NO~EL EPOXY RESIN HARDENING AGENTS
The present invention relates to novel epoxy resin hardening agents. More particularly, it relates to epoxy resin hardening agents which have rapid cold hardening ability and a high degree of sa~ety and which provide hardened products excellent in heat resistance.
Hitherto, aliphatic polyamines such as diethylene-triamine, triethylenetetramine, xylylenediamine, etc. ha~e been generally used as rapid hardening agents for epoxy resins.
The products hardened with these amines have some heat resistance, but the mechanical properties of such products especially at high temperatures such as 120C or higher are not necessarily satisfactory. Moreover, these amines have problems as to safety of thehUman body because they have relatively high vapor pressures.
Therefore, use of modified amines have been proposed, but these modified amines are liable to further decrease mechanical properties of the hardened products at high temperatures.
Aromatic polyamines such as m-phenylenediamine, diaminodiphenyl methane, diaminodiphenyl sulfone, etc. provide hardened products which have excellent mechanical properties at high temperatures, so that they are industrially widely used, but they have the defect that they cannot harden epoxy resins at normal temperatures.
The present inventors earnestly studied epoxy resin hardening agents and succeeded in finding that 1,3,5-tris-~aminomethyl)benzene (sometimes referred to as "MTA" herein-a~ter) and 1,3,5-tris(aminomethyl)cyclohexane (sometimes referred to a "H6MTA" hereinafter) per se have much lower vapor pressures and so have a high degree of safety, have rapid cold hardening ability~and provide hardened products which have excellent mechanical properties at high temperatures.
The present invention, in one aspect, resides in a method for hardening an epoxy resin which comprises mixing the epoxy resin with a compound of the formula:
' - la -C~2N~2 f~
H2NCH2~--CH2NH2 ~herein ~ is ~ ~r ~ ~
In another aspect, the inven.tion resides in a method for hardening an epoxy resin which comprises mixing the epoxy resin with a prepolymer obtained by reacting one mole of the diglycidyl ether of bisphenol ~ wi~h two or more moles of a compound of the formula:
wherein ~ is ~ or ~
In related Canadian Patent Application No. 365,707 of I. Minato et al, filed November 28, 1980, there are disclosed and claimed epoxy resin hardening-agents represented by the general formula '~c~
(wherein ~ represents ~ or ~ ).
The MTA and H6MTA which are the hardening agents of the present invention are novel polyamines obtained by the methods disclosed in Japanese Patent Applications No. 67169/79 and No. 67170/79. That is, MTA can be produced by reducing, in the presence of a catalyst such as Raney nickel, a starting material of 1,3,5-tricyanobenzene obtained 15 by ammoxydation of mesitylene. H6MTA can be produced by further reducing the aromatic ring of the MT~-in the presence of a reducing catalyst. Moreover, H6MTA can also be obtained directly from 1,3,5-tricyanobenzene by reducing cyano groups and the aromatic ring at once.
The thus obtained H6MTA includes both the cis and trans types, the cis type being thermally more stable than the trans type.
Therefore, H6MTA high in proportion of cis type is preferred, and the proportion of the cis type is preferably at least 60 mol.%.
Epoxy resins to which these MTA and H6MTA hardening agents can be applied include polyepoxide compounds having at least an average of one epoxy group per one molecule, ~or instance, various general-purpose-epoxy resins. Examples of these known epoxy resins are those of bisphenol A type, bisphenol F type, hydrogenated bisphenol A and F types, alicyclic type, novolak type, polyoxyalkylene type, polyhydroxybenæene type, methylepichlorohydrin type, glycidylamine type, epoxy resins derived from dimer acid, phthalic acid, tetrahydrophthalic acid or p-oxybenzoic acid and epichlorohydrin, halogen-containing epoxy resins, etc.
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These MTA and H6MTA hardening agents may be used alone or in admixture and moreover may also be used in com-bination with other known hardening agents. For example, the hardening agents of the present invention may be used in combination with aliphatic or aromatic polyamines and various modified products thereof, polyamides, imidazoles, mercaptans, phenols, various acid anhydrides, BF3 complex compounds, etc.
Furthermore, MTA and H6MTA may be modified with organic acids, epoxy compounds, etc. Moreover, prepolymers having diamines at both terminals may also be used as hardening agents. Such prepolymers can be obtained by modifying MTA or H6MTA with any epoxy resins. For example, one mole of the di~lycidyl ether of bisphenol A is reacted with two or more moles of MTA or H6MTA to obtain a prepolymer.
The hardening agents of the present invention may be added to epoxy resins as they are or may be dissolved in a solvent such as toluene and then added as a solution to epoxy resins. The hardening time may be suitably adjusted according to such way of addition.
If necessary, various additives may also be added.
For example, there may be added inorganic fillers such as metal powder, silica, zinc oxide, titanium oxide, magnesium oxide, calcium oxide, calcium carbonate, aluminum sulfate, talc, clay, alumina white, barium sulfate, calcium sulfate, pumice powder, asbestos, diatomaceous earth, glass fiber, mica, molybdenum disulfide, carbon black, graphite, lithopone, etc., phenolic resins, petroleum resins, phthalic esters, other various pigments, etc.
The triamine hardening agents of the present inven-tion may be used in an amount of 0.1 - 2 times, preferably 0.5 - 1.5 times the number of amine equivalent of the tri-amine divided by epoxy equivalent.
Epoxy resins hardened with the hardening agents of '~`
the present invention exhibit extremely high heat distortiontemperatures. Furthermore, the vapor pressure of the hardening agents per se is, for example, about 1/20 (20C) of m-xylylenediamine which is the ordinarily used hardening agent , so that the hardening agents of the present invention are very useful hardening agents with a high degree of safety.
