MXPA98002889A - Reduction of content of ionic impurities in polycarbon resins - Google Patents

Abstract

An aromatic polycarbonate composition having less than 300 parts per billion each of ionic impurities, particularly sulfate and chloride ions, devolatilizing the ionic impurities from a polycarbonate composition employing an aqueous medium of about 1% by weight with base on the weight of the polycarbonate composition, preferably, the devolatilization is carried out in an extruder during the combination of the polycarbonate composition and preferably under vacuum, also, the extruded polycarbonate resin strands are extinguished in a water bath which has a sulfate and chloride ion content of less than 300 ppb each u

Description

REDUCTION OF THE CONTENT OF IONIC IMPURITIES IN POLYCARBONATE RESINS FIELD OF THE INVENTION The present invention is directed to a thermoplastic aromatic polycarbonate composition having reduced ionic impurities while maintaining good processing quality properties. The product is a superior quality polycarbonate resin for producing high quality molded articles such as computer hard disk drive plate carriers or pre-microcircuit silicon wafer carriers for the computer industry. Very specifically, this invention is directed to an improved process and to an improved product from said process as described herein.

BACKGROUND OF THE INVENTION The polycarbonate resin can often contain certain impurities which in turn affect the performance of its quality in the final molded article. For example, sulfate and chloride ions, if in sufficient quantities, will affect the color and processing quality of polycarbonate resins to produce pre-microcircuit silicon wafer carriers, or hard disk drive card carriers for computer. The sulfate ions can react with residual ammonia on the surface of the silicon wafer to form ammonium sulfate which forms a white residue on the surface of a silicon pre-microcircuit wafer. The wafer then requires cleaning before being processed into a computer microcircuit. Exposure to the additional heat phase, such as injection molding, extrusion or combination thereof, can also induce discoloration of the polycarbonate resin. Even with phosphite stabilizers, polycarbonate yellowing and hydrolysis of the phosphite can occur particularly at processing temperatures. It is believed that phosphites, which are susceptible to hydrolysis at elevated temperatures or processing, form acidic species in situ that can then react with polycarbonate, possibly increasing chain cleavage and giving rise to side reactions that can finally generate color in the molded article. This may occur during the extrusion, combination, or molding of the polycarbonate resin. Also, to achieve certain improved properties or properties, some additives are used with the polycarbonate resin during extrusion, by combining or injection molding the polycarbonate composition. The addition of said additives to achieve better properties should not affect the quality of processing. Furthermore, it is known how to stabilize the polycarbonate resin against discoloration using phosphites and / or epoxy materials as stabilizing additives. These are described extensively in US patents. such as 4,381,358, 4,358,563 and 3,673,146. However, if certain impurities can be removed without the use of additives to neutralize the impurities, the removal of the impurities would greatly increase their properties without affecting the processing quality as may occur with the additives. Therefore, an object of the present invention is to provide a method for reducing ionic impurities in a polycarbonate resin. Another object of this invention is to reduce ionic impurities in a polycarbonate resin during the melt blending of the polycarbonate composition. Still another object of the invention is to reduce sulfate and chloride ions in a polycarbonate resin. Yet another object of this invention is to produce a polycarbonate resin having reduced ionic impurities.

