Adhesive sheet and display with touch sensor

Abstract

To provide an adhesive sheet exhibiting excellent impact resistance and high peel resistance against a load in the thickness direction.SOLUTION: The adhesive sheet of the present invention includes an adhesive layer, the adhesive layer containing a crosslinked polymer having a structure in which an acrylic polymer (P) is crosslinked with a multifunctional monomer, wherein the acrylic polymer (P) contains 15 to 40 pts.mass of a vinyl monomer unit a2 having a non-cyclic substituent containing a nitrogen atom per 100 pts.mass of the acrylic polymer (P), the content of a long-chain alkyl (meth)acrylate unit a1 having an alkyl group of 10 to 18 carbon atoms with a cyclic or branched structure being 40 pts.mass or less per 100 pts.mass of the acrylic polymer (P), the gel fraction of the adhesive layer being 30% to 80%, and the storage elastic modulus of the adhesive layer being 101 to 500 kPa.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, with the demand for narrower picture frames for displays, there has been a demand for pressure-sensitive adhesive sheets with improved adhesive strength, and it is particularly important that they have excellent impact resistance and are able to suppress peeling even when a predetermined load is applied in the thickness direction. Although technologies for improving adhesive strength have been widely studied to date, as disclosed in the aforementioned Patent Document 1 and the like, impact resistance and peel resistance when a predetermined load is applied in the thickness direction have not necessarily been sufficient. From this perspective, there has been an urgent need to develop a pressure-sensitive adhesive sheet that has excellent impact resistance and excellent peel resistance against a load in the thickness direction.

[0006] The present invention has been made in view of the above, and has an object to provide a pressure-sensitive adhesive sheet that has excellent impact resistance and excellent peel resistance against a load in the thickness direction. [Means for solving the problem]

[0007] As a result of extensive research into achieving the above-mentioned object, the inventors have discovered that the above-mentioned object can be achieved by applying a pressure-sensitive adhesive layer containing a specific acrylic polymer, 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 contains a crosslinked polymer having a structure in which an acrylic polymer (P) is crosslinked with a polyfunctional monomer, the acrylic polymer (P) contains 15 to 40 parts by mass of vinyl monomer units a2 having an acyclic substituent containing a nitrogen atom, relative to 100 parts by mass of the acrylic polymer (P); the content of the long-chain alkyl (meth)acrylate unit a1 having a cyclic or branched alkyl group having 10 to 18 carbon atoms is 40 parts by mass or less relative to 100 parts by mass of the acrylic polymer (P), the pressure-sensitive adhesive layer has a gel fraction of 30% to 80%; The pressure-sensitive adhesive sheet has a storage modulus at 23°C of 101 to 500 kPa. Section 2 Item 1. A pressure-sensitive adhesive sheet according to Item 1, wherein the pressure-sensitive adhesive layer is a cured product of an active energy ray-curable pressure-sensitive adhesive. Section 3 Item 3. The pressure-sensitive adhesive sheet according to item 1 or 2, wherein the content of the monomer unit having a hydroxyl group is 10 parts by mass or less per 100 parts by mass of the acrylic polymer (P). Section 4 Item 4. The pressure-sensitive adhesive sheet according to any one of items 1 to 3, having a relative dielectric constant of 4.0 or less at a frequency of 100 kHz. Section 5 Item 5. The pressure-sensitive adhesive sheet according to item 4, having a relative dielectric constant of 3.5 or less at a frequency of 100 kHz. Section 6 Item 6. The pressure-sensitive adhesive sheet according to any one of items 1 to 5, which is for a display with a touch sensor. Section 7 Item 7. A display with a touch sensor, comprising the adhesive sheet according to item 6. [Effects of the Invention]

[0009] The pressure-sensitive adhesive sheet according to the present invention has excellent impact resistance and excellent peel resistance against a load in the thickness direction. [Brief explanation of the drawings]

[0010] [Figure 1] 1A and 1B are schematic diagrams showing a method for measuring the peel resistance value of the pressure-sensitive adhesive sheet of the present invention, in which (a) is a side view and (b) is a plan view. DETAILED DESCRIPTION OF THE INVENTION

[0011]

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

[0012] 1. Adhesive sheet The pressure-sensitive adhesive sheet of the present invention includes a pressure-sensitive adhesive layer, which contains a crosslinked polymer having a structure in which an acrylic polymer (P) is crosslinked with a polyfunctional monomer, and the acrylic polymer (P) contains 15 to 40 parts by mass of vinyl monomer units a2 having an acyclic substituent containing a nitrogen atom, relative to 100 parts by mass of the acrylic polymer (P); The content of long-chain alkyl (meth)acrylate units a1 having a cyclic or branched alkyl group having 10 to 18 carbon atoms is 40 parts by mass or less relative to 100 parts by mass of the acrylic polymer (P). In the pressure-sensitive adhesive sheet of the present invention, the pressure-sensitive adhesive layer has a gel fraction of 30% to 80%, and a storage modulus at 23°C of 101 to 500 kPa.

