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
2002-09-25
2004-10-12
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...
C525S209000, C525S240000, C521S073000, C521S075000, C428S542800
Reexamination Certificate
active
06803417
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a polyolefin composition in powder form comprising (i) a crosslinkable, vinyl silane-grafted blend of a olefinic interpolymer, optionally containing a crystalline polypropylene homopolymer or interpolymer; and (ii) a crosslinked vinyl silane-grafted olefinic interpolymer containing a cure or crosslinking catalyst; the above blend optionally containing a crystalline polyolefin powder. In another aspect, this invention relates to a process for preparing these polyolefin powders, and applications for using these powders. In a further aspect, this invention relates to laminates, both foamed and unfoamed, prepared from these polyolefin powders. In yet another aspect, this invention relates to processes to prepare these laminates.
BACKGROUND OF THE INVENTION
Automotive interior coatings are produced by a variety of techniques including vacuum molding and thermoforming of calendered or extruded sheets. If the mold has sharp corners or deep draw regions, then the molding process can lead to thinning of the material in these areas and significant loss of grain texture. Vacuum formed sheets, after cooling, can also contain a high residual molding stress caused during the molding process which, when reheated in subsequent back-foaming steps, can result in release of this stress. This, in turn, can cause shrinkage and dimensional stability problems. These stress areas can also lead to cracks forming over time as the skin ages.
An alternative process which is less susceptible to these problems is slush molding. In the slush molding technique, a free-flowing, powdered polymer is charged to an open top container or box, i.e., a slush box. A heated mold in the form of the article or object to be molded is clamped on top of the slush box, and the container rotated in a manner such that the free-flowing polymer powder contacts the hot mold where the powder melts and flows over the mold. The container is then returned to its original position, the mold removed from the container, and the article removed from the mold. This technique can realize complex shapes with sharp edges and excellent grain retention.
Introduction of passenger and door airbags has changed the requirement for automotive interior coverings from predominately appearance only criteria to that of a safety composition. Until recently, polyvinyl chloride (PVC) resins were the material of choice for interior coverings, and they are ideally suited for slush molding. However, PVC formulations suffer from migration and volatilization of the plasticizers over time, and this leads both to physical property changes in the PVC as it ages and to fogging of the car window glass. PVC also suffers from being heavier than alternative polyolefin materials (an important consideration in the current design of automobiles with the emphasis on lighter materials to reduce the overall weight of the vehicle and thus increase its gas efficiency). Additionally, the hardness, storage modulus, and brittleness of PVC increases as the ambient temperature decreases, and thus at low temperatures, e.g., about minus 40° C., the instrument panel skin upon airbag deployment could splinter.
An alternative to PVC is thermoplastic polyurethanes (TPU) which can be engineered to have the necessary flow characteristics required for slush molding. Such TPUs have good scratch and mar properties but the aromatic based TPUs have poor ultraviolet (UV) light resistance. Aliphatic isocyanates can be used to prepare TPUs having good UV-resistance but at a significant cost penalty.
Another problem with many existing compositions used in the slush molding process is poor hot tear resistance which can sometimes cause tearing of the molded product if it is removed from the mold while still hot. Having to wait for the molded article to cool increases production time and reduces efficiency.
Thus, there is a need by the automobile manufacturers and others to develop a polymer composition for automotive interior applications, especially polymer powder for slush molding operations, which has good hot tear properties, excellent low temperature properties, low hardness and no glossing after heat aging.
SUMMARY OF THE INVENTION
One embodiment of this invention is a polyolefin powder comprising about 80 to 95 wt % of component A, about 5 to 10 wt % of component B, and, optionally, 0 to 10 wt % of component C. Component A comprises a first powder of about 60 to about 99.9 wt % of a crosslinkable, silane-grafted, olefinic interpolymer, and, optionally, about 0.1 to about 40 wt % of a crosslinkable, silane-grafted, crystalline polypropylene homopolymer or interpolymer. Component B comprises a second powder of about 98 to 99.9 wt % of a crosslinked, silane-grafted, olefinic interpolymer, and from about 0.1 to 2 wt % of a cure catalyst. Component C comprises a crystalline polyolefin powder having a particle size of not greater than 500 microns. Optionally, the polyolefin powder blend of A, B, and C contains a blowing agent, typically a chemical blowing agent. Components A and B are prepared independently and blended together, optionally with Component C, to prepare the polyolefin powders of this invention. If Component C is absent from the polyolefin blend powder of the invention, then Component A comprises a polypropylene homopolymer or interpolymer.
In another embodiment of the invention, a process for preparing a polyolefin powder comprises the steps of:
(A) Contacting under grafting conditions (i) at least one olefinic interpolymer (ii) an unsaturated silane compound, and (iii) a free radical generating compound, to form a first silane-grafted, olefinic interpolymer;
(B) Melt blending from about 60 to about 99.9 wt % of the first silane-grafted, olefinic interpolymer with about 0.1 to about 40 wt % of at least one crosslinkable, silane-grafted, crystalline polypropylene homopolymer or interpolymer to form a first polymer blend;
(C) Forming the first polymer blend into a first powder;
(D) Mixing under grafting conditions (i) an olefinic interpolymer (ii) an unsaturated silane compound, and (iii) a free radical generating compound, to form a second silane-grafted, olefinic interpolymer,
(E) Curing the second silane-grafted olefinic interpolymer to a gel content of at least 10%;
(F) Forming the second silane-grafted, olefinic interpolymer into a second powder; and
(G) Mixing the first and second powders to form a polyolefin powder comprising about 90 to 95 wt % of the first powder and about 5 to 10 wt % of the second powder.
Certain of the steps of the process can be practiced in any order, e.g., steps D-F can precede or be performed simultaneously with steps A-C. In addition, step (G) can further comprise mixing the first and second powders with about 0.1 to about 10, preferably about 1 to about 8 and more preferably about 2 to about 7, wt % of a crystalline polyolefin powder having a particle size of not greater than about 500 microns.
In another embodiment of the invention, a process for preparing a polyolefin powder comprises the steps of:
(A) Melt blending from about 60 to about 99.9 wt % of at least one olefinic interpolymer with about 0.1 to about 40 wt % of at least one crystalline polypropylene homopolymer or interpolymer into a olefinic interpolymer blend;
(B) Contacting under grafting conditions (i) an olefinic interpolymer blend from step (A) (ii) an unsaturated silane compound, and (iii) a free radical generating compound, to form a first silane-grafted, olefinic interpolymer blend;
(C) Forming the first silane-grafted olefinic interpolymer blend into a first powder;
(D) Mixing under grafting conditions (i) at least one olefinic interpolymer (ii) an unsaturated silane compound, and (iii) a free radical generating compound, to form a second silane-grafted, olefinic interpolymer,
(E) Curing the second silane-grafted olefinic interpolymer to a gel content of at least 10%;
(F) Forming the second silane-grafted, olefinic interpolymer into a second powder; and
(G) Mixing the first and second powders to form a polyolefin powder com
Clayfield Timothy E.
Cree Stephen H.
Dupont Dow Elastomers L.L.C.
Nutter Nathan M.
Whyte Hirschboeck Dudek SC
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