IONIZING RADIATION CURING OF EPOXY RESIN SYSTEMS INCORPORATING CATIONIC PHOTOINITIATORS

Abstract: Mixtures of toughened epoxy resins with cationic initiators are curable under high energy ionizing radiation such as electron beam radiation, X-ray radiation, and gamma radiation. The composition of this process consists of an epoxy resin, a cationic initiator such as a diaryliodonium or triarylsulfonium salt of specific anions, and a toughening agent such as a thermoplastic, hydroxy-containing thermoplastic oligomer, epoxy-containing thermoplastic oligomer, reactive flexibilizer, rubber, elastomer, or mixture thereof. Cured compositions have high glass transition temperatures, good mechanical properties, and good toughness. These properties are comparable to those of similar thermally cured epoxies. A mixture of epoxy resins such as a semi-solid triglycidyl ether of tris (hydroxyphenyl) methane and a low viscosity bisphenol A glycidyl ether and a cationic photoinitiator such as a diaryliodonium salt is cured by irradiating with a dosage of electron beams from about 50 to about 150 kGy forming a cross-linked epoxy resin polymer.

Description: i IONIZING RADIATION CURING QF EPQXY RESIN SYSTEMS INCORPORATING 2 CATΓONTΓ PHOTOINΓΠ ATORS 3 This invention was made with Government support under contract DE-AC05- 5 84OR21400 awarded by the U.S. Department of Energy to Lockheed Martin Energy 6 Systems, Inc. and the Government has certain rights in this Invention. 7 s CROSS REFERENCE TO RELATED APPLICATION 9 This application is a continuation-in-part application under 37 C.F.R. § 1.53 of io U.S. Patent Application Serial No.08/507,569, filed July 26, 1995, the entire disclosure u of which is incorporated herein by reference. 12 i3 FIELD OF THE INVENTION i4 The present invention relates to a epoxy resin system and a method of curing is epoxy resins, more particularly, to a toughened epoxy resin system and a method of 16 curing epoxy resin systems containing cationic photoinitiators. 17 is BACKGROUND OF THE INVENTION i9 For the most part the polymerization or curing of monomers to high molecular 20 weight or highly cross linked polymers by means of high energy electron beam 2i radiation has been limited to a few general types of monomers. Monomers containing 22 acrylate and methacrylate groups have been extensively used as electron beam 23 curable coatings and adhesives. Monomers containing carbon-carbon double bonds, 1 such as vinyls, allenes, and dienes, are also known to be electron beam curable. 2 These monomers react by means of free radical mechanisms and under high energy 3 ionizing radiation such as electron beam require no free radical initiators. However, 4 these monomers tend to be toxic and expensive. Of greater concern is the fact that the 5 polymers produced by cross linking these materials are of limited value for many β applications. Such drawbacks include low glass transition temperature (or low service 7 temperature), low mechanical properties such as toughness, strength, and modulus, 8 and high shrinkage when cured. 9 What is desired is a means by which higher performance resins can be io processed and cured by means of electron beam radiation, and still achieve the same u thermal and mechanical properties as when thermally cured. A recent patent by i2 Aerospatiale (Eur. Pat. Appl EP 499,542) described a process by which bismaleimides i3 can be cured at ambient temperature by electron beam radiation to yield materials with i4 good mechanical properties and glass transition temperatures in excess of 300°C. is Coreactive diluents were added to the bismaleimides to make them processable at i6 lower temperatures. i7 Epoxy resins are much more widely used than bismaleimides although their is thermal properties are not quite as high. Epoxies are produced in hundreds of millions i9 of pounds annually and are widely used in a variety of applications (LV. McAdams and 20 J. A. Gannon, 'Epoxy Resin", Encyclopedia of Poh/mer Science and Technolog y . John 2i Wiley & Sons). A method of curing epoxy resins by means of electron beam radiation 22 would therefore be of considerable value. Visible-ultraviolet curing of thin films of 23 cycloaliphatic epoxies using a cationic initiator is well known (J Crivello, Advances in SUBSTITUTE SHEET (RULE 26> 1 Polvmer Science. Vol. 61 , p.1 , 1984). 2 However, these processes are limited to thin coatings due to the low penetration 3 of visible-ultraviolet radiation. Thermal and mechanical properties of these materials are low and curing is incomplete. There has been little reported success with the s electron beam curing of epoxies. Crivello (J. V. Crivello, M. Fan, and D. Bi:, Journal of 6 Applied Polvmer Science. Vol. 44, p.9, 1992; U.S. Pat. 5,260,349) has recently 7 disclosed a series of highly reactive cycloaliphatic siiicone epoxies which are electron 8 beam curable in the presence of certain cationic photoinitiators (diaryliodonium and 9 triarylsulfonium salts). Crivello further reported that cycloaliphatic epoxies and io conventional bisphenol A based epoxies cured poorly under the same conditions. u Massive doses of electron beam radiation were required. Others (R.S Davidson and S. 12 A. Wilkinson, Journal of Photochemistry and Photobioloqv A: Chemistry. Vol. 58, i3 p.123, 1991 and T. Okada, T. Asano, M. Hatada, J. Takezaki, and K. Ochi, Kobunshi 14 Ronbunshu, Vol.44, p. 761 , 1987) have also reported that examples of these same is types of photoinitiators do not lead to complete electron beam curing of certain i6 cycloaliphatic epoxies and bisphenol A based glycidyl ethers. Thermal postcuring is 17 required to achieve a more complete degree of cure. is The U.S. Patent Application, parent to this application, disclosed that i9 conventional epoxy resins can be fully cured at ambient temperature to high glass 20 transition temperatures (essentially the same or higher as with thermal curing). 2i Cationic initiators are also required for this process. The process also requires ionizing 22 radiation produced by an electron beam accelerator. The main difficulty associated 23 with the cured epoxy resins is that they are brittle. While much research has been 1 devoted to the toughening of thermally cured epoxies, there are no reports in the 2 literature of any means to toughen epoxies which are radiation cured using cationic 3 initiators. 4 Radiation cured epoxy resins incorporating cationic photoinitiators tend to be s very brittle. Resins for many structural and non-structural applications including 6 composites, adhesives, and coatings for use in aircraft, aerospace, marine, transportation, sporting goods, and other consumer products must have sufficient 8 toughness and impact resistance to endure many years of harsh service. What is needed is a means by which radiation cured cationic epoxies can be toughened and io still retain the good thermal and mechanical properties of the original composition. This li invention describes a variety of toughening agents which can be incorporated into the i2 epoxy resin initiator mixture. These toughening agents include thermoplastics, i3 hydroxy-containing thermoplastic oligomers epoxy-containing thermoplastic oligomers, i4 reactive flexibilizers, elastomers, rubbers, and mixtures thereof. An additional is advantage obtained by the use of low viscosity reactive flexibilizers is reduction of the 16 overall viscosity of the uncured resin mixture. Incorporation of one or more of these i7 toughening agents has resulted in increases in toughness of more than 230% over that is of the untoughened epoxy resin. 19 0 OBJECTS OF THE INVENTION 2i Accordingly, it is an object of the present invention to provide a method of curing 22 epoxy resin systems containing cationic photoinitiators and to provide a toughened 23 epoxy resin composition. It is an additional object of the present invention to provide a i method for making a toughened epoxy resin system from the toughened epoxy resin 2 composition. 3 Further and other objects of the present invention will become apparent from the 4 description contained herein. s SUMMARY OF THE INVENTION 6 In accordance with one aspect of the present invention, a new and improved 7 method of curing an epoxy resin system comprises the following steps: 8 Step 1. Provide a blend of an epoxy resin system. The epoxy resin system 9 comprises an epoxy resin and a cationic photoinitiator. The epoxy resin is selected from to th* group consisting oft glycidyl ethers of bisphenol A, epoxy phenolic novolacs, epoxy u cresol novolacs, bisphenol F epoxies, tetraglyάdyl ether of tetrakis (4-bydroxyphenyI) 12 ethane, diglyάdyl ether of 9, 9- bis (4-hydroxyphenyI) fluorene, glyάdyl ether of the 13 condensation product of dicydopentadiene and phenol, triglyάdyl ether of tris 14 (hydroxyphenyl) methane, 3',4'-epoxycydohexylmethyl 3,4-epoxycydohexanecarboxylate, is diglyddylester of hexahydrophthalic anhydride, bis (3,4-epoxycydohexylmethyI) adipate, 16 isomeric mixture of bis (2,3-epoxycydopentyI) ether, isomeric mixture of bis (2,3- 17 epoxycydopentyl) ether reacted with ethylene glycol, isomeric mixture of bis (2,3- 18 epoxycydopentyl) ether blended with a bisphenol A based glyάdyl ether, and mixtures 19 thereof. The cationic photoinitiator is sdected from the group consisting of: 20 diaryliodonium salts, triarylsulfonium salts, and mixtures thereof. The diaryliodonium 2i salts have the following formula: R. where R, and R 2 are sdected from the group consisting of: H, methyl, ethyl, n- propyl, isopropyl, n-butyl, tert-butyl, Cl, Br, OC B H 2 , +1 , OCH 2 CH(CH 3 )CJEϊ 2 . + „ OCH 2 CH(C 2 H 5 )C Ir H 2lI+1 , OCH 2 CH(OH)C B H 2a+I , OCH 2 C0 2 C lt H 2B+1> OCH(CH 3 )CO,C n H 2n+1 , OCH(C j H j )CO 2 C B H 2jl+ „ and mixtures thereof where n is an integer between 0 and 18. An ' is an anion selected from the goup consisting of: hexafluoroarsenate (AsF ( * ), hexafluoroantimonate (SbF c , hexafluorophosphate (FF 4 "), boron tetrafluoride (BF 4 , trifluoromethane sulfonate (€7 3 80 3 , and tetrakis (pentafluorophenylborate) (B FJ ), and mixtures thereof. The triarylsulf onium salts have the following formulas: Λ, -©- * r\ - Ar. " +S-©- * ■ © ■ { * A ' where R 3 is selected from the group consisting of: H, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, phenylsulfide (FhS), phenoxy (PhO), and mixtures thereof. An ' is an anion selected from the group consisting of: hexafluoroarsenate (AsF 4 " )» hexafluoroantimonate (SbF<")» hexafluorophosphate (P Y), boron tetrafluoride (BF ), trifluoromethane sulfonate (CFjSOj * ), and tetrakis (pentafluorophenylborate) (Bt FiUO, and mixtures thereof. 1 Step 2. Irradiate the blend with ionizing radiation to form a cross-linked epoxy 2 resin polymer. 