DD140256A1 - PROCESS FOR PREPARING ACTIVATED EPOXY RESIN - Google Patents

Abstract

Process for the preparation of activated epoxy resin for the Hardening with dicyandiamide. It is used for the production of impregnating solutions for laminates and pressed materials. The activation is here by treating the epoxy resin solution with an alkaline Connection achieved. The process is different from before known by, - That it provides products with high reactivity, which is a high and uniform processing speed when curing with Dicyandiamid'ermöglichen, - That the concentration of accelerator additive kept small can be, i - that the mechanical, electrical and thermal Properties of the impregnated fabrics do not deteriorate, - That the process for both one- and two-component systems is applicable, - That the method due to its simple reaction is very economical.

Description

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VEB Leuna-Werke Merseburg, 24. 11. 1978

"Walter Ulbricht" DC.Hi / Sch

0- '. 'wl. IP 7865,

Title of the invention

Process for the preparation of activated epoxy resin Field of application of the invention;

The invention relates to a process for the preparation of epoxy resin systems, which are characterized by an increased reactivity in the reaction with hardeners, especially with dicyandiamide · Dicyandiamide cured epoxy resins are widely used for coatings, for impregnating fabrics, glass fibers and laminates

Characteristic of known technical users ·

The processing of the epoxy resins for impregnation solutions of glass fiber fabrics or fabrics is usually carried out via the intermediate stage of a prepreg.

The prepregs are prepared by passing the support material through the impregnating solution consisting of an epoxy resin solution, a hardener and an accelerator, and then evaporating the solvent in a heated drying channel.

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During the passage of the impregnated carrier material through the drying channel, a partial crosslinking takes place, which leads to a tack-free and storage-stable intermediate product, the prepreg. For laminate manufacture a plurality of such prepregs are superposed and cured in a press at temperatures of 120 to 200 ⁰ C and pressures of 1 to 100 atm.

The data of the impregnation system which are critical for processing are the residence time of the impregnated material in the drying channel, the storage stability of the prepreg and the rapid and error-free curing of the prepregsin the press. All these criteria determine the processing speed and thus the cost-effectiveness of the processing.

It is known that mixtures of a medium or high molecular weight resin and dicyandiamide (CH Pat. No. 257,115) can be used as the impregnating solution. To cure such mixtures, very long curing times are required at temperatures around 150 ° C. It is known that the curing rates by addition of accelerators, such as quaternary ammonium salts (US-PS 2,811) acrylic guamidine (UL PS 6,614,563) 'hexamethylenetetramine (BE-PS 697 383) substituted triazines (US Patent 3,366,601) tert , Amines (DE-OS 2,131,929, US-PS 3,360,199) pyrrolidines (DE-OS 1,908,752) and novolacs (DE-OS 1,643,309), can accelerate.

As advantageous accelerators have tert in practice. Amines, especially substituted aromatic amines, such as dimethylbenzylamine, proved (DE-OS 2,131,929). As negative has been found in these amine accelerators that they are very much dependent on the content of readily versible chlorine of the epoxy resin and thus have different activities in the acceleration.

In general, each epoxy resin batch has a different chlorine content and thus a different processing condition. "The uniformity of processing is in practice adjusted by varying the accelerator concentration." However, this leads to undesired increases in chlorine content

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Hebenwirungen; einer · Β · a change in the polymer structure (DE-OS 2,521,813), which leads to a deterioration of the mechanical and dielectric properties and an undesirable

: discoloration and a decrease in the storage stability of the prepregs leads.

Another way to speed up the processability is by. Addition of Uovolak achieved (DE-OS 1 643 309). However, the addition of Sbvblak leads to a deterioration of the mechanical and electrical properties. "Another variant of the increase in reactivity is achieved in the one-component system by a precondensation of the 'epoxide resin with the dicyandiamide.' This variant leads to

^ long boiler occupation times and is therefore uneconomical ·

Object of the invention

The aim of the invention is to produce an activated epoxy resin for curing with dicyandiamide, which guarantees a constant reactivity and a high processing speed and avoids or largely avoids the mentioned negative effects of the known processes.

