Shock-absorbing sheet

Abstract

Provided is a shock absorbing sheet which has excellent shock absorbing performance, durability against repeated bending, and flexibility at low temperatures. The shock absorbing sheet comprises a resin foam layer obtained by curing a resin composition containing monofunctional urethane (meth)acrylate, wherein the monofunctional urethane (meth)acrylate is one or more monomers selected from reaction products of a compound containing a certain (meth)acryloyloxy group.

Description

[Technical Field]

[0001] The present invention relates to an impact absorbing sheet suitable for electronic devices and the like. [Background technology]

[0002] When mobile devices such as smartphones, tablets, and laptops are dropped or hit, the impact can cause damage to the casing or display panel. To prevent such damage, shock-absorbing sheets are used, for example, between the cover panel and the housing, between a display device such as a liquid crystal or organic electroluminescence (organic EL) display and a touch screen panel, and on the back side of the display device.

[0003] As such impact absorbing sheets, foam sheets of olefin resins, such as polyethylene, and acrylic resins are known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 013258 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, development of foldable mobile devices equipped with foldable displays, i.e., foldable devices, has progressed. Shock-absorbing sheets provided in foldable devices are required to have not only shock-absorbing performance but also durability against repeated bending (hereinafter also referred to as "repeated bending durability"). Furthermore, since mobile devices can be carried around and used in a variety of environments, the shock-absorbing sheets installed on mobile devices must be flexible enough to provide shock-absorbing performance and durability against repeated bending, even in extremely cold environments with temperatures below 0°C.

[0006] However, conventional impact absorbing sheets made of foamed sheets of olefin resin or acrylic resin do not have sufficient durability against repeated bending and flexibility at low temperatures.

[0007] The present invention is intended to solve these problems, and has an object to provide an impact absorbing sheet that has excellent impact absorbing performance, durability against repeated bending, and flexibility at low temperatures. [Means for solving the problem]

[0008] The present invention is based on the discovery that a resin foam layer produced using a specific urethane acrylate having a polyether chain and a urethane bond can provide an impact absorbing sheet with excellent impact absorption performance, repeated bending durability, and flexibility at low temperatures.

[0009] The present invention provides the following means. [1] An impact absorbing sheet having a resin foam layer formed by curing a resin composition containing a monofunctional urethane (meth)acrylate, wherein the monofunctional urethane (meth)acrylate is one or more monomers selected from the reaction products of the following (i) to (iii): (i) A reaction product of an equimolar reaction between a polyether monool and a compound having a (meth)acryloyloxy group, wherein the compound having a (meth)acryloyloxy group has one isocyanate group in one molecule and one or two (meth)acryloyloxy groups in one molecule. (ii) A reaction product of an equimolar reaction of a polyether monool, a diisocyanate, and a compound having a (meth)acryloyloxy group, wherein the compound having a (meth)acryloyloxy group has one group reactive with an isocyanate group in one molecule and one or two (meth)acryloyloxy groups in one molecule. (iii) A reaction product of an equimolar reaction of a polyether polyol and a compound having a (meth)acryloyloxy group, wherein the compound having a (meth)acryloyloxy group has one isocyanate group in one molecule and one or two (meth)acryloyloxy groups in one molecule. [2] The impact absorbing sheet according to [1], wherein the molecular weight of the monomer is 3,000 to 30,000. [3] The impact absorbing sheet according to [1] or [2], wherein the glass transition temperature of the cured product of the resin composition is −55° C. or lower. [4] The impact absorbing sheet according to any one of [1] to [3], wherein the monomer is a reaction product of (i). [5] The impact absorbing sheet according to any one of [1] to [4], wherein the resin foam layer contains hollow particles. [6] The impact absorbing sheet according to any one of [1] to [5], wherein the resin foam layer is formed by a mechanical flossing method. [7] The impact absorbing sheet according to any one of [1] to [6], which has a thickness of 300 μm or less. [8] The shock-absorbing sheet according to any one of [1] to [7], which is used in an electronic device. [9] The impact absorbing sheet according to any one of [1] to [8], which is placed on the back side of a display device.

[10] An adhesive tape comprising the impact absorbing sheet according to any one of [1] to [9] and an adhesive material provided on at least a part of at least one surface of the impact absorbing sheet. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an impact absorbing sheet that has excellent impact absorbing performance, durability against repeated bending, and flexibility at low temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0011] The definitions and meanings of terms and notations used in this specification are shown below. The term "(meth)acryloyloxy group" is a general term for an acryloyloxy group and a methacryloyloxy group. "(Meth)acrylate" is a general term for acrylate and methacrylate. Similarly, "(meth)acrylic acid" is a general term for acrylic acid and methacrylic acid. Unless otherwise specified, the term "functionality" refers to the number of (meth)acryloyloxy groups in one molecule. Unless otherwise specified, the term "average functionality" refers to the average number of (meth)acryloyloxy groups in one molecule, where the formula weight or number average molecular weight based on the chemical formula is one unit. The term "monofunctional urethane (meth)acrylate" refers to a urethane (meth)acrylate in which the average number of functional groups per molecule is substantially 1, and a urethane (meth)acrylate in which the average number of functional groups per molecule is 0.7 to 1.4, preferably 0.8 to 1.3, is considered to be a urethane (meth)acrylate having substantially one (meth)acryloyloxy group per molecule, i.e., a monofunctional urethane (meth)acrylate. The term "equimolar reaction product" means that the molar ratio of the reacting compounds is substantially 1, and a reaction product in which the molar ratio is 0.7 to 1.4, preferably 0.8 to 1.3, is considered to be an equimolar reaction product. Similarly, "the molar ratio of the reactive groups (or compounds) is equal" means that the molar ratio of the reactive groups (or compounds) is substantially 1, and when the molar ratio is 0.7 to 1.4, preferably 0.8 to 1.3, the molar ratio of the reactive groups (or compounds) is considered to be equal. The "hydroxyl value" is determined by measurement in accordance with JIS K 1557:2007. The "hydroxyl value-equivalent molecular weight" is a value calculated from the formula 56,100 / (hydroxyl value) x (number of active hydrogen atoms in the initiator). The "NCO index" in the reaction of an isocyanate group-containing compound with a hydroxyl group-containing compound is the equivalent ratio of the isocyanate groups of the isocyanate group-containing compound to the hydroxyl groups of the hydroxyl group-containing compound, expressed as a percentage. Unless otherwise specified, "molecular weight" refers to the formula weight based on the chemical formula, or, in the case of a compound with a molecular weight distribution, the number average molecular weight. The "number average molecular weight" is the polystyrene-equivalent molecular weight determined by gel permeation chromatography (GPC) based on a calibration curve prepared using standard polystyrene samples.

[0012] The impact absorbing sheet of the present invention has a resin foam layer formed by curing a resin composition containing a monofunctional urethane (meth)acrylate, and the monofunctional urethane (meth)acrylate is one or more monomers (hereinafter also referred to as "first monomers") selected from the reaction products of the following (i) to (iii): (i) an equimolar reaction product of a polyether monool and a compound having a (meth)acryloyloxy group, The compound having a (meth)acryloyloxy group is a reaction product having one isocyanate group in one molecule and one or two (meth)acryloyloxy groups in one molecule. (ii) an equimolar reaction product of a polyether monool, a diisocyanate, and a compound having a (meth)acryloyloxy group, The compound having a (meth)acryloyloxy group is a reaction product, which is a compound having one group reactive with an isocyanate group in one molecule and one or two (meth)acryloyloxy groups in one molecule. (iii) an equimolar reaction product of a polyether polyol and a compound having a (meth)acryloyloxy group, The compound having a (meth)acryloyloxy group is a reaction product having one isocyanate group in one molecule and one or two (meth)acryloyloxy groups in one molecule.

[0013] The impact absorbing sheet of the present invention having the above-described resin foam layer is excellent in impact absorbing performance, durability against repeated bending, and flexibility at low temperatures.

[0014] [Resin foam layer] The resin foam layer is formed by curing a resin composition containing a monofunctional urethane (meth)acrylate, and contains a cured product of the resin composition and air bubbles. Resin compositions containing monofunctional urethane (meth)acrylates can be photopolymerized or thermally polymerized by the (meth)acryloyloxy groups of the monofunctional urethane (meth)acrylates. Furthermore, since the monofunctional urethane (meth)acrylates have flexible graft chains that do not contribute to crosslinking, cured products with excellent flexibility can be obtained, and resin foam layers formed from the cured products can exhibit excellent impact absorption performance. Furthermore, the cured products exhibit little temperature dependence of their storage modulus over a wide temperature range from -20 to 80°C, and can maintain excellent flexibility even at low temperatures below 0°C. The (meth)acryloyloxy group of the monofunctional urethane (meth)acrylate is preferably an acryloyloxy group from the viewpoint of the curing rate of the resin composition.

