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

Abstract

To provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive material which has superior low-temperature characteristics and exhibits strong adhesive strength at ambient temperature.SOLUTION: A pressure-sensitive adhesive composition comprises (meth)acrylic polymer (A), (meth)acrylic polymer (B), and a crosslinking agent, wherein the (meth)acrylic polymer (A) has a weight-average molecular weight (MwA) of from 1,000,000 to 3,000,000, the (meth)acrylic polymer (B) has a weight-average molecular weight (MwB) of from 50,000 to 500,000, and the dipole interaction term (δpA(J1 / 2 / cm3 / 2)) of the Hansen solubility parameter in the (meth)acrylic polymer (A) and the dipole interaction term (δpB(J1 / 2 / cm3 / 2)) of the Hansen solubility parameter in the (meth)acrylic polymer (B) satisfy the relationships of formulae (1) and (2): -1.00≤(δpA-δpB)≤0.05 (1) and 5.00≤(δpA+δpB)≤6.00 (2).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an adhesive composition, an adhesive material, and an adhesive sheet.

Background Art

[0002] In various displays such as televisions, mobile phones, and smartphones, and flexible displays such as foldable displays that can be folded and rollable displays that can be rolled into a cylindrical shape, etc., an adhesive material is generally used for joining the members that make up these. The adhesive material is provided in the form of an adhesive sheet with a substrate having an adhesive layer on a support substrate, a substrate-free pressure-sensitive adhesive sheet, etc., and the members are bonded together. Examples of the adhesive material used for the adhesive sheet include acrylic-based adhesive materials, silicone-based adhesive materials, urethane-based adhesive materials, rubber-based adhesive materials, etc. Among these, acrylic-based adhesive materials are excellent in transparency, weather resistance, heat resistance, solvent resistance, etc., and also, by monomer selection, the properties can be adjusted according to various required physical properties. Therefore, acrylic-based adhesive materials are becoming the mainstream in adhesive material development.

[0003] However, since acrylic-based adhesive materials tend to become hard when the temperature decreases, low-temperature characteristics (such as warping and adhesiveness in a low-temperature environment) may become a problem. As a method for solving such problems, a method of adding a plasticizer to an acrylic copolymer (1); a method of using an acrylic copolymer copolymerized with an alkyl (meth)acrylate having a long alkyl group with a large number of carbon atoms (2) have been proposed.

[0004] In the method of adding a plasticizer of the above method (1), due to the deterioration of the processability of the adhesive composition and the possibility of the plasticizer bleeding out from the formed adhesive layer, the addition amount of the plasticizer cannot be increased, and the low-temperature characteristics cannot be sufficiently improved.

[0005] As an example of the above method (2), for instance, Patent Document 1 describes an optical adhesive layer formed from an optical acrylic adhesive. The optical acrylic adhesive has a monomer unit of an alkyl (meth)acrylate with 2 to 18 carbon atoms in a linear or branched alkyl group as the main skeleton, and further contains a copolymer monomer copolymerized with the alkyl (meth)acrylate as a monomer unit. The acrylic polymer having a weight average molecular weight of 300,000 to 2,500,000 is used as a base polymer, and the optical adhesive layer is characterized in that the Tg is -35°C or lower (see Patent Document 1 (Claim 1)).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the method described in Patent Document 1, which is an example of the above method (2), although there is no risk of bleed-out and the low-temperature characteristics are improved, there is a problem that the adhesive force at room temperature (23°C) decreases. The present invention has been made in view of the above circumstances, and an object thereof is to provide an adhesive composition capable of forming an adhesive material having excellent low-temperature characteristics and excellent adhesive force at room temperature.

Means for Solving the Problems

[0008] The adhesive composition of the present invention that has solved the above problems contains a (meth)acrylic polymer (A), a (meth)acrylic polymer (B), and a crosslinking agent. The weight average molecular weight (MwA) of the (meth)acrylic polymer (A) is 1,000,000 to 3,000,000, the weight average molecular weight (MwB) of the (meth)acrylic polymer (B) is 50,000 to 500,000, and the dipole-dipole force term (δ of the Hansen solubility parameter in the (meth)acrylic polymer (A)p A(J 1 / 2 / cm 3 / 2 )) and the dipole-dipole force term (δ p B(J 1 / 2 / cm 3 / 2 )) of the Hansen solubility parameter in the (meth)acrylic polymer (B) satisfy the relationships of Formula (1) and Formula (2). -1.00 ≦ (δ p A - δ p B) ≦ 0.05 ···(1) 5.00 ≦ (δ p A + δ p B) ≦ 6.00 ···(2)

[0009] The pressure-sensitive adhesive composition contains a (meth)acrylic polymer (A) and a (meth)acrylic polymer (B), and by satisfying the relationships of Formula (1) and Formula (2) for the dipole-dipole force terms of the Hansen solubility parameters of the (meth)acrylic polymer (A) and the (meth)acrylic polymer (B), it is possible to suppress an increase in the glass transition temperature of the pressure-sensitive adhesive formed and increase the adhesive force at room temperature.

Advantages of the Invention

[0010] By using the pressure-sensitive adhesive composition of the present invention, a pressure-sensitive adhesive excellent in low-temperature characteristics and excellent in adhesive force at room temperature can be formed.

Modes for Carrying Out the Invention

[0011] (Definition) In this specification, “(meth)acryl” means “at least one of acrylic and methacrylic”. “(meth)acrylate” means “at least one of acrylate and methacrylate”. “(meth)acrylate” means “an ester compound in which a hydrogen atom of a carboxy group of (meth)acrylic acid is substituted with an organic group”. “(meth)acryloyl” means “at least one of acryloyl and methacryloyl”. “(meth)acrylic monomer” means “a monomer having a (meth)acryloyl group in the molecule” and includes “(meth)acrylate”. “Vinyl monomer” means “a monomer having a radically polymerizable carbon-carbon double bond in the molecule” and includes “(meth)acrylate” and “(meth)acrylic monomer”.

[0012] In this specification, “structural unit derived from (meth)acrylate” means “a structural unit in which a radically polymerizable carbon-carbon double bond of (meth)acrylate has polymerized to become a carbon-carbon single bond”. “Structural unit derived from (meth)acrylic monomer” means “a structural unit in which a radically polymerizable carbon-carbon double bond of (meth)acrylic monomer has polymerized to become a carbon-carbon single bond”. “Structural unit derived from vinyl monomer” means “a structural unit in which a radically polymerizable carbon-carbon double bond of vinyl monomer has polymerized to become a carbon-carbon single bond”.

[0013] In this specification, when described as “X to Y” (X and Y are arbitrary numbers), it means “X or more and Y or less”. Also, when described as “X or more” (X is an arbitrary number), it includes the meaning of “X or more than X”, and when described as “Y or less” (Y is an arbitrary number), it also includes the meaning of “Y or less than Y”. Furthermore, “X and / or Y” (X and Y are arbitrary components) means “at least one of X and Y” and means three cases: “only X”, “only Y”, and “X and Y”.

[0014] [Adhesive composition] The pressure-sensitive adhesive composition of the present invention contains a (meth)acrylic polymer (A), a (meth)acrylic polymer (B), and a crosslinking agent, wherein the weight-average molecular weight (MwA) of the (meth)acrylic polymer (A) is 1,000,000 to 3,000,000, the weight-average molecular weight (MwB) of the (meth)acrylic polymer (B) is 50,000 to 500,000, and the dipole-dipole force term (δ p A (J 1 / 2 / cm 3 / 2 )) of the Hansen solubility parameter in the (meth)acrylic polymer (A) and the dipole-dipole force term (δ p B (J 1 / 2 / cm 3 / 2 )) of the Hansen solubility parameter in the (meth)acrylic polymer (B) satisfy the relationships of Formula (1) and Formula (2). -1.00 ≦ (δ p A - δ p B) ≦ 0.05 ···(1) 5.00 ≦ (δ p A + δ p B) ≦ 6.00 ···(2)

[0015] The Hansen solubility parameter (HSP) is a value used for predicting the solubility of a substance calculated by the method proposed by Hansen et al.

[0016] Specifically, HSP is a value calculated by the following formula (Mathematical Formula (10)). In Mathematical Formula (10), δ represents the HSP of the polymer. δ d represents the London dispersion force term of HSP. δ p represents the dipole-dipole force term of HSP. δ h represents the hydrogen bonding force term of HSP. δ 2 = δ d 2 + δ p 2 + δ h 2 (10)

[0017] δ d 、δ p and δ his a value calculated by the following equations (Equations (11) to (13)) using the molar attraction constants (F di , F pi , E hi ) and molar volume V i of atomic group i that constitutes the structural unit of the polymer. The unit of F di is "J 1 / 2 ·cm 3 / 2 ·mol -1 ", the unit of F pi is "J 1 / 2 ·cm 3 / 2 ·mol -1 ", the unit of E hi is "J·mol -1 ", and the unit of V i is "cm 3 ·mol -1 ". δ d = ΣF di / ΣV i (11) δ p = (ΣF pi 2 ) 1 / 2 / ΣV i (12) δ h = (ΣE hi / ΣV i ) 1 / 2 (13)

[0018] The molar attraction constants (F di , F pi , E hi ) and molar volume V i of representative atomic groups are shown in Table 1.

[0019]

Table 1

[0020] For a polymer having a plurality of structural units, the HSP of each homopolymer of each structural unit constituting the polymer is calculated, and the results are summed up after multiplying by the molar fraction of each structural unit of those HSPs.

[0021] δ d , δp and δ h The three parameters of and δ can be regarded as coordinates in three-dimensional space (Hansen space). When the HSPs of two substances are placed in Hansen space, the closer the distance between the two points, the easier they are to dissolve or be compatible with each other. The distance (R) between the HSP of polymer (A) and the HSP of polymer (B) can be calculated by the following formula (Equation (14)). In Equation (14), δ d A represents the London dispersion force term of the HSP of polymer (A). δ p A represents the dipole-dipole force term of the HSP of polymer (A). δ h A represents the hydrogen bonding force term of the HSP of polymer (A). δ d B represents the London dispersion force term of the HSP of polymer (B). δ p B represents the dipole-dipole force term of the HSP of polymer (B). δ h B represents the hydrogen bonding force term of the HSP of polymer (B). (R) 2 =4(δ d A - δ d B) 2 +(δ p A - δ p B) 2 +(δ h A - δ h B) 2 (14)

[0022] Here, the dipole-dipole force term of the HSP is an index of the entanglement between polymers. Therefore, if the difference (δ p A - δ p B) is -1.00 or more, the bleed-out of the polymer component from the formed pressure-sensitive adhesive can be suppressed, and if it is 0.05 or less, the adhesive force caused by the polymer component is appropriately exhibited. Also, if the sum (δ p A + δ p B) is 5.00 or more, the adhesive force at room temperature is good, and if it is 6.00 or less, the rise in the glass transition temperature can be suppressed. Therefore, by satisfying the relationships of the above formulas (1) and (2), the rise in the glass transition temperature can be suppressed, and a pressure-sensitive adhesive excellent in adhesive force at room temperature can be formed. Note that δp A and δ p The unit of B is J 1 / 2 / cm 3 / 2 It is.

[0023] The difference (δ p A - δ p B) is -1.00 or more, preferably -0.90 or more, more preferably -0.80 or more, and 0.05 or less, preferably 0.00 or less. The sum (δ p A + δ p B) is 5.00 or more, preferably 5.15 or more, more preferably 5.30 or more, and 6.00 or less, preferably 5.90 or less, more preferably 5.85 or less.

[0024] The dipole - dipole force term (δ p A) of the Hansen solubility parameter in the (meth)acrylic polymer (A) is preferably 2.00 or more, more preferably 2.20 or more, still more preferably 2.40 or more, and preferably 3.00 or less. If the δ p A is 2.00 or more, the adhesive strength at room temperature is further improved, and if it is 3.00 or less, the increase in the glass transition temperature can be further suppressed.

[0025] The dipole - dipole force term (δ p B) of the Hansen solubility parameter in the (meth)acrylic polymer (B) is preferably 2.00 or more, more preferably 2.20 or more, still more preferably 2.40 or more, and preferably 4.00 or less, more preferably 3.80 or less, still more preferably 3.60 or less. If the δ p B is 2.00 or more, the adhesive strength at room temperature is further improved, and if it is 4.00 or less, the increase in the glass transition temperature can be further suppressed.

[0026] (Polymer component) The pressure - sensitive adhesive composition contains, as a polymer component, a (meth)acrylic polymer (A) and a (meth)acrylic polymer (B).

[0027] ((Meth)acrylic polymer (A)) The above-mentioned (meth)acrylic polymer (A) may be a copolymer having structural units derived from (meth)acrylic monomers as the main component (50 mol% or more). The above-mentioned (meth)acrylic polymer (A) may be one kind or two or more kinds. Further, the above-mentioned (meth)acrylic polymer (A) may contain structural units derived from vinyl monomers other than (meth)acrylic monomers. The content of the structural units derived from (meth)acrylic monomers in the above-mentioned (meth)acrylic polymer (A) is preferably 80 mol% or more, more preferably 90 mol% or more, based on 100 mol% of all the structural units. Incidentally, the above-mentioned (meth)acrylic polymer (A) may be composed only of structural units derived from (meth)acrylic monomers.

