TW202444854A - Optical adhesive sheet - Google Patents

Abstract

An adhesive sheet (10) (optical adhesive sheet) comprises a base polymer and an oligomer having a glass transition temperature of 40 DEG C or higher, and has a shear storage elastic modulus of 100 kPa or less at -10 DEG C. In the adhesive sheet (10), the hydrogen bond term [delta]H1 of the Hansen solubility parameter of the base polymer and the hydrogen bond term [delta]H2 of the Hansen solubility parameter of the oligomer satisfy the formula: 0.1 ≤ [delta]H2 - [delta]H1 ≤ 1.3.

Description

Optical adhesive sheet

The present invention relates to an optical adhesive sheet.

The display panel, for example, has a laminated structure including components such as a pixel panel, a polarizing film, a touch panel, and a cover film. In the manufacturing process of such a display panel, in order to bond the components included in the laminated structure to each other, for example, a transparent adhesive sheet (optical adhesive sheet) is used.

On the other hand, a display panel that can be bent repeatedly (foldable) is being developed for use in, for example, smart phones and tablet terminals. Specifically, a foldable display panel can be repeatedly deformed between a curved shape and a flat non-curved shape. Each element in the laminated structure of such a foldable display panel is made to be able to be bent repeatedly, and a thinner optical adhesive sheet is used to bond such elements to each other. Optical adhesive sheets for flexible devices such as foldable display panels are described, for example, in the following patent document 1. [Prior art document] [Patent document]

[Patent Document 1] Japanese Patent Publication No. 2018-111754

[The problem the invention is trying to solve]

For optical adhesive sheets used in soft devices, they are required to be highly soft so that they can fully follow the adherend when the device is deformed, and have excellent stress relaxation properties. However, the softer the previous optical adhesive sheet, the lower the adhesive force.

In the past, optical adhesive sheets were easily peeled off from the components as adherends at the bends of foldable display panels. The reason is that when the display panel is bent, a relatively large shear force is applied to the bend of the optical adhesive sheet in the direction of the adherend. The peeling of the optical adhesive sheet will cause the display to malfunction, so it is not desirable. For optical adhesive sheets used in foldable display panels, it is required at a higher level that they are not easily peeled off from the components (adherends) when the display is bent.

As a flexible device, the development of rollable (curled) display panels is also advancing. For example, a rollable display panel can be repeatedly deformed between a rolled-up shape after being rolled up in whole or in part and a flat shape after being rolled out in whole. Each element in the layered structure of such a rollable display panel is made to be able to be repeatedly deformed, and a thinner optical adhesive sheet is used to bond such elements to each other. When the rollable display panel is in a rolled-up shape, the optical adhesive sheet bonded to the rolled-up element is continuously subjected to shear force in the direction of the adherend. Such optical adhesive sheets are required to be not easily peeled off from a device (adherend) when the display is in a rolled-up state at a very high level.

The present invention provides an optical adhesive sheet suitable for use in flexible devices. [Technical means for solving the problem]

The present invention [1] comprises an optical adhesive sheet comprising a base polymer and an oligomer having a glass transition temperature of 40°C or higher, and having a shear storage modulus of 100 kPa or lower at -10°C, wherein the hydrogen bonding term _δH1 of the Hansen solubility parameter of the base polymer and the hydrogen bonding term _δH2 of the Hansen solubility parameter of the oligomer satisfy 0.1≦ _δH2 - _δH1 ≦1.3.

The present invention [2] comprises the optical adhesive sheet as described in the above-mentioned [1], which has a haze of less than 1%.

The present invention [3] comprises an optical adhesive sheet as described in the above [1] or [2], wherein the adhesive force of the optical adhesive sheet in a peeling test conducted at 25°C, a peeling angle of 180° and a tensile speed of 300 mm/min is 7.6 N/20 mm or more.

The present invention [4] comprises an optical adhesive sheet as described in any one of the above [1] to [3], which has an adhesion force F1 in a peeling test conducted at 25°C, a peeling angle of 180° and a tensile speed of 300 mm/min, and has an adhesion force F2 in a peeling test conducted at 25°C, a peeling angle of 180° and a tensile speed of 60 mm/min, and the ratio of the adhesion force F2 to the adhesion force F1 is greater than 0.5 and less than 1.1.

The present invention [5] comprises the optical adhesive sheet as described in any one of the above [1] to [4], wherein the ratio of the shear storage modulus at 60°C to the shear storage modulus at -10°C is 0.2 or more and 1.0 or less.

The present invention [6] comprises an optical adhesive sheet as described in any one of the above [1] to [5], which has a gel fraction of 60 mass % or more and 87 mass % or less. [Effect of the invention]

As described above, the optical adhesive sheet of the present invention has a shear storage modulus of 100 kPa or less at -10°C. Thus, the soft optical adhesive sheet is suitable for relieving the stress generated by the optical adhesive sheet and the adherend when the adherend to which the adhesive sheet is attached is deformed (stress relieving function). Stress relieving in the optical adhesive sheet is suitable for ensuring the tracking property of the optical adhesive sheet to the adherend. Stress relieving in the adherend is suitable for suppressing damage such as cracking of the adherend. In addition, as described above, the optical adhesive sheet of the present invention includes a base polymer and an oligomer having a glass transition temperature (Tg) of 40°C or higher, and the hydrogen bonding term _δH1 of the Hansen solubility parameter (HSP) of the base polymer and the hydrogen bonding term _δH2 of the HSP of the oligomer satisfy 0.1≦ _δH2 - _δH1 ≦1.3. This structure is suitable for ensuring the overall softness of the optical adhesive sheet, and will make the oligomer with a Tg of 40°C or higher segregate on the surface (adhesive surface) of the optical adhesive sheet and its vicinity, thereby achieving good adhesion of the adhesive sheet. The high adhesion of the optical adhesive sheet is suitable for suppressing the peeling of the optical adhesive sheet from the repeatedly deformed adherend. The optical adhesive sheet as described above is suitable for flexible device applications.

As shown in FIG1 , an adhesive sheet 10 as an embodiment of the optical adhesive sheet of the present invention has a sheet shape with a specific thickness and expands in a direction (surface direction) orthogonal to the thickness direction. The adhesive sheet 10 has an adhesive surface 11 and an adhesive surface 12 on the opposite side of the adhesive surface 11. FIG1 shows, by way of example, a state in which peel-off pads L1 and L2 are attached to the adhesive surfaces 11 and 12 of the adhesive sheet 10. The peel-off pad L1 is arranged on the adhesive surface 11. The peel-off pad L2 is arranged on the adhesive surface 12. In addition, the adhesive sheet 10 is a transparent adhesive sheet (optical adhesive sheet) arranged in a light-passing portion of a flexible device. As a flexible device, for example, a flexible display panel can be cited. As a flexible display panel, for example, a foldable display panel and a rollable display panel can be cited. The flexible display panel, for example, has a laminated structure including components such as a pixel panel, a polarizing film, a touch panel, and a cover film. The adhesive sheet 10 is used to bond the components contained in the laminated structure to each other during the manufacturing process of the flexible display panel. The peeling pads L1 and L2 are peeled off at specific points in time when the adhesive sheet 10 is used.

The adhesive sheet 10 is formed of an adhesive composition. The adhesive composition includes a base polymer and an oligomer having a glass transition temperature (Tg) of 40°C or higher. That is, the adhesive sheet 10 includes a base polymer and an oligomer having a Tg of 40°C or higher. The adhesive sheet 10 has a shear storage modulus of 100 kPa or less at -10°C. In addition, in the adhesive sheet 10, the hydrogen bonding term _δH1 of the Hansen solubility parameter (HSP) of the base polymer and the hydrogen bonding term _δH2 of the HSP of the oligomer satisfy the following formula (1).

0.1≦δH ₂ -δH ₁ ≦1.3 (1)

As described above, the adhesive sheet 10 has a shear storage modulus of less than 100 kPa at -10°C. Thus, the soft adhesive sheet 10 is suitable for relieving the stress generated by the adhesive sheet 10 and the adherend when the adherend to which the adhesive sheet 10 is attached is deformed (stress relief function). The stress relief in the adhesive sheet 10 is suitable for ensuring the tracking property of the adhesive sheet 10 to the adherend. The stress relief in the adherend is suitable for suppressing damage such as rupture of the adherend. Therefore, the adhesive sheet 10 is suitable for achieving good repeated deformation of the soft device using the adhesive sheet 10.

Furthermore, as described above, the adhesive sheet 10 includes a base polymer and an oligomer having a Tg of 40° C. or higher, and the hydrogen bonding term δH ₁ of the HSP of the base polymer and the hydrogen bonding term δH ₂ of the HSP of the oligomer satisfy 0.1≦δH ₂ −δH ₁ ≦1.3. The difference ΔH (=δH ₂ −δH ₁ ) between the hydrogen bonding term δH ₁ of the HSP of the base polymer and the hydrogen bonding term δH ₂ of the HSP of the oligomer is an indicator of the compatibility of the base polymer and the oligomer in the adhesive sheet 10. When the difference ΔH is 0.1 or more and 1.3 or less, it is suitable to realize moderately low compatibility between the base polymer and the oligomer, so that the oligomer is concentrated on the surface (adhesive surface 11, 12) and its vicinity of the adhesive sheet 10. Therefore, when the difference ΔH is 0.1 or more and 1.3 or less, it is suitable to ensure the above-mentioned overall softness of the adhesive sheet 10, and oligomers with a Tg of 40°C or more are concentrated on the surface (adhesive surface 11, 12) and its vicinity of the adhesive sheet 10, thereby realizing high adhesion in the adhesive sheet 10. The high adhesion of the adhesive sheet 10 is suitable for suppressing the peeling of the adhesive sheet 10 from the repeatedly deformed adherend.

The adhesive sheet 10 as described above is suitable for the use of flexible devices. That is, the adhesive sheet 10 is suitable for realizing good repeated deformation of the flexible device using the adhesive sheet 10.

From the perspective of stress relief at the deformed portion when the adhesive sheet 10 is deformed (bending and bending, etc.), the shear storage modulus G1 of the adhesive sheet 10 at -10°C is preferably 90 kPa or less, more preferably 85 kPa or less, and further preferably 80 kPa or less. From the perspective of ensuring the cohesive force of the adhesive sheet 10 in the low temperature area, the shear storage modulus G1 (-10°C) is preferably 30 kPa or more, more preferably 40 kPa or more, further preferably 50 kPa or more, and further preferably 60 kPa or more. The shear storage modulus G1 is obtained by the dynamic viscoelasticity measurement described below in the embodiment (the same applies to the shear storage moduli G2 and G3 described below). As a method for adjusting the shear storage modulus of the adhesive sheet 10, for example, there can be cited: selection of the type of base polymer in the adhesive sheet 10, adjustment of the molecular weight, and adjustment of the blending amount, and selection of the type of crosslinking agent and adjustment of the blending amount (the same applies to the shear storage moduli G2 and G3 described below).

From the viewpoint of the above stress relaxation in the adhesive sheet 10, the shear storage modulus G2 of the adhesive sheet 10 at 60°C is preferably 35 kPa or less, more preferably 32 kPa or less, and further preferably 27 kPa or less. From the viewpoint of ensuring the cohesive force of the adhesive sheet 10 in the high temperature region, the shear storage modulus G2 (60°C) is preferably 10 kPa or more, more preferably 15 kPa or more, further preferably 20 kPa or more, and further preferably 22 kPa or more.

From the perspective of ensuring the stable stress relief function of the adhesive sheet 10 within a wider temperature range, the ratio of the shear storage modulus G2 to the shear storage modulus G1 (G2/G1) is preferably greater than 0.2, more preferably greater than 0.25, and further preferably greater than 0.3, and further preferably less than 1.0, more preferably less than 0.5, and further preferably less than 0.4.

From the viewpoint of stress relaxation in the adhesive sheet 10, the shear storage modulus G3 of the adhesive sheet 10 at -20°C is preferably 150 kPa or less, more preferably 130 kPa or less, and further preferably 120 kPa or less. From the viewpoint of ensuring the cohesive force of the adhesive sheet 10 in the low temperature region, the shear storage modulus G3 (-20°C) is preferably 40 kPa or more, more preferably 50 kPa or more, more preferably 70 kPa or more, and further preferably 90 kPa or more.

