Resin composition for adhesive sheet and adhesive sheet for flexible printed wiring board

Abstract

This resin composition for an adhesive sheet contains: an acrylic copolymer having a structural unit (A) derived from a (meth)acrylic acid ester, a structural unit (B) derived from (meth)acrylonitrile, and a structural unit (C) derived from an unsaturated carboxylic acid; an epoxy resin; and a curing agent. The structural unit (A) includes a structural unit derived from a (meth)acrylic acid ester having a number average molecular weight (Mn) of 1,300-36,000.

Description

Resin composition for adhesive sheet and adhesive sheet for flexible printed wiring board

[0001] The present invention relates to a resin composition for an adhesive sheet and an adhesive sheet for a flexible printed wiring board.

[0002] In recent years, flexible printed circuit boards (FPCs) have come into widespread use as electronic and electrical devices become lighter and thinner. When mounting electronic components such as resistors and ICs on an FPC, the FPC is bonded to a rigid reinforcing plate via an adhesive sheet to improve handling. The adhesive sheet must have the following characteristics: (i) heat resistance (solder heat resistance) sufficient to withstand solder reflow during mounting, (ii) adhesion to the FPC and reinforcing plate, and (iii) flexibility.

[0003] As an adhesive sheet that satisfies the above-mentioned required properties, for example, it is known that an acrylic adhesive composition comprising an acrylic resin and an epoxy resin can be used as the adhesive sheet (see, for example, Patent Document 1).

[0004] It is also known that an acrylic adhesive composition comprising an acrylic resin, an epoxy resin, and an epoxy curing agent can be used as an adhesive sheet (see, for example, Patent Document 2).

[0005] Furthermore, it is known that a resin composition for adhesive sheets containing a specific acrylic copolymer, an epoxy resin, and a curing agent containing at least one selected from Lewis acid amine complexes can be used as an adhesive sheet (see, for example, Patent Document 3).

[0006] However, with adhesive sheets formed from conventional resin compositions for adhesive sheets, it has been difficult to improve the foldability while maintaining heat resistance and adhesiveness.

[0007] Japanese Patent Application Laid-Open No. 62-174283 Japanese Patent Application Laid-Open No. 2003-231873 Japanese Patent Application Laid-Open No. 2008-24772

[0008] In view of the above problems, the present invention aims to provide a resin composition for an adhesive sheet that can be used to prepare an adhesive sheet that has improved foldability while maintaining heat resistance and adhesion, and an adhesive sheet for flexible printed wiring boards that uses the resin composition for an adhesive sheet.

[0009] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that an adhesive sheet having improved foldability while maintaining heat resistance and adhesion can be produced by using a resin composition for an adhesive sheet containing an acrylic copolymer having structural units (A) derived from a (meth)acrylic acid ester containing a monomer having a number average molecular weight (Mn) of 1,300 to 36,000, structural units (B) derived from (meth)acrylonitrile, and structural units (C) derived from an unsaturated carboxylic acid, together with an epoxy resin and a curing agent, and have thus completed the present invention. That is, the present invention is as follows: [1] A resin composition for an adhesive sheet containing an acrylic copolymer having structural units (A) derived from a (meth)acrylic acid ester, structural units (B) derived from (meth)acrylonitrile, and structural units (C) derived from an unsaturated carboxylic acid, together with an epoxy resin and a curing agent, wherein the structural units (A) contain structural units derived from a (meth)acrylic acid ester having a number average molecular weight (Mn) of 1,300 to 36,000. [2] The resin composition for adhesive sheets according to [1] above, wherein the (meth)acrylic acid ester having a number average molecular weight (Mn) of 1,300 to 36,000 is a monofunctional monomer having one (meth)acryloyloxy group per molecule. [3] The resin composition for adhesive sheets according to [2] above, wherein the monofunctional monomer contains a curable component obtained by a urethanization reaction between a polyoxyalkylene monool represented by the following formula (1a) and a compound represented by the following formula (1b): (In formula (1a), R １２ is an alkylene group having 2 to 4 carbon atoms, and R １３ is an alkyl group having 1 to 20 carbon atoms or a carboxylic acid residue having 1 to 20 carbon atoms, and b is an integer of 20 to 600. In formula (1b), R １１is a hydrogen atom or a methyl group, and a is an integer of 1 to 4.) [4] The resin composition for an adhesive sheet according to [1] or [2] above, wherein the structural unit (A) further contains a unit based on butyl acrylate. [5] The resin composition for an adhesive sheet according to any one of [1] to [4] above, wherein the content of the structural unit derived from a (meth)acrylic acid ester having a number average molecular weight (Mn) of 1,300 to 36,000 per 100 parts by mass of the acrylic copolymer is 1 to 30 parts by mass. [6] The resin composition for an adhesive sheet according to any one of [1] to [5] above, wherein the content of the structural unit (A) per 100 parts by mass of the acrylic copolymer is 50 to 95 parts by mass. [7] The resin composition for an adhesive sheet according to any one of [1] to [6] above, wherein the content of the structural unit (B) per 100 parts by mass of the acrylic copolymer is 5 to 45 parts by mass. [8] The resin composition for adhesive sheets according to any one of [1] to [7] above, wherein the content of the structural unit (C) per 100 parts by mass of the acrylic copolymer is 1 to 6 parts by mass. [9] The resin composition for adhesive sheets according to any one of [1] to [8] above, wherein the content of the curing agent per 100 parts by mass of the epoxy resin is 0.1 part by mass or more and less than 1.0 part by mass.

[10] The resin composition for adhesive sheets according to any one of [1] to [9] above, wherein the acrylic copolymer is synthesized by solution polymerization.

[11] The resin composition for adhesive sheets according to any one of [1] to

[10] above, wherein the equivalent ratio of epoxy groups of the epoxy resin to carboxy groups of the structural unit (C) is 1:1 to 2:1.

[12] An adhesive sheet for flexible printed wiring boards, comprising the resin composition for adhesive sheets according to any one of [1] to

[11] above.

[0010] According to the present invention, there are provided a resin composition for an adhesive sheet that can be used to prepare an adhesive sheet that has improved foldability while maintaining heat resistance and adhesion, and an adhesive sheet for a flexible printed wiring board that uses the resin composition for an adhesive sheet.

[0011] Next, an embodiment of the present invention will be described. The following embodiment is an example for explaining the present invention, and is not intended to limit the present invention to this embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention.

