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
1998-11-05
2001-06-19
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...
C525S241000, C057S244000, C057S400000, C428S373000, C428S392000, C428S394000
Reexamination Certificate
active
06248835
ABSTRACT:
BACKGROUND OF THE INVENTION
Without limiting the scope of the present invention, the background of the invention is described with reference to polymer blends, in particular, polymer blends useful and particularly adapted for the production of carpets and rugs. Due to widespread availability and economic factors, polypropylene is a material particularly suitable for use in carpet manufacture. However, polypropylene fiber, texturized and woven into carpets or rugs, typically does not possess all of the most desired properties for use as a material for carpet fibers.
In particular, polypropylene fibers, texturized and woven into carpets and rugs, typically do not possess the high resiliency characteristics of nylon or polyester fibers because of the relatively low glass transition temperature, (T
g
), of the polypropylenes utilized to produce such fibers. Since the glass transition temperature of the polypropylenes utilized to produce carpet fibers is typically below room temperature, the molecular mobility of the polypropylene molecules is such that the fibers deform, without substantial recovery, in the direction of the applied load. Consequently the use of polypropylene fibers in the manufacture of carpets and rugs has been limited.
Typically, the glass transition temperature of commercially available polypropylene is in the range of 0° C. Thus, at room temperature, portions of polypropylene molecules, especially amorphous segments, retain mobility over a significant range of the segment length. Consequently, if a load is placed upon a carpet produced from polypropylene fibers at room temperature, the polypropylene molecules tend to relax in the direction of stress and retain the imposed deformation after the load is removed. One way of minimizing non-reversible fiber deformation is to raise the glass transition temperature of the polymer. If the glass transition temperature of the material can be increased, the effect of segmental molecular deformations can be reduced or significantly reduced. Thus, if the glass transition temperature of the polymer is increased, the fiber will be more likely to recover from the deformation after the load is removed.
One way of increasing the glass transition temperature of a polymer is to increase the size of the pendant groups on the polymer backbone. For example, in the case of polypropylene, increasing the glass transition temperature could theoretically be accomplished by replacing some of the pendant methyl groups with larger pendant groups. One way of achieving this result would be to copolymerize propylene with bulkier olefins. However, as a practical matter, copolymerization with a higher olefin is not necessarily a commercially feasible solution due to numerous factors, including loss of productivity due to decreased polymerization rates and a decrease in the control over the physical properties of the resulting copolymer.
Another approach to increasing the glass transition temperature of polypropylene is to physically mix another polymer with a higher glass transition temperature with the polypropylene. The added polymer must, however, be physically compatible with polypropylene and economically feasible to use in the desired application. Because physical mixtures of different polymers adhere to each other via secondary bonding forces, the chemical composition, crystal structure, morphology and molecular weight all impact on the compatibility of the polymers. Finally, the polymer blend should be adaptable to processing, utilizing existing process equipment and conditions.
One article, Gupta et al., “Processability and properties of yarns made from polypropylene containing small amounts of polystyrene”,
J. Appl. Polm. Sci.
60, 1952 (1996), reports higher drawability and elongation with the addition of polystyrene to polypropylene. However, the maximum draw ratio reported in the Gupta article was 5.1 at a wind up speed of 750 (m/sec). Additionally, the reported tenacity of the resultant fiber was relatively low and the reported thermal shrinkage of the fibers was relatively high.
Thus, there exists a need for an improved blended polypropylene for use in the manufacture of fibers, and in particular, polypropylene fibers that exhibit improved resiliency, tenacity, processability and thermal resistance.
SUMMARY OF THE INVENTION
In one embodiment, the present invention provides a polymer blend comprising from 92 wt % to 98.5 wt % of a base polypropylene having a melt flow rate of less than 30 g/10 min, and a maximum draw ratio D
1
and a Crimp Stability of CS
1
when drawn into filaments at 1000 m/sec and from 8 wt % to 1.5 wt % of an amorphous polystyrene having a melt flow rate of less than 15 g/10 min. The polymer blend is drawable at greater than 800 m/sec to produce filaments having a maximum draw ratio of D
2
the ratio of D
2
: D
1
being greater than 1.15:1 and a Crimp Stability of CS
2
, the ratio of CS
2
: CS
1
being greater than 1.45. Preferably, the base polypropylene has a melt flow rate of between 8 and 30 g/10 min. More preferably, the base polypropylene has a melt flow rate of between 10 and 14 g/10 min. Most preferably, the base polypropylene has a melt flow rate of about 12 g/10 min.
The base polypropylene is characterized by a density between about 0.904 and 0.906 g/cc., and fibers produced from the base polypropylene exhibit a tenacity of about 4.0 g/denier and an elongation of about 35%. The base polypropylene is further characterized by a tensile strength of between 4000 and 6000 psi, a modulus of between 250,000 and 500,000 psi, a Vicat softening point of between 150° C. and 220° C., and a DSC melting point between 150° C. and 180° C.
The base polypropylene is blended with an amorphous polystyrene having a melt flow between 2 and 15 g/10 min., a tensile strength of between 6000 and 9000 psi, a modulus of between 250,000 and 500,000 psi, a flexural strength of between 8000 and 16,000 psi, a flexural modulus of between 300,000 and 500,000 psi, a Vicat softening point of between 180° F. and 240° F., and an annealed heat distortion of between 170° F. and 220° F. Preferably, the polymer blend comprises from 2 wt % to 6 wt % of the amorphous polystyrene. More preferably, the polymer blend comprises from about 3 wt % to 5 wt % of an amorphous polystyrene.
In another aspect, the present invention provides a method of producing fibers and bulk continuous filament including the steps of:
(1) blending from 92 wt % to 98.5 wt % of a base polypropylene having a melt flow rate of less than 20 g/10 min, a maximum draw ratio D
1
and a Crimp Stability of CS
1
when drawn into filaments at 1000 m/sec;
(2) from 8 wt % to 1.5 wt % of an amorphous polystyrene having a melt flow rate of less than 15 g/10 min to produce a polymer blend. The polymer blend is drawable at greater than 800 m/sec to produce filaments having a maximum draw ratio of D
2
, the ratio of D
2
: D
1
being greater than 1.15:1 and a Crimp Stability of CS
2
, the ratio of CS
2
: CS
1
being greater than 1.45. The method includes the step of heating the polymer blend to a melt temperature between 220° C. and 240° C. and spinning the blend into filaments at a speed of between 500 m/sec and 3000 m/sec, preferably at a rate of about 1000 m/sec.
In another embodiment, the present invention provides a polymer fiber or filament produced from a polymer blend comprising:
(1) from 92 wt % to 98.5 wt % of a base polypropylene having a melt flow rate of less than 20 g/10 min, and a maximum draw ratio D
1
and a Crimp Stability of CS
1
when drawn into filaments at 1000 m/sec; and
(2) from 8 wt % to 1.5 wt % of an amorphous polystyrene having a melt flow rate of less than 15 g/10 min.
The fibers or filaments may be drawn at greater than 800 m/sec to produce filaments having a maximum draw ratio of D
2,
the ratio of D
2
: D
1
being greater than 1.15:1 and a Crimp Stability of CS
2
, the ratio of CS
2
: CS
1
being greater than 1.45.
REFERENCES:
patent: 5616412 (1997-04-01), Lin
patent: 0194147 (1986-09-01), None
patent: 0353386 (1990-02-01), None
Gownder Mohan
Nguyen Jay
Reddy Baireddy Raghava
Fina Technology, Inc.
Nutter Nathan M.
Wheelington Jim D.
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