Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J133/00—Adhesives based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Adhesives based on derivatives of such polymers
  • C09J133/04—Homopolymers or copolymers of esters
  • C09J133/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, the oxygen atom being present only as part of the carboxyl radical
  • C09J133/08—Homopolymers or copolymers of acrylic acid esters
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2/00—Processes of polymerisation
  • C08F2/46—Polymerisation initiated by wave energy or particle radiation
  • C08F2/48—Polymerisation initiated by wave energy or particle radiation by ultraviolet or visible light
  • C08F2/50—Polymerisation initiated by wave energy or particle radiation by ultraviolet or visible light with sensitising agents
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
  • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
  • C08F220/10—Esters
  • C08F220/12—Esters of monohydric alcohols or phenols
  • C08F220/16—Esters of monohydric alcohols or phenols of phenols or of alcohols containing two or more carbon atoms
  • C08F220/18—Esters of monohydric alcohols or phenols of phenols or of alcohols containing two or more carbon atoms with acrylic or methacrylic acids
  • C08F220/1808—C8-(meth)acrylate, e.g. isooctyl (meth)acrylate or 2-ethylhexyl (meth)acrylate
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
  • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
  • C08F220/10—Esters
  • C08F220/34—Esters containing nitrogen, e.g. N,N-dimethylaminoethyl (meth)acrylate
  • C08F220/343—Esters containing nitrogen, e.g. N,N-dimethylaminoethyl (meth)acrylate in the form of urethane links
  • C08F220/346—Esters containing nitrogen, e.g. N,N-dimethylaminoethyl (meth)acrylate in the form of urethane links and further oxygen
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F265/00—Macromolecular compounds obtained by polymerising monomers on to polymers of unsaturated monocarboxylic acids or derivatives thereof as defined in group C08F20/00
  • C08F265/04—Macromolecular compounds obtained by polymerising monomers on to polymers of unsaturated monocarboxylic acids or derivatives thereof as defined in group C08F20/00 on to polymers of esters
  • C08F265/06—Polymerisation of acrylate or methacrylate esters on to polymers thereof
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J4/00—Adhesives based on organic non-macromolecular compounds having at least one polymerisable carbon-to-carbon unsaturated bond ; adhesives, based on monomers of macromolecular compounds of groups C09J183/00 - C09J183/16
  • C09J4/06—Organic non-macromolecular compounds having at least one polymerisable carbon-to-carbon unsaturated bond in combination with a macromolecular compound other than an unsaturated polymer of groups C09J159/00 - C09J187/00
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J7/00—Adhesives in the form of films or foils
  • C09J7/30—Adhesives in the form of films or foils characterised by the adhesive composition
  • C09J7/38—Pressure-sensitive adhesives [PSA]
  • C09J7/381—Pressure-sensitive adhesives [PSA] based on macromolecular compounds obtained by reactions involving only carbon-to-carbon unsaturated bonds
  • C09J7/385—Acrylic polymers
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J7/00—Adhesives in the form of films or foils
  • C09J7/40—Adhesives in the form of films or foils characterised by release liners
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/30—Polarising elements
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K77/00—Constructional details of devices covered by this subclass and not covered by groups H10K10/80, H10K30/80, H10K50/80 or H10K59/80
  • H10K77/10—Substrates, e.g. flexible substrates
  • H10K77/111—Flexible substrates
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J2203/00—Applications of adhesives in processes or use of adhesives in the form of films or foils
  • C09J2203/318—Applications of adhesives in processes or use of adhesives in the form of films or foils for the production of liquid crystal displays
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J2301/00—Additional features of adhesives in the form of films or foils
  • C09J2301/30—Additional features of adhesives in the form of films or foils characterized by the chemical, physicochemical or physical properties of the adhesive or the carrier
  • C09J2301/312—Additional features of adhesives in the form of films or foils characterized by the chemical, physicochemical or physical properties of the adhesive or the carrier parameters being the characterizing feature

Definitions

• the present invention relates to an adhesive sheet, an adhesive sheet with a release film using the same, a laminate for an image display device, a flexible image display device, an adhesive sheet for a component of a flexible image display device, and an adhesive composition, and more specifically to an adhesive sheet having a low refractive index and flexibility, an adhesive sheet with a release film using the same, a laminate for an image display device, a flexible image display device, an adhesive sheet for a component of a flexible image display device, and an adhesive composition.
• Flexible image display devices include bendable devices whose image display surface has a curved shape, foldable devices that can be repeatedly folded, rollable devices that can be rolled up, and stretchable devices that can be expanded and contracted.
• a plurality of component sheets such as a surface protective film, a cover lens, a circular polarizing plate, a touch film sensor, and a light-emitting element, are laminated together with a transparent adhesive sheet, and each laminate structure can be regarded as a laminate sheet formed by laminating a component sheet and an adhesive sheet.
• Bendable flexible display devices have various problems caused by interlayer stress when folded. For example, there is a demand for a laminated sheet that quickly restores to a flat state without sustaining any effects from being bent when the screen is opened from a folded state. Furthermore, repeated folding operations may cause the adhesive sheet to peel off or stress to be applied to the adherend member, causing the member to crack and ultimately break. Therefore, there is a demand for a laminated sheet that is durable enough to withstand repeated folding operations at low temperatures, which are particularly harsh conditions. Furthermore, in addition to durability at low temperatures, a higher elastic modulus is also required at high temperatures in order to prevent the adhesive sheet itself from overflowing and to prevent creases caused by deformation of the adhesive sheet when bent at high temperatures.
• the pressure-sensitive adhesive sheet in such a flexible image display device is required to have not only optical properties but also flexibility and, in particular, high durability against bending.
• Patent Document 1 discloses a laminated film with an adhesive layer that is free from the risk of causing distortion of the image displayed at the folded portion after repeated folding.
• Patent Document 2 discloses a laminate comprising a double-sided pressure-sensitive adhesive sheet having a glass transition temperature and storage modulus within a specified range, and a flexible member for an image display device, which does not break or peel off even in a bending test approximating an actual usage environment.
• such laminated sheets have the problem that light scattering occurs at the interface between the adhesive sheet and the component sheet due to the difference in refractive index between the adhesive sheet and the component sheet, reducing the light transmittance of the laminated sheet and causing unevenness in the displayed image.
• Such problems become more pronounced when the surface of the component sheet is uneven or in the curved parts of a flexible image display device. For this reason, there is a growing demand for adhesive sheets with a low refractive index to reduce the difference in refractive index between the adhesive sheet and the component sheet.
• Patent Document 3 discloses an adhesive that contains an acrylic polymer that includes a fluorine-containing acrylic monomer (M1) as a monomer unit, and has a refractive index of 1.46 or less.
• Patent Documents 1 and 2 take into consideration durability when folded, they do not take into consideration the refractive index of the pressure-sensitive adhesive sheet.
• the refractive index is low, the flexibility that has been required in recent years is not taken into consideration in Patent Document 3, and further improvement is required in terms of achieving both flexibility and a low refractive index.
• the present invention provides an adhesive sheet that has a low refractive index and excellent flexibility, an adhesive sheet with a release film that uses the same, a flexible image display device, an adhesive sheet for use as a component of a flexible image display device, and an adhesive composition.
• a pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive composition containing an acrylic copolymer and a radically polymerizable compound (x),
• the refractive index of the pressure-sensitive adhesive sheet is 1.470 or less
• the pressure-sensitive adhesive sheet has a shear storage modulus ratio (G'(-30°C)/G'(80°C)) of the shear storage modulus at -30°C (G'(-30°C)) to the shear storage modulus at 80°C (G'(80°C)), which is 1 to 65, as determined by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz.
• the acrylic copolymer is an acrylic copolymer having a structural portion derived from a (meth)acrylate (a1) having an alkyl group having 3 or more alkyl carbon atoms, and a structural portion derived from a hydroxyl group-containing (meth)acrylate (a2).
• the refractive index of the pressure-sensitive adhesive sheet is 1.470 or less
• the pressure-sensitive adhesive sheet has a shear storage modulus ratio (G'(-30°C)/G'(80°C)) of the shear storage modulus at -30°C (G'(-30°C)) to the shear storage modulus at 80°C (G'(80°C)), which is 1 to 65, as determined by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz.
• a pressure-sensitive adhesive sheet with a release film comprising the pressure-sensitive adhesive sheet according to any one of [1] to [14] and a release film laminated on the pressure-sensitive adhesive sheet.
• a laminate for an image display device comprising two components of an image display device and the pressure-sensitive adhesive sheet according to any one of [1] to [14] interposed between the two components of the image display device.
• a flexible image display device comprising the laminate for an image display device according to [16].
• a pressure-sensitive adhesive sheet for use as a component of a flexible image display device comprising the pressure-sensitive adhesive sheet according to any one of [1] to [14].
• a pressure-sensitive adhesive composition comprising an acrylic copolymer and a radically polymerizable compound (x),
• the weight average molecular weight of the acrylic copolymer is 500,000 or more,
• the refractive index of the radical polymerizable compound (x) is less than 1.46,
• the content of the radically polymerizable compound (x) is 20 to 95% of the total mass of the pressure-sensitive adhesive composition.
• the adhesive sheet of the present invention has a low refractive index and excellent flexibility. Therefore, it can be suitably used as an adhesive sheet for flexible image display devices.
• film conceptually includes a sheet, a film, and a tape.
• panel such as an image display panel or a protective panel, it encompasses a plate, a sheet, and a film.
• x and/or y (x and y are optional configurations) means at least one of x and y, and means three possibilities: x only, y only, and x and y.
• (meth)acrylic refers to a comprehensive definition of acrylic and methacrylic
• (meth)acrylate refers to a comprehensive definition of acrylate and methacrylate
• (meth)acryloyl refers to a comprehensive definition of acryloyl and methacryloyl.
• a pressure-sensitive adhesive sheet according to an example of a first embodiment of the present invention (hereinafter referred to as "the pressure-sensitive adhesive sheet 1") is formed from a pressure-sensitive adhesive composition containing an acrylic copolymer and a radically polymerizable compound (x), and the pressure-sensitive adhesive sheet has a refractive index of 1.470 or less, and further has a shear storage modulus ratio (G'(-30°C)/G'(80°C)) of the shear storage modulus at -30°C (G'(-30°C)) to the shear storage modulus at 80°C (G'(80°C)), obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, of 1 to 65.
• the pressure-sensitive adhesive sheet 1 is formed from a pressure-sensitive adhesive composition containing an acrylic copolymer and a radically polymerizable compound (x), and the pressure-sensitive adhesive sheet has a refractive index of 1.470 or less, and further has a shear storage modulus ratio
• a pressure-sensitive adhesive sheet according to an example of a second embodiment of the present invention is a pressure-sensitive adhesive sheet having an acrylic pressure-sensitive adhesive layer, the acrylic pressure-sensitive adhesive layer being a cured reaction product formed from a syrup composition containing an alkyl (meth)acrylate (a1) having an alkyl group with 3 or more carbon atoms [hereinafter referred to as “alkyl (meth)acrylate (a1)”], a hydroxyl group-containing (meth)acrylate (a2), and a radically polymerizable compound (x), the pressure-sensitive adhesive sheet having a refractive index of 1.470 or less, and further having a shear storage modulus ratio (G'(-30°C)/G'(80°C)) of the shear storage modulus at -30°C (G'(-30°C)) to the shear storage modulus at 80°C (G'(80°C)) of 1 to 65, as obtained by
• the pressure-sensitive adhesive sheet 1 is formed from a pressure-sensitive adhesive composition containing an acrylic copolymer and a radically polymerizable compound (x). Each component contained in the pressure-sensitive adhesive composition will be described in detail below.
