JPH09137142A - Pressure-sensitive adhesive and adhesive sheet using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a pressure-sensitive adhesive which has excellent adhesion by adding a photopolymerizable initiator and a polyfunctional (meth)acrylate to a mixture of an alkyl (meth)acrylate represented by a particular formula with a copolymerizable monomer having a polar group and conducting copolymerization. SOLUTION: A photopolymerization initiator in an amt. of 0.1 to 3.0 pts.wt. (hereinafter referred to as 'pts.') is added to 100 pts. mixture of 70 to 99wt.% alkyl (meth) acrylate monomer represented by the formula, CH2 =C(R<1> )COOR<2> (wherein R<1> represents H or methyl; and R<2> represents a 4-14C alkyl), such as isononyl acrylate, with 30 to 1wt.% copolymerizable monomer having a polar group, such as acrylic acid, and the mixture is irradiated with ultraviolet light to conduct prepolymerization. Thereafter, 0.02 to 5.0 pts. polyfunctional (meth)acrylate monomer, such as trimethylolpropane tri(meth)acrylate, and 0.01 to 20 pts. photopolymerization initiator having not less than 3, per molecule, peroxide groups are added to and mixed with 100 pts. prepolymer to prepare a pressure-sensitive adhesive. The pressure-sensitive adhesive is coated on a substrate of a PE film or the like, and the coating is irradiated with ultraviolet light to cure the coating, thus preparing an adhesive tape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photopolymerizable acrylic pressure-sensitive adhesive and adhesive sheets in the form of a sheet, a tape or the like.

[0002]

2. Description of the Related Art In industries such as home electric appliances, construction, and automobiles, with various kinds of industrial products, parts made of various materials and shapes are used. Recently, from the standpoint of improving the working environment and workability, these parts have been bonded using pressure-sensitive adhesives such as sheets and tapes instead of liquid adhesives. It is often joined.

By the way, in recent years, due to the high functionality of products,
These pressure-sensitive adhesives are also required to have heat resistance higher than ever before. As a pressure-sensitive adhesive having heat resistance, a photopolymerization type pressure-sensitive adhesive has been conventionally known.

[0004]

However, the photopolymerizable pressure-sensitive adhesive is generally crosslinked with a crosslinking agent, and if the crosslink density becomes dense, the cohesive force increases and the heat resistance improves. Adhesion is reduced. On the contrary, if the crosslink density becomes sparse, the adhesiveness improves, but the heat resistance decreases. As described above, the conventionally known photopolymerizable pressure-sensitive adhesive has a problem that it is difficult to achieve both adhesiveness and heat resistance.

In view of the above conventional circumstances, it is an object of the present invention to provide a photopolymerizable pressure-sensitive adhesive excellent in adhesiveness and heat resistance and its adhesive sheet.

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a specific acrylic monomer is photopolymerized with a specific photopolymerization initiator. The present inventors have completed the present invention by knowing that a pressure sensitive adhesive having excellent adhesiveness and heat resistance can be obtained.

That is, the present invention comprises a) the general formula (1);
Alkyl (meth) acrylate monomer represented by CH ₂ ═C (R ¹ ) COOR ² (wherein R ¹ is hydrogen or a methyl group, R ² is an alkyl group having 4 to 14 carbon atoms) 7
0 to 99% by weight and polar group-containing copolymerizable monomer 30 to 1
B) 1 to 100 parts by weight of a monomer mixture consisting of
0.01 to 20 parts by weight of a cleavage type photopolymerization initiator having 3 or more peroxide groups in the molecule, and c) 0.02 to 5 parts by weight of a polyfunctional (meth) acrylate monomer. In addition, a pressure sensitive adhesive that is polymerized and cured by light irradiation,
An adhesive sheet in the form of a sheet or tape having a layer made of the above pressure-sensitive adhesive on one or both sides of the substrate
It is related to the kind.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The monomer mixture as the component a in the present invention comprises an alkyl (meth) acrylate monomer and a polar group-containing copolymerizable monomer. ) The acrylate monomer is obtained by substituting a part of it with various vinyl monomers known as monomers for modifying general acrylic pressure-sensitive adhesives, such as vinyl acetate and styrene. Good. These vinyl-based monomers account for 30% of the total amount with the alkyl (meth) acrylate monomer.
It is preferably not more than wt%.

