JP2022095505A - Adhesive composition, adhesive and adhesive sheet - Google Patents

Abstract

To provide an adhesive composition having multistage curability, which can obtain excellent adhesive physical properties even in a low crosslinked state after primary curing.SOLUTION: An adhesive composition contains an acrylic resin (A) and a crosslinking agent (B), in which the acrylic resin (A) is a copolymer obtained by copolymerization of a copolymerization component (a) containing 5 pts.wt. or more of alkyl acrylate (a1) having a glass transition temperature of -27 to 50°C when a homopolymer is formed, 10 wt.% or more of alkyl methacrylate (a2) having a glass transition temperature of 0 to 100°C when the homopolymer is formed, and a hydroxyl group-containing (meth)acrylate monomer (a3), and a glass transition temperature of the acrylic resin (A) is -10 to 15°C.SELECTED DRAWING: None

Description

The present invention relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition, and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer composed of the pressure-sensitive adhesive. The pressure-sensitive adhesive composition of the present invention can be suitably used as a pressure-sensitive adhesive for a multi-stage curable pressure-sensitive adhesive sheet that cures in a plurality of stages, and excellent pressure-sensitive adhesive properties can be obtained even in a low-crosslinked state after primary curing.

In recent years, touch panels that combine displays and position input devices have become widely used in mobile devices such as televisions, monitors for personal computers, laptop computers, mobile phones, smartphones, and tablet terminals. Among them, capacitive touch panels have become popular. It has increased.
The touch panel is usually composed of a display made of an organic EL or a liquid crystal, a transparent conductive film substrate (ITO substrate), and a protective film (protective glass), and a transparent adhesive sheet is used for bonding these members.

Since it is necessary to bond members of various shapes to the transparent pressure-sensitive adhesive sheet, the pressure-sensitive adhesive for the transparent pressure-sensitive adhesive sheet is bonded in a low cross-linked state before it is completely cured, and is sufficient in the process until the pressure-sensitive adhesive layer is completely cured. Adhesive properties are required.
Specifically, when bonding to a member having a complicated shape, poor bonding such as sticking of a transparent adhesive sheet to a place other than the target location is likely to occur, so transparency with low tackiness even in a low cross-linking state. Adhesive sheets are required. Further, in order to fix the members having a complicated shape to each other, it is required to suppress the peeling of the transparent adhesive sheet from the members under stress. Therefore, it is required to be a transparent adhesive sheet having a high constant load holding force even in a low crosslinked state.
Therefore, the pressure-sensitive adhesive for a transparent pressure-sensitive adhesive sheet is required to have not only normal pressure-sensitive adhesive properties such as adhesive strength after complete curing, but also excellent pressure-sensitive adhesive properties even in a low-crosslinked state after primary curing. Generally, primary curing is cross-linked by thermal cross-linking or irradiation with active energy rays, and complete curing is cross-linked and cured by irradiation with active energy rays.
Examples of the pressure-sensitive adhesive sheet using such a multi-stage curable pressure-sensitive adhesive include the pressure-sensitive adhesive sheets described in Patent Documents 1 to 3.

In Patent Document 1, an organic solvent that easily volatilizes under general drying conditions is further used in a solvent-based pressure-sensitive adhesive made of an acrylic resin, and an ethylenically unsaturated monomer that does not easily volatilize is blended in a specific ratio. It is disclosed that thick coating is possible and a clean pressure-sensitive adhesive layer on the surface of the coating film can be obtained.
Further, in Patent Document 2, a hydrogen extraction type photoinitiator is used in order to form a three-dimensional network structure of a solvent-type acrylic acid ester-based pressure-sensitive adhesive without using a cross-linking agent, and light irradiation is performed after the coating drying step. It is disclosed that the aging step is omitted by doing so.
Further, Patent Document 3 discloses that an acrylic resin having a high glass transition temperature can be used to obtain a pressure-sensitive adhesive having high step followability and blister resistance.
However, none of Patent Documents 1 to 3 considered the adhesive physical properties in the low crosslinked state at the time of primary curing.

Japanese Unexamined Patent Publication No. 2012-111939 JP-A-2017-210542 International Publication No. 2017/022770

The problem to be solved by the present invention is a pressure-sensitive adhesive composition that can be used for multi-stage curing, and provides a pressure-sensitive adhesive composition that can obtain excellent pressure-sensitive adhesive properties even in a low-crosslinked state after primary curing. Further, it is to provide a pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive.

As a result of diligent studies by the present inventor in order to solve the above problems, by using a pressure-sensitive adhesive composition containing an acrylic resin obtained by using a copolymerization component having a specific composition, low cross-linking after primary curing is used. It has been found that excellent adhesive properties such as low tackiness and high constant load holding force can be obtained even in the state.
Specifically, the present invention has the following configurations.

(1) A pressure-sensitive adhesive composition containing an acrylic resin (A) and a cross-linking agent (B).
The acrylic resin (A) contains 5% by weight or more of the alkyl acrylate (a1) having a glass transition temperature of −27 to 50 ° C. when the homopolymer is formed, and the glass transition temperature when the homopolymer is formed is 0 to 0 to 0. A copolymer obtained by polymerizing a copolymerization component (a) containing an alkyl methacrylate (a2) at 100 ° C. in an amount of 10% by weight or more and a hydroxyl group-containing (meth) acrylic acid ester monomer (a3).
A pressure-sensitive adhesive composition, wherein the acrylic resin (A) has a glass transition temperature of −10 to 15 ° C.

(2) A pressure-sensitive adhesive characterized in that the pressure-sensitive adhesive composition is crosslinked.

(3) A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the above-mentioned pressure-sensitive adhesive.

The pressure-sensitive adhesive composition of the present invention has excellent pressure-sensitive adhesive properties such as low tackiness and high constant load holding power even in a low cross-linking state after primary curing, so that workability and reliability are improved. Therefore, it is particularly useful as an adhesive or an adhesive sheet used for a touch panel, an image display device, or the like.

Hereinafter, the present invention will be described in detail, but these are examples of desirable embodiments.
In the present invention, "(meth) acrylic" means acrylic or methacrylic, "(meth) acryloyl" means acryloyl or methacryloyl, and "(meth) acrylate" means acrylate or methacrylate. , "Acrylic resin" is a resin obtained by polymerizing a monomer component containing at least one (meth) acrylic monomer. Further, the "sheet" conceptually includes a sheet, a film, and a tape.

<Adhesive composition>
The pressure-sensitive adhesive composition of the present invention contains an acrylic resin (A) and a cross-linking agent (B).
The acrylic resin (A) is a copolymer obtained by polymerizing a copolymerization component (a) containing at least an alkyl acrylate (a1), an alkyl methacrylate (a2) and a hydroxyl group-containing monomer (a3).
Hereinafter, each component will be described.

[Alkyl acrylate (a1)]
The alkyl acrylate (a1) has a glass transition temperature (hereinafter referred to as “Tg”) of -25 to 27 to 50 ° C, preferably −10 to 45 ° C, and more preferably −5 to 10 ° C. When such Tg is within the range, the effect of the present invention can be obtained.
The Tg of the alkyl acrylate (a1) is a homopolymer glass transition temperature made of the alkyl acrylate (a1), and standard analytical values described in Wiley Publishing "POLYMER HANDBOOK" and the like can be adopted.

Examples of the alkyl acrylate (a1) include methyl acrylate (Tg = 8 ° C.), ethyl acrylate (Tg = -22 ° C.), isobutyl acrylate (Tg = −26 ° C.), and t-butyl acrylate (Tg = 41 ° C.). , Cyclohexyl acrylate (Tg = 15 ° C.) and the like. Of these, methyl acrylate is preferable from the viewpoint of adhesive properties. One type selected from these may be used alone, or two or more types may be used in combination.

