Polyhydric phenol and epoxy resin obtained using the same

Abstract: The present invention provides polyhydric phenols which are starting materials for glycidyl ether compounds which can provide cured products having low moisture absorption, high heat resistance and improved crack resistance and can be used for encapsulating semiconductor devices. The polyhydric phenols are represented by the following formula: wherein R¹ independently represents a halogen atom, an alkyl or cycloalkyl group of 1-9 carbon atoms, an alkoxy group of 4 or less carbon atoms or an aryl group and R¹ may be identical or different when ℓ is 2 or more, R² independently represents a halogen atom, an alkoxy group of 4 or less carbon atoms or an alkyl group of 6 or less carbon atoms and R² may be identical or different when m is 2 or more, R³ independently represents a hydrogen atom or an alkyl group of 6 or less carbon atoms, the average recurring unit number n is 0-10, ℓ is 0-4 and m is 0-7, and can be contained as a curing agent in an epoxy resin composition which is used not only for giving cured products but also for encapsulating semiconductor devices.

Description: BACKGROUND OF THE INVENTION The present invention relates to epoxy resin compositions comprising a glycidyl ether compound and a polyhydric phenol as curing agent as well as the use thereof as encapsulants for electronic parts. Recently, transfer molding of epoxy resin compositions which are economically advantageous has been carried out for encapsulation of semiconductors such as LSI, IC and transistors. Especially, surface mounting has been carried out for LSI and direct dipping in bath of solder has often been conducted. In this case, since encapsulants are exposed to high temperatures of higher than 200°C, water absorbed and contained therein expands to cause cracking. Therefore, epoxy resin encapsulants are required to be low in moisture absorption and have resistance to cracking and at present, glycidyl ethers of o-cresol novolak are mainly used. Further, encapsulants comprising glycidyl ethers of tetramethylbiphenol were developed to improve the moisture absorption. [Japanese Patent Kokai (Laid-Open) No. Hei 1-283241] Moreover, glycidyl ethers of condensates of α-naphthol with aldehydes have been known as epoxy resins low in water absorption and excellent in heat resistance. [Japanese Patent Kokai No. Sho 62-25116). Encapsulants mainly composed of glycidyl ethers of o-cresol novolak are excellent in heat resistance and are somehow superior in balancing of heat resistance and low moisture absorption, but they are not necessarily satisfactory in the use which requires low moisture absorption of higher level as mentioned above and improvement has been demanded. The glycidyl ethers of tetramethylbiphenol are superior in low moisture absorption, but are not necessarily enough in heat resistance. Therefore, they are limited in their use as encapsulants. Furthermore, glycidyl ethers of condensates of α-naphthol with aldehydes are low in moisture absorption, but high in melt viscosity even in the case of low polymerization degree and inferior in operability and besides, insufficient in heat resistance. US-A-4 960 634 discloses a resin composition of enhanced thermal conductivity which comprises a tetrabrominated diglycidyl ether of a phenol polyepoxide and an epoxy polymer obtained by the reaction of a haloepoxy-alkane with a novolak which in turn is prepared by reacting a phenol compound with an aldehyde as well as additional components. SUMMARY OF THE INVENTION An object of the present invention is to provide epoxy resin composition comprising glycidyl ether compounds and polyhydric phenols which give cured products lower in moisture absorption, improved in crack resistance and high in heat resistance. The present invention is characterized in the claims. DESCRIPTION OF THE PREFERRED EMBODIMENTS The polyhydric phenols which are starting materials for glycidyl compounds are synthesized by condensation of phenols with naphthaldehydes. Examples of the phenols are phenol and cresol, ethylphenol, propylphenol, butylphenol, amylphenol, hexylphenol, cyclohexylphenol, octylphenol, nonylphenol, xylenol, methylbutylphenol, chlorophenol, bromophenol, dichlorophenol and dibromophenol (including isomers thereof). These phenols may be used each alone or in combination of two or more. Examples of the naphthaldehydes are naphthaldehyde, methylnaphthaldehyde, ethylnaphthaldehyde, methyl naphthyl ketone and methoxynaphthaldehyde (including isomers thereof). These naphthaldehydes may be used each alone or in combination of two or more. Other aldehydes may be added to the above naphthaldehydes as far as the effects of the present invention are not damaged. As other aldehydes, mention