Patent Application
20080021156
The method of the invention involves a step of blending in an extruder thermoplastic polymer material comprising or consisting essentially of an olefin resin and a barrier resin selected from polyvinyl alcohol, copolymers of ethylene-vinyl alcohol, polyamides, and mixtures of these, wherein the temperature of the thermoplastic polymer material in the extruder is controlled to be not higher than at or about 10° C. above the melting point of the barrier resin.
Preferred polyolefin resins are selected from high-density polyethylene (HDPE), low density polyethylene (LDPE) and polypropylene (PP), and mixtures of these. The method of the invention is particularly suited to HDPE.
The barrier resin is selected from polyvinyl alcohol, copolymers of ethylene-vinyl alcohol, polyamides, and mixtures of these. Preferred barrier resins are ethylene vinyl alcohol copolymers (EVOH), particularly with at or about 20 to 40 mol % of repeat units derived from ethylene, and at or about 60 to 80 mol % of repeat units derived from vinyl alcohol, more preferably at or about 24 to 36 mol % of repeat units derived from ethylene, and at or about 64 to 76 mol % of repeat units derived from vinyl alcohol. Also contemplated are mixtures of such polymers and copolymers.
The barrier resin may additionally comprise an optional compatibilizer at up to about 75 wt % or preferably at or about 10 to 75 wt %, or more preferably at or about 15 to 50 wt %, or yet more preferably at or about 20 to 45 wt %, or even more preferably at or about 25 to 40 wt %, based on the weight of polymers in the barrier resin. Examples of compatibilizer include maleic anhydride grafted HDPE, or maleic anhydride grafted ethylene propylene diene (EPDM). The grafting agent is preferably used at about 0.3 to 2 weight percent relative to the weight of grafted polymer.
Also preferred as barrier resin is PA6, PA6,66, and mixtures of these. Also preferred are PA6 and/or PA6,66 in combination with PVOH, particularly PA6,66 in combination with PVOH, wherein the weight percent of PVOH is at or about 20 to 50 wt %, more preferably at or about 30 to 45 wt %, particularly preferably at or about 35 to 45 wt %, and wherein the weight percentage of PA6,66 is at or about 5 to 65 wt %, preferably at or about 10 to 50 wt %, more preferably at or about 15 to 40 wt %, wherein these weight percentages are based on the total weight of polymers in the barrier resin.
Also preferred as high thermal stability barrier resins are blends of one or more polyamides having a melting point of about 180 to about 230° C., or preferably about 190 to about 220° C. with EVOH, wherein the weight percent of EVOH is at or about 20 to 60 wt %, more preferably at or about 30 to 50 wt %, particularly preferably at or about 35 to 50 wt %, and wherein the weight percentage of the polyamides is at or about 5 to 40 wt %, preferably at or about 10 to 40 wt %, more preferably at or about 15 to 35 wt %, wherein these weight percentages are based on the total weight of polymers in the barrier resin. The ethylene vinyl alcohol copolymers (EVOH) preferably contain about 20 to 40 mol % of repeat units derived from ethylene, and at or about 60 to 80 mol % of repeat units derived from vinyl alcohol, or more preferably at or about 20 to 30 mol % of repeat units derived from ethylene, and at or about 70 to 80 mol % of repeat units derived from vinyl alcohol. A preferred polyamide is polyamide 10,10. These barrier resins are particularly useful in preparing blow-molded articles using accumulator head blow-molded machines.
The barrier resin (particularly a vinyl alcohol containing polymer or copolymer), including any compatibilizers, is preferably present at or about 2 to 30 wt %, more preferably at or about 3 to 15 wt %, particularly preferably at or about 5 to 10 wt %, or 7 to 9 wt % based on the total weight of the barrier resin and polyolefin resin in the blend of the invention.