[0013] The pressure-sensitive adhesive sheet of the present invention has excellent impact resistance and excellent peel resistance against a load in the thickness direction due to the pressure-sensitive adhesive layer described above, and can therefore be suitably used as a pressure-sensitive adhesive sheet for a display with a touch sensor.

[0014] (Active energy ray curable adhesive) As described above, in the pressure-sensitive adhesive sheet of the present invention, the pressure-sensitive adhesive layer contains a crosslinked polymer having a structure in which an acrylic polymer (P) is crosslinked with a polyfunctional monomer. Such a pressure-sensitive adhesive layer can be formed, for example, using an active energy ray-curable pressure-sensitive adhesive. Specifically, the pressure-sensitive adhesive layer is obtained by irradiating an active energy ray-curable pressure-sensitive adhesive with active energy rays to cure it. Hereinafter, the active energy ray-curable pressure-sensitive adhesive will be simply abbreviated as "pressure-sensitive adhesive."

[0015] The pressure-sensitive adhesive may contain at least the acrylic polymer (P), the polyfunctional monomer, and a photopolymerization initiator. More specifically, the pressure-sensitive adhesive contains at least an adhesive resin containing the acrylic polymer (P), a polyfunctional monomer, and a photopolymerization initiator.

[0016] <Adhesive resin containing acrylic polymer (P)> The adhesive resin contains an acrylic polymer (P) as an essential component and may further contain a (meth)acrylic ester monomer. More specifically, the adhesive resin may contain the acrylic polymer (P) and the same (meth)acrylic ester monomer as the monomer constituting the acrylic polymer (P). In this case, the adhesive resin is a solution (also called a syrup) in which the acrylic polymer (P) is dissolved in the (meth)acrylic ester monomer, and may also be referred to as a partial polymerization product of the acrylic polymer (P).

[0017] The acrylic polymer (P) contains, in its structural units, vinyl monomer units a2 having an acyclic substituent containing at least a nitrogen atom. The content of such vinyl monomer units a2 is 15 to 40 parts by mass (i.e., 15 parts by mass or more and 40 parts by mass or less) per 100 parts by mass of the acrylic polymer (P). In this specification, the expression "vinyl monomer units a2" refers to vinyl monomer units a2 having an acyclic substituent containing a nitrogen atom.

[0018] If the content of the vinyl monomer unit a2 is less than 15 parts by mass relative to 100 parts by mass of the acrylic polymer (P), the peel resistance against a load in the thickness direction of the pressure-sensitive adhesive sheet may decrease, or impact resistance may decrease. Furthermore, if the content of the vinyl monomer unit a2 is less than 15 parts by mass relative to 100 parts by mass of the acrylic polymer (P), transparency in a humid and heat-resistant environment is likely to decrease. If the content of the vinyl monomer unit a2 exceeds 40 parts by mass relative to 100 parts by mass of the acrylic polymer (P), the dielectric constant of the pressure-sensitive adhesive sheet increases, and the peel resistance against a load in the thickness direction also decreases.

[0019] The content of the vinyl monomer unit a2 is preferably 18 parts by mass or more, more preferably 20 parts by mass or more, and is preferably 38 parts by mass or less, more preferably 35 parts by mass or less, and even more preferably 25 parts by mass or less, relative to 100 parts by mass of the acrylic polymer (P).

[0020] The vinyl monomer unit a2 is a structural unit formed by polymerization of a vinyl compound having a non-cyclic substituent containing a nitrogen atom. Hereinafter, the vinyl compound having a non-cyclic substituent containing a nitrogen atom will be referred to as the "nitrogen-containing vinyl compound A2."

[0021] The nitrogen-containing vinyl compound A2 is a vinyl compound having an acyclic substituent containing a nitrogen atom in the molecule and capable of copolymerizing with the long-chain alkyl (meth)acrylate compound A1 described below. For example, the nitrogen-containing vinyl compound A2 is a vinyl compound capable of radical polymerization with the long-chain alkyl (meth)acrylate compound A1.

[0022] In the acyclic substituent containing a nitrogen atom in the nitrogen-containing vinyl compound A2, 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.

[0023] The nitrogen-containing vinyl compound A2 preferably has an amide bond in its molecule. That is, the vinyl monomer unit a2 in the acrylic polymer (P) preferably has an amide bond. In this case, the dielectric constant of the pressure-sensitive adhesive sheet is likely to be low, and the peel resistance against a load in the thickness direction is likely to be improved.

[0024] Specific examples of the nitrogen-containing vinyl compound A2 include (meth)acrylamide and N-substituted (meth)acrylamide. Examples of N-substituted (meth)acrylamides include (meth)acrylamides 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 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and even 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.

[0025] In this specification, "(meth)acrylic" means "acrylic" or "methacrylic." For example, "(meth)acrylate" means "acrylate" or "methacrylate," and "(meth)acrylamide" means "acrylamide" or "methacrylamide."

