JP7573373B2 - Liquid crystal polyester fiber and its manufacturing method - Google Patents

Description

The present invention relates to continuous liquid crystal polyester fibers and a method for producing the same.

It has been known that excellent fibers with high strength of 18 cN/dtex or more can be obtained by melt spinning liquid crystal polyester resin and heat treating the resulting spun yarn. For example, Patent Document 1 (JP Patent Publication 55-20008) discloses a method for improving the strength of a melt-molded article formed from a synthetic linear polymer capable of forming an anisotropic melt, by heat treating the article to improve its strength by at least 50%.

Patent Document 2 (JP Patent Publication 1-92408 A) discloses a method for producing an aromatic polyester fiber, which comprises spinning an aromatic polyester capable of forming an anisotropic melt from a nozzle at a temperature 10° C. or more higher than the flow temperature of the polymer and at a shear rate of 10 ³ sec ^-1 or more, heat treating the spun fiber in an inert atmosphere at a temperature equal to or lower than the flow temperature of the fiber for a time such that the strength of the fiber does not increase by 50% or more, and then further heat treating the fiber in an active atmosphere for a time such that the strength increases by 50% or more.

Patent document 3 (JP Patent Publication 2013-133575A) discloses a liquid crystal polyester multifilament for splitting, characterized in that the degree of fusion between single fibers (F) is 1≦F≦5. This invention describes that it is preferable to heat treat (solid-phase polymerization) the fibers obtained by melt spinning in a packaged state in order to improve productivity.

Taking advantage of their high strength and low water absorption compared to other high strength fibers such as aramid fibers, these high strength liquid crystal polyester fibers are widely used in general industrial materials such as ropes, cords, and slings, as well as tension members for undersea telegraph cables and optical cables.

Many of these applications involve long total distances. For example, when used for marine ropes and undersea cables, the deepest point in the world is about 11,000 meters deep, and the length of undersea cables for information and communications is over 30 km in the Straits of Dover and several thousand km in the Atlantic and Pacific Oceans. Taking into account that tension members used in cables may be processed into a spiral shape, bending during use, and the undulations of the seabed, raw fiber materials with total lengths even longer than these linear distances are required. Currently, these marine ropes and undersea cables are operated by adding short fiber materials or setting up relay points.

Special Publication No. 55-20008 Japanese Unexamined Patent Publication No. 1-92408 JP 2013-133575 A

However, in such long-length applications, when fiber materials are joined together until they reach the desired length, structures such as knots, adhesive points, and joint parts are required to connect the end points, which is undesirable because the weight and size of the relevant parts increase and they become more susceptible to tensile breakage. Furthermore, even for product applications that are shorter than the raw fiber material, long lengths are advantageous in the process of continuously manufacturing products, and with short fibers, the manufacturing equipment must be stopped or slowed down every time a fiber end appears, and the raw fiber material must be switched to the next lot, resulting in high manufacturing costs and low production efficiency.

Therefore, for long-length applications, if raw fiber material could be continuously supplied over a distance equivalent to the total length, it would be unnecessary to relay such discontinuous structures, and it is believed that the manufacturing of the target product and the use of the raw fiber material would become dramatically more efficient. Furthermore, even if the product is shorter than the raw fiber material, if longer fiber material could be used, the number of times that fiber material lots need to be switched in the process of continuously manufacturing products could be reduced, leading to reduced manufacturing costs and improved production efficiency.

However, in the conventional manufacturing method of liquid crystal polyester fiber, when the amount of fiber is large, it is difficult to manufacture continuous long fibers having more uniform physical properties over the entire length of the fiber. That is, liquid crystal polyester fiber is first melt-spun as a raw yarn with low strength (for example, 10 cN/dtex or less) using liquid crystal polyester resin as a raw material, and then heat-treated (this is called solid-phase polymerization) to exhibit high strength (for example, 18 cN/dtex or more). In solid-phase polymerization, a batch method is generally used in which a fiber package in which a spun raw yarn is wound at a predetermined winding density on a bobbin with holes is heat-treated in a heat treatment furnace. Since long objects are generally heavy, when solid-phase polymerization is performed by the batch method, if the weight of the fiber wound on the bobbin becomes large, the size of the package in the thickness direction or height direction of the bobbin becomes large, and unevenness in the inner and outer layers of heat and air flow and unevenness in the height direction occur. As a result, the degree of improvement in mechanical properties also varies, making it difficult to obtain a heat-treated yarn without variation in mechanical properties.

In Patent Documents 1 to 3, solid-state polymerization is carried out in a batch manner while the fiber is wound around a bobbin, and the fiber weight of the fiber package used in solid-state polymerization is 6 kg in Patent Document 2 and in the range of 1.0 kg to 6.0 kg in Patent Document 3. None of the documents involve solid-state polymerization of fibers weighing 10 kg or more. For this reason, it is still not possible to obtain a long liquid crystal polyester fiber with small variations in strength over its entire length.

Therefore, the object of the present invention is to provide a liquid crystal polyester fiber that is long and has little variation in strength over its entire length, and a method for producing the same.

As a result of intensive research into achieving the above-mentioned object, the inventors of the present invention discovered that by conveying the liquid crystal polyester fiber spinning raw yarn at a specific elongation ratio, subjecting it to continuous heat treatment, and solid-phase polymerization, it is possible to perform the heat treatment in a more uniform environment in the longitudinal direction of the fiber, thereby suppressing the variation in strength over the entire length of the fiber, even for heavy fibers, and thus completing the present invention.

