Improved thermoplastic process

Abstract: The present invention relates to a method for processing a thermoplastic polymer which is melt incompatible with polybutylene comprising adding a high melt index polybutylene to the thermoplastic prior to processing.

Description: The present invention relates to a means for extruding a thermoplastic polymer. More particularly, this invention relates to increasing polymer processing rates, by incorporating a high melt index polybutylene into melt incompatible thermoplastic polymers especially polyethylene. It is well known that some thermoplastics, including thermoplastic elastomers, have excellent properties, but lack good melt processability. Even among readily processable polymers, high toughness and good melt strength are attributes of higher molecular weight grades, and as a result, melt processing machine outputs tend to be inversely related to the toughness required for, e.g. durable goods, and melt strength needed for, e.g. film, thermoforming, blow molding, and injection molding. With the addition of a high melt index polybutylene, polymers which are otherwise difficult to melt process may be processed more easily. Thus, desirable performance properties may be largely retained with little or no sacrifice to melt processability. Therefore, these polymers may be efficiently melt processed while the desirable performance properties of the final product are retained. Blends of polypropylene and polybutylene have been described, e.g. see U.S. 3,900,534. US-A-4,675,982 discloses extruding blends of polyethylene, and two polybutenes having different molecular weights, in specified proportions. These blends are extruded to form films which are said to exhibit better stretch-cling properties than blends made from a single polybutene. EP-A-0343943 is directed at specific combinations of polymers of but-1-ene and propylene which give rise, on moulding, to shaped articles and film having improved properties, especially stretch properties. However the incorporation of high melt index polybutylene polymers to improve extrusion efficiency has not been disclosed. The present invention provides the use of a high melt index (or low molecular weight) polybutylene, said polybutylene being used in an amount from 0.2 to 20% by weight of the mixture of polybutylene and thermoplastic polymer for improving the extrusion efficiency of a thermoplastic polymer other than polypropylene which is substantially melt incompatible with polybutylene. This use involves less power and significantly increases polymer throughput without significantly diminishing the properties of the parent polymer. The high melt index polybutylene appears to lubricate the polymer melt and, because it is incompatible with the thermoplastic, continues to operate at the surface of the blend. This procedure may be used to more efficiently recycle waste thermoplastic polymers by allowing a wide diversity of polymer grades to be melt processed with less concern for their melt processability. The amount of polybutylene added is from 0.2% to 20%, preferably from 1% to 10%, and most preferably 2% to 7% by weight of the resulting mixture and is preferably dry blended with the polymer in powder form, prior to extrusion. The high melt index polybutylene referred to herein is at least one butene-1 polymer generally containing from 90%, preferably from 95%, and more preferably from 97%, by weight of isotactic portions. For example, isotactic poly-1-butenes having a low molecular weight, e.g. less than about 280,000 as determined by solution viscosity in "Decalin" (decahydronaphthalene) may be used. Suitable poly-1-butenes have a density of from 0.900 to 0.925, preferably from 0.905 to 0.920 and most preferably from 0.910 to 0.915. The poly-1-butenes used have melt indices in the range of from 10 to 1000, more preferably from 20 to 650, and most preferably from 100 to 500, as determined by ASTM D-1238 Condition E, at 190°C. The intrinsic viscosity of the polybutylene generally ranges from 0.03 to 0.20, preferably from 0.06 to 0.11 at 130°C. A butene-1 polymer (PB) usable herein is either a butene-1 homopolymer or a copolymer or a terpolymer. If a butene-1 copolymer is used, the non-butene comonomer content is preferably from 1 to 30 mole % of either ethylene, propylene, or an alpha olefin having from 5 to 8 carbon atoms. The poly-1-butenes can be modified to increase