[0012] The definitions and meanings of terms and notations used in this specification are as follows: "(Meth)acrylic acid ester" is a general term for acrylic acid esters and methacrylic acid esters, and "(meth)acrylonitrile" is a general term for acrylonitrile and methacrylonitrile. "(Meth)acryloyloxy group" is a general term for acryloyloxy group and 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. "Number of functional groups" refers to the number of (meth)acryloyloxy groups per molecule, unless otherwise specified. "Average number of functional groups" refers to the average number of (meth)acryloyloxy groups per molecule, where the formula weight or number average molecular weight (Mn) obtained based on the chemical formula is one unit. "Curable component" refers to a compound having a (meth)acryloyloxy group. The "index" in the reaction between an isocyanate group-containing compound and a hydroxyl group-containing compound is the value obtained by multiplying the number of moles of isocyanate groups in the isocyanate group-containing compound by the number of moles of hydroxyl groups in the hydroxyl group-containing compound by 100. The hydroxyl value of the hydroxyl group-containing compound is obtained by measurement in accordance with JIS K1557 (2007 edition). The hydroxyl value-based molecular weight is calculated by applying the hydroxyl value to the formula "56100 / (hydroxyl value) x (number of active hydrogen atoms in the initiator)". The number average molecular weight (Mn) is the polystyrene-equivalent molecular weight obtained by measurement with gel permeation chromatography (GPC) using a calibration curve prepared using standard polystyrene samples of known molecular weight. The molecular weight distribution refers to the value obtained by dividing the weight average molecular weight (Mw) (polystyrene-equivalent molecular weight obtained by GPC in the same way as the number average molecular weight (Mn)) by the number average molecular weight (Mn). In the GPC measurement, if a peak of an unreacted low molecular weight component (monomer, etc.) appears, the peak is excluded from the number average molecular weight (Mn) to be determined. Even if the number average molecular weight (Mn) is specified, if there is no molecular weight distribution, it is substituted with the molecular weight represented by the formula weight obtained based on the chemical formula.

[0013] [Resin Composition for Adhesive Sheet] The resin composition for an adhesive sheet according to the present invention contains an acrylic copolymer, an epoxy resin, and a curing agent, and may further contain other optional components as required.

[0014] <Acrylic Copolymer> The acrylic copolymer has a structural unit (A) derived from a (meth)acrylic acid ester (component (A)), a structural unit (B) derived from (meth)acrylonitrile (component (B)), and a structural unit (C) derived from an unsaturated carboxylic acid (component (C)), and may have other structural units as necessary.

[0015] The (meth)acrylic acid ester is not particularly limited, and examples thereof include (meth)acrylic acid ester monomers having a number average molecular weight (Mn) of 1,300 to 36,000, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl acrylate, 2-hydroxyethyl acrylate, and 4-hydroxybutyl acrylate. These may be used alone or in combination of two or more. The unsaturated carboxylic acid is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, and itaconic acid. These may be used alone or in combination of two or more. Other structural units include structural units derived from acryloylmorpholine and structural units derived from acrylamide.

[0016] The content of the acrylic copolymer in the resin composition for an adhesive sheet is not particularly limited, but from the viewpoint of obtaining sufficient flexibility after curing, it is preferably 20 to 96% by mass, more preferably 40 to 93% by mass, and particularly preferably 60 to 90% by mass.

[0017] The content of the structural unit (A) per 100 parts by mass of the acrylic copolymer is not particularly limited, but is preferably 50 to 95 parts by mass, more preferably 55 to 90 parts by mass, and particularly preferably 60 to 85 parts by mass. When the content of the structural unit (A) per 100 parts by mass of the acrylic copolymer is within the above range, sufficient flexibility and adhesiveness can be obtained after curing.

[0018] The content of the structural unit (B) per 100 parts by mass of the acrylic copolymer is not particularly limited, but is preferably 5 to 45 parts by mass, more preferably 10 to 40 parts by mass, and particularly preferably 10 to 35 parts by mass. When the content of the structural unit (B) per 100 parts by mass of the acrylic copolymer is within the above range, sufficient flexibility and high adhesiveness can be obtained after curing.

[0019] The content of the structural unit (C) per 100 parts by mass of the acrylic copolymer is not particularly limited, but is preferably 1 to 6 parts by mass, more preferably 1 to 5 parts by mass, and particularly preferably 3 to 5 parts by mass. When the content of the structural unit (C) per 100 parts by mass of the acrylic copolymer is within the above range, good room temperature storage stability, solder heat resistance after curing, and high adhesiveness can be obtained.

[0020] The content of the other structural units relative to 100 parts by mass of the acrylic copolymer is not particularly limited, but is preferably 0 to 30 parts by mass, more preferably 0 to 20 parts by mass, and particularly preferably 0 to 15 parts by mass.

[0021] The total content of the structural unit (A), the structural unit (B), and the structural unit (C) per 100 parts by mass of the acrylic copolymer is not particularly limited, but is preferably 70 to 100 parts by mass, more preferably 80 to 100 parts by mass, and particularly preferably 85 to 100 parts by mass.

[0022] The (meth)acrylic acid ester constituting the structural unit (A) contains a (meth)acrylic acid ester having a number average molecular weight (Mn) of 1,300 to 36,000. Such a (meth)acrylic acid ester having a number average molecular weight (Mn) of 1,300 to 36,000 is preferably a monofunctional monomer, as described below. The content of the structural unit derived from the (meth)acrylic acid ester having a number average molecular weight (Mn) of 1,300 to 36,000 relative to 100 parts by mass of the acrylic copolymer is not particularly limited, but is preferably 1 to 30 parts by mass, more preferably 3 to 25 parts by mass, and particularly preferably 5 to 20 parts by mass.

[0023] From the viewpoint of flexibility, the (meth)acrylic acid ester constituting the structural unit (A) preferably further contains butyl acrylate. When the (meth)acrylic acid ester constituting the structural unit (A) further contains butyl acrylate, the content of butyl acrylate relative to 100 parts by mass of the acrylic copolymer is not particularly limited, but is preferably 30 to 70 parts by mass, more preferably 40 to 65 parts by mass, and particularly preferably 45 to 60 parts by mass.

[0024] From the viewpoint of adhesive strength, it is preferable that the (meth)acrylic acid ester constituting the structural unit (A) further contains isobornyl acrylate. When the (meth)acrylic acid ester constituting the structural unit (A) contains isobornyl acrylate, the content of isobornyl acrylate per 100 parts by mass of the acrylic copolymer is not particularly limited, but is preferably 2 to 45 parts by mass, more preferably 3 to 30 parts by mass, and particularly preferably 4 to 20 parts by mass.

[0025] (Monofunctional Monomer) The monofunctional monomer has one (meth)acryloyloxy group per molecule, and preferably further has a polyoxyalkylene chain and a urethane bond derived from an isocyanate group-containing compound. When the resin composition for an adhesive sheet of the present invention is ultraviolet-curable, the (meth)acryloyloxy group in the monofunctional monomer is preferably an acryloyloxy group.

[0026] The monofunctional monomer suppresses shrinkage during curing, reduces the elastic modulus after curing, and easily suppresses whitening when repeatedly bent. In addition, since the monofunctional monomer has one (meth)acryloyloxy group, it has better stability after curing and suppresses bleed-out.

[0027] The monofunctional monomer preferably has a polyoxyalkylene chain. Examples of the polyoxyalkylene chain include a polymer chain having an ethylene oxide unit, a polymer chain having a propylene oxide unit, a polymer chain having an ethylene oxide unit and a propylene oxide unit, a polymer chain consisting of an ethylene oxide unit, a polymer chain consisting of a propylene oxide unit, a polymer chain consisting of a butylene oxide unit, a polymer chain consisting of a tetramethylene oxide unit, a polymer chain consisting of an ethylene oxide unit and a propylene oxide unit, and a polymer chain consisting of a propylene oxide unit and a butylene oxide unit. A polymer chain having a propylene oxide unit, or a polymer chain having an ethylene oxide unit and a propylene oxide unit is preferred, with a polymer chain consisting of a propylene oxide unit being particularly preferred. When the monofunctional monomer has a polyoxyalkylene chain, the number of alkylene oxide units in one molecule is preferably 20 to 600, and more preferably 50 to 500.

