TW202344649A - Optical adhesive sheet - Google Patents

Abstract

This invention provides an optical adhesive sheet suitable for use in flexible devices. An adhesive sheet 10 (optical adhesive sheet) of this invention contains a base polymer having a first glass transition temperature and an oligomer having a second glass transition temperature higher than the first glass transition temperature, and has an adhesive surface 11 and an adhesive surface 12. A component analysis in the thickness direction H from the adhesive surface 12 side to the adhesive surface 11 side is performed by TOF-SIMS method for the adhesive sheet 10 in a state in which a substrate S is adhered to the adhesive surface 11. A detection maximum peak of an ion strength of a first fragment derived from the oligomer is detected between a detection start time of a second fragment derived from the substrate and a detection end time of a third fragment derived from the base polymer after the detection start time. A ratio of the ion strength of the detection maximum peak to the average value of the ion strength of the first fragment is 1.2 or more. The average value of the ion strength of the first fragment refers to the average value from the time deviating from 10 [sigma] to 5 [sigma] from the half-value width [sigma] (sec) of the detection maximum peak toward the analysis start time side.

Description

Optical adhesive sheet

The invention relates to an optical adhesive sheet.

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

On the other hand, for example, a display panel that can be bent repeatedly (folded) is developed for use in smartphones and tablet terminals. Specifically, the foldable display panel can repeatedly deform between a curved shape and a flat, non-curved shape. In this kind of foldable display panel, each component in the stacked structure is made to be foldable repeatedly, and a thinner optical adhesive sheet is used to join the components. An optical adhesive sheet for flexible devices such as foldable display panels is described in the following Patent Document 1, for example. [Prior technical literature] [Patent Document]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2018-111754

[Problem to be solved by the invention]

Optical adhesive sheets for foldable display panels are required to be highly soft in order to have sufficient followability to the adherend when the device is bent and excellent stress relaxation properties. However, the softer the previous optical adhesive sheet, the lower the adhesive force.

On the other hand, regarding the repeatedly bent portions of the foldable display panel, previously, the optical adhesive sheet was easily peeled off from the adherend component. The reason is that when the display panel is bent, stress such as shear stress will locally act on the optical adhesive sheet at the bent portion. Peeling off of the optical adhesive sheet will cause malfunction of the display panel, so it is undesirable. Therefore, optical adhesive sheets for foldable display panels are required to have a high level of adhesion to the adherend.

The present invention provides an optical adhesive sheet suitable for use in flexible devices. [Technical means to solve problems]

The present invention [1] includes an optical adhesive sheet, which includes a base polymer having a first glass transition temperature and an oligomer having a second glass transition temperature higher than the above-mentioned first glass transition temperature, and has a first surface , and the second surface on the opposite side of the first surface, the optical adhesive sheet in the state where the substrate is bonded to the first surface is measured from the second surface side by time-of-flight secondary ion mass spectrometry. In the component analysis in the thickness direction of the first surface side, the maximum detected peak of ion intensity derived from the first fragment of the oligomer starts from the detection of the second fragment derived from the base material. time, and the detection end time of the third fragment derived from the above-mentioned base polymer which is later than the detection start time, and the ionic intensity of the above-mentioned detection maximum peak is relative to the average value of the ionic intensity of the above-mentioned first fragment. When the ratio is 1.2 or more, the average value of the ion intensity of the first fragment is the average value from the time interval 10σ to the time interval 5σ between the half-peak width σ (seconds) of the maximum detected peak and the analysis start time.

The present invention [2] includes the optical adhesive sheet according to the above [1], wherein the oligomer forms an aggregate having a maximum length of 0.4 μm or less.

The present invention [3] includes the optical adhesive sheet according to the above [1] or [2], wherein the second glass transition temperature is 50° C. or higher.

The present invention [4] includes the optical adhesive sheet according to any one of the above [1] to [3], wherein the ratio of the melting temperature (°C) of the above-mentioned oligomer to the above-mentioned second glass transition temperature (°C) is 1.5 or above.

The present invention [5] includes the optical adhesive sheet according to any one of [1] to [4] above, wherein the oligomer has a weight average molecular weight of 2,000 or more.

The present invention [6] includes the optical adhesive sheet according to any one of the above [1] to [5], wherein the sum of the first glass transition temperature and the second glass transition temperature is 0° C. or higher. [Effects of the invention]

As mentioned above, the optical adhesive sheet of the present invention includes a base polymer with a first glass transition temperature, an oligomer with a second glass transition temperature higher than the first glass transition temperature, and an oligomer with a higher glass transition temperature. Object agglomeration exists on and near the surface of the optical adhesive sheet. Specifically, in the time-of-flight secondary ion mass spectrometry (component analysis in the thickness direction from the second surface to the first surface of the optical adhesive sheet with the substrate bonded to the first surface), the source The detected maximum peak P of ion intensity I ₁ from the first fragment of the oligomer is detected later than the detection start time of the second fragment derived from the substrate, and the maximum detected ion intensity I ₁ of the peak P is relatively The ratio to the specific average value of ionic strength I ₁ is more than 1.2, so oligomers with a glass transition temperature higher than that of the base polymer are concentrated on and near the surface of the optical adhesive sheet. This structure is suitable for ensuring the overall softness of the optical adhesive sheet and achieving good adhesion to the adherend on the surface (adhesive surface) of the optical adhesive sheet. If the optical adhesive sheet is soft, it is suitable for ensuring sufficient tracking of the adherend and excellent stress relaxation when the adherend bends. Therefore, it is suitable for realizing flexible devices using optical adhesive sheets. Good repeated deformation. The optical adhesive sheet has high adhesion to the adherend, which is suitable for preventing the optical adhesive sheet from peeling off the adherend due to repeated deformation. Therefore, the optical adhesive sheet of the present invention is suitable for flexible device applications.

As shown in FIG. 1 , the adhesive sheet 10 as one embodiment of the optical adhesive sheet of the present invention has a sheet shape with a specific thickness and expands in a direction (surface direction) orthogonal to the thickness direction. The adhesive sheet 10 has an adhesive surface 11 and an adhesive surface 12 opposite to the adhesive surface 11 . FIG. 1 schematically shows a state where release liners L1 and L2 are bonded to the adhesive surfaces 11 and 12 of the adhesive sheet 10 . The release liner L1 is arranged on the adhesive surface 11 . The release liner L2 is arranged on the adhesive surface 12 . In addition, the adhesive sheet 10 is an optically transparent adhesive sheet arranged at a light-passing portion of the flexible device. An example of the flexible device is a flexible display panel. Examples of flexible display panels include foldable display panels and rollable display panels. The flexible display panel has, for example, a laminated structure including a pixel panel, a film-shaped polarizing plate (polarizing film), a touch panel, a cover film, and other components. The adhesive sheet 10 is used, for example, in the manufacturing process of a flexible display panel to join components included in the stacked structure to each other. The release liners L1 and L2 are respectively released at specific points when the adhesive sheet 10 is used.

The adhesive sheet 10 is formed from an adhesive composition. The adhesive composition includes base polymers and oligomers. That is, the adhesive sheet 10 contains a base polymer and a first oligomer. The base polymer has a glass transition temperature Tg ₁ (first glass transition temperature) (when the base polymer has a cross-linked structure, the glass transition temperature Tg ₁ is the glass transition temperature of the base polymer having the cross-linked structure). The oligomer has a glass transition temperature Tg ₂ (second glass transition temperature) higher than the glass transition temperature Tg ₁ . The methods for measuring the glass transition temperatures Tg ₁ and Tg ₂ are as described in the examples below.

The adhesive sheet 10 is an adhesive sheet in which a base material is bonded to one side (the first side of one of the adhesive surfaces 11 and 12). Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS: Time-of-Flight Secondary Ion Mass Spectrometry) is used to perform component analysis in the thickness direction H from the second surface (the other of the adhesive surfaces 11 and 12) side to the first surface side. , in this component analysis, the following measurement results are shown.

The detected maximum peak P of ionic strength I ₁ derived from the first fragment of the oligomer is between the detection start time of the second fragment derived from the base material and the detection start time of the second fragment derived from the base polymer which is later than the detection start time. Detected between the detection end time of the third segment. The ratio (I ₁ /I ₂ ) of the detected ion intensity I ₁ of the maximum peak P to the average value of the ion intensity I ₁ of the first fragment (average ion intensity I ₂ ) is 1.2 or more, and the ion intensity of the first fragment is The average value of I ₁ refers to the average value from the time 10σ apart from the half-peak width σ (seconds) of the maximum detected peak P to the time 5σ apart from the analysis start time.

