CS215733B1 - Process for preparing low molecular weight epoxy resins - Google Patents

Abstract

The preparation is carried out by the addition of polyhydric phenols to epichlorohydrin and multi-stage dehydrochlorination of the resulting chlorohydrin ethers by the gradual addition of alkali hydroxides. The last stage of dehydrochlorination is carried out in an inert solvent after removal of unreacted epichlorohydrin and before its commencement, the solution of the intermediate product in this solvent is subjected to washing at a temperature of 20 to 90 °C with water or diluted aqueous solutions of specified acids or aqueous solutions of inorganic acid salts, or the solution is purified by the addition of adsorbents.

Description

The invention relates to a novel process for the preparation of low molecular weight epoxy resins, which consists in a special technological process in the dehydrohalogenation phase of production.

Epoxy resins are commonly prepared by reacting divalent or polyvalent phenols with epichlorohydrin in an alkaline medium. Most often it is based on bisphenol A (dianu, ie 2,2- (4,4-dihydroxidiphenyl) propane) and epichlprhydrins using sodium hydroxide. Depending on the molar ratio of dian to epichlorohydrin used, the resins are obtained in the form of viscous liquids to solids, which can be chemically defined as glycyl ethers of the corresponding phenols.

For the purpose of casting, casting, casting, laminating, impregnating, and for sealants and some adhesives, liquid resins at normal temperature are particularly preferred. These resins are prepared with a molar excess of epichlorohydrin so that the average molecular weight is as low as possible. It is possible either to carry out all phases of the reaction in an epichlorohydrin medium or to work in the epichlorohydrin only in the first part of the synthesis and to complete the preparation of the resin in a suitable inert solvent. The preparation of low molecular weight epoxy resins can be roughly divided into the following phases:

An addition in which a major part of the phenoxide anion is added to the epoxide group of epichlorohydrin to form the chlorohydrin ether of the corresponding phenol. By the appropriate choice of reaction conditions, the addition reaction is preferred and the dehydrohalogenation reaction is suppressed, so that it proceeds only to a small extent,

- The first dehydrohalogenation in which the addition of the phenoxide anion to epichlorohydrin is completed to form a new epoxy group which already forms part of the resin.

- Second dehydrohalogenation, which completes the dehydrohalogenation of the remaining chlorohydrinether groups of the resin. This phase of the reaction takes place in a strongly alkaline medium, since the sodium hydroxide must be in excess in order for the dehydrohalogenation to proceed sufficiently.

- The final phase in which the resin is washed and freed from residues of sodium chloride, by-products, alkali and isolated.

In the original technological processes for the preparation of low molecular weight epoxy resins, these 4 phases were carried out in an excess of epichlorohydrin by a so-called one-step method (NSR Pat. No. 2,656,865, GDR Pat. No. 118,663, US Pat. No. 425 929, British Patent No. 752 226, Japanese Patent No. 78 65835), which is simpler to operate. Its disadvantage is the increased hydrolysis of epichlorohydrin in the final phase of dehydrohalogenation and its loss in the final wash. Therefore, the resin yield based on the epichlorohydrin used is low and the process is uneconomical in terms of raw material consumption.

Newer methods of preparing these resins emphasize improved use of raw materials and minimization of waste products. Therefore, the so - called two - stage procedure (NSR Pat.

533,505, US Pat. Nos. 2,913,095 and 3,331,730, French. U.S. Pat. δ. 1 336 444; U.S. Pat. No. 413,086), wherein the initial phases of the synthesis, i.e. addition and first dehydrohalogenation, are carried out in excess of epichlorohydrin, but the final phase in a suitable inert solvent after distillation of unreacted epichlorohydrin. Although this process is technologically somewhat more complicated, it gives a high yield relative to the epichlorohydrin used and also the waste balance is more advantageous. In practice, only the theoretical or even below theoretical amounts of sodium hydroxide are used for the addition and first dehydrohalogenation phases, then any unreacted epichlorohydrin is distilled off and the remaining crude resin is dissolved in an inert solvent. However, the resulting resin solution contains a considerable amount of solid sodium chloride (formed by dehydrohalogenation), which is removed either by centrifugation or by dissolving in water and separating the brine from the organic resin layer. In the subsequent second dehydrohalogenation, the resin solution is treated with additional sodium hydroxide and the process ends with a final neutralization and a purification and isolation operation.

