Adhesive composition, adhesive, and adhesive sheet

Abstract

To provide an adhesive composition which is excellent in bending durability and high temperature reliability while being excellent in adhesive force to an adherend, and is also excellent in shape restorability after an adhesive layer has been deformed.SOLUTION: An adhesive composition contains an acrylic resin (A), in which the acrylic resin (A) contains at least two acrylic resins having different glass transition temperatures (T) read from a temperature at which a loss tangent of dynamic viscoelasticity is maximum, and at least one acrylic resin contains an active energy ray-curable site.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an adhesive composition, an adhesive, and an adhesive sheet. Specifically, it has excellent adhesive force to an adherend, and also has excellent bending durability (durability when repeatedly bent) and reliability in a high-temperature environment (hereinafter sometimes referred to as "high-temperature reliability"), and further, an adhesive composition, an adhesive, and an adhesive sheet that are also excellent in shape recoverability (hereinafter sometimes referred to as "shape recoverability") after the adhesive layer is deformed.

Background Art

[0002] In recent years, in mobile devices such as televisions, monitors for personal computers, notebook computers, mobile phones, tablet terminals, and wearable terminals, a protective layer formed of a plastic sheet or the like is usually provided on the viewing side of the display, and a space (air layer) is provided between the display and the protective layer to prevent damage to the display due to external impact. However, there is a problem that reflection occurs at the interface between the protective layer and the air layer and at the interface between the air layer and the display, causing a decrease in visibility. Therefore, in recent years, in order to ensure impact resistance while improving visibility and further thinning mobile devices (plastic sheets), an impact-absorbing adhesive layer is used instead of the air layer.

[0003] In order for the adhesive layer to exhibit sufficient impact-absorbing performance, it is necessary to have a certain thickness. For thick coating applications, a solvent-based acrylic adhesive that has been commonly used conventionally, a hot-melt adhesive that can be a solvent-free adhesive, and an active energy ray-curable adhesive have been proposed (see, for example, Patent Document 1). Among solvent-free adhesives, hot-melt adhesives do not require a drying process for volatilizing the solvent after coating, and an adhesive layer can be efficiently obtained in a short time even when thick coating is performed.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-214280 [Summary of the Invention] [Problems to be Solved by the Invention]

[0005] In recent years, due to the high functionality, multifunctionality, and further diversification of designs of mobile devices, the curvature and flexibility of flat displays have been demanded. Along with this, adhesives with durability for repeated bending, such as the substrate not cracking even when bent and no cracks or the like entering the substrate even when repeatedly bent, and durability in a bent state such as reliability in a high-temperature and high-humidity environment in a bent state have been required. Furthermore, from the viewpoint of suppressing the deformation of the adhesive layer after bending, it is also required to quickly recover from deformation (strain) caused by an external force.

[0006] However, in the technology disclosed in the above Patent Document 1, these bending durabilities are not considered, and an improvement as an adhesive composition is required. In addition, an adhesive with a low elastic modulus can be considered from the viewpoint of improving bending durability, but there is a concern that only this may reduce the adhesive strength and the like. Furthermore, further improvement is required to balance all of the resilience to deformation of the adhesive layer, bending durability, adhesive strength, reliability in a high-temperature environment, etc. to be excellent.

[0007] Therefore, in the present invention, under such a background, an object is to provide an adhesive composition that is excellent in adhesive strength to an adherend, excellent in bending durability and high-temperature reliability, and further excellent in shape recoverability after the adhesive layer is deformed. [Means for Solving the Problems]

[0008] However, as a result of intensive research in view of such circumstances, the present inventors have found that in an adhesive composition containing an acrylic resin, by containing at least two kinds of acrylic resins having different glass transition temperatures (T), and containing an active energy ray curable site in at least one of the acrylic resins, the adhesive has excellent adhesion to an adherend, excellent bending durability and high temperature reliability, and further excellent shape recoverability after the adhesive layer is deformed, and thus completed the present invention.

[0009] That is, the first aspect of the present invention is an adhesive composition containing an acrylic resin (A), wherein the acrylic resin (A) contains at least two kinds of acrylic resins having different glass transition temperatures (T) read from the temperature at which the loss tangent of dynamic viscoelasticity is maximum, and at least one of the acrylic resins contains an active energy ray curable site.

[0010] Furthermore, in the present invention, the second aspect is an adhesive using the adhesive composition of the first aspect, and the third aspect is an adhesive sheet having an adhesive layer using the adhesive composition of the first aspect.

Effects of the Invention

[0011] The adhesive composition of the present invention is an adhesive composition containing an acrylic resin (A), wherein the acrylic resin (A) contains at least two kinds of acrylic resins having different glass transition temperatures (T) read from the temperature at which the loss tangent of dynamic viscoelasticity is maximum, and at least one of the acrylic resins contains an active energy ray curable site. Therefore, it has excellent adhesion to an adherend, excellent bending durability and high temperature reliability, and further excellent shape recoverability after the adhesive layer is deformed. Therefore, it is particularly useful as an adhesive and an adhesive sheet used for touch panels, image display devices, etc., especially touch panels and image display devices such as foldable or rollable smartphones.

Modes for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in detail, which shows an example of a preferred embodiment. In the present invention, “(meth)acryl” means acrylic or methacrylic, “(meth)acryloyl” means acryloyl or methacryloyl, and “(meth)acrylate” means acrylate or methacrylate, respectively.

[0013] The pressure-sensitive adhesive composition of the present invention contains an acrylic resin (A). First, the acrylic resin (A) will be described.

[0014] <Acrylic resin (A)> In the present invention, the above acrylic resin (A) contains at least two acrylic resins having different glass transition temperatures (T) read from the temperature at which the loss tangent of dynamic viscoelasticity is maximum, from the viewpoints of adhesive strength, bending durability, and shape recovery. Furthermore, at least one of the acrylic resins contains an active energy ray-curable site.

[0015] In the present invention, furthermore, it is preferable from the viewpoint of compatibility that the temperature difference between the glass transition temperature (T1) of the acrylic resin (A1) having the highest glass transition temperature and the glass transition temperature (T2) of the acrylic resin (A2) having the lowest glass transition temperature among the above acrylic resins (A) is 20°C or less. The above glass transition temperature can be read from the temperature at which the loss tangent of dynamic viscoelasticity is maximum, and more specifically, it is measured under the conditions used in the examples described later.

[0016] The acrylic resin (A) containing at least two acrylic resins having different glass transition temperatures is usually obtained by mixing acrylic resins having different glass transition temperatures produced separately. The acrylic resin (A) containing at least two acrylic resins having different glass transition temperatures can also be obtained, for example, by devising a polymerization method such as two-stage polymerization.

[0017] When mixing acrylic resins with different glass transition temperatures produced separately, the number of acrylic resins is usually 2 to 4, preferably 2 to 3, and particularly preferably 2. The productivity and economy tend to decrease as the number of acrylic resins contained in the acrylic resin (A) increases. First, the acrylic resin used in the present invention will be described.

[0018] The acrylic resin is preferably obtained by polymerizing a polymerization component containing a hydroxyl group-containing monomer (a1), and more preferably further contains at least one copolymerizable monomer (a2) selected from (meth)acrylic acid alkyl ester monomers and vinyl ester monomers having an alkyl group with 5 to 14 carbon atoms (excluding (a1)), at least one copolymerizable monomer (a3) selected from (meth)acrylic acid alkyl ester monomers and vinyl ester monomers having an alkyl group with 1 to 4 carbon atoms (excluding (a1) and (a2)), optionally a functional group-containing ethylenically unsaturated monomer (a4) (excluding (a1)), and other copolymerizable monomers (a5) as polymerization components.

[0019] 〈Hydroxyl group-containing monomer (a1)〉 Examples of the hydroxyl group-containing monomer (a1) include hydroxy (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate; caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth) acrylate; oxyalkylene-modified monomers such as diethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate; primary hydroxyl group-containing monomers such as 2-acryloyloxyethyl-2-hydroxyethyl phthalate; secondary hydroxyl group-containing monomers such as 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-chloro-2-hydroxypropyl (meth) acrylate; and tertiary hydroxyl group-containing monomers such as 2,2-dimethyl-2-hydroxyethyl (meth) acrylate. These can be used alone or in combination of two or more.

[0020] Among the above hydroxyl group-containing monomers (a1), 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, particularly 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate are particularly preferably used in terms of excellent balance between moisture and heat resistance and heat resistance.

[0021] When producing the acrylic resin (A2) described later, from the viewpoint of achieving both adhesiveness and bending durability, it is preferable to use a hydroxyl group-containing monomer containing 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate as a polymerization component, and it is particularly preferable to contain only 2-hydroxy (meth) acrylate and 4-hydroxybutyl (meth) acrylate as the hydroxyl group-containing monomer.

[0022] In the present invention, the polymerization ratio of the above 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate [2-hydroxyethyl (meth) acrylate / 4-hydroxybutyl (meth) acrylate] is preferably 95 / 5 to 30 / 70 on a weight basis, more preferably 80 / 20 to 40 / 60, particularly preferably 75 / 25 to 45 / 55, and especially preferably 70 / 30 to 50 / 50. If the amount of 2-hydroxyethyl (meth) acrylate is too small, the adhesive strength when used as an adhesive tends to decrease, and if it is too large, the bending durability when used as an adhesive tends to decrease.