[0026] 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-octylacrylamide.

[0027] 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.

[0028] The vinyl monomer unit a2 contained in the acrylic polymer (P) may be one type or two or more types.

[0029] The acrylic polymer (P) may also contain, in its structural units, long-chain alkyl (meth)acrylate units a1 having a cyclic or branched alkyl group having 10 to 18 carbon atoms. In this case, the content of the long-chain alkyl (meth)acrylate units a1 having a cyclic or branched alkyl group having 10 to 18 carbon atoms is 40 parts by mass or less per 100 parts by mass of the acrylic polymer (P). Hereinafter, in this specification, the long-chain alkyl (meth)acrylate units a1 having a cyclic or branched alkyl group having 10 to 18 carbon atoms will be referred to as "long-chain alkyl (meth)acrylate units a1."

[0030] If the content of the long-chain alkyl (meth)acrylate units a1 exceeds 40 parts by mass relative to 100 parts by mass of the acrylic polymer (P), the peel resistance against load in the thickness direction of the pressure-sensitive adhesive sheet may decrease, or impact resistance may decrease. Furthermore, if the content of the long-chain alkyl (meth)acrylate units a1 exceeds 40 parts by mass relative to 100 parts by mass of the acrylic polymer (P), transparency in a humid and heat-resistant environment is likely to decrease.

[0031] The content of the long-chain alkyl (meth)acrylate units a1 is preferably 38 parts by mass or less, more preferably 35 parts by mass or less, and even more preferably 30 parts by mass or less, relative to 100 parts by mass of the acrylic polymer (P). The acrylic polymer (P) may not contain the long-chain alkyl (meth)acrylate units a1, i.e., the content of the long-chain alkyl (meth)acrylate units a1 may be 0 part by mass relative to 100 parts by mass of the acrylic polymer (P).

[0032] The long-chain alkyl (meth)acrylate unit a1 is a structural unit formed by polymerization of a long-chain alkyl (meth)acrylate compound having an alkyl group with 10 to 18 carbon atoms. Hereinafter, the long-chain alkyl (meth)acrylate compound having an alkyl group with 10 to 18 carbon atoms will be referred to as "long-chain alkyl (meth)acrylate compound A1."

[0033] Examples of the long-chain alkyl (meth)acrylate compound A1 include compounds in which an alkyl group (long-chain alkyl group) having 10 to 18 carbon atoms is bonded to the ester oxygen of a (meth)acrylate. The number of carbon atoms in such an alkyl group is preferably 12 or more, and more preferably 14 or more. The alkyl group having 10 to 18 carbon atoms preferably does not have a hydroxyl group or a carboxyl group.

[0034] In the long-chain alkyl (meth)acrylate compound A1, the alkyl group having 10 to 18 carbon atoms has a cyclic or branched structure. The alkyl group having 10 to 18 carbon atoms may have other substituents as long as the effects of the present invention are not impaired.

[0035] Specific examples of the long-chain alkyl (meth)acrylate compound A1 include isobornyl (meth)acrylate, lauryl (meth)acrylate, isomistyryl (meth)acrylate, isostearyl (meth)acrylate, isotridecyl (meth)acrylate, isopentadecyl (meth)acrylate, isohexadecyl (meth)acrylate, and isoheptadecyl (meth)acrylate.

[0036] Among these, the long-chain alkyl (meth)acrylate compound A1 is preferably isostearyl (meth)acrylate or isobornyl (meth)acrylate, since this tends to reduce the dielectric constant of the pressure-sensitive adhesive sheet and tends to improve peel resistance against load in the thickness direction.

[0037] The long-chain alkyl (meth)acrylate units a1 contained in the acrylic polymer (P) may be of one type or two or more types.

[0038] The acrylic polymer (P) may contain other structural units in addition to the long-chain alkyl (meth)acrylate units a1 and vinyl monomer units a2. For example, the acrylic polymer (P) may contain alkyl (meth)acrylate units other than the long-chain alkyl (meth)acrylate units a1. The (meth)acrylate units other than the long-chain alkyl (meth)acrylate units a1 are referred to as "(meth)acrylate units a3."

[0039] The monomer for forming the (meth)acrylate unit a3 can be, for example, a wide range of (meth)acrylic compounds copolymerizable with the long-chain alkyl (meth)acrylate compound A1 and the nitrogen-containing vinyl compound A2. The (meth)acrylic compound for forming the (meth)acrylate unit a3 is referred to as "(meth)acrylic compound A3."

[0040] The (meth)acrylic compound A3 may be a (meth)acrylate having an alkyl group with 9 or less carbon atoms or a (meth)acrylate having an aromatic ring, and among these, a (meth)acrylate having an alkyl group with 9 or less carbon atoms is preferred. The alkyl group with 9 or less carbon atoms preferably does not have a hydroxyl group or a carboxyl group.