That is, the present invention can be configured in the following manner.
[Aspect 1]
A liquid crystal polyester fiber, which is a continuous fiber weighing 10 kg or more, the entire length of the continuous fiber is divided into 50 equal parts in the longitudinal direction, and an average value (A ₁ ) obtained from strength measurement data of the 50 points is 18 cN/dtex or more (preferably 20 cN/dtex or more, more preferably 23 cN/dtex or more), and a strength variation calculated according to the following formula using the average value (A ₁ ) and standard deviation (σ ₁ ) obtained from the strength measurement data is 8.0% or less (preferably 5.0% or less, more preferably 3.0% or less).
Strength variation=(σ ₁ /A ₁ )×100
[Aspect 2]
The liquid crystal polyester fiber according to embodiment 1, having a total fineness of 220 dtex or more (preferably 500 to 50,000 dtex, more preferably 1,000 to 30,000 dtex).
[Aspect 3]
A highly processed product at least partly using the liquid crystal polyester fiber according to embodiment 1 or 2.
[Aspect 4]
A method for producing the liquid crystal polyester fiber according to aspect 1 or 2,
A method for producing a liquid crystal polyester fiber, comprising at least a step of heat-treating a raw spun yarn of a liquid crystal polyester fiber, wherein in the heat-treating step, the raw spun yarn is transported at an elongation ratio of 1.000 to 1.200 times (preferably 1.001 to 1.150 times, more preferably 1.002 to 1.100 times, and even more preferably 1.003 to 1.050 times) to be heat-treated.
[Aspect 5]
The method for producing a liquid crystalline polyester fiber according to embodiment 4, wherein the strength ratio before and after the heat treatment is 1.5 times or more (preferably 1.8 times or more, more preferably 2.0 times or more).
[Aspect 6]
A method for producing a liquid crystalline polyester fiber according to aspect 4 or 5, wherein in the heat treatment step, the heat treatment is performed while the raw spun yarn is transported by a roll-to-roll method.

The liquid crystal polyester fiber of the present invention is a heavy and long product, but has little variation over its entire length, making it suitable for use in long applications and improving the production efficiency of processed products using the liquid crystal polyester fiber.

In addition, the manufacturing method of the present invention makes it possible to efficiently produce heavy, long liquid crystal polyester fibers with little variation in strength over their entire length.

The present invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are merely for illustration and explanation, and should not be used to define the scope of the present invention, which is defined by the appended claims.
1 is a process schematic diagram of the production of a liquid crystal polyester fiber of Example 1.

[Liquid crystal polyester fiber]
The liquid crystal polyester fiber of the present invention is composed of liquid crystal polyester. The liquid crystal polyester is composed of repeating units derived from, for example, aromatic diol, aromatic dicarboxylic acid, aromatic hydroxycarboxylic acid, etc., and the chemical structure of the aromatic diol, aromatic dicarboxylic acid, aromatic hydroxycarboxylic acid-derived units is not particularly limited as long as it does not impair the effects of the present invention. In addition, the liquid crystal polyester may contain a structural unit derived from an aromatic diamine, aromatic hydroxyamine, or aromatic aminocarboxylic acid, so long as it does not impair the effects of the present invention. For example, examples of preferred structural units are shown in Table 1.

In the structural units in Table 1, m is an integer of 0 to 2, and Y in the formula, in the range of 1 to the maximum number of possible substitutions, each independently represents a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (e.g., a methoxy group, an ethoxy group, a isopropoxy group, a n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an aralkyl group (e.g., a benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.), an aryloxy group (e.g., a phenoxy group), an aralkyloxy group (e.g., a benzyloxy group), etc.).

More preferred structural units include the structural units described in examples (1) to (18) in Tables 2, 3, and 4 below. When a structural unit in the formula is a structural unit that can exhibit multiple structures, two or more of such structural units may be combined and used as structural units that constitute the polymer.

In the structural units of Tables 2, 3 and 4, n is an integer of 1 or 2, and each structural unit n=1, n=2 may exist alone or in combination, and Y ₁ and Y ₂ may each independently be a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (e.g., a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an aralkyl group (e.g., a benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.), an aryloxy group (e.g., a phenoxy group, etc.), an aralkyloxy group (e.g., a benzyloxy group, etc.), etc. Of these, a hydrogen atom, a chlorine atom, a bromine atom, or a methyl group is preferred.

Examples of Z include the substituents represented by the following formula:

The liquid crystal polyester may preferably be a combination having a naphthalene skeleton as a structural unit. It is particularly preferable to include both a structural unit (A) derived from hydroxybenzoic acid and a structural unit (B) derived from hydroxynaphthoic acid. For example, the structural unit (A) may be represented by the following formula (A), and the structural unit (B) may be represented by the following formula (B). From the viewpoint of improving melt moldability, the ratio of the structural unit (A) to the structural unit (B) may be preferably in the range of 9/1 to 1/1, more preferably 7/1 to 1/1, and even more preferably 5/1 to 1/1.

The sum of the structural units (A) and the structural units (B) may be, for example, 65 mol% or more of the total structural units, more preferably 70 mol% or more, and even more preferably 80 mol% or more. Liquid crystal polyesters in which the structural units (B) account for 4 to 45 mol% of the polymer are particularly preferred.

The liquid crystal polyester may contain 50 mol% or more of the structural unit (A), i.e., the structural unit derived from 4-hydroxybenzoic acid, preferably 53 mol% or more, and more preferably 60 mol% or more. There is no particular upper limit to the content of the structural unit derived from 4-hydroxybenzoic acid in the liquid crystal polyester, but it may be, for example, 90 mol% or less, preferably 88 mol% or less, and more preferably 85 mol% or less.

