GB2095680A

GB2095680A - Reactive accelerators for acid- anhydride-hardened resin systems

Info

Publication number: GB2095680A
Application number: GB8209168A
Authority: GB
Original assignee: Elektro Apparate Werke VEB
Current assignee: Elektro Apparate Werke VEB
Priority date: 1981-03-31
Filing date: 1982-03-29
Publication date: 1982-10-06
Also published as: DE3204170A1; JPS57174317A; FR2503169A1; DD160225A3; CS269755B1; BG41044A1

Abstract

The invention relates to the acceleration of epoxide resin systems hardened with acid anhydride, which resins may be used as low pressure moulding compounds, adhesive, laminating or casting resins in electrical engineering or electronics. The invention seeks to allow complete integration of the accelerator into the hardened resin and improve its physical properties. The accelerators are bismaleic imides of general formula (1> <IMAGE>

Description

SPECIFICATION Reactive accelerators for acid-anhydride-hardened resin systems The invention relates to reactive accelerators for use in acid-anhydride-hardened epoxide resin systems, whereby not only rapid hardening is obtained but also production of exhalate forming substances which detract from the dielectric properties is avoided.

Epoxide resin systems accelerated in this manner can be advantageously used as low pressure moulding compounds and also as adhesive, casting and laminating resins, particularly in electrical engineering and electronics.

The hardening of epoxide resins, e.g. with amines, acid an hydrides or polymerization catalysts, does not in itself lead to the formation of any volatile products. This is why epoxide resins are given preference, in many branches of industry, for use as adhesive, casting and laminating resins. Nonaccelerated systems of epoxide resin and acid anhydride require relatively long reaction times of several hours at high temperatures of over 1 500 C. Various accelerator systems are known for reducing the reaction time. Among the usual accelerators for systems of acid an hydride and epoxide resin are polyalcohols, such as glycol or glycerine, tertiary amines, such as dimethyl benzyl amine, triethanol amine or 2,4,6-tris(N,N'-diamino ethyl)phenol.

Among the accelerators recently developed for systems of acid anhydride and epoxide resin are phenyl tin trichloride enabling a hardening point of between 20 and 700C to be obtained, dialkyl pyridine, polymercaptans containing hydroxyl groups and a combination of chromium tricarboxylate and tertiary amines. Other known accelerators include phosphonium halides, reaction products of melamine and dicarboxylic acid, the salts of aliphatic carbonic acids with titanium, zirconium and cerium and tetraphenyl phosphonium tetraphenyl borate.

These resin systems, however, suffer from the drawback that they are not incorporated into the hardened moulded material, or not completely and thereby reduce the dielectric, thermal, optical and/or mechanical properties. Metal compounds or halogen compounds contained in certain accelerators also have a disadvantageous effect, particularly on the dielectric properties. It has also been proposed to accelerate mixtures of epoxide resin and hardening agents by synergistic mixtures of cresol resol resins and aromatic amines.

Epoxide resin polymerization with BF3 complex compounds, suffers from the same drawbacks.

A rapidly hardening epoxide resin composition is known for injection moulding, based on liquid epoxide resin, methyl hexahydrophthalic acid anhydride and 2,4,6-tris-(dimethyl aminomethyl)-phenol as an accelerator.

In the above system the accelerator is not completely incorporated into the hardened product.

Moulding materials are also known which have been produced by the hardening of epoxide resins together with bismaleic imides and polyamines.

Thermally hardenable resin compounds are also known which contain the reaction mixture and an expoxide compound, the former being produced by melting a diamine with a polycarbonic acid anhydride.

These systems differ from the present invention in that they use different systems of epoxide resin and hardening agent.

Maleic acid monoallylesters have been added for hardening of epoxide resins, while polycarbonic acid an hydrides have been added in the hardening process.

Thermally hardenable combinations containing epoxide resin-carbonic acid anhydrides and bismaleic imides (BMI) are known in which proportions of BMI are used within 40 to 250% by mass of the epoxide resin. Resin combinations have also been described in which the proportion of bis-maleic imides ranges from 30 to 80 parts by mass in relation to 100 parts by mass of the total resin. The other components of these resin compositions are epoxide resins and carbonic acid anhydrides.