FIG. 2 schematically shows the measurement results of the adhesive sheet 10 measured by TOF-SIMS. FIG. 3 is an enlarged view of part of the measurement results shown in FIG. 2 . In the graphs shown in Figures 2 and 3, the horizontal axis represents analysis time (seconds), and the vertical axis represents normalized ion intensity. In Figures 2 and 3, the solid line represents the change in ionic strength derived from the first segment of the oligomer, the single-point chain line represents the change in ionic strength derived from the second segment of the substrate, and the two-point chain line represents The line represents the change in ionic strength originating from segment 3 of the base polymer. The intensity of the ionic strength of a particular fragment corresponds to the amount of the component that has that fragment. The detection time of the ion intensity of a specific fragment corresponds to the position where the component containing the fragment exists in the thickness direction of the adhesive sheet (the depth direction from the second surface side). As shown in Figures 2 and 3, in the adhesive sheet 10, the detection time _t1 of the maximum peak P of the ionic strength derived from the first fragment of the oligomer is between the second fragment derived from the polyimide base material. Between the detection start time t ₂ (the detection amount start time of the second segment) and the detection end time t ₃ of the third segment derived from the base polymer (later than the detection start time t ₂ ) (t ₂ < t ₁ < t ₃ ). This means that the amount of oligomers having the first segment is greater on the first surface of the adhesive sheet 10 and its vicinity than in other areas. In addition, in the adhesive sheet 10, the ratio (I ₁ /I ₂ ) of the ion intensity I ₁ of the maximum detected peak P to the average ion intensity I ₂ of the first segment is 1.2 or more (the average ion intensity I ₂ refers to The half-peak width σ (seconds) of the maximum detected peak P is the average value of the ion intensity I ₁ of the first segment from the time 10σ apart to the time 5σ apart from the analysis start time; the half-peak width σ refers to the maximum peak detected P is the half-maximum half-width of the analysis start time side). This means that the amount of oligomers having the first segment is significantly greater on the first surface of the adhesive sheet 10 and its vicinity than in other areas.

In TOF-SIMS, ions (secondary ions) are released from the sample surface by irradiating the sample with an ion beam (primary ions), and the flight time (proportional to the square root of the mass) of the secondary ions until they reach the detector is used. ) to separate the quality. Thereby, the mass spectrum of secondary ions is obtained. That is, component analysis of the sample surface can be performed. In TOF-SIMS, changes in the mass spectrum in the thickness direction can be detected by alternately repeating irradiation of the sample with an ion beam for etching and then irradiation with an ion beam for measurement (primary ion beam). That is, component analysis in the thickness direction of the sample can be performed. The method of TOF-SIMS is specifically described in the examples below.

As mentioned above, the adhesive sheet 10 includes a base polymer with a glass transition temperature Tg ₁ and an oligomer with a glass transition temperature Tg ₂ higher than the glass transition temperature Tg _1. The oligomers with a higher glass transition temperature are concentrated. Exists on the surface of the adhesive sheet 10 and its vicinity. Specifically, in TOF-SIMS (composition analysis in the thickness direction H from the second surface to the first surface of the adhesive sheet 10 in a state where the base material is bonded to the first surface), the oligomer-derived The maximum detected peak P of the ion intensity I ₁ of the first fragment is detected later than the detection start time of the second fragment derived from the substrate, and the maximum detected ion intensity I ₁ of the maximum peak P is relative to the above ion The ratio of the average strength I ₂ (I ₁ /I ₂ ) is 1.2 or more, so oligomers with a glass transition temperature higher than that of the base polymer are concentrated on the surface of the adhesive sheet 10 and in its vicinity. This structure is suitable for ensuring the overall softness of the adhesive sheet 10 and achieving good adhesion to the adherend on the surface (adhesive surface) of the adhesive sheet 10 . If the adhesive sheet 10 is soft, it is suitable for the adhesive sheet 10 to ensure sufficient tracking of the adherend when the adherend bends and excellent stress relaxation properties. Therefore, it is suitable for realizing flexible devices using the adhesive sheet 10. Good repeated deformation. The adhesive force of the adhesive sheet 10 to the adherend is relatively high, which is suitable for preventing the adhesive sheet 10 from peeling off from the adherend that undergoes repeated deformation. Therefore, the adhesive sheet 10 is suitable for flexible device applications.

An example of a method for causing the oligomers to be concentrated on the surface of the adhesive sheet 10 and in its vicinity is to adjust the compatibility of the oligomers with the base polymer (to adjust the compatibility to a certain level). range), and adjust the molecular weight of the oligomer (adjust the ease of movement of the oligomer). As an indicator of the compatibility of the oligomers with respect to the base polymer, the Hansen solubility parameter (HSP value) can be used, for example. The HSP value is represented by the following formula (1).

HSP value = (δD ² + δP ² + δH ² ) ^1/2

In the above formula, δD represents a dispersion term of energy derived from the dispersion force between molecules. δP is a polarization term representing energy derived from polar forces between molecules. δH is a hydrogen bond term representing energy derived from hydrogen bonding force between molecules. Substances with similar HSP values are known to exhibit similar physical properties to each other. The HSP value is described in, for example, "Chemical Industry Society, Chemical Industry, March 2010 issue, Hiroshi Yamamoto, Steven Abbott, Charles M. Hansen".

Regarding the ratio (I ₁ /I ₂ ), from the viewpoint of ensuring good adhesion in the adhesive sheet 10, it is preferably 1.4 or more, more preferably 1.6 or more, and still more preferably 1.7 or more. The ratio (I ₁ /I ₂ ) is, for example, 5 or less, 3.5 or less, or 2.7 or less.

On the surface of the adhesive sheet 10 and its vicinity, from the viewpoint of ensuring the cohesion of the adhesive surfaces 11 and 12, it is preferable that oligomers form aggregates (crystalline domains). The maximum length of the oligomer aggregate is preferably 0.05 μm or more, and more preferably 0.1 μm or more. From the viewpoint of high dispersion of oligomers, the maximum length of oligomer aggregates is preferably 0.4 μm or less, more preferably 0.3 μm or less, further preferably 0.2 μm or less. The method for measuring the size of oligomer aggregates is specifically described in the Examples below.

The glass transition temperature Tg ₂ of the oligomer is preferably 50°C or higher, more preferably 60°C or higher, and still more preferably from the viewpoint of high adhesion on the surface of the adhesive sheet 10 (adhesive surfaces 11 and 12 ). It is 70°C or higher, and preferably 130°C or lower, more preferably 120°C or lower, still more preferably 110°C or lower.

Regarding the ratio (Tm/Tg ₂ ) of the melting temperature Tm (°C) of the oligomer to the glass transition temperature Tg ₂ (°C), the viewpoint of high adhesion on the surface of the adhesive sheet 10 (adhesive surfaces 11 and 12 ) is Specifically, it is preferably 1.5 or more, more preferably 1.6 or more, and it is preferably 3 or less, more preferably 2.5 or less, and still more preferably 2 or less. The method for measuring the melting temperature Tm of the oligomer is specifically described in the Examples below.

The weight average molecular weight Mw of the oligomer is preferably 2,000 or more, more preferably 2,500 or more, and still more preferably 3,000 or more from the viewpoint of high adhesion on the surface of the adhesive sheet 10 (adhesive surfaces 11, 12). , more preferably 3,500 or more, particularly preferably 4,000 or more. From the viewpoint of the segregation of the oligomer on the surface of the adhesive sheet 10 and its vicinity (mobility to the surface), the weight average molecular weight Mw of the oligomer is preferably 30,000 or less, more preferably 15,000 or less. More preferably, it is 10,000 or less. The method for measuring the weight average molecular weight Mw of the oligomer is specifically described in the Examples below.

The sum of the glass transition temperature Tg ₁ and the glass transition temperature Tg ₂ is preferably 0°C or higher, and more preferably 10°C or higher from the viewpoint of high adhesion on the surface of the adhesive sheet 10 (adhesive surfaces 11 and 12 ). , more preferably 20°C or more, more preferably 100°C or less, more preferably 80°C or less, still more preferably 60°C or less.

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

The acrylic polymer is a copolymer containing a monomer component of (meth)acrylate in a ratio of 50% by mass or more. "(Meth)acrylic" means acrylic acid and/or methacrylic acid.

As the (meth)acrylate, a (meth)acrylic acid alkyl ester is preferably used, and a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 20 carbon atoms is more preferably used. The alkyl (meth)acrylate may have a linear or branched alkyl group, or may have a cyclic alkyl group such as an alicyclic alkyl group.

