Epoxy resin composition and method for producing the same

Abstract: Provided is an epoxy resin composition comprising a crystalline epoxy resin (A) and an amorphous epoxy resin as an essential component, wherein the crystalline epoxy resin (A) being uniformly dispersed in the amorphous epoxy resin (B) as a crystallite. The epoxy resin composition has a high softening point, hardly causes blocking during the storage and has an excellent handling property.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method for producing an epoxy resin composition, which is superior in workability and useful for adhesives, paints, insulation materials and electrical/electronic materials (e.g. laminated plate, etc.), particularly useful for encapsulating electronic devices. Description of the Related Art For encapsulation of semiconductors such as LSI, IC, transistor, etc., economically useful transfer molding of an epoxy resin composition has recently been carried out. In this case, a softening point of the resin composition is important in view of handling. The resin composition having a low softening point sometimes causes blocking during the storage to result in deterioration of the workability. Therefore, the composition is stored generally with cooling in a refrigerator, but there has been a problem that the productive efficiency is poor. JP-A-2-300 255 discloses a heat-curable uncured epoxy resin composition which is solid at ordinary temperature, obtained by melt-mixing components comprising a crystalline epoxy resin which is solid at ordinary temperature in an amount of 30 wt% or more based on the total amount of epoxy resins, a non-crystalline epoxy resin which is solid at ordinary temperature and an epoxy resin-curing agent. JP-A-7-179 564 discloses a method for producing a crystalline epoxy resin having lower viscosity wherein to 100 parts by weight of an epoxy resin in liquid condition represented by the following general formula (1): (wherein, G represents a glycidyl group, R represents a monovalent group, n represents an integer from 0 to 4, and X represents a divalent group) is added 0.05 to 10 parts by weight of a crystalline fine powder of said epoxy resin separately prepared, and the mixture is crystallized with stirring under condition wherein the mixture is maintained in liquid condition at a temperature 20°C lower than the melting temperature of said epoxy resin. EP-A-0 724 006 discloses a polymer-dispersed liquid crystal composite having a polymer continuous phase and a liquid crystal discontinuous phase characterized in that the polymer continuous phase contains a liquid crystalline main chain thermoset epoxy resin as a compatible component of that phase; and a method of making the composite and devices incorporating the composite. US-A-5 206 313 discloses a process for the preparation of a powder coating composition, comprising the steps of: (a) providing a crystalline material consisting of two or more crystalline substances each of which has a melting point of at least 90°C, and one of which has a melting point Mp that is lower than those of the other crystalline substances, said crystalline substances consisting of at least one crystalline epoxy resin and at least one crystalline curing agent; (b) providing a non-crystalline material consisting of one or more non-crystalline substances each of which has a softening point of at least 50°C, and one of which has a glass transition point Tg which is lower than those of the other non-crystalline substances and which is lower than said melting point Mp, said non-crystalline substances being selected from the group consisting of non-crystalline epoxy resins, non-crystalline curing agents and mixtures thereof; (c) blending said crystalline material with said non-crystalline material to obtain a mixture having a content of said crystalline material of 55-90% by weight based on the total weight of said crystalline and non-crystalline materials and 5-45% by weight of said at least one crystalline curing agent based on the total weight of said crystalline and non-crystalline materials; (d) pressing said mixture at a temperature which is higher than said glass transition point Tg but lower than said melting point Mp and which is lower than any softening point of said one or more non-crystalline substances so that said crystalline substances and non-crystalline substances