The content of the alkyl acrylate (a1) is 5% by weight or more, preferably 8 to 50% by weight, more preferably 10 to 30% by weight, and particularly preferably 12 to 10% by weight in the copolymerization component (a). It is 28% by weight, particularly preferably 15 to 25% by weight.
If the content is too small, the adhesive property in the primary cured state tends to decrease, and if the content is too large, the adhesive property after complete curing tends to decrease.

[Alkyl methacrylate (a2)]
The alkyl methacrylate (a2) has a Tg of 0 to 100 ° C, preferably 20 to 85 ° C, and more preferably 40 to 70 ° C. When such Tg is within the range, the effect of the present invention can be obtained.
The Tg of the alkyl methacrylate (a2) is the homopolymer glass transition temperature composed of the alkyl methacrylate (a2), and the standard analytical value described in Wiley Publishing "POLYMER HANDBOOK" or the like can be adopted.

Examples of the alkyl methacrylate (a2) include ethyl methacrylate (Tg = 65 ° C.), n-butyl methacrylate (Tg = 20 ° C.), isobutyl methacrylate (Tg = 48 ° C.), cyclohexyl methacrylate (Tg = 66 ° C.), and the like. Can be mentioned. One type selected from these may be used alone, or two or more types may be used in combination. Of these, ethyl methacrylate and isobutyl methacrylate are preferable.

The content of the alkyl methacrylate (a2) is 10% by weight or more, preferably 12 to 40% by weight, and more preferably 15 to 30% by weight in the copolymerization component (a). If the content is too small, the adhesive property in the primary cured state tends to decrease, and if the content is too large, the adhesive property after complete curing tends to decrease.

Further, in the copolymerization component (a) used in the present invention, the content ratio (a1 / a2) of the alkyl acrylate (a1) and the alkyl methacrylate (a2) is preferably 20/80 to 55/45 by weight, more preferably 20/80 to 55/45. It is 30/70 to 52/48, particularly preferably 35/65 to 50/50.
When the content ratio of (a1 / a2) is within the above range, the adhesive physical properties in the primary cured state are excellent.

The total content of the alkyl acrylate (a1) and the alkyl methacrylate (a2) is preferably 30 to 70% by weight, more preferably 38 to 65% by weight, and particularly preferably 38% by weight, based on the copolymerization component (a). It is 40 to 60% by weight.
When the total content of both monomers is in the above range, the adhesive properties in the low crosslinked state in the primary curing state are good, which is preferable.

[Hydroxy group-containing (meth) acrylic acid ester monomer (a3)]
The hydroxyl group-containing (meth) acrylic acid ester monomer is a (meth) acrylic acid ester having one or more hydroxyl groups, and examples of the monomer (a3) include 2-hydroxyethyl (meth) acrylate and 4-hydroxy. Acrylic acid hydroxyalkyl esters such as butyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate; caprolactone-modified 2-hydroxyethyl (meth) acrylate. Caprolactone-modified monomers such as diethylene glycol (meth) acrylate, oxyalkylene-modified monomers such as polyethylene glycol (meth) acrylate; In addition, 2-acryloyloxyethyl-2-hydroxyethylphthalic acid, N-methylol (meth) acrylamide, hydroxy Primary hydroxyl group-containing monomer such as ethylacrylamide; Secondary hydroxyl group-containing monomer such as 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-chloro2-hydroxypropyl (meth) acrylate; 2,2 -Examples include tertiary hydroxyl group-containing monomers such as dimethyl 2-hydroxyethyl (meth) acrylate. Of these, 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate are preferable, and 2-hydroxyethyl (meth) acrylate is particularly preferable because they have few impurities such as di (meth) acrylate and are easy to manufacture. Is preferable. One type selected from these may be used alone, or two or more types may be used in combination.

The content of the hydroxyl group-containing (meth) acrylic acid ester monomer (a3) is preferably 5% by weight or more, more preferably 10 to 40% by weight, and particularly preferably 12 to 30% by weight in the copolymerization component (a). % By weight. If the content is too small, the moist heat resistance tends to decrease, and if the content is too large, the self-crosslinking reaction of the acrylic resin tends to occur, and the heat resistance tends to decrease.

The hydroxyl group-containing (meth) acrylic acid ester monomer (a3) used in the present invention contains a small amount of di (meth) acrylate contained as an impurity in the hydroxyl group-containing (meth) acrylic acid ester monomer (a3). It is preferable to use a hydroxyl group-containing (meth) acrylic acid ester monomer (a3) containing 0.5% by weight or less of di (meth) acrylate, and more preferably 0. .2% by weight or less, particularly preferably 0.1% by weight or less, still more preferably 0% by weight.

Further, the hydroxyl group-containing (meth) acrylic acid ester monomer (a3) often contains acrylic acid as an impurity, and the content thereof is usually in the hydroxyl group-containing (meth) acrylic acid ester monomer (a3). It is about 0.001 to 0.5% by weight, and it is preferable to use a smaller amount.

[Active energy ray-curable structural site-containing (meth) acrylic acid ester monomer (a4)]
The acrylic resin (A) used in the present invention can also have an active energy ray crosslinkable structural site.
The active energy ray crosslinkable structure site is a structure capable of forming a crosslinked structure by reacting with a part of the acrylic resin (A) or other curing components contained in the pressure-sensitive adhesive composition by irradiation with the active energy ray. It is a part.
In the present invention, as the active energy ray crosslinkable structural moiety, a benzophenone-based crosslinkable structural moiety is preferable because it has high reactivity and is excellent in improving cohesive force.

Therefore, in the present invention, the copolymerization component (a) for polymerizing the acrylic resin (A) may further contain the active energy ray crosslinkable structural site-containing (meth) acrylic acid ester monomer (a4). preferable.
As the (meth) acrylic acid ester monomer (a4) containing an active energy ray crosslinkable structural site, a (meth) acrylic acid ester monomer having a benzophenone-based crosslinkable structural site is more efficient with active energy rays such as ultraviolet rays and electron beams. It is preferable in that it can form a crosslinked structure, and examples thereof include 4- (meth) acryloyloxybenzophenone.

The content of the (meth) acrylic acid ester monomer (a4) containing the active energy ray crosslinkable structural site is preferably 0.01 to 5% by weight in the copolymerization component (a), and among them, the benzophenone type. The content of the (meth) acrylic acid ester monomer having a crosslinkable structural moiety is preferably 0.01 to 5% by weight, more preferably 0.1 to 2% by weight, based on the copolymerization component (a). , More preferably 0.2 to 1% by weight. If the content is too small, the holding power when forming the crosslinked structure by the active energy rays tends to decrease, and further, the active energy when forming the crosslinked structure for producing a processable pressure-sensitive adhesive sheet. A large dose is required, a large amount of energy is required when producing the adhesive sheet, and efficient production tends to be difficult. Further, if the content is too large, the cohesive force of the entire system tends to increase too much, and the adhesive force tends to decrease.

In addition to copolymerizing the (meth) acrylic acid ester monomer (a4) containing the active energy ray-crosslinkable structural site, when introducing the active energy ray-crosslinkable structural moiety into the acrylic resin (A), the acrylic resin (A4) is acrylic-based. It is also possible to contain a hydroxyl group in the resin (A) and react the hydroxyl group with an ethylenically unsaturated group-containing isocyanate compound to introduce an ethylenically unsaturated group as an active energy ray crosslinkable structural site.

