JPH08239405A - Process for producing polymer for adhesive, its adhesive and adhesive member - Google Patents

Abstract

(57) [Abstract] [Purpose] A compact polymer, low manufacturing energy, and bulk polymerization method that does not use organic solvent due to easy maintenance. Acrylic polymer for adhesives has good molecular weight stability due to less gel formation. Obtain and easily prepare a solventless coating type UV curable adhesive. [Structure] The bulk polymerization method uses a static mixer to carry out the polymerization while maintaining the temperature at which the radical polymerization initiator decomposes and further removing the reaction heat by the polymerization to suppress the temperature rise of the reaction system. A method for producing a polymer for pressure-sensitive adhesives by obtaining an acrylic polymer by advancing, a radiation-curable pressure-sensitive adhesive comprising 100 parts by weight of the acrylic polymer and 3 to 50 parts by weight of a compound having a double bond, and the method. An adhesive member having a radiation-cured layer made of an adhesive on one side or both sides of a support. [Effect] A non-gel type acrylic polymer having excellent water resistance can be easily and efficiently prepared.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a polymer for pressure-sensitive adhesives which can obtain an acrylic polymer with a stable molecular weight by a bulk polymerization method, and a solventless coating type radiation-curable pressure-sensitive adhesive using the same. The present invention relates to an adhesive member.

[0002]

2. Description of the Related Art From the viewpoint of environmental hygiene and safety, it is an important issue to reduce the use of organic solvents as much as possible. The same is true in the field of pressure-sensitive adhesives, and there is a demand for a method for producing a polymer for pressure-sensitive adhesives that does not use an organic solvent, and a solventless coating type pressure-sensitive adhesive that can be coated without using a solvent or a small amount of solvent. Conventionally, as such a solventless coating type adhesive,
A radiation-curable type has been known, and an emulsion polymerization method using an emulsion has been known as a method for producing a polymer for an adhesive without using an organic solvent.

However, emulsion type polymers for pressure-sensitive adhesives have a drawback that they are poor in water resistance, and that they require the removal of water in order to be cured by radiation. As a method for producing a polymer that does not use an organic solvent, there is also a method by bulk polymerization, but the molecular weight of the obtained polymer is not stable, a gel insoluble in an organic solvent is generated, and a polymer for an adhesive, particularly a solventless coating. It has been unsuitable for the formation of polymers used for the preparation of engineered pressure-sensitive adhesives. A bulk polymerization method using an extruder has been proposed, but there are drawbacks such as enlargement of equipment such as a motor for driving a screw, increase in production energy, and complicated maintenance (Japanese Patent Laid-Open No. 58-58).
-53901 publication). Therefore, the emulsion polymerization method has been exclusively adopted as a method for producing a pressure-sensitive adhesive polymer that does not use an organic solvent.

[0004]

SUMMARY OF THE INVENTION The present invention uses a bulk polymerization method that does not use an organic solvent due to a compact apparatus, a small amount of manufacturing energy, and easy maintenance. The objective is to easily prepare a solventless coating type pressure-sensitive adhesive with good stability.

[0005]

Means for Solving the Problems The present invention is based on a bulk polymerization method in which a static mixer is used to maintain a temperature at which a radical-type polymerization initiator decomposes and at the same time remove reaction heat by polymerization to carry out a reaction. A method for producing a polymer for pressure-sensitive adhesives, characterized in that an acrylic polymer is obtained by proceeding with polymerization while suppressing an increase in temperature of the system, and 3 to 10 parts by weight of a compound having a double bond in 100 parts by weight of the acrylic polymer. The present invention provides a radiation-curable pressure-sensitive adhesive characterized by being mixed in an amount of 50 parts by weight, and a pressure-sensitive adhesive member having a radiation-curable layer comprising such a pressure-sensitive adhesive on one side or both sides of a support.

[0006]

With the above-mentioned constitution using the static mixer, it is possible to obtain an acrylic polymer suitable for a pressure-sensitive adhesive because gel hardly occurs even in the bulk polymerization method which does not use an organic solvent and the molecular weight can be stably controlled. It is possible to use it to easily prepare a solventless coating type pressure-sensitive adhesive. Such a bulk polymerization method can obtain a polymer having excellent compactness of the apparatus, small amount of energy required for production, easy maintenance, and excellent water resistance.