[0028] The above-mentioned (meth)acrylic polymer (A) is preferably a (meth)acrylate copolymer. The (meth)acrylate copolymer may be a copolymer having structural units derived from (meth)acrylates as the main component (50 mol% or more), and may contain structural units derived from vinyl monomers other than (meth)acrylates. The content of the structural units derived from (meth)acrylates in the above-mentioned (meth)acrylic polymer (A) is preferably 80 mol% or more, more preferably 90 mol% or more, based on 100 mol% of all the structural units.

[0029] The above-mentioned (meth)acrylic polymer (A) may be any of a random copolymer, a block copolymer, and a graft copolymer, and is preferably a random copolymer.

[0030] The weight average molecular weight (MwA) of the (meth)acrylic polymer (A) is 1,000,000 or more, preferably 1,100,000 or more, more preferably 1,300,000 or more, and 3,000,000 or less, preferably 2,600,000 or less, more preferably 2,400,000 or less. If the MwA of the (meth)acrylic polymer (A) is 1,000,000 or more, the number of the first reactive groups per one (meth)acrylic polymer (A) increases, making it easier to adjust the gel fraction and showing suitable resilience. If it is 3,000,000 or less, the coatability and workability of the pressure-sensitive adhesive composition become better. The method for measuring the weight average molecular weight (Mw) will be described later.

[0031] The molecular weight distribution (Mw / Mn) of the (meth)acrylic polymer (A) is preferably 3.0 or less, more preferably 2.7 or less, still more preferably 2.5 or less. The smaller the Mw / Mn, the narrower the molecular weight distribution width, and the polymer has a more uniform molecular weight. When the value is 1.0, the molecular weight distribution width is the narrowest. If the Mw / Mn is 3.0 or less, compared with the designed molecular weight of the polymer, the content of those with a small molecular weight or a large molecular weight is low, and a pressure-sensitive adhesive material with excellent flex resistance can be obtained. In the present invention, the molecular weight distribution is a value calculated by (weight average molecular weight (Mw)) / (number average molecular weight (Mn)), and the measurement methods of Mw and Mn will be described later.

[0032] The glass transition temperature of the (meth)acrylic polymer (A) according to the FOX equation is preferably -70°C or higher, more preferably -65°C or higher, still more preferably -63°C or higher, and -50°C or lower, preferably -53°C or lower, still more preferably -56°C or lower. If the glass transition temperature according to the FOX equation is -70°C or higher, sufficient cohesive force is given to the pressure-sensitive adhesive material, and the durability of the formed pressure-sensitive adhesive material is improved. If it is -50°C or lower, the adhesion of the formed pressure-sensitive adhesive material to the adherend is increased, peeling at low temperatures, etc. are suppressed, and the durability is improved.

[0033] The glass transition temperature of the (meth)acrylic polymer according to the FOX equation is the value calculated by the following FOX equation (Equation (20)). In Equation (20), Tg represents the glass transition temperature (°C) of the polymer according to the FOX equation. Tgi represents the glass transition temperature (°C) of vinyl monomer i when it forms a homopolymer according to the FOX equation. Wi represents the mass ratio of vinyl monomer i in all vinyl monomers forming the copolymer, and ΣWi = 1. i is a natural number from 1 to n.

[0034]

Number

[0035] The (meth)acrylic polymer (A) may or may not have a reactive group for forming a crosslinked structure, but it is preferably provided with a reactive group. The reactive group is a functional group that binds with other reactive groups to form a crosslinked structure, or a functional group that reacts with a reactive group of a crosslinking agent described later to form a crosslinked structure. Examples of the reactive group include a hydroxy group, a carboxy group, an epoxy group, a vinyl group (ethylenically unsaturated group), etc.

[0036] The (meth)acrylic polymer (A) preferably has a first reactive group as the reactive group. The first reactive group is a functional group having high reactivity with a second reactive group of a crosslinking agent described later. Examples of the functional group that can be the first reactive group include reactive functional groups. Examples of the first reactive group include a hydroxy group, a carboxy group, an epoxy group, a vinyl group (ethylenically unsaturated group), etc., and preferably a hydroxy group and / or a carboxy group.

[0037] When the (meth)acrylic polymer (A) has a reactive group (first reactive group), the amount of the reactive group (first reactive group) of the (meth)acrylic polymer (A) is preferably 0.002 mmol / g or more, more preferably 0.005 mmol / g or more, still more preferably 0.010 mmol / g or more, and preferably 1.0 mmol / g or less, more preferably 0.8 mmol / g or less, still more preferably 0.7 mmol / g or less. If the amount of the reactive group (first reactive group) is within the above range, a suitable crosslinked structure is formed in the pressure-sensitive adhesive material, and the adhesive strength becomes more excellent.

[0038] When the carboxy group is the first reactive group in the (meth)acrylic polymer (A), it is preferable that the (meth)acrylic polymer (A) further has a hydroxy group as a functional group other than the first reactive group. In this case, the amount of the hydroxy group of the (meth)acrylic polymer (A) is preferably 0.002 mmol / g or more, more preferably 0.005 mmol / g or more, still more preferably 0.002 mmol / g or more, and preferably 1.0 mmol / g or less, more preferably 0.6 mmol / g or less, still more preferably 0.4 mmol / g or less.

[0039] When the (meth)acrylic polymer (A) has a carboxy group as the first reactive group and has both a carboxy group and a hydroxy group, the molar ratio (carboxy group / hydroxy group) of the carboxy group and the hydroxy group per unit mass of the (meth)acrylic polymer (A) is preferably 0.01 or more, more preferably 0.05 or more, still more preferably 0.1 or more, and preferably 7.0 or less, more preferably 5.0 or less, still more preferably 3.0 or less. If the molar ratio (carboxy group / hydroxy group) is within the above range, the adhesive strength of the pressure-sensitive adhesive material becomes more excellent.

[0040] When the hydroxy group is the first reactive group, the (meth)acrylic polymer (A) preferably further has a carboxy group as a functional group other than the first reactive group. In this case, the amount of the carboxy group in the (meth)acrylic polymer (A) is preferably 0.01 mmol / g or more, more preferably 0.05 mmol / g or more, still more preferably 0.1 mmol / g or more, and preferably 0.8 mmol / g or less, more preferably 0.6 mmol / g or less, still more preferably 0.4 mmol / g or less.

[0041] When the hydroxy group is the first reactive group and the (meth)acrylic polymer (A) has both a carboxy group and a hydroxy group, the molar ratio of the carboxy group to the hydroxy group (carboxy group / hydroxy group) per unit mass of the (meth)acrylic polymer (A) is preferably 0.01 or more, more preferably 0.05 or more, still more preferably 0.1 or more, and preferably 0.8 or less, more preferably 0.6 or less, still more preferably 0.4 or less. When the molar ratio (carboxy group / hydroxy group) is within the above range, the adhesive strength of the pressure-sensitive adhesive material becomes more excellent.

[0042] ((meth)acrylic polymer (B)) The (meth)acrylic polymer (B) may be a copolymer having a structural unit derived from a (meth)acrylic monomer as a main component (50 mol% or more). The (meth)acrylic polymer (B) may be one kind or two or more kinds. Further, the (meth)acrylic polymer (B) can contain a structural unit derived from a vinyl monomer other than the (meth)acrylic monomer. The content of the structural unit derived from the (meth)acrylic monomer in the (meth)acrylic polymer (B) is preferably 80 mol% or more, more preferably 90 mol% or more, in 100 mol% of all the structural units. Incidentally, the (meth)acrylic polymer (B) may be composed only of the structural unit derived from the (meth)acrylic monomer.

[0043] The above-mentioned (meth)acrylic polymer (B) is preferably a (meth)acrylate copolymer. The (meth)acrylate copolymer may be a copolymer having structural units derived from (meth)acrylate as the main component (50 mol% or more), and may contain structural units derived from vinyl monomers other than (meth)acrylate. The content of the structural units derived from (meth)acrylate in the above-mentioned (meth)acrylic polymer (B) is preferably 80 mol% or more, more preferably 90 mol% or more, based on 100 mol% of all the structural units.

[0044] The above-mentioned (meth)acrylic polymer (B) may be any of a random copolymer, a block copolymer, and a graft copolymer, and is preferably a random copolymer.

[0045] The weight average molecular weight (MwB) of the above-mentioned (meth)acrylic polymer (B) is preferably 50,000 or more, more preferably 80,000 or more, still more preferably 90,000 or more, and preferably 500,000 or less, more preferably 400,000 or less, still more preferably 300,000 or less. If the MwB of the above-mentioned (meth)acrylic polymer (B) is within the above range, better adhesiveness can be obtained.

[0046] The molecular weight distribution (Mw / Mn) of the above-mentioned (meth)acrylic polymer (B) is preferably 3.0 or less, more preferably 2.5 or less, still more preferably 2.0 or less. If Mw / Mn is 3.0 or less, compared with the designed molecular weight of the polymer, the content of those with a small molecular weight or a large molecular weight is low, and an adhesive material excellent in flex resistance can be obtained. The molecular weight distribution (Mw / Mn) of the above-mentioned (meth)acrylic polymer (B) is 1.0 or more.

[0047] The glass transition temperature of the above-mentioned (meth)acrylic polymer (B) according to the FOX equation is preferably -70°C or higher, more preferably -69°C or higher, still more preferably -68°C or higher, and preferably -50°C or lower, more preferably -53°C or lower, still more preferably -55°C or lower. If the glass transition temperature according to the FOX equation is -70°C or higher, sufficient cohesive force can be imparted to the pressure-sensitive adhesive, and the durability of the formed pressure-sensitive adhesive is improved. If it is -50°C or lower, the adhesion of the formed pressure-sensitive adhesive to the adherend is increased, peeling at low temperatures is suppressed, and the durability is improved.

[0048] The above-mentioned (meth)acrylic polymer (B) may or may not have a reactive group (first reactive group), but from the viewpoint of flex resistance, it is preferably substantially free of it. The reactive group is a functional group that combines with other reactive groups to form a crosslinked structure or a functional group that reacts with the reactive group of a crosslinking agent described later to form a crosslinked structure. The first reactive group is a functional group that has a high reactivity with the second reactive group of the crosslinking agent described later. Examples of the functional group that can be the reactive group (first reactive group) include reactive functional groups. Examples of the reactive group include a hydroxy group, a carboxy group, an epoxy group, a vinyl group (ethylenically unsaturated group), etc., and preferably a hydroxy group and / or a carboxy group.

[0049] When the above-mentioned (meth)acrylic polymer (B) is substantially free of a reactive group (first reactive group), the amount of the reactive group (first reactive group) of the (meth)acrylic polymer (B) is 0.50 mmol / g or less, preferably 0.30 mmol / g or less, more preferably 0.10 mmol / g or less.

[0050] The mass ratio of the (meth)acrylic polymer (A) to the (meth)acrylic polymer (B) in the pressure-sensitive adhesive composition ((meth)acrylic polymer (A) / (meth)acrylic polymer (B)) is preferably 0.5 or more, more preferably 0.7 or more, still more preferably 1.0 or more, and preferably 5.0 or less, more preferably 4.0 or less, still more preferably 3.0 or less. If the mass ratio ((meth)acrylic polymer (A) / (meth)acrylic polymer (B)) is 0.5 or more, the adhesive strength is further improved, and if it is 5.0 or less, the pressure-sensitive adhesive formed has suitable stretchability.

[0051] The total content of the (meth)acrylic polymer (A) and the (meth)acrylic polymer (B) in the pressure-sensitive adhesive composition is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more in 100% by mass of the solid content. The solid content is a component other than the solvent in the pressure-sensitive adhesive composition.

[0052] The difference (MwA - MwB) between the weight average molecular weight (MwA) of the (meth)acrylic polymer (A) and the weight average molecular weight (MwB) of the (meth)acrylic polymer (B) is preferably 500,000 or more, more preferably 700,000 or more, still more preferably 1,000,000 or more, and preferably 2,950,000 or less, more preferably 2,520,000 or less, still more preferably 2,310,000 or less. If the difference (MwA - MwB) is within the above range, the pressure-sensitive adhesive is appropriately crosslinked and both suitable stretchability and suitable adhesive strength are achieved. In the case of containing a plurality of (meth)acrylic polymers (A), the molecular weight measurement is performed on the mixture of the plurality of (meth)acrylic polymers (A), and the obtained measured value is taken as the weight average molecular weight (MwA). Further, in the case of containing a plurality of (meth)acrylic polymers (B), the molecular weight measurement is performed on the mixture of the plurality of (meth)acrylic polymers (B), and the obtained measured value is taken as the weight average molecular weight (MwB).

[0053] The pressure-sensitive adhesive composition may contain only the (meth)acrylic polymer (A) or the (meth)acrylic polymer (B) as the polymer component, or may contain a (meth)acrylic polymer (C) that is not classified as the (meth)acrylic polymer (A) or the (meth)acrylic polymer (B).

[0054] ((meth)acrylic polymer (C)) The (meth)acrylic polymer (C) may be a copolymer having a structural unit derived from a (meth)acrylic monomer as a main component (50 mol% or more). The (meth)acrylic polymer (C) may be one kind or two or more kinds.

[0055] The (meth)acrylic polymer (C) is preferably a (meth)acrylate copolymer. The (meth)acrylate copolymer may be a copolymer having a structural unit derived from a (meth)acrylate as a main component (50 mol% or more), and may contain a structural unit derived from a vinyl monomer other than the (meth)acrylate. The content of the structural unit derived from the (meth)acrylate in the (meth)acrylic polymer (C) is preferably 80 mol% or more, more preferably 90 mol% or more, per 100 mol% of all structural units.

