Adhesive composition for optical member protective film and optical member protective film

Abstract

The present invention provides an adhesive composition for an optical component protective film and an optical component protective film. The adhesive composition for an optical component protective film comprises: a (meth)acrylic polymer (A) having at least one of a hydroxyl group and a carboxyl group and having a weight-average molecular weight of more than 200,000 and less than 2,000,000; a (meth)acrylic polymer (B) having at least one of a hydroxyl group and a carboxyl group, a glass transition temperature of 0°C to 45°C, and a weight-average molecular weight of 6,000 to 150,000; a (meth)acrylic polymer (C) having a glass transition temperature of -30°C or less and a weight-average molecular weight of 6,000 to 150,000; and an isocyanate crosslinking agent (D). The content of the (meth)acrylic polymer (B) is 7 to 70 parts by mass relative to 100 parts by mass of the (meth)acrylic polymer (A), and the content of the (meth)acrylic polymer (C) is 0.5 to 5 parts by mass relative to 100 parts by mass of the (meth)acrylic polymer (A).

Description

Technical Field

[0001] The present invention relates to a pressure-sensitive adhesive composition for an optical member protective film and an optical member protective film. Background Art

[0002] Protective films having an adhesive layer are widely used to protect the surfaces of various articles, and are particularly commonly used for various optical components, such as polarizing plates.

[0003] For example, Japanese Patent Application Laid-Open No. 2005-146151 discloses a surface protection sheet formed by coating a support with a pressure-sensitive adhesive, wherein the pressure-sensitive adhesive is formed by cross-linking a cross-linkable composition so as to have a gel fraction of 80% or more, wherein the cross-linkable composition comprises (A) a (meth)acrylic polymer having a glass transition temperature of -40°C or lower, obtained by copolymerizing at least an alkyl (meth)acrylate and a monomer containing a functional group; (B) a (meth)acrylic polymer having a glass transition temperature of 80°C or higher, containing an alkyl (meth)acrylate as a main component; and (C) a cross-linking agent, wherein 5 to 20 parts by weight of (B) are added to 100 parts by weight of (A).

[0004] In addition, Japanese Patent Application Publication No. 2013-216769 discloses a surface protection sheet in which an adhesive layer is formed on at least one side of a support, wherein the adhesive layer is composed of an adhesive composition containing 100 parts by mass of a polymer (A) having a glass transition temperature of less than 0°C, 0.05 to 3 parts by mass of a (meth)acrylic polymer (B) having a weight-average molecular weight of 1,000 to less than 50,000 and a glass transition temperature of 30 to 300°C, and an organopolysiloxane compound (C) having a specific polyoxyalkylene chain. Summary of the Invention

[0005] The adhesive composition used in the protective film used in the optical component (hereinafter also referred to as "adhesive composition for protective film for optical component") is required to be able to form the following adhesive layer: after the protective film is affixed to the surface of the optical component, it is not easy to cause undesirable conditions such as peeling or deviation from the optical component during the period when protection is required, and it can be efficiently peeled from the optical component at the stage when protection is not required.

[0006] Here, an adhesive layer that is less likely to experience undesirable conditions such as peeling or deviation from an optical component can be evaluated by measuring the adhesive strength when the protective film is peeled off from the optical component at a low speed (i.e., 0.3 m / min) (so-called low-speed peel strength). Alternatively, an adhesive layer that can be efficiently peeled off from an optical component can be evaluated by measuring the adhesive strength when the protective film is peeled off from the optical component at a high speed (i.e., 30 m / min) (so-called high-speed peel strength).

[0007] However, when the protective film is peeled off from the optical component, a phenomenon called zipping (hereinafter also referred to as "tearing phenomenon") sometimes occurs in which the protective film is not peeled off smoothly and is peeled off with a clicking sound. If the tearing phenomenon occurs, a rib-like defect (so-called tear line) can be confirmed on the surface of the optical component after peeling off the protective film. Therefore, it is required for the adhesive composition for the optical component protective film to form an adhesive layer that can suppress the tearing phenomenon. In particular, since it is assumed that the optical component with the protective film is to be kept for a long time, it is preferred that the adhesive composition for the optical component protective film can form an adhesive layer that can suppress the tearing phenomenon even when it is attached to the optical component for a long time.

[0008] However, if one wishes to control the low-speed peel force and high-speed peel force of the adhesive layer of a protective film, it is difficult to adjust the balance between the low-speed peel force and the high-speed peel force because both exhibit the same behavior. In recent years, in particular, with the rise of flexible displays, the chances of attaching protective films to curved surfaces have increased. If a protective film is attached to a curved surface, it is more likely to peel off or deviate from the optical component than when attached to a flat surface. Therefore, there is a tendency for the adhesive layer of a protective film to require a higher low-speed peel force than before, making it more difficult to adjust the balance between the low-speed peel force and the high-speed peel force.

[0009] In addition, in recent years, from the perspective of further improving workability, there has been a trend to increase the speed at which the protective film is peeled off from the optical component. In addition, as the optical component becomes thinner, there is a tendency for the surface defects of the optical component to be more easily caused by the tearing phenomenon when the protective film is peeled off. It is believed that the tearing phenomenon is caused by the strength of the adhesive layer. Generally speaking, after being attached to the adherend, the adhesive strength of the adhesive layer tends to increase over time. Therefore, if the protective film is attached to the optical component for a long period of time, such as 6 months, the tearing phenomenon is likely to occur. In addition, the adhesive strength of the adhesive layer tends to increase as the peeling speed increases. Therefore, the tearing phenomenon is also likely to occur when the protective film is peeled off from the optical component at high speed.

[0010] Therefore, it is difficult to realize an adhesive composition for an optical member protective film that can form an adhesive layer having a good balance between low-speed peel strength and high-speed peel strength and that is less likely to tear even when peeled from an optical member at high speed after being adhered to the optical member for a long time.

[0011] Regarding the above-mentioned point, Japanese Patent Application Laid-Open Nos. 2005-146151 and 2013-216769 do not mention anything about suppressing the tearing phenomenon when the optical material is peeled off from the optical member at high speed after being attached to the optical member for a long time.

[0012] The problem to be solved by the present invention is to provide an adhesive composition for an optical component protective film and an optical component protective film that can form an adhesive layer with a good balance between low-speed peeling force and high-speed peeling force and is not easily torn even when peeled from the adherend at high speed after being adhered to the adherend for a long time.

[0013] Specific methods for solving the problem include the following.

[0014] <1> An adhesive composition for an optical member protective film, comprising:

[0015] A (meth)acrylic polymer (A) having at least one of a hydroxyl group and a carboxyl group and having a weight average molecular weight of more than 200,000 and not more than 2,000,000,

[0016] a (meth)acrylic polymer (B) having at least one of a hydroxyl group and a carboxyl group, a glass transition temperature in the range of 0° C. to 45° C., and a weight average molecular weight in the range of 6,000 to 150,000,

[0017] a (meth)acrylic polymer (C) having a glass transition temperature of -30°C or lower and a weight average molecular weight of 6,000 or more and 150,000 or less, and

[0018] Isocyanate crosslinking agent (D);

[0019] The content of the (meth)acrylic polymer (B) is in the range of 7 parts by mass or more and 70 parts by mass or less relative to 100 parts by mass of the (meth)acrylic polymer (A).

[0020] The content of the (meth)acrylic polymer (C) is in the range of 0.5 parts by mass or more and 5 parts by mass or less relative to 100 parts by mass of the (meth)acrylic polymer (A).

[0021] <2> The adhesive composition for an optical member protective film according to <1>, wherein the (meth)acrylic polymer (A) has a hydroxyl group and has a hydroxyl value in the range of 0.3 mgKOH / g to 40 mgKOH / g.

[0022] <3> The adhesive composition for an optical member protective film according to <1> or <2>, wherein the (meth)acrylic polymer (A) has a carboxyl group and has an acid value within a range of 0.7 mgKOH / g to 24 mgKOH / g.

[0023] <4> The adhesive composition for an optical member protective film according to any one of <1> to <3>, wherein the (meth)acrylic polymer (B) has a hydroxyl group and has a hydroxyl value within a range of 0.3 mgKOH / g to 40 mgKOH / g.

[0024] <5> The adhesive composition for an optical member protective film according to any one of <1> to <4>, wherein the (meth)acrylic polymer (B) has a carboxyl group and has an acid value within a range of 0.7 mgKOH / g to 24 mgKOH / g.

[0025] <6> The pressure-sensitive adhesive composition for an optical member protective film according to any one of <1> to <5>, wherein the (meth)acrylic polymer (C) has a hydroxyl value of 40 mgKOH / g or less.

[0026] <7> The pressure-sensitive adhesive composition for an optical member protective film according to any one of <1> to <6>, wherein the weight average molecular weight of the (meth)acrylic polymer (C) is smaller than the weight average molecular weight of the (meth)acrylic polymer (B).

[0027] <8> The adhesive composition for an optical member protective film according to any one of <1> to <7>, further comprising an antistatic agent.

[0028] <9> The adhesive composition for an optical member protective film according to any one of <1> to <8>, further comprising a polyether-modified silicone compound.

[0029] <10> An optical member protective film comprising a substrate and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer is provided on the substrate and is formed from the pressure-sensitive adhesive composition for an optical member protective film according to any one of <1> to <9>.

[0030] According to the present invention, a pressure-sensitive adhesive composition for an optical member protective film and an optical member protective film are provided, which can form a pressure-sensitive adhesive layer having a good balance between low-speed peel strength and high-speed peel strength and which is less likely to tear even when peeled from an adherend at high speed after being adhered to the adherend for a long time. DETAILED DESCRIPTION

[0031] Hereinafter, specific embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be implemented by adding appropriate modifications within the scope of the purpose of the present invention.

[0032] In this specification, the numerical range expressed using "to" means a range including the numerical values described before and after "to" as the minimum value and the maximum value, respectively.

[0033] In the numerical ranges described in this specification, the upper limit or lower limit described in a certain numerical range may be replaced by the upper limit or lower limit of another numerical range described in another stage. In addition, in the numerical ranges described in this specification, the upper limit or lower limit described in a certain numerical range may also be replaced by the value shown in the Examples.

[0034] In this specification, a combination of two or more preferred embodiments is a more preferred embodiment.

[0035] In this specification, when there are a plurality of substances corresponding to each component, the amount of each component means the total amount of the plurality of substances unless otherwise specified.

[0036] In this specification, a "(meth)acrylic polymer" refers to a polymer in which the content of constitutional units derived from a monomer having a (meth)acryloyl group is 50% by mass or more of all constitutional units (ie, all constitutional units of the (meth)acrylic polymer).

[0037] In this specification, a "(meth)acrylic monomer" refers to a monomer having a (meth)acryloyl group.

[0038] In this specification, “(meth)acrylic acid” is a term including both “acrylic acid” and “methacrylic acid”, “(meth)acrylate” is a term including both “acrylate” and “methacrylate”, and “(meth)acryloyl” is a term including both “acryloyl” and “methacryloyl”.

[0039] In this specification, "n-" represents normal, "i-" represents iso, "s-" represents secondary, and "t-" represents tertiary.

[0040] In this specification, the "adhesive composition" refers to a liquid or paste-like substance before completion of the cross-linking reaction.

[0041] In this specification, the "adhesive layer" refers to a film composed of a substance after the cross-linking reaction of the adhesive composition is completed.

[0042] In this specification, "adherend" refers to an optical member.

[0043] In this specification, "low-speed peel strength" refers to the adhesive strength measured when a protective film attached to an adherend is peeled 180° from the adherend along the longitudinal direction of the protective film at a low speed (i.e., 0.3 m / min). The detailed measurement method is described in the Examples below.

[0044] In this specification, "appropriate low-speed peeling strength" refers to an adhesive strength strong enough to prevent problems such as peeling or deviation from an adherend from occurring.

[0045] In this specification, "high-speed peel strength" refers to the adhesive strength measured when a protective film attached to an adherend is peeled 180° from the adherend along the longitudinal direction of the protective film at a high speed (i.e., 30 m / min). The detailed measurement method is described in the Examples below.

[0046] In this specification, "appropriate high-speed peeling force" refers to an adhesive force having a strength that allows efficient peeling from an adherend.

[0047] In this specification, a "PSA layer having a good balance between low-speed peeling force and high-speed peeling force" means a PSA layer having an adhesive force strong enough to prevent peeling or deviation from an adherend and to enable efficient peeling from the adherend.

[0048] [Adhesive composition for optical member protective film]

[0049] The adhesive composition for an optical member protective film of the present invention (hereinafter also referred to as the "adhesive composition") comprises: a (meth)acrylic polymer (A) having at least one of a hydroxyl group and a carboxyl group and having a weight average molecular weight of more than 200,000 and less than 2,000,000 [hereinafter also referred to as the "specific (meth)acrylic polymer (A)"], a (meth)acrylic polymer (B) having at least one of a hydroxyl group and a carboxyl group, having a glass transition temperature of 0°C to 45°C and having a weight average molecular weight of 6,000 to 150,000 [hereinafter also referred to as the "specific (meth)acrylic polymer (B)"], a glass a (meth)acrylic polymer (C) [hereinafter also referred to as a specific (meth)acrylic polymer (C)] having a chemical transition temperature of -30°C or lower and a weight average molecular weight of 6,000 to 150,000, and an isocyanate crosslinking agent (D); wherein the content of the (meth)acrylic polymer (B) is in the range of 7 parts by mass to 70 parts by mass relative to 100 parts by mass of the (meth)acrylic polymer (A), and the content of the (meth)acrylic polymer (C) is in the range of 0.5 parts by mass to 5 parts by mass relative to 100 parts by mass of the (meth)acrylic polymer (A).

[0050] The PSA composition of the present invention can form a PSA layer having a good balance between low-speed peel strength and high-speed peel strength and being less susceptible to tearing even when peeled from an adherend at high speed after being attached to the adherend for a long time.

[0051] The reason why the adhesive composition of the present invention can exhibit such effects is not yet clear, but the present inventors speculate as follows. However, the following speculation is not intended to limit the interpretation of the adhesive composition of the present invention, but is provided as an example.

[0052] The adhesive composition of the present invention comprises: a specific (meth)acrylic polymer (A) having at least one of a hydroxyl group and a carboxyl group and having a high weight-average molecular weight; a specific (meth)acrylic polymer (B) having at least one of a hydroxyl group and a carboxyl group, having a high glass transition temperature and a low weight-average molecular weight; a specific (meth)acrylic polymer (C) having a low glass transition temperature and a low weight-average molecular weight; and an isocyanate crosslinking agent (D). The content of the specific (meth)acrylic polymer (B) is less than that of the specific (meth)acrylic polymer (A), and the content of the specific (meth)acrylic polymer (C) is less than that of the specific (meth)acrylic polymer (B).

[0053] Since the adhesive composition of the present invention has the above-mentioned structure, it is believed that in the adhesive layer formed by the adhesive composition of the present invention, the specific (meth) acrylic polymer (B) is moderately localized near the surface (so-called interface with the adherend) and reacts with the isocyanate crosslinking agent (D) to form a crosslinked structure. It is believed that the glass transition temperature of the specific (meth) acrylic polymer (B) is high and the crosslinked structure formed is relatively hard. Therefore, it is believed that a relatively hard part is moderately present near the surface of the adhesive layer. In addition, it is believed that in the adhesive layer formed by the adhesive composition of the present invention, the specific (meth) acrylic polymer (C) is moderately localized near the surface (so-called interface with the adherend). The glass transition temperature of the specific (meth) acrylic polymer (C) is low, so it is believed that a relatively soft part is moderately present near the surface of the adhesive layer.

[0054] When such an adhesive layer is attached to an adherend, the relatively hard portion exists appropriately near the interface between the adhesive layer and the adherend, which prevents excessive wetting of the adherend by the adhesive layer and allows the adhesive layer to exhibit appropriate high-speed peel strength. Therefore, it is speculated that the adhesive composition of the present invention can form an adhesive layer with a good balance between low-speed peel strength and high-speed peel strength.

[0055] On the other hand, if the adhesive layer is not moistening enough to adherend, then after being pasted on adherend for a long time, from the situation of adherend high speed peeling, easily tearing phenomenon occurs.In contrast, the adhesive layer formed by adhesive composition of the present invention is owing to the relatively soft part that is moderately present near the interface with adherend, so thinks to adherend moderately moistening.Therefore, think that can suppress the tearing phenomenon that is caused by the adhesive layer wetting not moistening enough to adherend.Therefore, infer: even can form the adhesive layer that is not easy to tear phenomenon after being pasted on adherend for a long time, from the situation of adherend high speed peeling, also can form according to adhesive composition of the present invention.

[0056] Specifically, in the adhesive layer formed from the adhesive composition of the present invention, the specific (meth)acrylic polymer (B) and the specific (meth)acrylic polymer (C) are appropriately localized near the interface with the adherend, forming relatively hard and relatively soft areas, thereby appropriately adjusting the wetting of the adhesive layer to the adherend. Therefore, it is speculated that the adhesive layer formed from the adhesive composition of the present invention exhibits a good balance between low-speed and high-speed peel strengths, and is less likely to tear even when peeled from the adherend at high speed after being adhered to the adherend for a long time.

[0057] Hereinafter, in this specification, the specific (meth)acrylic polymer (A), the specific (meth)acrylic polymer (B), and the specific (meth)acrylic polymer (C) are collectively referred to as "specific (meth)acrylic polymers."

[0058] [Specific (meth)acrylic polymer (A)]

[0059] The pressure-sensitive adhesive composition of the present invention comprises a (meth)acrylic polymer (A) having at least one of a hydroxyl group and a carboxyl group and having a weight average molecular weight of more than 200,000 and not more than 2,000,000 [ie, a specific (meth)acrylic polymer (A)].

[0060] The pressure-sensitive adhesive composition of the present invention may contain only one specific (meth)acrylic polymer (A), or may contain two or more specific (meth)acrylic polymers (A).

[0061] The specific (meth)acrylic polymer (A) may be a homopolymer or a copolymer. Furthermore, the specific (meth)acrylic polymer (A) may be a polymer having only hydroxyl groups among hydroxyl groups and carboxyl groups, a polymer having only carboxyl groups, or a polymer having both hydroxyl groups and carboxyl groups.

