JP7504485B2 - High strength silk thread and its manufacturing method - Google Patents

Description

The present invention relates to silkworm silk thread with high strength, a method for producing the same, and an apparatus for producing the silk thread.

The threads that make up insect cocoons and the hair of mammals have been used as animal fibers for clothing and other purposes since ancient times. In particular, silk threads derived from silkworms, the larvae of the silkworm moth (Bombyx mori) (often referred to as "silkworm silk threads" in this specification) are highly valued as a high-quality natural material even today, due to their excellent moisture absorption and release properties, moisture retention, and heat retention, as well as their unique luster and smooth texture.

Although silkworm silk has the excellent properties mentioned above, its range of use has been limited because its strength is not necessarily sufficient. If the strength of silkworm silk can be improved, it is expected that it will be used in the same or different fields as a new material that takes advantage of the inherent properties of silkworm silk.

It is generally known that applying tension to fibers orients the molecular chains and improves their strength (Patent Document 1). However, in the case of flexible fibers such as silkworm silk, efforts have focused on technologies to reduce the tension applied to the silk thread during the reeling process, for example, in order to preserve its texture (Non-Patent Document 1). On the other hand, from an academic perspective, research has also been conducted into applying tension to silkworm silk during reeling (Non-Patent Document 2), but with conventional technology, applying tension could actually reduce strength, and it was not possible to sufficiently increase strength.

GB 2042414

Masaaki Okajima et al., Nippon Silk Gakkaishi, 24, 25-32 (2016) Junichi Shimada, Seiji Ogihara, Japanese Journal of Sericulture 39(5), 359-362, 1970

In one embodiment, the present invention aims to provide high-strength silkworm silk thread and a method or apparatus for producing high-strength silkworm silk thread.

The inventors discovered that silkworm silk thread with increased strength can be produced by applying a specific tension in the longitudinal direction of the silkworm silk thread, and thus completed the present invention.

The present invention includes the following aspects.
(1) A method for producing high-strength silk thread, comprising a tensioning step of applying a tension of 2.5 g/d or more and 10 g/d or less in the longitudinal direction of silkworm silk thread.
(2) The method according to (1), in which tension is applied under reduced local friction on the silkworm silk.
(3) The method according to (1) or (2), wherein the tensioning is carried out continuously.
(4) Tensioning is performed using two or more rotors;
A method according to any one of (1) to (3), in which tension is generated by the difference in rotational speed between rotors rotating at the same speed as the silkworm silk thread, or by the difference in rotational speed between a rotor rotating at the same speed as the silkworm silk thread and a rotor rotating at a speed different from that of the silkworm silk thread.
(5) A method according to any one of (1) to (4), in which a tensioning step is carried out while the silkworm silk thread contains moisture, and which includes a step of treating the silkworm silk thread with a lower alcohol and/or a step of heat treating the silkworm silk thread after the tensioning step, and a step of drying the silkworm silk thread simultaneously with or after the lower alcohol treatment step and/or the heat treatment step.
(6) The method according to any one of (1) to (5), wherein the high-strength silk thread has a strength of 5 g/d or more.
(7) A high-strength silk thread produced by the method according to any one of (1) to (6).
(8) Two or more rotating parts; and a control unit that controls the speed of the rotating parts.
A tension applying device for use in the manufacturing method described in any one of (1) to (6), comprising: at least one of the rotating parts rotating at the same speed as the silkworm silk thread.
(9) A silk reeling machine including the tensioning device according to (8).

The present invention provides high-strength silkworm silk thread, and a manufacturing method and device for obtaining high-strength silkworm silk thread.

