BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to a paper machine clothing, and more particularly, to the composition of monofilaments used in the paper machine clothing.

2. Description of the Related Art

[0002] A paper machine clothing (PMC) fabric is typically carried by a number of rolls in a paper machine, and travels at a high speed. Vacuum boxes are used to pull moisture from the web through the PMC. This creates multiple friction points within the paper machine that wear down the PMC fabric and cause an increase in power consumption. The individual yarns making up a PMC fabric require several desirable physical properties, such as modulus of elasticity, relative elongation, abrasion resistance, fibrillation resistance, water absorbency, and a low coefficient of friction.

[0003] PMC fabrics, particularly in the forming and press sections of a papermaking machine, come into contact with large volumes of water. In the forming section, water based pulp is deposited on a porous forming fabric and water is extracted from the pulp by gravity and suction through the forming fabric. In the next stage, the wet fibrous web is transported on a felt and passes through nip rollers to squeeze out additional water remaining in the web. Finally, the web is completely dried by the application of heat on a porous dryer fabric to generate a paper sheet. [0004] Polyamides such as PA6 and PA6,6 have been utilized in the paper machine clothing industry. However, a common problem associated with each of these polyamides is that they absorb a considerable amount of water in the papermaking process due to the hydrogen bonding capacity of the amide linkages present in the polymer structure. This results in a decrease in advantageous monofilament properties and dimensional changes to the fabric, which can lead to marking of the fibrous material web being produced thereon.

[0005] Attempts have been made to improve the absorption of polyamide fabrics by the use of additives. For example, one approach to overcome the issue has been to incorporate carbon nanotubes (CNT), molybdenum disulfide (MoS ₂ ), tungsten disulphide (WS ₂ ) or glass fibers. However, these approaches may result in adverse effects on the yarn tensile properties. [0006] What is needed in the art is a PMC fabric yarn which has lower water absorption than the state of the art and improved tenacity, loop and knot strength. The PMC fabric yarn should further be simple and cost effective to produce.

SUMMARY OF THE INVENTION

[0007] The present invention provides a paper machine clothing (PMC) fabric with monofilaments having a composition which is a thermoplastic resin, namely polyamide 6/6T

(PA6/6T) copolymer resin. The polyamide copolymer is formed from polyamide 6 and polyamide 6T. The resulting monofilament has a decreased water absorption over a monofilament formed of polyamide 6 (PA6) alone. Polyamide 6T (PA6T) contains an aromatic component which helps in reducing the moisture content or water uptake of the PA6/6T copolymer resin. This structural component is also responsible for improvement in the tensile properties such as tenacity, loop strength and knot strength of the material. The PA6/6T copolymer resin also has improved loop tenacity over PA6 alone.

[0008] The invention in one form is directed to a PMC fabric including a plurality of monofilament yarns. At least some of the yarns have a composition which is a PA6/6T copolymer resin. The yarns formed of the PA6/6T copolymer resin have a water absorption of less than approximately 6% and a loop tenacity of greater than approximately 8.0 grams/denier.

[0009] The invention in another form is directed to a PMC fabric yarn for use in a PMC fabric.

The PMC yarn has a composition which is a PA6/6T copolymer resin. The PMC fabric yarn has a water absorption of less than approximately 6% and a loop tenacity of greater than approximately 8.0 grams/denier.

[0010] The invention in yet another form is directed to a method of manufacturing a PMC fabric yarn for use in a PMC fabric. The method includes the steps of: providing a PA6/6T resin; forming the PA6/6T copolymer resin into a filament; and drawing the filament into a monofilament PMC fabric yarn having a water absorption of less than 6 percent (%) and a loop tenacity of greater than 8.0 grams per denier.

[0011] Advantageously, the PA6/6T copolymer resin composition of the PMC yarns according to the present invention provide for reduced water uptake, improved tensile properties, simplicity in processing and does not require the use of additives to effectively stand the test of time.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] 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:

[0013] Fig. 1 is a fragmentary, perspective view of a portion of a fabric including an embodiment of a monofilament yarn of the present invention;

[0014] Fig. 2 is a side view of a portion of a press felt including monofilament yarns according to the present invention; and

[0015] Fig. 3 is a flowchart illustrating an embodiment of the method of making monofilament yarns of the present invention.