[0041] Examples of the (meth)acrylic 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. Among these, in terms of ease of control of adhesive properties, (meth)acrylates having an alkyl group containing 2 to 9 carbon atoms are more preferred, (meth)acrylates having an alkyl group containing 3 to 9 carbon atoms are even more preferred, and (meth)acrylates having an alkyl group containing 4 to 9 carbon atoms are particularly preferred. A specific preferred example of the (meth)acrylic compound A3 is 2-ethylhexyl (meth)acrylate.

[0042] In terms of ease of control of adhesive properties, the content of the (meth)acrylate units a3 is preferably 80 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 65 parts by mass or less, and particularly preferably 60 parts by mass or less, relative to 100 parts by mass of the acrylic polymer (P), and is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 35 parts by mass or more, and particularly preferably 40 parts by mass or more.

[0043] The structural unit a3 contained in the acrylic polymer (P) may be of one type or of two or more types.

[0044] The acrylic polymer (P) may contain other structural units in addition to the long-chain alkyl (meth)acrylate units a1, vinyl monomer units a2, and (meth)acrylate units a3. For example, the acrylic polymer (P) may contain a monomer unit having a hydroxyl group. An example of such a monomer unit having a hydroxyl group is a (meth)acrylate unit having a hydroxyl group.

[0045] Examples of monomers for forming (meth)acrylate units having a hydroxyl group include 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. Of these, 4-hydroxybutyl (meth)acrylate is preferred.

[0046] In order to easily control the adhesive properties, the content of the hydroxyl group-containing monomer unit is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, even more preferably 5 parts by mass or less, and particularly preferably 3 parts by mass or less, relative to 100 parts by mass of the acrylic polymer (P). The acrylic polymer (P) may not contain a hydroxyl group-containing monomer unit, i.e., the content of the hydroxyl group-containing monomer unit may be 0 parts by mass relative to 100 parts by mass of the acrylic polymer (P). In this case, the relative dielectric constant of the pressure-sensitive adhesive sheet is likely to be low.

[0047] The acrylic polymer (P) may contain units derived from a vinyl compound having a cyclic substituent (heterocycle) containing a nitrogen atom to the extent that the effects of the present invention are not impaired. However, in terms of further improving impact resistance, it is preferable that the acrylic polymer (P) does not contain (meth)acrylate units a3.

[0048] The acrylic polymer (P) may be composed solely of long-chain alkyl (meth)acrylate units a1, vinyl monomer units a2, and (meth)acrylate units a3.

[0049] The adhesive resin contains the acrylic polymer (P) and, as described above, may contain the same type of (meth)acrylic ester monomer as the monomer for constituting the acrylic polymer (P), and may 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 content (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 50 mass %, and preferably 20 to 40 mass %.

[0050] The weight-average molecular weight of the acrylic polymer (P) 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).

[0051] 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.

[0052] 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 (P) 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.

[0053] 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.

[0054] 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 type 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 the synthesis of the polymer. 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.

[0055] 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.

[0056] <Polyfunctional Monomer> The pressure-sensitive adhesive contains a polyfunctional monomer. Examples of the polyfunctional monomer include compounds 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.

[0057] 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).

[0058] 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.

[0059] 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.

[0060] 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.

[0061] When the adhesive contains a polyfunctional monomer, curing the adhesive with active energy rays forms a crosslinked polymer having a structure in which the acrylic polymer (P) is crosslinked with the polyfunctional monomer, which makes the adhesive sheet more likely to have excellent adhesive strength.

[0062] The content of the polyfunctional monomer in the pressure-sensitive adhesive is not particularly limited. For example, the pressure-sensitive adhesive 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, in order to facilitate adjustment of the gel fraction of the pressure-sensitive adhesive layer to a desired range. Furthermore, the pressure-sensitive adhesive may contain 0.01 parts by mass or more of the polyfunctional monomer per 100 parts by mass of the pressure-sensitive adhesive resin, more preferably 0.03 parts by mass or more, and even more preferably 0.05 parts by mass or more. The pressure-sensitive adhesive may contain one type of polyfunctional monomer alone or two or more types of polyfunctional monomers.

[0063] <Photopolymerization initiator> The pressure-sensitive adhesive contains a photopolymerization initiator. As the photopolymerization initiator, for example, a wide variety of known photopolymerization initiators can be used.

[0064] 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.

[0065] 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-hydroxycyclohexylphenylketone, manufactured by IGM Resins BV), and Omnirad 1173 (2-hydroxy-2-methyl-1-phenylpropanone, manufactured by IGM Resins BV).

[0066] 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).

[0067] Other examples of the photopolymerization initiator include benzoin ether initiators, benzophenone initiators, hydroxyalkylphenone initiators, thioxanthone initiators, and amine initiators.

[0068] The content of the photopolymerization initiator in the adhesive 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 adhesive resin. When the adhesive contains a photopolymerization initiator, one type of photopolymerization initiator may be used alone or two or more types may be used in combination. The adhesive may contain one type of photopolymerization initiator alone or two or more types.