[0056] The (meth)acrylic polymer (C) may be any of a random copolymer, a block copolymer, and a graft copolymer, and is preferably a random copolymer.

[0057] The (meth)acrylic polymer has a structural unit derived from a (meth)acrylic monomer. Further, the (meth)acrylic polymer may have a structure derived from a vinyl monomer other than the (meth)acrylic monomer. Hereinafter, the monomers constituting the (meth)acrylic polymer will be described.

[0058] Examples of the (meth)acrylic monomer include a (meth)acrylic monomer having a linear alkyl group, a (meth)acrylic monomer having a cyclic alkyl group, a (meth)acrylic monomer having an aryl group, a (meth)acrylic monomer having a hydroxy group, a (meth)acrylic monomer having an alkoxy group, a (meth)acrylic monomer having an acidic group, a (meth)acrylic monomer having an amino group, a (meth)acrylic monomer having an epoxy group, a (meth)acrylic monomer having an oxygen-containing heterocyclic group, a (meth)acrylic monomer having an amide group, and the like.

[0059] Examples of the (meth)acrylic monomer having a linear alkyl group include (meth)acrylate having a linear alkyl group and (meth)acrylate having a branched alkyl group.

[0060] Examples of the (meth)acrylate having a linear alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-lauryl (meth)acrylate, n-stearyl (meth)acrylate, and the like. The number of carbon atoms of the linear alkyl group is preferably 1 to 20, more preferably 1 to 15, and still more preferably 4 to 12.

[0061] Examples of the (meth)acrylate having a branched alkyl group include isopropyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, and the like. The number of carbon atoms of the branched alkyl group is preferably 3 to 20, more preferably 3 to 12, and still more preferably 3 to 10.

[0062] Examples of the (meth)acrylic monomer having the cyclic alkyl group include (meth)acrylates having a cyclic alkyl group with a monocyclic structure and (meth)acrylates having a cyclic alkyl group with a bridged ring structure. The cyclic alkyl group may have a chain portion.

[0063] Examples of the (meth)acrylate having a cyclic alkyl group with a monocyclic structure include cyclic alkyl esters of (meth)acrylic acid such as cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, and cyclododecyl (meth)acrylate. The number of carbon atoms of the cyclic alkyl group with a monocyclic structure is preferably 6 to 20, more preferably 6 to 12.

[0064] Examples of the (meth)acrylate having a cyclic alkyl group with a bridged ring structure include bornyl (meth)acrylate, isobornyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate, and norbornyl (meth)acrylate. The number of carbon atoms of the cyclic alkyl group with a bridged ring structure is preferably 6 to 20, more preferably 6 to 12.

[0065] Examples of the (meth)acrylic monomer having the aryl group include (meth)acrylates having an aryl group. The aryl group may have a chain portion such as an alkylaryl group, an aralkyl group, or an aryloxyalkyl group. That is, examples of the (meth)acrylate having an aryl group include a compound in which an aryl group is directly bonded to a (meth)acryloyloxy group, a compound in which an aralkyl group is directly bonded to a (meth)acryloyloxy group, and a compound in which an alkylaryl group is directly bonded to a (meth)acryloyloxy group. Specific examples of the (meth)acrylate having an aryl group include phenyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate. The number of carbon atoms of the aryl group is preferably 6 to 12, more preferably 6 to 9.

[0066] Examples of the (meth)acrylic monomer having a hydroxy group include (meth)acrylates having a hydroxyalkyl group, (meth)acrylates having a lactone-modified hydroxy group, (meth)acrylates having a polyalkylene glycol group, and the like. The hydroxyalkyl group is an alkyl group in which at least one hydrogen atom is substituted with a hydroxy group.

[0067] Examples of the (meth)acrylate having a hydroxyalkyl group include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, (4-hydroxymethylcyclohexyl) (meth)acrylate, and the like. The hydroxyalkyl group is preferably linear or branched. The number of carbon atoms of the hydroxyalkyl group is preferably 1 to 10, more preferably 1 to 5.

[0068] Examples of the (meth)acrylate having a lactone-modified hydroxy group include those obtained by adding lactone to the (meth)acrylate having a hydroxyalkyl group, and those obtained by adding caprolactone are preferred. The addition amount of lactone is preferably 1 mol to 10 mol, more preferably 1 mol to 5 mol. Examples of the (meth)acrylate having a lactone-modified hydroxy group include 1 mol adduct of caprolactone to 2-hydroxyethyl (meth)acrylate, 2 mol adduct of caprolactone to 2-hydroxyethyl (meth)acrylate, 3 mol adduct of caprolactone to 2-hydroxyethyl (meth)acrylate, 4 mol adduct of caprolactone to 2-hydroxyethyl (meth)acrylate, 5 mol adduct of caprolactone to 2-hydroxyethyl (meth)acrylate, 10 mol adduct of caprolactone to 2-hydroxyethyl (meth)acrylate, and the like.

[0069] Examples of the (meth)acrylate having a polyalkylene glycol group include terminal hydroxy group polyethylene glycol (degree of polymerization = 2 to 30) mono(meth)acrylate, terminal hydroxy group polypropylene glycol (degree of polymerization = 2 to 30) mono(meth)acrylate, and the like.

[0070] Examples of the (meth)acrylic monomer having an alkoxy group include (meth)acrylate having an alkoxyalkyl group, (meth)acrylate having an alkoxypolyalkylene glycol group, and the like.

[0071] Examples of the (meth)acrylate having an alkoxyalkyl group include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, and the like.

[0072] Examples of the (meth)acrylate having an alkoxypolyalkylene glycol group include (meth)acrylates having an alkoxypolyethylene glycol group such as polyethylene glycol (degree of polymerization = 2 to 30) methyl ether (meth)acrylate, polyethylene glycol (degree of polymerization = 2 to 30) ethyl ether (meth)acrylate, polyethylene glycol (degree of polymerization = 2 to 30) propyl ether (meth)acrylate, etc.; (meth)acrylates having an alkoxypolypropylene glycol group such as polypropylene glycol (degree of polymerization = 2 to 30) methyl ether (meth)acrylate, polypropylene glycol (degree of polymerization = 2 to 30) ethyl ether (meth)acrylate, polypropylene glycol (degree of polymerization = 2 to 30) propyl ether (meth)acrylate, etc.

[0073] Examples of the acidic group of the (meth)acrylic monomer having an acidic group include carboxy group (-COOH), sulfonic acid group (-SO 3 H), phosphoric acid group (-OPO 3 H 2 ), phosphonic acid group (-PO 3 H 2 ), phosphinic acid group (-PO 2 H 2) can be mentioned. Examples of the (meth)acrylic monomer having an acidic group include (meth)acrylic acid; 2-(meth)acryloyloxyethyl hydrogen succinate, 2-((meth)acryloyloxy)ethyl hydrogen hexahydrophthalate, 2-(meth)acryloyloxyethyl hydrogen phthalate, (meth)acrylate having a carboxy group such as a caprolactone adduct of (meth)acrylic acid; (meth)acrylate having a sulfonic acid group such as ethyl sulfonate (meth)acrylate, 2-(meth)acrylamide-2-methylpropane sulfone; (meth)acrylate having a phosphate group such as 2-(phosphonooxy)ethyl (meth)acrylate, etc.

[0074] Examples of the (meth)acrylic monomer having an amino group include (meth)acrylate having an amino group. Examples of the (meth)acrylate having an amino group include dimethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, dimethylaminobutyl (meth)acrylate, diethylaminoethyl (meth)acrylate, diethylaminopropyl (meth)acrylate, diethylaminobutyl (meth)acrylate, ethylaminoethyl (meth)acrylate, ethylaminopropyl (meth)acrylate, ethylaminobutyl (meth)acrylate, propylaminoethyl (meth)acrylate, propylaminopropyl (meth)acrylate, propylaminobutyl (meth)acrylate, etc.

[0075] Examples of the (meth)acrylic monomer having an epoxy group include (meth)acrylate having an epoxy group. Examples of the (meth)acrylate having an epoxy group include glycidyl (meth)acrylate, (3,4-epoxycyclohexyl)methyl (meth)acrylate, etc.

[0076] Examples of the (meth)acrylic monomer having an oxygen-containing heterocyclic group include (meth)acrylates having an oxygen-containing heterocyclic group. Examples of the (meth)acrylate having an oxygen-containing heterocyclic group include tetrahydrofurfuryl (meth)acrylate, (3-ethyloxetan-3-yl)methyl (meth)acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, (5-ethyl-1,3-dioxan-5-yl)methyl (meth)acrylate, 2-[(2-tetrahydropyranyl)oxy]ethyl (meth)acrylate, (1,3-dioxan-5-yl)methyl (meth)acrylate, etc. The oxygen-containing heterocyclic group is preferably a 4- to 6-membered ring.

[0077] Examples of the (meth)acrylic monomer having an amide group include N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-tert-butyl(meth)acrylamide, N-octyl(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-ethoxymethyl(meth)acrylamide, N-propoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, diacetone acrylamide, 4-(meth)acryloylmorpholine, etc. (Meth)acrylamides are (meth)acrylic monomers but are not included in (meth)acrylate monomers.

[0078] Examples of vinyl monomers other than (meth)acrylic monomers include styrene-based monomers, vinyl monomers having an acidic group, vinyl monomers containing an epoxy group, vinyl monomers having a nitrogen-containing heterocyclic group, vinyl monomers having a sulfur-containing heterocyclic group, vinylamides, nitriles, vinyl carboxylates, α-olefins, dienes, vinyl halide monomers, etc.

[0079] Examples of the styrenic monomer include substituted or unsubstituted styrene. Examples of the substituent that may substitute styrene include an alkyl group, an aryl group, an alkoxy group, an aryloxy group, etc. The styrenic monomer also includes a condensed cyclic compound having two or more benzene rings. Examples of the styrenic monomer include styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 4-methoxystyrene, 4-phenylstyrene, 1-vinylnaphthalene, etc., and preferably styrene or styrene having an alkyl group. The number of carbon atoms of the alkyl group in the styrene having an alkyl group is preferably 1 to 6.

[0080] Examples of the acidic group of the vinyl monomer having an acidic group include a carboxy group (-COOH), a sulfonic acid group (-SO 3 H), a phosphoric acid group (-OPO 3 H 2 ), a phosphonic acid group (-PO 3 H 2 ), and a phosphinic acid group (-PO 2 H 2 ). Examples of the vinyl monomer having an acidic group include vinyl monomers having a carboxy group such as crotonic acid, maleic acid, itaconic acid, citraconic acid, cinnamic acid; vinyl monomers having a sulfonic acid group such as vinylsulfonic acid, 1-propene-2-sulfonic acid; vinyl monomers having a phosphoric acid group such as vinyl phosphate, isopropenyl phosphate; vinyl monomers having a phosphonic acid group such as vinylphosphonic acid, isopropenylphosphonic acid; vinyl monomers having a phosphinic acid group such as vinylphosphinic acid, (1-methylethenyl)phosphinic acid, etc.

[0081] Examples of the vinyl monomer containing an epoxy group include 2-allyloxirane, glycidyl vinyl ether, 3,4-epoxycyclohexyl vinyl ether, etc.

[0082] Examples of the vinyl monomer having a nitrogen-containing heterocyclic group include vinyl monomers having a 5-membered lactam group such as N-vinylpyrrolidone, N-vinyl-5-methylpyrrolidone, N-vinyl-5-ethylpyrrolidone, N-vinyl-5-propylpyrrolidone, N-vinyl-5-butylpyrrolidone, 1-(2-propenyl)-2-pyrrolidone; vinyl monomers having a 6-membered lactam group such as N-vinylpiperidone; vinyl monomers having a 7-membered lactam group such as N-vinylcaprolactam; 2-vinylpyridine, 4-vinylpyridine; vinylpyrrole and the like. Among these, vinyl monomers having a 5-membered lactam group are preferred, and N-vinylpyrrolidone is more preferred.

[0083] Examples of the vinyl monomer having a sulfur-containing heterocyclic group include 2-vinylthiophene and the like. Examples of the vinylamides include N-vinylformamide, N-vinylacetamide and the like. Examples of the nitriles include acrylonitrile, methacrylonitrile and the like. Examples of the vinyl carboxylate include vinyl acetate, vinyl pivalate, vinyl benzoate and the like. Examples of the α-olefins include 1-hexene, 1-octene, 1-decene and the like. Examples of the dienes include butadiene, isoprene, 4-methyl-1,4-hexadiene, 7-methyl-1,6-octadiene and the like. Examples of the vinyl halide monomer include vinyl fluoride, vinylidene fluoride, trifluoroethylene, tetrafluoroethylene, tetrafluoropropylene, hexafluoropropylene, vinyl chloride, vinylidene chloride, 1-chloro-1-fluoroethylene, 1,2-dichloro-1,2-difluoroethylene, chlorotrifluoroethylene and the like.

[0084] The content ratio of the structural unit derived from the (meth)acrylic monomer having a chain alkyl group in 100 mol% of all the structural units of the (meth)acrylic polymer (A) is preferably 85 mol% or more, more preferably 90 mol% or more, preferably 99.9 mol% or less, more preferably 99.5 mol% or less, and still more preferably 99.0 mol% or less. If the content ratio of the structural unit derived from the (meth)acrylic monomer having a chain alkyl group is 85 mol% or more, the glass transition temperature of the pressure-sensitive adhesive can be further decreased, and if it is 99.9 mol% or less, the pressure-sensitive adhesive can be appropriately crosslinked to exhibit more excellent durability.

