JPH11140406A - Adhesive composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an adhesive composition excellent in both bond strength and stickiness at low temperatures to an adhered material having a low energy surface. SOLUTION: This adhesive composition mainly comprises an acrylic copolymer obtained by copolymerizing 100 pts.wt, of an alkyl (meth)acrylate having a 4-8C alkyl residue with 17-67 pts.wt. of an alkyl (meth)acrylate having a 12-14C alkyl residue and is made to have a compressive strength in the range of 0.2-5 kg/cm<2> under 25% compression.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acrylic pressure-sensitive adhesive composition, and more particularly to a pressure-sensitive adhesive composition exhibiting excellent adhesive strength to plastics such as acrylic resins and melamine resins and painted steel plates.

[0002]

2. Description of the Related Art Japanese Patent No. 2558142 discloses a pressure-sensitive adhesive capable of increasing the adhesive strength to an adherend having a low energy surface such as a plastic material. In this pressure-sensitive adhesive, the alkyl group has 2 to 1 carbon atoms.
The surface energy of the pressure-sensitive adhesive is reduced by copolymerizing an acrylic long-chain alkyl ester having an alkyl group of 15 to 20 with the acrylic alkyl ester of No. 4 to bring the surface energy close to the surface energy of the adherend. This increases the bonding strength.

[0003] When a long-chain acrylic alkyl ester is contained, the glass transition temperature of the pressure-sensitive adhesive becomes high, the sticking property at low temperatures is reduced, and there is a problem that it is difficult to stick to an adherend in winter. Therefore, in the above prior art, a long-chain acrylic alkyl ester having 15 to 20 carbon atoms cannot be contained in a large amount, and the copolymer is copolymerized so as to account for 5 to 25% by weight of the copolymer.

[0004] Accordingly, there is a limit in reducing the surface energy by including a long-chain acrylic alkyl ester, and the adhesion to an adherend having a low surface energy is sufficiently reduced without lowering the sticking property at low temperatures. It was difficult to increase.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to reduce the surface energy by increasing the content of long-chain alkyl (meth) acrylate to lower the surface energy. An object of the present invention is to provide a pressure-sensitive adhesive composition that can sufficiently increase the adhesive strength to a body and that has excellent low-temperature application properties.

[0006]

The pressure-sensitive adhesive composition according to the present invention has a carbon number of 1 to 100 parts by weight of an alkyl (meth) acrylate having an alkyl group having 4 to 8 carbon atoms.
It contains an acrylic copolymer in which 17 to 67 parts by weight of an alkyl (meth) acrylate having an alkyl group of 2 to 14 is copolymerized, and has a compressive strength at 25% compression of 0.2 to 5 kg / at 5 ° C. cm ² . In this specification, (meth) acrylate is
Acrylate and methacrylate shall be generically referred to.

The above alkyl (meth) acrylate having an alkyl group having 4 to 8 carbon atoms is used as a main component for exhibiting adhesiveness in the acrylic copolymer of the adhesive composition according to the present invention. Are not particularly limited, for example, n-butyl (meth) acrylate, isobutyl (meth) acrylate,
Isoamyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, n-octyl (meth) acrylate, and the like can be used. These alkyl (meth) acrylates having an alkyl group having 4 to 8 carbon atoms may be used alone or in combination of two or more.

The alkyl (meth) acrylate having an alkyl group having 12 to 14 carbon atoms is used in the pressure-sensitive adhesive composition according to the present invention to enhance the low-temperature sticking property. The (meth) acrylate is not particularly limited,
For example, lauryl acrylate, isomyristyl acrylate, and the like can be given.