Examples of the (meth)acrylic acid alkyl ester having a linear or branched alkyl group include: (meth)acrylic acid methyl ester, (meth)acrylic acid ethyl ester, (meth)acrylic acid n-butyl ester Ester, isobutyl (meth)acrylate, second butyl (meth)acrylate, third butyl (meth)acrylate, amyl (meth)acrylate, isopentyl (meth)acrylate, (meth)acrylate Neopentyl acrylate, n-hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, iso(meth)acrylate Octyl ester, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, (meth)acrylate (Basic) dodecyl acrylate (i.e. lauryl (meth)acrylate), isotridecyl (meth)acrylate, myristyl (meth)acrylate, isotetradecyl (meth)acrylate Alkyl ester, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, (meth) Isostearyl acrylate, and nonadecyl (meth)acrylate.

Examples of the (meth)acrylic acid alkyl ester having an alicyclic alkyl group include: (meth)acrylic acid cycloalkyl ester, (meth)acrylic acid ester having a bicyclic aliphatic hydrocarbon ring, and (meth)acrylic acid ester having a bicyclic aliphatic hydrocarbon ring. (Meth)acrylate with more than three rings of aliphatic hydrocarbon ring. Examples of (meth)acrylic acid cycloalkyl esters include: (meth)acrylic acid cyclopentyl ester, (meth)acrylic acid cyclohexyl ester, (meth)acrylic acid cycloheptyl ester, and (meth)acrylic acid cycloalkyl ester. Octyl ester. Examples of the (meth)acrylate having a bicyclic aliphatic hydrocarbon ring include iso(meth)acrylate. Examples of the (meth)acrylate having an aliphatic hydrocarbon ring with three or more rings include: (meth)acrylic acid dicyclopentyl, (meth)acrylic acid dicyclopentoxyethyl, (meth)acrylic acid tricyclic Cyclopentyl ester, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate .

As the alkyl (meth)acrylate, from the viewpoint of balancing the softness and adhesive force required for an adhesive sheet for flexible device applications in the adhesive sheet 10, it is preferable to use an adhesive sheet having a carbon number of 3. At least one alkyl (meth)acrylate with an alkyl group having ∼12 carbon atoms, more preferably, one selected from alkyl (meth)acrylates having an alkyl group with 3 to 12 carbon atoms. At least one first (meth)acrylic acid alkyl ester having a relatively large number of carbon atoms and at least one second (meth)acrylic acid alkyl ester having a relatively small carbon number in the alkyl group are used in combination. The first alkyl (meth)acrylate is preferably at least one selected from the group consisting of 2-ethylhexyl acrylate (2EHA) and lauryl acrylate (LA). The second alkyl (meth)acrylate is preferably n-butyl acrylate.

The ratio of alkyl (meth)acrylate in the monomer component is preferably 50 mass % or more, and more preferably 70 mass % from the viewpoint of appropriately expressing basic characteristics such as adhesiveness in the adhesive sheet 10 % or more, and more preferably 90 mass% or more. The above ratio is, for example, 99% by mass or less. When the first and second alkyl (meth)acrylates are used together, from the viewpoint of the balance between softness and adhesive force of the adhesive sheet 10, the first alkyl (meth)acrylate among the monomer components The ratio of the base ester is preferably 50 mass% or more, more preferably 60 mass% or more, further preferably 70 mass% or more, and further preferably 85 mass% or less, more preferably 80 mass% or less. From the viewpoint of the balance between softness and adhesive force of the adhesive sheet 10, the ratio of the second alkyl (meth)acrylate in the monomer component is preferably 10 mass% or more, more preferably 15 mass% or more. , more preferably 20 mass% or more, more preferably 30 mass% or less, more preferably 25 mass% or less.

The monomer component may also include a copolymerizable monomer capable of being copolymerized with alkyl (meth)acrylate. Examples of the copolymerizable monomer include monomers having a polar group. Examples of the polar group-containing monomer include a hydroxyl group-containing monomer, a carboxyl group-containing monomer, and a monomer having a nitrogen atom-containing ring. Monomers containing polar groups help to modify the acrylic polymer, such as introducing cross-linking points into the acrylic polymer and ensuring the cohesion of the acrylic polymer.

Examples of the hydroxyl-containing monomer include: (meth)acrylic acid 2-hydroxyethyl ester, (meth)acrylic acid 2-hydroxypropyl ester, (meth)acrylic acid 2-hydroxybutyl ester, (meth)acrylic acid 3-hydroxypropyl ester, 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. As the hydroxyl group-containing monomer, it is preferable to use at least one selected from the group consisting of 2-hydroxyethyl (meth)acrylate and 2-hydroxybutyl (meth)acrylate.

The ratio of the hydroxyl-containing monomer in the monomer component is preferably 0.2% by mass or more, and more preferably 0.2% by mass or more, from the viewpoint of introducing a cross-linked structure into the acrylic polymer and ensuring the cohesion of the adhesive sheet 10 0.5% by mass or more, more preferably 1% by mass or more. From the viewpoint of adjusting the polarity of the acrylic polymer (the compatibility of various additive components in the adhesive sheet 10 with the acrylic polymer), the above ratio is preferably 10 mass % or less, more preferably 5 mass % or less. .

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

The ratio of the carboxyl group-containing monomer in the monomer component is from the perspective of introducing a cross-linked structure into the acrylic polymer, ensuring the cohesion of the adhesive sheet 10, and ensuring the adhesion of the adhesive sheet 10 to the adherend. , preferably 0.1 mass% or more, more preferably 0.5 mass% or more, further preferably 0.8 mass% or more. From the viewpoint of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend due to acid, the above ratio is preferably 10 mass% or less, more preferably 5 mass% or less.

Examples of the monomer having a nitrogen-containing ring include: N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinyl pyrimidine, N-vinyl piperazole, N-vinyl pyrrole, N-vinyl pyrrole, N-vinylimidazole, N-vinyl 㗁azole, N-(meth)acrylyl-2 -pyrrolidinone, N-(meth)acrylylpiperidine, N-(meth)acrylylpyrrolidine, N-vinyl𠰌line, N-vinyl-3-𠰌linone, N-ethylene Acetyl-2-caprolactamide, N-vinyl-1,3-㗁𠯤-2-one, N-vinyl-3,5-𠰌lindione, N-vinylpyrazole, N-vinyl Isothiazole, N-vinylthiazole, and N-vinylisothiazole. As the monomer having a nitrogen atom-containing ring, N-vinyl-2-pyrrolidone is preferably used.

The ratio of the monomer having a nitrogen-containing ring among the monomer components is preferably 0.1 mass % or more from the viewpoint of ensuring the cohesive force of the adhesive sheet 10 and ensuring the adhesive force of the adhesive sheet 10 to the adherend. , more preferably 0.5% by mass or more, further preferably 0.8% by mass or more. From the viewpoint of adjusting the glass transition temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (the compatibility of various additive components in the adhesive sheet 10 with the acrylic polymer), the above ratio is preferably 10 mass% or less, more preferably 5 mass% or less.

The monomer component may also include other copolymerizable monomers. Examples of other copolymerizable monomers include acid anhydride monomers, sulfonic acid group-containing monomers, phosphate group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, and alkoxy group-containing monomers. monomers, and aromatic vinyl compounds. These other copolymerizable monomers may be used alone, or two or more types may be used in combination.

The base polymer preferably has a cross-linked structure. An example of a method for introducing a cross-linked structure into a base polymer is as follows: a base polymer having a functional group capable of reacting with a cross-linking agent, and a cross-linking agent are blended into an adhesive composition, and the base polymer is polymerized. The reaction between the substance and the cross-linking agent in the adhesive sheet (first method); and the monomer component forming the base polymer contains a multi-functional monomer as a cross-linking agent, and the monomer component is polymerized to form a A base polymer having a branched structure (cross-linked structure) is introduced into the polymer chain (second method). These methods can also be used together.

Examples of the crosslinking agent used in the first method include compounds that react with functional groups (hydroxyl groups, carboxyl groups, etc.) contained in the base polymer. Examples of such cross-linking agents include isocyanate cross-linking agents, peroxide cross-linking agents, epoxy cross-linking agents, azoline cross-linking agents, aziridine cross-linking agents, and carbodiimide cross-linking agents. linking agent, and metal chelate cross-linking agent. The cross-linking agent may be used alone, or two or more types may be used in combination. As the cross-linking agent, in terms of its high reactivity with the hydroxyl and carboxyl groups in the base polymer and the ease of introducing a cross-linked structure, isocyanate cross-linking agents, peroxide cross-linking agents, and epoxy cross-linking agents are preferably used. Cross-linking agent.