[0085] As the structural unit derived from the (meth)acrylic monomer having a chain alkyl group that constitutes the (meth)acrylic polymer (A), the structural unit derived from the (meth)acrylic monomer having a chain alkyl group with 1 to 20 carbon atoms is preferable, more preferably the structural unit derived from the (meth)acrylic monomer having a chain alkyl group with 4 to 12 carbon atoms, and still more preferably the structural unit derived from the (meth)acrylic monomer having a chain alkyl group with 5 to 12 carbon atoms.

[0086] The content ratio of the structural unit derived from the (meth)acrylic monomer having a linear alkyl group in 100 mol% of all the structural units of the (meth)acrylic polymer (A) is preferably 10 mol% or more, more preferably 15 mol% or more, still more preferably 20 mol% or more, preferably 35 mol% or less, more preferably 30 mol% or less, and still more preferably 25 mol% or less. If the content ratio of the structural unit derived from the (meth)acrylic monomer having a linear alkyl group is 10 mol% or more, the glass transition temperature of the pressure-sensitive adhesive can be further decreased, and if it is 35 mol% or less, the increase in the glass transition temperature due to the crystallinity of the linear alkyl side chain can be suppressed.

[0087] As the structural unit derived from the (meth)acrylic monomer having a linear alkyl group constituting the (meth)acrylic polymer (A), a structural unit derived from a (meth)acrylic monomer having a linear alkyl group with 1 to 20 carbon atoms is preferable, more preferably a structural unit derived from a (meth)acrylic monomer having a linear alkyl group with 4 to 12 carbon atoms, and even more preferably a structural unit derived from a (meth)acrylic monomer having a linear alkyl group with 5 to 12 carbon atoms.

[0088] When the (meth)acrylic polymer (A) has a hydroxy group, as the structural unit having a hydroxy group, a structural unit derived from a (meth)acrylate having a hydroxyalkyl group with 1 to 10 carbon atoms is preferable, and a structural unit derived from a (meth)acrylate having a hydroxyalkyl group with 1 to 5 carbon atoms is more preferable. Further, the hydroxyalkyl group is preferably linear. When the (meth)acrylic polymer (A) has a carboxy group, as the structural unit having a carboxy group, a structural unit derived from (meth)acrylic acid is preferable.

[0089] In the (meth)acrylic polymer (B), the content of the structural unit derived from the (meth)acrylic monomer having a chain alkyl group in 100 mol% of all structural units is preferably 80 mol% or more, more preferably 85 mol% or more, even more preferably 90 mol% or more, and preferably 99 mol% or less, more preferably 98 mol% or less, even more preferably 97 mol% or less. If the content of the structural unit derived from the (meth)acrylic monomer having a chain alkyl group is 80 mol% or more, the glass transition temperature of the pressure-sensitive adhesive can be further reduced and the adhesive force can be further increased. If it is 99 mol% or less, the cohesive force of the pressure-sensitive adhesive becomes high and the durability is improved.

[0090] As the structural unit derived from the (meth)acrylic monomer having a linear alkyl group that constitutes the (meth)acrylic polymer (B), a structural unit derived from a (meth)acrylic monomer having a linear alkyl group with 1 to 20 carbon atoms is preferable, more preferably a structural unit derived from a (meth)acrylic monomer having a linear alkyl group with 4 to 12 carbon atoms, and even more preferably a structural unit derived from a (meth)acrylic monomer having a linear alkyl group with 5 to 12 carbon atoms.

[0091] In the (meth)acrylic polymer (B), the content of the structural unit derived from the (meth)acrylic monomer having a linear alkyl group in 100 mol% of all structural units is preferably 10 mol% or more, more preferably 15 mol% or more, even more preferably 20 mol% or more, and preferably 35 mol% or less, more preferably 30 mol% or less, and even more preferably 25 mol% or less. If the content of the structural unit derived from the (meth)acrylic monomer having a linear alkyl group is 10 mol% or more, the glass transition temperature of the pressure-sensitive adhesive can be further lowered, and if it is 35 mol% or less, an increase in the glass transition temperature due to the crystallinity of the linear alkyl side chain can be suppressed.

[0092] As the structural unit derived from the (meth)acrylic monomer having a linear alkyl group that constitutes the (meth)acrylic polymer (B), a structural unit derived from a (meth)acrylic monomer having a linear alkyl group with 1 to 20 carbon atoms is preferable, more preferably a structural unit derived from a (meth)acrylic monomer having a linear alkyl group with 4 to 12 carbon atoms, and even more preferably a structural unit derived from a (meth)acrylic monomer having a linear alkyl group with 5 to 12 carbon atoms.

[0093] The (meth)acrylic polymer (B) preferably contains a structural unit having a heterocyclic group. By the (meth)acrylic polymer (B) containing a structural unit having a heterocyclic group, the cohesive force is improved and the adhesive force is further improved. Examples of the heterocyclic group include nitrogen-containing heterocyclic groups, oxygen-containing heterocyclic groups (excluding epoxy groups), sulfur-containing heterocyclic groups, and the like.

[0094] When the (meth)acrylic polymer (B) contains a structural unit having a heterocyclic group, the content of the structural unit having a heterocyclic group in 100 mol% of all the structural units is preferably 0.50 mol% or more, more preferably 0.70 mol% or more, still more preferably 1.00 mol% or more, and preferably 8.00 mol% or less, more preferably 6.00 mol% or less, still more preferably 5.00 mol% or less. When the content of the structural unit having a heterocyclic group is 0.50 mol% or more, the effect of improving the adhesive strength due to the improvement of the cohesive force is further improved. When it is 8.00 mol% or less, an increase in δp of the Hansen solubility parameter can be suppressed, and it becomes easy to control the glass transition temperature of the pressure-sensitive adhesive within a suitable range.

[0095] Examples of the structural unit having a heterocyclic group include a structural unit derived from a (meth)acrylic monomer and a structural unit derived from a vinyl monomer other than a (meth)acrylic monomer. Examples of the structural unit having a heterocyclic group include a structural unit derived from a (meth)acrylic monomer having an oxygen-containing heterocyclic group (excluding epoxy groups), a structural unit derived from a vinyl monomer having a nitrogen-containing heterocyclic group, and a structural unit derived from a vinyl monomer having a sulfur-containing heterocyclic group. Among these, a structural unit derived from a (meth)acrylic monomer having an oxygen-containing heterocyclic group of 4 to 6 members and a structural unit derived from a vinyl monomer having a lactam group of 5 to 7 members are preferable.

[0096] It is also preferable that the (meth)acrylic polymer (B) contains a structural unit derived from a styrene monomer. By containing a structural unit derived from a styrene monomer in the (meth)acrylic polymer (B), δp of the Hansen solubility parameter can be decreased, and it becomes easy to control the glass transition temperature of the pressure-sensitive adhesive within a suitable range.

[0097] When the (meth)acrylic polymer (B) contains a structural unit derived from a styrene monomer, the content of the structural unit derived from the styrene monomer in 100 mol% of all the structural units is preferably 0.05 mol% or more, more preferably 0.1 mol% or more, still more preferably 0.15 mol% or more, and preferably 4.0 mol% or less, more preferably 3.0 mol% or less, still more preferably 2.0 mol% or less. If the content of the structural unit derived from the styrene monomer is within the above range, the δp of the Hansen solubility parameter can be decreased, and it becomes easy to control the glass transition temperature of the pressure-sensitive adhesive to a suitable range.

[0098] (Production method of (meth)acrylic polymer) The (meth)acrylic polymer can be produced by polymerizing the monomer using a conventionally known polymerization method.

[0099] Examples of the polymerization method include a radical polymerization method (also referred to as a free radical polymerization method), a cationic polymerization method, an anionic polymerization method, a living polymerization method, etc. Among these, the living polymerization method is preferable. That is, as the (meth)acrylic polymer, those polymerized by the living polymerization method are preferable. In the living polymerization method, among the four elementary reactions of initiation reaction, growth reaction, termination reaction, and chain transfer reaction in chain polymerization, side reactions such as termination reaction and chain transfer reaction are not substantially involved, and the vinyl monomer reacts without the reaction point (polymerization growth end) being deactivated, and the polymer chain grows. Therefore, a polymer with a small molecular weight distribution and a uniform composition can be produced. The living polymerization method includes a living radical polymerization method, a living anionic polymerization method, a living cationic polymerization method, etc. Among these, from the viewpoint of the simplicity of polymerization, the living radical polymerization method is preferable. Also, the living radical polymerization method is preferable in that it maintains the simplicity and versatility of the free radical polymerization method, and it is easy to precisely control the molecular weight distribution and produce a polymer with a uniform composition.

[0100] (Free radical polymerization method) The free radical polymerization method may adopt a conventionally known method. Examples of the polymerization initiator used in the free radical polymerization method include azo polymerization initiators and peroxide polymerization initiators. Examples of the azo polymerization initiators include 2,2'-azobis(isobutyronitrile) (AIBN), 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN), 1,1'-azobis(1-cyclohexanecarbonitrile) (ACHN), dimethyl-2,2'-azobisisobutyrate (MAIB), 4,4'-azobis(4-cyanovaleric acid) (ACVA), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70), 2,2'-azobis(N-butyl-2-methylpropionamide) (VAm-110), and the like.

[0101] The polymerization reaction can be carried out without a solvent, but it may also be carried out by using an aprotic solvent or a protic solvent generally used in radical polymerization and stirring a mixture of vinyl monomers. Examples of the aprotic solvents include acetonitrile, methyl ethyl ketone, anisole, benzene, toluene, propylene glycol monomethyl ether acetate, ethyl acetate, tetrahydrofuran (THF), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), acetone, dioxane, chloroform, carbon tetrachloride, and the like. Examples of the protic solvents include water, methanol, ethanol, isopropanol, n-butanol, ethyl cellosolve, butyl cellosolve, 1-methoxy-2-propanol, hexafluoroisopropanol, diacetone alcohol, and the like. The solvent may be used alone or in combination of two or more.

[0102] The amount of the solvent used may be adjusted as appropriate. For example, with respect to 1 g of the vinyl monomer, it is preferably 0.01 ml to 50 ml, more preferably 0.05 ml to 10 ml, and even more preferably 0.1 ml to 1 ml.

[0103] The reaction temperature and reaction time may be appropriately adjusted according to the molecular weight or molecular weight distribution of the resulting polymer component, but usually, stirring is carried out at 0°C to 150°C for 1 minute to 100 hours. At this time, the pressure is usually carried out at normal pressure, but it may be pressurized or depressurized. After the completion of the polymerization reaction, the target polymer can be separated from the obtained reaction mixture by ordinary separation and purification means, such as removing the used solvent and residual vinyl monomer.

[0104] (Living Radical Polymerization Method) In the living radical polymerization method, due to the difference in the method of stabilizing the polymerization growing end, there are methods using compounds capable of generating nitroxide radicals (nitroxide method; NMP method); methods using metal complexes such as copper and ruthenium, using a halogenated compound as a polymerization initiation compound, and polymerizing livingly from the polymerization initiation compound (ATRP method); methods using dithiocarboxylic acid esters or xanthate compounds (RAFT method); methods using organic tellurium compounds (TERP method); methods using organic iodine compounds (ITP method); methods using an iodine compound as a polymerization initiation compound and using an organic compound such as a phosphorus compound, nitrogen compound, oxygen compound, or hydrocarbon as a catalyst (reversible transfer catalyst polymerization; RTCP method, reversible catalyst-mediated polymerization; RCMP method), etc. Among these, from the viewpoints of the diversity of monomers that can be used, molecular weight control in the polymer region, uniform composition, or coloring, it is preferable to use the TERP method.

[0105] The TERP method is a method of polymerizing a radical polymerizable compound (vinyl monomer) using an organic tellurium compound as a chain transfer agent, for example, the methods described in International Publication No. 2004 / 14848, International Publication No. 2004 / 14962, International Publication No. 2004 / 072126, International Publication No. 2004 / 096870, and International Publication No. 2020 / 116144.

[0106] Specific polymerization methods of the TERP method include the following (a) to (d). (a) A method of polymerizing a vinyl monomer using an organic tellurium compound represented by the formula (T1). (b) A method for polymerizing a vinyl monomer using a mixture of an organic tellurium compound represented by formula (T1) and an azo-based polymerization initiator. (c) A method for polymerizing a vinyl monomer using a mixture of an organic tellurium compound represented by formula (T1) and an organic ditelluride compound represented by formula (T2). (d) A method for polymerizing a vinyl monomer using a mixture of an organic tellurium compound represented by formula (T1), an azo-based polymerization initiator, and an organic ditelluride compound represented by formula (T2).