In the present invention, the above-mentioned alkyl (meth) acrylate having an alkyl group having 4 to 8 carbon atoms,
An acrylic copolymer obtained by copolymerizing an alkyl (meth) acrylate having an alkyl group having 12 to 14 carbon atoms is used. Regarding the copolymerization ratio, an alkyl group having 4 to 8 carbon atoms is used. The alkyl (meth) acrylate having an alkyl group having 12 to 14 carbon atoms is 17 to 100 parts by weight of the alkyl (meth) acrylate having
The proportion is 67 parts by weight, preferably 25 to 38 parts by weight. When the copolymerization ratio of the alkyl (meth) acrylate having an alkyl group having 12 to 14 carbon atoms is less than 17 parts by weight, the surface energy of the pressure-sensitive adhesive composition cannot be reduced sufficiently, and If the adhesive strength of such a low energy surface to the adherend decreases, and if it exceeds 67 parts by weight, the glass transition temperature of the pressure-sensitive adhesive composition increases, and the adhesiveness at low temperatures decreases.

In the pressure-sensitive adhesive composition according to the present invention, in addition to the above alkyl (meth) acrylate, a modifying monomer may be further copolymerized in order to impart crosslinkability and improve cohesion.

As the modifying monomer for increasing the cohesion, a carboxyl group-containing monomer such as acrylic acid, maleic acid, fumaric acid and itaconic acid or an anhydride thereof;
Nitrogen-containing monomers such as acrylonitrile, N-vinylpyrrolidone, N-vinylcaprolactone, acryloylmorpholine, (meth) acrylamide, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylamide; Hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, modified caprolactone (meth) acrylate, polyoxyethylene (meth) acrylate, polyoxypropylene (meth) acrylate, etc. Hydroxy group-containing monomers can be exemplified.

With respect to the copolymerization ratio of the above-mentioned modified monomer for increasing the cohesive strength, the above-mentioned alkyl (meth) acrylate is used in an amount of 100 parts by weight (alkyl (meth) acrylate having an alkyl group having 4 to 8 carbon atoms and 12 to 12 carbon atoms) (Total amount of alkyl (meth) acrylate having 14 alkyl groups) is preferably 10% by weight or less. 1
If the amount exceeds 0 parts by weight, the cohesive force of the pressure-sensitive adhesive composition may become too high, and the compressive strength may decrease.

Further, various other modifying monomers copolymerizable with the above-mentioned alkyl (meth) acrylate monomer may be copolymerized. Examples of such a monomer include vinyl acetate, vinyl propionate, and styrene. be able to. About the copolymerization ratio of such a copolymerizable modifying monomer, 10% by weight of the whole acrylic copolymer is used.
It is desirable to make the following. If it exceeds 10% by weight, the cohesive strength becomes too high, and the pressure-sensitive adhesiveness may decrease.

If necessary, the acrylic copolymer may be crosslinked with an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, an aziridine-based crosslinking agent, or the like in order to enhance heat resistance and creep characteristics. Good.

The method for polymerizing the acrylic copolymer is not particularly limited, and the acrylic copolymer may be polymerized by any known method such as solution polymerization, bulk polymerization, emulsion polymerization, and pearl polymerization. When the solution polymerization method is used, copolymerization can be performed using a thermal polymerization initiator such as azobisisobutyronitrile or benzoyl peroxide in the presence of a solvent such as ethyl acetate or toluene.

In the case of the bulk polymerization method, it is most preferable to use a photopolymerization method using ultraviolet light because a sheet having a large thickness is easily obtained and a uniform polymer is easily obtained. In this case, a photopolymerization initiator is added to the monomer composition, and polymerization is performed by irradiating ultraviolet rays.

Examples of the photopolymerization initiator include, for example, 4-
(2-hydroxyethoxy) phenyl (2-hydroxy-2-propyl) ketone [trade name: Darocure 295]
9, Merck Ltd.]; α-hydroxy-α, α′-dimethyl-acetophenone [trade name: Darocur 1173, Merck Ltd.]; methoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone [trade name: Irgacure 651] Manufactured by Ciba Geigy]; 2-hydroxy-2
Acetophenone-based initiators such as cyclohexyl acetophenone (trade name: Irgacure 184, manufactured by Ciba Geigy); ketal-based initiators such as benzyl dimethyl ketal; and other examples include halogenated ketones, acylphosphinoxides, and acylphosphonates. Can be.

