JP2017210610A - Solventless type acrylic resin composition, solventless type acrylic adhesive using the same, and adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solventless type acrylic resin composition capable of obtaining an adhesive which shows little change in a molecular weight by heating, is excellent in thermal stability, enables thick coating when used as an adhesive, and is excellent in impact absorption property and step followability.SOLUTION: The solventless type acrylic resin composition contains an acrylic resin (A) and an antioxidizing agent (B), where the acrylic resin (A) is obtained by polymerization of a polymerization component containing 3-50 wt.% of a hydroxyl group-containing monomer (a1), a glass transition temperature of the acrylic resin (A) is -100 to 50°C, a content of the antioxidizing agent (B) is 0.2-10 pts.wt. with respect to 100 pts.wt. of the acrylic resin (A), and a change ratio M (%) of a weight average molecular weight represented by formula 1 is 20 or less. [Formula 1] M(%)=(|M2-M1|/M1)×100, where M2 represents a weight average molecular weight of the solventless type acrylic resin composition after a heating treatment at 120°C for 4 days, and M1 represents a weight average molecular weight of the solventless type acrylic resin composition before the heating treatment.SELECTED DRAWING: None

Description

  The present invention relates to a solventless acrylic resin composition, and a pressure-sensitive adhesive and pressure-sensitive adhesive sheet using the solventless acrylic resin composition. Specifically, the molecular weight change due to heating is small, and heat stability is achieved. The present invention relates to a solventless acrylic resin composition having excellent properties.

In mobile devices such as TVs, monitors for personal computers, notebook computers, mobile phones, and tablet devices, a protective layer made of a plastic sheet or the like is usually provided on the viewing side of the liquid crystal display. In order to prevent the damage, 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, in recent years, an impact-absorbing pressure-sensitive adhesive layer is used in place of an air layer for the purpose of improving visibility and further reducing the thickness of a mobile device (plastic sheet) while ensuring impact resistance. .

  In order for the pressure-sensitive adhesive layer to exhibit sufficient shock absorption performance, it needs to have a certain thickness, but a solvent-based acrylic pressure-sensitive adhesive that has been generally used in the past is used for thick coating applications. In the case where the pressure-sensitive adhesive layer is thick at the time of coating, dripping of the coating occurs or the solvent does not easily evaporate in the drying process after coating, and the adhesive layer remains as foam. was there.

On the other hand, the use of a solventless pressure-sensitive adhesive has been proposed, and a hot-melt pressure-sensitive adhesive and an active energy ray-curable pressure-sensitive adhesive have been proposed (for example, Patent Document 1).
Among solventless adhesives, hot-melt adhesives do not require a drying process to volatilize the solvent after coating, and even when thick coating is applied, the adhesive layer can be efficiently formed in a short time. It can be obtained. In addition, it is often used without blending an active energy ray-curable monomer, and in that case, a curing step by irradiation with active energy rays is not essential, so a thick adhesive layer can be obtained more efficiently. It is something that can be done.

JP, 2014-214280, A

  However, hot-melt pressure-sensitive adhesives are not fluid at normal temperatures and usually need to be heated to about 100 to 150 ° C. for coating, and hot-melt pressure-sensitive adhesives using solvent-free acrylic resins are hot. When subjected to conditions, the molecular weight of the acrylic resin increases due to the residual monomers and residual catalysts during production contained in the acrylic resin, and depending on the acrylic resin of a specific composition, There has been a problem that the adhesiveness is lowered or a pressure-sensitive adhesive satisfying desired physical properties cannot be obtained.

  Therefore, in the present invention, under such a background, there is little change in molecular weight due to heating, excellent thermal stability, thick coating can be applied when used as an adhesive, impact absorption, step followability, An object is to provide a solventless acrylic resin composition capable of obtaining a pressure-sensitive adhesive having excellent heat and humidity resistance.

  However, as a result of intensive studies in view of such circumstances, the present inventors have polymerized a polymerization component containing a specific amount of a hydroxyl group-containing monomer more than usual in the solventless acrylic resin composition, and By adding a specific amount of antioxidant to a solvent-free acrylic resin with a specific glass transition temperature, it is possible to suppress an increase in molecular weight due to heating, and thick coating can be applied when used as an adhesive. It has been found that an adhesive having excellent absorbability and step following ability can be obtained, and further an acrylic resin composition having excellent moisture and heat resistance can be obtained.

That is, the present invention
Contains acrylic resin (A) and antioxidant (B),
The acrylic resin (A) is obtained by polymerizing a polymerization component containing 3 to 50% by weight of the hydroxyl group-containing monomer (a1),
The glass transition temperature of the acrylic resin (A) is −100 to 50 ° C.,
The content of the antioxidant (B) is 0.2 to 10 parts by weight with respect to 100 parts by weight of the acrylic resin (A),
The present invention relates to a solventless acrylic resin composition having a weight average molecular weight change rate M (%) represented by the following formula 1 of 20 or less.

[Formula 1]
M (%) = (| M2-M1 | / M1) × 100
M2: Weight average molecular weight of solventless acrylic resin composition after heat treatment at 120 ° C. for 4 days M1: Weight average molecular weight of solventless acrylic resin composition before heat treatment

  Furthermore, the present invention relates to a solventless acrylic pressure-sensitive adhesive containing the solventless acrylic resin composition, and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the solventless acrylic resin composition. .

  The solventless acrylic resin composition of the present invention has a small increase in molecular weight due to heating, is excellent in thermal stability, and can be applied by thick coating, and is a pressure-sensitive adhesive comprising the solventless acrylic resin composition. Is excellent in shock absorption and step following property, and also in heat and moisture resistance, and is therefore particularly useful as an adhesive used in touch panels, image display devices, 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 solventless acrylic resin composition of the present invention contains an acrylic resin (A) and an antioxidant (B).

