Alcohol-peelable optical adhesive sheet

Abstract

An adhesive sheet (10) as an alcohol-peelable optical adhesive sheet according to the present invention contains a photopolymerizable polymer as a base polymer. The adhesive sheet (10) has an adhesive force Fn1 in a predetermined initial normal temperature peeling test of 9.0 N / 25 mm or more, an adhesive force Fa1 in a predetermined first ethanol peeling test of 3.0 N / 25 mm or less, and an adhesive force Fh in a predetermined high temperature and high humidity peeling test of 2.0 N / 25 mm or more.

Description

Alcohol-peelable optical adhesive sheet

[0001] The present invention relates to an optical pressure-sensitive adhesive sheet.

[0002] A display panel has a laminated structure including elements such as a pixel panel, a polarizing film, and a cover film. In the manufacturing process of a display panel, for example, an optically transparent adhesive sheet (optical adhesive sheet) is used to bond the elements included in the laminated structure.

[0003] On the other hand, optical adhesive sheets having water releasability are known. A water-releasable optical adhesive sheet is an optical adhesive sheet whose adhesive strength can be reduced by allowing water droplets to penetrate into the interface between the adherend and the adhesive sheet after it has been attached to the adherend. After being attached to the adherend, such an optical adhesive sheet can be easily peeled from the adherend using water, as necessary. For example, in the manufacturing process of a display panel, if a defect (such as misalignment) occurs in the attachment of an optical adhesive sheet to the adherend, the adhesive sheet can be peeled from the adherend using water (water releasability), and a replacement optical adhesive sheet can be used for the attachment. Such an optical adhesive sheet having water releasability is described, for example, in Patent Document 1 listed below.

[0004] Japanese Patent Application Laid-Open No. 2020-23679

[0005] The optical pressure-sensitive adhesive sheet described in Patent Document 1 contains an acrylic-based polymer and a surfactant. In this pressure-sensitive adhesive sheet, the acrylic-based polymer ensures adhesion to an adherend. Furthermore, in this pressure-sensitive adhesive sheet, the presence of a surfactant on the adhesive surface allows water releasability to be exhibited. However, the optical pressure-sensitive adhesive sheet of Patent Document 1 has low moisture resistance due to the presence of a surfactant on the adhesive surface. For example, the optical pressure-sensitive adhesive sheet of Patent Document 1 has low adhesive strength in a high-humidity environment. Such an optical pressure-sensitive adhesive sheet does not provide good adhesion reliability to an adherend.

[0006] The present invention provides an alcohol-peelable optical pressure-sensitive adhesive sheet that is suitable for achieving both adhesive reliability to an adherend and reworkability.

[0007] The present invention [1] contains a photopolymerized polymer as a base polymer, and has an adhesive strength Fn in the following initial room temperature peel test. １ The adhesive strength in the first ethanol peeling test below is 9.0 N / 25 mm or more. １ The alcohol-peelable optical pressure-sensitive adhesive sheet includes an alcohol-peelable optical pressure-sensitive adhesive sheet having an adhesive strength Fh of 3.0 N / 25 mm or less and an adhesive strength Fh of 2.0 N / 25 mm or more in the high-temperature, high-humidity peel test described below.

[0008] Initial room temperature peel test: First, a 25 mm wide x 100 mm long adhesive sheet piece of the alcohol-peelable optical adhesive sheet is bonded to an alkali glass plate prepared by the float method to obtain a laminate (preparation step). Next, the laminate is heated and pressurized at 50°C, 0.5 MPa, and 15 minutes (heating and pressurizing step). Next, the laminate is left standing at room temperature for 72 hours (standing step). Next, the adhesive sheet piece is peeled from the alkali glass plate by pulling one end of the adhesive sheet piece in the longitudinal direction under first conditions of 25°C, 50% relative humidity, a peel angle of 180°, and a pulling speed of 300 mm / min, and the adhesive strength is measured (measurement step).

[0009] First ethanol peeling test: This test is the same as the initial room temperature peeling test, except for the following: In the standing step, the laminate is stood at 50°C for 168 hours; After the standing step and before the measurement step, an ethanol supplying step is carried out; In the ethanol supplying step, 10 μL of ethanol is supplied onto the alkali glass plate of the laminate so that the ethanol contacts one end of the adhesive sheet piece in the longitudinal direction at the interface between the alkali glass plate and the adhesive sheet piece.

[0010] High-temperature, high-humidity peel test: This is the same as the initial room-temperature peel test, except for the following: In the standing step, the laminate is left standing at room temperature for 24 hours; After the standing step and before the measurement step, a high-temperature, high-humidity treatment step is carried out; In the high-temperature, high-humidity treatment step, the laminate after the standing step is subjected to high-temperature, high-humidity treatment under conditions of 60°C, 93% relative humidity, and 15 minutes; In the measurement step, a 180° peel test is carried out under second conditions, instead of the first conditions, of 60°C, 93% relative humidity, a peel angle of 180°, and a pulling speed of 300 mm / min.

[0011] The present invention [2] has an adhesive strength Fa in the second ethanol peeling test described below. ２ and the adhesive strength Fa ２ The adhesive force Fa １ The alcohol-peelable optical pressure-sensitive adhesive sheet according to the above [1], wherein the fluctuation rate of is -50% to 100%.

[0012] Second Ethanol Peeling Test: This test was the same as the first ethanol peeling test, except that in the leaving step, the laminate was left standing at room temperature for 72 hours.

[0013] The present invention [3] includes the alcohol-peelable optical pressure-sensitive adhesive sheet according to the above [2], wherein the ethanol peeling duration in the second ethanol peeling test is 20 mm or more.

[0014] The present invention [4] includes the alcohol-peelable optically adhesive sheet according to any one of the above [1] to [3], which does not contain a surfactant.

[0015] As described above, the alcohol-peelable optical adhesive sheet of the present invention has a base polymer that is a photopolymerized polymer, and an initial adhesive strength Fn １ The adhesive strength in the first ethanol peel test is 9.0 N / 25 mm or more. １ The adhesive strength Fn is 3.0 N / 25 mm or less, and the adhesive strength Fh in a high temperature and high humidity peel test is 2.0 N / 25 mm or more. １A high adhesive strength of 9.0 N / 25 mm or more (adhesive strength under conditions where ethanol is not supplied) is suitable for ensuring the adhesive reliability of the alcohol-peelable optical adhesive sheet to the adherend after the sheet is attached to the adherend. １ A low adhesive strength (Fh) of 3.0 N / 25 mm or less (adhesion strength after storage under ethanol supply conditions) is suitable for ensuring good alcohol releasability and reworkability in the alcohol-releasable optical adhesive sheet over a long period of time after it is attached to an adherend. A high adhesive strength (Fh) of 2.0 N / 25 mm or more (adhesion strength under conditions where ethanol is not supplied and at high temperature and humidity) is suitable for ensuring the adhesion reliability of the optical adhesive sheet to the adherend even in a high-humidity environment. Therefore, the alcohol-releasable optical adhesive sheet of the present invention is suitable for achieving both adhesion reliability to the adherend and reworkability.

[0016] 4A is a cross-sectional schematic diagram of an alcohol-releasable optical adhesive sheet according to one embodiment of the present invention; FIG. 4B is a schematic representation of an ethanol peeling test; FIG. 4C is a schematic representation of an example of a peel force-peel length curve obtained in an ethanol peeling test; and FIG. 4C is a schematic representation of an example of a method for using the alcohol-releasable optical adhesive sheet shown in FIG. 1. FIG. 4A shows a step of bonding the alcohol-releasable optical adhesive sheet to a first adherend, FIG. 4B shows a step of joining the first adherend and a second adherend via the alcohol-releasable optical adhesive sheet, and FIG. 4C shows an aging step.

[0017] As shown in Fig. 1 , a pressure-sensitive adhesive sheet 10 as one embodiment of the alcohol-peelable optical pressure-sensitive adhesive sheet of the present invention has a sheet shape of a predetermined thickness and extends in a direction (plane direction) perpendicular to the thickness direction H. The pressure-sensitive adhesive sheet 10 has an adhesive surface 11 and an adhesive surface 12 opposite to the adhesive surface 11. Fig. 1 exemplarily shows a state in which release liners L1 and L2 are bonded to the adhesive surfaces 11 and 12 of the pressure-sensitive adhesive sheet 10. The release liner L1 is disposed on the adhesive surface 11. The release liner L2 is disposed on the adhesive surface 12.

[0018] The pressure-sensitive adhesive sheet 10 is an optically transparent pressure-sensitive adhesive sheet (optical pressure-sensitive adhesive sheet). The pressure-sensitive adhesive sheet 10 is an optical pressure-sensitive adhesive sheet that has alcohol releasability. That is, the pressure-sensitive adhesive sheet 10 is an optical pressure-sensitive adhesive sheet whose adhesive strength can be reduced by infiltrating alcohol (e.g., alcohol droplets) into the interface between the adherend and the pressure-sensitive adhesive sheet 10 after it has been attached to the adherend (alcohol releasability).

[0019] The pressure-sensitive adhesive sheet 10 is a sheet-like pressure-sensitive adhesive. The pressure-sensitive adhesive sheet 10 contains a photopolymerizable polymer as a base polymer. Specifically, the base polymer is a polymer formed by photopolymerization of a polymerizable component such as a monomer component. Photopolymerization is a polymerization method in which a polymerization reaction of a polymerizable component is promoted by irradiation with active energy rays such as ultraviolet light. The pressure-sensitive adhesive sheet 10 also has an adhesive strength Fn in the initial room temperature peel test described below. １ The adhesive strength in the first ethanol peeling test below is 9.0 N / 25 mm or more. １ The adhesive strength Fh in the high temperature and high humidity peel test described below is 2.0 N / 25 mm or more.

[0020] Initial room temperature peel test: First, a 25 mm wide x 100 mm long adhesive sheet piece of the adhesive sheet 10 is bonded to an alkali glass plate prepared by the float method to obtain a laminate (preparation step). In this step, the adhesive sheet piece is bonded to the tin side of the alkali glass plate (the same applies to other peel tests described below). Next, the laminate is heated and pressurized at 50 ° C, 0.5 MPa, and 15 minutes (heating and pressurizing step). Next, the laminate is left standing at room temperature for 72 hours (standing step). Next, the adhesive sheet piece is peeled from the alkali glass plate by pulling one end of the adhesive sheet piece in the longitudinal direction under first conditions of 25 ° C, relative humidity 50%, peel angle 180 °, and pulling speed 300 mm / min, and the adhesive strength is measured (measurement step). The initial room temperature peel test method is more specifically described below in the examples.

