Adhesive composition, adhesive and adhesive sheet

Abstract

To provide an adhesive composition that is usable for multi-stage curing which can obtain excellent adhesive physical properties in a low crosslinked state after primary curing, can be efficiently cured even with a small quantity of an active energy ray in curing, and is excellent in adhesive physical property, reliability and shape stability after final curing.SOLUTION: An adhesive composition contains an acrylic resin (A) and a photopolymerization initiator (B), wherein a glass transition temperature calculated from dynamic viscoelasticity of the acrylic resin (A) is 12 to 40°C, and the adhesive composition has a structural unit derived from alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms, and a structural unit derived from an amide group-containing ethylenically unsaturated monomer (a3).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive, and a pressure-sensitive adhesive sheet. [Background technology]

[0002] In recent years, touch panels that combine a display and a position input device have been widely used in mobile devices such as televisions, PC monitors, laptops, mobile phones, smartphones, and tablet terminals. Among them, capacitive touch panels are the most popular. A touch panel is usually composed of components such as an organic electroluminescence (EL) or liquid crystal display, a transparent conductive film substrate (ITO substrate), a protective film (protective glass), etc. A transparent adhesive sheet is used to bond these components of the touch panel together.

[0003] In recent years, displays with complex shapes such as curved surfaces have been developed due to the improved freedom of design of shapes, such as organic EL displays. In the case of a transparent adhesive sheet for laminating a laminate consisting of such displays with complex shapes such as curved surfaces, the laminate is laminated in a low crosslinked state (primary curing) before final curing, and then the adhesive layer is finally cured. Therefore, sufficient adhesive properties are required until the adhesive layer in the low crosslinked state (primary curing) is finally cured. For example, when a transparent adhesive sheet is attached to a component with a complex shape, poor attachment is likely to occur due to the sheet sticking to places other than the intended location. Therefore, there is a demand for a transparent adhesive sheet with low tackiness. At the same time, in order to fix components with complex shapes together, it is necessary to suppress the transparent adhesive sheet from peeling off from the component when stress is applied. Therefore, there is also a demand for a transparent adhesive sheet with high constant load retention even in a low crosslinking state (primary curing).

[0004] In addition, in recent years, there has been a trend toward thinner and more omitted components for the purpose of reducing the weight and power consumption of mobile terminals, which has resulted in a tendency for the mechanical strength of the entire laminate to decrease. Therefore, adhesives for transparent adhesive sheets are required to increase the strength of the entire structure after final curing, and at the same time, to have excellent adhesive properties such as adhesive strength, and reliability when bonding various components such as polarizing plates and glass. For example, in order to obtain excellent durability after final curing, a low degree of crosslinking is required until the adhesive is attached to an adherend, and the degree of crosslinking is required to be efficiently increased during final curing.

[0005] Therefore, there is a demand for a transparent adhesive sheet that can adhere sufficiently to an adherend by being attached to the adherend in a low cross-linked state (primary curing). It is expected that this transparent adhesive sheet will have a high cross-linking degree and improved durability by being finally cured while attached to the adherend in a low cross-linked state (primary curing).

[0006] The transparent adhesive sheet is generally crosslinked by heat or by irradiation with active energy rays to cause primary curing, and then crosslinked by irradiation with active energy rays to cause final curing. Examples of adhesive sheets using such multi-stage curing adhesives include the adhesive sheets described in Patent Documents 1 to 3. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2013-522393 [Patent Document 2] JP 2022-063964 A [Patent Document 3] International Publication No. 2021 / 181767

[0008] Furthermore, in order to improve the mechanical strength of the laminate, it is believed that increasing the elasticity of the pressure-sensitive adhesive layer is effective. However, if a large amount of cross-linking components is introduced to increase the cross-linking density in order to increase the elasticity, the adhesive strength cannot be maintained, so the acrylic resin itself used in the pressure-sensitive adhesive is required to have a high elastic modulus. Summary of the Invention [Problem to be solved by the invention]

[0009] However, none of Patent Documents 1 to 3 considers the adhesive properties in a low crosslinked state during primary curing. Therefore, the adhesive sheets disclosed in Patent Documents 1 to 3 have insufficient adhesive properties in a low crosslinked state during primary curing, and there is room for improvement. In addition, in order to increase the strength of the entire structure after final curing, it is required to increase the elasticity of the adhesive layer, and at the same time, it is required to have excellent adhesive properties and reliability.

[0010] Therefore, the present invention aims to provide a pressure-sensitive adhesive composition that can be used for multi-stage curing, which provides excellent adhesive properties in a low crosslinked state after primary curing, can be efficiently multi-stage cured even with a small amount of active energy radiation during curing, and can provide a high elasticity adhesive layer after final curing, and can provide excellent adhesive properties, reliability, and shape stability. Another object of the present invention is to provide a pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition, and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive. [Means for solving the problem]

[0011] In order to solve the above problems, the present inventors have conducted extensive research and found that by using a pressure-sensitive adhesive composition containing an acrylic resin having a specific structural unit and a photopolymerization initiator, it is possible to realize excellent adhesive properties such as low tackiness and high constant load retention even in a low crosslinked state after primary curing, and it is possible to efficiently cure even with a small amount of active energy radiation during curing, and further, after final curing, it is possible to obtain a pressure-sensitive adhesive composition that is excellent in adhesive properties, reliability, and shape stability.The present inventors have also found that a laminate laminated using a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of a pressure-sensitive adhesive obtained by crosslinking such a pressure-sensitive adhesive composition has excellent mechanical strength.

[0012] The gist of the present invention is as follows. [1] A pressure-sensitive adhesive composition comprising an acrylic resin (A) and a photopolymerization initiator (B), The acrylic resin (A) has a glass transition temperature calculated from the dynamic viscoelasticity of 12 to 40° C., The pressure-sensitive adhesive composition, wherein the acrylic resin (A) has a structural unit derived from an alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms and a structural unit derived from an amide group-containing ethylenically unsaturated monomer (a3). [2] The pressure-sensitive adhesive composition according to [1], wherein the content of the structural unit derived from the alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms is 20 to 70 mass % based on the total mass of the acrylic resin (A). [3] The pressure-sensitive adhesive composition according to [1] or [2], wherein the content of the structural unit derived from the amide group-containing ethylenically unsaturated monomer (a3) ​​is 5 to 40 mass % based on the total mass of the acrylic resin (A). [4] The pressure-sensitive adhesive composition according to any one of [1] to [3], wherein the acrylic resin (A) has a structural unit derived from an alkyl (meth)acrylate (a2) having an alkyl group having 1 to 4 carbon atoms. [5] The pressure-sensitive adhesive composition according to any one of [1] to [4], wherein the acrylic resin (A) has a weight average molecular weight of 50,000 to 600,000. [6] The pressure-sensitive adhesive composition according to any one of [1] to [5], wherein the photopolymerization initiator (B) contains a hydrogen abstraction type photopolymerization initiator (b). [7] The pressure-sensitive adhesive composition according to any one of [1] to [6], further comprising a crosslinking agent (C). [8] A pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition according to any one of [1] to [7]. [9] The pressure-sensitive adhesive described in [8], wherein the crosslinking is performed by irradiation with active energy rays.

[10] An adhesive sheet having an adhesive layer made of the adhesive described in [8].

[11] An adhesive sheet having an adhesive layer made of the adhesive described in [9].

[12] The pressure-sensitive adhesive sheet according to

[10] , wherein the pressure-sensitive adhesive layer exhibits multi-stage curing properties, that is, curing in multiple stages.

[13] The pressure-sensitive adhesive sheet according to

[11] , wherein the pressure-sensitive adhesive layer exhibits multi-stage curing properties, that is, curing in multiple stages. Effect of the Invention

[0013] According to the present invention, there is provided a pressure-sensitive adhesive composition that can be used for multi-stage curing, which has excellent adhesive properties in a low crosslinked state after primary curing, can be cured efficiently even with a small amount of active energy radiation during curing, and has excellent adhesive properties, reliability, and shape stability even after final curing. In addition, a laminate laminated with a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of a pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition has excellent mechanical strength. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention will be described in detail below, but these are merely examples of preferred embodiments. In addition, the following terms used in this specification have the following meanings: "(Meth)acrylic" means acrylic and / or methacrylic. "(Meth)acryloyl" means acryloyl and / or methacryloyl. "(Meth)acrylate" means acrylate and / or methacrylate. The "acrylic resin" is a resin obtained by polymerizing a monomer component containing at least one (meth)acrylic monomer, and the monomer component containing at least one (meth)acrylic monomer is preferably the main component of the entire polymerization components. Here, the main component is usually 50% by weight or more, preferably 60% by weight or more, and particularly preferably 70% by weight or more of the polymerization components. The term "sheet" conceptually encompasses a sheet, a film, and a tape. The symbol "~" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. In this specification, "x and / or y (x and y are optional configurations)" means at least one of x and y, and means three possibilities: x only, y only, and x and y. In the present specification, the upper limit or lower limit of a numerical range described in stages can be arbitrarily combined with the upper limit or lower limit of a numerical range of another stage. In addition, in the numerical range described in this specification, the upper limit or lower limit of the numerical range can be replaced with a value shown in the examples.

[0015] <<Adhesive composition>> The pressure-sensitive adhesive composition according to one embodiment of the present invention (hereinafter referred to as "the pressure-sensitive adhesive composition") contains an acrylic resin (A) and a photopolymerization initiator (B). In addition to the acrylic resin (A) and the photopolymerization initiator (B), the pressure-sensitive adhesive composition may further contain a crosslinking agent (C), a silane coupling agent (D), and other optional components, as necessary. Each component will be described in turn below.

[0016] <Acrylic resin (A)> The acrylic resin (A) has a structural unit derived from an alkyl (meth)acrylate (a1) having an alkyl group with 5 or more carbon atoms and a structural unit derived from an amide group-containing ethylenically unsaturated monomer (a3), preferably a structural unit derived from an alkyl (meth)acrylate (a2) having an alkyl group with 1 to 4 carbon atoms, and, if necessary, a structural unit derived from another polymerizable monomer (a4). The acrylic resin (A) can be obtained by copolymerizing an alkyl(meth)acrylate (a1) having an alkyl group with 5 or more carbon atoms and an amide group-containing ethylenically unsaturated monomer (a3), preferably an alkyl(meth)acrylate (a2) having an alkyl group with 1 to 4 carbon atoms, and, if necessary, other polymerizable monomers (a4) (hereinafter, these may be collectively referred to as "copolymerization components"). The copolymerization component is a general term for monomer components having a polymerizable double bond, and does not include a polymerization initiator or a polymerization solvent. Each copolymer component will be explained in turn below.

