Optical adhesive sheet

Abstract

To provide an optical adhesive sheet suitable to a use for a flexible device.SOLUTION: An optical adhesive sheet includes a base polymer and an oligomer being a polymer of a monomer component containing a (meth)acrylate monomer. The (meth)acrylate monomer includes a hydroxy group-containing (meth)acrylate monomer. In the optical adhesive sheet, a shear storage modulus is 300 kPa or less at -30°C. Furthermore, 6.0≤F1 and 0.7≤F2 / F1≤1.3 are satisfied by an adhesive force F1 (N / 20 mm) to glass at a first peeling test and an adhesive force F2 (N / 20 mm) to glass at a second peeling test.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, for example, a pixel panel, a polarizing film, a touch panel, a cover film, etc. In such a display panel, for example, a transparent adhesive sheet (optical adhesive sheet) is used to bond each layer in the laminated structure.

[0003] Furthermore, in recent years, development of repeatedly foldable display panels for smartphones and tablet devices has progressed. Furthermore, development of rollable display panels has also progressed. In such flexible devices such as foldable display panels and rollable display panels, each layer in the laminate structure is made to be repeatedly foldable. In flexible devices, optical adhesive sheets are used to bond each layer together (see, for example, Patent Document 1 below). The optical adhesive sheet for flexible devices described in Patent Document 1 has excellent flexibility so as to be able to withstand repeated bending, and also has excellent adhesiveness to adherends. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-122140 Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, optical adhesive sheets for flexible devices are required to have excellent flexibility and adhesiveness, and furthermore, to be able to prevent excessive deterioration of adhesiveness even when used in high-temperature, high-humidity environments, i.e., to be highly reliable.

[0006] In particular, at the folding points of a foldable display panel, a relatively large shear force is applied in the direction along the adherend, which makes the optical adhesive sheet prone to peeling. Furthermore, when a rollable display panel is rolled up, the optical adhesive sheet is prone to peeling due to the continuous shear force in the direction along the adherend. In other words, optical adhesive sheets for such applications are required to have even better adhesion to the adherend, and are also required to have even better reliability.

[0007] The present invention provides an optical pressure-sensitive adhesive sheet that is suitable for flexible device applications, has excellent flexibility and adhesiveness, and further has excellent reliability in high-temperature, high-humidity environments. [Means for solving the problem]

[0008] The present invention [1] is an optical adhesive sheet comprising a base polymer and an oligomer, wherein the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester monomer, and the (meth)acrylic acid ester monomer contains a hydroxy group-containing (meth)acrylic acid ester monomer, and the optical adhesive sheet has a shear storage modulus of 300 kPa or less at -30°C, and the adhesive strength F1 (N / 20 mm) to glass in the first peel test described below and the adhesive strength F2 (N / 20 mm) to glass in the second peel test described below satisfy the following formulas (1) and (2). 6.0≦F1 (1) 0.7≦F2 / F1≦1.3 (2) (First peel test) A polyethylene terephthalate film is attached to one side of the optical adhesive sheet, and the other side is attached to a glass plate, followed by heating and pressure treatment to prepare a measurement sample. The measurement sample is left standing at room temperature for 30 minutes, and then a test piece (the polyethylene terephthalate film with the optical adhesive sheet) is peeled from the glass plate. The measurement conditions are a temperature of 25°C, a relative humidity of 55%, a peel angle of 180°, a pulling speed of 300 mm / min, and a peel length of 50 mm. (Second peel test) A measurement sample is prepared in the same manner as in the first peel test. The measurement sample is left standing for 500 hours in an environment at a temperature of 85°C and a relative humidity of 85%, and then the measurement sample is removed and conditioned for one day in an environment at a temperature of 25°C and a relative humidity of 55%. Thereafter, the test piece is peeled off from the glass plate of the measurement sample. The measurement conditions are the same as in the first peel test.

[0009] The present invention [2] includes an optical adhesive sheet described in [1] above, in which the adhesive strength F1 (N / 20 mm) to glass in the first peel test and the adhesive strength F3 (N / 20 mm) to glass in the third peel test described below satisfy the following formula (3). 0.7≦F3 / F1≦1.3 (3) (Third peel test) A measurement sample is prepared in the same manner as in the first peel test. The measurement sample is left standing for 500 hours in an environment at a temperature of 60°C and a relative humidity of 90%, and then the measurement sample is removed and conditioned for one day in an environment at a temperature of 25°C and a relative humidity of 55%. Thereafter, the test piece is peeled off from the glass plate of the measurement sample. The measurement conditions are the same as in the first peel test.

[0010] The present invention [3] includes an optical adhesive sheet described in [1] or [2] above, in which the adhesive strength F1 (N / 20 mm) to glass in the first peel test and the adhesive strength F4 (N / 20 mm) to glass in the fourth peel test described below satisfy the following formula (4). 0.7≦F4 / F1≦1.3 (4) (4th peel test) A measurement sample is prepared in the same manner as in the first peel test. The measurement sample is left standing in an environment at a temperature of 0°C for 500 hours, then removed and conditioned for one day in an environment at a temperature of 25°C and a relative humidity of 55%. Thereafter, the test piece is peeled off from the glass plate of the measurement sample. The measurement conditions are the same as in the first peel test.

[0011] The present invention [4] includes the optical adhesive sheet according to any one of the above [1] to [3], wherein the glass transition temperature of the oligomer is 100°C or higher.

[0012] The present invention [5] includes the optical adhesive sheet according to any one of the above [1] to [4], wherein the (meth)acrylic acid ester monomer further includes a fused ring-containing (meth)acrylic acid ester monomer.

[0013] The present invention [6] includes an optical adhesive sheet described in any one of [1] to [5] above, wherein the oligomer is a polymer of a monomer component containing a methacrylic acid ester monomer, the methacrylic acid ester monomer includes the hydroxy group-containing methacrylic acid ester monomer and the condensed ring-containing methacrylic acid ester monomer, and the content of the methacrylic acid ester monomer in the monomer component exceeds 90 mass%.

[0014] The present invention [7] includes an optical adhesive sheet described in any one of [1] to [6] above, wherein the content of the hydroxy group-containing (meth)acrylic acid ester monomer in the monomer component is 0.5 mass% or more and 15 mass% or less.

[0015] The present invention [8] includes an optical adhesive sheet described in [5] or [6] above, in which the content of the fused ring-containing (meth)acrylic acid ester monomer in the monomer component is 20 mass% or more and 80 mass% or less.

[0016] The present invention [9] includes an optical adhesive sheet described in any one of [1] to [8] above, in which the amount of the oligomer blended per 100 parts by mass of the base polymer is 0.1 parts by mass or more and less than 3 parts by mass.

[0017] The present invention

[10] includes the optical pressure-sensitive adhesive sheet according to any one of the above [1] to [9], which has a haze of 1% or less. [Effects of the Invention]

[0018] As described above, the optical adhesive sheet of the present invention has a shear storage modulus of 300 kPa or less at -30°C. Such an optical adhesive sheet has excellent flexibility and can relieve stresses that occur in the optical adhesive sheet and adherend upon deformation (stress relaxation). Stress relaxation in the optical adhesive sheet can ensure the conformability of the optical adhesive sheet to the adherend, and stress relaxation in the adherend can suppress damage such as cracking of the adherend.

[0019] Furthermore, as described above, the optical pressure-sensitive adhesive sheet of the present invention has an adhesive strength F1 (N / 20 mm) to glass in the first peel test that satisfies 6.0≦F1. In other words, it has excellent adhesive properties. The excellent adhesive properties of the optical pressure-sensitive adhesive sheet can prevent the optical pressure-sensitive adhesive sheet from peeling off from an adherend that is repeatedly deformed.

[0020] In addition, in the optical pressure-sensitive adhesive sheet of the present invention, as described above, the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester monomer, and the (meth)acrylic acid ester monomer contains a hydroxy group-containing (meth)acrylic acid ester monomer, and the adhesive strength to glass in the first peel test F1 (N / 20 mm) and the adhesive strength to glass in the second peel test F2 (N / 20 mm) satisfy 0.7≦F2 / F1≦1.3. In other words, such an optical pressure-sensitive adhesive sheet can suppress excessive deterioration in adhesiveness even when used in a high-temperature, high-humidity environment. In other words, it has excellent reliability in a high-temperature, high-humidity environment.

