TWI794504B - Adhesive sheet - Google Patents

Abstract

An object of the present invention is to provide an adhesive sheet that is excellent in sebum resistance and chemical resistance, is less prone to foaming even under high temperature and high humidity, and has excellent optical properties. The present invention is an adhesive sheet, which has an adhesive layer containing an acrylic copolymer, and the swelling rate of the adhesive layer after immersion in oleic acid for 24 hours under the conditions of 65°C and 90% humidity is 100% by weight or more and 130% by weight. The difference (A-B) between the maximum value (A) and the minimum value (B) of the storage elastic modulus of the above-mentioned adhesive layer in the temperature range between 100°C and 140°C is 1.2×10 ⁴ Pa the following.

Description

Adhesive sheet

The invention relates to an adhesive sheet.

Adhesive sheets were widely used when fixing parts in electronic machines. Specifically, it is used for bonding a cover for protecting the surface of a portable electronic device to a touch panel module or a display panel module, or bonding a touch panel module to a display panel module. Adhesive sheet. Moreover, in order to fix a polarizing plate, an adhesive sheet is also used. In addition to high adhesiveness, the adhesive sheets used for fixing electronic equipment parts also require functions such as heat resistance, thermal conductivity, and impact resistance depending on the environment of the used part (for example, patent documents 1 to 3). prior art literature patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2015-052050 Patent Document 2: Japanese Patent Laid-Open No. 2015-021067 Patent Document 3: Japanese Patent Laid-Open No. 2015-120876

[Problem to be Solved by the Invention]

In recent years, mobile phones, smart phones, wearable terminals, and other portable electronic devices that are often carried around or placed at hand have been widely popularized. Due to the frequent use of portable electronic devices and the use of touch panels, etc., due to bare-handed operations, there are problems such as: sebum or chemicals attached to the hands penetrate into the inside and the adhesive sheet peels off, or due to the swelling of the adhesive sheet Visibility decreases due to whitening. In recent years, the narrowing of the outer frame (bezel) of the display, that is, so-called narrowing of the border, has been progressing, and this problem has become more and more serious. In addition, when electronic equipment is exposed to high temperature and high humidity, there are also problems in that outgassing occurs from parts that easily absorb moisture such as polarizers, and foaming occurs on the bonding surface with the adhesive sheet. Such foaming also causes the visibility of the display to decrease.

An object of the present invention is to provide an adhesive sheet that is excellent in sebum resistance and chemical resistance, is less prone to foaming even under high temperature and high humidity, and has excellent optical properties. [Technical means to solve the problem]

The present invention is an adhesive sheet, which has an adhesive layer containing an acrylic copolymer, and the swelling rate of the adhesive layer after immersion in oleic acid for 24 hours under the conditions of 65°C and 90% humidity is 100% by weight or more and 130% by weight. The difference (A-B) between the maximum value (A) and the minimum value (B) of the storage elastic modulus of the above-mentioned adhesive layer in the temperature range between 100°C and 140°C is 1.2×10 ⁴ Pa the following. The present invention will be described in detail below.

The inventors of the present invention have found that, in an adhesive sheet having an adhesive layer containing an acrylic copolymer, the sebum resistance can be improved by adjusting the swelling rate of the adhesive layer after immersing the adhesive layer in oleic acid, which is the main component of sebum, to a specific range for a certain period of time. resistance and chemical resistance. On the other hand, in order to suppress foaming under high temperature and high humidity, it is considered to adjust the storage elastic modulus of the adhesive layer, especially the storage elastic modulus at a high temperature (about 80-100°C) where foaming occurs to a relatively high range. However, the storage elastic modulus in the temperature region where foaming occurs may not necessarily correlate with the actual easiness of foaming. The reason for this is considered to be that the deformation speed of the adhesive layer when foaming occurs is very low. That is, according to the temperature-speed conversion law, the foaming behavior of the adhesive layer at low speed is regarded as the foaming behavior in a higher temperature region than the foaming temperature region, if it is in such a high temperature region The storage elastic modulus is considered to be more related to the ease of actual foaming. However, there is a problem that accurate measurement cannot be performed due to occurrence of decomposition of the adhesive in a higher temperature region than the temperature region where foaming occurs. In contrast, the present inventors focused on the change degree of the storage elastic modulus of the adhesive layer in the temperature range above 100°C and below 140°C, and thought that if the change degree of the storage elastic modulus in this temperature range is small, The storage modulus of elasticity can then be kept high even in regions of further high temperature. The present inventors found that by adjusting the difference (AB) between the maximum value (A) and the minimum value (B) of the storage elastic modulus of the adhesive layer in the temperature range between 100°C and 140°C to a specific Below the value, the foaming that occurs under high temperature and high humidity can be suppressed, thereby completing the present invention.

The adhesive sheet of the present invention has an adhesive layer containing an acrylic acid copolymer, and the swelling rate of the above adhesive layer after being immersed in oleic acid for 24 hours under the conditions of 65°C and 90% humidity (also called "oleic acid swelling rate") It is 100 weight% or more and 130 weight% or less. When the said oleic acid swelling rate is 100 weight% or more, it shows that an adhesive component is not eluted by oleic acid. The sebum resistance and chemical resistance of the said adhesive agent layer will improve that the said oleic acid swelling rate is 130 weight% or less. The preferable upper limit of the above-mentioned oleic acid swelling rate is 120% by weight, and the more preferable upper limit is 115% by weight. In addition, the oleic acid swelling ratio is a value representing the ratio of the weight of the adhesive layer after dipping in oleic acid and drying to the weight of the adhesive layer before dipping in oleic acid as a percentage, as shown in the following formula. Swelling ratio of oleic acid (weight %) = 100 x (W ₃ -W ₁ )/(W ₂ -W ₁ ) (W ₁ : weight of substrate, W ₂ : weight of adhesive sheet before dipping in oleic acid, W ₃ : The weight of the adhesive sheet soaked in oleic acid and dried)

As a method of adjusting the said oleic acid swelling rate to the said range, the method of adjusting the monomer composition, weight average molecular weight, etc. of the said acrylic copolymer is mentioned, for example. More specifically, for example, the method of (a) making the said acrylic copolymer contain the structural unit derived from the fluoroalkyl (meth)acrylate as follows is mentioned, for example. Moreover, the method of (b) making the said acrylic copolymer contain the structural unit derived from the alkyl (meth)acrylate which has an alkyl group with 2 or less carbon atoms is mentioned. The methods (a) and (b) above can be used alone or in combination.

