Adhesive composition

Abstract

To provide a superior adhesive composition that exhibits low temperature dependence of storage modulus both in weak-adhesion and strong-adhesion urethane adhesives, and achieves high adhesion or bonding reliability from low to high temperatures.SOLUTION: This adhesive composition comprises a urethane prepolymer (A) obtained by reacting a polyether polyol (a1) having carbonate bonds with an isocyanate compound (b). Preferably, the adhesive composition further contains a crosslinking agent such that a reaction equivalent ratio (x) / (y) of a reactive functional group (x) in the crosslinking agent to an active hydrogen group (y) in the urethane prepolymer (A) is 0.5 to 1.25.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a novel urethane-based pressure-sensitive adhesive composition. [Background technology]

[0002] Pressure-sensitive adhesives are used in, for example, tapes, labels, stickers, cosmetic sheets, anti-slip sheets, double-sided pressure-sensitive adhesive tapes, and the like, and in recent years have been used in various fields, such as for adhesion or bonding of liquid crystal displays and touch panels of personal computers, televisions, smartphones, and the like.

[0003] Known examples of adhesives include acrylic adhesives, rubber adhesives, silicone adhesives, urethane adhesives, and oxyalkylene adhesives. Recently, there has been a trend toward the use of acrylic adhesives in a wide range of applications, from strong adhesives with strong adhesive strength to weak adhesives with very little adhesive strength.

[0004] However, acrylic adhesives have problems such as odor and skin irritation when acrylic monomers remain in the adhesive. Furthermore, acrylic adhesives tend to increase their adhesive strength and migration over time after application to an adherend. This can lead to problems such as adhesive residue on the adherend and insufficient removability. Furthermore, acrylic adhesives use comonomers with high glass transition temperatures to exert cohesive strength, which increases their storage modulus at low temperatures, resulting in insufficient adhesive strength and poor low-temperature properties.

[0005] Therefore, if a comonomer with a low glass transition temperature is used to obtain low-temperature properties, or if the crosslinking agent is reduced and reactive functional groups in the acrylic polymer remain to form an adhesive, the storage modulus at low temperatures will decrease and adhesive strength will improve, but conversely, heat sagging will occur at high temperatures, making it more likely that adhesive will remain on the adherend, and there will also be problems with peeling during application.

[0006] In contrast, urethane-based adhesives have a lower temperature dependency of storage modulus compared to acrylic-based adhesives, and are therefore said to be more likely to achieve both low-temperature and high-temperature properties. However, while conventional urethane adhesives have been able to achieve low temperature dependence of storage modulus in weak adhesives, strong adhesives have had the problem of their storage modulus easily decreasing, especially at high temperatures. A decrease in storage modulus not only leads to poor removability (e.g., adhesive residue) and poor adhesion reliability (e.g., peeling during application), but also to poor productivity due to poor punching processability. For these reasons, there has been a demand for the development of a urethane-based adhesive with low temperature dependence of the storage modulus over a wide range of adhesive strength, from weak to strong.

[0007] For example, Patent Document 1 discloses a urethane pressure-sensitive adhesive composition that has flexibility at room temperature and maintains elasticity at high temperatures while ensuring adhesive strength over a wide range of temperatures. However, the urethane pressure-sensitive adhesive composition disclosed in Patent Document 1, which has a storage modulus of 0.02 MPa at 80°C, is not sufficiently hard for high-temperature durability, and there is a concern that the pressure-sensitive adhesive composition may peel or lift off from the adherend during long-term use.

[0008] Patent Document 2 discloses a pressure-sensitive adhesive composition in which 5 to 30 parts by weight of a polyisocyanate curing agent is added to 100 parts by weight of a urethane resin. The pressure-sensitive adhesive composition in Patent Document 2 has a storage modulus of 0.5 to 1.6 MPa at 23°C and a storage modulus of 0.5 to 1.0 MPa at 80°C, which are higher values ​​than the pressure-sensitive adhesive composition described in Patent Document 1. However, this reflects a decrease in adhesive strength, raising concerns about peeling from the adherend.

[0009] Patent Document 3 discloses a pressure-sensitive adhesive containing a polyurethane resin whose essential constituent monomers are a polyol component having no amino group and an isocyanate component. The pressure-sensitive adhesive of Patent Document 3 has a sufficiently high adhesive strength to glass of 5 to 50 N / 25 mm, but has a weight-average molecular weight of 80,000 to 500,000, which may make the resulting pressure-sensitive adhesive difficult to handle. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-204467 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-026418 [Patent Document 3] International Publication No. 2021 / 075558 Summary of the Invention [Problem to be solved by the invention]

[0011] The object of the present invention is to solve the above problems and to provide an excellent pressure-sensitive adhesive composition that has low temperature dependence of storage modulus and can achieve high adhesion or adhesive reliability from low to high temperatures, not only for weakly adhesive urethane pressure-sensitive adhesives but also for strongly adhesive urethane-based pressure-sensitive adhesives. [Means for solving the problem]

[0012] As a result of extensive research to solve the above-mentioned problems, the present inventors have found that a specific urethane prepolymer obtained using a polyether polyol containing a carbonate bond as a raw material not only makes it possible to obtain urethane-based pressure-sensitive adhesives with a wide range of adhesive strengths, but also makes it possible to maintain a high storage modulus even at high temperatures, particularly in strong adhesive urethane-based pressure-sensitive adhesives, and have thus completed the present invention. That is, the gist of the present invention is as follows.

[0013] [1] A pressure-sensitive adhesive composition comprising a urethane prepolymer (A) obtained by reacting a polyether polyol (a1) having a carbonate bond with an isocyanate compound (b).

[0014] [2] The pressure-sensitive adhesive composition according to [1], wherein the urethane prepolymer (A) has a number average molecular weight, calculated as a standard polystyrene molecular weight, of 15,000 or more and 50,000 or less.

[0015] [3] The pressure-sensitive adhesive composition according to [1] or [2], wherein the hydroxyl value of the carbonate bond-containing polyether polyol (a1) is 45 mgKOH / g or more and 130 mgKOH / g or less.

[0016] [4] The pressure-sensitive adhesive composition according to any one of [1] to [3], wherein the number average molecular weight calculated from the hydroxyl value of the polyether polyol (a1) having a carbonate bond is 860 or more and 2,500 or less.

[0017] [5] The urethane prepolymer (A) has a storage modulus (G') at -30°C after curing under the following curing conditions: -30 ) and storage modulus at 100°C (G' 100 ) ratio (G' -30 ) / (G' 100 The pressure-sensitive adhesive composition according to any one of [1] to [4], which provides a cured product in which the value of (a) is 50 or less. [Curing conditions] A pressure-sensitive adhesive composition (i) is obtained by blending a urethane prepolymer (A) with a crosslinking agent, Takenate® D-101E (Mitsui Chemicals, Inc.), so that the reactive functional group (x) of the crosslinking agent and the active hydrogen group (y) of the urethane prepolymer (A) are in a reaction equivalent ratio (x) / (y) of 0.5 to 1.25. The resulting pressure-sensitive adhesive composition (i) is applied to the release surface of a release-treated polyethylene terephthalate film (75 μm thick) "SP-PET-03-BU" (Mitsui Chemicals Tocello, Inc.) using an applicator to give a film thickness of 1 mm after curing. The composition is then dried at 130°C for 5 minutes and then aged at 40°C for one week to allow it to cure.

[0018] [6] The pressure-sensitive adhesive composition according to any one of [1] to [5], wherein the urethane prepolymer (A) provides a cured product having a gel fraction of 30 mass % or more after curing under the following curing conditions: [Curing conditions] A pressure-sensitive adhesive composition (i) is obtained by blending a urethane prepolymer (A) with a crosslinking agent, Takenate® D-101E (Mitsui Chemicals, Inc.), so that the reactive functional group (x) of the crosslinking agent and the active hydrogen group (y) of the urethane prepolymer (A) are in a reaction equivalent ratio (x) / (y) of 0.5 to 1.25. The resulting pressure-sensitive adhesive composition (i) is applied to the adhesion-treated surface of an adhesion-friendly polyethylene terephthalate film (38 μm thick) "Cosmoshine A4360" (Toyobo Co., Ltd.) using an applicator so that the cured film thickness is 25 μm. The film is then dried at 130°C for 5 minutes and then aged at 40°C for one week to allow it to cure.

[0019] [7] The pressure-sensitive adhesive composition according to any one of [1] to [6], further comprising a crosslinking agent.

[0020] [8] The pressure-sensitive adhesive composition according to [7], which contains the urethane prepolymer (A) and the crosslinking agent so that the reaction equivalent ratio (x) / (y) between the reactive functional group (x) of the crosslinking agent and the active hydrogen group (y) of the urethane prepolymer (A) is 0.5 to 1.25.

[0021] [9] The storage modulus (G') at -30°C of the cured product obtained by the reaction of the active hydrogen group (y) with the reactive functional group (x) -30 ) and storage modulus at 100°C (G' 100 ) ratio (G' -30 ) / (G' 100 ) is 50 or less.