[0021] The optical pressure-sensitive adhesive sheet described above is suitable for use in flexible devices. [Brief explanation of the drawings]

[0022] [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

[0023] One embodiment of the optical pressure-sensitive adhesive sheet of the present invention will be described with reference to FIG.

[0024] The optical adhesive sheet 10 has a sheet shape with a predetermined thickness and extends in a direction (plane direction) perpendicular to the thickness direction. The optical adhesive sheet 10 has a first adhesive surface 11 and a second adhesive surface 12 opposite to the first adhesive surface 11.

[0025] 1 exemplarily shows a state in which release liners L1 and L2 are bonded to a first adhesive surface 11 and a second adhesive surface 12 of an optical adhesive sheet 10. The first release liner L1 is disposed on the first adhesive surface 11. The second release liner L2 is disposed on the second adhesive surface 12.

[0026] The optical adhesive sheet 10 is an optically transparent adhesive sheet that is placed at a light passage location of 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 that includes, for example, a pixel panel, a polarizing film, a touch panel, and a cover film. The optical adhesive sheet 10 is used, for example, to bond the layers in the laminated structure of a flexible display panel. The release liners L1 and L2 are each peeled off at a predetermined timing when the optical adhesive sheet 10 is used.

[0027] The optical adhesive sheet 10 is formed from a pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition includes a base polymer and an oligomer. That is, the optical adhesive sheet 10 includes a base polymer and an oligomer. The oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester monomer, and the (meth)acrylic acid ester monomer includes a hydroxy group-containing (meth)acrylic acid ester monomer. The optical adhesive sheet 10 also has a shear storage modulus of 300 kPa or less at -30°C. Furthermore, the optical adhesive sheet 10 has an adhesive strength F1 (N / 20 mm) to glass in a first peel test described below and an adhesive strength F2 (N / 20 mm) to glass in a second peel test described below, which satisfy the following formulas (1) and (2).

[0028] 6.0≦F1 (1) 0.7≦F2 / F1≦1.3 (2)

[0029] As described above, the optical adhesive sheet 10 has a shear storage modulus of 300 kPa or less at -30°C. Such an optical adhesive sheet has excellent flexibility and can relieve stresses that occur in the optical adhesive sheet and the adherend when deformed (stress relaxation). Stress relaxation in the optical adhesive sheet ensures the conformability of the optical adhesive sheet to the adherend, and stress relaxation in the adherend can prevent damage such as cracking of the adherend.

[0030] Furthermore, as described above, the adhesive strength F1 (N / 20 mm) of the optical adhesive sheet 10 to glass in the first peel test satisfies 6.0≦F1. In other words, the optical adhesive sheet has excellent adhesive properties. The excellent adhesive properties of the optical adhesive sheet can prevent the optical adhesive sheet from peeling off from an adherend that is repeatedly deformed.

[0031] Additionally, in the optical adhesive sheet 10, as described above, the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester monomer, and the (meth)acrylic acid ester monomer contains a hydroxy group-containing (meth)acrylic acid ester monomer, and the adhesive strength to glass F1 (N / 20 mm) in the first peel test and the adhesive strength to glass F2 (N / 20 mm) in the second peel test satisfy 0.7≦F2 / F1≦1.3. In other words, such an optical adhesive sheet can suppress excessive deterioration in adhesiveness even when used in a high-temperature, high-humidity environment. In other words, it has excellent reliability in a high-temperature, high-humidity environment.

[0032] The optical adhesive sheet 10 as described above is suitable for flexible device applications. That is, the optical adhesive sheet 10 is suitable for achieving good repeated deformation of a flexible device in which the optical adhesive sheet 10 is used.

[0033] The shear storage modulus of the optical adhesive sheet 10 at -30°C is 300 kPa or less, preferably 280 kPa or less, more preferably 250 kPa or less, from the viewpoint of stress relaxation during deformation (bending, curvature, etc.) of the optical adhesive sheet 10. Also, from the viewpoint of ensuring the cohesive strength of the optical adhesive sheet 10 in the low temperature range, it is, for example, 150 kPa or more, preferably 180 kPa or more, more preferably 200 kPa or more, and even more preferably 230 kPa or more. The shear storage modulus is determined by dynamic viscoelasticity measurement, and specific details are described in the Examples below. Methods for adjusting the shear storage modulus of the optical adhesive sheet 10 include, for example, selecting the type and adjusting the amount of the base polymer, oligomer, and crosslinking agent, and adjusting the molecular weight of the base polymer and oligomer.

[0034] From the viewpoint of improving the adhesiveness of the optical adhesive sheet 10, the glass transition temperature (Tg) of the oligomer is, for example, 90°C or higher, preferably 100°C or higher, more preferably 105°C or higher, even more preferably 110°C or higher, particularly preferably 115°C or higher, and for example, 150°C or lower, preferably 140°C or lower, more preferably 130°C or lower, even more preferably 120°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 of the oligomer and adjusting the molecular weight.

[0035] The Tg of an oligomer is the glass transition temperature (theoretical value) calculated based on the Fox equation below. The Fox equation is a relational expression between the glass transition temperature Tg of a polymer (oligomer) and the glass transition temperature Tgi of a homopolymer of the monomers constituting the polymer (oligomer). In the Fox equation below, Tg represents the glass transition temperature (°C) of the polymer (oligomer), Wi represents the weight fraction of the monomer mi constituting the polymer (oligomer), and Tgi represents the glass transition temperature (°C) of the homopolymer formed from the monomer mi. Literature values ​​can be used for the glass transition temperature of homopolymers. For example, the "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) lists the glass transition temperatures of various homopolymers. Meanwhile, the glass transition temperature of a homopolymer of a monomer can also be calculated by the method specifically described in JP 2007-51271 A.

[0036] Fox formula 1 / (273+Tg)=Σ[Wi / (273+Tgi)]

[0037] In the first peel test described below, the adhesive strength F1 (initial adhesive strength) of the optical adhesive sheet 10 to glass is 6.0 N / 20 mm or more, preferably 7.0 N / 20 mm or more, more preferably 8.0 N / 20 mm or more, even more preferably 8.3 N / 20 mm or more, particularly preferably 8.5 N / 20 mm or more, from the viewpoint of suppressing peeling of the optical adhesive sheet 10 from the adherend. It is also, for example, 15 N / 20 mm or less, preferably 12 N / 20 mm or less, more preferably 10 N / 20 mm or less. Methods for adjusting the adhesive strength F1 of the optical adhesive sheet 10 to glass include, for example, selecting the type of base polymer in the optical adhesive sheet 10, adjusting the molecular weight, and adjusting the blending amount. Note that selecting the type of base polymer includes adjusting the composition of the monomers that form the base polymer. Other methods include, for example, selecting the type of components other than the base polymer in the optical adhesive sheet 10 and adjusting the blending amount of these components. Components other than the base polymer include a crosslinking agent, a silane coupling agent, and an oligomer. The method for adjusting the adhesive strength F1 of the optical adhesive sheet 10 to glass is also similar to the method for adjusting the adhesive strength of the optical adhesive sheet 10 to glass in other peel tests described below.

[0038] (First peel test) A measurement sample is prepared by laminating one side of the optical adhesive sheet 10 to a polyethylene terephthalate film, laminating the other side to a glass plate, and then heating and pressurizing. The measurement sample is left to stand at room temperature for 30 minutes, and then the test piece (polyethylene terephthalate film with optical adhesive sheet) is peeled from the glass plate. The measurement conditions are a temperature of 25°C, a relative humidity of 55%, a peel angle of 180°, a tensile speed of 300 mm / min, and a peel length of 50 mm.

[0039] Details of the first peel test and the method for measuring the adhesive strength F1 (initial adhesive strength) of the optical adhesive sheet 10 to glass in the first peel test are specifically described in the examples described below (the same applies to the other peel tests described below and the adhesive strength of the optical adhesive sheet 10 to glass in other peel tests).

[0040] In the second peel test described below, the adhesive strength F2 of the optical adhesive sheet 10 to glass (adhesion strength after storage at 85°C / 85% RH / 500 hours) is, from the viewpoint of suppressing peeling of the optical adhesive sheet 10 from the substrate in a high temperature and high humidity environment, for example, 5.0 N / 20 mm or more, preferably 6.0 N / 20 mm or more, more preferably 7.0 N / 20 mm or more, even more preferably 8.0 N / 20 mm or more, and for example, 15 N / 20 mm or less, preferably 12 N / 20 mm or less, more preferably 10 N / 20 mm or less.