• the acrylic copolymer used in the pressure-sensitive adhesive sheet 1 is preferably an acrylic copolymer containing a structural portion derived from an alkyl (meth)acrylate and a structural portion derived from a hydroxyl group-containing (meth)acrylate, and is particularly preferably an acrylic copolymer containing a structural portion derived from an alkyl (meth)acrylate (a1) having 3 or more carbon atoms in the alkyl group and a structural portion derived from a hydroxyl group-containing (meth)acrylate (a2) from the viewpoint of adhesive properties.
• Such an acrylic copolymer is obtained by polymerizing copolymerization components containing an alkyl (meth)acrylate (a1) having 3 or more carbon atoms in the alkyl group and a hydroxyl group-containing (meth)acrylate (a2).
• the copolymerization components may also contain components other than the alkyl (meth)acrylate (a1) having an alkyl group with 3 or more carbon atoms and the hydroxyl group-containing (meth)acrylate (a2), such as at least one copolymerizable monomer (a3) selected from alkyl (meth)acrylates having an alkyl group with 1 or 2 carbon atoms and vinyl ester monomers (hereinafter referred to as "copolymerizable monomer (a3)”), a functional group-containing ethylenically unsaturated monomer (a4), other copolymerizable monomers (a5), and the like.
• alkyl (meth)acrylate (a1) examples include aliphatic (meth)acrylates such as linear alkyl (meth)acrylates and branched alkyl (meth)acrylates, and alicyclic (meth)acrylates.
• Examples of the aliphatic (meth)acrylate include n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, lauryl (meth)acrylate, n-tridecyl (meth)acrylate, stearyl (meth)acrylate, icosyl (meth)acrylate, henicosyl (meth)acrylate, and behenyl (meth)acrylate.
• alkyl (meth)acrylates such as isopropyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, isostearyl (meth)acrylate, and isoicosyl (meth)acrylate.
• isopropyl (meth)acrylate isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, 2-ethylhexyl (meth
• alicyclic (meth)acrylate examples include cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, and adamantyl (meth)acrylate. These may be used alone or in combination of two or more.
• linear alkyl (meth)acrylates are preferred from the viewpoint of adhesion and resilience.
• linear and branched alkyl (meth)acrylates having an alkyl group with 3 to 18 carbon atoms, further 3 to 16, particularly 3 to 12, and especially 3 to 8 carbon atoms are preferred, such as n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, decyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.
• alkyl (meth)acrylates having an alkyl group with 4 or more carbon atoms, particularly 6 or more, and especially 8 or more and 18 or less, particularly 16 or less, and especially 12 or less carbon atoms are preferred.
• the alkyl (meth)acrylate (a1) is an acrylate.
• the content of the structural portion derived from alkyl (meth)acrylate (a1) in the acrylic copolymer is usually 40 to 95% of the total mass of the acrylic copolymer, preferably 45 to 90%, and particularly preferably 50 to 85% by mass, in order to suppress an increase in the shear storage modulus (G') at low temperatures. If the content of the structural portion derived from alkyl (meth)acrylate (a1) is equal to or greater than the lower limit, an increase in the shear storage modulus (G') at low temperatures can be suppressed, and if it is equal to or less than the upper limit, it is preferable in terms of compatibility with other physical properties such as adhesion.
• hydroxyl group-containing (meth)acrylate (a2) examples include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; caprolactone-modified hydroxy (meth)acrylates such as caprolactone-modified 2-hydroxyethyl (meth)acrylate; diethylene glycol (meth)acrylate; polyethylene glycol (meth)acrylate; and polypropylene glycol (meth)acrylate polytetrafluoroethylene.
• hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (
• acrylates examples include (meth)acrylates having an oxyalkylene glycol structure, such as lamethylene glycol (meth)acrylate and polyoxyethylene polyoxypropylene glycol (meth)acrylate, primary hydroxyl group-containing (meth)acrylates, such as 2-acryloyloxyethyl-2-hydroxyethyl phthalate, secondary hydroxyl group-containing (meth)acrylates, such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate and 3-chloro-2-hydroxypropyl (meth)acrylate, and tertiary hydroxyl group-containing (meth)acrylates, such as 2,2-dimethyl 2-hydroxyethyl (meth)acrylate, etc. These may be used alone or in combination of two or more.
• hydroxyl group-containing (meth)acrylates (a2) from the viewpoint of reducing the shear storage modulus (G') at low temperatures, hydroxyl group-containing (meth)acrylates having a hydroxyalkyl group with 1 to 10 carbon atoms, further 1 to 6, and especially 2 to 4 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate, are preferred, and primary hydroxyl group-containing (meth)acrylates, such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate, are particularly preferred.
• the ratio [2-hydroxyethyl (meth)acrylate/4-hydroxybutyl (meth)acrylate] is preferably 95/5 to 30/70 by mass, more preferably 80/20 to 40/60, particularly preferably 75/25 to 45/65, and especially preferably 70/30 to 50/50. If the amount of 2-hydroxyethyl (meth)acrylate is too small, the adhesive strength decreases when used as an adhesive, and if the amount is too large, the bending durability tends to decrease when used as an adhesive.
• the hydroxyl group-containing (meth)acrylate (a2) preferably has a low content of di(meth)acrylate as an impurity, specifically, 0.5% by mass or less, more preferably 0.2% by mass or less, and even more preferably 0.1% by mass or less.
• the content of the structural portion derived from the hydroxyl group-containing (meth)acrylate (a2) in the acrylic copolymer is usually 5 to 60% of the total mass of the acrylic copolymer, preferably 8 to 45%, particularly preferably 10 to 35%, further preferably 11 to 30%, and particularly preferably 12 to 25%. If the content is too low, the moist heat resistance when used as an adhesive tends to decrease, whereas if the content is too high, the acrylic resin is more likely to undergo a self-crosslinking reaction, tending to decrease the heat resistance.
• Copolymerizable monomer (a3) In the present invention, it is preferable to further contain a copolymerizable monomer (a3) as a copolymerization component from the viewpoint of improving the cohesive strength and further improving the adhesive strength when used as a pressure-sensitive adhesive.
• Examples of the copolymerizable monomer (a3) include methyl (meth)acrylate, ethyl (meth)acrylate, vinyl acetate, and the like. These copolymerizable monomers (a3) may be used alone or in combination of two or more. Among them, methyl (meth)acrylate and ethyl (meth)acrylate are preferred from the viewpoint of improving cohesive strength when used as an adhesive.
• the content is usually preferably 1 to 70% of the total mass of the acrylic copolymer, particularly preferably 10 to 60%, and even more preferably 15 to 45%. If the content of such copolymerizable monomer (a3) is too low, the adhesive strength tends to decrease when used as an adhesive, and if the content is too high, the durability tends to decrease when used as an adhesive when the molecular weight of the acrylic copolymer is small.
• the content of structural moieties derived from methyl (meth)acrylate and/or ethyl (meth)acrylate in the acrylic copolymer is usually 1 to 40% of the total mass of the acrylic copolymer, preferably 2 to 30%, more preferably 3 to 25%, and particularly preferably 4 to 10%. If the content of structural moieties derived from methyl (meth)acrylate and/or ethyl (meth)acrylate is too high, the viscosity increases, tending to reduce the handleability during processing, and if it is too low, the adhesive strength tends to decrease when used as an adhesive.
• a functional group-containing ethylenically unsaturated monomer (a4) (excluding the hydroxyl group-containing (meth)acrylate (a2)) can be used as a copolymerization component of the acrylic copolymer, if necessary.
• Examples of the functional group-containing ethylenically unsaturated monomer (a4) include functional group-containing monomers having a nitrogen atom, carboxy group-containing monomers, acetoacetyl group-containing monomers, isocyanate group-containing monomers, and glycidyl group-containing monomers.
• functional group-containing monomers having a nitrogen atom are preferred, amino group-containing monomers and amide group-containing monomers are particularly preferred, and amino group-containing monomers are even more preferred.
• the above amino group-containing monomers include, for example, primary amino group-containing (meth)acrylates such as aminomethyl (meth)acrylate and aminoethyl (meth)acrylate; secondary amino group-containing (meth)acrylates such as t-butylaminoethyl (meth)acrylate and t-butylaminopropyl (meth)acrylate; and tertiary amino group-containing (meth)acrylates such as ethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, diethylaminopropyl (meth)acrylate, and dimethylaminopropylacrylamide.
• primary amino group-containing (meth)acrylates such as aminomethyl (meth)acrylate and aminoethyl (meth)acrylate
• amide group-containing monomer examples include (meth)acrylamide; N-alkyl (meth)acrylamides such as N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-propyl (meth)acrylamide, N-n-butyl (meth)acrylamide, diacetone (meth)acrylamide, and N,N'-methylene bis (meth)acrylamide; N,N-dialkyl (meth)acrylamides such as N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N,N-dipropyl (meth)acrylamide, N,N-ethylmethyl acrylamide, and N,N-diallyl (meth)acrylamide; hydroxyalkyl (meth)acrylamides such as N-hydroxymethyl (meth)acrylamide and N-hydroxyethyl (meth)acrylamide; and alkoxyalkyl (meth)acrylamides such as N-meth
• carboxyl group-containing monomer examples include (meth)acrylic acid, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxypropylhexahydrophthalic acid, 2-(meth)acryloyloxyethylphthalic acid, 2-(meth)acryloyloxypropylphthalic acid, 2-(meth)acryloyloxyethylmaleic acid, 2-(meth)acryloyloxypropylmaleic acid, 2-(meth)acryloyloxyethylsuccinic acid, 2-(meth)acryloyloxypropylsuccinic acid, crotonic acid, fumaric acid, maleic acid, and itaconic acid.
• acetoacetyl group-containing monomer examples include 2-(acetoacetoxy)ethyl (meth)acrylate and allyl acetoacetate.
• isocyanate group-containing monomer examples include 2-(meth)acryloyloxyethyl isocyanate and its alkylene oxide adducts.
• glycidyl group-containing monomer examples include glycidyl (meth)acrylate, allyl glycidyl (meth)acrylate, etc.
• These functional group-containing ethylenically unsaturated monomers (a4) may be used alone or in combination of two or more.
• the content is usually 30% or less of the total mass of the acrylic copolymer, preferably 20% or less, more preferably 10% or less, and especially preferably 5% or less. If the content of the structural portion derived from the functional group-containing ethylenically unsaturated monomer (a4) is too high, the heat resistance of the acrylic copolymer tends to decrease.