In the above method the effect of small additions of BMI upon the hardening of mixtures of epoxide resin -and carbonic acid anhydride is not disclosed.

Epoxide resin mixtures are also known which contain not only bismaleic imides but also epoxide resins and carbonic acid anhydrides. These mixtures, however, have been confined to epoxide compounds containing allyl groups. In these mixtures use is generally made of accelerators for the hardening process.

The disadvantage of these resin systems is that the accelerators used therein are not completely bound, either by polymerization or by polyaddition of the initial substances.

The object of this invention is to provide complete integration of the accelerator into the hardened system and at the same time to enable the thermal, thermo-oxidizing and dielectric properties and vacuum-resistance of the resulting moulded bodies to be improved.

The invention further seeks to provide for systems of epoxide resin and acid anhydride, accelerators having suitable reactive groups which ensure complete incorporation into the polymer network.

It has surprisingly been found that bismaieic imides of the general formula 1 have been found suitable as accelerators in hardening systems of epoxide resin and acid anhydride: Formula 1

wherein R=

where n is an integer from 0 to 10, R' and R" can be but need not be equal.

Bismaleic imides in which R' and R" denote the following are particularly suitable: R'=R" below bismaleic imide C6H4-C6H4 4,4'-bis-(maleic imide)-biphenylene C6H4-CH2-C6H4 4,4'-bis-(maleic imide)-diphenylmetha ne C6H4-O-C6H4 4,4'-bis-(maleic imide)-diphenyl ether C6H4-S02-C6H2 4,4'-bis-(maleic imide)-diphenyl sulphone C6H4-C3H6-C6H4 4,4'-bis-(maleic imidophenyl)-2,2-propane C6H4-CH(C6H5)-C6H4 4,4'-bis-(maleic imidophenyl)-phenyl methane C6H4-C6K10-C6H4 4,4'-bis-(maleic imidophenyl)-1 ,4-cyclohexane C6H4COC6H4 4,4'-bis-(maleic imide)-benzophenone m-C6H4 1,3-bis-(maleic imide)-benzene p-C6 H4 1 ,4-bis-(maleic imide)-benzene C2H4 1,2-bis-(maleic imide)-ethane C6H10-CH2-C6H10 4,4'-bis-(maleic imide)-dicyclohexyl methane CH2-C6H10-C6H10-CH2 bis-(maleic imide-4,4'-ethyl cyclohexane) 1 ,3-(CH3)2-C6H2 2,4-bis-(maleic imide)-m-xylene 1 ,4-(CH1 )2-C6H2 2,5-bis-(maleic imide)-p-xylene [C6H4C2N2(C6H5)C6H3]20 4,4'-bis[3-phenyl-6-maleic imide-quinoxalin 2-yl]-diphenyl ether Such bismaleic imides, known per se, are produced by a method in which the corresponding diamines are converted, with twice quantities of maleic acid anhydride in solvents such as mixture of chloroform and dimethyl formamide, to form amidocarbonic acid, the latter being converted by means of acetanhydride to the corresponding imides (U.S. Pat. 30 18 290 and Brit. Pat. 11 37 592). Further information can be found in: Macromolecular Syntheses-Vol. 6-James E. Mulvaney (edit.)-p. 92.

J. V. Crivello. John Wiley 8 Sons-New York, London, Sydney 8 Toronto-1 977.

Oligomaieic imides, which have a similar catalytic effect on systems of epoxide resin and acid anhydride, are produced in a known manner (Europ. Polymer Journal 14 (1978) 12, pp. 985-990), by a method in which diamines are reacted with bismalein imides in a polar solvent, in a molar ratio of less than 1:1.25, at about 1000C. When the reaction is complete the compounds are isolated by precipitation in methanol, filtration and extraction with methanol.

Bismaleic imides of this kind, in accordance with the general formula 1, in which n > O, are usually produced by a process in which a surplus of bismaleic imides, in which n=O, is reacted with diamines in m-cresol in the presence of acetic acid and at 1 00-1 600 C.