surface activity by reaction with, for example, maleic anhydride. Suitable poly-1-butenes can be obtained, for example, in accordance with Ziegler-Natta low-pressure polymerization of butene-1, e.g. by polymerizing butene-1 with catalysts of TiCl₃ or TiCl₃.AlCl₃ and Al(C₂H₅)₂Cl at temperatures of 10-50°C, preferably 20-40°C, e.g. according to the process described in DE-A-1,570,353. High melt indices are obtainable by further processing the polymer by peroxide cracking, thermal treatment or irradiation to induce scissons leading to a higher melt flow material. Duraflex® DP0800, a developmental polybutylene polymer produced by Shell Chemical Company, of Houston, Texas is a particularly suitable polymer. This novel polymer is a homopolymer with a melt index of 200 g/10 min. at 190°C and 490 g/10 min. at 210°C and a molecular weight of 108,000. Duraflex® PB0400, a commercial polybutylene polymer produced by Shell Chemical Company, is another suitable polymer. The polymer is a homopolymer with a melt index of 20 g/10 min. at 190°C and a molecular weight to 202,000. The thermoplastics suitable for use in the present invention are any thermoplastics which are incompatible in the melt with polybutylene. Melt incompatible thermoplastic polymers which can be processed using the present method include a broad range of melt incompatible thermoplastics and thermoplastic elastomers. These thermoplastics include but are not limited to low melt index polyethylene including high density polyethylene, low density polyethylene, linear low density polyethylene and other polyethylene copolymers. Other thermoplastics include polyamides (nylons), polyesters, polycarbonates, poly-4-methyl pentene, polyimides, polysulfones, polyketones, polyphenylene oxide, ethylene vinyl alcohol, polyvinyl chloride, polyacetals, polystyrene, and similar polymers and copolymers. Melt incompatible thermoplastic elastomers include styrenic block copolymers, polyesters, polyolefins, and polyurethanes. Uncured thermosetting materials may be used in the present invention and many include epoxides, crosslinkable polyesters, thermoset polyurethanes, cyanoacrylates, phenolics, urea formaldehydes, and silicones. Thermoplastic polymers usable herein can be either homopolymers or copolymers. If copolymers are used, they can be random or block copolymers. For example, a suitable thermoplastic polymer is a polyolefin homopolymer or a polyolefin copolymer comprising from 1 to 30 mole% of an alpha-olefin having from 2 to 8 carbon atoms. Suitable thermoplastic polymers preferably have a melt index of less than 60, preferably less than 20, more preferably less than 15, and most preferably less than 10, as measured by ASTM D-1238, Condition L at 230°C. A preferred method uses 5% by weight of a high melt index butene-1 homopolymer having a melt index equal to or greater than 20, and 95% by weight of a thermoplastic, e.g. a linear low density polyethylene. Blending of the components can occur by, for example, dry tumble blending, masterbatch, or melt compounding techniques. The method of combining the ingredients of the formulation is important. For example, in most cases, it is desirable to use the least amount of energy to merge the components into an effective blend. Therefore the preferred method of blending is dry blending the components in a powder form. This mixture may, of course, be shaped in an additional step. EXAMPLES Blends were prepared with GRSN-7047 linear low density polyethylene (LLDPE) with a 1.0 melt index available from Union Carbide Corporation, Duraflex® DP0800, polybutylene and Duraflex® PB0400 polybutylene, available from Shell Chemical Company, Houston, Texas. The components were dry blended before extruding. The typical physical properties of the high index polybutylene (DP0800) are listed below. Typical Physical Properties of DP0800 Polybutylene ASTM Polybutylene DP0800 Units Test Method Metric English Melt Index @ 190°C D1238 "E" 200g/10min - @ 230°C D1238 "L" 490g/10min - Density D1505 0.915g/cm³ 57.1 lb/ft Tensile strength @ yield D638 13.8 MPa 2000 psi Tensile strength @ break D638 29.0 MPa 4200 psi Elongation at break D638 350% - Modulus of elasticity D638 241 MPa 35000 psi Hardness, Shore D2240 55 D Scale - Brittleness temperature D746 -18°C 0°F Melting point range DSC 124-126°C 225-259°F Soft point, Vicat D1525 116°C 241°F Thermal conductivity at 25°C (77°F) C177 