• Examples of the other copolymerizable monomers (a5) include (meth)acrylates having an alkoxyalkylene glycol skeleton, such as methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, butoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, butoxypolypropylene glycol (meth)acrylate, methoxypolytetramethylene glycol (meth)acrylate, butoxypolytetramethylene glycol (meth)acrylate, methoxypolyoxyethylene polyoxypropylene glycol (meth)acrylate, butoxypolyoxyethylene polyoxypropylene glycol (meth)acrylate, and the like; phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyl Examples of such monomers include aromatic (meth)acrylic acid ester mono
• a small amount of a compound having two or more ethylenically unsaturated groups such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, or divinylbenzene, can also be used in combination.
• these compounds having two or more ethylenically unsaturated groups are highly reactive, and when used as a polymerization component of the acrylic copolymer, they usually do not remain unreacted. However, if too much is used, these compounds having two or more ethylenically unsaturated groups will remain unreacted, and the acrylic copolymer will tend to gel.
• the acrylic copolymer contains a structural portion derived from another copolymerizable monomer (a5)
• the content is usually 50% or less of the total mass of the acrylic copolymer, preferably 40% or less, and more preferably 20% or less. If the content of the other copolymerizable monomer (a5) is too high, the heat resistance and adhesive strength tend to decrease.
• the acrylic copolymer used in this adhesive sheet 1 can be obtained by appropriately selecting and polymerizing the above copolymerization components.
• Examples of the method for polymerizing the acrylic copolymer include conventionally known methods such as solution polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization. Among these, solution polymerization is preferred in that it can safely and stably produce an acrylic copolymer with any monomer composition. An example of a preferred method for producing the acrylic copolymer used in the present invention will be described below.
• the copolymerization components and polymerization initiator are mixed or dropped into an organic solvent, and solution polymerization is carried out to obtain an acrylic resin solution.
• Organic solvents used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as hexane, esters such as ethyl acetate and butyl acetate, aliphatic alcohols such as n-propyl alcohol and isopropyl alcohol, and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. These can be used alone or in combination of two or more. Among these solvents, ethyl acetate is preferred.
• azo-based polymerization initiators and peroxide-based polymerization initiators which are ordinary radical polymerization initiators, can be used.
• the azo-based polymerization initiator include 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, (1-phenylethyl)azodiphenylmethane, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile).
• peroxide-based polymerization initiator examples include benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, lauroyl peroxide, t-butyl peroxypivalate, t-hexyl peroxypivalate, t-hexyl peroxyneodecanoate, diisopropyl peroxycarbonate, and diisobutyryl peroxide. These may be used alone or in combination of two or more of them. Among them, 2,2'-azobis(2,4-dimethylvaleronitrile) is preferred.
• the amount of the polymerization initiator used is usually 0.001 to 10 parts by mass, preferably 0.1 to 8 parts by mass, particularly preferably 0.5 to 6 parts by mass, even more preferably 1 to 4 parts by mass, especially preferably 1.5 to 3 parts by mass, and most preferably 2 to 2.5 parts by mass, per 100 parts by mass of the copolymerization components. If the amount of the polymerization initiator used is too small, the polymerization rate of the acrylic copolymer tends to decrease, the amount of residual monomers tends to increase, and the weight average molecular weight of the acrylic copolymer tends to increase. If the amount used is too large, gelation of the acrylic copolymer, as described below, tends to occur.
• the solution polymerization may be carried out under known polymerization conditions.
• the polymerization components and a polymerization initiator may be mixed or dropped into a solvent, and polymerization may be carried out under predetermined polymerization conditions.
• the polymerization temperature in the above polymerization reaction is usually 40 to 120°C, but in the present invention, 50 to 90°C is preferred from the viewpoint of stable reaction, with 55 to 75°C being particularly preferred, and 60 to 70°C being even more preferred. If the polymerization temperature is too high, the acrylic copolymer tends to gel easily, and if it is too low, the activity of the polymerization initiator decreases, so the polymerization rate decreases and the amount of residual monomers tends to increase.
• the polymerization time in the polymerization reaction (the time until the start of the follow-up heating in the case where the follow-up heating described later is carried out) is not particularly limited, but is preferably 0.5 hours or more from the addition of the final polymerization initiator, particularly preferably 1 hour or more, further preferably 2 hours or more, and particularly preferably 5 hours or more.
• the upper limit of the polymerization time is usually 72 hours.
• the polymerization reaction is preferably carried out while refluxing the solvent in order to facilitate heat removal.
• the drive-in heating temperature is preferably higher than the 10-hour half-life temperature of the polymerization initiator, and specifically is usually 40 to 150° C., preferably 55 to 130° C. from the viewpoint of suppressing gelation, and particularly preferably 75 to 95° C. If the drive-in heating temperature is too high, the acrylic copolymer tends to turn yellow, whereas if it is too low, the polymerization components and polymerization initiator tend to remain, and the temporal stability and thermal stability of the acrylic copolymer tend to decrease. Thus, an acrylic copolymer can be obtained.
• the acrylic copolymer may also have a photoactive site, such as a polymerizable carbon double bond group, introduced into the side chain. This can increase the crosslinking efficiency of the pressure-sensitive adhesive composition, allowing the pressure-sensitive adhesive composition to be crosslinked in a shorter time, thereby increasing productivity.
• a photoactive site such as a polymerizable carbon double bond group
• a method for introducing a polymerizable carbon double bond group into the side chain of an acrylic copolymer for example, a method can be given in which a copolymer containing the above-mentioned hydroxyl group-containing (meth)acrylate (a2) or functional group-containing ethylenically unsaturated monomer (a4) is prepared, and then a compound having a functional group that can react with these functional groups and a polymerizable carbon double bond group is subjected to a condensation or addition reaction while maintaining the activity of the polymerizable carbon double bond group.
• a copolymer containing the above-mentioned hydroxyl group-containing (meth)acrylate (a2) or functional group-containing ethylenically unsaturated monomer (a4) is prepared, and then a compound having a functional group that can react with these functional groups and a polymerizable carbon double bond group is subjected to a condensation or addition reaction while maintaining the activity of the polymerizable carbon double bond group.
• Combinations of these functional groups include epoxy groups (glycidyl groups) and carboxy groups, amino groups and carboxy groups, amino groups and isocyanate groups, epoxy groups (glycidyl groups) and amino groups, hydroxyl groups and epoxy groups, and hydroxyl groups and isocyanate groups.
• the combination of hydroxyl groups and isocyanate groups is preferred because of the ease of reaction control.
• a combination in which the copolymer has a hydroxyl group and the compound has an isocyanate group is particularly suitable.
• isocyanate compounds having a polymerizable carbon double bond group examples include the above-mentioned 2-(meth)acryloyloxyethyl isocyanate and its alkylene oxide adducts.
• the content of the compound having a functional group capable of reacting with the functional group and a polymerizable carbon double bond group is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 1 part by mass or less, and particularly preferably 0.1 parts by mass or less, per 100 parts by mass of the acrylic copolymer, from the viewpoint of improving adhesion and stress relaxation properties.
• the lower limit is usually 0 parts by mass.
• the glass transition temperature (Tg) of the acrylic copolymer is preferably -20°C or lower in order to suppress an increase in the shear storage modulus (G') at low temperatures, more preferably -23°C or lower, even more preferably -25°C or lower, particularly preferably -30°C or lower, and especially preferably -40°C or lower. Due to concerns about glue overflow due to a decrease in the shear storage modulus at high temperatures, the lower limit of the glass transition temperature (Tg) is usually -70°C, and preferably -50°C.
• the glass transition temperature (Tg) is determined by reading the temperature at which the loss tangent (tan ⁇ ) becomes maximum when the dynamic viscoelasticity is measured in a shear mode at a frequency of 1 Hz using a dynamic viscoelasticity measuring device.
• the acrylic copolymer is molded into a cylinder having a diameter of 8 mm (height of 1.0 mm), and the loss tangent (tan ⁇ ) of this cylinder is measured using a viscoelasticity measuring device (manufactured by T.A. Instruments, Inc., "DHR 2”) under the following measurement conditions.
• Measurement condition Measurement tool: ⁇ 8mm parallel plate Distortion: 0.1% Frequency: 1Hz Measurement temperature: -60 to 100°C Heating rate: 5°C/min
• the weight average molecular weight (Mw) of the acrylic copolymer is preferably 400,000 or more, more preferably 500,000 or more, even more preferably 550,000 or more, and particularly preferably 600,000 or more.
• the upper limit of the weight average molecular weight (Mw) of the acrylic copolymer is preferably 1.5 million or less, more preferably 1.2 million or less, even more preferably 1.1 million or less, and particularly preferably 1 million or less, from the viewpoints of handleability and uniform stirrability.
• the weight average molecular weight (Mw) can be determined, for example, as follows. (Method of measuring weight average molecular weight) 4 mg of the acrylic copolymer is dissolved in 12 mL of tetrahydrofuran (THF) to prepare a measurement sample, and a molecular weight distribution curve is measured under the following conditions using a gel permeation chromatography (GPC) analyzer ("HLC-8320GPC” manufactured by Tosoh Corporation), whereby the weight average molecular weight (Mw) can be determined.
• GPC gel permeation chromatography
• the content of the acrylic copolymer is usually 10 to 75% of the total mass of the adhesive composition, preferably 12 to 73%, more preferably 20 to 71%, and particularly preferably 30 to 69%.
• the pressure-sensitive adhesive composition contains, in addition to the acrylic copolymer, a radically polymerizable compound (x).
• the radically polymerizable compounds may be used alone or in combination of two or more kinds.
• the radically polymerizable compound (x) preferably has a monomer refractive index of less than 1.46, more preferably 1.45 or less, and particularly preferably 1.44 or less.
• the refractive index of an acrylic copolymer is about 1.47, and when a pressure-sensitive adhesive sheet is produced using this acrylic copolymer, it is difficult to make the refractive index of the pressure-sensitive adhesive sheet 1.470 or less.
• the refractive index of the pressure-sensitive adhesive sheet tends to be low.
• the radical polymerizable compound (x) preferably has an alkylene glycol skeleton from the viewpoint of lowering the refractive index. There is a relationship between the refractive index and chemical structure, and it is known that compounds having an ether bond have a low refractive index. Therefore, by using a radical polymerizable compound having an alkylene glycol skeleton, the refractive index of the adhesive sheet tends to be 1.470 or less.
• the alkylene glycol skeleton is preferably an alkylene chain having 2 to 10 carbon atoms, further 2 to 8 carbon atoms, particularly 2 to 6 carbon atoms, and especially 2 to 4 carbon atoms, and particularly preferably an ethylene glycol skeleton, a propylene glycol skeleton, a butylene glycol skeleton, etc., and more preferably a propylene glycol skeleton.
• the radical polymerizable compound (x) has a urethane bond from the viewpoint of flexibility.
• the content of the radically polymerizable compound (x) is preferably 25 to 1900 parts by mass, more preferably 35 to 740 parts by mass, even more preferably 40 to 400 parts by mass, and particularly preferably 45 to 240 parts by mass, relative to 100 parts by mass of the acrylic copolymer.
• the content of the radically polymerizable compound (x) is preferably 20 to 95% of the total mass of the adhesive composition, more preferably 27 to 88%, even more preferably 29 to 80%, and particularly preferably 31 to 70%.
• Examples of the radically polymerizable compound (x) include monofunctional radically polymerizable compounds and polyfunctional radically polymerizable compounds. Among these, monofunctional radically polymerizable compounds are preferred.
