Sheet-like sealing material, layered product, and display device

Abstract

The present invention addresses the problem of providing a layered product able to form a member in which cracking and hollowing are unlikely to occur even if a localized load is applied from the outside, and in which peeling is unlikely to occur at an interface between a thin glass film and a sheet-like sealing material. This layered product for solving the foregoing problem has a thin glass film and a sheet-like sealing material disposed on the thin glass film. The sheet-like sealing material contains: (A) an alicyclic epoxy compound represented by a specific formula; and (B) an aromatic ring-containing epoxy resin having at least one aromatic ring in the molecule. The sheet-like sealing material has a storage elastic modulus at 25°C of 0.31-3.1 GPa, as determined by dynamic viscoelasticity measurements carried out at a frequency of 1 Hz at a temperature increase rate 5°C / min after heating for an hour at 100ºC.

Description

Sheet-like sealing material, laminate, and display device

[0001] The present invention relates to a sheet-like sealing material, a laminate, and a laminate including the laminate.

[0002] Display devices in which various display elements (e.g., LED elements, liquid crystal display elements, etc.) and a touch panel are stacked are widely used (see, for example, Patent Document 1). Such display devices are operated by a user touching a cover film (also called a cover window) arranged on the display surface side with a finger, a touch pen, or the like. In recent years, display devices with foldable display surfaces have also been developed. For foldable display devices, the use of a member stacked with a thin film glass and an adhesive layer as a part of the cover film has been considered.

[0003] On the other hand, flexibility is also being demanded in display devices that do not have touch panels (for example, display devices that use organic EL elements), and the use of a member that is a laminate of thin film glass and an adhesive layer, etc., as a cover film that covers the surface of a display element is being considered.

[0004] Furthermore, a cover member for protecting the touch panel device and the display device is usually disposed on the display surface side of the display device. The cover member generally has a structure in which a base film, a sheet-like sealing material (adhesive layer), and a protective film are laminated. In recent years, display devices with foldable display surfaces have been developed, and there is a demand for a cover member that can be repeatedly folded and unfolded.

[0005] JP 2013-20529 A

[0006] For example, in a display device with a built-in touch panel, it has been considered to provide a cover film with a laminated structure consisting of a resin film (e.g., polyethylene terephthalate (PET) or transparent polyimide (CPI) / interlayer adhesive layer / planar sealing material / thin film glass / first adhesive layer / transparent film layer (PET or polyimide (PI) / second adhesive layer). However, when a local load is applied to the cover film by a finger, a touch pen, or the like, the thin film glass may crack, peeling may occur between the thin film glass and the planar sealing material, or dents may occur on the surface due to deformation of the planar sealing material or the interlayer adhesive layer.

[0007] Furthermore, even in display devices that do not have a touch panel, local loads may be applied to the cover film during transport or use. In such cases, if a member in which thin film glass and a planar sealing material are laminated is used as the cover film, the thin film glass may crack, the planar sealing material may be dented and leave marks, or peeling may occur at the interface between the thin film glass and the planar sealing material.

[0008] The first embodiment of the present invention has been made in view of the above-mentioned problems, and specifically aims to provide a laminate including a thin film glass and a sheet-like sealing material, which can form a member that is resistant to cracking or denting even when subjected to a localized external load, and that is resistant to peeling at the interface between the thin film glass and the cured product of the sheet-like sealing material.

[0009] Furthermore, the cover members of conventional display devices have low bending resistance, and when bent, the base film or protective film may crack, or peeling may occur at the interface between the sheet-shaped sealing material and the base film, or between the sheet-shaped sealing material and the protective film.

[0010] The second embodiment of the present invention aims to provide a laminate having two films and a sheet-like sealing material sandwiched between the two films, which has high bending resistance and is less likely to peel at the interface between the layers.

[0011] The third embodiment of the present invention aims to provide a laminate having a pair of films and a sealing material sandwiched between the pair of films, which has high bending resistance and is less likely to peel at the interface between the films and the sealing material, and a display device using the same.

[0012] Furthermore, the inventors' investigations revealed that with conventional cover films, whitening of the planar sealing material is likely to occur when a local load is applied by a finger, a touch pen, etc., or when the cover film is bent.

[0013] The fourth embodiment of the present invention has been made in view of the above-mentioned problems. Specifically, an object of the present invention is to provide a sheet-like sealing material that has excellent adhesion to various members and, when used as a surface sealing material, is resistant to whitening even when subjected to an external load, and a laminate using the same.

[0014] An object of the present invention is to provide a display device using these.

[0015] A first embodiment of the present invention provides the following sheet-like sealing material and laminate: [1] A sheet-like sealing material comprising an alicyclic epoxy compound containing two or more epoxy groups and two or more cyclic structures in the molecule, and an aromatic ring-containing epoxy resin having one or more aromatic rings in the molecule. [2] The sheet-like sealing material according to [1], wherein the alicyclic epoxy compound is a compound represented by the following formula: [3] The sheet-like sealing material according to [1] or [2], which has a storage modulus at 25°C of 0.31 GPa or more and 3.1 GPa or less, as measured by dynamic viscoelasticity measurement at a temperature rise rate of 5°C / min and a frequency of 1 Hz after heating at 100°C for 1 hour. [4] The sheet-like sealing material according to any one of [1] to [3], which has a thickness of 3 µm or more. [5] The sheet-like sealing material according to any one of [1] to [4], which has a thickness of 7 µm or more. [6] A sealing sheet comprising a thin film glass and a sealing sheet disposed on the thin film glass, wherein the sealing sheet comprises (A) an alicyclic epoxy compound represented by the following formula: (B) an aromatic ring-containing epoxy resin having one or more aromatic rings in the molecule, wherein the storage modulus at 25°C of the sheet-like sealing material, as determined by dynamic viscoelasticity measurement at a temperature rise rate of 5°C / min and a frequency of 1 Hz after heating at 100°C for 1 hour, is 0.31 GPa or more and 3.1 GPa or less. [7] The laminate according to [6], which is used in a touch panel type display device.

[0016] A second embodiment of the present invention provides the following laminate. [8] A laminate comprising a first film, a sheet-like sealing material disposed on the first film, and a second film disposed on the sheet-like sealing material, wherein a test piece of the sheet-like sealing material having a length of 50 mm, a width of 10 mm, and a thickness of 20 μm is prepared and a tensile test is conducted in accordance with JIS K7127:1999 at a tensile speed of 300 mm / min, and the gradient of the initial linear portion of the load-strain curve is 2.5 N / % or more and 4.0 N / % or less. [9] The laminate according to [8], wherein the sheet-like sealing material is a cured product of a resin composition containing an alicyclic epoxy compound represented by the following formula:

[10] The laminate according to [8] or [9], wherein the first film and / or the second film contains at least one material selected from the group consisting of glass, alicyclic polyimide, polyethylene terephthalate, and polyethylene.

[11] The laminate according to any one of [8] to

[10] , wherein the film thickness of the sheet-like sealing material is 5 μm or more and 150 μm or less.

[0017] A third embodiment of the present invention provides the following laminate and display device.

[12] A laminate comprising a pair of films, a first sealant and a second sealant having a higher elastic modulus than the first sealant, disposed between the pair of films, wherein a test piece of the first sealant having a length of 50 mm, a width of 10 mm, and a thickness of 20 μm is prepared and a tensile test is conducted in accordance with JIS K7127:1999 at 25°C and a tensile speed of 300 mm / min, and the slope of the initial linear portion of the load-strain curve is 0.4 N / % or more and 2.0 N / % or less.

[13] The laminate according to

[12] , wherein the first sealant is a cured product of a resin composition containing an alicyclic epoxy compound represented by the following formula:

[14] The laminate according to

[12] or

[13] , wherein the second sealant has a tensile modulus of 2 GPa or more and 4 GPa or less at 25°C, as measured in accordance with JIS K7127:1999.

[15] The laminate according to any one of

[12] to

[14] , wherein at least one of the pair of films contains at least one material selected from the group consisting of glass, alicyclic polyimide, polyethylene terephthalate, and polyethylene.

[16] The laminate according to any one of

[12] to

[15] , wherein the first sealant has a film thickness of 5 μm or more and 50 μm or less, and the second sealant has a film thickness of 5 μm or more and 50 μm or less.

[17] A display device comprising a display element and the laminate according to any one of

[12] to

[16] , disposed on the display element, wherein the laminate is disposed so that the second sealant is closer to the display element than the first sealant.

[0018] A fourth embodiment of the present invention provides the following sheet-like sealing material and laminate.

[18] A sheet-like sealing material comprising an epoxy compound and a tackifier, wherein, when the surface of the sheet-like sealing material is observed with a scanning electron microscope, the number of islands in a sea-island structure contained in an area of ​​200 μm × 200 μm is 10 or less.

[19] The sheet-like sealing material according to

[18] , wherein the epoxy compound comprises an alicyclic epoxy compound represented by the following formula:

[20] The sheet-like sealing material according to

[18] or

[19] , wherein the tackifier contains a terpene resin and a phenolic resin, and the amount of the terpene resin is less than 50 mass% based on the total amount of the terpene resin and the phenolic resin.

[21] A laminate comprising a substrate and the sheet-like sealing material according to any one of

[18] to

[20] or a cured product thereof, disposed on the substrate.

[22] The laminate according to

[21] , which is used in a touch panel type display device.

[0019] The present invention further provides the following display device:

[23] A display device comprising the laminate according to any one of [6], [8],

[12] , and

[21] above.

[24] The display device according to

[23] , which has a radius of curvature of 0.5 to 5 mm when bent.

[0020] According to the laminate of the first embodiment of the present invention, a component is obtained that is less likely to crack or dent even when subjected to a localized external load, and is also less likely to peel at the interface between the thin film glass and the cured product of the sheet-like sealing agent.

[0021] According to the second embodiment of the present invention, a laminate is provided which has high bending resistance and is less susceptible to peeling at the interfaces between layers.

[0022] According to a third embodiment of the present invention, there is provided a laminate having a pair of films and a sealing material sandwiched between the pair of films, which has high bending resistance and is less susceptible to peeling at the interface between the films and the sealing material, and a display device using the same.

[0023] According to the fourth embodiment of the present invention, there is provided a sheet-like sealing material that has excellent adhesiveness to various members and is resistant to whitening even when subjected to a localized external load or the like.

[0024] FIG. 1A is a photograph of a typical sheet-shaped sealant observed with a scanning electron microscope, and FIG. 1B is a photograph of a sheet-shaped sealant according to the fourth embodiment observed with a scanning electron microscope.

[0025] 1. First Embodiment A laminate according to a first embodiment of the present invention includes at least a thin film glass and a sheet-like sealing material. The sheet-like sealing material in the laminate is hardened by heating to form a surface sealing material that fills the gap between the thin film glass and other structures. The laminate is suitable for use, for example, in manufacturing display devices, and is particularly useful as a material for cover films. Hereinafter, an example will be described in which the laminate is used to manufacture a cover film for a display device. However, the uses of the laminate according to this embodiment are not limited to these, and it may also be used for purposes other than display devices or in locations other than the cover film of a display device.

[0026] Here, the laminate of this embodiment includes thin film glass and a sheet-like sealing material, and the sheet-like sealing material contains (A) an alicyclic epoxy compound with a specific structure and (B) an aromatic ring-containing epoxy resin. Furthermore, the storage modulus at 25°C, as obtained by dynamic viscoelasticity measurement at a temperature rise rate of 5°C / min and a frequency of 1 Hz after heating the sheet-like sealing material at 100°C for 1 hour, is 0.31 GPa or more and 3.1 GPa or less. The inventors have diligently studied and found that when the storage modulus of the sheet-like sealing material is within the above range, the cured product of the sheet-like sealing material (hereinafter also referred to as "plane sealing material") easily absorbs external stress and has excellent restoring force. Furthermore, it has also been found that when the sheet-like sealing material contains (A) an alicyclic epoxy compound with a specific structure and (B) an aromatic ring-containing epoxy resin, the adhesion between the thin film glass and the plane sealing material is very good, and the plane sealing material easily follows the deformation of the thin film glass.

[0027] As a result, in a component having a thin film glass and a planar sealing material obtained from the laminate of this embodiment, even when subjected to a local load from the outside, the thin film glass is less likely to break and the planar sealing material is less likely to be dented. Furthermore, peeling at the interface between the thin film glass and the planar sealing material is less likely to occur. The laminate of this embodiment will be described in detail below.

[0028] (1) Thin Film Glass In this specification, "thin film" refers to a film having a thickness of 150 μm or less, and "thin film glass" refers to a film having a thickness of 100 μm or less and made of glass. The thin film glass is a film generally referred to as UTG (Ultra Thin Glass). The size of the thin film glass is not particularly limited and is selected appropriately depending on the application of the laminate.

[0029] The thickness of the thin film glass is preferably 10 μm or more and 150 μm or less, more preferably 30 μm or more and 100 μm or less. Furthermore, the thin film glass preferably has bending resistance, and the minimum bending radius is preferably 10 mm or less, more preferably 5 mm or less. When the thin film glass has such a minimum bending radius, the laminate can be used in applications requiring flexibility, such as a cover film for a bendable display device.

[0030] The thin film glass may be a commercially available product, examples of which include G-Leaf (manufactured by Nippon Electric Glass Co., Ltd.), Dinorex UTG (manufactured by Nippon Electric Glass Co., Ltd.), and SCHOTT UTG (manufactured by SCHOTT).

[0031] (2) Sheet-like sealing material The sheet-like sealing material may be a layer disposed on the thin film glass and containing (A) an alicyclic epoxy compound having a specific structure and (B) a specific aromatic ring-containing epoxy resin. Preferably, the layer has a storage modulus at 25°C of 0.31 GPa or more and 3.1 GPa or less, as determined by dynamic viscoelasticity measurement at a temperature rise rate of 5°C / min and a frequency of 1 Hz after heating at 100°C for 1 hour.

[0032] The sheet-like sealing material may be disposed on one or both surfaces of the thin film glass. Furthermore, when the laminate is viewed from above, the sheet-like sealing material may be disposed so as to cover the entire one surface of the thin film glass, or may be disposed only in a partial region.

[0033] The thickness of the sheet-like sealing material is appropriately selected depending on the application of the laminate, but is preferably 3 μm to 100 μm, more preferably 7 μm to 40 μm. When the thickness of the sheet-like sealing material is 3 μm or more, the planar sealing material obtained from it is more likely to absorb or alleviate stress applied to the thin-film glass and the components including the planar sealing material, making it easier to suppress cracking of the thin-film glass and dents in the components. It also makes it easier to suppress peeling at the interface between the thin-film glass and the planar sealing material. On the other hand, when the thickness is 100 μm or less, it becomes easier to reduce the thickness and weight of the display device.

[0034] The sheet-shaped sealing material may also contain components other than (A) the alicyclic epoxy compound having a specific structure and (B) the specific aromatic ring-containing epoxy resin, and typically contains (D) a thermal cationic polymerization initiator. If necessary, it may further contain (C) other epoxy resins, (E) a tackifier, (F) various additives, etc. Each component and the physical properties of the sheet-shaped sealing material are described in detail below.

[0035] (A) Alicyclic Epoxy Compound (A) Alicyclic epoxy compound is a compound represented by the following formula:

[0036] The alicyclic epoxy compound (A) may be a synthetic product or a commercially available product. An example of a commercially available product is CEL2021P manufactured by Daicel Corporation. When the sheet-shaped sealing material contains the alicyclic epoxy compound, the alicyclic skeleton tends to improve the bending resistance and heat resistance of the cured product. Furthermore, since the alicyclic epoxy compound has a low viscosity when unreacted, handling during processing is also improved.

[0037] The amount of the alicyclic epoxy compound (A) relative to the total amount of the sheet-like sealing material is preferably 5% by mass to 40% by mass, more preferably 10% by mass to 30% by mass. When the amount of the alicyclic epoxy compound (A) is within this range, the storage modulus (described below) is more likely to fall within a desired range, and the peel strength between the sheet-like sealing material and thin-film glass is also likely to be increased.

[0038] (B) Aromatic Ring-Containing Epoxy Resin The aromatic ring-containing epoxy resin (B) is a resin having at least one epoxy group and at least one aromatic ring in the molecule. The sheet-like sealing material may contain only one type of aromatic ring-containing epoxy resin (B), or may contain two or more types.

[0039] The type of (B) aromatic ring-containing epoxy resin is not particularly limited, but it is preferable to include a resin that is solid at room temperature (23°C) and has a weight-average molecular weight of 3,000 to 100,000. The weight-average molecular weight of the aromatic ring-containing epoxy resin is preferably 6,000 to 60,000, more preferably 7,000 to 40,000. When the molecular weight of the (B) aromatic ring-containing epoxy resin is 3,000 or more, the (B) aromatic ring-containing epoxy resin tends to solidify at room temperature. On the other hand, when the (B) aromatic ring-containing epoxy resin has a weight-average molecular weight of 1,000,000 or less, the fluidity of the sheet-like sealing material can be increased when the laminate is bonded to various structures via the sheet-like sealing material, making it easier to adhere to various structures. The weight-average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0040] Furthermore, the epoxy equivalent of the aromatic ring-containing epoxy resin (B) having the above weight-average molecular weight is preferably 900 g / eq or more and 20,000 g / eq or less, more preferably 1,000 g / eq or more and 200,000 g / eq or less. When the epoxy equivalent of the aromatic ring-containing epoxy resin is 900 g / eq or more, the tackiness of the sheet-shaped sealing material at room temperature is reduced. As a result, the sheet-shaped sealing material is more likely to be easily handled when bonded to various structures, making it easier to bond accurately to various structures. On the other hand, if the epoxy equivalent of the aromatic ring-containing epoxy resin (B) having the above weight-average molecular weight is excessively large, the solubility of the aromatic ring-containing epoxy resin (B) in solvents may decrease or its compatibility with the alicyclic epoxy compound (A) may deteriorate during the preparation of the sheet-shaped sealing material. Therefore, the epoxy equivalent of the aromatic ring-containing epoxy resin (B) is preferably 20,000 g / eq or less. When the epoxy equivalent of the aromatic ring-containing epoxy resin (B) is within the above range, the melting temperature of the sheet-like sealing material falls within an appropriate range, and it becomes possible to attach it to various structures at a desired temperature. When a plurality of epoxy resins are used as the aromatic ring-containing epoxy resin (B), it is preferable that the epoxy equivalent of each epoxy resin is within the above range.

[0041] On the other hand, the aromatic ring-containing epoxy resin may be a resin having a weight average molecular weight of 3,000 or less. In either case, the aromatic ring-containing epoxy resin (B) may contain one or more epoxy groups in the molecule, but preferably contains a plurality of epoxy groups so as to satisfy the above-mentioned epoxy equivalent. Furthermore, the aromatic ring-containing epoxy resin (B) may contain one or more aromatic rings in the molecule, and the number of aromatic rings is not particularly limited.

[0042] Examples of (B) aromatic ring-containing epoxy resins include bisphenol-type epoxy resins such as bisphenol A type, bisphenol F type, bisphenol E type, bisphenol S type, bisphenol AD ​​type, and mixtures thereof; diphenyl ether-type epoxy resins; novolac-type epoxy resins such as phenol novolac type, cresol novolac type, biphenyl novolac type, bisphenol novolac type, naphthol novolac type, trisphenol novolac type, and dicyclopentadiene novolac type; biphenyl-type epoxy resins; naphthyl-type epoxy resins; and triphenolalkane-type epoxy resins such as triphenolmethane type, triphenolethane type, and triphenolpropane type.

[0043] Among the above, the aromatic ring-containing epoxy resin (B) is preferably a bisphenol-type epoxy resin or a biphenyl-type epoxy resin. Note that, as the amount of bisphenol F skeleton in the aromatic ring-containing epoxy resin (B) increases, the softening point of the aromatic ring-containing epoxy resin (B) tends to decrease. Therefore, when the melting temperature of the sheet-like sealing material is set to a relatively high temperature, it is preferable to use an epoxy resin with a small amount of bisphenol F skeleton.

[0044] The total amount of the aromatic ring-containing epoxy resin (B) relative to the total amount of the sheet-like sealing material is preferably 5% by mass or more and 60% by mass or less, more preferably 10% by mass or more and 50% by mass or less, and even more preferably 20% by mass or more and 40% by mass or less. When the amount of the aromatic ring-containing epoxy resin (B) in the sheet-like sealing material is within this range, the shape stability of the sheet-like sealing material is improved, and the lamination temperature is likely to be appropriate. In addition, the storage stability of the laminate is likely to be improved.

[0045] (C) Other Epoxy Resins As described above, the sheet-like sealing material may further contain an epoxy resin (hereinafter also referred to as "other epoxy resin") that does not correspond to the above (A) alicyclic epoxy compound and (B) aromatic ring-containing epoxy resin. The sheet-like sealing material may contain only one type of (C) other epoxy resin, or may contain two or more types.

[0046] Examples of (C) other epoxy resins include alicyclic epoxy resins other than the above (A) alicyclic epoxy resins, and aliphatic epoxy resins.

[0047] The other epoxy resin (C) may be a resin having only one epoxy group in the molecule, or may be a resin having two or more epoxy groups. The type of the other epoxy resin (C) is preferably selected appropriately in accordance with the storage modulus described below.

[0048] The total amount of the (C) other epoxy resins relative to the total amount of the sheet-like sealing material is preferably 10% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 40% by mass or less. When the amount of the (C) other epoxy resins in the sheet-like sealing material is within this range, the amounts of the above-mentioned (A) alicyclic epoxy compound and (B) aromatic ring-containing epoxy resin tend to be sufficiently large. Furthermore, when the amount of the (C) other epoxy resins is within this range, the storage modulus of the sheet-like sealing material tends to fall more easily within the desired range.

[0049] (D) Thermal Cationic Polymerization Initiator The (D) thermal cationic polymerization initiator may be any compound that generates an active species capable of initiating cationic polymerization upon heating and is capable of polymerizing the above-mentioned (A) alicyclic epoxy compound, (B) aromatic ring-containing epoxy resin, or (C) other epoxy resin.

[0050] Examples of the thermal cationic polymerization initiator (D) include sulfonium salts, phosphonium salts, quaternary ammonium salts, diazonium salts, and iodonium salts, among which quaternary ammonium salts and sulfonium salts are preferred. The anion moiety of these is AsF ６ － , SbF ６ － , P.F.６ － , B(C ６ F ５ ) ４ － The sheet-shaped sealing material may contain only one type of thermal cationic polymerization initiator, or may contain two or more types.

[0051] The total amount of the (D) thermal cationic polymerization initiator relative to the total amount of the sheet-like sealing material is preferably 0.5% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 5% by mass or less. When the amount of the (D) thermal cationic polymerization initiator is 1% by mass or more, the curability of the sheet-like sealing material is further improved. On the other hand, when the amount of the (D) thermal cationic polymerization initiator is 5% by mass or less, the storage stability of the sheet-like sealing material, and therefore the laminate, is further improved.

[0052] (E) Tackifier The sheet-like sealing material may further contain a tackifier (E). When the sheet-like sealing material contains a tackifier (E), the storage modulus of the sheet-like sealing material is easily adjusted, and the storage modulus is more likely to fall within a desired range. Such a tackifier (E) is preferably a resin selected from the group consisting of petroleum resins (aliphatic hydrocarbon resins, alicyclic hydrocarbon resins, and / or aromatic hydrocarbon resins), terpene resins, phenolic resins, and rosin resins. The sheet-like sealing material may contain only one type of tackifier (E), or may contain two or more types.