[0022]

[10] The pressure-sensitive adhesive composition according to [8] or [9], wherein a gel fraction of a cured product obtained by the reaction of the active hydrogen group (y) with the reactive functional group (x) is 30 to 90 mass %. [Effects of the Invention]

[0023] The pressure-sensitive adhesive composition of the present invention can reduce the temperature dependence of storage modulus not only in weakly adhesive pressure-sensitive adhesives but also in strongly adhesive pressure-sensitive adhesives, thereby enabling the adhesive properties to be maintained even in high temperature ranges, and not only can the adhesive properties be excellent in removability but also high adhesion and adhesive reliability can be expected from low to high temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0024] Representative embodiments for carrying out the present invention will be specifically described below. However, the embodiments described below are examples (representative examples) of embodiments of the present invention, and the present invention is not limited to the embodiments described below as long as they do not depart from the gist of the present invention.

[0025] [Adhesive composition of the present invention] The pressure-sensitive adhesive composition of the present invention is a pressure-sensitive adhesive composition containing a urethane prepolymer (A) (hereinafter sometimes referred to as "urethane prepolymer (A) of the present invention") obtained by reacting a polyether polyol (a1) having a carbonate bond (hereinafter sometimes referred to as "the polyether polyol (a1) of the present invention" or simply "the polyether polyol (a1)" or "the polyol (a1)") with an isocyanate compound (b). The urethane prepolymer (A) of the present invention may be produced by reacting a polyether polyol (a1) having a carbonate bond together with a polyol (a2) other than the polyether polyol (a1) having a carbonate bond (hereinafter, sometimes simply referred to as "polyol (a2)") with an isocyanate compound (b). As will be described later, the urethane prepolymer (A) of the present invention is preferably dissolved in an organic solvent to form a urethane prepolymer solution.

[0026] <Polyether polyol (a1) having carbonate bond> The polyether polyol (a1) having a carbonate bond used in the present invention must have a carbonate bond in the polyether polyol structure. The polyether polyol structure other than the carbonate bond is not particularly limited, but preferably contains a structural unit derived from a polyalkylene ether glycol.

[0027] A preferred embodiment of the polyether polyol (a1) is one in which polyalkylene ether glycols are linked by carbonate bonds, and the polyalkylene ether glycols may be directly linked to each other by carbonate bonds, or may be indirectly linked by carbonate bonds via a polyol or the like that is different from the polyalkylene ether glycol.

[0028] The hydroxyl value of the polyether polyol (a1) is preferably 35 or more and 250 or less, more preferably 40 or more and 200 or less, even more preferably 42.5 or more and less than 150, and particularly preferably 45 or more and 130 or less. The hydroxyl value in the present invention is a value measured by a hydroxyl value (mgKOH / g) measurement method using an acetylation method in accordance with JIS K1557-1:2007.

[0029] If the hydroxyl value of the polyether polyol (a1) is too low, the pressure-sensitive adhesive composition of the present invention containing the urethane prepolymer (A) of the present invention will not exhibit adhesive strength, holding power, or compatibility with the adherend, and will no longer function as a pressure-sensitive adhesive. The same applies if the hydroxyl value of the polyether polyol (a1) is too high.

[0030] The number average molecular weight of the polyether polyol (a1) can be determined from the hydroxyl value. The number average molecular weight of the polyether polyol (a1) of the present invention is preferably 450 to 3,200, more preferably 560 to 2,800, even more preferably 750 to 2,640, and particularly preferably 860 to 2,500. If the number average molecular weight of the polyether polyol (a1) is too low or too high, problems tend to occur such that the excellent adhesive strength, holding power, compatibility with the adherend, and the like, which are the characteristics of the present invention, are not easily exhibited.

[0031] The number average molecular weight of the polyether polyol (a1) can be determined from the hydroxyl value (mgKOH / g) determined by the acetylation method in accordance with JIS K1557-1:2007.

[0032] The properties of the polyether polyol (a1) are not particularly limited, but are liquid or waxy at room temperature, and the properties and form of the polyether polyol (a1) may be selected according to the application.

[0033] <Polyalkylene ether glycol> In the present invention, the polyether polyol (a1) may contain a structural unit derived from a polyalkylene ether glycol. A polyalkylene ether glycol is usually a polyhydroxy compound having one or more ether bonds in the main skeleton of the molecule.

[0034] Examples of the repeating units in the main skeleton of the polyalkylene ether glycol include a 1,2-ethylene glycol unit, a 1,2-propylene glycol unit, a 1,3-propanediol (trimethylene glycol) unit, a 2-methyl-1,3-propanediol unit, a 2,2-dimethyl-1,3-propanediol unit, a 1,4-butanediol (tetramethylene glycol) unit, a 2-methyl-1,4-butanediol unit, a 3-methyl-1,4-butanediol unit, a 3-methyl-1,5- Examples of the repeating unit include saturated hydrocarbon groups having 1 to 20 carbon atoms, such as pentanediol units, neopentyl glycol units, 1,6-hexanediol units, 1,7-heptanediol units, 1,8-octanediol units, 1,9-nonanediol units, 1,10-decanediol units, and 1,4-cyclohexanedimethanol units. A single repeating unit may form a polyalkylene ether glycol, or two or more repeating units may form a copolymerized polyalkylene ether glycol. While the raw materials providing these repeating units are not particularly limited, cyclic ethers are preferred. Furthermore, the raw materials providing these repeating units may be derived from petroleum or biomass.

[0035] As the polyalkylene ether glycol, among polyalkylene ether glycols having the above repeating units in the main skeleton, polytetramethylene ether glycol, polytrimethylene ether glycol, copolymer polyether polyols obtained by reacting 1 to 20 mol % of 3-methyltetrahydrofuran with tetrahydrofuran (for example, "PTG-L1000," "PTG-L2000," and "PTG-L3500" manufactured by Hodogaya Chemical Co., Ltd.), and copolymer polyether glycols obtained by reacting neopentyl glycol with tetrahydrofuran are preferred, with polytetramethylene ether glycol being more preferred.

[0036] These polyalkylene ether glycols may be used alone or in combination of two or more, and may be selected according to the physical properties required for the urethane prepolymer (A) of the present invention.

[0037] In the present invention, the molecular weight of the polyalkylene ether glycol used as a raw material for the polyether polyol (a1) is usually 100 or more and 3,000 or less, preferably 125 or more and 2,000 or less, more preferably 150 or more and 1,500 or less, and even more preferably 200 or more and 1,250 or less, in terms of number average molecular weight. By setting the number-average molecular weight of the polyalkylene ether glycol to the above upper limit or less, it is possible to prevent the resulting polyether polyol (a1) from having an extremely high molecular weight and an excessively high viscosity, thereby improving workability and productivity during the production of the urethane prepolymer (A). On the other hand, by setting the number-average molecular weight of the polyalkylene ether glycol to the above lower limit or more, the resulting polyether polyol (a1) has a viscosity suitable for handling, allowing the production of a homogeneous urethane prepolymer (A).

[0038] The number average molecular weight of the polyalkylene ether glycol can be determined from the hydroxyl value (mgKOH / g) determined by the acetylation method in accordance with JIS K1557-1:2007.

[0039] <Method for producing polyether polyol (a1)> The polyether polyol (a1) of the present invention must contain a carbonate bond, and preferably further contains a structural unit derived from a polyalkylene ether glycol.

[0040] The method for producing the polyether polyol (a1) of the present invention is not particularly limited as long as it is a known method, but a method of reacting a polyether polyol such as the above-mentioned polyalkylene ether glycol with a carbonate compound is preferably used. Specifically, a transesterification reaction between polytetramethylene ether glycol and a carbonate diester can be used.

[0041] (carbonate compounds) Examples of carbonate compounds that can be used in the production of the polyether polyol (a1) of the present invention include dialkyl carbonates, diaryl carbonates, and alkylene carbonates. Specific examples include dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, diisobutyl carbonate, ethyl-n-butyl carbonate, and ethyl isobutyl carbonate; diaryl carbonates such as diphenyl carbonate, ditolyl carbonate, bis(chlorophenyl) carbonate, and m-cresyl carbonate; ethylene carbonate, trimethylene carbonate, and tetramethyl ... Examples of the alkylene carbonate include tetramethylene carbonate, 1,2-propylene carbonate, 1,2-butylene carbonate, 1,3-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 1,3-pentylene carbonate, 1,4-pentylene carbonate, 1,5-pentylene carbonate, 2,3-pentylene carbonate, and 2,4-pentylene carbonate, and alkylene carbonates such as neopentyl carbonate. These may be used alone or in combination of two or more.

[0042] Among carbonate compounds, carbonic acid diesters are preferred, and among these, dialkyl carbonates are preferred because they are inexpensive and easy to recover, and are therefore efficient and preferable for industrial production, and diethyl carbonate is more preferred because it is easily and inexpensively available as an industrial raw material.

