CA2080422A1

CA2080422A1 - Process for preparing latent curing agents for epoxy resins, and uses therefor

Info

Publication number: CA2080422A1
Application number: CA 2080422
Authority: CA
Inventors: Christian Burba; Werner Mrotzek; Joerg Volle
Original assignee: BERLIN und BERGKAMEN; Schering AG
Current assignee: BERLIN und BERGKAMEN; Bayer Pharma AG
Priority date: 1991-10-15
Filing date: 1992-10-13
Publication date: 1993-04-16
Also published as: EP0540895A1; DE4134081A1; JPH06179657A

Abstract

ABSTRACT
The invention relates to a process for preparing latent curing agents based on imidazole or N-aminoalkylimidazole/acrylic acid reaction products containing amido, and optionally amino, groups for epoxy resins and to their use in the manufacture of fiber-reinforced printed circuit boards for the electrical industry.

Description

- 20~22 The invention relates to a process for preparing latent curing agents based on imidazole or N-aminoalkylimidazole/acrylic acid reaction products containing amido, and optionally amino, groups for epoxy resins and to their use in the manufacture of ; 5 fiber-reinforced printed circuit boards for the electrical industry.
In modern technology, components have been employed for some time which use electric circuits in the ~orm of vapor~deposited conductors (printed circuit boards) in place of wiring. ~
With this technique, thin electrically conductive layers are applied to insulating base materials by various methods. For this end use, the homogeneity of the base material must meet stringent requirements, which become steadily more rigorous as miniaturization advances. ~ny inhomogeneity of the order of magnitude of the geometric dimensions of the conductors (width and thickness) can lead to serious malfunctions.
The base materials predominantly used today are ~iber-reinforced materials in which curable mixtures of epoxy resins and amine curing agents are used as binder.
As a rule, so-called prepregs are produced in a first step from the reinforcing materials and the binder. These prepregs can then be stored before they are thoroughly cured under pressure and at elevated temperatures.

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, ~; 2 ~ 2 2 In the prepregs, the binder is in what is known as the B
stage, that is, it has been partially cured. Consequently it is solid but still largely soluble in solvents and also fusible.
To achieve this stage, the curing agent must satisfy specific conditions:
It should make it possible to reach the B stage at a minimum expenditure of energy ~temperature and time), yet permit that stage to be maintained for a long period of time, without further modification, after cooling to room temperature.
Complete cure, on the other hand, should be achievable within a short time at the lowest possible temperature and without pronounced exothermicity.
The finished products must, of course, meet the actual physical and mechanical end-use requirements.
Epoxy resins cured with dicyandiamide substantially satisfy these requirements so far as physical and mechanical properties as well as storage and curing behavior are concerned, and dicyandiamide therefore is usPd predominantly at present, occasionally together with accelerators.
The advantageous storage and curing beha~i~r is due ~o the *act that at room temperature dicyandiamide is substantially insoluble in the usual epoxy resins.
When solid crystalline dicyandiamide is used, inhomo-geneities are observed in the cured substrates. These are due to-2~g~22 undissolved and unreacted particles.
While homogeneous substrates can be produced when dicyandiamide solutions are employed, the us~ of solvents gives rise to other problems.
Dicyandiamide is soluble in sufficient amounts only in a few solvents, notably dimethylformàmide and methyl glycol.
However, these solvents are toxicologically hazardous and cause problems, not only in the manufacture of the prepregs, that is, during the impregnation of the reinforcing materials and the 10 conversion to the B stage, but also in connection with the disposal t of wastes.
Because dicyandiamide i5 only sparingly soluble, large amounts of solvent must be used, which influences the impregnating viscosity in such a way that the binder content of the rein~orcing materials cannot be chosen at will.
Since the solvent cannot be eliminated completely during the cure, thermal stresses produced in components of the e~uipment employed also pose the danger that in the field the solvents will be discharged to the ambient air in an uncontrolled manner.
; 20 The object of the present invention is to overcome these drawbacks and to provide a process for the manufacture of fiber-reinforced base materials which can be used in the electrical indllstry, and par~icularly in electronics and microelectronics, to manu~acture printed circuit boards (PCBs).