The liquid crystal polyester may also contain a structural unit derived from 4-hydroxybenzoic acid as the aromatic hydroxycarboxylic acid, and may also contain a structural unit derived from an aromatic dicarboxylic acid and a structural unit derived from an aromatic diol. For example, at least one selected from the group consisting of the following formula (C) and the following formula (D) may be used as the structural unit derived from an aromatic dicarboxylic acid, and at least one selected from the group consisting of the following formula (E) and the following formula (F) may be used as the structural unit derived from an aromatic diol. Preferably, the liquid crystal polyester may include a structural unit (A) (above formula (A)) derived from 4-hydroxybenzoic acid, a structural unit (C) (below formula (C)) derived from terephthalic acid as an aromatic dicarboxylic acid, a structural unit (D) (below formula (D)) derived from isophthalic acid, and a structural unit (E) (below formula (E)) derived from 4,4'-dihydroxybiphenyl as an aromatic diol; a liquid crystal polyester may include a structural unit (A) (above formula (A)) derived from 4-hydroxybenzoic acid, a structural unit (C) (below formula (C)) derived from terephthalic acid as an aromatic dicarboxylic acid, a structural unit (D) (below formula (D)) derived from isophthalic acid, a structural unit (E) (below formula (E)) derived from 4,4'-dihydroxybiphenyl as an aromatic diol, and a structural unit (F) (below formula (F)) derived from hydroquinone.

The liquid crystal polyester may also contain a structural unit derived from hydroxynaphthoic acid containing a naphthalene skeleton as an aromatic hydroxycarboxylic acid, and may also contain a structural unit derived from an aromatic dicarboxylic acid and a structural unit derived from an aromatic diol. Preferably, the liquid crystal polyester may contain a structural unit (B) (above formula (B)) derived from 6-hydroxy-2-naphthoic acid, a structural unit (C) (below formula (C)) derived from terephthalic acid as an aromatic dicarboxylic acid, a structural unit (G) (below formula (G)) derived from 2,6-naphthalenedicarboxylic acid, and a structural unit (F) (below formula (F)) derived from hydroquinone as an aromatic diol.

The melting point (hereinafter, sometimes referred to as Mp ₀ ) of the liquid crystal polyester preferably used in the present invention is preferably in the range of 250 to 380°C, more preferably 255 to 370°C, even more preferably 260 to 360°C, and even more preferably 260 to 330°C. The melting point referred to here is the main absorption peak temperature observed when measured with a differential scanning calorimeter (DSC; Mettler "TA3000") in accordance with the JIS K 7121 test method. Specifically, 10 to 20 mg of a sample is taken and sealed in an aluminum pan in the DSC device, and then nitrogen is flowed as a carrier gas at 100 mL/min, and the endothermic peak is measured when the temperature is raised at 20°C/min. In cases where no clear peak appears in the first run in DSC measurement due to the type of polymer, the polymer should be heated at a rate of 50° C./min to a temperature 50° C. higher than the expected flow temperature, completely melted at that temperature for 3 minutes, then cooled to 50° C. at a rate of 80° C./min, and then the endothermic peak should be measured at a heating rate of 20° C./min.

The liquid crystal polyester may contain thermoplastic polymers such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyether ether ketone, and fluororesin, as long as the effects of the present invention are not impaired. It may also contain various additives such as inorganic substances such as titanium oxide, kaolin, silica, and barium oxide, colorants such as carbon black, dyes, and pigments, antioxidants, ultraviolet absorbers, and light stabilizers.

The liquid crystal polyester fiber of the present invention is a continuous fiber having a fiber weight of 10 kg or more. Continuous fiber refers to a monofilament or multifilament that is continuous without breaks for the length of the fiber weight. In the case of a multifilament, it is sufficient that the fiber bundle is continuous without breaks. In the present invention, for fibers that are continuous due to joint treatments such as knotting, splicing, end loop treatment, intertwining, heat fusion, adhesive, adhesive tape, and the use of joint parts, the fibers before and after the treatment are not continuous fibers. The length of the fiber varies depending on the total fineness, but the size of the package in the thickness direction or height direction of the bobbin when wound around the bobbin varies depending on the weight rather than the length of the fiber. Therefore, when a heavy fiber is solid-phase polymerized in a batch system, the size of the package in the thickness direction or height direction of the bobbin becomes large, which causes unevenness in the inner and outer layers of heat and air flow and unevenness in the height direction, resulting in unevenness in the degree of improvement of mechanical properties. Therefore, the manufacturing method described below makes it possible to reduce the strength unevenness over the entire length of the continuous fiber, even if it is heavy. From the viewpoint of improving productivity in subsequent product processing, the liquid crystal polyester fiber of the present invention may have a fiber weight of preferably 12 kg or more, more preferably 15 kg or more, and even more preferably 25 kg or more. The upper limit of the fiber weight is not particularly limited, but may be, for example, 100 kg or less, preferably 50 kg or less.

The liquid crystal polyester fiber of the present invention has a strength of 18 cN/dtex or more. From the viewpoint of improving the mechanical strength of general industrial materials and highly processed products such as tension members of submarine telegraph cables and optical cables, the strength may be preferably 20 cN/dtex or more, more preferably 23 cN/dtex or more. The upper limit of the strength is not particularly limited, but for example, the value that can be achieved by the present invention is about 30 cN/dtex. In the present invention, the strength of the liquid crystal polyester fiber refers to the tensile strength, and is the average value (A ₁ ) obtained from the strength measurement data of 50 points obtained by dividing the entire length of the continuous fiber into 50 equal parts in the longitudinal direction, and is a value measured by the method described in the examples described later.