[0053] Examples of petroleum resins include C5 monomers or oligomers thereof obtained from pentene, pentadiene, isoprene, etc.; C9 monomers or oligomers thereof obtained from indene, methylindene, vinyltoluene, styrene, α-methylstyrene, β-methylstyrene, etc.; copolymers of C5 and C9 monomers (C5-C9 copolymer resins); alicyclic monomers or polymers thereof obtained from cyclopentadiene, dicyclopentadiene, etc.; aromatic monomers such as isopropenyl toluene or polymers thereof; hydrogenated products of the above-mentioned various monomers or polymers thereof; and modified petroleum resins obtained by modifying the above-mentioned various monomers or polymers thereof with maleic anhydride, maleic acid, fumaric acid, (meth)acrylic acid, phenol, etc.

[0054] Examples of terpene resins include α-pinene resin, β-pinene resin, α-pinene monomer, aromatic-modified terpene resin obtained by copolymerizing terpenes such as β-pinene monomer with aromatic monomers such as styrene and phenol.

[0055] Examples of phenolic resins include condensates of phenols and formaldehyde. Examples of phenols include phenol, m-cresol, 3,5-xylenol, p-alkylphenol, resorcinol, etc. Examples of the phenolic resins include resols obtained by addition reaction of these phenols with formaldehyde using an alkali catalyst, and novolacs obtained by condensation reaction using an acid catalyst. Phenolic resins also include rosin phenolic resins obtained by adding phenol to rosin using an acid catalyst and thermally polymerizing the resulting mixture.

[0056] Examples of rosin resins include gum rosin, wood rosin, or tall oil rosin; stabilized rosins or polymerized rosins obtained by disproportionating or hydrogenating these rosins; modified rosins obtained by modifying these rosins with maleic anhydride, maleic acid, fumaric acid, (meth)acrylic acid, phenol, or the like; and esters thereof. The alcohol used to obtain the esters is preferably a polyhydric alcohol. Examples of polyhydric alcohols include dihydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, and neopentyl glycol; trihydric alcohols such as glycerin, trimethylolethane, and trimethylolpropane; tetrahydric alcohols such as pentaerythritol and diglycerin; and hexahydric alcohols such as dipentaerythritol. These may be used alone or in combination during esterification.

[0057] The total amount of the tackifier (E) relative to the total amount of the sheet-like sealing material is preferably 1% by mass or more and 40% by mass or less, more preferably 5% by mass or more and 30% by mass or less. When the amount of the tackifier (E) is 5% by mass or more, the storage modulus of the sheet-like sealing material can be easily adjusted to a desired range. On the other hand, when the amount of the tackifier (E) is 30% by mass or less, the amounts of the above-mentioned (A) alicyclic epoxy compound and (B) aromatic ring-containing epoxy resin tend to be sufficiently large. Furthermore, when the amount of the tackifier (E) is 5% by mass or more, the storage modulus of the sheet-like sealing material can be easily adjusted to a desired range by the tackifier (E).

[0058] (F) Other Components Examples of other components include the above-mentioned (A) alicyclic epoxy compound, (B) aromatic ring-containing epoxy resin, and (C) other resins other than epoxy resins, as well as fillers, modifiers, stabilizers, etc.

[0059] Examples of other resins include polyamide, polyamideimide, polyurethane, polybutadiene, polychloroprene, polyether, polyester, styrene-butadiene-styrene block copolymer, xylene resin, ketone resin, cellulose resin, fluorine-based oligomer, silicon-based oligomer, polysulfide-based oligomer, etc. The sheet-like sealing material may contain only one of these, or may contain two or more of them.

[0060] Examples of the filler include glass beads, styrene-based polymer particles, methacrylate-based polymer particles, ethylene-based polymer particles, propylene-based polymer particles, etc. The sheet-shaped sealing material may contain only one type of filler, or may contain two or more types of filler.

[0061] Specific examples of the modifier include a polymerization initiator, an antioxidant, a leveling agent, a wettability improver, a surfactant, a plasticizer, a solvent, a silane coupling agent, etc. The sheet-like sealing material may contain only one type of these modifiers, or may contain two or more types.

[0062] On the other hand, specific examples of stabilizers include ultraviolet absorbers, preservatives, antibacterial agents, etc. The sheet-like sealing material may contain only one of these, or may contain two or more of them.

[0063] (G) Physical Properties of Sheet-Like Sealing Material The storage modulus at 25°C, as determined by dynamic viscoelasticity measurement at a temperature rise rate of 5°C / min and a frequency of 1 Hz after heating the sheet-like sealing material at 100°C for 1 hour, is 0.31 GPa to 3.1 GPa, preferably 0.34 GPa to 1.8 GPa. When the storage modulus of the sheet-like sealing material is within this range, even when a local load is applied to the cured product of the laminate, the thin film glass is less likely to crack, and dents and peeling of the planar sealing material are also less likely to occur, as specifically shown in the examples described below. The storage modulus can be adjusted by the ratio of the above-mentioned (A) alicyclic epoxy compound and (B) aromatic-containing epoxy resin, or by the amount of other compounds (e.g., (E) tackifier), etc.

[0064] Furthermore, the melting temperature of the sheet-like sealing material is preferably 35°C or higher and 60°C or lower. However, this temperature is preferably adjusted appropriately depending on the lamination method of the laminate and the object to be laminated. For example, when lower tackiness during lamination is required, the melting temperature is preferably 40 to 56°C. When laminating the laminate (sheet-like sealing material) to various structures, softening (melting) the sheet-like sealing material reduces the occurrence of gaps with the various structures, enabling closer adhesion. When the melting temperature of the sheet-like sealing material is 60°C or lower, the laminate (sheet-like sealing material) can be laminated to various structures at a relatively low temperature (60°C or lower). On the other hand, when the melting temperature of the sheet-like sealing material is 35°C or higher, the tackiness of the sheet-like sealing material during operation (tackiness at room temperature) is low, and workability is likely to be improved. Furthermore, during storage, the sheet-like sealing material is less likely to deform and can maintain its shape.

[0065] The melting temperature can be measured as follows. A strip-shaped test piece is prepared by cutting a sheet-like sealing material into a length of approximately 30 mm and a width of approximately 5 mm. This test piece is then adhered to a glass plate heated on a hot plate. The test piece is then gradually peeled off from the glass plate in a 180° direction. This operation is started with the hot plate set at 40°C, and is repeated by preparing a new strip-shaped test piece every time the set temperature is increased by 1°C. The temperature at which the adhesive peelability of the layer made of the sheet-like sealing material is greatest upon peeling is taken as the melting temperature. However, if the adhesive peelability is already high at 40°C, the melting temperature is measured from 25°C.

[0066] Furthermore, the melting temperature of the sheet-shaped sealing material after storage at 40°C for 17 hours preferably falls within a range of ±10°C of the melting temperature of the sheet-shaped sealing material before storage, and more preferably within ±5°C. This temperature change serves as an indicator of the storage stability of the sheet-shaped sealing material, and if the temperature change is 10°C or less, it can be said that a curing reaction or the like is unlikely to occur during storage. Furthermore, if the melting temperature of the sheet-shaped sealing material changes significantly during storage, it becomes necessary to change the temperature, pressure, etc. when laminating the sheet-shaped sealing material in accordance with this fluctuation. In contrast, if the melting temperature change after storage at 40°C for 17 hours is within 10°C, there is an advantage that there is no need to significantly change the lamination conditions, and the laminate can be efficiently laminated.

[0067] On the other hand, the heat generation initiation temperature of the sheet-like sealing material measured by a differential scanning calorimeter (DSC) is preferably 60°C or higher and 90°C or lower, and more preferably 65 to 85°C. When the heat generation initiation temperature is 60°C or higher, the (A) alicyclic epoxy compound and (B) aromatic ring-containing epoxy resin are less likely to harden during the production of the laminate or during storage of the laminate, resulting in good storage stability. On the other hand, when the heat generation initiation temperature is 90°C or lower, the sheet-like sheet material can be cured at 90°C or lower, which is less likely to affect the laminated object. The heat generation initiation temperature can be measured by the following method. First, 10 mg of the sheet-like sealing material is sampled and placed in an aluminum cell for DSC measurement to prepare a measurement test sample. Then, the temperature characteristics of the measurement test sample are measured at a temperature rise rate of 5°C / min and a measurement temperature range of 20°C to 300°C, thereby determining the heat generation initiation temperature.

[0068] On the other hand, when the sheet-shaped sealing material is heated at 85°C for 50 minutes, the epoxy reaction rate is preferably 80% or more, and more preferably 85% or more. The epoxy reaction rate is an index of the curability when the sheet-shaped sealing material is cured at 85°C, and the higher the value, the easier the sheet-shaped sealing material is to cure even at low temperatures. If the epoxy reaction rate is 80% or more, it can be said that the sheet-shaped sealing material can be sufficiently cured even at 90°C or less.

[0069] The epoxy reaction rate can be measured as follows. First, a sheet-shaped sealing material (sample) is placed in an oven previously set to 85°C. Then, 50 minutes after the sample is placed in, the measurement sample is removed. The calorific value of the cured product is determined by DSC at a temperature rise rate of 5°C / min and a measurement temperature range of 20°C to 300°C. Then, based on the measured calorific value and the calorific value in the uncured state described above, the epoxy reaction rate is calculated using the following formula: Epoxy reaction rate (%) = (calorific value of uncured product - calorific value after curing) / calorific value of uncured product x 100

[0070] Furthermore, when a 20 μm-thick sheet-like sealing material is cured for 50 minutes at 85° C., the transmittance of light with a wavelength of 550 nm is preferably 90% or more, more preferably 95% or more, and even more preferably 97% or more. When the light transmittance of the cured product of the sheet-like sealing material is 90% or more, the laminate can be used as a cover film for a display device, etc.

[0071] The light transmittance of the cured product of the sheet-like sealing material can be measured by the following procedure. A laminate consisting of a substrate film and a 20 μm-thick sheet-like sealing material formed on the substrate film is cut into a length of approximately 60 mm and a width of approximately 40 mm to obtain a test piece. The layer consisting of the sheet-like sealing material of this test piece is transferred and bonded to a glass plate (No. 3, manufactured by Matsunami Glass, 0.3 mm thick, 70 mm x 50 mm) heated on a hot plate heated to 70°C using a roll, taking care not to introduce air bubbles. The test piece is removed from the hot plate and allowed to cool for 3 minutes. Thereafter, the substrate film is peeled off, and the sheet-like sealing material on the glass plate is heated in an oven at 85°C for 50 minutes to obtain a cured product. The light transmittance at a wavelength of 550 nm of the glass plate on which the cured product of the sheet-like sealing material has been formed is measured using an ultraviolet-visible spectrophotometer (Shimadzu Corporation UV-2550). In the measurement, the light transmittance of the glass plate alone is used as the baseline. The transmittance may be measured using a sheet-like sealing material having a thickness other than 20 μm. In this case, the obtained transmittance is converted into the transmittance when the thickness of the sheet-like sealing material is 20 μm.

[0072] (3) Other Configurations The laminate may have a configuration other than the thin film glass and sheet-like sealing material, as long as the purpose and effect of this embodiment are not impaired. For example, a protective film or the like may be disposed so as to cover the surface of the sheet-like sealing material opposite to the thin film glass. The protective film is preferably a film having moisture barrier properties or gas barrier properties, and may be, for example, a polyethylene terephthalate film. The thickness of the protective film may be about 20 to 100 μm, depending on the film material.

[0073] (4) Method for Producing Laminate The above-described laminate can be produced by any method as long as it does not impair the object and effect of this embodiment. For example, it can be produced by the following method, but is not limited to this method. First, a composition containing (A) an alicyclic epoxy compound, (B) an aromatic-containing epoxy resin, (C) other epoxy resins, (D) a thermal cationic polymerization initiator, (E) a tackifier, and (F) other components is dissolved in a solvent at 30°C or less to form a varnish. Then, the varnish is applied to a desired region of the above-described thin film glass to a desired thickness and dried. This produces the above-described laminate.

[0074] Examples of the solvent include aromatic solvents such as toluene and xylene; ketone solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone; ethers such as ether, dibutyl ether, tetrahydrofuran, dioxane, ethylene glycol monoalkyl ether, ethylene glycol dialkyl ether, propylene glycol or dialkyl ether; aprotic polar solvents such as N-methylpyrrolidone, dimethylimidazolidinone and dimethylformaldehyde; and esters such as ethyl acetate and butyl acetate.

[0075] In preparing the varnish, the (A) alicyclic epoxy compound, (B) aromatic-containing epoxy resin, (C) other epoxy resin, (D) thermal cationic polymerization initiator, (E) tackifier, (F) other components, and solvent may be mixed all at once, or the (A) alicyclic epoxy compound, (B) aromatic-containing epoxy resin, and (C) other epoxy resin may be dissolved in the solvent, and then the other components may be added. Examples of mixing methods include known stirring methods and triple-roll kneading methods.

[0076] The method for applying the varnish is not particularly limited, and examples thereof include screen printing, dispenser application, various roll methods, etc. The thickness of the applied varnish is appropriately selected depending on the desired thickness of the sheet-like sealing material.

[0077] The drying temperature and drying time of the varnish are set so that the (A) epoxy compound and (B) epoxy resin do not harden. For example, the drying temperature is 20 to 100°C, and the drying time can be, for example, about 1 minute to 3 hours. The drying method is not particularly limited, and examples include hot air drying and vacuum drying.

[0078] (5) Uses of the Laminate, etc. The laminate can be used to produce cover films for display devices including touch panels, as described above, and cover films for various display devices. The layer structure of such a cover film is not particularly limited. For example, it may have a structure in which, from the display surface side, a transparent resin film layer / planar sealing material, thin film glass / adhesive layer / transparent film layer / adhesive layer are laminated. Alternatively, it may have a structure in which, from the display surface side, a transparent resin film layer / interlayer adhesive layer / planar sealing material / thin film glass are arranged, or a structure in which, from the display surface side, a transparent resin film layer / planar sealing material / thin film glass are arranged, etc. The laminate may also be used to produce a cover film in which the thin film glass is arranged closer to the display surface than the planar sealing material. Furthermore, the laminate may also be used to produce a cover film in which the thin film glass is arranged as the outermost layer. In either embodiment, the thin film glass is less likely to break, and the planar sealing material is less likely to be dented. Furthermore, peeling is less likely to occur at the interface between the thin film glass and the planar sealing material.

[0079] The method for using the laminate is not particularly limited, and can be, for example, the following method. The laminate will be described using an example in which a transparent resin film (PET or CPI) / planar sealing material / thin film glass / first adhesive layer / transparent film (PET or PI) / second adhesive layer is laminated. When the laminate has the protective film, the protective film is peeled off from the laminate to expose the sheet-like sealing material. Then, the sheet-like sealing material and the transparent resin film (PET or CPI) are brought into close contact with each other. The sheet-like sealing material is cured in this state, and the laminate is laminated with a desired structure. The temperature for curing the sheet-like sealing material is appropriately selected depending on the composition of the sheet-like sealing material, but is preferably 60°C or higher and 200°C or lower, more preferably 70°C or higher and 120°C or lower. Furthermore, the heating time is more preferably 20 minutes or higher and 120 minutes or lower. In this manner, the upper layer is obtained.

[0080] Separately, a laminate is prepared by laminating a lower layer (first adhesive layer / resin film (PET or PI) / second adhesive layer). For example, if the first adhesive layer has protective films on both sides, one of the protective films is peeled off to expose the first adhesive layer. Then, the first adhesive layer is adhered to a desired transparent film (PET or PI). Then, the resin film (PET or PI) on the side not in contact with the first adhesive layer is adhered to the second adhesive layer to obtain the lower layer. Thereafter, the other protective film of the first adhesive layer in the lower layer is peeled off and adhered to the thin glass of the cover film described above to obtain a laminate.

[0081] 2. Second Embodiment A laminate according to a second embodiment of the present invention includes a first film, a sheet-like sealing material disposed on the first film, and a second film disposed on the sheet-like sealing material. That is, the laminate has a structure in which the first film and the second film are bonded together by the sheet-like sealing material. The laminate is suitable as a cover member for various display devices, particularly a cover member for a foldable display device. Hereinafter, an example in which the laminate is used as a cover member for a foldable display device will be described. However, the use of the laminate is not limited to this, and the laminate can be used as a component of various display devices.

[0082] Here, the sheet-like sealing material in the laminate of this embodiment not only serves to bond the first film and the second film, but also to relieve external loads on the laminate and prevent cracking or damage to the first film or the second film. As described above, conventionally known laminates (cover members) have insufficient performance. For example, when the laminate is repeatedly folded and unfolded, peeling occurs at the interface between the first film or the second film and the sheet-like sealing material, or the first film or the second film cracks or breaks. Furthermore, when a local load is applied by a touch pen or the like, peeling easily occurs at the interface between the first film or the second film and the sheet-like sealing material, and discoloration easily occurs.

[0083] In contrast, the inventors have conducted extensive research and found that when the initial slope of the load-strain curve of a sheet-like sealing material falls within a predetermined range, cracks are less likely to occur in the first film or the second film, even when the laminate is repeatedly bent or a local load is applied to its surface, and peeling between the sheet-like sealing material and the first film or the second film can be suppressed. More specifically, when a test piece having the same composition as the sheet-like sealing material and a length of 50 mm, a width of 10 mm, and a thickness of 20 μm is prepared and a tensile test is performed on the test piece at a tensile speed of 300 mm / min in accordance with JIS K7127:1999, it has been found that the above-mentioned effect can be achieved when the slope of the initial linear portion of the load-strain curve is 2.5 N / % or more and 4.0 N / % or less. It is more preferable that the slope is 2.7 N / % or more and 3.5 N / % or less.

[0084] Here, in this specification, the load-elongation diagram is a graph in which the tensile load (N) in the tensile test is on the vertical axis and the elongation (%) of the test piece of the sheet-like sealing material when the tensile load is applied is on the horizontal axis. The elongation of the test piece is a value expressed by the following formula: Elongation (%) = 100 × {(L １ -L ０ ) / L ０In this load-strain diagram, the elongation is usually proportional to the load in the range where the tensile load is small, i.e., in the range close to the origin. Therefore, in this specification, the load-strain line in the region where the load is proportional to the elongation in the range where the tensile load in the tensile test is sufficiently small (for example, 3 N or less) is referred to as the initial linear portion.

[0085] When the slope of the initial linear portion in the load-strain curve of the sheet-shaped sealing material is within the above range, the first and second films are less likely to be damaged and peeling is less likely to occur at the interface between the layers. The reason for this is believed to be as follows: Generally, the more easily the sheet-shaped sealing material disposed between the first and second films stretches, the more easily it follows the deformation of the first and second films and is more likely to deform under external force. Therefore, it is believed that the smaller the slope, the more effectively external stress can be alleviated and peeling at the interface between the first and second films and the sheet-shaped sealing material can be suppressed. However, the foldable display device is frequently folded and unfolded. Furthermore, a load may be locally applied from the outside using a touch pen or the like. In such applications, if the sheet-shaped sealing material is excessively elongated, it is prone to plastic deformation. As a result, the sheet-shaped sealing material becomes locally thin, losing its stress relaxation properties and creating gaps between the sheet-shaped sealing material and the first and second films. On the other hand, if the sheet-shaped sealing material is too difficult to stretch, it may be unable to follow the deformation of the first or second film and peel off, or the first or second film may be subjected to a load, resulting in the cracking or peeling. In contrast, if the inclination is within the above range, the sheet-shaped sealing material can have both moderate stretchability and shape recovery. In other words, even if it is repeatedly bent or subjected to a local load, gaps are unlikely to form between the sheet-shaped sealing material and the first or second film, and the sheet-shaped sealing material can fully absorb external stress. The laminate of this embodiment will be described in detail below.

[0086] (1) First Film and Second Film The first film and second film (hereinafter, simply referred to as "film" when there is no need to distinguish between them) in this specification are preferably foldable and have sufficient light transmittance. The first film and second film may each be a film made of an inorganic material or a film made of a resin. Preferred examples of materials constituting the film include inorganic materials such as glass; and organic materials such as alicyclic polyimide (CPI), polyethylene terephthalate (PET), and polyethylene (PE). The first film and second film may be the same film, but typically the first and second films are different types of films.

[0087] Furthermore, the shape of the film is not particularly limited, but it is preferable that both are thin films. In this specification, "thin film" refers to a film thickness of 150 μm or less. The film thickness of each film is preferably 10 μm or more and 150 μm or less, more preferably 30 μm or more and 100 μm or less. Furthermore, the minimum bending radius of each film is preferably 10 mm or less, more preferably 5 mm or less. When each film has this minimum bending radius, the laminate can be more easily used in a folding display device. On the other hand, the planar shape of the film is not particularly limited and can be appropriately selected depending on the application of the laminate.

[0088] In a more preferred embodiment, either the first film or the second film is thin film glass. Thin film glass refers to a film made of glass and having a thickness of 100 μm or less. This thin film glass is a film generally referred to as UTG (Ultra Thin Glass).

[0089] The thin film glass may be a commercially available product, examples of which include G-Leaf (manufactured by Nippon Electric Glass Co., Ltd.), Dinorex UTG (manufactured by Nippon Electric Glass Co., Ltd.), and SCHOTT UTG (manufactured by SCHOTT).

[0090] (2) Sheet-like sealing material The sheet-like sealing material is a layer disposed between the first film and the second film and bonds the first film and the second film together. As described above, the sheet-like sealing material may be a sheet-like member in which, when a test piece is prepared and a tensile test is performed on the test piece, the gradient of the initial linear portion of the load-strain curve falls within a predetermined range.

[0091] The film thickness of the sheet-like sealing material is appropriately selected depending on the application of the laminate, but is preferably 5 μm to 150 μm, more preferably 10 μm to 100 μm. When the film thickness of the sheet-like sealing material is 10 μm or more, the sheet-like sealing material can more easily relieve stress applied to the laminate. On the other hand, when the film thickness of the sheet-like sealing material is 100 μm or less, the film thickness of the entire laminate becomes thin, making it easier to reduce the film thickness and weight of the display device.

[0092] Here, the composition of the sheet-like sealing material is not particularly limited, but may be a cured product of a thermosetting resin composition or an ultraviolet-curable resin composition containing an epoxy compound. Hereinafter, the thermosetting resin composition for obtaining the sheet-like sealing material and the method for forming the sheet-like sealing material will be described in detail, but the present invention is not limited thereto.

[0093] (Thermosetting resin composition) The thermosetting resin composition for forming a sheet-like sealing material having the above-mentioned physical properties preferably contains (A) an alicyclic epoxy compound, (B) other epoxy compounds, (C) a thermal cationic polymerization initiator and / or a curing agent, and (D) a tackifier. If necessary, it may further contain components other than these. Each component will be described below.

[0094] (A) Alicyclic Epoxy Compound In this specification, the term "(A) alicyclic epoxy compound" refers to a compound having one or more epoxy groups and an alicyclic structure in one molecule. The (A) alicyclic epoxy compound is preferably a compound that is liquid at room temperature (25°C). The number of epoxy groups contained in the (A) alicyclic epoxy compound is preferably 2 or more, more preferably 2 or more and 4 or less. The thermosetting resin composition may contain only one type of (A) alicyclic epoxy compound, or may contain two or more types.

[0095] Examples of (A) alicyclic epoxy compounds include compounds having a cycloalkene oxide structure represented by the following general formula: The cycloalkene oxide structure is a structure obtained by epoxidizing a cycloalkene with an oxidizing agent such as a peroxide, and has an aliphatic ring and an epoxy group composed of two carbon atoms and an oxygen atom that constitute the aliphatic ring. In the above general formula, M represents an alicyclic structure, and the number of carbon atoms therein is preferably 4 to 8, and more preferably 5 to 6. When the number of carbon atoms in the alicyclic structure of the cycloalkene oxide structure is within this range, the slope of the initial linear portion of the load-strain curve of the sheet-like sealing material (cured product of the thermosetting resin composition) tends to fall within the desired range.

