Pressure-sensitive adhesive composition, pressure-sensitive adhesive, and pressure-sensitive adhesive sheet

Abstract

To provide an adhesive composition, adhesive and adhesive sheet which exhibit low tackiness, high step-following ability and excellent adhesive properties in a low crosslinked state after primary curing, can be cured in multiple stages even with a small amount of active energy radiation during curing, and exhibit excellent adhesive properties and reliability even after final curing. [Solution] A pressure-sensitive adhesive composition comprising an acrylic resin (A1) and an acrylic resin (A2), the acrylic resin (A) having a Tg of -10 to 20°C, and a crosslinking agent (B), wherein the acrylic resin (A1) (excluding the acrylic resin (A2)) has a structural unit derived from an alkyl (meth)acrylate (a11) having an alkyl group with 5 or more carbon atoms and a structural unit derived from a functional group-containing ethylenically unsaturated monomer (a12), and the acrylic resin (A2) has a structural unit derived from an alkyl (meth)acrylate (a21) having an alkyl group with 5 or more carbon atoms and a structural unit derived from an amide group-containing ethylenically unsaturated monomer (a22).

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 become widely used in mobile devices such as televisions, PC monitors, laptops, mobile phones, smartphones, and tablet devices. Among these, capacitive touch panels are the most popular. A touch panel is typically composed of an organic electroluminescence (EL) or liquid crystal display, a transparent conductive film substrate (ITO substrate), and a protective film (protective glass). A transparent adhesive sheet is used to bond these components together.

[0003] Due to their characteristics, displays made of flexible devices such as organic electroluminescence (EL) devices can be used in a variety of shapes, from flat to curved, and even foldable and rollable displays. Transparent adhesive sheets are used to bond laminates that make up displays with complex shapes, such as curved surfaces. Because it is necessary to bond components of various shapes, the adhesive for the transparent adhesive sheet is bonded in a low-crosslinked state before final curing. Therefore, sufficient adhesive properties are required in the process leading up to final curing of the low-crosslinked adhesive layer. On the other hand, with the progress of miniaturization and weight reduction of mobile devices, there is a demand for thinner transparent adhesive sheets. Therefore, even if the adhesive sheet is made thinner, it is still required to have the ability to conform to uneven surfaces such as ink. For example, when attaching to a component with a complex shape, adhesion defects are likely to occur due to the transparent adhesive sheet sticking to areas other than the intended location. Therefore, there is a demand for transparent adhesive sheets that have high conformability to uneven surfaces and low tackiness. Furthermore, in order to secure components with complex shapes together, it is necessary to prevent the transparent adhesive sheet from peeling off from the components when stress is applied, and therefore there is a demand for a transparent adhesive sheet that has high constant load holding power even in a low cross-linking state.

[0004] In addition, the adhesive layer after final curing is required to have not only normal adhesive properties but also excellent performance in terms of reliability when attached to various components such as polarizing plates, glass, etc. For example, to obtain excellent durability after final curing, it is required to have a low degree of crosslinking until attachment to the adherend and to efficiently increase the degree of crosslinking during final curing, as well as high strength of the adhesive layer after curing, excellent impact resistance at low temperatures (low-temperature properties), and high adhesive strength independent of peel speed.

[0005] By laminating the film to the adherend in a low cross-linking state, it is possible to achieve sufficient adhesion to the adherend, and it is expected that the film will have high conformability to uneven surfaces. Furthermore, by finally curing the adhesive sheet while it is attached to the adherend in a low crosslinked state, the adhesive sheet will have a high degree of crosslinking, which is expected to improve durability. Generally, in the primary curing step, the adhesive is cured by crosslinking through heat or irradiation with active energy rays, and in the final curing step, the adhesive is cured by crosslinking through irradiation with active energy rays. Examples of pressure-sensitive adhesive sheets using such multi-stage curing pressure-sensitive adhesives include the pressure-sensitive adhesive sheets described in Patent Documents 1 to 3.

[0006] Patent Document 1 discloses that by further using an organic solvent that is volatile under general drying conditions in a solvent-based adhesive made from an acrylic resin and blending in a specific ratio of an ethylenically unsaturated monomer that is less volatile, thick coating is possible and an adhesive layer with a clean coating surface can be obtained. Furthermore, Patent Document 2 discloses that in order to form a three-dimensional network structure of a solvent-based acrylate ester-based pressure-sensitive adhesive without using a crosslinking agent, a hydrogen abstraction photopolymerization initiator is used and light irradiation is performed after the coating and drying process, thereby eliminating the aging process. Furthermore, Patent Document 3 discloses that by using an acrylic resin with a high glass transition temperature, a pressure-sensitive adhesive with excellent conformability to unevenness and blister resistance can be obtained. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-111939 [Patent Document 2] Japanese Patent Application Publication No. 2017-210542 [Patent Document 3] International Publication No. 2017 / 022770 Summary of the Invention [Problem to be solved by the invention]

[0008] However, none of Patent Documents 1 to 3 takes into consideration the adhesive properties in a low crosslinked state during primary curing, and therefore there is room for improvement in adhesive properties such as tackiness, step-following ability, and constant load holding power in a low crosslinked state during primary curing. Furthermore, there is a demand for efficient curing, and excellent adhesive properties and reliability after final curing.

[0009] Therefore, the present invention aims to provide an adhesive composition that can be used for multi-stage curing, which gives low tackiness, high step-following ability, and excellent adhesive properties in a low crosslinked state after primary curing, and which can be efficiently multi-stage cured even with a small amount of active energy radiation during curing, and which gives excellent adhesive properties and reliability even after final curing; an adhesive obtained by crosslinking the adhesive composition, and an adhesive sheet having an adhesive layer made of the adhesive. [Means for solving the problem]

[0010] In order to solve the above problems, the present inventors have conducted extensive research and have found that by using a pressure-sensitive adhesive composition containing a combination of two acrylic resins obtained using copolymerization components of specific compositions, it is possible to achieve excellent adhesive properties such as high step-following ability and low tackiness even in a low crosslinked state after primary curing, and that the composition can be cured efficiently even with a small amount of active energy radiation during curing, and that it is also possible to achieve excellent adhesive properties and reliability after final curing.

[0011] That is, the present invention has the following constituent features [1] to

[19] . [1] A pressure-sensitive adhesive composition comprising an acrylic resin (A) including an acrylic resin (A1) and an acrylic resin (A2), and a crosslinking agent (B), the acrylic resin (A1) (excluding the acrylic resin (A2)) has a structural unit derived from an alkyl (meth)acrylate (a11) having an alkyl group having 5 or more carbon atoms and a structural unit derived from a functional group-containing ethylenically unsaturated monomer (a12), the acrylic resin (A2) has a structural unit derived from an alkyl (meth)acrylate (a21) having an alkyl group having 5 or more carbon atoms and a structural unit derived from an amide group-containing ethylenically unsaturated monomer (a22), A pressure-sensitive adhesive composition, wherein the acrylic resin (A) has a glass transition temperature of -10 to 20°C calculated from the dynamic viscoelasticity. [2] The pressure-sensitive adhesive composition according to [1] above, wherein the acrylic resin (A1) has a glass transition temperature (T1) based on dynamic viscoelasticity of -50 to -20°C. [3] The pressure-sensitive adhesive composition according to the above [1] or [2], wherein the acrylic resin (A2) has a glass transition temperature (T2) based on dynamic viscoelasticity of -10 to 40°C. [4] The pressure-sensitive adhesive composition according to any one of [1] to [3], wherein the temperature difference between the glass transition temperature (T1) of the acrylic resin (A1) and the glass transition temperature (T2) of the acrylic resin (A2) is 70°C or less. [5] The pressure-sensitive adhesive composition according to any one of the above [1] to [4], wherein the content of the acrylic resin (A2) is 5 to 60 mass % based on the total amount of the acrylic resin (A). [6] The pressure-sensitive adhesive composition according to any one of the above [1] to [5], wherein the acrylic resin (A1) has a weight-average molecular weight of 200,000 to 1,000,000. [7] The pressure-sensitive adhesive composition according to any one of the above [1] to [6], wherein the acrylic resin (A2) has a weight-average molecular weight of 100,000 to 500,000. [8] The pressure-sensitive adhesive composition according to any one of the above [1] to [7], wherein the difference between the weight-average molecular weight of the acrylic resin (A1) and the weight-average molecular weight of the acrylic resin (A2) is 0 to 900,000. [9] The pressure-sensitive adhesive composition according to any one of [1] to [8] above, wherein the functional group-containing monomer (a12) is a hydroxyl group-containing monomer (a12-1), and the hydroxyl group-containing monomer (a12-1) when made into a homopolymer has a glass transition temperature of less than 0°C.

[10] The pressure-sensitive adhesive composition according to any one of the above [1] to [9], wherein the amide group-containing ethylenically unsaturated monomer (a22) is a compound (a22-1) having a tertiary amide group.

[11] The pressure-sensitive adhesive composition according to any one of [1] to

[10] above, wherein the glass transition temperature of the homopolymer of the amide group-containing ethylenically unsaturated monomer (a22) is 50°C or higher.

[12] The pressure-sensitive adhesive composition according to any one of [1] to

[11] above, wherein the acrylic resin (A) has a maximum loss tangent (tan δ) of 1.5 or less at a frequency of 1 Hz as measured by dynamic viscoelasticity.

[13] A pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition according to any one of the above [1] to

[12] .

[14] The pressure-sensitive adhesive according to

[13] , wherein the crosslinking is carried out by irradiation with active energy rays.

[15] The pressure-sensitive adhesive composition according to any one of [1] to

[12] above is completely crosslinked; The gel fraction is 60 to 90%. The storage modulus at 25°C is 200 to 300 kPa, The glass transition temperature based on dynamic viscoelasticity is -5 to 10°C, The pressure-sensitive adhesive according to

[13] or

[14] , wherein the loss tangent at -20°C is more than 0.1 and not more than 1.0.

[16] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to any one of

[13] to

[15] above.

[17] A pressure-sensitive adhesive composition containing an acrylic resin (A1) and an acrylic resin (A2), the acrylic resin (A1) has a structural unit derived from an alkyl (meth)acrylate (a11) having an alkyl group having 5 or more carbon atoms and a structural unit derived from the hydroxyl group-containing monomer (a12-1), the glass transition temperature of the hydroxyl group-containing monomer (a12-1) when made into a homopolymer is less than 0°C; the acrylic resin (A2) has a structural unit derived from a tertiary amide group-containing ethylenically unsaturated monomer (a22-1), A pressure-sensitive adhesive composition, wherein the tertiary amide group-containing ethylenically unsaturated monomer (a22-1) when made into a homopolymer has a glass transition temperature of 50°C or higher. [Effects of the Invention]

[0012] According to the present invention, there are provided a pressure-sensitive adhesive composition that can be used for multi-stage curing, which exhibits low tackiness, high step-following ability, and excellent adhesive properties in a low crosslinked state after primary curing, and which can be efficiently multi-stage cured even with a small amount of active energy radiation during curing, and which exhibits excellent adhesive properties and reliability even after final curing; 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. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below, but these are examples of preferred embodiments. In addition, the following terms used in this specification have the following meanings: "(Meth)acrylic" means acrylic or methacrylic. "(Meth)acryloyl" means acryloyl or methacryloyl. "(Meth)acrylate" means acrylate or methacrylate. The term "copolymerization component" is a general term for monomer components having a polymerizable double bond, and does not include polymerization initiators or polymerization solvents. The term "acrylic resin" refers to a resin obtained by polymerizing a monomer component containing at least one (meth)acrylic monomer. The term "sheet" conceptually encompasses sheets, films, and tapes. The symbol "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits.

[0014] <Adhesive composition> The pressure-sensitive adhesive composition of the present invention contains an acrylic resin (A) and a crosslinking agent (B). In addition to the acrylic resin (A) and the crosslinking agent (B), the pressure-sensitive adhesive composition of the present invention may further contain one or more of a photopolymerization initiator (C), a silane coupling agent (D) and other optional components, as needed, within a range that does not impair the effects of the present invention. Each component will be explained in turn below.