[0041] (Second peel test) A measurement sample is prepared in the same manner as in the first peel test. The measurement sample is left standing for 500 hours in an environment at a temperature of 85°C and a relative humidity of 85%, and then the measurement sample is removed and conditioned for one day in an environment at a temperature of 25°C and a relative humidity of 55%. After that, the test piece is peeled off from the glass plate of the measurement sample. The measurement conditions are the same as in the first peel test.

[0042] The ratio (F2 / F1) of the adhesive strength F2 to the adhesive strength F1 is 0.7 or more, preferably 0.8 or more, more preferably 0.9 or more, even more preferably 0.95 or more, and 1.3 or less, preferably 1.2 or less, more preferably 1.1 or less, even more preferably 1.05 or less, from the viewpoint of ensuring the reliability of the optical adhesive sheet 10 in a high-temperature, high-humidity environment.

[0043] Furthermore, the ratio (F2 / F1) of the adhesive strength F2 to the adhesive strength F1 is 0.7 to 1.3, preferably 0.8 to 1.2, more preferably 0.9 to 1.1, and even more preferably 0.95 to 1.05, from the viewpoint of ensuring the reliability of the optical adhesive sheet 10 in a high-temperature, high-humidity environment.

[0044] In the third peel test described below, the adhesive strength F3 of the optical adhesive sheet 10 to glass (adhesion strength after storage at 60°C / 90% RH / 500 hours) is, from the viewpoint of suppressing peeling of the optical adhesive sheet 10 from the substrate in a high temperature and high humidity environment (particularly a higher humidity environment), for example, 5.0 N / 20 mm or more, preferably 6.0 N / 20 mm or more, more preferably 7.0 N / 20 mm or more, even more preferably 8.0 N / 20 mm or more, particularly preferably 9.0 N / 20 mm or more, and also, for example, 15 N / 20 mm or less, preferably 12 N / 20 mm or less, more preferably 10 N / 20 mm or less.

[0045] (Third peel test) A measurement sample is prepared in the same manner as in the first peel test. The measurement sample is left standing for 500 hours in an environment at a temperature of 60°C and a relative humidity of 90%, and then the measurement sample is removed and conditioned for one day in an environment at a temperature of 25°C and a relative humidity of 55%. After that, the test piece is peeled off from the glass plate of the measurement sample. The measurement conditions are the same as in the first peel test.

[0046] The ratio (F3 / F1) of the adhesive strength F3 to the adhesive strength F1 is, from the viewpoint of ensuring the reliability of the optical adhesive sheet 10 in a high temperature and high humidity environment (particularly a higher humidity environment), for example, 0.7 or more, preferably 0.8 or more, more preferably 0.9 or more, and for example, 1.3 or less, preferably 1.2 or less, more preferably 1.1 or less.

[0047] Furthermore, the ratio (F3 / F1) of the adhesive strength F3 to the adhesive strength F1 is 0.7 to 1.3, preferably 0.8 to 1.2, and more preferably 0.9 to 1.1, from the viewpoint of ensuring the reliability of the optical adhesive sheet 10 in a high temperature and high humidity environment (particularly a higher humidity environment).

[0048] In the fourth peel test described below, the adhesive strength F4 of the optical adhesive sheet 10 to glass (adhesion strength after storage at 0°C / 500 hours) is, from the viewpoint of suppressing peeling of the optical adhesive sheet 10 from the substrate in a low-temperature environment, for example, 5.0 N / 20 mm or more, preferably 6.0 N / 20 mm or more, more preferably 7.0 N / 20 mm or more, even more preferably 8.0 N / 20 mm or more, and for example, 15 N / 20 mm or less, preferably 12 N / 20 mm or less, more preferably 10 N / 20 mm or less, even more preferably 9.0 N / 20 mm or less.

[0049] (4th peel test) A measurement sample is prepared in the same manner as in the first peel test. The measurement sample is left standing in an environment at a temperature of 0°C for 500 hours, then removed and conditioned for one day in an environment at a temperature of 25°C and a relative humidity of 55%. After that, the test piece is peeled off from the glass plate of the measurement sample. The measurement conditions are the same as in the first peel test.

[0050] The ratio (F4 / F1) of the adhesive strength F4 to the adhesive strength F1 is, from the viewpoint of ensuring the reliability of the optical adhesive sheet 10 in a low-temperature environment, for example, 0.7 or more, preferably 0.8 or more, more preferably 0.9 or more, even more preferably 0.95 or more, and for example, 1.3 or less, preferably 1.2 or less, more preferably 1.1 or less, even more preferably 1.05 or less.

[0051] Furthermore, the ratio (F4 / F1) of the adhesive strength F4 to the adhesive strength F1 is 0.7 to 1.3, preferably 0.8 to 1.2, more preferably 0.9 to 1.1, and even more preferably 0.95 to 1.05, from the viewpoint of ensuring the reliability of the optical adhesive sheet 10 in low-temperature environments.

[0052] In the fifth peel test described below, the adhesive strength F5 of the optical adhesive sheet 10 to glass (adhesion strength after storage at 25°C / 55% RH / 500 hours) is, from the viewpoint of preventing peeling of the optical adhesive sheet 10 from the substrate during storage, for example, 5.0 N / 20 mm or more, preferably 6.0 N / 20 mm or more, more preferably 7.0 N / 20 mm or more, even more preferably 8.0 N / 20 mm or more, and for example, 15 N / 20 mm or less, preferably 12 N / 20 mm or less, more preferably 10 N / 20 mm or less, even more preferably 9.0 N / 20 mm or less.

[0053] (5th peel test) A measurement sample is prepared in the same manner as in the first peel test. The measurement sample is left to stand for 500 hours in an environment of 25°C and 55% relative humidity, and then removed. Then, the test piece is peeled off from the glass plate in the measurement sample. The measurement conditions are the same as in the first peel test.

[0054] From the viewpoint of ensuring the reliability of the optical adhesive sheet 10, the ratio (F5 / F1) of the adhesive strength F5 to the adhesive strength F1 is, for example, 0.7 or more, preferably 0.8 or more, more preferably 0.9 or more, even more preferably 0.95 or more, and for example, 1.3 or less, preferably 1.2 or less, more preferably 1.1 or less, even more preferably 1.05 or less.

[0055] Furthermore, the ratio (F5 / F1) of the adhesive strength F5 to the adhesive strength F1 is 0.7 to 1.3, preferably 0.8 to 1.2, more preferably 0.9 to 1.1, and even more preferably 0.95 to 1.05, from the viewpoint of ensuring the reliability of the optical adhesive sheet 10.

[0056] In the sixth peel test described below, the adhesive strength F6 of the optical adhesive sheet 10 to glass (adhesion strength after storage at 100°C / 500h) is, from the viewpoint of suppressing peeling of the optical adhesive sheet 10 from the substrate in a high temperature environment, for example, 5.0 N / 20 mm or more, preferably 6.0 N / 20 mm or more, more preferably 7.0 N / 20 mm or more, even more preferably 8.0 N / 20 mm or more, particularly preferably 9.0 N / 20 mm or more, and also, for example, 15 N / 20 mm or less, preferably 12 N / 20 mm or less, more preferably 10 N / 20 mm or less.

[0057] (6th peel test) A measurement sample is prepared in the same manner as in the first peel test. The measurement sample is left standing in an environment at 100°C for 500 hours, then removed and conditioned for one day in an environment at a temperature of 25°C and a relative humidity of 55%. After that, the test piece is peeled off from the glass plate of the measurement sample. The measurement conditions are the same as in the first peel test.

[0058] The ratio (F6 / F1) of the adhesive strength F6 to the adhesive strength F1 is, from the viewpoint of ensuring the reliability of the optical adhesive sheet 10 in a high-temperature environment, for example, 0.7 or more, preferably 0.8 or more, more preferably 0.85 or more, and for example, 1.3 or less, preferably 1.2 or less, more preferably 1.15 or less.