However, in the preparation of low molecular weight epoxy resins by known two-step processes, undesirable formation of a ballast polymer occurs by anionic polymerization of the epoxy resin by sodium hydroxide. This polymer has a spatially crosslinked structure (since the epoxy resin contains 2 to 3 epoxy groups per molecule) and is insoluble in conventional solvents. In addition to reducing yields, it mainly causes difficulties in the final purification and isolation of the product. The anionic polymerization of epoxides by alkali can be suppressed to some extent by adding more water (NSC Pat. No. 2,533,505) or lower alcohols (Japanese Pat. No. 76 68553) to the reaction mixture or by using dilute sodium hydroxide solution (NSC Pat. No. 2,335,199), but at the same time deteriorate the dehydrohalogenation conditions so that it is then necessary to increase the reaction temperature or extend the reaction time so that the final resin has the desired low bound chlorine content. In addition, washing of the alcohol-containing resin solution is very difficult, some of the alcohol is transferred to wastewater and, moreover, in an alkaline environment, the alcohol reacts to some extent with the epoxy groups of the resulting resin.

The present invention is directed to a process for the preparation of low molecular weight epoxy resins by the addition of polyhydric phenols, especially bisphenols and phenolic novolac, to epichlorohydrin and dehydrochlorination of the resulting chlorohydrin ethers by sequential addition of alkali hydroxides, wherein the final dehydrochlorination step is and after addition of at least 80 wt. theoretical amount of alkali hydroxide. The principle of the invention is that before starting the dehydrochlorination in an inert solvent, the solution of the intermediate in this solvent is subjected to a washing with water or 0.1 to 5% aqueous phosphoric, formic, acetic, oxalic, citric, tartaric acid solutions at 20 to 90 ° C. or mixtures thereof or 0.1 to 20% aqueous solutions of inorganic acid salts, preferably alkali chlorides, sulphates or phosphates, and / or purification by the addition of adsorbents, preferably silica gel, kaolin, siloxide or talc, with a particle size of not more than 100 µm. The washing and / or cleaning process consists of one to five separate washing or cleaning operations, each separate operation being carried out for 2 to 100 minutes, using washing liquids or adsorbents in an amount of 10 to 200% by weight. % based on the weight of the resin. Between each operation, the wash liquids or adsorbents used are removed from the solution of the resin in an inert solvent.

In this way, undesired products resulting from side reactions, in particular by alkaline hydrolysis of epichlohdrin, are removed from the reaction mixture before the final dehydrohalogenation stage. These substances are generally blpolarly protic in nature, so that they are water-soluble and act in conjunction with the actual reaction catalyst, i.e., the alkali hydroxide, as anionic polymerization epoxide catalysts, especially when present in small amounts. The most perfect removal of these substances can be achieved by washing or repeatedly washing the solution of the reaction intermediate in an inert solvent with pure water, and after each washing step it is necessary to separate the aqueous phase from the organic phase. However, the separation of the two phases when using pure water is relatively lengthy. Since the phase separation is significantly faster at a lower pH of the wash medium, it is preferable, in particular for large-scale production operations, to use acidified, ie weak, aqueous acidic solutions, namely phosphoric acid, formic acid, acetic acid, oxalic acid, for washing. , lemon and wine or mixtures thereof. Washing with dilute aqueous solutions of inorganic acid salts, preferably alkali metal chlorides, sulphates and phosphates, has a similar effect, where the different phase weights of the washing and washing solutions have a very favorable effect on the rate of phase separation. The wash aqueous phase remains as a bottom layer at the bottom of the reaction vessel after separation, so that it can be easily drained from the bottom of the vessel. These washing procedures can be combined with each other.