The difference (AB) between the maximum value (A) and the minimum value (B) of the storage elastic modulus of the adhesive layer in the temperature range of 100°C to 140°C is 1.2×10 ⁴ Pa or less. If the difference (A-B) of the above-mentioned storage modulus of elasticity is 1.2×10 ⁴ Pa or less, the degree of change in the storage modulus of elasticity in the temperature range above 100°C and below 140°C is small, even in the temperature range In the region of higher temperature, the storage modulus of elasticity of the above-mentioned adhesive layer is also kept high, which can suppress the foaming generated under high temperature and high humidity. A preferable upper limit of the above storage modulus difference (A-B) is 0.8×10 ⁴ Pa, and a more preferable upper limit is 0.4×10 ⁴ Pa. The lower limit of the difference (A-B) of the storage elastic modulus is not particularly limited, and the smaller the better, the lower limit is substantially about 0.01×10 ⁴ Pa. Furthermore, the storage elastic modulus can be measured using a dynamic viscoelasticity measuring device (such as DVA-200 manufactured by IT Measurement Co., Ltd.) at a heating rate of 5°C/min in the range of -40°C to 140°C.

As a method of adjusting the difference (AB) of the said storage elastic modulus to the said range, the method of adjusting the monomer composition, weight average molecular weight, etc. of the said acrylic copolymer is mentioned, for example. Moreover, the method which adjusts the type or amount of the monomer which has a crosslinkable functional group in the said acrylic copolymer, and the type or amount of the crosslinking agent added to the said adhesive agent layer, and the following method can also be mentioned. The gel fraction of the adhesive layer is adjusted to a relatively high range. In particular, it can be adjusted by increasing the weight average molecular weight; setting the gel fraction to a relatively high range. Also, by selecting the type of monomer used, the value of the modulus of elasticity can be finely adjusted. From the viewpoint of keeping the storage elastic modulus high in the high-temperature region, it is preferable to use an alkyl (meth)acrylate having a linear alkyl group or an alkyl (meth)acrylate having a ring structure ester. Also, it is preferable to use an alkyl (meth)acrylate having an alkyl group having 6 or less carbon atoms.

The above-mentioned acrylic copolymer preferably has an SP value calculated by the Fedors method of 9.3 or less. Portable electronic devices, etc. are frequently used, and are sometimes cleaned with detergent while wearing them. Among the cleaning agents in recent years, there are also strong alkaline cleaning agents obtained by mixing surfactants and alcohols in alkaline aqueous solutions, and sometimes the adhesive tape peels off due to this alkaline cleaning agent. By making the above-mentioned SP value 9.3 or less, it is possible to suppress penetration of alkaline detergents into the molecular chain, and to impart resistance to sebum and alkaline detergents, especially resistance to alkaline detergents, to the obtained adhesive sheet. High patience. The above SP value is preferably at most 9.25, more preferably at most 9.2. The lower limit of the SP value is not particularly limited, and about 8.5 is the lower limit because it is difficult to synthesize. Furthermore, the SP value is called the solubility parameter (Solubility Parameter), which is an index that can indicate the ease of dissolution. In this manual, the calculation of the SP value is based on the Fedors method (R. F. Fedors, Polym. Eng. Sci., 14 (2), 147 – 154 (1974)). In addition, the SP value of the acrylic copolymer can be calculated based on the SP value of each repeating unit in the copolymer alone, using the blend ratio (molar ratio).

It is preferable that the said acrylic copolymer contains the structural unit derived from the fluoroalkyl (meth)acrylate. The above-mentioned fluoroalkyl (meth)acrylate means that part or all of the hydrogen atoms of the alkyl group of the alkyl (meth)acrylate are fluorinated. By making the above-mentioned acrylic copolymer contain the constituent units derived from the above-mentioned fluoroalkyl (meth)acrylate, the penetration of oleic acid into the above-mentioned acrylic acid can be suppressed by utilizing the high water and oil repellency of fluorine itself and the close packing of fluorine atoms. within the molecular chain of the copolymer. As a result, the oleic acid swelling ratio tends to satisfy the above-mentioned range, and the sebum resistance and chemical resistance of the pressure-sensitive adhesive layer improve.

The above-mentioned fluoroalkyl (meth)acrylate is not particularly limited, and examples include: 2,2,2-trifluoroethyl (meth)acrylate, 1H,1H,3H-tetrafluoropropyl (meth)acrylate , 2,2,3,3,3-pentafluoropropyl (meth)acrylate, 2-(perfluorohexyl)ethyl (meth)acrylate, 1H-1-(trifluoromethyl)acrylate ) trifluoroethyl ester, 1H,1H,3H-hexafluorobutyl acrylate, 1,2,2,2-tetrafluoro-1-(trifluoromethyl)ethyl acrylate, (meth)acrylic acid 2-(perfluorobutyl)ethyl ester, etc. In addition, the term "(meth)acrylate" means either acrylate or methacrylate. These fluoroalkyl (meth)acrylates may be used alone or in combination. Among them, preferably selected from 2,2,2-trifluoroethyl (meth)acrylate, 2,2,3,3,3-pentafluoropropyl (meth)acrylate, 2-(meth)acrylate At least one selected from the group consisting of (perfluorobutyl)ethyl ester and 2-(perfluorohexyl)ethyl (meth)acrylate, more preferably these acrylates. In terms of very high sebum resistance and chemical resistance, 2-(perfluorohexyl)ethyl acrylate is particularly preferred.

The above-mentioned fluoroalkyl (meth)acrylate is preferably a (methyl) group in which fluorine is not bonded to the carbons at the 1st and 2nd positions of the alkyl group (the 1st and 2nd carbons from the side bonded to oxygen). ) fluoroalkyl acrylate. For example, 2-(perfluorohexyl)ethyl (meth)acrylate, 2-(perfluorobutyl)ethyl (meth)acrylate, 6-(perfluoroethyl)hexyl (meth)acrylate are preferred wait. Since the electron-withdrawing fluorine atoms of these fluoroalkyl (meth)acrylates are located far away from the ester group, it is considered that they are difficult to be hydrolyzed by alkaline detergents and can play a more excellent role in alkaline detergents. patience. Among these, it is preferable to use at least one kind selected from the group consisting of 2-(perfluorohexyl)ethyl acrylate and 2-(perfluorobutyl)ethyl (meth)acrylate. In addition, by using fluorine-containing (meth)acrylic alkyl groups with relatively low SP values such as 2-(perfluorohexyl)ethyl (meth)acrylate and 2-(perfluorobutyl)ethyl (meth)acrylate, Esters can easily adjust the SP value of the obtained acrylic copolymer to 9.3 or less.