are bonded with each other with said non-crystalline substance having the glass transition point Tg serving as a binder; (e) then cooling the mixture obtained in step (d) to a temperature lower than said glass transition point Tg; and (f) then pulverizing the cooled mixture obtained in step (e). SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing an epoxy resin composition, which has a high softening point and hardly causes blocking during the storage. That is, the present invention is as follows: (1) a method for producing an epoxy resin composition comprising a crystalline epoxy resin (A) and an amorphous epoxy resin (B) as an essential component, wherein the crystalline epoxy resin (A) is uniformly dispersed in the amorphous epoxy resin (B) as a crystallite, which method comprises mixing a crystalline epoxy resin (A) with an amorphous epoxy resin (B) with heating at a temperature of not higher than a melting point of the former and not lower than a softening point of the latter; and (2) a method for producing the epoxy resin composition comprising a crystalline epoxy resin (A) and an amorphous epoxy resin (B) as an essential component, wherein the crystalline epoxy resin (A) is uniformly dispersed in the amorphous epoxy resin (B) as a crystallite, which method comprises mixing a crystalline epoxy resin (A) with an amorphous epoxy resin (B) with heating at a temperature of not lower than a melting point of the former and not lower than that of the latter, cooling the resulting mixture to a temperature of not higher than the melting point of the former to deposit a crystal of the former and then kneading the mixture. DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing a resin composition having a high softening point by uniformly dispersing a crystalline epoxy resin in an amorphous epoxy resin in the form of a crystallite. In the composition, all or a part of the crystalline epoxy resin should be dispersed uniformly in the amorphous epoxy resin. Furthermore, the particle size of the crystallite is preferably not larger than 100 µm, and more preferably not larger than 50 µm. When the particle size is larger than the above range, the performance varies with the position and melting properties of the crystallite are lowered during the molding/curing to cause a defective molding. The method of producing the epoxy resin composition according to the present invention will be described in detail. The composition and the mixing temperature are important to obtain the epoxy resin composition by melt-mixing. Regarding the composition, the amount of the crystalline epoxy resin is preferably more than 5% by weight based on the total amount, more preferably more than 10% by weight, and most preferably more than 30% by weight. When the amount is 5% by weight or less, the effect of decreasing the viscosity of whole resin composition becomes low and it is difficult to uniformly disperse the crystalline epoxy resin in the amorphous epoxy resin as a crystallite, and the softening point of the composition may be lowered. The upper limit of the amount of the crystalline epoxy resin is not restricted, but it is preferably not more than 80% by weight based on the total amount. Regarding the mixing temperature, there is a method of melt-mixing with heating at a temperature of not lower than the softening point of the amorphous epoxy resin and not higher than the melting point of the crystalline epoxy resin. This temperature is preferably 10-30 °C lower than the melting point of the crystalline epoxy resin. When the mixing temperature is higher than the melting point of the crystalline epoxy resin, the proportion of the crystalline epoxy resin existing in the amorphous epoxy resin as a crystallite is lowered unfavorably. When the mixing temperature is lower than the softening point of the amorphous epoxy resin, numerous energy is required for kneading and it is industrially disadvantageous. On the other hand, a resin composition having an uniform phase structure wherein both amorphous epoxy resin and crystalline epoxy resin are compatiblized each other is prepared by melt-mixing at a temperature higher than the melting point of crystalline epoxy resin, then the resin composition is cooled to a temperature not higher than the melting point of the crystalline epoxy resin to deposit a crystallite, and the resin composition is further