WO1992019601A1

WO1992019601A1 - Diaminocyclohexane imidazolines and their use

Info

Publication number: WO1992019601A1
Application number: PCT/EP1991/002474
Authority: WO
Inventors: Christian Burba; Alwin Krotzek; Werner Mrotzek; Bernd Neffgen
Original assignee: Witco Gmbh
Priority date: 1991-04-27
Filing date: 1991-12-20
Publication date: 1992-11-12
Also published as: DE4113870A1

Abstract

The object of the invention consists of compounds of the general formula (I) in which R1 is a possibly branched alkyl radical with 1-9, preferably 1-5, C atoms and their use as curing agents for epoxy resins.

Description

Λ

The inocvclohexane imidazolines and their use

The invention relates to new imidazolyl derivatives, their use as curing agents in epoxy resin compositions, curable epoxy resin compositions comprising them, consisting of an epoxy resin and of the compounds of the general formula I and optionally conventional curing agents and solvents for the production of moldings.

In principle, two processes are used today for the production of composite materials.

In the wet-on-wet process, the reinforcing materials are impregnated with the curable mixture and cured in one step in the heat to the duromeric final state (one-step process).

In the two-stage process, so-called prepregs are first produced from the reinforcement materials and the curable mixture, which are then processed into finished parts in a second, separate process step. In terms of process engineering, a distinction is once again to be made between the use of solvent-containing and solvent-free procedures.

The prepregs are normally produced in a continuous process in which the reinforcing materials are either passed through an impregnating bath of the resin-hardener mixture to be used, or the impregnating agent is mixed only immediately before it is applied to the carrier material and knocked on using a special device. The control of the amount of impregnating agent to be applied to a certain web of carrier material takes place in addition to the viscosity of the impregnating agent via downstream squeeze rollers.

In the case of solvent-containing systems, the solvent contained in the impregnation solution is evaporated by the application of heat after the impregnation process, and the resin system is simultaneously converted from the A to the B state. Depending on the process conditions and the resin system used, the reinforcing materials soaked with liquid to highly tacky impregnating agent become a slightly tacky to almost dry prepreg. In this process step it is important that on the one hand the solvent is completely removed from the impregnation mixture, but on the other hand that the latent hardener required for the prepreg curing in the second process step does not yet start, in order to allow the impregnated reinforcing materials to react unintentionally to prevent.

In the case of solvent-free systems, depending on the chemical composition of the resin system, either a short heat treatment of the material is carried out after the impregnation, or the reinforcing materials are laminated with separating foils on both sides immediately after the impregnation, without a separate heat treatment, and the system is adequate Intermediate storage fed. in the

In the course of this intermediate storage either a gradual transition of the resin system into the B state occurs or the impregnating agent is fixed on the carrier materials solely by physical effects, largely without chemical changes.

The prepregs obtained in this way can be temporarily stored and transported as rolls before being used for the respective application. case, be cut accordingly and layered on top of each other in component thickness. The prepreg stack is cured into a high-strength molded part by the simultaneous action of pressure and temperature, the still low-molecular, flowable resins being converted into the high-molecular C state of the duromer.

While long open times and short curing times at low curing temperatures are required in the one-step process, the longest possible stability of the prepregs is an additional criterion in the two-step process. In practice, storage temperatures below room temperature are becoming less and less accepted.

Regardless of the prepreg production, they should be cured at the lowest possible temperatures within a short time, the temperature maximum of the exothermic reaction should remain at a low level even with larger layer thicknesses, and the level of physical properties of the end products should be adapted to practical requirements.

These requirements with regard to the curing behavior and property level also apply in the same way to the epoxy resin systems to be processed in the wet-on-wet process.

For certain applications, only a hardening up to the dimensional stability of the shaped bodies is necessary or even desired, the final hardening taking place after a possible intermediate storage in a subsequent tempering process at the required temperatures. It is important, however, that the The thermal resistance of the material rises above the hardening temperature, since otherwise demolding is only possible after the temperature of the molded part has been reduced.

Dicyandiamide, which has long been used as a latent hardener in curable mixtures based on epoxy resins, is generally combined with co-curing agents and / or accelerators to achieve the desired properties. A large number of proposals have therefore become known from the literature in this field.

Sufficient amounts of dicyandiamide are only soluble in a few solvents, in particular dimethylformamide or methylglycol. However, these solvents are toxicologically unsafe and cause problems both in the manufacture of the prepregs, that is to say when the reinforcing materials are impregnated and converted to the B state, and in the disposal.