As a light source for light irradiation used in photopolymerization, a light source having a light emission distribution at a wavelength of 400 nm or less is suitably used. Examples of such a light source include a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a chemical lamp, a black light lamp, a micro-wave excitation mercury lamp, and a metal halide lamp. Preferably, a chemical lamp is used, and the chemical lamp can efficiently emit light in the active wavelength region of the photopolymerization initiator and has a small light absorption of a composition other than the photopolymerization initiator. Light can be transmitted, and a high-thickness adhesive can be manufactured.

The irradiation intensity of light on the photopolymerizable composition is as follows:
Since it is a factor that affects the degree of polymerization of the obtained polymer or copolymer, it may be appropriately adjusted for each desired performance of the pressure-sensitive adhesive. When a cleavage type photopolymerization initiator having a normal acetophenone group is blended, a wavelength region effective for photodecomposition of the photopolymerization initiator (depending on the initiator, usually,
The light intensity of 365 to 420 nm is used)
It is desirable to set it in the range of 0.1 to 100 mW / cm ² . If the light intensity is less than 0.1 mW / cm ² , it may be difficult to increase the degree of polymerization, or it may take a long time for the polymerization. If the light intensity exceeds 100 mW / cm ² , the molecular weight becomes low and the Performance may be reduced.

In the present invention, the acrylic copolymer is polymerized by various methods as described above, and its final form is a so-called solvent-type acrylic pressure-sensitive adhesive which is polymerized in a solvent. It may be in the form of an emulsion-type acrylic pressure-sensitive adhesive polymerized in water, or may be obtained by irradiating the acrylic-type monomer composition with ultraviolet rays and performing bulk polymerization.

When an acrylic copolymer is obtained by UV bulk polymerization, a copolymerizable unsaturated double bond is used in place of the crosslinking agent in order to perform crosslinking for improving heat resistance and creep characteristics. A monomer having two or more monomers in the molecule may be added to the monomer mixture. Examples of such a monomer having two or more unsaturated double bonds in a molecule include hexanediol di (meth) acrylate, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, Neopentyl glycol di (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, allyl (meth) acrylate, vinyl (meth) acrylate, divinylbenzene And other epoxy acrylates, polyester acrylates, urethane acrylates and the like can be suitably used.

In the pressure-sensitive adhesive composition according to the present invention, a tackifier resin may be blended, if necessary, in addition to the acrylic copolymer. Rosin-based resins,
Modified rosin-based resins, terpene-based resins, terpene-phenol-based resins, C5 and C9-based petroleum resins, cumarone resins, and the like, and hydrogenated products thereof can be suitably used. These tackifying resins are used alone. May be
Two or more kinds may be used in combination. When a solvent-type pressure-sensitive adhesive is used, these tackifying resins may be used as the above-mentioned acrylic copolymer 1
It is preferable to mix 5 to 30 parts by weight with respect to 00 parts by weight.

However, when an acrylic copolymer is polymerized by photopolymerization, if a tackifying resin is blended with the photopolymerizable composition and polymerized, the polymerization rate decreases or the molecular weight of the acrylic copolymer decreases. Caution is required. In this case, if necessary, the amounts of the chain transfer agent and the crosslinking monomer may be adjusted. Preferred tackifying resins having low polymerization inhibition include hydrogenated products such as hydrogenated terpene resins, hydrogenated rosin resins, disproportionated rosin resins, and hydrogenated petroleum resins.

The pressure-sensitive adhesive composition according to the present invention further comprises:
If necessary, conventionally known various additives such as a plasticizer, a softener, an inorganic filler, an organic filler, a pigment, a dye, and the like may be contained.

