JPS61231211A - Production of high-strength polyethylene fiber - Google Patents

Abstract

PURPOSE:To spin a polyethylene solution very stably, draw the resultant fibers stably at a high draw ratio and obtain the titled fibers at a low cost, by extruding high molecular-weight polyethylene solution through a spinneret, cooling the extruded solution to give a fibrous material, extracting the solvent therefrom, shrinking the fibers, drying the shrunk fibers and hot-drawing the dried fibers. CONSTITUTION:A solution consisting of a high-molecular weight polyethylene and a solvent is extruded through a spinneret 3 of an extruder 2, and cooled in a water bath 4 to give a fibrous material 6. The solvent contained in the fibrous material 6 is then extracted in an extraction bath 7 to shrink substantially the fibrous material 6, which is then dried in a drying oven 10 to afford dried undrawn fibers 12. The resultant fibers 12 are led to a hot-drawing furnace 13 and hot-drawn to give a drawn yarn 15, which is then wound by a winder 16 to afford the aimed fibers. Preferably, the fibers are shrunk at >=10% in extracting the solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing high strength polyethylene fibers.

It is known that polyethylene fibers with high strength and high elastic modulus can be obtained by the so-called gel spun fiber manufacturing method, in which a solution obtained by dissolving high molecular weight polyethylene in a solvent is spun and stretched at a high magnification of 1:1. be. For example, P, 8. mi th
and various publications by A. J. Pennings et al. (e.g., Polymer Bullet
tin) 7 j j (/ri2ri), 77j (/
9♂θ)), Japanese Unexamined Patent Publication No. Shojj-6-107jO6,
Tokukai Akira! ! - It is disclosed in the No. 222 publication. In order to commercialize the conventional techniques described in these sections, stability of stretching, that is, long-term continuous stretchability in high-magnification stretching is an essential condition. However, conventional manufacturing methods have insufficient stretching stability. That is, high strength,
In order to obtain fibers with a tensile strength of at least 39 g'/ or more, it is necessary to draw the fibers at a draw ratio C2 of at least 70 times. However, when drawn at a high magnification, the drawing tension inevitably becomes extremely large, and thread breakage occurs due to slight scratches or speed fluctuations, making it impossible to stably produce fibers for a long period of time. Especially when it comes to high strength,
A stretching tension corresponding to this is required, and in actual production, there is a trade-off between strength and tension, and it is difficult to achieve both. In order to avoid this, the following measures were taken. That is, (1) lowering the strain rate by slowing down the stretching speed or increasing the length of the stretching furnace, and (2) performing multi-stage stretching. Note that these methods are also methods for increasing stretchability, that is, increasing the maximum stretching ratio.

In general, improving drawability leads to improving maximum draw ratio C:. This means that the larger the difference between the operating stretching ratio and the maximum stretching ratio, the easier and more stable stretching can be performed. Therefore, in order to obtain high-strength fibers, the operating draw ratio must be extremely high. This inevitably leads to the need to increase the maximum stretching ratio even more.

However, such known methods have the problem that the method (1) of slowing down the drawing speed lowers productivity, and the method of increasing the length of the drawing furnace increases equipment costs. Method (2) has the drawbacks of increased equipment costs and complicated stretching operations. Moreover, more importantly,
These methods are based on the technical idea of improving the stretchability only by devising the equipment, and do not attempt to increase the maximum stretching ratio by changing the structure of the unstretched body. That is,
This is a means for bringing the operating stretching ratio as close as possible to the maximum stretching ratio indicated by the structure of the unstretched body. This means that the temperature and speed of the equipment must be controlled very precisely. As mentioned above, it has the serious disadvantage that it is extremely difficult to strictly control the speed and temperature of an apparatus with an extremely slow speed or an extremely long furnace length or a multi-stage stretching apparatus, and it requires a large amount of cost.

The above method takes measures in terms of drawing conditions and drawing equipment, but another method is to optimize the fine structure of the undrawn yarn as described above. In the case of crystalline synthetic resin fibers, it is generally said that in order to improve high-magnification drawability, it is preferable that the undrawn yarn be as unoriented and non-structural as possible.

