Optical adhesive sheet

Abstract

To provide an optical adhesive sheet suitable to a use for a flexible device.SOLUTION: An adhesive sheet 10 is an optical adhesive sheet including a base polymer and an oligomer with a glass-transition temperature 40°C or higher, and has a shear storage modulus of 100 kPa or less at -10°C. In the adhesive sheet 10, 0.1≤δH2-δH1≤1.3 is satisfied by a hydrogen bond term δH1 of Hansen solubility parameter of the base polymer and a hydrogen bond term δH2 of Hansen solubility parameter of the oligomer. The oligomer is a polymer of a monomer component containing (meth)acrylate. The monomer component further includes a hydroxy group-containing monomer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

[0003] Meanwhile, development of repeatedly foldable display panels for, for example, smartphones and tablet terminals is progressing. Specifically, foldable display panels can be repeatedly deformed between a bent shape and a flat, non-bent shape. In such foldable display panels, each element in the laminated structure is made to be repeatedly foldable, and a thin optical adhesive sheet is used to bond such elements. Optical adhesive sheets for flexible devices such as foldable display panels are described, for example, in Patent Document 1 listed below. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-111754 Summary of the Invention [Problem to be solved by the invention]

[0005] Optical adhesive sheets for flexible devices are required to be highly flexible so that they can conform to the adherend when the device is deformed and have excellent stress relaxation properties. However, conventional optical adhesive sheets have lower adhesive strength as they become softer. In particular, the adhesive strength is reduced under high temperature and high humidity environments.

[0006] Conventionally, optical adhesive sheets tend to peel off from the elements (adherends) at the bending points of foldable display panels. This is because, when the display panel is bent, a relatively large shear force is applied to the bent portion of the optical adhesive sheet in the direction along the adherend. Peeling is undesirable as it can cause malfunctions of the display. Optical adhesive sheets for foldable display panels are highly required to resist peeling off from the elements (adherends) when the display is bent.

[0007] As a flexible device, development of rollable display panels is also progressing. Rollable display panels can be repeatedly deformed, for example, between a rolled shape after being completely or partially rolled up and a flat shape after being completely unrolled. In such rollable display panels, each element in the laminated structure is made to be repeatedly deformable, and a thin optical adhesive sheet is used to bond such elements. When the rollable display panel is in a rolled shape, the optical adhesive sheet bonded to the rolled element continues to be subjected to a shear force in a direction along the adherend. Such optical adhesive sheets are required to be highly resistant to peeling from the element (adherend) when the display is in a rolled shape.

[0008] The present invention provides an optical pressure-sensitive adhesive sheet suitable for flexible device applications. [Means for solving the problem]

[0009] The present invention [1] is an optical adhesive sheet comprising a base polymer and an oligomer having a glass transition temperature of 40°C or higher, having a shear storage modulus of 100 kPa or less at -10°C, wherein the hydrogen bond term δH1 of the Hansen solubility parameter of the base polymer and the hydrogen bond term δH2 of the Hansen solubility parameter of the oligomer satisfy 0.1≦δH2-δH1≦1.3, wherein the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester, and the monomer component further contains a hydroxy group-containing monomer.

[0010] The present invention [2] includes the optical pressure-sensitive adhesive sheet according to the above [1], which has a haze of 1% or less.

[0011] The present invention [3] includes an optical adhesive sheet according to the above [1] or [2], which has an adhesive strength of 7.6 N / 20 mm or more in a peel test under conditions of 25°C, a peel angle of 180°, and a tensile speed of 300 mm / min.

[0012] The present invention [4] has an adhesive strength F in a peel test under the conditions of 25°C, a peel angle of 180°, and a pulling speed of 300 mm / min. 11 The adhesive strength F 21 and has adhesive strength F 11 Adhesion strength F 21 The optical pressure-sensitive adhesive sheet according to any one of [1] to [3] above, wherein the ratio is 0.65 or more and 1.1 or less.

[0013] The present invention [5] includes an optical adhesive sheet according to any one of [1] to [4] above, which has an adhesive strength of 4.0 N / 20 mm or more in a peel test under conditions of 60°C, relative humidity of 90%, a peel angle of 180°, and a tensile speed of 300 mm / min.

[0014] The present invention [6] has an adhesive strength F in a peel test under the conditions of 25°C, relative humidity 55%, peel angle 180°, and pulling speed 300 mm / min. 11The adhesive strength F was measured in a peel test under the conditions of 60°C, 90% relative humidity, a peel angle of 180°, and a pulling speed of 300 mm / min. 12 and has adhesive strength F 11 Adhesion strength F 12 The optical pressure-sensitive adhesive sheet according to any one of [1] to [5] above, wherein the ratio is 0.5 or more and 1.1 or less.

[0015] The present invention [7] includes the optical pressure-sensitive adhesive sheet according to any one of the above [1] to [6], which has a gel fraction of 60% by mass or more and 87% by mass or less.

[0016] The present invention [8] includes an optical adhesive sheet according to any one of the above [1] to [7], wherein the hydrogen bond parameter δH1 and the hydrogen bond parameter δH2 satisfy 1.04≦δH2 / δH1≦1.28.

[0017] The present invention [9] includes the optical adhesive sheet according to any one of the above [1] to [8], wherein the proportion of the hydroxy group-containing monomer in the monomer components is 0.5 mass% or more.

[0018] The present invention

[10] includes the optical adhesive sheet according to any one of the above [1] to [9], wherein the proportion of the hydroxy group-containing monomer in the monomer components is 15 mass % or less. [Effects of the Invention]

[0019] As described above, the optical adhesive sheet of the present invention has a shear storage modulus of 100 kPa or less at -10°C. Such a soft optical adhesive sheet is suitable for alleviating stresses that occur in the optical adhesive sheet and the adherend when the adherend to which the optical adhesive sheet is attached deforms (stress relaxation function). Stress relaxation in the optical adhesive sheet is suitable for ensuring the conformability of the optical adhesive sheet to the adherend. Stress relaxation in the adherend is suitable for suppressing damage such as cracking of the adherend.

[0020] In addition, as described above, the optical pressure-sensitive adhesive sheet of the present invention comprises a base polymer and an oligomer with a glass transition temperature (Tg) of 40°C or higher, and the hydrogen bond term δH1 of the Hansen solubility parameter (HSP) of the base polymer and the hydrogen bond term δH2 of the HSP of the oligomer satisfy 0.1≦δH2−δH1≦1.3. This configuration is suitable for achieving good adhesive strength of the optical pressure-sensitive adhesive sheet by unevenly distributing the oligomer with a Tg of 40°C or higher on and near the surface (adhesive surface) of the optical pressure-sensitive adhesive sheet while ensuring the overall softness of the optical pressure-sensitive adhesive sheet. The high adhesive strength of the optical pressure-sensitive adhesive sheet is suitable for suppressing peeling of the optical pressure-sensitive adhesive sheet from an adherend that is repeatedly deformed.

[0021] In addition, as described above, in the optical pressure-sensitive adhesive sheet of the present invention, the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester, and the monomer component further contains a hydroxyl group-containing monomer. An oligomer having such a monomer composition is suitable for ensuring good adhesive strength in a high-temperature, high-humidity environment.

[0022] The optical pressure-sensitive adhesive sheet described above is suitable for use in flexible devices. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a cross-sectional schematic view of one embodiment of the optical pressure-sensitive adhesive sheet of the present invention. [Figure 2] 2A shows an example of a method for using the optical pressure-sensitive adhesive sheet of the present invention, in which Fig. 2A shows a step of attaching the optical pressure-sensitive adhesive sheet to a first adherend, Fig. 2B shows a step of joining the first adherend and a second adherend via the optical pressure-sensitive adhesive sheet, and Fig. 2C shows an aging step. DETAILED DESCRIPTION OF THE INVENTION

[0024] As shown in FIG. 1 , a pressure-sensitive adhesive sheet 10 as one embodiment of the optical pressure-sensitive adhesive sheet of the present invention has a sheet shape with a predetermined thickness and extends in a direction (plane direction) perpendicular to the thickness direction. The pressure-sensitive adhesive sheet 10 has a pressure-sensitive adhesive surface 11 and a pressure-sensitive adhesive surface 12 opposite the pressure-sensitive adhesive surface 11. FIG. 1 exemplarily shows a state in which release liners L1 and L2 are bonded to the pressure-sensitive adhesive surfaces 11 and 12 of the pressure-sensitive adhesive sheet 10. The release liner L1 is disposed on the pressure-sensitive adhesive surface 11. The release liner L2 is disposed on the pressure-sensitive adhesive surface 12. The pressure-sensitive adhesive sheet 10 is an optically transparent pressure-sensitive adhesive sheet (optical pressure-sensitive adhesive sheet) that is disposed at a light-transmitting location in a flexible device. Examples of flexible devices include flexible display panels. Examples of flexible display panels include foldable display panels and rollable display panels. Flexible display panels have a laminated structure including elements such as a pixel panel, a polarizing film, a touch panel, and a cover film. The pressure-sensitive adhesive sheet 10 is used, for example, to bond elements included in the laminated structure during the manufacturing process of a flexible display panel. Release liners L1 and L2 are each peeled off at a predetermined timing when adhesive sheet 10 is used.

