SUPER-HIGH-MOLECULAR-WEIGHT POLYOLEFIN YARN, METHOD FOR PRODUCING SAME, AND DRAWING DEVICE

Abstract

An ultrahigh molecular weight polyolefin yarn of the present invention has been drawn and has a melting point that is determined as a maximum peak temperature measured by a differential scanning calorimeter (DSC) at a temperature rise rate of 20° C./min, and the melting point is higher than a melting point of the yarn before drawing. In a production method of the present invention, a drawing bath (3) that includes a hollow yarn path (14) and a jacket portion (13) in which a heated liquid circulates is placed in a drawing zone, and the yarn is heated and drawn while passing through the yarn path (14) in a non-contact manner. A drawing device of the present invention includes a feeder (1) for feeding a yarn, a drawing bath (3) for heating and drawing the yarn, and a winder (5) for winding up the drawn yarn. The drawing bath (3) includes a hollow yarn path (14) and a jacket portion (13) in which a heated liquid circulates. Thus, the present invention provides a drawing method in which a high strength ultrahigh molecular weight polyolefin yarn can be drawn stably even at a high draw ratio, a drawing device, and a yarn obtained by the drawing method.

Description

TECHNICAL FIELD

The present invention relates to a high strength ultrahigh molecular weight polyolefin yarn, a method for producing the same, and a drawing device.

BACKGROUND ART

High strength polyolefin filaments, typified by gel spun ultrahigh molecular weight polyethylene filaments, have high tenacity, light weight, and excellent light and abrasion resistance, and therefore are used for ropes, fishing lines, reinforcing materials, protective clothing, or the like.

It is known that raw yarns, twisted yarns, or braided yarns of high strength ultrahigh molecular weight polyolefin that have been drawn can be postdrawn (redrawn). Postdrawing is also called redrawing. In the present specification, postdrawing or redrawing simply may be referred to as “drawing”. The melting point of the high strength ultrahigh molecular weight polyolefin is 120 to 240° C., although it depends on the type of the resin. As a typical example, ultrahigh molecular weight polyethylene has a melting point of 138 to 162° C. The following documents are directed to polyethylene. Patent Document 1 discloses that drawing is performed at a temperature not higher than the melting point (140 to 153° C.). Patent Document 2 discloses that a braided fishing line is fused and drawn to 1.01 to 2.2 times at a temperature within the melting point range (150 to 155° C.). Patent Document 2 also discloses that the fishing line thus drawn under the above conditions increases the transparency due to the fusion and becomes like a monofilament.

Patent Documents 3, 4, 5, etc. disclose drawing at a high draw ratio. In Patent Document 3, a forced convection oven is used as a drawing device, and a yarn is drawn to 3 times or more at 130 to 160° C. In Patent Document 4, a yarn is drawn to 2.7 times or more at 150 to 157° C. In Patent Document 5, a polyolefin yarn is drawn to 2 times or more to have a single fiber fineness of 0.55 deci tex or less. Patent Documents 3 and 4 use filaments having a large single fiber fineness and a large total fineness. Patent Document 5 teaches that it is desirable that yarns are doubled to increase the total fineness and then drawn, thereby achieving a small single fiber fineness.

According to the studies conducted by the present inventors, the temperature of a drawing bath needs to be controlled with high precision so that drawing can be performed at a high draw ratio within a narrow melting point range, as described above, to establish industrially stable production. As an example of a drawing device for high strength polyolefin, Patent Document 3 uses a forced convection oven. Although Patent Document 4 does not specifically teach a drawing device, Patent

Document 6 (by the same applicant as Patent Document 4) discloses an air-blow drawing device that provides a gas flow in the direction perpendicular to the yarn.

The drawing system that blows and circulates a heated gas such as air generally has been used for the drawing of a monofilament When this drawing system requires high-precision temperature control, it is desirable that the gas flow rate is increased so as to increase the number of circulations of the gas per unit time. However, a strong gas flow can cause the yarn to sway and tangle, and thus makes the drawing unstable. On the other hand, if the gas flow rate is reduced, the number of circulations of the gas per unit time is reduced. This is likely to result in an uneven temperature distribution in the drawing bath (e.g., between the inlet and the outlet, the center and the ends, or the like) and temperature variations over time. In particular, when the total fineness and the single fiber fineness of the yarn are small, the yarn and the single fiber are broken easily even by a relatively small fluctuation, and it is more difficult to perform the drawing stably.

PRIOR ART DOCUMENTS

Patent Documents

Patent Document 1: JPS 61(1986)-289111 A

Patent Document 2: JPH 9(1997)-98698 A

Patent Document 3: JP 2008-512573 A

Patent Document 4: JP 2008-517168 A

Patent Document 5: 2008-266843 A

Patent Document 6: 2004-512436 A

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

To solve the above conventional problems, the present invention provides a method for producing a high strength ultrahigh molecular weight polyolefin yarn, in which the yarn can be drawn stably even at a high draw ratio, a drawing device, and a yarn produced by this method.

Means for Solving Problem

An ultrahigh molecular weight polyolefin yarn of the present invention has been drawn and has a melting point that is determined as a maximum peak temperature measured by a differential scanning calorimeter (DSC) at a temperature rise rate of 20° C./min. The melting point is higher than a melting point of the yarn before drawing.

A method for producing an ultrahigh molecular weight polyolefin yarn of the present invention includes heating and drawing the ultrahigh molecular weight polyolefin yarn. A drawing bath that includes a hollow yarn path and a jacket portion in which a heated liquid circulates is placed in a drawing zone. The yarn is heated and drawn while passing through the yarn path in a non-contact manner.