[0017] [Alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms] Examples of the alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms (hereinafter may be referred to as "alkyl (meth)acrylate (a1)")] include alkyl (meth)acrylate (a1-1) containing a linear alkyl group having 5 or more carbon atoms (hereinafter may be referred to as "linear alkyl (meth)acrylate (a1-1)"] and branched alkyl (meth)acrylate (a1-2) having an alkyl group having 5 or more carbon atoms (hereinafter may be referred to as "branched alkyl (meth)acrylate (a1-2)"). The number of carbon atoms in the alkyl group of the alkyl (meth)acrylate (a1) is preferably 8 or more. The upper limit is 24 or less, preferably 18 or less.

[0018] Examples of the linear alkyl (meth)acrylate (a1-1) include n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, lauryl (meth)acrylate, n-tridecyl (meth)acrylate, n-stearyl (meth)acrylate, and behenyl (meth)acrylate. Examples of the branched alkyl (meth)acrylate (a1-2) include alkyl group-containing (meth)acrylates such as isoamyl (meth)acrylate, 1-methylheptyl (meth)acrylate, 2-ethylhexyl acrylate (Tg = -70°C), 2-ethylhexyl methacrylate (Tg = -10°C), isononyl acrylate (Tg = -58°C), isononyl methacrylate, isodecyl acrylate (Tg = -62°C), isodecyl methacrylate (Tg = -41°C), isotridecyl (meth)acrylate, isomyristyl (meth)acrylate, and isostearyl (meth)acrylate. These may be used alone or in combination of two or more. Among them, as the alkyl (meth)acrylate (a1), a branched chain alkyl (meth)acrylate (a1-2) is preferable since it can be efficiently cured by active energy rays. Among the branched alkyl (meth)acrylates (a1-2), 2-ethylhexyl (meth)acrylate and isodecyl (meth)acrylate are preferred because they have excellent active energy ray curability during curing.

[0019] The alkyl (meth)acrylate (a1) preferably has a glass transition temperature (Tg) when it forms a homopolymer of −80 to 0° C., particularly preferably −75 to −20° C. By using an alkyl (meth)acrylate (a1) having a glass transition temperature (Tg) within the above range, it tends to be possible to improve the active energy ray curability and adhesive properties after curing when the adhesive is made into an adhesive.

[0020] [Alkyl (meth)acrylate (a2) having an alkyl group having 1 to 4 carbon atoms] Examples of the alkyl (meth)acrylate (a2) having an alkyl group having 1 to 4 carbon atoms (hereinafter, sometimes referred to as "alkyl (meth)acrylate (a2)") include methyl acrylate (Tg = 8°C), methyl methacrylate (Tg = 105°C), ethyl acrylate (Tg = -22°C), ethyl methacrylate (Tg = 65°C), n-butyl acrylate (Tg = -55°C), n-butyl methacrylate (Tg = 20°C), isobutyl acrylate (Tg = -26°C), isobutyl methacrylate (Tg = 48°C), t-butyl acrylate (Tg = 14°C), t-butyl methacrylate (Tg = 107°C), etc. These may be used alone or in combination of two or more. Among these, the alkyl (meth)acrylate (a2) is preferably an alkyl (meth)acrylate having an alkyl group with a carbon number of 1 to 2. By using the alkyl (meth)acrylate (a2) having the alkyl group with a carbon number within the above range, the polarity of the acrylic resin (A) can be increased, and when used as an adhesive, the adhesive strength to a highly polar adherend such as glass tends to be improved.

[0021] The alkyl (meth)acrylate (a2) preferably has a glass transition temperature (Tg) of −30 to 150° C. when it forms a homopolymer, more preferably 0 to 120° C., and particularly preferably 5 to 105° C. By using an alkyl (meth)acrylate (a2) having a glass transition temperature (Tg) within the above range, the elastic modulus of the acrylic resin (A) can be improved, and when used as a pressure-sensitive adhesive, there is a tendency that the tackiness during primary curing can be reduced and the shape stability after final curing can be improved.

[0022] [Amide group-containing ethylenically unsaturated monomer (a3)] Examples of the amide group-containing ethylenically unsaturated monomer (a3) ​​include primary and secondary amide group-containing monomers such as (meth)acrylamide, N-butyl(meth)acrylamide, and N-butoxymethyl(meth)acrylamide; N,N'-disubstituted (meth)acrylamides such as N,N'-dimethyl(meth)acrylamide, N-methyl-N'-ethyl(meth)acrylamide, N,N'-diethyl(meth)acrylamide, N,N'-dibutyl(meth)acrylamide, N,N'-dihexyl(meth)acrylamide, and N,N'-dioctyl(meth)acrylamide; acryloylmorpholine; and methacryloylmorpholine. Among these, N,N'-disubstituted (meth)acrylamide is preferred in terms of excellent tackiness during primary curing, excellent active energy ray curing properties during curing, and excellent shape stability after curing when used as an adhesive, and more preferred are N,N'-dimethyl(meth)acrylamide, N-methyl-N'-ethyl(meth)acrylamide, and N,N'-diethyl(meth)acrylamide, further more preferred are N,N'-dimethyl(meth)acrylamide and N,N'-diethyl(meth)acrylamide, and particularly preferred is N,N'-dimethyl(meth)acrylamide.

[0023] [Other polymerizable monomers (a4)] Examples of the other polymerizable monomer (a4) include ethylenically unsaturated monomers having one ethylenically unsaturated group, and ethylenically unsaturated monomers having two or more ethylenically unsaturated groups.

[0024] Examples of the ethylenically unsaturated monomer having one ethylenically unsaturated group include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, N-methylol (meth)acrylamide, hydroxyethyl acrylamide, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2,2-dimethyl 2-hydroxyethyl Hydroxyl group-containing monomers such as (meth)acrylates; aromatic ring-containing monomers such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyl diethylene glycol (meth)acrylate, phenoxy polyethylene glycol (meth)acrylate, phenoxy polyethylene glycol-polypropylene glycol-(meth)acrylate, orthophenylphenoxyethyl (meth)acrylate, and nonylphenol ethylene oxide adduct (meth)acrylate; cyclohexyloxy Alicyclic monomers such as alkyl (meth)acrylates; 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 Ether chain-containing monomers such as ethylene glycol (meth)acrylate, octoxy polyethylene glycol-polypropylene glycol mono(meth)acrylate, lauroxy polyethylene glycol mono(meth)acrylate, and stearoxy polyethylene glycol mono(meth)acrylate; carboxy group-containing monomers such as (meth)acrylic acid, acrylic acid dimers such as β-carboxyethyl acrylate, crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, N-glycolic acid, and cinnamic acid;Benzophenone-containing monomers such as 4-(meth)acryloyloxybenzophenone; other examples include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, itaconic acid dialkyl esters, fumaric acid dialkyl esters, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone; Furthermore, examples of the ethylenically unsaturated monomer having two or more ethylenically unsaturated groups include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, and divinylbenzene. These other polymerizable monomers (a4) may be used alone or in combination of two or more.

[0025] [Composition of acrylic resin (A)] The content of the structural unit derived from the alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms in the acrylic resin (A) is preferably 20 to 70 mass %, more preferably 25 to 65 mass %, and particularly preferably 30 to 55 mass %, based on the total mass of the acrylic resin (A) (100 mass %). If the content of the structural unit derived from the alkyl (meth)acrylate (a1) is too low, the active energy ray curability tends to decrease, whereas if the content is too high, the adhesive properties such as tackiness during primary curing and the shape stability after curing tend to decrease when used as an adhesive.

[0026] In addition, when the acrylic resin (A) contains a structural unit derived from a branched alkyl (meth)acrylate (a1-2), the content thereof is usually 50 mass% or more, preferably 80 mass% or more, and particularly preferably 90 mass% or more, in the structural unit derived from the alkyl (meth)acrylate (a1). By setting the content within the above range, when the adhesive is used, the active energy ray curability and the adhesive properties after final curing tend to be excellent.

[0027] When the acrylic resin (A) has a structural unit derived from an alkyl (meth)acrylate (a2) having an alkyl group having 1 to 4 carbon atoms, the content thereof is usually 15 to 70 mass%, preferably 20 to 60 mass%, more preferably 25 to 55 mass%, and particularly preferably 30 to 50 mass%, based on the entire acrylic resin (A) (100 mass%). If the content is too low, the adhesive properties such as tackiness during primary curing when used as an adhesive tend to decrease, while if the content is too high, the active energy ray curability tends to decrease.

[0028] The content of the structural unit derived from the amide group-containing ethylenically unsaturated monomer (a3) ​​in the acrylic resin (A) is preferably 5 to 40 mass%, more preferably 10 to 35 mass%, and particularly preferably 15 to 30 mass%, based on the total mass of the acrylic resin (A) (100 mass%). If the content is too low, the adhesive properties such as active energy ray curability and tackiness during primary curing and the shape stability after curing tend to decrease when used as an adhesive, while if the content is too high, the adhesive strength tends to decrease due to the decrease in adhesion.

[0029] When the acrylic resin (A) has a structural unit derived from another polymerizable monomer (a4), the content of the structural unit derived from the other polymerizable monomer (a4) is usually 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, based on the total acrylic resin (A) (100% by mass). If the content of the other polymerizable monomer (a4) is too high, the balance of the adhesive properties tends to be reduced.

[0030] The mass ratio of the content of the structural unit derived from the alkyl (meth)acrylate (a2) to the content of the structural unit derived from the amide group-containing ethylenically unsaturated monomer (a3) ​​in the acrylic resin (A) [(a2):(a3)] is usually 75:25 to 25:75, preferably 70:30 to 35:65, and particularly preferably 65:35 to 45:55. By setting the mass ratio of the contents within the above range, the pressure-sensitive adhesive tends to have excellent active energy ray curability and shape stability after final curing.