[0096] Specific examples of the cycloalkene oxide structure include cyclohexene oxide and cyclopentene oxide, with cyclohexene oxide being preferred.

[0097] The number of cycloalkene oxide structures contained in one molecule of the (A) alicyclic epoxy compound may be one (monofunctional) or two or more (polyfunctional). In particular, the number of cycloalkene oxide structures contained in one molecule of the alicyclic epoxy compound is preferably two or more (polyfunctional).

[0098] Examples of the alicyclic epoxy compound (A) having a cycloalkene oxide structure include compounds represented by the following general formulas (A-1) to (A-3).

[0099]

[0100] M in the above general formula (A-1) １ and M ２ represents an alicyclic structure, and as described above, the number of carbon atoms therein is preferably 4 to 8, more preferably 5 to 6. １is a single bond or a linking group. Examples of the linking group include a divalent hydrocarbon group, a carbonyl group, an ether group (ether bond), a thioether group (thioether bond), an ester group (ester bond), a carbonate group (carbonate bond), an amide group (amide bond), or a group in which a plurality of these groups are linked together.

[0101] Examples of divalent hydrocarbon groups that can be the linking group include alkylene groups having 1 to 18 carbon atoms and divalent alicyclic hydrocarbon groups. Examples of alkylene groups having 1 to 18 carbon atoms include methylene, methylmethylene, dimethylmethylene, ethylene, propylene, and trimethylene. Examples of divalent alicyclic hydrocarbon groups include divalent cycloalkylene groups (including cycloalkylidene groups) such as 1,2-cyclopentylene, 1,3-cyclopentylene, cyclopentylidene, 1,2-cyclohexylene, 1,3-cyclohexylene, 1,4-cyclohexylene, and cyclohexylidene.

[0102] Among them, X １ is preferably a single bond or a linking group having an oxygen atom. The linking group having an oxygen atom is more preferably —CO— (carbonyl group), —O—CO—O— (carbonate group), —COO— (ester group), —O— (ether group), —CONH— (amide group), a group in which a plurality of these groups are linked together, or a group in which one or more of these groups are linked to one or more divalent hydrocarbon groups.

[0103] Specific examples of the alicyclic epoxy compound represented by general formula (A-1) include the following compounds. In the following formula, l is an integer of 1 to 10, and m is an integer of 1 to 30. R is an alkylene group having 1 to 8 carbon atoms (preferably an alkylene group having 1 to 3 carbon atoms, such as a methylene group, an ethylene group, a propylene group, or an isopropylene group). n1 and n2 are each an integer of 1 to 30.

[0104]

[0105] Commercially available examples of the alicyclic epoxy compound (A) represented by the general formula (A-1) include Celloxide 2021P, Celloxide 2081, Celloxide 8000, and Celloxide 8010 (manufactured by Daicel Corporation).

[0106] On the other hand, the alicyclic epoxy compound (A) having a cycloalkene oxide structure may be, for example, a compound having a structure represented by the following general formula (A-2) or (A-3). M in the above general formulae (A-2) and (A-3) ３ , M ４ , and M ５ represents an alicyclic structure, the number of carbon atoms of which is preferably 4 to 8, more preferably 5 to 6. X in the above general formula (A-3) ２ is a single bond or a linking group. The linking group is the same as the linking group in the general formula (A-1) described above. In addition, the compounds represented by the general formulas (A-2) and (A-3) may have an alkyl group or the like bonded to a carbon that constitutes an alicyclic structure or an epoxy group.

[0107] Examples of the alicyclic epoxy compound (A) represented by the general formula (A-2) or (A-3) above include 3,4:7,8-diepoxybicyclo[4.3.0]nonane, limonene dioxide, etc. Examples of commercially available products of these compounds include THI-DE (manufactured by JX-TG Corporation) and LDO (manufactured by Nagase Chemtec Corporation).

[0108] In any of the above-mentioned (A) alicyclic epoxy compounds, the weight-average molecular weight is preferably 180 or more, more preferably 190 or more, and even more preferably 200 or more. The upper limit of the weight-average molecular weight is appropriately selected depending on the viscosity of the composition, but is preferably 500 or less. When the weight-average molecular weight of the alicyclic epoxy compound is 180 or more, the slope of the initial linear portion of the load-strain curve of the sheet-like sealing material (cured product of the thermosetting resin composition) tends to fall within the desired range. The weight-average molecular weight of the alicyclic epoxy compound is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0109] The (A) alicyclic epoxy compound is particularly preferably a compound represented by the following formula, from the viewpoint that the slope of the initial linear portion of the load-strain curve of the sheet-like sealing material (cured product of the thermosetting resin composition) is more likely to fall within a desired range.

[0110] The total amount of the alicyclic epoxy compound (A) relative to the total amount of the thermosetting resin composition is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 30% by mass or less. When the amount of the alicyclic epoxy compound (A) is within this range, the slope of the initial linear portion of the load-strain curve of the sheet-like sealing material is more likely to fall within the desired range.

[0111] (B) Other Epoxy Compounds In this specification, the term "(B) other epoxy compounds" refers to compounds having an epoxy group that do not correspond to the above-mentioned (A) alicyclic epoxy compounds. Examples of (B) other epoxy compounds include aromatic epoxy compounds and aliphatic epoxy compounds. The thermosetting resin composition may contain only one (B) other epoxy compound, or two or more (B) other epoxy compounds. Among these, the (B) other epoxy compounds preferably contain a high-molecular-weight epoxy compound having a weight-average molecular weight of 3,000 or more and a flexibility-imparting epoxy compound having a weight-average molecular weight of 300 or more but less than 3,000. The high-molecular-weight epoxy compound is usually solid at room temperature (25°C). When the thermosetting resin composition contains a high-molecular-weight epoxy compound as the (B) other epoxy compound, the thermosetting resin composition can be easily formed into a sheet-like film. On the other hand, the flexibility-imparting epoxy compound is liquid or solid at room temperature (25°C). When the thermosetting resin composition contains a flexibility-imparting epoxy compound as the (B) other epoxy compound, the resulting sheet-like sealing material tends to have good bending resistance. Furthermore, by combining these, the gradient of the initial linear portion of the load-strain curve of the sheet-like sealing material described above tends to fall within a desired range. The weight average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0112] The weight average molecular weight of the high molecular weight epoxy compound is preferably from 3,000 to 100,000, more preferably from 6,000 to 60,000, and even more preferably from 7,000 to 40,000. The high molecular weight epoxy compound may be an aromatic epoxy compound or an aliphatic epoxy compound, but a compound having an aromatic ring is more preferred.

[0113] Specific examples of aromatic epoxy compounds that can be the high-molecular-weight epoxy compounds include bisphenol-type epoxy resins such as bisphenol A, bisphenol F, bisphenol E, bisphenol S, bisphenol AD, and mixtures thereof; diphenyl ether-type epoxy resins; novolac-type epoxy resins such as phenol novolac, cresol novolac, biphenyl novolac, bisphenol novolac, naphthol novolac, trisphenol novolac, and dicyclopentadiene novolac; biphenyl-type epoxy resins; naphthyl-type epoxy resins; and triphenolalkane-type epoxy resins such as triphenolmethane, triphenolethane, and triphenolpropane.

[0114] Among the above aromatic epoxy compounds, bisphenol-type epoxy resins or biphenyl-type epoxy resins are preferred. However, as the amount of bisphenol F skeleton in the thermosetting resin composition increases, the softening point of the thermosetting resin composition tends to decrease. Therefore, when a sheet-shaped thermosetting resin composition is bonded to a first film or a second film at a relatively high temperature, it is preferred that the thermosetting resin composition mainly contain an aromatic epoxy compound other than a bisphenol F skeleton.

[0115] Furthermore, the number of epoxy groups possessed by the high molecular weight epoxy compound is not particularly limited, but the epoxy equivalent is preferably 900 g / eq or more and 20,000 g / eq or less, and more preferably 1,000 g / eq or more and 20,000 g / eq or less. When the epoxy equivalent of the high molecular weight epoxy compound is 900 g / eq or more, the tackiness of the thermosetting resin composition at room temperature is reduced. Therefore, the handleability of the thermosetting resin composition when producing a laminate is likely to be improved. On the other hand, if the epoxy equivalent of the high molecular weight epoxy compound is excessively large, the solubility of the high molecular weight aromatic epoxy compound in solvents may decrease, or the compatibility with the above-mentioned (A) alicyclic epoxy compound may become poor. Therefore, the epoxy equivalent of the high molecular weight epoxy compound is preferably 20,000 g / eq or less.

[0116] On the other hand, the weight average molecular weight of the flexibility-imparting epoxy compound is more preferably from 500 to 2000. The flexibility-imparting epoxy compound may be an aromatic epoxy compound or an aliphatic epoxy compound.

[0117] Specific examples of the flexibility-imparting epoxy compound that is an aromatic epoxy compound include the aromatic epoxy compounds listed above as the high molecular weight epoxy compounds and similar resins (however, the molecular weight is 300 or more and less than 3,000).

[0118] On the other hand, when the flexibility-imparting epoxy compound is an aliphatic epoxy compound, the aliphatic epoxy compound may be a compound having one or more epoxy groups in the molecule and an aliphatic chain (excluding those corresponding to the above (A) alicyclic epoxy compound and aromatic epoxy compound). The aliphatic epoxy compound may have only one epoxy group or may have two or more epoxy groups. Furthermore, the length of the aliphatic chain contained in the aliphatic epoxy compound is not particularly limited, but the number of carbon atoms in the molecule is preferably 10 to 1,000, more preferably 50 to 200. When the number of carbon atoms in the molecule is 10 or more, flexibility is easily imparted to the sheet-like sealing material. On the other hand, when the number of carbon atoms in the molecule is 1,000 or less, compatibility with other components is improved.

[0119] The number of epoxy groups in the flexibility-imparting epoxy compound is not particularly limited, but is preferably two or more, and the epoxy equivalent is preferably 150 g / eq or more and 3000 g / eq or less, and more preferably 300 g / eq or more and 1500 g / eq or less. When the epoxy equivalent of the flexibility-imparting epoxy compound is 150 g / eq or more, the bending resistance of the resulting sheet-like sealing material tends to be good. On the other hand, when the epoxy equivalent of the flexibility-imparting epoxy compound is 3000 g / eq or less, the flexibility of the thermosetting resin composition tends to be increased.

[0120] The total amount of the high-molecular-weight epoxy compound relative to the total amount of the thermosetting resin composition is preferably 5% by mass to 60% by mass, more preferably 10% by mass to 50% by mass, and even more preferably 20% by mass to 40% by mass. When the amount of the high-molecular-weight epoxy compound in the thermosetting resin composition is within this range, the thermosetting resin composition can be easily formed into a sheet, and the lamination temperature with the first film and the second film tends to be appropriate.

[0121] On the other hand, the total amount of the flexibility-imparting epoxy compound relative to the total amount of the thermosetting resin composition is preferably 50% by mass or less. When the flexibility-imparting epoxy compound is contained, the lower limit is preferably 5% by mass, and more preferably 5% by mass or more and 40% by mass or less. When the amount of the flexibility-imparting epoxy compound in the thermosetting resin composition is within this range, the physical properties of the sheet-like sealing material tend to fall within the desired range.

[0122] (C) Thermal Cationic Polymerization Initiator and Curing Agent The (C) thermal cationic polymerization initiator and curing agent are components for curing the above-mentioned (A) alicyclic epoxy compound and (B) other epoxy compounds. The thermal cationic polymerization initiator may be any compound that generates active species capable of initiating cationic polymerization upon heating and is capable of cationic polymerizing the above-mentioned (A) alicyclic epoxy compound and (B) other epoxy compounds. On the other hand, the curing agent may be any compound that is capable of reacting with the above-mentioned (A) alicyclic epoxy compound and (B) other epoxy compounds to cure them. The thermosetting resin composition generally needs to contain either the thermal cationic polymerization initiator or the curing agent.

[0123] Examples of the thermal cationic polymerization initiator include sulfonium salts, phosphonium salts, quaternary ammonium salts, diazonium salts, and iodonium salts, among which quaternary ammonium salts or sulfonium salts are preferred. The anion moiety of these is AsF ６ － , SbF ６ － , P.F. ６ － , B(C ６ F ５ ) ４ － The thermosetting resin composition may contain only one type of thermal cationic polymerization initiator, or may contain two or more types of thermal cationic polymerization initiators.

[0124] The total amount of the thermal cationic polymerization initiator relative to the total amount of the thermosetting resin composition is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less. When the amount of the thermal cationic polymerization initiator is 0.5% by mass or more, the curability of the thermosetting resin composition becomes even better. On the other hand, when the amount of the thermal cationic polymerization initiator is 10% by mass or less, the storage stability of the thermosetting resin composition becomes even better.

[0125] On the other hand, the curing agent is preferably a thermal latent curing agent having a melting point of 50° C. or more and 250° C. or less, and more preferably a melting point of 50° C. or more and 150° C. or less. When the melting point of the curing agent is within this range, the (A) alicyclic epoxy compound or (B) other epoxy compound is unlikely to react with the curing agent at room temperature, and the storage stability of the thermosetting resin composition is improved.

[0126] Examples of the curing agent include dihydrazide-based thermal latent curing agents, imidazole-based thermal latent curing agents, amine adduct-based thermal latent curing agents, polyamine-based thermal latent curing agents, etc. The thermosetting resin composition may contain only one of these, or may contain two or more of them.

[0127] Examples of the dihydrazide-based thermal latent curing agent include adipic acid dihydrazide (melting point 181°C), 1,3-bis(hydrazinocarboethyl)-5-isopropylhydantoin (melting point 120°C), 7,11-octadecadiene-1,18-dicarbohydrazide (melting point 160°C), dodecanedioic acid dihydrazide (melting point 190°C), sebacic acid dihydrazide (melting point 189°C), and the like.

[0128] Examples of the imidazole-based thermal latent curing agent include 2,4-diamino-6-[2'-ethylimidazolyl-(1')]-ethyltriazine (melting point: 215 to 225°C), 2-phenylimidazole (melting point: 137 to 147°C), and the like.

[0129] The amine adduct thermal latent curing agent is a thermal latent curing agent consisting of an addition compound obtained by reacting an amine compound having catalytic activity with an arbitrary compound, and examples thereof include Amicure PN-40 (melting point 110°C), Amicure PN-23 (melting point 100°C), Amicure PN-31 (melting point 115°C), Amicure PN-H (melting point 115°C), Amicure MY-24 (melting point 120°C), and Amicure MY-H (melting point 131°C) (all manufactured by Ajinomoto Fine-Techno Co., Inc.).

[0130] The polyamine-based thermal latent curing agent is a thermal latent curing agent having a polymer structure obtained by reacting an amine with an epoxy, and examples thereof include ADEKA HARDNER EH4339S (softening point 120 to 130°C) and ADEKA HARDNER EH4357S (softening point 73 to 83°C) (both manufactured by ADEKA Corporation).

[0131] The amount of the curing agent relative to the total amount of the thermosetting resin composition is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 5% by mass. When the amount of the curing agent is within this range, the curability and storage stability of the thermosetting resin composition become even better.

[0132] (D) Tackifier When the thermosetting resin composition contains a tackifier (D), the adhesion between the sheet-like sealing material and the first film and the second film tends to be further improved. The tackifier (D) is preferably a resin selected from the group consisting of petroleum resins (aliphatic hydrocarbon resins, alicyclic hydrocarbon resins, and / or aromatic hydrocarbon resins), terpene resins, phenolic resins, and rosin resins. The thermosetting resin composition may contain only one type of tackifier (D), or may contain two or more types.

[0133] Examples of petroleum resins include C5 monomers or oligomers thereof obtained from pentene, pentadiene, isoprene, etc.; C9 monomers or oligomers thereof obtained from indene, methylindene, vinyltoluene, styrene, α-methylstyrene, β-methylstyrene, etc.; copolymers of C5 and C9 monomers (C5-C9 copolymer resins); alicyclic monomers or polymers thereof obtained from cyclopentadiene, dicyclopentadiene, etc.; aromatic monomers such as isopropenyl toluene or polymers thereof; hydrogenated products of the above-mentioned various monomers or polymers thereof; and modified petroleum resins obtained by modifying the above-mentioned various monomers or polymers thereof with maleic anhydride, maleic acid, fumaric acid, (meth)acrylic acid, phenol, etc.

[0134] Examples of terpene resins include α-pinene resin, β-pinene resin, α-pinene monomer, aromatic-modified terpene resin obtained by copolymerizing terpenes such as β-pinene monomer with aromatic monomers such as styrene and phenol.

[0135] Examples of phenolic resins include condensates of phenols and formaldehyde. Examples of phenols include phenol, m-cresol, 3,5-xylenol, p-alkylphenol, resorcinol, etc. Examples of the phenolic resins include resols obtained by addition reaction of these phenols with formaldehyde using an alkali catalyst, and novolacs obtained by condensation reaction using an acid catalyst. Phenolic resins also include rosin phenolic resins obtained by adding phenol to rosin using an acid catalyst and thermally polymerizing the resulting mixture.

[0136] Examples of rosin resins include gum rosin, wood rosin, or tall oil rosin; stabilized rosins or polymerized rosins obtained by disproportionating or hydrogenating these rosins; modified rosins obtained by modifying these rosins with maleic anhydride, maleic acid, fumaric acid, (meth)acrylic acid, phenol, or the like; and esters thereof. The alcohol used to obtain the esters is preferably a polyhydric alcohol. Examples of polyhydric alcohols include dihydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, and neopentyl glycol; trihydric alcohols such as glycerin, trimethylolethane, and trimethylolpropane; tetrahydric alcohols such as pentaerythritol and diglycerin; and hexahydric alcohols such as dipentaerythritol. These may be used alone or in combination during esterification.

[0137] The total amount of the tackifier (D) relative to the total amount of the thermosetting resin composition is preferably 1% by mass or more and 40% by mass or less, more preferably 5% by mass or more and 30% by mass or less. When the amount of the tackifier (D) is 5% by mass or more, the adhesion between the obtained sheet-like sealing material and the first film and the second film tends to be further improved. On the other hand, when the amount of the tackifier (D) is 30% by mass or less, the amounts of the above-mentioned (A) alicyclic epoxy compound and (B) other epoxy compound tend to be sufficiently large.

[0138] (E) Other Components Examples of other components include various resins, fillers, modifiers, stabilizers, etc. Examples of various resins include polyamide, polyamideimide, polyurethane, polybutadiene, polychloroprene, polyether, polyester, styrene-butadiene-styrene block copolymer, xylene resin, ketone resin, cellulose resin, fluorine-based oligomer, silicon-based oligomer, polysulfide-based oligomer, etc. The thermosetting resin composition may contain only one of these, or may contain two or more of them.

[0139] Examples of the filler include glass beads, styrene-based polymer particles, methacrylate-based polymer particles, ethylene-based polymer particles, propylene-based polymer particles, etc. The thermosetting resin composition may contain only one type of filler, or may contain two or more types of fillers.

[0140] Examples of the modifier include a polymerization initiator, an antioxidant, a leveling agent, a wettability improver, a surfactant, a plasticizer, a solvent, a silane coupling agent, etc. The thermosetting resin composition may contain only one type of these modifiers or may contain two or more types thereof.

[0141] Examples of the stabilizer include an ultraviolet absorber, an antiseptic, an antibacterial agent, etc. The thermosetting resin composition may contain only one kind of these, or may contain two or more kinds thereof.

[0142] (Method for forming a sheet-like sealing material) The sheet-like sealing material can be formed by dissolving the thermosetting resin composition in a solvent to form a varnish, applying the varnish to a desired film thickness, and drying (removing the solvent). Thereafter, the sheet-like thermosetting resin composition is laminated with the first film and the second film, and curing (A) the alicyclic epoxy compound and (B) other epoxy compounds in the sheet-like thermosetting resin composition.

[0143] Examples of the solvent include aromatic solvents such as toluene and xylene; ketone solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone; ethers such as ether, dibutyl ether, tetrahydrofuran, dioxane, ethylene glycol monoalkyl ether, ethylene glycol dialkyl ether, propylene glycol or dialkyl ether; aprotic polar solvents such as N-methylpyrrolidone, dimethylimidazolidinone and dimethylformaldehyde; and esters such as ethyl acetate and butyl acetate.

[0144] In preparing the varnish, the thermosetting resin composition containing (A) the alicyclic epoxy compound, (B) other epoxy compounds, (C) the thermal cationic polymerization initiator and / or curing agent, (D) the tackifier, and (E) other components as needed, as well as the solvent may be mixed all at once, or the other components may be added after dissolving the (A) alicyclic epoxy compound and (B) other epoxy compounds in the solvent. Examples of methods for mixing the components include known stirring methods and triple-roll kneading methods.

[0145] The method for applying the varnish is not particularly limited, and examples thereof include screen printing, dispenser application, various roll methods, etc. The thickness of the applied varnish is appropriately selected depending on the desired film thickness of the sheet-like sealing material.

[0146] The method for drying the varnish, i.e., the method for removing the solvent, is not particularly limited, and examples thereof include heating. The heating temperature and drying time are preferably set so that the (A) alicyclic epoxy compound and the (B) other epoxy compounds do not harden. For example, the drying temperature is 20 to 100°C, and the drying time can be, for example, about 1 minute to 3 hours. The drying method is not particularly limited, and examples thereof include hot air drying and vacuum drying.

[0147] Alternatively, the varnish may be applied directly to the first film or the second film to form the thermosetting resin composition into a sheet. However, a more preferred method involves applying the varnish to a known separate film, removing the solvent to obtain a sheet-like thermosetting resin composition, and then laminating the sheet-like thermosetting resin composition to the first film or the second film. This method makes it less likely that the first film or the second film will be altered or deteriorated by the solvent or the heat generated during solvent removal.

[0148] The method for bonding the sheet-like thermosetting resin composition to the first film and the second film is not particularly limited, and lamination can be performed by thermocompression bonding, for example. For example, the first film and the second film may be placed on both sides of the sheet-like thermosetting resin composition, respectively, and the first film and the second film may be simultaneously thermocompression bonded to the thermosetting resin composition. However, it is more preferable to first superpose the thermosetting resin composition on one of the first film and the second film and thermocompression bond it, and then thermocompression bond the other film to the thermosetting resin composition. When sequential thermocompression bonding is performed, the temperature for at least the first thermocompression bonding is preferably 50°C or higher and 120°C or lower, more preferably 70°C or higher and 100°C or lower. By performing thermocompression bonding for a short time at this temperature, it is possible to laminate the (A) alicyclic epoxy compound and (B) other epoxy compound without curing them.

[0149] After laminating the first film, the thermosetting resin composition, and the second film, the laminate is further heated to cure the (A) alicyclic epoxy compound and the (B) other epoxy compound. The heating temperature is preferably 60°C or higher and 200°C or lower, and more preferably 70°C or higher and 120°C or lower. Furthermore, the heating time is more preferably 20 minutes or higher and 120 minutes or lower. By using the heating temperature and heating time, the (A) alicyclic epoxy compound and the (B) other epoxy compound in the thermosetting resin composition can be sufficiently cured.

[0150] (Preferred physical properties of sheet-like sealing material) The sheet-like sealing material preferably has sufficient visible light transmittance. Specifically, at a thickness of 20 μm, the transmittance of light with a wavelength of 550 nm is preferably 90% or more, more preferably 95% or more, and even more preferably 97% or more. When the sheet-like sealing material has a transmittance of 90% or more at a wavelength of 550 nm, the laminate can be suitably used as a cover member for a display device, etc. The light transmittance can be measured by the following method. The above-mentioned thermosetting resin composition is applied to a glass plate so that the film thickness after curing is 20 μm. Then, the coating film is cured under the same curing conditions as when the sheet-like sealing material was produced. The light transmittance of the laminate of the glass plate and the sheet-like sealing material is then measured using an ultraviolet-visible spectrophotometer (Shimadzu Corporation UV-2550). In the measurement, the light transmittance of the glass plate alone is used as a baseline. The transmittance may be measured using a sheet-like sealing material with a thickness other than 20 μm. In this case, the measured transmittance is converted to the transmittance when the thickness of the sheet-like sealing material is 20 μm.

