A PROCESS FOR REDUCING THE TOTAL HALIDE CONTENT OF AN EPOXY RESIN

Abstract: The total halide content of epoxy resins is reduced by heating a resin containing halide dissolved in a solvent mixture containing at least one ketone, at least one aromatic hydrocarbon and optionally at least one compound containing at least one aliphatic hydroxyl group in the presence of an alkali metal hydroxide for a time sufficient to reduce the total halide content.

Description: A PROCESS FOR REDUCING THE TOTAL HALIDE CONTENT OF AN EPOXY RESIN The present invention pertains to a process 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 resultant end products. The higher the halide content, the greater the detriment. The present invention provides a pro¬ cess for reducing the total (hydrolyzable and/or bound) halide content of epoxy resins. The present invention pertains to a process for reducing the total halide content of an epoxy resin containing hydrolyzable and/or bound halide which pro¬ cess comprises (A) dissolving said epoxy resin in a solvent system which comprises (1) from 25 to 75, preferably from 50 to 75 percent by weight of at least one ketone and (2) from 75 to 25, preferably from 50 to 25 percent by weight of at least one aromatic hydrocarbon; (B) adding from 0.1 to 5, preferably from 0.2 to 1 percent by weight based upon the weight of said epoxy resin of at least one compound having at least one aliphatic hydroxyl group per molecule as a cosolvent; (C) heating the resultant solution to a temper¬ ature of from 50°C up to 200°C; (D) adding from 0.25 to 10, preferably from 1 to 5, most preferably from 1 to 3 moles of an alkali metal hydroxide per equivalent of total, halide; (E) continuing the heating for a time sufficient 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, acid salt or a combination thereof; and (G) recovering the resultant epoxy resin having a reduced total halide content from the product of step (F) . Suitable epoxy resins which can be employed herein include any epoxy resin containing an average of more than one vicinal epoxy group per molecule and which contains an undesirable quantity of total, hydro¬ lyzable 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, for example, glycidyl ethers of bisphenols, glycidyl ethers of phenol formaldehyde epoxy resins, cresol formaldehyde epoxy resins, and mixtures thereof. Suitable ketones which can be employed herein include, for example, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and mixtures thereof. Suitable aromatic hydrocarbons which can be employed herein include, for example, benzene, toluene, xylene, and mixtures thereof. Suitable compounds having at least one ali¬ phatic hydroxyl group per molecule include, for example, aliphatic alcohols, diols and triols and polyoxyalkylene compounds having from 1 to 3 hydroxyl groups per molecule having an average molecular weight of from 100 to 600, preferably from 200 to 400, and mixtures thereof. Particularly suitable are the polyoxyethylene glycols sometimes referred to as polyethylene glycols, and mixtures thereof. Suitable alkali metal hydroxides include, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, and mixtures thereof. The alkali metal can be employed in solid form or as an aqueous solution, preferably as an aqueous solution in a concentration of from 10 to 70, preferably from 40 to 60 percent alkali metal hydroxide by weight. The heating can be conducted at atmospheric or superatmospheric pressure. When relatively low boiling solvents are employed, superatmospheric pres¬ sure is usually required. It is preferred to employ a temperature of from 50°C up to 200°C, more preferably from 100° to 130°C. It is preferable to not employ a temperature above the boiling point of the solvent system. For low boiling solvent systems, pressure can be employed so that temperatures above the boiling point can be employed. When washing the epoxy resin to remove the salt formed and any unreacted alkali metal hydroxide, it is preferred to employ a plurality of washing steps employing as the first wash 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 from 2 to 7. Suitable acids and acid salts include, for example, phosphoric acid, mono-sodium phosphate, di-sodiu phosphate, carbonic acid, boric acid, and mixtures thereof. The epoxy resin is ultimately recovered by subjecting the organic phase from the washing procedure to distillation to remove the solvents from the epoxy resin. The following examples are illustrative of the present invention, but are not to be construed as to limiting the scope thereof in any manner. EXAMPLE 1 75 G of a cresol-formaldehyde epoxy novolac resin having an average epoxide equivalent weight (EEW) of about 220 and an average epoxy functionality of about 6 containing 3536 ppm hydrolyzable chloride by weight was dissolved in 75 g of a 75/25 by weight mixture of methyl ethyl ketone ( EK) and toluene. 0.38 G (0.5 weight percent based on epoxy resin) of poly¬ ethylene glycol having an average molecular weight of about 400 was added to the solution and the solution was heated to 80°C with stirring. 