[0015] [First Monomer] The monofunctional urethane (meth)acrylate is one or more first monomers selected from the reaction products of the (i) to (iii) (hereinafter also referred to as "monomer (1-1)," "monomer (1-2)," and "monomer (1-3)"). That is, the resin composition contains a monofunctional urethane (meth)acrylate as a first monomer. The first monomer in the resin composition may be one type alone or two or more types in combination.

[0016] The molecular weight of the first monomer is preferably 3,000 to 30,000, more preferably 4,000 to 20,000, and even more preferably 5,000 to 17,000. When the molecular weight is 3,000 or more, the cured product of the resin composition tends to be flexible, and when it is 30,000 or less, the viscosity of the resin composition is easily adjusted. When two or more types of first monomers are used in combination, it is preferable that the molecular weight of each be within the above range.

[0017] <Monomer (1-1)> The monomer (1-1) is a reaction product of the above (i), which is an equimolar reaction product of the polyether monool (i-1) and the compound (i-2) having a (meth)acryloyloxy group, and the compound (i-2) having a (meth)acryloyloxy group is a compound having one isocyanate group in one molecule and one or two (meth)acryloyloxy groups in one molecule.

[0018] The monomer (1-1) is preferably a compound represented by formula (1).

[0019] [ka]

[0020] In formula (1), R 1 is a monovalent organic group having one or two (meth)acryloyloxy groups. R 12 is preferably an alkylene group having 2 to 8 carbon atoms, and more preferably an alkylene group having 2 to 4 carbon atoms. 12 may be the same or different. Two or more types of R 12 If present, -OR 12 - The chain can be block or random. 12 is preferably at least one selected from an ethylene group, a propylene group, a 1,2-dimethylethylene group and a 1-ethylethylene group, and more preferably at least one selected from an ethylene group and a propylene group.

[0021] Also, (OR 12 ) is also preferably a unit based on a monomer (a) described below, which has one epoxy group and an ether bond other than the ether bond of the epoxy group in one molecule. The unit based on the monomer (a) is preferably a unit represented by formula (11). The monomer (a) may be used alone or in combination of two or more types.

[0022] [ka]

[0023] In formula (11), R 101 -R 103 -OR 104 is a monovalent group represented by R 102 is a hydrogen atom or -R 105 -OR 106 R is a monovalent group represented by 103 , R 105 are each independently a linear or branched alkylene group having 1 to 3 carbon atoms, and R 104 , R 106 are each independently a linear or branched alkyl group having 1 to 18 carbon atoms. R 103 , R 105 The alkylene groups are each independently preferably a methylene group, an ethylene group, an n-propylene group, or an isopropylene group, more preferably a methylene group or an ethylene group, and even more preferably a methylene group. R 104 , R 106 The number of carbon atoms in each of the groups independently is preferably 1 to 14, more preferably 1 to 12, and even more preferably 2 to 10. R 104 , R 106 Examples of the linear alkyl group include methyl, ethyl, n-propyl, n-butyl, n-octyl, n-decyl, lauryl, cetyl, and stearyl, with methyl, ethyl, and n-butyl being preferred. The branched alkyl group has a structure in which the hydrogen atoms in the linear alkyl group (excluding the hydrogen atoms bonded to the terminal carbon) are substituted with alkyl groups. Examples of the substituting alkyl groups include methyl and ethyl groups. The branched alkyl group is preferably a 2-ethylhexyl group.

[0024] The monomer (a) is preferably a monomer represented by formula (12). [ka]

[0025] R in equation (12) 101 and R102 has the same meaning as the same symbol in equation (11).

[0026] Examples of the monomer represented by formula (12) include methyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, lauryl glycidyl ether, and hexyl glycidyl ether. Of these, butyl glycidyl ether and 2-ethylhexyl glycidyl ether are preferred because they result in a cured product of the resulting resin composition with better flexibility.

[0027] In formula (1), R 13 is an alkyl group having 1 to 20 carbon atoms. 13 is preferably an alkyl group having 1 to 8 carbon atoms, more preferably a methyl group, an ethyl group or a butyl group, and even more preferably a butyl group. a is an integer of 20 to 600. a is preferably an integer of 35 to 500, and more preferably an integer of 65 to 250.

[0028] (Polyether monool (i-1)) The polyether monool (i-1) in the monomer (1-1) is a compound obtained by ring-opening polymerization of an initiator having an active hydrogen-containing group and having one or more active hydrogen atoms with an alkylene oxide and / or the monomer (a), and having an initiator residue, a polyether chain, and hydroxyl groups corresponding to the number of active hydrogen atoms in the initiator.

[0029] The mass ratio of the monomer (a) to the total mass of the alkylene oxide and the monomer (a) is preferably 0 to 90 mass%, more preferably 0 to 85 mass%, and even more preferably 10 to 80 mass%, from the viewpoint of adjusting the flexibility and strength of the cured product of the resin composition.

[0030] The alkylene oxide is preferably an alkylene oxide having 2 to 8 carbon atoms, and more preferably an alkylene oxide having 2 to 4 carbon atoms. Specific examples of the alkylene oxide include propylene oxide, ethylene oxide, 1,2-butylene oxide, and 2,3-butylene oxide.

[0031] Examples of the active hydrogen-containing group contained in the initiator include a hydroxyl group, a carboxyl group, and an amino group having one hydrogen atom bonded to a nitrogen atom. The active hydrogen-containing group contained in the initiator is preferably a hydroxyl group or a carboxyl group, more preferably a hydroxyl group, and even more preferably an alcoholic hydroxyl group.

[0032] Examples of initiators having one active hydrogen include monohydric alcohols, monohydric phenols, monocarboxylic acids, and amine compounds having one hydrogen atom bonded to a nitrogen atom.Preferably, the initiator is a monohydric aliphatic alcohol or a monohydric aliphatic carboxylic acid, and more preferably a monohydric aliphatic alcohol.Also, a polyoxyalkylene monool having a lower molecular weight than the target polyether monool may be used as the initiator.

[0033] The number of carbon atoms in the monohydric aliphatic alcohol as the initiator is preferably 1 to 20, more preferably 2 to 8. Specific examples of the monohydric aliphatic alcohol as the initiator include ethanol, propanol, 2-propanol, and butanol. The monovalent aliphatic carboxylic acid as the initiator preferably has 2 to 20 carbon atoms, and more preferably 2 to 8 carbon atoms, including the carbon atoms of the carboxy group.

[0034] The oxyalkylene group in the polyether monool (i-1) preferably consists of only an oxypropylene group or a combination of an oxypropylene group and another group, and the oxyalkylene group other than an oxypropylene group is preferably an oxyethylene group. The ratio of oxypropylene groups to all oxyalkylene groups in the polyether monool (i-1) is preferably 50 to 100 mass%, more preferably 80 to 100 mass%. When the initiator is a polyoxyalkylene monool having a lower molecular weight than the target polyether monool, the oxyalkylene groups in the initiator are considered to be oxyalkylene groups in the obtained polyether monool.

[0035] In the polyether monool (i-1), a polyoxyalkylene monool having a low hydroxyl value, i.e., a high molecular weight, can be produced by ring-opening polymerization of an alkylene oxide having 3 or more carbon atoms, particularly propylene oxide, as an initiator in the presence of a composite metal cyanide complex catalyst. Examples of polyoxyalkylene monools with a low hydroxyl value include polyoxyalkylene monools with a hydroxyl value of 40 mgKOH / g or less. A polyoxyalkylene monool having an oxyethylene group and a low hydroxyl value can be produced by ring-opening polymerization of an alkylene oxide having 3 or more carbon atoms, particularly propylene oxide, using a polyoxyalkylene monool having an oxyethylene group and a high hydroxyl value, for example, a hydroxyl value of 50 mgKOH / g or more, as an initiator in the presence of a composite metal cyanide complex catalyst. A polyoxyalkylene monool having a high hydroxyl value can be produced by the ring-opening polymerization in the presence of an alkali catalyst such as potassium hydroxide.

[0036] In the production of polyoxyalkylene monool, the initiator and alkylene oxide introduced into the reaction system are usually those with low water content, with water removed by degassing under reduced pressure or the like. Usually, the lower the water content of the initiator in the production of polyoxyalkylene monool, the better, preferably 500 mass ppm or less, more preferably 300 mass ppm or less. When the water content is within the above range, the amount of polyoxyalkylene diol produced from water is suppressed, and as a result, the amount of by-products caused by polyoxyalkylene diol is suppressed, and it is easy to adjust the upper limit of the average number of hydroxyl groups of the obtained polyoxyalkylene monool to 1.2 or less.