[0069] <Adhesive> As described above, the pressure-sensitive adhesive contains at least an adhesive resin containing an acrylic polymer (P), a polyfunctional monomer, and a photopolymerization initiator. The pressure-sensitive adhesive may also contain a silane coupling agent, a solvent, etc. Furthermore, a dye or 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.

[0070] The method for preparing the pressure-sensitive adhesive is not particularly limited, and for example, a wide variety of known methods can be employed. For example, the pressure-sensitive adhesive can be prepared by mixing a pressure-sensitive adhesive resin containing an acrylic polymer (P), a polyfunctional monomer, and a photopolymerization initiator.

[0071] (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 (active energy ray-curable pressure-sensitive adhesive). That is, the pressure-sensitive adhesive sheet of the present invention can be produced using, for example, the pressure-sensitive adhesive.

[0072] The method for curing the pressure-sensitive adhesive 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 to a substrate to form a coating film, and a step of irradiating the coating film with active energy rays to obtain a cured product of the pressure-sensitive adhesive. This allows the pressure-sensitive adhesive layer to be formed by curing the pressure-sensitive adhesive.

[0073] The pressure-sensitive adhesive 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.

[0074] The substrate used for coating the adhesive is not particularly limited. For example, the adhesive can be coated onto various substrates such as resin substrates and glass substrates. When the substrate has a release sheet as described below, the adhesive can also be coated onto this release sheet. The adhesive can also be coated directly onto the member to be adhered. The thickness of the adhesive after coating is also not particularly limited and can be appropriately set depending on the desired thickness of the adhesive layer (or adhesive sheet). After forming the coating film, the coating film may be subjected to a heat treatment or a drying treatment, if necessary.

[0075] The step of irradiating the coating film with active energy rays can be, for example, a step similar to a known method. This step, for example, allows the reaction of photopolymerizable components in the adhesive (e.g., monomers in the adhesive resin, polyfunctional monomers, photopolymerization initiators, etc.) to proceed, resulting in a cured product. For example, when the adhesive contains the adhesive resin, polyfunctional monomers, and photopolymerization initiator, the polymerization reaction of the monomers and polyfunctional monomers in the adhesive resin can also proceed to form a cured product. This can improve the strength of the adhesive layer and also improve the adhesive force.

[0076] 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, and ultraviolet rays are particularly preferred. Examples of light sources that can be used for ultraviolet rays 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 irradiation output of ultraviolet rays is such that the cumulative light amount is 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:

[0077] 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.

[0078] In the pressure-sensitive adhesive sheet of the present invention, the gel fraction of the pressure-sensitive adhesive layer is 30% to 80% (i.e., 30% or more and 80% or less). If the gel fraction of the pressure-sensitive adhesive layer is less than 30%, the adhesive strength of the pressure-sensitive adhesive sheet decreases, and peel resistance against a load in the thickness direction is also likely to be impaired. If the gel fraction of the pressure-sensitive adhesive layer exceeds 80%, the peel resistance against a load in the thickness direction of the pressure-sensitive adhesive sheet is also likely to be impaired, and impact resistance is also likely to be impaired.

[0079] The gel fraction of the pressure-sensitive adhesive layer is preferably 33% or more, more preferably 35% or more, and even more preferably 40% or more, and is preferably 70% or less, more preferably 65% ​​or less, and even more preferably 60% or less.

[0080] The gel fraction of the pressure-sensitive adhesive layer can be adjusted by changing the type of acrylic polymer (P) in the pressure-sensitive adhesive, and other factors such as the type and content of the polyfunctional monomer and the type and content of the photopolymerization initiator can also be adjusted.

[0081] The gel fraction of the adhesive layer is a value measured by the following method. First, approximately 0.1 g of the adhesive sheet (adhesive layer) is placed in a sample bottle, 30 ml of ethyl acetate is added, and the mixture is shaken for 24 hours. The contents of the sample bottle are then filtered through a 150-mesh stainless steel wire mesh, and the residue on the wire mesh is dried at 100°C for 1 hour to measure the dry mass (g). The obtained dry mass is then calculated using the following formula: Gel fraction (mass%) = (dry mass / collected mass of adhesive sheet) × 100 Equation 1 Calculate the gel fraction using 1.

[0082] The storage modulus of the pressure-sensitive adhesive layer at 23°C is 101 to 500 kPa (i.e., 101 kPa or more and 500 kPa or less). Hereinafter, the storage modulus at 23°C will be simply referred to as "storage modulus." If the storage modulus of the pressure-sensitive adhesive layer is less than 101 kPa, the adhesive strength of the pressure-sensitive adhesive sheet will decrease and peel resistance against load in the thickness direction will also be likely to be impaired. If the storage modulus of the pressure-sensitive adhesive layer exceeds 500 kPa, impact resistance will also likely be reduced.

[0083] The storage modulus of the pressure-sensitive adhesive layer is preferably 110 kPa or more, more preferably 130 kPa or more, and even more preferably 150 kPa or more, and is preferably 450 kPa or less, more preferably 400 kPa or less, and even more preferably 350 kPa or less.