[0007]

Examples of constituent elements of the present invention: The production method of the present invention is a bulk polymerization method in which a static mixer is used to maintain the temperature at which a radical polymerization initiator decomposes and at the same time remove heat of reaction due to polymerization. Polymerization proceeds while suppressing an increase in the temperature of the reaction system to obtain a pressure-sensitive adhesive polymer made of an acrylic polymer.

In the present invention, as the static mixer, an appropriate mixer equipped with a non-driving type mixing element for realizing a mixing action such as division, movement, recombining of liquids in the pipe can be used. According to this, by supplying the liquid into the pipe through the pump or the like and allowing the liquid to pass through the mixing element, the liquid can be mixed without the need for the mixing operation via the driving source such as the screw. Therefore, any of the known static mixers can be used.

A static mixer that can be preferably used is one in which a pipe for medium flow is provided inside or outside the pipe.
The medium flow conduit in the tube may form a mixing element. The medium flow pipe is supplied with a heat medium or a refrigerant to maintain the temperature of the reaction system at a temperature at which the polymerization initiator can be decomposed, or to remove the reaction heat due to the progress of polymerization to remove the reaction system temperature. It is used to prevent rising.

The main monomer used for forming the acrylic polymer has a carbon number of 4 such as butyl group, isobutyl group, isoamyl group, hexyl group, 2-ethylhexyl group, isooctyl group, isononyl group and isodecyl group.
Examples thereof include esters of acrylic acid and methacrylic acid having an alkyl group of 14 to 14.

Further, esters of (meth) acrylic acid having an alkyl group having 3 or less carbon atoms such as methyl group, ethyl group and propyl group, vinyl esters such as vinyl acetate and vinyl propionate, styrene and α- Styrene compounds such as methylstyrene, other vinylpyrrolidone,
(Meth) acrylonitrile, (meth) acrylamide,
A monomer such as N-methylol can also be used for the purpose of modifying the glass transition point and the like of the acrylic polymer. The amount of the modifying monomer used is generally equal to or less than the amount of the main monomer.

Further, (meth) acrylic acid and itaconic acid,
Functional group-containing monomers such as maleic acid, crotonic acid, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and glycidyl (meth) acrylate are also used for the purpose of modifying acrylic polymers. Can be used. The functional group-containing monomer is particularly effective for modifying adhesive properties such as cohesive strength, and the amount used is generally 0.5 to 10% by weight of all monomers. Further, the functional group-containing monomer also contributes to modification of crosslinkability such as radiation crosslinkability.

As the polymerization initiator, radical type ones such as peroxides typified by benzoyl peroxide and azo type compounds typified by azobisisobutyronitrile are used. Known radical type polymerization initiators are used. Any of these can be used. An azo type polymerization initiator is preferably used in view of controlling polymerization by preventing induced decomposition. The polymerization initiator can also be used as a mixture with a monomer.

The polymerization operation is carried out by the bulk polymerization method using the static mixer as described above. In that case, the polymerization operation can be started using one or more monomers as a raw material, or the polymerization operation can be started using an oligomer or polymer, and further a prepolymer containing a monomer as a raw material.

In the polymerization operation using a prepolymer as a starting material, the viscosity may be increased as compared with the case where a monomer is used as a starting material, and the difference in viscosity with the target polymer may be reduced to facilitate polymerization control. is there. When the viscosity of the starting raw material is low and the viscosity difference with the target polymer is large, it may be difficult to control the feed rate of the starting raw material and the polymerization operation may be complicated. The prepolymer can be prepared by an appropriate method such as a method of prepolymerization or a method of dissolving an oligomer or a polymer in a monomer.

In the polymerization operation, it is preferable to preheat the static mixer to a temperature at which the polymerization initiator decomposes in order to smoothly proceed the polymerization. In addition, it is preferable to supply the raw material at a constant rate using an appropriate device such as a gear pump from the viewpoint of stability of polymerization and suppression of variation in molecular weight of formed polymer.

