POLYMER COMPOSITION

Abstract: The invention relates to opaque polymer compositions and moulded articles having improved scratch resistance wherein the polymer composition comprises a blend of a matrix polymer selected from the group consisting of polypropylene, high density polyethylene and poly-4-methylpenten-1; at least one impact modifier wherein said impact modifier is a copolymer or terpolymer of ethylene and at least one other alpha -olefin or diolefin; at least one opacifier selected from the group consisting of colourants and fillers and combinations thereof; and at least one block copolymer of at least one styrenic monomer and at least one olefinic or diolefinic monomer.

Description: POLYMER COMPOSITION The present invention relates to scratch-resistant polymer compositions and moulded articles. Plastics materials are utilised in a wide variety of applications, many of which require the material to maintain its aesthetic appeal notwithstanding various scratches and scuffs to which it is subjected during its useful life. Plastics materials are particularly susceptible to degradation of surface finish and the subsequent loss of aesthetic appeal. In particular, opaque plastics materials show a far greater loss of aesthetic appeal than either transparent or translucent plastics materials. It is believed that micro-tearing and stress whitening of the plastics material occurs around any scratches in the surface of the plastics material. This damage is far more visible, and hence much more of a problem, in opaque plastics materials. Opaque plastics materials find considerable use in applications which require a resistance to scratches and scuffs. For example car manufacturers utilise coloured plastics materials (typically polypropylene) for the interior trim of their vehicles. The interior trim of a car is subjected to considerable scratching and scuffing. Accordingly there is a need for a plastics material which may be pigmented as desired but is able to resist the scratches and scuffs of everyday use. There are a considerable number of other applications where scratch resistance is required in opaque materials. ' We have now found an opaque plastics material which provides a surface finish with improved scratch-resistance and alleviates some of the abovementioned problems. Accordingly we therefore provide an opaque polymer composition comprising a blend of: a matrix polymer selected from the group consisting of polypropylene, high density polyethylene and poly- 4-methylpentene -1; at least one impact modifier wherein said impact modifier is a copolymer or terpolymer of ethylene and at least one other α-olefin or diolefin; at least one opacifier selected from the group consisting of colourants and fillers and combinations thereof; and at least one block copolymer of at least one styrenic monomer and at least one olefinic or diolefinic monomer. In practice, we have found that polymer compositions of the present invention comprising polypropylene as matrix polymer exhibits particularly marked resistance to damage associated with scratching. Wherein polypropylene is utilised as matrix polymer we have found that it is preferable that the polypropylene be selected from is isotactic polypropylene homopolymers and random copolymers of ethylene and propylene. Commercial available isotactic polypropylene typically comprises approximately 3% atactic polypropylene. It is preferred that the amount of atactic polypropylene is less than 8%. The random copolymer of ethylene and propylene may be manufactured by introducing the ethylene monomer into the copolymer in a mixed feed with propylene. This generates random statistical ethylene-propylene copolymer (EP copolymer) chains. The overall proportion of ethylene units in the random copolymer used in the invention is typically from 3 to 15, more usually 5 to 12 and especially about 6 (for example 5 to 7), mole % based on total monomer. The remainder of the units are derived from propylene although a small proportion of other olefin monomers can be included, for example up to 10% by weight of the propylene units of C 4 to C 10 alpha olefin monomers. Preferably the polypropylene has a melt flow index, ASTM D1238 CONDITION L of 0.5-60 g/10 min and a xylene- soluble content of from 2-6% w/w. More preferably the melt flow index ASTM D1238 CONDITION L of the polypropylene is in the range of 4 to 20 g/10 min