Adhesive sheet and display with touch sensor

Abstract

To provide an adhesive sheet exhibiting a low dielectric constant and reduced temperature dependence of relative permittivity.SOLUTION: The adhesive sheet of the present invention is an adhesive sheet including an adhesive layer, the adhesive layer containing a cured product of an adhesive composition comprising at least an acrylic polymer (P), wherein the acrylic polymer (P) is a polymer having predetermined monomer units, has a relative permittivity at 100 kHz of 3.0 or less at 25°C, and has values of relative permittivity at 100 kHz measured at -20°C, 0°C, 40°C, 60°C, 80°C, and 100°C, all of which are within ±0.5 points relative to the value of relative permittivity measured at 25°C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an adhesive sheet and a display with a touch sensor including the adhesive sheet. [Background technology]

[0002] The pressure-sensitive adhesive sheet is a material formed with a pressure-sensitive adhesive layer whose main component is, for example, an acrylic polymer, and is used for bonding various optical components such as light-control films, touch panels, liquid crystal displays (LCDs), etc. When the pressure-sensitive adhesive layer is of an active energy ray curing type, the pressure-sensitive adhesive layer is further cured by irradiating the pressure-sensitive adhesive layer with active energy rays such as UV, and various components (adherends) can be bonded together with high adhesive strength.

[0003] In recent years, low-dielectric-constant adhesive sheets have been proposed as adhesive sheets for bonding displays with touch sensors (see, for example, Patent Document 1). This is because the use of low-dielectric-constant adhesive sheets for bonding displays with touch sensors is expected to improve the sensitivity of the touch function. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-82880 Summary of the Invention [Problem to be solved by the invention]

[0005] Recently, there has been an increasing demand for even higher functionality in touch sensor displays, and there is a strong demand for touch sensor displays whose touch sensitivity is particularly less affected by temperature. Therefore, adhesive sheets for bonding touch sensor displays are required to have a low temperature dependency of their relative dielectric constant, but conventional adhesive sheets have not necessarily had such a property. From this perspective, there has been an urgent need to develop an adhesive sheet with a low temperature dependency of its relative dielectric constant.

[0006] The present invention has been made in view of the above, and an object of the present invention is to provide a pressure-sensitive adhesive sheet that has a low dielectric constant and in which the temperature dependency of the relative dielectric constant is low. [Means for solving the problem]

[0007] As a result of extensive research into achieving the above object, the present inventors have found that the above object can be achieved by forming an adhesive layer from a cured product of an adhesive composition having a specific composition, and have thus completed the present invention.

[0008] That is, the present invention includes, for example, the subject matter described in the following sections. Item 1 A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer comprises a cured product of a pressure-sensitive adhesive composition containing at least an acrylic polymer (P1); The acrylic polymer (P1) is nitrogen-containing monomer units a2; and (Meth)acrylate units a3 having a branched alkyl group having less than 12 carbon atoms; and is a polymer having no monomer unit having a hydroxyl group, the nitrogen-containing monomer unit a2 has a nitrogen-containing cyclic substituent and an acryloyl group, and the nitrogen-containing monomer unit a2 is contained in an amount of 5 to 40 parts by mass per 100 parts by mass of the acrylic polymer (P1); the content of (meth)acrylate units a1 having a branched alkyl group having 12 to 24 carbon atoms is 80 parts by mass or less per 100 parts by mass of the acrylic polymer (P1); The relative dielectric constant at 25°C and a frequency of 100 kHz is 3.5 or less, and An adhesive sheet whose dielectric constant values ​​at 100 kHz measured at -20°C, 0°C, 40°C, 60°C, 80°C and 100°C are all within ±0.5 points of the dielectric constant value measured at 25°C. Section 2 A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer contains a cured product of a pressure-sensitive adhesive composition containing at least an acrylic polymer (P2), The acrylic polymer (P2) is a (meth)acrylate unit a1 having a branched alkyl group having 12 to 24 carbon atoms, and a nitrogen-containing monomer unit a2; acrylate units a3(1) having a branched alkyl group with less than 12 carbon atoms; methacrylate units a3(2) having a branched alkyl group with less than 12 carbon atoms; a monomer unit a4 having a hydroxyl group; A polymer having at least the nitrogen-containing monomer unit a2 has a nitrogen-containing cyclic substituent and an acryloyl group, and the (meth)acrylate unit a1 is contained in an amount of less than 19 parts by mass per 100 parts by mass of the acrylic polymer (P2); the nitrogen-containing monomer unit a2 is contained in an amount of 5 to 30 parts by mass per 100 parts by mass of the acrylic polymer (P2); the hydroxyl group-containing monomer unit a4 is contained in an amount of less than 5 parts by mass per 100 parts by mass of the acrylic polymer (P2), The relative dielectric constant at 25°C and a frequency of 100 kHz is 3.5 or less, and An adhesive sheet whose dielectric constant values ​​at 100 kHz measured at -20°C, 0°C, 40°C, 60°C, 80°C and 100°C are all within ±0.5 points of the dielectric constant value measured at 25°C. Section 3 the acrylic polymer (P1) further contains a nitrogen-containing monomer unit a5 other than the nitrogen-containing monomer unit a2, the nitrogen-containing monomer unit a5 is a vinyl monomer unit having an acyclic substituent containing a nitrogen atom, Item 2. The pressure-sensitive adhesive sheet according to Item 1, wherein the nitrogen-containing monomer unit a5 is contained in an amount of 5 parts by mass or less per 100 parts by mass of the acrylic polymer (P1). Section 4 Item 2. The pressure-sensitive adhesive sheet according to item 1, wherein the (meth)acrylate unit a3 is contained in an amount of less than 50 parts by mass per 100 parts by mass of the acrylic polymer (P1). Section 5 the acrylic polymer (P2) further contains a nitrogen-containing monomer unit a5 other than the nitrogen-containing monomer unit a2, the nitrogen-containing monomer unit a5 is a vinyl monomer unit having an acyclic substituent containing a nitrogen atom, Item 3. The pressure-sensitive adhesive sheet according to Item 2, wherein the nitrogen-containing monomer unit a5 is contained in an amount of 5 parts by mass or less per 100 parts by mass of the acrylic polymer (P2). Section 6 the acrylate unit a3(1) is contained in an amount of less than 50 parts by mass per 100 parts by mass of the acrylic polymer (P2), Item 3. The pressure-sensitive adhesive sheet according to Item 2, wherein the methacrylate unit a3(2) is contained in an amount of less than 50 parts by mass per 100 parts by mass of the acrylic polymer (P2). Section 7 Item 7. The pressure-sensitive adhesive sheet according to any one of items 1 to 6, wherein the nitrogen-containing monomer unit a2 is an acryloylmorpholine unit. Section 8 Item 8. The pressure-sensitive adhesive sheet according to any one of items 1 to 7, which is for a display with a touch sensor. Section 9 Item 9. A display with a touch sensor, comprising the adhesive sheet according to item 8. [Effects of the Invention]

[0009] The pressure-sensitive adhesive sheet according to the present invention has a low dielectric constant, and the temperature dependency of the relative dielectric constant is low. DETAILED DESCRIPTION OF THE INVENTION

[0010]

[0023] In the present specification, the terms "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0011] 1. Adhesive sheet The pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer comprises a cured product of a pressure-sensitive adhesive composition containing at least a specific acrylic polymer (P) described below. The pressure-sensitive adhesive sheet of the present invention has a dielectric constant of 3.5 or less at a frequency of 100 kHz at 25°C, and the values ​​of the dielectric constant at 100 kHz measured at -20°C, 0°C, 40°C, 60°C, 80°C and 100°C are all within a range of ±0.5 points (i.e., -0.5 points or more and +0.5 points or less) of the value of the dielectric constant measured at 25°C.

[0012] The pressure-sensitive adhesive sheet of the present invention has a low dielectric constant and also has a low temperature dependency of the dielectric constant. Low temperature dependency of the dielectric constant means that the dielectric constant is less likely to fluctuate even when the temperature of the pressure-sensitive adhesive sheet changes. In particular, this means that the dielectric constants of the pressure-sensitive adhesive sheet at 100 kHz measured at -20°C, 0°C, 40°C, 60°C, 80°C, and 100°C all differ by within 0.5 points from the dielectric constant measured at 25°C.

