JP5168491B2 - Thermosetting resin composition - Google Patents

Description

  The present invention relates to a thermosetting resin composition used by thermosetting. More specifically, thermosetting is suitably used as an optical electronic member such as an optical semiconductor sealant, an electronic circuit sealant, an optical waveguide, an optical communication lens, an organic EL element sealant, and an optical film. The present invention relates to a resin composition.

  In recent years, for higher output and shorter wavelength of light sources using light-emitting diodes (LEDs) and other optical semiconductors, flat panel displays using liquid crystal, organic EL, etc. have higher definition, higher image quality, and higher viewing angle. Furthermore, the performance of optical and electronic parts has been remarkably advanced, such as higher frequency of electronic circuits and circuits / communications using light. In applications in these fields, a thermosetting resin composition (hereinafter also referred to as a silicone resin) using a polysiloxane compound has been used (see, for example, Patent Documents 1 and 2). However, since the silicone resin generally has a low hardness, it has a surface tack, and there is a problem that a foreign matter adheres to the surface, or a portion receiving a strong light amount such as a light emitting surface is damaged. In general, the silicone resin has a problem of poor adhesion to an organic material such as PPA and an inorganic material such as silver.

  In order to solve this problem, it is conceivable to introduce an epoxy resin curing system by introducing a rigid component into the silicone resin. In order to apply an acid / epoxy resin curing system to a thermosetting resin composition having a polysiloxane skeleton, a technique for introducing an acid-modified site or an epoxy-modified site into polysiloxane is known. For example, Patent Document 3 discloses a resin composition in which an epoxy-modified silicone (polysiloxane) in which a commercially available epoxy resin and an acid anhydride curing agent are respectively introduced into a molecular chain and an acid anhydride-modified silicone are blended. . When the resin composition according to this disclosed technique is used, the problem of surface tack is solved, but the proportion of polysiloxane is relatively reduced, causing problems in light resistance, and high output in a short wavelength region. It is difficult to meet strict light resistance requirements recently required such as sealing of light emitting elements.

  On the other hand, a cage-type silsesquioxane has been studied as a substance having a hard structure while having a siloxane skeleton having high light resistance and heat yellowing resistance, and has been attempted to be applied to fields such as electronics and photonics. For example, Patent Document 4 discloses a resin composition comprising an epoxy ring-containing silsesquioxane, an epoxy resin, an acid anhydride curing agent, and a curing catalyst. According to this disclosed technology, the problem of surface tack is solved and the resin composition is excellent in light resistance. However, since an acid anhydride is used as a curing agent, whitening of the cured product and reduction in heat yellowing are reduced. May occur.

  In addition, from the viewpoint of adhesion and rigidity, a technique for introducing an acrylic component into a polysiloxane skeleton is known. For example, Patent Document 5 discloses a photocurable resin composition containing a silicone-modified acrylate resin and an epoxy-modified acrylate. When this disclosed technique is used, a resin composition having excellent adhesive strength by introduction of an acrylic component can be obtained, but a problem arises in heat-resistant yellowing, and the use conditions for high-performance optical semiconductor devices are increased. I'm not satisfied.

Thus, there is a need for a thermosetting resin composition that improves surface non-tackiness while taking advantage of the excellent light resistance of polysiloxane and is excellent in light resistance, heat yellowing resistance and adhesion.
JP 2001-2922 A (pages 2 and 8) JP 2004-186168 A (page 2, page 3 and page 8) Japanese Patent Laid-Open No. 06-306084 (pages 2 and 14) Japanese Patent Laying-Open No. 2005-263869 (Pages 2, 3, and 14) JP 2004-189942 A (page 2, page 3 and page 11)

  Therefore, the object of the present invention is that the cured product has good surface non-tackiness, is transparent, excellent in light resistance, heat-resistant yellowing and adhesion, sealing a light-emitting element with high output in a short wavelength region, etc. It is providing the thermosetting resin composition which can be used also for a severe use.

  As a result of intensive studies in view of the above problems, the present inventors have determined that a specific amount ratio of a specific structure of an alicyclic epoxy group-containing cage silsesquioxane and a specific structure of a hemiacetal ester bond-containing acrylic copolymer. The present invention was completed by obtaining the knowledge that the above-mentioned problems can be solved by blending and using.

  That is, the thermosetting resin composition of the present invention contains the following component (A) and component (B), and the ratio of the content of both components is component (A): component (B) = 20 on a mass basis. : 80-70: 30.

  Component (A): An alicyclic epoxy group-containing cage silsesquioxane having two or more alicyclic epoxy groups and a structure represented by the following formula (1).

Wherein (1), ^{R 1} and ^{R 2} is an alkylene group or alkylene oxyalkylene group having 1 to 10 carbon atoms, ^{R 3} and ^{R 4} is an alkyl group having 1 to 4 carbon atoms, m is 1 to 3 Integer, R ⁵ is a substituted or unsubstituted alkyl group, r is a number selected from 6, 8, 10, and 12, p is an integer of 2 to r, and q is an integer of 0 to (rp). ]
Component (B): a structural unit (b1) having an alkoxysilyl group represented by the following formula (2);

(Wherein R ⁶ is hydrogen or a methyl group, R ⁷ and R ⁸ are alkyl groups having 1 to 3 carbon atoms, k is an integer of 0 to 2 and n is an integer of 0 or 1)
A structural unit (b2) having a hemiacetal bond represented by the following formula (3);

(Wherein R ⁹ is hydrogen or a methyl group, R ¹⁰ is an alkyl group having 1 to 18 carbon atoms, and s is an integer of 0 to 10)
A structural unit (b3) having a polydimethylsiloxane structure represented by the following formula (4):

Wherein R ¹¹ is hydrogen or a methyl group, R ¹² is an alkyl group having 1 to 4 carbon atoms, t is an integer of 0 or 1, u is an integer of 0 to 20, and w is an integer of 1 to 3. )
And the proportion of each of the structural units b1 to b3 is b1 = 3 to 30 mol%, b2 = 25 to 60 mol% and b3 = 20 to 60 mol%, provided that the total amount of the structural units b2 and b3 (b2 + b3) = A hemiacetal ester bond-containing acrylic copolymer having a weight average molecular weight of 3,000 to 20,000 and a weight average molecular weight of 70 to 97 mol%.