3 In accordance with another aspect of the present invention, a new and improved 4 method of curing an epoxy resin system comprises the following steps: s Step 1. Provide a blend of an epoxy resin system. The epoxy resin system 6 comprises epoxy resins and a cationic photoinitiator. The epoxy resins are a blend of a 7 semi-solid epoxy, triglyddyl ether of tris (hydroxyphenyl) methane, and a low viscosity s epoxy, glycidyl ether of bisphenol A. The cationic photoinitiator is (4-octyloxyphenyI) 9 phenyliodonium hexafluoroantimonate. io Step 2. Irradiate the blend of an epoxy resin system with ionizing radiation to n form a crosslinked epoxy resin polymer. 12 In accordance with another aspect of the present invention, a new and improved 13 method of curing an epoxy resin system comprises the following steps: 14 Step 1. Provide a blend of an epoxy resin system. The epoxy resin system is comprises epoxy resins and a cationic photoinitiator. The epoxy resins are a blend of a 16 glycidyl ether of the condensation product of dicydopentadiene and phenol, and a low 17 viscosity epoxy, glycidyl ether of bisphenol A. The cationic photoinitiator is is (4-octyloxyphenyl) phenyliodonium hexafluoroantimonate. 19 Step 2. Irradiate the blend of an epoxy resin system with ionizing radiation to 20 form a crosslinked epoxy resin polymer. 2i In accordance with another aspect of the present invention, a new and improved 22 epoxy resin system comprises a blend of an epoxy resin and a cationic photoinitiator. 23 The epoxy resin is selected from the group consisting of: glyddyl ethers of bisphenol A, 24 epoxy phenolic novolacs, epoxy cresol novolacs, bisphenol F epoxies, tetraglyddyl ether 25 of tetrakis (4-hydroxyphenyl) ethane, diglycidyl ether of 9, 9- bis (4-hydroxyphenyI) 26 fluorene, glycidyl ether of the condensation product of dicydopentadiene and phenol, 27 triglyddyl ether of tris (hydroxyphenyl) methane, 3' ,4'-epoxycydohexylmethyl 3,4- 1 epoxycyclohexanecarboxylate, diglyddylester of hexahydrophthalic anhydride, bis (3,4- 2 epoxycydohexyhnethyl) adipate, isomeric mixture of bis (2,3-epoxycydopentyI) ether, 3 isomeric mixture of bis (2,3-epoxycydopentyl) ether reacted with ethylene glycol, isomeric 4 mixture of bis (2,3-epoxycydopentyl) ether blended with a bisphenol A based glyddyl s ether, and mixtures thereof. The cationic photoinitiator is sdected from the group 6 consisting of: diaryliodonium salts, triarylsulfonium salts, and mixtures thereof. The 7 diaryliodonium salts have the following formula: 8 9 16 17 is where R, and R 2 are seleded from the group consisting of: H, methyl, ethyl, n- 19 propyl, isopropyl, n-butyl, tert-butyl, CI, Br, OC H J . +J , OCH 2 CH(CH 3 )C It H 2 . +l , 20 OCH 2 CH(CjH 5 )C 11 H 2ll+ „ OCH 2 CH(OH)C„H 2 . +1 , OCHJCOJCfi^u 2i OCH(CH 3 )C0 2 C B H 2ll+I , OCH(C 2 H 5 )C0 2 CJH 2a+1 , and mixtures thereof where n is 22 an integer between 0 and 18. 23 An ' is an anion selected from the goup consisting of: hexafluoroarsenate (AsF^, 24 hexafluoroantimonate (SbF c , hexafluorophosphate (PF β ")» boron tetrafluoride 25 (BF 4 , trifluoromethane sulfonate (CFaSOj " ), and tetrakis 26 (pentafluorophenylborate) (BICjFJ , and mixtures thereof. 27 i The triaryisuifonium salts have the following formulas: 3 8 9 0 i where R 3 is selected from the group consisting of: H, methyl, ethyl, n-propyl, 2 isopropyl, n-butyl, tert-butyl, phenylsulfide (FhS), phenoxy (PhO), and mixtures 3 thereof. 4 An ' is an anion sdected from the group consisting of: is hexafluoroarsenate (AsF 4 "), hexafluoroantimonate (SbF t "), hexafluorophosphate 16 (PF c , boron tetrafluoride (BF/), trifluoromethane sulfonate (CFjSOjl, and 17 tetrakis (pentafluorophenylborate) (BIC^F^"), and mixtures thereof. is In accordance with another aspect of the present invention, a new and improved i9 toughened epoxy resin system mixture composition comprises an epoxy resin, a 20 cationic initiator, and a toughening agent. The cationic initiator is selected from the 2i group consisting of a diaryliodonium salt of a specific anion, a triaryisuifonium salt of a 22 specific anion and combination thereof. The toughening agent is selected from the 23 group consisting of a thermoplastic, hydroxy-containing thermoplastic oligomer, epoxy- 24 containing thermoplastic oligomer, reactive flexibilizer, rubber, elastomer, and mixtures 25 thereof. 26 in accordance with another aspect of the present invention, a new and improved 1 method for making a toughened epoxy resin system comprises the following steps: 2 Step 1. A toughened epoxy resin system mixture composition is provided. The 3 toughened epoxy resin system mixture composition comprises an epoxy resin, a 4 cationic initiator, and a toughening agent. The cationic initiator is selected from the 5 group consisting of a diaryliodonium salt of a specific anion, a triaryisuifonium salt of a specific anion and combination thereof. 7 Step 2. The toughened epoxy resin system mixture composition is exposed to 8 high energy ionizing radiation for a period of time sufficient to cure the epoxy resin 9 system forming a cured toughened epoxy resin system. io In accordance with another aspect of the present invention, a new and improved u method for making a toughened epoxy resin system mixture comprises the following 12 steps: i3 Step 1. A toughened epoxy resin system mixture composition is provided. The i4 toughened epoxy resin system mixture composition comprises an epoxy resin, a is cationic initiator, and a toughening agent. The cationic initiator is selected from the i6 group consisting of a diaryliodonium salt of a specific anion, a triaryisuifonium salt of a i7 specific anion and combination thereof. is Step 2. The toughened epoxy resin system mixture composition is exposed to 19 high energy radiation from the sun for a period of time sufficient to cure the epoxy resin 0 system forming a cured toughened epoxy resin system. 1 2 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 3 This invention describes toughened epoxy resins and a method thereof which 1 are cured or cross linked by means of radiation induced cationic polymerization. It was 2 found that conventional epoxy resins can be cured at, below, or above ambient 3 temperatures to high glass transition temperatures (essentially the same or higher as 4 with thermal curing), while still exhibiting the same mechanical properties. A cationic s initiator at a concentration of 0.25 to 10 parts per hundred of the epoxy resin is required 6 for this process. Upon irradiation by ionizing radiation the initiator produces a cationic 7 species (positively charged ion) which initiates the cationic cure of the epoxy resins. 8 The mechanism of the cationic curing of epoxies is well known (L. V. McAdams and J. 9 A. Gannnon, "Epoxy Resins", Encyclopedia of polymer Science and Engineering, John io Wiley and Sons). Ionizing radiation refers to high energy radiation such as X-rays, u gamma rays, and electron beam (e-beam) radiation. E-beam radiation as produced by 12 an accelerator is particularly useful. In addition, high energy radiation from the sun i3 and high energy ultraviolet radiation can be used. i4 Additional advantages obtained from this process are the lack of mechanical is stresses, which result from thermal curing, and reduced manufacturing expenses i6 related to faster curing times, lower energy requirements, and the elimination of 17 expensive thermal processing equipment. is Uses of the process of this invention include coatings, encapsulants for i electronic devices, adhesives, molded and cast parts, and laminates and composites 2o with fiber reinforcement. Unlike the cationic curing of epoxy resins with visible or 2i ultraviolet light, the use of a penetrating high energy electron beam to initiate the curing 22 reaction means that thick sections of material can be completely and uniformly cured. 3 Thus, thick composite parts can now be fabricated and cured at any temperature at or 1 above the glass transition temperature of the epoxy monomers in relatively short 2 periods of time with minimal residual mechanical stresses. 3 The primary problem associated with epoxy resins cured by this process is that 4 they are too brittle to be used for many applications. What is needed is a toughening s agent which can be added to the epoxy resin/initiator blend. Requirements of this 6 toughening agent are: that it be miscible with or form a stable suspension with the 7 epoxy resin/initiator composition; that it not interfere with the cationic curing 8 mechanism; and, that it not significantly reduce the thermal and mechanical properties 9 of the cured resin. There is no mention in the literature of any tougheners for use with io epoxy resins which are cured by means of ionizing radiation induced cationic li polymerization. A variety of toughening agents and flexibilizers have been used with 12 thermally cured epoxy resins, which typically use an amine coreactant or hardener for i3 cross linking. These tougheners include: rubbers or elastomers, either as discrete i4 particles or reacted with epoxy resin, epoxy functionalized flexibilizers, engineering is thermoplastics, and amine or hydroxy-terminated thermoplastic oligomers. However, i6 the utility of these materials in toughening epoxy resins cured by the previously i7 described process cannot be predicted. is Specifically, this invention relates to the radiation curing of an epoxy resin or i9 mixtures of epoxy resins (Part A) which contains an initiator (Part B), and a toughener 20 (Part C). 