Adhesive composition and adhesive sheet

Abstract

Provided is an adhesive composition that has excellent processability, that can be easily peeled immediately after affixation to an adherend, that can firmly adhere to the adherend by photocuring of the adhesive after affixation to the adherend, and that can form an adhesive layer in which peeling is unlikely to occur at a bent portion.　An adhesive composition according to the present invention exhibits a ratio ΔG'(25) of shear storage modulus (G'1(25)) at 25°C after photocuring to shear storage modulus (G'0(25)) at 25°C before photocuring of not more than 200%. Before photocuring, the 180° peeling adhesive force (F0) with respect to a polyimide under the peeling conditions of a temperature of 25°C, a relative humidity of 50%, and a tensile speed of 300 mm / minute is 0.01-1 N / 25 mm, and after photocuring, the 180° peeling adhesive force (F1) with respect to the polyimide under the peeling conditions of a temperature of 25°C, a relative humidity of 50%, and a tensile speed of 300 mm / minute is greater than 1 N / 25 mm.

Description

Pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet

[0001] The present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet.

[0002] By temporarily attaching an adhesive film to the surface of a device or a device component before use, such as during device assembly, processing, transportation, etc., it is possible to prevent the adherend from being scratched or damaged. Patent Document 1 discloses a reinforcing film having an adhesive layer made of a photocurable adhesive composition on a film substrate.

[0003] This reinforcing film has a high gel fraction of adhesive and low adhesiveness immediately after application to the adherend, making it easy to peel off from the adherend. This allows for reworking from the adherend, and also allows for selective peeling and removal of the reinforcing film from areas of the adherend that do not require reinforcement. The adhesive of the reinforcing film firmly bonds to the adherend upon photocuring, permanently bonding the film substrate to the surface of the adherend, making it usable as a reinforcing material for protecting the surface of devices, etc.

[0004] In recent years, organic EL panels using foldable substrates (flexible substrates) such as resin films have been put to practical use, and foldable flexible displays have been proposed. In foldable flexible displays (foldable displays), bending occurs repeatedly at the same location. At the bending point, compressive stress is applied to the inside and tensile stress is applied to the outside, causing distortion at the bending point and its surroundings, which may result in peeling of the adhesive from the adherend. Patent Document 2 proposes using a soft adhesive sheet to bond components in a foldable display to relieve stress distortion at the bending point (e.g., Patent Documents 2 and 3).

[0005] However, when the reinforcing film disclosed in Patent Document 1 is applied to a flexible device, peeling may occur at bending points because the adhesive is hard after photocuring. The adhesive sheets described in Patent Documents 2 and 3 do not have photocurable properties and exhibit high adhesiveness immediately after being attached to an adherend, making them difficult to peel off or process.

[0006] Patent Document 4 discloses a reinforcing film having a photocurable adhesive layer, and describes that the reinforcing film is easy to peel off immediately after being attached to an adherend because it has not yet been photocured, and that the adhesive can be photocured after being attached to the adherend, thereby enabling strong adhesion to the adherend, and that the modulus of elasticity of the adhesive layer after photocuring is within a specific range and is relatively flexible, making peeling less likely to occur at bending points.

[0007] JP 2020-41113 A JP 2018-45213 A JP 2017-119801 A International Publication No. 2022 / 050009

[0008] When applied to the bent portions of a flexible display, particularly a foldable display, one way to make peeling of the adhesive sheet less likely to occur at the bent portions is to increase the flexibility of the adhesive layer after photocuring. Photocurable adhesive layers usually harden upon photocuring, so it is necessary to increase the flexibility of the adhesive layer before photocuring. However, if the flexibility of the adhesive layer is high before photocuring, problems such as glue overflow, glue chipping, and process contamination caused by these can easily occur when cutting an adhesive sheet having such an adhesive layer with, for example, a punching blade, resulting in poor processability.

[0009] The present invention has been made to solve these problems, and an object of the present invention is to provide a pressure-sensitive adhesive composition that has excellent processability, is easily peeled off immediately after being attached to an adherend, can be firmly bonded to an adherend by photo-curing the pressure-sensitive adhesive after being attached to the adherend, and is capable of forming a pressure-sensitive adhesive layer that is less likely to peel off at bending points.

[0010] The present invention is directed to a shear storage modulus (G') at 25°C before photocuring. ０（２５） ) versus shear storage modulus (G') at 25°C after photocuring １（２５） ) ratio ΔG' （２５） The 180° peel adhesion strength (F) to polyimide before photocuring under peel conditions of a temperature of 25°C, a relative humidity of 50%, and a pulling rate of 300 mm / min is 200% or less. ０) is 0.01 to 1 N / 25 mm, and the 180° peel adhesive strength (F) to polyimide after photocuring is 0.01 to 1 N / 25 mm under peel conditions of a temperature of 25°C, a relative humidity of 50%, and a pulling speed of 300 mm / min. １ ) is greater than 1 N / 25 mm.

[0011] The shear storage modulus (G' ０（２５） ) is 20 kPa or more, and the shear storage modulus (G' １（２５） ) is preferably 200 kPa or less.

[0012] The pressure-sensitive adhesive composition preferably contains the following components (a), (b), and (c): component (a): a polymer (a1) having a reversibly decomposable bond in the molecule that can be cleaved by light irradiation and then recombined, and / or a compound (a2) capable of introducing the reversibly decomposable bond into the polymer; component (b): a compound that inhibits the recombination; and component (c): a compound that reacts and hardens by light irradiation.

[0013] The present invention also provides a pressure-sensitive adhesive composition comprising the following components (a), (b), and (c): component (a): a polymer (a1) having in its molecule a reversibly degradable bond that can be cleaved by an external stimulus and then rebonded, and / or a compound (a2) capable of introducing the reversibly degradable bond into the polymer; component (b): a compound that inhibits the rebonding; and component (c): a compound that reacts and hardens in response to an external stimulus.

[0014] The component (a) is preferably an acrylic polymer having the reversibly decomposable bond in the molecule.

[0015] The component (c) preferably contains a compound having a polymerizable functional group and a polymerization initiator.

[0016] The component (c) preferably contains a polyfunctional (meth)acrylate and a radical polymerization initiator.

[0017] The pressure-sensitive adhesive composition is preferably for optical applications.

[0018] The present invention also provides a pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition.

[0019] The pressure-sensitive adhesive sheet preferably comprises a substrate and the pressure-sensitive adhesive layer laminated on one surface of the substrate.

[0020] The pressure-sensitive adhesive sheet is preferably a reinforcing film for an optical member.

[0021] The pressure-sensitive adhesive composition of the present invention can form a pressure-sensitive adhesive layer that has excellent processability, is easy to peel immediately after lamination with an adherend, can be firmly bonded to an adherend by photo-curing the pressure-sensitive adhesive after lamination with an adherend, and is less likely to peel at bending points.

[0022] 1 is a schematic diagram (cross-sectional view) illustrating one embodiment of a pressure-sensitive adhesive sheet of the present invention.

[0023] [Adhesive composition] In this specification, "adhesion" refers to the property of two surfaces adhering to each other in response to external pressure (e.g., minute pressure) based on the cohesive force of the chemical structure of the composition, and allowing separation as needed. In contrast, "adhesion" refers to the property of two surfaces being firmly joined together by a chemical reaction (curing) of the composition to produce a cured product, without the intention of separation.

[0024] The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention has adhesiveness and can be peeled from an adherend before photocuring, and is firmly adhered to an adherend after photocuring. Thus, the pressure-sensitive adhesive composition of the present invention has the properties of both a pressure-sensitive adhesive composition and an adhesive composition.

[0025] In addition, in this specification, the form of the "pressure-sensitive adhesive" is not particularly limited, and it may be a liquid at room temperature (for example, a solid (paste-like) having fluidity, a pressure-sensitive adhesive composition, etc.), or it may be a solid at room temperature. In addition, the form of the "pressure-sensitive adhesive" is not particularly limited, and it may be in sheet form. In this specification, the "pressure-sensitive adhesive layer" is a sheet-like (layer-like) pressure-sensitive adhesive layer that does not have fluidity.

[0026] The pressure-sensitive adhesive composition according to one embodiment of the present invention has a shear storage modulus (G' ０（２５） ) versus shear storage modulus (G') at 25°C after photocuring １（２５）) ratio ΔG' （２５） The above ΔG′ is 200% or less. （２５） When ΔG′ is 200% or less, the change in elastic modulus at 25° C. before and after photocuring is small, the pressure-sensitive adhesive layer has excellent processability before photocuring, and peeling is unlikely to occur at bent portions of the adherend after photocuring. （２５） is preferably 180% or less, more preferably 150% or less, and even more preferably 120% or less, and may be 100% or less or 80% or less. （２５） is, for example, 10% or more, and may be 30% or more, or 50% or more. （２５） is a value calculated by the following formula: （２５） (%) = G' １（２５） / G' ０（２５） ×100

[0027] The shear storage modulus (G' ０（２５） The shear storage modulus (G') is preferably 20 kPa or more, more preferably 25 kPa or more, and may be 30 kPa or more, 50 kPa or more, or 100 kPa or more. ０（２５） When the shear storage modulus (G') is 20 kPa or more, the pressure-sensitive adhesive layer has low flexibility before photocuring, and has excellent processability. ０（２５） ) is the shear storage modulus (G' １（２５） ) within an appropriate range and from the viewpoint of achieving better processability, it may be, for example, 500 kPa or less, 400 kPa or less, 300 kPa or less, or 200 kPa or less.

[0028] The shear storage modulus (G' １（２５） The shear storage modulus (G') is preferably 200 kPa or less, more preferably 150 kPa or less, even more preferably 100 kPa or less, and particularly preferably 80 kPa or less. １（２５） When the shear storage modulus (G') is 200 kPa or less, the pressure-sensitive adhesive layer has excellent flexibility after photocuring, and peeling is less likely to occur at bent portions of the adherend. １（２５） From the viewpoint of excellent handleability, the pressure may be, for example, 10 kPa or more, 20 kPa or more, or 30 kPa or more.

[0029] The shear storage modulus (G' ０（２５） ) and the shear storage modulus (G' １（２５） ) is a value obtained by measuring a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition, and can be calculated using a dynamic viscoelasticity measurement (DMA) device.

[0030] The pressure-sensitive adhesive composition according to one embodiment of the present invention has a 180° peel adhesive strength (F ０ ) is 0.01 to 1 N / 25 mm. When the peel adhesive strength is 0.01 N / 25 mm or more, the film can exhibit appropriate adhesiveness when attached to an adherend. When the peel adhesive strength is 1 N / 25 mm or less, the film can be easily peeled from the state where it is attached to an adherend before photocuring. ０ ) is preferably 0.03 to 0.8 N / 25 mm, more preferably 0.06 to 0.7 N / 25 mm.

[0031] The pressure-sensitive adhesive composition according to one embodiment of the present invention has a 180° peel adhesive strength (F １ When the peel adhesive strength is more than 1 N / 25 mm, the composition can be firmly adhered to the adherend after photocuring. １ The peel adhesive strength (F) is preferably 2 N / 25 mm or more, more preferably 3 N / 25 mm or more. １ ) is not particularly limited because the higher the strength, the stronger the adhesion to the adherend, but may be, for example, 100 N / 25 mm or less.