[0107] [Chemical formula] [In formula (T1), R a represents an alkyl group, aryl group, or aromatic heterocyclic group having 1 to 8 carbon atoms. R b and R c each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. R d represents an alkyl group, aryl group, substituted aryl group, aromatic heterocyclic group, alkoxy group, acyl group, amide group, oxycarbonyl group, cyano group, allyl group, or propargyl group having 1 to 8 carbon atoms. In formula (T2), R a represents an alkyl group, aryl group, or aromatic heterocyclic group having 1 to 8 carbon atoms. ]

[0108] Specific examples of the organic tellurium compound represented by formula (T1) include ethyl = 2-methyl-2-n-butyltellanyl-propionate, ethyl = 2-n-butyltellanyl-propionate, (2-hydroxyethyl) = 2-methyl-methyltellanyl-propionate, etc., and the organic tellurium compounds described in International Publication No. 2004 / 14848, International Publication No. 2004 / 14962, International Publication No. 2004 / 072126, International Publication No. 2004 / 096870, and International Publication No. 2020 / 116144. Specific examples of the organic ditelluride compound represented by formula (T2) include dimethylditelluride, dibutylditelluride, etc.

[0109] The azo polymerization initiator can be used without particular limitation as long as it is an azo polymerization initiator used in ordinary radical polymerization, and examples thereof include 2,2'-azobis(isobutyronitrile) (AIBN), 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN), 1,1'-azobis(1-cyclohexanecarbonitrile) (ACHN), dimethyl-2,2'-azobisisobutyrate (MAIB), 4,4'-azobis(4-cyanovaleric acid) (ACVA), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70), 2,2'-azobis(N-butyl-2-methylpropionamide) (VAm-110), and the like.

[0110] In the polymerization step, in a container substituted with an inert gas, a vinyl monomer, an organic tellurium compound of formula (T1), and, depending on the type of vinyl monomer, for the purposes of promoting the reaction, controlling the molecular weight and molecular weight distribution, etc., an azo polymerization initiator and / or an organic ditelluride compound of formula (T2) are further mixed. At this time, examples of the inert gas include nitrogen, argon, helium, etc. Argon and nitrogen are preferred. The amount of the vinyl monomer used in the above (a), (b), (c) and (d) may be appropriately adjusted according to the physical properties of the target polymer component.

[0111] The polymerization reaction can be carried out without a solvent, or it may be carried out by using an aprotic solvent or a protic solvent commonly used in radical polymerization and stirring the mixture. Examples of the aprotic solvent include acetonitrile, methyl ethyl ketone, anisole, benzene, toluene, propylene glycol monomethyl ether acetate, ethyl acetate, tetrahydrofuran (THF), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), acetone, dioxane, chloroform, carbon tetrachloride, etc. Examples of the protic solvent include, for example, water, methanol, ethanol, isopropanol, n-butanol, ethyl cellosolve, butyl cellosolve, 1-methoxy-2-propanol, hexafluoroisopropanol, diacetone alcohol, etc. The solvent may be used alone or in combination of two or more. The amount of the solvent used may be adjusted as appropriate. For example, 0.01 ml to 50 ml is preferable per 1 g of the vinyl monomer. In the polymerization reaction, in addition to the solvent, a surfactant and / or a dispersant can also be used.

[0112] The reaction temperature and reaction time may be appropriately adjusted according to the molecular weight or molecular weight distribution of the obtained polymer, but usually, it is stirred at 0 °C to 150 °C for 1 minute to 100 hours. At this time, the pressure is usually carried out at normal pressure, but it may be pressurized or depressurized. Further, the polymerization reaction may be carried out by light irradiation. After the completion of the polymerization reaction, from the obtained reaction mixture, the used solvent, the removal of the residual vinyl monomer, etc. can be carried out by ordinary separation and purification means to separate the target polymer.

[0113] The polymerization growing end of the polymer obtained by the polymerization reaction is -TeR derived from a tellurium compound a is (wherein R ais in the same form as described above), and is removed from the polymerization growth terminal by an operation in air after the polymerization reaction, although tellurium atoms may remain. Since the polymer with tellurium atoms remaining at the terminal may be colored or have poor thermal stability, it is preferable to remove the tellurium atoms. Examples of methods for removing tellurium atoms include radical reduction methods; methods of adsorbing with activated carbon or the like; methods of adsorbing metals with ion exchange resins or the like, and these methods can also be used in combination. Note that the other end of the polymer obtained by the polymerization reaction (the end opposite to the polymerization growth terminal) is -CR b R c R d (wherein R b 、R c and R d are the same as R b 、R c and R d in formula (T1).). Therefore, the polymer obtained by the TERP method does not have a substituent containing a sulfur atom at the terminal.

[0114] (Crosslinking agent) The pressure-sensitive adhesive composition contains a crosslinking agent. The crosslinking agent introduces a crosslinked structure into the cured product of the pressure-sensitive adhesive composition. The crosslinked structure may be a crosslinked structure formed only from the crosslinking agent, or a crosslinked structure formed from the molecular chain of the (meth)acrylic polymer and the crosslinking agent. The crosslinking agent has two or more reactive groups in the molecule. The reactive groups are functional groups that bond with each other to form a crosslinked structure, or functional groups that react with the first reactive group of the (meth)acrylic polymer. Examples of the reactive groups include a hydroxy group, a carboxy group, a vinyl group (ethylenically unsaturated group), an amino group, an isocyanate group, an epoxy group, an alidylin group, a carbodiimide group, an oxazoline group, and the like.

[0115] The average number of reactive groups contained in one molecule of the crosslinking agent is 2 or more, preferably 8 or less, and more preferably 6 or less. The molecular weight of the crosslinking agent is preferably 200 or more, more preferably 250 or more, still more preferably 300 or more, and preferably 1500 or less, more preferably 1000 or less, still more preferably 700 or less.

[0116] The content of the reactive groups of the crosslinking agent is preferably 1.5 mmol / g or more, more preferably 2.0 mmol / g or more, and preferably 10 mmol / g or less, more preferably 8 mmol / g or less. By setting the content of the reactive groups of the crosslinking agent within the above range, it becomes possible to design the adhesive strength and durability within a suitable range.

[0117] Examples of the crosslinking agent include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, radical polymerization-based crosslinking agents, aziridine-based crosslinking agents, oxazoline-based crosslinking agents, carbodiimide-based crosslinking agents, metal chelate-based crosslinking agents, melamine resin-based crosslinking agents, urea resin-based crosslinking agents, and the like. The crosslinking agent may be used alone or in combination of two or more. Among these, isocyanate-based crosslinking agents and / or epoxy-based crosslinking agents are preferred.

[0118] (Isocyanate-based crosslinking agent) The isocyanate-based crosslinking agent is preferably a compound having two or more isocyanate groups (including isocyanate regenerable functional groups in which the isocyanate group is temporarily protected by a blocking agent or oligomerization, etc.) in one molecule as reactive groups. The isocyanate-based crosslinking agent may be used alone or in combination of two or more.

[0119] Examples of the isocyanate-based crosslinking agent include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates, and polyisocyanates polyfunctionalized by adducts of these with various polyols, isocyanurate bonds, biuret bonds, allophanate bonds, and the like. Specifically, examples include a compound having two isocyanate groups (including an isocyanate regenerable functional group in which the isocyanate group is temporarily protected by a blocking agent or oligomerization, etc.) in one molecule (a bifunctional isocyanate crosslinking agent), or a compound having three isocyanate groups (including an isocyanate regenerable functional group in which the isocyanate group is temporarily protected by a blocking agent or oligomerization, etc.) in one molecule (a trifunctional isocyanate crosslinking agent), or a compound having six isocyanate groups (including an isocyanate regenerable functional group in which the isocyanate group is temporarily protected by a blocking agent or oligomerization, etc.) in one molecule (a hexafunctional isocyanate crosslinking agent), etc.

[0120] Examples of the bifunctional isocyanate crosslinking agent include diisocyanate compounds such as aliphatic diisocyanate compounds, alicyclic diisocyanate compounds, and aromatic diisocyanate compounds, and adducts of these diisocyanate compounds and diol compounds can also be used. A diisocyanate compound is a compound represented by the general formula "O=C=N-X-N=C=O" (X is a divalent aliphatic group, a divalent alicyclic group, a divalent aromatic group, etc.). A diol compound is a compound represented by the general formula "HO-Y-OH" (Y is a divalent aliphatic group, a divalent alicyclic group, a divalent aromatic group, etc.).

[0121] Examples of the aliphatic diisocyanate compound include ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, etc. Among these, aliphatic diisocyanate compounds having 4 to 30 carbon atoms are preferred, and aliphatic diisocyanate compounds having 4 to 10 carbon atoms are more preferred.

[0122] Examples of the alicyclic diisocyanate compound include isophorone diisocyanate, cyclopentyl diisocyanate, cyclohexyl diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylylene diisocyanate, etc. Among these, alicyclic diisocyanate compounds having 7 to 30 carbon atoms are preferred.

[0123] Examples of the aromatic diisocyanate compound include phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthylene diisocyanate, diphenyl ether diisocyanate, diphenylmethane diisocyanate, diphenylpropane diisocyanate, etc. Aromatic diisocyanate compounds having 8 to 30 carbon atoms are preferred.

[0124] Examples of the diol compound include aliphatic diol compounds such as 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, polyethylene glycol, polypropylene glycol, etc. Among these, aliphatic diol compounds having 3 to 10 carbon atoms are preferred.

[0125] Examples of the trifunctional isocyanate crosslinking agent and the hexafunctional isocyanate crosslinking agent include adducts of the diisocyanate compound, biuret bodies of the diisocyanate compound, isocyanurate bodies of the diisocyanate compound (cyclic multimers of diisocyanate compounds), etc.

[0126] As the isocyanate-based crosslinking agent, a bifunctional isocyanate-based crosslinking agent selected from the group consisting of an aliphatic diisocyanate compound and an adduct of an aliphatic diisocyanate compound and an aliphatic diol compound; a trifunctional or hexafunctional isocyanate-based crosslinking agent selected from the group consisting of an adduct of aliphatic diisocyanate compounds, a biuret of an aliphatic diisocyanate compound, and an isocyanurate of an aliphatic diisocyanate compound is preferred. If the crosslinking agent is a trifunctional or hexafunctional aliphatic isocyanate-based crosslinking agent, crosslinking over time due to unreacted reactive groups is suppressed, and a stable pressure-sensitive adhesive can be prepared.

[0127] (Epoxy-based crosslinking agent) The epoxy-based crosslinking agent is preferably a compound having two or more epoxy groups as reactive groups in one molecule. The epoxy-based crosslinking agent may be used alone or in combination of two or more.

[0128] Examples of the epoxy-based crosslinking agent include aliphatic epoxy compounds, alicyclic epoxy compounds, aromatic epoxy compounds, and heterocyclic epoxy compounds.

[0129] Examples of the aliphatic epoxy compound include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, trimethylolpropane diglycidyl ether, trimethylolpropane polyglycidyl ether, diglycidylamine, neopentyl glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, polyglycerol polyglycidyl ether, adipic acid diglycidyl ester, and the like.

[0130] Examples of the alicyclic epoxy compound include 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and the like.

[0131] Examples of the aromatic epoxy compound include bisphenol A epichlorohydrin type epoxy resin, diglycidylaniline, o-phthalic acid diglycidyl ester, resorcin diglycidyl ether, bisphenol-S-diglycidyl ether, and the like.

[0132] Examples of the heterocyclic epoxy compound include triglycidyl-tris(2-hydroxyethyl) isocyanurate, 1,3,5-tris-(2,3-epoxybutyl)-isocyanurate, 1,3,5-tris-(3,4-epoxybutyl)-isocyanurate, 1,3,5-tris-(4,5-epoxypentyl)-isocyanurate, sorbitan polyglycidyl ether, and the like.

[0133] As the epoxy crosslinking agent, a compound having two epoxy groups in one molecule (bifunctional epoxy crosslinking agent), a compound having three epoxy groups in one molecule (trifunctional epoxy crosslinking agent), or a compound having four epoxy groups in one molecule (tetrafunctional epoxy crosslinking agent) is preferable. If the crosslinking agent is a bifunctional epoxy crosslinking agent, a trifunctional epoxy crosslinking agent, or a tetrafunctional epoxy crosslinking agent, crosslinking over time due to unreacted reactive groups can be suppressed, and a stable adhesive material can be prepared.

[0134] (Radical polymerization type crosslinking agent) The radical polymerization type crosslinking agent is preferably a compound having two or more ethylenically unsaturated groups as reactive groups in one molecule. The radical polymerization type crosslinking agent may be used alone or in combination of two or more.

[0135] The number of ethylenically unsaturated groups in one molecule of the radical polymerization crosslinking agent is preferably 2 or more, preferably 4 or less, and more preferably 3 or less. Examples of the radical polymerization crosslinking agent include compounds having 2 or more (meth)acryloyl groups, and polyfunctional monomers and polyfunctional oligomers are preferred.

[0136] Examples of the compound having 2 or more (meth)acryloyl groups include hexanediol di(meth)acrylate, butanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, ethylene oxide-modified isocyanuric acid tri(meth)acrylate, allyl (meth)acrylate, vinyl (meth)acrylate, urethane (meth)acrylate, and the like.

[0137] The content of the crosslinking agent in the pressure-sensitive adhesive composition is preferably 0.05 parts by mass or more, more preferably 0.08 parts by mass or more, still more preferably 0.1 parts by mass or more, and preferably 0.5 parts by mass or less, more preferably 0.4 parts by mass or less, still more preferably 0.3 parts by mass or less, based on 100 parts by mass of the (meth)acrylic polymer (A). When the content of the crosslinking agent is within the above range, appropriate cohesive force is exhibited, and the adhesive strength and durability are within a suitable range.