From the viewpoint of appropriately reducing the compatibility between the base polymer and the oligomer so that the oligomer is sufficiently segregated on the adhesive surfaces 11 and 12 and their vicinities, the difference ΔH (δH ₂ - δH ₁ ) between the hydrogen bonding term δH ₁ of the HSP of the base polymer and the hydrogen bonding term δH ₂ of the HSP of the oligomer is preferably 0.2 or more, more preferably 0.3 or more. From the viewpoint of preventing the compatibility between the base polymer and the oligomer from becoming too low, the difference ΔH (δH ₂ - δH ₁ ) is preferably 1.26 or less. By ensuring the compatibility between the base polymer and the oligomer, it is helpful to achieve low haze in the adhesive sheet 10. As a method for adjusting _δH1 of a base polymer, for example, adjustment of the monomer composition of the base polymer can be cited. As a method for adjusting _δH2 of an oligomer, for example, adjustment of the monomer composition of the oligomer can be cited.

From the viewpoint of appropriately reducing the compatibility between the base polymer and the oligomer so that the oligomer is sufficiently segregated on the adhesive surfaces 11 and 12 and their vicinities, the ratio of the hydrogen bond term δH ₂ of the HSP of the oligomer to the hydrogen bond term δH ₁ of the HSP of the base polymer (δH ₂ /δH ₁ ) is preferably 1.04 or more, more preferably 1.06 or more, further preferably 1.08 or more, further preferably 1.10 or more. From the viewpoint of preventing the compatibility between the base polymer and the oligomer from becoming too low, the ratio (δH ₂ /δH ₁ ) is preferably 1.28 or less, more preferably 1.25 or less, further preferably 1.22 or less. The ratio (δH ₂ /δH ₁ ) is also an indicator of the compatibility of the base polymer and the oligomer in the adhesive sheet 10 .

The Hansen Solubility Parameter (HSP) is represented by the following formula (2), where δH is a hydrogen bonding term representing the energy derived from hydrogen bonding forces between molecules, δD is a dispersion term representing the energy derived from dispersion forces between molecules, and δP is a polarization term representing the energy derived from polar forces between molecules.

HSP=(δD ² +δP ² +δH ₂ ) ^1/2 (2)

The δH of a polymer is determined by the following formula (3) based on the molar fraction _xi of the monomer _mi forming the polymer and the hydrogen bonding term _δhi of the monomer _mi . The δH of an oligomer is determined in the same manner. The hydrogen bonding term δh of a monomer can be calculated, for example, by computer software HSPiP (Hansen Solubility Parameters in Practice). Specifically, the method for determining δH is described below in connection with the Examples.

δH＝ _Σxi × _δhi (3)

As for the Tg of the oligomer, as described above, from the viewpoint of making the surface of the soft adhesive sheet 10 highly adhesive, it is preferably 50°C or more, more preferably 60°C or more, and further preferably 70°C or more, and further, preferably 145°C or less, more preferably 135°C or less, and further preferably 130°C or less. The Tg of the oligomer is preferably higher than the Tg of the base polymer. As a method for adjusting the Tg of the oligomer, the adjustment of the monomer composition of the oligomer and the adjustment of the molecular weight can be cited. Specifically, the method for measuring the Tg of the oligomer is described below in relation to the embodiment.

Regarding the glass transition temperature Tg of the oligomer, the glass transition temperature (theoretical value) calculated based on the following Fox formula can be used. 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 a monomer constituting the polymer. In the following Fox formula, Tg represents the glass transition temperature of the oligomer (°C), _Wi represents the weight fraction of the monomer _mi constituting the polymer, and _Tgi represents the glass transition temperature of the homopolymer formed by the monomer _mi (°C). Regarding the glass transition temperature of a homopolymer, a literature value can be used. For example, the glass transition temperatures of various homopolymers are listed in the "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999). On the other hand, the glass transition temperature of the homopolymer of the monomer can also be obtained by the method specifically described in Japanese Patent Application Laid-Open No. 2007-51271.

Fox formula 1/(273+Tg)=Σ[W _i /(273+Tg _i )]

The haze of the adhesive sheet 10 is preferably less than 1%, more preferably less than 0.8%, further preferably less than 0.7%, and further preferably less than 0.5%. The haze is, for example, greater than 0.01%. The haze of the adhesive sheet 10 can be measured using a haze meter in accordance with JIS K7136 (2000). Examples of the haze meter include "NDH2000" manufactured by Nippon Denshoku Industries, Ltd., and "HM-150" manufactured by Murakami Color Technology Laboratory, Inc. Specifically, the method for measuring the haze is described below in connection with the embodiments.

The total light transmittance of the adhesive sheet 10 is preferably 60% or more, more preferably 80% or more, and further preferably 85% or more. The total light transmittance of the adhesive sheet 10 is, for example, 100% or less. The total light transmittance of the adhesive sheet 10 can be measured according to JIS K 7375 (2008).

From the viewpoint of ensuring the cohesive force of the adhesive sheet 10 in the high temperature region, the gel fraction of the adhesive sheet 10 is preferably 60% by mass or more, more preferably 70% by mass or more, and further preferably 73% by mass or more. From the viewpoint of ensuring the softness of the adhesive sheet 10, the gel fraction of the adhesive sheet 10 is preferably 87% by mass or less, more preferably 85% by mass or less, and further preferably 83% by mass or less. As a method for adjusting the gel fraction of the adhesive sheet 10, for example, the selection of the type of base polymer in the adhesive sheet 10, the adjustment of the molecular weight, and the adjustment of the blending amount can be cited. As a method for adjusting the gel fraction, the selection of the type of crosslinking agent and the adjustment of the blending amount can also be cited. In addition, the method for measuring the gel fraction is described below in connection with the examples.

From the viewpoint of inhibiting the adhesive sheet 10 from peeling off from the adherend, the adhesive force F1 of the adhesive sheet 10 in the peeling test (the first peeling test) conducted at 25°C, a peeling angle of 180° and a tensile speed of 300 mm/minute is preferably 7.6 N/20 mm or more, more preferably 7.8 N/20 mm or more, further preferably 8.0 N/20 mm or more, further preferably 8.2 N/20 mm or more, further preferably 8.4 N/20 mm or more, further preferably 8.6 N/20 mm or more, and particularly preferably 8.8 N/20 mm or more. The adhesive force F1 is, for example, 15 N/20 mm or less. Specifically, the method for measuring the adhesive force F1 is as described below in connection with the embodiments. As a method for adjusting the adhesion F1, for example, there can be cited: selection of the type of base polymer in the adhesive sheet 10, adjustment of the molecular weight, and adjustment of the blending amount. The selection of the type of base polymer includes adjustment of the composition of the monomers forming the base polymer. As a method for adjusting the adhesion F1, there can also be cited the selection of the type of components other than the base polymer in the adhesive sheet 10, and adjustment of the blending amount of the components. As such components, there can be cited crosslinking agents, silane coupling agents, and oligomers. The above-mentioned method for adjusting the adhesion is also applicable to the following adhesion F2.

From the viewpoint of suppressing the peeling of the adhesive sheet 10 from the adherend, the adhesive force F2 of the adhesive sheet 10 in the peeling test (the second peeling test) conducted under the conditions of 25°C, a peeling angle of 180° and a tensile speed of 60 mm/min is preferably 4.1 N/20 mm or more, more preferably 6.0 N/20 mm or more, further preferably 6.4 N/20 mm or more, further preferably 6.8 N/20 mm or more, further preferably 7.2 N/20 mm or more, further preferably 7.6 N/20 mm or more, and particularly preferably 8.0 N/20 mm or more. The adhesive force F2 is, for example, 12 N/20 mm or less.

From the perspective of ensuring stable adhesion in the adhesive sheet 10, the ratio of the adhesion F2 to the adhesion F1 (F2/F1) is preferably greater than 0.5, more preferably greater than 0.6, more preferably greater than 0.7, more preferably greater than 0.75, further preferably greater than 0.8, and preferably less than 1.1, more preferably less than 1.0.

The base polymer is an adhesive component that exhibits adhesiveness in the adhesive sheet 10. Examples of the base polymer include acrylic polymers, silicone polymers, polyester polymers, polyurethane polymers, polyamide polymers, polyvinyl ether polymers, vinyl acetate/vinyl chloride copolymers, modified polyolefin polymers, epoxy polymers, fluoropolymers, and rubber polymers. The base polymer may be used alone or in combination of two or more. From the perspective of ensuring good transparency and adhesiveness in the adhesive sheet 10, an acrylic polymer is preferred as the base polymer.

The acrylic polymer is a polymer containing a monomer component (first monomer component) of an alkyl (meth)acrylate at a ratio of 50 mass % or more. "(Meth)acrylic acid" means acrylic acid and/or methacrylic acid.

As the alkyl (meth)acrylate, it is preferred to use an alkyl (meth)acrylate having an alkyl group with a carbon number of 1 to 20. Examples of the alkyl (meth)acrylate include alkyl (meth)acrylates having a chain alkyl group (chain alkyl (meth)acrylates) and alkyl (meth)acrylates having an alicyclic alkyl group (alicyclic alkyl (meth)acrylates).

Examples of the chain alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, iso-pentyl (meth)acrylate, neopentyl (meth)acrylate, n-hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, iso-octyl (meth)acrylate, 2 ... The present invention also includes the following: nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, 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.

Examples of the cycloalkyl (meth)acrylate include cycloalkyl (meth)acrylate, (meth)acrylate having a dicyclic aliphatic hydrocarbon ring, and (meth)acrylate having a tricyclic or higher aliphatic hydrocarbon ring. Examples of the cycloalkyl (meth)acrylate include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, cyclooctyl (meth)acrylate, and cyclododecyl (meth)acrylate. Examples of the (meth)acrylate having a dicyclic aliphatic hydrocarbon ring include isobutyl (meth)acrylate. Examples of the (meth)acrylate having a tricyclic or more aliphatic hydrocarbon ring include dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

As the alkyl (meth)acrylate, from the viewpoint of achieving a balance between softness and adhesiveness required for an adhesive sheet for a flexible device in the adhesive sheet 10, it is preferred to use at least one selected from the group consisting of alkyl (meth)acrylates having a first alkyl group with a carbon number of 8 to 12, or at least one selected from the group consisting of alkyl (meth)acrylates having a first alkyl group with a carbon number of 8 to 12 and at least one selected from the group consisting of alkyl (meth)acrylates having an alkyl group with a carbon number of 1 to 4. The first alkyl (meth)acrylate is preferably at least one selected from the group consisting of 2-ethylhexyl acrylate (2EHA), n-octyl acrylate (NOAA), isononyl acrylate (INAA), and lauryl acrylate (LA). The second alkyl (meth)acrylate is preferably n-butyl acrylate (BA).

From the viewpoint of appropriately showing softness and adhesiveness in the adhesive sheet 10, the ratio of the alkyl (meth)acrylate in the first monomer component is preferably 80 mass % or more, more preferably 85 mass % or more, further preferably 88 mass % or more, and particularly preferably 90 mass % or more. The ratio is, for example, 99.9 mass % or less, 99.5 mass % or less, or 99 mass % or less. When a first alkyl (meth)acrylate selected from alkyl (meth)acrylates having an alkyl group with 8 to 12 carbon atoms and another second alkyl (meth)acrylate selected from alkyl (meth)acrylates having an alkyl group with 1 to 4 carbon atoms are used in combination, the ratio of the first alkyl (meth)acrylate in the monomer component is preferably 60 mass% or more, more preferably 65 mass% or more, further preferably 70 mass% or more, further preferably 85 mass% or less, further preferably 80 mass% or less, further preferably 75 mass% or less, and the ratio of the second alkyl (meth)acrylate in the monomer component is preferably 10 mass% or more, more preferably 15 mass% or more, further preferably 20 mass% or more, further preferably 35 mass% or less, further preferably 30 mass% or less, further preferably 25 mass% or less.

The first monomer component may also include a copolymerizable monomer that can copolymerize with the (meth)acrylic acid alkyl ester. Examples of the copolymerizable monomer include monomers having a polar group. Examples of the polar group-containing monomer include: hydroxyl group-containing monomers, monomers having a ring containing a nitrogen atom, and carboxyl group-containing monomers. The polar group-containing monomer helps to introduce crosslinking points into the acrylic polymer, ensure the cohesive force of the acrylic polymer, and other modifications of the acrylic polymer. The copolymerizable monomers may be used alone or in combination of two or more.

Examples of the hydroxyl-containing monomer 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, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. The hydroxyl-containing monomer is preferably at least one selected from the group consisting of 2-hydroxyethyl acrylate (2HEA) and 4-hydroxybutyl acrylate (4HBA).