[0015] [Acrylic resin (A)] The acrylic resin (A) of the present invention contains an acrylic resin (A1) and an acrylic resin (A2).

[0016] [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 -10 to 20°C, preferably -8 to 15°C, more preferably -5 to 10°C, and even more preferably -3 to 10°C. If the temperature at which the loss tangent of the dynamic viscoelasticity of the acrylic resin (A) is maximized is equal to or lower than the upper limit, the adhesive strength tends to improve along with the improvement in the step-following ability and adhesion of the pressure-sensitive adhesive layer.If the temperature at which the loss tangent of the dynamic viscoelasticity of the acrylic resin (A) is maximized is equal to or higher than the lower limit, the adhesive properties tend to improve in the low-crosslinked state during primary curing.

[0017] The Tg based on dynamic viscoelasticity can be determined by the following measurement method. An appropriate organic solvent is added to prepare an acrylic resin solution containing only the acrylic resin (A) and the organic solvent. After adjusting the concentration of the acrylic resin solution, it is coated onto a release sheet so that the thickness after drying is 50 μm. The organic solvent is then removed by drying at 90 to 105°C for 5 to 10 minutes, and the resulting solution is then attached to a release sheet to prepare an acrylic resin sheet containing 99% by mass or more of the acrylic resin (A). Multiple acrylic resin sheets are then laminated to prepare an acrylic resin sheet with a thickness of approximately 800 μm. The dynamic viscoelasticity of the prepared sheet having a thickness of approximately 800 μm is measured under the following conditions, and the temperature at which the loss tangent (loss modulus G'' / storage modulus G'=tanδ) becomes maximum is read and taken as the Tg based on the dynamic viscoelasticity of the acrylic resin (A).

[0018] The temperature difference between the glass transition temperature (T1) of the acrylic resin (A1) and the glass transition temperature (T2) of the acrylic resin (A2) is preferably 70°C or less, more preferably 20 to 70°C, even more preferably 30 to 60°C, and particularly preferably 35 to 50°C. When the difference in glass transition temperature is equal to or less than the upper limit, the acrylic resins tend to have good compatibility with each other and the adhesive layer tends to have excellent transparency.When the difference in glass transition temperature is equal to or more than the lower limit, the adhesive layer tends to have excellent step-following ability during primary curing.

[0019] (Dynamic viscoelasticity measurement conditions) Measuring equipment: Dynamic viscoelasticity measuring device (product name: DVA-225, manufactured by IT Measurement and Control Co., Ltd.) Deformation mode: Shear Distortion: 0.1% Measurement temperature: -100~60℃ Measurement frequency: 1Hz

[0020] The calculated glass transition temperature (Tg') can be determined by the following FOX formula, and is a value different from the glass transition temperature (Tg) based on dynamic viscoelasticity in the present invention.

number

[0021] That is, it is a value calculated by applying the glass transition temperature and weight fraction of each of the monomers constituting the acrylic resin (A) to the Fox formula when they are made into a homopolymer. The glass transition temperature of the homopolymer of the monomers constituting the acrylic resin (A) is usually measured by a differential scanning calorimeter (DSC), and can be measured by a method in accordance with JIS K7121-1987 or JIS K 6240.

[0022] The temperature difference between the calculated glass transition temperature (T'1) of the acrylic resin (A1) and the calculated glass transition temperature (T'2) of the acrylic resin (A2) is preferably 70°C or less, more preferably 20 to 70°C, even more preferably 30 to 60°C, and particularly preferably 35 to 50°C. When the difference in calculated glass transition temperature is equal to or less than the upper limit, the acrylic resins tend to have good compatibility with each other and the adhesive layer tends to have excellent transparency.When the difference in glass transition temperature is equal to or more than the lower limit, the adhesive layer tends to have excellent step-following ability during primary curing.

[0023] The weight-average molecular weight (Mw) of the acrylic resin (A) is preferably 50,000 to 700,000, more preferably 150,000 to 600,000, and even more preferably 200,000 to 500,000. When the weight-average molecular weight of the acrylic resin (A) is not more than the above upper limit, the viscosity does not increase more than necessary, and coatability and handleability tend to be improved. When the weight-average molecular weight of the acrylic resin (A) is not less than the above lower limit, the cohesive strength of the acrylic resin (A) is improved, and adhesive properties and durability after final curing tend to be improved. 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 heated or otherwise subjected to any treatment after production.

[0024] The weight-average molecular weight of the acrylic resin (A) is the weight-average molecular weight converted to standard polystyrene molecular weight. The weight-average molecular weight was measured using a high-performance liquid chromatograph (manufactured by Nihon Waters K.K., "Waters 2695 (main unit)" and "Waters 2414 (detector)") with a Shodex GPC KF-806L column (exclusion limit molecular weight: 2 × 10 7 Separation range: 100 to 2 × 10 7 Measurements can be performed by connecting three columns in series: theoretical plate number: 10,000 / column, filler material: styrene-divinylbenzene copolymer, filler particle size: 10 μm. The number average molecular weight can also be measured using a similar method.

[0025] The difference in weight average molecular weight (Mw) between the acrylic resin (A1) and the acrylic resin (A2) is preferably from 0 to 900,000, more preferably from 50,000 to 600,000, and even more preferably from 100,000 to 400,000. When the difference in weight-average molecular weight (Mw) is equal to or less than the upper limit, the handling of the acrylic resin on the high molecular weight side tends to be improved, and the cohesive force of the acrylic resin (A) tends to be improved as the molecular weight of the acrylic resin on the low molecular weight side becomes higher, and the adhesive properties during primary curing tend to be improved.

[0026] The difference in number average molecular weight (Mn) between the acrylic resin (A1) and the acrylic resin (A2) is preferably from 0 to 500,000, more preferably from 5,000 to 200,000, and even more preferably from 10,000 to 100,000. When the difference in number average molecular weight (Mn) is equal to or less than the upper limit, the handling of the acrylic resin on the high molecular weight side tends to be improved, and the cohesive force of the acrylic resin (A) tends to be improved as the molecular weight of the acrylic resin on the low molecular weight side becomes higher, and the adhesive properties during primary curing tend to be improved.

[0027] 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 the above upper limit or less, the durability of the pressure-sensitive adhesive layer tends to be improved and foaming and the like tends to be more easily suppressed. If the dispersity of the acrylic resin (A) is the above lower limit or more, handleability tends to be improved. The lower limit of the dispersity can be set to 1.1 in view of production limitations. The degree of dispersion can be determined from the weight average molecular weight and the number average molecular weight.

[0028] [Acrylic resin (A1)] The acrylic resin (A1) used in the present invention has a structural unit derived from an alkyl (meth)acrylate (a11) having an alkyl group with 5 or more carbon atoms and a structural unit derived from a functional group-containing ethylenically unsaturated monomer (a12). The acrylic resin (A1) used in the present invention may, if necessary, have at least one of a structural unit derived from an alkyl (meth)acrylate (a13) having an alkyl group with 1 to 4 carbon atoms and another ethylenically unsaturated monomer (a14). The acrylic resin (A1) does not include the acrylic resin (A2), in other words, the acrylic resin (A1) does not have a structural unit derived from the amide group-containing ethylenically unsaturated monomer (a22) described below.

[0029] The acrylic resin (A1) of the present invention can be obtained by copolymerizing an alkyl(meth)acrylate (a11) having an alkyl group with 5 or more carbon atoms, a functional group-containing ethylenically unsaturated monomer (a12), an alkyl(meth)acrylate (a13) having an alkyl group with 1 to 4 carbon atoms, which is used as needed, and another ethylenically unsaturated monomer (a14). Each copolymer component of the acrylic resin (A1) will be explained in turn below.

[0030] (Alkyl (meth)acrylate (a11) having an alkyl group with 5 or more carbon atoms) The number of carbon atoms in the alkyl group of the alkyl (meth)acrylate (a11) having 5 or more carbon atoms used in the present invention is preferably 8 or more. The upper limit is preferably 24 or less, more preferably 18 or less.

[0031] The glass transition temperature (Tg) of the alkyl (meth)acrylate (a11) having an alkyl group having 5 or more carbon atoms used in the present invention when formed into a homopolymer is preferably −80° C. to 0° C., more preferably −75° C. to −20° C. By using an alkyl (meth)acrylate having a Tg within the above range, it is possible to improve the active energy ray curability and the adhesive properties after curing. The alkyl (meth)acrylate (a11) having an alkyl group having 5 or more carbon atoms may be used alone or in combination of two or more.

[0032] Examples of the alkyl(meth)acrylate (a11) having an alkyl group having 5 or more carbon atoms used in the present invention include a linear alkyl(meth)acrylate (a11-1) containing a linear alkyl group and a branched alkyl(meth)acrylate (a11-2) containing a branched alkyl group.

[0033] The number of carbon atoms in the alkyl group of the linear alkyl (meth)acrylate (a11-1) is preferably 8 or more. The upper limit is preferably 24 or less, and more preferably 18 or less. Examples of the linear alkyl (meth)acrylate (a11-1) 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.

[0034] The number of carbon atoms in the alkyl group of the branched alkyl (meth)acrylate (a11-2) is preferably 8 or more. The upper limit is preferably 24 or less, more preferably 18 or less. Examples of the branched alkyl (meth)acrylate (a11-2) 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. The Tg values ​​shown for the branched alkyl (meth)acrylates (a11-2) exemplified above are glass transition temperatures when each branched alkyl (meth)acrylate (a11-2) is made into a homopolymer.

[0035] The acrylic resin (A1) preferably has a structural unit derived from a branched alkyl (meth)acrylate (a11-2) in that it can be efficiently cured by active energy rays. Among these, it is preferable to have a structural unit derived from 2-ethylhexyl (meth)acrylate or a structural unit derived from isodecyl (meth)acrylate, because these have excellent active energy ray curability during curing.

[0036] (Functional Group-Containing Ethylenically Unsaturated Monomer (a12)) Examples of the functional group-containing ethylenically unsaturated monomer (a12) include a hydroxyl group-containing monomer (a12-1), a nitrogen atom-containing functional group (excluding amide groups)-containing monomer (a12-2), a carboxyl group-containing monomer, an acetoacetyl group-containing monomer, an isocyanate group-containing monomer, and a glycidyl group-containing monomer. Among these, the hydroxyl group-containing monomer (a12-1) and the carboxyl group-containing monomer are preferred, and the hydroxyl group-containing monomer (a12-1) is more preferred. That is, the acrylic resin (A1) used in the present invention preferably has a structural unit derived from the hydroxyl group-containing monomer (a12-1).

[0037] Examples of the hydroxyl group-containing monomer (a12-1) include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 2,2-dimethyl 2-hydroxyethyl (meth)acrylate.

[0038] The glass transition temperature (Tg) of the homopolymer of the hydroxyl group-containing monomer (a12-1) is preferably less than 0°C, from the viewpoint of lowering the glass transition temperature (Tg) of the acrylic resin (A1). The Tg of the homopolymer of the hydroxyl group-containing monomer (a12-1) is more preferably from -50 to -5°C, and even more preferably from -40 to -15°C.

[0039] Examples of the functional group-containing monomer (a12-2) having a nitrogen atom include amino group-containing monomers. Examples of amino group-containing monomers include primary amino group-containing (meth)acrylates such as aminomethyl (meth)acrylate and aminoethyl (meth)acrylate; secondary amino group-containing (meth)acrylates such as t-butylaminoethyl (meth)acrylate and t-butylaminopropyl (meth)acrylate; and tertiary amino group-containing (meth)acrylates such as ethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, and diethylaminopropyl (meth)acrylate.

[0040] Examples of carboxy group-containing monomers include (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.

[0041] Examples of acetoacetyl group-containing monomers include 2-(acetoacetoxy)ethyl (meth)acrylate and allyl acetoacetate. Examples of isocyanate group-containing monomers include 2-acryloyloxyethyl isocyanate, 2-methacryloyloxyethyl isocyanate, and alkylene oxide adducts of these monomers. Examples of the glycidyl group-containing monomer include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate.

