Epoxy resins cured with mixed methylene bridged poly(cyclohexyl-aromatic)amine curing agents

Abstract: This invention pertains to epoxy resins having increased chemical resistance to solvents, and good cured mechanical properties which are prepared by curing the epoxy resins with a curing agent comprising a mixture of methylene bridged poly(cyclohexyl-aromatic)amines. The methylene bridged poly(cyclohexyl-aromatic)amine curing agents are the residue obtained from the distillation of a mixture of poly(cyclohexyl-aromatic)amines formed by the hydrogenation of crude methylenedianiline or crude di(4-amino-3-methylcyclohexyl)methane.

Description: TECHNICAL FIELD This invention pertains to epoxy resins cured with mixed methylene bridged poly(cyclohexyl-aromatic)amines and a process for producing such epoxy resins. BACKGROUND OF THE INVENTION Aliphatic and aromatic polyamines have been used in the past for curing epoxy resins. It is well known that the aliphatic amines have accelerated reaction with epoxy resins and react at a faster rate than do aromatic polyamines. Aliphatic polyamines can effect cure at room temperature while aromatic polyamines generally require more rigorous cure conditions or additives which act as accelerators. Epoxy resins by their very nature are generally chemically resistant and have utility as coatings, encapsulating agents and composite matrices. Even so, the properties of epoxy resins also are affected by the type of curing agent used for curing the polyepoxide. Cycloaliphatic curatives permit rapid, subambient or low temperature cure cycles but also leave residual NH functionality in the cured epoxy resin which may react with ambient carbon dioxide to form surface carbamates. These carbamates lead to water spotting and poor interfacial adhesion and, as a result, the resins may be unsuited for subsequent coating and architectural applications. In addition, either incompatibility or rapid cures effected by cycloaliphatic polyamines often result in incomplete incorporation of the curative in the final epoxy matrix. Amine exudation and degradation of surface and interfacial properties of the epoxy resin may result because of such lack of incorporation. Aromatic amines, on the other hand, because they are less basic and nucleophilic than their cycloaliphatic counterparts, do not react with carbon dioxide to form surface carbamates and thus do not suffer from the inadequacies imparted by cycloaliphatic amines. In addition, chemical resistance of epoxy resins cured with aromatic amines is superior to that of cycloaliphatic cured systems. However, there are problems associated with the use of common aromatic polyamines. One problem associated with such common aromatic diamines relates to their hygienic considerations in the workplace. Many single ring and double ring diamines are toxic or carcinogenic. Representative patents which describe epoxy resins and the utilization of aromatic and cycloaliphatic amines as curatives, therefore are as follows: U.S. Patent 2,817,644 discloses a process for curing and resinifying polyepoxides by reacting the polyepoxides with hydrogenated aromatic primary or secondary amines. Examples of aromatic amines which could be hydrogenated to form the cycloaliphatic counterparts include p,p' -methylenedianiline, 2,4-diaminotoluene, and the like. The hydrogenated aromatic amines provide epoxy resin products having excellent hardness and excellent resistance to solvents and water. U.S. 2,981,711 discloses the use of amines as hardening agents for epoxy resins formed by the reaction of a polyglycidylether of a polyhydric phenol with epichlorohydrin. Both aromatic and cycloaliphatic amines are represented and these include para.para'-diaminodiphenylmethane, para.para'-diaminodiphenylpropane, and cycloaliphatic amines include diaminodicyclohexylmethane (often referred to as PACM), diaminodicyclohexylpropane and diaminotricyclohexylmethane. U.S. 2,999,826 discloses epoxy resins cured with a polyamide adduct incorporating both aliphatic and aromatic amines. The polyamide adduct when used to cure the epoxy resins provides an epoxy product which has a balance of properties