According to the present invention, the following effects can be exhibited.
In the thermosetting resin composition of the present invention, the specific component (A) alicyclic epoxy group-containing cage silsesquioxane and the specific component (B) hemiacetal ester bond-containing acrylic copolymer are included, The ratio of the content of these components (A) and components (B) is set within a predetermined range. Since the component (A) alicyclic epoxy group-containing cage silsesquioxane has a rigid cage structure, it can exhibit excellent non-surface tackiness and also has a siloxane skeleton. Excellent light resistance and heat yellowing can be expressed.

  On the other hand, the component (B) hemiacetal ester bond-containing acrylic copolymer has an acrylic copolymer structure in the main chain and is crosslinked when it becomes a crosslinked body after thermosetting due to the rigidity of the main chain. Excellent non-surface tackiness can be expressed without increasing the number of points. A polysiloxane chain is bonded to the side chain of this acrylic main chain structure, and this action makes it difficult for the fragile chemical bond of the carbon-carbon bond or carbon-oxygen bond to break down, suppressing the deterioration of heat resistance and light resistance. can do. In addition, the adhesion can be remarkably enhanced by the action of both the alkoxysilane in component (A) and component (B) and the hydroxyl group produced by the acid-epoxy reaction.

  Therefore, the thermosetting resin composition has a good surface non-tack property of the cured product, is transparent, excellent in light resistance, heat-resistant yellowing and adhesion, sealing a light-emitting element having a high output in a short wavelength region, etc. It can also be used for severe applications.

In the following, embodiments that are considered to be the best of the present invention will be described in detail.
The thermosetting resin composition of this embodiment contains the following component (A) alicyclic epoxy group-containing cage silsesquioxane and component (B) hemiacetal ester bond-containing acrylic copolymer. And the ratio of content of both components is component (A): component (B) = 20: 80-70: 30 on a mass basis. A cured product obtained by thermosetting or photocuring the thermosetting resin composition is particularly suitably used as an optical electronic member such as an optical semiconductor encapsulant and an electronic circuit encapsulant. Below, component (A) alicyclic epoxy group-containing cage silsesquioxane, component (B) hemiacetal ester bond-containing acrylic copolymer, content ratio of both components and curing of thermosetting resin composition Will be described in order.
[Component (A): Cage-type silsesquioxane containing alicyclic epoxy group]
This alicyclic epoxy group-containing cage silsesquioxane is a siloxane having a polyhedral structure and has a structure represented by the following formula (1).

Wherein (1), ^{R 1} and ^{R 2} is an alkylene group or alkylene oxyalkylene group having 1 to 10 carbon atoms, ^{R 3} and ^{R 4} is an alkyl group having 1 to 4 carbon atoms, m is 1 to 3 An integer, R ⁵ is a substituted or unsubstituted alkyl group, r is a number selected from 6, 8, 10 and 12, p is an integer of 2 to r, and q is an integer of 0 to (rp). ]
That is, the alicyclic epoxy group-containing cage silsesquioxane is a substituent having the alicyclic epoxy group represented by the following formula (6) on the silsesquioxane skeleton represented by the following formula (5), A cage-type silsesquioxane having p, q, and rpq substituents each having an alkoxysilyl group represented by the formula (7) and an alkyl group represented by the following formula (8): It is.

R ¹ in Formula (6) is preferably an alkylene group having 1 to 3 carbon atoms. Specifically, an ethylene group [— (CH ₂ ) ₂ —] is preferable as the alkylene group.

R ² in Formula (7) is preferably an alkylene group having 1 to 3 carbon atoms. Such an alkylene group is preferably an ethylene group. R ³ and R ⁴ are preferably alkyl groups having 1 to 3 carbon atoms, and specifically, a methyl group (—CH ₃ ) is preferred.

The substituted or unsubstituted alkyl group of R ⁵ in formula (8) is an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms such as a phenyl group, Selected from the group consisting of a C1-C20 hydrocarbon group containing an ether bond, a C1-C20 hydrocarbon group containing an ester bond, and a C1-C12 alkyl group containing a triorganosiloxy group At least one selected.

  Specifically, examples of the alkyl group having 1 to 20 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group. . Examples of the cycloalkyl group having 5 to 12 carbon atoms include a cyclopentyl group, a cyclohexyl group, and a norbornyl group. Examples of the alkyl group having 1 to 12 carbon atoms containing a triorganosiloxy group are usually straight chain having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms such as methylene group, ethylene group, propylene group and butylene group. Examples thereof include a triorganosiloxy-substituted alkyl group in which a triorganosiloxy group is bonded to a chain, cyclic or branched alkylene group. Among these, a C1-C10 alkyl group is preferable.

R in the formula (1) is a number selected from 6, 8, 10 and 12, and is preferably 8. p is an integer of 2 to r, preferably an integer of 4 to r. When p is less than 2, a crosslinked structure is not formed in the cured product, and the cured product does not have the desired physical properties. q is an integer of 0 to (rp), and when it is an integer of 1 or more, in addition to the ring-opening esterification reaction between an epoxy group and a carboxyl group formed by heat cleavage of a hemiacetal ester bond, alkoxy Bonding by reaction of hydrolysis and polycondensation of groups can form a crosslinked structure and increases hardness, which is preferable from the viewpoint of surface non-tackiness.

  As a method for synthesizing the above cage silsesquioxane, a method of introducing a substituent into a synthesized cage structure of a cage silsesquioxane, or a hydrolysis of a trifunctional organosilicon monomer having a substituent. Although methods are known, any of them may be used. The skeleton structure of cage silsesquioxanes can be synthesized by various methods, for example, see Chem. Rev. 1995, 95, 1431 and J.H. Am. Che. Soc. 1989, 111, 1741 or Organometallics. 1991, 10, 2526 and the like. Further, for example, an alkyl group can be introduced onto the silicon at the apex by using a hydrosilylation reaction to octakis (hydridosilsesquioxane) in which each apex of the hexahedron is made of silicon and each side is made of oxygen (for example, (See Japanese Patent No. 3020164).

In addition, some cage-type silsesquioxanes having a substituent are available on the market. For example, POSS (registered trademark) series silsesquioxanes (manufactured by Hybrid Plastics) may be used. .
[Component (B): Hemiacetal ester bond-containing acrylic copolymer]
Such a hemiacetal ester bond-containing acrylic copolymer comprises a structural unit (b1) having an alkoxysilyl group, a structural unit (b2) having a hemiacetal ester bond, and a structural unit (b3) having a polydimethylsiloxane structure. Become. Each structural unit (b1), (b2), and (b3) is respectively represented by the following formulas (2), (3), and (4).

