False twist beaded yarn
To make a monofilament yarn having synthetic polymeric materials, a multifilament or monofilament core yarn is coated with a polymer using a specially designed die during an extrusion process. Flow instabilities created in the die resulting in a yarn that develops a non-uniform cross-sectional beading of the coating material. The beaded material forms a helical pattern around the yarn core, producing a false twist effect.
Yarn comprises continuous strands of twisted threads of natural or synthetic materials, which are used in weaving or knitting. Threads used to make yarn are fine cords of fibrous material, such as cotton, flax, wool or nylon, which are twisted together to form the threads.
With the advent of synthetic plastic coating materials, fabrics created from coated yarn can gain the benefit of increased durability, increased resistance to abrasion, weathering, burning, chemical attack, microbial and fungal attack, improved aesthetic appearance, increased blocking of sunlight and harmful ultraviolet radiation, and can be used effectively as a thermal insulator.
Other fabrics can have a decorative appearance if they are woven from a beaded yarn. In the prior art, coated yarns have been created by running a monofilament or multifilament yarn through a plastic coating extruder. However, such yarns are not beaded. A plastic coated, beaded yarn can provide the aforementioned benefits of a coated yarn and additionally provide unique and exotic aesthetic qualities brought by new product patterns and designs in specialty and niche markets. Thus, there is a need for creating a plastic coated, beaded yarn.
BRIEF SUMMARY OF THE INVENTIONTo make a monofilament yarn having synthetic polymeric materials, a multifilament or monofilament core yarn is coated with a polymer using a specially designed die during an extrusion process. Flow instabilities created in the die resulting in a yarn that develops a non-uniform cross-sectional beading of the coating material. The beaded material forms a helical pattern around the yarn core, producing a false twist effect.
In one aspect, the present invention is directed to a polymeric coated yarn, comprising: a core yarn strand; and a polymeric coating over said core yarn strand; wherein said coating is non-uniform along a radial direction of said strand.
In another aspect of the present invention, said coating forms a helical bead along an axial direction of said strand.
In another aspect of the present invention, said helical bead is non-uniformly distributed along the axial direction, thereby forming a zigzag appearance.
In another aspect of the present invention, an outer edge of a radial cross section of said coating is substantially circular.
In another aspect of the present invention, an outer edge of a radial cross section of said coating is substantially circular.
In another aspect of the present invention, said core yarn strand comprises artificial fibers.
In another aspect of the present invention, said core yarn strand comprises more than one filament.
In another aspect of the present invention, each filament comprises a different type of fiber.
In another aspect of the present invention, said core yarn strand comprises a material different from a polymeric material.
In another aspect of the present invention, said coating is extruded over said core yarn strand.
In another aspect of the present invention, the yarn further comprises a pigment, wherein the coating is extruded with said pigment.
In another aspect, the present invention is directed to a polymeric yarn, comprising a single polymeric strand having an axial axis, wherein an outer surface of said strand is non-uniform along a radial direction from said axial axis.
In another aspect, the present invention is directed to a method of coating yarn, comprising: creating an instability in flow of a polymeric coating through a die attached to an extruder; extruding a core yarn strand with said coating through said die; and forming a non-uniform coating along a radial direction of said strand.
In another aspect of the present invention, the method further comprises varying one or more processing parameters from the group of extruder pressure, extruder barrel temperature, die temperature, and yarn draw speed.
In another aspect of the present invention, the method further comprises extruding a pigment with said core yarn strand and coating.
In another aspect of the present invention, the method further comprises cooling said coated yarn in a chilled water tank.
In another aspect of the present invention, the method further comprises rolling said coated yarn through nip rollers.
In another aspect, the present invention is directed to a crosshead extrusion die for forming a polymeric coating over a strand of yarn, comprising: a die head; a feed zone to admit said strand and said coating; a flow balance zone to orient a flow of said coating; and a die cap having an orifice through which said coating and said strand is extruded, and a reservoir to create a flow instability in said coating; wherein a non-uniform coating along a radial direction of said strand is formed.
In another aspect of the present invention, said orifice is circular.
In another aspect of the present invention, said die comprises more than one orifice to simultaneously extrude more than one polymeric coated strand of yarn.
BRIEF DESCRIPTION OF THE DRAWINGS
Coating 120 is any material that can be conventionally extruded, including polyvinyl chloride (PVC) compounds, polypropylene, polyester, and the like. Preferably, coating 120 is a compound containing several ingredients shown in Table 1 below:
The coating ingredients shown in Table 1 provides a combination of PVC resin, plasticizer, and lubricant that results in flow properties required in the production of false twist beaded yarn over a relatively wide range of processing conditions.
Coating 120 may have a clear formulation, but may also have streaks of coloring material by mixing a pigment into the coating, preferably by using a secondary extruder. In addition, yarn can be extruded with two or more pigmentation colors at various percentages, using a typical coextrusion process.
Now, the extrusion process will be described in more detail. Referring to
Preferably, secondary extruder 660 optionally creates bi-color streaks on some false twist beaded yarns. In such case, a compound with a secondary pigment is extruded into the primary melt stream of main 2-inch extruder 620 just prior to flow into the static mixing section. This process is not limited to a single secondary extruder, and extrudate with multicolored streaks can be produced in this fashion. The final product is then run through a chilled water tank 640 before being pulled through nip rolls 650 and rolled onto a tube using a precision winder 660.
