DE2166606C3 - Heat-curable, solid epoxy resin compounds - Google Patents

Description

Monomeies cyanamide in the form of aqueous solutions and derivatives of cyanamide have been around for some time Time spent in various areas of chemistry. The dimeric form of cyanamide, the dicyandiamide, is also used to harden epoxy resins, especially when processing prepregs, Molding compounds and powder coatings are used. In the case of dicyandiamide, however, it is necessary to harden it relatively high temperatures are required even when accelerators are also used, and Attempts have been made again and again with little success to lower the curing temperature z-u.

With the use of solid dicyandiamide it is also not possible at room temperature or elevated temperatures liquid epoxy resins are solvent-free into a solid, still fusible one B-stage to transfer.

Using aromatic amines as hardeners in conjunction with liquid epoxy resins Although a B-stage can be achieved smoothly, amine-cured epoxy resins show in the cured one Condition has very poor heat aging behavior, i. H. a strong embrittlement.

Epoxy resins include those with more than one To understand epoxy group per molecule, especially di- and polyglycidyl ethers that are liquid at room temperature, which differ on the one hand from polyhydric phenols, in particular bisphenols, and novolaks and polyhydric alcohols, especially dialcohols, e.g. B. Polypropylene Glycol. and on the other hand from Epichlorohydrin and, if appropriate, methylepichlorohydrin, derive. There are also glycidyl esters of di- and polycarboxylic acids, especially the aromatic series, e.g. B. phthalic acid, and the aliphatic Row suitable. The epoxy resins obtained by the epoxidation of olefinic compounds can also be used but are not preferred. Mixtures can also be used the listed epoxy resins with one another or with so-called reactive thinners, d. H.

in particular monoglycidyl ethers of alcohols or phenols or monoglycidyl esters of carboxylic acids, in particular of the aromatic and aliphatic series can be used.

The amount of cyanamide to be used can be varied considerably without affecting the properties be changed significantly. With ratios of 0.5 Mo! per equivalent of epoxy will give good results achieved, with larger amounts (0.6 mol)

ίο the reactivity increases.

According to the simplest embodiment of the invention, anhydrous, monomeric cvanamid is im Dissolved epoxy resin heated to about 50 ° C, after which the solution at room temperature depending on the impurities contained in the epoxy resin and the stabilization of the cyanamide from days to remains unchanged for weeks. Larger amounts can, however, after this »intimation period« React spontaneously with strong warming, while in the case of layer thicknesses in the order of magnitude from 1 cm a B-stage is established.

This simplest, quasi-latent system according to the invention can be used in practice to z. B. glass fiber reinforced plastics, e.g. B. Moldings, plates, pipes, bonds or coatings, directly from the liquid phase by heating to temperatures above about 100 to about 200 ° C to create. This system is also suitable for cast resin purposes, provided that none Excessively high heat build-up leads to cracks or even charring. This is usually the easiest to do by adding fillers and heat dissipation.

It has also been found that the reaction between epoxy resins and anhydrous monomers Cyanamide by adding small amounts of accelerating substances can control that for the purposes mentioned, the curing temperatures or times while shortening the pot life considerably

be lowered. Amines are used as accelerators, such as those used in conjunction with others in the epoxy resin sector Hardening mills are customary, especially tertiary amines, suitable.

From the large number of tertiary amines that can be used, some particularly favorable ones are mentioned below and easily accessible ones called: triethylamine, diethylmethylamine, butylamine, Ν, Ν'-tetramethylethylenediamine, Dimethyl- and diethylethanolamine, benzyldimethylamine, (dimethylaminomethyl) phenol,

Tri- (dimethylaminomethyl) phenol and the like. Tertiary amines can also be used in situ from primary or secondary Amines are formed by reaction with epoxy compounds and are effective.

The invention relates to thermosetting, solid ones

Epoxy resin compounds made from

a) liquid di- and / or polyglycidyl ethers of di- and / or polyphenols or from liquid mixtures of these glycidyl ethers with

up to 20 percent by weight, based on the

entire epoxy resin component, on Mcno- or diglycidyl compounds, namely glycidyl ethers of mono- or polyhydric phenols or alcohols or glycidyl esters of

⁶ S mono- or polybasic carboxylic acids and from

b) anhydrous monomeric cyanamide in amounts of 0.3 to 0.6 mol per epoxide equivalent and, if necessary, off

c) accelerators and / or

d) fillers and / or strengthening agents with Pigments and auxiliaries

by converting to the B-stage in the temperature range from about 20 to about 130 ° C below Cooling down. The main component of these epoxy resin compounds is glycidyl ether based on Bisphenols with epoxy equivalent weights of 190 to about 400 are particularly suitable.