<Acrylic resin (A)>
First, the acrylic resin (A) that the solventless acrylic resin composition of the present invention contains as an essential component will be described.

  The acrylic resin (A) used in the present invention is obtained by polymerizing a polymerization component containing 3 to 50% by weight of the hydroxyl group-containing monomer (a1), preferably further having 5 carbon atoms having a branched structure. At least one copolymerizable monomer (a2) selected from (meth) acrylic acid alkyl ester monomers and vinyl ester monomers having an alkyl group of -14, (meth) acrylic acid alkyl ester monomers (a3) (provided that , (A1) and (a2) are excluded.), Functional group-containing monomer (a4) (however, excluding (a1)), and other copolymerizable monomer (a5) may be contained as a polymerization component. is there.

  Examples of the hydroxyl group-containing monomer (a1) include 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8- Hydroxy (meth) acrylates such as hydroxyoctyl (meth) acrylate, caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth) acrylate, oxyalkylene-modified monomers such as diethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, etc. Primary hydroxyl group-containing monomers such as 2-acryloyloxyethyl-2-hydroxyethylphthalic acid; 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) ) Acrylate, secondary hydroxyl group-containing monomers such as 3-chloro-2-hydroxypropyl (meth) acrylate; may be mentioned 2,2-dimethyl-2-hydroxyethyl (meth) tertiary hydroxyl group-containing monomers such as acrylates.

  Among the hydroxyl group-containing monomers (a1), it is particularly preferable to use 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, or 2-hydroxypropyl acrylate from the viewpoint of excellent balance between heat and moisture resistance and heat resistance.

  In addition, as a hydroxyl-containing monomer used by this invention, it is preferable to use the thing with the content rate of di (meth) acrylate which is an impurity 0.5% or less, Especially 0.2% or less, Furthermore, 0 It is preferable to use a material of 1% or less.

In the present invention, the content of the hydroxyl group-containing monomer (a1) needs to be 3 to 50% by weight, preferably 5 to 45% by weight, more preferably 8 to 40% by weight, based on the entire polymerization component. Particularly preferably, it is 10 to 35% by weight, particularly preferably 11 to 30% by weight.
When the content is too small, the heat and moisture resistance when used as a pressure-sensitive adhesive is lowered, and when it is too large, the acrylic resin tends to undergo a self-crosslinking reaction, and the heat resistance tends to be lowered.

  In the present invention, it is preferable that the polymerization component further contains a copolymerizable monomer having a structure in which hydrogen abstraction is likely to occur at a high temperature, and as a result, a crosslink is easily formed. It is preferable to contain at least one copolymerizable monomer (a2) selected from (meth) acrylic acid alkyl ester monomers having a C 5-14 alkyl group and vinyl ester monomers, and more specifically. , 2-ethylhexyl (meth) acrylate, vinyl acetate and the like.

In the present invention, the content of the copolymerizable monomer (a2) is preferably 15 to 85% by weight, more preferably 20 to 80% by weight, particularly 30 to 75% by weight, based on the entire polymerization component. In particular, it is preferably 40 to 70% by weight, more preferably 45 to 65% by weight.
If the content is too small, the (meth) acrylic acid alkyl ester monomer having a C 5-14 alkyl group having a branched structure tends to decrease the step following ability when used as an adhesive, With vinyl ester monomers, the durability when formed into a sheet tends to decrease due to a decrease in cohesive strength. On the other hand, when the amount of the copolymerizable monomer (a2) is too large, the acrylic resin tends to undergo a self-crosslinking reaction, and the heat resistance tends to decrease.

  In the present invention, it is preferable to further contain a (meth) acrylic acid alkyl ester monomer (a3) (excluding (a1) and (a2)) as a polymerization component, and (meth) acrylic acid alkyl ester. Examples of the system monomer (a3) include aliphatic (meth) acrylic acid alkyl ester monomers and alicyclic structure-containing (meth) acrylic acid alkyl ester monomers.

  As the aliphatic (meth) acrylic acid ester monomer, for example, a (meth) acrylic acid alkyl ester in which the alkyl group usually has 1 to 24 carbon atoms, particularly preferably 1 to 20 carbon atoms, and further preferably 1 to 18 carbon atoms. Is mentioned.

  Specific examples of the aliphatic (meth) acrylic acid alkyl ester monomers include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, tert-butyl (meth) acrylate, n -Propyl (meth) acrylate, n-hexyl (meth) acrylate, n-octyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, cetyl (meth) acrylate, stearyl (meth) acrylate, isostearyl ( (Meth) acrylate, isotetracosyl (meth) acrylate, etc. are mentioned.

  Examples of the alicyclic structure-containing (meth) acrylic acid alkyl ester-based monomer include cyclohexyl (meth) acrylate and isobornyl (meth) acrylate.

Among the above (meth) acrylic acid alkyl ester monomers (a3), methyl (meth) acrylate, tert-butyl (meth) acrylate, 2-isobornyl (meth) are used in terms of improving cohesion when used as an adhesive. Acrylate is preferred.
From the viewpoint of reducing the dielectric constant, it is preferable to use a (meth) acrylic acid alkyl ester having 8 or more carbon atoms, more preferably lauryl (meth) acrylate, tridecyl (meth) acrylate, isostearyl (meth). Acrylate and stearyl (meth) acrylate.

  These (meth) acrylic acid alkyl ester monomers (a3) may be used alone or in combination of two or more.

