Polyolefin sheets and polyolefin coatings of substrates

Details Polyolefin sheets and polyolefin coatings of substrates Polyolefin sheets and polyolefin coatings of substrates

1999-03-24

2001-06-26

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...

C525S240000

Reexamination Certificate

active

06251995

ABSTRACT:

The invention relates to polyolefin sheets and/or polyolefin coatings of substrates, such as textile fabrics, plastic sheets, paper, cardboard and metal with a high dimensional accuracy and a thermal shock stability, which are suitable for use in the sectors of packaging, foods, pharmacy, textile and hygiene industry, in automobile construction, equipment construction and machine construction, electrical engineering, electronics, domestic appliances, medicine, the building industry, transport systems and transport packaging, as well as to a method for their production.
Polyolefin sheets and polyolefin coatings based on polyolefins such as polyethylene or polypropylene are known (G. Schenkel, Kunststoff-Extrudertechnik, Carl-Hanser-Verlag, Munich, 1963; W. Pred{umlaut over (Hl)}, Folienextrusion mit Coextrusion (Sheet Extrusion with Coextrusion, VDI-Verlag, Dusseldorf 1980).
Polyethylene can be processed into sheets and coatings with good dimensional accuracy. However, the disadvantage of sheets and coatings, based on polyethylene, lies in the low thermal shock stability (Vicat B softening temperature of 78° C.), so that sheets and coatings cannot be used in fields, in which they are subjected to brief thermal stresses of more than 100° C., such as those caused by steam or by a thermal shock stress exerted on vehicle or equipment parts or by a short-circuit stress of electrical equipment or cables up to a power failure.
Known methods of increasing the thermal shock stability of polyethylene sheets and coatings are the cross linking by ionizing radiation (N. Brooks, J. of Indust. Irradiation Tech. 1 (3), 237-257), the graffing of silane compounds and the hydrolytic cross linking of grafted copolymers (H. Vogt, Kunststoffe 82, (1992) 9, 830-833), as well as the cross linking by peroxides (M. Dorn, Kunststoffe 90 (1990), 7, 830-837). A thermal shock stability of up to 100° C. is achieved for polyethylene by cross linking. The high expense of the additional processing steps and the inability to recycle the products are, however, disadvantages.
Sheets and coatings of polypropylene, with a Vicat B temperature of 86°-94° C., can be exposed briefly to a thermal shock stress of up to 140° C. The low dimensional accuracy is a disadvantage of sheets and coatings of polypropylene. During the production of sheets and coatings, “neck ins” transversely to the take-off direction occur already at medium take-off speeds and express themselves in a fluctuating width and thickness of the sheets and coatings.
For flat film extrusion, such as the chill roll extrusion, the extrusion coating and glazing roller methods, there are extreme flow irregularities, especially in the edge region, as the take-off speed or the output increases. These “draw variations” make it impossible to produce a sheet or a film coating with a uniform distribution of thicknesses and a constant sheet width. In many cases, this leads to plant stoppages because of tears, holes or to uncontrollable take-off or winding up or to an uneconomic production due to the low take-off speeds or the low output.
In the blown film process, there are instabilities in the blown film of conventional polypropylenes as the throughput or speed of the plant increases and this, in turn, leads to fluctuations in thickness and width. In many cases, the pumping of the blown film results in tears and, consequently, to a complete stoppage of the plant.
Known methods of improving the dimensional accuracy of sheets and coatings of polypropylene consist of using blends of polypropylene and 5 to 20% polyethylene (U.S. Pat. No. 4,526,919, Japanese patent 53 128 662, Japanese patent 59 049 921), blends of polypropylene, polystyrene and polybutadiene (German patent 2937528) or blends of polypropylene and poly(meth)acrylates (U.S. Pat. No. 5,506,307, European patent 570,221) for the production of sheets or coatings. However, it is a disadvantage of these additions that the thermal shock stability is decreased and the transparency of the sheets and coatings is decreased greatly.