[0025] The pressure-sensitive adhesive sheet 10 is formed from a pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition includes a base polymer and an oligomer having a glass transition temperature (Tg) of 40°C or higher. That is, the pressure-sensitive adhesive sheet 10 includes a base polymer and an oligomer having a Tg of 40°C or higher. The pressure-sensitive adhesive sheet 10 has a shear storage modulus of 100 kPa or less at -10°C. Furthermore, in the pressure-sensitive adhesive sheet 10, the hydrogen bond term δH1 of the Hansen solubility parameter (HSP) of the base polymer and the hydrogen bond term δH2 of the HSP of the oligomer satisfy the following formula (1). In addition, the oligomer in the pressure-sensitive adhesive sheet 10 is a polymer of a monomer component containing a (meth)acrylic acid ester, and the monomer component further contains a hydroxy group-containing monomer.

[0026] 0.1≦δH2-δH1≦1.3 (1)

[0027] As described above, the adhesive sheet 10 has a shear storage modulus of 100 kPa or less at -10°C. Such a soft adhesive sheet 10 is suitable for alleviating stresses that occur in the adhesive sheet 10 and the adherend when the adherend to which the adhesive sheet 10 is attached deforms (stress relaxation function). The stress relaxation in the adhesive sheet 10 is suitable for ensuring the conformability of the adhesive sheet 10 to the adherend. The stress relaxation in the adherend is suitable for suppressing damage such as cracking of the adherend. Therefore, the adhesive sheet 10 is suitable for achieving good repeated deformation of flexible devices in which the adhesive sheet 10 is used.

[0028] Additionally, as described above, the PSA sheet 10 comprises a base polymer and an oligomer having a Tg of 40°C or higher, and the hydrogen bond term δH1 of the HSP of the base polymer and the hydrogen bond term δH2 of the HSP of the oligomer satisfy the relationship 0.1≦δH2−δH1≦1.3. The difference ΔH (=δH2−δH1) between the hydrogen bond term δH1 of the HSP of the base polymer and the hydrogen bond term δH2 of the HSP of the oligomer is an index of the compatibility between the base polymer and the oligomer in the PSA sheet 10. Such a difference ΔH of 0.1 or more and 1.3 or less achieves a moderately low compatibility between the base polymer and the oligomer, which is suitable for localizing the oligomer on the surface (adhesive surfaces 11 and 12) of the PSA sheet 10 and in the vicinity thereof. Therefore, a difference ΔH of 0.1 or more and 1.3 or less is suitable for ensuring the above-mentioned overall softness of adhesive sheet 10 while unevenly distributing oligomers with a Tg of 40°C or more on the surface (adhesive surfaces 11, 12) of adhesive sheet 10 and its vicinity, thereby achieving high adhesive strength in adhesive sheet 10. High adhesive strength of adhesive sheet 10 is suitable for suppressing peeling of adhesive sheet 10 from an adherend that is repeatedly deformed.

[0029] In addition, as described above, the oligomer of the optical adhesive sheet 10 is a polymer of a monomer component containing a (meth)acrylic acid ester, and the monomer component further contains a hydroxyl group-containing monomer. An oligomer with such a monomer composition is suitable for ensuring good adhesive strength in a high-temperature, high-humidity environment.

[0030] The pressure-sensitive adhesive sheet 10 described above is suitable for use in flexible devices. That is, the pressure-sensitive adhesive sheet 10 is suitable for achieving good repeated deformation of the flexible device in which the pressure-sensitive adhesive sheet 10 is used.

[0031] The shear storage modulus G1 of the pressure-sensitive adhesive sheet 10 at -10°C is preferably 90 kPa or less, more preferably 85 kPa or less, and even more preferably 80 kPa or less, from the viewpoint of stress relaxation at the deformed portion when the pressure-sensitive adhesive sheet 10 is deformed (such as by bending or curving). The shear storage modulus G1 (-10°C) is preferably 30 kPa or more, more preferably 40 kPa or more, even more preferably 50 kPa or more, and even more preferably 60 kPa or more, from the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive sheet 10 in the low temperature range. The shear storage modulus G1 is determined by dynamic viscoelasticity measurement, which will be described later in the examples (the same applies to the shear storage moduli G2 and G3 described later). Methods for adjusting the shear storage modulus of the pressure-sensitive adhesive sheet 10 include, for example, selecting the type of base polymer in the pressure-sensitive adhesive sheet 10, adjusting the molecular weight and amount of base polymer, and selecting the type of crosslinker and amount of crosslinker (the same applies to the shear storage moduli G2 and G3 described later).

[0032] The shear storage modulus G2 of the pressure-sensitive adhesive sheet 10 at 20°C is preferably 80 kPa or less, more preferably 60 kPa or less, and even more preferably 50 kPa or less, from the viewpoint of the above-mentioned stress relaxation in the pressure-sensitive adhesive sheet 10. The shear storage modulus G2 (20°C) is preferably 20 kPa or more, more preferably 30 kPa or more, and more preferably 35 kPa or more, from the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive sheet 10 in the room temperature range.

[0033] The shear storage modulus G3 of the pressure-sensitive adhesive sheet 10 at 60°C is preferably 35 kPa or less, more preferably 32 kPa or less, and even more preferably 30 kPa or less, from the viewpoint of the above-mentioned stress relaxation in the pressure-sensitive adhesive sheet 10. The shear storage modulus G3 (60°C) is preferably 10 kPa or more, more preferably 15 kPa or more, even more preferably 20 kPa or more, and even more preferably 22 kPa or more, from the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive sheet 10 in the high temperature range.

[0034] The difference ΔH (= ΔH2 - ΔH1) between the hydrogen bond term ΔH1 of the HSP of the base polymer and the hydrogen bond term ΔH2 of the HSP of the oligomer is preferably 0.2 or more, more preferably 0.4 or more, and even more preferably 0.6 or more, from the viewpoint of appropriately reducing the compatibility between the base polymer and the oligomer and sufficiently unevenly distributing the oligomer on and near the PSA surfaces 11 and 12. The difference ΔH (ΔH2 - ΔH1) is preferably 1.26 or less, more preferably 1.20 or less, even more preferably 1.15 or less, and even more preferably 1.00 or less, from the viewpoint of preventing the compatibility between the base polymer and the oligomer from becoming too low. Ensuring compatibility between the base polymer and the oligomer helps to achieve low haze in the PSA sheet 10. Examples of methods for adjusting the ΔH1 of the base polymer include adjusting the monomer composition of the base polymer. Examples of methods for adjusting the ΔH2 of the oligomer include adjusting the monomer composition of the oligomer.

[0035] The ratio (δH2 / δH1) of the hydrogen bond term δH2 of the HSP of the oligomer to the hydrogen bond term δH1 of the HSP of the base polymer is preferably 1.04 or more, more preferably 1.06 or more, even more preferably 1.08 or more, and even more preferably 1.10 or more, from the viewpoint of appropriately reducing the compatibility between the base polymer and the oligomer and sufficiently unevenly distributing the oligomer on and near the adhesive surfaces 11 and 12. The ratio (δH2 / δH1) is preferably 1.28 or less, more preferably 1.25 or less, and even more preferably 1.21 or less, from the viewpoint of preventing the compatibility between the base polymer and the oligomer from becoming too low. The ratio (δH2 / δH1) also serves as an indicator of the compatibility between the base polymer and the oligomer in the adhesive sheet 10.

[0036] The Hansen Solubility Parameter (HSP) is expressed by the following formula (2), where δH is the hydrogen bond term representing the energy derived from intermolecular hydrogen bonding forces, δD is the dispersion term representing the energy derived from intermolecular dispersion forces, and δP is the polarization term representing the energy derived from intermolecular polar forces.

[0037] HSP = (δD 2 +δP 2 +δH 2 ) 1 / 2 (2)

[0038] The δH of a polymer is determined by the ratio of the monomers m i Mole fraction x i and the monomer m i The hydrogen bond term δh i From this, it can be calculated by the following formula (3). The δH of the oligomer can be calculated in the same way. The hydrogen bond term δh of the monomer can be calculated, for example, by computer software HSPiP (Hansen Solubility Parameters in Practice). The specific method for calculating δH is as described below in the Examples.

