Method for preparing a polyphenylene ether composition having high melt flow characteristics

Abstract: An improved polyphenylene ether composition is described herein, comprising at least two polyphenylene ether resins, one having an intrinsic viscosity of at least about 0.38 dl/g, and another having an intrinsic viscosity of no greater than about 0.33 dl/g.

Description: This invention relates generally to thermoplastic compositions, and more specifically to polyphenylene ether-based compositions suitable for a wide range of processing techniques. Polyphenylene ether resin (sometimes referred to by the terms "polyphenylene oxide", "PPE", or PPO® resin) has enjoyed wide acceptance in the plastics industry because of its desirable physical and chemical properties, such as high heat resistance and dimensional stability. One area in which PPE compositions have required improvement is melt flow capability, ie., the ability to flow freely at elevated temperatures during various processing stages, such as extrusion and molding. Poor melt flow capability or "processability" can result in the commercial exclusion of materials which otherwise possess an enviable set of properties. As pointed out in the teachings of G. Lee, Jr.'s U.S. Patent 4,154,712, processability can be improved by decreasing the molecular weight of the PPE. However, lower molecular weights sometimes adversely affect other properties, such as impact strength. Impact strength in the Lee, Jr. patent is maintained by the presence of an elastomeric block copolymer of a vinyl aromatic compound and a conjugated diene, along with a plasticizer such as triphenyl phosphate. Even in the relatively short period since the issuance of the Lee, Jr. patent, extrusion and molding methods for thermoplastics have undergone improvements so that processing times could be reduced, and larger parts could be fabricated more efficiently. However, these improvements have required concurrent improvements in the resins themselves, ie, ever-higher levels of melt flow, without substantial sacrifice of any of the other key physical properties of the material, Thus, one can readily discern the need for new thermoplastic compositions which satisfy all of these requirements. SUMMARY OF THE INVENTION The present invention provides a method for preparing a polyphenylene ether composition having high melt flow characteristics and good physical properties, wherein said method comprises: combining as a premix blend (a) a polyphenylene ether resin having an intrinsic viscosity of at least about 0.46 dl/g and (b) a polyphenylene ether resin having an intrinsic viscosity of no greater than about 0.19 dl/g; wherein component (a) constitutes at least about 70% by weight of the total polyphenylene ether resin in the composition; and component (b) constitutes at least 10.85% by weight of the total polyphenylene ether resin in the composition; extruding in an extruder; cooling; and chopping into pellets The use of a blend of two PPE resins as specified above unexpectedly resulted in a level of increased melt flow which was much greater than one would predict from the calculated melt flow for a PPE resin having an intrinsic viscosity (IV) which was the average of that of two such PPE resins. Furthermore, the desirable physical properties, such as heat distortion temperature, tensile strength, and flexural modulus, are substantially maintained. Furthermore, various embodiments of this invention include the presence of other suitable components, such as plasticizers, flame retardants, fillers, and various block copolymer materials, as also described below. DETAILED DESCRIPTION OF THE INVENTION PPE resins are generally well-known and readily available. Many are described in EP-A 0347539 and EP-A-0347828. Both homopolymer and copolymer polyphenylene ethers are within the scope of this invention. The preferred PPE resins are homo- and copolymers of the formula wherein the oxygen ether atom of one unit is connected to the benzene nucleus of the next adjoining unit; n is an integer of at least 50; and each Q is a monovalent substituent such as hydrogen, halogen, hydrocarbon groups, halohydrocarbon groups having at least two carbon atoms between the halogen atom and the phenyl nucleus, hydrocarbonoxy groups, and halohydrocarbonoxy groups having at least two carbon atoms between the halogen atom and the phenyl nucleus. In preferred