Removal of the above-mentioned undesirable by-products from a solution of the reaction intermediate in an inert solvent can also be achieved to some extent by the addition or repeated addition of powdered adsorbents. Essentially all known substances with adsorptive properties in the form of particles having a size of not more than 100 .mu.m can be used as the adsorbents. the smaller the particles, i.e., the larger the adsorbent surface, the greater the cleaning effect. Also in this case, the adsorbent must be removed from the solution after each individual operation, usually by filtration or centrifugation. However, filtering too small particles, especially if they contain adsorbed impurities, is relatively difficult, so that under operating conditions it may be necessary to choose a certain compromise between adsorbent particle size and adsorption efficiency or the number of individual operations. The type of adsorbents is not essential here, from the point of view of large-scale use, in particular, economically advantageous adsorbents such as powdered bentonite, kaolin, silica gel, talc, siloxide and others are suitable.

Example 1

A 1.5 L flask equipped with a stirrer, thermometer, separating funnel and azeotropic reflux condenser was charged with 228 g dianne and 740 g epichlorohydrin. While stirring, the reaction mixture is heated to 65 ° C and 56 g of 42.8% aqueous sodium hydroxide solution are added dropwise from the addition funnel over 2 hours at this temperature. When the lye is dripped, the reaction mixture is azeotropically drained to 100 ° C and then 112 g of a 42.8% aqueous sodium hydroxide solution is added dropwise over 75 minutes at a reaction temperature of 97 to 100 ° C while dewatering through the azeotrope, where the distillate is separated into aqueous and organic layers. The organic epichlorohydrin layer is continuously returned to the reaction mixture. After the dropwise addition of the caustic soda, the azeotrope is replaced by a descending condenser and the unreacted epichlorohydrin is distilled off at a pressure of 5 to 10 kPa to a temperature of 150 ° C. The contents of the flask were cooled to 100 ° C, diluted with 315 g of toluene and filtered through a paper filter. The filter cake was washed on the filter with 100 g of toluene and the combined filtrates were returned to the reaction flask. To this was added 100 g of water with stirring and the resin solution was washed at 60 ° C for 10 minutes. The aqueous layer was then separated and 48 g of a 42.8% aqueous sodium hydroxide solution was added dropwise at 60 ° C over 20 minutes. After the liquor was added dropwise, the reaction mixture was heated to 80 ° C and stirred at this temperature for 60 minutes. After the reaction, 40 g of water were added to dissolve the resulting sodium chloride and the mixture was filtered through a paper filter. The trapped polymer on the filter was washed with acetone, water, ethanol and dried. An epoxy resin having the following properties is isolated from the filtrate by conventional means:

content of epoxy groups content of organically bound chlorine viscosity time gelatin ce with phthalic anhydride resin yield epichlorohydrin yield polymer amount

0.532 gek./100 g,

0.19% by weight,

12.4 Pa.s / 25 ° C

195 minutes at 140 ° C 337 g, ie 99.1% of theory 93.2% of theory

0.08% by weight of resin.

If the toluene solution of the reaction product is not washed with water before the second dehydrogenation, then under the same reaction conditions a curd polymer is formed in an amount of 1.82% by weight of the resin. In this case, if 35 g of water are added to the reaction mixture before the second dehydrohalogenation, only 0.36% of the polymer by weight of the resin is formed under the same reaction conditions, but the isolated product contains 0.38% by weight of water. % organically bound chlorine.

Example 2

The procedure is as in Example 1 except that the toluene resin solution is washed with 150 g of water containing 1 g of concentrated orthophosphoric acid before the second dehydrohalogenate. The resin obtained has the following characteristics:

content of epoxide groups content of organically bound chlorine viscosity dry matter time of gelation with phthalic anhydride resin yield makes yield per epichlorohydrin amount of polymer formed

0,530 gekv./100 g i

0.18 wt. %

12.3 Pa.s / 25 ° C

99.7 wt. (1h / 140 ° C)

180 minutes at 140 ° C 336 g, i.e. 98.8% of theory 93.0% of theory

0.06% resin by weight

Example 3

The procedure was as in Example 1 except that the toluene resin solution was washed with 120 g of 5% aqueous sodium chloride solution prior to the second dehydrohalogenation. The resin obtained has similar properties as in the previous examples, the amount of polymer formed being

0.22% by weight of resin.