[0059] Furthermore, the ratio (F6 / F1) of the adhesive strength F6 to the adhesive strength F1 is 0.7 to 1.3, preferably 0.8 to 1.2, and more preferably 0.85 to 1.15, from the viewpoint of ensuring the reliability of the optical adhesive sheet 10 in a high-temperature environment.

[0060] The haze of the optical adhesive sheet 10 is, for example, 1% or less, preferably 0.8% or less, more preferably 0.5% or less, and for example, 0.01% or more. The haze of the optical adhesive sheet 10 can be measured using a haze meter in accordance with JIS K7136 (2000).

[0061] The total light transmittance of the optical adhesive sheet 10 is, for example, 60% or more, preferably 80% or more, more preferably 85% or more, and for example, 100% or less. The total light transmittance of the optical adhesive sheet 10 can be measured in accordance with JIS K 7375 (2008).

[0062] <Base polymer> The base polymer is the adhesive component of the optical 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. Acrylic polymers are preferred from the viewpoint of ensuring good transparency and adhesiveness. The base polymers may be used alone or in combination of two or more.

[0063] 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 monomer. Note that "(meth)acrylic" refers to acrylic and / or methacrylic.

[0064] Examples of the (meth)acrylic acid ester monomer include a (meth)acrylic acid ester monomer having an alkyl group having 1 to 20 carbon atoms (an alkyl group-containing (meth)acrylic acid ester monomer) and a (meth)acrylic acid ester monomer having a hydroxy group (a hydroxy group-containing (meth)acrylic acid ester monomer). Examples of the alkyl group-containing (meth)acrylic acid ester monomer include a (meth)acrylic acid ester monomer having a chain alkyl group (a chain alkyl group-containing (meth)acrylic acid ester monomer) and a (meth)acrylic acid ester monomer having an alicyclic alkyl group (an alicyclic alkyl group-containing (meth)acrylic acid ester monomer).

[0065] Examples of the chain alkyl group-containing (meth)acrylic acid ester monomer 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, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, and lauryl (meth)acrylate.

[0066] Examples of the alicyclic alkyl group-containing (meth)acrylic acid ester monomer include the alicyclic alkyl group-containing (meth)acrylic acid ester monomer in the second monomer component described below.

[0067] In order to achieve a balance between the flexibility and adhesive strength required for an optical adhesive sheet for flexible devices, the alkyl group-containing (meth)acrylic acid ester monomer in the optical adhesive sheet 10 is preferably at least one selected from first alkyl group-containing (meth)acrylic acid ester monomers having an alkyl group of 8 to 12 carbon atoms and at least one selected from second alkyl group-containing (meth)acrylic acid ester monomers having an alkyl group of 1 to 4 carbon atoms. The first alkyl group-containing (meth)acrylic acid ester monomer is preferably n-octyl acrylate (NOAA). The second alkyl group-containing (meth)acrylic acid ester monomer is preferably n-butyl acrylate (BA). More preferably, NOAA and BA are used in combination.

[0068] The content of the alkyl group-containing (meth)acrylic acid ester monomer in the first monomer component is, for example, 80% by mass or more, preferably 85% by mass or more, more preferably 88% by mass or more, and for example, less than 100% by mass, preferably 99% by mass or less, from the viewpoint of balancing flexibility and adhesive strength in the optical adhesive sheet 10. When the first alkyl group-containing (meth)acrylic acid ester monomer and the second alkyl group-containing (meth)acrylic acid ester monomer are used in combination, the content of the first alkyl group-containing (meth)acrylic acid ester monomer in the monomer component is, for example, 60% by mass or more, preferably 65% ​​by mass or more, more preferably 68% by mass or more, and for example, 85% by mass or less, preferably 80% by mass or less, more preferably 75% by mass or less. The content of the second alkyl group-containing (meth)acrylic acid ester monomer in the monomer components is, for example, 10% by mass or more, preferably 15% by mass or more, more preferably 18% by mass or more, and for example, 35% by mass or less, preferably 30% by mass or less, more preferably 25% by mass or less.

[0069] Examples of hydroxy group-containing (meth)acrylic acid ester 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. 4-hydroxybutyl acrylate (4HBA) is preferred.

[0070] The content ratio of the hydroxy group-containing (meth)acrylic acid ester monomer in the first monomer component is, for example, 1 mass% or more, preferably 3 mass% or more, more preferably 5 mass% or more, from the viewpoint of introducing a crosslinked structure into the acrylic polymer and ensuring cohesive strength in the optical adhesive sheet 10, and, from the viewpoint of adjusting the polarity of the acrylic polymer (which is related to the compatibility between various additive components in the optical adhesive sheet 10 and the acrylic polymer), is, for example, 15 mass% or less, preferably 12 mass% or less, more preferably 10 mass% or less.

[0071] The first monomer component may also contain a copolymerizable monomer copolymerizable with the (meth)acrylic acid ester monomer. Examples of the copolymerizable monomer include a monomer having a polar group. Examples of the polar group-containing monomer include a monomer having a nitrogen atom-containing ring and a carboxy group-containing monomer. In the first monomer component, the polar group-containing monomer can modify the acrylic polymer, for example, by introducing crosslinking points into the acrylic polymer or ensuring the cohesive strength of the acrylic polymer. The copolymerizable monomer may be used alone or in combination of two or more types. The polar group-containing monomer excludes the above-mentioned hydroxy group-containing (meth)acrylic acid ester monomer.

[0072] Examples of monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, 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, N-vinyl-2-pyrrolidone (NVP) is used.

[0073] When a monomer having a nitrogen atom-containing ring is used, the content ratio of the monomer having a nitrogen atom-containing ring in the first monomer component is, for example, 0.5 mass% or more, preferably 1 mass% or more, more preferably 1.5 mass% or more, from the viewpoint of ensuring the cohesive strength of the optical adhesive sheet 10 and ensuring the adhesion strength of the optical adhesive sheet 10 to the substrate, and is, for example, 10 mass% or less, preferably 5 mass% or less, more preferably 3 mass% or less, from the viewpoint of adjusting the glass transition temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (which is related to the compatibility between various additive components in the optical adhesive sheet 10 and the acrylic polymer).

[0074] The first monomer component may contain other copolymerizable monomers in addition to those described above. 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. The other copolymerizable monomers may be used alone or in combination of two or more.

[0075] The first monomer component preferably contains a first alkyl group-containing (meth)acrylic acid ester monomer having an alkyl group of 8 to 12 carbon atoms, a second alkyl group-containing (meth)acrylic acid ester monomer having an alkyl group of 1 to 4 carbon atoms, a hydroxy group-containing (meth)acrylic acid ester monomer, and a monomer having a nitrogen atom-containing ring. More preferably, it contains NOAA, BA, 4HBA, and NVP.

[0076] The base polymer preferably has a crosslinked structure. Methods for introducing a crosslinked structure into the base polymer include, for example, a first method and a second method. In the first method, a base polymer having a functional group reactive with the crosslinking agent and a crosslinking agent are blended into an adhesive composition, and the base polymer and the crosslinking agent are reacted in an optical adhesive sheet. In the second method, a first monomer component forming the base polymer contains a multifunctional 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.

[0077] 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 the crosslinking agent include isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, and carbodiimide crosslinking agents. Isocyanate crosslinking agents are preferred because they have high reactivity with the hydroxyl groups and carboxyl groups in the base polymer and facilitate the introduction of crosslinked structures. The crosslinking agents may be used alone or in combination of two or more.

[0078] In the first method, the amount of crosslinking agent per 100 parts by mass of base polymer is, from the viewpoint of ensuring the cohesive strength of the optical adhesive sheet 10, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and from the viewpoint of ensuring good tackiness in the optical adhesive sheet 10, for example, 5 parts by mass or less, preferably 1 part by mass or less, more preferably 0.2 parts by mass or less.

[0079] 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, first, a monofunctional monomer for forming a base polymer is polymerized (prepolymerization), 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 to the prepolymer composition, and the mixture containing the partial polymer and the polyfunctional compound is polymerized (main polymerization). In the main polymerization, a pre-prepared oligomer (described below) can also be blended with the mixture containing the partial polymer and the polyfunctional compound. A silane coupling agent (described below) can also be blended with the mixture.

[0080] Examples of polyfunctional compounds include polyfunctional monomers and polyfunctional oligomers containing two or more ethylenically unsaturated double bonds in one molecule, and polyfunctional monomers include polyfunctional (meth)acrylates.

