Optical adhesive sheet and laminate

Abstract

The present invention provides an adhesive sheet having high adhesive force at high temperature, excellent step followability, and excellent durability. The present invention further provides a laminate including the optical adhesive sheet.　The present invention is an optical adhesive sheet containing a cured product of an adhesive composition, wherein the adhesive composition contains an acrylic polymer, and the acrylic polymer has a hydroxyl value of 70 mg KOH / g or more. This optical adhesive sheet satisfies the following physical properties (1) and (2). Physical property (1); a probe is pressed into the surface of the adhesive sheet at a speed of 5 μm / s in an environment of 25°C, and the pressing is stopped when the tip of the probe reaches a depth of 20% of the thickness of the adhesive sheet. A stress value F2, measured when this state is held for 60 seconds, is 60% or less of a maximum stress value F1. Physical property (2); the adhesive force at 110°C is 2 N / 25 mm or more.

Description

Optical adhesive sheets and laminates

[0001] This invention relates to optical adhesive sheets and laminates.

[0002] Adhesive sheets are adhesive materials formed by curing an adhesive composition, primarily composed of acrylic polymer, with heat or ultraviolet light. They are used for bonding optical components such as touch panels and liquid crystal displays (LCDs). For example, in display applications, there is a problem in that it is difficult to apply adhesive sheets when the surface shape is complex.

[0003] To solve this problem, Patent Document 1 proposes an adhesive sheet in which the adhesive strength at 23°C and the indentation hardness of the adhesive layer at 70°C are adjusted to a predetermined range when the adhesive layer contained in the adhesive sheet is attached to a polyimide film. Such an adhesive sheet is said to achieve both step-following ability and peelability.

[0004] Japanese Patent Publication No. 2021-175789

[0005] However, due to the increasing complexity of electronic component shapes in recent years, the demand for adhesive sheets to conform to uneven surfaces is also growing, and further improvements in durability are required. In particular, for full lamination applications, there are printing steps (e.g., 10 μm or more) to conceal wiring, so adhesive sheets are required to have the ability to fill in such printing steps.

[0006] The present invention has been made in view of the above, and aims to provide an adhesive sheet that has high adhesive strength at high temperatures, excellent ability to follow steps, and excellent durability, as well as a laminate equipped with such an optical adhesive sheet.

[0007] The inventors of this invention conducted extensive research to achieve the above objectives and discovered that these objectives can be achieved by using an acrylic polymer having a specific hydroxyl value as an essential component and by giving the adhesive sheet the desired flexibility. As a result, the inventors of this invention have completed the present invention.

[0008] In other words, the present invention encompasses, for example, the subject matter described in the following sections. Section 1 An optical adhesive sheet containing a cured product of an adhesive composition, wherein the adhesive composition contains an acrylic polymer, the acrylic polymer has a hydroxyl value of 70 mgKOH / g or more, and satisfies the following physical properties (1) and (2): Physical property (1): When a probe is pressed into the surface of the adhesive sheet at a speed of 5 μm / second in a 25°C environment, and the pressing is stopped when the tip of the probe reaches a depth of 20% of the thickness of the adhesive sheet, the stress value F2 measured when this state is held for 60 seconds is 60% or less of the maximum stress value F1; Physical property (2): The adhesive force at 110°C is 2 N / 25 mm or more. Section 2 The optical adhesive sheet according to Section 1, wherein the glass transition temperature of the acrylic polymer is -10°C or less. Item 3 An optical adhesive sheet according to Item 1 or 2, wherein the acrylic polymer comprises (meth)acrylate units having linear or branched alkyl groups, (meth)acrylate units having alicyclic structures in their side chains, and monomer units having hydroxyl groups in their side chains. Item 4 An optical adhesive sheet according to any one of Items 1 to 3, wherein the adhesive composition comprises a silane coupling agent having an isocyanurate structure. Item 5 An optical adhesive sheet according to any one of Items 1 to 4, wherein the adhesive composition contains a photoinitiator, and the cured product is an ultraviolet-cured product. Item 6 An optical adhesive sheet according to Item 5, wherein the adhesive composition comprises an ultraviolet absorber. Item 7 An optical adhesive sheet according to any one of Items 1 to 6, having a thickness of 100 μm or more. Item 8 An optical adhesive sheet according to any one of Items 1 to 7, wherein the acrylic polymer contains 2-octyl acrylate units derived from biomass raw materials. Item 9 A laminate comprising an optical adhesive sheet according to any one of Items 1 to 8.

[0009] The optical adhesive sheet of the present invention exhibits high adhesive strength at high temperatures, excellent conformability to uneven surfaces, and superior durability. For these reasons, the optical adhesive sheet of the present invention is suitable as an adhesive sheet for various optical applications.

[0010] Embodiments of the present invention will be described in detail below. In this specification, the expressions "containing" and "including" include the concepts of "containing," "including," "substantially consisting of," and "consisting only of."

[0011] In the numerical ranges described stepwise in this specification, the upper or lower limit of a numerical range in one step can be arbitrarily combined with the upper or lower limit of a numerical range in another step. In the numerical ranges described in this specification, the upper or lower limit of a numerical range may be replaced with values ​​shown in the examples or values ​​that can be uniquely derived from the examples. Furthermore, in this specification, numbers connected by "~" mean a numerical range that includes the numbers before and after "~" as the lower and upper limits.

[0012] The optical adhesive sheet of the present invention contains a cured product of an adhesive composition, the adhesive composition contains an acrylic polymer, the acrylic polymer has a hydroxyl value of 70 mgKOH / g or more, and satisfies the following physical properties (1) and (2). Physical property (1): When a probe is pressed into the surface of the adhesive sheet at a speed of 5 μm / second in a 25°C environment, and the pressing is stopped when the tip of the probe reaches a depth of 20% of the thickness of the adhesive sheet, the stress value F2 measured when this state is held for 60 seconds is 60% or less of the maximum stress value F1. Physical property (2): The adhesive strength at 110°C is 2 N / 25 mm or more.

[0013] The optical adhesive sheet of the present invention satisfies all of the physical properties (1) and (2), resulting in high adhesive strength at high temperatures (for example, in an environment of 110°C), excellent step-following ability, and superior durability. Specifically, the optical adhesive sheet of the present invention has high adhesive strength at high temperatures, is relatively flexible, and can exhibit excellent step-following ability, and can particularly suppress step lifting that occurs when heated. Furthermore, the optical adhesive sheet of the present invention also has excellent resistance to moisture and heat whitening. Therefore, the optical adhesive sheet of the present invention is suitable for use as an adhesive sheet for various optical applications, and is particularly suitable for full lamination applications.

[0014] 1. Adhesive Composition The optical adhesive sheet of the present invention contains a cured product of the adhesive composition. That is, the optical adhesive sheet of the present invention is formed by curing the adhesive composition. Such an adhesive composition contains an acrylic polymer as an essential component.

[0015] (Acrylic Polymer) Acrylic polymer is the main component of adhesive compositions and is a component that can impart adhesive properties to optical adhesive sheets. Note that acrylic polymer includes methacrylic polymer.

[0016] Acrylic polymers are polymers having (meth)acrylic monomer units, that is, polymers of (meth)acrylic monomers. In this specification, "(meth)acrylic" means "acrylic" or "methacrylic," and "(meth)acrylate" means "acrylate" or "methacrylate." In this specification, monomer units and monomer units mean the smallest unit (i.e., structural unit) formed by the polymerization (radical polymerization) of monomers.