[0062] The specific (meth)acrylic polymer (A) may be, for example, a homopolymer of a (meth)acrylic monomer having at least one of a hydroxyl group and a carboxyl group, a homopolymer obtained by introducing at least one of a hydroxyl group and a carboxyl group into a homopolymer of a (meth)acrylic monomer having neither a hydroxyl group nor a carboxyl group by substitution, a copolymer of a (meth)acrylic monomer having at least one of a hydroxyl group and a carboxyl group, a copolymer of a (meth)acrylic monomer having at least one of a hydroxyl group and a carboxyl group and a monomer other than a (meth)acrylic monomer having neither a hydroxyl group nor a carboxyl group, or a copolymer of a monomer other than a (meth)acrylic monomer having at least one of a hydroxyl group and a carboxyl group and a (meth)acrylic monomer having neither a hydroxyl group nor a carboxyl group.

[0063] A preferred embodiment of the specific (meth)acrylic polymer (A) is an embodiment in which the specific (meth)acrylic polymer (A) contains at least one of a structural unit derived from a monomer having a hydroxyl group and a structural unit derived from a monomer having a carboxyl group, which will be described later, and thus has at least one of a hydroxyl group and a carboxyl group.

[0064] <Constitutional Units Derived from Monomers Having a Hydroxyl Group>

[0065] The specific (meth)acrylic polymer (A) preferably includes a structural unit derived from a monomer having a hydroxyl group.

[0066] In the present specification, the "constituent unit derived from a monomer having a hydroxyl group" refers to a constituent unit formed by addition polymerization of a monomer having a hydroxyl group.

[0067] The type of the monomer having a hydroxyl group is not particularly limited.

[0068] Specific examples of the monomer having a hydroxyl group include hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, 3-methyl-3-hydroxybutyl (meth)acrylate, 1,1-dimethyl-3-hydroxybutyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3-hydroxyhexyl (meth)acrylate, N-hydroxyethyl (meth)acrylamide, glycerol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, and poly(ethylene glycol-propylene glycol) mono(meth)acrylate.

[0069] The monomer having a hydroxyl group is preferably a hydroxyalkyl (meth)acrylate, more preferably a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 1 to 5 carbon atoms, further preferably a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms, and particularly preferably 4-hydroxybutyl acrylate.

[0070] When the specific (meth)acrylic polymer (A) contains a structural unit derived from a monomer having a hydroxyl group, it may contain only one type of structural unit derived from a monomer having a hydroxyl group, or may contain two or more types.

[0071] When the specific (meth)acrylic polymer (A) contains a constituent unit derived from a monomer having a hydroxyl group, the content of the constituent unit derived from a monomer having a hydroxyl group in the specific (meth)acrylic polymer (A) is not particularly limited, but is, for example, preferably in the range of 0.1% by mass to 10% by mass, more preferably in the range of 0.5% by mass to 8% by mass, and even more preferably in the range of 1% by mass to 5% by mass, relative to all the constituent units of the specific (meth)acrylic polymer (A).

[0072] The content of the structural units derived from the monomer having a hydroxyl group in the specific (meth)acrylic polymer (A) is 0.1% by mass or more relative to all the structural units of the specific (meth)acrylic polymer (A). This means that the specific (meth)acrylic polymer (A) actively contains the structural units derived from the monomer having a hydroxyl group.

[0073] When the content of the structural units derived from the monomer having a hydroxyl group in the specific (meth)acrylic polymer (A) is 10% by mass or less relative to the total structural units of the specific (meth)acrylic polymer (A), a PSA layer tends to be less susceptible to tearing even when peeled from an adherend at high speed after being adhered to the adherend for a long period of time.

[0074] <Constitutional Unit Derived from a Monomer Having a Carboxyl Group>

[0075] The specific (meth)acrylic polymer (A) preferably includes a structural unit derived from a monomer having a carboxyl group.

[0076] In the present specification, the "constituent unit derived from a monomer having a carboxyl group" refers to a constituent unit formed by addition polymerization of a monomer having a carboxyl group.

[0077] The type of the monomer having a carboxyl group is not particularly limited.

[0078] Specific examples of the monomer having a carboxyl group include acrylic acid, methacrylic acid, crotonic acid, maleic anhydride, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, ω-carboxy-polycaprolactone mono(meth)acrylate [e.g., ω-carboxy-polycaprolactone (n≈2) monoacrylate], and succinate [e.g., 2-acryloyloxyethyl succinate].

[0079] As the monomer having a carboxyl group, acrylic acid is preferred.

[0080] When the specific (meth)acrylic polymer (A) contains a structural unit derived from a monomer having a carboxyl group, it may contain only one type of structural unit derived from a monomer having a carboxyl group, or may contain two or more types.

[0081] When the specific (meth)acrylic polymer (A) contains a structural unit derived from a monomer having a carboxyl group, the content of the structural unit derived from a monomer having a carboxyl group in the specific (meth)acrylic polymer (A) is not particularly limited, but is, for example, preferably in the range of 0.1% by mass to 5% by mass, more preferably in the range of 0.3% by mass to 3% by mass, and even more preferably in the range of 0.5% by mass to 1.5% by mass, relative to all the structural units of the specific (meth)acrylic polymer (A).

[0082] The content of the structural units derived from the monomer having a carboxyl group in the specific (meth)acrylic polymer (A) is 0.1% by mass or more relative to all the structural units of the specific (meth)acrylic polymer (A). This means that the specific (meth)acrylic polymer (A) actively contains the structural units derived from the monomer having a carboxyl group.

[0083] When the content of the structural units derived from the monomer having a carboxyl group in the specific (meth)acrylic polymer (A) is 5% by mass or less relative to the total structural units of the specific (meth)acrylic polymer (A), a PSA layer tends to be less susceptible to tearing even when peeled from an adherend at high speed after being adhered to the adherend for a long period of time.

[0084] <Constitutional Units Derived from Alkyl (Meth)acrylate Monomers>

[0085] The specific (meth)acrylic polymer (A) preferably includes a structural unit derived from an alkyl (meth)acrylate monomer.

[0086] The structural unit derived from the alkyl (meth)acrylate monomer contributes to the adjustment of adhesive strength.

[0087] In the present specification, the "constituent unit derived from an alkyl (meth)acrylate monomer" refers to a constituent unit formed by addition polymerization of an alkyl (meth)acrylate monomer.

[0088] In addition, the "alkyl (meth)acrylate monomer" in this specification does not include an alkyl (meth)acrylate monomer having at least one of a hydroxyl group and a carboxyl group.

[0089] The type of the alkyl (meth)acrylate monomer is not particularly limited.

[0090] As the (meth)acrylic acid alkyl ester monomer, an unsubstituted (meth)acrylic acid alkyl ester monomer is preferable.

[0091] The alkyl group of the (meth)acrylate monomer may be linear, branched, or cyclic.

[0092] From the viewpoint of adhesive strength, the number of carbon atoms in the alkyl group is, for example, preferably in the range of 1 or more and 18 or less, more preferably in the range of 1 or more and 12 or less, and even more preferably in the range of 1 or more and 8 or less.

[0093] In particular, when the number of carbon atoms in the alkyl group is within the range of 1 to 8, the formed pressure-sensitive adhesive layer tends to wet the adherend appropriately and exhibit more appropriate low-speed peeling strength.

[0094] Specific examples of the alkyl (meth)acrylate monomer include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate.

[0095] As the (meth)acrylic acid alkyl ester monomer, at least one selected from n-butyl acrylate and 2-ethylhexyl acrylate is preferred.

[0096] When the specific (meth)acrylic polymer (A) contains a structural unit derived from an alkyl (meth)acrylate monomer, it may contain only one type of structural unit derived from an alkyl (meth)acrylate monomer, or may contain two or more types.

[0097] When the specific (meth)acrylic polymer (A) contains a constituent unit derived from an alkyl (meth)acrylate monomer, the content of the constituent unit derived from an alkyl (meth)acrylate monomer in the specific (meth)acrylic polymer (A) is not particularly limited, but is, for example, preferably 50% by mass or more, more preferably in the range of 50% by mass or more and 99% by mass or less, further preferably in the range of 60% by mass or more and 99% by mass or less, and particularly preferably in the range of 70% by mass or more and 99% by mass or less, relative to all the constituent units of the specific (meth)acrylic polymer (A).

[0098] Here, the content of the structural units derived from the alkyl (meth)acrylate monomer in the specific (meth)acrylic polymer (A) is 50% by mass or more relative to all the structural units of the specific (meth)acrylic polymer (A). This means that the structural units derived from the alkyl (meth)acrylate monomer are contained as the main components of the structural units constituting the specific (meth)acrylic polymer (A).

[0099] <Other components>

[0100] The specific (meth)acrylic polymer (A) may contain structural units other than the above-mentioned structural units (so-called other structural units) within a range in which the effects of the present invention are exhibited.

[0101] Examples of monomers constituting other structural units include (meth)acrylates having an aromatic ring, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; alkoxyalkyl (meth)acrylates, such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; monovinyl aromatics, such as styrene, α-methylstyrene, tert-butylstyrene, p-chlorostyrene, chloromethylstyrene, and vinyltoluene; vinyl cyanides, such as acrylonitrile and methacrylonitrile; and vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate. Various derivatives of these monomers are also included.

[0102] When the specific (meth)acrylic polymer (A) contains other structural units, it may contain only one type of other structural units, or may contain two or more types.

[0103] When the specific (meth)acrylic polymer (A) contains other structural units, the content of the other structural units in the specific (meth)acrylic polymer (A) is not particularly limited and can be appropriately set depending on the intended purpose.

[0104] <<Glass Transition Temperature of Specific (Meth)Acrylic Polymer (A)>>

[0105] The glass transition temperature (also referred to as "Tg") of the specific (meth)acrylic polymer (A) is not particularly limited, but is, for example, preferably -40°C or lower, more preferably -50°C or lower, and further preferably -60°C or lower.

[0106] When the glass transition temperature of the specific (meth)acrylic polymer (A) is -40°C or lower, a PSA layer having a better balance between low-speed peel strength and high-speed peel strength tends to be formed. Furthermore, a PSA layer that is less likely to tear when peeled from an adherend at high speed after being adhered to the adherend for a long period of time tends to be formed.

[0107] The lower limit of the glass transition temperature of the specific (meth)acrylic polymer (A) is not particularly limited, but is preferably -70°C or higher, for example.

[0108] The glass transition temperature of the specific (meth)acrylic polymer (A) is a value obtained by converting the absolute temperature (unit: K; the same shall apply hereinafter) obtained by calculation using the following formula 1 into Celsius temperature (unit: ° C.; the same shall apply hereinafter).

[0109] 1 / Tg=m1 / Tg1+m2 / Tg2+···+m(k-1) / Tg(k-1)+mk / Tgk (Formula 1)

[0110] In Formula 1, Tg1, Tg2, ..., Tg(k-1), and Tgk each represent the glass transition temperature expressed as the absolute temperature when each monomer constituting the specific (meth)acrylic polymer (A) is converted into a homopolymer. m1, m2, ..., m(k-1), and mk each represent the mole fraction of each monomer constituting the specific (meth)acrylic polymer (A), where m1 + m2 + ... + m(k-1) + mk = 1.

[0111] It should be noted that the absolute temperature can be converted into the Celsius temperature by subtracting 273 from the absolute temperature, and the Celsius temperature can be converted into the absolute temperature by adding 273 to the Celsius temperature.

[0112] In this specification, the “glass transition temperature expressed by the absolute temperature when forming a homopolymer” means the glass transition temperature expressed by the absolute temperature of a homopolymer produced by polymerizing the monomer alone.

[0113] The glass transition temperature of the homopolymer was measured using a differential scanning calorimeter (DSC) [Model: EXSTAR6000, Seiko Instruments Inc.] under the conditions of a 10 mg sample and a heating rate of 10°C / min in a nitrogen stream. The inflection point of the obtained DSC curve was defined as the glass transition temperature of the homopolymer.

[0114] The glass transition temperatures (in degrees Celsius) of representative monomers as homopolymers are: -76°C for 2-ethylhexyl acrylate (2EHA), -10°C for 2-ethylhexyl methacrylate (2EHMA), -57°C for n-butyl acrylate (n-BA), 21°C for n-butyl methacrylate (n-BMA), 41°C for tert-butyl acrylate (t-BA), 107°C for tert-butyl methacrylate (t-BMA), 48°C for isobutyl methacrylate (i-BMA), 5°C for methyl acrylate (MA), 103°C for methyl methacrylate (MMA), 155°C for isobornyl methacrylate (IBXMA), and 157°C for isobornyl methacrylate (IBXMA). Isobornyl acrylate (IBXA) is 96°C, ethyl acrylate (EA) is -27°C, methacrylic acid (MAA) is 185°C, 4-hydroxybutyl acrylate (4HBA) is -39°C, 2-hydroxyethyl acrylate (2HEA) is -15°C, 2-hydroxyethyl methacrylate (2HEMA) is 55°C, 2-hydroxypropyl acrylate (2HPA) is -7°C, acrylic acid (AA) is 163°C, isooctyl acrylate (i-OA) is -75°C, dimethylaminoethyl methacrylate (DM) is 18°C, ω-carboxy-polycaprolactone (n≈2) monoacrylate is -30°C, and 2-acryloyloxyethyl succinate is -40°C.

[0115] The glass transition temperature of the specific (meth)acrylic polymer (A) can be appropriately adjusted by, for example, using two or more monomers having different glass transition temperatures when forming a homopolymer.

[0116] <<Weight Average Molecular Weight of Specific (Meth)Acrylic Polymer (A)>>

[0117] The weight average molecular weight (also referred to as "Mw") of the specific (meth)acrylic polymer (A) is in the range of more than 200,000 and 2,000,000 or less, preferably in the range of more than 200,000 and 1,800,000 or less, more preferably in the range of more than 200,000 and 1,600,000 or less, further preferably in the range of more than 200,000 and 1,400,000 or less, and particularly preferably in the range of more than 200,000 and 1,200,000 or less.

[0118] When the weight average molecular weight of the specific (meth)acrylic polymer (A) exceeds 200,000, the formed pressure-sensitive adhesive layer tends to easily obtain cohesive strength.

[0119] When the weight average molecular weight of the specific (meth)acrylic polymer (A) is 2,000,000 or less, the coating properties of the pressure-sensitive adhesive composition tend to be improved.

[0120] The weight average molecular weight of the specific (meth)acrylic polymer (A) is a value measured by the following method. Specifically, it is measured according to the following (1) to (3).

[0121] (1) A solution of a specific (meth)acrylic polymer (A) is applied to release paper and dried at 100° C. for 1 minute to obtain a film-like specific (meth)acrylic polymer (A).

[0122] (2) Using the film-like specific (meth)acrylic polymer (A) obtained in (1) above and tetrahydrofuran, a sample solution having a solid content concentration of 0.2% by mass is obtained. It should be noted that the "solid content concentration" herein refers to the mass ratio of the specific (meth)acrylic polymer (A) in the sample solution.

[0123] (3) The weight average molecular weight of the specific (meth)acrylic polymer (A) was measured as a standard polystyrene equivalent value under the following conditions using gel permeation chromatography (GPC).

[0124] ~Conditions~

[0125] Measuring device: High-speed GPC [Model: HLC-8220GPC, manufactured by Tosoh Corporation]

[0126] Detector: Differential refractometer (RI) [Built-in HLC-8220, manufactured by Tosoh Corporation]

[0127] Column: 4 TSK-GEL GMH XL [Made by Tosoh Corporation]

[0128] Column temperature: 40°C

[0129] Eluent: tetrahydrofuran

[0130] Injection volume of sample solution: 100 μL

[0131] Flow rate: 0.8 mL / min

[0132] The weight average molecular weight of the specific (meth)acrylic polymer (A) can be adjusted to a desired value by adjusting the polymerization temperature, polymerization time, the amount of the organic solvent used, the type of the polymerization initiator, the amount of the polymerization initiator used, and the like.

[0133] <<Hydroxy Value of Specific (Meth)Acrylic Polymer (A)>>

[0134] When the specific (meth)acrylic polymer (A) has a hydroxyl group, the hydroxyl value of the specific (meth)acrylic polymer (A) is not particularly limited, but is, for example, preferably in the range of 0.3 mgKOH / g to 40 mgKOH / g, more preferably in the range of 0.5 mgKOH / g to 30 mgKOH / g, and even more preferably in the range of 1 mgKOH / g to 20 mgKOH / g.

[0135] When the hydroxyl value of the specific (meth)acrylic polymer (A) is 0.3 mgKOH / g or more, a pressure-sensitive adhesive layer having a better balance between low-speed peel strength and high-speed peel strength tends to be formed.

[0136] When the hydroxyl value of the specific (meth)acrylic polymer (A) is 40 mgKOH / g or less, a pressure-sensitive adhesive layer tends to be less susceptible to tearing even when peeled from an adherend at high speed after being adhered to the adherend for a long period of time.

[0137] The hydroxyl value of the specific (meth)acrylic polymer (A) is a value determined by the following calculation formula: In the following calculation formula, 56.1 is the molecular weight of KOH.

[0138] Hydroxyl value (mgKOH / g) = {(A1 / 100) ÷ A2} × 56.1 × 1000 × A3

[0139] A1: Ratio of monomers having a hydroxyl group in all monomers used to produce the specific (meth)acrylic polymer (A) (unit: mass %)

[0140] A2: Molecular weight of the monomer having a hydroxyl group used to produce the specific (meth)acrylic polymer (A)

[0141] A3: The number of hydroxyl groups contained in one molecule of the monomer having hydroxyl groups

[0142] When two or more monomers having a hydroxyl group are used to produce the specific (meth)acrylic polymer (A), the hydroxyl value is determined for each monomer according to the above calculation formula, and the obtained values are totaled to determine the hydroxyl value.

[0143] <<Acid Value of Specific (Meth)Acrylic Polymer (A)>>

[0144] When the specific (meth)acrylic polymer (A) has a carboxyl group, the acid value of the specific (meth)acrylic polymer (A) is not particularly limited, but is, for example, preferably in the range of 0.7 mgKOH / g to 24 mgKOH / g, more preferably in the range of 1 mgKOH / g to 20 mgKOH / g, and even more preferably in the range of 2 mgKOH / g to 10 mgKOH / g.

[0145] When the acid value of the specific (meth)acrylic polymer (A) is 0.7 mgKOH / g or more, a pressure-sensitive adhesive layer having a better balance between low-speed peeling force and high-speed peeling force tends to be formed.

[0146] When the acid value of the specific (meth)acrylic polymer (A) is 24 mgKOH / g or less, a pressure-sensitive adhesive layer tends to be less susceptible to tearing even when peeled from an adherend at high speed after being adhered to the adherend for a long period of time.