Bismaleic imide additions of about 130% result in a considerable acceleration of the hardening reaction of low to high-molecular epoxide resins on the basis of polyphenols, novolacs, triazines, polyenes, siloxans, aliphatic and cyclo-aliphatic olefin oxides as well as amines with aromatic, alicyclic, mono- or polyfunctional acid anhydrides containing double bonds and/or halogen. A remarkable feature of this method is that by using bismaleic imides a combination can be obtained which has a medium "service life" and a short overall hardening time.

Favourable results can be obtained with the following acid anhydrides: Phthalic acid anhydride.

Tetrahydrophthalic acid anhydride.

Hexahydrophthalic acid anhydride.

Endomethylene tetrahydrophthalic acid anhydride.

Methylendomethylene tetrahydrophthalic acid anhydride.

Hexachlorendomethylene tetrahydrophthalic acid anhydride.

Tetrachlorophthalic acid anhydride.

Trimellithic acid anhydride.

Maleic acid anhydride.

Succinic acid anhydride.

Pyromellithic acid dianhydride.

Benzophenonetetracarbonic acid dianhydride.

Cyclopentatetracarbonic acid dianhydride.

Bismaleic imides act as reactive accelerators which by a complex reaction mechanism are completely incorporated into the moulding material. This ensures high vacuum-resistance and freedom from exhalate for a considerable period, even under extreme conditions. Owing to the proportion of thermally stable groups these accelerators contribute to an improvement in the thermal and thermally oxidizing properties of the product.

The addition of the bismaleic imides to the system of epoxide resin and acid anhydride is carried out by a method in which the hardening agent is added in the proportion calculated to the mixture of accelerator and epoxide resin and the system is then melted. In this form it can be used as an adhesive, moulding and laminating resin. The hardening operation is preferably carried out in two stages: (A) Hardening until stability of shape is obtained.

(B) Removal from mould and hardening in the 2nd stage.

In the pressing or transfer moulding or injection moulding process the melting operation in the machine takes place at temperatures of 100--2850C and the hardening to the point where stability of shape is obtained (first stage) is effected in the tool at temperatures of about 100--2850C according to the particular system used.

The hardening in the second stage (re-hardening) can be effected at 1 20-3000C after the workpiece has been withdrawn from the tool.

The variations of the proportions in which the accelerator according to the invention is used enables the hardening time in the tool to be reduced and the efficiency of processing the moulding compound to be optimised. This optimisation of processing and hardening times allows considerable saving of energy and is an increase in productivity. The addition of 2% of 1,3-bismaleic imidobenzene reduces the hardening time of a mixture of dian epoxide resin and acid anhydride to about 50% of the non-accelerated system.By using bismaleic imides with a greater molar mass, e.g. 4,4'-bis[3-phenyi- 6(7) maleic imide quinoxalin-2-yl]diphenyl ether, the acceleration effect is less marked; however, compounds of this type enable the accelerator to be used in greater proportions, which improves such properties of moulding materials as thermal stability, thermal oxidation resistance, dielectric strength and vacuum-resistance at higher temperatures. In addition, the use of such compounds favourably alters viscosity of the melt for subsequent processing.

An addition of 5% of the aforementioned bismaleic imide to a mixture of dian epoxide resin and acid anhydride enables the hardening time to be reduced by 50%. In cases in which additional acceleration appears desirable, co-catalysts can be used, such as tertiary amines, Lewis acids, polyalcohols, carbonic acid salts of chromium, cerium, titanium, zirconium and/or polymercaptan derivatives.

The following examples describe embodiments of the invention, the special possibilities for its use and the advantages which it offers: Example 1 For the hardening of a system consisting of 100 parts by mass of a low-molecular epoxide resin with an epoxide equivalent of 1 90 and 70 parts by mass of phthalic acid anhydride, 118 minutes are required in which to reach the B state at 1 300 C. By the addition of 10 parts by mass of 4,4'-bis-(3phenyl-6-maleicimide-quinoxalin-2-yl)-diphenyl ether to this system the time required for reaching the B state at 1 300C is reduced to 52 minutes.