2i The epoxy resin (Part A) may be virtually any of a variety of commercially 22 available materials. The glycidyl ethers of various phenolic compounds are particularly 23 important. These include the glycidyl ethers of bisphenol A as given by the following 1 formula where n ranges from 0 to 12: 5 6 These resins are widely available from a number of manufacturers such as Shell 7 Chemical Company, DOW Chemical Company, and Ciba-Geigy Corporation in a 8 variety of molecular weights and viscosities. Examples include: D.E.R. 332, D.E.R. 9 330, D.E.R. 331 , D.E.R. 383, D.E.R. 661 , Tactix 123, Tactix 138, and Tactix 177 (DOW io trademarks); Epon 825, Epon 826, and Epon 828 (Shell trademarks); and, Araldite GY ιι 6008, Araldite GY 6010, and Araldite GY2600 (Ciba-Geigy trademarks). i 2 Additionally, flame retardant epoxy resins can be used including fiuorinated or 13 brominated bisphenol type epoxy resins, such as D.E.R. 542 and D.E.R.566-A80 from i4 DOW Chemical Company. is Another important class of glycidyl ethers are those of phenolic novolac and i 6 cresol novolac resins as given by the following formula where n ranges from 0 to 8: 17 21 22 For epoxy phenolic novolacs, R=H, and for epoxy cresol novolacs, R=CH 3 . For 23 bisphenol F epoxy resins R=H and the value of n is low (0 to 0.15). These materials are also widely available from a number of manufacturers in a variety of molecular weights and viscosities. Examples include Epon 862, Epon 155, SU-8 (Shell trademarks); D.E.R. 354, D.E.N. 431, D.E.N. 438, and D.E.N. 439 (DOW trademarks); and Araldite PY 306, Araldite EPN 1139, Araldite EPN 1138, Araldite GY281, Araldite GY 285, Araldite GY 302-2, Araldite LY 9703, Araldite XD 4955, and Araldite ECN 9511 (Ciba-Geigy trademarks). Several other polyfunctional glycidyl ethers are of significant importance for high performance applications i.e. heavy mechanical loads under conditions of high temperature and harsh environment. The materials include: The tetraglyddyl ether of tetrakis (4-hydroxyphenyl) ethane, which is commercially available as Epon 1031 (Shell Chemical trademark) and Araldite MT 0163 (Ciba-Geigy trademark). The diglycidyl ether of 9, 9- bis (4-hydroxyphenyl) fluorene is available as Epon HPT 1079 (Shell Chemical trademark). A glycidyl ether of the condensation product of dicydopentadiene and phenol is available as Tadix 556 (DOW Chemical trademark) as given by the following formula where n is approximately 0.2: The triglyddyl ether of tris (hydroxyphenyl) methane is available as Tadix 742 (DOW Chemical trademark) or as XD9053. These latter materials, Epon 1031, Epon HPT 1079, Tadix 556, Tadix 742 and XD9053, are either high viscosity liquids or solids at room temperature. Therefore it is β advantageous to blend these materials with a low viscosity bisphenol A or bisphenol F based diglycidyl ether or readive diluents. The resulting blends are less viscous at ambient temperatures and are more easily processed. Some heating may be required for adequate flow, but not temperatures high enough to cause thermal curing of the io epoxy group. Specific blends were found to have a good overall combination of low u viscosity in the uncured state and high glass transition temperature, flexural strength, i2 and modulus when cured. It was found to be particularly advantageous to blend a high i3 performance semi-solid epoxy such as Tadix 556, Tadix 742 or Epon HPT 1079 with a i4 low viscosity bisphenol A or bisphenol F based glycidyl ether epoxy such as Epon 862, is Tadix 123, or a readive diluent. i6 Cycloaliphatic epoxies represent another group of epoxies useful in the present i7 invention. They are usually low viscosity liquids at room temperature and can either be is used alone or as readive diluents in blends with the semi-solid glycidyl ether epoxies. i9 These materials include 3',4'-epoxycyclohexylmethyl 3,4- 20 epoxycyciohexanecarboxylate, which is available as ERL-4221 (Union Carbide 2i Corporation trademark) and Araldite CY-179 (Ciba-Geigy trademark); diglyddylester of 22 hexahydrophthalic anhydride which is available as CY 184 (Ciba-Geigy trademark); bis 23 (3,4-epoxycyclohexylmethyl) adipate, which is available as ERL-4299 (Union Carbide 1 trademark); the isomeric mixture of bis (2,3-epoxycyclopentyl) ether, which was once 2 available as ERL-4205 (Union Carbide trademark); ERL-4205 readed with ethylene 3 glycol or blended with a bisphenol A based diglycidyl ether, which were once available 4 from Union Carbide as ERLB-4617 and ERL-2258(Union Carbide trademarks), 5 respedively. 6 The epoxy resin (Part A) as just described may also be advantageously modified 7 by mixing with various additives. Such additives include glycols such as ethylene s glycol, propylene glycol, 1 ,3-butylene glycol, 1.4-butylene glycol, and other polyols. 9 Aromatic diphenols and polyphenolic compounds may also be used to modify the epoxy io resin. Other readive diluents, which contain vinyl, acrylate, or methacrylate may be ii employed to change readivity, glass transition temperature, or mechanical properties. 12 In addition, readive diluents based on monofundional or polyfundional glycidyl ethers i3 may also be used to reduce the viscosity or modify the resin systems. Additionally, i4 nonreadive diluents, such as acetone, have been found to be useful for reducing the is viscosity of the resin system which improves the processibility of the material before it is i6 cured for certain applications, such as solvent based prepreg. i7 The initiator (Part B) for the present invention is a material which produces a is positively charged species (cation) when subjeded to ionizing radiation. This positively i9 charged species must then be capable of initiating the cationic polymerization of the 20 epoxy (Part A). Much research has been devoted to the development of cationic 2i photoinitators (J.V. Crivello, Advances in Polvmer Science. Vol. 62, p. 1, 1984). 22 Cationic initiators read when subjeded to visible or ultraviolet light of a particular 23 wavelength to produce a cationic species, typically a Bronstead add. It was previously 1 determined that some of these initiators also read to generate cations when subjeded 2 to ionizing radiation. The behavior of these materials when subjeded to higher energy 3 ionizing radiation, such as produced by an eledron beam accelerator or a gamma cell, 4 cannot be predided. Diaryliodonium salts and triarylsulfonuim salts of certain anions s are particularly effective as initiators for the ionizing radiation induced cationic 6 polymerization of epoxies. Many examples of each have been reported and some are 7 commercially available. Almost all could be useful in the present invention. s Specific examples of diaryliodonium salts are given by the following formula, 9 where R, and R 2 are radicals such as H, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert- 10 butyl, Cl, Br, C^,, OC^,, OCH 2 CH(CH 3 )C n H 2lv . 1 , OCH^C^C^., i2 and mixtures thereof where n is an integer between 0 and 18: 13 14 IS Λ. 16 20 21 22 An " denotes the anion which may be hexafluoroarsenate (AsF β " ), 23 hexafluoroantimonate (SbF 6 " ), hexafluorophosphate (PF β * ), boron tetrafluoride (BF 4 " ), trifluoromethane sulfonate (CF 3 SO 3 " ), tetrakis (pentafluorophenylborate), (BtC β F^ " ), or tetrakis [3,5-bis(trifluoromethyl) phenyljborate (B[C 6 H 3 (CF 3 ) 2 1 4 " ). For example, OPPI of Tables 1-4 denotes (4-odyloxyphenyl) phenyliodonium hexafluoroantimonate (R, = H, R 2 = OC 8 H 17 , An " = SbF 6 " ). This initiator, which was obtained from General Eledric Corporation as Aryl Fluoroantimonate Produd 479-2092 as well as CD-1012 from the Sartomer Company were found to be particularly effedive with certain epoxy resins. However, initiators with other R,and R 2 substituents would be expeded to exhibit similar readivities. Specific examples of triaryisuifonium salts are given by the following formulas, where R 3 is H, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, phenylsulfide (PhS), phenoxy (PhO) and An " denotes the anion, which may be the same as those of the diaryliodonium salts: Examples of commercially available triaryisuifonium salts are Cyracure UVI-6974 and Cyracure UVI-6990 which are available from Union Carbide Corporation. These are mixtures of the triaryisuifonium salts given by the formulas where R 3 is phenylsulfide and An - are the hexafluoroantimonate and hexafluorophosphate anions, respedively. Degussa Corporation Degacure KI-85 and 3M Corporation FX-512 are both mixtures of triaryisuifonium hexafluorophosphate salts. 1 The toughener or flexibilizer (Part C) may be any of a variety of materials. High 2 molecular weight engineering thermoplastics are particularly effedive in increasing the 3 toughness of the radiation cured epoxy mixture as measured by fradure toughness 4 (K,^. Polysulfones such as Udel and Radel (Amoco Performance Produds, Inc.) can s be dissolved in the epoxy resin/initiator composition to form a viscous homogeneous 6 mixture. Toughness of the cured composition is significantly improved in comparison 7 with the untoughened epoxy resin (Examples 1 and 2, Table 1). Similar results were 8 obtained with a polyetherimide such as Ultem (General Eledric Company) as given by 9 Example 3. It is not necessary for the thermoplastic to be miscible with the epoxy io resin/initiator composition. The addition of Nylon 12 and Nylon 6/12 particles, Elf π Atochem Orgasol 2001 and Orgasol 3501 , respedively, resulted in improved fradure i2 toughness even though these materials were insoluble in the epoxy resin mixture, is Similar results were obtained using insoluble polyimide particles, Imitec X-902. Other i4 thermoplastics such as polyamideimides, poly(arylene ethers), polyesters, polyarytates, is polycarbonates, poiyurethanes, and others are potentially useful as Part C of the 16 present invention. Examples can be found in "Engineering Plastics," D. C. Clagett, 17 Encyclopedia of Polvmer Science and Engineering. John Wiley and Sons. is Engineering thermoplastics are typically endcapped with nonreadive fundional i9 groups. It may also be advantageous for the toughening agent of Part C to be a low 20 molecular weight segment or oligomer of a previously described engineering 2i thermoplastic, which contains fundional groups that are capable of readion with the 22 epoxy resin during radiation induced cationic polymerization. To this end hydroxy- 23 terminated polysulfone oligomers based on the Udel P-1700 polymer backbone were 19 SUBSTITUTE SHbtUrUJLE 26) 1 synthesized at various molecular weights (Example 4 and Table 1). These materials 2 are more easily blended with the epoxy resin/initiator mixture and the resulting 3 compositions are less viscous than with the same percentage of high molecular weight 4 polymer of similar backbone. These materials were also found to be very effedive in 5 increasing fradure toughness. Oligomers with other backbones could also be used, 6 particularly those of poly(arylene ethers), polyarylates, and polyester. Conceivably, the 7 oligomer backbone could be that of any of the previously referenced thermoplastics. 8 Readive groups are limited to those which read with the epoxy resin during cationic polymerization. These groups include hydroxy, epoxy, and carboxylate. io Flexible molecules which contain two or more epoxy groups represent a class of n material which is also useful as Part C of this invention. These compounds typically i2 contain long aliphatic groups which ad to reduce crosslink density in the cured epoxy 13 resin. In addition to increasing the fradure toughness of the cured epoxy resin, the i4 addition of low viscosity flexibilizers can also significantly reduce the overall viscosity of is the uncured epoxy resin/initiator/flexibilizer mixture. Specific examples are given in i6 Examples 5 and 6, and in Table 2. Useful flexibilizers include but are not limited to: i7 1 ,4-butanediol diglycidyl ether (Shell Heloxy Modifier 67), neopentlyglycol diglyddyl is ether (Shell Heloxy Modifier 68), cyclohexane dimethanol diglycidyl ether (Shell Heloxy i9 Modifier 107), trimethylol ethane triglyddyl ether (Shell Heloxy Modifier 44), 20 dibromoneopentyl glycol glycidyl ether (Shell Heloxy Modifier 56), propoxylated glycerol 2i poryglycidyl ether (Shell Heloxy Modifier 84), polypropylene glycol glyddyl ether (Shell 22 Heloxy Modifier 32), polyglycidyl ether of castor oil (Shell Heloxy Modifier 505), dimer 23 acid diglycidyl ester (Shell Heloxy Modifier 71), resorcinol diglycidyl ether (Rhone- 1 Poulenc Heloxy 69), epoxidized soybean oil (Elf Atochem Vikoflex 7170), epoxidized 2 linseed oil (Elf Atochem Vikoflex 7190, methyl epoxy soyate (Elf Atochem Vikoflex 3 7010), epoxidized propylene glycol dioleate (Elf Atochem Vikoflex 5075), epoxy ester 4 (Elf Atochem Vikoflex 4050), 1 ,2-tetradecane oxide (Elf Atochem Vikolox 14), internally 5 epoxidized 1,3-butadiene homopolymer (Elf Atochem Poly bd 600 and Poly bd 605), 6 diglycidyl ether, glycidyl glycidate, bis(2,3-epoxy-2-methylpropyl)ether, and 7 polyglycoldiepoxides (Dow Chemical DER 732 and DER 736). Flexible molecules s which contain two or more hydroxy groups are also useful as Part C of this invention. 