[0021] First ethanol peeling test: This test is the same as the initial room-temperature peeling test, except for the following: In the standing step, the laminate is left standing at 50°C for 168 hours; and after the standing step and before the measurement step, an ethanol supplying step is performed. In the ethanol supplying step, 10 μL of ethanol (100% ethanol) is supplied onto the alkali glass plate of the laminate so that the ethanol contacts one end of the adhesive sheet piece in the longitudinal direction at the interface between the alkali glass plate and the adhesive sheet piece. Specifically, as shown in FIG. 2 , 10 μL of ethanol 22 is supplied onto the alkali glass plate 21 of the laminate W so that the ethanol 22 contacts one end 10a in the longitudinal direction D of the adhesive sheet piece 10A at the interface B between the alkali glass plate 21 and the adhesive sheet piece 10A. In the measurement step after the ethanol supplying step, the adhesive sheet piece 10A is peeled from the alkali glass plate by pulling one end side in the longitudinal direction (one end 10e in FIG. 2 ) of the adhesive sheet piece 10A, and the adhesive strength is measured. The method of the first ethanol peeling test is described more specifically below in relation to the examples.

[0022] Figure 3 shows an example of a peel force-peel length curve obtained in an ethanol peel test (first ethanol peel test, second ethanol peel test described below). In the graph of Figure 3, the horizontal axis represents the peel length (mm) from the start of peeling of the PSA sheet piece in the measurement step (peel length 0 mm), and the vertical axis represents the peel force (N / 25 mm) required to peel the PSA sheet piece during the peeling process. In the measurement step of the ethanol peel test, the peel length d when the peel force begins to stabilize during the peeling process of the PSA sheet piece is １ and peel length d １ When the peeling force increases by 10% compared to the peeling force at ２ (If the peel force does not increase by 10%, the peel length d ２ is the length of the adhesive sheet piece 100 mm - d １ The peel length d １ From peel length d ２ The average value of the peel strength measured up to the end of the test was used as the adhesive strength (adhesive strength Fa in the ethanol peel test). １ ,Fa ２ )

[0023] High-temperature, high-humidity peel test: This is the same as the initial room-temperature peel test, except for the following: In the resting step, the laminate is left to rest at room temperature for 24 hours; After the resting step and before the measurement step, a high-temperature, high-humidity treatment step is carried out; In the high-temperature, high-humidity treatment step, the laminate after the resting step is subjected to high-temperature, high-humidity treatment under conditions of 60°C, 93% relative humidity, and 15 minutes; In the measurement step, a 180° peel test is carried out under second conditions of 60°C, 93% relative humidity, a peel angle of 180°, and a pulling speed of 300 mm / min, instead of the first conditions. The method of the high-temperature, high-humidity peel test is more specifically as described below in the examples.

[0024] As described above, the adhesive sheet 10 has a base polymer that is a photopolymerized polymer, and an initial adhesive strength Fn １ The adhesive strength in the first ethanol peel test is 9.0 N / 25 mm or more. １ The adhesive strength Fn is 3.0 N / 25 mm or less, and the adhesive strength Fh in a high temperature and high humidity peel test is 2.0 N / 25 mm or more. １ A high adhesive strength of 9.0 N / 25 mm or more (adhesive strength under the condition of no ethanol supply) is suitable for ensuring the adhesive reliability of the adhesive sheet 10 to the adherend after the adhesive sheet 10 is attached to the adherend. １ A low adhesive strength of 3.0 N / 25 mm or less (adhesive strength after storage under ethanol supply conditions) is suitable for ensuring good alcohol removability and reworkability in the adhesive sheet 10 for a long period of time after the adhesive sheet 10 is attached to an adherend (long-term reworkability). A high adhesive strength Fh (adhesive strength under conditions where ethanol is not supplied and at high temperature and humidity) of 2.0 N / 25 mm or more is suitable for ensuring the adhesive reliability of the adhesive sheet 10 to an adherend even in a high humidity environment. Therefore, the adhesive sheet 10 is suitable for achieving both adhesive reliability to an adherend and reworkability (alcohol reworkability).

[0025] Furthermore, unlike the optical pressure-sensitive adhesive sheet of Patent Document 1, which exhibits water releasability dependent on a surfactant, the present inventors have discovered that an optical pressure-sensitive adhesive sheet can exhibit alcohol releasability over a relatively long period of time without relying on a surfactant. The present invention is based on this discovery. Not relying on a surfactant is suitable for ensuring the adhesion reliability of the optical pressure-sensitive adhesive sheet to the adherend even in a high-humidity environment.

[0026] Adhesive force Fn １ From the viewpoint of ensuring the above-mentioned adhesive reliability, the adhesive strength Fn is preferably 9.5 N / 25 mm or more, and more preferably 10 N / 25 mm or more. １ From the viewpoint of ensuring the reworkability, the adhesive strength Fn is preferably 19 N / 25 mm or less, more preferably 18 N / 25 mm or less, and even more preferably 17 N / 25 mm or less. １ From the viewpoint of achieving both adhesive reliability and reworkability, the adhesive strength Fn is preferably 9.0 to 19 N / 25 mm, more preferably 9.5 to 18 N / 25 mm, and even more preferably 10 to 17 N / 25 mm. １ Examples of methods for adjusting the adhesive strength Fn include selecting the type of base polymer in the pressure-sensitive adhesive sheet 10, adjusting the molecular weight, adjusting the degree of crosslinking, and adjusting the blending amounts. Examples of methods for these adjustments include selecting the type and adjusting the blending amounts of monofunctional monomers, polyfunctional polymerizable compounds (crosslinking agents), and polymerization initiators when forming the base polymer. １ The adhesive strength Fa can be adjusted by selecting the type of components other than the base polymer in the pressure-sensitive adhesive sheet 10 and adjusting the amount of the components. Examples of the components include oligomers (hydrophilic oligomers, hydrophobic oligomers), surfactants, and silane coupling agents. １ , Fh and adhesive force Fn described below ２ ,Fa ２ The same is true for .

[0027] Adhesive strength Fa １From the viewpoint of ensuring the alcohol reworkability of the pressure-sensitive adhesive sheet 10, the adhesive strength Fa is preferably 2.7 N / 25 mm or less, more preferably 2.4 N / 25 mm or less, and even more preferably 2.0 N / 25 mm or less. １ From the viewpoint of preventing unintended peeling of the adhesive sheet 10 when an alcohol-containing liquid (such as a disinfectant) is applied to the adhesive sheet 10, the adhesive strength Fa is preferably 0.5 N / 25 mm or more, more preferably 0.8 N / 25 mm or more, even more preferably 1.0 N / 25 mm or more, and even more preferably 1.2 N / 25 mm or more. １ From the viewpoint of achieving both the alcohol reworkability of the pressure-sensitive adhesive sheet 10 and the suppression of unintended peeling, the adhesive strength is preferably 0.5 to 3.0 N / 25 mm, more preferably 0.8 to 2.7 N / 25 mm, even more preferably 1.0 to 2.4 N / 25 mm, and even more preferably 1.2 to 2.0 N / 25 mm.

[0028] The adhesive strength Fh is preferably 2.1 N / 25 mm or more, more preferably 2.2 N / 25 mm or more, from the viewpoint of ensuring the adhesive reliability of the adhesive sheet 10 in a high-humidity environment. The adhesive strength Fh is preferably 10 N / 25 mm or less, more preferably 7.0 N / 25 mm or less, and even more preferably 5.0 N / 25 mm or less, from the viewpoint of ensuring reworkability. １ From the viewpoint of achieving both the adhesive reliability and reworkability of the pressure-sensitive adhesive sheet 10 in a high-humidity environment, the applied pressure is preferably 2.0 to 10 N / 25 mm, more preferably 2.1 to 7.0 N / 25 mm, and even more preferably 2.2 to 5.0 N / 25 mm.

[0029] The adhesive sheet 10 had an adhesive strength of Fn in the following room temperature peel test after storage. ２ It has.

[0030] Post-storage room temperature peel test: This was the same as the initial room temperature peel test, except that in the resting step, the laminate was left to stand at 50° C. for 168 hours. The method for the post-storage room temperature peel test was specifically as described below in the examples.

[0031] Adhesive force Fn ２From the viewpoint of ensuring long-term adhesive reliability of the pressure-sensitive adhesive sheet 10, the adhesive strength Fn is preferably 9.0 N / 25 mm or more, more preferably 9.5 N / 25 mm or more, and even more preferably 10 N / 25 mm or more. ２ From the viewpoint of ensuring the reworkability, the adhesive strength Fn is preferably 19 N / 25 mm or less, more preferably 18 N / 25 mm or less, and even more preferably 17 N / 25 mm or less. ２ From the viewpoint of achieving both long-term adhesive reliability and reworkability, the adhesive strength is preferably 9.0 to 19 N / 25 mm, more preferably 9.5 to 18 N / 25 mm, and even more preferably 10 to 17 N / 25 mm.

[0032] The adhesive sheet 10 had an adhesive strength of Fa in the second ethanol peeling test described below. ２ It has.

[0033] Second ethanol peeling test: The second ethanol peeling test was the same as the first ethanol peeling test, except that the laminate was left to stand at room temperature for 72 hours in the standing step. The method of the second ethanol peeling test was specifically as described below in the examples.

[0034] Adhesive strength Fa ２ Adhesion force Fa １ From the viewpoint of ensuring stable alcohol reworkability of the PSA sheet 10, the fluctuation rate represented by the following formula is preferably −50% to 100%, more preferably −20% to 70%, and even more preferably 0% to 60%.

[0035] Fluctuation rate (%) = [(Fa １ -Fa ２ ) / Fa ２ ] x 100

[0036] Adhesive strength Fa ２ From the viewpoint of ensuring the alcohol reworkability of the pressure-sensitive adhesive sheet 10, the adhesive strength Fa is preferably 2.5 N / 25 mm or less, more preferably 2.0 N / 25 mm or less, and even more preferably 1.8 N / 25 mm or less. ２From the viewpoint of preventing unintended peeling of the adhesive sheet 10 when an alcohol-containing liquid is applied to the adhesive sheet 10, the adhesive strength Fa is preferably 0.5 N / 25 mm or more, more preferably 0.8 N / 25 mm or more, and even more preferably 1.0 N / 25 mm or more. ２ From the viewpoint of achieving both alcohol reworkability in the pressure-sensitive adhesive sheet 10 and suppression of unintended peeling, the adhesive strength is preferably 0.5 to 2.5 N / 25 mm, more preferably 0.8 to 2.0 N / 25 mm, and even more preferably 1.0 to 1.8 N / 25 mm.