[0017] Acrylic polymers can contain various (meth)acrylic monomer units as long as their hydroxyl value is 70 mgKOH / g or more. Examples of (meth)acrylic monomers for forming (meth)acrylic monomer units include various monofunctional monomers, such as (meth)acrylic monomers having hydroxyl groups, and (meth)acrylic monomer M, which is other than (meth)acrylic monomers having hydroxyl groups. Examples of (meth)acrylic monomer M include (meth)acrylic monomers having linear or branched alkyl groups, and (meth)acrylic monomers having a ring structure in the side chain.

[0018] Examples of (meth)acrylic monomers having hydroxyl groups include (meth)acrylates having hydroxyl groups. Examples of hydroxyl group-containing (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2,2-dimethyl-2-hydroxyethyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, and polyalkylene glycol mono(meth)acrylate. In particular, the (meth)acrylate having a hydroxyl group is preferably 4-hydroxybutyl (meth)acrylate.

[0019] Examples of (meth)acrylic monomers having linear or branched alkyl groups include (meth)acrylates having linear or branched alkyl groups.

[0020] As a (meth)acrylic monomer having a linear or branched alkyl group, the number of carbon atoms in the alkyl group can be, for example, 1 to 20, preferably 1 to 15, more preferably 2 to 14, and even more preferably 3 to 12.

[0021] Specific examples of (meth)acrylic monomers having linear or branched alkyl groups include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, isopropyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-octyl acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, and behenyl (meth)acrylate. These can be used individually or in combination of two or more. In particular, the (meth)acrylate having linear or branched alkyl groups is preferably selected from the group consisting of 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, and 2-octyl acrylate.

[0022] Examples of acrylic monomers having a ring structure in the side chain include (meth)acrylates having a ring structure in the side chain, and among these, (meth)acrylates having an alicyclic or aromatic ring in the side chain are preferred, and (meth)acrylic monomers having an alicyclic ring are more preferred. Examples of alicyclic rings include cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane, cyclododecane, norbornene, norbornadiene, dicyclopentane, isobornyl, tetrahydrofuran, and tetrahydropyran. The alicyclic ring may also have a spiro structure. Examples of aromatic rings include benzene, naphthalene, anthracene, pyridine, furan, benzofuran, pyrrole, thiophene, imidazole, and oxazole. Among these, the ring structure is preferably alicyclic, more preferably at least one selected from cyclohexane, dicyclopentane, and isobornyl, and particularly preferably cyclohexane or isobornyl.

[0023] The ring structure described above may have further substituents. Examples of substituents include substituted substituents selected from halogen atoms, alkyl halides, alkyl groups, alkenyl groups, acyl groups, hydroxyl groups, hydroxyalkyl groups, alkoxy groups, aryl groups, heteroaryl groups, alicyclic groups, cyano groups, epoxy groups, oxetanyl groups, mercapto groups, amino groups, and the like.

[0024] When the acrylic polymer contains (meth)acrylate units having a ring structure in its side chains, the optical adhesive sheet of the present invention tends to exhibit improved adhesion to resins other than glass (e.g., polarizing plates, etc.).

[0025] Specific examples of (meth)acrylates having a ring structure in the side chain include, for example, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, 3-phenoxybenzyl (meth)acrylate, and O-phenylphenoxyethyl (meth)acrylate. Among these, the (meth)acrylate having a ring structure in the side chain is more preferably one or more selected from the group consisting of cyclohexyl (meth)acrylate and isobornyl (meth)acrylate, with cyclohexyl (meth)acrylate being particularly preferred, as it particularly improves adhesion between the optical adhesive sheet and the glass substrate and particularly enhances durability.

[0026] In addition to acrylic monomers having linear or branched alkyl groups and acrylic monomers having a ring structure in the side chain, other examples of the acrylic monomer M include acrylic monomers having a nitrogen atom and monomers having a carboxyl group.

[0027] The acrylic polymer preferably has (meth)acrylate units having linear or branched alkyl groups, (meth)acrylate units having alicyclic structures in the side chains, and monomer units having hydroxyl groups in the side chains. In this case, the adhesive sheet for optical applications of the present invention tends to have improved adhesive strength and durability.

[0028] The acrylic polymer preferably contains 30% by mass or more of acrylic monomer units having a linear or branched alkyl group, more preferably 40% by mass or more, even more preferably 50% by mass or more, particularly preferably 55% by mass or more, more preferably 90% by mass or less, even more preferably 85% by mass or less, and particularly preferably 80% by mass or less.

[0029] The acrylic polymer preferably contains 1% by mass or more of acrylic monomer units having a ring structure in the side chain, more preferably 3% by mass or more, even more preferably 5% by mass or more, preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and particularly preferably 15% by mass or less.

[0030] The acrylic polymer preferably contains 10% by mass or more of acrylic monomer units having hydroxyl groups, more preferably 15% by mass or more, even more preferably 18% by mass or more, preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, and particularly preferably 35% by mass or less.

[0031] The acrylic polymer more preferably contains 80% by mass or more in total amounts of (meth)acrylic monomer units having linear or branched alkyl groups, (meth)acrylic monomer units having a ring structure in the side chain, and (meth)acrylic monomer units having a hydroxyl group, and is even more preferably 85% by mass or more, and particularly preferably 90% by mass or more.

[0032] Furthermore, the proportion (molar ratio) of each unit contained in the acrylic polymer may be the same as the molar ratio of each monomer used in the production of the acrylic polymer.

[0033] It is preferable that the monomer units constituting the acrylic polymer include monomer units derived from biomass raw materials. For example, it is preferable that the acrylic polymer contains monomer units such as lauryl (meth)acrylate, stearyl (meth)acrylate, 2-octyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and isobornyl (meth)acrylate derived from biomass raw materials.

[0034] As mentioned above, the hydroxyl value of the acrylic polymer is 70 mg KOH / g or more. This makes it easier for the optical adhesive sheet of the present invention to have improved resistance to humid heat whitening and superior durability. If the hydroxyl value of the acrylic polymer is less than 70 mg KOH / g, it becomes difficult to satisfy all of physical properties (1) and (2), and the step-following ability and durability of the resulting optical adhesive sheet tend to be impaired, and in particular, the resistance to humid heat whitening tends to deteriorate.

[0035] The hydroxyl value of the acrylic polymer is preferably 75 mg KOH / g or more, more preferably 200 mg KOH / g or less, more preferably 180 mg KOH / g or less, even more preferably 160 mg KOH / g or less, and particularly preferably 150 mg KOH / g or less.

[0036] In the present invention, the hydroxyl value of the acrylic polymer can be measured in accordance with JIS K 0070. On the other hand, if the amount of acrylic monomer having hydroxyl groups used in preparing the acrylic polymer is known, the hydroxyl value calculated based on that amount can be used as the hydroxyl value of the acrylic polymer. Furthermore, if the amount of acrylic monomer having hydroxyl groups or its units contained in the acrylic polymer is known, the hydroxyl value calculated based on that amount can be used as the hydroxyl value of the acrylic polymer.

[0037] Preferably, the acrylic polymer has a glass transition temperature of -10°C or lower. In this case, it becomes easier for the optical adhesive sheet of the present invention to satisfy physical properties (1) and (2), and its ability to follow steps and its durability are more easily improved.