associated with cycloaliphatic and aromatic curatives. More specifically, these epoxy resins exhibit great toughness, excellent resistance to impact and excellent machinability. Volatility of the adduct is much lower than the corresponding amines and hygienic safety is improved. The patentees do point out in the background portion of the invention that when mixtures of aliphatic and aromatic polyamines were simply blended together and reacted with epoxy resins, the resulting product was quite brittle and had poor machining characteristics. In addition the simple blending of the aliphatic and aromatic amines did not overcome the volatility and toxicity of the blend. U.S. Patents 4,226,737 and 4,321,353 disclose epoxy curatives which are methylene bridged polycycloaliphatic polyamines represented by the structural formulas: and wherein x and y are from 0-2 and the sum of x plus y is from 1 to 4. Typically the curative consists essentially of from 50 to 75% of the methylene bridged tricyclohexyltriamine and from 15 to 30% of the tetracyclohexyltetramine. The patentees report that the curing agents overcome substantial problems encountered with prior art amine curatives in that they have lower volatility and reduced toxicological properties. In addition the patentees report higher glass transition temperatures, and thus improved thermal properties, can be achieved vis-a-vis 1,2-cyclohexanediamine. U.S. Patent No. 3,321,438 discloses aliphatic and cycloaliphatic amines, including piperazines as curing agents for fluidized bed epoxy coating compositions. Examples of aliphatic amines include diethylenetriamine and triethylenetetramine; cycloaliphatic diamines include di(4-aminocyclohexyl)methane, di(3-methyl-4-aminocyclohexyl)methane and the N-substituted derivatives. U.S. Patent No. 3,629,181 discloses various cycloaliphatic and cycloaliphatic-aliphatic di-primary amines for use in preparing adducts as curing agents for polyepoxide resin systems. Representative amines include 1,4-diamino-3,6-diethylcyclohexane; 2,2-di(4-aminocyclohexyl)propane which is commonly referred to as hydrogenated bisaniline A and 3-aminomethyl-3,5,5-trimethyl-1-cyclohexylamine, which is commonly referred to as isophoronediamine. U.S. Patent No. 4,447,586 discloses a process for producing polyepoxide resins by incorporating therein a metal fluoborate and a hindered aromatic amine curing agent. Examples of the hindered aromatic amines include diethyltoluenediamine, methylenebis(2,6-diisopropylaniline), methylenebis(2,6-diethylaniline) and methylenebis(2-methyl-6-ethylaniline). U.S. 4,946,925 discloses various bridged bis(cyclohexylamine) derivatives as curing agents. Each cyclohexylamine group has two alkyl groups where the alkyl groups are in the 2 and the 5 positions and the amine groups are in the 4 position. Specific curing agents include 2,2',5,5'-tetramethylmethylenedicyclohexylamine and 2,2',5,5'-tetraethylmethylenedicyclohexylamine. The tetraalkyl substitution pattern in the bridged cyclohexylamine derivative provides for extended pot life by retarding activity of the amine as a curative and the tetraalkyl substitution also enhances thermal properties of the epoxy resin. British Patent 1,536,808 discloses a process for the hydrogenation of methylene bridged aromatic amines, such as, methylenedianiline. The patentees suggest that it is well known that the mixed isomeric methylene bridged polycyclohexylpolyamines are useful as curing agents for vicinal epoxides. SUMMARY OF THE INVENTION This invention relates to polyepoxide resins cured with a mixture of methylene bridged poly(cycloaliphatic-aromatic)amines (sometimes referred to as "MPCA") and a process for preparing such polyepoxide resins. In the preparation of the MPCA mixture, a condensation product of formaldehyde and aniline or toluidine containing substantial amounts of oligomer is partially hydrogenated and the partially hydrogenated product separated by distillation. The heavier components of the distillation mixture or bottoms are represented by the formula: wherein R is hydrogen or methyl, x is 1-3, y is 0-2 and the sum of x and y is from 2 to 4. An MPCA mixture contains