[0042] The acrylic resin (A1) used in the present invention may further contain at least one of a structural unit derived from an alkyl (meth)acrylate (a11) having an alkyl group with 5 or more carbon atoms and a structural unit derived from a functional group-containing ethylenically unsaturated monomer (a12), a structural unit derived from an alkyl (meth)acrylate (a13) having an alkyl group with 1 to 4 carbon atoms, and a structural unit derived from another ethylenically unsaturated monomer (a14).

[0043] (Alkyl (meth)acrylate (a13) having an alkyl group having 1 to 4 carbon atoms) The alkyl group of the alkyl (meth)acrylate (a13) has 1 to 4 carbon atoms, and preferably 1 to 2 carbon atoms. By setting the number of carbon atoms within the above range, the polarity of the polymer can be increased, and the adhesive strength to highly polar adherends such as glass can be improved. The alkyl (meth)acrylate (a13) may be used alone or in combination of two or more kinds.

[0044] The glass transition temperature (Tg) of the alkyl (meth)acrylate (a13) having an alkyl group of 1 to 4 carbon atoms used in the present invention when formed into a homopolymer is preferably -30°C to 150°C, more preferably 0°C to 110°C, and even more preferably 5°C to 105°C. By using an alkyl (meth)acrylate having a Tg within the above range, it is possible to reduce tackiness during primary curing and improve adhesive strength after final curing. Two or more types of alkyl (meth)acrylate (a13) having different Tgs may be used in combination, but it is preferred that at least one type of alkyl (meth)acrylate (a13) has a Tg of 0°C or higher.

[0045] Examples of the alkyl (meth)acrylate (a13) having an alkyl group having 1 to 4 carbon atoms 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), and t-butyl methacrylate (Tg: 107°C). The Tg values ​​shown for the alkyl (meth)acrylates (a13) exemplified above are glass transition temperatures when each alkyl (meth)acrylate (a13) is made into a homopolymer.

[0046] (Other ethylenically unsaturated monomers (a14)) Examples of other ethylenically unsaturated monomers (a14) include aromatic ring-containing monomers such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyldiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, orthophenylphenoxyethyl (meth)acrylate, and nonylphenol ethylene oxide adduct (meth)acrylate; alicyclic ring-containing monomers such as cyclohexyloxyalkyl (meth)acrylate; 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-butoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxytriethylene glycol (meth)acrylate, and ethoxydiethylene glycol (meth)acrylate. ether chain-containing monomers such as acrylate, methoxydipropylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, octoxypolyethylene glycol-polypropylene glycol mono(meth)acrylate, lauroxypolyethylene glycol mono(meth)acrylate, and stearoxypolyethylene glycol mono(meth)acrylate; benzophenone-containing monomers such as 4-(meth)acryloyloxybenzophenone; and others such as acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyl toluene, vinylpyridine, vinylpyrrolidone, itaconic acid dialkyl esters, fumaric acid dialkyl esters, acrylic chloride, methyl vinyl ketone, allyl trimethylammonium chloride, and dimethyl allyl vinyl ketone. The ethylenically unsaturated monomer (a14) may be used alone or in combination of two or more kinds.

[0047] Furthermore, ethylenically unsaturated monomers having two or more ethylenically unsaturated groups such as 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 can also be used in combination.

[0048] (Composition of acrylic resin (A1)) The content of the structural units derived from the alkyl (meth)acrylate (a11) having an alkyl group with 5 or more carbon atoms in the acrylic resin (A1) is preferably 40 to 95 mass%, more preferably 50 to 92 mass%, and even more preferably 65 to 90 mass%, based on the total mass of the acrylic resin (A1) (100 mass%). When the content of the structural units derived from the alkyl (meth)acrylate (a11) having an alkyl group with 5 or more carbon atoms is equal to or greater than the above lower limit, the active energy ray curability tends to be improved. When the content of the structural units derived from the alkyl (meth)acrylate (a11) having an alkyl group with 5 or more carbon atoms is within the above range, the adhesive properties such as tackiness during primary curing and the adhesive strength after curing are excellent.

[0049] The content of structural units derived from branched alkyl (meth)acrylate (a11-2) is preferably 50% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more, of the structural units derived from alkyl (meth)acrylate (a11) having an alkyl group having 5 or more carbon atoms. By setting the content of structural units derived from branched alkyl (meth)acrylate (a11-2) to the above-mentioned lower limit or more, excellent active energy ray curability and adhesive strength after final curing are achieved.

[0050] The content of the structural unit derived from the functional group-containing ethylenically unsaturated monomer (a12) in the acrylic resin (A1) is preferably 5 to 25 mass %, more preferably 8 to 20 mass %, and even more preferably 10 to 15 mass %, based on the total mass of the acrylic resin (A1) (100 mass %). When this content is equal to or greater than the lower limit, the active energy ray curability, adhesive strength after final curing, and moist heat resistance tend to improve, while when the content is equal to or less than the upper limit, the adhesive strength tends to improve along with the improved adhesion.

[0051] The content of the structural unit derived from the hydroxyl group-containing monomer (a12-1) in the acrylic resin (A1) is preferably 5 to 25 mass %, more preferably 8 to 20 mass %, and even more preferably 10 to 15 mass %, based on the total mass of the acrylic resin (A) (100 mass %). When this content is equal to or greater than the lower limit, the active energy ray curability, adhesive strength after final curing, and moist heat resistance tend to improve, while when the content is equal to or less than the upper limit, the adhesive strength tends to improve along with the improved adhesion.

[0052] When the acrylic resin (A1) contains a structural unit derived from an alkyl (meth)acrylate (a13) having an alkyl group with 1 to 4 carbon atoms, the content of the structural unit derived from an alkyl (meth)acrylate (a13) having an alkyl group with 1 to 4 carbon atoms in the acrylic resin (A1) is preferably 20 mass % or less, more preferably 10 mass % or less, and even more preferably 5 mass % or less, based on the total acrylic resin (A1) (100 mass %). When the content is equal to or less than the above upper limit, the active energy ray curability is improved and the dielectric properties of the adhesive layer tend to be easily adjusted.

[0053] When the acrylic resin (A1) contains a structural unit derived from an ethylenically unsaturated monomer (a14), the content of the structural unit derived from the ethylenically unsaturated monomer (a14) is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, based on the total acrylic resin (A1) (100% by mass). When the content of the ethylenically unsaturated monomer (a14) is not more than the above upper limit, the balance of adhesive properties tends to be good.

[0054] (Physical properties of acrylic resin (A1)) The glass transition temperature (T1) based on the dynamic viscoelasticity of the acrylic resin (A1), i.e., the temperature at which the loss tangent of the dynamic viscoelasticity is maximum, is preferably -50 to -20°C, more preferably -45 to -25°C, and even more preferably -40 to -30°C. When the glass transition temperature (T1) based on the dynamic viscoelasticity of the acrylic resin (A1) is not more than the upper limit, the adhesive strength tends to be improved along with the improvement in the step-following ability, low-temperature properties, and adhesion of the pressure-sensitive adhesive layer.When the temperature at which the loss tangent of the dynamic viscoelasticity of the acrylic resin (A1) is maximum is not less than the lower limit, the adhesive properties tend to be improved during primary curing and after final curing.

[0055] The Tg based on dynamic viscoelasticity can be determined in the same manner as for the acrylic resin (A).

[0056] The weight-average molecular weight (Mw) of the acrylic resin (A1) is preferably 200,000 to 1,000,000, more preferably 300,000 to 700,000, and even more preferably 400,000 to 600,000. When the weight-average molecular weight of the acrylic resin (A1) is not more than the above upper limit, the viscosity does not increase more than necessary, and the coatability and handleability tend to be improved. When the weight-average molecular weight of the acrylic resin (A1) is not less than the above lower limit, the cohesive strength and adhesive properties tend to be improved, and the durability after final curing tends to be improved. The weight-average molecular weight of the acrylic resin (A1) is the weight-average molecular weight at the time of completion of production. The weight-average molecular weight is measured on the acrylic resin (A1) that has not been heated or otherwise subjected to any treatment after production.

[0057] The weight average molecular weight, number average molecular weight and dispersity of the acrylic resin (A1) can be determined in the same manner as for the acrylic resin (A).

[0058] The dispersity (weight average molecular weight / number average molecular weight) of the acrylic resin (A1) is preferably 15 or less, more preferably 10 or less, even more preferably 7 or less, and particularly preferably 5 or less. When the dispersity of the acrylic resin (A1) is equal to or less than the above upper limit, the durability of the pressure-sensitive adhesive layer tends to be improved and foaming and the like tends to be more easily suppressed. The lower limit of the dispersity of the acrylic resin (A1) can be 1.1, from the viewpoint of a tendency for improved handleability and from the viewpoint of production limitations.

[0059] The content of the acrylic resin (A1) is preferably 5 to 60% by mass, more preferably 10 to 50% by mass, and even more preferably 30 to 40% by mass, based on the total mass of the acrylic resin (A). When the content of the acrylic resin (A1) is equal to or greater than the lower limit, the step-following ability during primary curing tends to be excellent. When the content of the acrylic resin (A1) is equal to or less than the upper limit, the tackiness during primary curing and the adhesive strength after final curing tend to be excellent.

[0060] (Method for producing acrylic resin (A1)) The acrylic resin (A1) can be produced by polymerizing the alkyl(meth)acrylate (a11) having an alkyl group with 5 or more carbon atoms and the functional group-containing ethylenically unsaturated monomer (a12). The acrylic resin (A1) may be produced, if necessary, by further polymerizing at least one of the alkyl(meth)acrylate (a13) having an alkyl group with 1 to 4 carbon atoms and the ethylenically unsaturated monomer (a14) in addition to the alkyl(meth)acrylate (a11) having an alkyl group with 5 or more carbon atoms and the functional group-containing ethylenically unsaturated monomer (a12). Hereinafter, the alkyl(meth)acrylate (a11) having an alkyl group with 5 or more carbon atoms, the functional group-containing ethylenically unsaturated monomer (a12), the alkyl(meth)acrylate (a13) having an alkyl group with 1 to 4 carbon atoms, and the ethylenically unsaturated monomer (a14) are collectively referred to as copolymerization component (a1).

[0061] Examples of the polymerization method for the acrylic resin (A1) 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 (A1) with any monomer composition. An example of a preferred method for producing the acrylic resin (A1) will be described below.

[0062] First, the copolymerization component (a1) and a polymerization initiator are mixed or dropped into an organic solvent to carry out solution polymerization. Examples of organic solvents 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; halogenated aliphatic 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 more preferred. The organic solvent may be used alone or in combination of two or more kinds.

[0063] As the polymerization initiator used in the polymerization reaction, azo-based polymerization initiators and peroxide-based polymerization initiators, which are common 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 peroxide polymerization initiators 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. Of 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.

[0064] 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, even more preferably 1 to 4 parts by mass, particularly preferably 1.5 to 3 parts by mass, and most preferably 2 to 2.5 parts by mass, per 100 parts by mass of the copolymerization component (a1). When the amount of the polymerization initiator used is equal to or greater than the lower limit, the polymerization rate of the acrylic resin (A) tends to be improved, and the reaction rate of the monomers tends to be improved. Furthermore, the weight-average molecular weight of the acrylic resin (A) tends to be lower. When the amount of the polymerization initiator used is equal to or less than the upper limit, gelation of the acrylic resin (A) tends to be suppressed.

[0065] The polymerization conditions for solution polymerization are not particularly limited, and polymerization can be carried out according to conventionally known polymerization conditions. For example, polymerization can be carried out by mixing or dropping the copolymerization component (a1) and a polymerization initiator into an organic solvent.

[0066] The polymerization temperature in the polymerization reaction can be set to 40 to 120° C., but in the present invention, from the viewpoint of ensuring a stable reaction, it is preferably 50 to 90° C. If the polymerization temperature is equal to or lower than the above upper limit, gelation of the acrylic resin (A) tends to be suppressed, and if the polymerization temperature is equal to or higher than the above lower limit, the activity of the polymerization initiator is improved, which tends to improve the polymerization rate and the reaction rate of the monomer. The polymerization time in the polymerization reaction is not particularly limited, but is preferably 0.5 hours or more, more preferably 1 hour or more, even 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, since this facilitates heat removal.