[0147] The acid value of the specific (meth)acrylic polymer (A) is a value determined by the following calculation formula: In the following calculation formula, 56.1 is the molecular weight of KOH.

[0148] Acid value (mgKOH / g) = {(a1 / 100) ÷ a2} × 56.1 × 1000 × a3

[0149] a1: Ratio of the monomer having a carboxyl group in all monomers used to produce the specific (meth)acrylic polymer (A) (unit: mass %)

[0150] a2: Molecular weight of the monomer having a carboxyl group used to produce the specific (meth)acrylic polymer (A)

[0151] a3: The number of carboxyl groups contained in one molecule of the monomer having a carboxyl group

[0152] When there are two or more monomers having a carboxyl group used for producing the specific (meth)acrylic polymer (A), the acid value is determined for each monomer according to the above calculation formula, and the obtained values are totaled to determine the acid value.

[0153] <<Content of specific (meth)acrylic polymer (A)>>

[0154] The content of the specific (meth)acrylic polymer (A) in the adhesive composition of the present invention is not particularly limited, but is preferably in the range of 55% by mass or more and 92% by mass or less, more preferably in the range of 55% by mass or more and 90% by mass or less, further preferably in the range of 60% by mass or more and 90% by mass or less, and particularly preferably in the range of 60% by mass or more and 88% by mass or less, relative to the total solid content in the adhesive composition.

[0155] In this specification, “the total solid content in the adhesive composition” refers to the total mass of the adhesive composition when the adhesive composition does not contain a solvent, and refers to the mass of the residue after removing the solvent from the adhesive composition when the adhesive composition contains a solvent.

[0156] In this specification, "solvent" refers to water and organic solvents.

[0157] [Specific (meth)acrylic acid polymer (B)]

[0158] The adhesive composition of the present invention comprises a (meth)acrylic polymer (B) (specific (meth)acrylic polymer (B)) having at least one of a hydroxyl group and a carboxyl group, a glass transition temperature in the range of 0°C to 45°C, and a weight-average molecular weight in the range of 6,000 to 150,000. The content of the specific (meth)acrylic polymer (B) in the adhesive composition of the present invention is in the range of 7 to 70 parts by mass relative to 100 parts by mass of the specific (meth)acrylic polymer (A).

[0159] The pressure-sensitive adhesive composition of the present invention may contain only one specific (meth)acrylic polymer (B), or may contain two or more specific (meth)acrylic polymers (B).

[0160] The specific (meth)acrylic polymer (B) may be a homopolymer or a copolymer. Furthermore, the specific (meth)acrylic polymer (B) may be a polymer having only hydroxyl groups among hydroxyl groups and carboxyl groups, a polymer having only carboxyl groups, or a polymer having both hydroxyl groups and carboxyl groups.

[0161] The specific (meth)acrylic polymer (B) may be, for example, a homopolymer of a (meth)acrylic monomer having at least one of a hydroxyl group and a carboxyl group, a homopolymer obtained by introducing at least one of a hydroxyl group and a carboxyl group into a homopolymer of a (meth)acrylic monomer having neither a hydroxyl group nor a carboxyl group by substitution, a copolymer of a (meth)acrylic monomer having at least one of a hydroxyl group and a carboxyl group, a copolymer of a (meth)acrylic monomer having at least one of a hydroxyl group and a carboxyl group and a monomer other than a (meth)acrylic monomer having neither a hydroxyl group nor a carboxyl group, or a copolymer of a monomer other than a (meth)acrylic monomer having at least one of a hydroxyl group and a carboxyl group and a (meth)acrylic monomer having neither a hydroxyl group nor a carboxyl group.

[0162] A preferred embodiment of the specific (meth)acrylic polymer (B) is an embodiment in which the specific (meth)acrylic polymer (B) contains at least one of a structural unit derived from a monomer having a hydroxyl group and a structural unit derived from a monomer having a carboxyl group, which will be described later, and thus has at least one of a hydroxyl group and a carboxyl group.

[0163] <Constitutional Units Derived from Monomers Having a Hydroxyl Group>

[0164] The specific (meth)acrylic polymer (B) preferably includes a structural unit derived from a monomer having a hydroxyl group.

[0165] The type of the monomer having a hydroxyl group is not particularly limited.

[0166] Specific examples of the monomer having a hydroxyl group in the specific (meth)acrylic polymer (B) are the same as the specific examples of the monomer having a hydroxyl group in the specific (meth)acrylic polymer (A), and therefore description thereof is omitted here.

[0167] The monomer having a hydroxyl group is preferably a hydroxyalkyl (meth)acrylate, more preferably a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 1 to 5 carbon atoms, further preferably a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms, and particularly preferably 4-hydroxybutyl acrylate.

[0168] When the specific (meth)acrylic polymer (B) contains a structural unit derived from a monomer having a hydroxyl group, it may contain only one type of structural unit derived from a monomer having a hydroxyl group, or may contain two or more types.

[0169] When the specific (meth)acrylic polymer (B) contains a constituent unit derived from a monomer having a hydroxyl group, the content of the constituent unit derived from a monomer having a hydroxyl group in the specific (meth)acrylic polymer (B) is not particularly limited, but is, for example, preferably in the range of 0.1% by mass to 10% by mass, more preferably in the range of 0.5% by mass to 8% by mass, and even more preferably in the range of 1% by mass to 5% by mass, relative to all the constituent units of the specific (meth)acrylic polymer (B).

[0170] The content of the structural units derived from the monomer having a hydroxyl group in the specific (meth)acrylic polymer (B) is 0.1% by mass or more relative to all the structural units of the specific (meth)acrylic polymer (B). This means that the specific (meth)acrylic polymer (B) actively contains the structural units derived from the monomer having a hydroxyl group.

[0171] When the content of the structural units derived from the monomer having a hydroxyl group in the specific (meth)acrylic polymer (B) is 10% by mass or less relative to the total structural units of the specific (meth)acrylic polymer (B), a PSA layer tends to be less susceptible to tearing even when peeled from an adherend at high speed after being adhered to the adherend for a long period of time.

[0172] <Constitutional Unit Derived from a Monomer Having a Carboxyl Group>

[0173] The specific (meth)acrylic polymer (B) preferably includes a structural unit derived from a monomer having a carboxyl group.

[0174] The type of the monomer having a carboxyl group is not particularly limited.

[0175] Specific examples of the monomer having a carboxyl group in the specific (meth)acrylic polymer (B) are the same as the specific examples of the monomer having a carboxyl group in the specific (meth)acrylic polymer (A), and therefore description thereof is omitted here.

[0176] As the monomer having a carboxyl group, acrylic acid is preferred.

[0177] When the specific (meth)acrylic polymer (B) contains a structural unit derived from a monomer having a carboxyl group, it may contain only one type of structural unit derived from a monomer having a carboxyl group, or may contain two or more types.

[0178] When the specific (meth)acrylic polymer (B) contains a structural unit derived from a monomer having a carboxyl group, the content of the structural unit derived from a monomer having a carboxyl group in the specific (meth)acrylic polymer (B) is not particularly limited, but is, for example, preferably in the range of 0.1% by mass to 5% by mass, more preferably in the range of 0.3% by mass to 3% by mass, and even more preferably in the range of 0.5% by mass to 1.5% by mass, relative to all the structural units of the specific (meth)acrylic polymer (B).

[0179] The content of the structural units derived from the monomer having a carboxyl group in the specific (meth)acrylic polymer (B) is 0.1% by mass or more relative to all the structural units of the specific (meth)acrylic polymer (B). This means that the specific (meth)acrylic polymer (B) actively contains the structural units derived from the monomer having a carboxyl group.

[0180] When the content of the structural units derived from the monomer having a carboxyl group in the specific (meth)acrylic polymer (B) is 5% by mass or less relative to the total structural units of the specific (meth)acrylic polymer (B), a PSA layer tends to be less susceptible to tearing even when peeled from an adherend at high speed after being adhered to the adherend for a long period of time.

[0181] <Constitutional Units Derived from Alkyl (Meth)acrylate Monomers>

[0182] The specific (meth)acrylic polymer (B) preferably includes a structural unit derived from an alkyl (meth)acrylate monomer.

[0183] The type of the alkyl (meth)acrylate monomer is not particularly limited.

[0184] As the (meth)acrylic acid alkyl ester monomer, an unsubstituted (meth)acrylic acid alkyl ester monomer is preferable.

[0185] The alkyl group of the (meth)acrylate monomer may be linear, branched, or cyclic.

[0186] From the viewpoint of adhesive strength, the number of carbon atoms in the alkyl group is, for example, preferably in the range of 1 or more and 18 or less, more preferably in the range of 1 or more and 12 or less, and even more preferably in the range of 1 or more and 8 or less.

[0187] Specific examples of the alkyl (meth)acrylate monomer in the specific (meth)acrylic polymer (B) are the same as those of the alkyl (meth)acrylate monomer in the specific (meth)acrylic polymer (A), and therefore description thereof is omitted here.

[0188] As the (meth)acrylic acid alkyl ester monomer, at least one selected from the group consisting of methyl acrylate, n-butyl acrylate, and n-butyl methacrylate is preferred.

[0189] When the specific (meth)acrylic polymer (B) contains a structural unit derived from an alkyl (meth)acrylate monomer, it may contain only one type of structural unit derived from an alkyl (meth)acrylate monomer, or may contain two or more types.

[0190] When the specific (meth)acrylic polymer (B) contains a constituent unit derived from an alkyl (meth)acrylate monomer, the content of the constituent unit derived from an alkyl (meth)acrylate monomer in the specific (meth)acrylic polymer (B) is not particularly limited, but is, for example, preferably 50% by mass or more, more preferably in the range of 50% by mass or more and 99% by mass or less, further preferably in the range of 60% by mass or more and 99% by mass or less, and particularly preferably in the range of 70% by mass or more and 99% by mass or less, relative to all the constituent units of the specific (meth)acrylic polymer (B).

[0191] Here, the content of the structural units derived from the alkyl (meth)acrylate monomer in the specific (meth)acrylic polymer (B) is 50% by mass or more relative to all the structural units of the specific (meth)acrylic polymer (B). This means that the structural units derived from the alkyl (meth)acrylate monomer are contained as the main components of the structural units constituting the specific (meth)acrylic polymer (B).

[0192] <Other components>

[0193] The specific (meth)acrylic polymer (B) may contain structural units other than the above-mentioned structural units (so-called other structural units) within a range in which the effects of the present invention are exhibited.

[0194] Specific examples of monomers constituting other structural units in the specific (meth)acrylic polymer (B) are the same as those of monomers constituting other structural units in the specific (meth)acrylic polymer (A), and therefore description thereof is omitted here.

[0195] When the specific (meth)acrylic polymer (B) contains other structural units, it may contain only one type of other structural units, or may contain two or more types.

[0196] When the specific (meth)acrylic polymer (B) contains other structural units, the content of the other structural units in the specific (meth)acrylic polymer (B) is not particularly limited and can be appropriately set depending on the intended purpose.

[0197] <<Glass Transition Temperature of Specific (Meth)Acrylic Polymer (B)>>

[0198] The glass transition temperature of the specific (meth)acrylic polymer (B) is in the range of 0°C to 45°C, preferably 5°C to 43°C, more preferably 10°C to 40°C, and even more preferably 15°C to 35°C.

[0199] When the glass transition temperature of the specific (meth)acrylic polymer (B) is 0° C. or higher, a pressure-sensitive adhesive layer having a good balance between low-speed peeling force and high-speed peeling force tends to be formed.

[0200] When the glass transition temperature of the specific (meth)acrylic polymer (B) is 45° C. or lower, a pressure-sensitive adhesive layer that is unlikely to tear even when peeled from an adherend at high speed after being attached to the adherend for a long period of time can be formed.

[0201] The glass transition temperature of the specific (meth)acrylic polymer (B) is a value determined by the same method as the glass transition temperature of the specific (meth)acrylic polymer (A).

[0202] The glass transition temperature of the specific (meth)acrylic polymer (B) can be appropriately adjusted by, for example, using two or more monomers having different glass transition temperatures when forming a homopolymer.

[0203] <<Weight Average Molecular Weight of Specific (Meth)Acrylic Polymer (B)>>

[0204] The weight average molecular weight of the specific (meth)acrylic polymer (B) is in the range of 6,000 to 150,000, preferably 10,000 to 150,000, more preferably 15,000 to 150,000, and even more preferably 20,000 to 100,000.

[0205] When the weight average molecular weight of the specific (meth)acrylic polymer (B) is 6,000 or more, a pressure-sensitive adhesive layer having a good balance between low-speed peeling force and high-speed peeling force tends to be formed.

[0206] When the weight average molecular weight of the specific (meth)acrylic polymer (B) is 150,000 or less, a pressure-sensitive adhesive layer that is unlikely to tear even when peeled from an adherend at high speed after being adhered to the adherend for a long period of time can be formed.

[0207] The weight average molecular weight of the specific (meth)acryl-based polymer (B) is a value measured by the same method as that for the weight average molecular weight (Mw) of the specific (meth)acryl-based polymer (A).

[0208] The weight average molecular weight of the specific (meth)acrylic polymer (B) can be adjusted to a desired value by adjusting the polymerization temperature, polymerization time, the amount of the organic solvent used, the type of the polymerization initiator, the amount of the polymerization initiator used, and the like.

[0209] <<Hydroxy Value of Specific (Meth)Acrylic Polymer (B)>>

[0210] When the specific (meth)acrylic polymer (B) has a hydroxyl group, the hydroxyl value of the specific (meth)acrylic polymer (B) is not particularly limited, but is, for example, preferably in the range of 0.3 mgKOH / g to 40 mgKOH / g, more preferably in the range of 0.5 mgKOH / g to 30 mgKOH / g, and even more preferably in the range of 1 mgKOH / g to 20 mgKOH / g.

[0211] When the hydroxyl value of the specific (meth)acrylic polymer (B) is 0.3 mgKOH / g or more, a pressure-sensitive adhesive layer having a better balance between low-speed peel strength and high-speed peel strength tends to be formed.

[0212] When the hydroxyl value of the specific (meth)acrylic polymer (B) is 40 mgKOH / g or less, a pressure-sensitive adhesive layer tends to be less susceptible to tearing even when peeled from an adherend at high speed after being adhered to the adherend for a long period of time.

[0213] The hydroxyl value of the specific (meth)acryl-based polymer (B) is a value calculated by the same method as the hydroxyl value of the specific (meth)acryl-based polymer (A).

[0214] <<Acid Value of Specific (Meth)Acrylic Polymer (B)>>

[0215] When the specific (meth)acrylic polymer (B) has a carboxyl group, the acid value of the specific (meth)acrylic polymer (B) is not particularly limited, but is, for example, preferably in the range of 0.7 mgKOH / g to 24 mgKOH / g, more preferably in the range of 1 mgKOH / g to 20 mgKOH / g, and even more preferably in the range of 2 mgKOH / g to 10 mgKOH / g.

[0216] When the acid value of the specific (meth)acrylic polymer (B) is 0.7 mgKOH / g or more, a pressure-sensitive adhesive layer having a better balance between low-speed peeling force and high-speed peeling force tends to be formed.

[0217] When the acid value of the specific (meth)acrylic polymer (B) is 24 mgKOH / g or less, a PSA layer that is less likely to tear even when peeled from an adherend at high speed after being adhered to the adherend for a long period of time tends to be formed. This is presumably because the formed PSA layer does not excessively inhibit wetting of the adherend.

[0218] The acid value of the specific (meth)acryl-based polymer (B) is a value calculated by the same method as the acid value of the specific (meth)acryl-based polymer (A).

[0219] <<Content of specific (meth)acrylic polymer (B)>>

[0220] The content of the specific (meth)acrylic polymer (B) in the adhesive composition of the present invention is in the range of 7 parts by mass or more and 70 parts by mass or less, preferably in the range of 10 parts by mass or more and 60 parts by mass or less, more preferably in the range of 15 parts by mass or more and 55 parts by mass or less, and even more preferably in the range of 20 parts by mass or more and 50 parts by mass or less, relative to 100 parts by mass of the specific (meth)acrylic polymer (A).

[0221] When the content of the specific (meth)acrylic polymer (B) in the adhesive composition of the present invention is 7 parts by mass or more relative to 100 parts by mass of the specific (meth)acrylic polymer (A), a adhesive layer having a good balance between low-speed peel strength and high-speed peel strength tends to be formed.

[0222] When the content of the specific (meth)acrylic polymer (B) in the adhesive composition of the present invention is 70 parts by mass or less relative to 100 parts by mass of the specific (meth)acrylic polymer (A), a adhesive layer that is unlikely to tear even when peeled from an adherend at high speed after being adhered to the adherend for a long period of time can be formed.

[0223] [Specific (meth)acrylic acid polymer (C)]

[0224] The adhesive composition of the present invention comprises a (meth)acrylic polymer (C) (i.e., a specific (meth)acrylic polymer (C)) having a glass transition temperature of -30°C or lower and a weight-average molecular weight of 6,000 to 150,000. Furthermore, the content of the specific (meth)acrylic polymer (C) in the adhesive composition of the present invention is in the range of 0.5 to 5 parts by mass relative to 100 parts by mass of the specific (meth)acrylic polymer (A).

[0225] The pressure-sensitive adhesive composition of the present invention may contain only one specific (meth)acrylic polymer (C), or may contain two or more specific (meth)acrylic polymers (C).

[0226] The specific (meth)acrylic polymer (C) may be a homopolymer or a copolymer.

[0227] Hereinafter, preferred structural units contained in the specific (meth)acrylic polymer (C) will be described in detail.

[0228] <Constitutional Units Derived from Alkyl (Meth)acrylate Monomers>

[0229] The specific (meth)acrylic polymer (C) preferably includes a structural unit derived from an alkyl (meth)acrylate monomer.

[0230] The type of the alkyl (meth)acrylate monomer is not particularly limited.

[0231] As the (meth)acrylic acid alkyl ester monomer, an unsubstituted (meth)acrylic acid alkyl ester monomer is preferable.

[0232] The alkyl group of the (meth)acrylate monomer may be linear, branched, or cyclic.

[0233] From the viewpoint of adhesive strength, the number of carbon atoms in the alkyl group is, for example, preferably in the range of 1 or more and 18 or less, more preferably in the range of 1 or more and 12 or less, and even more preferably in the range of 1 or more and 8 or less.

