DD223456A1 - METHOD FOR PRODUCING EPOXY RESINS HAVING LOW CHLORINE CONTENT - Google Patents

Abstract

Process for the preparation of low chlorine content epoxy resins. These are used to produce resin systems of defined reactivity, which result in end products of high crosslink density. For the preparation of these resins, the distillation of the epichlorohydrin is carried out in the presence of alkali metal carbonates or bicarbonates at temperatures up to 453 K and vacua of 5 to 100 Torr after condensation.

Description

VEB Leuna-Werke>.

Walter Ulbricht Leuna, the

LP 83165 Title of the invention

Process for the preparation of low chlorine content epoxy resins

Field of application of the invention

The invention relates to a process for the preparation of epoxy resins with low chlorine content, which is used for the production of. Resin systems of defined reactivity can be used, thereby yielding end products of high crosslink density.

Characteristic of the known technical solutions

For the preparation of epoxy resins with low chlorine content, numerous processes are known.

Thus, for example, the reaction of polyhydric phenols with epichlorohydrin is carried out in two stages, the dehydrohalogenation taking place in the second stage in the absence of epichlorohydrin using mostly aqueous solutions of alkali hydroxides with azeotropic removal of the water (CS-PS 105 716 and 105 800, US Pat -PS 33 09 384). An analogous procedure is also disclosed in Japanese Patent Publication Nos. 57-133116 and 58-24

described.

The reaction with aqueous alkalis of low concentration, for example with 10 to 23% by mass aqueous sodium hydroxide solution, is proposed in DE-OS 24-07 092 and HU-PS 1 54 181.

The disadvantage here is the emergence of higher molecular weight and rapeseed products which, for example, have an adverse effect on the crosslinking density of the cured resin and thus limit its applicability.

Another disadvantage of the known processes is the tendency to form relatively stable emulsions, for example, when taking up the reaction products in inert organic solvents such as toluene, xylene or methyl ethyl ketone.

In a further method using a 0.2 to 2.0% by mass aqueous sodium hydroxide solution in the absence of organic solvents side reactions are largely avoided, but the tendency to emulsify when working up the reaction mixture using inert solvent is still. In addition, the required relatively long reaction times are to be regarded as disadvantageous.

To avoid long reaction times, which occur in particular in organic solvents such as toluene, the use of onium surfactants has been proposed as a catalyst (DE-OS 29 47 469). Again, the disadvantageous for the implementation of the method emulsion formation is not excluded. In addition, since the incorporation of the onium compounds into the reaction product is to be expected, reactivity and thus processing problems are to be expected when using the products obtained in this way.

Furthermore, it is known to avoid these disadvantages

To use onium compounds in combination with a buffer system consisting of an alkali salt of a weak acid and aqueous alkali hydroxide solution. Again, however, is to be expected with the formation of emulsions.

Object of the invention

The object of the invention is the development of a process for the preparation of low chlorine content epoxy resins which avoids the occurrence of emulsions often leading to high resin losses without the introduction of additional process steps.

Explanation of the essence of the invention

The invention has for its object to develop a process for the preparation of epoxy resins with low chlorine content for the production of resin systems of defined reactivity, the end products with high crosslinking density, develop.

This object is achieved by a method in which the preparation by condensation of epihalohydrin with bisphenols and / or novolacs in an alkaline medium at elevated temperatures while simultaneously separating the water of reaction by azeotropic distillation with epihalohydrin, then aborting the excess epihalohydrin, taking up the reaction mixture in a solvent and its work-up is carried out in a known manner, wherein according to the invention the condensation of the epihalohydrin, preferably epichlorohydrin, in Gegenv / art from 2.0 to 20.0 parts by mass, preferably 8.0 to 16.0 parts by mass, based on 100 parts by weight of resin , an alkali carbonate or bicarbonate, preferably sodium carbonate, which may be added individually or in admixture, at temperatures up to 453 K, preferably from 413 to 438 K, and a vacuum of 5 to 100 Torr, preferably 10 to 50 Torr ,

Exemplary embodiments Example 1

-114 parts by weight of bisphenol A are dissolved in 465 parts by weight of epichlorohydrin and reacted in a known manner with 45 parts by weight of sodium hydroxide in the form of a '48% by mass aqueous solution, the water being azeotropically removed.

After completion of the condensation, the epichlorohydrin is distilled off in the presence of 16.8 parts by weight of sodium bicarbonate to a temperature of 438 K and a vacuum of 10 Torr. The reaction mixture obtained is then worked up in a known manner.

The epoxy resin thus prepared has a chlorine content of 0.14 mass%.

Example 2

As Example 1, except that 21.2 parts by weight of sodium carbonate are used.

The epoxy resin has a chlorine content of 0.13 mass%. Example 3

As Example 1, except that distilled to a temperature of 430 K at a vacuum of 15 Torr.

The chlorine content of the epoxy resin is 0.26 mass%.

Example 4 '

102 parts by weight of phenol novolak having a molecular weight of 350 are dissolved in 465 parts by weight of epichlorohydrin and reacted in a known manner with 42.5 parts by weight of sodium hydroxide in the form of a 48% by mass aqueous solution, the water being azeotropically removed.

After completion of the condensation, the epichlorohydrin is distilled off in the presence of 8.9 parts by weight of sodium bicarbonate to a temperature of 433 K and a vacuum of 30 Torr. The reaction mixture obtained is then worked up in a known manner.

The resulting epoxy resin has a chlorine content of 0.12% by mass.

Example 5

As Example 4 with the exception that 11.3 parts by mass of sodium carbonate are used.

The epoxy resin has a chlorine content of 0.14% by mass

 Comparative example

As Example 4 with the exception that working without sodium bicarbonate.

The chlorine content of the resin is 0.45 mass%.

Claims (2)

Claim of invention. 1 A process for the preparation of low chlorine content epoxy resins, which can be used to produce resin systems of defined reactivity, thereby yielding end products of high crosslink density, by condensation of epihalohydrin with bisphenols and / or hovolaks in alkaline medium at elevated temperatures with simultaneous removal of the water of reaction by azeotropic distillation with epihalohydrin, followed by stripping off the excess epihalohydrin, taking up the reaction mixture in a solvent and working up the same in a known manner, characterized, that after the condensation, the driving off of the epihalohydrin, preferably epichlorohydrin, in the presence of 2.0 to 20.0 parts by weight, based on 100 parts by weight of resin, of an alkali carbonate or bicarbonate> which can be used individually or in a mixture, at temperatures up to 453 K and a vacuum of 5 to 100 Torr. 2. The method according to item 1, characterized in that after the condensation, the driving off of Epihalohydrins, preferably epichlorohydrin, in the presence of 8 to 16 parts by mass of sodium carbonate or sodium bicarbonate at temperatures of 413.bis 438 K and a vacuum of 10 to 50 Torr.