[0067] [Acrylic resin (A2)] The acrylic resin (A2) used in the present invention has a structural unit derived from an alkyl(meth)acrylate (a21) having an alkyl group with 5 or more carbon atoms and a structural unit derived from an amide group-containing ethylenically unsaturated monomer (a22). The acrylic resin (A2) may, if necessary, have at least one of a structural unit derived from an alkyl(meth)acrylate (a23) having an alkyl group with 1 to 4 carbon atoms and a structural unit derived from another ethylenically unsaturated monomer (a24).

[0068] The acrylic resin (A2) of the present invention can be obtained by copolymerizing an alkyl(meth)acrylate (a21) having an alkyl group with 5 or more carbon atoms, an amide group-containing ethylenically unsaturated monomer (a22), an alkyl(meth)acrylate (a23) having an alkyl group with 1 to 4 carbon atoms, which is used as needed, and another ethylenically unsaturated monomer (a24). Each copolymer component of the acrylic resin (A2) will be explained in turn below.

[0069] (Alkyl (meth)acrylate (a21) having an alkyl group with 5 or more carbon atoms) The number of carbon atoms in the alkyl group of the alkyl (meth)acrylate (a21) having 5 or more carbon atoms used in the present invention is preferably 8 or more. The upper limit is preferably 24 or less, more preferably 18 or less.

[0070] The glass transition temperature (Tg) of a homopolymer formed from the alkyl(meth)acrylate (a21) having an alkyl group having 5 or more carbon atoms used in the present invention is preferably −80° C. to 0° C., more preferably −75° C. to −20° C. By using an alkyl(meth)acrylate having a Tg in the above range, it is possible to improve the active energy ray curability and the adhesive properties after curing. The alkyl (meth)acrylate (a21) having an alkyl group having 5 or more carbon atoms may be used alone or in combination of two or more.

[0071] Examples of the alkyl(meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms used in the present invention include a linear alkyl(meth)acrylate (a21-1) containing a linear alkyl group and a branched alkyl(meth)acrylate (a21-2) containing a branched alkyl group.

[0072] The number of carbon atoms in the alkyl group of the linear alkyl (meth)acrylate (a21-1) is preferably 8 or more. The upper limit is preferably 24 or less, and more preferably 18 or less. Examples of the linear alkyl (meth)acrylate (a21-1) 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.

[0073] The number of carbon atoms in the alkyl group of the branched alkyl (meth)acrylate (a21-2) is preferably 8 or more. The upper limit is preferably 24 or less, more preferably 18 or less. Examples of the branched alkyl (meth)acrylate (a21-2) 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. The Tg values ​​shown for the branched alkyl (meth)acrylates (a21-2) exemplified above are glass transition temperatures when each branched alkyl (meth)acrylate (a21-2) is made into a homopolymer.

[0074] The acrylic resin (A) preferably has a structural unit derived from a branched alkyl (meth)acrylate (a21-2) in that it can be efficiently cured by active energy rays. Among these, it is preferable to have structural units derived from 2-ethylhexyl (meth)acrylate or isodecyl (meth)acrylate, because these have excellent active energy ray curability during curing.

[0075] (Amide group-containing ethylenically unsaturated monomer (a22)) As the amide group-containing ethylenically unsaturated monomer (a22), a tertiary amide group-containing ethylenically unsaturated monomer (a22-1) is preferred in terms of excellent active energy ray curability during curing, excellent reliability after curing, and excellent adhesive strength after curing. In particular, among the tertiary amide group-containing ethylenically unsaturated monomers (a22-1), the number of carbon atoms in the N-substituted alkyl group is preferably 2 or less, and more preferably 1.

[0076] The glass transition temperature (Tg) of the homopolymer of the amide group-containing ethylenically unsaturated monomer (a22) is preferably 50°C or higher, more preferably 50 to 180°C, and even more preferably 80 to 120°C. When the Tg of the homopolymer of the amide group-containing ethylenically unsaturated monomer (a22) is at least the above lower limit, the adhesive properties such as tackiness during primary curing and the strength after final curing are excellent. When the Tg of the homopolymer of the amide group-containing ethylenically unsaturated monomer (a22) is at most the above upper limit, the active energy ray curability during curing is excellent. The same applies to the preferred range of the glass transition temperature (Tg) when the tertiary amide group-containing ethylenically unsaturated monomer (a22-1) is made into a homopolymer.

[0077] Examples of the amide group-containing ethylenically unsaturated monomer (a22) include primary and secondary amide group-containing monomers such as (meth)acrylamide, N-butyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-methylol(meth)acrylamide, hydroxyethylacrylamide, and dimethylaminopropylacrylamide; 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. Of these, N,N'-dimethylacrylamide, N,N'-dimethylmethacrylamide, N,N'-diethylacrylamide, and N,N'-diethylmethacrylamide are preferred, and N,N'-dimethylacrylamide and N,N'-dimethylmethacrylamide are more preferred.

[0078] The acrylic resin (A2) used in the present invention may further contain at least one of a structural unit derived from an alkyl (meth)acrylate (a23) having an alkyl group with 1 to 4 carbon atoms and a structural unit derived from another ethylenically unsaturated monomer (a24), in addition to the structural unit derived from an alkyl (meth)acrylate (a21) having an alkyl group with 5 or more carbon atoms and the structural unit derived from an amide group-containing ethylenically unsaturated monomer (a22).

[0079] (Alkyl (meth)acrylate (a23) having an alkyl group having 1 to 4 carbon atoms) The alkyl group of the alkyl (meth)acrylate (a23) has 1 to 4 carbon atoms, and preferably 1 to 2 carbon atoms. By setting the number of carbon atoms within the above range, the polarity of the polymer can be increased, and the adhesive strength to highly polar adherends such as glass can be improved. The alkyl (meth)acrylate (a23) may be used alone or in combination of two or more kinds.

[0080] The glass transition temperature (Tg) of the alkyl (meth)acrylate (a23) having an alkyl group having 1 to 4 carbon atoms used in the present invention when formed into a homopolymer is preferably -30°C to 150°C, more preferably 0°C to 110°C, and even more preferably 5°C to 105°C. By using an alkyl (meth)acrylate having a Tg within the above range, it is possible to reduce tackiness during primary curing and improve adhesive strength and strength after final curing. Two or more types of alkyl (meth)acrylate (a23) having different Tgs may be used in combination, but it is preferred that at least one type of alkyl (meth)acrylate (a23) has a Tg of 0°C or higher.

[0081] Examples of the alkyl (meth)acrylate (a23) having an alkyl group having 1 to 4 carbon atoms 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), and t-butyl methacrylate (Tg: 107°C). The Tg values ​​shown for the alkyl (meth)acrylates (a23) exemplified above are glass transition temperatures when each alkyl (meth)acrylate (a23) is made into a homopolymer.

[0082] (Other ethylenically unsaturated monomers (a24)) Examples of other ethylenically unsaturated monomers (a24) include hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 2,2-dimethyl 2-hydroxyethyl (meth)acrylate; aromatic ring-containing monomers such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyldiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, orthophenylphenoxyethyl (meth)acrylate, and nonylphenol ethylene oxide adduct (meth)acrylate; alicyclic ring-containing monomers such as cyclohexyloxyalkyl (meth)acrylate; 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, and the like. Ether chain-containing monomers such as acrylate, 3-methoxybutyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-butoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxytriethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, octoxypolyethylene glycol-polypropylene glycol mono(meth)acrylate, lauroxypolyethylene glycol mono(meth)acrylate, and stearoxypolyethylene 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 ether, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, itaconic acid dialkyl ester, fumaric acid dialkyl ester, acrylic chloride, methyl vinyl ketone, allyl trimethyl ammonium chloride, and dimethyl allyl vinyl ketone. The ethylenically unsaturated monomer (a24) may be used alone or in combination of two or more kinds.

[0083] Furthermore, ethylenically unsaturated monomers having two or more ethylenically unsaturated groups such as 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 can also be used in combination.

[0084] (Composition of acrylic resin (A2)) The content of the structural unit derived from the alkyl (meth)acrylate (a21) having an alkyl group with 5 or more carbon atoms in the acrylic resin (A2) is preferably 30 to 80 mass%, more preferably 40 to 70 mass%, and even more preferably 50 to 65 mass%, relative to the total acrylic resin (A) (100 mass%). When the content of the structural unit derived from the alkyl (meth)acrylate (a21) having an alkyl group with 5 or more carbon atoms is equal to or greater than the above lower limit, the active energy ray curability tends to be improved. When the content of the structural unit derived from the alkyl (meth)acrylate (a21) having an alkyl group with 5 or more carbon atoms is within the above range, the adhesive properties such as tackiness during primary curing and the adhesive strength after final curing are excellent.

[0085] The content of structural units derived from branched alkyl (meth)acrylate (a21-2) is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, of the structural units derived from alkyl (meth)acrylate (a21) having an alkyl group having at least 5 carbon atoms. By setting the content of such structural units derived from branched alkyl (meth)acrylate (a21-2) to 50% by mass or more, the active energy ray curability and adhesive strength after final curing are excellent.

[0086] The content of the amide group-containing ethylenically unsaturated monomer (a22) in the acrylic resin (A2) is preferably 5 to 30% by mass, more preferably 10 to 27% by mass, and even more preferably 15 to 25% by mass, based on the total mass of the acrylic resin (A2) (100% by mass). When this content is at least the lower limit, the active energy ray curability, adhesive strength after final curing, moist heat resistance, and strength tend to improve, while when the content is at most the upper limit, the adhesive strength tends to improve along with the improved adhesion.

[0087] The content of structural units derived from alkyl (meth)acrylate (a23) having an alkyl group having 1 to 4 carbon atoms in the acrylic resin (A2) is preferably 10 to 50 mass%, more preferably 12.5 to 40 mass%, and even more preferably 15 to 30 mass%, relative to the total mass of the acrylic resin (A2) (100 mass%). If this content is at least the lower limit, adhesive properties such as tackiness during primary curing and strength during final curing tend to be improved, while if it is at most the upper limit, active energy ray curability tends to be improved.

[0088] Furthermore, among the structural units derived from alkyl(meth)acrylate (a23) having an alkyl group having 1 to 4 carbon atoms, the content of structural units derived from alkyl(meth)acrylate having a glass transition temperature (Tg) of 0° C. or higher when forming a homopolymer is preferably 50% by mass or more, more preferably 80% by mass or more. When such a content is equal to or higher than the above-mentioned lower limit, adhesive properties such as tackiness during primary curing tend to be improved.

[0089] When the acrylic resin (A2) contains a structural unit derived from the ethylenically unsaturated monomer (a24), the content of the structural unit derived from the ethylenically unsaturated monomer (a4) is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, based on the total acrylic resin (A) (100% by mass). When the content of the ethylenically unsaturated monomer (a24) is equal to or greater than the above lower limit, the balance of adhesive properties tends to be good.

[0090] (Physical properties of acrylic resin (A2)) The glass transition temperature (T2) based on the dynamic viscoelasticity of the acrylic resin (A2), i.e., the temperature at which the loss tangent of the dynamic viscoelasticity is maximum, is preferably from -10 to 40°C, more preferably from -5 to 30°C, even more preferably from 0 to 25°C, and particularly preferably from 5 to 20°C. When the glass transition temperature (T2) based on the dynamic viscoelasticity of the acrylic resin (A2) is not more than the upper limit, the adhesive strength tends to be improved along with the improvement in the step-following ability and adhesion of the pressure-sensitive adhesive layer. When the temperature at which the loss tangent of the dynamic viscoelasticity of the acrylic resin (A2) is maximum is not less than the lower limit, the adhesive properties tend to be improved in a low-crosslinked state during primary curing.

[0091] The Tg based on dynamic viscoelasticity can be determined in the same manner as for the acrylic resin-based resins (A and A1).