[0234] Specific examples of the (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic acid-based polymer (C) are the same as those of the specific (meth)acrylic acid-based polymer (A), and therefore description thereof is omitted here.

[0235] As the (meth)acrylic acid alkyl ester monomer, at least one selected from the group consisting of methyl acrylate and n-butyl acrylate is preferred.

[0236] When the specific (meth)acrylic polymer (C) contains a structural unit derived from an alkyl (meth)acrylate monomer, it may contain only one type of structural unit derived from an alkyl (meth)acrylate monomer, or may contain two or more types.

[0237] When the specific (meth)acrylic polymer (C) contains a constituent unit derived from an alkyl (meth)acrylate monomer, the content of the constituent unit derived from an alkyl (meth)acrylate monomer in the specific (meth)acrylic polymer (C) is not particularly limited, but is, for example, preferably in the range of 50% by mass or more and 100% by mass or less, more preferably in the range of 60% by mass or more and 100% by mass or less, and even more preferably in the range of 70% by mass or more and 100% by mass or less, relative to all the constituent units of the specific (meth)acrylic polymer (C).

[0238] Here, the content of the structural units derived from the alkyl (meth)acrylate monomer in the specific (meth)acrylic polymer (C) is 50% by mass or more relative to all the structural units of the specific (meth)acrylic polymer (C). This means that the structural units derived from the alkyl (meth)acrylate monomer are contained as the main components of the structural units constituting the specific (meth)acrylic polymer (C).

[0239] <Constitutional Units Derived from Monomers Having a Hydroxyl Group>

[0240] The specific (meth)acrylic polymer (C) preferably includes a structural unit derived from a monomer having a hydroxyl group.

[0241] The type of the monomer having a hydroxyl group is not particularly limited.

[0242] Specific examples of the monomer having a hydroxyl group in the specific (meth)acrylic polymer (C) are the same as the specific examples of the monomer having a hydroxyl group in the specific (meth)acrylic polymer (A), and therefore description thereof is omitted here.

[0243] The monomer having a hydroxyl group is preferably a hydroxyalkyl (meth)acrylate, more preferably a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 1 to 5 carbon atoms, further preferably a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms, and particularly preferably 4-hydroxybutyl acrylate.

[0244] When the specific (meth)acrylic polymer (C) contains a structural unit derived from a monomer having a hydroxyl group, it may contain only one type of structural unit derived from a monomer having a hydroxyl group, or may contain two or more types.

[0245] When the specific (meth)acrylic polymer (C) contains a constituent unit derived from a monomer having a hydroxyl group, the content of the constituent unit derived from a monomer having a hydroxyl group in the specific (meth)acrylic polymer (C) is not particularly limited, but is, for example, preferably in the range of 0.1% by mass to 10% by mass, more preferably in the range of 0.5% by mass to 10% by mass, and even more preferably in the range of 1% by mass to 8% by mass, relative to all the constituent units of the specific (meth)acrylic polymer (C).

[0246] When the content of the structural units derived from the monomer having a hydroxyl group in the specific (meth)acrylic polymer (C) is 0.1% by mass or more relative to all the structural units of the specific (meth)acrylic polymer (C), a cross-linked structure is appropriately formed, and thus there is a tendency to suppress the migration of the adhesive layer components to the adherend during peeling.

[0247] When the content of the structural units derived from the monomer having a hydroxyl group in the specific (meth)acrylic polymer (C) is 10% by mass or less relative to the total structural units of the specific (meth)acrylic polymer (C), a PSA layer tends to be less susceptible to tearing even when peeled from an adherend at high speed after being adhered to the adherend for a long period of time.

[0248] <Constitutional Unit Derived from a Monomer Having a Carboxyl Group>

[0249] The specific (meth)acrylic polymer (C) may include a structural unit derived from a monomer having a carboxyl group.

[0250] The type of the monomer having a carboxyl group is not particularly limited.

[0251] Specific examples of the monomer having a carboxyl group in the specific (meth)acrylic polymer (C) are the same as the specific examples of the monomer having a carboxyl group in the specific (meth)acrylic polymer (A), and therefore description thereof is omitted here.

[0252] When the specific (meth)acrylic polymer (C) contains a structural unit derived from a monomer having a carboxyl group, it may contain only one type of structural unit derived from a monomer having a carboxyl group, or may contain two or more types.

[0253] When the specific (meth)acrylic polymer (C) contains a structural unit derived from a monomer having a carboxyl group, the content of the structural unit derived from a monomer having a carboxyl group in the specific (meth)acrylic polymer (C) is not particularly limited.

[0254] For example, from the viewpoint of being able to form a PSA layer that is less likely to tear even when peeled from an adherend at high speed after being adhered to the adherend for a long time, the specific (meth)acrylic polymer (C) preferably contains no constitutional units derived from a monomer having a carboxyl group, or the content of constitutional units derived from a monomer having a carboxyl group is in the range of more than 0% by mass and not more than 1% by mass relative to the total constitutional units of the specific (meth)acrylic polymer (C). More preferably, it contains no constitutional units derived from a monomer having a carboxyl group, or the content of constitutional units derived from a monomer having a carboxyl group is in the range of more than 0% by mass and not more than 0.5% by mass relative to the total constitutional units of the specific (meth)acrylic polymer (C). Even more preferably, it contains no constitutional units derived from a monomer having a carboxyl group, or the content of constitutional units derived from a monomer having a carboxyl group is in the range of more than 0% by mass and not more than 0.1% by mass relative to the total constitutional units of the specific (meth)acrylic polymer (C). It is particularly preferred that it contains no constitutional units derived from a monomer having a carboxyl group.

[0255] <Other components>

[0256] The specific (meth)acrylic polymer (C) may contain structural units other than the above-mentioned structural units (so-called other structural units) within a range in which the effects of the present invention are exhibited.

[0257] Specific examples of monomers constituting other structural units in the specific (meth)acrylic polymer (C) are the same as the specific examples of monomers constituting other structural units in the specific (meth)acrylic polymer (A), and therefore description thereof is omitted here.

[0258] When the specific (meth)acrylic polymer (C) contains other structural units, it may contain only one type of other structural units, or may contain two or more types.

[0259] When the specific (meth)acrylic polymer (C) contains other structural units, the content of other structural units in the specific (meth)acrylic polymer (C) is not particularly limited and can be appropriately set depending on the intended purpose.

[0260] <<Glass Transition Temperature of Specific (Meth)Acrylic Polymer (C)>>

[0261] The glass transition temperature of the specific (meth)acrylic polymer (C) is -30°C or lower, preferably -65°C to -30°C, more preferably -65°C to -40°C, and even more preferably -65°C to -45°C.

[0262] When the glass transition temperature of the specific (meth)acrylic polymer (C) is -30°C or lower, a pressure-sensitive adhesive layer that is unlikely to tear even when peeled off at high speed after being attached to an adherend for a long time can be formed.

[0263] The glass transition temperature of the specific (meth)acrylic polymer (C) is a value determined by the same method as the glass transition temperature of the specific (meth)acrylic polymer (A).

[0264] The glass transition temperature of the specific (meth)acrylic polymer (C) can be appropriately adjusted by, for example, using two or more monomers having different glass transition temperatures when forming a homopolymer.

[0265] <<Weight Average Molecular Weight of Specific (Meth)Acrylic Polymer (C)>>

[0266] The weight average molecular weight of the specific (meth)acrylic polymer (C) is in the range of 6,000 to 150,000, preferably 7,000 to 130,000, more preferably 8,000 to 100,000, and even more preferably 9,000 to 80,000.

[0267] When the weight average molecular weight of the specific (meth)acrylic polymer (C) is 6,000 or more, a pressure-sensitive adhesive layer having a good balance between low-speed peeling force and high-speed peeling force tends to be formed.

[0268] When the weight average molecular weight of the specific (meth)acrylic polymer (C) is 150,000 or less, a pressure-sensitive adhesive layer that is unlikely to tear even when peeled from an adherend at high speed after being attached to the adherend for a long period of time can be formed.

[0269] The weight average molecular weight of the specific (meth)acryl-based polymer (C) is a value measured by the same method as that for the weight average molecular weight (Mw) of the specific (meth)acryl-based polymer (A).

[0270] The weight average molecular weight of the specific (meth)acrylic polymer (C) can be adjusted to a desired value by adjusting the polymerization temperature, polymerization time, the amount of the organic solvent used, the type of the polymerization initiator, the amount of the polymerization initiator used, and the like.

[0271] The weight average molecular weight of the specific (meth)acrylic polymer (C) is preferably smaller than the weight average molecular weight of the specific (meth)acrylic polymer (B).

[0272] When the weight average molecular weight of the specific (meth)acrylic polymer (C) is smaller than the weight average molecular weight of the specific (meth)acrylic polymer (B), a PSA layer tends to be less susceptible to tearing even when the PSA layer is peeled off from an adherend at high speed after being adhered to the adherend for a long period of time.

[0273] <<Hydroxy Value of Specific (Meth)Acrylic Polymer (C)>>

[0274] The hydroxyl value of the specific (meth)acrylic polymer (C) is not particularly limited, but is, for example, preferably 40 mgKOH / g or less, more preferably in the range of 0 mgKOH / g to 40 mgKOH / g, further preferably in the range of 0.3 mgKOH / g to 40 mgKOH / g, and particularly preferably in the range of 0.5 mgKOH / g to 30 mgKOH / g.

[0275] In this specification, the fact that the hydroxyl value of the specific (meth)acrylic polymer (C) is 0 mgKOH / g means that the specific (meth)acrylic polymer (C) does not contain a hydroxyl group.

[0276] When the hydroxyl value of the specific (meth)acrylic polymer (C) is 40 mgKOH / g or less, the formed pressure-sensitive adhesive layer tends to exhibit more appropriate high-speed peeling strength.

[0277] The hydroxyl value of the specific (meth)acryl-based polymer (C) is a value calculated by the same method as the hydroxyl value of the specific (meth)acryl-based polymer (A).

[0278] <<Acid Value of Specific (Meth)Acrylic Polymer (C)>>

[0279] The acid value of the specific (meth)acrylic polymer (C) is not particularly limited, but is, for example, preferably 7 mgKOH / g or less, more preferably in the range of 0 mgKOH / g to 7 mgKOH / g, further preferably in the range of 0 mgKOH / g to 3.5 mgKOH / g, and particularly preferably 0 mgKOH / g.

[0280] In this specification, the fact that the acid value of the specific (meth)acrylic polymer (C) is 0 mgKOH / g means that the specific (meth)acrylic polymer (C) does not contain a carboxyl group.

[0281] When the acid value of the specific (meth)acrylic polymer (C) is 7 mgKOH / g or less, a pressure-sensitive adhesive layer that is unlikely to tear even when peeled from an adherend at high speed after being adhered to the adherend for a long period of time can be formed.

[0282] The acid value of the specific (meth)acryl-based polymer (C) is a value calculated by the same method as the acid value of the specific (meth)acryl-based polymer (A).

[0283] As the specific (meth)acrylic polymer (C), a commercially available item can be used.

[0284] Examples of commercially available products of the specific (meth)acrylic polymer (C) include UP-1080 [trade name, glass transition temperature: -61°C, weight average molecular weight: 6000, manufactured by Toagosei Co., Ltd.], UP-1170 [trade name, glass transition temperature: -57°C, weight average molecular weight: 8000, manufactured by Toagosei Co., Ltd.], UH-2000 [trade name, (meth)acrylic polymer having a hydroxyl group, glass transition temperature: -55°C, weight average molecular weight: 11000, manufactured by Toagosei Co., Ltd.], and UH-2190 [trade name, (meth)acrylic polymer having a hydroxyl group, glass transition temperature: -47°C, weight average molecular weight: 6000, manufactured by Toagosei Co., Ltd.].

[0285] <<Content of specific (meth)acrylic polymer (C)>>

[0286] The content of the specific (meth)acrylic polymer (C) in the adhesive composition of the present invention is in the range of 0.5 parts by mass or more and 5 parts by mass or less, preferably in the range of 0.5 parts by mass or more and 4.5 parts by mass or less, more preferably in the range of 1 part by mass or more and 4 parts by mass or less, and even more preferably in the range of 1.5 parts by mass or more and 3 parts by mass or less, relative to 100 parts by mass of the specific (meth)acrylic polymer (A).

[0287] When the content of the specific (meth)acrylic polymer (C) in the adhesive composition of the present invention is 0.5 parts by mass or more relative to 100 parts by mass of the specific (meth)acrylic polymer (A), a adhesive layer that is unlikely to tear even when peeled from an adherend at high speed after being adhered to the adherend for a long period of time can be formed.

[0288] When the content of the specific (meth)acrylic polymer (C) in the adhesive composition of the present invention is 5 parts by mass or less relative to 100 parts by mass of the specific (meth)acrylic polymer (A), a adhesive layer having a good balance between low-speed peel strength and high-speed peel strength tends to be formed.

[0289] As a preferred embodiment of the adhesive composition of the present invention, the weight average molecular weight of the specific (meth)acrylic polymer (C) is smaller than the weight average molecular weight of the specific (meth)acrylic polymer (B), and the content of the specific (meth)acrylic polymer (C) is smaller than the content of the specific (meth)acrylic polymer (B).

[0290] According to the above aspect, there is a tendency to form a PSA layer that is less likely to be peeled off even when peeled off from an adherend at high speed after being attached to the adherend for a long time.

[0291] [Method for producing specific (meth)acrylic acid polymer]

[0292] The production method of the specific (meth)acrylic polymer (A), the specific (meth)acrylic polymer (B), and the specific (meth)acrylic polymer (C) [ie, the specific (meth)acrylic polymer] is not particularly limited.

[0293] The specific (meth)acrylic polymer can be produced, for example, by polymerizing the above-mentioned monomers using a known polymerization method such as solution polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization. Furthermore, the specific (meth)acrylic polymer can be produced by polymerizing a monomer having neither a hydroxyl group nor a carboxyl group using a known polymerization method such as solution polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization to produce a (meth)acrylic polymer, and then introducing at least one of a hydroxyl group and a carboxyl group into the produced (meth)acrylic polymer by substitution.

[0294] From the viewpoint that the handling steps are relatively simple and can be performed in a short time when preparing the adhesive composition of the present invention after production, the solution polymerization method is preferred as the polymerization method.

[0295] In solution polymerization, a predetermined organic solvent, monomers, a polymerization initiator, and, if necessary, a chain transfer agent are generally placed in a polymerization tank. The mixture is then heated and reacted for several hours at the reflux temperature of the organic solvent under a nitrogen stream while stirring. In this case, at least a portion of the organic solvent, monomers, polymerization initiator, and / or chain transfer agent may be added gradually.

[0296] Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbon compounds, aliphatic or alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, and alcohol compounds.

[0297] More specifically, examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbon compounds represented by benzene, toluene, ethylbenzene, n-propylbenzene, tert-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha; aliphatic or alicyclic hydrocarbon compounds represented by n-hexane, n-heptane, n-octane, isooctane, n-decane, dipentene, petroleum spirit, naphtha, and turpentine; ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, acetic acid; Ester compounds represented by 2-butoxyethyl ester, 3-methoxybutyl acetate and methyl benzoate; ketone compounds represented by acetone, methyl ethyl ketone, methyl isobutyl ketone, isophorone, cyclohexanone and methylcyclohexanone; glycol ether compounds represented by ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether and diethylene glycol monobutyl ether; and alcohol compounds represented by methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol and tert-butanol.

[0298] When producing the specific (meth)acrylic polymer, it is preferred to use an organic solvent such as an aromatic hydrocarbon compound, an ester compound, or a ketone compound that is less likely to cause chain transfer during the polymerization reaction. In particular, from the viewpoints of the solubility of the specific (meth)acrylic polymer and the ease of the polymerization reaction, it is preferred to use at least one selected from ethyl acetate, toluene, and methyl ethyl ketone.

[0299] During the polymerization reaction, only one organic solvent may be used, or two or more organic solvents may be used.

[0300] Examples of the polymerization initiator include organic peroxides and azo compounds used in general solution polymerization methods.

[0301] Examples of the organic peroxide include tert-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, hexanoyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, tert-butyl peroxypivalate, 2,2-bis(4,4-di-tert-butylperoxycyclohexyl)propane, 2,2-bis(4,4-di-tert-amylperoxycyclohexyl)propane, 2,2-bis(4,4-di-tert-octylperoxycyclohexyl)propane, 2,2-bis(4,4-di-α-cumylperoxycyclohexyl)propane, 2,2-bis(4,4-di-tert-butylperoxycyclohexyl)butane, and 2,2-bis(4,4-di-tert-octylperoxycyclohexyl)butane.

[0302] Examples of the azo compound include 2,2'-azobisisobutyronitrile [AIBN], 2,2'-azobis(2,4-dimethylvaleronitrile) [ABVN], 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), and 2,2'-azobis(dimethylisobutyrate).

[0303] When producing the specific (meth)acrylic polymer, it is preferred to use a polymerization initiator that does not cause a graft reaction during the polymerization reaction, and it is particularly preferred to use an azo compound.

[0304] During the polymerization reaction, only one polymerization initiator may be used, or two or more polymerization initiators may be used.

[0305] The amount of the polymerization initiator used is not particularly limited and can be appropriately set according to, for example, the molecular weight of the intended specific (meth)acrylic polymer.

[0306] When producing the specific (meth)acrylic polymer, a chain transfer agent may be used as needed.

[0307] Examples of the chain transfer agent include cyanoacetic acid, alkyl ester compounds of cyanoacetic acid having 1 to 8 carbon atoms, bromoacetic acid, alkyl ester compounds of bromoacetic acid having 1 to 8 carbon atoms, aromatic compounds represented by α-methylstyrene, anthracene, phenanthrene, fluorene and 9-phenylfluorene, aromatic nitro compounds represented by p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol and p-nitrotoluene, benzoquinone derivatives represented by benzoquinone and 2,3,5,6-tetramethyl-p-benzoquinone, and borane derivatives represented by tributylborane. , halogenated hydrocarbon compounds represented by carbon tetrabromide, carbon tetrachloride, 1,1,2,2-tetrabromoethane, tribromoethylene, trichloroethylene, bromotrichloromethane, bromoform and 3-chloro-1-propene, aldehyde compounds represented by chloral and furfural, alkyl mercaptan compounds having 1 to 18 carbon atoms, aromatic mercaptan compounds represented by thiophenol and toluene mercaptan, thioglycolic acid, alkyl ester compounds having 1 to 10 carbon atoms of thioglycolic acid, hydroxyalkyl mercaptan compounds having 1 to 12 carbon atoms, and terpene compounds represented by pinene and terpinolene.