  The content of the (meth) acrylic acid alkyl ester monomer (a3) is preferably from 5 to 70% by weight, more preferably from 10 to 60% by weight, particularly from 15 to 45% by weight, based on the entire polymerization component. % Is preferred. If the content of the (meth) acrylic acid alkyl ester monomer (a3) is too small, the adhesive strength when used as a pressure-sensitive adhesive tends to decrease, and if it is too large, the acrylic resin has a low molecular weight. When used as an agent, durability tends to decrease.

In the present invention, the functional group-containing ethylenically unsaturated monomer (a4) (excluding (a1)) includes, for example, a carboxyl group-containing monomer, a functional group-containing monomer having a nitrogen atom, an acetoacetyl group-containing monomer, An isocyanate group containing monomer, a glycidyl group containing monomer, etc. are mentioned.
Among these, a functional group-containing monomer having a nitrogen atom is preferable from the viewpoint of imparting a cohesive force and a crosslinking promoting action, particularly an amino group-containing monomer and an amide group-containing monomer, and more preferably an amino group-containing monomer.

  Examples of the carboxyl group-containing monomer include (meth) acrylic acid, acrylic acid dimer, crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, acrylamide N-glycolic acid, and cinnamic acid. Etc. Of these, (meth) acrylic acid is preferably used.

  Examples of the amino group-containing monomer include primary amino group-containing (meth) acrylates such as aminomethyl (meth) acrylate and aminoethyl (meth) acrylate; t-butylaminoethyl (meth) acrylate, t-butylaminopropyl Secondary amino group-containing (meth) acrylates such as (meth) acrylate; ethylaminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, diethylaminopropyl And tertiary amino group-containing (meth) acrylates such as (meth) acrylate and dimethylaminopropylacrylamide.

  Examples of the amide group-containing monomer include (meth) acrylamide; N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-propyl (meth) acrylamide, Nn-butyl (meth) acrylamide, and diacetone. N-alkyl (meth) acrylamides such as (meth) acrylamide and N, N′-methylenebis (meth) acrylamide; N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N, N-dipropyl N, N-dialkyl (meth) acrylamides such as (meth) acrylamide, N, N-ethylmethylacrylamide, N, N-diallyl (meth) acrylamide; N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) Hydroxylases such as acrylamide And alkylalkyl (meth) acrylamides such as N-methoxymethyl (meth) acrylamide and N- (n-butoxymethyl) (meth) acrylamide;

  Examples of the acetoacetyl group-containing monomer include 2- (acetoacetoxy) ethyl (meth) acrylate and allyl acetoacetate.

  Examples of the isocyanate group-containing monomer include 2-acryloyloxyethyl isocyanate, 2-methacryloyloxyethyl isocyanate, and alkylene oxide adducts thereof.

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

  These functional group-containing monomers (a4) may be used alone or in combination of two or more.

  The content of the functional group-containing monomer (a4) is preferably 0.01 to 30% by weight, more preferably 0.05 to 20% by weight, particularly 0.1 to 10%, based on the entire polymerization component. % By weight, in particular 0.5 to 5% by weight is preferred. If the content of the functional group-containing monomer (a4) is too small, the reactivity with the cross-linking agent tends to decrease, or the cross-linking density tends to decrease and the cohesive force tends to decrease, while if too large, the heat resistance of the resin tends to decrease. There is.

  In the present invention, as other polymerizable monomer (a5), for example, phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenyldiethylene glycol (meth) acrylate, 2-hydroxy-3-phenoxy Aromatic (meth) acrylic acid ester monomers such as propyl (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, phenoxypolyethylene glycol-polypropylene glycol- (meth) acrylate, nonylphenol ethylene oxide adduct (meth) acrylate, Acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl Ether, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, itaconic acid dialkyl ester, fumaric acid dialkyl ester, allyl alcohol, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinylketone, etc. Monomer.

  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) A small amount of a compound having two or more ethylenically unsaturated groups such as acrylate and divinylbenzene may be used in combination. At this time, these compounds having two or more ethylenically unsaturated groups are highly reactive, and usually do not remain unreacted when used as a polymerization component of an acrylic resin. In addition, when there is too much usage-amount, the compound which has two or more of these ethylenically unsaturated groups will remain unreacted, and since an acrylic resin tends to gelatinize, it is unpreferable.

  The content of the other polymerizable monomer (a5) is preferably 50% by weight or less, more preferably 40% by weight or less, and particularly preferably 20% by weight or less based on the entire polymerization component. When there is too much content rate of the said other polymerizable monomer (a5), there exists a tendency for heat resistance to fall or for adhesive force to fall.

The acrylic resin (A) can be produced by polymerizing the above polymerization components.
As a polymerization method of the acrylic resin (A), for example, a conventionally known polymerization method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization or the like can be used, but in the present invention, it is produced by solution polymerization. It is preferable that the acrylic resin (A) can be produced safely and stably with an arbitrary monomer composition.
Hereinafter, an example of the preferable manufacturing method of acrylic resin (A) used by this invention is shown.

  First, the above polymerization component and polymerization initiator are mixed or dropped in an organic solvent, and solution polymerization is performed to obtain an acrylic resin (A) solution.

〔Organic solvent〕
Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as hexane, esters such as ethyl acetate and butyl acetate, N-propyl alcohol, and isopropyl alcohol. Aliphatic alcohols such as acetone, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Among these solvents, a solvent having a boiling point of 70 ° C. or less is used in that the solvent can be distilled off from the acrylic resin solution obtained by solution polymerization to efficiently produce a solventless acrylic resin. preferable.