[0038] The glass transition temperature of the acrylic polymer is more preferably -20°C or lower, even more preferably -30°C or lower, particularly preferably -33°C or lower, and also preferably -80°C or higher, more preferably -70°C or higher, and even more preferably -65°C or higher.

[0039] The method for adjusting the glass transition temperature of the acrylic polymer is not particularly limited. For example, it can be adjusted to a desired range by changing the monomer species and composition ratio constituting the acrylic polymer. In the present invention, the glass transition temperature of the acrylic polymer refers to Tg determined by the following Fox's equation based on the composition of the monomers used in the synthesis of the polymer. Fox's equation: 1 / Tg = (W1 / Tg1) + (W2 / Tg2) +... + (Wm / Tgm) Here, W1 + W2 +... + Wm = 1 In the formula, Tg is the glass transition temperature of the acrylic polymer (unit: K), Tg1, Tg2,..., Tgm are the glass transition temperatures of the respective homopolymers of the m types of monomers (m is an integer) constituting the acrylic polymer, and W1, W2,..., Wm are the mass fractions of the respective constitutional units in the acrylic polymer. Note that Tg1 and W1 are in a corresponding relationship with each other. That is, the monomer constituting the homopolymer showing the glass transition temperature of Tg1 is the same as the monomer for forming the constitutional unit having a mass fraction of W1. Similarly, Tg2 and W2,..., Tgm and Wm are in a corresponding relationship with each other.

[0040] As the glass transition temperature of the homopolymer mentioned above, for example, the value listed in Polymer Handbook 4th Edition (Wiley-Interscience 2003) can be used. If it is not listed in such a handbook, the glass transition temperature of the homopolymer can be measured by differential scanning calorimeter (DSC), for example. The measurement conditions for DSC are as follows: 5 mg of sample, under a nitrogen atmosphere, the temperature is raised from -100°C to 200°C at a heating rate of 5°C / min in the first measurement (1st RUN), then cooled to -100°C at a cooling rate of 5°C / min, and then the temperature is raised again from -100°C to 200°C at a heating rate of 5°C / min in the second measurement (2nd RUN). Here, the glass transition temperature is defined as the point where, in the region where the baseline of the DSC curve measured when the temperature is raised from -100°C to 200°C in the 2nd RUN changes in a sigmoid shape in the endothermic direction, the extension of the baseline on the lower temperature side of the region where the curve changes in a sigmoid shape intersects with the tangent line to the inflection point in the sigmoid curve.

[0041] The weight-average molecular weight of the acrylic polymer is preferably greater than 10,000, more preferably 100,000 or more, even more preferably 200,000 or more, and particularly preferably 300,000 or more. Furthermore, the weight-average molecular weight of the acrylic polymer is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,000,000 or less.

[0042] Incidentally, the weight-average molecular weight referred to in the present invention means the polystyrene-equivalent weight-average molecular weight measured by gel permeation chromatography (GPC) method. There is no particular limitation on the GPC apparatus used in the GPC method, and commercially available GPC measuring machines can be used, for example, LC-2000 Plus series manufactured by JASCO Corporation, RI-2031 Plus, UV-2075 Plus, etc. as detectors. In this case, for example, a GPC column formed by connecting four of "Shodex KF801", "Shodex KF803L", "Shodex KF800L" and "Shodex KF800D" manufactured by Showa Denko K.K. is used. The column temperature can be set to 40 °C. Tetrahydrofuran is used as the eluent and the measurement is carried out at a flow rate of 1.0 ml / min. Usually, a calibration curve is prepared using standard polystyrene, and the weight-average molecular weight (Mw) can be obtained by conversion to polystyrene.

[0043] The acrylic polymer can be produced by a known method. For example, an acrylic polymer can be produced by polymerizing a monomer mixture for forming each structural unit in the acrylic polymer by a known polymerization method. As the polymerization method, for example, solution polymerization, bulk polymerization, suspension polymerization, emulsion polymerization, etc. can be adopted. The acrylic polymer can also be obtained from commercially available products, etc. In the adhesive composition, the acrylic polymer can exist, for example, in a state of a solution dissolved in a (meth)acrylic monomer. In other words, the adhesive composition can contain a solution (so-called syrup) in which the acrylic polymer is dissolved in a (meth)acrylic monomer. The acrylic polymer may be in a form other than syrup, for example, a solution dissolved in a solvent (excluding acrylic monomers), that is, the adhesive composition may be a solvent-type adhesive.

[0044] The adhesive composition preferably contains a so-called syrup, which is formed by dissolving the acrylic polymer in a (meth)acrylic monomer. Examples of (meth)acrylic monomers for forming the syrup include various monomers used to form the acrylic polymer. From this viewpoint, it is preferable that the (meth)acrylic monomers for forming the syrup include all of the following: (meth)acrylic monomers having a linear or branched alkyl group, (meth)acrylic monomers having a ring structure in the side chain, and (meth)acrylic monomers having a hydroxyl group. The content ratio of each monomer contained in the syrup can be the same as or close to the content ratio of the corresponding monomer constituting the (meth)acrylic polymer. The (meth)acrylic monomers for forming the syrup are preferably monofunctional monomers.

[0045] The proportion of acrylic polymer in the syrup can be 1 to 70% by mass, preferably 5 to 50% by mass, relative to the total mass of the acrylic polymer and (meth)acrylic monomer. The syrup may consist only of the acrylic polymer and the acrylic monomer.

[0046] (Polyfunctional Monomers) The adhesive composition may also contain polyfunctional monomers. Examples of such polyfunctional monomers include compounds having two or more polymerizable double bonds in the molecule. The polyfunctional monomer has two or more polymerizable double bonds (e.g., radical polymerizable double bonds), preferably two or more but less than five, and more preferably two or more but less than four. By containing polyfunctional monomers in the adhesive composition, a crosslinked polymer may be formed by a reaction with the monofunctional monomers in the syrup. That is, when the adhesive composition contains polyfunctional monomers, a polymer having a crosslinked structure due to the polyfunctional monomers may be contained in the optical adhesive sheet.

[0047] Examples of polyfunctional monomers include, as difunctional monomers (monomers with two polymerizable double bonds), polyethylene glycol diacrylate, polypropylene diacrylate, alkyl diacrylate, polytetramethylene glycol diacrylate, polypropylene glycol diacrylate, dioxane diacrylate, tricyclodecanol diacrylate, and fluororange acrylate. Furthermore, examples of polyfunctional monomers with three or more functions include alkoxylated trimethylolpropane triacrylate, alkoxylated glycerin triacrylate, caprolactone-modified isocyanurate triacrylate, pentaerythritol acrylate, alkoxylated pentaerythritol acrylate, (alkoxylated) pentaerythritol acrylate, (alkoxylated) ditrimethylolpropane acrylate, (alkoxylated) dipentaerythritol acrylate, and (ethoxylated) polyglycerin acrylate.

[0048] The polyfunctional monomer may have a bisphenol skeleton within a single molecule. Examples of such polyfunctional monomers include diacrylates of bisphenol A diglycidyl ether, diacrylates of propoxylated bisphenol A, and diacrylates of bisphenol F diglycidyl ether.