substantial amounts of 3 ring and higher aliphatic-aromatic rings. Typically the weight ratio of 3 ring to 4 ring and higher aliphatic-aromatic ring components will be from 50 to 90 parts of the 3 ring component to 10 to 50 parts of the 4 ring and higher components. The ratio of cycloaliphatic rings to aromatic rings in said MPCA will range from 0.5 to 2:1, and preferably 1.3 to 1.9:1. The utilization of the MPCA mixture of methylene-bridged poly(cycloaliphatic-aromatic) amines, as described above, overcomes major problems associated with prior art epoxy curatives and these advantages include: an ability to produce epoxy coating compositions having excellent gloss and water spotting resistance; an ability to formulate epoxy resin compositions with reduced environmental problems due to the low toxicity of the curing agent as compared to aromatic amines; an ability to generate epoxy compositions having excellent thermal properties, chemical resistance, and mechanical properties including fracture toughness, flexibility, elongation, strength and so forth required for composites and for structural applications; an ability to produce an epoxy resin having reduced resistance to amine exudation; an ability to enhance part integrity for molding operations and minimize resin loss because of higher room temperature viscosity, and yet, on heating, the resin becomes less viscous and has excellent flowability; and, an ability to enhance throughput of molded products due to excellent reaction rates. DETAILED DESCRIPTION OF THE INVENTION According to the present invention a polyepoxide resin comprises the reaction product of a polyglycidyl polyether of a polyhydric alcohol having terminal 1,2-epoxy groups with a curing agent which comprises a polyamine represented by the formula: wherein R is hydrogen or methyl, x is 1-3 and y is 0-2 and the sum of x and y is from 2 to 4. The methylene bridged poly(cyclohexyl-aromatic)amines are known and can be synthesized in conventional manner, e.g., condensing aniline or toluidine with formaldehyde, followed by hydrogenation. The crude reaction product obtained with the condensation of aniline generally contains from about 15 to 50% by weight of the 3 ring and higher molecular weight oligomers with the balance being methylenedianiline. Hydrogenation of the crude methylenedianiline or di(4-amino-3-methylphenyl)methane can be effected by well known processes using a hydrogenation catalyst. Typically a ruthenium or rhodium catalyst or mixture of the two catalysts is used to effect hydrogenation. Many of the impurities in crude methylenedianiline or di(4-amino-3-methylphenyl)methane act as poisons to hydrogenation catalysts and some precautions must be taken to effect hydrogenation. Conditions of hydrogenation will range from a hydrogen pressure of from 35.5 to 277 bar (500 to 4000 psig) and preferably 49.3 to 104.5 bar (700-1500 psig) and a temperature ranging from 150 to 250°C, preferably from 170° to 190°C. To convert substantially all of the methylenedianiline or di(4-amino-3-methylphenyl)methane to at least partially hydrogenated product, reaction times may extend for a period of 1 to 4 hours. Monitoring of the hydrogenation process by sampling is the best method of determining when the desired degree of hydrogenation is obtained. In the preferred low pressure process (49.3 to 104.5 bar) (700-1500 psig) from about 10 to 65% by weight of the hydrogenation reaction product (containing 2 ring components and the higher oligomers) is comprised of a mixture of methylene bridged poly(cycloaliphatic-aromatic)amines. In contrast, the high pressure process is capable of complete hydrogenation of the crude aromatic product. In that case, the reaction should be terminated after substantially all of the methylenedianiline or di(4-amino-3-methylphenyl)methane is converted to partially hydrogenated product and prior to complete hydrogenation of all of the aromatic rings of the 3 ring component. An example of a process for hydrogenating methylenedianiline and derivatives is shown in US 4,754,070 and the process described therein is incorporated by reference. In a distilled form, an MPCA containing