A drawing device of the present invention is used in the above method for producing an ultrahigh molecular weight polyolefin yarn, and includes a feeder for feeding a yarn, a drawing bath for heating and drawing the yarn, and a winder for winding up the drawn yarn. The drawing bath includes a hollow yarn path and a jacket portion in which a heated liquid circulates.

Effects of the Invention

The melting point of the drawn ultrahigh molecular weight polyolefin yarn of the present invention, which is determined as a maximum peak temperature measured by a differential scanning calorimeter (DSC) at a temperature rise rate of 20° C./min, shifts to a higher temperature than the melting point of the yarn before drawing. This indicates that crystallization or melt-recrystallization of the amorphous portion proceeds by uniform drawing, and a skin-core structure composed of the surface layer and the inside of a filament is reduced or eliminated, so that the filament is changed into a crystal structure that is uniform in the cross-sectional direction. According to the present invention, the high strength ultrahigh molecular weight polyolefin yarn can be drawn stably even at a high draw ratio, and an extra-fine drawn yarn having a small total fineness can be provided. Moreover, the present invention can provide an ultrahigh molecular weight polyolefin yarn that has a small coefficient of variation in strength and excellent uniformity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic process diagram showing the whole of a drawing device of an example of the present invention.

FIG. 2 is a perspective view of a drawing bath of an example of the present invention.

FIGS. 3A to 3C are cross-sectional views of a drawing bath of an example of the present invention.

FIG. 4A is a DSC chart of a yarn before drawing in Examples 1 and 4. FIG. 4B is a DSC chart of a yarn after drawing in Example 1.

FIG. 5 is a DSC chart of a yarn at a draw ratio of 2.0 times in Example 4.

FIG. 6 is a DSC chart of a yarn at a draw ratio of 2.5 times in Example 4.

FIG. 7 is a DSC chart of a yarn at a draw ratio of 3.0 times in Example 4.

FIG. 8 is a DSC chart of a yarn at a draw ratio of 5.6 times in Example 4.

FIG. 9 is a DSC chart of a yarn at a draw ratio of 1.5 times in Comparative Example 4.

FIG. 10 is a DSC chart of a yarn at a draw ratio of 2 0 times in Comparative Example 4.

DESCRIPTION OF THE INVENTION

The present inventors have found that when an ultrahigh molecular weight polyolefin yarn is drawn uniformly by the drawing method of the present invention, the melting point of the resulting drawn yarn, which is determined as a maximum peak temperature measured by a differential scanning calorimeter (DSC) at a temperature rise rate of 20° C./min in the unconstrained state, shifts to higher temperatures due to the drawing, and the maximum peak temperature (melting point) is even higher than the melting point of the yarn before drawing.

With respect to the ultrahigh molecular weight polyethylene yarn, a commercially available high tenacity polyethylene yarn, i.e., a conventional drawn yarn has a melting point of about 147 to 153° C. The present invention demonstrates that the drawn yarn obtained by redrawing the conventional drawn yarn has a maximum peak temperature of 155 to 162° C. (i.e., a high temperature peak). This high temperature peak may exist independently or in conjunction with a shoulder or small peak that is in the vicinity of the melting point (147 to 153° C.) before drawing. In either case, if the draw ratio is high, the maximum peak temperature reaches a high temperature of 155 to 162° C. The melting point after drawing is higher than the drawing temperature, indicating that the drawing has changed a large proportion of the structure and made the structure highly uniform. Such a component having a high melting point also can be recognized as a small peak or shoulder in the DSC of the raw yarn before drawing. However, in the conventional raw yarn and drawing method, it is not known that the component having a high melting point shows the main peak. Therefore, the above phenomenon may indicate that crystallization and melt-recrystallization of the amorphous portion proceeds by uniform drawing, and a skin-core structure composed of the surface layer and the inside of a filament is reduced or eliminated, so that the filament is changed into a crystal structure that is uniform in the cross-sectional direction.

The degree of crystallinity calculated from the amount of heat of fusion is 72 to 85% after drawing, which is likely to be the same as or slightly larger than the degree of crystallinity (65 to 80%) before drawing. These features can support the fact that the drawing of the present invention is performed uniformly under high-precision temperature control.

On the other hand, in the conventional hot air circulation drawing, the main peak appears at a temperature of 147 to 153° C. on the low temperature side even after drawing, and the structural change due to the drawing is smaller than that in the drawing method of the present invention. The degree of crystallinity calculated from the amount of heat of fusion is 70 to 85% after drawing.

The ultrahigh molecular weight polyolefin of the present invention includes polyethylene, polypropylene, polybutene-1, poly(4-methylpentene-1), and copolymers or mixtures thereof The ultrahigh molecular weight is preferably an average molecular weight of at least about 200,000, and more preferably at least about 600,000. Here, the molecular weight represents a weight average molecular weight (Mw) and can be calculated by Mw =5.37×10⁴×[IV]^1.37, where [IV] is an intrinsic viscosity in decalin at 135° C. (Patent Document 4 etc.).

The polyolefin yarn of the present invention is preferably a high strength filament that is produced by a so-called “gel spinning” method and has a strength of at least 15 CN/dtex.

In particular, a high strength ultrahigh molecular weight polyethylene filament is suitable. Examples of the high strength polyethylene filament include “Dyneema” (trade name) manufactured by TOYOBO CO., LTD. and DSM Corporation, and “Spectra” (trade name) manufactured by Honeywell Inc.