[0308] When a chain transfer agent is used in producing the specific (meth)acrylic polymer, the amount of the chain transfer agent used is not particularly limited and can be appropriately set according to, for example, the molecular weight of the intended specific (meth)acrylic polymer.

[0309] The polymerization temperature is not particularly limited and can be appropriately set according to, for example, the molecular weight of the intended specific (meth)acrylic polymer.

[0310] [Isocyanate crosslinking agent (D)]

[0311] The adhesive composition of the present invention contains an isocyanate-based crosslinking agent (D).

[0312] In this specification, "isocyanate-based crosslinking agent (D)" refers to a compound having two or more isocyanate groups in the molecule (so-called polyisocyanate compound).

[0313] The isocyanate-based crosslinking agent (D) is not particularly limited.

[0314] Examples of the isocyanate crosslinking agent (D) include aromatic polyisocyanate compounds such as xylene diisocyanate (XDI), diphenylmethane diisocyanate, triphenylmethane triisocyanate, and toluene diisocyanate (TDI); and aliphatic or alicyclic polyisocyanate compounds such as hexamethylene diisocyanate (HMDI), pentamethylene diisocyanate (PDI), isophorone diisocyanate, and hydrogenated aromatic polyisocyanate compounds.

[0315] Examples of the isocyanate crosslinking agent (D) include dimers, trimers, or pentamers of the polyisocyanate compounds, adducts of the polyisocyanate compounds with polyol compounds such as trimethylolpropane, and biuret forms of the polyisocyanate compounds.

[0316] Examples of the isocyanate crosslinking agent (D) include compounds having two or more isocyanate groups, a polysiloxane structure, and an oxyalkylene structure in the molecule (so-called silicone polyisocyanate compounds).

[0317] Specific examples of the silicone polyisocyanate compound include the exemplary compounds of the silicone isocyanate compound (C) described in paragraphs

[0102] to

[0118] of JP-A-2019-35066.

[0318] Among them, hexamethylene diisocyanate is preferred as the isocyanate-based crosslinking agent (D).

[0319] When the isocyanate-based crosslinking agent (D) is hexamethylene diisocyanate, a pressure-sensitive adhesive layer having a release strength more suitable for use as a protective film tends to be formed.

[0320] As the isocyanate-based crosslinking agent (D), a commercially available item can be used.

[0321] Examples of commercially available isocyanate crosslinking agents (D) include "CORONATE (registered trademark) HX", "CORONATE (registered trademark) HL-S", "CORONATE (registered trademark) L", "CORONATE (registered trademark) L-45E", "CORONATE (registered trademark) 2031", "CORONATE (registered trademark) 2030", "CORONATE (registered trademark) 2234", "CORONATE (registered trademark) 2785", "AQUANATE (registered trademark) 200" and "AQUANATE (registered trademark) 210" [all manufactured by Tosoh Corporation], "SUMIDUR (registered trademark) N3300", "DESMODUR (registered trademark) N3400" and "SUMIDUR (registered trademark) N75" [all manufactured by Sumika Covestro Urethane Co., Ltd.], "DURANATE (registered trademark) E-405-80T", "DURANATE (registered trademark) AE700-100", "DURANATE (registered trademark) 24A-100", and "DURANATE (registered trademark) TSE-100" [all manufactured by Asahi Kasei Corporation], and "TAKENATE (registered trademark) D-110N", "TAKENATE (registered trademark) D-120N", "TAKENATE (registered trademark) M-631N", "MT-OLESTER (registered trademark) NP1200", and "STABIO (registered trademark) XD-340N" [all manufactured by Mitsui Chemicals, Inc.].

[0322] The adhesive composition of the present invention may contain only one isocyanate crosslinking agent (D), or may contain two or more types.

[0323] The content of the isocyanate crosslinking agent (D) in the adhesive composition of the present invention is not particularly limited, but is preferably in the range of 0.1 parts by mass or more and 7.0 parts by mass or less, more preferably in the range of 0.3 parts by mass or more and 7.0 parts by mass or less, further preferably in the range of 0.5 parts by mass or more and 5.0 parts by mass or less, and particularly preferably in the range of 0.5 parts by mass or more and 3.0 parts by mass or less, relative to 100 parts by mass of the specific (meth)acrylic polymer (A).

[0324] When the content of the isocyanate crosslinking agent (D) in the adhesive composition of the present invention is 0.1 parts by mass or more relative to 100 parts by mass of the specific (meth)acrylic polymer (A), an adhesive layer having a better balance between low-speed peel strength and high-speed peel strength tends to be formed.

[0325] When the content of the isocyanate crosslinking agent (D) in the adhesive composition of the present invention is 7.0 parts by mass or less relative to 100 parts by mass of the specific (meth)acrylic polymer (A), a adhesive layer tends to be less susceptible to tearing even when the adhesive is peeled off from an adherend at high speed after being adhered to the adherend for a long period of time.

[0326] [Organic solvent]

[0327] The adhesive composition of the present invention may contain an organic solvent.

[0328] When the adhesive composition of the present invention contains an organic solvent, coating properties can be improved.

[0329] Examples of the organic solvent include the same organic solvents as those used in the polymerization reaction of the above-mentioned specific (meth)acrylic polymer.

[0330] When the adhesive composition of the present invention contains an organic solvent, it may contain only one organic solvent or two or more organic solvents.

[0331] When the adhesive composition of the present invention contains an organic solvent, the content of the organic solvent is not particularly limited and can be appropriately set according to the intended purpose.

[0332] 〔Antistatic Agent〕

[0333] The adhesive composition of the present invention may contain an antistatic agent.

[0334] The antistatic agent is not particularly limited, and examples thereof include ionic compounds.

[0335] Examples of the ionic compound include alkali metal salts and organic salts.

[0336] Among them, alkali metal salts are preferred as ionic compounds.

[0337] If the alkali metal salt is lithium ion (Li + ), sodium ion (Na + ), potassium ion (K + ), rubidium ions (Rb + ) etc. are not particularly limited.

[0338] The alkali metal salt is preferably selected from Li + 、Na + and K + At least one cation selected from Cl － Br － , I － 、BF4 － PF6 －、SCN － 、ClO4 － CF3SO3 － 、(FSO2)2N － 、(CF3SO2)2N － 、(C2F5SO2)2N － and (CF3SO2)3C － The metal salt is composed of at least one anion, more preferably a lithium salt such as LiBr, LiI, LiBF4, LiPF6, LiSCN, LiClO4, LiCF3SO3 (so-called LiTFS), Li(FSO2)2N, Li(CF3SO2)2N, Li(C2F5SO2)2N, Li(CF3SO2)3C, and further preferably at least one lithium salt selected from LiClO4, LiCF3SO3, Li(CF3SO2)2N, Li(C2F5SO2)2N and Li(CF3SO2)3C.

[0339] When the adhesive composition of the present invention contains an antistatic agent, it may contain only one antistatic agent or two or more antistatic agents.

[0340] When the adhesive composition of the present invention contains an antistatic agent, the content of the antistatic agent is not particularly limited and can be appropriately set according to the purpose.

[0341] [Polyether-modified silicone compounds]

[0342] The adhesive composition of the present invention may include a polyether-modified organic silicon compound.

[0343] It should be noted that the "polyether-modified silicone compound" in this specification does not include the above-mentioned silicone-based polyisocyanate compound.

[0344] In the adhesive composition of the present invention, the polyether-modified silicone compound can function as a release regulator.

[0345] In addition, the polyether-modified silicone compound in the adhesive composition of the present invention can function as an antistatic agent. Therefore, the adhesive composition of the present invention preferably contains a polyether-modified silicone compound and an antistatic agent in combination.

[0346] The polyether-modified silicone compound is not particularly limited, but is preferably at least one silicone compound selected from the group consisting of silicone compounds having an oxyalkylene structure having a terminal hydroxyl group bonded to a part of the side chain of a polysiloxane chain serving as a main chain, silicone compounds having an oxyalkylene structure having an acetyl group bonded to a terminal, and silicone compounds having an oxyalkylene structure having a terminal hydroxyl group bonded to both ends of a polysiloxane chain serving as a main chain (hereinafter also referred to as "specific polyether-modified silicone compound").

[0347] The specific polyether-modified silicone compound is preferably a polysiloxane compound containing a structural unit derived from a dialkylsiloxane and a structural unit derived from an alkylsiloxane to which an oxyalkylene structure having a terminal hydroxyl group is bonded.

[0348] The number of carbon atoms of the alkyl group in the dialkylsiloxane is preferably 1 to 4, more preferably 1.

[0349] The number of carbon atoms in the alkylsiloxane having an oxyalkylene structure having a terminal hydroxyl group bonded thereto is preferably 2 to 4, more preferably 2 or 3.

[0350] The alkyl group in the alkylsiloxane to which an oxyalkylene structure having a terminal hydroxyl group is bonded preferably has 1 to 4 carbon atoms.

[0351] The number of oxyalkylene chains contained in the alkylsiloxane to which an oxyalkylene structure having a terminal hydroxyl group is bonded is preferably 1 to 100, more preferably 10 to 100.

[0352] When the specific polyether-modified silicone compound contains constituent units derived from dialkylsiloxane and constituent units derived from alkylsiloxane to which an oxyalkylene structure having a terminal hydroxyl group is bonded, the number of constituent units derived from dialkylsiloxane is preferably 100 or less, more preferably 1 to 80.

[0353] The number of constituent units derived from an alkylsiloxane to which an oxyalkylene structure having a terminal hydroxyl group is bonded is preferably 2 to 100, more preferably 2 to 80.

[0354] As the specific polyether-modified silicone compound, a compound represented by the following formula (A) or formula (B) is preferred.

[0355]

[0356] In formula (A), p is the number of repetitions of the dimethylsiloxane structural unit, which is an integer from 0 to 100; q is the number of repetitions of the methylpropylenesiloxane structural unit having a polyoxyethylene chain, which is an integer from 2 to 100; and a is the number of repetitions of the ethylene oxide structural unit, which is an integer from 1 to 100.

[0357] When the compound represented by formula (A) is an aggregate of a plurality of compounds, p, q, and a are average values of the aggregate of the compounds and are rational numbers.

[0358] In formula (A), the number of repetitions of the ethylene oxide structural unit represented by a is preferably an integer of 10 to 100.

[0359] In formula (A), the number of repetitions of the dimethylsiloxane structural unit represented by p is preferably an integer of 1 to 80.

[0360] In formula (A), the number of repetitions of the methylpropylenesiloxane structural unit represented by q is preferably an integer of 2 to 80.

[0361] As the compound represented by formula (A), a commercially available product can be used.

[0362] Examples of commercially available products of the compound represented by formula (A) include "DOWSIL (registered trademark) SF-8428", "DOWSIL (registered trademark) FZ-2162", "DOWSIL (registered trademark) SH-3773M", "DOWSIL (registered trademark) FZ-77", "DOWSIL (registered trademark) FZ-2104", "DOWSIL (registered trademark) FZ-2110", "DOWSIL (registered trademark) L-7001", "DOWSIL (registered trademark) L-7002" and "DOWSIL (registered trademark) SH-3749" [all manufactured by Dow Toray Industries, Ltd.].

[0363]

[0364] In formula (B), R 1 and R 2 Each independently represents an alkylene group having 1 to 6 carbon atoms, c is the number of repetitions of the dimethylsiloxane structural unit and is an integer from 10 to 80, d is the number of repetitions of the ethylene oxide structural unit and is an integer greater than or equal to 1, e is the number of repetitions of the propylene oxide structural unit and is an integer greater than or equal to 0, and d+e is an integer from 1 to 30. The order of the ethylene oxide structural unit and the propylene oxide structural unit may be random.

[0365] As the compound represented by formula (B), a commercially available product can be used.

[0366] Examples of commercially available products of the compound represented by formula (B) include "DOWSIL (registered trademark) BY-16-201" and "DOWSIL (registered trademark) SF-8427" [both manufactured by Dow Toray Industries, Ltd.].

[0367] The weight average molecular weight of the polyether-modified silicone compound is not particularly limited, but is preferably in the range of 1,000 to 20,000, and more preferably in the range of 3,000 to 15,000.

[0368] The weight average molecular weight of the polyether-modified silicone compound is a value measured by the same method as the method for measuring the weight average molecular weight of the above-mentioned specific (meth)acrylic polymer (A).

[0369] When the adhesive composition of the present invention contains a polyether-modified silicone compound, it may contain only one type of polyether-modified silicone compound or two or more types.

[0370] When the adhesive composition of the present invention contains a polyether-modified silicone compound, the content of the polyether-modified silicone compound in the adhesive composition of the present invention is not particularly limited, but is preferably in the range of 0.1 mass part or more and 3.0 mass parts or less, more preferably in the range of 0.1 mass part or more and 1.5 mass parts or less, and even more preferably in the range of 0.1 mass part or more and 1.0 mass part or less, relative to 100 mass parts of the specific (meth)acrylic polymer (A).

[0371] 〔Cross-linking catalyst〕

[0372] The adhesive composition of the present invention may contain a cross-linking catalyst.

[0373] The cross-linking catalyst is not particularly limited, and a known cross-linking catalyst can be used.

[0374] Examples of the cross-linking catalyst include organometallic compounds represented by dioctyltin dilaurate (DOTDL) and 1,3-diacetoxytetrabutyldistannoxane, and tertiary amine compounds represented by triethylenediamine and N-methylmorpholine.

[0375] When the adhesive composition of the present invention contains a cross-linking catalyst, it may contain only one type of cross-linking catalyst or two or more types of cross-linking catalysts.

[0376] When the adhesive composition of the present invention contains a cross-linking catalyst, the content of the cross-linking catalyst is not particularly limited and can be appropriately set according to the purpose.

[0377] [Other ingredients]

[0378] The adhesive composition of the present invention may contain components other than the above components (so-called other components) as needed within a range not impairing the effects of the present invention.

[0379] Examples of other components include crosslinking agents other than isocyanate crosslinking agents (eg, metal chelate crosslinking agents), antioxidants, colorants (eg, dyes and pigments), and light stabilizers (eg, ultraviolet absorbers).

[0380] When the adhesive composition of the present invention contains other components, the content of the other components can be appropriately set within a range in which the effects of the present invention are exhibited.

[0381] [use]

[0382] The adhesive composition of the present invention is preferably used in films for protecting optical components (so-called optical component protective films) because it can form an adhesive layer that has a good balance between low-speed peel strength and high-speed peel strength and is not easily torn even when peeled from the adherend at high speed after being attached to the adherend for a long time. In other words, the adhesive composition of the present invention is suitable for use in applications where protective films are attached to optical components.

[0383] The optical member is not particularly limited, and examples thereof include members constituting devices such as image display devices and input devices (so-called optical devices) or members used in these devices.

[0384] Specific examples of optical components include polarizing plates, AG (anti-glare) polarizing plates, wavelength plates, phase difference plates including 1 / 2, 1 / 4 and other wavelength plates, viewing angle compensation films, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflection films, transparent conductive films such as ITO (indium tin oxide) films, prism sheets, lens sheets, diffuser plates, etc.

[0385] Examples of materials for optical components include polyethylene resins, polyester resins, acetate resins (e.g., cellulose triacetate resins), polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, acrylic resins, vinyl chloride resins, ABS (acrylonitrile-butadiene-styrene) resins, and fluorine resins.

[0386] [Optical component protective film]

[0387] The optical member protective film of the present invention (hereinafter also referred to as "protective film") comprises a substrate and an adhesive layer, wherein the adhesive layer is provided on the substrate and is formed from the adhesive composition of the present invention described above. Specifically, the protective film of the present invention comprises a substrate and an adhesive layer formed from the adhesive composition of the present invention laminated together.

[0388] The protective film of the present invention comprises an adhesive layer formed from the adhesive composition of the present invention. Therefore, after being attached to the surface of an adherend, the film is less likely to peel or stray from the adherend while protection is required. Furthermore, the film can be efficiently peeled from the adherend when protection is no longer required. In other words, the film exhibits a good balance between low-speed and high-speed peel forces.

[0389] The protective film of the present invention includes a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention, and therefore is less likely to tear even when it is peeled off from an adherend at high speed after being attached to the adherend for a long time.

[0390] The substrate is not particularly limited as long as a pressure-sensitive adhesive layer can be formed on the substrate.

[0391] Examples of the substrate include films comprising resins such as polyolefin resins (e.g., polyethylene and polypropylene), polyester resins [e.g., polyethylene terephthalate (PET)], acetate resins (e.g., cellulose triacetate resin), polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, acrylic resins, vinyl chloride resins, ABS (acrylonitrile-butadiene-styrene) resins, and fluorine-based resins.

[0392] For example, from the perspective of inspection and management of optical components based on perspective, the substrate is preferably a film comprising at least one resin selected from polyester resins, acetate resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins and acrylic resins.

[0393] Furthermore, for example, from the viewpoint of surface protection performance, a film composed of a polyester resin is preferred, and in consideration of practicality, a film composed of polyethylene terephthalate (PET) is particularly preferred.

[0394] The substrate may contain various additives such as plasticizers, colorants (such as dyes and pigments), heat stabilizers, light stabilizers, antistatic agents, flame retardants, antioxidants, and the like.

[0395] The substrate may be patterned over a portion or the entirety.

[0396] The thickness of the substrate is not particularly limited, but is generally 500 μm or less, preferably 300 μm or less, and more preferably 200 μm or less.

[0397] For example, from the viewpoint of the strength of the protective film, the lower limit of the thickness of the substrate is preferably 5 μm or more, and more preferably 10 μm or more.

[0398] Antistatic layer can be set on the single side or double sides of base material.In addition, from the viewpoint of improving the adhesion of base material and adhesive layer, surface treatments such as corona discharge treatment, plasma discharge treatment can be implemented on the surface that is provided with adhesive layer one side of base material.

[0399] The method for forming the pressure-sensitive adhesive layer is not particularly limited, and a commonly used method can be employed.

[0400] As a method for forming the pressure-sensitive adhesive layer on the substrate, for example, the following method can be employed.

[0401] The adhesive composition of the present invention is applied to a substrate in its original state or diluted with a solvent as needed to form a coating film. The formed coating film is then dried to form an adhesive film on the substrate. The adhesive film formed on the substrate is then aged to form an adhesive layer on the substrate.