[0049] For example, commercially available polyfunctional monomers can be used. Examples of commercially available products include Shin Nakamura Chemical's NK Ester series of difunctional polyethylene glycol acrylates, such as "A-200" (polyethylene glycol #200 diacrylate), "A-400" (polyethylene glycol #400 diacrylate), and "A-600" (polyethylene glycol #600 diacrylate); the trifunctional monomer A-TMPT ((alkoxylated) trimethylolpropane acrylate); Toagosei Co., Ltd.'s trifunctional monomers M310 (trimethylolpropane PO-modified triacrylate) and M321 (trimethylolpropane propylene oxide-modified triacrylate); Toagosei Co., Ltd.'s difunctional monomers M211B (bisphenol A EO-modified diacrylate) and M240 (polyethylene glycol diacrylate); and the tetrafunctional monomer M-408 (ditrimethylolpropane tetraacrylate). Other commercially available polyfunctional monomers include, for example, A-DOG, A-DCP, A-9300, and A-9200YN from Shin-Nakamura Chemical, FA-731A from Hitachi Chemical, and AOMA from Nippon Shokubai.

[0050] In the adhesive composition, the content of polyfunctional monomer is preferably 0.01 parts by mass or more, more preferably 0.03 parts by mass or more, even more preferably 0.05 parts by mass or more, particularly preferably 0.07 parts by mass or more, and also preferably 1 part by mass or less, more preferably 0.5 parts by mass or less, even more preferably 0.3 parts by mass or less, even more preferably 0.13 parts by mass or less, and particularly preferably 0.1 parts by mass or less, based on 100 parts by mass of the total mass of acrylic polymer and (meth)acrylic monomer in the adhesive composition.

[0051] The polyfunctional monomer contained in the adhesive composition may be one type alone or two or more types.

[0052] (Silane coupling agent) The adhesive composition may also contain a silane coupling agent, which can increase the adhesion to the adherend at high temperatures. In addition, it becomes easier for the optical adhesive sheet of the present invention to satisfy physical properties (1) and (2), and its ability to follow steps and its durability are improved.

[0053] A wide range of known compounds can be used as silane coupling agents, such as γ-acryloxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyldialkoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltriacoxysilane, γ-methacryloxypropyltrialkoxysilane, γ-chloropropyltrialkoxysilane, γ-methacryloxypropyldialkoxysilane, γ-mercaptopropyltrialkoxysilane, tris(trimethoxysilylpropyl)isocyanurate, vinyltrialkoxysilane, etc. The silane coupling agent may also be an oligomer of various alkoxysiloxanes.

[0054] The silane coupling agent can, for example, have an isocyanurate structure. That is, the adhesive composition can contain a silane coupling agent having an isocyanurate structure. In this case, the optical adhesive sheet of the present invention can more easily satisfy physical properties (1) and (2), and its step-following ability and durability can be more easily improved.

[0055] Silane coupling agents having an isocyanurate structure include, for example, a "-R" compound on each nitrogen atom of the isocyanurate skeleton. １ -Si(OR ２ ) ３ Compounds having a structure in which " is bonded can be listed. Here, R １ For example, an alkylene group, R ２For example, this is an alkyl group. The alkylene group preferably has 1 or more carbon atoms, more preferably 2 or more, more preferably 10 or fewer carbon atoms, and more preferably 8 or fewer carbon atoms. Examples of alkyl groups include those with 1 to 10 carbon atoms, specifically methyl, ethyl, n-propyl, and isopropyl groups.

[0056] Silane coupling agents can be obtained by known manufacturing methods or from commercially available products. For example, commercially available silane coupling agents having an isocyanurate structure include Shin-Etsu Silicone's "KBM-9659". Other examples include Shin-Etsu Silicone's "KBM-403" (3-glycidoxypropyltrimethoxysilane).

[0057] The silane coupling agent contained in the adhesive composition may be one or more types.

[0058] The content of the silane coupling agent in the adhesive composition is not particularly limited. The content of the silane coupling agent is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, and 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, and particularly preferably 0.4 parts by mass or less, based on 100 parts by mass of the total mass of the acrylic polymer and (meth)acrylic monomer in the adhesive composition.

[0059] (UV absorber) The adhesive composition may further contain a UV absorber. The UV absorber is intended to provide a function of absorbing ultraviolet light in the optical adhesive sheet.

[0060] The type of UV absorber is not particularly limited, and for example, a wide range of known UV absorbers can be cited. Examples of UV absorbers include at least one UV absorber selected from the group consisting of hydroxyphenyltriazine, benzotriazole, and benzophenone types. In this case, the optical adhesive sheet formed from the adhesive composition can have its weather resistance and durability further improved.

[0061] Examples of hydroxyphenyltriazine-based UV absorbers include Tinuvin 477 (registered trademark), Tinuvin 400 (registered trademark), Tinuvin 405 (registered trademark), and Tinuvin 460 (registered trademark) from BASF Japan. Examples of benzotriazole-based UV absorbers include Tinuvin 970 (registered trademark), Tinuvin PS (registered trademark), Tinuvin 99-2 (registered trademark), Tinuvin 326 (registered trademark), Tinuvin 384-2 (registered trademark), Tinuvin 900 (registered trademark), Tinuvin 928 (registered trademark), and Tinuvin 1130 (registered trademark) from BASF Japan.

[0062] The ultraviolet absorber may also contain ultraviolet absorbers other than hydroxyphenyltriazine-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, and benzophenone-based ultraviolet absorbers, as long as the effects of the present invention are not inhibited.

[0063] The content of the ultraviolet absorber in the adhesive composition is not particularly limited. For example, the content of the ultraviolet absorber is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, even more preferably 0.5 parts by mass or more, particularly preferably 0.8 parts by mass or more, and also preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 4 parts by mass or less, and particularly preferably 3 parts by mass or less, based on 100 parts by mass of the total mass of the acrylic polymer and (meth)acrylic monomer.

[0064] The adhesive composition may contain one or more types of ultraviolet absorbers.

[0065] (Photoinitiator) The adhesive composition may further contain a photoinitiator (also called a photopolymerization initiator). The photoinitiator initiates the polymerization of the acrylic monomer in the syrup upon irradiation with active energy rays. In this specification, "active energy rays" means electromagnetic waves or charged particle beams that have energy quanta, and examples include ultraviolet rays, electron beams, visible light, X-rays, and ion beams. Among these, ultraviolet rays or electron beams are preferred from the viewpoint of versatility, and ultraviolet rays are particularly preferred.

[0066] When an adhesive composition contains a photoinitiator, the adhesive composition becomes, for example, UV-curable. That is, an adhesive composition containing a photoinitiator, and the cured product obtained when the adhesive composition hardens, can be called a UV-cured product.

[0067] The type of photoinitiator is not particularly limited, and for example, a wide range of known photoinitiators can be listed. Examples of photoinitiators include acetophenone-based photoinitiators such as 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-henylpropanone, 1-[4-(2-hydroxyethoxyl)-phenyl]-2-hydroxy-methylpropanone, and 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methyl-1-propanone, 2,4 Examples of photoinitiators include acyl phosphine oxide-based photoinitiators such as 6-trimethylbenzoyl-diphenylphosphine oxide, 2,4,6-trimethylbenzoyl)phenylphosphine oxide, and di-p-tolyl(2,4,6-trimethylbenzoyl)phosphine oxide, as well as intramolecular hydrogen abstraction type photoinitiators such as methyl benzoylformate and 4-methylbenzophenone, and oil-soluble polymerization initiators such as oxime ester-based photoinitiators and cationic-based photoinitiators.