[0037] The water content of the polyether monool (i-1) used as a raw material for the monomer (1-1) is preferably as low as possible, and is preferably 300 ppm by mass or less, more preferably 250 ppm by mass or less, and even more preferably 50 to 200 ppm by mass, relative to the polyether monool (i-1). When the water content is within the above range, the generation of by-products between the water and the isocyanate group-containing compound is reduced, and the stability of the reaction product, the monomer (1-1), is improved. Furthermore, it is easy to suppress changes in the appearance of the resin composition over time, and it is easy to obtain a cured resin composition having good flexibility.

[0038] The average number of hydroxyl groups in one molecule of the polyether monool (i-1) is preferably from 0.80 to 1.20, more preferably from 0.90 to 1.10. The hydroxyl value of the polyether monool (i-1) is preferably from 1.6 to 18.1 mgKOH / g, more preferably from 2.8 to 14 mgKOH / g, and even more preferably from 3.1 to 11.2 mgKOH / g.

[0039] The polyether monool (i-1) in the monomer (1-1) may be a mixture of two or more polyether monools, in which case each polyether monool is preferably a polyoxyalkylene monool falling within the above category.

[0040] Examples of the polyether monool (i-1) include those represented by the formula (1a).

[0041] [ka]

[0042] In formula (1a), R 12 , R 13 and a have the same meaning as the same symbols in formula (1).

[0043] (Compound (i-2) having a (meth)acryloyloxy group) The compound (i-2) having a (meth)acryloyloxy group is a compound having one isocyanate group per molecule and one or two (meth)acryloyloxy groups per molecule. The compound (i-2) having a (meth)acryloyloxy group is preferably a (meth)acrylate having an isocyanate group bonded to an aliphatic hydrocarbon group or an alicyclic hydrocarbon group, and more preferably an isocyanate alkyl (meth)acrylate. The number of carbon atoms in the alkylene group excluding the isocyanate group of the isocyanate alkyl group is preferably 8 or less, more preferably 4 or less.

[0044] An example of the compound (i-2) having a (meth)acryloyloxy group is a compound represented by formula (1b).

[0045] [ka]

[0046] In formula (1b), R 11 is a hydrogen atom or a methyl group. 11 is preferably a hydrogen atom. s is an integer of 1 to 4, and an integer of 1 or 2 is preferred.

[0047] Specific examples of the compound (i-2) having a (meth)acryloyloxy group include 2-isocyanate ethyl (meth)acrylate, isocyanate methyl methacrylate, etc. Commercially available products include, for example, Karenz (registered trademark; hereinafter, abbreviated) AOI and Karenz MOI (both manufactured by Showa Denko K.K.).

[0048] An example of the compound (i-2) having a (meth)acryloyloxy group is a compound represented by formula (1c).

[0049] [ka]

[0050] In formula (1c), R 11 is a hydrogen atom or a methyl group. 11 is preferably a hydrogen atom. R 14 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. 14 is preferably a methyl group. t is an integer of 1 to 8. t is preferably an integer of 1 to 4, and more preferably an integer of 1 or 2. u is an integer of 0 to 4. u is preferably an integer of 0 to 2.

[0051] Specific examples of the compound (i-2) having a (meth)acryloyloxy group include 2,2-(bisacryloyloxymethyl)propyl isocyanate and 1,1-(bisacryloyloxymethyl)ethyl isocyanate (trade name "Karenz BEI", manufactured by Showa Denko K.K.), and 1,1-(bisacryloyloxymethyl)ethyl isocyanate is preferred.

[0052] The monomer (1-1) is preferably at least one selected from the group consisting of compounds represented by formula (1-1-1), compounds represented by formula (1-1-2) and compounds represented by formula (1-1-3).

[0053] [ka]

[0054] In formula (1-1-1), formula (1-1-2) and formula (1-1-3), m, n1 and n2 are each independently preferably an integer of 20 to 600, more preferably an integer of 35 to 500, and even more preferably an integer of 65 to 250. Bu is a butyl group.

[0055] <Monomer (1-2)> The monomer (1-2) is a reaction product of the above (ii), which is an equimolar reaction product of a polyether monool (ii-1), a diisocyanate (ii-2), and a compound (ii-3) having a (meth)acryloyloxy group, and the compound (ii-3) having a (meth)acryloyloxy group is a compound having one group reactive with an isocyanate group in one molecule and one or two (meth)acryloyloxy groups in one molecule.

[0056] The monomer (1-2) is preferably a compound represented by formula (2).

[0057] [ka]

[0058] In formula (2), R 2 is a monovalent organic group having one or two (meth)acryloyloxy groups. R 22 is preferably an alkylene group having 2 to 8 carbon atoms, and more preferably an alkylene group having 2 to 4 carbon atoms. 22 may be the same or different. Two or more types of R 22 If present, -OR 22 - The chain can be block or random. 22 is preferably one or more selected from an ethylene group, a propylene group, a 1,2-dimethylethylene group, and a 1-ethylethylene group, and more preferably one or two selected from an ethylene group and a propylene group. Also, (OR 22 ) in formula (1) 12 Similarly to the monomer (1-1), it is also preferred that the monomer (a) is a unit based on the monomer (a) having one epoxy group and an ether bond other than the ether bond of the epoxy group in one molecule. The preferred embodiments of the monomer (a) are the same as those of the monomer (1-1). R 23 is an alkyl group having 1 to 20 carbon atoms. 23is preferably an alkyl group having 2 to 8 carbon atoms, more preferably a butyl group. R 24 is a divalent group obtained by removing two isocyanate groups from a diisocyanate. Examples of diisocyanates are described below. b is an integer of 20 to 600. b is preferably an integer of 35 to 500, and more preferably an integer of 65 to 250.

[0059] (Polyether monool (ii-1)) The polyether monool (ii-1) is the same as the polyether monool (i-1) in the monomer (1-1), and the preferred embodiments are also the same.

[0060] Examples of the polyether monool (ii-1) include those represented by the formula (2a).

[0061] [ka]

[0062] In formula (2a), R 22 , R 23 and b have the same meaning as the same symbols in formula (2).

[0063] (Diisocyanate (ii-2)) Diisocyanate (ii-2) is a compound having two isocyanate groups in one molecule. Examples of the diisocyanate (ii-2) include non-yellowing aromatic diisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, and various modified products of these diisocyanates (modified products having two isocyanate groups). The diisocyanates may be used alone or in combination of two or more. As the diisocyanate (ii-2), from the viewpoint of flexibility and repeated bending durability of the cured product of the resin composition, one or more types selected from aliphatic diisocyanates and alicyclic diisocyanates are preferred.

[0064] Specific examples of non-yellowing aromatic diisocyanates include xylylene diisocyanate and tetramethylxylylene diisocyanate. Specific examples of the aliphatic diisocyanate include 1,6-hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate. Alicyclic diisocyanates include isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 2,5-norbornane diisocyanate, and 2,6-norbornane diisocyanate.

[0065] The diisocyanate (ii-2) may, for example, be a compound represented by formula (2b).

[0066] [ka]

[0067] In formula (2b), R 24 has the same meaning as the same symbol in formula (2). As the diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate are preferred from the viewpoint of flexibility and repeated bending durability of the cured product of the resin composition.

[0068] (Compound (ii-3) having a (meth)acryloyloxy group) The compound (ii-3) having a (meth)acryloyloxy group is a compound having one group reactive with an isocyanate group in one molecule and one or two (meth)acryloyloxy groups in one molecule. Examples of the group reactive with an isocyanate group include a hydroxyl group and an amino group having a nitrogen atom bonded to a hydrogen atom. The number of hydroxyl groups and the number of hydrogen atoms bonded to the nitrogen atom in the group reactive with an isocyanate group are preferably one each. Furthermore, the group reactive with an isocyanate group is preferably a hydroxyl group bonded to an aliphatic hydrocarbon group or an alicyclic hydrocarbon group.

[0069] The compound (ii-3) having a (meth)acryloyloxy group is preferably a hydroxyalkyl (meth)acrylate or a hydroxycycloalkyl (meth)acrylate, and particularly preferably a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group with 8 or less carbon atoms.

[0070] An example of the compound (ii-3) having a (meth)acryloyloxy group is a compound represented by formula (2c).

[0071] [ka]

[0072] In formula (2c), R 21 is a hydrogen atom or a methyl group. 21 is preferably a hydrogen atom. p is an integer of 1 to 4. p is preferably an integer of 1 or 2.

[0073] Specific examples of the compound (ii-3) having a (meth)acryloyloxy group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, etc. Commercially available products include Light Ester HO-250(N), Light Ester HOP(N), Light Ester HOA(N), Light Ester HOP-A(N), Light Ester HOB(N) (all manufactured by Kyoeisha Chemical Co., Ltd.), and 4-HBA (manufactured by Osaka Organic Chemical Industry Ltd.).

[0074] An example of the compound (ii-3) having a (meth)acryloyloxy group is a compound represented by formula (2d).