16Kcal/m²/hr/°C/cm 1.25Btu/ft²/hr/°F/in In Tables II to V the blends were extruded using a 3.18 cm (1¼") Brabender extruder with temperatures at Zone 1 of 190°C and at Zones 2-5 of 215°C and a L/D of 24:1. In Table VI the blends and control were extruded using a 1.91 cm (3/4 inch) Brabender extruder with temperatures at Zones 1-4, 175°C and 234°C at the die. The L/D was 25:1. The results are recorded in Tables II to V below. It can be seen from the data that significant improvements in throughput and power required are achieved using the claimed process. Polybutylene with a melt index as low as 20 g/10 min. and concentrations as low as 1.0w% showed improvements in processability. 30 RPM Extrusion Conditions for LLDPE + DP0800 BACK PRESSURE CURRENT THROUGHPUT MPa (psi) AMP kg/hr (lbs/hr) Control 7.929 (1150) 6.75 3.60 (7.93) 2.5w% PB 6.72 (975) 5.25 3.03 (6.68) 5.0W% PB 6.55 (950) 5.0 3.0 (6.7) 60 RPM Extrusion Conditions for LLDPE + DP0800 BACK PRESSURE CURRENT THROUGHPUT MPa (psi) AMP kg/hr (lbs/hr) Control 10.51 (1525) 8.5 7.158 (15.78) 1.0w% PB 9.480 (1375) 7.25 6.319 (13.93) 2.5w% PB 8.791 (1275) 6.75 5.620 (12.39) 5.0w% PB 7.929 (1150) 6.25 5.529 (12.19) 90 RPM Extrusion Conditions for LLDPE + DP0800 BACK PRESSURE CURRENT THROUGHPUT MPa (psi) (amps) kg/hr(lbs/hr) Control 11.79 (1710) 7.5 11.1 (24.4) 2.5w% PB 9.825 (1425) 6.25 8.550 (18.85) 5.0w% PB 9.136 (1325) 6.25 8.110 (17.88) 60 RPM Extrusion Conditions for LLDPE + PB0400 BACK PRESSURE CURRENT THROUGHPUT MPa (psi) (amps) kg/hr(lbs/hr) Control 10.51 (1525) 8.5 7.158 (15.78) 2.5w% 9.584 (1390) 7.5 6.146 (13.55) control = 100% LLDPE In Table VI the back pressure was raised by increasing the RPM for the blends containing PB to levels approaching the control back pressure. Polymer throughput was significantly increased as can be seen in the last two runs containing PB with extruder speed at 175 and 174 RPM. Although the invention has been described with preferred embodiments it is to be understood that modifications and variations may be made without departing from the spirit and scope of this invention as claimed.

Claims: Use of polybutylene in improving the extrusion efficiency of a thermoplastic polymer other than polypropylene which is substantially melt incompatible with polybutylene, said polybutylene being used in an amount from 0.2% to 20% by weight of the mixture of polybutylene and the thermoplastic polymer, and having a melt index of from 10 to 1000, as determined by ASTM D-1238 Condition E, at 190°C. Use according to claim 1 wherein the thermoplastic polymer is a polyolefin homopolymer or a polyolefin copolymer comprising from 1 to 30 mole% of an alpha-olefin having from 2 to 8 carbon atoms. Use according to claim 1 wherein the thermoplastic polymer is a low melt index polyethylene homopolymer or copolymer. Use according to any one of the preceding claims wherein the thermoplastic polymer is high density polyethylene, low density polyethylene or linear low density polyethylene. Use according to any one of the preceding claims wherein the thermoplastis polymer is a thermoplastic elastomer. Use according to claim 1 wherein the thermoplastic polymer is an uncured thermosetting polymer. Use according to any one of the preceding claims wherein the thermoplastic polymer has a melt index of less than 20, as measured by ASTM D-1238, Condition L at 230°C. Use according to claim 7 wherein the thermoplastic polymer has a melt index of less than 10. Use according to any one of claims 1 to 8 wherein the polybutylene has a melt index of from 20 to 650. Use according to claim 9 wherein the polybutylene has a melt index of from 100 to 500. Use according to any one of the preceding claims wherein the polybutylene is used in an amount from 1% to 10% ny weight of the mixture. Use according to claim 11 wherein the amount of polybutylene is from 2% to 7% by weight of the mixture. Use according to any one of the preceding claims wherein the polybutylene is a butene-1 homopolymer or a butene-1 copolymer comprising from 1 to 30 mole% of an alpha-olefin having from 2 to 8 carbon atoms. Use according to any one of the preceding claims wherein the mixture is shaped in an additional step.

Inventors: HWO CHARLES C, MCCULLOUGH JAMES D DR, HWO, CHARLES C., MCCULLOUGH, JAMES D., DR.
Applicants: SHELL OIL CO, SHELL OIL COMPANY
Application year: 1991
Main classification: C08L23
IPC codes: C08L23, B29K23, C08L101, B29C47