[0138] In the pressure-sensitive adhesive composition, it is preferable that the (meth)acrylic polymer (A) and / or the (meth)acrylic polymer (B) (preferably the (meth)acrylic polymer (A)) has a first reactive group, and the crosslinking agent is a compound having two or more second reactive groups that react with the first reactive group in one molecule. As the second reactive group, a hydroxy group, a carboxy group, a vinyl group (ethylenically unsaturated group), an amino group, an isocyanate group, an epoxy group, an aziridine group, a carbodiimide group, an oxazoline group, etc. are preferable, and an isocyanate group and / or an epoxy group are more preferable.

[0139] Examples of the combination of the first reactive group of the (meth)acrylic polymer (A) and / or the (meth)acrylic polymer (B) (preferably the (meth)acrylic polymer (A)) and the second reactive group of the crosslinking agent include the following combinations. When the second reactive group of the crosslinking agent is an epoxy group, a carboxy group can be mentioned as the first reactive group. When the second reactive group of the crosslinking agent is an isocyanate group, a hydroxy group can be mentioned as the first reactive group. When the second reactive group of the crosslinking agent is an ethylenically unsaturated group, an ethylenically unsaturated group can be mentioned as the first reactive group. When the (meth)acrylic polymer does not have an ethylenically unsaturated group, a crosslinked structure is formed between the crosslinking agents.

[0140] Examples of the combination of the first reactive group of the (meth)acrylic polymer and the second reactive group of the crosslinking agent include (1) a combination in which the first reactive group is a hydroxy group and the second reactive group is an isocyanate group; (2) a combination in which the first reactive group is a carboxy group and the second reactive group is an epoxy group.

[0141] The molar ratio (the first reactive group / the second reactive group) of the second reactive group possessed by the crosslinking agent and the first reactive group possessed by the (meth)acrylic polymer is preferably 1.0 or more, preferably 30.0 or less, more preferably 20.0 or less, still more preferably 10.0 or less, and particularly preferably 5.0 or less. When the molar ratio (the first reactive group / the second reactive group) is 1.0 or more, the crosslinking agent reacts without excess or deficiency, there is no excess in the second reactive group, high flexibility is exhibited, and when it is 30.0 or less, sufficient reaction proceeds and high resilience is exhibited.

[0142] The pressure-sensitive adhesive composition preferably contains only an isocyanate-based crosslinking agent, only an epoxy-based crosslinking agent, an isocyanate-based crosslinking agent and a radical polymerization-based crosslinking agent, or an epoxy-based crosslinking agent and a radical polymerization-based crosslinking agent as the crosslinking agent, and more preferably contains only an isocyanate-based crosslinking agent or only an epoxy-based crosslinking agent as the crosslinking agent. When containing only an isocyanate-based crosslinking agent as the crosslinking agent, it is preferable to contain only a bifunctional isocyanate-based crosslinking agent having 2 isocyanate groups in one molecule, a trifunctional isocyanate-based crosslinking agent having 3 isocyanate groups in one molecule, or a hexafunctional isocyanate-based crosslinking agent having 6 isocyanate groups in one molecule. Further, when containing only an epoxy-based crosslinking agent as the crosslinking agent, it is preferable to contain only a bifunctional epoxy-based crosslinking agent having 2 epoxy groups in one molecule, a trifunctional epoxy-based crosslinking agent having 3 epoxy groups in one molecule, or a tetrafunctional epoxy-based crosslinking agent having 4 epoxy groups in one molecule.

[0143] As the pressure-sensitive adhesive composition, there are preferred embodiments in which the (meth)acrylic polymer (A) has a hydroxy group as the first reactive group and contains an isocyanate-based crosslinking agent as the crosslinking agent; the (meth)acrylic polymer (A) has a carboxy group as the first reactive group and contains an epoxy-based crosslinking agent as the crosslinking agent; and the (meth)acrylic polymer (A) has a hydroxy group and a carboxy group as the first reactive group and contains an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent as the crosslinking agent.

[0144] (Other additives) In addition to the (meth)acrylic polymer (A), (meth)acrylic polymer (B), and crosslinking agent, other additives can be blended and used in the pressure-sensitive adhesive composition. Examples of other additives include crosslinking accelerators, crosslinking retardants, tackifying resins (tackifiers), photopolymerization initiators, silane coupling agents, plasticizers, softeners, release aids, dyes, pigments, colorants, fluorescent brighteners, antistatic agents, wetting agents, surfactants, thickeners, antifungal agents, preservatives, oxygen absorbers, ultraviolet absorbers, antioxidants, near-infrared absorbers, water-soluble matting agents, fragrances, metal deactivators, nucleating agents, alkylating agents, flame retardants, lubricants, processing aids, and the like. These are appropriately selected and blended for use according to the application and purpose of use of the pressure-sensitive adhesive material.

[0145] (Crosslinking accelerator) The pressure-sensitive adhesive composition can contain a crosslinking accelerator as needed. Examples of crosslinking accelerators include organotin compounds and metal chelate compounds. The crosslinking accelerator may be used alone or in combination of two or more.

[0146] Examples of the organotin compound include dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin dioctylate, and the like. The metal chelate compound is a complex in which a ligand having two or more coordinating atoms forms a ring and binds to a central metal.

[0147] The content of the crosslinking accelerator in the pressure-sensitive adhesive composition is preferably 0.01 part by mass or more, more preferably 0.02 part by mass or more, still more preferably 0.04 part by mass or more, and preferably 0.5 part by mass or less, more preferably 0.4 part by mass or less, still more preferably 0.3 part by mass or less, based on 100 parts by mass of the polymer component. By setting the content of the crosslinking accelerator within the above range, it is possible to obtain an excellent crosslinking acceleration effect.

[0148] (Crosslinking retardant) In the above-mentioned pressure-sensitive adhesive composition, a crosslinking retarder can be blended and used as required. The crosslinking retarder is a compound that can suppress excessive viscosity increase of the pressure-sensitive adhesive composition by blocking the functional groups of the crosslinking agent in the pressure-sensitive adhesive composition containing the crosslinking agent. As the crosslinking retarder, β-diketones such as acetylacetone, hexane-2,4-dione, heptane-2,4-dione, octane-2,4-dione; β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, propyl acetoacetate, butyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, stearyl acetoacetate; benzoylacetone, etc. can be used. As the crosslinking retarder, those that can act as a chelating agent are preferred, and β-diketones and β-ketoesters are preferred.

[0149] The content of the crosslinking retarder that can be blended in the pressure-sensitive adhesive composition is preferably 0.1 part by mass or more, more preferably 0.2 part by mass or more, still more preferably 0.5 part by mass or more, and preferably 4.0 parts by mass or less, more preferably 3.0 parts by mass or less, still more preferably 1.5 parts by mass or less with respect to 100 parts by mass of the polymer component. If the content of the crosslinking retarder is within the above range, after blending the crosslinking agent into the pressure-sensitive adhesive composition, excessive viscosity increase and gelation of the pressure-sensitive adhesive composition can be suppressed, and the storage stability (pot life) of the pressure-sensitive adhesive composition can be extended.

[0150] (Photoinitiator) When a radical polymerization crosslinking agent is used as the crosslinking agent, it is preferable to blend a photoinitiator in the pressure-sensitive adhesive composition and irradiate it with active energy rays. By blending a photoinitiator, the reaction during irradiation with active energy rays can be promoted. The photoinitiator is not particularly limited as long as it generates radicals by the action of light. For example, photoinitiators such as acetophenones, benzoins, benzophenones, thioxanthones, and acylphosphine oxides can be mentioned. These photoinitiators can be used alone or in combination of two or more. Among these photoinitiators, hydrogen abstraction type benzophenones and intramolecular cleavage type acetophenone photoinitiators are preferable from the viewpoint of efficient crosslinking between molecules or within molecules.

[0151] When a photoinitiator is blended in the pressure-sensitive adhesive composition, the content of the photoinitiator is preferably 0.01 parts by mass to 5 parts by mass, more preferably 0.1 parts by mass to 10 parts by mass, and still more preferably 0.3 parts by mass to 2 parts by mass with respect to 100 parts by mass of the polymer component.

[0152] In addition, the pressure-sensitive adhesive composition may contain an auxiliary agent for the photoinitiator. As the auxiliary agent, triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Michler's ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethyl benzoate, ethyl 4-dimethylaminobenzoate, (n-butoxy)ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, etc. can be used in combination. These auxiliary agents may be used alone or in combination of two or more.

[0153] (Silane coupling agent) The above-mentioned pressure-sensitive adhesive composition can be used by blending a silane coupling agent as required. Examples of the silane coupling agent include epoxy group-containing silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; amino group-containing silane coupling agents such as 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, and N-phenyl-γ-aminopropyltrimethoxysilane; (meth)acrylic group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane; isocyanate group-containing silane coupling agents such as 3-isocyanatopropyltriethoxysilane, and the like.

[0154] The content of the silane coupling agent that can be blended in the above-mentioned pressure-sensitive adhesive composition is preferably 0.01 part by mass to 1 part by mass, more preferably 0.15 part by mass to 0.8 part by mass, and still more preferably 0.02 part by mass to 0.6 part by mass, based on 100 parts by mass of the polymer component. By setting the content of the silane coupling agent within the above range, the water resistance at the interface can be improved when the pressure-sensitive adhesive is applied to a hydrophilic adherend such as glass.

[0155] (Plasticizer) In the above-mentioned pressure-sensitive adhesive composition, a plasticizer can be blended and used as necessary. Examples of the plasticizer include oils such as paraffin oil and process oil; liquid rubbers such as liquid polyisoprene, liquid polybutadiene, and liquid ethylene-propylene rubber; tetrahydrophthalic acid, azelaic acid, benzoic acid, phthalic acid, trimellitic acid, pyromellitic acid, adipic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid, citric acid, and their derivatives; dioctyl phthalate (DOP), dibutyl phthalate (DBP), dioctyl adipate, diisononyl adipate (DINA), isodecyl succinate, and the like. The plasticizer may be used alone or in combination of two or more. Among these, liquid rubber is preferred.

[0156] The weight average molecular weight (Mw) of the above-mentioned liquid rubber is preferably 5,000 to 60,000, more preferably 10,000 to 50,000. By setting the Mw of the liquid rubber within the above range, a pressure-sensitive adhesive excellent in flexibility can be formed while suppressing bleed-out. The method for measuring the weight average molecular weight (Mw) will be described later.

[0157] When a plasticizer is blended in the pressure-sensitive adhesive composition, the content of the plasticizer is preferably 1 to 50 parts by mass, more preferably 5 to 40 parts by mass, and still more preferably 10 to 30 parts by mass with respect to 100 parts by mass of the polymer component. By adjusting the content of the plasticizer within the above range, a pressure-sensitive adhesive excellent in adhesive force and resilience can be formed.

[0158] (Method for producing the pressure-sensitive adhesive composition) The pressure-sensitive adhesive composition can be produced by mixing the above-mentioned (meth)acrylic polymer, cross-linking agent, and other additives used as necessary. The pressure-sensitive adhesive composition may contain a solvent derived from the production of the (meth)acrylic polymer, or may be a solution diluted with an appropriate solvent to have a viscosity suitable for forming a pressure-sensitive adhesive layer.

[0159] Examples of the solvent include aliphatic hydrocarbons such as hexane and heptane; aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as methylene chloride and ethylene chloride; ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; cellosolve solvents such as ethyl cellosolve; and glycol ether solvents such as propylene glycol monomethyl ether. These solvents may be used alone or in combination of two or more.

[0160] The amount of the solvent used may be appropriately adjusted so that the pressure-sensitive adhesive composition has a viscosity suitable for coating, and there is no particular limitation. However, from the viewpoint of coatability, 1% by mass to 90% by mass is preferable, more preferably 10% by mass to 80% by mass, and still more preferably 20% by mass to 70% by mass.

[0161] (Use of the pressure-sensitive adhesive composition) The pressure-sensitive adhesive composition is used for forming a pressure-sensitive adhesive. As described later, the pressure-sensitive adhesive is preferably used for a flexible display and a member used for curved surface bonding. Therefore, the pressure-sensitive adhesive composition is useful as a pressure-sensitive adhesive composition for flexible displays for bonding one flexible member and another flexible member constituting a flexible display.

[0162] [Pressure-sensitive adhesive] The pressure-sensitive adhesive of the present invention is characterized in that it is a cured product of the pressure-sensitive adhesive composition. The use of the pressure-sensitive adhesive is not particularly limited, and it can be used for a wide range of applications. In particular, it is preferably used for flexible displays that can be repeatedly bent and stretched and members used for flexible displays. That is, the pressure-sensitive adhesive can be used as a pressure-sensitive adhesive for flexible displays for bonding one flexible member and another flexible member constituting a flexible display.

[0163] Examples of the flexible display that can be used by repeatedly bending and stretching include a foldable display that can be folded and a rollable display that can be rolled into a cylindrical shape. The flexible display is expected to be used in portable terminals such as smartphones and tablet terminals, and stationary displays that can be stored.

[0164] The gel fraction of the cured product is preferably 40% by mass or more and preferably 95% by mass or less, more preferably 90% by mass or less, and still more preferably 80% by mass or less. By setting the gel fraction within the above range, an adhesive material having excellent adhesiveness can be formed. The gel fraction can be controlled by the type and blending amount of the polymer in the adhesive composition, as well as the blending amount of the crosslinking agent, the crosslinking treatment temperature, the crosslinking treatment time, and the like.