In the context of the present invention, the yarn is preferably an untwisted, interlaced, twisted, or braided multifilament yarn.

Next, examples of a drawing method and a manufacturing apparatus of the present invention will be described with reference to the schematic drawings. The same components or materials are denoted by the same reference numerals. FIG. 1 is a schematic process diagram showing the whole of a drawing device in an example of the present invention. FIG. 1 is an overall view of a one-stage drawing device. A plurality of feed yarns 8 (8 yarns in FIG. 1) are pulled out of a yarn feeder 1, fed to a first roller group 2 rotating at a speed V1, heated and drawn in a drawing bath 3, drawn on a second roller group 4 at a speed V2, and then the drawn yarns 9 are wound up by a winder 5. The total draw ratio is expressed by V2/V1. A yarn path 14 of the drawing bath 3 is hollow, and the yarns are heated and drawn in the yarn path 14. A heated liquid circulates in a jacket portion 13 enclosed by a housing portion 16 of the drawing bath 3. The circulating liquid is heated at a predetermined temperature by a heater 6, and is forced to circulate using a pump 7 that is located upstream or downstream of the heater 6. Although this example shows one-stage drawing, multi-stage drawing (with two or more stages) may be used. The number of drawing baths and the length of the drawing bath are not particularly limited, and can be appropriately selected.

FIG. 2 is a perspective view of the drawing bath 3 in an example of the present invention. The yarn path 14 is in the form of a continuous cavity. The feed yarns 10a to 10c are heated and drawn so as not to be in contact with the drawing bath 3, and the drawn yarns 11a to 11c are wound up. The drawing bath 3 may have any length L as long as it is long enough to be able to heat and draw the feed yarns 10a to 10c uniformly, although the length L depends on the speed of the yarn and the draw ratio. The practically favorable length L of the drawing bath 3 is 0.3 to 10 m, and more preferably 0.5 to 5 m. If the length L is too long, temperature variations are likely to occur in the length direction. Therefore, it is desirable that two or more units are coupled as needed.

FIGS. 3A to 3C are cross-sectional views (taken along the direction perpendicular to the traveling direction of the yarns) of the drawing bath 3 in an example of the present invention. In FIG. 3A, both the drawing bath 3 and the yarn path 14 have an elliptical cross section. The yarns 10a to 10c are heated and drawn so as not to be in contact with an inner wall 12 of the drawing bath 3. The heated liquid circulates in the jacket portion 13. The yarn path 14 is in the form of a continuous cavity. In FIG. 3B, both the drawing bath 3 and the yarn path 14 have a rectangular cross section. However, each of the corners is formed in an arc shape. In FIG. 3C, the drawing bath 3 has a rectangular cross section, and the yarn path 14 has a circular cross section. The minor axis 15, the height 15, and the diameter 15 of the yarn paths 14 in FIGS. 3A, 3B, and 3C are preferably in the range of 10 to 300 mm, and more preferably in the range of 10 to 150 mm, respectively.

The heated liquid circulates through a temperature-controlled heating medium heater. The heated liquid is not directly in contact with the yarns, and therefore can circulate at a high speed. Moreover, if the capacity of the jacket is made sufficiently large compared to the yarns, there is almost no temperature change due to the traveling of the yarns. The heated liquid is not particularly limited, and a general heating medium liquid such as oils preferably can be used. Although not shown, it is desirable that the outer wall of the drawing bath 3 is covered with a heat insulating material.

In the present invention, it is preferable that positive air ventilation is not provided in the drawing bath. In this case, the “positive air ventilation” means forced air ventilation with the use of a fan or the like. When the positive air ventilation is not provided, the internal temperature hardly varies and the yarns do not sway, so that stable drawing can be performed. Incidentally, natural convection is tolerated.

The drawing method of the present invention has the following advantages over the hot air circulation drawing that is generally used as a postdrawing method of a polyolefin yarn.

(1) The present invention ensures excellent temperature control accuracy

(2) Since the present invention does not provide the positive air ventilation, the yarn is stable even if it is a fine filament.

(3) The present invention mainly uses radiant heat from the inner wall and natural convection, while the yarn is heated by the forced circulation of hot air in the hot air circulation system. Such a difference may also be one of the advantages of the present invention.

For the temperature control, the ambient temperature (drawing temperature) of the drawing bath is preferably 150 to 157° C. and is controlled within ±0.2° C., and more preferably controlled within the ambient temperature (drawing temperature) ±0.1° C. In this manner, the drawing bath of the present invention enables stable temperature control. On the other hand, the conventional air-blow (hot air circulation) drawing bath has a variation of about ±1.0° C. This is described in Example 1 of Patent Document 3. The heating system of the present invention uses a liquid as a heating medium and forces the liquid to circulate, thereby improving the temperature accuracy.

It has been confirmed that there is less variation in temperature according to the location in the drawing bath. In the air-blow drawing bath, the circulation velocity (blowing speed) may be limited due to the swaying of the yarn, and the temperature control accuracy may be limited because the heat capacity of a gas is smaller than that of a liquid, and a nonuniform gas flow is likely to occur in the device.

The cross section of the yarn path 14 can be elliptical, rectangular, and circular, as shown in FIGS. 3A to 3C. However, the cross section of the yarn path 14 is not limited thereto, and may be appropriately designed in accordance with the number of yarns to be drawn. Moreover, it is preferable that the entire surface of the inner wall of the drawing bath, except for the inlet and the outlet through which the yarns pass, is jacket heated so as to make the temperature more uniform.

