JP6847040B2 - Method for Producing (Meta) Acrylic Polymer and Method for Producing Adhesive Layer - Google Patents

Description

The present invention relates to a method for producing a (meth) acrylic polymer and a method for producing an adhesive layer.

In recent years, personal computers and mobile phones equipped with a touch panel have become widespread. The touch panel is made of a cover film made of glass or polyethylene terephthalate, an indium tin oxide transparent conductive film, or the like, and these are laminated via an adhesive layer.

As the pressure-sensitive adhesive layer for the touch panel, for example, a pressure-sensitive adhesive having a controlled relative permittivity and a specific pressure-sensitive adhesive layer containing a polymer obtained by polymerizing a monomer component containing a long-chain alkyl monomer in order to realize a low dielectric constant. There are known pressure-sensitive adhesives having excellent adhesive strength, which include the acrylic pressure-sensitive adhesive and a specific resin (Patent Documents 1 and 2).

The adhesive layer for a touch panel is further required to have step followability and durability. The step followability can be improved by using a soft adhesive layer, but the soft adhesive layer has high fluidity and foams and floats in a high temperature and high humidity environment, resulting in poor durability. On the contrary, when a hard adhesive layer is used, the durability is excellent, but the step followability is inferior, and there is a trade-off relationship between the step followability and the durability.

As a solution to the above problem, for example, the use of a two-layer structure adhesive and the use of an ultraviolet semi-curable adhesive are known, but there is a problem that productivity is poor.

Japanese Unexamined Patent Publication No. 2012-246477 Japanese Unexamined Patent Publication No. 2015-13925

An object of the present invention is a method for producing a (meth) acrylic polymer capable of forming a pressure-sensitive adhesive layer having excellent step-following property and durability by using it as a component contained in a pressure-sensitive adhesive composition, and the above-mentioned. It is an object of the present invention to provide a method for producing a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition containing a (meth) acrylic polymer.

The present inventor has diligently studied to solve the above problems. As a result, they have found that the above problems can be solved by, for example, the following method for producing a (meth) acrylic polymer, and have completed the present invention.

The present invention is, for example, the following [1] to [6].
[1] In a method for producing a (meth) acrylic polymer by polymerizing a monomer component containing a (meth) acrylic acid alkyl ester, methacrylic acid is added to the polymerization system when the polymerization rate of the monomer component is 50 to 95%. A method for producing a (meth) acrylic polymer to which an alkyl ester is added.

[2] The method for producing a (meth) acrylic polymer according to [1], wherein the methacrylic acid alkyl ester is continuously added dropwise to the polymerization system.

[3] The method for producing a (meth) acrylic polymer according to [1] or [2], wherein the initial charged monomer component contains an acrylic acid alkyl ester and a methacrylic acid alkyl ester.

[4] When the polymerization rate of the monomer component is 50 to 95% in 30% by mass or more of 100% by mass of the methacrylic acid alkyl ester contained in all the monomer components used for forming the (meth) acrylic polymer. The method for producing a (meth) acrylic polymer according to any one of [1] to [3], which is added to the polymerization system.

[5] 30 to 89.9% by mass of an acrylic acid alkyl ester having a homopolymer glass transition temperature of less than −45 ° C. in 100% by mass of all the monomer components used to form the (meth) acrylic polymer. [1] ~, the homopolymer contains 10 to 69.9% by mass of an alkyl methacrylate having a glass transition temperature of −45 ° C. or higher, and 0.05 to 20% by mass of a crosslinkable group-containing monomer. The method for producing a (meth) acrylic polymer according to any one of [4].

[6] A step of producing a (meth) acrylic polymer by the production method according to any one of [1] to [5], and an adhesive containing the (meth) acrylic polymer and a cross-linking agent. A method for producing a pressure-sensitive adhesive layer, which comprises a step of forming a pressure-sensitive adhesive layer from the composition.

According to the production method of the present invention, a (meth) acrylic polymer capable of forming a pressure-sensitive adhesive layer having excellent step-following property and durability can be produced by using it as a component contained in the pressure-sensitive adhesive composition. .. Further, according to the production method of the present invention, an adhesive layer having excellent step followability and durability can be produced by using the pressure-sensitive adhesive composition containing the (meth) acrylic polymer.

Hereinafter, a method for producing the (meth) acrylic polymer of the present invention and a method for producing a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition containing the (meth) acrylic polymer will be described.
As used herein, "(meth) acrylic" is used to indicate both acrylic and methacrylic, and "(meth) acrylate" is used to indicate both or one of acrylate and methacrylate. Further, "polymer" is used in the sense of including not only a polymer formed from one kind of monomer but also a copolymer formed from a plurality of kinds of monomers.

[Method for producing (meth) acrylic polymer]
In the present invention, in the method for producing a (meth) acrylic polymer by polymerizing a monomer component containing a (meth) acrylic acid alkyl ester, the polymerization system is methacrylic when the polymerization rate of the monomer component is 50 to 95%. A (meth) acrylic polymer is produced by a method of adding an acid alkyl ester.

In the present invention, it is preferable that the initial charged monomer component contains at least one selected from an acrylic acid alkyl ester and a methacrylic acid alkyl ester. The initial charged monomer component refers to a monomer component present in the reaction system at the start of polymerization of the monomer component forming the (meth) acrylic polymer.

The initial charged monomer component can further contain at least one selected from a crosslinkable group-containing monomer and other monomers, if necessary.
It is more preferable that the initial charged monomer component contains an acrylic acid alkyl ester and a methacrylic acid alkyl ester.

