JP2017048384A - Manufacturing method of acrylic resin and acrylic resin for non-solvent-type adhesive, non-solvent-type adhesive composition, adhesive and adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an acrylic resin for non-solvent-type adhesive capable of providing an adhesive capable of thick coating and excellent in impact absorption property and step followability.SOLUTION: There is provided a manufacturing method of an acrylic resin having weight average molecular weight of 50,000 or more for use in a non-solvent-type adhesive, including a process [I] of preparing an acrylic resin solution by solution polymerizing a polymerization component containing a (meth)acrylic monomer and a process [II] for distilling a solvent from the resin solution and using a solvent having the boiling point of 70°C or less as the solvent during solution polymerization.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing an acrylic resin, an acrylic resin for solventless pressure-sensitive adhesive, a solventless pressure-sensitive adhesive composition using the same, a pressure-sensitive adhesive, and a pressure-sensitive adhesive sheet. Acrylic resin for solvent-free pressure-sensitive adhesives, a method for producing an acrylic resin capable of producing an acrylic resin suitable for thick coating, and an acrylic resin for solvent-free pressure-sensitive adhesives obtained thereby The present invention relates to a resin, a solventless pressure-sensitive adhesive composition, a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet using the same.

  Conventionally, acrylic adhesives are strong adhesives that are intended to bond adherends firmly for a long period of time, or peel-off types based on the premise that they are peeled off from adherends after being attached. There are various types of pressure-sensitive adhesives such as pressure-sensitive adhesives, and pressure-sensitive adhesives having optimized adhesive properties are designed and used in various fields.

  In recent years, not only adhesive properties such as adhesive strength when used for bonding glass substrates in the field of portable image display devices such as mobile phones and liquid crystal display devices as performance required for adhesives in recent years. The pressure-sensitive adhesive layer itself is required to have transparency and impact resistance.

For example, in mobile devices such as TVs, monitors for personal computers, notebook computers, mobile phones, and tablet terminals, a protective layer formed from a plastic sheet or the like is usually provided on the viewing side of the liquid crystal display, or due to external impacts. In order to prevent damage to the liquid crystal display, a space (air layer) is provided between the liquid crystal display and the protective layer.
However, there is a problem that reflection occurs at the interface between the protective layer and the air layer and at the interface between the air layer and the liquid crystal display, resulting in a decrease in visibility. Therefore, an impact-absorbing pressure-sensitive adhesive layer is used instead of an air layer for the purpose of improving visibility and reducing the thickness of plastic sheets (mobile devices) while ensuring impact resistance. In order to improve the impact absorbing performance, it has been proposed to increase the thickness of the pressure-sensitive adhesive layer.

  However, when solvent-based pressure-sensitive adhesives are used for thick coating applications, the thickness of the pressure-sensitive adhesive layer at the time of coating is so thick that the solvent is less likely to volatilize in the pressure-sensitive adhesive layer during the drying process after coating. In more detail, the solvent near the surface of the pressure-sensitive adhesive layer that is likely to be volatilized first hardens the surface of the pressure-sensitive adhesive layer, and even if the solvent inside the pressure-sensitive adhesive layer continues to volatilize, it does not volatilize. In addition, there is a problem that it remains as foam inside the pressure-sensitive adhesive layer.

  On the other hand, as a technique for thickening the pressure-sensitive adhesive layer using an acrylic resin (coating with a thick film), a dilution monomer ((meta) is added to the acrylic resin ((meth) acrylic acid derivative polymer (B)). ) Acrylic acid derivative (A)) and a polyfunctional compound (polyfunctional (meth) acrylic acid derivative (C)) that is a curing component are known. (For example, refer to Patent Document 1).

  The active energy ray-curable pressure-sensitive adhesive generally does not contain a solvent used for viscosity adjustment with a normal acrylic pressure-sensitive adhesive, and a photopolymerizable unsaturated monomer as a dilution monomer instead of the solvent. Since it is a solvent-free pressure-sensitive adhesive to be used, there is no need for a drying step to remove the solvent after the pressure-sensitive adhesive has been applied, and it is possible to efficiently obtain a pressure-sensitive adhesive layer even in the case of thick coating. It can be done.

JP 2009-57550 A

  However, it is possible to use only an acrylic resin produced by a considerably limited method for the solventless pressure-sensitive adhesive. For example, (i) an acrylic resin produced by bulk polymerization, or (ii) once It was necessary to use an acrylic resin produced by a method in which an acrylic resin was produced by solution polymerization or suspension polymerization and then dried to remove the solvent.

Here, in the case of producing by the method (i), it is difficult to produce an acrylic resin with good reproducibility because of poor polymerization stability, the reaction heat is difficult to control and the safety is low, and there are many reaction components and the reaction There was a problem that it was difficult to remove heat and production efficiency was poor because it was intense.
Furthermore, even in the case of producing by the method (ii), usually when producing an acrylic resin by solution polymerization or suspension polymerization, ethyl acetate, butyl acetate, toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, etc. Organic solvents and water are used as solvents, but they have a high boiling point, and it takes a lot of energy and time to remove the solvent and water from the acrylic resin containing the solvent (solvent and water) once produced. Was bad. In addition, it is difficult to completely remove the solvent, and the residual solvent may adversely affect the physical properties of the pressure-sensitive adhesive.

  Therefore, in the present invention, under such a background, when used as a pressure-sensitive adhesive, a thick coating can be applied, and a pressure-sensitive adhesive having excellent shock absorption and step following characteristics can be obtained. It aims at providing the method of manufacturing the acrylic resin for agents.

  However, as a result of intensive studies in view of such circumstances, the present inventors have carried out solution polymerization of a polymerization component containing a (meth) acrylic monomer in a method for producing an acrylic resin for solventless adhesives ( ) Including the step [I] of preparing an acrylic resin solution and the step [II] of distilling off the solvent from the resin solution, and using a low-boiling solvent having a boiling point of 70 ° C. or less as a solvent during solution polymerization, Thus, the inventors have found that an acrylic resin that does not contain a solvent can be efficiently produced, and completed the present invention.

  That is, the gist of the present invention is a method for producing an acrylic resin having a weight average molecular weight of 50,000 or more for use in a solvent-free pressure-sensitive adhesive, wherein a polymerization component containing a (meth) acrylic monomer is solution-polymerized. An acrylic resin solution comprising a step [I] of producing an acrylic resin solution and a step [II] of distilling off the solvent from the resin solution, wherein a solvent having a boiling point of 70 ° C. or less is used as a solvent during solution polymerization. The present invention relates to a method for producing a resin.

  Furthermore, the present invention provides an acrylic resin for solventless pressure-sensitive adhesives produced by the above acrylic resin production method, a solventless pressure-sensitive adhesive composition comprising the same, and a solventless pressure-sensitive adhesive composition And a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the solvent-free pressure-sensitive adhesive composition.

  The method for producing an acrylic resin of the present invention includes a step [I] for producing an acrylic resin solution by solution polymerization of a (meth) acrylic monomer, and a step [II] for distilling off the solvent from the resin solution. Since a solvent having a boiling point of 70 ° C. or lower is used as a solvent during polymerization, the solvent can be efficiently removed even in solution polymerization. And the pressure-sensitive adhesive made of the solvent-free pressure-sensitive adhesive acrylic resin manufactured by this manufacturing method can be applied by thick coating and has excellent shock absorption and step following performance. It is useful for pressure-sensitive adhesives used in display devices and the like, shock absorbing sheets and the like.