[0032] The peel adhesion strength (F ０ ) and the peel adhesion strength (F １ ) is a value obtained by measuring a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition.

[0033] The peel adhesion strength (F ０ ) to the peel adhesion strength (F １The ratio (rate of change in adhesive strength) ΔF of the peel strength before and after photocuring is preferably 500% or more, more preferably 750% or more, and even more preferably 900% or more. When the ΔF is 500% or more, the change in peel adhesive strength before and after photocuring is large, and the film can be easily peeled from the state where it is stuck to the adherend before photocuring, and can be firmly adhered to the adherend after photocuring. The higher the ΔF, the more effective it is, but it may be, for example, 5000% or less. The ΔF is a value calculated by the following formula: ΔF (%) = F １ / F ０ ×100

[0034] The pressure-sensitive adhesive composition according to one embodiment of the present invention has a shear storage modulus (G' ０（－２０） ) versus shear storage modulus (G') at -20°C after photocuring １（－２０） ) ratio ΔG' （－２０） is preferably 200% or less, more preferably 180% or less, more preferably 150% or less, even more preferably 130% or less, and may be 100% or less or 80% or less. （－２０） When ΔG' is 200% or less, the change in modulus of elasticity at -20°C before and after photocuring is small, and peeling is unlikely to occur at the bent portion of the adherend even in a low temperature environment or when subjected to sudden bending after photocuring. （－２０） is, for example, 10% or more, and may be 30% or more, or 50% or more. （－２０） is a value calculated by the following formula: （－２０） (%) = G' １（－２０） / G' ０（－２０） ×100

[0035] The shear storage modulus (G' ０（－２０） The shear storage modulus (G') is preferably 20 kPa or more, more preferably 25 kPa or more, and may be 30 kPa or more, 50 kPa or more, or 100 kPa or more. ０（－２０） When the shear storage modulus (G') is 20 kPa or more, the pressure-sensitive adhesive layer has low flexibility before photocuring, and has excellent processability. ０（－２０） ) is the shear storage modulus (G'１（－２０） ) within an appropriate range and from the viewpoint of achieving better processability, it may be, for example, 500 kPa or less, 400 kPa or less, 300 kPa or less, or 200 kPa or less.

[0036] The shear storage modulus (G' １（－２０） The shear storage modulus (G') is preferably 140 kPa or less, more preferably 120 kPa or less, even more preferably 100 kPa or less, and particularly preferably 80 kPa or less. １（－２０） When the shear storage modulus (G') is 140 kPa or less, the pressure-sensitive adhesive layer has excellent flexibility, and peeling is less likely to occur at the bent portion of the adherend even in a low-temperature environment or when subjected to sudden bending. １（－２０） From the viewpoint of excellent handleability, the pressure may be, for example, 10 kPa or more, 20 kPa or more, or 30 kPa or more.

[0037] The shear storage modulus (G' ０（－２０） ) and the shear storage modulus (G' １（－２０） ) is a value obtained by measuring a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition, and can be calculated using a dynamic viscoelasticity measurement (DMA) device.

[0038] The pressure-sensitive adhesive composition according to one embodiment of the present invention has a shear storage modulus (G' ０（２５） ) versus shear storage modulus (G') at -20°C after photocuring １（―２０） ) is preferably 500% or less. When the ΔG' is 500% or less, the pressure-sensitive adhesive layer has excellent processability before photocuring, and peeling is unlikely to occur at the bent portion of the adherend even in a low-temperature environment or when subjected to sudden bending after photocuring. The ΔG' is preferably 400% or less, more preferably 300% or less, and even more preferably 200% or less, and may be 100% or less or 80% or less. The ΔG' may be, for example, 10% or more, 30% or more, or 50% or more. The ΔG' is a value calculated by the following formula: ΔG' (%) = G' １（－２０） / G' ０（２５） ×100

[0039] In this specification, the term "after photocuring" refers to a state in which at least a part of the pressure-sensitive adhesive layer has been cured by irradiating it with light, for example, using a 340 nm LED light source with an integrated light dose of 20,000 mJ / cm. ２ The photocuring may be performed after the pressure-sensitive adhesive layer has been incompletely cured, or after the pressure-sensitive adhesive layer has been cured to a state where the curing hardly progresses any further (complete curing) (for example, after the pressure-sensitive adhesive layer has been incompletely cured and then further cured).

[0040] Furthermore, a pressure-sensitive adhesive composition according to another embodiment of the present invention preferably contains the following component (a), component (b), and component (c): The pressure-sensitive adhesive composition can form a pressure-sensitive adhesive layer that exhibits the effects of having a small change in elastic modulus before and after application of an external stimulus, being easy to peel immediately after application of the composition to an adherend, and being able to firmly adhere to the adherend by applying an external stimulus to the pressure-sensitive adhesive after application of the composition to the adherend. Component (a): a polymer (a1) having in its molecule a reversibly degradable bond that can be cleaved by an external stimulus and then rebonded, and / or a compound (a2) capable of introducing the reversibly degradable bond into a polymer; component (b): a compound that inhibits the rebonding; and component (c): a compound that reacts and hardens in response to an external stimulus.

[0041] Degradable bonds that are cleaved by the application of an external stimulus are classified into reversibly degradable bonds that can recombine after cleavage, and irreversibly degradable bonds in which the cleavage reaction proceeds irreversibly and no recombination occurs. In the present invention, the polymer in component (a) is a compound having a reversibly degradable bond. The polymer in component (a) may be referred to as "polymer (a1)," and the compound capable of introducing the reversibly degradable bond into the polymer may be referred to as "compound (a2)."

[0042] The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition includes polymer (a1) as component (a), component (b), and component (c). When an external stimulus is applied to the pressure-sensitive adhesive layer, the external stimulus cleaves the reversibly decomposable bond in polymer (a1), and component (b) reacts with at least one of the groups generated by the cleavage of the reversibly decomposable bond, thereby suppressing the recombination. The external stimulus (typically an external stimulus that cleaves the reversibly decomposable bond) simultaneously promotes the curing of component (c). Therefore, when an external stimulus is applied, the elastic modulus of polymer (a1) decreases due to chain scission, and at the same time, the elastic modulus increases due to the curing of component (c). As a result, the change in the elastic modulus of the pressure-sensitive adhesive layer before and after the external stimulus is small. Furthermore, it is presumed that when the pressure-sensitive adhesive layer is attached to the adherend before the application of an external stimulus, at least a portion of the component (c) in the pressure-sensitive adhesive layer penetrates into the adherend, and when the external stimulus is applied, the component (c) in the pressure-sensitive adhesive layer and the component (c) in the adherend are bonded by polymerization, and after the application of the external stimulus, the pressure-sensitive adhesive layer can be firmly adhered to the adherend.

[0043] The external stimulus that causes the cleavage reaction of the reversibly decomposable bond is appropriately selected depending on the type of the reversibly decomposable bond in the component (a), and is not particularly limited, but examples thereof include light or heat. In particular, when the polymer (a1) is a thermosetting resin or a photocurable resin such as active energy ray, from the viewpoint of allowing the thermosetting reaction or photocuring reaction and the cleavage to occur separately, it is preferable that the external stimulus be different from the type of curing when the polymer (a1) has curability.

[0044] The pressure-sensitive adhesive composition according to one embodiment of the present invention is preferably the pressure-sensitive adhesive composition according to the other embodiment, in which the external stimulus is light (light irradiation).

[0045] The light is not particularly limited, and examples thereof include ionizing radiation such as α-rays, β-rays, γ-rays, neutron beams, and electron beams, and active energy rays such as ultraviolet light and visible light. Active energy rays are particularly preferred, and ultraviolet light is more preferred. The light irradiation energy, irradiation time, irradiation method, etc. are not particularly limited. In addition, examples of light sources for irradiating ultraviolet light or visible light include low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, metal halide lamps, and LED lamps.

[0046] The pressure-sensitive adhesive composition preferably contains at least a base polymer and / or its raw material monomer. In particular, it preferably contains a base polymer from the viewpoint of ensuring that the resulting pressure-sensitive adhesive layer exhibits adhesiveness. The base polymer is polymer (a1) and / or other polymers (i.e., polymers without reversibly decomposable bonds). Only one type of base polymer may be used, or two or more types may be used.

[0047] When the base polymer is the other polymer, the pressure-sensitive adhesive composition further contains a compound (a2). In this case, the pressure-sensitive adhesive composition may further contain a monomer component (sometimes referred to as "monomer component (d)") reactive with the compound (a2). The compound (a2) is reactive with the other polymer and / or the monomer component (d). When the compound (a2) is reactive with the other polymer, the other polymer reacts with the compound (a2) in the pressure-sensitive adhesive layer by heat or light irradiation to form, for example, a polymer chain, and the polymer chain and the other polymer bond to form a network structure, thereby obtaining a pressure-sensitive adhesive layer containing the polymer (a1). When the pressure-sensitive adhesive layer contains the compound (a2) and the monomer component (d), the compound (a2) reacts with the monomer component (d) in the pressure-sensitive adhesive layer by heat or light irradiation to form, for example, a polymer chain, and the polymer chain and the other polymer become entangled to form a network structure, thereby obtaining a pressure-sensitive adhesive layer containing the polymer (a1). Only one type of monomer component (d) may be used, or two or more types may be used.

[0048] When the PSA composition contains the raw material monomer, compound (a2) is incorporated into the base polymer during polymerization of the raw material monomer to form polymer (a1). Alternatively, the raw material monomer is polymerized to form the other polymer, which is then reacted with compound (a2) to form polymer (a1). Monomer component (d) can be used as the raw material monomer.

[0049] The pressure-sensitive adhesive compositions mainly include (i) pressure-sensitive adhesive compositions containing polymer (a1), (ii) pressure-sensitive adhesive compositions containing polymer (a1) and the other polymers described above, (iii) pressure-sensitive adhesive compositions containing the other polymers described above, compound (a2), and, if necessary, monomer component (d), and (iv) pressure-sensitive adhesive compositions containing compound (a2), monomer component (d), and, if necessary, other polymers.

[0050] Thus, polymer (a1) may be a reaction product of the other polymer, compound (a2), and monomer (d), or may be a (particularly entangled) polymer containing the other polymer and a reaction product of the other polymer and compound (a2), or may be a reaction product of monomer component (d) and compound (a2). When the base polymer is polymer (a1), the PSA layer obtained from the PSA composition may contain unreacted compound (a2) and / or unreacted monomer component (d).

[0051] Preferably, polymer (a1) contains a structure derived from compound (a2). Compound (a2) has the reversibly decomposable bond. Examples of compound (a2) include a monomer component, oligomer component, crosslinking agent, etc., each having the reversibly decomposable bond. That is, polymer (a1) may contain a structural unit derived from a monomer component and / or oligomer component having the reversibly decomposable bond, or may contain a structural portion derived from the crosslinking agent. When compound (a2) is a monomer component or oligomer component, polymer (a1) having the reversibly decomposable bond can be obtained by polymerizing or copolymerizing the monomer component or oligomer component with another monomer component. In this specification, the term "crosslinking agent" refers to a compound capable of crosslinking a resin, and may also be referred to as a "curing agent." In this specification, the term "monomer component" refers to a compound having one polymerizable functional group, and does not refer to a compound having two or more polymerizable functional groups.

