NO165078B - PROCEDURE FOR REDUCING THE TOTAL HALOGEN CONTENT IN AN EPOXY RESIN. - Google Patents

Description

The invention relates to a method for reducing

the hydrolyzable and/or bound (total) halide content of an epoxy resin.

Epoxy resins are used in the electronics industry as encapsulants, potting compounds, electrical laminates and the like. This industry has discovered that the halide content of the epoxy resin adversely affects the electrical properties of the resulting end products. The higher the halide content, the greater the harmful impact. The present invention provides a method for reducing the total (hydrolysable and/or bound) halide content in epoxy resins.

The invention thus relates to a method for reducing the total halide content in an epoxy resin which contains on average more than one vicinal epoxy group per molecule, containing hydrolyzable and/or bound halide, which comprises

(A) dissolving the epoxy resin in a solvent system comprising

(1) 25-75% by weight of at least one ketone and

(2) 75-25% by weight of at least one aromatic hydrocarbon; and the characteristic of the method is the following additional feature: (B) adding 0.1-5% by weight, based on the weight of said epoxy resin, of at least one compound having at least one

aliphatic hydroxyl group per molecule, as co-solvent;

(C) heating the resulting solution to a temperature of

from 50°C up to 200°C; (D) adding 0.25-10 mol of an alkali metal hydroxide per equivalent of total halide; (E) continuing the heating to reduce the total halide content of said epoxy resin;

(F) washing the product from step (E) with either water, a

dilute aqueous solution of a weak inorganic acid, et

acid salt or a combination thereof;

(G) recovering the resulting epoxy resin having a

reduced total halide content from the product in step (F).

Preferably, in point (B) 0.2-1% by weight of said compound is added as co-solvent, and in (D) preferably 1-5, preferably 1-3, moles of alkali metal hydroxide are added.

Suitable epoxy resins which may be used herein include any epoxy resin containing an average of more than one vicinal epoxy group per molecule and containing an undesirable amount of total, hydrolyzable and/or bound halide.

Particularly suitable epoxy resins include the polyglycidyl ether of compounds having an average of more than one hydroxyl group per molecule and which contains at least 10 parts per million total halide such as glycidyl ethers of bisphenols, glycidyl ethers of phenol formaldehyde epoxy resins, cresol/formaldehyde epoxy resins, as well as mixtures thereof.

Suitable ketones which can be used herein include e.g. acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and mixtures thereof.

Suitable aromatic hydrocarbons which can be used herein include e.g. benzene, toluene, xylene, and mixtures thereof.

Suitable compounds which have at least one aliphatic hydroxyl group per molecule includes e.g. aliphatic alcohols, diols and triols and polyoxyalkylene compounds which have 1-3 hydroxyl groups per molecule with an average molecular weight of 100-600, preferably 200-400, as well as mixtures thereof.

Particularly suitable are the polyoxyethylene glycols which are sometimes referred to as polyethylene glycols, as well as mixtures thereof.

Suitable alkali metal hydroxides include e.g. sodium hydroxide, potassium hydroxide, lithium hydroxide and mixtures thereof. The alkali metal can be used in solid form or as an aqueous solution, preferably as an aqueous solution in a concentration of from 10 to 70, preferably 40-60, percent alkali metal hydroxide by weight.

The heating can be carried out at atmospheric pressure or superatmospheric pressure. If relatively low-boiling solvents are used, superatmospheric pressure is usually required. It is preferred to use a temperature of from 50 and up to 200°C, more preferably from 100 to 130°C. It is preferred not to use a temperature above the boiling point of the solvent system. For

(7

low boiling solvent systems; -pressure can be used so that temperatures above the boiling point can be used.

When washing the epoxy resin to remove the salt that has formed and possibly unreacted alkali metal hydroxide, it is preferred to use several washing steps, where a dilute solution of an inorganic acid or a dilute solution of an inorganic acid salt, preferably acids or acid salts having a pKa value of from 2 to 10, preferably 2-7.

Suitable acids and acid salts include e.g. phosphoric acid, monosodium phosphate, disodium phosphate, carbonic acid, boric acid, as well as mixtures thereof.

The epoxy resin is finally recovered by subjecting the organic phase from the washing process to distillation to remove the solvents from the epoxy resin.

The following examples illustrate the present invention.

Example 1

75 grams of a cresol/formaldehyde epoxy novolak resin with an average epoxy equivalent weight (EEV) of approx. 22 0 and an average epoxy functionality of approx. 6, containing 3536 ppm hydrolyzable chloride, by weight, was dissolved in 75 grams of a 75/25 weight mixture of methyl ethyl ketone (MEK) and toluene. 0.38 grams (0.5% by weight based on epoxy resin) of polyethylene glycol which had an average molecular weight of approx. 400 was added to the solution, and the solution was heated to 80°C with stirring. 1.05 grams of 50% aqueous potassium hydroxide (1.25 eq. KOH to 1 eq. of hydrolyzable chloride) was added, all at once, and the reaction mixture was held at 80° for 2 h (7200 s) under good stirring.