(In the formula, R ⁶ hydrogen or methyl group, R ⁷ and R ⁸ are alkyl groups having 1 to 3 carbon atoms, k is an integer of 0 to 2, and n is an integer of 0 or 1.)

Wherein R ¹¹ is hydrogen or a methyl group, R ¹² is an alkyl group having 1 to 4 carbon atoms, t is an integer of 0 or 1, u is an integer of 0 to 20, and w is an integer of 1 to 3. )
<Constitutional Unit Having Alkoxysilyl Group (b1)>
The structural unit (b1) having an alkoxysilyl group has a structure represented by the following formula (2) and has an alkoxysilyl group. This can improve the adhesion of the cured product.

In formula (2), R ⁶ is hydrogen or a methyl group, and n is an integer of 0 or 1. That is, when R ⁶ = hydrogen and n = 0, a vinyl group is represented, when R ⁶ = hydrogen and n = 1, an acrylic group is represented, and when R ⁶ = methyl group and n = 1, methacryl is represented. Represents a group. When R ⁶ is not hydrogen or a methyl group, the copolymerizability is lowered. R ⁷ and R ⁸ are alkyl groups having 1 to 3 carbon atoms. When the carbon number is 4 or more, the heat resistance of the cured product is lowered. k is an integer of 0 to 2, and in the case of 3, since the alkoxysilyl group disappears, the adhesion of the cured product decreases.

  The structural unit (b1) having an alkoxysilyl group is derived from a monomer represented by the following formula (9).

R ⁶ , R ⁷ , R ⁸ , k and m in the formula (9) are the same as those in the formula (2).

  Specific examples of the monomer forming the structural unit (b1) include 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltriisopropoxysilane. Trialkoxysilanes such as 3-acryloxypropyltrimethoxysilane and 3-acryloxypropyltriethoxysilane; methylvinyldimethoxysilane, methylvinyldiethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyl Dialkoxysilanes such as diethoxysilane, 3-acryloxypropylmethyldimethoxysilane, 3-acryloxypropylmethyldiethoxysilane; dimethylvinylmethoxysilane, dimethylvinylethoxy Silane, 3-methacryloxypropyl dimethyl silane, 3-methacryloxypropyl dimethyl ethoxysilane, 3-acryloxypropyl dimethyl methoxy silane, 3-acryloxypropyl monoalkoxysilane and dimethyl ethoxy silane. Among these monomers, 3-methacryloxypropyltrimethoxysilane and 3-methacryloxypropylmethyldiethoxysilane are preferable from the viewpoints of copolymerizability and cured product adhesion.

The structural unit (b1) having an alkoxysilyl group is contained in the component (B) hemiacetal ester bond-containing acrylic copolymer in an amount of 3 to 30 mol%, preferably 5 to 25 mol%. When the content of the structural unit (b1) is less than 3 mol%, the adhesiveness of the cured product is deteriorated, and when it exceeds 30 mol%, the toughness of the cured product is reduced and cracks are generated in the cured product.
<Structural unit (b2) having a hemiacetal ester bond>
The structural unit (b2) having such a hemiacetal ester bond is represented by the formula (3). When the hemiacetal ester bond is heated, it is decomposed into a carboxyl group and vinyl ether, and the generated carboxyl group undergoes a curing reaction with the epoxy group. The adhesion of the cured product is improved by the action of the hydroxyl group produced by the ring opening of the epoxy group by the carboxyl group.

  The structural unit (b2) having a hemiacetal ester bond is superior in compatibility because it is less polar than the structural unit containing a carboxyl group, and the viscosity of the copolymer with time increases due to the protective effect of the carboxyl group. Behavior is suppressed.

In formula (3), R ⁹ is hydrogen or a methyl group. If it is not hydrogen or a methyl group, copolymerizability will fall. R ¹⁰ is an alkyl group having 1 to 18 carbon atoms. When the alkyl group has 19 or more carbon atoms, the vinyl ether of the protecting group is not eliminated during curing, and the carboxyl group is not regenerated. Therefore, the component (A) cage silsesquioxane containing alicyclic epoxy group A curing failure occurs in the curing reaction with the epoxy group. s is an integer of 0-10. When s becomes 11 or more, the heat resistance and light resistance of the cured product decrease.

  The structural unit (b2) having a hemiacetal ester bond is derived from a monomer having a hemiacetal ester bond represented by the following formula (10).

R ⁹ , R ¹⁰ and s in the formula are the same as those in the formula (3).

  The monomer having a hemiacetal ester bond represented by the formula (10) includes a carboxylic acid containing an ethylenically unsaturated bond represented by the following formula (11) and a vinyl ether compound represented by the following formula (12): Is obtained by reaction with

R ⁹ and s in the formula (11) are the same as those in the formula (3), and R ¹⁰ in the formula (12) is the same as in the formula (3).

  Specific examples of the carboxylic acid containing an ethylenically unsaturated bond represented by the formula (11) include acrylic acid, methacrylic acid, butenoic acid, pentenoic acid, hexenoic acid, heptenoic acid, decenoic acid, and undecenoic acid. It is done. Since the heat resistance of the cured product decreases when the alkyl group becomes a long chain, s is preferably an integer of 0 to 4, and more preferably s = 0. That is, acrylic acid and methacrylic acid are particularly preferable.

Specific examples of the vinyl ether compound represented by the formula (12) include methyl vinyl ether, ethyl vinyl ether, isopropyl vinyl ether, n-propyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, t-butyl vinyl ether, t-amyl vinyl ether, 2- Examples thereof include ethylhexyl vinyl ether, dodecyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether and the like. Among these, from the viewpoint of elimination of the protective group and volatilization of the vinyl ether compound after elimination, R ¹⁰ preferably has 1 to 10 carbon atoms, and more preferably 1 to 4 carbon atoms. Specific examples thereof include n-propyl vinyl ether having 3 carbon atoms.

  The hemiacetal esterification reaction between a carboxylic acid containing an ethylenically unsaturated bond and a vinyl ether compound can be performed by a known method, for example, in an organic solvent at a temperature of room temperature to 200 ° C. Preferably, it is room temperature-150 degreeC. The reaction time for this reaction may be appropriately selected according to the progress of the reaction, but is usually 1 to 100 hours.