Furthermore, in particular when using broken epoxy resins, the end products increasingly demand higher thermal resistances, which cannot be achieved by dicyandiamide hardening. On the other hand, however, the use of brominated epoxy resins for products with reduced flammability cannot be dispensed with.

If solid crystalline dicyandiamide is used in liquid epoxy resins without the use of solvents, the dicyandiamide is either dispersed directly in the required amount in the epoxy resin or a highly filled dicyandiamide / epoxy resin paste is prepared beforehand, which is subsequently added to the main amount Epoxy resin and the accelerator to the desired resin / hardener concentrations is set.

The choice of the accelerator represents a compromise between the level of the required curing temperature and the prepeg storage stability. A strong accelerator not only reduces the curing temperature of an epoxy-dicyandiamide mixture to a technically desirable temperature level, but also there is also the danger that this accelerator reacts with the epoxy resin already during the prepreg storage, whereby the stability of the prepreg storage is permanently reduced.

When a comparatively weak accelerator is also used, however, very high curing temperatures are necessary for curing the dicyandiamide, as a result of which u. a. undesirably strong thermal stresses are introduced into the end product.

When dicyandiamide and accelerator are introduced into a melt of epoxy resins solid at RT, the same problems occur in a time-compressed form as when using a liquid epoxy resin, especially since the behavior of the accelerators at higher temperatures is even more difficult to control. It does not matter whether the system is used as a matrix material for fiber composites or as a hot melt for reactive adhesives or as a powder for coatings.

The object of the present invention was, while avoiding the disadvantages of the prior art, curable mixtures based on epoxy compounds and latent and in the To find epoxy resins soluble or homogeneously distributable curing agents which, at relatively low temperatures, harden within a short time without high exothermic temperature peaks to the dimensionally stable state or harden to the final final state, have a thermal resistance which corresponds to the requirements of practice , and which have sufficient storage stability in prepregs at room temperature.

This object is achieved by using a new hardening agent, if appropriate also using conventional latent hardening agents.

The invention therefore relates to imidazolyl compounds of the general formula (I)

wherein R ^{1 is} an optionally branched alkyl radical with 1-9, preferably 1-5, carbon atoms.

The invention further relates to imidazolyl compounds of the general formula II,

ü _'

and the general formula III,

( in )

in which R ^{1 is} an optionally branched alkyl radical with 1-9, preferably 1-5, carbon atoms, in which R ² = - (Cfo.a-, in which a = 2-10, preferably 4-6, in which R ³ =

with b = 0-5 and where R ⁴ and R ^{s can be} independently H or CH3 -.

Another object of the invention are curing agents for glycidyl compounds which can be prepared by reacting

a) 1, 2-diaminocyclohexane with

b) monocarboxylic acids of the general formula V R ¹ -C-OH (V)

O

in which R ^{1 is} an optionally branched alkyl radical having 1-9 carbon atoms, preferably 1-5 carbon atoms, to the imidazolyl compounds of the general formula I

and optionally further reaction of these compounds with diacrylates of the general formula II a

CH _Z = CH-C-0-R ² -0-C-CH = CH ₂ (II a)

to compounds of the general formula II

or with Diglvcidvlethern of the general formula III a

CH ₂ -CH-CH2 -OR ³ -O-CH2 -CH-CH2 {III a) \ / \ / o 0 to compounds of the general formula III,

( in )

in which R ^{1 is} an optionally branched alkyl radical with 1-9, preferably 1-5 C atoms, in which R ² = - (CH∑la-, in which a = 2-10, preferably 4-6, in which R ³ =

with b = 0-5, and wherein R ⁴ and R ^{5 can} independently be H or CH3 -.

The products of the formula III according to the invention can also be prepared via the isolated adducts of 1,2-diaminocyclohexane and glycidyl compounds by reaction with monocarboxylic acids.

Another object of the invention is the use of compounds of the general formula I - III, optionally with the use of conventional amine compounds, auxiliaries and additives, as curing agents for glycidyl compounds. Another object of the invention are Epoxidharzform¬ body, which are characterized in that in the first stage, the reinforcing or insert materials with the binder consisting of

a) a glycidyl compound with an average of more than one glycidyl group per molecule and

b) Compounds of the general formulas I - III and optionally

c) usual solvents, fillers, reinforcing or insert materials, pigments, auxiliaries and, if necessary

d) usual nitrogen-containing heterocyclic A compounds

impregnated and converted into the solid and dimensionally stable state, and in the second stage are cured at a temperature below the softening temperature of the shaped bodies formed in stage 1.

The imidazolyl compounds of the formula I according to the invention can be prepared by condensing 1,2-diaminocylohexane with monocarboxylic acids of the general formula V.

