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
1994-10-11
2001-05-22
Woodward, Ana (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...
C525S179000, C525S182000, C525S183000, C428S409000
Reexamination Certificate
active
06235837
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to articles of manufacture that are based on a mixture of polyamide and polyolefin resins. Such articles are made by multi-port injection molding processes, and as a result of these processes, the articles include a weld line. One of the preferred aspects of the present invention involves the configuration of such articles as automobile fenders.
BACKGROUND OF THE INVENTION
Polyamide polyolefin mixtures are known to combine the advantages of polyolefins (ease of injection molding, chemical resistance, insensitivity to moisture) and of polyamides (good mechanical properties).
Mixtures based on polyamide and polyolefin have been described in Patent Application publication EP 342066. Since polyamides and polyolefins are not very compatible, it is necessary either to graft a proportion of the polyolefin, for example with maleic anhydride (forming a maleinized polyolefin), or to add a third substance (compatibilizing agent). EP 342066 shows the advantage of some third substances for obtaining mixtures of polyamides and polyolefin which have good mechanical properties. However, if these mixtures of polyamide and polyolefin are employed for making articles which have a weld line, ruptures may occur along this line.
The weld line in an article is the meeting of two flows of molten polymers when the article is manufactured, for example by injection molding at two or more points in the mold. At the junction of two or more molten polymer flow fronts, characteristic regions are formed, called weld lines or knit lines. Injection molding of complex articles is practically impossible to carry out without weld lines.
The morphology and the mechanical properties of articles with weld lines differ substantially from those that are devoid of them. In general, the weld lines exhibit an orientation of the material which is parallel to the plane of welding, and give rise to a considerable embrittlement of the articles. In the case of mixtures of incompatible polymers the weld lines have particularly dramatic effects because of the heterogeneous nature of these materials. Increasing the temperatures of the mold and of the material does not suffice to improve appreciably the toughness of the weld lines.
An article by B. Fisa et al., “Effect of an Ionomer Compatibilizer on the Structure and Mechanical Properties of Injection molded PA6/HDPE Blends”, which appeared in ANTEC '91, pages 1135-1139, describes the effect of a compatibilizing agent for improving the tensile strength of the weld lines. This agent is an ethylene/methacrylic acid/isobutyl acrylate copolymer. The methacrylic acid is 70% neutralized with zinc.
Patent Application JP 1 284785 of Nov. 2, 1989 published on Jun. 21, 1991 under no. JP 3146552 describes mixtures including 80 to 40% of polyamide, 1 to 40% of a modified polyolefin, and 20 to 60% of polypropylene and such that the ratio of the viscosity of the polypropylene to the viscosity of the polyamide is higher than 0.75 when these viscosities are measured at the molding temperature and at a shear rate of 3500 s
−1
. These mixtures are particularly suitable for being painted or metallized. Nothing is mentioned concerning the behaviour of weld lines.
SUMMARY OF THE INVENTION
A new mixture of polyamide and polyolefin has now been-found which has a satisfactory elongation at break at the weld lines. This elongation may be obtained without the use of a compatibilizing agent. When such an agent is employed, the present invention allows a great degree of latitude in its selection.
The present invention makes it possible to solve to a large extent the problems linked with the process of injection molding of polyamide/polyolefin mixtures, in particular improving the behaviour of the weld lines and reducing the phenomenon of surface delamination. Furthermore, injection-molded articles made in accordance with the present invention have improved mechanical properties.
The present invention includes an article that is based on a mixture of polyamide and polyolefin and that has at least one weld line, characterized in that:
the ratio of the viscosities of the polyolefin to the polyamide, measured at a shear rate higher than 100 s
−1
, is greater than 0.70,
the quantity of polyamide is sufficient for the elongation at break to be greater than 10 percent.
Thus, in one aspect, the present invention provides an article of manufacture made by injection-molding a resinous mixture comprising polyamide and polyolefin through two or more mold ports wherein (a) the relative amount of polyamide resin in said resinous mixture is from 58-75 weight-percent and (b) the elongation at break of said article is greater than 10%.
Another aspect of the present invention relates to articles of manufacture made by injection-molding resinous mixtures through two or more mold ports wherein said resinous mixtures comprise from 60-70 weight-percent polyamide, from 20-30 weight-percent polyolefin, from 3-10 weight-percent compatibilizing agent, and optionally approximately 10 weight-percent of a shock resistance agent.
Still another aspect of the present invention is a method of making an automobile fender which comprises providing an openable mold comprising a cavity having the shape of the automobile fender to be made and a plurality of injection ports, providing a resinous mixture comprising from 60-70 weight-percent polyamide, from 20-30 weight-percent polyolefin, and from 3-10 weight-percent compatibilizing agent in a reservoir outside of said mold cavity, heating said resinous mixture to a temperature sufficiently high to maintain said mixture in a flowable condition, injecting the flowable mixture into the mold cavity via the plurality of injection ports, cooling the mold and resinous mixture to a temperature sufficiently low to maintain said mixture in a solid condition, opening said mold, and removing the solid resinous mixture in the form of an automobile fender.
Finally, in order to accomplish aspects thereof such as those outlined above, the present invention makes use of various novel compositions of matter. Among them are compositions of matter comprising 60-70 weight-percent polyamide resin, 20-30 weight percent polypropylene, 3-10 weight-percent maleinized polypropylene grafted with polyamide, and optionally about 10 weight-percent maleinized ethylene-propylene copolymer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The resinous mixture according to the present invention comprises a polyamide matrix. Any polyamide may be employed. Nylon polyamides such as PA6, PA66, PA11, and PA12 have been found to be particularly suitable.
A person skilled in the art can determine the quantity of polyamide to obtain an elongation at break higher than 10%. For example, if PA6 or 66 is employed, the mixture must contain at least 58% by weight of polyamide and preferably will contain 60 to 70%.
The polyolefin may be polyethylene, polypropylene, their copolymers, or ethylene/butene copolymers, and the like. Polypropylene homopolymer or copolymer is advantageously employed, for example block or statistical propylene/ethylene copolymers and propylene/butene copolymers. Polypropylene is currently the preferred polyolefin. Most preferred are polypropylenes having a melt flow index (MFI), measured at 230° C./2.16 kg, lower than 0.5.
The polyolefin may be a wholly or partially modified polyolefin. It may be, for example, a polyolefin that has at least one functional group chosen from carboxylic acids, carboxylic esters, acid anhydrides, and epoxy groups, for example the following copolymers: ethylene/alkyl (meth)acrylate, ethylene/alkyl (meth)acrylate/maleic anhydride, ethylene/alkyl (meth)acrylate/glycidyl (meth)acrylate, ethylene/vinyl acetates ethylene/vinyl acetate/maleic anhydride, ethylene/vinyl acetate/glycidyl (meth)acrylate, ethylene/vinyl acetate grafted with maleic anhydride, ethylene/alkyl (meth)acrylate grafted with maleic anhydride, and homo- or copolyolefins optionally grafted with maleic anhydride.
The viscosities that characterize the components of th
Basset Dominique
Bouilloux Alain
Le Du Yves
Atofina
Pennie & Edmonds LLP
Woodward Ana
LandOfFree
Article including a weld line based on a mixture of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Article including a weld line based on a mixture of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Article including a weld line based on a mixture of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2499763