embodiments, each Q is an alkyl group having from 1-4 carbon atoms, such as methyl, ethyl, propyl. In the most preferred embodiments, at least one of the polyphenylene ether resins is derived from a monomer selected from the group consisting of 2,6-dimethyl phenol; 2,3,6-trimethyl phenol; and mixtures of these monomers. The preparation of PPE resins is well-known in the art and is described, for example, in U.S. Patents 3,306,874; 3,306,875; and 3,432,469 of Allan Hay; and U.S. patents 3,257,357 and 3,257,358 of Gelu Stamatoff, As noted above, one of the PPE resins must have an "intrinsic viscosity" (a measurement well-known in the art, which generally correlates with molecular weight) of at least about 0.46 dl/g, while the other must have an intrinsic viscosity of no greater than about 0.19 dl/g. Methods of preparing PPE resins and controlling the molecular weight thereof are known in the art, as shown, for example, in U.S. Patents 4,252,913 and 4,154,712, issued to Katchman et al and Lee, Jr., respectively. The PPE composition prepared by the method of the present invention may contain other suitable components. In some instances, it is desirable that the composition contain very high levels of PPE resin. For example, when greater heat resistance is required, the composition may comprise at least about 80% by weight PPE resin, based on total composition weight. In still other circumstances, the composition may comprise at least about 85% (or even 90%) by weight PPE resin. Materials which sometimes enhance the impact strength of the compositions are sometimes desirable. They are usually of high molecular weight, and include natural rubbers, synthetic rubbers, and thermoplastic elastomers. They may by homopolymers as well as copolymers, including random, block and graft copolymers derived from various suitable monomers such as butadiene, possibly in combination with a vinyl aromatic compound like styrene. Specific examples of such materials are elastomeric block copolymers and core/shell polymers. The block copolymers are well-known in the art and are described, for example in EP-A-362,660, EP-A-358 993 and EP-A-395 994. Some of the patents mentioned above also contain descriptions of suitable block copolymers. Commercial examples of block copolymers are the Kraton® D and Kraton® materials, available from Shell Chemical Company. The preferred block copolymers useful in the present invention are characterized by an A-B-A 1 structure, wherein terminal blocks A and A 1 are the same or different, and are polymerized vinyl aromatic hydrocarbons, and center block B is a polymerized conjugated diene, the molecular weight of B being higher than the combined molecular weights of A and A 1 . The conjugated diene block can be non-hydrogenated, partially hydrogenated, or entirely hydrogenated. In some especially preferred embodiments, each A and A 1 block of this type of copolymer is styrene, and the B block is ethylene-butylene, often derived from post-hydrogenated butadiene. Core-shell materials are described in U.S. Patents 3,944,631 of Yu et al; 4,681,915 of Bates et al; and 4,684,696 of Bates et al,. Preferred core-shell materials include a cross-linked acrylate rubber core, such as polybutyl acrylate. Surrounding this core is a shell-like structure of cross-linked vinyl aromatic resin, preferably polystyrene, which surrounds and interpenetrates the cross-linked core. The impact modifier is generally present at 1 percent to 10 percent by weight, based on the weight of the entire composition; a specific amount will of course be determined by end use requirements for the composition. The compositions sometimes include at least one polyolefin resin, usually present at 0.1% to 10% by weight, based on the total weight of the composition. Polyolefin resins and methods for their preparation are known in the art and described, for example, in European Patent 0,095,098; in the above-mentioned EP 362 660, and in U.S. patent 4,166,055, Illustrative polyolefin resins are polyethylene, polypropylene, and polyisobutylene, with the preferred homopolymer being polyethylene. Copolymers of polyolefins may also be used, such as copolymers of ethylene with alpha olefins like propylene and 4-methylpentene-1. In preferred embodiments, the polyolefin resin has a melt index of less than about 30 grams/10 minutes, and for some applications, less than about 5 grams/10 