Examples of the isocyanate cross-linking agent include toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, and diphenylmethane diisocyanate. , hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate. Furthermore, examples of the isocyanate cross-linking agent include derivatives of these isocyanates. Examples of the isocyanate derivative include isocyanurate modified products and polyol modified products. Examples of commercially available isocyanate crosslinking agents include Coronate L (trimethylolpropane adduct of toluene diisocyanate, manufactured by Tosoh), Coronate HL (trimethylolpropane of hexamethylene diisocyanate). Adduct, manufactured by Tosoh), Coronate HX (isocyanurate form of hexamethylene diisocyanate, manufactured by Tosoh), Takenate D110N (trimethylolpropane adduct of xylylene diisocyanate, Mitsui Chemicals Manufactured by Mitsui Chemicals Co., Ltd.), and Takenate 600 (1,3-bis(isocyanatomethyl)cyclohexane, manufactured by Mitsui Chemicals Co., Ltd.).

Examples of peroxide cross-linking agents include dibenzoyl peroxide, di(2-ethylhexyl)peroxydicarbonate, di(4-tert-butylcyclohexyl)peroxydicarbonate, Di-second-butyl peroxydicarbonate, tert-butyl peroxyneodecanoate, tert-hexyl peroxypivalate, and tert-butyl peroxypivalate.

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

As for the compounding amount of the cross-linking agent in the first method, from the viewpoint of ensuring the cohesion of the adhesive sheet 10, it is, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, based on 100 parts by mass of the base polymer. More preferably, it is 0.1 part by mass or more. From the viewpoint of ensuring good tackiness in the adhesive sheet 10, the compounding amount of the cross-linking agent is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, and more preferably 100 parts by mass or less based on 100 parts by mass of the base polymer. 3 parts by mass or less.

In the above-mentioned second method, the monomer components (including polyfunctional monomers and other monomers used to introduce a cross-linked structure) can be polymerized in one go or in multiple stages. In the multi-stage polymerization method, first, the monofunctional monomers used to form the base polymer are polymerized (prepolymerization), thereby preparing a polymer containing part of the polymer (a mixture of polymers with a low degree of polymerization and unreacted monomers). Prepolymer composition. Next, after adding a polyfunctional monomer as a crosslinking agent to the prepolymer composition, a part of the polymer and the polyfunctional monomer are polymerized (main polymerization).

Examples of the polyfunctional monomer include polyfunctional (meth)acrylates containing two or more ethylenically unsaturated double bonds in one molecule. As a polyfunctional monomer, a polyfunctional acrylate is preferable from the viewpoint that a crosslinked structure can be introduced by active energy ray polymerization (photopolymerization).

Examples of polyfunctional (meth)acrylates include difunctional (meth)acrylates, trifunctional (meth)acrylates, and polyfunctional (meth)acrylates having four or more functions.

Examples of the difunctional (meth)acrylate include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate. Tetraethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerol di(meth)acrylate , neopentyl glycol di(meth)acrylate, stearic acid modified pentaerythritol di(meth)acrylate, dicyclopentenyl di(meth)acrylate, isocyanuric acid di(meth)acrylate ester, and alkylene oxide modified bisphenol di(meth)acrylate.

Examples of the trifunctional (meth)acrylate include: trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and isocyanuric acid tris(acryloyloxyethyl) ester.

Examples of the polyfunctional (meth)acrylate having four or more functions include di-trimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol monohydroxypenta(meth)acrylate. acrylate, alkyl-modified dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

As the polyfunctional (meth)acrylate, a polyfunctional (meth)acrylate having four or more functions is preferably used, and dipentaerythritol hexaacrylate is more preferably used.

As for the compounding amount of the polyfunctional monomer as the cross-linking agent in the second method among the monomer components, from the viewpoint of ensuring the cohesion of the adhesive sheet 10, it is, for example, 0.01 parts by mass relative to 100 parts by mass of the monofunctional monomer. Parts by mass or more, preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more. From the viewpoint of ensuring good tackiness in the adhesive sheet 10, the blending amount of the polyfunctional monomer is, for example, 10 parts by mass or less, preferably 3 parts by mass or less, relative to 100 parts by mass of the monofunctional monomer. It is preferably 1 part by mass or less, more preferably 0.5 part by mass or less, still more preferably 0.2 part by mass or less, and particularly preferably 0.1 part by mass or less.

The acrylic polymer can be formed by polymerizing the above-mentioned monomer components. Examples of the polymerization method include solution polymerization, solvent-free photopolymerization (for example, UV (Ultraviolet, ultraviolet) polymerization), block polymerization, and emulsion polymerization. As a solvent for solution polymerization, ethyl acetate and toluene can be used, for example. Moreover, as a polymerization initiator, for example, a thermal polymerization initiator and a photopolymerization initiator can be used. The polymerization initiator may be used alone, or two or more types may be used in combination. The usage amount of the polymerization initiator is preferably 0.05 parts by mass or more, more preferably 0.08 parts by mass or more, further preferably 0.1 parts by mass or more, and more preferably 1 part by mass, based on 100 parts by mass of the monomer component. parts or less, more preferably 0.5 parts by mass or less, still more preferably 0.3 parts by mass or less.

Examples of the thermal polymerization initiator include azo polymerization initiators and peroxide polymerization initiators. Examples of the azo polymerization initiator include: 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis( 2-Methylpropionic acid) dimethyl ester, 4,4'-azobis-4-cyanovaleric acid, azobisisovaleronitrile, 2,2'-azobis(2-amidinopropane)bis Hydrochloride, 2,2'-Azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride, 2,2'-Azobis(2-methyl propionamidine) disulfate, and 2,2'-azobis(N,N'-dimethyleneisobutylamidine) dihydrochloride. Examples of the peroxide polymerization initiator include dibenzoyl peroxide, tert-butyl peroxymaleate, and lauryl peroxide.

Examples of the photopolymerization initiator include: benzoin ether-based photopolymerization initiator, acetophenone-based photopolymerization initiator, α-ketool-based photopolymerization initiator, and aromatic sulfonyl chloride-based photopolymerization initiator. Initiator, photoactive oxime-based photopolymerization initiator, benzoin-based photopolymerization initiator, benzyl-based photopolymerization initiator, benzophenone-based photopolymerization initiator, ketal-based photopolymerization initiator , 9-oxysulfur𠮿 It is a photopolymerization initiator and a phosphine oxide-based photopolymerization initiator.

The weight average molecular weight of the base polymer is preferably 500,000 or more, more preferably 800,000 or more, further preferably 1,000,000 or more, and still more preferably 1,500,000, from the viewpoint of ensuring the cohesion of the adhesive sheet 10 above. The weight average molecular weight of the base polymer is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene.

The glass transition temperature Tg ₁ of the base polymer is preferably 0°C or lower, more preferably -20°C or lower, and further preferably -40°C or lower from the viewpoint of ensuring sufficient softness in the adhesive sheet 10 , further preferably below -45°C. The glass transition temperature Tg ₁ is, for example, -80°C or higher.

Regarding the glass transition temperature of the base polymer, the glass transition temperature (theoretical value) calculated based on the following Fox formula can be used. Fox's formula is a relationship between the glass transition temperature Tg of a polymer and the glass transition temperature Tgi of the homopolymer of the monomers constituting the polymer. In the following Fox formula, Tg represents the glass transition temperature (℃) of the polymer, Wi represents the weight fraction of the monomer i that constitutes the polymer, and Tgi represents the glass transition temperature of the homopolymer formed from the monomer i. (°C). Literature values can be used for the glass transition temperature of homopolymers. For example, in "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) and "New Polymer Library 7: Introduction to Synthetic Resins for Coatings" (authored by Kyozo Kitaoka, Polymer Publishing Association , 1995) gives examples of the glass transition temperatures of various homopolymers. On the other hand, the glass transition temperature of the homopolymer of the monomer can also be determined by the method specifically described in Japanese Patent Application Laid-Open No. 2007-51271.

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

When an acrylic polymer is used as the base polymer, the oligomer is preferably an acrylic oligomer. The acrylic oligomer is a copolymer containing a monomer component of alkyl (meth)acrylate at a ratio of 50 mass % or more, and its weight average molecular weight is, for example, 1,000 to 30,000.

The acrylic oligomer is preferably a polymer of a monomer component including (meth)acrylic acid alkyl ester having a chain alkyl group ((meth)acrylic acid chain alkyl ester), and Alkyl (meth)acrylate having an alicyclic alkyl group (alicyclic alkyl (meth)acrylate). Specific examples of the (meth)acrylic acid alkyl esters include the above-mentioned (meth)acrylic acid alkyl esters described above as monomer components of the acrylic polymer.

As the chain alkyl (meth)acrylate, methyl methacrylate is preferable in that the glass transition temperature is relatively high and the compatibility with the base polymer is relatively high. As the alicyclic alkyl (meth)acrylate, preferred are dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate. That is, the acrylic oligomer is preferably a polymer of a monomer component selected from the group consisting of dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate. One or more of the group consisting of methyl methacrylate.

