Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-07-31
2004-03-16
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S210000, C525S213000, C525S239000, C525S240000, C525S241000, C524S425000
Reexamination Certificate
active
06706815
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to improved impact resistant vinyl chloride polymer compositions. More specifically, this invention relates to impact resistant compositions of hydrocarbon rubber impact modifiers and polyvinyl chloride compatibilized with randomly chlorinated polyethylene.
BACKGROUND OF THE INVENTION
Polyvinyl chloride (PVC) is widely used in both its rigid and flexible forms in such applications as films, siding, sheets, pipe and tubing. Because rigid PVC is a hard, brittle thermoplastic polymer, it is often mixed with a modifier to form a composition that is less prone to failure on impact. Known PVC modifiers include polyacrylic resins, butadiene-containing polymers such as methacrylate butadiene styrene terpolymers (MBS), and chlorinated polyethylene (CPE) resins. For example, in U.S. Pat. Nos. 3,006,889 and 3,209,055 the use of a broad range of chlorinated and chlorosulfonated polyethylenes in blends with PVC is disclosed. These modifiers form small rubbery microdomains when mixed in PVC compositions that improve the impact resistance of these compositions.
Hydrocarbon rubbers such as ethylene/alpha-olefin copolymers have advantages over the aforementioned modifiers in that they are low density, have excellent stability at PVC processing temperatures (e.g. 170-210° C.) and are UV resistant. For example, in U.S. Pat. No. 5,925,703 Betso et al. teach the use of linear ethylene/alpha-olefins to improve impact performance of filled thermoplastic compositions, including polyvinyl chlorides. However, the use of these hydrocarbon rubbers as impact modifiers for rigid PVC applications has been hampered by the fact that the small rubbery microdomains have not formed in the size range for effective impact modification when the hydrocarbon rubbers are mixed in PVC compounds.
More recently, impact modifiers that are mixtures containing chlorinated polyethylenes and other polymers have been disclosed. As an example, Aono et al., in Japanese Published Patent Application No.
7-11085
, disclose the use of a mixture of a chlorinated polyethylene prepared from a polyethylene of molecular weight 50,000 to 400,000 and AES resin (acrylonitrile-EPDM-styrene), optionally in combination with other polymers, as an impact modifier for PVC. Further, in U.S. Pat. No. 6,124,406 Cinadr et al. teach that blocky chlorinated polyethylenes can be used to compatibilize hydrocarbon rubber and PVC to give a PVC composition with improved impact resistance. The Cinadr patent also teaches that randomly chlorinated polyethylenes, such as Tyrin® chlorinated polyethylene, are ineffective as compatibilizers due to poor interfacial adhesion between the PVC and hydrocarbon rubber. Blocky chlorinated polyethylenes have regions of high chlorine concentration as well as regions of very low chlorine concentration. However, blocky chlorinated polyethylenes have poor thermal stability at PVC processing temperatures, which increases the possibility of degradation during PVC processing. Blocky chlorinated polyethylenes are also time consuming to manufacture since the chlorination reactions must take place at temperatures which retain the crystallinity of the polyethylene, thereby slowing the reaction rates down.
SUMMARY OF THE INVENTION
Surprisingly, and in contrast to what has been suggested in the Cinadr patent, we have found that randomly chlorinated polyethylenes, such as Tyrin®, can be used to compatibilize blends of vinyl chloride polymers and hydrocarbon rubber and that their mixture with hydrocarbon rubbers improves the impact resistance of PVC compositions. We have also found that randomly chlorinated polyethylenes are effective compatibilizers for hydrocarbon rubbers at lower levels in PVC-hydrocarbon rubber compositions than what has been demonstrated in the prior art using blocky chlorinated polyethylenes. We have also found that with some PVC compositions there is a synergistic effect between components used as fillers in PVC compositions, such as calcium carbonate, and the hydrocarbon rubber used as the impact modifier, where the impact strength of the composition is improved as the concentration of filler in the composition is increased. These highly filled PVC compositions are economical and advantageous for their improved impact resistance.
The present invention is specifically directed to improved polyvinyl chloride compositions having excellent impact strength. In particular, the impact resistant composition comprises a) a vinyl chloride polymer, b) at least one ethylene/alpha-olefin copolymer, said copolymer having a density of 0.858 to 0.91 g/cc and having a melt index from an I
10
value of 0.1 to an I
2
value of 10, and c) at least one randomly chlorinated olefin polymer having a chlorine content of from 20-40 percent by weight, the feedstock for said chlorinated olefin polymer having a melt index from an I
10
value of 0.1 to an I
2
value of 10. Optionally, these impact resistant polyvinyl chloride compositions may have inorganic filler levels from 5 to 50 parts per hundred parts of the polyvinyl chloride polymer.
DETAILED DESCRIPTION OF THE INVENTION
The impact resistant compositions of the present invention comprise a vinyl chloride polymer, a hydrocarbon rubber, and a randomly chlorinated olefin polymer both having specific chemical composition and physical properties. Another aspect of the current invention additionally comprises an inorganic filler in the impact resistant compositions.
The vinyl chloride polymer component is a solid, high molecular weight polymer that may be a polyvinyl chloride homopolymer or a copolymer of vinyl chloride having copolymerized units of one or more additional comonomers. When present, such comonomers will account for up to 20 weight percent of the copolymer, preferably from 1-5 weight percent of the copolymer. Examples of suitable comonomers include C
2
-C
6
olefins, for example ethylene and propylene; vinyl esters of straight chain or branched C
2
-C
4
carboxylic acids, such as vinyl acetate, vinyl propionate, and vinyl 2-ethyl hexanoate; vinyl halides, for example vinyl fluoride, vinylidene fluoride or vinylidene chloride; vinyl ethers, such as vinyl methyl ether and butyl vinyl ether; vinyl pyridine; unsaturated acids, for example maleic acid, fumaric acid, methacrylic acid and their mono- or diesters with C
1
-C
10
mono- or dialcohols; maleic anhydride, maleic acid imide as well as the N-substitution products of maleic acid imide with aromatic, cycloaliphatic and optionally branched aliphatic substituents; acrylonitrile and styrene. Such homopolymers and copolymers are commercially available from Borden Chemicals and Plastics and Shintech. They may also be prepared by any suitable polymerization method. Polymers prepared using a suspension process are preferred.
Graft copolymers of vinyl chloride are also suitable for use in the invention. For example, ethylene copolymers, such as ethylene vinyl acetate, and ethylene copolymer elastomers, such as EPDM (copolymers comprising copolymerized units of ethylene, propylene and dienes) and EPR (copolymers comprising copolymerized units of ethylene and propylene) that are grafted with vinyl chloride may be used as the vinyl chloride polymer component. A commercially available example of such a polymer is Vinnol® 500, available from Wacker Chemie GmbH.
The randomly chlorinated olefin polymer component of the compositions of the invention is selected from the group consisting of a) randomly chlorinated polyethylene homopolymers prepared from polyethylenes having a melt index from an I
10
value of 0.1 to an I
2
value of 10 and b) randomly chlorinated copolymers prepared from polyolefins having a melt index from an I
10
value of 0.1 to an I
2
value of 10 that contain copolymerized units of i) ethylene and ii) a copolymerizable monomer. The chlorinated olefin polymer may optionally include chlorosulfonyl groups. That is, the polymer chain will have pendant chlorine groups and chlorosulfonyl groups. Such polymers are known as chlorosulfonated olefin polymers.
Representative chlorinate
Berard Mark T.
Marchand Gary R.
DuPont Dow Elastomers L.L.C.
Nutter Nathan M.
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