For this reason, undrawn yarn produced by melt spinning is generally produced by rapid cooling to prevent crystallization after spinning the molten resin. However, polyethylene has a slow crystallization rate. Even if the molten resin is rapidly cooled, it is unlikely to become a non-quality fiber.Also, in the case of polyethylene, it is better to slowly cool the molten resin and grow spherulites, which improves high-magnification drawability. There are also known documents that say that it is good.Academically, it is known that single crystal polymers have extremely good stretchability, and the maximum stretching ratio can reach nearly 30θ times.However, it is known that such a structure can be There have been no announcements about how to achieve this industrially, and no specific method is known. At present, almost no technology has been published.Among them, only the following method is known.In other words, in the gel spinning method, a method is used to extract material from the fine structure of an unstretched material to improve high-magnification drawability. As a solution, a method has been proposed in which the polymer concentration in the spinning solution is extremely lowered.The improvement in drawability with this method is explained to be due to a reduction in the entanglement of molecular chains.Problems with this method The point is that the polymer concentration must be extremely low, so the amount of solvent used for spinning t1 is large, and the cost of recovering the solvent is high.Therefore, it is almost impossible to apply it industrially. be.

Problems to be Solved by the Invention The object of the present invention is to provide a method for producing gel-spun fibers that can extremely stably produce high-strength polyethylene fibers. Furthermore, the present invention relates to a method for producing gel-spun fibers, and it is an object of the present invention to provide a pretreatment method for a stretching method that allows extremely stable stretching at a high magnification.

Means for Solving the Problems The present inventors have conducted extensive studies with the aim of improving the stability of drawing in the gel-spun fiber manufacturing method (= manufacturing method of high-strength polyethylene fibers), and as a result, have resolved the problems. The present invention was achieved by discovering a new method capable of stabilizing ζ stretching and increasing strength without using conventionally known methods.

That is, in the present invention, a solution consisting of high molecular weight polyethylene and a solvent is extruded from a spinneret, cooled to form a fibrous material, and then the solvent contained in the fibrous material is extracted, dried, and hot-stretched. In the method for producing high-strength polyethylene fibers, the method includes substantially shrinking the two fibers during extraction of the solvent.

The present invention described above does not depend on stretching conditions such as a reduction in strain rate or the number of stretching stages. The present invention is an optimization of the microstructure of undrawn yarn (1), which significantly improves high-magnification drawability. As a result of this optimization, the density, which is one of the macroscopic properties of the undrawn yarn, has been significantly increased. In crystalline polymers, it has been common knowledge that crystallized undrawn yarns have a higher stretching stress than non-quality undrawn yarns, and therefore can only be drawn at a low ratio. The present invention is a method that solves these problems, and can be easily carried out within conventional manufacturing processes.

An important point of the present invention is that the undrawn yarn is substantially shrunk during the extraction step of the manufacturing process. The present inventors conducted a detailed study on the shrinkage and drawability of the fibrous material during the extraction process, and the physical properties of the drawn yarn. The results are shown in FIG. In other words, as the shrinkage rate of undrawn yarn (referred to as wet gel fiber) obtained by extruding a high molecular weight polyethylene solution from a spinneret and cooling it increases during extraction, the tensile strength of the drawn yarn increases. I understand. λ0 in the figure is the elongation of the drawn yarn with respect to the wet gel fiber unit length after spinning, that is, the deformation ratio. λ0 is expressed by the following formula.

t.

20=π LD = Length after stretching Lo = length of wet gel fiber dD = fineness of drawn yarn Do: Fineness of wet gel fiber ρD = density of drawn yarn ρ0 = density of wet gel fiber However, in the present invention, the following equation is used as a simple method.

λ0=5D Regarding the fineness of the wet gel fiber, undrawn yarn was used which was extracted and dried (shrinkage rate: 0) without changing the length. This deformation magnification λ0 (as a binary example, it can be seen that the tensile strength of the drawn yarn increases.Furthermore, the higher the shrinkage rate when extracting the wet gel fiber, the better the stability of the drawing. I also understood.

For example, an undrawn yarn that is not shrunk has a deformation magnification of 2! When stretched twice, the stretching stability is extremely poor (approximately 70 minutes of continuous stretching time), but when the shrinkage is reduced, the stretching stability is extremely improved (more than 7 hours of continuous stretching time).

The shrinkage rate referred to here is the shrinkage rate of the wet gel fiber in the yarn direction, and is expressed by the following formula.

1゜8B= /-■ S, = Shrinkage rate during extraction, = Length of wet gel fiber after gel spinning (after water cooling and collection) and before extraction t8 = Length of wet gel fiber after extraction In the invention, the following equation is used as a simple method.

8B=/-'! 5L B Do = Fineness of fiber before extraction and shrinkage dB = Fineness of fiber after extraction and shrinkage However, in this case, the fineness was determined by excluding the solvent and extraction solvent.