In the above-mentioned acrylic copolymer, the preferable lower limit of the content of the constituent unit derived from the above-mentioned fluoroalkyl (meth)acrylate is 30% by weight, and the preferable upper limit is 80% by weight. When the above content is 30% by weight or more, penetration of oleic acid into the molecular chain of the acrylic copolymer can be further suppressed, and the sebum resistance and chemical resistance of the adhesive layer can be improved. If the said content is 80 weight% or less, the said adhesive agent layer will not become hard too much, and sufficient adhesive force can be exhibited. A more preferable lower limit of the above content is 40% by weight, a more preferable upper limit is 70% by weight, a more preferable lower limit is 45% by weight, and a more preferable upper limit is 60% by weight.

It is preferable that the said acrylic copolymer contains the structural unit derived from the alkyl (meth)acrylate which has an alkyl group with 2 or less carbon atoms. When the said acrylic copolymer contains the structural unit derived from the alkyl (meth)acrylate which has the said C2 or less alkyl group, the cohesive force of the said pressure-sensitive adhesive layer becomes high. As a result, the oleic acid swelling ratio tends to satisfy the above-mentioned range, and the sebum resistance and chemical resistance of the pressure-sensitive adhesive layer improve.

Examples of the alkyl (meth)acrylate having an alkyl group having 2 or less carbon atoms include methyl (meth)acrylate and ethyl (meth)acrylate. These alkyl (meth)acrylates which have an alkyl group having 2 or less carbon atoms may be used alone or in combination. Among these, methyl acrylate is preferable in terms of exerting a high cohesive force.

In the said acrylic copolymer, content of the structural unit derived from the alkyl (meth)acrylate which has the said C2 or less alkyl group is not specifically limited. When the above-mentioned acrylic copolymer contains both the above-mentioned structural unit derived from fluoroalkyl (meth)acrylate and the above-mentioned structural unit derived from alkyl (meth)acrylate having an alkyl group having 2 or less carbon atoms In this case, the preferable lower limit of the content of the constituent unit derived from the alkyl (meth)acrylate having an alkyl group having 2 or less carbon atoms is 10% by weight. When the said content is 10 weight% or more, the cohesive force of the said adhesive agent layer will become higher, and sebum resistance and chemical resistance will improve. Moreover, the preferable upper limit of the said content is 40 weight%. If the said content is 40 weight% or less, the said adhesive agent layer will not become hard too much, and sufficient adhesive force can be exhibited. The more preferable lower limit of the said content is 14 weight%, and the more preferable upper limit is 30 weight%. On the other hand, the above-mentioned acrylic copolymer does not contain the structural unit derived from the above-mentioned fluoroalkyl (meth)acrylate, but contains the above-mentioned alkyl (meth)acrylate derived from an alkyl group having 2 or less carbon atoms. In the case of the constituent unit, the preferable lower limit of the content of the constituent unit derived from the alkyl (meth)acrylate having an alkyl group having 2 or less carbon atoms is 50% by weight. When the said content is 50 weight% or more, the cohesive force of the said adhesive agent layer will become higher, and sebum resistance and chemical resistance will improve. Moreover, the preferable upper limit of the said content is 99 weight%. If the said content is 99 weight% or less, the said adhesive agent layer will not become hard too much, and sufficient adhesive force can be exhibited. The more preferable lower limit of the said content is 70 weight%, and the more preferable upper limit is 95 weight%.

The above-mentioned acrylic copolymer contains: 50% by weight or more of a constituent unit derived from an alkyl (meth)acrylate having an alkyl group having a carbon number of 2 or less, as the (methyl) group having an alkyl group having a carbon number of 2 or less The alkyl acrylate preferably contains at least methyl acrylate. By setting it as such a structure, sebum resistance and chemical resistance can be improved.

The above-mentioned acrylic copolymer is preferably used: a constituent unit derived from an alkyl (meth)acrylate derived from a straight-chain alkyl group having 8 or more carbon atoms, a (methyl) group derived from an alkyl group having a branch ) acrylic acid copolymer (hereinafter also referred to as source From "Constituent units of long-chain, branched, and cyclic alkyl esters of (meth)acrylate"). The above constituent units derived from long-chain, branched, and cyclic alkyl esters of (meth)acrylic acid reduce the SP value of the obtained acrylic acid copolymer, making it difficult for alkaline detergents to penetrate into the molecular chain, Therefore, excellent resistance to alkaline detergents can be imparted to the resulting adhesive sheet.

The content of the structural units derived from the long-chain, branched, and cyclic alkyl esters of (meth)acrylic acid in the above-mentioned acrylic copolymer is preferably 10% by weight or more. By making content of this structural unit 10 weight% or more, the tolerance with respect to the alkaline cleaning agent more excellent can be exhibited. The content of the constituent unit is more preferably at least 15% by weight. The content of the constituent units derived from long-chain, branched, and cyclic alkyl (meth)acrylic acid esters is preferably at most 60% by weight, more preferably at most 50% by weight.

In the above-mentioned acrylic copolymer, the content of the constituent unit derived from an alkyl (meth)acrylate having an alkyl group having 8 or more carbon atoms is preferably 10% by weight or less from the viewpoint of sebum resistance . By adjusting the content of this structural unit to 10% by weight or less and adjusting the SP value to the above-mentioned range, both resistance to alkaline detergents and resistance to sebum can be achieved. Likewise, from the viewpoint of sebum resistance, the (meth)acrylic copolymer preferably contains a constituent unit derived from an alkyl (meth)acrylate having an alkyl group having 2 or less carbon atoms. . By containing this constituent unit and adjusting the SP value to the above-mentioned range, it is possible to have both resistance to alkaline detergents and resistance to sebum.