Example 2 For the hardening of a system consisting of 100 parts by mass of a low-molecular epoxide resin with an epoxide equivalent of 1 90 and 70 parts by mass of tetrahydrophthalic acid anhydride, 127 minutes are required to reach the B state at 1 300 C. By the addition of 10 parts by mass of 4,4'-bis[3phenyl-6-maleimide-quinoxalin-2-yl]-diphenyl ether to this system the time required to reach the B state at 1 300C is reduced to 57 minutes.

Example 3 For the hardening of a system consisting of 100 parts by mass of a low-molecular epoxide resin with an epoxide equivalent of 1 90 and 75 parts by mass of hexahydrophthalic acid anhydride, 226 minutes are required for reaching the B state at 1300 C. By the addition of 10 parts by mass of 4,4' bis[3-phenyl-6-maleimide-quinoxalin-2-yljdiphenyl ether to this system the time for reaching the B state at 1 300C is reduced to 117 minutes.

Example 4 For the hardening of a system consisting of 100 parts by mass of a medium-molecular epoxide resin with an epoxide equivalent of 350 and 30 parts by mass of phthalic acid anhydride, 38 minutes are required for reaching the B state at 1 300 C. By the addition of 10 parts by mass of 4,4'-bis[3 phenyl-6-maleimide-quinoxalin-2-yi]diphenyl ether to this system the time required for reaching the B state at 1 300C is reduced to 19 minutes.

Example 5 For the hardening of a system consisting of 100 parts by mass of a medium-molecular epoxide resin with an epoxide equivalent of 350 and 30 parts by mass of tetrahydrophthalic acid anhydride, 39 minutes are required for reaching the B state at 130"C. By the addition of 10 parts by mass of 4,4' bis[3-phenyl-6-maleimide-quinoxaline-2-yljdiphenyl ether to this system the time required for reaching the B state at 1 300C is reduced to 21 minutes.

Example 6 For the hardening of a system consisting of 100 parts by mass of a medium-molecular epoxide resin with an epoxide equivalent of 350 and 35 parts by mass of hexahydrophthalic acid anhydride, 53 minutes are required for reaching the B state at 130"C. By the addition of 10 parts by mass of 4,4' bis[3-phenyl-maleimido-quinoxaline-2-yl]diphenyl ether to this system the time for reaching the B state at 1 300C is reduced to 33 minutes.

Example 7 For the hardening of a system consisting of 100 parts by mass of a novolac epoxide resin with an epoxide equivalent of 1 80 and 70 parts by mass of phthalic acid anhydride, 69 minutes are required for reaching the B state at 1300 C. By the addition of 10 parts by mass of 4,4'-bis[3-phenyl-6-maleimidoquinoxaline-2-yl]diphenyl ether to this system the time required for reaching the B state at 1 300C is reduced to 32 minutes.

Example 8 For the hardening of a system consisting of 100 parts by mass of a novolac epoxide resin with an epoxide equivalent of 180 and 75 parts by mass of tetrahydrophthalic acid, 72 minutes are required for reaching the B state at 1300 C. By the addition of 10 parts by mass of 4,4'-bis[3-phenyl-6-maleimide- quinoxalin-2-yl]diphenyl ether to this system the time required for reaching the B state at 1 3O0C is reduced to 40 minutes.

Example 9 For the hardening of a system consisting of 100 parts by mass of a novolac epoxide resin with an epoxide equivalent of 1 80 and 80 parts by mass of hexahydrophthalic acid anhydride, 228 minutes are required for reaching the B state at 1300 C. By the addition of 10 parts by mass of 4,4'-bis[3-phenyl-6maleimido-quinoxalin-2-yl]diphenyl ether to this system the time required for reaching the B state at 1 3O0C is reached to 98 minutes.

