Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Staple length fiber
Reexamination Certificate
2003-04-24
2004-11-16
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Staple length fiber
C528S295000, C528S298000, C528S302000, C528S306000, C528S307000, C528S308000, C528S308600, C525S438000, C524S126000, C524S128000, C428S364000, C428S373000
Reexamination Certificate
active
06818293
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to fibers and films prepared from polyesters of a dicarboxylic acid and a diol selected from 1,3-cyclohexanedimethanol, 1,4-cyclohexane-dimethanol, or 1,3-propanediol. The fibers and films contain an epoxide additive and, optionally, an antioxidant, and show an increased dry heat stability when exposed to elevated temperatures in the presence of air. The fibers and films are particularly useful in applications requiring elevated temperatures.
BACKGROUND OF THE INVENTION
Polyester materials are widely used as extrusion and molding resins for applications such as fibers, films, automotive parts, food packaging, beverage containers, and the like. Commonly used polyesters include poly(ethylene terephthalate), herein abbreviated as “PET”, poly(1,4-butylene terephthalate), herein abbreviated as “PBT”, poly(1,3-propylene terephthalate), herein abbreviated as “PTT”, and poly(1,4-cyclohexylenedimethylene terephthalate), herein abbreviated as “PCT”. PET polymers are widely used because of their availability and modest price. PET polymers have relatively good heat resistance in dry conditions but tend to degrade readily under moist conditions at elevated temperatures. Similarly, PET fibers, yarns, and fabrics are known to exhibit excellent dimensional stability, that is, low shrinkage or growth during service. Although PET has a high resistance to thermal degradation, PET fibers can exhibit loss of tensile strength under continuous exposure to elevated temperatures. Because of these limitations, PET polymers have limited usefulness in certain durable and semi-durable applications which require elevated temperatures, such as, for example, paper making machine clothing, dryer felts, industrial belts, high temperature tape backing, filter media for hot air or liquid filtration, autoclavable products, and other applications involving extended exposure to steam or superheated steam.
Efforts to remedy this problem have been directed to producing a high molecular weight linear polyester having a low content of free carboxyl groups. One approach is to reduce the number of free carboxyls by the use of “end-capping agents”, such as diazomethane, as disclosed by U.S. Pat. No. 3,051,212, or carbodiimides, as disclosed by U.S. Pat. Nos. 3,975,329 and 5,169,499, which react with the free carboxyl groups and thereby prevent their further reaction. These end-capping materials, however, are expensive, often toxic, and thus not suitable for commercial applications.
Polyester compositions containing epoxides are known (see, for example, U.S. Pat. Nos. 3,657,191; 3,627,867; 3,869,427; 4,016,142; 4,130,541; 4,115,350; 3,560,605; 4,374,960; and Japanese Kokai Patent Nos. 07166419; 55012871; and 54131695. The addition of epoxides to polyesters, however, can be problematic. For example, the epoxides may show a low reactivity which, in turn, can create processing and operational difficulties and give uncertain results. For example, U.S. Pat. No. 3,869,427 discloses that styrene oxide appears to increase the level of carboxyl groups when added to molten PET and that diepoxides are “unsuitable for the formation of fibers”. Various polyester blends and composites in combination with epoxides also are described, for example in U.S. Pat. Nos. 4,348,500 and 4,222,928. Such blends, however, are expensive and can require complicated processing. In addition, reinforced polymer composites are not suitable for the preparation of fibers. Thus, the compositions described in the above references do not adequately address the inherent susceptibility of PET to hydrolysis or provide compositions which show excellent stability to high temperatures under both dry and moist conditions.
In contrast to PET, polyester polymers based on poly(1,4-cyclohexylene-dimethylene terephthalate), i.e., “PCT”, have excellent high temperature hydrolytic stability, are essentially free of cyclic trimers and surface oligomers, and are well suited for filtration applications. PCT fibers have an inherent advantages, with melting points (abbreviated herein as “Tm”) up to 290° C., glass transition temperatures (abbreviated herein as “Tg”) up to 90° C., high resiliency, and softness in comparison with other polyester fibers. PCT polymers, however, are susceptible to oxidation and tend to degrade when heated at high temperatures in the presence of air. Although PCT polymers containing epoxides and antioxidants for molding and reinforced compositions also are known (see, for example, Minnick et al. in U.S. Pat. No. 5,428,086), the deficiencies of PCT polymers in dry-heat stability for fiber and film applications have not been addressed. We have now discovered that fibers and films prepared from PCT and PTT homo- and copolyesters melt-blended with multifunctional epoxides show excellent stability at elevated temperatures in the presence of air and under both moist and dry conditions. Our discovery is unexpected because fibers and films prepared from PET melt-blended with multifunctional epoxides show no improvement, and sometimes, a reduction in both dry and wet stability at elevated temperatures.
SUMMARY OF THE INVENTION
It has been found that certain polyester blends containing selected epoxide compounds and, optionally, antioxidants, such as hindered phenols and/or phosphites, have excellent elevated temperature stability in fiber and film form under both dry and moist conditions. Accordingly the present invention provides a polyester fiber comprising:
i) dicarboxylic acid residues comprising about 60 to 100 mole % of a first dicarboxylic acid residue selected from the group consisting of terephthalic acid, naphthalenedicarboxylic acids, cyclohexanedicarboxylic acids, and mixtures thereof; and from 0 to about 40% of a second dicarboxylic acid residue selected from the group consisting of aromatic dicarboxylic acids containing from about 8 to about 16 carbon atoms, aliphatic dicarboxylic acids containing from about 4 to about 16 carbon atoms, cycloaliphatic dicarboxylic acids containing from about 6 to about 16 carbon atoms, and mixtures thereof;
ii) diol residues comprising about 50 to 100 mole % of a first diol residue selected from the group consisting of 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,3-propanediol, and mixtures thereof, and from 0 to about 50 mole % of a second diol residue selected from the group consisting of aliphatic diols containing from 2 to about 16 carbon atoms, cycloaliphatic diols containing from about 6 to about 16 carbon atoms, and mixtures thereof; and
iii) about 0.05 weight % (wt %) to about 5 wt %, based on the total weight of said polyester, of an epoxide additive comprising an epoxide compound with at least 2 epoxy groups per molecule.
The fiber compositions may take any of the following forms, namely monofilaments, multifilaments, tows, staple or cut fibers, staple yarns, cords, woven, tufted and knitted fabrics, nonwoven fabrics, including melt blown fabrics and spunbond fabrics, and multilayer nonwovens, laminates, and composites from such fibers. Because of their good resistance to degradation at elevated temperatures, our novel stabilized fibers are useful in dryer felts and other paper machine clothing, belting, filter media for hot air or hot liquid filtration, electrical, autoclavable, sterizable products, and other industrial applications.
The instant invention also provides stabilized polyester films. Thus, another embodiment of our invention is polyester film comprising:
i) a polyester comprising about 60 to 100 mole % of a dicarboxylic acid residue selected from the group consisting of terephthalic acid, naphthalenedicarboxylic acids, cyclohexanedicarboxylic acids, and mixtures thereof; about 50 to: 100 mole % of a diol residue selected from the group consisting of 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,3-propanediol, and mixtures thereof; and
ii) about 0.05 weight % (wt %) to about 5 wt %, based on the total weight of said polyester, of an epoxide additive comprising an epoxide compound with at least 2 epoxy groups per molecu
Haile William Alston
Keep Gerald Timothy
Tincher Mark Elliott
Acquah Samuel A.
Eastman Chemical Company
Graves, Jr. Bernard J.
Middlemas Eric D.
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