  The mixing ratio of the carboxylic acid and the vinyl ether compound can be arbitrarily set according to the purpose, but usually 1 to 5 mol, particularly 1.2 to 1.5 mol of vinyl ether group per mol of carboxyl group. It is suitable to use a vinyl ether compound. In the blocking reaction, an acid catalyst such as an acidic phosphate can be used for the purpose of promoting the reaction.

  An organic solvent may be used for the purpose of making the reaction system uniform and facilitating the reaction. Examples thereof include glycol derivatives such as aromatic hydrocarbons, ethers, esters, ether esters, ketones, phosphate esters, aprotic polar solvents, and propylene glycol monoethyl ether acetate. Of these organic solvents, propylene glycol monomethyl ether acetate (PMA) is preferred. These organic solvents can be used alone or in combination of two or more. Although the usage-amount of an organic solvent in particular is not restrict | limited, It is 5-95 mass parts normally with respect to 100 mass parts of reaction raw materials, Preferably it is 20-80 mass parts. After the reaction, the organic solvent used may be distilled off with an apparatus such as an evaporator.

  When the compound of the formula (10) obtained by reacting carboxylic acid and vinyl ether is used in, for example, a resin composition for encapsulating an optical semiconductor, the acid value is usually preferably 20 mgKOH / g or less from the viewpoint of storage stability, and 10 mgKOH / g g or less is more preferable, and 5 mgKOH / g or less is particularly preferable.

  In the thermosetting resin composition, the adhesion of the cured product can be improved by increasing the concentration of the alkoxysilyl group in the acrylic copolymer. However, when the concentration of the alkoxysilyl group in the copolymer is increased, the adhesion of the cured product is improved because a siloxy bond having inferior toughness is preferentially generated. On the other hand, the cured product is brittle and easily cracked. End up.

  By introducing the structural unit (b2) having a hemiacetal ester bond into the component (B) hemiacetal ester bond-containing acrylic copolymer, the hemiacetal ester bond is thermally dissociated to generate a carboxyl group. The produced carboxyl group generates a hydroxyl group by a ring-opening esterification reaction with the epoxy group of the component (A) alicyclic epoxy group-containing cage silsesquioxane, and the adhesion of the cured product is good due to the action of the hydroxyl group. Become. Moreover, since the bond produced | generated by acid-epoxy hardening reaction is excellent in toughness, the crack of hardened | cured material does not arise.

The structural unit (b2) having a hemiacetal ester bond is contained in the component (B) hemiacetal ester bond-containing acrylic copolymer in an amount of 25 to 60 mol%, preferably 25 to 50 mol%. When the content of the structural unit (b2) is less than 25 mol%, the adhesiveness of the cured product is lowered, and when it exceeds 60 mol%, the heat resistance and light resistance of the cured product are lowered and the transparency is impaired.
<Constitutional unit (b3) having a polydimethylsiloxane structure>
The structural unit (b3) having this polydimethylsiloxane structure is a structure represented by the formula (4), and since the main skeleton has a polydimethylsiloxane structure, the cured product has good light resistance and heat yellowing resistance. Become.

In formula (4), R ¹¹ is hydrogen or a methyl group, and t is an integer of 0 or 1. That is, when R ¹¹ = hydrogen and t = 0, it represents a vinyl group, when R ¹¹ = hydrogen and t = 1, an acrylic group is represented, and when R ¹¹ = methyl group and t = 1, methacryl is represented. Represents a group. When R ¹¹ is not hydrogen or a methyl group, the copolymerizability is lowered. R ¹² is an alkyl group having 1 to 4 carbon atoms. When carbon number is 5 or more, the heat resistance of hardened | cured material falls. u is an integer of 0-20, preferably an integer of 0-15. When u is 21 or more, the compatibility with the monomer (b2) containing a hemiacetal ester bond is deteriorated, the copolymerizability is lowered, or in some cases, it becomes cloudy or the monomer component is separated. To do. w is an integer of 1 to 3, and in the case of 0, since the polysiloxane component is lost, the light resistance and heat resistance of the cured product are lowered.

  The structural unit (b3) having a polydimethylsiloxane structure is derived from a monomer represented by the following formula (13).

R ¹¹ , R ¹² , t, u and w in the formula (13) are the same as those in the formula (4).

  The monomer represented by the above formula (13) has a polymerizable ethylenically unsaturated bond for constituting an acrylic main chain structure at the molecular end, and a silicone macromonomer whose main skeleton is polydimethylsiloxane. It is a monomer (monomer). The mass average molecular weight of the monomer is preferably 300 to 10,000, and more preferably 400 to 5,000. When the mass average molecular weight is lower than 300, the characteristics based on the silicone unit are hardly exhibited, and the heat resistance and light resistance of the cured product may be lowered. On the other hand, when the mass average molecular weight is higher than 10,000, the reactivity is lowered, so that the amount of free silicone not copolymerized may increase. Commercially available products such as FM-0711, FM-0721, FM-0725 [manufactured by Chisso Corporation], X-22-174DX [manufactured by Shin-Etsu Chemical Co., Ltd.] can be used as the monomer.

The structural unit (b3) having a polydimethylsiloxane structure is contained in the component (B) hemiacetal ester bond-containing acrylic copolymer in an amount of 20 to 60 mol%, preferably 30 to 60 mol%. When the content of the structural unit (b3) is less than 20 mol%, the heat resistance and light resistance of the cured product are lowered, and when it exceeds 60 mol%, the adhesion and surface tackiness of the cured product are lowered.

However, regarding content of the said structural unit (b2) and (b3), the total amount (b2 + b3) of those structural units is 70-97 mol%, Preferably it is 75-95 mol%. When the total amount (b2 + b3) exceeds 95 mol%, the content of the structural unit (b1) is excessively small, resulting in insufficient adhesion of the cured product. When the total amount (b2 + b3) is less than 70 mol%, the structural unit (b1) is derived. The amount of crosslinking becomes excessive, the toughness of the cured product is lowered, and cracks are likely to occur in the cured product.
<Preparation of component (B) hemiacetal ester bond-containing acrylic copolymer>
This hemiacetal ester bond-containing acrylic copolymer comprises an alkoxysilyl group-containing monomer (b1), a hemiacetal ester bond-containing monomer (b2), and a polydimethylsiloxane structure-containing monomer (b3). It can be obtained by copolymerization. The molecular form is linear and may be in the form of either a random copolymer or a block copolymer.