[0028] The number of urethane bonds in one molecule of the monofunctional monomer is one or more, and is preferably one or two, more preferably one, because this inhibits shrinkage during curing and facilitates a reduction in the modulus of elasticity after curing. The concentration (abundance ratio) of urethane bonds in one molecule of the monofunctional monomer is not particularly limited, but from the viewpoint of obtaining better adhesiveness, it is preferably 0.35 to 1.9 mass%, more preferably 0.4 to 1.3 mass%, and particularly preferably 0.5 to 1.2 mass%. The concentration of urethane bonds can be calculated using the following formula, assuming that all of the isocyanate groups in the isocyanate group-containing compound used in producing the monofunctional monomer form urethane bonds: (number of moles of isocyanate groups in the isocyanate group-containing compound × molecular weight of urethane bonds (59) / mass of monofunctional monomer) × 100 (%)

[0029] The number-average molecular weight (Mn) of the monofunctional monomer is not particularly limited as long as it is 1,300 to 36,000, but is preferably 3,000 to 35,000, more preferably 4,000 to 20,000, and particularly preferably 5,000 to 18,000. When the number-average molecular weight (Mn) of the monofunctional monomer is within the above range, it is easy to adjust the viscosity of the resin composition for an adhesive sheet. Furthermore, when the number-average molecular weight (Mn) of the monofunctional monomer is 3,000 or more, the cure shrinkage rate of the resin composition for an adhesive sheet is likely to be low. When the resin composition for an adhesive sheet contains two or more monofunctional monomers, it is preferable that the number-average molecular weight (Mn) of each monofunctional monomer is within the above range.

[0030] In the production process of a monofunctional monomer, a by-product having a polyoxyalkylene chain other than the monofunctional monomer may be generated in the product. Examples of by-products having a polyoxyalkylene chain include compounds having two (meth)acryloyloxy groups, compounds having no (meth)acryloyloxy groups, and compounds having no urethane bonds. The content of the monofunctional monomer in the product is not particularly limited, but from the viewpoint of fully exhibiting the function as a monofunctional monomer, it is preferably 80 to 100% by mass, more preferably 85 to 100% by mass, and particularly preferably 90 to 100% by mass. When the product contains the monofunctional monomer in the above content, the function of the monofunctional monomer is fully exhibited, and the product can be considered a monofunctional monomer.

[0031] When the above product can be considered a monofunctional monomer, the average functionality calculated from the number average molecular weight (Mn) and the number of functional groups of the product can be considered the average functionality of the monofunctional monomer. In this case, the average functionality of the product is not particularly limited, but is preferably 0.7 to 1.3, more preferably 0.8 to 1.2, and particularly preferably 0.9 to 1.1. A product having an average functionality within the above range is likely to fully exhibit the function of a monofunctional monomer. The average functionality can be adjusted to this range by adjusting the amount of impurities contained in the raw materials for producing the monofunctional monomer or by adjusting the index described below. Furthermore, in this specification, the average functionality can be calculated using the average functionality of the raw materials and the index described below.

[0032] Specific examples of monofunctional monomers include reaction product (1), reaction product (2), and reaction product (3) shown below. These may be used alone or in combination of two or more. In particular, it is preferable that the monofunctional monomer in the resin composition for an adhesive sheet contains one or more selected from the group consisting of reaction product (1) and reaction product (2). In particular, reaction product (1) is more preferable as the monofunctional monomer, since it has a lower content of by-products than other reaction products and can provide a resin composition for an adhesive sheet that is excellent in flexibility and cure shrinkage.

[0033] The total content of reaction product (1) and reaction product (2) relative to the monofunctional monomer is not particularly limited, but is preferably 50% by mass or more, more preferably 80% by mass or more, and particularly preferably 100% by mass. When the total content of reaction product (1) and reaction product (2) is equal to or greater than the lower limit of the above range, flexibility and cure shrinkage rate are excellent. When the monofunctional monomer contains reaction product (1) and reaction product (2), the mass ratio thereof (reaction product (1):reaction product (2)) is preferably greater than 1:0 to 1:1.

[0034] Reaction product (1): An equimolar reaction product of a polyoxyalkylene monool and a compound having an isocyanate group and a (meth)acryloyloxy group. Reaction product (2): An equimolar reaction product of a polyoxyalkylene monool, a diisocyanate, and a compound having a group reactive with an isocyanate group and a (meth)acryloyloxy group. Reaction product (3): An equimolar reaction product of a polyoxyalkylene polyol and a compound having an isocyanate group and a (meth)acryloyloxy group.

[0035] The compound having an isocyanate group and a (meth)acryloyloxy group, which is the raw material for the reaction products (1) and (3), is preferably a (meth)acrylate having one isocyanate group, more preferably an isocyanate alkyl (meth)acrylate.

[0036] Examples of diisocyanates that are raw materials for the reaction product (2) include non-yellowing aromatic diisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, and various modified products of these diisocyanates (modified products having two isocyanate groups). These may be used alone or in combination of two or more. Among these, aliphatic diisocyanates and alicyclic diisocyanates are preferred because they have excellent light resistance, weather resistance, and heat resistance and can maintain transparency.

[0037] The non-yellowing aromatic diisocyanate is not particularly limited, and examples thereof include xylylene diisocyanate, tetramethylxylylene diisocyanate, etc. These may be used alone, or two or more types may be used in combination. The aliphatic diisocyanate is not particularly limited, and examples thereof include 1,6-hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, etc. These may be used alone, or two or more types may be used in combination. The alicyclic diisocyanate is not particularly limited, and examples thereof include isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 2,5-norbornane diisocyanate, 2,6-norbornane diisocyanate, etc. These may be used alone, or two or more types may be used in combination. The compound having a group reactive with an isocyanate group and a (meth)acryloyloxy group, which is a raw material for the reaction product (2), is not particularly limited, but is preferably a (meth)acrylate having one hydroxyl group, more preferably a hydroxyalkyl (meth)acrylate or a hydroxycycloalkyl (meth)acrylate, and particularly preferably a hydroxyalkyl (meth)acrylate having 8 or less carbon atoms in the hydroxyalkyl group.

[0038] The average number of hydroxyl groups per molecule of the polyoxyalkylene monool, which is the raw material for the reaction products (1) and (2), is not particularly limited, but is preferably 0.7 to 1.3, more preferably 0.8 to 1.2, and particularly preferably 0.9 to 1.1. The hydroxyl value of the polyoxyalkylene monool is not particularly limited, but is preferably 1.6 to 18.1 mgKOH / g, more preferably 2.8 to 14 mgKOH / g, and particularly preferably 3.1 to 11.2 mgKOH / g, in order to obtain a monofunctional monomer having a urethane bond concentration within a predetermined range.

[0039] Polyoxyalkylene monool is a compound obtained by ring-opening addition polymerization of alkylene oxide with an initiator having an active hydrogen-containing group and one or more active hydrogens, and having an initiator residue, a polyoxyalkylene chain, and hydroxyl groups corresponding to the number of active hydrogens in the initiator.

[0040] The alkylene oxide is not particularly limited, and suitable examples include alkylene oxides having 2 to 4 carbon atoms, such as propylene oxide, ethylene oxide, 1,2-butylene oxide, and 2,3-butylene oxide. These may be used alone or in combination of two or more.