[0402] In the protective film of the present invention, the exposed adhesive layer can be protected by a release film. The release film is not particularly limited as long as it can be easily peeled from the adhesive layer. For example, a resin film that has been surface-treated with a release agent on one or both sides (so-called easy-peel treatment) can be used. The resin film can be, for example, a polyester film represented by polyethylene terephthalate (PET) film.

[0403] Examples of the release agent include fluorine-based release agents (eg, fluorine-based resins), wax-based release agents (eg, paraffin wax), silicone-based release agents (eg, silicone), and long-chain alkyl compounds.

[0404] The release film protects the surface of the adhesive layer before the protective film is actually applied and is peeled off during use.

[0405] As another method for forming a pressure-sensitive adhesive layer on a substrate, for example, the following method can be adopted.

[0406] The adhesive composition of the present invention is applied to a release film such as paper or resin film that has been surface-treated with a release agent, either in its original state or diluted with a solvent as needed, to form a coating film on the release film. The formed coating film is then dried to form an adhesive film on the release film. The exposed surface of the formed adhesive film is then brought into contact with a substrate and pressure is applied to transfer the adhesive film to the substrate, thereby forming an adhesive film on the substrate. The formed adhesive film is then aged to form an adhesive layer on the substrate.

[0407] The method for coating the adhesive composition on the substrate or the release film is not particularly limited, and examples thereof include known methods using a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a knife coater, a spray coater, a bar coater, an applicator, and the like.

[0408] The amount of the adhesive composition applied to the substrate or the release film is appropriately set depending on the thickness of the adhesive layer to be formed.

[0409] The thickness of the adhesive layer can be appropriately set according to the adhesive strength required of the protective film, the type of adherend (eg, material and shape), the surface roughness of the adherend, and the like.

[0410] The thickness of the adhesive layer is not particularly limited, but is generally in the range of 1 μm to 100 μm, preferably 5 μm to 50 μm, and more preferably 10 μm to 30 μm.

[0411] The method for drying the coating film formed on the substrate or the release film is not particularly limited, and examples thereof include natural drying, heat drying, hot air drying, and vacuum drying.

[0412] The drying temperature and drying time of the coating film are not particularly limited and are appropriately set depending on the thickness of the coating film, the amount of the organic solvent in the coating film, and the like.

[0413] An example of drying conditions is drying at 70° C. to 120° C. for 1 to 3 minutes using a hot air dryer.

[0414] The aging is performed, for example, in an environment of 20°C to 35°C for 4 to 7 days.

[0415] By aging, the crosslinking reaction of the adhesive composition is completed, and an adhesive layer is formed.

[0416] When the peeling speed is 0.3 m / min (i.e., low-speed peeling), the adhesive strength (so-called peeling force) of the adhesive layer when the protective film attached to the adherend is peeled off 180° is preferably 0.09 N / 25 mm or more, more preferably 0.13 N / 25 mm or more, and even more preferably 0.18 N / 25 mm or more.

[0417] When the protective film attached to the adherend is peeled off 180° at a peeling speed of 30 m / min (i.e., high-speed peeling), the adhesive strength of the adhesive layer (so-called peeling force) is preferably less than 1.00 N / 25 mm, more preferably less than 0.75 N / 25 mm, and further preferably less than 0.50 N / 25 mm.

[0418] In this specification, a PSA layer having a good balance between low-speed and high-speed peel forces is evaluated based on the value obtained by dividing the low-speed peel force by the high-speed peel force (ie, "low-speed peel force / high-speed peel force").

[0419] The ratio of “low-speed peel force / high-speed peel force” is preferably 0.10 or more, more preferably 0.20 or more, and even more preferably 0.30 or more.

[0420] Example

[0421] The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist of the present invention.

[0422] [Production of (meth)acrylic acid polymer A]

[0423] [Production Example A-1]

[0424] 70.0 parts by mass of ethyl acetate (organic solvent) were added to a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, a reflux cooler, and a gradual dropping device.

[0425] Separately, 60.0 parts by mass of n-butyl acrylate [n-BA; an alkyl acrylate monomer], 36.3 parts by mass of 2-ethylhexyl acrylate [2EHA; an alkyl acrylate monomer], 3.0 parts by mass of 4-hydroxybutyl acrylate [4HBA; a monomer having a hydroxyl group], and 0.7 parts by mass of acrylic acid [AA; a monomer having a carboxyl group] were added to another container and mixed to prepare a monomer mixture.

[0426] 25.0% by mass of the monomer mixture was added to the above-mentioned reaction vessel. The atmosphere in the reaction vessel was then replaced with nitrogen, and 0.01 parts by mass of 2,2'-azobisisobutyronitrile (AIBN; polymerization initiator) was added. The temperature of the contents of the reaction vessel was raised to 85°C while stirring under a nitrogen atmosphere to initiate an initial reaction.

[0427] After the initial reaction is substantially completed, a mixture of the remaining monomer mixture (75.0% by mass), 20.0 parts by mass of ethyl acetate, and 0.02 parts by mass of AIBN is gradually added to the reaction vessel over a period of about 2 hours, while the contents of the reaction vessel are reacted. After the addition is completed, the reaction is continued for another 2 hours to obtain the reactant (a1).

[0428] Then, a solution prepared by dissolving 0.25 parts by mass of t-butyl peroxypivalate (polymerization initiator) in 25.0 parts by mass of ethyl acetate was added dropwise to the reaction product (a1) in the reaction vessel over 1 hour. After completion of the dropwise addition, the reaction was continued for 1.5 hours to obtain a reaction product (a2). The obtained reaction product (a2) was diluted with ethyl acetate to obtain a solution of (meth)acrylic polymer A-1 having a solid content concentration of 45% by mass.

[0429] The “solid content concentration” referred to here refers to the mass ratio of the (meth)acrylic acid-based polymer A-1 in the solution of the (meth)acrylic acid-based polymer A-1.

[0430] The same applies to each solution of the following (meth)acrylic polymers A-2 to A-6.

[0431] [Production Examples A-2 and A-4 to A-6]

[0432] In Production Examples A-2 and A-4 to A-6, except that the monomer composition of the (meth)acrylic polymer A was changed to the monomer composition shown in Table 1, and the weight average molecular weight (Mw) of the (meth)acrylic polymer A was adjusted to the weight average molecular weight (Mw) shown in Table 1 by adjusting at least one of the amount of the organic solvent used and the amount of the polymerization initiator used, the same procedures as in Production Example A-1 were carried out to obtain solutions of the (meth)acrylic polymers A-2 and A-4 to A-6 having a solid content concentration of 45% by mass.

[0433] [Production Example A-3]

[0434] In Production Example A-3, except that the weight average molecular weight (Mw) of the (meth)acrylic polymer A was adjusted to the weight average molecular weight (Mw) shown in Table 1 by adjusting at least one of the amount of the organic solvent used and the amount of the polymerization initiator used, the same procedures as in Production Example A-1 were performed to obtain a solution of the (meth)acrylic polymer A-3 having a solid content concentration of 45% by mass.

[0435] The monomer composition (unit: mass %), hydroxyl value (unit: mgKOH / g), acid value (unit: mgKOH / g), weight average molecular weight (Mw, unit: ten thousand (indicated as "×10 4 ”)] and glass transition temperature (Tg, unit: °C) are shown in Table 1.

[0436] The weight average molecular weight (Mw) of the (meth)acrylic polymers A-1 to A-6 is measured by the same method as the method for measuring the weight average molecular weight (Mw) of the above-mentioned specific (meth)acrylic polymer (A).

[0437] The glass transition temperature (Tg) of the (meth)acrylic polymers A-1 to A-6 is calculated by the same method as the method for calculating the glass transition temperature (Tg) of the above-mentioned specific (meth)acrylic polymer (A).

[0438] The hydroxyl value and acid value of the (meth)acrylic polymers A-1 to A-6 were calculated by the same method as the method for calculating the hydroxyl value and acid value of the specific (meth)acrylic polymer (A).

[0439] For example, the hydroxyl value of (meth)acrylic polymer A-1 is calculated as follows. The 4HBA content (A1) in (meth)acrylic polymer A-1 is 3.0% by mass, and the molecular weight (A2) of 4HBA is 144.17. Furthermore, the number (A3) of hydroxyl groups contained in one molecule of 4HBA is 1.

[0440] Hydroxyl value of (meth)acrylic polymer A-1 (mgKOH / g) = {(A1 / 100) ÷ A2} × 56.1 × 1000 × A3 = {(3.0 / 100) ÷ 144.17} × 56.1 × 1000 × 1 = 11.67 ≈ 11.7

[0441] The acid value of (meth)acrylic polymer A-1 was calculated as follows. The AA content (a1) in (meth)acrylic polymer A-1 was 0.7% by mass, and the molecular weight (a2) of AA was 72.06. Furthermore, the number (a3) of carboxyl groups contained in one molecule of AA was 1.

[0442] Acid value of (meth)acrylic polymer A-1 (mgKOH / g) = {(a1 / 100) ÷ a2} × 56.1 × 1000 × a3 = {(0.7 / 100) ÷ 72.06} × 56.1 × 1000 × 1 = 5.44 ≈ 5.4

[0443] Among the (meth)acrylic polymers A-1 to A-6 obtained above, the (meth)acrylic polymers A-1 to A-5 correspond to the specific (meth)acrylic polymer (A) in the present invention.

[0444] Table 1

[0445]

[0446] The details of each monomer described in Table 1 are as follows.

[0447] "n-BA": n-butyl acrylate (alkyl acrylate monomer)

[0448] "2EHA": 2-ethylhexyl acrylate (alkyl acrylate monomer)

[0449] "4HBA": 4-hydroxybutyl acrylate (a monomer containing a hydroxyl group)

[0450] "AA": acrylic acid (monomer with carboxyl group)

[0451] In Table 1, “-” in the monomer composition column indicates that the monomer corresponding to that column is not contained.

[0452] In Table 1, “weight average molecular weight” is indicated as “Mw”, and “glass transition temperature” is indicated as “Tg”.

[0453] [Production of (meth)acrylic acid polymer B]

[0454] [Production Example B-1]

[0455] 70.0 parts by mass of ethyl acetate (organic solvent) were added to a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, a reflux cooler, and a gradual dropping device.

[0456] Separately, 96.3 parts by mass of n-butyl methacrylate [n-BMA; alkyl methacrylate monomer], 3.0 parts by mass of 4-hydroxybutyl acrylate [4HBA; monomer having a hydroxyl group], and 0.7 parts by mass of acrylic acid [AA; monomer having a carboxyl group] were added to another container and mixed to prepare a monomer mixture.

[0457] 25.0% by mass of the monomer mixture was added to the above-mentioned reaction vessel. The atmosphere in the reaction vessel was then replaced with nitrogen, and 1.80 parts by mass of 2,2'-azobisisobutyronitrile (AIBN; polymerization initiator) was added. The temperature of the contents of the reaction vessel was raised to 85°C while stirring under a nitrogen atmosphere to initiate an initial reaction.

[0458] After the initial reaction is substantially completed, the remaining monomer mixture (75.0% by mass) and a mixture of 20.0 parts by mass of ethyl acetate and 2.0 parts by mass of AIBN are gradually added to the reaction vessel over about 2 hours, while the contents in the reaction vessel are reacted. After the addition is completed, the reaction is continued for about 1 hour to obtain the reactant (b1).

[0459] Then, a solution prepared by dissolving 0.25 parts by mass of t-butyl peroxypivalate (polymerization initiator) in 25.0 parts by mass of ethyl acetate was added dropwise to the reaction product (b1) in the reaction vessel over 1 hour. After completion of the dropwise addition, the reaction was continued for another 2 hours to obtain a reaction product (b2). The obtained reaction product (b2) was diluted with ethyl acetate to obtain a solution of (meth)acrylic polymer B-1 having a solid content concentration of 45% by mass.

[0460] The “solid content concentration” referred to here refers to the mass ratio of the (meth)acrylic acid-based polymer B-1 in the solution of the (meth)acrylic acid-based polymer B-1.

[0461] The same applies to each solution of the following (meth)acrylic polymers B-2 to B-12.

[0462] [Production Examples B-2 to B-5 and B-8 to B-10]

[0463] In Production Examples B-2 to B-5 and B-8 to B-10, except that the monomer composition of the (meth)acrylic acid polymer B was changed to the monomer composition shown in Table 2, and the weight average molecular weight (Mw) of the (meth)acrylic acid polymer B was adjusted to the weight average molecular weight (Mw) shown in Table 2 by adjusting at least one of the amount of the organic solvent used and the amount of the polymerization initiator used, the same procedures as in Production Example B-1 were performed to obtain solutions of the (meth)acrylic acid polymers B-2 to B-5 and B-8 to B-10 having a solid content concentration of 45% by mass.

[0464] [Production Examples B-6, B-7, B-11, and B-12]

[0465] In Production Examples B-6, B-7, B-11, and B-12, except that the weight average molecular weight (Mw) of the (meth)acrylic polymer B was adjusted to the weight average molecular weight (Mw) shown in Table 2 by adjusting at least one of the amount of the organic solvent used and the amount of the polymerization initiator used, the same procedures as in Production Example B-1 were performed to obtain solutions of the (meth)acrylic polymers B-6, B-7, B-11, and B-12 having a solid content concentration of 45% by mass.

[0466] The monomer composition (unit: mass %), hydroxyl value (unit: mgKOH / g), acid value (unit: mgKOH / g), weight average molecular weight (Mw, unit: ten thousand (indicated as "×10 4 ”)] and glass transition temperature (Tg, unit: ° C. are shown in Table 2.

[0467] The weight average molecular weight (Mw) of the (meth)acrylic polymers B-1 to B-12 is measured by the same method as the method for measuring the weight average molecular weight (Mw) of the above-mentioned specific (meth)acrylic polymer (A).

[0468] The glass transition temperature (Tg) of the (meth)acrylic polymers B-1 to B-12 was calculated by the same method as the calculation method of the glass transition temperature (Tg) of the above-mentioned specific (meth)acrylic polymer (A).

[0469] The hydroxyl value and acid value of the (meth)acrylic polymers B-1 to B-12 were calculated by the same method as the method for calculating the hydroxyl value and acid value of the above-mentioned specific (meth)acrylic polymer (A), respectively.

[0470] Among the (meth)acrylic polymers B-1 to B-12 obtained above, (meth)acrylic polymers B-1 to B-7 correspond to the specific (meth)acrylic polymer (B) in the present invention.

[0471]

[0472] The details of each monomer described in Table 2 are shown below.

[0473] "n-BA": n-butyl acrylate (alkyl acrylate monomer)

[0474] "n-BMA": n-butyl methacrylate (alkyl methacrylate monomer)

[0475] "MA": methyl acrylate (alkyl acrylate monomer)

[0476] "MMA": methyl methacrylate (alkyl methacrylate monomer)

[0477] "2EHMA": 2-ethylhexyl methacrylate (alkyl methacrylate monomer)

[0478] "4HBA": 4-hydroxybutyl acrylate (a monomer containing a hydroxyl group)

[0479] "AA": acrylic acid (monomer with carboxyl group)

[0480] In Table 2, “-” in the monomer composition column indicates that the monomer corresponding to that column is not contained.

[0481] In Table 2, the “weight average molecular weight” is indicated as “Mw”, and the “glass transition temperature” is indicated as “Tg”.

[0482] [Production of (meth)acrylic acid polymer C]

[0483] [Production Example C-1]

[0484] 100.0 parts by mass of methyl ethyl ketone (organic solvent) was added to a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux cooler.

[0485] After the air in the reaction vessel was replaced with nitrogen, the temperature in the reaction vessel was raised to 87°C. Methyl ethyl ketone was then stirred while maintaining the temperature in the reaction vessel at 87°C. A monomer mixture of 95.0 parts by mass of n-butyl acrylate (n-BA; alkyl acrylate monomer) and 5.0 parts by mass of 4-hydroxybutyl acrylate (4HBA; hydroxyl group-containing monomer) and a mixture of 100.0 parts by mass of methyl ethyl ketone and 5.0 parts by mass of 2,2'-azobisisobutyronitrile (AIBN; polymerization initiator) were gradually added to the stirred methyl ethyl ketone over approximately 2 hours. The contents in the reaction vessel were allowed to react simultaneously. After the additions were completed, the reaction was continued for approximately 4 hours to obtain a reaction product (c1). The obtained reaction product (c1) was diluted with methyl ethyl ketone to obtain a solution of (meth)acrylic polymer C-1 having a solids concentration of 45% by mass.

[0486] The “solid content concentration” referred to here refers to the mass ratio of the (meth)acrylic acid-based polymer C-1 in the solution of the (meth)acrylic acid-based polymer C-1.

[0487] The same applies to each solution of the following (meth)acrylic acid-based polymers C-2 to C-8.

[0488] [Production Examples C-2, C-5 and C-6]

[0489] In Production Examples C-2, C-5, and C-6, except that the monomer composition of the (meth)acrylic acid polymer C was changed to the monomer composition shown in Table 3, and the weight average molecular weight (Mw) of the (meth)acrylic acid polymer C was adjusted to the weight average molecular weight (Mw) shown in Table 3 by adjusting at least one of the amount of the organic solvent used and the amount of the polymerization initiator used, the same procedures as in Production Example C-1 were performed to obtain solutions of the (meth)acrylic acid polymers C-2, C-5, and C-6 having a solid content concentration of 45% by mass.

[0490] [Production Examples C-3, C-4, C-7 and C-8]

[0491] In Production Examples C-3, C-4, C-7, and C-8, except that the weight average molecular weight (Mw) of the (meth)acrylic polymer C was adjusted to the weight average molecular weight (Mw) shown in Table 3 by adjusting at least one of the amount of the organic solvent used and the amount of the polymerization initiator used, the same procedures as in Production Example C-1 were performed to obtain solutions of the (meth)acrylic polymers C-3, C-4, C-7, and C-8 having a solid content concentration of 45% by mass.

[0492] The monomer composition (unit: mass %), hydroxyl value (unit: mgKOH / g), acid value (unit: mgKOH / g), weight average molecular weight (Mw, unit: ten thousand (indicated as "×10 4 ”)] and glass transition temperature (Tg, unit: ° C. are shown in Table 3.

[0493] The weight average molecular weight (Mw) of the (meth)acrylic polymers C-1 to C-8 is measured by the same method as the method for measuring the weight average molecular weight (Mw) of the above-mentioned specific (meth)acrylic polymer (A).