[0037] The ethanol peeling duration d in the second ethanol peeling test is preferably 20 mm or more, more preferably 26 mm or more, and even more preferably 28 mm or more, from the viewpoint of ensuring the alcohol reworkability of the PSA sheet 10. The ethanol peeling duration d is, for example, 100 mm or less. The ethanol peeling duration d is the above-mentioned peeling length d ２ and peel length d １ The difference between (d ２ -d １ The specific method for measuring the ethanol peeling duration d is as will be described later in the examples.

[0038] The pressure-sensitive adhesive sheet 10 is a sheet-shaped pressure-sensitive adhesive formed from a pressure-sensitive adhesive composition. The pressure-sensitive adhesive sheet 10 (pressure-sensitive adhesive composition) contains at least the above-mentioned photopolymerization polymer as a base polymer.

[0039] Examples of base polymers include acrylic polymers, polyurethane polymers, polyamide polymers, and polyvinyl ether polymers. The base polymers may be used alone or in combination of two or more. From the viewpoint of ensuring good adhesiveness and transparency in the pressure-sensitive adhesive sheet 10, the base polymer is preferably an acrylic polymer. The acrylic polymer is a copolymer of monomer components containing 50% or more by mass of (meth)acrylic acid ester. "(Meth)acrylic" refers to acrylic and / or methacrylic.

[0040] In this embodiment, the acrylic polymer is a polymer (photopolymerized polymer) obtained by photopolymerization of a polymerizable component including a monofunctional monomer and a polyfunctional polymerizable compound as a crosslinking agent. The acrylic polymer is, for example, a polymer obtained by photopolymerization of a partial polymer (a mixture of a polymer of a monofunctional monomer and an unreacted monofunctional monomer) obtained by photopolymerization of a monofunctional monomer and a polyfunctional polymerizable compound.

[0041] Such acrylic polymers include a photopolymerized polymer (first photopolymerized polymer) having a photocrosslinked structure. The photocrosslinked structure is a structure in which linear chain structures formed by units derived from monofunctional monomers are crosslinked by units derived from a crosslinking agent. The base polymer may also include a photopolymerized polymer (second photopolymerized polymer) that does not have such a photocrosslinked structure. The second photopolymerized polymer is a polymer of a monofunctional monomer.

[0042] The monofunctional monomer preferably includes a monofunctional (meth)acrylic acid alkyl ester, and more preferably includes a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms. The (meth)acrylic acid alkyl ester may have a linear or branched alkyl group, or may have a cyclic alkyl group (alicyclic alkyl group).

[0043] Examples of (meth)acrylic acid alkyl esters having a linear or branched alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, Examples include nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (i.e., (meth)acrylate laurate), isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, and nonadecyl (meth)acrylate.

[0044] Examples of (meth)acrylic acid alkyl esters having an alicyclic alkyl group include (meth)acrylic acid cycloalkyl esters, (meth)acrylic acid alkyl esters having a bicyclic aliphatic hydrocarbon ring, and (meth)acrylic acid alkyl esters having a tricyclic or higher aliphatic hydrocarbon ring. Examples of (meth)acrylic acid cycloalkyl esters include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate. Examples of (meth)acrylic acid alkyl esters having a bicyclic aliphatic hydrocarbon ring include isobornyl (meth)acrylate. Examples of (meth)acrylic acid alkyl esters having three or more aliphatic hydrocarbon rings include dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

[0045] The monofunctional (meth)acrylic acid alkyl ester may be used alone or in combination of two or more kinds. The monofunctional (meth)acrylic acid alkyl ester is preferably an acrylic acid alkyl ester having an alkyl group having 6 to 12 carbon atoms, and more preferably at least one selected from the group consisting of 2-ethylhexyl acrylate (2EHA) and acrylic laurate (LA).

[0046] The proportion of the (meth)acrylic acid alkyl ester in the monofunctional monomer is preferably 70 to 99.9% by mass, more preferably 80 to 99.5% by mass, and even more preferably 90 to 99% by mass. The proportion of the (meth)acrylic acid alkyl ester in the monofunctional monomer is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. When the proportion of the (meth)acrylic acid alkyl ester is equal to or greater than the above-mentioned lower limit, basic properties such as adhesiveness can be appropriately exhibited in the PSA sheet 10. Furthermore, the proportion of the monofunctional (meth)acrylic acid alkyl ester in the monofunctional monomer is, for example, 99.9% by mass or less, 99.5% by mass or less, or 99% by mass or less.

[0047] The monofunctional monomer may include a copolymerizable monomer copolymerizable with the (meth)acrylic acid alkyl ester. Examples of the copolymerizable monomer include polar group-containing monomers. Examples of the polar group-containing monomer include hydroxy group-containing monomers, monomers having a nitrogen atom-containing ring, and carboxy group-containing monomers. The copolymerizable monomers may be used alone or in combination of two or more. The polar group-containing monomer is useful for modifying the acrylic polymer, such as ensuring the cohesive strength of the acrylic polymer. The polar group-containing monomer is preferably at least one selected from the group consisting of hydroxy group-containing monomers and monomers having a nitrogen atom-containing ring.

[0048] Examples of hydroxy group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate. The hydroxy group-containing monomer is preferably at least one selected from the group consisting of 2-hydroxyethyl acrylate (2HEA), 4-hydroxyethyl acrylate (4HEA), and 4-hydroxybutyl acrylate (4HBA).

[0049] The proportion of the hydroxy group-containing monomer in the monofunctional monomer is preferably 0.1 to 20% by mass, more preferably 0.5 to 15% by mass, and even more preferably 1 to 12% by mass. The proportion of the hydroxy group-containing monomer in the monofunctional monomer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more. When this proportion of the hydroxy group-containing monomer is equal to or greater than the above-mentioned lower limit, the cohesive strength of the PSA sheet 10 can be ensured, and the adhesive strength of the PSA sheet 10 to the adherend can be ensured. Furthermore, the proportion of the hydroxy group-containing monomer in the monomer components is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less. When this proportion of the hydroxy group-containing monomer is equal to or less than the above-mentioned upper limit, the polarity of the acrylic polymer (which is related to the compatibility of the acrylic polymer with various additive components in the PSA sheet 10) can be appropriately adjusted.

[0050] Examples of monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, and acryloylmorpholine. The monomer having a nitrogen atom-containing ring is preferably N-vinyl-2-pyrrolidone (NVP).

[0051] The proportion of the monomer having a nitrogen atom-containing ring in the monofunctional monomer is preferably 0.1 to 20% by mass, more preferably 0.5 to 12% by mass, and even more preferably 1 to 8% by mass. The proportion of the monomer having a nitrogen atom-containing ring in the monofunctional monomer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more. When this proportion of the monomer having a nitrogen atom-containing ring is equal to or greater than the above-mentioned lower limit, the cohesive strength of the PSA sheet 10 can be ensured, and the adhesive strength of the PSA sheet 10 to the adherend can be ensured. Furthermore, the proportion of the monomer having a nitrogen atom-containing ring in the monofunctional monomer is preferably 20% by mass or less, more preferably 12% by mass or less, and even more preferably 8% by mass or less. When this proportion of the monomer having a nitrogen atom-containing ring is equal to or less than the above-mentioned upper limit, the glass transition temperature of the acrylic polymer can be appropriately adjusted, and the polarity of the acrylic polymer (which is related to the compatibility of the acrylic polymer with various additive components in the PSA sheet) can be appropriately adjusted.

[0052] Examples of carboxy group-containing monomers include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

[0053] The proportion of the carboxy group-containing monomer in the monofunctional monomer is preferably 0.0 to 3 mass%, more preferably 0.0 to 1 mass%, even more preferably 0.0 to 0.5 mass%, and even more preferably 0.0 to 0.1 mass%. The proportion of the carboxy group-containing monomer in the monofunctional monomer is preferably 3 mass% or less, more preferably 1 mass% or less, even more preferably 0.5 mass% or less, even more preferably 0.1 mass% or less, and particularly preferably 0.0 mass%. When the proportion of the carboxy group-containing monomer in the monofunctional monomer is the above-mentioned upper limit or less, acid corrosion of the adherend of the PSA sheet 10 can be suppressed.

[0054] The monofunctional monomer may contain other copolymerizable monomers, such as acid anhydride monomers, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, alkoxy group-containing monomers, and aromatic vinyl compounds.

[0055] Examples of polyfunctional polymerizable compounds include polyfunctional monomers containing two or more ethylenically unsaturated double bonds in one molecule. Examples of polyfunctional monomers include polyfunctional (meth)acrylates. Examples of polyfunctional (meth)acrylates include difunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional or higher polyfunctional (meth)acrylates.

[0056] Examples of bifunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol dimethacrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerin di(meth)acrylate, neopentyl glycol di(meth)acrylate, stearic acid-modified pentaerythritol di(meth)acrylate, dicyclopentenyl diacrylate, di(meth)acryloyl isocyanurate, and ethoxylated bisphenol A diacrylate (BPAEODE).

[0057] Examples of trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl)isocyanurate.

[0058] Examples of tetrafunctional or higher polyfunctional (meth)acrylates include ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, alkyl-modified dipentaerythritol pentaacrylate, and dipentaerythritol hexa(meth)acrylate.

[0059] The polyfunctional polymerizable compound may be used alone or in combination of two or more kinds. The polyfunctional polymerizable compound is preferably at least one selected from the group consisting of dipentaerythritol hexaacrylate (DPHA) and 1,9-nonanediol diacrylate (NDDA).

[0060] The amount of the polyfunctional polymerizable compound in the polymerizable component is preferably 0.01 to 2 parts by mass, more preferably 0.03 to 1.5 parts by mass, and even more preferably 0.05 to 1.2 parts by mass, per 100 parts by mass of the monofunctional monomer. When the amount of the polyfunctional polymerizable compound is equal to or greater than the above-mentioned lower limit, the cohesive strength of the pressure-sensitive adhesive sheet 10 can be increased, and the adhesive reliability after being laminated to an adherend can be improved. When the amount of the polyfunctional polymerizable compound is equal to or less than the above-mentioned upper limit, the wettability of the pressure-sensitive adhesive sheet 10 to the adherend can be ensured, and the initial adhesive strength of the pressure-sensitive adhesive sheet 10 to the adherend can be ensured.

[0061] In this embodiment, the acrylic polymer is formed by photopolymerization of the polymerizable components. The polymerizable components (including a monofunctional monomer and a multifunctional polymerizable compound as a crosslinking agent) may be polymerized in one step or in multiple steps. In the multistep polymerization method, a monofunctional monomer is first polymerized to prepare a prepolymer composition containing a partial polymer (a mixture of a monofunctional monomer polymer and unreacted monofunctional monomer) (preliminary polymerization). Next, a multifunctional polymerizable compound as a crosslinking agent is added to the prepolymer composition, and then a polymerization reaction is allowed to proceed in a reaction system containing the partial polymer and the multifunctional polymerizable compound (main polymerization). A photopolymerization initiator may be used in the photopolymerization.