and more preferably in the range of 15 to 20 g/10 min. Wherein high density polyethylene (HDPE) is selected as matrix polymer it is preferred that the HDPE has a melt flow index ASTM D1238 CONDITION E in the range of from 0.5 to 80 g/10 min, more preferably in the range of from 4 to 40 g/10 min. It is preferred that the density of the HDPE is in the range of from 940 to 965 kg/m , more preferably in the range of from 950 to 960 kg/m 3 . The matrix polymer may also contain effective amounts of additional polymers such as nylon 6, nylon 66 and polyphenylene oxide. The impact modifier, the polymer of ethylene and α- olefin, typically has a density in the range from 860 to 930 kg/m 3 , preferably 890 to 920 kg/m 3 . The melt flow index ASTM D1238 CONDITION E of the polymer of ethylene and α-olefin is typically in the range of from 0.1 to 40 g/10 min, preferably in the range of from 0.3 to 4 g/10 min. The polymer of ethylene and α-olefin typically comprises up to 70 mole percent of α-olefin. The crystalinity of the polymer of ethylene and α-olefin is related to the α-olefin content. Preferably the α-olefin content is in the range of from 2 to 30 mole percent. The α-olefin is preferably selected from propene, butene, hexene, octene and 1-methylρentene. It is preferred that the impact modifier be selected from the group consisting of linear low density polyethylene (LLDPE), low density polyethylene (LDPE), ethylene-propylene terpolymer (EPT or EPDM) and ethylene- propylene rubber (EPR) . Preferably the impact modifier is LLDPE and has a melt flow index ASTM D1238 CONDITION E in the range of from 0.5 to 80 g/10 min, more preferably in the range of from 4 to 40 g/10 min. The LLDPE typically has a density in the range of from 860 to 930 kg/m 3 , more preferably 890 to 920 kg/m 3 . The impact modifier may be blended with the matrix polymer or manufactured in situ with the matrix polymer. Wherein the impact modifier is manufactured in situ with the matrix polymer it is conveniently manufactured utilising a 2 step cascade reactor. For example polypropylene/EPR block copolymers and polypropylene/LLDPE block copolymers may be manufactured in this manner. We have found it preferable that the block copolymer of at least one styrenic monomer and at least one olefinic or diolefinic monomer be grafted with from 0.1 to 20, more preferably 1 to 6, mole percent of a carboxylic acid, acid anhydride or sulphonate functionality. The block copolymers are preferably selected from the group consisting of: A - B; A - B - A; and (A - B)nX wherein A is a styrenic block preferably polymerised from styrene or methylstyrene monomers or combinations thereof, wherein B is an olefinic or diolefinic block preferably polymerised from isoprene, butadiene or combinations thereof, and optionally halogenated to form blocks of ethylene/butylene or ethylene/propylene sequences. and wherein X is a multivalent cation or a multifunctional moiety and n is the valency or functionality of X. Typically X is silicon or organosilane. The styrenic monomers for use in this invention are elected from styrene itself and homologues such as α-methyl styrene and the mixed isomers sold commercially as "vinyl toluene". It is preferred that the copolymers contain from 25-35 mole percent of styrenic monomer. It is preferred that B is a random copolymer block of ethylene and either butylene or propylene made by halogenating butadiene or isoprene blocks. Typically block copolymers of the type A-B-A are selected from the group consisting of styrene/ethylene/ -butylene/styrene and styrene/ethylene/ propylene/styrene block copolymers (hereinafter SEBS and SEPS respectively) and may be selected from any such polymers known to the art which comply with the parameters mentioned herein. The SEBS and SEPS copolymers may be prepared by the sequential anionic polymerisation of the monomers using known initiators such as alkyl lithium initiators. Typically block copolymers of the type (A-B) n X are selected from the group consisting of radial SEB and radial SEP block copolymers. The SEB and SEP copolymers for the radial block copolymers may be prepared by sequential anionic polymerisation using known initiators. The polymers are then coupled together by using multifunctional coupling agents known to the art, for example polychlorosilanes. The block copolymers for use in this invention are preferably grafted with from 