[0031] [Physical properties of acrylic resin (A)] The glass transition temperature (Tg) based on the dynamic viscoelasticity of the acrylic resin (A), i.e., the temperature at which the loss tangent of the dynamic viscoelasticity is maximum, is 12 to 40°C, preferably 14 to 35°C, more preferably 16 to 30°C, and particularly preferably 18 to 27°C. If the glass transition temperature of the acrylic resin (A) is too high, the adhesive strength tends to decrease with the decrease in adhesion when used as an adhesive. On the other hand, if the glass transition temperature of the acrylic resin (A) is too low, the adhesive properties such as tackiness and the shape stability after curing tend to decrease when used as an adhesive in a low crosslinking state during primary curing.

[0032] The glass transition temperature (Tg) based on the dynamic viscoelasticity is determined by the following measurement method. An acrylic resin solution containing only the acrylic resin (A) and the organic solvent is prepared by adding an appropriate organic solvent to the acrylic resin (A). This acrylic resin solution is applied onto a release sheet so that the thickness after drying is 50 μm. After that, the solution is dried by heating at 90 to 105° C. for 5 to 10 minutes to remove the organic solvent, and then the solution is attached to a release sheet to prepare an acrylic resin sheet containing 99% by mass or more of the acrylic resin (A). Then, a plurality of these acrylic resin sheets are laminated to prepare an acrylic resin sheet having a thickness of about 800 μm. The dynamic viscoelasticity of the produced acrylic resin sheet is measured under the following conditions, and the temperature at which the loss tangent (loss modulus G" / storage modulus G'=tan δ) becomes maximum is read and regarded as the glass transition temperature of the acrylic resin (A) based on the dynamic viscoelasticity.

[0033] (Dynamic viscoelasticity measurement conditions) Measuring equipment: Dynamic viscoelasticity measuring device (product name: DVA-225, manufactured by IT Instrument and Control Co., Ltd.) Deformation mode: Shear Distortion: 0.1% Measurement temperature: -100~60℃ Measurement frequency: 1Hz

[0034] In contrast, the calculated glass transition temperature (calculated Tg) is calculated by the following Fox formula: The "glass transition temperature (Tg) based on the dynamic viscoelasticity of the acrylic resin (A)" in the present invention is different from the calculated Tg.

[0035]

number

[0036] Tg: Glass transition temperature of the copolymer (K) Tga: Glass transition temperature of homopolymer of monomer A (K) Wa: Mass fraction of structural units derived from monomer A in the copolymer Tgb: Glass transition temperature of homopolymer of monomer B (K) Wb: Mass fraction of structural units derived from monomer B in the copolymer Tgn: Glass transition temperature of homopolymer of monomer N (K) Wn: Mass fraction of structural units derived from monomer N in the copolymer (Wa+Wb+···+Wn=1)

[0037] The weight average molecular weight (Mw) of the acrylic resin (A) is preferably 50,000 to 600,000, more preferably 100,000 to 500,000, and particularly preferably 150,000 to 400,000. If the weight average molecular weight of the acrylic resin (A) is too large, the viscosity becomes too high, and the coating property and handling property tend to be deteriorated. On the other hand, if the weight average molecular weight of the acrylic resin (A) is too small, the cohesive force decreases, and the adhesive property tends to decrease, and the durability after final curing tends to decrease. The weight average molecular weight of the acrylic resin (A) is the weight average molecular weight at the time of completion of production. The weight average molecular weight is measured on the acrylic resin (A) that has not been subjected to heating or the like after production.

[0038] The weight-average molecular weight of the acrylic resin (A) is the weight-average molecular weight converted into the standard polystyrene molecular weight. The weight-average molecular weight was measured by a high-performance liquid chromatograph (Waters Japan, "Waters2695 (main body)" and "Waters2414 (detector)") using a Shodex GPC KF-806L column (exclusion limit molecular weight: 2 × 10 7 , Separation range: 100~2×10 7 The measurement is performed using three columns in series: theoretical plate number: 10,000 plates / column, filler material: styrene-divinylbenzene copolymer, filler particle size: 10 μm. The number average molecular weight of the acrylic resin (A) can also be measured by the same method. The dispersity is determined from the weight average molecular weight and the number average molecular weight.

[0039] 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, even more preferably 7 or less, and particularly preferably 5 or less. If the dispersity of the acrylic resin (A) is too high, the durability of the adhesive layer tends to decrease and foaming and the like tends to occur easily. If the dispersity of the acrylic resin (A) is too low, the handleability tends to decrease. The lower limit of the dispersity is usually 1.1 in terms of production limitations.

[0040] [Method for producing acrylic resin (A)] The acrylic resin (A) can be produced by polymerizing the above-mentioned alkyl(meth)acrylate (a1) having an alkyl group with 5 or more carbon atoms, the amide group-containing ethylenically unsaturated monomer (a3), and, as necessary, the alkyl(meth)acrylate (a2) having an alkyl group with 1 to 4 carbon atoms, and other polymerizable monomers (a4) [copolymerization components].

[0041] Examples of the polymerization method for the acrylic resin (A) include conventionally known polymerization methods such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. Solution polymerization is preferred in terms of the safety and stability of the reaction and the ability to produce the acrylic resin (A) with any monomer composition. An example of a preferred method for producing the acrylic resin (A) will be described below.

[0042] First, the copolymerization components and a polymerization initiator are mixed or dropped into 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; aliphatic alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, and isopropyl alcohol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; aliphatic ethers such as dimethyl ether and diethyl ether; aliphatic halogenated hydrocarbons such as methylene chloride and ethylene chloride; and cyclic ethers such as tetrahydrofuran. Among these organic solvents, esters and ketones are preferred, and ethyl acetate, acetone and methyl ethyl ketone are particularly preferred. The organic solvent may be used alone or in combination of two or more kinds.

[0043] As the polymerization initiator used in the polymerization reaction, azo-based polymerization initiators and peroxide-based polymerization initiators, which are ordinary radical polymerization initiators, can be used. Examples of the azo polymerization initiator include 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, (1-phenylethyl)azodiphenylmethane, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Examples of the peroxide polymerization initiator include benzoyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide, lauroyl peroxide, tert-butyl peroxypivalate, tert-hexyl peroxypivalate, tert-hexyl peroxyneodecanoate, diisopropyl peroxycarbonate, and diisobutyryl peroxide. Among these, azo-based polymerization initiators are preferred, and 2,2'-azobisisobutyronitrile and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) are more preferred. The polymerization initiator may be used alone or in combination of two or more kinds.

[0044] The amount of the polymerization initiator used is usually 0.001 to 10 parts by mass, preferably 0.1 to 8 parts by mass, more preferably 0.5 to 6 parts by mass, particularly preferably 1 to 4 parts by mass, even more preferably 1.5 to 3 parts by mass, and most preferably 2 to 2.5 parts by mass, based on 100 parts by mass of the copolymerization components. If the amount of the polymerization initiator used is too small, the polymerization rate of the acrylic resin (A) tends to decrease and the amount of residual monomers tends to increase. In addition, the weight average molecular weight of the acrylic resin (A) tends to increase. If the amount of the polymerization initiator used is too large, the acrylic resin (A) tends to gel.

[0045] The polymerization conditions for the solution polymerization are not particularly limited, and the polymerization can be carried out according to conventionally known polymerization conditions. For example, the copolymerization components and a polymerization initiator can be mixed or dropped into an organic solvent to carry out the polymerization.

[0046] The polymerization temperature in the polymerization reaction is usually 40 to 120° C., but in the present invention, from the viewpoint of stable reaction, it is preferably 50 to 90° C. 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 decreases and the amount of residual monomers tends 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 from the final addition of the polymerization initiator. The polymerization reaction is preferably carried out while refluxing the solvent in order to facilitate removal of heat.

[0047] <Photopolymerization initiator (B)> The pressure-sensitive adhesive composition contains a photopolymerization initiator (B) in addition to the acrylic resin (A). The photopolymerization initiator (B) preferably contains a hydrogen abstraction type photopolymerization initiator (b). The hydrogen abstraction type photopolymerization initiator (b) includes an intramolecular hydrogen abstraction type photopolymerization initiator (b1) and an intermolecular hydrogen abstraction type photopolymerization initiator (b2), with the intramolecular hydrogen abstraction type photopolymerization initiator (b1) being preferred. The photopolymerization initiator (B) may further contain a photopolymerization initiator (b3) other than the intramolecular hydrogen abstraction type photopolymerization initiator (b1) and the intermolecular hydrogen abstraction type photopolymerization initiator (b2) within a range that does not impair the effects of the invention. The photopolymerization initiator (B) may be used alone or in combination of two or more kinds.

[0048] [Intramolecular hydrogen abstraction type photopolymerization initiator (b1)] The intramolecular hydrogen abstraction type photopolymerization initiator (b1) has a structure capable of generating radicals by abstracting hydrogen from the photopolymerization initiator itself, specifically, a phenyl glyoxylate structure or the like. Examples of the intramolecular hydrogen abstraction type photopolymerization initiator (b1) include oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester, [4-(4-methoxyoxalyl-phenoxy)-phenyl]-oxoacetic acid methyl ester, [4-(4-butoxyoxalyl-phenoxy)-phenyl]-oxoacetic acid butyl ester, [4-(4-methoxyoxalyl-phenylsulfanyl)-phenyl]-oxoacetic acid methyl ester, [4-(4-ethoxyoxalyl-phenylsulfanyl)-phenyl]-oxoacetic acid methyl ester, [4-(4-butoxyoxalyl-phenylsulfanyl)-phenyl]-oxoacetic acid methyl ester, [4-(4-methoxyoxalyl-benzyl)-phenyl]-oxoacetic acid methyl ester, and methyl phenylglyoxylate. Among these, oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester, which has multiple crosslinking points in the molecule, is preferred in terms of crosslinking efficiency during final curing. Commercially available products include "Omnirad MBF" and "Omnirad 754" manufactured by IGM RESINS BV. The intramolecular hydrogen abstraction photopolymerization initiator (b1) may be used alone or in combination of two or more kinds.