• the monofunctional radically polymerizable compound preferably has a glass transition temperature of ⁇ 40° C. or lower, more preferably ⁇ 45° C. or lower, and further preferably ⁇ 50° C. or lower, when homopolymerized.
• the monofunctional radically polymerizable compound preferably has a glass transition temperature of ⁇ 80° C. or higher, more preferably ⁇ 75° C. or higher, and even more preferably ⁇ 70° C. or higher, when homopolymerized, in consideration of concerns about overflow of the paste due to a decrease in shear storage modulus at high temperatures.
• Examples of the monofunctional radically polymerizable compound include monofunctional (meth)acrylic monomers and monofunctional (meth)acrylic oligomers. Among these, monofunctional (meth)acrylic oligomers are preferred.
• the monofunctional (meth)acrylic monomers include, for example, aliphatic alkyl (meth)acrylates and alicyclic alkyl (meth)acrylates, specifically, n-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, and other monofunctional linear aliphatic (meth)acrylates, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl monofunctional branched aliphatic (
• the monofunctional (meth)acrylic oligomer may, for example, be one represented by the following general formula (1).
• R 1 represents hydrogen or a methyl group.
• R 2 represents an alkylene group having 1 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms, which may have an ether bond or a cyclic structure in the chain.
• R 4 represents an alkyl group having 1 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms, which may have an ether bond or a cyclic structure in the chain.
• Z represents a linking group selected from a urethane bond, an ester bond, an ether bond, a carbonate bond, an amide bond, and a urea bond.
• R 3 represents an alkylene group which is an ethylene group or a propylene group.
• k represents r+s, which is the total number of repeating units of the repeating units (C 2 H 4 O) r and (C 3 H 6 O) s , and is an integer of 1 to 500.
• an oxyethylene structure and an oxypropylene structure coexist, they may be of a random type or a block type.
• the positive number "k" in the general formula (1) is preferably 10 to 500, more preferably 100 to 450, and even more preferably 200 to 400, from the viewpoint of reducing the refractive index and lowering the shear storage modulus at low temperatures while maintaining high recovery when bent.
• monofunctional (meth)acrylic oligomers are monofunctional urethane (meth)acrylates, monofunctional polyester (meth)acrylates, monofunctional epoxy (meth)acrylates, etc., and more preferred are monofunctional urethane (meth)acrylates.
• the monofunctional urethane (meth)acrylate is particularly effective because it has high polarity and a long chain length, resulting in high recovery due to the entanglement of polymer chains, and because it has an oxypropylene structure with high molecular rotation, it has a low shear storage modulus.
• the weight average molecular weight (Mw) of the monofunctional (meth)acrylic oligomer is preferably 30,000 or less, more preferably 28,000 or less, and even more preferably 25,000 or less, from the viewpoint of reducing the shear storage modulus at low temperatures while maintaining high recovery property when bent.
• the lower limit of the weight average molecular weight (Mw) of the monofunctional (meth)acrylic oligomer is preferably 3,000 or more, more preferably 4,000 or more, and even more preferably 5,000 or more, from the viewpoint of preventing a decrease in adhesiveness due to bleed-out while maintaining high recovery property when bent.
• the weight average molecular weight (Mw) of the monofunctional (meth)acrylic oligomer can be determined in accordance with the "Method of measuring weight average molecular weight" of the acrylic copolymer described above.
• Polyfunctional radically polymerizable compound examples include polyfunctional (meth)acrylic monomers and polyfunctional (meth)acrylic oligomers.
• polyfunctional (meth)acrylic monomers examples include 1,4-butanediol di(meth)acrylate, glycerin di(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin glycidyl ether di(meth)acrylate, tricyclodecane dimethacrylate, tricyclodecane dimethanol di(meth)acrylate, bisphenol A polyethoxy di(meth)acrylate, bisphenol A polypropoxy di(meth)acrylate, and bisphenol F polyethoxy di(meth)acrylate.
• difunctional (meth)acrylates such as ethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, and di(meth)acrylate of hydroxypivalic acid neopentyl glycol adduct with ⁇ -caprolactone; trimethylolpropane trioxyethyl (meth)acrylate acrylate, ⁇ -caprolactone-modified tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propoxylated pentaerythritol tri(meth)acrylate, ethoxylated pentaerythritol tri(meth
• polyfunctional (meth)acrylic oligomer examples include polyfunctional (meth)acrylic oligomers such as polyfunctional polyester (meth)acrylate oligomers, polyfunctional epoxy (meth)acrylate oligomers, polyfunctional urethane (meth)acrylate oligomers, and polyfunctional polyether (meth)acrylate oligomers.
• polyfunctional (meth)acrylic monomer or a polyfunctional (meth)acrylic oligomer it also acts as a crosslinking agent.
• the pressure-sensitive adhesive composition preferably further contains a photopolymerization initiator in addition to the acrylic copolymer and the radically polymerizable compound (x).
• the photopolymerization initiator may be any compound that generates radicals by the action of active energy rays.
• Photopolymerization initiators are broadly classified into two types based on the radical generation mechanism: cleavage-type photopolymerization initiators, which can generate radicals by cleaving the single bond of the initiator itself, and hydrogen abstraction-type photopolymerization initiators, which form an exciplex between the excited initiator and the hydrogen donor in the system and transfer the hydrogen from the hydrogen donor.
• the photopolymerization initiator may be either a cleavage type photopolymerization initiator or a hydrogen abstraction type photopolymerization initiator, and may be used alone or in combination with the two, or may be used in combination with one or more of each.
• the acrylic copolymer itself does not require a functional group such as a polymerizable carbon double bond group and crosslinking can be efficiently performed.
• Examples of the cleavage-type photopolymerization initiator include 2,2-dimethoxy-1,2-diphenylethane-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-(4-(2-hydroxyethoxy)phenyl)-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-[4- ⁇ 4-(2-hydroxy-2-methyl-propionyl)benzyl ⁇ phenyl]-2-methyl-propan-1-one, oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone), methyl phenylglyoxylate, and 2-benzyl-2-dimethylamino
• Examples of such compounds include 1-(4-morpholinophenyl)butan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-(dimethylamino)-2-
• Examples of the hydrogen abstraction type photopolymerization initiator include benzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3'-dimethyl-4-methoxybenzophenone, 4-(meth)acryloyloxybenzophenone, methyl 2-benzoylbenzoate, methyl benzoylformate, bis(2-phenyl-2-oxoacetate)oxybisethylene, 4-(1,3-acryloyl-1,4,7,10,13-pentaoxotridecyl)benzophenone, thioxanthone, 2-chlorothioxanthone, 3-methylthioxanthone, 2,4-dimethylthioxanthone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-t-butylanthraquinone, 2-aminoanthraquinone, and derivatives thereof.
• the photopolymerization initiator When the photopolymerization initiator is used, its content is usually 0.1 to 10 parts by mass, preferably 0.5 to 6 parts by mass, and more preferably 1 to 4 parts by mass, per 100 parts by mass of the acrylic copolymer. If the content is equal to or greater than the lower limit, curing failure tends to be prevented, and if it is equal to or less than the upper limit, it tends to be easier to prevent a decrease in solution stability, such as precipitation from the adhesive composition, and to prevent problems such as embrittlement and coloration.
• the pressure-sensitive adhesive composition may contain a thermal crosslinking agent in order to further increase the crosslink density and improve long-term reliability.
• thermal crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, aldehyde-based crosslinking agents, amine-based crosslinking agents, and metal chelate-based crosslinking agents.
• the thermal crosslinking agent When the thermal crosslinking agent is used, its content is usually 0.01 to 10 parts by mass, preferably 0.02 to 7 parts by mass, and more preferably 0.1 to 5 parts by mass, per 100 parts by mass of the acrylic copolymer.
• the pressure-sensitive adhesive composition may contain, as "other components", as necessary, various additives such as a silane coupling agent, an ultraviolet absorber, an anti-rust agent, a tackifier resin, an antioxidant, a light stabilizer, a metal deactivator, an anti-aging agent, a moisture absorber, an anti-rust agent, inorganic particles, and a refractive index adjuster, to the extent that the effects of the present invention are not impaired.
• a reaction catalyst such as a tertiary amine compound, a quaternary ammonium compound, or a tin laurate compound may be appropriately contained. These may be used alone or in combination of two or more.
• Silane coupling agent is an organic silicon compound that contains one or more reactive functional groups and one or more alkoxy groups bonded to silicon atoms in its structure.
• the reactive functional groups include, for example, epoxy groups, (meth)acryloyl groups, mercapto groups, hydroxyl groups, carboxy groups, amino groups, amide groups, and isocyanate groups, and among these, epoxy groups and mercapto groups are preferred from the viewpoint of durability balance.
• the alkoxy group bonded to the silicon atom preferably contains an alkoxy group having 1 to 8 carbon atoms from the viewpoint of durability and storage stability, and is particularly preferably a methoxy group or an ethoxy group.
• the silane coupling agent may also have an organic substituent other than the reactive functional group and the alkoxy group bonded to the silicon atom, such as an alkyl group or a phenyl group.
• the silane coupling agent may be, for example, a monomeric epoxy group-containing silane coupling agent which is a silane compound such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, or 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, or a silane coupling agent in which a part of the silane compound is hydrolyzed and condensed, or a silane compound and methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane ...
• a silane compound such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-
• oligomer-type epoxy group-containing silane coupling agents which are silane compounds obtained by co-condensation of alkyl group-containing silane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, ⁇ -mercaptopropyldimethoxymethylsilane, 3-mercaptopropylmethyldimethoxysilane, and monomer-type mercapto group-containing silane compounds such as silane compounds obtained by hydrolysis and condensation polymerization of a part of the silane compounds, or methyltriethoxysilane, ethyltriethoxysilane, ...
• oligomeric mercapto group-containing silane coupling agents which are silane compounds obtained by co-condensation of alkyl group-containing silane compounds such as ethyltrimethoxysilane and ethyltrimethoxysilane; (meth)acryloyl group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane and 3-acryloxypropyltrimethoxysilane; N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane;
• suitable silane coupling agents include amino group-containing silane coupling agents such as N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-
• epoxy group-containing silane coupling agents and mercapto group-containing silane coupling agents are preferably used because of their excellent durability, and among these, epoxy group-containing silane coupling agents are more preferred.
• the content of the silane coupling agent is preferably 0.005 to 10 parts by mass, particularly preferably 0.01 to 5 parts by mass, and even more preferably 0.05 to 1 part by mass, per 100 parts by mass of the acrylic copolymer. If the content is equal to or greater than the lower limit, durability tends to improve, and if the content is equal to or less than the upper limit, durability tends to improve.
• ultraviolet absorbent examples include benzophenone-based ultraviolet absorbents, benzotriazole-based ultraviolet absorbents, triazine-based ultraviolet absorbents, salicylic acid-based ultraviolet absorbents, cyanoacrylate-based ultraviolet absorbents, benzoxazine-based ultraviolet absorbents, etc. These ultraviolet absorbents can be used alone or in combination of two or more kinds.