From the viewpoint of introducing a cross-linked structure into the acrylic polymer and ensuring the cohesive force in the adhesive sheet 10, the ratio of the hydroxyl-containing monomer in the first monomer component is preferably 1% by mass or more, more preferably 3% by mass or more, and further preferably 5% by mass or more. From the viewpoint of adjusting the polarity of the acrylic polymer (related to the compatibility of various additive components in the adhesive sheet 10 with the acrylic polymer), the ratio is preferably 12% by mass or less, more preferably 10% by mass or less, and further preferably 9% by mass or less.

Examples of the monomer having a ring containing a nitrogen atom include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperidone, N-vinylpyrrolidone, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, 4-acryloyloxazolidine, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazol-2-one, N-vinyl-3,5-oxazolidinedione, N-vinylpyrazole, N-vinylisooxazolone, N-vinylthiazole, and N-vinylisothiazole. The monomer having a ring containing a nitrogen atom is preferably N-vinyl-2-pyrrolidone (NVP).

When a monomer having a ring containing a nitrogen atom is used, the ratio of the monomer having a ring containing a nitrogen atom in the first monomer component is preferably 0.5 mass % or more, more preferably 1 mass % or more, and further preferably 1.5 mass % or more, from the viewpoint of ensuring the cohesive force in the adhesive sheet 10 and the close contact of the adhesive sheet 10 to the adherend. From the viewpoint of adjusting the glass transition temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (related to the compatibility of various additive components in the adhesive sheet 10 and the acrylic polymer), the ratio is preferably 10 mass % or less, more preferably 6 mass % or less, and further preferably 4 mass % or less.

Examples of the carboxyl group-containing monomer include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and methacrylonic acid.

When a carboxyl group-containing monomer is used, the ratio of the carboxyl group-containing monomer in the monomer component is preferably 0.1 mass % or more, more preferably 0.5 mass % or more, and further preferably 0.8 mass % or more, from the viewpoint of introducing a cross-linked structure into the acrylic polymer, ensuring the cohesive force in the adhesive sheet 10, and ensuring the close contact of the adhesive sheet 10 to the adherend. From the viewpoint of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend caused by acid, the ratio is preferably 3 mass % or less, and more preferably 1 mass % or less.

The first monomer component may also contain other copolymerizable monomers. Examples of other copolymerizable monomers include 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. These other copolymerizable monomers may be used alone or in combination of two or more.

The first monomer component preferably includes: a first alkyl (meth)acrylate having an alkyl group with 8 to 12 carbon atoms, a second alkyl (meth)acrylate having an alkyl group with 1 to 4 carbon atoms, a hydroxyl group-containing monomer, and a monomer having a ring containing a nitrogen atom. The first monomer component more preferably includes NOAA, BA, NVP, and 4HBA.

The base polymer preferably has a crosslinking structure. As a method for introducing a crosslinking structure into the base polymer, for example, the following first method and second method can be cited. In the first method, a base polymer having a functional group capable of reacting with a crosslinking agent and a crosslinking agent are mixed into an adhesive composition, and the base polymer and the crosslinking agent react in an adhesive sheet; in the second method, a multifunctional compound as a crosslinking agent is included in the first monomer component forming the base polymer, and a base polymer having a branched structure (crosslinking structure) introduced into the polymer chain is formed by polymerization of the first monomer component. These methods can also be used in combination.

As the crosslinking agent used in the above-mentioned first method, for example, a compound that reacts with the functional groups (hydroxyl and carboxyl groups, etc.) contained in the base polymer can be cited. As such a crosslinking agent, for example, isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, and carbodiimide crosslinking agents can be cited. The crosslinking agent in the first method can be used alone or in combination of two or more. As the crosslinking agent in the first method, it is preferred to use an isocyanate crosslinking agent in terms of its high reactivity with the hydroxyl and carboxyl groups in the base polymer and its ease of introduction into a crosslinked structure.

As the isocyanate crosslinking agent, for example, toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate can be cited. In addition, as the isocyanate crosslinking agent, derivatives of the isocyanates can also be cited. As the isocyanate derivative, for example, isocyanurate modified bodies and polyol modified bodies can be cited. Examples of commercially available isocyanate crosslinking agents include Coronate L (trihydroxymethylpropane adduct of toluene diisocyanate, manufactured by Tosoh Corporation), Coronate HL (trihydroxymethylpropane adduct of hexamethylene diisocyanate, manufactured by Tosoh Corporation), Coronate HX (isocyanurate of hexamethylene diisocyanate, manufactured by Tosoh Corporation), Takenate D110 N (trihydroxymethylpropane adduct of xylylenediisocyanate, manufactured by Mitsui Chemicals Co., Ltd.), and Takenate 600 (1,3-bis(isocyanatomethyl)cyclohexane, manufactured by Mitsui Chemicals Co., Ltd.).

Examples of the peroxide crosslinking agent include dibenzoyl peroxide, di(2-ethylhexyl) peroxydicarbonate, di(4-t-butylcyclohexyl) peroxydicarbonate, di-t-butyl peroxydicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxypivalate, and t-butyl peroxypivalate.

Examples of the epoxy crosslinking agent include bisphenol A, epichlorohydrin type epoxy resin, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, 1,6-hexanediol glycidyl ether, trihydroxymethylpropane triglycidyl ether, diglycidyl aniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane.

As for the amount of the crosslinking agent in the first method, from the viewpoint of ensuring the cohesive force of the adhesive sheet 10, the amount is, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, and more preferably 0.1 parts by mass or more per 100 parts by mass of the base polymer. From the viewpoint of ensuring good adhesion in the adhesive sheet 10, the amount of the crosslinking agent is, for example, 5 parts by mass or less, preferably 1 part by mass or less, and more preferably 0.2 parts by mass or less per 100 parts by mass of the base polymer.

In the above-mentioned second method, the first monomer component (including the multifunctional compound and the monofunctional compound for introducing the crosslinking structure) can be polymerized at once or in multiple stages. In the multistage polymerization method, first, the monofunctional monomer used to form the base polymer is polymerized (prepolymerization) to prepare a prepolymer composition containing a partial polymer (a mixture of a polymer with a low degree of polymerization and unreacted monofunctional monomer). Then, after adding the multifunctional compound as a crosslinking agent to the prepolymer composition, a polymerization reaction (main polymerization) is carried out in a reaction system containing the partial polymer and the multifunctional compound.

Examples of the polyfunctional compound include polyfunctional monomers and polyfunctional oligomers having two or more ethylenically unsaturated double bonds in one molecule. Examples of the polyfunctional monomer include polyfunctional (meth)acrylates.

Examples of the polyfunctional (meth)acrylate include difunctional (meth)acrylate, trifunctional (meth)acrylate, and tetrafunctional or higher polyfunctional (meth)acrylate.

Examples of the difunctional (meth)acrylate include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerol di(meth)acrylate, ethoxylated bisphenol A diacrylate (BPAEODE), and neopentyl glycol di(meth)acrylate.

Examples of the trifunctional (meth)acrylate include trihydroxymethylpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tri(acryloxyethyl)isocyanurate.

Examples of the tetrafunctional or higher polyfunctional (meth)acrylate include di-trihydroxymethylpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxy penta(meth)acrylate, alkyl-modified dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

Examples of the polyfunctional oligomer include urethane (meth)acrylic oligomers, polyester (meth)acrylic oligomers, polyether (meth)acrylic oligomers, polyol (meth)acrylic oligomers, epoxy (meth)acrylic oligomers, polyethylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate.

The multifunctional compound used as a crosslinking agent in the second method may be used alone or in combination of two or more. As the multifunctional compound, it is preferred to use a multifunctional monomer, and it is more preferred to use at least one selected from the group consisting of 1,9-nonanediol diacrylate, dipentaerythritol hexaacrylate, 1,6-hexanediol diacrylate, and trihydroxymethylpropane triacrylate.

As for the amount of the multifunctional compound as a crosslinking agent in the first monomer component, from the viewpoint of ensuring the cohesive force of the adhesive sheet 10, it is preferably 0.02 mass parts or more, more preferably 0.05 mass parts or more, and further preferably 0.07 mass parts or more per 100 mass parts of the monofunctional monomer. As for the amount of the multifunctional compound, from the viewpoint of ensuring good adhesion in the adhesive sheet 10, it is preferably 3 mass parts or less, more preferably 2 mass parts or less, and further preferably 1 mass part or less per 100 mass parts of the monofunctional monomer.

The acrylic polymer (base polymer) can be formed by polymerizing the first monomer component. Examples of the polymerization method include solution polymerization, emulsion polymerization, and photopolymerization without a solvent (e.g., ultraviolet polymerization). Examples of solvents for solution polymerization include ethyl acetate and toluene. In the polymerization, a chain transfer agent can also be used. In addition, examples of polymerization initiators include thermal polymerization initiators and photopolymerization initiators. The polymerization initiators can be used alone or in combination of two or more. The amount of the polymerization initiator used is preferably 0.03 parts by mass or more, more preferably 0.05 parts by mass or more, and further preferably 0.07 parts by mass or more per 100 parts by mass of the first monomer component, and is preferably 1 part by mass or less, more preferably 0.5 parts by mass or less, and further preferably 0.3 parts by mass or less.

Examples of the thermal polymerization initiator include azo polymerization initiators and peroxide polymerization initiators. Examples of the azo polymerization initiator include 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionic acid) dimethyl ester, 4,4'-azobis-4-cyanovaleric acid, azobisisovaleronitrile, and 2,2'-azobis(2-amidinopropane) dihydrochloride. Examples of the peroxide polymerization initiator include dibenzoyl peroxide, tert-butyl peroxymaleate, and lauryl peroxide.

Examples of the photopolymerization initiator include radical photopolymerization initiators, cationic photopolymerization initiators, and anionic photopolymerization initiators.

Examples of the radical photopolymerization initiator include acylphosphine oxide photopolymerization initiators, benzoin ether photopolymerization initiators, and acetophenone photopolymerization initiators.

Examples of the acylphosphine oxide-based photopolymerization initiator include bis(2,4,6-trimethylbenzyl)phenylphosphine oxide, bis(2,4,6-trimethylbenzyl)-2,4-di-n-butoxyphenylphosphine oxide, 2,4,6-trimethylbenzyldiphenylphosphine oxide, and bis(2,6-dimethoxybenzyl)-2,4,4-trimethylpentylphosphine oxide. Examples of the benzoin ether-based photopolymerization initiator include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and 2,2-dimethoxy-1,2-diphenylethane-1-one. Examples of the acetophenone-based photopolymerization initiator include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, and 4-(tert-butyl)dichloroacetophenone.

From the viewpoint of ensuring the cohesive force in the adhesive sheet 10, the weight average molecular weight of the base polymer is preferably 100,000 or more, more preferably 300,000 or more, and further preferably 500,000 or more. The weight average molecular weight of the base polymer is measured by gel permeation chromatography (GPC) and calculated by polystyrene conversion.

The glass transition temperature (Tg) of the base polymer is preferably 0°C or lower, more preferably -10°C or lower, and further preferably -20°C or lower. The glass transition temperature is, for example, -80°C or higher. The glass transition temperature (theoretical value) obtained based on the above-mentioned Fox equation can be used for the glass transition temperature (Tg) of the base polymer.

When an acrylic polymer is used as the base polymer, an acrylic oligomer is preferably used as the oligomer. The acrylic oligomer is a copolymer containing a monomer component (second monomer component) of an alkyl (meth)acrylate at a ratio of 50 mass % or more, and has a weight average molecular weight of, for example, 1000 or more and 30000 or less. The oligomer may be used alone or in combination of two or more.

When two or more oligomers are used in combination, at least one oligomer satisfies the specified parameters (e.g., glass transition temperature, difference ΔH (= δH ₂ - δH ₁ ) between hydrogen bonding term δH ₁ of HSP of base polymer and hydrogen bonding term δH ₂ of HSP of oligomer), weight average molecular weight). That is, when two or more oligomers are used in combination, oligomers that do not satisfy the specified parameters (e.g., glass transition temperature, difference ΔH (= δH 2 - δH 1 ) between hydrogen bonding term δH ₁ of HSP of base polymer and hydrogen bonding term δH ₂ of _HSP of _oligomer ), weight average molecular weight) may be included within the scope that does not impair the effect of the present invention. It is preferred that all oligomers used in combination meet the specified parameters.