[0049] [Intermolecular hydrogen abstraction type photopolymerization initiator (b2)] The intermolecular hydrogen abstraction photopolymerization initiator (b2) has a structure capable of generating radicals by abstracting hydrogen from a site other than the photopolymerization initiator itself, specifically, a benzophenone structure, a thioxanthone structure, or the like. Examples of the intermolecular hydrogen abstraction type photopolymerization initiator (b2) include benzophenone, 4-methyl-benzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3'-dimethyl-4-methoxybenzophenone, 4-(meth)acryloyloxybenzophenone, 4-[2-((meth)acryloyloxy)ethoxy]benzophenone, 4-(meth)acryloyloxy-4'-methoxybenzophenone, and carboxymethoxymethoxybenzophenone-polyethylene. benzophenones such as ethylene glycol 250 diester, 2-benzoylbenzoate methyl, and 4-(1,3-acryloyl-1,4,7,10,13-pentaoxotridecyl)benzophenone; and thioxanthones such as 2,4-diethylthioxanthone, 2-isopropylthioxanthone, 2,4-diisopropylthioxanthone, 1-chloro-4-propoxythioxanthone, 2-acryloyloxythioxanthone, and 2-(2-acryloyloxyethoxy)thioxanthone. Among these, 4-(meth)acryloyloxybenzophenone, 4-[2-((meth)acryloyloxy)ethoxy]benzophenone, 4-(meth)acryloyloxy-4'-methoxybenzophenone, and carboxymethoxymethoxybenzophenone-polyethylene glycol 250 diester, which have multiple crosslinking points within the molecule, are preferred because they allow high crosslinking. Commercially available products include "MBP" manufactured by Shinryo Corporation, and "OmniradBP", "Omnirad 4MBZ", "Esacure TZT", and "Omnipol BP" manufactured by IGM RESINS BV. The intermolecular hydrogen abstraction photopolymerization initiator (b2) may be used alone or in combination of two or more kinds.

[0050] [Other photopolymerization initiators (b3)] Other examples of the photopolymerization initiator (b3) include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-2-morpholino(4-thiomethylphenyl)propan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, 2-hydroxy-2-methyl-1-[4-(1-methylvinyl acetophenones such as bis(2,6-phenyl)propanone oligomer; benzoins such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether; and acyl phosphonoxides such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. The other photopolymerization initiators (b3) may be used alone or in combination of two or more.

[0051] As an auxiliary for the photopolymerization initiator (B), it is also possible to use triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Michler's ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethylbenzoic acid, ethyl 4-dimethylaminobenzoate, (n-butoxy)ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, etc. in combination. The auxiliary for the photopolymerization initiator (B) may be used alone or in combination of two or more kinds.

[0052] <Crosslinking agent (C)> The pressure-sensitive adhesive composition preferably further contains a crosslinking agent (C) in addition to the acrylic resin (A) and the photopolymerization initiator (B). The crosslinking agent (C) may be an active energy ray crosslinking agent (c1) or a thermal crosslinking agent (c2). The crosslinking agent (C) may be used alone or in combination of two or more kinds.

[0053] When the crosslinking agent (C) contains only the active energy ray crosslinking agent (c1), multi-stage curing is possible by simply controlling the amount of active energy radiation. When the crosslinking agent (C) contains both the active energy ray crosslinking agent (c1) and the thermal crosslinking agent (c2), multi-stage curing is also possible by using both thermal curing and active energy ray curing. By controlling the crosslinking reaction in this manner, the cohesive strength of the entire pressure-sensitive adhesive layer can be adjusted, and stable adhesive properties can be obtained after primary curing and final curing.

[0054] [Active energy ray crosslinking agent (c1)] The active energy ray crosslinking agent (c1) may be a polyfunctional crosslinking agent containing two or more ethylenically unsaturated groups in one molecule. For example, hexanediol di(meth)acrylate, butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)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 Examples of the acrylates include glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, EO-modified glycerin tri(meth)acrylate, isocyanuric acid ethylene oxide-modified tri(meth)acrylate, and polyfunctional urethane (meth)acrylate. Among these, in terms of the balance between adhesive properties after curing and shape stability, (meth)acrylates containing 2 to 6 ethylenically unsaturated groups are preferred, and (meth)acrylates containing 2 to 4 ethylenically unsaturated groups are more preferred. In particular, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, (poly)tetramethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and pentaerythritol tri(meth)acrylate are preferred. The active energy ray crosslinking agent (c1) may be used alone or in combination of two or more kinds.

[0055] [Thermal crosslinking agent (c2)] The thermal crosslinking agent (c2) can exhibit excellent adhesive strength by reacting mainly with the functional group derived from the functional group-containing monomer, which is a constituent monomer of the acrylic resin (A). Examples of the thermal crosslinking agent (c2) include isocyanate-based crosslinking agents (c2-1), epoxy-based crosslinking agents (c2-2), aziridine-based crosslinking agents (c2-3), melamine-based crosslinking agents (c2-4), aldehyde-based crosslinking agents (c2-5), amine-based crosslinking agents (c2-6), and metal chelate-based crosslinking agents (c2-7). Among these, isocyanate-based crosslinking agents (c2-1) are preferably used in terms of improving adhesion to the substrate and reactivity with the acrylic resin (A). The thermal crosslinking agent (c2) may be used alone or in combination of two or more kinds.

[0056] Examples of the isocyanate crosslinking agent (c2-1) include tolylene diisocyanate compounds such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, xylylene diisocyanate compounds such as 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate and tetramethyl xylylene diisocyanate, aromatic isocyanate compounds such as 1,5-naphthalene diisocyanate and triphenylmethane triisocyanate, hexamethylene diisocyanate compounds such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate, and aliphatic isocyanate compounds such as lysine diisocyanate, alicyclic isocyanate compounds such as isophorone diisocyanate, and adducts of these isocyanate compounds with polyol compounds such as trimethylolpropane, biuret compounds and isocyanurate compounds of these isocyanate compounds, and the like. Among the isocyanate-based crosslinking agents (c2-1), aromatic isocyanate-based compounds are preferred from the viewpoint of excellent reactivity, and tolylene diisocyanate-based compounds are particularly preferred, while aliphatic isocyanate-based compounds are preferred from the viewpoint of suppressing yellowing, and hexamethylene diisocyanate-based compounds are particularly preferred.

[0057] Examples of the epoxy crosslinking agent (c2-2) include bisphenol A-epichlorohydrin type epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl erythritol, and diglycerol polyglycidyl ether.

[0058] Examples of the aziridine-based crosslinking agent (c2-3) include tetramethylolmethane-tri-β-aziridinylpropionate, trimethylolpropane-tri-β-aziridinylpropionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), and N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide).

[0059] Examples of the melamine-based crosslinking agent (c2-4) include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexaptoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, and melamine resins.

[0060] Examples of the aldehyde crosslinking agent (c2-5) include glyoxal, malondialdehyde, succindialdehyde, maleic dialdehyde, glutaric dialdehyde, formaldehyde, acetaldehyde, and benzaldehyde.

[0061] Examples of the amine-based crosslinking agent (c2-6) include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetraamine, diethylenetriamine, triethyltetraamine, isophoronediamine, amino resins, and polyamides.

[0062] Examples of the metal chelate crosslinking agent (c2-7) include acetylacetone and acetoacetyl ester coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium.

[0063] <Silane coupling agent (D)> The pressure-sensitive adhesive composition preferably further contains a silane coupling agent (D) as a compound other than the acrylic resin (A), the photopolymerization initiator (B) and the crosslinking agent (C) in order to improve durability.

[0064] The silane coupling agent (D) is an organosilicon compound that contains, in its structure, at least one reactive functional group and at least one alkoxy group bonded to a silicon atom. The silane coupling agent (D) may be of the monomer type or oligomer type. Examples of the reactive functional group in the silane coupling agent (D) include an epoxy group, a (meth)acryloyl group, a mercapto group, a hydroxyl group, a carboxy group, an amino group, an amide group, an isocyanate group, etc. Among these, an epoxy group and a mercapto group are preferred from the viewpoints of excellent durability and reworkability.

[0065] The content of reactive functional groups in the silane coupling agent (D) is usually 3,000g / mol or less, preferably 1,500g / mol or less, more preferably 1,000g / mol or less. The lower limit is 200g / mol. When the content of reactive functional groups is within the above numerical range, the balance between durability and reworkability tends to be improved. The lower limit of the content of reactive functional groups in the silane coupling agent (D) is 200g / mol.

[0066] As the alkoxy group bonded to a silicon atom in the silane coupling agent (D), from the viewpoints of durability and storage stability, an alkoxy group having 1 to 8 carbon atoms is preferred, and a methoxy group or an ethoxy group is more preferred. The silane coupling agent (D) may also have an organic functional group other than the reactive functional group and the alkoxy group bonded to the silicon atom, such as an alkyl group or a phenyl group.

[0067] Examples of the silane coupling agent (D) include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyldimethoxymethylsilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, methyltri(glycidyl)silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, etc. Among them, γ-glycidoxypropyltrimethoxysilane is preferred from the viewpoint of heat resistance. The silane coupling agent (D) may be used alone or in combination of two or more kinds.

[0068] <Optional ingredients> The pressure-sensitive adhesive composition may contain a pressure-sensitive adhesive as an optional component, if necessary. The pressure-sensitive adhesive composition may contain conventionally known additives such as carbodiimide, antioxidant, ultraviolet absorber, crosslinking accelerator, antistatic agent, tackifier, and functional dye.

[0069] <Composition of Pressure-Sensitive Adhesive Composition> The content of the acrylic resin (A) in the present pressure-sensitive adhesive composition is usually 80% by mass or more, preferably 90 to 99.9% by mass, and more preferably 92 to 99.9% by mass, based on the total pressure-sensitive adhesive composition. When the content of the acrylic resin (A) is within the above range, excellent adhesive properties tend to be obtained in a low crosslinking state after primary curing.

[0070] The content of the photopolymerization initiator (B) is usually 0.1 to 5 parts by mass, preferably 0.5 to 4 parts by mass, and more preferably 1.0 to 3 parts by mass, based on 100 parts by mass of the acrylic resin (A). When the content of the photopolymerization initiator (B) is within the above range, sufficient curability tends to be obtained when curing is performed.