BRIEF DESCRIPTION OF THE INVENTION The invention is directed to a polycarbonate composition having reduced ionic impurities and to a process for producing reduced ionic impurities in polycarbonate resins. This invention is also directed to an aromatic polycarbonate composition having reduced ionic impurities. The polycarbonate composition can be injection molded, extruded in a sheet or film, extruded in profile, coextruded or extruded blow molded. The process of this invention comprises the devolatilization of the impurities downstream in a melt mixing process such as an extruder, during the combination of the aromatic polycarbonate resin formulation using an aqueous medium. A small amount of the aqueous medium, preferably water, can be added to the formulation during mixing under melting in an extruder and then removing the ionic impurities by devolatilization, generally, under a downstream vacuum in an extruder. Although the removal of sulfate ions is the preferred ion removal, it has been found that other ions such as chloride ions are also removed. The sulfate and chloride ions are removed each to less than 300 parts per billion (hereafter ppmm). In a melt blending process, the formulation is extruded through a die into strips with which pellets are then formed. The strips, before forming pellets, are passed through a cooling bath or extinction of aqueous medium. Since the water has a very high ionic concentration, ie, sulfate and chloride ions, the polycarbonate resin strips are re-contaminated with these ions. Therefore, the process of this invention further requires the use of an aqueous cooling bath through which strands and truidas having a low concentration of ions are passed, particularly a low content of sulfate and chloride ions. Therefore, the water bath should be analyzed at least for the concentration of sulfate and chloride ions, which should be less than about 300 ppb each, or using at least deionized water. The process of combining or melting the aromatic polycarbonate resin of the present invention is well known to those skilled in the art of blending and blending an aromatic polycarbonate formulation, and are described in numerous articles and patents for preparing formulations of polycarbonate molding. Preferably, the composition is first combined or mixed under fusion with the additive materials, generally, in an extruder. The combined formulation is extruded into strands that are usually extinguished in an aqueous bath converted into pellets, dried and processed under heat and pressure in the finished article. The finished article can be injection molded, extruded into profile, extruded into sheet or film, blow molded or extruded into hollow shapes such as single layer or multi layer plastic objects such as bottles, disk drive plate carriers hard for computer or silicon pre-microcircuit wafer carriers for the computer industry. A small amount of an aqueous medium is added to the combination formulation to increase the removal of ionic impurities as well as the use of an aqueous quench bath having a low ion concentration. The amount of aqueous medium, preferably water, is that amount sufficient to reduce ionic impurities, particularly sulfate and chloride ions to less than about 300 ppb. The amount of aqueous medium added is from about 0.25 to about 2.0% by weight, based on the weight of the polycarbonate formulation, and preferably about 0.75 to about 1.5% by weight. A value of approximately 1.0% has been found optimal. The aqueous cooling or extinguishing bath should have a low ionic concentration, preferably wherein the concentration of sulfate or chloride ions is each less than about 300 ppb, and in particular each being no more than about 100 ppb, and very particularly each being less than about 50 ppb. The aqueous medium can be added with the ingredients in the feed hopper of the extruder or can be added downstream to the molten bath. Obviously, the medium must be added before the devolatilization of the aqueous medium and the removal of ionic impurities. The medium can be added as a shot, or it can be added in several increments such as one part in the feed hopper and the rest downstream or in the extruder, or in increments to the feed hopper.