[0039] δH=Σ x i ×δh i (3)

[0040] From the viewpoint of increasing the surface adhesion of the soft pressure-sensitive adhesive sheet 10 as described above, the Tg of the oligomer is preferably 50°C or higher, more preferably 70°C or higher, even more preferably 90°C or higher, even more preferably 100°C or higher, and even more preferably 116°C or higher, and is preferably 145°C or lower, more preferably 135°C or lower, even more preferably 130°C or lower, and even more preferably 125°C or lower. The Tg of the oligomer is preferably higher than the Tg of the base polymer. Methods for adjusting the Tg of the oligomer include adjusting the monomer composition and molecular weight of the oligomer. Specific methods for measuring the Tg of the oligomer are as described below in the examples.

[0041] The glass transition temperature Tg of an oligomer can be calculated using the theoretical glass transition temperature (Tg) calculated based on the Fox formula below. The Fox formula is based on the glass transition temperature Tg of a polymer and the glass transition temperature Tg of a homopolymer of the monomers that make up the polymer. i In the Fox formula below, Tg represents the glass transition temperature (°C) of the oligomer, and W i is the monomer m constituting the polymer i represents the weight fraction of Tg i is the monomer m i The glass transition temperature (°C) of a homopolymer formed from the above monomers is shown. The glass transition temperature of a homopolymer can be determined from literature values. For example, the glass transition temperatures of various homopolymers are listed in "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999). The glass transition temperature of a homopolymer of a monomer can also be determined by the method specifically described in JP-A-2007-51271.

[0042] Fox's formula 1 / (273+Tg)=Σ[W i / (273+Tg i )]

[0043] The haze of the pressure-sensitive adhesive sheet 10 is preferably 1% or less, more preferably 0.8% or less, even more preferably 0.7% or less, and even more preferably 0.5% or less. The haze is, for example, 0.01% or more. The haze of the pressure-sensitive adhesive sheet 10 can be measured using a haze meter in accordance with JIS K7136 (2000). Examples of haze meters include the "NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd. and the "HM-150" manufactured by Murakami Color Research Laboratory Co., Ltd. Specific methods for measuring haze are described below in connection with the examples.

[0044] The total light transmittance of the pressure-sensitive adhesive sheet 10 is preferably 60% or more, more preferably 80% or more, and even more preferably 85% or more. The total light transmittance of the pressure-sensitive adhesive sheet 10 is, for example, 100% or less. The total light transmittance of the pressure-sensitive adhesive sheet 10 can be measured in accordance with JIS K 7375 (2008).

[0045] The gel fraction of the adhesive sheet 10 is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 73% by mass or more, from the viewpoint of ensuring the cohesive strength of the adhesive sheet 10 in high temperature regions. The gel fraction of the adhesive sheet 10 is preferably 87% by mass or less, more preferably 85% by mass or less, from the viewpoint of ensuring the flexibility of the adhesive sheet 10. Methods for adjusting the gel fraction of the adhesive sheet 10 include, for example, selecting the type of base polymer in the adhesive sheet 10, adjusting the molecular weight, and adjusting the blending amount. Methods for adjusting the gel fraction also include selecting the type of crosslinking agent and adjusting the blending amount. The method for measuring the gel fraction is as described below in the examples.

[0046] The adhesive strength F of the pressure-sensitive adhesive sheet 10 in a peel test (first peel test) under the conditions of 25°C, a peel angle of 180°, and a pulling speed of 300 mm / min 11From the viewpoint of suppressing peeling of the pressure-sensitive adhesive sheet 10 from the adherend, the adhesive strength F is preferably 7.6 N / 20 mm or more, more preferably 7.8 N / 20 mm or more, even more preferably 8.0 N / 20 mm or more, even more preferably 8.2 N / 20 mm or more, still more preferably 8.4 N / 20 mm or more, particularly preferably 8.6 N / 20 mm or more, and particularly preferably 8.8 N / 20 mm or more. 11 For example, the adhesive strength F is 15N / 20mm or less. 11 The specific method for measuring adhesive strength F is as described below in the examples. 11 Examples of methods for adjusting the adhesive strength F include selecting the type of base polymer in the adhesive sheet 10, adjusting the molecular weight, and adjusting the amount of base polymer blended. Selecting the type of base polymer includes adjusting the composition of the monomers that form the base polymer. 11 The adhesive strength can be adjusted by selecting the type of components other than the base polymer in the adhesive sheet 10 and adjusting the amount of these components. Examples of these components include crosslinking agents, silane coupling agents, and oligomers. The above-mentioned adhesive strength adjustment method is also applicable to the adhesive strength F described below. 11 ,F 21 ,F 22 The same is true for .

[0047] The adhesive strength F of the adhesive sheet 10 in a peel test (second peel test) under the conditions of 60°C, relative humidity 90%, peel angle 180°, and pulling speed 300 mm / min 12 From the viewpoint of preventing the adhesive sheet 10 from peeling off from the adherend in a high-temperature, high-humidity environment, the adhesive strength F is preferably 4.0 N / 20 mm or more, more preferably 4.5 N / 20 mm or more, even more preferably 5.0 N / 20 mm or more, and even more preferably 5.2 N / 20 mm or more. 12 is, for example, 10N / 20mm or less.

[0048] Adhesive force F 11 Adhesion strength F 12 The ratio (F 12 / F 11) is preferably 0.5 or more, more preferably 0.6 or more, even more preferably 0.62 or more, and is preferably 1.1 or less, more preferably 1.0 or less, from the viewpoint of ensuring stable adhesive strength of the adhesive sheet 10 in a high-temperature, high-humidity environment.

[0049] The adhesive strength F of the pressure-sensitive adhesive sheet 10 in a peel test (second peel test) under the conditions of 25°C, a peel angle of 180°, and a pulling speed of 60 mm / min 21 From the viewpoint of preventing peeling of the pressure-sensitive adhesive sheet 10 from the adherend, the adhesive strength F is preferably 5.9 N / 20 mm or more, more preferably 6.0 N / 20 mm or more, and even more preferably 6.1 N / 20 mm or more. 21 is, for example, 12N / 20mm or less.

[0050] Adhesive force F 11 Adhesion strength F 21 The ratio (F 21 / F 11 ) is preferably 0.65 or more, more preferably 0.7 or more, even more preferably 0.73 or more, and is preferably 1.1 or less, more preferably 1.0 or less, from the viewpoint of ensuring stable adhesive strength in the adhesive sheet 10.

[0051] The adhesive strength F of the adhesive sheet 10 in a peel test (fourth peel test) under the conditions of 60°C, relative humidity 90%, peel angle 180°, and pulling speed 60 mm / min 22 From the viewpoint of preventing the adhesive sheet 10 from peeling off from the adherend in a high-temperature, high-humidity environment, the adhesive strength F is preferably 2.8 N / 20 mm or more, more preferably 3.0 N / 20 mm or more, and even more preferably 3.2 N / 20 mm or more. 22 is, for example, 8N / 20mm or less.

[0052] Adhesive force F 21 Adhesion strength F 22 The ratio (F 22 / F 21) is preferably 0.48 or more, more preferably 0.5 or more, and is preferably 1.1 or less, more preferably 1.0 or less, from the viewpoint of ensuring stable adhesive strength of the adhesive sheet 10 in a high-temperature, high-humidity environment.

[0053] The base polymer is an adhesive component that imparts adhesiveness to the pressure-sensitive adhesive sheet 10. Examples of base polymers 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 polymers may be used alone or in combination of two or more. From the viewpoint of ensuring good transparency and adhesiveness in the pressure-sensitive adhesive sheet 10, acrylic polymers are preferred as the base polymer.

[0054] An acrylic polymer is a polymer of a monomer component (first monomer component) containing 50% by mass or more of a (meth)acrylic acid ester. "(Meth)acrylic" refers to acrylic and / or methacrylic.

[0055] The (meth)acrylic acid ester is preferably a (meth)acrylic acid ester having an alkyl group having 1 to 20 carbon atoms. Examples of the (meth)acrylic acid ester include a (meth)acrylic acid ester having a chain alkyl group (a chain alkyl (meth)acrylate ester) and a (meth)acrylic acid ester having an alicyclic alkyl group (alicyclic alkyl (meth)acrylate ester).

[0056] Examples of the chain alkyl (meth)acrylate esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, n-hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, and isooctyl (meth)acrylate. , nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (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.

[0057] Examples of (meth)acrylic acid alicyclic alkyl esters include (meth)acrylic acid cycloalkyl esters, (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring, and (meth)acrylic acid esters having a tricyclic or higher aliphatic hydrocarbon ring. Examples of (meth)acrylic acid cycloalkyl esters 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 (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring include isobornyl (meth)acrylate. Examples of (meth)acrylic acid esters having three or more aliphatic hydrocarbon rings include dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

[0058] In order to achieve a balance between the flexibility and adhesive strength required for adhesive sheets for flexible devices, the (meth)acrylic acid ester used in the adhesive sheet 10 is preferably at least one selected from (meth)acrylic acid esters having a first alkyl group having 8 to 12 carbon atoms, or at least one selected from (meth)acrylic acid esters having a first alkyl group having 8 to 12 carbon atoms and at least one selected from a second (meth)acrylic acid ester having an alkyl group having 1 to 4 carbon atoms. The first (meth)acrylic acid ester 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 (meth)acrylic acid ester is preferably n-butyl acrylate (BA).