Referring to
Processing conditions which affect the appearance of beaded yarn are listed below in Table 2. A wide range of processing conditions result in the production of false twist beaded yarn. Different process settings combined with a different sized die cap orifice or different coating compound materials could also result in the same yarn characteristics as those noted above. In addition, the following variables have been considered and have been determined to affect the characteristics of false twist beaded yarn to create a variety of patterns and textures:
More specifically, the following processing conditions illustrated in Table 3 below were found to create the first and second preferred embodiments:
The extruder temperature is maintained according to a heat temperature profile. The heat temperature profile comprises 3 barrel temperatures shown in Table 3 for each of the two embodiments. The extruder barrel has three separate heating zones along its length. Each temperature value shown in the table corresponds to an individual zone. The first temperature (152) corresponds to the zone closest to the feed (entrance) end of the extruder and the last temperature (161) corresponds to the zone at the metering (exit) end of the extruder. Likewise, the die is maintained according to the temperature profile shown in Table 3.
The parameters as shown in Table 3 are typical of conditions that were determined through experimentation to produce two distinctive yarn designs that represent points near the upper and lower limits that produce beaded yarn on the preferred extrusion equipment. Process conditions that also produce beaded yarn exist at many different setpoints, and at least include those setpoints between the first and second preferred embodiment setpoints shown.
Multiple experiments were conducted to study the complex interaction of multiple processing, equipment, and material related variables. The results of these experiments are reflected in the parametric value setpoints disclosed in Table 3. Changes in any parameter affects the other settings, and can add or diminish the formation of beaded yarn 100. Generally, the effect generated by changing each process parameter will now be explained.
Screw and Line Speed: In general, plastic melt fracture depends on a specific combination of shear stress, melt viscosity, flow rate, melt elasticity, and flow channel geometry at the die orifice. Screw speed directly affects the first three listed conditions and a range of required screw speeds can be used to create beading. Deviating outside of the range results in a smooth coating rather then a fractured (beaded) coating. The actual range over which this phenomenon occurs depends on the material, extruder screw design, die design, and temperature set points. The die recommended in the preferred embodiment can be used over a wide range of screw speeds. Beaded yarn can be produced with screw speeds ranging from 40 rpm up to the maximum screw speed for the extruder (110 rpm). The exact appearance of the beaded yarn will depend on a combination of the screw speed and line speed with higher screw speed and lower line speed generating a thicker yarn with an appearance similar to that shown in
Temperature Settings: Temperature set points affect melt viscosity, shear stress, and flow rate at the die orifice and will thus have a similar affect as screw speed. In general, a range of temperature settings is required. Deviation from these settings, either below or above, will result in the production of a smooth coating rather then a fractured (beaded) coating. Because PVC compounds are temperature sensitive and require a relatively narrow temperature processing range, the absolute range of barrel temperatures that can be used to produce beaded yarn has not yet been determined.
Having thus described at least illustrative embodiments of the invention, various modifications and improvements will readily occur to those skilled in the art and are intended to be within the scope of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention is limited only as defined in the following claims and the equivalents thereto.
Claims
1. A polymeric coated yarn, comprising:
- a core yarn strand; and
- a polymeric coating over said core yarn strand;
- wherein said coating is non-uniform along a radial direction of said strand.
2. The yarn of claim 1, wherein said coating forms a helical bead along an axial direction of said strand.
3. The yarn of claim 2, wherein said helical bead is non-uniformly distributed along the axial direction, thereby forming a zigzag appearance.
4. The yarn of claim 3, wherein an outer edge of a radial cross section of said coating is substantially circular.
5. The yarn of claim 1, wherein an outer edge of a radial cross section of said coating is substantially circular.
6. The yarn of claim 1, wherein said core yarn strand comprises artificial fibers.
7. The yarn of claim 2, wherein said core yarn strand comprises more than one filament.
8. The yarn of claim 7, wherein each filament comprises a different type of fiber.
9. The yarn of claim 1, wherein said core yarn strand comprises a material different from a polymeric material.
10. The yarn of claim 1, wherein said coating is extruded over said core yarn strand.
11. The yarn of claim 10 further comprising a pigment, wherein the coating is extruded with said pigment.
12. A polymeric yarn, comprising a single polymeric strand having an axial axis, wherein an outer surface of said strand is non-uniform along a radial direction from said axial axis.
13. A method of coating yarn, comprising:
- creating an instability in flow of a polymeric coating through a die attached to an extruder;
- extruding a core yarn strand with said coating through said die; and
- forming a non-uniform coating along a radial direction of said strand.
14. The method of claim 13, further comprising varying one or more processing parameters from the group of extruder pressure, extruder barrel temperature, die temperature, and yarn draw speed.
15. The method of claim 13, further comprising extruding a pigment with said core yarn strand and coating.
16. The method of claim 13, further comprising cooling said coated yarn in a chilled water tank.
17. The method of claim 13, further comprising rolling said coated yarn through nip rollers.
18. A crosshead extrusion die for forming a polymeric coating over a strand of yarn, comprising:
- a die head;
- a feed zone to admit said strand and said coating;
- a flow balance zone to orient a flow of said coating; and
- a die cap having an orifice through which said coating and said strand is extruded, and a reservoir to create a flow instability in said coating;
- wherein a non-uniform coating along a radial direction of said strand is formed.
19. The die of claim 18, wherein said orifice is circular.
20. The die of claim 18, wherein said die comprises more than one orifice to simultaneously extrude more than one polymeric coated strand of yarn.
Type: Application
Filed: Jul 18, 2005
Publication Date: Jan 18, 2007
Inventors: Coley Mathis (Dothan, AL), Ali Ahmed (Dothan, AL)
Application Number: 11/183,524
International Classification: D02G 3/00 (20060101);