acrylic copolymer in which the above-mentioned monomer having a benzotriazole group and having a copolymer unsaturated double bond is copolymerized. As an ingredient. Since this monomer contains a benzotriazole group and exerts an ultraviolet absorbing action, as is apparent from the examples described later, even if ultraviolet rays are radiated, the pressure-sensitive adhesive is unlikely to be transformed, and the adhesion is reduced. The durability of the body is enhanced. In addition, since the above-mentioned monomer containing a benzotriazole group has an OH group in the molecule and thus functions as a cross-linking base point, it also acts to enhance the adhesive physical properties of the acrylic adhesive. Therefore, the acrylic pressure-sensitive adhesive composition of the present invention can enhance the weather resistance of the pressure-sensitive adhesive itself and the adherend while maintaining a high balance of pressure-sensitive adhesive properties.

[0030]

EXAMPLES The present invention will be clarified below by giving Examples and Comparative Examples of the present invention. In the following, "parts" means "parts by weight" unless otherwise specified.

Example 1 72.7 parts of n-butyl acrylate, 24 parts of 2-ethylhexyl acrylate according to the composition shown in Table 1 below,
Acrylic acid 3 parts, 2- (2'-hydroxy-5'-methacryloxyethylphenyl) -2H-benzotriazole (hereinafter abbreviated as MHB) (Otsuka Chemical Co., Ltd., trade name:
RUVA-93) 0.3 parts and lauryl mercaptan 0.03 parts together with 80 parts of ethyl acetate were placed in a five-necked flask equipped with a stirrer, a reflux condenser, a thermometer, a dropping funnel and a nitrogen gas inlet, and stirred. Dissolved into a uniform mixture. After that, nitrogen gas was purged for about 30 minutes to remove oxygen existing in the monomer solution.

Next, the air in the flask was replaced with nitrogen gas, the temperature was raised with stirring, the system was kept at 70 ° C., and 0.03 part of benzoyl peroxide was dissolved in 1 part of ethyl acetate. The solution was dropped from the dropping funnel. Then, a polymerization reaction was carried out at the same temperature for 10 hours to obtain an acrylic copolymer solution.

In the acrylic copolymer solution obtained as described above, an ethyl acetate solution of a tolylene diisocyanate adduct of trimethylolpropane (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name: Coronate L55E, solid content 55 parts by weight) After adding 1.5 parts to 100 parts of the acrylic copolymer and mixing them uniformly, the mixture was applied on a release sheet having a release-treated surface to form a pressure-sensitive adhesive layer having a thickness after drying of 25 μm. Then, the surface was transferred to a corona discharge treated polyester film having a thickness of 38 μm to obtain an adhesive tape.

Examples 2 to 7 and Comparative Examples 1 to 5 Acrylic copolymers were prepared in the same manner as in Example 1 except that the compounding composition shown in Table 2 below was charged in a five-necked flask together with 80 parts of ethyl acetate. A polymer solution was obtained. In addition, Example 1
However, in Examples 6 and 7, the tackifying resins shown in Table 1 were mixed in the proportions shown in Table 1 to prepare adhesive tapes.

Evaluation As the evaluation of the adhesive physical properties, the adhesive strength (SP adhesive strength) to the stainless steel plate, the holding power and the weather resistance were evaluated according to the following procedures.

(1) SP adhesive strength ... According to JIS Z0237, 2 adhesive tapes are attached to a stainless steel plate (SUS304).
After bonding at 0 mm and leaving at 23 ° C. for 20 minutes, 180 ° peel strength was measured at a pulling speed of 300 mm / min.

(2) Holding power (80 ° C.) ... SP at normal temperature
Attach the adhesive tape to the stainless steel plate used to measure the adhesive strength.
Laminated so that the adhesion area is × 20 mm, 23 ° C
Left for 20 minutes. Then, leave it in the system at 80 ° C for 20 minutes, arrange the adhesive tape that is adhered downward, and apply a load of 1 kg to the adhesive tape, and evaluate the deviation (or drop) after 1 hour. did.

(3) Evaluation of weather resistance: The adhesive tape was immersed in warm water of 40 ° C. for 24 hours, and the ultraviolet absorption spectrum was measured to determine whether the absorbance at the peak value of 340 mm changed from that before warm water immersion (initial value). Were compared. For this weather resistance evaluation, three-stage evaluation was performed as indicated by the following symbols.

⊚ ... Absorbance did not decrease after immersion. ◯ ... Absorbance after immersion was 80% or more of the initial value. B: Absorbance after immersion decreased to less than 80% of the initial value.

The evaluation results are shown in Tables 1 and 2 below.
In addition, TF in Table 1 indicates a tackifying resin, SEA
115 and SEA 125 mean the following contents, respectively.

SEA115 ... Arakawa Chemical Industry Co., Ltd., trade name: Superester A115, a disproportionated rosin mixed ester of glycerin and pentaerythritol. SEA125 ... Arakawa Chemical Industry Co., Ltd., trade name: Super Ester A125, pentaerythritol ester of disproportionated rosin.

Further, tinuvin in Table 2 means the following contents. Cinubin ... Ciba Geigy, trade name: Tinubin-32
7,2- (2-hydroxy-3 ', 5', di-tert
-Butylphenyl) -5-chlorobenzotriazole.

[0043]

[Table 1]

[0044]

[Table 2]

As is clear from Table 2, in Comparative Example 1,
The weather resistance was not sufficient, probably because the mixing ratio of MHB was as low as 0.05 part with respect to 100 parts of (meth) acrylic acid alkyl ester.

In Comparative Example 2, the weather resistance was sufficient, but the peeling force was 40, probably because MHB was used in a large amount of 35 parts with respect to 100 parts of (meth) acrylic acid alkyl ester.
It was as low as 0 gf / 20 mm.

In Comparative Example 3, MHB was not used, but 1 part of tinuvin was used, but the weather resistance was not sufficient.
In Comparative Example 4, tinuvin was 1 as the ultraviolet absorber.
Due to the large amount of 0 parts, the bleed-out of tinuvin showed a decrease in weather resistance and the peel strength was 6
It is as low as 10 gf / 20 mm.

On the other hand, in Examples 1 to 7, the weather resistance was good, and the peeling force and the holding force also showed a sufficient value. Therefore, the peeling force and the holding force were highly balanced. You can see that

[0049]

As described above, according to the acrylic pressure-sensitive adhesive composition of the present invention, a monomer having a (meth) acrylic acid alkyl ester and a benzotriazole group and having a copolymerizable unsaturated double bond is used. Since the main component is a copolymer obtained by copolymerizing the monomer in the above-mentioned specific ratio, ultraviolet rays are absorbed by the action of the monomer having the benzotriazole group, and thus the weather resistance of the pressure-sensitive adhesive itself and the adherend. In addition to effectively increasing the viscosity, the monomer functions as a cross-linking base because it has an OH group in the molecule, providing an acrylic pressure-sensitive adhesive with a highly balanced adhesive physical property such as peeling power and holding power. It becomes possible to do.

Claims (1)

[Claims] 1. The general formula CH ₂ ═CR ¹ COOR ² (wherein R ¹ is hydrogen or a methyl group, and R ² has ^{2 to 2} carbon atoms).
At least one kind of (meth) acrylic acid alkyl ester (which represents an alkyl group of 12) of 70 to 99.9% by weight, and a monomer having a benzotriazole group and a copolymerizable unsaturated double bond. An acrylic pressure-sensitive adhesive composition, characterized in that the main component is a copolymer copolymerized with 1 to 30% by weight as an essential component.