[0041] The active hydrogen-containing group of the initiator is not particularly limited, and examples thereof include a hydroxyl group, a carboxyl group, and an amino group having one hydrogen atom bonded to a nitrogen atom. These may be used alone or in combination of two or more. Among these, a hydroxyl group and a carboxyl group are preferred, and an alcoholic hydroxyl group is more preferred.

[0042] Examples of initiators having one active hydrogen include monohydric alcohols, monohydric phenols, monovalent carboxylic acids, and amine compounds having one hydrogen atom bonded to a nitrogen atom. These may be used alone or in combination of two or more. Among these, monohydric aliphatic alcohols and monohydric aliphatic carboxylic acids are preferred. The number of carbon atoms in the monohydric aliphatic alcohol is not particularly limited, but is preferably 1 to 20, more preferably 1 to 14, and particularly preferably 2 to 8. The number of carbon atoms in the monohydric aliphatic carboxylic acid is not particularly limited, but is preferably 2 to 20, more preferably 2 to 14, and particularly preferably 2 to 8, including the carbon atoms of the carboxy group. In addition, a polyoxyalkylene monool having a lower molecular weight than the target polyoxyalkylene monool may be used as the initiator.

[0043] The oxyalkylene groups in the polyoxyalkylene monool preferably consist solely of oxypropylene groups or of a combination of oxypropylene groups and other oxyalkylene groups. The oxyalkylene groups other than oxypropylene groups are preferably oxyethylene groups. The proportion of oxypropylene groups relative to all oxyalkylene groups in the polyoxyalkylene monool is not particularly limited, but is preferably 50 to 100% by mass, more preferably 65 to 100% by mass, and particularly preferably 80 to 100% by mass. When the initiator is a polyoxyalkylene monool having a lower molecular weight than the target polyoxyalkylene monool, the oxyalkylene groups in the initiator are considered to be the oxyalkylene groups in the resulting polyoxyalkylene monool.

[0044] A low hydroxyl value (i.e., high molecular weight) polyoxyalkylene monool can be produced by ring-opening addition polymerization of an alkylene oxide having 3 or more carbon atoms (preferably propylene oxide) to an initiator in the presence of a composite metal cyanide complex catalyst. A low hydroxyl value polyoxyalkylene monool having an oxyethylene group can also be produced by ring-opening addition polymerization of an alkylene oxide having 3 or more carbon atoms (particularly propylene oxide) to an initiator in the presence of a composite metal cyanide complex catalyst. A high hydroxyl value polyoxyalkylene monool can also be produced using an alkali catalyst such as KOH.

[0045] In the production of polyoxyalkylene monools, initiators and alkylene oxides are typically introduced into the reaction system with low water content, typically obtained by removing water by vacuum degassing or the like. The water content of the initiator used in the production of polyoxyalkylene monools is not particularly limited, but the lower the content, the better. It is preferably 500 ppm by mass or less, more preferably 400 ppm by mass or less, and particularly preferably 300 ppm by mass or less. When the water content is within the above range, the amount of polyoxyalkylene diol produced from water is suppressed, thereby ultimately suppressing the amount of by-products produced due to the polyoxyalkylene diol, and making it easier to adjust the upper limit of the average number of hydroxyl groups in the resulting polyoxyalkylene monool to 1.2 or less. The water content of the polyoxyalkylene monool used as a raw material for reaction products (1) and (2) is not particularly limited, but the lower the content, the better. It is preferably 300 ppm by mass or less, more preferably 250 ppm by mass or less, and particularly preferably 50 to 200 ppm by mass relative to the polyoxyalkylene monool. When the water content is within the above range, the production of by-products, which are reaction products of water and the isocyanate group-containing compound, is reduced, improving the stability of the reaction products (1) and (2).Furthermore, it is easy to suppress changes in the appearance of the curable composition containing the reaction products (1) and (2) over time, and the elastic modulus of the cured product is easy to improve.

[0046] The polyoxyalkylene polyol used as the raw material for reaction product (3) is preferably a polyoxyalkylene diol. The average number of hydroxyl groups per molecule of the polyoxyalkylene polyol is not particularly limited, but is preferably 1.6 to 2.1, more preferably 1.7 to 2.0, and particularly preferably 1.8 to 1.96. That is, the polyoxyalkylene polyol used as the raw material for reaction product (3) is preferably a polyoxyalkylene diol. The content of oxypropylene groups relative to all oxyalkylene groups in the polyoxyalkylene polyol is not particularly limited, but is preferably 80 to 100% by mass. The hydroxyl value of the polyoxyalkylene polyol is not particularly limited, but is preferably 1.6 to 19 mgKOH / g, more preferably 2.2 to 16 mgKOH / g, and particularly preferably 2.8 to 14 mgKOH / g, from the viewpoint of obtaining a monofunctional monomer having a urethane bond concentration within a predetermined range.

[0047] [Reaction Product (1)] The reaction product (1) is an equimolar reaction product of a polyoxyalkylene monool and a compound having an isocyanate group and a (meth)acryloyloxy group. The compound having an isocyanate group and a (meth)acryloyloxy group is not particularly limited, and a suitable example is an isocyanate alkyl (meth)acrylate.

[0048] Because the polyoxyalkylene monool and the isocyanate alkyl (meth)acrylate each have one group capable of urethanization per molecule, it is easy to control the number of urethane bonds per molecule of the reaction product (1) to one. A low number of urethane bonds per molecule of the reaction product (1) tends to result in low viscosity. Therefore, it is preferable that the monofunctional monomer in the resin composition for adhesive sheets contains the reaction product (1), as this results in a low viscosity and a cured product with excellent flexibility. Furthermore, because both the polyoxyalkylene monool and the isocyanate alkyl (meth)acrylate are compounds with one reactive group, they are less likely to produce by-products, making it easier to remove unreacted material and obtain a highly pure reaction product (1). If unreacted material remains, it is preferable that the unreacted material be a polyoxyalkylene monool from the perspective of the stability of the reaction product. To obtain a reaction product with minimal unreacted material, it is preferable to react the two at an index of 90 to 100, and more preferably at an index of 100. The average number of functional groups in the reaction product (1) is not particularly limited, but is preferably 0.9 to 1.1. A resin composition for an adhesive sheet containing the reaction product (1) within the above range is likely to reduce shrinkage during curing and is likely to reduce the elastic modulus after curing.

