THERMOSET EPOXY COMPOSITION

Abstract: These compositions contain the reaction product of a liquid cycloaliphatic epoxy resin having more than one 1,2-epoxy group per molecule with a diphenolic compound. This reaction product, which is solid, may be employed with curing agent, filler and the like in any conventional manner or, as preferred, as molding compound.

Description: THERMQSET EPOXY COMPOSITION Background of the Invention . Epoxy resins are well known for a variety of different uses. The liquid resins are commonly employed for such applications as casting, potting, coating, impregnation and the like. Solid epoxy resins are most popular for injection, compression and transfer molding. In general, the more rapidly curing cycloaliphatic epoxies do not lend themselves to molding in conventional equipment. However, because they possess generally superior characteristics of weathering resistance, heat distortion temperature and electrical properties the liquid cycloaliphatic epoxy resins would be preferred if articles could be produced by conventional solid resin techniques. Such articles would find particular utility in the field of electric or electronic parts. It is further known that many epoxy resins may be modified by reaction with an adduct to provide different properties. The results of such an adduct reaction, however, are often unpredictable. By way of illustration, Japanese Patent application 50,921 of Osaka Soda Co. Ltd., describes the production of thermoset resins from diglycidyl compounds. Those compounds are reacted with divalent phenols in the presence of ammonium bicarbonate or acetate. British patent 915,767 of Shell Internationale Research Maatshappij N.V. relates to thermoplastic materials. These materials are produced by reaction of a diglycidyl ether with a dihydroxy compound in the presence of a sodium salt. U.S. Patent No. 3,364,178 of Kreps et al describes production of thermoplastic materials. Equi olar amounts of a dihydic phenol and a diglycidyl ether of a dihydric phenol (at least one of which contains a diarylsulfone group) are reacted in the presence of an alkaline catalyst. OMPI U.S. Patent No. 3,694,407 of Krikorian describes the reaction of certain polyepoxides having more than one vicepoxide group with special polyhydric phenols. The reaction takes place in the presence of an organic phosphine or hydrocarbon phosphonium halide to produce a thermoset product. U.S. Patent No. 3,733,305 of Loewrigkeit et al again relates to thermoset products. These are produced without a catalyst by reaction of sulfonyl diphenol (bisphenol-S) with a bis (glycidyloxyphenyl) sulfone (diepoxy bisphenol S) in molten condition. Not only do the reactions and results for such adduct formation differ, but the prior art lacks particular teaching as to the modification of liquid cycloaliphatic (or alicyclic) epoxy resins. The production of thermoset materials capable of use in solid molding techniques from these resins therefore remains an especially desirable- objective. Introduction of the Invention The present invention involves improved thermoset compositions. These compositions relate to the reaction product of a liquid cycloaliphatic epoxy resin having more than one 1,2-epoxy group per molecule with a dipheno¬ lic compound. The diphenolic coirpound is utilized in an amount effective to convert the epoxy resin from a normally liquid to solid form. The present compositions are particularly useful in molding applications. They may additionally contain a curing agent, such as metal acetylacetonate and phenolic accelerator, or a filler. In preferred compositions useful as molding compounds , they contain both these additional components. Description of the Invention The epoxy resins employed in this invention can be cycloaliphatic 1,2-epoxy resins having more than 1 epoxy group per molecule. They include resins such as 3,4-epoxycyclohexylmethyl-(3,4-epoxy) cyclohexane carboxylate (sold under the trademarks ERL 4221 by Union Carbide Plastics Company or Araldite CY . 179 by Ciba Products Company); bis(3,4-epoxy-6-methylcyclo- hexylmethyl) adipate (sold under the trademarks ERI 4289 by Union Carbide Plastics Company of Araldite CY 178 by Ciba Products Company) ; vinylcyclohexane dioxide (ERL 4206 made by Union Carbide Plastics Company); bis(2,3- epoxy-cyclopentyl) ether resins (sold under the trademark ERL 4205 by Union Carbide Plastics Company); 2-(3,4-epoxy) cyclohexyl-5-j5-spiro (3,4-epoxy) cyclohexane-m-dioxane (sold tinder the trademark ERL 4234 by-Union Carbide Corp. of Araldite CY 175 by Ciba Products Company) . These and other suitable cycloaliphatic epoxy resins are readily available and/or may 'be made in accordance with conventional techniques. In addition to the cycloaliphatic resins, other epoxy resins may also be present in the compositions of this invention. These ancillary epoxy resins need not be cycloaliphatics but desirably are solid, thermoset resins. In this manner, they are most compatible with the preferred properties and applications of the present composition. The other essential reactant for the present composi¬ tions is a diphenolic, and preferably a bisphenol, compound. An amount of diphenolic compound effective to transform the liquid cycloaliphatic epoxy resin into a solid thermoset reaction product should be utilized. The equivalent ratio of. liquid cycloaliphatic epoxy resin and the diphenolic compound is desirably between about 40:1 and 2:1, more preferably 20:1 to 3:1, respectively. Preferably, the diphenolic compound utilized in accordance with the present invention has the formula: wherein X is selected from the group consisting of lower