The polyolefin is preferably present in the composition at or about 55 to 97 wt %, more preferably at or about 85 to 96 wt %, particularly preferably at or about 83 to 94 wt %, based on the total weight of polymers in the blend of the invention.
In the method according to the invention, the temperature of the melt throughout the extruder is controlled to be not higher than at or about 10° C. above the melting point of the barrier resin. As used herein, the term “the melting point of the barrier resin” refers to the highest melting point if the barrier resin exhibits two or more melting points. While not wishing to be limited by theory, the inventors believe that such a temperature profile results in just barely melting the barrier resin, allowing a laminar structure to be formed with the olefin resin. The melting point of the barrier resin may be determined according to ISO 11357-3:1999(E). The temperature of the melt should not be lower than the melting point of the barrier resin.
Particularly preferred are the following barrier resins: A barrier resin consisting of an ethylene-vinyl alcohol copolymer (EVOH), with at or about 26 mol % of repeat units derived from ethylene and at or about 74 mol % derived from vinyl alcohol, and the following compatibilizers: maleic anhydride grafted HDPE, or maleic anhydride grafted ethylene propylene diene (EPDM). This barrier resin has a melting point of approximately 195° C.
A barrier consisting of polyvinyl alcohol (PVOH) (47.75 wt %) mixed with copolymer PA6,66 (18.6 wt %) and the following compatibilizers: maleic anhydride grafted HDPE, or maleic anhydride grafted ethylene propylene diene (EPDM). This barrier resin has a melting point of approximately 225° C.
Particularly preferred is a barrier resin showing high thermal stability comprising an ethylene-vinyl alcohol copolymer (EVOH) in which at or about 26 mol % of repeat units are derived from ethylene and at or about 74 mol % of repeat units are derived from vinyl alcohol mixed with polyamide 1010, and at least one maleic-anhydride grafted HDPE or maleic-anhydride grafted EPDM compatibilizer. This barrier resin has a melting point of approximately 195° C.
The thermoplastic polymer blends made using the method of the invention can be injection- or blow-molded, or extruded. A preferred use for thermoplastic polymer blends made using the method of the invention is blow-molded articles, for example, bottles, canisters, reservoirs or tanks. In a particularly preferred embodiment, the thermoplastic polymer blend made with the method of the invention is used to make fuel or solvent reservoirs, such as a heating oil tank, an automotive fuel tank, an antifreeze reservoir, a motorcycle fuel tank, and a jerrycan.
In another preferred embodiment, the thermoplastic polymer blend may be extruded, particularly for making hollow articles, such as pipes.
Thermoplastic polymer blends compounded by the method of the invention and molded, particularly blow-molded, or extruded, particularly into hollow articles, have a laminar structure that can be observed under an optical microscope. Using the method of the invention, thermoplastic polymer blends are produced wherein the laminar structure has an aspect ratio of greater than at or about 10, preferably between at or about 10 to 10,000, more preferably greater than at or about 20, particularly preferably greater than at or about 35, even more particularly preferably greater than at or about 50. The aspect ratio can be measured using microtoming procedure, followed by image analysis. In particular, the molded resin is sliced laterally across the direction of elongation during molded (e.g. a cross-section of the wall of a blow-molded article) into slices of 10 to 20 micrometer thickness. The slices may be stained with iodine to increase contrast, and they are then examined at a suitable magnification (e.g. 50 to 100×), and the aspect ratio determined by calculation from the lamellae thickness assuming that the initial volume of the pellet remains constant. A schematic of microtomes of polymer blends is shown in
Articles made from the thermoplastic polymer blends of the invention have enhanced barrier properties as compared with articles made with conventional thermoplastic polymer blends. The barrier properties extend to hydrocarbons, particularly straight-chain and branched hydrocarbons (e.g. C1-C18, particularly C5-C12), m- p- and o-xylene, ethanol, benzene, ethylbenzene, toluene, ethyl-benzene, methanol, and methyl-t-butyl ether (MTBE). Also included are halogenated hydrocarbons and oxygen containing hydrocarbons, such as alcohols, CE10 type fuel and mixtures of all of these. Barrier properties may be measured by determining permeability to various solvents, for example, according to ASTM D2684. When measured according to this standard, molded and extruded articles (particularly blow-molded articles) preferably have permeabilities to hydrocarbons or C-fuel type containing alcohol of less than at or about 0.0787 g·mm/day·100 cm2 when measured after 3, 4, 5 or 6 weeks soaking, at a steady-state of mass transfer of hydrocarbon, or more preferably of less than at or about 0.07 g·mm/day·100 cm2, yet more preferably of less than at or about 0.06 g·mm/day·100 cm2, or still more preferably of less than at or about 0.04 g·mm/day·100 cm2, or particularly preferably of less than at or about 0.02 g·mm/day·100 cm2.