minutes. Specific examples of polyolefins in this category are the linear low density polyethylene (LLDPE) copolymers, such as those described in US Patents 4,584,334 and 4,076,698, and in the above-mentioned EP 362 660. Various vinyl aromatic polymers may sometimes also be included in the compositions such as homopolystyrene, polychlorostyrene, polyvinyl toluene, and rubber-modified polystyrene (sometimes referred to as "HIPS"), as well as mixtures of these materials. Mention should also be made of styrene-containing copolymers such as styrene-acrylonitrile copolymers (SAN), styrene-maleic anhydride copolymers, polyalpha-methylstyrene, and copolymers of ethylvinylbenzene and divinylbenzene. The amount of vinyl aromatic polymer present depends upon the particular properties contemplated, and usually ranges from about 5% to about 90% by weight (based on total composition weight), and more preferably, 20% to 60% by weight. Various additives which impart a variety of attributes to these compositions are well-known in the art, as are their effective levels and methods of incorporation. Examples of such additives are flame retardants, plasticizers, stabilizers (eg., oxidative, thermal, and ultraviolet light), fillers, reinforcing agents, lubricants, colorants, dyes, pigments, drip retardants, and other processing aids. Some of these additives are mentioned in the following examples; others are disclosed in many of the references described above. In the method of this invention, the ingredients are combined as a premix blend, and then extruded on a single or twin screw extruder, cooled, and chopped into pellets. The pellets are then molded into articles of a desired shape and size. EXAMPLES Unless otherwise indicated, the PPE resins were each poly(2,6-dimethyl-1,4-phenylene) ether. Intrinsic viscosity (IV) was measured in chloroform at 25°C. The components in each example were dry-blended and compounded, using a 30 mm Werner & Pfleiderer twin-screw extruder. The components are expressed as parts by weight, unless otherwise indicated. The extrudate was quenched and pelletized. The products were then molded on a Toshiba injection molding machine (8 oz. barrel capacity) into various test specimens. EXAMPLE 1 The following compositions were prepared as described above: Sample Number Component 1 2 3 PPE (0.46 IV) 44.9 0 0 PPE (0.40 IV) 0 44.9 38.0 PPE (0.19 IV) 0 0 6.9 HIPS 44.9 44.9 44.9 F.R./Plasticizer 13.0 13.0 13.0 TDP 0.45 0.45 0.45 Polyethylene 1.4 1.4 1.4 ZnS 0.13 0.13 0.13 ZnO 0.13 0.13 0.13 Tests on molded pieces resulted in the following properties: Property Sample Number 1 2 3 Flame Retardance 3.175mm (1/8") 2.4,V0 3.6,V0 3.7,V0 Flame Retardance 1.587mm (1/16") 4.9,V0 4.7,V0 6.0,V1 Heat Distortion Temperature (264 psi) 1.82MPa 178 182 183 Flow Channel (inches)cm (24.5)62.2 (26.4) 67.1 (30.0) 76.2 Izod Impact (notched) (4.5) 240 (2.9) 155 (1.8) 96 Strength (ft.lb/in) J/m Dynatup Impact (230) 253 (120) 13.2 (67) 7.4 Strength (in-lbs) Nm Melt Viscosity (540°F) 282°C 1500 sec -1 1101 960 934 100 sec -1 5099 4405 3714 The flow channel length for sample 3, which contains the mixture of PPE resins, is much higher than the value predicted for a sample having an IV equal to the average IV of the components in sample 3. Furthermore, although there is some decrease in flame retardance and impact values as compared to control samples 1 and 2, the overall physical properties for sample 3 are still acceptable for many end use applications. EXAMPLE 2 The following compositions were prepared as described above. Each component is identical to that used in Example 1, unless otherwise indicated. Sample Number Component 4 5 6 PPE (0.46 IV) 67.3 0 60 PPE (0.40 IV) 0 67.3 0 PPE (0.19 IV) 0 0 7.3 HIPS 22.4 22.4 22.4 F.R./Plasticizer 13.0 13.0 13.0 TDP 0.45 0.45 0.45 Polyethylene 1.4 1.4 1.4 ZnS 0.13 0.13 0.13 ZnO 0.13 0.13 0.13 Tests on molded pieces resulted in the following properties, as measured according to the standards described in Table 1. Property Sample Number 4 5 6 Flame Retardance 3.175mm (1/8") 1.6,V0 1.6,V0 1.9,V0 Flame Retardance 1.587mm (1/16") 2.8,V0 2.4,V0 3.3,V0 Heat Distortion Temperature (264 psi) 1.82 MPa 211 207 209 Flow Channel (inches) cm (13.2) 33.5 (15.7) 39.8 (16.1) 40.9 Izod Impact (Notched) (3.2) 171 (2.5) 133 (2.5) 133 Strength (ft.lb/in) J/m Dynatup Impact (406) 44.7 (125) 13.8 (172) 18.9 Strength (in-lbs) Nm Melt Viscosity (540°F) 