[0068] Commercially available acetophenone-based photoinitiators include EsacureOne (oligo(2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenylpropanone], manufactured by IGM RESINS B.V.), Omnirad 651 (2,2-dimethoxy-2-phenylacetophenone, manufactured by IGM RESINS B.V.), Omnirad 184 (1-hydroxycyclohexyl-phenyl ketone, manufactured by IGM RESINS B.V.), and Omnirad 1173 (2-hydroxy-2-methyl-1-phenylpropanone, manufactured by IGM RESINS B.V.). Commercially available acylphosphine oxide-based photoinitiators include Omnirad 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide) Examples include IGMRESINS B.V. (manufactured by IGMRESINS B.V.), Omnirad TPO (2,4,6-trimethylbenzoyl-diphenylphosphine oxide, manufactured by IGMRESINS B.V.), and Ltcure TMO (di-p-tolyl(2,4,6-trimethylbenzoyl)phosphine oxide, manufactured by Anquing Phichem). A commercially available oxime ester photoinitiator is Irgacure OXE03 (BASF Japan).

[0069] In the adhesive composition, the content of the photoinitiator is not particularly limited. For example, it is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, and particularly preferably 1.5 parts by mass or less, based on 100 parts by mass of the total mass of the acrylic polymer and (meth)acrylic monomer.

[0070] (Adhesive Composition) The adhesive composition may optionally include tackifying resins, solvents, plasticizers, antioxidants, metal corrosion inhibitors, light stabilizers, etc. Dyes and pigments may also be added for coloring purposes. The adhesive composition does not necessarily have to contain substantially any solvent; that is, the adhesive composition may be solvent-free.

[0071] The adhesive composition may contain a total amount of 50% by mass of an acrylic polymer or its syrup, a polyfunctional monomer, a silane coupling agent, an ultraviolet absorber, and a photoinitiator, preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, and particularly preferably 85% by mass or more. The adhesive composition may also consist only of an acrylic polymer or its syrup, a polyfunctional monomer, a silane coupling agent, an ultraviolet absorber, and a photoinitiator.

[0072] The adhesive composition can form an optical adhesive sheet by curing. For example, the adhesive composition can be cured by irradiation with active energy rays such as ultraviolet light, which accelerates the curing process and causes it to form a sheet (becoming an ultraviolet-cured product), thereby forming an optical adhesive sheet.

[0073] The method for preparing the adhesive composition is not particularly limited. For example, the adhesive composition can be prepared by mixing an acrylic polymer or its syrup with raw materials such as a polyfunctional monomer, a silane coupling agent, an ultraviolet absorber, and a photoinitiator in predetermined proportions.

[0074] 2. Optical Adhesive Sheet The optical adhesive sheet of the present invention is formed by irradiating the above-mentioned adhesive composition with active energy rays such as ultraviolet light to create a sheet. Therefore, the optical adhesive sheet can be said to be an adhesive material comprising an adhesive layer containing a cured product of the adhesive composition.

[0075] To form an optical adhesive sheet using an adhesive composition, it is necessary to cure the adhesive composition. The method for curing the adhesive composition is not particularly limited, and for example, a wide range of known methods can be employed. Specifically, the process may include the steps of coating the adhesive composition onto a substrate to form a coating film, and irradiating this coating film with active energy rays to obtain a cured adhesive product. This allows for the formation of an adhesive layer in which the adhesive composition has been cured, and thus an optical adhesive sheet can be obtained.

[0076] The adhesive composition can be coated using known coating equipment. Examples of coating equipment include blade coaters, air knife coaters, roll coaters, bar coaters, gravure coaters, microgravure coaters, rod blade coaters, lip coaters, die coaters, and curtain coaters.

[0077] The substrate used for coating with the adhesive composition is not particularly limited. For example, the adhesive composition can be coated on various substrates such as resin substrates and glass substrates. The substrate may also be a release sheet as described below. In this case, an optical adhesive sheet with a release sheet as described below is easily obtained. The adhesive composition can also be coated directly onto the components to be bonded. The thickness of the adhesive composition after coating can be appropriately set according to the desired thickness of the adhesive layer (or optical adhesive sheet). After the coating film is formed, the coating film may be subjected to heat treatment or drying treatment as needed.

[0078] The step of irradiating the coating film with active energy rays can be, for example, the same as known methods. In such a step, the photoinitiator in the adhesive composition generates radicals due to the active energy rays, and the polymerizable components in the adhesive composition also initiate and proceed with a polymerization reaction due to the generated radicals, thereby becoming a polymerized cured product. This forms an adhesive layer in which the adhesive composition has hardened.

[0079] Examples of active energy rays include ultraviolet light, electron beams, visible light, X-rays, and ion beams, which can be appropriately selected depending on the photoinitiator contained in the adhesive composition. Among these, ultraviolet light or electron beams are preferred from the standpoint of versatility, and ultraviolet light is particularly preferred. Examples of ultraviolet light sources that can be used include chemical lamps, high-pressure mercury lamps, low-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, carbon arcs, xenon arcs, and electrodeless ultraviolet lamps. The irradiation output of the ultraviolet light should be such that the integrated light amount is 100 to 10,000 mJ / cm². ２ It is preferable to have a concentration of 200 to 5000 mJ / cm². ２ It is more preferable to have the following. In the step of irradiating the coating with active energy rays, the active energy rays may be irradiated in two stages.

[0080] The cured product formed as described above can be used as the adhesive layer of the optical adhesive sheet of the present invention. The adhesive layer may consist only of the cured adhesive product, or it may contain other components in addition to the cured adhesive product.

[0081] The optical adhesive sheet of the present invention may include other layers as long as it has the adhesive layer, or it may be formed only of the adhesive layer. That is, it is preferable that the optical adhesive sheet consists only of the adhesive layer. The adhesive layer is, for example, a single-layer structure.

[0082] The optical adhesive sheet of the present invention may also be an optical adhesive sheet equipped with a base material such as a release sheet on one or both sides. That is, the present invention also includes an optical adhesive sheet with a release sheet, which comprises an optical adhesive sheet and a release sheet.

[0083] Examples of release sheets include a release sheet substrate and a release agent layer provided on one side of the release sheet substrate, or a low-polarity substrate such as a polyethylene film or polyolefin film. Paper and polymer films are used as the release sheet substrate in the release sheet laminate. As the release agent constituting the release agent layer, for example, a general-purpose addition-type or condensation-type silicone release agent or a long-chain alkyl group-containing compound can be used. Commercially available products may also be used as the release sheet laminate. For example, heavy separator film, which is a release-treated polyethylene terephthalate film manufactured by Teijin DuPont Films, and light separator film, which is a release-treated polyethylene terephthalate film manufactured by Teijin DuPont Films, can be used.

[0084] As described above, the optical adhesive sheet of the present invention satisfies physical properties (1) and (2). As a result, the optical adhesive sheet of the present invention has high adhesive strength at high temperatures (for example, in an environment of 110°C), excellent ability to follow steps, and in particular suppresses lifting of steps that occurs when heated, and also has excellent durability.

[0085] If the optical adhesive sheet of the present invention does not satisfy physical property (1), that is, if the stress value F2 measured when a probe is pressed into the surface of the adhesive sheet at a speed of 5 μm / second in a 25°C environment, and the pressing is stopped when the tip of the probe reaches a depth of 20% of the thickness of the adhesive sheet, and this state is held for 60 seconds, does not satisfy the requirement of being 60% or less of the maximum stress value F1, the step-following ability will deteriorate, and it will become difficult to suppress step lifting that occurs when heating.