[0062] Examples of the photopolymerization initiator include a radical photopolymerization initiator, a cationic photopolymerization initiator, and an anionic photopolymerization initiator.

[0063] Examples of the radical photopolymerization initiator include an acylphosphine oxide photopolymerization initiator, a benzoin ether photopolymerization initiator, an acetophenone photopolymerization initiator, an α-ketol photopolymerization initiator, and an aromatic sulfonyl chloride photopolymerization initiator.

[0064] Examples of acylphosphine oxide photopolymerization initiators include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-2,4-di-n-butoxyphenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. Examples of benzoin ether photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and 2,2-dimethoxy-1,2-diphenylethan-1-one. Examples of acetophenone photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of α-ketol photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of aromatic sulfonyl chloride photopolymerization initiators include 2-naphthalenesulfonyl chloride. Photopolymerization initiators may be used alone or in combination. The photopolymerization initiator is preferably at least one selected from the group consisting of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,2-dimethoxy-2-phenylacetophenone, and 1-hydroxycyclohexyl phenyl ketone.

[0065] The amount of photopolymerization initiator is preferably 0.03 to 0.5 parts by mass, more preferably 0.06 to 0.3 parts by mass, and even more preferably 0.08 to 0.2 parts by mass, per 100 parts by mass of the polymerizable component. The amount of photopolymerization initiator is preferably 0.03 parts by mass or more, more preferably 0.06 parts by mass or more, and even more preferably 0.08 parts by mass or more, per 100 parts by mass of the polymerizable component. When the amount of photopolymerization initiator is equal to or greater than the above-mentioned lower limit, a crosslinked network with sufficient crosslinking density is formed in the acrylic polymer, thereby ensuring the adhesive strength of the PSA sheet 10. The amount of photopolymerization initiator is preferably 0.5 parts by mass or less, more preferably 0.3 parts by mass or less, and even more preferably 0.2 parts by mass or less, per 100 parts by mass of the polymerizable component. When the amount of photopolymerization initiator is equal to or less than the above-mentioned upper limit, cohesive failure of the adhesive surface of the PSA sheet 10 can be suppressed when peeling the PSA sheet 10 from the adherend. This is useful, for example, for ensuring alcohol reworkability. When the acrylic polymer is photopolymerized by prepolymerization and main polymerization, a photopolymerization initiator may be added after the prepolymerization and during the main polymerization.

[0066] From the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive sheet 10, the weight-average molecular weight of the base polymer is preferably 100,000 to 5,000,000, more preferably 300,000 to 3,000,000, and even more preferably 500,000 to 2,000,000. The weight-average molecular weight of the base polymer is preferably 100,000 or more, more preferably 300,000 or more, and even more preferably 500,000 or more. When the weight-average molecular weight of the base polymer is equal to or greater than the above-mentioned lower limit, the cohesive strength of the pressure-sensitive adhesive sheet 10 can be ensured. The weight-average molecular weight of the base polymer is preferably 5,000,000 or less, more preferably 3,000,000 or less, and even more preferably 2,000,000 or less. When the weight-average molecular weight of the base polymer is equal to or less than the above-mentioned upper limit, the flexibility of the pressure-sensitive adhesive sheet 10 can be ensured. The weight-average molecular weight of the acrylic polymer is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene.

[0067] The glass transition temperature (Tg) of the base polymer is preferably 0°C or lower, more preferably -10°C or lower, and even more preferably -20°C or lower. The glass transition temperature is, for example, -80°C or higher. That is, the glass transition temperature of the base polymer is preferably -80°C to 0°C, more preferably -80°C to -10°C, and even more preferably -80°C to -20°C.

[0068] The glass transition temperature of the base polymer may be determined using the theoretical glass transition temperature (Tg) calculated based on the Fox formula below. The Fox formula is a relationship between the glass transition temperature (Tg) of a polymer and the glass transition temperature (Tgi) of a homopolymer of the monomers constituting the polymer. In the Fox formula below, Tg represents the glass transition temperature (°C) of the polymer, Wi represents the weight fraction of the monomer i constituting the polymer, and Tgi represents the glass transition temperature (°C) of the homopolymer formed from the monomer i. Literature values ​​can be used for the glass transition temperature of the homopolymer. For example, the "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) lists the glass transition temperatures of various homopolymers. Meanwhile, the glass transition temperature of a homopolymer of a monomer can also be determined using the method specifically described in JP 2007-51271 A.

[0069] Fox's formula: 1 / (273+Tg)=Σ[Wi / (273+Tgi)]

[0070] The hydrogen bond term δH of the Hansen solubility parameter (HSP) of the base polymer is preferably 3.5 or more, preferably 3.8 or more, preferably 4.0 or more, from the viewpoint of ensuring the alcohol affinity of the PSA sheet 10. The hydrogen bond term δH of the HSP of the base polymer is preferably 4.9 or less, preferably 4.7 or less, preferably 4.6 or less, from the viewpoint of suppressing the hydrophilicity of the PSA sheet 10. The hydrogen bond term δH of the HSP of the base polymer is preferably 3.5 to 4.9, preferably 3.8 to 4.7, preferably 4.0 to 4.6, from the viewpoint of simultaneously ensuring the alcohol affinity and suppressing the hydrophilicity of the PSA sheet 10. Methods for adjusting the δH of the base polymer include, for example, adjusting the monomer composition of the base polymer.

[0071] The Hansen solubility parameter (HSP) is expressed by the following formula (1), where δH is the hydrogen bond term representing the energy derived from intermolecular hydrogen bonding forces, δD is the dispersion term representing the energy derived from intermolecular dispersion forces, and δP is the polarization term representing the energy derived from intermolecular polar forces.

[0072] HSP = (δD ２ +δP ２ +δH ２ ) １／２ (1)

[0073] The δH of a polymer is determined by the ratio of the monomers m that form the polymer. ｉ Molar fraction x ｉ and the monomer m ｉ The hydrogen bond term δh ｉ From this, it can be calculated by the following formula (2). The hydrogen bond term δh of the monomer can be calculated, for example, by computer software HSPiP (Hansen Solubility Parameters in Practice). The specific method for calculating δH is as described below in the examples.

[0074] δH=Σ x ｉ ×δh ｉ (2)

[0075] The polarization term δP of the HSP of the base polymer is preferably 2.5 or more, preferably 2.8 or more, preferably 3.0 or more, from the viewpoint of ensuring the alcohol affinity of the PSA sheet 10. The polarization term δP of the HSP of the base polymer is preferably 3.7 or less, preferably 3.5 or less, preferably 3.3 or less, from the viewpoint of suppressing the hydrophilicity of the PSA sheet 10. The polarization term δP of the HSP of the base polymer is preferably 2.5 to 3.7, preferably 2.8 to 3.5, preferably 3.0 to 3.3, from the viewpoint of simultaneously ensuring the alcohol affinity of the PSA sheet 10 and suppressing the hydrophilicity. An example of a method for adjusting the δP of the base polymer is adjusting the monomer composition of the base polymer. The δP of a polymer is determined by the ratio of the monomer m forming the polymer to the total monomer m. ｉ Molar fraction x ｉ and the monomer m ｉ Polarization term δp ｉ From this, it can be calculated by the following formula (3): The polarization term δp of the monomer can be calculated, for example, by computer software HSPiP (Hansen Solubility Parameters in Practice). The specific method for calculating δP is as described later in the examples.

[0076] δP = Σ x ｉ ×δp ｉ (3)

[0077] The base polymer content in the pressure-sensitive adhesive sheet 10 is preferably 80 to 99.9% by mass, more preferably 85 to 99.5% by mass, and even more preferably 90 to 99.0% by mass. The base polymer content in the pressure-sensitive adhesive sheet 10 is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more. When the base polymer content is equal to or greater than the above-mentioned lower limit, basic properties such as adhesiveness can be appropriately exhibited in the pressure-sensitive adhesive sheet 10. The base polymer content in the pressure-sensitive adhesive sheet 10 is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99.0% by mass or less. When the base polymer content is equal to or less than the above-mentioned upper limit, the oligomer content described below can be ensured.

[0078] The pressure-sensitive adhesive sheet 10 may contain an oligomer. Examples of oligomers include hydrophilic oligomers and hydrophobic oligomers. The hydrophilic oligomer refers to an oligomer formed as a polymer of a monomer component containing 3% or more by mass of a hydrophilic monomer. The hydrophobic oligomer refers to an oligomer formed as a polymer of a monomer component containing less than 3% by mass of a hydrophilic monomer. The weight-average molecular weight of the oligomer is, for example, 1,000 or more and 30,000 or less. The weight-average molecular weight of the oligomer is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene.

[0079] When the base polymer is an acrylic polymer, the oligomer is preferably an acrylic oligomer. That is, the hydrophilic oligomer is preferably a hydrophilic acrylic oligomer. The hydrophobic oligomer is preferably a hydrophobic acrylic oligomer. The acrylic oligomer is an oligomer as a polymer of a monomer component containing 50% by mass or more of a (meth)acrylic acid alkyl ester.

[0080] The hydrophilic acrylic oligomer is preferably a polymer of monomer components including a (meth)acrylic acid alkyl ester having a chain alkyl group (chain alkyl (meth)acrylate), a (meth)acrylic acid alkyl ester having an alicyclic alkyl group (alicyclic alkyl (meth)acrylate), and a hydrophilic monomer. Specific examples of the (meth)acrylic acid alkyl ester include the (meth)acrylic acid alkyl esters described above as monomer components of the acrylic polymer. Specific examples of the hydrophilic monomer include hydroxy group-containing monomers and carboxy group-containing monomers. Specific examples of the hydroxy group-containing monomers and carboxy group-containing monomers include the hydroxy group-containing monomers and carboxy group-containing monomers described above as monomer components of the acrylic polymer.

[0081] The linear alkyl (meth)acrylate is preferably methyl methacrylate (MMA) because it has a high glass transition temperature and relatively high compatibility with the base polymer. The alicyclic alkyl (meth)acrylate is preferably at least one selected from the group consisting of dicyclopentanyl acrylate (DCPA), dicyclopentanyl methacrylate (DCPMA), cyclohexyl acrylate (CHA), and cyclohexyl methacrylate (CHMA). The hydrophilic monomer is preferably at least one selected from the group consisting of 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl methacrylate (HPMA), and 4-hydroxybutyl methacrylate (HBMA). That is, the acrylic oligomer is preferably a polymer of monomer components including at least one selected from the group consisting of DCPA, DCPMA, CHA, and CHMA, at least one selected from the group consisting of HEMA, HPMA, and HBMA, and MMA.