Examples of the alkyl (meth)acrylate in the second monomer component include cyclic alkyl (meth)acrylate and chain alkyl (meth)acrylate.

As the (meth) cycloalkyl acrylate in the second monomer component, for example, the (meth) cycloalkyl acrylate described above for the first monomer component can be cited. The (meth) cycloalkyl acrylate in the second monomer component is preferably at least one selected from the group consisting of cyclohexyl methacrylate (CHMA), methyl cyclohexyl methacrylate, tert-butyl cyclohexyl methacrylate, cyclododecyl methacrylate, isoindigoyl methacrylate (IBXMA), dicyclopentyl methacrylate (DCPMA), dicyclopentenyl methacrylate, and 1-adamantyl methacrylate (ADMA), and more preferably at least one selected from the group consisting of DCPMA, CHMA, IBXMA, and ADMA.

From the viewpoint of increasing the Tg of the oligomer, the ratio of the (meth) cycloalkyl acrylate in the second monomer component is preferably 30% by mass or more, more preferably 35% by mass or more, and further preferably 40% by mass or more. From the viewpoint of the polymerizability of the second monomer component, the ratio of the (meth) cycloalkyl acrylate in the second monomer component is preferably 80% by mass or less, more preferably 75% by mass or less, and further preferably 65% by mass or less.

As the chain alkyl (meth)acrylate in the second monomer component, for example, the chain alkyl (meth)acrylate described above for the first monomer component can be cited. The chain alkyl (meth)acrylate in the second monomer component is preferably an alkyl (meth)acrylate having an alkyl group with 1 to 6 carbon atoms, more preferably methyl methacrylate (MMA). MMA is preferred because the glass transition temperature of the homopolymer is high and the compatibility with the base polymer is high.

From the viewpoint of ensuring a high Tg of the oligomer and adjusting the compatibility of the oligomer with the base polymer, the ratio of the chain alkyl (meth)acrylate in the second monomer component is preferably 15 mass % or more, more preferably 20 mass % or more, further preferably 25 mass % or more, further preferably 30 mass % or more, and further preferably 60 mass % or less, more preferably 55 mass % or less, further preferably 50 mass % or less.

From the viewpoint of increasing the Tg of the oligomer and adjusting the compatibility of the oligomer with the base polymer, the mass ratio of the cyclic alkyl (meth)acrylate to the chain alkyl (meth)acrylate in the second monomer component is preferably 0.6 or more, more preferably 0.8 or more, and preferably 9.0 or less, more preferably 5.0 or less, and further preferably 2.0 or less.

The second monomer component may also include a copolymerizable monomer that can copolymerize with the (meth) alkyl acrylate. Examples of the copolymerizable monomer include hydrophilic monomers. Examples of the hydrophilic monomer include hydroxyl-containing monomers, monomers having a ring containing a nitrogen atom, carboxyl-containing monomers, and ether-containing monomers. Preferably, the hydrophilic monomer is at least one selected from the group consisting of hydroxyl-containing monomers, monomers having a ring containing a nitrogen atom, carboxyl-containing monomers, and ether-containing monomers. The hydrophilic monomer may be used alone or in combination of two or more.

As the hydroxyl-containing monomer in the second monomer component, for example, the hydroxyl-containing monomers described above for the first monomer component can be cited. The hydroxyl-containing monomer in the second monomer component is preferably at least one selected from the group consisting of 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl methacrylate (HPMA), and 4-hydroxybutyl acrylate (4HBA).

From the viewpoint of adjusting the compatibility of the oligomer with the base polymer, the ratio of the hydroxyl group-containing monomer in the second monomer component is preferably 1 mass % or more, more preferably 3 mass % or more, further preferably 5 mass % or more, and preferably 18 mass % or less, more preferably 15 mass % or less, further preferably 12 mass % or less.

Examples of the monomer having a nitrogen atom-containing ring in the second monomer component include the monomer having a nitrogen atom-containing ring described above with respect to the first monomer component. The monomer having a nitrogen atom-containing ring in the second monomer component is preferably 4-acryloylmoline (ACMO).

From the viewpoint of adjusting the compatibility of the oligomer with the base polymer, the ratio of the monomer having a ring containing a nitrogen atom in the second monomer component is preferably 5 mass % or more, more preferably 10 mass % or more, and further preferably 15 mass % or more. From the viewpoint of controlling the molecular weight of the oligomer, the ratio of the monomer having a ring containing a nitrogen atom in the second monomer component is preferably 30 mass % or less, more preferably 25 mass % or less, and further preferably 22 mass % or less.

Examples of the carboxyl group-containing monomer in the second monomer component include the carboxyl group-containing monomers described above for the first monomer component. The carboxyl group-containing monomer in the second monomer component is preferably acrylic acid (AA).

From the viewpoint of adjusting the compatibility of the oligomer with the base polymer, the ratio of the carboxyl group-containing monomer in the second monomer component is preferably 1 mass % or more, more preferably 3 mass % or more, further preferably 5 mass % or more, and further preferably 18 mass % or less, more preferably 15 mass % or less, further preferably 12 mass % or less.

Examples of the ether group-containing monomer include ethyl carbitol (meth)acrylate, 2-methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, phenoxyethyl (meth)acrylate, and vinyloxyethoxyethyl (meth)acrylate. The ether group-containing monomer is preferably ethyl carbitol acrylate (CBA).

From the viewpoint of adjusting the compatibility of the oligomer with the base polymer, the ratio of the ether group-containing monomer in the second monomer component is preferably 3 mass % or more, more preferably 5 mass % or more, further preferably 7 mass % or more, and further preferably 40 mass % or less, more preferably 35 mass % or less, further preferably 32 mass % or less.

The second monomer component preferably includes a cyclic alkyl (meth)acrylate, a chain alkyl (meth)acrylate, and a hydrophilic monomer. That is, the acrylic oligomer is preferably a copolymer of the second monomer component including a cyclic alkyl (meth)acrylate, a chain alkyl (meth)acrylate, and a hydrophilic monomer.

From the viewpoint of increasing the Tg of the oligomer and adjusting the compatibility of the oligomer with the base polymer, the ratio of the hydrophilic monomer in the second monomer component is preferably 1 mass % or more, more preferably 3 mass % or more, further preferably 5 mass % or more, and further preferably 40 mass % or less, more preferably 35 mass % or less, further preferably 32 mass % or less.

As described above, the acrylic oligomer may be used alone or in combination of two or more. When two or more acrylic oligomers are used in combination, it is preferred that at least one or more of the oligomers is a copolymer of a second monomer component comprising a (meth)acrylate cyclic alkyl ester, a (meth)acrylate chain alkyl ester, and a hydrophilic monomer. Specifically, examples include a copolymer of a second monomer component comprising a (meth)acrylate cyclic alkyl ester and a (meth)acrylate chain alkyl ester, and a copolymer of a second monomer component comprising a (meth)acrylate cyclic alkyl ester, a (meth)acrylate chain alkyl ester, and a hydrophilic monomer.

When two or more acrylic oligomers are used in combination, the content ratio of each copolymer (each acrylic oligomer) in the total amount of acrylic oligomers is not particularly limited, and is appropriately adjusted within the range where the two or more acrylic oligomers used in combination meet the specified parameters. Specifically, the content ratio of the copolymer (one acrylic oligomer) containing a second monomer component of a (meth)acrylate cyclic alkyl ester, a (meth)acrylate chain alkyl ester, and a hydrophilic monomer in the total amount of acrylic oligomers is preferably 50% by mass or more, more preferably 55% by mass or more, and further preferably 58% by mass or more.

The acrylic oligomer is obtained by polymerizing the second monomer component of the acrylic oligomer. Examples of the polymerization method include solution polymerization, emulsion polymerization, and photopolymerization without a solvent (e.g., ultraviolet polymerization). Examples of solvents for solution polymerization include ethyl acetate and toluene. During the polymerization, a chain transfer agent may be used to adjust the molecular weight. Furthermore, examples of polymerization initiators include thermal polymerization initiators and photopolymerization initiators. The polymerization initiators may be used alone or in combination of two or more. The amount of the polymerization initiator used is preferably 0.03 parts by mass or more, more preferably 0.05 parts by mass or more, and further preferably 0.07 parts by mass or more per 100 parts by mass of the second monomer component, and is preferably 1 part by mass or less, more preferably 0.5 parts by mass or less, and further preferably 0.3 parts by mass or less.

From the viewpoint of high adhesion of the surface (adhesive surfaces 11, 12) of the adhesive sheet 10, the weight average molecular weight Mw of the oligomer is preferably 4300 or more, more preferably 4500 or more, and further preferably 4700 or more. From the viewpoint of the oligomer's segregation on the surface and vicinity of the adhesive sheet 10 (property of migration to the surface), the weight average molecular weight Mw of the oligomer is preferably 10000 or less, more preferably 8000 or less, and further preferably 6000 or less. Specifically, the method for determining the weight average molecular weight Mw of the oligomer is as described below in connection with the embodiments.

In order to fully improve the adhesive force of the adhesive sheet 10, the content of the acrylic oligomer in the adhesive sheet 10 is preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, and further preferably 0.5 parts by mass or more, relative to 100 parts by mass of the base polymer. From the viewpoint of ensuring the transparency of the adhesive sheet 10, the content of the acrylic oligomer in the adhesive sheet 10 is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and further preferably 3 parts by mass or less, relative to 100 parts by mass of the base polymer. When the content of the acrylic oligomer in the adhesive sheet 10 is too large, there is a tendency that the compatibility of the acrylic oligomer decreases, resulting in an increase in haze and a decrease in transparency.

The adhesive composition may also contain a silane coupling agent. The content of the silane coupling agent in the adhesive composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, relative to 100 parts by mass of the base polymer. The content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less.

The adhesive composition may also contain other components as needed. Examples of other components include solvents, adhesive agents, plasticizers, softeners, antioxidants, fillers, colorants, ultraviolet absorbers, antioxidants, surfactants, and antistatic agents. Examples of solvents include polymerization solvents used as needed when polymerizing acrylic polymers and solvents added to the polymerization reaction solution after polymerization. Examples of the solvent include ethyl acetate and toluene.

The adhesive sheet 10 can be manufactured, for example, by applying the adhesive composition on the peeling pad L1 (first peeling pad) to form a coating, and then irradiating the coating with ultraviolet rays or drying the coating. The adhesive sheet 10 can also be manufactured by applying the adhesive composition on the peeling pad L1 (first peeling pad) to form a coating, laminating the peeling pad L2 (second peeling pad) on the coating, and then irradiating the coating between the peeling pads with ultraviolet rays or drying the coating.

As the release liner L1, for example, a flexible plastic film can be cited. As the plastic film, for example, polyester films such as polyethylene terephthalate films, polyethylene films, and polypropylene films can be cited. The thickness of the release liner L1 is, for example, not less than 3 μm, and, for example, not more than 200 μm. The surface of the release liner L1 is preferably subjected to a release treatment.

Examples of the coating method of the adhesive composition include roller coating, contact roller coating, gravure coating, reverse coating, roller brush coating, spray coating, dip roller coating, rod coating, scraper coating, air knife coating, curtain coating, die lip coating, and die nozzle coating. The drying temperature of the coating film is, for example, 50° C. to 200° C. The drying time is, for example, 5 seconds to 20 minutes.

The peeling pad L2 is preferably a flexible plastic film with a peeling treatment on the surface. As the peeling pad L2, the plastic film described above for the peeling pad L1 can be used.

The adhesive sheet 10 can be manufactured in the above manner. The adhesive sheet 10 is formed by covering and protecting the adhesive surfaces 11 and 12 with the release pads L1 and L2.

2A to 2C show an example of a method of using the adhesive sheet 10. FIG.

In this method, first, as shown in FIG. 2A , an adhesive sheet 10 is attached to one surface of the first component 21 (adhered body) in the thickness direction H. The first component 21 is, for example, a component in a laminated structure of a flexible display panel. Examples of such components include: a pixel panel, a polarizing film, a touch panel, and a cover film (the same applies to the second component 22 described below). By this step, an adhesive sheet 10 is provided on the first component 21 for bonding with other components.

2B, one side of the first member 21 in the thickness direction H is bonded to the other side of the second member 22 in the thickness direction H via the adhesive sheet 10 on the first member 21. The second member 22 is, for example, another element in the laminated structure of the flexible display panel.

