Optical adhesive sheet

Abstract

To provide an optically clear adhesive sheet suitable for flexible device applications.SOLUTION: There is provided an adhesive sheet 10 (optically clear 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 first glass transition temperature, and has an adhesive surface 11 and an adhesive surface 12. In the component analysis in a thickness direction H from the adhesive surface 12 side to the adhesive surface 11 side by a TOF-SIMS method for the adhesive sheet 10 in a state in which a base material S is laminated to the adhesive surface 11, the maximum detection peak of the ion intensity of a first fragment derived from the oligomer is detected between a detection start time of a second fragment derived from the base material and a detection end time of a third fragment derived from the base polymer after the detection start time, a ratio of the ion intensity of the maximum detection peak with respect to an average value of the ion intensity of the first fragment from a time 10 σ away to a time 5 σ away from a half width σ (seconds) of the maximum detection peak to an analysis start time is 1.2 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an optical adhesive sheet. [Background technology]

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

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

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-111754 [Overview of the project] [Problems that the invention aims to solve]

[0005] Optical adhesive sheets for foldable display panels are required to be highly flexible in order to have sufficient conformability to the substrate when the device is bent and to have excellent stress relaxation properties. However, with conventional optical adhesive sheets, the more flexible they are, the lower their adhesive strength becomes.

[0006] On the other hand, in foldable display panels, the optical adhesive sheet tends to peel off from the substrate at areas that are repeatedly folded. This is because when the display panel is folded, stresses such as shear stress act locally on the optical adhesive sheet at the folded area. Peeling of the optical adhesive sheet is undesirable as it can cause malfunction of the display panel. Therefore, optical adhesive sheets for foldable display panels require a high level of adhesive strength to the substrate.

[0007] This invention provides an optical adhesive sheet suitable for flexible device applications. [Means for solving the problem]

[0008] The present invention [1] includes an optical adhesive sheet comprising 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 having a first surface and a second surface opposite to the first surface, wherein in a component analysis of the optical adhesive sheet with a substrate bonded to the first surface by time-of-flight secondary ion mass spectrometry in the thickness direction from the second surface to the first surface, the maximum detection peak of the ionic intensity of a first fragment derived from the oligomer is detected between the detection start time of a second fragment derived from the substrate and the detection end time of a third fragment derived from the base polymer, which is after the detection start time, and the ratio of the ionic intensity of the maximum detection peak to the average value of the ionic intensity of the first fragment from a time 10σ away from the half-width σ(seconds) of the maximum detection peak to a time 5σ away from the analysis start time is 1.2 or more.

[0009] The present invention [2] includes the optical adhesive sheet described in [1] above, wherein the oligomer forms aggregates with a maximum length of 0.4 μm or less.

[0010] The present invention [3] includes the optical adhesive sheet described in [1] or [2] above, wherein the second glass transition temperature is 50°C or higher.

[0011] The present invention [4] includes an optical adhesive sheet according to any one of [1] to [3] above, wherein the ratio of the melting temperature (°C) of the oligomer to the second glass transition temperature (°C) is 1.5 or more.

[0012] The present invention [5] includes an optical adhesive sheet according to any one of [1] to [4] above, wherein the oligomer has a weight-average molecular weight of 2000 or more.

[0013] The present invention [6] includes an optical adhesive sheet according to any one of [1] to [5] above, wherein the sum of the first glass transition temperature and the second glass transition temperature is 0°C or higher. [Effects of the Invention]

[0014] As described above, the optical adhesive sheet of the present invention includes 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 the oligomer having a higher glass transition temperature is unevenly distributed on the surface of the optical adhesive sheet and in its vicinity. Specifically, in time-of-flight secondary ion mass spectrometry (component analysis in the thickness direction from the second surface to the first surface in a state where a substrate is bonded to the first surface of the optical adhesive sheet), the detection maximum peak P of the ion intensity I1 of the first fragment derived from the oligomer is detected after the detection start time of the second fragment derived from the substrate, and the ratio of the ion intensity I1 of the detection maximum peak P to the predetermined average value of the ion intensity I1 is 1.2 or more, the oligomer having a higher glass transition temperature than the base polymer is unevenly distributed on the surface of the optical adhesive sheet and in its vicinity. Such a configuration is suitable for realizing good adhesion to the adherend on the surface (adhesive surface) of the optical adhesive sheet while ensuring the overall softness of the optical adhesive sheet. The softness of the optical adhesive sheet is suitable for ensuring sufficient followability to the adherend and excellent stress relaxation properties when the adherend is bent in the optical adhesive sheet. Therefore, it is suitable for realizing good repeated deformation of the flexible device in which the optical adhesive sheet is used. The high adhesion of the optical adhesive sheet to the adherend is suitable for suppressing the peeling of the optical adhesive sheet from the repeatedly deformed adherend. Therefore, the optical adhesive sheet of the present invention is suitable for flexible device applications.

Brief Description of Drawings

[0015] [Figure 1] It is a schematic cross-sectional view of an embodiment of the optical adhesive sheet of the present invention. [Figure 2] It schematically shows the measurement results of the optical adhesive sheet of the present invention by time-of-flight secondary ion mass spectrometry (TOF-SIMS). [Figure 3] A part of the measurement results shown in FIG. 2 is enlarged and shown. [Figure 4]This shows an example of how to use the optical adhesive sheet of the present invention. Figure 4A shows the step of attaching the optical adhesive sheet to a first adherend, Figure 4B shows the step of joining the first adherend and the second adherend via the optical adhesive sheet, and Figure 4C shows the aging step. [Figure 5] This shows the TOF-SIMS measurement results for the optical adhesive sheet of Example 1. [Figure 6] A magnified view of a portion of the measurement results shown in Figure 5. [Figure 7] This shows the TOF-SIMS measurement results for the optical adhesive sheet of Comparative Example 2. [Modes for carrying out the invention]

[0016] As one embodiment of the optical adhesive sheet of the present invention, the adhesive sheet 10 has a sheet shape of a predetermined thickness, as shown in Figure 1, and extends in a direction perpendicular to the thickness direction (surface direction). The adhesive sheet 10 has an adhesive surface 11 and an adhesive surface 12 opposite to the adhesive surface 11. Figure 1 illustrates a state in which release liners L1 and L2 are attached to the adhesive surfaces 11 and 12 of the adhesive sheet 10. The release liner L1 is placed on the adhesive surface 11. The release liner L2 is placed on the adhesive surface 12. The adhesive sheet 10 is also an optically transparent adhesive sheet placed at a light-passing location in a flexible device. Examples of flexible devices include flexible display panels. Examples of flexible display panels include foldable display panels and rollable display panels. A flexible display panel has a laminated structure including elements such as a pixel panel, a polarizing plate, a touch panel, and a cover film. The adhesive sheet 10 is used, for example, in the manufacturing process of a flexible display panel to bond elements included in the laminated structure. The release liners L1 and L2 are peeled off at predetermined timings when the adhesive sheet 10 is used.

[0017] The adhesive sheet 10 is formed from an adhesive composition. The adhesive composition includes a base polymer and an oligomer. That is, the adhesive sheet 10 includes a base polymer and a first oligomer. The base polymer has a glass transition temperature Tg1 (first glass transition temperature) (if the base polymer has a crosslinked structure, the glass transition temperature Tg1 is the glass transition temperature of the base polymer having the crosslinked structure). The oligomer has a glass transition temperature Tg2 (second glass transition temperature) that is higher than the glass transition temperature Tg1. The methods for measuring the glass transition temperatures Tg1 and Tg2 are described later with reference to the examples.