[0165] The glass transition temperature measured using the dynamic viscoelasticity measuring device of the cured product is preferably -60°C or higher and preferably -47°C or lower, more preferably -45°C or lower. If the glass transition temperature measured using the dynamic viscoelasticity measuring device is within the above range, it is possible to design an adhesive material that does not float or peel off against deformation at low temperatures or high speeds.

[0166] The shear storage modulus G -20 ' at -20°C measured using the dynamic viscoelasticity measuring device of the cured product is preferably 0.02 MPa or more, more preferably 0.05 MPa or more, still more preferably 0.07 MPa or more, and preferably 0.2 MPa or less, more preferably 0.15 MPa or less, still more preferably 0.13 MPa or less. The shear storage modulus G -20 ' within the above range makes it possible to design an adhesive material that does not float or peel off against deformation at low temperatures or high speeds.

[0167] The shear storage modulus G 25' is preferably 0.01 MPa or more, more preferably 0.015 MPa or more, still more preferably 0.025 MPa or more, and preferably 0.1 MPa or less, more preferably 0.07 MPa or less, still more preferably 0.05 MPa or less. The shear storage modulus G at 25°C measured using the dynamic viscoelasticity measuring device 25 ' exhibits suitable adhesive strength at room temperature if it is 0.01 MPa or more, and it is possible to produce an adhesive material that sufficiently follows deformation at room temperature if it is 0.07 MPa or less.

[0168] The shear storage modulus G at 60°C measured using the dynamic viscoelasticity measuring device of the cured product 60 ' is preferably 0.01 MPa or more, more preferably 0.015 MPa or more, and preferably 0.1 MPa or less, more preferably 0.07 MPa or less, still more preferably 0.05 MPa or less. The shear storage modulus G at 60°C measured using the dynamic viscoelasticity measuring device 60 ' exhibits suitable adhesive strength even at high temperature (60°C) if it is 0.01 MPa or more, and it is possible to produce an adhesive material that sufficiently follows deformation even at high temperature (60°C) if it is 0.07 MPa or less.

[0169] [Adhesive sheet] The adhesive sheet of the present invention has an adhesive layer and a base material sheet disposed on at least one surface of the adhesive layer, and is characterized in that the adhesive layer is formed from the adhesive material.

[0170] Generally, a "sheet" refers to a flat product that is thin and generally has a small thickness relative to its length and width as defined in JIS. Generally, a "film" refers to a thin flat product with an extremely small thickness compared to its length and width, and its maximum thickness is arbitrarily limited, and it is usually supplied in the form of a roll (Japanese Industrial Standard JIS K6900). For example, in terms of thickness, in a narrow sense, those with a thickness of 100 μm or more may be referred to as sheets, and those with a thickness of less than 100 μm may be referred to as films. However, the boundary between sheets and films is not clear, and since there is no need to distinguish between the two in the language of the present invention, in the present invention, when referring to "sheets", it includes "films", and when referring to "films", it also includes "sheets".

[0171] (Adhesive layer) The adhesive layer is formed from the adhesive material. From the viewpoint of sufficiently ensuring the adhesiveness with the adherend, etc., the film thickness of the adhesive layer is preferably 2 μm or more, more preferably 5 μm or more, and still more preferably 10 μm or more. Also, from the viewpoint of suppressing the protrusion of the adhesive layer, etc., the thickness of the adhesive layer is preferably 100 μm or less, more preferably 70 μm or less, and still more preferably 50 μm or less.

[0172] (Base sheet) The base sheet is a sheet member that supports the adhesive layer. The material of the base sheet can be appropriately selected according to the use of the adhesive sheet. Examples of the base sheet include resin sheets, glass sheets, release sheets, etc. The release sheet protects the adhesive layer until the adhesive layer is adhered to the adherend, and is peeled off from the adhesive layer before the adhesive layer is adhered to the adherend.

[0173] The base sheet may be a functional sheet member. Examples of the functional sheet member include cover films, barrier films, polarizing films, retardation films, optical compensation films, brightness enhancement films, diffusion films, antireflection films, etc.

[0174] The thickness of the base sheet is not particularly limited, but from the viewpoint of excellent handleability, etc., it is preferably 2 μm to 500 μm, more preferably 2 μm to 200 μm.

[0175] The pressure-sensitive adhesive sheet is a pressure-sensitive adhesive sheet for a flexible display, which has a pressure-sensitive adhesive layer used for bonding one flexible member and another flexible member constituting the flexible display, and a flexible sheet member adhered to at least one surface of the pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer is preferably a pressure-sensitive adhesive sheet for a flexible display formed from the pressure-sensitive adhesive.

[0176] As the configuration of the pressure-sensitive adhesive sheet for a flexible display, there are embodiments having a pressure-sensitive adhesive layer and a first flexible sheet member adhered to one surface of the pressure-sensitive adhesive layer; embodiments having a pressure-sensitive adhesive layer, a first flexible sheet member adhered to one surface of the pressure-sensitive adhesive layer, and a second flexible sheet member adhered to the other surface of the pressure-sensitive adhesive layer.

[0177] Examples of the flexible sheet member include a base sheet having flexibility, a release sheet, etc. The base sheet is a sheet member that supports the pressure-sensitive adhesive layer, and this sheet member may be a functional sheet member. Examples of the functional sheet member include a cover film, a barrier film, a polarizing film, a retardation film, an optical compensation film, a brightness enhancement film, a diffusion film, an antireflection film, etc. The release sheet protects the pressure-sensitive adhesive layer until the pressure-sensitive adhesive layer is adhered to an adherend, and is peeled off from the pressure-sensitive adhesive layer before the pressure-sensitive adhesive layer is adhered to the adherend.

[0178] Examples of the flexible sheet member include a sheet of a polymer material, a glass sheet, etc. The thickness of the flexible sheet member is not particularly limited, but from the viewpoint of excellent handleability, etc., it is preferably 2 μm to 500 μm, more preferably 2 μm to 200 μm.

[0179] Examples of the polymer material include polyimide resin; polyester resins such as polyethylene terephthalate resin and polyethylene naphthalate resin; polycarbonate resin; poly(meth)acrylate resin; polystyrene resin; polyamide resin; polyacrylonitrile resin; polyolefin resins such as polypropylene resin, polyethylene resin, and polycycloolefin resin; polyphenylene sulfide resin; polyvinyl chloride resin; polyvinylidene chloride resin; and polyvinyl alcohol resin.

[0180] The flexible sheet member may be composed of a single layer including one or more of the above polymer materials, or may be composed of two or more layers such as a layer including one or more of the above polymer materials and a layer including one or more polymer materials different from this layer.

[0181] The flexible sheet member is preferably a release sheet having a release treatment on the surface in contact with the adhesive layer. Examples of the release agent used for the release treatment include release agents such as silicone-based, fluorine-based, alkyd-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents.

[0182] The adhesive sheet has a first flexible sheet member adhered to one surface of the adhesive layer and a second flexible sheet member adhered to the other surface of the adhesive layer. The first flexible sheet member is a first release sheet, the second flexible sheet member is a second release sheet, and it is preferable that the first release sheet and the second release sheet are adhered so that their release surfaces are in contact with the adhesive layer. When the adhesive layer is sandwiched between two release sheets, it is preferable that one release sheet is a heavy release type release sheet with a large release force and the other release sheet is a light release type release sheet with a small release force.

[0183] (Manufacture of Adhesive Sheet) The adhesive sheet can be manufactured, for example, by applying the above-described adhesive composition onto a flexible sheet member and curing it by drying heat treatment as necessary to form an adhesive layer.

[0184] For the coating of the pressure-sensitive adhesive composition, for example, various coating methods such as reverse gravure coating method, direct gravure coating method, die coating method, bar coating method, wire bar coating method, roll coating method, spin coating method, dip coating method, spray coating method, knife coating method, kiss coating method, etc.; inkjet method; various printing methods such as offset printing, screen printing, flexographic printing, etc. can be adopted. Further, before applying the pressure-sensitive adhesive composition, the surface of the release sheet may be subjected to surface treatment such as corona treatment, plasma treatment, hot air treatment, ozone treatment, ultraviolet treatment, etc.

[0185] The drying and heating process is not particularly limited as long as it can remove the solvent etc. used in the pressure-sensitive adhesive composition and cure it, but it is preferably carried out at a temperature of 60°C to 150°C for 20 seconds to 300 seconds. In particular, the heating temperature is preferably 100°C to 130°C.

[0186] When arranging the first flexible sheet member on one surface of the pressure-sensitive adhesive layer and the second flexible sheet member on the other surface, apply the pressure-sensitive adhesive composition to the first flexible sheet member, form a pressure-sensitive adhesive layer on the first flexible sheet member, and then attach the second flexible sheet member to this pressure-sensitive adhesive layer. Further, the pressure-sensitive adhesive layer may be cured as needed. Examples of the curing conditions include, for example, 60°C for 3 days to 7 days.

Examples

[0187] Hereinafter, the present invention will be described in more detail based on specific examples. The present invention is not limited to the following examples at all, and can be appropriately modified and implemented within the scope of not changing the gist. The polymerization rate of the polymerization composition, the weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the polymer component, the thickness of the pressure-sensitive adhesive layer, and the evaluation of the pressure-sensitive adhesive were evaluated according to the following methods.

[0188] The meanings of the abbreviations are as follows. EHA: 2-Ethylhexyl acrylate IDA: Isodecyl acrylate LA: n-Lauryl acrylate LMA: n-Lauryl methacrylate AA: Acrylic acid HBA: 4-Hydroxybutyl acrylate MEDOLMA: (2-Methyl-2-ethyl-1,3-dioxolan-4-yl)methyl acrylate VP: N-Vinyl-2-pyrrolidone St: Styrene BTEE: Ethyl 2-methyl-2-n-butyltellanyl-propionate AIBN: Azobisisobutyronitrile AcOEt: Ethyl acetate

[0189] (Polymerization rate) Using a nuclear magnetic resonance (NMR) measuring device (manufactured by Bruker BioSpin, model: AVANCE500 (frequency 500 MHz)), 1 1H-NMR was measured (solvent: deuterated chloroform, internal standard: trimethylsilane (TMS)). For the obtained NMR spectrum, the integration ratio of the signals derived from the monomer and the signals derived from the polymer was determined, and the polymerization rate of the monomer was calculated.

[0190] (Weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn)) Gel permeation chromatography (GPC) was performed using a high-performance liquid chromatograph (manufactured by Tosoh Corporation, model HLC-8320GPC). Two TSKgel Super HZM-H columns (manufactured by Tosoh Corporation) were used, a tetrahydrofuran solution was used as the mobile phase, and a differential refractometer was used as the detector. The measurement conditions were a column temperature of 40 °C, a sample concentration of 0.5 mg / mL, a sample injection volume of 10 μL, and a flow rate of 0.6 mL / min. A calibration curve was created using polystyrene (molecular weights 9,840,000, 5,480,000, 2,890,000, 1,090,000, 775,000, 427,000, 190,000, 96,400, 37,900, 10,200, 2,630, 440) as the standard substance, and the weight-average molecular weight (Mw) and number-average molecular weight (Mn) were measured. The molecular weight distribution (Mw / Mn) was calculated from these measured values.

[0191] (Thickness of the adhesive layer) The total thickness of the entire adhesive sheet was measured using a thickness measuring machine (manufactured by Tester Sangyo Co., Ltd., "TH-104"), and the thickness of the adhesive layer was determined by subtracting the thickness of the release sheet from this total thickness.

[0192] (Gel fraction) The mass M2 of a wire mesh (400 mesh) cut into a size of 50 mm in width and 120 mm in length was measured. 80 mg to 120 mg of the adhesive layer (adhesive material) constituting the adhesive sheet was collected and the mass M1 was measured. A test piece was prepared by wrapping it with a wire mesh so that the adhesive material would not fall off. The test piece was placed in a glass bottle, 40 g of ethyl acetate was poured in, and it was gently shaken, then left standing at room temperature (23 °C) for 72 hours. After standing, the test piece was taken out of the glass bottle and left at room temperature for 12 hours, and further dried in a vacuum oven at 100 °C for 4 hours. The dried test piece was cooled to room temperature and the mass M3 was measured, and the gel fraction was calculated from the following formula. Gel fraction (mass %) = (M3 - M2) / M1 × 100

[0193] (Dynamic viscoelasticity test) The adhesive layer (adhesive material) constituting the adhesive sheet was laminated by bonding using a hand roller to produce a laminate with a thickness of 1 mm, which was used as a test piece. The measurement was carried out using a dynamic viscoelasticity measuring device (MCR702 manufactured by Anton Paar), and the sample was sandwiched between parallel plates with a diameter of 8 mm. The measurement conditions were a temperature range of -70°C to 150°C, a heating rate of 3°C / min, and a frequency of 1 Hz. The strain was changed stepwise according to the elastic modulus, with 0.1% from the start of measurement to 10 MPa, 0.2% to 0.5 MPa, 0.5% to 0.09 MPa, 1.5% to 0.05 MPa, and 3% below 0.05 MPa. From the dynamic viscoelasticity measurement results, the glass transition temperature (°C) was read from the maximum value of Tanδ, and the shear storage elastic modulus G’ at -20°C, 25°C, and 60°C was read.