The present invention will be described in detail below, but these show examples of desirable embodiments.
In the present invention, (meth) acryl means acryl or methacryl, (meth) acryloyl means acryloyl or methacryloyl, and (meth) acrylate means acrylate or methacrylate. The acrylic resin is a resin obtained by polymerizing a monomer component containing at least one (meth) acrylic monomer. The “sheet” conceptually includes a sheet, a film, and a tape.

The process for producing an acrylic resin for solvent-free pressure-sensitive adhesives of the present invention includes a step [I] for producing an acrylic resin solution by solution polymerization of a (meth) acrylic monomer, and a step for distilling off the solvent from the resin solution [ II], and a solvent having a boiling point of 70 ° C. or lower is used as a solvent during solution polymerization.
Each process will be described sequentially.

[Step [I]]
First, process [I] is demonstrated.
This step is a step of obtaining an acrylic resin solution by solution polymerization of a polymerization component containing a (meth) acrylic monomer.

<Polymerization component>
In the present invention, the (meth) acrylic monomer preferably contains the (meth) acrylic acid ester monomer (a1), and if necessary, the functional group-containing monomer (a2) and other polymerizable monomers ( a3) can also be used as a polymerization component.

  Examples of the (meth) acrylic acid ester monomer (a1) include, for example, aliphatic (meth) acrylic acid ester monomers such as (meth) acrylic acid alkyl ester, and aromatic monomers such as (meth) acrylic acid phenyl ester. Examples include (meth) acrylic acid ester monomers.

  Examples of such aliphatic (meth) acrylic acid ester monomers include alkyl (meth) acrylates in which the alkyl group usually has 1 to 24 carbon atoms, particularly preferably 1 to 20 carbon atoms, and more preferably 1 to 18 carbon atoms. Examples thereof include esters and (meth) acrylic acid esters having an alicyclic structure.

  As such (meth) acrylic acid alkyl ester, specifically, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl ( (Meth) acrylate, n-propyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, tridecyl ( (Meth) acrylate, isotridecyl (meth) acrylate, isomyristyl (meth) acrylate, cetyl (meth) acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, isotetracosyl (meth) acryl Over doors and the like.

  Specific examples of the (meth) acrylic acid ester having an alicyclic structure include cyclohexyl (meth) acrylate and isobornyl (meth) acrylate.

  Examples of aromatic (meth) acrylic acid ester monomers include phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenyldiethylene glycol (meth) acrylate, and 2-hydroxy-3-phenoxypropyl. (Meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, phenoxypolyethylene glycol-polypropylene glycol- (meth) acrylate, nonylphenol ethylene oxide adduct (meth) acrylate, and the like.

  Examples of other (meth) acrylic acid ester monomers include tetrahydrofurfuryl (meth) acrylate. These may be used alone or in combination of two or more.

  Among these (meth) acrylic acid ester monomers (a1), aliphatic (meth) acrylic acid esters are excellent in terms of copolymerizability, coating film strength, ease of handling, and availability of raw materials. Monomers are preferable, and methyl (meth) acrylate, n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and isobornyl (meth) acrylate are particularly preferable.

  The content ratio of the (meth) acrylic acid ester monomer (a1) in the polymerization component is preferably 10 to 100% by weight, particularly preferably 50 to 95% by weight, and further preferably 60 to 90% by weight. If the content of the (meth) acrylic acid ester monomer (a1) is too small, the adhesive strength when used as an adhesive tends to be insufficient.

  The functional group-containing monomer (a2) may be any monomer containing a functional group that can become a crosslinking point by reacting with a cross-linking agent described later, such as a hydroxyl group-containing monomer, a carboxyl group-containing monomer, an alkoxy group-containing monomer, Phenoxy group-containing monomer, amide group-containing monomer, amino group-containing monomer, nitrogen atom-containing monomer (excluding the amide group-containing monomer and amino group-containing monomer), glycidyl group-containing monomer, phosphate group-containing monomer, sulfonic acid And group-containing monomers. These may be used alone or in combination of two or more.

  Among these, it is preferable to use a hydroxyl group-containing monomer, a carboxyl group-containing monomer, and an alkoxy group-containing monomer from the viewpoint that the crosslinking reaction can be efficiently performed. In addition, a hydroxyl group-containing monomer is preferably used from the viewpoint of excellent transparency when used under high temperature and high humidity, and a carboxyl group is preferably used from the viewpoint of easy adjustment of adhesive strength.

  Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl ( Primary (meth) acrylic acid hydroxyalkyl esters such as (meth) acrylate, 10-hydroxydecyl (meth) acrylate, (4-hydroxymethylcyclohexyl) methyl (meth) acrylate, caprolactone-modified 2-hydroxyethyl (meth) Contains primary hydroxyl group such as caprolactone-modified monomer such as acrylate, 2-acryloyloxyethyl-2-hydroxyethylphthalic acid, N-methylol (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, etc. Monomer; 2-hydroxypropyl (meth) acrylate 2-hydroxybutyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 3-chloro-2-hydroxypropyl (meth) acrylate, 2-hydroxy-3 -Secondary hydroxyl group-containing monomers such as phenoxypropyl (meth) acrylate; tertiary hydroxyl group-containing monomers such as 2,2-dimethyl-2-hydroxyethyl (meth) acrylate.

  In addition, polyethylene glycol esters of (meth) acrylic acid such as diethylene glycol mono (meth) acrylate and polyethylene glycol mono (meth) acrylate, polypropylene glycol esters of (meth) acrylic acid such as polypropylene glycol mono (meth) acrylate, polyethylene glycol- Oxyalkylene-modified monomers such as polypropylene glycol-mono (meth) acrylate, poly (ethylene glycol-tetramethylene glycol) mono (meth) acrylate, poly (propylene glycol-tetramethylene glycol) mono (meth) acrylate may be used.

  Among the above hydroxyl group-containing monomers, a primary hydroxyl group-containing monomer is preferable from the viewpoint of excellent reactivity with a crosslinking agent, and 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are particularly preferable.

  Examples of the carboxyl group-containing monomer include Michael addition of acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, fumaric acid, acrylamide N-glycolic acid, cinnamic acid, and (meth) acrylic acid. (Eg, acrylic acid dimer, methacrylic acid dimer, acrylic acid trimer, methacrylic acid trimer, acrylic acid tetramer, methacrylic acid tetramer, etc.), 2- (meth) acryloyloxyethyl dicarboxylic acid monoester (eg, 2-acryloyloxyethyl) Succinic acid monoester, 2-methacryloyloxyethyl succinic acid monoester, 2-acryloyloxyethyl phthalic acid monoester, 2-methacryloyloxyethyl phthalic acid monoester, 2-acryloyloxyethyl hexahi Rofutaru acid monoester, 2-methacryloyloxyethyl hexahydrophthalic acid mono ester) and the like. Such a carboxyl group-containing monomer may be used as an acid, or may be used in the form of a salt neutralized with an alkali.

  Examples of the alkoxy group-containing monomer include 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, 2-butoxyethyl (meth) acrylate, and 2-butoxydiethylene glycol. (Meth) acrylate, methoxydiethylene glycol (meth) acrylate, methoxytriethylene glycol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxydipropylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, octoxypolyethylene glycol- Polypropylene glycol-mono (meth) acrylate, lauroxypolyethylene glycol mono (meth) acrylate, steer Alkoxy polyethylene glycol mono (meth) acrylate aliphatic of (meth) acrylic acid ester.