The polymerization temperature and the feed rate of the raw materials are appropriately determined depending on the type and amount of the polymerization initiator. The general polymerization temperature is 60 to 200 ° C, especially 80 to 150 ° C.
Further, the general amount of the polymerization initiator used is 0.01 to 10% by weight, preferably 0.03 to 3% by weight, based on all the monomers. If the polymerization temperature is too high or the amount of the polymerization initiator used is too large, it will be difficult to control the polymerization, and the gel will be generated due to abnormal heat generation locally, or the mixer will be clogged due to gel adhesion. . If the polymerization temperature is too low or the amount of the polymerization initiator used is too small, it takes a lot of time for the polymerization operation, which is disadvantageous in terms of production efficiency.

In the reaction system in the static mixer, the measures for maintaining the temperature at which the polymerization initiator decomposes and removing the reaction heat due to the polymerization to suppress the temperature rise of the reaction system are as follows: It may be performed by an appropriate method such as a method of using a medium of a predetermined temperature that functions as a refrigerant for the above and acts as a heat medium for the low temperature side, or a method of using both heat treatment and cooling treatment in combination. In the present invention, while maintaining the decomposition temperature of the polymerization initiator to measure the progress of polymerization when the reaction system passes through the static mixer, formation of gel due to excessive temperature rise of the reaction system due to heat of reaction is prevented. An appropriate temperature control method can be adopted.

A preferred acrylic polymer for use as a pressure-sensitive adhesive is a polymer which has a weight average molecular weight of 100,000 to 500,000 and is insoluble in an organic solvent (gel). ) Is not contained as much as possible, and the gel content is 5% by weight or less, especially 2% by weight or less. If the molecular weight of the polymer is too low, the adhesive properties will be poor, and if it is too high, the workability during polymerization will be poor and the coatability will also be poor. Further, the gel tends to cause coating unevenness such as roughness of the coated surface.

The molecular weight can be controlled by the polymerization operation by controlling the polymerization temperature, the feed rate of the raw materials, and the amount of the polymerization initiator used as described above, and the method using a chain transfer agent represented by mercaptan. But you can do it. The method using a chain transfer agent has an advantage that the molecular weight can be easily controlled with good reproducibility. Incidentally, in the polymerization operation, the use of a small amount of solvent does not hinder the purpose of improving workability such as passage of the raw material through the static mixer, but when using the obtained polymer as an adhesive, the solvent is removed. It is preferable.

The radiation-curable pressure-sensitive adhesive is double coated on 100 parts by weight of a non-gel type acrylic polymer having a weight average molecular weight of 100,000 to 500,000 and a glass transition point of 250 K or less obtained by the method of the present invention. 3 to 50 compounds having a bond
It can be prepared by blending parts by weight. By satisfying the above weight average molecular weight and glass transition point, it is possible to form a radiation-cured layer having excellent adhesive properties and the like.

As the compound having a double bond, one kind or two or more kinds can be used. If the compounding amount of the compound having a double bond is less than 3 parts by weight, a hardened layer having poor cohesive force will be obtained, and if it exceeds 50 parts by weight, a hardened layer will be formed and adhesiveness will be poor.

Examples of the compound having a double bond include (meth) acrylamide, N-methyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide and N.
Examples thereof include -t-butyl (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide and N, N-diethylaminoethyl (meth) acrylate.

Diethylene glycol di (meth) acrylate, ethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate,
1,6-hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, divinylbenzene, vinyl (meth) acrylate, adipic acid Divinyl, N, N′-methylenebisacrylamide and the like can also be used as the compound having a double bond.

The radiation-curable pressure-sensitive adhesive can be prepared by mixing the ingredients. At that time, if necessary, additives usually used for the pressure-sensitive adhesive, for example, tackifiers, glass fibers and hollow particles, fillers such as metal powder, pigments, colorants and the like can be added in usual amounts.

An antioxidant and a polymerization inhibitor may be added for the purpose of preventing denaturation and the like, and these may be added during the above-mentioned polymerization operation. In particular, the method of adding a hindered phenol anti-aging agent during the polymerization operation is effective in preventing gel formation. The addition amount is preferably 0.05 to 2% by weight. If the amount added is too large, the curability and the polymerizability may be reduced.