[0075] [ka]

[0076] In formula (2d), R 21 is a hydrogen atom or a methyl group. 21 is preferably a hydrogen atom. R 25 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. 25 is preferably a methyl group. q is an integer of 1 to 8. q is preferably an integer of 1 to 4, and more preferably an integer of 1 or 2. r is an integer of 0 to 4. r is preferably an integer of 0 to 2.

[0077] Specific examples of the compound (ii-3) having a (meth)acryloyloxy group include 2,2-(bisacryloyloxymethyl)propan-1-ol and 1,1-(bisacryloyloxymethyl)ethan-1-ol, and 1,1-(bisacryloyloxymethyl)ethan-1-ol is preferred.

[0078] <Monomer (1-3)> Monomer (1-3) is a reaction product of the above-mentioned (iii), which is an equimolar reaction product of polyether polyol (iii-1) and compound (iii-2) having a (meth)acryloyloxy group, and compound (iii-2) having a (meth)acryloyloxy group is a compound having one isocyanate group per molecule and one or two (meth)acryloyloxy groups per molecule.

[0079] The monomer (1-3) is preferably a compound represented by formula (III). R 3 -NH-C(=O)-Z 1 (III) In formula (III), R 3 is a monovalent organic group having one or two (meth)acryloyloxy groups. Z 1 is a residue of a polyether polyol obtained by removing one hydrogen atom from one of the hydroxyl groups in the polyether polyol.

[0080] The monomer (1-3) is more preferably a compound represented by formula (3).

[0081] [ka]

[0082] In formula (3), R 3 is R in formula (III) 3 The same meaning as the same symbol in the figure. R 32 is preferably an alkylene group having 2 to 8 carbon atoms, and more preferably an alkylene group having 2 to 4 carbon atoms. 32 may be the same or different. Two or more types of R 32 If present, -OR 32 The chain of - can be block or random. 32 is preferably one or more selected from an ethylene group, a propylene group, a 1,2-dimethylethylene group, and a 1-ethylethylene group, and more preferably one or two selected from an ethylene group and a propylene group. Also, (OR 32 ) in formula (1) 12 As with the monomer (1-1), it is also preferred that the monomer (a) is a unit based on a monomer (a) having one epoxy group and an ether bond other than the ether bond of the epoxy group in one molecule. The preferred embodiments of the monomer (a) are the same as those of the monomer (1-1). c is an integer of 20 to 600. c is preferably an integer of 35 to 500, and more preferably an integer of 65 to 250.

[0083] (Polyether polyol (iii-1)) The polyether polyol (iii-1) is a compound obtained by ring-opening polymerization of an initiator having an active hydrogen-containing group and having two or more active hydrogen atoms with an alkylene oxide and / or the monomer (a), and has an initiator residue, a polyether chain, and hydroxyl groups corresponding to the number of active hydrogen atoms in the initiator.

[0084] The alkylene oxide is preferably an alkylene oxide having a carbon number of 2 to 4. Specific examples of the alkylene oxide having a carbon number of 2 to 4 include propylene oxide, ethylene oxide, 1,2-butylene oxide, and 2,3-butylene oxide. Furthermore, as the monomer (a), a monomer represented by the formula (12) is preferred. Examples of the monomer represented by the formula (12) include methyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, lauryl glycidyl ether, and hexyl glycidyl ether. Of these, butyl glycidyl ether and 2-ethylhexyl glycidyl ether are preferred because they result in a cured product of the resulting resin composition with better flexibility.

[0085] The mass ratio of the monomer (a) to the total mass of the alkylene oxide and the monomer (a) is preferably 0 to 90 mass%, more preferably 0 to 85 mass%, and even more preferably 10 to 80 mass%, from the viewpoint of adjusting the flexibility and strength of the cured product of the obtained resin composition.

[0086] Examples of the active hydrogen-containing group contained in the initiator include a hydroxyl group, a carboxyl group, and an amino group having a hydrogen atom bonded to a nitrogen atom. The active hydrogen-containing group contained in the initiator is preferably a hydroxyl group, and more preferably an alcoholic hydroxyl group.

[0087] Examples of initiators having two or more active hydrogen atoms include water, polyhydric alcohols, polyhydric phenols, polycarboxylic acids, and amine compounds having two or more hydrogen atoms bonded to nitrogen atoms. The initiator is preferably water or a dihydric aliphatic alcohol, more preferably a dihydric aliphatic alcohol. Alternatively, a polyoxyalkylene polyol having a lower molecular weight than the target polyether polyol may be used as the initiator.

[0088] The carbon number of the dihydric aliphatic alcohol as the initiator is preferably 2 to 8. Specific examples of the dihydric aliphatic alcohol as the initiator include ethylene glycol, propylene glycol, polypropylene glycol such as dipropylene glycol, and 1,4-butanediol.

[0089] The oxyalkylene groups in the polyether polyol (iii-1) preferably consist solely of oxypropylene groups or a combination of oxypropylene groups with other groups, and the oxyalkylene groups other than oxypropylene groups are preferably oxyethylene groups or oxytetramethylene groups. The proportion of oxypropylene groups to all oxyalkylene groups in the polyether polyol is preferably 50 to 100 mass%, more preferably 80 to 100 mass%. When the initiator is a polyoxyalkylene polyol having a lower molecular weight than the target polyether polyol, the oxyalkylene group in the initiator is considered to be the oxyalkylene group in the resulting polyether polyol.

[0090] Among the polyether polyols (iii-1), polyoxyalkylene polyols having a low hydroxyl value, i.e., a high molecular weight, can be produced by ring-opening polymerization of an alkylene oxide having 3 or more carbon atoms, particularly propylene oxide, as an initiator in the presence of a composite metal cyanide complex catalyst. Examples of polyoxyalkylene polyols with a low hydroxyl value include polyoxyalkylene polyols with a hydroxyl value of 40 mgKOH / g or less. Among the polyether polyols (iii-1), a polyoxyalkylene polyol having an oxyethylene group and a low hydroxyl value can be produced by ring-opening polymerization of an alkylene oxide having 3 or more carbon atoms, particularly propylene oxide, using a polyoxyalkylene polyol having an oxyethylene group and a high hydroxyl value, for example, a hydroxyl value of 50 mgKOH / g or more, as an initiator in the presence of a composite metal cyanide complex catalyst. Among the polyether polyols (iii-1), the polyoxyalkylene polyol having a high hydroxyl value and the polyoxyalkylene polyol having a high hydroxyl value as the initiator can also be produced using an alkali catalyst such as KOH.

[0091] The average number of hydroxyl groups in one molecule of the polyether polyol (iii-1) is preferably 1.60 to 2.00, more preferably 1.70 to 2.00, and even more preferably 1.80 to 1.96. A polyether polyol having an average number of hydroxyl groups in one molecule of 1.60 to 2.00 is sometimes called a polyether diol. The hydroxyl value of the polyether polyol (iii-1) is preferably from 1.6 to 18.1 mgKOH / g, more preferably from 2.8 to 14 mgKOH / g.

[0092] The polyether polyol (iii-1) may be a mixture of two or more polyether polyols, in which case each polyether polyol is preferably a polyether polyol within the above-mentioned category, and each polyether polyol is preferably a polyether diol within the above-mentioned category.

[0093] An example of the polyether polyol (iii-1) is one represented by the formula (3a).

[0094] [ka]

[0095] In formula (3a), R 32 and c have the same meaning as the same symbols in formula (3).

[0096] (Compound (iii-2) having a (meth)acryloyloxy group) The compound (iii-2) having a (meth)acryloyloxy group is a compound having one isocyanate group per molecule and one or two (meth)acryloyloxy groups per molecule. The compound (iii-2) having a (meth)acryloyloxy group is the same as the compound (i-2) having a (meth)acryloyloxy group in the monomer (1-1), and preferred embodiments are also the same.

[0097] [Second Monomer] In addition to the first monomer, the resin composition preferably contains one or more second monomers selected from the reaction products (hereinafter also referred to as "monomer (2-1)" and "monomer (2-2)") of the following (iv) and (v). That is, the resin composition preferably contains the first monomer and the second monomer. The second monomer in the resin composition may be one type alone or two or more types in combination. (iv) A reaction product of a polyether polyol and a compound having a (meth)acryloyloxy group, The compound having a (meth)acryloyloxy group is a compound having one isocyanate group in one molecule and one or two (meth)acryloyloxy groups in one molecule, A reaction product in which the number of moles of hydroxyl groups in the polyether polyol is equal to the number of moles of the compound having a (meth)acryloyloxy group. (v) A reaction product of a polyol (A), a polyisocyanate, and a compound having a (meth)acryloyloxy group, the polyol (A) is at least one selected from polyoxyalkylene polyols, polyester polyols, poly(meth)acrylic polyols, polycarbonate polyols, castor oil-based polyols, and polyolefin polyols; The compound having a (meth)acryloyloxy group is a compound having one group reactive with an isocyanate group in one molecule and one or two (meth)acryloyloxy groups in one molecule, A reaction product in which the total number of moles of hydroxyl groups in the polyol (A) and groups reactive with isocyanate groups in the compound having a (meth)acryloyloxy group is equal to the number of moles of isocyanate groups in the polyisocyanate.