In the method for producing a (meth) acrylic polymer of the present invention, an alkyl methacrylate ester is added to the polymerization system when the polymerization rate of the monomer component is 50 to 95%. In the present invention, the methacrylic acid alkyl ester may be added to the polymerization system when the polymerization rate of the monomer component is 50 to 95%, and the monomer component is added to the polymerization system when the polymerization rate of the monomer component is less than 50%. It does not prevent you from doing so. Hereinafter, adding the monomer component to the polymerization system after the start of the polymerization of the initial charged monomer component and before the completion of the polymerization is also referred to as additional addition.

The monomer component to be additionally added may contain at least one selected from an acrylic acid alkyl ester, a crosslinkable group-containing monomer and other monomers, in addition to the methacrylic acid alkyl ester. Above all, it is preferable that the monomer component to be additionally added contains a crosslinkable group-containing monomer.

[Methacrylic acid alkyl ester]
The methacrylic acid alkyl ester is represented by, for example, the following formula (1).
CH ₂ = C (CH ₃ ) -COOR ¹ ... (1)
R ¹ is usually an alkyl group having 1 to 22 carbon atoms, preferably 4 to 20 carbon atoms, and more preferably 4 to 18 carbon atoms.

Examples of the methacrylic acid alkyl ester include methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate, and iso. Examples thereof include decyl methacrylate, lauryl methacrylate, isotridecyl methacrylate, tetradecyl methacrylate, hexadecyl methacrylate, stearyl methacrylate, isostearyl methacrylate and behenyl methacrylate.

The methacrylic acid alkyl ester may be used alone or in combination of two or more.
From the viewpoint of forming a pressure-sensitive adhesive layer having excellent durability, the methacrylic acid alkyl ester preferably has a homopolymer glass transition temperature (hereinafter, also referred to as “Tg”) of −45 ° C. or higher, more preferably 45 to 120 ° C. It is preferable to use the monomer component of. For the Tg, for example, the value described in Polymer Handbook Fourth edition (Wiley-Interscience 2003) can be used.

Examples of the methacrylic acid alkyl ester in which the Tg of the homopolymer is −45 ° C. or higher include methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, and hexyl methacrylate, 2 -Ethylhexyl methacrylate, octyl methacrylate, isodecyl methacrylate, isotridecyl methacrylate, hexadecyl methacrylate, stearyl methacrylate, isostearyl metallicate can be mentioned.

[Acrylic acid alkyl ester]
The acrylic acid alkyl ester is represented by, for example, the following formula (2).
CH ₂ = CH-COOR ² ... (2)
R ² is usually an alkyl group having 1 to 18 carbon atoms, preferably 4 to 18 carbon atoms, and more preferably 4 to 12 carbon atoms.

Examples of the acrylic acid alkyl ester include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, and isooctyl acrylate. Examples thereof include nonyl acrylate, decyl acrylate, isodecyl acrylate, lauryl acrylate, tetradecyl acrylate, hexadecyl acrylate, stearyl acrylate and isostearyl acrylate.

The acrylic acid alkyl ester may be used alone or in combination of two or more.
From the viewpoint of forming a pressure-sensitive adhesive layer having excellent step followability, the acrylic acid alkyl ester may use a monomer component having a homopolymer Tg of preferably less than −45 ° C., more preferably −80 to −50 ° C. preferable. For the Tg, for example, the value described in Polymer Handbook Fourth edition (Wiley-Interscience 2003) can be used.

Examples of the acrylic acid alkyl ester in which the Tg of the homopolymer is less than −45 ° C. include butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, isooctyl acrylate, and nonyl acrylate.

[Crosslinkable group-containing monomer]
The crosslinkable group-containing monomer is a monomer having at least one crosslinkable group. By using the crosslinkable group-containing monomer, it becomes possible to introduce a crosslink point to be crosslinked when forming the pressure-sensitive adhesive layer from the pressure-sensitive adhesive composition described later into the (meth) acrylic polymer. Examples of the crosslinkable group include a hydroxyl group and a carboxyl group.

Examples of the crosslinkable group-containing monomer include a hydroxyl group-containing monomer and a carboxyl group-containing monomer.
Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroshikibutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate and 8-hydroxyoctyl ( Examples thereof include hydroxyl group-containing (meth) acrylates such as meta) acrylates.

Examples of the carboxyl group-containing monomer include β-carboxyethyl (meth) acrylate, 5-carboxypentyl (meth) acrylate, mono (meth) acryloyloxyethyl ester of succinate, and ω-carboxypolycaprolactone mono (meth) acrylate. Carboxyl group-containing (meth) acrylates such as (meth) acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid and other ethylenically unsaturated carboxylic acids.
The crosslinkable group-containing monomer may be used alone or in combination of two or more.

[Other monomers]
The monomer component forming the (meth) acrylic polymer is, for example, alkoxyalkyl (meth) acrylate, alkoxypolyalkylene glycol mono (meth) acrylate, as long as the physical properties of the (meth) acrylic polymer are not impaired. Other monomers such as alicyclic groups or aromatic ring-containing (meth) acrylates, amino group-containing monomers, amide group-containing monomers, and acidic group-containing monomers other than carboxyl groups can be included.

Examples of the alkoxyalkyl (meth) acrylate include methoxymethyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxypropyl (meth) acrylate, and 3-ethoxypropyl (meth) acrylate. Examples thereof include meta) acrylate, 4-methoxybutyl (meth) acrylate, and 4-ethoxybutyl (meth) acrylate.