It is an object of the present invention to develop sheets and coatings based on polypropylene, which have a high dimensional accuracy and thermal shock stability, as well as to develop a method for their production.
The inventive objective was accomplished by polyolefin sheets and/or polyolefin coatings of substrates, such as textile fabrics, plastic sheets, paper, cardboard and metal with a high dimensional accuracy and thermal shock stability, the polyolefin sheets and/or polyolefin coatings consisting of modified polypropylenes, which are present up to 100% by weight and preferably from 5 to 50% by weight in admixture with unmodified polypropylenes, and the unmodified polypropylenes consisting preferably of 95 to 50% by weight of
1) conventional polypropylene polymers, preferably propylene homopolymers and/or copolymers of propylene, ethylene and/or &agr;-olefins, which were produced using Ziegler-Natta catalysts or metallocene catalysts and contain 4 to 18 carbon atoms and have a propylene content of 80.0 to 99.9% by weight, in the form of random copolymers, block copolymers and/or random block copolymers with melt indexes of 0.1 to 300 g/10 min at 230° C./2.16 kg and preferably 1 to 100 g/10 min at 230° C./2.16 kg, and/or
2) a polyolefin mixture with an Mw/Mn ratio of 2 to 6 and a melt index of 1 to 40 g/10 min at 230° C./2.16 kg, which consists of
 2.1) 60 to 98% by weight of a crystalline copolymer of 85 to 99.5% by weight of propylene and 15 to 0.5% by weight of ethylene and/or an &agr;-olefin of the general formula CH
2
═CHR, in which R is a linear or branched alkyl group with 2 to 8 carbon atoms,
 2.2) 2 to 40% by weight of an elastic copolymer of 20 to 70% by weight of ethylene and 80 to 30% by weight of propylene and/or an &agr;-olefin of the general formula CH
2
═CHR, in which R is a linear or branched alkyl group with 2 to 8 carbon atoms, and/or
3) largely amorphous polypropylenes or propylene copolymers with a crystalline polypropylene or crystalline propylene copolymer content of less than 10% by weight, an enthalpy of melting of less than 40 J/g and a melt index of 0.1 to 100 g/10 min at 230° C./2.16 kg, the largely amorphous polypropylene being a homopolymer of propylene and/or a copolymer of propylene of at least 80 mole percent of propylene and not more than 20 mole percent of one or more &agr;-olefins of the general formula CH
2
=CHR, in which R is a linear or branched alkyl group with 2 to 8 carbon atoms, and/or
4) non-isotactic propylene homopolymers with a melting point of 145° to 165° C. and a melt viscosity of 200,000 cps at 190° C., a heat of crystallization of 4 to 10 cal/g and a 35% by weight to 55% by weight solubility in diethyl ether,
 the polypropylenes containing 0.01 to 2.5% by weight of stabilizers, 0.01 to 1% by weight of processing aids and, optionally, 0.1 to 1% by weight of antistats, 0.2 to 3% by weight of pigments, 0.05 to 1% by weight of nucleating agents, 2 to 20% by weight of flame retardants, in each case based on the sum of the polypropylenes, as auxiliary materials and/or optionally 10 to 70% by weight and preferably 20 to 50% by weight, based on the sum of the polypropylenes, of inorganic and/or organic fillers and/or reinforcing materials,
 the modified polypropylenes, pursuant to the invention, being modified propylene polymers with melt indexes of 0.1 to 50 g/10 min at 230° C./2.16 kg and preferably of 1 to 40 g/10 min at 230° C./2.16 kg, and a ratio of the intrinsic viscosity of the modified polypropylene to the intrinsic viscosity of the unmodified polypropylene of largely the same weight average molecular weight being 0.20 to 0.95, and being produced
a) by the treatment of propylene homopolymers and/or copolymers of propylene and ethylene or &agr;-olefins with 4 to 18 carbon atoms as well as of mixtures of said polypropylenes with multi-functional ethylenically unsaturated monomers in the presence of ionizing radiation or of thermally decomposing free radical-forming agents or
b) by the reaction o

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