JP7613064B2 - Resin sheet and laminate - Google Patents

Description

The present invention relates to a resin sheet and laminate that have excellent coverage of uneven parts, high flexibility and heat resistance.

In recent years, a large number of electronic control technologies have been adopted in vehicles to assist with driving and improve fuel efficiency. As a result, electronic control units have become larger and the number of units installed has increased. This has resulted in issues such as increased vehicle weight and a lack of installation space, making it desirable to reduce the size of electronic control units.

On the other hand, electronic circuit boards equipped with electronic components such as IC chips mounted on electronic control units are generally sealed with sealing resin to protect the board from changes in the external environment such as water and dust. Various sealing methods have been used so far, including potting, dipping, coating and spraying, but these methods have the problem that they require a thick coat of paint, making it difficult to achieve sufficient miniaturization. Furthermore, even if the sealing layer can be made thinner, there are problems with material waste and long process times due to cumbersome work.

To address these issues, for example, Patent Documents 1 and 2 propose a method in which a resin sheet made of epoxy resin, a hardener, an inorganic filler, and a flame retardant is softened by heat under its own weight to cover the irregularities of electronic components, and then hardened in that state to form a sealing film.

However, although these methods can simplify the sealing process of electronic circuit boards, if the inorganic filler is loaded heavily to suppress fluidity, cross-linking is insufficient and heat resistance is lost, and if the loading amount of inorganic filler is reduced, the fluidity of the epoxy resin is too high and the resin cannot adequately cover the protrusions, making it difficult to achieve both fluidity and heat resistance. In addition, since the coating film after curing is hard and brittle, repeated heat cycles can cause peeling from the board and cracks, and excessive stress can be applied to the board, electronic components, and solder joints, resulting in short circuits, breaks, current leakage, and other problems that can lead to malfunction of the equipment.

JP 2011-246596 A JP 2012-054363 A

The object of the present invention is to provide a resin sheet that has excellent coverage of uneven parts, high flexibility and heat resistance, and can easily seal electronic circuit boards.

As a result of intensive research, the present inventors have found that a resin sheet formed from a resin composition containing a urethane-acrylic composite resin having a structural unit derived from a crystalline (meth)acrylic monomer and a structural unit derived from a (meth)acrylic monomer having a crosslinkable group, and a crosslinking agent, can solve the above problems.

The resin sheet according to one aspect of the present invention is a resin sheet formed from a resin composition containing a urethane-acrylic composite resin and a crosslinking agent, the urethane-acrylic composite resin being a resin in which a urethane unit (A) and a (meth)acrylic unit (B) are linked by a chain transfer agent residue, and the (meth)acrylic unit (B) has a structural unit derived from a crystalline (meth)acrylic monomer (b1) and a structural unit derived from a (meth)acrylic monomer (b2) having a crosslinkable group (excluding the structural unit derived from (b1)).

The resin sheet according to another embodiment of the present invention is characterized in that the crystalline (meth)acrylic monomer (b1) is a (meth)acrylate having a linear alkyl group having 16 or more carbon atoms.

A resin sheet according to another aspect of the present invention is characterized in that the urethane-acrylic composite resin contains urethane units (A) in a range of 30 to 70% by mass based on the mass of the urethane-acrylic composite resin.

A resin sheet according to another aspect of the present invention is characterized in that it is used for sealing electronic devices.

A laminate according to another aspect of the present invention is characterized by having the above-mentioned resin sheet and a release material.

The present invention provides a resin sheet that has excellent coverage of uneven areas, high flexibility and heat resistance, and can easily seal electronic circuit boards at low temperatures in a short time.

<Resin sheet>
The resin sheet of the present invention is formed from a resin composition containing a urethane-acrylic composite resin in which a urethane unit (A) and a (meth)acrylic unit (B) are linked by a chain transfer agent residue, and a crosslinking agent, and is characterized in that the (meth)acrylic unit (B) has a constituent unit derived from a crystalline (meth)acrylic monomer (b1) and a constituent unit derived from a (meth)acrylic monomer (b2) having a crosslinkable group (excluding the constituent unit derived from (b1)).
By adopting such a configuration, the flexible urethane portion and the acrylic portion having self-assembly properties form a microphase separation structure, and even before curing, the resin sheet maintains a solid shape at room temperature due to the crystallization effect of the crystalline (meth)acrylic monomer (b1), while at a relatively low temperature 20 to 40 ° C. higher than the crystallization temperature of the crystalline (meth)acrylic monomer (b1), the resin sheet softens due to the elimination of the crystallization effect while maintaining a certain cohesive force due to the cohesive force derived from the urethane unit (A), and quickly follows the unevenness. After crosslinking, the resin sheet exhibits excellent extensibility and adhesion due to the urethane portion, and excellent heat resistance due to the crosslinked structure of the acrylic portion. As a result, the resin sheet of the present invention can exhibit excellent coverage of uneven portions and high flexibility and heat resistance under low-temperature conditions of about 80 ° C. for 1 minute for a short time.
Therefore, the resin sheet of the present invention can be suitably used for protecting various electronic circuit boards, that is, various boards such as rigid boards and FPC boards.
In this specification, the term "chain transfer agent residue" refers to a partial structure of a composite resin that can be identified as being derived from a chain transfer agent, and "crystalline" refers to a melting point in the range of 30 to 100°C and a clear endothermic peak rather than a stepwise endothermic change in differential scanning calorimetry (DSC).

<Urethane/acrylic composite resin>
The urethane-acrylic composite resin in the present invention may have a structure in which a urethane unit (A), and a (meth)acrylic unit (B) having a structural unit derived from a crystalline (meth)acrylic monomer (b1) and a structural unit derived from a (meth)acrylic monomer (b2) having a crosslinkable group (excluding the structural unit derived from (b1)), are linked together via a chain transfer agent residue, and the method for producing the resin is not limited, but it can be preferably produced by the following method.
First, a urethane prepolymer having isocyanato groups at both ends is formed by reacting a polyol with a polyisocyanate (hereinafter, step 1).
Next, a chain transfer agent is added to synthesize a urethane unit (A) having chain transfer agent residues at both ends of the urethane prepolymer (hereinafter, step 2).
Thereafter, using the chain transfer agent residue contained in the obtained urethane unit (A), an ethylenically unsaturated monomer including a structural unit derived from the crystalline (meth)acrylic monomer (b1) and a structural unit derived from the (meth)acrylic monomer (b2) having a crosslinkable group (excluding the structural unit derived from (b1)) is chain transfer polymerized to form an ethylenically unsaturated monomer polymer unit (B) (hereinafter, Step 3).
In this manner, a urethane-acrylic composite resin in which the urethane unit (A) and the polymer unit (B) of an ethylenically unsaturated monomer are linked together via a chain transfer agent residue can be obtained.
All of these reactions may be carried out with or without a solvent, and when a solvent is used, the solvent may be removed under reduced pressure or at normal pressure during or after the reaction.