  Examples of the amide group-containing monomer include acrylamide, methacrylamide, N- (n-butoxyalkyl) acrylamide, N- (n-butoxyalkyl) methacrylamide, N, N-dimethyl (meth) acrylamide, N, N- Examples include diethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, acrylamide-3-methylbutylmethylamine, dimethylaminoalkylacrylamide, and dimethylaminoalkylmethacrylamide.

  Examples of the amino group-containing monomer include dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, and a quaternized product thereof.

  Examples of the nitrogen atom-containing monomer include acryloylmorpholine.

  Examples of the glycidyl group-containing monomer include glycidyl (meth) acrylate and allyl glycidyl ether.

  Examples of the phosphoric acid group-containing monomer include 2- (meth) acryloyloxyethyl acid phosphate (for example, “Light Ester P-1M”, “Light Acrylate P-1A” manufactured by Kyoeisha Chemical Co., Ltd.), bis (2- (Meth) acryloyloxyethyl) acid phosphate, phosphate ester of polyethylene glycol monomethacrylate (for example, “Sipomer PAM100” and “Sipomer PAM4000” manufactured by Rhodia Nikka Co., Ltd.), phosphate ester of polyethylene glycol monoacrylate (for example, Rhodia Nikka Co., Ltd. “Sipomer PAM5000”, etc.), Polypropylene glycol monomethacrylate phosphate ester (eg, Rhodia Nikka Corporation “Sipomer PAM200”, etc.), Polypro Polyalkylene glycol mono (meth) acrylate phosphate ester such as phosphate ester of lenglycol monoacrylate (for example, “Sipomer PAM300” manufactured by Rhodia Nikka Co., Ltd.), methylene phosphate (meth) acrylate, trimethylene phosphate ( Examples thereof include alkylene (meth) acrylates such as (meth) acrylate, propylene phosphate (meth) acrylate, and tetramethylene (meth) acrylate phosphate.

Examples of the sulfonic acid group-containing monomer include olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, styrene sulfonic acid, and salts thereof. .
These functional group-containing monomers (a2) can be used alone or in combination of two or more.

  The content of the functional group-containing monomer (a2) in the polymerization component is preferably 0 to 50% by weight, particularly preferably 1 to 35% by weight, and more preferably 2 to 20% by weight. When there is too much content rate of the said functional group containing monomer (a2), there exists a tendency for a viscosity to become high or for stability of resin to fall.

  Examples of the other polymerizable monomer (a3) include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, and vinyl. Pyridine, vinylpyrrolidone, itaconic acid dialkyl ester, fumaric acid dialkyl ester, allyl alcohol, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinylketone, 4- (meth) acryloyloxy And monomers such as benzophenone.

  It is preferable to use 4- (meth) acryloyloxybenzophenone in that a crosslinking reaction can be efficiently performed with active energy rays such as ultraviolet rays and electron beams.

  For the purpose of increasing the molecular weight, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate A compound having two or more ethylenically unsaturated groups such as divinylbenzene can also be used in combination.

  The content of the other polymerizable monomer (a3) is preferably 0 to 80% by weight, particularly preferably 0 to 50% by weight, and further preferably 0 to 30% by weight with respect to the entire polymerization component. When there is too much content rate of the said other polymerizable monomer (a3), there exists a tendency for heat resistance to fall or for adhesive force to fall.

<Solvent>
In solution polymerization of the polymerization component containing the (meth) acrylic monomer, it is necessary to use a solvent having a boiling point of 70 ° C. or lower as the solvent.
Examples of the solvent having a boiling point of 70 ° C. or lower include hydrocarbon solvents such as n-hexane (67 ° C.), alcohol solvents such as methanol (65 ° C.), and esters such as methyl acetate (54 ° C.). Solvents, ketone solvents such as acetone (56 ° C.), diethyl ether (35 ° C.), methylene chloride (40 ° C.), tetrahydrofuran (66 ° C.), among others, versatility and safety In this respect, acetone and methyl acetate are preferably used, and acetone is particularly preferable.
In addition, the numerical value in () described following each said solvent name is a boiling point.

  The amount of the solvent used is usually 5 to 1,000 parts by weight, preferably 20 to 500 parts by weight with respect to a total of 100 parts by weight of the polymerization components of the acrylic resin, and is efficient by keeping the temperature during the reaction high. From the viewpoint of causing a polymerization reaction to increase the reaction rate, it is particularly preferably 30 to 100 parts by weight. If the amount of the solvent used is too small, it tends to be difficult to adjust the weight average molecular weight of the acrylic resin, and if it is too large, the amount of the solvent to be distilled off is too large and the production efficiency tends to decrease.

<Polymerization initiator>
In the method for producing an acrylic resin of the present invention, as a polymerization initiator used for solution polymerization of the polymerization component containing the (meth) acrylic monomer, an azo polymerization initiator that is a normal radical polymerization initiator, A peroxide polymerization initiator can be used. Examples of the azo polymerization initiator include 2,2′-azobis (2-methylbutyronitrile) (67 ° C.), 2,2′-azobis. Isobutyronitrile (65 ° C.), (1-phenylethyl) azodiphenylmethane (58 ° C.), 2,2′-azobis (2,4-dimethylvaleronitrile) (52 ° C.), 2,2′-azobis (2 -Cyclopropylpropionitrile) (49.6 ° C.), 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile) (30 ° C.) and the like. Is For example, benzoyl peroxide (74 ° C.), di-t-butyl peroxide, cumene hydroperoxide, lauroyl peroxide (61.6 ° C.), t-butyl peroxypivalate (54.6 ° C.), t-hexyl peroxy Examples include pivalate (53.2 ° C.), t-hexyl peroxyneodecanoate (44.5 ° C.), diisopropyl peroxycarbonate (40.5 ° C.), diisobutyryl peroxide (32.7 ° C.) and the like.
These may be used alone or in combination of two or more.
In addition, the numerical value in () described following each compound name is the 10-hour half-life temperature of each compound.

Especially, in this invention, it is preferable to use the polymerization initiator whose 10-hour half life temperature is less than 60 degreeC from the point which performs process [II] stably, Especially, 2,2'- azobis (2 , 4-dimethylvaleronitrile) (52 ° C.), 2,2′-azobis (2-cyclopropylpropionitrile) (49.6 ° C.), 2,2′-azobis (4-methoxy 2,4-dimethylvalero) Nitrile) (30 ° C), t-butylperoxypivalate (54.6 ° C), t-hexylperoxypivalate (53.2 ° C), t-hexylperoxyneodecanoate (44.5 ° C), diisopropylperoxy Carbonate (40.5 ° C.) and diisobutyryl peroxide (32.7 ° C.) are preferable, and 2,2′-azobis (2,4-dimethylvaleronitrile) ( 52 ° C.), t-hexyl peroxypivalate (53.2 ° C.).
In the present invention, in the solution polymerization in step [I], a polymerization initiator having a low 10-hour half-life temperature is used because polymerization is performed at a relatively low reaction temperature using a reaction solvent having a boiling point as low as 70 ° C. or lower. When is used, the polymerization initiator tends to remain. If the polymerization initiator remains, gelation may occur in step [II].

  The amount of the polymerization initiator used is usually 0.001 to 10 parts by weight, preferably 0.1 to 8 parts by weight, particularly preferably 0.5 to 6 parts by weight, more preferably 100 parts by weight of the polymerization component. Is 1 to 4 parts by weight, particularly preferably 1.5 to 3 parts by weight, most preferably 2 to 2.5 parts by weight. If the amount of the polymerization initiator used is too small, the polymerization rate of the acrylic resin decreases and the residual monomer tends to increase, or the polymerization average molecular weight of the acrylic resin tends to increase. In the step [II], the acrylic resin tends to gel easily.