The aromatic polycarbonate resin employed herein may be any of the condonated aromatic polycarbonates or copolymers or terpolyols thereof, or mixtures of polycarbonates with other polymers, copolymers or terpolymers thereof. The aromatic polycarbonate used in the practice of this invention can be prepared by reacting a dihydric phenol with a carbonate precursor in the presence of an acid receptor and generally a molecular weight regulator. Any dihydric phenol can be used in the preparation of polycarbonate resin described herein. Preferably, they are mononuclear or polynuclear aromatic compounds containing as functional groups two hydroxyl radicals, each of which is directly attached to a carbon atom of an aromatic nucleus. Examples of some of the dihydric phenols which can be used in the practice of this invention are bisphenols such as l, l-bis (4-hydroxyphenyl) methane, 2,2-bis (4-hydroxyphenyl) -propane, 4,4- bis (4-hydroxy phenyl) heptane, etc .; dihydric phenolic ethers such as bis (4-hydroxyphenyl) ether, bis (3,5-dichloro-4-hydroxyphenyl) ether, etc., dihydroxy-diphenyls such as p, p'-dihydroxydiphenyl, 3,3'-dichloro-4, 4'-dihydroxy-diphenyl, etc., dihydroxyarylsulphones such as bis (4-hydroxy phenyl) sulfone, bis (3,5-dime i 1 -4-hyd roxy phenyl) -sulfone, bis (3-methyl-5-ethyl) 4-hydroxyphenyl) sulfone, etc., dihydroxybenzenes, resorcinol, hydroquinone, dihydroxybenzenes substituted with halogen and alkyl such as l, 4-dihydroxy-2-chlorobenzene, 1,4-dihydroxy-2,3-dichlorobenzene, 1,4- dihydroxy-2-methylbenzene, etc., and dihydroxydiphenylsulphoxides such as bis (4-hydroxyphenyl) sulfide, bis (3,5-dibromo-4-hydroxyphenyl) -sulfoxide, etc. The carbonate precursors used in the practice of This invention may be either carbonyl halogenide or halogenoformate The carbonyl halides which may be used herein are carbonyl bromide, carbonyl chloride, carbonyl fluoride, etc., or mixtures thereof. The halogen formates suitable for use herein include bishalogenoformates of dihydric phenols (hydroquinone bichlorophoriates, etc.) or glycols (ethylene glycol bishaloformates, neopentyl glycol, polyethylene glycol, etc.). Although other carbonate precursors will occur to those skilled in the art, carbonyl chloride, also known as phosgene, is preferred. The reaction described above is preferably known as an interfacial process or reaction between the dihydric compound and a carbonyl chloride such as phosgene. Another process for preparing the aromatic polycarbonate of this invention is the transesterification process which involves the transesterification of an aromatic dihydroxy compound and a diester carbonate. This procedure is known as the interfacial fusion process. In the practice of this invention, the process of producing the aromatic polycarbonate is not critical. The critical aspect of this invention is to prepare the aromatic polycarbonate resin formulation by devolatilization of the attentive medium containing the ionic impurities as described above. As used herein, aromatic polycarbonate will mean and include any of the aromatic polycarbonates and combinations thereof as set forth above. The polycarbonate composition of the invention may also include additives such as UV stabilizers, thermal stabilizers, releasing agents, fillers and reinforcing fillers such as glass fibers (short or long glass fibers), carbon fibers, talc, silica and other known additives used in polycarbonate compositions.

DETAILED DESCRIPTION OF THE EXAMPLES OF THIS INVENTION This invention is further described by means of the following examples, it being understood however that this invention will not be restricted in any way by these examples. In the examples where the amounts are in terms of percent, they are percent by weight.

EXAMPLE 1 Four samples of approximately 1000 grams each, of a polycarbonate resin, were prepared as follows: Sample A was an aromatic polycarbonate powder having an intrinsic viscosity of approximately 0.50 deciliters per gram (dl / g) as measured at 20 ° C in methylene chloride. The polycarbonate powder was not extruded by melting in an extruder. Sample B was prepared using the polycarbonate powder of Sample A by mixing under fusion in an extruder a polycarbonate powder formulation of Sample A and standard mold release additives, thermal stabilizers and colorants. This mueetra was mixed under melting in a vented extruder at about 330 ° C and at an extrusion pressure of about 84.36 g / cm2. The extruded strands of sample B were extinguished in a water bath using regular tap water. Sample C was also an aromatic polycarbonate powder but had an intrinsic viscosity of about 0.45 dl / g, as determined under the conditions employed with sample A. Sample C was also not extruded under melting in an extruder. Sample D was prepared using the polycarbonate powder of sample C and mixed under melting in an extruder under the same extruder conditions as used in example B. The formulation was essentially the same as the formulation of sample B, except that about 1% by weight of water was added to the formulation based on the weight of the formulation. Downstream in the extruder, the formulation was devolatilized under vacuum of more than about 50.8 cm of mercury through the vent in the extruder. The water bath used to extinguish the extruded polycarbonate strands was deionized water having a sulphate content of approximately 12 ppb and a chloride content of approximately 12 ppb. Each formulation contained the same weight percent of standard additives. Each formulation was analyzed by ion chromatography (Cl) analysis for sulfate and chloride ion content. The results obtained were as shown below in table 1. The test method consists of dissolving approximately 3-5 grams of the polycarbonate sample in 25 ml of methylene chloride. The ions are then extracted with 15 to 20 ml of deionized water. A 5 ml aliquot of extracted deionized water was injected into an ion chromatograph to determine the total free ions in the sample.