The liquid crystal polyester fiber of the present invention has a strength variation of 8.0% or less over the entire fiber length. The liquid crystal polyester fiber of the present invention has a reduced strength variation over the entire fiber length, even though it is long. From the viewpoint of improving the mechanical properties of the entire highly processed product, the strength variation may be preferably 5.0% or less, more preferably 3.0% or less. The lower limit of the strength variation is not particularly limited, but may be, for example, about 0.1%. In the present invention, the strength variation is calculated according to the following formula using the average value (A ₁ ) and standard deviation (σ ₁ ) obtained from the strength measurement data of the 50 points obtained by dividing the entire length of the continuous fiber into 50 equal parts in the longitudinal direction, and is a value measured by the method described in the examples described later.
Strength variation=(σ ₁ /A ₁ )×100

The total fineness of the liquid crystal polyester fiber of the present invention can be adjusted appropriately depending on the application, etc., and may be, for example, 220 dtex or more. In addition, it may be preferably 500 to 50,000 dtex, and more preferably 1,000 to 30,000 dtex.

The liquid crystal polyester fiber of the present invention is not particularly limited in total length of the fiber as long as the weight is 10 kg or more, and can be appropriately adjusted depending on the application, etc. For example, when the total fineness is 220 dtex or more and less than 500 dtex, the total length of the fiber may be 200,000 to 2,300,000 m, and preferably 240,000 to 2,300,000 m.
When the total fineness is 500 dtex or more and less than 1000 dtex, it may be 100,000 to 1,000,000 m, and preferably 120,000 to 1,000,000 m.
When the total fineness is 1000 dtex or more and less than 3000 dtex, it may be 33000 to 500000 m, and preferably 40000 to 500000 m.
When the total fineness is 3000 dtex or more and less than 10000 dtex, it may be 10000 to 170000 m, preferably 12000 to 170000 m.
When the total fineness is 10,000 dtex or more and less than 50,000 dtex, it may be 2,000 to 50,000 m, preferably 2,400 to 50,000 m.

The single fiber fineness of the liquid crystal polyester fiber of the present invention can be appropriately adjusted depending on the application, etc. For example, the single fiber fineness may be 0.5 to 50 dtex, preferably 1.0 to 15 dtex, and more preferably 1.5 to 10 dtex.

When the liquid crystal polyester fiber of the present invention is a multifilament fiber, the number of filaments can be appropriately adjusted depending on the application, etc. For example, the number of filaments may be 5 to 20,000, preferably 10 to 4,000, and more preferably 30 to 3,000.

The liquid crystal polyester fiber of the present invention may be in the form of a fiber package wound around a bobbin. The bobbin used to form the fiber package is not particularly limited as long as it is cylindrical, and may be a fiber package in a known winding form such as a pirn, cheese, or cone. Since the liquid crystal polyester fiber of the present invention is heavy, the fiber package may be wound around a bobbin so as not to collapse, and may have a winding density of, for example, 0.7 to 1.4 g/ ^cm3 .

[Method of producing liquid crystal polyester fiber]
The method for producing a liquid crystal polyester fiber of the present invention includes at least a step of heat-treating a raw spun yarn of the liquid crystal polyester fiber, and in the heat-treating step, the raw spun yarn may be transported at an elongation ratio of 1.000 to 1.200 times to perform the heat treatment.

The inventors of the present invention have found that in the solid-state polymerization of liquid crystal polyester fiber spinning raw yarn, it is not possible to sufficiently suppress strength variations by simply carrying out continuous heat treatment while transporting the fiber to create a more uniform heating environment in the longitudinal direction of the fiber, but that by carrying the fiber at a specific elongation ratio and carrying out continuous heat treatment, it is possible to suppress strength variations over the entire length of the fiber, even for heavy fibers.

The method of fiberization of liquid crystal polyester fiber spinning raw yarn is not limited, but fibers obtained by melt spinning can usually be used. Melt spinning can be performed by known or conventional methods, for example, by melting a fiber-forming resin for obtaining spinning raw yarn composed of liquid crystal polyester in an extruder, and then discharging it from a nozzle at a predetermined spinning temperature.

In the heat treatment process, the raw yarn is heat-treated to perform solid-phase polymerization, thereby improving the strength of the raw yarn. The heat treatment temperature may be 230°C or higher, preferably 240°C or higher, and more preferably 250°C or higher, from the viewpoint of improving strength. The heat treatment temperature may be lower than the melting point (Mp) of the liquid crystal polyester fiber (raw yarn) subjected to the heat treatment to prevent melting, and may be, for example, in the range of 230°C or higher, (Mp-80)°C or higher but lower than (Mp)°C, preferably (Mp-50)°C or higher but lower than (Mp)°C, and more preferably (Mp-30)°C or higher but lower than (Mp)°C. However, since the melting point of the liquid crystal polyester fiber increases as the solid-phase polymerization progresses, it is sufficient to set the initial temperature in the heat treatment process lower than the melting point (Mp) of the liquid crystal polyester fiber (raw yarn), and by gradually increasing the heat treatment temperature according to the progress of the solid-phase polymerization, the heat treatment can be performed at a higher temperature than when the heat treatment is performed at a constant temperature. In addition, increasing the heat treatment temperature stepwise or continuously over time is preferable because it prevents fusion and increases the time efficiency of solid-state polymerization.

From the viewpoint of improving strength and manufacturing efficiency, the heat treatment time may be 5 to 1000 minutes, preferably 8 to 500 minutes, more preferably 10 to 100 minutes, and even more preferably 15 to 60 minutes. Here, the heat treatment time refers to the time for which the same part of the spun raw yarn is heat treated.