<Solution polymerization>
Regarding polymerization conditions for solution polymerization, polymerization may be performed in accordance with conventionally known polymerization conditions. For example, a polymerization component containing a (meth) acrylic monomer and a polymerization initiator are mixed or dropped in a solvent to a predetermined polymerization condition. Can be polymerized.

  When the above polymerization components are charged, any charging method may be used, such as batch charging, multistage split charging, or the like. And in the case of the division | segmentation preparation by a multistep, what is necessary is just to prepare in 2-10 steps normally, Preferably it is preparation by 2-3 steps. In addition, in the multi-stage split charging, 1 to 99 parts by weight of the polymerization components are charged in the initial (first stage) charging, and the remaining polymerization components are charged by splitting or dropping, so that the temperature during the polymerization reaction can be increased. Since the temperature can be higher than the boiling point of the selected solvent species, it is preferable from the viewpoint of improving the reaction efficiency.

  When the above polymerization components are charged, it is preferably dropped in 15 minutes to 10 hours, particularly preferably 30 minutes to 4 hours.

  The polymerization initiator may be charged in the same manner as in the case of the polymerization component, or may be batch charging, multi-stage split charging, or any charging method. And in the case of division | segmentation by a multistage, it is sufficient to charge normally in 2-10 steps, Preferably it is the preparation by 3-5 steps. In the case of this multi-stage charging, a method in which 1 to 50% by weight of the total amount of the polymerization initiator is charged in the first half and 50 to 99% by weight in the second and subsequent stages is preferable.

  As described above, when the polymerization initiator is divided into multiple stages, after the pass-through rate of the entire reaction component to the polymer is 60% or more, 50% by weight or more of the total amount of the polymerization initiator is used. It is preferable to charge, and particularly preferably, after the conversion rate reaches 80% or more, particularly preferably 90% or more, it is preferable to charge 50% or more of the polymerization initiator.

From the viewpoint of improving the pass-through rate to the final polymer, that is, from the viewpoint of reducing the residual monomer, the solvent concentration in the system when the conversion rate is 80% or more is desirably 30 to 1%, particularly preferably. 25 to 2%, particularly preferably 20 to 5%.
This is because the reaction rate of the residual monomer is improved by increasing the radical concentration in the system. When the solvent concentration is reduced to less than 1%, the reaction of the residual monomer becomes difficult due to the increase in viscosity, which causes conversion. It tends to be difficult to improve the rate.

  The polymerization initiator may be added, for example, before the polymerization component is charged, after the polymerization component is charged, or at the same time as the polymerization component is dropped. You may make it melt | dissolve in a component, or may melt | dissolve a polymerization initiator in a solvent separately, and may be dripped simultaneously with a polymerization component.

  The polymerization temperature in the above polymerization reaction is usually 40 to 120 ° C., but in the present invention, it is preferably 50 to 90 ° C., particularly preferably 55 to 75 ° C., and more preferably 60 to 70 from the viewpoint of enabling a stable reaction. ° C. If the polymerization temperature is too high, gelation tends to occur, and if it is too low, the activity of the polymerization initiator decreases, the polymerization rate decreases, and the residual monomer tends to increase.

In addition, the polymerization time in the polymerization reaction (in the case of performing after-heating, which will be described later) is not particularly limited, but is 0.5 hours or more, preferably 1 hour from the last addition of the polymerization initiator. Above, more preferably 2 hours or more, particularly preferably 5 hours or more.
The polymerization reaction is preferably performed while refluxing the solvent from the viewpoint of easy heat removal.

In the method for producing an acrylic resin of the present invention, it is preferable to perform additional heating in order to thermally decompose the polymerization initiator.
In the present invention, the heating operation (heating operation at a temperature higher than the 10-hour half-life temperature of the polymerization initiator) after the state in which the reaction rate of the polymerization component in the reaction solution is 80% or more is “push-in”. It is defined as “heating”.

  Thus, the reaction rate of the polymerization component at the start of the rushing heating is preferably 80% or more, particularly preferably 90% or more, and particularly preferably 95% or more. The upper limit of the reaction rate is usually 100%.

In addition, the reaction rate of a polymerization component can be measured and confirmed as follows, for example.
The reaction rate of the polymerization component, that is, the reaction rate (%) of the acrylic resin, precisely weighed 1 g of a sample of the resin whose reaction rate is desired to be confirmed on an aluminum foil, and a ket (infrared dryer, 185 W, high The solid content during the reaction is calculated from the remaining amount after heating for 45 minutes at 5 cm), and the reaction rate is calculated from the monomer content (solid content assuming that all monomers have reacted) by the following formula: Can do.
Reaction rate (%) = [(solid content during reaction) / (monomer content)] × 100

  And it is preferable to perform the said driving-in heating temperature at the temperature higher than the 10-hour half-life temperature of the said polymerization initiator, and specifically it is 40-150 degreeC normally, and 55-130 degreeC from the point of gelatinization suppression. Is preferable, and in particular, the temperature is preferably 75 to 95 ° C. If the driving-in heating temperature is too high, the acrylic resin tends to yellow, and if it is too low, the monomer and the polymerization initiator remain, and the stability of the produced resin tends to decrease.

  In addition, the follow-up can be performed at normal pressure or by raising the boiling point under pressure.

  The time required for the follow-up heating is preferably 30 minutes or more, particularly preferably 1 hour or more, more preferably 2 hours or more, and particularly preferably 3 hours or more. There is no particular upper limit for the time required for the forced heating, but it is usually within 48 hours from the viewpoint of product efficiency.

  The smaller the amount of residual polymerization initiator (calculated value) at the end of the above polymerization reaction or at the end of the follow-up heating performed as necessary, the better. Specifically, the amount of the residual polymerization initiator calculated is preferably 1000 ppm or less, particularly preferably 300 ppm or less, more preferably 100 ppm or less, particularly preferably 50 ppmpp or less, and most preferably 10 ppm or less. When the amount of the residual polymerization initiator is too large, the temporal stability of the obtained resin tends to decrease.

Thus, an acrylic resin solution can be obtained in step [I].
The solid content of the acrylic resin solution obtained above is preferably 40 to 90%, particularly preferably 45 to 80%, and still more preferably 50 to 70%. If the solid content of the acrylic resin solution is too high, the viscosity will increase too much and it will be difficult to carry out the polymerization reaction in the step [I] stably. If it is too low, the amount of solvent to be distilled off will increase, so the production efficiency energy It is not preferable in terms of efficiency.

[Step [II]]
Next, step [II] will be described.
In this step, the solvent is distilled off from the acrylic resin solution obtained in the step [I].

The step of distilling off the solvent from the acrylic resin solution can be performed by a known general method.
For example, after completion of the step [I], the step [II] may be performed with the reaction vessel used in the step [I], or the step [II] may be performed by transferring to a distillation apparatus. In the latter case, batch distillation in a distillation kettle or continuous distillation may be used.

  As a method of distilling off the solvent, there are a method of distilling off the solvent by heating, a method of distilling off the solvent by reducing the pressure, and the like.

  The temperature when the solvent is distilled off by heating is preferably 60 to 150 ° C., in particular, the reaction solution after polymerization of the acrylic resin is maintained at 60 to 80 ° C., and the solvent is distilled off. It is preferable to distill the solvent at 80 to 150 ° C. from the viewpoint of extremely reducing the residual solvent amount. In view of suppressing the gelation of the acrylic resin, it is preferable to carry out the solvent distillation at a temperature of 150 ° C. or lower.