Examples of the alkyl (meth) acrylate monomer include n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate. Any of those having an alkyl group having 4 to 14 carbon atoms, such as G, can be used.

The polar group-containing copolymerizable monomer includes
Acid group-containing monomers such as (meth) acrylic acid, itaconic acid and 2-acrylamidopropanesulfonic acid, and hydroxyl group-containing monomers such as 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate. A quantity or the like is used.

An alkyl (meth) acrylate monomer (a part of which may be substituted with a vinyl monomer such as vinyl acetate or styrene) and a polar group-containing copolymerizable monomer The usage ratio of the former is 70 to 99% by weight, and the latter is 3
It is 0 to 1% by weight, and outside this range, favorable results cannot be obtained in terms of adhesive properties. Particularly preferred use ratios are 80 to 95% by weight for the former and 20 to 5% by weight for the latter.

The cleavage type photopolymerization initiator having three or more peroxide groups in one molecule as the component b in the present invention produces a large number of the above-mentioned radicals in one molecule by the cleavage thereof. It is presumed that when a polymer molecule extends from one of the two, the polymer molecule also extends from other radicals in the same molecule, resulting in the formation of a three-dimensional polymer structure.

Therefore, even if the length from the initiation point to the reaction termination point is as short as in the case of the conventional photopolymerization initiator,
Since the polymer molecule has a three-dimensional polymer structure, the polymer as a whole has a high molecular weight, the adhesive force of the adhesive is not impaired, the cohesive force is increased, and good results are obtained in heat resistance. It seems to be.

As such a photopolymerization initiator, a benzophenone group-containing polyvalent peroxy ester is preferably used. Specifically, 3,3 ′, 4,4′-tetra (t
-Butylperoxycarbonyl) benzophenone, 3,
3 ', 4,4'-tetra (t-amylpa-oxycarbonyl) benzophenone, 3,3', 4,4'-tetra (t-hexylper-oxycarbonyl) benzophenone, 3,3 ', 4,4'- Tetra (t-octylper-oxycarbonyl) benzophenone, 3,3 ′, 4,4 ′
-Tetra (cumylpa-oxycarbonyl) benzophenone, 3,3 ', 4,4'-tetra (p-isopropylcumylpa-oxycarbonyl) benzophenone and the like.

The amount of the photopolymerization initiator used is 100 parts by weight of the monomer mixture of the component a.
It is 0.01 to 20 parts by weight, preferably 0.1 to 3 parts by weight. If the amount of this photopolymerization initiator used is too small, it will be consumed early due to light energy, so the polymerization rate will decrease. On the contrary, if it is too large, the polymerization rate will increase but the molecular weight will decrease and the cohesive force will be insufficient. However, neither is preferable.

The polyfunctional (meth) acrylate monomer of the component c in the present invention can be obtained by simply photopolymerizing the monomer mixture of the component a with the photopolymerization initiator of the component b. Despite the peculiar function based on the above-mentioned, since it is still insufficient in heat resistance, it is intended to further improve this heat resistance without adversely affecting the adhesiveness. It becomes possible to fully satisfy the high degree of heat resistance that is required as the functionality of these products increases.

Such polyfunctional (meth) acrylate monomers include trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, and 1,2-ethylene glycol. (Meth) acrylic
1,6-Hexanediolge (meth) acrylate
To, 1,12-dodecane diorge (meth) acrylate
Bifunctional or higher polyvalent alkyl (meth) acrylate such as
G.

The amount of the polyfunctional (meth) acrylate monomer used varies somewhat depending on the number of functional groups, etc., but is generally 0.0 per 100 parts by weight of the component a.
It is 2 to 5 parts by weight, preferably 0.2 to 3 parts by weight. By using the polyfunctional (meth) acrylate monomer in such a ratio, a good cohesive force is maintained due to the cross-linking structure of the polymer molecule, and high heat resistance can be obtained.