<Urethane unit (A)>
First, the urethane unit (A) of the urethane-acrylic composite resin will be described below.
The urethane-acrylic composite resin of the present invention can be formed by reacting a polyol with a polyisocyanate in a solvent or without a solvent. The urethane unit is flexible and has excellent adhesion to substrates, so that it can exhibit excellent coating properties.

[Polyol]
Examples of the polyol constituting the urethane unit (A) include polyether polyols, polyester polyols, polycarbonate polyols, polyolefin polyols, vegetable oil-based polyols, other polyols including acrylic polyols, and complexes thereof.
These polyols may be used alone or in combination of two or more.

(Polyether polyol)
The polyether polyol may be any compound having two or more hydroxyl groups and two or more ether bonds in the molecule, and examples thereof include polymers or copolymers of methylene oxide, ethylene oxide, propylene oxide, tetrahydrofuran, and the like, and specific examples thereof include polyethylene glycol, polypropylene glycol, poly(ethylene/propylene) glycol, and polytetramethylene glycol.
Examples of the polyether polyol include polyether polyols obtained by condensation of hexanediol, methylhexanediol, heptanediol, octanediol, or mixtures thereof.

Further examples of polyether polyols include polyols obtained by adding alkylene oxides such as methylene oxide, ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, or polyoxytetramethylene oxide to a starting material that has at least two active hydrogen groups, such as low molecular weight polyols, aliphatic amine compounds, aromatic amine compounds, alkanolamines, or bisphenols.

Among the compounds having two or more active hydrogen groups, examples of low molecular weight polyols include bifunctional low molecular weight polyols and trifunctional or higher functional low molecular weight polyols.

Examples of the bifunctional low molecular weight polyols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, hexanediol, octanediol, nonanediol, dipropylene glycol, diethylene glycol, triethylene glycol, 3-methyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-ethyl-1,3-hexanediol, 2-methyl-1,8-octanediol, and the like. , polyoxyethylene glycol (10 or less moles added), polyoxypropylene glycol (10 or less moles added), cyclohexanediol, cyclohexanedimethanol, tricyclodecane dimethanol, cyclopentadiene dimethanol, dimer diol, bisphenol B, N,N-bis(2-hydroxypropyl)aniline, dimethylolacetic acid, dimethylolpropionic acid, dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolpentanoic acid, dihydroxysuccinic acid, dihydroxypropionic acid, and dihydroxybenzoic acid.

Examples of the trifunctional low molecular weight polyols include trimethylolethane, trimethylolpropane, 1,1,1-trimethylolbutane, 1,2,3-butanetriol, 1,2,4-butanetriol, 1,2,6-butanetriol, trimethylolbutene, trimethylolpentene, trimethylolhexene, trimethylolheptene, trimethyloloctene, trimethylolnonene, trimethyloldecene, trimethylolundecene, trimethyloldodecene, trimethyloltridecene, trimethylolpentadecene, trimethylolhexene, Sadecene, Trimethololheptadecene, Trimethyloloctadecene, 1,1,1-trimethylol-2-methyl-hexane, 1,1,1-trimethylol-3-methyl-hexane, 1,1,1-trimethylol-2-ethyl-hexane, 1,1,1-trimethylol-3-ethyl-hexane, Trimethylolhexene, 1,2,3-octanetriol, 1,3,7-octanetriol, 3,7-dimethyl-1,2,3-octanetriol, 1,1,1-, 1,1,1-trimethyloldecane, 1,2,10-decanetriol ...2,10-trimethyloldecane, 1,2,10-tri Tyrol isoheptadecane, 1,1,1-trimethylol-seA-butane, 1,1,1-trimethylol-tert-pentane, 1,1,1-trimethylol-tert-nonane, 1,1,1-trimethylol-tert-tridecane, 1,1,1-trimethylol-tert-heptadecane, 1,1,1-trimethylol-2-methyl-hexane, 1,1,1-trimethylol-3-methyl-hexane, 1,1,1-trimethylol-2-ethyl-hexane, 1,1,1-trimethylol-3-ethyl-hexane, 1,1,1-trimethylol isoheptadecane These include decane, 1,2,3,4-butanetetraol, pentaerythritol, dipentaerythritol, tripentaerythritol, glycerin, diglycerin, triglycerin, polyglycerin, ditrimethylolethane, ditrimethylolpropane, tris(2-hydroxyethyl)isocyanurate, benzene-1,3,5-triol, benzene-1,2,3-triol, stilbene-3,4',5-triol, sucrose, inositol, sorbitan, sorbitol, mannitol, saccharose, cellulose, and xylitol.

Among the compounds having two or more active hydrogen groups, examples of aliphatic amine compounds include ethylenediamine, isophoronediamine, triethylenetetramine, diethylenetriamine, and triaminopropane. Examples of aromatic amine compounds include toluenediamine and diphenylmethane-4,4-diamine. Examples of alkanolamines include ethanolamine and diethanolamine. Examples of bisphenols include bisphenol B, bisphenol BP, bisphenol C, bisphenol A, bisphenol E, and bisphenol F.

(Polyester polyol)
The polyester polyol may be, for example, a polyester polyol obtained by condensation reaction of the above-mentioned low molecular weight polyol with a dibasic acid component.

Examples of dibasic acid components include aliphatic or aromatic dibasic acids such as terephthalic acid, adipic acid, azelaic acid, sebacic acid, dimer acid, hydrogenated dimer acid, phthalic anhydride, isophthalic acid, trimellitic acid, glutaric acid, pimelic acid, suberic acid, and sebacic acid, as well as their anhydrides.