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, 2 ~ 2 In accordance with the invention, this object is accomplished by using a curable mixture of epoxy resins and latent curing agents based on imidazole and/or N-aminoalkyl-imidazole/acrylic acid reaction products containing amido, and optionally amino, groups.
Thus, the invention relates to compounds based on imidazole and/or N-aminoalkylimidazole/acrylic acid reaction products and containing amido, and optionally amino, groups which can be prepared -(A) through the addition in a first step of acrylic acid or acrylic esters to optionally substituted imidazoles and/or N-aminoalkylimidazoles in approximately equivalent amounts, based on reactive amino hydxogen atoms and double bonds, and (B) by reacting these adducts in a second step with polyamines and/or amino alcohols which on average have two or more reactive hydrogen atoms per molecule, under condensation conditions, to give polyamides and/or polyaminoamides or polyamido alcohols, (C) the reaction products (A) and (B) being optionally extended in a third step with approximately equivalent amounts of mono and/or polyglycidyl compounds, mono-and/or polyacrylates, or mono- and/or polycarboxylic acids.

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2 ~ 2 These compounds can also ~e used as curing agents.
Additionally, the invention relates to glycidyl ethers based on bisphenol A, bisphenol F and novolacs with epoxy values of from 0.18 to 0.6, and more particularly from 0.39 to 0.55, used as epoxy resins. Commercial halogenatcd, and particularly brominated, epoxy resins with approximately 18 percent by weight of bromine, :,~
;~- based on the aforesaid raw materials, are prPferably used.
Because of the occasionally rather high viscosities of the epo~y resins used, the fiber-reinforced base matérials for ` 10 printed circuit boards are pr~dominantly manufactured by the two-step process since only then can the viscosity of the binder system be varied over a wide range by adding solvents.
With this process, prepregs are first produced from the reinforcing materials and the curable mixture, and these prepregs are then processed into finished parts in a separate second step.
The prepregs are usually formed in a continuous process in which the reinforcing materials are passed t~rough an impregnating bath of the resin/curing agent mixture being used.
;, ~ he quankity of impregnant to be deposited on a particular base-material web is xegulated both through the viscosity of the impregnant and through squeegee rolls located downstream.
With solvent-containing systems, the solvent contained in the impregnating solution is evaporated through the input of heat after the impregnating operation and the resin system is at the , , ,"': ' ' ,' ' ` 2~8~22 same time converted from the A stage to the B stage. Depending on the process conditions and on the resin system used, the reinforcing materials impregnated with liquid to highly viscid impregnant are thus turned into a prepreg that is slightly tacky to almost dry. It is important that in this process step the solvent generally be completely eliminated from the impregnating mixture and that the latent curing agent needed ~or the prepreg cure in the second process step not be activated just yet as this generally would cause the reaction of the impregnated reinforcing materials to go prematurely to completion.
With solvent-free systems, impregnation is also followed by a brief heat treatment of the material, depending on the chemical composition of the resin system, to convert the impregnant to the B stage, or then the reinforcing materials are faced on both sides with release sheets immediately after impregnation, without any heat treatment, and placed into intermediate storage adequate to the system. During this storage, either a gradual transition of the resin system to the B stage takes place or the impregnant is fixed on the base materials through physical effects alone and largely without undergoing chemical modification.
The prepregs so obtained can be stored and shipped as rolls before they are cut to 5iZ2 for a given end use and stacked to the thickness of a circuit board. Under the simultaneous action of pressure and heat, the prepreg stack is fully cured into a ': :
' ~ . 2~8~22 -~ high-strength molded part, with the still fluid low-molecular-weight resins passing into the high-molecular-weight C stage of a thermoset.
While in the one-step process, long open times and short cure times at low curing temperatures may be all that is required;
however, prolonged storage stability of the prepregs is additionally used in the two-step process. Storage temperatures bélow room temperature are increasingly considered unacceptable.
It can also be important that, depending on the pre-pregging procedure, the viscoæity of the ready-for-use curable mixture remain substantially constant for the longest possible period of time. This can be necessary, particularly when a ~ large-volume impregnating bath is used, for achieving a nonvarying q resin deposition and a constant B stage, since the conditions of 5' 15 production cannot be continually adjusted to changing relationships in the curable mixture, and since fluctuations in the viscosity have an adverse effect on the physical properties of the fully cured ~inished product.
What is desired in practice is a curable mixture whose 2 0 YiSCosity remains constant over an extended period o~ time in the impregnating bath and which reacts at low temperatures in a short time to the B stage and can then be stored as a prepreg at room temperature for a long period of time without undergoing chemical changes.