The heat treatment can be carried out by a known method, such as atmospheric heating or contact heating. The atmosphere is preferably air, an inert gas (e.g., nitrogen, argon), or a combination thereof. The heat treatment can also be carried out under reduced pressure.

The transport method in the heat treatment step may be either contact transport (e.g., conveyor method, support roll method, heat treatment method on heated rollers) or non-contact transport (roll-to-roll method). However, from the viewpoint of avoiding uneven heat caused by contact, performing treatment in a more uniform environment, and suppressing variation in mechanical properties in the longitudinal direction of the fiber, it is preferable to perform heat treatment using a heat treatment furnace while transporting the raw spun yarn by the roll-to-roll method. In addition, the treatment path does not have to be a straight line, and the length, angle, curvature, etc. of the treatment path may be appropriately changed by arranging return rollers or guides within the device and performing heat treatment.

For example, when a heat treatment furnace capable of non-contact continuous heat treatment is used, there is no particular restriction on its structure. It may be a structure in which the fiber transport path is in a straight line from the inlet to the outlet of the heat treatment furnace without any contact body, or it may have a fiber transport path with two or more stages of folding back, with rollers arranged inside the furnace or on the side of the furnace. The folding back rollers may be ones that rotate by themselves, or they may be ones that rotate in dependence on the fibers being transported. In this case, in order to prevent the generation of fibrils and perform uniform processing, the temperature of the part of the rollers arranged to fold back the fiber transport path that comes into contact with the fibers is preferably (Mp-50)°C or lower, and more preferably room temperature (40°C or lower).

In the heat treatment process, the raw spun yarn may be transported at a stretch ratio of 1.000 to 1.200. By stretching and transporting at a specific stretch ratio, in the case of multifilament, the single fibers can be aligned parallel to each other without slack at all points in the longitudinal direction of the fiber, thereby suppressing variation in the mechanical properties in the longitudinal direction of the fiber and suppressing the decrease in strength due to stretching.

The extension ratio is a value that indicates how many times the liquid crystal polyester fiber is extended before and after extension. When extension is performed using two rollers with a speed difference, it is calculated from the speed ratio. When extension is performed using a device that cannot be expressed by a speed ratio, such as stretching using the load of a dancer roller, it is calculated from the total fineness ratio of the fiber before and after extension (before and after heat treatment). The extension ratio is not limited to a range as long as the strength is not significantly reduced by the extension, but from the viewpoint of aligning the single fibers, it may be preferably 1.001 to 1.150 times, more preferably 1.002 to 1.100 times, and even more preferably 1.003 to 1.050 times.

The method of this stretching is not particularly limited to a specific stretch ratio, but examples include a method in which the rotation speed of the downstream drive roller is made faster than the rotation speed of the upstream transport roller when performing heat treatment using the roll-to-roll method, a method in which heat treatment is performed while applying a constant load using a dancer roller during transport, a method in which the yarn is passed through a heated Nelson roller, and a method in which the yarn is fixed with a pin or the like and transported and heat-treated, thereby stretching the liquid crystal polyester fiber by utilizing its negative thermal expansion coefficient in the fiber axis direction.

The stretching technique is widely known as a technique for performing heat treatment while stretching the fiber, but this stretching technique is applied to fibers with low molecular orientation to improve the strength and elastic modulus of the yarn, and is not intended to be applied to fibers that already have a highly oriented higher-order structure, such as the liquid crystal polyester fiber of the present invention. In addition, the suitable processing conditions are also different. In the stretching technique, the stretching ratio is often set to 1.5 times or more to increase the orientation as much as possible, but in the present invention, it is sufficient to stretch the single fibers so that they are aligned with each other, so the stretching ratio is preferably in the range of 1.000 to 1.200 times. If the processing is performed at a ratio exceeding this range, defects will occur in the higher-order structure due to slippage of the molecular chains, etc., and the strength is likely to decrease. As described above, the stretching technique of the present invention is a different technique from the stretching technique, and therefore the term stretching ratio is used in the present invention instead of the stretching ratio.

The tension applied during the heat treatment can be adjusted according to the total fineness of the liquid crystal polyester fiber to be heat treated, but from the viewpoint of stabilizing the yarn path and suppressing yarn breakage, it may be, for example, 0.001 to 0.06 cN/dtex, preferably 0.003 to 0.05 cN/dtex, and more preferably 0.005 to 0.04 cN/dtex.

In the method for producing liquid crystal polyester fiber of the present invention, the strength ratio of the liquid crystal polyester fiber before and after the heat treatment may be 1.5 times or more, preferably 1.8 times or more, and more preferably 2.0 times or more. Here, the strength ratio before and after the heat treatment refers to the value obtained by dividing the tensile strength of the liquid crystal polyester fiber after the heat treatment by the tensile strength of the liquid crystal polyester fiber (raw spinning yarn) before the heat treatment. Since the strength of the raw spinning yarn of liquid crystal polyester fiber is generally 12 cN/dtex or less, the strength of the liquid crystal polyester fiber can be improved by performing solid-phase polymerization under appropriate conditions so that the strength ratio before and after the heat treatment is in the above range.

The liquid crystal polyester fiber of the present invention is long and has reduced strength variation over its entire length, so it can be used suitably for long applications and can improve production efficiency when manufacturing advanced processed products. Therefore, the liquid crystal polyester fiber of the present invention can be used suitably for general industrial materials such as ropes, cords, and slings, and advanced processed products such as tension members for submarine telegraph cables and optical cables.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited by these examples. In the following examples and comparative examples, various physical properties were measured by the following methods.