[0071] When a hydrogen abstraction type photopolymerization initiator (b) is used as the photopolymerization initiator (B), the content is usually 0.1 to 5 parts by mass, preferably 0.5 to 4 parts by mass, and more preferably 1.0 to 3 parts by mass, based on 100 parts by mass of the acrylic resin (A). When the content of the photopolymerization initiator (B) is within the above numerical range, sufficient curability tends to be obtained when curing is performed.

[0072] When an intramolecular hydrogen abstraction type photopolymerization initiator (b1) is used as the photopolymerization initiator (B), the content is usually 0.1 to 5 parts by mass, preferably 0.5 to 3 parts by mass, based on 100 parts by mass of the acrylic resin (A). If the content of the intramolecular hydrogen abstraction type photopolymerization initiator (b1) is too high, the color tends to easily change after humidity and heat durability. If the content of the intramolecular hydrogen abstraction type photopolymerization initiator (b1) is too low, the degree of crosslinking does not increase, and therefore the adhesive properties during primary curing and the durability after final curing tend to decrease.

[0073] When the intermolecular hydrogen abstraction type photopolymerization initiator (b2) is used as the photopolymerization initiator (B), the content is usually 0.1 to 5 parts by mass, preferably 0.5 to 3 parts by mass, based on 100 parts by mass of the acrylic resin (A). If the content of the intermolecular hydrogen abstraction type photopolymerization initiator (b2) is too high, durability tends to decrease due to bleed-out. On the other hand, if the content of the intermolecular hydrogen abstraction type photopolymerization initiator (b2) is too low, the degree of crosslinking does not increase, and therefore the adhesive properties during primary curing and durability after final curing tend to decrease.

[0074] When an intramolecular hydrogen abstraction type photopolymerization initiator (b1) and an intermolecular hydrogen abstraction type photopolymerization initiator (b2) are used, the content ratio thereof, in terms of mass ratio [(b1) / (b2)], is usually 1 / 9 to 9 / 1, and preferably 5 / 5 to 8 / 2.

[0075] In addition, when the photopolymerization initiator (B) contains another photopolymerization initiator (b3), the content of the other photopolymerization initiator (b3) is usually 2 parts by mass or less, and preferably 1 part by mass or less, per 100 parts by mass of the acrylic resin (A).

[0076] When the pressure-sensitive adhesive composition contains a crosslinking agent (C), the content of the crosslinking agent (C) is usually 30 parts by mass or less, preferably 0.001 to 10 parts by mass, and more preferably 0.1 to 7.5 parts by mass, based on 100 parts by mass of the acrylic resin (A). If the content of the crosslinking agent (C) is too high, the adhesive strength tends to decrease. On the other hand, if the content of the crosslinking agent (C) is too low, the durability tends to decrease.

[0077] When the active energy ray crosslinking agent (c1) is used as the crosslinking agent (C), the content of the active energy ray crosslinking agent (c1) is usually 0.1 to 20 parts by mass, preferably 0.5 to 15 parts by mass, and more preferably 1.0 to 10 parts by mass, based on 100 parts by mass of the acrylic resin (A). If the content of the active energy ray crosslinking agent (c1) is too small, the cohesive force tends to decrease and sufficient durability tends not to be obtained. Also, if the content of the active energy ray crosslinking agent (c1) is too large, the adhesive properties during primary curing tend to decrease.

[0078] When the thermal crosslinking agent (c2) is used as the crosslinking agent (C), the content of the thermal crosslinking agent (c2) is usually 0.001 to 5 parts by mass, preferably 0.02 to 1 part by mass, and more preferably 0.05 to 0.5 parts by mass, based on 100 parts by mass of the acrylic resin (A). If the content of the thermal crosslinking agent (c2) is too small, the cohesive strength decreases, and the adhesive properties tend to decrease during primary curing. If the content of the thermal crosslinking agent (c2) is too large, the adhesive strength tends to decrease during final curing.

[0079] When the pressure-sensitive adhesive composition contains a silane coupling agent (D), the content of the silane coupling agent (D) is usually 0.001 to 3 parts by mass, preferably 0.005 to 1 part by mass, more preferably 0.01 to 0.5 parts by mass, and particularly preferably 0.015 to 0.3 parts by mass, based on 100 parts by mass of the acrylic resin (A). If the content of the silane coupling agent (D) is too low, the effect of improving durability tends to be difficult to obtain. On the other hand, if the content of the silane coupling agent (D) is too high, the adhesive strength tends to decrease due to the influence of bleed-out, etc.

[0080] When the present pressure-sensitive adhesive composition contains other pressure-sensitive adhesives or additives, the content of the other pressure-sensitive adhesives or additives is usually 10 parts by mass or less, and preferably 5 parts by mass or less, per 100 parts by mass of the acrylic resin (A).

[0081] <Preparation of Pressure-Sensitive Adhesive Composition> The pressure-sensitive adhesive composition can be obtained by mixing an acrylic resin (A), a photopolymerization initiator (B), and, if necessary, a crosslinking agent (C), a silane coupling agent (D), and other optional components. There are no particular limitations on the mixing method, and various methods can be used, such as a method of mixing each component at once, or a method of mixing optional components and then mixing the remaining components at once or sequentially.

[0082] <Application> The adhesive composition can be suitably used as an adhesive for adhesive sheets exhibiting multi-stage curing properties that cure in multiple stages. The adhesive has low tackiness even in a low crosslinking state after primary curing, high constant load holding power, can be cured efficiently even with a small amount of active energy radiation during curing, and has excellent adhesive properties, reliability, and shape stability after final curing. Therefore, a laminate laminated using a multi-stage curing adhesive sheet made of such an adhesive has excellent mechanical strength. Therefore, the present pressure-sensitive adhesive composition can be suitably used for applications such as pressure-sensitive adhesives and pressure-sensitive adhesive sheets used in touch panels and image display devices.

[0083] <Adhesive> An adhesive according to one embodiment of the present invention (hereinafter referred to as "the adhesive") is obtained by crosslinking the above-mentioned adhesive composition. When the adhesive composition is crosslinked (cured), the acrylic resin (A) contained in the adhesive composition forms a crosslinked structure at least intramolecularly and / or intermolecularly. As a result, the adhesive composition is crosslinked to become the adhesive. When the acrylic resin (A) has an active energy ray crosslinkable structural site, a crosslinked structure can be formed by irradiation with active energy rays.

[0084] This adhesive exhibits multi-stage curing properties, allowing it to be cured in multiple stages. This adhesive is in a low cross-linked state through primary curing, and is finally cured by further cross-linking (curing). Although it is not always possible to clearly distinguish between final curing and primary curing, they can be distinguished based on differences in gel fraction and dynamic viscoelasticity.

[0085] The means for carrying out the primary curing and final curing are not particularly limited, and may be, for example, any of heating and irradiation with active energy rays. The primary curing may be carried out in multiple steps to carry out multi-stage curing, and the final curing may also be carried out in multiple steps to carry out multi-stage curing. The present pressure-sensitive adhesive has excellent adhesive properties after primary curing, and is therefore suitable for use in bonding optical members constituting touch panels, image display devices, and the like.

[0086] It can be said that the present pressure-sensitive adhesive contains at least a crosslinked product of the acrylic resin (A). The crosslinked product may be a partially crosslinked product in which at least a part of the acrylic resin (A) is partially crosslinked, or a completely crosslinked product in which the entire acrylic resin (A) is entirely crosslinked. The present pressure-sensitive adhesive may contain both a partially crosslinked product and a completely crosslinked product of the acrylic resin (A).

[0087] <<Adhesive sheet>> An adhesive sheet according to one embodiment of the present invention (hereinafter referred to as "the adhesive sheet") has an adhesive layer made of the adhesive. The adhesive sheet can exhibit multi-stage curing properties in which the adhesive layer is cured in multiple stages. A pressure-sensitive adhesive layer made of the pressure-sensitive adhesive can be provided on a substrate sheet to form a pressure-sensitive adhesive sheet. The pressure-sensitive adhesive sheet can also be provided on a release sheet to form a double-sided pressure-sensitive adhesive sheet. The pressure-sensitive adhesive sheet can also be provided as a substrate-less double-sided pressure-sensitive adhesive sheet by forming a pressure-sensitive adhesive layer on a release sheet instead of a substrate sheet, and attaching a release sheet to the opposite side of the pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet can also be provided as a thick pressure-sensitive adhesive layer by forming a further pressure-sensitive adhesive layer on the formed pressure-sensitive adhesive layer. When the obtained pressure-sensitive adhesive sheet or double-sided pressure-sensitive adhesive sheet is used, the release sheet is peeled off from the pressure-sensitive adhesive layer.

[0088] Examples of methods for producing the present pressure-sensitive adhesive sheet include the following methods (i) and (ii). (i) A method in which the present pressure-sensitive adhesive composition is dissolved in a solvent and coated to form a pressure-sensitive adhesive sheet. (ii) A method in which the present pressure-sensitive adhesive composition is melted by heating to form a pressure-sensitive adhesive sheet.

[0089] Method (i) will now be explained. When the adhesive composition is dissolved in a solvent and applied to prepare an adhesive sheet, the concentration of the coating solution containing the adhesive composition is adjusted with an appropriate organic solvent, and the adhesive sheet is directly applied onto a substrate sheet. After that, the adhesive sheet is dried, for example, by heat treatment at 80 to 105°C for 0.5 to 10 minutes, and then attached to a substrate sheet or a release sheet. After that, the adhesive composition is crosslinked (cured) by irradiation with active energy rays or aging, and an adhesive sheet having an adhesive layer made of an adhesive can be prepared.

[0090] As the organic solvent used for adjusting the concentration, those exemplified as the organic solvent used in the polymerization reaction of the acrylic resin (A) can be used. The concentration of the pressure-sensitive adhesive composition is usually 20 to 60 mass %, preferably 30 to 50 mass %, as solid content.

[0091] Method (ii) will now be explained. When the pressure-sensitive adhesive composition is melted by heating to form a pressure-sensitive adhesive sheet, a pressure-sensitive adhesive layer having a desired thickness is formed on one or both sides of a substrate sheet by a method in which the pressure-sensitive adhesive composition in a molten state is applied to one or both sides of a substrate sheet and then cooled, or by a method in which the pressure-sensitive adhesive composition is extruded and laminated onto a substrate sheet using a T-die or the like. Next, a release sheet can be attached to the surface of the pressure-sensitive adhesive layer as necessary to produce a pressure-sensitive adhesive sheet. In addition, after forming the adhesive layer on the base sheet, if necessary, an active energy ray irradiation treatment can be carried out, and then aging can be carried out to produce an adhesive sheet having an adhesive layer in which the adhesive composition is cured (crosslinked). Furthermore, a substrate-less double-sided pressure-sensitive adhesive sheet can also be produced by forming a pressure-sensitive adhesive layer on a release sheet and laminating a release sheet to the opposite side of the pressure-sensitive adhesive layer.

