JP2001220564A - Process for preparing pressure-sensitive adhesive composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for preparing a solvent-free type, pressure- sensitive adhesive composition which process is a polymerization by an ultraviolet ray irradiation, at a fast rate of the polymerization, with little vaporization of a monomer when polymerizing and with little limitation on the monomer constitution and gives a polymer having a high molecular weight. SOLUTION: The process for preparing a pressure-sensitive adhesive composition is characterized by using, as the chief ingredient of the pressure-sensitive adhesive composition, an acrylic polymer that is formed by carrying out a polymerization while irradiating an ultraviolet ray having a substantially single wave length onto a composition consisting of a monomer of the main component of an alkyl (meth)acrylate and a photo-free radical generator and that has a glass transition temperature of 250 K or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently producing a pressure-sensitive adhesive composition containing an acrylic polymer as a main component without using a solvent.

[0002]

2. Description of the Related Art Conventionally, a pressure-sensitive adhesive has been prepared by preparing an organic solvent solution such as an acrylic polymer and mixing additives such as a tackifying resin and a cross-linking agent into a solvent-type adhesive composition. It was common to apply this on a support and dry it to produce an adhesive sheet (sheet, tape, etc.). However, in recent years, from the viewpoint of environmental measures, the development of solvent-free pressure-sensitive adhesives has been actively performed.

[0003] As a method for eliminating the solvent, there are emulsification, hot melt and the like.
Drying and removal of water after coating is troublesome, and there is also a problem with water resistance. In the case of hot melt, there is a problem with heat resistance and the like, and both types are inferior in practical use. As another method, a composition containing a monomer and a photo-radical generator is irradiated with ultraviolet rays to carry out a polymerization reaction, thereby producing a solvent-free polymer to produce a pressure-sensitive adhesive or an adhesive sheet thereof. Methods have been proposed.

[0004] The above-mentioned polymerization method by ultraviolet irradiation is a preferable method without problems such as emulsion formation and hot melt formation, but has a drawback that productivity is inferior because the polymerization rate is generally slow. On the other hand, the amount of the photo-radical generator used has been increased, and a photo-radical generator having a high initiator efficiency has been devised to increase the polymerization rate. Greatly decreases. Further, there is a contrivance for increasing the polymerization rate by increasing the intensity of ultraviolet rays. However, in this case, the molecular weight is also reduced, and problems such as volatilization of the monomer are likely to occur.

To overcome such a problem, Japanese Patent Application Laid-Open No.
Japanese Patent Application Laid-Open No. 504809 proposes a two-stage irradiation method in which ultraviolet light is irradiated at a low intensity at first and then at a higher intensity. However, this two-stage irradiation method is complicated in that two types of ultraviolet lamps are combined, and requires cooling to prevent volatilization of the monomer, which is not always practical. In addition, Tokio Table 7-
In Japanese Patent Application Laid-Open No. 505425, when irradiating ultraviolet rays, 180
Using a pulsed laser ultraviolet light of ~ 400 nm,
Although it has been proposed to form a thick pressure-sensitive adhesive layer up to 5,000 μm, problems still tend to occur in terms of molecular weight characteristics and the like.

[0006]

As described above, in the prior art for producing a solventless pressure-sensitive adhesive by a polymerization method using ultraviolet irradiation, the polymerization rate is increased without volatilizing the monomer during polymerization. In addition, the production of a high molecular weight polymer involves considerable difficulties, and at present, there are great restrictions on the surface of the apparatus and the monomer composition.

In view of the above circumstances, the present invention provides a method for producing a solvent-free pressure-sensitive adhesive by a polymerization method using ultraviolet irradiation, which can produce a polymer having a high polymerization rate and a high molecular weight. It is an object of the present invention to provide the above-mentioned production method in which the volatilization of the monomer during polymerization is small and the restrictions on the monomer composition and the like are small.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, irradiated a composition containing an acrylic monomer and a photo radical generator with ultraviolet light of a single wavelength. Sometimes, the polymerization reaction occurs in a short time, without being greatly restricted by the composition of the monomer, etc., and the molecular weight of the acrylic polymer to be generated can be increased, and the volatilization of the monomer during the polymerization is also reduced. I found little. When the composition is sprayed in a particle state in an inert gas atmosphere and irradiated with ultraviolet light of a single wavelength,
It has been found that the polymerization rate is further increased and the volatilization of the monomer can be further reduced. The present invention has been completed based on these findings.