[0098] The second monomer is a polyfunctional urethane (meth)acrylate having two or more (meth)acryloyloxy groups and can act as a crosslinking monomer that crosslinks the first monomer. A resin composition containing the first monomer and the second monomer has a reduced cure shrinkage rate of the resin composition, and a cured product of the resin composition has excellent flexibility.

[0099] The second monomer preferably has a molecular weight of 6,000 to 60,000, more preferably 8,000 to 40,000, and even more preferably 10,000 to 34,000. When the molecular weight is 6,000 or more, flexibility is easily obtained in the cured product of the resin composition, and when it is 60,000 or less, the viscosity of the resin composition is low, making it easier to mix the resin composition.

[0100] <Monomer (2-1)> Monomer (2-1) is a reaction product of the above-mentioned (iv), which is a reaction product of polyether polyol (iv-1) and compound (iv-2) having a (meth)acryloyloxy group, and compound (iv-2) having a (meth)acryloyloxy group has one isocyanate group per molecule and one or two (meth)acryloyloxy groups per molecule, and the number of moles of hydroxyl groups in polyether polyol (iv-1) is equal to the number of moles of compound (iv-2) having a (meth)acryloyloxy group.

[0101] The monomer (2-1) is preferably a compound represented by formula (IV). R 4 -NHC(=O)-Z2 -C(=O)NH-R 4 (IV) In formula (IV), R 4 is a monovalent organic group having one or two (meth)acryloyloxy groups. Z 2 is a residue of polyether polyol (iv-1) obtained by removing two hydrogen atoms from two hydroxyl groups in polyether polyol (iv-1).

[0102] The monomer (2-1) is more preferably a compound represented by formula (4).

[0103] [ka]

[0104] In formula (4), R 4 has the same meaning as the same symbol in formula (IV). R 42 is preferably an alkylene group having 2 to 8 carbon atoms, and more preferably an alkylene group having 2 to 4 carbon atoms. 42 may be the same or different. Two or more types of R 42 If present, -OR 42 The chain of - can be block or random. 42 is preferably one or more selected from an ethylene group, a propylene group, a 1,2-dimethylethylene group, and a 1-ethylethylene group, and more preferably one or two selected from an ethylene group and a propylene group. Also, (OR 42 ) in formula (1) 12 As with the monomer (1-1), it is also preferred that the monomer (a) is a unit based on a monomer (a) having one epoxy group and an ether bond other than the ether bond of the epoxy group in one molecule. The preferred embodiments of the monomer (a) are the same as those of the monomer (1-1). d is an integer of 20 to 600. d is preferably an integer of 35 to 500, and more preferably an integer of 65 to 250.

[0105] The polyether polyol (iv-1) is the same as the polyether polyol (iii-1) in the monomer (1-3), and the preferred embodiments are also the same.

[0106] The compound (iv-2) having a (meth)acryloyloxy group is the same as the compound (i-2) having a (meth)acryloyloxy group in the monomer (1-1), and the preferred embodiments are also the same.

[0107] <Monomer (2-2)> Monomer (2-2) is a reaction product of (v) above, which is a reaction product of polyol (A), polyisocyanate (v-1), and compound (v-2) having a (meth)acryloyloxy group, in which polyol (A) is one or more selected from polyether polyols, polyester polyols, poly(meth)acrylic polyols, polycarbonate polyols, castor oil-based polyols, and polyolefin polyols, and compound (v-2) having a (meth)acryloyloxy group is a compound having one group reactive with an isocyanate group per molecule and one or two (meth)acryloyloxy groups per molecule, and the total number of moles of hydroxyl groups in polyol (A) and groups reactive with isocyanate groups in compound (v-2) having a (meth)acryloyloxy group is equal to the number of moles of isocyanate groups in polyisocyanate (v-1).

[0108] The monomer (2-2) is preferably a compound represented by formula (5).

[0109] [ka]

[0110] In formula (5), R 5 is a monovalent organic group having one or two (meth)acryloyloxy groups. R 52is preferably an alkylene group having 2 to 8 carbon atoms, and more preferably an alkylene group having 2 to 4 carbon atoms. 52 may be the same or different. Two or more types of R 52 If present, -OR 52 -The chain can be block or random. 52 is preferably one or more selected from an ethylene group, a propylene group, a 1,2-dimethylethylene group, and a 1-ethylethylene group, and more preferably one or two selected from an ethylene group and a propylene group. Also, (OR 52 ) in formula (1) 12 As with the monomer (1-1), it is also preferred that the monomer (a) is a unit based on a monomer (a) having one epoxy group and an ether bond other than the ether bond of the epoxy group in one molecule. The preferred embodiments of the monomer (a) are the same as those of the monomer (1-1). R 54 is a divalent group obtained by removing two isocyanate groups from a diisocyanate. The diisocyanate is the same as the diisocyanate in the monomer (1-2), and the preferred embodiments are also the same. e is an integer of 20 to 600. e is preferably an integer of 35 to 500, and more preferably an integer of 65 to 250.

[0111] Of the polyols (A), the polyether polyol is the same as the polyether polyol (iii-1) in the monomer (1-3), and the preferred embodiments are also the same. In the polyol (A), polyether polyols, polyester polyols, poly(meth)acrylic polyols, polycarbonate polyols, castor oil-based polyols, and polyolefin polyols described in

[0016] to

[0028] of JP 2020-37689 A can be used without any particular limitation. The polyether polyol may be a polymer polyol in which a polymer having units based on a (meth)acrylate monomer is dispersed in a polyether polyol. The polymer polyol may be a commercially available product, such as the "ULTIFLOW (registered trademark)" series or the "SHARPFLOW (registered trademark)" series (both manufactured by Sanyo Chemical Industries, Ltd.), or the "EXCENOL (registered trademark)" series (manufactured by AGC Inc.).

[0112] The polyisocyanate (v-1) is a compound having two or more isocyanate groups in one molecule. The polyisocyanate is preferably a compound having two or three isocyanate groups in one molecule, and more preferably a diisocyanate. The diisocyanate is the same as the diisocyanate (ii-2) in the monomer (1-2), and the preferred embodiments are also the same. Specific examples of polyisocyanate (v-1) include tolylene diisocyanate, hexamethylene diisocyanate, diphenylmethylene diisocyanate, and isophorone diisocyanate. From the viewpoint of ease of adjusting the elongation and strength of the cured product of the resin composition, hexamethylene diisocyanate or isophorone diisocyanate is preferred.

[0113] The compound (v-2) having a (meth)acryloyloxy group is the same as the compound (ii-2) having a (meth)acryloyloxy group in the monomer (1-2), and the preferred embodiments are also the same.

[0114] [Contents of first monomer and second monomer] The content of the first monomer relative to 100 parts by mass of the resin composition is preferably 50 to 98 parts by mass, more preferably 70 to 95 parts by mass, and even more preferably 80 to 90 parts by mass, from the viewpoint of appropriate flexibility and repeated bending durability of the cured product of the resin composition. Monomer (1-1), monomer (1-2), and monomer (1-3) may be used alone or in combination of two or more. It is more preferable that the first monomer contains one or more selected from monomer (1-1) and monomer (1-2). From the viewpoints of reducing the cure shrinkage of the resin composition and improving the flexibility of the cured product of the resin composition, the total content of monomer (1-1) and monomer (1-2) per 100 parts by mass of the first monomer is preferably 50 parts by mass or more, more preferably 80 parts by mass or more, and particularly preferably 100 parts by mass. In this case, the content of monomer (1-1) is preferably 50 to 100 parts by mass per 100 parts by mass of the total content of monomer (1-1) and monomer (1-2).

[0115] When the resin composition contains a second monomer, from the viewpoint of appropriate flexibility and repeated bending durability of the cured product of the resin composition, the content of the second monomer per 100 parts by mass of the resin composition is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 15 parts by mass or less.

[0116] [Other ingredients] The resin composition may contain components other than the first monomer and the second monomer from the viewpoint of improving the flexibility and repeated bending durability of the cured product of the resin composition, etc. Examples of the other components include monomers other than the first monomer and the second monomer (hereinafter also referred to as "other monomers"), polymerization initiators, etc. Furthermore, if necessary, optional components such as catalysts (tertiary amine compounds, quaternary ammonium compounds, tin laurate compounds, etc.), colorants such as pigments and dyes, silane coupling agents, tackifying resins, antioxidants, light stabilizers, metal deactivators, rust inhibitors, antiaging agents, moisture absorbents, hydrolysis inhibitors, antistatic agents, foam stabilizers, fillers, etc. may also be included. A solvent may also be included. These other components are blended into the resin composition in an amount within a range that does not impair the effects of the present invention.