[0082] The proportion of alicyclic alkyl (meth)acrylate in the monomer component of the hydrophilic acrylic oligomer is preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and preferably 80% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. Having the proportion of alicyclic alkyl (meth)acrylate at or above the above-mentioned lower limit helps to ensure the adhesive strength and cohesive strength of the pressure-sensitive adhesive sheet 10. Having the proportion of alicyclic alkyl (meth)acrylate at or below the above-mentioned upper limit helps to ensure compatibility between the acrylic polymer and the hydrophilic oligomer in the pressure-sensitive adhesive sheet 10. The proportion of chain alkyl (meth)acrylate in the monomer component of the hydrophilic acrylic oligomer is preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and preferably 80% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. Having the proportion of the chain alkyl (meth)acrylate equal to or greater than the above-mentioned lower limit helps to ensure compatibility between the acrylic polymer and the hydrophilic oligomer in the pressure-sensitive adhesive sheet 10. Having the proportion of the chain alkyl (meth)acrylate equal to or less than the above-mentioned upper limit helps to ensure the adhesive strength and cohesive strength of the pressure-sensitive adhesive sheet 10. The proportion of the hydrophilic monomer in the monomer components of the hydrophilic acrylic oligomer is preferably 6% by mass or more, more preferably 8% by mass or more, even more preferably 10% by mass or more, and is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 12% by mass or less. When the proportion of the hydrophilic monomer is equal to or greater than the above-mentioned lower limit, the adhesive strength and cohesive strength of the pressure-sensitive adhesive sheet 10 can be ensured. When the proportion of the hydrophilic monomer is equal to or less than the above-mentioned upper limit, the compatibility between the acrylic polymer and the hydrophilic oligomer in the pressure-sensitive adhesive sheet 10 can be ensured.

[0083] The hydrophilic acrylic oligomer can be obtained by polymerizing the monomer components of the acrylic oligomer (the same applies to the hydrophobic acrylic oligomer described below). Polymerization methods include, for example, solution polymerization, active energy ray polymerization (e.g., UV polymerization), bulk polymerization, and emulsion polymerization. In the polymerization of the acrylic oligomer, a polymerization initiator may be used, and a chain transfer agent may be used for the purpose of adjusting the molecular weight.

[0084] The content of the hydrophilic oligomer in the pressure-sensitive adhesive sheet 10 is preferably 0.1 to 3 parts by mass, more preferably 0.3 to 2 parts by mass, and even more preferably 0.4 to 1.2 parts by mass, per 100 parts by mass of the base polymer. The content of the hydrophilic oligomer in the pressure-sensitive adhesive sheet 10 is preferably 0.1 part by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.4 parts by mass or more. When the content of the hydrophilic oligomer is equal to or greater than the above-mentioned lower limit, the adhesive strength of the pressure-sensitive adhesive sheet 10 (particularly adhesive strength in a high-humidity environment) can be increased. The content of the hydrophilic oligomer in the pressure-sensitive adhesive sheet 10 is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1.2 parts by mass or less, per 100 parts by mass of the base polymer. When the content of the hydrophilic oligomer is equal to or less than the above-mentioned upper limit, the transparency of the pressure-sensitive adhesive sheet 10 can be ensured. When the content of the oligomer in the pressure-sensitive adhesive sheet 10 is too high, the compatibility of the oligomer decreases, which tends to increase haze and reduce transparency.

[0085] The hydrophobic acrylic oligomer is preferably a polymer of monomer components including a chain alkyl (meth)acrylate and an alicyclic alkyl (meth)acrylate. The chain alkyl (meth)acrylate is preferably MMA because it has a high glass transition temperature and relatively high compatibility with the base polymer. The alicyclic alkyl (meth)acrylate is preferably at least one selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate. That is, the acrylic oligomer is preferably a polymer of monomer components including MMA and one or more selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate.

[0086] The proportion of alicyclic alkyl (meth)acrylate in the monomer component of the hydrophobic acrylic oligomer is preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and preferably 90% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. Having the proportion of alicyclic alkyl (meth)acrylate at or above the above-mentioned lower limit helps to ensure the adhesive strength and cohesive strength of the pressure-sensitive adhesive sheet 10. Having the proportion of alicyclic alkyl (meth)acrylate at or below the above-mentioned upper limit helps to ensure compatibility between the acrylic polymer and the hydrophobic oligomer in the pressure-sensitive adhesive sheet 10. The proportion of chain alkyl (meth)acrylate in the monomer component of the hydrophobic acrylic oligomer is preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and preferably 90% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. Having the proportion of the chain alkyl (meth)acrylate equal to or greater than the above-mentioned lower limit helps to ensure compatibility between the acrylic polymer and the hydrophobic oligomer in the pressure-sensitive adhesive sheet 10. Having the proportion of the chain alkyl (meth)acrylate equal to or less than the above-mentioned upper limit helps to ensure the adhesive strength and cohesive strength of the pressure-sensitive adhesive sheet 10.

[0087] The content of the hydrophobic oligomer in the pressure-sensitive adhesive sheet 10 is preferably 0.1 to 3 parts by mass, more preferably 0.3 to 2 parts by mass, and even more preferably 0.4 to 1.2 parts by mass, per 100 parts by mass of the base polymer. The content of the hydrophobic oligomer in the pressure-sensitive adhesive sheet 10 is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and even more preferably 0.4 part by mass or more. When the content of the hydrophobic oligomer is equal to or greater than the above-mentioned lower limit, the adhesive strength of the pressure-sensitive adhesive sheet 10 can be increased. The content of the hydrophobic oligomer in the pressure-sensitive adhesive sheet 10 is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1.2 parts by mass or less, per 100 parts by mass of the base polymer. When the content of the hydrophobic oligomer is equal to or less than the above-mentioned upper limit, the transparency of the pressure-sensitive adhesive sheet 10 can be ensured.

[0088] The total content of the hydrophilic oligomer and hydrophobic oligomer in the pressure-sensitive adhesive sheet 10 is preferably 0.2 parts by mass or more, more preferably 0.6 parts by mass or more, even more preferably 0.8 parts by mass or more, and is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less, relative to 100 parts by mass of the base polymer. When the total content of the oligomers is equal to or greater than the above-mentioned lower limit, the adhesive strength of the pressure-sensitive adhesive sheet 10 can be increased. When the total content of the oligomers is equal to or less than the above-mentioned upper limit, the transparency of the pressure-sensitive adhesive sheet 10 can be ensured.

[0089] The pressure-sensitive adhesive sheet 10 may contain other components, such as a silane coupling agent, an ultraviolet absorber, an antioxidant, a surfactant, and a rust inhibitor.

[0090] Examples of silane coupling agents include silane coupling agents containing an epoxy group. Examples of epoxy group-containing silane coupling agents include 3-glycidoxydialkyldialkoxysilane and 3-glycidoxyalkyltrialkoxysilane. Examples of 3-glycidoxydialkyldialkoxysilane include 3-glycidoxypropylmethyldimethoxysilane and 3-glycidoxypropylmethyldiethoxysilane. Examples of 3-glycidoxyalkyltrialkoxysilane include 3-glycidoxypropyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane. As the silane coupling agent, preferably 3-glycidoxyalkyltrialkoxysilane is used, and more preferably 3-glycidoxypropyltrimethoxysilane is used. The silane coupling agents may be used alone or in combination of two or more. The proportion of the silane coupling agent in the adhesive sheet 10 is preferably 0.1 mass% or more, more preferably 0.2 mass% or more, even more preferably 0.3 mass% or more, from the viewpoint of suppressing the adhesive sheet 10's adhesion to glass and exhibiting good alcohol peelability, and is also preferably 3 mass% or less, more preferably 2 mass% or less, even more preferably 1 mass% or less.

[0091] The pressure-sensitive adhesive sheet 10 preferably does not contain a surfactant. From the viewpoint of ensuring the adhesive strength of the pressure-sensitive adhesive sheet 10 in a high-humidity environment, the content of the surfactant in the pressure-sensitive adhesive sheet 10 is preferably 0.3 mass % or less, more preferably 0.2 mass % or less, even more preferably 0.1 mass % or less, and particularly preferably 0.0 mass %.

[0092] Examples of the release liner L1 include a release liner having a release treatment layer on the surface of the liner substrate, and a release liner formed from a low-adhesion material. Examples of the liner substrate include resin films and paper. Examples of resins for resin films include polyester resins and polycarbonate resins. Examples of polyester resins include polyethylene terephthalate (PET) and polybutylene terephthalate. The release layer can be formed by surface treating the liner substrate with a release agent. Examples of release agents include silicone release agents, long-chain alkyl release agents, and fluorine release agents. Examples of low-adhesion materials include polyolefin resins and fluorine-based polymers. Examples of polyolefin resins include polyethylene, polypropylene, and cycloolefin polymer (COP). Examples of fluorine-based polymers include polytetrafluoroethylene.

[0093] Examples of the release liner L2 include a release liner having a release-treated layer on the surface of a liner substrate and a release liner made of a low-adhesion material. Specific examples of the release liner L2 are the same as those described above for the release liner L1.

[0094] The pressure-sensitive adhesive sheet 10 can be produced, for example, as follows.

[0095] First, a prepolymer composition is prepared. Specifically, a mixture (liquid) containing the monofunctional monomer for forming the base polymer and a photopolymerization initiator is prepared. Next, the mixture is irradiated with ultraviolet light to photopolymerize a portion of the monofunctional monomer in the mixture, thereby obtaining a prepolymer composition. Examples of light sources for ultraviolet irradiation include ultraviolet LED lights, black light lamps, high-pressure mercury lamps, and metal halide lamps. In the ultraviolet irradiation, the illuminance is, for example, 5 to 200 mW / cm. ２ The cumulative irradiation amount is, for example, 100 to 5000 mJ / cm ２ The ultraviolet irradiation is preferably continued until the viscosity of the composition reaches approximately 15 to 25 Pa·s. This viscosity is measured using a Brookfield viscometer with a No. 5 rotor at a rotor rotation speed of 10 rpm and a temperature of 30°C. The prepolymer composition contains a photopolymerized product of a monofunctional monomer and an unreacted monofunctional monomer (residual monomer). The prepolymer composition does not contain a solvent.