[0013] As described above, the pressure-sensitive adhesive sheet of the present invention has a low dielectric constant and, in addition, the temperature dependency of the relative dielectric constant is low, and therefore, can be suitably used as a pressure-sensitive adhesive sheet for a display with a touch sensor.

[0014] In the pressure-sensitive adhesive sheet of the present invention, the acrylic polymer (P) includes, for example, an "acrylic polymer (P1)" and an "acrylic polymer (P2)".

[0015] The acrylic polymer (P1) is nitrogen-containing monomer units a2; and (Meth)acrylate units a3 having a branched alkyl group having less than 12 carbon atoms; and The polymer does not have any monomer units having a hydroxyl group. In the polymer, the nitrogen-containing monomer units a2 have a cyclic substituent containing nitrogen and an acryloyl group, and the nitrogen-containing monomer units a2 are contained in an amount of 5 to 40 parts by mass per 100 parts by mass of the acrylic polymer (P1). In the acrylic polymer (P1), the content of (meth)acrylate units a1 having a branched alkyl group having 12 to 24 carbon atoms is 80 parts by mass or less in 100 parts by mass of the acrylic polymer (P1).

[0016] The acrylic polymer (P2) is a (meth)acrylate unit a1 having a branched alkyl group having 12 to 24 carbon atoms, and a nitrogen-containing monomer unit a2; acrylate units a3(1) having a branched alkyl group with less than 12 carbon atoms; methacrylate units a3(2) having a branched alkyl group with less than 12 carbon atoms; a monomer unit a4 having a hydroxyl group; In the polymer, the nitrogen-containing monomer units a2 have a nitrogen-containing cyclic substituent and an acryloyl group, the (meth)acrylate units a1 are contained in an amount of less than 19 parts by mass per 100 parts by mass of the acrylic polymer (P2), the nitrogen-containing monomer units a2 are contained in an amount of 5 to 30 parts by mass per 100 parts by mass of the acrylic polymer (P2), and the hydroxyl group-containing monomer units a4 are contained in an amount of less than 5 parts by mass per 100 parts by mass of the acrylic polymer (P).

[0017] First, each monomer unit contained in the acrylic polymer (P1) or the acrylic polymer (P2) will be described. Note that the monomer unit refers to a repeating structural unit formed when a monomer is polymerized.

[0018] <(Meth)acrylate unit a1> The (meth)acrylate unit a1 is a structural unit derived from a (meth)acrylate monomer having a branched alkyl group with 12 to 24 carbon atoms (12 or more and 24 or less). The (meth)acrylate monomer having a branched alkyl group with 12 to 24 carbon atoms is referred to as "(meth)acrylate compound A1."

[0019] In this specification, "(meth)acrylic" means "acrylic" or "methacrylic", and "(meth)acrylate" means "acrylate" or "methacrylate".

[0020] Examples of the (meth)acrylate compound A1 include a compound in which an alkyl group (branched alkyl group) having 12 to 24 carbon atoms is bonded to the ester oxygen of a (meth)acrylate. In the (meth)acrylate compound A1, the number of carbon atoms in the branched alkyl group is more preferably 14 or more, even more preferably 16 or more, and more preferably 22 or less, even more preferably 20 or less. The branched alkyl group may have another substituent as long as the effects of the present invention are not impaired.

[0021] Specific examples of the (meth)acrylate compound A1 include isomistyryl (meth)acrylate, isostearyl (meth)acrylate, isotridecyl (meth)acrylate, isopentadecyl (meth)acrylate, isohexadecyl (meth)acrylate, and isoheptadecyl (meth)acrylate.

[0022] Among these, the (meth)acrylate compound A1 is preferably isostearyl (meth)acrylate, since this tends to reduce the dielectric constant of the PSA sheet and the temperature dependency of the dielectric constant. That is, the (meth)acrylate unit a1 is preferably a structural unit derived from isostearyl (meth)acrylate.

[0023] <Nitrogen-containing monomer unit a2> The nitrogen-containing monomer unit a2 is a monomer unit having a nitrogen-containing cyclic substituent and an acryloyl group, and is a constituent unit derived from a monomer having a nitrogen-containing cyclic substituent and an acryloyl group. The monomer having a nitrogen-containing cyclic substituent and an acryloyl group is referred to as "nitrogen-containing monomer A2."

[0024] The nitrogen-containing monomer A2 is a polymerizable compound having a nitrogen-containing cyclic substituent and an acryloyl group. Therefore, a specific example of the nitrogen-containing monomer A2 is acryloylmorpholine.

[0025] Among these, the nitrogen-containing monomer A2 is preferably acryloylmorpholine, since this tends to reduce the dielectric constant of the pressure-sensitive adhesive sheet and the temperature dependency of the dielectric constant. That is, the nitrogen-containing monomer unit a2 is preferably a structural unit derived from acryloylmorpholine (acryloylmorpholine unit).

[0026] <(Meth)acrylate unit a3> The (meth)acrylate unit a3 is a structural unit derived from a (meth)acrylate monomer having a branched alkyl group with a carbon number of less than 12. The (meth)acrylate monomer having a branched alkyl group with a carbon number of less than 12 is referred to as "(meth)acrylate compound A3."

[0027] In this specification, in the (meth)acrylate unit a3, an acrylate unit having a branched alkyl group with less than 12 carbon atoms is sometimes referred to as an "acrylate unit a3(1)," and a methacrylate unit having a branched alkyl group with less than 12 carbon atoms is sometimes referred to as a "methacrylate unit a3(2)." Furthermore, the term "(meth)acrylate unit a3" refers to "acrylate unit a3(1)" or "methacrylate unit a3(2)." Similarly, in the (meth)acrylate compound A3, an acrylate having a branched alkyl group with less than 12 carbon atoms is sometimes referred to as "acrylate compound A3(1)," and a methacrylate having a branched alkyl group with less than 12 carbon atoms is sometimes referred to as "methacrylate compound A3(2)." Furthermore, the term "(meth)acrylate compound A3" refers to "acrylate compound A3(1)" or "methacrylate compound A3(2)."

[0028] The (meth)acrylate compound A3 may be a compound in which an ester oxygen of a (meth)acrylate is bonded to a branched alkyl group having a carbon number of less than 12. The branched alkyl group may have a cyclic structure.

[0029] In the (meth)acrylate compound A3, the number of carbon atoms in the branched alkyl group is more preferably 4 or more, even more preferably 6 or more, and more preferably 10 or less, even more preferably 8 or less. The branched alkyl group may have another substituent as long as the effects of the present invention are not impaired.

[0030] Specific examples of the (meth)acrylate compound A3 include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, isopropyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, and benzyl (meth)acrylate.

[0031] Among these, the (meth)acrylate compound A3 is more preferably a (meth)acrylate having an alkyl group with two or more carbon atoms, even more preferably a (meth)acrylate having an alkyl group with three or more carbon atoms, and particularly preferably a (meth)acrylate having an alkyl group with four or more carbon atoms, in that the dielectric constant of the PSA sheet is likely to be low and the temperature dependency of the dielectric constant is likely to be low. Specific preferred examples of the (meth)acrylic compound A3 include 2-ethylhexyl (meth)acrylate and isobornyl (meth)acrylate, with 2-ethylhexyl (meth)acrylate being particularly preferred. That is, the (meth)acrylate unit a3 is preferably a structural unit derived from 2-ethylhexyl (meth)acrylate or isobornyl (meth)acrylate, and particularly preferably a structural unit derived from 2-ethylhexyl (meth)acrylate.

[0032] The (meth)acrylate units a3 contained in the acrylic polymer (P) may consist solely of structural units derived from 2-ethylhexyl (meth)acrylate.

[0033] <Monomer unit a4 having a hydroxyl group> The monomer unit a4 having a hydroxyl group is a structural unit derived from a polymerizable monomer having a hydroxyl group. The polymerizable monomer having a hydroxyl group is referred to as a "monomer A4 having a hydroxyl group."