[0086] Here, "the stress value F2 is 60% or less of the maximum stress value F1" means that the ratio (%) of the stress value F2 to the maximum stress value F1 is 60% or less, and specifically, that the value of (F2 / F1) × 100 is 60% or less. Hereafter, the value of (F2 / F1) × 100 will be abbreviated as "stress maintenance rate".

[0087] The stress maintenance ratio is preferably 59% or less, more preferably 58% or less, even more preferably 55% or less, even more preferably 53% or less, even more preferably 50% or less, and also preferably 10% or more, more preferably 20% or more, even more preferably 30% or more, and particularly preferably 35% or more.

[0088] In the optical adhesive sheet of the present invention, when the composition of the acrylic polymer, the glass transition temperature, the amount of polyfunctional monomer used, etc. are adjusted to the above-mentioned range, it becomes easier to satisfy physical property (1).

[0089] In the present invention, the physical property (1) of the optical adhesive sheet, that is, the stress retention rate, can be measured using the "TAC-1000" manufactured by Resca. A stainless steel probe can be used for this measurement, and the diameter of such a probe is 5 mm. Specifically, the probe is pressed against the surface of the sample (adhesive sheet) at a speed of 5 μm / second, and the probe is pushed into the adhesive sheet until the tip of the probe reaches a depth of 20% of the thickness of the adhesive sheet. The stress is measured while the probe is being pushed in, and the maximum value of the stress is recorded as the maximum stress value F1. As described above, when the probe reaches a depth of 20% of the thickness of the adhesive sheet, the pushing of the probe is stopped and it is held, and the stress is measured while holding it in that state, and the stress is measured 1 minute after the hold is measured, and this value is recorded as the stress value F2. From the maximum stress value F1 and stress value F2 obtained in this way, the stress retention rate is calculated by the following formula (I). Stress retention rate (%) = (F2 / F1) × 100 (I) Here, in equation (I), F2 represents the stress value F2, and F1 represents the maximum stress value F1. In the measurement of physical property (1), the thickness of the adhesive sheet to be measured is preferably 100 μm or more, more preferably 500 μm or less, more preferably 400 μm or less, even more preferably 300 μm or less, and particularly preferably 250 μm or less.

[0090] If the optical adhesive sheet of the present invention does not satisfy physical property (2), that is, if the adhesive strength at 110°C is less than 2 N / 25 mm, the adhesive strength at high temperatures will be insufficient, and the optical adhesive sheet of the present invention will not be suitable for optical applications, especially display applications. Preferably, the optical adhesive sheet of the present invention has an adhesive strength of 2.5 N / 25 mm or more at 110°C. There is no particular upper limit to the adhesive strength at 110°C, but considering the ease of manufacturing, for example, it is 30 N / 25 mm or less.

[0091] In the optical adhesive sheet of the present invention, when the composition of the acrylic polymer, the glass transition temperature, the amount of polyfunctional monomer used, etc. are adjusted to the above-mentioned range, it becomes easier to satisfy physical property (2).

[0092] The optical adhesive sheet of the present invention is suitable for use as an adhesive sheet for various optical applications because it has high adhesive strength at high temperatures, is relatively flexible, has excellent ability to follow uneven surfaces, and is also highly durable.

[0093] In particular, the optical adhesive sheet of the present invention makes it easier to suppress step filling during lamination and step lifting and delay valves that occur during heating, especially when a large deformation is required, such as when the printed step difference is 10 μm or more.

[0094] For example, in the technology described in Patent Document 1 mentioned above, hardness is defined by a nanoindenter as a factor that improves step-following ability. However, due to the characteristics of the nanoindenter, the hardness of the adhesive sheet can only be measured in the very surface layer, and the indentation depth that is specifically being considered is very shallow, only a few micrometers.

[0095] In contrast, as described above, the present invention observes the stress relaxation characteristics using probe tack, controls the deformation at room temperature and at high temperatures during bonding, and further adjusts the adhesive strength at high temperatures, thereby increasing the adhesive strength at high temperatures (for example, in an environment of 110°C), providing excellent step-following ability, and also excellent durability.

[0096] Furthermore, the optical adhesive sheet of the present invention can firmly adhere to substrates such as displays without requiring irradiation with active energy rays such as ultraviolet light after the substrates have been bonded to it.

[0097] The thickness of the optical adhesive sheet of the present invention is not particularly limited. For example, the thickness is preferably 100 μm or more, preferably 1000 μm or less, more preferably 700 μm or less, even more preferably 500 μm or less, and particularly preferably 400 μm or less.

[0098] The optical adhesive sheet of the present invention can be used for various applications to bond optical substrates together, for example, to bond display components. In particular, the optical adhesive sheet of the present invention is suitable for full lamination applications.

[0099] Examples of display component materials include glass, polycarbonate, polyethylene terephthalate, polymethyl methacrylate, polyethylene naphthalate, cycloolefin polymer, triacetylcellulose, polyimide, and cellulose acylate. Among these, examples of adherends include glass, polycarbonate, and polymethyl methacrylate.

[0100] The optical adhesive sheet of the present invention can form a laminate together with an adherend. In other words, the laminate includes the optical adhesive sheet of the present invention and an adherend.

[0101] In specifying the inventions contained herein, the components (properties, structures, functions, etc.) described in each embodiment of this disclosure may be combined in any way. That is, this disclosure encompasses all subject matter consisting of any combination of the combinatable components described herein.

[0102] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to the embodiments of these examples.

[0103] The following acrylic monomers ((meth)acrylic monomers) were prepared to produce the acrylic polymers used in each example and comparative example: • 2EHA: 2-ethylhexyl acrylate • 2OA: 2-octyl acrylate (biomass-derived) • BA: butyl acrylate • CHMA: cyclohexyl methacrylate • IBXA: isobornyl acrylate (biomass-derived) • 4HBA: 4-hydroxybutyl acrylate

[0104] Furthermore, the following were prepared as the "polyfunctional monomer," "silane coupling agent," and "photoinitiator" to be used in each example.

[0105] (Polyfunctional monomers) ・A-200: Difunctional monomer (Polyethylene glycol #200 diacrylate, manufactured by Shin-Nakamura Chemical Industry Co., Ltd., NK Ester A-200 (registered trademark)) ・A-400: Difunctional monomer (Polyethylene glycol #400 diacrylate, manufactured by Shin-Nakamura Chemical Industry Co., Ltd., NK Ester A-400 (registered trademark))

[0106] (Silane coupling agent) ・KBM-9659 (Shin-Etsu Chemical Co., Ltd. "KBM-9659" (registered trademark), tris(trimethoxysilylpropyl) isocyanurate ・KBM-403 (Shin-Etsu Chemical Co., Ltd. "KBM-403" (registered trademark), 3-glycidoxypropyltrimethoxysilane

[0107] (UV absorber) ・Tinuvin 477: Hydroxyphenyltriazine-based UV absorber (BASF Japan)

[0108] (Photoinitiator) - ESACURE ONE: IGM Resins B. V. ・Omnirad819: IGM Resins B. V.