9 These compounds also contain long aliphatic groups. Useful polyols include E- 10 caproladone triol (Union Carbide Tone 0301 , 0305, 0310). u Elastomers or rubbers may also be used as Part C. Examples of these materials i2 include, but are not limited to, the copolymers of styrene, butadiene, and ethylene or i3 styrene, butyiene, and ethylene (Shell Kraton rubber), butadiene, styrene copolymers, i4 the copolymer of butadiene and styrene, butyl rubber, neoprene rubber, and poly is (siloxanes). Fundionalized versions of these materials such as carboxyl terminated i6 poly (α - butylacrylate) rubber are particularly useful. Epoxy resins of Part A may be 17 readed with these materials to form an epoxy terminated elastomer which is useful as is Part C. Maleic anhydride terminated Kraton rubber (Shell Chemical - FG 1901X), and i9 epoxy fundionalized liquid Kraton rubbers (Shell Chemical - EXP-206 and EKP-207) 20 are especially useful as Part C. Specific examples are given in Examples 7 - 9 and in 2i Table 3. 22 It is also advantageous to blend the various types of tougheners or flexibilizers in 23 order to achieve toughness through different toughening mechanisms and to adjust the 1 overall viscosity of the uncured epoxy resin/initiatorΛoughener composition i.e. Parts A, 2 B, and C combined. A flexibilizer may be added to a mixture of a thermoplastic or 3 thermoplastic oligomer dissolved in an epoxy resin. Overall viscosity may be reduced 4 and toughness may be improved compared with using toughener or flexibilizer alone, s The thermoplastic may separate from the radiation cured epoxy to form a two phase 6 moφhology while the flexibilizer provides long flexible groups to conned crosslink sites 7 in the epoxy network. Specific examples are given in Table 4. s The following examples illustrate the formulation and curing of the toughened 9 epoxy mixtures. The invention is not limited to these examples, io Example 1 - 10% Udel P-1700 NT with Tadix 123 li Amoco Udel P-1700 NT Polysulfone (30 g) in pellet form was added to 270 g of 12 Dow Tadix 123 (high purity bisphenol A based glycidyl ether) in a three neck flask i3 equipped with a mechanical stirrer, nitrogen inlet, and a thermocouple probe. The i4 mixture was stirred under nitrogen at approximately 150°C until the thermoplastic is dissolved to form a high viscosity solution (24 h). The temperature of the solution was i6 reduced to approximately 90°C and 9.00 g of (4-octyloxyphenyl)phenyliodonium i7 hexafluoroantimonate, OPPI, was added to the stirred mixture. Mixing was complete is after 0.5 h. At 60°C the vicosity of the mixture was 7300 cp. The mixture was i9 degassed under vacuum at approximately 80°C, poured hot into aluminum molds, and 20 the specimens irradiated using an eledron beam accelerator (Energy, 10 MeV; Power, 2i 1 kW). Specimens were irradiated in three passes of 50 kGy per pass for a total 22 dosage of 150 kGy. Fradure toughness (K 1c ) as determined according to ASTM E399 23 was 0.680 MPa m 12 at 25°C and 0.899 MPa m 12 at -100°C. Glass transition 1 temperature (Tg) as determined by Dynamic Mechanical Analysis (DMA) was 168°C 2 (peak, Tan delta curve) and 156°C (peak, loss modulus curve, G"). Flexural modulus 3 was estimated by DMA to be 2.94 GPa at 25°C. The temperature at which the 4 modulus was 50% of the 25°C value was 132°C (initial service temperature). After 48 h s in boiling water the specimens absorbed 1.25% moisture. 6 Example 2 - 20% Radel A-200NT with Tadix 123 7 Amoco Radel A-200 NT (60 g) in pellet form was dissolved in approximately 300 s mL of methylene chloride. The Radel solution was mixed at room temperature with 240 9 g of Dow Tadix 123 (mixture complete in 1-2 h with stirring) and the methylene chloride io removed under vacuum at 90°C (approximately 0.5 h). OPPI (9 g) was added and u dissolved in the stirred mixture at 90°C (approximately 0.5 h). Viscosity of the mixture i2 at 60°C was 24,000 cp. Specimens were cured as described in Example 1. Fradure 13 toughness was determined to be 0.494 and 0.612 Mpa m 12 at 25 β C and -100°C, i4 respedively. Glass transition temperature was 168°C (Tan delta) and 143°C (G"). is Flexural modulus was 2.68 GPa at 25°C with an initial service temperature of 129°C. i6 Water absorption after 48 h water boil was 1.37%. 17 Example 3 - 10% Ultem 1000 with Tadix 123 is General Eledric Ultem 1000-1000 polyetherimide (60 g) in pellet form was i9 dissolved in approximately 300 mL of methylene chloride. The Ultem solution was 20 mixed at room temperature with 540 g of Dow Tadix 123 (mixture complete in 1-2 h 2i with stirring) and the methylene chloride removed under vacuum at 90 β C. OPPI (18 g) 22 was added and dissolved in the stirred mixture at 90°C (approximately 0.5 h). 23 Specimens were cured as described in Example 1. Fradure toughness was 0.696 and 23 T 1 0.877 MPa m 1/2 at 25°C and -100°C, respedively. Glass transition temperature was 2 175°C (Tan delta) and 157°C (G"). Flexural modulus was 3.07 GPa at 25°C with an 3 initial service temperature of 136°C. Water absorption after 48 h water boil was 1.37%. 4 Exam p le 4 -30% Hydroxy-Terminated Polysulfone Oligomer (Mn, 6000 g/mole) 5 with Tadix 123 6 Hydroxy-terminated polysulfone oligomers were prepared according to a method 7 described in the literature [J. E. McGrath, T. C. Ward, E. Shehori, and A. J. Wnuk, s Polvm. Eng. Sci. 17. 647 (1977)]. The following example illustrates the preparation of a hydroxy-terminated polysulfone oligomer with a calculated molecular weight (Mn) of io 6000 g/mole, based on a stoichiometric imbalance (r=0.929) using excess hydroxy- n containing monomer. This example further illustrates the use of this material to i2 toughen a bisphenol A based glycidyl ether mixture which was cured by means of i3 eledron beam radiation. 2,2-Bis (4-hydroxyphenyl) propane, (bisphenol A), (228.29 g, 14 1.000 mole), bis (4-chlorophenyl) sulfone (266.78, 0.929 mole), powdered anhydrous is potassium carbonate (282.5 g, 2.044 mole), N,N-dimethylacetamide (1173 mL), and i6 toluene (125 mL) were added to a 2 L three necked flask equipped with a i7 thermocouple, nitrogen inlet, mechanical stirrer, and a Dean-Stark trap topped by a is reflux condenser. With heating provided by a heating mantle the stirred mixture was i9 slowly heated to approximately 140°C under an atmosphere of flowing nitrogen. Water 2o was removed over a period of several hours, then the toluene was removed through the 2i Dean-Stark trap and the temperature of the readion mixture allowed to reach 155°C. 22 The readion mixture was maintained at 155°C overnight (20 h), cooled to 23 approximately 100°C, and filtered through a fritted glass funnel. The filtrate was 1 acidified by the addition of glacial acetic acid (57 mL, 1.00 mole) mixed with 200 mL of 2 N,N-dimethylacetamide and precipitated into a total of 4-5 L of water in a blender. The s precipitated polymer was colleded by filtration, washed with water, and dried in air at 4 105°C and under vacuum at 90°C. Yield of hydroxy-terminated polysulfone oligomer 5 was 423.8 g (99.2% yield). Glass transition temperature as determined by Differential 6 Scanning Calorimetry was 169°C and inherent viscosity was 0.13 dlJg at 0.5% 7 concentration in chloroform at 25°C. The hydroxy-terminated polysulfone oligomer (90 s g) was added to 210 g of Dow Tadix 123 and the mechanically stirred mixture heated 9 at 120-130°C until the polysulfone oligomer dissolved (1-2 h). The temperature of the io solution was reduced to approximately 90°C and OPPI (9 g) added to the stirred u mixture. After 0.5 h mixing was complete. Viscosity of the solution was 29,000 cp at i2 60°C. Specimens were cured as described in Example 1. Fradure toughness was i3 0.705 and 1.114 MPa m 1Λ at 25 and -100°C, respedively. Glass transition temperature i4 was 161 °C (Tan delta) and 149°C (G"). Flexural modulus was 3.02 GPa at 25°C with is an initial service temperature of 134 β C. The percent weight gain after 48 hour water 16 boil was 1.64%. 17 Example 5 10% Vikoflex 7170 with Tadix 123 is Elf Atochem ATO Vikoflex 7170 (epoxidized soybean oil), (60 g), OPPI (18 g), i and Dow Tadix 123 (540 g) was mixed at approximately 80°C. Viscosity of the solution 20 was 3600 cp at 24°C. Specimens were cured as described in Example 1. Fradure 2i toughness was 0.598 and 0.752 MPa m 12 at 25 and -100°C, respedively. Glass 22 transition temperature was 151 °C (Tan delta) and 133°C (G"). Flexural modulus was 23 2.79 GPa at 25°C with an initial service temperature of 117°C. Water absorption after 1 48 h water boil was 2.02%. 2 Example 6 10% Elf Atochem ATO Poly bd 600 with Tadix 123 3 Elf Atochem ATO Poly bd 600 VM 312051 (internally epoxidized 1 ,3-butadiene 4 homopolymer), (60 g), OPPI (18 g), and Dow Tadix 123 (540 g) was mixed at 5 approximately 80°C. Viscosity of the solution was 6120 cp at 24°C. Specimens were 6 cured as described in Example 1. Fradure toughness was 0.594 MPa m 1/2 and 0.463 7 MPa m 1/2 at 25°C and -100°C, respedively. Glass transition temperature was 166°C s (Tan delta) and 151 β C (G"). Flexural modulus was 2.68 GPa at 25°C with an initial 9 service temperature of 123°C. Water absorption after 48 h water boil was 1.28%. io Example 7 10% Paraloid EXL-2330 with Tadix 123 u Rohm and Haas Paraloid EXL-2330 methacry late-butadiene core shell rubber i2 (30 g) was stirred overnight with 30 g of acetone. The suspension was mixed with Dow i3 Tadix 123 (270 g) at room temperature and the acetone removed under vacuum at 14 approximately 80°C. OPPI (9 g) was added with mixing at 80°C until it was in solution is (0.5 h). Specimens were cured as described in Example 1. Fradure toughness was i6 0.585 MPa m 1/2 at 25°C. Glass transition temperature was 132 β C ( Tan delta) and i7 132°C (G"). Flexural modulus was 2.69 GPa at 25°C with an initial service is temperature of 109°C. Water absorption after 48 h water boil was 2.59%. 