In the pressure-sensitive adhesive composition according to the present invention, the compressive strength at the time of 25% compression is 0.1 to improve the adhesion at low temperatures.
2-5 kg / cm ² , preferably 0.5-3 kg / c
m ² . Compressive strength is 5kg / cm
^If it exceeds ² , the sticking property at low temperature will decrease,
If it is less than g / cm ^2, it is too soft and the tackiness is reduced.

The pressure-sensitive adhesive composition according to the present invention may be used as it is as a pressure-sensitive adhesive, or may be used in the form of a pressure-sensitive adhesive tape. When the pressure-sensitive adhesive tape is used, the pressure-sensitive adhesive tape may be in the form of a double-sided pressure-sensitive adhesive tape having no substrate, or may be a pressure-sensitive adhesive tape with a substrate in which a pressure-sensitive adhesive layer is formed on one or both surfaces of the substrate.

The pressure-sensitive adhesive composition according to the present invention is preferably used for bonding various adherends, and is particularly preferably used for low-energy adherends such as plastics and resin-coated steel sheets. Can be.

(Action) In the pressure-sensitive adhesive composition according to the present invention,
For 100 parts by weight of the alkyl (meth) acrylate having an alkyl group having 4 to 8 carbon atoms, 1 alkyl (meth) acrylate having an alkyl group having 12 to 14 carbon atoms is used.
Since the main component is an acrylic copolymer copolymerized at a ratio of 7 to 67 parts by weight, the latter compound reduces the surface energy and is excellent in adhesion strength to an adherend having a low surface energy. Not only that, the adhesion at low temperatures can be improved. In addition, the compression strength at the time of 25% compression,
Since it is in the range of 0.2 to 5 kg / cm ² at 5 ° C., the adhesive strength to an adherend having a low surface energy;
The balance of low-temperature sticking properties is further enhanced.

[0029]

The present invention will be described in more detail by way of the following non-limiting examples. In the following, parts mean parts by weight unless otherwise specified.

(Example 1) Lauryl acrylate 20
Parts, 2-ethylhexyl acrylate 80 parts, acrylic acid 2 parts, n-dodecanethiol 0.02 parts and 2,2-
After stirring and mixing in a separable flask until 0.1 part of dimethyl-2-phenylacetophenone (trade name: Irgacure 651 manufactured by Ciba Geigy) was uniformly dispersed,
Dissolved oxygen was removed by purging with nitrogen gas.
The composition was then added to the composition using a black light lamp.
When the composition was irradiated with ultraviolet light having a wavelength of 5 nm for 1 minute, the viscosity of the composition increased at the same time as the temperature of the composition increased. When the temperature of the composition increased by 5 ° C., the light irradiation was stopped. As a result, the conversion of the obtained partially photopolymerized thickening composition was 3.7%, and the viscosity was 2200 cps (23 ° C.).

Thereafter, 0.05 part of hexanediol diacrylate was added to the system, kneaded, and then polymerized on a release-treated surface of a 38 μm-thick polyethylene terephthalate (PET) film whose surface was release-treated. The composition was applied so that the thickness after the completion was 2.0 ± 0.1 mm, and the same PET film was coated on the coated surface so that the release-treated surface was in contact with the coated surface.

Next, the height of the lamp was adjusted using a chemical lamp so that the irradiation intensity on the PET film was ² mW / cm ^2, and ultraviolet light having a wavelength of 365 nm was irradiated for 10 minutes, and the film was sandwiched between the PET films. An adhesive sheet was obtained.

(Example 2) 30 parts of isomiristyl acrylate, 70 parts of butyl acrylate, 4 parts of acrylic acid,
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that a partial photopolymerizable composition was obtained using a composition comprising 0 parts of n-dodecanethiol.