  The acrylic polymer containing a hemiacetal ester bond can be obtained by polymerization according to a conventional polymerization method. That is, the polymerization method is not particularly limited, and a polymerization method such as a radical polymerization method or an ionic polymerization method can be employed. More specifically, a bulk polymerization method using a polymerization initiator, a solution polymerization method, a suspension polymerization method, A polymerization method such as an emulsion polymerization method can be employed.

  The mass average molecular weight of the component (B) hemiacetal ester bond-containing acrylic copolymer is 3,000 to 20,000, preferably 5,000 to 10,000. When the mass average molecular weight is less than 3,000, the hardness of the cured product is lowered, and when it exceeds 20,000, the miscibility with the component (A) becomes insufficient and the curability is adversely affected. Further, when the phosphor is dispersed in the thermosetting resin composition, the viscosity becomes high and proper dispersion becomes difficult. The mass average molecular weight is a polystyrene-reduced mass average molecular weight determined by gel permeation chromatography (GPC).

In the thermosetting resin composition, the component (B) hemiacetal ester bond-containing acrylic copolymer may be used by mixing two or more types of copolymers having different molecular weights and monomer types.
[Ratio of content of component (A) and component (B)]
In the thermosetting resin composition, the ratio of the content of component (A) alicyclic epoxy group-containing cage silsesquioxane and component (B) hemiacetal ester bond-containing acrylic copolymer is component (A ): Component (B) = 20: 80 to 70:30, preferably 30:70 to 60:40. If the component (A): component (B) = 20: 80 is removed and the content of the component (B) is excessively large, there will be many unreacted carboxyl groups in the cured product, and the moisture resistance of the cured product Gets worse. In addition, in this case, since the ratio of the component (A) decreases, the rigid properties of the cage silsesquioxane skeleton are hardly expressed, and the surface non-tackiness of the cured product is insufficient. On the other hand, if the component (A): component (B) = 70: 30 is removed and the content of the component (B) is too small, the curability of the thermosetting resin composition becomes insufficient and the cured product The heat resistance of will deteriorate.

Furthermore, the compounding amount of the component (A) alicyclic epoxy group-containing cage silsesquioxane and the component (B) hemiacetal ester bond-containing acrylic copolymer is derived from (the hemiacetal ester bond-containing acrylic copolymer). The ratio (molar ratio) of (molar concentration of hemiacetal ester bond) / (molar concentration of epoxy group derived from alicyclic epoxy group-containing cage silsesquioxane) is usually 0.2 to 2.0, preferably 0. .7 to 1.2, more preferably 0.8 to 1.1. If the ratio is less than 0.2, the adhesiveness of the cured product may be reduced. If the ratio is more than 2.0, curing failure may occur due to an excessive amount of carboxyl groups generated from a hemiacetal ester bond by a heating reaction. Decrease in transparency of cured product may occur.
[Curing of thermosetting resin composition]
By thermosetting or photocuring the thermosetting resin composition, a cured product used as an optical semiconductor sealing agent or the like is obtained. In this case, when the thermosetting resin composition is cured at a low temperature in a short time, the curing reaction is accelerated, and an acid catalyst may be added for the purpose of imparting good chemical performance and physical performance to the cured product. Good. Examples of the acid catalyst include proton acids such as phosphoric acid, sulfonic acid, and boric acid; Lewis acids such as BF ₃ , FeCl ₃ , SnCl ₄ , AlCl ₃ , ZnCl ₂ , and organometallic complexes. Of these, tin-based organometallic complexes are particularly preferable from the viewpoints of curability and transparency.

  This acid catalyst may be used alone or in combination of two or more. Moreover, the addition amount of an acid catalyst is 0.01-10 mass parts normally with respect to 100 mass parts of total solid content of a thermosetting resin composition. When the addition amount of the acid catalyst is less than 0.01 parts by mass, the catalytic effect is not sufficiently exhibited, and when it exceeds 10 parts by mass, the finally obtained cured product may be colored or the water resistance may be lowered. Is not preferable.

  The thermosetting resin composition can be used after diluted with an organic solvent. Examples of the organic solvent include aromatic hydrocarbons, alicyclic hydrocarbons, esters, halogen-containing aliphatic hydrocarbons, ketones, ethers, and the like. An organic solvent may be used individually by 1 type, and may be used in combination of 2 or more type. The amount of the organic solvent used is usually 30 parts by mass or less, preferably 7 parts by mass or less with respect to 100 parts by mass of the thermosetting resin composition.

  The thermosetting resin composition has a coupling agent, an antioxidant, an ultraviolet absorber, a visible light absorber, an infrared absorber, a modifier, a filler, as necessary, as long as the effect is not impaired. Conventionally known additives such as flame retardants and thixotropy imparting agents can be added. These additives may be used alone or in combination of two or more. Moreover, the addition amount is 0.01-10 mass parts normally with respect to 100 mass parts of total solid content of a thermosetting resin composition.

When using a thermosetting resin composition as a sealing material, it can implement by thermosetting or photocuring a thermosetting resin composition. In that case, a method in which the thermosetting resin composition is applied and cured by an overcoat method, a dip coat method, or the like, or the composition is placed in a container and the element is dipped and cured as it is It can be set as the sealing material of an optical semiconductor element by such as.
[Summary of actions and effects exhibited by the embodiment]
Generally, an epoxy compound and a carboxyl compound (carboxylic acid) that is a curing agent thereof are inferior in light resistance and heat resistance when compared with a polysiloxane compound. Polysiloxane compounds are composed of chains of siloxane bonds (silicon-oxygen bonds) with high atomic bond energy, whereas epoxy compounds and carboxyl compounds have carbon-carbon bonds or carbon-carbons with much lower bond energies. This is because it is composed of oxygen bonds. In order to improve the non-surface tackiness of the polysiloxane composition, in order to compensate for the low glass transition temperature and hardness of the polysiloxane chain even if a crosslinked structure by reaction of carboxyl group and epoxy group is introduced, a number of crosslinking points are required. These cross-linking points increase the vulnerability to light resistance and heat yellowing as they are. Alternatively, blending acrylic resin with high glass transition temperature and hardness instead of epoxy compound or carboxyl compound can reduce the light resistance and heat yellowing resistance even if the non-surface tackiness can be improved. Will be invited.