[0081] Examples of the polyfunctional (meth)acrylate include difunctional (meth)acrylate, trifunctional (meth)acrylate, and tetrafunctional or higher polyfunctional (meth)acrylate.

[0082] Examples of bifunctional (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.

[0083] Examples of trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl)isocyanurate.

[0084] 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.

[0085] 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.

[0086] The polyfunctional compound as the crosslinking agent may be used alone or in combination of two or more kinds. The polyfunctional compound is preferably a polyfunctional monomer. More preferably, the polyfunctional compound is at least one selected from the group consisting of 1,9-nonanediol diacrylate, dipentaerythritol hexaacrylate, 1,6-hexanediol diacrylate, and trimethylolpropane triacrylate.

[0087] In the second method, the amount of polyfunctional compound per 100 parts by mass of the monofunctional monomer of the first monomer component is, from the viewpoint of ensuring the cohesive strength of the optical adhesive sheet 10, for example, 0.02 parts by mass or more, preferably 0.05 parts by mass or more, more preferably 0.07 parts by mass or more, and from the viewpoint of ensuring good tackiness in the optical adhesive sheet 10, for example, 3 parts by mass or less, preferably 1 part by mass or less, more preferably 0.5 parts by mass or less.

[0088] The base polymer can be formed by polymerizing the first monomer component. Examples of polymerization methods include solution polymerization, emulsion polymerization, and solventless photopolymerization (e.g., ultraviolet polymerization). Examples of solvents for 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. For example, in the second method, the polymerization initiator is added first during prepolymerization and then second during main polymerization. The polymerization initiator may be used alone or in combination of two or more. The amount of the polymerization initiator per 100 parts by mass of the first monomer component is, for example, 0.03 parts by mass or more, preferably 0.05 parts by mass or more, and more preferably 0.07 parts by mass or more, and for example, 1 part by mass or less, preferably 0.5 parts by mass or less, and more preferably 0.3 parts by mass or less.

[0089] 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.

[0090] Examples of photopolymerization initiators include radical photopolymerization initiators, cationic photopolymerization initiators, and anionic photopolymerization initiators. Examples of radical photopolymerization initiators include acylphosphine oxide photopolymerization initiators, acetophenone photopolymerization initiators, and benzoin ether photopolymerization initiators. 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 acetophenone-based photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of benzoin ether-based 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.

[0091] The weight average molecular weight of the base polymer is, for example, 100,000 or more, preferably 300,000 or more, and more preferably 500,000 or more, from the viewpoint of ensuring cohesive strength in the optical 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.

[0092] The Tg of the base polymer is, for example, 0° C. or lower, preferably −10° C. or lower, more preferably −20° C. or lower, and for example, −80° C. or higher. The Tg of the base polymer can be determined by the glass transition temperature (theoretical value) calculated based on the Fox formula described above.

[0093] The content of the base polymer in the optical adhesive sheet 10 is, for example, 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more, from the viewpoint of properly expressing basic properties such as adhesiveness, and, from the viewpoint of ensuring the content of other components in the optical adhesive sheet 10, is, for example, 99.9% by mass or less, preferably 99.5% by mass or less, and more preferably 99.0% by mass or less.

[0094] <Oligomer> The oligomer is a polymer of a monomer component (second monomer component) containing a (meth)acrylic acid ester monomer. Preferably, it is a polymer of a monomer component (second monomer component) containing a methacrylic acid ester monomer. The oligomer may be used alone or in combination of two or more kinds.

[0095] When two or more oligomers are used in combination, it is sufficient that at least one oligomer satisfies the specified parameters (e.g., glass transition temperature). In other words, when two or more oligomers are used in combination, an oligomer that does not satisfy the specified parameters (e.g., glass transition temperature) may also be included within a range that does not impair the effects of the present invention. Preferably, all oligomers used in combination satisfy the specified parameters.

[0096] Examples of the (meth)acrylic acid ester monomer in the second monomer component include alkyl group-containing (meth)acrylic acid ester monomers and hydroxy group-containing (meth)acrylic acid ester monomers. Examples of the alkyl group-containing (meth)acrylic acid ester monomer include chain alkyl group-containing (meth)acrylic acid ester monomers and alicyclic alkyl group-containing (meth)acrylic acid ester monomers. The (meth)acrylic acid ester monomer in the second monomer component also includes hydroxy group-containing (meth)acrylic acid ester monomers.

[0097] Examples of the (meth)acrylic acid ester monomer containing a chain alkyl group in the second monomer component include the chain alkyl group-containing (meth)acrylic acid ester monomers described above for the first monomer component. Preferably, a (meth)acrylic acid ester monomer containing a chain alkyl group having an alkyl group of 1 to 6 carbon atoms is used. More preferably, a methacrylic acid ester monomer containing a chain alkyl group having an alkyl group of 1 to 6 carbon atoms is used. Even more preferably, methyl methacrylate (MMA) is used. MMA has a high glass transition temperature as a homopolymer and is relatively compatible with the base polymer.

[0098] The proportion of the chain alkyl group-containing (meth)acrylic acid ester monomer in the second monomer component is, from the viewpoint of ensuring a high Tg of the oligomer and adjusting the compatibility of the oligomer with the base polymer, for example, 15% by mass or more, preferably 20% by mass or more, more preferably 25% by mass or more, even more preferably 30% by mass or more, particularly preferably 35% by mass or more, and for example, 60% by mass or less, preferably 55% by mass or less, more preferably 50% by mass or less, even more preferably less than 50% by mass.

[0099] Examples of the (meth)acrylic acid ester monomer containing an alicyclic alkyl group in the second monomer component include a (meth)acrylic acid cycloalkyl ester monomer, a (meth)acrylic acid ester monomer having a bicyclic aliphatic hydrocarbon ring, and a (meth)acrylic acid ester monomer having a tricyclic or higher aliphatic hydrocarbon ring.Preferably, among the (meth)acrylic acid ester monomers having a bicyclic aliphatic hydrocarbon ring and the (meth)acrylic acid ester monomers having a tricyclic or higher aliphatic hydrocarbon ring, a (meth)acrylic acid ester monomer containing a condensed ring (condensed ring-containing (meth)acrylic acid ester monomer) is used.More preferably, a condensed ring-containing methacrylic acid ester monomer is used.

[0100] Examples of (meth)acrylic acid cycloalkyl ester monomers 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 a tricyclic or higher aliphatic hydrocarbon ring 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.

[0101] The alicyclic alkyl group-containing (meth)acrylic acid ester monomer in the second monomer component is preferably a fused ring-containing (meth)acrylic acid ester monomer, more preferably a fused ring-containing methacrylic acid ester monomer, and even more preferably dicyclopentanyl methacrylate (DCPMA).

[0102] The proportion of the alicyclic alkyl group-containing (meth)acrylic acid ester monomer in the second monomer component is, from the viewpoint of increasing the Tg of the oligomer, for example, 30% by mass or more, preferably 35% by mass or more, and more preferably 40% by mass or more, and from the viewpoint of the polymerizability of the second monomer component, for example, 80% by mass or less, preferably 70% by mass or less, more preferably 60% by mass or less, even more preferably 50% by mass or less, and particularly preferably less than 50% by mass.

[0103] The mass ratio of the alicyclic alkyl group-containing (meth)acrylic acid ester monomer to the chain alkyl group-containing (meth)acrylic acid ester monomer in the second monomer component is, from the viewpoint of increasing the Tg of the oligomer and adjusting the compatibility of the oligomer with the base polymer, for example, 0.6 or more, preferably 0.8 or more, and for example, 5.0 or less, preferably 3.0 or less, more preferably 1.5 or less.

[0104] The proportion of the fused ring-containing methacrylic acid ester monomer in the second monomer component is, from the viewpoint of increasing the Tg of the oligomer, for example, 20% by mass or more, preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more, and from the viewpoint of the polymerizability of the second monomer component, for example, 80% by mass or less, preferably 70% by mass or less, more preferably 60% by mass or less, even more preferably 50% by mass or less, and particularly preferably less than 50% by mass.

[0105] The mass ratio of the fused ring-containing methacrylic acid ester monomer to the chain alkyl group-containing (meth)acrylic acid ester monomer in the second monomer component is, from the viewpoint of increasing the Tg of the oligomer and adjusting the compatibility of the oligomer with the base polymer, for example, 0.6 or more, preferably 0.8 or more, and for example, 5.0 or less, preferably 3.0 or less, more preferably 1.5 or less.