(Total fineness, single fiber fineness)
Based on JIS L 1013:2010 8.3.1 A method, a 100m reel of liquid crystal polyester fiber was taken using a measuring device "Wrap Reel by Motor Drive" manufactured by Daiei Scientific Instruments Co., Ltd., and the weight (g) was multiplied by 100 to perform two measurements per level, and the average value was taken as the total fineness (dtex) of the liquid crystal polyester fiber obtained. The quotient obtained by dividing this value by the number of filaments was taken as the single fiber fineness (dtex).

(Melting Point)
The melting point was determined as the main absorption peak temperature observed using a differential scanning calorimeter (DSC; Mettler, "TA3000") in accordance with JIS K 7121. Specifically, 10 to 20 mg of a sample was placed in an aluminum pan and sealed in the DSC device, and nitrogen was passed as a carrier gas at a flow rate of 100 mL/min, and the endothermic peak was measured when the temperature was raised at a rate of 20° C./min.

(Strength, strength variation)
Fifty 1 m measurement samples were taken from a continuous liquid crystal polyester fiber without any break. These measurement samples were taken from the range of ±0.5% from each of the 50 points that were equally divided in the longitudinal direction of the entire fiber length. The entire fiber length was calculated from the fiber weight and the total fineness measured above.
Next, referring to JIS L 1013:2010 8.5.1, a tensile test was performed using an autograph "AGS-100B" manufactured by Shimadzu Corporation under conditions of a test length of 10 cm, an initial load of 2.94 mN/dtex, and a tensile speed of 10 cm/min. The strength at break was measured once for each of the 50 measurement samples, and the average value (A ₁ ) of the total 50 measurements was taken as the strength (cN/dtex).
Further, the standard deviation (σ ₁ ) of the 50 measurement results was divided by the average value (A ₁ ), and the quotient was multiplied by 100 to obtain the strength variation (%).
Strength variation (%)=(σ ₁ /A ₁ )×100

[Example 1]
A liquid crystal polyester (α) (Mp ₀ : 281° C.) was used in which the structural units (A) and (B) shown in the following formula were (A)/(B)=73/27 (molar ratio). This was melt-extruded by an extruder, and the polymer was supplied to the spinning head while being metered by a gear pump. The spinning head was equipped with a spinneret with a hole diameter of 0.125 mmφ, a land length of 0.175 mm, and 300 holes, and the polymer was discharged at a discharge rate of 167 g/min and wound around a bobbin at a winding speed of 1000 m/min to obtain a spun raw yarn. At this time, a 2 wt % aqueous solution of sodium dodecyl phosphate (manufactured by Wako Pure Chemical Industries, Ltd., Wako First Grade) was applied to the spun raw yarn from an oiling guide arranged directly under the spinneret. The amount of this aqueous solution applied was 8.4 g/min, and the adhesion ratio of sodium dodecyl phosphate to the spun raw yarn was calculated to be 0.1 wt %. The melting point (Mp) of the raw yarn was 281°C.