[0092] The weight-average molecular weight (Mw) of the acrylic resin (A2) is preferably 100,000 to 500,000, more preferably 100,000 to 450,000, and even more preferably 150,000 to 400,000. When the weight-average molecular weight of the acrylic resin (A2) is not more than the upper limit, the viscosity does not increase more than necessary, and coatability and handleability tend to be improved. When the weight-average molecular weight of the acrylic resin (A2) is not less than the lower limit, the cohesive strength is improved, the adhesive properties during primary curing are improved, and durability after final curing tends to be improved. The weight average molecular weight of the acrylic resin (A2) is the weight average molecular weight at the time of completion of production. The weight average molecular weight is measured on the acrylic resin (A2) that has not been heated or otherwise subjected to any treatment after production.

[0093] The weight average molecular weight, number average molecular weight and dispersity of the acrylic resin (A2) can be determined in the same manner as for the acrylic resin (A).

[0094] The dispersity (weight average molecular weight / number average molecular weight) of the acrylic resin (A2) is preferably 15 or less, more preferably 10 or less, even more preferably 7 or less, and particularly preferably 5 or less. When the dispersity of the acrylic resin (A2) is equal to or less than the above upper limit, the durability of the pressure-sensitive adhesive layer tends to be improved and foaming and the like tends to be more easily suppressed. The lower limit of the dispersity of the acrylic resin (A2) can be 1.1, from the viewpoint of a tendency for handleability to be improved and from the viewpoint of the dispersity production limit.

[0095] The content of the acrylic resin (A2) is preferably 30 to 95 mass%, more preferably 50 to 85 mass%, and even more preferably 60 to 75 mass%, based on the total mass of the acrylic resin (A). When the content of the acrylic resin (A2) is equal to or greater than the above lower limit, the tackiness during primary curing is excellent. When the content of the acrylic resin (A2) is equal to or less than the above upper limit, the conformability to unevenness during primary curing is excellent.

[0096] (Method for producing acrylic resin (A2)) The acrylic resin (A2) can be produced by polymerizing the alkyl(meth)acrylate (a21) having an alkyl group with 5 or more carbon atoms and the amide group-containing ethylenically unsaturated monomer (a22). The acrylic resin (A2) may be produced, if necessary, by further polymerizing at least one of the alkyl(meth)acrylate (a23) having an alkyl group with 1 to 4 carbon atoms and the ethylenically unsaturated monomer (a24) in addition to the alkyl(meth)acrylate (a21) having an alkyl group with 5 or more carbon atoms and the amide group-containing ethylenically unsaturated monomer (a22). Hereinafter, the alkyl(meth)acrylate (a21) having an alkyl group with 5 or more carbon atoms, the amide group-containing ethylenically unsaturated monomer (a22), the alkyl(meth)acrylate (a23) having an alkyl group with 1 to 4 carbon atoms, and the ethylenically unsaturated monomer (a24) are collectively referred to as copolymerization component (a2).

[0097] The acrylic resin (A2) can be produced by the same production method as that for the acrylic resin (A1), except that the copolymerization component (a1) is replaced with the copolymerization component (a2).

[0098] (Crosslinking agent (B)) The pressure-sensitive adhesive composition of the present invention contains an acrylic resin (A) and a crosslinking agent (B). Examples of the crosslinking agent (B) include an active energy ray crosslinking agent (b1) and a thermal crosslinking agent (b2). The active energy ray crosslinking agent (b1) and the thermal crosslinking agent (b2) may be used alone or in combination.

[0099] When the crosslinking agent (B) contains only the active energy ray crosslinking agent (b1), multi-stage curing is possible simply by controlling the amount of active energy rays. When the crosslinking agent (B) contains both the active energy ray crosslinking agent (b1) and the thermal crosslinking agent (b2), multi-stage curing is also possible by using both thermal curing and active energy ray curing. By controlling the crosslinking reaction in this way, 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.

[0100] [Active energy ray crosslinking agent (b1)] The active energy ray crosslinking agent (b1) 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, acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(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, tetramethylolmethane tri(meth)acrylate, isocyanuric acid ethylene oxide-modified tri(meth)acrylate, and multifunctional urethane (meth)acrylate. Among these, in terms of the balance of adhesive properties after curing, (meth)acrylates containing two ethylenically unsaturated groups are preferred, and (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, and (poly)tetramethylene glycol di(meth)acrylate are particularly preferred. The polyfunctional crosslinking agent may be used alone or in combination of two or more kinds.

[0101] [Thermal crosslinking agent (b2)] The thermal crosslinking agent (b2) exhibits excellent adhesive strength by reacting with the functional group derived from the functional group-containing ethylenically unsaturated monomer (a12), which is a constituent monomer of the acrylic resin (A). Examples of suitable crosslinking agents include isocyanate-based crosslinking agents (b2-1), epoxy-based crosslinking agents (b2-2), aziridine-based crosslinking agents (b2-3), melamine-based crosslinking agents (b2-4), aldehyde-based crosslinking agents (b2-5), amine-based crosslinking agents (b2-6), and metal chelate-based crosslinking agents (b2-7). Among these, isocyanate-based crosslinking agents (b2-1) are preferred for their improved adhesion to the substrate and reactivity with the acrylic resin (A). The thermal crosslinking agent (b2) may be used alone or in combination of two or more.

[0102] As the isocyanate-based crosslinking agent (b2-1), aromatic isocyanate compounds are preferred, more preferably tolylene diisocyanate compounds, due to their excellent reactivity, and aliphatic isocyanate compounds are preferred, more preferably hexamethylene diisocyanate compounds, due to the prevention of yellowing.

[0103] Examples of the isocyanate crosslinking agent (b2-1) 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 tetramethylxylylene diisocyanate, and 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; and biuret and isocyanurate forms of these isocyanate compounds.

[0104] Examples of the epoxy crosslinking agent (b2-2) 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.

[0105] Examples of the aziridine crosslinking agent (b2-3) 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).

[0106] Examples of the melamine-based crosslinking agent (b2-4) include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexaptoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, and melamine resins.

[0107] Examples of the aldehyde crosslinking agent (b2-5) include glyoxal, malondialdehyde, succindialdehyde, maleic dialdehyde, glutaric dialdehyde, formaldehyde, acetaldehyde, and benzaldehyde.

[0108] Examples of the amine-based crosslinking agent (b2-6) include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetraamine, diethylenetriamine, triethyltetraamine, isophoronediamine, amino resins, and polyamides.

[0109] Examples of the metal chelate crosslinking agent (b2-7) 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.

[0110] (Photopolymerization initiator (C)) The pressure-sensitive adhesive composition of the present invention preferably contains a photopolymerization initiator (C) in addition to the acrylic resin (A) and the crosslinking agent (B). The photopolymerization initiator (C) preferably contains a hydrogen abstraction type photopolymerization initiator. Examples of the hydrogen abstraction photopolymerization initiator include an intramolecular hydrogen abstraction photopolymerization initiator (c1) and an intermolecular hydrogen abstraction photopolymerization initiator (c2), and it is more preferable to contain an intramolecular hydrogen abstraction photopolymerization initiator (c1). The photopolymerization initiator (C) may further contain a photopolymerization initiator (c3) other than the intramolecular hydrogen abstraction photopolymerization initiator (c1) and the intermolecular hydrogen abstraction photopolymerization initiator (c2), as long as the effects of the invention are not impaired.

[0111] [Intramolecular hydrogen abstraction photopolymerization initiator (c1)] The intramolecular hydrogen abstraction photopolymerization initiator (c1) has a structure that can generate radicals by abstracting hydrogen from the photopolymerization initiator itself, and specifically has a phenyl glyoxylate structure or the like. The intramolecular hydrogen abstraction photopolymerization initiator (c1) may be used alone or in combination of two or more kinds.

[0112] Examples of the intramolecular hydrogen abstraction photopolymerization initiator (c1) include 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl oxyphenyl-acetic acid, methyl [4-(4-methoxyoxalyl-phenoxy)-phenyl]-oxoacetic acid, butyl [4-(4-butoxyoxalyl-phenoxy)-phenyl]-oxoacetic acid, methyl [4-(4-methoxyoxalyl-phenylsulfanyl)-phenyl]-oxoacetic acid, methyl [4-(4-methoxyoxalyl-benzyl)-phenyl]-oxoacetic acid, and methyl phenylglyoxylate. Among these, in terms of crosslinking efficiency at the time of final curing, oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester and [4-(4-methoxyoxalyl-phenoxy)-phenyl]-oxoacetic acid methyl ester, which have multiple crosslinking points within the molecule, are preferred. Commercially available products include "Omnirad MBF" and "Omnirad 754" manufactured by IGM RESINS BV.

[0113] [Intermolecular hydrogen abstraction photopolymerization initiator (c2)] The intermolecular hydrogen abstraction photopolymerization initiator (c2) has a structure that can generate radicals by abstracting hydrogen from a site other than the photopolymerization initiator itself, and specifically has a benzophenone structure, a thioxanthone structure, or the like. The intermolecular hydrogen abstraction photopolymerization initiator (c2) may be used alone or in combination of two or more kinds.

[0114] Examples of the intermolecular hydrogen abstraction photopolymerization initiator (c2) include benzophenones such as benzophenone, 4-methylbenzophenone, 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, carboxymethoxymethoxybenzophenone-polyethylene glycol 250 diester, methyl 2-benzoylbenzoate, and 4-(1,3-acryloyl-1,4,7,10,13-pentaoxotridecyl)benzophenone; and thioxanthones such as 2,4-diethylthioxanthone, 2-isopropylthioxanthone, 2,4-diisopropylthioxanthone, and 1-chloro-4-propoxythioxanthone. 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 for 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.

[0115] [Other photopolymerization initiators (c3)] Other examples of the photopolymerization initiator (c3) 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 benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether; and acylphosphine oxides 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 (c3) may be used singly or in combination of two or more.

[0116] As an auxiliary agent for the photopolymerization initiator (C), it is also possible to use in combination 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. The auxiliary for the photopolymerization initiator (C) may be used alone or in combination of two or more.

[0117] (Silane coupling agent (D)) The pressure-sensitive adhesive composition of the present invention preferably further contains a silane coupling agent (D) as a compound other than the acrylic resin (A), the crosslinking agent (B), and the photopolymerization initiator (C) in order to improve durability.

[0118] The silane coupling agent (D) is an organosilicon compound containing, 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 monomeric or oligomeric 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 viewpoint of excellent durability and reworkability.

[0119] The content of the reactive functional group in the silane coupling agent (D) is preferably 3,000 g / mol or less, more preferably 1,500 g / mol or less, and even more preferably 1,000 g / mol or less. When the reactive functional group is within the above numerical range, the balance between durability and reworkability is improved. The lower limit of the content of the reactive functional group in the silane coupling agent (D) is 200 g / mol.

[0120] The alkoxy group bonded to the silicon atom in the silane coupling agent (D) is preferably an alkoxy group having 1 to 8 carbon atoms from the viewpoint of durability and storage stability, with methoxy and ethoxy groups being more preferred. The silane coupling agent (D) may have an organic functional group other than a reactive functional group and an alkoxy group bonded to a silicon atom, such as an alkyl group or a phenyl group.

[0121] 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 these, 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.

[0122] (optional ingredient) The pressure-sensitive adhesive composition of the present invention may contain a pressure-sensitive adhesive as an optional component, if necessary. The pressure-sensitive adhesive composition of the present invention may contain conventionally known additives such as a carbodiimide, an antioxidant, an ultraviolet absorber, a crosslinking accelerator, an antistatic agent, a tackifier, and a functional dye.

[0123] (Composition of Pressure-Sensitive Adhesive Composition) The content of the acrylic resin (A) is preferably 80% by mass or more, more preferably 85 to 99% by mass, and even more preferably 90 to 98% by mass, based on the total mass of the adhesive composition. When the content of the acrylic resin (A) is within this range, excellent adhesive properties are likely to be obtained in a low crosslinked state after primary curing.

[0124] The content of the crosslinking agent (B) is preferably 20 parts by mass or less, more preferably 0.1 to 10 parts by mass, and even more preferably 0.5 to 5 parts by mass, relative to 100 parts by mass of the acrylic resin (A). When the content of the crosslinking agent (B) is equal to or less than the upper limit, the adhesive properties and step-conforming ability after primary curing tend to be improved. When the content of the crosslinking agent (B) is equal to or more than the lower limit, the durability tends to be improved.