kneaded at a temperature of not lower than the softening point of the amorphous epoxy resin and not higher than the melting point of the crystalline epoxy resin to uniformly disperse a crystallite of the crystalline epoxy resin in the amorphous epoxy resin. The kneading temperature in this case is preferably 20-30°C lower than the melting point. In these production methods, a mixer, a twin roll, an extruder, etc. are used. The dispersion state of the crystallite in the resin composition prepared according to the present invention can be confirmed by using a polarized light microscope. The crystalline epoxy resin as the component (A) used in the present invention may be any epoxy resins having crystallizability, but is not particularly limited. Examples thereof include those having a mesogen skeleton or a bisphenol skeleton and low molecular weight, etc. Specific examples of those having a mesogen skeleton include an epoxy resin represented by the following general formula (1). wherein X represents a single bond or a group selected from -N=N-, -CH=CH-, -O-CO-, -CH=C(CH 3 )-, -CH=C(CN)-, -C≡C- and -CH=CH-CO-; and R 1 to R 8 independently represent an acyclic or cyclic alkyl group having 1 to 6 carbon atoms, hydrogen atom or a halogen atom. In the formula, the glycidyl group can substitute at any position to the X group on the ring. Usually, the glycidyl group substitutes at the para- and/or ortho-position to the X group, and the epoxy resins can be used as a mixture of these isomers. Among them, para-substituted epoxy resin is preferably used. Specific examples of the epoxy resins represented by the above general formula (1) include glycidyl ethers such as 2,2'-dihydroxy-3,3',5,5'-tetramethylstilbene, 4,4'-dihydroxy-3,3',5,5'-tetramethylstilbene, 4,4'-dihydroxy-3,3'-di-t-butyl-5,5'-dimethylstilbene, 4,4'-dihydroxy-3,3'-di-t-butyl-6,6'-dimethylstilbene, 2,2'-dihydroxy-3,3'-di-t-butyl-6,6'-dimethylstilbene, 2,4'-dihydroxy-3,3'-di-t-butyl-6,6'-dimethylstilbene, 3-t-butyl-4,4'-dihydroxy-3',5,5'-trimethylstilbene, 3-t-butyl-2,4'-dihydroxy-3,5',6-trimethylstilbene, 3-t-butyl-4,4'-dihydroxy-3',5',6-trimethylstilbene, bisphenol2,2',4,4'-tetramethylbisphenol, etc. Examples of those having a bisphenol skeleton and low molecular weight include those represented by the following general formula (2), wherein X represents a group selected from ; R 1 to R 6 independently represent an acyclic or cyclic alkyl group having 1 to 6 carbon atoms, a hydrogen atom or a halogen atom; and n represents a value of 0.05 or less. These epoxy resins may be used in combination thereof. The melting point of these epoxy resins is preferably from 80 to 150°C in view of the handling properties. The epoxy resin as the component (B) used in the present invention may be any amorphous one, and is not particularly limited, preferably those which are solid at room temperature and have a softening point of not higher than 100°C. Among them, a novolak epoxy resin is preferred in view of the heat resistance and low water absorption. As the novolak epoxy resin, known resins can be used, and examples thereof include polyphenol and polynaphthol novolak resins as a reaction product of phenols (e.g. phenol, o-cresol, catechol, etc.) or naphthols (e.g. hydroxynaphthalene, dihydroxynaphthalene, etc.) and aldehydes (e.g. formaldehyde, etc.); polyaralkylphenol resins as a reaction product of phenols (e.g. phenol, o-cresol, catechol, etc.) or naphthols (e.g. hydroxynaphthalene, dihydroxynaphthalene, etc.) and xylylenedichloride or bis(hydroxymethyl)benzenes; and glycidyl ether compounds derived from polyaralkylnaphthol resins, etc. These epoxy resins may be used alone or in combination thereof. To the epoxy resin composition prepared according to the present invention, known epoxy resin curing agents, curing accelerators, fillers (e.g. silica, alumina, titanium white, aluminum hydroxide, talc, clay, glassfiber,etc.,), natural wax, synthetic wax, higher fatty acid and a metallic salt thereof, releasants (e.g. paraffin, etc.), colorants (e.g. carbon black, etc.) and surface treat ing agents (e.g. such as silane coupling aqent, etc.) may be added. The epoxy resin composition prepared according to the present invention is used as adhesives, paints, insulating materials and electrical/electronic materials (e.g. laminated plate, etc.), particularly encapsulant for electronic parts. EXAMPLES