[0043] The amount of these carbonate compounds used, expressed as a molar ratio relative to the polyether polyol such as polyalkylene ether glycol that is the raw material for the polyether polyol (a1), is preferably 0.2 or more, more preferably 0.3 or more, even more preferably 0.4 or more, and particularly preferably 0.5 or more, and the upper limit is preferably 3.0 or less, more preferably 2.0 or less, and even more preferably 1.5 or less.

[0044] If the amount of carbonate compound used exceeds the upper limit, the proportion of terminal groups of the resulting polyether polyol (a1) that are not hydroxyl groups may increase, or the molecular weight may become larger than desired. If the amount is below the lower limit, the polymerization reaction may not proceed to the desired molecular weight.

[0045] <Polyol (a2) other than polyether polyol (a1)> When producing the urethane prepolymer (A) of the present invention, a polyol (a2) other than the polyether polyol (a1) may be used in combination, if necessary. Here, the polyol (a2) other than the polyether polyol (a1) is not particularly limited as long as it is one that is used in the production of a normal prepolymer, and examples thereof include polyether polyols, polyester polyols, and polycarbonate diols. This polyol (a2) is distinguished from the chain extender (c) described below in that the molar concentration (eq / kg) of hydroxyl groups contained per unit weight is 8.0 or less.

[0046] The number average molecular weight of the polyol (a2) can be appropriately selected depending on the adhesive properties desired for the urethane prepolymer (A) of the present invention and / or the adhesive composition of the present invention, but is preferably 100 to 3,000, more preferably 150 to 2,750, and even more preferably 200 to 2,500.

[0047] When polyol (a2) is used, from the viewpoint of more effectively obtaining the above-mentioned effects obtained by using polyether polyol (a1) of the present invention, the amount of polyol (a2) used is preferably 60 mass % or less, particularly preferably 50 mass % or less, based on the total amount of polyether polyol (a1) and polyol (a2).

[0048] <Isocyanate compound (b)> The isocyanate compound (b) used in the present invention is not particularly limited, and examples thereof include aromatic diisocyanates such as 2,4- or 2,6-tolylene diisocyanate, xylylene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), 2,4'-MDI, paraphenylene diisocyanate, 1,5-naphthalene diisocyanate, and tolidine diisocyanate; isocyanates having an aromatic ring such as α,α,α',α'-tetramethylxylylene diisocyanate; Aliphatic diisocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, 2,2,4- or 2,4,4-trimethylhexamethylene diisocyanate, and 1,6-hexamethylene diisocyanate; and 1,4-cyclohexane diisocyanate, methylcyclohexane diisocyanate (H6TDI), isophorone diisocyanate (IPDI), 4,4'-methylenebis(cyclohexyl isocyanate) (H 12 Examples of suitable diisocyanates include alicyclic diisocyanates such as methyl methyl diisocyanate (MDI) and isopropylidenedicyclohexyl-4,4'-diisocyanate. Other examples include triisocyanates such as triphenylmethane triisocyanate and triisocyanate triphenylthiophosphate; and polyisocyanates such as isocyanate trimers having an isocyanurate ring, reaction products of urea derivatives having a biuret bond with isocyanate compounds, and adduct reaction products of trimethylolpropane with isocyanate compounds. These may be used alone or in combination of two or more.

[0049] Suitable isocyanate compounds (b) vary depending on the applications of the urethane prepolymer (A) and the pressure-sensitive adhesive composition to be produced. For example, for applications requiring weather resistance such as surface protection films, masking films, and sign displays, it is preferable to use aliphatic diisocyanates and / or alicyclic diisocyanates, as they are less likely to yellow due to light. Among these, 1,6-hexamethylene diisocyanate, isophorone diisocyanate (IPDI), 4,4'-methylenebis(cyclohexyl isocyanate) (H 12It is preferable to use aromatic diisocyanates (TDI, MDI). On the other hand, for applications requiring low contamination of the substrate, such as maintaining electrical and electronic components or optical members until they are shipped to the next process, it is preferable to use aromatic diisocyanates with high cohesive strength, and tolylene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI) are particularly preferable because of their good physical properties and easy availability. In addition, some of the NCO groups of the isocyanate compound may be modified with urethane, urea, biuret, allophanate, carbodiimide, oxazolidone, amide, imide, etc., and polynuclear compounds may also contain isomers other than those mentioned above.

[0050] <Chain extender (c)> When producing the urethane prepolymer (A) of the present invention, a chain extender (c) may be further used in addition to the polyether polyol (a1), the polyol (a2) other than the polyether polyol (a1) that is used as needed, and the isocyanate compound (b).

[0051] The chain extender (c) that may be used in the present invention is mainly classified into compounds having two or more hydroxyl groups, compounds having two or more amino groups, and water. Among these, short-chain polyols, specifically compounds having two or more hydroxyl groups, are preferred for producing the urethane prepolymer (A) of the present invention. Furthermore, polyamine compounds, specifically compounds having two or more amino groups, are preferred for producing a prepolymer having a urethane urea bond.

[0052] Examples of the compound having two or more hydroxyl groups include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-butyl-2-hexyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2-methyl aliphatic glycols such as 2,4-pentanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, neopentyl glycol, 1,6-hexanediol, 2-ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol, 1,8-octanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol; alicyclic glycols such as bishydroxymethylcyclohexane; and glycols having an aromatic ring such as xylylene glycol and bishydroxyethoxybenzene. Among these, ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, and 2-methyl-1,3-propanediol are preferred, and 1,4-butanediol is particularly preferred because the resulting urethane prepolymer (A) has an excellent balance of physical properties.

[0053] Examples of compounds having two or more amino groups include aromatic diamines such as 2,4- or 2,6-tolylenediamine, xylylenediamine, and 4,4'-diphenylmethanediamine; aliphatic diamines such as ethylenediamine, 1,2-propylenediamine, 2,2-dimethyl-1,3-propanediamine, 1,3-pentanediamine, 2-methyl-1,5-pentanediamine, 2-butyl-2-ethyl-1,5-pentanediamine, 1,6-hexanediamine, 2,2,4- or 2,4,4-trimethylhexanediamine, 1,8-octanediamine, 1,9-nonanediamine, and 1,10-decanediamine; and 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane (IPDA), 4,4'-dicyclohexylmethanediamine (H 12 Alicyclic diamines such as ethylenediamine, 1,2-propylenediamine, 1,3-pentanediamine, 2-methyl-1,5-pentanediamine, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane (IPDA), 4,4'-dicyclohexylmethanediamine (HMDA), isopropylidenecyclohexyl-4,4'-diamine, 1,4-diaminocyclohexane, and 1,3-bisaminomethylcyclohexane are also included. Among these, ethylenediamine, 1,2-propylenediamine, 1,3-pentanediamine, 2-methyl-1,5-pentanediamine, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane (IPDA), 4,4'-dicyclohexylmethanediamine (HMDA), and the like are also included. 12 MDA) is preferred.

[0054] Furthermore, the chain extender (c) may be derived from biomass resources.

[0055] The amount of these chain extenders (c) used is preferably 0.1 to 5.0 equivalents, more preferably 0.8 to 2.0 equivalents, and even more preferably 0.9 to 1.5 equivalents, where the equivalent obtained by subtracting the total hydroxyl group equivalents of the polyether polyol (a1) and the polyol (a2) used as needed from the equivalent of the isocyanate compound (b) is taken as 1.

[0056] <Other additives, etc.> When producing the urethane prepolymer (A) of the present invention, a crosslinking agent having three or more active hydrogen groups or isocyanate groups may be used as needed to improve the heat resistance and strength of the resulting urethane prepolymer (A). Examples of such crosslinking agents include trimethylolpropane, glycerin, and their isocyanate-modified products, and polymeric MDI.

[0057] Furthermore, other additives may be added as needed during the production of the urethane prepolymer (A) of the present invention. These additives include antioxidants such as "CYANOX 1790" (manufactured by SOLVAY), "IRGANOX 245" and "IRGANOX 1010" (all manufactured by BASF), "Sumilizer GA-80" (manufactured by Sumitomo Chemical Co., Ltd.) and 2,6-dibutyl-4-methylphenol (BHT); "TINUVIN 622LD" and "TINUVIN 765" (all manufactured by BASF), "SANOL LS-2626" and "SANOL LS-765 (both manufactured by Sankyo Co., Ltd.), ultraviolet absorbers such as TINUVIN328 and TINUVIN234 (both manufactured by BASF), tackifying compounds such as rosin-based resins, terpene-based resins, xylene-based resins, phenolic resins, coumarone-based resins, pinene-based polymers, hydrogenated petroleum resins, hydrocarbon resins and petroleum resins, silicone compounds such as dimethylsiloxane polyoxyalkylene copolymers, additives and reactive flame retardants such as red phosphorus, organic phosphorus compounds, phosphorus- and halogen-containing organic compounds, bromine- or chlorine-containing organic compounds, ammonium polyphosphate, aluminum hydroxide, and antimony oxide, pigments such as titanium dioxide, dyes, colorants such as carbon black, hydrolysis inhibitors such as carbodiimide compounds, fillers such as short glass fiber, carbon fiber, alumina, talc, graphite, melamine, and clay, lubricants, oils, surfactants, other inorganic extenders, and organic solvents.