[0125] When the pressure-sensitive adhesive composition contains an active energy ray crosslinking agent (b1), the content of the active energy ray crosslinking agent (b1) is preferably 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, and even more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the acrylic resin (A). When the content of the active energy ray crosslinking agent (b1) is equal to or greater than the lower limit, the cohesive strength is sufficient and sufficient durability tends to be obtained. When the content of the active energy ray crosslinking agent (b1) is equal to or less than the upper limit, the adhesive properties and step-following ability during primary curing tend to be improved.

[0126] When the pressure-sensitive adhesive composition contains a thermal crosslinking agent (b2), the content of the thermal crosslinking agent (b2) is preferably 0.001 to 5 parts by mass, more preferably 0.02 to 1 part by mass, and even more preferably 0.05 to 0.5 parts by mass, per 100 parts by mass of the acrylic resin (A). When the content of the thermal crosslinking agent (b2) is equal to or greater than the lower limit, the cohesive strength is sufficient, and adhesive properties such as holding power during primary curing tend to be improved. When the content of the thermal crosslinking agent (b2) is equal to or less than the upper limit, the conformability to unevenness during primary curing tends to be improved, and adhesive strength during final curing tends to be improved.

[0127] When the pressure-sensitive adhesive composition contains a photopolymerization initiator (C), the content of the photopolymerization initiator (C) is preferably 0.1 to 5.0 parts by mass, more preferably 0.5 to 4.0 parts by mass, and even more preferably 1.0 to 3.0 parts by mass, relative to 100 parts by mass of the acrylic resin (A). When the content of the photopolymerization initiator (C) is within the above range, sufficient curability can be obtained when final curing is performed.

[0128] The content of the intramolecular hydrogen abstraction photopolymerization initiator (c1) is preferably 0.1 to 5.0 parts by mass, more preferably 0.2 to 3.0 parts by mass, based on 100 parts by mass of the acrylic resin (A). If the content of the intramolecular hydrogen abstraction photopolymerization initiator (c1) is less than the above upper limit, discoloration tends to occur after humidity and heat resistance. If the content of the intramolecular hydrogen abstraction photopolymerization initiator (c1) 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 deteriorate.

[0129] The content of the intermolecular hydrogen abstraction photopolymerization initiator (c2) is preferably 0.1 to 5.0 parts by mass, more preferably 0.5 to 3.0 parts by mass, per 100 parts by mass of the acrylic resin (A). When the content of the intermolecular hydrogen abstraction photopolymerization initiator (c2) is equal to or less than the upper limit, deterioration of durability due to bleed-out tends to be suppressed. When the content of the intermolecular hydrogen abstraction photopolymerization initiator (c2) is equal to or more than the lower limit, the degree of crosslinking becomes sufficient, and adhesive properties during primary curing and durability after final curing tend to be good.

[0130] When the intramolecular hydrogen abstraction photopolymerization initiator (c1) and the intermolecular hydrogen abstraction photopolymerization initiator (c2) are used in combination, the weight ratio of the contents of the intramolecular hydrogen abstraction photopolymerization initiator (c1) and the intermolecular hydrogen abstraction photopolymerization initiator (c2), (c1) / (c2), is preferably 1 / 9 to 9 / 1, and more preferably 5 / 5 to 8 / 2.

[0131] When the photopolymerization initiator (C) contains another photopolymerization initiator (c3), the content of the photopolymerization initiator (c3) is preferably 2.0 parts by mass or less, more preferably 1.0 part by mass or less, per 100 parts by mass of the acrylic resin (A).

[0132] When the pressure-sensitive adhesive composition contains a silane coupling agent (D), the content of the silane coupling agent (D) is preferably 0.001 to 3 parts by mass, more preferably 0.005 to 1 part by mass, even more preferably 0.01 to 0.5 parts by mass, and particularly preferably 0.015 to 0.3 parts by mass, per 100 parts by mass of the acrylic resin (A). When the content of the silane coupling agent (D) is equal to or greater than the lower limit, the effect of improving durability tends to be easily obtained. When the content of the silane coupling agent (D) is equal to or less than the upper limit, the decrease in adhesive strength due to the influence of bleed-out and the like tends to be suppressed.

[0133] When the pressure-sensitive adhesive composition contains other pressure-sensitive adhesives or additives, the content of the other pressure-sensitive adhesives or additives is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the acrylic resin (A).

[0134] (Preparation of Pressure-Sensitive Adhesive Composition) The pressure-sensitive adhesive composition of the present invention can be obtained by mixing the acrylic resin (A), the crosslinking agent (B), the photopolymerization initiator (C) used as needed, the silane coupling agent (D), and other optional components. The mixing method is not particularly limited, and various methods can be used, such as mixing the components all at once, or mixing optional components and then mixing the remaining components all at once or sequentially.

[0135] (Application) The pressure-sensitive adhesive composition of the present invention can be suitably used as a pressure-sensitive adhesive for multi-stage curing pressure-sensitive adhesive sheets that are cured in multiple stages. Even in a low-crosslinked state after primary curing, excellent adhesive properties are obtained, and after final curing, not only do the composition retain typical adhesive properties such as adhesive strength, but it also exhibits excellent durability when bonded to components of various types and shapes, such as polarizing plates and glass. The pressure-sensitive adhesive composition of the present invention has excellent adhesive properties, such as low tackiness and high constant load holding power, even in a low-crosslinked state after primary curing, and therefore improves workability and reliability, making it particularly suitable for use as a pressure-sensitive adhesive or pressure-sensitive adhesive sheet for use in touch panels, image display devices, etc.

[0136] <Adhesive> The pressure-sensitive adhesive of the present invention is obtained by crosslinking the pressure-sensitive adhesive composition of the present invention described above. When the pressure-sensitive adhesive composition of the present invention is crosslinked (cured), the acrylic resin (A) contained in the pressure-sensitive adhesive composition forms a crosslinked structure at least intramolecularly and / or intermolecularly. As a result, the pressure-sensitive adhesive composition of the present invention is crosslinked to become the pressure-sensitive adhesive according to the present invention. When the acrylic resin (A) has an active energy ray crosslinkable structural moiety, a crosslinked structure can be formed by irradiation with active energy rays.

[0137] The pressure-sensitive adhesive of the present invention exhibits multi-stage curing properties, allowing it to be cured in multiple stages. The pressure-sensitive adhesive of the present invention is in a low-crosslinked state through primary curing before final curing. Although the final curing and primary curing are not necessarily clearly distinguishable, they can be distinguished by differences in gel fraction and dynamic viscoelasticity.

[0138] The curing method for both the primary curing step and the final curing step is not particularly limited, and may be either heating or irradiation with active energy rays. The primary curing step may be carried out in multiple steps, or multi-stage curing may be carried out to achieve the final cured state. The pressure-sensitive adhesive of the present invention 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.

[0139] It can also be said that the pressure-sensitive adhesive of the present invention contains at least a crosslinked product of the acrylic resin (A) of the present invention. The crosslinked product may be a partially crosslinked product in which at least a portion of the acrylic resin (A) is partially crosslinked, or a fully crosslinked product in which the entire acrylic resin (A) is entirely crosslinked. Furthermore, the pressure-sensitive adhesive of the present invention may contain both a partially crosslinked product and a fully crosslinked product of the acrylic resin (A).

[0140] (Crosslinking method) The pressure-sensitive adhesive of the present invention is obtained by crosslinking the pressure-sensitive adhesive composition of the present invention described above, and examples of the crosslinking method include a method of irradiating with active energy rays, a method of heating (aging), etc. Among these, the method of irradiating with active energy rays is preferred from the viewpoints of production efficiency and adjustment of physical properties during primary curing. The irradiation conditions for active energy rays are 100 to 1000 (W / cm) using a UV lamp (high-pressure mercury lamp, metal halide lamp, etc.) or UV LED. 2 ) illuminance, a specific cumulative light amount (mJ / cm 2 ) is preferably irradiated.

[0141] <Adhesive sheet> The pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive of the present invention. The pressure-sensitive adhesive sheet of the present invention can exhibit multi-stage curing properties in which the pressure-sensitive adhesive layer is cured in multiple stages. A pressure-sensitive adhesive sheet can be produced by providing a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive of the present invention on a substrate sheet. Alternatively, a double-sided pressure-sensitive adhesive sheet can be produced by providing the pressure-sensitive adhesive layer on a release sheet. Furthermore, a substrate-less double-sided pressure-sensitive adhesive sheet can be produced by forming the pressure-sensitive adhesive layer on a release sheet instead of a substrate sheet, and then laminating a release sheet to the opposite side of the pressure-sensitive adhesive layer. A thick pressure-sensitive adhesive layer can be further formed by forming another 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.

[0142] Examples of methods for producing the pressure-sensitive adhesive sheet include the following methods (i) and (ii). (i) A method in which the pressure-sensitive adhesive composition of the present invention is dissolved in a solvent and coated to form a pressure-sensitive adhesive sheet. (ii) A method in which the pressure-sensitive adhesive composition of the present invention is melted by heating to form a pressure-sensitive adhesive sheet.

[0143] Method (i) will now be explained. When the pressure-sensitive adhesive composition of the present invention is dissolved in a solvent and coated to form a pressure-sensitive adhesive sheet, the concentration of the coating solution containing the pressure-sensitive adhesive composition of the present invention is adjusted with an appropriate organic solvent and directly coated onto a substrate sheet. The coating is then 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. The pressure-sensitive adhesive composition is then crosslinked (cured) by irradiation with active energy rays or aging, to produce a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive.

[0144] As the organic solvent used for adjusting the concentration, those listed as organic solvents used in the polymerization reaction of the acrylic resin (A) can be used. The concentration of the pressure-sensitive adhesive composition can be 20 to 60 mass % as solid content, and preferably 30 to 50 mass %.

[0145] Method (ii) will now be explained. When the pressure-sensitive adhesive composition of the present invention 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 such as applying the molten composition to one or both sides of a substrate sheet and then cooling, or by extrusion laminating the composition onto the substrate sheet using a T-die, etc. Next, a release sheet can be attached to the surface of the pressure-sensitive adhesive layer as needed to produce a pressure-sensitive adhesive sheet. Furthermore, after forming a pressure-sensitive adhesive layer on a substrate sheet, if necessary, an active energy ray irradiation treatment is carried out, and further aging is carried out, whereby a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer in which the pressure-sensitive adhesive composition is cured (crosslinked) can be produced. Furthermore, a substrate-less double-sided PSA sheet can also be produced by forming a PSA layer on a release sheet and then laminating a release sheet to the opposite side of the PSA 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.

[0146] Examples of substrate sheets 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 and nonwoven fabrics made of glass fiber, natural fiber, synthetic fiber, etc. These substrate sheets can be used as a single layer or as a multi-layered body in which two or more types are laminated together. Among these, synthetic resin sheets are preferred from the viewpoint of weight reduction.

[0147] As the release sheet, for example, various synthetic resin sheets exemplified as the base material sheet, paper, woven fabric, nonwoven fabric, etc., which have been subjected to a release treatment can be used. As the release sheet, for example, a silicone-based release sheet is preferably used.

[0148] The method for applying the pressure-sensitive adhesive composition is not particularly limited, and examples thereof include roll coating, die coating, gravure coating, comma coating, slot coating, and screen printing.

[0149] Examples of 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 gamma rays; electron beams; proton beams; and neutron beams. Curing with ultraviolet rays is preferred in terms of curing speed, availability of irradiation equipment, cost, etc.

[0150] The gel fraction of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet before final curing is preferably 0.5 to 70 mass %, more preferably 1 to 50 mass %, and even more preferably 5 to 45 mass %, because the sheet can be easily attached to the adherend regardless of its shape, and the pressure-sensitive adhesive layer can hold the adherend in place after attachment.