[Ethylene unsaturated monomer (a5)]
In the present invention, the copolymerization component (a) may further contain other copolymerizable ethylenically unsaturated monomers (a5) other than the monomers (a1) to (a4), if necessary.
Examples of the other copolymerizable ethylenically unsaturated monomer (a5) include alkyl (meth) acrylates such as n-butyl acrylate and 2-ethylhexyl (meth) acrylate (provided that the monomers (a1) and (a2) are used. Excludes); phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenyldiethylene glycol (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, phenoxypolyethylene glycol-polypropylene glycol- (meth) acrylate, Aromatic ring-containing monomers such as orthophenylphenoxyethyl (meth) acrylate, nonylphenolethylene oxide adduct (meth) acrylate; cyclohexyloxyalkyl (meth) acrylate, tert-butylcyclohexyloxyethyl (meth) acrylate, isobornyl (meth) acrylate, Alicyclic-containing monomers such as dicyclopentanyl (meth) acrylate; 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, 2-butoxyethyl (meth) acrylate. , 2-Butoxydiethylene glycol (meth) acrylate, methoxydiethylene glycol (meth) acrylate, methoxytriethylene glycol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxydipropylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, Octoxypolyethylene glycol-ether chain-containing monomers such as polypropylene glycol mono (meth) acrylate, lauroxypolyethylene glycol mono (meth) acrylate, stearoxypolyethylene glycol mono (meth) acrylate; (meth) acrylic acid, β-carboxyethyl acrylate. Acrylate dimer such as crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, N-glycolic acid, carboxy group-containing monomers such as silicic acid; (meth) acrylamide, N- Amid group-containing monomers such as (n-butoxyalkyl) (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N, N-dimethylaminoalkyl (meth) acrylamide; Others, acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, vinyl pyridine, vinylpyrrolidone, itaconic acid dialkyl ester, fumal Examples thereof include acid dialkyl esters, allyl alcohols, acrylic chlorides, methyl vinyl ketones, N-acrylamide methyltrimethylammonium chlorides, allyltrimethylammonium chlorides, and dimethylallylvinyl ketones.
One type selected from these may be used alone, or two or more types may be used in combination.

Further, when the purpose is to increase the molecular weight of the acrylic resin (A), ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, Compounds having two or more ethylenically unsaturated groups such as propylene glycol di (meth) acrylate and divinylbenzene can also be used in combination.

The content of the other copolymerizable ethylenically unsaturated monomer (a5) is usually 60% by weight or less, preferably 48% by weight or less, and more preferably 38% by weight or less in the copolymerization component (a). be.
If the content is too large, the sticky physical properties at the time of low cross-linking tend to decrease.

[Acrylic resin (A)]
The acrylic resin (A) used in the present invention contains the above-mentioned alkyl acrylate (a1), alkyl methacrylate (a2) and hydroxyl group-containing (meth) acrylic acid ester monomer (a3) as essential components, and if necessary, the above-mentioned It can be produced by copolymerizing the copolymerization component (a) further containing the optional polymerization components (a4) and (a5).

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

First, the copolymerization component (a) and the polymerization initiator are mixed or dropped in an organic solvent to carry out solution polymerization.

Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as n-hexane; esters such as methyl acetate, ethyl acetate and butyl acetate; methyl alcohols. , Ethyl alcohols, n-propyl alcohols, isopropyl alcohols and other aliphatic alcohols; acetone, methyl ethyl ketones, methyl isobutyl ketones, cyclohexanones and other ketones; dimethyl ethers, diethyl ethers and other aliphatic ethers; methylene chloride, ethylene chloride and the like. Examples thereof include aliphatic halogenated hydrocarbons; cyclic ethers such as tetrahydrofuran. One type selected from these may be used alone, or two or more types may be used in combination. Among these solvents, esters and ketones are preferable, and ethyl acetate and acetone are particularly preferable.

As the polymerization initiator used in the above-mentioned polymerization reaction, an azo-based polymerization initiator, a peroxide-based polymerization initiator, or the like, which are ordinary radical polymerization initiators, can be used.
Examples of the azo-based polymerization initiator include 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, (1-phenylethyl) azodiphenylmethane, and 2,2'. -Azobis (2,4-dimethylvaleronitrile), 2,2'-Azobis (2-cyclopropylpropionitrile), 2,2'-Azobis (4-methoxy-2,4-dimethylvaleronitrile), etc. Be done.
Examples of the peroxide-based polymerization initiator include benzoyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide, lauroyl peroxide, tert-butylperoxypivalate, tert-hexylperoxypivalate, and tert-hexyl. Examples thereof include peroxyneodecanoate, diisopropylperoxycarbonate, and diisobutyryl peroxide.
One type selected from these may be used alone, or two or more types may be used in combination.
Of these, the azo-based polymerization initiator is preferable, and more preferably 2,2'-azobisisobutyronitrile and 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile).

The amount of the polymerization initiator used is usually 0.001 to 10 parts by weight, preferably 0.1 to 8 parts by weight, and more preferably 0.5 with respect to 100 parts by weight of the copolymerization component (a). It is up to 6 parts by weight, particularly preferably 1 to 4 parts by weight, more 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 (A) tends to decrease, the residual monomers tend to increase, and the weight average molecular weight of the acrylic resin (A) tends to increase. If the amount is too large, the acrylic resin (A) tends to gel.

The polymerization conditions of solution polymerization are not particularly limited, and polymerization can be carried out according to conventionally known polymerization conditions. For example, the copolymerization component (a) and the polymerization initiator can be mixed or dropped in the organic solvent to polymerize under predetermined polymerization conditions.

The polymerization temperature in the above polymerization reaction is usually 40 to 120 ° C., but in the present invention, it is preferably 50 to 90 ° C. from the viewpoint of stable reaction. If the polymerization temperature is too high, the acrylic resin (A) tends to gel easily, and if it is too low, the activity of the polymerization initiator decreases, so that the polymerization rate tends to decrease and the residual monomers tend to increase.

The polymerization time in the polymerization reaction is not particularly limited, but is 0.5 hours or more, preferably 1 hour or more, more preferably 2 hours or more, and particularly preferably 5 hours or more after the last addition of the polymerization initiator.
The polymerization reaction is preferably carried out while refluxing the solvent because it is easy to remove heat.
Thus, the acrylic resin (A) used in the present invention can be produced.

As described above, the acrylic resin (A) used in the present invention can be produced, and the acrylic resin (A) preferably has a weight average molecular weight of 10,000 to 1,000,000, more preferably 5. It is 10,000 to 400,000, particularly preferably 100,000 to 300,000, and even more preferably 150,000 to 280,000. If the weight average molecular weight is too large, the viscosity tends to be too high, and the coatability and handling tend to be deteriorated. If the weight average molecular weight is too small, the cohesive force tends to be lowered and the adhesive characteristics tend to be lowered.
The weight average molecular weight of the acrylic resin (A) is the weight average molecular weight at the time of completion of production, and is the weight average molecular weight of the acrylic resin (A) that has not been heated after production.

The dispersity (weight average molecular weight / number average molecular weight) of the acrylic resin (A) is preferably 15 or less, more preferably 10 or less, particularly preferably 7 or less, and further preferably 5 or less. If the degree of dispersion is too high, the durability of the pressure-sensitive adhesive layer is lowered, and foaming or the like tends to occur easily. If the degree of dispersion is too low, the handleability tends to be lowered. The lower limit of the dispersity is usually 1.1 from the point of view of the manufacturing limit.

The above weight average molecular weight is a weight average molecular weight converted to a standard polystyrene molecular weight, and is used on a high performance liquid chromatograph (“Waters 2695 (main body)” and “Waters 2414 (detector)” manufactured by Japan Waters Co., Ltd.). : Chromatography GPC KF-806L (exclusion limit molecular weight: 2 × 10 ⁷ , separation range: 100 to 2 × 10 ⁷ , theoretical number of stages: 10000 stages / piece, filler material: styrene-divinylbenzene copolymer, filler particle size : 10 μm) is measured by using three in series, and the number average molecular weight can also be measured by the same method. The degree of dispersion is obtained from the weight average molecular weight and the number average molecular weight.

