Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-06-30
2002-08-13
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S488000, C524S504000
Reexamination Certificate
active
06433063
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to directly paintable thermoplastic olefin compositions comprising an epichlorohydrin rubber; said compositions have improved electrical conductivity and therefore are particularly suitable to electrostatic painting. The TPO compositions of the invention are useful for making injection molded parts, such as automobile bumpers, and exhibit excellent paint adhesion and durability.
BACKGROUND OF THE INVENTION
Thermoplastic olefins (TPOS) are uncrosslinked blends of olefin polymers and polyolefin elastomers. They can be made by physically blending in an internal mixer, or by polymerizing in a reactor. These materials are not paintable or coatable, because the paints or coatings consist of polar materials like urethanes, acrylics, epoxies, or melamines that have very poor adhesion to non-polar materials like polyolefins. Typically an adhesion promoter is used as the tie layer between the TPO substrate and the paint coating. This extra step adds to the cost of the product, and the coating is not very durable.
U.S. Pat. No. 5,962,573 discloses a directly paintable polymer composition comprising: (1) a thermoplastic olefin, (2) a propylene homopolymer or a propylene copolymer with ethylene or a C
4-8
&agr;-olefin, grafted with an anhydride of an aliphatic &agr;,&bgr;-unsaturated dicarboxylic acid; (3) an oxidized polyethylene wax having a melting point of less than 116° C. and an acid number of less than 40; (4) a functionalized polymer that is reactive with the anhydride groups of the grafted polymers and, optionally, (5) a polyolefin rubber grafted with an anhydride of an aliphatic &agr;,&bgr;-unsaturated dicarboxylic acid, and (6) an ethylene polymer grafted with an anhydride of an aliphatic &agr;,&bgr;-unsaturated dicarboxylic acid.
Injections molded parts such as automobile bumpers made from this composition are directly paintable with polar paints or coatings without the need for a layer of adhesion promoter between the thermoplastic olefin surface and the paint, and exhibit good paint adhesion an durability.
An important parameter in the paint process is the efficiency of the paint being sprayed; in fact, since the paint is airborne, some of it does not arrive onto the part to be treated and some is lost in the environment. Electrostatic painting of substrates tends to reduce paint waste and emissions, as compared to non-electrostatic painting techniques.
Electrostatic painting techniques require the substrate to be electrically conducting and common TPOs for injection molded articles are electrically insulating; one of the methods to solve this problem, according to the prior art, consists in applying an electrically conductive primer prior to painting, in order to display an increased paint transfer efficiency. Nevertheless, this further step is costly and time consuming.
An alternative technique is to use a grounding clip, but this causes higher film buildup near the grounding clip with film buildup decreasing as the distance from the grounding clip increases. In addition, after several passes through the paint spraying booth, significant resistance to ground may be encountered due to multiple paint layers on the substrate itself
A further way of improving the electrical conductivity is to incorporate additives, such as stainless steel fibers, into the thermoplastic polymer itself; nevertheless said additives are not suitable for TPO-based compositions because they lead to a degradation of their desirable mechanical properties, such as impact strength and tensile elongation. Moreover, said additives significantly increase the brittleness of such TPO compositions.
U.S. Pat. No. 5,484,838 describes thermoplastic olefin compositions having improved electrical conductivity due to the addition of electrically conductive carbon black; in these compositions, at least a portion of the carbon black has to be dispersed within the crystalline polymer component of the TPO. Nevertheless, carbon black or additives of similar nature are difficult to handle and, as a consequence. their exact dispersion and the morphology needed for the TPO matrix are very difficult to control.
In addition, conductive carbon black may cause a reduction in the effectiveness of the directly paintable functionalized polymers, presumably by absorbing the materials onto the surface of the carbon black itself.
Thus, there is still a need for a TPO composition having an improved electrical conductivity and therefore allowing a better paint efficiency, at the same time meeting the stringent requirements for paint adhesion and durability of today's marketplace, particularly in the automotive industry.
SUMMARY OF THE INVENTION
The composition of the present invention comprises, by weight:
(1) 100 parts of a thermoplastic olefin comprising an olefin polymer having an isotactic index of at least 80 and an olefin polymer rubber, the thermoplastic olefin having a rubber content of at least 20%;
(2) about 5 to about 20 parts per hundred parts of the thermoplastic olefin of a propylene homopolymer or propylene copolymer with ethylene or a C
4-8
&agr;-olefin having an ethylene or &agr;-olefin content of about 0.5% to about 20%, grafted with an anhydride of an aliphatic &agr;,&bgr;-unsaturated dicarboxylic acid and having an anhydride content of about 2% to about 5%;
(3) about 3 to about 20 parts per hundred parts of the thermoplastic olefin of an oxidized polyethylene wax having a melting point of less than 116° C. and an acid number of less than 40;
(4) a functionalized polymer that is reactive with the anhydride groups of the grafted polymers, selected from the group consisting of:
(a) about 2 to about 6 parts per hundred parts of the thermoplastic olefin of an amine-terminated polyalkylene glycol;
(b) about 2 to about 6 parts per hundred parts of the thermoplastic olefin of a hydroxy-terminated polyolefin;
(c) about 2 to about 6 parts per hundred parts of the thermoplastic olefin of a hydroxy-terminated polybutadiene;
(d) about 2 to about 8 parts per hundred parts of the thermoplastic olefin of a hydroxy-terminated olefin/alkylene oxide copolymer;
(e) about 2 to about 8 parts per hundred parts of the thermoplastic olefin of a hydroxy-terminated polyalkylene oxide;
(f) about 2 to about 8 parts per hundred parts of the thermoplastic olefin of a methoxy-terminated polyalkylene oxide;
(g) about 2 to about 8 parts per hundred parts of the thermoplastic olefin of an amine-terminated olefin/alkylene oxide copolymer, and
(h) mixtures thereof;
(5) about 2 to about 20 parts per hundred parts of the thermoplastic olefin of an epichlorohydrin rubber;
(6) optionally, about 5 to about 30 parts per hundred parts of the thermoplastic olefin of a polyolefin rubber grafted with an anhydride of an aliphatic &agr;,&bgr;-unsaturated dicarboxylic acid, having an anhydride content of at least 0.3% but less than 3% and comprising a polymer of ethylene and a C
3-8
&agr;-olefin, optionally containing about 0.5% to about 10% of a diene, having an ethylene content of about 30% to about 70%;
(7) optionally, about 5 to about 20 parts per hundred parts of the thermoplastic olefin of an ethylene polymer grafted with an anhydride of an aliphatic &agr;,&bgr;-unsaturated dicarboxylic acid, having an anhydride content of about 1% to about 16% and a number average molecular weight Mn of about 500 to about 5000, provided that at least 5 parts of anhydride-grafted polypropylene or propylene copolymer and 3 parts of oxidized polyethylene wax per hundred parts of the thermoplastic elastomer are also present;
(8) optionally, about 5 to about 20 parts per hundred parts of the thermoplastic olefin of a thermoplastic resin selected from the group consisting of:
(a) an hydrogenated polymer consisting essentially of terpene hydrocarbons, having a drop softening point greater than about 70° C., and a number average molecular weight M
n
greater than about 500; and
(b) an hydrogenated polymer of styrene or alkyl-substituted styrene, having a number average molecular weight M
n
ranging between about 600 and about 20
Basell Technology Company BV
Mullis Jeffrey
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