[0034] Examples of the monomer A4 having a hydroxyl group include a wide range of (meth)acrylate compounds having a hydroxyl group, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2,2-dimethyl-2-hydroxyethyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, and polyalkylene glycol mono(meth)acrylate. Among these, the hydroxyl group-containing monomer A4 is preferably 4-hydroxybutyl(meth)acrylate.

[0035] <Nitrogen-containing monomer unit a5> The acrylic polymer (P) may further contain a nitrogen-containing monomer unit a5. In particular, the acrylic polymer (P1) may further contain a nitrogen-containing monomer unit a5. The nitrogen-containing monomer unit a5 is a monomer unit other than the nitrogen-containing monomer unit a2, and is particularly a unit derived from a monomer having an acyclic substituent containing a nitrogen atom. A monomer having an acyclic substituent containing a nitrogen atom is referred to as a "nitrogen-containing monomer A5."

[0036] The nitrogen-containing monomer A5 may be a vinyl compound having an acyclic substituent containing a nitrogen atom in the molecule, and particularly may be a vinyl monomer copolymerizable with the (meth)acrylate compound A1. That is, the nitrogen-containing monomer A5 may be a vinyl monomer capable of radical polymerization with the (meth)acrylate compound A1. Therefore, the nitrogen-containing monomer unit a5 is preferably a vinyl monomer unit having an acyclic substituent containing a nitrogen atom.

[0037] In the acyclic substituent containing a nitrogen atom in the nitrogen-containing monomer A5, the number of nitrogen atoms is 1 or more, and preferably 2 or less. In the acyclic substituent containing a nitrogen atom, the number of nitrogen atoms is particularly preferably 1.

[0038] The nitrogen-containing monomer A5 preferably has an amide bond in the molecule, that is, the nitrogen-containing monomer unit a5 preferably has an amide bond, which tends to reduce the relative dielectric constant of the PSA sheet.

[0039] Specific examples of the nitrogen-containing monomer A5 include (meth)acrylamide and N-substituted (meth)acrylamide. N-substituted (meth)acrylamide is exemplified by (meth)acrylamide in which one or two alkyl groups are substituted on the nitrogen atom. In the N-substituted (meth)acrylamide, the alkyl group may be, for example, an alkyl group having 1 to 8 carbon atoms, preferably an alkyl group having 1 to 3 carbon atoms, and more preferably an alkyl group having 1 or 2 carbon atoms. When two alkyl groups are substituted on the nitrogen atom, the alkyl groups may be the same or different, and preferably the alkyl groups are the same.

[0040] Specific examples of N-substituted (meth)acrylamides include N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, and tert-octyl(meth)acrylamide.

[0041] The nitrogen-containing vinyl compound A2 is more preferably an N-substituted (meth)acrylamide, and among these, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, and the like are even more preferred.

[0042] <Acrylic polymer (P1)> The acrylic polymer (P1) is a polymer that contains at least the above-mentioned (meth)acrylate unit a1, nitrogen-containing monomer unit a2, and (meth)acrylate unit a3, but does not contain any monomer unit having a hydroxyl group. For example, the acrylic polymer (P1) does not contain the above-mentioned monomer unit a4 having a hydroxyl group.

[0043] The acrylic polymer (P1) may contain, for example, other monomer units in addition to those described above. Examples of the other monomers include the nitrogen-containing monomer unit a5, a carboxyl group-containing monomer such as (meth)acrylic acid, and a (meth)acrylic ester compound having an epoxy group.

[0044] In the acrylic polymer (P1), the content of the (meth)acrylate units a1 is 80 parts by mass or less per 100 parts by mass of the acrylic polymer (P1). More specifically, the acrylic polymer (P1) may not contain the (meth)acrylate units a1 (i.e., the content of the (meth)acrylate units a1 may be 0 parts by mass). Alternatively, if the acrylic polymer (P1) contains the (meth)acrylate units a1, the content of the (meth)acrylate units a1 is 80 parts by mass or less per 100 parts by mass of the acrylic polymer (P1). In either case, a pressure-sensitive adhesive sheet having a low dielectric constant and a low temperature dependence of the dielectric constant is easily formed. If the content of the (meth)acrylate units a1 exceeds 80 parts by mass per 100 parts by mass of the acrylic polymer (P1), the optical properties may be deteriorated. However, this does not apply when the acrylic polymer (P2) is contained in the pressure-sensitive adhesive sheet.

[0045] When the acrylic polymer (P1) contains the (meth)acrylate units a1, the content of the (meth)acrylate units a1 is, per 100 parts by mass of the acrylic polymer (P1), preferably 25 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 35 parts by mass or more, particularly preferably 40 parts by mass or more, and is preferably 78 parts by mass or less, more preferably 75 parts by mass or less, even more preferably 70 parts by mass or less, particularly preferably 65 parts by mass or less.

[0046] In the acrylic polymer (P1), the nitrogen-containing monomer unit a2 is contained in an amount of 5 to 40 parts by mass (i.e., 5 parts by mass or more and 40 parts by mass or less) per 100 parts by mass of the acrylic polymer (P1). This makes it easy to form a pressure-sensitive adhesive sheet having a low relative dielectric constant and low temperature dependency of the relative dielectric constant. If the content of the nitrogen-containing monomer unit a2 is less than 5 parts by mass or more than 40 parts by mass per 100 parts by mass of the acrylic polymer (P1), the balance of cohesive force may be lost, and adhesive properties may be impaired.

[0047] In the acrylic polymer (P1), the content of the nitrogen-containing monomer units a2 is preferably 6 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of the acrylic polymer (P1). When the acrylic polymer (P1) contains (meth)acrylate units a1, the content of the nitrogen-containing monomer units a2 is preferably 28 parts by mass or less, more preferably 25 parts by mass or less, even more preferably 23 parts by mass or less, and particularly preferably 20 parts by mass or less, per 100 parts by mass of the acrylic polymer (P1). When the acrylic polymer (P1) does not contain (meth)acrylate units a1, the content of the nitrogen-containing monomer units a2 is preferably 38 parts by mass or less, more preferably 36 parts by mass or less, even more preferably 35 parts by mass or less, and preferably 25 parts by mass or more, and even more preferably 30 parts by mass or more, per 100 parts by mass of the acrylic polymer (P1).

[0048] In the acrylic polymer (P1), the (meth)acrylate units a3 are preferably contained in an amount of less than 50 parts by mass per 100 parts by mass of the acrylic polymer (P1). In this case, a pressure-sensitive adhesive sheet having a low dielectric constant and low temperature dependency of the dielectric constant is easily formed. In the acrylic polymer (P1), the (meth)acrylate units a3 are preferably contained in an amount of 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and particularly preferably 20 parts by mass or more per 100 parts by mass of the acrylic polymer (P1), and are preferably contained in an amount of 49 parts by mass or less, more preferably 45 parts by mass or less, and even more preferably 40 parts by mass or less. However, this does not apply when the acrylic polymer (P1) does not contain the (meth)acrylate units a1. For example, when the acrylic polymer (P1) does not contain (meth)acrylate units a1, the content of the (meth)acrylate units a3 is preferably 50 parts by mass or more and 70 parts by mass or less, and more preferably 60 parts by mass or more and 68 parts by mass or less, per 100 parts by mass of the acrylic polymer (P1).

[0049] When the acrylic polymer (P1) contains the nitrogen-containing monomer unit a5, the nitrogen-containing monomer unit a5 is preferably contained in an amount of 5 parts by mass or less per 100 parts by mass of the acrylic polymer (P1), which makes it easier to form a pressure-sensitive adhesive sheet having a low temperature dependence of the dielectric constant.

[0050] In the acrylic polymer (P1), the nitrogen-containing monomer unit a5 is contained in an amount of more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of the acrylic polymer (P1). The nitrogen-containing monomer unit a5 may not be contained in the acrylic polymer (P1) (i.e., the content of the nitrogen-containing monomer unit a5 in the acrylic polymer (P1) may be 0 part by mass).

[0051] The acrylic polymer (P1) may be composed only of nitrogen-containing monomer units a2 and (meth)acrylate units a3. Alternatively, the acrylic polymer (P1) may be composed only of (meth)acrylate units a1, nitrogen-containing monomer units a2 and (meth)acrylate units a3. Furthermore, the acrylic polymer (P1) may be composed only of (meth)acrylate units a1, nitrogen-containing monomer units a2, (meth)acrylate units a3 and nitrogen-containing monomer units a5.