Fig. 1 shows a schematic diagram of the multiple reeling machine used in Example 1. In the figure, 101 indicates a cord collector, 102 indicates a first wheel, 103 indicates a second wheel, 104 indicates a third wheel, 105 indicates a fourth wheel, 106 indicates a hook, 107 indicates a frame, 108 indicates a kennel twist, and 109 indicates a tension measurement site. Figure 2 shows a schematic diagram of the modified multi-row silk reeling machine used in Example 1. The modified parts from the multi-row silk reeling machine shown in Figure 1 are indicated by dashed circles. In the figure, 201 indicates a cord collector, 202 indicates a first wheel, 203 indicates a second wheel, 204 indicates a third wheel, 205 indicates a fourth wheel, 206 indicates a fifth wheel, 207 indicates a sixth wheel, 208 indicates a frame, 209 indicates a kennel twist, 210 indicates a tension equalizer, and 211 indicates a tension measurement site. FIG. 3 is a plot showing the relationship between tension and strength of silkworm silk produced by applying tension. FIG. 4 is a plot showing the relationship between tension and elongation of silkworm silk produced by applying tension. FIG. 5 is a plot showing the relationship between tension and Young's modulus for silkworm silk produced under tension. FIG. 6 is a plot showing the correlation between strength and elongation in three varieties of silkworm silk (Japan No. 137 x China No. 146, China No. 515 and MC502). FIG. 7 is a plot showing the relationship between tension and strength in silkworm silk of three varieties (Japan No. 137 x China No. 146, China No. 515 and MC502) produced under tension. FIG. 8 is a plot showing the relationship between tension and elongation in silkworm silk of three varieties (Japanese No. 137 x Chinese No. 146, Chinese No. 515 and MC502) produced under tension. FIG. 9 is a plot showing the relationship between tension and Young's modulus for three varieties of silkworm silk (Japan No. 137 x China No. 146, China No. 515 and MC502) produced under tension. FIG. 10 is a plot diagram showing the relationship between tension and strength when tension is applied to raw silk after reeling. FIG. 11 is a plot diagram showing the relationship between tension and elongation when tension is applied to raw silk after reeling. FIG. 12 is a plot diagram showing the relationship between tension and Young's modulus when tension is applied to raw silk after reeling.

1. Method for producing high-strength silk thread In one aspect, the present invention relates to a method for producing high-strength silk thread, which includes a step of applying tension in the longitudinal direction of silkworm silk thread.

In this specification, "silk thread" refers to thread derived from insects, a protein thread spun by insect larvae and adults for the purposes of nesting, moving, fixing, spinning cocoons, capturing food, etc., and when simply referred to as "silk thread" in this specification, it means silkworm silk thread unless otherwise specified. In this specification, "silkworm silk thread" refers to silk thread derived from the silkworm moth (Bombyx mori) that is spun by silkworms.

In this specification, silk thread includes cocoon thread obtained from cocoons, raw silk obtained by reeling cocoon thread, and degummed silk obtained by treating raw silk with soap, lye, alkaline chemicals such as sodium carbonate and urea, and enzymes to remove the gelatinous sericin.

In this specification, unless otherwise specified, "strength" means breaking strength, which refers to the tensile load required to break fibers such as silk thread. In this specification, strength is expressed in g/d (grams/denier). Here, denier is a unit that indicates the thickness of a thread, and should originally be expressed in meters or the like. However, since it is difficult to directly measure the thickness of a thread, it is common to express the thickness of a thread by the mass of a certain length of thread. Specifically, denier refers to the weight (g) of a 9,000m long thread.

In this specification, "high-strength silk thread" means silk thread that has higher strength than silk thread that has not been tensioned. The range of strength of high-strength silk thread is not particularly limited, but may be, for example, 5.0 g/d or more, 5.5 g/d or more, 6.0 g/d or more, 6.5 g/d or more, or 7.0 g/d or more.

Although the strength can be easily measured by a person skilled in the art, the strength values in this specification are values measured by the method described in the Examples. That is, first, fineness yarn (raw silk wound to a specified length using a measuring machine (1.125 m per revolution)) is prepared, and left to stand for 24 hours or more in an environment with a temperature of 20°C and a humidity of 65%, and then weighed on an electronic balance to determine the fineness (d: denier). Next, the strength is measured using a Tensilon universal material testing machine RTA-100 (ORIENTEC) installed in an environment with a temperature of 20°C and a humidity of 65%. The sample length used for the measurement is 100 mm, the stretching speed is 150 mm/min, and the number of tests is 50. At this time, the elongation and Young's modulus may be measured at the same time. In this specification, "elongation" means breaking elongation unless otherwise specified, and breaking elongation refers to the elongation rate (%) of a fiber when a tensile load is applied to break the fiber such as silk thread. In this specification, "Young's modulus" is a proportionality coefficient that represents the proportional relationship between stress and strain in the elastic range.