[0023] In addition, as the hydroxyl group-containing monomer (a1) used in the present invention, the lower the content ratio of di (meth) acrylate contained as an impurity in the hydroxyl group-containing monomer (a1), the more preferable it is. Specifically, it is preferably those having 0.5% by weight or less, particularly preferably 0.2% by weight or less, more preferably 0.1% by weight or less, and most preferably 0% by weight.

[0024] In the present invention, the content of the hydroxyl group-containing monomer (a1) is usually 5 to 60% by weight, preferably 7 to 40% by weight, particularly preferably 8 to 30% by weight, more preferably 11 to 25% by weight, and especially preferably 12 to 20% by weight with respect to the total polymerization components. If such a content is too small, the wet heat resistance when used as an adhesive tends to decrease, and if it is too large, the self-crosslinking reaction of the acrylic resin tends to occur, and the heat resistance tends to decrease.

[0025] <At least one copolymerizable monomer (a2) selected from (meth) acrylic acid alkyl ester monomers and vinyl ester monomers having an alkyl group having 5 to 14 carbon atoms> In the present invention, as the polymerization component, it is further preferred to contain a copolymerizable monomer having a structure in which hydrogen abstraction easily occurs in a high-energy state such as high temperature or ultraviolet irradiation, and as a result, crosslinking is easily formed, and after copolymerization, it is possible to lower the glass transition temperature of the acrylic resin. In particular, it is particularly preferred to contain at least one copolymerizable monomer (a2) selected from (meth)acrylic acid alkyl ester monomers and vinyl ester monomers having an alkyl group with 5 to 14 carbon atoms. More preferably, it is a (meth)acrylic acid alkyl ester monomer having an alkyl group with 5 to 14 carbon atoms having a branched structure, and particularly preferably 2-ethylhexyl (meth)acrylate. These can be used alone or in combination of two or more.

[0026] The content of the copolymerizable monomer (a2) is preferably 15 to 90% by weight based on the total polymerization components, particularly preferably 20 to 85% by weight, more preferably 30 to 80% by weight, particularly preferably 40 to 75% by weight, and most preferably 45 to 70% by weight. When such content is too small, the step-following property and durability when used as an adhesive tend to decrease. On the other hand, when the copolymerizable monomer (a2) is too much, the adhesive strength when used as an adhesive tends to decrease.

[0027] 〈At least one copolymerizable monomer (a3) selected from (meth)acrylic acid alkyl ester monomers and vinyl ester monomers having an alkyl group with 1 to 4 carbon atoms〉 In the present invention, as the polymerization component, it is preferred to contain at least one copolymerizable monomer (a3) selected from (meth)acrylic acid alkyl ester monomers and vinyl ester monomers having an alkyl group with 1 to 4 carbon atoms (excluding (a1) and (a2)) from the viewpoints of improving cohesion, further improving the adhesive strength when used as an adhesive, and improving the reliability in a high-temperature environment.

[0028] Examples of the copolymerizable monomer (a3) include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, isobutyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, vinyl propionate, vinyl acetate and the like. These copolymerizable monomers (a3) may be used alone or in combination of two or more. Among the copolymerizable monomers (a3), it is preferable to use methyl (meth) acrylate, ethyl (meth) acrylate, or t-butyl (meth) acrylate from the viewpoint of improving the cohesive force when used as an adhesive.

[0029] Among the copolymerizable monomers (a3), it is preferable to use at least one of methyl (meth) acrylate and ethyl (meth) acrylate, i.e., (meth) acrylate (a3-1), in order to further exert the effects of the present invention.

[0030] The content of the copolymerizable monomer (a3) is preferably 5 to 70% by weight, particularly preferably 10 to 60% by weight, and still more preferably 15 to 45% by weight based on the total polymerization components. If the content of the copolymerizable monomer (a3) is too small, the adhesive strength tends to decrease when used as an adhesive. If it is too large, the bending durability tends to decrease when used as an adhesive.

[0031] When using at least one of methyl (meth) acrylate and ethyl (meth) acrylate, i.e., (meth) acrylate (a3-1), as the component (a3), the content is preferably 5 to 40% by weight, particularly preferably 7 to 30% by weight, and still more preferably 10 to 25% by weight based on the total polymerization components. If the content of (a3-1) is too large, the handleability during processing tends to decrease due to an increase in viscosity. If it is too small, the adhesive strength tends to decrease when used as an adhesive.

[0032] 〈Functional group-containing ethylenically unsaturated monomer (a4)〉 In the present invention, a functional group-containing ethylenically unsaturated monomer (a4) (excluding (a1)) can be used as a polymerization component of the acrylic resin as needed.

[0033] Examples of the functional group-containing ethylenically unsaturated monomer (a4) include a functional group-containing monomer having a nitrogen atom, an acetoacetyl group-containing monomer, an isocyanate group-containing monomer, a glycidyl group-containing monomer, and the like. Among these, a functional group-containing monomer having a nitrogen atom is preferable in terms of imparting cohesive force and crosslinking promoting action, particularly preferably an amino group-containing monomer or an amide group-containing monomer, and more preferably an amino group-containing monomer.

[0034] Examples of the amino group-containing monomer include primary amino group-containing (meth)acrylates such as aminomethyl (meth)acrylate and aminoethyl (meth)acrylate; secondary amino group-containing (meth)acrylates such as t-butylaminoethyl (meth)acrylate and t-butylaminopropyl (meth)acrylate; tertiary amino group-containing (meth)acrylates such as ethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, diethylaminopropyl (meth)acrylate, and dimethylaminopropylacrylamide; and the like.

[0035] Examples of the amide group-containing monomer include (meth)acrylamide; N-alkyl(meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-n-butyl(meth)acrylamide, diacetone(meth)acrylamide, and N,N'-methylenebis(meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-ethylmethylacrylamide, and N,N-diallyl(meth)acrylamide; hydroxyalkyl(meth)acrylamides such as N-hydroxymethyl(meth)acrylamide and N-hydroxyethyl(meth)acrylamide; alkoxyalkyl(meth)acrylamides such as N-methoxymethyl(meth)acrylamide and N-(n-butoxymethyl)(meth)acrylamide; and the like.

[0036] Examples of the acetoacetyl group-containing monomer include 2-(acetoacetoxy)ethyl (meth)acrylate and allyl acetoacetate.

[0037] Examples of the isocyanate group-containing monomer include 2-acryloyloxyethyl isocyanate, 2-methacryloyloxyethyl isocyanate, and their alkylene oxide adducts.

[0038] Examples of the glycidyl group-containing monomer include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate.

[0039] These functional group-containing ethylenically unsaturated monomers (a4) may be used alone or in combination of two or more.

[0040] The content of the above functional group-containing ethylenically unsaturated monomer (a4) is preferably 30% by weight or less, particularly preferably 20% by weight or less, more preferably 10% by weight or less, and especially preferably 5% by weight or less, based on the total polymerization components. The lower limit is usually 0% by weight. If the content of the functional group-containing ethylenically unsaturated monomer (a4) is too high, the heat resistance of the resin tends to decrease.

[0041] 〈Other copolymerizable monomer (a5)〉 In the present invention, other copolymerizable monomer (a5) can be used as needed as a polymerization component of the acrylic resin.

[0042] Examples of the above other copolymerizable monomer (a5) include aromatic (meth)acrylate monomers such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyldiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol - polypropylene glycol - (meth)acrylate, nonylphenol ethylene oxide adduct (meth)acrylate, and monomers such as acrylonitrile, methacrylonitrile, styrene, α - methylstyrene, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, dialkyl itaconate, dialkyl fumarate, allyl alcohol, acrylic chloride, methyl vinyl ketone, N - acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinyl ketone. These can be used alone or in combination of two or more.

[0043] When aiming to increase the molecular weight of the acrylic resin, for example, a small amount of a compound having two or more ethylenically unsaturated groups such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, divinylbenzene, etc. can be used in combination. At this time, these compounds having two or more ethylenically unsaturated groups have high reactivity and usually do not remain unreacted when used as a polymerization component of the acrylic resin. However, if the usage amount is too large, these compounds having two or more ethylenically unsaturated groups will remain unreacted, and the acrylic resin tends to gel.

[0044] The content of the above-mentioned other copolymerizable monomer (a5) is preferably 50% by weight or less, particularly preferably 40% by weight or less, and more preferably 20% by weight or less, based on the total polymerization components. The lower limit is usually 0% by weight. If the content ratio of the above-mentioned other copolymerizable monomer (a5) is too high, the resin may have reduced temporal stability such as thickening over time or a tendency for the adhesive strength to decrease. The thickening can be confirmed by measuring the viscosity change over time at normal temperature or in a 40°C atmosphere.

[0045] The acrylic resin used in the present invention can be produced by appropriately selecting the above-mentioned polymerization components so as to obtain a desired glass transition temperature and then polymerizing them.

[0046] As the above-mentioned polymerization method, for example, conventionally known polymerization methods such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. can be used. In the present invention, solution polymerization is preferred in that an acrylic resin can be produced safely, stably, and with an arbitrary monomer composition. Hereinafter, an example of a preferred production method of the acrylic resin used in the present invention is shown.

[0047] First, in an organic solvent, the above-mentioned polymerization components and a polymerization initiator are mixed or dropped, and solution polymerization is carried out to obtain an acrylic resin solution.

