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
2000-05-12
2002-01-29
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
06342565
ABSTRACT:
TECHNICAL FIELD
The invention relates to an elastic fiber including at least one and preferably two polyolefin thermoplastic components.
BACKGROUND
Ethylene—propylene copolymers and blends of isotactic polypropylene and ethylene propylene rubber are well known in the prior art. However, the traditional Ziegler-Natta catalysts used to make the ethylene propylene elastomer have limitations. Thus polymers which are simultaneously uniform in compositional distribution, have substantially stereospecific propylene residues and have less than 35 wt. % ethylene are not available with these catalysts. These limitations in the synthesis have lead to the absence of elastic fibers from blends of ethylene propylene copolymers and isotactic polypropylene.
U.S. Pat. No. 3,882,197 suggests blends of stereoregular propylene/alpha-olefin copolymers, stereoregular propylene, and ethylene copolymer rubbers.
U.S. Pat. No. 3,888,949 suggests the synthesis of blend compositions containing isotactic polypropylene and copolymers of propylene and an alpha-olefin, containing between 6-20 carbon atoms, which have improved elongation and tensile strength over either the copolymer or isotactic polypropylene. Copolymers of propylene and alpha-olefin are described wherein the alpha-olefin is hexene, octene or dodecene. However, the copolymer is made with a heterogeneous titanium catalyst resulting in copolymers with non-uniform composition distribution and a broad molecular weight distribution. Non-uniform intramolecular compositional distribution is evident in U.S. Pat. No. 3,888,949 by the use of the term “block” in the description of the polymer where the copolymer is described as having “sequences of different alpha-olefin content.” Within the context of the invention described above the term sequences describes a number of olefin monomer residues linked together by chemical formed during polymerization.
U.S. Pat. No. 4,461,872, improved on the properties of the blends described in U.S. Pat. No. 3,888,949 by using another heterogeneous catalyst system which is expected to form copolymers which have statistically significant intermolecular and intramolecular compositional differences.
Two successive publications in the journal of Macromolecules, 1989, V22, pages 3851-3866 described blends of isotactic polypropylene and partially atactic polypropylene which purportedly have desirable tensile elongation properties. However, the partially atactic propylene has a broad molecular weight distribution as shown in
FIG. 8
of the first publication. The partially atactic polypropylene is also composed of several fractions, which differ in the level of tacticity of the propylene units as shown by the differences in the solubility in different solvents. This is shown by the corresponding physical decomposition of the blend which is separated by extraction with different solvents to yield individual components of uniform solubility characteristics as shown in Table IV of the above publications.
More recently several authors have shown the formation of more refined structures of partially atactic, partially isotactic polypropylene which have elastomeric properties. It is believed that in these components each molecule consists of portions which are isotactic and therefore crystallizable while the other portions of the same polypropylene molecule are atactic and therefore amorphous and not crystallizable. Examples of these propylene homopolymers containing different levels of isotacticity in different portions of the molecule are described in U.S. Pat. No. 5,594,080, in the article in the Journal American Chemical Society (1995), 117, p. 11586, in the article in the Journal American Chemical Society (1997), 119, p. 3635, in the journal article in the Journal of the American Chemical Society (1991), 113, pp. 8569-8570, and in the journal article in the Journal Macromolecules (1995), 28, pp. 3771-3778. These articles describe the copolymer of the present composition but do not describe the compositions obtained in blends with a more crystalline polymer such as isotactic polypropylene, nor its resultant desirable physical properties.
U.S. Pat. Nos. 3,853,969 and 3,378,606, suggest the formation of in situ blends of isotactic polypropylene and “stereo block” copolymers of propylene and another olefin of 2 to 12 carbon atoms, including ethylene and hexene. The copolymers of this invention are necessarily heterogeneous in intermolecular and intramolecular composition distribution. This is demonstrated by the synthesis procedures of these copolymers which involve sequential injection of monomer mixtures of different compositions to synthesize polymeric portions of analogously different compositions. In addition,
FIG. 1
of both patents shows that the “stereo block” character, which is intra or intermolecular compositional differences in the context of the description of the present invention, is essential to the benefit of the tensile and elongation properties of the blend of these patents. Moreover, all of these compositions either do not meet all of the desired properties for various applications.
Similar results are purportedly achieved in U.S. Pat. No. 3,262,992 wherein the authors suggest that the addition of a stereoblock copolymer of ethylene and propylene to isotactic polypropylene leads to improved mechanical properties of the blend compared to isotactic polypropylene alone. However, these benefits are described only for the stereoblock copolymers of ethylene and propylene. These copolymers were synthesized by changing the monomer concentrations in the reactor with time. This is shown in examples 1 and 2. The stereoblock character of the polymer is graphically shown in the molecular description (column 2, line 65) and contrasted with the undesirable random copolymer (column 2, line 60). The presence of stereoblock character in these polymers is shown by the high melting point of these polymers and the poor solubility in hydrocarbons at ambient temperature.
Notwithstanding these descriptions of the polymer blends containing isotactic propylene segments it is apparent that useful articles such as elastic fibers have not been constructed from any of these materials. The utility of elastic fibers is that they (a) are soft to the touch, and (b) can recover partly from temporary tensile deformation to less than 100% increase in their original length, this latter affording the wearer of garments based on such fibers more comfort. In addition, there is a need for elastic fibers which are easily processible in conventional thermoplastic plastics fiber equipment using conditions similar to that used for conventional thermoplastic fibers. Further, any or all of the conventional processes used for fiber fabrication should be usable to fabricate the elastic fiber blend. These include but are not limited to the following: continuous filament, bulked continuous filament, staple fibers, melt blown fibers, spun bonded fibers. It is also further desirable to have elastic fibers composed essentially completely of polyolefins such that they are thermally stable, heat resistant, light resistant and generally suitable for thermoplastic applications.
SUMMARY
There is a need therefore for soft elastic fibers composed generally essentially completely of polyolefins but having simultaneously a crystalline stereospecific polypropylene component to obtain good tensile strength as well as a crystallizable ethylene-propylene copolymer to provide good elastic recoverability, resistance to elastic flow at a load sustained for specified period as well as a glass transition temperature below that of polypropylene.
Embodiments of our invention include forming soft elastic fibers from predominantly crystallizable, semicrystalline polyolefin copolymers. Further embodiments include improving the aforementioned properties of fibers by blending a generally minor amount of a crystalline polyolefin where the type of crystallinity of the two components are similar, as for instance both will be substantially isotactic or substantially syndiotactic. Isotactic
Agarwal Pawan Kumar
Cheng Chia Yung
Datta Sudhin
ExxonMobil Chemical Patent Inc.
Muller William G.
Nutter Nathan M.
Schmidt Paige
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