Epoxy resin composition and process for producing the same

Abstract: Provided is an epoxy resin composition comprising a crystalline epoxy resin and an amorphous epoxy curing agent, wherein the crystalline epoxy resin is dispersing uniformly in the amorphous epoxy curing agent as crystallites. The epoxy resin composition is excellent in preservation stability.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a process for producing an epoxy resin composition which is useful for adhesives, coating materials, electric and electronic materials such as insulating materials and laminated plates, particularly useful to encapsulate electronic parts, and excellent in preservation stability, and an epoxy resin composition obtainable by said process. Description of the Related Art An epoxy resin is used generally as a resin composition, by being mixed with a curing agent, a cure accelerator, a filler, etc., and the composition has a problem of preservation stability. In recent years, transfer molding of an economically useful epoxy resin composition has been performed for encapsulating semiconductors, such as LSI, IC, and a transistor, and in this field, the preservation stability is especially important in view of productivity and economical efficiency. However, the preservation stability of the conventional compositions has not been sufficient. Especially in case of using a crystalline epoxy resin, when the crystallinity is lost in a kneading process, the softening point of the composition falls remarkably, and the preservation stability is remarkably lowered. For this reason, the composition is necessary to be stored cool until just before molding. If it is left at room temperature for some time, it may become unusable. US-A-5 414 058 discloses a powder coating composition including one or more crystalline substances the lowest melting point of which is Mp and one or more non-crystalline substances the lowest glass transition point of which is -Tg and is lower than Mp, wherein the crystalline and non-crystalline substances are selected from epoxy resins and curing agents and bonded to each other. The bonding is effected by maintaining a powdery mixture containing the crystalline and non-crystalline substances at a temperature higher than Tg but lower than Mp and the softening point of any of the non-crystalline substances, optionally under a pressure, and cooling and pulverizing the resulting mixture. Chemical Abstracts, Vol. 113, 7407 describes oriented structures obtained in polyethylenepolyamine-cured epoxy resin ED-20 by orientational drawing or extrusion of the resin in the initial stages of curing, when the crosslink density is low and the resin exhibits high elasticity. The oriented structures are stabilized by crystallites formed during subsequent crystallization and retained after completion of the curing process. Drawing and extrusion of the partially cured resin led to improved mechanical properties and anisotrophy of the thermal expansion coefficient above the glass temperature for the completely cured resin. JP-A-71-38502 discloses a process for producing a powdery coating composition having a low melt viscosity and improved in flowability, anti-block property and heat resistance, wherein in a first step a 2,5-di-t-butylhydroquinone is reacted with epichlorohydrin in the presence of an alkali catalyst to obtain a crystalline epoxy resin having an epoxy equivalent of 180 g or lower and a melting point (measured with a differential scanning calorimeter at a heating rate of 10°C/min) of 140°C or higher, and in a second step a noncrystalline hardener having a softening point of 50-120°C is incorporated into this epoxy resin in such a manner that the amount of the functional groups contained in the hardener is 0.5-1.5 equivalents based on the epoxy groups of the resin. SUMMARY OF THE INVENTION The purpose of the present invention is to provide an epoxy resin composition excellent in preservation stability, which comprises a crystalline epoxy resin and an amorphous epoxy curing agent as indispensable components. As a result of extensive studies, the inventors found that the dispersion state of a crystalline epoxy resin and an amorphous epoxy curing agent affects the preservation stability of the composition, and accomplished this invention. That is, the present invention is as follows. (1) A process for producing an epoxy resin composition characterized by that a crystalline epoxy resin (A) represented by formula (1) below and an amorphous epoxy curing agent (B) are mixed uniformly at a temperature of lower than the melting point of the crystalline epoxy