Autoclave resistant blends of poly(ester-carbonate) and polyetherimide resins

Abstract: Compositions which comprise blends of a poly(ester-carbonate) resin and a polyetherimide or a poly(ether sulfone) resin are provided. The compositions are useful for preparing articles that are resistant to autoclave sterilization conditions.

Description: BACKGROUND OF THE INVENTION Field of The Invention The invention relates to thermoplastic molding compositions and more particularly to autoclave resistant molding compositions which are blends of poly(ester-carbonate) and polyetherimide resins. Brief Description of the Related Art Poly(ester-carbonate) (PEC) resins have been useful as ingredients in the preparation of blends of thermoplastic molding resins. These blends can be attractive to mold particular articles having certain desirable physical properties. For example, U. S. Patent 4,430,484 (Quinn) issued February 7, 1984, describes blends of poly(ester-carbonate) resins with aromatic polyamides, polyimides, polyamideimides and polyetherimides showing improved properties, such as higher heat distortion temperature under load. However, articles molded from some of these blends can exhibit some brittleness and blistering when subjected to autoclave conditions typical for sterilization of medical equipment. In copending application EP-A-0519657, ternary blends of polyetherimides, siloxane polyetherimide copolymers and polycarbonate resins including poly(ester-carbonate) resins are described broadly as thermoplastically moldable to obtain ductile articles with improved flame retardancy and strength properties useful in engineering thermoplastics. In copending and commonly owned U. S. Patent Application Serial No. 965,484, filed October 23, 1992, blends of polyetherimides and siloxane polyetherimide copolymers and polycarbonate resins including poly(ester-carbonate) resins are described broadly as a method for improving the stress crack resistance of articles. In copending application EP-A-0594386, ternary blends of polyetherimides, thermoplastic aromatic polyarylate resins and polycarbonate resins including poly(ester-carbonate) resins are described broadly as thermoplastically moldable to obtain ductile articles. Many of these same blends would be useful for the manufacture of articles, such as surgical trays, for the medical industry except for the stringent and harsh sterilization conditions required for this industry. Useful articles made from these compositions for the medical industry would have to be able to withstand autoclave sterilization at temperatures of at least 270°F for as many as 500 cycles without deforming or blistering while maintaining their physical properties. Additionally, these compositions would have to be sufficiently ductile to avoid cracking and breakage from routine handling, including dropping. Although poly(ester-carbonate) resins have the impact strength needed for these applications, they are unable to withstand the autoclave sterilization procedure. Conversely, polyetherimide resins can withstand the autoclave sterilization procedure but are too brittle to meet the toughness requirement. Thus, there is a long felt need for the development of ductile compositions that are able to withstand repeated autoclave sterilization conditions without distorting or blistering. SUMMARY OF THE INVENTION The present invention provides thermoplastic molding compositions which meet the long felt needs for ductile, autoclave resistant articles, which comprise blends of: (a) a poly(ester-carbonate) resin; and (b) an effective amount of a resin to provide autoclave resistance to at least 500 cycles at 132°C (270°F) and wherein the notched Izod impact resistance of a test specimen of the composition is at least 90 J/m (1.7 ft-lb/in) after the 500 cycles wherein the resin comprising a polyetherimide comprising repeat units of the formula: wherein f is an integer of from 10 to 500; R 2 is para-phenylene and R 1 is the divalent moiety of formula: DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION The poly(ester-carbonate) resins (referred to hereinafter as "PEC") used as ingredient (a) in the blends of the present invention may be prepared by either melt polymerization or by interfacial polymerization. Melt polymerization involves coreacting, for example, diphenyl carbonate with various mixtures of dihydric phenols and ester precursors such as, for example, diphenyl derivatives of iso- and terephthalates, and their mixtures. Various catalysts or mixtures of catalysts such as, for example, lithium hydroxide and lithium stearate can also be used to accelerate the polymerization reactions. In general, the method of interfacial polymerization comprises the reaction of a dihydric phenol with a carbonate precursor in the presence of an ester