R ⁱ -COOH CV) wherein R ^{1 is} an optionally branched alkyl radical with 1-9 carbon atoms, such as the methyl, ethyl, n-propyl, i-propyl, primary, sec, tert-butyl radical, 2-ethylpentyl radical, 3.3 .5 (3.5.5) -trimethylpentyl radical, in the molar ratio of amine to acid from 1: 1 to 3: 1, the aminoamide at reaction temperatures of about 180 ° C. in the first stage and by heating to 180 ° C. 200 ° C in a vacuum in the second stage the imidazoline is produced.

According to the invention, the reaction is preferably carried out in such a way that the excess amine and the water resulting from the imidazoline formation are removed in vacuo.

These imidazolyl compounds of the general formula I prepared in the first stage

can be reacted in a further stage with difunctional glycidyl compounds and / or acrylates to give the imidazolyl compounds of the general formula II

of the general formula III

("I)

in which R ^{1 is} an optionally branched alkyl radical with 1-9, preferably 1-5, carbon atoms in which R ² = - (CH2) a-, in which a = 2-10, preferably 4-6, in which R ³ =

with b = 0-5, and wherein R ⁴ and R ^{s can} independently be H or CH3.

The known aliphatic, cycloaliphatic, aromatic and araliphatic compounds, in particular the commercially available glycidyl ethers, as described in the Handbook of Epoxy Resins, Lee & Neville, 1967, Chapter 2, can be used here as glycidyl compounds.

According to the invention, preference is given to using the glycidyl ethers based on polyhydric phenols, in particular those based on 2,2-bis (4-hydroxyphenyl) propane (bisphenol A) Epoxy values from 0.2 - 0.6. In addition, the glycidyl ethers based on bisphenol F and polypropylene glycols have also proven to be advantageous.

The compounds of the general formula I are reacted with the diglycidyl ethers mentioned by processes known per se. According to the invention, the procedure is preferably such that the imidazolyl compounds of the general formula I are reacted with stoichiometric amounts of the diglycidyl ethers at 60-80 ° C. with or without a solvent.

The acrylate compounds used according to the invention for the preparation of the addition compounds are transesterification or transesterification products of dihydric alcohols and acrylic acids or their esters. These reactions take place in accordance with the methods belonging to the known prior art. The straight-chain or branched dihydric aliphatic alcohols such as ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, decanediol or their isomers can be used here as alcohols.

According to the invention, the diacrylates are reacted with the compounds of the formula I, preferably with stoichiometric amounts, based on acrylic double bonds, at about 60-80 ° C.

The reaction of the glycidyl compounds and / or the acrylates with the imidazoline compounds of the general formula I is carried out according to the methods known for the respective reactive groups, the ratio of mono-imidazolyl compound to the other reactive group preferably being 1: 1 is. The compounds of the formulas I, II, III according to the invention can be used as curing agents alone or as a mixture, 5-50 g, preferably 5-40 g, but especially 5-30 g curing agent being used per 100 g epoxy resin. The quantities depend on the structure of the respective hardening agent and can be optimized by simple orienting tests.

It is also possible to use the compounds of the general formula I-III in the form of their salts. The organic and inorganic salt formers known in this field can be used here. However, the mono- or polyvalent organic carboxylic acids are preferred according to the invention.

The epoxy resins used as a binder component according to the invention are glycidyl esters and ethers with two or more epoxy groups per molecule (as described in Lee & Neville, Handbook of Epoxy esins, 1967 Chapter 2), but preferably the glycidyl ethers based on mono- or polyvalent ones Phenols. According to the invention, preference is given to glycidyl ethers of 2,2-bis (4-hydroxyphenyl) propane (bisphenol A) with epoxy values of 0.2-0.6, in particular the compounds which are liquid at room temperature and have epoxy values of around 0.45 to 0.55 . In addition, the glycidyl ethers based on bisphenol F and the novolaks have also proven to be advantageous.

The commercially available halogenated, in particular brominated, epoxy resins based on the phenols listed above can also be used, in particular for products which are to be used in the electronics sector (printed circuit boards). To achieve particularly desired properties, the imidazoline compounds according to the invention can also be used in a mixture with the aminic curing agents customary in this field.

In combination with dicyandiamide, they can act both as co-hardening agents and as accelerators and accordingly can be used in the desired mixing ratio. The hardening or acceleration / hardening behavior achieved is influenced by the respective structures and quantitative ratios.

In addition to other epoxy resins, modification or auxiliary substances such as phenolic resins, melamine resins, silicone resins, inorganic and organic fillers such as quartz powder, titanium dioxide, carbon black, silicone rubber or butadiene rubber can also be used to modify the properties of the end product.