distillation fraction substantially free of two ring components and substantially free of non elutables as determined by gas chromatographic analysis contains: 10-37% 2,4-di(4-aminocycl,ohexylmethyl)cyclohexylamine; 67-85% 2,4-di(4-aminocyclohexylmethyl)aniline; 0-20% 4,4'-di(4-cyclohexylmethyl)dicyclohexylamine; and, 5-14% partially hydrogenated trimethylenetetraaniline and analogs thereof. In a partially distilled form, and therefore a form containing substantial amounts of two ring components but substantially free of non elutables, a typical MPCA containing curative as determined by gas chromatographic analysis (hereinafter sometimes referred to as "MPCA Blend") comprises the following components: 2-10% di(4-aminocyclohexyl)methane (PACM); 0.5-2% 4-aminocyclohexyl-4-hydroxycyclohexylmethane; 5-17% 4-(4'-aminobenzyl)cyclohexylamine; (ABCHA) 5-25% 2,4-di(4-aminocyclohexylmethyl)cyclohexylamine; 35-55% 2,4-di(4-aminocyclohexylmethyl)aniline; 0-15% 4,4'-di(4-cyclohexylmethyl)dicyclohexylamine; and, 3-8% partially hydrogenated trimethylenetetraaniline and analogs thereof. The amine hydrogen equivalent of an MPCA containing mixture as described above containing the two ring components typically will range from 50 to 60 and preferably be within the range of from 54-56. The methylene bridged poly(cyclohexyl-aromatic)amines can also be converted to epoxy adducts and used in that form as a curative for polyepoxides. To use the MPCA in such form, an excess of amine is reacted with the epoxide. The adduct containing unreacted amine hydrogens then can be reacted with a polyepoxide to produce a cured epoxy resin product. An example of such adduct is one where a diglycidylether of bisphenol A is reacted with the MPCA or the MPCA Blend in furfuryl alcohol. The polyepoxides can be cured in conventional manner by effecting reaction with the methylene bridged poly(cyclohexyl-aromatic)amine. Typically the amount of methylene bridged poly(cyclohexyl-aromatic)amine curative which is reacted with the polyepoxide will range from a level of 0.6 to 1.7 times the stoichiometric or equivalent amount of polyepoxide resin present. Preferably, the level of methylene bridged poly(cyclohexyl-aromatic)amine to polyepoxide is from about 0.9 to 1.1 times the stoichiometric amount, stoichiometric being one equivalent weight of epoxide per equivalent weight of amine hydrogen. Other polyamine curing agents can be used in combination with MPCA and these include aromatic polyamines such as diethyltoluenediamine, and methylenedianiline; and cycloaliphatic amines such as di(4-aminocyclohexyl)methane (PACM), isophoronediamine, 1,3-xylylenediamine, and polyalkylenepolyamines such as diethylenetriamine and triethylenetetramine and the mixed methylene bridged poly(cyclohexyl-aromatic)amine, 4-(4'-aminobenzyl)cyclohexylamine (ABCHA). In many cases the amine functionality for curing is provided by a mixture of a cycloaliphatic amine such as PACM or ABCHA or both. When a mixture of polyamines is used as the curative, the MPCA will range from 5 to 70% by weight of the curative. A polyamine mixture which has been found to be excellent comprises the MPCA and ABCHA or PACM or both in an amount of from 15-70% MPCA and from 30 to 85% by weight of 4-(4'-aminobenzyl)cyclohexylamine, di(4-aminocyclohexyl)methane or combinations thereof. Conventional accelerators, plasticizers, fillers, glass and carbon fibers, pigments, solvents, etc. used in formulating epoxy coatings, mold compositions, lacquers, etc. can be used. Selection and amount of these additives is at the option of the formulator. The adjustment of cure temperatures and curing times for polyepoxide resins is within the discretion of the formulator. Representative accelerators which may be used, although not mandatory, include: boron trifluoride amine complexes and metal fluoroborate systems, e.g. copper fluoroborate; substituted phenolics, and tertiary amines, such as imidazole, 2,4,6-tri(dimethylaminomethyl)phenol, and benzyldimethylamine. The following examples are intended to illustrate various embodiments of the invention and are not intended to restrict the scope thereof. Example 1 Preparation of Epoxy