The ratio of alicyclic alkyl (meth)acrylate in the monomer component of the acrylic oligomer is preferably 10 mass% or more, more preferably 20 mass% or more, and still more preferably 30 mass% or more , preferably more than 35% by mass. The above ratio is preferably 90 mass% or less, more preferably 80 mass% or less, further preferably 70 mass% or less, particularly preferably 65 mass% or less. The ratio of the (meth)acrylic acid chain alkyl ester in the monomer component of the acrylic oligomer is preferably 90 mass% or less, more preferably 80 mass% or less, and still more preferably 70 mass% or less. The above-mentioned ratio is preferably 10 mass% or more, more preferably 20 mass% or more, and still more preferably 30 mass% or more.

The acrylic oligomer is obtained by polymerizing the monomer component of the acrylic oligomer. Examples of the polymerization method include solution polymerization, active energy ray polymerization (for example, UV polymerization), block polymerization, and emulsion polymerization. In the polymerization of acrylic oligomers, a polymerization initiator may be used, and a chain transfer agent may be used to adjust the molecular weight.

Regarding the content of the acrylic oligomer in the adhesive sheet 10, in order to fully improve the adhesive force of the adhesive sheet 10, it is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, based on 100 parts by mass of the base polymer. Furthermore, it is more preferable that it is 0.3 parts by mass or more, and particularly preferably it is 0.4 parts by mass or more. On the other hand, from the viewpoint of ensuring the transparency of the adhesive sheet 10, the content of the acrylic oligomer in the adhesive sheet 10 is preferably 5 parts by mass or less, more preferably 4 parts by mass, based on 100 parts by mass of the base polymer. Parts by mass or less, more preferably 3 parts by mass or less. In the adhesive sheet 10, when the content of the acrylic oligomer is too large, the haze tends to increase and the transparency tends to decrease because the compatibility of the acrylic oligomer decreases.

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

The adhesive composition may also contain other ingredients if necessary. Examples of other components include solvents, tackifiers, plasticizers, softeners, antioxidants, fillers, colorants, ultraviolet absorbers, surfactants, and antistatic agents. Examples of the solvent include a polymerization solvent used if necessary when polymerizing an acrylic polymer, and a solvent added to a polymerization reaction solution after polymerization. As the solvent, for example, ethyl acetate and toluene can be used.

The adhesive sheet 10 can be produced, for example, by applying the adhesive composition to the release liner L1 (first release liner) to form a coating film, and then drying the coating film.

Examples of the release liner L1 include a flexible plastic film. Examples of the plastic film include polyethylene terephthalate film, polyethylene film, polypropylene film, and polyester film. The thickness of the release liner L1 is, for example, 3 μm or more, and may be, for example, 200 μm or less. The surface of the release liner L1 is preferably subjected to a release treatment.

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

A release liner L2 (second release liner) may be further laminated on the adhesive sheet 10 on the release liner L1. The release liner L2 is preferably a flexible plastic film whose surface has been released. As the release liner L2, the plastic film described above with respect to the release liner L1 can be used.

In the above manner, the adhesive sheet 10 can be manufactured by covering and protecting the adhesive surfaces 11 and 12 with the release liners L1 and L2.

The thickness of the adhesive sheet 10 is preferably 10 μm or more, more preferably 15 μm or more, from the viewpoint of ensuring sufficient adhesion to the adherend and handleability. From the viewpoint of thinning the flexible device, the thickness of the adhesive sheet 10 is preferably 300 μm or less, more preferably 200 μm or less, further preferably 100 μm or less, particularly preferably 50 μm or less.

The haze of the adhesive sheet 10 is preferably 3% or less, more preferably 2% or less, further preferably 1% or less. The haze of the adhesive sheet 10 can be measured using a haze meter in accordance with JIS K7136 (2000). Examples of the haze meter include "NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd. and "HM-150 type" manufactured by Murakami Color Technology Research Institute Co., Ltd.

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

4A to 4C illustrate an example of how to use the adhesive sheet 10 .

In this method, first, as shown in FIG. 4A , the adhesive sheet 10 is bonded to one surface in the thickness direction H of the first member 21 (adherent). The first member 21 is, for example, one element in the multilayer structure of the flexible display panel. Examples of this element include a pixel panel, a film-shaped polarizing plate (polarizing film), a touch panel, and a cover film (the same applies to the second member 22 described below). Through this step, the adhesive sheet 10 for joining with another member (the second member 22 described below) is provided on the first member 21 .

Then, as shown in FIG. 4B , one side of the first member 21 in the thickness direction H is joined to the other side of the second member 22 in the thickness direction H through the adhesive sheet 10 on the first member 21 . The second member 22 is, for example, another element in the multilayer structure of the flexible display panel.

Then, as shown in FIG. 4C , the adhesive sheet 10 between the first member 21 and the second member 22 is aged. By aging, the cross-linking reaction of the base polymer proceeds in the adhesive sheet 10, thereby improving the bonding strength between the first member 21 and the second member 22. The aging temperature is, for example, 20°C to 160°C. The aging time ranges from 1 minute to 21 days, for example. When performing autoclave treatment (heating and pressure treatment) as aging, the temperature is, for example, 30°C to 80°C, the pressure is, for example, 0.1 to 0.8 MPa, and the treatment time is, for example, 15 minutes or more.

As mentioned above, the adhesive sheet 10 includes a base polymer with a glass transition temperature Tg ₁ and an oligomer with a glass transition temperature Tg ₂ higher than the glass transition temperature Tg ₁ , and the oligomer with a higher glass transition temperature is partial. The collection exists on the surface of the adhesive sheet 10 and its vicinity. This adhesive sheet 10 is suitable for use in flexible devices as described above. [Example]

Hereinafter, an Example is shown and this invention is demonstrated concretely. However, the present invention is not limited to the examples. In addition, the specific numerical values of the blending amount (content), physical property values, parameters, etc. described below can be replaced by the corresponding upper limits of the blending amount (content), physical property values, parameters, etc. described in the above "Embodiments" ( A value defined as "below" or "under") or a lower limit (a value defined as "above" or "exceeds").

<Preparation of acrylic polymer> In a reaction vessel equipped with a mixer, a thermometer, a reflux condenser, and a nitrogen introduction pipe, 68 parts by mass of 2-ethylhexyl acrylate (2EHA) and 10 parts of lauryl acrylate (LA) were placed 20 parts by mass of n-butyl acrylate (BA), 1 part by mass of 4-hydroxybutyl acrylate (4HBA), 1 part by mass of N-vinyl-2-pyrrolidone (NVP), as a thermal polymerization initiator A mixture of 0.1 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) and ethyl acetate as a solvent (solid content concentration 47% by mass) was stirred at 56°C for 6 hours in a nitrogen atmosphere (polymerization reaction). Thereby, a polymer solution containing an acrylic polymer is obtained. The weight average molecular weight (Mw) of the acrylic polymer in the polymer solution is about 2 million. The glass transition temperature (first glass transition temperature Tg ₁ ) of the acrylic polymer is -46.4°C. The solid content concentration of the mixture is adjusted by adjusting the amount of solvent.

<Preparation of acrylic oligomer M1> First, in a reaction container equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen introduction pipe, 60 parts by mass of dicyclopentyl methacrylate (DCPMA), methyl methacrylate 40 parts by mass of ester (MMA), 9 parts by mass of α-thioglycerol as a chain transfer agent, 0.3 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and as a solvent The mixture of ethyl acetate (solid content concentration: 26% by mass) was reacted at 70°C for 2 hours in a nitrogen atmosphere, and then reacted at 80°C for 3 hours (polymerization reaction). Next, the reaction solution was heated at 130° C. for 2 hours to volatilize and remove the ethyl acetate, chain transfer agent, and unreacted monomer. Thereby, a solid acrylic oligomer M1 (dry solid) which is a hydrophobic oligomer without a polar group is obtained. The weight average molecular weight (Mw) of the acrylic oligomer M1 is 2,500. The glass transition temperature (second glass transition temperature Tg ₂ ) of the acrylic oligomer M1 is 61°C. The melting temperature Tm of the acrylic oligomer M1 is 120°C.

<Preparation of acrylic oligomer M2> The same operation as acrylic oligomer M1 was carried out except that the amount of chain transfer agent (α-thioglycerol) added in the polymerization reaction was changed from 9 parts by mass to 6 parts by mass. An acrylic oligomer M2 with a weight average molecular weight of 3600 was obtained. The glass transition temperature (second glass transition temperature Tg ₂ ) of the acrylic oligomer M2 is 73°C. The melting temperature Tm of the acrylic oligomer M2 is 130°C.