precursor. Examples of interfacial polymerization techniques can be found in U. S. Patent Nos. 3,169,121 and 4,487,896. Although the reaction conditions of the preparative processes may vary, several of the preferred processes typically involve dissolving or dispersing dihydric phenol reactants in aqueous caustic, combining the resulting mixture with a suitable water immiscible solvent medium and contacting the reactants with the carbonate precursor, such as, for example, phosgene, in the presence of a suitable catalyst and under controlled pH conditions. The most commonly used water immiscible solvents include methylene chloride, 1,2-dichloroethane, chlorobenzene, toluene, and the like. Advantageously a catalyst may be added to the reaction mixture to promote the reaction. The catalyst typically accelerates the rate of polymerization of the dihydric phenol reactants with the carbonate precursors. Representative catalysts include but are not limited to, for example, tertiary amines such as triethylamine, quaternary phosphonium compounds, quaternary ammonium compounds. The preferred process for preparing PEC comprises a phosgenation reaction. The temperature at which the phosgenation reaction proceeds may vary from below 0°C to 100°C. The phosgenation reaction preferably proceeds at temperatures of from about room temperatures (23°C) to 50°C. Since the reaction is exothermic, the rate of phosgene addition may be used to control the reaction temperature. The amount of phosgene required will generally depend upon the amount of the dihydric phenol reactants added. The dihydric phenols employed are known, and the reactive groups are thought to be the phenolic hydroxyl groups. Some of the dihydric phenols are represented by the general formula (XIII): wherein A is a divalent hydrocarbon radical containing from 1 to 15 carbon atoms or a substituted divalent hydrocarbon radical containing from 1 to 15 carbon atoms and substituent groups such as halogen;-S-; -SS-; -S(O)-; -S(O) 2 -; -O-; or -S(O)-; each X is independently selected form the group consisting of hydrogen, halogen, and a monovalent hydrocarbon radical such as an alkyl group of from 1 to 8 carbon atoms, an aryl group of from 6 to 18 carbon atoms, an aralkyl group of from 7 to 14 carbon atoms, and alkaryl group of from 7 to 14 carbon atoms, and alkoxy group of from 1 to 8 carbon atoms; and m is 0 or 1 and n is an integer of from 0 to 5. Typical of some of the dihydric phenols employed are bis-phenols such as (4-hydroxy-phenyl)methane, 2,2-bis(4-hydroxyphenyl)propane (also known as bisphenol-A), 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane; dihydric phenol ethers such as bis(4-hydroxyphenyl)ether, bis(3,5-dichloro-4-hydroxyphenyl)ether; dihydroxydiphenyl such as p,p'-dihydroxydiphenyl, 3,3'-dichloro-4,4'-dihydroxydiphenyl; dihydroxyaryl sulfone such as bis(4-hydroxyphenyl)sulfone, bis(3,5-dimethyl-4-hydroxyphenyl)sulfone, dihydroxy benzenes such as resorcinol, hydroquinone, halo- and alkylsubstituted dihydroxybenzenes such as 1,4-clihydroxy-2,5-dichlorobenzene, 1,4-dihydroxy-3-methylbenzene; and dihydroxydiphenyl sulfides and sulfoxides such as bis(4-hydroxyphenyl)sulfide, bis(4-hydroxy-phenyl)sulfoxide and bis(3,5-dibromo-4-hydroxy-phenyl)sulfoxide. A variety of additional dihydric phenols are available and are disclosed in U. S. Patent Nos. 2,999,835, 3,028,365 and 3,153,008. It is, of course, possible to employ two or more different dihydric phenols or a combination of a dihydric phenol with a glycol. The carbonate precursors are typically a carbonyl halide, a diarylcarbonate, or a bishaloformate. The carbonyl halides include, for example, carbonyl bromide, carbonyl chloride, and mixtures thereof. The bishaloformates include the bishaloformates of dihydric phenols such as bischloroformates of 2,2-bis(4-hydroxy-3,5-dichlorophenyl)-propane, hydroquinone, or bishaloformates of glycol. While all of the above carbonate precursors are useful, carbonyl chloride, also known as phosgene, is preferred. In general, any dicarboxylic acid conventionally used in the preparation of polyesters may be utilized in the preparation of poly(ester-carbonate) resins. However, the PEC used in the present invention are prepared with aromatic dicarboxylic acids, and in particular terephthalic acid, and mixtures thereof with isophthalic acid wherein the weight ratio of terephthalic acid to isophthalic acid is in the range of from 5:95 to 95:5, especially preferred are weight ratios of terephthalic acid to isophthalic acid is in the range of from 40:60 to 60:40. Rather that utilizing the dicarboxylic acid per se, it is possible, and sometimes even preferred, to employ various derivatives of the acid moiety. Illustrative of these reactive derivatives are the acid halides. The preferred acid halides are the acid dichlorides