The acrylic resin (A) used in the present invention has a glass transition temperature (Tg) of −10 to 15 ° C., preferably −7 to 12 ° C., more preferably −5 to 10 ° C., and particularly preferably 0 to 0 to It is 8 ° C. If the glass transition temperature is too high, the adhesive strength tends to decrease as the step followability of the adhesive layer decreases and the adhesiveness decreases. If the glass transition temperature is too low, the sticky physical properties at the time of low cross-linking tend to decrease.

The glass transition temperature (Tg) of the acrylic resin (A) is determined by the following measuring method.
The release sheet is peeled off from the pressure-sensitive adhesive sheet before irradiation with active energy rays, which will be described later, and a plurality of pressure-sensitive adhesive sheets are laminated to prepare a pressure-sensitive adhesive sheet having a thickness of about 800 μm in an uncrosslinked state. The dynamic viscoelasticity of the prepared sheet was measured under the following conditions, and the temperature at which the loss positive contact (loss elastic modulus G'' / storage elastic modulus G'= tanδ) was maximized was read, and the acrylic resin (A) was used. The glass transition temperature (Tg) of.

(Measurement condition)
Measuring equipment: Dynamic viscoelasticity measuring device (trade name: DVA-225, manufactured by IT Measurement Control Co., Ltd.)
Deformation mode: Shear strain: 0.1%
Measurement temperature: -100 to 60 ° C
Measurement frequency: 1Hz

The pressure-sensitive adhesive composition of the present invention preferably contains the acrylic resin (A) in an amount of 80% by weight or more, more preferably 90 to 99.9% by weight, and particularly preferably 92, based on the entire pressure-sensitive adhesive composition. The content is ~ 99.9% by weight.

[Crosslinking agent (B)]
The pressure-sensitive adhesive composition of the present invention contains a cross-linking agent (B). As the cross-linking agent (B), it is preferable to contain an active energy ray cross-linking agent (B1) and / or a thermal cross-linking agent (B2) such as a monofunctional cross-linking agent and a polyfunctional cross-linking agent.
When only the active energy ray cross-linking agent (B1) is contained as the cross-linking agent (B), multi-stage curing is possible by controlling the active energy dose, and the active energy ray cross-linking agent (B1) is used as the cross-linking agent (B). In the case of containing the heat curing agent (B2), multi-stage curing is possible by using both heat curing and active energy ray curing. By controlling the cross-linking reaction in this way, the cohesive force of the entire pressure-sensitive adhesive layer can be adjusted, and stable pressure-sensitive physical properties can be obtained after primary curing or complete curing.

(Active energy ray cross-linking agent (B1))
The active energy ray cross-linking agent (B1) is a monofunctional cross-linking agent containing one ethylenically unsaturated group in one molecule, and a polyfunctional cross-linking agent containing two or more ethylenically unsaturated groups in one molecule. Examples thereof include a sex cross-linking agent (B1-1), and a polyfunctional cross-linking agent (B1-1) is particularly preferable.

Examples of the polyfunctional cross-linking agent (B1-1) include hexanediol di (meth) acrylate, butanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, and 1,10-decanediol di. (Meta) acrylate, (poly) ethylene glycol mono (meth) acrylate, (poly) butylene glycol mono (meth) acrylate, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, ( Poly) tetramethylene glycol di (meth) acrylate, (poly) pentamethylene glycol di (meth) acrylate, (poly) hexamethylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, pentaerythritol di (meth) Acrylic, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, trimethylolpropane tri (meth) acrylate, EO-modified trimethylolpropane tri (meth) acrylate, glycerintri (meth) acrylate, EO-modified glycerintri Examples thereof include (meth) acrylate, tetramethylolmethanetri (meth) acrylate, isocyanuric acid ethylene oxide-modified tri (meth) acrylate, allyl (meth) acrylate, vinyl (meth) acrylate, and urethane (meth) acrylate.
In addition, one kind selected from the said polyfunctional cross-linking agent (B1-1) may be used alone, or two or more kinds may be used in combination. Among them, (meth) acrylate containing two ethylenically unsaturated groups is preferable, and (poly) ethylene glycol di (meth) acrylate and (poly) propylene glycol are particularly preferable in terms of the balance of the adhesive property after curing. Di (meth) acrylate and (poly) tetramethylene glycol di (meth) acrylate are preferred.

The content of the active energy ray cross-linking agent (B1) is usually preferably 0.01 to 20 parts by weight, more preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the acrylic resin (A). It is particularly preferably 0.5 to 7.5 parts by weight.
If the amount of the active energy ray cross-linking agent (B1) is too small, the cohesive force tends to be insufficient and sufficient durability tends not to be obtained, and if it is too large, the adhesive physical properties at the time of primary curing tend to decrease.

(Thermal crosslinker (B2))
The heat crosslinking agent (B2) used in the present invention exhibits excellent adhesive strength mainly by reacting with a functional group derived from a functional group-containing monomer which is a constituent monomer of the acrylic resin (A). Examples thereof include isocyanate-based cross-linking agents, epoxy-based cross-linking agents, aziridine-based cross-linking agents, melamine-based cross-linking agents, aldehyde-based cross-linking agents, amine-based cross-linking agents, and metal chelate-based cross-linking agents. Among these, the isocyanate-based cross-linking agent (B2-1) is preferably used in terms of improving the adhesion to the substrate and the reactivity with the acrylic resin (A).

Examples of the isocyanate-based cross-linking agent (B2-1) include tolylene diisocyanate compounds such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, and 1,4-. Xylylene diisocyanate compounds such as xylylene diisocyanate and tetramethylxylylene diisocyanate, aromatic isocyanate compounds such as 1,5-naphthalenedi isocyanate and triphenylmethane triisocyanate; hexamethylene diisocyanate such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate. Hydroisocyanate compounds such as lysine diisocyanates and aliphatic isocyanate compounds; alicyclic isocyanate compounds such as isophorone diisocyanates; and adducts of these isocyanate compounds and polyol compounds such as trimethylolpropane; Isocyanurates; etc.
Among the above isocyanate-based cross-linking agents (B2-1), it is preferable to use an aromatic isocyanate-based compound from the viewpoint of excellent reactivity, and a tolylene-based isocyanate-based compound is particularly preferable. Further, from the viewpoint of suppressing yellowing, it is preferable to use an aliphatic isocyanate-based compound, and a hexamethylene diisocyanate-based compound is particularly preferable.

Examples of the epoxy-based cross-linking agent include bisphenol A / epichlorohydrin type epoxy resin, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, and 1,6-hexanediol diglycidyl ether. , Trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl erythritol, diglycerol polyglycidyl ether and the like.

Examples of the aziridine-based cross-linking agent include tetramethylolmethane-tri-β-aziridinylpropionate, trimethylolpropane-tri-β-aziridinylpropionate, and N, N'-diphenylmethane-4,4. ′ -Bis (1-aziridine carboxylamide), N, N'-hexamethylene-1,6-bis (1-aziridine carboxylamide) and the like can be mentioned.

Examples of the melamine-based cross-linking agent include hexmethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexaptoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, and melamine resin. ..

Examples of the aldehyde-based cross-linking agent include glioxal, malondialdehyde, succindialdehyde, maleindialdehyde, glutardaldehyde, formaldehyde, acetaldehyde, and benzaldehyde.

Examples of the amine-based cross-linking agent include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetraamine, diethylenetriamine, triethyltetraamine, isophoronediamine, amino resin, and polyamide.

Examples of the metal chelate-based cross-linking agent include acetylacetone and acetoacetyl ester coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, panadium, chromium and zirconium. Can be mentioned.

Further, these thermal cross-linking agents (B2) may be used alone or in combination of two or more.

The content of the heat-crosslinking agent (B2) is usually preferably 0.001 to 5 parts by weight, more preferably 0.02 to 1 part by weight, based on 100 parts by weight of the acrylic resin (A). Particularly preferably, it is 0.05 to 0.5 parts by weight.
If the amount of the heat-crosslinking agent (B2) is too small, the cohesive force is insufficient and the adhesive physical properties tend to decrease at the time of primary curing, and if it is too large, the adhesive force tends to decrease at the time of complete curing.