[0117] The resin foam layer may also contain hollow particles, and the hollow portions of the hollow particles may form bubbles in the resin foam layer. In this case, the hollow particles are blended into the resin composition.

[0118] <Other monomers> The other monomer is a compound that copolymerizes with the first monomer (or the first monomer and the second monomer, if the resin composition contains a second monomer), and may be used alone or in combination of two or more types. Examples of the other monomer include (meth)acrylates such as alkyl (meth)acrylates, hydroxyl group-containing (meth)acrylates, and amino group-containing (meth)acrylates, from the viewpoints of ease of copolymerization with the first monomer and the second monomer, ease of adjusting the viscosity of the resin composition, etc.

[0119] Examples of the alkyl(meth)acrylate include alkyl(meth)acrylates having a linear or branched alkyl group, and the alkyl group preferably has 1 to 18 carbon atoms, more preferably 1 to 14 carbon atoms, and even more preferably 1 to 10 carbon atoms. Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-undecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, and n-tetradecyl (meth)acrylate. Examples of hydroxyl group-containing (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, caprolactone-modified (meth)acrylate, polyoxyethylene (meth)acrylate, and polyoxypropylene (meth)acrylate. Examples of amino group-containing (meth)acrylates include aminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate, and dimethylaminomethyl (meth)acrylate.

[0120] The other monomer may be a crosslinkable monomer having two or more functional groups capable of crosslinking the first monomer. The crosslinkable monomer may be used alone or in combination of two or more. The functional group of the crosslinkable monomer is preferably at least one selected from the group consisting of (meth)acryloyloxy, epoxy, isocyanate, carboxy, hydroxy, carbodiimide, oxazoline, aziridine, vinyl, amino, imino, and amide groups. The functional group may be protected with a deprotectable protecting group. The number of functional groups in one molecule of the crosslinkable monomer is preferably 2 to 4, more preferably 2 or 3.

[0121] Examples of crosslinkable monomers include bifunctional alkyl (meth)acrylates such as 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, and neopentyl glycol di(meth)acrylate; bifunctional (meth)acrylates having a polyoxyalkylene chain such as polyethylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, polyethylene glycol-polypropylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate; trifunctional or higher functional (meth)acrylates such as trimethylolpropane tri(meth)acrylate, ε-caprolactone-modified tris(acryloxyethyl) isocyanurate, pentaerythritol tri(meth)acrylate, and pentaerythritol penta(meth)acrylate; and triallyl isocyanurate. From the viewpoints of ease of copolymerization with the first monomer and the second monomer and ease of adjusting the viscosity of the resin composition, polypropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ε-caprolactone-modified tris(acryloxyethyl)isocyanurate, and triallyl isocyanurate are preferred, and polypropylene glycol di(meth)acrylate and ε-caprolactone-modified tris(acryloxyethyl)isocyanurate are more preferred.

[0122] When a crosslinkable monomer is blended, the content of the crosslinkable monomer in the resin composition is preferably 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, and even more preferably 1.0 to 5 parts by mass, per 100 parts by mass of the first monomer (or the first monomer and the second monomer, if the resin composition contains a second monomer), from the viewpoint of flexibility of the cured product of the resin composition at low temperatures.

[0123] <Polymerization initiator> The resin composition may be cured by photocuring or heat curing. When the resin composition is cured in the device fabrication process, photocuring has a high curing rate and does not require high temperatures, so that the device is not damaged by heat. In the case of photocuring, it is preferable to contain a photopolymerization initiator.

[0124] From the viewpoint of controlling the polymerization reaction, the photopolymerization initiator is preferably one that can be used with ultraviolet irradiation at a wavelength of 380 nm or less. The photopolymerization initiator may be used alone or in combination of two or more kinds. Examples of the photopolymerization initiator include those described in paragraphs

[0147] to

[0151] of WO 2018 / 173896. The photopolymerization initiator is preferably a hydrogen abstraction photopolymerization initiator in which a photoexcited initiator and a hydrogen donor in the system form an exciplex, transferring hydrogen from the hydrogen donor. Specific examples of hydrogen abstraction photopolymerization initiators include benzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3'-dimethyl-4-methoxybenzophenone, 4-(meth)acryloyloxybenzophenone, 4-[2-((meth)acryloyloxy)ethoxy]benzophenone, 4-(meth)acryloyloxy-4'-methoxybenzophenone, methyl 2-benzoylbenzoate, and methyl benzoylformate. Furthermore, as the photopolymerization initiator, from the viewpoint of high sensitivity to light, an acylphosphine oxide photoinitiator such as phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, or bis(2,6-dimethoxybenzoyl)2,4,4-trimethylpentylphosphine oxide is preferred.

[0125] As the thermal polymerization initiator, a known thermal polymerization initiator used in polymerization of (meth)acrylate can be used by a known method, and examples thereof include azo compounds such as 2,2'-azobisbutyronitrile, peroxides such as benzoyl peroxide, etc. The thermal polymerization initiator may be used alone or in combination of two or more types.

[0126] From the viewpoint of ensuring appropriate progress of curing accompanying the polymerization of the resin composition, the content of the polymerization initiator in the resin composition is preferably 0.01 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, and even more preferably 0.2 to 5 parts by mass, relative to 100 parts by mass of the total of the first monomer and the second monomer.

[0127] <Hollow particles> The hollow particles are not particularly limited and may be hollow inorganic or organic microspheres, or hollow organic-inorganic composite microspheres. Examples of hollow inorganic microspheres include hollow glass balloons and other glass hollow balloons, hollow metal compound balloons such as hollow silica balloons and hollow alumina balloons, and hollow porcelain balloons such as hollow ceramic balloons. Examples of hollow organic microspheres include hollow resin balloons such as hollow acrylic balloons, hollow vinylidene chloride balloons, phenol balloons, and epoxy balloons.

[0128] The average particle size of the hollow particles is not particularly limited as long as it is equal to or less than the thickness of the resin foam layer, but from the viewpoint of good impact absorption performance, it is preferably 10 to 150 μm, more preferably 20 to 130 μm, and even more preferably 30 to 100 μm. The average particle size of the hollow particles can be measured by, for example, a laser diffraction method or a low-angle laser light scattering method.

[0129] The ratio of the average particle diameter of the hollow particles to the thickness of the resin foam layer (average particle diameter / thickness) is preferably 0.1 to 0.9, more preferably 0.2 to 0.85, from the viewpoint of uniformly distributing air bubbles in the resin foam layer.

[0130] The density of the hollow particles is not particularly limited, but is preferably 0.01 to 0.4 g / cm from the viewpoint of uniformly distributing the bubbles in the resin foam layer. 3 is preferable, and 0.02 to 0.3 g / cm 3 is more preferred.

[0131] The content of hollow particles in the resin composition varies depending on the density of the hollow particles, but from the viewpoints of the impact absorption properties, flexibility at low temperatures, and repeated bending durability of the resin foam layer, it is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and even more preferably 1 to 3 parts by mass, per 100 parts by mass of the resin composition.

[0132] [Glass transition temperature] The resin composition has a glass transition temperature (Tg) of -55°C or lower, more preferably -58°C or lower, and even more preferably -60°C or lower. When the Tg is -55°C or lower, the cured resin composition has excellent flexibility at low temperatures and durability against repeated bending. From the viewpoint of enabling the resin foam layer formed from the cured resin composition to exhibit excellent impact absorption performance, the lower limit of the Tg is preferably -85°C or higher, more preferably -80°C or higher. The Tg of the cured product of the resin composition of the present invention can be calculated by Fox's formula based on the Tg values ​​of the homopolymers of the respective monomer components in the resin composition.

[0133] [Air bubbles] The resin foam layer contains a cured product of the resin composition and bubbles. The bubbles in the resin foam layer may be formed by hollow portions of hollow particles blended in the resin composition, as described above, or by mixing a gas or a foaming agent into the resin composition, followed by foaming and curing. When cells are formed using hollow particles, it is easy to make the cell diameter uniform, and it is easy to control the cell distribution by using closed cells. From the viewpoint of sufficient impact absorption, a uniform cell distribution is preferable. When bubbles are formed by foaming, unlike hollow particles, the bubbles are covered with the resin composition and do not have an outer shell, making it easier to obtain a resin foam layer that is excellent in flexibility and durability against repeated bending. The cells in the resin foam layer may be closed cells, open cells, or both closed cells and open cells.

[0134] [Apparent density] The apparent density of the resin foam layer is 0.3 to 0.8 g / cm from the viewpoint of sufficient shock absorption performance. 3 is preferable, and 0.45 to 0.8 g / cm 3 More preferably, 0.6 to 0.79 g / cm 3 is more preferable. The apparent density is determined by measurement based on JIS K 7222:2005.