Examples of polyester polyols include polyester polyols obtained by ring-opening polymerization of cyclic ester compounds such as lactones, such as ε-caprolactone, poly(β-methyl-γ-valerolactone), and polyvalerolactone.

(Polycarbonate polyol)
Examples of the polycarbonate polyol include reaction products of the above-mentioned low molecular weight polyols and carbonate compounds such as dialkyl carbonates, alkylene carbonates, and diaryl carbonates.
The dialkyl carbonate may be dimethyl carbonate, diethyl carbonate, etc. The alkylene carbonate may be ethylene carbonate, etc. The diaryl carbonate may be diphenyl carbonate, etc.

(Polyolefin polyol)
Examples of polyolefin polyols include hydroxyl-containing polybutadiene, hydrogenated hydroxyl-containing polybutadiene, hydroxyl-containing polyisoprene, hydrogenated hydroxyl-containing polyisoprene, hydroxyl-containing chlorinated polypropylene, and hydroxyl-containing chlorinated polyethylene.

(Vegetable oil-based polyol)
Examples of vegetable oil-based polyols include polyols made from castor oil, dimer acid, or soybean oil, which are derived from plants.

The number average molecular weight of these polyols is preferably 500 or more and less than 5,000, and more preferably 700 or more and less than 3,500.

In addition, the above-mentioned low molecular weight polyols, aliphatic amine compounds, and aromatic amine compounds can be used in combination to adjust the urethane bond concentration and introduce various functional groups.

[Polyisocyanate]
Examples of the polyisocyanate constituting the urethane unit (A) include aromatic, aliphatic, and alicyclic polyisocyanates. These may be used alone or in combination of two or more.

Examples of aromatic polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, tolidine diisocyanate, xylylene diisocyanate, m-tetramethylxylene diisocyanate, p-tetramethylxylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 3,3'-dichloro-4,4'-biphenylene diisocyanate, and 1,5-tetrahydronaphthalene diisocyanate.

Examples of aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, lysine ester triisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate tetramethylene diisocyanate, pentamethylene diisocyanate, and trimethylhexamethylene diisocyanate.

Examples of alicyclic polyisocyanates include isophorone diisocyanate, 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), 1,4-bis(isocyanatemethyl)cyclohexane, hydrogenated xylylene diisocyanate, dimer acid diisocyanate, and norbornene diisocyanate.

The reaction between the polyol and the polyisocyanate can be carried out preferably in the absence of a solvent using a known urethane reaction, and by using an excess of polyisocyanate, a urethane prepolymer having isocyanato groups at both ends can be obtained. The molar ratio of isocyanato groups to hydroxyl groups (NCO moles/OH moles) during the reaction is preferably 1.05 to 2.00, more preferably 1.10 to 1.50.
In the urethanization reaction, a catalyst may be used for the purpose of adjusting the reactivity.

The catalyst may be a known metal catalyst, amine catalyst, or the like. Examples of metal catalysts include dibutyltin dilaurate, tin octoate, dibutyltin di(2-ethylhexoate), lead 2-ethylhexoate, 2-ethylhexyl titanate, titanium ethyl acetate, iron 2-ethylhexoate, cobalt 2-ethylhexoate, zinc naphthenate, cobalt naphthenate, and tetra-n-butyltin. Examples of amine catalysts include tertiary amines such as tetramethylbutanediamine. The amount of catalyst used is preferably in the range of 0.05 to 1 mol% based on the mass of the polyol.

<Chain Transfer Agent>
The chain transfer agent in the present invention is not particularly limited, but is preferably a chain transfer agent having a sulfanyl group. As the chain transfer agent having a sulfanyl group, one having a functional group capable of reacting with an isocyanato group and a sulfanyl group in the molecule is preferably used. When the chain transfer agent is used, the terminal isocyanato group in the urethane prepolymer reacts with the functional group capable of reacting with an isocyanato group in the chain transfer agent, and a urethane unit (A) having a sulfanyl group at both ends can be formed. The chain transfer agent can be used alone or in combination of two or more of known chain transfer agents.

The functional group capable of reacting with the isocyanato group may be a hydroxyl group or an amino group, with the amino group being preferred from the viewpoint of reactivity. Since the amino group is more reactive than the sulfanyl group, it reacts preferentially with the terminal isocyanato group of the urethane prepolymer to form a urea bond, and the sulfanyl group can be efficiently introduced to the end of the urethane unit (A). A more preferred chain transfer agent is a compound having one amino group and one sulfanyl group in the molecule.

Examples of compounds having one amino group and one sulfanyl group in the molecule include aminoalkanethiols such as 2-aminoethanethiol, 3-aminopropyl-1-thiol, 1-aminopropyl-2-thiol, and 4-amino-1-butanethiol; and aminobenzenethiols such as 2-aminothiophenol, 3-aminothiophenol, and 4-aminothiophenol. Among these, aminoalkanethiols are preferred, and 2-aminoethanethiol is more preferred.

[Content of urethane unit (A)]
The urethane-acrylic composite resin in the present invention preferably contains 30 to 70% by mass of the urethane unit (A) based on the mass of the urethane-acrylic composite resin, and more preferably contains 35 to 65% by mass of the urethane unit (A). When the content of the urethane unit (A) is 30 to 70% by mass, the cured film is excellent in terms of its unevenness covering ability and its flexibility and heat resistance.

The weight average molecular weight of the urethane unit (A) is not particularly limited, but is preferably in the range of 3,000 to 200,000. If it is 3,000 or more, the adhesive strength is excellent, and if it is 200,000 or less, the viscosity can be easily adjusted.