Resins A series of epoxy resins was prepared in conventional manner using various amine curing agents. The formulations were made with commercial epoxy resins including D.E.R. 383 (Dow), Epon 826 and Epon 828 (both by Shell). The formulations were cured with stoichiometric levels of curing agents. Both commercial amine curatives and blends containing the MPCA poly(cyclohexyl-aromatic)amines were compared. The blend containing the MPCA obtained by the hydrogenation of crude methylenedianiline and partial distillation thereof (hereinafter referred to as "MPCA Blend") comprised the following components and amounts: 5.0% di(4-aminocyclohexyl)methane; (PACM) 0.5% 4-aminocyclohexyl-4-hydroxycyclohexyl methane; 5.4% 4-(4'-aminobenzyl)cyclohexylamine; (ABCHA) 17.9% 2,4-di(4-aminocyclohexylmethyl)cyclohexylamine; 49.8% 2,4-di(4-aminocyclohexylmethyl)aniline; 6.5% 4,4'-di(4-cyclohexylmethyl)dicyclohexylamine; 7.5% partially hydrogenated trimethylenetraaniline and analogs thereof; and 7.4% non elutables. The polyepoxides and amine curatives as described above were mixed at temperatures between 25 and 50°C. Entrained air was removed by one of two methods: 1) by applying a vacuum for about 1-15 minutes until foaming stopped indicating most of the air had been removed, or 2) by placing the mixture in a centrifuge until the mixture of polyepoxide and curative was clear. After removal of the entrained air, the mixture of amine curative and polyepoxide was poured into 3.175 mm (1/8 inch) molds preheated to 80°C for the elevated cure systems. The elevated cure systems were placed in an 80°C circulating air oven and cured at that temperature for 2 hours and then for 3 hours at 150°C. Molds were allowed to cool to room temperature and the 3.175 mm (1/8 inch) castings were removed. Samples of the resulting resin were prepared for mechanical and physical testing. The mechanical and physical properties then were determined by standard methods. The results are set forth in Table 1. PROPERTIES OF DGEBA HEAT CURED SYSTEMS PROPERTIES AMICURE PACM ANCAMINE 2049 MDA MPCA 50/50 PACM/MPCA VISCOSITY @ 25°C (CPS) Pa.s.10⁻³ 80 112 Solid - - 2175 @ 40°C (CPS) Pa.s.10⁻³ - - - - - - 60,000 - - EQ. WEIGHT 52.5 59.5 50 55.1 54 FORMULATION VISCOSITY (CPS) Pa.s.10⁻³ @ 25°C 4250 5345 - - - - 6250 @ 40°C - - - - - - 3730 - - @ 60°C 250 220 170 - - - - GEL TIME (MIN) @ 25°C 175 295 >8 HRS - - - - @ 40°C - - - - - - 94 - - @ 60°C 27 59 - - - - - - @ 80°C 9 - - 93 - - - - DSC REACTIVITY ONSET °C 88 - - 130 87 89 PEAK °C 116 - - 163 118 119 ΔH (J/g) 447 - - 300 437 457 Tg °C 156 150 160 182 175 MECHANICAL PROPERTIES TENSILE STRENGTH (MPa) 71.6 69.6 70.3 56.5 71.0 TENSILE MODULUS (MPa) 2240 2412 3164 2572.8 2516.3 % ELONGATION 5.5 3.8 4.0 3.0 4.6 FLEXURAL STRENGTH (MPa) 164.7 147.5 175.8 - - - - FLEXURAL MODULUS (MPa) 3522 3558.4 3440.1 - - - - FRACTURE TOUGHNESS GIC kJ/M² 0.29 0.22 0.22 - - - - CHEMICAL RESISTANCE % WT GAIN AFTER 120 DAYS) ACETONE 8.51 16.52 10.69 5.64 - - TOLUENE 0.66 0.33 0.24 0.73 - - ETHANOL 1.20 1.47 0.83 0.51 - - METHANOL - - - - - - 5.21 - - AMMONIUM HYDROXIDE, 10% 4.20 1.59 1.65 1.81 - - SODIUM HYDROXIDE, 10% - - - - - - 1.48 - - NITRIC ACID, 10% 7.42 5.72 0.89 3.64 - - ACETIC ACID, 25% 16.6 12.95 1.44 6.73 - - SULFURIC ACID, 30% - - - - - - 2.16 - - DI WATER 1.97 1.65 1.64 1.71 - - DGEBA polyepoxide is a diglycidyl ether of bisphenol A epoxy having an epoxide equivalent weight between 176 and 192. ANCAMINE 2049 is a trademark of Air Products and Chemicals, Inc. identifying dimethyl PACM. AMICURE PACM is a trademark of Air Products and Chemicals, Inc. identifying PACM. MDA is methylenedianiline. Example 2 Preparation of Epoxy Resins A series of heat cured epoxy resins was synthesized in accordance with the procedure of Example 1. The MPCA Blend of Example 1 was combined with additional amounts of other aliphatic and cycloaliphatic-aromatic amine curatives. The results of physical and mechanical tests are shown in Tables 2 and 3. PROPERTIES OF DGEBA HEAT CURED SYSTEMS CURATIVE 50% MPCA 33.3% MPCA 70% MPCA 40% MPCA ABCHA 50% ABCHA 33.3% ABCHA 17% ABCHA 60% DETDA 33.3% PACM 13% PACM VISCOSITY @ 25 C (CPS) Pa.s.10⁻³ semi-solid 3072 