The content of the cross-linking agent (B) is usually 20 parts by weight or less, preferably 0.001 to 15 parts by weight, and more preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the acrylic resin (A). It is a part by weight. If the amount of such a cross-linking agent is too large, the adhesive strength tends to decrease. If the amount is too small, the adhesive property under high temperature conditions tends to decrease.

As the cross-linking agent (B), it is preferable to use an active energy ray cross-linking agent (B1) and a thermal cross-linking agent (B2) in combination. When used in combination, the content ratio (weight ratio) of the active energy ray cross-linking agent (B1) and the thermal cross-linking agent (B2) is preferably 100/1 to 100/50, more preferably 100/4 to 100/10.

[Photopolymerization initiator]
The pressure-sensitive adhesive composition of the present invention can be crosslinked (cured) into a pressure-sensitive adhesive, but may further contain a photopolymerization initiator in order to carry out the cross-linking efficiently. In particular, when the acrylic resin (A) does not have the above-mentioned active energy ray-crosslinkable structural site, it is preferable to add a photopolymerization initiator.

The photopolymerization initiator is not particularly limited as long as it generates radicals by the action of active energy rays, and for example, photopolymerization of acetophenones, benzoins, benzophenones, thioxanthones, acylphosphine oxides and the like. Initiators are mentioned. These photopolymerization initiators may be used alone or in combination of two or more. Further, among these photopolymerization initiators, it is preferable to use hydrogen abstraction type benzophenones and intramolecular cleavage type acetophenones photopolymerization initiators from the viewpoint of being able to efficiently crosslink between molecules or within molecules.

Examples of the photopolymerization initiator of benzophenones include benzophenone, 4-methylbenzophenone, 2,4,6-trimethylmethylbenzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone and the like. Be done. One type selected from these may be used alone, or two or more types may be used in combination.

Examples of the intramolecular cleavage type acetophenone photopolymerization initiator include oxyphenyl-acetic acid 2- [2-oxo-2-phenylacetoxyethoxy] ethyl ester.

Other photopolymerization initiators include, for example, diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethylketal, 4- (2-hydroxyethoxy) phenyl- (2-hydroxy). -2-propyl) Ketone, 1-Hydroxycyclohexylphenyl Ketone, 2-Methyl-2-morpholino (4-thiomethylphenyl) propan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) ) Butanone, acetophenones such as 2-hydroxy-2-methyl-1- [4- (1-methylvinyl) phenyl] propanone oligomer; benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, etc. Phenyl benzoins; 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, 1-chloro-4-propoxythioxanthone, 2- (3-dimethylamino-2-hydroxy)- Thioxanthones such as 3,4-dimethyl-9H-thioxanthone-9-onemesochloride; 2,4,6-trimethylbenzoyl-diphenylphosphinoxide, bis (2,6-dimethoxybenzoyl) -2,4,4- Examples thereof include acylphosphon oxides such as trimethyl-pentylphosphine oxide and bis (2,4,6-trimethylbenzoyl) -phenylphosphin oxide.

The content of the photopolymerization initiator is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, particularly preferably 0.1 part by weight, based on 100 parts by weight of the acrylic resin (A). Is 0.5 to 2 parts by weight. When the content of the photopolymerization initiator is within the above range, sufficient curability can be obtained even when the acrylic resin (A) does not have the above-mentioned active energy ray-crosslinkable structural site, for example. can.

In addition, as an auxiliary agent for these photopolymerization initiators, triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Mihiler ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethyl benzoic acid, 4- Ethyl dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate (n-butoxy), isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 2,4-diethylthioxanson, 2,4- It is also possible to use diisopropylthioxanson or the like in combination. One type selected from these may be used alone, or two or more types may be used in combination.

[Carbodiimide compound]
In addition to the acrylic resin (A) and the cross-linking agent (B), it is preferable to further contain a carbodiimide-based compound as a constituent component of the pressure-sensitive adhesive composition of the present invention from the viewpoint of heat resistance.
Examples of the carbodiimide-based compound include bis (2,6-diisopropylphenyl) carbodiimide, dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, and di-t-butylcarbodiimide. , Monocarbodiimide such as didodecylcarbodiimide, polycarbodiimide in which a plurality of carbodiimides are present, cyclic carbodiimide, and the like. One of these can be used alone or in combination of two or more. Among these, monocarbodiimide-based compounds and bis (2,6-diisopropylphenyl) carbodiimide are preferable from the viewpoint of heat resistance.

The content of the carbodiimide-based compound in the present invention is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, particularly, with respect to 100 parts by weight of the acrylic resin (A). It is preferably 0.2 to 2 parts by weight, more particularly preferably 0.3 to 1 part by weight.
If the content of the carbodiimide-based compound is too small, the thermal stability of the acrylic resin (A) tends to decrease, and if it is too large, the durability tends to decrease due to the influence of bleed-out or the like.

Further, the pressure-sensitive adhesive composition of the present invention may contain other pressure-sensitive adhesives as necessary, or may contain conventionally known additives such as a cross-linking accelerator, an antistatic agent, a pressure-sensitive adhesive, and a functional dye. You may.
The content of the other pressure-sensitive adhesives and additives is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, based on 100 parts by weight of the acrylic resin (A).

Thus, the pressure-sensitive adhesive composition of the present invention can be obtained by mixing an acrylic resin (A), a cross-linking agent (B), a photopolymerization initiator and other optional components, if necessary. The mixing method is not particularly limited, and various methods such as a method of mixing each component in a batch, a method of mixing an arbitrary component, and then a method of mixing the remaining components in a batch or sequentially are adopted. can do.

<Adhesive>
The pressure-sensitive adhesive composition of the present invention is adhered by cross-linking (curing) the pressure-sensitive adhesive composition or, when the acrylic resin (A) has an active energy ray-crosslinkable structural site, by irradiation with active energy rays. The acrylic resin (A) contained in the agent composition forms a crosslinked structure in at least one of the molecules and in the molecule, and becomes the pressure-sensitive adhesive according to the present invention.
The pressure-sensitive adhesive of the present invention has multi-stage curability that can be cured in a plurality of stages, and is in a low crosslinked state by primary curing before complete curing. Complete curing and primary curing are not clearly distinguishable, but can be distinguished by differences in gel fraction and dynamic viscoelasticity.
In any of the primary curing step and the complete curing step, the curing means is not particularly limited, and either heating or irradiation with active energy rays may be used. Further, the primary curing step may be performed in a plurality of times, or multi-stage curing may be performed in order to achieve a completely cured state.
The pressure-sensitive adhesive of the present invention has excellent adhesive physical properties after primary curing, and is suitably used for bonding optical members constituting a touch panel, an image display device, or the like.

<Adhesive sheet>
The pressure-sensitive adhesive layer made of the pressure-sensitive adhesive of the present invention can be provided on a base sheet to form a pressure-sensitive adhesive sheet, and the pressure-sensitive adhesive layer can be provided on a release sheet to form a double-sided pressure-sensitive adhesive sheet. .. Further, a double-sided pressure-sensitive adhesive sheet without a base material can be produced by forming an adhesive layer on the release sheet instead of the base material sheet and attaching the release sheet to the pressure-sensitive adhesive layer surface on the opposite side. .. It is also possible to further form a pressure-sensitive adhesive layer on the formed pressure-sensitive adhesive layer to form a thick-film pressure-sensitive adhesive layer.
At the time of use, the obtained pressure-sensitive adhesive sheet or double-sided pressure-sensitive adhesive sheet is used by peeling the release sheet from the pressure-sensitive adhesive layer.