[0084] The storage modulus of the pressure-sensitive adhesive layer can be adjusted by changing the type of acrylic polymer (P) in the pressure-sensitive adhesive, and other factors such as the type and content of the polyfunctional monomer and the type and content of the photopolymerization initiator can also be adjusted.

[0085] The storage modulus of the pressure-sensitive adhesive layer means a value measured using Rheogel-E4000 manufactured by UBM by a solid shear method under conditions of a temperature rise rate of 3°C / min, a frequency of 1 Hz, and 23°C.

[0086] 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.

[0087] 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 10 to 1000 μm, more preferably 20 to 500 μm, and even more preferably 100 to 400 μm. In order to adjust the thickness of the pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet), the same type of pressure-sensitive adhesive can be overcoated (i.e., after forming a coating film of pressure-sensitive adhesive, another pressure-sensitive adhesive is coated on the coating film to overlay the coating film). The pressure-sensitive adhesive sheet thus formed is also considered to have a single-layer structure.

[0088] 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.

[0089] The pressure-sensitive adhesive sheet of the present invention has a relative dielectric constant at a frequency of 100 kHz of, for example, 4.0 or less, preferably 3.5 or less, more preferably 3.3 or less, even more preferably 3.1 or less, and particularly preferably 3.0 or less.

[0090] The pressure-sensitive adhesive sheet of the present invention has a low dielectric constant and excellent peel resistance against a load in the thickness direction, due to the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive described above. In addition, the pressure-sensitive adhesive sheet of the present invention exhibits high adhesive strength to various substrates such as glass and polarizing plates, and also has high transparency.

[0091] Therefore, the pressure-sensitive adhesive sheet of the present invention can be suitably used as a pressure-sensitive adhesive sheet for displays with touch sensors, and specifically, is suitable for laminating liquid crystal displays or organic EL displays with touch sensor functions. A display with a touch sensor including the pressure-sensitive adhesive sheet of the present invention has a low dielectric constant and excellent peel resistance against loads in the thickness direction, and therefore has excellent durability, for example.

[0092] 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.

[0093] 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]

[0094] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0095] The following monomers (long-chain alkyl (meth)acrylate compound A1, nitrogen-containing vinyl compound A2, (meth)acrylic compound A3, monomers for forming (meth)acrylate units having a hydroxyl group, and other monomers) were prepared for producing the "adhesive resin containing an acrylic polymer (P)" used in each example.

[0096] [Long-chain alkyl (meth)acrylate compound A1] ISTA: Isostearyl acrylate IBXA: Isobornyl acrylate

[0097] [Nitrogen-containing vinyl compound A2] ·DMAA: N,N-dimethylacrylamide DEAA: N,N-diethylacrylamide

[0098] [(Meth)acrylic compound A3] 2EHA: 2-Ethylhexyl acrylate

[0099] [Monomer for forming a (meth)acrylate unit having a hydroxyl group] 4HBA: 4-hydroxybutyl acrylate

[0100] [Other monomers] ACMO: Acryloylmorpholine

[0101] Example 1 An adhesive resin containing an acrylic polymer (P) 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, DMAA, and DEAA (mass ratio 40:35:15:10) 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 heat generation, and then cooled to obtain an adhesive resin containing a partial polymer of the acrylic polymer (P) with a polymer fraction of 31%.

[0102] Next, 0.15 parts by mass of Shin-Nakamura Chemical Co., Ltd.'s "ATM-4PL" as a polyfunctional monomer and 1 part by mass of Omnirad TPO (2,4,6-trimethylbenzoyl-diphenylphosphine oxide, IGM Resins BV) as a photopolymerization initiator were mixed with a planetary stirrer to prepare an adhesive. This adhesive 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 "50E-0010KFAS") was further placed on top of that to obtain a laminate. This laminate was then irradiated with 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 2000mJ / 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.

[0103] Examples 2 to 11 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.

[0104] (Comparative Examples 1 to 6) 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.

[0105] (dielectric constant) The first and second release films were peeled off from the adhesive sheet with release sheet to obtain an adhesive sheet, which was then sandwiched between two copper foils 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 in accordance with JIS C 2138 using a dielectric measurement system (Solartron, 1260A). The measurement was performed at a frequency of 100 kHz, 23°C, and a relative humidity of 50%.

[0106] (peel resistance) Using jig A shown in Figure 1, peel resistance values ​​(mm) were measured according to the method described above, and peel resistance was evaluated from these values. Figure 1 is a schematic diagram illustrating how the peel resistance value of the pressure-sensitive adhesive sheet of the present invention is measured. Figure 1(a) is a side view of jig A, and Figure 1(b) is a plan view of jig A from above.