In this regard, if there is an opening or gap that is not jacket heated in the inner wall of the drawing bath, such a structure is not suitable. Moreover, an opening and closing structure of the drawing bath is also not suitable, since the temperature is changed by opening and closing operations, and it takes time before the temperature becomes constant.

The inlet and outlet of the drawing bath of the present invention are open. However, if the opening space is large, the temperature varies as the heated air comes in and out of the drawing bath. Therefore, it is preferable that a temperature difference is reduced, e.g., by shielding the opening other than the portion where the yarn is traveling, or by disposing a heat insulating material or a heating unit at a temperature lower than the drawing bath temperature in front of the inlet and/or behind the outlet of the drawing bath.

The length (L) of the drawing bath (unit) is not particularly limited, and a plurality of drawing baths may be coupled, or multi-stage drawing may be performed as needed. In this case, the length (L) of the drawing bath means the total length of the drawing bath units.

The capacity of the heating medium and the size of the inside of the jacket are not particularly limited, and any structure may be used as long as the internal temperature is uniform and does not vary even if many yarns are processed together.

However, if the cross section of the yarn path 14 is too large, temperature variations occur. On the other hand, if the cross section of the yarn path 14 is too small, the workability such as threading of the yarns through the yarn path is poor. Therefore, the preferred height, diameter, or minor axis of the cross section is about 10 to 300 mm. It is desirable that the yarns 10a to 10c pass through near the central portion of the yarn path 14 in terms of uniform heating.

In the present invention, the yarn to be drawn is a drawn ultrahigh molecular weight polyolefin multifilament yarn. The drawn feed yarn can be an untwisted yarn, an interlaced yarn, a twisted yarn, or a braided yarn. It is possible to use either a method in which the raw yarns such as the untwisted yarns, the interlaced yarns, or the single-twisted yarns are drawn and then braided to form a product or a method in which the braided yarns are drawn to form a product, or both of these methods. The above methods may be selected as needed, and the raw yarns before braiding can be drawn at a higher draw ratio. If necessary, these yarns may contain oils such as mineral oil and vegetable oil, waxes, and resins such as polyolefin resin, modified polyolefin resin, and ethylene-acrylic acid copolymer resin. Moreover, the resins may contain a coloring agent.

The thickness (fineness) of the yarn to be drawn is not particularly limited. Compared to the conventional air-blow heating, the drawing method of the present invention has the advantage of drawing a fine yarn. In view of this, it is particularly preferable that the fineness of the feed yarn is 400 dtex or less.

In the present invention, extra-fine yarns having a fineness of 50 dtex or less after drawing, which have been difficult to produce industrially, can be produced and also applied to braided yarns. Such extra-fine braided yarns can be obtained by a method in which the raw yarns before braiding are drawn by the drawing method of the present invention and then braided, a method in which the braided yarns are drawn by the drawing method of the present invention, or a combination of these methods. Although the single fiber fineness depends on that of the raw yarns before drawing, commercially available yarns with a single fiber fineness of 1.1 dtex can be drawn into ultrafine yarns with a single fiber fineness of 0.2 dtex or less. Such fine yarns and fine braided yarns are particularly suitable for fishing lines of a small line size number. Moreover, since those yarns cannot be seen easily by the naked eye and have high tenacity, they are suitable for strings for hanging, sutures, thin knitted fabrics, nets, or the like.

The ultrahigh molecular weight polyethylene yarn is drawn under the conditions that the temperature is preferably 150 to 157° C. and the draw ratio is about 1.5 to 10 times. Setting the drawing conditions is important because if the temperature and the time are insufficient, the yarn is broken during the drawing, and if the temperature is too high and the time is too long, the yarn is broken by melting or becomes weak due to excessive fusion. The residence time in the drawing bath is preferably 0.1 to 8 minutes, although it depends on the temperature and the draw ratio.

The drawing method of the present invention has the following advantages over the conventional hot air circulation heating method.

(1) The present invention suppresses the breakage of the yarn during the drawing and reduces fuzz on the yarn.

(2) The present invention allows the drawing to be performed at a high draw ratio such that the maximum draw ratio is higher at the same drawing temperature.

(3) There is only a small variation in the physical properties of the drawn yarn.

(4) The present invention ensures high stability at the time of an increase in quantity.

In addition to the general uniform drawing at a constant draw ratio, the present invention also can produce a tapered braided yarn with a thickness ratio of about 1:5 to 1:8 by variably controlling the draw ratio.

EXAMPLES

Hereinafter, the present invention will be described in more detail by way of Examples and Comparative Examples. However, the present invention is not limited to the following examples.

Examples 1 to 3 used a drawing bath having a length of 3 m and a hollow rectangular cross section, as shown in FIG. 3B, in combination with a one-stage drawing device, as shown in FIGS. 1 and 2. Comparative Examples used a hot air circulation drawing bath having the same length in place of the drawing bath in Examples 1 to 3.

Examples and Comparative Examples were evaluated in the following manner.

Physical Properties Test

The strength-elongation was measured according to the measurement method of JIS L1013. The fineness (dtex) was determined by cutting a yarn into a length of 1 m, measuring the weight of the cut yarn in units of 0.1 mg, and multiplying the result by 10000.

Evaluation of Drawing Properties

The drawing properties were evaluated by the following criteria under the respective drawing conditions.

A: No yarn breakage occurred for 5 minutes or more.

B: A yarn breakage occurred within 5 minutes, but the yarn was wound up.