  The pressure when the solvent is distilled off under reduced pressure is preferably 20 to 101.3 kPa, and in particular, after the solvent in the reaction solution is distilled by holding in the range of 50 to 101.3 kPa. It is preferable to distill the residual solvent at 0 to 50 kPa from the viewpoint of extremely reducing the residual solvent amount.

  From the viewpoint of efficiently distilling off the solvent, a method of distilling off by heating under reduced pressure is preferred.

  Note that the above temperature range and the degree of reduced pressure are only examples, and the appropriate temperature range and the reduced pressure range vary depending on the content of the solvent and residual monomer in the reaction solution, etc. If the distillation operation is carried out, the solvent can be distilled off in other systems.

  The time from the start to the end of the evaporation of the solvent is not particularly limited, but in the case of batch distillation, it is preferably 3 to 48 hours, and particularly preferably 5 to 24 hours. In the case of continuous distillation, it is preferably 1 hour or less, and particularly preferably 10 minutes or less. If the time for evaporating the solvent is too long, the production efficiency tends to decrease.

By the production method of the present invention including the above steps [I] and [II], the solventless pressure-sensitive adhesive acrylic resin of the present invention is obtained.
The weight average molecular weight of the acrylic resin of the present invention thus obtained is required to be 50,000 or more, more preferably 7 to 1.5 million, particularly preferably 100,000 to 1,000,000, particularly preferably 20 to 80. In particular, it is preferably 300 to 600,000.
If the weight average molecular weight is too large, the viscosity tends to be too high and coating properties and handling tend to decrease. If it is too small, the cohesive force tends to decrease and durability tends to decrease.

  Further, the dispersity (weight average molecular weight / number average molecular weight) of the acrylic resin is preferably 1.1 to 20, particularly preferably 2 to 15, more preferably 3 to 10, especially 4 ~ 7 is preferred. If the degree of dispersion is too high, the durability performance of the pressure-sensitive adhesive layer tends to be reduced, and foaming or the like tends to occur. If it is too low, the handleability tends to be lowered.

Ｔｇ：共重合体のガラス転移温度（Ｋ）
Ｔga：モノマーＡのホモポリマーのガラス転移温度（Ｋ） Ｗａ：モノマーＡの重量分率
Ｔgb：モノマーＢのホモポリマーのガラス転移温度（Ｋ） Ｗｂ：モノマーＢの重量分率
Ｔgn：モノマーＮのホモポリマーのガラス転移温度（Ｋ） Ｗｎ：モノマーＮの重量分率
（Ｗａ＋Ｗｂ＋・・・＋Ｗｎ＝１） In addition, said weight average molecular weight is a weight average molecular weight by standard polystyrene molecular weight conversion, and it is a column in high performance liquid chromatography (The Japan Waters company "Waters 2695 (main body)" and "Waters 2414 (detector)"). : Shodex GPC KF-806L (exclusion limit molecular weight: 2 × 10 ⁷ , separation range: 100 to 2 × 10 ⁷ , theoretical plate number: 10,000 plates / piece, filler material: styrene-divinylbenzene copolymer, filler The particle diameter is measured by using three series of 10 μm), and the same method can be used for the number average molecular weight. The degree of dispersion is determined from the weight average molecular weight and the number average molecular weight. The glass transition temperature is calculated from the following Fox equation.

Tg: Glass transition temperature of copolymer (K)
Tga: Glass transition temperature (K) of monomer A homopolymer Wa: Weight fraction of monomer A Tgb: Glass transition temperature of homopolymer of monomer B (K) Wb: Weight fraction of monomer B Tgn: Homogeneity of monomer N Glass transition temperature (K) of polymer Wn: weight fraction of monomer N (Wa + Wb +... + Wn = 1)

  The glass transition temperature (Tg) of the acrylic resin is usually −100 to 80 ° C., preferably −80 to 0 ° C., particularly preferably −70 to −10 ° C., and more preferably −60 to −20 ° C. It is. If the glass transition temperature is too high, the tackiness tends to decrease, and if it is too low, the thermal durability tends to decrease.

  The acrylic resin has a melt viscosity (mPa · s) at 100 ° C. of preferably 1,000 to 10,000,000 mPa · s, particularly preferably 50,000 to 1,000,000 mPa · s, and more preferably 200. , 000-600,000. If the viscosity is too low, the durability tends to be insufficient due to a decrease in molecular weight, and if the viscosity is too high, the handleability tends to decrease and coating tends to be difficult.

  In addition, said viscosity is the value which measured the load 30kg, the orifice diameter 1.0mm, die | dye length 10mm, and the measurement temperature at 100 degreeC using the Shimadzu Corporation Koka type flow tester.

  In the present invention, the solvent content of the acrylic resin obtained by the above production method is preferably 2% by weight or less, particularly preferably 0.00001 to 2% by weight, more preferably 0.0001 to 1% by weight. Particularly preferred is 0.001 to 0.1% by weight. When the solvent content is too high, bubbles are generated in the pressure-sensitive adhesive, and the durability after the coating tends to decrease. When the content is too small, the adhesion tends to decrease.

  Further, the residual monomer amount in the acrylic resin obtained by the above production method is preferably 2% by weight or less, particularly preferably 0.00001 to 1.5% by weight, more preferably 0.0001 to 1.2. % By weight. If the amount of the residual monomer is too large, bubbles are generated in the pressure-sensitive adhesive, and the durability tends to decrease.

Thus, the solvent-free pressure-sensitive adhesive acrylic resin of the present invention can be produced. The solvent-free pressure-sensitive adhesive acrylic resin of the present invention is useful as a hot-melt pressure-sensitive adhesive component, and is based on a pressure-sensitive adhesive layer comprising a pressure-sensitive adhesive composition containing the solvent-free pressure-sensitive adhesive acrylic resin of the present invention. It can be used as an adhesive sheet on the material.
The pressure-sensitive adhesive layer may be the pressure-sensitive adhesive composition itself of the present invention or may be formed by curing the pressure-sensitive adhesive composition. Examples of the curing method include a method of curing by crosslinking using a crosslinking agent, a method of curing with active energy rays, a method of combining these, and the like.

  The pressure-sensitive adhesive composition of the present invention contains the acrylic resin for solvent-free pressure-sensitive adhesive of the present invention as a main component, and if necessary, an ethylenically unsaturated group-containing compound, other acrylic pressure-sensitive adhesives, etc. Such as photopolymerization initiator, crosslinking agent, crosslinking accelerator, silane coupling agent, antistatic agent, urethane resin, rosin, rosin ester, hydrogenated rosin ester, phenol resin, aromatic modified terpene resin Tackifiers such as aliphatic petroleum resins, alicyclic petroleum resins, styrene resins, xylene resins, plasticizers, softeners, colorants, fillers, anti-aging agents, UV absorbers, functional dyes A conventionally well-known additive, such as these, can be mix | blended.

  From the viewpoint that handling properties and other physical properties can be imparted, it is preferable to contain an ethylenically unsaturated group-containing compound. In this case, curing with active energy rays is performed, and the acrylic resin and the ethylenically unsaturated compound in the pressure-sensitive adhesive composition are polymerized with active energy rays, and desired adhesive properties are exhibited.

  Examples of the ethylenically unsaturated group-containing compound include ethylenically unsaturated monomers having one or more ethylenically unsaturated groups in one molecule, such as monofunctional monomers, bifunctional monomers, trifunctional or higher monomers, and urethane. (Meth) acrylate compounds can be used.