[0151] (4) Uses of the Laminate The laminate can be used as a cover member for a display device including a touch panel as described above. It can also be used as a cover member for various display devices (e.g., an organic EL display device), to protect a vibration-sensitive part of a sensor, or as a protective layer for the surface of an in-vehicle instrument panel.

[0152] 3. Third Embodiment 3-1. Laminate A third laminate of the present invention includes a pair of films, a first sealant disposed between the pair of films, and a second sealant having a higher elastic modulus than the first sealant. That is, the laminate has a structure in which the first sealant and the second sealant are sandwiched between a pair of films (hereinafter, the film disposed adjacent to the first sealant will be referred to as the "first film" and the other film as the "second film"). The laminate is suitable as a cover member for various display devices, particularly a cover member for a foldable display device. Hereinafter, the laminate will be described using an example in which it is used as a cover member for a foldable display device. However, the use of the laminate is not limited to this, and it can be used as a component of various display devices.

[0153] The first and second sealing materials in the laminate of this embodiment not only serve to bond the first and second films together, but also to relieve external loads on the laminate and prevent cracking or damage to the first and second films. As described above, in conventionally known laminates (cover members) consisting of a first film, a sealing material, and a second film, repeated folding and unfolding of the laminate can result in peeling at the interface between the first or second film and the sealing material, or cracking or damage to the first or second film. Furthermore, when a localized load is applied by a touch pen or the like, peeling and discoloration can easily occur at the interface between the first or second film and the sealing material.

[0154] In response to this, the inventors have found through extensive research that by constructing a sealing material from two layers, setting the initial slope of the load-strain curve in a tensile test of one of the layers (the first sealing material) within a predetermined range, and making the tensile modulus of the other (the second sealing material) higher than that of the first sealing material, cracks are less likely to occur in the first film or the second film even when the laminate is repeatedly bent or a local load is applied to the film surface. It has also been found that this laminate is less likely to experience peeling between the sealing material and the interface between the film and the sealing material.

[0155] The reason why the above-described effect is achieved in the laminate of this embodiment is believed to be as follows. Generally, the more easily the sealing material disposed between a pair of films stretches, the more it can accommodate deformation of the pair of films. Furthermore, it is believed that when each film is subjected to external force, the stress can be alleviated. On the other hand, cover members for foldable display devices are frequently folded and unfolded. In addition, loads may be applied locally from the outside using a touch pen or the like. Therefore, in such applications, if the sealing material undergoes plastic deformation due to external force, it will not be able to restore its original shape and will not be able to accommodate repeated folding. As a result, wrinkles and peeling occur at the folded portions of the first film and the second film. Furthermore, when a load is applied locally from the outside using a touch pen or the like, depressions will occur at the loaded areas, impairing the smoothness of the surface.

[0156] Therefore, it has been considered to provide the sealing material with elongation and recovery. It has been revealed that such elongation and recovery correlate with the slope (N / %) of the load-elongation curve during a tensile test of the sealing material. Specifically, if the slope is excessively small, the stress relaxation is high, but the sealing material is subject to large deformation even with a slight external force, making it more likely to reach the plastic deformation region. On the other hand, if the slope is excessively large, the plastic deformation due to external force is small, but the stress relaxation for the first film and the second film is low. As a result, a load is applied to the first film and the second film, causing the cracking and peeling described above.

[0157] In contrast, in the present embodiment, a first sealant having an appropriate range of elasticity is combined with a second sealant having a higher tensile modulus. This allows the laminate of the first sealant and the second sealant to have both appropriate stretchability and restorability. In other words, even if the laminate is repeatedly bent or subjected to localized loads, peeling is unlikely to occur between each film (the first film or the second film) and the first sealant or the second sealant, and the first sealant or the second sealant can sufficiently absorb external stress. The laminate of this embodiment will be described in detail below.

[0158] (1) Pair of Films The pair of films in this specification is not particularly limited as long as they are foldable, light-transmitting, and have the desired optical properties. The first film and the second film may each be a film made of an inorganic material or a film made of a resin. Preferred examples of materials constituting the films include inorganic materials such as glass; and organic materials such as alicyclic polyimide (CIP), polyethylene terephthalate (PET), and polyethylene (PE). The first film and the second film may be the same film or different types of films.

[0159] The thickness of each film is not particularly limited, but it is preferable that each film is thin. In this specification, "thin" means a thickness of 150 μm or less. The thickness of each film is preferably 10 μm or more and 150 μm or less, and more preferably 30 μm or more and 100 μm or less. On the other hand, the planar shape of the film is not particularly limited and is selected appropriately depending on the application of the laminate. Furthermore, the minimum bending radius of each film is preferably 10 mm or less, and more preferably 5 mm or less. When each film has this minimum bending radius, the laminate can be easily bent freely, making the laminate more usable as a cover member for a folding display device, etc.

[0160] Here, it is more preferable that at least one of the films is thin film glass. Thin film glass can be easily broken, but the laminate of this embodiment contains the first sealant and second sealant described below, so it is less likely to break even if it contains thin film glass. Note that thin film glass refers to a film made of glass and having a thickness of 100 μm or less. The thin film glass is a film generally referred to as UTG (Ultra Thin Glass).

[0161] The thin film glass may be a commercially available product, examples of which include G-Leaf (manufactured by Nippon Electric Glass Co., Ltd.), Dinorex UTG (manufactured by Nippon Electric Glass Co., Ltd.), and SCHOTT UTG (manufactured by SCHOTT).

[0162] (2) First sealing material The first sealing material may be a layered member that can be laminated with the above-mentioned film, and that has a slope of 0.4 N / % or more and 2.0 N / % or less in the initial linear portion of the load-strain curve when a test piece having the same composition as the first sealing material, 50 mm in length, 10 mm in width, and 20 μm in thickness is prepared and subjected to a tensile test at 25°C at a tensile speed of 300 mm / min in accordance with JIS K7127:1999. More preferably, the slope is 0.7 N / % or more and 1.8 N / % or less.

[0163] Here, in this specification, the load-elongation diagram is a graph in which the vertical axis represents the tensile load (N) in the tensile test and the horizontal axis represents the elongation (%) of a test piece having the same composition as the first sealing material when the tensile load is applied. The elongation of the test piece is a value expressed by the following formula: Elongation (%) = 100 × {(L １ -L ０ ) / L ０ In this load-strain diagram, the elongation is usually proportional to the load in the range where the tensile load is small, i.e., in the range close to the origin. Therefore, in this specification, the load-strain line in the region where the load is proportional to the elongation in the range where the tensile load in the tensile test is sufficiently small (for example, 3 N or less) is referred to as the initial linear portion.

[0164] The tensile modulus of the first sealing material measured in accordance with JIS K7127:1999 at 25°C and a film thickness of 20 μm is 1×10 ６ Pa or more 5×10 ９ Pa or less is preferable, and 1×10 ７ Pa or more 3×10 ９ It is more preferable that the modulus of elasticity of the first sealant is in this range. When the modulus of elasticity of the first sealant is in this range, not only is it easy to achieve the above-mentioned slope, but the modulus of elasticity when the first sealant and the second sealant are laminated is likely to be in the desired range, and further, the bending resistance of the laminate is likely to be good. The tensile modulus of elasticity of the first sealant is a value determined by preparing a test piece in the same way as when measuring the above-mentioned slope and performing a tensile test in the same way.

[0165] Furthermore, the first sealant preferably has sufficient visible light transmittance. Specifically, at a thickness of 20 μm, the transmittance of light with a wavelength of 550 nm is preferably 90% or more, more preferably 95% or more, and even more preferably 97% or more. When the sealant has a transmittance of 90% or more at a wavelength of 550 nm, the laminate can be easily used as a cover member for a display device, etc. The light transmittance of the first sealant can be measured by the following method. A composition for producing the first sealant (e.g., a thermosetting resin composition described below) is applied to a glass plate so that the film thickness after curing is 20 μm. The composition is then cured under the same curing conditions as when producing the first sealant. The light transmittance of the laminate of the glass plate and the sealant is then measured using an ultraviolet-visible spectrophotometer (Shimadzu Corporation UV-2550). In the measurement, the light transmittance of the glass plate alone is used as the baseline. Note that the transmittance measurement may also be performed using a sealant with a thickness other than 20 μm. In this case, the measured transmittance is converted into the transmittance when the thickness of the sealing material is 20 μm.

[0166] The film thickness of the first sealant is appropriately selected depending on the application of the laminate, but is preferably 5 μm to 50 μm, more preferably 10 μm to 40 μm. When the film thickness of the first sealant is 10 μm or more, the sealant can more easily relieve stress applied to the laminate. On the other hand, when the film thickness of the first sealant is 40 μm or less, the film thickness of the entire laminate becomes thin, making it easier to reduce the film thickness and weight of the display device.

[0167] Here, the composition of the first sealing material is not particularly limited as long as it has the above-mentioned physical properties, but it is preferably a cured product of a thermosetting resin composition containing an epoxy compound or an ultraviolet-curable resin composition containing an epoxy compound, as described below.

[0168] (3) Second sealing material On the other hand, the second sealing material may be a layered member that has a tensile modulus at 25°C, measured in accordance with JIS K7127:1999, higher than that of the first sealing material and can be laminated with the above-mentioned film. The tensile modulus of the second sealing material at 25°C is 1 x 10 ９ Pa or more 1×10 １０Pa or less is preferable, and 2×10 ９ Pa or more 5×10 ９ It is more preferable that the tensile modulus of the second sealant is in this range. When the tensile modulus of the second sealant is in this range, the modulus of elasticity when the first sealant and the second sealant are laminated is likely to be in the desired range, and further, the bending resistance of the laminate is likely to be good. The tensile modulus of the second sealant can be measured in the same way as the tensile modulus of the first sealant.

[0169] Furthermore, the second sealant preferably has sufficient visible light transmittance. Specifically, at a thickness of 20 μm, the transmittance of light with a wavelength of 550 nm is preferably 90% or more, more preferably 95% or more, and even more preferably 97% or more. When the sealant has a transmittance of light with a wavelength of 550 nm of 90% or more, the laminate can be easily used as a cover member for a display device, etc. The light transmittance of the second sealant is measured using the same method as that for the light transmittance of the first sealant.

[0170] The thickness of the second sealant is appropriately selected depending on the application of the laminate, but is preferably 5 μm to 50 μm, more preferably 10 μm to 40 μm. When the thickness of the second sealant is 10 μm or more, the second sealant can more easily relieve stress applied to the laminate. On the other hand, when the thickness of the second sealant is 40 μm or less, the thickness of the entire laminate is thin, making it easier to reduce the thickness and weight of the display device.

[0171] The thickness of the second sealant is preferably 25% to 75%, more preferably 40% to 60%, of the total thickness of the first and second sealants. When the ratio of the thickness of the second sealant to the total thickness of the first and second sealants is within this range, the bending resistance of the laminate tends to be further improved.

[0172] Here, the composition of the second sealant is not particularly limited, but it is preferably a thermosetting resin composition containing an epoxy compound described below, or a cured product of an ultraviolet-curable resin composition containing an epoxy compound. Note that, although the following mainly describes thermosetting resin compositions, when an ultraviolet-curable resin composition is used, the thermal cationic polymerization initiator and curing agent described below may be a known photopolymerization agent (e.g., Omnirad 184, Omnirad 651, Omnirad 907, etc., manufactured by IGM Resins B.V.).

[0173] (Thermosetting Resin Composition) Hereinafter, the thermosetting resin composition for obtaining the first sealing material and the second sealing material will be described in detail, but is not limited thereto. The thermosetting resin composition preferably contains (A) an epoxy compound, (B) a thermal cationic polymerization initiator and / or a curing agent, and (C) a tackifier. If necessary, it may further contain components other than these. Each component will be described.

[0174] (A) Epoxy Compound In this specification, the epoxy compound may be any compound having an epoxy group, and its structure is not particularly limited. The (A) epoxy compound may contain only one type, or two or more types. In both the thermosetting resin composition for obtaining the first sealant and the thermosetting resin composition for obtaining the second sealant, the thermosetting resin composition preferably contains multiple types of (A) epoxy compounds. This allows the physical properties of the first sealant and the second sealant to be adjusted as described above. In both the thermosetting resin composition for obtaining the first sealant and the thermosetting resin composition for obtaining the second sealant, the thermosetting resin composition preferably contains (i) an epoxy compound having a cycloalkene oxide structure and / or (ii) an epoxy compound having a cyclopentadiene structure, (iii) a high-molecular-weight epoxy compound having a weight-average molecular weight of 3,000 or more, and (iv) a flexibility-imparting epoxy compound having a weight-average molecular weight of 300 or more but less than 3,000. When the thermosetting resin composition contains these components, it becomes easier to obtain a first sealant or a second sealant having the above-described physical properties. In particular, the thermosetting resin composition for the first sealant contains a larger amount of the flexibility-imparting epoxy compound (iv) than the thermosetting resin composition for the second sealant, which makes it easier to achieve the above-mentioned gradient. Each of these compounds will be described below.

[0175] (i) In the epoxy compound having a cycloalkene oxide structure, the "cycloalkene oxide structure" is a structure represented by the following general formula, which is obtained by epoxidizing a cycloalkene with an oxidizing agent such as a peroxide, and which has an aliphatic ring and an epoxy group composed of two carbon atoms and an oxygen atom constituting the aliphatic ring. In the above general formula, M represents an alicyclic structure, and the number of carbon atoms therein is preferably 4 to 8, and more preferably 5 to 6. (i) When the number of carbon atoms in the alicyclic structure of the cycloalkene oxide structure is within this range, the physical properties of the first sealing material and the second sealing material tend to fall within desired ranges.

[0176] Specific examples of the cycloalkene oxide structure include cyclohexene oxide and cyclopentene oxide, with cyclohexene oxide being preferred.

[0177] (i) The number of cycloalkene oxide structures contained in one molecule of an epoxy compound having a cycloalkene oxide structure may be one (monofunctional) or two or more (polyfunctional). In particular, the number of cycloalkene oxide structures contained in one molecule is preferably two or more (polyfunctional).

[0178] (i) Examples of the epoxy compound having a cycloalkene oxide structure include compounds represented by the following general formulas (i-1) to (i-3).

[0179]

[0180] M in the above general formula (i-1) １ and M ２ represents an alicyclic structure, and as described above, the number of carbon atoms therein is preferably 4 to 8, more preferably 5 to 6. X in the above general formula (i-1) １ is a single bond or a linking group. Examples of the linking group include a divalent hydrocarbon group, a carbonyl group, an ether group (ether bond), a thioether group (thioether bond), an ester group (ester bond), a carbonate group (carbonate bond), an amide group (amide bond), or a group in which a plurality of these groups are linked together.

[0181] Examples of divalent hydrocarbon groups that can be the linking group include alkylene groups having 1 to 18 carbon atoms and divalent alicyclic hydrocarbon groups. Examples of alkylene groups having 1 to 18 carbon atoms include methylene, methylmethylene, dimethylmethylene, ethylene, propylene, and trimethylene. Examples of divalent alicyclic hydrocarbon groups include divalent cycloalkylene groups (including cycloalkylidene groups) such as 1,2-cyclopentylene, 1,3-cyclopentylene, cyclopentylidene, 1,2-cyclohexylene, 1,3-cyclohexylene, 1,4-cyclohexylene, and cyclohexylidene.

[0182] Among them, X １is preferably a single bond or a linking group having an oxygen atom. The linking group having an oxygen atom is more preferably —CO— (carbonyl group), —O—CO—O— (carbonate group), —COO— (ester group), —O— (ether group), —CONH— (amide group), a group in which a plurality of these groups are linked together, or a group in which one or more of these groups are linked to one or more divalent hydrocarbon groups.

[0183] Specific examples of the alicyclic epoxy compound represented by the general formula (i-1) above include the following compounds. In the following formula, l is an integer of 1 to 10, and m is an integer of 1 to 30. R is an alkylene group having 1 to 8 carbon atoms (preferably an alkylene group having 1 to 3 carbon atoms, such as a methylene group, an ethylene group, a propylene group, or an isopropylene group). n1 and n2 are each an integer of 1 to 30.

[0184]

[0185] Examples of commercially available epoxy compounds represented by the general formula (i-1) include Celloxide 2021P, Celloxide 2081, Celloxide 8000, and Celloxide 8010 (manufactured by Daicel Corporation).

[0186] On the other hand, (i) the epoxy compound having a cycloalkene oxide structure may be, for example, a compound having a structure represented by the following general formula (i-2) or (i-3). M in the above general formulae (i-2) and (i-3) ３ , M ４ , and M ５ represents an alicyclic structure, the number of carbon atoms of which is preferably 4 to 8, more preferably 5 to 6. X in the above general formula (i-3) ２ is a single bond or a linking group. The linking group is the same as the linking group in the above-mentioned general formula (i-1). In addition, the compounds represented by general formulas (i-2) and (i-3) may have an alkyl group or the like bonded to a carbon that constitutes an alicyclic structure or an epoxy group.

[0187] Examples of the epoxy compound represented by the general formula (i-2) or (i-3) include 3,4:7,8-diepoxybicyclo[4.3.0]nonane, limonene dioxide, etc. Examples of commercially available products of these compounds include THI-DE (manufactured by JX-TG Corporation) and LDO (manufactured by Nagase Chemtec Corporation).

[0188] In any of the above-mentioned (i) epoxy compounds having a cycloalkene oxide, the weight average molecular weight is preferably 180 or more, more preferably 190 or more, and even more preferably 200 or more. The upper limit of the weight average molecular weight is appropriately selected depending on the viscosity of the composition, but is preferably 500 or less. When the weight average molecular weight of the (i) epoxy compound having a cycloalkene oxide is 180 or more, the physical properties of the first sealant and the second sealant tend to fall within the desired range. The weight average molecular weight of the epoxy compound is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0189] In particular, (i) the epoxy compound having a cycloalkene oxide is preferably a compound represented by the following formula, from the viewpoint that the physical properties of the first sealant and the second sealant are more likely to fall within the desired ranges:

[0190] When the thermosetting resin composition contains (i) an epoxy compound having a cycloalkene oxide, the total amount thereof is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 30% by mass or less, relative to the total amount of the thermosetting resin composition. When the amount of the epoxy compound is within this range, the physical properties of the first sealant and the second sealant are more likely to fall within the desired ranges.

[0191] On the other hand, examples of (ii) epoxy compounds having a dicyclopentadiene skeleton include compounds having a structure represented by the following general formula: Here, the bonding position of the group bonded to the dicyclopentadiene skeleton is not particularly limited. The thermosetting resin composition may contain only one type of compound having a structure represented by the following general formula, or may contain two or more types.

[0192] The epoxy compound is liquid at 25°C. (ii) The epoxy compound having a dicyclopentadiene skeleton may be prepared by a known method, or may be a commercially available product. Examples of commercially available products include EP-4088L and EP-4088S manufactured by ADEKA Corporation.

[0193] Furthermore, when the thermosetting resin composition contains (ii) an epoxy compound having a dicyclopentadiene skeleton, the total amount thereof is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 30% by mass or less, relative to the total amount of the thermosetting resin composition. When the amount of the epoxy compound is within this range, the physical properties of the first sealant and the second sealant are more likely to fall within the desired ranges.

[0194] (iii) A high-molecular-weight epoxy compound having a weight-average molecular weight of 3,000 or more is solid at room temperature (25°C). The weight-average molecular weight of the (iii) high-molecular-weight epoxy compound is preferably 3,000 to 100,000, more preferably 6,000 to 60,000, and even more preferably 7,000 to 40,000. When the thermosetting resin composition contains the (iii) high-molecular-weight epoxy compound, the physical properties of the first and second sealing materials tend to fall within the desired range, making them easier to mold into a sheet. Furthermore, when the (iii) high-molecular-weight epoxy compound has a weight-average molecular weight of 100,000 or less, the flowability of the thermosetting resin composition is improved, making it easier to bond the sheet-shaped thermosetting resin composition to each film when producing a laminate. The weight-average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0195] (iii) The high molecular weight epoxy compound may be an aromatic epoxy compound or an aliphatic epoxy compound, but a compound having an aromatic ring is more preferred.

[0196] Specific examples of aromatic epoxy compounds that can be the (iii) high-molecular-weight epoxy compounds include bisphenol-type epoxy resins such as bisphenol A, bisphenol F, bisphenol E, bisphenol S, bisphenol AD, and mixtures thereof; diphenyl ether-type epoxy resins; novolac-type epoxy resins such as phenol novolac, cresol novolac, biphenyl novolac, bisphenol novolac, naphthol novolac, trisphenol novolac, and dicyclopentadiene novolac; biphenyl-type epoxy resins; naphthyl-type epoxy resins; and triphenolalkane-type epoxy resins such as triphenolmethane, triphenolethane, and triphenolpropane.

[0197] Among the above, the aromatic epoxy compound is preferably a bisphenol-type epoxy resin or a biphenyl-type epoxy resin. However, as the amount of bisphenol F skeleton in the thermosetting resin composition increases, the softening point of the thermosetting resin composition tends to decrease. Therefore, when a sheet-like thermosetting resin composition and each film are laminated at a relatively high temperature, it is preferable that the thermosetting resin composition mainly contains an aromatic epoxy compound other than a bisphenol F skeleton.

[0198] Furthermore, the number of epoxy groups possessed by the (iii) high-molecular-weight epoxy compound is not particularly limited, but the epoxy equivalent is preferably 900 g / eq or more and 20,000 g / eq or less, and more preferably 1,000 g / eq or more and 20,000 g / eq or less. When the epoxy equivalent of the (iii) high-molecular-weight epoxy compound is 900 g / eq or more, the tackiness of the thermosetting resin composition at room temperature is reduced. Therefore, the handleability of the thermosetting resin composition when producing a laminate is likely to be improved. On the other hand, if the epoxy equivalent of the (iii) high-molecular-weight epoxy compound is excessively large, the solubility of the (iii) high-molecular-weight epoxy compound in solvents may decrease or its compatibility with other epoxy compounds may become poor. Therefore, the epoxy equivalent of the (iii) high-molecular-weight epoxy compound is preferably 20,000 g / eq or less.

[0199] The total amount of the (iii) high-molecular-weight epoxy compound relative to the total amount of the thermosetting resin composition is preferably 1% by mass to 50% by mass, more preferably 5% by mass to 40% by mass, and even more preferably 10% by mass to 35% by mass. When the amount of the (iii) high-molecular-weight epoxy compound in the thermosetting resin composition is within this range, the thermosetting resin composition can be easily formed into a sheet, and the lamination temperature with a film tends to be appropriate.

[0200] The (iv) flexibility-imparting epoxy compound may be an epoxy compound having a weight-average molecular weight of 300 or more but less than 3,000, and more preferably a weight-average molecular weight of 500 or more but less than 2,000. The (iv) flexibility-imparting epoxy compound may be either a solid or liquid at room temperature (25°C). The (iv) flexibility-imparting epoxy compound may be either an aromatic epoxy compound or an aliphatic epoxy compound.

[0201] Specific examples of the (iv) flexibility-imparting epoxy compound that is an aromatic epoxy compound include the aromatic epoxy compounds listed above as the (iii) high-molecular-weight epoxy compounds and similar resins (with the proviso that the molecular weight is 300 or more and less than 3,000).

