WO2008144477A1

WO2008144477A1 - Alternate twist ply yarn with low residual twist

Info

Publication number: WO2008144477A1
Application number: PCT/US2008/063839
Authority: WO
Inventors: Peter Popper; Donia Elkhamy; Paul Yngve; Frank Ko
Original assignee: Drexel University
Priority date: 2007-05-18
Filing date: 2008-05-16
Publication date: 2008-11-27
Also published as: US20110016841A1

Abstract

ATP yarns having high twist efficiency (low residual twist) as well as methods for increasing the self plying action that occurs in ATP yarn processing. The self plying action and the ATP yarn structure may be improved by increasing the convergence angle of the singles twist yarns to above 50 degrees (compared to current values of 0 to 35 degrees). The increased convergence angle permits an increase in the ply twist above the level possible by self plying alone. This results in a yarn with reduced residual singles twist. An array of singles torque jets and an optional ply torque jet has been developed to achieve a high convergence angle. The angle between the singles torque jet axes can be varied from 0 to 180 degrees.

Description

ALTERNATE TWIST PLY YARN WITH LOW RESIDUAL TWIST

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to alternate twist ply yarns (hereinafter "ATP yarns"), methods for manufacturing alternate twist ply yarns and to apparatus used in the manufacturing methods.

2. Description of the Related Technology

ATP yarns can be produced at much higher rates, for example, greater than ten times as fast as conventional ply yarns that do not alternate the twist direction. However, ATP yarns suffer from several problems that limit their use. Most significant is the excessive level of residual singles twist (typically the twist efficiency for ATP yarns is about 0.65). Conventional unidirectional twist ply yarns have zero residual twist (which equates to a twist efficiency of 1). In ATP yarns, the residual twist prevents the individual fibers from achieving their full bulk because they are tightly held in the structure (see for example Fig. 3B). In addition, in the case of carpet yarns, current ATP yarns can only be used in loop pile constructions (less than half of the United States carpet market). Cut pile carpets cannot now be made successfully with these ATP yarns due to the low twist efficiency of the ATP yarns.

Past attempts to reduce the residual twist have been generally unsuccessful. In particular, although adding a ply torque jet to the manufacturing apparatus and process to increase ply twist did produce a reduction in residual twist, this reduction was only by a relatively small amount. Thus, there is a need in the art for a way to overcome the problem of low twist efficiency in ATP yarns.

SUMMARY OF THE INVENTION

In a first aspect, the present invention relates to ATP yarns having a high twist efficiency.

In a second aspect, the present invention relates to a method for increasing the self plying action that occurs in ATP yarn processing. The self plying action and the ATP yarn structure may be improved by increasing the convergence angle of the singles yarns to above 50 degrees. The increased convergence angle permits an increase in the ply twist above the level possible by self plying alone. This results in a yarn with reduced residual twist.

In a third aspect, the present invention relates to an array of singles torque jets, an optional ply torque jet and optional other apparatus developed to achieve a high convergence angle. The angle between the jet axes can be varied from 0 to 180 degrees and the convergence angle is at least 50 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a schematic representation of an ATP apparatus with a high convergence angle.

Fig. 2 shows an alternate twist ply (ATP) yarn. Fig 3 A shows a balanced ply yarn with zero residual twist. Fig 3 B shows a ply yarn with a high amount of residual twist (reverse twist direction as the ply twist). Fig. 4 shows the portion of the ATP process in which the yarns converge and self-ply was modeled mathematically. The force and torque equilibrium equations are shown in Fig. 4.

Fig. 5 shows the results of the equations plotted in terms of singles torque versus convergence angle with parameter ply torque. Fig. 6 shows a plot of ply twist versus singles twist with and without a ply jet, using the procedure of comparative example A.

Fig. 7 shows a plot of twist efficiency versus convergence angle without ply torque along with a control test of the low convergence angle ATP machine as obtained using the procedure of Example 1. Fig. 8 shows a plot of twist efficiency versus convergence angle with added ply torque along with a control test run on the low convergence angle ATP machine using the procedure of Example 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to alternate twist ply (ATP) yarns as shown, for example, in Fig. 2, as well as to methods and apparatus for making ATP yarns. The following terminology is employed in this application. Twist - Turns/length along a singles or ply yarn, Singles - A yarn that is twisted and then plied together with other yams by twisting in the opposite twist direction in order to reduce or substantially eliminate residual singles twist.

Ply Yarn - A yarn made of two or more singles yarns. The singles are individually twisted and then twisted as a bundle in the opposite direction to form the ply yarn.

Balanced Ply Yarn - A ply yarn in which the singles twist equals the ply twist, but wherein the singles twist is in the opposite twist direction to the ply twist.

