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
2002-04-26
2004-04-06
Acquah, Samuel A. (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...
C525S063000, C525S073000, C525S074000, C525S078000, C525S263000
Reexamination Certificate
active
06716926
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the modification of polyolefins to give them improved adhesion performances.
RELATED ART
Polyolefins are known to present poor adhesion to paints, glues and inks. To improve their adhesion properties they need to be chemically modified with polar groups. This could be achieved by blending or alloying the polyolefin resin with engineering polymers, by the functionalization of the polyolefin with specific monomers, or by applying post-treatment methods, such as the use of oxygen plasma and flaming. Polyolefins being modified by graft reactions performed in melt processing equipment, such as single or multiple screw extruders, include well known technologies widely reported in the technical literature.
U.S. Pat. No. 5,001,197 discloses a process for functionalization and preferably maleation of a polypropylene by the use of a selected class of peroxides that will not significantly decreased the molecular weight of the polypropylene.
EP 0 634 424 discloses a compound comprised of polypropylene and the reaction product of a maleated polypropylene and polyether amine. A process for producing the polymer compound involves two steps, first preparation of the maleated polypropylene, then reacting this maleated polypropylene with the polyether amine by melting the components in the presence of a polypropylene in a customary mixing apparatus.
U.S. Pat. No. 5,281,670 discloses a blend comprising polybutylene and functionalized polyolefins having an improved adhesion to metals and polar polymers. The blend can be made by any conventional blending process, which in general include the steps of tumbling the polybutylene and functionalized polyolefin in a mixer, feeding the mixture into a melt mixing device, such as a Brabender mixer or continuous single or twin screw extruder.
WO 96/06872 discloses a method of grafting a polypropylene resin with an allyl epoxy compound in the presence of styrene. The polypropylene mixed with the allyl epoxy compound, styrene and a peroxide initiator is heated to a suitable reaction temperature at conditions of continuous mixing, preferably in an extruder, until a desired degree of grafting has been obtained. The disclosures of this publication is included herein by reference.
U.S. Pat. No. 5,424,367 discloses an extruder having multiple reaction zones. Each reaction zone is provided with means for introducing reagents, mixing the reagents with polymer and removal of bi/co-products or unreacted reagents. Each reaction zone is followed by a purification zone where volatile products are vented off. This extruder is used in grafting a polyolefin with maleic anhydride, followed by imidization of the grafted anhydride with a primary amine in the second reaction zone.
The prior art grafting methods used to modify polyolefins will not result in a sufficient level of polar molecules in the surface layer of the final article to obtain an acceptable paintability. Moreover, the overall desired mechanical properties will become significantly reduced. Blending methods normally involve several compounding steps and the cost of the resulting material will hardly be justified. The post-treatment methods mentioned above, which are used to increase directly the polarity of the surface to be painted, are normally very time-consuming, and often high investments in special equipment will be needed. Therefore, it still exists a need for polyolefin resins that are available at an acceptable cost and which can be manufactured into final articles having an inherent paintability.
It has now surprisingly been found that an extrusion process may be used to obtain a modified polyolefin blend comprising polypropylene resins that are selectively functionalized with polar molecules. In a final article obtained according to the present invention the polar molecules will become localized in the surface layer of the article and thus make it paintable.
SUMMARY OF THE INVENTION
The present invention provides a process for obtaining a polyolefin composition endowed with improved adhesion performance, comprising the steps of premixing a high-flow polyolefin resin with one or more grafting monomers and initiator, optionally also one or more comonomers, feeding the obtained premix and a low-flow polyolefin resin into a mixing device, and gradually heating the components to above their melting points while being subjected to mixing forces.
The present invention also provides process for obtaining a polyolefin composition endowed with improved adhesion performance, comprising the steps of premixing a high-flow polypropylene polymer with one or more grafting monomers and initiator, optionally also one or more comonomers, feeding the obtained premix and a low-flow polyolefin resin into an extruder or a series of extruders provided with mixing elements, gradually heating the components to above their melting points while being subjected to mixing forces, and introducing at least one polyether amine into the extruder through a second inlet feed opening, downstream of the first inlet opening, localized at a point where at least a main part of the already introduced components are in a molten state.
DETAILED DESCRIPTION OF THE INVENTION
To obtain a polyolefin based article that can be painted, at least the surface layer of the article must contain polar groups that make the surface material compatible with the applied paint film material. By the present invention the polyolefin material is blended with a polar component that will migrate to the surface of the article and selectively provide the surface layer with polar groups which make the article paintable. To maintain the favourable properties of polyolefins both components should be based on polyolefin resins, preferably polypropylene based resins. Consequently, the polyolefin resin to be grafted is selected from polypropylenes having relatively short chain lengths. However, such polypropylene grades will not alone have an acceptable range of properties and therefore must be-supported by another polyolefin resin. Thus, in a final article the grafted polypropylene component will provide the paintability, and the other polyolefin components will provide the required mechanical properties.
According to the present invention it is provided a process for sequentially grafting a high-flow polypropylene resin and then blending this grafted resin with a low-flow polyolefin resin. The selected polypropylene and polyolefin grades must be matched with each other in such a way that the one to be grafted will melt first and react with the grafting monomers before any substantial part of the low-flow polypropylene component has melted. This is achieved by the process of the present invention.
In this application the term “high-flow resin” is used to describe a resin that melts relatively easy and has a lower melt viscosity, while the term “low-flow resin” is used to describe a resin that has a higher melt viscosity.
Suitable high-flow polypropylene resins to be used by the present process comprise all polypropylene homopolymers and copolymers that can be grafted with reactive, functionalizing agents. Particularly preferred polypropylenes are polypropylene homopolymers, and copolymers of propylene with ethylene, containing up to 30% of ethylene. These polypropylenes should preferably have a weight average molecular weight (MW) of 5000 to 500.000, preferably from 10.000 to 200.000. The melt flow index (MFI) should be in the range from 0.1 to 1000 g/10 min, preferably from 20 to 1000 g/10 min, more preferably from 20 to 100 g/10 min, determined according to the method of ASTM D 1238 (230° C. and 2.16 kg load). The polypropylene resins may be used as pellets or as a powder, preferably as a powder. The powder may be milled granules or corresponding material, or it may be the polymer substance as obtained from a polymerisation reactor, stabilized or non-stabilized.
Suitable low-flow polyolefin resins to be used by the present process in-principle comprise all polypropylene homopolymers and copolymers ha
Acquah Samuel A.
Asinovsky Olga
Borealis Technology Oy
Fay Sharpe Fagan Minnich & McKee LLP
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