Examples of the alkoxypolyalkylene glycol mono (meth) acrylate include methoxydiethylene glycol mono (meth) acrylate, methoxydipropylene glycol mono (meth) acrylate, ethoxytriethylene glycol mono (meth) acrylate, and ethoxydiethylene glycol mono (meth) acrylate. Examples thereof include methoxytriethylene glycol mono (meth) acrylate.

Examples of the alicyclic group or aromatic ring-containing (meth) acrylate include cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, and phenoxyethyl (meth) acrylate. ..

Examples of the amino group-containing monomer include amino group-containing (meth) acrylates such as dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate.

Examples of the amide group-containing monomer include N-mono such as (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-propyl (meth) acrylamide, and N-hexyl (meth) acrylamide. Alkyl-substituted acrylamide; N, N-dialkyl-substituted acrylamides such as N, N-dimethylacrylamide, N, N-dimethylmethacrylicamide and the like can be mentioned.

Examples of the monomer containing an acidic group other than the carboxyl group include maleic anhydride, itaconic anhydride, a (meth) acrylic acid ester having a phosphate group in the side chain, and a (meth) acrylic acid ester having a sulfate group in the side chain. Can be mentioned.

Further, the monomer component forming the (meth) acrylic polymer is a copolymerizable monomer such as a styrene monomer or vinyl acetate as long as the physical properties of the (meth) acrylic polymer are not impaired. Can be included as other monomers.

Examples of the styrene-based monomer include styrene; alkyl styrene such as methyl styrene, dimethyl styrene, trimethyl styrene, propyl styrene, butyl styrene, hexyl styrene, heptyl styrene, and octyl styrene; fluorostyrene, chloro styrene, and bromo styrene. Halogenized styrene such as dibromostyrene and styrene iodide; nitrostyrene, acetylstyrene, methoxystyrene and the like.
The other monomers may be used alone or in combination of two or more.

[Polymerization initiator]
In the present invention, a polymerization initiator may be used if necessary.
Examples of the polymerization initiator include an azo-based initiator and a peroxide-based polymerization initiator.
Examples of the azo-based initiator include 2,2'-azobisisobutyronitrile, 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), and 2,2'-azobis (2-). Cyclopropylpropionitrile), 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (2-methylbutyronitrile), 1,1'-azobis (cyclohexane-1-carbo) Nitrile), 2- (carbamoylazo) isobutyronitrile, 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile, 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'- Azobis (N, N'-dimethyleneisobutyramidine), 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) -propionamide], 2,2'-azobis (isobutylamide) dihydrate, 4 , 4'-azobis (4-cyanopentanoic acid), 2,2'-azobis (2-cyanopropanol), dimethyl-2,2'-azobis (2-methylpropionate) and the like.

Examples of the peroxide-based polymerization initiator include t-butyl hydroperoxide, cumene hydrooxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, and di-i-propylperoxydicarbonate. , Di-2-ethylhexyl peroxydicarbonate, t-butyl peroxyvivarate, 2,2-bis (4,5-di-t-butylperoxycyclohexyl) propane, 2,2-bis (4,5-bis) Di-t-amylperoxycyclohexyl) propane, 2,2-bis (4,5-di-t-octylperoxycyclohexyl) propane, 2,2-bis (4,5-di-α-cumylperoxycyclohexyl) ) Propane, 2,2-bis (4,5-di-t-butylperoxycyclohexyl) butane, 2,2-bis (4,5-di-t-octylperoxycyclohexyl) butane.
The polymerization initiator may be used alone or in combination of two or more.

[Polymerization solvent]
In the present invention, a polymerization solvent may be used if necessary.
Examples of the polymerization solvent include aromatic hydrocarbons such as benzene, toluene and xylene; aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane and n-octane; cyclopentane, cyclohexane and cycloheptane. , Cyclooctane and other alicyclic hydrocarbons; diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, dibutyl ether, tetrahydrofuran, dioxane, anisole, phenylethyl ether, diphenyl ether and other ethers; chloroform, carbon tetrachloride, etc. Halogenized hydrocarbons such as 1,2-dichloroethane and chlorobenzene; esters such as ethyl acetate, propyl acetate, butyl acetate and methyl propionate; ketones such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone and cyclohexanone; N , N-Dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone and other amides; acetonitrile, benzonitrile and other nitriles; dimethylsulfoxide, sulfolane and other sulfoxides and the like.
The polymerization solvent may be used alone or in combination of two or more.

[Production conditions for (meth) acrylic polymer]
The (meth) acrylic polymer can be produced by, for example, a conventionally known polymerization method such as a solution polymerization method, a bulk polymerization method, an emulsion polymerization method, or a suspension polymerization method, and among these, the solution polymerization method is preferable. Specifically, a polymerization solvent, an initial charge monomer component, and a polymerization initiator are charged in the reaction vessel, and the reaction start temperature is usually set to 40 to 100 ° C., preferably 50 to 90 ° C., and usually The reaction system is maintained at a temperature of 50-90 ° C, preferably 60-90 ° C. The reaction is usually carried out for 0.5 to 20 hours until the polymerization rate (mass%) of the monomer component becomes 50 to 95%, preferably 55 to 95%, more preferably 60 to 90%. The polymerization reaction can be carried out in an atmosphere of an inert gas such as nitrogen gas, for example.

The polymerization rate can be measured by, for example, the following method.
During the polymerization, the reaction solution in the polymerization system is taken out and the heating residue is measured. The heating residue can be measured according to JIS K 5407: 1997. The polymerization rate is calculated from the following formula using the measured heating residue.
-Polymerization rate (%) = 100 x [X / Y]
X: Actually measured heating residue (mass)
Y: Ideal heating residue (mass) when all the monomer components contained in the reaction system are polymerized.