and the acid dibromides. Thus, for example instead of using terephthalic acid or mixtures thereof with isophthalic acid, it is possible to employ terephthaloyl dichloride, and mixtures thereof with isophthaloyl dichloride In the conventional interfacial polymerization methods of preparing PEC, polycarbonates and polyarylates, a molecular weight regulator (a chain stopper) is generally added to the reaction mixture prior to or during the polymerization reactions with carbonate and/or ester precursors. Useful molecular weight regulators include, for example, monohydric phenols such as phenol, chroman-I, para-t-butylphenol, p-cumylphenol. The preferred PEC for use as the ingredient (a) in the blends of the present invention are those derived from reaction of bisphenol-A and phosgene with iso- and terephthaloyl chloride and having an intrinsic viscosity of 0.5 to 0.65 deciliters per gram (measured in methylene chloride at a temperature of 25°C). Additional embodiments of the invention include thermoplastic molding compositions containing polycarbonate homopolymers. Polycarbonate homopolymer resins and their method of preparation by interfacial polymerization are provided in U. S. Patent Nos. 3,028,365, 3,334,154, 3,275,601, 3,915,926, 3,303,331, 3,169,121, 3,027,814 and 4,188,314. In general, the method is as described above for preparing PEC, but in the absence of an ester precursor. Also included within the blends of the present invention is the presence of randomly branched polycarbonates, randomly branched PEC, randomly branched poly(aryl ether)s and/or randomly branched polyarylates. These randomly branched materials are sometimes useful for altering the rheological characteristics of the blends containing the linear polymers for fabrication techniques such as pressure forming or blow molding and can be used as partial or full replacements for the linear materials. The randomly branched polymers are prepared by co-reacting a polyfunctional organic compound with the afore-described dihydric phenols, carbonate and/or ester precursors. The polyfunctional organic compounds useful in making the branched polycarbonates are set forth in U. S. Patent Nos. 3,544,514, 3,635,895 and 4,001,184. The polyfunctional compounds are generally aromatic and contain at least three functional groups which are carboxyl, carboxylic anhydrides, phenols, haloformyls or mixtures thereof. Some nonlimiting examples of these polyfunctional aromatic compounds include 1,1,1-tri(4-hydroxyphenyl)ethane, 1,3,5,-trihydroxybenzene, trimellitic anhydride, trimellitic acid, trimellityl trichloride, 4-chloroformyl phthalic anhydride, pyromellitic acid, pyromellitic dianhydride, mellitic acid, mellitic anhydride, trimesic acid, benzophenonetetracarboxylic acid, benzophenone-tetracarboxylic dianhydride. The preferred polyfunctional aromatic compounds are 1,1,1-tri(4-hydroxyphenyl)ethane, trimellitic anhydride or trimellitic acid or their haloformyl derivatives. The polyetherimide resins (referred to hereinafter as PEI) comprising ingredient (b) in the blends of the present invention are also known compounds whose preparation and properties are described in U. S. Patent Nos. 3,803,085 and 3,905,942. The PEI according to claim 1 used for preparing the blends of this invention can be prepared by any of the methods well known to those skilled in the art. The PEI is generally present in an amount up to 50% by weight of the composition, preferably between 5-30% by weight of the composition and especially preferred between 10-25% by weight of the composition. The blend compositions of the present invention may be modified by the addition of other additives conventionally used in the art of plastics compounding. Such additives can include fillers (such as, for example, clay, mica or talc), supplementary delustrants, reinforcing agents (such as, for example, glass fibers), impact modifiers (such as, for example, epoxy modified polyolefins), plasticizers, flow promoters and other processing aids, stabilizers, colorants, pigments, mold release agents, ultraviolet screening agents, drip inhibitors (such as, for example, polytetrafluoroethylene (PTFE)), supplementary or synergistic flame retardant. The preparation of the compositions of the present invention is normally achieved by merely blending the ingredients under conditions for the formation of an intimate blend. Such conditions often include mixing in single or twin screw type extruders or similar mixing devices which can apply a shear to the components. It is often advantageous to apply a vacuum to the melt through at least one vent port in the extruder to remove volatile impurities in the composition. Intrinsic Viscosity (I.V.) The intrinsic viscositv was measured at a temperature of 25°C in methylene chloride and is reported in deciliters/gram (dl/g). Molecular Weight (Mw) The weight average molecular weight (Mw) is determined by gel permeation chromatography (GPC) in methylene chloride relative to polycarbonate standards using a UV detector at 254 nm. Autoclave Conditions Test specimens were subjected to autoclave conditioning to simulate medical sterilization conditions. An American Sterilizer Autoclave (AMSCO) Series 2023 Vac-A-Matic was used for the rapid autoclave cycle testing. A single autoclave cycle consists of the following steps: 1. A pre-vacuum step to heat and condition the parts. The pre-vacuum step consists of alternating pulses of steam followed by evacuation, each pulse lasting for approximately 15 seconds. The pulse cycle is repeated approximately 5 times to condition the parts. 2. A sterilization step consisting of 5 minutes of steam at about 270°F The 270°F is an important temperature distinction for this cycle as it is higher than that for a traditional gravity displacement cycle of about 250°F. 3. The third step is a drying step which consists of evacuating the chamber for approximately 4 minutes utilizing a vacuum drawdown of approximately 30 in. of Hg. After the vacuum drying, there is a 1 minute delay followed by returning to Step 1. After subjecting the test specimens to 500 autoclave cycles consisting of steps 1-3, a visual observance of the test specimens for cracks and blisters was performed followed by testing the notched Izod impact resistance of the specimens according to ASTM D-256. Samples failing the test typically form blisters and/or cracks which negatively affects the notched Izod impact performance. Test specimens having a notched Izod impact value of less than about 90 J/m (1.7 ft-lbs/in) are too brittle to be acceptable and these compositions are defined as failing the autoclave test It should also be clear that autoclave resistant articles prepared from the compositions of the present invention represent an additional embodiment of this invention. The following examples are provided to illustrate some embodiments of the present invention. All percentages are by weight based on the total weight of the entire composition, unless otherwise indicated. Preparation 1 This preparation is of a poly(ester-carbonate) (PEC) resin. To a 38 liter reactor vessel there are added 8 liters of methylene chloride, 6 liters of water, 1,906 grams (8.36 moles) of bisphenol A, 20 milliliters of triethylamine, 4 grams of sodium gluconate, and 65 grams of p-tertiary butylphenol molecular weight regulator. At a pH of between about 9-10.5, 2544 grams (12.54 moles) of a mixture of 50% by weight of isophthaloyl dichloride and 50% by weight of terephthaloyl dichloride in 4 liters of methylene chloride are added over about a 20 minute interval while controlling the pH at about 9-10.5 with 35 weight percent aqueous caustic. After the addition of the diacid chloride mixture, phosgene is added at a rate of about 36 grams per minutes for about 20 minutes while controlling the pH at about 10-11 with 35 weight percent aqueous caustic. The polymer mixture is diluted with about 5 liters of methylene chloride and the brine phase is separated by centrifuge. The resulting polymer phase is washed with aqueous acid and water and is then recovered by high pressure steam precipitation to yield a white powder having an Intrinsic Viscosity of 0.5 dl/g in methylene chloride at 25°C. Optionally, to this resin powder is added a minor amount (about 0.1 parts by weight per hundred parts by weight of resin) of a stabilizer mixture containing a phosphite color stabilizer and an epoxy stabilizer. This resin product is then fed to an extruder operating at temperature of about 316°C to extrude the resin into strands and the extruded strands are chopped into pellets. Preparation 2. This preparation is of "PEI-1", a polyetherimide utilizing m-phenylene diamine. A mixture of bisphenol A dianhydride (BPA-DA) and m-phenylene diamine (mPD) in o-dichlorobenzene was prepared by first dissolving 5.0225 g (9.650 millimoles) of BPA-DA and 1.0814 g (10.00 millimoles) mPD in about 50 mL of o-dichlorobenzene at about 150°C for approximately 1 hour, and thereafter adding 0.1037 g (0.70 millimoles) phthalic anhydride (PA). The solution was slowly warmed to about 180°C. and refluxed under nitrogen for 3 hours at this temperature to produce a prepolymer. A 0.10 g sample was then removed to a small test tube and heated at about 350°C. for about 15 minutes under nitrogen to substantially finish the conversion to PEI. The resulting polymer was dissolved in dichloromethane and its molecular weight was determined, by gel permeation chromatography (GPC) against a polystyrene standard, to be 24,700 M N (typical of the desired polyetherimides). Preparation 3. This preparation is of "PEI-2", a polyetherimide utilizing p-phenylene