[0052] The acrylic polymer (P1) may contain one type of each monomer unit, or two or more different types.

[0053] <Acrylic polymer (P2)> The acrylic polymer (P2) is a polymer having at least (meth)acrylate units a1, nitrogen-containing monomer units a2, acrylate units a3(1), methacrylate units a3(2), and monomer units a4 having a hydroxyl group.

[0054] The acrylic polymer (P2) may contain, for example, other monomer units in addition to those described above. Examples of the other monomers include the nitrogen-containing monomer unit a5, as well as carboxyl group-containing monomers such as (meth)acrylic acid, and (meth)acrylic ester compounds having an epoxy group.

[0055] The acrylic polymer (P2) may consist solely of (meth)acrylate units a1, nitrogen-containing monomer units a2, acrylate units a3(1), methacrylate units a3(2), and hydroxyl group-containing monomer units a4, or may consist solely of (meth)acrylate units a1, nitrogen-containing monomer units a2, acrylate units a3(1), methacrylate units a3(2), hydroxyl group-containing monomer units a4, and nitrogen-containing monomer units a5.

[0056] The acrylic polymer (P2) may contain one type of each monomer unit, or two or more different types.

[0057] In the acrylic polymer (P2), the (meth)acrylate units a1 are contained in an amount of less than 19 parts by mass per 100 parts by mass of the acrylic polymer (P2). This makes it easier to form a pressure-sensitive adhesive sheet with an excellent balance between dielectric constant and adhesive properties. If the content of the (meth)acrylate units a1 is 19 parts by mass or more per 100 parts by mass of the acrylic polymer (P2), the balance of cohesive force may be lost, and adhesive properties may be impaired. However, this does not apply when the acrylic polymer (P1) is contained in the pressure-sensitive adhesive sheet.

[0058] In the acrylic polymer (P2), the (meth)acrylate units a1 are contained in an amount of preferably 5 parts by mass or more, more preferably 8 parts by mass or more, even more preferably 10 parts by mass or more, and particularly preferably 13 parts by mass or more per 100 parts by mass of the acrylic polymer (P2).

[0059] In the acrylic polymer (P2), the nitrogen-containing monomer unit a2 is contained in an amount of 5 to 30 parts by mass (5 parts by mass or more and 30 parts by mass or less) per 100 parts by mass of the acrylic polymer (P2). This makes it easier to form a pressure-sensitive adhesive sheet having a low dielectric constant and low temperature dependency of the dielectric constant, and also makes the cohesive strength of the polymer components in the pressure-sensitive adhesive sheet appropriate, making it easier to improve adhesive properties. If the content of the nitrogen-containing monomer unit a2 is less than 5 parts by mass or more than 30 parts by mass per 100 parts by mass of the acrylic polymer (P2), the cohesive strength may be unbalanced, resulting in impaired adhesive properties.

[0060] In the acrylic polymer (P2), the nitrogen-containing monomer unit a2 is contained in an amount of preferably 6 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 10 parts by mass or more per 100 parts by mass of the acrylic polymer (P2), and is contained in an amount of preferably 28 parts by mass or less, more preferably 25 parts by mass or less, even more preferably 23 parts by mass or less, and particularly preferably 20 parts by mass or less.

[0061] In the acrylic polymer (P2), the acrylate unit a3(1) may be contained in an amount of, for example, less than 50 parts by mass per 100 parts by mass of the acrylic polymer (P2).

[0062] In the acrylic polymer (P2), the acrylate unit a3(1) is contained in an amount of preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and particularly preferably 20 parts by mass or more per 100 parts by mass of the acrylic polymer (P2), and is contained in an amount of preferably 49 parts by mass or less, more preferably 45 parts by mass or less, and even more preferably 40 parts by mass or less.

[0063] In the acrylic polymer (P2), the methacrylate unit a3(2) may be contained in an amount of, for example, less than 50 parts by mass per 100 parts by mass of the acrylic polymer (P2).

[0064] In the acrylic polymer (P2), the methacrylate units a3(2) are contained in an amount of preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and particularly preferably 20 parts by mass or more per 100 parts by mass of the acrylic polymer (P2), and are contained in an amount of preferably 49 parts by mass or less, more preferably 45 parts by mass or less, and even more preferably 43 parts by mass or less.

[0065] In the acrylic polymer (P2), the hydroxyl group-containing monomer unit a4 is contained in an amount of less than 5 parts by mass per 100 parts by mass of the acrylic polymer (P2). This makes it easy to form a pressure-sensitive adhesive sheet having a low dielectric constant and low temperature dependency of the dielectric constant. If the content of the monomer unit a4 is 5 parts by mass or more per 100 parts by mass of the acrylic polymer (P2), the dielectric constant may become high and the temperature dependency of the dielectric constant may become high.

[0066] In the acrylic polymer (P2), the hydroxyl group-containing monomer unit a4 is contained in an amount of preferably 4 parts by mass or less, more preferably 3.5 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of the acrylic polymer (P2), and is contained in an amount of preferably 0.1 part by mass or more, and more preferably 0.5 part by mass or more.

[0067] When the acrylic polymer (P2) contains the nitrogen-containing monomer unit a5, the nitrogen-containing monomer unit a5 is preferably contained in an amount of 5 parts by mass or less per 100 parts by mass of the acrylic polymer (P2), which makes it easier to form a pressure-sensitive adhesive sheet with a low temperature dependence of the dielectric constant.

[0068] In the acrylic polymer (P2), the nitrogen-containing monomer unit a5 is contained in an amount of more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of the acrylic polymer (P2). The nitrogen-containing monomer unit a5 may not be contained in the acrylic polymer (P2) (i.e., the content of the nitrogen-containing monomer unit a5 in the acrylic polymer (P2) may be 0 part by mass).

[0069] <Acrylic polymer (P)> In the present invention, the weight-average molecular weight of the acrylic polymer (P) (including the acrylic polymer (P1) and the acrylic polymer (P2)) is not particularly limited, and from the viewpoint of preventing a decrease in adhesive strength in the pressure-sensitive adhesive sheet, it can be, for example, 100,000 to 2,000,000, and more preferably 300,000 to 1,000,000. Note that the weight-average molecular weight referred to in the present invention refers to the weight-average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC).

[0070] There are no particular limitations on the GPC apparatus used in the GPC method. Commercially available GPC measuring instruments, such as the LC-2000Plus series manufactured by JASCO Corporation, with detectors such as RI-2031Plus and UV-2075Plus, can be used. In this case, for example, a GPC column consisting of four columns connected together, including "Shodex KF801," "Shodex KF803L," "Shodex KF800L," and "Shodex KF800D" manufactured by Showa Denko K.K., can be used. The column temperature can be set to 40°C. Tetrahydrofuran is used as the eluent, and measurements are performed at a flow rate of 1.0 ml / min. Typically, a calibration curve is prepared using standard polystyrene, and the weight-average molecular weight (Mw) can be calculated in terms of polystyrene.

[0071] The acrylic polymer (P) can be produced, for example, by polymerizing a monomer mixture for forming each structural unit by a known polymerization method. Examples of the polymerization method that can be used include solution polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization. The ratio of each structural unit in the acrylic polymer corresponds to the ratio of each monomer used during polymerization. The types of solvent and polymerization initiator used in the polymerization are not particularly limited, and for example, solvents and polymerization initiators used in the production of known acrylic polymers can be used.

[0072] The glass transition temperature (Tg) of the acrylic polymer (P) is not particularly limited and can be, for example, from -60 to 0°C, preferably from -50 to -10°C, and more preferably from -40 to -20°C.