When the monomer component is additionally added before the polymerization rate measurement, the polymerization rate calculated by the above method is the polymerization rate of all the monomer components which is the total of the initial charged monomer and the monomer component additionally added before the polymerization rate measurement.

When the polymerization rate of the monomer component is 50 to 95%, an alkyl methacrylate ester and, if necessary, at least one monomer component selected from an acrylic acid alkyl ester, a crosslinkable group-containing monomer and other monomers are added. Added. Specifically, the additional addition may be started when the polymerization rate of the monomer component is 50 to 95%, and even if the polymerization rate of the monomer component becomes other than 50 to 95% during the additional addition, it is particularly limited. Not done. At this time, the monomer component to be additionally added may be dissolved in a polymerization solvent or the like and added, if necessary. The polymerization solvent may be the same as or different from the polymerization solvent used when carrying out the polymerization reaction of the initial charged monomer.

The additional addition of the monomer component may be performed once or twice or more. The method of addition is not particularly limited, but it is preferable to add by continuously dropping. When the monomer component is added dropwise, it is usually added dropwise over 0.5 to 4 hours, preferably 1 to 2 hours.

An additional polymerization initiator may be added. The additional addition of the polymerization initiator may be performed at the same time as the additional addition of the monomer component, or may be performed at a different timing. At this time, if necessary, the polymerization initiator may be dissolved in a polymerization solvent or the like and added. The polymerization solvent may be the same as or different from the polymerization solvent used when carrying out the polymerization reaction of the initial charged monomer and the polymerization solvent for dissolving the monomer component to be additionally added. The additional addition of the polymerization initiator may be performed once, twice or more, or may be added dropwise.

Further, a chain transfer agent and a polymerization solvent may be additionally added as appropriate during the polymerization reaction.
The reaction is usually carried out for 1 to 6 hours, preferably 2 to 5 hours from the start of additional addition of the monomer component.
In 100% by mass of all the monomer components used for forming the (meth) acrylic polymer, the methacrylic acid alkyl ester is usually 10 to 69.9% by mass, preferably 15 to 64.9% by mass, more preferably. It contains 20 to 59.8% by mass. Here, the total monomer component means the total of the initial charged monomer and all the monomer components to be additionally added.

Acrylic acid alkyl ester is usually contained in an amount of 30 to 89.9% by mass, preferably 35 to 84.9% by mass, and more preferably 40 to 79.8% by mass in 100% by mass of the total monomer components.

In 100% by mass of the total monomer components, the crosslinkable group-containing monomer is usually contained in an amount of 0.05 to 20% by mass, preferably 0.1 to 15% by mass, and more preferably 0.2 to 12% by mass.
In particular, among all the monomer components used to form the (meth) acrylic polymer, an acrylic acid alkyl ester having a homopolymer Tg of less than −45 ° C. and an alkyl methacrylate having a homopolymer Tg of −45 ° C. or higher are included. It is preferable that the ester and the crosslinkable group-containing monomer are contained.

Polymerization of the monomer component is preferably 30% by mass or more, more preferably 40 to 90% by mass, still more preferably 50 to 80% by mass of the methacrylic acid alkyl ester contained in all the monomer components. It is preferable to add it to the polymerization system when the ratio is 50 to 95%. By adding the methacrylic acid alkyl ester in an amount within the above range, the methacrylic acid alkyl ester can be reacted from the early stage to the late stage of polymerization, and the variation in the amount of structural unit derived from the methacrylic acid alkyl ester is small (meth) acrylic type. A polymer can be obtained. As a result, by blending the (meth) acrylic polymer with the pressure-sensitive adhesive composition, a pressure-sensitive adhesive layer having excellent step followability and durability can be formed.

The monomer component to be additionally added preferably contains a crosslinkable group-containing monomer in addition to the methacrylic acid alkyl ester. Of 100% by mass of the crosslinkable group-containing monomer contained in all the monomer components, preferably 30% by mass or more, more preferably 40 to 90% by mass, still more preferably 50 to 80% by mass of the crosslinkable group-containing monomer as the monomer component. It is preferable to add it to the polymerization system when the polymerization rate is 50 to 95%. By additionally adding a crosslinkable group-containing monomer, crosslink points can be uniformly present in the (meth) acrylic polymer, and the (meth) acrylic polymer can be blended into the pressure-sensitive adhesive composition. It is possible to form an adhesive layer having excellent durability.

The polymerization initiator is usually used in an amount in the range of 0.001 to 5 parts by mass, preferably 0.005 to 3 parts by mass with respect to 100 parts by mass of all the monomer components.
The reason why the pressure-sensitive adhesive layer having excellent step followability and durability can be formed by blending the (meth) acrylic polymer obtained by the production method of the present invention into the pressure-sensitive adhesive composition is as follows. I guess there is.

The methacrylic acid alkyl ester tends to proceed with the polymerization reaction relatively faster than other monomers other than the methacrylic acid alkyl ester from the viewpoint of polymerizability. Therefore, for example, when a monomer component containing an acrylic acid alkyl ester and a methacrylic acid alkyl ester is polymerized by a usual method, many methacrylic acid alkyl esters react in the initial stage of the polymerization reaction, and react in the latter stage of the polymerization reaction. Less methacrylic acid alkyl ester. The result is a (meth) acrylic polymer with varying amounts of structural units derived from methacrylic acid alkyl esters. The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition using the (meth) acrylic polymer having a variation in the amount of structural units is inferior in durability.