The method for producing high-strength silk thread according to one embodiment of the present invention includes a step of applying tension to the silkworm silk thread in the longitudinal direction (i.e., the direction in which the thread is stretched). In this specification, "tension" refers to a force acting on a part of an object in a direction that pulls the part apart. In this specification, tension refers specifically to the force that pulls the thread, and is expressed in g/d (grams/denier).

The method of applying tension is not limited, but for example, tension may be applied by fixing one end of the silk thread and pulling the other end with a weight or mechanical force, or by pulling both ends of the silk thread in different directions with a mechanical force. Tension may also be applied by attaching weights to both ends of the silk thread hung on a pulley or the like. From the viewpoint of the production efficiency of high-strength silk thread, it is preferable to use a system that can continuously apply tension to a part or the entire silk thread. In this specification, "continuously applying tension to silk thread" means, but is not limited to, applying tension to a silk thread of, for example, 1 m or more, 5 m or more, 10 m or more, 100 m or more, 1 km or more, or 10 km or more. In this case, it is preferable to continuously change the part to which tension is applied while applying tension to a part of the silk thread, and finally apply tension to the entire silk thread. An example of continuous tension application is when, during reeling or for raw silk after reeling, two or more rotors are used to rotate and move the thread, and rotors with different rotation speeds are used, generating tension by the difference in the speed at which the thread moves between the rotor with the faster rotation speed and the rotor with the slower rotation speed. Examples of rotors include rollers and drum wheels.

The strength of the tension in the tension application step may be, for example, 2.5 g/d or more, 2.6 g/d or more, 2.7 g/d or more, 2.8 g/d or more, 2.9 g/d or more, preferably 3.0 g/d or more, 3.5 g/d or more, 4.0 g/d or more, or 4.5 g/d or more, and may be 10.0 g/d or less, 9.0 g/d or less, preferably 8.0 g/d or less, 7.0 g/d or less, 6.0 g/d or less, or 5.0 g/d or less. For example, the range of the tension in the tension application step may be 2.5 g/d to 10.0 g/d, 2.8 g/d to 6.0 g/d, or 3.0 g/d to 5.0 g/d.

The strength of tension in the above tension application process is the value measured using the method described in the Examples. In other words, it is the value when a tensiometer (Nakaasa Sokki Co., Ltd.) is applied to the area where tension is applied. It is believed that similar values can be obtained using a tension meter (Yokogawa Electronics Co., Ltd., model T-101-10-00), which is the successor to the tensiometer (Nakaasa Sokki Co., Ltd.). The desired tension can be applied to the silk thread by using the tensiometer to set the conditions for the rotation speed of the rotor.

The time for which tension is applied to the silkworm silk thread is not particularly limited. For example, it may be on the order of a few seconds (1 to 10 seconds or 2 to 4 seconds), or it may be on the order of several tens of seconds or several minutes.

Preferably, tension is applied under reduced local friction on the silkworm silk thread. Generally, "friction" is considered to mean rubbing or rubbing against each other, but in this specification, "friction" includes any force received from the surface with which the thread is in contact, in addition to the above meaning. In this specification, "local friction" refers to friction occurring in a specific limited part of the silkworm silk thread. When local friction occurs, the silk thread is damaged at that point, resulting in a decrease in strength. For example, in a speed suppression means such as a ring tenser or hysteresis tenser that contacts the silkworm silk thread at a point to slow down the silkworm silk thread and apply tension, local friction occurs at the contact point between the silkworm silk thread and the speed suppression means. Therefore , in one embodiment, reduced local friction on the silkworm silk thread means a state in which local friction is reduced compared to the friction that occurs when the speed suppression means contacts the silkworm silk thread at a point to slow down the silkworm silk thread and generate tension.

Tension application under reduced local friction can be achieved, for example, by using two or more rotors to apply tension, and generating tension by the difference in rotational speed between rotors that rotate at the same speed as the silkworm silk thread, or by the difference in rotational speed between a rotor that rotates at the same speed as the silkworm silk thread and a rotor that rotates at a different speed than the silkworm silk thread.