[0059] The proportion of the (meth)acrylic acid ester in the first monomer component is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 88% by mass or more, and particularly preferably 90% by mass or more, from the viewpoint of appropriately exhibiting softness and adhesive strength in the pressure-sensitive adhesive sheet 10. This proportion is, for example, 99.9% by mass or less, 99.5% by mass or less, or 99% by mass or less. When a first (meth)acrylic acid ester selected from (meth)acrylic acid esters having an alkyl group of 8 to 12 carbon atoms is used in combination with a second (meth)acrylic acid ester selected from (meth)acrylic acid esters having an alkyl group of 1 to 4 carbon atoms, the proportion of the first (meth)acrylic acid ester in the monomer components is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, and preferably 85% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less, and the proportion of the second (meth)acrylic acid ester in the monomer components is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less.

[0060] The first monomer component may contain a copolymerizable monomer copolymerizable with the (meth)acrylic acid ester. Examples of the copolymerizable monomer include a monomer having a polar group. Examples of the polar group-containing monomer include a hydroxy group-containing monomer, a monomer having a nitrogen atom-containing ring, and a carboxy group-containing monomer. The polar group-containing monomer is useful for modifying the acrylic polymer, such as by introducing crosslinking points into the acrylic polymer and ensuring the cohesive strength of the acrylic polymer. The copolymerizable monomer may be used alone or in combination of two or more types.

[0061] Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. The hydroxyl group-containing monomer is preferably at least one selected from the group consisting of 2-hydroxyethyl acrylate (2HEA) and 4-hydroxybutyl acrylate (4HBA).

[0062] The proportion of the hydroxy group-containing monomer in the first monomer component is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, from the viewpoint of introducing a crosslinked structure into the acrylic polymer and ensuring cohesive strength in the pressure-sensitive adhesive sheet 10. From the viewpoint of adjusting the polarity of the acrylic polymer (which is related to the compatibility between the acrylic polymer and various additive components in the pressure-sensitive adhesive sheet 10), this proportion is preferably 12% by mass or less, more preferably 10% by mass or less, and even more preferably 9% by mass or less.

[0063] Examples of the monomer having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, 4-acryloylmorpholine, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, and N-vinylisothiazole.Preferably, the monomer having a nitrogen atom-containing ring is N-vinyl-2-pyrrolidone (NVP).

[0064] When a monomer having a nitrogen atom-containing ring is used, the proportion of the monomer having a nitrogen atom-containing ring in the first monomer component is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 1.5% by mass or more, from the viewpoints of ensuring the cohesive strength of the pressure-sensitive adhesive sheet 10 and ensuring the adhesive strength to the adherend of the pressure-sensitive adhesive sheet 10. This proportion is preferably 10% by mass or less, more preferably 6% by mass or less, and even more preferably 4% by mass or less, from the viewpoints of adjusting the glass transition temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (which is related to the compatibility of the acrylic polymer with various additive components in the pressure-sensitive adhesive sheet 10).

[0065] Examples of carboxy group-containing monomers include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

[0066] When a carboxyl group-containing monomer is used, the proportion of the carboxyl group-containing monomer in the monomer components is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 0.8% by mass or more, from the viewpoints of introducing a crosslinked structure into the acrylic polymer, ensuring the cohesive strength of the pressure-sensitive adhesive sheet 10, and ensuring the adhesive strength to the adherend in the pressure-sensitive adhesive sheet 10. The proportion is preferably 3% by mass or less, more preferably 1% by mass or less, from the viewpoints of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend by acid.

[0067] The first monomer component may contain other copolymerizable monomers. Examples of the 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.

[0068] The first monomer component preferably includes a first (meth)acrylic acid ester having an alkyl group with 8 to 12 carbon atoms, a second (meth)acrylic acid ester having an alkyl group with 1 to 4 carbon atoms, a hydroxy group-containing monomer, and a monomer having a nitrogen atom-containing ring. The first monomer component more preferably includes NOAA, BA, NVP, and 4HBA.

[0069] The base polymer preferably has a crosslinked structure. Examples of methods for introducing a crosslinked structure into a base polymer include the following first and second methods. In the first method, a base polymer having a functional group reactive with the crosslinking agent and the crosslinking agent are blended into a pressure-sensitive adhesive composition, and the base polymer and the crosslinking agent are reacted in a pressure-sensitive adhesive sheet. In the second method, a first monomer component forming the base polymer contains a polyfunctional compound as a crosslinking agent, and polymerization of the first monomer component forms a base polymer in which a branched structure (crosslinked structure) is introduced into the polymer chain. These methods may be used in combination.

[0070] Examples of the crosslinking agent used in the first method include compounds that react with functional groups (such as hydroxyl groups and carboxyl groups) contained in the base polymer. Examples of such crosslinking agents include isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, and carbodiimide crosslinking agents. The crosslinking agents used in the first method may be used alone or in combination of two or more. As the crosslinking agent in the first method, an isocyanate crosslinking agent is preferably used because it has high reactivity with the hydroxyl groups and carboxyl groups in the base polymer and facilitates the introduction of a crosslinked structure.

[0071] Examples of isocyanate crosslinking agents include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenylisocyanate. Also included as isocyanate crosslinking agents are derivatives of these isocyanates. Examples of the isocyanate derivatives include isocyanurate-modified products and polyol-modified products. Commercially available isocyanate crosslinking agents include, for example, Coronate L (a trimethylolpropane adduct of tolylene diisocyanate, manufactured by Tosoh), Coronate HL (a trimethylolpropane adduct of hexamethylene diisocyanate, manufactured by Tosoh), Coronate HX (an isocyanurate of hexamethylene diisocyanate, manufactured by Tosoh), Takenate D110N (a trimethylolpropane adduct of xylylene diisocyanate, manufactured by Mitsui Chemicals), and Takenate 600 (1,3-bis(isocyanatomethyl)cyclohexane, manufactured by Mitsui Chemicals).

[0072] Peroxide crosslinking agents include dibenzoyl peroxide, di(2-ethylhexyl)peroxydicarbonate, di(4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butylperoxydicarbonate, t-butylperoxyneodecanoate, t-hexylperoxypivalate, and t-butylperoxypivalate.

[0073] Epoxy crosslinkers include bisphenol A, epichlorohydrin-type epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane.

[0074] The amount of crosslinking agent in the first method 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 base polymer, from the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive sheet 10. From the viewpoint of ensuring good tackiness in the pressure-sensitive adhesive sheet 10, the amount of crosslinking agent in ...

[0075] In the second method, the first monomer component (including a polyfunctional compound and a monofunctional monomer for introducing a crosslinked structure) may be polymerized in one step or in multiple steps. In the multi-step polymerization method, a monofunctional monomer for forming a base polymer is first polymerized (pre-polymerization), thereby preparing a prepolymer composition containing a partial polymer (a mixture of a low-polymerization polymer and unreacted monofunctional monomer). Next, a polyfunctional compound is added as a crosslinking agent to the prepolymer composition, and then a polymerization reaction is allowed to proceed in a reaction system containing the partial polymer and the polyfunctional compound (main polymerization).

[0076] Examples of polyfunctional compounds include polyfunctional monomers and polyfunctional oligomers containing two or more ethylenically unsaturated double bonds in one molecule, and examples of polyfunctional monomers include polyfunctional (meth)acrylates.

[0077] Examples of the polyfunctional (meth)acrylate include difunctional (meth)acrylate, trifunctional (meth)acrylate, and tetrafunctional or higher polyfunctional (meth)acrylate.

[0078] Examples of difunctional (meth)acrylates 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, glycerin di(meth)acrylate, ethoxylated bisphenol A diacrylate (BPAEODE), and neopentyl glycol di(meth)acrylate.

[0079] Examples of trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl)isocyanurate.

[0080] Examples of tetrafunctional or higher polyfunctional (meth)acrylates include ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, alkyl-modified dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0081] Examples of polyfunctional oligomers include urethane (meth)acrylate oligomers, polyester (meth)acrylate oligomers, polyether (meth)acrylate oligomers, polyol (meth)acrylate oligomers, epoxy (meth)acrylate oligomers, polyethylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate.

[0082] The polyfunctional compound as the crosslinking agent in the second method may be used alone or in combination of two or more kinds. As the polyfunctional compound, a polyfunctional monomer is preferably used, and more preferably at least one selected from the group consisting of dipentaerythritol hexaacrylate, 1,6-hexanediol diacrylate, and trimethylolpropane triacrylate is used.