[0092] Examples of the base sheet include polyester-based resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate / isophthalate copolymer; polyolefin-based resins such as polyethylene, polypropylene, and polymethylpentene; polyethylene fluoride resins such as polyvinyl fluoride, polyvinylidene fluoride, and polyethylene fluoride; polyamides such as nylon 6 and nylon 6,6; vinyl polymers such as polyvinyl chloride, polyvinyl chloride / vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, and vinylon; cellulose-based resins such as cellulose triacetate and cellophane; acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, and polybutyl acrylate; polystyrene; polycarbonate; polyarylate; and synthetic resin sheets such as polyimide; metal foils such as aluminum, copper, and iron; paper such as fine paper and glassine paper; and woven fabrics and nonwoven fabrics made of glass fiber, natural fiber, synthetic fiber, and the like. These substrate sheets can be used as a single layer or as a multi-layered body in which two or more types are laminated. Among these, synthetic resin sheets are preferred from the viewpoint of weight reduction, etc.

[0093] As the release sheet, for example, various synthetic resin sheets, papers, woven fabrics, nonwoven fabrics, etc. exemplified as the base material sheet, which have been subjected to a release treatment, can be used. As the release sheet, for example, it is preferable to use a silicone-based release sheet.

[0094] The method for applying the pressure-sensitive adhesive composition is not particularly limited, but examples thereof include roll coating, die coating, gravure coating, comma coating, slot coating, and screen printing.

[0095] Examples of the active energy rays that can be used include light rays such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, and infrared rays; electromagnetic waves such as X-rays and γ-rays; electron beams; proton beams; neutron beams, etc. Curing with ultraviolet rays is preferred in terms of curing speed, availability of an irradiation device, cost, etc.

[0096] The gel fraction of the adhesive layer of this adhesive sheet after primary curing is typically 0.1 to 60 mass%, preferably 0.5 to 55 mass%, and particularly preferably 1 to 50 mass%, because the adhesive sheet can be easily bonded to the adherend regardless of its shape and the adhesive layer can hold the adherend after bonding.

[0097] The gel fraction of the adhesive layer of the present adhesive sheet after final curing is preferably 60-90% by mass, more preferably 65-87% by mass, and particularly preferably 70-85% by mass, from the viewpoints of durability and adhesive strength. If the gel fraction is too low, the cohesive strength tends to decrease, leading to a decrease in durability. If the gel fraction is too high, the cohesive strength tends to increase, leading to a decrease in adhesive strength.

[0098] The gel fraction can be appropriately adjusted, for example, by the following method. (1) A method for adjusting the amount of active energy ray irradiation. (2) A method of adjusting the content of active energy ray crosslinkable structural moieties in the acrylic resin (A). (3) A method of adjusting the type and amount of the photopolymerization initiator (B) and crosslinking agent (C).

[0099] The gel fraction is a measure of the degree of crosslinking (degree of curing) and is calculated, for example, by the following method. That is, an adhesive sheet (without a release sheet) in which an adhesive layer is formed on a polymer sheet (e.g., a polyethylene terephthalate (PET) film, etc.) serving as a substrate is wrapped in a 200-mesh SUS wire net and immersed in toluene maintained at 23°C for 24 hours, and the mass percentage of the undissolved adhesive component remaining in the wire net is taken as the gel fraction. However, the mass of the substrate is calculated by subtracting the mass before and after dissolution in toluene.

[0100] The thickness of the adhesive layer of the present adhesive sheet is preferably 50 to 3000 μm, more preferably 75 to 1000 μm, and particularly preferably 100 to 350 μm. If the adhesive layer is too thin, the impact absorption properties tend to decrease. If the adhesive layer is too thick, for example, when it is attached to an optical member, the overall thickness increases, and the practicality tends to decrease.

[0101] The thickness of the adhesive layer in this adhesive sheet was determined using a Mitutoyo ID-C112B by subtracting the measured thickness of the constituent members other than the adhesive layer from the measured thickness of the entire adhesive layer-containing laminate.

[0102] The storage modulus G' of the adhesive layer of this adhesive sheet after final curing is usually 400 kPa or more at 25°C, preferably 600 kPa or more, more preferably 700 kPa or more, and particularly preferably 800 kPa or more. When the storage modulus G' is within the above range, the adhesive layer has excellent shape stability, and the laminate laminated using the adhesive sheet composed of such an adhesive layer tends to have excellent mechanical strength. The upper limit is usually 5000 kPa. The storage modulus G' can be obtained by measuring the pressure-sensitive adhesive layer at a frequency of 1 Hz using a dynamic viscoelasticity device.

[0103] In addition, the tensile modulus of elasticity of the adhesive layer of this adhesive sheet after final curing is usually 0.35 MPa or more, preferably 0.40 MPa or more, more preferably 0.45 MPa or more, at 23°C and 50% RH. When the tensile modulus of elasticity is within the above range, the adhesive layer has excellent shape stability, and the laminate laminated using the adhesive sheet composed of such an adhesive layer tends to have excellent mechanical strength. The upper limit is usually 10 MPa. The tensile modulus is obtained by measuring the pressure-sensitive adhesive layer at a tensile speed of 10 mm / min using a tensile tester, and determining the rate of change between tensile strain and tensile stress.

[0104] The haze value of the adhesive layer (thickness 100 μm) of the present adhesive sheet is usually 2% or less, preferably 0 to 1.5%, and particularly preferably 0 to 1%. If the haze value is too high, the adhesive layer tends to whiten and lose transparency. The haze value is calculated by measuring the diffuse transmittance and total light transmittance using a HAZE MATER NDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.) and substituting the obtained diffuse transmittance (DT) and total light transmittance (TT) into the following [Equation 1]. This machine complies with JIS K7361-1. Haze value (%) = (DT / TT) × 100 [Formula 1]

[0105] In the present invention, the present pressure-sensitive adhesive composition is used to laminate a pressure-sensitive adhesive layer on an optical member to obtain an optical member with a pressure-sensitive adhesive layer. For example, the pressure-sensitive adhesive layer surface of the present pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed on a release sheet is attached to an optical member, and then the release sheet is peeled off to obtain an optical member with a pressure-sensitive adhesive layer. In addition, the above-mentioned double-sided pressure-sensitive adhesive sheet can be used to bond optical members together.

[0106] Examples of optical components include components that constitute touch panels and image display devices, such as displays (organic electroluminescence, liquid crystal), transparent conductive film substrates (ITO substrates), protective films (glass), transparent antennas (films), and transparent wiring. EXAMPLES

[0107] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following description. In the examples, "parts" and "%" refer to mass standards. The weight average molecular weight of the acrylic resin (A), the glass transition temperature based on dynamic viscoelasticity, the thickness of the pressure-sensitive adhesive layer, and the haze value (%) were measured according to the method described in the above embodiment.

[0108] Prior to the examples, the following raw materials were prepared.

[0109] <Acrylic resin (A)> [Alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms] 2EHA: 2-Ethylhexyl acrylate (Tg of homopolymer: -70℃) IDMA: Isodecyl methacrylate (Tg of homopolymer: -41°C)

[0110] [Alkyl (meth)acrylate (a2) having an alkyl group having 1 to 4 carbon atoms] MA: Methyl acrylate (Tg of homopolymer: 8°C) MMA: Methyl methacrylate (Tg of homopolymer: 105℃)

[0111] [Amide group-containing ethylenically unsaturated monomer (a3)] ·DMAA: Dimethylacrylamide (Tg of homopolymer: 119℃) ACMO: acryloylmorpholine (Tg of homopolymer: 145°C)

[0112] [Other polymerizable monomers (a4)] HEMA: Hydroxyethyl methacrylate (Tg of homopolymer: 55°C)

[0113] [Polymerization initiator] ADVN: 2,2'-azobis(2,4-dimethylvaleronitrile) (10 hour half-life temperature 52℃)

[0114] <Photopolymerization initiator (B)> [Intramolecular hydrogen abstraction type photopolymerization initiator (b1)] Omnirad 754 (Omn754): A blend of oxyphenylacetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester and oxyphenylacetic acid 2-[2-hydroxy-ethoxy]-ethyl ester, manufactured by IGM Resins BV [Intermolecular hydrogen abstraction type photopolymerization initiator (b2)] MBP: 4-methacryloyloxybenzophenone, manufactured by Shinryo Corporation

[0115] <Crosslinking agent (C)> NK Ester APG400 (APG400): Polypropylene glycol #400 diacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd.

[0116] <Silane coupling agent (D)> KBM403: 3-glycidoxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.

[0117] <Production Example: Production of Acrylic Resin (A-1)> In a 2L flask equipped with a condenser, 24 parts of ethyl acetate (boiling point 77°C), 16 parts of methyl ethyl ketone (boiling point 80°C), 0.01 parts of ADVN, 4.5 parts of 2EHA, 1.7 parts of MA, 1.8 parts of MMA, and 2 parts of DMAA were placed as polymerization solvents, and the mixture was heated and refluxed in the flask. Then, 10 parts of ethyl acetate, 0.18 parts of ADVN, 40.5 parts of 2EHA, 15.3 parts of MA, 16.2 parts of MMA, and 18 parts of DMAA were added dropwise over 3 hours. After 30 minutes of addition, a mixture of 10 parts of ethyl acetate and 0.13 parts of ADVN was added dropwise over 1 hour and reacted to obtain a solution of acrylic resin (A-1). The polymer composition, weight average molecular weight (Mw), glass transition temperature based on dynamic viscoelasticity, and storage modulus at 25°C of the acrylic resin (A-1) are shown in Table 1 below.

[0118] <Production Example: Production of Acrylic Resins (A-2) and (A-3)> Acrylic resins (A-2) and (A-3) 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 below. The physical properties of the obtained acrylic resins (A-2) and (A-3) are shown in Table 1 below.