Here, the rotor rotates at the same speed as the silkworm silk thread means that the rotor rotates completely or substantially at the same speed as the silkworm silk thread. "Substantially the same speed" means that the speeds are equal to the extent that no local friction occurs between the rotor and the silkworm silk thread. For example, the difference in speed may be within 10%, 5%, or 1% of the faster rotation speed of the rotor or the silkworm silk thread. There are no limitations on the configuration for the rotor to rotate completely or substantially at the same speed as the silkworm silk thread, but for example, the thread may be wound around a rotor having a predetermined width (at least several times the width of the thread) and a smooth contact surface with the silkworm silk thread multiple times, for example, two or more turns, three or more turns, four or more turns, or five or more turns. By winding the silkworm silk thread around the rotating part multiple times, not only can the rotor and the silkworm silk thread rotate at the same speed, but friction occurring at the contact point between the rotating part and the thread can also be reduced. Here, the thread may be wound around one rotor, or around two or more rotors.

"The rotor rotates at a different speed than the silkworm silk thread" means that the rotor rotates at a substantially different speed than the silkworm silk thread. Here, "substantially different speed" means, for example, that the difference in speed is 1% or more, 5% or more, 10% or more, 20% or more, or 50% or more different from the faster rotation speed of the rotor or the silkworm silk thread. When tension is applied by the difference in rotation speed between a rotor that rotates at the same speed as the silkworm silk thread (same-speed rotor) and a rotor that rotates at a different speed than the silkworm silk thread (different-speed rotor), it is preferable that the different-speed rotor rotates at a faster speed than the same-speed rotor.

In one embodiment, the tensioning step is performed when the silkworm silk thread contains moisture. By absorbing moisture into the silkworm silk thread, the thread becomes easier to unravel, making it easier to apply tension. In this case, it is preferable that the manufacturing method of the present invention further includes a lower alcohol treatment step and/or a heat treatment step, and a drying step. When hydrated silkworm silk thread is dried, breakage may occur in the single fibers of the silkworm silk thread during drying, but breakage can be avoided by going through a lower alcohol treatment step and/or a heat treatment step.

In this specification, the lower alcohol treatment step is a step of treating the silkworm silk after the tensioning step with a lower alcohol. In this specification, examples of lower alcohols include methanol, ethanol, propanol, and mixtures thereof. It is believed that lower alcohols increase the cohesive force between the fibroin molecular chains of raw silk and improve crystallinity. Taking advantage of such properties, lower alcohols are also used as silk insolubilizing solvents to make water-soluble regenerated silk water-insoluble. The method of lower alcohol treatment is not limited, but can be, for example, spraying 70-80% lower alcohol on raw silk, immersing raw silk in 70-80% lower alcohol, immersing a device (e.g., a small frame) used for tensioning or reeling in 70-80% lower alcohol before performing tensioning treatment or reeling, or installing an alcohol treatment device in the tensioning path. Examples of alcohol treatment devices include devices that have a configuration for continuously or intermittently immersing a portion of the yarn in an alcohol solution for a certain period of time, for example, a few seconds or less than a few seconds, such as a device that has a rotor and an alcohol storage section for immersing a part or all of the rotor in alcohol.

The heat treatment process is a process of heating the silkworm silk. The heating temperature may be any temperature that can reduce breakage, for example, 40°C or higher, 50°C or higher, 80°C or higher, preferably 100°C or higher, 120°C or higher, or 140°C or higher, and the upper limit can be set to a temperature below the melting point (decomposition point) of the silkworm silk, for example, 300°C or lower, 250°C or lower, 220°C or lower, preferably 200°C or lower, 180°C or lower, or 160°C or lower. For example, the heating temperature can be 40°C to 300°C, 50°C to 250°C, preferably 100°C to 200°C, 120°C to 180°C, or 140°C to 160°C. The time of the heat treatment process is not limited, and can be, for example, 1 second or more, 5 seconds or more, 10 seconds or more, 30 seconds or more, or 1 minute or more. The upper limit can be 1 hour or less, 30 minutes or less, 20 minutes or less, 10 minutes or less, or 5 minutes or less. Specific heating temperature ranges can be, for example, 5 seconds to 30 minutes, 30 seconds to 10 minutes, or 1 minute to 5 minutes.