[0135] [Thickness] The thickness of the resin foam layer is preferably 300 μm or less, more preferably 20 to 280 μm, and even more preferably 50 to 250 μm, from the viewpoints of the impact absorbing performance of the impact absorbing sheet and the installation space in the device. The impact-absorbing sheet of the present invention is preferably composed only of a resin foam layer. Furthermore, from the viewpoints of imparting light-blocking properties and improving processability and handling, other layers such as skin layers composed of various resins may be provided on one or both sides of the resin foam layer. Examples of resins constituting the skin layer include the resins constituting the resin composition, other acrylic resins, thermoplastic elastomers, polyolefin resins, polyester resins, urethane resins, polyimide resins, etc. Other layers include rubber, metal foil, nonwoven fabric, etc. The thickness of the other layer is within a range that does not impair the function of the resin foam layer, and is preferably less than the thickness of the resin foam layer. The thickness of the other layer is, for example, about 1 to 100 μm. The thickness can be measured using a micrometer.

[0136] [Method for forming resin foam layer] The formation of the resin foam layer is not particularly limited. When air bubbles in the resin foam layer are formed by hollow particles, the resin foam layer can be formed, for example, by applying a resin composition containing hollow particles to a support such as a release film or a substrate, and then curing the resin composition. The resin composition is prepared by mixing a first monomer, hollow particles, and optionally a second monomer and other components. The order in which the components are mixed is not particularly limited. From the viewpoint of handling for mixing and application, a solvent may be added to the resin composition. In this case, it is preferable to remove the solvent during or after curing. The method for applying the resin composition is not particularly limited, and can be a conventional method, such as a slot die method, a reverse gravure coating method, a microgravure coating method, a dipping method, a spin coating method, a brush coating method, a roll coating method, or a flexographic printing method. As described above, the resin composition may be cured by photocuring or heat curing.

[0137] In addition, when forming bubbles in the resin foam layer by mixing gas, the bubbles can be formed, for example, by mixing gas into the resin composition using a mechanical froth method, applying the resin composition containing the bubbles onto a support such as a release film or a substrate, and curing it. In this case, from the viewpoint of uniform bubble formation, etc., an emulsion in which a polymer is dispersed in a dispersion medium such as water can also be used as the resin composition. The emulsion can be obtained, for example, by polymerizing a monomer component by a method such as emulsion polymerization, suspension polymerization, or dispersion polymerization in the presence of a polymerization initiator, an emulsifier, a dispersion stabilizer, etc., which are added as needed. A foaming agent such as a surfactant may be added to the emulsion as needed. The dispersion medium of the emulsion preferably contains water, and may contain polar solvents other than water, such as methanol, ethanol, isopropanol, acetone, dipropylene glycol, tripropylene glycol, etc. The solid content of the emulsion is, for example, 30 to 70% by mass, and preferably 35 to 60% by mass, from the viewpoint of handleability in the mechanical froth method.

[0138] Specifically, the mechanical froth method involves mixing a gas into a resin composition while kneading the resin composition using a kneader such as a high-speed shearing or vibration kneader. Examples of gases that can be used include air, nitrogen, carbon dioxide, and argon. Gases may also be mixed into the resin composition using a device that discharges pressurized gas. The amount of gas mixed in is preferably adjusted appropriately so that a resin foam layer with the desired density is obtained. The bubble diameter in the resin composition is approximately the same as the bubble diameter in the resin foam layer, and can be adjusted by adding a foam stabilizer or the like to the resin composition or adjusting the kneading time. The method of applying and curing the resin composition is the same as in the case of forming cells in the resin foam layer using hollow particles.

[0139] [Usage] The shock-absorbing sheet of the present invention can be suitably used in, for example, electronic devices, particularly mobile devices such as smartphones, tablet terminals, laptop computers, etc. Specifically, it is disposed between the cover panel and housing of these mobile devices, between a display device such as a liquid crystal or organic EL display and a touch screen panel, or on the back side of the display device, and absorbs shocks that these mobile devices, displays, etc. receive. The impact absorbing sheet of the present invention has excellent impact absorbing performance even though it is thin, and therefore contributes to preventing breakage of electronic devices while making them thinner. Furthermore, the impact absorbing sheet of the present invention has excellent flexibility at low temperatures, and can exhibit excellent impact absorbing performance even in electronic devices used in low temperature environments of 0°C or below. Furthermore, the impact absorbing sheet of the present invention has excellent durability against repeated bending, and therefore can continuously exhibit excellent impact absorbing performance even in areas where loads are applied due to repeated bending of a foldable device.

[0140] The impact absorbing sheet may be used by laminating a resin sheet on one or both sides thereof as needed. Examples of resins used for the resin sheet include thermoplastic resins such as polyolefin resins such as polyethylene and polypropylene; and polyester resins such as polyethylene terephthalate. Each resin sheet is preferably thinner than the impact absorbing sheet, and has a thickness of, for example, 10 to 300 μm, preferably 10 to 200 μm. The resin sheet can be bonded to the impact absorbing sheet by thermocompression bonding, or can also be bonded to the impact absorbing sheet using an adhesive or the like.

[0141] The impact absorbing sheet can also be used as an adhesive tape by providing an adhesive material on at least a portion of one or both surfaces. The adhesive material of the adhesive tape allows the impact absorbing sheet to be easily attached to components such as the housing of an electronic device. The adhesive material has at least an adhesive layer, and preferably consists of only an adhesive layer laminated on the surface of the impact absorbing sheet. The adhesive material is also preferably a double-sided adhesive sheet having a substrate and adhesive layers provided on both sides of the substrate, and is attached to the surface of the impact absorbing sheet. The double-sided adhesive sheet can adhere one adhesive layer to the impact absorbing sheet, and the other adhesive layer to components of an electronic device, etc. The adhesive constituting the adhesive layer is not particularly limited, and for example, an acrylic adhesive, a urethane adhesive, a rubber adhesive, etc. can be used. From the viewpoint of thinning the adhesive sheet, the thickness of the adhesive is preferably 5 to 200 μm, more preferably 7 to 150 μm. Furthermore, a release film such as release paper may be further laminated on the adhesive, and the adhesive layer of the adhesive sheet before use may be protected by the release film. [Example]

[0142] The present invention will be specifically described below based on examples, but the present invention is not limited to the following examples.

[0143] [Production of resin composition] Resin compositions for producing impact-absorbing sheet samples are produced according to the following synthesis examples and production examples.

[0144] [Measurement of number average molecular weight] The number average molecular weight of the products obtained in the synthesis examples was measured by gel permeation chromatography (GPC) under the following measurement conditions. <Measurement conditions> Equipment used: "HLC-8120GPC", manufactured by Tosoh Corporation Columns used: The following two columns are connected in series: "TSKgel (registered trademark) G7000HXL," manufactured by Tosoh Corporation, 1 bottle "TSKgel (registered trademark) GMHXL," manufactured by Tosoh Corporation, 2 bottles Column temperature: 40℃ Detector: Refractive index (RI) detector Eluent: tetrahydrofuran ·Flow rate: 0.8mL / min Sample concentration: 0.5% by mass Sample injection volume: 100 μL Standard sample: Polystyrene

[0145] [Raw material compound] Details of the raw material compounds used in the synthesis examples and production examples are as follows. DMC-TBA: Zinc hexacyanocobaltate-tert-butanol complex AOI: 2-acryloyloxyethyl isocyanate; Karenz AOI, manufactured by Showa Denko K.K. Photopolymerization initiator: phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide; "Irgacure (registered trademark) 819" manufactured by BASF ADP-400: Polypropylene glycol diacrylate; "Blenmer (registered trademark) ADP-400" manufactured by NOF Corporation; number average molecular weight approximately 400 (catalog value); crosslinkable monomer; homopolymer Tg -18°C M-325: ε-caprolactone-modified tris(acryloxyethyl) isocyanurate; "Aronix (registered trademark) M-325" manufactured by Toagosei Co., Ltd.; crosslinkable monomer; Tg of homopolymer: 195°C BA: n-butyl acrylate; homopolymer Tg -54°C MA: methyl acrylate; homopolymer Tg -8℃ Hollow particles: "Expancel (registered trademark) 920DE80d30", manufactured by Nippon Phillite Co., Ltd., average particle diameter 80 μm

[0146] [Synthesis Example 1] A pressure-resistant reactor equipped with a stirrer and a nitrogen inlet tube was charged with 0.2 g of DMC-TBA and 30 g of n-butanol, and then 3970 g of propylene oxide was added at a constant rate over 7 hours at 130° C. under a nitrogen atmosphere. After confirming that the internal pressure of the pressure-resistant reactor had stopped decreasing, 4000 g of polyoxypropylene monool having a hydroxyl value of 5.6 mg KOH / g (hydroxyl value-based molecular weight of 10,000) and an average number of hydroxyl groups of 1.08 was obtained. 964.9 g of the polyoxypropylene monool and 13.1 g of AOI (NCO index 100) were added to a reaction vessel equipped with a stirrer and a nitrogen inlet tube, and the mixture was stirred at 70°C for 3 hours in the presence of 0.08 g of a 25% by weight toluene solution of bismuth 2-ethylhexanoate to obtain a product containing a monofunctional urethane acrylate (number average molecular weight 16,000). The Tg of the homopolymer of this product was -65°C.