resin and not lower than the softening point of the amorphous epoxy curing agent, and the crystalline epoxy resin is dispersing uniformly in the amorphous epoxy curing agent as crystallites. (2) A process for producing an epoxy resin composition characterized by that a crystalline epoxy resin (A) represented by formula (1) below and an amorphous epoxy curing agent (B) are melt-mixed uniformly at a temperature of not lower than the melting point of the crystalline epoxy resin, subsequently treated at a temperature of lower than the melting point of the crystalline epoxy resin and not lower than the softening point of the amorphous epoxy curing agent, and the crystalline epoxy resin is dispersing uniformly in the amorphous epoxy curing agent as crystallites. (3) A process for producing an epoxy resin composition characterized by that a crystalline epoxy resin (A) represented by formula (1) below, an amorphous epoxy curing agent (B), a cure accelerator (C), and an inorganic filler (D) are mixed uniformly at a temperature of lower than the melting point of the crystalline epoxy resin and not lower than the softening point of the amorphous epoxy curing agent, and the crystalline epoxy resin is dispersing uniformly in the amorphous epoxy curing agent as crystallites. (4) A process for producing an epoxy resin composition characterized by that a crystalline epoxy resin (A) represented by formula (1) below, an amorphous epoxy curing agent (B), a cure accelerator (C), and an inorganic filler (D) are melt-mixed uniformly at a temperature of not lower than the melting point of the crystalline epoxy resin, subsequently treated at a temperature of lower than the melting point of the crystalline epoxy resin and not lower than the softening point of the amorphous epoxy curing agent, and the crystalline epoxy resin is dispersing uniformly in the amorphous epoxy curing agent as crystallites. (5) An epoxy resin composition obtainable by any of the processes described in above (1) to (4). (6) A cured product of the epoxy resin composition of above (5). DETAILED DESCRIPTION OF THE INVENTION The crystalline epoxy resin which is (A) component used in this invention is not especially limited as long as it is an epoxy resin having crystallinity. Examples are those having a mesogen skelton or those having a bisphenol skelton and low molecular weight. Examples of those having a mesogen skelton include epoxy resins represented by general formula (1). In the formula, X represents -N=N-, -CH=CH-, -O-CO-, -CH=C(CH3)-, -CH=C(CN)-, -C≡C-, -CH=CH-CO- or a single bond. X is preferably -CH=CH-, -CH=C(CH3)-, -O-CO- or -CH=CH-CO-, and more preferably -CH=CH- and -CH=C(CH3)-. R 1 -R 8 represent each independently an alkyl group having 1-6 carbon atoms, hydrogen atom or halogen atom. Concrete examples of the alkyl group include groups such as methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, pentyl, hexyl and cyclohexyl. Concrete examples of a halogen atom include chlorine, bromine, etc. As concrete examples of the epoxy resin represented by general formula (1), following compounds are included. Although the curing agent which is the component (B) used in this invention is not limited as long as it is amorphous, preferably it is solid-like at a room temperature, and the softening point is 100 °C or lower. Concrete examples of the curing agent include: polyphenolic and the polynaphtholic novolak resins which are the reaction products of phenols such as phenol, o-cresol and catechol, or naphthols such as hydroxynaphthalene and dihydroxynaphthalene, with aldehydes such as formaldehyde; trityl skelton containing polyphenols obtained by the condensation of phenols such as phenol, cresol and methyl-t-butyl phenol, with aromatic aldehydes such as hydroxy benzaldehyde. Trityl skelton containing polyphenol novolaks which are the reaction product of trityl skelton containing poly phenols with formaldehyde; polyaralkyl phenol resins and polyaralkyl naphthol resins which are reaction products of phenols such as phenol, o-cresol and catechol, or naphthols such as hydroxy naphthalene and dihydroxy naphthalene, with xylylene dichloride and bis (hydroxymethyl)benzene; alicyclic hydrocarbon containing polyphenol resins and the polynaphthol resins which are the reaction product of phenols such as phenol, o-cresol and catechol, or naphthols such as hydroxynaphthalene, dihydroxynaphthalene, with unsaturated alicyclic hydrocarbons such as dicyclopentadiene and limonene; alicyclic hydrocarbon containing polyphenol novolak resins and the polynaphthol novolak resins which are the reaction product of alicyclic