In the present invention, the photopolymerizable composition is prepared by adding the photopolymerization initiator of the component b and the polyfunctional (meth) acrylate monomer of the component c to the monomer mixture of the component a. To do. In terms of handling the composition, the monomer mixture of the component a can be prepolymerized to some extent by using a photopolymerization initiator different from the photopolymerization initiator of the component b.
If the component b photopolymerization initiator is used during the prepolymerization, gelation may occur. Therefore, the component b photopolymerization initiator is preferably added after the preliminary polymerization.

As another photopolymerization initiator used here,
4- (2-hydroxyethoxy) phenyl (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2,2-dimethylacetophenone, methoxyacetophenone, 2,2
-Acetophenone-based initiators such as dimethoxy-2-phenylacetophenone, benzoin-ether-based initiators such as benzoin ethyl ether, benzoin isopropyl ether, and ketetal-based initiators such as benzyl dimethyl ketal, etc. Examples thereof include halogenated ketones, acyl phosphinoxides, acyl phosphonates and the like, and two or more kinds may be used in combination.

In addition to the above-mentioned three components a to c which are essential components, such a photopolymerizable composition may further include an optional component such as a tackifier, a polar monomer, a plasticizer, a softening agent,
Various conventionally known additives such as fillers, pigments, dyes, and anti-aging agents can be appropriately added within a range that does not inhibit the photopolymerization.

The above polar monomers include N- (meth) acryloylmorpholine, N- (meth) acryloylpyrrolidone, N- (meth) acryloylpiperidine, N-
Monomers considered to have a chemical interaction with the adherend interface such as (meth) acryloylpyrrolidine and N- (meth) acryloyl-4-piperidone.

In the present invention, such a photopolymerizable composition is directly coated on an adherend or once coated on a release paper and then exposed to light, for example, 400 to 1,500 mj.
A pressure-sensitive acrylic pressure-sensitive adhesive having a pressure-sensitive adhesive per se can be obtained by irradiating with ultraviolet rays of about / cm ² and polymerizing and curing. Polymerization cure
It is desirable to perform the coating layer in an air blocking state such as a substitution atmosphere with an inert gas such as nitrogen gas or a coating state with a light-transmitting film. This is because more favorable results can be obtained in terms of development of adhesive properties.

Instead of coating on an adherend or release paper, various base materials such as synthetic resin film such as polyester film and fiber base material are used, and the base material is coated on one side or both sides. Then, by polymerizing and curing this in the same manner as described above, it is possible to obtain an adhesive sheet in the form of a sheet, a tape, or the like.

The acrylic pressure-sensitive adhesive thus obtained and its adhesive sheet have a three-dimensional polymer structure and a high molecular weight, as described above. As a pressure-sensitive adhesive and its product, which has a high degree of adhesiveness and cohesiveness due to the cross-linking effect of a polyfunctional (meth) acrylate monomer, has particularly high holding power at high temperatures, and has excellent heat resistance. , Used in a wide range of applications.

[0026]

Next, an embodiment of the present invention will be described in more detail. In the following, “parts” means “parts by weight”.

Example 1 90 parts of isononyl acrylate, 10 parts of acrylic acid, and 0.05 part of 2,2-dimethoxy-2-phenylacetophenone as a photopolymerization initiator were placed in a four-necked flask. Then
A syrup (viscosity 30 poise) was obtained by exposing it to ultraviolet rays in a nitrogen atmosphere and partially photopolymerizing it.

100 parts of this partially polymerized syrup, 0.2 part of trimethylolpropane triacrylate, and 3,3 ', 4,4'-tetra (t-butylperoxycarbonyl) as a photopolymerization initiator 0.1 part of benzophenone,
The components were mixed uniformly to prepare a photopolymerizable composition.