<(Meth)acrylic unit (B)>
The (meth)acrylic unit (B) in the present invention has a structural unit derived from a crystalline (meth)acrylic monomer (b1) and a structural unit derived from a (meth)acrylic monomer (b2) having a crosslinkable group (excluding the structural unit derived from (b1)), and is specifically a polymer of an ethylenically unsaturated monomer containing a crystalline (meth)acrylic monomer (b1) and a (meth)acrylic monomer (b2) having a crosslinkable group (excluding (b1)). Specifically, the urethane unit (A) having a chain transfer agent residue at both ends obtained in step 2, and the ethylenically unsaturated monomer containing the crystalline (meth)acrylic monomer (b1) and the (meth)acrylic monomer (b2) having a crosslinkable group (excluding (b1)) are polymerized in the presence of a polymerization initiator to obtain a urethane-acrylic composite resin, which is a block polymer in which the urethane unit (A) and the (meth)acrylic unit (B) are linked by a chain transfer agent residue.

The structural units derived from the crystalline (meth)acrylic monomer (b1) cause the (meth)acrylic unit (B) to crystallize at room temperature, increasing the cohesive force of the urethane-acrylic composite resin, allowing it to maintain its sheet shape even when uncured. On the other hand, when the crystallization temperature is exceeded, the cohesive force is immediately eliminated, the resin sheet softens, and forms a film that conforms to the irregularities of the electronic circuit board. Furthermore, by crosslinking the (meth)acrylic unit (B) with a crosslinking agent, the resulting cured film becomes a tough film that is waterproof, stain-resistant, and heat-resistant, and can seal the electronic circuit board.

[Crystalline (meth)acrylic monomer (b1)]
The crystalline (meth)acrylic monomer is not particularly limited as long as it is a (meth)acrylic monomer having the above-mentioned "crystallinity", and for example, a (meth)acrylate having a linear alkyl group having 16 or more carbon atoms can be used. Examples of such (meth)acrylates having a linear alkyl group having 16 or more carbon atoms include cetyl (meth)acrylate, stearyl (meth)acrylate, eicosyl (meth)acrylate, and behenyl (meth)acrylate. From the viewpoint of crystallinity, those having a linear alkyl group having 18 or more carbon atoms are preferable.

[Content of crystalline (meth)acrylic monomer (b1)]
The content of the crystalline (meth)acrylic monomer (b1) is preferably in the range of 50 to 95% by mass, more preferably in the range of 55 to 90% by mass, based on the total mass of the monomers constituting the (meth)acrylic unit (B). When the content of the crystalline (meth)acrylic monomer (b1) is 50% by mass or more, the unevenness covering ability is excellent, and when it is 95% by mass or less, the flexibility and heat resistance of the cured film are excellent.

[(Meth)acrylic monomer (b2) having a crosslinkable group (excluding (b1)]
The (meth)acrylic monomer (b2) having a crosslinkable group is not particularly limited as long as it has a crosslinkable group in the molecule that can react with a crosslinking agent described below. Examples of such crosslinkable groups include a hydroxyl group, an epoxy group, a carboxyl group, an isocyanato group, and blocked forms thereof.

Examples of (meth)acrylic monomers having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-hydroxy-3-allyloxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, or caprolactone adducts of these monomers (number of moles added: 1 to 5), polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, and glycerin mono(meth)acrylate.

Examples of (meth)acrylic monomers having an epoxy group include glycidyl (meth)acrylate, 3,4-epoxybutyl (meth)acrylate, 4,5-epoxypentyl (meth)acrylate, 6,7-epoxypentyl (meth)acrylate, 3,4-epoxycyclohexyl (meth)acrylate, 4-hydroxybutyl acrylate glycidyl ether, and lactone-modified 3,4-epoxycyclohexyl (meth)acrylate.

Examples of (meth)acrylic monomers having a carboxy group include (meth)acrylic acid, acrylic acid dimer, itaconic acid, maleic acid, fumaric acid, crotonic acid, α-(hydroxymethyl)(meth)acrylic acid, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxypropyl phthalate, 2-(meth)acryloyloxyethyl hexahydrophthalate, 2-(meth)acryloyloxypropyl hexahydrophthalate, β-carboxyethyl (meth)acrylate, ethylene oxide modified succinic acid (meth)acrylate, ω-carboxypolycaprolactone (meth)acrylate, and p-vinylbenzoic acid.

Examples of (meth)acrylate monomers having an isocyanato group and their blocked monomers include (meth)acryloyl isocyanate, 2-isocyanatoethyl (meth)acrylate, 2-(meth)acryloyloxyethoxyethyl isocyanate, 1,1-(bis(meth)acryloyloxymethyl)ethyl isocyanate, m-(meth)acryloylphenyl isocyanate, and α,α-dimethyl-4-isopropenylbenzyl isocyanate.

[Content of (meth)acrylic monomer (b2) having crosslinkable group]
The content of the (meth)acrylic monomer (b2) having a crosslinkable group is preferably in the range of 5 to 35 mass % based on the total mass of the monomers constituting the (meth)acrylic unit (B). When the content of the (meth)acrylic monomer (b2) having a crosslinkable group is 5 to 35 mass %, the unevenness covering property and the flexibility and heat resistance of the cured film are excellent.

