NO137207B - PROCEDURES FOR THE MANUFACTURE OF WATER INSULATION MEMBRANES - Google Patents

Description

Process for cleaning curable epoxy resin precursors.

The present invention relates to a

improved method for purification of

curable epoxy resins obtained by

turnover of bis- or poly-phenols

with one or more nuclei, with epichlorohydrin or dihalohydrins in the presence

of alkali.

It is known that under the influence of

epichlorohydrin or dihalohydrins on

mono- or multi-nuclear bis-respectively poly-phenols, especially those of the type p,p'-dihydr-oxydiphenyldimethylmethane, condensation products are formed which upon addition of acidic

or basic cold curing components

or hot condition can be transferred to

synthetic resins that do not melt and do not

dissolve. These synthetic resins are based on

of its special properties particularly suitable

for the production of castings, as an adhesive, especially for bonding metal, glass and porcelain, as an insulating material

and for the production of protective coatings.

During the production and cleaning of these

resins generally become one mole of bis-

phenol dissolved in 1-2 mol of aqueous alkali hydroxide in a warm state, after which at approx. At 40° C, 1-2 mol of epichlorohydrin are added at once and recondensed between 90 and 100° C for one hour. After completion of the reaction, the secreted resin is separated from the aqueous solution by decantation and washed with hot water, possibly with the addition of a little acid, free of excess alkali that still had to adhere to it and of sodium chloride that was formed during the reaction. When heated to approx. 150° C, a clear anhydrous epoxy resin precursor is then obtained where the molecular size and number of epoxy groups contained in 100 g of resin depends on the molar ratio between bisphenol and epichlorohydrin used. In general, work is carried out with an alkali surplus of approx. 3-20 percent

When p,p'-dihydroxydiphenyldimethylmethane is used, the resin that is formed can be described by the following formula

where R is an aromatic residue and n is an integer.

Flawless synthetic resins must contain

more than one epoxy group per moles of poly-glycidethers.

In addition to the simple bisphenols, the condensation products of phenol or their substitutes with aldehydes can also be used for this reaction.

According to another method for the production and purification of epoxy resins, the bisphenol can also initially be dissolved in part of the alkali, preferably 1 mol of alkali per mol of bisphenol, and the remainder is added at a higher temperature only after the addition of the epichlorohydrin.

In all cases, however, the complete washing out of the excess alkali from the sodium chloride presents great difficulties, as at least six to ten washings with fresh washing water are needed to obtain fault-free products. If some sodium chloride or alkali remains, the quality of the cured resin is greatly reduced. While the condensation only requires approx. 90 min., the washout lasts approx. 3-5 hours for washing periods of approx. 30 min.

It has already been proposed to decant the crude resin formed after the end of the condensation from the aqueous phase and to take it up in organic solvents which do not contain any groups which can react with the epoxy resin pre-product. According to US patent no. 2,824,855, the raw resin is neutralized with hydrochloric acid and then taken up in a solvent which together with water forms an azeotropic mixture and as such boils at between 71 and 99°. The necessity of this boiling point range is derived from the assumption that at higher temperatures and in the presence of salts a certain hardening of the epoxy resin already occurs. After the water has been removed, the salt that has still been separated is removed over filter soil (dicalite 4200). In another patent, US patent no. 2,879,259, reference is made to the fact that solutions of epoxy resins in organic solvents can only be separated from the aqueous phase with difficulty, and in order to get the washing water to separate more quickly, solutions of inorganic salts are used, e.g. sodium dihydrogen phosphate.

Already in the Swiss patent no. 211,116 regarding the production of epoxy resins, it is referred to dissolve the formed resin in acetone, and filter from the separated salts and to free the resin from solvents. According to experience, the formed resin cannot be completely freed from the aqueous phase and in order to achieve a complete dissolution of the aqueous resin in acetone, it is necessary to use large amounts of acetone, as the water content greatly reduces the solubility of the resin in acetone. Moreover, the water contained even in clear solutions constantly acts as a solvent for inorganic salts, and it is only then possible to obtain error-free products after the removal of the solvent, if the dry resin is taken up several times in acetone and filtered until complete clarification.