may be made of, for example, formaldehyde, acetaldehyde, benzaldehyde, acrolein, crotonaldehyde, cinnamic aldehyde and glyoxal (including derivatives thereof). The condensation reaction of phenols with naphthaldehydes can be carried out at 40-150°C in the presence of acid catalysts, for example, inorganic acids such as HCl and H 2 SO 4 , organic acids such as acetic acid, p-toluenesulfonic acid and thioglycollic acid, and Lewis acids or ion-exchange resins which show strong acidity, followed by known after-treatments such as washing with water and distilling off of unreacted phenols. Furthermore, for imparting flame retardance to said polyhydric phenols, they may be substituted with halogens such as chlorine and bromine. In this way, the polyhydric phenols represented by the following formula (1) can be prepared. wherein R 1 (s) each independently represents a halogen atom, an alkyl or cycloalkyl group of 1-9 carbon atoms, an alkoxy group of 4 or less carbon atoms or an aryl group, with a proviso that R 1 (s) may be identical or different when ℓ is 2 or more, R 2 (s) each independently represents a halogen atom, an alkoxy group of 4 or less carbon atoms or an alkyl group of 6 or less carbon atoms, with a proviso that R 2 (s) may be identical or different when m is 2 or more, R 3 (s) each independently represents a hydrogen atom or an alkyl group of 6 or less carbon atoms and may be identical or different, the average recurring unit number n is 0-10, ℓ is 0-4 and m is 0-7. In the compounds represented by the formula (1), the average recurring unit number n can be adjusted by the synthesis conditions such as molar ratio of the charged phenols and naphthaldehydes and amount of the catalysts. When n is 0, the melting point or melt viscosity of the condensates is the lowest and handling of the condensates is easy. But considering the balance of the properties of cured products of glycidyl ether compounds (epoxy resins) referred to hereinafter, the polyhydric phenols may be mixtures containing polyfunctional component in which n is more than 0 and in some uses, mixtures are rather preferred. Ordinarily, the number n can be in the range of about 0-10. For use as encapsulants, the average recurring unit number n is 0-5, preferably 0-3, more preferably 0-1.5 considering both the easiness in handling and the properties of cured products. When n exceeds 5, the softening point or melt viscosity of the desired products is high and this is not preferred for encapsulants. When the products are diluted with solvents for use, for example, as laminate sheets, the high melt viscosity is not necessarily disadvantageous for practical use and thus, the average recurring unit number n can be optionally adjusted depending on the objects. The glycidyl ether compounds to be used in the present invention can be obtained by the well known process which comprises glycidyl-etherifying the polyhydric phenols of the first invention. A typical process comprises reacting the polyhydric phenols with epihalohydrins such as epichlorohydrin in the presence of alkalis such as sodium hydroxide. Especially when products of high purity are desired, the reaction is preferably carried out in an aprotic solvent as described in Japanese Patent Kokai (Laid-Open) No. Sho 60-31517. The resulting glycidyl ether compounds can be used as epoxy resins. The epoxy resin composition comprises besides the above glycidyl ether compound a polyhydric phenol as a curing agent. Examples of the curing agent are polyhydric phenols such as phenol novolaks, eg polycondensates of one or more phenols such as phenol, various alkylphenols and naphthols with aldehydes such as formaldehyde, acetaldehyde, acrolein, glyoxal, benzaldehyde, naphthaldehyde and hydroxybenzaldehyde or ketones such as cyclohexanone and acetophenone, vinyl polymerization type polyhydric phenols such as polyvinylphenol and polyisopropenylphenols, the polyhydric phenols of the formula (1), Friedel-Crafts type reaction products of phenols with diols such as those represented by the formula (3): dialkoxy compounds represented by the following formula (4): or, dihalogens represented by the following formula (5): and Friedel-Crafts type reaction products of phenols with diolefins such as dicyclopentadiene and diisopropenylbenzene. Amount of these curing agents used is 0.7-1.2 equivalent to epoxy group. When it is less than 0.7 equivalent or more than 1.2 equivalent to epoxy group, curing cannot be completed. Furthermore, known additives such as fillers, curing accelerators, flame retardants, mold-releasing agents and surface treating agents can be added to the compositions depending on uses. The fillers include, for example, silica, alumina, aluminum hydroxide, talc, clay and glass fibers. These