Example 3 Lauryl acrylate 25 was placed in a separable flask equipped with a cooling pipe, a thermometer and a stirrer.
, 75 parts of 2-ethylhexyl acrylate, 4 parts of acrylic acid and 0.01 part of n-dodecanethiol were charged together with 90 parts of ethyl acetate, heated to reflux under a nitrogen gas atmosphere, and held for 20 minutes. A solution prepared by dissolving 0.1 part of oxide in 5 parts of ethyl acetate was added dropwise and reacted for 4 hours. Thereafter, a solution in which 0.1 part of benzoyl peroxide was dissolved in 5 parts of ethyl acetate was added dropwise to the system, and the mixture was further reacted for 3 hours. Next, 50 parts of toluene was stirred and mixed to obtain a solvent-type pressure-sensitive adhesive having a viscosity of 12,000 cps (23 ° C.). The weight average molecular weight of the polymer in the obtained solvent-type pressure-sensitive adhesive was 600,000.

An aziridine crosslinking agent (manufactured by Mutual Pharmaceutical Co., Ltd., trade name: H
After adding and mixing 0.1 part of DU), the above-mentioned pressure-sensitive adhesive solution was applied on a separator so that the thickness after drying became 2 mm, to obtain a pressure-sensitive adhesive sheet.

Comparative Example 1 100 parts of 2-ethylhexyl acrylate, 4 parts of acrylic acid, 0.02 part of n-dodecanethiol and 2,2-dimethyl-2-phenylacetophenone (trade name: Irgacure 6 manufactured by Ciba Geigy)
51) After stirring and mixing in a separable flask until 0.1 part was uniformly dispersed, dissolved oxygen was removed by purging with nitrogen gas. Next, when this composition was irradiated with ultraviolet rays using a black light lamp, the viscosity of the composition increased at the same time as the temperature of the composition increased. Light irradiation was stopped when the temperature of the composition increased by 5 ° C. as a result,
The conversion in the obtained partially photopolymerized thickening composition was 3.9.
% And viscosity was 2500 cps (23 ° C.).

Next, 0.05 parts of hexanediol diacrylate was added and kneaded, and then, on a release-treated surface of a 38 μm-thick PET film whose surface had been release-treated, the thickness after polymerization was 2. The composition was coated so as to have a thickness of 0 ± 0.1 mm, and the same PET film was coated on the coated surface such that the release-treated surface was in contact with the coated surface.

Next, the height of the lamp was adjusted using a chemical lamp so that the irradiation intensity on the PET film was ² mW / cm ^2, and ultraviolet light having a wavelength of 365 nm was irradiated for 10 minutes, and the film was sandwiched between the PET films. An adhesive sheet was obtained.

Comparative Example 2 60 parts of isomiristyl acrylate, 40 parts of butyl acrylate, 4 parts of acrylic acid,
A pressure-sensitive adhesive sheet was obtained in the same manner as in Comparative Example 1, except that a partially photopolymerizable composition was obtained using a composition comprising 0.01 parts of n-dodecanethiol.

Comparative Example 3 Lauryl Acrylate 10
Comparative Example 1 except that a partially photopolymerizable composition was obtained using a composition consisting of 90 parts of 2-ethylhexyl acrylate, 2 parts of acrylic acid, and 0.01 part of n-dodecanethiol.
In the same manner as in the above, an adhesive sheet was obtained.

Comparative Example 4 Lauryl Acrylate 20
Part, 2-ethylhexyl acrylate, 80 parts, acrylic acid, 12 parts, n-dodecanethiol, except that a partial photopolymerizable composition was obtained using a composition comprising 0.01 part, a pressure-sensitive adhesive sheet was prepared in the same manner as in Comparative Example 1. Obtained.

(Evaluation of PSA Sheets of Examples and Comparative Examples)
25% compressive strength, low temperature stickability, 1
The 80 degree peel test and shear adhesion test were evaluated. The results are shown in Table 1 below. 25% compressive strength When a plurality of adhesive tapes of 25 mm x 25 mm are overlapped at 23 ° C so that the thickness becomes 10 mm, and compressed to 25% of the total thickness at a rate of 10 mm / min by a Tensilon type testing machine. (Kg / cm ² ) was measured.