Using this photopolymerizable composition as a base material, a polyethylene terephthalate film having a thickness of 25 μm, which has been subjected to a low-adhesion release treatment, is coated with the above composition, and then in a nitrogen gas atmosphere. Ultraviolet rays at 900 mj / cm
^{It was} irradiated and polymerized and cured. Then, it was cut into a width of 20 mm to produce an adhesive tape having an adhesive layer thickness of 50 μm.

Example 2 A photopolymerizable composition was prepared in the same manner as in Example 1 except that 90 parts of isooctyl acrylate was used instead of 90 parts of isononyl acrylate. An adhesive tape was prepared in the same manner as in Example 1.

Comparative Example 1 As a post-addition of a photopolymerization initiator, 2,2-dimethoxy-2 was used instead of 0.1 part of 3,3 ', 4,4'-tetra (t-butylperoxycarbonyl) benzophenone. A photopolymerizable composition was prepared in the same manner as in Example 1 except that 0.1 part of phenylacetophenone was added. Further, an adhesive tape was produced in the same manner as in Example 1 using this photopolymerizable composition.

Comparative Example 2 As post-addition of a photopolymerization initiator, 2,2-dimethoxy-2 was used instead of 0.1 part of 3,3 ', 4,4'-tetra (t-butylperoxycarbonyl) benzophenone. A photopolymerizable composition was prepared in the same manner as in Example 2 except that 0.1 part of phenylacetophenone was added. Further, an adhesive tape was produced in the same manner as in Example 1 using this photopolymerizable composition.

Comparative Example 3 A photopolymerizable composition was prepared in the same manner as in Example 1 except that 0.2 part of trimethylolpropane triacrylate was not added. Similar to 1,
An adhesive tape was prepared.

The adhesive properties and heat resistance of the adhesive tapes of Examples 1 and 2 and Comparative Examples 1 to 3 were examined by the following methods. The results were as shown in Table 1.

<Adhesiveness> According to JIS Z-1522, using a stainless steel plate as an adherend, the adhesive force (g / g)
20 mm width).

<Heat resistance> An adhesive tape having a width of 10 mm is attached to an aluminum plate with an adhesive area of 10 mm × 20 mm, and 2
After 0 minutes, leave it at 120 ° C for 20 minutes, hang down the aluminum plate, apply a uniform load of 1 kg to the free end of the adhesive tape, and drop the adhesive tape at 120 ° C ) Was measured. In addition, in this test, for those that did not drop for 3 hours or more, the deviation distance (mm) was measured.

[0037]

As is clear from the results shown in Table 1, the adhesive tapes of Examples 1 and 2 of the present invention were the adhesive tapes of Comparative Examples 1 to 3.
It is clear that not only the adhesiveness, but also the heat resistance is superior to that of the resin, and it is possible to easily achieve both properties.

[0039]

As described above, according to the present invention, a monomer mixture comprising an alkyl (meth) acrylate monomer and a polar group-containing copolymerizable monomer contains 3 monomers per molecule. Good adhesion is obtained by adding the above-mentioned cleavage type photopolymerization initiator having a peroxide group and a polyfunctional (meth) acrylate monomer, and polymerizing and curing by light irradiation. At the same time, it is possible to provide an acrylic pressure-sensitive adhesive that exhibits excellent heat resistance and its adhesive sheet.

Claims (2)

[Claims] 1. a) General formula (1); CH ₂ ═C (R ¹ ).
70 to 99% by weight of an alkyl (meth) acrylate monomer represented by COOR ² (wherein R ¹ is hydrogen or a methyl group, and R ² is an alkyl group having 4 to 14 carbon atoms) and a polar group 100 parts by weight of a monomer mixture consisting of 30 to 1% by weight of a copolymerizable monomer contained therein, b) a cleavage type photopolymerization initiator having 3 or more peroxide groups in one molecule. 01
˜20 parts by weight, and c) 0.02 to 5 parts by weight of a polyfunctional (meth) acrylate monomer, and a polymerization-curable adhesive which is polymerized and cured by light irradiation. 2. Adhesive sheets having a layer comprising the pressure-sensitive adhesive according to claim 1 on one side or both sides of a base material.