• the content of the ultraviolet absorber is preferably 0.01 to 20 parts by mass, particularly preferably 0.1 to 15 parts by mass, and even more preferably 0.5 to 10 parts by mass, per 100 parts by mass of the acrylic copolymer. If the content is equal to or greater than the lower limit, the light resistance reliability tends to improve, and if the content is equal to or less than the upper limit, the yellowing resistance tends to improve.
• rust inhibitor for example, triazoles, benzotriazoles, etc. are preferable, which can prevent corrosion of optical members. These may be used alone or in combination of two or more kinds.
• the content of the rust inhibitor is preferably 0.01 to 5 parts by mass, and more preferably 0.1 to 3 parts by mass, based on 100 parts by mass of the acrylic copolymer.
• the content of the other components is preferably 5 parts by mass or less per 100 parts by mass of the acrylic copolymer, particularly preferably 1 part by mass or less, and even more preferably 0.5 parts by mass or less. If the content is too high, the compatibility with the acrylic copolymer decreases, and durability tends to decrease.
• the adhesive composition is prepared by mixing a predetermined amount of each of the acrylic copolymer, the radical polymerizable compound (x), preferably a photopolymerization initiator, and, if necessary, a thermal crosslinking agent and other components.
• an adhesive composition for forming the adhesive sheet 1 is prepared, which contains an acrylic copolymer, a radically polymerizable compound (x), a photopolymerization initiator, and optionally a thermal crosslinking agent and other components, and the adhesive composition is formed into a sheet, crosslinked, i.e., polymerized, to harden the composition, and then processed as necessary to produce the adhesive sheet 1.
• an adhesive composition for forming the adhesive sheet 1 may be prepared in the same manner as described above, and then coated onto a member sheet or a component of a flexible image display device, and the adhesive composition may be cured to form the adhesive sheet 1.
• the method for manufacturing the adhesive sheet 1 is not limited to this method.
• the raw materials may be kneaded using a temperature-controllable kneader (e.g., a single-screw extruder, a twin-screw extruder, a planetary mixer, a twin-screw mixer, a pressure kneader, etc.).
• a temperature-controllable kneader e.g., a single-screw extruder, a twin-screw extruder, a planetary mixer, a twin-screw mixer, a pressure kneader, etc.
• various additives such as silane coupling agents and antioxidants may be blended together with the resin in advance and then fed to the kneader, or all of the materials may be melt-mixed in advance and then fed, or a master batch in which only the additives are concentrated in the resin may be prepared and then fed.
• the adhesive composition can be formed into a sheet by any known method, such as wet lamination, dry lamination, extrusion casting using a T-die, extrusion lamination, calendaring, inflation, injection molding, or liquid injection curing.
• wet lamination, extrusion casting, and extrusion lamination methods are preferred.
• the adhesive composition can be cured by irradiating it with active energy rays, and the adhesive sheet 1 can be produced by irradiating a molded product of the adhesive composition, for example, a sheet, with active energy rays. In addition to irradiating it with active energy rays, the adhesive composition can also be heated to further cure it.
• the present pressure-sensitive adhesive sheet 1 is preferably cured using a hydrogen abstraction type photopolymerization initiator.
• the active energy rays in the active energy ray irradiation include, for example, light rays such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, infrared rays, and visible light rays, as well as ionizing radiation such as X-rays, alpha rays, beta rays, gamma rays, electron beams, proton beams, and neutron beams.
• light rays such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, infrared rays, and visible light rays
• ionizing radiation such as X-rays, alpha rays, beta rays, gamma rays, electron beams, proton beams, and neutron beams.
• X-rays alpha rays
• beta rays beta rays
• gamma rays electron beams
• proton beams proton beams
• neutron beams are preferred from the viewpoints
• Light sources for ultraviolet irradiation include high-pressure mercury lamps, ultra-high-pressure mercury lamps, low-pressure mercury lamps, carbon arc lamps, metal halide lamps, xenon lamps, chemical lamps, electrodeless discharge lamps, LEDs, etc. that emit light in the 150 to 450 nm wavelength range. Of these, it is preferable to use a high-pressure mercury lamp.
• the exposure dose of active energy rays is preferably from 0.03 to 3 J/cm 2 , more preferably from 0.1 to 2 J/cm 2 , and even more preferably from 0.3 to 1.5 J/cm 2 .
• the pressure-sensitive adhesive composition can be dissolved in an appropriate solvent and various coating methods can be used.
• various coating methods in addition to the above-mentioned curing by irradiation with active energy rays, it is also possible to obtain the present pressure-sensitive adhesive sheet 1 by thermal curing.
• the thickness of the present pressure-sensitive adhesive sheet 1 can be adjusted by the coating thickness and the solids concentration of the coating liquid.
• the adhesive composition can be dissolved in a solvent, coated on a release film, dried, and cured by irradiating with active energy rays to form the present adhesive sheet.
• a release film may be laminated as necessary.
• the adhesive composition may be coated on a release film, dried, cured by irradiating with active energy rays, and a release film may be laminated on top of the coating, or the adhesive composition may be coated on a release film, dried, and then cured by irradiating with active energy rays to form the present adhesive sheet 1.
• the solvent is not particularly limited as long as it dissolves the adhesive composition, and examples include ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, methyl acetoacetate, and ethyl acetoacetate; ketone-based solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aromatic solvents such as toluene and xylene; and alcohol-based solvents such as methanol, ethanol, and propyl alcohol. These can be used alone or in combination of two or more.
• ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, methyl acetoacetate, and ethyl acetoacetate
• ketone-based solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone
• aromatic solvents such as toluen
• ethyl acetate acetone, methyl ethyl ketone, and toluene are preferred from the standpoint of solubility, drying property, cost, etc., and ethyl acetate is particularly preferred.
• the content of the solvent is preferably 600 parts by mass or less, more preferably 500 parts by mass or less, even more preferably 400 parts by mass or less, and particularly preferably 300 parts by mass or less, relative to 100 parts by mass of the acrylic copolymer, while it is preferably 1 part by mass or more, more preferably 50 parts by mass or more, even more preferably 100 parts by mass or more, and particularly preferably 150 parts by mass or more.
• the coating method may be a conventional method such as roll coating, die coating, gravure coating, comma coating, screen printing, or bar coating.
• the solvent content in the adhesive composition after drying is preferably 1% by mass or less, more preferably 0.5% by mass or less, particularly preferably 0.1% by mass or less, and most preferably 0% by mass.
• the drying temperature is usually 40 to 150°C, more preferably 45 to 140°C, even more preferably 50 to 130°C, and particularly preferably 55 to 120°C.
• the drying temperature is within the above temperature range, the solvent can be removed efficiently and relatively safely while suppressing thermal deformation of the release film.
• the drying time is usually 1 to 30 minutes, more preferably 3 to 25 minutes, and even more preferably 5 to 20 minutes. If the drying time is within the above range, the solvent can be removed efficiently and sufficiently.
• Drying methods include, for example, drying with a dryer, drying with a heated roll, and drying by blowing hot air onto the film.
• a dryer is preferred because it allows for uniform and easy drying. These can be used alone or in combination of two or more types.
• a release film can be provided on at least one side of the adhesive sheet 1 obtained above to prevent blocking and adhesion of foreign matter.
• the present adhesive sheet 1 can also be provided as an adhesive sheet with a release film (adhesive sheet laminate) having a configuration in which a release film is laminated on one or both sides of an adhesive layer (the present adhesive sheet) made of an adhesive composition.
• a release film adhesive sheet laminate
• the present adhesive sheet made of an adhesive composition.
• release films are provided on both sides of the present pressure-sensitive adhesive sheet 1, it is preferable to use a laminate configuration in which a light release film with a relatively low release strength and a heavy release film with a relatively high release strength are laminated together.
• one release film (light release film) is peeled off to expose one side of the adhesive sheet, and the adhesive sheet is then bonded to a component sheet or a flexible image display device component (referred to as the first component), and the other release film (heavy release film) is peeled off to expose the other side of the adhesive sheet, and the component sheet or a flexible image display device component (referred to as the second component) is then bonded to the other side of the adhesive sheet.
• any known release film can be appropriately used.
• a film such as a polyester film, a polyolefin film, a polycarbonate film, a polystyrene film, an acrylic film, a triacetyl cellulose film, or a fluororesin film that has been subjected to a release treatment by coating with a release agent such as a silicone resin, or release paper, etc.
• a release agent such as a silicone resin, or release paper, etc.
• polyester films, and more particularly polyethylene terephthalate (PET) films, particularly biaxially stretched PET films are preferred because they are excellent in transparency, mechanical strength, heat resistance, flexibility, etc.
• a release film having a release layer formed by curing a curable silicone-based release agent containing silicone resin as a main component on the above-mentioned substrate can be used.
• the release film particularly the light release film, used in the highly flexible adhesive sheet is preferably a release film that can be peeled off with even less force than the light release type release films that have been conventionally used for general purposes.
• the thickness of the release agent layer is increased in order to make the release film easier to release, depending on the type of release agent used, components from the release agent layer may transfer to the surface of the adhesive sheet, compromising the reliability of the adhesive sheet. For this reason, it is preferable for the release film to have good releasability from the adhesive sheet and little migration of the release agent to the adhesive sheet.
• the peel strength between the adhesive sheet 1 and the release film is preferably 0.05 to 1.5 N/cm, more preferably 0.06 to 1.2 N/cm, and even more preferably 0.07 to 1.0 N/cm.
• the peel strength between the adhesive sheet 1 and the release film is a measurement value obtained by a 180° peel test at a test speed of 300 m/min. If the peel strength between the adhesive sheet 1 and the release film is within the above range, peel marks can be prevented when the release film is peeled off from the adhesive sheet 1.
• the peak intensity of silicon atoms on the adhesive surface exposed by peeling the release film off of the adhesive sheet 1, as measured using an X-ray fluorescence analyzer is preferably 100 cps or less. If the peak intensity is 100 cps or less, this is preferable because the release agent that has migrated to the adhesive sheet surface does not impair the reliability of the adhesive sheet when it is used as a laminate for constituting an image display device. From this perspective, the peak intensity is more preferably 90 cps or less, even more preferably 80 cps or less, and especially preferably 70 cps or less. The lower limit is usually 0 cps.
• the thickness of the release film is not particularly limited. From the standpoint of processability and handling, for example, it is preferably 10 to 250 ⁇ m, more preferably 25 to 200 ⁇ m, and even more preferably 35 to 190 ⁇ m.
• embossing or various other uneven processing may be performed.
• various surface treatments such as corona treatment, plasma treatment, and primer treatment may be performed on the surface.
• the adhesive sheet 1 may be a single-layer sheet consisting of only an acrylic adhesive layer formed from an adhesive composition, or a multi-layer sheet in which multiple acrylic adhesive layers and/or other adhesive layers are laminated.
• the adhesive sheet 2 has an acrylic adhesive layer, and the acrylic adhesive layer is a cured reaction product formed from a syrup composition containing an alkyl (meth)acrylate (a1), a hydroxyl group-containing (meth)acrylate (a2), and a radical polymerizable compound (x).