Examples of the method for producing the pressure-sensitive adhesive sheet include (i) a method in which the pressure-sensitive adhesive composition of the present invention is dissolved in a solvent and coated to obtain a pressure-sensitive adhesive sheet, and (ii) the pressure-sensitive adhesive composition of the present invention is melted by heating. Examples include a method of using an adhesive sheet.

First, the method (i) will be described.
When the pressure-sensitive adhesive composition of the present invention is dissolved in a solvent and coated to obtain a pressure-sensitive adhesive sheet, the concentration of the coating liquid containing the pressure-sensitive adhesive composition of the present invention is adjusted with an appropriate organic solvent to obtain a base material. Apply directly on the sheet. Then, for example, it is dried by heat treatment at 80 to 105 ° C. for 0.5 to 10 minutes, and this is attached to a base sheet or a release sheet. After that, the pressure-sensitive adhesive composition is crosslinked (cured) by aging, and further irradiated with active energy rays as needed, whereby a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the above-mentioned pressure-sensitive adhesive can be produced.

As the organic solvent used for the concentration adjustment, those listed as the organic solvent used for the polymerization reaction of the acrylic resin (A) can be used. The concentration of the pressure-sensitive adhesive composition is usually 20 to 60% by weight, preferably 30 to 50% by weight as a solid content.

Next, the method (ii) will be described.
When the pressure-sensitive adhesive composition of the present invention is melted by heating to form a pressure-sensitive adhesive sheet, a method of applying the pressure-sensitive adhesive composition to one or both sides of the base material sheet in the melted state and then cooling the base sheet, or using a T-die or the like on the base material sheet. An adhesive layer is formed on one side or both sides of the base sheet so as to have a predetermined thickness by a method of extruding and laminating. Then, if necessary, the release sheet can be attached to the pressure-sensitive adhesive layer surface to produce a pressure-sensitive adhesive sheet.
Further, after forming the pressure-sensitive adhesive layer on the base material sheet, an active energy ray irradiation treatment is performed as necessary, and further aging is performed to cure (crosslink) the pressure-sensitive adhesive composition. Sheets can be made.
Further, by forming a pressure-sensitive adhesive layer on the release sheet and attaching the release sheet to the pressure-sensitive adhesive layer surface on the opposite side, a substrate-less double-sided pressure-sensitive adhesive sheet can be produced.
At the time of use, the obtained pressure-sensitive adhesive sheet or double-sided pressure-sensitive adhesive sheet is used by peeling the release sheet from the pressure-sensitive adhesive layer.

Examples of the base sheet include polyester resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate / isophthalate copolymers; polyolefin resins such as polyethylene, polypropylene, and polymethylpentene; Polyfluoroethylene resin such as polyvinylidene polyfluoride and ethylene polyfluoride; polyamide such as nylon 6, nylon 6,6; polyvinyl chloride, polyvinyl chloride / vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl Vinyl polymers such as alcohol copolymers, polyvinyl alcohol and vinylon; cellulose-based resins such as cellulose triacetate and cellophane; acrylic resins such as methyl polymethacrylate, ethyl polymethacrylate, ethyl polyacrylate and butyl polyacrylate. ; Polystyrene; Polycarbonate; Polyallylate; Synthetic resin sheets such as polyimide, metal foils such as aluminum, copper, and iron, high-quality paper, paper such as glassin paper, glass fibers, natural fibers, synthetic fibers, and other textiles and non-woven fabrics. Be done. These base material sheets can be used as a single layer or as a multi-layer in which two or more kinds are laminated. Among these, the synthetic resin sheet is preferable from the viewpoint of weight reduction and the like.

As the release sheet, for example, various synthetic resin sheets, paper, woven fabrics, non-woven fabrics and the like exemplified for the above-mentioned base material sheet can be used after being released. As the release sheet, for example, it is preferable to use a silicon-based release sheet.

The method for applying the pressure-sensitive adhesive composition is not particularly limited, and examples thereof include roll coating, die coating, gravure coating, comma coating, slot coating, and screen printing.

As the active energy rays, far-ultraviolet rays, ultraviolet rays, near-ultraviolet rays, infrared rays and the like; electromagnetic waves such as X-rays and γ-rays; electron beams; proton rays; neutron rays and the like can be used. It is preferable to cure with ultraviolet rays because of its availability and price.

Regarding the gel fraction before the adhesive layer of the adhesive sheet is completely cured, it can be easily bonded regardless of the shape of the adherend, and the adhesive layer holds the adherend after bonding. From the possible point of view, it is preferably 5 to 60% by weight, more preferably 10 to 50% by weight, and particularly preferably 20 to 48% by weight.

The gel fraction after complete curing of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is preferably 40 to 100% by weight, more preferably 45 to 90% by weight, and particularly preferably 45 to 90% by weight from the viewpoint of durability and adhesive strength. It is 48 to 80% by weight. If the gel fraction is too low, the cohesive force tends to decrease and the durability tends to decrease. If the gel fraction is too high, the cohesive force tends to increase and the adhesive force tends to decrease.

Adjusting the gel fraction to the above range may, for example, adjust the amount of active energy ray irradiation, the content of the active energy ray crosslinkable structural part in the acrylic resin (A), the crosslinker (B), or light. This is achieved by adjusting the type and amount of the polymerization initiator.

The gel fraction is a measure of the degree of cross-linking (curing degree), and is calculated by, for example, the following method. That is, an adhesive sheet (without a release sheet) having an adhesive layer formed on a polymer sheet (for example, polyethylene terephthalate (PET) film) as a base material is wrapped with a 200 mesh SUS wire mesh. , Immersed in toluene maintained 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 base material is subtracted from the weight before and after the dissolution of toluene.

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 100 to 350 μm. If the thickness of the pressure-sensitive adhesive layer is too thin, the shock absorption tends to decrease, and if it is too thick, the entire thickness tends to increase when the adhesive layer is attached to an optical member, for example, and the practicality tends to decrease.

The thickness of the pressure-sensitive adhesive layer in the present invention is a measured value of the thickness of the constituent members other than the pressure-sensitive adhesive layer from the measured value of the entire thickness of the pressure-sensitive adhesive layer-containing laminate using "ID-C112B" manufactured by Mitutoyo. It is a value obtained by subtracting.

The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention preferably has a haze value of 2% or less when the thickness of the pressure-sensitive adhesive layer is 100 μm, more preferably 0 to 1.5%, and particularly preferably 0 to 1%. Is. If the haze value is too high, the adhesive layer tends to whiten and the transparency tends to decrease.
The haze value is the value of the diffuse transmittance (DT) and the total light transmittance (TT) obtained by measuring the diffuse transmittance and the total light transmittance using HAZE MATER NDH4000 (manufactured by Nippon Denshoku Kogyo Co., Ltd.). Was calculated by substituting into the following equation 1. This machine complies with JIS K7361-1.
[Equation 1] Haze value (%) = (DT / TT) × 100

In the present invention, the optical member with the pressure-sensitive adhesive layer can be obtained by laminating and forming the pressure-sensitive adhesive layer on the optical member. For example, an optical member with an adhesive layer can be obtained by attaching the adhesive layer surface of the adhesive sheet of the present invention having an adhesive layer formed on the release sheet to an optical member and then peeling off the release sheet. Can be done. Further, the optical members can be bonded to each other by using the above-mentioned double-sided adhesive sheet.

Examples of the optical member include a member constituting a touch panel and an image display device, for example, a display (organic EL, liquid crystal display), a transparent conductive film substrate (ITO substrate), a protective film (glass), a transparent antenna (film), and the like. Examples include transparent wiring.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In the example, "part" and "%" mean the weight standard. Further, the weight average molecular weight and the glass transition temperature of the acrylic resin (A) were measured according to the above-mentioned method.