19 Example 8 30% Dow XU 71790.04L with Tadix 123 and Tadix 556 (28:42) 20 Dow XU 71790.04L (bisphenol A based glycidyl ether readed with acrylic 2i rubber), (90 g), Dow Tadix 123 (84 g), Dow Tadix 556 (126 g), and OPPI (9 g) was 22 mixed at approximately 90°C. Specimens were cured as described in Example 1. 23 Fradure toughness was 0.411 MPa m 1/2 and 0.520 MPa m 12 at 25 and -100°C, 1 respedively. Glass transition temperature was 176°C (Tan delta) and 161 β C (G"). 2 Flexural modulus was 2.48 GPa at 25°C with an initial service temperature of 137°C. 3 Water absorption after 48 h water boil was 2.22%. 4 Example 9 10% Kraton FG 1901 X with Tadix 123 s Shell Kraton FG 1901X, a styrene-ethylene/butylene-styrene block copolymer 6 terminated with maleic anhydride, (60g) was dissolved in 300 mL of toluene. The 7 Kraton solution was added to 540g of Dow Tadix 123 and the mixture stirred overnight s at approximately 60°C. Toluene was removed under vacuum at approximately 90°C. 9 OPPI (18g) was added and dissolved in the stirred mixture at 90°C (approximately 0.5 io hour). The final mixture was a milky white suspension with a viscosity of 1100 cPs at u 60°C. Specimens were cured as described in Example 1. Fradure toughness was i2 determined to be 0.92 MPa m 1/2 at 25°C and 1.224 Mpa m 1/z at -100 β C. Glass i3 transition temperature was 171 °C (Tan delta). The temperature at which the flexural i4 modulus drops to one-half its value from 25°C was 131 °C. is In addition to solvent mixing, Kraton FG 1901X was also mechanically blended i6 into the epoxy resin by using a Silverson high shear mixer/emulsifier. The solid rubber 17 was blended into the epoxy at approximately 7000 RPM for 0.5 hour at 190-200°C. is Additionally, it is expeded that the toughened resin system may be reinforced i9 with fibers which may include carbon, graphite, glass, aramid, polyethylene, or other 20 reinforcement fibers to form a composite. Fillers such as clay, minerals, glass particles, 2i silica particles, alumina particles, aluminum powder and other inert materials may also 22 be added. 23 Mechanical, thermal, and physical properties for eledron beam cured carbon- SUBSTITUTi ' feHEET (RULE 26) 1 fiber-reinforced composite laminates, incorporating some of the above described 2 toughened epoxy resin systems as well as examples of some untoughened epoxy resin 3 systems, are described in Table 5 and Table 6. These properties include those tested 4 at room temperature as well as those determined after cycling several times from low 5 temperatures (-194°C or -79°C) to elevated temperatures (121 β C). 6 The impetus for developing Eledron Beam (EB) curing of polymer matrix 7 composites (PMCs) that incorporate toughened epoxy resins is based primarily on 8 reducing the manufaduring costs and cycle times in comparison with traditional thermal curing processes. One of the primary cost drivers in manufaduring with PMCs, and to one of the elements having the greatest effed on quality and performance, is the it standard thermal cure process. Thermal cure of PMCs requires relatively long cure i2 times and high-energy consumption, creates residual thermal stresses, produces 13 volatile toxic by-produds during cure, requires the use of hardeners (curing agents) i4 which limit the shelf life of the resin system, requires resin systems to be stored and is transported under low temperature conditions before cure, and requires expensive i6 tooling that is tolerant to high temperatures (i.e., 250 to 750°F). 17 EB curing is a nonthermal curing method that uses high-energy, high-power is eledrons to initiate polymerization and cross-linking readions at controlled rates in EB i9 curable materials to enhance specific physical, mechanical, and chemical properties. 2o EB curing can eliminate or reduce many of the shortcomings of thermal curing and 2i facilitate technical developments that are presently unachievable utilizing thermal curing 22 technology. 23 Four advantages are offered by EB curing compared to traditional Thermal 1 Curing: 2 Lower Manufaduring Costs: resulting from faster cures, lower energy 3 consumption, the ability to use lighter and lower cost tooling, simplified transportation 4 and storage of resin systems, and easier waste cleanup after fabrication. 5 Simplified Processing: resulting from seledable cure temperatures, minimal part 6 and tool thermal mismatches, uniform and efficient cross-linking, unlimited resin pot life, 7 elimination of hardeners in the resin system, redudion in resin viscosity variations, s greater material integration flexibility, in-situ fabrication and curing capability, ability to cure parts up to about 12-inches thick, no part size limitations, and its ability to be io retrofittable to traditional fabrication methods (i.e., automated tape and tow and fiber u placement, filament winding, pultrusion, resin transfer molding). 12 Environmentally Friendly: because it reduces toxic and volatile emissions and i3 minimizes the use of solvents normally required for waste clean-up operations. i4 Improved Produd Performance: by lowering residual and internal stresses, is improving dimensional part quality, and the ability to tailor the material properties by 16 controlling the cure depth and the degree of cure. i7 This subjed invention provides the user an almost unlimited number of epoxy is resin systems, incoφorating epoxy resins, cationic initiators, and toughening materials i 9 and combinations thereof, to choose from which meet the necessary performance 20 requirements for given applications. 2 i The benefits of PMCs have long been recognized for high-performance 22 applications, but American industry has not capitalized on the advantages of these 23 materials because large-scale manufaduring of PMCs is cost prohibitive. One of the i primary cost drivers in manufaduring PMC parts and strudures is the manufaduring 2 cycle times required to cure the materials. By utilizing these toughened EB-curable 3 materials discussed in this subjed invention one can dramatically shorten the 4 manufaduring time for producing these materials, thereby greatly improving the s affordability and use of PMCs in many areas of the commercial sedor, including 6 aircraft, aerospace, automotive, marine, sporting goods, infrastrudure, and construdion 7 industries. 8 Many companies involved in the manufadure of aircraft and aerospace produds, automobiles, chemicals, adhesives, polymer matrix composites, marine io produds, reinforcement fibers, oil drilling platforms, and eledron beam accelerators are u extremely interested in this technology area. 12 The toughened epoxy materials described in this invention also have enormous i3 potential for reducing the final cost and improving the performance for produds used in i4 applications such as thick and thin coatings; tooling for manufaduring PMCs; is encapsulants for eledronic devices; adhesives for bonding PMCs, metals, ceramics, i6 and other materials; and for manufaduring molded and cast parts. 17 This invention describes a method or process by which conventional epoxy resins is can be cured (crosslinked) by the application of ionizing radiation. The currently used 19 thermal processes for curing epoxies with an amine, anhydride, or other coreactive 20 curing agent or with a catalyst require that the mixture be heated above its final glass 2i transition temperature. For many resin mixtures this may require a complex heating 22 cycle which may reach temperatures as high as 150 - 300° C. If not completely cured the 23 resin suffers from poor mechanical properties. The process of this invention allows the 24 epoxy resin to be rapidly cured to a high glass transition temperature (essentially the 1 same or higher in some cases as with thermal curing) at any temperature at or above the 2 glass transition temperature of the epoxy monomers, while still exhibiting the same 3 mechanical properties. Additional advantages obtained from this process are the lack of 4 mechanical stresses, which result from thermal curing, and reduced manufacturing s expenses related to faster curing times, lower energy requirements, and the elimination of 6 expensive thermal processing equipment. This process is potentially useful in the 7 manufacture and application of coatings, encapsulants, adhesives, and composite 8 matrices. 9 Specifically, this invention relates to the radiation curing of an epoxy resin or o mixtures of epoxy resins (Part A) which contains an initiator (Part B). When the initiator i is subjected to ionizing radiation a cationic species (positively charged ion) is produced 2 which initiates the cationic cure of the epoxy resin. The mechanism of the cationic curing 13 of epoxies is well known (L.V. McAdams and J.A. Gannon, "Epoxy Resins", 14 Encyclopedia of Polymer Science and Technology, John Wiley & Sons). is Ionizing radiation refers to high energy radiation such as x-rays, gamma rays, and 16 electron beam (e-beam) radiation. Electron beam radiation as produced by an 17 accelerator is particularly useful. is The epoxy resin (Part A) may be virtually any of a variety of commercially 19 available materials. The glycidyl ethers of various phenolic compounds are particularly 20 important. These include the glycidyl ethers of bisphenol A as given by the following 2i formula where n ranges from 0 to 12: 22 26 27 These resins are widely available from a number of manufacturers such as Shell Chemical Company, DOW Chemical Company, and Ciba-Geigy Corporation in a variety of molecular weights and viscosities. Examples include: D.E.R. 332, D.EJL 330, D.E.R. 331, D.E.R. 383, Tactix 123, Tactix 138, and Tactix 177 (DOW trademarks); Epon 825, Epon 826, and Epon 828 (SheU trademarks); and, Araldite GY 6008, Araldite GY 6010, and Araldite GY 2600 (Ciba-Geigy trademarks). Another important class of glycidyl ethers are those of phenolic novolac and cresol novolac resins as given by the following formula where n ranges from 0 to 5: For epoxy phenolic novolacs, R=H, and for epoxy cresol novolacs, R=CH 3 . For bisphenol F epoxy resins R=H and the value of n is low (0 to 0.15). These materials are also widely available from a number of manufacturers in a variety of molecular weights and viscosities. Examples include Epon 862, Epon 155 (Shell trademarks); D.E.R. 354, D.E.N. 431, D.E.N. 438, and D.E.N. 439 (DOW trademarks); and Araldite PY 306, Araldite EPN 1139, Araldite EPN 1138, Araldite GY 281, Araldite GY 285, Araldite GY 302-2, Araldite LY 9703, Araldite XD 4955, and Araldite ECN 9511 (Ciba-Geigy trademarks). Several other poiyfunctional glycidyl ethers are of significant importance for high performance applications i.e. heavy mechanical loads under conditions of high temperature and harsh