[0049] [Reaction Product (2)] Reaction product (2) is an equimolar reaction product of a polyoxyalkylene monool, a diisocyanate, and a compound having a group reactive with an isocyanate group and a (meth)acryloyloxy group. The diisocyanate is not particularly limited, and suitable examples thereof include aliphatic diisocyanates and alicyclic diisocyanates. The compound having a group reactive with an isocyanate group and a (meth)acryloyloxy group is not particularly limited, and suitable examples thereof include hydroxyalkyl (meth)acrylates in which the hydroxyalkyl group has 8 or less carbon atoms. Examples of reaction product (2) include (a) a reaction product obtained by reacting a polyoxyalkylene monol with a diisocyanate at an index of 200, and then reacting the resulting reaction product (a reaction product having an isocyanate group) with a hydroxyalkyl (meth)acrylate at an index of 100; and (b) a reaction product obtained by simultaneously reacting a polyoxyalkylene monol with an equimolar amount of hydroxyalkyl (meth)acrylate relative to the polyoxyalkylene monol, and an amount of diisocyanate with an index of 100 relative to the total amount of the polyoxyalkylene monol and the hydroxyalkyl (meth)acrylate. Among these, reaction product (a) is preferred because it produces fewer by-products. Note that when producing reaction product (a), the hydroxyalkyl (meth)acrylate may be used in excess, and the excess hydroxyalkyl (meth)acrylate can be incorporated into the resin composition for adhesive sheets together with the reaction product (a). The average number of functional groups in the reaction product (2) is not particularly limited, but is preferably 0.7 to 1.3, more preferably 0.8 to 1.2, and particularly preferably 0.9 to 1.1. A resin composition for an adhesive sheet containing a reaction product (2) within the above range is likely to reduce shrinkage during curing and is likely to reduce the elastic modulus after curing.

[0050] [Reaction Product (3)] The reaction product (3) is an equimolar reaction product of a polyoxyalkylene polyol and a compound having an isocyanate group and a (meth)acryloyloxy group. The polyoxyalkylene polyol is not particularly limited, and a suitable example thereof is a polyoxyalkylene diol. The compound having an isocyanate group and a (meth)acryloyloxy group is not particularly limited, and a suitable example thereof is an isocyanate alkyl (meth)acrylate. Note that the reaction product (3) is a reaction product having a hydroxyl group, and the number of hydroxyl groups is not limited to one. Therefore, as long as the compound having an isocyanate group and a (meth)acryloyloxy group is a compound having one isocyanate group and is an equimolar reaction product, the raw material polyoxyalkylene polyol may be a compound having more than two hydroxyl groups. The average number of functional groups in the reaction product (3) is not particularly limited, but is preferably 0.7 to 1.3, more preferably 0.8 to 1.2, and particularly preferably 0.9 to 1.1. A reaction product (3) within the above range is likely to have reduced shrinkage during curing and a reduced elastic modulus after curing.

[0051] The monofunctional monomer contributes to reducing shrinkage during curing and reducing the elastic modulus of the cured product, and since it has a (meth)acryloyloxy group as a curable functional group, the cured product has excellent stability and is less likely to bleed out.

[0052] A specific example of the monofunctional monomer is the monomer (IB-1).

[0053] Monomer (IB-1) Monomer (IB-1) contains a curable component having one curable functional group and represented by the following formula (1): The curable component represented by the following formula (1) is obtained by subjecting a polyoxyalkylene monool (1a) represented by the following formula (1a) and a compound (1b) represented by the following formula (1b) to a urethane reaction.

[0054]

[0055] In formulas (1), (1a), and (1b), R １１is a hydrogen atom or a methyl group, preferably a hydrogen atom. １２ is an alkylene group having 2 to 4 carbon atoms, and multiple R １２ may be the same or different. Two or more types of R １２ If there is -OR １２ The chain of - may be block or random. １２ is preferably an ethylene group or a propylene group. １３ is an alkyl group having 1 to 20 carbon atoms or a carboxylic acid residue having 1 to 20 carbon atoms. The carboxylic acid residue is a monovalent group obtained by removing one hydrogen atom from a monocarboxylic acid having 1 to 20 carbon atoms, including the carbon atom in the carboxy group (—COOH). R １３ In terms of ease of reaction, a is preferably an alkyl group, more preferably an alkyl group having 2 to 8 carbon atoms. a is an integer of 1 to 4, preferably an integer of 1 or 2. b is an integer of 20 to 600, preferably an integer of 35 to 500, more preferably an integer of 65 to 250.

[0056] In producing the curable component represented by formula (1), the polyoxyalkylene monool (1a) represented by formula (1a) may be used in the form of a composition containing a diol as a by-product in addition to the polyoxyalkylene monool (1a) represented by formula (1a), which is produced as follows: The obtained curable component is used as monomer (IB-1).

[0057] Since the polyoxyalkylene monool (1a) represented by formula (1a) and the compound (1b) represented by formula (1b) each have one group capable of urethanization reaction present in one molecule, the number of urethane bonds per molecule of the monomer (IB-1) can be easily controlled to one on average. If the number of urethane bonds per molecule of the monomer (IB-1) is small, the viscosity tends to be low. Therefore, by including the monomer (IB-1), the resin composition for adhesive sheets has a low viscosity, and a cured product with excellent flexibility can be easily obtained.

[0058] The hydroxyl value of the polyoxyalkylene monool (1a) represented by formula (1a) is not particularly limited, but is preferably 1.6 to 56.1 mgKOH / g, more preferably 2.8 to 14.0 mgKOH / g, and particularly preferably 3.5 to 12.5 mgKOH / g. The molecular weight calculated from the hydroxyl value of the polyoxyalkylene monool (1a) represented by formula (1a) is not particularly limited, but is preferably 1,000 to 35,000, more preferably 4,000 to 20,000, and particularly preferably 4,500 to 16,000.

[0059] The polyoxyalkylene monool (1a) component containing the polyoxyalkylene monool (1a) represented by formula (1a) can be obtained, for example, by ring-opening addition polymerization of an alkylene oxide with an initiator such as a monohydric alcohol or a carboxylic acid. The catalyst used in the ring-opening addition polymerization is not particularly limited, and examples thereof include alkali metal compound catalysts, composite metal cyanide complex catalysts (hereinafter also referred to as DMC catalysts), phosphazene compound catalysts, and boron-based cation catalysts which are Lewis acids. These may be used alone or in combination of two or more. Among these, DMC catalysts are preferred because they can reduce the contamination of low-molecular-weight bifunctional polyols, i.e., diols, which are by-produced using water as an initiator during ring-opening addition polymerization, and also because they facilitate the production of high-molecular-weight monools. The molecular weight calculated from the hydroxyl value of the polyoxyalkylene monool (1a) produced using a DMC catalyst is not particularly limited, but is preferably 1,000 to 35,000, more preferably 4,000 to 20,000, and particularly preferably 4,500 to 16,000.

[0060] The molecular weight of the by-produced low-molecular-weight diol is twice that of the polyoxyalkylene monool (1a). It is preferable to produce a polyoxyalkylene monool (1a) component containing the polyoxyalkylene monool (1a) represented by formula (1a) so that the amount of the low-molecular-weight diol is reduced. When a polyoxyalkylene monool (1a) component produced using a DMC catalyst is used, Zn and Co are present as residues in a total amount of 0.01 to 100 ppm by mass in the resin composition for adhesive sheets.

[0061] The polyoxyalkylene monool (1a) component thus obtained may contain, in addition to the polyoxyalkylene monool (1a) represented by formula (1a), a diol by-produced during the production, but the amount of the diol is preferably 30 mass% or less, more preferably 25 mass% or less, and even more preferably 18 mass% or less, based on the total amount of the polyoxyalkylene monool (1a) component produced. In the production of the polyoxyalkylene monool (1a) represented by formula (1a), the amount of the diol by-produced can be kept within the above-mentioned range by reducing the amount of water in the reaction system.