[0109] (Example 1) <Production of Syrup> A syrup containing an acrylic polymer was synthesized according to the formulation of the (meth)acrylic syrup composition shown in Table 1. Specifically, 100 parts by mass of a mixed monomer consisting of 2EHA, CHMA, and 4HBA (mass ratio 70:10:20) prepared in the proportions shown in Table 1, and 0.0035 parts by mass of n-dodecyl mercaptan were placed in a 2 L flask equipped with a stirrer, nitrogen inlet tube, condenser, and thermometer. The mixture was then heated to 65°C in a water bath, and 0.015 parts by mass of AIBN was added. The mixture was reacted for 30 minutes while controlling the exothermic reaction, and then cooled to room temperature. Additional monomers (2EHA, CHMA, and 4HBA) were added to the flask to maintain the aforementioned mass ratio of monomers, and the solid content concentration was adjusted to 30%. In this way, a syrup containing an acrylic polymer with a solid content concentration of 30% by mass and a weight-average molecular weight of 900,000 was obtained.

[0110] <Preparation of Adhesive Composition> Next, an optical adhesive sheet was obtained from the adhesive composition prepared according to the adhesive composition preparation conditions shown in Table 1. First, as shown in Table 1, 0.1 parts by mass of A-200 as a polyfunctional monomer, 0.1 parts by mass of KBM-9659 as a silane coupling agent, 0.8 parts by mass of an ultraviolet absorber, and 0.85 parts by mass of Omnirad819 as a photoinitiator were added to 100 parts by mass of the total amount of syrup, and the mixture was stirred and defoamed to obtain adhesive composition 1.

[0111] <Manufacture of Optical Adhesive Sheet> The obtained adhesive composition 1 was coated onto a 100-μm-thick polyester film (release sheet) coated with a silicone release agent to a thickness of 250 μm, laminated with a 75-μm-thick polyester film (release sheet) coated with a silicone release agent, and then irradiated with a chemical lamp at an illuminance of 3 mW / cm ２ and an integrated illuminance of 200 mJ / cm ２ Thereafter, it was irradiated with a high-pressure mercury lamp at an illuminance of 200 mW / cm ２ and an integrated illuminance of 2000 mJ / cm ２ to form an adhesive layer, and an optical adhesive sheet 1 with a thickness of 250 μm provided with release sheets on both sides was obtained.

[0112] (Example 2) <Manufacture of Syrup> A syrup containing an acrylic polymer with a weight average molecular weight of 900,000 was obtained in the same manner as in the manufacture of the syrup in Example 1, except that the (meth)acrylic syrup composition was changed to the composition shown in Table 1. <9000236>

[0113] <Manufacture of Adhesive Composition> An adhesive composition 2 was obtained in the same manner as in the manufacture of the adhesive composition in Example 1, except that the conditions for preparing the adhesive composition were changed to the conditions shown in Table 1.

[0114] <Manufacture of Optical Adhesive Sheet> An optical adhesive sheet ٢ was obtained in the same manner as in the manufacture of the optical adhesive sheet in Example 1, except that the adhesive composition 2 was used instead of the adhesive composition 1.

[0115] (Example 3) <Manufacture of Syrup> A syrup containing an acrylic polymer with a weight average molecular weight of <900,000> was obtained in the same manner as in the manufacture of the syrup in Example 1, except that the (meth)acrylic syrup composition was changed to the composition shown in Table 1.

[0116] <Manufacture of Adhesive Composition> An adhesive composition 3 was obtained in the same manner as in the manufacture of the adhesive composition in Example 1, except that the conditions for preparing the adhesive composition were changed to the conditions shown in Table 1.

[0117] <Manufacturing of Optical Adhesive Sheet> An optical adhesive sheet 3 was obtained in the same manner as in the manufacturing of the optical adhesive sheet in Example 1, except that adhesive composition 3 was used instead of adhesive composition 1 and the coating thickness was changed to 150 μm.

[0118] (Example 4) <Production of syrup> Except for changing the (meth)acrylic syrup composition to the composition shown in Table 1, a syrup containing an acrylic polymer with a weight-average molecular weight of 900,000 was obtained by the same method as in the production of the syrup in Example 1.

[0119] <Preparation of Adhesive Composition> Adhesive composition 4 was obtained in the same manner as the preparation of the adhesive composition in Example 1, except that the preparation conditions for the adhesive composition were changed to the conditions shown in Table 1.

[0120] <Manufacturing of optical adhesive sheet> An optical adhesive sheet 4 was obtained in the same manner as in the manufacturing of the optical adhesive sheet in Example 1, except that adhesive composition 4 was used instead of adhesive composition 1.

[0121] (Example 5) <Production of syrup> Except for changing the (meth)acrylic syrup composition to the composition shown in Table 1, a syrup containing an acrylic polymer with a weight-average molecular weight of 900,000 was obtained by the same method as in the production of the syrup in Example 1.

[0122] <Preparation of the adhesive composition> Adhesive composition 5 was obtained in the same manner as the preparation of the adhesive composition in Example 1, except that the preparation conditions for the adhesive composition were changed to the conditions shown in Table 1.

[0123] <Manufacturing of Optical Adhesive Sheet> An optical adhesive sheet 5 was obtained in the same manner as in the manufacturing of the optical adhesive sheet in Example 1, except that adhesive composition 5 was used instead of adhesive composition 1.

[0124] (Comparative Example 1) <Syrup Production> Except for changing the (meth)acrylic syrup composition to the composition shown in Table 1, a syrup containing an acrylic polymer with a weight-average molecular weight of 900,000 was obtained by the same method as in the production of the syrup in Example 1.

[0125] <Preparation of Adhesive Composition> Adhesive composition 1a was obtained in the same manner as the preparation of the adhesive composition in Example 1, except that the preparation conditions for the adhesive composition were changed to the conditions shown in Table 1.

[0126] <Manufacturing of optical adhesive sheet> An optical adhesive sheet 1a was obtained in the same manner as in the manufacturing of the optical adhesive sheet in Example 1, except that adhesive composition 1a was used instead of adhesive composition 1.

[0127] (Comparative Example 2) <Syrup Production> Except for changing the (meth)acrylic syrup composition to the composition shown in Table 1, a syrup containing an acrylic polymer with a weight-average molecular weight of 900,000 was obtained by the same method as in the production of the syrup in Example 1.

[0128] <Preparation of Adhesive Composition> Adhesive composition 1b was obtained in the same manner as the preparation of the adhesive composition in Example 1, except that the preparation conditions for the adhesive composition were changed to the conditions shown in Table 1.

[0129] <Manufacturing of optical adhesive sheet> Optical adhesive sheet 1b was obtained in the same manner as in the manufacturing of the optical adhesive sheet in Example 1, except that adhesive composition 1b was used instead of adhesive composition 1.

[0130] (Comparative Example 3) <Syrup Production> Except for changing the (meth)acrylic syrup composition to the composition shown in Table 1, a syrup containing an acrylic polymer with a weight-average molecular weight of 900,000 was obtained by the same method as in the production of the syrup in Example 1.

[0131] <Preparation of Adhesive Composition> Adhesive composition 1c was obtained in the same manner as the preparation of the adhesive composition in Example 1, except that the preparation conditions for the adhesive composition were changed to the conditions shown in Table 1.

[0132] <Manufacturing of Optical Adhesive Sheet> An optical adhesive sheet 1c was obtained in the same manner as in the manufacturing of the optical adhesive sheet in Example 1, except that adhesive composition 1c was used instead of adhesive composition 1 and the coating thickness was changed to 150 μm.

[0133] Evaluation Method The weight-average molecular weight (Mw), glass transition temperature, and hydroxyl value of the acrylic polymers obtained in each example and comparative example were derived by the method described above. Probe tack evaluation (measurement of the stress retention rate), high-temperature adhesion strength measurement, step-filling ability evaluation, and durability tests of the obtained adhesive sheets were performed according to the following procedure.