[Manufacturing Example 1: Production of Acrylic Resin [A-1]]
In a 2 L flask equipped with a cooler, 24 parts of ethyl acetate (boiling point 77 ° C.), 16 parts of methyl ethyl ketone (boiling point 80 ° C.) as the polymerization solvent, and 2,2'-azobis (2,4-dimethylvaleronitrile) as the polymerization initiator (2,4-dimethylvaleronitrile) ( ADVN: 10-hour half-life temperature 52 ° C.) 0.01 part, premixed monomer solution (15 parts methyl acrylate (MA: a1, Tg = -7 ° C), ethyl methacrylate (EMA: a2, Tg = 65 ° C) 25 Add 10% of 100 parts of a mixed solution of 15 parts of 2-hydroxyethyl acrylate (HEA: a3) and 45 parts of 2-ethylhexyl acrylate (2EHA: a5), heat and reflux in the flask, and then ADVN0. .2 parts, the remaining 90% of the above-mentioned monomer solution was added dropwise over 3 hours. Further, 30 minutes after the dropping, a mixture of 10 parts of ethyl acetate and 0.17 part of ADVN was dropped over 1 hour to react, and the acrylic resin [A-1] (weight average molecular weight: 260,000, dispersity: 3.05). , Glass transition temperature -2 ° C) solution was obtained.

[Production Example 2, Production Example 3, Comparative Production Example 1]
Acrylic resins [A-2], [A-3] and [A'-1] were produced in the same manner as in Production Example 1 except that the copolymerization components of the acrylic resin were as shown in Table 1.
The acrylic resin [A-2] had a weight average molecular weight of 260,000, a dispersity of 2.97, and a glass transition temperature of −7 ° C.
The acrylic resin [A-3] had a weight average molecular weight of 180,000, a dispersity of 2.73, and a glass transition temperature of 5 ° C.
The acrylic resin [A'-1] had a weight average molecular weight of 260,000, a dispersity of 3.45, and a glass transition temperature of -13 ° C.

* MA: Methyl acrylate EMA: Ethyl methacrylate HEA: 2-Hydroxyethyl acrylate 2EHA: 2-Ethylhexyl acrylate

<Example 1>
Coronate L55E (manufactured by Tosoh Corporation) 0.3 part (solid content equivalent) and polypropylene glycol # 400 diacrylate (solid content equivalent) as a cross-linking agent for 100 parts (solid content equivalent) of the acrylic resin [A-1] solution. NK Ester APG400) (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.) 5.0 parts (in terms of solid content), Omnirad 184 (manufactured by IGM Resins B.V.) as a photopolymerization initiator, 0.25 parts (in terms of solid content) and 0.75 parts (in terms of solid content) of Polymer 754 (manufactured by IGM Resins B.V.) was mixed to obtain a pressure-sensitive adhesive composition. The obtained pressure-sensitive adhesive composition solution is adjusted to a solid content concentration of 50% with ethyl acetate, applied to a polyester-based mold release sheet so that the thickness after drying is about 50 μm, and dried at 100 ° C. for 5 minutes. , A pressure-sensitive adhesive composition layer was formed.

Two polyester-based mold release sheets on which the pressure-sensitive adhesive composition layer was formed were prepared in this way, and both pressure-sensitive adhesive composition layers were laminated so as to face each other. A pressure-sensitive adhesive layer is formed by allowing the laminated pressure-sensitive adhesive composition layer to stand at 40 ° C. for 3 days with both sides sandwiched between polyester-based release sheets (primary curing), and the thickness of the pressure-sensitive adhesive layer is 100 μm. A substrate-less double-sided adhesive sheet was obtained.
Further, the release sheet on one side is peeled off from the pressure-sensitive adhesive layer of the base-less double-sided pressure-sensitive adhesive sheet obtained above, and the exposed pressure-sensitive adhesive layer side is pressed against an easy-adhesion-treated polyethylene terephthalate (PET) sheet (thickness 125 μm). Then, a PET sheet with an adhesive layer having a thickness of 100 μm was obtained.

<Examples 2 to 4, Comparative Example 1>
Both sides without a base material in the same manner as in Example 1 except that the acrylic resin [A-1] is changed to the acrylic resin [A-2], the acrylic resin [A-3] or [A'-1]. A pressure-sensitive adhesive sheet and a PET sheet with a pressure-sensitive adhesive layer were obtained, respectively.
The composition of each pressure-sensitive adhesive composition is summarized in Table 2.

[Gel fraction: before complete curing (after primary curing)]
After cutting the base material-less double-sided adhesive sheet to 40 mm × 40 mm and allowing it to stand for 30 minutes under the condition of 23 ° C. × 50% RH, one of the release sheets is peeled off, and the exposed adhesive layer side is 50 mm ×. It was affixed to a 100 mm SUS mesh sheet (200 mesh). The remaining release sheet was peeled off, folded back from the center in the longitudinal direction of the SUS mesh sheet, and the adhesive layer was wrapped with the SUS mesh sheet. The gel fraction (%) was measured by the weight change when the product was immersed in a sealed container containing 250 g of toluene maintained at 23 ° C. for 24 hours.

[Gel fraction: after complete curing]
The base material-less double-sided adhesive sheet is irradiated with ultraviolet rays with a high-pressure mercury UV irradiation device at a peak illuminance of 150 mW / cm ² and an integrated exposure amount of 3000 mJ / cm ² (1000 mJ / cm ² x 3 passes), and then 40 mm. It was cut into × 40 mm and allowed to stand for 30 minutes under the conditions of 23 ° C. × 50% RH. Then, one of the release sheets was peeled off, and the exposed adhesive layer side was attached to a 50 mm × 100 mm SUS mesh sheet (200 mesh). The remaining release sheet was peeled off, folded back from the center in the longitudinal direction of the SUS mesh sheet, and the adhesive layer was wrapped with the SUS mesh sheet. The gel fraction (%) was measured by the weight change when the product was immersed in a sealed container containing 250 g of toluene maintained at 23 ° C. for 24 hours.
Table 2 summarizes the gel fractions before and after complete curing (after primary curing) and after complete curing.

[Probe Tack: Before complete curing (after primary curing)]
The PET sheet with the pressure-sensitive adhesive layer is cut into a size of 12 mm in width × 12 mm in length, the release sheet is peeled off, and the PET sheet is added using a probe tack tester (Probe Tuck Tester TE-6001 manufactured by Tester Sangyo Co., Ltd.). Probe tack (unit: N / 2 kPa) is measured under the conditions of pressure time 1 second, pasting pressure 20.4 gf / cm ² , pushing speed 120 mm / min, pulling speed 600 mm / min, and probe diameter 5.1 mm (diameter). did. The evaluation criteria are as follows. The results are summarized in Table 3.
(Evaluation criteria)
◎ ・ ・ ・ Probe tack (unit: N / 2kPa) is less than 3 〇 ・ ・ ・ Probe tack (unit: N / 2kPa) is 3 or more and less than 6 △ ・ ・ ・ Probe tack (unit: N / 2kPa) is 6 More than 9 × ・ ・ ・ Probe tack (unit: N / 2kPa) is 9 or more

[Constant load holding force (50 ° C): Before complete curing (after primary curing)]
The PET sheet with the adhesive layer is cut into a size of 25 mm in width × 75 mm in length (width 25 mm × length 50 mm of the adhesive layer portion + width 25 mm × length 25 mm of the non-adhesive layer portion), and the release sheet is cut. It peeled off. The exposed adhesive layer side was pressure-bonded (pasting area 25 mm × 50 mm) by reciprocating a 2 kg roller on a stainless steel plate (SUS304), and allowed to stand in an atmosphere of 50 ° C. for 20 minutes. After that, a 50 g weight is hung at the end in the length direction of the non-attached portion (area 25 mm × 25 mm), a load of 50 g is applied in the direction of 90 ° to the flat surface of the stainless steel plate, and the mixture is allowed to stand for 60 minutes in that state. , The distance from which the PET sheet was peeled off was measured. The evaluation criteria are as follows. The results are summarized in Table 3.
(Evaluation criteria)
◎ ・ ・ ・ Peeling distance is less than 5 mm ○ ・ ・ ・ Peeling distance is 5 mm or more and less than 10 mm △ ・ ・ ・ Peeling distance is 10 mm or more and less than 50 mm × ・ ・ ・ Drop