[0194] (Strain at 10 kPa stress, recovery rate after applying 10 kPa stress) The adhesive layer (adhesive material) constituting the adhesive sheet was laminated by bonding using a hand roller to produce a laminate with a thickness of 1 mm, which was used as a test piece. The measurement was carried out using a viscoelasticity measuring device (MCR302 manufactured by Anton Paar), and the sample was sandwiched between parallel plates with a diameter of 8 mm (the adhesive surface was roughened with 240-grit sandpaper), and the measurement was carried out in a 25°C atmosphere. In the measurement, after leaving the test piece compressed with an axial force of 2 N for 5 minutes, a shear stress of 10 kPa was applied and a creep test was carried out for 10 minutes, and the strain after 10 minutes (10 kPa strain) was measured. Next, the shear stress was released (0 kPa) and left for 10 minutes, and the final strain after 10 minutes was measured to obtain the recovery rate. The recovery rate was calculated based on the following formula. Recovery rate (%) = {(10 kPa strain - final strain) / 10 kPa strain} × 100

[0195] <Manufacture of (meth)acrylic polymer> (Synthesis Example 1: Polymer No. 1) Into a flask equipped with an argon gas inlet tube and a stirrer, EHA (402.6 g), LA (180.0 g), AA (2.4 g), HBA (15.0 g), AIBN (26 mg), and AcOEt (352 g) were charged. After purging with argon, BTEE (120 mg) was added, and the mixture was reacted at 60 °C for 23 hours to effect polymerization. The polymerization rate was 90%. After completion of the reaction, AcOEt was added to the reaction solution to obtain a solution containing Polymer No. 1. The Mw of the obtained Polymer No. 1 was 1.618 million, and Mw / Mn was 2.1.

[0196] (Synthesis Examples 2 to 18: Polymers No. 2 to 18) In the same manner as the production method of Polymer No. 1, Polymers No. 2 to 18 were prepared. Table 2 shows the monomers, organic tellurium compounds, azo polymerization initiators, solvents, reaction temperatures, reaction times, and polymerization rates used.

[0197] Table 2 shows the polymerization conditions and the like of each polymer. The amounts of carboxy groups, hydroxy groups, and glass transition temperatures according to the FOX equation were calculated from the charging ratios of the monomers used in the polymerization reaction and the polymerization rate.

[0198] [Table 2]

[0199] [Production of Pressure-Sensitive Adhesive Composition] (Pressure-Sensitive Adhesive Composition No. 1) To the solution of Polymer No. 1 obtained in Synthesis Example 1 (100 parts by mass of polymer component) and the solution of Polymer No. 10 obtained in Synthesis Example 10 (53.0 parts by mass of polymer component), 0.126 part by mass of Crosslinking Agent No. 1 was added and stirred to obtain Pressure-Sensitive Adhesive Composition No. 1. In Pressure-Sensitive Adhesive Composition No. 1, the first reactive group of Polymer No. 1 is a carboxy group, and the second reactive group of the crosslinking agent is an epoxy group.

[0200] (Pressure-Sensitive Adhesive Compositions No. 2 to 14) Adhesive compositions No. 2 to 14 were prepared in the same manner as Adhesive Composition No. 1, except that the formulation was changed as shown in Table 3. In Adhesive Compositions No. 2 to 8 and 10 to 14, the first reactive group of the (meth)acrylic polymer is a carboxy group, and the second reactive group of the crosslinking agent is an epoxy group. In Adhesive Composition No. 9, the first reactive group of the (meth)acrylic polymer is a hydroxy group, and the second reactive group of the crosslinking agent is an isocyanate group.

[0201]

Table 3

[0202] <Production of Adhesive Sheet> An adhesive composition was applied to the release surface of the first release sheet (PET film with a release treatment on the surface, Clean Sepa (registered trademark) HY-US20: manufactured by Toyama Film, thickness 75 μm) using a Baker applicator so that the film thickness after drying would be 50 μm, and then heated using a constant-temperature dryer at 60°C for 3 minutes and subsequently at 150°C for 3 minutes. Next, the release surface of the second release sheet (PET film with a release treatment on the surface, Clean Sepa (registered trademark) HY-S10: manufactured by Toyama Film, thickness 38 μm) was bonded to the adhesive layer formed on the first release sheet, and then aged at 60°C for 3 days to produce an adhesive layer sandwiched between the two release sheets.

[0203] (Adhesive Strength) One release sheet of the adhesive sheet was peeled off from the adhesive layer, and the corona-treated surface of a polyethylene terephthalate (PET) film (Toyobo Estar (registered trademark) film E5100, manufactured by Toyobo, thickness 50 μm) was bonded to the adhesive layer surface, and an adhesive sheet with a substrate was cut into a size of 25 mm in width and 100 mm in length. Regarding this adhesive sheet with a substrate, as an adherend, the adhesive force to glass was measured by changing the time from bonding to measurement to 24 hours according to the method of JIS Z 0237 (2009). Specifically, the release sheet was peeled off from the adhesive layer, and a white plate glass (S9112, manufactured by Matsunami Glass Industry Co., Ltd., thickness 1.0 - 1.2 mm) was pressure-bonded with a 2 kg roller for 2 reciprocations and left standing in an environment of 23°C and 50% RH for 24 hours. Next, using a precision universal testing machine "AUTOGRAPH (registered trademark) AGS-1kNX, 50N load cell" manufactured by Shimadzu Corporation, the adhesive force of the adhesive sheet was measured under the conditions of a peeling speed of 300 mm / min and a peeling angle of 180°. All the measurement operations were carried out in an environment of 23°C and 50% RH.

[0204] The evaluation results of the adhesive material and the adhesive sheet are shown in Table 4.

[0205]

Table 4

[0206] The adhesive compositions No. 1 to 11 contain a (meth)acrylic polymer (A), a (meth)acrylic polymer (B), and a crosslinking agent, and the dipole-dipole force terms of the Hansen solubility parameters of the (meth)acrylic polymer (A) and the (meth)acrylic polymer (B) satisfy the relationships of Formula (1) and Formula (2). The adhesives No. 1 to 11 composed of the cured products of these adhesive compositions No. 1 to 11 have a glass transition temperature of -47°C or lower and excellent low-temperature properties. In addition, the adhesive sheets having an adhesive layer formed from these adhesives No. 1 to 11 have excellent adhesive force at room temperature.

[0207] The pressure-sensitive adhesive compositions No. 12 to 14 contain a (meth)acrylic polymer (A), a (meth)acrylic polymer (B), and a crosslinking agent, and the dipole-dipole force term of the Hansen solubility parameter of the (meth)acrylic polymer (A) and the (meth)acrylic polymer (B) does not satisfy the relationship of formula (1). The pressure-sensitive adhesives No. 12 to 14 made of the cured products of these pressure-sensitive adhesive compositions No. 12 to 14 have a glass transition temperature of -47°C or lower and excellent low-temperature characteristics. However, the pressure-sensitive adhesive sheets having a pressure-sensitive adhesive layer formed from these pressure-sensitive adhesives No. 12 to 14 have poor adhesive strength at room temperature.

[0208] The present invention includes the following embodiments. (Embodiment 1) A pressure-sensitive adhesive composition containing a (meth)acrylic polymer (A), a (meth)acrylic polymer (B), and a crosslinking agent, wherein the weight average molecular weight (MwA) of the (meth)acrylic polymer (A) is 1,000,000 to 3,000,000, and the weight average molecular weight (MwB) of the (meth)acrylic polymer (B) is 50,000 to 500,000, and the dipole-dipole force term (δ p A (J 1 / 2 / cm 3 / 2 )) of the Hansen solubility parameter of the (meth)acrylic polymer (A) and the dipole-dipole force term (δ p B (J 1 / 2 / cm 3 / 2 )) of the Hansen solubility parameter of the (meth)acrylic polymer (B) satisfy the relationships of formula (1) and formula (2). -1.00 ≦ (δ p A - δ p B) ≦ 0.05 ···(1) 5.00 ≦ (δ p A + δ p B) ≦ 6.00 ···(2)

[0209] (Embodiment 2) The pressure-sensitive adhesive composition according to Embodiment 1, wherein the mass ratio of the (meth)acrylic polymer (A) to the (meth)acrylic polymer (B) in the pressure-sensitive adhesive composition is 0.5 to 5.0 ((meth)acrylic polymer (A) / (meth)acrylic polymer (B)).

[0210] (Embodiment 3) The pressure-sensitive adhesive composition according to Embodiment 1 or 2, wherein the molecular weight distribution (Mw / Mn) of the (meth)acrylic polymer (A) and / or the (meth)acrylic polymer (B) is 3.0 or less.

[0211] (Embodiment 4) The pressure-sensitive adhesive composition according to any one of Embodiments 1 to 3, wherein the (meth)acrylic polymer (A) has a first reactive group and the crosslinking agent has a second reactive group that reacts with the first reactive group.

[0212] (Embodiment 5) The pressure-sensitive adhesive composition according to Embodiment 4, wherein the molar ratio of the first reactive group to the second reactive group in the pressure-sensitive adhesive composition is 1.0 to 30.0 (first reactive group / second reactive group).

[0213] (Embodiment 6) The pressure-sensitive adhesive composition according to Embodiment 4 or 5, wherein the amount of the first reactive group of the (meth)acrylic polymer (A) is 0.002 mmol / g to 1.0 mmol / g.

[0214] (Embodiment 7) The pressure-sensitive adhesive composition according to any one of Embodiments 4 to 6, wherein the first reactive group is a carboxy group and / or a hydroxy group.

[0215] (Embodiment 8) The pressure-sensitive adhesive composition according to any one of Embodiments 4 to 7, wherein the (meth)acrylic polymer (B) substantially does not contain a first reactive group.

[0216] (Embodiment 9) The pressure-sensitive adhesive composition according to any one of Embodiments 1 to 8, wherein the crosslinking agent is an epoxy-based crosslinking agent and / or an isocyanate-based crosslinking agent.

[0217] (Embodiment 10) The pressure-sensitive adhesive composition according to any one of Embodiments 1 to 9, which is a pressure-sensitive adhesive composition for a flexible display for bonding one flexible member and another flexible member constituting the flexible display.

[0218] (Embodiment 11) A pressure-sensitive adhesive comprising a cured product of the pressure-sensitive adhesive composition according to any one of Embodiments 1 to 10.

[0219] (Embodiment 12) The pressure-sensitive adhesive according to Embodiment 11, wherein the gel fraction of the cured product is 40% by mass to 95% by mass.

[0220] (Embodiment 13) A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer and a base material sheet disposed on at least one surface of the pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer is formed from the pressure-sensitive adhesive according to Embodiment 11 or 12.

Claims

1. Contains a (meth)acrylic polymer (A), a (meth)acrylic polymer (B), and a crosslinking agent; The (meth)acrylic polymer (A) has a weight average molecular weight (MwA) of 1,000,000 to 3,000,000; The weight average molecular weight (MwB) of the (meth)acrylic polymer (B) is 50,000 to 500,000; The dipole-dipole term (δ) of the Hansen solubility parameter in the (meth)acrylic polymer (A) p A (J 1 / 2 / cm 3 / 2 )) and the dipole-dipole term (δ) of the Hansen solubility parameter in the (meth)acrylic polymer (B). p B (J 1 / 2 / cm 3 / 2 )) satisfies the relationship of formula (1) and formula (2). -1.00≦(d) p A-d p B)≦0.05 ・・・(1) 5.00≦(d) p A+d p B)≦6.00 ・・・(2)

2. The pressure-sensitive adhesive composition according to claim 1, wherein a mass ratio of the (meth)acrylic polymer (A) to the (meth)acrylic polymer (B) in the pressure-sensitive adhesive composition ((meth)acrylic polymer (A) / (meth)acrylic polymer (B)) is 0.5 to 5.

0.

3. The pressure-sensitive adhesive composition according to claim 1 , wherein the (meth)acrylic polymer (A) and / or the (meth)acrylic polymer (B) has a molecular weight distribution (Mw / Mn) of 3.0 or less.

4. The (meth)acrylic polymer (A) has a first reactive group, The adhesive composition according to claim 1 , wherein the crosslinker has a second reactive group that reacts with the first reactive group.

5. The adhesive composition according to claim 4, wherein a molar ratio of the first reactive group to the second reactive group (first reactive group / second reactive group) in the adhesive composition is 1.0 to 30.

0.

6. The pressure-sensitive adhesive composition according to claim 4, wherein the amount of the first reactive group in the (meth)acrylic polymer (A) is 0.002 mmol / g to 1.0 mmol / g.

7. The adhesive composition according to claim 4 , wherein the first reactive group is a carboxy group and / or a hydroxy group.

8. The pressure-sensitive adhesive composition according to claim 4 , wherein the (meth)acrylic polymer (B) is substantially free of a first reactive group.

9. The pressure-sensitive adhesive composition according to claim 1 or 4, wherein the crosslinking agent is an epoxy-based crosslinking agent and / or an isocyanate-based crosslinking agent.

10. The adhesive composition according to claim 1 or 4, which is an adhesive composition for a flexible display, for bonding one flexible member and another flexible member constituting a flexible display.

11. An adhesive material comprising a cured product of the adhesive composition according to claim 1 or 4.

12. The adhesive material according to claim 11, wherein the gel fraction of the cured product is 40% by mass to 95% by mass.

13. The adhesive layer has a base sheet disposed on at least one surface of the adhesive layer, An adhesive sheet, wherein the adhesive layer is formed from the adhesive material according to claim 11.

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