Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-11-29
2003-08-12
Shosho, Callie (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S212000, C525S101000, C525S179000, C524S506000, C524S536000, C524S538000
Reexamination Certificate
active
06605656
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a thermoplastic resin composition that demonstrates improved surface durability properties. More specifically, the invention relates to a polyolefin alloy blended with a polyamide and manipulated in such a manner as to selectively segregate the polyamide toward the front of a melt flow of the resin. Also, the invention relates to the addition of a compatibilizing agent in relatively small amounts to increase the interphase strength between the polyolefin and polyamide components, thereby overcoming the natural incompatibility of these two materials. The invention affords improved resistance to scratching, marring and gouging while maintaining the other well-recognized benefits of polyolefin alloys, such as superior moldability.
BACKGROUND OF THE INVENTION
Thermoplastic resins are commonly used in automotive interior components, such as instrument panels, and exterior components, such as bumpers and/or trim. Polypropylene resins are often used for these articles due at least in part to their superior moldability. Polypropylene resins offer a material that can be readily formed into components of various shapes and sizes by techniques well known in the art, such as injection and blow molding. Unfortunately, polypropylene demonstrates poor resistance to various types of surface impacts. Consequently, components manufactured from polypropylene resins often exhibit susceptibility to scratching, marring, and gouging.
Various techniques have been proposed for increasing the resistance of polyolefin resins, such as polypropylene, to surface impacts. For example, some current components utilize a migratory scratch protection package to bolster resistance to these defects. For example, work reported by Jack Chu (SPE ANTEC Proceedings, 1999) indicated that the use of high molecular weight “euracamides”, when added to a thermoplastic olefin material, could increase the scratch propensity of the material. Work described by Dow Corning (SPE TPO in Automotive Proceedings, 2000) indicates that the use of high molecular weight siloxane masterbatches, when used in conjunction with thermoplastic olefins, can also increase the scratch resistance of the material. Unfortunately, while these add-ins may confer some protection against damage, they greatly limit other aspects of components manufactured from the modified polyolefin resin. For example, the scratch protection add-in may limit the paintability of the component, thereby reducing the ability to make the component visually appealing. Also, the add-in may evaporate or whiten over time, thereby causing a displeasing change in the visual appearance of the component over time. Other approaches include the addition of filer materials, such as silica, to a polyolefin material. JP 1318051 (Toray Siliconekk) discloses polyolefins that are modified in this manner. The silica filler may have been treated with silicone type compounds. The disclosed polyolefins, however, are not alloys.
The use of polyamides as add-ins to improve desirable qualities of polypropylene has been attempted. However, the natural incompatibility of these two materials causes a delamination effect and no desired material can be obtained by simple melt mixing. Therefore, if a polyamide is to be used to improve the qualities of polypropylene, the incompatibility of materials must be addressed. One approach to addressing this incompatibility is presented in Japanese Patent Publication No. 30945. The approach of this reference involves grafting a polypropylene with an unsaturated carboxylic acid or a derivative thereof. This approach makes a polypropylene and a polyamide compatible with each other. However, the approach of this reference is not satisfactory when an ordinary polyamide, such as nylon-6, nylon-6,6, and nylon-12, or the like, is used. To significantly improve the impact resistance of polypropylene by addition of a polyamide, the physical location of the polyamide in the alloy is critical.
U.S. Pat. No. 5,206,284 to Fukui, et al. teaches a polypropylene thermoplastic resin comprising, in part, a modified polypropylene obtained by grafting an unsaturated carboxylic acid or a derivative thereof, and a modified polyamide obtained by partially or wholly modifying a polyamide with a clay mineral. In this reference, the authors overcame the incompatibility of polypropylene and polyamide by modifying both the polypropylene and the polyamide. While this approach does overcome the incompatibility of these two materials and does not increase the heat stability of molded components, resins according to this approach still are prone to surface damage and have poor paintability.
Consequently, there is a need for a thermoplastic resin composition that retains the desirable attributes of a polyolefin alloy, e.g., superior moldability, while improving surface durability without imparting adverse properties, such as poor paintability and whitening, or decreased impact resistance, onto the polyolefin alloy.
SUMMARY OF THE INVENTION
The current invention provides the desired resin by teaching a resin comprising a polyolefin alloy, a polyamide, and a compatibilizing agent. The materials utilized in the resin have a difference between their respective melt flow rates such that the polyamide is selectively segregated to the surface of the component during the molding process. In this configuration, the polyamide, preferably nylon, provides excellent resistance to surface impacts. Compatibility between the polyolefin alloy and polyamide phases is obtained by the addition in small amounts of a compatibilizing agent. Also, the stiffness or modulus of molded parts can be increased by adding inorganic nanocomposite materials, such as clay, talc, silica, and wollastonite, to the resin.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a thermoplastic resin that comprises a blend of a polyolefin alloy, a polyamide, and a compatibilizing agent. The polyolefin alloy, also commonly referred to as a thermoplastic olefin alloy, and polyamide components of the thermoplastic resin are selected so that the melt flow of each component is such that the polyamide selectively segregates itself towards the front of a melt flow of molten resin. This allows the thermoplastic resin of the present invention to achieve the desired results. That is, this property allows the polyamide to confer its resistance to surface impacts onto parts molded from the thermoplastic resin. The compatibilizing agent increases the strength between the polyolefin alloy and polyamide phases, thereby overcoming the natural incompatibility between these two phases. The thermoplastic resin of the present invention can also include a filler material to increase the stiffness or modulus of parts molded from the resin.
Polyolefin alloys are frequently used in the art as thermoplastic resins. These alloys are blends of a polyolefin with an alloy component, such as rubber. Essentially any polyolefin alloy can be used in the current invention, as long as its melt flow rate is sufficient as compared to that of the polyamide component. That is, the polyolefin alloy must have a lower melt flow rate than that of the polyamide. Having a lower melt flow rate, the alloy is the more viscous component of the blend and, therefore, is more resistant to flow than the polyamide component. This ensures that the polyamide component will migrate to the front of the melt flow during manufacturing of the resin and parts made therefrom. In preferred compositions, the polyolefin component can be any polyolefin suitable for use as a thermoplastic resin and able to form a desired alloy, such as polypropylene, polyethylene, blends of polypropylene with high density polyethylene, polypropylene blended with ethylene propylene copolymer, and polypropylene blended with ethylene butene copolymer. In preferred resin compositions according to the present invention, the alloy component can be rubber, styrene, acrylic, or ionomer. The alloying component is selected such that it imparts toughn
Ryntz Rose A.
Wichterman Beth M.
Brinks Hofer Gilson & Lione
Shosho Callie
Visteon Global Technologies Inc.
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