[0018] The adhesive sheet 10 is an adhesive sheet in which a substrate is bonded to one side (the first side, one of the adhesive surfaces 11 and 12), and in a time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis of the components in the thickness direction H from the second side (the other side of the adhesive surfaces 11 and 12) to the first side, the following measurement results are obtained.

[0019] The maximum detection peak P of the ionic intensity I1 of the first fragment derived from the oligomer is detected between the detection start time of the second fragment derived from the substrate and the detection end time of the third fragment derived from the base polymer, which occurs after the detection start time. The ratio of the ionic intensity I1 of the maximum detection peak P to the average value of the ionic intensity I1 of the first fragment (average ionic intensity I2) from a time 10σ away from the half-width σ (seconds) of the maximum detection peak P to a time 5σ away from the analysis start time (I1 / I2) is 1.2 or greater.

[0020] FIG. 2 schematically shows such measurement results by TOF-SIMS for the adhesive sheet 10. FIG. 3 shows an enlarged view of a part of the measurement results shown in FIG. 2. In the graphs shown in FIGS. 2 and 3, the horizontal axis represents the analysis time (seconds), and the vertical axis represents the normalized ion intensity. In FIGS. 2 and 3, the change in the ion intensity of the first fragment derived from the oligomer is represented by a solid line, the change in the ion intensity of the second fragment derived from the base material is represented by a one-dot chain line, and the change in the ion intensity of the third fragment derived from the base polymer is represented by a two-dot chain line. The intensity of the ion of a predetermined fragment corresponds to the amount of the component having the fragment. The detection time of the ion intensity of a predetermined fragment corresponds to the position of the component having the fragment in the thickness direction of the adhesive sheet (depth direction from the second surface side). As shown in FIGS. 2 and 3, in the adhesive sheet 10, the detection time t1 of the detection maximum peak P of the ion intensity of the first fragment derived from the oligomer is between the detection start time t2 of the second fragment derived from the polyimide base material (the start time of the rise in the detection amount of the second fragment) and the detection end time t3 of the third fragment derived from the base polymer (after the detection start time t2) (t2 < t1 < t3). This means that the abundance of the oligomer having the first fragment in the first surface of the adhesive sheet 10 and its vicinity is larger than that in other regions. In addition, in the adhesive sheet 10, the ratio (I1 / I2) of the ion intensity I1 of the detection maximum peak P to the average ion intensity I2 of the first fragment is 1.2 or more (the average ion intensity I2 is the average value of the ion intensity I1 of the first fragment from the time 10σ away from the analysis start time side to the time 5σ away from the half-width σ (seconds) of the detection maximum peak P. This half-width σ is the half-width on the analysis start time side of the detection maximum peak P). This means that the abundance of the oligomer having the first fragment in the first surface of the adhesive sheet 10 and its vicinity is significantly larger than that in other regions.

[0021] In TOF-SIMS, an ion beam (primary ions) is irradiated onto the sample surface, causing ions (secondary ions) to be emitted. The difference in the time of flight (proportional to the square root of the mass) of these secondary ions to reach the detector is used to separate the masses. This allows for the acquisition of a mass spectrum of the secondary ions, enabling component analysis of the sample surface. Furthermore, TOF-SIMS allows for the detection of changes in the mass spectrum in the thickness direction by alternately irradiating the sample with an etching ion beam and then with a measurement ion beam (primary ion beam). This enables component analysis of the sample in the thickness direction. The specific method of TOF-SIMS is described in detail in the examples below.

[0022] As described above, the adhesive sheet 10 contains a base polymer having a glass transition temperature Tg1 and an oligomer having a glass transition temperature Tg2 that is higher than Tg1, with the oligomer having the higher glass transition temperature being concentrated on and near the surface of the adhesive sheet 10. Specifically, in TOF-SIMS (component analysis in the thickness direction H from the second surface to the first surface when the substrate is bonded to the first surface of the adhesive sheet 10), the maximum detection peak P of the ionic intensity I1 of the first fragment derived from the oligomer is detected after the detection start time of the second fragment derived from the substrate, and the ratio of the ionic intensity I1 of the maximum detection peak P to the average ionic intensity I2 (I1 / I2) is 1.2 or higher, the more concentrated the oligomer with a higher glass transition temperature than the base polymer is on and near the surface of the adhesive sheet 10. This configuration is suitable for achieving good adhesion to the adherend on the surface (adhesive surface) of the adhesive sheet 10 while ensuring the overall softness of the adhesive sheet 10. The flexibility of the adhesive sheet 10 is suitable for ensuring sufficient conformability to the adherend and excellent stress relaxation properties when the adherend is bent, and therefore, it is suitable for achieving good repeated deformation in flexible devices in which the adhesive sheet 10 is used. The high adhesive strength of the adhesive sheet 10 to the adherend is suitable for suppressing peeling of the adhesive sheet 10 from the adherend that undergoes repeated deformation. Therefore, the adhesive sheet 10 is suitable for flexible device applications.

[0023] Methods for unevenly distributing oligomers on and near the surface of the adhesive sheet 10 include, for example, adjusting the compatibility of the oligomers with respect to the base polymer (adjusting the compatibility to a range that is relatively low), and adjusting the molecular weight of the oligomers (adjusting the ease of oligomer migration). As an indicator of the compatibility of oligomers with respect to the base polymer, for example, Hansen's solubility parameter (HSP value) can be used. The HSP value is expressed by the following formula (1).

[0024] HSP value = (δD 2 +δP 2 +δH 2 ) 1 / 2

[0025] In the above formula, δD is the dispersion term (representing the energy derived from intermolecular dispersion forces). δP is the polarization term, representing the energy derived from intermolecular polar forces. δH is the hydrogen bonding term, representing the energy derived from intermolecular hydrogen bonding forces. Substances with similar HSP values ​​are known to exhibit similar physical properties. For more information on HSP values, see, for example, "Chemical Industry Co., Ltd., Chemical Industry, March 2010 issue, Hiroshi Yamamoto, Steven Abbott, Charles M. Hansen".

[0026] The ratio (I1 / I2) is preferably 1.4 or higher, more preferably 1.6 or higher, and even more preferably 1.7 or higher, from the viewpoint of ensuring good adhesive strength in the adhesive sheet 10. The ratio (I1 / I2) is, for example, 5 or less, 3.5 or less, or 2.7 or less.

[0027] On the surface of the adhesive sheet 10 and its vicinity, it is preferable that the oligomers form aggregates (domains) from the viewpoint of ensuring cohesive force on the adhesive surfaces 11 and 12. The maximum length of the oligomer aggregates is preferably 0.05 μm or more, more preferably 0.1 μm or more. From the viewpoint of high dispersion of the oligomers, the maximum length of the oligomer aggregates is preferably 0.4 μm or less, more preferably 0.3 μm or less, and even more preferably 0.2 μm or less. The method for measuring the size of the oligomer aggregates will be specifically described later with reference to the examples.

[0028] The glass transition temperature Tg2 of the oligomer is preferably 50°C or higher, more preferably 60°C or higher, even more preferably 70°C or higher, and also preferably 130°C or lower, more preferably 120°C or lower, and even more preferably 110°C or lower, from the viewpoint of increasing the tackiness of the surface (adhesive surfaces 11, 12) of the adhesive sheet 10.

