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
2000-06-07
2002-11-05
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
06476135
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a polyolefin composition containing a crystalline propylene homopolymer having a high melt flow rate, and an olefin polymer composition, as well as fiber and nonwoven fabric prepared therefrom. Nonwoven fabrics prepared from fibers of this polyolefin composition exhibit a desirable combination of acceptable tensile strength, superior cross-directional fabric elongation, good processability, and improved fabric softness and drape.
U.S. Pat. No. 5,460,884 discloses a nonwoven fabric prepared from a polyolefin composition having a highly crystalline propylene homopolymer as a major component and a heterophasic ethylene/propylene random copolymer as a minor component. The nonwoven fabric is said to be very strong but yet soft in comparison to comparable nonwoven fabrics.
Nonwoven fabrics have gained acceptance in various products, including diapers, disposable medical products and personal hygiene products. Nonwoven fabrics destined for use in these applications may be subjected to post-manufacturing finishing operations such as coating or stretching. Fabrics having high tensile strength can be difficult to process, and also may exhibit inadequate suppleness (“drape”) as well as reduced fabric elongation.
Nonwoven fabrics prepared from polyolefin fibers having a high melt flow rate have been proposed. Thus, U.S. Pat. No. 5,529,850 discloses fibers and nonwoven fabrics produced from crystalline propylene polymers and copolymers having a polydispersity index of 2.5 to 3.7 and a melt flow rate of from 600 to 2000 g/10 minutes.
An object of this invention is to provide a polyolefin composition capable of being formed into fibers of fine diameter.
Another object of this invention is to provide a polyolefin fiber capable of being formed into a nonwoven fabric having a combination of desirable properties, including acceptable tensile strength, superior cross-directional fabric elongation, good processability, and improved fabric softness and drape.
A feature of this invention is a polyolefin composition which includes an as-polymerized, high melt flow rate (MFR) propylene homopolymer and a random copolymer of propylene and ethylene and/or a C
4-10
alpha-olefin.
Another feature of this invention is a fiber prepared from this polyolefin composition and which has a diameter of from 15 to 23 microns.
Yet another feature of this invention is a nonwoven fabric prepared from this polyolefin fiber and which has superior cross-directional fabric elongation, as measured by peak tensile elongation.
An advantage of the nonwoven fabric of the present invention is that it has improved processability, softness and drape.
SUMMARY OF THE INVENTION
The present invention relates to a polyolefin composition comprising:
A. 45 to 5 weight percent of a low viscosity propylene homopolymer having an as polymerized MFR of from 250 to 550 g/10 minutes, as measured by D-1238, Condition L (230° C./2.16 Kg); and
B. 55 to 95 weight percent of an olefin polymer composition selected from the group consisting of
(1) a random copolymer of propylene and ethylene and/or a C
4-10
alpha-olefin, with the copolymer containing from 90 to 99 weight percent propylene;
(2) a propylene polymer composition consisting essentially of:
(a) from 30 to 65% of a copolymer of propylene with a C
4-8
alpha-olefin, which contains from 80 to 98% propylene, and
(b) from about 35 to 70% of a copolymer of propylene with ethylene having an ethylene content of from 1 to 10% or a terpolymer of propylene with ethylene and a C
4-8
alpha-olefin having a total comonomer content is from 2 to 10%;
(3) an olefin polymer composition consisting essentially of:
(a) from 10 to 50% of a propylene homopolymer having an isotactic index of from 80 to greater than 99%, or a copolymer selected from the group consisting of (i) propylene and ethylene, (ii) propylene, ethylene and a CH
2
═CHR alpha-olefin, where R is a C
2-8
straight or branched alkyl, and (iii) propylene and a CH
2
═CHR alpha-olefin, where R is a C