The drying process is a process of drying the silkworm silk thread simultaneously with or after the lower alcohol treatment process and/or heat treatment process. There are no limitations on the drying method as long as it can reduce the moisture content in the silkworm silk thread, but examples include a natural drying method in which the silkworm silk thread is exposed to the outside air, a dehumidification drying method in which the silkworm silk thread is placed in an enclosed space with a dehumidifier for a certain period of time, an air drying method in which hot or cold air is blown using a blower or the like, a heat drying method in which the silkworm silk thread is heated at a temperature at which it does not deteriorate or denature, and a vacuum drying method in which the inside of a container is deaerated to evaporate the moisture.

In the manufacturing method of the present invention, tension may be applied during or at the time of reeling, or to silkworm silk after reeling, such as raw silk. In this specification, "reeling" refers to the process of converging several cocoon threads according to the desired thickness of raw silk, and then joining the cocoon threads in sequence as necessary to form a raw silk thread. The basic flow of reeling is as follows. First, the cocoon threads are peeled off from the surface of the cocoon layer (cord), and the tangled cocoon threads are straightened out to pull out one correct thread (cord strip). A certain number of cocoons with threads found (correct thread cocoons) are collected (cord strips), and are gathered into raw silk consisting of several drums with the function of thread-like conjugation and dehydration, and reeled onto a small frame (Revised Introduction to Sericulture, published in 2002, edited by the Japanese Society of Sericulture, p. 285).

The tensioning in the manufacturing method of the present invention can be performed using the tensioning device described in "2. Tensioning Device" below, or the silk-reeling machine described in "3. Silk-reeling Machine".

In one aspect, the present invention relates to high-strength silk thread produced according to the above-mentioned method for producing high-strength silk thread. Without being limited by theory, it is believed that the high-strength silk thread of the present invention has high strength due to the molecular chains being oriented by applying tension.

The high-strength silk thread of the present invention may be used as is, or may be mixed with other silk threads, cotton threads, wool, and/or synthetic fibers to impart new physical properties.

2. Tensioning device In one aspect, the present invention relates to a tensioning device for use in the method described in "1. Method for producing high-strength silk thread." The tensioning device of the present invention includes two or more rotating parts and a control part that controls the speed of the rotating parts, and at least one of the rotating parts rotates at the same speed as the silkworm silk thread.

In this specification, the term "rotating part" refers to a part that adjusts the rotation (movement) speed and/or the direction of the silkworm silk thread (thread path) by rotating in contact with the silkworm silk thread, and specific examples include a roller and a drum wheel. The tensioning device of the present invention includes one or more rotating parts, for example, two or more, three or more, four or more, five or more, six or more, seven or more, eight or more, nine or more, or ten or more. In the tensioning device of the present invention, one or more of the rotating parts, for example, two or more, three or more, or all of them may rotate at the same speed as the silkworm silk thread. There are no limitations on the configuration for the rotating parts to rotate completely or substantially at the same speed as the silkworm silk thread, but it is sufficient that the rotating parts are configured to have a predetermined width (at least several times the width of the thread) and a smooth contact surface with the silkworm silk thread, so that the thread can be wound around the rotor multiple times, for example, two or more, three or more, four or more, or five or more.

The tensioning device of the present invention includes a control unit that controls the speed of the rotating part. The "control unit" includes one or both of a driving means that increases the speed of the rotating part and a speed suppression means that decreases the speed of the rotating part. The control unit may further include an adjustment means (e.g., a CPU) that adjusts the strength of the motor or brake according to specified conditions or according to certain conditions.

The tensioning device of the present invention may have, in addition to a rotating part and a control part, a shaft and bearings corresponding to the rotating part, etc.

3. Silk-reeling machine In one aspect, the present invention relates to a silk-reeling machine including the tensioning device described in "2. Tensioning device".