One of the effects obtained by further shrinking is that the stretching tension is reduced. It has been found that in order to obtain a drawn yarn with the same tensile strength, an undrawn yarn with a high shrinkage rate can be drawn at a lower tension. It can be considered that this characteristic works effectively for stretching stability and high-magnification stretchability. This phenomenon is surprising because it has been said that the higher the crystallinity of the undrawn yarn, the higher the drawing stress and the difficulty in drawing it.

As explained above, by using the present invention, the stretching tension during stretching can be reduced, and as a result, the maximum stretching ratio can be significantly increased. Therefore, it can be easily and stably stretched even at high magnification. Therefore, according to the present invention, it has become possible to produce fibers with high strength and high elastic modulus extremely easily using ordinary equipment and methods without using special equipment as in conventionally known methods.

Next, a method of implementing the present invention will be explained.

A general method for producing high-strength, high-modulus polyethylene fibers using the gel-spun fiber production method is as follows.

That is, a solution consisting of high molecular weight polyethylene and a solvent is first prepared, extruded from a spinneret using a plunger type extruder, etc., cooled to form a wet gel fiber containing the solvent,
Next, the solvent is removed from the gel fiber containing the solvent, and the fiber is hot-stretched to a high magnification.

As high molecular weight polyethylene, the viscosity average molecular weight is 4
t, OX/0s or higher is used, but preferably in small amounts! Alkenes such as propylene and butylene having a molar mass or more may be copolymerized.

As a solvent for dissolving high molecular weight polyethylene,
Aliphatic hydrocarbons, cyclic hydrocarbons, aromatic hydrocarbons, etc. are used. Preferred are aliphatic and cyclic hydrocarbons such as dodecane and decalin. Dissolve by heating to increase the dissolved concentration. At this time, it is important to avoid creating density spots.

Additionally, small amounts of additives such as antioxidants are also used as appropriate.

As an extruder that uses two C phases during spinning, a screw extruder or a container pressurized with air or nitrogen gas can be used for short-term stretching.

Cooling of the extruded fibrous material is usually carried out with water.

The solvent can be removed by simple drying or extraction with an extraction solvent.

Extraction of the solvent from the wet gel fibers can be carried out using extraction solvents that are miscible with the solvent, such as hydrocarbons such as hexane and cyclohexane, alcohols such as ethanol, dichloromethane, /, /, 2-)lichloro/, 29. Halogenated hydrocarbons such as 2-fluoroethane, aromatic hydrocarbons such as toluene and xylene, etc. are used.

Drying of the extraction solvent is generally carried out in an open hot air chamber. When using an extraction solvent that generates flexible gas, it is heated in an inert gas and dried.

For stretching, a heating zone is installed between the rolls whose speed can be adjusted.
This is done by stretching at a stretching ratio depending on the roll speed ratio.

Heating is usually performed using hot air, hot plates, steam, or the like. Rolls such as godet rolls and nip rolls are used to prevent fibers from slipping.

Further, the present invention will be explained in detail.

A general polyethylene gel spinning and hot stretching apparatus is shown in FIG. A high molecular weight polyethylene solution 1 is extruded from a spinneret 3 connected to the plunger type extruder 2 to form a fibrous material, dropped into a water tank 4, cooled, and then passed through a take-up roll and extraction roll 5. It is taken off at a constant speed to form wet gel fibers 6.

This is immersed in an extraction tank 7 containing an extraction solvent, the solvent is extracted, and the product is taken up by a take-up roll/drying roll 8. Next, the gel fibers 9 after extraction are introduced into an extraction solvent drying oven 10, dried, and taken up by a take-up roll/drawing roll 11 for drawing to form undrawn gel fibers 12. Next, the undrawn gel fibers are introduced into a heated drawing furnace 13 having hot air or a hot plate. Stretching is carried out by increasing the speed of the take-up roll 14 at the exit of the stretching furnace relative to the speed of the take-up roll/drawing roll 11 of the drying furnace. Thereafter, the drawn yarn 15 is wound up by a winding machine 16.

The conventional method for producing high-strength, high-modulus polyethylene fibers is to run the fibrous material after spinning at the same speed or with a slight tension to the extraction step, that is, a wet gel fiber take-up roll and extraction roll 5 and an extraction roll 5. Generally, the subsequent take-up roll 8 is operated at the same speed or slightly faster.