The epoxy resins hardened with the hardening agents of the present invention may be effectively used as, for example, paints, adhesives, case materials, coating agents, electrical insulating materials, etc.,like the conventional epoxy resins.
Reference Example 1 Preparation of 1,3,5-tricyanobenzene 18.2 parts of vanadium pentoxide was added to 150 parts of a 33% aqueous solution of oxalic acid and the mixture was heated to about 100C on a water bath to dissolve the vanadium pentoxide. The solution was referred to as solution A. A
solution obtained by dissolving 20 parts of chromium oxide ~VI) in 150 parts of a 33% aqueous solution of oxalic acid as mentioned above was referred to as solution B. Solutions A and B were homogeneously mixed.
To this mixed solution was added 300 parts of anatase type titanium oxide powder burned at 800C,and water was evaporated while they were mixed. The thus obtained wet slurry was molded by extruder into a cylindrical shape having a diameter of 4 mm and a length of 5 mm. The resulting molded products were dried at 100C for 15 hours and thereafter burned at 500C for 4 hours in air to obtain a catalyst.
About 200 me f the t`hus obtained catalyst was packed in an ordinary fixed bed reactor and a mixed gas consisting of 0.5 mol.~ of mesitylene, 7 mol.% of ammonia and 92.5 mol.
of air was reacted under normal pressure at a space velocity of 1000 hr 1 ~at normal temperature and pressure) while , ~ :
maintaining the temperature of the medium in a bath at 360C to obtain 1,3,5-tricyanobenzene (MTN) in a yield of 51.2 mol.%.
Reference Example 2 Preparation of 1,3,5-tris(aminomethyl) benzene 1000 g of 1,3,5-tricyanobenzene (MTN) was charged in an autoclave having a 20 e capacity together with 400 g of Raney nickel-chromium catalyst (atomic ratio Ni:Cr=49:1), 1800 m~ of methanol, 4.2 e of m-xylene and 32.6 g of sodium hydroxide. Hydrogen was injected thereinto under an initial pressure of 140 kg/cm2G and reaction was effected at 60 -102C to cause absorption of nearly the theoretical amount of hydrogen for 31 minutes. The catalyst was filtered off and the solvent was distilled out. Then, distillation under reduced pressure was effected to obtain 874 g of colorless crystals of 1,3,5-tris(aminomethyl)benzene (MTA). The product had a melting point of 49 - 51C and a boiling point of 136 -139C/0.4 mmHg.
Reference Example 3 Preparation of 1,3,5-tris(aminomethyl~cyclohexane 200 g of 1,3,5-tris(aminomethyl)benzene (MTA) obtained in Reference Example 2 together with 15 g of 5%
ruthenium-alumina catalyst(manufactured by Japan Engelhard Co., Ltd.), 100 g of water and 2 g of sodium hydroxide were charged into a magnetically stirring type autoclave having a 1~ capacity. High pressure hydrogen was injected there-into under an initial pressure of 120 kg/cm2G and reaction was effected at 110 - 135C for 3.5 hours to cause absorption of 3.8 mols of hydrogen.
The catalyst was filtered off and the solvent was distilled out. Thereafter, distillation under reduced pres-sure was carried out to obtain 164 g of 1,3,5-tris(aminomethyl)-cyclohexane (H6MTA), about 85 mol.% of which was cis typeOThis H6MTA was a colorless and transparent liquid of low vis-cosity which had a boiling point of 127 - 128C/l mm~g.
Example 1 Each of 100 g of bisphenol A type epoxy resin (Trade mark 'Epikote 828)"having an epoxy equivalent of 188.7 and 87.5 g of MTA was heated to 60C and they were quickly mixed. To this mixture was further added 500 9 of a bisphenol A type epQxy resin which was at ro~m tempe~ature and they were inti-mately mixed. Thereafter, the mixture was deaerated under reduced pressure of 10 mmHg, then subjected to procedures necessary for ordinary casting and poured into a mold. After about 21 minutes, heat was abruptly generated and a slighly yellow transparent cast plate was obtained. Properties of the thus obtained cast plate are shown in Table 1.
Example 2 To 600 g of the same epoxy resin as used in Example 1 was added gO.8 g of H6MTA and they were homogeneously mixed.
Then, the mixture was cast in accordance with usual procedures.
In about 25 minutes after casting, heat generation occurred and a colorless and transparent cas~ plate was obtained.
Properties of the thus obtained cast plate are shown in Table 1.
Comparative Example 1 600 g of the same epoxy resin as used in Example 1 was mixed with 108.2 g of xylylenediamine (XDA) and the mix-ture was cast in the same manner as in Example 2. After about 75 minutes, the mixture was hardened with generation of heat to obtain a slightly yellow cast plate.
Comparative Example 2 Casting was effected in the same manner as in Comparative Example 1 except that XDA was substituted by 113.0 g of bis(aminomethyl)cyclohexane (H6XDA). After about 83 minutes, the mixture was hardened with generation of heat to obtain a colorless and transparent cast plate.
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X X ~ X pil Example 3 Preparation of prepolymer To 10 g of'lEpikote 828"(having an epoxy equivalent of 187.6) was added 14.7 g of 1,3,5-tris(aminomethyl)benzene (MTA) and they were reacted at 70C Eor 3 hours to obtain a prepolymer which had a viscosity of 17,000 poises at 25C.
The yellowish cast plate was obtained by mixing 50 g of"Epikote 828"with 13.7 g of the prepolymer.
* Trademark . . .