On the other hand, in the production method of the present invention, since the methacrylic acid alkyl ester is additionally added, the methacrylic acid alkyl ester can be reacted even in the latter stage of the polymerization reaction, and the amount of the structural unit derived from the methacrylic acid alkyl ester varies. It is considered that a (meth) acrylic polymer having a small amount of acrylic acid can be obtained. The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition using the (meth) acrylic polymer having little variation in the amount of structural units is excellent in durability and step-following property.

Further, in the present invention, the reason for using the methacrylic acid alkyl ester as the monomer component to be additionally added is that the methacrylic acid alkyl ester has an α-methyl group, and therefore the (meth) acrylic weight produced by using the methacrylic acid alkyl ester. This is because the coalescence is considered to have high rigidity. Therefore, the pressure-sensitive adhesive composition containing the (meth) acrylic polymer can form a pressure-sensitive adhesive layer having excellent durability.

Absolute difference between the amount of methacrylic acid ester used in all monomer components and the amount of structural unit derived from methacrylic acid ester of the polymer contained in the sol content in the pressure-sensitive adhesive layer obtained from the (meth) acrylic polymer. The value is preferably 0 to 10% by mass, more preferably 0 to 8% by mass.

The amount of structural unit derived from the methacrylic acid ester of the polymer contained in the sol content can be measured by, for example, the following method.
An appropriate amount of a cross-linking agent or the like is mixed with the polymer solution of the (meth) acrylic polymer to prepare a pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition is applied to a support and dried to form a pressure-sensitive adhesive layer. A part of the obtained pressure-sensitive adhesive layer is collected, ethyl acetate is added, and the mixture is shaken and then filtered through a wire mesh. The filtrate is concentrated and dried on a PET film, measured by an infrared spectroscopic spectrum, and the amount of structural unit derived from the methacrylic acid ester of the polymer contained in the sol content is calculated.

When the absolute value of the difference is within the above range, it can be said that the methacrylic acid ester reacted in a well-balanced manner not only in the early stage of the polymerization reaction but also in the late stage during the production of the (meth) acrylic polymer. Therefore, it is considered that a (meth) acrylic polymer having a small variation in the amount of structural units in the polymer was obtained, and the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition containing the (meth) acrylic polymer is Excellent step followability and durability.

[Adhesive composition]
The pressure-sensitive adhesive composition contains the (meth) acrylic polymer and a cross-linking agent. The pressure-sensitive adhesive composition may further contain additives, if necessary. Moreover, it is preferable that the pressure-sensitive adhesive composition contains an organic solvent.

[Crosslinking agent]
The pressure-sensitive adhesive composition preferably contains a cross-linking agent. The cross-linking agent is appropriately selected depending on the cross-linking group that can be introduced into the (meth) acrylic polymer, and for example, an isocyanate compound, an epoxy compound, and a metal chelate compound can be used.

By cross-linking the (meth) acrylic polymer with a cross-linking agent, a cross-linked product (network polymer) can be formed, and a pressure-sensitive adhesive layer having excellent heat resistance can be obtained.
The cross-linking agent may be used alone or in combination of two or more.
The content of the cross-linking agent is appropriately selected according to the (meth) acrylic polymer, and is preferably 0.01 to 7 parts by mass with respect to 100 parts by mass of the (meth) acrylic polymer. More preferably, it is 0.01 to 5 parts by mass.

As the isocyanate compound, an isocyanate compound having 2 or more isocyanate groups in one molecule is usually used, preferably 2 to 8, and more preferably 3 to 6. When the number of isocyanate groups is within the above range, it is preferable in terms of the cross-linking reaction efficiency between the (meth) acrylic polymer and the isocyanate compound and in terms of maintaining the flexibility of the pressure-sensitive adhesive layer.

Examples of the diisocyanate compound having 2 isocyanate groups in one molecule include aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates.
Aliphatic diisocyanates include ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and 2,2,4-trimethyl. Examples thereof include aliphatic diisocyanates having 4 to 30 carbon atoms such as -1,6-hexamethylene diisocyanate.

As the alicyclic diisocyanate, an alicyclic having 7 to 30 carbon atoms such as isophorone diisocyanate, cyclopentyl diisocyanate, cyclohexyl diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and hydrogenated tetramethylxylylene diisocyanate. Group diisocyanates can be mentioned.

Examples of the aromatic diisocyanate include aromatic diisocyanates having 8 to 30 carbon atoms such as phenylenediocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthylene diisocyanate, diphenyl ether diisocyanate, diphenylmethane diisocyanate, and diphenyl propane diisocyanate.

Examples of the isocyanate compound having 3 or more isocyanate groups in one molecule include aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates. Specific examples thereof include 2,4,6-triisocyanate toluene, 1,3,5-triisocyanatebenzene, and 4,4', 4 "-triphenylmethane triisocyanate.

Examples of the isocyanate compound include multimers (for example, dimer or trimer, biuret, isocyanurate) and derivatives (for example, polyhydric alcohol) of the above isocyanate compound having 2 or 3 or more isocyanate groups. Addition reaction products with two or more molecules of diisocyanate compounds) and polymers. Examples of the polyhydric alcohol in the derivative include trihydric or higher valent alcohols such as trimethylolpropane, glycerin, and pentaerythritol as low molecular weight polyhydric alcohols; and examples of high molecular weight polyhydric alcohols include polyether polyols. Examples thereof include polyester polyols, acrylic polyols, polybutadiene polyols, and polyisoprene polyols.