[0106] Examples of the hydroxy group-containing (meth)acrylic acid ester monomer in the second monomer component include the hydroxy group-containing (meth)acrylic acid ester monomers described above in the first monomer component. Preferred examples include the hydroxy group-containing methacrylic acid ester monomers. More preferred examples include 2-hydroxyethyl methacrylate (HEMA).

[0107] The proportion of the hydroxy group-containing (meth)acrylic acid ester monomer in the second monomer component is, from the viewpoint of ensuring good adhesive strength in high temperature and high humidity environments in the optical adhesive sheet 10, for example, 0.5 mass% or more, preferably 1 mass% or more, more preferably 2 mass% or more, and even more preferably 5 mass% or more, and from the viewpoint of adjusting the compatibility of the oligomer with the base polymer, for example, 15 mass% or less, preferably 13 mass% or less, and more preferably 12 mass% or less.

[0108] From the viewpoint of increasing the Tg of the oligomer, the proportion of the methacrylic acid ester monomer in the second monomer component is, for example, 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass.

[0109] The second monomer component may contain a polar group-containing monomer. Preferably, the second monomer component does not contain a polar group-containing monomer. Examples of the polar group-containing monomer include a monomer having a nitrogen atom-containing ring and a carboxy group-containing monomer. The polar group-containing monomer does not include the above-mentioned hydroxy group-containing (meth)acrylic acid ester monomer.

[0110] The proportion of the polar group-containing monomer in the second monomer component is, for example, 10% by mass or less, preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0% by mass, from the viewpoint of ensuring good adhesive strength in the optical adhesive sheet 10 in a high-temperature, high-humidity environment and adjusting the compatibility of the oligomer with the base polymer.

[0111] The second monomer component preferably contains a chain alkyl group-containing (meth)acrylic acid ester monomer, an alicyclic alkyl group-containing (meth)acrylic acid ester monomer, and a hydroxy group-containing (meth)acrylic acid ester monomer. More preferably, it contains a chain alkyl group-containing methacrylic acid ester monomer having an alkyl group of 1 to 6 carbon atoms, a condensed ring-containing methacrylic acid ester monomer, and a hydroxy group-containing methacrylic acid ester monomer. Even more preferably, it is composed of a chain alkyl group-containing methacrylic acid ester monomer having an alkyl group of 1 to 6 carbon atoms, a condensed ring-containing methacrylic acid ester monomer, and a hydroxy group-containing methacrylic acid ester monomer. Specifically, it is composed of MMA, DCPMA, and HEMA.

[0112] As described above, the oligomer can be obtained by polymerizing a monomer component (second monomer component) containing a (meth)acrylic acid ester monomer. 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 the thermal polymerization initiators and photopolymerization initiators described above. The polymerization initiators may be used alone or in combination of two or more. The amount of the polymerization initiator used is, per 100 parts by mass of the second monomer component, for example, 0.05 parts by mass or more, preferably 0.1 parts by mass or more, and for example, 1 part by mass or less, preferably 0.5 parts by mass or less.

[0113] The oligomer has a weight average molecular weight Mw of 1,000 or more and 30,000 or less. From the viewpoint of increasing adhesion on the surface (adhesive surfaces 11 and 12) of the optical adhesive sheet 10, the weight average molecular weight Mw of the oligomer is, for example, 4,300 or more, preferably 4,500 or more, more preferably 4,700 or more, and even more preferably 4,900 or more. From the viewpoint of uneven distribution of the oligomer on and near the surface of the optical adhesive sheet 10 (mobility to the surface), the weight average molecular weight Mw is, for example, 10,000 or less, preferably 8,000 or less, more preferably 6,000 or less, and even more preferably 5,800 or less. The weight average molecular weight Mw of the oligomer is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene.

[0114] The content of the oligomer in the pressure-sensitive adhesive composition (optical adhesive sheet 10) is, from the viewpoint of sufficiently increasing the adhesive strength of the optical adhesive sheet 10, for example, 0.1 parts by mass or more, preferably 0.3 parts by mass or more, 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; from the viewpoint of ensuring the transparency of the optical adhesive sheet 10, it is, for example, 5 parts by mass or less, preferably 3 parts by mass or less, more preferably less than 3 parts by mass, even more preferably 2 parts by mass or less, and particularly preferably 1.5 parts by mass or less. In the optical adhesive sheet 10, if the content of the oligomer is too large, the compatibility of the oligomer decreases, which tends to increase haze and reduce transparency.

[0115] The PSA composition may contain a silane coupling agent. The content of the silane coupling agent in the PSA composition is, per 100 parts by mass of the base polymer, for example, 0.1 parts by mass or more, preferably 0.2 parts by mass or more, and for example, 5 parts by mass or less, preferably 3 parts by mass or less.

[0116] The PSA composition may contain other components as needed. Examples of the other components include solvents, tackifiers, plasticizers, softeners, antioxidants, fillers, colorants, UV absorbers, antioxidants, surfactants, and antistatic agents. Examples of the solvent include polymerization solvents used as needed during polymerization of the acrylic polymer, and solvents added to the polymerization reaction solution after polymerization. Specifically, ethyl acetate and toluene are used as the solvent.

[0117] The optical adhesive sheet 10 can be produced, for example, by applying the above-mentioned pressure-sensitive adhesive composition to a first release liner L1 to form a coating film, and then irradiating the coating film with ultraviolet light or drying the coating film. The optical adhesive sheet 10 may also be produced by applying the above-mentioned pressure-sensitive adhesive composition to a first release liner L1 to form a coating film, laminating a second release liner L2 on the coating film, and then irradiating the coating film between the release liners with ultraviolet light or drying the coating film.

[0118] Examples of the first release liner L1 include a release liner having a release treatment layer on the surface of the liner substrate, and a release liner made of a low-adhesion material. Examples of the liner substrate include a resin film and paper. Examples of the resin for the resin film include a polyester resin and a polycarbonate resin. Examples of polyester resins include polyethylene terephthalate (PET) and polybutylene terephthalate. The release treatment layer can be formed by treating the surface of the liner substrate with a release treatment agent. Examples of the release treatment agent include a silicone release treatment agent, a long-chain alkyl release treatment agent, and a fluorine release treatment agent. Examples of low-adhesion materials include a polyolefin resin and a fluorine-based polymer. Examples of polyolefin resins include polyethylene, polypropylene, and cycloolefin polymer (COP). Examples of fluorine-based polymers include polytetrafluoroethylene.

[0119] 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.

[0120] Examples of the second 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. Specifically, the second release liner L2 is the same as that described above for the first release liner L1.

[0121] In this manner, an optical pressure-sensitive adhesive sheet 10 can be produced in which the pressure-sensitive adhesive surfaces 11, 12 are covered and protected by the release liners L1, L2.

[0122] A method of using the optical adhesive sheet 10 will be described with reference to FIGS. 2A to 2C.

[0123] 2A, the optical adhesive sheet 10 is attached to one surface in the thickness direction of a first member 21 (adherend). The first member 21 is, for example, part of the laminated structure of a flexible display panel. Specifically, the first member 21 can be a pixel panel, a polarizing film, a touch panel, or a cover film (the same applies to the second member 22 described below).

[0124] 2B, one surface in the thickness direction of the first member 21 is bonded to the other surface in the thickness direction of the second member 22 via the optical adhesive sheet 10 on the first member 21. The second member 22 is, for example, part of a laminated structure of a flexible display panel.

[0125] Next, as shown in FIG. 2C, the optical adhesive sheet 10 between the first member 21 and the second member 22 is aged. Aging increases the bonding strength between the optical 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 autoclaving (heat and pressure treatment) is used for aging, 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]

[0126] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. The specific numerical values ​​of the blending amounts (contents), physical properties, parameters, etc. described below can be substituted for the upper limits (numerical values ​​defined as "not more than" or "less than") or lower limits (numerical values ​​defined as "not less than" or "exceeding") of the corresponding blending amounts (contents), physical properties, parameters, etc. described in the above-mentioned "Description of the Invention."