Examples of the organic 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 methyl acetate (54 ° C.). Examples include ester 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 preferably used.
In addition, the numerical value in () described following each said organic solvent name is a boiling point.

(Polymerization initiator)
As the polymerization initiator used in the polymerization reaction, an azo polymerization initiator or a peroxide polymerization initiator which is a normal radical polymerization initiator can be used, and as the azo polymerization initiator, for example, 2,2′-azobis (2-methylbutyronitrile), 2,2′-azobisisobutyronitrile, (1-phenylethyl) azodiphenylmethane, 2,2′-azobis (2,4-dimethylvaleronitrile) ), 2,2′-azobis (2-cyclopropylpropionitrile), 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), and the like. Is, for example, benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, lauroyl peroxide, t-butyl peroxypivalate, - hexyl peroxypivalate, t-hexyl peroxyneodecanoate, diisopropyl peroxycarbonate, diisobutyryl peroxide and the like.
These may be used alone or in combination of two or more.

  In the production of the acrylic resin (A) of the present invention, it is preferable to perform polymerization at a relatively low temperature using a solvent having a boiling point of 70 ° C. or lower as a reaction solvent for solution polymerization. When a high polymerization initiator is used, the polymerization initiator tends to remain, and when the polymerization initiator remains, gelation of the acrylic resin tends to occur in the process of distilling off the solvent from the acrylic resin solution, which will be described later. There is.

Therefore, in the present invention, from the viewpoint of stably performing the process of distilling off the solvent from the acrylic resin solution obtained by solution polymerization, among the above polymerization initiators, the polymerization start having a 10-hour half-life temperature of less than 60 ° C. It is preferable to use an agent, 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-butyl peroxypivalate (54.6 ° C.), t-hexyl peroxypivalate (53.2 ° C.), t-hexyl peroxyneodecanoate (44.5 ° C.) diisopropyl peroxycarbonate (40.5 ° C.) and diisobutyryl peroxide (32.7 ° C.) are preferred, especially 2,2′-azobis (2
, 4-dimethylvaleronitrile) (52 ° C.) and t-hexyl peroxypivalate (53.2 ° C.).
In addition, the numerical value in () described following each compound name is the 10-hour half-life temperature of each compound.

  As the usage-amount of the said polymerization initiator, it is 0.001-10 weight part normally with respect to 100 weight part of polymerization components, Preferably it is 0.1-8 weight part, Most preferably, it is 0.5-6 weight part. More preferably, it is 1 to 4 parts by weight, particularly preferably 1.5 to 3 parts by weight, and 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, the residual monomer increases, or the weight average molecular weight of the acrylic resin tends to increase, and if the amount used is too large, In the step of distilling off the solvent from the acrylic resin solution described later, gelation of the acrylic resin tends to occur.

[Polymerization conditions, etc.]
Regarding polymerization conditions for solution polymerization, polymerization may be performed according to conventionally known polymerization conditions. For example, a polymerization component and a polymerization initiator may be mixed or dropped in a solvent, and polymerization may be performed under predetermined polymerization conditions.

  The polymerization temperature in the polymerization reaction is usually 40 to 120 ° C., but in the present invention, 50 to 90 ° C. is preferable from the viewpoint of stable reaction, more preferably 55 to 75 ° C., particularly 60 to 70 ° C. preferable. If the polymerization temperature is too high, the acrylic resin tends to be gelled, and if it is too low, the activity of the polymerization initiator decreases, so that 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 it is 0.5 hours or more, preferably 1 hour or more after the last addition of the polymerization initiator. More preferably, it is 2 hours or more, particularly preferably 5 hours or more. The upper limit of the polymerization time is usually 72 hours.
The polymerization reaction is preferably performed while refluxing the solvent from the viewpoint of easy heat removal.

  In the production of the acrylic resin (A) of the present invention, in order to reduce the amount of the residual polymerization initiator, it is preferable to perform additional heating in order to thermally decompose the polymerization initiator.

  The driving-in heating temperature is preferably higher than the 10-hour half-life temperature of the polymerization initiator, specifically 40 to 150 ° C., and preferably 55 to 130 ° C. from the viewpoint of suppressing gelation. In particular, the temperature is preferably 75 to 95 ° C. If the heating temperature is too high, the acrylic resin tends to yellow, and if it is too low, the polymerization components and the polymerization initiator remain, and the aging stability and thermal stability of the acrylic resin (A) tend to decrease. There is.

Thus, an acrylic resin (A) solution can be obtained.
Next, the solvent is distilled off from the obtained acrylic resin (A) solution.
The step of distilling off the solvent from the acrylic resin (A) solution can be performed by a publicly known general method. As a method of distilling off the solvent, a method of distilling off the solvent by heating or a pressure reduction There is a method of distilling off the solvent, but from the viewpoint of efficiently distilling off the solvent, a method of distilling off by heating under reduced pressure is preferred.

  The temperature when the solvent is distilled off by heating is preferably 60 to 150 ° C., and in particular, the reaction solution after polymerization of the acrylic resin is maintained at 60 to 80 ° C. to distill the solvent. Then, it is preferable to distill the solvent at 80 to 150 ° C. from the viewpoint of extremely reducing the amount of residual solvent. In addition, it is preferable not to perform the temperature at the time of solvent distillation at 150 degreeC or more from the point which suppresses gelatinization of an acrylic resin.

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.
Thus, the acrylic resin (A) used in the present invention can be produced.

  The acrylic resin (A) used in the present invention needs to have a glass transition temperature (Tg) of −100 to 50 ° C., preferably −80 to 0 ° C., and further −70 to −10. It is preferable that it is (degreeC), especially -60--20 degreeC. If the glass transition temperature is too high, the melt viscosity of the acrylic resin becomes high, which increases the heating temperature required during coating, and may impair the stability of the acrylic resin. Tends to decrease. If the glass transition temperature is too low, the thermal durability tends to decrease.