0.1 to 20 mole percent of a carboxylic acid, acid anhydride or sulphonate functionality. The preferred acid is acrylic acid and the preferred acid anhydride is maleic anhydride. It is preferred that block copolymers for use in the present invention are hydrogenated. Hydrogenated block copolymers provide improved weatherability characteristics in the polypropylene composition. The olefins may be hydrogenated by known means. By the term "opaque" it is meant that the polymer composition is substantially opaque to visible light. The opacifier is present in amounts sufficient to render the polymer composition substantially opaque. The opacifier is either a colourants or a filler or a combination thereof. Typically colourants are present in amounts in the range of 0.1 to 5% by weight of the polymer composition. Colourants for us in the present invention may be any of those known to the art and which comply with the parameters mentioned hereinabove. Examples of colourants useful in polymer compositions of the present invention include titanium dioxide, carbon black, iron oxide pigments, phthalocyanines, lead chromates and the like. Typically fillers are present in amounts in the range of from 5 to 50 percent by weight of the polymer composition. Fillers for use in the present invention may be any of those known to the art and which comply with the parameters mentioned hereinabove. Examples of fillers useful in polymer compositions of the present invention include chalk, dolomite, fibrous and plate-like inorganic fillers. "Plate-like fillers" are those fillers whose particles have a length and width substantially greater than their depth. The presence of a plate like inorganic filler in the composition of the invention gives the composition increased stiffness. Suitable plate like inorganic fillers include mineral fillers such as clays, mica and especially talc. A particularly useful talc is LUZENAC 15 MOO (Talc de Luzenac) . Fibrous fillers include aramid glass and carbon fibres. In practice, we have found that polymer compositions in accordance with the present invention exhibit improved scratch resistance when the matrix polymer/impact modifier blend contains one or more multivalent metal cations. The multivalent metal cations may preferably be selected from the group consisting of calcium, zinc, titanium, chronium and vanadium. More preferably the multivalent metal cation is zinc. The multivalent metal cations may be residues from catalysts used in the manufacture of the matrix polymer or impact modifier. The multivalent metal cations may also be in the form of acid acceptors used in the compounding of the matrix polymer or impact modifier. Examples of acid acceptors useful in providing multivalent metal cations are zinc oxide, zinc stearate and calcium stearate. It is preferred that the multivalent metal cation is provided in the form of zinc stearate in amounts in the range of from 100 to 3000 ppm based on the total weight of polymer. While not wishing to be bound by theory it is believed that the block copolymer forms an interface between the matrix polymer and the impact modifier. It is believed that the compatibility of the olefinic or diolefinic block with both the matrix polymer and the impact modifier is important in allowing the block copolymer to form the interface between the matrix polymer and the impact modifier. It is believed the styrenic blocks form glassy vinyl/aromatic domains on both sides of the interface forming melt reversible crosslinks which generally add to the interfacial strength. Wherein the block copolymer is grafted as hereinabove defined, it is believed that inside these glassy domains the grafted acidic groups form ionic domains with multivalent metal ions, such as those residual from the catalyst or acid acceptors used in the manufacture of the matrix polymer. These ionic bonds within the ionic domains are also melt reversible and further increase the strength of the interface between the matrix polymer and the impact modifier. In practice, we have found the addition of a fatty acid amide to the polymer composition has the effect of substantially improving the scratch-resistance of the polymer composition. This effect appears to be synergistic. Suitable fatty acid amides are of fatty acids with CIO to C25, especially C16 to C22, carbon chains. A particularly suitable fatty acid amide is erucamide, available as