ATP - Alternate Twist Ply yarn. A ply yarn in which the twist direction alternates along the length. This yarn is twisted in one direction (typically for several feet) and then twisted in the opposite direction. The yarn is usually bonded or entangled where the twist reverses.

Self Ply - The process step in which twisted singles yarns converge and rotate about each other to form a ply yarn. Residual Singles Twist - The singles twist that remains in a singles yarn after plying which does not equal the ply twist. For a balanced ply yarn, since ply twist = singles twist, the residual twist is zero. This occurs because each turn of ply twist untwists a turn of singles twist. If the ply twist is less than the singles twist, some residual twist will remain. Thus, the Residual Singles Twist can be expressed as:

Residual singles twist = (twist imparted in the singles yarns - twist in the resulting plied yarn) (Equation 1)

Twist efficiency - Twist efficiency is defined as the ratio of ply twist to singles twist imparted in a ply yarn. The twist efficiency may be determined by measuring the ply yarn twist and singles yarn twist in the produced yarns using a standard twist tester (e.g. ITC-5 hand operated unit). First, a 40cm sample length of yarn is placed between the two jaws of the twist tester. A 5g weight is applied to the test sample at the spring loaded left jaw, creating tension in the yarn. The counter dial is then set to zero, and the crank handle is turned manually to unwind the ply twist. The counter reading, which represents the ply twist in turns per 40cm, is then recorded. With the unwound ply yarn still held between the jaws of the twist tester, one of the singles yarns is cut and removed. The counter dial is then reset to zero and the crank handle is turned in the opposite direction to unwind the twist in the remaining singles yarn.

The twist in the singles yarn may be measured using the Untwist-Retwist Method according to ASTM standard D 1422-99. In this method, the singles yarn is first untwisted. The twist is then reinserted until the tension loaded left jaw returned to its initial position. The counter reading is then recorded and divided by 2 to determine the singles twist in turns per 40cm. Yarn twist efficiency is calculated using Equation 2. The yarn twist efficiency of the ATP yarn was subsequently determined by calculating the average twist efficiency of five samples. In a balanced ply yarn, the Twist Efficiency = 1. If the ply twist is less than the singles twist, the twist efficiency will be less than 1. If the ply twist is greater than the singles twist, the twist efficiency will be greater than 1. The relationship between Twist Efficiency and singles twist is:

Twist efficiency = (Ply twist /singles twist) (Equation 2)

The ATP yarn of Fig. 2 shows twist alternatives section 4 and a bond section 5. Fig 3 A shows sections of alternating twist and thus having a twist efficiency of 1. Fig 3B shows a ply yarn with a high amount of residual singles twist in the reverse twist direction as the ply twist. A negative residual twist means the singles twist is in the same direction as the ply twist - since both the singles and the ply are twisted in the same direction. Yarns of that type are produced by a process called Sirospun.™

Both Twist Efficiency and Residual Twist may be expressed as a ratio or as a percentage. Both are measures of the same property in slightly different terms and thus these terms may be used interchangeably in this application.

BCF - Bulked continuous filament yarn. All fibers in this yarn are crimped to increase bulk.

The present invention can be used to increase the self plying action that occurs in ATP yarn processing. Known ATP yarns typically suffer from a specific technical problem - excessive residual twist of the singles yarns. This problem can be overcome by modifying the yarn processing method and apparatus in accordance with the present invention. The self plying action and the ATP yarn structure can be improved by increasing the convergence angle 3 of the singles yarns to above 50 degrees. Optionally, an additional ply torque jet 1 can be added to assist plying. The increased convergence angle 3 permits the ply torque jet 1 or other suitable apparatus to increase the ply twist above the level possible by self plying of parallel yarns alone. This results in a yarn with reduced residual twist.

In one exemplary embodiment of the apparatus of the present invention, an array of singles torque jets 2 and an optional ply torque jet 1 was developed to achieve a high convergence angle 3. The angle between the jet axes of the singles torque jets 2 can be varied from (0 degrees - jet axis parallel - to 180 degrees - jets facing each other). The convergence angle between the jet axes of the singles torque jets 2 may be from 50 to 180 degrees, from 70 to 150 degrees, or from 90-120 degrees. In another exemplary embodiment of the apparatus of the present application, the ATP yarn manufactured according to the method of the present invention, at high convergence angles 3 and using helper jets, produces substantially high twist efficiency. By increasing the ATP yarn convergence angle 3 to about 90 degrees and using a helper jet, the ATP yarn may have a twist efficiency of at least 0.70. In all known ATP processes, the torque in the singles yarns causes them to rotate around each other to form the ply yarn. But, the amount of ply twist is not as high as the singles twist. Consequently, all of the twist in the singles is not removed and undesirable singles twist remains.