Next, as shown in FIG. 2C , the adhesive sheet 10 between the first component 21 and the second component 22 is aged. By the aging, the bonding force between the adhesive sheet 10 and the components 21 and 22 is improved. The aging temperature is, for example, 20°C to 160°C. The aging time is, for example, 1 minute to 21 days. When the aging is performed by autoclave treatment (heating 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, more than 15 minutes. [Example]

The following examples are given to specifically illustrate the present invention. However, the present invention is not limited to the examples. In addition, the specific numerical values of the blending amounts (contents), physical property values, parameters, etc. described below can be replaced by the upper limits (defined as values "below" or "less than") or lower limits (defined as values "above" or "exceeding") of the corresponding blending amounts (contents), physical property values, parameters, etc. described in the above-mentioned "Implementation Method".

<Preparation of the first prepolymer composition> In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, 0.05 parts by weight of the first photopolymerization initiator (product name "Omnirad 184", 1-hydroxycyclohexyl phenyl ketone, manufactured by IGM Resins) and 0.05 parts by weight of the second photopolymerization initiator (product name "Omnirad 651", 2,2-dimethoxy-1,2-diphenylethane-1-one, manufactured by IGM Resins) were added to a monomer mixture of 70 parts by weight of n-octyl acrylate (NOAA), 20 parts by weight of n-butyl acrylate (BA), 8 parts by weight of 4-hydroxybutyl acrylate (4HBA), and 2 parts by weight of N-vinyl-2-pyrrolidone (NVP). Resins Co., Ltd.) was added, and then the mixture was irradiated with ultraviolet rays in a nitrogen atmosphere, thereby polymerizing a portion of the monomer components in the mixture to obtain the first prepolymer composition. A black light was used for ultraviolet irradiation. The ultraviolet irradiation was continued until the viscosity of the composition reached 10-20 Pa·s. The viscosity was measured using a B-type viscometer (product name "TVB-10M", manufactured by Toki Sangyo Co., Ltd.) under the conditions of rotor No. 22, rotor speed 6 rpm, and temperature 30°C (the same applies to the viscosity described below). The first prepolymer composition obtained contains a partial polymer of acrylic polymer P1 and monomer components (residual monomers) that have not undergone polymerization reaction. The weight average molecular weight of acrylic polymer P1 in the first prepolymer composition is approximately 4.3 million.

<Preparation of the second prepolymer composition> In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, 0.05 parts by mass of the first photopolymerization initiator (Omnirad 184) and 0.05 parts by mass of the second photopolymerization initiator (Omnirad 651) were added to a monomer mixture of 48 parts by mass of lauryl acrylate (LA), 51 parts by mass of 2-ethylhexyl acrylate (2EHA), and 1 part by mass of 4-hydroxybutyl acrylate (4HBA), and then the mixture was irradiated with ultraviolet light in a nitrogen atmosphere to polymerize part of the monomer components in the mixture to obtain the second prepolymer composition. A black light was used for ultraviolet irradiation. Ultraviolet irradiation was continued until the viscosity of the composition reached 10 to 20 Pa·s. The obtained second prepolymer composition contains acrylic polymer P2 and a partial polymer of monomer components that have not undergone polymerization reaction (residual monomers). The weight average molecular weight of acrylic polymer P2 in the second prepolymer composition is about 4.8 million.

<Preparation of the third prepolymer composition> In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, 0.05 parts by mass of the first photopolymerization initiator (Omnirad 184) and 0.05 parts by mass of the second photopolymerization initiator (Omnirad 651) were added to a monomer mixture of 70 parts by mass of n-octyl acrylate (NOAA), 20 parts by mass of n-butyl acrylate (BA), 30 parts by mass of lauryl acrylate (LA), 8 parts by mass of 4-hydroxybutyl acrylate (4HBA), and 2 parts by mass of N-vinyl-2-pyrrolidone (NVP), and then the mixture was irradiated with ultraviolet light in a nitrogen atmosphere to polymerize part of the monomer components in the mixture to obtain the third prepolymer composition. A black light was used for ultraviolet irradiation. The ultraviolet irradiation is continued until the viscosity of the composition reaches 10-20 Pa·s. The third prepolymer composition obtained contains acrylic polymer P3 and a partial polymer of monomer components that have not undergone polymerization reaction (residual monomers). The weight average molecular weight of acrylic polymer P3 in the third prepolymer composition is about 5 million.

<Preparation of acrylic oligomer M1> First, in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, a mixture containing 45 parts by mass of isobutyl methacrylate (IBXMA), 45 parts by mass of methyl methacrylate (MMA), 10 parts by mass of carbitol acrylate (CBA), 3 parts by mass of α-thioglycerol as a chain transfer agent, 0.3 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and ethyl acetate as a solvent (solid content concentration 26% by mass) was reacted at 72°C to 74°C for 6 hours under a nitrogen atmosphere (polymerization reaction). Then, the reaction solution was heated at 90°C for 12 hours to volatilize and remove ethyl acetate, chain transfer agent and unreacted monomers. Thus, a solid acrylic oligomer M1 was obtained. The weight average molecular weight (Mw) of the acrylic oligomer M1 was 4880. The glass transition temperature (Tg) of the acrylic oligomer M1 was 98.5°C.

<Preparation of acrylic oligomer M2> A solid acrylic oligomer M2 was obtained in the same manner as acrylic oligomer M1 except that the blending amount of IBXMA was 35 parts by mass, the blending amount of MMA was 35 parts by mass, and the blending amount of CBA was 30 parts by mass. The Mw of acrylic oligomer M2 was 5400. The Tg of acrylic oligomer M2 was 50.9°C.

<Preparation of acrylic oligomer M3> First, in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, a mixture containing 45 parts by mass of dicyclopentyl methacrylate (DCPMA), 45 parts by mass of MMA, 10 parts by mass of CBA, 3 parts by mass of α-thioglycerol as a chain transfer agent, 0.3 parts by mass of AIBN as a thermal polymerization initiator, and ethyl acetate as a solvent (solid content concentration 26% by mass) was reacted at 72°C to 74°C for 6 hours under a nitrogen atmosphere (polymerization reaction). Then, the reaction solution was heated at 90°C for 12 hours to volatilize and remove ethyl acetate, chain transfer agent, and unreacted monomers. In this way, a solid acrylic oligomer M3 was obtained. The Mw of acrylic oligomer M3 is 5230. The Tg of acrylic oligomer M3 is 97.7℃.

<Preparation of acrylic oligomer M4> The acrylic oligomer M4 was obtained in a solid form in the same manner as the acrylic oligomer M1, except that the amount of IBXMA was set to 40 parts by mass, the amount of MMA was set to 40 parts by mass, and 20 parts by mass of 4-acryloyl methoxyphene (ACMO) was used instead of 10 parts by mass of CBA. The Mw of the acrylic oligomer M4 was 4940. The Tg of the acrylic oligomer M4 was 129.2°C.

<Preparation of acrylic oligomer M5> Solid acrylic oligomer M5 was obtained in the same manner as acrylic oligomer M3 except that the amount of DCPMA was set to 40 parts by mass, the amount of MMA was set to 40 parts by mass, and 20 parts by mass of ACMO was used instead of 10 parts by mass of CBA. The Mw of acrylic oligomer M5 was 5110. The Tg of acrylic oligomer M5 was 128.3°C.

<Preparation of acrylic oligomer M6> Solid acrylic oligomer M6 was obtained in the same manner as acrylic oligomer M1 except that 10 parts by mass of acrylic acid (AA) was used instead of 10 parts by mass of CBA. The Mw of acrylic oligomer M6 was 5670. The Tg of acrylic oligomer M6 was 121.9°C.

<Preparation of acrylic oligomer M7> Solid acrylic oligomer M7 was obtained in the same manner as acrylic oligomer M3 except that 10 parts by mass of 2-hydroxyethyl methacrylate (HEMA) was used instead of 10 parts by mass of CBA. The Mw of acrylic oligomer M7 was 5600. The Tg of acrylic oligomer M7 was 115.8°C.

<Preparation of acrylic oligomer M8> Solid acrylic oligomer M8 was obtained in the same manner as acrylic oligomer M3 except that the amount of DCPMA was set to 60 parts by mass, the amount of MMA was set to 30 parts by mass, and 10 parts by mass of HEMA was used instead of 10 parts by mass of CBA. The Mw of acrylic oligomer M8 was 5570. The Tg of acrylic oligomer M8 was 123.9°C.

<Preparation of acrylic oligomer M9> First, in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, a mixture containing 45 parts by mass of cyclohexyl methacrylate (CHMA), 45 parts by mass of MMA, 10 parts by mass of HEMA, 3 parts by mass of α-thioglycerol as a chain transfer agent, 0.3 parts by mass of AIBN as a thermal polymerization initiator, and ethyl acetate as a solvent (solid content concentration 26% by mass) was reacted at 72°C to 74°C for 6 hours under a nitrogen atmosphere (polymerization reaction). Then, the reaction solution was heated at 90°C for 12 hours to volatilize and remove ethyl acetate, chain transfer agents, and unreacted monomers. In this way, a solid acrylic oligomer M9 was obtained. The Mw of acrylic oligomer M9 is 5920. The Tg of acrylic oligomer M9 is 85.4℃.

<Preparation of acrylic oligomer M10> Solid acrylic oligomer M10 was obtained in the same manner as acrylic oligomer M9 except that 10 parts by mass of 4HBA was used instead of 10 parts by mass of HEMA. The Mw of acrylic oligomer M10 was 5740. The Tg of acrylic oligomer M10 was 72.2°C.

<Preparation of acrylic oligomer M11> Solid acrylic oligomer M11 was obtained in the same manner as acrylic oligomer M9 except that 10 parts by mass of 2-hydroxypropyl methacrylate (HPMA) was used instead of 10 parts by mass of HEMA. The Mw of acrylic oligomer M11 was 5840. The Tg of acrylic oligomer M11 was 82.4°C.

<Preparation of acrylic oligomer M12> Acrylic oligomer M12 was obtained in the same manner as acrylic oligomer M1, except that 10 parts by mass of 4HBA was used instead of 10 parts by mass of CBA. The Mw of acrylic oligomer M12 was 5320. The Tg of acrylic oligomer M12 was 99.2°C.

<Preparation of acrylic oligomer M13> First, in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, a mixture containing 50 parts by mass of IBXMA, 50 parts by mass of NVP, 3 parts by mass of α-thioglycerol as a chain transfer agent, 0.3 parts by mass of AIBN as a thermal polymerization initiator, and ethyl acetate as a solvent (solid content concentration 26% by mass) was reacted at 72°C to 74°C for 6 hours under a nitrogen atmosphere (polymerization reaction). Then, the reaction solution was heated at 90°C for 12 hours to volatilize and remove ethyl acetate, chain transfer agent, and unreacted monomers. In this way, a solid acrylic oligomer M13 was obtained. The Mw of acrylic oligomer M13 is 10200. The Tg of acrylic oligomer M13 is 193℃.

<Preparation of acrylic oligomer M14> First, in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, a mixture containing 50 parts by mass of n-pentyl acrylate (NPA) (product name "LIMA", manufactured by Osaka Organic Chemical Industry Co., Ltd.), 50 parts by mass of MMA, 3 parts by mass of α-thioglycerol as a chain transfer agent, 0.3 parts by mass of AIBN as a thermal polymerization initiator, and ethyl acetate as a solvent (solid content concentration 26% by mass) was reacted at 72°C to 74°C for 6 hours under a nitrogen atmosphere (polymerization reaction). Then, the reaction solution was heated at 90°C for 12 hours to volatilize and remove ethyl acetate, the chain transfer agent, and unreacted monomers. In this way, a solid acrylic oligomer M14 was obtained. The Mw of the acrylic oligomer M14 was 5220. The Tg of the acrylic oligomer M14 was 20.6°C.

<Preparation of acrylic oligomer M15> Solid acrylic oligomer M15 was obtained in the same manner as acrylic oligomer M1, except that the amount of IBXMA was set to 90 parts by mass and MMA was not added. The Mw of acrylic oligomer M15 was 4230. The Tg of acrylic oligomer M15 was 123.4°C.

<Preparation of acrylic oligomer M16> A solid acrylic oligomer M16 was obtained in the same manner as acrylic oligomer M3 except that the amount of DCPMA was set to 40 parts by mass, the amount of MMA was set to 40 parts by mass, and 20 parts by mass of 4HBA was used instead of 10 parts by mass of CBA. The Mw of acrylic oligomer M16 was 5350. The Tg of acrylic oligomer M16 was 76.8°C.