[Other monomers]
The other monomers other than the monomers (b1) and (b2) used for forming the (meth)acrylic unit (B) are not particularly limited as long as they are copolymerizable with the monomers (b1) and (b2), and can be appropriately selected from known ethylenically unsaturated monomers.
Examples of such other ethylenically unsaturated monomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tertiary butyl (meth)acrylate, isoamyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, and isodecyl (meth)acrylate. linear or branched alkyl (meth)acrylates such as cyclohexyl (meth)acrylate, tertiary butyl cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, etc. fluoroalkyl (meth)acrylates such as trifluoroethyl (meth)acrylate, octafluoropentyl (meth)acrylate, perfluorooctylethyl (meth)acrylate, and tetrafluoropropyl (meth)acrylate; heterocyclic (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate and 3-methyl-3-oxetanyl (meth)acrylate; aromatic (meth)acrylates such as benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, and nonylphenoxypolyethylene glycol (meth)acrylate; methoxypolyethylene glycol mono(meth)acrylate, octoxypolyethylene glycol polypropylene glycol mono(meth)acrylate, lauroxypolyethylene glycol mono(meth)acrylate, phenoxypolyethylene glycol mono(meth)acrylate, phenoxypolyethylene glycol polypropylene glycol mono(meth)acrylate, and polyethylene (Meth)acrylates having an alkyl ether group such as ethylene glycol monomethyl ether (meth)acrylate, lauroxy polyethylene glycol mono(meth)acrylate, nonylphenoxy polyethylene glycol mono(meth)acrylate, nonylphenoxy polypropylene glycol mono(meth)acrylate, nonylphenoxy polyethylene glycol polypropylene glycol mono(meth)acrylate, phenoxy polyethylene glycol mono(meth)acrylate, methoxypolyethylene glycol (meth)acrylate, n-butoxyethyl (meth)acrylate, n-butoxydiethylene glycol (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate; vinyls such as styrene, α-methylstyrene, vinyl acetate; (meth)acrylamide, N-methyl(meth)acrylamide, N-butyl(meth)acrylamide, diacetone(meth)acrylamide, N-methoxymethyl-(meth)acrylamide, N-ethoxymethyl-(meth)acrylamide, N-propanol, N-butoxymethyl-(meth)acrylamide, N-pentoxymethyl-(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-dibenzyl(meth)acrylamide, methacrylformamide, N-methyl-N-vinylacetamide, N-vinylpyrrolidone, N,N-di(methoxymethyl)acrylamide, N-ethoxymethyl-N-methoxymethyl(meth)acrylamide, N,N-di(ethoxymethyl)(meth)acrylamide, N-ethoxymethyl-N- (meth)acrylates having a nitrogen atom, such as propoxymethyl(meth)acrylamide, N,N-di(propoxymethyl)(meth)acrylamide, N-butoxymethyl-N-(propoxymethyl)(meth)acrylamide, N,N-di(butoxymethyl)(meth)acrylamide, N-butoxymethyl-N-(methoxymethyl)(meth)acrylamide, N,N-di(pentoxymethyl)(meth)acrylamide, N-methoxymethyl-N-(pentoxymethyl)(meth)acrylamide, and cinnamic acid amide, are included.
These may be used alone or in combination of two or more.

[Polymerization initiator]
As the polymerization initiator, known azo compounds and organic peroxides can be used.
Examples of azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), dimethyl 1,1'-azobis(1-cyclohexanecarboxylate), dimethyl 2,2'-azobis(2-methylpropionate), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), and 2,2'-azobis[2-(2-imidazolin-2-yl)propane].
Examples of organic peroxides include benzoyl peroxide, t-butyl peroxy 2-ethylhexaate, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(2-ethoxyethyl)peroxydicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxypivalate, (3,5,5-trimethylhexanoyl)peroxide, dipropionyl peroxide, and diacetyl peroxide.
These may be used alone or in combination of two or more.

The amount of the polymerization initiator used is preferably 0.001 to 15% by mass based on the total mass of the ethylenically unsaturated monomers that form the (meth)acrylic unit (B). A range of 0.001 to 15% by mass is preferable because chain transfer polymerization proceeds effectively.

[Weight average molecular weight of (meth)acrylic unit (B)]
The weight average molecular weight of the (meth)acrylic unit (B) is not particularly limited, but is preferably from 2,000 to 200,000. If it is 2,000 or more, the unevenness covering ability is excellent, and if it is 200,000 or less, the viscosity can be easily adjusted.

[Weight average molecular weight of urethane-acrylic composite resin]
The weight average molecular weight of the urethane-acrylic composite resin is not particularly limited, but is preferably in the range of 5,000 to 300,000, and more preferably in the range of 10,000 to 100,000. If it is 5,000 or more, it has excellent unevenness covering ability, and if it is 300,000 or less, it is easy to adjust the viscosity.

<Solvent>
The reaction for producing the urethane-acrylic composite resin may be carried out using a solvent. These solvents may be used alone or in combination of two or more.
The solvent that may be used in the reaction of the polyol with the polyisocyanate is not particularly limited as long as it does not react with an isocyanato group, and examples thereof include acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, propyl acetate, toluene, xylene, anisole, propylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, N-vinylpyrrolidone, N-methylcaprolactam, dimethylsulfoxide, tetramethylurea, pyridine, dimethylsulfone, hexamethylsulfoxide, m-cresol, γ-butyrolactone, and γ-valerolactone.
As the solvent that may be used in the reaction between the urethane prepolymer and the chain transfer agent, in addition to the above-mentioned solvents, alcohols such as ethanol, isopropanol, tertiary butanol, and diacetone alcohol can be used.

<Crosslinking Agent>
The resin sheet of the present invention is formed from a resin composition containing the above-mentioned urethane-acrylic composite resin and a crosslinking agent. The crosslinking group derived from the (meth)acrylic monomer (b2) reacts with the crosslinking agent to cure, thereby obtaining a cured product having excellent flexibility and heat resistance.
The crosslinking agent is not particularly limited as long as it has a functional group capable of reacting with the crosslinkable group in the molecule, and examples of such functional groups include an epoxy group, an acid anhydride group, a phenol group, an isocyanato group and its block, an amino group, a hydroxyl group, and a carboxy group. The crosslinking agent may be used alone or in combination of two or more kinds.

Examples of crosslinking agents having an epoxy group include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidylaminophenylmethane, triglycidyl isocyanurate, and triglycidyl-p-aminophenol.

Examples of crosslinking agents having an acid anhydride group include phthalic anhydride, trimellitic anhydride, and maleic anhydride.

The crosslinking agent having a phenol group may be a monomer compound or a polymer compound. The crosslinking agent having a phenol group, which is a polymer compound, may be a polymer (homopolymer) of a single monomer or a copolymer (copolymer) of multiple types of monomers. The crosslinking agent having a phenol group may be any of a random copolymer, a block copolymer, or a graft copolymer.
Examples of crosslinking agents having a phenol group include bisphenol A, bisphenol F, bisphenol S, resorcin, catechol, hydroquinone, fluorene bisphenol, 4,4'-biphenol, 4,4',4"-trihydroxytriphenylmethane, naphthalene diol, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, calixarene, novolak-type phenolic resins (e.g., polyhydric phenol novolak resins synthesized from polyhydric hydroxy compounds and formaldehyde, such as phenol novolak resins, cresol novolak resins, bisphenol A novolak resins, bisphenol S novolak resins, and resorcin novolak resins), naphthol-phenol co-condensed novolak resins, naphthol-cresol co-condensed novolak resins, naphthol novolak resins, and alco Examples of suitable phenol compounds include polyhydric phenol compounds such as alkoxy group-containing aromatic ring-modified novolak resins (polyhydric phenol compounds in which a phenol nucleus and an alkoxy group-containing aromatic ring are linked by formaldehyde)), aralkyl-type phenol resins (for example, phenol aralkyl resins and naphthol aralkyl resins such as Xylok resin), aromatic hydrocarbon formaldehyde resin-modified phenol resins, dicyclopentadiene phenol addition type resins, trimethylolmethane resins, tetraphenylolethane resins, biphenyl-modified phenol resins (polyhydric phenol compounds in which a phenol nucleus is linked by a bismethylene group), biphenyl-modified naphthol resins (polyhydric naphthol compounds in which a phenol nucleus is linked by a bismethylene group), and aminotriazine-modified phenol resins (polyhydric phenol compounds in which a phenol nucleus is linked by melamine, benzoguanamine, or the like).