It is preferable that the said acrylic copolymer contains the structural unit derived from the alkyl (meth)acrylate represented by following general formula (1). An acrylic copolymer containing a constituent unit derived from an alkyl (meth)acrylate represented by the following general formula (1) is less likely to be hydrolyzed by an alkaline detergent and exhibits particularly excellent performance against an alkaline detergent patience. It is considered that the reason is that in the alkyl (meth)acrylate represented by the following general formula (1), the carbon directly bonded to the ester structure becomes a secondary or tertiary bulky structure, so the basic The detergent is less likely to permeate into the ester structure and thus less likely to be hydrolyzed.

In the general formula (1), R represents hydrogen or a methyl group, and R ¹ , R ² , and R ³ represent hydrogen or an alkyl group. In the general formula (1), at least two of R ¹ , R ² , and R ³ are alkyl groups, or two of R ¹ , R ² , and R ³ form a ring structure.

Specific examples of the alkyl (meth)acrylate represented by the general formula (1) include: 1-methylheptyl (meth)acrylate, tertiary butyl (meth)acrylate, ( Isocamphoryl meth)acrylate, cyclohexyl (meth)acrylate, etc.

From the standpoint of having both resistance to alkaline detergents and resistance to sebum, it is preferable that the above-mentioned acrylic copolymer contains (meth)acrylic alkyl derived from a branched alkyl group having 4 or less carbon atoms. A constituent unit of at least one of an alkyl ester and an alkyl (meth)acrylate having a ring structure. Specifically, it is preferable to contain, for example, a structural unit derived from t-butyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, or the like.

The content of the structural unit derived from the alkyl (meth)acrylate represented by the general formula (1) in the acrylic copolymer is preferably 10% by weight or more. By making content of this structural unit 10 weight% or more, the tolerance with respect to the alkaline cleaning agent which was more excellent can be exhibited. The content of the constituent unit is more preferably at least 15% by weight. The content of the constituent units derived from the alkyl (meth)acrylate represented by the general formula (1) is preferably at most 60% by weight, more preferably at most 50% by weight.

It is preferable that the said acrylic copolymer further contains the structural unit derived from the monomer which has a crosslinkable functional group. By making the said acrylic copolymer contain the structural unit derived from the said monomer which has a crosslinkable functional group, when using a crosslinking agent together, the interchain of the said acrylic copolymer is crosslinked. At this time, by adjusting the degree of crosslinking, the gel fraction of the adhesive layer can be adjusted. In particular, by adjusting the gel fraction of the adhesive layer to a relatively high range, the difference (A-B) of the storage elastic modulus can be easily adjusted to the above range, and it is more suppressed under high temperature and high humidity. The resulting foaming.

As said crosslinkable functional group, a hydroxyl group, a carboxyl group, a glycidyl group, an amino group, an amide group, a nitrile group etc. are mentioned, for example. Among them, a hydroxyl group or a carboxyl group is preferable, and a hydroxyl group is more preferable from the viewpoint of easy adjustment of the gel fraction of the adhesive layer and the difference (AB) in the storage modulus of elasticity. As a monomer which has the said hydroxyl group, the (meth)acrylate which has a hydroxyl group, such as 4-hydroxybutyl (meth)acrylate and 2-hydroxyethyl (meth)acrylate, is mentioned, for example. As a monomer which has the said carboxyl group, (meth)acrylic acid is mentioned, for example. As a monomer which has the said glycidyl group, glycidyl (meth)acrylate is mentioned, for example. Examples of the monomer having the amide group include hydroxyethylacrylamide, isopropylacrylamide, dimethylaminopropylacrylamide, and the like. As a monomer which has the said nitrile group, acrylonitrile etc. are mentioned, for example. These monomers having a crosslinkable functional group may be used alone or in combination.

In the above-mentioned acrylic copolymer, the content of the above-mentioned constituent units derived from monomers having crosslinkable functional groups is not particularly limited, but the lower limit is preferably 0.05% by weight, the upper limit is 10% by weight, and the lower limit is 1% by weight, more preferably the upper limit is 5% by weight. By making the said content into the said range, it becomes easy to adjust the difference (A-B) of the gel fraction of the said adhesive agent layer and the said storage elastic modulus.

The said acrylic copolymer may further contain the structural unit derived from another monomer within the range which does not inhibit the effect of this invention. The above-mentioned other monomers are not particularly limited, for example, propyl (meth)acrylate, butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, Octyl (meth)acrylate, nonyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, vinyl acetate, and the like.

In addition, when the above-mentioned acrylic copolymer is prepared by ultraviolet polymerization, it is preferable that the above-mentioned acrylic copolymer further contains polyfunctional monomers such as divinylbenzene and trimethylolpropane tri(meth)acrylate. Constituent unit.

The weight average molecular weight of the above-mentioned acrylic copolymer is not particularly limited, but the lower limit is preferably 300,000. When the weight average molecular weight of the acrylic copolymer is 300,000 or more, the adhesive layer has improved sebum resistance and chemical resistance, and can further suppress foaming under high temperature and high humidity. The lower limit of the weight average molecular weight of the said acrylic copolymer is more preferably 400,000, more preferably 500,000, and most preferably 1 million. The upper limit of the weight average molecular weight of the said acrylic copolymer is not specifically limited, but a preferable upper limit is 2 million, and a more preferable upper limit is 1.8 million. In addition, the weight average molecular weight is the polystyrene-equivalent molecular weight obtained by GPC measurement, and can be adjusted by polymerization conditions (for example, the kind or amount of a polymerization initiator, polymerization temperature, monomer concentration, etc.).

When synthesizing the said acrylic copolymer, what is necessary is just to make the monomer which becomes the source of the said structural unit carry out a radical reaction in presence of a polymerization initiator. The form of the radical reaction is not particularly limited, and examples thereof include living radical polymerization, radical polymerization, and the like. According to living radical polymerization, compared with radical polymerization, a copolymer having a more uniform molecular weight and composition can be obtained, and the formation of low molecular weight components and the like can be suppressed, and the cohesive force of the above-mentioned adhesive agent layer can be increased. The polymerization method is not particularly limited, and a previously known method can be used. For example, solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, block polymerization, etc. are mentioned. Among them, solution polymerization is preferred in terms of synthesis convenience.