The B-stage can inter alia at room temperature within z. B. 24 hours, provided that the formation of ready * crosslinked products is avoided by excessive heat build-up. With a higher content of z. As fillers, glass fibers od. The like., As given in the formulation of molding compositions or prepreg to be sufficiently intercepted the inorganic material in general, the reaction heat du ^r ch. In the case of non-filled or weakly filled formulations, e.g. B. in the production of powder coatings, an unacceptably high build-up of heat is avoided most simply by leaving the formulation in shallow dishes to harden or solidify, ie the hardening takes place in a layer that is not too thick.

The thermosetting epoxy resin compositions can either be used without further additives or with them from the start incorporated fillers, pigments, reinforcing fibers and / or auxiliaries, e.g. B. as adhesives, Coatings, molding compounds, etc. are processed. It is especially possible on normal Roller mills at room temperature - instead of in the heat using special extruders - powder coating formulations to prepare.

These epoxy resin compositions are also suitable for producing so-called prepregs by using the initially liquid resin / hardener approaches fiber mats or fabrics, z. B. Glass fiber mats or fabrics, soaks and this then at room temperature or elevated temperature to the B-stage leads.

example 1

11.4 g of anhydrous monomeric cyanamide were dissolved in 100 g of the diglycidyl ether of diphenylolpropane (epoxy equivalent weight 190) at 50.degree. After cooling to room temperature, 0.1 g of benzyldimethylamine was stirred in and the liquid mixture was stored in flat dishes in a layer thickness of about 1 cm for 2 days at room temperature. The approach was then solidified to a hard, brittle, clear mass (B-state). This was broken and ground. Using this B-stage powder, overlapped steel bonds were produced which, after curing for 30 minutes at 125 ° C., had a tensile shear strength of 2.5 kp / mm ² .

You can also create the B stage with the same recipe by using the liquid mixture " Heated for about 4 minutes to 120 ° C in a layer thickness of up to about 1 mm and then cooled. So can a solid adhesive layer in the B-state is also produced on the adhesive surface and the bond continues for a longer period of time Intermediate storage can be carried out.

Example 2

1000 g of the epoxy resin as in Example 1 were heated to about 50 ° C., whereupon 114 g of anhydrous, monomeric cyanamide were stirred in and dissolved. After cooling to almost room temperature, 1 g of benzyldimethylamine and then 2228 g of finely divided chalk were added. The mixture was homogenized on a 3-roll chair and a layer thickness of about 5 to 6 cm was set aside for 2 days at room temperature. The mass was then brittle and hard and could be broken easily. From the hard mass, 4 mm thick plates were pressed in 5 minutes at 170 ° C., which had a value of 108 ° C. and a flexural strength of 998 kp / cm ² .

. After 100 h at 140 ° C. (heat aging), the value was 130 ° C. and the flexural strength was 882 kg / cm ² . Practically the same result is obtained when the pressing temperature is 120 ° C. and the pressing time is 60 minutes.

Example 3

400 g of a diglycidyl ether based on diphenylolpropane of epoxy equivalent weight 260 were heated to about 50 ° C, whereupon 32 g of anhydrous, monomeric cyanamide were stirred in. The cooling clear mixture was added 0.8 g of benzyldimethylamine and 4 g of a leveling agent based on acrylic resin and 185 g of titanium dioxide pigment were added and the whole thing is homogenized on a roller mill. The liquid mass was in a layer thickness Set aside from 2 to 3 cm in shallow dishes for 2 days. It was down to the hard, brittle B-state stiffens.

The hard mass was ground and passed through a sieve with a mesh size of 90 μ . The powder obtained was sprayed electrostatically onto metal sheets and the powder coating was ^{cured at 180 °} C. for 7 minutes. A glossy, white coating that ran well and had an Erichsen cupping of 6 was obtained.

The powder coating can alternatively also z. B. cured at 150 ° C for 25 min.

In order to obtain an even more flexible coating, one can use a part, e.g. B. 10 to 20% of the above diglycidyl ether used, by the diglycidyl ether of polypropylene glycol used in Example 4 substitute.

Claims (1)

Claim: Heat-curable, solid epoxy resin compounds made from a) liquid di- and / or polyglycidyl ethers of di- and / or polyphenols or from liquid mixtures of these glycidyl ethers with up to 20 percent by weight, based on the entire epoxy resin component, of mono- or diglycidyl compounds, namely glycidyl ethers of mono- or polyhydric phenols or alcohols or glycidyl esters of mono- or polybasic carboxylic acids and from b) anhydrous monomeric cyanamide in amounts of 0.3 to 0.6 mol per epoxide equivalent and, if necessary, off c) accelerators and / or d) fillers and / or reinforcing agents with pigments and auxiliaries by converting to the B stage in the temperature range from about 20 to about 130 ° C below subsequent cooling.