[0134] (Probe Tack Evaluation) The stress retention rate, i.e., the ratio (%) of the stress value F2 to the maximum stress value F1, was measured using the "TAC-1000" manufactured by Resca. For this measurement, a stainless steel probe was used, with a probe diameter of 5 mm. In an environment of 25°C, an adhesive sheet was cut to a size of 30 mm x 30 mm, the light separator surface was peeled off from the adhesive sheet, and the sheet was placed on the measuring base with the adhesive side facing the probe. Next, the probe was pressed against the surface of the sample (adhesive sheet) at a speed of 5 μm / second, and the probe was pushed into the adhesive sheet until the tip of the probe reached a depth of 20% of the thickness of the adhesive sheet. The stress was measured while the probe was being pushed in, and the maximum value of the stress was recorded as the maximum stress value F1. As described above, when the probe reached a depth of 20% of the thickness of the adhesive sheet, the probe was stopped being pushed in and held, and the stress was measured while holding it in that state. The stress was measured 1 minute after the hold and this value was recorded as the stress value F2. From the maximum stress value F1 and stress value F2 obtained in this way, the stress retention rate was calculated using the following formula (I): Stress retention rate (%) = (F2 / F1) × 100 (I) Here, in formula (I), F2 represents the stress value F2, and F1 represents the maximum stress value F1.

[0135] (Measuring Adhesion at High Temperatures) The adhesive sheets obtained in each example and comparative example were laminated to a 100 μm thick easily bonded polyester film (Toyobo A4360), and the adhesive strength measurement section was cut to a width of 25 mm and a length of 50 mm. Next, this was attached to a 1.1 mm thick float glass (Hiraoka Glass Industry Co., Ltd.), and then pressed down by two passes with a 2 kg roller. After that, it was treated in an autoclave at a temperature of 30°C and a pressure of 0.5 MPa for 30 minutes, and then left to stand for one day at atmospheric pressure and room temperature to obtain the evaluation laminate. The evaluation laminate was left to stand for one hour in a tensile testing machine with a constant temperature chamber (A&D RTC-1210A) at a temperature of 110°C, and then the adhesive strength was measured at a speed of 300 mm / min at an angle of 180° in the same environment, and this was taken as the measured value of the high-temperature adhesive strength of the adhesive sheet.

[0136] (Evaluation of step-filling ability) A substrate was prepared by laminating a printed section with a frame shape (frame size 50 mm wide, 90 mm long) of approximately 10 mm in width onto a float glass with a width of 70 mm, a length of 120 mm, and a thickness of 0.7 mm. The total thickness of the printed section was set to 10% of the thickness of the adhesive sheet to be evaluated. After cutting the adhesive sheets obtained in each example and comparative example to a width of 55 mm and a length of 95 mm, the light separator was peeled off and the sheets were laminated so that they overlapped the printed section by about 2.5 mm. Then the heavy separator was peeled off and a float glass with a width of 70 mm, a length of 120 mm, and a thickness of 0.7 mm was laminated onto the exposed adhesive layer. The substrate was then treated in an autoclave at a temperature of 30°C and a pressure of 0.5 MPa for 30 minutes, left to stand for 1 day at atmospheric pressure and room temperature, and then left to stand for 1 day in a constant temperature bath at 95°C. The appearance was visually observed and the step-filling ability was evaluated according to the following criteria. ≪Evaluation Criteria≫ A: No peeling bubbles or other defects were observed at the stepped sections, indicating excellent conformability to the stepped surface. B: 1 to 5 bubbles were observed at the stepped sections, indicating excellent conformability to the stepped surface. C: 6 or more bubbles were observed at the stepped sections. Lifting was observed at the stepped sections, indicating poor conformability to the stepped surface.

[0137] (Durability Test) The adhesive sheets obtained in each example and comparative example were cut to the same size onto a glass plate (manufactured by Matsunami Glass Industry Co., Ltd.) with a thickness of 1 mm, a width of 76 mm, and a length of 52 mm. The light-release film of the adhesive sheet was peeled off and adhered to the glass surface. Then, the heavy-release film was peeled off, and a glass plate of the same size was bonded onto the exposed adhesive layer. The laminate was then pressed together under autoclave conditions of 40°C and 0.5 MPa for 30 minutes to obtain a laminate. After the laminate was left to stand at room temperature (25°C) for one day, it was left to stand in a constant temperature and humidity chamber at a temperature of 85°C and a humidity of 85% for 500 hours. After that, it was left to stand at room temperature for one hour, and the haze value was measured using Murakami Color Technology Research Institute's HM-150, and the durability was evaluated according to the following criteria: A: The haze value was less than 1, indicating excellent durability. B: The haze value was 1 or more and less than 2, indicating good durability. C: The haze value was 2 or more, indicating poor durability.

[0138] Table 1 of the evaluation results shows the (meth)acrylic syrup composition, weight-average molecular weight, glass transition temperature, and hydroxyl value (OHV) of the acrylic polymer used in the production of the optical adhesive sheets obtained in each example and comparative example, the preparation conditions of the adhesive composition, the thickness of the obtained optical adhesive sheets, and various evaluation results. A blank space in Table 1 indicates that the raw material was not used.

[0139] Table 1 shows that the optical adhesive sheets obtained in the examples satisfy all of the above-mentioned physical properties (1) (stress retention rate) and (2) (high-temperature adhesive strength), exhibiting high adhesive strength at high temperatures (e.g., under a 110°C environment), excellent step-following ability, and superior durability. Therefore, the optical adhesive sheets obtained in the examples have high adhesive strength at high temperatures, are relatively flexible, and possess excellent step-following ability, and in particular can suppress step lifting that occurs when heated.

[0140]

Claims

1. An optical adhesive sheet containing a cured product of an adhesive composition, wherein the adhesive composition contains an acrylic polymer, the acrylic polymer has a hydroxyl value of 70 mgKOH / g or more, and satisfies the following physical properties (1) and (2): Physical property (1): When a probe is pressed into the surface of the adhesive sheet at a speed of 5 μm / second in a 25°C environment, the pressing is stopped when the tip of the probe reaches a depth of 20% of the thickness of the adhesive sheet, and this state is held for 60 seconds, the measured stress value F2 is 60% or less of the maximum stress value F1; Physical property (2): The adhesive force at 110°C is 2 N / 25 mm or more.

2. The optical adhesive sheet according to claim 1, wherein the glass transition temperature of the acrylic polymer is -10°C or lower.

3. The optical adhesive sheet according to claim 1, wherein the acrylic polymer comprises (meth)acrylate units having a linear or branched alkyl group, (meth)acrylate units having an alicyclic structure in the side chain, and monomer units having a hydroxyl group in the side chain.

4. The optical adhesive sheet according to claim 1, wherein the adhesive composition comprises a silane coupling agent having an isocyanurate structure.

5. The optical adhesive sheet according to claim 1, wherein the adhesive composition contains a photoinitiator, and the cured product is an ultraviolet cured product.

6. The optical adhesive sheet according to claim 5, wherein the adhesive composition comprises an ultraviolet absorber.

7. The optical adhesive sheet according to claim 1, wherein the thickness is 100 μm or more.

8. The optical adhesive sheet according to claim 1, wherein the acrylic polymer contains 2-octyl acrylate units derived from biomass raw materials.

9. A laminate comprising an optical adhesive sheet according to any one of claims 1 to 8.

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