[0202] On the other hand, when the (iv) flexibility-imparting epoxy compound is an aliphatic epoxy compound, the aliphatic epoxy compound may be a compound having one or more epoxy groups in the molecule and an aliphatic chain (excluding those corresponding to the epoxy compounds (i) to (iii) above). The aliphatic epoxy compound may have only one epoxy group, or may have two or more epoxy groups. Furthermore, the length of the aliphatic chain contained in the aliphatic epoxy compound is not particularly limited, but the number of carbon atoms in the molecule is preferably 10 to 1,000, and more preferably 50 to 200. Having 10 or more carbon atoms in the molecule makes it easier to impart flexibility to the first sealing material and the second sealing material. On the other hand, having 1,000 or less carbon atoms in the molecule makes it easier to be compatible with other components.

[0203] The total amount of the (iv) flexibility-imparting epoxy compound relative to the total amount of the thermosetting resin composition is preferably 15% by mass to 45% by mass, more preferably 20% by mass to 40% by mass, and even more preferably 25% by mass to 35% by mass. When the amount of the (iv) flexibility-imparting epoxy compound in the thermosetting resin composition is within this range, the physical properties of the first sealant and the second sealant tend to fall within desired ranges.

[0204] (B) Thermal Cationic Polymerization Initiator and Curing Agent The (B) thermal cationic polymerization initiator and curing agent are components for curing the above-mentioned (A) epoxy compound. The thermal cationic polymerization initiator may be any compound that generates active species capable of initiating cationic polymerization upon heating and is capable of cationic polymerizing the above-mentioned (A) epoxy compound. On the other hand, the curing agent may be any compound that is capable of reacting with the above-mentioned (A) epoxy compound to cure it. The thermosetting resin composition may contain either the thermal cationic polymerization initiator or the curing agent.

[0205] Examples of the thermal cationic polymerization initiator include sulfonium salts, phosphonium salts, quaternary ammonium salts, diazonium salts, and iodonium salts, among which quaternary ammonium salts or sulfonium salts are preferred. The anion moiety of these is AsF ６ － , SbF ６ － , P.F. ６ － , B(C ６ F ５ ) ４ － The thermosetting resin composition may contain only one type of thermal cationic polymerization initiator, or may contain two or more types of thermal cationic polymerization initiators.

[0206] The total amount of the thermal cationic polymerization initiator relative to the total amount of the thermosetting resin composition is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less. When the amount of the thermal cationic polymerization initiator is 0.5% by mass or more, the curability of the thermosetting resin composition becomes even better. On the other hand, when the amount of the thermal cationic polymerization initiator is 10% by mass or less, the storage stability of the thermosetting resin composition becomes even better.

[0207] On the other hand, the curing agent is preferably a thermal latent curing agent having a melting point of 50° C. or more and 250° C. or less, and more preferably a melting point of 50° C. or more and 150° C. or less. When the melting point of the curing agent is within this range, the epoxy compound (A) and the curing agent are unlikely to react at room temperature, and the storage stability of the thermosetting resin composition is improved.

[0208] Examples of the curing agent include dihydrazide-based thermal latent curing agents, imidazole-based thermal latent curing agents, amine adduct-based thermal latent curing agents, polyamine-based thermal latent curing agents, etc. The thermosetting resin composition may contain only one of these, or may contain two or more of them.

[0209] Examples of the dihydrazide-based thermal latent curing agent include adipic acid dihydrazide (melting point 181°C), 1,3-bis(hydrazinocarboethyl)-5-isopropylhydantoin (melting point 120°C), 7,11-octadecadiene-1,18-dicarbohydrazide (melting point 160°C), dodecanedioic acid dihydrazide (melting point 190°C), sebacic acid dihydrazide (melting point 189°C), and the like.

[0210] Examples of the imidazole-based thermal latent curing agent include 2,4-diamino-6-[2'-ethylimidazolyl-(1')]-ethyltriazine (melting point: 215 to 225°C), 2-phenylimidazole (melting point: 137 to 147°C), and the like.

[0211] The amine adduct thermal latent curing agent is a thermal latent curing agent consisting of an addition compound obtained by reacting an amine compound having catalytic activity with an arbitrary compound, and examples thereof include Amicure PN-40 (melting point 110°C), Amicure PN-23 (melting point 100°C), Amicure PN-31 (melting point 115°C), Amicure PN-H (melting point 115°C), Amicure MY-24 (melting point 120°C), and Amicure MY-H (melting point 131°C) (all manufactured by Ajinomoto Fine-Techno Co., Inc.).

[0212] The polyamine-based thermal latent curing agent is a thermal latent curing agent having a polymer structure obtained by reacting an amine with an epoxy, and examples thereof include ADEKA HARDNER EH4339S (softening point 120 to 130°C) and ADEKA HARDNER EH4357S (softening point 73 to 83°C) (both manufactured by ADEKA Corporation).

[0213] The amount of the curing agent relative to the total amount of the thermosetting resin composition is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 5% by mass. When the amount of the curing agent is within this range, the curability and storage stability of the thermosetting resin composition become even better.

[0214] (C) Tackifier When the thermosetting resin composition contains a tackifier (C), the adhesion between the first and second sealing materials and the film tends to be further improved. The tackifier (C) is preferably a resin selected from the group consisting of petroleum resins (aliphatic hydrocarbon resins, alicyclic hydrocarbon resins, and / or aromatic hydrocarbon resins), terpene resins, phenolic resins, and rosin resins. The thermosetting resin composition may contain only one type of tackifier (C), or may contain two or more types.

[0215] Examples of petroleum resins include C5 monomers or oligomers thereof obtained from pentene, pentadiene, isoprene, etc.; C9 monomers or oligomers thereof obtained from indene, methylindene, vinyltoluene, styrene, α-methylstyrene, β-methylstyrene, etc.; copolymers of C5 and C9 monomers (C5-C9 copolymer resins); alicyclic monomers or polymers thereof obtained from cyclopentadiene, dicyclopentadiene, etc.; aromatic monomers such as isopropenyl toluene or polymers thereof; hydrogenated products of the above-mentioned various monomers or polymers thereof; and modified petroleum resins obtained by modifying the above-mentioned various monomers or polymers thereof with maleic anhydride, maleic acid, fumaric acid, (meth)acrylic acid, phenol, etc.

[0216] Examples of terpene resins include α-pinene resin, β-pinene resin, α-pinene monomer, aromatic-modified terpene resin obtained by copolymerizing terpenes such as β-pinene monomer with aromatic monomers such as styrene and phenol.

[0217] Examples of phenolic resins include condensates of phenols and formaldehyde. Examples of phenols include phenol, m-cresol, 3,5-xylenol, p-alkylphenol, resorcinol, etc. Examples of the phenolic resins include resols obtained by addition reaction of these phenols with formaldehyde using an alkali catalyst, and novolacs obtained by condensation reaction using an acid catalyst. Phenolic resins also include rosin phenolic resins obtained by adding phenol to rosin using an acid catalyst and thermally polymerizing the resulting mixture.

[0218] Examples of rosin resins include gum rosin, wood rosin, or tall oil rosin; stabilized rosins or polymerized rosins obtained by disproportionating or hydrogenating these rosins; modified rosins obtained by modifying these rosins with maleic anhydride, maleic acid, fumaric acid, (meth)acrylic acid, phenol, or the like; and esters thereof. The alcohol used to obtain the esters is preferably a polyhydric alcohol. Examples of polyhydric alcohols include dihydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, and neopentyl glycol; trihydric alcohols such as glycerin, trimethylolethane, and trimethylolpropane; tetrahydric alcohols such as pentaerythritol and diglycerin; and hexahydric alcohols such as dipentaerythritol. These may be used alone or in combination during esterification.

[0219] The total amount of the tackifier (C) relative to the total amount of the thermosetting resin composition is preferably 1% by mass or more and 40% by mass or less, more preferably 5% by mass or more and 30% by mass or less. When the amount of the tackifier (C) is 5% by mass or more, the adhesion between the resulting first and second seal materials and the film tends to be even better. On the other hand, when the amount of the tackifier (C) is 30% by mass or less, the amount of the epoxy compound (A) mentioned above tends to be sufficiently large.

[0220] (D) Other Components Examples of other components include various resins, fillers, modifiers, stabilizers, etc. Examples of various resins include polyamide, polyamideimide, polyurethane, polybutadiene, polychloroprene, polyether, polyester, styrene-butadiene-styrene block copolymer, xylene resin, ketone resin, cellulose resin, fluorine-based oligomer, silicon-based oligomer, polysulfide-based oligomer, etc. The thermosetting resin composition may contain only one of these, or may contain two or more of them.

[0221] Examples of the filler include glass beads, styrene-based polymer particles, methacrylate-based polymer particles, ethylene-based polymer particles, propylene-based polymer particles, etc. The thermosetting resin composition may contain only one type of filler, or may contain two or more types of fillers.

[0222] Examples of the modifier include a polymerization initiator, an antioxidant, a leveling agent, a wettability improver, a surfactant, a plasticizer, a solvent, a silane coupling agent, etc. The thermosetting resin composition may contain only one type of these modifiers or may contain two or more types thereof.

[0223] Examples of the stabilizer include an ultraviolet absorber, an antiseptic, an antibacterial agent, etc. The thermosetting resin composition may contain only one kind of these, or may contain two or more kinds thereof.

[0224] (Method for Producing Laminate) The method for producing the laminate described above is not particularly limited, and it can be produced, for example, by the following method. The pair of films described above is prepared. Furthermore, the thermosetting resin composition for forming the first sheet and the thermosetting resin composition for forming the second sheet are each prepared. These thermosetting resin compositions are each dissolved in a solvent to form a varnish. Next, each is applied to a separate film or the like to a desired film thickness, and dried (to remove the solvent). Thereafter, the sheet-like thermosetting resin compositions (the thermosetting resin for the first sealant and the thermosetting resin for the second sealant) after solvent removal are bonded together. Furthermore, the pair of films are laminated by thermocompression bonding or the like. Thereafter, the epoxy compound (A) in each thermosetting resin composition is cured to obtain the laminate described above.

[0225] Examples of solvents that can dissolve the thermosetting resin composition include aromatic solvents such as toluene and xylene; ketone-based solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone; ethers such as ether, dibutyl ether, tetrahydrofuran, dioxane, ethylene glycol monoalkyl ether, ethylene glycol dialkyl ether, propylene glycol or dialkyl ether; aprotic polar solvents such as N-methylpyrrolidone, dimethylimidazolidinone and dimethylformaldehyde; and esters such as ethyl acetate and butyl acetate.

[0226] When preparing a varnish containing the thermosetting resin composition, the components may be mixed at once, or only the epoxy compound (A) may be dissolved in a solvent and then the other components may be mixed in. Examples of methods for mixing the components include known stirring methods and triple-roll kneading methods.

[0227] The method for applying the varnish is not particularly limited, and examples thereof include screen printing, dispenser application, various roll methods, etc. The thickness of the applied varnish is appropriately selected depending on the desired film thickness of the sealing material.

[0228] The method for drying the varnish, i.e., the method for removing the solvent, is not particularly limited, and examples thereof include heating. The heating temperature and drying time are preferably set to a temperature and time that do not cause the epoxy compound (A) to cure. For example, the drying temperature is 20 to 100°C, and the drying time can be, for example, about 1 minute to 3 hours. The drying method is not particularly limited, and examples thereof include hot air drying and vacuum drying.

[0229] Alternatively, the varnish may be applied directly onto a film to form the thermosetting resin composition into a sheet. However, a more preferred method involves applying the varnish onto a known separate film, removing the solvent to obtain a sheet-like thermosetting resin composition, and then laminating the sheet-like thermosetting resin composition and the film. This method makes it difficult for the solvent or the heat generated during solvent removal to alter or deteriorate the film.

[0230] Furthermore, the method for laminating two layers of sheet-like thermosetting resin composition together and then laminating them with the first film and the second film is not particularly limited, and lamination can be performed, for example, by thermocompression bonding. For example, a first film and a second film may be placed on both sides of a two-layer thermosetting resin composition, respectively, and the first film and the second film may be simultaneously thermocompression bonded to the thermosetting resin composition. However, it is more preferable to first superpose the thermosetting resin composition on one of the first film and the second film and thermocompression bond it, and then thermocompression bond the other film to the thermosetting resin composition. When sequential thermocompression bonding is performed, the temperature for at least the first thermocompression bonding is preferably 50°C or higher and 120°C or lower, more preferably 70°C or higher and 100°C or lower. By performing thermocompression bonding at this temperature for a short period of time, lamination is possible without curing the epoxy compound (A) in each thermosetting resin composition.

[0231] After laminating the first film, the two-layer thermosetting resin composition, and the second film, the laminate is further heated to cure the epoxy compound (A) in the thermosetting resin composition. The heating temperature is preferably 60°C or higher and 200°C or lower, and more preferably 70°C or higher and 120°C or lower. The heating time is more preferably 20 minutes or higher and 120 minutes or lower. By using the heating temperature and heating time, the epoxy compound (A) in the thermosetting resin composition can be sufficiently cured.

[0232] (4) Others The laminate may include the pair of films described above and the first and second sealing materials disposed therebetween, and may include other layers as long as the purpose and effect of this embodiment are not impaired.

[0233] The laminate can be used as a cover member for a display device including a touch panel as described above, a cover member for various display devices (e.g., an organic EL display device), a protective layer for an in-vehicle instrument panel, or a protective layer for a vibration-sensing portion or a light-receiving portion of a sensor or the like.

[0234] 3-2. Display Device This embodiment also provides a display device including the above-described laminate. Specifically, the present invention provides a display device including a display element and the above-described laminate disposed on the display element. The display element and the laminate can be bonded with a known optical adhesive or the like. Furthermore, a touch panel element or the like may be further disposed between the display element and the laminate.

[0235] Here, the laminate is preferably disposed on the display surface side of the display device, preferably in a position that directly contacts the cover member, i.e., the user. The orientation of the laminate, i.e., the relative positions of the first and second sealants, is appropriately selected depending on the type and structure of the display element. However, it is generally preferable that the second sealant be disposed closer to the display element than the first sealant. By disposing the second sealant, which has a high elastic modulus, on the display element side, stress can be absorbed by the first sealant, and the second sealant can protect the display element, for example, when a load is applied by a touch pen.

[0236] 4. Fourth Embodiment 4-1. Sheet-Like Sealing Material The sheet-like sealing material of the fourth embodiment of the present invention is cured by heating and is suitable for use as a surface sealing material for adhering two members together or filling the gap between them. The sheet-like sealing material of the present invention is particularly suitable as a material for a cover film of a foldable display device. Hereinafter, an example will be described in which the sheet-like sealing material is used as a cover film for a display device. However, the use of the sheet-like sealing material is not limited to this use.

[0237] As described above, when a surface sealing material, which is a cured product of a conventional sheet-like sealing material, is subjected to a local load or is bent, whitening tends to occur in the area where the load is applied. After extensive research, the present inventors have found that a typical sheet-like sealing material (and a surface sealing material) contains a base resin and a tackifier, forming a sea-island structure in which the base resin forms the sea and the tackifier forms the islands. Figure 1A shows a photograph of a typical sheet-like sealing material observed with a scanning electron microscope (SEM). It has been found that when a load is applied to the cured product (surface sealing material), cracks tend to occur at the interface between the sea and island parts of the sea-island structure, and these cracks cause whitening.

[0238] Therefore, in this embodiment, when the surface of a sheet-shaped sealing material containing an epoxy resin and a tackifier is observed with a scanning electron microscope, the number of islands in the sea-island structure contained in a 200 μm × 200 μm area is set to 10 or less. Figure 1B shows a scanning electron microscope (SEM) photograph of the sheet-shaped sealing material of this embodiment (example). By limiting the number of islands per unit area to 10 or less, cracks are less likely to occur in the sheet-shaped sealing material, and whitening is suppressed. The number of islands is preferably 10 or less, and more preferably 0. The number of islands in the sea-island structure is determined by observing a 200 μm × 200 μm area at any location where the resin of the sheet-shaped sealing material is exposed with a scanning electron microscope. The number of islands contained in each area is then calculated, and the average value is used as the number of islands per unit area of ​​the sheet-shaped sealing material. Note that the number of islands is highly dependent on the compatibility between the epoxy resin and the tackifier. Therefore, it can be adjusted by the type, composition, ratio, etc. of the epoxy compound and tackifier described below.

[0239] The sheet-like sealing material may be a composition containing, for example, (A) an epoxy compound, (B) a tackifier, and (C) a thermal cationic polymerization initiator and / or a curing agent. If necessary, other components may also be included. Each component will be described in detail below.

[0240] (A) Epoxy Compound In this specification, the term "epoxy compound" refers to a compound having one or more epoxy groups in one molecule. The epoxy compound is not particularly limited as long as it has high compatibility with the tackifier (B) described below and can impart the desired strength, impact absorption, etc. to the sheet-like sealing material. In particular, the epoxy compound (A) preferably includes an alicyclic epoxy compound (A-1) and an aromatic ring-containing epoxy compound (A-2).

[0241] (A-1) Alicyclic Epoxy Compound In this specification, (A-1) alicyclic epoxy compound refers to a compound having one or more epoxy groups and an alicyclic structure in one molecule. The (A-1) alicyclic epoxy compound is preferably a compound that is liquid at room temperature (23°C). The number of epoxy groups contained in the (A-1) alicyclic epoxy compound is preferably 2 or more, more preferably 2 or more and 4 or less. The sheet-like sealing material may contain only one type of (A-1) alicyclic epoxy compound, or may contain two or more types.

[0242] Examples of the (A-1) alicyclic epoxy compound include compounds having a cycloalkene oxide structure represented by the following general formula: The cycloalkene oxide structure is a structure obtained by epoxidizing a cycloalkene with an oxidizing agent such as a peroxide, and has an aliphatic ring and an epoxy group composed of two carbon atoms and an oxygen atom that constitute the aliphatic ring. In the above general formula, M represents an alicyclic structure, and the number of carbon atoms therein is preferably 4 to 8, and more preferably 5 to 6. When the number of carbon atoms in the alicyclic structure of the cycloalkene oxide structure is within this range, compatibility between the epoxy compound (A) and the tackifier (B) tends to be good, and when the composition is made into a sheet-like sealing material, a sea-island structure is unlikely to occur.

[0243] Specific examples of the cycloalkene oxide structure include cyclohexene oxide and cyclopentene oxide, with cyclohexene oxide being preferred.

[0244] The number of cycloalkene oxide structures contained in one molecule of the alicyclic epoxy compound (A-1) may be one (monofunctional) or two or more (polyfunctional). Of these, the number of cycloalkene oxide structures contained in one molecule of the alicyclic epoxy compound is preferably two or more (polyfunctional).

[0245] Examples of the alicyclic epoxy compound (A-1) having a cycloalkene oxide structure include compounds represented by the following general formulas (a-1) to (a-3).

[0246]

[0247] M in the above general formula (a-1) １ and M ２ represents an alicyclic structure, and as described above, the number of carbon atoms therein is preferably 4 to 8, more preferably 5 to 6. X in the above general formula (a-1) １ is a single bond or a linking group. Examples of the linking group include a divalent hydrocarbon group, a carbonyl group, an ether group (ether bond), a thioether group (thioether bond), an ester group (ester bond), a carbonate group (carbonate bond), an amide group (amide bond), or a group in which a plurality of these groups are linked together.

[0248] Examples of divalent hydrocarbon groups that can be the linking group include alkylene groups having 1 to 18 carbon atoms and divalent alicyclic hydrocarbon groups. Examples of alkylene groups having 1 to 18 carbon atoms include methylene, methylmethylene, dimethylmethylene, ethylene, propylene, and trimethylene. Examples of divalent alicyclic hydrocarbon groups include divalent cycloalkylene groups (including cycloalkylidene groups) such as 1,2-cyclopentylene, 1,3-cyclopentylene, cyclopentylidene, 1,2-cyclohexylene, 1,3-cyclohexylene, 1,4-cyclohexylene, and cyclohexylidene.

[0249] Among them, X １ is preferably a single bond or a linking group having an oxygen atom. The linking group having an oxygen atom is more preferably —CO— (carbonyl group), —O—CO—O— (carbonate group), —COO— (ester group), —O— (ether group), —CONH— (amide group), a group in which a plurality of these groups are linked together, or a group in which one or more of these groups are linked to one or more divalent hydrocarbon groups.

[0250] Specific examples of the alicyclic epoxy compound represented by general formula (a-1) include the following compounds. In the following formula, l is an integer of 1 to 10, and m is an integer of 1 to 30. R is an alkylene group having 1 to 8 carbon atoms (preferably an alkylene group having 1 to 3 carbon atoms, such as a methylene group, an ethylene group, a propylene group, or an isopropylene group). n1 and n2 are each an integer of 1 to 30.

[0251]

[0252] Examples of commercially available alicyclic epoxy compounds represented by the general formula (a-1) include Celloxide 2021P, Celloxide 2081, Celloxide 8000, and Celloxide 8010 (manufactured by Daicel Corporation).

[0253] As described above, the alicyclic epoxy compound (A-1) may be, for example, a compound having a structure represented by the following general formula (a-2) or (a-3). M in the above general formulae (a-2) and (a-3) ３ , M ４ , and M ５ represents an alicyclic structure, the number of carbon atoms of which is preferably 4 to 8, more preferably 5 to 6. X in the above general formula (a-3) ２ is a single bond or a linking group. The linking group is the same as the linking group in the above-mentioned general formula (a-1). In addition, the compounds represented by general formulas (a-2) and (a-3) may have an alkyl group or the like bonded to a carbon that constitutes an alicyclic structure or an epoxy group.

[0254] Examples of the alicyclic epoxy compounds represented by the general formula (a-2) or (a-3) include 3,4:7,8-diepoxybicyclo[4.3.0]nonane, limonene dioxide, etc. Commercially available examples of these compounds include THI-DE (manufactured by JX-TG Corporation) and LDO (manufactured by Nagase Chemtec Corporation).

[0255] In any of the above-mentioned (A-1) alicyclic epoxy compounds, the weight average molecular weight is preferably 180 or more, more preferably 190 or more, and even more preferably 200 or more. The upper limit of the weight average molecular weight is appropriately selected depending on the desired viscosity of the sheet-like sealing material, but is preferably 500 or less. When the weight average molecular weight of the alicyclic epoxy compound is 180 or more, the handleability of the sheet-like sealing material is improved. The weight average molecular weight of the (A-1) alicyclic epoxy compound is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0256] From the viewpoints of compatibility with the tackifier and the likelihood that the sheet-shaped sealing material will have the desired physical properties, the alicyclic epoxy compound (A-1) is particularly preferably a compound represented by the following formula: In addition, the alicyclic epoxy compound has low viscosity when uncured, which improves handleability during processing.

[0257] The total amount of the alicyclic epoxy compound (A-1) relative to the total amount of the sheet-like sealing material is preferably 5% by mass to 40% by mass, more preferably 10% by mass to 30% by mass. When the amount of the alicyclic epoxy compound (A-1) is within this range, the sheet-like sealing material tends to be easy to handle, and the adhesive strength between the sheet-like sealing material and various members (e.g., substrates) tends to be good.

[0258] (A-2) Aromatic Ring-Containing Epoxy Compound The (A-2) aromatic ring-containing epoxy compound may be any compound having at least one epoxy group and at least one aromatic ring in the molecule. The sheet-like sealing material may contain only one type of (A-2) aromatic ring-containing epoxy compound, or may contain two or more types.