[0073] The method for adjusting the glass transition temperature of the acrylic polymer (P) is not particularly limited, and the glass transition temperature can be adjusted to a desired range by, for example, changing the types and composition ratio of the monomers constituting the acrylic polymer (P). In the present invention, the glass transition temperature of the acrylic polymer (P) refers to Tg calculated by the following Fox formula based on the composition of the monomers used in synthesizing the copolymer. Fox formula: 1 / Tg = (W1 / Tg1) + (W2 / Tg2) + + (Wm / Tgm) where W1+W2+···+Wm=1 In the formula, Tg is the glass transition temperature (unit: K) of the acrylic polymer (P), Tg1, Tg2, ..., Tgm are the glass transition temperatures of the respective homopolymers of m types of monomers (m is an integer) that constitute the acrylic polymer (P), and W1, W2, ..., Wm are the mass fractions of each structural unit in the acrylic polymer (P). Note that Tg1 and W1 correspond to each other; that is, the monomer that constitutes the homopolymer that exhibits the glass transition temperature of Tg1 is the same as the monomer that forms the structural unit whose mass fraction is W1. Similarly, Tg2 and W2, ..., Tgm and Wm correspond to each other.

[0074] The glass transition temperature of the homopolymer can be determined, for example, from the value described in the Polymer Handbook, 4th Edition (Wiley-Interscience, 2003). If no such reference is found, the glass transition temperature of the homopolymer can be measured, for example, by a differential scanning calorimeter (DSC). The DSC measurement conditions are as follows: 5 mg of sample, under a nitrogen atmosphere, the temperature is increased from -100°C to 200°C at a rate of 5°C / min in the first measurement (1st run), then cooled to -100°C at a rate of 5°C / min, and then increased from -100°C to 200°C at a rate of 5°C / min in the second measurement (2nd run). Here, the glass transition temperature refers to the intersection of the extension of the baseline on the lower temperature side of the region where the baseline of the DSC curve measured when the temperature is raised from -100°C to 200°C changes to a sigmoid shape in the endothermic direction and the tangent to the inflection point of the sigmoid.

[0075] (Adhesive composition) As described above, the pressure-sensitive adhesive sheet of the present invention includes a pressure-sensitive adhesive layer containing a cured product of a pressure-sensitive adhesive composition. That is, the pressure-sensitive adhesive layer is obtained by curing the pressure-sensitive adhesive composition. Examples of the pressure-sensitive adhesive composition include active energy ray-curable pressure-sensitive adhesive compositions that have the property of being cured by irradiation with active energy rays. The active energy ray-curable pressure-sensitive adhesive composition can contain, for example, at least an adhesive resin containing an acrylic polymer (P), a polyfunctional monomer, and a photopolymerization initiator.

[0076] In the active energy ray-curable pressure-sensitive adhesive composition, the adhesive resin containing the acrylic polymer (P) can contain the acrylic polymer (P) and the same type of (meth)acrylic ester monomer as the monomer constituting the acrylic polymer (P). Therefore, the adhesive resin containing the acrylic polymer (P) can be in the form of a so-called syrup. The monomer contained in the adhesive resin preferably has the same composition as the monomer composition constituting the monomer unit contained in the acrylic polymer. In other words, the adhesive resin is preferably a partial polymer of the acrylic polymer (P). In this case, the polymer fraction is not particularly limited. The polymer fraction is the proportion (mass %) of the resin component relative to the total mass of the resin component (acrylic polymer (P)) and the monomer. The polymer fraction can be, for example, 1 to 80 mass %, and preferably 20 to 50 mass %.

[0077] When the pressure-sensitive adhesive composition is an active energy ray-curable pressure-sensitive adhesive composition, the acrylic polymer (P) constituting the pressure-sensitive adhesive resin is preferably an acrylic polymer (P1).

[0078] The polyfunctional monomer may be, for example, a compound having two or more polymerizable double bonds in the molecule. The polyfunctional monomer has two or more polymerizable double bonds (e.g., radically polymerizable double bonds), preferably two or more but less than five, and more preferably two or more but less than four.

[0079] Examples of polyfunctional monomers include bifunctional monomers (monomers having two polymerizable double bonds), such as polyethylene glycol diacrylate, polypropylene diacrylate, alkyl diacrylate, polytetramethylene glycol diacrylate, polypropylene glycol diacrylate, dioxane diacrylate, tricyclodecanol diacrylate, and fluorene diacrylate. Examples of polyfunctional monomers include trifunctional or higher functional monomers, such as alkoxylated trimethylolpropane triacrylate, alkoxylated glycerin triacrylate, caprolactone-modified isocyanurate triacrylate, pentaerythritol acrylate, alkoxylated pentaerythritol acrylate, (alkoxylated) pentaerythritol acrylate, (alkoxylated) ditrimethylolpropane acrylate, (alkoxylated) dipentaerythritol acrylate, (ethoxylated) polyglycerin acrylate, polyfunctional urethane acrylate, and polyfunctional oligomers such as acrylic-terminated polybutadiene (olefin).

[0080] When the polyfunctional monomer is a polyfunctional monomer having an alkylene glycol group in one molecule, the number of alkylene glycol groups in one molecule is preferably 1 to 20. Examples of such polyfunctional monomers include polyethylene glycol diacrylate and trimethylolpropane propylene oxide modified triacrylate.

[0081] Commercially available polyfunctional monomers include, for example, "A-200" (polyethylene glycol #200 diacrylate) and "A-400" (polyethylene glycol #400 diacrylate) from the NK Ester series, which are bifunctional polyethylene glycol acrylates manufactured by Shin-Nakamura Chemical Co., Ltd., the trifunctional "ATM-4PL" (pentaerythritol triacrylate), the trifunctional monomer M310 (trimethylolpropane PO-modified triacrylate) and the trifunctional monomer M321 (trimethylolpropane propylene oxide-modified triacrylate) manufactured by Toagosei Co., Ltd., and the bifunctional monomer M211B (bisphenol A EO-modified diacrylate) manufactured by Toagosei Co., Ltd.

[0082] The polyfunctional monomer may have a bisphenol skeleton in one molecule, such as diacrylate of bisphenol A diglycidyl ether, diacrylate of propoxylated bisphenol A, and diacrylate of bisphenol F diglycidyl ether.

[0083] When the adhesive composition contains a polyfunctional monomer, the adhesive resin (acrylic polymer) can form a crosslinked structure by curing the adhesive with active energy rays, which makes the adhesive sheet more likely to have excellent adhesive strength.

[0084] The content of the polyfunctional monomer in the pressure-sensitive adhesive composition is not particularly limited. For example, the pressure-sensitive adhesive composition may contain 1 part by mass or less of the polyfunctional monomer per 100 parts by mass of the pressure-sensitive adhesive resin, preferably 0.5 parts by mass or less, more preferably 0.3 parts by mass or less, even more preferably 0.2 parts by mass or less, and particularly preferably 0.15 parts by mass or less. Furthermore, the pressure-sensitive adhesive preferably contains 0.001 parts by mass or more of the polyfunctional monomer per 100 parts by mass of the pressure-sensitive adhesive resin, more preferably 0.01 parts by mass or more, and even more preferably 0.02 parts by mass or more. The pressure-sensitive adhesive composition may contain one type of polyfunctional monomer alone or two or more types of polyfunctional monomers.

[0085] As the photopolymerization initiator, for example, a wide variety of known photopolymerization initiators can be used.

[0086] The photopolymerization initiator is not particularly limited, and examples thereof include acetophenone-based photopolymerization initiators such as 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropanone, 1-[4-(2-hydroxyethoxyl)-phenyl]-2-hydroxy-methylpropanone, and 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methyl-1-propanone; acylphosphine oxide-based photopolymerization initiators such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and 2,4,6-trimethylbenzoyl)phenylphosphine oxide; intramolecular hydrogen abstraction photopolymerization initiators such as methyl benzoylformate and 4-methylbenzophenone; and oil-soluble polymerization initiators such as oxime ester-based photopolymerization initiators and cationic photopolymerization initiators. Among these, the photopolymerization initiator is preferably at least one selected from the group consisting of acetophenone-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, and oxime ester-based photopolymerization initiators.

[0087] Commercially available acetophenone-based photopolymerization initiators include EsacureOne (oligo(2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenylpropanone], manufactured by IGM Resins BV), Omnirad 651 (2,2-dimethoxy-2-phenylacetophenone, manufactured by IGM Resins BV), Omnirad 184 (1-hydroxycyclohexylphenyl ketone, manufactured by IGM Resins BV), and Omnirad 1173 (2-hydroxy-2-methyl-1-phenylpropanone, manufactured by IGM Resins BV).