environment. The materials include: The tetraglyddyl ether of tetrakis (4-hydroxyphenyI) ethane, which is commercially available as Epon 1031 (Shell Chemical trademark) and Araldite MT 0163 (Ciba-Geigy trademark). The diglycidyl ether of 9, 9- bis (4-hydroxyphenyI) fluorene is available as Epon HPT 1079 (Shell Chemical trademark). A glycidyl ether of the condensation product of dicydopentadiene and phenol is available as Tactix 556 (DOW Chemical trademark) as given by the following formula where n is approximately 0.2: The triglyddyl ether of tris (hydroxyphenyl) methane is available as Tactix 742 (DOW Chemical trademark). These latter materials, Epon 1031, Epon HPT 1079, Tactix 556, and Tactix 742, are either high viscosity liquids or solids at room temperature. Therefore it is advantageous to blend these materials with a low viscosity bisphenol A or bisphenol F based glyddyl ether. The resulting blends are less viscous at ambient temperatures and are more easily processed. Some heating may be required for adequate flow, but not temperatures high enough to cause thermal curing of the epoxy group. Cydoaliphatic epoxies represent another group of epoxies useful in the present invention. They are usually low viscosity liquids at room temperature and can either be used alone or as reactive diluents in blends with the semi-solid glyddyl ether epoxies. These materials indude 3',4'-epoxycyclohexylmethyI 3,4-epoxycydohexanecarboxylate, which is available as ERL-4221 (Union Carbide Corporation trademark) and Araldite CY 1 179 (Ciba-Geigy trademark); diglyddylester of hexahydrophthalic anhydride which is 2 available as CY 184 (Ciba-Geigy trademark); bis(3,4-epoxycyclohexylmethyl) adipate, 3 which is available as ERL-4299 (Union Carbide trademark); the isomeric mixture of bis 4 (2,3-epoxycydopentyl) ether, which was once available as ERL-4205 (Union Carbide s trademark); ERL-4205 reacted with ethylene glycol or blended with a bisphenol A based 6 glycidyl ether, which were once available from Union Carbide as ERLB-4617 and 7 ERL-2258 (Union Carbide trademarks), respectively. s The epoxy resin (Part A) as just described may also be advantageously modified by 9 mixing with ten percent or less of various additives. Such additives indude glycols sudi as io ethylene glycol, propylene glycol, 1,3-butylene glycol, 1 ,4-butylene glycol, and other u polyols. Aromatic diphenols and polyphenolic compounds may also be used to modify the 12 epoxy resin. Other reactive diluents, which contain vinyl, acrylate, or methacrylate may 13 be employed to increase reactivity, glass transition temperature, or mechanical 14 properties. In addition, reactive diluents based on monofunctional or polyfunctional is glycidyl ethers may also be used to reduce the viscosity or modify the resin systems. 16 The most useful application of this invention lies in the blending of two or more of 17 the Part A epoxy resins in order to optimize overall resin viscosity for ease of processing. is Resin blending may also be used to enhance the thermal and mechanical properties of the 19 cured resin. 20 Specific blends were found to have a good overall combination of low viscosity in 2i the uncured state and high glass transition temperature, flexural strength, and modulus 22 when cured. It was found to be particularly advantageous to blend a high performance 23 semi-solid epoxy such as Tactix 556, Tactix 742 or Epon HPT 1079 with a low viscosity 24 bisphenol A or bisphenol F based glycidyl ether epoxy such as Epon 862. Specific 25 examples are listed in Tables 7-9. A description of the materials are listed in Table 10. 26 (4-Octyloxyphenyl) phenyliodonium hexafluoroantimonate (OPPI) at concentrations of 27 one and three parts per hundred of the epoxy blend was used as the initiator although 1 any of the initiators described as Part B could potentially be used at concentrations 2 ranging from 0.25 to 10 parts per hundred of active initiator. Ionizing radiation was 3 provided by an electron beam accelerator (Energy 10 MeV; Power, 1 kW). Specimens 4 were irradiated in single or multiple passes. Total dosage received by the specimens s ranged between 50 and 150 kGy, although possible curing dosages of between 10 and 500 6 kGy could be used. Accelerators with different energy and power levels could also be 7 used. X-ray or gamma sources could also be used as the source of ionizing radiation. s While the cured resins exhibit good thermal and mechanical properties they tend, 9 like most epoxies, to be somewhat brittle. It is envisioned that this short-coming will be io overcome by the addition of toughening agents to the resin system (Part A plus Part B). u Toughening agents such as elastomeric microspheres and thermoplastics (e.g. polyarylene 12 ethers, polysulfones and polyimides) may be added in concentrations ranging from 2 to 13 40 percent of the resin system. Three different resin systems containing three different 14 molecular weights of hydroxy-terminated polyether sulfone having molecular weights of is 2650, 5360, or 8890 g/mole at 20% loading each were added to Dow's Tactix 123 resin 16 containing 3 phr of OPPI and electron beam cured at 150 kGy to toughen the resin π system. Results indicate that all three of these resin systems approximately doubled the is K, c values compared to the control resin system (Control - Tactix 123 with 3 phr OPPI; 19 cured at 150 kGy with no added toughening agent) which had a value of 352 psi»in βJ 20 compared to values of 637, 665, and 672 psi-in" for the 2650, 5360, and 8890 molecular 2i weights, respectively of the hydroxy-terminated thermoplastic material. Additionally, it 22 is expected that the resin system may be reinforced with fibers which may indude 23 carbon, glass, aramid, polyethylene, or other reinforcement fibers to form a composite. 2 Fillers such as clay, minerals, and other inert materials may also be added. 25 Uses of the process of this invention indude coatings, encapsulants for electronic 26 devices, adhesives, molded and cast parts, and laminates and composites with fiber 27 reinforcement. Unlike the cationic curing of epoxy resins with visible or ultraviolet light, 1 the use of a penetrating high energy electron beam to initiate the curing reaction means 2 that thick sections of material can be completely and uniformly cured. Thus, thick 3 composite parts can now be fabricated and cured at any temperature at or above the 4 glass transition temperature of the epoxy monomers in relatively short periods of time s with minimal residual mechanical stresses. 6 The initiator (Part B) for the present invention is a material which produces a 7 positively charged spedes (cation) when subjected to ionizing radiation. Tnis positively 8 charged species must then be capable of initiating the cationic polymerization of the 9 epoxy (Part A). Much research has been devoted to the development of cationic io photoinitators (J.V. Crivello, Advances in Polymer Science, Vol. 62, p. 1, 1984). u Cationic photoinitiators react when subjected to visible or ultraviolet light of a particular 12 wavelength to produce a cationic species, typically a Bronstead add. The behavior of 13 these materials when subjected to higher energy ionizing radiation as produced by an 14 - electron beam accelerator or a gamma cell cannot be predicted. is In order to determine which, if any, of the many commercially available and 16 noncommercially available cationic photoinitiators were effective when subjected to 17 ionizing radiation, a variety of cationic photoinitiators were evaluated using a "Co is gamma cell. The photoinitiator at a concentration of one part per hundred active 19 materials was mixed with each of a variety of epoxy resins. The mixture was then placed 20 in a gamma cell at a dose rate of 100 Gy per minute. The temperature increase 2i (exotherm of the curing reactions) of the sample versus that of an inert reference material 22 (water or cured resin) was measured (Tables 8 and 9). The dose at the exotherm peak 23 and the effect of gamma radiation (total dosage, up to approximately 25 kGy) on the 24 resins are listed. Some liquid resins in combination with certain initiators exhibited large 25 exotherms and crosslinked to form hard cured materials. Other combinations exhibited 26 little or no temperature increase and only small viscosity increases. This behavior could 27 not have been predicted. From the Tables 7-10 it is dear that diaryliodonium salts and triarylsulfonuim salts of certain anions are particularly effective as initiators for the ionizing radiation induced cationic polymerization of epoxies. Many examples of each have been reported and some are commercially available. Almost all could be useful in the present invention. Specific examples of diaryliodonium salts are given by the following formula, where R, and R 2 are radicals such as H, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert- butyl, Cl, Br, OC-H^,, OCH 2 CH(CH 3 )C I1 H 2ll+1 , OCH 2 CH(C^H s )C H ta+1 , OCH 2 CH(OH)C B H 2lI+1 , OCH J CO J C-H J ^,, OCH(CH 3 )C0 2 C,H 2 , +1 , OCH(C 2 H 5 )C0 2 C n H 2 , + „ and mixtures thereof where n is an integer between 0 and 18: R, 1 * Λ„- An ' denotes the anion which may be hexafluoroarsenate (AsF β , hexafluoroantimonate (SbF ( , hexafluorophosphate (PF t " ), boron tetrafluoride (BF 4 " ), trifluoromethane sulfonate (CFjSO j "), or tetrakis (pentafluorophenylborate), For example, OPPI of Tables 7-10 denotes (4-octyloxyphenyI) phenyliodonium hexafluoroantimonate (R, = H, R 2 = OC, H 17 , An' = SbF ). This initiator, which was obtained from General Electric Corporation as Aryl Fluoroantimonate Product 479-2092 was found to be particularly effective with certain epoxy resins. However, initiators with other R j and R 2 substituents would be expected to exhibit similar reactivities. Specific examples of triaryisuifonium salts are given by the following formulas, where R 3 is H, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, phenylsulfide (PhS), or phenoxy (PhO) and An ' denotes the anion, which may be the same as those of l the diaryliodonium salts: 2 In Table 10, 6974 and 6990 refer to Cyracure UVI-6974 and Cyracure UVI-6990, which were obtained from Union Carbide Corporation. These are mixtures of the 2 triaryisuifonium salts given by the formulas where R 3 is phenylsulfide and An ' are the 3 hexafluoroantimonate and hexafluorophosphate anions, respectively. KI-85 and FX-512 4 in Table 9 denote Degussa Corporation Degacure KI-85 and 3M Corporation FX-512, 5 respectively. These materials are both mixtures of triaryisuifonium hexafluorophosphate 6 salts. 7 Table 7 lists glass transition temperatures and flexual moduli for various resin s systems (Part A plus Part B) after curing by electron beam radiation. 