A schematic of an extrusion blow-molded machine is shown in
Alternatively, the temperature of the thermoplastic polymer material at the rear of the extruder may be maintained at or about 5-20° C. below, preferably 5-15° C. below, the melting point of the barrier resin. The temperature of the thermoplastic polymer material is then gradually raised as it passes through the extruder, until it is at or about 0-10° C. above the melting point of the barrier resin at the die.
The expression “rear” means at or about the first 30-40 cm after entry of polymer material into the barrel of the extruder. Similarly, the expression “front” means at or about the last 30-40 cm of the barrel, before entry of the polymer into the die.
Thermoplastic polymer blends were made comprising HDPE as olefin resin with a barrier resin was incorporated at 7 wt %. The barrier resin was a copolymer of ethylene and vinyl alcohol, with 26 mol % of repeat units derived from ethylene and about 74 mol % of repeat units derived from vinyl alcohol, and a melt flow rate measured at 210° C. under 2160 g of 3.2 g/10 minutes. The resin includes maleic anhydride grafted HDPE, or maleic anhydride grafted ethylene propylene diene (EPDM). The melting point of the barrier resin was 195° C.
The dry resins were mixed as granules in the hopper of an extruder, and then passed through the extruder with the temperature profiles shown in
For run 20, which is shown for comparative purposes, thermoplastic polymer blend at the rear of the extruder was heated to 15° C. above the melting point of the barrier resin. It was then allowed to cool to approximately the melting point of the barrier resin while passing through the extruder.
Runs 9, 15 and 16, are according to the method of the invention.
For run 9, the temperature at the rear of the extruder was maintained at approximately 175° C., i.e. approximately 20° C. below the melting point of the barrier resin (195° C.). It was then raised from the rear to the middle of the barrel to approximately 200° C. (i.e. approximately 5° C. above the melting point of the barrier resin), and maintained at 200° C. as it passed through the barrel.
For run 15, the temperature at the rear of the extruder was maintained at approximately 195° C., i.e. at the melting point of the barrier resin. It was allowed to cool somewhat as it passed down the barrel, to approximately 190° C.
For run 16, the temperature at the rear of the extruder was maintained at approximately 190° C, i.e. slightly below the melting point of the barrier resin. It was maintained at this temperature throughout the barrel.
The blends produced from comparative run 20 and invention runs 9, 15 and 16 were blow-molded using a continuous process to produce a standard test bottle of 1.5 litre, with an external area of 645 cm2 (100 inch2) and a wall thickness of 1.4 mm. The blow-molded bottles were tested for permeability to CE10 type fuel (i.e. a mixture of 45 vol % isooctane, 45 vol % toluene and 10 vol % ethanol), over time, according to ASTM D2684.
Permeability, P, is calculated according to the following equation:
wherein R is the rate of loss of hydrocarbon (in g/day), t is the wall thickness (in mm), and A is the external area (in cm2).