That is, the present invention provides a composition containing a monomer having an alkyl (meth) acrylate as a main component and a photoradical generator, which is irradiated with ultraviolet rays having substantially a single wavelength to carry out a polymerization reaction. Producing an acrylic polymer having a glass transition point of 250 K or less, and using the acrylic polymer as a main component of the pressure-sensitive adhesive composition, a method for producing a pressure-sensitive adhesive composition, In particular,
A composition comprising the above monomer and a photoradical generator,
The present invention relates to a method for producing a pressure-sensitive adhesive composition having the above-described structure, in which the composition is sprayed in a particle state in an inert gas atmosphere, and the polymerization reaction is performed by irradiating ultraviolet rays having substantially a single wavelength. .

[0010] The present invention also relates to the present invention, wherein the monomer having the above-mentioned alkyl (meth) acrylate as a main component has 4 to 4 carbon atoms.
The method for producing a pressure-sensitive adhesive composition having the above constitution, which comprises at least 50% by weight of an alkyl acrylate having 12 alkyl groups, and the method wherein the amount of the photo-radical generator used is an alkyl (meth) acrylate. The method for producing the pressure-sensitive adhesive composition having the above composition in which the composition is 0.05 to 10 parts by weight with respect to 100 parts by weight of the monomer as a main component, and the above composition in which ultraviolet light having a single wavelength is 308 nm or 222 nm. And a method for producing the pressure-sensitive adhesive composition. .

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The monomers used in the present invention are:
(Meth) acrylic acid alkyl ester, that is, an ester of acrylic acid or methacrylic acid and an alcohol having 12 or less carbon atoms as a main component, wherein the homopolymer or the copolymer has a glass transition point of 250K or less. If so, there is no particular limitation on the composition. Particularly preferably, it contains 50% by weight or more of an alkyl acrylate having an alkyl group having 4 to 12 carbon atoms, such as n-butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, nonyl acrylate and the like. What you do is good.

If necessary, other modifying monomers may be used together with the above-mentioned alkyl (meth) acrylate as a main component in an amount not exceeding 50% by weight of all monomers. Examples of such modifying monomers include vinyl acetate, vinyl propionate, styrene or derivatives thereof, (meth) acrylamide, mono- or diesters of maleic acid, N-methylol (meth) acrylamide, glycidyl (meth) Acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, 2-hydroxypropyl (meth) acrylate, (meth) acrylic acid, oligoester ( Various monomers and oligomers such as (meth) acrylate and ε-caprolactone (meth) acrylate are exemplified. The type and amount of these monomers and the like are appropriately selected in consideration of the glass transition point of the copolymer and the required adhesive properties of the pressure-sensitive adhesive.

The photo-radical generator used in the present invention comprises:
It is not particularly limited as long as it can be decomposed by ultraviolet rays to generate radicals and initiate polymerization of the monomer. Depending on the type of the monomer, an appropriate one can be selected in consideration of the solubility in the monomer. Specifically, 1-phenyl-2-hydroxy-2-methylpropan-1-one, 1-hydroxycyclohexylphenyl ketone, 2
-Methyl-1- (4-methylthiophenyl) -2-morpholino-propan-1-one, α, α-dimethoxy-α
-Phenylacetophenone, benzyl dimethyl ketal
And benzophenone. In addition, auxiliary agents such as amines and sulfones can be used together with these compounds, if necessary.

These photo-radical generators include monomers 10
It is used in an amount of usually 0.05 to 10 parts by weight, preferably 0.1 to 5 parts by weight, based on 0 parts by weight. If the amount of the photoradical generator is too small, the polymerization reaction will be slowed down and the polymerization rate will not be improved. On the other hand, if the amount of the photo-radical generator is too large, the molecular weight of the acrylic polymer to be produced is reduced, and the cost is disadvantageous.