19 The impetus for developing Electron Beam (EB) curing of polymer matrix 0 composites (PMCs) that incorporate epoxy resins is based primarily on reducing the i manufacturing costs and cycle times in comparison with traditional thermal curing 2 processes. One of the primary cost drivers in manufacturing with PMCs, and one of the 3 elements having the greatest effect on quality and performance, is the standard thermal 24 cure process. Thermal cure of PMCs requires relatively long cure times and high-energy 25 consumption, creates residual thermal stresses, produces volatile toxic by-products during 26 cure, requires the use of hardeners (curing agents) which limit the shelf life of the resin 27 system, requires resin systems to be stored and transported under low temperature conditons before cure, and requires expensive tooling that is tolerant to high temperatures (i.e., 250 to 750°F). EB curing is a nontheπnal curing method that uses high-energy, high-power electrons to initiate polymerization and cross-linking reactions at controlled rates in EB curable materials to enhance specific physical, mechanical, and chemical properties. EB curing can eliminate or reduce many of the shortcomings of thermal curing and facilitate technical developments that are presently unachievable utilizing thermal curing technology. Four advantages are offered by EB curing compared to traditional Thermal Curing: Lower Manufacturing Costs, resulting from faster cures, lower energy consumption, the ability to use lighter and lower cost tooling, simplified transportation and storage of resin systems, and easier waste deanup after fabrication. Simplified Processing! resulting from selectable cure temperatures, minimal part and tool thermal mismatches, uniform and effident cross-linking, unlimited resin pot life, elimination of hardeners in the resin system, reduction in resin viscosity variations, greater material integration flexibility, in-situ fabrication and curing capability, ability to cure parts up to about 12-inches thick, no part size limitations, and its ability to be retroflttable to traditional fabrication methods (i.e., automated tape and tow and fiber placement, filament winding, pultrusion, resin transfer molding), and the ability to be cured in either on-line or batch operations. Environmentally Friendly: because it reduces toxic and volatile emissions and minimizes the use of solvents normally required for waste clean-up operations. Improved Product Performance: by lowering residual and internal stresses, improving dimensional part quality, and the ability to tailor the material properties by controlling the cure depth and the degree of cure. This subject invention provides the user an almost unlimited number of epoxy 39 SUBSTITUTE SHEET (R UU 26) 1 resin systems to choose from which meet the necessary performance requirements for 2 given applications. 3 The benefits of PMCs have long been recognized for high-performance applications, but 4 Amercian industry has not capitalized on the advantages of these materials because 5 large-scale manufacturing of PMCs is cost prohibitive. One of the primary cost drivers 6 in manufacturing PMC parts and structures is the manufacturing cyde times required to 7 cure the mateirals. By utilizing the radiation curable materials discussed in this subject s invention one can dramatically shorten the manufacturing time for producting these 9 materials, thereby greatly improving the affordability and use of PMCs in many areas of o the commercial sector, including aircraft, aerospace, automotive, marine, sporting goods, i infrastructure, and construction industries. 2 Many companies involved in the manufacture of aircraft and aerospace products, 3 automobiles, chemicals, adhesives, polymer matrix composites, marine products, 4 reinforcement fibers, oil drilling platforms, and electron beam accderators are extremdy s interested in this technology area. 6 The materials described in this invention also have enormous potential for 7 reducing the final cost for products used in applications such as thick and thin coatings; s tooling for manufacturing PMCs; encapsulants for electronic devices; adhesives for 9 bonding PMCs, metals, ceramics, and other materials; and for manufacturing molded 0 and cast parts. i While there has been shown and described what is at present considered the 2 preferred embodiments of the invention, it will be obvious to those skilled in the art that 3 various changes and modifications may be made therein without departing from the 4 scope of the invention as defined by the appended claims. 5 Table 1. Toughening of Radiation Cured Epoxy Resins with Engineering Thermoplastics and Hydroxy-Terminated Thermoplastic Oligomers 1 ' 2 cn Fl t 3 1. All formulations contained OPPI at a concentration of 3 phr. 2. All specimens were cured using a total dosage of 150 kGy. 3. Initial service temperature is defined as the temperature at which the modulus is at 50% of its value at 25°C. Table 1. Toughening of Radiation Cured Epoxy Resins with Engineering Thermoplastics and Hydroxy-Terminated Thermoplastic Oligomers 1,2 Continued c :xn Bl * 53 cz ro . All formulations contained OPPI at a concentration of 3 phr. 2. All specimens were cured using a total dosage of 150 kGy. 3. Initial service temperature is defined as the temperature at which the modulus is at 50% of its value at 25°C. Table 1. Toughening of Radiation Cured Epoxy Resins with Engineering Thermoplastics and Hydroxy-Terminated Thermoplastic Oligomers 1,2 Continued 1. All formulations contained OPPI at a concentration of 3 phr. 2. All specimens were cured using a total dosage of 150 kGy. 3. Initial service temperature is defined as the temperature at which the modulus is at 50% of its value at 25°C. LO I r Table 2. Toughening of Radiation Cured Epoxy Resins with Reactive Flexibilizers 1,2 1. All formulations contained OPPI at a concentration of 3 phr. 2. All specimens were cured using a total dosage of 150 kGy. 3. Initial service temperature is defined as the temperature at which the modulus is at 50% of its value at 25°C. Table 2. Toughening of Radiation Cured Epoxy Resins with Reactive Flexibilizers 1,2 c Continued Ui 1. All formulations contained OPPI at a concentration of 3 phr. 2. All specimens were cured using a total dosage of 150 kGy. 3. Initial service temperature is defined as the temperature at which the modulus is at 50% of its value at 25°C. r r Bi 1. All formulations contained OPPI at a concentration of 3 phr. 2. All specimens were cured using a total dosage of 150 kGy. 3. Initial service temperature is defined as the temperature at which the modulus is at 50% of its value at 25°C. Table 3. Toughening of Radiation Cured Epoxy Resins with Rubbers and Elastomers 1,2 Continued 1. All formulations contained OPPI at a concentration of 3 phr. 2. All specimens were cured using a total dosage of 150 kGy. 3. Initial service temperature is defined as the temperature at which the modulus is at 50% of its value at 25°C. Table 4. Toughening of Radiation Cured Epoxy Resins with Mixtures of Tougheners π 1. All formulations contained OPPI at a concentration of 3 phr. 2. All specimens were cured using a total dosage of 150 kGy. 3. Initial service temperature is defined as the temperature at which the modulus is at 50% of its value at 25°C. Table 4. Toughening of Radiation Cured Epoxy Resins with Mixtures of Tougheners Continued -No 1. All formulations contained OPPI at a concentration of 3 phr. 2. All specimens were cured using a total dosage of 150 kGy. 3. Initial service temperature is defined as the temperature at which the modulus is at 50% of its value at 25°C. Table 5. Electron Beam Cured Composite Laminate Properties Continued O'- 1 n Table 6. Electron Beam Cured Composite Laminate Thermal Properties Tg, °C (Tan Delta by Resin Viscosity Prepreg Resin System 4 Dynamic Mechanical @70°C (cps) Analysis) Tactix 123 (74%)/DER 661 (13%)/Udel P- 182 44,750 1700 NT (13%)/Sartomer CD-1012 (3 phr) Tactix 123 (55%)/Tactix 556 (35%)/Udel P- 202 21,700 tn 1700 NT (10%)/Sartomer CD-1012 (3 phr) Nl Tactix 123 (55%)/Tactix 742 (35%)/Udel P- 212 25,700 1700 NT (10%)/Sartomer CD-1012 (3 phr) Tactix 123 (50%)/DEN 438 (40%)/Udel P- 212 27,400 1700 NT (10%)/Sartomer CD-1012 (3 phr) 'Unidirectional carbon fiber prepreg (Hercules carbon fiber, IM7/GP-12K) laminates electron beam cured with a dose of 150 kGy. i 4* » 3 33 cr Table 8. Gamma Screening Studies Using the OPPI Photoinitiator and Various Resin Systems Continued r "b>. : 1! Table 10. Description of Materials. ? Table 10. Description of Materials. Continued Table 10. Description of Materials. Continued Table 10. Description of Materials. Continued n

Claims: What te claimed te; ι 1. A toughened epoxy resin system mixture composition comprising an epoxy 2 resin, a cationic initiator, and a toughening agent; said cationic initiator having a specific a anion selected from the group consisting of a diaryliodonium salt, a triaryisuifonium salt 4 and combinations thereof. 1 2. A toughtened epoxy resin system mixture composition in accordance with 2 claim 1 wherein said toughening agent is selected from the group consisting of a 3 thermoplastic, hydroxy-containing thermoplastic oligomer, epoxy-containing 4 thermoplastic oligomer, reactive flexibilizer, rubber, elastomer, and mixtures thereof. 1 3. A toughtened epoxy resin system mixture composition in accordance with 2 claim 1 wherein said anion is selected from the group consisting of hexafluoroarsenate 3 (AgF β " ), hexafluoroantimonate (SbF β " ), hexafluorophosphate (PF β " ), boron tetrafluoride 4 (BF 4 " ), trifluoromethane sulfonate (CF 3 SO 3 " ), tetrakis (pentafluorophenylborate), s (BIC β Fsl, " ), tetrakis [3,5-bis(trifluoromethyl) phenyljborate 1 4. A toughtened epoxy resin system mixture composition in accordance with 2 claim 1 wherein said cationic initiator comprises a diaryliodonium salt. 1 5. A toughtened epoxy resin system mixture composition in accordance with 2 claim 1 wherein said cationic initiator comprises a triaryisuifonium salt. 1 6. A toughtened epoxy resin system mixture composition in accordance with 2 claim 1 wherein said toughtened epoxy resin system mixture composition includes 3 fibers selected from the group consisting of carbon, graphite, glass, aramid , polyethylene and mixtures thereof. ι 7. A toughtened epoxy resin system mixture composition in accordance with 2 claim 1 wherein said toughtened epoxy resin system mixture composition includes s fillers selected from the group consisting of clay, minerals, glass particles, silica 4 particles, alumina particles, aluminum powder and mixtures thereof. i 8. A toughtened epoxy resin system mixture composition in accordance with 2 claim 1 wherein said cationic initiator is about 0.25 to about 10 pph of said toughtened 3 epoxy resin system mixture composition. 