C: A yarn breakage occurred immediately, and the yarn was not wound up.

Measurement of Melting Point and Degree of Crystallinity by Differential Scanning Calorimeter (DSC)

Using a differential scanning calorimeter DSC-60 manufactured by Shimadzu Corporation, the yarn was measured in the unconstrained state at a temperature rise rate of 20° C./min. The maximum peak temperature at a melting endothermic peak was defined as a melting point. The degree of crystallinity was determined by the following formula based on the amount of endotherm Δ Hm (J/g) obtained from the peak area.

Degree of crystallinity (%)=100 ×Δ Hm/Δ H

where Δ H represents the amount of heat of fusion of a perfect crystal. In the case of polyethylene, the calculation was performed with Δ H=293 J/g. When the sample yarns appeared to be in the constrained state as a result of braiding, resin finish, or the like, the yarns were disentangled before measurement.

The following yarns were used as raw yarns before drawing.

Raw Yarn Before Drawing

Raw yarn A: manufactured by TOYOBO CO., LTD., trade name: “Dyneema”, 110T-96F-410, single twisted (s-twist) with 90 twists per meter

Braided yarn B: manufactured by TOYOBO CO., LTD., trade name: “Dyneema”, 55T-48F-410, a set of four yarns

Braided yarn C: manufactured by TOYOBO CO., LTD., trade name: “Dyneema”, 165T-144F-410, a set of eight yarns

Example 1

A drawing test was performed using a single-twisted high strength ultrahigh molecular weight polyethylene raw yarn A, which had been drawn by the conventional method, as a feed yarn. In this example, the raw yarn A was obtained by twisting (s-twist) a raw yarn manufactured by TOYOBO CO., LTD., trade name: “Dyneema”, 110T-96F (total fineness: 110 Tex; number of filaments: 96) with 90 twists per meter. The raw yarn used had a tensile strength of 31.8 CN/dtex, an elongation of 4.8%, a DSC melting point of 150.3° C., and a degree of crystallinity of 75%. FIG. 4A shows a DSC chart of the yarn before drawing. In FIG. 4A, a dotted line is an auxiliary line that is automatically added by the analyzer to determine a peak area. The same is true for the following DSC charts. The drawing bath of the drawing device used had a length of 3 m and a hollow rectangular cross section, as shown in FIG. 3B. The drawing test was performed with the one-stage drawing device, as shown in FIGS. 1 and 2. The measured temperature of the drawing bath was 154±0.1° C., and the temperature was stable. The draw ratio was changed from 3.6 to 4.7 times, and consequently the maximum draw ratio was 4.6 times, as shown in Table 1. The drawn yarn at this draw ratio had a strength of 35.7 CN/dtex, an elongation of 2.4%, a DSC melting point of 157.5° C., and a degree of crystallinity of 80%. The melting point was raised by about 8° C. and the degree of crystallinity was increased by 5% due to the drawing. FIG. 4B shows a DSC chart of the drawn yarn at a maximum draw ratio of 4.6 times.

Comparative Example 1

A one-stage drawing test was performed on three yarns while increasing the draw ratio using the same device as Example 1, except that a hot air circulation drawing bath having a length of 3 m was used instead of the drawing bath in Example 1. As shown in Table 1, the drawn yarn at a draw ratio of 3.6 times could be wound up for 5 minutes or more. However, the drawn yarn at a draw ratio of 3.7 times was broken in a little more than 1 minute, and the drawn yarn at a draw ratio of 3.8 times was frequently broken and could not be wound up. Therefore, the maximum draw ratio was 3.6 times in accordance with the criteria described above. The drawn yarn at this draw ratio had a strength of 30.6 CN/dtex and an elongation of 2.5%. The measured temperature of the drawing bath was 154±1.0° C. The drawn yarn at a draw ratio of 3 6 times had a DSC melting point of 151.5° C. and a degree of crystallinity of 79%. Tables 1 and 2 show the conditions and the results of Example 1 and Comparative Example 1.

TABLE 1
Example/			Feed	Winding		Jacket heating	Internal		Fineness	Fineness
Compar-			speed	speed	Draw	medium	temperature of		before	after
ative	Exper.		V1	V2	ratio	temperature	drawing bath		drawing	drawing
Example	No.	Sample	(m/min)	(m/min)	(V2/V1)	(° C.)	(° C.)	Results of drawing	(dtex)	(dtex)
Ex. 1	1-1	Raw yarn A:	0.91	3.30	3.6	154.0	154 ± 0.1	A: No problem	109.5	30.5
		110T
	1-2	Raw yarn A:	0.72	3.30	4.6	154.0	154 ± 0.1	A: Maximum draw ratio	109.5	23.8
		110T
Comp.	1-3	Raw yarn A:	0.91	3.30	3.6	154*	154 ± 1.0	A: Maximum draw ratio	109.5	30.6
Ex. 1		110T
	1-4	Raw yarnA:	0.89	3.30	3.7	154*	154 ± 1.0	B: The yarn was broken in 1	109.5	29.0
		110T						minute and 15 seconds.
	1-5	Raw yarn A:	0.87	3.30	3.8	154*	154 ± 1.0	C: The yarn was frequently	109.5	—
		110T						broken.
(Note)
*Set temperature of a hot air circulation drawing bath