"Shrinking" as used in the present invention means reducing the speed of the take-up roll 8 relative to the extracting delivery roll 5 to actively shrink the wet gel fibers. This is extremely effective in increasing strength and stretching stability. The amount of shrinkage is preferably at least the /θ factor. More preferably, the gel fibers are shrunk to the limit of self-shrinkage.

To achieve shrinkage during extraction, the speed of the take-off roll 8 is reduced as described above. When shrinking extremely or to the limit of self-shrinkage, the fibrous material is kept in a tensionless state in the extraction tank so that no tension is applied to the material by the take-up roll 8, and the fibrous material is extracted. For example, molecular weight! , θ×106 high-density polyethylene dissolved in decalin at 770°C and cooled with room temperature water to form wet gel fibers at room temperature /, /.

Coat rechrolow/,,2.2-')! When extracted with J fluoroethane under no tension, it can be contracted from 1.2 tons to 30 tons.

It is presumed that shrinkage during extraction of wet gel fibers gives the unstretched body a fine structure that makes it easier to stretch, but it is unclear what this is and how it improves stretchability.

In the present invention, since the fine structure of the undrawn yarn is determined by the amount of shrinkage C, the relationship between the drawing ratio and the tensile strength obtained from the undrawn yarn from which the solvent has been removed before entering the drawing process is This means that if the amount of contraction is not constant, it cannot be determined uniquely. In fact, in the case of undrawn yarns made by changing the extraction time contraction ratio according to the present invention, the relationship between the stretching ratio from the undrawn yarn before stretching and the tensile strength of the drawn yarn does not follow a single line. was recognized. The higher the shrinkage rate, the higher the stretching ratio.

Example The present invention will be explained by examples.

Example/, Comparative Example/ High-density polyethylene (manufactured by Asahi Kasei Corporation, molecular weight j, θ×
706) 2.0 Tidecalin solution /,! Extrude with high pressure N2 gas from a pressure vessel equipped with mω spinneret, cool in water, 3. It was taken up with ♂yyl/mix and wound onto a bobbin. Immediately, the wet gel fiber is wrapped around a metal frame whose outer circumference can be changed, so as not to overlap or slack in order to prevent threads from sticking together, and then the metal frame is wired by a predetermined amount. 1: Therefore, by reducing the circumference of the metal frame, /, /,, 2-trichloro-/, 2. ．． The gel fibers were immersed in an extraction tank containing 2-trifluoroethane to extract the solvent and simultaneously shrink the gel fibers by a predetermined amount.

The gel fibers after extraction, which were wound around a metal frame without any slack, were dried at 70°C in an open air circulation system with a shrinkage rate of 10. ．． A 2/% undrawn yarn was made.

In addition, an undrawn yarn with a shrinkage rate of 26 cm was prepared by keeping the wet gel fiber in an untensioned state in the extraction tank, shrinking it to the limit, and drying it without causing any change in the length of the fiber. As a comparative example, an undrawn yarn was made without shrinkage by extraction and drying.

Table 1 shows the fineness and density of the undrawn yarn.

Table 7: Density increased in proportion to shrinkage rate. Density is ethanol-
2 with water-based density gradient tube! Measured at °C.

These undrawn yarns are drawn with a device as shown in Fig. 2 at a drawing temperature of //! ~/33-℃, feeding speed θ, /! Stretched with my fake.

FIG. 3 shows the relationship between the deformation ratio λ0 of the wet gel fiber and the tensile strength of the drawn yarn.

The fineness of the drawn yarn is determined by λ0 if the wet gel fiber is the same regardless of the shrinkage rate during extraction, so looking at the strength of the drawn yarn at the same λ0 from Figure 3, the shrinkage rate is It can be seen that the higher the value, the higher the strength. The relationship between the shrinkage rate and the tensile strength of the drawn yarn (obtained by interpolation and extrapolation from Fig. 3 for the case of 20275% 20.2!) is shown in Fig. 1, and the more it shrinks, the higher the strength becomes. , the contraction rate is 10tl
It can be seen that r or more is preferable.

During stretching, as shown in FIG.
During this time, a tensiometer was set to measure the drawing tension, and the relationship with the tensile strength of the obtained drawn yarn was investigated. The results are shown in FIG. OC to obtain the same strength: The higher the shrinkage rate, the lower the stretching tension.If you look at it from another perspective, it can be seen that the higher the shrinkage rate, the higher the strength, if stretched at the same stretching tension. Note that the drawing tension is a value divided by the fineness of the drawn yarn.