The pressure-sensitive adhesive member can be formed by providing a radiation-curable layer made of the above-mentioned pressure-sensitive adhesive on one side or both sides of the support. As the support, for example, a suitable material such as plastic film, paper, non-woven fabric, woven fabric or metal foil can be used. The thickness can be appropriately determined depending on the material and the like, but is generally about 12 to 200 μm.

The radiation-curable pressure-sensitive adhesive can be coated by using an appropriate coating machine such as a roll coater or a die coater. From the viewpoint of applying a uniform thickness without using a solvent, it is preferable to apply heat treatment with a die coater or the like. In that case, it is also possible to apply a plurality of pressure-sensitive adhesives having different compositions by a method in which the manifold of the die coater is made plural.

The coating thickness can be appropriately determined according to the purpose of use, etc., and is generally 1 to 500 μm in the case of a single layer structure, especially 5 to 150 μm, and 1 to 800 μm in the case of a laminated structure.
The unit thickness is 5 to 1500 μm, especially 40 to 1200 μm.

The coating layer is cured by, for example, α rays, β rays,
It is carried out by irradiating ionizing radiation such as γ ray, neutron ray and electron beam, and appropriate radiation such as ultraviolet ray. The irradiation dose is appropriately determined depending on the type of radiation. Generally, in the case of ionizing radiation, it is 0.5 to 20 Mrad, especially 1 to 1
0 Mrad is preferred. In the case of ultraviolet rays, irradiation with 400 to 3000 mj / cm ² is generally preferable using a suitable ultraviolet ray source such as a mercury lamp or a metal halide lamp.

In the case of curing with ultraviolet rays, it is desirable to add a photoreaction initiator (photosensitizer) together with the adhesive in advance. The addition amount is generally 0.1 to 10% by weight. As the photoreaction initiator, an appropriate one such as benzophenone, benzoin, benzoin methyl ether, benzoin ethyl ether, dibenzyl, benzyl dimethyl ketal can be used.

The pressure-sensitive adhesive member may be one in which the pressure-sensitive adhesive layer composed of the radiation-cured layer is fixed to the support, or one which is peelable from the support. The peelable type can be formed by, for example, a method using a support treated with a release agent.

[0033]

According to the present invention, a non-gel type acrylic polymer excellent in water resistance can be obtained with a stable molecular weight even in a bulk polymerization method without using an organic solvent. A coating type radiation-curable pressure-sensitive adhesive can be easily and efficiently prepared. Further, the bulk polymerization method according to the present invention is excellent in the compactness of the apparatus, the small amount of energy required for production, and the ease of maintenance.

[0034]

【Example】

Example 1 Inner diameter 50 mm, length 700 mm, volume 6 equipped with a mixing element that also serves as a supply pipe and has a diameter of 5 mm
After supplying a heating medium of 110 ° C. to the supply pipe of the static mixer of 60 ml to preheat it, 2-ethylhexyl acrylate 7
0 parts (parts by weight, the same applies hereinafter), 20 parts ethyl acrylate,
A mixture of 10 parts of acrylic acid and 0.2 part of 2,2'-azobisisobutyronitrile was added to 400 parts of the mixture under nitrogen substitution.
It is supplied at a rate of g / min, and is polymerized while preventing overheating with the above-mentioned heat medium, and has a weight average molecular weight of 270,000 (polystyrene conversion by gel permeation chromatography, the same applies below) and an acrylic resin having a glass transition point of 238K. A polymer was obtained. The polymerization rate of the polymer flowing out from the static mixer is 9
It was 6.3%. The gel content of ethyl acetate was 1.
5%.

Example 2 A mixture of 70 parts of 2-ethylhexyl acrylate, 20 parts of ethyl acrylate, 10 parts of acrylic acid, and 0.2 parts of 2,2'-azobisisobutyronitrile was pre-purged under nitrogen substitution. The polymerization liquid obtained by the polymerization and having a polymerization rate of 7.5% and a viscosity of 70 poise was subjected to a polymerization treatment according to Example 1 to obtain an acrylic polymer having a weight average molecular weight of 300,000 and a glass transition point of 238K. The polymerization rate of the polymer flowing out from the static mixer was 98.4%, and the gel content with ethyl acetate was 0.8%.