TABLE 2
Example/				DSC peak temperature	DSC peak temperature	Degree of
Comparative	Exper.	Strength	Elongation	on low temperature	on high temperature	crystallinity	DSC chart
Example	No.	(CN/dtex)	(%)	side (° C.)	side (° C.)	(%)	No.
Before drawing	1-0	31.8	4.8	◯ 150.3	—	75	FIG. 4A
Ex. 1	1-2	35.7	2.4	—	◯ 158.6	80	FIG. 4B
Comp. Ex. 1	1-3	34.9	2.5	◯ 151.8	158.8	78	—
	1-4	34.5	2.5	—	—	—	—
	1-5	—	—	—	—	—	—
(Note)
◯ Maximum peak temperature (melting point)

As is evident from Table 1, Example 1 can significantly improve the maximum draw ratio compared to Comparative Example 1, and thus can stably provide the drawn yarn with a small fineness. The drawn yarn also has a high strength. Moreover, as is evident from Table 2, it can be confirmed that the melting point measured as a maximum peak temperature by the differential scanning calorimeter (DSC) at a temperature rise rate of 20° C/min in the unconstrained state shifts 8.3° C. to the high temperature side from the melting point of the yarn before drawing, and the melting point thus measured is 7° C. higher than that of Comparative Example 1. Further, the degree of crystallinity is higher in Example 1 than in Comparative Example 1.

Example 2

A drawing test was performed using a braided yarn B as a feed yarn. In this example, the braided yarn B was obtained by braiding four raw yarns manufactured by TOYOBO CO., LTD., trade name: “Dyneema”, 55T-48F (total fineness: 55 Tex, number of filaments: 48). The braided yarn B used had a tensile strength of 25.4 CN/dtex and an elongation of 4.9%. The drawing test was performed with the same jacket heating drawing bath as Example 1. As shown in Tables 3 and 4, the maximum draw ratio was 3 2 times in Example 2, which was improved compared to Comparative Example 2. The drawn yarn at this draw ratio had a strength of 27.0 CN/dtex and an elongation of 2.9%.

Comparative Example 2

The maximum draw ratio was examined using a hot air circulation drawing bath in the same manner as Comparative Example 1. As shown in Table 2, the maximum draw ratio was 2.7 times. The drawn yarn at a draw ratio of 2.9 times was frequently broken and could not be wound up. The drawn yarn at the maximum draw ratio had a strength of 26.5 CN/dtex and an elongation of 3.1%. Tables 3 and 4 show the conditions and the results of Example 2 and Comparative Example 2.

TABLE 3
			Feed	Winding		Jacket heating	Internal		Fineness	Fineness
Example/			speed	speed	Draw	medium	temperature of		before	after
Comparative	Exper.		V1	V2	ratio	temperature	drawing bath		drawing	drawing
Example	No.	Sample	(m/min)	(m/min)	(V2/V1)	(° C.)	(° C.)	Results of drawing	(dtex)	(dtex)
Ex. 2	2-1	Braided yarn B	0.78	2.50	3.2	154.0	154 ± 0.1	A: Maximum draw ratio	205.2	64.5
Comp. Ex. 2	2-2	Braided yarn B	0.93	2.50	2.7	154*	154 ± 1.0	A: Maximum draw ratio	205.2	76.3
	2-3	Braided yarn B	0.89	2.50	2.8	154*	154 ± 1.0	B: The yarn was broken	205.2	73.6
								in 1 minute.
	2-4	Braided yarn B	0.86	2.50	2.9	154*	154 ± 1.0	C: The yarn was frequently	205.2	—
								broken.
(Note)
*Set temperature of a hot air circulation drawing bath

TABLE 4
Example/				DSC peak temperature	DSC peak temperature	Degree of
Comparative	Exper.	Strength	Elongation	on low temperature	on high temperature	crystallinity
Example	No.	(CN/dtex)	(%)	side (° C.)	side (° C.)	(%)
Before drawing	2-0	25.4	4.9	◯ 150.3	157.9	72
Ex. 2	2-1	27.0	2.9	—	◯ 161.6	80
Comp. Ex. 2	2-2	26.5	3.1	◯ 150.5	158.3	78
	2-3	—	—	—	—	—
	2-4	—	—	—	—	—
(Note)
◯ Maximum peak temperature (melting point)

As is evident from Table 3, Example 2 can significantly improve the maximum draw ratio compared to Comparative Example 2, and thus can stably provide the drawn yarn with a small fineness. Moreover, as is evident from Table 4, it can be confirmed that the melting point measured as a maximum peak temperature by the differential scanning calorimeter (DSC) at a temperature rise rate of 20° C./min in the unconstrained state shifts 11.3° C. to the high temperature side from the melting point of the yarn before drawing, and the melting point thus measured is 11.1° C. higher than that of Comparative Example 2. Further, the degree of crystallinity is higher in Example 2 than in Comparative Example 2.

Example 3

A drawing test was performed using a relatively thick braided yarn C as a feed yarn. In this example, the braided yarn C was obtained by braiding eight raw yarns manufactured by TOYOBO CO., LTD., trade name: “Dyneema”, 165T-144F (total fineness: 165 Tex, number of filaments: 144). The braided yarn C used had a tensile strength of 23.7 CN/dtex and an elongation of 5.9%. The drawing test was performed with the same jacket heating drawing bath as Example 1. As shown in Table 3, the maximum draw ratio was 2.4 times in Example 3, which was improved compared to Comparative Example 3. The drawn yarn at this draw ratio had a strength of 26.0 CN/dtex and an elongation of 3.5%.