[0062] In the production of polyoxyalkylene monool represented by formula (1a), the total amount of water in the reaction system is not particularly limited, but is preferably 250 ppm by mass or less, more preferably 225 ppm by mass or less, and particularly preferably 200 ppm by mass or less. When the amount of water in the reaction system is within this range, the production of diol initiated by water, which is a by-product of polyoxyalkylene monool represented by formula (1a), is suppressed. In the production of monomer (IB-1), using a polyoxyalkylene monool (1a) component with a reduced diol content makes it easy to suppress the production of diol-derived bifunctional monomers, and monomer (IB-1) containing a predetermined amount of curable component represented by formula (1) can be easily obtained.

[0063] To adjust the water content in the reaction system to the above range, water may be removed under reduced pressure after supplying the initiator to the reaction vessel. Alternatively, the water content in the reaction system can be adjusted by adjusting the water content of the alkylene oxide to be added to 200 ppm by mass or less. Therefore, the water content of the alkylene oxide to be added is preferably 200 ppm by mass or less, more preferably 150 ppm by mass or less. When the ring-opening addition polymerization catalyst is an alkali metal compound catalyst, it is typically used as an aqueous solution containing the catalyst and having a solids content of 85% to 95% by mass. Since the water content in the reaction system tends to be high, water is removed under reduced pressure after alcoholating the hydroxyl groups of the initiator. DMC catalysts are preferred because they contain a low amount of water. Furthermore, the use of a DMC catalyst allows the production of a polyoxyalkylene monool (1a) represented by formula (1a) with a narrow molecular weight distribution.

[0064] The content ratio of the polyoxyalkylene monool (1a) represented by formula (1a) and the diol in the polyoxyalkylene monool (1a) component can be determined by GPC measurement of the produced polyoxyalkylene monool (1a) component. The average number of hydroxyl groups in the polyoxyalkylene monool (1a) represented by formula (1a) can be determined by GPC measurement of the produced monool (1a) component.

[0065] When the polyoxyalkylene monool (1a) represented by formula (1a) is reacted with the compound (1b) represented by formula (1b) using the polyoxyalkylene monool (1a) component, the compounding ratio of the compound represented by formula (1b) to the polyoxyalkylene monool (1a) component is not particularly limited, but is preferably an index (NCO / OH ratio) of 80 to 100, more preferably 90 to 100, and particularly preferably 100. By setting the index within the above range, the number of curable functional groups per molecule of the monomer (IB-1) can be brought close to one on average.

[0066] In particular, R present in one molecule of the curable component represented by formula (1) １２ It is preferable that the monomer (IB) contains a monomer (IB-1-PO) containing a monomer (1-PO) having a propylene group content of 50 to 100% by mass based on the total amount of the monomer (1-PO). １２ The proportion of propylene groups relative to the total amount of R is not particularly limited, but is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and particularly preferably 100% by mass. １２ Among these, the alkylene group other than the propylene group is preferably an ethylene group.

[0067] Furthermore, when the monomer (IB-1-PO) is used, the content of the monomer (IB-1-PO) relative to the monomer (IB) is not particularly limited, but is preferably 50 to 100% by mass, more preferably 65 to 100% by mass, and particularly preferably 80 to 100% by mass. When the content of the monomer (IB-1-PO) is equal to or greater than the lower limit of the above range, the viscosity is low and flexibility is excellent.

[0068] The polymerization method for the acrylic copolymer is not particularly limited, and can be, for example, emulsion polymerization, suspension polymerization, solution polymerization, or the like. These may be used alone or in combination of two or more. Among these, solution polymerization is preferred because it contains almost no metal ions such as Na, and therefore has good electrical insulation properties (migration characteristics).

[0069] When the acrylic copolymer is polymerized by solution polymerization, the initiator is preferably azobisisobutyronitrile, benzoyl peroxide, etc., the polymerization solvent is preferably ethyl acetate, butyl acetate, etc., and the other additives are preferably chain transfer agents, etc. When the acrylic copolymer is polymerized by solution polymerization, the polymerization temperature is preferably 50 to 100°C, the polymerization pressure is preferably 0.1 to 0.5 MPa, and the polymerization time is preferably 4 to 10 hours.

[0070] <Epoxy Resin> The epoxy resin is not particularly limited, and examples thereof include bisphenol-type epoxy resins such as bisphenol A, bisphenol F, and bisphenol S; novolac-type epoxy resins such as phenol novolac and cresol novolac; biphenyl-type epoxy resins; naphthalene ring-containing epoxy resins; and alicyclic epoxy resins. These may be used alone or in combination of two or more. Among these, bisphenol A-type epoxy resins and phenol novolac-type epoxy resins are preferred in terms of providing good adhesion and solder heat resistance.

[0071] The content of the epoxy resin is preferably an amount in the range where the ratio of the epoxy group equivalent of the epoxy resin to the carboxy group equivalent of the structural unit (C) is 1: 1 to 2: 1. This allows the reaction between the epoxy groups of the epoxy resin and the carboxy groups of the structural unit (C) to proceed sufficiently, leaving almost no carboxy groups remaining and forming a three-dimensional network crosslinked structure, thereby achieving sufficient solder heat resistance and high adhesiveness after curing.

[0072] The content of the epoxy resin relative to 100 parts by mass of the acrylic copolymer is not particularly limited, but is preferably 1 to 30 parts by mass, more preferably 3 to 25 parts by mass, and particularly preferably 5 to 20 parts by mass.

[0073] The equivalent ratio of the epoxy groups of the epoxy resin to the carboxy groups of the structural unit (C) is not particularly limited, but is preferably 1:1 to 2:1, more preferably 1:1 to 1.7:1, and particularly preferably 1:1 to 1.4:1.

[0074] <Curing Agent> The curing agent is not particularly limited, and examples thereof include Lewis acid amine complexes, imidazole-based, phenol-based, amine-based, acid anhydride-based, and organic peroxide-based curing agents. These may be used alone or in combination of two or more. Among these, Lewis acid amine complexes are preferred because they make the curing reaction at room temperature less likely to proceed and provide good room temperature storage stability. Furthermore, the Lewis acid amine complexes act as a catalyst during the curing reaction, promoting the reaction between the carboxy group of the acrylic copolymer and the epoxy group of the epoxy resin, and the hydroxyl group generated by the reaction provides high adhesiveness.

[0075] The Lewis acid amine complexes are not particularly limited, and examples thereof include BF ３ , BCl ３ , TiCl ４ , SnCl ４ , SnCl ３ , ZnBr ２ , ZnCl ２ , Zn(CH ３ COO) ２ , AlCl ３ , AlBr ３ , SiCl ４ , FeCl３ and the like, and complexes of Lewis acids such as monoethylamine, n-hexylamine, benzylamine, triethylamine, aniline, piperidine, and the like. These may be used alone or in combination of two or more. Among these, BF ３ BF complex with monoethylamine ３ Complexes are preferred.

[0076] The content of the curing agent per 100 parts by mass of the acrylic copolymer is not particularly limited, but is preferably 0.01 part by mass or more but less than 1.0 part by mass, more preferably 0.05 to 0.8 parts by mass, and particularly preferably 0.05 to 0.7 parts by mass. When the content of the curing agent per 100 parts by mass of the acrylic copolymer is within the above range, good room temperature storage stability, solder heat resistance after curing, and high adhesiveness are obtained. The content of the curing agent per 100 parts by mass of the epoxy resin is not particularly limited, but is preferably 0.1 part by mass or more but less than 1.0 part by mass, more preferably 0.2 to 0.8 parts by mass, and particularly preferably 0.3 to 0.7 parts by mass. When the content of the curing agent per 100 parts by mass of the epoxy resin is within the above range, good room temperature storage stability, solder heat resistance after curing, and high adhesiveness are obtained.