Examples of such isocyanate compounds include trimer of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, hexamethylene diisocyanate or biuret or isocyanurate of tolylene diisocyanate, trimethyl propane and tolylene diisocyanate or xylylene diisocyanate. Reaction products with (for example, three-molecule adduct of tolylene diisocyanate or xylylene diisocyanate), reaction products of trimethylolpropane and hexamethylene diisocyanate (for example, three-molecule adduct of hexamethylene diisocyanate), polyether polyisocyanate, Examples include polyester polyisocyanate.

Among the isocyanate compounds, a tolylene diisocyanate-based cross-linking agent (L-45 manufactured by Soken Chemical Co., Ltd., etc.) is preferable from the viewpoint of pot life.
Examples of the epoxy compound include compounds having two or more epoxy groups in the molecule, for example, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexane. Didiol diglycidyl ether, trimethylpropan triglycidyl ether, diglycidyl aniline, diamine glycidyl amine, N, N, N', N'-tetraglycidyl-m-xylylene diamine, 1,3-bis (N, N'- Diamine glycidyl aminomethyl). Examples of commercially available products include E-5CM manufactured by Soken Chemical Co., Ltd. and E-5XM manufactured by Soken Chemical Co., Ltd.

As the metal chelate compound, for example, alkoxide, acetylacetone, ethyl acetoacetate and the like are coordinated with polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium and zirconium. Examples include compounds. Specific examples thereof include aluminum isopropylate, aluminum secondary butyrate, aluminum ethyl acetoacetate / diisopropirate, aluminum tris ethyl acetoacetate, and aluminum tris acetyl acetonate.

[Additive]
Additives may be added to the pressure-sensitive adhesive composition if necessary. As the additive, for example, one or 2 selected from a silane coupling agent, an antistatic agent, an antioxidant, a light stabilizer, a metal corrosion inhibitor, a tackifier, a plasticizer, a cross-linking accelerator and a reworking agent. It may contain more than a seed.

[Organic solvent]
The pressure-sensitive adhesive composition preferably contains an organic solvent in order to adjust its coatability. Examples of the organic solvent include the polymerization solvent described in the [Polymerization solvent] column. In the pressure-sensitive adhesive composition, the content of the organic solvent is usually 30 to 90% by mass, preferably 40 to 90% by mass.
In addition, in this specification, "solid content" means all components except an organic solvent in a pressure-sensitive adhesive composition.

<Preparation of adhesive composition>
The pressure-sensitive adhesive composition can be prepared by mixing the (meth) acrylic polymer, a cross-linking agent, and if necessary, an additive by a conventionally known method. As a method for adjusting the pressure-sensitive adhesive composition, for example, a cross-linking agent and, if necessary, a cross-linking agent are added to a polymer solution containing the (meth) acrylic polymer obtained when the (meth) acrylic polymer is synthesized. Blending with an additive can be mentioned.

<Conditions for forming the adhesive layer, etc.>
The pressure-sensitive adhesive layer is formed from the pressure-sensitive adhesive composition described above. For example, the pressure-sensitive adhesive layer can be obtained by advancing the cross-linking reaction in the above-mentioned pressure-sensitive adhesive composition, specifically, by cross-linking the (meth) acrylic polymer with a cross-linking agent.
The conditions for forming the pressure-sensitive adhesive layer are as follows, for example. The pressure-sensitive adhesive composition is applied onto the support and dried at 50 to 150 ° C., preferably 60 to 100 ° C., usually 1 to 5 minutes, preferably 3 to 5 minutes, depending on the type of solvent. The solvent is removed to form a coating film.

As a method for applying the pressure-sensitive adhesive composition, a predetermined thickness is obtained by a known method, for example, a spin coating method, a knife coating method, a roll coating method, a bar coating method, a blade coating method, a die coating method, or a gravure coating method. As described above, a method of applying and drying can be used.

Examples of the support include a polyester film such as polyethylene terephthalate (PET); and a plastic film such as a polyolefin film such as polyethylene, polypropylene, and an ethylene-vinyl acetate copolymer.

The film thickness of the dry coating film is usually 10 to 300 μm, preferably 20 to 200 μm. The film thickness can be measured with a dial thickness gauge.
Then, the coating film is cured in an environment of usually 3 days or more, preferably 7 to 10 days, usually 5 to 60 ° C., preferably 15 to 40 ° C., usually 20 to 80% RH, preferably 30 to 70% RH. To do. When cross-linking is performed under the above-mentioned aging conditions, a cross-linked product (network polymer) can be efficiently formed.

The gel fraction of the pressure-sensitive adhesive layer is preferably 20 to 98% by mass, more preferably 30 to 98% by mass, and further preferably 35 to 95% by mass from the viewpoint of cohesive force, adhesive force, and removability. ..
The pressure-sensitive adhesive layer of the present invention can be suitably used as a pressure-sensitive adhesive particularly for a touch panel.

Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to these Examples. In the description of the following examples and the like, "parts" means "parts by mass" unless otherwise specified.

[Polymerization rate]
The synthesis reaction of the (meth) acrylic polymer was carried out under the same conditions as in the following Examples and Comparative Examples, and the reaction solution was taken out from the reaction apparatus according to the reaction time, and the polymerization rate was calculated.
About 1 g of a reaction solution containing a monomer component was put into a finely weighed tin petri dish, the total weight was finely weighed, and then the mixture was heated at 105 ° C. for 5 hours to measure the heating residue. The heating residue was measured according to JIS K 5407: 1997. The polymerization rate was calculated from the following formula.
-Polymerization rate (%) = 100 x [X / Y]
X: Actually measured heating residue (mass)
Y: Ideal heating residue (mass) when all the monomer components contained in the reaction system are polymerized.