17,380 2820 solid FORMULATION VISCOSITY (CPS) Pa.s.10⁻³ @ 25 C - - 7143 11,600 10,700 - - GEL TIME (MIN) @ 25 C - - 181 170 - - - - @ 40 C - - 291 80 - - - - DSC REACTIVITY ONSET C 79 83 84 79 77.5 PEAK C - - - - - - 127/184 - - ΔH (J/g) 410 426 388 363 437 Tg C 175 166 167 184 169 MECHANICAL PROPERTIES TENSILE STRENGTH (MPa) - - - - - - 71.70 77.9 TENSILE MODULUS (MPa) - - - - - - 2640 2295 % ELONGATION - - - - - - 5.1 5.8 cured for 2 hrs @ 80 C followed by 3 hrs at 150 C. MPCA refers to the MPCA Blend of Example 1. ABCHA refers to 4-(4'aminobenzyl)cyclohexylamine. DETDA refers to diethyltoluenediamine. PROPERTIES OF DGEBA HEAT CURED SYSTEMS CURATIVE 66.7% ABCHA 66.7% MPCA 80% PACM 40% PACM 13.3% PACM 33.3% ABCHA 20% MPCA 60% MPCA 20% MPCA VISCOSITY @ 25° C (CPS) Pa.s.10⁻³ semi-solid 84820 208 3772 FORMULATION VISCOSITY (CPS) Pa.s.10⁻³ @ 25°C - - 17300 2340 7340 GEL TIME (MIN) @ 25°C - - - - - - 183 @ 40°C - - - - 142 122 DSC REACTIVITY ONSET °C 79 83 88 85 PEAK °C 115 118 115 118 ΔH (J/g) 410 411 442 429 Tg °C 167 178 164 171 MECHANICAL PROPERTIES** TENSILE STRENGTH (MPa) 75.8 64.1 75.8 62.0 TENSILE MODULUS (MPa) 2295 2516 2564 2550 % ELONGATION 3.0 3.6 5.2 4.1 The above results in Tables 1-3 from Examples 1 and 2 show that the MPCA cured resin generally has significantly better chemical resistance to many conventional organic solvents than do the PACM, ANCAMINE 2049 curative and MDA cured resins. In many instances the chemical resistance approached that of the aromatic amine, MDA, but the mechanical properties approached those of the cycloaliphatic amines, i.e., PACM and ANCAMINE 2049 curatives. Gel times for the MPCA cured epoxy resin were significantly shorter than those obtained with MDA. The mixture of PACM and MPCA provided benefits intermediate to those of PACM and MPCA alone. Formulating a curative based on PACM and MPCA offers a processing benefit with respect to viscosity and reactivity while retaining many of the benefits offered by MPCA with respect to chemical resistance and mechanical properties. The MPCA Blend of Example 1 with additional amounts of PACM, ABCHA, and both, as noted in Table 3, offered excellent physical properties. Example 3 Resistance to Caustic Using Epoxy Resin Formulations Based On High Molecular Weight Polyepoxides The procedure of Example 1 was repeated except that the Epon 830 resin was substituted for the Epon 828. The test samples were exposed to a 10% sodium hydroxide solution for 7 days at 75°C. Properties are set forth in Table 4. SODIUM HYDROXIDE RESISTANCE FOR PACM/MPCA AND PACM CURED EPON 830 PROPERTIES 50/50 PACM/MPCA CURED EPON 830 PACM CURED EPON 830 STORAGE MODULUS (E'), MPa (BEFORE IMMERSION) 2762 2630 STORAGE MODULUS (E'), MPa (AFTER IMMERSION) 2691 2546 AVERAGE % DROP IN MODULUS 2.6 3.2 GLASS TRANSITION (Tg), °C (BEFORE IMMERSION) 156 146 GLASS TRANSITION (Tg), °C (AFTER IMMERSION) 143 134 AVERAGE % DROP IN GLASS TRANSITION TEMPERATURE 8.22 8.28 % WEIGHT CHANGE AFTER IMMERSION +1.332 +1.349 The data in Table 4 show that the mixture of PACM and MPCA gave improved retention of modulus and thermal properties after exposure to dilute caustic, demonstrating improved chemical resistance compared to PACM alone. Example 4 Low Temperature Cured Epoxy Resin Test coatings for use in coatings and civil engineering applications were prepared in conventional manner using the MPCA amine curative of Example 1. More particularly, the formulation comprised the following: 90 parts of D.E.R. 351 blend of bisphenol A and bisphenol F diglycidyl ether and 10 parts of Epodil C₁₂₋₁₄ glycidyl ether by weight cured with a stoichiometric amount of test amine curative. Table 5 below sets forth the results for films cured at 10 and 25°C cure temperatures. Low Temperature Cured Epoxy Resins CURATIVE 1888 2257 DB272 MXA1 DB272 MXA2 VISCOSITY @ 25°C/CPS Pa.s.10⁻³ 5300 840 140 220 MIXED VISCOSITY @ 25°C/CPS Pa.s.10⁻³ 1470 800 380 480 COLOR GARDNER 12 8 6 6 GEL TIME @ 25°C/MIN 24 32 31 35 PEAK EXOTHERM @ 25°C 145 114 153 155 TIME TO PEAK EXOTHERM/MIN 30 39 40 42 LOADING/PHR 60 65 50 50 CARBAMATION RESISTANCE/DAYS: (NOTE: ALL LEVELS OF CARBAMATION WERE VERY LOW, IF PRESENT AT ALL) @ 10°C 0 