[180 degree peel strength (23 ° C): after complete curing]
The PET sheet with the adhesive layer is cut into a size of 25 mm in width × 100 mm in length, and a high-pressure mercury UV irradiation device is used to achieve a peak illuminance of 150 mW / cm ² and an integrated exposure amount of 3000 mJ / cm ² (1000 mJ / cm). After irradiating with ultraviolet rays in ² × 3 passes), the release sheet was peeled off. The exposed adhesive layer side is pressure-bonded to non-alkali glass (Corning's "Eagle XG", thickness 1.1 mm) at 23 ° C and 50% RH with 2 reciprocating 2 kg rubber rollers, and under the same atmosphere. It was allowed to stand for 30 minutes. After that, the peel strength (N / 25 mm) of 180 degrees was measured at a peeling speed of 300 mm / min at room temperature (23 ° C.). The results are summarized in Table 3.

[Holding power (80 ° C): after complete curing]
The PET sheet with the adhesive layer is cut into a size of 25 mm × 50 mm, and a high-pressure mercury UV irradiation device is used to achieve a peak illuminance of 150 mW / cm ² and an integrated exposure amount of 3000 mJ / cm ² (1000 mJ / cm ² × 3). After irradiating with ultraviolet rays in the pass), the release sheet was peeled off. The exposed adhesive layer side is reciprocated on a stainless steel plate (SUS304) with a 2 kg roller to apply pressure (pasting area 25 mm x 25 mm), and a creep tester (manufactured by Tester Sangyo Co., Ltd., holding force test with constant temperature and humidity chamber). Using the machine BE-501), a load of 1 kg was applied for 24 hours in an atmosphere of 80 ° C., and the holding force was measured. The evaluation criteria are as follows. The results are summarized in Table 3.
(Evaluation criteria)
〇 ・ ・ ・ No deviation △ ・ ・ ・ Misalignment is less than 1.0 mm × ・ ・ ・ Misalignment is 1.0 mm or more, or drops

[Constant load holding force (80 ° C): after complete curing]
The PET sheet with the adhesive layer is cut into a size of 25 mm in width × 75 mm in length (width 25 mm × length 50 mm of the adhesive layer portion + width 25 mm × length 25 mm of the non-adhesive layer portion) and irradiated with high-pressure mercury UV. After irradiating with ultraviolet rays at a peak illuminance of 150 mW / cm ² and an integrated exposure amount of 3000 mJ / cm ² (1000 mJ / cm ² × 3 passes), the release sheet was peeled off. The exposed adhesive layer side was pressure-bonded (pasting area 25 mm × 50 mm) by reciprocating a 2 kg roller on a stainless steel plate (SUS304), and allowed to stand in an atmosphere of 80 ° C. for 20 minutes. After that, a 50 g weight is hung at the end in the length direction of the non-attached portion (area 25 mm × 25 mm), a load of 50 g is applied in the direction of 90 ° to the flat surface of the stainless steel plate, and the mixture is allowed to stand for 60 minutes in that state. , The distance from which the PET sheet was peeled off was measured. The evaluation criteria are as follows. The results are summarized in Table 3.
(Evaluation criteria)
○ ・ ・ ・ Peeling distance is less than 10 mm △ ・ ・ ・ Peeling distance is 10 mm or more and less than 50 mm × ・ ・ ・ Drop

[Moisture resistance: after complete curing]
The PET sheet with the adhesive layer is cut into a size of 30 mm × 50 mm, and a high-pressure mercury UV irradiation device is used to obtain a peak illuminance of 150 mW / cm ² and an integrated exposure amount of 3000 mJ / cm ² (1000 mJ / cm ² × 3). After irradiating with ultraviolet rays in the pass), the release sheet was peeled off. The exposed adhesive layer side is bonded to non-alkali glass (Corning's "Eagle XG", thickness 1.1 mm) and then autoclaved (50 ° C, 0.5 MPa, 20 minutes) at 23 ° C, 50. It was allowed to stand for 30 minutes in an atmosphere of% RH to prepare a test piece having a composition of "non-alkali glass / adhesive layer / PET".

Using the obtained test piece, a moist heat resistance test was conducted for 7 days (168 hours) in an atmosphere of 60 ° C. and 90% RH, and haze values were measured before the start of the moist heat resistance test and after the moist heat resistance test.
The haze value is the value of the diffuse transmittance (DT) and the total light transmittance (TT) obtained by measuring the diffuse transmittance and the total light transmittance using HAZE MATER NDH4000 (manufactured by Nippon Denshoku Kogyo Co., Ltd.). Was calculated by substituting into the following equation 1. Further, the rate of increase (%) of the haze value was calculated from the following equation 2. This machine complies with JIS K7361-1. The results are summarized in Table 3.
[Equation 1] Haze value (%) = (DT / TT) × 100
[Equation 2] Haze value increase rate (%) = {(Haze value after moisture resistance test-Haze value before start of moisture resistance test) / Haze value before start of moisture resistance test} × 100
(Evaluation criteria)
○ ・ ・ ・ Rise rate is less than 100% × ・ ・ ・ Rise rate is 100% or more

The pressure-sensitive adhesive sheet using the pressure-sensitive adhesive compositions of Examples 1 to 4 has excellent pressure-sensitive adhesive properties such as low tackiness and high constant load holding power even in a low cross-linking state before complete curing (after primary curing). There was, and the adhesive property was excellent even after complete curing.
On the other hand, the pressure-sensitive adhesive sheet using the pressure-sensitive adhesive composition of Comparative Example 1 in which the glass transition temperature of the acrylic resin (A) is outside the range of −10 to 15 ° C. is primary cured as compared with Examples 1 to 4. It was inferior in adhesive properties in the later hypocrosslinked state.

The pressure-sensitive adhesive using the pressure-sensitive adhesive composition of the present invention has excellent adhesive properties in a low-crosslinked state after primary curing, and is particularly suitable for bonding optical members constituting a touch panel, an image display device, or the like, or an organic EL display. It is useful as an adhesive used for sealing applications and the like.

Claims (8)

A pressure-sensitive adhesive composition containing an acrylic resin (A) and a cross-linking agent (B).
The acrylic resin (A) is
Alkyl acrylate (a1) having a glass transition temperature of −27 to 50 ° C. when homopolymer is formed is 5% by weight or more.
A copolymerization component (a) containing 10% by weight or more of an alkyl methacrylate (a2) having a glass transition temperature of 0 to 100 ° C. when forming a homopolymer and a hydroxyl group-containing (meth) acrylic acid ester monomer (a3). It is a copolymer obtained by polymerization,
A pressure-sensitive adhesive composition, wherein the acrylic resin (A) has a glass transition temperature of −10 to 15 ° C. The pressure-sensitive adhesive composition according to claim 1, wherein the total content of the alkyl acrylate (a1) and the alkyl methacrylate (a2) is 30 to 70% by weight in the copolymerization component (a). thing. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the acrylic resin (A) has a weight average molecular weight of 50,000 to 400,000. The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the cross-linking agent (B) contains an active energy ray cross-linking agent (B1) and a thermal cross-linking agent (B2). A pressure-sensitive adhesive comprising the cross-linked pressure-sensitive adhesive composition according to any one of claims 1 to 4. The pressure-sensitive adhesive according to claim 5, wherein the cross-linking is performed by irradiation with active energy rays. A pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to claim 5. The pressure-sensitive adhesive sheet according to claim 7, wherein the pressure-sensitive adhesive layer has a multi-stage curability that cures in a plurality of stages.