The reaction mixture was diluted to 20% resin concentration with MEK/toluene solvent mix, neutralized with dilute H3PO4 and then washed with water 3-4 times to remove NaCl.

The organic phase from the water washings was placed on a rotary evaporator under full vacuum and at 170°C to completely remove the solvent. A purified cresole epoxy novolac resin with a hydrolyzable chloride content of 7 ppm was obtained.

Example 2

The procedure of Example 1 was followed using the following components and conditions.

100 grams of a cresol/formaldehyde epoxy novolak resin having an average EEV of 220 and an average epoxy functionality of 6 and containing 3700 ppm hydrolyzable chloride.

100 grams of a 75/25 mixture of MEK/toluene. Sufficient amounts of various co-solvents such that the amount of co-solvent was 0.5% by weight based on the epoxy resin. 1 gram (1.2 equiv. per hydrolysable chlorine equiv.) of a 50% aqueous solution of NaOH.

The reactions were carried out at 80°C for 2 hours (7200 s). The results are given in the following table I.

Example 3

The procedure of Example 1 was followed using the following components and conditions.

100 grams of a cresol/formaldehyde epoxy novolac resin with an average EEV of 220, an average epoxy functionality of 6, and 3536 ppm hydrolyzable chloride.

100 grams of a 75/25 mixture, by weight, of MEK/toluene.

Several reactions were carried out at 80°C for 2 hours (7200 s) using varying amounts of either NaOH or KOH and with and without polyethylene glycol having an average MV of 400. The results are shown in the following Table II.

Example 4

To a 1 liter reaction vessel equipped with temperature and pressure control and indicating aids, aid for continuous addition of aqueous sodium hydroxide, aid for condensation and separation of water from a co-distillate mixture of water, solvent and epichlorohydrin and aid for returning the solvent and epichlorohydrin, 118.5 grams (1 eq.) of cresol/formaldehyde novolak resin with an average hydroxide equivalent weight of 118.5 and with an average functionality of approx. 6, 370 grams (4 equiv.) of epichlorohydrin and 247 grams of the methyl ether of propylene glycol (1-methoxy-2-hydroxypropane) as solvent. After stirring at room temperature and atmospheric pressure to thoroughly mix the contents, the temperature was raised to 65°C, and the pressure was reduced to 180 mm Kg (24 kPa) absolute. To the resulting solution was continuously added 75.2 grams (0.94 eq.) of 50% aqueous sodium hydroxide solution at a constant rate over a period of 4 hours (14400 s). During the addition of the sodium hydroxide, the water was removed by co-distillation with epichlorohydrin and solvent. The distillate was condensed to form two separate phases, a water phase (top) and an organic epichlorohydrin solvent phase (bottom). The organic phase was continuously returned to the reactor. After completion of the sodium hydroxide addition, the reaction mixture was maintained at a temperature of 65° and a pressure of approx. 180 mm Hg (24 kPa) absolute for another 30 minutes (1800 s). The resulting cresol/formaldehyde-epoxy-novolac resin was then distilled under full vacuum and at temperatures up to 170°C to remove all epichlorohydrin and 1-methoxy-2-hydroxypropane.

To the molten cresol/formaldehyde epoxy novolak resin was added an equal weight of a 75/25 mixture, by weight, of methyl ethyl ketone (MEK) and toluene. A sample of the slurry was taken and found to contain 1200 ppm hydrolyzable chloride. 0.87 grams (0.5% by weight based on epoxy resin) of polyethylene glycol having an average molecular weight of 400 was added to the mixture and the mixture was heated to 80°C with stirring. 0.86 grams of 50% aqueous potassium hydroxide (1.3 eq. KOH to 1 eq. hydrolyzable chloride) was added, all at once, and the reaction mixture was held at 80°C for 2 hours (7200 s) with good agitation.

The reaction mixture was diluted to 20% resin concentration with MEK/toluene (75/25) solvent mixture, neutralized with CC>2 and then washed with water 4-5 times to remove NaCl.

The organic phase from the water washings was placed on a rotary evaporator under full vacuum and at a temperature of 170°C to remove the solvent completely. A purified cresol/formaldehyde epoxy novolak resin with a hydrolyzable chloride content of 7 ppm was obtained.

Example 5

625 grams of cresol-epoxy-novolac containing 553 ppm hydrolyzable chloride and 930 ppm bound chloride (total chloride = 1483 ppm) was dissolved in 625 grams of 75/25, by weight, MEK/toluene solvent mixture. 1.875 grams (0.3% by weight based on resin) of polyethylene glycol having an average molecular weight of 400 was added to the solution, and the solution was heated to 85°C under

stirring. 6.7 grams of 45% aqueous potassium hydroxide (2.1 equiv caustic to 1 equiv chlorine) was added, all at once, and the reaction mixture was held at 85°C for 6 hours (21,600 s) with good agitation.

