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
2001-02-07
2004-08-17
Short, Patricia A. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S175000, C525S176000, C525S183000, C525S184000, C525S217000, C525S218000, C525S220000, C525S221000, C525S222000, C525S227000, C525S240000, C525S425000
Reexamination Certificate
active
06777496
ABSTRACT:
BACKGROUND OF THE INVENTION
Today numerous different thermoplastic polymers are commercially used because each has a combination of physical characteristics that make it well-suited for particular applications. In many instances, it is an undesirable characteristic that prevents a thermoplastic polymer from fully participating in some applications. For example, thermoplastic polyester has a good combination of strength, dimensional stability, and cost, but surface related problems such as adhesion, UV resistance, abrasion resistance, etc. inhibit its potential.
Polyester fiber replaced nylon fiber in passenger tire bodies because polyester was more dimensionally stable and hence the resulting tires did not exhibit objectionable flat-spotting. Due to its combination of strength and dimensional stability, polyester remained the preferred tire body reinforcement as passenger tires went from bias to radial constructions. Polyester's poor adhesion to rubber was overcome by using aggressive adhesion promoters in combination with higher temperatures and residence times in down-stream dipping and heat-setting operations. See for example U.S. Pat. No. 4,300,972 and W. G. Perkins, “Complexities in PET Tire Yarn Processing and Characteristics”,
International Fiber Journal
42 (September 1987) and R. Iyengar, “Adhesion of tire cords—the total picture”, RUBBER WORLD 197(2) 24(1987). This added cost from reduced output, higher energy input, and control equipment for containing the added environmentally unfriendly chemicals makes the conventionally used dip additives for adhesive promotion unattractive. Even with its objectionable flat-spotting, nylon is preferred over polyester in tire cap plies due to at least partly its inherently better hot adhesion. Thus, an article having a combination of polyester physical properties with a “nylon-like” surface would be highly desirable for tire applications.
Reduced friction during polymeric fiber processing and abrasion during end-use are also currently addressed by topically applying a finish during fiber spinning and drawing. These finishes are applied as solutions or emulsions and hence have the difficulties discussed above. Similarly, a polymeric fiber having a permanent outer layer exhibiting low friction and/or abrasion resistance would be a highly desirable solution.
Ultraviolet (“UV”) resistance is currently improved by introducing UV “screens” via topically applied coatings or additives to the polymer melt. Coatings lack permanency. Uniform addition to the fiber adds extra cost, but little benefit from “screens” located well below the surface. Preferential location of a UV stabilizer in a permanent layer near the surface would be a highly desirable solution.
A seldom used approach for fiber production has been the incorporation of low molecular weight additives which “bloom” to the surface during fiber extrusion, fiber drawing, and/or during subsequent use. This approach avoids the environmental issues associated with the above approaches, but it does not produce the sought-after permanent surface for applications where abrasion or shear at the fiber/matrix surface is present. Blooming is disclosed in U.S. Pat. No. 3,973,068 wherein a surfactant is added to polyolefin and the surfactant migrates to the fiber surface and reduces secondary bonding. U.S. Pat. No. 4,640,962 teaches a silicone-sheathed polyester fiber wherein (1) the silicone is added from 0.1 to 10 weight percent to the polyester, (2) per column 8, lines 24-27, microdomains (preferably less than 1 micron) are formed “so that the endgroups of all of the polysiloxane block polymer have an opportunity to condense with the polyester,” and (3) the microdomain migrates to the fiber surface during spinning and drawing. Per column 8, lines 50-53, “surprisingly, the migration of the silicone domains has been found to continue during drawing, including cold drawing . . . .” The low inherent surface energy for the polysiloxane and resulting driving force to occupy a surface geometry was sufficient for the formation of a “silicone sheath.”
Similarly, U.S. Pat. No. 5,069,970 teaches the use of low surface energy organic polymers to preferentially locate at the surface of PET fibers for use as high capacity air filter fibers. Polypropylene and poly(methylpentene) are the only additives in the patent examples. A wider range of polymers is suggested in the patent text, but all the polymers are inherently inert and incapable of thermally reacting with PET.
In contrast in the present invention, additives with higher surface energies are preferentially located at the article surface. Therefore, although not wishing to be bound by theory, it is believed that the mechanism for this invention is fundamentally different in a manner that provides much greater opportunity for surface engineering. Furthermore, the surprising ability to incorporate reactive groupings such as amides, esters, unsaturated olefins, etc. into melt formed articles while maintaining the base thermoplastic properties and achieving the desired propensity for bonding is a further differentiating feature.
This invention relates to heterogeneous or immiscible blends of two or more polymers. The Encyclopedia of Polymer Science and Engineering 12, 403-424 (1988) reviews the various methods for establishing blend heterogeneity. Thermal (DSC & DTA), Dynamical Mechanical, and Microscopy (optical, TEM, SEM) methods are particularly useful. As general guide, blend miscibility can be estimated using solubility parameters (see M. M. Coleman et. al. Polymer 31, 1187 (1990)). A lower solubility parameter signifies a lower surface energy and hence a greater propensity to preferentially locate at the article surface. For this invention, solubility parameters are defined in terms of the values calculated using Coleman's methodology and his constitutive molar volumes and attraction constants. When using copolymeric additives, the relative abundance of the constitutive functional units is proportionated in accordance with their mole fraction. Therefore, the calculated solubility parameter for a Nylon 6/Nylon 11 copolymer with 33 mole % Nylon 6 would be calculated as follows:
{0.33[5×132+405]+0.67[10×132+405]}/{0.33[5×16.5+19.2]+0.67[10×16.5+19.2]}=9.6
End-capping agents would also be included in the analysis and would also be proportionated on a mole fraction basis. For ease of reference these calculated solubility parameters will be referred to as “CSP” values.
The CSP value is 7.4 for both the polypropylene and poly(methyl pentene) exemplified in above U.S. Pat. No. 5,069,970. In the broadest patent claim, polybutylene has the highest CSP value at 7.6. This patent teaches the most preferred polyolefins have high molecular weight in the 50,000 to 500,000 range.
The desire to have a certain base fiber for mechanical properties and cost and a permanent outer layer or sheath with markedly different physical characteristics has been a major driving force for bi-component spinning. While this approach does provide the basic fiber structures desired as solutions for the above problems, it has disadvantages. First, additional equipment is required including an additional extruder to introduce the sheath polymer and sophisticated spinnerettes to channel that sheath polymer to extrude it as the outer layer of the individual filaments. For current day multi-end processes, these spinnerettes can have 1000 extrusion holes. Second, it is quite difficult to make sheath-core filaments where the sheath is present at 5% or less of the fiber volume. Both factors represent significant added cost in terms of added equipment, excess sheath weight, and scrap arising from added process control difficulties. Also, the melt viscosity of the sheath and core must be similar in order to be spinnable. Finally and possibly most importantly, poor adhesion between the fiber core and the sheath often occurs resulting in a propensity for failure via
Mares Frank
Mohajer Yousef
Nelson Charles Jay
Patel Kundan M.
Twomey Conor
Bingham & McCutchen LLP
Honeywell International , Inc.
Short Patricia A.
Thompson Sandra P.
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