[0052] When the compound (a2) is a monomer component or an oligomer component, the reversibly decomposable bond may be present in a portion constituting a side chain of the polymer (a1) or in a portion constituting the main chain. When the reversibly decomposable bond is present in a portion constituting a side chain, it is preferable from the viewpoint of being less susceptible to stress when greatly deformed and maintaining handleability in the temperature range of actual use (assumed to be room temperature). On the other hand, when the reversibly decomposable bond is present in a portion constituting the main chain, it is preferable from the viewpoint of further reducing the molecular weight of the polymer after cleavage of the reversibly decomposable bond, further improving flexibility, and enabling significant changes in physical properties to be exhibited.

[0053] From the viewpoint of forming a polymer (a1) by polymerization, crosslinking, or the like, the compound (a2) preferably has a reactive functional group other than the reversibly decomposable bond. When the compound (a2) has two or more reactive functional groups, the compound (a2) functions as a crosslinking agent. When the reactive functional group is a polymerizable functional group, the compound (a2) functions as a monomer component or an oligomer component.

[0054] Examples of the polymerizable functional group include a cationically polymerizable group, an anionically polymerizable group, and a radically polymerizable group. Of these, a radically polymerizable group is preferred. Examples of the radically polymerizable group include groups having a radically polymerizable carbon-carbon double bond, such as a (meth)acryloyl group, a vinyl group, a vinyl ether group, and a (meth)allyl group.

[0055] Examples of reactive functional groups other than the above polymerizable functional groups include thiol groups, carboxy groups, hydroxy groups, amino groups, epoxy groups, and isocyanate groups, from the viewpoint of achieving an appropriate crosslinking density and ensuring a certain degree of flexibility of the adhesive or the like.

[0056] In addition, the number of reactive functional groups of the compound (a2) is preferably 2 or more, from the viewpoint of increasing the molecular weight after introduction into the polymer (a1) and imparting a certain degree of hardness to the polymer before the application of an external stimulus, while further reducing the molecular weight of the polymer after cleavage to exhibit flexibility. On the other hand, if the number of functional groups is large, crosslinking with many polymers will occur, making it difficult to obtain the effect of cleavage of the reversibly decomposable bond. Therefore, from the viewpoint of ensuring a certain degree of flexibility of the pressure-sensitive adhesive layer by maintaining an appropriate crosslinking density, the number of functional groups is preferably 4 or less, more preferably 3 or less. Among these, the compound (a2) is preferably a polyfunctional compound having the reversibly decomposable bond in its main chain and the reactive functional groups at both ends.

[0057] The reactive functional group is preferably a radically polymerizable group, more preferably a (meth)acryloyl group, i.e., the polyfunctional compound is preferably a di(meth)acrylate compound having a (meth)acryloyl group as the reactive functional group.

[0058] It is preferable that the polymer (a1) contains a structural portion derived from the crosslinking agent. That is, it is preferable that the polymer (a1) contains a crosslinking moiety having the reversibly decomposable bond. In this case, the crosslinking moiety can be cleaved by an external stimulus, which makes it easy to control the crosslink density.

[0059] The number of atoms in the linear chain at the crosslinked site is preferably 6 or more, more preferably 10 or more, and even more preferably 14 or more. When the number of atoms is 6 or more, the polymer has appropriate flexibility before the reversibly decomposable bond is cleaved. From the viewpoint of obtaining an appropriate crosslink density, the number of atoms is, for example, 40 or less, preferably 35 or less.

[0060] The reversibly decomposable bond is preferably a bond that can be cleaved by the external stimulus with a C-C bond or a C-O bond as a terminal. That is, the reversibly decomposable bond preferably has a C-C bond and / or a C-O bond, and after cleavage, the terminal is a C-C bond or a C-O bond (on the carbon atom side). The carbon atom on the cleavage side of the C-C bond and C-O bond is preferably a tertiary or quaternary carbon atom before cleavage. The bond between C and O in the C-O bond may be a single bond (C-O) or a double bond (C=O).

[0061] The reversibly decomposable bond is particularly preferably —O—C—C(═O)—. —O—C—C(═O)— generates a C—O bond terminal upon cleavage. Both terminals of —O—C—C(═O)— are bonded to other groups, and the above “—O—C—C(═O)—” contains the bilaterally symmetric bond “—C(═O)—C—O—”.

[0062] -O-C-C(=O)- is cleaved into -O-C and -C(=O)- by an external stimulus. It is preferred that -O-C-C(=O)- generates a radical upon cleavage. That is, it is preferred that -O-C-C(=O)- is cleaved into -O-C· and ·C(=O)- by an external stimulus.

[0063] The reactive functional group in compound (a2) is preferably capable of reacting with light and / or heat. Furthermore, the reversibly decomposable bond is preferably capable of being cleaved by light. When the reactive functional group is photoreactive and the reversibly decomposable bond is capable of being cleaved by light, it is preferable that the peak wavelengths of the light from which the reaction of compound (a2) and the cleavage of the reversibly decomposable bond occur are different, and it is more preferable that the wavelength ranges are different, from the viewpoint of preventing the reaction of compound (a2) and the cleavage of the reversibly decomposable bond from occurring simultaneously. Specifically, it is preferable that the reactive functional group in compound (a2) is capable of reacting with light and / or heat having a wavelength of 370 nm or more. Furthermore, it is preferable that the reversibly decomposable bond is capable of being cleaved by light having a wavelength of less than 370 nm.

[0064] Examples of the compound (a2) include the above-mentioned polyfunctional compounds, and among them, a di(meth)acrylate having an acetophenone skeleton (sometimes referred to as "compound (a2-1)") is preferred, and a di(meth)acrylate having an α-hydroxyacetophenone skeleton is particularly preferred. As the compound (a2-1), a compound represented by the following formula (1), a compound represented by the following formula (2), and a compound represented by the following formula (3) are preferred.

[0065] In formula (1), two R １ are the same or different and represent a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms. ２ are the same or different and represent a hydrogen atom, an alkyl group, or an aryl group, and may be bonded to each other to form a ring. X represents a direct bond, a divalent hydrocarbon group which may have an ester bond, or a divalent hydrocarbon group which may have an ether bond. Y represents a divalent hydrocarbon group which may have an ester bond or a divalent hydrocarbon group which may have an ether bond. The hydrocarbon group, alkyl group, and aryl group may each have a substituent. m and n each independently represent an integer of 1 or more.

[0066]

[0067] In formula (2), two R １ are the same or different and represent a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms.２ are the same or different and represent a hydrogen atom, an alkyl group, or an aryl group. ２ may be bonded to each other to form a ring. Two X's may be the same or different and represent a direct bond, a divalent hydrocarbon group which may have an ester bond, or a divalent hydrocarbon group which may have an ether bond. The hydrocarbon group, alkyl group, and aryl group may each have a substituent. Two m's may be the same or different and represent an integer of 1 or more. L represents a direct bond or a linking group.

[0068]

[0069] In formula (3), two R １ are the same or different and represent a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms. ２ are the same or different and represent a hydrogen atom, an alkyl group, or an aryl group, and may be bonded to each other to form a ring. X represents a direct bond, a divalent hydrocarbon group which may have an ester bond, or a divalent hydrocarbon group which may have an ether bond. The hydrocarbon group, alkyl group, and aryl group may each have a substituent. m represents an integer of 1 or more. k represents the number of repetitions of the parentheses.

[0070] In formulas (1) to (3), R １ Examples of the hydrocarbon group having 1 to 4 carbon atoms in include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an s-butyl group, and a t-butyl group.

[0071] In formulas (1) to (3), R ２ The alkyl group in is preferably an alkyl group having 1 to 4 carbon atoms, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an s-butyl group, and a t-butyl group. ２ is preferably an alkyl group having 1 to 4 carbon atoms, and more preferably a methyl group.

[0072] In formulas (1) to (3), R ２Examples of the aryl group in the formula (I) include groups having 1 to 3 benzene rings, such as a phenyl group, a naphthyl group, a phenanthrenyl group, an anthracenyl group, etc. Of these, a phenyl group is preferred.

[0073] Two R's ２ Examples of the ring that can be formed by bonding include hydrocarbon rings such as alicyclic hydrocarbon rings such as a cyclohexyl ring. The number of carbon atoms in the ring is, for example, 3 to 10, and preferably 5 to 8.

[0074] In formulas (1) to (3), the divalent hydrocarbon group in X and Y which may have an ester bond and the divalent hydrocarbon group in the divalent hydrocarbon group which may have an ether bond are preferably alkylene groups having 1 to 6 carbon atoms, more preferably alkylene groups having 2 to 4 carbon atoms. Examples of the alkylene group include methylene, dimethylene, trimethylene, methylmethylene, and tetramethylene.

[0075] In formulas (1) to (3), m represents the number of repetitions of (-X-O) and is an integer of 1 or more, preferably 1 to 10, more preferably 1 to 4, and even more preferably 1 to 2. In formula (1), n ​​represents the number of repetitions of (-Y-O) and is an integer of 1 or more, preferably 1 to 10, more preferably 1 to 4, and even more preferably 1 to 2.

[0076] In formula (2), L represents a direct bond or a linking group. Examples of the linking group include an alkylene group, an ether bond, an ester bond, and a group in which two or more of these are bonded.

[0077] The compounds represented by the above formulas (1) to (3) are C(=O)-C(R ２ ) ２ is cleaved, and the C—O bond (C═O) becomes the terminal after cleavage. ２ When X is a hydrocarbon group, the C—C bond also becomes an end after cleavage, and when X is a direct bond, the C—O bond (C—O) also becomes an end after cleavage.

[0078] Specific examples of the compound (a2) include compounds represented by the following formulas (1-1) and (1-2), compounds represented by the following formulas (2-1) and (2-2), and compounds represented by the following formula (3-1).

[0079]

[0080]

[0081]

[0082] The component (a) may be used alone or in combination of two or more. That is, the pressure-sensitive adhesive composition may contain either the polymer (a1) or the compound (a2), or both. Furthermore, the polymer (a1) and the compound (a2) may each be used alone or in combination of two or more.

[0083] The content of compound (a2) in the pressure-sensitive adhesive composition (the total content of one or more selected from the group consisting of compound (a2), structural units derived from compound (a2), and structural moieties derived from compound (a2)) is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, relative to 100% by mass of the total amount of the pressure-sensitive adhesive composition (excluding components that do not remain when the layer is formed, such as organic solvents), from the viewpoint of bringing about sufficient changes in physical properties by cleavage and shredding after the application of an external stimulus. Furthermore, in order to achieve an appropriate crosslinking density and impart appropriate flexibility to the resin before the application of an external stimulus, the content is preferably 50% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0084] Examples of the polymer (a1) include thermoplastic resins, thermosetting resins, and active energy ray-curable resins. Among these, thermoplastic resins and thermosetting resins are preferred. A pressure-sensitive adhesive composition containing a thermoplastic resin can exhibit adhesiveness that allows it to adhere to an adherend, for example, when subjected to external pressure. A pressure-sensitive adhesive containing a thermosetting resin can be cured by heating, for example, to adhere to an adherend. Only one type of polymer (a1) may be used, or two or more types may be used.