fillers may be mixtures of those which are different in shape (sphere or fragment) or in size to increase filling amount. The amount of the inorganic fillers when the epoxy resin composition is used for encapsulation of semiconductors is 25-90% by weight, preferably 60-85% by weight based on the total amount of the epoxy resin composition. When it is less than 25% by weight, the composition is inferior in moisture resistance and when it is more than 90% by weight, the composition has problems in moldability. The curing accelerators include, for example, imidazoles, tertiary amines and phosphorus compounds. The flame retardants include, for example, brominated epoxy resins and antimony trioxide. The mold-releasing agents include, for example, waxes and metal salts of higher fatty acids such as zinc stearate. The surface treating agents include, for example, silane coupling agents. Furthermore, various elastomers may be added to reduce the stress of cured products. Examples are addition type or reaction type elastomers such as polybutadienes, butadiene-acrylonitrile copolymers and silicone rubber. Encapsulation of electronic parts such as semiconductors by the resin composition of the present invention can be performed by conventional methods such as transfer molding, compression molding and injection molding. The glycidyl ethers of the condensates of phenols and naphthaldehydes can provide cured products lower in moisture absorption than those provided by conventional glycidyl ethers of o-cresol novolaks and furthermore can provide cured products lower in moisture absorption and higher in heat resistance than those provided by glycidyl ethers of tetramethylbiphenol which are known to be low moisture absorption resins. Therefore, the composition can be used in the wide variety of the fields such as adhesives, coatings, prepregs, laminate sheets, molding materials and casting materials. Furthermore, the glycidyl ether compounds of formula (2) are lower in viscosity than glycidyl the second invention are lower in viscosity than glycidyl ethers of o-cresol novolak and when compositions are prepared with the glycidyl ether compounds, fillers can be used in a large amount and thus, the moisture absorption can be further lowered and the strength can be further increased and the compositions are useful as resin compositions for obtaining surface mounting as well as encapsulants for electronic parts. Moreover, the resin encapsulated type semiconductor devices are superior in solder crack resistance. The present invention is illustrated by way of the following Examples, but not limited thereby. In the Examples, the "epoxy equivalent weight" is defined as the molecular weight of epoxy resin per one epoxy group. Furthermore, the "hydrolyzable chlorine content" means chlorine ion which is released when an epoxy resin is dissolved in dioxane, an alcoholic potassium hydroxide solution is added thereto and the mixture is heated for 30 minutes under refluxing and which is expressed by concentration in parts per million (ppm) in the compound obtained by subjecting the chlorine ion to back titration with aqueous silver nitrate solution. The cured moldings were evaluated in the following manners. Glass transition temperature: This was measured using a thermo-mechanical analyzing instrument (SHIMADZU DT-30). Flexural strength and flexural modulus: This was measured in accordance with JIS K-6911 using an Instron universal testing machine (SHIMADZU IS-10T). Water absorption (index for moisture absorption): Change in weight was measured using a thermohygrostat (TABAI PR-2) under the conditions of 85°C/85%RH. Spiral flow: This was measured in accordance with EMMI-1-66 under the conditions of 175°C and 70 kg/cm 2 . Preparation of condensates of phenols and naphthaldehydes and glycidyl-etherification of the condensates. Example 1 244.4 g (2.00 mol) of 2,6-xylenol, 78.1 g (0.50 mol) of 1-naphthaldehyde, 225.8 g of toluene and 9.5 g of p-toluenesulfonic acid monohydrate were charged in a 1 liter four-necked flask provided with a stirrer, a thermometer and a condenser attaching a water separator and stirred to perform dissolution. The inner temperature was elevated to a refluxing temperature of 130°C and water produced by the reaction was distilled off from the reaction system by the water separator. The reaction was carried out at 130°C for 7 hours. After completion of the reaction, 258 g of toluene was added to the reaction mixture, followed by neutralization with aqueous sodium hydrogencarbonate solution and separation into layers and thereafter repeating washing with water and separation into layers. The toluene layer was dried and thereafter, toluene and 2,6-xylenol were distilled off by a rotary evaporator to obtain 193.5 g of