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The complete cure of the prspreg which follows should occur within a short time at the lowest possible temperature, the maximum temperature of the exothermic reaction should remain at a low level even with moderately thick layers, and the profile of physical properties of the finished products should meet practical requirements.
Dicyandiamide, long used as a curing agent in curable mixtures based on epoxy resins, is usually combined with co-curing agents andtor accelerators to achieve the desired properties. A
great many proposals are known from the literature in this area.
However, to obtain homogeneous substrates, dicyandiamide should be used in dissolved form as otherwise crystalline unreacted particles will remain in the substrates.
But the few solvents in which dicyandiamide is soluble in sufficient amounts are physiologically hazardous and give rise to i processing problems.
In contrast thereto, the curing agents used in accordance with the invention are soluble in sufficient amounts in all commonly used solvents, including highly volatile and physiologically safe solvents. Consequently, the impregnating ~ viscosity of the curable mixture can be adjusted to actual ; requirements and the solvent can be eliminated practically completely without any difficulty in the conversion to the B stage.
- Solvents suitable for use in accordance with the "~
~ 8 ;

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invention are those commonly used in this field, for example, alcohols, aliphatic and aromatic hydrocarbons, and glycol ethers, as well as mixtures of alcohols and ketones, for example.
Short-chain alcohols such as ethanol or propanol, or mixtures thereof, are preferred in accordance with the invention.
The compounds used in accordance with the invention act both as curing agents and ~s accelerators, and the concurrent use : of commonly employed accelerators and curing agents can therefore be dispensed with. On the other hand, the inventive compounds can be used successfully as accelerators in commercial curing agents, -~or example, dicyandiamide.
The curing agents of the invention can be prepared, by individual processes which are known per se, by adding acrylic acid or acrylic acid derivatives of the general formula 15C~2=C-C00R ~I) .

Rl ..

where R represents H or a short-chain alkyl group having from 1 to 4 carbon atoms, and more par~icularly a methyl or ethyl group, and R1 represents H or CH3-, to imidaæoles of the general formula .

~:: 2~ 2 :: NR4 (II) ` l I
~ 5 RZ

:' ,~ where R2 and R3 may represent, independently o~ each other, ~, C~3, .; C2H5- or phenyl groups and R4 may represent the group 0 -(CH2)a-NH2~ a being 2 or 3, and more particularly the compounds - imidazole, 2 methylimidazole, 2-ethyl-4~methylimidazole or 1-(3-aminopropyl)imidazole.
:- Both the acrylates and the imidazoles can be used alone or as mixtures. As a rule, the imidazole is heated to ~. 15 30-90 C, and preferably to 50-70 C, optionally together with a .. ~ solvent, and the acrylate is slowly added dropwise at that tem-jf perature. The quantity ratios, based on reactivs amino hydrogen `~f atoms and double bonds, are equivalent.
\
These addition products, which, idealized, have the general ~ormula ,, .
~' - L~ C ~ 2 1 a - ~ - LC ~ 2 - C ~ - C O O R
,', R2 R
,. . .

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,, ~ , , ,, ~' '' , ,, ' , . . , 2~A~,~f where R, R1, R2, R3 and a have the meanings given above, b may be 0 or 1, and c may be 1 or 2, subject to the provision that c can be 1 or 2 only when b is 1, and that c can be 1 only when b is 0, are reacted in a second step with polyamines or alkanolamines to give the corresponding compounds containing amido, and optionally amino, groups and/or hydroxyl groups.
Suitable for use as polyamines or alkanolamines are, in accordance with t~e invention, all amines and amino alcohols which : contain two or more reactive hydrogen atoms per molecule and which 10 under the conditions stated will react with the acid group of the addition compounds of formula (III). These are mono- and/or polyfunctional aliphatic, cycloaliphatic, heterocyclic and optionally aromatic or araliphatic amines or amino alcohols which : optionally may contain heteroatoms, such as oxygen and/or nitrogen . .
. 15 in particular, and which optionally may be branched. Preferred - are, in accordance with the invention, heterocyclic amines such as N-aminoethylpiperazine, aliphatic amines such as diethylene tri-amine, and amino alcohols such as diglycolamine.
~-The condensation reaction is carried out by methods which . 20 are known per se~ As a rule, the procedure will be to add the compounds of the general formula (III) to the initial charge of . amine or amino alcohol and to heat the mixture to 180-220 C with stirring, optionally in the presence of an entrainer; to eliminate most of the water of reaction at that temperature by azeotropic ~, .