[GPC]
The weight average molecular weight (Mw) of the (meth) acrylic polymer was determined by the gel permeation chromatography method (GPC method) under the following conditions.
-Measuring device: HLC-8320GPC (manufactured by Tosoh Corporation)
-GPC column configuration: The following 4-column column (all manufactured by Tosoh Corporation)
(1) TSKgel HxL-H (guard column)
(2) TSKgel GMHxL
(3) TSKgel GMHxL
(4) TSKgel G2500HxL
・ Flow velocity: 1.0 mL / min
-Column temperature: 40 ° C
-Sample concentration: 1.5% (w / v) (diluted with tetrahydrofuran)
・ Mobile phase solvent: Tetrahydrofuran ・ Standard polystyrene conversion

[Example 1]
(1) Preparation of Polymer Solution of (Meta) Acrylic Polymer In a reaction device equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen introduction tube, 13 parts of isodecyl methacrylate, 55 parts of 2-ethylhexyl acrylate, 2- 1.0 part of hydroxyethyl acrylate, 2.0 parts of dimethylacrylamide and 50 parts of ethyl acetate were charged, and the temperature was raised to 80 ° C. while introducing nitrogen gas. Then, 0.3 part of 2,2'-azobisisobutyronitrile was added, and the reaction was started at 80 ° C. under a nitrogen gas atmosphere. One hour after the start of the reaction at a polymerization rate of 80%, a solution prepared by dissolving 26 parts of isodecyl methacrylate and 3 parts of 2-hydroxyethyl acrylate in 10 parts of ethyl acetate and 2,2'-azobisisobutyronitrile A solution prepared by dissolving 0.5 part in 10 parts of ethyl acetate was added dropwise over 1 hour, and then the polymerization reaction was carried out for 4 hours for a total of 6 hours from the start of the reaction. After completion of the reaction, the mixture was diluted with ethyl acetate to prepare a polymer solution having a solid content concentration of 50% by mass. The Mw of the obtained (meth) acrylic polymer was 360,000.

(2) Preparation of Adhesive Composition L-45 (Soken Kagaku (Soken Kagaku)) as an isocyanate-based cross-linking agent with respect to 100 parts of the solid content contained in the polymer solution (solid content concentration 50% by mass) obtained in the above (1). Manufactured by Co., Ltd .: Tolylene diisocyanate-based cross-linking agent, solid content concentration 45% by mass) 0.1 part (solid content amount) was mixed to obtain a pressure-sensitive adhesive composition.

(3) Preparation of Adhesive Sheet After defoaming the adhesive composition obtained in (2) above on the peeled PET film, it is applied at a liquid temperature of 25 ° C. using a doctor blade, and 4 at 90 ° C. The film was dried for a minute to remove the solvent to form a coating film. The peeled PET film is further attached to the surface of the coating film opposite to the surface on which the PET film is attached, and is aged in an environment of 23 ° C./50% RH for 7 days to have an adhesive layer having a film thickness of 50 μm. An adhesive sheet was obtained.

[Examples 2 to 4, Comparative Examples 3 and 5]
The same procedure as in Example 1 was carried out except that the monomer components used in the polymerization reaction were changed as shown in Table 1, to prepare a polymer solution having a solid content concentration of 50% by mass. Further, the same procedure as in Example 1 was carried out to prepare a pressure-sensitive adhesive composition and prepare a pressure-sensitive adhesive sheet.

[Comparative Example 1]
Preparation of Polymer Solution of (1') (Meta) Acrylic Polymer 39 parts of isodecyl methacrylate, 55 parts of 2-ethylhexyl acrylate, 2 in a reactor equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen introduction tube. -Hydroxyethyl methacrylate (4.0 parts), dimethylacrylamide (2.0 parts) and ethyl acetate (50 parts) were charged, and the temperature was raised to 80 ° C. while introducing nitrogen gas. Next, 0.5 part of 2,2'-azobisisobutyronitrile was added, and a polymerization reaction was carried out at 80 ° C. for 6 hours in a nitrogen gas atmosphere. After completion of the reaction, the mixture was diluted with ethyl acetate to prepare a polymer solution having a solid content concentration of 50% by mass. The Mw of the obtained (meth) acrylic polymer was 360,000.

In the same manner as in Example 1 except that the polymer solution prepared in (1') was used, (2') the pressure-sensitive adhesive composition and (3') the pressure-sensitive adhesive sheet were prepared, and the film thickness was 50 μm. An adhesive sheet having an adhesive layer was obtained.

[Comparative Examples 2 and 4]
A polymer solution having a solid content concentration of 50% by mass was prepared in the same manner as in Comparative Example 1 except that the monomer components used in the polymerization reaction were changed as shown in Table 1. Further, the same procedure as in Comparative Example 1 was carried out to prepare an adhesive composition and prepare an adhesive sheet.

[Evaluation]
<Gel fraction>
From the pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples, about 0.1 g of a pressure-sensitive adhesive layer was collected in a sampling bottle, 30 mL of ethyl acetate was added, and the mixture was shaken for 4 hours. It was filtered through a wire mesh, and the residue on the wire mesh was dried at 100 ° C. for 2 hours, and the dry weight was measured. The gel fraction of the pressure-sensitive adhesive layer was determined by the following formula. The results are shown in Table 1.
-Gel fraction (%) = (dry weight / adhesive collection weight) x 100 (%)

<Amount of structural unit derived from methacrylic acid alkyl ester of polymer contained in sol content>
The filtrate obtained by measuring the <gel fraction> was concentrated and dried on a PET film at 80 ° C. for 6 hours to form a coating film. Then, the non-contact surface of the coating film having a sufficient thickness with respect to the PET film was measured by an infrared spectroscopic spectrum (FT-IR Nexus 470: manufactured by Thermo Fisher Scientific Co., Ltd.) and derived from an alkyl methacrylate ester. The peak absorbance was calculated. A calibration curve was prepared to calculate the structural unit amount derived from the methacrylic acid alkyl ester from the absorbance of the peak derived from the methacrylic acid alkyl ester, using several samples for which the structural unit amount derived from the methacrylic acid alkyl ester was known. Using the calibration curve, the amount of structural unit derived from the methacrylic acid alkyl ester of the polymer contained in the sol was calculated. The results are shown in Table 1.