1-2 2-3 3-4 @ 25°C 0 0 0-1 1 CONICAL MANDREL ELONGATION/% <2 <30 <30 <30 DIRECT IMPACT RESISTANCE/KG.M 1.04 <1.80 0.90 1.22 REVERSE IMPACT RESISTANCE/KG.M 0.018 0.36 0.108 0.19.8 1888 is a mixture of methylenedianiline, 20% Epon 828, 6% Cordura E-10, 19% benzyl alcohol, and 49% salicyclic acid. 2257 is a mixture of 50% of the MPCA Blend of Example 1, 45% benzyl alcohol, and 5% salicylic acid. The results show that epoxy resins cured at subambient temperature with the MPCA blend of Example 1 did not suffer from surface carbamate contamination. The MPCA Blend when used alone or in combination with meta xylylene diamine, provides effective cure of epoxy resin, good resistance to surface carbamation, and good application viscosity. Example 5 Ambient Cured Castings The procedure of Example 1 was repeated, except that mixtures of the amine curative and polyepoxide were cured at ambient temperature in the molds for seven days before the castings were removed. Table 6 sets forth the results of the tests. PROPERTIES OF DGEBA AMBIENT CURED SYSTEMS CURING AGENTS 2280 1884 1693 MCA VISCOSITY @ 25°C/CPS Pa.s.10⁻³ 500 300 150 150 COLOR (GARDNER) 8 2 3 3 USE LEVEL (PHR) 60 45 50 55 GEL TIME (MIN) 50 70 50 30 COMPRESSIVE STRENGTH (MPA) 71.5 92.4 69.2 85.2 CHEMICAL RESISTANCE XYLENE 0.1 2.3 1.0 0.4 TOLUENE 2.3 DESTROYED 6.6 3.3 BUTYL CELLOSOLVE 2.4 6.2 2.5 6.5 ETHANOL 6.9 5.2 5.0 10.7 SKYDROL 500 -0.3 -0.3 -0.1 D. I. WATER 1.2 0.8 1.1 0.9 10% ACETIC ACID 5.4 12.2 4.6 5.0 10% LACTIC ACID 1.9 8.7 1.7 2.5 70% SULFURIC ACID 0.2 1.0 0.0 0.2 50% NAOH -0.2 -0.1 -0.2 -0.2 2280 is the MPCA Blend of Example 1 with benzyl alcohol and salicylic acid. 1884 is a 1,2-cyclohexanediamine-epoxy adduct modified with polyoxypropylene amine and benzyl alcohol. 1693 is a 1,2-cyclohexanediamine adduct modified with benzyl alcohol. MCA is a mannich base of isophoronediamine with phenol and formaldehyde, modified with benzyl alcohol. The above results show that the MPCA cured resin has significantly better chemical resistance especially against hydrocarbons such as xylene and toluene.

Claims: A polyepoxide resin comprising the reaction product of a polyglycidyl polyether of a polyhydric alcohol having terminal 1,2-epoxy groups with a curing agent which comprises a polyamine represented by the formula: wherein R is hydrogen or methyl, x is 1-3 and y is 0-2 and the sum of x and y is from 2 to 4. The polyepoxide resin of Claim 1 wherein R is hydrogen. The polyepoxide resin of Claim 2 wherein in the polyamine the weight ratio of 3 ring to 4 ring and higher aliphatic-aromatic ring components is from 50 to 90 parts of the 3 ring component to 10 to 50 parts of the 4 ring and higher components. The polyepoxide resin of Claim 3 wherein the ratio of cycloaliphatic rings to aromatic rings is from 0.5 to 2:1. The polyepoxide resin of Claim 4 wherein the ratio of cycloaliphatic rings to aromatic rings is from 1.3 to 1.9:1. The polyepoxide resin of Claim 3 wherein the curing agent comprises 2,4-di(4-aminocyclohexylmethyl)cyclohexylamine and the resulting blend based on the 3 ring and higher ring components, as determined by gas chromatographic analysis, comprises the following weight percentages: 10-37% 2,4-di(4-aminocyclohexylmethyl)cyclohexylamine; 67-85% 2,4-di(4-aminocyclohexylmethyl)aniline; 0-20% 4,4'di(4-cyclohexylmethyl)cyclohexylamine; and, 5-14% partially hydrogenated trimethylenetetraaniline and analogs thereof. The polyepoxide resin of Claim 6 wherein the curing agent is present as a partially distilled hydrogenation product from the hydrogenation of crude methylenedianiline and comprises the following: 2-10% di(4-aminocyclohexyl)methane; 0.5-2% 4-aminocyclohexyl-4-hydroxycyclohexyl methane; 5-17% 4-(4'aminobenzyl)cyclohexylamine; 5-25% 2,4-di(4-aminocyclohexylmethyl)cyclohexylamine; 35-55% 2,4-di(4-aminocyclohexylmethyl)aniline; 0-15% 4,4'di(4-cyclohexylmethyl)cyclohexylamine; and, 3-8% partially hydrogenated trimethylenetetraaniline and analogs thereof. The polyepoxide resin of Claim 7 wherein the amine hydrogen equivalent of said product is from 50-60. The polyepoxide resin of Claim 2 wherein the ratio of polyamine to polyglycidyl ether of a