[0088] Commercially available acylphosphine oxide photopolymerization initiators include Omnirad 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, manufactured by IGM Resins BV) and Omnirad TPO (2,4,6-trimethylbenzoyl-diphenylphosphine oxide, manufactured by IGM Resins BV). Commercially available oxime ester photopolymerization initiators include Irgacure OXE01 (1,2-octanedione, 1-[4-(phenylthio)phenyl[-, 2-(o-benzoyloxime) manufactured by BASF) and Irgacure OXE02 (ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(o-acetyloxime) manufactured by BASF).

[0089] Other examples of the photopolymerization initiator include benzoin ether initiators, benzophenone initiators, hydroxyalkylphenone initiators, thioxanthone initiators, and amine initiators.

[0090] The content of the photopolymerization initiator in the pressure-sensitive adhesive composition is not particularly limited. For example, the photopolymerization initiator may be contained in an amount of 0.01 to 5 parts by mass, and more preferably 0.05 to 1 part by mass, per 100 parts by mass of the pressure-sensitive adhesive resin. When the pressure-sensitive adhesive composition contains a photopolymerization initiator, one type of photopolymerization initiator may be used alone, or two or more types may be used in combination.

[0091] When the pressure-sensitive adhesive composition is not an active energy ray-curable pressure-sensitive adhesive composition, i.e., when the pressure-sensitive adhesive composition does not contain a polyfunctional monomer and a photopolymerization initiator, the pressure-sensitive adhesive composition may be a thermosetting pressure-sensitive adhesive composition. The thermosetting pressure-sensitive adhesive composition may contain, for example, an adhesive resin containing an acrylic polymer (P) and a crosslinking agent. In the case of a thermosetting pressure-sensitive adhesive composition, the adhesive resin preferably does not contain a monomer, and also preferably does not contain a solvent.

[0092] When the pressure-sensitive adhesive composition is a thermosetting pressure-sensitive adhesive composition, the acrylic polymer (P) constituting the adhesive resin is preferably an acrylic polymer (P2), and the adhesive resin preferably consists solely of the acrylic polymer (P2).

[0093] In the thermosetting pressure-sensitive adhesive composition, the crosslinking agent can be appropriately selected, for example, taking into consideration the reactivity with the crosslinkable functional groups (hydroxyl groups, etc.) of the acrylic polymer (P2), and examples thereof include a wide range of known crosslinking agents contained in pressure-sensitive adhesive sheets. Specific crosslinking agents can be selected from known crosslinking agents such as isocyanate compounds, epoxy compounds, oxazoline compounds, aziridine compounds, metal chelate compounds, and butylated melamine compounds. Of these, it is preferable that the crosslinking agent contains at least one selected from isocyanate compounds, epoxy compounds, and metal chelate compounds.

[0094] The pressure-sensitive adhesive composition may further contain a silane coupling agent, a solvent, etc. Furthermore, a dye or a pigment may be added to the pressure-sensitive adhesive for the purpose of coloring. It is also preferable that the pressure-sensitive adhesive does not contain a solvent, i.e., is solvent-free.

[0095] The method for preparing the pressure-sensitive adhesive composition is not particularly limited, and for example, a wide variety of known methods can be employed. For example, an active energy ray-curable pressure-sensitive adhesive composition can be prepared by mixing a pressure-sensitive adhesive resin containing an acrylic polymer (P1) with a polyfunctional monomer and a photopolymerization initiator. Alternatively, a heat-curable pressure-sensitive adhesive composition can be prepared by mixing a pressure-sensitive adhesive resin containing an acrylic polymer (P2) with a crosslinking agent.

[0096] (adhesive sheet) The pressure-sensitive adhesive sheet of the present invention comprises a pressure-sensitive adhesive layer made of a cured product obtained by curing a pressure-sensitive adhesive composition (e.g., an active energy ray-curable pressure-sensitive adhesive composition or a heat-curable pressure-sensitive adhesive composition). That is, the pressure-sensitive adhesive sheet of the present invention can be produced, for example, using the pressure-sensitive adhesive composition.

[0097] The method for curing the pressure-sensitive adhesive composition is not particularly limited, and for example, a wide variety of known methods can be adopted. Specifically, the method can include a step of applying the pressure-sensitive adhesive composition to a substrate to form a coating film, and a step of irradiating the coating film with active energy rays or heating it to obtain a cured product of the pressure-sensitive adhesive composition. This allows the pressure-sensitive adhesive composition to be cured to form a pressure-sensitive adhesive layer.

[0098] The PSA composition can be applied using a known coating device, such as a blade coater, air knife coater, roll coater, bar coater, gravure coater, microgravure coater, rod blade coater, lip coater, die coater, or curtain coater.

[0099] The substrate used for coating the pressure-sensitive adhesive composition is not particularly limited. For example, the pressure-sensitive adhesive composition can be coated onto various substrates such as resin substrates and glass substrates. When the substrate has a release sheet as described below, the pressure-sensitive adhesive can also be coated onto this release sheet. The pressure-sensitive adhesive composition can also be directly coated onto the member to be adhered. The thickness of the pressure-sensitive adhesive composition after coating is not particularly limited, and can be appropriately set depending on the desired thickness of the pressure-sensitive adhesive layer (or pressure-sensitive adhesive sheet). After forming the coating film, the coating film may be subjected to a heat treatment or a drying treatment, if necessary.

[0100] When irradiating the coating film with active energy rays, the irradiation method can employ the same steps as known methods. Irradiating with active energy rays, for example, causes a reaction of photopolymerizable components in the pressure-sensitive adhesive composition (e.g., monomers in the adhesive resin, polyfunctional monomers, photopolymerization initiators, etc.) to proceed, resulting in a cured product. Examples of active energy rays include ultraviolet rays, electron beams, visible light, X-rays, and ion beams, and can be appropriately selected depending on the photopolymerization initiator contained in the pressure-sensitive adhesive layer. Among these, ultraviolet rays or electron beams are preferred from the viewpoint of versatility, with ultraviolet rays being particularly preferred. Examples of ultraviolet light sources that can be used include chemical lamps, high-pressure mercury lamps, low-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, carbon arcs, xenon arcs, and electrodeless ultraviolet lamps. The ultraviolet irradiation output is an integrated light amount of 100 to 10,000 mJ / cm. 2 It is preferable to set the value to 200 to 5000 mJ / cm 2 It is more preferable to set it so that:

[0101] The cured product formed as described above can be used as the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention. The pressure-sensitive adhesive layer may consist of only the cured product of the pressure-sensitive adhesive, or may contain other components in addition to the cured product of the pressure-sensitive adhesive.

[0102] The pressure-sensitive adhesive sheet of the present invention may comprise other layers as long as it comprises the pressure-sensitive adhesive layer. Alternatively, it may be formed of only the pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer may have, for example, a single-layer structure.

[0103] The thickness of the pressure-sensitive adhesive sheet of the present invention can be appropriately set depending on the application, and is, for example, preferably from 10 to 1000 μm, more preferably from 20 to 500 μm, and even more preferably from 100 to 400 μm.

[0104] The pressure-sensitive adhesive sheet of the present invention is produced using the pressure-sensitive adhesive described above, and is a so-called low-dielectric-constant pressure-sensitive adhesive sheet having a low relative dielectric constant.

[0105] The pressure-sensitive adhesive sheet of the present invention has a relative dielectric constant at 25° C. and a frequency of 100 kHz of 3.5 or less, preferably 3.3 or less, more preferably 3.0 or less, and even more preferably 2.9 or less.

[0106] Furthermore, the pressure-sensitive adhesive sheet of the present invention has a dielectric constant at 100 kHz measured at -20°C, 0°C, 40°C, 60°C, 80°C, and 100°C that differs by ±0.5 points from the dielectric constant measured at 25°C. In other words, when the dielectric constant at 100 kHz measured at T°C (T=-20°C, 0°C, 40°C, 60°C, 80°C, or 100°C) is defined as ε1 and the dielectric constant measured at 25°C is defined as ε2, the absolute value of the difference between ε1 and ε2 is 0.5 or less. This results in a pressure-sensitive adhesive sheet of the present invention with low temperature dependency of the dielectric constant, and the dielectric constant is less likely to fluctuate even when the temperature of the pressure-sensitive adhesive sheet changes.