When solution polymerization is used as a polymerization method, examples of the reaction solvent include ethyl acetate, toluene, methyl ethyl ketone, methyl sulfoxide, ethanol, acetone, diethyl ether and the like. These reaction solvents may be used alone or in combination.

The said polymerization initiator is not specifically limited, For example, an organic peroxide, an azo compound, etc. are mentioned. Examples of the above-mentioned organic peroxides include: 1,1-bis(tertiary hexyl peroxide)-3,3,5-trimethylcyclohexane, tertiary hexyl peroxypivalate, tertyl peroxide tert-butyl valerate, 2,5-dimethyl-2,5-bis(2-ethylhexyl peroxide) hexane, tert-hexyl 2-ethylhexanoate, peroxide 2 - tert-butyl ethylhexanoate, tert-butyl peroxyisobutyrate, tert-butyl peroxy-3,5,5-trimethylhexanoate, tert-butyl peroxylaurate, etc. As said azo compound, azobisisobutyronitrile, azobiscyclohexylcarbonitrile, etc. are mentioned, for example. These polymerization initiators may be used alone or in combination. Moreover, in the case of living radical polymerization, as said polymerization initiator, an organotellurium polymerization initiator is mentioned, for example. The above-mentioned organotellurium polymerization initiator is not particularly limited as long as it is generally used in living radical polymerization, and examples thereof include organotellurium compounds, organotelluride compounds, and the like. Furthermore, in the living radical polymerization, in addition to the above-mentioned organotellurium polymerization initiator, an azo compound may be used as the above-mentioned polymerization initiator for the purpose of accelerating the polymerization rate.

It is preferable that the said adhesive agent layer contains a crosslinking agent other than the said acrylic copolymer. When the said acrylic copolymer contains the said structural unit derived from the monomer which has a crosslinkable functional group, a crosslinked structure can be constructed between the chains of the said acrylic copolymer by the said crosslinking agent. At this time, the gel fraction of the adhesive layer can be adjusted by adjusting the degree of crosslinking. In particular, by adjusting the gel fraction of the adhesive layer to a relatively high range, the difference (A-B) of the storage elastic modulus can be easily adjusted to the above range, and it is more suppressed under high temperature and high humidity. The resulting foaming.

The said crosslinking agent is not specifically limited, For example, an isocyanate type crosslinking agent, an aziridine type crosslinking agent, an epoxy type crosslinking agent, a metal chelate type crosslinking agent etc. are mentioned. Among them, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred, and are more preferred in terms of easy adjustment of the gel fraction of the adhesive layer and the difference (A-B) in the storage elastic modulus. It is an isocyanate-based crosslinking agent. In the above-mentioned adhesive layer, the content of the above-mentioned crosslinking agent is not particularly limited, but relative to 100 parts by weight of the above-mentioned acrylic copolymer, the lower limit is preferably 0.01 parts by weight, the upper limit is preferably 10 parts by weight, and the lower limit is more preferably 0.1 parts by weight. parts by weight, the more preferable upper limit is 5 parts by weight.

It is preferable that the said adhesive layer further contains a silane coupling agent. By making the said adhesive layer contain the said silane coupling agent, the adhesiveness of the said adhesive layer with respect to an adherend improves. As a result, the sebum resistance and chemical resistance of the above-mentioned adhesive layer are improved, and foaming generated under high temperature and high humidity can be further suppressed.

The above-mentioned silane coupling agent is not particularly limited, for example, vinyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltrimethylsilane, 3-methacryloxypropyltrimethylsilane, Dimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyl Diethoxysilane, 3-glycidoxypropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethylmethoxysilane, N-(2-aminoethyl)3-aminopropyltriethoxysilane, N- (2-aminoethyl)3-aminopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, mercaptobutyltrimethoxysilane , 3-mercaptopropylmethyldimethoxysilane, 3-isocyanatopropyltriethoxysilane, etc. Among them, a silane coupling agent having a glycidyl group, an isocyanato group, or a mercapto group is preferable. Especially preferred are 3-glycidoxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, or a combination thereof.

In the adhesive layer, the content of the silane coupling agent is not particularly limited, but the lower limit is preferably 0.1 parts by weight and the upper limit is 10 parts by weight relative to 100 parts by weight of the acrylic copolymer. If the content of the above-mentioned silane coupling agent is 0.1 parts by weight or more, the adhesiveness of the above-mentioned adhesive layer to the adherend will be improved, the resistance to sebum and chemicals will be improved, and it will be more suppressed. of foaming. When the content of the above-mentioned silane coupling agent is 10 parts by weight or less, the paste residue when the adhesive sheet is peeled off can be suppressed, and the secondary processability of the adhesive sheet can be improved. The more preferable lower limit of the content of the said silane coupling agent is 0.5 weight part, and the more preferable lower limit is 1 weight part. A more preferable upper limit of the content of the above-mentioned silane coupling agent is 5 parts by weight, and a more preferable upper limit is 3 parts by weight.

The above-mentioned adhesive layer may optionally contain additives such as plasticizers, emulsifiers, softeners, fillers, pigments, and dyes; adhesion-imparting agents such as rosin-based resins and terpene-based resins; and other resins.

The gel fraction of the adhesive layer is preferably at least 70% by weight. When the said gel fraction is 70 weight% or more, the said storage elastic modulus difference (AB) becomes easy to satisfy|fill the said range, and the foaming which arises under high temperature and high humidity can be suppressed more. The more preferable lower limit of the said gel fraction is 80 weight%. The upper limit of the above-mentioned gel fraction is not particularly limited, but a preferable upper limit is 99% by weight. Furthermore, the gel fraction is a value representing the ratio of the weight of the adhesive layer after being dipped in ethyl acetate and dried to the weight of the adhesive layer before dipping in ethyl acetate, which can be expressed by the following formula figured out. Gel fraction (weight %) = 100 x (W ₅ -W ₃ )/(W ₄ -W ₃ ) (W ₃ : the weight of the substrate, W ₄ : the weight of the adhesive sheet before dipping in ethyl acetate, W ₅ : The weight of the adhesive sheet soaked in ethyl acetate and dried)

It is preferable that the said acrylic copolymer contains the structural unit derived from the (meth)acrylate which has a hydroxyl group, and the gel fraction of the said adhesive agent layer is 70 weight% or more. By setting it as such a structure, the difference (AB) of the said storage elastic modulus becomes easy to satisfy|fill the said range, and the foaming which arises under high temperature and high humidity can be suppressed more.