CRODAMIDE E (Croda Chemicals). The amount of fatty acid amide will usually be up to 1 weight % of the composition, particularly 0.1 to 0.8%, and especially about 0.5% by weight of the composition. In addition to the essential components, the compositions of the invention may also contain ingredients well known to the art to be useful in such compositions, these being included in art-recognised quantities. Such ingredients include antioxidants, UV stabilisers and nucleating agents. The invention is further described with reference to the following invention. Example : A series of compositions 1 to 4 were prepared according to conventional automotive interior formulations and compared with the example constructed according to the invention, composition 5. The composition of Examples 1 to 5 are shown in Table 1.TABLE 1 COMPOSITIONS Propathene LZM186, GWMlOl and GYM45 are polypropylene grades ex ICI Australia. Chimmasorb 944 and Tinuvin 770 are ex Ciba-Geigy. LLDPE; NUC MG 265 is ex Nippon ϋnicar and Kraton FG190IX is ex Shell. Propathene LZM186 and GWMlOl are ethylene propylene block copolymers and GYM45 is a propylene hom polymer having a melt flow indices (MED) of 24, 4.5 and 15 respectively (ASTM D1238 CONDITION L) . Each has been adequately heat stabilised and contains between 500 and 1000 ppm Zinc Stearate. NUC MG2 5 is a hexene-based LLDPE of MFI 5.0 (ASTM D1238 CONDITION E) . The compositions 1 to 4 were prepared by tumble blending all ingredients for 15 minutes prior to compounding in a 50mm Farrel Continuous Mixer. Composition 5 was prepared by first compounding the homopoly er, LLDPE and Kraton in a cavity transfer mixer (CTM, Rapra Technologies) of 50mm diameter. The resultant granulated compound was tumble blended with the remaining ingredients prior to extrusion compounding on a 38mm single screw extruder. Each compounded composition was injection moulded into textured plaques of size 160 x 130mm with four automotive grained surfaces ranging from fine stipple to cowhide look. The plaques were set aside for seven days to allow annealing and scratched using a hand operated scratch tester using weights of 100 to 900g in lOOg increments applied to a 1mm hemispherical tungsten stylus which was drawn across the grained surface. The scratches were visually assessed by a panel of four independent observers. The plaques ranked according to the visibility of the visible scratch) . The rankings of the panel were aggregated to give an overall ranking. Table 1 shows the results. On the polished surface of the plaque, the results were identical, but no damage was found for Composition 5 whilst the other plaques showed considerable scratching. The results clearly show that the composition which is the subject of this patent, composition 5, gave moulded plaques which were far superior to the conventional compositions of Examples 1 to 4. TABLE 2 SCRATCH RESULTS Observer

Claims: The claims defining the invention are as follows: 1. An opaque polymer composition comprising a blend of a matrix polymer selected from the group consisting of polypropylene, high density polyethylene and poly-4- methylpenten-1; at least one impact modifier wherein said impact modifier is a copolymer or terpolymer of ethylene and at least one other «-olefin or diolefin; at least one opacifier selected from the group consisting of colourants and fillers and combinations thereof; and at least one block copolymer of at least one styrenic monomer and at least one olefinic or diolefinic monomer. 2. An opaque polymer composition according to claim 1 wherein matrix polymer is selected from isotactic polypropylene homopolymers and random copolymers of ethylene and propylene. 3. An opaque polymer composition according to either of claims 1 or 2 wherein the matrix polymer is high density polyethylene and has a melt flow index ASTM D1238 CONDITION E in the range of from 4 to 40 g/10 min and has a density is in the range of from 950 to 960 kg/m . 4. An opaque polymer composition according to any one of claims 1 to 3 wherein the impact modifier has a density in the range from 890 to 920 kg/m 3 and a melt flow index ASTM D1238 CONDITION E in the range of from 0.3 to 4 g/10 min. 5. An opaque polymer composition according to any one claims 1 to 4 wherein the impact modifier is selected from the group consisting of linear low density . polyethylene, low density polyethylene ethylene- propylene terpolymer and ethylene-propylene rubber. 