  Examples of such monofunctional monomers include styrene monomers such as styrene, vinyl toluene, chlorostyrene, α-methylstyrene, methyl (meth) acrylate, ethyl (meth) acrylate, acrylonitrile, 2-methoxyethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, phenoxyethyl (meth) acrylate, 2-phenoxy-2-hydroxypropyl (meth) acrylate, 2-hydroxy -3-phenoxypropyl (meth) acrylate, 3-chloro-2-hydroxypropyl (meth) acrylate, glycerin mono (meth) acrylate, glycidyl (meth) acrylate, cyclohexyl (meta Acrylate, isobornyl (meth) acrylate, tricyclodecanyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, dicyclopentanyl (meth) acrylate, (2-methyl- 2-ethyl-1,3-dioxolan-4-yl) -methyl (meth) acrylate, cyclohexanespiro-2- (1,3-dioxolan-4-yl) -methyl (meth) acrylate, 3-ethyl-3- Oxetanylmethyl (meth) acrylate, γ-butyrolactone (meth) acrylate, n-butyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) Acry , Isodecyl (meth) acrylate, dodecyl (meth) acrylate, n-stearyl (meth) acrylate, isostearyl (meth) acrylate, benzyl (meth) acrylate, phenol ethylene oxide modified (n = 2) (meth) acrylate, Half (meth) of phthalic acid derivatives such as nonylphenol propylene oxide modified (n = 2.5) (meth) acrylate, 2- (meth) acryloyloxyethyl acid phosphate, 2- (meth) acryloyloxy-2-hydroxypropyl phthalate Acrylate, furfuryl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, carbitol (meth) acrylate, benzyl (meth) acrylate, butoxyethyl (meth) acrylate, allyl ( (Meth) acrylate monomers such as (meth) acrylate, (meth) acryloylmorpholine, polyoxyethylene secondary alkyl ether acrylate, 2-hydroxyethylacrylamide, N-methylol (meth) acrylamide, N-vinylpyrrolidone, 2- Examples thereof include vinyl pyridine and vinyl acetate.

  Examples of such bifunctional monomers include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, and di Propylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, butylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, ethylene oxide modified bisphenol A type di (meth) acrylate, propylene oxide modified bisphenol A Type di (meth) acrylate, cyclohexanedimethanol di (meth) acrylate, ethoxylated cyclohexanedimethanol di (me ) Acrylate, dimethylol dicyclopentane di (meth) acrylate, tricyclodecane dimethanol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, glycerin di (meth) acrylate, pentaerythritol di (meth) Acrylate, ethylene glycol diglycidyl ether di (meth) acrylate, diethylene glycol diglycidyl ether di (meth) acrylate, diglycidyl phthalate di (meth) acrylate, hydroxypivalic acid modified neopentyl glycol di (meth) acrylate, ethylene isocyanurate Examples thereof include oxide-modified diacrylate.

  Examples of the tri- or higher functional monomer include trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa ( (Meth) acrylate, tri (meth) acryloyloxyethoxytrimethylolpropane, glycerin polyglycidyl ether poly (meth) acrylate, isocyanuric acid ethylene oxide modified triacrylate, caprolactone modified dipentaerythritol penta (meth) acrylate, caprolactone modified dipentaerythritol hexa (Meth) acrylate, caprolactone-modified pentaerythritol tri (meth) acrylate, capro Kuton modified pentaerythritol tetra (meth) acrylate, ethylene oxide modified dipentaerythritol penta (meth) acrylate, ethylene oxide modified dipentaerythritol hexa (meth) acrylate, ethylene oxide modified pentaerythritol tri (meth) acrylate, ethylene oxide modified pentaerythritol Examples include tetra (meth) acrylate and ethoxylated glycerin triacrylate.

  Such a urethane (meth) acrylate compound is a (meth) acrylate compound having a urethane bond in the molecule, and a (meth) acrylic compound containing a hydroxyl group and a polyvalent isocyanate compound, and if necessary, a polyol Can be produced by a known general method, and the weight average molecular weight thereof is usually 300 to 4,000. It is also effective to leave the isocyanate group consciously, make urethane acrylate having an isocyanate group and an unsaturated bond in the molecule, create a crosslinking point with the acrylic resin, and increase the cohesive strength of the adhesive.

  These ethylenically unsaturated group-containing compounds are used alone or in combination of two or more.

  Among these, it is preferable to use (meth) acrylates such as isostearyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, cyclohexyl (meth) acrylate and the like from the viewpoint of excellent adhesive properties. Is an isodecyl (meth) acrylate because it has a good balance between compatibility and adhesive properties.

  Moreover, from the point which can adjust the cohesion force of the whole adhesive layer, the ethylenically unsaturated monomer which contains two or more ethylenically unsaturated groups in 1 molecule, for example, a bifunctional monomer, a trifunctional or more monomer, It is preferable to use a urethane (meth) acrylate compound.

The content of the ethylenically unsaturated group-containing compound is preferably 0 to 1000 parts by weight, particularly preferably 10 to 300 parts by weight, and more preferably 100 to 200 parts by weight with respect to 100 parts by weight of the acrylic resin. is there.
If the content is too large, the cohesive force is increased too much, so that the adhesive performance tends to be lowered. If the content is too small, the holding force is insufficient, or the cohesive force is lowered and durability tends to be lowered. .

  Moreover, when hardening by an active energy ray, it is preferable to contain a photoinitiator at the point which can stabilize reaction at the time of active energy ray irradiation.

  Such a photopolymerization initiator is not particularly limited as long as it generates radicals by the action of light, and examples thereof include polymerization initiators such as acetophenones, benzoins, benzophenones, thioxanthones, and acyl phosphooxides. can give. In addition, these photoinitiators may be used independently and may use 2 or more types together.

  Further, auxiliary agents for these photopolymerization initiators include triethanolamine, triisopropanolamine, 4,4′-dimethylaminobenzophenone (Michler ketone), 4,4′-diethylaminobenzophenone, 2-dimethylaminoethylbenzoic acid, 4- Ethyl dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate (n-butoxy), isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 2,4-diethylthioxanthone, 2,4- Diisopropylthioxanthone and the like can be used in combination. These auxiliaries may be used alone or in combination of two or more.

  About the compounding quantity of this photoinitiator, it is usually preferable that it is 0.01-10 weight part with respect to 100 weight part of ethylenically unsaturated group containing compounds, Most preferably, it is 0.1-1 weight part. It is. If the amount is too small, the curing rate tends to decrease, and if too large, the curability is not improved and the economy tends to decrease.

  The crosslinking agent mainly reacts with a functional group derived from the functional group-containing monomer (a2), which is a constituent monomer of the acrylic resin (A), and becomes a pressure-sensitive adhesive having excellent adhesive force. Examples of the crosslinking agent include an epoxy crosslinking agent, an aziridine crosslinking agent, a melamine crosslinking agent, an aldehyde crosslinking agent, an amine crosslinking agent, and a metal chelate crosslinking agent. Among these, an isocyanate-based cross-linking agent is preferably used from the viewpoint of improving the adhesion to the substrate and the reactivity with the acrylic resin. These crosslinking agents may be used independently and may use 2 or more types together.

  In general, the content of the crosslinking agent is preferably 0.01 to 10 parts by weight, more preferably 0.05 to 5 parts by weight, and particularly preferably 0.1 to 100 parts by weight of the acrylic resin. ~ 2 parts by weight. If the amount of the crosslinking agent is too small, there is a tendency that the cohesive force is lowered and sufficient durability cannot be obtained. If the amount is too large, the flexibility and the adhesive strength are lowered, the durability is lowered, and peeling easily occurs. There is a tendency to become.