[0259] The type of aromatic ring-containing epoxy compound (A-2) is not particularly limited. For example, it may be an aromatic ring-containing polymeric epoxy compound that is solid at room temperature (23°C) and has a weight-average molecular weight of 3,000 to 100,000. The weight-average molecular weight of the aromatic ring-containing polymeric epoxy compound is preferably 6,000 to 60,000, more preferably 7,000 to 40,000. When the molecular weight of the aromatic ring-containing polymeric epoxy compound is 3,000 or more, the aromatic ring-containing polymeric epoxy compound (A-2) tends to become solid at room temperature. On the other hand, when the weight-average molecular weight of the aromatic ring-containing polymeric epoxy compound is 100,000 or less, the fluidity of the sheet-like sealing material can be increased when it is bonded to other components, making it easier to adhere to various structures. The weight-average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0260] Furthermore, the epoxy equivalent of the aromatic ring-containing polymeric epoxy compound having the above weight-average molecular weight is preferably 900 g / eq or more and 20,000 g / eq or less, more preferably 1,000 g / eq or more and 200,000 g / eq or less. When the epoxy equivalent of the aromatic ring-containing polymeric epoxy compound is 900 g / eq or more, the tackiness of the sheet-like sealing material at room temperature is reduced. As a result, the handling ability when laminating the sheet-like sealing material to various components is improved, making it easier to accurately laminate it onto various components. On the other hand, if the epoxy equivalent of the aromatic ring-containing polymeric epoxy compound having the above weight-average molecular weight is excessively large, the solubility of the aromatic ring-containing polymeric epoxy compound in solvents may decrease or the compatibility with the (A-1) alicyclic epoxy compound may become poor during the preparation of the sheet-like sealing material. Therefore, the epoxy equivalent of the aromatic ring-containing polymeric epoxy compound is preferably 20,000 g / eq or less. When the epoxy equivalent of the aromatic ring-containing polymeric epoxy compound is within the above range, the melting temperature of the sheet-like sealing material is within an appropriate range, and it becomes possible to attach it to a member at a desired temperature. When a plurality of epoxy compounds are used as the aromatic ring-containing polymeric epoxy compound, it is preferable that the epoxy equivalent of each epoxy compound is within the above range.

[0261] On the other hand, the aromatic ring-containing epoxy compound (A-2) may be an aromatic ring-containing low-molecular-weight epoxy compound having a weight-average molecular weight of less than 3,000.

[0262] Here, whether the aromatic ring-containing epoxy compound (A-2) is an aromatic ring-containing high molecular weight epoxy compound or an aromatic ring-containing low molecular weight epoxy compound, the aromatic ring-containing epoxy compound (A-2) is sufficient as long as it contains one or more epoxy groups in the molecule, but preferably contains multiple epoxy groups so as to satisfy the above-mentioned epoxy equivalent. Furthermore, the aromatic ring-containing epoxy compound (A-2) is sufficient as long as it contains one or more aromatic rings in the molecule, and the number of aromatic rings is not particularly limited.

[0263] Examples of the aromatic ring-containing epoxy compound (A-2) include bisphenol-type epoxy resins such as bisphenol A type, bisphenol F type, bisphenol E type, bisphenol S type, bisphenol AD ​​type, and mixtures thereof; diphenyl ether-type epoxy resins; novolac-type epoxy resins such as phenol novolac type, cresol novolac type, biphenyl novolac type, bisphenol novolac type, naphthol novolac type, trisphenol novolac type, and dicyclopentadiene novolac type; biphenyl-type epoxy resins; naphthyl-type epoxy resins; and triphenolalkane-type epoxy resins such as triphenolmethane type, triphenolethane type, and triphenolpropane type.

[0264] Among the above, the aromatic ring-containing epoxy compound (A-2) is preferably a bisphenol-type epoxy resin or a biphenyl-type epoxy resin. Note that, as the amount of bisphenol F skeleton in the aromatic ring-containing epoxy compound (A-2) increases, the softening point of the aromatic ring-containing epoxy compound (A-2) tends to decrease. Therefore, when the lamination temperature of the sheet-like sealing material is set to a relatively high temperature, it is preferable to use an epoxy resin with a small amount of bisphenol F skeleton.

[0265] The total amount of the aromatic ring-containing epoxy compound (A-2) relative to the total amount of the sheet-like sealing material is preferably 5% by mass to 60% by mass, more preferably 10% by mass to 50% by mass, and even more preferably 20% by mass to 40% by mass. When the amount of the aromatic ring-containing epoxy compound (A-2) in the sheet-like sealing material is within this range, the shape stability of the sheet-like sealing material is improved, and the lamination temperature is likely to be appropriate.

[0266] The sheet-like sealing material may further contain an epoxy compound (hereinafter also referred to as "other epoxy compound") that does not correspond to the above-mentioned (A-1) alicyclic epoxy compound or (A-2) aromatic ring-containing epoxy compound. The sheet-like sealing material may contain only one type of other epoxy compound, or may contain two or more types.

[0267] Examples of other epoxy compounds include aliphatic epoxy compounds. The aliphatic epoxy compound may be a resin having only one epoxy group in the molecule, or may be a resin having two or more epoxy groups. The structure of the aliphatic chain is not particularly limited. The type and amount of the other epoxy compound are preferably determined taking into consideration the compatibility with the tackifier (B).

[0268] (B) Tackifier As described above, the sheet-like sealing material contains a tackifier (B). The tackifier (B) is a component that imparts adhesiveness when the sheet-like sealing material is bonded to another component. As described above, if the compatibility between the epoxy compound (A) and the tackifier (B) is low, a sea-island structure is likely to be formed on the surface of the sheet-like sealing material. The sheet-like sealing material may contain only one type of tackifier (B), or may contain two or more types.

[0269] The type of (B) tackifier is not particularly limited as long as it is a component that is compatible with the (A) epoxy compound and does not readily form a sea-island structure. Examples of (B) tackifiers that do not readily form a sea-island structure with the (A) epoxy compound include tackifiers with relatively high polarity, such as mixtures of terpene resins and phenolic resins, i.e., terpene-phenol tackifiers; xylene-based tackifiers (Y-50, Y-100, etc., manufactured by Fudow Co., Ltd.); and alkylphenol tackifiers (Tackifiers 510, 7509, etc., manufactured by Arakawa Chemical Industries, Ltd.). Among these, mixtures of terpene resins and phenolic resins, i.e., terpene-phenol tackifiers, are particularly preferred. Furthermore, in this case, it is preferable that the amount of the terpene resin is less than 50% by mass relative to the total amount of the terpene resin and phenolic resin. If the amount of the terpene resin in a terpene-phenol PSA is less than 50% by mass, it becomes significantly more difficult to form a sea-island structure.

[0270] Examples of the terpene resin in the terpene phenol-based tackifier include α-pinene resin, β-pinene resin, α-pinene monomer, β-pinene monomer, or other terpenes copolymerized with aromatic monomers such as styrene and phenol.

[0271] Examples of phenolic resins in the terpene phenol-based tackifiers include condensates of phenols and formaldehyde. Examples of phenols include phenol, m-cresol, 3,5-xylenol, p-alkylphenol, resorcinol, etc. Examples of the phenolic resins include resols obtained by addition reaction of these phenols with formaldehyde using an alkali catalyst, and novolaks obtained by condensation reaction using an acid catalyst. Phenolic resins also include rosin phenolic resins obtained by adding phenol to rosin using an acid catalyst and thermally polymerizing the resulting mixture.

[0272] The content of the tackifier (B) relative to 100 parts by mass of the epoxy compound (A) is preferably 1 part by mass or more and 40 parts by mass or less, and more preferably 5 parts by mass or more and 30 parts by mass or less. When the ratio of the amount of the epoxy compound (A) to the amount of the tackifier (B) is within this range, the formation of the above-mentioned sea-island structure becomes even more unlikely.

[0273] (C) Thermal Cationic Polymerization Initiator or Curing Agent The sheet-like sealing material may contain (C) a thermal cationic polymerization initiator or curing agent for curing the above-mentioned (A) epoxy compound. The thermal cationic polymerization initiator may be any compound that generates active species capable of initiating cationic polymerization upon heating and is capable of cationic polymerizing the above-mentioned (A) epoxy compound. On the other hand, the curing agent may be any compound that is capable of reacting with the above-mentioned (A) epoxy compound to cure it. The sheet-like sealing material may contain both a thermal cationic polymerization initiator and a curing agent, but it is usually preferable to contain either one of them.

[0274] Examples of the thermal cationic polymerization initiator include sulfonium salts, phosphonium salts, quaternary ammonium salts, diazonium salts, and iodonium salts, among which quaternary ammonium salts or sulfonium salts are preferred. The anion moiety of these is AsF ６ － , SbF ６ － , P.F. ６ － , B(C ６ F ５ )４ － The sheet-shaped sealing material may contain only one type of thermal cationic polymerization initiator, or may contain two or more types.

[0275] The total amount of the thermal cationic polymerization initiator relative to the total amount of the sheet-shaped sealing material is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less. When the amount of the thermal cationic polymerization initiator is 0.5% by mass or more, the curability of the sheet-shaped sealing material is further improved. On the other hand, when the amount of the thermal cationic polymerization initiator is 10% by mass or less, the storage stability of the sheet-shaped sealing material is further improved.

[0276] On the other hand, the curing agent is preferably a thermal latent curing agent having a melting point of 50° C. or more and 250° C. or less, and more preferably a melting point of 50° C. or more and 150° C. or less. When the melting point of the curing agent is within this range, the epoxy compound (A) and the curing agent are unlikely to react at room temperature, and the storage stability of the sheet-like sealing material is improved.

[0277] Examples of the curing agent include dihydrazide-based thermal latent curing agents, imidazole-based thermal latent curing agents, amine adduct-based thermal latent curing agents, polyamine-based thermal latent curing agents, etc. The sheet-like sealing material may contain only one of these, or may contain two or more of them.

[0278] Examples of the dihydrazide-based thermal latent curing agent include adipic acid dihydrazide (melting point 181°C), 1,3-bis(hydrazinocarboethyl)-5-isopropylhydantoin (melting point 120°C), 7,11-octadecadiene-1,18-dicarbohydrazide (melting point 160°C), dodecanedioic acid dihydrazide (melting point 190°C), sebacic acid dihydrazide (melting point 189°C), and the like.

[0279] Examples of the imidazole-based thermal latent curing agent include 2,4-diamino-6-[2'-ethylimidazolyl-(1')]-ethyltriazine (melting point: 215 to 225°C), 2-phenylimidazole (melting point: 137 to 147°C), and the like.

[0280] The amine adduct thermal latent curing agent is a thermal latent curing agent consisting of an addition compound obtained by reacting an amine compound having catalytic activity with an arbitrary compound, and examples thereof include Amicure PN-40 (melting point 110°C), Amicure PN-23 (melting point 100°C), Amicure PN-31 (melting point 115°C), Amicure PN-H (melting point 115°C), Amicure MY-24 (melting point 120°C), and Amicure MY-H (melting point 131°C) (all manufactured by Ajinomoto Fine-Techno Co., Inc.).

[0281] The polyamine-based thermal latent curing agent is a thermal latent curing agent having a polymer structure obtained by reacting an amine with an epoxy, and examples thereof include ADEKA HARDNER EH4339S (softening point 120 to 130°C) and ADEKA HARDNER EH4357S (softening point 73 to 83°C) (both manufactured by ADEKA Corporation).

[0282] The amount of the curing agent relative to the total amount of the sheet-like sealing material is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 5% by mass. When the amount of the curing agent is within this range, the curability and storage stability of the sheet-like sealing material are further improved.

[0283] (D) Other Components The sheet-like sealing material may contain a resin other than the above-described (A) epoxy-based compound, as long as the purpose and effect of this embodiment are not impaired. Examples of other resins include polyamide, polyamideimide, polyurethane, polybutadiene, polychloroprene, polyether, polyester, styrene-butadiene-styrene block copolymer, xylene resin, ketone resin, cellulose resin, fluorine-based oligomer, silicon-based oligomer, polysulfide-based oligomer, etc. The sheet-like sealing material may contain only one of these, or may contain two or more of them.

[0284] Furthermore, the sheet-like sealing material may further contain fillers, modifiers, stabilizers, etc., within the scope that does not impair the object and effect of this embodiment. Examples of fillers include glass beads, styrene-based polymer particles, methacrylate-based polymer particles, ethylene-based polymer particles, propylene-based polymer particles, etc. The sheet-like sealing material may contain only one type of filler, or may contain two or more types of fillers.

[0285] Specific examples of the modifier include a polymerization initiator, an antioxidant, a leveling agent, a wettability improver, a surfactant, a plasticizer, a solvent, a silane coupling agent, etc. The sheet-like sealing material may contain only one type of these modifiers, or may contain two or more types.

[0286] On the other hand, specific examples of stabilizers include ultraviolet absorbers, preservatives, antibacterial agents, etc. The sheet-like sealing material may contain only one of these, or may contain two or more of them.

[0287] However, the amount of other components is preferably 10% by mass or less, and more preferably 5% by mass or less, based on the total amount of the sheet-shaped sealing material.

[0288] (E) Physical Properties of Sheet-Like Sealing Material The sheet-like sealing material may be a resin composition containing the above-mentioned (A) epoxy compound, (B) tackifier, (C) thermal cationic polymerization initiator or curing agent, and, if necessary, (D) other components, molded into a sheet shape. The sheet-like sealing material has adhesive properties. The sheet-like sealing material may have a separator disposed on one or both surfaces, for example. Furthermore, as described below in the laminate, a desired substrate may be disposed on one or both surfaces.

[0289] The thickness of the sheet-like sealing material is appropriately selected depending on the application of the sheet-like sealing material, but when used as a surface sealing material for a cover film, it is preferably 3 μm or more and 100 μm or less, and more preferably 7 μm or more and 40 μm or less. When the thickness of the sheet-like sealing material is 3 μm or more, the surface sealing material made of the cured product of the sheet-like sealing material can easily absorb and relieve stress applied to the substrate and other components, making it easier to suppress cracks and dents in the substrate, etc. In addition, whitening of the surface sealing material is also less likely to occur. On the other hand, when the thickness of the sheet-like sealing material is 100 μm or less, it becomes easier to reduce the thickness and weight of the display device.

[0290] The storage modulus at 25°C of the sheet-like sealing material, obtained by dynamic viscoelasticity measurement at a temperature rise rate of 5°C / min and a frequency of 1 Hz after heating at 100°C for 1 hour, is preferably 0.31 GPa to 3.1 GPa, more preferably 0.34 GPa to 1.8 GPa. When the storage modulus of the sheet-like sealing material is within this range, even if a local load is applied to a laminate including a planar sealing material made of a cured product of the sheet-like sealing material, the planar sealing material can easily absorb or disperse the load. The storage modulus of the cured product of the sheet-like sealing material can be adjusted by the type of epoxy compound (A) and the amount of tackifier (B) described above.

[0291] The melting temperature of the sheet-shaped sealing material is preferably 35° C. or higher and 60° C. or lower. However, it is preferable to adjust the temperature appropriately depending on the lamination method when laminating the sheet-shaped sealing material to another member and the object to be laminated. For example, when lower tackiness during lamination is required, the melting temperature is preferably set to 40 to 56° C.

[0292] Furthermore, when the sheet-shaped sealing material is bonded to various components, the sheet-shaped sealing material is softened (melted), making it less likely to form gaps between the various components. If the melting temperature of the sheet-shaped sealing material is 60°C or lower, the sheet-shaped sealing material can be bonded to various components at a relatively low temperature (60°C or lower). On the other hand, if the melting temperature of the sheet-shaped sealing material is 35°C or higher, the tackiness of the sheet-shaped sealing material during operation (tackiness at room temperature) is reduced, making it easier to work with. Furthermore, the sheet-shaped sealing material is less likely to deform during storage, and can maintain its shape.

[0293] The melting temperature can be measured as follows. A strip-shaped test piece is prepared by cutting a sheet-like sealing material into a length of approximately 30 mm and a width of approximately 5 mm. This test piece is then adhered to a glass plate heated on a hot plate. The test piece is then gradually peeled off from the glass plate in a 180° direction. This operation is started with the hot plate set at 40°C, and is repeated by preparing a new strip-shaped test piece every time the set temperature is increased by 1°C. The temperature at which the adhesive peelability of the layer made of the sheet-like sealing material is greatest upon peeling is taken as the melting temperature. However, if the adhesive peelability is already high at 40°C, the melting temperature is measured from 25°C.

[0294] Furthermore, the melting temperature of the sheet-shaped sealing material after storage at 40°C for 17 hours preferably falls within a range of ±10°C of the melting temperature of the sheet-shaped sealing material before storage, and more preferably within ±5°C. This temperature change serves as an indicator of the storage stability of the sheet-shaped sealing material, and if the temperature change is 10°C or less, it can be said that a curing reaction or the like is unlikely to occur during storage. Furthermore, if the melting temperature of the sheet-shaped sealing material changes significantly during storage, it becomes necessary to change the temperature, pressure, etc. when laminating the sheet-shaped sealing material in accordance with this change. In contrast, if the melting temperature change after storage at 40°C for 17 hours is within 10°C, there is no need to significantly change the lamination conditions, and there is also the advantage that the sheet-shaped sealing material can be efficiently laminated to other components.

[0295] On the other hand, the heat generation onset temperature of the sheet-like sealing material measured by a differential scanning calorimeter (DSC) is preferably 60°C or higher and 90°C or lower, and more preferably 65 to 85°C. If the heat generation onset temperature is 60°C or higher, the epoxy compound (A) is less likely to harden when the sheet-like sealing material is used to produce a laminate described below, or when the produced laminate is stored, resulting in good storage stability. On the other hand, if the heat generation onset temperature is 90°C or lower, the sheet-like sheet material can be cured at 90°C or lower, and is less likely to affect the object to be bonded. The heat generation onset temperature can be measured by the following method. First, 10 mg of the sheet-like sealing material is sampled and placed in an aluminum cell for DSC measurement to prepare a measurement test sample. Then, the temperature characteristics of the measurement test sample are measured at a temperature rise rate of 5°C / min and a measurement temperature range of 20°C to 300°C, thereby determining the heat generation onset temperature.

[0296] On the other hand, when the sheet-shaped sealing material is heated at 85°C for 50 minutes, the epoxy reaction rate is preferably 80% or more, and more preferably 85% or more. The epoxy reaction rate is an index of the curability when the sheet-shaped sealing material is cured at 85°C, and the higher the value, the easier the sheet-shaped sealing material is to cure even at low temperatures. If the epoxy reaction rate is 80% or more, it can be said that the sheet-shaped sealing material can be sufficiently cured even at 90°C or less.

[0297] The epoxy reaction rate can be measured as follows. First, a sheet-shaped sealing material (sample) is placed in an oven previously set to 85°C. Then, 50 minutes after the sample is placed in, the measurement sample is removed. The calorific value of the cured product is determined by DSC at a temperature rise rate of 5°C / min and a measurement temperature range of 20°C to 300°C. Then, based on the measured calorific value and the calorific value in the uncured state described above, the epoxy reaction rate is calculated using the following formula: Epoxy reaction rate (%) = (calorific value of uncured product - calorific value after curing) / calorific value of uncured product x 100

[0298] Furthermore, when a 20 μm-thick sheet-like sealing material is cured for 50 minutes at 85° C., the transmittance of light with a wavelength of 550 nm is preferably 90% or more, more preferably 95% or more, and even more preferably 97% or more. When the cured product of the sheet-like sealing material has a light transmittance of 90% or more, the optical properties tend to be even better when the sheet-like sealing material is used as a surface sealing material for a cover film.

[0299] The light transmittance of the cured product of the sheet-like sealing material can be measured by the following procedure. A laminate consisting of a substrate film and a 20 μm-thick sheet-like sealing material formed on the substrate film is cut into a length of approximately 60 mm and a width of approximately 40 mm to obtain a test piece. The layer consisting of the sheet-like sealing material of this test piece is transferred and bonded to a glass plate (No. 3, manufactured by Matsunami Glass, 0.3 mm thick, 70 mm x 50 mm) heated on a hot plate heated to 70°C using a roll, taking care not to introduce air bubbles. The test piece is removed from the hot plate and allowed to cool for 3 minutes. Thereafter, the substrate film is peeled off, and the sheet-like sealing material on the glass plate is heated in an oven at 85°C for 50 minutes to obtain a cured product. The light transmittance at a wavelength of 550 nm of the glass plate on which the cured product of the sheet-like sealing material has been formed is measured using an ultraviolet-visible spectrophotometer (Shimadzu Corporation UV-2550). In the measurement, the light transmittance of the glass plate alone is used as the baseline. The transmittance may be measured using a sheet-like sealing material having a thickness other than 20 μm. In this case, the obtained transmittance is converted into the transmittance when the thickness of the sheet-like sealing material is 20 μm.

[0300] 4-2. Laminate The laminate may have a substrate and the above-mentioned sheet-like sealing material or a cured product thereof disposed on the substrate. In the laminate, the substrate may be disposed on only one side of the sheet-like sealing material, or on both sides. Furthermore, when substrates are disposed on both sides, these may be the same substrate or different substrates. Furthermore, the sheet-like sealing material may be in an uncured state (before the above-mentioned epoxy compound (A) is cured) or in a cured state.

[0301] Here, the substrate to be laminated with the sheet-like sealing material is appropriately selected depending on the application. When the laminate is used as a cover film, the substrate is preferably a film that is foldable, light-transmitting, and has desired optical properties. The substrate may be a film made of an inorganic material or a film made of a resin. Examples of preferred materials for the film include inorganic materials such as glass; and organic materials such as polyimide, transparent polyimide (CPI), polyethylene terephthalate (PET), and polyethylene (PE).

[0302] The thickness of the substrate is not particularly limited, but is preferably a thin film. In this specification, "thin film" refers to a film thickness of 150 μm or less. The film thickness of the substrate is preferably 10 μm or more and 150 μm or less, more preferably 30 μm or more and 100 μm or less. On the other hand, the planar shape of the substrate is not particularly limited and is appropriately selected depending on the application of the laminate. Furthermore, the minimum bending radius of the substrate is preferably 10 mm or less, more preferably 5 mm or less. When the substrate has this minimum bending radius, the laminate becomes easier to bend freely, making the laminate more usable as a cover film for a folding display device, etc.

[0303] Here, it is more preferable that at least one substrate constituting the laminate is thin film glass. Thin film glass can be easily broken, but the laminate of this embodiment contains the above-mentioned sheet-like sealing material, so it is less likely to break even if it contains thin film glass. Thin film glass refers to a film made of glass with a film thickness of 100 μm or less. This thin film glass is a film generally referred to as UTG (Ultra Thin Glass).

[0304] The thin film glass may be a commercially available product, examples of which include G-Leaf (manufactured by Nippon Electric Glass Co., Ltd.), Dinorex UTG (manufactured by Nippon Electric Glass Co., Ltd.), and SCHOTT UTG (manufactured by SCHOTT).

[0305] Here, the laminate may have a configuration other than the above-mentioned substrate and sheet-like sealing material, as long as the purpose and effect of this embodiment are not impaired. For example, a substrate may be disposed on one side of the above-mentioned sheet-like sealing material, and a protective film (separator) or the like may be disposed on the other side. The protective film is preferably a film having moisture barrier properties or gas barrier properties, and can be, for example, a polyethylene terephthalate film. The thickness of the protective film can be about 20 to 100 μm, depending on the film material.

[0306] 4-3. Method for Producing Sheet-Like Sealing Material and Laminate The above-described sheet-like sealing material and laminate can be produced by any method as long as the object and effect of this embodiment are not impaired. For example, they can be produced by the following method, but are not limited to this method. First, a composition containing (A) an epoxy compound, (B) a tackifier, (C) a thermal cationic polymerization initiator or curing agent, and other components as necessary is prepared, and this is dissolved in a solvent at 30°C or below to form a varnish.

[0307] Examples of the solvent include aromatic solvents such as toluene and xylene; ketone solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone; ethers such as ether, dibutyl ether, tetrahydrofuran, dioxane, ethylene glycol monoalkyl ether, ethylene glycol dialkyl ether, propylene glycol or dialkyl ether; aprotic polar solvents such as N-methylpyrrolidone, dimethylimidazolidinone and dimethylformaldehyde; and esters such as ethyl acetate and butyl acetate.