Adding a ply torque jet 1 to existing systems which typically employ convergence angles 3 of 0-35 degrees, to increase ply twist yields only a small improvement because only a small amount of residual twist is removed by this measure. The reason for this limited improvement was found to be a "singles twist reduction" phenomenon. When torque is added to the ply yarns, the geometry of the yarn path requires the singles torque to drop - because of tension and torque equilibrium requirements. That means that adding ply torque, although it can increase ply twist, also reduces singles torque, the driving force for self plying. A ply torque jet 1 added to a conventional system employing a convergence angle 3 of 0-35 degrees thus causes two effects, one advantageous and one detrimental.

Fig. 4 shows the yarn mechanics in the convergence zone highlighting the two effects of a ply torque jet 1. The results of this analysis were plotted in FIG 5. These results confirm that if the process is run at a high convergence angle 3, the detrimental effect of the ply torque jet 1 is minimized while the benefits of the ply torque jet 1 are still obtained. This is a useful feature of the present invention. The method and apparatus of the invention can be used to produce an alternate twist ply yarn with a twist efficiency greater than 0.70, more particularly, an alternate twist ply yarn with a twist efficiency of 0.75 to 1.25, an alternate twist ply yarn with a twist efficiency of 0.85 to 1.15, or an alternate twist ply yarn with a twist efficiency of 0.95 to 1.05.

Basic Mechanical Action of Self Plying

The portion of the ATP process in which the yarns converge and self-ply was modeled mathematically as shown in Fig. 4. The force (Equation 3) and torque equilibrium equations (Equation 4) used to quantify how increasing convergence angle 3 prevents the ply torque jet from reducing torque on the individual singles yarns:

Tp = 2Ts cos θ (Equation 3) τ_p+2τ_s cos θ - T_SD_S sin θ = 0 (Equation 4)

Where τ_p,τ_s represents torque in singles and ply yarn for opposite direction twists, Tp Ts represents tension in singles and ply yarn, θ represents half convergence angle 3, and Ds represents singles yarn diameter. The torque on the ply yarn may be applied by a ply torque jet 1 (or other suitable means) to increase ply twist. The torque in the singles yarns is applied by the individual singles torque jets 2. The singles yarn torque causes rotation and plying and the amount of plying may be increased by the ply jet.

Fig. 5 shows the results of the equations plotted in terms of singles torque versus convergence angle 3 with parameter ply torque. For a given convergence angle 3, as the ply torque is increased, the singles torque is reduced. This means that the basic driving torque for the process is reduced when a ply jet 1 is turned on. In other words, increasing the ply torque to achieve more ply twist has the opposite effect as the singles torque is reduced. In fact, it can be reduced so much that the singles torque is in the opposite direction. (Yarns of that type can be made. They do not alternate twist and are made in a completely different way - the Sirospun™ process.)

The undesirable effect described can be overcome by operating at a high convergence angle 3. Because of the non- linear relation between the variables, at a high convergence angle 3, ply torque can be added without driving the singles torque to low levels that prevent self plying.

Fig. 1 shows a schematic representation of an ATP apparatus with a high convergence angle 3. The singles jets twist downstream (because the twist direction reverses in time cycles) and the ply jet increases the ply twist from what it would be if only self-plying occurred. The high convergence angle 3 is facilitated by the angle between the jet axes. High convergence angle 3 might also be achieved with parallel axis jets, but that would require extensive rubbing on the jet wall and result in a relatively inefficient torque application and thus is less preferred. Addition of a small guide or guide pins downstream of parallel singles torque jets 2 might also be used to increase the convergence angle 3. The guide or guide pins would fit between the singles yarns and prevent them from converging at a low angle. Alternatively, high convergence angles 3 can be achieved by deflecting yarns with directed air flow. This flow can come from added air jets or from the exhaust of the singles yarns jets. Yet another way of increasing convergence angle 3 is to set the process parameters (such as feed tension) to achieve a low singles yarn tension. At lower tension, the convergence angle 3 increases. Other process adjustments or combinations of the above could also increase convergence angle 3. In each of these scenarios, the convergence angle 3 between the axes of the singles torque jets 2 could, for example, be anywhere in the range of 0- 180 degrees with the other means assuring the desired convergence angle 3 downstream of the outlets of the singles torque jets 2 and upstream of the optional ply torque jet 1.

One alternative to use of the optional ply torque jet 1 to apply ply torque to the converging singles yarns would be the use of rollers as in the conventional Repco process.