It has now been shown that it is possible in a simple way to arrive at very clean and error-free epoxy resin precursors, when the surplus of free alkali, after completion of condensation, is neutralized with organic or inorganic acids, that the raw resin which is contaminated with alkali salts by decanting or tearing off the aqueous layer is separated from this and dewatered under vacuum in a hot state at bath temperatures of 130° C. The resin containing alkali salts is then taken up in acetone and filtered until complete clarification, after which the solvent is first distilled off under normal pressure, towards the end under vacuum . It has been established that an epoxy resin precursor that was contaminated with sodium chloride even after standing for two days in a drying cabinet at 130° C does not polymerize, and only after standing for several days at the same temperature only a polymeric layer settles directly about the sodium chloride crystal.

This phenomenon can also be confirmed by the fact that, when comparing experiments with the same molar ratio between bisphenol and epichlorohydrin purified by washing out several times with hot water, and experiments using the method just described, no difference is found in the number of epoxides per 100 g of resin.

The new method can be carried out particularly well if the moist resin separated from the aqueous layer is heated while stirring to approx. 100° C and only then slowly put under vacuum. In this way, excessive foaming of the resin is avoided, which under particularly unfavorable conditions can lead to constipation. If a vacuum of approx. 20-100 mm Hg and the bath temperature is raised after the removal of the main amount of water to 130° C, the drying is finished after an average of 30-60 min. The drying time also depends on the softening point of the resin, which in turn depends on the mole ratio used between bisphenol and epichlorohydrin. Resins with low softening points dry faster than resins with higher softening points. Epoch sewing number per 100 g of resin is also not affected by the length of the drying time. The end of drying can very well be recognized by the fact that the product is no longer cloudy and only permeated with alkali salt crystals.

The advantages of the new method compared to the older ones consist in particular in the fact that the long-term washing out of the condensation product is eliminated, which, especially in the case of resins with higher softening points, entails major difficulties and in the fact that the necessary purification of the raw resin takes significantly less time time. The narrow cleaning can be carried out in the apparatus that has already been used for the condensation.

The method according to the invention for the production of epoxy resins shall be described in more detail by means of the following examples.

Example 1:

In a three-necked flask equipped with a stirrer, reflux condenser and thermometer, 228 g bisphenol (1 mol) was dissolved in 64 g sodium hydroxide (1.6 mol) and 426 g water by heating to approx. 55° C. After cooling to 40° C, 148 g (1.6 mol) of epichlorohydrin were added at once and stirred vigorously. The exothermic reaction mixture was then over the course of 80 min. heated to 90° C and stirring continued for one hour between 90 and 100° C.

Then the alkaline reacting reaction mixture was mixed with acetic acid until a slightly acidic reaction and the stirring continued for a further approx. 10 minutes at the same temperature. Even after this time, the reaction mixture must react acidic. Now the upper resin layer was separated from the lower aqueous layer and washed out with the same amount of boiling water for 15 min. under vigorous stirring. After separation of the washing water, a vacuum of approx. 50-100 mm Hg and the resin heated with stirring to a bath temperature of 130° C. After approx. 30 min. in the flask there was dewatered resin which had been permeated with sodium chloride and which, after cooling, was dissolved in 400 cm<3> of acetone. The dissolved resin was then freed from undissolved matter by filtration and then heated to a bath temperature of 130° C, first under normal pressure, later under vacuum to remove the rest of the solvent. A clear anhydrous epoxy resin precursor was left in the flask, which on analysis gave the following data: Epoxide number per 100 g resin 0.254 Softening point (Dur r ans

Hg method) 52° C Molecular weight (measured in acetone) 752 Appearance strongly amber colored product.