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distillation; and to s~op the reaction at a vacuum of about 10-50 mbar.
Depending on the starting material and the desired reaction products, the molar ratios may be approximately equivalent or select~d so that free amino hydrogen atoms remain in the reaction product.
Reaction products with free amino hydrogen atoms can then be extended with reactive mono- or polyfunctional compounds in a further step. Suitable reactive compounds are, in principle, all compounds which will react with the amino hydrogen atoms at room temperature or under the condensation conditions. In accordance with the invention, mon~- and/or diglycidyl compounds, mono- and/or diacrylates, and mono- and/or dicarboxylic acids are preferred.
These compounds may ke reacted alone or as any desired mixture with the compounds containing amino groups. The molar ratios are preferably selected so that no excess of any component, and especially no free amino hydrogen atoms, remain in the reaction mixture.
Butanediol diglycidyl ether and hexanediol diglycidyl ether are preferred as mono- and/or diglycidyl compounds which in accordance with the invention may be used.
Butanediol diacrylate and hexanediol diacrylate ~re preferred as mono- and/or diacrylates which in accordance with the invention may be used.

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2~8~7, , Aliphatic, cycloaliphatic, aromatic and araliphatic mono-and polyfunctional compounds which under the conditions stated will react with the amines or amino alcohols may be used as carboxylic acids. Preferred are, in accordance with the invention, aliphatic dicarboxylic acids such as adipic acid and azelaic acid, and dimerized fatty acids prepared from unsaturated monomeric monobasic acids having from 12 to 18 carbon atoms by known methods and having dimer contents of about 65 weight percent and higher.
Adipic acid, azelaic acid and dimerized fatty acids are preferred as mono- and/or dicarboxylic acids which in accordance with the invention may be used.
The quantity of curing agents or accelerators may be varied over a wide range. It is determined by the intended end use and the curing conditions which it may impose. In accordance with ; 15 the invention, quantities ranging from 4 to 20, and preferably from 5 to 10, parts by weight, based on 100 parts by weight of epoxy compound, are used.
The epoxy resins used in the preparation of the curable mixture are glycidyl esters and ethers having two or more epoxy groups per molecule, and preferably glycidyl ethers based on mono-or polyhydric phenols. Preferred are, in accordance with the ; inYention, the glycidyl ethers of 2,~bis (4-hydroxyphenyl)propane (bisphenol A) with epoxy values of from 0.2 to 0.6, and particularly the compounds with epoxy values of about 0.39 to 0.5~
,,. ;. .

'' which at room temperature are semisolid and range from highly viscous to moderately viscous. The glycidyl ethers based on bisphenol F and the novolacs have also proved advantageous.
Advantageously, commercial halogenated, and preferably brominated, epoxy resins with the usual bromine contents and based on the aforesaid resins are used.
For modification of the properties of the end product, modifying or auxiliary substances such as phenolic resins, melamine resins or silicone resins may be used, in addition to other epoxy resins. --To obtain the desired viscosity, resins of different viscosities or diluents may be used, as may commonly used solvents such as dimethylformamide, acetone, methyl ethyl ketone, methyl glycol or propylene glycol monomethyl ether or mixtures thereof.
In prepegging, organic and insrganic ~ibers, nonwoven and woven fabrics and particularly glass are used.
The solvent-containing prepregs are ~ormed by the con-ventional method, the base materials being impregnated in an impregnating bath with the reactive resin mixture and, a~ter the excess resin has been squeegeed off, being continuously converted ~rom the A stage to the B stage with input of energy (mostly heat) and simultaneous elimination of the solvent. Depending on the desir~d prepreg consistency (viscid to solid), the prepregs are -~ then provided on both sides with a release sheet and rolled up for , . . .

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storage and shipping. The further processing consists of cutting the individual prepreg layers to siæe and placing them one on top of the other to form a stack, from which a highly crosslinked part is produced by molding with simultaneous heat input.
The curing agents of the invention can also be used successfully in solvent-free prepregs based on epoxy resins and, optionally, commonly used curing agents. The base materials are impregnated at elevated temperature, if indicated, with the binder systems by methods which are known per se and then appropriately stored before they are further processed like the solvent-containing systems.
Further examples of solvent-free systems are heat-curing one-component adhesives, for example, for the adhesive-bonding of body sections in the automotive industry, and epoxy-resin coatings ;~ 15 applied either wet or as a powder.

