Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2000-10-05
2001-09-04
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S271000
Reexamination Certificate
active
06284864
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to the manufacture of copolyester fibers for textile applications, and in particular relates to an enhanced copolyester fiber, which demonstrates improved dye permanence properties and dyeing characteristics. In particular, the present invention relates to employing a small amount of pentaerythritol and a combination of at least two different dicarboxylic acids, or their anhydride or ester equivalents, copolymerized with the raw materials used to make polyethylene terephthalate (PET). The present invention has deeper dye characteristics while maintaining the physical properties compared to the addition of pentaetriitol and adipic acid alone.
2) Prior Art
Copolyester has long been recognized as a desirable material for textile applications. The basic processes for the manufacture of copolyester are relatively well known. Copolyester fibers can be blended with other fibers such as wool or cotton to produce fabrics, which have the enhanced strength and durability of copolyester, while retaining many of the desired qualities of the natural fiber with which the copolyester is blended.
Conventional PET fibers are typically dyed at temperatures of about at least 265° F. so as to achieve uniform dyeing, adequate dye intensity, and acceptable dye permanence. However, the conventional dyeing processes are too harsh for certain heat sensitive natural fibers, causing excess shrinkage or a loss of physical properties of the heat sensitive fibers. When conventional PET fibers are dyed under less harsh conditions, dye uptake by the polyester fiber is lessened as is dye permanence.
However, dye permanence continues to be a problem with conventional PET because it is not as easily dyeable as most natural fibers under the same conditions. Most natural fibers are dyed at low temperatures. Low temperature dyeing of conventional PET will cause the dye to rapidly fade or bleed from the polyester. While various additives have been used in the past to provide a deeper dye uptake (dye intensity) in polyester fibers, such additives have not resulted in dye permanence for PET as required for many end use applications. As a consequence, PET in which dye permanence is an objective must be dyed under conditions of high temperature, high pressure, or both.
It is known in the art that adipic acid can be added to PET to produce a copolyester with improved dyeability. Adding increased amounts of adipic acid during production of the copolyester will increase the dyeability. However, adipic acid increases the shrinkage of the fiber and weakens the strength of the fiber. Consequently, using more than about 4 wt. % (based on the amount of terephthalic acid or its ester equivalent) is not recommended.
It is also known in the art that pentaerythritol at low levels of less than about 700 parts per million (ppm) based on the weight of the terephthalic acid (TA) or dimethyl terephthalate (DMT) can be incorporated into PET for improved dyeability. However, at levels greater than about 700 ppm, the pentaerytliritol often results in decreased strength of the fiber.
U.S. Pat. Nos. 5,135,697 and 5,272,246 to Roderiguez et al disclose the incorporation into PET of 175 to 700 ppm of pentaelythntol and 1.3 to 3.1 wt. percent adipic acid (based on the amount of TA or DMT in the PET). As set forth in Table 1 of these patents, the atmospheric dye rating of PET is defined as being 100. The combination of the addition of pentaerythritol, adipic acid, and PET resulted in a copolymer with an improved atmospheric dye rating of 112. This result is better than using adipic acid and PET, or pentaerythritol and PET. The dyeing temperature was 210° F., which is substantially lower than the normal dyeing temperature of 265° F. for PET. This copolyester is a great advantage over PET.
Nevertheless, there continues to be a need for improved copolyester fibers that possess enhanced, superior dyeing properties, maintain the stability of the incorporated dye, and possess suitable characteristics of tenacity, shrinkage, dyeability and dye retention.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a copolyester fiber and a method of producing a copolyester fiber that has improved dyeability and dye retention properties, while maintaining other physical properties of tenacity and shrinkage. The resulting copolyester fiber may be dyed to a desired intensity level using atmospheric, low temperature conditions to achieve a comparable or greater dye intensity to that achieved from a standard copolyester fiber (of PET and adipic acid, with a small amount of pentaerythritol). The present invention surprisingly enhances the dyeability and dye permanence beyond that of the copolyester of PET, pentaerythritol, and adipic acid; maintains the physical properties; and enables the use of mild dyeing conditions. Thus, the present invention provides a unique balance of physical properties with improved dyeability and dye permanence compared with PET, or with the copolyester of PET and adipic acid (with a small amount of pentaerythritol).
The copolyester of the present invention is formed from a batch or continuous process of reacting TA or DMT and ethylene glycol in an esterification stage followed by a polycondensation stage. A mixture comprising about 2-4 mole percent and, more preferably, about 3½ mole percent of Dibasic Esters (DBEs), sold by E.I. du Pont Nemours and Co., and about 100-700 ppm of pentaerythritol is added to the reaction. The resulting copolymer is melt extruded into a fiber having increased dyeability and dye permanence, while maintaining good physical properties.
The improved copolyester fiber retains a useful range of physical properties, which lend themselves to use of the fibers in a variety of textile applications. In particular, the improved dyeability and dye permanence enables the deep-dye copolyester fibers to be integrated into various fabric blends, which include heat sensitive natural and synthetic fibers. The resulting fibers can be safely dyed at the lower temperatures required of the heat sensitive component, the deep dye copolyester fibers achieving a dye intensity level matching that of the other blended, non-copolyester fibers. The invention also provides a copolyester fiber, which dyes darker and with a substantial increase in dye permanence under more economical dyeing conditions than a standard PET fiber.
In the broadest sense, the present invention comprises: a) copolymer of: a) polyethylene terephthalate prepared from either terephthalic acid or its ester equivalent; b) at least two dicarboxylic acids, or their anhydride or ester equivalents; and c) pentaerythritol.
The foregoing and other objects, advantages and features of the invention, and the manner in which the same are accomplished, will become more readily apparent upon consideration of the following detailed description of the invention taken in conjunction with the examples, which illustrate exemplary embodiments.
REFERENCES:
patent: 5135697 (1992-08-01), Roderiguez
patent: 5272246 (1993-12-01), Roderiguez
Flores Rodolfo Agustin
Fulcomer Katherine Keever
Roderiguez Joseph Anthony
Sutherland J. Michael
Arteva North America S.a.r.l.
Boykin Terressa M.
Clements Gregory N.
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