<Preparation of acrylic oligomer M17> Acrylic oligomer M17 was obtained in the same manner as acrylic oligomer M1, except that 10 parts by mass of lauryl methacrylate (LMA) was used instead of 10 parts by mass of CBA. The Mw of acrylic oligomer M17 was 5780. The Tg of acrylic oligomer M17 was 125.5°C.

<Preparation of acrylic oligomer M18> Solid acrylic oligomer M18 was obtained in the same manner as acrylic oligomer M1, except that the amount of IBXMA was set to 75 parts by mass, the amount of MMA was set to 20 parts by mass, and 5 parts by mass of HEMA was used instead of 10 parts by mass of CBA. The Mw of acrylic oligomer M18 was 4610. The Tg of acrylic oligomer M18 was 141.0℃.

<Preparation of acrylic oligomer M19> Solid acrylic oligomer M19 was obtained in the same manner as acrylic oligomer M7 except that 10 parts by mass of 4HBA was used instead of 10 parts by mass of HEMA. The Mw of acrylic oligomer M19 was 5430. The Tg of acrylic oligomer M19 was 99.2°C.

<Preparation of acrylic oligomer M20> A solid acrylic oligomer M20 was obtained in the same manner as acrylic oligomer M1 except that the amount of IBXMA was set to 80 parts by mass, the amount of CMA was set to 20 parts by mass, and MMA was not added. The Mw of acrylic oligomer M20 was 3820. The Tg of acrylic oligomer M20 was 80.8°C.

<Preparation of acrylic oligomer M21> Except that the amount of IBXMA was 70 parts by mass, the amount of MMA was 20 parts by mass, and the amount of CBA was 10 parts by mass, a solid acrylic oligomer M21 was obtained in the same manner as the acrylic oligomer M1. The Mw of the acrylic oligomer M21 was 4060. The Tg of the acrylic oligomer M21 was 109.3°C.

<Preparation of acrylic oligomer M22> Except that the amount of DCPMA was set to 47.5 parts by mass, the amount of MMA was set to 47.5 parts by mass, and the amount of HEMA was set to 5 parts by mass, a solid acrylic oligomer M22 was obtained in the same manner as the acrylic oligomer M8. The Mw of the acrylic oligomer M22 was 5150. The Tg of the acrylic oligomer M22 was 120.0°C.

<Preparation of acrylic oligomer M23> Except that the amount of DCPMA was set to 70 parts by mass, the amount of MMA was set to 20 parts by mass, and the amount of HEMA was set to 10 parts by mass, a solid acrylic oligomer M23 was obtained in the same manner as the acrylic oligomer M8. The Mw of the acrylic oligomer M23 was 5840. The Tg of the acrylic oligomer M23 was 130.8°C.

<Preparation of acrylic oligomer M24> Solid acrylic oligomer M24 was obtained in the same manner as acrylic oligomer M23 except that 70 parts by mass of 1-adamantyl methacrylate (ADMA) was used instead of 70 parts by mass of DCPMA. The Mw of acrylic oligomer M24 was 5150. The Tg of acrylic oligomer M24 was 160.7°C.

<Preparation of acrylic oligomer M25> A solid acrylic oligomer M25 was obtained in the same manner as acrylic oligomer M8 except that the amount of DCPMA was 60 parts by mass, the amount of MMA was 40 parts by mass, and HEMA was not used. The Mw of acrylic oligomer M25 was 4940. The Tg of acrylic oligomer M25 was 130.6°C.

[Example 1] <Preparation of adhesive composition> 3.0 parts by mass of acrylic oligomer M1 and 0.07 parts by mass of crosslinking agent (product name "Viscoat #260", 1,9-nonanediol diacrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd.) were added to the first prepolymer composition for every 100 parts by mass of monomer components (monomer components forming the base polymer in the adhesive layer described below in this example) in the composition and mixed to prepare the first adhesive composition. The relative parts of the acrylic oligomer per 100 parts by mass of the base polymer in the adhesive layer described below in this example are set as "parts" and shown in Tables 1 and 2.

<Formation of Adhesive Layer> Next, the first adhesive composition is applied to the release-treated surface of the first release liner treated with silicone release on one side to form a coating film. The first release liner is a polyethylene terephthalate (PET) film treated with silicone release on one side (product name "DIAFOIL MRE#75", thickness 75 μm, manufactured by Mitsubishi Chemical Co., Ltd.). Next, the release-treated surface of the second release liner treated with silicone release on one side is attached to the coating film on the first release liner. The second release pad is a PET film (product name "DIAFOIL MRF#75", thickness 75 μm, manufactured by Mitsubishi Chemical Co., Ltd.) with silicone release treatment on one side. Then, the coating between the release pads is irradiated with ultraviolet light to photoharden the coating to form an adhesive layer (thickness 50 μm). When irradiating with ultraviolet light, a black light is used as the irradiation light source, the irradiation intensity is set to about 2.5 mW/cm ² , and the irradiation time is set to 16 minutes. The adhesive sheet (thickness 50 μm) of Example 1 with a release pad is prepared in the above manner.

[Examples 2 to 12] When preparing the adhesive composition, the type and amount of the acrylic oligomer to be prepared were changed as shown in Tables 1 and 2. In addition, the adhesive sheets with peel-off pads of Examples 2 to 12 were prepared in the same manner as the adhesive sheets with peel-off pads of Example 1.

[Comparative Example 1] The adhesive sheet with a peel-off liner of Comparative Example 1 was prepared in the same manner as the adhesive sheet with a peel-off liner of Example 1 except that no acrylic oligomer was added when preparing the adhesive composition.

[Comparative Examples 2 to 6] When preparing the adhesive composition, the type and amount of the acrylic oligomer to be formulated were changed as shown in Table 2. In addition, the adhesive sheets with peel-off pads of Comparative Examples 2 to 6 were prepared in the same manner as the adhesive sheets with peel-off pads of Example 1.

[Example 13] <Preparation of adhesive composition> 1.0 mass part of acrylic oligomer M18 and 0.07 mass part of crosslinking agent (product name "Viscoat #260", 1,9-nonanediol diacrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd.) were added to the second prepolymer composition for every 100 mass parts of monomer components (monomer components forming the base polymer in the adhesive layer described below in this example) in the composition and mixed to prepare the second adhesive composition. The relative parts of the acrylic oligomer per 100 mass parts of the base polymer in the adhesive layer described below in this example are set as "parts" and are shown in Table 3.

<Formation of adhesive layer> In addition to using the second adhesive composition instead of the first adhesive composition, an adhesive layer with a thickness of 50 μm is formed between the peeling pads in the same manner as the formation of the adhesive layer described above in Example 1. The adhesive sheet (thickness 50 μm) of Example 13 with a peeling pad is prepared in the above manner.

[Comparative Example 7] The adhesive sheet with a peel-off liner of Comparative Example 7 was prepared in the same manner as the adhesive sheet with a peel-off liner of Example 13 except that no acrylic oligomer was added when preparing the adhesive composition.

[Comparative Examples 8 and 9] When preparing the adhesive composition, the type of the acrylic oligomer to be formulated was changed as shown in Table 3. Except for this, the adhesive sheets with peel-off pads of Comparative Examples 8 and 9 were prepared in the same manner as the adhesive sheet with peel-off pads of Example 13.

[Example 14] <Preparation of adhesive composition> 1.0 mass part of acrylic oligomer M8 and 0.07 mass part of crosslinking agent (product name "Viscoat #260", 1,9-nonanediol diacrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd.) were added to the third prepolymer composition for every 100 mass parts of monomer components (monomer components forming the base polymer in the adhesive layer described below in this example) in the composition and mixed to prepare the third adhesive composition. The relative parts of the acrylic oligomer per 100 mass parts of the base polymer in the adhesive layer described below in this example are set as "parts" and shown in Table 4.

<Formation of adhesive layer> In addition to using the third adhesive composition instead of the first adhesive composition, an adhesive layer with a thickness of 50 μm is formed between the peeling pads in the same manner as the formation of the adhesive layer described above in Example 1. The adhesive sheet (thickness 50 μm) of Example 14 with a peeling pad is prepared in the above manner.

[Example 15] When preparing the adhesive composition, the type of the acrylic oligomer to be formulated was changed as shown in Table 4. Except for this, the adhesive sheet with a peel-off liner of Example 15 was prepared in the same manner as the adhesive sheet with a peel-off liner of Example 15.

[Comparative Example 10] The adhesive sheet with a peel-off liner of Comparative Example 10 was prepared in the same manner as the adhesive sheet with a peel-off liner of Example 14 except that no acrylic oligomer was added when preparing the adhesive composition.

[Comparative Examples 11 and 12] When preparing the adhesive composition, the type of acrylic oligomer to be formulated was changed as shown in Table 4. Except for this, the adhesive sheets with peel-off pads of Comparative Examples 11 and 12 were prepared in the same manner as the adhesive sheets with peel-off pads of Example 14.

[Example 16] ＜Preparation of adhesive composition＞ To the first prepolymer composition, 1.5 parts by weight of acrylic oligomer M22, 0.11 parts by weight of dipentaerythritol hexaacrylate (DPHA), 0.02 parts by weight of additional photopolymerization initiator (product name "Omnirad 819", bis(2,4,6-trimethylbenzyl)phenylphosphine oxide, IGM were added per 100 parts by weight of the monomer components in the composition (monomer components forming the base polymer in the adhesive layer described below in this example). Resins Co., Ltd.), 0.02 mass parts of silane coupling agent (product name "KBM-403", 3-glyceryloxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) and 0.5 mass parts are mixed to prepare the fourth adhesive composition. The relative proportion of the acrylic oligomer per 100 mass parts of the base polymer in the following adhesive layer in this embodiment is set as "parts" and shown in Table 5.

<Formation of adhesive layer> In addition to using the fourth adhesive composition instead of the first adhesive composition, an adhesive layer with a thickness of 50 μm is formed between the peeling pads in the same manner as the formation of the adhesive layer described above in Example 1. The adhesive sheet (thickness 50 μm) of Example 16 with a peeling pad is prepared in the above manner.

[Examples 17 to 19] When preparing the adhesive composition, the type of acrylic oligomer to be prepared was changed as shown in Table 5. Except for this, each peel-off liner-attached adhesive sheet of Examples 17 to 19 was prepared in the same manner as the peel-off liner-attached adhesive sheet of Example 16. Furthermore, in Example 19, two types of acrylic oligomers were prepared (0.5 parts by mass of acrylic oligomer M25 and 1.0 parts by mass of acrylic oligomer M22 were added to the first prepolymer composition per 100 parts by mass of the monomer component in the composition).

<First measurement method of weight average molecular weight> Under the following first measurement conditions, the weight average molecular weight (Mw) of each of the acrylic polymers and acrylic oligomers not containing nitrogen-containing monomers is measured by gel permeation chromatography (GPC) and is calculated as a polystyrene conversion value. For the measurement, a GPC measurement device (product name "HLC-8120GPC", manufactured by Tosoh) is used. The sample solution is prepared as follows. First, the above-mentioned acrylic polymer or acrylic oligomer not containing nitrogen-containing monomers is used as a sample, and a tetrahydrofuran (THF) solution (containing 10 mM phosphoric acid) with a sample concentration of 0.20 mass% is prepared, and the THF solution is left to stand for 20 hours. Then, the THF solution was filtered using a membrane filter with an average pore size of 0.45 μm to obtain the filtrate as the sample solution for molecular weight determination.

[GPC 1st measurement condition] Column: G7000H _XL + GMH _XL + GMH _XL , each TSKgel (Tosoh) Column temperature: 40°C Eluent: THF solution (phosphoric acid concentration 10 mM) Flow rate: 0.8 mL/min Sample injection volume: 100 μL Standard sample: Polystyrene (Agilent) Detector: Differential refractometer (RI)

<Second measurement method of weight average molecular weight> Under the following second measurement conditions, the weight average molecular weight (Mw) of each of the acrylic polymers and acrylic oligomers containing nitrogen-containing monomers is measured by gel permeation chromatography (GPC) and is calculated as a polystyrene conversion value. For the measurement, a GPC measurement device (product name "HLC-8120GPC", manufactured by Tosoh) is used. The sample solution is prepared as follows. First, the above-mentioned acrylic polymer or acrylic oligomer containing nitrogen-containing monomer is used as a sample, and a dimethylformamide (DMF) solution (salt added) with a sample concentration of 0.20 mass% is prepared, and the DMF solution is allowed to stand for 20 hours. Next, the DMF solution was filtered using a membrane filter with an average pore size of 0.45 μm to obtain a filtrate, which was used as a sample solution for molecular weight determination.