a condensate of 2,6-xylenol and 1-naphthaldehyde. The resulting condensate had a molecular weight of 382 measured by FD-MASS spectrum and a melting point of 95-105°C. 100.0 g of the resulting condensate of 2,6-xylenol and 1-naphthaldehyde was charged in a reactor provided with a thermometer, a stirrer, a dropping funnel and a condenser attaching a water separator and dissolved in 343.2 g of epichlorohydrin and 171.6 g of dimethyl sulfoxide. With keeping the pressure in the reaction system at 5,466.10 3 Pa (41 Torr), 43.6 g of 48.6% aqueous sodium hydroxide solution was continuously dropped to the solution at 48°C over a period of 1.5 hour, during which reaction was carried out with cooling and liquefying the co-boiling epichlorohydrin and water and returning the organic layer to the reaction system keeping the temperature at 48°C. After completion of the reaction, unreacted epichlorohydrin was removed by concentration under reduced pressure and the glycidyl ether compound containing by-product salts and dimethyl sulfoxide were dissolved in methyl isobutyl ketone, and the by-product salts and the dimethyl sulfoxide were removed by washing with water. Epoxy equivalent weight and hydrolyzable chlorine content of the thus obtained glycidyl ether compound were 258 g/eq and 260 ppm, respectively. Example 2 Reaction was carried out in the same manner as in Example 1 except that 81.1 g (0.75 mol) of o-cresol was used in place of 2,6-xylenol and 1-naphthaldehyde was charged in an amount of 78.1 g (0.50 mol), thereby to obtain 137.7 g of a condensate of o-cresol and 1-naphthaldehyde. Fragments of 354, 600, 846, 1092, 1338 and 1584 were detected in FD-MASS spectrum of the condensate. The average recurring unit number n obtained by GPC was 1.61. In the same manner as in Example 1, 123.6 g of the resulting condensate of o-cresol and 1-naphthaldehyde was charged in a reactor provided with a thermometer, a stirrer, a dropping funnel and a condenser attaching a water separator and dissolved in 389.4 g of epichlorohydrin and 194.7 g of dimethyl sulfoxide. With keeping the pressure in the reaction system at 5,466.10 3 Pa (41 Torr), 37.5 g of 48.6% aqueous sodium hydroxide solution was continuously dropped to the solution at 48°C over a period of 1.5 hour, during which reaction was carried out with cooling and liquefying the co-boiling epichlorohydrin and water and returning the organic layer to the reaction system keeping the temperature at 48°C, followed by subjecting to after-treatments to obtain the desired glycidyl ether compound. Epoxy equivalent weight and hydrolyzable chlorine content of the thus obtained glycidyl ether compound were 302 g/eq and 260 ppm, respectively. Example 3 Reaction was carried out in the same manner as in Example 2 except that o-cresol was charged in an amount of 378.4 g (3.50 mol) and 1-naphthaldehyde was charged in an amount of 109.3 g (0.70 mol), thereby to obtain 230.2 g of a condensate of o-cresol and 1-naphthaldehyde. Fragments of 354 and 600 were detected in FD-MASS spectrum of the condensate. The average recurring unit number n obtained by GPC was 0.24. In the same manner as in Example 1, 146.4 g of the resulting condensate of o-cresol and 1-naphthaldehyde was charged in a reactor provided with a thermometer, a stirrer, a dropping funnel and a condenser attaching a water separator and dissolved in 518.0 g of epichlorohydrin and 259.0 g of dimethyl sulfoxide. With keeping the pressure in the reaction system at 5,466.10 3 Pa (41 Torr), 62.5 g of 48.6% aqueous sodium hydroxide solution was continuously dropped to the solution at 48°C over a period of 1.5 hour, during which reaction was carried out with cooling and liquefying the co-boiling epichlorohydrin and water and returning the organic layer to the reaction system keeping the temperature at 48°C, followed by subjecting to after-treatments to obtain the desired product. Epoxy equivalent weight and hydrolyzable chlorine content of the thus obtained glycidyl ether compound were 279 g/eq and 220 ppm, respectively. Example 4 Reaction was carried out in the same manner as in Example 1 except that 100.0 g (0.61 mol) of 2-t-butyl-4-methyl-phenol was charged in place of 2,6-xylenol and 1-naphthaldehyde was charged in an amount of 47.5 g (0.30 mol). After toluene was distilled off, the precipitated crystal was washed and dried to obtain 137.3 g of a condensate of 2-t-butyl-4-methyl-phenol and 1-naphthaldehyde. Molecular weight of the condensate according to FD-MASS spectrum was 466. In the same manner as in Example 1, 100.3 g of the resulting condensate was charged in a reactor provided with a thermometer, a stirrer, a dropping funnel and a condenser attaching a water separator and dissolved in 278.4 g of epichlorohydrin and 139.2 g of