• a1 alkyl (meth)acrylate
• a2 hydroxyl group-containing (meth)acrylate
• x radical polymerizable compound
• alkyl (meth)acrylate (a1) examples include those similar to the alkyl (meth)acrylate (a1) described in the present adhesive sheet 1, and the types of preferred monomers, etc. are also similar to those of the alkyl (meth)acrylate (a1) described in the present adhesive sheet 1.
• the content of the structural moiety derived from the alkyl (meth)acrylate (a1) is preferably 2 to 80% of the total mass of the acrylic adhesive layer (syrup composition) in order to suppress an increase in the shear storage modulus (G') at low temperatures, more preferably 5 to 55%, and particularly preferably 10 to 50%. If the content of the structural moiety derived from the alkyl (meth)acrylate (a1) is equal to or more than the lower limit, an increase in the shear storage modulus (G') at low temperatures can be suppressed, and if it is equal to or less than the upper limit, it is preferable in terms of compatibility with other physical properties such as adhesion.
• hydroxyl group-containing (meth)acrylate (a2) examples include the same as the hydroxyl group-containing (meth)acrylate (a2) described in the present adhesive sheet 1, and the types of preferred monomers, etc. are also the same as the hydroxyl group-containing (meth)acrylate (a2) described in the present adhesive sheet 1.
• the content of the structural moiety derived from the hydroxyl group-containing (meth)acrylate (a2) is usually 0.5 to 60% by mass of the total mass of the acrylic pressure-sensitive adhesive layer (syrup composition), preferably 0.5 to 30%, particularly preferably 1 to 25%, further preferably 1.5 to 20%, and especially preferably 2 to 20%.
• the radical polymerizable compound (x) may be any of the radical polymerizable compounds (x) described in the present pressure-sensitive adhesive sheet 1 that do not overlap with (a3) to (a5).
• the preferred compounds and physical properties of the radical polymerizable compound (x) are the same as those of the radical polymerizable compound (x) described in the present pressure-sensitive adhesive sheet 1.
• the content of the structural portion derived from the radically polymerizable compound (x) is preferably 20 to 95% of the total mass of the acrylic adhesive layer (syrup composition), more preferably 27 to 88%, even more preferably 29 to 80%, and particularly preferably 31 to 70%.
• the syrup composition may also contain the copolymerizable monomer (a3), functional group-containing monomer (a4), and other copolymerizable monomers (a5) described in the present adhesive sheet 1.
• the types of these preferred monomers are the same as those described in the present adhesive sheet 1.
• the acrylic adhesive layer contains a structural portion derived from copolymerizable monomer (a3), the content thereof is usually 1 to 70%, preferably 10 to 60%, and particularly preferably 15 to 45%, of the total mass of the acrylic adhesive layer (syrup composition).
• the acrylic adhesive layer contains a structural portion derived from the functional group-containing monomer (a4)
• the content thereof is usually 30% or less, preferably 20% or less, particularly preferably 10% or less, and especially preferably 5% or less of the total mass of the acrylic adhesive layer (syrup composition).
• the acrylic adhesive layer contains a structural portion derived from another copolymerizable monomer (a5), the content thereof is usually 50% or less, preferably 40% or less, and particularly preferably 20% or less of the total mass of the acrylic adhesive layer (syrup composition).
• the acrylic adhesive layer preferably contains a photopolymerization initiator as described above in the present adhesive sheet 1, and may also contain a thermal crosslinking agent and other components as described above in the present adhesive sheet 1.
• the photopolymerization initiator is not particularly limited as long as it is the same as the photopolymerization initiator described above in the present pressure-sensitive adhesive sheet 1, but from the viewpoint of efficiently progressing the polymerization reaction, it is preferable to include a cleavage-type photopolymerization initiator, and among the above-mentioned cleavage-type photopolymerization initiators, 2,2-dimethoxy-1,2-diphenylethan-1-one, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide are particularly preferred.
• the photopolymerization initiator may include two or more types selected from the group consisting of cleavage type photopolymerization initiators and/or hydrogen abstraction type photopolymerization initiators.
• the photopolymerization initiator When the photopolymerization initiator is used, its content is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 6 parts by mass, and even more preferably 1 to 4 parts by mass, per 100 parts by mass of the copolymer components, such as the alkyl (meth)acrylate (a1), hydroxyl group-containing (meth)acrylate (a2), radical polymerizable compound (x), copolymerizable monomer (a3), functional group-containing monomer (a4), and other copolymerizable monomer (a5), contained in the syrup composition.
• the copolymer components such as the alkyl (meth)acrylate (a1), hydroxyl group-containing (meth)acrylate (a2), radical polymerizable compound (x), copolymerizable monomer (a3), functional group-containing monomer (a4), and other copolymerizable monomer (a5), contained in the syrup composition.
• the content is equal to or greater than the lower limit, poor curing tends to be prevented, and if it is equal to or less than the upper limit, it tends to be easier to prevent a decrease in stability, such as precipitation from the adhesive sheet, and to prevent problems such as embrittlement and coloration.
• thermal crosslinking agent As the thermal crosslinking agent, it is preferable to use an isocyanate-based crosslinking agent because of its excellent reactivity with the acrylic copolymer.
• the thermal crosslinking agent When the thermal crosslinking agent is used, its content is usually 1 to 30% of the total mass of the acrylic adhesive layer (syrup composition), and preferably 5 to 20%.
• a silane coupling agent As other components, a silane coupling agent, an ultraviolet absorber, and an anti-rust agent are preferable.
• the preferable types of the silane coupling agent, the ultraviolet absorber, and the anti-rust agent are the same as those explained in the present pressure-sensitive adhesive sheet 1.
• silane coupling agent When the silane coupling agent is used, its content is usually 0.005 to 5%, preferably 0.01 to 3%, and more preferably 0.05 to 1% of the total mass of the acrylic adhesive layer (syrup composition). When the content is within the above range, durability tends to improve.
• the acrylic adhesive layer contains an ultraviolet absorber
• the content is usually 0.001 to 20%, preferably 0.1 to 15%, and more preferably 0.5 to 10% of the total mass of the acrylic adhesive layer (syrup composition). If the content is equal to or greater than the lower limit, the light resistance reliability tends to improve, and if the content is equal to or less than the upper limit, the yellowing resistance tends to improve.
• the acrylic adhesive layer contains a rust inhibitor
• its content is usually 5% or less of the total mass of the acrylic adhesive layer (syrup composition), preferably 1% or less, and more preferably 0.5% or less. If the content is too high, compatibility decreases and durability tends to decrease.
• a syrup composition is prepared by kneading copolymer components such as alkyl (meth)acrylate (a1), hydroxyl group-containing (meth)acrylate (a2), radical polymerizable compound (x), and, if necessary, copolymerizable monomer (a3), functional group-containing monomer (a4), and other copolymerizable monomer (a5), and a photopolymerization initiator.
• this syrup composition is irradiated with active energy rays to perform prepolymerization.
• the syrup composition to which additional photopolymerization initiator, thermal crosslinking agent, and other components have been added is coated on a release film or the like using various coating methods, and then cured by irradiating active energy rays or heating, thereby obtaining the present adhesive sheet 2.
• the radical polymerizable compound (x), the thermal crosslinking agent, and other components may be added to the syrup composition from the beginning, or may be added to the syrup composition after the prepolymerization is completed. Furthermore, the prepolymerization and curing may be carried out in one step.
• the syrup composition is dissolved in a solvent, coated on a release film, dried, and prepolymerized and cured by irradiation with active energy rays to form the adhesive sheet 2.
• the release film, active energy rays, solvent, kneading method, coating method, drying conditions, etc. may be the same as those described above for the adhesive sheet 1.
• the adhesive sheet 2 thus obtained may be a single layer sheet having only an acrylic adhesive layer, or a multilayer sheet having multiple laminated acrylic adhesive layers and other adhesive layers.
• the adhesive sheet 2 may also be provided as an adhesive sheet with a release film (adhesive sheet laminate) having a configuration in which a release film is laminated on one or both sides of an adhesive layer (the adhesive sheet) made of an adhesive composition.
• the present pressure-sensitive adhesive sheets 1 and 2 (hereinafter simply referred to as “the present pressure-sensitive adhesive sheets”) can have the following physical properties.
• the refractive index of the present pressure-sensitive adhesive sheet is 1.470 or less, preferably 1.469 or less, more preferably 1.467 or less, even more preferably 1.465 or less, and even more preferably 1.464 or less.
• the lower limit of the refractive index of the present pressure-sensitive adhesive sheet is preferably 1.450 or more, and more preferably 1.460 or more.
• the method of adjusting the refractive index of the pressure-sensitive adhesive sheet includes, for example, a method of using a monomer having a relatively low refractive index among the above-mentioned alkyl (meth)acrylates (a1) as a constituent part of the acrylic copolymer, for example, an alkyl (meth)acrylate having 4 or more carbon atoms, particularly 6 or more, and especially 8 or more carbon atoms in the alkyl group, and adjusting the content thereof, a method of using a (meth)acrylate monomer having an alkylene glycol structure as a constituent part, and a method of adjusting the structure or amount of the radical polymerizable compound (x).
• a refractive index adjuster may be added within a range that does not impair the compatibility or transparency of the pressure-sensitive adhesive composition.
• the refractive index refers to the refractive index of the surface (acrylic adhesive layer) of this adhesive sheet.
• the refractive index can be measured using a commercially available refractive index measuring device (Abbe refractometer) at a measurement wavelength of 589 nm and a measurement temperature of 25°C, and specifically, can be measured by the method described in the Examples below.
• the pressure-sensitive adhesive sheet has a shear storage modulus at -30°C (G'(-30°C)), obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, of preferably 1200 kPa or less, more preferably 1000 kPa or less, even more preferably 800 kPa or less, particularly preferably 700 kPa or less, especially preferably 500 kPa or less, even more preferably 400 kPa or less, even more preferably 300 kPa or less, and especially preferably 200 kPa or less.
• the lower limit of the shear storage modulus (G'(-30°C)) of the present pressure-sensitive adhesive sheet is preferably 100 kPa or more in terms of the balance with the shear storage modulus at high temperatures.
• the shear storage modulus (G' (-30°C)) of this adhesive sheet within the above range, for example, when the adhesive sheet is attached to a component sheet to form a laminate or a laminate for an image display device, the interlayer stress during bending of the laminate or the laminate for an image display device can be reduced, particularly at low to high temperatures, and delamination or cracking of the component sheet or the component of a flexible image display device can be suppressed.
• the pressure-sensitive adhesive sheet preferably has a shear storage modulus at -20°C (G'(-20°C)), obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, of 500 kPa or less, more preferably 400 kPa or less, particularly preferably 300 kPa or less, and even more preferably 250 kPa or less.
• the lower limit of the shear storage modulus (G'(-20°C)) of the present pressure-sensitive adhesive sheet is preferably 50 kPa or more in view of the balance with the shear storage modulus at high temperatures.
• the shear storage modulus (G' (-20°C)) of the adhesive sheet is within the above range, for example, when the adhesive sheet is attached to a component sheet to form a laminate or a laminate for an image display device, the interlayer stress during bending of the laminate or the laminate for an image display device can be reduced, particularly at low to high temperatures, and delamination or cracking of the component sheet or the component of a flexible image display device can be suppressed.