Example 2

In an apparatus which was equipped with a stirrer, reflux condenser, thermometer and drop-

funnel, 228 g of bisphenol (1 mol) and 148 g of epichlorohydrin (1.6 mol) were heated to 60° C and slowly mixed with a solution of 64 g of sodium hydroxide (1.6 mol) in 300 g

water until the highly exothermic reaction began. The temperature rose to approx. 73° C, and only after the reaction was finished was the rest of the alkali added between 60 and 70° C. The reaction was then no longer exothermic. The reaction mixture was now heated to 90° C and the stirring continued for one hour between 90 and 100° C. Then a few drops of acetic acid or inorganic acid were mixed in to form a slightly acidic reaction, and the stirring continued for another 10 min. The aqueous layer should also react slightly acidic after this time. The resin obtained in this way was then washed out for approx. 15 min. with boiling water and after separation of the wash water dried under a vacuum of 50-100 mm Hg and a bath temperature of up to 130° C within 30 min. After the resin was taken up in 400 cm<3> of acetone, the solution was prepared for undissolved salts by filtration and solvents distilled off at a bath temperature of up to 130° C, first under normal pressure and later under vacuum to remove residues that still accompanied. The analysis of the resin thus obtained showed the following values:

Example 3:

In the same apparatus as in example 2, 228 g of bis-phenol (1 mol) was dissolved in 40 g of sodium hydroxide (1 mol) and 200 g of water by heating to 55° C and after cooling to 40° C, 148 g of epichlorohydrin became (1.6 mole) added at once. The temperature in the flask then rose to 62° C. After completion of the reaction, a further 24 g of sodium hydroxide dissolved in 60 cm<3> of water were introduced at a temperature between 60 and 70° C and the reaction mixture was heated to 90° C. After one hour, at the same temperature a few drops of acetic acid were added until a slightly acidic reaction and the stirring continued for a further 10 min. The resin was then separated from the aqueous phase and washed out for 15 min. with the same amount of boiling water. Dewatering was then carried out by applying a vacuum of 50-100 mm Hg and a bath temperature of 130° C and dissolving in 400 cm<3> of acetone. After filtering off the undissolved part, the solvent was distilled off, first at normal pressure and later under vacuum at a bath temperature of up to 130° C. The resin obtained in this way had the following analytical values:

Example 4:

In the same apparatus as in example 2, 228 g of bisphenol (1 mol) was dissolved at 55° C in 40 g of sodium hydroxide (1 mol) and 200 g of water, cooled to 40° C and at this temperature simultaneously mixed with 148 g of epichlorohydrin (1.6 moles). The temperature then rose to 62° C. and between 60 and 70° C. a further 24 g of sodium hydroxide (0.6 mol), dissolved in 60 g of water, was introduced. After completion of the alkali addition, heating was then carried out to 90° C and 6.4 g of sodium hydroxide (10% excess), dissolved in 20 cm<3> of water was introduced and the reaction mixture was stirred for one hour at between 90 and 100° C Then acetic acid was added until a slightly acidic reaction, stirred for a further approx. 10 minutes and the resin separated from the aqueous layer. After washing out the crude resin once with an equal amount of boiling water, this was then dewatered under vacuum at a bath temperature of up to 130° C and taken up in 400 cm<3> of acetone. By filtration, a clear resin solution was obtained, from which the solvent was removed first under normal pressure, later to remove the residue under vacuum at a bath temperature of up to 130° C. The analysis of raw resin

Example 5:

In the same apparatus as in the previous examples, 228 g of bisphenol (1 mol) was heated together with 148 g of epichlorohydrin (1.6 mol) to 60° C and at this temperature slowly mixed with a solution of 20 g of sodium hydroxide in 200 cm<3 > water. At the beginning of the strongly exothermic reac tion, the alkali addition was interrupted and then regulated so that the temperature in the reaction mixture did not exceed 70° C. A further 44 g of sodium hydroxide, dissolved in 100 cm<3> of water, were then introduced. The total addition of alkali was finished within 30 min.