EXAMPLES

A number of experiments were conducted to demonstrate the technology and the invention. Each will be described in detail along with the method of measuring residual twist. Method of Measuring Residual Twist

1. Select a 20 inch length of ATP with twist in one direction.

2. Using a standard twist counter and constant tension, measure the ply twist (turns/2.54 cm). 3. When all the ply twist has been removed, continue to grip the yarn and remove all but one singles yarn (which will be restored to the twist level it had before plying). 4. Measure the twist in the remaining singles yarn (the point of zero twist corresponds to the maximum untwisting length). 5. Calculate Twist Efficiency as the ratio of ply to singles twist.

6. Convert to Residual Twist, if needed, by Equation 1 given above.

On the Static Test Machine, the Twist Efficiency was measured on photographs of the converging singles yarns and the adjacent ply. Black tracer filaments were used to simplify identification of singles twist.

Comparative Example A - Effect of Ply Jet on Residual Twist

A laboratory ATP machine was used with and without a ply jet. Ply twist was measured for a range of singles twists and plotted on a graph that indicates twist efficiency levels. In addition, a static test machine was also used to prepare similar samples. In the static test machine, yarns were put into a "Y" configuration to simulate the actual process.

Key ATP Machine Conditions Bonding method - ultrasonic bond

Twist reversal length - 3 ft

Convergence angle - -35°

Singles - Nylon BCF 1250 denier

Output - 2 ply yarn

Static Test Machine Conditions

Convergence angle ~ 35°

Singles - Nylon BCF 1250 denier

Output - 2 ply yarn Results

Ply twist versus singles twist (with and without) ply jet is plotted in Fig. 6.

Twist efficiency decreases as twist increase (a twist efficiency of 100% corresponds to the ratio of ply twist/singles twist equaling 1). The static tester results are very close to those of the ATP machine

Ply jet increases Twist Efficiency (reduces Residual Twist) by negligible amount

It was found that adding a ply jet to a standard process with low convergence angle does not significantly reduce residual twist.

Example 1 - Effect of a High Convergence Angle on Residual Twist

The purpose of this test was to evaluate the effect of convergence angle on residual twist with and without an added ply torque jet 1. The experiment was run on the Static Tester because an ATP machine with the hardware needed for high convergence angle was not immediately available. The Static Tester was qualified as being a prototypic representation of the ATP machine in of Comparative Example A.

Static Test Machine Conditions Convergence angle - varied throughout experiment

Singles - Nylon BCF 1250 denier Output - 2 ply yarn Ply torque - experiment run with and without

Results

Twist efficiency versus convergence angle without ply torque are plotted in Fig. 7 along with a control test of the low convergence angle ATP machine. The results show that higher convergence angles improve twist efficiency by a relatively small amount over the control system. A twist efficiency of 100% corresponds to the ratio of ply twist/singles twist equaling 1.

Twist efficiency versus convergence angle with added ply torque are plotted in Fig. 8 along with a control test run on the low convergence angle ATP machine. The results show a very significant increase in twist efficiency relative to the control experiment. Levels well over 1 were reached. This experiment demonstrates that twist efficiency can be increased to required levels (and residual twist can be removed) by operating the process with a ply jet and a high convergence angle of 100-180 degrees.

Example 2 - Operating Test for High Convergence Angle Singles Torque Jets

The purpose of this example was to demonstrate the operability of the torque jet assembly of the present invention.

Jet Description Two singles torque jets mounted on a plate that permits their axes to be angled up to 180°.

Test

Install the jet in ATP machine Yarn speed - 400 yards/minute

Singles yarns - two 1245 denier Nylon 6,6 BCF

Air pressure - 40 to 90 psig

Evaluate operability, no attempt to produce ATP

Yarn feed geometry - parallel yarns into jets

Results

Yarns ran well through the jets at 0, 50, 90°

A new angled jet device was successfully fabricated and operated on an ATP machine at 400 yards/min with angles up to 90°. ATP yarns were not made in this example.

Example 3 - Effect of High Convergence Angle and Helper Jet on Twist Efficiency

The purpose of this experiment was to evaluate the effect of convergence angle on the residual twist of yarn with and without an added ply torque jet. Test

The following is a list of equipment and materials used to conduct the experiment: Drexel ATP Lab Machine Two 1245 BCF nylon feed yarns Main torque-jet pressure 30 psi Singles yarn tension 34g Helper torque-jet pressure 75 psi

Results Fig. 9 shows the measured twist efficiency for ATP yarn with and without a ply torque jet over a range of convergence angles. As shown by Fig. 9, using a helper torque-jet substantially improves twist efficiency. Furthermore, increasing the convergence angle, preferably to about 90 degrees between yarns, also substantially enhanced twist efficiency when a helper jet is used, but increasing the convergence angle was found to decrease efficiency without a helper jet. Based on this experiment, the highest twist efficiency, about 78%, was achieved at a high convergence angle of about 90 degrees and by using a helper torque-jet.