<Preparation of acrylic oligomer M3> The same operation as acrylic oligomer M1 was performed except that the amount of chain transfer agent (α-thioglycerol) added in the polymerization reaction was changed from 9 parts by mass to 3 parts by mass. An acrylic oligomer M3 with a weight average molecular weight of 6400 was obtained. The glass transition temperature (second glass transition temperature Tg ₂ ) of the acrylic oligomer M3 is 89°C. The melting temperature Tm of the acrylic oligomer M3 is 150°C.

<Preparation of acrylic oligomer M4> The same operation as acrylic oligomer M1 was carried out except that the amount of chain transfer agent (α-thioglycerol) added in the polymerization reaction was changed from 9 parts by mass to 2 parts by mass. An acrylic oligomer M4 with a weight average molecular weight of 8100 was obtained. The glass transition temperature (second glass transition temperature Tg ₂ ) of the acrylic oligomer M4 is 92°C. The melting temperature Tm of the acrylic oligomer M4 is 150°C.

<Preparation of acrylic oligomer M5> The same operation as acrylic oligomer M1 was performed except that the amount of chain transfer agent (α-thioglycerol) added in the polymerization reaction was changed from 9 parts by mass to 1 part by mass. An acrylic oligomer M5 with a weight average molecular weight of 17,000 was obtained. The glass transition temperature (second glass transition temperature Tg ₂ ) of the acrylic oligomer M5 is 100°C. The melting temperature Tm of the acrylic oligomer M5 is 170°C.

<Preparation of acrylic oligomer M6> The same operation as acrylic oligomer M1 was performed except that the amount of chain transfer agent (α-thioglycerol) added in the polymerization reaction was changed from 9 parts by mass to 0.5 parts by mass. An acrylic oligomer M6 with a weight average molecular weight of 25,000 was obtained. The glass transition temperature (second glass transition temperature Tg ₂ ) of the acrylic oligomer M6 is 110°C. The melting temperature Tm of the acrylic oligomer M6 is 190°C.

<Acrylic oligomer M7> A carboxyl group-containing polyacrylic acid-2-ethylhexyl ester (product name "ACTFLOW CB3098", Mw3000, manufactured by Soken Chemical Co., Ltd.) was prepared as the acrylic oligomer M7. The glass transition temperature (second glass transition temperature Tg ₂ ) of the acrylic oligomer M7 is -44°C. The melting temperature Tm of the acrylic oligomer M6 is less than 25°C (it is not a melting temperature that can be accurately measured within the following measurement temperature range).

[Example 1] ＜Preparation of adhesive composition＞ To the polymer solution, 0.5 parts by mass of the acrylic oligomer M1, the first cross-linking agent (product name "Nyper BMT-40SV", peroxide per 100 parts by mass of the solid content of the polymer solution) were added. Benzoate, manufactured by Nippon Oils and Fats Co., Ltd.) 0.3 parts by mass, second cross-linking agent (product name "Takenate D110N", trimethylolpropane adduct of xylylene diisocyanate, manufactured by Mitsui Chemicals Co., Ltd.) 0.015 parts by mass , and 0.2 parts by mass of a silane coupling agent (product name "A100", a silane coupling agent containing an acetyl acetyl group, manufactured by Soken Chemical Co., Ltd.) and mixed them to prepare an adhesive composition.

＜Formation of adhesive layer＞ Next, the adhesive composition is applied to the release-treated surface of the first release liner that has been subjected to silicone release treatment on one side to form a coating film. The first release liner is a polyethylene terephthalate (PET) film (product name "DIAFOIL MRF #75", thickness 75 μm, manufactured by Mitsubishi Chemical Co., Ltd.) with silicone release treatment on one side. Next, the coating film on the first release liner is bonded to the release-treated surface of the second release liner that has been subjected to silicone release treatment on one side. The second release liner is a PET film (product name "DIAFOIL MRF #75", thickness 75 μm, manufactured by Mitsubishi Chemical Co., Ltd.) that has been subjected to silicone release treatment on one side. Next, the coating film on the first release liner was dried by heating at 100°C for 1 minute and then at 150°C for 3 minutes to form a transparent adhesive layer with a thickness of 50 μm. In the above manner, the adhesive sheet (thickness 50 μm) of Example 1 with a release liner was produced.

[Examples 2 to 6, Comparative Example 2] In the preparation of the adhesive composition, the acrylic oligomer shown in Table 1 was prepared instead of the acrylic oligomer M1. Except for this, the same operation was performed as the adhesive sheet of Example 1 to prepare Examples 2 to 6 and each adhesive sheet of Comparative Example 2.

[Comparative example 1] The adhesive sheet of Comparative Example 1 was produced in the same manner as the adhesive sheet of Example 1, except that the acrylic oligomer M1 was not blended in the preparation of the adhesive composition.

＜Weight average molecular weight＞ The weight average molecular weight (Mw) of each of the acrylic polymers and acrylic oligomers was measured by gel permeation chromatography (GPC) under the following measurement conditions and calculated as polystyrene-converted values. . In the measurement, a GPC measurement device (product name "HLC-8120GPC", manufactured by Tosoh) was used. The sample solution is prepared as follows. First, an acrylic polymer or an acrylic oligomer was used as a sample, a tetrahydrofuran (THF) solution (containing 10 mM phosphoric acid) with a sample concentration of 0.15% by mass was prepared, and the THF solution was left to stand for 20 hours. Then, the THF solution was filtered using a membrane filter with an average pore size of 0.45 μm to obtain a filtrate, which was used as a sample solution for molecular weight measurement.

[GPC measurement conditions] Column: TSKgel GMH-H(S), manufactured by Tosoh Tube string temperature: 40℃ Eluent: tetrahydrofuran solution containing phosphoric acid (phosphoric acid concentration 10 mM) Flow rate: 0.5 mL/min Sample injection volume: 100 μL Standard sample: polystyrene (PS) Detector: Differential Refractometer (RI)

＜Measurement of dynamic viscoelasticity of acrylic polymer＞ The glass transition temperature of acrylic polymers was determined by dynamic viscoelasticity measurements. Specifically, it is as follows.

First, a sample for measurement is prepared. Specifically, first, a first cross-linking agent (product name "Nyper BMT-40SV", dibenzoyl peroxide, was added to the polymer solution per 100 parts by mass of the solid content of the polymer solution. Nippon Oils and Fats Co., Ltd.) 0.3 parts by mass, and 0.015 parts by mass of the second cross-linking agent (product name "Takenate D110N", trimethylolpropane adduct of xylylene diisocyanate, manufactured by Mitsui Chemicals Co., Ltd.), and prepare an adhesive composition. Then, this adhesive composition was used instead of the adhesive composition described above for Example 1. Except for this, the same operation was performed as the adhesive sheet (thickness 50 μm) of Example 1 with a release liner to prepare Adhesive sheet with release liner (thickness 50 μm). Then, a plurality of small pieces of the adhesive sheet cut out from the adhesive sheet were laminated together to produce an adhesive sheet with a thickness of approximately 1 mm. Then, the sheet was punched to obtain cylindrical particles (diameter 7.9 mm) as a sample for measurement.

Then, using a dynamic viscoelasticity measuring device (product name "Discovery Hybrid Rheometer (DHR)", manufactured by TA Instruments), the sample for measurement was fixed on a parallel plate jig with a diameter of 7.9 mm, and the dynamic viscoelasticity was measured. In this measurement, the measurement mode was set to shear mode, the measurement temperature range was set to -50°C to 110°C, the temperature rise rate was set to 5°C/min, and the frequency was set to 1 Hz. From the measurement results (the values of loss modulus, storage modulus and loss tangent tanδ [=loss modulus/storage modulus] over the entire measurement temperature range), read the temperature at which the loss tangent tanδ becomes maximum. This value is shown in Table 1 as the glass transition temperature Tg ₁ (° C.) of the acrylic polymer.

<TMA (thermomechanical analysis) measurement of acrylic oligomer> The softening temperature and melting temperature of acrylic oligomer were measured by thermomechanical analysis (TMA: thermomechanical analysis). First, the acrylic oligomer (dry solid matter) to be measured is pulverized into powder, and then the powder is put into a sample container (made of aluminum) as a measurement sample. Next, an aluminum cover is placed on the measurement sample in the sample container, and a probe (connected to the load generating part) is placed on the cover. Then, using a TMA device (product name "TMA/SS6000", manufactured by Hitachi High-Tech Science), a certain load is applied to the measurement sample in the sample container through the probe and the cap, and in this state, the sum of the measurement sample and Deformation corresponding to temperature (compression and expansion measurement). In this measurement, the measurement mode is set to the compression-expansion mode, the measurement load is set to 19.6 mN (equivalent to 2 g), nitrogen (flow rate 200 ml/min) is used as the ambient gas, and the measurement temperature range is set to 20°C to 200°C. ℃, set the heating rate to 10℃/min. The measured softening temperature is shown in Table 1 as the glass transition temperature Tg ₂ (°C) of the acrylic oligomer, and the measured melting temperature Tm (°C) is also shown in Table 1. The sum of the above-mentioned glass transition temperature Tg ₁ and glass transition temperature Tg ₂ and the ratio of the melting temperature Tm to the glass transition temperature Tg ₂ (Tm/Tg ₂ ) are also shown in Table 1.