[0107] The pressure-sensitive adhesive sheet of the present invention has high transparency, a low dielectric constant, and a low temperature dependency of the relative dielectric constant, and therefore can be suitably used as a pressure-sensitive adhesive sheet for a display with a touch sensor. Specifically, the pressure-sensitive adhesive sheet of the present invention is suitable for use in laminating a liquid crystal display or an organic EL display with a touch sensor function.

[0108] The pressure-sensitive adhesive sheet of the present invention can also be a pressure-sensitive adhesive sheet provided with a substrate such as a release sheet on one or both sides. Examples of release sheets include a release laminate sheet having a release sheet substrate and a release agent layer provided on one side of the release sheet substrate, or a polyolefin film such as a polyethylene film or a polypropylene film as a low-polarity substrate. Paper or a polymer film is used as the release sheet substrate in the release laminate sheet. Examples of release agents that constitute the release agent layer include general-purpose addition-type or condensation-type silicone-based release agents and long-chain alkyl group-containing compounds. Commercially available release laminate sheets may also be used. Examples include a heavy-duty separator film, which is a release-treated polyethylene terephthalate film manufactured by Teijin DuPont Films, and a light-duty separator film, which is a release-treated polyethylene terephthalate film manufactured by Teijin DuPont Films.

[0109] In specifying the inventions included in the present disclosure, the components (properties, structures, functions, etc.) described in the embodiments of the present disclosure may be combined in any manner. In other words, the present disclosure includes all subject matter consisting of all combinations of the components that can be combined as described in this specification. [Example]

[0110] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0111] The following monomers ((meth)acrylate compound A1, nitrogen-containing monomer A2, (meth)acrylate compound A3, hydroxyl group-containing monomer A4, and nitrogen-containing monomer A5) for producing the acrylic polymer (P1) and acrylic polymer (P2) used in each example were prepared.

[0112] [(Meth)acrylate compound A1] ISTA: Isostearyl acrylate

[0113] [Nitrogen-containing monomer A2] ACMO: Acryloylmorpholine

[0114] [(Meth)acrylate compound A3] 2EHA: 2-Ethylhexyl acrylate (Acrylate Compound A3(1)) IBXA: Isobornyl acrylate 2EHMA: 2-Ethylhexyl methacrylate (Methacrylate compound A3(2))

[0115] [Hydroxyl group-containing monomer A4] 4HBA: 4-hydroxybutyl acrylate

[0116] [Nitrogen-containing monomer A5] ·DMAA: N,N-dimethylacrylamide DEAA: N,N-diethylacrylamide

[0117] Example 1 An adhesive resin containing an acrylic polymer (P1) was synthesized according to the compounding conditions of the adhesive resin preparation recipe shown in Table 1. Specifically, 100 parts by mass of a monomer mixture consisting of 2EHA, ISTA, and ACMO (mass ratio 45:45:10) in the compounding amounts shown in Table 1 were added to a flask, and 0.15 g of AIBN was added. The mixture was reacted for 30 minutes while controlling the heat generation, and then cooled to obtain an adhesive resin containing a partial polymer of the acrylic polymer (P1) with a polymer fraction of 23%.

[0118] Next, 0.03 parts by mass of Shin-Nakamura Chemical Co., Ltd.'s "ATM-4PL" as a polyfunctional monomer and 0.2 parts by mass of Omnirad 184 (IGM Resins BV) as a photopolymerization initiator were mixed with planetary stirring to prepare a pressure-sensitive adhesive composition, relative to a total of 100 parts by mass of the above adhesive resin. This pressure-sensitive adhesive composition was applied to a heavy separator (Fujimori Kogyo Co., Ltd.'s "100E-0010NT1AS") to a thickness of 150 μm to form a coating film, and a light separator (Fujimori Kogyo Co., Ltd.'s "75E-0010KFAS") was further placed on top of that to obtain a laminate. This laminate was then exposed to a chemical lamp at 4 mW / cm. 2 The light intensity is 240mJ / cm 2 After irradiating the sample to a temperature of 150 mW / cm with a high-pressure mercury lamp, 2 The cumulative light intensity is 3000mJ / cm 2 By irradiating the light so as to obtain a pressure-sensitive adhesive layer having a thickness of 150 μm as a pressure-sensitive adhesive sheet.

[0119] Examples 2 to 7 An adhesive sheet was obtained in the same manner as in Example 1, except that the compounding conditions for the adhesive resin preparation formulation were changed to those shown in Table 1 and the amounts of the multifunctional monomer and photopolymerization initiator used were changed to the formulations shown in Table 1.

[0120] Example 8 An adhesive resin containing an acrylic polymer (P2) was synthesized according to the formulation conditions of the adhesive resin preparation recipe shown in Table 1. Specifically, 100 parts by mass of a monomer mixture consisting of 2EHA, ISTA, ACMO, IBXA, 2EHMA, and 4HBA (mass ratio 28:18:15:4:32:3) in the amounts shown in Table 1 and ethyl acetate were added to a flask, and the atmosphere was purged with nitrogen at a nitrogen flow rate of 300 mL / min for 60 minutes. After that, the nitrogen flow rate was reduced to 100 mL / min, and the mixture was heated to 70 °C in a water bath. 0.1 g of AIBN was added, and the reaction was allowed to proceed for 1 hour while controlling the heat generation. After that, an additional 0.5 g of AIBN was added, and the reaction was allowed to proceed for 6 hours, after which the mixture was cooled to 50 °C. In this manner, an acrylic polymer (P2) with a solids concentration of 40% by mass and a weight-average molecular weight of approximately 590,000 was obtained.

[0121] Next, as shown in Table 1, 0.2 parts by mass of a crosslinker (Tosoh's Coronate HX) was added to 100 parts by mass of the acrylic polymer (P2), and the mixture was stirred and degassed to obtain a pressure-sensitive adhesive composition. The obtained pressure-sensitive adhesive composition was applied to a 100 μm thick polyester film (release sheet) coated with a silicone release agent so that the thickness of the pressure-sensitive adhesive layer after drying would be 150 μm, and the mixture was dried in a dryer at 100°C for 3 minutes. Thereafter, a pressure-sensitive adhesive layer obtained in the same manner was laminated and left to stand at room temperature for 7 days to obtain a 150 μm thick pressure-sensitive adhesive sheet.

[0122] Examples 9 to 10 A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 7, except that the compounding conditions for the pressure-sensitive adhesive resin preparation recipe were changed to the conditions shown in Table 1.

[0123] (Comparative Examples 1 to 4) An adhesive sheet was obtained in the same manner as in Example 1, except that the compounding conditions for the adhesive resin preparation formulation were changed to those shown in Table 1 and the amounts of the multifunctional monomer and photopolymerization initiator used were changed to the formulations shown in Table 1.

[0124] (dielectric constant) The first and second release films were peeled off from the pressure-sensitive adhesive sheet with a release sheet to obtain a pressure-sensitive adhesive sheet, which was then sandwiched between two sheets of copper foil and autoclaved (treatment conditions: 40°C, 0.5 MPa, 30 minutes) to obtain a measurement sample. The dielectric constant of this measurement sample was measured using a dielectric measurement system (Solartron, 1260A) in accordance with JIS C 2138. The measurement was performed at a frequency of 100 kHz, at temperatures of -20°C, 0°C, 25°C, 40°C, 60°C, 80°C, and 100°C, and at a relative humidity of 50%.

[0125] (Adhesion to glass) The light separator of the adhesive sheet (adhesive layer) was peeled off, and the sheet was laminated to a 50 μm-thick PET film and cut to a 25 mm width. After cleaning the non-tin side of the float glass with ethanol, the heavy separator of the adhesive sheet was peeled off, and the adhesive side of the adhesive sheet was laminated to the glass by rolling a 2 kg roller back and forth. The resulting sample with a PET / adhesive layer / glass configuration was autoclaved (40°C, 0.5 MPa, 30 min), and then the other end of the sample was peeled off at a speed of 300 mm / min in a 180-degree peeling direction, and the adhesive strength to the glass was measured.