[0048] 〔Organic solvent〕 Examples of the organic solvent used in the above polymerization reaction include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as hexane, esters such as ethyl acetate and butyl acetate, aliphatic alcohols such as N-propyl alcohol and isopropyl alcohol, and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. These can be used alone or in combination of two or more. Among these solvents, it is preferable to use ethyl acetate, acetone, methyl ethyl ketone, and methyl acetate from the viewpoints of solubility, drying property during coating, price, etc., and it is particularly preferable to use ethyl acetate and acetone.

[0049] 〔Polymerization initiator〕 As the polymerization initiator used in the above polymerization reaction, an azo-based polymerization initiator or a peroxide-based polymerization initiator, which are ordinary radical polymerization initiators, can be used. Examples of the azo-based polymerization initiator include 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, (1-phenylethyl)azodiphenylmethane, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), etc. Examples of the peroxide-based polymerization initiator include benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, lauroyl peroxide, t-butyl peroxy pivalate, t-hexyl peroxy pivalate, t-hexyl peroxy neodecanoate, diisopropyl peroxydicarbonate, diisobutyryl peroxide, etc. These can be used alone or in combination of two or more.

[0050] In the production of the above acrylic resin, it is preferable to use an organic solvent with a boiling point of 80°C or lower as the reaction solvent for solution polymerization and carry out the polymerization at a relatively low temperature. At this time, if a polymerization initiator with a high 10-hour half-life temperature is used, the polymerization initiator tends to remain. When the polymerization initiator remains, the stability of the acrylic resin solution over time decreases, and gelation of the acrylic resin tends to occur.

[0051] Therefore, from the viewpoint of improving the stability of the acrylic resin solution over time, it is preferable to use a polymerization initiator having a 10-hour half-life temperature of 70°C or lower among the above polymerization initiators. Among them, particularly preferably, 2,2'-azobis(2-methylbutyronitrile) (67°C), 2,2'-azobisisobutyronitrile (65°C), 2,2'-azobis(2,4-dimethylvaleronitrile) (52°C), 2,2'-azobis(2-cyclopropylpropionitrile) (49.6°C), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (30°C), t-butylperoxypivalate (54.6°C), t-hexylperoxypivalate (53.2°C), t-hexylperoxyneodecanoate (44.5°C), diisopropylperoxycarbonate (40.5°C), diisobutyrylperoxide (32.7°C), and more preferably 2,2'-azobis(2,4-dimethylvaleronitrile) (52°C), t-hexylperoxypivalate (53.2°C). The numerical value in the parentheses described following each of the above compound names is the 10-hour half-life temperature of each compound.

[0052] The amount of the above polymerization initiator used is usually 0.001 to 10 parts by weight, preferably 0.1 to 8 parts by weight, particularly preferably 0.5 to 6 parts by weight, more preferably 1 to 4 parts by weight, especially preferably 1.5 to 3 parts by weight, and most preferably 2 to 2.5 parts by weight based on 100 parts by weight of the polymerization components. If the amount of the above polymerization initiator used is too small, the polymerization rate of the acrylic resin tends to decrease and the residual monomer tends to increase. If the amount used is too large, gelation of the acrylic resin occurs, etc., and the stability of the acrylic resin solution over time tends to decrease.

[0053] 〔Coincidence conditions, etc.〕 Regarding the polymerization conditions for solution polymerization, polymerization may be carried out according to conventionally known polymerization conditions. For example, in a solvent, a polymerization component and a polymerization initiator can be mixed or dropped and polymerized under predetermined polymerization conditions.

[0054] The polymerization temperature in the above polymerization reaction is usually 40 to 120 °C. However, in the present invention, from the viewpoint of stable reaction, 50 to 90 °C is preferable, particularly preferably 55 to 75 °C, and more preferably 60 to 70 °C. If the polymerization temperature is too high, the acrylic resin tends to gel. If it is too low, the activity of the polymerization initiator decreases, resulting in a decrease in the polymerization rate and an increase in residual monomers.

[0055] Also, the polymerization time in the polymerization reaction (when the subsequent forced heating is carried out, it is the time until the start of forced heating) is not particularly limited, but it is preferably 0.5 hours or more from the addition of the last polymerization initiator, particularly preferably 1 hour or more, more preferably 2 hours or more, and particularly preferably 5 hours or more. The upper limit of the polymerization time is usually 72 hours. Note that the polymerization reaction is preferably carried out while refluxing the solvent because heat removal is easy.

[0056] In the production of the above acrylic resin, in order to reduce the amount of residual polymerization initiator, it is preferable to thermally decompose the polymerization initiator by forced heating.

[0057] The above forced heating temperature is preferably carried out at a temperature higher than the 10-hour half-life temperature of the above polymerization initiator. Specifically, it is usually 40 to 150 °C, preferably 55 to 130 °C from the viewpoint of gelation suppression, and particularly preferably 75 to 95 °C. If the forced heating temperature is too high, the acrylic resin tends to turn yellow. If it is too low, the polymerization components and polymerization initiator remain, and the gelation and thickening of the acrylic resin occur, resulting in a tendency for the stability over time and thermal stability to decrease. Thus, an acrylic resin solution can be obtained.

[0058] In the present invention, it is necessary that at least one of the above acrylic resins (A) contains an active energy ray curable site. Preferably, in the above acrylic resin (A), both the acrylic resin (A1) having the highest glass transition temperature and the acrylic resin (A2) having the lowest glass transition temperature contain an active energy ray curable site.

[0059] The above active energy ray curable site is a structural site that can react with a part of the acrylic resin or other curing components contained in the acrylic resin composition upon irradiation with active energy rays to form a crosslinked structure.

[0060] Among these, a benzophenone structure and an ethylenically unsaturated group are preferable in that they can be crosslinked efficiently. Therefore, as the active energy ray curable site of the acrylic resin, at least one selected from a benzophenone structure and an ethylenically unsaturated group is preferably used.

[0061] The benzophenone structure means a group having at least a benzophenone skeleton. Examples thereof include a monovalent benzophenone group which may have a substituent and a divalent dibenzophenone group which may have a substituent. Specific examples of the monovalent benzophenone group which may have a substituent include 4,4'-bis(diethylamino)benzophenone having one free valence and 4-methylbenzophenone having one free valence.

[0062] On the other hand, the ethylenically unsaturated group means an ethenyl group which may have a substituent. Specific examples of the ethenyl group which may have a substituent include an ethenyl group and a 1-methylethenyl group.

[0063] The above active energy ray curable site can be introduced by copolymerizing as a monomer when producing the acrylic resin, or can be introduced by using an addition reaction or the like after producing the acrylic resin.

[0064] When introducing by copolymerization, as the monomer, a monomer (α) having an ethylenically unsaturated group and an active energy ray curable site may be used. For example, a monomer having two or more ethylenically unsaturated groups, a monomer having an ethylenically unsaturated group and a photo radical generating group, etc. may be mentioned. In the "ethylenically unsaturated group and active energy ray curable site" of the above monomer (α), the ethylenically unsaturated group means a site for copolymerization, while the active energy ray curable site means a site for imparting photocurability by hanging on an acrylic resin.

[0065] Among these, a monomer having an ethylenically unsaturated group and a photo radical generating group is preferable in terms of excellent stability during polymerization, and further, a monomer having an ethylenically unsaturated group and a benzophenone structure is preferable in terms of reactivity. Specific examples of the monomer having an ethylenically unsaturated group and a benzophenone structure include 4-acryloyloxybenzophenone, 4-methacryloyloxybenzophenone (4MBP), etc.

[0066] The content ratio of the structural unit derived from the monomer (α) having an ethylenically unsaturated group and an active energy ray curable site in the acrylic resin is preferably 0.001 to 10% by weight, more preferably 0.01 to 5% by weight, still more preferably 0.015 to 1% by weight, even more preferably 0.02 to 0.5% by weight, and particularly preferably 0.05 to 0.25% by weight with respect to the whole polymerization components. When the content ratio of the structural unit derived from the monomer (α) having an ethylenically unsaturated group and an active energy ray curable site in the acrylic resin is within the above range, a crosslinked structure can be efficiently formed by active energy rays, the crosslink density becomes constant, and it is possible to obtain a sufficient molecular weight between crosslinking points. Therefore, when used as an adhesive, the shape recovery of the adhesive layer can be enhanced while maintaining the adhesive strength.

[0067] In addition, as a method of performing an addition reaction after producing an acrylic resin, there is a method of introducing a compound having a functional group in the acrylic resin and a site reactive with such a functional group and an active energy ray curable site by reacting with the acrylic resin having the functional group.

[0068] For example, there are a method of urethanizing and adding a compound having an active energy ray curable site and an isocyanate group to a hydroxyl group-containing acrylic resin, a method of esterifying and adding a compound having an active energy ray curable site and a carboxyl group, and the like. Further, methods of reacting a carboxyl group-containing acrylic resin with a compound having an active energy ray curable site and an epoxy group, a compound having an active energy ray curable site and an oxetanyl group, and a method of esterifying and adding a compound having an active energy ray curable site and a hydroxyl group are exemplified.

[0069] Among these methods, a method of adding a compound having an active energy ray curable site and an isocyanate group to an acrylic resin having a hydroxyl group is preferable in terms of excellent stability and addition efficiency during addition. Examples of the compound having an active energy ray curable site and an isocyanate group include 2-acryloyloxyethyl isocyanate (AOI), 2-methacryloyloxyethyl isocyanate (MOI), and 2-(2-methacryloyloxyethyloxy)ethyl isocyanate.