Low Temperature Adhesion (90 ° Peeling Test) Under a 5 ° C. atmosphere, the pressure-sensitive adhesive sheet sandwiched by PET films was cut into a width of 20 mm × length of 150 mm.
Under an atmosphere of ° C, one of the PET films was peeled off to expose the adhesive sheet, and the width was 25 mm, the length was 200 mm, and the thickness was 2
A pressure-sensitive adhesive sheet was attached to an acrylic coated steel sheet (manufactured by Nippon Test Panel Co., Ltd.) from the exposed pressure-sensitive adhesive sheet surface side so as to have a bonding length of 100 mm. Next, the other PET film of the pressure-sensitive adhesive sheet was peeled off, a polyester film having a thickness of 25 μm was adhered to the exposed pressure-sensitive adhesive sheet surface as a backing material, and a roller having a weight of 2 kg was reciprocated two times from the back side of the backing material. Immediately after crimping
The 90 ° peel force was measured at a pulling speed of 300 mm / min using a tensile tester in an atmosphere of ° C.

180 ° Peeling Test Under an atmosphere of 23 ° C., the pressure-sensitive adhesive sheet sandwiched between PET films was cut into a width of 20 mm and a length of 150 mm.
Under an atmosphere of 3 ° C., one of the PET films is peeled off, the adhesive sheet is exposed, and an adhesive coated steel sheet having a width of 25 mm, a length of 200 mm and a thickness of 2 mm (manufactured by Nippon Test Panel Co., Ltd.) has a length of 100 mm. The adhesive sheet was stuck from the exposed adhesive sheet surface side. Next, the other PET film of the pressure-sensitive adhesive sheet was peeled off, a polyester film having a thickness of 25 μm was adhered to the exposed pressure-sensitive adhesive sheet surface as a backing material, and a roller having a weight of 2 kg was reciprocated two times from the back side of the backing material. 23 ℃
At 24 ° C. for 24 hours, and a 180 ° peeling force was measured in an atmosphere of 23 ° C. using a tensile tester at a tensile speed of 50 mm / min.

Shear Adhesion Test The obtained adhesive tape was cut into a width of 20 mm × 20 mm,
23mm, 65% RH atmosphere, width 50mm x 50m
m, 2 mm thick acrylic coated steel sheets (manufactured by Nippon Test Panel Co., Ltd.), and the center parts are bonded together via an adhesive sheet from which PET films on both sides have been peeled off, and 15 kg under a load of 5 kg.
After pressure bonding for 24 minutes, the film was pulled in the shearing direction at a pulling speed of 50 mm / min after 24 hours, and the shear adhesive strength was measured.

[0046]

[Table 1]

[0047]

The pressure-sensitive adhesive composition according to the present invention has a long chain having an alkyl group having 12 to 14 carbon atoms per 100 parts by weight of an alkyl (meth) acrylate having an alkyl group having 4 to 8 carbon atoms. Alkyl (meth) acrylate 17
The main component is an acrylic copolymer obtained by copolymerization of up to 67 parts by weight, and the compression strength at 25% compression is 0.2 to 5 at 5 ° C.
Since it is in the range of kg / cm ² , it is possible to provide a pressure-sensitive adhesive composition that is excellent in both adhesive strength and low-temperature stickability to an adherend having a low energy surface such as a plastic surface.

Therefore, by using the pressure-sensitive adhesive composition according to the present invention, the adhesive composition can be easily adhered to an adherend having a low energy surface such as plastic and various adherends can be obtained even at a low temperature such as in winter. It is possible to provide a pressure-sensitive adhesive product that can be easily attached to a product.

Claims (1)

[Claims] 1. An alkyl (meth) having an alkyl group having 12 to 14 carbon atoms per 100 parts by weight of an alkyl (meth) acrylate having an alkyl group having 4 to 8 carbon atoms.
An adhesive comprising an acrylic copolymer in which 17 to 67 parts by weight of an acrylate is copolymerized, and having a compressive strength at 25% compression of 0.2 to 5 kg / cm ² at 5 ° C. Composition.