[0058] [Method for producing the urethane prepolymer (A) of the present invention] The urethane prepolymer (A) of the present invention can be produced by any of the production methods generally used in experiments or industry, using the polyether polyol (a1), the polyol (a2) used as needed, and the isocyanate compound (b) as main production raw materials in the amounts described above, either in the absence of a solvent or in the presence of a solvent.

[0059] Examples of the production method include a method of simultaneously reacting the polyether polyol (a1), the polyol (a2) used as needed, the isocyanate compound (b), and the chain extender (c) (hereinafter referred to as a one-step method); a method of first reacting the polyether polyol (a1), the polyol (a2) used as needed, and the isocyanate compound (b) to prepare a prepolymer having isocyanate groups at both ends, and then reacting the prepolymer with the chain extender (c) (hereinafter referred to as an isocyanate-terminated two-step method); and a method of reacting the polyether polyol (a1), the polyol (a2) used as needed, and the isocyanate compound (b) to prepare a prepolymer having hydroxyl groups at both ends, and then reacting the prepolymer with an isocyanate compound (hereinafter referred to as a hydroxyl-terminated two-step method).

[0060] <Solvent> When the urethane prepolymer (A) of the present invention is produced in the presence of a solvent, the solvent to be used is not particularly limited, and examples thereof include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ethers such as dioxane and tetrahydrofuran; hydrocarbons such as hexane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; esters such as ethyl acetate and butyl acetate; halogenated hydrocarbons such as chlorobenzene, trichlene, and perclene; and aprotic polar solvents such as γ-butyrolactone, dimethyl sulfoxide, acetonitrile, N-methyl-2-pyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide, as well as mixtures of two or more thereof.

[0061] Among these organic solvents, aprotic polar solvents are preferred from the viewpoint of solubility. Specific examples of preferred aprotic polar solvents include methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide, and more preferred are the aprotic amide solvents N,N-dimethylformamide and N,N-dimethylacetamide.

[0062] The urethane prepolymer (A) solution obtained by the reaction in the presence of a solvent has good storage stability, such as being less prone to gelation and exhibiting little change in viscosity over time, and also has little thixotropy, making it convenient for processing into an adhesive film.

[0063] The concentration of the urethane prepolymer (A) of the present invention in the urethane prepolymer (A) solution obtained by reaction in the presence of a solvent is preferably 10 to 90 mass %, more preferably 20 to 80 mass %, and even more preferably 30 to 70 mass %, based on the total mass of the urethane prepolymer (A) solution. By keeping the urethane prepolymer (A) concentration in the urethane prepolymer (A) solution at or below the upper limit, it becomes unnecessary to remove a large amount of solvent in a subsequent step, thereby improving productivity. On the other hand, by keeping the concentration at or above the lower limit, the viscosity of the solution can be reduced, improving processability.

[0064] When the urethane prepolymer (A) solution is to be stored for a long period of time, it is preferably stored at room temperature or lower in an inert gas atmosphere such as nitrogen or argon.

[0065] <One step method> The one-stage method, also called a one-shot method, is a method in which the polyether polyol (a1), the polyol (a2) used as needed, the isocyanate compound (b), and the chain extender (c) used as needed are all charged together to carry out the reaction. The reaction is usually carried out at a temperature of 0 to 250°C, more preferably 50 to 150°C. The reaction temperature varies depending on the amount of solvent, the reactivity of the raw materials used, the reaction equipment, etc. If the temperature is too low, the reaction may proceed too slowly or the solubility of the raw materials and polymer may decrease, resulting in a decrease in productivity. If the temperature is too high, side reactions or decomposition of the polyurethane may occur.

[0066] <Two step method> The two-stage method is also called the prepolymer method.

[0067] (Isocyanate-terminated two-step method) In the isocyanate-terminated two-stage method, first, polyether polyol (a1) and optionally used polyol (a2) are reacted with isocyanate compound (b) and, optionally, chain extender (c) at a reaction equivalent ratio of (b) / {((a1) + (a2)) + (c)} of preferably 1.5 to 5 to produce an intermediate product having isocyanate groups at both ends. In particular, when chain extender (c) is a diamine, the reaction rate with the isocyanate groups differs significantly between the total hydroxyl groups of polyether polyol (a1) and polyol (a2) and the amino groups of the diamine, so it is preferable to carry out the reaction after synthesis of the intermediate product having isocyanate groups at both ends. In some cases, an active hydrogen compound component such as a polyhydric alcohol and / or an amine compound can be added to this isocyanate-terminated intermediate product to carry out a two-step reaction to synthesize a prepolymer having hydroxyl groups at both ends.

[0068] When synthesizing an isocyanate-terminated urethane prepolymer, (1) first, without using a solvent, the isocyanate compound (b) is reacted directly with the polyether polyol (a1) and the polyol (a2) used as needed to synthesize an intermediate product, which can then be used as is in the reaction with the chain extender (c); (2) the intermediate product can be synthesized by the method of (1) and then dissolved in a solvent for use; or (3) a solvent can be used from the beginning to react the isocyanate compound (b) with the polyether polyol (a1) and the polyol (a2) used as needed.

[0069] In the case of (1), in the present invention, when reacting with the chain extender (c), it is preferable to obtain the urethane prepolymer in the coexistence with the solvent by a method such as dissolving the chain extender (c) in a solvent or introducing the intermediate product and the chain extender (c) into the solvent simultaneously. The reaction equivalent ratio of NCO / active hydrogen group (polyether polyol (a1) + polyol (a2) + chain extender (c)) is preferably 1 or more, more preferably 1.5 or more. Also, it is preferably 10 or less, more preferably 5 or less, and even more preferably 3 or less. The amount of the chain extender (c) used is not particularly limited, but is preferably 0.5 or more, more preferably 0.8 or more, relative to the equivalent weight of the isocyanate groups contained in the intermediate product, and is preferably 5.0 or less, more preferably 2.0 or less.

[0070] In the chain extension reaction in which the intermediate product having isocyanate groups at both ends is reacted with the chain extender (c), it is usually preferable to react each component at 0 to 250° C. When the chain extender (c) is a polyhydric alcohol, the temperature is 50 to 150° C., and when the chain extender (c) is a diamine, the temperature is more preferably 0 to 60° C. The reaction temperature varies depending on the amount of solvent, the reactivity of the raw materials used, the reaction equipment, etc., but if the temperature is too low, the reaction will proceed too slowly and the solubility of the raw materials and polymer will be low, resulting in poor productivity, while if the temperature is too high, side reactions and decomposition of the polyurethane will occur, which are undesirable.

[0071] (Two-step method for hydroxyl-terminated groups) In the two-stage hydroxyl-terminated method, first, a polyether polyol (a1) and an optionally used polyol (a2) are reacted with an isocyanate compound (b) and, optionally, a chain extender (c) at a reaction equivalent ratio of (b) / {((a1)+(a2))+(c)} of preferably 0.3 to 0.9 to synthesize a prepolymer having hydroxyl groups at both ends. The two-stage process can be carried out in the absence of a solvent or in the presence of a solvent. When carried out in the presence of a solvent, the above-mentioned solvent can be used in an amount such that the concentration of the urethane prepolymer (A) in the resulting urethane prepolymer (A) solution falls within the above-mentioned range.

[0072] When synthesizing a hydroxyl-terminated urethane prepolymer, (1) first, the isocyanate compound (b) may be directly reacted with the polyether polyol (a1) and the polyol (a2) used as needed without using a solvent, and the prepolymer may be used as is; (2) an intermediate product may be synthesized by the method of (1), and then the intermediate product may be dissolved in a solvent and used; or (3) a solvent may be used from the beginning to react the isocyanate compound (b) with the polyether polyol (a1) and the polyol (a2) used as needed.

[0073] The reaction equivalent ratio of NCO / active hydrogen group (polyether polyol (a1) + polyol (a2) + chain extender (c)) is preferably 0.3 or more, more preferably 0.6 or more. Also, it is preferably 1 or less, more preferably 0.9 or less.

[0074] By setting the reaction equivalent ratio of NCO / active hydrogen group (polyether polyol (a1) + polyol (a2)) to the upper limit or less, it is possible to prevent the molecular weight of the resulting urethane prepolymer from becoming too high, which could result in poor handleability. Furthermore, by setting it to the lower limit or more, it is possible to shorten the time required for the subsequent chain extension reaction. The isocyanate compound used as the chain extender (c) may be the same compound as the isocyanate compound (b) used in the synthesis of the urethane prepolymer, or may be a different isocyanate compound.

[0075] The amount of the isocyanate compound used as the chain extender (c) is not particularly limited, but the total isocyanate equivalent of the isocyanate compound (b) used in the synthesis of the urethane prepolymer (A) and the isocyanate compound used as the chain extender (c) relative to the active hydrogen group equivalent of the polyether polyol (a1), polyol (a2), etc. used in the synthesis of the intermediate product is usually preferably 0.5 or more, more preferably 0.8 or more, and usually preferably 1.5 or less, more preferably 1.2 or less.