[0308] When preparing the varnish, the components may be mixed at once, or the epoxy compound (A) may be dissolved in a solvent and then the other components may be mixed in. Examples of methods for mixing the components include known stirring methods and triple-roll kneading methods.

[0309] Next, the varnish is applied onto a separator, and the solvent is removed. The method for applying the varnish is not particularly limited, and examples include screen printing, dispenser application, various roll methods, etc. The thickness of the applied varnish is appropriately selected depending on the desired film thickness of the sheet-like sealing material. The drying temperature and drying time of the varnish are preferably those at which the epoxy compound (A) does not harden. For example, the drying temperature is 20 to 100°C, and the drying time can be, for example, about 1 minute to 3 hours. The drying method is not particularly limited, and examples include hot air drying and vacuum drying. This results in the above-mentioned sheet-like sealing material.

[0310] The sheet-like sealing material thus obtained can be laminated to a desired substrate and cured as necessary to obtain the laminate. The method for laminating the sheet-like sealing material and the substrate is not particularly limited, and lamination can be performed, for example, by thermocompression bonding. For example, desired substrates (films) can be placed on both sides of the sheet-like sealing material, and these and the sheet-like sealing material can be simultaneously thermocompression bonded. However, it is more preferable to place a substrate on one side of the sheet-like sealing material and thermocompression bond it, and then place another substrate on the other side of the sheet-like sealing material and thermocompression bond them.

[0311] When the sheet-shaped sealing material is thermally cured, the heating temperature is preferably 60° C. or higher and 200° C. or lower, and more preferably 70° C. or higher and 120° C. or lower. The heating time is more preferably 20 minutes or higher and 120 minutes or lower. By using the heating temperature and heating time in this range, the epoxy compound (A) in the sheet-shaped sealing material can be sufficiently cured.

[0312] Although the laminate manufacturing method described above involves forming a sheet-like sealing material on a separator in advance and then laminating this to a substrate, the laminate may also be formed by directly applying the above-mentioned varnish to the substrate, removing the solvent on the substrate, and forming a sheet-like sealing material. However, the former method is preferable because it is less likely to alter or deteriorate the substrate due to the solvent or the heat generated during solvent removal.

[0313] 4-4. Uses of the Laminate The laminate can be used as a cover film for touch panel-type display devices, including touch panels, as described above, or as a cover film for various display devices. When forming a cover film, additional layers may be laminated on the laminate. For example, a structure in which, from the display surface side of the display device, a transparent resin film layer (substrate) / a surface sealing material (cured product of the sheet-like sealing material) / a thin film glass (substrate) / a pressure-sensitive adhesive layer / a transparent film layer / a pressure-sensitive adhesive layer may be laminated. Alternatively, a structure in which, from the display surface side, a transparent resin film layer (substrate) / an interlayer adhesive layer / a surface sealing material (cured product of the sheet-like sealing material) / a thin film glass (substrate) may be arranged. Furthermore, a structure in which, from the display surface side, a transparent resin film layer (substrate) / a surface sealing material (cured product of the sheet-like sealing material) / a thin film glass (substrate) may be arranged. In either embodiment, the surface sealing material (cured product of the sheet-like sealing material) is resistant to whitening, enabling the display device to be used stably for a long period of time.

[0314] 5. Fifth Embodiment The fifth embodiment relates to a display device including the laminate described in the first to fourth embodiments. The display device may include any of the laminates described above, and other configurations may be appropriately selected depending on the application.

[0315] The display device preferably has a bending radius of 0.5 to 5 mm, which is measured by a known method.

[0316] The present invention will be described below with reference to examples, which should not be construed as limiting the scope of the present invention.

[0317] 1. Examples of the First Embodiment [Materials] The following materials were used in the examples and comparative examples.

[0318] (A) Alicyclic epoxy compound CEL2021P: a compound represented by the following formula (CEL2021P, manufactured by Daicel Corporation), having a viscosity of 220 to 270 mPa·s when measured with a Brookfield viscometer at 25°C.

[0319] (B) Aromatic-containing epoxy resins YX6954-B35: biphenyl-type epoxy resin (YX6954-B35, manufactured by Mitsubishi Chemical Corporation), weight-average molecular weight (Mw) 36,691 EXA-4850-150: bisphenol A-type epoxy resin (EPICRON EXA-4850-150, manufactured by DIC Corporation), weight-average molecular weight (Mw) 900 jER-4005P: bisphenol F-type epoxy resin (jER-4005P, manufactured by Mitsubishi Chemical Corporation), weight-average molecular weight (Mw) 2000 EP-4003: bisphenol F-type epoxy resin (EP-4003, manufactured by ADEKA Corporation), weight-average molecular weight (Mw) 1000

[0320] (C) Other epoxy resins EP-4040L: A mixed system of monofunctional and difunctional epoxy resins with flexible molecular chains (EP-4040L, manufactured by ADEKA Corporation), weight average molecular weight (Mw) 1000

[0321] (D) Thermal cationic polymerization initiator CXC-1821: a thermal cationic polymerization initiator represented by the following formula (K-Pure CXC-1821, manufactured by King Industries)

[0322] (E) Tackifier K-125: Terpene phenol resin (YS Polystar K-125), softening point 125°C ± 5°C G-125: Terpene phenol resin (YS Polystar G-125), softening point 125°C ± 5°C

[0323] (F) Leveling agent BYK302: Polyether-modified polydimethylsiloxane (BYK302, manufactured by BYK-Chemie)

[0324] Example 1 (A) alicyclic epoxy compound, (B) aromatic ring-containing epoxy resin, (C) other epoxy resin, (D) thermal cationic polymerization initiator, (E) tackifier, (F) leveling agent, and MEK solvent were added to a flask in the mass ratios shown in Table 1, and the mixture was stirred and dissolved at room temperature to prepare a varnish.

[0325] The prepared varnish was applied to a separator (PET75-H270, 75 μm thick, manufactured by Nichiei Shinka Co., Ltd.) using an applicator to a thickness of approximately 20 μm after drying. Furthermore, the varnish was applied to another separator (PET75-H270, 75 μm thick, manufactured by Nichiei Shinka Co., Ltd.) to a thickness of approximately 40 μm after drying. These laminates were dried in an inert oven at 80°C for 3 minutes to dry and remove the methyl ethyl ketone (MEK) in the varnish coating film. Furthermore, a sheet-like sealing material was adhered to a thin film glass (Dinorex UTG, 50 μm, manufactured by Nippon Electric Glass Co., Ltd.) and thermocompressed at 70°C to obtain a laminate. Subsequently, a CPI polyimide film (manufactured by Kolon, 80 μm) was laminated on the sheet-like sealing material using the same procedure to obtain a thin film glass / sheet-like sealing material / polyimide film laminate.

[0326] Examples 2 to 9 and Comparative Example 1 Laminates were obtained in the same manner as in Example 1, except that the amounts of the components used in preparing the varnish were changed as shown in Table 1.

[0327] Comparative Example 2 A laminate was obtained in the same manner as in Example 1, except that a commercially available SANCYUARY DH425 (a commercially available acrylic adhesive, manufactured by San-A Kaken Co., Ltd.) was used.

[0328] [Evaluation] The sheet-like sealing materials and laminates produced in the examples and comparative examples were evaluated by the following methods. The results are shown in Table 1.

[0329] (1) Storage modulus E' of sheet-shaped sealing material at 25°C The sheet-shaped sealing materials prepared in the examples and comparative examples were cured at 100°C for 1 hour. Then, dynamic viscoelasticity measurements were performed from 20°C to 150°C at a temperature increase rate of 5°C / min and a frequency of 1 Hz. The storage modulus (E') at 25°C at this time was determined.

[0330] (2) Peel Strength A sheet-like sealing material was adhered to alkali-free glass (manufactured by Matsunami Glass Co., Ltd., 50 mm x 70 mm, thickness 0.2 mm) and thermocompression-bonded at 70 °C to obtain a laminate. A silver-deposited PET film (Alpet 9-100 manufactured by Panac Corporation) was adhered to the sheet-like sealing material on the side opposite the alkali-free glass and thermocompression-bonded at 70 °C to obtain a test specimen. The sheet-like sealing material and silver-deposited PET film were 25 mm wide and 100 mm long. The alkali-free glass was then fixed vertically to the jig of a universal testing machine (2200X manufactured by Intesco Co., Ltd.), and the silver-deposited PET film was peeled vertically at a peel rate of 30 mm / min to measure the adhesive strength.

[0331] (3) Pen-press test (film thickness 20 μm, 40 μm) The above-mentioned laminate consisting of thin-film glass / sheet-like sealing material / polyimide film was heated for a predetermined time to obtain a laminate structure consisting of thin-film glass / planar sealing material / CPI polyimide film. The thin-film glass of this laminate structure was bonded to a first adhesive layer of a laminate structure consisting of a first adhesive layer (OCA, SANCYUARY DH425, manufactured by San-A Chemical Co., Ltd., 50 μm) / polyimide layer (manufactured by Kapton Corporation, 50 μm) / second adhesive layer (OCA, SANCYUARY DH425, manufactured by San-A Chemical Co., Ltd., 50 μm) to obtain a structure. In addition, a rigid plate was prepared, and the second adhesive layer side of the structure was placed on the rigid plate. Then, a predetermined load was applied from the top of the structure (transparent resin film layer side) using a jig with a spherical tip. The tip of the jig had a diameter of 2 mm, and the pen pressing speed was 0.5 mm / min. The test was terminated when the specified load was reached. A universal testing machine (Intesco 2200X) was used as the testing equipment. The test results were evaluated using an optical microscope (Olympus BX63 upright microscope) to determine whether or not there was damage to each layer at the load point. Measurements were then taken under different loads, and the maximum load at which no damage occurred was identified. Similar tests were conducted for both cases where the film thickness of the sheet-like sealing material was 20 μm and 40 μm.

[0332] (4) Bending test The structure consisting of the above-mentioned CPI polyimide film (80 μm) / planar sealing material (40 μm) / thin film glass (50 μm) / first adhesive layer (OCA, 50 μm) / polyimide layer (50 μm) / second adhesive layer (OCA, 50 μm) was placed across two stages of a bending tester (Yuasa System Co., Ltd. tabletop durability tester, Tension-Free Folding Clamshell-type DMS-CS), and the angle between the two stages was repeatedly moved between 180 ° and 0 °. The bending radius was 5 mm, the bending speed was 30 times / min, and the test was terminated when the number of bending times reached 10,000 times. The test results were evaluated using an optical microscope (Olympus BX63 upright microscope) to determine whether or not there was damage to each layer at the bent portion, with a ◯ indicating no damage and an X indicating damage. The same test was conducted for both cases where the film thickness of the sheet-like sealing material was 20 μm and 40 μm.

[0333]

[0334] As shown in Table 1 above, in the laminates obtained by laminating thin film glass with a sheet-like sealing material containing (A) an alicyclic epoxy compound and (B) an aromatic ring-containing epoxy resin and having a storage modulus E' of 0.31 GPa or more and 3.1 GPa or less at 25°C after curing, the results of the pen push test were excellent, with values ​​of 40 N or more in both the 20 μm and 40 μm film thicknesses (Examples 1 to 9).Furthermore, the results of the bending test were good.

[0335] In contrast, even if the composition contained (A) an alicyclic epoxy compound and (B) an aromatic ring-containing epoxy resin, when the storage modulus E' of the cured product at 25°C was not 0.31 GPa or more and 3.1 GPa or less, the results of the pen push test showed values ​​of 30 N or less in both the case where the film thickness was 20 μm and the case where the film thickness was 40 μm (Comparative Examples 1 and 2).

[0336] 2. Examples of the Second Embodiment [Materials] The following materials were used in the examples and comparative examples.

[0337] (A) Alicyclic epoxy compound CEL2021P: a compound represented by the following formula (CEL2021P, manufactured by Daicel Corporation, viscosity at 25°C as measured with a Brookfield viscometer: 220 to 270 mPa·s)

[0338] (B) Other epoxy compounds EXA-4850-150: bisphenol A type epoxy resin (EPICRON EXA-4850-150, manufactured by DIC Corporation), weight average molecular weight (Mw) 900 JER-4005P: bisphenol F type epoxy resin (jER-4005P, manufactured by Mitsubishi Chemical Corporation), weight average molecular weight (Mw) 2000 EP-4040L: epoxy resin with flexible molecular chain, mixed system of monofunctional and difunctional resins (EP-4040L, manufactured by ADEKA Corporation), weight average molecular weight (Mw) 1000 EP-4003: bisphenol F type epoxy resin (EP-4003, manufactured by ADEKA Corporation), weight average molecular weight (Mw) 1000 YX6954-B35: Biphenyl-type epoxy resin (YX6954-B35, manufactured by Mitsubishi Chemical Corporation), weight average molecular weight (Mw) 36,691

[0339] (C) Thermal cationic polymerization initiator or curing agent CXC-1733: thermal cationic polymerization initiator (K-Pure CXC-1733, manufactured by King Industries) CXC-1821: thermal cationic polymerization initiator represented by the following formula (K-Pure CXC-1821, manufactured by King Industries) 2E4MZ: 2-ethyl-4-methylimidazole (Curezol 2E4MZ, manufactured by Shikoku Chemical Industries, Ltd.)

[0340] (D) Tackifier K-125: Terpene phenol resin (YS Polystar K-125), softening point 125°C ± 5°C G-125: Terpene phenol resin (YS Polystar G-125), softening point 125°C ± 5°C FTR8120: Styrene oligomer (FTR8120, manufactured by Mitsui Chemicals, Inc.)

[0341] Example 1 (A) an alicyclic epoxy compound, (B) another epoxy compound, (C) a thermal cationic polymerization initiator or curing agent, (D) a tackifier, and methyl ethyl ketone (MEK) as a solvent were added to a flask in the mass ratios shown in Table 2, and the mixture was stirred and dissolved at room temperature to obtain a varnish of a thermosetting resin composition.

[0342] The varnish was applied with an applicator onto a separator (PET75-H270, film thickness 75 μm, manufactured by Nichiei Shinka Co., Ltd.) so that the film thickness after drying would be approximately 20 μm. Furthermore, the same varnish was applied onto another separator (PET75-H270, film thickness 75 μm, manufactured by Nichiei Shinka Co., Ltd.) so that the film thickness after drying would be approximately 40 μm.

[0343] These were dried in an inert oven at 80°C for 3 minutes to dry and remove the MEK. Then, a thin film glass (NEG, 50 μm, manufactured by Nippon Electric Glass Co., Ltd.) and the sheet-like thermosetting resin composition from which the MEK had been removed were closely attached and thermocompressed at 70°C to obtain a laminate. Furthermore, the separator was removed, and an alicyclic polyimide film (80 μm, manufactured by Kolon) was laminated on the surface opposite to the thermosetting resin composition to obtain a laminate consisting of thin film glass / thermosetting resin composition / polyimide film.

[0344] The laminate was heated at 100°C for 1 hour to cure the alicyclic epoxy compound (A) and the other epoxy compound (B) in the thermosetting resin composition, thereby obtaining a laminate of the present invention consisting of thin film glass / sealing sheet / polyimide film.

[0345] (Preparation of a sheet-like load-strain curve and the slope of its initial linear portion) Separately, the above varnish was applied to a separator using an applicator so that the film thickness after drying would be approximately 20 μm. The varnish was then dried in an inert oven at 80°C for 3 minutes to dry and remove the MEK. The sample was then heated at 100°C for 1 hour to cure (A) the alicyclic epoxy compound and (B) other epoxy compounds. The sample was then cut into a length of 50 mm and a width of 10 mm, and the separator was peeled off to obtain the desired test specimen.

[0346] The test piece was fixed to a universal testing machine (2200X manufactured by Intesco Co., Ltd.) in accordance with JIS K7127:1999, and a tensile test was carried out at a speed of 300 mm / min. The relationship between the tensile load (N) and the elongation (%) of the test piece was plotted on a graph with the tensile load (N) on the vertical axis and the elongation (%) on the horizontal axis. The elongation was calculated by dividing the initial length of the test piece by L ０ , the length of the sample under test is L １ When the elongation rate is 100×{(L １ -L ０ ) / L ０ The graph showed a linear region (initial linear portion) near the origin. The slope of the initial linear portion was calculated to be 2.6 N / %.

[0347] [Examples 2 to 9 and Comparative Examples 1 to 4] Laminates were obtained in the same manner as in Example 1, except that the formulation of the thermosetting resin composition was changed as shown in Table 2. The slope of the initial linear portion was determined in the same manner as above. The results are shown in Table 2.

[0348] Comparative Example 5 A laminate was obtained in the same manner as in Example 1, except that commercially available SANCUARY DH425 (a commercially available acrylic adhesive manufactured by San-A Kaken Co., Ltd.) was used. The slope of the initial straight portion was determined in the same manner as above. The results are shown in Table 2.

[0349] [Evaluation] The laminates and sheet-like sealing materials produced in the examples and comparative examples were evaluated by the following methods. The results are shown in Table 2.

[0350] (1) Measurement of Peel Strength of Sheet-Like Sealing Material Similar to the laminate manufacturing method described above, a varnish was applied to a separator to a dry film thickness of 20 μm, and then dried in an inert oven at 80°C for 3 minutes to dry and remove the MEK. The resulting sheet-like curable resin composition was adjusted to a width of 25 mm and a length of 100 mm, and then adhered to alkali-free glass (manufactured by Matsunami Glass Co., Ltd., 50 mm x 70 mm, film thickness 0.2 mm) and thermocompression-bonded at 70°C. Next, the separator was peeled from the curable resin composition, and an aluminum-vapor-deposited PET film (Alpet 9-100 manufactured by Panac Corporation) was adhered to the surface opposite the alkali-free glass and thermocompression-bonded at 70°C. The laminate was heated at 100°C for 1 hour to cure (A) the alicyclic epoxy compound and (B) other epoxy compounds. The sheet-like sealing material and aluminum-vapor-deposited PET film were adjusted to a width of 25 mm and a length of 100 mm.

[0351] Thereafter, the alkali-free glass was fixed vertically to the jig of a universal testing machine (2200X manufactured by Intesco), and the aluminum-deposited PET film was peeled off vertically at a peeling rate of 30 mm / min to measure the adhesive strength (peel strength) between the sheet-like sealing material and the alkali-free glass.

[0352] (2) Pen Push Test (Film Thickness: 20 μm, 40 μm) The thin-film glass laminates prepared in the Examples and Comparative Examples were bonded to the first adhesive layer of an adhesive laminate consisting of a first adhesive layer (OCA, SANCUARY DH425, manufactured by San-A Chemical Co., Ltd., 50 μm) / a polyimide layer (Kapton Corporation, 50 μm) / a second adhesive layer (OCA, SANCUARY DH425, manufactured by San-A Chemical Co., Ltd., 50 μm). A rigid plate was then prepared, and the second adhesive layer of the adhesive laminate was attached to the surface of the rigid plate. A predetermined load was then applied from the top (polyimide film side) of the laminate using a spherical-tipped jig. The jig tip had a diameter of 2 mm, and the pen push speed was 0.5 mm / min. The test was terminated when the predetermined load was reached. A universal testing machine (Intesco 2200X) was used as the testing device. The test was performed using an optical microscope (Olympus Corporation, upright microscope BX63) to determine whether or not each layer was damaged at the load point. Then, measurements were taken under different loads to identify the maximum load at which each layer was not damaged. The same test was performed for both cases where the film thickness of the sheet-like sealing material was 20 μm and 40 μm.

[0353] (3) Bending Test As in the pen push test described above, the thin film glass of the laminate prepared in the examples and comparative examples was bonded to the first adhesive layer of an adhesive laminate consisting of a first adhesive layer (OCA, SANCUARY DH425, manufactured by San-ei Kaken Co., Ltd., 50 μm) / a polyimide layer (manufactured by Kapton Corporation, 50 μm) / a second adhesive layer (OCA, SANCUARY DH425, manufactured by San-ei Kaken Co., Ltd., 50 μm). The laminate was then placed across the two stages of a bending tester (Yuasa System Equipment Co., Ltd., tabletop durability tester, Tension-Free Folding Clamshell-type DMS-CS), and the second adhesive layer was bonded to the stage. Next, the stages were each moved so that the angle between the two stages repeatedly fluctuated between 180 ° and 0 °. The bending radius was 5 mm, the bending speed was 30 times / min, and the test was terminated when the number of bending times reached 50,000. The test was performed using an optical microscope (Olympus BX63 upright microscope) to determine whether or not each layer at the bending point was damaged. The evaluation was performed as follows.

[0354] (Evaluation criteria: film thickness of sheet-shaped sealing material 20 μm) ◯: No damage after 50,000 bendings ×: Damage after 50,000 bendings ◯ is within the range where there is no problem in practical use.

[0355] (Evaluation criteria: film thickness of sheet-shaped sealing material 40 μm) ◯: No damage after 50,000 folds △: Damage observed after 50,000 folds, but no damage after 30,000 folds ×: Damage observed after 35,000 folds △ and ◯ are within the range where there are no problems in practical use.

[0356]

[0357] As shown in Table 2 above, in Examples 1 to 8, in which the slope of the initial linear portion of the load-strain curve of the sheet-shaped sealing material was 2.5 N / % or more and 4.0 N / % or less, the peel strength was sufficiently high. Furthermore, in these Examples, when the film thickness of the sheet-shaped sealing material was 20 μm and when it was 40 μm, the results of the pen push test were 40 N or more, and good results were obtained. Furthermore, in these Examples, when the film thickness of the sheet-shaped sealing material was 20 μm, no problems were observed even after repeated folding more than 50,000 times. Furthermore, when the film thickness of the sheet-shaped sealing material was 40 μm, all of them could be folded more than 30,000 times, which is within the range of practically acceptable problems.

[0358] On the other hand, when the gradient of the initial linear portion of the load-strain curve is less than 2.5 N / %, the sheet-shaped sealing material is stretched too much and plastically deformed, which tends to cause peeling during a bending test. On the other hand, when the gradient of the initial linear portion of the load-strain curve is more than 4.0 N / %, the sheet-shaped sealing material is unable to relax the stress, which causes a load to be applied to the thin glass, etc., which tends to break.

[0359] 3. Examples of the Third Embodiment [Materials] The following materials were used in the examples and comparative examples.

[0360] (A) Epoxy Compound CEL2021P: a compound represented by the following formula (CEL2021P, manufactured by Daicel Corporation, viscosity at 25°C as measured with a Brookfield viscometer: 220 to 270 mPa s) EP-4088S: Dicyclopentadiene-type epoxy resin represented by the following formula (EP-4040L, manufactured by ADEKA Corporation), weight average molecular weight (Mw) 300 JER-4005P: bisphenol F type epoxy resin (jER-4005P, manufactured by Mitsubishi Chemical Corporation), weight average molecular weight (Mw) 2000 EP-4003: bisphenol F type epoxy resin (EP-4003, manufactured by ADEKA Corporation), weight average molecular weight (Mw) 1000 EP-4010: bisphenol A type epoxy resin (EP-4010, manufactured by ADEKA Corporation), weight average molecular weight (Mw) 1000 EP-4040L: epoxy resin with flexible molecular chain, monofunctional and difunctional mixed system (EP-4040L, manufactured by ADEKA Corporation), weight average molecular weight (Mw) 1000 YX6954-B35: biphenyl type epoxy resin (YX6954-B35, manufactured by Mitsubishi Chemical Corporation), weight average molecular weight (Mw) 36,691 EXA-4850-150: Bisphenol A type epoxy resin (EPICRON EXA-4850-150, manufactured by DIC Corporation), weight average molecular weight (Mw) 900

[0361] (B) Thermal cationic polymerization initiator and curing agent CXC-1733: thermal cationic polymerization initiator (K-Pure CXC-1733, manufactured by King Industries) CXC-1821: thermal cationic polymerization initiator represented by the following formula (K-Pure CXC-1821, manufactured by King Industries) 2E4MZ: 2-ethyl-4-methylimidazole (Curezol 2E4MZ, manufactured by Shikoku Chemical Industries, Ltd.)