[GPC second measurement condition] Column: SuperAWM-H + SuperAW4000 + SuperAW2500, each TSKgel (Tosoh) Column temperature: 40°C Solvent: DMF solution (with added salt) Flow rate: 0.4 mL/min Sample injection volume: 40 μL Standard sample: Polystyrene (Agilent) Detector: Differential refractometer (RI)

<Tg of oligomer> Based on the above-mentioned Fox formula, the glass transition temperature (Tg) of acrylic oligomers M1 to M25 was calculated. The values are shown in Tables 1 to 5.

<Hydrogen bonding term of HSP> The hydrogen bonding term of the Hansen solubility parameter (HSP) of each of the acrylic oligomers M1 to M25 was determined. Specifically, it is as follows.

First, the hydrogen bonding term ( _δhi ) of each monomer _mi forming the acrylic oligomer is calculated by the computer software HSPiP (Hansen Solubility Parameters in Practice). Then, the hydrogen bonding term (δH) of the acrylic oligomer is calculated by the following formula based on the molar fraction _xi of the monomer _mi in the acrylic oligomer and the hydrogen bonding term _δhi of the monomer _mi . For example, the hydrogen bonding term of acrylic oligomer M1 is 5.39 MPa ^{1/2 as calculated from the molar fraction of 0.289 and hydrogen bonding term of 2.4 MPa 1/2 of} IBXMA (molecular weight 220.0), the molar fraction of 0.636 and hydrogen bonding term of 6.6 MPa ^1/2 of MMA (molecular weight 100.1), and the molar fraction of 0.075 and hydrogen bonding term of 6.5 MPa ^1/2 of CBA (molecular weight 188.2). The hydrogen bonding term of acrylic oligomers M1 to M25 is shown as δH ₂ in Tables 1 to 5.

δH＝ _Σxi × _δhi

Similarly, the hydrogen bonding term (δH ₁ ) of the HSP of the acrylic polymer was determined. For example, in the acrylic polymer comprising the first prepolymer composition, the value was 5.07 MPa ^1/2 . The ratio of δH ₂ of the acrylic oligomer to δH ₁ of the acrylic polymer in the adhesive sheet (δH ₂ /δH ₁ ) and the difference ΔH between δH ₂ and δH ₁ (=δH ₂ -δH ₁ ) are also shown in Tables 1 to 5.

<Gel fraction> For each adhesive sheet of Examples 1 to 19 and Comparative Examples 1 to 12, the gel fraction was measured as follows.

First, take about 500 mg of adhesive sample from the adhesive sheet between the peeling pads. Then, measure the mass of the adhesive sample (W ₁ ). Then, immerse the adhesive sample in 40 g of ethyl acetate in a container for 7 days. Then, recover all the components that are insoluble in ethyl acetate (insoluble part). Then, dry the insoluble part at 130°C for 2 hours (to remove ethyl acetate). Then, measure the mass of the insoluble part (W ₂ ). Then, calculate the gel fraction (mass %) of the adhesive sheet after light curing based on the following formula. The values are shown in Tables 1 to 5.

Gel fraction (mass %) = (W ₂ /W ₁ ) × 100

<Fog> The fog of each adhesive sheet of Examples 1 to 19 and Comparative Examples 1 to 12 was measured as follows.

First, prepare a sample for measurement. Specifically, after peeling the first peelable liner from the adhesive sheet, adhere the sheet to alkaline glass (thickness 1.0 mm, total light transmittance 92%, haze 0.4%, manufactured by Matsunami Glass Co., Ltd.). Next, peel the first peelable liner from the adhesive sheet on the glass. In this way, a sample for measurement is prepared. Next, use a haze meter (product name "HM-150", manufactured by Murakami Color Technology Laboratory) to measure the haze of each adhesive sheet in the sample. The measurement is based on JIS K7136 (2000). In this measurement, the sample is placed in the device in a manner such that light is irradiated from its alkaline glass side. The measured haze values of the adhesive sheets are shown in Tables 1-5.

<Shear storage modulus> Dynamic viscoelasticity was measured for each adhesive sheet of Examples 1 to 19 and Comparative Examples 1 to 12 (first measurement).

The required number of samples for measurement were prepared for each adhesive sheet. Specifically, first, a plurality of adhesive sheet sections cut from the adhesive sheet were bonded together to prepare a sample sheet with a thickness of about 1.0 mm. Then, the sheet was punched to obtain cylindrical particles (diameter 7.9 mm) as the sample for measurement.

Then, using a dynamic viscoelasticity measuring device (product name "Advanced Rheometric Expansion System (ARES)", manufactured by Rheometric Scientific), the sample for measurement was fixed to a parallel plate jig with a diameter of 7.9 mm, and then the dynamic viscoelasticity measurement was performed. In this measurement, the measurement mode was set to shear mode, the measurement temperature range was set to -65℃ to 200℃, the heating rate was set to 5℃/min, and the frequency was set to 1 Hz. The shear storage modulus at specific temperatures (-20℃, -10℃, 60℃) was read from the measurement results. The shear storage modulus G1 (kPa) at -10°C, the shear storage modulus G2 (kPa) at 60°C, the shear storage modulus G3 (kPa) at -20°C, and the ratio of the shear storage modulus G2 to the shear storage modulus G1 (G2/G1) are shown in Tables 1 to 5.

<Peeling test> For each adhesive sheet of Examples 1 to 19 and Comparative Examples 1 to 12, the adhesive force to the adherend was investigated by a peeling test.

Specifically, first, the required number of test samples were prepared for each adhesive sheet. In the process of preparing the test samples, first, the first peeling pad was peeled off from the adhesive sheet, and the exposed surface was bonded to a polyethylene terephthalate (PET) film (product name "Lumirror S10", thickness 25 μm, manufactured by Toray) whose surface was plasma-treated to obtain a laminate. In the plasma treatment, a plasma irradiation device (product name "AP-TO5", manufactured by Sekisui Industries) was used, and the voltage was set to 160 V, the frequency was set to 10 kHz, and the treatment speed was set to 5000 mm/min (the same applies to the plasma treatment described below). Next, a test piece (20 mm wide x 100 mm long) is cut out from the laminate (PET film/adhesive sheet/second peeling pad). Next, the second peeling pad is peeled off from the adhesive sheet in the test piece, and the exposed surface is bonded to a glass substrate (acrylic glass manufactured by Matsunami Glass Co., Ltd.). Next, the glass substrate with the adhesive sheet (test piece) attached is heated and pressurized at a temperature of 50°C and a pressure of 0.5 MPa for 15 minutes. In this way, the test piece is pressed against the glass substrate. The test sample is prepared in the above manner.

Next, after the test sample was left at room temperature for 30 minutes, a 180° peeling test was performed to peel the test piece from the glass substrate in the test sample, and the force required for peeling (peeling strength) was measured (first peeling test). In this test, a tensile testing machine (product name "Autograph AG-50NX plus" manufactured by Shimadzu Corporation) was used. In this test, the measuring temperature was set to 25°C, the relative humidity was set to 55%, the angle of peeling the test piece from the glass substrate was set to 180°, the tensile speed of the test piece was set to 300 mm/min, and the peeling length was set to 50 mm. The average value of the measured peel strength is shown in Tables 1 to 5 as adhesion force F1 (N/20 mm).

On the other hand, a peeling test (second peeling test) was performed under the same conditions as the first peeling test except that the tensile speed was changed to 60 mm/min. The measurement results are shown in Tables 1 to 5 as adhesion F2 (N/20 mm). In addition, the ratio of the above-mentioned adhesion F2 to the adhesion F1 (F2/F1) is also shown in Tables 1 to 5.

[Evaluation] The adhesive sheet of Comparative Example 1 is a soft adhesive sheet with a shear storage modulus G1 of less than 100 kPa at -10°C, but does not contain oligomers with a Tg of more than 40°C, and the adhesion forces F1 and F2 are relatively small.

The adhesive sheet of Comparative Example 2 contains an oligomer (acrylic oligomer M13) having a Tg of 40°C or higher, but the difference ΔH (=δH ₂ -δH ₁ ) is less than 0.1, and the adhesive forces F1 and F2 are small. In the adhesive sheet of Comparative Example 2, the acrylic oligomer M13 is not segregated on the adhesive surface and its vicinity.

The adhesive sheet of Comparative Example 3 does not contain an oligomer having a Tg of 40° C. or higher, and the adhesive forces F1 and F2 are relatively small.

The adhesive sheet of Comparative Example 4 contains an oligomer (acrylic oligomer M15) having a Tg of 40°C or higher, but the difference ΔH (=δH ₂ -δH ₁ ) is less than 0.1, and the adhesive forces F1 and F2 are small. In the adhesive sheet of Comparative Example 4, the acrylic oligomer M15 is not segregated on the adhesive surface and its vicinity.

The adhesive sheet of Comparative Example 5 contains an oligomer (acrylic oligomer M16) with a Tg of 40°C or higher, but the difference ΔH (=δH ₂ -δH ₁ ) exceeds 1.3, and the haze is too large. In the adhesive sheet of Comparative Example 5, the compatibility of acrylic oligomer M16 with the base polymer is low, and crystal nuclei are formed to generate light scattering.

The adhesive sheet of Comparative Example 6 contains an oligomer (acrylic oligomer M17) having a Tg of 40°C or higher, but the difference ΔH (=δH ₂ -δH ₁ ) is less than 0.1, and the adhesive forces F1 and F2 are small. In the adhesive sheet of Comparative Example 6, the acrylic oligomer M17 is not sufficiently segregated on the adhesive surface and its vicinity.

In contrast, the shear storage modulus G1 of each adhesive sheet of Examples 1 to 12 at -10°C is less than 100 kPa, which is relatively soft, and contains oligomers with a Tg of 40°C or more, and the δH ₁ of the HSP of the base polymer and the δH ₂ of the HSP of the oligomer satisfy 0.1≦δH ₂ -δH ₁ ≦1.3. The adhesive force F1 of such adhesive sheets of Examples 1 to 12 is greater than 8.0 N/20 mm. In each adhesive sheet of Examples 1 to 12, the oligomers with a Tg of 40°C or more are sufficiently segregated on the adhesive surface and its vicinity.

The adhesive sheet of Comparative Example 7 is a soft adhesive sheet with a shear storage modulus G1 of 100 kPa or less at -10°C, but does not contain an oligomer with a Tg of 40°C or more, and the adhesive forces F1 and F2 are small. The adhesive sheet of Comparative Example 8 contains an oligomer with a Tg of 40°C or more (acrylic oligomer M19), but the difference ΔH (= δH ₂ - δH ₁ ) exceeds 1.3, the haze is too large, and the adhesive forces F1 and F2 are small. The adhesive sheet of Comparative Example 9 contains an oligomer with a Tg of 40°C or more (acrylic oligomer M20), but the difference ΔH (= δH ₂ - δH ₁ ) is less than 0.1, and the adhesive forces F1 and F2 are small. In the adhesive sheet of Comparative Example 9, the acrylic oligomer M20 is not concentrated on the adhesive surface and its vicinity. Compared with the adhesive sheets of Comparative Examples 7 to 9, the adhesive sheet of Example 13 has a shear storage modulus G1 of 100 kPa or less at -10°C, is softer, and contains an oligomer with a Tg of 40°C or more, and the δH ₁ of the HSP of the base polymer and the δH ₂ of the HSP of the oligomer satisfy 0.1≦δH ₂ -δH ₁ ≦1.3. The adhesive force F1 of the adhesive sheet of Example 13 is 7.7 N/20 mm, which is greater than the adhesive force F1 of the adhesive sheets of Comparative Examples 7 to 9 (the base polymer is the same as that of Example 13). In each adhesive sheet of Example 13, the oligomers with a Tg of 40°C or higher are sufficiently segregated on the adhesive surface and its vicinity. The shear storage modulus G1 of the adhesive sheet of Example 13 at -10°C is 40 kPa or less, and is very soft, having both softness and adhesiveness.