[0494] The glass transition temperature (Tg) of the (meth)acrylic polymers C-1 to C-8 is calculated by the same method as the method for calculating the glass transition temperature (Tg) of the above-mentioned specific (meth)acrylic polymer (A).

[0495] The hydroxyl value and acid value of the (meth)acrylic polymers C-1 to C-8 are calculated by the same method as the method for calculating the hydroxyl value and acid value of the above-mentioned specific (meth)acrylic polymer (A).

[0496] Among the (meth)acrylic polymers C-1 to C-8 obtained above, (meth)acrylic polymers C-1 to C-5 correspond to the specific (meth)acrylic polymer (C) in the present invention.

[0497] Table 3

[0498]

[0499] The details of each monomer described in Table 3 are shown below.

[0500] "n-BA": n-butyl acrylate (alkyl acrylate monomer)

[0501] "MA": methyl acrylate (alkyl acrylate monomer)

[0502] "4HBA": 4-hydroxybutyl acrylate (a monomer containing a hydroxyl group)

[0503] In Table 3, "-" in the monomer composition column indicates that the monomer corresponding to that column is not contained.

[0504] In Table 3, the “weight average molecular weight” is indicated as “Mw”, and the “glass transition temperature” is indicated as “Tg”.

[0505] [Production of Silicone Polyisocyanate Compound X]

[0506] In a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen inlet tube, a reflux cooler, and a dropping funnel, 118.0 parts by mass of TAKENATE (registered trademark) 500 (trade name, xylene diisocyanate (XDI), manufactured by Mitsui Chemicals, Inc.) and 82.0 parts by mass of DOWSIL (registered trademark) SH-3773M (trade name, polyether-modified silicone compound, manufactured by Dow Toray Industries, Ltd.) were added. After the air in the flask was replaced with nitrogen, the temperature in the flask was raised to 50°C. Subsequently, the contents in the flask were stirred for 6 hours while maintaining the temperature at 50°C, thereby obtaining a silicone polyisocyanate compound X serving as an isocyanate crosslinking agent.

[0507] [Preparation of Adhesive Composition]

[0508] [Example 1]

[0509] In a four-necked flask equipped with a stirring blade, a thermometer, a cooler, and a dropping funnel, 222.2 parts by mass (100 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer A-1 as the specific (meth)acrylic polymer (A), 66.7 parts by mass (30 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer B-1 as the specific (meth)acrylic polymer (B), 3.0 parts by mass (1 part by mass in terms of solid content) of a solution of a (meth)acrylic polymer C-1 as the specific (meth)acrylic polymer (C), and 0.36 parts by mass of DOWSIL (registered trademark) SH-3773M [trade name, compound represented by formula (A), manufactured by Dow Toray Industries, Ltd.] as a polyether-modified silicone compound were added, and the mixture was stirred for 4 hours while the liquid temperature of the contents in the flask was maintained at approximately 25°C.

[0510] Next, 6.0 parts by mass (2.0 parts by mass based on solid content) of a diluted product of DESMODUR (registered trademark) N3400 (trade name, dimer of hexamethylene diisocyanate (HMDI), manufactured by Sumika Covestro Urethane Co., Ltd.) as an isocyanate crosslinking agent (D) was added to the flask and thoroughly stirred to obtain the adhesive composition of Example 1.

[0511] [Examples 2 and 3]

[0512] In Examples 2 and 3, the same procedures as in Example 1 were carried out except that the blending amount of the (meth)acrylic polymer C-1 as the specific (meth)acrylic polymer (C) was changed to the blending amount shown in Table 4, thereby obtaining the respective PSA compositions of Examples 2 and 3.

[0513] [Examples 4 to 7]

[0514] In Examples 4 to 7, except that the type of the specific (meth)acrylic polymer (C) was changed to the type shown in Table 4, the same operation as in Example 2 was carried out to obtain each pressure-sensitive adhesive composition of Examples 4 to 7.

[0515] [Examples 8 and 9]

[0516] In Examples 8 and 9, the same procedures as in Example 2 were carried out except that the type of the specific (meth)acrylic polymer (A) was changed to the type shown in Table 4, thereby obtaining pressure-sensitive adhesive compositions of Examples 8 and 9.

[0517] [Example 10]

[0518] In a four-necked flask equipped with a stirring blade, a thermometer, a cooler, and a dropping funnel, 222.2 parts by mass (100 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer A-4 as a specific (meth)acrylic polymer (A), 66.7 parts by mass (30 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer B-1 as a specific (meth)acrylic polymer (B), 6.0 parts by mass (2 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer C-1 as a specific (meth)acrylic polymer (C), and 0.36 parts by mass of DOWSIL (registered trademark) SH-3773M [trade name, compound represented by formula (A), manufactured by Dow Toray Industries, Ltd.] as a polyether-modified silicone compound were added, and the mixture was stirred for 4 hours while the liquid temperature of the contents in the flask was maintained at approximately 25°C.

[0519] Next, 15.0 parts by mass (5.0 parts by mass based on solid content) of a diluted product of DESMODUR (registered trademark) N3400 (trade name, dimer of hexamethylene diisocyanate (HMDI), manufactured by Sumika Covestro Urethane Co., Ltd.) as an isocyanate crosslinking agent (D) and 0.02 parts by mass of dioctyltin dilaurate (DOTDL) as a crosslinking catalyst were added to the flask and thoroughly stirred to obtain the adhesive composition of Example 10.

[0520] [Example 11]

[0521] In a four-necked flask equipped with a stirring blade, a thermometer, a cooler, and a dropping funnel, 222.2 parts by mass (100 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer A-5 as a specific (meth)acrylic polymer (A), 66.7 parts by mass (30 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer B-1 as a specific (meth)acrylic polymer (B), 6.0 parts by mass (2 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer C-1 as a specific (meth)acrylic polymer (C), and 0.36 parts by mass of DOWSIL (registered trademark) SH-3773M [trade name, compound represented by formula (A), manufactured by Dow Toray Industries, Ltd.] as a polyether-modified silicone compound were added, and the mixture was stirred for 4 hours while the liquid temperature of the contents in the flask was maintained at approximately 25°C.

[0522] Next, 15.0 parts by mass (5.0 parts by mass as solid content) of a diluted product of DESMODUR (registered trademark) N3400 (trade name, dimer of hexamethylene diisocyanate (HMDI), manufactured by Sumika Covestro Urethane Co., Ltd.) as an isocyanate crosslinking agent (D) was added to the flask and thoroughly stirred to obtain the adhesive composition of Example 11.

[0523] [Example 12]

[0524] In a four-necked flask equipped with a stirring blade, a thermometer, a cooler, and a dropping funnel, 222.2 parts by mass (100 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer A-1 as the specific (meth)acrylic polymer (A), 66.7 parts by mass (30 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer B-2 as the specific (meth)acrylic polymer (B), 6.0 parts by mass (2 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer C-1 as the specific (meth)acrylic polymer (C), and 0.36 parts by mass of DOWSIL (registered trademark) SH-3773M [trade name, compound represented by formula (A), manufactured by Dow Toray Industries, Ltd.] as a polyether-modified silicone compound were added, and the mixture was stirred for 4 hours while the liquid temperature of the contents in the flask was maintained at approximately 25°C.

[0525] Next, 15.0 parts by mass (5.0 parts by mass based on solid content) of a diluted product of DESMODUR (registered trademark) N3400 (trade name, dimer of hexamethylene diisocyanate (HMDI), manufactured by Sumika Covestro Urethane Co., Ltd.) as an isocyanate crosslinking agent (D) and 0.02 parts by mass of dioctyltin dilaurate (DOTDL) as a crosslinking catalyst were added to the flask and thoroughly stirred to obtain the adhesive composition of Example 12.

[0526] [Example 13]

[0527] In a four-necked flask equipped with a stirring blade, a thermometer, a cooler, and a dropping funnel, 222.2 parts by mass (100 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer A-1 as the specific (meth)acrylic polymer (A), 66.7 parts by mass (30 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer B-3 as the specific (meth)acrylic polymer (B), 6.0 parts by mass (2 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer C-1 as the specific (meth)acrylic polymer (C), and 0.36 parts by mass of DOWSIL (registered trademark) SH-3773M [trade name, compound represented by formula (A), manufactured by Dow Toray Industries, Ltd.] as a polyether-modified silicone compound were added, and the mixture was stirred for 4 hours while the liquid temperature of the contents in the flask was maintained at approximately 25°C.

[0528] Next, 15.0 parts by mass (5.0 parts by mass as solid content) of a diluted product of DESMODUR (registered trademark) N3400 [trade name, dimer of hexamethylene diisocyanate (HMDI), manufactured by Sumika Covestro Urethane Co., Ltd.] as an isocyanate crosslinking agent (D) was added to the flask and thoroughly stirred to obtain the adhesive composition of Example 13.

[0529] [Examples 14 and 15]

[0530] In Examples 14 and 15, the same procedures as in Example 2 were carried out except that the blending amount of the specific (meth)acrylic polymer B-1 was changed to the blending amount shown in Table 4, thereby obtaining respective PSA compositions of Examples 14 and 15.

[0531] [Examples 16 to 19]

[0532] In Examples 16 to 19, except that the type of the specific (meth)acrylic polymer (B) was changed to the type shown in Table 5, the same operation as in Example 2 was carried out to obtain each pressure-sensitive adhesive composition of Examples 16 to 19.

[0533] [Examples 20 and 21]

[0534] In Examples 20 and 21, the same procedures as in Example 2 were carried out except that the amount of DESMODUR (registered trademark) N3400 as the isocyanate crosslinking agent (D) was changed to the amounts shown in Table 5, thereby obtaining adhesive compositions of Examples 20 and 21.

[0535] [Examples 22 and 23]

[0536] In Examples 22 and 23, the same procedures as in Example 2 were carried out except that the type of the isocyanate crosslinking agent (D) was changed to the types shown in Table 5, thereby obtaining adhesive compositions of Examples 22 and 23.

[0537] [Example 24]

[0538] In Example 24, the same procedures as in Example 2 were carried out except that the type and blending amount of the isocyanate crosslinking agent (D) were changed to the type and blending amount shown in Table 5, thereby obtaining a pressure-sensitive adhesive composition of Example 24.

[0539] [Example 25]

[0540] In Example 25, the same procedures as in Example 2 were carried out except that DOWSIL (registered trademark) SH-3773M as a polyether-modified silicone compound was not added to obtain a pressure-sensitive adhesive composition of Example 25.

[0541] [Example 26]

[0542] In a four-necked flask equipped with a stirring blade, a thermometer, a cooler, and a dropping funnel, 222.2 parts by mass (100 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer A-1 as the specific (meth)acrylic polymer (A), 66.7 parts by mass (30 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer B-1 as the specific (meth)acrylic polymer (B), 6.0 parts by mass (2 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer C-1 as the specific (meth)acrylic polymer (C), and 0.36 parts by mass of DOWSIL (registered trademark) SH-3773M [trade name, compound represented by formula (A), manufactured by Dow Toray Industries, Ltd.] as a polyether-modified silicone compound were added, and the mixture was stirred for 4 hours while the liquid temperature of the contents in the flask was maintained at approximately 25°C.

[0543] Next, 6.0 parts by mass (2.0 parts by mass based on solid content) of a diluted product of DESMODUR (registered trademark) N3400 [trade name, dimer of hexamethylene diisocyanate (HMDI), manufactured by Sumika Covestro Urethane Co., Ltd.] as an isocyanate-based crosslinking agent (D) and 0.1 parts by mass of a metal chelate-based crosslinking agent, i.e., aluminum chelate A [trade name, aluminum triacetylacetonate, manufactured by Kawaken Fine Chemicals Co., Ltd.] as another crosslinking agent were added to the flask and stirred thoroughly to obtain the adhesive composition of Example 26.

[0544] [Example 27]

[0545] In a four-necked flask equipped with a stirring blade, a thermometer, a cooler, and a dropping funnel, 222.2 parts by mass (100 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer A-1 as a specific (meth)acrylic polymer (A), 66.7 parts by mass (30 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer B-1 as a specific (meth)acrylic polymer (B), and 100 parts by mass (30 parts by mass in terms of solid content) of a (meth)acrylic polymer B-2 as a specific (meth)acrylic polymer (C) were added. 6.0 parts by mass of a solution of compound C-1 (2 parts by mass in terms of solid content), 0.36 parts by mass of DOWSIL (registered trademark) SH-3773M [trade name, compound represented by formula (A), manufactured by Dow Toray Industries, Ltd.] as a polyether-modified silicone compound, and 0.25 parts by mass of LiTFS [LiCF3SO3 (lithium trifluoromethanesulfonate), manufactured by Morita Chemical Industry Co., Ltd.] as an antistatic agent were added, and stirred for 4 hours while maintaining the liquid temperature of the contents in the flask at around 25°C.

[0546] Next, 6.0 parts by mass (2.0 parts by mass as solid content) of a diluted product of DESMODUR (registered trademark) N3400 [trade name, dimer of hexamethylene diisocyanate (HMDI), manufactured by Sumika Covestro Urethane Co., Ltd.] as an isocyanate crosslinking agent (D) was added to the flask, and the mixture was thoroughly stirred to obtain the adhesive composition of Example 27.

[0547] [Example 28]

[0548] In a four-necked flask equipped with a stirring blade, a thermometer, a cooler, and a dropping funnel, 222.2 parts by mass (100 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer A-1 as the specific (meth)acrylic polymer (A), 66.7 parts by mass (30 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer B-1 as the specific (meth)acrylic polymer (B), 6.0 parts by mass (2 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer C-1 as the specific (meth)acrylic polymer (C), and 0.36 parts by mass of DOWSIL (registered trademark) SH-3773M [trade name, compound represented by formula (A), manufactured by Dow Toray Industries, Ltd.] as a polyether-modified silicone compound were added, and the mixture was stirred for 4 hours while the liquid temperature of the contents in the flask was maintained at approximately 25°C.

[0549] Next, 6.0 parts by mass (2.0 parts by mass as solid content) of a diluted product of DESMODUR (registered trademark) N3400 (trade name, dimer of hexamethylene diisocyanate (HMDI), manufactured by Sumika Covestro Urethane Co., Ltd.) as an isocyanate crosslinking agent (D) and 0.25 parts by mass of a silicone polyisocyanate compound X as an isocyanate crosslinking agent (D) were added to the flask and thoroughly stirred to obtain the adhesive composition of Example 28.

[0550] [Example 29]

[0551] In a four-necked flask equipped with a stirring blade, a thermometer, a cooler, and a dropping funnel, 222.2 parts by mass (100 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer A-1 as the specific (meth)acrylic polymer (A), 66.7 parts by mass (30 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer B-1 as the specific (meth)acrylic polymer (B), 6.0 parts by mass (2 parts by mass in terms of solid content) of a solution of a (meth)acrylic polymer C-1 as the specific (meth)acrylic polymer (C), and 0.36 parts by mass of DOWSIL (registered trademark) SH-3773M [trade name, compound represented by formula (A), manufactured by Dow Toray Industries, Ltd.] as a polyether-modified silicone compound were added, and the mixture was stirred for 4 hours while the liquid temperature of the contents in the flask was maintained at approximately 25°C.

[0552] Next, 6.0 parts by mass (2.0 parts by mass based on solid content) of a diluted product of DESMODUR (registered trademark) N3400 (trade name, dimer of hexamethylene diisocyanate (HMDI), manufactured by Sumika Covestro Urethane Co., Ltd.) as an isocyanate crosslinking agent (D) and 0.02 parts by mass of dioctyltin dilaurate (DOTDL) as a crosslinking catalyst were added to the flask and thoroughly stirred to obtain the adhesive composition of Example 29.

[0553] [Comparative Example 1]

[0554] In Comparative Example 1, the same procedures as in Example 2 were carried out except that 100 parts by mass of (meth)acrylic polymer A-6 was added as a comparative polymer instead of 100 parts by mass of (meth)acrylic polymer A-1 as the specific (meth)acrylic polymer (A). Thus, a pressure-sensitive adhesive composition of Comparative Example 1 was obtained.

[0555] [Comparative Example 2]

[0556] In Comparative Example 2, the same procedures as in Example 2 were carried out except that 30 parts by mass of (meth)acrylic polymer B-8 was added as a comparative polymer instead of 30 parts by mass of (meth)acrylic polymer B-1 as the specific (meth)acrylic polymer (B). Thus, a pressure-sensitive adhesive composition of Comparative Example 2 was obtained.

[0557] [Comparative Example 3]

[0558] In Comparative Example 3, the same operation as in Example 2 was carried out except that the specific (meth)acrylic polymer (B) was not blended, thereby obtaining a pressure-sensitive adhesive composition of Comparative Example 3.

[0559] [Comparative Examples 4 and 5]

[0560] In Comparative Examples 4 and 5, the same procedures as in Example 2 were carried out except that the blending amount of the specific (meth)acrylic polymer B-1 was changed to the blending amount shown in Table 6, thereby obtaining respective PSA compositions of Comparative Examples 4 and 5.

[0561] [Comparative Example 6]

[0562] In Comparative Example 6, the same procedures as in Example 2 were carried out except that 30 parts by mass of (meth)acrylic polymer B-9 was added as a comparative polymer instead of 30 parts by mass of (meth)acrylic polymer B-1 as the specific (meth)acrylic polymer (B). A pressure-sensitive adhesive composition of Comparative Example 6 was obtained.

[0563] [Comparative Example 7]

[0564] In Comparative Example 7, the same procedures as in Example 2 were carried out except that 30 parts by mass of the (meth)acrylic polymer B-10 as a comparative polymer was added instead of 30 parts by mass of the (meth)acrylic polymer B-1 as the specific (meth)acrylic polymer (B). A pressure-sensitive adhesive composition of Comparative Example 7 was obtained.

[0565] [Comparative Example 8]

[0566] In Comparative Example 8, the same procedures as in Example 2 were carried out except that 30 parts by mass of the (meth)acrylic polymer B-11 as a comparative polymer was added instead of 30 parts by mass of the (meth)acrylic polymer B-1 as the specific (meth)acrylic polymer (B) to obtain a pressure-sensitive adhesive composition of Comparative Example 8.

[0567] [Comparative Example 9]

[0568] In Comparative Example 9, the same procedures as in Example 2 were carried out except that 30 parts by mass of the (meth)acrylic polymer B-12 was added as a comparative polymer instead of 30 parts by mass of the (meth)acrylic polymer B-1 as the specific (meth)acrylic polymer (B) to obtain a PSA composition of Comparative Example 9.