In the present invention, first, a composition is prepared by uniformly mixing the monomer and the photoradical generator.
At that time, the presence of dissolved oxygen in the composition not only slows down the polymerization reaction in the subsequent ultraviolet irradiation step, but also
The adverse effect that the molecular weight of the produced polymer decreases is observed. For this reason, after mixing the two components, it is desirable to sufficiently displace the mixture with an inert gas such as nitrogen to reduce dissolved oxygen as much as possible, particularly to reduce dissolved oxygen to 2 ppm or less.

Next, the composition in which dissolved oxygen is reduced is irradiated with ultraviolet rays in a state in which oxygen is cut off to decompose the photo-radical generator, and the generated radical causes a polymerization reaction of the monomer. Is performed. At this time, the present invention is characterized by irradiating ultraviolet rays having substantially a single wavelength. This makes it possible to accelerate the polymerization reaction and increase the molecular weight of the acrylic polymer to be produced. A special effect that volatilization of the monomer can be reduced is achieved.

In particular, when the composition containing the monomer and the photo-radical generator is sprayed into an inert gas atmosphere in the form of particles and irradiated with ultraviolet light of substantially a single wavelength, the polymerization rate is further increased. Thus, the volatilization of the monomer can be further reduced. For example, when the composition is sprayed in the form of particles as droplets while introducing nitrogen gas from the lower part to the upper part along the tube wall into the glass cylindrical tube, and the above-mentioned single wavelength ultraviolet light is irradiated, Polymerization can be performed without volatilizing the body to the outside, and a high molecular weight acrylic polymer can be continuously produced from the lower part of the glass cylindrical tube.

On the other hand, when conventional ordinary ultraviolet light is used, the wavelength range is wide, so that the effect of the present invention cannot be obtained. In particular, the temperature of the composition rises due to heat rays contained in the ultraviolet light. As a result, the termination reaction of the polymerization reaction becomes active as the temperature rises, and the molecular weight of the produced polymer tends to decrease. For this reason, for example, when the above-described method of spraying and polymerizing the composition in a glass cylindrical tube is employed, the amount of the acrylic polymer produced from the lower portion decreases, and a desired polymerization rate cannot be obtained. The molecular weight of the polymer is also very low.

In the present invention, as the "single-wavelength ultraviolet light", a lamp capable of generating ordinary ultraviolet light such as a high-pressure mercury lamp or a metal halide lamp is used.
The wavelength filter can be used with a single wavelength in a cut filter. More preferably, an excimer UV lamp that generates ultraviolet light of a single wavelength is used. It is desirable to use “222 nm ultraviolet light” enclosing the “.

In the present invention, the above-mentioned "single-wavelength ultraviolet light" is described as "substantially a single-wavelength ultraviolet light". This is because, in the present invention, it is desired that the ultraviolet rays by the above-mentioned method have a single wavelength of 100%, but as long as the effect of the present invention is not significantly impaired (for example, 3
If it is within the range of 0% or less), it means that low-intensity ultraviolet rays other than the specific wavelength may be contained.

Further, in the present invention, when irradiating the above-mentioned substantially single-wavelength ultraviolet ray, as described above, it is preferable that the oxygen is cut off so as not to adversely affect the polymerization reaction. It is important. In the above-described technique of spraying and polymerizing the composition in the glass cylindrical tube, the above-mentioned oxygen can be shut off by introducing nitrogen gas from the lower portion to the upper portion along the tube wall surface. Separately from this, for example, by applying a composition containing the above monomer and a photoradical generator on a support, and irradiating the composition with the ultraviolet ray, a release liner is further laminated on the composition. The above-described oxygen can be cut off by, for example, placing the whole of the coated support in a nitrogen gas atmosphere.

The acrylic polymer thus obtained has a glass transition point of 250 K or less, preferably 240 K or less.
K or less, the polymerization rate is usually 90% by weight or more, preferably 95% by weight or more, and the weight average molecular weight in terms of polystyrene by gel permeation chromatography is usually 400,000 or more, preferably 500,000 or more. More preferably, it has a high molecular weight of 700,000 or more (usually up to 1.5 million). By using this as a main component of the pressure-sensitive adhesive composition, it is possible to obtain an excellent adhesive property satisfying adhesive strength and cohesive strength. A pressure-sensitive adhesive composition is obtained.