` PREPARATION OF INVENTIVE CURING AGENTS
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EX~MPLES

1. Reaction of imidazole/acrylic acid adduct with N-aminoethylpiperazine 1,068.6 g of imidazole is dissolved at room temperature in 3,300 g of distilled water~ The solution is heated to approximately 40-50 C and 1,131.4 g of acrylic acid is added ''~ -. ~ , '~ ' .

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dropwise. On completion of this addition, the mixture is allowed to react for another 2 hrs at 50 C.
The reaction product (a 40% solution in water) is ~reed of water in a vacuum and at about 120 C slowly mixed with 2,026 g of N-aminoethylpiperazine. The mixture is heated to approximately 180 C, and the theoretically possible quantity of water is distilled off by the use of a dephlegmator.

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Upon cooling, a pastelike, highly viscous product is ' obtained.
:,.... .
~ 10 Viscosity at 60 C: Approx~ 50 Pa-s c Amine number: Approx. 670 f.
i~ Acid number: 1.3 .:
It corresponds to the product obtained with an equivalent amount of methyl acrylate (in place of acrylic acid).

: 15 : 2. Reaction of aminopro~ylimidazole/acrylic acid adduct with N-aminoethvl~iperazine 500 g of aminopropylimidazole is introduced as initial charge in 360 g of distilled water. The solution is heated to 50-- 20 60 C and 5~6 g of acrylic acid is added dropwise. ~n completion ;
of this addition, the mixture is allowed to react for another hour ; at 60 C. The reaction product is a 75% solution in water.

320 g of this product is carefully mixed with 248 g ~an approximat~ly 10% excess) of N-aminoethylpiperazine. Upon heating to about 120 C, the amount of water used distills off, and from ~; 16 ,' ., `

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about 180 C, approximately 32 g of water formed through amide formation distills off. The mixture is heated to about 210 C and maintained at that temperatur~ for approximately 2 hrs, and excess amine is then drawn off in a vacuum of 10 mbar. The product has the following characteristics:
Amine number: 599 Acid number: 0.5 It has the consistency of lard.

0 3. Reaction of a 2-methylimidazols/acrylic acid adduct with diethylene triamine 164 g of 2-methylimidazole is dissolved in 308 g of distilled water at approximately 40 C and at that temperature slowly mixed with 144 g of acrylic acid. On completion of this addition, the mixture is stirred for another 2 hrs at 50 C. The 50% solution obtained is used in further reactions.
51.5 g of diethylene triamine is slowly mixed with 308 g of the aforesaid 2-methylimidazole/water solution. Upon heating, the amount of water used distills off. Upon further heating to about 180 C, approximately 1 mol of water of reaction can be distilled off. The product has the following characteristics:
Amine number: 429 Acid number: 8.2 2 ~ 2 2 4. Reaction of imidazole/acrylic acid adduct : of Example 1 with di~lycolamine .. 350 g of the imidazole/acrylic acid adduct (40% in water) ~ 5 of Example 1 is slowly added to 115 g (a 10% excess) of .~ diglycolamine. Upon heating, the amount of water used distills ~: off. Upon further heating, water of reaction forms from 160 C on.
The mixture is maintained at 190 C for 2 hrs, and the remaining ~ water and the excess amine are finally eliminated in a vacuum. The: 10 reaction product has the following characteristics:
Amine number: 2S1 ~. Hydroxyl number: 257 ;~
-` Acid number: 5.9 ,.:
'. 15 5~ Reaction of imidazole/acrylic acid~N-aminoethYl~iperazine ; reaction product of Example ~ with hexanediol dialycidyl . ether 125.5 g of the aforesaid adduct of Example 1 is intro-duced as initial charge, heated to 100-120 C and slowly mixed with 79.5 g of hexanediol diglycidyl ether (epoxy value 0.63). Stirring , is continued for another 2 hrs at 120 C.
Amine number: 410 ,, ~ 18 .'~ .