Comparative Example 3

The maximum draw ratio was examined using a hot air circulation drawing bath in the same manner as Comparative Example 1. As shown in Table 3, the maximum draw ratio was 2.1 times. The drawn yarn at the maximum draw ratio had a strength of 25.5 CN/dtex and an elongation of 3.5%. Tables 5 and 6 show the conditions and the results of Example 3 and Comparative Example 3.

TABLE 5
			Feed	Winding		Jacket heating	Internal		Fineness	Fineness
Example/			speed	speed	Draw	medium	temperature of		before	after
Comparative	Exper.		V1	V2	ratio	temperature	drawing bath		drawing	drawing
Example	No.	Sample	(m/min)	(m/min)	(V2/V1)	(° C.)	(° C.)	Results of drawing	(dtex)	(dtex)
Ex. 3	3-1	Braided yarn C	0.63	1.50	2.4	154.0	154 ± 0.1	A: Maximum draw ratio	1260	603
Comp. Ex. 3	3-2	Braided yarn C	0.71	1.50	2.1	154*	154 ± 1.0	A: Maximum draw ratio	1260	528
(Note)
*Set temperature of a hot air circulation drawing bath

TABLE 6
Example/				DSC peak temperature	DSC peak temperature	Degree of
Comparative	Exper.	Strength	Elongation	on low temperature	on high temperature	crystallinity
Example	No.	(CN/dtex)	(%)	side (° C.)	side (° C.)	(%)
Before drawing	3-0	23.7	5.9	◯ 150.4	157.5	75
Ex. 3	3-1	26.0	3.5	—	◯ 157.2	85
Comp. Ex. 3	3-2	25.5	3.5	◯ 150.5	157.5	82
(Note)
◯ Maximum peak temperature (melting point)

As is evident from Table 5, Example 3 can significantly improve the maximum draw ratio compared to Comparative Example 3, and thus can stably provide the drawn yarn with a small fineness. Moreover, as is evident from Table 6, it can be confirmed that the melting point measured as a maximum peak temperature by the differential scanning calorimeter (DSC) at a temperature rise rate of 20° C./min in the unconstrained state shifts 6.8° C. to the high temperature side from the melting point of the yarn before drawing, and the melting point thus measured is 7° C. higher than that of Comparative Example 3. Further, the degree of crystallinity is higher in Example 3 than in Comparative Example 3.

Example 4,

Comparative Example 4

A quantitative test was performed on eight yarns using a two-stage drawing device that included two drawing baths in Example 1 as a drawing device. For comparison, drawing was performed using two hot air circulation drawing baths in the same manner. As the drawing properties, the drawing state in an 8-hour operation was evaluated, while the drawing properties were evaluated for 5 minutes in Examples 1 to 3 and Comparative Examples 1 to 3. Table 7 shows the results. The drawing speed of all the sample yarns except the sample yarn with a draw ratio of 5.6 times in this example was set to 9 m/min (the drawing speed of the sample yarn with a draw ratio of 5.6 was 4.8 m/min). In the comparative example, since the drawing stability was low, the draw ratio had to be reduced even with two-stage processing. Therefore, in order to maintain the drawing stability for 8 hours at the above drawing speed, the upper limit of the draw ratio was only 2 times. However, in the drawing method of this example, the drawing was performed at a draw ratio of 2.5 times and was not a problem. When the drawing speed was reduced, the drawing could be performed even at a draw ratio of 5.6 times without any yarn breakage. Moreover, a variation (coefficient of variation) in strength of the sample yarns of this example was improved. The sample yarns were drawn at various draw ratios and then taken for DSC measurement. Table 8 shows the results of the measurements. The DSC charts are shown in FIGS. 5 to 10.

TABLE 7
Example/			Draw			Coefficient of
Comparative	Exper.		ratio	Drawing state	Strength	variation in	Elongation
Example	No.	Sample	(times)	(8 hours)	(CN/dtex)	strength (%)	(%)
Ex. 4	4-1	110T single-twisted yarn	2.5	A: No yarn breakage	37.1	1.51	3.2
	4-2	110T single-twisted yarn	5.6	A: No yarn breakage	38.2	1.36	2.6
Comp. Ex. 4	4-3	110T single-twisted yarn	2.0	A: No yarn breakage	35.1	2.76	3.4
	4-4	110T single-twisted yarn	2.5	B: The yarn was broken	32.6	5.53	3.2
				two times.

TABLE 8
Example/			Draw	DSC peak temperature	DSC peak temperature	Degree of
Comparative	Exper.		ratio	on low temperature	on high temperature	crystallinity	DSC chart
Example	No.	Sample	(tims)	side (° C.)	side (° C.)	(%)	No.
Before drawing	4-0	110T single-twisted yarn	—	◯ 150.3	—	75	FIG. 4A
Ex. 4	4-5	110T single-twisted yarn	2.0	151.1	◯ 158.8	76	FIG. 5
	4-1	110T single-twisted yarn	2.5	151.3	◯ 158.8	77	FIG. 6
	4-6	110T single-twisted yarn	3.0	152.0	◯ 158.6	79	FIG. 7
	4-2	110T single-twisted yarn	5.6	—	◯ 159.1	81	FIG. 8
Comp. Ex. 4	4-7	110T single-twisted yarn	1.5	◯ 150.5	157.3	78	FIG. 9
	4-3	110T single-twisted yarn	2.0	◯ 151.5	158.6	78	FIG. 10
(Note)
◯ Maximum peak temperature (melting point)

As is evident from Tables 7 to 8 and FIGS. 5 to 10, in the drawing method of this example, the main peak appears on the high temperature side even at a low draw ratio of about 1.5 times. On the other hand, in the conventional drawing method (Comparative Example 4 and FIGS. 9 to 10), although a small peak is observed on the high temperature side at a draw ratio of 2 times, the main peak temperature is substantially unchanged from the peak temperature before drawing. Thus, the results confirmed that there is a difference between the yarns of this example and the yarns by the conventional drawing method in terms of a change in the fine structure of the yarn.