[0070] The amount of the compound to be added is preferably 0.001 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, still more preferably 0.015 to 1 part by weight, even more preferably 0.02 to 0.5 part by weight, and particularly preferably 0.05 to 0.25 part by weight with respect to 100 parts by weight of the acrylic resin having a functional group. When the amount of the compound to be added is within the above range, the addition reaction proceeds efficiently, and a crosslinked structure can be efficiently formed by active energy rays, the crosslink density becomes constant, and a sufficient molecular weight between crosslinking points can be obtained. Therefore, when used as an adhesive, the shape recoverability of the adhesive layer can be enhanced while maintaining the adhesive strength.

[0071] The average molecular weight between structural units derived from the monomer (α) having an ethylenically unsaturated group and an active energy ray curable site in the acrylic resin is preferably from 10,000 to 2,000,000, more preferably from 30,000 to 1,500,000. When the weight average molecular weight of the acrylic resin is less than 800,000, the average molecular weight between structural units derived from the monomer (α) having an ethylenically unsaturated group and an active energy ray curable site in the acrylic resin is preferably from 30,000 to 700,000, more preferably from 50,000 to 500,000, particularly preferably from 70,000 to 350,000. On the other hand, when the weight average molecular weight of the acrylic resin is 800,000 or more, the average molecular weight between structural units derived from the monomer (α) having an ethylenically unsaturated group and an active energy ray curable site in the acrylic resin is preferably from 50,000 to 2,000,000, more preferably from 100,000 to 1,000,000, particularly preferably from 150,000 to 850,000.

[0072] The average molecular weight between structural units derived from the monomer (α) having an ethylenically unsaturated group and an active energy ray curable site is calculated by the following formula. [Formula 1] Average molecular weight between structural units derived from the monomer (α) having an ethylenically unsaturated group and an active energy ray curable site = 100 / number of moles of structural units derived from the monomer (α) in 100 g of the acrylic resin

[0073] Thus, an acrylic resin containing an active energy ray curable site is obtained. In the present invention, as described above, it is necessary that at least one of the acrylic resins (A) contains an active energy ray curable site. Preferably, in the above acrylic resin (A), both the acrylic resin (A1) having the highest glass transition temperature and the acrylic resin (A2) having the lowest glass transition temperature contain an active energy ray curable site.

[0074] In the present invention, the content ratio of the active energy ray curable site in the acrylic resin (A) is preferably 0.001 to 10% by weight, more preferably 0.01 to 1% by weight, still more preferably 0.015 to 0.5% by weight, and particularly preferably 0.02 to 0.25% by weight, from the viewpoints of the shape recoverability and the adhesive strength of the adhesive layer. If such a content ratio is too small, the shape recoverability of the adhesive layer tends to decrease, and if it is too large, the adhesive strength tends to decrease.

[0075] Furthermore, the content ratio of the active energy ray curable site in the acrylic resin (A1) is preferably 0.001 to 10% by weight, more preferably 0.01 to 1% by weight, still more preferably 0.015 to 0.5% by weight, and particularly preferably 0.02 to 0.2% by weight, from the viewpoints of the shape recoverability and the adhesive strength of the adhesive layer. If such a content ratio is too small, the shape recoverability of the adhesive layer tends to decrease, and if it is too large, the adhesive strength tends to decrease.

[0076] Also, the content ratio of the active energy ray curable site in the acrylic resin (A2) is preferably 0.001 to 10% by weight, more preferably 0.01 to 1% by weight, still more preferably 0.015 to 0.5% by weight, and particularly preferably 0.02 to 0.2% by weight, from the viewpoints of the shape recoverability and the adhesive strength of the adhesive layer. If such a content ratio is too small, the shape recoverability of the adhesive layer tends to decrease, and if it is too large, the adhesive strength tends to decrease.

[0077] In the present invention, the acrylic resins (A1) and (A2) preferably contain a structural site derived from the hydroxyl group-containing monomer (a1), and the content of the structural site derived from the hydroxyl group-containing monomer (a1) in the acrylic resin is usually 5 to 60% by weight, preferably 7 to 40% by weight, particularly preferably 8 to 30% by weight, still more preferably 11 to 25% by weight, and especially preferably 12 to 20% by weight based on the total polymerization components.

[0078] In addition, the above acrylic resins (A1) and (A2) preferably contain, in addition to the structural moiety derived from the hydroxyl group-containing monomer (a1), a structural moiety derived from at least one of methyl (meth) acrylate and ethyl (meth) acrylate, i.e., (meth) acrylate (a3-1). The content of the structural moiety derived from such (meth) acrylate (a3-1) is usually 5 to 40% by weight, preferably 7 to 30% by weight, and particularly preferably 10 to 25% by weight based on the acrylic resin.

[0079] In the above acrylic resin (A1), from the viewpoint of excellent adhesion, it is particularly preferable that the (meth) acrylate (a3-1) contains a structural moiety derived from methyl (meth) acrylate and ethyl (meth) acrylate.

[0080] In addition, in the above acrylic resin (A2), from the viewpoints of excellent bending durability and adhesion, it is particularly preferable that the (meth) acrylate (a3-1) contains a structural moiety derived from ethyl (meth) acrylate.

[0081] Here, the proportion (composition ratio) of the structural moiety derived from each component of the above acrylic resin can be determined, for example, by NMR.

[0082] The glass transition temperature (T1) of the above acrylic resin (A1) is preferably -25 to -10 °C, more preferably -23 to -12 °C, and particularly preferably -21 to -15 °C. If the glass transition temperature is too low, the adhesion tends to decrease, and if the glass transition temperature is too high, the bending durability tends to decrease.

[0083] On the premise that the glass transition temperature (T2) of the above acrylic resin (A2) is lower than the glass transition temperature of the above acrylic resin (A1), it is preferably -40 to -20 °C, more preferably -35 to -23 °C, and particularly preferably -30 to -25 °C. If the glass transition temperature is too low, the adhesion and the reliability under high-temperature environments tend to decrease, and if the glass transition temperature is too high, the bending durability tends to decrease.

[0084] Furthermore, from the viewpoints of compatibility of the acrylic resins, and further the balance between adhesive strength and bending durability, it is preferable that the temperature difference between the glass transition temperature (T1) of the acrylic resin (A1) with the highest glass transition temperature and the glass transition temperature (T2) of the acrylic resin (A2) with the lowest glass transition temperature is 20°C or less, more preferably 15°C or less, particularly preferably 10°C or less, and even more preferably 8°C or less. If the temperature difference of the glass transition temperature is too large, the compatibility of the resins tends to decrease. The lower limit value of such a temperature difference is preferably 3°C, particularly preferably 4°C. If the temperature difference is too small, either the adhesive strength or the bending durability tends to decrease.

[0085] Also, as the glass transition temperature (T) of the acrylic resin (A), it is preferably -40 to -15°C, more preferably -35 to -17°C, and particularly preferably -30 to -18°C in terms of adhesive strength and bending durability. If such a glass transition temperature is too low, the adhesive strength and the reliability in a high-temperature environment tend to decrease. If it is too high, the bending durability tends to decrease.

[0086] The weight average molecular weight of the above acrylic resins (A1) and (A2) is preferably 100,000 or more, particularly preferably 300,000 to 2,000,000, more preferably 400,000 to 1,800,000, especially preferably 500,000 to 1,500,000, and most preferably 600,000 to 1,200,000. If such a weight average molecular weight is too small, the cohesive force decreases, and the reliability in a high-temperature environment tends to decrease. If it is too large, the viscosity becomes too high, and the coatability and handleability tend to decrease.

[0087] The dispersity (weight average molecular weight / number average molecular weight) of the above acrylic resins (A1) and (A2) is preferably 15 or less, more preferably 10 or less, particularly preferably 7 or less, more preferably 5.5 or less, and especially preferably 5 or less. If such a dispersity is too high, the durability performance of the adhesive layer tends to decrease, and foaming or the like tends to occur easily. If it is too low, the handleability tends to decrease. The lower limit of the dispersity is usually 1.1 from the viewpoint of manufacturing limitations.

[0088] Moreover, the difference (|M1 - M2|) between the weight average molecular weight (M1) of the acrylic resin (A1) with the highest glass transition temperature and the weight average molecular weight (M2) of the acrylic resin (A2) with the lowest glass transition temperature is preferably 700,000 or less, more preferably 500,000 or less, and particularly preferably 300,000 or less from the viewpoints of adhesion and reliability in a high-temperature environment. If it is outside the above range, either the adhesion or the reliability in a high-temperature environment tends to decrease.

[0089] In addition, the weight average molecular weight (M) of the acrylic resin (A) is preferably 400,000 to 2,000,000, more preferably 500,000 to 1,500,000, and particularly preferably 600,000 to 1,200,000 from the viewpoint of reliability in a high-temperature environment. If such a weight average molecular weight (M) is too low, the reliability in a high-temperature environment tends to decrease, and if it is too high, the adhesion tends to decrease. Furthermore, the dispersity (weight average molecular weight / number average molecular weight) of the acrylic resin (A) is preferably 15 or less, more preferably 10 or less, particularly preferably 7 or less, still more preferably 5.5 or less, and especially preferably 5 or less. If such a dispersity is too high, the durability performance of the adhesive layer tends to decrease, and foaming or the like is likely to occur. If it is too low, the handleability tends to decrease. The lower limit of the dispersity is usually 1.1 from the viewpoint of manufacturing limitations.