Examples 10 to 16 For the hardening of a system consisting of 100 parts by mass of a medium-molecular epoxide resin with an epoxide resin equivalent of 350 and 30 parts by mass of tetrahydrophthalic acid anhydride, 39 minutes are required for reaching the B state at 1300 C. By the addition of A parts by mass of 4,4'-bis[3-phenyl-6-maleimido-quinoxalin-2-yl]diphenyl-ether to this system the time required for reaching the B state at 1 3O0C is reduced to B minutes-see Table 1.

Table 1 Example 10 11 12 13 14 15 16 Addition of bismaleic imide, in parts by mass: A 0 1 2 6 10 15 20 30 B time in minutes: B 39 37 32 25 21 15 10 6 Examples 17 to 19 For the hardening of a system consisting of 100 parts by mass of a medium-molecular epoxide resin with an epoxide equivalent of 350 and 30 parts by mass of tetrahydrophthalic acid anhydride, 39 minutes are required for reaching the B state at 1 300 C. By the addition of A parts by mass of 1,4bis(maleimide)benzene to this mixture, the time required for reaching the B state at 1 300C is reduced to B minutes-see Table 2.

Table 2 Example 17 18 19 Addition of bis maleic imide, in parts by mass: A 0 1 2 3 B time in minutes: B 39 32 30 26 Example 20 For the production of a moulded body from a moulded compound consisting of 100 parts by mass of a low-molecular epoxide resin with an epoxide equivalent of 190 and 70 parts by mass of phthalic acid anhydride, a hardening time of about 15 hours at 1300C is required. By the addition of 10 parts by mass of 4,4'-bis(3-phenyl-6-maleimido-quinoxaline-2-yl)diphenyl ether the hardening time is reduced to below 120 minutes. Moulded bodies of the moulding compound modified with the bismaleic imide have a bending strength of about 75 N/mm2 after a hardening time of 120 minutes.

This value is not changed by any increase in the hardening time. The Vicat temperatures of moulded bodies hardened for different periods are as follows: Hrs: 2 3 4 5 6 7 12 24 T( C): 128 139 138 138 140 137 146 146 The water absorption found in test bodies measuring 50x50x4 mm3 was as follows: 4 days 12 days 20 days 40 days 0.25% 0.45% 0.57% 0.73%

Claims

1. An acclerator for accelerating the hardening of epoxide resin systems with an acid anhydride, the accelerator comprising a bismaleic imide of general formula (1).

wherein R is denoted by:

wherein n is an integer from 0 to 10, R' and/or R" being selected from the group consisting of: C6H4 < 6H4 C6H4-CH2-C6H4 C6H--O--C6H4 C6H4-S02-C6H4 C6H4--C3H6--C6H4 C6H4-CH(C6H6)-C6H4 C6H446H 10-C6H4 C6H4O-C6H4 1,3-C6H4 1 ,4-C6H4 C2H4 C6H 1o C6H 10-CH2C6H10 CH2C6H10C6H10CH2 1,3-(CH3)2C6H2 1,4-(CH3-C6H2 [C6H42N2(C6H)-C6H 20

2. An accelerator according to Claim 1 wherein R'=R".

3. An epoxide resin system comprising an epoxide resin, an acid anhydride and an accelerator according to either Claim 1 or 2, wherein the amount of accelerator is in the proportion of 0.5 to 20% in relation to the overall mass of the resin hardener system.

4. An accierator according to Claim 1 or 2, in combination with a cocatalyst.

5. An accelerator and cocatalyst according to Claim 4 wherein the cocatalyst is selected from the group consisting of tertiary amines, Lewis acids, polyalcohols, carbonic acid salts of chromium, cerium, titanium, zirconium and polymercaptan derivatives.

6. A process for hardening an epoxide resin system comprising an expoxide resin, an acid anhydride and an accelerator according to either claim 1 or 2, wherein first stage hardening is effected by heating to a temperature from 1000C to about 2200C within 1 to 30 minutes.

7. An accelerator substantially as herein described with reference to the examples.

8. An epoxide resin system substantially as herein described and with reference to the examples.

9. A process for hardening an epoxide resin system substantially as herein described and with reference to the examples.