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6. Reaction of imidazole/acrylic acid/N-aminoethylpiperazine reaction product of ExamPle 1 with hexanediol diacrvlate ,;.
125.5 g of the aforesaid adduct of Example 1 is intro-; 5 duced as initial charge, heated to 100-120 C and slowly mixed with 56.5 g of hexanediol diacrylate. Stirring is continued for another ` 2 hrs at 120 C.
Amine number: 460 7. Reaction of 2-methylimidazole~acrylic acid adduct and dimeric fatty acid with diethylene triamine 308 g of 2-methylimidazole/acrylic acid adduct (50~ in water) is introduced as initial charge and reacted with 51.5 g of diethylene triamine as in Example 3 and then mixed at 180 C with 290 g (excess acid) of dimeric fatty acid (dimer content 96%, acid number 193). The mixture is heated for 2 hrs at 230 C until all w~ter of reaction has been distilled off.
; Amine number: 133 Acid number: 55 The analytical values given in the foregoing examples ; (amine number, acid number, hydroxyl number) are determined by the methods customarily employed in this field and are given in mg XOH/g of substance.

2 ~ 2 Determination of effect of curin~ aaent in the case of brominated epoxy resins ;
Example 1 100 g of a brominated epoxy resin (epoxy value about 0.18, bromine content about 18%) dissolved in 25 g of methyl ethyl ketone (MEK) is mixed with 10 g of a 50% curing-agent solution of the inventive reaction product and ethanol and used in prepregging.
The curing-agent solution is prepared at room temperature. Its ,; concentration may generally be chosen at will. -For prepregging on the laboratory scale, a woven glass-filament fabric about 0.1 m2 in size is first impregnated -~
with the resin/curing agent solution. This is followed by a two-minute heat treatment at 120 C in a forced-air oven of the reinforcing material so impregnated. During prepregging, the solvent is removed from the impregnant and the reactants are converted from the A stage to the B stage. Almost dry, flexible prepregs are so obtained which after cooling can be stored at room temperature for several wesks until they are processed further.
The further processing o~ the prepregs to laminates about 1 mm thick is carried out in one hour at 150 C with a compacting pressure of about 1 bar. The thoroughly cured end product so obtained exhibits no flaws so far as adhesion of the individual prepreg layers is concerned.

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To determine the heat resistance of the matrix material, test specimens measuring 100 x 10 mm are then taken from the laminates and subjected to a torsion pendulum test in conformity with DIN 53,455. The results of this test are presented in Table 1 for various mixing ratios.
The glass-transition temperatures also listed in Table 1 for Examples 2 to 7 were determined as in Example 1 with the epoxy resin there specified. For comparison, the glass-transition temperature of a matrix material much used at present, with dicyandiamide as curing agent and N-methylimidazole as accelerator, is included in the table. (Mixing ratio brominated epoxy resinjdicyandiamide/N-methylimidazole:
100:5:0.8.) . ., ,., ,":

2 ~ 2 2 ., .

Table 1 Heat resistance of laminates . _ . .
Mixing Glass-trannition temperature (C) Example ratio after prepreg ntorage for ~curing re~in: _ agent) agent 1 day 4 weeks 12 week~ 26 week~
! _. _ _ ' _ I 1 100:5 127 116 116 115 l 100:10 125 .
l . 11 2 100:5 124 120 118 100:10 129 121 120 3 100:5 145 131 127 100:10 151 136 l . ~ . . __ _ 11 4 100:5 126 122 119 100:10 123 _ I
100:5 124 118 117 117 100:10 118 . _ I
l 6 100:5 128 115 110 110 . I lO0:10 130 l ... ... .. ... . .. .. 11 : 7 100:5 119 119 100:10 1~5 123 l . . . 11 Compar-atlve100:5:0.8 118 . 20 Determination of effect of curinq agent ; in the_case of epoxy_resins based on bisphenol A
To determine the properties of the material when selected curing agents are used, mixtures consisting solely of epoxy resin and curing-agent were fully cured and tested so as to exclude the 2~8~
:.
distorting influence of reinforcements and additives.
; In the examples listed in Table 2, a glycidyl ether based on bisphenol A with an epoxy value of 0.53 ~as used as epoxy resin.
To make the test specimens, 100 g of the epoxy resin was mixed in each case at room temperature with the quantity of curing agent indicated in Table 2 and thoroughly cured in a steel mold to give flat molded pieces 4 mm thick. From these molded pieces, test specimens were taken by sawing or milling, and on these the values of the properties listed in Table 2, determined in conformity with the test standards specified below, are based.