[0090] Note that the weight average molecular weight in the present invention is the weight average molecular weight in terms of standard polystyrene molecular weight conversion. For high-performance liquid chromatography (manufactured by Tosoh Corporation, "HLC-8320GPC"), column: TSKgel GMHXL (exclusion limit molecular weight: 4×10 8 , separation range: 100 to 4×10 8 , theoretical plate number: 14,000 plates / column, packing material: styrene-divinylbenzene copolymer, packing particle size: 9 μm, column size: 7.8 mm I.D. × 30 cm) and 3 columns of column: TSKgel G2000HXL (exclusion limit molecular weight: 1×10 4 , separation range: 100 to 1×10 4It is measured by using one column of [[ID=]], theoretical plate number: 16,000 plates / book, filler material: styrene-divinylbenzene copolymer, filler particle size: 5 μm, column size: 7.8 mm I.D. × 30 cm) in series, and the number average molecular weight (Mn) can also be measured by using a similar method. In addition, the dispersity is determined from the weight average molecular weight (Mw) and the number average molecular weight (Mn).

[0091] When the acrylic resin (A) contains the acrylic resin (A1) and the acrylic resin (A2), the content ratio [(A1) / (A2)] of the acrylic resin (A1) and the acrylic resin (A2) is preferably 70 / 30 to 30 / 70, more preferably 65 / 35 to 40 / 60, and particularly preferably 60 / 40 to 50 / 50 in terms of weight ratio from the viewpoint of achieving both adhesiveness and bending durability. If the content of the acrylic resin (A1) is too small [the content of the acrylic resin (A2) is too large], the adhesiveness tends to decrease and the reliability in a high-temperature environment tends to decrease. If the content of the acrylic resin (A1) is too large [the content of the acrylic resin (A2) is too small], the bending durability tends to decrease.

[0092] Furthermore, the weight ratio [(a1) amount of the acrylic resin (A1):(a1) amount of the acrylic resin (A2)] of the amount of the hydroxyl group-containing monomer (a1) constituting the acrylic resin (A1) to the amount of the hydroxyl group-containing monomer (a1) constituting the acrylic resin (A2) is preferably 3:1 to 1:3, particularly preferably 2:1 to 1:2, and more preferably 1:1 to 1:1.5. If the amount of the hydroxyl group-containing monomer (a1) constituting the acrylic resin (A1) is too small, the adhesiveness when used as an adhesive decreases, and if the amount of the hydroxyl group-containing monomer (a1) is too large, the bending durability when used as an adhesive tends to decrease. If the difference in the amount of the hydroxyl group-containing monomer (a1) between the two is too large, the compatibility of the resin tends to decrease, and the heat and humidity resistance also tends to decrease.

[0093] In addition, the total content ratio of the acrylic resin (A1) and the acrylic resin (A2) to the acrylic resin (A) is usually 50% by weight or more, preferably 80% by weight or more, more preferably 90% by weight or more, and still more preferably 100% by weight.

[0094] The acid value of the acrylic resin (A) is preferably 0.001 to 2 mgKOH / g, particularly preferably 0.001 to 1 mgKOH / g, and still more preferably 0.001 to 0.5 mgKOH / g. If the acid value is too high, depending on the type of adherend, there is a tendency to corrode the adherend.

[0095] Here, the acid value in the present invention is determined by neutralization titration based on JIS K 0070.

[0096] The acrylic resin (A) is the main component of the pressure-sensitive adhesive composition of the present invention. That is, the content of the acrylic resin (A) in the pressure-sensitive adhesive composition is preferably 70% by weight or more based on the whole, particularly preferably 80 to 99.9% by weight, and still more preferably 90 to 98% by weight from the viewpoint of reliability during durability.

[0097] In the present invention, the acrylic resin (A) contains two or more kinds of acrylic resins having different glass transition temperatures. As a method for confirming these, for example, using tetrahydrofuran (THF), the acrylic resin (A) [or the pressure-sensitive adhesive composition] is dissolved to prepare a sample solution of about 0.1% by weight. This sample solution can be confirmed by analyzing it by gradient method using a high performance liquid chromatograph (HPLC) with an ODS (octadecylsilyl) column. Further, examples of the gradient method include a method of using acetonitrile and THF as the mobile phase and changing the mixing ratio of acetonitrile and THF.

[0098] <Photoinitiator> The pressure-sensitive adhesive composition of the present invention becomes a pressure-sensitive adhesive layer when cured. When curing is performed by active energy rays described later, it is preferable to use a photopolymerization initiator in that the reaction during active energy ray irradiation can be stabilized.

[0099] Such a photopolymerization initiator is not particularly limited as long as it generates radicals by the action of light. For example, photopolymerization initiators such as acetophenones, benzoins, benzophenones, thioxanthones, and acylphosphine oxides can be mentioned. These photopolymerization initiators can be used alone or in combination of two or more. Among these photopolymerization initiators, it is preferable to use hydrogen abstraction type benzophenones and intramolecular cleavage type acetophenone photopolymerization initiators from the viewpoint of efficient crosslinking between molecules or within molecules.

[0100] The blending amount of such a photopolymerization initiator is preferably 0.01 to 10 parts by weight, particularly preferably 0.1 to 5 parts by weight, and more preferably 0.5 to 2 parts by weight with respect to 100 parts by weight of the acrylic resin (A). If the blending amount is too small, the curing rate tends to decrease or the curing becomes insufficient. If it is too large, the curability does not improve and the economy tends to decrease.

[0101] In addition, as auxiliaries for these photopolymerization initiators, for example, triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Michler's ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethyl benzoate, ethyl 4-dimethylaminobenzoate, (n-butoxy)ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, etc. can also be used in combination. These auxiliaries may be used alone or in combination of two or more.

[0102] <Active energy ray curable monomer> When curing is performed by active energy rays, it is preferable to use an active energy ray-curable monomer. By doing so, the cohesive force of the entire adhesive layer can be adjusted, and stable adhesive physical properties can be obtained.

[0103] As the active energy ray-curable monomer, a polyfunctional monomer or oligomer containing two or more ethylenically unsaturated groups in one molecule is preferable. For example, hexanediol di(meth)acrylate, butanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, ethylene oxide-modified tri(meth)acrylate of isocyanuric acid, allyl (meth)acrylate, vinyl (meth)acrylate, urethane (meth)acrylate, etc. can be mentioned. The above polyfunctional monomers can be used alone or in combination of two or more.

[0104] The number of ethylenically unsaturated groups of the above active energy ray-curable monomer is preferably 2 to 4, and more preferably 2 to 3.

[0105] The blending amount of such an active energy ray-curable monomer is preferably 0 to 30 parts by weight, particularly preferably 2.5 to 20 parts by weight, based on 100 parts by weight of the acrylic resin (A).

[0106] <Other optional components> As components of the adhesive composition of the present invention, in addition to the above photoinitiator and active energy ray-curable monomer, other optional components may be included.

[0107] Examples of other optional components include carbodiimide compounds, antioxidants, plasticizers, tackifiers, crosslinking agents, crosslinking accelerators, silane coupling agents, antistatic agents, functional dyes, etc. These can be used alone or in combination of two or more. The content of other optional components may be within a range that does not impair the effects of the present invention, preferably 10% by weight or less in the pressure-sensitive adhesive composition, and more preferably 0.1 to 5% by weight.

[0108] In addition, when a carbodiimide compound is blended as another component, it is preferable to blend it into the acrylic resin (A) prior to the photopolymerization initiator, the active energy ray curable monomer, and other optional components from the viewpoint of the chemical stability of the resulting resin composition. Particularly preferably, the acrylic resin (A) and the carbodiimide compound are mixed at 0 to 140 °C, and more preferably at 20 to 100 °C.

[0109] The pressure-sensitive adhesive layer obtained by curing the above pressure-sensitive adhesive composition is excellent in adhesion to an adherend, bending durability, and reliability in a high-temperature environment, and thus is useful as a pressure-sensitive adhesive layer of a pressure-sensitive adhesive sheet. Further, the above pressure-sensitive adhesive composition is also useful when used as a material component of a pressure-sensitive adhesive.

[0110] <Pressure-sensitive adhesive sheet> The pressure-sensitive adhesive composition of the present invention is preferably used as a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer obtained by curing this on a base sheet, a double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer provided on a release sheet, or an optical member with a pressure-sensitive adhesive layer having a pressure-sensitive adhesive layer provided on an optical member. Examples of the above curing method include a method of curing by active energy rays, a method of curing by crosslinking using a crosslinking agent, and a method combining these. Among them, the method of curing by active energy rays is preferable in that it enables two-stage curing and aging treatment is not required.

[0111] The above pressure-sensitive adhesive sheet can be produced, for example, as follows. In the present invention, the term "sheet" is not particularly distinguished from "film" or "tape", and is described in a sense that includes these as well.

[0112] First, a method of applying the pressure-sensitive adhesive composition diluted with a solvent to one or both sides of a base sheet and then drying it, or a method of melting the pressure-sensitive adhesive composition by heating and extrusion laminating it onto the base sheet using a T-die or the like, is used to form a pressure-sensitive adhesive layer having a predetermined thickness on one or both sides of the base sheet. Subsequently, a pressure-sensitive adhesive sheet can be produced by laminating a release sheet on the pressure-sensitive adhesive layer surface as needed.