  In contrast, the thermosetting resin composition of the present embodiment includes component (A) alicyclic epoxy group-containing cage silsesquioxane and component (B) hemiacetal ester bond-containing acrylic copolymer. The ratio of the content of these components (A) and (B) is set within a predetermined range. For this reason, the thermosetting resin composition can achieve significant improvements in non-surface tackiness and adhesion without impairing the excellent light resistance and heat-resistant yellowing properties of conventional polysiloxane compositions.

  About this mechanism, it is guessed as follows. Component (A) The alicyclic epoxy group-containing cage silsesquioxane has a siloxane skeleton, but has a rigid cage structure, so it has excellent non-surface tackiness and excellent siloxane skeleton. Light resistance and heat yellowing. In addition, since the component (B) hemiacetal ester bond-containing acrylic copolymer has an acrylic copolymer structure in the main chain, it is mischievous when it becomes a cross-linked body after thermosetting due to the rigidity of the main chain. In addition, excellent non-surface tackiness can be exhibited without increasing the number of crosslinking points. On the other hand, in this acrylic main chain structure, a polysiloxane chain is bonded to the side chain, and the kinetic energy of the molecular chain due to heat and light is dissipated well. For this reason, even when a thermal history or light load is applied, the fragile chemical bonds such as carbon-carbon bonds and carbon-oxygen bonds are hardly decomposed, and heat resistance and light resistance are not impaired. Further, the adhesion is remarkably improved by the action of both the alkoxysilane in the component (A) and the component (B) and the hydroxyl group generated by the acid-epoxy reaction.

  Accordingly, the thermosetting resin composition has good surface non-tackiness of the cured product obtained, is transparent, excellent in light resistance, heat-resistant yellowing and adhesion, sealing a light-emitting element having a high output in a short wavelength region, etc. It can also be suitably used for demanding applications.

Hereinafter, the embodiment will be described more specifically with reference to synthesis examples, polymerization examples, examples, and comparative examples.
[Synthesis Example 1, synthesis of hemiacetal ester (b2-1)]
In a four-necked flask equipped with a thermometer, a reflux condenser, a stirrer, and a dropping funnel, 90.84 g of methacrylic acid, 0.02 g of hydroquinone and AP-8 [produced by Daihachi Chemical Industry Co., Ltd., acidic phosphate ester] 10 g was charged and heated to 50 ° C. while stirring. Subsequently, 109.04 g of n-propyl vinyl ether was added dropwise while maintaining the temperature at 50 ° C., and the reaction temperature was raised to 75 ° C. after the completion of the addition. The reaction was terminated when the acid value of the mixture became 2.0 mgKOH / g or less to obtain a colorless and transparent hemiacetal ester (b2-1).
[Synthesis Example 2, synthesis of hemiacetal ester (b2-2)]
A four-necked flask equipped with a thermometer, a reflux condenser, a stirrer, and a dropping funnel was charged with 74.82 g of acrylic acid and 0.04 g of hydroquinone, and heated to 60 ° C. while stirring. Next, 145.36 g of n-butyl vinyl ether was added dropwise while maintaining the temperature at 60 ° C., and the reaction temperature was raised to 75 ° C. after completion of the addition. The reaction was terminated when the acid value of the mixture became 2.0 mgKOH / g or less to obtain a colorless and transparent hemiacetal ester (b2-2).
[Synthesis Example 3, synthesis of hemiacetal ester (b2-3)]
A 4-necked flask equipped with a thermometer, a reflux condenser and a stirrer was charged with 92.0 g of undecenoic acid and 60.2 g of isopropyl vinyl ether, and heated to 60 ° C. while stirring. The reaction was terminated when the acid value of the mixture became 2.0 mgKOH / g or less to obtain a colorless and transparent hemiacetal ester (b2-3).
[Synthesis Example 4, Synthesis of alicyclic epoxy group-containing cage silsesquioxane (A-1)]
10.18 g (10 mmol) of octakis [hydridodimethylsiloxy] silsesquioxane (OHSS), 4-vinylcyclohexene-1 in a 300 mL four-neck flask equipped with a thermometer, reflux condenser and stirrer under a nitrogen atmosphere , 2-epoxide 4.97 g (40 mmol), 1-octene 4.49 g (40 mmol) and dehydrated toluene 30 g. After OHSS was dissolved, 0.03 mL of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum 0.1M xylene solution was added as a catalyst and reacted at 70 ° C. for 3 hours. Thereafter, the catalyst was removed with activated carbon, and the solvent was distilled off to obtain 18.7 g (9.5 mmol) of a colorless transparent viscous liquid. As a result of measuring the obtained reaction product by a 1H-NMR spectrum, it was confirmed that it was a cage silsesquioxane (A-1) represented by the following formula (14). The yield of A-1 obtained was 95%, and the epoxy equivalent was 491 g / mol.

[Synthesis Example 5, Synthesis of alicyclic epoxy group-containing cage silsesquioxane (A-2)]
To a 300 mL four-neck flask equipped with a thermometer, a reflux condenser and a stirrer, under a nitrogen atmosphere, 10.18 g (10 mmol) of OHSS, 4.97 g (40 mmol) of 4-vinylcyclohexene-1,2-epoxide, 5.29 g (40 mmol) of dimethoxymethylvinylsilane and 30 g of dehydrated toluene were added. After OHSS was dissolved, 0.03 mL of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum 0.1M xylene solution was added as a catalyst and reacted at 70 ° C. for 3 hours. Thereafter, the catalyst was removed with activated carbon, and the solvent was distilled off to obtain 19.2 g (9.4 mmol) of a colorless transparent viscous liquid. As a result of measuring the obtained reaction product by a 1H-NMR spectrum, it was confirmed that it was a cage silsesquioxane (A-2) represented by the following formula (15). The yield of A-2 obtained was 94%, and the epoxy equivalent was 511 g / mol.

[Synthesis Example 6, synthesis of alicyclic epoxy group-containing cage silsesquioxane (A-3)]
To a 300 mL four-neck flask equipped with a thermometer, a reflux condenser and a stirrer, under a nitrogen atmosphere, 10.18 g (10 mmol) of OHSS, 3.72 g (30 mmol) of 4-vinylcyclohexene-1,2-epoxide, 1.48 g (10 mmol) of dimethoxymethylvinylsilane , 5.60 g (40 mmol) of 1-decene and 30 g of dehydrated toluene were added. After OHSS was dissolved, 0.03 mL of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum 0.1M xylene solution was added as a catalyst and reacted at 70 ° C. for 3 hours. Thereafter, the catalyst was removed with activated carbon, and the solvent was distilled off to obtain 19.9 g (9.5 mmol) of a colorless transparent viscous liquid. As a result of measuring the obtained reaction product by 1H-NMR spectrum, it was confirmed that it was a cage silsesquioxane (A-3) represented by the following formula (16). The yield of A-3 obtained was 95%, and the epoxy equivalent was 700 g / mol.