dimethyl sulfoxide. With keeping the pressure in the reaction system at 5,466.10 3 Pa (41 Torr), 35.4 g of 48.6% aqueous sodium hydroxide solution was continuously dropped to the solution at 48°C over a period of 1.5 hour, during which reaction was carried out with cooling and liquefying the co-boiling epichlorohydrin and water and returning the organic layer to the reaction system keeping the temperature at 48°C, followed by subjecting to after-treatments to obtain the desired glycidyl ether compound. Epoxy equivalent weight and hydrolyzable chlorine content of the thus obtained glycidyl ether compound were 339 g/eq and 268 ppm, respectively. Comparative Example 1 500 g of 2,6-xylenol was treated in the same manner as in Example 1 of Japanese Patent Kokai (Laid-Open) No. Hei 1-283241 to obtain 3,3',5,5'-tetramethylbiphenol. Then, 100 g of the resulting 3,3',5,5'-tetramethylbiphenol was charged in a reactor provided with a thermometer, a stirrer, a dropping funnel and a condenser attaching a water separator and dissolved in 535.0 g of epichlorohydrin and 267.0 g of dimethyl sulfoxide. With keeping the pressure in the reaction system at 5,466.10 3 Pa (41 Torr), 48.6% aqueous sodium hydroxide solution was continuously dropped to the solution at 48°C over a period of 5 hours. Thereafter, treatments were carried out in the same manner as in Example 1 to obtain the glycidyl ether compound. Epoxy equivalent weight and hydrolyzable chlorine content of the thus obtained glycidyl ether compound were 194 g/eq and 220 ppm, respectively. Comparative Example 2 A glycidyl ether compound of o-cresol novolak (Sumi-epoxy ESCN-195, a trade name, manufactured by sumitomo Chemical Co., Ltd.) was used as a conventional glycidyl ether compound. Comparative Example 3 A glycidyl ether compound of bisphenol A (Sumi-epoxy ELA-070, a trade name, manufactured by Sumitomo Chemical Co., Ltd.) was used as a conventional glycidyl ether compound. Evaluation of the epoxy resin compositions Examples 5-8 and Comparative Examples 4-6 Cured moldings of the glycidyl ether compounds (epoxy resins) prepared in Examples 1-4 and Comparative Examples 1-3 were evaluated. To each of the epoxy resins were added a phenol novolak (Tamanol 759 manufactured by Arakawa Chemical Co., Ltd.) as a curing agent, triphenylphosphine as a curing accelerator, a fused silica (FS-891 manufactured by Denki Kagaku Kogyo K.K.) as a filler, carnauba wax as a releasing agent and a coupling agent (SH-6040 manufactured by Toray Dow-Corning Co.) in the amounts (g) as shown in Table 1. The mixture was kneaded with heating by a roll of 110°C/50°C and transfer molded under the conditions of 175°C/70 kg/cm 2 /90 sec. The molding was further subjected to postcuring in an oven at 180°C for 5 hours to obtain a cured molding. Glass transition temperature, water absorption, flexural strength and flexural modulus of the cured molding were measured and the results are shown in Table 2.

Claims: An epoxy resin composition which comprises a glycidyl ether compound represented by the following formula: wherein R 1 independently represents a halogen atom, an alkyl or cycloalkyl group having 1 - 9 carbon atoms, an alkoxy group having 4 or less carbon atoms or an aryl group and may be identical or different when 1 is 2 more; R 2 independently represents a halogen atom, an alkoxy group having 4 or less carbon atoms or an alkyl group having 6 or less carbon atoms and may be identical or different when m is 2 or more; R 3 independently represents a hydrogen atom or an alkyl group having 6 or less carbon atoms and may be identical or different; the average recurring unit number n is 0 - 10, ℓ is 0 - 4 and m is 0 - 7, and a polyhydric phenol, wherein the amount of the polyhydric phenol is 0.7 - 1.2 equivalent to the epoxy group of the compound represented by the formula (2). An epoxy resin composition according to claim 1, wherein the polyhydric phenol is a phenol novolak. An epoxy resin composition according to claim 1, wherein the average recurring unit number n in the formula of a glycidylether compound is 0 - 5. An epoxy resin composition according to claim 1, wherein the average recurring unit number n in the formula of a glycidylether compound is 0 - 3. A process for using the epoxy resin composition of claim 1 comprising encapsulating a semiconductor device.

Inventors: KAMIO KUNIMASA, KANAGAWA SHUICHI, MORIMOTO TAKASHI, NAITOH SHIGEKI, SAITO NORIAKI, SHIOMI YUTAKA, SUGIYAMA YASUHIDE, TAKEBE KAZUO, KAMIO, KUNIMASA, KANAGAWA, SHUICHI, MORIMOTO, TAKASHI, NAITOH, SHIGEKI, SAITO, NORIAKI, SHIOMI, YUTAKA, SUGIYAMA, YASUHIDE, TAKEBE, KAZUO
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY LIMITED
Application year: 1992
Main classification: C08G8
IPC codes: C07D303, C08G59, C08G8, H01L23