[0083] The amount of the polyfunctional compound as a crosslinking agent in the first monomer component is preferably 0.02 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.07 parts by mass or more per 100 parts by mass of the monofunctional monomer, from the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive sheet 10. The amount of the polyfunctional compound is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less per 100 parts by mass of the monofunctional monomer, from the viewpoint of ensuring good tackiness in the pressure-sensitive adhesive sheet 10.

[0084] The acrylic polymer (base polymer) can be formed by polymerizing the first monomer component described above. Examples of polymerization methods include solution polymerization, emulsion polymerization, and solvent-free photopolymerization (e.g., ultraviolet polymerization). Examples of solvents used in solution polymerization include ethyl acetate and toluene. A chain transfer agent may be used in the polymerization. Examples of polymerization initiators include thermal polymerization initiators and photopolymerization initiators. The polymerization initiators may be used alone or in combination. 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 even more preferably 0.07 parts by mass or more, per 100 parts by mass of the first monomer component. 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 even more preferably 0.07 parts by mass or more, and is preferably 1 part by mass or less, more preferably 0.5 parts by mass or less, and even more preferably 0.3 parts by mass or less.

[0085] Examples of thermal polymerization initiators include azo polymerization initiators and peroxide polymerization initiators. Examples of azo polymerization initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionic acid) dimethyl, 4,4'-azobis-4-cyanovaleric acid, azobisisovaleronitrile, and 2,2'-azobis(2-amidinopropane) dihydrochloride. Examples of peroxide polymerization initiators include dibenzoyl peroxide, t-butyl permaleate, and lauroyl peroxide.

[0086] Examples of the photopolymerization initiator include a radical photopolymerization initiator, a cationic photopolymerization initiator, and an anionic photopolymerization initiator.

[0087] Examples of the radical photopolymerization initiator include an acylphosphine oxide photopolymerization initiator, a benzoin ether photopolymerization initiator, and an acetophenone photopolymerization initiator.

[0088] Examples of acylphosphine oxide photopolymerization initiators include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-2,4-di-n-butoxyphenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. Examples of benzoin ether photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and 2,2-dimethoxy-1,2-diphenylethan-1-one. Examples of acetophenone-based photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone.

[0089] The weight average molecular weight of the base polymer is preferably 100,000 or more, more preferably 300,000 or more, and even more preferably 500,000 or more, from the viewpoint of ensuring cohesive strength in the pressure-sensitive adhesive sheet 10. The weight average molecular weight of the base polymer is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene.

[0090] The glass transition temperature (Tg) of the base polymer is preferably 0° C. or lower, more preferably −10° C. or lower, and even more preferably −20° C. or lower. The glass transition temperature is, for example, −80° C. or higher. The glass transition temperature (Tg) of the base polymer can be the theoretical glass transition temperature calculated based on the Fox equation.

[0091] The content of the base polymer in the pressure-sensitive adhesive sheet 10 is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, from the viewpoint of appropriately exhibiting basic properties such as adhesiveness in the pressure-sensitive adhesive sheet 10. The content of the base polymer in the pressure-sensitive adhesive sheet 10 is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99.0% by mass or less, from the viewpoint of ensuring the content of other components in the pressure-sensitive adhesive sheet 10.

[0092] The oligomer is a polymer of a monomer component (second monomer component) containing 50% by mass or more of a (meth)acrylic acid ester, and has a weight-average molecular weight of, for example, 1,000 or more and 30,000 or less. As described above, the second monomer component further contains a hydroxy group-containing monomer. That is, the oligomer is a polymer of a monomer component (second monomer component) containing 50% by mass or more of a (meth)acrylic acid ester and a hydroxy group-containing monomer. The oligomer may be used alone or in combination of two or more types.

[0093] When two or more oligomers are used in combination, at least one oligomer satisfies the specified parameters (e.g., glass transition temperature, the difference ΔH between the hydrogen bond term ΔH1 of the HSP of the base polymer and the hydrogen bond term ΔH2 of the HSP of the oligomer (= ΔH2 - ΔH1), the ratio of the hydrogen bond term ΔH2 of the HSP of the oligomer to the hydrogen bond term ΔH1 of the HSP of the base polymer (ΔH2 / ΔH1)). In other words, when two or more oligomers are used in combination, oligomers that do not satisfy the specified parameters (e.g., glass transition temperature, the difference ΔH between the hydrogen bond term ΔH1 of the HSP of the base polymer and the hydrogen bond term ΔH2 of the HSP of the oligomer (= ΔH2 - ΔH1), the ratio of the hydrogen bond term ΔH2 of the HSP of the oligomer to the hydrogen bond term ΔH1 of the HSP of the base polymer (ΔH2 / ΔH1)) may also be included as long as the effects of the present invention are not impaired. Preferably, all oligomers used in combination meet the specified parameters.

[0094] Examples of the (meth)acrylic acid ester in the second monomer component include alicyclic (meth)acrylic acid alkyl esters and chain (meth)acrylic acid alkyl esters.

[0095] Examples of the (meth)acrylic acid alicyclic alkyl ester in the second monomer component include the (meth)acrylic acid alicyclic alkyl esters described above with respect to the first monomer component. The (meth)acrylic acid alicyclic alkyl ester in the second monomer component is preferably at least one selected from the group consisting of cyclohexyl methacrylate (CHMA), methylcyclohexyl methacrylate, tert-butylcyclohexyl methacrylate, cyclododecyl methacrylate, isobornyl methacrylate (IBXMA), dicyclopentanyl 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.

[0096] The proportion of the (meth)acrylic acid alicyclic alkyl ester in the second monomer component is preferably 30% by mass or more, more preferably 35% by mass or more, even more preferably 40% by mass or more, and even more preferably 45% by mass or more, from the viewpoint of increasing the Tg of the oligomer. The proportion of the (meth)acrylic acid alicyclic alkyl ester in the second monomer component is preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less, from the viewpoint of the polymerizability of the second monomer component.

[0097] Examples of the (meth)acrylic acid chain alkyl ester in the second monomer component include the (meth)acrylic acid chain alkyl esters described above for the first monomer component. The (meth)acrylic acid chain alkyl ester in the second monomer component is preferably a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 6 carbon atoms, more preferably methyl methacrylate (MMA). MMA is preferred because its homopolymer has a high glass transition temperature and is relatively compatible with the base polymer.

[0098] From the viewpoints of ensuring a high Tg of the oligomer and adjusting the compatibility of the oligomer with the base polymer, the proportion of the chain alkyl (meth)acrylate in the second monomer component is preferably 15% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, still more preferably 30% by mass or more, and even more preferably 35% by mass or more, and is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less.

[0099] The mass ratio of the (meth)acrylic acid alicyclic alkyl ester to the (meth)acrylic acid chain alkyl ester in the second monomer component is preferably 0.6 or more, more preferably 0.8 or more, from the viewpoint of increasing the Tg of the oligomer and adjusting the compatibility of the oligomer with the base polymer, and is also preferably 9.0 or less, more preferably 5.0 or less, and even more preferably 2.0 or less.

[0100] Examples of the hydroxy group-containing monomer in the second monomer component include the hydroxy group-containing monomers described above with respect to the first monomer component. The hydroxy group-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).

[0101] The proportion of the hydroxy group-containing monomer in the second monomer component is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 1.8% by mass or more, from the viewpoint of ensuring good adhesive strength in high-temperature, high-humidity environments in the pressure-sensitive adhesive sheet 10. The proportion of the hydroxy group-containing monomer in the second monomer component is preferably 15% by mass or less, more preferably 12% by mass or less, even more preferably 10% by mass or less, and even more preferably 8% by mass or less, from the viewpoint of adjusting the compatibility of the oligomer with the base polymer.

[0102] The second monomer component may contain a polar group-containing monomer other than the hydroxy group-containing monomer. Examples of the polar group-containing monomer other than the hydroxy group-containing monomer include a monomer having a nitrogen atom-containing ring and a carboxy group-containing monomer. The second monomer component preferably does not contain a carboxy group-containing monomer.

[0103] The proportion of polar group-containing monomers other than hydroxy group-containing monomers in the second monomer component is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and even more preferably 0% by mass, from the viewpoint of ensuring good adhesive strength in the adhesive sheet 10 under high temperature and high humidity environments and adjusting the compatibility of the oligomer with the base polymer.

[0104] The second monomer component preferably contains a (meth)acrylic acid alicyclic alkyl ester, a (meth)acrylic acid chain alkyl ester, and a hydroxy group-containing monomer. That is, the acrylic oligomer is preferably a copolymer of the second monomer component containing a (meth)acrylic acid alicyclic alkyl ester, a (meth)acrylic acid chain alkyl ester, and a hydroxy group-containing monomer.