[0113] Further, after forming a pressure-sensitive adhesive layer on the base sheet, a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer in which the pressure-sensitive adhesive composition is cured (crosslinked) can be produced by performing an active energy ray irradiation treatment and further aging as needed.

[0114] Also, a pressure-sensitive adhesive layer can be formed on a release sheet, and a double-sided pressure-sensitive adhesive sheet without a base material can be produced by laminating a release sheet on the opposite pressure-sensitive adhesive layer surface. When the obtained pressure-sensitive adhesive sheet or double-sided pressure-sensitive adhesive sheet is used, the release sheet is peeled off from the pressure-sensitive adhesive layer and used.

[0115] As the base sheet, for example, polyester resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate / isophthalate copolymer; polyolefin resins such as polyethylene, polypropylene, and polymethylpentene; polyfluoroethylene resins such as polyvinyl fluoride, polyvinylidene fluoride, and polyfluoroethylene; 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 resins such as triacetate cellulose and cellophane; acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, and polybutyl acrylate; polystyrene; polycarbonate; polyarylate; polyimide; etc. A sheet made of at least one synthetic resin selected from the group consisting of these, metal foils such as aluminum, copper, and iron, papers such as high-quality paper and glassine paper, and woven or non-woven fabrics made of glass fibers, natural fibers, synthetic fibers, etc. can be mentioned. These base sheets can be used as a single layer or as a multi-layer body in which two or more kinds are laminated. Among these, from the viewpoint of weight reduction, etc., a sheet made of a synthetic resin is preferable.

[0116] Furthermore, as the release sheet, for example, those obtained by subjecting various synthetic resin sheets, papers, cloths, non-woven fabrics, etc. exemplified by the above support base material to a release treatment can be used. As the release sheet, it is preferable to use a silicon-based release sheet.

[0117] Also, as the coating method of the above adhesive composition, there is no particular limitation as long as it is a general coating method. For example, methods such as roll coating, die coating, gravure coating, comma coating, and screen printing can be mentioned.

[0118] By irradiating active energy rays, the acrylic resin (A) in the adhesive composition forms a crosslinked structure at least in one of intramolecular and intermolecular.

[0119] As the active energy rays, for example, rays such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, and infrared rays, electromagnetic waves such as X-rays and γ-rays, and in addition, electron beams, proton beams, neutron beams, etc. can be used, but ultraviolet rays are preferred in terms of curing speed, availability of irradiation devices, price, etc.

[0120] When irradiating with ultraviolet rays for curing, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a carbon arc lamp, a metal halide lamp, a xenon lamp, a chemical lamp, an electrodeless discharge lamp, an LED lamp, etc. that emit light in the wavelength range of 150 to 450 nm is used, and usually 30 to 3000 mJ / cm 2 , preferably 100 to 1500 mJ / cm 2 of ultraviolet rays may be irradiated.

[0121] The above aging treatment is preferably carried out especially when a cross-linking agent is used in the adhesive composition. As the conditions of the above aging treatment, the temperature is usually room temperature (23°C) to 100°C, and the time is usually 1 to 30 days. Specifically, for example, it can be carried out under conditions such as 1 to 20 days at 23°C, preferably 3 to 10 days at 23°C, 1 to 7 days at 40°C, etc.

[0122] And in the present invention, by laminating and forming the above adhesive layer on an optical member, an optical member with an adhesive layer can be obtained. Also, the above double-sided adhesive sheet can be used to bond optical members together.

[0123] Regarding the gel fraction of the adhesive layer of the above adhesive sheet, it is preferably 20 to 100% by weight from the viewpoints of durability performance and adhesive strength, particularly preferably 50 to 90% by weight, and especially preferably 70 to 85% by weight. If the gel fraction is too low, the cohesive force decreases, and the durability tends to decrease. Also, if the gel fraction is too high, the adhesive strength tends to decrease, and the bending durability and the shape recovery of the adhesive layer tend to decrease.

[0124] The gel fraction serves as an indication of the degree of crosslinking (degree of curing). For example, it is calculated by the following method. That is, an adhesive sheet (one without a separator) in which an adhesive layer is formed on a polymer sheet serving as a base material (e.g., a polyethylene terephthalate (PET) film, etc.) is wrapped with a 200-mesh SUS wire mesh and immersed in toluene at 23°C for 24 hours. The gel fraction is defined as the weight percentage of the insoluble adhesive layer remaining in the wire mesh with respect to the weight of the adhesive layer before the toluene immersion. However, the weight of the base material is subtracted.

[0125] In adjusting the gel fraction to the above range, for example, it can be achieved by adjusting the active energy ray irradiation dose, the amount of photoinitiator, adjusting the type and amount of the active energy ray curable monomer, and when using a crosslinking agent, by adjusting the type and amount of the crosslinking agent, etc.

[0126] The thickness of the adhesive layer of the above adhesive sheet is usually preferably 15 to 3000 μm, more preferably 20 to 1000 μm, and particularly preferably 50 to 350 μm. If the thickness of the adhesive layer is too thin, the impact absorbency tends to decrease, and if it is too thick, the thickness of the entire optical member increases and the practicality tends to decrease.

[0127] The film thickness in the present invention is a value obtained by subtracting the measured value of the thickness of the constituent members other than the adhesive layer from the measured value of the thickness of the entire laminate containing the adhesive layer using "ID-C112B" manufactured by Mitutoyo Corporation.

[0128] The adhesive obtained by curing the adhesive composition of the present invention is excellent in adhesive force, bending durability, reliability under high-temperature environments, and shape recoverability of the adhesive. Therefore, it can be suitably used for double-sided adhesion applications and as an adhesive having impact resistance and strong adhesiveness. Specifically, it is useful as an adhesive component for applications such as attaching optical sheets such as glass, ITO transparent electrode sheets, polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), and clear polyimide (CPI), polarizing plates, retardation plates, optical compensation films, and brightness enhancement films. Furthermore, it can be suitably used for image display devices such as touch panels including these optical members, particularly touch panels and image display devices such as foldable smartphones. In addition, the adhesive composition of the present invention can also be used as an adhesive for various labels and a masking adhesive, and is particularly suitably used for electronic component applications and the like.

Examples

[0129] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In the examples, “parts” and “%” mean weight basis. Also, regarding the weight average molecular weight and dispersity of the acrylic resin, they were measured according to the above-described method for measuring the weight average molecular weight of the acrylic resin.

[0130] Also, regarding the measurement of the glass transition temperature of the acrylic resin, it was measured as follows. Note that the content of the structural site of the acrylic resin after completion (after polymerization) is substantially the same as the blending content of the polymerization components.

[0131] <Glass transition temperature (Tg) of acrylic resin> An acrylic resin solution before solvent removal was applied to a polyester release sheet and dried, and then laminated to produce a pressure-sensitive adhesive sheet with a thickness of about 650 μm in an uncrosslinked state. The dynamic viscoelasticity of the produced pressure-sensitive adhesive sheet was measured under the following conditions, and the temperature at which the loss tangent (loss elastic modulus G" / storage elastic modulus G' = tan δ) was maximized was read and taken as the glass transition temperature (Tg) of the acrylic resin. · Measuring instrument: DVA-225 (manufactured by IT Measurement and Control Co., Ltd.) · Deformation mode: shear · Strain: 0.1% · Measuring temperature: -100 to 20 °C · Measuring frequency: 1 Hz

[0132] Prior to the examples, an acrylic resin was produced as follows.

[0133] 〈Production of acrylic resins (A-1), (A-3), (A-7) to (A-9)〉 Into a 2 L flask equipped with a cooler, 25 parts of ethyl acetate (boiling point 77 °C) as a polymerization solvent and 0.01 part of 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN, half-life temperature 52 °C) as a polymerization initiator were heated to reflux in the flask. A solution prepared by previously mixing 100 parts of the polymerization components having the composition shown in Table 1, 10 parts of acetone, and 0.11 part of ADVN was added dropwise over 3 hours. After the addition, 0.14 part of ADVN was added dropwise over 1 hour and reacted to obtain an acrylic resin solution. The glass transition temperatures and weight average molecular weights of the obtained acrylic resins (A-1), (A-3), (A-7) to (A-9) were as shown in Table 1.

[0134] 〈Production of acrylic resin (A-2)〉 Into a 2 L flask equipped with a cooler, 93 parts of ethyl acetate (boiling point 77 °C), 20 parts of acetone (boiling point 56 °C) as a polymerization solvent, 0.01 part of 2,2'-azobisisobutyronitrile (AIBN, half-life temperature 65 °C) as a polymerization initiator, and 100 parts of the polymerization components having the composition shown in Table 1 were heated to reflux in the flask. After 60 minutes, 20 parts of ethyl acetate and 0.01 part of AIBN were added dropwise over 2 hours and reacted to obtain an acrylic resin solution. The glass transition temperature and weight average molecular weight of the obtained acrylic resin (A-2) were as shown in Table 1.