[Synthesis Example 7, Synthesis of alicyclic epoxy group-containing cage silsesquioxane (A-4)]
To a 300 mL four-neck flask equipped with a thermometer, a reflux condenser and a stirrer, under a nitrogen atmosphere, 10.18 g (10 mmol) of OHSS, 6.21 g (50 mmol) of 4-vinylcyclohexene-1,2-epoxide, 1.37 (30 mmol) of 1- decene and 30 g of dehydrated toluene were added. After OHSS was dissolved, 0.03 mL of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum 0.1M xylene solution was added as a catalyst and reacted at 70 ° C. for 3 hours. Thereafter, the catalyst was removed with activated carbon, and the solvent was distilled off to obtain 18.8 g (9.5 mmol) of a colorless transparent viscous liquid. As a result of measuring the obtained reaction product by 1H-NMR spectrum, it was confirmed that it was a cage silsesquioxane (A-4) represented by the following formula (17). The yield of A-4 obtained was 95%, and the epoxy equivalent was 395 g / mol.

[Comparative Synthesis Example 1, Synthesis of Epoxy Group-Containing Cage Silsesquioxane (A′-1)]
In a 300 mL four-neck flask equipped with a thermometer, reflux condenser and stirrer, under a nitrogen atmosphere, 10.18 g (10 mmol) of OHSS, 4.57 g (40 mmol) of allyl glycidyl ether, and 4.49 g of 1-octene. (40 mmol) and 30 g of dehydrated toluene were added. After OHSS was dissolved, 0.03 mL of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum 0.1M xylene solution was added as a catalyst and reacted at 70 ° C. for 3 hours. Thereafter, the catalyst was removed with activated carbon, and the solvent was distilled off to obtain 18.1 g (9.5 mmol) of a colorless transparent viscous liquid. As a result of measuring the obtained reaction product by a 1H-NMR spectrum, it was confirmed that it was a cage silsesquioxane (A′-1) represented by the following formula (18). The yield of A′-1 was 94%, and the epoxy equivalent was 481 g / mol.

[Comparative Synthesis Example 2, Synthesis of Epoxy Group-Containing Cage-type Silsesquioxane (A′-2)]
Under a nitrogen atmosphere, 10.18 g (10 mmol) of OHSS, 9.13 (80 mmol) of allyl glycidyl ether, and 30 g of dehydrated toluene were charged into a 300 mL four-round flask equipped with a thermometer, a reflux condenser, and a stirrer. After OHSS was dissolved, 0.03 mL of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum 0.1M xylene solution was added as a catalyst and reacted at 70 ° C. for 3 hours. Thereafter, the catalyst was removed with activated carbon, and the solvent was distilled off to obtain 18.2 g (9.4 mmol) of a colorless transparent viscous liquid. As a result of measuring the obtained reaction product by 1H-NMR spectrum, it was confirmed that it was a cage silsesquioxane (A′-2) represented by the following formula (19). The yield of A′-2 was 94%, and the epoxy equivalent was 241 g / mol.

The meanings of the abbreviations shown in the following polymerization examples are as shown below.

MTM: methacryloxypropyltrimethoxysilane represented by formula (20) MDE: methacryloxypropylmethyldiethoxysilane represented by formula (21) ATM: acryloxypropyltrimethoxysilane represented by formula (22) VTM : Vinyltrimethoxysilane represented by formula (23) b3-1: methacryl group-containing polysiloxane represented by formula (24) b3-2: acrylic group-containing polysiloxane represented by formula (25) b3-3 : Methacryl group-containing polysiloxane represented by formula (26) b3-4: vinyl group-containing polysiloxane represented by formula (27)

[Polymerization Example 1, Synthesis of Hemiacetal Ester Bond-Containing Acrylic Copolymer (B-1)]
A 4-necked flask equipped with a thermometer, a reflux condenser, a stirrer, and a dropping funnel was charged with 76.0 g of PMA and heated to 95 ° C. while introducing nitrogen. There, the monomers [the MTM 16.4g (17.5mol%), b2-1 and 33.8g (51.5mol%) and b3-1 a 49.7g (31.0mol%)], the polymerization An initiator (manufactured by NOF Corporation, Perhexyl O) was added dropwise while maintaining a mixture of 16.0 g and PMA 8.0 g at 98 ° C. After dropping, the reaction was terminated by reacting at 95 ° C. for 5 hours. After allowing to cool, PMA as a solvent was distilled off with an evaporator to obtain a colorless and transparent hemiacetal ester bond-containing acrylic copolymer (B-1, Mw 5,500).
[Polymerization examples 2 to 6, synthesis of hemiacetal ester bond-containing acrylic copolymer (B-2 to B-6)]
The operations shown in Table 1 were carried out in the same manner as in Polymerization Example 1 to obtain hemiacetal ester bond-containing acrylic copolymers (B-2 to B-6). Table 1 shows the composition, mass average molecular weight and acid equivalent of each raw material together with the polymerization results.
[Comparative Polymerization Examples 1 to 3, Synthesis of Component (B) Analogue (B′-1 to B′-3)]
The operation shown in Table 2 was carried out in the same manner as in Polymerization Example 1, and component (B) analogues (B′-1 to B′-3) were obtained. Table 2 shows the composition, mass average molecular weight, and acid equivalent of each raw material together with the polymerization results.