The reaction mixture was diluted to 20% solids concentration with MEK/toluene solvent mixture, neutralized with dilute H₂PO₂ and then washed with water several times to remove NaCl.

The organic phase from the washings was placed on a rotary evaporator under full vacuum and at 170°C to remove the solvent completely. A purified cresol epoxy novolac with hydrolyzable chloride content of 7 ppm and bound chloride content of 263 ppm (total chloride = 270) was obtained.

Example 6

100 grams of a diglycidyl ether of bisphenol A epoxy resin containing 300 ppm hydrolyzable chloride and 900 ppm bound chloride (total chloride = 1200 ppm) was dissolved in 100 grams of a MEK/toluene solvent mixture. 0.5 grams (0.5% by weight based

on resin) of polyethylene glycol with a molecular weight of 400 was added to the solution, and the solution was heated to 80°C with stirring. 0.84 grams of 45% aqueous potassium hydroxide (2 equiv caustic to 1 equiv chlorine) was added, all at once, and the reaction mixture was held at 80°C for 2 hours (7200 s) with good agitation.

The reaction mixture was diluted to 20% solids concentration with MEK/toluene solvent mixture, neutralized with CO 2 and then washed with water several times to remove NaCl.

The organic phase from the washings was placed on a rotary evaporator under full vacuum and at 170°C for complete removal of the solvent. A purified diglycidyl ether of bisphenol A epoxy resin with hydrolyzable chloride of 3 ppm and bound chloride of 540 ppm (total chloride = 543 ppm) was obtained.

Example 7

In a 2-liter stainless steel pressure reaction vessel was

625 grams of cresol-epoxy-novolac containing 553 ppm hydrolyzate-

bare chloride and 930 ppm bound chloride (total chloride = 1483 ppm)

dissolved in 625 grams of a 75/25, by weight, MEK/toluene solvent mixture. 1.875 grams (0.3% by weight based on resin) of 400 average molecular weight polyethylene glycol was added to the solution, and the solution was heated to 120°C with stirring. 3.9 grams of 45% aqueous potassium hydroxide (1.2 eq. caustic to 1 eq. chloride) was added, all at once, and the reaction mixture was held at 120°C for 1 hour (3600 s) with good agitation .

The reaction mixture was diluted to 20% solids concentration with MEK/toluene solvent mixture, neutralized with CO 2 and then washed with water several times to remove NaCl.

The organic phase from the washings was placed on a rotary evaporator under full vacuum and at 170°C so that the solvent was completely removed. A purified cresol epoxy novolac with hydrolyzable chloride content of 8 ppm and bound chloride content of 260 ppm (total chloride = 268) was obtained.

Claims (6)

1. Method for reducing the total halide content in an epoxy resin which contains on average more than one vicinal epoxy group per molecule, containing hydrolyzable and/or bound halide, comprising (A) dissolving the epoxy resin in a solvent system comprising (1) 25-75% by weight of at least one ketone and (2) 75-25% by weight of at least one aromatic hydrocarbon; characterized in that it further comprises (B) adding 0.1-5% by weight, based on the weight of said epoxy resin, of at least one compound which has at least one aliphatic hydroxyl group per molecule, as co-solvent; (C) heating the resulting solution to a temperature of from 50°C up to 200°C; (D) adding 0.25-10 mol of an alkali metal hydroxide per equivalent of total halide; (E) continuing the heating to reduce the total halide content of said epoxy resin; (F) washing the product from step (E) with either water, a dilute aqueous solution of a weak inorganic acid, a acid salt or a combination thereof; (G) recovering the resulting epoxy resin having a reduced total halide content from the product in step (F). 2. Procedure as stated in claim 1, characterized in that (i) in step (B) said co-solvent is present in an amount of 0.2-1% by weight, based on the weight of the epoxy resin; (ii) in step (C) the heating is carried out at a temperature of from 100°C to 130°C; and (iii) in step (D), the alkali metal hydroxide is present in an amount of 1-5 mol per equivalent of total halide. 3. Procedure as stated in claim 2, characterized in that (i) said co-solvent is a polyoxyethylene glycol or polyoxypropylene glycol having an average molecular weight of from 100 to 600; (ii) said alkali metal hydroxide is sodium hydroxide or potassium hydroxide; and (iii) in step (D), the alkali metal hydroxide is present in an amount of from 1 to 3 moles per equivalent of total halide. 4. Procedure as stated in claim 3, characterized in that (i) said co-solvent is polyoxyethylene glycol with an average molecular weight of 200-400; and (ii) said alkali metal hydroxide is potassium hydroxide. 5. Procedure as stated in claim 4, characterized in that in step (F) said product from step (E) is washed at least once with a dilute solution of a weak inorganic acid. 6. Procedure as stated in claim 5, characterized in that phosphoric acid or carbonic acid is used as a weak inorganic acid.