[0076] By using an amount of the isocyanate compound as the chain extender (c) that is equal to or greater than the lower limit, the molecular weight of the resulting urethane prepolymer (A) can be increased sufficiently to obtain the desired adhesive strength and holding power. By using an amount that is equal to or less than the upper limit, it is possible to prevent unreacted isocyanate compound from causing a side reaction that would otherwise deteriorate the adhesive properties.

[0077] In the chain extension reaction in which an isocyanate compound is reacted with a prepolymer having hydroxyl groups at both ends, the components are usually reacted at a temperature of 0 to 250° C., more preferably 50 to 150° C. The reaction temperature varies depending on the amount of solvent, the reactivity of the raw materials used, the reaction equipment, etc., but if the temperature is too low, the reaction will proceed too slowly and the solubility of the raw materials and polymer will be low, which tends to reduce productivity, while if the temperature is too high, side reactions and decomposition of the polyurethane will occur, which tends to be undesirable.

[0078] <Reaction catalysts and stabilizers> When producing the urethane prepolymer (A) of the present invention, a reaction catalyst (z), a stabilizer, etc. may be added as needed, regardless of the reaction method.

[0079] Examples of the reaction catalyst (z) include triethylamine, tributylamine, dibutyltin dichloride, dibutyltin oxide, dibutyltin dibromide, dibutyltin dimaleate, dibutyltin dilaurate (DBTL), dibutyltin diacetate, dibutyltin sulfide, tributyltin sulfide, tributyltin oxide, tributyltin acetate, triethyltin ethoxide, tributyltin ethoxide, dioctyltin oxide, tributyltin chloride, and tributyltin trichloroacetate. titanium-based compounds such as lead oleate, lead 2-ethylhexanoate, lead benzoate, and lead naphthenate; iron-based compounds such as iron 2-ethylhexanoate and iron acetylacetonate; cobalt-based compounds such as cobalt benzoate and cobalt 2-ethylhexanoate; zinc-based compounds such as zinc naphthenate and zinc 2-ethylhexanoate; zirconium naphthenate; acetic acid, phosphoric acid, sulfuric acid, hydrochloric acid, and sulfonic acid.

[0080] Examples of stabilizers include 2,6-dibutyl-4-methylphenol, distearyl thiodipropionate, di-β-naphthylphenylenediamine, and tri(dinonylphenyl)phosphite.

[0081] However, when the chain extender (c) is a highly reactive one such as a short-chain aliphatic amine, it is preferable to carry out the reaction without adding a catalyst. Furthermore, the reaction may be carried out in the presence of a monofunctional organic amine and an alcohol.

[0082] [Physical Properties of the Urethane Prepolymer (A) of the Present Invention] The urethane prepolymer (A) of the present invention produced by carrying out a reaction in the presence of a solvent is obtained in a state of being dissolved in the solvent, but the urethane prepolymer (A) of the present invention may be in a solution state or a solid state, and there are no particular limitations on the form in which it exists.

[0083] The number average molecular weight (Mn) of the urethane prepolymer (A) of the present invention, as determined by gel permeation chromatography (GPC), varies depending on the application, but is usually 6,000 to 70,000, preferably 8,000 to 65,000, more preferably 10,000 to 60,000, still more preferably 12,000 to 55,000, and particularly preferably 15,000 to 50,000. The number-average molecular weight is the number-average molecular weight converted into the molecular weight of standard polystyrene, and is measured using a high-performance liquid chromatograph (Waters, "ACQUITY APC System") equipped with four columns in series: one ACQUITY APC XT 450, one ACQUITY APC XT 200, and two ACQUITY APC XT 45.

[0084] If the number average molecular weight of the urethane prepolymer (A) is too low, the viscosity of the prepared pressure-sensitive adhesive composition will be too low, which may result in repellency when applied to an adherend, or the resulting pressure-sensitive adhesive coating film may not cure sufficiently and be too soft to function as a pressure-sensitive adhesive. Conversely, if the number average molecular weight of the urethane prepolymer (A) is too high, the viscosity of the prepared pressure-sensitive adhesive composition will be too high, which may result in the composition being unable to be uniformly applied to an adherend, or the resulting cured coating film may be too hard to function as a pressure-sensitive adhesive.

[0085] The urethane prepolymer (A) of the present invention is reacted with a crosslinking agent described below in a reaction equivalent ratio (x) / (y) described below to be cured, and the cured product has a gel fraction (G') described below. -30 ) / (G' 100 ) and storage modulus.

[0086] The cured product obtained by curing the urethane prepolymer (A) of the present invention can exhibit a variety of properties by changing the type and amount of the polyether polyol (a1) used in the synthesis of the urethane prepolymer (A), the polyol (a2) used as needed, and the isocyanate compound (b), and / or the type and amount of the crosslinking agent (described below) used when curing the urethane prepolymer (A). For example, if the adhesive strength is increased, it can be used to bond touch panels, display components, etc., while if the adhesive strength is decreased, it can be used as a protective film to prevent scratches and dirt during the production and shipping of electronic materials, optical films, etc.

[0087] [Adhesive composition of the present invention] The pressure-sensitive adhesive composition of the present invention is used as a pressure-sensitive adhesive composition containing the crosslinking agent described below used for curing the urethane prepolymer (A) of the present invention, and, if necessary, other optional additives such as antistatic agents, antioxidants, plasticizers, fillers, pigments, diluents, antioxidants, UV absorbers, UV stabilizers, tackifying resins, etc. In addition to these additives, the pressure-sensitive adhesive composition of the present invention may also contain small amounts of impurities contained in the raw materials for producing the components of the urethane prepolymer (A).

[0088] <Crosslinking agent> The crosslinking agent is blended into the pressure-sensitive adhesive composition of the present invention to form a crosslinked structure with the urethane prepolymer (A) of the present invention and thereby increase adhesive strength.

[0089] Examples of the crosslinking agent include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, oxazoline-based crosslinking agents, melamine-based crosslinking agents, aldehyde-based crosslinking agents, and amine-based crosslinking agents. These crosslinking agents may be used alone or in combination of two or more.

[0090] Among these, it is preferable to use an isocyanate-based crosslinking agent in terms of improving adhesion to the adherend and reactivity with the urethane prepolymer (A).

[0091] Examples of the isocyanate crosslinking agent include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylylene diisocyanate, hexamethylene diisocyanate, diphenylmethane-4,4'-diisocyanate, isophorone diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, tetramethylxylylene diisocyanate, 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate, adducts of these polyisocyanate compounds with polyol compounds such as trimethylolpropane, and biurets and isocyanurates of these polyisocyanate compounds.

[0092] Among these, in terms of chemical resistance and reactivity with functional groups, an isocyanurate of hexamethylene diisocyanate, 2,4-tolylene diisocyanate, an adduct of 2,4-tolylene diisocyanate or 2,6-tolylene diisocyanate with trimethylolpropane, an isocyanurate of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, and an adduct of tetramethylxylylene diisocyanate with trimethylolpropane are preferred.

[0093] Examples of the epoxy crosslinking agent include bisphenol A-epichlorohydrin epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl erythritol, diglycerol polyglycidyl ether, 1,3'-bis(N,N-diglycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidyl-m-xylylenediamine.

[0094] Examples of the aziridine crosslinking agent include tetramethylolmethane-tri-β-aziridinylpropionate, trimethylolpropane-tri-β-aziridinylpropionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), and N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide).

[0095] Examples of the oxazoline-based crosslinking agent include 2,2'-bis(2-oxazoline), 1,2-bis(2-oxazolin-2-yl)ethane, 1,4-bis(2-oxazolin-2-yl)butane, 1,8-bis(2-oxazolin-2-yl)butane, 1,4-bis(2-oxazolin-2-yl)cyclohexane, 1,2-bis(2-oxazolin-2-yl)benzene, and 1,3-bis(2-oxazolin-2-yl) Examples include bisoxazoline compounds containing aliphatic or aromatic groups such as benzene, and polymers of one or more addition-polymerizable oxazolines such as 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

[0096] Examples of the melamine-based crosslinking agent include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexabutoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, and melamine resins.

[0097] Examples of the aldehyde crosslinking agent include glyoxal, malondialdehyde, succindialdehyde, maleic dialdehyde, glutaric dialdehyde, formaldehyde, acetaldehyde, and benzaldehyde.

[0098] Examples of the amine-based crosslinking agent include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetraamine, diethylenetriamine, triethyltetraamine, isophoronediamine, amino resins, and polyamides.

[0099] The content of the crosslinking agent is usually such that the reaction equivalent ratio (x) / (y) between the reactive functional group (x) of the crosslinking agent and the active hydrogen group (y) of the urethane prepolymer (A) is preferably 0.3 to 2.0, more preferably 0.4 to 1.75, even more preferably 0.5 to 1.5, and most preferably 0.5 to 1.25. If the amount of crosslinking agent is too small, the cohesive strength of the urethane prepolymer (A) tends to decrease, which can cause adhesive residue, while if the amount is too large, the adhesive strength tends to decrease, which can cause problems with adhesion to the adherend.