Example 3 70 parts of isononyl acrylate, 25 parts of methyl acrylate
Parts, acrylic acid 5 parts, 2,2′-azobisisobutyronitrile 0.3 parts, and pentaerythrityl-tetrakis {3- (3,5-dit-butyl-4-hydroxyphenyl) propionate} 1 Part of the mixture was prepolymerized under nitrogen substitution to obtain a polymerization liquid having a polymerization rate of 6.0% and a viscosity of 55 poise, which was subjected to a polymerization treatment according to Example 1 to give a weight average molecular weight of 220,000 and a glass transition point of 234K. An acrylic polymer was obtained. The polymerization rate of the polymer flowing out from the static mixer is 9
7.5% and 0.2% gel content with ethyl acetate.

Example 4 100 parts of the acrylic polymer obtained in Example 1 was mixed with 20 parts of pentaerythritol ester of polymerized rosin and 5 parts of tetraethylene glycol dimethacrylate to obtain a radiation-curable pressure-sensitive adhesive. A 25 μm thick polyester film was continuously coated with a curtain coater heated to 0 ° C. and cured by irradiation with an electron beam at 5 Mrad to obtain an adhesive member having an adhesive layer of 25 μm thickness.

Example 5 100 parts of the acrylic polymer obtained in Example 2 was mixed with N, N
A radiation-curable pressure-sensitive adhesive was obtained by blending 5 parts of dimethylaminopropyl methacrylamide, 5 parts of trimethylolpropane trimethacrylate and 1 part of benzyl dimethyl ketal, and using a die coater heated to 120 ° C., a thickness of 3
50μm thickness is continuously coated on a separator consisting of 8μm polyester film release-treated product.
It was adhered to both sides of a 2 μm polyester film and irradiated with ultraviolet rays at 1000 mj / cm ² with a high pressure mercury lamp for curing treatment to obtain a double-sided adhesive type adhesive member.

Example 6 100 parts of the acrylic polymer obtained in Example 3 was mixed with N, N
A mixture of 10 parts of diethylaminoethyl acrylate and 5 parts of dipentaerythritol hexaacrylate to obtain a radiation-curable adhesive, which was continuously coated on a polyester film having a thickness of 25 μm with a curtain coater heated to 110 ° C., The adhesive was irradiated with 5 Mrad of an electron beam and cured to obtain an adhesive member having an adhesive layer with a thickness of 25 μm.

Evaluation Test The adhesive members obtained in Examples 4, 5 and 6 were subjected to the following tests. Peeling adhesive strength Adhesive surface of 20mm x 100mm adhesive member on stainless plate (sandpaper # 280 sanding surface) 2
Pressure was applied by a method in which a kg roller was reciprocated once, and after 30 minutes, the force required for peeling was measured (180 degree peeling,
(Pulling speed 300 mm / min, 23 ° C, 65% RH).

Holding power 10 mm width of the adhesive member of the adhesive member on the phenol resin plate
After adhering with an adhesive area of mm × 20 mm for 20 minutes, 80
It was left at 20 ° C. for 20 minutes, then a phenol resin plate was hung down to apply a load of 500 g to the free end of the adhesive member, and the time until the adhesive member dropped was measured.

The above results are shown in the table below.

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Claims (4)

[Claims] 1. A bulk polymerization method, which uses a static mixer to maintain the temperature at which a radical polymerization initiator decomposes, and removes reaction heat due to polymerization to suppress an increase in the temperature of the reaction system. A method for producing a polymer for pressure-sensitive adhesive, which comprises subjecting an acrylic polymer to polymerization. 2. A reaction system using a monomer or a prepolymer as a raw material is maintained at a predetermined temperature via a medium flowing in a pipe line provided inside or outside a static mixer, and an azo polymerization initiator is added to the reaction system. The method according to claim 1, wherein a non-gel type acrylic polymer having a weight average molecular weight of 100,000 to 500,000 and a glass transition point of 250 K or less is used. 3. A compound having a double bond in an amount of 3 to 50 is added to 100 parts by weight of the acrylic polymer obtained in claim 1.
A radiation-curable pressure-sensitive adhesive characterized by being mixed in parts by weight. 4. A pressure-sensitive adhesive member having a radiation-curable layer comprising the pressure-sensitive adhesive according to claim 3 on one side or both sides of a support.