<Durability test>
The peeled PET film on one side of the pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples was peeled off, and the exposed pressure-sensitive adhesive layer surface was attached to a PET film having a thickness of 100 μm and cut into a size of 50 mm × 50 mm. Next, the other peeled PET film was peeled off, and the exposed pressure-sensitive adhesive layer surface was attached to a non-alkali glass plate having a thickness of 2 mm. The obtained laminate was held in an autoclave adjusted to 50 ° C./5 atm for 20 minutes to prepare a test plate. The test plate was left for 24 hours under the conditions of 85 ° C./85% RH. Appearance defects such as foaming from the pressure-sensitive adhesive layer of the test plate, cracks in the test plate, and peeling of the pressure-sensitive adhesive layer were visually observed and evaluated according to the following criteria.
AA: No appearance defects are observed BB: Slight appearance defects are observed CC: Appearance defects are clearly observed

<Whitening test>
A test plate was prepared in the same manner as described in the above <Durability test>. The test plate was left for 24 hours under the conditions of 85 ° C./85% RH. After allowing to stand at room temperature for another 1 hour, the haze was measured and the haze value (%) after the durability test was calculated. MH-150 (manufactured by Murakami Color Technology Research Institute Co., Ltd.) was used for haze measurement.

<Step followability>
The peeled PET film on one side of the pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples was peeled off, the exposed pressure-sensitive adhesive layer surface was attached to a PET film having a thickness of 100 μm, and the pressure-sensitive adhesive sheet was cut into a size of 50 mm × 50 mm. A test piece was prepared. Next, a PET film having a thickness of 25 μm cut into a size of 15 mm × 15 mm was placed on a glass plate to create a step for evaluation. The other peeled PET film of the test piece is peeled off, and the test piece (50 mm × 50 mm) is covered with the adhesive layer over the entire surface of the PET film (15 mm × 15 mm) on the glass plate of the evaluation step. Was attached and held in an autoclave adjusted to 50 ° C./5 atm for 20 minutes, and then left at room temperature for 1 hour, and the appearance of the stepped portion was visually observed and evaluated according to the following criteria.
AA: No voids or bubbles are observed around the steps BB: Slight voids or bubbles are observed around the steps CC: Voids or bubbles are clearly observed around the steps

In Examples 1 to 4 in which the production method of the present invention was adopted, an adhesive sheet having an adhesive layer having excellent durability and step followability was obtained. The (meth) acrylic polymer produced in Comparative Example 1 or Comparative Example 2 is produced from a monomer component having the same composition as the (meth) acrylic polymer produced in Example 1 or Example 3, respectively. Since no additional monomer component is added, the durability of the obtained pressure-sensitive adhesive layer is inferior. Further, since the (meth) acrylic polymers produced in Comparative Examples 3 and 4 do not contain the methacrylic acid alkyl ester as a monomer component, the durability of the obtained pressure-sensitive adhesive sheet is inferior. Further, in the (meth) acrylic polymer produced in Comparative Example 5, the durability of the obtained pressure-sensitive adhesive sheet is inferior because the methacrylic monomer is not contained in the monomer component to be additionally added.

Claims (3)

In a method for producing a (meth) acrylic polymer by polymerizing a (meth) acrylic acid alkyl ester (excluding a crosslinkable group-containing monomer) and a monomer component containing a crosslinkable group-containing monomer.
The crosslinkable group-containing monomer is a hydroxyl group-containing monomer , and the crosslinkable group-containing monomer is a hydroxyl group-containing monomer.
Initially charged monomer component in the acrylic acid alkyl ester, include methacrylic acid alkyl esters and the crosslinkable group-containing monomer,
At the time of the polymerization rate is 50% to 95% monomer component polymerization system methacrylic acid alkyl ester and the crosslinkable group-containing monomer was continuously added dropwise to, and forming the (meth) acrylic polymer All monomers methacrylic acid alkyl ester in 100% by mass contained in the component used to, by adding 40 to 90 wt% methacrylic acid alkyl ester to the polymerization system,
20 to 59.8% by mass of methacrylic acid alkyl ester and 40 to 79.8% by mass of acrylic acid alkyl ester are contained in 100% by mass of all the monomer components used for forming the (meth) acrylic polymer. The crosslinkable group-containing monomer is contained in an amount of 0.2 to 12% by mass.
A method for producing a (meth) acrylic polymer. The (meth) on the total monomer in Ingredient used to form the acrylic polymer, the glass transition temperature is lower than -45 ° C. acrylic acid alkyl ester le homopolymer, a homopolymer glass transition temperature of -45 ° C. and more methacrylic acid alkyl ester le, the include and crosslinkable group-containing monomer over method of (meth) acrylic polymer of claim 1. A pressure-sensitive adhesive layer is formed from a step of producing a (meth) acrylic polymer by the production method according to claim 1 or 2 and a pressure-sensitive adhesive composition containing the (meth) acrylic polymer and a cross-linking agent. A method for producing an adhesive layer, which comprises a step of making an adhesive layer.