[0569] [Comparative Example 10]

[0570] In Comparative Example 10, a pressure-sensitive adhesive composition of Comparative Example 10 was obtained by performing the same operation as in Example 2, except that the specific (meth)acrylic polymer (C) was not blended.

[0571] [Comparative Examples 11 and 12]

[0572] In Comparative Examples 11 and 12, the same procedures as in Example 2 were carried out except that the blending amount of the specific (meth)acrylic polymer C-1 was changed to the blending amount shown in Table 6, thereby obtaining respective PSA compositions of Comparative Examples 11 and 12.

[0573] [Comparative Example 13]

[0574] In Comparative Example 13, the same procedures as in Example 2 were carried out except that 2 parts by mass of the (meth)acrylic polymer C-6 was added as a comparative polymer instead of 2 parts by mass of the (meth)acrylic polymer C-1 as the specific (meth)acrylic polymer (C). Thus, a pressure-sensitive adhesive composition of Comparative Example 13 was obtained.

[0575] [Comparative Example 14]

[0576] In Comparative Example 14, the same procedures as in Example 2 were carried out except that 2 parts by mass of the (meth)acrylic polymer C-7 was added as a comparative polymer instead of 2 parts by mass of the (meth)acrylic polymer C-1 as the specific (meth)acrylic polymer (C) to obtain a PSA composition of Comparative Example 14.

[0577] [Comparative Example 15]

[0578] In Comparative Example 15, the same procedures as in Example 2 were carried out except that 2 parts by mass of the (meth)acrylic polymer C-8 was added as a comparative polymer instead of 2 parts by mass of the (meth)acrylic polymer C-1 as the specific (meth)acrylic polymer (C), to obtain a pressure-sensitive adhesive composition of Comparative Example 15.

[0579] [Comparative Example 16]

[0580] In Comparative Example 16, the same operations as in Example 2 were performed except that TETRAD (registered trademark)-X [trade name, manufactured by Mitsubishi Gas Chemical Co., Ltd.], an epoxy crosslinking agent, was used as a comparative crosslinking agent instead of the isocyanate crosslinking agent (D). To obtain the adhesive composition of Comparative Example 16,

[0581]

[0582]

[0583]

[0584] In Tables 4 to 6, “-” indicates that the corresponding component is not contained.

[0585] All the blending amounts in Tables 4 to 6 are values based on solid content.

[0586] In Table 5, “silicone-based polyisocyanate compound X” is described as “compound X”.

[0587] The details of each cross-linking agent described in Tables 4 to 6 are shown below.

[0588] Isocyanate crosslinking agent (D)

[0589] "N3400" [Trade name: DESMODUR (registered trademark) N3400, dimer of hexamethylene diisocyanate (HMDI), manufactured by Sumika Covestro Urethane Co., Ltd.]

[0590] "N3300" [Trade name: SUMIDUR (registered trademark) N3300, a trimer of hexamethylene diisocyanate (HMDI), manufactured by Sumika Covestro Urethane Co., Ltd.]

[0591] "L-45E" [Trade name: CORONATE (registered trademark) L-45E, an adduct of toluene diisocyanate (TDI) and trimethylolpropane (TMP), manufactured by Tosoh Corporation]

[0592] "D-120" [Trade name: TAKENATE (registered trademark) D-120, an adduct of xylene diisocyanate (XDI) and trimethylolpropane (TMP), manufactured by Mitsui Chemicals, Inc.]

[0593] "Compound X": Silicone polyisocyanate compound X

[0594] <Other cross-linking agents>

[0595] "Aluminum Chelate A" [trade name, aluminum triacetylacetonate, manufactured by Kawaken Fine Chemicals Co., Ltd.]: Metal chelate-based crosslinking agent

[0596] Comparison of crosslinking agents

[0597] "TETRAD-X" [Trade name: TETRAD (registered trademark)-X, manufactured by Mitsubishi Gas Chemical Co., Ltd.]: Epoxy crosslinking agent

[0598] [evaluate]

[0599] The following evaluations were performed using the adhesive compositions prepared above.

[0600] The results are shown in Tables 7 to 9.

[0601] 1. Peel force

[0602] <Preparation of protective film for peel strength evaluation>

[0603] The coating amount after drying is 15 g / m 2 The adhesive composition was applied to a polyethylene terephthalate (PET) film substrate (trade name: TEIJIN (registered trademark) TETORON (registered trademark) film, model: G2, thickness: 38 μm, manufactured by Teijin Film Solutions Limited) to form a coating film. The resulting coating film was then dried at 100°C for 60 seconds using a hot air circulation dryer to form an adhesive film on the substrate.

[0604] Next, the exposed surface of the adhesive film formed on the substrate was overlaid with the treated surface of a release film (trade name: FILMBYNA (registered trademark) 100E-0010 No. 23, thickness: 100 μm, manufactured by Fujimori Industries, Ltd.), which had been surface-treated with a silicone release agent. The two films were then pressed together and bonded using a pressure nip roller. The adhesive film was then aged for 96 hours in an environment of 23°C and 50% RH to produce a protective film for peel strength evaluation having a laminated structure of substrate / adhesive layer / release film.

[0605] <Evaluation Test>

[0606] (1) Initial

[0607] (1-1) Low-speed peeling force

[0608] The protective film for evaluating the peeling strength produced above was cut into a size of 25 mm×150 mm to prepare a protective film sheet for evaluating the peeling strength.

[0609] Next, the peeling film was peeled off from the protective film sheet prepared for peeling strength evaluation, and the surface of the adhesive layer exposed by the peeling was overlapped with the surface of a polyethylene terephthalate (PET) film [trade name: COSMOSHINE (registered trademark) A4300, thickness: 300 μm, manufactured by Toyobo Co., Ltd.] as the adherend, and then press-bonded using a desktop laminator to prepare a test sample.

[0610] The test sample was left in an environment at 23°C and 50% RH for 24 hours. Next, using a single-column materials testing machine (Model: STA-1225, manufactured by A&D Company, Limited), the peel strength (unit: N / 25 mm) was measured when a protective film sheet for peel strength evaluation (composition: adhesive layer / substrate) was peeled 180° along the long side (150 mm) from a PET film at a peel speed of 0.3 m / min in an environment at 23°C and 50% RH. The low-speed peel strength was then evaluated according to the following evaluation criteria.

[0611] If the evaluation result was "AA," "A," or "B," the pressure-sensitive adhesive layer was judged to exhibit appropriate low-speed peeling strength.

[0612] -Evaluation Criteria-

[0613] AA: Peel force is 0.18 N / 25 mm or more.

[0614] A: The peel force is 0.13 N / 25 mm or more and less than 0.18 N / 25 mm.

[0615] B: The peel force is 0.09 N / 25 mm or more and less than 0.13 N / 25 mm.

[0616] C: Peel force is less than 0.09N / 25mm.

[0617] (1-2) High-speed peeling force

[0618] A test sample was obtained by the same procedure as in the above-mentioned "(1-1) Low-speed peeling force".

[0619] The test sample was left in an environment at 23°C and 50% RH for 24 hours. Next, using a peel tester (Model: Horizontal TE-720, manufactured by Tester Sangyo Co., Ltd.), the peel strength (unit: N / 25 mm) was measured when a protective film sheet for peel strength evaluation (composition: adhesive layer / substrate) was peeled 180° along the long side (150 mm) from a PET film at a peel speed of 30 m / min in an environment at 23°C and 50% RH. High-speed peel strength was then evaluated according to the following evaluation criteria.

[0620] If the evaluation result was "AA", "A", or "B", it was determined that the pressure-sensitive adhesive layer exhibited appropriate high-speed peeling force.

[0621] -Evaluation Criteria-

[0622] AA: Peel force is less than 0.50N / 25mm.

[0623] A: The peel force is 0.50 N / 25 mm or more and less than 0.75 N / 25 mm.

[0624] B: The peel force is 0.75 N / 25 mm or more and less than 1.00 N / 25 mm.

[0625] C: Peel force is 1.00 N / 25 mm or more.

[0626] (1-3) Balance between low-speed peeling force and high-speed peeling force

[0627] The balance between the low-speed peel force and the high-speed peel force was evaluated based on the low-speed peel force value measured in the above “(1-1) Low-speed peel force” and the high-speed peel force value measured in the above “(1-2) High-speed peel force”.

[0628] Specifically, the balance between the low-speed peel force and the high-speed peel force was evaluated according to the following evaluation criteria based on the value obtained by dividing the low-speed peel force value by the high-speed peel force value and rounding off to the third decimal place.

[0629] If the evaluation result is "AA", "A", or "B", it is judged that the pressure-sensitive adhesive layer has a good balance between the low-speed peeling force and the high-speed peeling force.

[0630] -Evaluation Criteria-

[0631] AA: "Low-speed peel force / high-speed peel force" is 0.30 or more.

[0632] A: "Low-speed peel force / high-speed peel force" is 0.20 or more and less than 0.30.

[0633] B: "Low-speed peel force / high-speed peel force" is 0.10 or more and less than 0.20.

[0634] C: "Low-speed peel force / high-speed peel force" is less than 0.10.

[0635] (2) After accelerated test

[0636] (2-1) Suppression of tearing phenomenon

[0637] A test sample was obtained by the same procedure as in the above-mentioned "(1-1) Low-speed peeling force".

[0638] The test sample was subjected to an accelerated test in a hot air circulation dryer (Model: PHH-200, manufactured by ESPECCORP.) set at 80°C for 250 hours. After the accelerated test, the test sample was removed from the hot air circulation dryer and allowed to stand for 24 hours in an environment with an ambient temperature of 23°C and 50% RH. Next, a protective film sheet for evaluating peel strength (composition: adhesive layer / substrate) was peeled 180° along its long side (150 mm) from the PET film using a peel tester (Model: Horizontal TE-720, manufactured by Tester Sangyo Co., Ltd.) at a peel rate of 30 m / min in an environment with an ambient temperature of 23°C and 50% RH. After blowing air onto the surface of the peeled PET film, the surface condition was visually observed. The suppression of peeling was then evaluated according to the following evaluation criteria.

[0639] If the evaluation result is "AA", "A" or "B", it is judged that the pressure-sensitive adhesive layer is unlikely to be torn off even when peeled off from the adherend at high speed after being attached to the adherend for a long time.

[0640] -Evaluation Criteria-

[0641] AA: No streaky defects were observed.

[0642] A: Slightly skeletal defects were detected.

[0643] B: Slight streaky defects were observed, but within an acceptable range.

[0644] C: Streak-like defects were clearly observed.

[0645]

[0646]

[0647]

[0648] As shown in Tables 7 and 8, it was confirmed that the adhesive layers formed from the adhesive compositions of Examples 1 to 29 had a good balance between low-speed peeling force and high-speed peeling force, and were less likely to tear even when peeled from an adherend at high speed after being attached to the adherend for a long time. The adhesive compositions of Examples 1 to 29 comprised: a (meth)acrylic polymer (A) having at least one of a hydroxyl group and a carboxyl group and a weight-average molecular weight in the range of more than 200,000 and less than 2,000,000 [i.e., a specific (meth)acrylic polymer (A)]; a (meth)acrylic polymer (A) having at least one of a hydroxyl group and a carboxyl group, a glass transition temperature in the range of 0°C to 45°C, and a weight-average molecular weight in the range of 6,000 to 150,000. an acrylic polymer (B) [i.e., a specific (meth)acrylic polymer (B)], a (meth)acrylic polymer (C) having a glass transition temperature of -30°C or lower and a weight average molecular weight of 6,000 to 150,000 [i.e., a specific (meth)acrylic polymer (C)], and an isocyanate crosslinking agent (D); wherein the content of the specific (meth)acrylic polymer (B) is in the range of 7 parts by mass to 70 parts by mass relative to 100 parts by mass of the specific (meth)acrylic polymer (A), and the content of the specific (meth)acrylic polymer (C) is in the range of 0.5 parts by mass to 5 parts by mass relative to 100 parts by mass of the specific (meth)acrylic polymer (A).

[0649] On the other hand, as shown in Table 9, the PSA layer formed from the PSA composition of Comparative Example 1 in which the (meth)acrylic polymer (A) had neither hydroxyl nor carboxyl groups did not peel from the adherend, and the evaluation test could not be performed.

[0650] It was confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 2, in which the (meth)acrylic polymer (B) did not have a hydroxyl group or a carboxyl group, had a poor balance between low-speed peeling force and high-speed peeling force.

[0651] It was confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 3 that did not contain the specific (meth)acrylic polymer (B) had a poor balance between low-speed peeling force and high-speed peeling force.

[0652] It was confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 4, in which the content of the specific (meth)acrylic polymer (B) was less than 7 parts by mass per 100 parts by mass of the specific (meth)acrylic polymer (A), had a poor balance between low-speed peel strength and high-speed peel strength.

[0653] It was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 5, in which the content of the specific (meth)acrylic polymer (B) exceeded 70 parts by mass relative to 100 parts by mass of the specific (meth)acrylic polymer (A), was easily torn off when adhered to an adherend for a long time and then peeled off from the adherend at high speed.

[0654] It was confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 6, in which the (meth)acrylic polymer (B) had a glass transition temperature of less than 0° C., had a poor balance between low-speed peel strength and high-speed peel strength.

[0655] It was confirmed that the PSA layer formed from the PSA composition of Comparative Example 7, in which the glass transition temperature of the (meth)acrylic polymer (B) exceeded 45° C., was easily torn off when adhered to an adherend for a long time and then peeled off at high speed.

[0656] It was confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 8, in which the (meth)acrylic polymer (B) had a weight-average molecular weight of less than 6,000, had a poor balance between low-speed peeling force and high-speed peeling force.

[0657] It was confirmed that the PSA layer formed from the PSA composition of Comparative Example 9 in which the (meth)acrylic polymer (B) had a weight average molecular weight exceeding 150,000 was easily torn off when adhered to an adherend for a long time and then peeled off at high speed.

[0658] It was confirmed that the PSA layer formed from the PSA composition of Comparative Example 10 not containing the specific (meth)acrylic polymer (C) was easily torn off when adhered to an adherend for a long time and then peeled off at high speed.

[0659] It was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 11, in which the content of the specific (meth)acrylic polymer (C) is less than 0.5 parts by mass relative to 100 parts by mass of the specific (meth)acrylic polymer (A), is easily torn off when it is adhered to an adherend for a long time and then peeled off from the adherend at high speed.

[0660] It was confirmed that the PSA layer formed from the PSA composition of Comparative Example 12, in which the content of the specific (meth)acrylic polymer (C) exceeded 5 parts by mass relative to 100 parts by mass of the specific (meth)acrylic polymer (A), had a poor balance between low-speed peel strength and high-speed peel strength.

[0661] It was confirmed that the PSA layer formed from the PSA composition of Comparative Example 13, in which the glass transition temperature of the (meth)acrylic polymer (C) exceeded -30°C, was easily torn off when adhered to an adherend for a long time and then peeled off at high speed.

[0662] It was confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 14, in which the (meth)acrylic polymer (C) had a weight-average molecular weight of less than 6,000, had a poor balance between low-speed peeling force and high-speed peeling force.

[0663] It was confirmed that the PSA layer formed from the PSA composition of Comparative Example 15 in which the (meth)acrylic polymer (C) had a weight average molecular weight exceeding 150,000 was easily torn off when adhered to an adherend for a long time and then peeled off at high speed.

[0664] It was confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 16 containing an epoxy-based crosslinking agent instead of an isocyanate-based crosslinking agent had an unfavorable balance between low-speed peeling force and high-speed peeling force.

Claims

1. An adhesive composition for an optical member protective film, comprising: A (meth)acrylic polymer A having at least one of a hydroxyl group and a carboxyl group, a hydroxyl value in the range of 0.3 mgKOH / g to 40 mgKOH / g, or an acid value in the range of 0.7 mgKOH / g to 24 mgKOH / g, a glass transition temperature of -40°C or lower, and a weight-average molecular weight of more than 200,000 to 2,000,000. A (meth)acrylic polymer B having at least one of a hydroxyl group and a carboxyl group, wherein the content of the structural unit derived from the monomer having a hydroxyl group is in the range of 0.1% by mass to 10% by mass relative to all the structural units, or the content of the structural unit derived from the monomer having a carboxyl group is in the range of 0.1% by mass to 5% by mass relative to all the structural units, wherein the glass transition temperature is in the range of 0°C to 45°C, and the weight average molecular weight is in the range of 6,000 to 150,000. A (meth)acrylic polymer C having a glass transition temperature of -30°C or lower, containing no structural units derived from a monomer having a carboxyl group, or containing structural units derived from a monomer having a carboxyl group in a range of more than 0% by mass and less than 1% by mass relative to all structural units, and having a weight-average molecular weight of 6,000 or more and 150,000 or less, and Isocyanate crosslinking agent D; The content of the (meth)acrylic polymer B is in a range of 7 parts by mass or more and 70 parts by mass or less relative to 100 parts by mass of the (meth)acrylic polymer A. The content of the (meth)acrylic polymer C relative to 100 parts by mass of the (meth)acrylic polymer A is in the range of 0.5 parts by mass or more and 5 parts by mass or less.

2. The adhesive composition for an optical member protective film according to claim 1, wherein The (meth)acrylic polymer B has a hydroxyl group and has a hydroxyl value in a range of 0.3 mgKOH / g to 40 mgKOH / g.

3. The adhesive composition for an optical member protective film according to claim 1 or claim 2, wherein The (meth)acrylic polymer B has a carboxyl group and has an acid value in a range of 0.7 mgKOH / g to 24 mgKOH / g.

4. The adhesive composition for an optical member protective film according to claim 1 or claim 2, wherein The (meth)acrylic polymer C has a hydroxyl value of 40 mgKOH / g or less.

5. The adhesive composition for an optical member protective film according to claim 1 or claim 2, wherein The weight average molecular weight of the (meth)acrylic polymer C is smaller than the weight average molecular weight of the (meth)acrylic polymer B.

6. The adhesive composition for an optical member protective film according to claim 1 or claim 2, wherein Contains antistatic agent.

7. The adhesive composition for an optical member protective film according to claim 1 or claim 2, wherein Contains polyether-modified silicone compounds. 8 . An optical member protective film comprising a substrate and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer is provided on the substrate and is formed from the pressure-sensitive adhesive composition for an optical member protective film according to claim 1 .

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