In the case where the composition is applied onto a support and the polymerization reaction is carried out by the above-mentioned ultraviolet irradiation, a pressure-sensitive adhesive composition comprising an acrylic polymer formed by the polymerization reaction is used as an adhesive layer. -Sheets (tapes, sheets, etc.) are obtained. In this case, as the support, various plastic films such as polyester film, paper,
Any conventionally known materials such as metal foil, nonwoven fabric, cloth and foam can be used. The thickness of the adhesive layer provided on the support as described above is not particularly limited, but can be usually 20 to 1,000 μm.

Further, in the present invention, the above-mentioned adhesive sheet
Are prepared by obtaining a pressure-sensitive adhesive composition comprising an acrylic polymer by the above method without coating the composition on a support, and then applying a melt coating on the support. You may. In this case, in the pressure-sensitive adhesive composition before coating,
Various additives such as a tackifier resin, a filler, a pigment, and a crosslinking agent may be blended. These additives may optionally be
It can also be added in advance to the composition before the polymerization reaction by ultraviolet irradiation.

[0025]

The present invention will be described more specifically with reference to the following examples. In the following, “parts” means “parts by weight”.

Example 1 1-hydroxycyclohexyl was added to a monomer mixture consisting of 70 parts of 2-ethylhexyl acrylate, 20 parts of n-butyl acrylate, 7 parts of isobornyl acrylate and 3 parts of acrylic acid. 0.3 parts of phenyl ketone are uniformly mixed and sufficiently replaced with nitrogen, and the amount of dissolved oxygen is 1.5 pp.
m. This composition was coated on a 38 μm-thick polyester film as a support with a coating thickness of 5 μm.
It was applied so as to have a thickness of 0 μm, and a release-treated polyester film was laminated thereon. In this state, a polymerization reaction was carried out by irradiating ultraviolet rays (single wavelength: 308 nm) twice on a 3 m / min conveyor with an excimer UV lamp manufactured by Heraeus.

In this manner, an adhesive sheet having an adhesive layer comprising a pressure-sensitive adhesive composition containing, as a main component, an acrylic polymer produced by the above-mentioned polymerization reaction on a support was produced. . The resulting acrylic polymer had a glass transition point of 231K, a polymerization rate of 96.7% by weight, and a polystyrene-equivalent weight average molecular weight of 820,000 as determined by gel permeation chromatography.

Example 2 0.3 part of α, α-dimethoxy-α-phenylacetophenone was added to a monomer mixture consisting of 70 parts of isooctyl acrylate, 20 parts of ethyl acrylate and 10 parts of acrylic acid. And 0.3 part of 1-hydroxycyclohexylphenyl ketone were uniformly mixed and sufficiently substituted with nitrogen to obtain a composition having a dissolved oxygen amount of 1.5 ppm. This composition was sprayed as droplets onto a glass cylindrical tube having a diameter of 20 cm and a length of 1 m, which was replaced with nitrogen gas, while introducing a nitrogen gas flow (flow rate: 5 liters / minute) from the bottom to the top of the glass tube wall. And a 30cm long Heraeus excimer U
Ultraviolet light (single wavelength: 308 nm) was irradiated by a V lamp.

In this way, the acrylic polymer formed at the lower receptacle of the glass cylindrical tube was taken out. The acrylic polymer had a glass transition point of 225K, a polymerization rate of 94.5% by weight, and a polystyrene-equivalent weight average molecular weight of 760,000 by gel permeation chromatography. Next, a pressure-sensitive adhesive composition was formed using the acrylic polymer as a main component, and melt-coated so as to have a thickness of 50 μm on a 38 μm-thick polyester film as a support, An adhesive sheet was prepared.