After the reaction mixture had been stirred for one hour between 90 and 100° C, a few drops of hydrochloric acid were introduced until an acidic reaction and the stirring continued for a further 10 min. The resin thus obtained was then washed with an approximately equal volume of boiling water for 15 min. and after separation of the washing water completely dewatered under vacuum at a bath temperature up to 130° C. After taking up the resin, which is still contaminated with sodium chloride, in 400 cm<3> of acetone, the solution was freed of the undissolved salts by filtration and the solvent distilled from, first at normal pressure, later under vacuum at a bath temperature of up to 130° C. The raw resin gave the following values when analyzed:

Example 6:

In an apparatus equipped with a stirrer, thermometer, reflux condenser and dropping funnel, 456 g of bisphenol (2 mol) and 296 g of epichlorohydrin (3.2 mol) were heated to 90° C and at this temperature slowly and with vigorous stirring mixed with a solution of 128 g of sodium hydroxide (3.2 mol) in 600 cm<3> of water. At the beginning of the introduction, the temperature rose to 105° C. and until the end of the reaction the addition of alkali was interrupted.

The further addition of alkali was then no longer noticeably exothermic and had to be terminated within 30 minutes. after which the stirring was continued for another hour between 90 and 100° C. Then the reaction mixture was acidified with a few drops of acetic acid, stirred for a further 10 min. and then the resin was separated from the aqueous layer. When stirring for 15 min. with approximately the same amount of boiling water, the resin was washed out and, after separation of the washing water, it was dewatered under vacuum at a bath temperature of up to 130° C. After the absorption of the resin which had been permeated with sodium chloride in 800 cm<3> of acetone, the solution was filtered and then the solvent was distilled off, first under normal pressure and then under vacuum to remove the rest of the solvent. As a residue, the completely clear epoxy precursor was left.

Example 7: Instead of a molar ratio of 1 mol of bisphenol to 1.6 mol of epichlorohydrin, as in the previous example, only 1.4 mol of epichlorohydrin per moles of bisphenol. The working method was the same as in example 6. A resin with the following properties was obtained.

Example 8.

Using the same method as in example 6, 1 mol of bisphenol was reacted with 1.8 mol of epichlorohydrin. The resin obtained gave the following values after analysis:

Example 9.

Following the same procedure as already described in the previous examples, after reacting 1 mol of bisphenol with 2 mol of epichlorohydrin, a resin with the following analytical data was obtained:

Example 10.

By reacting 1 mol of bisphenol with 2.2 mol of epichlorohydrin in the manner described in the preceding examples,

an epoxy resin precursor with the following properties was obtained:

Example 11: In a reaction vessel equipped with a stirrer, reflux condenser, thermometer and dropping funnel, 110 g of resorcinol (1 mol) and 148 g of epichlorohydrin (1.6) mol were heated to 60° C under vigorous stirring and during 30 min. mixed with a solution of 64 g of sodium hydroxide (1.6 mol) in 300 cm<3> of water. The reaction, which was initially strongly exothermic, was regulated by interrupting the addition of alkali so that the temperature did not exceed 70° C as far as possible. The stirring was then continued for a further hour between 90 and 100° C and the alkaline reacting reaction mixture was then mixed long with acetic acid that it reacts slightly acidic to litmus. After further stirring for 10 min. should it still react slightly sour. The resin was, after being separated from the aqueous phase, washed out well for 15 min. with an equal amount of boiling water and after separation of the washing water, dewatered completely under vacuum and a bath temperature of up to 130° C. After the resin contaminated with sodium chloride was taken up in 200 cm<3> of acetone and after filtering off the undissolved salts, the solvent was distilled from, first under normal pressure, later under vacuum at a bath temperature of up to 130°C to remove the residue. In the flask what remained was clear, pure recorcin poly-glycidether.

Claims (1)

Procedure for the purification of curable epoxy resin precursors which have been produced by reacting mono- or multi-core bis- ref. polyphenols with epichlorohydrin or dihalohydrin in the presence of alkali and subsequent high-tralization of excess alkali by adding an organic or inorganic acid and subsequent treatment of the reaction product containing resin and salts with acetone and filtering off the undissolved inorganic salts, characterized in that the reaction product containing resin and salts prior to the treatment with acetone is separated from the aqueous part of the reaction mixture, washed in boiling water and then completely dewatered by heating under vacuum to a bath temperature of approx. 130°C.