[0029] The ratio of the melting temperature Tm (°C) of the oligomer to the glass transition temperature Tg2 (°C) (Tm / Tg2) is preferably 1.5 or higher, more preferably 1.6 or higher, and also preferably 3 or lower, more preferably 2.5 or lower, and even more preferably 2 or lower, from the viewpoint of increasing the tackiness of the surface (adhesive surfaces 11, 12) of the adhesive sheet 10. The method for measuring the melting temperature Tm of the oligomer is described in detail later with reference to the examples.

[0030] The weight-average molecular weight Mw of the oligomer is preferably 2000 or more, more preferably 2500 or more, even more preferably 3000 or more, even more preferably 3500 or more, and particularly preferably 4000 or more, from the viewpoint of increasing the tackiness of the surface (adhesive surfaces 11, 12) of the adhesive sheet 10. The weight-average molecular weight Mw of the oligomer is preferably 30000 or less, more preferably 15000 or less, and even more preferably 10000 or less, from the viewpoint of uneven distribution of the oligomer to and near the surface of the adhesive sheet 10 (migration to the surface). The method for measuring the weight-average molecular weight Mw of the oligomer is described in detail in the examples below.

[0031] The sum of the glass transition temperature Tg1 and the glass transition temperature Tg2 is preferably 0°C or higher, more preferably 10°C or higher, even more preferably 20°C or higher, and also preferably 100°C or lower, more preferably 80°C or lower, and even more preferably 60°C or lower, from the viewpoint of increasing the tackiness of the surface (adhesive surfaces 11, 12) of the adhesive sheet 10.

[0032] In the adhesive sheet 10, the base polymer is an adhesive component that provides tackiness. Examples of base polymers include acrylic polymers, silicone polymers, polyester polymers, polyurethane polymers, polyamide polymers, polyvinyl ether polymers, vinyl acetate / vinyl chloride copolymers, modified polyolefin polymers, epoxy polymers, fluoropolymers, and rubber polymers. The base polymer may be used alone or in combination of two or more types. From the viewpoint of ensuring good transparency and tackiness in the adhesive sheet 10, an acrylic polymer is preferably used as the base polymer.

[0033] Acrylic polymers are copolymers of monomer components containing 50% or more by mass of (meth)acrylic acid ester. "(Meth)acrylic" means acrylic and / or methacrylic.

[0034] Preferably, an alkyl (meth)acrylate ester is used as the (meth)acrylic acid ester, and more preferably, an alkyl (meth)acrylate ester having 1 to 20 carbon atoms in the alkyl group. The alkyl (meth)acrylate ester may have a linear or branched alkyl group, or a cyclic alkyl group such as an alicyclic alkyl group.

[0035] Examples of alkyl (meth)acrylates having linear or branched alkyl groups include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, n-hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, iso-octyl (meth)acrylate. Examples include (meth)acrylate nonyl, (meth)acrylate isononyl, (meth)acrylate decyl, (meth)acrylate isodecyl, (meth)acrylate undecyl, (meth)acrylate dodecyl (i.e., lauryl acrylate), (meth)acrylate isotridecyl, (meth)acrylate tetradecyl, (meth)acrylate isotetradecyl, (meth)acrylate pentadecyl, (meth)acrylate cetyl, (meth)acrylate heptadecyl, (meth)acrylate octadecyl, (meth)acrylate isooctadecyl, and (meth)acrylate nonadecyl.

[0036] Examples of alkyl (meth)acrylates having an alicyclic alkyl group include cycloalkyl (meth)acrylates, (meth)acrylates having a bicyclic aliphatic hydrocarbon ring, and (meth)acrylates having three or more aliphatic hydrocarbon rings. Examples of cycloalkyl (meth)acrylates include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate. An example of a (meth)acrylate ester having a bicyclic aliphatic hydrocarbon ring is isobornyl (meth)acrylate. Examples of (meth)acrylic acid esters having three or more aliphatic hydrocarbon rings include dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

[0037] As the alkyl (meth)acrylate ester, in the adhesive sheet 10, from the viewpoint of balancing the flexibility and adhesive strength required for adhesive sheets for flexible device applications, preferably at least one selected from alkyl (meth)acrylate esters having an alkyl group with 3 to 12 carbon atoms is used, and more preferably, at least one first alkyl (meth)acrylate ester having a relatively large number of carbon atoms in the alkyl group and at least one second alkyl (meth)acrylate ester having a relatively small number of carbon atoms in the alkyl group are used in combination, selected from alkyl (meth)acrylate esters having an alkyl group with 3 to 12 carbon atoms. The first alkyl (meth)acrylate ester is preferably at least one selected from the group consisting of 2-ethylhexyl acrylate (2EHA) and lauryl acrylate (LA). The second alkyl (meth)acrylate ester is preferably n-butyl acrylate.

[0038] The proportion of alkyl (meth)acrylate in the monomer component is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, from the viewpoint of appropriately exhibiting basic properties such as tackiness in the adhesive sheet 10. This proportion is, for example, 99% by mass or less. When the first and second alkyl (meth)acrylates are used in combination, the proportion of the first alkyl (meth)acrylate in the monomer component is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and also preferably 85% by mass or less, and even more preferably 80% by mass or less, from the viewpoint of balancing the flexibility and tackiness of the adhesive sheet 10. The proportion of the second alkyl (meth)acrylate in the monomer component is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and also preferably 30% by mass or less, and even more preferably 25% by mass or less, from the viewpoint of balancing the flexibility and tackiness of the adhesive sheet 10.

[0039] The monomer component may include copolymerizable monomers that can copolymerize with alkyl (meth)acrylate esters. Examples of copolymerizable monomers include monomers having polar groups. Examples of polar group-containing monomers include monomers containing hydroxyl groups, monomers containing carboxyl groups, and monomers having nitrogen atom-containing rings. Polar group-containing monomers are useful for modifying acrylic polymers, such as introducing crosslinking sites into acrylic polymers and ensuring the cohesive strength of acrylic polymers.

[0040] Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. Preferably, at least one selected from the group consisting of 2-hydroxyethyl (meth)acrylate and 2-hydroxybutyl (meth)acrylate is used as the hydroxyl group-containing monomer.

[0041] The proportion of hydroxyl group-containing monomers in the monomer components is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, from the viewpoint of introducing a crosslinked structure into the acrylic polymer and ensuring cohesive force in the adhesive sheet 10. From the viewpoint of adjusting the polarity of the acrylic polymer (which is related to the compatibility between the various additive components in the adhesive sheet 10 and the acrylic polymer), the proportion is preferably 10% by mass or less, and more preferably 5% by mass or less.

[0042] Examples of monomers containing a carboxyl group include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

[0043] The proportion of carboxyl group-containing monomers in the monomer component is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 0.8% by mass or more, from the viewpoint of introducing a crosslinked structure into the acrylic polymer, ensuring cohesive force in the adhesive sheet 10, and ensuring adhesion force to the adherend in the adhesive sheet 10. The same proportion is preferably 10% by mass or less, more preferably 5% by mass or less, from the viewpoint of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend by acid.

[0044] Examples of monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholindione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, and N-vinylisothiazole. Preferably, N-vinyl-2-pyrrolidone is used as the monomer having a nitrogen atom-containing ring.