[0085] Examples of the thermoplastic resin include polystyrene resins, vinyl acetate resins, polyester resins, polyolefin resins (polyethylene resins, polypropylene resins, etc.), polyimide resins, acrylic polymers, etc. Among these, acrylic polymers are preferred because they can impart cohesive strength and appropriate flexibility to the pressure-sensitive adhesive layer.

[0086] The design of acrylic polymers varies widely depending on the purpose, and it is preferable to appropriately select the monomer type, copolymerization composition ratio, molecular weight, molecular weight distribution, crosslinking agent, compounding composition ratio, etc. depending on the target values, such as mechanical properties such as flexibility and elastic modulus, thermal properties such as glass transition point, optical properties such as transmittance, haze, and refractive index, and characteristic values ​​specific to pressure-sensitive adhesives, such as adhesive strength and adhesion strength.

[0087] An acrylic polymer is a resin containing an acrylic monomer (a monomer having a (meth)acryloyl group in the molecule) as a monomer component constituting the polymer. That is, the acrylic polymer contains a constituent unit derived from the acrylic monomer. The acrylic polymer is preferably a polymer containing a (meth)acrylic acid alkyl ester as a monomer component constituting the polymer. In this specification, "(meth)acrylic" refers to "acrylic" and / or "methacrylic" (either one or both of "acrylic" and "methacrylic"), and the same applies to other terms.

[0088] The (meth)acrylic acid alkyl ester as an essential monomer component is preferably a (meth)acrylic acid alkyl ester having a linear or branched alkyl group, and the (meth)acrylic acid alkyl ester may be used singly or in combination of two or more.

[0089] The (meth)acrylic acid alkyl ester having a linear or branched alkyl group is not particularly limited, and examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, and methyl (meth)acrylate. Examples of the alkyl (meth)acrylate esters having a linear or branched alkyl group having 1 to 20 carbon atoms include isononyl acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (n-lauryl (meth)acrylate), tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate (stearyl (meth)acrylate), isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

[0090] As the (meth)acrylic acid alkyl ester having a linear or branched alkyl group, a (meth)acrylic acid alkyl ester having a linear or branched (particularly linear) alkyl group having 2 or more carbon atoms (preferably 4 to 18, more preferably 6 to 14) is preferred. Furthermore, from the viewpoint of good compatibility with the adherend when the pressure-sensitive adhesive layer is laminated to the adherend and excellent adhesion at the time of rising, the (meth)acrylic acid alkyl ester having a linear or branched alkyl group is particularly preferably at least one selected from the group consisting of n-octyl acrylate (NOAA) and n-lauryl acrylate (LA). n-Octyl acrylate and n-lauryl acrylate have low Tg of the homopolymer and low G' １（２５） and G' １（－２０）In particular, by using these in combination, it is possible to suppress crystallization while lowering G'. １（２５） and G' １（－２０） can be lowered.

[0091] The content of the structural units derived from (meth)acrylic acid alkyl ester in the acrylic polymer is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 96% by mass or more, relative to 100% by mass of the total amount of the monomer components constituting the acrylic polymer. The content may be 99% by mass or less, or may be 98% by mass or less. Of course, depending on the application and required properties, the content of the structural units derived from (meth)acrylic acid alkyl ester in the acrylic polymer may be less than 70% by mass, relative to 100% by mass of the total amount of the monomer components constituting the acrylic polymer.

[0092] The acrylic polymer may contain, as a monomer component constituting the polymer, the alkyl (meth)acrylate and another monomer (copolymerizable monomer) copolymerizable with the alkyl (meth)acrylate. That is, the acrylic polymer may contain a copolymerizable monomer as a constituent unit. Only one type of copolymerizable monomer may be used, or two or more types may be used.

[0093] The copolymerizable monomer can be appropriately selected depending on the reactive functional group, for example, when the compound (a2) is a polyfunctional compound. Examples of the copolymerizable monomer include polar group-containing monomers such as carboxy group-containing monomers, acid anhydride monomers, hydroxy group-containing monomers, glycidyl group-containing monomers, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, and nitrogen atom-containing monomers. Only one type of the copolymerizable monomer components may be used, or two or more types may be used.

[0094] Examples of the hydroxy group-containing monomer include 2-hydroxyethyl (meth)acrylate, 2-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.

[0095] Examples of the carboxy group-containing monomer include acrylic acid, methacrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, etc. Examples of the acid anhydride monomer include maleic anhydride, itaconic anhydride, etc.

[0096] Examples of the nitrogen atom-containing monomer include amide group-containing monomers, amino group-containing monomers, cyano group-containing monomers, and monomers having a nitrogen atom-containing ring. Examples of the amide group-containing monomer include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methylolpropane(meth)acrylamide, N-methoxymethyl(meth)acrylamide, and N-butoxymethyl(meth)acrylamide. Examples of the amino group-containing monomer include aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, and t-butylaminoethyl(meth)acrylate. Examples of the cyano group-containing monomer include acrylonitrile and methacrylonitrile. 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, N-vinylmorpholine, N-vinylcaprolactam, and N-(meth)acryloylmorpholine.

[0097] The copolymerizable monomer is preferably a hydroxy group-containing monomer and / or a carboxy group-containing monomer. By introducing a crosslinked structure into the base polymer, the cohesive strength is improved, and the peelability of the pressure-sensitive adhesive layer from the adherend before curing tends to be improved.

[0098] The content of the structural unit derived from the copolymerizable monomer in the acrylic polymer may be 0.1% by mass or more, or may be 0.3% by mass or more, relative to 100% by mass of the total amount of the monomer components constituting the acrylic polymer. The content is preferably 30% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and may even be 1% by mass or less. Of course, depending on the application and desired properties, the content of the structural unit derived from the copolymerizable monomer in the acrylic polymer may be less than 0.1% by mass, relative to 100% by mass of the total amount of the monomer components constituting the acrylic polymer.

[0099] The proportion of the hydroxy group-containing monomer and / or carboxy group-containing monomer in the total amount (100% by mass) of all monomer components constituting the polymer (a1) is preferably 0.5 to 15% by mass, more preferably 1 to 10% by mass, and even more preferably 2 to 7% by mass.

[0100] The polymer (a1) may be substantially free of nitrogen atoms. The proportion of nitrogen atoms in the constituent elements of the polymer (a1) may be 0.1 mol% or less, 0.05 mol% or less, 0.01 mol% or less, 0.005 mol% or less, 0.001 mol% or less, or 0 mol%. By using a polymer (a1) that is substantially free of nitrogen atoms, when an adherend is subjected to a surface activation treatment, an increase in the adhesive strength (initial adhesive strength) of the pressure-sensitive adhesive layer before curing tends to be suppressed. By not using the nitrogen-atom-containing monomer as a constituent monomer component of the polymer (a1), a polymer (a1) that is substantially free of nitrogen atoms can be obtained. The proportion of the nitrogen-atom-containing monomer in the total amount (%) of the constituent monomer components of the polymer (a1) may be 1 mass% or less, 0.5 mass% or less, 0.1 mass% or less, 0.05 mass% or less, or 0 mass%.

[0101] The acrylic polymer may contain a structural unit derived from a polyfunctional compound copolymerizable with the monomer components constituting the acrylic polymer in order to form a crosslinked structure in the polymer skeleton. Examples of the polyfunctional compound include polyfunctional monomers and polyfunctional oligomers containing two or more ethylenically unsaturated double bonds per molecule. Examples of the polyfunctional monomer include polyfunctional (meth)acrylates. Compound (a2) may be used as the polyfunctional compound. Only one type of the polyfunctional compound may be used, or two or more types may be used.

[0102] The monomer component (d) may be any of those exemplified and described as the monomer component constituting the polymer (a1).When the pressure-sensitive adhesive composition contains the monomer component (d) and the compound (a2), the monomer component (d) preferably has a polymerizability different from that of the external stimulus so that the reversible decomposition bond in the compound (a2) is not decomposed during the polymerization of the monomer component (d).For example, when the external stimulus is light irradiation, the monomer component (d) preferably has thermal polymerizability.

[0103] Component (b) is a compound reactive with at least one of the groups generated by cleavage of the reversibly decomposable bond. It is preferable that component (b) is reactive with one of the groups (two groups) generated by cleavage of the reversibly decomposable bond per molecule. For example, when the reversibly decomposable group is -O-C-C(=O)-, component (b) is reactive with -O-C and / or C(=O)-. When one molecule of component (b) is reactive with both -O-C and C(=O)-, component (b) is interposed between -O-C and C(=O)-, and, for example, the molecular chain becomes longer and the elastic modulus decreases compared to before cleavage of the reversibly decomposable bond. On the other hand, when one molecule of component (b) is reactive with either —O—C or C(═O)—, component (b) blocks at least one of —O—C and C(═O)—, thereby suppressing the recombination of the two groups generated by cleavage, making it easier to change the elastic modulus. Only one type of component (b) may be used, or two or more types may be used.

[0104] When the polymer (a1) generates radicals upon cleavage, the component (b) is preferably a compound having radical scavenging ability (radical scavenger). Examples of the radical scavenger include a photoradical polymerization initiator, a spin scavenger, an antioxidant, a polymerization inhibitor, and a hydrogen donor.

[0105] From the viewpoint of excellent reactivity with —O—C·, the component (b) is preferably a compound (b1) having a phenolic hydroxyl group. The compound (b1) is a compound having a phenol structure, and examples thereof include phenol, hindered phenols (trade names "Irganox 1076", "Irganox 1135", "Irganox 1520L", etc.), catechol, t-butylcatechol, cresol, naphthol, bisphenols (bisphenol A, bisphenol F, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol S, tetrachlorobisphenol A, tetrabromobisphenol A, etc.), dihydroxide, Examples of the phenol derivatives include hydroxynaphthalene, phenol novolac, cresol novolac, bisphenol A novolac, brominated phenol novolac, resorcinol, 4,4'-dihydroxydiphenyl ether, 9,9'-bis(4-hydroxyphenyl)fluorene, 9,9-bis(3-methyl-4-hydroxyphenyl)fluorene, 3,3,3',3'-tetramethyl-1,1'-spirobiindan-6,6'-diol, 3-(4-hydroxyphenyl)-1,1,3-trimethyl-5-indanol, and gallic acid esters. Each of the compounds exemplified as compound (b1) may have a substituent.

[0106] From the viewpoint of exhibiting an appropriate recombination-inhibiting effect, the content of component (b) is preferably 10 parts by mass or more, more preferably 50 parts by mass or more, and even more preferably 75 parts by mass or more, relative to 100 parts by mass of the total amount of compound (a2) (the total amount of one or more selected from the group consisting of compound (a2), structural units derived from compound (a2), and structural moieties derived from compound (a2)). The content may be, for example, 1,000 parts by mass or less, 700 parts by mass or less, or 500 parts by mass or less.

[0107] Component (c) is a compound that reacts and hardens in response to an external stimulus. Specifically, it is a compound that reacts and hardens in response to an external stimulus that cleaves the reversibly decomposable bond. Component (c) does not have a decomposable bond that is cleaved by the application of the external stimulus. Component (c) preferably exhibits compatibility with component (a), and is more preferably a liquid at room temperature. Examples of component (c) include a compound having a polymerizable functional group and a polymerization initiator. Of these, component (c) preferably contains a compound having a polymerizable functional group and a polymerization initiator.