6. An opaque polymer composition according to any one of claims 1 to 5 wherein the impact modifier is linear low density polyethylene and has a melt flow index ASTM D1238 CONDITION E in the range of from 4 to 40 g/10 min and has a density in the range of from 890 to 920 kg/m 3 . 7. An opaque polymer composition according to any one of claims 1 to 6 wherein the impact modifier may be blended with the matrix polymer or manufactured in situ with the matrix polymer. 8. An opaque polymer composition according to any one of claims 1 to 7 wherein the block copolymer is grafted with from 1 to 6 mole percent of a carboxylic acid, acid anhydride or sulphonate functionality. 9. An opaque polymer composition according to any one of claims 1 to 8 wherein the block copolymers are selected from the group consisting of: A - B; A - B - A; and (A - B)nX wherein A is a styrenic block polymerised from styrene or methylstyrene monomers or combinations thereof; wherein B is an olefinic or diolefinic block polymerised from isoprene, butadiene or combinations thereof to form blocks of ethylene/butylene or ethylene/propylene sequences; and wherein X is a multivalent cation or a multifunctional moiety and n is the valency or functionality of X. 10.An opaque polymer composition according to any one of claims 1 to 9 wherein the styrenic monomers are selected from styrene itself and homologues such as <*- methyl styrene and the mixed isomers sold commercially as "vinyl toluene". 11. An opaque polymer composition according to any one of claims 1 to 10 wherein the copolymers contain from 25 to 35 mole percent of styrenic monomer. 12. An opaque polymer composition according to any one of claims 1 to 11 wherein B is a random copolymer block of ethylene and either butylene or propylene made by halogenating butadiene or isoprene blocks. 13. An opaque polymer composition according to any one of claims 1 to 12 wherein block copolymers of the type A-B-A are selected from the group consisting of styrene/ethylene/butylene/styrene and styrene/ ethylene/propylene/styrene block copolymers. 14. An opaque polymer composition according to any one of claims 1 to 13 wherein block copolymers of the type (A-B)-.X are selected from the group consisting of radial SEB and radial SEP block copolymers. 15. An opaque polymer composition according to any one of claims 1 to 14 wherein the block copolymers are grafted with from 0.1 to 20 mole percent of a carboxylic acid, acid anhydride or sulphonate functionality. 16. An opaque polymer composition according to any one of claims 1 to 15 wherein the carboxylic acid is acrylic acid. 17. An opaque polymer composition according to any one of claims 1 to 16 wherein the acid anhydride is maleic anhydride. 18. An opaque polymer composition according to any one of claims 1 to 17 wherein the copolymers for use in the present invention are hydrogenated. 19. An opaque polymer composition according to any one of claims 1 to 18 wherein colourants are present in amounts in the range of 0.1 to 5% by weight of the opaque polymer composition. 20. An opaque polymer composition according to any one of claims 1 to 19 wherein fillers are present in amounts in the range of from 5 to 50 percent by weight of the polymer composition. 21. An opaque polymer composition according to any one of claims 1 to 20 wherein the matrix polymer/impact modifier blend contains one or more multivalent metal cations selected from the group consisting of calcium, zinc, titanium, chronium and vanadium. 22. An opaque polymer composition according to any one of claims 1 to 21 wherein the multivalent metal cation is provided in the form of zinc stearate in amounts in the range of from 100 to 3000 ppm based on the total weight of opaque polymer composition. 23. An opaque polymer composition according to any one of claims 1 to 22 further comprising a fatty acid amide of C 16 to C 22 carbon chains. 24. An opaque polymer composition according to any one of claims 1 to 23 wherein the fatty acid amide is erucamide. 25. An opaque polymer composition substantially as hereinabove described with reference to the examples.

Inventors: MUSGRAVE STUART, O'LEARY JOHN, MUSGRAVE, STUART, O'LEARY, JOHN
Applicants: ICI AUSTRALIA OPERATIONS, ICI AUSTRALIA OPERATIONS PROPRIETARY LIMITED
Application year: 1993
Main classification: C08L23
IPC codes: C08L23, C08L51, C08L53