<Adhesive sheet>
The acrylic resin of the present invention includes a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising a pressure-sensitive adhesive composition containing an acrylic resin on a base sheet, a double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer provided on a release sheet, and pressure-sensitive adhesive. The adhesive layer is preferably used as an optical member with an adhesive layer provided on the optical member.
An adhesive sheet can be produced as follows, for example.

First, the pressure-sensitive adhesive composition is applied to one or both sides of the base sheet in a melted state by heating, and then cooled, or the pressure-sensitive adhesive composition is melted by heating, and the base sheet is formed by T dice or the like. The pressure-sensitive adhesive layer is formed to have a predetermined thickness on one side or both sides of the substrate sheet by a method such as extrusion lamination. Then, a pressure-sensitive adhesive sheet can be produced by attaching a release sheet to the pressure-sensitive adhesive layer surface as necessary.
Moreover, after forming an adhesive layer on a base material sheet, an active energy ray irradiation treatment is performed, and an adhesive sheet having an adhesive layer formed by crosslinking and curing the adhesive composition is produced by aging as necessary. be able to.
Moreover, a base material-less double-sided adhesive sheet can also be produced by forming an adhesive layer on the release sheet and bonding the release sheet to the opposite adhesive layer surface.
In use, the obtained pressure-sensitive adhesive sheet or double-sided pressure-sensitive adhesive sheet is peeled off from the pressure-sensitive adhesive layer for use.

  Examples of the base sheet include polyester resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate / isophthalate copolymer; polyolefin resins such as polyethylene, polypropylene, and polymethylpentene; polyvinyl fluoride, Polyfluorinated ethylene resins such as polyvinylidene fluoride and polyfluorinated ethylene; polyamides such as nylon 6 and nylon 6,6; polyvinyl chloride, polyvinyl chloride / vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl Alcohol copolymers, vinyl polymers such as polyvinyl alcohol and vinylon; cellulose resins such as cellulose triacetate and cellophane; polymethyl methacrylate, polyethyl methacrylate, polyacrylate Acrylic resins such as polybutyl acrylate, polystyrene, polycarbonate, polyarylate, synthetic resin sheets such as polyimide, aluminum, copper, iron metal foil, fine paper, glassine paper, glass fiber, natural fiber, synthetic Examples thereof include woven fabrics and nonwoven fabrics made of fibers. These base material sheets can be used as a single layer body or a multilayer body in which two or more kinds are laminated. Among these, a synthetic resin sheet is preferable from the viewpoint of weight reduction.

  Furthermore, as the release sheet, for example, various synthetic resin sheets exemplified for the support substrate, paper, cloth, non-woven fabric and the like can be used. As the release sheet, it is preferable to use a silicon-based release sheet.

  In addition, the application method of the pressure-sensitive adhesive composition is not particularly limited as long as it is a general application method, and examples thereof include roll coating, die coating, gravure coating, comma coating, and screen printing. can give.

  For irradiation with active energy rays, rays such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, infrared rays, electromagnetic waves such as X rays and γ rays, electron beams, proton rays, neutron rays, etc. can be used. Curing by ultraviolet irradiation is advantageous from the viewpoint of easy availability and price. In addition, when performing electron beam irradiation, it can harden | cure even if it does not use the said photoinitiator.

  The aging treatment is preferably carried out particularly when a crosslinking agent is used in the pressure-sensitive adhesive composition. As conditions for the aging treatment, the temperature is usually from room temperature (25 ° C.) to 100 ° C., and the time is usually from 1 day to 30 days. Specifically, for example, the treatment may be performed at 23 ° C. for 1 day to 20 days, preferably at 23 ° C. for 3 to 10 days, at 40 ° C. for 1 day to 7 days, and the like.

  Furthermore, in this invention, the said optical member with an adhesive layer can be obtained by carrying out the lamination formation of the adhesive layer which consists of the said adhesive composition on an optical member. Moreover, optical members can also be bonded together using said double-sided adhesive sheet.

  The gel fraction of the pressure-sensitive adhesive sheet, the double-sided pressure-sensitive adhesive sheet, and the pressure-sensitive adhesive layer of the optical member with the pressure-sensitive adhesive layer is preferably 10 to 100%, particularly 30 to 90% from the viewpoint of durability and adhesive strength. Is preferable, and 50 to 80% is particularly preferable. When the gel fraction is too low, durability tends to be reduced due to a decrease in cohesive force. On the other hand, if the gel fraction is too high, the adhesive force tends to decrease due to an increase in cohesive force.

  In addition, in adjusting a gel fraction to the said range, it is achieved by adjusting the kind and quantity, such as a kind and quantity of a crosslinking agent, an ethylenically unsaturated group containing compound, etc., for example.

  The gel fraction is a measure of the degree of crosslinking (curing degree), and is calculated, for example, by the following method. That is, a pressure-sensitive adhesive sheet (without a separator) formed by forming a pressure-sensitive adhesive layer on a polymer sheet (eg, polyethylene terephthalate (PET) film) as a base material is wrapped in a 200 mesh SUS wire mesh, and toluene It is immersed in the solution at 23 ° C. for 24 hours, and the weight percentage of the insoluble adhesive component remaining in the wire mesh is defined as the gel fraction. However, the weight of the substrate is subtracted.

  The thickness of the pressure-sensitive adhesive sheet, the double-sided pressure-sensitive adhesive sheet, and the pressure-sensitive adhesive layer of the optical member with the pressure-sensitive adhesive layer is usually preferably 50 to 3000 μm, more preferably 75 to 1000 μm, particularly 80 to It is preferable that it is 350 micrometers. If the thickness of the pressure-sensitive adhesive layer is too thin, the impact absorbability tends to decrease, and if it is too thick, the thickness of the entire optical member tends to increase too much.

  In addition, the film thickness in this invention subtracts the measured value of the thickness of structural members other than an adhesive layer from the measured value of the thickness of the adhesive layer containing laminated body whole using "ID-C112B" by Mitutoyo Corporation. It is the value calculated | required by.

  The adhesive strength of the pressure-sensitive adhesive sheet, the double-sided pressure-sensitive adhesive sheet, and the pressure-sensitive adhesive layer of the optical member with the pressure-sensitive adhesive layer is appropriately determined according to the material of the adherend. When sticking to a methyl methacrylate plate and a PET sheet having an ITO layer deposited thereon, it preferably has an adhesive strength of 5 N / 25 mm to 500 N / 25 mm, more preferably 10 N / 25 mm to 100 N / 25 mm.

  In addition, the said adhesive force is computed as follows, for example. An easy-adhesive PET (polyethylene terephthalate) film with a thickness of 125 μm is peeled off from the pressure-sensitive adhesive layer (thickness: 80 μm) of the substrate-less double-sided pressure-sensitive adhesive sheet using a polyester-based release sheet (polyethylene terephthalate sheet). To produce a PET film with an adhesive layer. The PET film with the pressure-sensitive adhesive layer is cut into a width of 25 mm × a length of 100 mm, the release sheet is peeled off, the pressure-sensitive adhesive layer side is brought into close contact with the adherend, and the atmosphere is at 23 ° C. and a relative humidity of 50%. 2 kg rubber roller 2 pressure reciprocating, left in the same atmosphere for 30 minutes, and then measured 180 ° peel strength (N / 25 mm) at a peel rate of 300 mm / min at room temperature (23 ° C.).