aliphatic, sulfide and sulfonyl radicals. Examplary of these diphenolic compounds are 4,4'- sulfonyldiphenol, ,4'-(3,3' ,5,5 * tetramethyl) sulfonyl diphenol, ,4 * -diphenolsulfide and bis(4-hydroxphenyl) methane, ethane, propane or butane. The reaction between the cycloaliphatic epoxy resin and diphenolic compound is readily achieved. They need only be admixed and, desirably, heated to yield the present reaction product. Preferably, the admixture is heated to between about 100° and 180°C. This ensures rapid and complete reaction. The resultant solid product is an improved thermoset epoxy resin. This thermoset resin may be admixed with curing agent where it is to be utilized in conventional manner. hile there is no criticality as to the curing agent utilized, it is preferred to employ the combination of a metal acetylacetonate and a phenolic accelerator. This is particularly true where the composition is to be employed as a molding compound. In this embodiment of the present invention, such a curing agent imparts improved properties of storage stability with activatable rapid curing. The metal acetylacetonates of the present invention desirably have the following structural formula: wherein M is a metal ion and n is 1 to 4 corresponding to the valence number of the metal ion. They are characterized by the presence of solely metal to oxygen bonds. Included within the scope of the invention are metal acetylacetonates in which one or more hydrogen atoms of the methyl or methylene groups are substituted by a halogen atom or by a alkyl, aryl, or an alkaryl substituent. An example of a halogen-substituted metal acetylacetonate is a metal hexafluoroacetylacetonate or trifluoracetylacetonate. An example of an alkyl- substituted acetylacetonate is dipivaloyle hane in which the three hydrogen atoms on each of the methyl groups are substituted with a methyl group. The acetylacetonate hardeners of the present invention should not be confused with similar compositions containing a labile halogen atom. In the present compositions, the halogens, if present, are attached directly to a carbon atom of the methylene or methyl groups and are therefore extremely stable. Labile halogen atoms in epoxy resin curing agents normally form halogen acids, and the presence of such an ionic constituent in the cured resin would raise many problems, including poor electrical properties. Metal acetylacetonates in which the metal is aluminum, titanium, zinc or zirconium are a particularly preferred class of metal acetylacetonates within the scope of the OMPI Yλ invention. However, essentially any metallic acetyl¬ acetonate may be used, including aluminum, barium, beryllium, cadmium, calcium, cerous, chromic, cobaltic, cobaltous, cupric, ferric, ferrous, gallium, hafnium, indium, lead, lithium, magnesium, manganic, manganous, molybdenum,molybdenyl, nickel, palladium, platiu , potassium, rhodium,- tungstyl, uranyl, vandium,. vanadyl, zinc, and zirconium. Acetylacetonates of the rare earth elements, scandium, cerium, yttrium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium are known and can reasonably be expected to be useful in the practice of the present invention. The metal acetylacetonates are used in small catalytic quantities of from 0.01 to 5.0 percent, based upon the weight of the epoxy resin. Optimum results have been achieved with from 0.05 t * p 3.0 percent. It is important to note that the acetylacetonates of the invention are catalytic hardeners, which do not in a significant way become a part of the hardened epoxy molecule as do curing agents added in much larger or near stoichiometric amounts. Among the phenolic accelerators which can be effectively used in this invention are bisphenol A (i.e., 2,2-bis (4-hydrophenyl) propane) , pyrogallol, dihydroxydiphenyls as well as ortho-, meta- and para- hydroxbenzaldehydes, (such as salicylaldehyde) , catechol, resorcinol, hydro- quinone, " and phenol-formaldehyde and resorcinol-formal- dehyde condensates. Examples of other phenolic accelera- tors suitably employed in this invention also include halogenated phenols such as ortho-, meta- and para- chlorophenols or bromophenols and ortho-, meta-, and para- nitrophenols. The phenolic accelerator may be present in concentrations ranging from 0.1 to 30 percent ■ based on epoxy resin, with optimum cure rates being OMPI - produced with phenolic accelerator concentration between 0.5 and 10 percent by weight of the epoxy resin. As in the case of the acetylacetonate, the phenolics are added in relatively small amounts because they are accelerators or catalysts rather than curing agents of the stoichio- etric type which form a significant reaction with the epoxy resin and become a significant part of the epoxy molecule. Another preferred but optional component of the present compositions is a filler. Filler is again especially important where these compositions are to be utilized as molding compounds. The fillers of the present invention are generally chemically inert. They ordinarily will not react with any of the epoxy resins , metal acetylacetonate or accelerator. They instead function by stabilizing the physical properties of the molding compound, particularly during and after resin cure. Any conventional filler may be utilized in the present compositions. Representative fillers include: clays, like kaolin and calcined clays; silica, like novaculities, ground sand and amorphous glass; mica; talc; carbon black; alumina; and wollastonite. Alternatively or in addition, a structural filler may be employed. These fillers include such fibrous materials as glass fiber, mineral wool and the like which may provide enhanced product