polyhydric phenol is 0.6-1.7 amine hydrogens per epoxide equivalent of polyglycidyl polyether of a polyhydric phenol. The polyepoxide resin of Claim 9 wherein the polyglycidyl ether of a polyhydric phenol is the glycidyl ether of bisphenol A. The polyepoxide resin of Claim 9 wherein the curing agent comprises from 5-70 percent of said polyamine by weight and from 30 to 95% by weight of added polyamine. The polyepoxide resin of Claim 11 wherein the added polyamine i isophoronediamine. The polyepoxide resin of Claim 11 wherein the added polyamine i di(4-aminocyclohexyl)methane. The polyepoxide resin of Claim 11 wherein the added polyamine i 1,3-xylylenediamine. The polyepoxide resin of Claim 11 wherein the added polyamine i 4-(4'-aminobenzyl)cyclohexylamine. The polyepoxide resin of Claim 11 wherein the curing agent comprises 15-70% of said polyamine, and from 30 to 85% by weight of di(4-aminocyclohexyl)methane, 4-(4'-aminobenzyl)cyclohexylamine and combinations thereof. A process for forming an epoxy resin by reacting a polyglycidyl ether of a polyhydric phenol with a polyamine curing agent, wherein the ratio of polyglycidyl ether to polyamine is from 0.6-1.7 amine hydrogens per epoxide equivalent of polyglycidyl polyether, said polyamine being represented by the formula: wherein R is hydrogen or methyl, x is 1-3 and y is 0-2 and the sum of x and y is from 2 to 4 as at least a portion of said polyamine curative. The process of Claim 17 wherein R is hydrogen. The process of Claim 18 wherein in the polyamine the weight ratio of 3 ring to 4 ring and higher aliphatic-aromatic ring components is from 50 to 90 parts of the 3 ring component to 10 to 50 parts of the 4 ring and higher components. The process of Claim 19 wherein the ratio of cycloaliphatic rings to aromatic rings is from 0.5 to 2:1. The process of Claim 20 wherein the ratio of cycloaliphatic rings to aromatic rings is from 1.3 to 1.9:1. The polyepoxide resin of Claim 20 wherein the curing agent contains 2,4-di(4-aminocyclohexylmethyl)cyclohexylamine and the resulting blend based on the 3 ring component and higher ring components, as determined by gas chromatographic analysis, comprises the following weight percentages: 10-37% 2,4-di(4-aminocyclohexylmethyl)cyclohexylamine; 67-85% 2,4-di(4-aminocyclohexylmethyl)aniline; 0-20% 4,4'di(4-cyclohexylmethyl)cyclohexylamine; and, 5-14% partially hydrogenated trimethylenetetraaniline and analogs thereof. The polyepoxide resin of Claim 22 wherein the curing agent is present a partially distilled hydrogenation product obtained by the hydrogenation of crude methylenedianiline and distillation thereof and comprises the following: 2-10% di(4-aminocyclohexyl)methane; 0.5-2% 4-aminocyclohexyl-4-hydroxycyclohexyl methane; 5-17% 4-(4'aminobenzyl)cyclohexylamine; 5-25% 2,4-di(4-aminocyclohexylmethyl)cyclohexylamine; 35-55% 2,4-di(4-aminocyclohexylmethyl)aniline; 0-15% 4,4'di(4-cyclohexylmethyl)cyclohexylamine; and, 3-8% partially hydrogenated trimethylenetetraaniline and analogs thereof. The process of Claim 23 wherein the amine hydrogen equivalent of said product is from 50-60. The process of Claim 18 wherein the polyglycidyl ether of a polyhydric phenol is the glycidyl ether of bisphenol A. The process of Claim 18 wherein the curing agent comprises from 5-70 percent of said polyamine weight and 30 to 95% by weight of added polyamine. The process of Claim 26 wherein the added polyamine is isophoronediamine. The process of Claim 26 wherein the added polyamine is di(4-aminocyclohexyl)methane. The process of Claim 26 wherein the added polyamine is 1,3-xylylenediamine. The process of Claim 26 wherein the added polyamine is 4-(4'-aminobenzyl)cyclohexylamine. The polyepoxide resin of Claim 26 wherein the curative comprises 15-70% of said polyamine and from 30-85% by weight of di(4-aminocyclohexyl)methane, 4-(4'-aminobenzyl)cyclohexylamine or combinations thereof.

Inventors: DUBOWIK DAVID ALAN, LUCAS PETER ANDREW, SMITH ANDREA KAREN, DUBOWIK, DAVID ALAN, LUCAS, PETER ANDREW, SMITH, ANDREA KAREN
Applicants: AIR PROD & CHEM, AIR PRODUCTS AND CHEMICALS, INC.
Application year: 1993
Main classification: C08G59
IPC codes: C08G59, C07C211