[0105] 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, preferably, at least one of the oligomers is a copolymer of a second monomer component containing a (meth)acrylic acid alicyclic alkyl ester, a (meth)acrylic acid chain alkyl ester, and a hydroxy group-containing monomer. Specific examples include a copolymer of a second monomer component containing a (meth)acrylic acid alicyclic alkyl ester and a (meth)acrylic acid chain alkyl ester, and a copolymer of a second monomer component containing a (meth)acrylic acid alicyclic alkyl ester, a (meth)acrylic acid chain alkyl ester, and a hydroxy group-containing monomer.

[0106] When two or more types of 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 a range in which the two or more types of acrylic oligomers used in combination satisfy the specified parameters. Specifically, the content ratio of the copolymer (one acrylic oligomer) of the second monomer component containing a (meth)acrylic acid alicyclic alkyl ester, a (meth)acrylic acid chain alkyl ester, and a hydroxy group-containing monomer in the total amount of acrylic oligomers is preferably 50 mass% or more, more preferably 55 mass% or more, and even more preferably 58 mass% or more.

[0107] The acrylic oligomer is obtained by polymerizing the second monomer component of the acrylic oligomer. Examples of polymerization methods include solution polymerization, emulsion polymerization, and solvent-free photopolymerization (e.g., ultraviolet polymerization). Examples of solvents used in solution polymerization include ethyl acetate and toluene. A chain transfer agent may be used in the polymerization to adjust the molecular weight. Examples of polymerization initiators include thermal polymerization initiators and photopolymerization initiators. The polymerization initiators may be used alone or in combination. 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 even more 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 even more preferably 0.3 parts by mass or less.

[0108] The weight average molecular weight Mw of the oligomer is preferably 4300 or more, more preferably 4500 or more, even more preferably 4700 or more, and even more preferably 4900 or more, from the viewpoint of increasing the adhesion of the surface (adhesive surfaces 11, 12) of the pressure-sensitive adhesive sheet 10. The weight average molecular weight Mw of the oligomer is preferably 10000 or less, more preferably 8000 or less, even more preferably 6000 or less, and even more preferably 5800 or less, from the viewpoint of uneven distribution of the oligomer on and near the surface of the pressure-sensitive adhesive sheet 10 (mobility to the surface). The method for measuring the weight average molecular weight Mw of the oligomer is specifically as described below in the examples.

[0109] The content of the acrylic oligomer in the pressure-sensitive adhesive sheet 10 is preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, even more preferably 0.5 parts by mass or more, and even more preferably 0.8 parts by mass or more, relative to 100 parts by mass of the base polymer, in order to sufficiently increase the adhesive strength of the pressure-sensitive adhesive sheet 10. From the viewpoint of ensuring the transparency of the pressure-sensitive adhesive sheet 10, the content of the acrylic oligomer in the pressure-sensitive adhesive sheet 10 is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less, relative to 100 parts by mass of the base polymer. If the content of the acrylic oligomer in the pressure-sensitive adhesive sheet 10 is too high, the compatibility of the acrylic oligomer will decrease, which will tend to increase haze and reduce transparency.

[0110] The PSA composition preferably contains a silane coupling agent. The content of the silane coupling agent in the PSA composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.3 parts by mass or more, per 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, and even more preferably 1 part by mass or less.

[0111] The PSA composition may contain other components as needed. Examples of other components include solvents, tackifiers, plasticizers, softeners, antioxidants, fillers, colorants, UV absorbers, antioxidants, surfactants, and antistatic agents. Examples of solvents include polymerization solvents used as needed during polymerization of the acrylic polymer, and solvents added to the polymerization reaction solution after polymerization. Examples of such solvents include ethyl acetate and toluene.

[0112] The PSA sheet 10 can be produced, for example, by applying the PSA composition described above to a release liner L1 (first release liner) to form a coating film, and then irradiating the coating film with ultraviolet light or drying the coating film. The PSA sheet 10 may also be produced by applying the PSA composition described above to a release liner L1 (first release liner) to form a coating film, laminating a release liner L2 (second release liner) on top of the coating film, and then irradiating the coating film between the release liners with ultraviolet light or drying the coating film.

[0113] Examples of the release liner L1 include a release liner having a release treatment layer on the surface of the liner substrate, and a release liner formed from a low-adhesion material. Examples of the liner substrate include resin film and paper. Examples of the resin for the resin film include polyester resin and polycarbonate resin. Examples of polyester resin include polyethylene terephthalate (PET) and polybutylene terephthalate. The release treatment layer can be formed by surface treating the liner substrate with a release treatment agent. Examples of the release treatment agent include silicone release treatment agents, long-chain alkyl release treatment agents, and fluorine release treatment agents. Examples of low-adhesion materials include polyolefin resins and fluorine-based polymers. Examples of polyolefin resins include polyethylene, polypropylene, and cycloolefin polymer (COP). Examples of fluorine-based polymers include polytetrafluoroethylene.

[0114] Examples of methods for applying the pressure-sensitive adhesive composition include roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, and die coating. The drying temperature for the coating film is, for example, 50°C to 200°C. The drying time is, for example, 5 seconds to 20 minutes.

[0115] Examples of the release liner L2 include a release liner having a release-treated layer on the surface of a liner substrate and a release liner made of a low-adhesion material. Specific examples of the release liner L2 are the same as those described above for the release liner L1.

[0116] In this manner, adhesive sheet 10 can be manufactured in which adhesive surfaces 11, 12 are covered and protected by release liners L1, L2.

[0117] 2A to 2C show an example of how the adhesive sheet 10 can be used.

[0118] In this method, first, as shown in FIG. 2A, an adhesive sheet 10 is attached to one surface in the thickness direction H of a first member 21 (adherend). The first member 21 is, for example, one element in the laminated structure of a flexible display panel. Examples of such elements include a pixel panel, a polarizing film, a touch panel, and a cover film (the same applies to the second member 22 described below). This step provides the adhesive sheet 10, which will be used for bonding to other members, on the first member 21.

[0119] 2B, one surface of the first member 21 in the thickness direction H is bonded to the other surface 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.

[0120] Next, as shown in FIG. 2C, the adhesive sheet 10 between the first member 21 and the second member 22 is aged. Aging increases the bonding strength between the adhesive sheet 10 and the members 21 and 22. The aging temperature is, for example, 20°C to 160°C. The aging time is, for example, 1 minute to 21 days. When aging is performed by autoclave treatment (heat and pressure treatment), the temperature is, for example, 30°C to 80°C, the pressure is, for example, 0.1 to 0.8 MPa, and the treatment time is, for example, 15 minutes or more. [Example]

[0121] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples. Furthermore, the specific numerical values ​​of the blending amounts (contents), physical property values, parameters, etc. described below can be substituted for the upper limits (numerical values ​​defined as "equal to or less than") or lower limits (numerical values ​​defined as "equal to or more than") of the corresponding blending amounts (contents), physical property values, parameters, etc. described in the above-mentioned "Description of the Invention."

[0122] Preparation of First Prepolymer Composition In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, 0.05 parts by mass of a first photoinitiator (product name "Omnirad 184", 1-hydroxycyclohexyl phenyl ketone, IGM Resins) and 0.05 parts by mass of a second photoinitiator (product name "Omnirad 819", bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, IGM Resins) 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), 8 parts by mass of 4-hydroxybutyl acrylate (4HBA), and 2 parts by mass of N-vinyl-2-pyrrolidone (NVP). The mixture was then irradiated with ultraviolet light under a nitrogen atmosphere to polymerize a portion of the monomer components in the mixture, yielding a first prepolymer composition. A black light was used for UV irradiation. UV irradiation was continued until the viscosity of the composition reached 10-20 Pa·s. This viscosity was measured using a Brookfield viscometer (product name "TVB-10M", manufactured by Toki Sangyo Co., Ltd.) with rotor No. 22, rotor rotation speed of 6 rpm, and temperature of 30°C. The obtained prepolymer composition was a partial polymer containing acrylic polymer P1 and unreacted monomer components (residual monomers). The weight-average molecular weight of acrylic polymer P1 in the prepolymer composition was approximately 4.3 million.

[0123] Preparation of Acrylic Oligomer M1 First, in a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, a mixture containing 49 parts by mass of dicyclopentanyl methacrylate (DCPMA), 49 parts by mass of MMA, 2 parts by mass of 2-hydroxyethyl methacrylate (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 (solids concentration 26% by mass) was reacted under a nitrogen atmosphere at 72 to 74°C for 6 hours (polymerization reaction). Next, the reaction solution was heated at 90°C for 12 hours to volatilize and remove the ethyl acetate, chain transfer agent, and unreacted monomer. This yielded a solid acrylic oligomer M1. The Mw of the acrylic oligomer M1 was 5030. The Tg of the acrylic oligomer M1 was 122.6°C.