hydrocarbon containing polyphenol resins, or poly naphthol resins, with formaldehyde. Examples of a cure accelerator which is the component (C) used in the present invention include; organic phosphine compounds, for example, triphenyl phosphine, tri-4-methylphenyl phosphine, tri-4-methoxyphenyl phosphine, tributyl phosphine, trioctyl phosphine, tri-2-cyanoethyl phosphine, and tetra phenyl borate salts thereof; tertiary amines such as tributyl amine, triethyl amine, 1,8-diazabicyclo(5,4,0)undecene-7 and triamyl amine; quarternary ammonium salts such as benzylchloride trimethyl ammonium, benzylhydroxide trimethyl ammonium, and triethyl ammonium tetraphenylborate; and imidazoles. Among these, organic phosphine compounds, 1,8-diazabicyclo(5,4,0) undecene-7, and imidazoles are preferable from the point of moisture resistance and curability. Especially triphenyl phosphine is preferable. Examples of the inorganic filler which is the component (D) used in the present invention include; silica, alumina, titanium white, aluminium hydroxide, talc, clay and glass fiber. In the epoxy resin composition obtainable according to the present invention, the ratio of the epoxy group of the crystalline epoxy resin (A) to the functional group of the amorphous epoxy curing agent (B) is in the range of 0.5-1.5. The ratio outside the above range may result in insufficient heat resistance of the epoxy resin composition. The ratio is preferably in the range of 0.8-1.2 The cure accelerator (C) can be used optionally in an amount as desired. However, the component (C) is preferably used so as to make the gel-time of the epoxy resin composition 10 to 180 seconds at 150-230°C, especially for use the composition as an encapsulating material. The inorganic filler (D) is used in an amount of 10-96% by weight, preferably 70-90 % by weight, in the total amount of the epoxy resin composition. In the epoxy resin composition obtainable according to the present invention, mold releasing agents such as a natural wax, a synthetic wax, a higher fatty acid and its metal salts and paraffin, colorants like carbon black, surface treatment agents such as a silane coupling agent, can be added. As for the process for producing the epoxy resin composition of the present invention, the method includes mixing in molten state. The temperature at the time of mixing is important for obtaining the epoxy resin composition of the present invention by melt mixing. As one method, it includes the method of heating the mixture of a crystalline epoxy resin and an amorphous curing agent (additives such as a cure accelerator and inorganic filler can be added further, if necessary) at a temperature of lower than the melting point of the crystalline epoxy resin and not lower than the softening point of the amorphous curing agent. The temperature is preferably 10°C - 30°C lower than the melting point of the crystalline epoxy resin. At a temperature higher than the melting point of the crystalline epoxy resin , the rate to which a crystalline epoxy resin exists in a curing agent as crystallites becomes low and it is not preferable. Moreover, at a temperature lower than the softening point of the amorphous curing agent, it needs great energy for kneading, and it is disadvantageous industrially. On the other hand, mixtures of the crystalline epoxy resin and the amorphous curing agent can be mixed with heating at a temperature of not lower than the melting point of a crystalline epoxy resin to produce a resin composition having an uniform phase structure where both the crystalline epoxy resin and the amorphous curing agent are melt-mixed uniformly. And then, the mixture can be melt kneaded at a temperature of lower than the melting point of a crystalline epoxy resin and not lower than the softening point of an amorphous curing agent to disperse the crystallite of a crystalline epoxy resin uniformly in the curing agent. The temperature here is preferably 20 to 30°C lower than the melting point of the crystalline epoxy resin. For these manufacture methods, a kneading mixer, a twin-roller, an extruder, etc. can be used. In the resin composition obtainable according to the present invention, comprising a crystalline epoxy resin and an amorphous epoxy curing agent, the crystalline epoxy resin is dispersing as a shape of crystallites in an amorphous curing agent, and the reaction of the curing agent with an epoxy resin during the storage is prevented and the preservation stability is raised. Here, the epoxy resin must be dispersed in an amorphous curing agent uniformly. If the dispersion is ill-balanced, partial unevenness of the