[0108] The (c) component may be used singly or in combination of two or more. For example, by using a (c) component having a relatively high compatibility with the polymer (a1) in combination with a (c) component having a relatively low compatibility with the polymer (a1), it is possible to adjust the properties of the pressure-sensitive adhesive layer before and after curing, such as increasing the storage modulus of the pressure-sensitive adhesive layer at room temperature after curing while keeping the initial adhesive strength low.

[0109] The compound having the polymerizable functional group may be a monomer component, an oligomer component, a polyfunctional compound, etc. Among these, a polyfunctional compound is preferred, and a polyfunctional (meth)acrylate is more preferred.

[0110] The polyfunctional (meth)acrylate is typically an ester of a polyol and (meth)acrylic acid. Specific examples of the polyfunctional (meth)acrylate include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, alkanediol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, isocyanuric acid di(meth)acrylate, isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, and trimethylolpropanediol di(meth)acrylate. Examples of the acrylate include ethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol poly(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin di(meth)acrylate, urethane (meth)acrylate, epoxy (meth)acrylate, butadiene (meth)acrylate, and isoprene (meth)acrylate.

[0111] The polyfunctional (meth)acrylate may be an ester of an alkylene oxide-modified polyol and (meth)acrylic acid. Examples of the alkylene oxide include ethylene oxide (EO) and propylene oxide (PO). The alkylene oxide may be a polyalkylene oxide such as polyethylene glycol or polypropylene glycol. The chain length n of the alkylene oxide is, for example, about 1 to 10. By adjusting the type and chain length of the alkylene oxide, the compatibility with the polymer (a1) when the polymer (a1) is an acrylic polymer can be adjusted to an appropriate range.

[0112] Specific examples of alkylene oxide-modified polyfunctional (meth)acrylates include bisphenol A ethylene oxide-modified di(meth)acrylate, bisphenol A propylene oxide-modified di(meth)acrylate, trimethylolpropane ethylene oxide-modified tri(meth)acrylate, trimethylolpropane propylene oxide-modified tri(meth)acrylate, isocyanuric acid ethylene oxide-modified di(meth)acrylate, isocyanuric acid propylene oxide-modified di(meth)acrylate, isocyanuric acid ethylene oxide-modified tri(meth)acrylate, isocyanuric acid propylene oxide-modified tri(meth)acrylate, pentaerythritol ethylene oxide-modified tetra(meth)acrylate, and pentaerythritol propylene oxide-modified tetra(meth)acrylate.

[0113] The polyfunctional (meth)acrylate may be a metal (meth)acrylate such as zinc (meth)acrylate, magnesium (meth)acrylate, calcium (meth)acrylate, barium (meth)acrylate, strontium (meth)acrylate, nickel (meth)acrylate, copper (meth)acrylate, or aluminum (meth)acrylate.

[0114] The smaller the molecular weight of component (c), the higher the compatibility with polymer (a1) tends to be. From the viewpoint of compatibility with polymer (a1), the molecular weight of component (c) is preferably 1,500 or less, more preferably 1,000 or less, and may be 800 or less, 600 or less, 500 or less, 450 or less, or 400 or less.

[0115] Furthermore, the smaller the functional group equivalent weight of component (c) (i.e., the greater the number of functional groups per unit molecular weight), the higher the compatibility with polymer (a1). From the viewpoint of compatibility with polymer (a1), the functional group equivalent weight (g / eq) of component (c) is preferably 80 to 300, more preferably 90 to 200, and even more preferably 100 to 170, and may be 110 to 160 or 120 to 150.

[0116] When the polymer (a1) and the component (c) are not completely miscible, the liquid component (c) bleeds out to the surface, forming an adhesion-preventing layer (Weak Boundary Layer; WBL) at the adhesive interface with the adherend, strengthening the liquid properties. When the WBL is formed, the liquid properties of the surface (adhesive interface) become stronger while maintaining the bulk properties of the PSA layer, such as shear storage modulus, and the adhesive strength with the adherend tends to decrease.

[0117] When the polymer (a1) and the component (c) are moderately compatible but not completely compatible, a WBL is formed in the pressure-sensitive adhesive layer before curing, resulting in a low initial adhesive strength and easy peeling from the adherend. On the other hand, after curing, the liquid properties of the component (c) disappear and a crosslinked structure is uniformly introduced into the pressure-sensitive adhesive layer, resulting in a significant improvement in adhesive strength to the adherend.

[0118] The compatibility between the polymer (a1) and the component (c) is mainly affected by the structure of the compound. The structure and compatibility of the compound can be evaluated, for example, by the Hansen solubility parameter (HSP). The Hansen solubility parameter (HSP) is calculated by multiplying the Hildebrand solubility parameter δ by the dispersion term δ. ｄ , polarity term δ ｐ , and the hydrogen bond term δ ｈ and expressed in three-dimensional space, and δ ２ = δ ｄ ２ +δ ｐ ２ +δ ｈ ２ The following relationship holds: Dispersion term δ ｄ is the effect of dispersion forces, and the polar term δ ｐ is the effect of dipole-dipole forces, and the hydrogen bond term δ ｈ indicates the effect of hydrogen bonding force. The distance Ra between the HSPs of two substances is the difference Δδ between the dispersion terms of the two substances. ｄ , the difference in polar terms Δδ ｐ , and the difference in hydrogen bond terms Δδ ｈ From this, Ra = {4Δδ ｄ ２ +Δδ ｐ ２ +Δδ ｈ ２} １／２The smaller the Ra, the higher the compatibility, and the larger the Ra, the lower the compatibility.

[0119] Details of Hansen solubility parameters are described in Hansen Solubility Parameters: A Users Handbook (CRC Press, 2007) by Charles M. Hansen, and for substances for which literature values ​​are unknown, the values ​​can be calculated using computer software Hansen Solubility Parameters in Practice (HSPiP).

[0120] The polymer (a1) having a low glass transition temperature has a high ratio of (meth)acrylic acid ester in the constituent monomer components, and a low ratio of highly polar monomers such as hydroxyl group-containing monomers, carboxyl group-containing monomers, and nitrogen atom-containing monomers. Thus, when using a polymer (a1) having a low glass transition temperature and low polarity, by using a polyfunctional (meth)acrylate containing alkylene oxide such as ethylene oxide or propylene oxide as component (c), the HSP distance Ra between the polymer (a1) and component (c) can be adjusted to a suitable range. The longer the chain length n of the alkylene oxide in the alkylene oxide-modified polyfunctional (meth)acrylate, the larger the HSP distance Ra tends to be.

[0121] If the HSP distance Ra between the polymer (a1) and the component (c) is excessively large, although the initial adhesive strength is low, contamination due to bleed-out of the component (c) may occur, or the increase in adhesive strength upon curing may be insufficient. Therefore, the chain length n of the alkylene oxide is preferably 1 to 5, more preferably 1 to 3. For example, when the component (c) is trimethylolpropane ethylene oxide-modified triacrylate, the chain length n of ethylene oxide (EO) attached to each of the three methylol groups of the trimethylolpropane is preferably 1 or 2.

[0122] The type and amount of the (c) component affect not only the adhesive strength but also the bulk properties of the adhesive. If the polymer (a1) in the adhesive composition is the same, the effect on the change in the storage modulus of the adhesive layer before curing is small, even if the type of the (c) component is different. On the other hand, as the content of the (c) component increases, the content of the polymer (a1) in the composition becomes relatively small, so the storage modulus of the adhesive layer before curing tends to decrease. The smaller the functional group equivalent of the (c) component and the higher the content of the (c) component, the higher the crosslinking density upon curing, so the higher the storage modulus of the adhesive layer after curing tends to increase. That is, the higher the content of the (c) component, the lower the storage modulus of the adhesive layer before curing and the higher the storage modulus of the adhesive layer after curing tends to increase. From the viewpoint of increasing the adhesive strength of the pressure-sensitive adhesive layer after curing while minimizing the change in elastic modulus, the content of the component (c) in the pressure-sensitive adhesive composition is preferably 1 to 50 parts by mass, more preferably 3 to 30 parts by mass, and may also be 4 to 25 parts by mass, or 5 to 20 parts by mass, relative to 100 parts by mass of the total amount of the polymer (a1) or the components constituting the polymer (a1) (monomer components and compound (a2)).

[0123] The polymerization initiator is appropriately selected depending on the type of compound having the polymerizable functional group, but a radical polymerization initiator is preferred. Furthermore, the polymerization initiator is preferably a photopolymerization initiator. Examples of the photopolymerization initiator include a radical photopolymerization initiator, a cationic photopolymerization initiator, and an anionic photopolymerization initiator. Only one type of the polymerization initiator may be used, or two or more types may be used.

[0124] Examples of the radical photopolymerization initiator include an acylphosphine oxide photopolymerization initiator, a benzoin ether photopolymerization initiator, an acetophenone photopolymerization initiator, an α-ketol photopolymerization initiator, an aromatic sulfonyl chloride photopolymerization initiator, a photoactive oxime photopolymerization initiator, a benzoin photopolymerization initiator, a benzyl photopolymerization initiator, a benzophenone photopolymerization initiator, a ketal photopolymerization initiator, and a thioxanthone photopolymerization initiator.

[0125] Examples of acylphosphine oxide photopolymerization initiators include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-2,4-di-n-butoxyphenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. Examples of benzoin ether photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and 2,2-dimethoxy-1,2-diphenylethan-1-one. Examples of acetophenone photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of α-ketol photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of aromatic sulfonyl chloride photopolymerization initiators include 2-naphthalenesulfonyl chloride. Examples of photoactive oxime photopolymerization initiators include 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. Examples of benzoin photopolymerization initiators include benzoin. Examples of benzyl photopolymerization initiators include benzyl. Examples of benzophenone photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, and polyvinylbenzophenone. Examples of ketal photopolymerization initiators include benzyl dimethyl ketal. Examples of thioxanthone photopolymerization initiators include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.

[0126] The photopolymerization initiator is preferably at least one selected from the group consisting of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,2-dimethoxy-1,2-diphenylethan-1-one, and 1-hydroxycyclohexyl phenyl ketone.

[0127] The content of the photopolymerization initiator is, for example, 0.001 parts by mass or more, preferably 0.01 parts by mass or more, and more preferably 0.03 parts by mass or more, relative to 100 parts by mass of the total amount of the polymer (a1) or the constituent components of the polymer (a1) (monomer components and compound (a2)), and is, for example, 10 parts by mass or less, preferably 3 parts by mass or less, and more preferably 1 part by mass or less.

[0128] The pressure-sensitive adhesive composition may also contain other components in addition to the above-mentioned components as needed. Examples of such other components include curing catalysts, crosslinking agents other than the compound (a2), crosslinking accelerators, tackifying resins (rosin derivatives, polyterpene resins, petroleum resins, oil-soluble phenols, etc.), oligomers, antioxidants, fillers (metal powders, organic fillers, inorganic fillers, etc.), colorants (pigments, dyes, etc.), antioxidants, plasticizers, softeners, surfactants, antistatic agents, surface lubricants, leveling agents, light stabilizers, UV absorbers, polymerization inhibitors, granular materials, foil-like materials, flame retardants, silane coupling agents, ion trapping agents, thickeners, etc. The other components may each be used singly or in combination of two or more.