[0100] When the above-mentioned other optional components are used, the content thereof is preferably 5 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less, relative to 100 parts by mass of the urethane prepolymer (A). If the content is too high, the crosslinking reaction of the pressure-sensitive adhesive composition tends to be inhibited and the adherend tends to be easily contaminated.

[0101] The gel fraction of the pressure-sensitive adhesive composition of the present invention after curing is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, and particularly preferably 30% by mass or more, from the viewpoints of durability and adhesive strength. If the gel fraction is too low, the cohesive strength decreases, and durability tends to decrease.

[0102] The gel fraction is an index of the degree of crosslinking and is calculated, for example, by the following method. A cured coating sheet (without a release film) consisting of a cured coating film formed on a polymer sheet (e.g., a PET film) serving as a substrate is wrapped in a 200-mesh SUS wire netting and immersed in toluene at 23°C for 48 hours. The gel fraction is calculated as the mass percentage of the insoluble cured coating components remaining in the wire netting after immersion relative to the mass of the cured coating components before immersion, excluding the mass of the substrate.

[0103] The storage modulus of the pressure-sensitive adhesive composition of the present invention after curing, i.e., the storage modulus of the cured product obtained by curing the urethane prepolymer (A) of the present invention with a crosslinking agent, is the storage modulus at −30° C. (G′ -30 ) and storage modulus at 100°C (G' 100 ) ratio (G' -30 ) / (G' 100 ) is preferably 50 or less, not only for weak adhesives but also for strong adhesives, because it can reduce the temperature dependence of the storage modulus, maintain adhesive properties even in high temperature ranges, provide excellent removability, and achieve high adhesion or adhesive reliability from low to high temperatures. -30 ) / (G' 100 ) is more preferably 30 or less, and even more preferably 10 or less. (G' -30 ) / (G' 100 ) is preferably small, but usually (G' -30 ) / (G' 100 ) is 1.5 or more.

[0104] The storage modulus (G') of the cured product at -30°C -30 The storage modulus (G') at 100°C is preferably in the range of 0.5 to 20 MPa, particularly 3 to 10 MPa, from the viewpoint of obtaining good adhesive properties and adhesive reliability in the low temperature range. 100 ) is preferably in the range of 0.05 to 5 MPa, particularly 0.2 to 2 MPa, from the viewpoint of obtaining good adhesive properties and adhesive reliability in the low temperature range.

[0105] In the present invention, the storage modulus (G') at -30°C -30 ) and storage modulus at 100°C (G' 100 ) is the storage modulus at -30°C and 100°C measured by the following method.

[0106] (Storage modulus measurement method) Measuring device: Rheogel-E4000 (manufactured by UBM) Measurement jig: solid shear Measurement temperature: -80~180℃ Heating rate: 5℃ / min Measurement frequency: 1Hz

[0107] [Adhesive sheet] A pressure-sensitive adhesive sheet (hereinafter, sometimes referred to as "the pressure-sensitive adhesive sheet of the present invention") can be produced using the pressure-sensitive adhesive composition of the present invention. The pressure-sensitive adhesive sheet of the present invention comprises a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition of the present invention containing the urethane prepolymer (A) of the present invention, a crosslinking agent, and other optional components, a substrate sheet, and, if necessary, a release film. To prepare such a pressure-sensitive adhesive sheet, first, the pressure-sensitive adhesive composition of the present invention is applied directly onto a release film or a substrate sheet, either as is or after adjusting the concentration with an appropriate organic solvent. The composition is then dried and crosslinked by, for example, heat treatment at 80 to 200°C for 0.5 to 60 minutes, and then attached to a substrate sheet or a release film to obtain a pressure-sensitive adhesive sheet. Furthermore, to balance the adhesive properties, further aging may be performed after drying.

[0108] Examples of the substrate sheet include polyester-based resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate / isophthalate copolymer; polyolefin-based resins such as polyethylene, polypropylene, and polymethylpentene; polyethylene fluoride resins such as polyvinyl fluoride, polyvinylidene fluoride, and polyethylene fluoride; polyamides such as nylon 6 and nylon 6,6; vinyl polymers such as polyvinyl chloride, polyvinyl chloride / vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, and vinylon; cellulose-based resins such as cellulose triacetate and cellophane; acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, and polybutyl acrylate; polystyrene; polycarbonate; polyarylate; polyimide; and synthetic resin sheets such as polyurethane; metal foils such as aluminum, copper, and iron; paper such as fine paper and glassine paper; and woven and nonwoven fabrics made of glass fiber, natural fiber, or synthetic fiber. These substrate sheets can be used as a single layer or as a multi-layered body in which two or more types are laminated. Among these, synthetic resin sheets are preferred because they can impart various properties to the substrate sheet.

[0109] As the release film, for example, any of the various synthetic resin sheets, paper, woven fabrics, nonwoven fabrics, etc. exemplified above as the base sheet, which have been subjected to a release treatment can be used.

[0110] The coating device used to coat the pressure-sensitive adhesive composition of the present invention on various substrate sheets can be any commonly used coating device, such as a roll knife coater, a die coater, a roll coater, a bar coater, a gravure roll coater, a reverse roll coater, a dipping coater, a blade coater, etc.

[0111] The thickness of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is preferably 1 to 200 μm, more preferably 5 to 150 μm, and even more preferably 10 to 100 μm.

[0112] The aging conditions are generally room temperature (23°C) to 70°C, and the time is generally 1 to 30 days, for example, 3 to 10 days at 23°C, or 1 to 7 days at 40°C. [Example]

[0113] 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 as long as it does not depart from the gist of the invention. In the following, "parts" and "%" are based on mass.

[0114] [Production of urethane prepolymer] <Polyether polyol (a1)> "PEPCD (registered trademark) NT1002": polyether polyol having a carbonate group (hydroxyl value: 111.6 mg KOH / g, number average molecular weight: 1,005), manufactured by Mitsubishi Chemical Corporation (referred to as "NT1002" in the tables). "PEPCD (registered trademark) NT2002": Polyether polyol having a carbonate group (hydroxyl value: 55.2 mg KOH / g, number average molecular weight: 2,032), manufactured by Mitsubishi Chemical Corporation (referred to as "NT2002" in the table). "PEPCD (registered trademark) NT2006": polyether polyol having a carbonate group (hydroxyl value: 58.6 mg KOH / g, number average molecular weight: 1,915), manufactured by Mitsubishi Chemical Corporation (referred to as "NT2006" in the table).

[0115] <Polyol (a2)> "BioPTMG2000": polyether polyol (hydroxyl value: 58.2 mg KOH / g, number average molecular weight: 1,928) manufactured by Mitsubishi Chemical Corporation (referred to as "PTMG2000" in the table). "SANNICS (registered trademark) PP-2000": Polyether polyol (hydroxyl value: 55.3 mg KOH / g, number average molecular weight: 2,029) manufactured by Sanyo Chemical Industries, Ltd. (referred to as "PP-2000" in the table). "Kuraray Polyol (registered trademark) P-1012": polyester polyol (hydroxyl value: 114.1 mg KOH / g, number average molecular weight: 983) manufactured by Kuraray Co., Ltd. (referred to as "P-1012" in the table). "Kuraray Polyol (registered trademark) P-2012": polyester polyol (hydroxyl value: 57.4 mg KOH / g, number average molecular weight: 1,955) manufactured by Kuraray Co., Ltd. (referred to as "P-2012" in the table).

[0116] <Isocyanate compound (b)> "4,4'-Diphenylmethane diisocyanate (MDI)": manufactured by Tokyo Chemical Industry Co., Ltd. (NCO group content: 34 g / 100 g) (referred to as "MDI" in the table) "VESTANAT (registered trademark) H 12 MDI": Evonik Industries (NCO group content: 32 g / 100 g) (in the table, "H 12 (Write "MDI"). "VESTANAT (registered trademark) IPDI": manufactured by Evonik Industries (NCO group content: 38 g / 100 g) (referred to as "IPDI" in the table). "Duranate (registered trademark) TLA-100": manufactured by Asahi Kasei Corporation (isocyanate trimer having an isocyanurate ring, NCO group content: 23 g / 100 g) (referred to as "TLA-100" in the table) "Duranate (registered trademark) LE300-100": manufactured by Asahi Kasei Corporation (hexamethylene diisocyanate adduct, NCO group content: 12 g / 100 g) (referred to as "LE300-100" in the table).

[0117] <Production Example 1: Production of urethane prepolymer (A-1)> A flask equipped with an internal thermometer, a stirrer, and a condenser was charged with 100.0 parts of PEPCD (registered trademark) NT1002 as the polyether polyol (a1), 20.7 parts of 4,4'-diphenylmethane diisocyanate (MDI) as the isocyanate compound (b), 66.7 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst, and the mixture was reacted at 80°C. The reaction was terminated when the remaining isocyanate groups reached 0.3% or less, yielding a composition containing a urethane prepolymer (A-1) (number average molecular weight (Mn): 13,000).

