CS254841B1 - Process for preparing dicyandiamide condensates - Google Patents

Abstract

The solution concerns the preparation of dicyandiamide condensates usable for curing epoxy resins and compositions based on them. The essence of the solution consists in first subjecting dicyandiamide to mutual reaction at a temperature of 30 to 70 °C with an aliphatic aldehyde and a cyclic ketone and/or aminotriazine and/or phenol in a specified molar ratio and the resulting intermediate product is then allowed to react at a temperature of 30 to 100 with a more specifically specified type of aliphatic amine. The obtained reaction product is finally dewatered, preferably by distillation under reduced pressure.

Description

The invention relates to the preparation of mixed dicyandiamide condensates suitable for curing epoxy resins treated at higher temperatures.

Commonly used hardener for this type of epoxy resins is dicyandiamide (e.g., Swiss Pat. No. 291,647) and its derivatives. Dicyandiamide itself has the disadvantage of low solubility and high melting point, which only exerts its hardening effect at very high temperatures.

Derivatives derived therefrom, such as arylbiguanides (U.S. Pat.

120 978), although they melt at a lower temperature, however, their drawback is poor curing ability and, as a result, cured resins have inferior mechanical properties and chemical resistance. Various mixtures of dicyandiamide and its derivatives require the addition of suitable accelerators, which, however, again adversely affect the storage stability of the epoxy resins.

The present invention is directed to a process for preparing dicyandiamide condensates suitable in particular for curing epoxy resins. It is based on the fact that it is first reacted at 30 to 70 ° C for 30 to 200 minutes with dicyandiamide β aliphatic aldehyde of carbon number

254,841 atoms of 1 to 2 and a cyclic ketone of the cyclohexanone or methylcyclohexanone type and / or aminotriazine selected from the group consisting of melamine, benzoguanamine and acetoguanamine and / or phenol from the group comprising phenol, cresol, resorcinol and dian, in mol. ratio of components 1 to 3 ϊ 1 to 3 »5: 0.5 to 1.5. The resulting intermediate is then reacted at 30 to 100 ° C for 30 to 100 minutes with 0.1 to 0.2 mol, based on 1 mole of the starting dicyandiamide, an aliphatic amine selected from the group consisting of dialkylamines having a carbon number of alkyl groups of 1 to 3, di (hydroxyalkyl) amines having 2 to 3 hydroxyalkyl groups and 2 to 3 dimethylaminoalkylamines having 2 to 3 alkyl chains. Finally, the reaction product is dewatered, preferably by distillation under subatmospheric pressure.

An advantage of the dicyandiamide mixed condensates of the present invention is their easy preparation from commercially available raw materials. The two-stage condensation and the immediately subsequent product dewatering can be carried out in the same universal-type reaction vessel. In terms of performance, these condensates as hardeners of epoxy resins have a suitably reduced softening point while maintaining long-term stability when mixed with them. Because of their high curing efficiency, epoxy resins cured with these condensates have excellent mechanical properties and good chemical resistance.

The most common aldehyde is formaldehyde, usually of varying concentration in aqueous solution, acetaldehyde, glyoxal and the like can be used. In addition to the cyclic ketones mentioned, their homologues can also be used. Of the aminotriazines, in particular melamine and guanamines are suitable, among phenols, in addition to the common phenol, cresols, resorcinol, dian and the like are among the most preferred.

254 841 more suitable amines with one primary and one tertiary and amino group, the most common being dimethylaminopropylamine.

The preparation of the mixed condensate according to the present invention consists in a two-stage condensation. In the first stage, the dicyandiamide is reacted with foraaldehyde and a cyclic ketone, optionally with another aminotriazine or phenol type component in a suitable molar ratio. Reaction conditions can be selected over a wide range of temperatures and times.

The condensates according to the invention find application as hardeners in epoxy powder adhesives and powder coatings with high hardening effect and good storage stability, eventually in other technical products based on epoxy resins.

The process for preparing dicyandiamide condensates according to the invention is illustrated by the following examples.

Example 1

168 wt. parts of dicyandiamide are dissolved in 187 parts by weight of neutralized 37% formaldehyde, 100 parts by weight are added. of cyclohexanone and heated at 60 ° C for 1 h. Then 31 parts by weight of dimethylaminopropylamine are added gradually over a period of 100 minutes at 60 to 80 ° C and heated at 80 ° C for a further 1 hour. Thereafter, the reaction solution is dewatered by distillation at normal pressure. After cooling the product, a light yellow resin is obtained having a softening point of 84.5 ° C (ball-ring method).

Example 2

210 wt. parts by weight of dicyandiamide and 12 parts by weight of melamine are dissolved in 300 parts by weight of dicyandiamide; 30% neutral formaldehyde4

254,841 du at 70 ° C. Then 140 parts by weight of methylcyclohexanone are added and the mixture is heated at the same temperature for 30 minutes. Thereafter, 38 parts by weight of dimethyl aminopnopylamine are gradually added to the reaction solution and heated at 80 DEG C. for 1 hour. cooling the product to give a pale yellow resin having a softening temperature of 91 ° C (ball-ring method).

Example 3

168 wt. parts of dicyandiamide are dissolved in 227 parts by weight of neutralized 37% formaldehyde, 35 parts by weight are added. parts of cyclohexanone and 65 parts by weight of phenol and the mixture was heated at 65 ° C for 2 hours. Thus, 40 parts by weight of a 35% aqueous dimethylamine solution are added gradually over 1 hour at 50-55 ° C and the reaction mixture is heated at 85 ° C for 1 hour after addition of the amine. Finally, the reaction mixture is dewatered under reduced pressure to a temperature of 120 ° C. After cooling the product, a yellow-brown resin is obtained with a softening point of 88 ° C (ball-ring method).

Claims (1)

SUBJECT OF THE INVENTION 254 841 Process for preparing dicyandiaaid condensates suitable in particular for curing epoxy resins, characterized in that it is first reacted at 30 to 70 ° C for 30 to 200 minutes with dicyandiamide with an aliphatic aldehyde having 1 to 2 carbon atoms and a cyclohexanone-type cyclic ketone or methylcyclohexanone and / or aminotriazine from the group consisting of melamine, benzoguanamine and acetoguanamine and / or phenol from the group comprising phenol, cresol, resorcinol and dian, in a molar ratio of components from 1 to 3: 1 to 3.5: 0.5 to 1 The resulting intermediate is then reacted at 30 to 100 ° C for 30 to 100 minutes β 0.1 to 0.2 mol, based on 1 mole of the starting dicyandiamide, an aliphatic amine selected from the group consisting of dialkylamines having carbon numbers in the alkyl groups of 1 to 3, di (hydroxyalkyl) amines having the number of carbon atoms in the hydroxyalkyl groups of 2 to 3, and dimethylaminoalkylamines having the number of carbon and finally the reaction product is dewatered, preferably by distillation under subatmospheric pressure.