[0096] Next, a multifunctional polymerizable compound (crosslinking agent) and, if necessary, other components are added to the prepolymer composition to prepare a pressure-sensitive adhesive composition. Examples of other components include an oligomer, an additional photopolymerization initiator, a silane coupling agent, an antioxidant, and a rust inhibitor. This pressure-sensitive adhesive composition does not contain a solvent. That is, the pressure-sensitive adhesive composition prepared in this step is a solventless pressure-sensitive adhesive composition.

[0097] Next, a pressure-sensitive adhesive composition is applied to release liner L1 to form a coating film, and then release liner L2 is laminated onto the coating film on release liner L1. Examples of methods for applying the pressure-sensitive adhesive composition include roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, and die coating.

[0098] Next, the coating film between the release liners L1 and L2 is irradiated with ultraviolet light to photocure it, forming a pressure-sensitive adhesive layer. The ultraviolet irradiation causes a polymerization reaction in the coating film in a reaction system containing the residual monomer and the polyfunctional polymerizable compound, forming a first photopolymerized polymer having a photocrosslinked structure. The pressure-sensitive adhesive layer may then be dried by heating. The drying temperature is, for example, 80°C to 150°C. The drying time is, for example, 30 seconds to 10 minutes. The drying process allows the unreacted monomer in the pressure-sensitive adhesive layer to be volatilized and removed.

[0099] In this manner, it is possible to manufacture a pressure-sensitive adhesive sheet 10 in which the adhesive surfaces 11, 12 are covered and protected by the release liners L1, L2. The release liners L1, L2 are peeled off from the pressure-sensitive adhesive sheet 10 as needed when using the pressure-sensitive adhesive sheet 10.

[0100] The pressure-sensitive adhesive sheet 10 can be formed from a solvent-free pressure-sensitive adhesive composition. Such a pressure-sensitive adhesive sheet 10 is suitable for reducing the environmental load. That is, a pressure-sensitive adhesive sheet 10 formed from a solvent-free pressure-sensitive adhesive composition is environmentally friendly and preferable from the viewpoint of sustainable development.

[0101] The thickness of the pressure-sensitive adhesive sheet 10 is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more, from the viewpoint of ensuring sufficient adhesiveness to the adherend. The thickness of the pressure-sensitive adhesive sheet 10 is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 100 μm or less, from the viewpoint of ease of handling and thinning of the pressure-sensitive adhesive sheet 10. The thickness of the pressure-sensitive adhesive sheet 10 is preferably 10 to 300 μm, more preferably 20 to 200 μm, and even more preferably 30 to 100 μm, from the viewpoint of achieving both the above-mentioned adhesiveness and the above-mentioned ease of handling and thinning.

[0102] The total light transmittance of the pressure-sensitive adhesive sheet 10 is preferably 90% or more, more preferably 95% or more, and is, for example, 100% or less, from the viewpoint of ensuring the transparency of the pressure-sensitive adhesive sheet 10. The total light transmittance can be measured in accordance with JIS K 7375 (2008).

[0103] 4A to 4C show an example of how the adhesive sheet 10 is used.

[0104] 4A , in this method, first, the pressure-sensitive adhesive sheet 10 is bonded to one surface of a member 31 (first adherend) in the thickness direction H (bonding step). Examples of the member 31 include a pixel panel and a polarizing film in a display panel. In this step, the pressure-sensitive adhesive sheet 10 for bonding to another member is provided on the member 31.

[0105] 4B, the member 31 and a member 32 (second adherend) are joined via the pressure-sensitive adhesive sheet 10 on the member 31 (joining step). An example of the member 32 is a cover film for a display panel.

[0106] Next, as shown in Figure 4C, the adhesive sheet 10 between the members 31 and 32 is aged (aging process). This process increases the bonding strength between the adhesive sheet 10 and the members 31 and 32. The aging temperature is, for example, 20°C to 160°C. The aging time is, for example, 1 minute to 21 days. When aging is performed by autoclave treatment (heat and pressure treatment), the temperature is, for example, 30°C to 80°C, the pressure is, for example, 0.1 to 0.8 MPa, and the treatment time is, for example, 15 minutes or more.

[0107] According to the pressure-sensitive adhesive sheet 10, after the bonding step or the aging step, the bonded state between the members 31 and 32 can be easily released using alcohol as needed (alcohol rework). Specifically, this is as follows.

[0108] By infiltrating alcohol into the interface between member 31 and adhesive sheet 10, the adhesive strength of the adhesive sheet 10 to member 31 is reduced, and then member 32 with adhesive sheet 10 attached can be easily separated from member 31. Thereafter, for example, a replacement member 32 with adhesive sheet 10 can be bonded to member 31 via that adhesive sheet 10. Alternatively, by infiltrating alcohol into the interface between member 32 and adhesive sheet 10, the adhesive strength of the adhesive sheet 10 to member 32 is reduced, and then member 31 with adhesive sheet 10 can be easily separated from member 32. Thereafter, for example, a replacement member 31 with adhesive sheet 10 can be bonded to member 32 via that adhesive sheet 10. Examples of alcohol include methanol, ethanol, propanol, and butanol.

[0109] The adhesive sheet 10 had an adhesive strength Fa in the first ethanol peeling test. １ Since the thickness is 3.0 / 25 mm or less, the above-mentioned alcohol rework is possible.

[0110] The pressure-sensitive adhesive sheet 10 is, for example, an optical pressure-sensitive adhesive sheet that is placed at a light-transmitting portion of a display panel. Examples of display panels include liquid crystal panels and organic EL panels. Display panels have a laminated structure that includes elements such as a pixel panel, a polarizing film, a touch panel, and a cover film. The pressure-sensitive adhesive sheet 10 is used, for example, to bond elements included in the laminated structure during the manufacturing process of the display panel.

[0111] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples. The specific numerical values ​​of the blending amounts (contents), physical property values, parameters, etc. described below can be substituted with the upper limits (numerical values ​​defined as "equal to or less than") or lower limits (numerical values ​​defined as "equal to or more than") of the corresponding blending amounts (contents), physical property values, parameters, etc. described in the above-mentioned "Description of the Invention."

[0112] <Oligomer M １Preparation of acrylic oligomer (oligomer M)> First, in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, a mixture containing 60 parts by mass of dicyclopentanyl methacrylate (DCPMA), 40 parts by mass of methyl methacrylate (MMA), 3.5 parts by mass of α-thioglycerol as a chain transfer agent, and 100 parts by mass of toluene as a polymerization solvent was stirred at 70°C for 1 hour under a nitrogen atmosphere. Next, 0.2 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was added to the mixture to prepare a reaction solution, which was reacted under a nitrogen atmosphere at 70°C for 2 hours and then at 80°C for 2 hours (polymerization reaction). Next, the reaction solution was heated at 130°C to volatilize and remove the toluene, chain transfer agent, and unreacted monomer. This produced a solid acrylic oligomer (oligomer M) １ ) was obtained. １ The weight average molecular weight of oligomer M was 5,100 and the glass transition temperature was 130°C. １ is a hydrophobic oligomer.

[0113] <Oligomer M ２ Preparation of acrylic oligomer (oligomer M)> First, in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, a mixture containing 45 parts by mass of DCPMA, 45 parts by mass of MMA, 10 parts by mass of 2-hydroxyethyl methacrylate (HEMA), 3.5 parts by mass of α-thioglycerol as a chain transfer agent, and 100 parts by mass of toluene as a polymerization solvent was stirred at 70°C for 1 hour under a nitrogen atmosphere. Next, 0.2 parts by mass of AIBN as a thermal polymerization initiator was added to the mixture to prepare a reaction solution, which was reacted under a nitrogen atmosphere at 70°C for 2 hours and then at 80°C for 2 hours (polymerization reaction). Next, the reaction solution was heated at 130°C to volatilize and remove the toluene, chain transfer agent, and unreacted monomer. This produced a solid acrylic oligomer (oligomer M) ２ ) was obtained. ２ The weight average molecular weight of oligomer M was 5,300 and the glass transition temperature was 115°C. ２ is a hydrophilic oligomer.

[0114] Example 1 Preparation of Prepolymer Composition First, 58 parts by weight of 2-ethylhexyl acrylate (2EHA), 39 parts by weight of acrylic laurate (LA), 3 parts by weight of 4-hydroxybutyl acrylate (4HBA), 0.05 parts by weight of a first photopolymerization initiator (trade name "Omnirad 184", 1-hydroxycyclohexyl phenyl ketone, manufactured by IGM Resins), and 0.05 parts by weight of a second photopolymerization initiator (trade name "Omnirad 651", 2,2-dimethoxy-2-phenylacetophenone, manufactured by IGM Resins) were mixed in a flask, and the mixture was then irradiated with ultraviolet light under a nitrogen atmosphere to polymerize a portion of the monomer components in the mixture, thereby obtaining a prepolymer composition with a polymerization rate of approximately 10%. This prepolymer composition was a partially polymerized product containing a photopolymerized product (photopolymerized polymer P1a) and unreacted monomer components (residual monomers).

[0115] <Preparation of Pressure-Sensitive Adhesive Composition> Next, 100 parts by mass of the prepolymer composition and oligomer M １ 1.0 part by mass of the acrylic acid acrylate (acrylic acid acrylate), 0.06 part by mass of dipentaerythritol hexaacrylate (DPHA) (trade name "KAYARAD DPHA" manufactured by Nippon Kayaku Co., Ltd.) as a polyfunctional polymerizable compound, and 0.3 part by mass of a silane coupling agent (trade name "KBM-403" manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed together to obtain a pressure-sensitive adhesive composition C1.

[0116] <Preparation of Pressure-Sensitive Adhesive Sheet> Next, the PSA composition C1 was applied to the release-treated surface of a first release liner (trade name "Diafoil MRF", thickness 38 μm, manufactured by Mitsubishi Chemical Corporation) having a release-treated surface on one side to form a coating film. Next, the release-treated surface of a second release liner (trade name "Diafoil MRN", thickness 38 μm, manufactured by Mitsubishi Chemical Corporation) having a release-treated surface on one side was laminated onto the coating film on the first release liner. Next, the coating film between the release liners was irradiated with ultraviolet light from the second release liner side, and the coating film was photocured to form a 50 μm thick PSA layer (ultraviolet light irradiation step). For ultraviolet light irradiation, a black light lamp (manufactured by Toshiba) was used as the light source, and the illuminance was 5.0 mW / cm. ２ The cumulative irradiation dose was 1500 mJ / cm ２In the ultraviolet irradiation step, a photopolymerization reaction proceeds in the coating film in a reaction system containing the residual monomer and the polyfunctional polymerizable compound, forming a photopolymerized polymer P1b having a photocrosslinked structure. Furthermore, since the photopolymerization reaction proceeds around the photopolymerized polymer P1a, the photopolymerized polymer P1b is formed around the photopolymerized polymer P1a. The pressure-sensitive adhesive layer formed in this step contains such photopolymerized polymer P1a and photopolymerized polymer P1b as base polymers.