The thickness of the adhesive layer is not particularly limited, but the lower limit is preferably 5 μm, and the upper limit is 150 μm. When the thickness of the above-mentioned adhesive layer is 5 μm or more, the adhesive force of the adhesive sheet increases. When the thickness of the said adhesive layer is 150 micrometers or less, the processability of an adhesive sheet will improve.

The adhesive sheet of the present invention may be a supported type having a substrate, or may be an unsupported type having no substrate. In the case of a support type, the above-mentioned adhesive layer may be formed on one side of the substrate, or may be formed on both sides.

The said base material is not specifically limited, For example, Polyolefin-type resin films, such as a polyethylene film and a polypropylene film; Polyester-type resin films, such as a PET film, etc. are mentioned. Further examples include polyolefin foam sheets such as ethylene-vinyl acetate copolymer films, polyvinyl chloride resin films, polyurethane resin films, polyethylene foam sheets, and polypropylene foam sheets; polyurethane foam sheets; Foam tablets, etc. Among them, a PET film is preferable. Also, from the viewpoint of impact resistance, a polyolefin foam sheet is preferred. In addition, as the above-mentioned substrate, a substrate printed black to prevent light transmission, a substrate printed white to improve light reflectivity, a substrate deposited with metal, and the like can also be used.

The adhesive sheet of the present invention is also excellent in optical properties. The total light transmittance of the adhesive sheet of the present invention is not particularly limited, but the lower limit is preferably 90%, and the lower limit is more preferably 95%. The haze of the adhesive sheet of the present invention is not particularly limited, but the upper limit is preferably 1%, and the upper limit is more preferably 0.5%. When the total light transmittance and the haze are within the above-mentioned ranges, an adhesive sheet having excellent optical characteristics and suitable for optical use can be obtained. Furthermore, regarding the total light transmittance and haze, a haze meter (for example, manufactured by Nippon Denshoku Kogyo Co., Ltd.) can be used in accordance with JIS K 7361 for a measurement sample obtained by attaching an adhesive sheet to a glass plate with a thickness of 1 mm. Haze Meter NDH4000, etc.) for measurement.

The tone of the adhesive sheet of the present invention is not particularly limited, but the value of L* is preferably 98 or more. Also, the value of a* is preferably not less than -0.5 and not more than 0.5. Also, the value of b* is preferably not less than -0.5 and not more than 0.5. When the values of L*, a*, and b* are within the above-mentioned ranges, it becomes an adhesive sheet excellent in optical characteristics and suitable for optical use. Furthermore, the values of L*, a*, and b* can be measured using a colorimeter (for example, Konica Minolta Co., Ltd., SPECTROPHOTOMETER CM-3700d, etc.) for measurement.

The manufacturing method of the adhesive sheet of this invention is not specifically limited, For example, when the adhesive sheet of this invention is an unsupported type which does not have a base material, the following methods are mentioned. First, a solvent is added to an acrylic copolymer, an optional crosslinking agent, a silane coupling agent, and the like to prepare a solution of the acrylic adhesive a. The obtained solution of acrylic adhesive a is coated on the release surface of the release film treated with silicone release, and the solvent in the solution is completely dried and removed to form the adhesive layer a. Next, on the formed adhesive layer a, a release film different from the above-mentioned release film was stacked so that the release treatment surface faced the adhesive layer a. In addition, by pressing the above-mentioned laminate with a rubber roller or the like, an unsupported adhesive sheet having no base material can be obtained.

The application of the adhesive sheet of the present invention is not particularly limited, and it can be preferably used for optical applications. For example, it can be used for fixing members constituting a display device. Among them, the adhesive sheet of the present invention is excellent in sebum resistance and chemical resistance, so it can be used especially for fixing electronic equipment parts that are frequently touched by human hands, and because it is difficult to generate foaming even under high temperature and high humidity, Therefore, it can also be used especially for fixing parts that easily absorb moisture and produce outgassing, such as polarizers. Specifically, the adhesive sheet of the present invention can be suitably used for fixing covers, fixing touch panels, fixing polarizers, car navigation, etc. in portable electronic devices such as smart phones and tablet terminals. The fixing of the cover plate in the vehicle electronic equipment, the fixing of the display panel part, the fixing of the polarizer, etc.

The shape of the adhesive sheet of the present invention is not particularly limited, and may be a rectangle, etc., may also be in the shape of a roll, or may be in the shape of a sheet. [Effect of Invention]

According to the present invention, it is possible to provide an adhesive sheet that is excellent in sebum resistance and chemical resistance, hardly generates foaming even under high temperature and high humidity, and has excellent optical characteristics.

Hereinafter, although an Example is disclosed and this invention is demonstrated in more detail, this invention is not limited only to these Examples.

(Example 1) (1) Manufacture of acrylic acid copolymer Ethyl acetate was added in the reaction container as a polymerization solvent, and after blowing nitrogen gas, the reaction container was heated while flowing nitrogen gas, and reflux was started. Then, put 0.1 parts by weight of azobisisobutyronitrile as a polymerization initiator into the reaction container obtained by diluting 0.1 parts by weight of azobisisobutyronitrile with ethyl acetate, and add 67.5 parts by weight of butyl acrylate dropwise over 2 hours. 30 parts by weight of 2,2,2-trifluoroethyl acrylate, 0.5 parts by weight of acrylic acid, and 2 parts by weight of 2-hydroxyethyl acrylate. After the dropwise addition, the polymerization initiator solution obtained by diluting 0.1 parts by weight of azobisisobutyronitrile as a polymerization initiator with 10 times of ethyl acetate was put into the reaction container again, and the polymerization reaction was carried out for 4 hours to obtain A solution containing an acrylic acid copolymer.

(2) Determination of weight average molecular weight A measurement sample was prepared by filtering a 50-fold dilution of the obtained acrylic copolymer with tetrahydrofuran (THF) through a filter (material: polytetrafluoroethylene, pore size: 0.2 μm). The measurement sample was supplied to a gel permeation chromatography (manufactured by Waters, 2690 Separations Model), and GPC measurement was performed under the conditions of a sample flow rate of 1 ml/min and a column temperature of 40°C to measure the polystyrene content of an acrylic copolymer. The molecular weight was converted to obtain the weight average molecular weight. As a column, GPC LF-804 (manufactured by Showa Denko Co., Ltd.) was used, and as a detector, a differential refractometer was used.