〔Test method〕
The test methods for heat yellowing resistance, light resistance, adhesion and surface non-tackiness in Examples and Comparative Examples are shown below.
(1) Heat-resistant yellowing The thermosetting resin composition was cured to produce a cured product having a thickness of 1 mm. The produced cured product was stored at 150 ° C. for 1 month, and then the transmittance (%) of the cured product was measured with a spectrophotometer [manufactured by Shimadzu Corporation, UV-2450]. Evaluation was performed by calculating a transmittance reduction rate with respect to the initial transmittance. When the transmittance reduction rate was 90% or more, the heat-resistant transparency was judged to be good.
(2) Light resistance The thermosetting resin composition was cured to produce a cured product having a thickness of 1 mm. This was stored for 1 month using a weather meter (manufactured by Suga Test Instruments Co., Ltd.) under the conditions of irradiation intensity of 0.4 kW / m ² and black panel temperature of 63 ° C., and then a spectrophotometer [Co., Ltd.] The transmittance (%) of the cured product was measured with UV-2450 manufactured by Shimadzu Corporation. Evaluation was performed by calculating a transmittance reduction rate with respect to the initial transmittance. When the transmittance reduction rate was 90% or more, light resistance was judged to be good.
(3) Adhesion After performing a high-temperature and high-humidity test (temperature 85 ° C., relative humidity 85%) of the LED for evaluation sealed with a thermosetting resin composition for 1000 hours, whether or not peeling occurs from the chip and the package Observations were made. A test was performed using 20 samples, and evaluation was performed according to the following criteria.

○: No peeling sample. Δ: 9 or less exfoliation samples. X: 10-20 peeling samples.
(4) Surface non-tackiness The thermosetting resin composition was cured to produce a cured product having a thickness of 1 mm. About the produced hardened | cured material, the tack property of the surface of a test piece was observed by finger observation, and the surface non-tack property was evaluated on the following reference | standard.

○: Tack was not recognized. X: Tack was recognized.
[Examples 1-7 and Comparative Examples 1-8]
The thermosetting resin compositions used in Examples 1 to 7 and Comparative Examples 1 to 8 are shown in Tables 3 and 4 so that the acid / epoxy molar ratio (molar ratio) is 0.9. According to the composition, each raw material was blended and prepared by uniformly dissolving. The thermosetting resin composition described in Table 3 and Table 4 is molded into a shape according to the test method shown above, defoamed for 30 minutes, and then cured at 150 ° C. for 4 hours to obtain a cured product. Got. In addition, the meaning of the symbol in Table 4 is shown below.
<Epoxy compound other than component (A)>
CE2021P: Alicyclic epoxy resin [manufactured by Daicel Chemical Industries, Ltd.]
<Compounds other than component (B)>
Me-HHPA: 4-methylhexahydrophthalic acid [manufactured by Shin Nippon Rika Co., Ltd.]

From the test results shown in Table 3, in the cured products of the thermosetting resin compositions of Examples 1 to 7, the transmittance reduction rate was 92% or more for heat-resistant yellowing, and the transmittance reduction rate was 93% or more for light resistance. Thus, there was no peeled sample for adhesion, no tack was observed for surface non-tackiness, and it was revealed that all physical properties were excellent.

  On the other hand, as shown in Table 4, a copolymer having a different structure from the component (B) hemiacetal ester bond-containing acrylic copolymer of the present invention (a copolymer not containing the structural unit (b1)) is used. In Comparative Example 1, the adhesion was inferior. In Comparative Example 2, since the component (B) was a copolymer outside the scope of the present invention (a copolymer not containing the structural unit (b3)), the cured product was inferior in light resistance and heat yellowing. . In Comparative Example 3, the component (B) was a copolymer outside the scope of the present invention (copolymers in which the proportion of the structural units (b2) and (b3) was outside the scope of the present invention). And could not be used as an LED sealant because of foreign matter adhesion problems.

  In Comparative Example 4, since a compound that was not a hemiacetal ester bond-containing acrylic copolymer was used as component (B), the light resistance and heat yellowing of the cured product were poor. In Comparative Example 5, the content of the component (A) was too small and the content of the component (B) was excessive, so the result was inferior in the adhesion and surface non-tackiness of the cured product. In Comparative Example 6, since an epoxy resin having a structure different from that of the component (A) alicyclic epoxy group-containing cage silsesquioxane of the present invention was used, the light resistance and heat yellowing of the cured product, adhesion and surface The tackiness was inferior. In Comparative Examples 7 and 8, since it was a copolymer or an epoxy resin other than the present invention as the component (A), it was confirmed that the cured product was inferior in heat yellowing resistance and light resistance.

  As described above, it has been shown that the present invention can provide a thermosetting resin composition excellent in light resistance, heat yellowing resistance, adhesion and surface non-tackiness. Therefore, the cured product of the thermosetting resin composition of the present invention is extremely useful as an optical electronic member including an encapsulant for optical semiconductors.

Claims (1)

It contains the following component (A) and component (B), and the ratio of the content of both components is component (A): component (B) = 20: 80 to 70:30 on a mass basis. Thermosetting resin composition.
Component (A): An alicyclic epoxy group-containing cage silsesquioxane having two or more alicyclic epoxy groups and a structure represented by the following formula (1).
Wherein (1), ^{R 1} and ^{R 2} is an alkylene group or alkylene oxyalkylene group having 1 to 10 carbon atoms, ^{R 3} and ^{R 4} is an alkyl group having 1 to 4 carbon atoms, m is 1 to 3 Integer, R ⁵ is a substituted or unsubstituted alkyl group, r is a number selected from 6, 8, 10, and 12, p is an integer of 2 to r, and q is an integer of 0 to (rp). ]
Component (B): a structural unit (b1) having an alkoxysilyl group represented by the following formula (2);
(Wherein R ⁶ is hydrogen or a methyl group, R ⁷ and R ⁸ are alkyl groups having 1 to 3 carbon atoms, k is an integer of 0 to 2 and n is an integer of 0 or 1)
A structural unit (b2) having a hemiacetal bond represented by the following formula (3);
(Wherein R ⁹ is hydrogen or a methyl group, R ¹⁰ is an alkyl group having 1 to 18 carbon atoms, and s is an integer of 0 to 10)
A structural unit (b3) having a polydimethylsiloxane structure represented by the following formula (4):
Wherein R ¹¹ is hydrogen or a methyl group, R ¹² is an alkyl group having 1 to 4 carbon atoms, t is an integer of 0 or 1, u is an integer of 0 to 20, and w is an integer of 1 to 3. )
And the proportion of each of the structural units b1 to b3 is b1 = 3 to 30 mol%, b2 = 25 to 60 mol% and b3 = 20 to 60 mol%, provided that the total amount of the structural units b2 and b3 (b2 + b3) = A hemiacetal ester bond-containing acrylic copolymer having a weight average molecular weight of 3,000 to 20,000 and a weight average molecular weight of 70 to 97 mol%.