[0124] <Preparation of Acrylic Oligomers M2 to M7> Acrylic oligomers M2 to M7 were prepared in the same manner as acrylic oligomer M1, except that the formulation of the monomer components was changed as shown in Tables 1 and 2. The Mw and Tg of acrylic oligomers M2 to M7 are as shown in Tables 1 and 2.

[0125] Example 1 <Preparation of Pressure-Sensitive Adhesive Composition> A pressure-sensitive adhesive composition was prepared by adding 1.0 part by mass of acrylic oligomer M1, 0.11 part by mass of dipentaerythritol hexaacrylate (DPHA), 0.02 part by mass of additional photoinitiator (trade name "Omnirad 819", bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, manufactured by IGM Resins), and 0.5 part by mass of silane coupling agent (trade name "KBM-403", 3-glycidoxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) to 100 parts by mass of the monomer components in the prepolymer composition (monomer components that form the base polymer in the pressure-sensitive adhesive layer described below) and mixing them. The relative parts of acrylic oligomer per 100 parts by mass of the base polymer in the pressure-sensitive adhesive layer described below are shown as "parts" in Tables 1 and 2.

[0126] <Formation of adhesive layer> Next, a pressure-sensitive adhesive composition was applied to the release-treated surface of a first release liner, one side of which had been treated with a silicone release agent, to form a coating film. The first release liner was a polyethylene terephthalate (PET) film (product name "Diafoil MRE#75", thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) with one side treated with a silicone release agent. Next, the release-treated surface of a second release liner, one side of which had been treated with a silicone release agent, was bonded to the coating film on the first release liner. The second release liner was a PET film (product name "Diafoil MRF#75", thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) with one side treated with a silicone release agent. Next, the coating film between the release liners was irradiated with ultraviolet light to photocure the coating film and form a pressure-sensitive adhesive layer (thickness 50 μm). For ultraviolet irradiation, a black light was used as the irradiation light source, and the irradiation intensity was approximately 2.5 mW / cm. 2 The irradiation time was 16 minutes. In this manner, a pressure-sensitive adhesive sheet (thickness: 50 μm) with a release liner of Example 1 was produced.

[0127] [Examples 2 to 17 and Comparative Examples 2 and 3] In preparing the adhesive composition, the adhesive sheets with release liners of Examples 2 to 17 and Comparative Examples 2 and 3 were produced in the same manner as the adhesive sheet with release liner of Example 1, except that the type and amount of acrylic oligomer added was changed as shown in Tables 1 and 2.

[0128] Example 18 The PSA sheet with release liner of Example 18 was produced in the same manner as the PSA sheet with release liner of Example 1, except that two types of acrylic oligomers were blended in the preparation of the PSA composition.

[0129] Comparative Example 1 A release-liner-attached PSA sheet of Comparative Example 1 was produced in the same manner as the release-liner-attached PSA sheet of Example 1, except that no acrylic oligomer was added in the preparation of the PSA composition.

[0130] <First measurement method of weight-average molecular weight> The weight-average molecular weight (Mw) of each of the above acrylic oligomers (excluding nitrogen-containing monomers) was measured by gel permeation chromatography (GPC) under the following first measurement conditions, and calculated as a polystyrene equivalent value. A GPC measurement device (product name "HLC-8120GPC", manufactured by Tosoh Corporation) was used for the measurement. The sample solution was prepared as follows: First, a tetrahydrofuran (THF) solution (containing 10 mM phosphoric acid) with a sample concentration of 0.20% by mass was prepared using the acrylic oligomer as a sample, and the THF solution was allowed to stand for 20 hours. Next, the THF solution was filtered through a membrane filter with an average pore size of 0.45 μm, and the filtrate was obtained as a sample solution for molecular weight measurement.

[0131] [GPC first measurement condition] Column: G7000H XL + GMH XL + GMH XL , each TSKgel (manufactured by Tosoh) Column temperature: 40℃ Eluent: THF solution (phosphoric acid concentration 10 mM) Flow rate: 0.8mL / min Sample injection volume: 100 μL Standard sample: Polystyrene (Agilent) Detector: Differential refractometer (RI)

[0132] <Second Measurement Method of Weight-Average Molecular Weight> The weight-average molecular weight (Mw) of each of the above acrylic polymers (including nitrogen-containing monomers) was measured by gel permeation chromatography (GPC) under the second measurement condition described below, and calculated as a polystyrene equivalent value. A GPC measurement device (product name "HLC-8120GPC", manufactured by Tosoh Corporation) was used for the measurement. The sample solution was prepared as follows: First, a dimethylformamide (DMF) solution (salt added) with a sample concentration of 0.20% by mass was prepared using the acrylic polymer as the sample, and the DMF solution was allowed to stand for 20 hours. Next, the DMF solution was filtered through a membrane filter with an average pore size of 0.45 μm, and the filtrate was used as the sample solution for molecular weight measurement.

[0133] [GPC second measurement conditions] Columns: SuperAWM-H + SuperAW4000 + SuperAW2500, each TSKgel (manufactured by Tosoh) Column temperature: 40℃ Eluent: DMF solution (salt added) Flow rate: 0.4mL / min Sample injection volume: 40 μL Standard sample: Polystyrene (Agilent) Detector: Differential refractometer (RI)

[0134] <Oligomer Tg> The glass transition temperatures (Tg) of the acrylic oligomers M1 to M7 were calculated based on the Fox formula above, and the values ​​are shown in Tables 1 and 2.

[0135] <Hydrogen bond term of HSP> The hydrogen bond term of the Hansen solubility parameter (HSP) was determined for each of the acrylic oligomers M1 to M7. Specifically, it is as follows.

[0136] First, the computer software HSPiP (Hansen Solubility Parameters in Practice) was used to determine the ratio of each monomer m that forms the acrylic oligomer. i Regarding the hydrogen bond term of HSP (δh i ) was calculated. Next, the monomer m i Mole fraction x i and the monomer m i The hydrogen bond term δh i From this, the hydrogen bond parameter (ΔH) of the acrylic oligomer was calculated using the following formula. For example, the hydrogen bond parameter of the acrylic oligomer M1 is calculated using the following formula: 1 / 2 , the mole fraction of MMA (molecular weight 100.1) is 0.673 and the hydrogen bond constant is 6.6 MPa 1 / 2 , the mole fraction of HEMA (molecular weight 130.2) is 0.021 and the hydrogen bond constant is 11.5 MPa 1 / 2From the formula below, it is 5.69 MPa 1 / 2 The hydrogen bond parameters of the acrylic oligomers M1 to M5 are shown in Tables 1 and 2 as ΔH2.

[0137] δH=Σ x i ×δh i

[0138] Similarly, the hydrogen bond term (δH1) of the HSP of the above acrylic polymer was calculated. The value was 5.07 MPa. 1 / 2 Tables 1 and 2 also show the difference ΔH (= δH2 - δH1) between δH2 of the acrylic oligomer and δH1 of the acrylic polymer in the pressure-sensitive adhesive sheet, and the ratio of δH2 to δH1 (δH2 / δH1).

[0139] <Gel fraction> The gel fraction of each of the pressure-sensitive adhesive sheets of Examples 1 to 18 and Comparative Examples 1 to 3 was measured as follows.

[0140] First, approximately 500 mg of an adhesive sample was collected from the adhesive sheet between the release liners. Next, the mass (W1) of the adhesive sample was measured. Next, the adhesive sample was immersed in approximately 40 g of ethyl acetate in a container for 7 days. Next, all components insoluble in ethyl acetate (insoluble portion) were collected. Next, the insoluble portion was dried at 130°C for 2 hours (removal of ethyl acetate). Next, the mass (W2) of the insoluble portion was measured. Then, the gel fraction (mass%) of the adhesive sheet after photocuring was calculated based on the following formula. The values ​​are shown in Tables 1 and 2.

[0141] Gel fraction (mass%) = (W2 / W1) × 100

[0142] Haze The haze of each of the pressure-sensitive adhesive sheets of Examples 1 to 18 and Comparative Examples 1 to 3 was measured as follows.

[0143] First, a sample for measurement was prepared. Specifically, the first release liner was peeled from the pressure-sensitive adhesive sheet, and then the sheet was attached to alkali glass (thickness 1.0 mm, total light transmittance 92%, haze 0.4%, manufactured by Matsunami Glass Co., Ltd.). Next, the first release liner was peeled from the pressure-sensitive adhesive sheet on the glass. This prepared a sample for measurement. Next, the haze of each of the pressure-sensitive adhesive sheets in the sample was measured using a haze meter (product name "HM-150", manufactured by Murakami Color Research Laboratory). The measurement was performed in accordance with JIS K7136 (2000). In this measurement, the sample was placed in the device so that light was shining on the alkali glass side of the sample. The measured haze of the pressure-sensitive adhesive sheet is shown in Tables 1 and 2.