In addition, about the glass transition temperature of the said acrylic resin (A), it calculates using the formula of Fox, The glass transition temperature at the time of setting it as the homopolymer of the monomer which comprises acrylic resin (A) is normally DSC. Literature values and catalog values measured were used.
The glass transition temperature is calculated from the following Fox equation.

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

  The acrylic resin (A) used in the present invention preferably has a weight average molecular weight of 50,000 or more, more preferably 100,000 to 1,500,000, particularly preferably 200,000 to 1,000,000, particularly preferably 250,000. ˜800,000, particularly preferably 300,000 to 600,000. When the weight average molecular weight is too small, the cohesive force is lowered and the durability tends to be lowered. In addition, when too large, a viscosity will become high too much and there exists a tendency for coating property and handling to fall.

  The degree of dispersion (weight average molecular weight / number average molecular weight) of the acrylic resin (A) is preferably 15 or less, more preferably 10 or less, particularly 7 or less, and particularly preferably 5 or less. 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. The lower limit of the degree of dispersion is usually 1.1 from the viewpoint of production limit.

In addition, said weight average molecular weight is a weight average molecular weight by standard polystyrene molecular weight conversion, a column: TSKgel GMHXL (exclusion limit molecular weight: 4 * 10 < ⁸ >, in the high performance liquid chromatography (Tosoh Corporation make, "HLC-8320GPC"). Separation range: 100 to 4 × 10 ⁸ , theoretical plate number: 14,000 plates / pack, filler material: styrene-divinylbenzene copolymer, filler particle size: 9 μm, column size: 7.8 mm ID 30 cm) and column: TSKgel G2000HXL (exclusion limit molecular weight: 1 × 10 ⁴ , separation range: 100 to 1 × 10 ⁴ , theoretical plate number: 16000 plate / tube, filler material: styrene-divinylbenzene copolymer, (Particle size: 5 μm, column size: 7.8 mm ID × 30 cm) Are those, it can be measured using a number average molecular weight same manner. Further, the degree of dispersion is calculated from the weight average molecular weight to number average molecular weight.

  The melt viscosity (mPa · s) of the acrylic resin (A) is preferably 1,000 to 10,000,000 mPa · s, particularly preferably 50,000 to 1,000,000 mPa · s at 100 ° C., More preferably, it is 200,000-600,000. If the viscosity is too low, durability tends to decrease due to a decrease in molecular weight. If the viscosity is too high, 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.

  The acrylic resin (A) of the present invention is preferably a solventless acrylic resin that does not substantially contain a solvent, and the solvent content of the acrylic resin (A) is preferably 2% by weight or less. Further, it is preferably 0.00001 to 2% by weight, more preferably 0.0001 to 1% by weight, and particularly preferably 0.001 to 0.1% by weight. When there is too much solvent content, when it uses as an adhesive, a bubble will generate | occur | produce in an adhesive layer and there exists a tendency for durability to fall.

  The residual monomer amount in the acrylic resin (A) of the present invention 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 residual monomer is too large, the molecular weight will increase when heated, and coating properties and adhesive properties will decrease, or bubbles will be generated in the adhesive, and durability will tend to decrease.

  The solvent content and the residual monomer amount in the acrylic resin (A) were obtained by diluting the acrylic resin 20 times with toluene and gas chromatography / mass fragment detector (GC: 7890A GC system, MSD: MSD: It is the value measured using Agilent Technologies 5975inert).

  In the present invention, the volatile content in the acrylic resin (A) (usually the solvent and the residual monomer are the main components) is preferably 2% by weight or less, particularly preferably 0.00001. It is -1.5 weight%, More preferably, it is 0.0001-1.2 weight%. If the amount of residual monomer is too large, the molecular weight of the acrylic resin will increase when heated, resulting in a decrease in coating properties, a decrease in adhesive properties when used as an adhesive, and generation of bubbles, resulting in durability. Tends to decrease.

  The volatile content in the acrylic resin (A) is a value calculated from the weight change before and after heating the acrylic resin in a hot air dryer at 130 ° C. for 1 hour. .

<Antioxidant (B)>
Examples of the antioxidant (B) used in the present invention include hindered phenol compounds, amine compounds, sulfur compounds, and phosphoric acid compounds. Among these, at least one selected from amine compounds and phosphate compounds is preferable.

  Examples of the hindered phenol compound include 2,6-di-t-butyl-p-cresol, 2,2′-methylenebis (4-methyl-6-t-butylphenol), triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], pentaerythritol-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] and octadecyl-3- ( 3,5-di-t-butyl-4-hydroxyphenyl) propionate and the like.

  Examples of amine compounds include hindered amine compounds and aromatic amine compounds. Among them, hindered amine compounds are preferable. Specifically, for example, tetrakis (1,2,2,6,6, -pentamethyl-4 -Piperidyl) butane-1,2,3,4-tetracarboxylate, tetrakis (2,2,6,6-tetramethyl-4-piperidyl) butane-1,2,3,4-tetracarboxylate, bis ( 1,2,2,6,6 pentamethyl 4-piperidyl) sebacate, octyldiphenylamine, Nn-butyl-p-aminophenol, N, N-diisopropyl-p-phenylenediamine and the like.

  Examples of the sulfur compound include dilauryl 3,3'-thiodipropionate and distearyl 3,3'-thiodipropionate.