(3) Manufacturing of adhesive sheets In the obtained solution containing the acrylic copolymer, 0.5 parts by weight of a crosslinking agent (isocyanate-based crosslinking agent, Coronate L-45, manufactured by Tosoh Corporation) and a silane coupling agent (KBM- 403, manufactured by Shin-Etsu Chemical Co., Ltd.) to prepare an adhesive solution by 1 part by weight. This adhesive solution was applied to a release-treated PET film having a thickness of 75 μm so that the thickness of the adhesive layer after drying was 15 μm, and then dried at 110° C. for 5 minutes. The adhesive layer was laminated on a 75 μm-thick release-treated PET film, and cured at 40°C for 48 hours to obtain an adhesive sheet (unsupported type).

(4) Determination of oleic acid swelling rate Peel off the release film on one side of the obtained adhesive sheet, stick it on a PET film with a thickness of 50 μm, and cut it into a flat rectangle shape of 20 mm×40 mm. Furthermore, the release film on the other side of the adhesive sheet was peeled off to make a test piece and measure its weight. After immersing the test piece in oleic acid for 24 hours at 65°C and 90% humidity, take the test piece out of the oleic acid, wash the surface with ethanol, and dry at 110°C for 3 hours. The weight of the test piece after drying was measured, and the oleic acid swelling ratio was calculated using the following formula (1). Swelling rate of oleic acid (weight %) = 100 x (W ₃ -W ₁ )/(W ₂ -W ₁ ) (1) (W ₁ : weight of the above PET film, W ₂ : test piece before dipping in oleic acid Weight, W ₃ : the weight of the test piece soaked in oleic acid and dried)

(5) Determination of gel fraction Peel off the release film on one side of the obtained adhesive sheet, stick it on a PET film with a thickness of 50 μm, and cut it into a flat rectangle shape of 20 mm×40 mm. Furthermore, the release film on the other side of the adhesive sheet was peeled off to make a test piece and measure its weight. After immersing the test piece in ethyl acetate at 23°C for 24 hours, the test piece was taken out from the ethyl acetate and dried at 110°C for 1 hour. The weight of the test piece after drying was measured, and the gel fraction was calculated using the following formula (2). Gel fraction (weight %) = 100 x (W ₅ -W ₃ )/(W ₄ -W ₃ ) (2) (W ₃ : the weight of the above PET film, W ₄ : the dipping of the test piece in ethyl acetate The weight before, W ₅ : the weight of the test piece dipped in ethyl acetate and dried)

(6) Determination of storage elastic modulus Using a dynamic viscoelasticity measuring device (DVA-200 manufactured by IT Measurement Co., Ltd.), the storage elastic modulus of the adhesive layer of the obtained adhesive sheet was measured at a heating rate of 5°C/min in the range of -40°C to 140°C. The maximum value (A), the minimum value (B) and the difference (A-B) of the storage modulus of elasticity in the temperature range from 100°C to 140°C were calculated.

(Examples 2-26, Comparative Examples 1-7) An adhesive sheet was obtained in the same manner as in Example 1, except that the monomer composition, the weight average molecular weight, and the type or amount of the crosslinking agent of the acrylic copolymer were changed as shown in Tables 1 to 3. In addition, the details of the materials shown in Table 1-Table 3 are as follows.

‧Crosslinking agent (epoxy crosslinking agent, Tetrad C, manufactured by Mitsubishi Gas Chemical Co., Ltd.) ‧Silane coupling agent (KBM-803, manufactured by Shin-Etsu Chemical Co., Ltd.) ‧Silane coupling agent (KBM-903, manufactured by Shin-Etsu Chemical Co., Ltd.)

＜Evaluation＞ The following evaluation was performed about the adhesive sheet obtained in the Example and the comparative example. The results are shown in Tables 1-4.

(1) Optical properties Peel off one of the release films of the adhesive sheet, attach it to a glass plate with a thickness of 1 mm, and peel off the other release film to prepare a measurement sample. About this measurement sample, the total light transmittance and the haze were measured using the haze meter (Nippon Denshoku Industries Co., Ltd., Haze Meter NDH4000) based on JIS K 7361. Moreover, the value of L*, a*, and b* was measured about this measurement sample using the colorimeter (SPECTROPHOTOMETER CM-3700d by Konica Minolta Co., Ltd.) based on JISZ 8730.

(2) Sebum resistance and chemical resistance Peel off one of the release films of the adhesive sheet, attach it to a PET film with a thickness of 50 μm, and cut it into a plane square shape of 30 mm×30 mm. Furthermore, the other release film of the adhesive sheet was peeled off and attached to a glass plate with a thickness of 2 mm to prepare a test piece. After immersing the test piece in oleic acid at 65°C and 90% humidity for 24 hours, the test piece was taken out, cleaned with ethanol, and dried at 110°C for 3 hours. Use an optical microscope to observe the end of the sample taken out at a magnification of 100 times, and measure the penetration distance of oleic acid. It can be said that the smaller the penetration distance of oleic acid, the better the sebum resistance and chemical resistance. The case where the oleic acid penetration distance was less than 1.0 mm was judged as "◎ (very excellent)", the case where the oleic acid penetration distance was 1.0 mm or more and less than 1.5 mm was judged as "○ (good)", and the oleic acid penetration distance was judged as "◎ (very excellent)". When the distance was 1.5 mm or more, it was judged as "× (poor)".

(3) Foaming inhibition under high temperature and high humidity (foaming resistance) Peel off one of the release films of the adhesive sheet, stick it on the COP film with a thickness of 50 μm, and cut it into a plane square of 100 mm×100 mm. Then peel off the other release film of the adhesive sheet, attach it to a glass plate (200 mm×300 mm, thickness 1 mm), and use an autoclave to press at 40°C and 0.4 MPa for 20 minutes to produce Measure the sample. At this time, it was confirmed that air bubbles did not exist at the interface between the adhesive sheet and the COP film. The measurement sample was placed in a humid heat oven at 85°C and humidity 85% and heated for 240 hours. Thereafter, the measurement sample was taken out from the humid heat oven, and the air bubbles at the interface between the adhesive sheet and the COP film were observed using an optical microscope at a magnification of 100 times within 3 minutes after the measurement sample was taken out. When the number of bubbles with a long diameter of 0.2 mm or more was one or less, it was judged as "0 (good)", and when the number of bubbles with a long diameter of 0.2 mm or more was two or more, it was judged "× (poor)".