The adhesive sheet of Comparative Example 10 is a soft adhesive sheet with a shear storage modulus G1 of 100 kPa or less at -10°C, but does not contain an oligomer with a Tg of 40°C or more, and the adhesive forces F1 and F2 are small. The adhesive sheet of Comparative Example 11 contains an oligomer with a Tg of 40°C or more (acrylic oligomer M19), but the difference ΔH (=δH ₂ -δH ₁ ) exceeds 1.3, and the adhesive forces F1 and F2 are small. The adhesive sheet of Comparative Example 12 contains an oligomer with a Tg of 40°C or more (acrylic oligomer M21), but the difference ΔH (=δH ₂ -δH ₁ ) is less than 0.1, and the adhesive forces F1 and F2 are small. In the adhesive sheet of Comparative Example 12, the acrylic oligomer M21 is not concentrated on the adhesive surface and its vicinity. Compared with the adhesive sheets of Comparative Examples 10 to 12, the adhesive sheets of Examples 14 and 15 have a shear storage modulus G1 of 100 kPa or less at -10°C, are softer, and contain oligomers with a Tg of 40°C or more, and the δH ₁ of the HSP of the base polymer and the δH ₂ of the HSP of the oligomer satisfy 0.1≦δH ₂ -δH ₁ ≦1.3. The adhesive force F1 of such adhesive sheets of Examples 14 and 15 is 7.6 N/20 mm or more, which is greater than the adhesive force F1 of the adhesive sheets of Comparative Examples 10 to 12 (the base polymer is the same as that of Examples 14 and 15). In each of the adhesive sheets of Examples 14 and 15, oligomers having a Tg of 40° C. or higher are sufficiently segregated on the adhesive surface and its vicinity.

In addition, the shear storage modulus G1 of each adhesive sheet of Examples 16 to 19 at -10°C is less than 100 kPa, which is relatively soft, and contains oligomers with a Tg of 40°C or more, and the δH ₁ of the HSP of the base polymer and the δH ₂ of the HSP of the oligomer satisfy 0.1≦δH ₂ -δH ₁ ≦1.3. The adhesive force F1 of such adhesive sheets of Examples 16 to 19 is greater than 7.9 N/20 mm. In each adhesive sheet of Examples 16 to 19, the oligomers with a Tg of 40°C or more are sufficiently segregated on the adhesive surface and its vicinity. Furthermore, the adhesive sheet of Example 19 includes two oligomers, each oligomer has a Tg of 40° C. or higher, and δH ₁ of the HSP of the base polymer and δH ₂ of the HSP of each oligomer satisfy 0.1≦δH ₂ -δH ₁ ≦1.3.

[Table 1] Table 1 Acrylic oligomer ∆H Gel fraction (mass %) Fog(%) Shear storage modulus (kPa) Adhesion force (N/20 mm) Type Number of copies M Tg (℃) δH ₂ G3 G1 G2 F1 F2 Embodiment 1 M1: IBXMA/MMA/CBA (45/45/10) 3 4880 98.5 5.39 1.06 0.32 76.1 0.20 110 70 twenty two 0.32 11.2 8.5 0.76 Embodiment 2 M2: IBXMA/MMA/CBA (35/35/30) 3 5400 50.9 5.58 1.10 0.51 78.5 0.22 97 63 twenty two 0.35 8.0 6.5 0.81 Embodiment 3 M3: DCPMA/MMA/CBA (45/45/10) 3 5230 97.7 5.64 1.11 0.57 74.0 0.26 119 73 twenty three 0.31 11.3 8.5 0.76 Embodiment 4 M4: IBXMA/MMA/ACMO (40/40/20) 3 4940 129.2 5.39 1.06 0.32 77.8 0.20 125 78 27 0.32 10.4 7.9 0.76 Embodiment 5 M5: DCPMA/MMA/ACMO (40/40/20) 3 5110 128.3 5.61 1.11 0.54 78.5 0.73 123 76 27 0.35 11.3 8.7 0.77 Embodiment 6 M6: IBXMA/MMA/AA (45/45/10) 3 5670 121.9 5.86 1.16 0.79 76.7 0.31 144 85 26 0.36 11.8 9.1 0.77 Embodiment 7 M7: DCPMA/MMA/HEMA (45/45/10) 1 5600 115.8 6.19 1.22 1.12 82.3 0.24 110 72 26 0.33 8.6 6.9 0.80 Embodiment 8 M8: DCPMA/MMA/HEMA (60/30/10) 1 5570 123.9 5.80 1.14 0.73 80.0 0.24 104 69 25 0.30 8.5 7.4 0.87 Embodiment 9 M9: CHMA/MMA/HEMA (45/45/10) 1 5920 85.4 6.33 1.25 1.26 82.1 0.28 123 82 31 0.36 8.6 6.9 0.80

[Table 2] Table 2 Acrylic oligomers ∆H Gel fraction (mass %) Fog(%) Shear storage modulus (kPa) Adhesion force (N/20 mm) Type Number of copies M Tg (℃) δH ₂ G3 G1 G2 F1 F2 Embodiment 10 M10: CHMA/MMA/4HBA (45/45/10) 1 5740 72.2 6.22 1.23 1.15 83.8 0.28 110 72 28 0.36 8.4 6.4 0.76 Embodiment 11 M11: CHMA/MMA/HPMA (45/45/10) 1 5840 82.4 6.25 1.23 1.18 76.4 0.27 126 83 30 0.38 8.7 6.8 0.78 Embodiment 12 M12: IBXMA/MMA/4HBA (45/45/10) 1 5320 99.2 5.82 1.15 0.75 80.9 0.28 98 64 twenty three 0.39 8.2 7.5 0.91 Comparison Example 1 - - - - - - - 83.5 0.20 102 69 27 0.40 3.7 2.8 0.76 Comparison Example 2 M13: IBXMA/NVP (50/50) 3 10200 193 5.00 0.99 -0.07 87.1 2.2 223 112 37 0.36 5.2 3.4 0.65 Comparison Example 3 M14: NPA/MMA (50/50) 3 5220 20.6 6.02 1.19 0.95 77.0 0.30 122 80 27 0.36 5.2 3.9 0.75 Comparison Example 4 M15: IBXMA/CBA (90/10) 3 4230 123.4 2.88 0.57 -2.19 78.4 0.23 95 61 twenty two 0.34 4.8 3.7 0.77 Comparison Example 5 M16: DCPMA/MMA/4HBA (40/40/20) 3 5350 76.8 6.58 1.30 1.51 78.6 6.36 119 80 27 0.24 9.3 8.8 0.95 Comparative Example 6 M17: IBXMA/MMA/LMA (45/45/10) 3 5780 125.5 5.16 1.02 0.09 76.7 0.23 130 79 25 0.36 7.5 6.6 0.87

[Table 3] Table 3 Acrylic oligomers ∆H Gel fraction (mass %) Fog(%) Shear storage modulus (kPa) Adhesion force (N/20 mm) Type Number of copies M Tg (℃) δH ₂ G3 G1 G2 F1 F2 Embodiment 13 M18: IBXMA/MMA/HEMA (75/20/5) 1 4610 141.0 4.46 1.18 0.69 73.6 0.16 47 34 11 0.33 7.7 4.1 0.53 Comparative Example 7 - - - - - - - 79.7 0.22 52 39 16 0.41 3.0 2.1 0.70 Comparative Example 8 M19: DCPMA/MMA/4HBA (45/45/10) 1 5430 99.2 6.07 1.61 2.3 76.9 1.97 50 37 14 0.36 4.0 2.0 0.50 Comparative Example 9 M20: IBXMA/CBA (80/20) 1 3820 80.8 3.33 0.88 -0.44 74.7 0.2 48 35 12 0.33 4.0 2.1 0.53

[Table 4] Table 4 Acrylic oligomer ∆H Gel fraction (mass %) Fog(%) Shear storage modulus (kPa) Adhesion force (N/20 mm) Type Number of copies M Tg (℃) δH ₂ G3 G1 G2 F1 F2 Embodiment 14 M8: DCPMA/MMA/HEMA (60/30/10) 1 5570 123.9 5.80 1.22 1.05 84.0 0.23 87 61 twenty four 0.40 7.6 5.9 0.77 Embodiment 15 M3: DCPMA/MMA/CBA (45/45/10) 1 5230 97.7 5.64 1.19 0.89 83.4 0.27 86 59 twenty four 0.41 8.1 6.2 0.77 Comparative Example 10 - - - - - - - 86.4 0.29 78 55 25 0.46 5.1 4.1 0.79 Comparative Example 11 M19: DCPMA/MMA/4HBA (45/45/10) 1 5430 99.2 6.07 1.39 1.83 84.3 0.40 89 62 26 0.42 6.4 6.0 0.93 Comparative Example 12 M21: IBXMA/MMA/CBA (70/20/10) 1 4060 109.3 4.26 0.90 -0.49 84.4 0.19 88 61 twenty four 0.40 5.0 3.9 0.77

[Table 5] Table 5 Acrylic oligomers ∆H Gel fraction (mass %) Fog(%) Shear storage modulus (kPa) Adhesion force (N/20 mm) Type Number of copies M Tg (℃) δH ₂ G3 G1 G2 F1 F2 Embodiment 16 M22: DCPMA/MMA/HEMA (47.5/47.5/5) 1.5 5150 120.0 5.88 1.16 0.81 77.6 0.27 123 84 twenty three 0.27 8.4 6.3 0.75 Embodiment 17 M23: DCPMA/MMA/HEMA (70/20/10) 1.5 5840 130.8 5.52 1.08 0.40 78.8 0.30 118 80 twenty four 0.30 7.9 5.4 0.68 Embodiment 18 M24: ADMA/MMA/HEMA (70/20/10) 1.5 5150 160.7 5.52 1.09 0.45 79.2 0.31 120 81 twenty four 0.30 8.3 5.4 0.65 Embodiment 19 M25: DCPMA/MMA (60/40) 0.5 4940 130.6 5.26 1.04 0.19 81.7 0.25 107 70 twenty four 0.34 8.4 6.1 0.73 M22: DCPMA/MMA/HEMA (47.5/47.5/5) 1.0 5150 120.0 5.88 1.16 0.81

Furthermore, although the above invention is provided in the form of the embodiment illustrated by the present invention, it is only a simple example and cannot be interpreted in a limiting sense. Variations of the present invention identified by the industry in the field of technology are included in the scope of the invention patent application described below. [Industrial Applicability]

The optical adhesive sheet of the present invention is suitable for use in the light-transmitting portion of a flexible device (such as a foldable display panel and a rollable display panel).

10: Adhesive sheet (optical adhesive sheet) 11: 1st surface 12: 2nd surface 21: 1st component 22: 2nd component H: Thickness direction L1: Peel-off pad L2: Peel-off pad

FIG1 is a cross-sectional schematic diagram of an embodiment of the optical adhesive sheet of the present invention. FIG2 shows an example of a method of using the optical adhesive sheet of the present invention. FIG2A shows a step of attaching the optical adhesive sheet to the first adherend, FIG2B shows a step of joining the first adherend to the second adherend via the optical adhesive sheet, and FIG2C shows a aging step.

10: Adhesive sheet (optical adhesive sheet)

11: Page 1

12: Page 2

H: thickness direction

L1: Peel off the liner

L2: Peel off the liner

Claims (6)

An optical adhesive sheet comprises a base polymer and an oligomer having a glass transition temperature of 40°C or higher and having a shear storage modulus of 100 kPa or lower at -10°C. The hydrogen bonding term _δH1 of the Hansen solubility parameter of the base polymer and the hydrogen bonding term _δH2 of the Hansen solubility parameter of the oligomer satisfy 0.1≦ _δH2 - _δH1 ≦1.3. The optical adhesive sheet of claim 1 has a haze of less than 1%. The optical adhesive sheet of claim 1 has an adhesive force of 7.6 N/20 mm or more in a peeling test conducted at 25° C., a peeling angle of 180°, and a tensile speed of 300 mm/min. The optical adhesive sheet of claim 1 has an adhesive force F1 in a peeling test conducted at 25°C, a peeling angle of 180°, and a tensile speed of 300 mm/min, and has an adhesive force F2 in a peeling test conducted at 25°C, a peeling angle of 180°, and a tensile speed of 60 mm/min, and the ratio of the adhesive force F2 to the adhesive force F1 is 0.5 or more and 1.1 or less. In the optical adhesive sheet of claim 1, a ratio of a shear storage modulus at 60°C to a shear storage modulus at -10°C is greater than 0.2 and less than 1.0. The optical adhesive sheet according to any one of claims 1 to 5 has a gel fraction of 60 mass % to 87 mass %.