The following examples further illustrate the present invention in detail but are not to be construed to limit the scope thereof. Moreover, softening point was measured by the ring and ball method according to JIS K 7234. Synthesis Example 1 An amount of 195.5 g (0.16 mol) 2,6-xylenol (hereinafter referred to "26XY"), 65.7 g (0.4 mol) of 2-t-butyl-5-methylphenol and 174.4 g (1.0 mol) of an aqueous 45% chloroacetoaldehyde solution were charged in a flask and stilbene bisphenol (yellow crystal 208 g) was obtained according to the method described in R. H. Siebe, Liebigs, Ann. Chem., 730, 31 (1969). Then, this stilbene bisphenol was epoxidized according to the method described in Japanese Patent Kokoku Publication No. Hei 7-91360 to obtain a desired product. The melting point of this product was 110-130°C, the epoxy equivalent was 208 g/eq. and the content of hydrolyzable chlorine was 170 ppm. Furthermore, the melt viscosity was 0.1 poise at 150°C. Example 1: Preparation of resin composition The crystalline epoxy resin obtained in Synthesis Example 1 and cresol novolak epoxy resin (trade name: Sumiepoxy ESCN-195XL3, manufactured by Sumitomo Chemical Co., Ltd.) as the amorphous epoxy resin were mixed at the composition shown in Table 1, and the mixture was molten and mixed in a beaker at 150°C to obtain an uniform resin composition. After cooling to room temperature, the composition was stirred over a hot plate heated to 80°C to obtain an opaque resin composition wherein the crystalline epoxy resin is uniformly dispersed in the amorphous epoxy resin. The softening point of this resin composition was measured as shown in Table 1. Comparative Example 1 The softening point of a cresol novolak epoxy resin (trade name: Sumiepoxy ESCN-195XL3, manufactured by Sumitomo Chemical Co., Ltd. ) was measured as shown in Table 1. Comparative example 2 The softening point of a low-molecular weight cresol novolak epoxy resin (trade name: Sumiepoxy ESCN-195LL, manufactured by Sumitomo Chemical Co., Ltd.) was measured as shown in Table 1. Comparative Example 3 A bisphenol epoxy resin (trade name: Sumiepoxy ELA-128, manufactured by Sumitomo Chemical Industries Co., Ltd.) as the amorphous epoxy resin and a cresol novolak epoxy resin (trade name: Sumiepoxy ESCN-195XL3, manufactured by Sumitomo Chemical Co., Ltd.) as the amorphous epoxy resin were mixed at the composition shown in Table 1, and the mixture was molten and mixed in a beaker at 150°C to obtain an uniform resin composition. The melting point of this resin composition was measured as shown in Table 1. Comparative Example 4 The resin composition mixed in the same composition as in Example 1 was molten and mixed in a beaker at 150°C and then cooled to room temperature to obtain an uniform resin composition. This resin was stirred over a hot plate heated to 130°C, but an opaque resin composition wherein the crystalline epoxy resin was uniformly dispersed in the amorphous epoxy resin was not obtained. The epoxy resin composition prepared according to the present invention has a high softening point and an excellent handling property.

Claims: A method for producing an epoxy resin composition comprising a crystalline epoxy resin (A) and an amorphous epoxy resin (B) as essential components, wherein the crystalline epoxy resin (A) is uniformly dispersed in the amorphous epoxy resin (B) as a crystallite, which method comprises mixing a crystalline epoxy resin (A) with an amorphous epoxy resin (B) with heating at a temperature of not higher than a melting point of the former and not lower than a softening point of the latter. A method for producing an epoxy resin composition comprising a crystalline epoxy resin (A) and an amorphous epoxy resin (B) as essential components, wherein the crystalline epoxy resin (A) is uniformly dispersed in the amorphous epoxy resin (B) as a crystallite, which method comprises mixing a crystalline epoxy resin (A) with an amorphous epoxy resin (B) with heating at a temperature of not lower than a melting point of the former and not lower than that of the latter, cooling the resulting mixture to a temperature of not higher than the melting point of the former to deposit a crystal of the former and then kneading the mixture.

Inventors: ARAI NORIYUKI, ARAI, NORIYUKI
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1998
Main classification: C08L63
IPC codes: C08L63