282°C x10 -1 Pa.s (Poises) 1500 sec -1 1556 1520 1413 100 sec -1 6148 6221 5221 The flow channel length for sample 6, which contains a mixture of PPE resins according to this invention, is much higher than one would expect for a sample having an IV equal to the average of that of the components in sample 6. The other physical properties for sample 6 were generally comparable to those of control samples 4 and 5, although flame-out times were slightly higher, and impact strength values were somewhat variable. In general, the impact strength of sample 6 can be enhanced by the presence of one of the impact modifiers discussed above. EXAMPLE 3 The following compositions were prepared as described above. Each component is identical to that used in Example 1, unless otherwise indicated. Sample Number Component 7 8 9 PPE (0.46 IV) 67.3 0 52 PPE (0.40 IV) 0 67.3 0 PPE (0.19 IV) 0 0 15.3 HIPS 22.4 22.4 22.4 F.R./Plasticizer 13.0 13.0 13.0 TDP 0.45 0.45 0.45 Polyethylene 1.4 1.4 1.4 ZnS 0.13 0.13 0.13 ZnO 0.13 0.13 0.13 Tests on molded pieces resulted in the following properties: Property Sample Number 7 8 9 Flame Retardance 3.175mm (1/8") 1.9,V0 1.3,V0 1.0,V0 Flame Retardance 1.587mm (1/16") 2.7,V0 3.3,V0 1.9,V0 Heat Distortion Temperature (264 psi) 1.82 MPa 214 215 212 Flow Channel (inches) cm (16.2) 41.1 (21.4) 54.4 (25.5) 64.8 Izod Impact (Notched) (2.9) 155 (2.1) 112 (1.4) 75 Strength (ft.lb/in) J/m Dynatup Impact (162) 17.8 (155) 17.1 (72) 7.9 Strength (in-lbs) Nm Melt Viscosity (540°F) 282°C x10 -1 Pa.s (Poises) 1500 sec 1 NA NA NA 100 sec -1 NA NA NA The flow channel length for sample 9, which contains a mixture of PPE resins according to this invention, is again higher than one would expect by averaging the IV values for the individual PPE components in sample 9 and then extrapolating a melt flow value. The physical properties for sample 9 are generally comparable to those of control samples 7 and 8, although impact values are somewhat decreased. These values can be increased as mentioned in Example 2. EXAMPLE 4 The following compositions were prepared as described above. Each component is identical to that used in Example 1, unless otherwise indicated. Sample Number Component 10 11 12 PPE (0.46 IV) 59.0 0.0 50.0 PPE (0.40 IV) 0 59.0 0 PPE (0.19 IV) 0 0 9.0 HIPS 41.0 41.0 41.0 F.R./Plasticizer 4.5 4.5 4.5 TDP 1.0 1.0 1.0 Polyethylene 1.5 1.5 1.5 ZnS 0.15 0.15 0.15 ZnO 0.15 0.15 0.15 Tests on molded pieces resulted in the following properties: Property Sample Number 10 11 12 Flame Retardance (3.175mm) (1/8") 5.1,V1 4.6,V0 4.2,V0 Flame Retardance 1.587mm (1/16") 10.8,V1 7.3,V1 9.7,V1 Heat Distortion Temperature (264 psi) 1.82MPa 224 235 233 Flow Channel (inches) cm (22.3) 56.6 (23.7) 60.2 (25.0) 63.5 Izod Impact (Notched) Strength (ft.lb/in) J/m (4.3) 229 (2.9) 155 (2.6) 139 Dynatup Impact Strength (in-lbs) Nm (267) 29.4 (304) 33.4 (158) 17.4 Melt Viscosity (540°F) 282°C x10 -1 Pa.s (Poises) 1500 sec -1 1756 1688 1739 100 sec -1 7879 7351 7564 The flow channel length for sample 12, which contains a mixture of PPE resins according to this invention, is again higher than one would predict by averaging the IV values for the individual PPE components in sample 12. The physical properties for sample 12 were somewhat similar to those of control samples 10 and 11, although Dynatup impact values were somewhat lower. These values could be increased by the use of an impact modifier, as described above.

Claims: A method for preparing a polyphenylene ether composition having high melt flow characteristics and good physical properties, wherein said method comprises: combining as a premix blend (a) a polyphenylene ether resin having an intrinsic viscosity of at least about 0.46 dl/g and (b) a polyphenylene ether resin having an intrinsic viscosity of no greater than about 0.19 dl/g; wherein component (a) constitutes at least about 70% by weight of the total polyphenylene ether resin in the composition: and component (b) constitutes at least 10.85% by weight of the total polyphenylene ether resin in the composition; extruding in an extruder; cooling; and chopping into pellets.

Inventors: HAAF WILLIAM ROBERT, LEE GIM FUN JR, SEBOK ERNESTO ESTEBAN TACHAUER, HAAF, WILLIAM ROBERT, LEE, GIM FUN, JR., SEBOK, ERNESTO ESTEBAN TACHAUER
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1990
Main classification: C08L71
IPC codes: C08L53, C08L71, C08L23, C08L25