Comparative Example 1 A high-pressure mercury lamp was used instead of an excimer UV lamp, and irradiation was performed in the same manner as in Example 2 except that ultraviolet rays were irradiated.
A polymerization reaction by ultraviolet irradiation was performed. However, one minute after the start of irradiation, the monomer vapor was filled in the glass cylindrical tube,
Even if a nitrogen stream is flowing over the liquid surface, it adheres to the inside of the glass tube,
A polymerization reaction has occurred. As a result, the amount of the acrylic polymer taken out to the lower receptacle became 50% by weight or less, the polymerization rate became 60.9% by weight, and the weight average molecular weight in terms of polystyrene by gel permeation chromatography was 320,000. And low. A pressure-sensitive adhesive composition was constituted using the removed acrylic polymer as a main component, and the adhesive sheet was used in the same manner as in Example 2 using this.
Was made.

With respect to each of the adhesive sheets of Examples 1 and 2 and Comparative Example 1, the adhesive force and the holding force were measured by the following methods. The results were as shown in Table 1.

<Adhesive force> An adhesive sheet cut into a size of 20 mm × 100 mm was pressure-bonded to a stainless steel plate sanded with a # 280 sandpaper as an adherend by reciprocating a 2 kg roller once. After 20 minutes at 23 ° C, 2
The force required for 180 ° peeling was measured under the conditions of 3 ° C., 65% RH atmosphere and a tensile speed of 300 mm / min.

<Holding force> An adhesive sheet was adhered to a phenol resin plate with an adhesive area of 10 mm × 20 mm, and after 20 minutes,
Leave it at 40 ° C for 20 minutes, then hang down the phenolic resin plate, apply a uniform load of 500g to the free end of the adhesive sheet, and let the adhesive sheet fall at 40 ° C (min). ) Was measured.

[0034]

As is clear from the results shown in Table 1 above, the adhesive sheets of Examples 1 and 2 in which the polymerization reaction was carried out by irradiating ultraviolet rays of a single wavelength were the acrylic polymer produced. It can be seen that-has a sufficiently high molecular weight and satisfies adhesive strength and cohesive strength and exhibits excellent adhesive properties. On the other hand, the adhesive sheet of Comparative Example 1 in which the polymerization reaction is performed by irradiating ordinary ultraviolet rays has a low molecular weight of the acrylic polymer to be produced and is inferior in cohesive strength,
Good adhesive properties cannot be obtained.

[0036]

As described above, according to the present invention, a composition containing an acrylic monomer and a photo-radical generator is irradiated with ultraviolet light having a single wavelength to cause a polymerization reaction. High-speed, high-molecular-weight acrylic polymer can be produced, monomer volatilization during polymerization is small, and restrictions on monomer composition are also reduced. A pressure-sensitive adhesive composition can be produced.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasushi Inoue 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Michiharu Yamamoto 1-1-2 Shimohozumi, Ibaraki-shi, Osaka No. F-term in Nitto Denko Corporation (reference) 4J040 DF041 DF051 HB13 HB19 HC26 JA01 JB09 KA13 LA02 LA11 QA01

Claims (5)

[Claims] 1. A composition containing a monomer containing an alkyl (meth) acrylate as a main component and a photo-radical generator is irradiated with a substantially single-wavelength ultraviolet ray to carry out a polymerization reaction, thereby causing a glass transition. A method for producing a pressure-sensitive adhesive composition, comprising producing an acrylic polymer having a temperature of 250K or less, and using the acrylic polymer as a main component of the pressure-sensitive adhesive composition. 2. A composition containing a monomer having a (meth) acrylic acid alkyl ester as a main component and a photo-radical generator is sprayed in an inert gas atmosphere in the form of particles, and a substantially single The method for producing a pressure-sensitive adhesive composition according to claim 1, wherein the polymerization reaction is performed by irradiating ultraviolet rays having a wavelength. 3. The monomer according to claim 1, wherein the monomer containing an alkyl (meth) acrylate as a main component contains at least 50% by weight of an alkyl acrylate having an alkyl group having 4 to 12 carbon atoms. A method for producing a pressure-sensitive adhesive composition. 4. The amount of the photo radical generator used is (meth)
Monomer 10 mainly composed of alkyl acrylate
The method for producing a pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the amount is 0.05 to 10 parts by weight based on 0 part by weight. 5. A single wavelength ultraviolet light having a wavelength of 308 nm or 2
The method for producing a pressure-sensitive adhesive composition according to any one of claims 1 to 4, wherein the thickness is 22 nm.