＜TEM (Electron Microscope, electron microscope) observation＞ An electron microscope (TEM) was used to observe the surface vicinity of each adhesive sheet of Examples 1 to 6 and Comparative Examples 1 and 2. In each of the adhesive sheets of Examples 1 to 6, aggregates (crystalline domains) of oligomers were confirmed. Table 1 shows the maximum length (μm) of the oligomer aggregates. In each of the adhesive sheets of Comparative Examples 1 and 2, no aggregates of oligomers were confirmed.

＜Peel Adhesion＞ For each of the adhesive sheets of Examples 1 to 6 and Comparative Examples 1 and 2, the peeling adhesive force was investigated by a peeling test.

First, test pieces were prepared for each adhesive sheet. In the preparation of the test piece, first, the adhesive sheet with the release liner was peeled off the second release liner, and a PET film (thickness 50 μm) was bonded to the exposed surface of the adhesive sheet thereby to obtain a laminated film (No. 1 release liner/adhesive sheet/PET film). During lamination, the adhesive sheet is press-bonded to the PET film by making a 2 kg roller reciprocate once. Next, a test piece (width 25 mm × length 100 mm) was cut out from the laminated film. Then, in an environment of 23°C and 50% relative humidity, the first release liner was peeled off from the adhesive sheet of the test piece, and the exposed surface of the adhesive sheet thus exposed was bonded to the alkali glass produced by the float method. The air surface of the plate (blue plate glass, manufactured by Shonami Glass Co., Ltd.) is obtained to obtain a laminate (alkali glass plate/adhesive sheet/PET film). The air surface refers to the exposed surface of the alkali glass plate when the alkali glass plate flows on the molten metal during the manufacturing process of the alkali glass plate (the opposite side to the surface that is in contact with the molten metal). During the lamination process, the test piece was pressed against the alkali glass plate by reciprocating the 2 kg roller once. Next, the laminated body is subjected to autoclave treatment (heating and pressure treatment). During the autoclave treatment, the temperature was set to 50°C, the pressure was set to 0.5 MPa, and the treatment time was set to 15 minutes. Then, in an environment of 23°C and a relative humidity of 50%, a peeling test was performed on the test piece from an alkali glass plate, and the force required for peeling was measured, which was used as the peeling adhesion force. In this measurement, a tensile testing machine (product name "Tensile Compression Testing Machine TCM-1kNB", manufactured by Minebea Co., Ltd.) was used. In this measurement, the peeling angle of the test piece relative to the adherend is set to 180°, the tensile speed of the test piece is set to 300 mm/min, and the peeling length is set to 50 mm (measurement conditions for peeling test). The measured peel adhesion force F (N/25 mm) is shown in Table 1.

＜TOF-SIMS＞ The components near the surface of each adhesive sheet of Examples 1 to 6 and Comparative Examples 1 and 2 were analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS).

The sample for TOF-SIMS analysis was prepared as follows. First, cut out a small piece (10 mm × 10 mm) of the adhesive sheet with release liner from the adhesive sheet with release liner. Then, the small piece of the adhesive sheet with the release liner is peeled off the first release liner. Then, the small piece of the adhesive sheet exposed by the peeling is bonded to the polyimide base material. Then, the second release liner is peeled off from the small piece of the adhesive sheet on the polyimide base material. A sample (small piece of polyimide base material/adhesive sheet) is thus obtained.

Then, by TOF-SIMS, on the adhesive sheet with the polyimide base material laminated on one side (the first side), conduct the operation from the second side (the side opposite to the first side) to the first side. Composition analysis in the thickness direction. In the analysis, a time-of-flight secondary ion mass spectrometer (product name "TRIFT-V, manufactured by ULVAC-PHI Co., Ltd.") was used. In this analysis, the irradiation of the ion beam for etching and the subsequent ion beam for measurement were alternately repeated. Beam (primary ion beam) irradiation. In the ion beam irradiation for etching, Ar gas cluster ions (Ar _n ⁺ ) are used, the acceleration voltage is set to 10 kV, and the irradiation range is set to 1000 μm × 1000 μm. Each irradiation time was set to 5 seconds. In the irradiation of the measurement ion beam, doubly charged ions (Bi ₃ ⁺⁺ ) of the bismuth cluster were used as primary ions for irradiation, the acceleration voltage was set to 30 kV, and the irradiation range was set to etching. The central part of the ion beam irradiation area is 100 μm × 100 μm, and a neutralization gun is used to correct the charge of the sample under analysis. In addition, this analysis is performed at room temperature.

Through this analysis, the distribution (depth distribution) of the mass spectrum of the secondary ion (negative ion) intensity in the depth direction (the thickness direction of the small piece of the adhesive sheet) is obtained. The fragments detected in the form of secondary ions (negative ions) in this analysis include: the first fragment derived from the acrylic oligomer, the CN ^- fragment (second fragment) derived from the polyimide substrate, and the source From the C ₃ H ₃ O ₂ ^-fragment (3rd fragment) of the acrylic base polymer. The first fragment is a C ₄ H ₅ O ₂ ^-fragment in Examples 1 to 6, and a C ₈ H ₁₅ ^O -fragment in Comparative Example 2 (Comparative Example 1 does not contain an acrylic oligomer). The ratio (m/z) of the secondary ion mass (m) to the secondary ion charge number (z) of the C ₄ H ₅ O ₂ ^-fragment is 85. The ratio (m/z) of the above-mentioned secondary ion mass (m) to the secondary ion charge number (z) of the C ₈ H ₁₅ O ^-fragment is 127. The ratio (m/z) of the above-mentioned secondary ion mass (m) to the secondary ion charge number (z) of the CN ^- fragment is 26. The ratio (m/z) of the above-mentioned secondary ion mass (m) to the secondary ion charge number (z) of the C ₃ H ₃ O ₂ ^-fragment is 71. The secondary ion intensity of each fragment was converted to the value when the ion intensity of the C ₂ H ^- fragment was set to the reference value of 1 (normalized).

Figure 5 shows the measurement results obtained by TOF-SIMS on the adhesive sheet of Example 1. FIG. 6 is an enlarged view of part of the measurement results shown in FIG. 5 . In the graphs shown in FIGS. 5 and 6 , the horizontal axis represents the analysis time (seconds), and the time indicating the analysis results at a specific midway position in the thickness direction of the adhesive sheet is represented as 0 seconds. The vertical axis in the above graph represents the normalized ionic strength (ionic strength relative to the ionic strength of the _C2H ^- fragment). In Figures 5 and 6, the change in ionic strength derived from the first segment (C ₄ H ₅ O ₂ ^-fragment ) of the acrylic oligomer is represented by a solid line, and the change in ionic strength derived from the polyimide is represented by a single-dot chain line. The change in ionic strength of the second segment (CN ^- fragment) of the base material is represented by a two-point chain line derived from the change in ionic strength of the third segment (C ₃ H ₃ O ₂ ^-fragment ) of the acrylic base polymer. As shown in Figures 5 and 6, the maximum peak P of the ionic intensity detected from the first fragment of the acrylic oligomer is detected at the detection time t ₁ , that is, the detection of the second fragment derived from the polyimide substrate. _{Detection ( _} t ₂ ＜ t ₁ ＜ t ₃ ). The ion intensity I ₁ of the maximum peak P detected and the detection time t ₁ (seconds) are shown in Table 1. Furthermore, in the adhesive sheet of Example 1, the ratio (I ₁ /I ₂ ) of the ion intensity I ₁ of the maximum detected peak P to the average value of the ion intensity of the first segment (average ion intensity I ₂ ) was 1.75. The average value of the ion intensity of the first segment refers to the average value from the half-peak width σ (seconds) of the detected maximum peak P to the time 5σ apart from the analysis start time, which is 10σ apart. The half-peak width σ (seconds) of the detected maximum peak P, the average ion intensity I ₂ , and the ratio (I ₁ /I ₂ ) are also shown in Table 1.