[0127] Example 1 <Preparation of Prepolymer Composition> In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, a monomer mixture of 70 parts by weight of n-octyl acrylate, 20 parts by weight of n-butyl acrylate, 8 parts by weight of 4-hydroxybutyl acrylate (4HBA), and 2 parts by weight of N-vinyl-2-pyrrolidone was added. 0.05 parts by weight of a photoinitiator (product name "Omnirad 184," 1-hydroxycyclohexyl phenyl ketone, IGM Resins) and 0.05 parts by weight of a second photoinitiator (product name "Omnirad 651," 2,2-dimethoxy-1,2-diphenylethan-1-one, IGM Resins) were then added. The mixture was then irradiated with UV light under a nitrogen atmosphere, polymerizing a portion of the monomer components in the mixture to obtain a prepolymer composition. A black light was used for UV irradiation. UV irradiation was continued until the viscosity of the prepolymer composition reached 10-20 Pa·s. The 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.

[0128] <Preparation of Oligomer> First, in a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, a mixture containing 45 parts by mass of dicyclopentanyl methacrylate (DCPMA), 45 parts by mass of methyl methacrylate (MMA), 10 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 azobisisobutyronitrile as a thermal polymerization initiator, and ethyl acetate as a solvent (solid content concentration 26% by mass) was reacted under a nitrogen atmosphere at 72°C 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 the solid oligomer used in Example 1. The Tg of the oligomer used in Example 1 was 115.8°C.

[0129] <Preparation of Pressure-Sensitive Adhesive Composition> To the prepolymer composition, 1.0 part by mass of the oligomer, 0.07 part by mass of a crosslinker (trade name "Viscoat #260", 1,9-nonanediol diacrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd.), and 0.02 part by mass of a second photoinitiator (trade name "Omnirad 651", 2,2-dimethoxy-1,2-diphenylethan-1-one, manufactured by IGM Resins) were added and mixed per 100 parts by mass of the monomer components (monomer components forming the base polymer) in the prepolymer composition to prepare a pressure-sensitive adhesive composition. The relative parts of the acrylic oligomer per 100 parts by mass of the base polymer in the pressure-sensitive adhesive layer described below are shown in Table 1 as "blended amount (parts by mass)."

[0130] <Formation of adhesive layer> Next, a pressure-sensitive adhesive composition was applied to the release-treated surface of a first release liner (product name "Diafoil MRE#75", polyethylene terephthalate film, thickness 75 μm, manufactured by Mitsubishi Chemical Corporation), one side of which had been treated for silicone release, to form a coating film. Next, the release-treated surface of a second release liner (product name "Diafoil MRE#75", polyethylene terephthalate film, thickness 75 μm, manufactured by Mitsubishi Chemical Corporation), one side of which had been treated for silicone release, was bonded to the coating film on the first release liner. Next, the coating film between the release liners was irradiated with ultraviolet light, and this coating film was photocured to 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, an optical pressure-sensitive adhesive sheet (thickness: 50 μm) with a release liner of Example 1 was produced.

[0131] Comparative Examples 1 to 5 The oligomers used in each Comparative Example were prepared in the same manner as the oligomer used in Example 1, except that the types and compositional ratios of the monomers used in the preparation of the oligomers were changed as shown in Table 1. CHMA represents cyclohexyl methacrylate, and CBA represents 2-(2-ethoxyethoxy)ethyl acrylate. The Tg of the oligomers used in each Comparative Example is as shown in Table 1.

[0132] Furthermore, in preparing the pressure-sensitive adhesive composition, the optical pressure-sensitive adhesive sheets with release liner of Comparative Examples 1 to 5 were produced in the same manner as the optical pressure-sensitive adhesive sheet with release liner of Example 1, except that the type and amount of oligomer added was changed as shown in Table 1. Note that in Comparative Example 1, no oligomer was added.

[0133] <Evaluation> [Oligomer Tg] The Tg values ​​of the oligomers used in Example 1 and each of the comparative examples were calculated based on the Fox formula. The values ​​are shown in Table 1.

[0134] [Shear storage modulus] The dynamic viscoelasticity was measured for each of the optical pressure-sensitive adhesive sheets of Example 1 and each of the comparative examples.

[0135] For each optical adhesive sheet, a measurement sample was prepared. Specifically, first, a plurality of optical adhesive sheet pieces cut out from the optical adhesive sheet were bonded together to prepare a sample sheet with a thickness of about 1.0 mm. Next, this sheet was punched to obtain a cylindrical pellet (diameter 7.9 mm) as a measurement sample.

[0136] Each of the prepared measurement samples was then fixed to a 7.9 mm diameter parallel plate jig using a dynamic viscoelasticity measuring device (product name: "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific) and subjected to dynamic viscoelasticity measurement. In this 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 -30°C was read from the measurement results. The results are shown in Table 1.

[0137] [Adhesive strength] For each of the optical pressure-sensitive adhesive sheets of Example 1 and each of the comparative examples, the adhesive strength to an adherend was measured by the following peel test.

[0138] (First peel test) A measurement sample was prepared for each optical adhesive sheet. Specifically, first, the first release liner was peeled from the optical adhesive sheet, and the exposed surface of the optical adhesive sheet was bonded to a plasma-treated polyethylene terephthalate film (product name "Lumirror S10", thickness 25 μm, 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.) with a voltage of 160 V, a frequency of 10 kHz, and a treatment speed of 5000 mm / min. Next, a test piece (width 20 mm × length 100 mm) was cut from the laminate (PET film / optical adhesive sheet / second release liner). Next, the second release liner was peeled from the optical adhesive sheet of this test piece, and the exposed surface of the optical adhesive sheet was bonded to a glass plate (alkali glass, manufactured by Matsunami Glass Co., Ltd.). Next, the glass plate with the optical adhesive sheet (test piece) was heated and pressurized for 15 minutes at a temperature of 50°C and a pressure of 0.5 MPa. This caused the test piece to be pressure-bonded to the glass plate. In this way, a measurement sample was prepared.

[0139] Next, the test sample was left to stand at room temperature for 30 minutes, and then the test piece (polyethylene terephthalate film with optical adhesive sheet) was peeled from the glass plate, and the force required for peeling (peel strength) was measured. The measurement conditions were a temperature of 25°C, a relative humidity of 55%, a peel angle of 180°, a tensile speed of 300 mm / min, and a peel length of 50 mm. A tensile tester (product name "Autograph AG-50NX plus", manufactured by Shimadzu Corporation) was used for the measurement. The average measured peel strength is shown in Table 1 as adhesive strength F1 (N / 20 mm).

[0140] (Second peel test) A measurement sample was prepared in the same manner as in the first peel test described above. Next, the measurement sample was left standing for 500 hours in an environment at a temperature of 85°C and a relative humidity of 85%, after which the measurement sample was removed and conditioned for one day in an environment at a temperature of 25°C and a relative humidity of 55%. Then, for the measurement sample, a test piece (polyethylene terephthalate film with optical adhesive sheet) was peeled from the glass plate, and the force required for peeling (peel strength) was measured. The measurement conditions were the same as in the first peel test described above. The average value of the measured peel strength is shown in Table 1 as adhesive strength F2 (N / 20 mm). The ratio of adhesive strength F2 to adhesive strength F1 (F2 / F1) is also shown in Table 1.

[0141] (Third peel test) A measurement sample was prepared in the same manner as in the first peel test described above. Next, the measurement sample was left to stand for 500 hours in an environment at a temperature of 60°C and a relative humidity of 90%, after which the measurement sample was removed and conditioned for one day in an environment at a temperature of 25°C and a relative humidity of 55%. Then, for the measurement sample, a test piece (polyethylene terephthalate film with optical adhesive sheet) was peeled from the glass plate, and the force required for peeling (peel strength) was measured. The measurement conditions were the same as in the first peel test described above. The average value of the measured peel strength is shown in Table 1 as adhesive strength F3 (N / 20 mm). The ratio of adhesive strength F3 to adhesive strength F1 (F3 / F1) is also shown in Table 1.

[0142] (4th peel test) A measurement sample was prepared in the same manner as in the first peel test described above. Next, the measurement sample was left to stand for 500 hours in an environment at 0°C, after which the measurement sample was removed and conditioned for 1 day in an environment at 25°C and 55% relative humidity. Then, for the measurement sample, a test piece (polyethylene terephthalate film with optical adhesive sheet) was peeled from the glass plate, and the force required for peeling (peel strength) was measured. The measurement conditions were the same as in the first peel test described above. The average value of the measured peel strength is shown in Table 1 as adhesive strength F4 (N / 20 mm). The ratio of adhesive strength F4 to adhesive strength F1 (F4 / F1) is also shown in Table 1.