  Examples of the phosphoric acid compound include triphenyl phosphite, triisodecyl phosphite (hereinafter abbreviated as TDP), tris (2,4-di-t-butylphenyl) phosphite, 2,2-methylenebis (4 , 6-di-t-butylphenyl) octyl phosphite and halo-substituted products thereof.

Among these, amine compounds, particularly hindered amine compounds, are preferred because they have high radical scavenging ability and can exhibit performance even in the absence of oxygen, and tetrakis (1,2,2,6,6) is particularly preferable. , -Pentamethyl-4-piperidyl) butane-1,2,3,4-tetracarboxylate. In addition, a phosphoric acid compound is preferable because it can efficiently decompose and stabilize the peroxide generated in the system and further capture radicals. Among them, tris (2,4-di-t-butyl is preferable. Phenyl) phosphite is preferred.
These antioxidants (B) may be used alone or in combination of two or more.

As content of antioxidant (B) in this invention, it is preferable that it is 0.2-10 weight part with respect to 100 weight part of acrylic resin (A), More preferably, it is 0.5-9 weight Parts, particularly preferably 1 to 7 parts by weight, particularly preferably 2 to 6 parts by weight.
If the content of the antioxidant (B) is too small, the thermal stability of the acrylic resin (A) tends to decrease. If the content is too large, the durability of the pressure-sensitive adhesive is increased due to the generation of bleed out and outgas with time. There is a tendency to decrease.

  The antioxidant (B) is preferably blended before or during the solvent distillation step in the production of the acrylic resin (A) (in the state where the solvent remains).

Thus, the solventless acrylic resin composition of the present invention comprising the acrylic resin (A) and the antioxidant (B) can be obtained.
The solventless acrylic resin composition of the present invention preferably contains 90% by weight or more of the acrylic resin (A) based on the whole composition, more preferably 95 to 99.9% by weight, particularly 98. It is preferable to contain ~ 99.9% by weight, particularly 99 ~ 99.9% by weight.

The solventless acrylic resin composition of the present invention has a weight average molecular weight change rate represented by the following formula 1, that is, a weight average molecular weight of the solventless acrylic resin composition after heating at 120 ° C. for 4 days as M2. The weight average molecular weight change rate M (%) when the weight average molecular weight of the solvent-free acrylic resin composition before heating is M1, is 20 or less, more preferably 0 to 10, particularly preferably 0 to 0. 5.
When the rate of change M is greater than 20, when used as an adhesive, the coatability is reduced and it is difficult to obtain desired adhesive properties.

[Formula 1]
M (%) = (| M2-M1 | / M1) × 100
M2: Weight average molecular weight of solventless acrylic resin composition after heat treatment at 120 ° C. for 4 days M1: Weight average molecular weight of solventless acrylic resin composition before heat treatment

Here, the measuring method of the weight average molecular weight of the solventless acrylic resin composition is as follows.
That is, the weight average molecular weight is a weight average molecular weight in terms of standard polystyrene molecular weight. High-performance liquid chromatography (manufactured by Tosoh Corporation, “HLC-8320GPC”, column: TSKgel GMHXL (exclusion limit molecular weight: 4 × 10 ⁸ , separation range) : 100 to 4 × 10 ⁸ , theoretical plate number: 14,000 plate / line, filler material: styrene-divinylbenzene copolymer, particle size of filler: 9 μm, column size: 7.8 mm ID × 30 cm) And columns: TSKgel G2000HXL (exclusion limit molecular weight: 1 × 10 ⁴ , separation range: 100 to 1 × 10 ⁴ , theoretical plate number: 16000 plates / column, packing material: styrene-divinylbenzene copolymer, packing material Measured by using one particle size: 5 μm, column size: 7.8 mm ID × 30 cm) in series There can be measured using a number average molecular weight same manner. Further, the degree of dispersion is calculated from the weight average molecular weight to number average molecular weight.

  The solventless acrylic resin composition of the present invention is useful as a pressure-sensitive adhesive component, and particularly useful as a hot-melt pressure-sensitive adhesive component.

<Adhesive sheet>
The solventless acrylic resin composition of the present invention comprises a pressure-sensitive adhesive sheet provided with a pressure-sensitive adhesive layer on the base sheet, a double-sided pressure-sensitive adhesive sheet provided with a pressure-sensitive adhesive layer on a release sheet, and a pressure-sensitive adhesive layer. Is preferably used as an optical member with an adhesive layer provided on the optical member. The pressure-sensitive adhesive layer may be the solventless acrylic resin composition itself of the present invention or may be formed by curing (crosslinking) the solventless acrylic resin composition of the present invention. . Examples of the curing method include a method of curing with active energy rays, a method of curing by crosslinking with a crosslinking agent, a method of combining these, and the like.

An adhesive sheet can be produced as follows, for example.
In the present invention, the “sheet” is not particularly distinguished from “film” or “tape”, and is described as meaning including these.

  First, a solventless acrylic resin composition is applied to one or both sides of a base sheet in a melted state by heating, and then cooled, or the pressure-sensitive adhesive composition is melted by heating, and a base such as a T-die is used. The pressure-sensitive adhesive layer is formed to have a predetermined thickness on one or both sides of the substrate sheet by a method such as extrusion lamination on the material sheet. 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 adhesive having an adhesive layer formed by curing (crosslinking) the adhesive composition by performing active energy ray irradiation treatment as necessary and further aging A sheet can be produced.

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.

  By irradiating active energy rays, the acrylic resin (A) in the solventless acrylic resin composition forms a cross-linked structure within and / or between molecules.

  When irradiating 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 because of the availability of the irradiation device and the price.