To set the desired viscosity, different viscous resins or diluents can be used, but also the customary solvents such as diethylformamide, acetone, methyl ethyl ketone, methyl glycol, propylene glycol monomethyl ether, short-chain alcohols or mixtures thereof.

Organic and inorganic fibers, nonwovens and fabrics based on aramid, carbon or cellulose, metals such as boron, steel etc., ceramics, but especially glass, are also used to produce the prepregs. The preparation of the solvent-containing prepregs takes place according to the method known per se, in which the carrier materials are impregnated with the reactive resin mixture in an impregnation bath and, after the excess amount of resin has been squeezed off, continuously with the supply of energy (usually heat), with simultaneous removal of the solvent means to be converted from the A to the B state. Depending on the desired prepreg consistency (sticky to firm), these are then provided with a release film on both sides and rolled up for storage and transport. The further processing takes place by cutting and folding the individual prepreg layers into a stack, from which a highly cross-linked workpiece is produced by shaping measures with simultaneous supply of heat.

The curing agents according to the invention can also be used successfully in solvent-free prepregs based on epoxy resins and, if appropriate, customary curing agents. In this case, the carrier materials are impregnated with the binder systems, if appropriate at elevated temperature, by methods known per se and stored appropriately for the system before they are further processed like the solvent-containing systems.

Further examples of solvent-free systems are wet laminates, in-situ fiber-reinforced molded parts (RTM), heat-curing one-component adhesives, for. B. for the bonding of body parts in the automotive industry and epoxy resin castings and epoxy resin coatings, which are applied either wet or as a powder. Preparation of the imidazoline compounds

Example 1;

2280 g (20 mol) of 1,2-diaminocyclohexane are introduced and 600 g (10 mol) of acetic acid are added dropwise so that the temperature of the reaction mixture does not exceed 50 ° C. The amount of water released by amide formation (about 180 g) is then distilled off by heating to about 180 ° C. The excess amine and the water resulting from the imidazoline formation are heated to approx. Distilled 200 ° C at 300 mbar. After about 2 hours at 200 ° C / 300 mbar, the distillation has largely ended.

The reaction product present in the bottom is purified by distillation at 200-230 ° C / 100 mbar. A colorless, semi-solid product at RT is obtained with the following key figures:

AZ: approx. 400

Imidazoline content (according to IR or NMR)> 90%

Example 2

Adduct of idazolin according to Example 1 and solid epoxy resin (MG 950)

237.5 g of solid epoxy resin with an average molecular weight of 950 are dissolved with 237.5 g of methyl ethyl ketone at RT and a solution of 69 g of imidazoline according to Example 1 in 69 g of methyl ethyl ketone is added. The mixture is heated for about 5 hours under reflux and then checked the completeness of the reaction by thin layer chromatography. The reaction product has a viscosity of approx. 800 mPas / 25 ° C.

Example 3

Adduct of imidazoline according to Example 1 and liquid epoxy resin (average molecular weight 380)

138 g of imidazoline are dissolved in 200 g of propylene glycol monomethyl ether, the solution is heated to 60 ° C. and 190 g of liquid epoxy resin (average molecular weight 380) are slowly added. After the addition, the mixture is left to react at 80 ° C. for 2 hours. After the solvent has been stripped off (up to 150 ° C. in vacuo), a solid product with an amine number of 174 is obtained.

Example 4

Additon product from imidazoline according to Example 1 and butanediol diacrylate

138 g (1.0 mol) of imidazoline according to Example 1 are dissolved in 100 g of ethanol and the solution is heated to about 40 ° C. 99.1 g (0.5 mol) of butanediol diacrylate are then added dropwise at 40-50 ° C. The mixture is stirred at about 80 ° C for 1 hour and then the ethanol is removed. The starting raw materials can no longer be detected after thin layer chromatography. The addition product has a viscosity of 11.9 Pas / 25 ° C. Determination of curing agent effects in connection with brominated resins

example 1

100 g of a brominated epoxy resin dissolved in 25 g methyl ethyl ketone (MEK) (epoxy value approx. 0.18, bromine content approx. 18) are mixed with 10 g of a 50% hardener solution from the reaction product according to the invention and MEK and used for prepreg production . The hardener solution is prepared at RT, and its concentration can in principle be chosen arbitrarily.

