Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2002-09-10
2004-07-20
Kelly, Cynthia (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S375000, C428S378000, C428S394000, C008S115510, C008S115600
Reexamination Certificate
active
06764762
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to fluoropolymer yarn having a coating of lubricant thereon to facilitate the drawing of the yarn
2. Problem
Japanese Patent Publication 53-52728 (May 13, 1978) discloses the melt spinning of ethylene/tetrafluoroethylene copolymer (ETFE) in which the resultant multifilament yarn contacts an oiling roller 17 after cooling but prior to stretching (orientation) between sets of rollers 18a-18b and 20a-20b at draw ratios of 2.9-3.1 (Table 1) and roller temperatures of 120° C. to 140° C. The oiling roller is disclosed to add an oiling liquid to the yarn to improve its antistatic property and stretchability. The composition of the oiling liquid, however, is not disclosed. The maximum tenacity of the yarn, shown in FIG. 8 is 2.5 g/den, which diminishes at stretching (draw) temperatures above 130° C. German Published patent application 41 31 746 (Sep. 24, 1991) also discloses the melt spinning of ETFE multifilament yarn and the application of a spin finish at the bottom of the spinning column and prior to the take-up rolls which take up the yarn at high speeds such that further drawing may not be necessary, or is further drawing is done, the draw ratio is between 1:1.1 to 1.5, and the draw temperature is 120° C. to 260° C.
Drawing is sometimes called cold drawing, to distinguish from the attenuation (spin stretch) of the yarn as it leaves the spinneret, wherein the yarn is at a temperature above the melting point of the polymer being melt spun. Drawing is carried out on the yarn after it has been cooled to a temperature below the melting point, but usually at an elevated temperature to facilitate the draw, so as to orient the polymer chains in the yarn in the direction of the yarn, to strengthen it. The primary function of cold drawing is to achieve the maximum orientation and thereby the maximum tenacity. The draw level may be varied to achieve other desired properties such as shrinkage which is defined by the end use. Some drawing occurs in the attenuation of the yarn as it solidifies and moves away from the spinneret, however, because this is done mostly in the molten state little orientation is achieved during this initial elongation. The yarn is cooled below the freeze point in the annealer and crystallization begins in the annealer before the yarn contacts the finish application device. The point at which the oil or spin finish is applied as in the references '728 and '746 cited above, however, separates the melt attenuation of the yarn (upstream) and the drawing of the yarn (downstream). Drawing is required, even after melt attenuation, to obtain high tenacity fluoropolymer yarn, e.g. at least 3 g/den tenacity.
The oiling liquid and spin finish disclosed in these references are understood to be serving the same purpose, namely that which is disclosed in 53-52728, but neither reference discloses the composition of the lubricant (spin finish). In order to make high tenacity ETFE yarn, e.g. tenacity greater than 3 g/den, and high production rates, e.g. at least 1000 m/min, without filament breakage within the yarn, it is important that the lubricant applied to the yarn prior to drawing effectively lubricate (cover) the yarn so that filament(s) making up the yarn do not break during drawing, to thereby enable high draw ratios to be reached in order to produce high tenacity yarn. The lubricant regulates inter-filament and fiber to metal frictional and properties which enable high draw ratios and a stable drawing process to be reached in order to achieve the highest tenacity yarn. It is the oil in the lubricant that provides the lubricating effect, by reducing friction between the yarn and processing equipment and in the case of multifilament yarn, between the filaments in the yarn (intra-yarn friction). The problem with lubricating fluoropolymer yarn, including ETFE yarn, is that fluoropolymers have an extremely low surface energy, characterized by exhibiting a surface tension of 16 dynes/cm to 26 dynes/cm at ambient temperature (20° C.) as compared to the much higher surface tensions of 41-43 dynes/cm for the more common polyester and polyamide yarns, as disclosed on pp. III-223 to -226 of J. Brandrup and E. H. Immergut, Polymer Handbook, 2
nd
Ed, published by John Wiley & Sons (1975). These surface tensions are called critical surface tensions. The determination of critical surface tension is described on pp. 181-193 of S. Wu, Polymer Interface and Adhesion, published by Marcel Dekker (1982). Because of the much lower surface energy of fluoropolymer as compared to polyester and polyamide yarn, lubricants that are operable with polyester and polyamide do not wet fluoropolymer and therefore cannot be used as lubricants for high speed/high draw ratio fluoropolymer yarn production. Typically lubricants are water based, i.e. an emulsion of an oil in water. Water-based lubricants do not wet fluoropolymer yarns, making such lubricants unsuitable for high-speed spin/high draw ratio fluoropolymer yarns.
The lubricant must not only be able to effectively wet and lubricate the fluoropolymer yarn, but it also has to satisfy additional criteria for practical application. After drawing of the yarn, and possibly as late as after the yarn is incorporated into a fabric, the lubricant must easily be removable from the yarn so that the fluoropolymer surface with its hydrophobic properties is exposed. In the textile industry, the preferred method of removing lubricant from textiles is to expose the textile to scouring, i.e. washing in an aqueous soap solution as will be described later herein. The lubricant must also be thermally stable so as not to decompose when exposed to temperatures of at least 120° C. normally encountered in the drawing process. Although the lubricant may be applied to the fluoropolymer yarn at or near room temperature, the yarn will be heated by the subsequent drawing process which will alter the lubricant properties and change spreading characteristics. Heating can be accomplished by heating the oil before application, by the use of heated rolls around which the yarn is wrapped for gripping and by internal heat generated by stretching the yarn.
BRIEF SUMMARY OF THE INVENTION
It has been found that oil-based lubricants that are thermally stable at the temperature of draw, at least 120° C. can be formulated to wet the fluoropolymer yarn when applied thereto and thereby spread over the surface of the yarn to effectively lubricate the yarn for the drawing process, which can be carried out to a high draw ratio, e.g. at least about 3.0:1, to provide high strength yarn without filament breakage, and that these lubricants satisfy the requirement of scourability. Thus, one aspect of the present invention can be defined as fluoropolymer yarn having a coating of lubricant thereon spread over the surface of the yarn, the lubricant being thermally stable at a temperature of at least about 120° C. and being removable from said yarn by scouring. By “spread over the surface of the yarn” is meant that the filaments or monofilament making up the yarn are wet by the lubricant so that it spreads out over the surface of the yarn, and in the case of multifilament yarn, e,g, containing at least 3 monofilaments, preferably at least 10 filaments, the surfaces of the individual filaments are coated with lubricant as well. In the case of mulifilament yarn, the ability of the lubricant to wet the yarn is assisted by capillary action to enable the lubricant to spread over the surfaces of the interior filaments of the yarn. The higher the draw ratio, the more critical is the need for lubrication of the yarn, i.e. spreading of the lubricant over the yarn surface, so that the high draw ratio can be achieved and the desired yarn properties obtained.
Another aspect of the present invention can be defined as the process for drawing fluoropolymer yarn, comprising coating said yarn with lubricant, said lubricant being thermally stable at a temperature of at least 120° C. and being removable from said yarn by scouring, and the
Potter Jerry Fuller
Seemuth Paul Douglas
E. I. du Pont de Nemours and Company
Gray Jill
Kelly Cynthia
LandOfFree
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