[0045] The proportion of monomers having nitrogen atom-containing rings in the monomer components is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 0.8% by mass or more, from the viewpoint of ensuring cohesive force in the adhesive sheet 10 and ensuring adhesion force to the adherend in the adhesive sheet 10. The same proportion is preferably 10% by mass or less, more preferably 5% by mass or less, from the viewpoint of adjusting the glass transition temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (which is related to the compatibility between the various additive components in the adhesive sheet 10 and the acrylic polymer).

[0046] The monomer component may also contain 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, alkoxy group-containing monomers, and aromatic vinyl compounds. These other copolymerizable monomers may be used individually or in combination of two or more types.

[0047] The base polymer preferably has a crosslinked structure. Methods for introducing a crosslinked structure to the base polymer include a first method in which a base polymer having a functional group reactive with a crosslinking agent and a crosslinking agent are blended into an adhesive composition and the base polymer and crosslinking agent are reacted in an adhesive sheet, and a second method in which a polyfunctional monomer as a crosslinking agent is included in the monomer component that forms the base polymer, and a base polymer in which a branched structure (crosslinked structure) is introduced into the polymer chain is formed by polymerization of the monomer component. These methods may be used in combination.

[0048] Examples of crosslinking agents used in the first method described above include compounds that react with functional groups (such as hydroxyl groups and carboxyl groups) contained in the base polymer. Examples of such crosslinking agents include isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, and metal chelate crosslinking agents. The crosslinking agent may be used alone or in combination of two or more types. As crosslinking agents, isocyanate crosslinking agents, peroxide crosslinking agents, and epoxy crosslinking agents are preferably used because they have high reactivity with hydroxyl groups and carboxyl groups in the base polymer and facilitate the introduction of crosslinked structures.

[0049] Examples of isocyanate crosslinking agents include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethyl xylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate. Derivatives of these isocyanates can also be used as isocyanate crosslinking agents. Examples of such isocyanate derivatives include isocyanurate-modified and polyol-modified derivatives. Examples of commercially available isocyanate crosslinking agents include Coronate L (trimethylolpropane adduct of tolylene diisocyanate, manufactured by Tosoh Corporation), Coronate HL (trimethylolpropane adduct of hexamethylene diisocyanate, manufactured by Tosoh Corporation), Coronate HX (isocyanurate of hexamethylene diisocyanate, manufactured by Tosoh Corporation), Takenate D110N (trimethylolpropane adduct of xylylene diisocyanate, manufactured by Mitsui Chemicals Corporation), and Takenate 600 (1,3-bis(isocyanatomethyl)cyclohexane, manufactured by Mitsui Chemicals Corporation).

[0050] Examples of peroxide crosslinking agents include dibenzoyl peroxide, di(2-ethylhexyl)peroxydicarbonate, di(4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butylperoxydicarbonate, t-butylperoxyneodecanoate, t-hexylperoxypivalate, and t-butylperoxypivalate.

[0051] Examples of epoxy crosslinking agents include bisphenol A, epichlorohydrin-type epoxy resins, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane.

[0052] From the viewpoint of ensuring the cohesive force of the adhesive sheet 10, the amount of crosslinking agent blended in the first method is, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, and more preferably 0.1 parts by mass or more, per 100 parts by mass of the base polymer. From the viewpoint of ensuring good tackiness in the adhesive sheet 10, the amount of crosslinking agent blended per 100 parts by mass of the base polymer is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, and more preferably 3 parts by mass or less.

[0053] In the second method described above, the monomer components (including polyfunctional monomers and other monomers for introducing a crosslinking structure) may be polymerized in a single step or in multiple steps. In the multi-step polymerization method, first, monofunctional monomers for forming the base polymer are polymerized (prepolymerization), thereby preparing a prepolymer composition containing a partially polymerized product (a mixture of a low-degree polymerized product and unreacted monomers). Next, a polyfunctional monomer as a crosslinking agent is added to the prepolymer composition, and then the partially polymerized product and the polyfunctional monomer are polymerized (main polymerization).

[0054] Examples of polyfunctional monomers include polyfunctional (meth)acrylates containing two or more ethylenically unsaturated double bonds in one molecule. From the viewpoint of being able to introduce crosslinked structures by active energy ray polymerization (photopolymerization), polyfunctional acrylates are preferred as polyfunctional monomers.

[0055] Examples of polyfunctional (meth)acrylates include difunctional (meth)acrylates, trifunctional (meth)acrylates, and polyfunctional (meth)acrylates with four or more functions.

[0056] Examples of difunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerin di(meth)acrylate, neopentyl glycol di(meth)acrylate, stearic acid-modified pentaerythritol di(meth)acrylate, dicyclopentenyl di(meth)acrylate, di(meth)acryloyl isocyanurate, and alkylene oxide-modified bisphenol di(meth)acrylate.

[0057] Examples of trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl) isocyanurate.

[0058] Examples of polyfunctional (meth)acrylates with four or more functions include ditrimethylolpropanetetra(meth)acrylate, pentaerythritoltetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, alkyl-modified dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0059] Preferably, a polyfunctional (meth)acrylate with four or more functions is used, and more preferably, dipentaerythritol hexaacrylate is used.

[0060] From the viewpoint of ensuring the cohesive force of the adhesive sheet 10, the amount of polyfunctional monomer used as a crosslinking agent in the monomer component is, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, and more preferably 0.1 parts by mass or more, per 100 parts by mass of monofunctional monomer. From the viewpoint of ensuring good tackiness in the adhesive sheet 10, the amount of polyfunctional monomer used is, for example, 10 parts by mass or less, preferably 3 parts by mass or less, more preferably 1 part by mass or less, even more preferably 0.5 parts by mass or less, even more preferably 0.2 parts by mass or less, and particularly preferably 0.1 parts by mass or less, per 100 parts by mass of monofunctional monomer.

[0061] Acrylic polymers can be formed by polymerizing the monomer components described above. Polymerization methods include, for example, solution polymerization, solvent-free photopolymerization (e.g., UV polymerization), bulk polymerization, and emulsion polymerization. For solvent polymerization, for example, ethyl acetate and toluene are used. For polymerization initiators, for example, thermal polymerization initiators and photopolymerization initiators are used. Polymerization initiators may be used alone or in combination of two or more types. The amount of polymerization initiator used is preferably 0.05 parts by mass or more, more preferably 0.08 parts by mass or more, even more preferably 0.1 parts by mass or more, and also preferably 1 part by mass or less, more preferably 0.5 parts by mass or less, and even more preferably 0.3 parts by mass or less, per 100 parts by mass of monomer components.

[0062] Examples of thermal polymerization initiators include azo polymerization initiators and peroxide polymerization initiators. Examples of azo polymerization initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionic acid)dimethyl, 4,4'-azobis-4-cyanovaleric acid, azobisisovaleronitrile, 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride, 2,2'-azobis(2-methylpropionamidine)disulfate, and 2,2'-azobis(N,N'-dimethyleneisobutylamidine)dihydrochloride. Examples of peroxide polymerization initiators include dibenzoyl peroxide, t-butyl permaleate, and lauroyl peroxide.

[0063] Examples of photopolymerization initiators include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and acylphosphine oxide-based photopolymerization initiators.

[0064] The weight-average molecular weight of the base polymer is preferably 500,000 or more, more preferably 800,000 or more, even more preferably 1,000,000 or more, and even more preferably 1,500,000 or more, from the viewpoint of ensuring cohesive force in the adhesive sheet 10. The weight-average molecular weight of the base polymer is measured by gel permeation chromatography (GPC) and calculated on a polystyrene basis.