[0129] The pressure-sensitive adhesive composition of the present invention may have any form, for example, a solvent type, an emulsion type, a thermal melt type (hot melt type), a solventless type, etc. Among these, an emulsion type using a thermally polymerizable polymer as a base polymer is preferred, from the viewpoints that photocuring does not occur and that it is suitable for reducing environmental load.

[0130] [Adhesive Layer] An adhesive layer can be formed using the adhesive composition described above. The adhesive layer formed using the adhesive composition of the present invention may be referred to as the "adhesive layer of the present invention."

[0131] The pressure-sensitive adhesive layer preferably contains at least a polymer (a1), a component (b), and a component (c). The polymer (a1) may be used singly or in combination of two or more kinds.

[0132] The pressure-sensitive adhesive layer may contain other components in addition to the above-mentioned components. Examples of the other components include those exemplified and explained as other components that may be contained in the pressure-sensitive adhesive composition. Only one of the other components may be used, or two or more of the other components may be used.

[0133] The content of polymer (a1) in the pressure-sensitive adhesive layer is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and particularly preferably 80% by mass or more, relative to the total amount (100% by mass) of the pressure-sensitive adhesive layer. When the content is 30% by mass or more, adhesiveness is easily imparted to the pressure-sensitive adhesive layer. The content is preferably 99.5% by mass or less, more preferably 99% by mass or less. When the content is 99.5% by mass or less, composition design by blending component (b) and component (c) is easily performed.

[0134] In the pressure-sensitive adhesive layer of the present invention, the polymer (a1) preferably forms a network structure. A network structure refers to a state in which molecules are entangled with each other, or a state in which molecular chains form long molecules via some kind of bond. That is, the polymer (a1) is preferably a polymer in which a network structure is formed by bonds or entanglement of molecules. A pressure-sensitive adhesive layer having such a configuration forms a network structure by bonds or entanglement of polymers with each other, and can have appropriate hardness, and the polymer structure is shredded by decomposition of the degradable bonds due to external stimuli.

[0135] The term "molecular entanglement" refers to a state in which polymers form a network structure without covalent bonds. To form such an entangled structure, it is preferable to contain different types of polymers that are unlikely to undergo crosslinking reactions with each other. From the viewpoint of ease of preparation, it is preferable that thermoplastic resins or thermosetting resins and thermoplastic resins form an entangled structure. This structure is suitable for a pressure-sensitive adhesive layer that is relatively flexible before the application of an external stimulus because it does not involve covalent bonds.

[0136] The state in which the molecular chains form a long molecule via some kind of bond indicates a polymer formed from a single polymer. To form such a long molecule, it is preferable to contain a single polymer, and it is preferable to contain the above-mentioned thermosetting resin. This structure allows the molecular chains to be covalently bonded to a long length, so that a relatively hard adhesive layer can be formed, and also increases the number of sites that are cleaved by external stimuli, making it suitable for an adhesive layer in which the molecular weight of the polymer changes significantly before and after external stimuli.

[0137] The pressure-sensitive adhesive layer of the present invention has a shear storage modulus (G' ０（２５） ), shear storage modulus (G') at 25°C after photocuring １（２５） ), shear storage modulus (G') at -20°C before photocuring ０（－２０） ), shear storage modulus (G') at -20°C after photocuring １（－２０） ), ΔG′ （２５） , ΔG′ （－２０） It is preferable that ΔG′ and ΔG′ each satisfy the above-mentioned preferred ranges for the PSA composition.

[0138] The pressure-sensitive adhesive layer can be produced, for example, by applying the pressure-sensitive adhesive composition to a release-treated surface of a release liner or a substrate to form a pressure-sensitive adhesive composition layer, and then solidifying the pressure-sensitive adhesive composition layer by removing the solvent through heating or by polymerization through irradiation with radiation.

[0139] The pressure-sensitive adhesive layer of the present invention is preferably a sheet-like pressure-sensitive adhesive (emulsion-type pressure-sensitive adhesive sheet) formed from an emulsion-type pressure-sensitive adhesive composition. Therefore, the pressure-sensitive adhesive layer of the present invention preferably contains at least a thermally polymerizable polymer as a base polymer. The thermally polymerizable polymer is a polymer formed by a polymerization method in which the polymerization reaction of a polymerizable component is advanced by heat.

[0140] The PSA composition may be applied (coated) using a known coating method, such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, comma coater, or direct coater.

[0141] The thickness of the pressure-sensitive adhesive layer of the present invention is not particularly limited, but is, for example, about 1 to 300 μm, preferably 3 to 100 μm, more preferably 5 to 50 μm, even more preferably 6 to 40 μm, and particularly preferably 8 to 30 μm. The greater the thickness of the pressure-sensitive adhesive layer, the more likely it is to improve adhesion to the adherend. On the other hand, if the pressure-sensitive adhesive layer is excessively thick, the fluidity before curing may be high, making handling difficult. From the perspective of reducing the thickness, the thickness of the pressure-sensitive adhesive layer may be 25 μm or less, 20 μm or less, or 18 μm or less.

[0142] [Adhesive Sheet] An adhesive sheet can be obtained using the adhesive layer of the present invention. In this specification, an adhesive sheet comprising the adhesive layer of the present invention may be referred to as the "adhesive sheet of the present invention." The adhesive sheet may be a so-called "substrate-less" adhesive sheet that does not have a substrate (substrate layer), or may be an adhesive sheet of a type that has a substrate. In this specification, an "adhesive-less" adhesive sheet may be referred to as a "substrate-less adhesive sheet," and an adhesive sheet of a type that has a substrate may be referred to as a "substrate-attached adhesive sheet." Examples of the substrate-less adhesive sheet include a double-sided adhesive sheet consisting of only the adhesive layer of the present invention, and a double-sided adhesive sheet consisting of the adhesive layer of the present invention and another adhesive layer (an adhesive layer other than the adhesive layer of the present invention). The substrate-attached adhesive sheet is an adhesive sheet comprising a substrate and the adhesive layer of the present invention formed on at least one side of the substrate. Examples include a single-sided adhesive sheet having the adhesive layer of the present invention on one side of the substrate, a double-sided adhesive sheet having the adhesive layer of the present invention on both sides of the substrate, and a double-sided adhesive sheet having the adhesive layer of the present invention on one side of the substrate and another adhesive layer on the other side. The above-mentioned "substrate (substrate layer)" refers to a support, and is the part that is attached to an adherend together with the PSA layer when the PSA sheet is used (attached) to the adherend. The release liner that is peeled off when the PSA sheet is used (attached) is not included in the above-mentioned substrate.

[0143] When the pressure-sensitive adhesive sheet of the present invention is a substrate-attached pressure-sensitive adhesive sheet or the like, the substrate is not particularly limited, and examples thereof include various optical films such as plastic films, anti-reflection (AR) films, anti-glare (AG) films, polarizing plates, and retardation plates. Examples of the substrate include porous materials such as paper, cloth, and nonwoven fabrics, nets, foam sheets, and metal foils. Examples of materials for the plastic film or the like include polyester resins such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate, triacetyl cellulose (TAC), polysulfone, polyarylate, polyimide, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, ethylene-propylene copolymers, and cyclic olefin polymers such as "ARTON" (a cyclic olefin polymer, manufactured by JSR Corporation) and "ZEONOR" (a cyclic olefin polymer, manufactured by Zeon Corporation). These plastic materials may be used alone or in combination of two or more.

[0144] The thickness of the substrate is not particularly limited, but is preferably 10 to 150 μm, more preferably 15 to 125 μm, and even more preferably 25 to 100 μm. The substrate may have either a single layer or multiple layers. The surface of the substrate may be appropriately subjected to a known or commonly used surface treatment, such as a physical treatment such as a corona discharge treatment or a plasma treatment, or a chemical treatment such as a primer treatment.

[0145] The pressure-sensitive adhesive sheet may have a release liner provided on the surface (adhesive surface or adhesive surface) of the pressure-sensitive adhesive layer until use. When the pressure-sensitive adhesive sheet is a double-sided pressure-sensitive adhesive sheet, each of the pressure-sensitive adhesive surfaces or adhesive surfaces may be protected by two release liners, or may be protected by a single release liner having release surfaces on both sides and wound into a roll (rolled body). The release liner is used as a protective material for the pressure-sensitive adhesive layer and is peeled off when the sheet is attached to the adherend. When the pressure-sensitive adhesive sheet is a substrate-less pressure-sensitive adhesive sheet, the release liner also serves as a support for the pressure-sensitive adhesive layer. The release liner is not necessarily provided.

[0146] The release liner protects the adhesive surface that comes into contact with the pressure-sensitive adhesive sheet until it is used, and is peeled off when the pressure-sensitive adhesive layer is to be used.

[0147] Examples of the substrate for the release liner include polyethylene films, polypropylene films, polybutene films, polybutadiene films, polymethylpentene films, polyvinyl chloride films, vinyl chloride copolymer films, polyethylene terephthalate films, polyethylene naphthalate films, polybutylene terephthalate films, polyurethane films, ethylene vinyl acetate films, ionomer resin films, ethylene-(meth)acrylic acid copolymer films, ethylene-(meth)acrylic acid ester copolymer films, polystyrene films, polycarbonate films, polyimide films, and fluororesin films. Crosslinked films of these may also be used. Laminated films of these may also be used.

[0148] The release surface of the release liner (particularly the surface that comes into contact with the pressure-sensitive adhesive layer, etc.) is preferably subjected to a release treatment. Examples of release agents used for the release treatment include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents.

[0149] The thickness of the release liner is not particularly limited, but is, for example, about 20 to 150 μm.

[0150] One embodiment of the pressure-sensitive adhesive sheet of the present invention is shown in Figure 1. The pressure-sensitive adhesive sheet 10 shown in Figure 1 is a single-sided pressure-sensitive adhesive sheet comprising a substrate 1 and a pressure-sensitive adhesive layer 21 of the present invention laminated on one side of the substrate 1. The adhesive surface of the pressure-sensitive adhesive layer 21 of the present invention is protected by a release liner 31.

[0151] [Uses] The pressure-sensitive adhesive composition of the present invention, the pressure-sensitive adhesive layer of the present invention, and the pressure-sensitive adhesive sheet of the present invention are preferably used for optical applications, i.e., for applications in which they are bonded to optical members. More specifically, they are used, for example, for applications in which optical members are bonded (for bonding optical members) and for manufacturing products (optical products) in which the optical members are used. The pressure-sensitive adhesive composition of the present invention, the pressure-sensitive adhesive layer of the present invention, and the pressure-sensitive adhesive sheet of the present invention are used for optical applications, and are therefore highly reliable.

[0152] The pressure-sensitive adhesive layer of the present invention and the pressure-sensitive adhesive sheet of the present invention are used, for example, in optical components of electrical and electronic devices, when attaching (mounting) various members or components to predetermined locations (e.g., housings, front panels, window portions, etc.). The term "electrical and electronic devices" refers to devices that fall into at least one of electrical and electronic devices. Examples of the electrical and electronic devices include image display devices such as liquid crystal displays, organic / inorganic electroluminescence displays, and plasma displays, as well as portable electronic devices. Examples of the image display devices include image display devices in portable electronic devices, in-vehicle displays, and digital signage (electronic signboards and electronic bulletin boards). The image display devices may be of a form (structure) such as a so-called "rigid type" or a so-called "flexible type," or may be of a form (structure) that can be bent or folded, such as a so-called "foldable type" or "rollable type."