strength. The present compositions , particularly where utilized as molding compounds, should contain from about 10 to 95% filler by total weight. More preferably, from about 50 to 95% filler is utilized. This optimizes the advantages of the present invention. In preparing the present compositions, the various optional ingredients may simply be admixed with the epoxy resin/diphenolic compound reaction product, usually at ambient temperatures. In thereafter utilizing the present compositions, conventional techniques may be employed. For example, the solid composition may be compression or transfer molded. While under molding pressure, the composition should be heated, generally to from about 50 to 200°C. Under these conditions, curing may occur in minutes. Molded articles having virtually any configuration or size may be formed. In some preferred embodiments of the present invention, the present compositions may contain one or more further auxiliary components. For example, up to about 10%, desirably from 1 to 5%, by weight of epoxy resin of a flame retardant may be used. Most commercial retardants, including antimony oxide or .halogenated hydrocarbon may be utilized. Mold release agent such as wax, ordinarily in an amount of from 0.2 to 4% by weight of epoxy resin are also highly desirable. These and other components may simply be admixed with the composition prior to molding to obtain the benefits for which they are already known. The following examples are given by way of illustration only and are not intended as a limitation on the scope of this invention. Many variations are possible without departing from its spirit and scope. Unless otherwise specified herein, all proportions are provided on a weight basis. EXAMPLE I 180 grams of liquid cycloaliphatic resin (ERL 4234 having the structure of epoxycyclohexylspiroepoxy-cyclo- hexane dioxide) is heated to 140°C under mechanical agitation. 20 grams of 4,4'-sulfonyldiphenol is added to the hot resin under rapid stirring. The admixture Is maintained at 140°C for about 40 minutes and until its Brookfield viscosity reaches 560 centipoises. The admixture is then cooled to yield a slightly yellow transparent solid having a resin/diphenol equivalent ratio of about 7.8. EXAMPLE II The process of Example 1 is repeated utilizing the epoxy resin and diphenolic compound in an equivalent ratio of 16.25. Under similar conditions a Brookfield viscosity of 460 is reached after 320 minutes. Upon then cooling, the results were cimilar. • EXAMPLE III The process of Example 1 is repeated, substituting 4,4'-(3,3' ,5,5' tetramethyl) sulfonyl diphenol as the diphenolic compound. An equivalent ratio of 2.24 is employed. The reagents are maintained at 150°C for 3 hours. On cooling, the resin separates as a transparent, but dark straw-colored solid. EXAMPLE V The process of Example 3 is repeated substituting bisphenol A as the diphenolic compound. An equivalent ratio of about 2.5 is utilized. The .resultant reaction product is a transparent solid. EXAMPLE V 85 grams of liquid cycloaliphatic resin (ERL 4221) having the structure of epoxy cyclohexyl methylepoxy- cyclohexane carboxylate is heated to 150°C under mechanical agitation. 15 grams of 4, '-sulfonyl diphenol is added and the admixture is maintained for 15 minutes at 150°C. On cooling, a solid transparent resin having an equivalent ratio of about 5.3 is separated. EXAMPLE VI Using the resin reaction product produced in Example IV, a molding compound is produced by dry blending the following composition: Cycloaliphatic resin adduct 97 grams Aluminum acetylacetonate 1 gram Phenolic resin 3 grams Amorphous silica 300 grams Ester lubricant 1 gram The composition is then roll milled at 65°C for 3 minutes and then sheeted and chopped. The chopped composition is transfer molded at 175°C for 2 minutes and then tempered for an additional 4 hours. The molded article has the following properties. Hot rigidity (175°C) 12 mils Linear Shrinkage .004 in/in Glass transition temperature 180°C —fi- Coefficient of linear expansion, 17 x.10 " in-_/in./?e. These properties reflect the superiority of the present compositions as molding compounds, especially for encapsu¬ lation of electronic parts. The above mentioned patents and/or publications are incorporated herein by reference. Obviously, other modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that changes may be made in the particu¬ lar embodiments of the invention described which are within the full intended scope of the invention as defined by the appended claims. O...PI

Claims: ■ CLAIMS 1. A thermoset composition comprising the solid reaction product of a liquid cycloaliphatic/epoxy resin having more than one 1,2-epoxy group per molecule with an effective amount of a diphenolic compound. 2. The composition of Claim 1, wherein the diphenolic compound is a bisphenol compound. 3. The composition of Claim 1, wherein the epoxy resin and diphenol compound are reacted in an equivalent ratio of between 40:1 and 2:1. 4. The composition of Claim 1, wherein the diphenol compound has the formula: wherein X is selected from the group consisting of lower aliphatic sulfide and sulfonyl radicals. 5. The composition of Claim 1, which"additionally contains an effective amount of curing agent for the reaction product. 6. The composition of Claim 5, wherein the curing agent comprises the combination of metal acetylacetonate and phenolic accelerator. 7. The composition of Claim 5, which additionally contains from 10 to 95% by total weight of filler.

Inventors: ALLEN RICHARD BRIAN
Applicants: GEN ELECTRIC
Application year: 1982
Main classification: C08G59
IPC codes: C08G59, C09D163