[0065] The glass transition temperature Tg1 of the base polymer is preferably 0°C or lower, more preferably -20°C or lower, even more preferably -40°C or lower, and even more preferably -45°C or lower, from the viewpoint of ensuring sufficient flexibility in the adhesive sheet 10. The glass transition temperature Tg1 is, for example, -80°C or higher.

[0066] For the glass transition temperature of the base polymer, the theoretical glass transition temperature (value) obtained based on Fox's equation below may be used. Fox's equation 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 Fox's equation below, Tg represents the glass transition temperature (°C) of the polymer, Wi represents the weight fraction of monomer i constituting the polymer, and Tgi represents the glass transition temperature (°C) of the homopolymer formed from monomer i. For the glass transition temperature of the homopolymer, literature values ​​can be used. For example, "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) and "New Polymer Library 7: Introduction to Synthetic Resins for Coatings" (by Kyozo Kitaoka, Polymer Publication Association, 1995) list the glass transition temperatures of various homopolymers. On the other hand, the glass transition temperature of the monomer homopolymer can also be determined by the method specifically described in Japanese Patent Publication No. 2007-51271.

[0067] Fox's formula 1 / (273+Tg)=Σ[Wi / (273+Tgi)]

[0068] When an acrylic polymer is used as the base polymer, an acrylic oligomer is preferred as the oligomer. The acrylic oligomer is a copolymer of monomer components containing 50% by mass or more of an alkyl (meth)acrylate, and has a weight-average molecular weight of, for example, 1,000 to 30,000.

[0069] Acrylic oligomers are preferably polymers of monomer components containing a (meth)acrylate (linear alkyl(meth)acrylate) having a chain-like alkyl group and an (meth)acrylate (alicyclic alkyl(meth)acrylate) having an alicyclic alkyl group. Specific examples of these (meth)acrylate (alkyl)esters include, for example, the above-mentioned (meth)acrylate (alkyl)esters used as monomer components in acrylic polymers.

[0070] As the linear alkyl (meth)acrylate, methyl methacrylate is preferred due to its high glass transition temperature and relatively high compatibility with the base polymer. As the alicyclic alkyl (meth)acrylate, dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferred. In other words, the acrylic oligomer is preferably a polymer of monomer components containing one or more selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate.

[0071] The proportion of alicyclic alkyl (meth)acrylate in the monomer component of the acrylic oligomer is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and particularly preferably 35% by mass or more. The same proportion is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 65% ​​by mass or less. The proportion of linear alkyl (meth)acrylate in the monomer component of the acrylic oligomer is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. The same proportion is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more.

[0072] Acrylic oligomers are obtained by polymerizing the monomer components of the acrylic oligomer. Examples of polymerization methods include solution polymerization, active energy ray polymerization (e.g., UV polymerization), bulk polymerization, and emulsion polymerization. In the polymerization of acrylic oligomers, polymerization initiators may be used, and chain transfer agents may be used for the purpose of adjusting the molecular weight.

[0073] To sufficiently increase the adhesive strength of the adhesive sheet 10, the acrylic oligomer content in the adhesive sheet 10 is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.3 parts by mass or more, and particularly preferably 0.4 parts by mass or more, per 100 parts by mass of the base polymer. On the other hand, from the viewpoint of ensuring the transparency of the adhesive sheet 10, the acrylic oligomer content in the adhesive sheet 10 is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of the base polymer. In the adhesive sheet 10, if the acrylic oligomer content is too high, the haze tends to increase and the transparency tends to decrease due to a decrease in the compatibility of the acrylic oligomer.

[0074] 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, more preferably 0.2 parts by mass or more, per 100 parts by mass of the base polymer. The content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less.

[0075] The adhesive composition may contain other components as needed. Examples of other components include solvents, tackifiers, plasticizers, softeners, antioxidants, fillers, colorants, UV absorbers, surfactants, and antistatic agents. Examples of solvents include polymerization solvents used as needed during the polymerization of acrylic polymers, and solvents added to the polymerization reaction solution after polymerization. Examples of such solvents include ethyl acetate and toluene.

[0076] The adhesive sheet 10 can be manufactured, for example, by applying the above-described adhesive composition onto a release liner L1 (first release liner) to form a coating film, and then drying the coating film.

[0077] Examples of the release liner L1 include a flexible plastic film. Examples of such plastic films 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 for example, 200 μm or less. The surface of the release liner L1 is preferably treated to release the coating.

[0078] Methods for applying the adhesive composition include, for example, roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, and die coating. The drying temperature of the coating film is, for example, 50°C to 200°C. The drying time is, for example, 5 seconds to 20 minutes.

[0079] A second release liner (L2) may be laminated on top of the adhesive sheet 10 on the release liner L1. Preferably, the release liner L2 is a flexible plastic film with a peel-off surface treatment. As the release liner L2, the plastic film described above with respect to the release liner L1 can be used.

[0080] In this manner, an adhesive sheet 10 can be manufactured in which the adhesive surfaces 11 and 12 are covered and protected by the release liners L1 and L2.

[0081] 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 ease of handling. From the viewpoint of making the flexible device thinner, the thickness of the adhesive sheet 10 is preferably 300 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less, and particularly preferably 50 μm or less.

[0082] The haze of the adhesive sheet 10 is preferably 3% or less, more preferably 2% or less, and more 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 haze meters include the "NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd. and the "HM-150" manufactured by Murakami Color Technology Laboratory Co., Ltd.

[0083] The total light transmittance of the adhesive sheet 10 is preferably 60% or more, more preferably 80% or more, and even more preferably 85% or more. The total light transmittance of the 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).

[0084] Figures 4A to 4C show an example of how to use the adhesive sheet 10.

[0085] In this method, first, as shown in Figure 4A, the adhesive sheet 10 is attached to one side of the first member 21 (adhered object) in the thickness direction H. The first member 21 is, for example, one element in the laminated structure of a flexible display panel. Examples of such elements include a pixel panel, a polarizing plate, a touch panel, and a cover film (the same applies to the second member 22 described later). Through this step, an adhesive sheet 10 for bonding with other members (the second member 22 described later) is provided on the first member 21.

[0086] Next, as shown in Figure 4B, one side of the first member 21 in the thickness direction H and the other side of the second member 22 in the thickness direction H are joined via an adhesive sheet 10 on the first member 21. The second member 22 is, for example, another element in the laminated structure of a flexible display panel.

[0087] Next, as shown in Figure 4C, the adhesive sheet 10 between the first member 21 and the second member 22 is aged. Aging promotes the crosslinking reaction of the base polymer in the adhesive sheet 10, increasing 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 is, for example, 1 minute to 21 days. When aging is performed by autoclave treatment (heat and pressure treatment), the temperature is, for example, 30°C to 80°C, the pressure is, for example, 0.1 to 0.8 MPa, and the treatment time is, for example, 15 minutes or more.

[0088] As described above, the adhesive sheet 10 comprises a base polymer having a glass transition temperature Tg1 and an oligomer having a glass transition temperature Tg2 higher than Tg1, with the oligomer with the higher glass transition temperature being unevenly distributed on and near the surface of the adhesive sheet 10. Such an adhesive sheet 10 is suitable for flexible device applications, as described above. [Examples]

[0089] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples. Furthermore, the specific numerical values ​​such as the amounts (contents), physical properties, and parameters described below can be substituted with the upper limits (numerical values ​​defined as "less than or equal to" or "less than") or lower limits (numerical values ​​defined as "greater than or equal to" or "greater than") of the corresponding amounts (contents), physical properties, and parameters described in the "Modes for Carrying Out the Invention" above.