diamine. The procedure as outlined in Preparation 2 was followed with the substitution of p-phenylene diamine (pPD) for the m-phenylene diamine (mPD). The desired polyetherimide was obtained. Examples In a series of runs, PEC prepared according to Preparation 1 was blended with 0.1 percent by weight of the blend of an antioxidant (Irgafos® 168; Ciba-Geigy Corp.), 2.0 percent by weight of titanium dioxide (TiO 2 ), and various proportions of a PEI as prepared according to Preparations 2 (PEI-1) and 3 (PEI-2). The blends were fed to an extruder at a temperature of about 340°C. to intimately mix the components and extruded into strands. The strands were chopped into pellets and injection molded under standard conditions into test samples for physical property testing. The composition of each blend and the notched Izod test results after completion of the previously described autoclave test are set forth in the Tables below. sample PEC PEI TiO 2 NI 1 98 0 2 dissolves 2 75 25 (PEI-1) 2 1.6 3 75 25 (PEI-2) 2 2.4 4 75 (PC*) 25 (PEI-2) 2 1.3 NI is notched Izod measured after 500 autoclave cycles; PC* is a polycarbonate, the phosgenation product of bisphenol-A (Lexan® 131; General Electric Co., Mount Vernon, Indiana). The data in Table 1 clearly illustrate the improved autoclave resistance of the compositions of the present invention. Sample 2, utilizing a PEI in which the diamine is m-phenylene diamine (PEI-1), fails the autoclave test A comparative sample, Sample 3, utilizing a PEI in which the diamine is p-phenylene diamine (PEI-2) surprisingly passes the autoclave test Comparative sample 4 utilizes the PEI-2 but contains a polycarbonate homopolymer of bis-phenol A and phosgene in place of the polyester carbonate. Comparison of this sample to sample 3 illustrates the utility of PEC resin in the compositions of the present invention. The samples in Table 2 were prepared as generally described for the samples in Table 1. sample PEC PEI-2 TiO 2 NI 5 75 25 2 2.4 6 85 15 2 2.5 7 90 10 2 1.8 8 95 5 2 0.4 9 98 2 2 0.4 10 99 1 2 0.6 NI is notched Izod measured after 500 autoclave cycles. The data in Table 2 illustrates the surprising effectiveness of the PEI-2 in the poly(ester-carbonate) (PEC) resins even at very low levels. At levels as low as 10 parts, significant improvement in autoclave resistance is realized. The samples in Table 3 were prepared as generally described for the samples in Table 1. sample PEC PEI-2 TiO 2 NI 11 84.5 15 0.5 2.9 12 84 15 1.0 2.3 13 83.5 15 1.5 2.2 14 80 15 5 0.3 NI is notched Izod measured after 500 autoclave cycles. The data in Table 3 illustrate that a fairly wide range of TiO 2 can be utilized in the compositions of the present invention while retaining acceptable impact strength. It is contemplated that other pigments, colorants and additives could also be utilized with similar positive results.

Claims: A resin composition comprising: (a) a poly(ester-carbonate) resin, and (b) an effective amount of a resin to provide autoclave resistance to at least 500 cycles at 132°C (270°F) and wherein the notched Izod impact resistance of a test specimen of the composition is at least 90 J/m (1.7 ft-lb/in) after the 500 cycles wherein the resin comprises a polyetherimide comprising repeat chain units of the formula: wherein f is an integer of from 10 to 500; R 2 is para-phenylene and R 1 is the divalent moiety of formula: The composition of any claim 1 wherein the notched Izod impact resistance of a test specimen made from the composition is at least 107 J/m (2 fl-lb/in) after 500 autoclave cycles at 132°C (270°F). The composition of claim 1 or claim 2 further comprising a polycarbonate resin. The composition of any preceding claim further comprising at least one member of the group consisting of fillers, supplementary delustrants, reinforcing agents, impact modifiers, plasticizers, flow promoters, processing aids, stabilizers, colorants, pigments, mold release agents, ultraviolet screening agents, drip inhibitors and flame retardants. A method to provide an autoclave resistant composition comprising the step of admixing a poly(ester-carbonate) resin, and an effective amount of a polyetherimide to provide autoclave resistance to at least 500 cycles at 132°C (270°F) and wherein a test specimen of the autoclove resistant composition has a notched Izod impact strength of at least 90 J/m (1.7 ft-lbs/in) after the 500 cycles, wherein the polyetherimide comprises repeating chain units of the formula: wherein f is an integer of from 10 to 500: R 2 is paraphenylene and R 1 is:

Inventors: COOPER STEPHEN MICHAEL, GREENBERG RONALD ALAN, NAZARETH DARRYL, COOPER, STEPHEN MICHAEL, GREENBERG, RONALD ALAN, NAZARETH, DARRYL
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1995
Main classification: C08L69
IPC codes: C08L79, C08L69, C08L67, C08L81