[0117] Next, after peeling the first release liner from the adhesive layer, the adhesive layer on the second release liner was dried in a hot air oven at 130°C for 3 minutes. This volatilized and removed unreacted monomers in the adhesive layer. After cooling at room temperature, the release-treated surface of a third release liner (product name "Diafoil MRF", thickness 38 μm, manufactured by Mitsubishi Chemical Corporation) having a release-treated surface on one side was bonded to the adhesive layer on the second release liner.

[0118] In this manner, a pressure-sensitive adhesive sheet with release liner of Example 1 (second release liner / pressure-sensitive adhesive sheet (thickness 50 μm) / third release liner) was prepared.

[0119] [Example 2] A release-liner-attached PSA sheet of Example 2 was produced in the same manner as the release-liner-attached PSA sheet of Example 1, except for the following: In preparing the PSA composition, oligomer M １ The amount of oligomer M ２ 0.5 parts by mass was blended.

[0120] Example 3 A release-lined PSA sheet of Example 3 was produced in the same manner as the release-lined PSA sheet of Example 1, except for the following: In preparing the prepolymer composition, the blend amount of 2EHA was 56 parts by mass, and 2 parts by mass of N-vinyl-2-pyrrolidone (NVP) was blended.

[0121] Example 4 A release-liner-attached PSA sheet of Example 4 was produced in the same manner as the release-liner-attached PSA sheet of Example 1, except for the following: In preparing the prepolymer composition, the blending amount of 2EHA was set to 52 parts by mass, and the blending amount of 4HBA was set to 9 parts by mass.

[0122] Example 5 A release-lined PSA sheet of Example 5 was produced in the same manner as the release-lined PSA sheet of Example 1, except for the following: The composition of the prepolymer composition was changed to the composition shown in Table 1. In the preparation of the PSA composition, oligomer M １ Instead of oligomer M ２ 1.0 part by mass of DPHA was blended, 0.08 part by mass of 1,9-nonanediol diacrylate (NDDA) (trade name "Viscoat #260", manufactured by Osaka Organic Chemical Industry Co., Ltd.) was blended in place of DPHA, and 0.1 part by mass of a first additional photopolymerization initiator (Omnirad 651) was blended.

[0123] Comparative Example 1: In the preparation of a prepolymer composition, oligomer M １ A release-liner-attached PSA sheet of Comparative Example 1 was prepared in the same manner as the release-liner-attached PSA sheet of Example 1, except that no compound was added.

[0124] Comparative Example 2 Preparation of Prepolymer Composition In a flask, a monomer mixture of 70 parts by mass of n-octyl acrylate (NOAA), 20 parts by mass of n-butyl acrylate (BA), 8 parts by mass of 4HBA, and 2 parts by mass of NVP was mixed with 0.05 parts by mass of a first photopolymerization initiator (Omnirad 184) and 0.05 parts by mass of a third photopolymerization initiator (trade name "Omnirad 819", bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, manufactured by IGM Resins). The mixture was then irradiated with ultraviolet light in a nitrogen atmosphere to polymerize a portion of the monomer components in the mixture, thereby obtaining a prepolymer composition with a polymerization rate of approximately 10%.

[0125] <Preparation of Pressure-Sensitive Adhesive Composition> Next, 100 parts by mass of the prepolymer composition and oligomer M １ 0.5 parts by mass of oligomer M ２0.5 parts by mass of the acrylic acid acrylate copolymer, 0.01 parts by mass of DPHA (KAYARAD DPHA) as a polyfunctional polymerizable compound, 0.3 parts by mass of a first reactive surfactant (trade name "ACRYT 8WX-046-NS", manufactured by Taisei Fine Chemical Co., Ltd.), 0.1 parts by mass of a non-reactive surfactant (trade name "Rheodol TW-L120", manufactured by Kao Corporation), and 0.04 parts by mass of a second additional photopolymerization initiator (Omnirad 819) were mixed together to prepare a pressure-sensitive adhesive composition C2.

[0126] <Preparation of Pressure-Sensitive Adhesive Sheet> A 50 μm thick pressure-sensitive adhesive layer was formed in the same manner as described above for Example 1, except that pressure-sensitive adhesive composition C2 was used instead of pressure-sensitive adhesive composition C1, and a pressure-sensitive adhesive sheet with release liner of Comparative Example 2 (second release liner / pressure-sensitive adhesive sheet (thickness 50 μm) / third release liner) was prepared.

[0127] Comparative Example 3 A release-liner-attached PSA sheet of Comparative Example 3 was produced in the same manner as the release-liner-attached PSA sheet of Comparative Example 2, except for the following: In preparing the PSA composition, the amount of DPHA blended was 0.02 parts by mass, no first reactive surfactant and no non-reactive surfactant were blended, and 0.3 parts by mass of a second reactive surfactant (trade name "Aqualon KH-10", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 0.1 parts by mass of a third reactive surfactant (trade name "Aminoion RE3000MA", manufactured by Nippon Nyukazai Co., Ltd.) were blended.

[0128] Comparative Example 4 A release-liner-attached PSA sheet of Comparative Example 4 was produced in the same manner as the release-liner-attached PSA sheet of Comparative Example 2, except for the following: In the preparation of the PSA composition, oligomer M １ The blending amount of oligomer M ２ The amount of DPHA was 0.045 parts by mass, and the first reactive surfactant and the non-reactive surfactant were not added.

[0129] Comparative Example 5 A release-liner-attached PSA sheet of Comparative Example 5 was produced in the same manner as the release-liner-attached PSA sheet of Comparative Example 2, except for the following: In the preparation of the PSA composition, oligomer M １ The blending amount of oligomer M ２was not blended, the blending amount of DPHA was 0.11 parts by mass, 0.5 parts by mass of a silane coupling agent (KBM-403) was blended, and the blending amount of a second additional photopolymerization initiator (Omnirad 819) was 0.02 parts by mass.

[0130] <Weight average molecular weight of oligomer> Oligomer M １ ,M ２ The weight average molecular weight (Mw) of each of the above was measured by gel permeation chromatography (GPC) under the following measurement conditions and calculated as a polystyrene equivalent value. A GPC measuring device (product name "HLC-8120GPC", manufactured by Tosoh Corporation) was used for the measurement. The sample solution was prepared as follows. First, a dimethylformamide (DMF) solution (salt added) with a sample concentration of 0.20% by mass was prepared using the acrylic oligomer as a sample, and the DMF solution was then left to stand for 20 hours. Next, the DMF solution was filtered through a membrane filter with an average pore size of 0.45 μm, and the filtrate was obtained as a sample solution for molecular weight measurement.

[0131] [GPC measurement conditions] Column: SuperAWM-H + SuperAW4000 + SuperAW2500, each TSKgel (manufactured by Tosoh) Column temperature: 40°C Eluent: DMF solution (salt added) Flow rate: 0.4 mL / min Sample injection amount: 40 μL Standard sample: polystyrene (manufactured by Agilent) Detector: differential refractometer (RI)

[0132] <HSP> The hydrogen bond parameter δH, dispersion parameter δD, and polarization parameter δP of the Hansen solubility parameter (HSP) were determined for each acrylic polymer used in the examples and comparative examples. Specifically, they are as follows.

[0133] Regarding the hydrogen bond term δH, first, the hydrogen bond parameters m of each monomer forming the acrylic polymer are calculated using computer software HSPiP (Hansen Solubility Parameters in Practice). ｉ Regarding the hydrogen bond term of HSP (δh ｉ Next, the monomer m ｉ Molar fraction x ｉ and the monomer mｉ The hydrogen bond term δh ｉ From this, the hydrogen bond parameter (δH) of the acrylic polymer was calculated using the following formula (2).

[0134] δH=Σ x ｉ ×δh ｉ (2)

[0135] Similarly, for the dispersion term δD, the computer software HSPiP is used to calculate the dispersion term m ｉ Regarding the dispersion term of HSP (δd ｉ ) and the monomer m ｉ Molar fraction x ｉ and the monomer m ｉ Dispersion term δd ｉ The dispersion term (δD) of the acrylic polymer was calculated from the above. Similarly, the polarization term δP was calculated by using the computer software HSPiP to calculate the dispersion term (δD) of the acrylic polymer. ｉ Regarding the polarization term of HSP (δp ｉ ) and the monomer m ｉ Molar fraction x ｉ and the monomer m ｉ Polarization term δp ｉ The hydrogen bond term δH, dispersion term δD, and polarization term δP of the acrylic polymer are shown in Tables 1 and 2.

[0136] <Initial Room Temperature Peel Test> An initial room temperature peel test was carried out on each of the pressure-sensitive adhesive sheets of the Examples and Comparative Examples to measure the adhesive strength Fn １ Specifically, the following was measured:

[0137] Preparation Step: First, the third release liner was peeled from the pressure-sensitive adhesive sheet with release liner (second release liner / pressure-sensitive adhesive sheet / third release liner). Next, the exposed pressure-sensitive adhesive sheet was bonded to a polyethylene terephthalate (PET) film (product name "Lumirror S10", 50 μm thick, manufactured by Toray Industries) whose surface had been plasma-treated. This resulted in a laminated film. For the plasma treatment, a plasma irradiation device (product name "AP-TO5", manufactured by Sekisui Kogyo Co., Ltd.) was used, with a voltage of 160 V, a frequency of 10 kHz, and a treatment speed of 5000 mm / min. For the bonding, the pressure-sensitive adhesive sheet was pressed onto the PET film by rolling it back and forth once with a 2 kg hand roller in an environment of 25°C. Next, a laminated film piece measuring 25 mm wide x 100 mm long was cut out from the laminated film. This laminated film comprised a PET film, a pressure-sensitive adhesive sheet piece, and a second release liner, in that order in the thickness direction. Next, the second release liner was peeled off from the adhesive sheet piece on the PET film, and the exposed adhesive sheet piece (25 mm wide x 100 mm long) was then bonded to the tin surface of an alkali glass plate prepared by the float method to obtain a laminate.

[0138] Heat and pressure step: Next, the laminate was subjected to a heat and pressure treatment at 50° C., 0.5 MPa and for 15 minutes, thereby pressure-bonding the adhesive sheet piece to the alkali glass plate.

[0139] Resting Step: Next, the laminate was allowed to rest at room temperature for 72 hours.