[0090] <Preparation of acrylic polymers> In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, a mixture containing 68 parts by mass of 2-ethylhexyl acrylate (2EHA), 10 parts by mass of lauryl acrylate (LA), 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), 0.1 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and ethyl acetate as a solvent (solid content concentration 47% by mass) was stirred at 56°C for 6 hours under a nitrogen atmosphere (polymerization reaction). This yielded a polymer solution containing an acrylic polymer. The weight-average molecular weight of the acrylic polymer in this polymer solution was approximately 2 million. The glass transition temperature (first glass transition temperature Tg1) of the acrylic polymer was -46.4°C. The solid content concentration of the above mixture was adjusted by adjusting the amount of solvent.

[0091] <Preparation of Acrylic Oligomer M1> First, in a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, a mixture (solid content 26% by mass) containing 60 parts by mass of dicyclopentanyl methacrylate (DCPMA), 40 parts by mass of methyl methacrylate (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 ethyl acetate as a solvent was reacted under a nitrogen atmosphere at 70°C for 2 hours, and then at 80°C for 3 hours (polymerization reaction). Next, the reaction solution was heated at 130°C for 2 hours to volatilize and remove ethyl acetate, the chain transfer agent, and unreacted monomers. This yielded a solid acrylic oligomer M1 (dry) as a hydrophobic oligomer without polar groups. The weight-average molecular weight Mw of acrylic oligomer M1 was 2500. The glass transition temperature (second glass transition temperature Tg2) of acrylic oligomer M1 was 61°C. The melting temperature Tm of acrylic oligomer M1 was 120°C.

[0092] <Preparation of Acrylic Oligomer M2> Acrylic oligomer M2 was obtained in the same manner as acrylic oligomer M1, 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. Acrylic oligomer M2 had a weight-average molecular weight of 3600. The glass transition temperature (second glass transition temperature Tg2) of acrylic oligomer M2 was 73°C. The melting temperature Tm of acrylic oligomer M2 was 130°C.

[0093] <Preparation of Acrylic Oligomer M3> Acrylic oligomer M3 was obtained in the same manner as acrylic oligomer M1, 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. Acrylic oligomer M3 had a weight-average molecular weight of 6400. The glass transition temperature (second glass transition temperature Tg2) of acrylic oligomer M3 was 89°C. The melting temperature Tm of acrylic oligomer M3 was 150°C.

[0094] <Preparation of Acrylic Oligomer M4> Acrylic oligomer M4 was obtained in the same manner as acrylic oligomer M1, 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. Acrylic oligomer M4 had a weight-average molecular weight of 8100. The glass transition temperature (second glass transition temperature Tg2) of acrylic oligomer M4 was 92°C. The melting temperature Tm of acrylic oligomer M4 was 150°C.

[0095] <Preparation of Acrylic Oligomer M5> Acrylic oligomer M5 was obtained in the same manner as acrylic oligomer M1, 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. Acrylic oligomer M5 had a weight-average molecular weight of 17,000. The glass transition temperature (second glass transition temperature Tg2) of acrylic oligomer M5 was 100°C. The melting temperature Tm of acrylic oligomer M5 was 170°C.

[0096] <Preparation of Acrylic Oligomer M6> Acrylic oligomer M6 was obtained in the same manner as acrylic oligomer M1, 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. The glass transition temperature (second glass transition temperature Tg2) of acrylic oligomer M6 was 110°C. The melting temperature Tm of acrylic oligomer M6 was 190°C.

[0097] <Acrylic oligomer M7> Carboxylate-containing polyacrylate-2-ethylhexyl (product name "Actflow CB3098", Mw3000, manufactured by Soken Chemical Co., Ltd.) was prepared as acrylic oligomer M7. The glass transition temperature (second glass transition temperature Tg2) of acrylic oligomer M7 was -44°C. The melting temperature Tm of acrylic oligomer M6 was less than 25°C (it was not a melting temperature that could be accurately measured within the measurement temperature range described later).

[0098] [Example 1] <Preparation of adhesive composition> To a polymer solution, 0.5 parts by mass of acrylic oligomer M1, 0.3 parts by mass of a first crosslinking agent (product name "Nipper BMT-40SV", dibenzoyl peroxide, manufactured by Nippon Oil & Fats Co., Ltd.), 0.015 parts by mass of a second crosslinking agent (product name "Takenate D110N", trimethylolpropane adduct of xylylene diisocyanate, manufactured by Mitsui Chemicals, Inc.), and 0.2 parts by mass of a silane coupling agent (product name "A100", acetoacetyl group-containing silane coupling agent, manufactured by Soken Chemical Co., Ltd.) were added and mixed to prepare an adhesive composition.

[0099] <Formation of the adhesive layer> Next, an adhesive composition was applied to the release surface of a first release liner, which had one side treated with silicone release treatment, to form a coating film. The first release liner was a polyethylene terephthalate (PET) film (product name "Diafoil MRF#75", thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) with one side treated with silicone release treatment. Next, the release surface of a second release liner, which had one side treated with silicone release treatment, was bonded to the coating film on the first release liner. The second release liner was a PET film (product name "Diafoil MRF#75", thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) with one side treated with silicone release treatment. 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 this way, an adhesive sheet (thickness 50 μm) of Example 1 with a release liner was prepared.

[0100] [Examples 2-6, Comparative Example 2] In preparing the adhesive composition, the adhesive sheets for Examples 2-6 and Comparative Example 2 were prepared in the same manner as the adhesive sheet for Example 1, except that the acrylic oligomers shown in Table 1 were used instead of acrylic oligomer M1.

[0101] [Comparative Example 1] The adhesive sheet of Comparative Example 1 was prepared in the same manner as the adhesive sheet of Example 1, except that the acrylic oligomer M1 was not included in the preparation of the adhesive composition.

[0102] <Weight average molecular weight> The weight-average molecular weight (Mw) of the acrylic polymer and acrylic oligomer described above was determined by gel permeation chromatography (GPC) under the following measurement conditions and expressed as a polystyrene equivalent. A GPC measuring device (product name "HLC-8120GPC", manufactured by Tosoh Corporation) was used for the measurement. The sample solution was prepared as follows: First, using the acrylic polymer or acrylic oligomer as the sample, a tetrahydrofuran (THF) solution with a sample concentration of 0.15% by mass (containing 10 mM phosphoric acid) was prepared, and the THF solution was left to stand for 20 hours. Next, the THF solution was filtered through a membrane filter with an average pore size of 0.45 μm, and the filtrate was obtained as the sample solution for molecular weight measurement.