[0147] [Production Example 1] Production of Resin Composition 1A 100 parts by mass of the product obtained in Synthesis Example 1, 2 parts by mass of ADP-400, 1 part by mass of M-325, 0.3 parts by mass of a photopolymerization initiator, and 2 parts by mass of hollow particles are mixed to prepare a resin composition 1A.

[0148] [Production Example 2] Production of Resin Composition 1B Resin composition 1B is prepared by mixing an emulsion of 100 parts by mass of a water dispersion (solid content 50% by mass) of the polymer obtained by emulsion polymerization of the product obtained in Synthesis Example 1 and 0.3 parts by mass of a photopolymerization initiator.

[0149] [Production Example 3] Production of Resin Composition 2A 25 parts by mass of BA, 75 parts by mass of MA, and 0.3 parts by mass of a photopolymerization initiator are mixed and partially polymerized by irradiating with ultraviolet light, and then 2 parts by mass of ADP-400, 1 part by mass of M-325, 0.3 parts by mass of the photopolymerization initiator, and 2 parts by mass of hollow particles are added and mixed to prepare Resin Composition 2A.

[0150] [Production Example 4] Production of Resin Composition 2B Resin composition 2B is prepared by mixing an emulsion of 100 parts by mass of an acrylic polymer obtained by emulsion polymerization of 25 parts by mass of BA and 75 parts by mass of MA in water (solid content 50% by mass) with 0.3 parts by mass of a photopolymerization initiator.

[0151] [Manufacturing impact absorbing sheet samples] Using each of the resin compositions obtained in Production Examples 1 to 4 above, impact absorbing sheet samples are prepared.

[0152] [Example 1] Resin composition 1A was applied onto a release film (a silicone-coated polyethylene terephthalate film: "SP-PET-O1-75BU", manufactured by Mitsui Chemicals Tocello Co., Ltd., thickness 75 μm; the same applies hereinafter), and then exposed to ultraviolet light (illuminance 100 mW / cm 2 , light intensity 1000mJ / cm 2 ) to prepare an impact absorbing sheet sample having a resin foam layer with a thickness of 200 μm.

[0153] [Example 2] Resin composition 1B was stirred at room temperature (25°C) with a stirrer for 1 minute, and air was mixed in by a mechanical froth method to form bubbles in resin composition 1B. Resin composition 1B with bubbles formed was applied to a release film and irradiated with ultraviolet light to prepare an impact-absorbing sheet sample having a resin foam layer with a thickness of 200 μm.

[0154] [Example 3] An impact-absorbing sheet sample is prepared in the same manner as in Example 1, except that Resin Composition 2A is used in place of Resin Composition 1A.

[0155] [Example 4] An impact-absorbing sheet sample is prepared in the same manner as in Example 2, except that Resin Composition 2B is used in place of Resin Composition 1B.

[0156] [Evaluation of impact absorbing sheet samples] When the impact absorbing sheet samples obtained in Examples 1 to 4 were evaluated for the following items, the evaluation results shown in Table 1 were obtained.

[0157] [Glass transition temperature] The values ​​were calculated using Fox's formula based on the glass transition temperature (Tg) and the amount of each monomer component homopolymer in the resin composition. For Examples 1 and 2, the Tg values ​​were calculated assuming that the product obtained in Synthesis Example 1 was the monomer.

[0158] [Impact test] A test piece (20 mm x 20 mm, 200 μm thick) was prepared by cutting out the impact-absorbing sheet sample and removing the release film. A total of five impacts were applied to this test piece within 10 seconds using a pendulum-type impact tester (test conditions: impactor mass 96 g, swing angle 47°, temperature 23°C). The initial impact absorption rate (first impact absorption rate) S1 [%] and the impact absorption rate after five impacts (fifth impact absorption rate) S5 [%] were measured, and the value SA calculated by S5 / S1 × 100 [%] was used as an index of repeated impact absorption. Evaluation was performed according to the following evaluation criteria. A rating of A indicates excellent impact absorption performance, and a rating of B indicates insufficient impact absorption performance. <Evaluation criteria> A: SA is 80% or more B: SA is less than 80%

[0159] [Repeated bending test] A Kapton film (polyimide film; "Kapton (registered trademark) 200EN" manufactured by Toray DuPont Co., Ltd., 50 μm thick) is attached to the side of the impact-absorbing sheet sample opposite the release film. Next, the release film is peeled off from the impact-absorbing sheet sample, and the corona-treated side of a corona-treated PET film (biaxially oriented polyethylene terephthalate film "Lumirror (registered trademark) S10" manufactured by Toray Industries, Inc.) is attached to this side to prepare a test specimen (width 50 mm, length 100 mm, thickness 200 μm). The test was conducted by repeatedly bending the test specimen into a U-shape at halfway along its length with the Kapton film side facing inward using a U-shaped planar bending tester ("DLDM111LH", manufactured by Yuasa System Co., Ltd.; test conditions: room temperature (25°C), bending radius 1.5 mm, bending at 180°C and releasing counted as one cycle, repeated 100,000 times at a speed of 60 cycles / min). The appearance of the test piece after the test is visually observed and evaluated according to the following evaluation criteria: A or B indicates no practical problem and excellent repeated bending durability, while C indicates insufficient repeated bending durability and is not suitable for practical use. <Evaluation criteria> A: No peeling, lifting or cracking occurs, and there is absolutely no change in appearance. B: Slight peeling, lifting, or cracking occurred. C: One or more of peeling, lifting, and cracking occurred significantly.

[0160] [Static bending test at -20°C] The same test piece as used in the repeated bending test was used, and the Kapton film side was placed in contact with the inside of a semicircular plate 3 mm in diameter and 3 mm thick so that the length of the test piece was aligned along the semicircle. The test piece was then fixed in this state using adhesive tape and left to stand at -20°C for 10 days. After the test, the appearance of the test piece is visually observed and evaluated using the same evaluation criteria as in the repeated bending test. If the test piece is rated A or B, it can be said that the flexibility at low temperatures is excellent, and if the test piece is rated C, it is judged that the flexibility at low temperatures is insufficient.

[0161] [Table 1]

[0162] As shown in Table 1, Examples 1 and 2 are excellent in impact absorption performance, durability against repeated bending, and flexibility at low temperatures.

Claims

1. An impact absorbing sheet having a resin foam layer formed by curing a resin composition containing a monofunctional urethane (meth)acrylate, wherein the monofunctional urethane (meth)acrylate is one or more monomers selected from the reaction products of the following (i) to (iii), and the cured product of the resin composition has a glass transition temperature of -85°C or higher and -58°C or lower: (i) An equimolar reaction product of a polyether monool and a compound having a (meth)acryloyloxy group, The compound having a (meth)acryloyloxy group is a reaction product having one isocyanate group in one molecule and one, or one and two (meth)acryloyloxy groups in one molecule. (ii) an equimolar reaction product of a polyether monool, a diisocyanate, and a compound having a (meth)acryloyloxy group, The compound having a (meth)acryloyloxy group is a compound having one group reactive with an isocyanate group in one molecule and one, or one and two (meth)acryloyloxy groups in one molecule. (iii) an equimolar reaction product of a polyether polyol and a compound having a (meth)acryloyloxy group, The compound having a (meth)acryloyloxy group is a reaction product having one isocyanate group in one molecule and one, or one and two (meth)acryloyloxy groups in one molecule.

2. 2. The impact absorbing sheet according to claim 1, wherein the molecular weight of the monomer is 3,000 to 30,000.

3. The impact absorbing sheet according to claim 1 or 2, wherein the monomer is a reaction product of (i).

4. The impact absorbing sheet according to any one of claims 1 to 3, wherein the resin foam layer contains hollow particles.

5. The impact absorbing sheet according to any one of claims 1 to 4, wherein the resin foam layer is formed by a mechanical flossing method.

6. The impact absorbing sheet according to any one of claims 1 to 5, having a thickness of 300 µm or less.

7. The impact absorbing sheet according to any one of claims 1 to 6, which is used in an electronic device.

8. The impact absorbing sheet according to any one of claims 1 to 7, which is disposed on the back side of a display device.

9. An adhesive tape comprising the impact absorbing sheet according to any one of claims 1 to 8 and an adhesive material provided on at least a portion of at least one surface of the impact absorbing sheet.

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