[0140] Measurement step: Next, a 180° peel test was performed to peel the adhesive sheet piece from the alkali glass plate in the laminate, and the force required for peeling (peel force) was measured. For this measurement, a tensile tester (product name "Autograph AG-50NX plus" manufactured by Shimadzu Corporation) was used. Specifically, in this measurement, under conditions (first conditions) of 25°C, relative humidity 50%, peel angle 180°, and tensile speed 300 mm / min, one end of the adhesive sheet piece on the alkali glass plate in the longitudinal direction was pulled to peel the adhesive sheet piece from the alkali glass plate, and the peel force was measured. The peel length (total length) was set to 50 mm, and the average value of the peel force measured between peel lengths of 10 mm and 40 mm was taken as the adhesive strength.

[0141] The adhesive force measured in the measurement step of the initial room temperature peel test is called adhesive force Fn １ (N / 25mm) are shown in Tables 1 and 2.

[0142] <Room Temperature Peel Test After Storage> A room temperature peel test was carried out on each of the pressure-sensitive adhesive sheets of the Examples and Comparative Examples after storage to measure the adhesive strength Fn ２ The room temperature peel test after storage was the same as the initial room temperature peel test, except that the laminate was left to stand at 50° C. for 168 hours in the standing step.

[0143] In the measurement step of the room temperature peel test after storage, the peel length (total length) was set to 50 mm, and the average value of the peel force measured between peel lengths of 10 mm and 40 mm was taken as the adhesive force. The adhesive force measured in the measurement step of the room temperature peel test after storage was taken as the adhesive force Fn ２ (N / 25mm) are shown in Tables 1 and 2.

[0144] <First Ethanol Peeling Test> The first ethanol peeling test was carried out on each of the pressure-sensitive adhesive sheets of the Examples and Comparative Examples to measure the adhesive strength Fa. １was measured. The first ethanol peeling test was the same as the initial room temperature peeling test, except for the following: In the standing step, the laminate was stood at 50°C for 168 hours. After the standing step and before the measurement step, an ethanol supplying step was carried out. In the ethanol supplying step, 10 μL of ethanol was supplied onto the alkali glass plate of the laminate so that the ethanol was in contact with one end of the adhesive sheet piece in the longitudinal direction at the interface between the alkali glass plate and the adhesive sheet piece.

[0145] In the measurement step of the first ethanol peeling test, the peel length d when the peel force begins to stabilize during the peeling process of the adhesive sheet piece is １ and peel length d １ The peel length d when the peel force increases by 10% compared to the peel force at ２ The peel length d １ From peel length d ２ The average value of the peel strengths measured up to this point was taken as the adhesive strength. The adhesive strength measured in the measurement step of the first ethanol peel test was taken as the adhesive strength Fa. １ (N / 25mm) are shown in Tables 1 and 2.

[0146] <Second Ethanol Peeling Test> A second ethanol peeling test was carried out on each of the pressure-sensitive adhesive sheets of the Examples and Comparative Examples to measure the adhesive strength Fa ２ The second ethanol peeling test was the same as the first ethanol peeling test, except for the following: In the resting step, the laminate was left to stand at room temperature for 72 hours.

[0147] In the measurement step of the second ethanol peeling test, the peel length d when the peel force begins to stabilize during the peeling process is measured. １ and peel length d １ The peel length d when the peel force increases by 10% compared to the peel force at ２ and the peel length d １ From peel length d ２ The average value of the peel strengths measured up to this point was taken as the adhesive strength. The adhesive strength measured in the measurement step of the second ethanol peel test was taken as the adhesive strength Fa ２ (N / 25mm) is shown in Tables 1 and 2. Peel length d ２ and peel length d １ The difference between (d ２ -d１ ) is shown in Tables 1 and 2 as the ethanol peeling duration d (mm). ２ Adhesion force Fa １ The fluctuation rate (%) of is also shown in Tables 1 and 2. This fluctuation rate is calculated using the following formula:

[0148] Fluctuation rate (%) = [(Fa １ -Fa ２ ) / Fa ２ ] x 100

[0149] <High-Temperature, High-Humidity Peel Test> A high-temperature, high-humidity peel test was conducted to measure the adhesive strength Fh for each of the pressure-sensitive adhesive sheets of the Examples and Comparative Examples. The high-temperature, high-humidity peel test was the same as the initial room-temperature peel test, except for the following: In the standing step, the laminate was left standing at room temperature for 24 hours. After the standing step and before the measurement step, a high-temperature, high-humidity treatment step was conducted. In the high-temperature, high-humidity treatment step, the laminate after the standing step was subjected to high-temperature, high-humidity treatment under conditions of 60°C, 93% relative humidity, and 15 minutes. In the measurement step, a 180° peel test was conducted under second conditions instead of the first conditions: 60°C, 93% relative humidity, a peel angle of 180°, and a pulling speed of 300 mm / min.

[0150] In the measurement step of the high-temperature, high-humidity peel test, the peel length (total length) was set to 50 mm, and the average value of the peel force measured between peel lengths of 10 mm and 40 mm was taken as the adhesive strength. The adhesive strength measured in the measurement step of the high-temperature, high-humidity peel test is shown in Tables 1 and 2 as adhesive strength Fh (N / 25 mm).

[0151] <First Water Peel Test> A first water peel test was carried out on each of the pressure-sensitive adhesive sheets of the comparative examples to measure the adhesive strength Fw. １ The first water peeling test was the same as the second ethanol peeling test, except that the following water supplying step was carried out instead of the ethanol supplying step.

[0152] Water supply step: After the standing step, 25 μL of water was supplied onto the alkali glass plate of the laminate so that the water was in contact with one longitudinal end of the adhesive sheet piece at the interface between the alkali glass plate and the adhesive sheet piece.

[0153] In the measurement step of the first water peeling test, the peel length d when the peel force begins to stabilize during the peeling process is １ and peel length d １ The peel length d when the peel force increases by 10% compared to the peel force at ２ and the peel length d １ From peel length d ２ The average value of the peel strengths measured up to this point was taken as the adhesive strength. The adhesive strength measured in the measurement step of the first water peel test was taken as the adhesive strength Fw １ (N / 25mm) are shown in Tables 1 and 2.

[0154] <Second Water Peel Test> A second water peel test was carried out on each of the comparative pressure-sensitive adhesive sheets to measure the adhesive strength Fw ２ The second water peeling test was the same as the first ethanol peeling test, except that the above water supplying step was carried out instead of the ethanol supplying step.

[0155] In the measurement step of the second water peel test, the peel length d when the peel force begins to stabilize during the peeling process is measured. １ and peel length d １ The peel length d when the peel force increases by 10% compared to the peel force at ２ and the peel length d １ From peel length d ２ The average value of the peel strengths measured up to this point was taken as the adhesive strength. The adhesive strength measured in the measurement step of the second water peel test was taken as the adhesive strength Fw ２ (N / 25mm) are shown in Tables 1 and 2.

[0156] A surfactant was used in the pressure-sensitive adhesive sheets of Comparative Examples 2 and 3. As a result, the pressure-sensitive adhesive sheets of Comparative Examples 2 and 3 had an adhesive strength Fw in the first water peel test. １ However, the adhesive sheets of Comparative Examples 2 and 3 have low adhesive strength Fh in the high temperature and high humidity peel test. Such adhesive sheets cannot ensure good adhesion reliability in a high humidity environment. Furthermore, the adhesive sheets of Comparative Examples 2 and 3 have low adhesive strength Fw in the second water peel test. ２ But the adhesive strength Fw １ That is, the PSA sheets of Comparative Examples 2 and 3 were unable to maintain water releasability (no long-term reworkability).

[0157]

[0158]

[0159] The above invention is provided as an exemplary embodiment of the present disclosure, but this is merely an example and should not be interpreted as limiting. Modifications of the present disclosure that are obvious to those skilled in the art are intended to be included in the scope of the following claims.

[0160] The alcohol-peelable optical adhesive sheet of the present invention is suitably used for display panels such as liquid crystal panels and organic EL panels.

[0161] 10 Adhesive sheet (alcohol-peelable optical adhesive sheet) H Thickness direction 11, 12 Adhesive surface 21 Alkaline glass plate 22 Ethanol L1, L2 Release liner

Claims

1. Contains a photopolymerized polymer as the base polymer, and has an initial adhesive strength Fn in the following room temperature peel test. １ The adhesive strength F in the first ethanol peeling test below is 9.0 N / 25 mm or more. １ and an adhesive strength Fh of 2.0 N / 25 mm or more in the high-temperature, high-humidity peeling test described below. Initial room-temperature peeling test: First, a 25 mm wide x 100 mm long adhesive sheet piece of the alcohol-peelable optical adhesive sheet is bonded to an alkali glass plate prepared by the float method to obtain a laminate (preparation step). Next, the laminate is subjected to a heating and pressurizing treatment under conditions of 50° C., 0.5 MPa and 15 minutes (heating and pressurizing step). Next, the laminate is left to stand at room temperature for 72 hours (standing step), and then one end of the adhesive sheet piece in the length direction is pulled under first conditions of 25° C., 50% relative humidity, a peeling angle of 180°, and a pulling speed of 300 mm / min to peel the adhesive sheet piece from the alkali glass plate and measure the adhesive strength (measurement step). First ethanol peeling test: The same as the initial room temperature peeling test except for the following. In the standing step, the laminate is stood at 50° C. for 168 hours. After the standing step and before the measuring step, an ethanol supplying step is carried out. In the ethanol supplying step, 10 μL of ethanol is supplied onto the alkali glass plate of the laminate so that the ethanol contacts one end of the adhesive sheet piece in the longitudinal direction at the interface between the alkali glass plate and the adhesive sheet piece. High temperature and high humidity peeling test: The same as the initial room temperature peeling test except for the following. In the standing step, the laminate is stood at room temperature for 24 hours. After the leaving step and before the measuring step, a high temperature and high humidity treatment step is carried out. In the high-temperature, high-humidity treatment step, the laminate after the standing step is subjected to high-temperature, high-humidity treatment under conditions of 60° C., a relative humidity of 93%, and 15 minutes. In the measuring step, instead of the first condition, a 180° peel test is performed under second conditions of 60° C., relative humidity 93%, a peel angle of 180°, and a tensile speed of 300 mm / min.

2. The adhesive strength F in the second ethanol peeling test described below ２ and the adhesive strength F a ２ The adhesive force F a １ The alcohol-peelable optical adhesive sheet according to claim 1, wherein the variation rate of is -50% to 100%. Second ethanol peeling test: The same as the first ethanol peeling test, except that in the standing step, the laminate is left standing at room temperature for 72 hours.

3. The alcohol-peelable optical adhesive sheet according to claim 2, wherein the ethanol peeling duration in the second ethanol peeling test is 20 mm or more.

4. The alcohol-peelable optical adhesive sheet according to any one of claims 1 to 3, which does not contain a surfactant.

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