[0119] <Comparative Production Example: Production of Acrylic Resin (A'-1)> In a 2L flask equipped with a condenser, 33.3 parts of ethyl acetate (boiling point 77°C) and 6.7 parts of methyl ethyl ketone (boiling point 80°C) were placed as polymerization solvents, and the mixture was heated to reflux in the flask, and then 10 parts of ethyl acetate, 0.2 parts of ADVN, 40 parts of 2EHA, 52 parts of MA, and 8 parts of DMAA were added dropwise over 3 hours. After 60 minutes of the dropwise addition, a mixture of 5 parts of ethyl acetate and 0.07 parts of ADVN was added and reacted, and then, after 60 minutes, a mixture of 5 parts of ethyl acetate and 0.07 parts of ADVN was added to obtain a solution of acrylic resin (A'-1). The polymer composition, weight average molecular weight (Mw), glass transition temperature based on dynamic viscoelasticity, and storage modulus at 25°C of the acrylic resin (A'-1) are shown in Table 1 below.

[0120] <Comparative Production Example: Production of Acrylic Resins (A'-2) to (A'-4)> Acrylic resins (A'-2) to (A'-4) were produced in the same manner as in Comparative Production Example 1, except that the copolymerization components of the acrylic resin were as shown in Table 1 below. The physical properties of the obtained acrylic resins (A'-2) to (A'-4) are shown in Table 1 below.

[0121] [Table 1]

[0122] <Example 1> 100 parts (solid content equivalent) of the solution of acrylic resin (A-1) was mixed with 2 parts (solid content equivalent) of Omnirad 754, 1 part (solid content equivalent) of MBP, 1.5 parts (solid content equivalent) of NK Ester APG400, and 0.1 parts (solid content equivalent) of KBM403 to obtain a pressure-sensitive adhesive composition. The obtained pressure-sensitive adhesive composition was adjusted to a solid content concentration of 45% with toluene, and applied to a polyester release sheet so that the thickness after drying was about 50 μm, and dried at 100 ° C. for 5 minutes to form a pressure-sensitive adhesive composition layer.

[0123] Two pressure-sensitive adhesive sheets each having a pressure-sensitive adhesive composition layer formed on a polyester-based release sheet as described above were prepared, and the two pressure-sensitive adhesive composition layers were laminated facing each other. In a state in which both sides of the laminated pressure-sensitive adhesive composition layer were sandwiched between polyester-based release sheets (release sheet / laminated pressure-sensitive adhesive composition layer / release sheet), the laminated pressure-sensitive adhesive composition layer was irradiated with a high-pressure mercury UV irradiation device at a peak irradiance of 150 mW / cm. 2 , Accumulative exposure: 2000mJ / cm 2 (1000mJ / cm 2 × 2 passes) to form an adhesive layer (primary curing), and a substrate-less double-sided adhesive sheet with an adhesive layer thickness of 100 μm was obtained. Next, the release sheet on one side was peeled off from the adhesive layer of the obtained substrate-less double-sided adhesive sheet, and the exposed adhesive layer side was pressed against an easy-adhesion treated polyethylene terephthalate (PET) sheet (thickness 125 μm) to obtain a PET sheet with an adhesive layer having a thickness of 100 μm.

[0124] <Examples 2 and 3, Comparative Examples 1 to 4> The pressure-sensitive adhesive compositions of each example were prepared in the same manner as in Example 1, except that the acrylic resin (A-1) was changed as shown in Table 2. Then, a substrate-less double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer thickness of 100 μm and a PET sheet with a pressure-sensitive adhesive layer were successively produced in the same manner as in Example 1. The composition of the pressure-sensitive adhesive composition of each example is shown in Table 2 below.

[0125] [Table 2]

[0126] <Measurement and evaluation methods> The substrate-less double-sided pressure-sensitive adhesive sheets and the PET sheets with a pressure-sensitive adhesive layer of the Examples and Comparative Examples were used to carry out the following evaluations. The results are shown in Tables 3 to 5 below.

[0127] (Gel fraction: after primary curing) The substrate-less double-sided adhesive sheet of each example was cut to 40 mm x 40 mm, and left to stand for 30 minutes under conditions of 23 ° C x 50% RH, and then one release sheet was peeled off, and the exposed adhesive layer side was attached to a 50 mm x 100 mm SUS mesh sheet (200 mesh). The remaining release sheet was peeled off, and the adhesive layer was wrapped in the SUS mesh sheet by folding back the center in the longitudinal direction. The gel fraction (%) was calculated from the mass change when this was immersed for 24 hours in a sealed container containing 250 g of toluene kept at 23 ° C.

[0128] (Constant load holding capacity (40℃): after primary curing) The PET sheet with adhesive layer of each example was cut to a size of 25 mm wide x 75 mm long (adhesive layer part width 25 mm x length 50 mm + non-adhesive layer part width 25 mm x length 25 mm), and the release sheet was peeled off. The exposed adhesive layer side was pressed and attached to a stainless steel plate (SUS304) by reciprocating a 2 kg roller (attached area 25 mm x 50 mm), and left to stand for 20 minutes in a 40°C atmosphere. Then, a 50 g weight was hung from the end of the length direction of the non-attached part (area 25 mm x 25 mm), and a 50 g load was applied in a direction of 90° to the plane of the stainless steel plate, and the plate was left to stand for 60 minutes in that state, and the distance the PET sheet peeled off was measured. The evaluation criteria are as follows. ◎ Peel distance is less than 5 mm. ○ The peeling distance is 5 mm or more and less than 10 mm. × The peeled distance was 10 mm or more, or the PET sheet peeled off completely and fell.

[0129] (Probe tack: after primary curing) The PET sheet with the adhesive layer of each example was cut to a size of 12 mm wide x 12 mm long, the release sheet was peeled off, and the probe tack (unit: N) was measured using a probe tack tester (Tester Sangyo Co., Ltd., Probe Tack Tester TE-6001) under the following conditions: pressure time 5 seconds, application pressure 1000 gf, pressing speed 600 mm / min, lifting speed 600 mm / min, probe diameter 5.1 mm (diameter). The evaluation criteria are as follows. ◎ Probe tack (unit: N) is less than 5. ○ Probe tack (unit: N) is 5 or more and less than 7.5. ×: Probe tack (unit: N) is 7.5 or more, 10 or more.

[0130] (Gel fraction: after final curing) The substrate-less double-sided adhesive sheet in each example was exposed to a high-pressure mercury UV irradiation device with a peak irradiance of 150 mW / cm 2 , Accumulative exposure: 3000mJ / cm 2 (1000mJ / cm 2 After irradiating the sample with ultraviolet light (3 passes), the sample was cut to 40 mm x 40 mm and left to stand for 30 minutes under conditions of 23 ° C x 50% RH. Then, one release sheet was peeled off, and the exposed adhesive layer side was attached to a 50 mm x 100 mm SUS mesh sheet (200 mesh). The remaining release sheet was peeled off, and the adhesive layer was wrapped in the SUS mesh sheet by folding back the center in the longitudinal direction. The gel fraction (%) was calculated from the mass change when the sample was immersed for 24 hours in a sealed container containing 250 g of toluene kept at 23 ° C.

[0131] (180 degree peel strength (23℃): after final curing) The PET sheet with adhesive layer of each example was cut into a size of 25 mm wide x 100 mm long, and irradiated with a high-pressure mercury UV irradiation device at a peak irradiance of 150 mW / cm. 2 , Accumulative exposure: 3000mJ / cm 2 (1000mJ / cm 2After irradiating the adhesive layer with ultraviolet light (3 passes), the release sheet was peeled off. The exposed adhesive layer side was attached to alkali-free glass (Corning's "Eagle XG", thickness 1.1 mm) using a 2 kg rubber roller under an atmosphere of 23°C and 50% RH, and then autoclaved (0.5 MPa x 50°C x 20 minutes) and left to stand for 24 hours under an atmosphere of 23°C and 50% RH. After this, the 180° peel strength (N / 25 mm) was measured at room temperature (23°C) and a peel speed of 60 mm / min.

[0132] The evaluation criteria for 180-degree peel strength are as follows. ○: The peel strength was 30 (N / 25 mm) or more, and peeling occurred at the adherend interface. △: The peel strength was 30 (N / 25 mm) or greater, and peeling occurred at a location other than the adherend interface. × Peel strength is less than 30 (N / 25 mm).

[0133] (Shape stability: storage modulus G' and tensile modulus: after final curing) The substrate-less double-sided adhesive sheet in each example was exposed to a high-pressure mercury UV irradiation device with a peak irradiance of 150 mW / cm 2 , Accumulative exposure: 3000mJ / cm 2 (1000mJ / cm 2 After irradiating the adhesive layer alone with ultraviolet light (×3 passes), eight sheets were laminated together to produce a substrate-less double-sided adhesive sheet with an adhesive layer thickness of approximately 800 μm. The release sheets on both sides of the prepared substrate-less double-sided pressure-sensitive adhesive sheet were peeled off, and the storage modulus G' of the exposed pressure-sensitive adhesive layer was measured under the conditions described below to determine the storage modulus G' at 25°C. (Measurement conditions for storage modulus G') Measuring equipment: Dynamic viscoelasticity measuring device (product name: DVA-225, manufactured by IT Instrument and Control Co., Ltd.) Deformation mode: Shear Distortion: 0.1% Measurement temperature: -80~80℃ Measurement frequency: 1Hz

[0134] In addition, the substrate-less double-sided adhesive sheets of each example were irradiated with a high-pressure mercury UV irradiation device at a peak irradiance of 150 mW / cm 2 , Accumulative exposure: 3000mJ / cm 2 (1000mJ / cm 2 After irradiating the adhesive layer alone with ultraviolet light (×3 passes), two sheets of the adhesive layer alone were laminated to produce a substrate-less double-sided adhesive sheet with an adhesive layer thickness of approximately 200 μm. The release sheets on both sides of the prepared substrate-less double-sided pressure-sensitive adhesive sheet were then peeled off, and the tensile modulus of elasticity of the exposed pressure-sensitive adhesive layer was measured under the following conditions.