[0077] <Other Optional Components> The other optional components are not particularly limited, and examples thereof include fluorine-based or silicon-based leveling agents, silane coupling agents, etc. These may be used alone or in combination of two or more. Among these, fluorine-based or silicon-based leveling agents are preferred in terms of improving the coating properties of the resin composition, and silane coupling agents are preferred in terms of further improving the solder heat resistance.

[0078] <Example of a method for synthesizing a resin composition for adhesive sheets> 100 parts by mass of ethyl acetate was added to a reaction vessel, and a total of 65 parts by mass of butyl acrylate and a monofunctional monomer as the (A) component constituting the structural unit (A), 31 parts by mass of acrylonitrile as the (B) component constituting the structural unit (B), 4 parts by mass of acrylic acid and 0.2 parts by mass of azobisisobutyronitrile (AIBN) as the (C) component constituting the structural unit (C) were added, followed by polymerization at 70°C for 8 hours with stirring while blowing in nitrogen gas. The mixture was then cooled to room temperature, and a diluent such as methyl ethyl ketone was added until a predetermined viscosity was achieved to obtain an acrylic copolymer. Next, 12.5 parts by mass of an epoxy resin was added to add epoxy groups in an amount approximately equivalent to the carboxyl groups of the acrylic acid contained in the acrylic copolymer, and boron trifluoride monoethylamine (BF) was added as a curing agent. ３ MEA) is added and stirred to obtain a resin composition for adhesive sheets.

[0079] [Adhesive Sheet for Flexible Printed Wiring Boards] The adhesive sheet for flexible printed wiring boards of the present invention is obtained by forming the above-mentioned resin composition for adhesive sheets into a film shape.

[0080] The adhesive sheet can be prepared, for example, by applying the adhesive sheet resin composition to a release film. More specifically, the adhesive sheet resin composition is applied to a release-treated surface of a PET (polyethylene terephthalate) film, PP (polypropylene) film, PE (polyethylene) film, or the like, at least one side of which has been subjected to a release treatment. The adhesive sheet is then cured and dried under specific curing and drying conditions (temperature: 80-180°C, time: 2-10 minutes) until it reaches a semi-cured state (hereinafter also referred to as B-stage), thereby obtaining an adhesive sheet. The coating thickness varies depending on the application, but is appropriately set between 10 and 100 μm. Depending on the coating thickness, a comma coater, die coater, gravure coater, or other suitable coating method can be used. A fully cured (C-stage) adhesive sheet can be obtained by treating a B-stage adhesive sheet under specific curing conditions (temperature: 160-180°C, pressure: 2-3 MPa, time: 30-60 minutes).

[0081] The present invention will be specifically described below based on examples, but the present invention is not limited to the following examples, and various modifications are possible within the scope of the gist of the present invention.

[0082] <Number Average Molecular Weight (Mn) and Weight Average Molecular Weight (Mw)> The number average molecular weight (Mn) and weight average molecular weight (Mw) of each sample are polystyrene-equivalent molecular weights obtained by gel permeation chromatography (GPC) measurement under the following conditions using a calibration curve prepared using standard polystyrene samples of known molecular weights. <<GPC Measurement Conditions>> Model used: HLC-8320GPC (manufactured by Tosoh Corporation) Columns used: G7000HXL+GMHXL+GMHXL (manufactured by Tosoh Corporation) Column size: each 7.8 mmφ×30 cm, total 90 cm Column temperature: 40°C Flow rate: 0.8 mL / min Injection volume: 100 μL Eluent: tetrahydrofuran Detector: differential refractometer (RI) Standard sample: polystyrene

[0083] (Examples 1 to 12) First, resin compositions for adhesive sheets were prepared containing the components shown in Table 1 (units of parts by weight). To a reaction vessel containing ethyl acetate, the parts by weight of components (A), (B), and (C) shown in Table 1 were added, and 0.2 parts by weight of azobisisobutyronitrile (AIBN, manufactured by Kanto Chemical Co., Inc.) was then added. After that, polymerization was carried out by solution polymerization at 70°C for 8 hours with stirring while blowing in nitrogen gas. The mixture was then cooled to room temperature, and methyl ethyl ketone was added until a predetermined viscosity (3000 to 5000 cps) was achieved, yielding an acrylic copolymer. The viscosity was measured at 25°C using a Brookfield viscometer. Next, epoxy resin and curing agent were added in the amounts shown in Table 1 to the acrylic copolymer, and after stirring, a resin composition for adhesive sheets was obtained. Of Examples 1 to 12, Examples 3 to 12 are working examples, and Examples 1 and 2 are comparative examples.

[0084] In Table 1, the details of each component are as follows: (1-1) Acrylic copolymer (A) component: butyl acrylate (monomer) (manufactured by Toagosei Co., Ltd.) (1-2) Acrylic copolymer (A) component: urethane acrylate (monomer): monofunctional monomer (1) produced by the following Production Example 1-1 and Production Example 2-1 (1-3) Acrylic copolymer (A) component: isobornyl acrylate (monomer) (manufactured by Osaka Organic Chemical Industry Ltd.) (1-4) Acrylic copolymer (B) component: acrylonitrile (monomer) (manufactured by Kanto Chemical Co., Inc.) (1-5) Acrylic copolymer (C) component: acrylic acid (monomer) (manufactured by Toagosei Co., Ltd.) (2) Epoxy resin: bisphenol A type epoxy resin (epoxy group equivalent 180 g / eq), AER260 (manufactured by Asahi Kasei Corporation) (3) Lewis acid amine complex: boron trifluoride monoethylamine (BF ３ MEA) (manufactured by Stella Chemifa Corporation)

[0085] Each of the obtained adhesive sheet resin compositions was applied to a release-treated PET film to a thickness of 25 μm, and then cured and dried under specific curing and drying conditions (temperature: 150° C., time: 5 minutes) until the adhesive sheet reached a semi-cured state (B stage), thereby obtaining an adhesive sheet. Each of the obtained adhesive sheets was subjected to the following evaluation tests.

[0086] <Production Example 1-1: Production of Monool (1)> A pressure-resistant reactor equipped with a stirrer and a nitrogen inlet tube was charged with 0.2 g of zinc hexacyanocobaltate-tert-butyl alcohol complex (hereinafter referred to as "DMC-TBA"), which is a composite metal cyanide complex catalyst, and 59 g of n-butanol, which is an initiator, and a nitrogen atmosphere was set at 130 ° C. 3941 g of propylene oxide (hereinafter also referred to as "PO") was added at a constant rate over 7 hours. After confirming that the internal pressure of the pressure-resistant reactor had stopped decreasing, 4000 g of the product was extracted. The main component of the product, excluding by-products and catalyst-derived metals, was polyoxypropylene monool (monool (1)) with a hydroxyl value of 11.2 mg KOH / g (hydroxyl value-based molecular weight: 5008), an average number of hydroxyl groups of 1.03, and a water content of 120 ppm by mass. The resulting product contained 8 ppm by mass of Zn and 2 ppm by mass of Co.

