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
2002-06-07
2004-03-23
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...
C525S192000, C525S197000, C525S232000, C525S240000, C524S424000, C524S425000, C524S449000, C524S451000
Reexamination Certificate
active
06710131
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to melt processable thermoplastic polyolefin blends and a process for the preparation of a melt processable thermoplastic polyolefin blend. More particularly, the present invention relates to a process for the preparation of a polypropylene copolymer blend with EPDM and other ingredients using a twin screw extruder or Buss co-kneader. The blends of this invention exhibit very high impact strength at moderate concentrations of EPDM and enable injection molding, thermoforming and other conventional techniques to be applied for making end products that demand high impact strength such as bumpers for cars/jeeps and other light automobile vehicles.
BACKGROUND OF THE INVENTION
In the early 1970's interesting opportunities arose in the automotive field for plastic materials having a specific requirement with respect to weight reduction, safety, production and maintenance costs. The first application was that of bumpers. Automobile bumpers were traditionally made of chromium plated metal and thus were heavy, expensive and too stiff. The use of polymer blends such as elastomer modified polypropylene in place of metal solved a majority of these problems. Elastomer modified isotactic polypropylene exhibits considerable impact strength, good dimensional stability, low weight, low production and maintenance costs.
Significant developments took place in Italy in respect of plastic automobile bumpers. The consumption of elastomer modified polypropylene expanded rapidly in Italian and then in other European markets. Other thermoplastic materials, particularly modified polycarbonate and modified polybutylene terephthalate were also considered for similar applications. However, elastomer modified polypropylene offered the same performance at a substantially lesser cost.
Plastic automobile bumpers entered the Indian market along with the Maruti car production in India. Initially, the bumpers were molded in India with an imported blend from Japan. JP 04,214,711 (1992) describes blends of thermoplastic polyolefins, polyurethanes from polyols, non-aromatic polyisocyanates and low molecular weight polyamines exhibiting appreciable impact strength and coatability properties. JP 03, 252, 436 (1991) claimed blends of ethylene-propylene block copolymer, ethylene-propylene rubber, non-crystalline nylon and modified polypropylene exhibiting excellent heat and impact resistance properties. JP 02,191,656 (1990) describes compounds of thermoplastic resins, rubbers, cross-linking monomers, and other additives possessing very high impact strength. JP 01,271,450 (1989) claims blends of ethylene-propylene block copolymer, ethylene-propylene rubber and talc exhibiting excellent impact strength and flexural modulus. U.S. Pat. No. 5,030,694 (1991) describes blends of ethylene-propylene copolymer with EPDM and organic peroxides exhibiting good melt flow, impact strength and flexural modulus. EP 435,247 (1991) illustrates blends of propylene polymer and multiphase propylene-vinyl monomer graft copolymer exhibiting good moldability, impact resistance and heat resistance properties. EP 373,834 (1990) describes compounds of hydrogenated diene-alkyl aromatic compound polymer, propylene polymer and polyoxyphenylene, polyamides, or thermoplastic polyesters possessing good impact strength.
In all the patents described above, the primary aim was to improve impact resistance. In an automobile bumper application, the primary concern is impact resistance (the item must remain undamaged when subjected to an impact of 4 kmph at −23° C., according to European regulations). In addition, higher stiffness, better aesthetics and environmental resistance are also important considerations. Further, since the bumper is to be assembled with metal parts, low linear thermal expansion coefficient is also required. Moreover, given that wide and thin shape of the bumper mold, enhanced flow at the molding temperature is also required.
The present invention takes into account all the above considerations in mind. The blends prepared in the invention can also be used for applications other than car bumpers where similar properties are required such as for molded luggage, furniture, automotive components and body panels and the like.
OBJECTS OF THE INVENTION
It is an object of this invention to provide blends of polypropylene copolymer with EPDM and other additives that allow injection molding, compression molding, thermoforming and other conventional techniques to be applied for making end products such as car bumpers that require, inter alia, high impact resistance.
It is another object of the invention to provide a process for the preparation of blends suitable for making car bumpers by injection molding.
It is another object of the invention to provide an improved process for the preparation of a blend with polypropylene copolymer, EPDM and other additives that exhibits suitable flow properties as well as mechanical properties (such as melt flow index: 10-15 g/10 minutes; flexural modulus: 8000-15000 kg/cm
2
; (notched Izod impact strength: 50-60 kg.cm/cm; and heat deflection temperature: 60-105° C.) necessary for injection molding of car bumpers as well as their property requirements.
It is another object of the present invention to provide an improved process for the preparation of blends for use in manufacture of car bumper with moderate concentrations of EPDM, filler, carbon black, and an organic peroxide using a twin screw extruder or a Buss co-kneader.
SUMMARY OF THE INVENTION
The present invention provides polypropylene copolymer blends with EPDM with or without a filler, carbon black, and an organic peroxide as well as a process for the preparation thereof by extruding the components in a twin screw extruder or a Buss co-kneader all together or in separate batches, while for example, the twin screw temperature is maintained in the range of 180 to 250° C. and the screws are rotated at a speed of 50 to 100 rpm.
Accordingly, the present invention relates to melt processable thermoplastic polyolefin blends comprising an intimate mixture of ethylene-propylene diene monomer (EPDM) in an amount of 5 to 25% by wt and a base block copolymer in an amount of 95 to 55% by wt, the balance if any comprising one or more conventional additives such as herein described, the polyolefin blend having a melt flow index in the range of 10 to 15 g/10 minutes when tested according to ASTM D1238.
The present invention also provides a process for the preparation of a melt processable thermoplastic polyolefin blend comprising, blending a base-block copolymer in an amount of 55 to 95% by wt of the total blend and EPDM in an amount of 25 to 5% by wt of the total blend, the balance if any comprising one or more of conventional additives, fillers, anti-oxidants, carbon black, melt flow enhancing additives.
In one embodiment of the invention, the blend has one or two melting peaks in the range of 160 to 170° C. when tested in a differential scanning calorimeter at a uniform heating rate of 10° C./minute in nitrogen environment.
In another embodiment of the invention, the ethylene content in EPDM is in the range of 55 to 65 wt %.
In yet another embodiment of the invention, the base block copolymer is a copolymer of ethylene and propylene.
In a further embodiment of the invention, an organic peroxide is added to the blend during blending operation in order to improve the melt flow index thereof.
In a further embodiment of the invention, the organic peroxide is selected from the group consisting of dicumyl peroxide, 2,5-dimethyl-2,5-di(tert.butyl peroxy)hexane and ditertiary butyl peroxide in the range of 0 to 2 wt %.
In yet another embodiment of the invention, carbon black is added in an amount of 0 to 20, preferably 12 wt % as a conventional additive.
In a further embodiment of the invention, conventional additive comprises of natural filler in an amount of 0 to 20 wt % and is selected from the group consisting of talc, calcium carbonate and mica.
In one embodiment of the invention, the polypropylene cop
Sastry Pendyala Veera Nageswara
Sodagudi Francis Xavier
Darby & Darby
Indian Petrochemicals Corporation Limited
Nutter Nathan M.
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