[0153] Examples of the portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (for example, wristwear devices worn on the wrist like a wristwatch, modular devices worn on a part of the body with a clip or strap, eyewear devices including eyeglasses (monocular and binocular, including head-mounted devices), clothing devices attached to shirts, socks, hats, etc. as accessories, earwear devices attached to the ears like earphones), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic organizers, e-books, in-car information devices, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, the term "portable" does not simply mean that the device is portable, but rather means that the device has a level of portability that allows an individual (average adult) to carry it relatively easily.

[0154] The pressure-sensitive adhesive layer of the present invention has excellent processability, is easily peeled immediately after being attached to an adherend, can be firmly adhered to an adherend by curing the pressure-sensitive adhesive after being attached to an adherend, and is less likely to peel at bending points. The pressure-sensitive adhesive layer of the present invention has excellent handleability before being attached to or adhered to a member during production, processing, storage, transportation, etc., and has excellent flexibility after being attached to or adhered to a member. Therefore, for example, when cutting with a punching blade, glue overflow and glue chipping, as well as process contamination caused by these, can be prevented, resulting in excellent processability. Furthermore, glue overflow due to its own weight is less likely to occur during storage, and glue chipping due to vibration or contact is less likely to occur during transportation. Furthermore, after being attached to or adhered to a member, for example, when used by being attached to a member, the excellent flexibility allows for excellent adhesion (adhesive strength), adhesive strength, bendability, foldability, flex resistance, etc.

[0155] [Reinforcing Film] The pressure-sensitive adhesive sheet of the present invention is preferably used as a reinforcing film for optical members such as devices and device components. The reinforcing film is used by being attached to the optical member. The pressure-sensitive adhesive sheet 10, which is a reinforcing film, has the pressure-sensitive adhesive layer 21 fixed to the substrate 1, and after being attached to the adherend, the adhesive strength to the adherend is low before the application of an external stimulus (for example, before photocuring). Therefore, the reinforcing film is easily peeled from the adherend before the application of an external stimulus.

[0156] The adherend to which the reinforced film is attached is not particularly limited, and examples thereof include the optical members described above. In one embodiment, the reinforced film is attached to the surface of a foldable device (flexible device). The flexible device has, for example, a hinge portion and can be folded around this hinge portion. The folding angle can be set arbitrarily, and the device may be bent (folded) 180°. When folding the flexible device, the device may be folded so that the adhesive surface of the reinforced film faces inward, or the device may be folded so that the reinforced film faces outward. When the device is a display device, the reinforced film may be attached to the surface on the screen side, or to the back side (housing). A flexible device that is configured to be bendable at a predetermined location such as a hinge portion repeatedly bends and stretches at the same location during use.

[0157] The reinforcing film may be attached to the entire surface of the adherend, or may be selectively attached only to the area requiring reinforcement (reinforcement target area). Alternatively, the reinforcing film may be attached to the entire area requiring reinforcement (reinforcement target area) and the area not requiring reinforcement (non-reinforcement target area), and then the reinforcing film attached to the non-reinforcement target area may be cut and removed. Before the external stimulus is applied, the reinforcing film is temporarily attached to the surface of the adherend, so the reinforcing film can be easily peeled and removed from the surface of the adherend. The reinforcing film may be attached to the area requiring reinforcement and the area not requiring reinforcement, and an external stimulus may be selectively applied to the area requiring reinforcement to harden the adhesive layer. Then, the reinforcing film may be selectively peeled and removed from the non-reinforcement target area where the adhesive layer is unhardened.

[0158] By laminating a reinforcing film, appropriate rigidity is imparted, which is expected to improve the handleability and prevent breakage of thin members such as flexible devices. When a reinforcing film is laminated to a work-in-progress in the device manufacturing process, the reinforcing film may be laminated to a large-sized work-in-progress before it is cut to the product size. The reinforcing film may also be laminated roll-to-roll to a mother roll of a device manufactured by a roll-to-roll process.

[0159] Before laminating the reinforcing film, the surface of the adherend may be subjected to an activation treatment for the purpose of cleaning, etc. Examples of surface activation treatments include plasma treatment, corona treatment, and glow discharge treatment. An adherend whose surface has been activated contains many active groups such as hydroxyl groups, carbonyl groups, and carboxyl groups, and the adhesive strength is likely to increase due to intermolecular interactions with the polar functional groups of the base polymer of the pressure-sensitive adhesive layer. In particular, when the adherend is a polyimide, the activation treatment activates amide acids, terminal amino groups, carboxyl groups (or carboxylic anhydride groups), etc., which interact strongly with the polar functional groups of the base polymer, and therefore the activation treatment may significantly increase the initial adhesive strength.

[0160] If the initial adhesive strength is excessively high, peeling operations such as reworking may become difficult. As described above, since the base polymer is substantially free of nitrogen atoms, an excessive increase in the initial adhesive strength to an adherend whose surface has been subjected to an activation treatment can be suppressed.

[0161] [Manufacturing Method] One embodiment of the manufacturing method of the pressure-sensitive adhesive layer etc. of the present invention will be described. For example, the pressure-sensitive adhesive sheet 10 with a substrate shown in Figure 1 can be manufactured by the following method. The pressure-sensitive adhesive composition that forms the pressure-sensitive adhesive layer 21 of the present invention is applied to the release-treated surface of the substrate 1 or a release-treated release liner 31 to form a coating layer, and then the coating layer is solidified by removing the solvent through heating or by curing by heat curing or the like, thereby manufacturing the pressure-sensitive adhesive layer 21 of the present invention.

[0162] When the pressure-sensitive adhesive composition contains polymer (a1), the pressure-sensitive adhesive layer is formed by heating, etc., when the coating layer is solidified. When the pressure-sensitive adhesive composition contains the other polymer and / or raw material monomer and compound (a2), the raw material monomer is polymerized as needed by heating, etc., when the coating layer is solidified, and compound (a2) forms a bond with a polymer of the raw material monomer or the other polymer, forming polymer (a1) and simultaneously forming the pressure-sensitive adhesive layer.

[0163] In this manner, the adhesive sheet 10 with the substrate shown in FIG. 1 is obtained.

[0164] The above-described embodiments have been described to facilitate understanding of the present invention, and are not intended to limit the present invention.

[0165] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The numerical values ​​of each component shown in Table 1 are in parts by mass.

[0166] Production Example 1 (Preparation of Acrylic Polymer A) 43 parts by mass of n-octyl acrylate (NOAA), 56 parts by mass of n-lauryl acrylate (LA), 1 part by mass of acrylic acid (AA), 1 part by mass of the photodegradable compound represented by the above formula (1-1), 0.034 parts by mass of α-pinene as a chain transfer agent, 2.70 parts by mass of an emulsifier (trade name "Aqualon KN-30", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and 53 parts by mass of ion-exchanged water were blended into a vessel and then stirred and mixed to prepare a monomer emulsion. Next, 0.3 parts by mass of an emulsifier (trade name "Aqualon KN-30", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 50 parts by mass of ion-exchanged water were added to a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and the mixture was purged with nitrogen at room temperature (25°C) for 1 hour with stirring. Thereafter, 0.1 parts by mass of a polymerization initiator (product name "VA-057", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added thereto, and the temperature was raised to 60°C. Next, the monomer emulsion was added dropwise to the reaction vessel over 3 hours, and polymerization was carried out for 3 hours with stirring while maintaining the liquid temperature in the reaction vessel at around 60°C. Thereafter, the mixture was cooled to room temperature, and the pH was adjusted to 7 using 10% aqueous ammonia, thereby obtaining an emulsion-based acrylic polymer containing acrylic polymer A and having a solids concentration of 50% by mass.

[0167] Production Example 2 (Preparation of Acrylic Polymer B) 43 parts by mass of n-octyl acrylate (NOAA), 56 parts by mass of n-lauryl acrylate (LA), 1 part by mass of acrylic acid (AA), 3 parts by mass of the photodegradable compound represented by the above formula (1-1), 0.034 parts by mass of α-pinene as a chain transfer agent, 2.70 parts by mass of an emulsifier (trade name "Aqualon KN-30", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and 53 parts by mass of ion-exchanged water were blended into a vessel and then stirred and mixed to prepare a monomer emulsion. Next, 0.3 parts by mass of an emulsifier (trade name "Aqualon KN-30", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 50 parts by mass of ion-exchanged water were added to a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and the mixture was purged with nitrogen at room temperature (25°C) for 1 hour with stirring. Thereafter, 0.1 parts by mass of a polymerization initiator (product name "VA-057", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added thereto, and the temperature was raised to 60°C. Next, the monomer emulsion was added dropwise to the reaction vessel over 3 hours, and polymerization was carried out for 3 hours with stirring while maintaining the liquid temperature in the reaction vessel at around 60°C. Thereafter, the mixture was cooled to room temperature, and the pH was adjusted to 7 using 10% aqueous ammonia, thereby obtaining an emulsion-based acrylic polymer containing acrylic polymer B and having a solids concentration of 50% by mass.

[0168] Production Example 3 (Preparation of Acrylic Polymer C) 43 parts by mass of n-octyl acrylate (NOAA), 56 parts by mass of n-lauryl acrylate (LA), 1 part by mass of acrylic acid (AA), 0.034 parts by mass of α-pinene as a chain transfer agent, 2.70 parts by mass of an emulsifier (trade name "Aqualon KN-30", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and 53 parts by mass of ion-exchanged water were blended in a vessel and then stirred and mixed to prepare a monomer emulsion. Next, 0.3 parts by mass of an emulsifier (trade name "Aqualon KN-30", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 50 parts by mass of ion-exchanged water were added to a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and the atmosphere was replaced with nitrogen at room temperature (25°C) for 1 hour while stirring. Thereafter, 0.1 parts by mass of a polymerization initiator (trade name "VA-057", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the mixture and the temperature was raised to 60°C. Next, the monomer emulsion was added dropwise to the reaction vessel over 3 hours, and polymerization was carried out for 3 hours with stirring while maintaining the liquid temperature in the reaction vessel at around 60° C. Thereafter, the mixture was cooled to room temperature, and the pH was adjusted to 7 with 10% aqueous ammonia, thereby obtaining an emulsion-based acrylic polymer containing acrylic polymer C and having a solids concentration of 50% by mass.

[0169] Examples 1 to 3 and Comparative Examples 1 to 4 (Preparation of Pressure-Sensitive Adhesive Compositions) To 100 parts by mass of the acrylic polymer obtained in the above Preparation Examples, a thickener, an interparticle crosslinking agent, a polymerization inhibitor, a photocuring agent, and a photoradical polymerization initiator were added in the types and amounts shown in Table 1, followed by stirring and mixing to obtain pressure-sensitive adhesive compositions (solutions) of Examples 1 to 3 and Comparative Examples 1 to 4. The amount (parts by mass) of the acrylic polymer in Table 1 indicates the amount (parts by mass) of the solid content in the acrylic polymer solution.