[0016] 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. DETAILED DESCRIPTION OF THE INVENTION

[0017] Referring now to the drawings, and more particularly to Fig. 1, there is shown a portion of an embodiment of a PMC fabric 10 including a plurality of woven monofilament yarns 12. Yarns 12 have a diameter of between approximately 0.05 and 0.70 millimeters, but this may vary between applications. The specific configuration of fabric 10 may vary, depending upon the application. For example, the specific weave pattern of fabric 10 may vary from one application to another. Moreover, fabric 10 need not necessarily be a woven fabric, but may include non- woven yarns, such as a press felt 10 including yarns 12, an example of which is illustrated in Fig. 2.

[0018] At least some of yarns 12 have a composition formed from a thermoplastic resin, such as a polyamide resin, and more particularly a polyamide 6/6T (PA6/6T) copolymer resin. The thermoplastic resin yarns have a water absorption of less than approximately 6%, for example approximately 5.5%. In any case, the composition of the thermoplastic yarns, and thus the yarns, has a water absorption which is less than polyamide 6 (PA6) alone. Further, the thermoplastic resin has a loop tenacity value of greater than 8.0 grams per denier, for example greater than 10 grams per denier or greater than 12 grams per denier.

[0019] The thermoplastic resin yarns 12 have a knot tenacity which is greater than 3.0 grams per denier, for example greater than 5.0 grams per denier. The tenacity of the composition, or more specifically of yarns formed of the same thermoplastic composition, is greater than 5.5 grams per denier, for example greater than 6.0 grams per denier. The thermoplastic resin yarns 12, for example the PA6,6T yarns according to the present invention, have an abrasion resistance which is greater than polyamide 6,12 alone, for example 50% greater than polyamide 6,12 alone, or 100% greater than polyamide 6,12 alone.

[0020] Optionally, the composition forming yarns 12 may further include at least one stabilizer, narticularly a stabilizer selected to improve antioxidant properties of the monofilament yarn formed, for example benzofuranones and hindered phenols.

[0021] Example

[0022] Table 1 below shows a comparison of the tensile properties of monofilament yarns produced with standard polyamide resins and a monofilament yarn produced with the PA6/6T copolymer resin according to the present invention. ASTM D2256-97 method was used to carry out the tensile testing of the yarns. The water absorption of the yarns was measured according to ASTM D570. The yarns were submerged in distilled water at approximately 23° C for 24 hours. The samples were then removed, pat dried using lint free cloth and weighed. Further, the abrasion resistance of the yarns was measured using the squirrel cage method, which consists of the use of a rotating drum of metal wires which are aligned perpendicular to the polymer strands. A pretension is used on each polymer strand prior to starting the drum. During the test, the strands are continually abraded by the rotation of the drum and the strand' s abrasion resistance is quantified by the number of cycles it takes for the strand to fail.

[0023] Table 1 : Comparison of yarn properties of standard polyamide resin (PA6, PA66, and PA6,12) and PA 6/6T

[0024] Referring now to Fig. 3, there is shown a flowchart illustrating an embodiment of a method of making the monofilament yarns of the present invention. During the manufacture of PMC fabric 10, PA6/6T is provided, for example in pellet form. A screw extruder is used, for example to melt the pelletized PA6/6T. (Fig. 3, block 14). Optionally, a stabilizer may be added into the pellets prior to the extrusion step (block 14) and the stabilizer melt blended with the pelletized PA6/6T. The extruded PA6/6T (and optionally the stabilizer mixture) is then spun into a filament. (Fig. 3, block 16). The filament is subsequently drawn into a monofilament PMC fabric yarn (Fig. 3, block 18) having a water absorption of less than approximately 6 percent and a loop tenacity of greater than 8.0 grams per denier.

[0025] 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.