[0118] <Production Example 2: Production of urethane prepolymer (A-2)> A flask equipped with an internal thermometer, a stirrer, and a condenser was charged with 100.0 parts of PEPCD (registered trademark) NT2006 as the polyether polyol (a1), 94.2 parts of BioPTMG2000 as the polyol (a2), 20.4 parts of 4,4'-diphenylmethane diisocyanate (MDI) as the isocyanate compound (b), 143.1 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst, and the mixture was reacted at 80°C. The reaction was terminated when the remaining isocyanate groups reached 0.3% or less, yielding a composition containing a urethane prepolymer (A-2) (number average molecular weight (Mn): 15,000).

[0119] <Production Example 3: Production of urethane prepolymer (A-3)> Into a flask equipped with an internal thermometer, a stirrer, and a condenser, 100.0 parts of "PEPCD (registered trademark) NT2002" as the polyether polyol (a1), 100.0 parts of "VESTANAT (registered trademark) H" as the isocyanate compound (b), 12 10.5 parts of MDI, 73.7 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst were added and reacted at 80°C. The reaction was terminated when the residual isocyanate groups reached 0.3% or less, yielding a composition containing urethane prepolymer (A-3) (number average molecular weight (Mn): 21,000).

[0120] <Production Example 4: Production of urethane prepolymer (A-4)> A flask equipped with an internal thermometer, a stirrer, and a condenser was charged with 100.0 parts of PEPCD (registered trademark) NT2002 as the polyether polyol (a1), 8.9 parts of VESTANAT (registered trademark) IPDI as the isocyanate compound (b), 58.6 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst, and the reaction was carried out at 80°C. The reaction was terminated when the remaining isocyanate groups reached 0.3% or less, yielding a composition containing a urethane prepolymer (A-4) (number average molecular weight (Mn): 21,000).

[0121] <Production Example 5: Production of urethane prepolymer (A-5)> Into a flask equipped with an internal thermometer, a stirrer, and a condenser, 100.0 parts of "PEPCD (registered trademark) NT2006" as the polyether polyol (a1), 100.0 parts of "VESTANAT (registered trademark) H" as the isocyanate compound (b), 12 10.5 parts of MDI, 59.5 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst were added and reacted at 80°C. The reaction was terminated when the residual isocyanate groups reached 0.3% or less, yielding a composition containing urethane prepolymer (A-5) (number average molecular weight (Mn): 20,000).

[0122] <Production Example 6: Production of urethane prepolymer (A-6)> A flask equipped with an internal thermometer, a stirrer, and a condenser was charged with 100.0 parts of PEPCD (registered trademark) NT2006 as the polyether polyol (a1), 9.7 parts of VESTANAT (registered trademark) IPDI as the isocyanate compound (b), 59.1 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst, and the reaction was carried out at 80°C. The reaction was terminated when the remaining isocyanate groups reached 0.3% or less, yielding a composition containing a urethane prepolymer (A-6) (number average molecular weight (Mn): 20,000).

[0123] <Production Example 7: Production of urethane prepolymer (A-7)> A flask equipped with an internal thermometer, a stirrer, and a condenser was charged with 100.0 parts of PEPCD (registered trademark) NT2002 as the polyether polyol (a1), 11.4 parts of 4,4'-diphenylmethane diisocyanate (MDI) as the isocyanate compound (b), 136.2 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst, and the mixture was reacted at 80°C. The reaction was terminated when the remaining isocyanate groups reached 0.3% or less, yielding a composition containing a urethane prepolymer (A-7) (number average molecular weight (Mn): 35,000).

[0124] <Production Example 8: Production of urethane prepolymer (A-8)> A flask equipped with an internal thermometer, a stirrer, and a condenser was charged with 100.0 parts of PEPCD (registered trademark) NT2006 as the polyether polyol (a1), 11.6 parts of 4,4'-diphenylmethane diisocyanate (MDI) as the isocyanate compound (b), 111.6 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst, and the mixture was reacted at 80°C. The reaction was terminated when the remaining isocyanate groups reached 0.3% or less, yielding a composition containing a urethane prepolymer (A-8) (number average molecular weight (Mn): 28,000).

[0125] <Production Example 9: Production of urethane prepolymer (A-9)> A flask equipped with an internal thermometer, a stirrer, and a condenser was charged with 100.0 parts of PEPCD (registered trademark) NT2002 as the polyether polyol (a1), 10.0 parts of 4,4'-diphenylmethane diisocyanate (MDI) and 1.1 parts of Duranate (registered trademark) TLA-100 as the isocyanate compound (b), 135.8 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst, and the mixture was reacted at 80°C. The reaction was terminated when the remaining isocyanate groups reached 0.3% or less, yielding a composition containing a urethane prepolymer (A-9) (number average molecular weight (Mn): 27,000).

[0126] <Production Example 10: Production of urethane prepolymer (A-10)> A flask equipped with an internal thermometer, a stirrer, and a condenser was charged with 100.0 parts of PEPCD (registered trademark) NT2002 as the polyether polyol (a1), 10.0 parts of 4,4'-diphenylmethane diisocyanate (MDI) and 2.1 parts of Duranate LE300-100 as the isocyanate compound (b), 137.0 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst, and the mixture was reacted at 80°C. The reaction was terminated when the remaining isocyanate groups reached 0.3% or less, yielding a composition containing a urethane prepolymer (A-10) (number average molecular weight (Mn): 32,000).

[0127] <Production Example 11: Production of urethane prepolymer (A-11)> A flask equipped with an internal thermometer, a stirrer, and a condenser was charged with 100.0 parts of PEPCD (registered trademark) NT2006 as the polyether polyol (a1), 10.2 parts of 4,4'-diphenylmethane diisocyanate (MDI) and 1.1 parts of Duranate (registered trademark) TLA-100 as the isocyanate compound (b), 136.0 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst, and the mixture was reacted at 80°C. The reaction was terminated when the residual isocyanate groups reached 0.3% or less, yielding a composition containing a urethane prepolymer (A-11) (number average molecular weight (Mn): 31,000).

[0128] <Production Example 12: Production of urethane prepolymer (A-12)> A flask equipped with an internal thermometer, a stirrer, and a condenser was charged with 100.0 parts of PEPCD (registered trademark) NT2006 as the polyether polyol (a1), 10.2 parts of 4,4'-diphenylmethane diisocyanate (MDI) and 2.2 parts of Duranate (registered trademark) LE300-100 as the isocyanate compound (b), 137.4 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst, and the mixture was reacted at 80°C. The reaction was terminated when the residual isocyanate groups reached 0.3% or less, yielding a composition containing a urethane prepolymer (A-12) (number average molecular weight (Mn): 29,000).

[0129] <Production Example 13: Production of urethane prepolymer (A'-1)> A flask equipped with an internal thermometer, a stirrer, and a condenser was charged with 100.0 parts of Kuraray Polyol (registered trademark) P-1012 as the polyol (a2), 20.2 parts of 4,4'-diphenylmethane diisocyanate (MDI) as the isocyanate compound (b), 80.1 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst, and the mixture was reacted at 80°C. The reaction was terminated when the remaining isocyanate groups reached 0.3% or less, yielding a composition containing a urethane prepolymer (A'-1) (number average molecular weight (Mn): 8,000).

[0130] <Production Example 14: Production of urethane prepolymer (A'-2)> A flask equipped with an internal thermometer, a stirrer, and a condenser was charged with 100.0 parts of Kuraray Polyol (registered trademark) P-2012 as the polyol (a2), 10.7 parts of 4,4'-diphenylmethane diisocyanate (MDI) as the isocyanate compound (b), 90.6 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst, and the mixture was reacted at 80°C. The reaction was terminated when the remaining isocyanate groups reached 0.3% or less, yielding a composition containing a urethane prepolymer (A'-2) (number average molecular weight (Mn): 12,000).

[0131] <Production Example 15: Production of urethane prepolymer (A'-3)> A flask equipped with an internal thermometer, a stirrer, and a condenser was charged with 100.0 parts of "Sanix (registered trademark) PP-2000" as polyol (a2), 10.3 parts of 4,4'-diphenylmethane diisocyanate (MDI) as isocyanate compound (b), 27.6 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst, and the mixture was reacted at 80°C. The reaction was terminated when the remaining isocyanate groups reached 0.3% or less, yielding a composition containing urethane prepolymer (A'-3) (number average molecular weight (Mn): 12,000).

[0132] <Production Example 16: Production of urethane prepolymer (A'-4)> A flask equipped with an internal thermometer, a stirrer, and a condenser was charged with 100.0 parts of "BioPTMG2000" as polyol (a2), 10.6 parts of 4,4'-diphenylmethane diisocyanate (MDI) as isocyanate compound (b), 24.9 parts of methyl ethyl ketone (MEK) as a solvent, and 0.02 parts of dibutyltin dilaurate (DBTL) as a reaction catalyst, and the mixture was reacted at 80°C. The reaction was terminated when the remaining isocyanate groups reached 0.3% or less, yielding a composition containing urethane prepolymer (A'-4) (number average molecular weight (Mn): 20,000).