performance is generated and it is not preferable. The size of the crystallite is preferably 100 µ m or less, and more preferably 50 µm or less. When the size of crystallite becomes larger than 100 µm, partial unevenness of the performance is generated, or the melting property of the crystallite deteriorates in molding and curing, and molding property becomes poor. One method of confirming the dispersion state of the crystallite of the epoxy resin in the resin composition of the present invention includes the observation by a polarizing microscope. The epoxy resin composition obtainable according to the present invention can be molded and heat-cured by a known method. The epoxy resin composition obtainable according to the present invention is used for electronic or electric use such as insulating materials and laminated plates, and for adhesives and coating materials. PREFERRED EMBODIMENTS OF THE INVENTION Examples of the present invention will be shown below, but the present invention is not limited to these. Referential Example 1 Synthesis of raw material phenol(1) In a 2 liter four-necked flask equipped with a thermometer, a stirrer and a condenser, 195.5 g (1.6 mol) of 2,6-xylenol (abbreviated to "26XY"), 65.7 g (0.4 mol) of 2-tertiary-butyl-5-methylphenol (abbreviated to "3M6B"), 124.5g (1.0 mol) of chloroacetaldehyde dimethylacetal and 376g of acetic acid were charged, stirred, dissolved and cooled to 5 °C. Next, a solution of conc. sulfuric acid 122g (1.2 mol) dissolved in acetic acid 84g was added dropwise at 10°C for 3 hours, and the reaction system was kept at 25°C for 6 hours, and stirred overnight at room temperature. Next, the reaction system was cooled to 5°C, and filtrated the depositted crystal. The crystal was washed 6 times with 500g of water, dried under reduced pressure at 40°C for 8 hours, and a crystal was obtained. Referential Example 2 Synthesis of raw material phenol(2) In a 2 liter four-necked flask equipped with a thermometer and a stirrer, 245.2g of 48.3% sodium hydroxide aqueous solutions, and 552 g of N-methyl pyrolidone were charged and the inner atomosphere was replaced with nitrogen. Under a nitrogen sealing, the temperature of the solution was raised to 140°C. A solution of the phenol intermediate 225.6 g obtained by the referential example 1 and N-methyl pyrolidone 676 g was added dropwise at 140°C for 1.5 hours, and kept at the said temperature for 2 hours. Then, the reaction system was cooled to 60°C and neutralized with 226 g of conc. hydrochloric acid. After recovering the solvent under a reduced pressure, the reaction mixture was charged into 1000g of ion-exchanged water, and the deposited crystal was filtrated. The crystal was washed 3 times with 1000 g of ion-exchanged water, and dried under reduced pressure at 80°C for 8 hours, and a crystal was obtained. Referential example 3 A synthesis of an epoxy resin In a reaction vessel equipped with a thermometer, a stirrer, a dropping funnel and the condenser with a separation pipe, the raw material obtained in the referential example 2 was charged, and dissolved in epichlorohydrin 485.6 g and dimethyl sulfoxide 243.1g. Keeping the inside of the reaction system at 43 torr, 61.71g of 48.3% sodium hydroxide was continuously added dropwise at temperature 48°C for 5 hours. In the meantime, keeping the temperature at 48°C, the azeotropically distilled epichlorohydrin and water were cooled to liquify, and the reaction was continued with returnig the organic layer to the reaction system. After the reaction, unreacted epichlorohydrin was removed by vacuum concentration. Glycidyl ether containing a by-produced salt and dimethyl sulfoxide was dissolved in 644g of methylisobutyl ketone, and the by-produced salt and dimethyl sulfoxide was removed by washing with water. Then, methylisobutyl ketone was distilled off under reduced pressure at 160°C and 10torr and the desired product was obtained. The melting point of this resin was 110°C measured by using a differential scanning calorimeter (produced by Seiko electron Co., Ltd., SSC5000 series, DSC200) under the condition of the temperature rising rate of 10°C/min. Here, the starting point of the heat-absorption peak due to melting was made to be the melting point. Example 1 Preparation of an epoxy resin composition Ten grams of the crystalline epoxy resin obtained in the referential example 3, and 8 g of an aralkyl phenol novolak resin (Mitsui Toatsu Company, tradename Milex XL-4L, softening point of 62°C) as a curing agent were mixed at 100°C for 15 minutes in a beaker. Then, triphenyl phosphine 0.35g was added as a cure accelerator