1 9. A method for making a toughened epoxy resin system comprising the 2 following steps: 3 Step 1. providing a toughened epoxy resin system mixture composition 4 comprising an epoxy resin, a cationic initiator, and a toughening agent; said cationic s initiator is selected from the group consisting of a diaryliodonium salt of a specific anion, 6 a triaryisuifonium salt of a specific anion and combination thereof; and 7 Step 2. exposing said toughened epoxy resin system to high energy ionizing 8 radiation for a period of time sufficient to cure said toughened epoxy resin system 9 forming a cured toughened epoxy resin system. 1 10. A method for making a toughtened epoxy resin system mixture composition in accordance with claim 9 wherein said toughening agent is selected from the group consisting of a thermoplastic, hydroxy-containing thermoplastic oligomer, epoxy- containing thermoplastic oligomer, reactive flexibilizer, rubber, elastomer, and mixtures therof. 1 11. A method for making a toughened epoxy resin system mixture composition in accordance with claim 9 wherein said anion is selected from the group consisting of hexafluoroarsenate (AgF β * ), hexafluoroantimonate (SbF β " ). hexafluorophosphate (PF β ' ), boron tetrafluoride (BF 4 " ), trifluoromethane sulfonate (CF 3 SO 3 " ), tetrakis (pentafluorophenylborate), (BfCeF j ^ " ), tetrakis [3,5-bis(trifluoromethyl) phenyl]borate (BlCeH CFJJ 1 12. A method for making a toughened epoxy resin system mixture composition 2 in accordance with claim 9 wherein said cationic initiator comprises a diaryliodonium 3 salt. ι 13. A method for making a toughened epoxy resin system mixture composition in accordance with claim 9 wherein said cationic initiator comprises a triaryisuifonium 3 salt. 70 SUBSTITUTE SHEET (RULE Q) 14. A method for making a toughened epoxy resin system mixture composition in accordance with claim 9 wherein said high energy ionizing radiation has a dose rate greater than about 0.75 kilogray/sec. 15. A method for making a toughened epoxy resin system mixture composition in accordance with claim 9 wherein said high energy ionizing radiation has a dose rate equal to or greater than about 100 kilogray/sec. 16. A method for making a toughened epoxy resin system comprising the following steps: Step 1. providing a toughened epoxy resin system mixture composition comprising an epoxy resin, a cationic initiator, and a toughening agent; said cationic initiator is selected from the group consisting of a diaryliodonium salt of a specific anion, a triaryisuifonium salt of a specific anion and combination thereof; and Step 2. exposing said toughened epoxy resin system to high energy radiation from the sun for a period of time sufficient to cure said toughened epoxy resin system forming a cured toughened epoxy resin system. 17. A method for making a toughened epoxy resin system mixture composition in accordance with claim 16 wherein said toughening agent is selected from the group consisting of a thermoplastic, hydroxy-containing thermoplastic oligomer, epoxy- containing thermoplastic oligomer, reactive flexibilizer, rubber, elastomer, and mixtures thereof. 1 18. A method for making a toughened epoxy resin system mixture composition 2 in accordance with claim 16 wherein said anion is selected from the group consisting of 3 hexafluoroarsenate (A g F β " ), hexafluoroantimonate (SbF β " ). hexafluorophosphate « ( pfr β " )» boron tetrafluoride (BF 4 " ), trifluoromethane sulfonate (CF 3 SO 3 " ), tetrakis 5 (pentafluorophenylborate), (BIC β F^ " ), tetrakis [3,5-bis(trifluoromethyl) phenyljborate 6 (B[C β H 3 (CF 3 ) 2 U* i 19. A method for making a toughened epoxy resin system mixture composition 2 in accordance with claim 16 wherein said cationic initiator comprises a diaryliodonium 3 salt. ι 20. A method for making a toughened epoxy resin system mixture composition 2 in accordance with claim 16 wherein said cationic initiator comprises a triaryisuifonium 3 salt. 1 21. A method for making a toughened epoxy resin system mixture composition 2 in accordance with claim 16 wherein said high energy radiation is ultraviolet radiation. 1 22. A method for curing an epoxy resin system comprising the following steps: 2 Step 1. providing a blend of an epoxy resin system, said epoxy resin system 3 comprising an epoxy resin and a cationic photoinitiator, said epoxy resin being selected 4 from the group consisting of: s glycidyl ethers of bisphenol A, epoxy phenolic novolacs, epoxy cresol novolacs, 6 bisphenol F epoxies, tetraglyddyl ether of tetrakis (4-hydroxyphenyI) ethane, 7 diglycidyl ether of 9, 9- bis (4-hydroxyphenyl) fluorene, glyddyl ether of the s condensation product of dicydopentadiene and phenol, triglyddyl ether of tris 9 (hydroxyphenyl) methane, 3',4'-epoxycyclohexylmethyl 3,4- o epoxycydohexanecarboxylate, diglyddylester of hexahydrophthalic anhydride, bis i (3,4-epoxycydohexylmethyI) adipate, isomeric mixture of bis (2,3- 2 epoxycydopentyl) ether, isomeric mixture of bis (2,3-epoxycydopentyI) ether 3 reacted with ethylene glycol, isomeric mixture of bis (2,3-epαxycydopentyI) ether blended with a bisphenol A based glyddyl ether, and mixtures thereof, 5 said cationic photoinitiator being selected from the group consisting of: diaryliodonium 6 salts, triaryisuifonium salts, and mixtures thereof, s&id diaryliodonium salts have the 7 following formula: 8 R. 19 0 24 25 26 where R, and R 2 are selected from the group consisting of: H, methyl, ethyl, n- 27 propyl, isopropyl, n-butyl, tert-butyl, Cl, Br, OCA.**, OCH,CH(CH 3 )C B H ta+ „ 28 OCH I CH(C 2 H s )C n H 2B+I , OCH,CH(OH)C B H 2 . + ι» OCH,CO,C,Hj, +1 , 29 OCH(CH 3 )C0 2 C I1 H 2ll+1 , OCH(C 2 H s )CO j C ιr H 2jl+l , and mixtures thereof, where n is 0 an integer between 0 and 18 and An' is an anion sdected from the goup consisting 3i of: hexafluoroarsenate (AsF t " )» hexafluoroantimonate (SbF« * ), 32 hexafluorophosphate (PF c , boron tetrafluoride (BF/), trifluoromethane sulfonate (CF- J SOJ " ), and tetrakis (pentafluorophenylborate) (BIC t Fj]/), and mixtures thereof and said triaryisuifonium salts have the following formulas: where R 3 is selected from the group consisting of: H, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, phenylsulfide (FhS), and phenoxy (PhO), An ' is an anion selected from tne group consisting of: hexafluoroarsenate (AsF ( "), hexafluoroantimonate (SbF , hexafluorophosphate (PF,"), boron tetrafluoride (BF/), trifluoromethane sulfonate (CFjSO, " ), and tetrakis (pentafluorophenylborate) (BtCJEy , and mixtures thereof; and Step 2. irradiating said blend with ionizing radiation to form a cross-linked epoxy resin polymer. 23. A method in accordance with claim 22 wherein said ionizing radiation is sdected from the group consisting of: dectron beam radiation, x-ray radiation, gamma- ray radiation, and combinations thereof. 24. A cross-linked epoxy resin polymer made by a method in accordance with claim 22. 25. A method for curing an epoxy resin system comprising the following steps: 2 Step 1. providing a blend of an epoxy resin system, said epoxy resin system 3 comprising epoxy resins and a cationic photoinitiator, said epoxy resins being a blend of 4 a semi-solid epoxy, triglyddyl ether of tris (hydroxyphenyl) methane, and a low viscosity 5 epoxy, glycidyl ether of bisphenol A, said cationic photoinitiator being (4-octyloxyphenyI) 6 phenyliodonium hexafluoroantimonate; and 7 Step 2. irradiating said blend of an epoxy resin system with ionizing radiation to s form a crosslinked epoxy resin polymer. 1 26. A method for curing an epoxy resin system comprising the following steps: 2 Step 1. providing a blend of an epoxy resin system, said epoxy resin system 3 comprising epoxy resins and a cationic photoinitiator, said epoxy resins being a blend of 4 a glyddyl ether of the condensation product of dicydopentadiene and phenol, and a low s viscosity epoxy, glyddyl ether of bispaenoϋ A, said cationic photoinitiator being 6 (4-octyloxyphenyI) phenyliodonium hexafluoroantimonate; and 7 Step 2. irradiating said blend of an epoxy resin system with ionizing radiation to 8 form a crosslinked epoxy resin polymer. 1 27. An epoxy resin system comprising a blend of an epoxy resin and a cationic 2 photoinitiator, said epoxy resin being selected from the group consisting of: 3 glyddyl ethers of bisphenol A, epoxy phenolic novolacs, epoxy cresol novolacs, 4 bisphenol F epoxies, tetraglyddyl ether of tetrakis (4-hydroxyphenyI) ethane, 5 diglycidyl ether of 9, 9- bis (4-hydroxyphenyl) fluorene, glyddyl ether of the 6 condensation product of dicydopentadiene and phenol, triglyddyl ether of tris 7 (hydroxyphenyl) methane, 3',4'-epoxycyclohexylinethyl 3,4- 8 epoxycydohexanecarboxylate, diglyddylester of hexahydrophthalic anhydride, bis 9 (3,4-epoxycycIohexylmethyl) adipate, isomeric mixture of bis (2,3- 0 epoxycydopentyl) ether, isomeric mixture of bis (2,3-epoxycydopentyl) ether reacted with ethylene glycol, isomeric mixture of bis (2,3-epoxycydopentyl) ether blended with a bisphenol A based glyddyl ether, and mixtures thereof, said cationic photoinitiator being selected from the group consisting of: diaryliodonium salts, triaryisuifonium salts, and mixtures thereof, said diaryliodonium salts have the following formula: R. where R t and R, are sdected from the group consisting of: H, methyl, ethyl, n- propyl, isopropyl, n-butyl, tert-butyl, Cl, Br, OCJB j ,.,.., OCH 1 CH(CH 3 )C ll H 2 . +1 , OCH 2 CH(C 2 H s )C B H ϊll+I , OCH 2 CH(OH)C B H 2 . +I , OCH,CO,C B H 2 . +i , OCH(CH 3 )CO 2 C Ir H 2 , +I , OCH(C ϊ H s )CO j C-P 2ll+1 , and mixtures thereof, where n is an integer between 0 and 18 and An' is an anion sdected from the goup consisting of: hexafluoroarsenate (AsF , hexafluoroantimonate (SbF,-), hexafluorophosphate (PF, " ), boron tetrafluoride (BF 4 " ), trifluoromethane sulfonate (CFjSOj , and tetrakis (pentafluorophenylborate) <&[€ &), and mixtures thereof and said triaryisuifonium salts have the following formulas: * * ~©-s »- +S-©- Σ-©-S+ A where R 3 is sdected from the group consisting of: H, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, phenylsulfide (PhS), and phenoxy (PhO), An ' an anion sdected from the group consisting of: hexafluoroarsenate (AsF<"), hexafluoroantimonate (SbF ( , hexafluorophosphate (PFV), boron tetrafluoride (BF 4 " ), trifluoromethane sulfonate (CFjSO, " ), and tetrakis (pentafluorophenylborate) (BIC^F j k"), and mixtures thereof.

Inventors: DORSEY GEORGE F, HAVENS STEPHEN J, JANKE CHRISTOPHER J, LOPATA VINCENT J, MOULTON RICHARD J, DORSEY, GEORGE, F., HAVENS, STEPHEN, J., JANKE, CHRISTOPHER, J., LOPATA, VINCENT, J., MOULTON, RICHARD, J.
Applicants: LOCKHEED MARTIN ENERGY SYS INC, LOCKHEED MARTIN ENERGY SYSTEMS, INC.
Application year: 1996
Main classification: C08F2
IPC codes: C08F2, C08F4, C08G59, C08G65, C08L63