[0143] (5th peel test) A measurement sample was prepared in the same manner as in the first peel test described above. The measurement sample was then left to stand for 500 hours in an environment at a temperature of 25°C and a relative humidity of 55%, after which the measurement sample was removed. The test piece (polyethylene terephthalate film with optical adhesive sheet) was then peeled from the glass plate of the measurement sample, and the force required for peeling (peel strength) was measured. The measurement conditions were the same as in the first peel test described above. The average value of the measured peel strength is shown in Table 1 as adhesive strength F5 (N / 20 mm). The ratio of adhesive strength F5 to adhesive strength F1 (F5 / F1) is also shown in Table 1.

[0144] (6th peel test) A measurement sample was prepared in the same manner as in the first peel test described above. Next, the measurement sample was left standing in an environment at 100°C for 500 hours, after which the measurement sample was removed and conditioned for one day in an environment at 25°C and 55% relative humidity. Then, for the measurement sample, a test piece (polyethylene terephthalate film with optical adhesive sheet) was peeled from the glass plate, and the force required for peeling (peel strength) was measured. The measurement conditions were the same as in the first peel test described above. The average value of the measured peel strength is shown in Table 1 as adhesive strength F6 (N / 20 mm). The ratio of adhesive strength F6 to adhesive strength F1 (F6 / F1) is also shown in Table 1.

[0145] [Table 1]

[0146] <Consideration> The optical pressure-sensitive adhesive sheet of Example 1 has a shear storage modulus of 300 kPa or less at -30°C, is excellent in flexibility, and can relieve stress generated in the optical pressure-sensitive adhesive sheet and adherend when used in a flexible device. On the other hand, the optical pressure-sensitive adhesive sheet of Comparative Example 3 has a shear storage modulus of more than 300 kPa at -30°C, is poor in flexibility, and is not suitable for flexible device applications.

[0147] Furthermore, the adhesive strength F1 (N / 20 mm) of the optical adhesive sheet of Example 1 to glass in the first peel test satisfies 6.0≦F1. In other words, it has excellent adhesiveness, and when used in a flexible device, peeling from the adherend can be suppressed. On the other hand, the adhesive strength F1 (N / 20 mm) of the optical adhesive sheets of Comparative Examples 1 and 2 to glass in the first peel test is 6.0>F1. In other words, it has poor initial adhesiveness and is not suitable for flexible device applications.

[0148] In addition, in the optical pressure-sensitive adhesive sheet of Example 1, the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester monomer, and the (meth)acrylic acid ester monomer contains a hydroxyl group-containing (meth)acrylic acid ester monomer, and the adhesive strength to glass in the first peel test F1 (N / 20 mm) and the adhesive strength to glass in the second peel test F2 (N / 20 mm) satisfy 0.7≦F2 / F1≦1.3. In other words, the optical pressure-sensitive adhesive sheet has excellent reliability in high-temperature, high-humidity environments. On the other hand, in the optical pressure-sensitive adhesive sheet of Comparative Example 4, the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester monomer, but the (meth)acrylic acid ester monomer does not contain a hydroxy group-containing (meth)acrylic acid ester monomer, and in the optical pressure-sensitive adhesive sheet of Comparative Example 5, the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester monomer, and the (meth)acrylic acid ester monomer contains a hydroxy group-containing (meth)acrylic acid ester monomer, but in both Comparative Examples 4 and 5, the adhesive strength to glass in the first peel test F1 (N / 20 mm) and the adhesive strength to glass in the second peel test F2 (N / 20 mm) are F2 / F1<0.7. In other words, the reliability in high temperature and high humidity environments is poor. [Explanation of symbols]

[0149] 10 Optical adhesive sheet 11 1st adhesive side 12 Second adhesive side L1, L2 release liner 21 First member 22 Second member

Claims

1. An optical adhesive sheet comprising a base polymer and an oligomer, the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester monomer, The (meth)acrylic acid ester monomer includes a hydroxy group-containing (meth)acrylic acid ester monomer, The optical adhesive sheet has a shear storage modulus of 300 kPa or less at −30° C., The adhesive strength F1 (N / 20 mm) to glass in the first peel test described below and the adhesive strength F2 (N / 20 mm) to glass in the second peel test described below satisfy the following formulas (1) and (2). An optical adhesive sheet. 6.0≦F1 (1) 0.7≦F2 / F1≦1.3 (2) (First Peel Test) A polyethylene terephthalate film is attached to one side of the optical adhesive sheet, and the other side is attached to a glass plate, followed by heating and pressurizing to prepare a measurement sample. After leaving the measurement sample at room temperature for 30 minutes, the test piece (the polyethylene terephthalate film with the optical adhesive sheet) is peeled from the glass plate. The measurement conditions are as follows: temperature 25 ° C, relative humidity 55%, peel angle of the test piece from the glass plate 180 °, tensile speed 300 mm / min, peel length 50 mm. (Second Peel Test) A measurement sample is prepared in the same manner as in the first peel test. The measurement sample is left standing for 500 hours in an environment at a temperature of 85°C and a relative humidity of 85%, and then the measurement sample is removed and conditioned for one day in an environment at a temperature of 25°C and a relative humidity of 55%. Thereafter, the test piece of the measurement sample is peeled off from the glass plate. The measurement conditions are the same as in the first peel test.

2. The adhesive strength F1 (N / 20 mm) to glass in the first peel test and the adhesive strength F3 (N / 20 mm) to glass in the third peel test described below satisfy the following formula (3). The optical adhesive sheet according to claim 1. 0.7≦F3 / F1≦1.3 (3) (Third Peel Test) A measurement sample is prepared in the same manner as in the first peel test. The measurement sample is left standing for 500 hours in an environment at a temperature of 60°C and a relative humidity of 90%, and then the measurement sample is removed and conditioned for one day in an environment at a temperature of 25°C and a relative humidity of 55%. Thereafter, the test piece of the measurement sample is peeled off from the glass plate. The measurement conditions are the same as in the first peel test.

3. The adhesive strength F1 (N / 20 mm) to glass in the first peel test and the adhesive strength F4 (N / 20 mm) to glass in the fourth peel test described below satisfy the following formula (4). The optical adhesive sheet according to claim 1. 0.7≦F4 / F1≦1.3 (4) (Fourth Peel Test) A measurement sample is prepared in the same manner as in the first peel test. The measurement sample is left standing in an environment at a temperature of 0°C for 500 hours, and then removed and conditioned for one day in an environment at a temperature of 25°C and a relative humidity of 55%. Thereafter, a test piece is peeled off from the glass plate of the measurement sample. The measurement conditions are the same as in the first peel test.

4. The optical adhesive sheet according to claim 1, wherein the glass transition temperature of the oligomer is 100°C or higher.

5. The optical adhesive sheet according to claim 1 , wherein the (meth)acrylic acid ester monomer further comprises a condensed ring-containing (meth)acrylic acid ester monomer.

6. the oligomer is a polymer of a monomer component containing a methacrylic acid ester monomer, the methacrylic acid ester monomers include hydroxy group-containing methacrylic acid ester monomers and fused ring-containing methacrylic acid ester monomers; The optical adhesive sheet according to claim 1 , wherein the content of the methacrylic acid ester monomer in the monomer component exceeds 90% by mass.

7. The optical adhesive sheet according to any one of claims 1 to 6, wherein the content of the hydroxy group-containing (meth)acrylic acid ester monomer in the monomer component is 0.5 mass% or more and 15 mass% or less.

8. The optical adhesive sheet according to claim 5 or 6, wherein the content of the fused ring-containing (meth)acrylic acid ester monomer in the monomer component is 20 mass% or more and 80 mass% or less.

9. The optical adhesive sheet according to any one of claims 1 to 6, wherein the amount of the oligomer blended is 0.1 parts by mass or more and less than 3 parts by mass relative to 100 parts by mass of the base polymer.

10. The optical pressure-sensitive adhesive sheet according to any one of claims 1 to 6, having a haze of 1% or less.

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