[0107] As shown in Fig. 1, jig A comprises an adhesive sheet 1 of the present invention, a glass plate 2 with a polarizing plate, a glass plate 3, and a weight G. As shown in Fig. 1(a), adhesive sheet 1 is disposed between glass plate 2 with a polarizing plate and glass plate 3, and adhesive sheet 1 bonds glass plate 2 with a polarizing plate and glass plate 3. Glass plate 2 with a polarizing plate is a laminated plate formed by bonding glass plate 2a and polarizing plate 2b together, and adhesive sheet 1 is bonded to the surface of such a laminated plate facing polarizing plate 2b.

[0108] In the method for measuring peel resistance, the size of the pressure-sensitive adhesive sheet 1 was 15 mm x 15 mm (thickness was optional). In the method for measuring peel resistance, the size of the glass plate 2a was 30 mm x 50 mm and the thickness was 4 mm. Soda glass was used for the glass plate 2a. In the method for measuring peel resistance, the size of the polarizing plate 2b was 30 mm x 50 mm and the thickness was 220 μm. Polarizing plate 2b used was "SKN-18243T-HC" manufactured by Polatechno Corporation. In the method for measuring peel resistance, the size of the glass plate 3 was 30 mm x 50 mm and the thickness was 0.7 mm. In the method for measuring peel resistance, the weight G was 400 g, 500 g, or 600 g.

[0109] As shown in Figure 1(a), the short end of glass plate 3 and the long end of polarizing plate-attached glass plate 2 were positioned in jig A so that they were parallel to each other and overlapped one another. As shown in Figure 1(b), the short end at the other end of glass plate 3 was positioned so that it protruded 20 mm from one end of polarizing plate-attached glass plate 2.

[0110] As shown in Figure 1(a), in jig A, adhesive sheet 1 was placed in the center of the overlapping area of ​​polarizing plate-attached glass plate 2 and glass plate 3, and was positioned so that a pair of diagonal lines of adhesive sheet 1 were parallel to the long and short sides of polarizing plate-attached glass plate 2, respectively.

[0111] 1(a) and (b), in jig A, weight G was connected to a string fixed to the center of the portion of glass plate 3 where polarizing plate-attached glass plate 2 did not overlap. Then, after the weight of weight G was continuously applied to glass plate 3 for 5 minutes, the maximum distance peeled from the edge of the pressure-sensitive adhesive sheet was measured, and this measurement value was taken as the peel resistance value of the pressure-sensitive adhesive sheet of the present invention. Using this procedure, the peel resistance values ​​of the pressure-sensitive adhesive sheets were measured using weights G of 400 g, 500 g, and 600 g, and the peel resistance was evaluated based on this peel resistance value and in accordance with the following criteria. <Judgment criteria> ⊚: The peel distance was less than 1 mm, and the film had extremely excellent peel resistance. ◯: The peel distance was 1 mm or more and less than 2 mm, and the film had excellent peel resistance. Δ: The peel distance was 2 mm or more and less than 3 mm, and the peel resistance was poor. ×: The peeling distance was 3 mm or more, and the peeling resistance was extremely poor.

[0112] (shock resistance) A PMMA plate (50 mm x 50 mm, 4 mm thick) with a polarizing plate (SKN-18243T-HC, manufactured by Polatechno Corporation) pre-bonded to it was prepared. A 20 mm x 20 mm, 4 mm thick PMMA piece was also prepared. An adhesive sheet, from which the first and second release films had been removed, was then bonded to the entire surface of one side of the PMMA piece. The adhesive sheet was then bonded to the center of the other side of the PMMA plate to obtain a laminate for evaluation. The PMMA plate and PMMA piece were bonded so that their centers overlapped. The laminate for evaluation was placed in an autoclave and heated at 40°C under a pressure of 0.5 MPa for 30 minutes. The laminate for evaluation was then placed on a horizontal table with the PMMA plate side facing upward. A 68-g, 1-inch-diameter stainless steel ball was dropped onto the center of the PMMA plate side of the laminate from a height of 150 mm from the center to conduct an impact test. If no PMMA delamination occurred after the impact test, the same impact test was repeated for a total of 10 impact tests. If no PMMA delamination occurred after the 10th impact test, the height was changed to 300 mm and the same impact test was repeated 10 more times. The presence or absence of PMMA delamination was confirmed in both tests at heights of 150 mm and 300 mm, and the impact resistance in both tests was evaluated according to the following criteria. If delamination was observed, the impact test at both heights of 150 mm and 300 mm was recorded. <Judgment criteria> Good: No peeling occurred and excellent impact resistance was observed. ×: Peeling occurred and impact resistance was poor.

[0113] (storage modulus) The storage modulus of the pressure-sensitive adhesive layer was measured using Rheogel-E4000 manufactured by UBM by a solid shear method under conditions of a temperature rise rate of 3°C / min, a frequency of 1 Hz, and 23°C.