1.05 G of 50 percent aqueous potassium hydroxide (1.25 eq. KOH to 1 eq. of hydrolyzable chloride) was added all at once and the reaction mixture was maintained at 80° for 2 hours (7200 s) with good agitation. The, reaction mixture was diluted to 20 per¬ cent resin concentration with MEK/toluene solvent mix, neutralized with dilute H 3 P0 and then washed with water 3 to 4 times to remove NaCl. The organic phase from the water washes was placed on a rotary evaporator under a full, vacuum and 170°C to remove the solvent completely. A purified cresol epoxy novolac resin with a hydrolyzable chloride content of 7 ppm was obtained. EXAMPLE 2 The procedure of Example 1 was followed employing the following components and conditions. 100 Grams of a cresol-formaldehyde epoxy novolac resin having an average EEW of 220 and an average epoxy functionality of 6 and containing 3700 ppm hydro¬ lyzable chloride. 100 Grams of a 75/25 mixture of MEK/toluene Sufficient quantity of different cosolvents such that the amount of cosolvent was 0.5 percent by weight based on the epoxy resin. 1 Gram (1.2 equiv. per hydrolyzable chlorine equiv. ) of a 50 percent aqueous solution of NaOH The reactions were conducted at 80°C for 2 hours (7200 s). The results are given in the following Table I. TABLE I COSOLVENT HYDROLYZABLE CHLORIDE, __£__ glycerine 181 methanol 95 isopropyl alcohol 84 monomethyl ether of propylene glycol 83 tetraethylene glycol 54 polyethylene glycol (200 MW) 60 polyethylene glycol (300 MW) 55 polyethylene glycol (400 MW) 54 polypropylene glycol (425 MW) 159 EXAMPLE 3 The procedure of Example 1 was followed employing the following components and conditions. 100 Grams of a cresol-formaldehyde epoxy novolac resin having an average EEW of 220, an average epoxy functionality of 6 and 3536 ppm hydrolyzable chloride. 100 Grams of a 75/25 by weight mixture of MEK/toluene. Several reactions were conducted at 80°C for 2 hours (7200 s) employing various quantities of either NaOH or KOH and with and without polyethylene glycol having an average MW of 400. The results are given in the following Table II. TABLE II EQUIV. CAUSTIC PER EQUIV. HYDROLYZABLE CAUSTIC HYDROLYZABLE POLYETHYLENE CHLORIDE TYPE CHLORIDE GLYCOL, Wt%* CONTENT,ppm NaOH 1.08 0 167 NaOH 1.08 0.5 107 KOH 1.08 0 113 KOH 1.08 0.5 48 NaOH 1.16 0.5 81 KOH 1.16 0.5 33 NaOH 1.25 0.5 34 KOH 1.25 0.5 7 *Based upon weight of epoxy resin. EXAMPLE 4 To a one liter reaction vessel equipped with temperature and pressure control and indicating means, a means for the continuous addition of aqueous sodium hydroxide, a means for condensing and separating water from a codistillate mixture of water, solvent and epichlorohydrin and means for returning the solvent and epichlorohydrin was added 118.5 g (1 equivalent) of cresol-formaldehyde novolac resin having an average hydroxyl equivalent wt. of 118.5 and average function¬ ality of about 6, 370 g (4 equivalents) of epichloro¬ hydrin and 247 g of the methyl ether of propylene glycol (l-methoxy-2-hydroxy propane) as a solvent. After stirring at room temperature and atmospheric pressure to thoroughly mix the contents, the tem¬ perature was raised to 65°C and the pressure was reduced to 180 mm Hg (24 kPa) absolute. To the resultant solution was continuously added 75.2 g (0.94 equivalent) of 50 percent aqueous sodium hydroxide solution at a constant rate over a period of 4 hours (14400 s). During the addition of the sodium hydrox¬ ide, the water was removed by codistilling with epi- chlorohydrin and solvent. The distillate was condensed thereby forming two distinct phases, an aqueous phase (top) and an organic epichlorohydrin-solvent phase (bottom) . The organic phase was continuously returned to the reactor. After completion of the sodium hydrox- ide addition, the reaction mixture was maintained at a temperature of 65° and a pressure of about 180 mm Hg (24 kPa) absolute for an additional 30 minutes (1800 s). The resulting cresol-formaldehyde epoxy novolac resin was then distilled under full vacuum and temperature up to 170°C .to remove all epichlorohydrin and l-methoxy-2- -hydroxy propane. To the molten cresol-formaldehyde epoxy novolac resin was added an equal weight of a 75/25 by weight mixture of methyl ethyl ketone (MEK) and tol- uene. A sample of the slurry was taken and was found to contain 1200 ppm hydrolyzable chloride. 0.87 g (0.5 weight percent 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 g of 50 percent aqueous potassium hydroxide (1.3 eq. KOH to 1 eq. hydrolyzable chloride) was added all at once and the reaction mixture was maintained at 80°C for 2 hours (7200 s) with good agitation. The reaction mixture was diluted to 20 per¬ cent resin concentration with MEK/toluene (75/25) solvent mixture, neutralized with C0 2 and then washed with water 4 to 5 times to remove NaCl. The organic phase from the water washes was placed on a rotary evaporator under a full vacuum and temperature of 170°C to remove the solvent completely. A purified cresol-formaldehyde epoxy novolac resin with a hydrolyzable chloride content of 7 ppm was obtained. EXAMPLE 5 625 G of cresol epoxy novolac containing 553 ppm hydrolyzable chloride and 930 ppm bound chloride (total chloride = 1483 ppm) was dissolved in 625 g of 75/25 by weight MEK/toluene solvent mixture. 