For prepreg production on a laboratory scale, an approximately 0.1 m ² large glass filament fabric is impregnated with the resin hardener solution. This is followed by a heat treatment of the reinforcing material impregnated in this way for 2 minutes at 120 ° C. in a forced-air drying cabinet. During this prepreg process, on the one hand the solvent is removed from the impregnating agent and, on the other hand, the reaction components are transferred from the A to the B state. The result is almost dry, flexible prepregs that can be stored for several weeks after cooling at RT until further processing.

The prepreg was further processed into approximately 1 mm thick laminates in one hour at 150 ° C with a pressing pressure of approximately 1 bar. The end product cured in this way showed no defects with regard to the liability of the individual prepreg layers. To determine the thermal resistance of the matrix material, 100 × 10 mm ² specimens were then removed from the laminates and examined in a torsional vibration test in accordance with DIN 53455. The results of this test are shown in Table 1 for various mixing ratios.

The other TG values of Examples 2-4, likewise listed in Table 1, were determined analogously to Example 1. As a comparison, the TG of a currently frequently used matrix material with dicyandiamide as hardener and N-methylimidazole as accelerator was also included in the table (mixing ratio: bro ured epoxy resin.: Dicyandiamide: N-methylimidazole = 100: 5: 0.8) .

Table 1

Thermal resistance of the laminates

Determination of curing agent effects in connection with BPA base resins

To determine the hardening agent properties as a function of the respective structure, the mixtures, consisting solely of epoxy resin and hardening agent, are hardened and tested in order to avoid falsifying influences from reinforcing and additional materials.

In the examples listed in Table 2, a glycidyl ether based on bisphenol A with an epoxy value of 0.53 is used as the epoxy resin.

To produce the test specimens, 100 g of the epoxy resin are mixed with the amount of curing agent mentioned in Table 2 at room temperature and cured in a steel tool to give 4 mm thick flat moldings. These molded parts are then bwz by sawing. Milling Test specimens taken on which the property values listed in Table 2 were determined in compliance with the test standards listed below. In addition to the curing agents according to the invention, the commercially available phenylimidazoline was also included in the table.

Specimen dimensions

Flexural strength DIN 53 482 80 x 10 x 4 mm ³

Deflection DIN 53 452 80 x 10 x 4 mm ³

Impact resistance DIN 53 453 50 x 6 x 4 mm ³

Tensile strength DIN 53 455 shoulder stick No. 3

Elongation DIN 53 455 shoulder stick no.3

Modulus of elasticity DIN 53 457 shoulder stick No. 3

Marten temperature DIN 53 458 Test specimen dimensions Heat Distortion Temperature (HDT) DIN 53 461 120 x 10 x 4 mm ³

Glass transition temperature (TG) DIN 53 445 80 x 10 x 1 mm ³

X ^"

Table 2

Properties of the unreinforced molding materials

* ■ HDT value without night temperature

Claims

1. Compounds of the general formula (I)

wherein R ^{1 is} an optionally branched alkyl radical with 1-9 carbon atoms.

2. imidazolyl compounds of the general formula II,

and the general formula III,

in which R ^{1 is} an optionally branched alkyl radical with 1-9 C atoms, in which R ² = - (CH2) a-, in which a = 2-10, in which R ³ =

with b = 0-5 and where R ⁴ and R ^{s can} independently be H or CHβ -.

3. Hardening agent for glycidyl compounds, can be prepared by reacting

a) 1,2-diaminocyclohexane with

b) monocarboxylic acids of the general formula V

R ¹ -C-OH (V)

O

in which R ^{1 is} an optionally branched alkyl radical having 1-9 carbon atoms, to the imidazolyl compounds of the general formula I.

8 8

0 0

to compounds of the general formula II

or with diglccidyl ethers of the general formula III a

CH2-CH-CHz-OR ³ -O-CH2-CH-CH2 (III a)

\ / \ /

0 0

to compounds of the general formula III,

⁽ III

in which R ^{1 is} an optionally branched alkyl radical with 1-9 C atoms, in which R ² = - (CH2) _a -, in which a = 2 - 10, in which R ³ =

with b = 0-5 and where R ⁴ and R ^{3 can} independently be H or CH3 -.

4. Use of compounds of the general formulas I - III, if appropriate with the use of conventional amine compounds, auxiliaries and additives, as curing agents for glycidyl compounds.

5. Epoxy resin molded body, characterized in that in the first stage the reinforcing or insert materials with the binder consisting of

b) Compounds of the general formulas I - III and optionally

c) usual solvents, fillers, reinforcing or insert materials, pigments, auxiliaries and optionally

d) customary nitrogen-containing heterocyclic amine compounds

impregnated and converted into the solid and dimensionally stable state, and are cured in a second stage at a temperature below the softening temperature of the shaped body formed in stage 1.