[0135] <Production of Acrylic Resins (A-4) to (A-6)> Into a 2 L flask equipped with a cooler, 100 parts of ethyl acetate (boiling point 77 °C) as a polymerization solvent, 20 parts of acetone (boiling point 56 °C), 0.01 part of 2,2'-azobisisobutyronitrile (AIBN, half-life temperature 65 °C) as a polymerization initiator, and 100 parts of a polymerization component having the composition shown in Table 1 were heated to reflux in the flask. After 60 minutes, 20 parts of ethyl acetate and 0.01 part of AIBN were added dropwise over 2 hours to react and obtain an acrylic resin solution. To the obtained acrylic resin solution (100 parts in terms of solid content), 2-methacryloyloxyethyl isocyanate (MOI) shown in Table 1 was charged and reacted at 40 °C for 12 hours to obtain an acrylic resin containing an ethylenically unsaturated group in the side chain. The glass transition temperature and weight average molecular weight of the obtained acrylic resins (A-4) to (A-6) were as shown in Table 1.

[0136]

Table 1

[0137] Using the acrylic resins (A-1) to (A-9) obtained above, adhesive compositions of Examples and Comparative Examples were produced.

[0138] <Example 1> An acrylic resin (A-i) solution was obtained by mixing an acrylic resin (A-1) solution (55 parts in terms of solid content) and an acrylic resin (A-3) solution (45 parts in terms of solid content). The difference in the glass transition temperature between the acrylic resin (A-1) and the acrylic resin (A-3) in the acrylic resin (A-i) was 6 °C, and the glass transition temperature of the acrylic resin (A-i) was -19 °C. Also, the weight average molecular weight (Mw) of the acrylic resin (A-i) was 680,000. To 100 parts (in terms of solid content) of the above acrylic resin (A-i) solution, 2.5 parts of trimethylolpropane triacrylate (TMPTA) and 0.25 part of Omnirad 184 (manufactured by IGM Resins B.V.) as a photopolymerization initiator were mixed to obtain an adhesive composition [I-1].

[0139] <Example 2> An acrylic resin (A-ii) solution was obtained by mixing an acrylic resin (A-2) solution (60 parts in terms of solid content) and an acrylic resin (A-3) solution (40 parts in terms of solid content). The difference in glass transition temperature between the acrylic resin (A-2) and the acrylic resin (A-3) in the acrylic resin (A-ii) was 5°C, and the glass transition temperature of the acrylic resin (A-ii) was -19°C. Also, the weight average molecular weight (Mw) of the acrylic resin (A-ii) was 960,000. To 100 parts (in terms of solid content) of the above acrylic resin (A-ii) solution, 2.5 parts of trimethylolpropane triacrylate and 0.25 part of Omnirad 184 (manufactured by IGM Resins B.V.) as a photopolymerization initiator were mixed to obtain an adhesive composition [I-2].

[0140] <Example 3> An acrylic resin (A-iii) solution was obtained by mixing an acrylic resin (A-4) solution (60 parts in terms of solid content) and an acrylic resin (A-5) solution (40 parts in terms of solid content). The difference in glass transition temperature between the acrylic resin (A-4) and the acrylic resin (A-5) in the acrylic resin (A-iii) was 6°C, and the glass transition temperature of the acrylic resin (A-iii) was -22°C. Also, the weight average molecular weight (Mw) of the acrylic resin (A-iii) was 1,010,000. To 100 parts (in terms of solid content) of the above acrylic resin (A-iii) solution, 5.0 parts of polypropylene glycol #400 diacrylate (NK ester APG400, manufactured by Shin-Nakamura Chemical Co., Ltd.), 0.25 part of Omnirad 184 (manufactured by IGM Resins B.V.) and 0.75 part of Omnirad 754 (manufactured by IGM Resins B.V.) as a photopolymerization initiator were mixed to obtain an adhesive composition [I-3].

[0141] <Example 4> An acrylic resin (A-4) solution (60 parts in terms of solid content) and an acrylic resin (A-6) solution (40 parts in terms of solid content) were mixed to obtain an acrylic resin (A-iv) solution. The difference in the glass transition temperature between the acrylic resin (A-4) and the acrylic resin (A-6) in the acrylic resin (A-iv) was 6 °C, and the glass transition temperature of the acrylic resin (A-iv) was -22 °C. Also, the weight average molecular weight (Mw) of the acrylic resin (A-iv) was 910,000. To 100 parts (in terms of solid content) of the above acrylic resin (A-iv) solution, 5.0 parts of polypropylene glycol #400 diacrylate (NK ester APG400, manufactured by Shin-Nakamura Chemical Co., Ltd.), 0.25 part of Omnirad 184 (manufactured by IGM Resins B.V.) and 0.75 part of Omnirad 754 (manufactured by IGM Resins B.V.) as a photopolymerization initiator were mixed to obtain an adhesive composition [I-4].

[0142] <Comparative Example 1> An acrylic resin (A-7) solution (55 parts in terms of solid content) and an acrylic resin (A-9) solution (45 parts in terms of solid content) were mixed to obtain an acrylic resin (A') solution. The difference in the glass transition temperature between the acrylic resin (A-7) and the acrylic resin (A-9) in the acrylic resin (A') was 4 °C, and the glass transition temperature of the acrylic resin (A-v) was -22 °C. Also, the weight average molecular weight (Mw) of the acrylic resin (A') was 680,000. To 100 parts (in terms of solid content) of the above acrylic resin (A') solution, 5 parts of trimethylolpropane triacrylate, 0.25 part of Omnirad 184 (manufactured by IGM Resins B.V.) and 0.50 part of Omnirad 754 (manufactured by IGM Resins B.V.) were mixed as a photopolymerization initiator to obtain an adhesive composition [I'-1].

[0143] <Comparative Example 2> To 100 parts (in terms of solid content) of an acrylic resin (A-8) solution, 5.0 parts of trimethylolpropane triacrylate, 0.25 part of Omnirad 184 (manufactured by IGM Resins B.V.) and 0.50 part of Omnirad 754 (manufactured by IGM Resins B.V.) were mixed as a photopolymerization initiator to obtain an adhesive composition [I'-2].

[0144] The formulation compositions of the adhesive compositions of Examples 1 to 4 and Comparative Examples 1 to 2 obtained above are shown in Table 2 below.

[0145]

Table 2

[0146] Using the adhesive compositions of Examples 1 to 4 and Comparative Examples 1 to 2 obtained above, a substrate-free double-sided adhesive sheet and a PET sheet with an adhesive layer were produced as follows.

[0147] <Production of Substrate-Free Double-Sided Adhesive Sheet and PET Sheet with Adhesive Layer> The above-obtained adhesive composition solution (solid content concentration 30%) was applied to a polyester release sheet so that the thickness after drying was about 50 μm, and dried at 100°C for 5 minutes to form an adhesive layer. After laminating three obtained adhesive layers, they were sandwiched between polyester release sheets, and further irradiated with a high-pressure mercury UV irradiation device at a peak illuminance of 150 mW / cm 2 , an integrated exposure amount of 1000 mJ / cm 2 (500 mJ / cm 2By performing ultraviolet irradiation in a ×2 pass, a substrate-free double-sided adhesive sheet was obtained. At this time, the adhesive composition becomes the adhesive. Also, the release sheet on one side was peeled off from the adhesive layer of the substrate-free double-sided adhesive sheet obtained above, and it was pressed against an easily adherable polyethylene terephthalate (PET) sheet (thickness 125 μm), and a PET sheet with an adhesive layer having an adhesive layer thickness of about 150 μm was obtained.

[0148] Using the substrate-free double-sided adhesive sheets and the PET sheets with an adhesive layer of Examples 1 to 4 and Comparative Examples 1 to 2 obtained above, evaluations were made on the gel fraction, adhesive strength, bending durability, high-temperature reliability (80°C constant load holding force, 80°C holding force), shape recovery, and stress relaxation (shear stress, relaxation rate). The results are shown in Table 3 below.

[0149] 〔Gel fraction〕 After cutting the substrate-free double-sided adhesive sheet into a size of 40 mm × 40 mm, with a high-pressure mercury UV irradiation device, peak illuminance: 150 mW / cm 2 , integrated exposure amount: 2000 mJ / cm 2 (1000 mJ / cm 2 ×2 pass), ultraviolet irradiation was performed, and after standing for 30 minutes under the conditions of 23°C × 50% RH, one release sheet was peeled off, the adhesive layer side was bonded to a SUS mesh sheet (200 mesh) with a size of 50 mm × 100 mm, then the other release sheet was peeled off, after folding back from the center part with respect to the longitudinal direction of the SUS mesh sheet to wrap the sample, it was immersed in a sealed container containing 250 g of toluene for 24 hours, and the weight percentage of the insoluble adhesive layer remaining on the SUS mesh sheet with respect to the weight of the adhesive layer before toluene immersion was taken as the gel fraction (%).

[0150] 〔Adhesive strength〕 Regarding the PET sheet with the adhesive layer above, it was cut into a size of 25 mm in width × 100 mm in length, and with a high-pressure mercury UV irradiation device, peak illuminance: 150 mW / cm 2 , integrated exposure amount: 2000 mJ / cm 2 (1000 mJ / cm 2After performing ultraviolet irradiation in a ×2 pass manner, the release sheet was peeled off, and the adhesive layer side was pressure-bonded to non-alkali glass (Corning's "Eagle XG", thickness 1.1 mm) with a 2 kg rubber roller reciprocated twice under an atmosphere of 23°C and 50% RH. After standing for 30 minutes under the conditions of 23°C × 50% RH, the 180-degree peel strength (N / 25 mm) at a peel rate of 300 mm / min was measured at room temperature (23°C).