(4) Determination of swelling rate of alkaline detergent The obtained adhesive sheet was cut into a plane rectangle shape of 20 mm×40 mm, a test piece was made and the weight was measured. After immersing the test piece in an alkaline detergent at 60°C and a humidity of 90% for 24 hours, take the test piece out of the alkaline detergent, clean the surface with ethanol, and dry at 110°C for 3 Hour. Furthermore, the alkaline cleaner uses Power Clean Keeper and solvents (water, ethanol) manufactured by Kao Corporation. The concentration of quaternary ammonium salt is adjusted to 0.5%, the concentration of ethanol to 5%, and the pH 10 while making. Measure the weight of the dried test piece, and calculate the alkaline detergent swelling rate of the adhesive sheet using the following formula. Swelling rate of alkaline cleaning solution (weight%) = (weight of test piece after immersion in alkaline cleaning solution - weight of substrate) / (weight of test piece before immersion in alkaline cleaning solution - weight of substrate )×100

(5) Evaluation of resistance to alkaline cleaners (peelability after immersion) Cut the obtained adhesive sheet into a plane square of 100 mm×100 mm, attach it to the center of a glass plate of 150 mm×150 mm, and perform autoclave treatment at 40°C and 0.4 MPa for 20 minutes, then at 23°C , Under the condition of 50% humidity, let it stand for 24 hours to make a test piece. Cover the adhesive sheet on the test piece with 50 ml of alkaline lotion, and let it stand for 24 hours at 60°C and 90% humidity. Furthermore, the alkaline cleaner uses Power Clean Keeper and solvents (water, ethanol) manufactured by Kao Corporation. The concentration of quaternary ammonium salt is adjusted to 0.5%, the concentration of ethanol to 5%, and the pH 10 while making. Return the test piece to 23°C, wash it with alkaline detergent, and observe the end with an optical microscope at 200 times to confirm the degree of peeling. Those who did not have peeling of more than 50 μm from the end were rated as "◎ (very excellent)", those with only peeling of more than 50 μm and less than 100 μm from the end were rated as "○ (good)", and those with The peeling of 100 μm or more from the end was rated as "× (poor)".

[Table 1]

[Table 2]

[table 3]

[產業上之可利用性][Table 4]

[Industrial availability]

According to the present invention, it is possible to provide an adhesive sheet that is excellent in sebum resistance and chemical resistance, hardly generates foaming even under high temperature and high humidity, and has excellent optical characteristics.

none

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Claims (13)

An adhesive sheet having an adhesive layer containing an acrylic copolymer, the acrylic copolymer containing a constituent unit derived from fluoroalkyl (meth)acrylate, and the adhesive layer being placed on the The swelling rate after 24 hours of oleic acid immersion is not less than 100% by weight and not more than 130% by weight, and the maximum value (A) and minimum value of the storage elastic modulus of the above-mentioned adhesive layer in the temperature range of 100°C to 140°C The difference (AB) between (B) is 1.2×10 ⁴ Pa or less. The adhesive sheet according to claim 1, wherein the acrylic copolymer contains a constituent unit derived from a (meth)acrylate having a hydroxyl group, and the gel fraction of the adhesive layer is 70% by weight or more. The adhesive sheet according to claim 1 or 2, wherein the acrylic copolymer contains 30% by weight or more of the structural unit derived from the fluoroalkyl (meth)acrylate. The adhesive sheet according to claim 3, wherein the fluoroalkyl (meth)acrylate is a fluoroalkyl (meth)acrylate in which fluorine is not bonded to the 1- and 2-carbons of the alkyl group. The adhesive sheet according to claim 4, wherein the fluoroalkyl (meth)acrylate is selected from 2-(perfluorohexyl)ethyl acrylate and 2-(perfluorobutyl)ethyl (meth)acrylate. At least one of the group consisting of esters. The adhesive sheet according to claim 1 or 2, wherein the acrylic copolymer contains a constituent unit derived from an alkyl (meth)acrylate having an alkyl group having 2 or less carbon atoms. The adhesive sheet according to claim 6, wherein the acrylic copolymer contains: 50% by weight or more of a constituent unit derived from an alkyl (meth)acrylate having an alkyl group having 2 or less carbon atoms, and as the above-mentioned The alkyl (meth)acrylate of an alkyl group having 2 or less carbon atoms includes at least methyl acrylate. The adhesive sheet according to claim 1 or 2, wherein the acrylic copolymer contains: a constituent unit derived from an alkyl (meth)acrylate having a linear alkyl group having 8 or more carbon atoms; At least one structural unit of the group consisting of a constituent unit of an alkyl (meth)acrylate having a branched alkyl group and a constituent unit derived from an alkyl (meth)acrylate having a ring structure. The adhesive sheet according to claim 8, wherein in the above-mentioned acrylic copolymer, the above-mentioned constituent units derived from alkyl (meth)acrylates having a straight-chain alkyl group having 8 or more carbon atoms, derived from Content of at least one constituent unit in the group consisting of branched alkyl (meth)acrylate constituent units and constituent units derived from alkyl (meth)acrylate having a ring structure 10% by weight or more. The adhesive sheet according to claim 1 or 2, wherein the acrylic copolymer contains a constituent unit derived from an alkyl (meth)acrylate represented by the following general formula (1);

In general formula (1), R represents hydrogen or methyl, R ¹ , R ² , R ³ represent hydrogen or alkyl; in general formula (1), at least two of R ¹ , R ² , R ³ are alkane group, or two of R ¹ , R ² , and R ³ form a ring structure. The adhesive sheet according to claim 10, wherein the alkyl (meth)acrylate represented by the above general formula (1) is 1-methylheptyl (meth)acrylate, tertiary butyl (meth)acrylate ester, isobornyl (meth)acrylate or cyclohexyl (meth)acrylate. The adhesive sheet according to claim 10, wherein the content of the structural unit derived from the alkyl (meth)acrylate represented by the general formula (1) in the acrylic copolymer is 10% by weight or more. The adhesive sheet according to claim 1 or 2, wherein the adhesive layer contains a silane coupling agent.