[0087] <Production Example 2-1: Production of Monofunctional Monomer (1)> In a reaction vessel equipped with a stirrer and a nitrogen inlet tube, 928.1 g of the monool (1) obtained in Production Example 1-1 and 26.8 g of 2-acryloyloxyethyl isocyanate (Karenzu AOI, product name of Showa Denko K.K.) were charged and reacted at 70°C for 3 hours in the presence of 0.0955 g of dioctyltin distearate (DOTDS) to obtain a monofunctional monomer (1). The number average molecular weight (Mn) of the obtained monofunctional monomer (1) was 7660. The content of 2-acryloyloxyethyl isocyanate relative to the monool (1) was 100 in terms of index (NCO / OH ratio).

[0088] [(1) Solder Heat Resistance Test Method] An adhesive sheet and a 25 μm polyimide film were laminated in this order on a 125 μm thick polyimide film, and then heated and pressed at 160°C, 2.45 MPa, and 30 minutes for thermocompression bonding to obtain a solder heat resistance sample. The 25 μm thick polyimide film and the adhesive sheet were temporarily bonded, and then laminated on a 125 μm thick polyimide film. Solder heat resistance was evaluated by floating the 125 μm polyimide film surface in a solder bath at a predetermined temperature and holding it for 1 minute. The sample was then visually observed for peeling, blistering, etc., and evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1. <Evaluation Criteria> A: No peeling or blistering after floating in a 300°C solder bath for 1 minute. B: No peeling or blistering after floating in a 260°C solder bath for 1 minute. C: Peeling and swelling observed after floating in a solder bath at 260°C for 1 minute.

[0089] [(2) Peeling Force Test Method] The peeling sample was prepared by laminating an adhesive sheet and a polyimide single-sided copper-clad laminate in this order on a 125 μm thick polyimide film, and then thermocompression bonding by heating and pressing at 160°C, 2.45 MPa, and 30 minutes. The peeling force (adhesion) was evaluated according to JPCA BM-02, and the peeling force (adhesion) when the polyimide single-sided copper-clad laminate was pulled at a 90° angle was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1. <Evaluation Criteria> A: The peeling force was 15 N / cm or more, and the adhesive strength was completely acceptable for practical use. B: The peeling force was 10 N / cm or more but less than 15 N / cm, and the adhesive strength was sufficient for practical use. C: The peeling force was less than 10 N / cm, and the adhesive strength was insufficient.

[0090] [(3) Flexibility Test Method] An adhesive sheet was laminated on one side of a 25 μm thick polyimide film, and then exposed to UV light (250 to 500 mj / cm ２), and then heat curing at 150°C for 30 to 60 minutes was carried out to prepare a test sample. The adhesive sheet surface was placed on the outside and folded 180 degrees in a mountain fold. At this time, a load of 300 gf / cm was applied using a rubber roller. The adhesive sheet surface was visually checked for cracks and evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1. <Evaluation criteria> A... No cracks B... Cracks present

[0091] [(4) Repeated Bending Test Method] Using a U-shaped planar bending tester (DLDM111LH, product name: Yuasa System Co., Ltd.), the test sample obtained in (3) was repeatedly bent at approximately halfway along its length. Specifically, the test sample was bent into a U-shape so that the bending radius was 1.5 mm and the Kapton film side was facing inward, and then the bending force was released (180° release). This operation was repeated 100,000 times at a rate of 60 times per minute. The appearance of the test sample after the test was visually observed and evaluated according to the following criteria. The evaluation results are shown in Table 1. <Evaluation Criteria> A: No whitening, peeling, lifting, or cracking occurred, and there was no change in appearance. B: One or more of whitening, peeling, lifting, or cracking occurred, but the degree was slight and did not pose a practical problem. C: One or more of whitening, peeling, lifting, or cracking occurred significantly, posing a practical problem.

[0092]

[0093] Table 1 shows that when the (meth)acrylic acid ester contains a monomer having a number average molecular weight (Mn) of 1,300 to 36,000, it is possible to produce an adhesive sheet that has improved foldability while maintaining heat resistance and adhesion.

[0094] The present invention has industrial applicability as a resin composition for adhesive sheets that can produce adhesive sheets that have improved foldability while maintaining heat resistance and adhesion, and as an adhesive sheet for flexible printed wiring boards that uses the resin composition for adhesive sheets.

Claims

1. A resin composition for adhesive sheets, comprising an acrylic copolymer having structural units (A) derived from a (meth)acrylic acid ester, structural units (B) derived from (meth)acrylonitrile, and structural units (C) derived from an unsaturated carboxylic acid, an epoxy resin, and a curing agent, wherein the structural units (A) contain structural units derived from a (meth)acrylic acid ester having a number average molecular weight (Mn) of 1,300 to 36,000.

2. The resin composition for adhesive sheets according to claim 1, wherein the (meth)acrylic acid ester having a number average molecular weight (Mn) of 1,300 to 36,000 is a monofunctional monomer having one (meth)acryloyloxy group per molecule.

3. A resin composition for adhesive sheets according to claim 2, wherein the monofunctional monomer contains a curable component obtained by a urethane reaction between a polyoxyalkylene monool represented by the following formula (1a) and a compound represented by the following formula (1b): (In formula (1a), R １２ is an alkylene group having 2 to 4 carbon atoms, and R １３ is an alkyl group having 1 to 20 carbon atoms or a carboxylic acid residue having 1 to 20 carbon atoms, and b is an integer of 20 to 600. In formula (1b), R １１ is a hydrogen atom or a methyl group, and a is an integer of 1 to 4.

4. The resin composition for adhesive sheets according to claim 1 or 2, wherein the structural unit (A) further contains a unit based on butyl acrylate.

5. A resin composition for adhesive sheets according to claim 1 or 2, wherein the content of structural units derived from the (meth)acrylic acid ester having a number average molecular weight (Mn) of 1,300 to 36,000 per 100 parts by mass of the acrylic copolymer is 1 to 30 parts by mass.

6. A resin composition for adhesive sheets according to claim 1 or 2, wherein the content of the structural unit (A) is 50 to 95 parts by mass per 100 parts by mass of the acrylic copolymer.

7. A resin composition for adhesive sheets according to claim 1 or 2, wherein the content of the structural unit (B) is 5 to 45 parts by mass per 100 parts by mass of the acrylic copolymer.

8. A resin composition for adhesive sheets according to claim 1 or 2, wherein the content of the structural unit (C) is 1 to 6 parts by mass per 100 parts by mass of the acrylic copolymer.

9. A resin composition for adhesive sheets according to claim 1 or 2, wherein the content of the curing agent per 100 parts by mass of the epoxy resin is 0.1 parts by mass or more and less than 1.0 part by mass.

10. The resin composition for adhesive sheets according to claim 1 or 2, wherein the acrylic copolymer is synthesized by solution polymerization.

11. A resin composition for adhesive sheets according to claim 1 or 2, wherein the equivalent ratio of the epoxy groups of the epoxy resin to the carboxy groups of the structural unit (C) is 1:1 to 2:

1.

12. An adhesive sheet for flexible printed wiring boards, comprising the resin composition for adhesive sheets according to claim 1 or 2.

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