[0151] [Bending Durability] Regarding the above PET sheet with an adhesive layer, the adhesive layer side of the adhesive sheet was pressed against a transparent polyimide sheet (thickness 50 μm) under an environment of 23°C and 50% RH to obtain a test piece with a layer structure of "PET sheet / adhesive layer / polyimide sheet". After that, for the above test piece, from the PET sheet side, using a high-pressure mercury UV irradiation device, peak illuminance: 150 mW / cm 2 , integrated exposure amount: 2000 mJ / cm 2 (1000 mJ / cm 2 ×2 pass) After performing ultraviolet irradiation, it was cut into a size of 40 mm in width × 120 mm in length, and the following repeated bending test was conducted. The repeated bending test was carried out under an environment of 23°C and 50% RH with the PET sheet side on the inside. The test conditions are as follows. [Test Conditions] ·Testing equipment: Flat specimen unloaded U-shaped expansion tester DLDM111LH (manufactured by Yuasa System Equipment Co., Ltd.) ·Bending speed: 45 times / min ·Bending radius: 2.5 mm In such a repeated bending test, the number of times without visual appearance change was measured and evaluated according to the following criteria. (Evaluation Criteria) ◎ ··· 200,000 times or more ○ ··· 100,000 times or more and less than 200,000 times × ··· Less than 100,000 times

[0152] [Constant Load Holding Force] Regarding the PET sheet with the above-mentioned adhesive layer, it was cut into a size of 25 mm × 75 mm (adhesive layer part: 25 mm × 50 mm + non-adhesive layer part: 25 mm × 25 mm), and irradiated with ultraviolet rays using a high-pressure mercury UV irradiation device at a peak illuminance of 150 mW / cm 2 , and an integrated exposure dose of 2000 mJ / cm 2 (1000 mJ / cm 2 × 2 passes). After that, the release sheet was peeled off, and it was pressure-bonded to a stainless steel plate (SUS304) by reciprocating a 2 kg roller (bonding area: 25 mm × 50 mm), and left standing for 20 minutes in an 80°C atmosphere. Then, a 50 g weight was hung at the end of the non-adhesive layer part (area: 25 mm × 25 mm), a 50 g load was applied in a direction perpendicular to the plane of the stainless steel plate, and it was left standing in that state for 60 minutes, and the distance by which the PET sheet peeled off was measured. The evaluation criteria are as follows. (Evaluation Criteria) ◎ ··· Peeling distance is less than 1 mm 〇 ··· Peeling distance is 1 mm or more and less than 25 mm △ ··· Peeling distance is 25 mm or more and 50 mm or less × ··· Falling off

[0153] 〔Retention Force〕 Regarding the PET sheet with the above-mentioned adhesive layer, it was cut into a size of 25 mm × 50 mm, and irradiated with ultraviolet rays using a high-pressure mercury UV irradiation device at a peak illuminance of 150 mW / cm 2 , and an integrated exposure dose of 2000 mJ / cm 2 (1000 mJ / cm 2 × 2 passes). After that, the release sheet was peeled off, and it was pressure-bonded to a stainless steel plate (SUS304) by reciprocating a 2 kg roller (bonding area: 25 mm × 25 mm), and the retention force was measured using a creep tester (manufactured by Tester Sangyo Co., Ltd., holding force tester with high-temperature and high-humidity chamber BE-501) by applying a load of 1 kg over 24 hours in an 80°C atmosphere. The evaluation criteria are as follows. (Evaluation Criteria) ◎ ··· No displacement 〇 ··· Displacement is less than 0.1 mm △ ··· Displacement is 0.1 mm or more and less than 1.0 mm × ··· Displacement is 1.0 mm or more, or falling off

[0154] [Shape recoverability after the adhesive layer is deformed] The substrate-free double-sided adhesive sheet was laminated to a thickness of about 650 μm and irradiated with ultraviolet light using a high-pressure mercury UV irradiation device at a peak illuminance of 150 mW / cm 2 and an integrated exposure amount of 2000 mJ / cm 2 (1000 mJ / cm 2 × 2 passes), then cut into a size of 25 mm in diameter to prepare a measurement sample. One release sheet of the sample was peeled off, bonded to a measurement jig (parallel plate), the other release sheet was peeled off, and bonded onto the lower plate of a rotational rheometer (Rotational Rheometer MCR301 manufactured by Anton Paar). After stretching by 200% under the condition of 23°C, the stress was released, and the strains 1 minute and 5 minutes after the stress release were measured respectively. The recovery rate (%) was calculated from the following formula and evaluated according to the following criteria. Recovery rate (%) = [(200 - strain) / 200] × 100 (Evaluation criteria) ◎ ··· The recovery rate 1 minute after is 55% or more, and the recovery rate 5 minutes after is 75% or more ○ ··· The recovery rate 1 minute after is 55% or more, and the recovery rate 5 minutes after is 65% or more and less than 75% × ··· The recovery rate 1 minute after is less than 55%

[0155] [Stress relaxation property] The substrate-free double-sided adhesive sheet was laminated to a thickness of about 650 μm and irradiated with ultraviolet light using a high-pressure mercury UV irradiation device at a peak illuminance of 150 mW / cm 2 and an integrated exposure amount of 2000 mJ / cm 2 (1000 mJ / cm 2Ultraviolet irradiation was performed in a ×2 pass, and then it was cut into a size of 25 mm in diameter to prepare a measurement sample. One release sheet of the sample was peeled off, bonded to a measurement jig (parallel plate), the other release sheet was peeled off, and it was bonded onto the lower plate of a rotational rheometer (Rotational Rheometer MCR301 manufactured by Anton Paar). After stretching by 200% under the condition of 23°C, the stress was controlled to maintain a strain of 200%. The time when the strain reached 200% was taken as 0 minutes, and the shear stress after 10 minutes was measured. The stress relaxation rate was calculated by the following formula. Stress relaxation rate (%) = [(Shear stress at 0 minutes - Shear stress after 10 minutes) / Shear stress at 0 minutes] × 100

[0156]

Table 3

[0157] As can be seen from Table 3 above, in Examples 1 to 4, all of the adhesive strength, bending durability, high-temperature reliability, shape recoverability after the adhesive layer was deformed, and stress relaxation property were excellently balanced. On the other hand, in Comparative Examples 1 to 2, none were excellently balanced in various physical properties aimed at by the present invention.

Industrial Applicability

[0158] The adhesive composition of the present invention is excellent in adhesive strength to an adherend, excellent in bending durability and high-temperature reliability, and further excellent in shape recoverability after the adhesive layer is deformed. Therefore, it can be suitably used for touch panels, image display devices, etc., and impact absorption sheets, etc.

Claims

1. An adhesive composition containing an acrylic resin (A), wherein the content of the structural site derived from the hydroxyl group-containing monomer (a1) in the acrylic resin (A) is 5 to 60% by weight based on the total polymerization components, and having an alkyl group with 5 to 14 carbon atoms, and the content of the structural site derived from at least one copolymerizable monomer (a2) selected from (meth)acrylic acid alkyl ester monomers and vinyl ester monomers is 15 to 90% by weight based on the total polymerization components, the acrylic resin (A) contains at least two acrylic resins with different glass transition temperatures (T) read from the temperature at which the loss tangent of dynamic viscoelasticity is maximum, the glass transition temperature (T1) of the acrylic resin (A1) with the highest glass transition temperature is -25 to -10 °C, the glass transition temperature (T2) of the acrylic resin (A2) with the lowest glass transition temperature is -40 to -20 °C, the content ratio (A1 / A2) of the acrylic resin (A1) and the acrylic resin (A2) is 70 / 30 to 30 / 70 by weight, the content ratio of the active energy ray curable site in the acrylic resin (A1) is 0.001 to 10% by weight, An adhesive composition characterized in that the content ratio of the active energy ray curable site in the acrylic resin (A2) is 0.001 to 10% by weight.

2. The adhesive composition according to Claim 1, characterized in that the temperature difference between the glass transition temperature (T1) of the acrylic resin (A1) with the highest glass transition temperature and the glass transition temperature (T2) of the acrylic resin (A2) with the lowest glass transition temperature is 20 °C or less.

3. The adhesive composition according to Claim 1 or 2, characterized in that the active energy ray curable site is at least one selected from a benzophenone structure and an ethylenically unsaturated group.

4. The adhesive composition according to any one of Claims 1 to 3, characterized in that the weight average molecular weight of the acrylic resin (A) is 400,000 to 2,000,000.

5. The adhesive composition according to any one of Claims 1 to 4, characterized in that the difference (|M1 - M2|) between the weight average molecular weight (M1) of the acrylic resin (A1) with the highest glass transition temperature and the weight average molecular weight (M2) of the acrylic resin (A2) with the lowest glass transition temperature is 700,000 or less.

6. The pressure-sensitive adhesive composition according to any one of claims 1 to 5, wherein the acrylic resin (A2) is an acrylic resin polymerized using a hydroxyl group-containing monomer containing 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate as polymerization components.

7. A pressure-sensitive adhesive characterized by being formed using the pressure-sensitive adhesive composition according to any one of claims 1 to 6.

8. A pressure-sensitive adhesive sheet characterized by having a pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition according to any one of claims 1 to 6.

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