As the crosslinking agent having an isocyanato group, for example, the description in the above [Polyisocyanate] section can be used. In addition, as the crosslinking agent having an isocyanato group, a biuret, a nurate, an adduct, or other condensation product of the above polyisocyanate may be used.
An example of the biuret is a biuret of hexamethylene diisocyanate.
Examples of the nurate form include a nurate form of hexamethylene diisocyanate, a nurate form of isophorone diisocyanate, and a nurate form of tolylene diisocyanate.
Examples of the adduct include an adduct of trimethylolpropane with hexamethylene diisocyanate, an adduct of trimethylolpropane with isophorone diisocyanate, and an adduct of toluene diisocyanate.
Other condensates include polyfunctional compounds having an isocyanato group, carbodiimide-modified compounds, biuret-modified compounds, and allophanate-modified compounds, such as polymethylene polyphenyl polyisocyanate, a biuret compound of hexamethylene diisocyanate, and carbodiimide-modified diphenylmethane diisocyanate.

Examples of crosslinking agents having blocked isocyanato groups include those obtained by blocking the above-mentioned crosslinking agents having isocyanato groups with a known blocking agent. Examples of blocking agents include phenols, alkylphenols, active methylene compounds, oximes, lactams, bisulfites, and imidazoles.

Examples of crosslinking agents having amino groups include the above-mentioned aliphatic amine compounds and aromatic amine compounds, as well as bifunctional or higher polyether amines such as JEFFAMINE D-230, D-400, D-2000, T-403, and T-3000 (all manufactured by HUNTSMAN).

As a crosslinking agent having a hydroxyl group, for example, the description of "low molecular weight polyol" in the above (Polyether polyol) section can be used.

Examples of crosslinking agents having a carboxy group include succinic acid, adipic acid, sebacic acid, maleic acid, phthalic acid, naphthalenedicarboxylic acid, methylphthalic acid, cyclohexanedicarboxylic acid, methylcyclohexanedicarboxylic acid, methylnorbornenedicarboxylic acid, tetrahydrophthalic acid, trimellitic acid, trimesic acid, pyromellitic acid, and naphthalenetetracarboxylic acid.

The molar ratio of the functional groups in the crosslinking agent to the crosslinkable groups in the urethane-acrylic composite resin (number of moles of functional groups in the crosslinking agent/number of moles of crosslinkable groups in the urethane-acrylic composite resin) is preferably 0.2 to 10.0, and more preferably 0.5 to 5.0. A molar ratio of 0.2 to 10.0 is preferred because it provides excellent flexibility.

<Resin sheet>
The resin sheet of the present invention can be obtained by molding the above-mentioned resin composition into a sheet. The method for producing the resin sheet is not particularly limited, and for example, the urethane-acrylic composite resin, the crosslinking agent, and the solvent are uniformly stirred and mixed to obtain a resin composition, which is then coated on a release film using a doctor blade or the like, dried in an oven, and then cooled to room temperature to solidify. The temperature of the oven is usually in the range of 60°C to 100°C, and the thickness of the resin sheet is preferably 100 μm to 3 mm.

[Filler]
The resin sheet of the present invention may contain a filler within a range that does not impair the effects of the present invention. Examples of the filler include colorants such as titanium oxide and carbon black; metal powders such as ferrite; inorganic fibers such as glass fibers and metal fibers; organic fibers such as carbon fibers and aramid fibers; heat-conducting agents such as aluminum nitride, boron nitride, aluminum hydroxide, alumina, magnesium oxide, carbon nanotubes, and expanded graphite; inorganic whiskers such as glass beads, glass balloons, glass flakes, glass fibers, calcium carbonate, magnesium carbonate, potassium titanate whiskers, and zinc oxide whiskers; and fillers such as talc, silica, calcium silicate, kaolin, diatomaceous earth, montmorillonite, graphite, pumice, ebonized powder, cotton flock, cork powder, barium sulfate, and fluororesin. The filler may be used alone or in combination of two or more types.

The resin sheet of the present invention may further contain known additives such as curing accelerators, antiaging agents, antioxidants, antistatic agents, weather resistance agents, UV absorbers, antiblocking agents, crystal nucleating agents, flame retardants, vulcanizing agents, vulcanization assistants, antibacterial and antifungal agents, dispersants, coloring inhibitors, foaming agents, and rust inhibitors, to the extent that the effects of the present invention are not impaired.

By using the resin sheet of the present invention, electronic devices can be sealed, for example, as follows. First, the resin sheet is laminated on an electronic circuit board and heated in an atmosphere of 60°C to 100°C for 30 to 60 seconds. It immediately softens and easily conforms to the irregularities of the electronic components under its own weight to form a coating film. It is then heated in an atmosphere of 80°C to 120°C for 10 to 60 minutes, hardened, and sealed. However, the method of sealing an electronic circuit board with the resin sheet of the present invention is not limited to the above.

The resin sheet of the present invention can greatly simplify the sealing process and can be sealed at low temperatures, making it suitable for use with electronic circuit boards that have low heat resistance. It also has excellent flexibility and heat resistance, making it suitable for use in protecting various types of electronic circuit boards, such as rigid boards and FPC boards.