[0151] The gel fraction of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet after final curing is preferably 60 to 90% by mass, more preferably 65 to 87% by mass, and even more preferably 70 to 85% by mass, from the viewpoints of durability and adhesive strength. If the gel fraction is equal to or greater than the lower limit, the cohesive strength is sufficient and sufficient durability tends to be exhibited. Meanwhile, if the gel fraction is equal to or less than the upper limit, sufficient adhesive strength tends to be exhibited without the cohesive strength being unnecessarily high.

[0152] The gel fraction can be adjusted appropriately, for example, by the following method. -Adjust the amount of active energy ray irradiation. Adjusting the content of active energy ray crosslinkable structural moieties in the acrylic resin (A). · Adjust the type and amount of crosslinking agent (B) and photopolymerization initiator (C).

[0153] The gel fraction is a measure of the degree of crosslinking (degree of cure) and is calculated, for example, by the following method. That is, an adhesive sheet (without a release sheet) consisting of an adhesive layer formed on a polymer sheet (e.g., polyethylene terephthalate (PET) film, etc.) serving as a substrate is wrapped in a 200-mesh SUS wire netting and immersed in toluene maintained at 23°C for 24 hours, and the weight percentage of the undissolved adhesive component remaining in the wire netting is taken as the gel fraction. However, the weight of the substrate is subtracted from the weight before and after dissolution in toluene to calculate the gel fraction.

[0154] The thickness of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is preferably 50 to 3000 μm, more preferably 75 to 1000 μm, and even more preferably 100 to 350 μm. If the thickness of the pressure-sensitive adhesive layer is equal to or greater than the above lower limit, sufficient impact absorption tends to be achieved. If the thickness of the pressure-sensitive adhesive layer is equal to or less than the above upper limit, the overall thickness is less likely to increase when the pressure-sensitive adhesive sheet is attached to, for example, an optical component, which is practical.

[0155] The thickness of the adhesive layer in the present invention is a value obtained 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 using a product named "ID-C112B" (manufactured by Mitutoyo Corporation).

[0156] When the thickness of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention is 100 μm, the haze value is preferably 2% or less, more preferably 0 to 1.5%, and even more preferably 0 to 1%. If the haze value is less than the above upper limit, whitening of the pressure-sensitive adhesive layer tends to be suppressed and sufficient transparency tends to be reduced. The haze value is calculated by measuring the diffuse transmittance and total luminous transmittance using a product called "HAZE MATER NDH4000" (manufactured by Nippon Denshoku Industries Co., Ltd.) and substituting the obtained diffuse transmittance (DT) and total luminous transmittance (TT) values ​​into the following [Equation 1]. This machine complies with JIS K7361-1:1997. Haze value (%) = (DT / TT) × 100 [Equation 1]

[0157] In the present invention, an optical member with a pressure-sensitive adhesive layer can be obtained by laminating a pressure-sensitive adhesive layer on an optical member. For example, an optical member with a pressure-sensitive adhesive layer can be obtained by attaching the pressure-sensitive adhesive layer side of the pressure-sensitive adhesive sheet of the present invention, in which a pressure-sensitive adhesive layer is formed on a release sheet, to an optical member and then peeling off the release sheet. In addition, optical members can also be attached to each other using the above-mentioned double-sided pressure-sensitive adhesive sheet.

[0158] Examples of optical components include components that constitute touch panels and image display devices, such as displays (organic EL, liquid crystal), transparent conductive film substrates (ITO substrates), protective films (glass), transparent antennas (films), and transparent wiring. [Example]

[0159] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following. The amounts of components used in each example are pure amounts unless otherwise specified. In the examples, "parts" and "%" are based on mass. 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 methods described in the above-mentioned embodiments.

[0160] <Abbreviations, raw materials> Alkyl (meth)acrylates having an alkyl group having 5 or more carbon atoms (a11, a21) 2EHA: 2-ethylhexyl acrylate (Tg of homopolymer: -70°C, manufactured by Mitsubishi Chemical Corporation) SLMA: A mixture of lauryl methacrylate and tridecyl methacrylate (polymer Tg: -64°C, manufactured by NOF Corporation)

[0161] Hydroxyl group-containing monomer (a12-1) HEA: 2-hydroxyethyl acrylate (Tg of homopolymer: -15°C, manufactured by Osaka Organic Chemical Industry Ltd.)

[0162] Amide group-containing ethylenically unsaturated monomers (a22) DMAA: Dimethylacrylamide (Tg of homopolymer: 119°C, manufactured by KJ Chemicals Co., Ltd.)

[0163] Alkyl (meth)acrylates (a13, a23) having an alkyl group having 1 to 4 carbon atoms MA: Methyl acrylate (Tg of homopolymer: 8°C, manufactured by Mitsubishi Chemical Corporation) MMA: Methyl methacrylate (Tg of homopolymer: 105°C, manufactured by Mitsubishi Chemical Corporation)

[0164] ADVN: 2,2'-azobis(2,4-dimethylvaleronitrile) (10-hour half-life temperature 52°C, V-65, Fujifilm Wako Pure Chemical Industries, Ltd.)

[0165] (Crosslinking agent (B)) DPHA: Dipentaerythritol hexaacrylate (KAYARAD DPHA, manufactured by Nippon Kayaku Co., Ltd.)

[0166] (Photopolymerization initiator (C)) [Intramolecular hydrogen abstraction photopolymerization initiator (c1)] c1-1: A blend of oxyphenylacetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester and oxyphenylacetic acid 2-[2-hydroxy-ethoxy]-ethyl ester (Omnirad 754, manufactured by IGM Resins BV) [Intermolecular hydrogen abstraction photopolymerization initiator (c2)] c2-1: 4-Methacryloyloxybenzophenone (MBP, manufactured by Shinryo Corporation)

[0167] (Silane coupling agent (D)) KBM403: 3-glycidoxypropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd.)

[0168] <Production of Acrylic Resins (A1-1) and (A'1-2)> A 2L flask equipped with a condenser was charged with 28 parts ethyl acetate (boiling point 77 ° C), 12 parts acetone (boiling point 56 ° C), 0.01 parts ADVN, 14 parts 2EHA, 2 parts HEA, and 4 parts SLMA as the polymerization solvent. The mixture was heated to reflux in the flask, and then 10 parts ethyl acetate, 0.1 parts ADVN, 56 parts 2EHA, 8 parts HEA, and 16 parts SLMA were added dropwise over 3 hours. After 45 minutes of addition, a mixture of 12 parts ethyl acetate and 0.13 parts ADVN was added dropwise over 1 hour and allowed to react. After 30 minutes, a mixture of 4 parts ethyl acetate and 0.06 parts ADVN was added. The mixture was then allowed to react for 2.5 hours to obtain a solution of acrylic resin (A1-1). Table 1 shows the polymer composition of the acrylic resin (A1-1), the glass transition temperature (Tg) based on the dynamic viscoelasticity of the acrylic resin (A1-1), the weight average molecular weight (Mw) and the polydispersity index (PDI). Acrylic resin (A'1-2) was produced by the same production method as for acrylic resin (A1-1), except for changing the monomer composition as shown in Table 1. The weight-average molecular weight (Mw), glass transition temperature (Tg) based on dynamic viscoelasticity, and polydispersity index (PDI) of acrylic resin (A'1-2) are shown in Table 1.

[0169] <Production of Acrylic Resins (A2-1), (A2-2), and (A'2-3)> 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, 5.5 parts of 2EHA, 0.5 parts of SLMA, 2.5 parts of DMAA, and 1.5 parts of MMA were added as polymerization solvents. The mixture was heated to reflux in the flask, and then 10 parts of ethyl acetate, 0.17 parts of ADVN, 49.5 parts of 2EHA, 4.5 parts of SLMA, 22.5 parts of DMAA, and 13.5 parts of MMA were added dropwise over 3 hours. After 45 minutes of addition, a mixture of 12 parts of ethyl acetate and 0.13 parts of ADVN was added dropwise over 1 hour, followed by reaction for 3 hours to obtain a solution of acrylic resin (A2-1). Table 1 shows the polymer composition of the acrylic resin (A2-1), the glass transition temperature (Tg) based on the dynamic viscoelasticity of the acrylic resin (A2-1), the weight average molecular weight (Mw) and the polydispersity index (PDI). Acrylic resins (A2-2) and (A'2-3) were produced using the same production method as for acrylic resin (A2-1), except for the monomer composition as shown in Table 1. Table 1 shows the weight-average molecular weight (Mw), glass transition temperature (Tg) based on dynamic viscoelasticity, and polydispersity index (PDI) of acrylic resins (A2-2) and (A'2-3).

[0170] [Table 1]

[0171] <Production of acrylic resin (A)> 100 parts (solids content equivalent) of the acrylic resin (A1-1) solution and 150 parts (solids content equivalent) of the acrylic resin (A2-1) solution were placed in a 2 L flask equipped with a condenser and stirred in the flask for 4 hours to obtain the acrylic resin (A) described in Example 1. Table 2 shows the polymer composition of the acrylic resin (A), the weight average molecular weight (Mw) of the acrylic resin (A), and the glass transition temperature based on dynamic viscoelasticity. The polymer composition was changed as shown in Table 2, and the acrylic resins (A) described in Example 2 and Comparative Examples 1 and 2 were produced by the same production method as for the acrylic resin (A) described in Example 1. The weight-average molecular weight (Mw), glass transition temperature (Tg) based on dynamic viscoelasticity, tan δ at Tg (tan δ peak value), tan δ at -20°C, -10°C, and 0°C, and haze value of the acrylic resin (A) of each example were measured, and the results are shown in Table 2.

[0172] [Table 2]

[0173] <Method of manufacturing pressure-sensitive adhesive composition> 100 parts (solid content equivalent) of the acrylic resin (A) of each example obtained above was mixed with 2.0 parts (solid content equivalent) of c1-1, 1.0 part (solid content equivalent) of c2-1, 1.5 parts (solid content equivalent) of DPHA, and 0.1 part (solid content equivalent) of KBM403 to obtain a pressure-sensitive adhesive composition.

[0174] <Method of manufacturing adhesive sheets> The obtained adhesive composition of each example was adjusted with toluene to a solids concentration of 45%, and then applied to a polyester release sheet so that the thickness after drying would be approximately 50 μm. The sheet was then dried at 100°C for 5 minutes to form an adhesive composition layer. Two polyester release sheets were prepared, and the two pressure-sensitive adhesive composition layers were laminated together with the polyester release sheets facing each other. With the laminated pressure-sensitive adhesive composition layer sandwiched between the polyester release sheets, the laminate was irradiated with a high-pressure mercury UV irradiation device at a peak irradiance of 150 mW / cm. 2 , cumulative exposure: 1000mJ / cm 2 (1000mJ / cm 2 A pressure-sensitive adhesive layer was formed by irradiating the sheet with ultraviolet light (1 pass x 1 pass) (primary curing), and a substrate-less double-sided pressure-sensitive adhesive sheet with a pressure-sensitive 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.

[0175] <Measurement and evaluation methods> The measurement and evaluation methods for the pressure-sensitive adhesive compositions and pressure-sensitive adhesive sheets of the Examples and Comparative Examples are shown below. Table 3 shows the results after primary curing, and Table 4 shows the results after final curing.

[0176] (G' (25°C), Tg and tanδ peak values: before final curing (after primary curing)) For eight substrate-less double-sided PSA sheets of each example, one release sheet was peeled off and the exposed PSA layers were repeatedly laminated together to produce substrate-less double-sided PSA sheets with a thickness of approximately 800 μm. Dynamic viscoelasticity was then measured using the method described above, and the storage modulus (G') at 25°C, Tg, and tanδ at Tg (tanδ peak value) were measured.

[0177] (Gel fraction: before final curing (after primary curing)) The substrate-less double-sided PSA 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. One release sheet was then peeled off, and the exposed PSA layer was attached to a 50 mm x 100 mm SUS mesh sheet (200 mesh). The remaining release sheet was peeled off, and the PSA layer was wrapped in the SUS mesh sheet by folding back the center longitudinally. This was immersed in a sealed container containing 250 g of toluene kept at 23 °C for 24 hours, and the gel fraction (%) was calculated from the change in weight.