2-8
straight or branched alkyl, wherein said copolymer contains from 85 to 99% propylene, and having an isotactic index greater than 80 to 98%,
(b) from 5 to 20% of a semi-crystalline, essentially linear copolymer fraction having a crystallinity of about 20 to 60%, by differential scanning calorimetry (DSC), wherein the copolymer is selected from the group consisting of (i) ethylene and propylene containing over 55% ethylene; (ii) ethylene, propylene, and a CH
2
═CHR alpha-olefin, where R is a C
2-8
straight or branched alkyl, containing from 1 to 10% of the alpha-olefin and over 55% up to 98% of both ethylene and alpha-olefin; and (iii) ethylene and a CH
2
═CHR alpha-olefin, where R is a C
2-8
straight or branched alkyl, containing over 55% up to 98% of said alpha-olefin, which copolymer is insoluble in xylene at room or ambient temperature, and
(c) from 40 to 80% of a copolymer fraction selected from the group consisting of a copolymer of (i) ethylene and propylene wherein the copolymer contains from 20% to less than 40% ethylene; (ii) ethylene, propylene, and a CH
2
═CHR alpha-olefin, where R is a C
2-8
straight or branched alkyl, wherein the alpha-olefin is present in an amount of from 1 to 10% and the amount of ethylene and alpha-olefin present is from 20% to less than 40%; and (iii) ethylene and a CH
2
═CHR alpha-olefin, where R is a C
2-8
straight or branched alkyl, containing from 20 to less than 40% of the alpha-olefin, and optionally with 0.5 to 10% of a diene, said copolymer fraction being soluble in xylene at ambient temperature, and having an intrinsic viscosity of from 1.7 to 3.0 dl/g, wherein the total amount of ethylene units or said alpha-olefin units in the olefin polymer composition, or of ethylene and said alpha-olefin units when both are present in the olefin polymer composition is from 15 to 35%, the total amount of (b) and (c) fractions, based on the total olefin polymer composition is from about 65% to 80%, the weight ratio of (b)/(c) is from 0.1 to about 0.3 and the total content of ethylene or C
4-8
alpha-olefin or combination thereof in (b+c) is less than 50%;
(4) a thermoplastic olefin composition consisting essentially of:
(a) from 10 to 60% of a propylene homopolymer having an isotactic index greater than 90 or a crystalline propylene copolymer with ethylene and/or C
4-8
alpha-olefin having a propylene content greater than 85% and an isotactic index of greater than 85%;
(b) from 30 to 60% of an amorphous ethylene-propylene copolymer fraction, optionally containing minor amount of a diene, which is xylene soluble at room temperature, and contains from 40 to 70% ethylene; and
(c) from 8 to 40% of a semi-crystalline ethylene-propylene copolymer which is xylene insoluble at room temperature,
(5) a linear low density polyethylene containing up to 20%, by weight, of a C
4-8
&agr;-olefin having a density of from 0.88 to 0.945 g/cm
3
and a melt index of from 0.1 to 35 g/10 min;
(6) a high melt strength propylene polymer having a branching index of less than 0.9 or a melt tension of 3 to 28 cN; and
(7) mixtures thereof.
The present invention also relates to fibers prepared from this polyolefin composition, with the fibers having a diameter of from 15 to 23 microns.
In another embodiment, the present invention is a nonwoven fabric prepared from fibers made from the polyolefin composition.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The polyolefin composition of the present invention contains from 5 to 45, preferably 5 to 40, and most preferably 10 to 40, weight percent of a low viscosity propylene homopolymer. The propylene homopolymer may be prepared by polymerization of propylene using known Ziegler-Natta catalyst systems and according to known methods operating in liquid phase comprising the propylene monomer or a solution thereof, in an aliphatic or aromatic hydrocarbon solvent, or in gas phase, or combining liquid and gas polymerization steps.
The polyolefin composition of the present invention also contains from 55 to
Bugada Daniele C.
Starsinic Michael E.
Basell Poliolefine Italia S.p.A.
Nutter Nathan M.
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