• the shear storage modulus (G'(25°C)) of this adhesive sheet at 25°C is preferably 100 kPa or less, more preferably 50 kPa or less, particularly preferably 40 kPa or less, and even more preferably 30 kPa or less.
• the lower limit of the shear storage modulus (G' (25°C)) of the present pressure-sensitive adhesive sheet is preferably 5 kPa or more from the viewpoints of preventing adhesive extrusion and maintaining the shape of the pressure-sensitive adhesive sheet.
• the shear storage modulus at 60°C (G'(60°C)) of this adhesive sheet is preferably 50 kPa or less, more preferably 40 kPa or less, particularly preferably 35 kPa or less, and even more preferably 30 kPa or less.
• the lower limit of the shear storage modulus (G'(60°C)) of the present pressure-sensitive adhesive sheet is preferably 1 kPa or more from the viewpoints of preventing adhesive extrusion and maintaining the shape of the pressure-sensitive adhesive sheet.
• the shear storage modulus (G'(80°C)) of this adhesive sheet at 80°C, obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is preferably 50 kPa or less, more preferably 40 kPa or less, particularly preferably 35 kPa or less, and even more preferably 30 kPa or less.
• the lower limit of the shear storage modulus (G'(80°C)) of this adhesive sheet is preferably 1 kPa or more, more preferably 3 kPa or more, even more preferably 5 kPa or more, particularly preferably 8 kPa or more, even more preferably 11 kPa or more, and especially preferably 15 kPa or more.
• This PSA sheet has a shear storage modulus ratio (G'(-30°C)/G'(80°C)) between the shear storage modulus at -30°C (G'(-30°C)) and the shear storage modulus at 80°C (G'(80°C)), as determined by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, of 1 to 65, preferably 1 to 50, more preferably 2 to 35, particularly preferably 3 to 30, and especially preferably 4 to 20. Since the shear storage modulus ratio (G'(-30°C)/G'(80°C)) of this pressure-sensitive adhesive sheet is in the above-mentioned range, it has excellent flexibility. In other words, this pressure-sensitive adhesive sheet has both flexibility and cohesive strength, and can prevent both destruction of members when folded at low temperatures and creases when folded at high temperatures.
• the maximum point of the loss tangent (tan ⁇ ) obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is preferably ⁇ 20° C. or lower, more preferably ⁇ 25° C. or lower, particularly preferably ⁇ 30° C. or lower, particularly preferably ⁇ 35° C. or lower, and even more preferably ⁇ 40° C. or lower.
• the lower limit is usually ⁇ 80° C.
• the maximum point of the loss tangent (tan ⁇ ) can be interpreted as the glass transition temperature (Tg), and by having the glass transition temperature (Tg) within the above range, it becomes easier to adjust the shear storage modulus (G'(-30°C)) of the pressure-sensitive adhesive sheet to 1200 kPa or less.
• the glass transition temperature (Tg) can be considered to be single.
• the "maximum point” of loss tangent (tan ⁇ ) refers to the peak value on the tan ⁇ curve, that is, the point that has the largest value within a specified range or the entire range among the inflection points where the value changes from positive (+) to negative (-) when differentiated.
• the shear storage modulus (G') and loss tangent (tan ⁇ ) at various temperatures can be measured using a rheometer.
• the shear storage modulus (G') and loss tangent (tan ⁇ ) can be adjusted to the above ranges by adjusting the types and weight average molecular weights of the components (e.g., the acrylic copolymer and the radically polymerizable compound) contained in the adhesive composition and syrup composition that make up this adhesive sheet, and by adjusting the gel fraction of the adhesive sheet.
• the components e.g., the acrylic copolymer and the radically polymerizable compound
• the adhesive strength of the acrylic adhesive layer of the present pressure-sensitive adhesive sheet is appropriately determined depending on the material of the adherend, etc., but for example, when it is attached to glass, polyethylene terephthalate (PET), polyimide (CPI), polycarbonate, polymethyl methacrylate, or PET with an ITO layer deposited thereon, it preferably has an adhesive strength of 1 to 50 N/cm, particularly preferably 2 to 30 N/cm, and further preferably 5 to 20 N/cm. Specifically, the adhesive strength can be measured by the method described in the Examples below.
• the pressure-sensitive adhesive sheet has a thickness of 0.5 to 1.2 mm, and the recovery rate calculated using the following formula from the strain ( ⁇ max(25) ) after a pressure of 10 kPa is applied for 600 seconds at a temperature of 25°C and the strain ( ⁇ min(25) ) 600 seconds after the stress is removed is preferably 80% or more, and more preferably 85% or more.
• Recovery rate (%) [( ⁇ max(25) - ⁇ min(25) ) / ⁇ max(25) ] x 100
• the pressure-sensitive adhesive sheet has a thickness of 0.5 to 1.2 mm, and the recovery rate calculated using the following formula from the strain ( ⁇ max(-20) ) after a pressure of 10 kPa is applied for 600 seconds at a temperature of -20°C and the strain ( ⁇ min(-20) ) 600 seconds after the stress is removed is preferably 70% or more, and more preferably 75% or more.
• Recovery rate (%) [( ⁇ max(-20) - ⁇ min(-20) ) / ⁇ max(-20) ] x 100
• the adhesive sheet has this kind of resilience, it can be made into an adhesive sheet with excellent flexibility that leaves no creases due to being placed in a bent state, even when the adhesive sheet is attached to a component sheet and folded at low or high temperatures. Since high resilience is preferable, the upper limit of resilience is 100%.
• this adhesive sheet it is preferable to use a monofunctional radically polymerizable compound having an alkylene glycol skeleton as the radically polymerizable compound (x), and it is even more preferable that the acrylic copolymer or acrylic adhesive layer contains a structural portion derived from a hydroxyl group-containing (meth)acrylate.
• the monofunctional radically polymerizable compound containing an oxyalkylene structure having an alkylene group having a certain range of length is bonded to the acrylic copolymer, which strengthens the entanglement of the polymer chains, thereby increasing the entropy difference before and after elongation, and improving the restorability due to the entropy elasticity.
• the method for adjusting the restorability is not limited to these methods.
• the gel fraction of the pressure-sensitive adhesive sheet is preferably 30 to 95% by mass, more preferably 50 to 90% by mass, even more preferably 55 to 85% by mass, and particularly preferably 60 to 85% by mass.
• the gel fraction is an index of the degree of crosslinking (degree of curing), and can be measured under the measurement conditions described in the examples below.
• This pressure-sensitive adhesive sheet has transparency when observed with the naked eye, and transparency indicates that each component is uniformly dissolved in the sheet.
• the pressure-sensitive adhesive sheet preferably has a haze of 1.0% or less, more preferably 0.8% or less, and particularly preferably 0.5% or less.
• the pressure-sensitive adhesive sheet has a haze of 1.0% or less, it tends to be suitable for use in image display devices.
• the present pressure-sensitive adhesive sheet does not contain particles such as organic particles.
• the thickness of the present pressure-sensitive adhesive sheet is not particularly limited, and if the thickness is 10 ⁇ m or more, the handleability is good, and if the thickness is 1000 ⁇ m or less, it can contribute to making the present pressure-sensitive adhesive sheet thinner. Therefore, the thickness of the present pressure-sensitive adhesive sheet is preferably 10 ⁇ m or more, more preferably 15 ⁇ m or more, even more preferably 20 ⁇ m or more, and even more preferably 25 ⁇ m or more.
• the upper limit is preferably 1000 ⁇ m or less, more preferably 500 ⁇ m or less, particularly preferably 250 ⁇ m or less, further preferably 100 ⁇ m or less, and particularly preferably 75 ⁇ m or less.
• the present pressure-sensitive adhesive sheet is suitable for use in bonding components of an image display device.
• the pressure-sensitive adhesive sheet is suitable for use in bonding components constituting a display member (also referred to as "display member"), particularly components of a flexible image display device used in producing a display, and is used as a pressure-sensitive adhesive sheet for components of a flexible image display device.
• a display member also referred to as "display member”
• the same components as those described later can be used for the flexible image display device.
• a laminate for an image display device (hereinafter, sometimes referred to as "the laminate for the image display device") is a laminate for an image display device having a configuration in which two components of the image display device are laminated via the present pressure-sensitive adhesive sheet.
• the laminate for the image display device is preferably a laminate for a flexible image display device (hereinafter, sometimes referred to as "the laminate for the flexible image display device") having a configuration in which two components of a flexible image display device are laminated via the present pressure-sensitive adhesive sheet.
• the adhesive sheet is as described above, and the components other than the adhesive sheet are described below.
• Examples of the image display device components constituting the present laminate for image display devices include flexible image display device components.
• Examples of the flexible image display device components include flexible displays such as organic electroluminescence (EL) displays, cover lenses (cover films), polarizing plates, polarizers, retardation films, barrier films, viewing angle compensation films, brightness improvement films, contrast improvement films, diffusion films, semi-transmissive reflective films, electrode films, transparent conductive films, metal mesh films, and touch sensor films. Any one of these or two of them may be used in combination. For example, a combination of a flexible display and other flexible image display device components, or a combination of a cover lens and other flexible image display device components may be used.
• flexible image display device components refer to bendable components, particularly components that can be repeatedly bent.
• the main components of the flexible image display device components include a resin sheet, glass, or the like.
• the material of such a resin sheet include polyester resin, cycloolefin resin, triacetyl cellulose resin, polymethyl methacrylate resin, polyurethane, epoxy resin, polyimide resin, and aramid resin, which may be one type of resin or two or more types of resin.
• a resin sheet containing at least one type of resin selected from the group consisting of polyester resin, cycloolefin resin, triacetyl cellulose resin, polymethyl methacrylate resin, epoxy resin, polyimide resin, aramid resin, and polyurethane resin as a main component is preferable.
• the term "main component” refers to a component that occupies the largest weight ratio among the components that make up the flexible image display device component, and specifically, it is a component that occupies 50 mass % or more of the resin composition (resin sheet) that forms the flexible image display device component, and preferably 55 mass % or more, and particularly preferably 60 mass % or more.
• the flexible image display device components may also be made of thin glass.
• one of the two flexible image display device components i.e., the first flexible image display device component
• ASTM D882 the 25° C. tensile strength
• the tensile strength at 25°C measured in accordance with ASTM D882 is preferably 10 to 900 MPa, more preferably 15 to 800 MPa, and even more preferably 20 to 700 MPa. If the 25° C. tensile strength (ASTM D882) of the other flexible image display device component is within the above range, it is preferable since it is less likely to crack even when bent.
• Examples of the flexible image display device constituent members having high tensile strength include polyimide films, polyester films, and aramid films, and the tensile strength of these films is generally 900 MPa or less.
• examples of flexible image display device components having a somewhat low tensile strength include triacetyl cellulose (TAC) film and cycloolefin polymer (COP) film, and the tensile strength of these films is usually 10 MPa or more. Even if the present laminate for flexible image display devices includes flexible image display device components made of such materials having a relatively low tensile strength, defects such as cracking can be suppressed by the action of the present pressure-sensitive adhesive sheet.
• the manufacturing method of the present laminate for an image display device is not particularly limited, and as described above, for example, the adhesive composition may be applied onto a component of an image display device, preferably onto a component of a flexible image display device, to form an adhesive sheet, or an adhesive sheet may be formed in advance and then laminated to a component of an image display device, preferably a component of a flexible image display device.