[0126] (Optical properties; heat resistance) The pressure-sensitive adhesive sheet with release sheet was cut into a size of 50 mm x 50 mm, and the light separator was peeled off. The exposed pressure-sensitive adhesive layer was then attached to a glass plate (S3112, manufactured by Matsunami Glass Co., Ltd.). Next, the heavy separator was peeled off, and a glass plate (S3112, manufactured by Matsunami Glass Co., Ltd.) was attached to the exposed pressure-sensitive adhesive layer to obtain a laminate. This laminate was placed in an autoclave in an atmosphere of 85°C for 10 days to obtain a measurement sample. Using this measurement sample, the haze (represented as "after 85°C durability" in Table 1) was measured using a haze meter ("NDH5000" manufactured by Nippon Denshoku Industries Co., Ltd.).

[0127] (Optical properties; humidity and heat resistance) The adhesive sheet with release sheet was cut into a size of 50 mm x 50 mm, and the light separator was peeled off. The exposed adhesive layer was attached to a glass plate (S3112, manufactured by Matsunami Glass Co., Ltd.). Next, the heavy separator was peeled off, and a glass plate (S3112, manufactured by Matsunami Glass Co., Ltd.) was attached to the exposed adhesive layer to obtain a laminate. This laminate was stored in an autoclave in an atmosphere of 60°C and 95% RH for 10 days to obtain a measurement sample. Using this measurement sample, the haze (represented as "after 60°C 95% durability" in Table 1) was measured using a haze meter ("NDH5000" manufactured by Nippon Denshoku Industries Co., Ltd.).

[0128] (Optical properties; UV durability) The adhesive sheet with release sheet was cut into a size of 50 mm x 50 mm, and the light separator was peeled off. The exposed adhesive layer was attached to a glass plate (S3112, manufactured by Matsunami Glass Co., Ltd.). Next, the heavy separator was peeled off, and a glass plate (S3112, manufactured by Matsunami Glass Co., Ltd.) was attached to the exposed adhesive layer to obtain a laminate. This laminate was irradiated with UV (0.65 W / m using a QUV tester (manufactured by Q-Lab Co., Ltd.)). 2 A measurement sample was obtained by irradiating the sample for 96 hours under the setting of 100°C. The haze (shown as "After UV durability" in Table 1) was measured using a haze meter ("NDH5000" manufactured by Nippon Denshoku Industries Co., Ltd.) of this measurement sample.

[0129] Table 1 shows the adhesive resin preparation formula and adhesive sheet preparation conditions for each example and comparative example. Table 1 also shows the weight-average molecular weight of the resulting acrylic polymer (P1) or acrylic polymer (P2), the theoretical Tg of the acrylic polymer (P1) or acrylic polymer (P2), and the evaluation results of the adhesive sheet's dielectric constant and difference (the absolute value of the difference between the dielectric constant measured at 25°C and the dielectric constant at each temperature other than 25°C), adhesive strength, and optical properties (haze). In the adhesive resin preparation formula in Table 1, blank cells indicate that the corresponding raw material was not used. The values ​​in the columns for multifunctional monomer, photopolymerization initiator, and crosslinking agent in Table 1 are in parts by mass, and the adhesive strength is expressed in units of N / 25 mm.

[0130] From Table 1, it can be seen that, as in Examples 1 to 10, adhesive sheets having an adhesive layer formed from an adhesive composition containing a specified acrylic polymer (P) (i.e., acrylic polymer (P1) or acrylic polymer (P2)) have a low dielectric constant, but also have a low temperature dependence of the dielectric constant, and the dielectric constant is less likely to fluctuate even when the temperature of the adhesive sheet changes.

[0131] [Table 1]

Claims

1. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer contains a cured product of a pressure-sensitive adhesive composition containing at least an acrylic polymer (P1), The acrylic polymer (P1) is a nitrogen-containing monomer unit a2; and (meth)acrylate units a3 having a branched alkyl group having less than 12 carbon atoms; and is a polymer having no monomer unit having a hydroxyl group, the nitrogen-containing monomer unit a2 has a nitrogen-containing cyclic substituent and an acryloyl group, and the nitrogen-containing monomer unit a2 is contained in an amount of 5 to 40 parts by mass per 100 parts by mass of the acrylic polymer (P1); the content of (meth)acrylate units a1 having a branched alkyl group having 12 to 24 carbon atoms is 80 parts by mass or less per 100 parts by mass of the acrylic polymer (P1); The dielectric constant at 25°C and a frequency of 100 kHz is 3.5 or less, and A pressure-sensitive adhesive sheet in which the values ​​of the relative dielectric constant at 100 kHz measured at -20°C, 0°C, 40°C, 60°C, 80°C and 100°C are all within a range of ±0.5 points of the value of the relative dielectric constant measured at 25°C.

2. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer contains a cured product of a pressure-sensitive adhesive composition containing at least an acrylic polymer (P2), The acrylic polymer (P2) is a (meth)acrylate unit a1 having a branched alkyl group having 12 to 24 carbon atoms, and a nitrogen-containing monomer unit a2; acrylate units a3(1) having a branched alkyl group having less than 12 carbon atoms; methacrylate units a3(2) having a branched alkyl group having less than 12 carbon atoms; a monomer unit a4 having a hydroxyl group; A polymer having at least the nitrogen-containing monomer unit a2 has a nitrogen-containing cyclic substituent and an acryloyl group, and the (meth)acrylate unit a1 is contained in an amount of less than 19 parts by mass per 100 parts by mass of the acrylic polymer (P2), the nitrogen-containing monomer unit a2 is contained in an amount of 5 to 30 parts by mass per 100 parts by mass of the acrylic polymer (P2), the hydroxyl group-containing monomer unit a4 is contained in an amount of less than 5 parts by mass per 100 parts by mass of the acrylic polymer (P2), The dielectric constant at 25°C and a frequency of 100 kHz is 3.5 or less, and A pressure-sensitive adhesive sheet in which the values ​​of the relative dielectric constant at 100 kHz measured at -20°C, 0°C, 40°C, 60°C, 80°C and 100°C are all within a range of ±0.5 points of the value of the relative dielectric constant measured at 25°C.

3. the acrylic polymer (P1) further contains a nitrogen-containing monomer unit a5 other than the nitrogen-containing monomer unit a2, the nitrogen-containing monomer unit a5 is a vinyl monomer unit having an acyclic substituent containing a nitrogen atom, The pressure-sensitive adhesive sheet according to claim 1 , wherein the nitrogen-containing monomer unit a5 is contained in an amount of 5 parts by mass or less per 100 parts by mass of the acrylic polymer (P1).

4. The pressure-sensitive adhesive sheet according to claim 1 , wherein the (meth)acrylate unit a3 is contained in an amount of less than 50 parts by mass per 100 parts by mass of the acrylic polymer (P1).

5. the acrylic polymer (P2) further contains a nitrogen-containing monomer unit a5 other than the nitrogen-containing monomer unit a2, the nitrogen-containing monomer unit a5 is a vinyl monomer unit having an acyclic substituent containing a nitrogen atom, The pressure-sensitive adhesive sheet according to claim 2 , wherein the nitrogen-containing monomer unit a5 is contained in an amount of 5 parts by mass or less per 100 parts by mass of the acrylic polymer (P2).

6. the acrylate unit a3(1) is contained in an amount of less than 50 parts by mass per 100 parts by mass of the acrylic polymer (P2), The pressure-sensitive adhesive sheet according to claim 2 , wherein the methacrylate unit a3(2) is contained in an amount of less than 50 parts by mass per 100 parts by mass of the acrylic polymer (P2).

7. The pressure-sensitive adhesive sheet according to any one of claims 1 to 6, wherein the nitrogen-containing monomer unit a2 is an acryloylmorpholine unit.

8. The pressure-sensitive adhesive sheet according to any one of claims 1 to 6, which is for a display with a touch sensor.

9. A display with a touch sensor, comprising the adhesive sheet according to claim 8.

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