[0114] (Hayes, b * value) The adhesive sheet with the release sheet was cut into a size of 50 mm x 50 mm, and the light separator was peeled off, and the exposed adhesive layer was attached to a glass plate (S9112, manufactured by Matsunami Glass Co., Ltd.). Next, the heavy separator was peeled off, and a glass plate (S9112, manufactured by Matsunami Glass Co., Ltd.) was attached to the exposed adhesive layer, and then the laminate was treated in an autoclave at 40°C and under a pressure of 0.5 MPa for 30 minutes to obtain a laminate. This laminate was used to measure the haze, b * The values ​​were measured and the optical properties were evaluated according to the following criteria. <Judgment criteria> ◯: Haze is 1% or less and b * The value was 1 or less, and the initial optical properties were excellent. ×: Haze exceeds 1% or b * The values ​​were less than or equal to 1 and were inferior to the initial optical properties.

[0115] (Optical properties (85℃ 10 days) The adhesive sheet with the release sheet was cut into a size of 50 mm x 50 mm, and the light separator was peeled off, and the exposed adhesive layer was attached to a glass plate (S9112, manufactured by Matsunami Glass Co., Ltd.). Next, the heavy separator was peeled off, and a glass plate (S9112, manufactured by Matsunami Glass Co., Ltd.) was attached to the exposed adhesive layer. The sheet was then placed in an autoclave and treated for 30 minutes under a pressure of 0.5 MPa at 40 ° C. to obtain a laminate as an evaluation sample. Next, this evaluation sample was treated in an autoclave for 10 days under an atmosphere of 85 ° C., after which the appearance was visually observed and the optical properties were evaluated based on the following criteria. <Judgment criteria> ◯: No whitening occurred and the optical properties were good. ×: Whitening was observed and the optical properties were poor.

[0116] (Optical properties (60℃95%RH10 days) The adhesive sheet with the release sheet was cut into a size of 50 mm x 50 mm, and the light separator was peeled off, and the exposed adhesive layer was attached to a glass plate (S9112, manufactured by Matsunami Glass Co., Ltd.). Next, the heavy separator was peeled off, and a glass plate (S9112, manufactured by Matsunami Glass Co., Ltd.) was attached to the exposed adhesive layer. The sheet was then placed in an autoclave and treated for 30 minutes under a pressure of 0.5 MPa at 40 ° C. to obtain a laminate as an evaluation sample. Next, this evaluation sample was treated in an autoclave for 10 days under an atmosphere of 60 ° C. and 95% RH, after which the appearance was visually observed and the optical properties were evaluated based on the following criteria. <Judgment criteria> ⊚: No whitening occurred and the optical properties were good. ◯: Whitening was observed only at the corners, and the optical properties were satisfactory for practical use. ×: Whitening was observed at the corners and along the periphery, and the optical properties were problematic for practical use. XX: Whitening was observed over the entire surface, and the optical properties were extremely poor.

[0117] (Evaluation results) 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 and Tg of the obtained acrylic polymer (P), as well as the evaluation results for the thickness, peel resistance, impact resistance, optical properties, and dielectric constant of the adhesive sheet. In the adhesive resin preparation formula in Table 1, a blank column indicates that the raw material was not used. In Table 1, the number in parentheses in the impact resistance column indicates the number of impact tests when peeling first occurred. The numbers in the columns for multifunctional monomer and photopolymerization initiator in Table 1 are parts by mass.

[0118] From Table 1, it can be seen that the adhesive sheets of Examples 1 to 11, which contain a specified acrylic polymer (P) and have an adhesive layer with a gel fraction within a specific range, have excellent impact resistance and excellent peel resistance against loads in the thickness direction, also have a low dielectric constant, and have excellent optical properties.

[0119] [Table 1]

Claims

1. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer contains a crosslinked polymer having a structure in which an acrylic polymer (P) is crosslinked with a polyfunctional monomer, the acrylic polymer (P) contains 15 to 40 parts by mass of vinyl monomer units a2 having an acyclic substituent containing a nitrogen atom, relative to 100 parts by mass of the acrylic polymer (P); the content of the long-chain alkyl (meth)acrylate units a1 having a cyclic or branched alkyl group having 10 to 18 carbon atoms is 40 parts by mass or less relative to 100 parts by mass of the acrylic polymer (P), the pressure-sensitive adhesive layer has a gel fraction of 30% to 80%; A pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer has a storage modulus at 23°C of 101 to 500 kPa.

2. The pressure-sensitive adhesive sheet according to claim 1 , wherein the pressure-sensitive adhesive layer is a cured product of an active energy ray-curable pressure-sensitive adhesive.

3. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the content of the hydroxyl group-containing monomer unit is 10 parts by mass or less per 100 parts by mass of the acrylic polymer (P).

4. The pressure-sensitive adhesive sheet according to claim 1 or 2, which has a relative dielectric constant of 4.0 or less at a frequency of 100 kHz.

5. The pressure-sensitive adhesive sheet according to claim 4, which has a relative dielectric constant of 3.5 or less at a frequency of 100 kHz.

6. The pressure-sensitive adhesive sheet according to claim 1 or 2, which is for a display with a touch sensor.

7. A display with a touch sensor, comprising the adhesive sheet according to claim 6.

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