Test-specimen dimensions Flexural strength DIN 53,482 80 x 10 x 4 mm Deflection DIN 53,452 80 x 10 x 4 mm Impact strength DIN 53,453 50 x 6 x 4 mm Tensile strength DIN 53,455 Dumbbell No. 3 Elongation DIN 53,455 Dumbbell NoO 3 Modulus of elasticity DIN 53,457 Dumbbell No. 3 Marten's temperature DIN 53,458 60 x 15 x 4 mm ~eat-distortion temperature DIN 53,461 120 x 10 x 4 mm Glass-transition temp~rature DIN 53,445 80 x 10 x 1 mm ,~

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Table 2 Properties of unreinforced molded materials .... _ I
Example 1 Example 6 . l .__ I
Quantity of curing agent g 14 14 ¦Curing conditions 2 hrs, 120C2 hrs, 120C
.,. l .. _ _ I
Flexural strength N/mm2 90 41 Deflection _~ 11 . Impact strength kJ/m2 20 : l Tensile strength N/mm2 50 30 .. .. _ ~r ~
: Elongation % 2.0 2.0 ¦
l Modulus of elasticity N/mm2 3,0003,000 _ 11 I ¦ ~arten's temperature C 113107 l ..
Heat-distortion temperature C 130 129 .' . .__ Glass-transition temperatureC 156 158 . ._ ~ ~
, 20 ,;

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Claims

1. A composition comprising at least one imidazole and/or N-alkylimidazole/acrylic acid reaction products and containing amido, and optionally amino, groups prepared by (A) adding, in a first step, acrylic acid or an acrylic ester to an acrylic ester to an optionally substituted imidazole and/or N-aminoalkylimidazole in approximately equivalent amounts, based on reactive amino hydrogen atoms and double bonds, to prepare an adduct and (B) reacting the adduct in a second step with a polyamine and/or amino alcohol which, on average, has two or more reactive hydrogen atoms per molecule, under condensation conditions, to give as a reaction product a polyamide and/or polyaminoamide or polyamido alcohol, (C) optionally extending the reaction product of (A) and (B) in a third step with approximately equivalent amounts of a mono-and/or polyglycidyl compound, mono- and/or polyacrylate or mono- and/or polycarboxylic acid.

2. The composition as defined in claim 1, wherein acrylic acid is reacted in a first step with imidazole and/or 2-methylimidazole and/or N-aminopropylimidazole, and the resulting adduct is reacted in a second step with diglycolamine and/or diethylene triamine and/or N-aminoethylpiperazine.

3. The composition as defined in claim 1, wherein the reaction product of steps (A) and (B) is extended in a third step, (C), with at least one compound selected from the group consisting of butanediol diglycidyl ether, hexanediol diglycidyl ether, butanediol diacrylate, hexanediol diacrylate and dimerized fatty acid.

4. A curing agent for epoxy resins comprising an amount of a composition according to claim 1 effective as a curing agent.

5. A curable epoxy-resin composition comprising (a) an epoxy resin having on average more than one epoxy group per molecule, and (b) a composition as defined in claim 1.

6. A curable epoxy-resin composition comprising reinforcements and embedments impregnated at room temperature with a binder comprising (a) an epoxy resin having on average more than one epoxy group per molecule;
(b) a composition as defined in claim 1; and optionally (c) solvents, fillers, pigments and auxiliary agents;
and converted to the semisolid but still fusible state (B stage), optionally at elevated temperature.

7. A method for preparing a molded epoxy-resin article including reinforcements and embodiments comprising impregnating the reinforcements and embedments at room temperature with a binder comprising (a) an epoxy resin having on average more than one epoxy group per molecule;
(b) a composition as defined in claim 1; and optionally (c) solvents, fillers, pigments and auxiliary agents;
converting to the B stage, molding or placing between substrates to be bonded laminates or prepregs, and thoroughly curing at elevated temperature and under pressure.

8. A process for manufacturing fiber-reinforced base materials for the electrical industry comprising converting reinforcing materials impregnated with a binder based on epoxy resins and amine curing agents to the B stage by the use of heat and optionally pressure, and thoroughly curing them in a second step at elevated temperature, wherein (a) brominated epoxy resins having on average more than one epoxy group per molecule are used as epoxy resins and (b) a composition as defined in claim 1 is used as amine curing agent.