The results are shown in
Thermoplastic polymer blends were made comprising HDPE as olefin resin with a barrier resin that was incorporated at 7 wt %. The components of the barrier resins for runs 30-32 are given in Table 2. In the case of runs 31 and 32, the barrier resin was an ethylene-vinyl alcohol copolymer in which with 26 mol % of repeat units were derived from ethylene and about 74 mol % of repeat units were derived from vinyl alcohol, and having a melt flow rate measured at 210° C. under 2160 g of 4.3 g/10 minutes, mixed with polyamide 10,10.
Compatibilizers 1-3 maleic-anhydride grafted HDPE resins. They have melt flow indexes (MFI) of 12, 3, and 2 g/10 min, respectively, where the MFI is measured at 190° C. under a weight of 2160 g. Compatibilizers 1 and 3 are grafted with 1.2 weight percent maleic anhydride, based on the weight of the HDPE plus maleic anhydride. Compatibilizer 2 is grafted with 0.65 weight percent maleic anhydride, based on the weight of the HDPE plus maleic anhydride. The plasticizer is trimethylolpropane. Each of the components of the barrier resins in each of runs 30-32 was melt blended prior to use with the exception of the compatibilizers, which were cube-blended with the melt-blended components. The barrier resins of runs 31 and 32 have a melting point of about 195° C. The barrier resin of run 30 had a melting point of about 225° C.
The dry resins (93 wt % HDPE and 7 wt % of the barrier resin) were mixed as granules in the hopper of an extruder, and then passed through the extruder with the temperature profiles shown in
In the case of runs 31 and 32, the temperature at the rear of the extruder was maintained at approximately 195° C., i.e. at around the melting point of the barrier resin. It was then raised from the rear to the middle of the barrel to approximately 200° C. (i.e. approximately 5° C. above the melting point of the barrier resin), and maintained at 200° C. as it passed through the barrel. As used in the case of run 9 above, a flat temperature profile was set on the blow-molded extruder.
In the case of run 30, the temperature at the rear of the extruder was maintained at approximately 220° C. It was then raised from the rear to the middle of the barrel to approximately 225° C. and maintained at 225° C. as it passed through the barrel. As used in the case of run 9 above, a flat temperature profile was set on the blow-molded extruder.
The blends produced from runs 30-32 were blow-molded to produce a standard test bottle of 1.5 litre, with an external area of 645 cm2 (100 inch2) and a wall thickness of 1.4 mm. One set of test bottles was made using a continuous extrusion/blow-molded process. Another set was made using a discontinuous process. In the discontinuous process the extruder was stopped for 10 minutes. One bottle was then molded. Then two more bottles were molded. The second two bottles were tested. Five more bottles were molded and the machine was again stopped for 10 minutes, whereupon the procedure was repeated and one bottle was molded and discarded and then two more were molded and tested and five more were molded before pausing the extruder for another 10 minute period.
The blow-molded bottles were tested for permeability to CE10 type fuel (i.e. a mixture of 45 vol % isooctane, 45 vol % toluene and 10 vol % ethanol), over time, according to ASTM D2684.
Permeability, P, is calculated according to the following equation:
wherein R is the rate of loss of hydrocarbon (in g/day), t is the wall thickness (in mm), and A is the external area (in cm2).
Five bottles were used for each set of testing conditions. The results were averaged and are shown in Table 3 and 4. It can be seen that bottles made from thermoplastic polymers of runs 31 and 32 in the discontinuous process under hold up time, have a permeability to CE10 type fuel after 7 weeks (steady state of mass transfer) of, 0.057 and 0.088 g·mm/day·100 cm2, respectively, whereas bottles made in run 30 have a permeability to CE10 type fuel after 7 weeks of over 0.141 g·mm/day·100 cm2. Permeability results are further listed in Table 3 and 4.
This application claims the benefit of U.S. Provisional Application No. 60/832,451, filed Jul. 21, 2006.
| Number | Date | Country | |
|---|---|---|---|
| 60832451 | Jul 2006 | US |