Example 4 - Examples of an ATP Yarn Having a High Twist Efficiency The twist efficiency for an ATP yarn manufactured according to the method of the present invention, at high convergence angles and using helper jets, was investigated. By increasing the ATP yarn convergence angle to 90 degrees and using a helper jet, it was possible to produce an ATP yarn with a twist efficiency of at least 70%.

Results

Table 1 shows the twist efficiency of the ATP yarn of the present invention in comparison to two control ATP yarns. Table I

Test The twist efficiency was determined by measuring the ply yarn twist and singles yarn twist in the produced yarns using a standard twist tester (e.g. ITC- 5 hand operated unit). First, a 40cm sample length of ATP yarn located between two successive bonds in the ATP yarn was placed between the two jaws of the twist tester. A 5g weight was applied to the test sample at the spring loaded left jaw, creating tension in the ATP yarn. The counter dial was then set to zero, and the crank handle was turned manually to unwind the ply twist. The counter reading, which represents the ply twist in turns per 40cm, was then recorded. With the unwound ply yarn still held between the jaws of the twist tester, one of the singles yarns was cut and removed. The counter dial was then set to zero again, and the crank handle was turned in the opposite direction to unwind the twist in the remaining singles yarn. The twist in the singles yarn was measured using the Untwist-Retwist Method according to ASTM standard D 1422-99. In this method, the singles yarn was first untwisted. The twist was then reinserted until the tension loaded left jaw returned to its initial position. The counter reading was then recorded and divided by 2 to determine the singles twist in turns per 40cm. Yarn twist efficiency was calculated using Equation 2. The yarn twist efficiency of the ATP yarn was subsequently determined by calculating the average twist efficiency of five samples.

For illustrative purposes, the principles of the present invention are described by referring to various exemplary embodiments thereof. Although the preferred embodiments of the invention are particularly disclosed herein, one of ordinary skill in the art will readily recognize that the same principles are equally applicable to, and can be implicated in other compositions and methods, and that any such variation would be within such modifications that do not part from the scope of the present invention. Before explaining the disclosed embodiments of the present invention in detail, it is to be understood that the invention is not limited in its application to the details of any particular embodiment shown. The terminology used herein is for the purpose of description and not of limitation. Further, although certain methods are described with reference to certain steps that are presented herein in certain order, in many instances, these steps may be performed in any order as may be appreciated by one skilled in the art, and the methods are not limited to the particular arrangement of steps disclosed herein.

Claims

1. An alternate twist ply yarn with a twist efficiency greater than 0.70.

2. An alternate twist ply yarn as claimed in claim 1 , with a twist efficiency of 0.75 to 1.25.

3. An alternate twist ply yarn as claimed in claim 1, with a twist efficiency of 0.85 to 1.15.

4. An alternate twist ply yarn as claimed in claim 1, with a twist efficiency of 0.95 to 1.05.

5. A method for making the yarn of claim 1 comprising the steps of: twisting singles in lengthwise alternating directions using a convergence angle of at least 50°; and bonding yarns at a twist reversal point.

6. A method as claimed in claim 5, wherein the convergence angle is 50-180°.

7. A method as claimed in claim 5, wherein the convergence angle is 70-150°.

8. A method as claimed in claim 5, wherein the convergence angle is 90-120°.

9. A method as claimed in claim 5, wherein at least one yarn ply torque jet is employed in said twisting step.

10. A method as claimed in claim 9, wherein at least two singles torque jets are employed in said twisting step.

11. A yarn torque jet assembly comprising at least two singles torque jets and wherein an angle between axes of two of said singles torque jets is from 0-180°.

12. A yarn torque jet assembly as claimed in claim 11, wherein the angle between axes of at least two of said singles torque jets is from 50-180°.

13. A yarn torque jet assembly as claimed in claim 11, wherein the angle between axes of at least two of said singles torque jets is from 70-150°.

14. A yarn torque jet assembly as claimed in claim 11 , wherein the angle between axes of at least two of said singles torque jets is from 90-120°.

15. A yarn torque jet assembly as claimed in claim 11, further comprising a guide which ensures that a yarn convergence angle is different from the angle between the axis of said at least two singles torque jets.

16. A yarn torque assembly as claimed in claim 11, further comprising a ply torque jet located downstream of said at least two singles torque jets.