and stirred at 100°C for 10 seconds, and an opaque resin composition was obtained. By observing this resin composition with a polarizing microscope (XTP-11; made by Nikon), it was confirmed that crystallites of 50 micrometers or less are dispersing uniformly. The resin compositions were kept in 23°C, 40°C, and 60°C oven for 10 days. For evaluating the preservation stability, the retention rate of the epoxy resin raw materials peak were pursued ( 28.9 minute: detected by a differential refractive index meter) in GPC. Results are shown in Table 1. Comparative example 1 An epoxy resin and a curing agent were mixed in a same manner as Example 1 except at a temperature of 120°C for 15 minutes. Then triphenyl phosphine 0.35g was added and stirred at 120°C for 10 seconds, and a transparent resin composition was obtained. By observing this resin composition with a polarizing microscope, crystallites were not observed, and it was confirmed that it is the structure where an epoxy resin and a curing agent are melt-mixed uniformly. Preservation stability test of the resin compositions was conducted as the same manner with Example 1. Results are shown in Table 1. Retention rate of the epoxy resin raw materials peak (%) Examples Referential Examples Preservation Temperture 23°C 40°C 60°C 23°C 40°C 60°C Preservation Days 3 days 99 63 37 91 58 21 7 days 91 51 31 84 50 16 10 days 77 44 21 77 40 15 The epoxy resin composition of the present invention is excellent in preservation stability, and it is a material advantageous for productivity and economical efficiency.

Claims: A process for producing a material to encapsulate electronic parts characterized by that (A) a crystalline epoxy resin represented by below formula (1) and (B) an amorphous epoxy curing agent are mixed uniformly at a temperature of lower than the melting point of the crystalline epoxy resin and not lower than the softening point of the amorphous epoxy curing agent, wherein, X represents -N=N-, -CH=CH-, -O-CO-, -CH=C(CH 3 )-, -CH=C(CN)-, -C≡C-, -CH=CH-CO- or a single bond; R 1 -R 8 represent each independently an alkyl group having 1-6 carbon atoms, hydrogen atom or halogen atom, and the crystalline epoxy resin is dispersing uniformly in the amorphous epoxy curing agent as crystallites. A process for producing a material to encapsulate electronic parts characterized by that (A) a crystalline epoxy resin represented by the above formula (1) and (B) an amorphous epoxy curing agent are melt-mixed uniformly at a temperature of not lower than the melting point of the crystalline epoxy resin, subsequently treated at a temperature of lower than the melting point of the crystalline epoxy resin and not lower than the softening point of the amorphous epoxy curing agent, and the crystalline epoxy resin is dispersing uniformly in the amorphous epoxy curing agent as crystallites. A process for producing a material to encapsulate electronic parts characterized by that (A) a crystalline epoxy resin represented by the above formula (1), (B) an amorphous epoxy curing agent, (C) a cure accelerator, and (D) an inorganic filler are mixed uniformly at a temperature of lower than the melting point of the crystalline epoxy resin and not lower than the softening point of the amorphous epoxy curing agent, and the crystalline epoxy resin is dispersing uniformly in the amorphous epoxy curing agent as crystallites. A process for producing a material to encapsulate electronic parts characterized by that (A) a crystalline epoxy resin represented by the above formula (1), (B) an amorphous epoxy curing agent, (C) a cure accelerator, and (D) an inorganic filler are melt-mixed uniformly at a temperature of not lower than the melting point of the crystalline epoxy resin, subsequently treated at a temperature of lower than the melting point of the crystalline epoxy resin and not lower than the softening point of the amorphous epoxy curing agent, and the crystalline epoxy resin is dispersing uniformly in the amorphous epoxy curing agent as crystallites. A material to encapsulate electronic parts obtainable by any one of the processes claimed in claims 1 to 4. A cured product of the material to encapsulate electronic parts of claim 5. A material to encapsulate electronic parts obtainable by any one of the processes claimed in claims 1 to 4, wherein the crystalline epoxy resin has the shape of crystallites and wherein the size of the crystallites is 100 µm or less.

Inventors: AKIBA MASATSUGU, ARAI NORIYUKI, AKIBA, MASATSUGU, ARAI, NORIYUKI
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1997
Main classification: C08G59
IPC codes: C08G59