The present invention will be explained in more detail below with reference to examples, but the following examples do not limit the scope of the invention in any way. In addition, unless otherwise specified, "parts" and "%" in the examples represent "parts by mass" and "% by mass", respectively.

<Weight average molecular weight (Mw)>
The weight average molecular weight (Mw) of the resin was determined by gel permeation chromatography (GPC) using a GPC-8020 (manufactured by Tosoh Corporation) as a GPC device, tetrahydrofuran as an eluent, and a column. The column was operated under conditions of a flow rate of 0.6 ml/min, an injection volume of 10 μl, and a column temperature of 40° C. using three TSKgel Super HM-M (manufactured by Tosoh Corporation) connected in series.

<Solid content>
The solid content concentration of the resin was measured in accordance with JIS K5601-1-2 at a heating temperature of 150° C. for a heating time of 20 minutes, and the heating residue was used.

The abbreviations for compounds used in this specification are shown below.
<Polyol>
T-5651: Bifunctional polycarbonate polyol, number average molecular weight 1,000, hydroxyl value 113 mgKOH/g, trade name "Duranol T5651", manufactured by Asahi Kasei Corporation PTG-1000SN: Bifunctional polytetramethylene ether glycol, number average molecular weight 1,000, hydroxyl value 112 mgKOH/g, manufactured by Hodogaya Chemical Co., Ltd. 112 mgKOH/g, manufactured by Adeka Corporation <Polyisocyanate>
IPDI: Isophorone diisocyanate

<(Meth)acrylic monomer>
SA: Stearyl acrylate, SMA: Stearyl methacrylate, VA: Behenyl acrylate, AA: Acrylic acid, HEMA: 2-hydroxyethyl methacrylate, BMA: Butyl methacrylate

<Crosslinking Agent>
jER630: p-aminophenol type liquid epoxy resin, product name "jER630", manufactured by Mitsubishi Chemical Corporation, epoxy equivalent 94.3 g/eq
BL3370: Aliphatic blocked isocyanate, product name "Desmodur BL3370", manufactured by Sumika Bayer Urethane Co., Ltd., solids concentration 70%, NCO content 8.9%

<Catalyst>
・C11Z-CN: 1-cyanoethyl-2-undecylimidazole, product name "Curezol C11Z-CN", manufactured by Shikoku Chemical Industry Co., Ltd. ・DBTDL: Dibutyltin dilaurate

<Production of urethane-acrylic composite resin>
(Production Example 1)
A reaction vessel equipped with a nitrogen gas inlet tube, a stirrer, a thermometer, and a reflux condenser was charged with 74.9 parts of T-5651 as a polyol, 25.1 parts of isophorone diisocyanate as a polyisocyanate, and 0.01 parts of dibutyltin dilaurate as a catalyst, and after uniform stirring, the mixture was reacted at 90° C. for 5 hours under a nitrogen atmosphere to obtain a urethane prepolymer.
Then, the mixture was cooled to 80° C., and 11.0 parts of methyl ethyl ketone as a solvent, 31.7 parts of toluene, and 5.5 parts of 2-aminoethanethiol as a chain transfer agent were added, followed by reaction for 2 hours at 75° C. to obtain a urethane unit. The end point of the reaction was confirmed by FT-IR based on the disappearance of the peak (near 2270 cm ⁻¹ ) derived from the isocyanato group.
Next, 135.4 parts of SA as the crystalline (meth)acrylic monomer (b1), 12.3 parts of AA as the (meth)acrylic monomer (b2) having a crosslinkable group, 98.5 parts of BMA as the other ethylenically unsaturated monomer, and toluene were added so that the ratio of the solvent in the reaction vessel was 40%, and after uniform stirring, the temperature was raised to 75° C. under a nitrogen atmosphere. 0.08 parts of 2,2′-azobis(2,4-dimethylvaleronitrile) was added thereto as a polymerization initiator in 13 divided portions every 30 minutes, and the mixture was allowed to react for another 2 hours after the addition of the polymerization initiator to form a (meth)acrylic unit.
Toluene was added to adjust the solid concentration to 60%, and a urethane-acrylic composite resin solution of Production Example 1 was obtained.

(Production Examples 2 to 15, Comparative Production Examples 1 to 2)
The same operations as in Production Example 1 were carried out except that the compounds and blending compositions were changed to those shown in Table 1, to obtain urethane-acrylic composite resin solutions of Production Examples 2 to 15 and Comparative Production Examples 1 and 2, respectively.

The weight average molecular weight of the obtained urethane-acrylic composite resin, the content (%) of urethane unit (A) in the urethane-acrylic composite resin, the content (%) of crystalline (meth)acrylic monomer (b1) in (meth)acrylic unit (B), and the content (b2) of (meth)acrylic monomer having a crosslinkable group in (meth)acrylic unit (B) are shown in Table 1.

(Comparative Production Example 3) Urethane resin In a reaction vessel equipped with a nitrogen gas inlet tube, a stirrer, a thermometer, and a reflux condenser, 100.0 parts of T-5651 as a polyol, 14.9 parts of isophorone diisocyanate as a polyisocyanate, and 0.01 parts of dibutyltin dilaurate as a catalyst were charged, and after uniform stirring, the mixture was reacted at 90°C for 5 hours under a nitrogen atmosphere, and 76.6 parts of toluene were added to obtain a comparative urethane resin solution. The weight average molecular weight of the obtained urethane resin was 8,300, and the solid content concentration was 60%.

(Comparative Production Example 4) Acrylic Resin In a reaction vessel equipped with a nitrogen gas inlet tube, a stirrer, a thermometer, and a reflux condenser, 137.3 parts of SA, 19.6 parts of AA, 39.2 parts of n-butyl methacrylate, 7.3 parts of 2-ethylhexyl thioglycolate, and 136.0 parts of toluene were added and stirred uniformly, and then heated to 75°C under a nitrogen atmosphere. 0.1 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) was added as a polymerization initiator in 13 portions every 30 minutes, and after all of the polymerization initiator was added, the reaction was continued for another 2 hours to obtain a comparative acrylic resin solution. The weight average molecular weight of the obtained acrylic resin was 8,900, and the solid content concentration was 60%.