  Since the acrylic resin for solvent-free pressure-sensitive adhesive of the present invention has little outgas and can be applied with thick coating, it is suitably used for double-sided pressure-sensitive adhesive applications and pressure-sensitive adhesives having impact resistance and strong adhesiveness. Specifically, glass, ITO transparent electrode sheet, polyethylene terephthalate (PET), polycarbonate (PC), optical sheets such as polymethyl methacrylate (PMMA), polarizing plate, retardation plate, optical compensation film, It is useful as an adhesive component for affixing optical members such as brightness enhancement films. Furthermore, it can be suitably used for an image display device such as a touch panel comprising these optical members.

  The solvent-free pressure-sensitive adhesive acrylic resin of the present invention can also be used as an acrylic resin for various label pressure-sensitive adhesives and masking pressure-sensitive adhesives, and since there is very little outgassing, it is particularly used for electronic parts. Is preferably used.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist. In the examples, “parts” and “%” mean weight basis. Moreover, regarding the measurement of the weight average molecular weight of acrylic resin, it measured according to the above-mentioned method.

<Example 1>
[Production of acrylic resin [A-1]]
(Process [I])
In a 2 L flask equipped with a condenser, 100 parts of acetone (boiling point 56 ° C.) as a polymerization solvent and 1 part of 2,2′-azobis (2,4-dimethylvaleronitrile) (ADVN; half temperature 52 ° C.) as a polymerization initiator. The mixture was heated to reflux in the flask, and a solution prepared by previously mixing 80 parts of 2-ethylhexyl acrylate (2EHA) and 20 parts of 2-hydroxyethyl acrylate (HEA) was added dropwise over 2 hours. After dropping, 2 hours, 4 hours, and 6 hours later, 1 part of ADVN was added and reacted to obtain an acrylic resin [A-1] solution.

(Process [II])
The acrylic resin [A-1] solution obtained above was reduced with an evaporator at a jacket temperature of 85 ° C. for 1 hour, further reduced to 10 kPa and left at a jacket temperature of 85 ° C. for 1 hour, and the return of the cooler was removed from the system. The solvent was distilled off in the form of taking out, and acrylic resin [A-1] (weight average molecular weight; 350,000) was obtained.

<Comparative Example 1>
[Production of acrylic resin [A'-1]]
(Process [I])
In a 2 L flask equipped with a condenser, 70 parts of ethyl acetate (boiling point 77 ° C.) as a polymerization solvent and 1 part of 2,2′-azobis (2,4-dimethylvaleronitrile) (ADVN; half-temperature 52 ° C.) as a polymerization initiator Was heated under reflux in a flask, and a solution prepared by previously mixing 80 parts of 2-ethylhexyl acrylate (2EHA) and 20 parts of 2-hydroxyethyl acrylate (HEA) was added dropwise over 2 hours. After reacting for 2 hours, 4 hours, and 6 hours after dropping, 1 part of ADVN was added and reacted, and then diluted with 30 parts of ethyl acetate to obtain a (meth) acrylic resin [A′-1] solution.

(Process [II])
The (meth) acrylic resin [A′-1] solution obtained above was reduced with an evaporator at a jacket temperature of 85 ° C. for 1 hour, further reduced to 10 kPa and left at a jacket temperature of 85 ° C. for 1 hour to return the cooler. The solvent was distilled off in a form that was taken out of the system to obtain (meth) acrylic resin [A′-1] (weight average molecular weight; 350,000).

  The solvent content and residual monomer amount in the acrylic resins [A-1] and [A′-1] produced in Example 1 and Comparative Example 1 were measured using GC-MS. The results are shown in Table 1 below.

0.1 g of the acrylic resins [A-1] and [A′-1] obtained above were weighed and each diluted 20 times with toluene. A toluene-diluted solution of the acrylic resins [A-1] and [A′-1] was put into a vial with a capacity of 2 ml and screw-capped.
This vial was autosampler (7693 Autosampler manufactured by Agilent Technologies), gas chromatography / mass fragment detector (GC: Agilent Technologies 7890A GCsystem, MSD: concentration manufactured by Agilent Technologies, and a concentration of 75 monomers) .
The column used was DB-1MS (30 m × 250 μmφ × 0.25 μm) manufactured by Agilent, the carrier gas was He, the flow rate was 1.0 ml / min, and the pressure was 7.0 psi (at 40 ° C.). The split ratio was 50: 1 and the inlet temperature was 250 ° C.
The oven temperature condition was 40 ° C. for 5 minutes, 10 ° C./minute, and after reaching 300 ° C., the oven was left for 3 minutes.
The transfer line temperature to the MSD was 320 ° C. and the SIM mode (target ion: 58 m / z, qualify ion 43 m / z, cycle / sec = 3.81).

  The acrylic resins [A-1] and [A′-1] produced in Example 1 and Comparative Example 1 were subjected to a heating test according to the following method and visually evaluated.

About 1 g of acrylic resins [A-1] and [A′-1] were collected, put into a vial and sealed. Thereafter, a heating test at 90 ° C. for 1 hour was performed, and the appearance of the acrylic resin was visually observed and evaluated as follows. The results are shown in Table 1.
(Evaluation criteria)
A: No more than 10 foams and 1 mm or more in diameter.
○ ... 10 or less foams but 1 or more foams with a diameter of 1 mm or more,
Or there were more than 10 foams, but there was no foam of 1 mm or more in diameter.
X: There were more than 10 foams and one or more foams with a diameter of 1 mm or more.

From Example 1 above, the acrylic resin obtained by the production method of the present invention had a low solvent content, and in the heating test, the foam was small and the foam size was small.
On the other hand, the acrylic resin produced by using a solvent other than the solvent specified in the present invention as a solvent at the time of solution polymerization in Comparative Example 1 has a large solvent content, and many large-sized foams are observed in the heating test. Met.

  The acrylic resin for solvent-free pressure-sensitive adhesives produced by the production method of the present invention has little outgas and can be applied with thick coating, so it has excellent shock absorption and step following ability, touch panel and image display It is useful for pressure-sensitive adhesives used in devices and the like, shock absorbing sheets and the like.

Claims (10)

  A process for producing an acrylic resin having a weight average molecular weight of 50,000 or more for use in a solvent-free pressure-sensitive adhesive, wherein a polymerization component containing a (meth) acrylic monomer is solution-polymerized to produce an acrylic resin solution [I], a method for producing an acrylic resin, which comprises the step [II] of distilling off the solvent from the resin solution, wherein a solvent having a boiling point of 70 ° C. or less is used as a solvent during solution polymerization.   The method for producing an acrylic resin according to claim 1, wherein a polymerization initiator having a 10-hour half-life temperature of less than 60 ° C is used in the step [I].   An acrylic resin for solventless pressure-sensitive adhesives, which is produced by the method for producing an acrylic resin according to claim 1.   4. The solvent-free pressure-sensitive adhesive acrylic resin according to claim 3, wherein the solvent content is 2% by weight or less.   A solventless pressure-sensitive adhesive composition comprising the solvent-free pressure-sensitive adhesive acrylic resin according to claim 3.   The solventless pressure-sensitive adhesive composition according to claim 5, comprising an ethylenically unsaturated group-containing compound.   A pressure-sensitive adhesive obtained by curing the solventless pressure-sensitive adhesive composition according to claim 5.   A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer made of the solventless pressure-sensitive adhesive composition according to claim 5.   The pressure-sensitive adhesive sheet according to claim 8, wherein the pressure-sensitive adhesive layer is a pressure-sensitive adhesive layer obtained by curing the solventless pressure-sensitive adhesive composition with active energy rays and / or heat.   The pressure-sensitive adhesive sheet according to claim 8 or 9, wherein the pressure-sensitive adhesive layer has a thickness of 50 to 3000 µm.