The tensile strength was measured according to JI8L/θ/3.

The fineness of the undrawn yarn and the drawn yarn was calculated by measuring the weight of a sample of a certain length (wax size) using a weight measuring device capable of measuring up to 0.0/cape.

Examples and Comparative Examples High-density polyethylene (manufactured by Asahi Kasei Kogyo ■), molecular weight! ,θ
×706 was dissolved in decalin to prepare a solution of θ. Spinning was carried out in the same manner as in Example 1, and extraction was carried out by changing the shrinkage rate. Drying after extraction was carried out without changing the length. The deformation magnification from the wet gel fiber is λ0=2, and the feeding speed is 0.72.
Stretching temperature with roux //! ~/3! °C, hot air heating stretching furnace length/
9! The film was stretched at m and the stretching stability was examined. For comparison, an undrawn yarn that was extracted without shrinkage and dried was also drawn in the same manner. Table 2 shows the continuous drawing time and the fineness of the undrawn yarn and the drawn yarn. It can be seen that the undrawn yarn that is shrunk during extraction has better stretching stability and greater tensile strength than the undrawn yarn that is not shrunk.

Table C Example 3, Comparative Example 3 Polyethylene (manufactured by Asahi Kasei Corporation, molecular weight 3.0X/θ6
)2. The θtidecalin solution was continuously subjected to the process from spinning to drying using the same spinning, extraction, drying, stretching, and winding equipment as shown in Figure 2, and once the undrawn yarn was wound, stretching was performed. . The extraction solvent is i, i, 2-trichloro-/, 2.
coated trifluoroethane was used.

The speed of the take-up roll 8 at the exit of the extraction tank is set at 3.4 m7m (with respect to the speed of the extraction roll 5, /roux).
/2 shrinkage), drying was carried out at a feed and take-up speed ratio of /:l at a temperature of ♂0°C, 20j denier, density 0. ri4
,? ? An undrawn Ad yarn was obtained. This undrawn yarn was let out at a undrawn speed of 0.20 m/m, and the drawing furnace temperature was set at 7 no.
At 37℃, λo = 23 times stretching can be performed stably, 7.4t denier, tensile strength 3♂・4tff/D
of monofilament was obtained. However, depending on the speed of the take-up roll 8 at the exit of the extraction tank, the dry undrawn yarn (fineness/7θ denier, density θ, 9J″, g f/ad) extracted without shrinkage is similarly Although it was stretched, 7
It broke in 0 minutes, and stable stretching was not possible.

Effects of the present invention According to the present invention, high-strength polyethylene fibers can be easily and stably produced.

Furthermore, according to the present invention, polyethylene fibers having the same tendency as strength and high tensile modulus can also be obtained easily and stably.

[Brief explanation of drawings]

FIG. 1 is a diagram plotting the relationship between the shrinkage rate of the wet gel fiber during extraction, the deformation ratio of the drawn yarn from the wet gel fiber, and the tensile strength of the drawn yarn. FIG. 2 shows a general polyethylene gel spinning and hot stretching apparatus. Figure 3 shows the deformation magnification λ0 of the drawn yarn from the wet gel fiber,
FIG. 3 is a diagram plotting the relationship between the shrinkage rate of wet gel fibers during extraction and the tensile strength of drawn yarn. FIG. 9 is a diagram plotting the relationship between the drawing tension, the shrinkage rate of the wet gel fiber during extraction, and the tensile strength of the drawn yarn. l...High molecular weight polyethylene solution 2...Plunger type extruder 3...Spinneret 4...Water tank 5...Take-up roll for spinning and delivery roll for extraction 6...
Wet gel fiber 7...Extraction tank 8...Extraction take-up roll/drying delivery roll 9...
Gel fiber 10 after extraction...Drying oven 11...Drying take-up roll/drawing roll 12/
... Dry undrawn gel fiber 13 ... Heating drawing furnace 14 ... Taking-off roll for drawing 15 ... Drawn yarn 16 ... Winding machine

Claims (2)

[Claims] (1) A solution consisting of high molecular weight polyethylene and a solvent is extruded from a spinneret, cooled to form a fibrous material, the solvent contained in the fibrous material is extracted, dried, and hot stretched to create a high strength product. A method for producing high-strength polyethylene fibers, the method comprising substantially shrinking the fibers when extracting the solvent. (2) A method for producing a high-strength polyethylene fiber according to claim (1), which comprises shrinking the fiber by 10% or more when extracting the solvent.