21573:

Example 4

The procedure is as in Example 1 except that the toluene resin solution is mixed with 10 g of finely ground bentonite having a particle size of about 80 µm before the second dehydrohalogenation and stirred for 30 minutes at 45 ° C. The bentonite is then filtered off and the filtrate is treated with sodium hydroxide in the same manner as in Example 1. The isolated resin has similar properties as in the previous examples, the amount of polymer formed being 0.48% by weight of the resin.

Example 5

The procedure was as in Example 1 except that the toluene resin solution was mixed with 50 g of finely ground silica gel with a particle size below 5 .mu.m before the second dehydrohalogenation, and 90 g of a 3% aqueous dipotassium hydrogenphosphate solution KgHPO4 was added. The mixture was stirred for 80 minutes at 25 ° C. After the lower aqueous layer was drained and the toluene resin layer was filtered to remove silica gel. The obtained organic filtrate is treated with sodium hydroxide in the same manner as in Example 1. The isolated resin has similar properties as in the previous examples, the amount of polymer formed being 0.12% by weight of the resin. The gelation time with phthalic anhydride is 210 minutes at 140 ° C.

Example 6

The procedure was as in Example 1, except that the toluene resin solution was washed with water and aqueous salts and kyaelin solutions prior to the second dehydrohalogenation, each aqueous phase being washed after each wash; separates. Washing is performed according to the following scheme:

Washing Washing agent Amount Temperature Time 1 water 70 g 80 ° C 5 minutes 2 5% NaCl 60 g 70 ° C 10 minutes 3 «« Η _? ρο ₄ 50 g 60 ° C 20 minutes 4 water 50 g Deň: 32 ° C 30 minutes

The washed organic layer was treated with sodium hydroxide in the same manner as in Example 1.

The isolated resin after the reaction has these properties; content of epoxide groups content of organically bound chlorine viscosity time of gelation with phthalic anhydride resin yield epichlorohydrin yield amount of polymer formed

0.539 geq / 100 g 0.21 wt. %

10.1 Pa.s / 25 ° C 236 minutes at 140 ° C

98.9% of theory

91.9% of theory

0.03% resin by weight

Example 7

The procedure is as in Example 1 except that the toluene solution of the resins is before the second; by dehydrohalogenation it undergoes multiple purification with adsorbents, after each purification operation the adsorbent used is removed by filtration. Purification is carried out according to the following scheme:

Cleaning Adsorbent Vel. max. Amount adsorb. Temperature Time 1 bentonite 10 yum 35 g Deň: 32 ° C 85 min. 2 silica gel 5./um 50 g 40 ° 0 60 min. 3 kaolin 15 Dec 50 g Deň: 29 ° C 90 min.

The obtained toluene filtrate was treated with sodium hydroxide in the same manner as in Example 1. The isolated pryslyria after reaction had similar properties to those in Examples 6; the amount of polymer formed is 0.01% by weight of the resin. The gelation time with phthalic anhydride is 248 minutes at 140 ° C.

Claims (3)

PREJEME OF THE WEEK · A process for the preparation of low molecular weight epoxy resins by the addition of polyvalent phenols, in particular bisphenols and phenolic novolaks, to epichlorohydrin and dehydrochlorination of the resulting chlorohydrin ethers by successive addition of alkali hydroxides, wherein the final dehydrochlorination is carried out after removal of unreacted epichlorohydrin. % of the theoretical amount of alkali hydroxide, characterized in that before starting the dehydrochlorination in an inert solvent, the solution of the intermediate in the solvent is subjected to a washing with water or 0.1 to 5% aqueous phosphoric, formic, acetic, oxalic acid solutions at 20 to 90 ° C , citric, tartaric or mixtures thereof, or 0.1 to 20% aqueous solutions of inorganic acid salts, preferably alkaline sulphate or phosphate chlorides, and / or purification by the addition of adsorbents, preferably silica gel, bentoriite, kaolin, siloxide or talc, of particle size not more than 100 µm. 2. A method according to claim 1, wherein the washing and / or cleaning process consists of one to five separate washing or cleaning operations, each separate operation being performed for 2 to 100 minutes using washing liquids or adsorbents in an amount of 10%. up to 200 wt. % based on the weight of the resin. 3. A process according to claim 1 or 2, characterized in that, between the individual operations, the wash liquids or adsorbents used are removed from the solution of the resin in an inert solvent.