[0362] (C) Tackifiers K-125: Terpene phenol resin (YS Polystar K-125), softening point 125°C ± 5°C G-125: Terpene phenol resin (YS Polystar G-125), softening point 125°C ± 5°C FTR8120: Styrene oligomer (FTR8120, manufactured by Mitsui Chemicals, Inc.) FTR8100: Styrene oligomer (FTR8120, manufactured by Mitsui Chemicals, Inc.)

[0363] 1. Preparation of Sheet-Shaped Thermosetting Resin Composition [Preparation of Sheet-Shaped Thermosetting Resin Composition 1] (A) an alicyclic epoxy compound, (B) another epoxy compound, (C) a thermal cationic polymerization initiator or curing agent, (D) a tackifier, and methyl ethyl ketone (MEK) as a solvent were added to a flask in the mass ratios shown in Table 3, and the mixture was stirred and dissolved at room temperature to obtain a varnish of a thermosetting resin composition.

[0364] The varnish was applied to a separator (PET75-H270, film thickness 75 μm, manufactured by Nichiei Shinka Co., Ltd.) using an applicator so that the film thickness after drying would be approximately 20 μm. This was dried in an inert oven at 80°C for 3 minutes to dry and remove the MEK, thereby obtaining a sheet-shaped thermosetting resin composition.

[0365] [Preparation of Sheet-Shaped Thermosetting Resin Compositions 2 to 19] Sheet-shaped thermosetting resin compositions were obtained in the same manner as in Example 1, except that the composition of the thermosetting resin composition was changed to the composition shown in Table 3.

[0366] [Preparation of Sheet-Shaped Thermosetting Resin Compositions 2 to 19] Sheet-shaped thermosetting resin compositions were obtained in the same manner as in Example 1, except that commercially available SANCUARY DH425 (manufactured by San-A Kaken Co., Ltd., acrylic adhesive) was used.

[0367] 2. Preparation of Laminate [Preparation of Laminate of Layer Structure 1] One surface of the sheet-shaped thermosetting resin composition 1 was bonded to one surface of the sheet-shaped thermosetting resin composition 16. Next, the separator was peeled from the sheet-shaped thermosetting resin composition 1, and an alicyclic polyimide film (manufactured by Kolon, 80 μm, first film) was superimposed on the other surface of the sheet-shaped thermosetting resin composition 1, followed by thermocompression bonding at 70°C. Furthermore, the separator was peeled from the sheet-shaped thermosetting resin composition 16, and the other surface of the sheet-shaped thermosetting resin composition 16 was superimposed on thin film glass (manufactured by NEG Corporation, G-Leaf, 30 μm, second film), followed by thermocompression bonding at 70°C. Thereafter, the films were heated at 100°C for 1 hour to cure the epoxy compound (A) in each thermosetting resin composition, thereby obtaining a laminate consisting of polyimide film / first sealant (cured product of thermosetting resin composition 1) / second sealant (cured product of thermosetting resin composition 16) / thin film glass.

[0368] Other laminates were similarly produced except that the type of the first sealing material was changed as shown in Table 4.

[0369] [Preparation of Laminate of Layer Structure 2] One surface of the sheet-shaped thermosetting resin composition 1 was bonded to one surface of a separately prepared sheet-shaped thermosetting resin composition 1. Next, the separator was peeled off from one of the sheet-shaped thermosetting resin compositions 1, and an alicyclic polyimide film (manufactured by Kolon, 80 μm, first film) was superimposed on the other surface of the sheet-shaped thermosetting resin composition 1, followed by thermocompression bonding at 70°C. Furthermore, the separator was peeled off from the other sheet-shaped thermosetting resin composition 1, and the other surface of the sheet-shaped thermosetting resin composition 1 was superimposed on thin film glass (manufactured by NEG Corporation, G-Leaf, 30 μm, second film), followed by thermocompression bonding at 70°C. Thereafter, the resultant was heated at 100°C for 1 hour to cure the epoxy compound (A) in each thermosetting resin composition, thereby obtaining a laminate consisting of polyimide film / first sealant (cured product of thermosetting resin composition 1) / second sealant (cured product of thermosetting resin composition 1) / thin film glass.

[0370] Other laminates were similarly produced, except that the types of the first sealing material and the second sealing material were changed as shown in Table 5.

[0371] [Preparation of Laminate with Layer Structure 3] As shown in Table 6, a laminate was prepared in the same manner as in Layer Structure 1, except that the second sealant was not laminated. Layer Structure 3 resulted in a laminate consisting of a polyimide film / first sealant (cured product of a thermosetting resin composition) / thin film glass.

[0372] [Preparation of Laminate with Layer Structure 4] A laminate was prepared in the same manner as in Layer Structure 1, except that the positions of the alicyclic polyimide film and the thin glass were changed as shown in Table 7.

[0373] 3. Evaluation The laminates and sealing materials produced in the examples and comparative examples were evaluated by the following methods. The results are shown in Tables 3 to 7.

[0374] (1) Creation of a load-strain curve for each sealing material and measurement of the slope of the initial linear portion and the tensile modulus. Each of the sheet-shaped thermosetting resin compositions 1 to 20 described above was heated at 100°C for 1 hour to cure the epoxy compound in each thermosetting resin composition. Thereafter, the separator was peeled off to obtain the desired test specimens.

[0375] The test piece was fixed to a universal testing machine (Intesco 2200X) in accordance with JIS K7127:1999, and a tensile test was carried out at 25°C and a speed of 300 mm / min. The relationship between the tensile load (N) and the elongation (%) of the test piece was plotted on a graph with the tensile load (N) on the vertical axis and the elongation (%) on the horizontal axis. The elongation was calculated by dividing the initial length of the test piece by L ０ , the length of the sample under test is L １ When the elongation rate is 100×{(L １ -L ０ ) / L ０ From the graphs thus created, the slope of the linear region (initial linear portion) near the origin was calculated. The tensile modulus of elasticity of each sealing material was also determined by the tensile test.

[0376] (2) Bending Test The second film of the laminate prepared in the above-mentioned Examples and Comparative Examples was bonded to the first adhesive layer of an adhesive laminate consisting of a first adhesive layer (OCA, SANCUARY DH425, manufactured by San-ei Kaken Co., Ltd., 50 μm) / a polyimide layer (manufactured by Kapton Corporation, 50 μm) / a second adhesive layer (OCA, SANCUARY DH425, manufactured by San-ei Kaken Co., Ltd., 50 μm). The laminate was then placed across the two stages of a bending tester (Yuasa System Equipment Co., Ltd., tabletop durability tester, Tension-Free Folding Clamshell-type DMS-CS), and the second adhesive layer was bonded to the stage. Next, the stages were each moved so that the angle between the two stages repeatedly moved between 180 ° and 0 °. The bending radius was 5 mm, the bending speed was 30 times / min, and the test was terminated when the number of bending times reached 50,000. The test was performed using an optical microscope (Olympus BX63 upright microscope) to determine whether or not there was damage to each layer at the bending point. If there was no damage after 50,000 bendings, it was marked as ◯, and if there was damage, it was marked as ×.

[0377] (3) Pen Push Test The second film of the laminate prepared in the Examples and Comparative Examples was bonded to the first adhesive layer of an adhesive laminate consisting of a first adhesive layer (OCA, SANCUARY DH425, manufactured by San-A Chemical Co., Ltd., 50 μm) / a polyimide layer (Kapton Corporation, 50 μm) / a second adhesive layer (OCA, SANCUARY DH425, manufactured by San-A Chemical Co., Ltd., 50 μm). A rigid plate was then prepared, and the second adhesive layer of the adhesive laminate was attached to the surface of the rigid plate. A predetermined load was then applied from the top (first film side) of the laminate using a spherical-tipped tool. The tip of the tool had a diameter of 2 mm, and the pen push speed was 0.5 mm / min. The test was terminated when the predetermined load was reached. A universal testing machine (Intesco 2200X) was used as the testing device. The test was performed using an optical microscope (Olympus BX63 upright microscope) to determine whether or not there was damage to each layer at the location where the load was applied. Measurements were then performed under different loads to identify the maximum load at which no damage occurred to each layer. A load of 50 N or more is considered to be within the range where there are no practical problems.

[0378]

[0379]

[0380]

[0381]

[0382]

[0383] As shown in Table 4 above, a laminate including a first sealant having an initial linear portion of a load-strain curve with a slope of 0.4 N / % or more and 2.0 N / % or less, and a second sealant having a tensile modulus higher than that of the first sealant, and in which the first sealant is positioned closer to the display surface, i.e., the user, than the second sealant, exhibited good results in all bending tests, and the results of the pen push test were all 50 N, which were very good results. Furthermore, as shown in Table 7, a laminate in which the second sealant is positioned closer to the user than the first sealant also exhibited very good results. Furthermore, when these results are compared with the comparative example in Table 6 that does not have a second sealant, it can be seen that the bending properties and the results of the pen push test are significantly better.

[0384] In contrast, as shown in Tables 4 and 7, when the slope of the initial linear portion of the load-strain curve of the first sealing material was less than 0.4 N / %, the first sealing material was stretched too much and underwent plastic deformation, and cracking and peeling were likely to occur in the first film and the second film when a bending test was performed. On the other hand, when the slope of the initial linear portion of the load-strain curve of the first sealing material exceeded 2.0 N / %, the first sealing material was unable to relieve stress, and load was applied to the first film and the second film, which were likely to crack and peel.

[0385] Furthermore, as shown in Table 5, when the tensile modulus of elasticity of the first sealant and the tensile modulus of elasticity of the second sealant were the same, the results of the bending test and the pen push test were not sufficiently improved.

[0386] 4. Examples of the Fourth Embodiment [Materials] The following materials were used in the examples and comparative examples.

[0387] (A-1) Alicyclic epoxy compound CEL2021P: a compound represented by the following formula (CEL2021P, manufactured by Daicel Corporation), having a viscosity of 220 to 270 mPa·s when measured with a Brookfield viscometer at 25°C.

[0388] (A-2) Aromatic ring-containing epoxy compounds jER-4005P: bisphenol F type epoxy resin (jER-4005P, manufactured by Mitsubishi Chemical Corporation), weight average molecular weight (Mw) 2000 EXA-4850-150: bisphenol A type epoxy resin (EPICRON EXA-4850-150, manufactured by DIC Corporation), weight average molecular weight (Mw) 900 YX6954-B35: biphenyl type epoxy resin (YX6954-B35, manufactured by Mitsubishi Chemical Corporation), weight average molecular weight (Mw) 36,691

[0389] (B) Tackifiers K-125: Terpene phenol resin system (YS Polystar K-125, manufactured by Yasuhara Chemical Co., Ltd.), softening point 125°C ± 5°C, terpene resin / phenol resin (mass ratio): 45 / 55 G-125: Terpene phenol resin system (YS Polystar G-125, manufactured by Yasuhara Chemical Co., Ltd.), softening point 125°C ± 5°C, terpene resin / phenol resin (mass ratio): 45 / 55 T-130: Terpene phenol resin system (YS Polystar T-130, manufactured by Yasuhara Chemical Co., Ltd.), softening point 130°C ± 5°C, terpene resin / phenol resin (mass ratio): 50 / 50 FTR8120: Aromatic monomer (manufactured by Mitsui Chemicals, Inc.) FTR8100: Aromatic monomer (manufactured by Mitsui Chemicals, Inc.)

[0390] (C) Thermal cationic polymerization initiator: 2E4MZ (2-ethyl-4-imidazole)

[0391] (D) Leveling agent BYK302: Polyether-modified polydimethylsiloxane (BYK302, manufactured by BYK-Chemie)

[0392] [Example 1] In a flask, (A-1) an alicyclic epoxy compound, (A-2) an aromatic ring-containing epoxy compound, (B) a tackifier, (C) a thermal cationic polymerization initiator, (D) a leveling agent, and MEK solvent were mixed in the mass ratios shown in Table 8. The mixture was then stirred and dissolved at room temperature to prepare a varnish.

[0393] The prepared varnish was applied to a separator (PET75-H270, manufactured by Nichiei Shinka Co., Ltd., thickness 75 μm) using an applicator with a coating machine so that the thickness after drying would be approximately 20 μm. The coating film was dried in an inert oven at 80°C for 3 minutes. This dried and removed the methyl ethyl ketone (MEK) in the varnish, yielding a sheet-like sealing material. Thereafter, a thin film glass (NEG, manufactured by Nippon Electric Glass Co., Ltd., 50 μm) and the sheet-like sealing material were overlaid and thermocompression bonded at 70°C. The separator was then peeled from the other side of the sheet-like sealing material, and the sheet-like sealing material and a CPI polyimide film (manufactured by Kolon, 80 μm) were overlaid and thermocompression bonded at 70°C. As a result, a laminate consisting of thin film glass / sheet-like sealing material / polyimide film was obtained.

[0394] Examples 2 to 4 and Comparative Examples 1 to 3 Laminates were obtained in the same manner as in Example 1, except that the amounts of the components used in preparing the varnish were changed as shown in Table 8.

[0395] [Evaluation] The sheet-like sealing materials and laminates produced in the examples and comparative examples were evaluated by the following methods. The results are shown in Table 8.

[0396] (1) Confirmation of the sea-island structure of the sheet-shaped sealing material The surfaces of the sheet-shaped sealing materials prepared in the examples and comparative examples were observed at three locations using a scanning electron microscope (SEM). The number of islands present in a 200 μm × 200 μm area was determined for each location, and the average value was calculated.

[0397] (2) Peel Strength A laminate consisting of a separator and a sheet-like sealing material was prepared in the same manner as in the Examples and Comparative Examples. Then, alkali-free glass (manufactured by Matsunami Glass Co., Ltd., 50 mm x 70 mm, 0.2 mm thick) was adhered to one side of the sheet-like sealing material (the side opposite the separator) and thermocompression-bonded at 70°C. The separator was then peeled off, and a silver-vapor-deposited PET film (Alpet 9-100 manufactured by Panac Corporation) was adhered to the sheet-like sealing material on the side opposite the alkali-free glass and thermocompression-bonded at 70°C to obtain a test specimen. The sheet-like sealing material and the silver-vapor-deposited PET film were 25 mm wide and 100 mm long. The laminate was then heated at 100°C for 60 minutes to cure the (A-1) alicyclic epoxy compound and (A-2) aromatic ring-containing epoxy compound in the sheet-like sealing material. Thereafter, the alkali-free glass was fixed vertically to the jig of a universal testing machine (2200X manufactured by Intesco Co., Ltd.), and the silver-deposited PET film was peeled off vertically at a peeling rate of 30 mm / min to measure the adhesive strength.

[0398] (3) Storage modulus E' of sheet-shaped sealing material at 25°C The sheet-shaped sealing materials prepared in the examples and comparative examples were cured as a single unit at 100°C for 1 hour. Then, dynamic viscoelasticity measurements were performed from 20°C to 150°C at a temperature increase rate of 5°C / min and a frequency of 1 Hz. The storage modulus (E') at 25°C at this time was determined.

[0399] (4) Tensile Test The sheet-like sealing materials produced in the Examples and Comparative Examples were cured as a single unit at 100° C. for 1 hour. The test specimen was fixed to a tensile tester (2200X manufactured by Intesco Co., Ltd.) in accordance with JIS K7127:1999, and a tensile test was carried out at 25° C. and a speed of 300 mm / min to determine the tensile modulus.

[0400] (5) Pen Press Test A laminate consisting of a separator and a sheet-like sealing material was prepared in the same manner as in the Examples and Comparative Examples. A CPI polyimide film (80 μm, manufactured by Kolon) was then placed on one side of the sheet-like sealing material and thermocompressed at 70°C. Paper (20 μm thick) was then placed on the separator side. The sheet-like sealing material was then heated at 100°C for 60 minutes to harden the sheet-like sealing material. A predetermined load was then applied from the CPI polyimide film using a spherical-tipped tool. The tip of the tool had a diameter of 2 mm, and the pen pressing speed was 0.5 mm / min. The test was terminated when the predetermined load was reached. A universal testing machine (2200X, manufactured by Intesco) was used as the testing equipment. The test results were evaluated using an optical microscope (Olympus, upright microscope BX63) to determine whether or not each layer was damaged at the load location. Then, measurements were taken under different loads to identify the maximum load at which no damage occurred to each layer. If there was no change before and after the test, the test was marked with an 'O'; if there was peeling or cracking in any of the layers, or if there was damage, the test was marked with an 'X'.

[0401] (5) Bending Test The laminates prepared in the above-described Examples and Comparative Examples were heated at 100°C for 60 hours to cure the sheet-like sealing material. Then, a structure consisting of a first adhesive layer (OCA, 50 μm) / polyimide layer (50 μm) / second adhesive layer (OCA, 50 μm) was prepared, and the first adhesive layer of the structure was bonded to the thin-film glass of the above-described laminate. Furthermore, the second adhesive layer side of the structure was placed across the two stages of a bending tester (Yuasa System Co., Ltd., tabletop durability tester, Tension-Free Folding Clamshell-type DMS-CS) and adhered. The two stages of the tester were then repeatedly moved back and forth so that the angle between them changed from 180° to 0°. The bending radius was 5 mm, the bending speed was 30 times / min, and the test was terminated when the number of bending times reached 10,000. The test results were evaluated using an optical microscope (Olympus BX63 upright microscope) to determine whether or not there was damage to each layer at the bending point, with a ◯ if there was no damage and an × if there was damage.

[0402]

[0403] As shown in Table 8 above, sheet-like sealing materials containing an epoxy compound and a tackifier, and having a surface observed with a scanning electron microscope in which the number of islands in the sea-island structure present in a 200 μm × 200 μm area was 10 or less, did not undergo whitening in the bending test (Examples 1 to 4). In contrast, sheet-like sealing materials having more than 10 islands in the sea-island structure present in a 200 μm × 200 μm area did undergo whitening in the bending test (Comparative Examples 1 to 3).

[0404] This application claims priority based on Japanese Patent Application No. 2023-108690 filed on June 30, 2023, Japanese Patent Application No. 2023-167698 filed on September 28, 2023, Japanese Patent Application No. 2023-167701 filed on September 28, 2023, and Japanese Patent Application No. 2023-183350 filed on October 25, 2023. The contents of the specifications and drawings of these applications are incorporated herein by reference in their entirety.

[0405] The laminate of the first embodiment can form a member that is resistant to cracking or denting even when subjected to a localized external load, and that is also resistant to peeling at the interface between the thin film glass and the cured sheet-like sealant, and therefore can be used as a cover film for various display devices.

[0406] The laminate of the second embodiment has very high bending resistance and is unlikely to peel at the interfaces between layers, making it suitable for use as a cover member for various display devices.

[0407] The laminate of the third embodiment has very high bending resistance and is unlikely to peel at the interfaces between layers, making it suitable for use as a cover member for various display devices.

[0408] The sheet-like sealing material of the fourth embodiment has excellent adhesiveness to various members and is less likely to whiten even when subjected to a localized external load, etc. Therefore, it can be used as a cover film for various display devices, etc.

Claims

1. A sheet-like sealing material comprising: an alicyclic epoxy compound containing two or more epoxy groups and two or more cyclic structures in the molecule; and an aromatic ring-containing epoxy resin having one or more aromatic rings in the molecule.

2. The sheet-like sealing material according to claim 1, wherein the alicyclic epoxy compound is a compound represented by the following formula:

3. The sheet-like sealing material according to claim 1, wherein the storage modulus at 25°C, as measured by dynamic viscoelasticity measurement at a heating rate of 5°C / min and a frequency of 1 Hz after heating at 100°C for 1 hour, is 0.31 GPa or more and 3.1 GPa or less.

4. The sheet-like sealing material according to claim 1, having a thickness of 3 μm or more.

5. The sheet-like sealing material according to claim 1, having a thickness of 7 μm or more.

6. A method for manufacturing a sealing material for a thin film glass, comprising: (B) an aromatic ring-containing epoxy resin having one or more aromatic rings in the molecule, wherein the storage modulus at 25°C of the sheet-like sealing material, as measured by dynamic viscoelasticity measurement at a temperature increase rate of 5°C / min and a frequency of 1 Hz after heating at 100°C for 1 hour, is 0.31 GPa or more and 3.1 GPa or less.

7. The laminate according to claim 6, which is used in a touch panel type display device.

8. A laminate comprising: a first film; a sheet-like sealing material disposed on said first film; and a second film disposed on said sheet-like sealing material, wherein a test piece of said sheet-like sealing material having a length of 50 mm, a width of 10 mm and a thickness of 20 μm is prepared and a tensile test is carried out in accordance with JIS K7127:1999 at a tensile speed of 300 mm / min., the gradient of the initial straight line portion of the load-strain curve is 2.5 N / % or more and 4.0 N / % or less.

9. The laminate according to claim 8, wherein the sheet-like sealing material is a cured product of a resin composition containing an alicyclic epoxy compound represented by the following formula:

10. The laminate according to claim 8, wherein the first film and / or the second film comprises at least one material selected from the group consisting of glass, alicyclic polyimide, polyethylene terephthalate, and polyethylene.

11. The laminate according to claim 8, wherein the film thickness of the sheet-like sealing material is 5 μm or more and 150 μm or less.

12. A laminate comprising a pair of films, a first sealant and a second sealant having a higher elastic modulus than the first sealant, disposed between the pair of films, wherein a test piece of the first sealant having a length of 50 mm, a width of 10 mm and a thickness of 20 μm is prepared and a tensile test is carried out in accordance with JIS K7127:1999 at 25°C at a tensile speed of 300 mm / min, where the slope of the initial straight line portion of the load-strain curve is 0.4 N / % or more and 2.0 N / % or less.

13. The laminate according to claim 12, wherein the first sealant is a cured product of a resin composition containing an alicyclic epoxy compound represented by the following formula:

14. The laminate according to claim 12, wherein the second sealing material has a tensile modulus at 25°C, measured in accordance with JIS K7127:1999, of 2 GPa or more and 4 GPa or less.

15. The laminate according to claim 12, wherein at least one of the pair of films contains at least one material selected from the group consisting of glass, alicyclic polyimide, polyethylene terephthalate, and polyethylene.

16. The laminate according to claim 12, wherein the film thickness of the first sealant is 5 μm or more and 50 μm or less, and the film thickness of the second sealant is 5 μm or more and 50 μm or less.

17. A display device comprising: a display element; and a laminate according to any one of claims 12 to 16, disposed on the display element; wherein the laminate is disposed such that the second sealant is located closer to the display element than the first sealant.

18. A sheet-like sealing material comprising an epoxy compound and a tackifier, wherein when the surface of the sheet-like sealing material is observed with a scanning microscope, the number of islands in a sea-island structure contained in an area of ​​200 μm x 200 μm is 10 or less.

19. The sheet-like sealing material according to claim 18, wherein the epoxy compound comprises an alicyclic epoxy compound represented by the following formula:

20. The sheet-like sealing material according to claim 18, wherein the tackifier contains a terpene resin and a phenol resin, and the amount of the terpene resin is less than 50 mass% based on the total amount of the terpene resin and the phenol resin.

21. A laminate comprising: a substrate; and the sheet-like sealing material or a cured product thereof according to claim 18, disposed on the substrate.

22. The laminate according to claim 21, which is used in a touch panel type display device.

23. A display device comprising a laminate according to any one of claims 6, 8, 12 and 21.

24. The display device according to claim 23, wherein the radius of curvature when folded is 0.5 to 5 mm.

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