1.875 G (0.3 weight percent 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 with stirring. 6.7 g of 45 percent aqueous potas- sium hydroxide (2.1 eq. caustic to 1 eq. chlorine) was added all at once and the reaction mixture was main¬ tained at 85°C for 6 hours (21,600 s) with good agita¬ tion. The reaction mixture was diluted to 20 per- cent solid concentration with MEK/toluene solvent ixture, neutralized with dilute H 3 P0 4 and then washed with water several times to remove NaCl. The organic phase from the washes was placed on a rotary evaporator under a full vacuum and 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 G 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 g of a MEK/toluene solvent mix¬ ture. 0.5 g (0.5 weight percent based on resin) of polyethylene glycol having a molecular weight of 400 was added to the solution and the solution was heated to 80°C with stirring. 0.84 G of 45 percent aqueous potassium hydroxide (2 eq. caustic to 1 eq. chlorine) was added all at once and the reaction mixture was maintained at 80°C for 2 hours (7200 s) with good agitation. The reaction mixture was diluted to 20 per¬ cent solid concentration with MEK/toluene solvent mixture, neutralized with C0 2 and then washed with water several times to remove NaCl. The organic phase from the washes was placed on a rotary evaporator under a full vacuum and 170°C to remove the solvent completely. 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 stainless steel 2-liter pressure reac¬ tion vessel, 625 g of cresol epoxy novolac containing 553 ppm hydrolyzable chloride and 930 ppm bound chlo- ride (total chloride = 1483 ppm) was dissolved in 625 g of a 75/25 by weight MEK/toluene solvent mixture. 1.875 G (0.3 weight percent based on resin) of poly¬ ethylene glycol having an average molecular weight of 400 was added to the solution and the solution was heated to 120°C with stirring. 3.9 G of 45 percent aqueous potassium hydroxide (1.2 eq. caustic to 1 eq. chlorine) was added all at once and the reaction mix¬ ture was maintained at 120°C for 1 hour (3600 s) with good agitation. The reaction mixture was diluted to 20 per¬ cent solid concentration with MEK/toluene solvent mixture, neutralized with C0 2 and then washed with water several times to remove NaCl. The organic phase from the washes was placed on a rotary evaporator under a full vacuum and 170°C to remove the solvent completely. 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: 1. A process for reducing the total halide content of an epoxy resin containing hydrolyzable and/or bound halide which process comprises (A) dissolving said epoxy resin in a solvent system which comprises (1) from 25 to 75 percent by weight of at least one ketone and (2) from 75 to 25 percent by weight of at least one aromatic hydrocarbon; (B) adding from 0.1 to 5 percent by weight based upon the weight of said epoxy resin of at least one compound having at least one ali¬ phatic hydroxyl group per molecule as a cosolvent; (C) heating the resultant solution to a temper¬ ature of from 50°C up to 200°C; (D) adding from 0.25 to 10 moles of an alkali metal hydroxide per equivalent of total halide; (E) continuing the heating for a time sufficient 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, acid salt or a combination thereof; and (G) recovering the resultant epoxy resin having a reduced total halide content from the product of step (F) . 2. A method of Claim 1 wherein (i) in step (A) said solvent system com¬ prises from 50 to 75 percent by weight of one ketone and said aromatic hydro¬ carbon is present in quantities of from 50 to 25 percent by weight; (ii) in step (B) said cosolvent is present in quantity of from 0.2 to 1 weight percent based upon the weight of the epoxy resin; (iii) in step (C), said heating is conducted at a temperature of from 100°C to 130°C; and (iv) in step (D), the alkali metal hydroxide is present in a quantity of from 1 to 5 moles per equivalent of total halide. 3. A method of Claim 2 wherein (i) said ketone is methyl ethyl ketone or methyl isobutyl ketone; (ii) said aromatic hydrocarbon is benzene, toluene or xylene; (iii) said cosolvent is a polyoxyethylene glycol or polyoxypropylene glycol having an average molecular weight of from 100 to 600; (iv) said alkali metal hydroxide is sodium hydroxide or potassium hydroxide; and (v) in step (D), the alkali metal hydroxide is present in a quantity of from 1 to 3 moles per equivalent of total halide. 4. A method of Claim 3 wherein (i) said ketone is methyl ethyl ketone; (ii) said aromatic hydrocarbon is toluene; (iii) said cosolvent is polyoxyethylene glycol having an average molecular weight of from 200 to 400; and (iv) said alkali metal hydroxide is potassium hydroxide. 5. A method of Claim 4 wherein in step (F), said product from step (E) is washed at least once with a dilute solution of a weak inorganic acid. 6. A method of Claim 5 wherein said weak inorganic acid is phosphoric acid or carbonic acid.

Inventors: BOWDEN ROBERT L, CHEN WUU N, WANG CHUN S, BOWDEN, ROBERT, L., CHEN, WUU, N., WANG, CHUN, S.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1985
Main classification: C08G59
IPC codes: C08G59