[0170] (Preparation of Pressure-Sensitive Adhesive Sheets) Each of the pressure-sensitive adhesive compositions (solutions) obtained above was applied to a 38 μm-thick polyethylene terephthalate (PET) film (trade name "Diafoil T100", manufactured by Mitsubishi Chemical Corporation) using an applicator so that the thickness after drying would be 18 μm. Heat drying was carried out at 130°C for 3 minutes, and the release-treated surface of a release liner (trade name "CA1", manufactured by Fujiko Co., Ltd.) was attached. Thereafter, aging treatment was carried out for 3 days in an atmosphere at 50°C, and pressure-sensitive adhesive sheets of Examples 1 to 3 and Comparative Examples 1 to 4 were obtained.

[0171] The components shown in Table 1 are as follows: Thickener: trade name "Aron B500", manufactured by Toagosei Co., Ltd. Interparticle crosslinking agent: trade name "TETRAD-C", epoxy crosslinking agent, manufactured by Mitsubishi Gas Chemical Company, Inc. Polymerization inhibitor: trade name "Irganox 1135", manufactured by BASF Japan Ltd. Photocuring agent: trade name "M-350", trimethylolpropane EO-modified triacrylate, manufactured by Toagosei Co., Ltd. Photoradical polymerization initiator: trade name "Omnirad 651", manufactured by IGM Resins Italia Srl.

[0172] <Evaluation> The pressure-sensitive adhesive sheets of the Examples and Comparative Examples were evaluated as follows. The evaluation results are shown in Table 1.

[0173] (1) Shear storage modulus A pressure-sensitive adhesive composition was applied to a release liner and crosslinked in the same manner as in the above-mentioned Examples and Comparative Examples to prepare a pressure-sensitive adhesive sheet. These pressure-sensitive adhesive sheets were laminated to prepare a measurement sample (before photocuring) with a thickness of approximately 1.0 mm. A release liner was attached to the exposed surface of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet to isolate it from oxygen, and the sample was exposed to a 340 nm LED light source with an integrated light intensity of 20,000 mJ / cm. ２ The adhesive sheets were laminated to prepare measurement samples (after photocuring) with a thickness of approximately 1.0 mm. These samples were subjected to dynamic viscoelasticity measurement under the following conditions using an Advanced Rheometric Expansion System (ARES) manufactured by Rheometric Scientific. The shear storage modulus at 25°C (before photocuring: G' ０ , after photocuring: G' １) was calculated, and the rate of change in shear storage modulus before and after photocuring, ΔG' (%) = G' １ / G' ０ × 100 was calculated. (Measurement conditions) Deformation mode: torsion Measurement frequency: 1 Hz Heating rate: 5°C / min Measurement temperature: -70 to 150°C Shape: parallel plate 8.0 mmφ

[0174] (2) Adhesive Strength: A 25 μm thick polyimide film (trade name "Upilex S," manufactured by UBE Corporation) was attached to a SUS plate via double-sided adhesive tape (trade name "No. 5000NS," manufactured by Nitto Denko Corporation) to obtain a polyimide film substrate for measurement. A 25 mm wide x 100 mm long sample was cut from the pressure-sensitive adhesive sheet obtained in the Examples and Comparative Examples. The release liner was peeled off from the surface, and the adhesive surface was placed on the polyimide film surface of the polyimide film substrate for measurement. The sample was then pressed with a 2 kg roller, rolling back and forth once, to bond the pressure-sensitive adhesive sheet to the polyimide film substrate for measurement, thereby producing a pre-photocuring sample. This pre-photocuring sample was then left to stand for 30 minutes in an environment at 25°C and 50% relative humidity, after which one end of the PET film on the pressure-sensitive adhesive sheet side was held with a chuck, and a 180° peel test was performed at a tensile speed of 300 mm / min in an environment at 25°C and 50% relative humidity to measure the peel strength (adhesive strength before photocuring F ０ After 30 minutes had passed since the bonding, an LED light source with a wavelength of 340 nm was used from the pressure-sensitive adhesive sheet side to measure an integrated light intensity of 20,000 mJ / cm. ２ The photocured sample was subjected to a 180° peel test in the same manner as the uncured sample, and the peel strength (adhesive strength after photocuring F １ From the measured adhesive strength values, the rate of change in adhesive strength before and after photocuring, ΔF (%) = F １ / F ０ × 100 was calculated.

[0175] (3) Processability The cross section of the adhesive sheet was touched with a finger, and evaluation was performed by rating it as "x" if it was adhesive and "o" if it was not adhesive. ０ If the adhesive strength is low, the glue (adhesive) will protrude from the cross section of the adhesive sheet, sticking to other objects and causing contamination, resulting in poor processability.

[0176]

[0177] As shown in Table 1, the pressure-sensitive adhesive sheets of the Examples have excellent processability before photocuring, suppressed increases in elastic modulus before and after photocuring, and improved adhesive strength. Therefore, they were evaluated as having excellent processability before photocuring, excellent flexibility after photocuring, and resistance to peeling at bending points. Furthermore, the adhesive strength before photocuring was low, while the adhesive strength after photocuring was high. The pressure-sensitive adhesive sheets were evaluated as being easily peelable from the adherend before photocuring and capable of firmly adhering to the adherend after photocuring. On the other hand, when the adhesive strength before photocuring was high (Comparative Examples 1 and 2), the pressure-sensitive adhesive sheets were evaluated as being difficult to peel from the adherend before photocuring. In particular, Comparative Example 3 had poor processability before photocuring, and the adhesive sheet underwent cohesive failure in the adhesive strength test before photocuring, resulting in a low adhesive strength F ０ , F １ Furthermore, when ΔG' at 25°C was large (Comparative Examples 3 and 4), the processability was poor before photocuring, and the increase in elastic modulus before and after photocuring was large, resulting in poor flexibility after photocuring and a tendency for peeling to occur at bent portions.

[0178] Variations of the present invention are described below. [Appendix 1] Shear storage modulus (G') at 25°C before photocuring ０（２５） ) versus shear storage modulus (G') at 25°C after photocuring １（２５） ) ratio ΔG' （２５） The 180° peel adhesion strength (F) to polyimide before photocuring under peel conditions of a temperature of 25°C, a relative humidity of 50%, and a pulling rate of 300 mm / min is 200% or less. ０ ) is 0.01 to 1 N / 25 mm, and the 180° peel adhesive strength (F) to polyimide after photocuring is 0.01 to 1 N / 25 mm under peel conditions of a temperature of 25°C, a relative humidity of 50%, and a pulling speed of 300 mm / min. １ [Appendix 2] The shear storage modulus (G') of the pressure-sensitive adhesive composition is greater than 1 N / 25 mm. ０（２５） ) is 20 kPa or more, and the shear storage modulus (G' １（２５）) is 200 kPa or less. [Appendix 3] The pressure-sensitive adhesive composition according to Appendix 1 or 2, comprising the following component (a), component (b), and component (c): component (a) : a polymer (a1) having in its molecule a reversibly decomposable bond that can be cleaved by light irradiation and then recombined, and / or a compound (a2) capable of introducing the reversibly decomposable bond into a polymer component (b): a compound that inhibits the recombination component (c): a compound that reacts and hardens by light irradiation [Appendix 4] The pressure-sensitive adhesive composition according to Appendix 1 or 2, comprising the following component (a), component (b), and component (c): Component (a): a polymer (a1) having a reversibly decomposable bond in its molecule that can be cleaved and subsequently recombined by an external stimulus, and / or a compound (a2) capable of introducing the reversibly decomposable bond into a polymer; Component (b): a compound that inhibits the recombination; and Component (c): a compound that reacts and hardens in response to an external stimulus. [Appendix 5] The pressure-sensitive adhesive composition according to Appendices 3 or 4, wherein the component (a) is an acrylic polymer having the reversibly decomposable bond in its molecule. [Appendix 6] The pressure-sensitive adhesive composition according to any one of Appendices 3 to 5, wherein the component (c) comprises a compound having a polymerizable functional group and a polymerization initiator. [Appendix 7] The pressure-sensitive adhesive composition according to any one of Appendices 3 to 6, wherein the component (c) comprises a polyfunctional (meth)acrylate and a radical polymerization initiator. [Appendix 8] The pressure-sensitive adhesive composition according to any one of Appendices 1 to 7, wherein the pressure-sensitive adhesive composition is for optical use. [Appendix 9] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of Appendices 1 to 8. [Appendix 10] The pressure-sensitive adhesive sheet according to Appendix 9, comprising a substrate and the pressure-sensitive adhesive layer laminated on one surface of the substrate. [Appendix 11] The pressure-sensitive adhesive sheet according to Appendix 9 or 10, which is a reinforcing film for an optical member.

[0179] 10 Pressure-sensitive adhesive sheet 1 Substrate 21 Pressure-sensitive adhesive layer of the present invention 31 Release liner

Claims

1. Shear storage modulus (G') at 25°C before photocuring ０（２５） ) versus shear storage modulus (G') at 25°C after photocuring １（２５） ) ratio ΔG' （２５） The 180° peel adhesion strength (F) to polyimide before photocuring under peel conditions of a temperature of 25°C, a relative humidity of 50%, and a pulling rate of 300 mm / min is 200% or less. ０ ) is 0.01 to 1 N / 25 mm, and the 180° peel adhesive strength (F) to polyimide after photocuring is 0.01 to 1 N / 25 mm under peel conditions of a temperature of 25°C, a relative humidity of 50%, and a pulling speed of 300 mm / min. １ ) is more than 1 N / 25 mm.

2. The shear storage modulus (G' ０（２５） ) is 20 kPa or more, and the shear storage modulus (G' １（２５） 2. The pressure-sensitive adhesive composition according to claim 1, wherein the compressive strength is 200 kPa or less.

3. The pressure-sensitive adhesive composition according to claim 1, comprising the following components (a), (b), and (c): component (a): a polymer (a1) having a reversibly decomposable bond in its molecule that can be cleaved by light irradiation and then recombined, and / or a compound (a2) capable of introducing the reversibly decomposable bond into a polymer; component (b): a compound that inhibits the recombination; and component (c): a compound that reacts and hardens when irradiated with light.

4. A pressure-sensitive adhesive composition comprising the following components (a), (b), and (c): component (a): a polymer (a1) having a reversibly degradable bond in the molecule that can be cleaved by an external stimulus and then rebonded, and / or a compound (a2) capable of introducing the reversibly degradable bond into the polymer; component (b): a compound that inhibits the rebonding; and component (c): a compound that reacts and hardens in response to an external stimulus.

5. The pressure-sensitive adhesive composition according to claim 3 or 4, wherein the component (a) is an acrylic polymer having the reversibly decomposable bond in the molecule.

6. The pressure-sensitive adhesive composition according to claim 3 or 4, wherein the component (c) comprises a compound having a polymerizable functional group and a polymerization initiator.

7. The pressure-sensitive adhesive composition according to claim 3 or 4, wherein the component (c) comprises a polyfunctional (meth)acrylate and a radical polymerization initiator.

8. The pressure-sensitive adhesive composition according to any one of claims 1 to 4, which is used for optical purposes.

9. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 4.

10. The pressure-sensitive adhesive sheet according to claim 9, comprising a substrate and the pressure-sensitive adhesive layer laminated on one surface of the substrate.

11. The pressure-sensitive adhesive sheet according to claim 10, which is a reinforcing film for an optical member.

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