Next, as shown in the process schematic diagram of FIG. 1, the raw spinning yarn 9 was unwound from the unwinder 1 and wound up through the first roller 2, the heat treatment furnace 3, the second roller 4, and the winder 5 in that order, thereby performing continuous heat treatment by conveying in a roll-to-roll manner, and 15 kg of the heat-treated yarn 12 of this embodiment was obtained continuously. Here, the heat treatment furnace 3 has a furnace tube 10 consisting of one ceramic tube and a control unit 11 having a heater unit for heating the atmosphere inside the furnace tube 10. The furnace tube 10 has three heating zones 6 to 8, and each heating zone 6 to 8 can be controlled at a different temperature by the control unit 11. The conditions for the continuous heat treatment were set as follows. The rotation speed of the first roller 2 was set so that the time to pass through the furnace tube 10 of the heat treatment furnace 3 (the distance the yarn sample passes through the furnace tube 10 of the heat treatment furnace 3/the conveying speed of the first roller 2) was 60 minutes. The rotation speed of the second roller 4 was set so that the elongation ratio (rotation speed of the second roller 4/rotation speed of the first roller 2) was 1.005. The heat treatment furnace 3 was filled with a nitrogen atmosphere, and the temperatures of the three heating zones 6 to 8 were 230°C, 260°C, and 290°C, respectively. To adjust the height of the yarn path, etc., ceramic rollers and ceramic guides (neither shown) for matte surface treatment were also used as appropriate. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Example 2]
A continuous heat-treated yarn (15 kg) was obtained in the same manner as in Example 1, except that a spinneret with a hole diameter of 0.100 mmφ, a land length of 0.140 mm, and 600 holes was used to obtain the raw spun yarn. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Example 3]
A continuous heat-treated yarn (15 kg) was obtained in the same manner as in Example 1, except that a spinneret with a hole diameter of 0.150 mmφ, a land length of 0.210 mm, and 50 holes was used to obtain the raw spinning yarn. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Example 4]
A continuous heat-treated yarn (15 kg) was obtained in the same manner as in Example 1, except that a spinneret with a hole diameter of 0.125 mmφ, a land length of 0.175 mm, and 20 holes was used, the polymer was discharged at a discharge rate of 11.2 g/min, and the amount of sodium dodecyl phosphate solution applied from the oiling guide was set to 0.56 g/min to obtain a raw spun yarn. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Example 5]
Two spinning heads and spinnerets used in Example 1 were used at the same time, and the polymer discharged from each at a discharge rate of 167 g/min was stacked as one thread and wound around a bobbin at a winding speed of 1000 m/min to obtain a spun raw yarn. Except for this, 15 kg of continuous heat-treated yarn was obtained in the same manner as in Example 1. The process of applying an aqueous sodium dodecyl phosphate solution from the oiling guide was performed at a stage prior to stacking as one thread, and was applied directly below each spinneret in the same manner as in Example 1. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Example 6]
Four spinning heads and spinnerets used in Example 1 were used simultaneously, and the polymer discharged from each at a discharge rate of 167 g/min was stacked as a single thread and wound around a bobbin at a winding speed of 1000 m/min to obtain a spun raw yarn. Except for this, 15 kg of continuous heat-treated yarn was obtained in the same manner as in Example 1. The process of applying an aqueous sodium dodecyl phosphate solution from the oiling guide was performed at a stage prior to stacking as a single thread, and was applied directly below each spinneret in the same manner as in Example 1. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Example 7]
A heat-treated yarn was obtained in the same manner as in Example 6, except that the continuous heat treatment was carried out for a long period of time to obtain 50 kg of continuous heat-treated yarn. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Example 8]
In the continuous heat treatment, the same spinning yarn and apparatus as in Example 1 were used, and the heat treatment time was 16 hours, and the rotation speeds of the first roller 2 and the second roller 4 were set so that the elongation ratio was 1.005 times, but otherwise the same procedure was followed as in Example 1 to obtain 15 kg of continuous heat-treated yarn. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Example 9]
In the continuous heat treatment, the same spinning yarn and device as in Example 1 were used, and except that the rotation speed of the second roller 4 was set so that the elongation ratio was 1.100 times, 15 kg of continuous heat-treated yarn was obtained in the same manner as in Example 1. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Example 10]
In the continuous heat treatment, the same spinning yarn and device as in Example 1 were used, and except that the rotation speed of the second roller 4 was set so that the elongation ratio was 1.000 times, 15 kg of continuous heat-treated yarn was obtained in the same manner as in Example 1. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Example 11]
A raw spinning yarn was obtained in the same manner as in Example 1, except that a liquid crystal polyester (β) (Mp ₀ : 348° C.) in which the molar ratio of each constituent unit shown in the following formula was (A)/(C)/(D)/(E)=65/10/5/20 was used instead of the liquid crystal polyester (α) described in Example 1. Thereafter, 15 kg of continuous heat-treated yarn was obtained in the same manner as in Example 1, except that in the continuous heat treatment, the temperatures of the three heating zones 6 to 8 were 280° C., 280° C., and 310° C. in the order of passing through. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Example 12]
A raw spinning yarn was obtained in the same manner as in Example 1, except that a liquid crystal polyester (γ) (Mp ₀ : 315° C.) in which the molar ratio of each constituent unit shown in the following formula is (A)/(C)/(D)/(E)/(F)=54/15/8/16/7 was used instead of the liquid crystal polyester (α) described in Example 1. Thereafter, 15 kg of continuous heat-treated yarn was obtained in the same manner as in Example 1, except that in the continuous heat treatment, the temperatures of the three heating zones 6 to 8 were 280° C., 280° C., and 310° C. in the order of passing through. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Example 13]
A raw spinning yarn was obtained in the same manner as in Example 1, except that a liquid crystal polyester (δ) (Mp ₀ : 363° C.) in which the molar ratio of each constituent unit shown in the following formula was (B)/(C)/(G)/(F)=58/5/16/21 was used instead of the liquid crystal polyester (α) described in Example 1. Thereafter, 15 kg of continuous heat-treated yarn was obtained in the same manner as in Example 1, except that in the continuous heat treatment, the temperatures of the three heating zones 6 to 8 were 300° C., 300° C., and 330° C. in the order of passing through. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Comparative Example 1]
15 kg of the raw spun yarn obtained in the same manner as in Example 1 was wound around a Kevlar felt (basis weight 280 g/ ^m2 , thickness 1.5 mm) on an aluminum bobbin with holes, and rewound at 400 m/min to obtain a bobbin package for heat treatment. At this time, the traverse width was 200 mm, the innermost diameter of the yarn layer was 100 mm, the average winding density was 0.60 g/ ^cm3 , and the thickness of the yarn layer was 160 mm. This was heat-treated under a nitrogen atmosphere in a batch-type box furnace using two heat sources, heated nitrogen flow and a wall-surface electric heater. In this case, the temperature was raised from 20°C to 230°C in 60 minutes (average 3.5°C/min), held at 230°C for 60 minutes, raised from 230°C to 260°C in 30 minutes (average 1°C/min), held at 260°C for 60 minutes, raised from 260°C to 290°C in 30 minutes (average 1°C/min), held at 290°C for 720 minutes, and then the use of the heat source was stopped, the inside of the furnace was opened to the outside air, and the furnace was left to cool for 3 hours to obtain 15 kg of heat-treated yarn. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Comparative Example 2]
15 kg of the raw spun yarn obtained in the same manner as in Example 6 was rewound in the same manner as in Comparative Example 1 to obtain a bobbin package for heat treatment. This was heat-treated in a batch manner in the same manner as in Comparative Example 1 to obtain 15 kg of heat-treated yarn. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Comparative Example 3]
15 kg of the liquid crystal polyester (β) spinning raw yarn obtained in the same manner as in Example 11 was rewound in the same manner as in Comparative Example 1 to obtain a bobbin package for heat treatment. This was heat-treated under a nitrogen atmosphere in a batch-type box furnace using two types of heat sources, heated nitrogen flow and wall electric heaters. In this case, the temperature was raised from 20°C to 280°C in 60 minutes (average 4.3°C/min), held at 280°C for 60 minutes, raised from 280°C to 310°C in 30 minutes (average 1°C/min), held at 310°C for 810 minutes, and then the use of the heat source was stopped, the furnace was opened to the outside air, and left for 3 hours to cool, thereby obtaining 15 kg of heat-treated yarn. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Comparative Example 4]
15 kg of the liquid crystal polyester (γ) spinning raw yarn obtained in the same manner as in Example 12 was rewound in the same manner as in Comparative Example 1 to obtain a bobbin package for heat treatment. This was heat-treated under a nitrogen atmosphere in a batch-type box furnace using two types of heat sources, heated nitrogen flow and wall electric heater. In this case, the temperature was raised from 20°C to 280°C in 60 minutes (average 4.3°C/min), held at 280°C for 60 minutes, raised from 280°C to 310°C in 30 minutes (average 1°C/min), held at 310°C for 810 minutes, and then the use of the heat source was stopped, the furnace was opened to the outside air, and left for 3 hours to cool, thereby obtaining 15 kg of heat-treated yarn. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Comparative Example 5]
15 kg of the liquid crystal polyester (δ) spinning raw yarn obtained in the same manner as in Example 13 was rewound in the same manner as in Comparative Example 1 to obtain a bobbin package for heat treatment. This was heat-treated under a nitrogen atmosphere in a batch-type box furnace using two types of heat sources, heated nitrogen flow and wall electric heater. In this case, the temperature was raised from 20°C to 300°C in 60 minutes (average 4.7°C/min), held at 300°C for 60 minutes, raised from 300°C to 330°C in 30 minutes (average 1°C/min), held at 330°C for 810 minutes, and then the use of the heat source was stopped, the furnace was opened to the outside air, and left for 3 hours to cool, thereby obtaining 15 kg of heat-treated yarn. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[Reference Example 1]
5 kg of the raw spun yarn obtained in the same manner as in Example 1 was rewound in the same manner as in Comparative Example 1 to obtain a bobbin package for heat treatment having an average winding density of 0.60 g/cm ³ and a yarn layer thickness of 75 mm. This was heat-treated in a batch manner in the same manner as in Comparative Example 1 to obtain 5 kg of heat-treated yarn. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