[0178] (Constant load holding capacity (40℃): Before final curing (after primary curing)) The PET sheet with adhesive layer for each example was cut to a size of 25 mm wide x 75 mm long (adhesive layer portion: 25 mm wide x 50 mm long + non-adhesive layer portion: 25 mm wide x 25 mm long), and the release sheet was peeled off. The exposed adhesive layer side was attached to a stainless steel plate (SUS304) by reciprocating pressure with a 2 kg roller (attachment area: 25 mm x 50 mm) and left to stand for 20 minutes in a 40°C atmosphere. A 50 g weight was then hung from the longitudinal end of the non-attached portion (area: 25 mm x 25 mm), and a 50 g load was applied at a 90° angle to the plane of the stainless steel plate. The sheet was left to stand in this state for 60 minutes, and the distance the PET sheet had peeled off was measured. The evaluation criteria are as follows: ◎ Peeling distance is less than 5 mm. ○ Peeling distance is 5mm or more and less than 10mm. × The peeled distance was 10 mm or more, or the PET sheet completely peeled off and fell.

[0179] (Probe Tack: before final curing (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 (Probe Tack Tester TE-6001, manufactured by Tester Sangyo Co., Ltd.) under the following conditions: pressure time 1 second, application pressure 500 gf, push-in speed 120 mm / min, pull-up 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 and less than 10. × The probe tack (unit: N) is 10 or more.

[0180] (G' (25°C), Tg and tanδ (-20°C, -15°C, -10°C): after final curing) Eight substrate-less double-sided PSA sheets for each example were subjected to a high-pressure mercury UV irradiation device with a peak irradiance of 150 mW / cm 2 , cumulative exposure: 3000mJ / cm 2 (1000mJ / cm 2 Then, one of the release sheets was peeled off, and the exposed pressure-sensitive adhesive layers were repeatedly laminated together to produce a substrate-less double-sided pressure-sensitive adhesive sheet with a thickness of approximately 800 μm. Thereafter, the dynamic viscoelasticity was measured by the method described above, and the storage modulus (G') at 25°C, Tg, and tan δ at -20°C, -15°C, and -10°C were measured.

[0181] (Strength: after final curing) The strength of the final cured product was evaluated in terms of storage modulus (G') at 25° C. The evaluation criteria for strength are as follows: ○ The storage modulus (G') at 25°C is 200 kPa or more. × The storage modulus (G') at 25°C is less than 200 kPa.

[0182] (Low temperature properties: after final curing) The low-temperature properties of the final cured product were evaluated by tan δ at −20° C., −15° C. and −10° C. The evaluation criteria for low-temperature properties are as follows: ◎ Tan δ at -20°C exceeds 0.2. ○ Tan δ at -15°C exceeds 0.2, and tan δ at -20°C is 0.2 or less. × Tan δ at -15°C is 0.2 or less.

[0183] (Gel fraction: after final curing) The substrate-less double-sided adhesive sheet in each example was subjected to high-pressure mercury UV irradiation with a peak irradiance of 150 mW / cm 2 , cumulative exposure: 3000mJ / cm 2 (1000mJ / cm 2 After irradiating the sample with ultraviolet light (3 passes x 3), it was cut into a 40 mm x 40 mm piece and left to stand for 30 minutes at 23°C x 50% RH. One of the release sheets was then peeled off, and the exposed pressure-sensitive adhesive layer was attached to a 50 mm x 100 mm SUS mesh sheet (200 mesh). The remaining release sheet was peeled off, and the SUS mesh sheet was folded back from the center in the longitudinal direction to encase the pressure-sensitive adhesive layer in the SUS mesh sheet. This was immersed for 24 hours in a sealed container containing 250 g of toluene kept at 23°C, and the gel fraction (%) was calculated from the change in weight.

[0184] (180° peel strength (23°C): 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 , cumulative exposure: 3000mJ / cm 2 (1000mJ / cm 2 After UV irradiation (×3 passes), the release sheet was peeled off. The exposed pressure-sensitive adhesive layer side was attached to alkali-free glass (Corning Eagle XG, 1.1 mm thick) under an atmosphere of 23°C and 50% RH by pressing with a 2 kg rubber roller twice in both directions, and left to stand in the same atmosphere for 30 minutes. After this, the 180-degree peel strength (N / 25 mm) was measured at room temperature (23°C) at peel speeds of 60 mm / min and 300 mm / min.

[0185] The evaluation criteria for 180-degree peel strength are as follows: ○ Peel strength is 25 (N / 25 mm) or more. × Peel strength is less than 25 (N / 25 mm).

[0186] (Speed ​​dependence: after final curing) The speed dependency of the 180-degree peel strength of the final cured product was evaluated as the rate of decrease in the 180-degree peel strength at 60 mm / min relative to the 180-degree peel strength at 300 mm / min. The reduction rate of 180-degree peel strength was calculated using the following [Equation 2]. Decrease rate of 180-degree peel strength (%) = 100 - (180-degree peel strength at 60 mm / min (N / 25 mm)) / (180-degree peel strength at 300 mm / min (N / 25 mm)) × 100 [Equation 2]

[0187] The evaluation criteria for speed dependency are as follows: ○ The reduction in 180-degree peel strength is less than 25%. △: The reduction rate of 180-degree peel strength is 25% or more and less than 40%. × The reduction rate of 180-degree peel strength is 40% or more.

[0188] (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 , cumulative 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 pressed back and forth to adhere the adhesive (adhesion area 25 mm × 25 mm). The adhesive strength was measured using a creep tester (Tester Sangyo Co., Ltd., constant humidity chamber equipped holding strength tester BE-501) under an 80°C atmosphere for 24 hours with a load of 1 kg. The evaluation criteria are as follows: ◎ No misalignment (NC). ○ The misalignment is less than 0.5 mm. × The misalignment is 0.5 mm or more, or the PET sheet has fallen.

[0189] (Optical properties: after final curing) The substrate-less double-sided PSA 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 at a peak irradiance of 150 mW / cm 2 , cumulative exposure: 3000mJ / cm 2 (1000mJ / cm 2 After irradiating the specimen with ultraviolet light (×3 passes), one of the release sheets was peeled off. The exposed adhesive layer side was attached to alkali-free glass (Corning Eagle XG, 1.1 mm thick). The specimen was then autoclaved at 50°C, 0.5 MPa, and left to stand for 30 minutes in an atmosphere of 23°C and 50% RH. The remaining release sheet was then peeled off to prepare a test specimen with an alkali-free glass / adhesive layer structure. The haze value was calculated using the obtained test piece by the above-mentioned method.

[0190] [Table 3]

[0191] As can be seen from Table 3, the primary cured products of the pressure-sensitive adhesive sheets of Examples 1 and 2 had excellent constant load holding power, low probe tack, and excellent step-following ability. In contrast, in the case of Comparative Example 1 in which no acrylic resin (A2) was used, the primary cured product of the pressure-sensitive adhesive sheet had high probe tack, was prone to problems in the lamination step, and had poor processability in lamination.

[0192] [Table 4]

[0193] As can be seen from Table 4, the final cured products of the pressure-sensitive adhesive sheets of Examples 1 and 2 were excellent in strength, low-temperature properties, speed dependency and holding power. In contrast, in the case of Comparative Example 1 in which no acrylic resin (A2) was used, the final cured product of the pressure-sensitive adhesive sheet was inferior in strength and speed dependency. Furthermore, in the case of Comparative Example 2 in which no acrylic resin (A1) was used, the final cured product of the pressure-sensitive adhesive sheet was inferior in low-temperature properties and rate dependency. [Industrial Applicability]

[0194] The pressure-sensitive adhesive composition of the present invention exhibits 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 exhibits excellent adhesive properties and reliability even after final curing. The pressure-sensitive adhesive composition of the present invention is particularly useful as a pressure-sensitive adhesive for use in bonding optical members constituting touch panels, image display devices, etc., and for sealing organic EL displays.

Claims

1. A pressure-sensitive adhesive composition comprising an acrylic resin (A) including an acrylic resin (A1) and an acrylic resin (A2), and a crosslinking agent (B), The acrylic resin (A1) (excluding the acrylic resin (A2)) ) has a structural unit derived from an alkyl (meth)acrylate (a11) having an alkyl group having 5 or more carbon atoms and a structural unit derived from a functional group-containing ethylenically unsaturated monomer (a12), the acrylic resin (A2) has a structural unit derived from an alkyl (meth)acrylate (a21) having an alkyl group having 5 or more carbon atoms and a structural unit derived from an amide group-containing ethylenically unsaturated monomer (a22), The pressure-sensitive adhesive composition, wherein the acrylic resin (A) has a glass transition temperature calculated from the dynamic viscoelasticity of −10 to 20° C.

2. The pressure-sensitive adhesive composition according to claim 1, wherein the acrylic resin (A1) has a glass transition temperature (T1) based on dynamic viscoelasticity of −50 to −20° C.

3. The pressure-sensitive adhesive composition according to claim 1, wherein the acrylic resin (A2) has a glass transition temperature (T2) based on dynamic viscoelasticity of -10 to 40°C.

4. The pressure-sensitive adhesive composition according to claim 1, wherein the temperature difference between the glass transition temperature (T1) of the acrylic resin (A1) and the glass transition temperature (T2) of the acrylic resin (A2) is 70°C or less.

5. The pressure-sensitive adhesive composition according to claim 1, wherein the content of the acrylic resin (A2) is 5 to 60 mass % based on the total mass of the acrylic resin (A).

6. 2. The pressure-sensitive adhesive composition according to claim 1, wherein the weight-average molecular weight of the acrylic resin (A1) is 200,000 to 1,000,000.

7. The pressure-sensitive adhesive composition according to claim 1, wherein the acrylic resin (A2) has a weight average molecular weight of 100,000 to 500,000.

8. 2. The pressure-sensitive adhesive composition according to claim 1, wherein the difference between the weight average molecular weight of the acrylic resin (A1) and the weight average molecular weight of the acrylic resin (A2) is 0 to 900,000.

9. 2. The pressure-sensitive adhesive composition according to claim 1, wherein the functional group-containing ethylenically unsaturated monomer (a12) is a hydroxyl group-containing monomer (a12-1), and the hydroxyl group-containing monomer (a12-1) has a glass transition temperature of less than 0°C when made into a homopolymer.

10. The pressure-sensitive adhesive composition according to claim 1, wherein the amide group-containing ethylenically unsaturated monomer (a22) is a tertiary amide group-containing ethylenically unsaturated monomer (a22-1).

11. The pressure-sensitive adhesive composition according to claim 1, wherein the amide group-containing ethylenically unsaturated monomer (a22) has a glass transition temperature of 50°C or higher when made into a homopolymer.

12. The pressure-sensitive adhesive composition according to claim 1, wherein the acrylic resin (A) has a maximum loss tangent (tan δ) of 1.5 or less at a frequency of 1 Hz as measured by dynamic viscoelasticity.

13. A pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition according to any one of claims 1 to 12.

14. The pressure-sensitive adhesive according to claim 13, wherein the crosslinking is carried out by irradiation with active energy rays.

15. The entire pressure-sensitive adhesive composition is completely crosslinked, The gel fraction is 60 to 90%; The storage modulus at 25°C is 200 to 300 kPa, a glass transition temperature based on dynamic viscoelasticity of −5 to 10° C.; The pressure-sensitive adhesive according to claim 13, having a loss tangent at -20°C of more than 0.1 and not more than 1.

0.

16. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to claim 13.

17. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to claim 14.

18. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to claim 15.

19. A pressure-sensitive adhesive composition containing an acrylic resin (A1) and an acrylic resin (A2), the acrylic resin (A1) has a structural unit derived from an alkyl (meth)acrylate (a11) having an alkyl group having 5 or more carbon atoms and a structural unit derived from a hydroxyl group-containing monomer (a12-1), the glass transition temperature of the homopolymer of the hydroxyl group-containing monomer (a12-1) is less than 0°C, the acrylic resin (A2) has a structural unit derived from a tertiary amide group-containing ethylenically unsaturated monomer (a22-1), The pressure-sensitive adhesive composition has a glass transition temperature of 50°C or higher when the tertiary amide group-containing ethylenically unsaturated monomer (a22-1) is made into a homopolymer.

Images