[0103] [GPC measurement conditions] Column: TSKgel GMH-H(S), manufactured by Tosoh Corporation Column temperature: 40℃ Eluent: Tetrahydrofuran solution containing phosphoric acid (phosphoric acid concentration 10 mM) Flow rate: 0.5mL / min Sample injection volume: 100 μL Standard sample: Polystyrene Detector: Differential refractometer (RI) Standard sample: Polystyrene (PS)

[0104] <Dynamic viscoelasticity measurement of acrylic polymers> The glass transition temperature of acrylic polymers was identified by dynamic viscoelasticity measurements. Specifically, the results are as follows:

[0105] First, a sample for measurement was prepared. Specifically, to a polymer solution, 0.3 parts by mass of a first crosslinking agent (product name "Niper BMT-40SV", dibenzoyl peroxide, manufactured by Nippon Oil & Fats Co., Ltd.) and 0.015 parts by mass of a second crosslinking agent (product name "Takenate D110N", trimethylolpropane adduct of xylylene diisocyanate, manufactured by Mitsui Chemicals, Inc.) were added and mixed to prepare an adhesive composition. Next, an adhesive sheet with a release liner (thickness 50 μm) was prepared in the same manner as the adhesive sheet with a release liner (thickness 50 μm) of Example 1, except that this adhesive composition was used in place of the adhesive composition described above for Example 1. Next, several pieces of adhesive sheet cut from this adhesive sheet were bonded together to prepare an adhesive sheet with a thickness of approximately 1 mm. Next, this sheet was punched out to obtain cylindrical pellets (diameter 7.9 mm) which were to be used as the measurement sample.

[0106] Then, dynamic viscoelasticity measurements were performed on the sample for measurement using a dynamic viscoelasticity measuring device (product name "Discovery Hybrid Rheometer (DHR)", manufactured by TA Instruments) after fixing it to a jig with a diameter of 7.9 mm parallel plate. In this measurement, the measurement mode was set to shear mode, the measurement temperature range to -50°C to 110°C, the heating rate to 5°C / min, and the frequency to 1 Hz. From the measurement results (values ​​of loss modulus, storage modulus, and loss tangent tanδ [= loss modulus / storage modulus] over the measurement temperature range), the temperature at which the loss tangent tanδ was maximum was read. This value is shown in Table 1 as the glass transition temperature Tg1 (°C) of the acrylic polymer.

[0107] <TMA measurement of acrylic oligomers> The softening and melting temperatures of acrylic oligomers were measured by thermomechanical analysis (TMA). First, the acrylic oligomer (dry state) to be measured was crushed into a powder, and this powder was placed in a sample container (made of aluminum) as the measurement sample. Next, an aluminum lid was placed on top of the measurement sample in the sample container, and a probe (connected to the load generating part) was placed on the lid. Then, using a TMA apparatus (product name "TMA / SS6000", manufactured by Hitachi High-Tech Science), a constant load was applied to the measurement sample in the sample container via the probe and lid, and the deformation of the measurement sample according to the temperature was measured (compression and expansion measurement). In this measurement, the measurement mode was set to compression and expansion mode, the measurement load was set to 19.6 mN (equivalent to 2 g), nitrogen gas (flow rate 200 ml / min) was used as the atmospheric gas, the measurement temperature range was from 20°C to 200°C, and the heating rate was set to 10°C / min. The measured softening temperature is shown in Table 1 as the glass transition temperature Tg2 (°C) of the acrylic oligomer. The measured melting temperature Tm (°C) is also shown in Table 1. The sum of the glass transition temperatures Tg1 and Tg2, and the ratio of the melting temperature Tm to the glass transition temperature Tg2 (Tm / Tg2) are also shown in Table 1.

[0108] <TEM observation> The surface vicinity of each adhesive sheet from Examples 1-6 and Comparative Examples 1 and 2 was observed using an electron microscope (TEM). Oligomer aggregates (domains) were confirmed in each adhesive sheet from Examples 1-6. The maximum length (μm) of the oligomer aggregates is shown in Table 1. No oligomer aggregates were confirmed in the adhesive sheets from Comparative Examples 1 and 2.

[0109] <Peelability> The peeling adhesive strength of each adhesive sheet in Examples 1-6 and Comparative Examples 1 and 2 was investigated by peel tests.

[0110] First, test specimens were prepared for each adhesive sheet. In preparing the test specimens, the second release liner was peeled off from the adhesive sheet with the release liner, and a PET film (thickness 50 μm) was bonded to the exposed surface of the adhesive sheet to obtain a laminated film (first release liner / adhesive sheet / PET film). For bonding, the adhesive sheet was pressed onto the PET film by running a 2 kg roller back and forth once. Next, test specimens (width 25 mm x length 100 mm) were cut from the laminated film. Then, under conditions of 23°C and 50% relative humidity, the first release liner was peeled off from the adhesive sheet of the test specimen, and the exposed surface of the adhesive sheet was bonded to the air surface of an alkali glass plate (blue glass, manufactured by Matsunami Glass Industry Co., Ltd.) prepared by the float method to obtain a laminate (alkali glass plate / adhesive sheet / PET film). The air surface refers to the exposed surface of the alkali glass sheet (the surface opposite to the surface in contact with the molten metal) when the alkali glass sheet flows over the molten metal during the alkali glass sheet manufacturing process. In the bonding process, the test specimen was pressed onto the alkali glass sheet by moving a 2kg roller back and forth once. Next, the laminate was autoclaved (heated and pressurized). In the autoclaving process, the temperature was set to 50°C, the pressure to 0.5MPa, and the processing time to 15 minutes. Next, a peel test was performed to peel the test specimen from the alkali glass sheet in an environment of 23°C and 50% relative humidity, and the force required for peeling was measured as the peel adhesive force. A tensile testing machine (product name "Tensile Compression Testing Machine TCM-1kNB", manufactured by Minebea Co., Ltd.) was used for this measurement. In this measurement, the peel angle of the test specimen relative to the adherend was set to 180°, the tensile speed of the test specimen was set to 300 mm / min, and the peel length was set to 50 mm (measurement conditions for the peel test). The measured peel-off adhesive strength F (N / 25mm) is shown in Table 1.

[0111] <TOF-SIMS> The surface vicinity of each adhesive sheet in Examples 1-6 and Comparative Examples 1 and 2 was analyzed for its components by time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0112] The sample for TOF-SIMS analysis was prepared as follows. First, a piece (10 mm × 10 mm) of the adhesive sheet with a release liner was cut out from the adhesive sheet with a release liner. Next, the first release liner was peeled off from the piece of the adhesive sheet with a release liner. Next, the exposed adhesive sheet piece by the peeling was bonded to the polyimide substrate. Next, the second release liner was peeled off from the adhesive sheet piece on the polyimide substrate. Thus, a sample (polyimide substrate / adhesive sheet piece) was obtained.

[0113] Then, by TOF-SIMS, component analysis in the thickness direction from the second surface (the surface opposite to the first surface) to the first surface of the adhesive sheet with the polyimide substrate bonded to one surface (the first surface) was performed. For the analysis, a time-of-flight secondary ion mass spectrometer (product name: "TRIFT-V", manufactured by ULVAC-PHI, Inc.) was used. In this analysis, irradiation with an etching ion beam and subsequent irradiation with a measurement ion beam (primary ion beam) were alternately repeated. In the irradiation with the etching ion beam, Ar gas cluster ions (Ar n + ) were used, the acceleration voltage was set to 10 kV, the irradiation range was set to 1000 μm × 1000 μm, and each irradiation time was set to 5 seconds. In the irradiation with the measurement ion beam, as the irradiation primary ion, double-charged ions of bismuth cluster (Bi3 ++ ) were used, the acceleration voltage was set to 30 kV, the irradiation range was set to 100 μm × 100 μm at the center of the etching ion beam irradiation region, and a neutral gun for correcting the charge of the sample during analysis was used. Also, this analysis was performed at room temperature.

