Patent Application
20140262099
1. Field of the Invention
The present invention relates to a paper machine clothing fabric, and more particularly, to monofilament yarns used in the paper machine clothing fabric.
2. Description of the Related Art
Polyethylene terephthalate (PET) is a polymer having good tensile properties, processability and low moisture absorption. PET is used extensively in apparel, home furnishings and industrial applications. Although PET has been utilized in the paper machine clothing (PMC) industry, due to the hostile conditions of the paper manufacturing process the mechanical life of PMC fabrics formed from PET is limited. During the operation of the papermaking machine the hostile conditions, such as mechanical stress, heat and moisture, work to break PET monofilament yarns down, thus shortening the life of a fabric formed from such yarns.
Although efforts have been made to increase the life of PMC fabrics formed from PET monofilament yarns, each proposed solution to the problem of low abrasion resistance has its disadvantages. For example, one approach to solving the problem of low abrasion resistance of PET monofilament yarns was to use high molecular weight PET, as evidenced by EP 0 158 710 A1. Other efforts have involved the utilization of various additives to improve the physical properties of PET monofilament yarns, such as abrasion resistance. Each of these proposed solutions, however, requires expensive resin, expensive additives, and/or longer processing times which lead to higher production costs.
What is needed in the art is a PMC fabric and, more particularly, a PMC fabric yarn having improved or higher abrasion resistance, which is cost effectively produced without the need for additional additives or expensive resin.
The present invention provides a paper machine clothing (PMC) fabric including a plurality of monofilament yarns, at least some of the monofilament yarns formed from polyethylene terephthalate (PET). The PET monofilament yarns according to the present invention have an abrasion resistance of between approximately 6,000 and 20,000 cycles.
The invention in another form is directed to a paper machine clothing (PMC) fabric yarn for use in a PMC fabric. The PMC fabric yarn formed from polyethylene terephthalate (PET) and has an abrasion resistance of greater than 6,000 cycles, for example greater than 10,000 cycles or greater than 15,000 cycles. The PMC fabric yarn formed from PET has an abrasion resistance of between 6,000 and 20,000 cycles.
The present invention further provides a method of manufacturing a paper machine clothing (PMC) fabric yarn for use in a PMC fabric including the steps of: melting polyethylene terephthalate (PET); spinning the PET into a filament; and drawing the filament into a monofilament PMC fabric yarn having an abrasion resistance of between 6,000 and 20,000 cycles.
An advantage of the present invention is the PET monofilament yarns exhibit excellent abrasion resistance without the use of additives or modifications to the molecular weight of the PET resin or the requirement of additional processing steps. Further, the increased abrasion resistance results in a longer life expectancy of the yarns and, thus, the fabric formed from the PET monofilament yarns.
An additional advantage of the PET monofilament processed according to the present invention is that the maximum shrink force temperature of the PET monofilament is lowered. The lower shrink force temperature will enable a lower heat set temperature for spiral and woven fabrics which should result in lower energy and production costs.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring now to the drawings, and more particularly to
Referring now to
PET monofilaments 12 according to the present invention may have a diameter between approximately 0.05 and 1.00 millimeters (mm), for example 0.55 mm or 0.30 mm.
It is feasible to add an additive or multiple additives to improve, for example, the chemical stability, hydrolytic stability or heat stability of the PET monofilament yarns. For example, Stabaxol® may be added to the PET in order to improve the hydrolytic stability of PMC monofilaments formed therefrom.
Referring now to
The drawing step (block 20) of the method of the present invention includes the step of processing the monofilament in at least one relaxation oven at a temperature less than approximately 320° F., for example less than approximately 290° F. or less than approximately 250° F. This lower relaxation temperature during processing of the PMC monofilament yarns, which is at least 30° F. less than the state of the art, yields an unexpected result in the form of improved abrasion resistance over PET monofilaments processed according to the known art.
The PET yarn was produced using the conditions listed in table 1. The 0.72 IV PET resin was commercially available.
Table 2 shows the comparison of the physical properties of the PET monofilament yarns produced with a standard process and modified processes. The target diameter of the monofilament was 0.55 millimeter. ASTM D2256-97 method was used to carry out the tensile testing of the yarns. The test utilized to determine abrasion resistance consisted of the squirrel cage method, which includes a rotating drum of metal wires which are positioned perpendicular to the polymer strands. A pretension (load 500 grams for 0.55 millimeter diameter yarn and 350 grams for 0.30 millimeter diameter yarn) is used on each polymer strand prior to starting the drum. One end of the monofilament is fixed and the other end is tied to a weight to normalize the monofilament pretension. For example, a 350 gram weight is used to pretension a 0.30 mm diameter yarn. The typical pretension is around 0.35 g/denier for monofilaments up to 0.50 mm. The monofilament comes in contact with about a quarter of the drum. The test begins by rotating the drum at 60 rpm. The metal wires on the rotating drum continuously abrade the strand and the number of cycles required to break the strand completely is quantified as an abrasion resistance of the yarn.
The maximum shrink force temperature of the monofilament is estimated using a Lenzing TST2 Machine. The yarn was mounted on the tester with one end fixed by a clamp and the other end pre-tensioned (0.01 gram per decitex) before the other end of the yarn was clamped to maintain the pretension prior to the start of the test. The distance between the clamps in this case was 13 inches. The mounted yarn was heated on the tester in a closed environment from 50° C. to 240° C. with a heating rate of 8° C. per minute. The development of the shrink force of the yarn was measured as a function of temperature by the machine. The temperature was then noted where the maximum shrink force value was observed on a shrink force curve. The maximum shrink force temperature of the PET monofilaments according to the present invention is equal to or less than approximately 311° F. (155° C.).
The PET yarn was produced using the conditions listed in Table 3 below. The 0.95 IV PET resin was commercially available.
Table 4 shows the comparison of the physical properties of the PET monofilament yarns produced with the standard process and with the inventive modified process. The target diameter of the monofilament was 0.30 millimeter. Tensile properties and abrasion resistance of the samples were measured by the same test methods as those described above with respect to Example 1.
While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
This is a continuation-in-part of U.S. patent application Ser. No. 13/835,737, entitled “MONOFILAMENT YARN FOR A PAPER MACHINE CLOTHING FABRIC”, filed Mar. 15, 2013, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13835737 | Mar 2013 | US |
| Child | 13937845 | US |