The basic configuration of a silk reeling machine is known to those skilled in the art. Examples of silk reeling machines include the Suwa-style silk reeling machine, the multi-row silk reeling machine, and the automatic silk reeling machine (see, for example, the 4th Japanese Silk Village Exhibition: Silk Reeling: Foundation of Modernization, Chapter 3, pp. 32-42, 2000; Hoshino, Nobuo, Okaya Silk Museum Bulletin 2, 31-43, 1997; and Kobayashi, Yasushi, Sen-i Gakkaishi Journal 18(10), 932-940, 1962). The silk reeling machine of this embodiment is not limited, and may be any type of silk reeling machine, including the previously described existing silk reeling machines. Here, the configuration of the multi-row silk reeling machine will be described with reference to the schematic diagram of FIG. 1. The cocoon thread obtained from the cocoon immersed in hot water is reeled onto the small frame by the tension generated by the rotation of the small frame 107 through the collecting device 101, the drum wheels 102-105, the hook 106, etc. The collecting device 101 gathers the cocoon threads into one and detects when the knot rises, and the hook 106 swings the thread from side to side so that the raw silk wound in a neat manner is not wound on top of each other in the same place. 108 refers to kennel twisting, which means that the threads that have passed through the collecting device are passed through a drum wheel to twist them together. Kennel twisting gives the threads a rounded shape to improve the adhesion (binding) between the cocoon threads, and may also remove moisture from the threads. The silk-reeling machine may optionally include a tension measuring site 109, which allows the tension generated in the thread during reeling to be measured.

A schematic diagram of an example of a modified multi-row silk-reeling machine incorporating the tensioning device of the present invention is shown in Figure 2. The modified parts from the multi-row silk-reeling machine shown in Figure 1 are indicated by dashed circles. In the modified multi-row silk-reeling machine shown in Figure 2, a tension equalizer 210 is added following the fourth reel 205. The rotation speed of the two rollers included in the tension equalizer 210 is slow, so the rotation speed (movement speed) of the yarn decreases, and tension is generated in the yarn path beyond the tension equalizer 210. In the modified multi-row silk-reeling machine shown in Figure 2, a fifth reel 206 is provided to ensure a location for accurately measuring the tension applied to the raw silk, as well as to ensure the distance and time for applying tension, and the hook is changed to a sixth reel 207 to reduce friction generated in the hook portion, but these configurations are optional.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[Example 1: Applying tension to silkworm silk during reeling]
Materials and Methods
(Reeling conditions)
The silkworm varieties from which the silk threads used in the test were derived were Japan No. 137 x China No. 146, China No. 515, and MC502.

The reeling equipment used was a multi-row reeling machine (Harada Co., Ltd.) whose schematic diagram is shown in Figure 1, or a modified multi-row reeling machine whose schematic diagram is shown in Figure 2. The specific configuration of the modified multi-row reeling machine is that a tension equalizer (Yuasa Shido Co., Ltd., model number: D510059-L) is installed between the fourth reeling wheel and the ayakage of the multi-row reeling machine, the ayakage is changed to the fifth reeling wheel, and a sixth reel is added.

The temperature during reeling was room temperature (approximately 15-30°C) and normal humidity (approximately 25-60%). Tension measurements were performed at the locations indicated by the arrowheads in Figures 1 and 2 using a tension meter (Nakaasa Sokki Co., Ltd.), model: AN Type 0-100G, measurement range: 0-100 g.

The reeling speed was approximately 51 m/min, and the length of the thread path where tension was applied was approximately 1.9 to 3.5 m.

(Strength and elongation test conditions)
The fineness and strength/elongation of the reeled silkworm silk were measured as follows.
Measurement of fineness First, fineness yarn (silkworm silk yarn wound to a specified length using a measuring machine (1.125 m per circumference)) was prepared and left to stand for more than 24 hours in a room at a temperature of 20°C and a humidity of 65%, after which it was weighed on an electronic balance (Sartorius, model 1702MP8) to determine the fineness (d: denier).
- Measurement of strength, elongation and Young's modulus
Measurements were performed using a Tensilon universal material testing machine RTA-100 (ORIENTEC) installed in a room at 20°C and 65% humidity. The sample length used for the measurement was 100 mm, the stretching speed was 150 mm/min, and the number of tests was 50. The items measured were strength, elongation, and Young's modulus.

<Results>
First, when reeling silkworm silk in a multi-row reeling machine, the screws on the drumwheel in the thread path were tightened to suppress rotation and apply tension, but friction in the thread path caused the silkworm silk to break, making reeling impossible (data not shown).