As shown in Table 5, in Examples 1 to 10, liquid crystal polyester fibers were produced by controlling the elongation ratio to a specific value and carrying out continuous heat treatment while transporting, so that, despite the long length, it was possible to suppress the strength variation over the entire length of the fiber. In particular, in Examples 1 to 9, in which the elongation ratio was set to 1.001 times or more, the strength variation was 3.0% or less, and it was possible to suppress the strength variation to a higher degree.

In Examples 11 to 13, a different liquid crystal polyester was used than in Example 1, but the liquid crystal polyester fiber was produced by controlling the elongation ratio to a specific value and carrying out continuous heat treatment while transporting, so that it was possible to suppress strength variations along the entire length of the fiber, regardless of the type of liquid crystal polyester.

On the other hand, in Comparative Examples 1 to 5, the heat treatment was performed on a heavy spun raw yarn using a batch method, which resulted in uneven heat and airflow in the package used for heat treatment, resulting in extremely large variations in strength over the entire length of the heat-treated yarn.

In Reference Example 1, the raw spun yarn was heat-treated using a batch method, which allowed for the suppression of strength variation. This is believed to be because the raw spun yarn was light in weight, and therefore there was little variation in the heat and airflow in the package used for heat treatment.

The liquid crystal polyester fiber of the present invention can be suitably used for general industrial materials such as ropes, cords, and slings, as well as for highly processed products such as tension members for submarine telegraph cables and optical cables.

As described above, a preferred embodiment of the present invention has been described, but various additions, modifications, and deletions are possible without departing from the spirit of the present invention, and such additions, modifications, and deletions are also included within the scope of the present invention.

Reference Signs List 1: Unwinder 2: First roller 3: Heat treatment furnace 4: Second roller 5: Winder 6, 7, 8: Heating zone 9: Spinning raw yarn 10: Furnace tube 11: Control unit 12: Heat-treated yarn

Claims (5)

A method for producing a liquid crystalline polyester fiber, the fiber being a continuous fiber weighing from 10 kg to 100 kg, the entire length of the continuous fiber being divided into 50 equal parts in the longitudinal direction, the average value (A ₁ ) obtained from strength measurement data of the 50 points being 18 cN/dtex or more, and the strength variation calculated from the average value (A ₁ ) and standard deviation (σ ₁ ) obtained from the strength measurement data according to the following formula being 8.0% or less,
A method for producing a liquid crystal polyester fiber, comprising at least a step of heat-treating a raw spun yarn of a liquid crystal polyester fiber, wherein in the heat-treating step, the raw spun yarn is transported at an elongation ratio of 1.000 to 1.200 times to be heat-treated.
Strength variation=(σ ₁ /A ₁ )×100 The method for producing a liquid crystal polyester fiber according to claim 1 , wherein a strength ratio before and after the heat treatment is 1.5 times or more. 3. The method for producing a liquid crystalline polyester fiber according to claim 1 , wherein in the heat treatment step, the raw spun yarn is heat-treated while being transported by a roll-to- roll method. The method for producing a liquid crystal polyester fiber according to any one of claims 1 to 3, wherein the total fineness of the obtained liquid crystal polyester fiber is 220 to 50,000 dtex. A method for producing a highly processed product, comprising at least a part of the liquid crystal polyester fiber obtained by the method according to any one of claims 1 to 4.

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