• a flexible image display device (hereinafter, sometimes referred to as "the flexible image display device") is an image display device incorporating a laminate for a flexible image display device having a configuration in which two flexible image display device constituent members are bonded together via the adhesive sheet of the present invention.
• the laminate for a flexible image display device having a configuration in which two flexible image display device constituent members are bonded together via the adhesive sheet of the present invention can be laminated onto another image display device constituent member to form the flexible image display device including the laminate.
• flexible image display device refers to an image display device that leaves no traces of folding even when repeatedly folded, can quickly restore to its original state when released from folding, and can display images without distortion even when folded. More specifically, examples of such image display devices include components capable of being curved and fixed into a curved shape with a radius of curvature of 25 mm or more, and in particular, components capable of withstanding repeated bending actions with a radius of curvature of less than 25 mm, and more preferably, less than 3 mm.
• This laminate can prevent delamination and cracking of the laminate even when folded in a high-temperature environment, and has good recovery properties, making it possible to manufacture flexible image display devices with excellent flexibility.
• a pressure-sensitive adhesive composition according to one embodiment of the present invention contains an acrylic copolymer and a radically polymerizable compound (x), wherein the weight-average molecular weight of the acrylic copolymer is 500,000 or more, the refractive index of the radically polymerizable compound (x) is less than 1.46, and the content of the radically polymerizable compound (x) is 20 to 95% of the total mass of the pressure-sensitive adhesive composition.
• the pressure-sensitive adhesive composition contains an acrylic copolymer and a radically polymerizable compound (x), wherein the weight-average molecular weight of the acrylic copolymer is 500,000 or more, the refractive index of the radically polymerizable compound (x) is less than 1.46, and the content of the radically polymerizable compound (x) is 20 to 95% of the total mass of the pressure-sensitive adhesive composition.
• acrylic copolymer examples include the same acrylic polymers as those described for the present pressure-sensitive adhesive sheet 1, and the types and contents of preferred monomers are also the same.
• the weight average molecular weight (Mw) of the acrylic copolymer is 500,000 or more, preferably 550,000 or more, and particularly preferably 600,000 or more, from the viewpoint of obtaining a pressure-sensitive adhesive composition with high cohesive strength.
• the upper limit of the weight average molecular weight (Mw) of the acrylic copolymer is preferably 1.5 million or less, more preferably 1.2 million or less, even more preferably 1.1 million or less, and particularly preferably 1 million or less, from the viewpoints of handleability and uniform stirrability.
• the glass transition temperature (Tg) of the acrylic copolymer is preferably -20°C or lower in order to suppress an increase in the shear storage modulus (G') at low temperatures, more preferably -23°C or lower, even more preferably -25°C or lower, particularly preferably -30°C or lower, and especially preferably -40°C. Due to concerns about glue overflow due to a decrease in the shear storage modulus at high temperatures, the lower limit of the glass transition temperature (Tg) is usually -70°C, and preferably -50°C.
• the content of the acrylic copolymer is usually 10 to 75% of the total mass of the adhesive composition, preferably 12 to 73%, more preferably 20 to 71%, and particularly preferably 30 to 69%.
• radical polymerizable compound (x) examples include the same compounds as the radical polymerizable compound (x) described in the present pressure-sensitive adhesive sheet 1, and preferred compounds and physical properties thereof are the same as those of the radical polymerizable compound (x) described in the present pressure-sensitive adhesive sheet 1.
• the radically polymerizable compound (x) has a monomer refractive index of less than 1.46, preferably 1.45 or less, and particularly preferably 1.44 or less.
• the refractive index of an acrylic copolymer is about 1.47, and when a pressure-sensitive adhesive sheet is produced from a pressure-sensitive adhesive composition containing this acrylic copolymer, it is difficult to make the refractive index of the pressure-sensitive adhesive sheet 1.470 or less.
• the refractive index of the pressure-sensitive adhesive sheet made of this pressure-sensitive adhesive composition tends to be low.
• the content of the radically polymerizable compound (x) is 20 to 95% of the total mass of the adhesive composition, preferably 27 to 88%, more preferably 29 to 80%, and particularly preferably 31 to 70%.
• the content of the radically polymerizable compound (x) is preferably 25 to 1900 parts by mass, more preferably 35 to 740 parts by mass, even more preferably 40 to 400 parts by mass, and particularly preferably 45 to 240 parts by mass, relative to 100 parts by mass of the acrylic copolymer.
• the adhesive composition preferably contains a photopolymerization initiator as described above in the adhesive sheet 1, and may also contain a thermal crosslinking agent and other components as described above in the adhesive sheet 1.
• the types, amounts, etc. of the preferred photopolymerization initiator, thermal crosslinking agent, and other components are the same as those of the adhesive sheet 1.
• the adhesive composition is prepared by mixing a predetermined amount of each of the acrylic copolymer, the radical polymerizable compound (x), preferably a photopolymerization initiator, and, if necessary, a thermal crosslinking agent and other components.
• the above-mentioned raw materials may be kneaded using a temperature-controllable kneader (for example, a single-screw extruder, a twin-screw extruder, a planetary mixer, a twin-screw mixer, a pressure kneader, etc.).
• a temperature-controllable kneader for example, a single-screw extruder, a twin-screw extruder, a planetary mixer, a twin-screw mixer, a pressure kneader, etc.
• various additives such as silane coupling agents and antioxidants may be blended together with the resin in advance and then fed to the kneader, or all of the materials may be melt-mixed in advance and then fed, or a master batch in which only the additives are concentrated in the resin may be prepared and then fed.
• part refers to parts by mass.
• the glass transition temperature and weight average molecular weight were measured according to the methods described above.
• acrylic copolymers (1) to (7) were produced using the copolymerization component compositions shown in Table 1.
• the results of the monomer composition structural units derived from the final component
• weight average molecular weight weight average molecular weight
• glass transition temperature (Tg) glass transition temperature
• refractive index of the obtained acrylic copolymers (1) to (7) are shown in the following Table 1.
• the content of the structural portion derived from the final component of the acrylic copolymer (after polymerization) is approximately the same as the composition of the copolymerization component.
• radical polymerizable compound As the radical polymerizable compound, the following was prepared. Monofunctional urethane acrylate containing an oxypropylene structure (manufactured by AGC, refractive index: 1.450, weight average molecular weight: about 10,000, glass transition temperature: -62°C)
• Esacure TZT Esacure TZT (IGM, a mixture of 4-methylbenzophenone and 2,4,6-trimethylbenzophenone (hydrogen abstraction type))
• the pressure-sensitive adhesive composition solution was coated onto a release film (a silicone release-treated polyester film "MRV” manufactured by Mitsubishi Chemical Corporation, thickness 100 ⁇ m) as a heavy release film so that the thickness after drying would be 50 ⁇ m. After coating, the coating was placed in a dryer heated to a temperature of 90° C. and held for 7 minutes to volatilize and dry the solvent contained in the pressure-sensitive adhesive composition.
• a release film a silicone release-treated polyester film "MRV” manufactured by Mitsubishi Chemical Corporation, thickness 100 ⁇ m
• a release film (“MHE” manufactured by Mitsubishi Chemical Corporation, a silicone release-treated polyester film, thickness 50 ⁇ m) was laminated as a light release film on the surface of the adhesive composition from which the solvent had been dried to form a laminate, and the adhesive composition was irradiated with ultraviolet rays through the release film using a high-pressure mercury lamp (see Table 2 for each irradiation amount), to obtain an adhesive sheet laminate (adhesive sheet with release film).
• the obtained pressure-sensitive adhesive sheet laminate was subjected to the following evaluations, and the results are shown in Tables 2 and 3 below.
• the release film was removed from each of the pressure-sensitive adhesive sheet laminates produced in the Examples and Comparative Examples, and the refractive index was determined using an Abbe refractometer (DR-A1-Plus) manufactured by Atago Co., Ltd. The refractive index was measured at 23° C. using sodium D line (589.3 nm).
• each adhesive strength measurement sample was peeled off at an angle of 180° to the glass at a peeling speed of 300 mm/min, and the tensile strength was measured with a load cell to measure the 180° peel strength (N/10 mm) of the adhesive sheet against the glass, which was taken as the adhesive strength (23°C).
• a double-sided adhesive tape ("No. 5000NS" manufactured by Nitto Denko Corporation) was roll-attached to the glass plate using a hand roller to obtain glass with adhesive tape.
• the pressure-sensitive adhesive sheet laminates of Example 3 and Reference Examples 1 to 3 were cut into strips of 50 mm width x 150 mm length.
• the heavy release film side of the cut pressure-sensitive adhesive sheet laminate was roll-bonded to the adhesive tape surface of the adhesive tape-attached glass using a hand roller to produce a laminate (sample for peel force measurement) consisting of glass/adhesive tape/heavy release film/adhesive sheet/light release film.
• the light release film of each peel strength measurement sample was peeled off at an angle of 180° to the adhesive sheet at a peel speed of 300 mm/min in an environment of 23°C, and the tensile strength was measured with a load cell to measure the 180° peel strength (N/cm) of the light release film against the adhesive sheet, which was taken as the peel strength of the release film.
• the pressure-sensitive adhesive sheets of Examples 1 to 10 had a low refractive index of 1.470 or less, and also had a shear storage modulus ratio between the shear storage modulus at -30°C and the shear storage modulus at 80°C within a specific range, and therefore had a low shear storage modulus at -30 to 80°C, excellent recovery rates at 25°C and -20°C, and excellent flexibility.
• the pressure-sensitive adhesive sheets of Comparative Examples 1 and 2 had a high refractive index exceeding 1.470, and also had a shear storage modulus ratio between the shear storage modulus at -30°C and the shear storage modulus at 80°C outside the specific range, so the recovery rate at -20°C was low and the recovery when folded was poor.
• the pressure-sensitive adhesive sheet of Comparative Example 2 had a high refractive index exceeding 1.470, and also had a high storage modulus at -30°C, and was poor in flexibility.
• Example 3 Furthermore, in the pressure-sensitive adhesive sheets with release film of Example 3 and Reference Examples 1 to 3, the peeling force of the release film was small, and the releasability from the pressure-sensitive adhesive sheet was good.
• Example 3 Reference Example 1 and Reference Example 2 used release films that had little migration of the release agent to the pressure-sensitive adhesive sheet, and were excellent in reliability in the bending test.
• the pressure-sensitive adhesive sheet with release film of Reference Example 3 had a high Si atom peak intensity in the fluorescent X-ray analysis of the pressure-sensitive adhesive sheet surface, suggesting that a large amount of the release agent component derived from the release film had migrated to the pressure-sensitive adhesive sheet surface. As a result, peeling occurred at the interface between the first member and the pressure-sensitive adhesive sheet in the reliability test, resulting in a decrease in reliability.
• the adhesive sheet of the present invention has a low refractive index and is flexible, making it useful as an adhesive sheet for obtaining various flexible image display devices, such as bendable, foldable, rollable, and stretchable devices, and is particularly suitable as an adhesive sheet for foldable image display devices that are repeatedly folded.

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