Explanation of the essence of the invention

The object of the invention bestehtjdarin to develop a method for modifi- _(<r \ fication of a reactive resin which by itself

It is characterized by simple reaction management and high efficiency, as well as products of consistent quality.

The stated object is achieved according to the invention "dissolved by 3 t, that the to be modified epoxy resin solution with 0.01 to 2.0 .%, Preferably 0.03 to 0.3 wt .-%, of an alkali or Alkalikarbonatesy preferably K ₂ CO ^ , up to 5 hours, preferably 30 to 60 minutes, at 20 to 150 ⁰ C, preferably 60 to 80 ⁰ C, treated ·

The implementation of the inventive method in such a way that T _e ile 100 a medium molecular weight epoxy resin having an Epojcydäquivalent from 200 to 1000, advantageously

From 400 to 600, in 50 or 100 parts of a solvent such as methyl ethyl ketone, acetone, ethyl glycol, methyl glycol or my mixture of said solvents, solves the dissolution of the resin 0.03 to 0.3 parts of alkali hydroxide or alkali carbonate in the form of a added to aqueous or alcoholic solution and treated at 60 G for 30 minutes. The resin thus treated shows a marked increase in reactivity upon curing with dicyandiamide and dimethylbenzylamine as accelerator.

The pretreated resin is also storage stable in the presence of dicyandiamide at room temperature. The addition of the alkali or the alkali carbonate has no negative effect on the mechanical or the electronic characteristics of the coated materials.

Compared to the known processes, the process according to the invention has the advantages that it provides products with high reactivity which enable a high and uniform processing speed in the case of hardening with dicyandiamide,

that the concentration of accelerator additive can be kept small,

that the mechanical, electrical and thermal properties of the impregnated substances do not deteriorate,

- that the method is applicable to both single- and two-component resin systems,

that the process is very economical due to its simple technology

embodiments

Example 1 .

500 parts of an epoxy resin with an epoxy equivalent of 400 and a chlorine content of 0.2 % are dissolved in 500 parts of ethyl glycol.

laughing loosening be ^COE ₂ 3 "" ^IiÖDun added 50 parts of an aqueous 0.5 η K and stirred at 70 ⁰ C for 30 minutes, "Hachf ^ em activating the thus treated resin solution with 21

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Add dicyandiamide and 2 parts of dimethylbenzylamine. B time at 150 ⁰ C 6 Y2 minutes

Dielectric characteristics of cured prepregs.

', .DK- ^:. ''\.'.". 5 ' ; -:.; ^: ·. ''' .. ···. : '':

tangens delta 6. 10 "· ^

Specific resistance 8,8. 10 ic. cm: surface area wideness 8. 10 ¹⁴

Example 2

500 parts of epoxy resin with an epoxide equivalent of 400 and a chlorine content of 0.2% are dissolved in 250 parts of ethyl glycol and stirred with 50 parts of 0.5 η ethanolic KOH 30 minutes at 70 ⁰ C.

The so-activated resin is mixed with 250 parts of a 8.5 to 9. -Sßigen Dicyandiamidamidhärterlösung (äthylglykolisch) and 2 parts of dimethylbenzylamine and gehärte'fv B-1§0 time at ⁰ C 7.0 minutes

The dielectric characteristics are similar to those of Example 1.

Example 3 (Comparative Example) V

500 parts of an epoxy resin, as used in Example 1, are dissolved in 500 parts of ethyl glycol and mixed with 21 parts of dicyandiamide. After dissolving the dicyandiamide (J), 2.0 parts of dimethylbenzylamine are added.

B-time at 150 ⁰ C 18 minutes V

The dielectric characteristics are similar to those of Example 1.

Claims (1)

Erfindungsansprach Process for the preparation of an activated epoxy resin for the curing with dicyandiamide, characterized in that the epoxy resin solution to be modified contains 0.01 to 2.0% by weight, preferably 0.03 to 0.3% by weight, of an alkali metal hydroxide or alkali metal carbonate, preferably KgCO-, up to 5 hours, preferably 30 to 60 minutes, at 20 to 150 ⁰ C _5, preferably 60 to 80 ⁰ C, treated.