As described above, the drawing method of the present invention is clearly distinguished from the hot air circulation drawing method in that the maximum draw ratio at which a yarn breakage may occur is higher under the same drawing conditions. This results in the following practical advantages.

(1) The present invention can provide a fine high strength polyolefin yarn at a high draw ratio, which has been difficult to produce.

(2) The present invention can suppress a yarn breakage and fuzz even at the same draw ratio, and therefore can reduce a defective rate, a loss, and a variation in the physical properties.

(3) Since low-cost yarns with a large fineness can be used as feed yarns, the material costs can be reduced.

Industrial Applicability

The drawn yarns obtained by the drawing method of the present invention are suitable for ropes, fishing lines, reinforcing materials, protective clothing, or the like. Moreover, since the drawn yarns cannot be seen easily by the naked eye and have high tenacity, they are suitable for strings for hanging, sutures, thin knitted fabrics, nets, or the like.

Description of Reference Numerals

1 Yarn Feeder

2 First Roller Group

3 Drawing Bath

4 Second roller group

5 Winder

6 Heater for circulating liquid

7 Pump

8, 10a-10c Feed Yarn

9, 11a-11c Drawn Yarn

12 Inner Wall of Drawing Bath

13 Jacket Portion

14 Yarn Path

15 Miner Axis, Height, or Diameter of Yarn Path

16 Housing Portion of Drawing Bath

Claims

1. An ultrahigh molecular weight polyolefin yarn that has been drawn, having a melting point that is determined as a maximum peak temperature measured by a differential scanning calorimeter (DSC) at a temperature rise rate of 20° C./min in an unconstrained state,

wherein the melting point is higher than a melting point of the yarn before drawing.

2. The ultrahigh molecular weight polyolefin yarn according to claim 1, wherein the melting point of the drawn ultrahigh molecular weight polyolefin yarn is at least 5° C. higher than the melting point of the yarn before drawing.

3. The ultrahigh molecular weight polyolefin yarn according to claim 1, wherein the drawn ultrahigh molecular weight polyolefin yarn has a total fineness of 50 dtex or less and a coefficient of variation in strength of 2% or less.

4. The ultrahigh molecular weight polyolefin yarn according to claim 1, wherein the ultrahigh molecular weight polyolefin is ultrahigh molecular weight polyethylene.

5. The ultrahigh molecular weight polyolefin yarn according to claim 4, wherein the ultrahigh molecular weight polyethylene yarn has been drawn and has a maximum melting peak temperature of 155 to 162° C., which is measured by a differential scanning calorimeter (DSC) at a temperature rise rate of 20° C./min in an unconstrained state.

6. The ultrahigh molecular weight polyolefin yarn according to claim 4, wherein the drawn ultrahigh molecular weight polyethylene yarn has a degree of crystallinity of 76 to 85%, which is determined from heat of fusion measured by a differential scanning calorimeter (DSC) at a temperature rise rate of 20° C./min in an unconstrained state.

7. A method for producing an ultrahigh molecular weight polyolefin yarn comprising:

heating and drawing the ultrahigh molecular weight polyolefin yarn,

wherein a drawing bath that includes a hollow yarn path and a jacket portion in which a heated liquid circulates is placed in a drawing zone,

positive air ventilation is not provided in the yarn path, and the yarn is heated by radiant heat from the jacket portion and natural convection,

an ambient temperature of the drawing bath is 150 to 157° C. and is controlled within ±0.2° C., and the yarn is heated and drawn while passing through the yarn path in a non-contact manner.

8. (canceled)

9. The method for producing an ultrahigh molecular weight polyolefin yarn according to claim 7, wherein a draw ratio in the drawing zone is 1.5 to 10 times.

10. (canceled)

11. The method for producing an ultrahigh molecular weight polyolefin yarn according to claim 7, wherein the yarn before drawing is an untwisted yarn, an interlaced yarn, a twisted yarn, or a braided yarn.

12. The method for producing an ultrahigh molecular weight polyolefin yarn according to claim 7, wherein the yarn before drawing has a fineness of 400 dtex or less.

13. A method for producing an ultrahigh molecular weight polyolefin yarn comprising:

drawing a raw yarn before braiding by the drawing process according to claim 7; and

subsequently braiding at least part of the drawn yarn.

14. A method for producing an ultrahigh molecular weight polyolefin yarn comprising:

drawing a raw yarn before braiding by the drawing process according to claim 7;

subsequently braiding at least part of the drawn yarn; and

further drawing the braided yarn.

15. A drawing device used in the method for producing an ultrahigh molecular weight polyolefin yarn according to claim 7, comprising:

a feeder for feeding a yarn;

a drawing bath for heating and drawing the yarn;

a winder for winding up the drawn yarn,

wherein the drawing bath includes a hollow yarn path and a jacket portion in which a heated liquid circulates.

16. The drawing device according to claim 15, wherein the heated liquid is heated outside the drawing bath, and is circulated by a pump.

17. The drawing device according to claim 15, wherein the yarn path has a height or diameter of 5 to 300 mm, and the drawing bath has a length of 0.3 to 10 m.