When curing with active energy rays, it is preferable to use a photopolymerization initiator in that the reaction during irradiation with active energy rays can be stabilized.
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 acylphosphine oxides. can give. Note that it is preferable to use a hydrogen abstraction type benzophenone photoinitiator from the viewpoint of efficient crosslinking between molecules or within a molecule.

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

  The blending amount of the photopolymerization initiator is preferably 0.01 to 10 parts by weight, particularly preferably 0.1 to 5 parts by weight, more preferably 100 parts by weight of the acrylic resin (A). Is 0.5 to 2 parts by weight. If the amount is too small, the curing rate tends to decrease or the curing tends to be insufficient, and if too large, the curability does not improve and the economy tends to decrease.

  Moreover, when hardening by an active energy ray, an active energy ray hardening monomer can be used. Thereby, the cohesion force of the whole adhesive layer can be adjusted, and the stable adhesive physical property can be obtained.

  The active energy ray-curable monomer is preferably a polyfunctional monomer containing two or more ethylenically unsaturated groups in one molecule. For example, hexanediol di (meth) acrylate, butanediol di (meth) acrylate, ( Poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (Meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylolmethane tri (meth) acrylate, isocyanuric acid ethylene oxide modified tri (meth) acrylate, allyl (meth) acryl Over DOO, such as vinyl (meth) acrylate or urethane (meth) acrylate. In addition, the said polyfunctional monomer can be used individually or in combination of 2 or more types.

  Such polyfunctional monomer is preferably used in an amount of 0 to 5 parts by weight, particularly preferably 0.01 to 2 parts by weight, and more preferably 0.1 to 1 part by weight with respect to 100 parts by weight of the acrylic resin (A). Part.

  In the pressure-sensitive adhesive sheet of the present invention, other pressure-sensitive adhesives may be blended in the pressure-sensitive adhesive layer as necessary, or a crosslinking agent, a crosslinking accelerator, a silane coupling agent, an antistatic agent, a tackifier, a functional dye, etc. These conventionally known additives may be blended.

  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.

  And in this invention, the optical member with an adhesive layer can be obtained by laminating | stacking and forming the said adhesive layer 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 layer of the pressure-sensitive adhesive sheet is preferably 10 to 100%, particularly preferably 30 to 90%, particularly 50 to 80% from the viewpoint of durability and adhesive strength. It is preferable. When the gel fraction is too low, durability tends to decrease 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 adjusting the gel fraction to the above range, for example, adjusting the amount of active energy ray irradiation and the amount of photopolymerization initiator, adjusting the type and amount of the active energy ray-curable monomer, and crosslinking In the case of using an agent, it is achieved by adjusting the type and amount of the crosslinking agent.

  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 layer of the pressure-sensitive adhesive sheet is usually preferably 50 to 3000 μm, more preferably 75 to 1000 μm, and particularly preferably 80 to 350 μm. 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 and the practicality tends to decrease.

  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 100 N / 25 mm, more preferably 10 N / 25 mm to 50 N / 25 mm.

  In addition, the said adhesive force is computed as follows, for example. Peel off the release sheet on one side from the pressure-sensitive adhesive layer of the substrate-less double-sided pressure-sensitive adhesive sheet using a polyester-based release sheet (polyethylene terephthalate sheet), and press it onto an easily adhesive PET (polyethylene terephthalate) film with a thickness of 125 μm. A PET film with an adhesive layer is prepared. 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.).

The solvent-free acrylic resin composition of the present invention is excellent in thermal stability, can be applied by thick coating, and has excellent heat and humidity resistance. Therefore, a pressure-sensitive adhesive using the solvent-free acrylic resin composition Can be suitably used as a double-sided adhesive application or as an adhesive having impact resistance and strong adhesiveness. Specifically, optical sheets such as glass, ITO transparent electrode sheet, polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), polarizing plate, retardation plate, optical compensation film, brightness enhancement film, etc. It is useful as a pressure-sensitive adhesive component for application of optical members. Furthermore, it can be suitably used for an image display device such as a touch panel comprising these optical members.
The solventless pressure-sensitive adhesive composition of the present invention can also be used as various label pressure-sensitive adhesives and masking pressure-sensitive adhesives, and is particularly suitable for use in electronic parts.

  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, about the measurement of the weight average molecular weight of an acrylic resin and an acrylic resin composition, and the glass transition temperature, it measured according to the above-mentioned method.

[Production of acrylic resin (A-1)]
In a 2 L flask equipped with a condenser, 100 parts of acetone (boiling point 56 ° C.) as a polymerization solvent and 2,2′-azobis (2,4-dimethylvaleronitrile) (ADVN;
1 part of half-temperature 52 ° C. is heated to reflux in the flask, 17 parts of 2-ethylhexyl acrylate (2EHA), 24 parts of 2-ethylhexyl methacrylate (2EHMA), 13 parts of 2-hydroxyethyl acrylate (HEA), t-butyl methacrylate A solution prepared by previously mixing 8 parts of (tBMA), 20 parts of lauryl methacrylate (LMA) and 18 parts of isostearyl acrylate (ISTA) was added dropwise over 2 hours. After dropping, 1 hour and 2 hours later, 1 part of ADVN was added and reacted to obtain an acrylic resin (A-1) solution.

  In a flask in which the acrylic resin (A-1) solution obtained above can be distilled out of the system by using a toroidal connecting tube, at a jacket temperature of 80 ° C. for 1 hour, and further The pressure was reduced to 10 kPa, and the solvent was distilled off by standing at a jacket temperature of 90 ° C. for 2 hours to remove the acrylic resin (A-1) (weight average molecular weight: 344,000, glass transition temperature: −31.0 ° C., Solvent content: 0.024%, volatile content: 0.9%).