[0114] By this analysis, a profile (depth profile) in the depth direction (thickness direction of the adhesive sheet piece) of the mass spectrum of the secondary ion (negative ion) intensity was obtained. Fragments detected as secondary ions (negative ions) in this analysis include a first fragment derived from an acrylic oligomer, a CN - fragment (second fragment) derived from the polyimide substrate, and C3H3O2 -A fragment (third fragment) is included. The first fragment is C4H5O2 in Examples 1-6. - As a fragment, in Comparative Example 2, C8H 15 O - The fragment was used (Comparative Example 1 does not contain acrylic oligomer). C4H5O2 - The ratio of the secondary ion mass (m) to the secondary ion charge number (z) of the fragment (m / z) is 85. C8H 15 O - The fragment ratio (m / z) is 127. CN - The fragment ratio (m / z) is 26. C3H3O2 - The ratio (m / z) of the fragments is 71. The secondary ion strength of each fragment is C2H - The ionic intensity of the fragment was converted to a value with a baseline of 1 (normalization).

[0115] Figure 5 shows the TOF-SIMS measurement results of the adhesive sheet of Example 1. Figure 6 shows a magnified view of a portion of the measurement results shown in Figure 5. In the graphs shown in Figures 5 and 6, the horizontal axis represents the analysis time (seconds), with the time showing the analysis results at a predetermined intermediate position in the thickness direction of the adhesive sheet being set to 0 seconds. The vertical axis in the same graph represents the normalized ionic intensity (C2H - This represents the ionic strength of the fragment relative to its ionic strength. Figures 5 and 6 show the first fragment (C4H5O2) derived from the acrylic oligomer. - The solid line shows the change in ionic strength of the second fragment (CN) derived from the polyimide substrate. - The dotted line shows the change in ionic strength of the fragment, and the third fragment (C3H3O2) originates from the acrylic-based polymer. -The change in the ion intensity of the (fragment) is represented by a two-dot chain line. As shown in FIGS. 5 and 6, the detection maximum peak P of the ion intensity of the first fragment derived from the acrylic oligomer is detected at the detection time t1 between the detection start time t2 of the second fragment derived from the polyimide substrate (the start time of the rise in the detection amount of the second fragment) and the detection end time t3 of the third fragment derived from the acrylic-based polymer (after the detection start time t2) (t2 < t1 < t3). The ion intensity I1 and the detection time t1 (seconds) of the detection maximum peak P are shown in Table 1. Also, the ratio (I1 / I2) of the ion intensity I1 of the detection maximum peak P to the average value of the ion intensity of the first fragment (ion intensity average value I2) from the time 10σ away from the analysis start time side to the time 5σ away from the half-width σ (seconds) of the detection maximum peak P was 1.75 for the adhesive sheet of Example 1. The half-width σ (seconds) of the detection maximum peak P, the ion intensity average value I2, and the ratio (I1 / I2) are also shown in Table 1.

[0116] In each of the adhesive sheets of Examples 2 to 6, similar to the adhesive sheet of Example 1, in TOF-SIMS, the detection maximum peak P of the ion intensity of the first fragment derived from the acrylic oligomer was detected between the detection start time t2 of the second fragment derived from the polyimide substrate and the detection end time t3 of the third fragment derived from the acrylic-based polymer (t2 < t1 < t3). For each of the adhesive sheets of Examples 2 to 6, the ion intensity I1, the detection time t1 (seconds), and the half-width σ (seconds) of the detection maximum peak P are shown in Table 1. For each of the adhesive sheets of Examples 2 to 6, the ion intensity average value I2 and the ratio (I1 / I2) are also shown in Table 1.

[0117] FIG. 7 shows the measurement results 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 predetermined intermediate position in the thickness direction of the adhesive sheet is represented as 0 seconds. The vertical axis in the same graph represents the normalized ion intensity (ion intensity relative to the ion intensity of the - fragment). In FIG. 7, the first fragment (C8H 15 O -The change in the ion intensity of the first fragment is represented by a solid line, and the change in the ion intensity of the second fragment (CN - fragment) derived from the polyimide substrate is represented by a dashed line, and the change in the ion intensity of the third fragment (C3H3O2 - fragment) derived from the acrylic-based polymer is represented by a dotted line. As shown in FIG. 7, between the detection start time t2 of the second fragment derived from the polyimide substrate (the start time of the rise in the detection amount of the second fragment) and the detection end time t3 of the third fragment derived from the acrylic-based polymer (after the detection start time t2), the maximum detection peak of the ion intensity of the first fragment derived from the acrylic oligomer was not detected. For the adhesive sheet of Comparative Example 2, the ion intensity I1, the detection time t1 (seconds), and the half-value width σ (seconds) of the detection maximum peak P are shown in Table 1. For the adhesive sheet of Comparative Example 2, the ion intensity average value I2 and the ratio (I1 / I2) are also shown in Table 1.

[0118] 〔Evaluation〕 The adhesive sheet of Comparative Example 1 does not contain an acrylic oligomer. The adhesive sheet of Comparative Example 2 contains an acrylic oligomer, but the acrylic oligomer is not unevenly distributed on the adhesive surface and its vicinity as described above. Such adhesive sheets of Comparative Examples 1 and 2 have a low adhesive force as shown in Table 1. On the other hand, in each of the adhesive sheets of Examples 1 to 6, the acrylic oligomer is unevenly distributed on the adhesive surface and its vicinity. Specifically, the detection maximum peak P of the ion intensity of the first fragment derived from the acrylic oligomer is detected between the detection start time t2 of the second fragment derived from the polyimide substrate and the detection end time t3 of the third fragment derived from the acrylic-based polymer (t2 < t1 < t3), and the ratio (I1 / I2) of the ion intensity I1 to the ion intensity average value I2 of the first fragment is 1.2 or more. Each of the adhesive sheets of Examples 1 to 6 has a higher adhesive force than the adhesive sheets of Comparative Examples 1 and 2.

[0119]

Table 1

Explanation of Symbols

[0120] 10 Adhesive sheets (optical adhesive sheets) 11 Page 1 12 Side 2 L1, L2 peel-off liner 21 First Member 22 Second Member H thickness direction

Claims

1. A base polymer having a first glass transition temperature, The oligomer having a second glass transition temperature higher than the first glass transition temperature, An optical adhesive sheet having a first surface and a second surface opposite to the first surface, In a component analysis of the optical adhesive sheet with a substrate bonded to the first surface, using time-of-flight secondary ion mass spectrometry, in the thickness direction from the second surface to the first surface, The maximum detection peak of the ionic intensity of the first fragment derived from the oligomer is detected between the detection start time of the second fragment derived from the substrate and the detection end time of the third fragment derived from the base polymer, which is after the detection start time. An optical adhesive sheet in which the ratio of the ionic intensity of the detected maximum peak to the average value of the ionic intensity of the first fragment from a time 10σ away from the half-width σ (seconds) of the detected maximum peak toward the start of analysis to a time 5σ away is 1.2 or more.

2. The optical adhesive sheet according to claim 1, wherein the oligomer forms aggregates with a maximum length of 0.4 μm or less.

3. The optical adhesive sheet according to claim 1 or 2, wherein the second glass transition temperature is 50°C or higher.

4. 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.

5. The optical adhesive sheet according to any one of claims 1 to 4, wherein the oligomer has a weight-average molecular weight of 2000 or more.

6. The optical adhesive sheet according to any one of claims 1 to 5, wherein the sum of the first glass transition temperature and the second glass transition temperature is 0°C or higher.

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