(Comparative Production Example 5)
20 parts of DER383J (bisphenol A type epoxy resin, epoxy equivalent 190 g/eq, manufactured by Dow Chemical Company), 80 parts of NC3300 (biphenyl skeleton-containing multifunctional epoxy resin, epoxy equivalent 285 g/eq, manufactured by Nippon Kayaku Co., Ltd.), 4 parts of dicyandiamide, 4 parts of U-CAT3502T (aromatic dimethylurea, manufactured by San-Apro Co., Ltd.), 300 parts of FB-959 (spherical silica, particle size 25 μm, manufactured by Denki Kagaku Kogyo Co., Ltd.), and 20 parts of H42M (aluminum hydroxide (particle size 1.5 μm, manufactured by Showa Denko Co., Ltd.) were charged into a kneader and mixed with stirring at 75° C. for 1 hour to obtain a comparative resin composition.

(Comparative Production Example 6)
15 parts of DER383J (bisphenol A type epoxy resin, epoxy equivalent 190 g/eq, manufactured by Dow Chemical Company), 85 parts of NC3300 (biphenyl skeleton-containing multifunctional epoxy resin, epoxy equivalent 285 g/eq, manufactured by Nippon Kayaku Co., Ltd.), 4 parts of dicyandiamide, 4 parts of U-CAT3502T (aromatic dimethylurea, manufactured by San-Apro Co., Ltd.), 10 parts of FB-959 (spherical silica, particle size 25 μm, manufactured by Denki Kagaku Kogyo Co., Ltd.), and 20 parts of H42M (aluminum hydroxide (particle size 1.5 μm, manufactured by Showa Denko Co., Ltd.) were charged into a kneader and mixed with stirring at 75° C. for 1 hour to obtain a comparative resin composition.

<Preparation of resin sheet>
[Example 1]
10.0 parts of the urethane-acrylic composite resin solution obtained in Production Example 1, 0.3 parts of jER630 as a crosslinking agent, 0.1 parts of C11Z-CN as a catalyst, and 2.4 parts of tetrahydrofuran were uniformly stirred and mixed at room temperature to obtain a resin composition. The obtained resin composition was applied onto a release film so that the thickness after drying was 300 μm, dried in a hot oven at 80 ° C. for 5 minutes, and after cooling, the release film was removed to prepare a resin sheet.

[Examples 2 to 15 and Comparative Examples 1 to 5]
Resin sheets of Examples 2 to 15 and Comparative Examples 1 to 5 were produced in the same manner as in Example 1, except that the blending composition was changed to that shown in Table 2. Note that the resin sheet of Comparative Example 1 had high viscosity, and it was difficult to remove the release film, so that a resin sheet could not be produced.

[Comparative Examples 6 to 7]
Resin sheets of Comparative Examples 6 and 7 were prepared in the same manner as in Example 1, except that the resin compositions were changed as shown in Table 2.

<Evaluation of Resin Sheet>
The obtained resin sheet was subjected to the following tests. The evaluation results are shown in Table 2. For Comparative Example 1 in which a resin sheet could not be produced, the following evaluations were not performed.

[Coating ability]
A chip measuring 10 mm in length, 10 mm in width, and 2 mm in thickness was mounted on an FR-4 substrate. A resin sheet cut to a size of 20 mm in length and 20 mm in width was placed on top of the chip and softened in a hot oven at 80°C for 1 minute. The coverage of the convex corners of the chip and the coverage of the contact points between the side of the chip and the substrate were evaluated and rated according to the following criteria.

(Evaluation Criteria for Coverage of Convex Corners)
○: The thickness of the coating is 20 μm or more (good)
△: The thickness of the coating is less than 20 μm, but there is no exposed tip (usable)
×: The tip is exposed in places (unusable)

(Evaluation criteria for contact coverage)
○: The contact area is completely covered with the resin sheet (good)
△: There is a slight gap between the resin sheet (usable)
×: There is a gap between the resin sheet (not suitable for use)

[Flexibility]
The resin sheet was cut into a 5 mm wide strip to prepare a test piece for evaluation. Using this test piece, a tensile test was performed at a tensile speed of 50 mm/min to measure the breaking elongation (%) and evaluate it according to the following criteria.

(Flexibility evaluation criteria)
○: Breaking elongation is 100% or more (good)
△: Breaking elongation is 50% or more and less than 100% (usable)
×: Breaking elongation is less than 50% (unusable)

[Heat resistance]
The test pieces after the above-mentioned coverage evaluation were left to stand in an environment of 120° C. for 500 hours, and then the coverage thickness of the salient corners was evaluated. The thickness change before and after the heat resistance test was evaluated according to the following criteria. Note that, for those in which the coverage of the salient corners before the heat resistance test was evaluated as ×, the heat resistance evaluation was not performed.

(Evaluation Criteria for Heat Resistance)
○: The change in thickness is less than 20% (good)
△: Thickness change rate is 20% or more and less than 35% (usable)
×: Thickness change rate is 35% or more (unusable)

The resin sheet of the present invention showed good results in terms of coverage, flexibility, and heat resistance. On the other hand, the adhesive of the comparative example showed results that were inferior to those of the examples in some or all of the coverage, flexibility, and heat resistance.

Claims (4)

A resin sheet formed from a resin composition containing a urethane-acrylic composite resin and a crosslinking agent,
the urethane-acrylic composite resin is a resin in which a urethane unit (A) and a (meth)acrylic unit (B) are linked together via a chain transfer agent residue,
the (meth)acrylic unit (B) has a structural unit derived from a crystalline (meth)acrylic monomer (b1) and a structural unit derived from a (meth)acrylic monomer (b2) having a crosslinkable group (excluding the structural unit derived from (b1)) ;
the crystalline (meth)acrylic monomer (b1) is a (meth)acrylate having a linear alkyl group having 16 or more carbon atoms,
A resin sheet , wherein the chain transfer agent residue is derived from a compound having one amino group and one sulfanyl group in the molecule . The resin sheet according to claim 1 , wherein the urethane-acrylic composite resin contains the urethane unit (A) in a range of 30 to 70 mass% based on the mass of the urethane-acrylic composite resin. The resin sheet according to claim 1 or 2 , which is used for sealing an electronic device. A laminate comprising the resin sheet according to any one of claims 1 to 3 and a release material.