In addition, the solvent content in the obtained acrylic resin (A-1) was measured by the following method.
0.1 g of acrylic resin (A-1) was weighed and diluted 20 times with toluene. The toluene-diluted solution of the acrylic resin (A-1) is put into a vial with a capacity of 2 ml, and an autosampler (Agilent Technologies 7893 Autosampler), gas chromatography / mass fragment detector (GC: Agilent Technologies 7890A GCsystems, : Agilent Technologies 5975inert), the solvent concentration and each monomer concentration were measured. The column used was Agilent DB-1MS (30 m × 250 μmφ × 0.25 μm), the carrier gas was He, the flow rate was 1.0 ml / min, and the pressure was 7.0 psi (when the oven temperature was 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).

Moreover, the volatile content in the obtained acrylic resin (A-1) was measured by the following method.
0.5 g of acrylic resin (A-1) was weighed in an aluminum cup, heated with a hot air dryer (130 ° C. × 1 hour), and calculated from the change in weight before and after heating.

[Manufacture of acrylic resins (A-2) to (A-4)]
In the production of (A-1) above, production was carried out in the same manner except that the polymerization component composition was as shown in Table 1, and various physical properties of the obtained acrylic resin were also measured.

<Example 1>
To 100 parts of the acrylic resin (A-1) obtained above, 0.5 part of an antioxidant (B-1) (manufactured by Adeka Corporation (trade name; ADK STAB LA-52) is added and heated. And mixed well to prepare a solventless acrylic resin composition.

<Examples 2 to 10 and Comparative Examples 1 to 4>
A solvent-free acrylic resin composition was prepared in the same manner as in Example 1 except that the type of acrylic resin (A) and the type and content of antioxidant (B) were as shown in Table 2.

  The following evaluation was performed using the solventless acrylic resin compositions obtained in Examples 2 to 10 and Comparative Examples 1 to 4. These results are also shown in Table 2 below.

[Thermal stability]
The solventless acrylic resin composition was placed in a glass bottle, purged with nitrogen, placed in an oven, and heated at 120 ° C. for 4 days. Thereafter, the polymerization average molecular weight of the solventless acrylic resin composition was measured by gel permeation chromatography, and the weight average of the acrylic resin composition after heat treatment at 120 ° C. for 4 days as shown in the following formula 1. The weight average molecular weight change rate M (%) when the molecular weight was M2 and the weight average molecular weight of the acrylic resin composition before heat treatment was M1, was calculated and evaluated according to the following evaluation criteria.

[Formula 1]
M (%) = (| M2-M1 | / M1) × 100
M2: Weight average molecular weight of solventless acrylic resin composition after heat treatment at 120 ° C. for 4 days M1: Weight average molecular weight of solventless acrylic resin composition before heat treatment

(Evaluation criteria)
◎ ・ ・ ・ M is 10 or less ○ ・ ・ ・ M is greater than 10 and 20 or less × ・ ・ ・ M is greater than 20

From the above Examples, it was found that the solventless acrylic resin composition of the present invention has little change in weight average molecular weight due to heating and is excellent in thermal stability.
On the other hand, the solventless acrylic resin composition of the comparative example which does not contain an antioxidant or whose antioxidant content does not satisfy the scope of the present invention has a large change in molecular weight due to heating and is inferior in thermal stability. It was a thing. When such a solvent-free acrylic resin composition is used as a hot-melt adhesive, the coating properties are lowered, resulting in poor coating properties and the desired adhesive properties cannot be obtained.

  The solventless resin composition of the present invention is excellent in thermal stability and can be applied by thick coating, so it has excellent shock absorption, step following ability, pressure-sensitive adhesive used for touch panels and image display devices, Useful for shock absorbing sheets.

Claims (8)

Contains acrylic resin (A) and antioxidant (B),
The acrylic resin (A) is obtained by polymerizing a polymerization component containing 3 to 50% by weight of the hydroxyl group-containing monomer (a1),
The glass transition temperature of the acrylic resin (A) is −100 to 50 ° C.,
The content of the antioxidant (B) is 0.2 to 10 parts by weight with respect to 100 parts by weight of the acrylic resin (A),
A solvent-free acrylic resin composition having a weight average molecular weight change rate M (%) represented by the following formula 1 of 20 or less.
[Formula 1]
M (%) = (| M2-M1 | / M1) × 100
M2: Weight average molecular weight of solventless acrylic resin composition after heat treatment at 120 ° C. for 4 days M1: Weight average molecular weight of solventless acrylic resin composition before heat treatment   The acrylic resin (A) is at least one copolymerizable monomer (a2) selected from a (meth) acrylic acid alkyl ester monomer and a vinyl ester monomer having a branched structure alkyl group having 5 to 14 carbon atoms. The solvent-free acrylic resin composition according to claim 1, which is obtained by polymerizing a polymerization component containing 15 to 85% by weight.   The solvent-free acrylic resin composition according to claim 1 or 2, wherein the acrylic resin (A) has a weight average molecular weight of 50,000 or more.   The solvent-free acrylic resin composition according to any one of claims 1 to 3, wherein the volatile content in the acrylic resin (A) is 2% by weight or less.   Content of acrylic resin (A) is 90 weight% or more, Solvent-free acrylic resin composition in any one of Claims 1-4 characterized by the above-mentioned.   The solventless acrylic resin composition according to any one of claims 1 to 5, wherein the antioxidant (B) is at least one selected from an amine compound and a phosphate compound.   A solventless acrylic pressure-sensitive adhesive comprising the solventless acrylic resin composition according to claim 1.   A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer using the solventless acrylic resin composition according to claim 1.