[0135] (Measurement conditions for tensile modulus) Measuring equipment: Tensile testing machine (product name: Autograph AG-X, manufactured by Shimadzu Corporation) Measurement environment: 23℃, 50% RH Tensile speed: 10mm / min Chuck distance: 20mm Sample width: 10mm Here, the tensile modulus is calculated from the rate of change in tensile strain (strain at 1% displacement to strain at 2% displacement) and tensile stress (tensile stress at 1% displacement to tensile stress at 2% displacement).

[0136] From the measured values ​​of storage modulus G' and tensile modulus, the shape stability was evaluated according to the following evaluation criteria. The storage modulus G' at 25°C is 700 kPa or more, and the tensile modulus is 0.70 MPa or more. ○The storage modulus G' at 25°C is 700 kPa or more, and the tensile modulus is 0.45 MPa or more and less than 0.70 MPa. ○The storage modulus G' at 25°C is 400 kPa or more and less than 700 kPa, and the tensile modulus is 0.70 MPa or more. ○The storage modulus G' at 25°C is 400 kPa or more and less than 700 kPa, and the tensile modulus is 0.45 kPa or more and less than 0.70 kPa. × The storage modulus G' at 25°C is less than 400 kPa, or the tensile modulus G' is less than 0.45 kPa.

[0137] (Holding force (80℃): after final curing) The PET sheet with adhesive layer of each example was cut into a size of 25 mm x 50 mm and irradiated with a high-pressure mercury UV irradiation device at a peak irradiance of 150 mW / cm. 2 , Accumulative exposure: 3000mJ / cm 2 (1000mJ / cm 2 After irradiating the adhesive with ultraviolet light (3 passes), the release sheet was peeled off. A stainless steel plate (SUS304) was placed on the exposed adhesive layer side, and a 2 kg roller was moved back and forth to apply pressure to the adhesive (application area 25 mm x 25 mm). The adhesive was then measured for its holding power by applying a load of 1 kg in an 80°C atmosphere for 24 hours using a creep tester (Tester Sangyo Co., Ltd., holding power tester BE-501 with humidity chamber). The evaluation criteria are as follows: ◎ No misalignment (NC). ○The deviation is less than 0.1 mm. × The deviation is 0.1 mm or more or the PET sheet has fallen.

[0138] (Optical properties: after final curing) The substrate-less double-sided adhesive sheet of each example was cut to a size of 30 mm x 50 mm and irradiated with a high-pressure mercury UV irradiation device with a peak irradiance of 150 mW / cm 2 , Accumulative exposure: 3000mJ / cm 2 (1000mJ / cm 2 After irradiating the specimen with ultraviolet light (3 passes x 3), one of the release sheets was peeled off. The exposed adhesive layer side was attached to alkali-free glass (Corning's "Eagle XG", thickness 1.1 mm). After that, autoclave treatment was performed under conditions of 50°C, 0.5 MPa, and 20 minutes, and the specimen was left to stand for 30 minutes in an atmosphere of 23°C and 50% RH. The remaining release sheet was peeled off to prepare a test specimen with a layer structure of "alkali-free glass / adhesive layer". The haze value and color difference b* value were measured using the obtained test pieces.

[0139] [Haze value] The haze value (%) was calculated by measuring the diffuse transmittance and total light transmittance using a HAZE MATER NDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.) and substituting the obtained diffuse transmittance (DT) and total light transmittance (TT) values ​​into the following formula 2. This machine complies with JIS K7361-1. Haze value (%) = (DT / TT) × 100 [Formula 2] [Color difference] The color difference b* value was measured in accordance with JIS K7105, and the measurement was performed under transmission conditions using a spectrophotometer (SE6000: manufactured by Nippon Denshoku Industries Co., Ltd.). In the present invention, the haze and color difference b* value are measured by attaching only the pressure-sensitive adhesive layer to non-alkali glass (haze=0.06, b* value=0.16).

[0140] (Moisture and heat resistance: after final curing) The PET sheet with adhesive layer of each example was cut into a size of 30 mm x 50 mm and irradiated with a high-pressure mercury UV irradiation device with a peak irradiance of 150 mW / cm. 2 , Accumulative exposure: 3000mJ / cm 2 (1000mJ / cm 2 After irradiating the sample with ultraviolet light (3 passes x 3), the release sheet was peeled off. The exposed adhesive layer side was attached to alkali-free glass (Corning's "Eagle XG", thickness 1.1 mm). After that, the sample was autoclaved at 50°C, 0.5 MPa, and 20 minutes, and then left to stand for 30 minutes in an atmosphere of 23°C and 50% RH to produce a test piece with a layer structure of "alkali-free glass / adhesive layer / PET". Using the obtained test pieces, a moist heat resistance test was carried out for 7 days (168 hours) in an atmosphere of 85°C and 85% RH, and the haze value before the moist heat resistance test (initial haze value) and the haze value after the moist heat resistance test (post-durability haze value) were measured. The haze value after durability was measured after leaving the sample to stand for 2 hours in an atmosphere of 23° C. and 50% RH after the moist heat resistance test.

[0141] The haze value (%) was calculated by measuring the diffuse transmittance and total light transmittance using a HAZE MATER NDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.) and substituting the obtained diffuse transmittance (DT) and total light transmittance (TT) values ​​into the following formula 3. Furthermore, the haze value difference (%) was calculated using the following formula 4. This machine complies with JIS K7361-1. Haze value (%) = (DT / TT) × 100 [Equation 3] Haze value difference (%) = haze value after durability test - initial haze value... [Formula 4]

[0142] The evaluation criteria for the moist heat resistance test are as follows. ◎ The haze value difference is less than 2.0%. ◯: The haze value difference is 2.0% or more and less than 3.5%. × The haze value difference is 3.5% or more.

[0143] (Polarizing plate durability: after final curing) The substrate-less double-sided adhesive sheet of each example was cut to a size of 60 mm x 100 mm, and one of the release sheets was peeled off. The exposed adhesive layer side was pressed and bonded to one of the TAC film surface polarizing plates of a polarizing plate in which a TAC film was laminated on both sides of a polarizer. Next, the other release sheet was peeled off, and the exposed adhesive layer side was bonded to alkali-free glass (Corning "Eagle XG", thickness 1.1 mm), and autoclaved (50°C, 0.5 MPa, 20 minutes). Thereafter, the peak irradiance from the alkali-free glass side was 150 mW / cm using a high-pressure mercury UV irradiation device. 2 , Accumulative exposure: 3000mJ / cm 2 (1000mJ / cm 2 The film was irradiated with ultraviolet light (1×3 passes) to prepare a sample for evaluating the durability of the polarizing plate. The polarizing plate durability evaluation sample was left to stand for one day in an atmosphere of 23°C and 50% RH, and then a durability test was carried out for 7 days (168 hours) in an atmosphere of 60°C and 90% RH, and the durability was evaluated according to the following criteria. Note that the durability evaluation was carried out by excluding air bubbles that were mixed in when the sample was attached to the alkali-free glass and evaluating the floating and air bubbles that occurred during the durability test. ○ Neither floating on the polarizing plate nor air bubbles with a diameter of 1 mm or more are found. ×: Either floating on the polarizing plate or air bubbles with a diameter of 1 mm or more are observed, or both.

[0144] [Table 3]

[0145] [Table 4]

[0146] [Table 5]

[0147] In Examples 1 to 3, which used the adhesive composition of the present invention, excellent adhesive properties were obtained in a low crosslinked state after primary curing, and efficient multi-stage curing was possible even with a small amount of active energy radiation during curing. An adhesive having excellent shape stability even after final curing was obtained, and such an adhesive had adhesive properties and reliability, and an adhesive sheet having an adhesive layer made of the adhesive was obtained. On the other hand, in Comparative Examples 1 to 4 in which the acrylic resin (A) specified in the present invention was not used, the adhesive properties during primary curing and the shape stability and adhesive properties after final curing were poor. [Industrial Applicability]

[0148] The adhesive obtained using this adhesive composition has excellent adhesive properties in a low crosslinked state after primary curing, and can be efficiently cured in multiple stages even with a small amount of active energy radiation during curing, and an adhesive having excellent shape stability even after final curing is obtained, and such an adhesive has excellent adhesive properties and reliability.The adhesive obtained using this adhesive composition is particularly useful as an adhesive used for bonding optical members constituting touch panels, image display devices, etc., and for sealing organic EL displays, etc.

Claims

1. A pressure-sensitive adhesive composition comprising an acrylic resin (A) and a photopolymerization initiator (B), The acrylic resin (A) has a glass transition temperature calculated from the dynamic viscoelasticity of 12 to 40° C., The pressure-sensitive adhesive composition, wherein the acrylic resin (A) has a structural unit derived from an alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms and a structural unit derived from an amide group-containing ethylenically unsaturated monomer (a3).

2. The pressure-sensitive adhesive composition according to claim 1, wherein the content of the structural unit derived from the alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms is 20 to 70 mass% based on the total acrylic resin (A).

3. The pressure-sensitive adhesive composition according to claim 1, wherein the content of the structural unit derived from the amide group-containing ethylenically unsaturated monomer (a3) ​​is 5 to 40 mass % based on the total mass of the acrylic resin (A).

4. The pressure-sensitive adhesive composition according to claim 1, wherein the acrylic resin (A) has a structural unit derived from an alkyl (meth)acrylate (a2) having an alkyl group having 1 to 4 carbon atoms.

5. The pressure-sensitive adhesive composition according to claim 1, wherein the acrylic resin (A) has a weight average molecular weight of 50,000 to 600,000.

6. The pressure-sensitive adhesive composition according to claim 1 , wherein the photopolymerization initiator (B) contains a hydrogen abstraction type photopolymerization initiator (b).

7. The pressure-sensitive adhesive composition according to claim 1 , further comprising a crosslinking agent (C).

8. A pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition according to any one of claims 1 to 7.

9. The pressure-sensitive adhesive according to claim 8, wherein the crosslinking is carried out by irradiation with active energy rays.

10. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to claim 8.

11. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to claim 9.

12. The pressure-sensitive adhesive sheet according to claim 10 , wherein the pressure-sensitive adhesive layer exhibits multi-stage curing properties in which the layer is cured in a plurality of stages.

13. The pressure-sensitive adhesive sheet according to claim 11 , wherein the pressure-sensitive adhesive layer exhibits multi-stage curing properties in which the layer is cured in a plurality of stages.

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