[0144] <Shear storage modulus> The dynamic viscoelasticity of each of the pressure-sensitive adhesive sheets of Examples 1 to 18 and Comparative Examples 1 to 3 was measured (first measurement).

[0145] For each pressure-sensitive adhesive sheet, the required number of measurement samples were prepared. Specifically, first, a plurality of pieces of pressure-sensitive adhesive sheet cut out from the pressure-sensitive adhesive sheet were laminated together to prepare a sample sheet with a thickness of approximately 1.0 mm. Next, this sheet was punched out to obtain cylindrical pellets (7.9 mm in diameter) as measurement samples.

[0146] The measurement sample was then fixed to a 7.9 mm diameter parallel plate fixture using a dynamic viscoelasticity measuring device (product name: "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific) and subjected to dynamic viscoelasticity measurement. The measurement mode was shear mode, the measurement temperature range was -65°C to 200°C, the heating rate was 5°C / min, and the frequency was 1 Hz. The shear storage modulus at predetermined temperatures (-10°C, 20°C, and 60°C) was read from the measurement results. The shear storage modulus G1 (kPa) at -10°C, G2 (kPa) at 20°C, and G3 (kPa) at 60°C are shown in Tables 1 and 2.

[0147] Peel test For each of the pressure-sensitive adhesive sheets of Examples 1 to 18 and Comparative Examples 1 to 3, the adhesive strength to the adherend was examined by a peel test.

[0148] Specifically, the required number of measurement samples were prepared for each pressure-sensitive adhesive sheet. To prepare the measurement samples, the first release liner was first peeled from the pressure-sensitive adhesive sheet, and the resulting exposed surface was bonded to a plasma-treated polyethylene terephthalate (PET) film (product name "Lumirror S10," 25 μm thick, manufactured by Toray Industries, Inc.) to obtain a laminate. The plasma treatment was performed using a plasma irradiation device (product name "AP-TO5," manufactured by Sekisui Kogyo Co., Ltd.) at a voltage of 160 V, a frequency of 10 kHz, and a treatment speed of 5,000 mm / min. Next, a test piece (20 mm wide x 100 mm long) was cut from the laminate (PET film / pressure-sensitive adhesive sheet / second release liner). Next, the second release liner was peeled from the pressure-sensitive adhesive sheet of this test piece, and the resulting exposed surface was bonded to a glass plate (acrylic glass manufactured by Matsunami Glass Co., Ltd.). Next, the glass plate with the adhesive sheet (test piece) was subjected to a heating and pressure treatment at a temperature of 50°C, a pressure of 0.5 MPa, and for 15 minutes. This caused the test piece to be pressure-bonded to the glass plate. In this way, a measurement sample was prepared.

[0149] Next, the measurement sample was left to stand at room temperature for 30 minutes, and then a 180° peel test was performed to peel the test piece from the glass plate of the measurement sample, and the force required for peeling (peel strength) was measured (first peel test). For this measurement, a tensile tester (product name "Autograph AG-50NX plus", manufactured by Shimadzu Corporation) was used. In this measurement, the measurement temperature was 25°C, the relative humidity was 55%, the peel angle of the test piece from the glass plate was 180°, the pulling speed of the test piece was 300 mm / min, and the peel length was 50 mm. The average value of the measured peel strength was taken as the adhesive strength F. 11 (N / 20mm) are shown in Tables 1 and 2.

[0150] On the other hand, the test sample was left to stand at 60°C and a relative humidity of 90% for 30 minutes, and then a 180° peel test was carried out to peel the test piece from the glass plate of the test sample, and the force required for peeling (peel strength) was measured (second peel test). In this measurement, the conditions were the same as those of the first peel test, except that the measurement temperature was 60°C and the relative humidity was 90%. The measurement results were recorded as adhesive strength F 12 (N / 20mm) are shown in Tables 1 and 2. Also, the adhesive strength F 11 Adhesion strength F 12 The ratio (F 12 / F 11 ) are also shown in Tables 1 and 2.

[0151] A peel test was carried out under the same conditions as the first peel test except that the pulling speed was changed to 60 mm / min (third peel test). The measurement results are shown as adhesive strength F 21 (N / 20mm) are shown in Tables 1 and 2. Also, the adhesive strength F 11 Adhesion strength F 21 The ratio (F 21 / F 11 ) are also shown in Tables 1 and 2.

[0152] A peel test was carried out under the same conditions as the second peel test except that the pulling speed was changed to 60 mm / min (fourth peel test). The measurement results were recorded as adhesive strength F 22 (N / 20mm) are shown in Tables 1 and 2. Also, the adhesive strength F 21 Adhesion strength F 22 The ratio (F 22 / F 21 ) are also shown in Tables 1 and 2.

[0153] 〔evaluation〕 The adhesive sheet of Comparative Example 1 is a soft adhesive sheet having a shear storage modulus G1 (-10°C) of 100 kPa or less, but does not contain an oligomer having a Tg of 40°C or higher, and has an adhesive strength F 11 ,F 21 Adhesion strength F under high temperature and humidity 12 ,F 22 Also low.

[0154] The PSA sheets of Comparative Examples 2 and 3 each have a shear storage modulus G1 (-10°C) of 100 kPa or less, contain an acrylic oligomer M5 with a Tg of 40°C or more, and have a difference ΔH (= ΔH2 - ΔH1) of 0.1 or more, but have an adhesive strength F at high temperature and high humidity. 12 ,F 22 is low.

[0155] In contrast, each PSA sheet of the Examples had a shear storage modulus G1 of 100 kPa or less at -10°C, making it soft, contained an oligomer with a Tg of 40°C or higher, and the δH1 of the HSP of the base polymer and the δH2 of the HSP of the oligomer satisfied the relationship 0.1≦δH2−δH1≦1.3. Each PSA sheet of the Examples had a high adhesive strength F at room temperature while suppressing haze. 11 ,F 21 In addition, the adhesive strength F of each of the pressure-sensitive adhesive sheets of the Examples at high temperature and high humidity was 12 ,F 22 was also expensive.

[0156] [Table 1]

[0157] [Table 2] [Explanation of symbols]

[0158] 10 Adhesive sheet (optical adhesive sheet) 11 Page 1 12 Side 2 L1, L2 release liner 21 First member 22 Second member H thickness direction

Claims

1. An optical adhesive sheet, The composition comprises a base polymer and an oligomer having a glass transition temperature of 40°C or higher, having a shear storage modulus of 100 kPa or less at −10° C., The hydrogen bond term δH of the Hansen solubility parameter of the base polymer １ and the hydrogen bond term δH of the Hansen solubility parameter of the oligomer. ２ But, 0.1≦δH ２ -δH １ ≦1.3 is satisfied, The optical adhesive sheet, wherein the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester, and the monomer component further contains a hydroxy group-containing monomer.

2. The optical pressure-sensitive adhesive sheet according to claim 1 , having a haze of 1% or less.

3. 2. The optical pressure-sensitive adhesive sheet according to claim 1, which has an adhesive strength of 7.6 N / 20 mm or more in a peel test under conditions of 25°C, a peel angle of 180°, and a tensile speed of 300 mm / min.

4. Adhesion strength F in a peel test under the conditions of 25°C, peel angle 180° and tensile speed 300 mm / min １１ and Adhesion strength F in a peel test under the conditions of 25°C, peel angle 180° and tensile speed 60 mm / min ２１ and Adhesive force F １１ Adhesion strength F ２１ The optical pressure-sensitive adhesive sheet according to claim 1, wherein the ratio is 0.65 or more and 1.1 or less.

5. 2. The optical pressure-sensitive adhesive sheet according to claim 1, wherein the adhesive strength is 4.0 N / 20 mm or more in a peel test under conditions of 60°C, relative humidity of 90%, a peel angle of 180°, and a pulling speed of 300 mm / min.

6. Adhesion strength F in a peel test under the conditions of 25°C, relative humidity 55%, peel angle 180° and tensile speed 300 mm / min １１ and Adhesion strength F in a peel test under the conditions of 60°C, relative humidity 90%, peel angle 180° and tensile speed 300 mm / min １２ and Adhesive force F １１ Adhesion strength F １２ The optical pressure-sensitive adhesive sheet according to claim 1, wherein the ratio is 0.5 or more and 1.1 or less.

7. The optical pressure-sensitive adhesive sheet according to claim 1, having a gel fraction of 60% by mass or more and 87% by mass or less.

8. The hydrogen bond term δH １ and the hydrogen bond term δH ２ But, 1.04≦δH ２ / δH １ The optical pressure-sensitive adhesive sheet according to claim 1, which satisfies ≦1.

28.

9. The optical adhesive sheet according to claim 1 , wherein the proportion of the hydroxy group-containing monomer in the monomer component is 0.5 mass % or more.

10. The optical adhesive sheet according to claim 1 , wherein the proportion of the hydroxy group-containing monomer in the monomer component is 15 mass% or less.

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