Therefore, in order to apply tension while reducing friction, a modified multi-reeling machine equipped with a tension equalizer was used for reeling. As a result, it became possible to apply tension of 3g/d or more, which increased the strength of the silkworm silk. The relationship between tension and strength of silkworm silk produced under tension is shown in Figure 3, the relationship between tension and elongation in Figure 4, and the relationship between tension and Young's modulus in Figure 5.

Next, silkworm silk threads of other varieties (Naka No. 515 and MC502) were similarly reeled using a modified multi-row reeling machine. Along with the results of the previous experiment with Ni No. 137 x H146, the correlation between strength and elongation for the Naka No. 515 and MC502 silkworm silk threads is shown in Figure 6, the relationship between tension and strength in Figure 7, the relationship between tension and elongation in Figure 8, and the relationship between tension and Young's modulus in Figure 9. As a result, a tendency was observed in all silkworm silk thread varieties that as tension increased, strength increased, elongation decreased, and Young's modulus increased.

In addition, silkworm silk threads sometimes broke during the drying process on the small frame after reeling. Breakage of silkworm silk threads was reduced by spraying 70-80% ethanol onto the silkworm silk threads until the ethanol was completely absorbed, or by installing a roller between the tension equalizer and the fifth drum, wrapping the silk thread around this roller once, and then immersing this roller in a 70-80% ethanol solution during reeling (data not shown).

[Example 2: Applying tension to raw silk]
Materials and Methods
(sample)
The raw silk after reeling prepared by Usui Silk Milling Co., Ltd. (silkworm variety: Gunma 200, silkworm silk reeled to a target fineness of 27d) was used as the sample.
(Treatment process)
First, an appropriate amount of raw silk was wound from a skein onto a small bobbin. Next, the raw silk was immersed in water at room temperature and soaked in water using a small frame permeator (Harada Co., Ltd.). The small frame permeator is a device for permeating water into the thread layer of the small frame before the rewinding process in order to improve the unraveling of the raw silk wound onto the small frame.

The tension was applied in the same manner as in Example 1, using the modified multi-reeling machine of Example 1. However, the kennel twisting portion in the yarn path was omitted.
The measurements of strength, elongation and Young's modulus were performed in accordance with Example 1.

<Results>
The relationship between tension and strength of silkworm silk thread obtained by applying tension to raw silk is shown in Figure 10, the relationship between tension and elongation in Figure 11, and the relationship between tension and Young's modulus in Figure 12. These results show that the application of tension to not only silkworm silk thread during reeling, but also to silkworm silk thread (raw silk) after reeling increases the strength and decreases the elongation.

In addition, during the drying process in the small frame, the raw silk sometimes broke, but this was reduced by spraying the small frame with 80% ethanol (data not shown).

Claims (7)

A method for producing high-strength silk thread, comprising a tensioning step of applying a tension of 3.0 g/d or more and 7.0 g/d or less in the longitudinal direction of silkworm silk thread after reeling,
The tension is applied by controlling the speed of movement of the silkworm silk thread caused by the rotation of the small frame at a portion of the silkworm silk thread using two or more rotors having a contact surface with the silkworm silk thread,
High-strength silk thread has a strength of 5 g/d or more.
The method. The method of claim 1 , wherein the tensioning is continuous. The method according to claim 1 or 2, wherein the tensioning step is carried out while the silkworm silk thread contains moisture, and the method further comprises a step of treating the silkworm silk thread with a lower alcohol and/or a step of heat-treating the silkworm silk thread after the tensioning step, and a step of drying the silkworm silk thread simultaneously with or after the lower alcohol treatment step and /or the heat treatment step. The method according to any one of claims 1 to 3, wherein the tension applied is 5.0 g/d or less. High-strength silk thread produced by the method according to any one of claims 1 to 4. Two or more rotating parts; and a control part for controlling the speed of the rotating parts.
A tension applying device for use in the manufacturing method described in any one of claims 1 to 4, comprising: at least one rotating part that rotates at the same speed as the silkworm silk thread. A silk reeling machine including the tensioning device according to claim 6.

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