[0133] The raw materials used in the production of the urethane prepolymers (A-1) to (A-12) and (A'-1) to (A'-4) produced in Production Examples 1 to 16 above, and the number average molecular weights thereof, are summarized in Tables 1 to 4.

[0134] [Examples 1 to 17 and Comparative Examples 1 to 6] <Preparation of Pressure-Sensitive Adhesive Composition> A crosslinking agent "Takenate (registered trademark) D-101E" (manufactured by Mitsui Chemicals, Inc.) was added to the urethane prepolymers shown in Tables 1 to 4 so as to achieve the reaction equivalent ratios (x) / (y) shown in Tables 1 to 4 (referred to as "NCO / OH equivalent ratio" in Tables 1 to 4), to prepare pressure-sensitive adhesive compositions.

[0135] <Preparation of adhesive sheets for measuring adhesive properties> The obtained adhesive composition was applied using an applicator to the easy-adhesion treated surface of an easy-adhesion treated polyethylene terephthalate film (thickness 38 μm) "Cosmoshine A4360" (manufactured by Toyobo Co., Ltd.) so that the film thickness after curing would be 25 μm, and the film was dried at 130°C for 5 minutes, and then cured by aging at 40°C for one week to obtain an adhesive sheet for measuring adhesive properties.

[0136] <Adhesive strength measurement> The resulting adhesive sheet for measuring adhesive properties was cut into 25mm x 150mm pieces and then pressed onto a stainless steel plate (SUS304BA plate) as an adherend, with a 2kg rubber roller rolling back and forth twice under an atmosphere of 23°C and 50% relative humidity, so that the adhesive area was 25 x 125mm, to prepare a test specimen. After leaving the test specimen in the same atmosphere for a predetermined time (30 minutes or 1 day), a 180° peel test was performed at a peel speed of 0.3m / min, and the adhesive strength (N / 25mm) was measured. The results are shown in Tables 1 to 4.

[0137] <Measuring holding power> The resulting adhesive sheet for measuring adhesive properties was cut into 25 mm x 75 mm pieces and then pressed onto a stainless steel plate (SUS304 #360 polished plate) as an adherend, with a 2 kg rubber roller moving back and forth twice in an atmosphere of 23°C and 50% relative humidity, so that the adhesive area was 25 x 25 mm, to prepare a test specimen. A 1 kg load was applied to this test specimen in an atmosphere of 40°C, and the displacement (mm) or the weight's fall time (min) after 24 hours was measured. The results are shown in Tables 1 to 4. Test specimens that showed no displacement after 24 hours were rated "NC."

[0138] <Gel fraction measurement> The resulting adhesive sheet for measuring adhesive properties was cut into 50 mm x 50 mm pieces and attached to a SUS mesh with a known mass to produce an adhesive sheet-attached SUS mesh. The mass of the adhesive sheet-attached SUS mesh was measured, and the mesh was immersed in toluene at 23°C for 48 hours. After immersion, the adhesive sheet-attached SUS mesh was dried at 100°C for 6 hours and then its mass was measured. The adhesive composition adhering to the substrate sheet was then removed, and the mass of the substrate sheet was measured to calculate the actual amount of adhesive composition in the adhesive sheet. The gel fraction was calculated using the following formula: The results are shown in Tables 1 to 4.

[0139]

number

[0140] <Preparation of adhesive sheet for dynamic viscoelasticity measurement> The obtained adhesive composition was applied using an applicator to the release surface of a release-treated polyethylene terephthalate film (75 μm thick) "SP-PET-03-BU" (manufactured by Mitsui Chemicals Tocello Co., Ltd.) so that the film thickness after curing would be 1 mm, and the composition was dried at 130°C for 5 minutes, and then cured by aging at 40°C for one week, yielding an adhesive sheet for dynamic viscoelasticity measurement. The storage modulus of the obtained adhesive sheet was measured using the method described above. In addition, the storage modulus (G ’-30 ) and storage modulus at 100°C (G' 100 ) and the ratio (G' -30 ) / (G' 100 ) was calculated and evaluated according to the following criteria. These results are shown in Tables 1 to 4. (Evaluation criteria) ◎:(G' -30 ) / (G' 100 ) is greater than 0 and less than or equal to 10.0. 〇:(G' -30 ) / (G' 100 ) is greater than 10.0 and less than or equal to 30.0. △:(G' -30 ) / (G' 100) is greater than 30.0 and less than or equal to 50.0. ×:(G' -30 ) / (G' 100 ) ratio is greater than 50.0.

[0141] [Table 1]

[0142] [Table 2]

[0143] [Table 3]

[0144] [Table 4]

[0145] From the above results, it can be seen that the adhesive composition of the present invention containing the urethane prepolymer (A) of the present invention can reduce the temperature dependence of the storage modulus not only in weakly adhesive adhesives but also in strongly adhesive adhesives, retains adhesive properties even in high temperature ranges, and not only has excellent removability but also can exhibit high adhesion or bonding reliability from low to high temperatures.

Claims

1. A pressure-sensitive adhesive composition comprising a urethane prepolymer (A) obtained by reacting a polyether polyol (a1) having a carbonate bond with an isocyanate compound (b).

2. The pressure-sensitive adhesive composition according to claim 1, wherein the urethane prepolymer (A) has a number average molecular weight of 15,000 or more and 50,000 or less in terms of standard polystyrene molecular weight.

3. The pressure-sensitive adhesive composition according to claim 1, wherein the polyether polyol (a1) having a carbonate bond has a hydroxyl value of 45 mgKOH / g or more and 130 mgKOH / g or less.

4. The pressure-sensitive adhesive composition according to claim 1, wherein the polyether polyol (a1) having a carbonate bond has a number average molecular weight calculated from a hydroxyl value of 860 or more and 2,500 or less.

5. The urethane prepolymer (A) has a storage modulus (G') at −30° C. after curing under the following curing conditions: －３０ ) and storage modulus at 100°C (G' １００ ) ratio (G' －３０ ) / (G' １００ 2. The pressure-sensitive adhesive composition according to claim 1, which provides a cured product having a modulus of elasticity of 50 or less. [Curing conditions] A pressure-sensitive adhesive composition (i) is obtained by blending a urethane prepolymer (A) with Takenate (registered trademark) D-101E (manufactured by Mitsui Chemicals, Inc.) as a crosslinking agent such that the reactive functional group (x) possessed by the crosslinking agent and the active hydrogen group (y) possessed by the urethane prepolymer (A) have a reaction equivalent ratio (x) / (y) of 0.5 to 1.

25. The resulting pressure-sensitive adhesive composition (i) is applied to the release surface of a release-treated polyethylene terephthalate film (thickness: 75 μm) "SP-PET-03-BU" (manufactured by Mitsui Chemicals Tocello, Inc.) using an applicator so that the film thickness after curing is 1 mm, dried at 130°C for 5 minutes, and then cured by aging at 40°C for one week.

6. The pressure-sensitive adhesive composition according to claim 1 , wherein the urethane prepolymer (A) provides a cured product having a gel fraction of 30 mass % or more after curing under the following curing conditions: [Curing conditions] A urethane prepolymer (A) and a crosslinking agent, Takenate (registered trademark) D-101E (manufactured by Mitsui Chemicals, Inc.), are blended so that the reaction equivalent ratio (x) / (y) between the reactive functional group (x) of the crosslinking agent and the active hydrogen group (y) of the urethane prepolymer (A) is 0.5 to 1.25, thereby obtaining a pressure-sensitive adhesive composition (i). The resulting pressure-sensitive adhesive composition (i) is applied using an applicator to the easy-adhesion-treated surface of an easy-adhesion-treated polyethylene terephthalate film (thickness: 38 μm) "Cosmoshine A4360" (manufactured by Toyobo Co., Ltd.) so that the film thickness after curing is 25 μm, and the composition is dried at 130°C for 5 minutes, and then aged at 40°C for one week to allow it to cure.

7. The pressure-sensitive adhesive composition according to any one of claims 1 to 6, further comprising a crosslinking agent.

8. 8. The pressure-sensitive adhesive composition according to claim 7, comprising the urethane prepolymer (A) and the crosslinking agent such that a reaction equivalent ratio (x) / (y) between a reactive functional group (x) of the crosslinking agent and an active hydrogen group (y) of the urethane prepolymer (A) is 0.5 to 1.

25.

9. The storage modulus (G') at -30°C of the cured product obtained by the reaction of the active hydrogen group (y) with the reactive functional group (x) －３０ ) and storage modulus at 100°C (G' １００ ) ratio (G' －３０ ) / (G' １００ 9. The pressure-sensitive adhesive composition according to claim 8, wherein the value of (a) is 50 or less.

10. The pressure-sensitive adhesive composition according to claim 8, wherein the gel fraction of a cured product obtained by the reaction of the active hydrogen group (y) with the reactive functional group (x) is 30 to 90 mass%.

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