For each of the adhesive sheets of Examples 2 to 6, similarly to the adhesive sheet of Example 1, in TOF-SIMS, the detected maximum peak P of ion intensity derived from the first fragment of the acrylic oligomer is at the source Detected between the detection start time t ₂ of the second segment derived from the polyimide base material and the detection end time t ₃ of the third segment derived from the acrylic base polymer (t ₂ < t ₁ < t ₃ ) . Regarding each adhesive sheet of Examples 2 to 6, Table 1 shows the ion intensity I ₁ of the maximum peak P detected, the detection time t ₁ (seconds), and the half-peak width σ (seconds). Table 1 also shows the average ionic strength I ₂ and the ratio (I ₁ /I ₂ ) of each adhesive sheet of Examples 2 to 6.

FIG. 7 shows the measurement results obtained by TOF-SIMS of the adhesive sheet of Comparative Example 2. In the graph shown in FIG. 7 , the horizontal axis represents the analysis time (seconds), and the time indicating the analysis result at a specific midway position in the thickness direction of the adhesive sheet is represented as 0 seconds. The vertical axis in the above graph represents the normalized ionic strength (ionic strength relative to the ionic strength of the _C2H ^- fragment). In Figure 7, the solid line represents the change in ionic strength of the first fragment (C ₈ H ₁₅ O ^- fragment) derived from the acrylic oligomer, and the single-dot chain line represents the change in the ionic strength derived from the polyimide base material. The change in the ionic strength of the 2 fragment (CN ^-fragment ) is represented by a two-point chain line as the change in the ionic strength derived from the 3rd fragment (C ₃ H ₃ O ₂ ^-fragment ) of the acrylic base polymer. As shown in Figure 7, the detection start time t ₂ of the second segment derived from the polyimide base material (the detection amount start time of the second segment) is different from the detection start time t 2 of the third segment derived from the acrylic base polymer. The detection maximum peak of the ion intensity derived from the first fragment of the acrylic oligomer was not detected between the detection end time t ₃ (later than the detection start time t ₂ ). Regarding the adhesive sheet of Comparative Example 2, the ion intensity I ₁ of the maximum peak P detected, the detection time t ₁ (seconds), and the half-peak width σ (seconds) are shown in Table 1. Regarding the adhesive sheet of Comparative Example 2, the ions The intensity mean value I ₂ and the ratio (I ₁ /I ₂ ) are also shown in Table 1.

[Evaluation] The adhesive sheet of Comparative Example 1 does not contain an acrylic oligomer. Although the adhesive sheet of Comparative Example 2 contains an acrylic oligomer, the acrylic oligomer is not concentrated on or near the adhesive surface as described above. As shown in Table 1, the adhesive sheets of Comparative Examples 1 and 2 have low adhesive force. On the other hand, in each of the adhesive sheets of Examples 1 to 6, acrylic oligomers were concentrated on the adhesive surface and its vicinity. Specifically, the detection maximum peak P of the ionic intensity derived from the first fragment of the acrylic oligomer is determined by the detection start time t 2 of the second fragment derived from the polyimide base material, and the detection start time t ₂ of the second fragment derived from the acrylic base material. The third fragment of the polymer is detected between the detection end time t ₃ (t ₂ < t ₁ < t ₃ ), and the ratio of the above-mentioned ionic intensity I ₁ of the first fragment to the average ionic intensity I ₂ (I ₁ /I ₂ ) is 1.2 or more. Each of the adhesive sheets of Examples 1 to 6 has higher adhesive force than the adhesive sheets of Comparative Examples 1 and 2.

[Table 1] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative example 1 Comparative example 2 Acrylic polymer Mw 2 million 2 million 2 million 2 million 2 million 2 million 2 million 2 million 1st glass transition temperature Tg ₁ (℃) -46.4 -46.4 -46.4 -46.4 -46.4 -46.4 -46.4 -46.4 Number of prepared portions 100 100 100 100 100 100 100 100 Acrylic oligomer Kind M1 M2 M3 M4 M5 M6 ― M7 Mw 2500 3600 6400 8100 17000 25000 ― 3000 2nd glass transition temperature Tg ₂ (℃) 61 73 89 92 100 110 ― -44 Melting temperature Tm(℃) 120 130 150 150 170 190 ― <25 Number of prepared portions 0.5 0.5 0.5 0.5 0.5 0.5 ― 0.5 Thickness(μm) 50 50 50 50 50 50 50 50 Maximum length of oligomer aggregates (μm) 0.26 0.24 0.25 0.27 0.26 0.26 ― not detected Tg ₁ +Tg ₂ (℃) 14.6 26.6 42.6 45.6 53.6 63.6 ― -90.4 Tm/Tg ₂ 1.97 1.78 1.69 1.63 1.70 1.73 ― ― Peel adhesion F (N/25 mm) 8.8 10.0 10.0 12.0 8.5 7.7 5.8 4.7 TOF-SIMS analysis The first fragment derived from oligomer (C ₄ H ₅ O ₂ ^- ) Detect the largest peak Ionic strength I ₁ 0.178 0.222 0.228 0.306 0.169 0.141 ― not detected Detection time t ₁ (seconds) 108 108 170 172 168 107 ― ― Half-peak width σ (seconds) 7 8 10 12 7 6 ― ― Average ionic strength I ₂ 0.102 0.109 0.110 0.121 0.101 0.095 ― ― I ₁ /I ₂ 1.75 2.04 2.07 2.53 1.67 1.48 ― ― Detection start time t ₂ (seconds) of the 2nd segment (CN ^- ) originating from the substrate 94 96 147 148 148 93 124 108 Detection end time t ₃ (seconds) of the third fragment (C ₃ H ₃ O ₂ ^- ) derived from the acrylic polymer 118 117 185 186 184 119 142 136

10: Adhesive sheet (optical adhesive sheet) 11: 1st side 12: 2nd side 21: 1st member 22: 2nd member H: Thickness direction L1: Release liner L2: Release liner P: Detection maximum peak t ₁ :Detection time of the maximum peak t ₂ :Detection start time of the second segment t ₃ :Detection end time of the third segment

FIG. 1 is a schematic cross-sectional view of an embodiment of the optical adhesive sheet of the present invention. FIG. 2 schematically shows the measurement results obtained by time-of-flight secondary ion mass spectrometry (TOF-SIMS) for the optical adhesive sheet of the present invention. FIG. 3 is an enlarged view of part of the measurement results shown in FIG. 2 . 4A to 4C illustrate an example of how to use the optical adhesive sheet of the present invention. Figure 4A shows the step of bonding the optical adhesive sheet to the first adherend. Figure 4B shows the step of joining the first adherend and the second adherend through the optical adhesive sheet. Figure 4C shows the curing step. . FIG. 5 shows the measurement results obtained by TOF-SIMS of the optical adhesive sheet of Example 1. FIG. 6 is an enlarged view of part of the measurement results shown in FIG. 5 . FIG. 7 shows the measurement results obtained by TOF-SIMS of the optical adhesive sheet of Comparative Example 2.

10: Adhesive sheet (optical adhesive sheet)

11:Side 1

12:Side 2

H:Thickness direction

L1: Release liner

L2: Release liner

Claims (6)

An optical adhesive sheet, which contains: A base polymer having a first glass transition temperature, and An oligomer having a second glass transition temperature higher than the above-mentioned first glass transition temperature, and Having a first side and a second side opposite to the first side, For the optical adhesive sheet with the base material bonded to the first surface, component analysis in the thickness direction from the second surface side to the first surface side is performed by time-of-flight secondary ion mass spectrometry. In this component analysis, The maximum detected peak of the ionic intensity derived from the first fragment of the oligomer is at the detection start time of the second fragment derived from the above-mentioned base material, and the detection start time of the second fragment derived from the above-mentioned base polymer is later than the detection start time. Detected between the detection end time of the third segment, The ratio of the ion intensity of the maximum detected peak to the average ion intensity of the first fragment is 1.2 or more. The average ion intensity of the first fragment refers to the half-peak width σ (seconds) of the maximum detected peak from the analysis The average value from the time that is 10σ apart from the starting time to the time that is 5σ apart. The optical adhesive sheet of claim 1, wherein the oligomers form aggregates with a maximum length of 0.4 μm or less. The optical adhesive sheet of claim 1, wherein the second glass transition temperature is above 50°C. The optical adhesive sheet according to any one of claims 1 to 3, wherein the ratio of the melting temperature (°C) of the oligomer to the second glass transition temperature (°C) is 1.5 or more. The optical adhesive sheet according to any one of claims 1 to 3, wherein the oligomer has a weight average molecular weight of more than 2000. The optical adhesive sheet according to any one of claims 1 to 3, wherein the sum of the above-mentioned first glass transition temperature and the above-mentioned second glass transition temperature is 0°C or above.