TABLE 1 Sample Total Content of Total Content of free sulfate ions free chloride ions A 565 1945 B 450 550 C 525 1555 D 276 156 EXAMPLE 2 This example is set forth to show the amount of sulfur ions and leachable chloride that accumulates on the surface of the polycarbonate resin strands from tap water as compared to deionized water, after passing the strands of the resin of polycarbonate through an aqueous extinguishing medium. The amount of leachable ions are mainly those ions on the surface of the polycarbonate strands collected from the water bath. In the test procedure, 25 ml of deionized water is added to approximately 10 grams of polycarbonate sample. The sample is then kept in an oven at 55 ° C for approximately 16-20 hours. An aliquot of 5 ml of deionized water extracted from the sample is injected into an ion chromatograph to determine the leachable free ions on the surface of the polycarbonate as it is collected from the water bath of extinction. Pellets of sample D of example 1 above and pellets of sample E which were prepared according to the procedure for preparing sample D above, except that the water bath of extinction used water from the tap instead of deionized water. The results obtained were the following: TABLE 2 Ions chloride leachable lixiviable sulfate ions Pellets from sample D 10 20 Pellets from sample E 50 100 As can be seen from the examples, a polycarbonate composition employing water in the formulation during the combination, after devolatilizing the water which is probably in the form of steam or steam under pressure and after cooling the extruded strands in a water bath having a low ion concentration, it reduces the ionic impurities in the polycarbonate formulations, particularly sulfate and chloride ions. Although the invention has been described by reference to particular illustrative embodiments thereof, many variations and modifications of the invention may be apparent to those skilled in the art without departing from the spirit and scope of the invention as set forth in the appended claims to the invention. same

Claims (6)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for preparing a polycarbonate composition having reduced ionic impurities, said process comprising mixing under melting a polycarbonate resin with sufficient aqueous medium to reduce the concentration of ionic impurities, most of which is composed of sulfate ions and chloride, to less than about 300 parts per billion each, as determined by ion chromatography, by devolatilizing the water with ionic impurities from the composition and then extruding the polycarbonate composition in an aqueous medium quenching bath. , said bath having a low concentration of ionic impurities. 2. The process according to claim 1, further characterized in that the mixture under melting and the devolatilization is carried out in an extruder under conditions of temperature and pressure, and said extruder having a vent and a die by which it leaves the Extruder through the vent in the extruder the aqueous medium containing the ionic impurities, before the polycarbonate composition leaves the die of the extruder and the water bath of extinction has a content of sulfate and chloride ions, each less than about 300 ppb. 3. - The method according to claim 2, further characterized in that the devolatilization is carried out under vacuum. 4. The process according to claim 1, further characterized in that the greater part of the ionic impurity is sulfate ions. 5. The process according to claim 1, further characterized in that the greater part of the ionic impurity is chloride ions. 6. The method according to claim 1, further characterized in that the ionic impurity is mainly a combination of sulfate and chloride ions. 7. The method according to claim 1, further characterized in that the amount of aqueous medium added is from about 0.25 to about

2. 0% by weight, based on the weight of the polycarbonate composition. 8. The process according to claim 6, further characterized in that the added aqueous medium is from about 0.75 to about 1.5% by weight. 9. The method of claim 1, further characterized in that the aqueous medium is water. 10. The process according to claim 2, further characterized in that the content of sulfate and chloride ions of the aqueous medium quench bath is each less than 110 ppb. 11. The compliance method cdn claim 2, further characterized in that the content of sulfate and chloride ions of the aqueous medium quenching bath is, each, not greater than 100 ppb. 12. The process according to claim 2, further characterized in that the content of sulfate and chloride ions of the aqueous medium quenching bath is each not greater than 50 ppb. 1

3. The process according to claim 1, further characterized in that the aqueous medium quenching bath is deionized water. 1

4. An aromatic polycarbonate composition having less than about 300 parts per billion, each of a combination of sulfate and chloride ions, said composition prepared by the process of claim 1. 1

5. An aromatic polycarbonate composition having less than about 300 parts per billion sulfate ions, said composition prepared by the process of claim 1. 1

6. An aromatic polycarbonate composition having less than about 300 parts per billion chloride ions, said composition prepared by the process of claim 1.