JP7239410B2 - Method for producing liquid crystal polyester fiber - Google Patents

Description

The present invention relates to a method for producing liquid crystalline polyester fibers.

Conventionally, it is known that excellent fibers having a high strength of 18 cN/dtex or more can be obtained by melt spinning and heat-treating a liquid crystalline polyester. This high-strength liquid crystal polyester fiber is widely used for general industrial materials, fishing nets, sporting goods, etc., taking advantage of its high strength and low water absorption. However, the liquid crystalline polyester fiber has a molecular chain structure that is highly oriented in the direction of the fiber axis, so there is a problem that it is weak against rubbing and inferior in abrasion resistance.

Therefore, in order to solve these problems, inorganic particles mainly composed of silicic acid and magnesium, which are chemically inactive and have appropriate hardness among inorganic particles, are used for the surface of the liquid crystal polyester fiber. A method has been proposed for improving the abrasion resistance of liquid crystal polyester fibers by imparting them (see, for example, Patent Document 1).

In addition, the liquid crystalline polyester fiber is heat-treated at a temperature higher than the endothermic peak temperature (Tm1) observed when measured under the temperature rising condition of 20 ° C./min from 50 ° C. in differential calorimetry, + 10 ° C. A method of relaxing the crystal orientation of the fiber surface and improving the wear resistance has been proposed. In this technology, the crystallinity of the fiber surface is reduced, and the difference in crystal/amorphous structure is reduced, thereby intentionally disturbing the fibril structure and softening the entire fiber, thereby improving It is described that fluff generation can be suppressed and abrasion resistance can be improved (see, for example, Patent Document 2).

JP 2004-107826 A Japanese Patent Application Laid-Open No. 2008-240228

However, in the method described in Patent Document 1, in a state in which the inorganic particles are strongly attached to the fiber surface or between the fibers, the inorganic particles act as a buffer against the impact of rubbing applied to the fiber surface. However, when the inorganic particles fall off from the surface of the fiber due to excessive rubbing or external load, there is a problem that the abrasion resistance is lowered.

Further, in the method described in Patent Document 2, there is a problem that the fiber surface is softened by the heat treatment at a temperature exceeding the endothermic peak temperature (Tm1), and the single fibers are fused to each other, resulting in deterioration of quality. .

Therefore, the present invention has been made in view of the above problems, and does not use materials such as inorganic particles that may peel off and fall, and has a smooth fiber surface and excellent abrasion resistance and strength. An object of the present invention is to provide a polyester fiber and a method for producing the liquid crystalline polyester fiber.

The inventors of the present invention have made intensive studies to solve the above problems, and found that by performing heat treatment by contact heating in which the liquid crystalline polyester fiber is directly brought into contact with a heating body heated to a predetermined temperature range, abrasion resistance and strength The present inventors have found that a liquid crystalline polyester fiber having an excellent thermal resistance can be obtained, and have completed the present invention. That is, the present invention provides the following preferred aspects.

[1] It includes a heat treatment step by contact heating in which the liquid crystal polyester fiber is brought into direct contact with a heating body, and the temperature of the heating body is Mp-50 ° C. or more and less than Mp, where Mp [° C.] is the melting point of the liquid crystal polyester fiber. A method for producing a liquid crystal polyester fiber, characterized by:
[2] The method for producing a liquid crystalline polyester fiber according to [1] above, wherein the heat treatment step is performed on a liquid crystalline polyester fiber having a tensile strength of 18 cN/dtex or more.
[3] The method for producing a liquid crystalline polyester fiber according to [1] or [2], wherein the heat treatment time of the heat treatment step is 10 seconds or less.
[4] The method for producing a liquid crystalline polyester fiber according to any one of [1] to [3], wherein the heater is a heat roller.

According to the present invention, a liquid crystalline polyester fiber having excellent abrasion resistance and strength can be obtained.

1 is a scanning electron microscope (SEM) photograph of a liquid crystal polyester multifilament (before heat treatment by contact heating) produced in Example 1. FIG. 1 is a scanning electron microscope (SEM) photograph of a liquid crystal polyester multifilament (after heat treatment by contact heating) produced in Example 1. FIG.

The liquid crystalline polyester fiber of the present invention and the method for producing the same will be described in detail below.
The liquid crystalline polyester used in the present invention includes, for example, repeating structural units derived from an aromatic diol, an aromatic dicarboxylic acid, an aromatic hydroxycarboxylic acid, and the like. Structural units derived from dicarboxylic acids and aromatic hydroxycarboxylic acids are not particularly limited in their chemical constitution. In addition, the liquid crystalline polyester may contain structural units derived from aromatic diamines, aromatic hydroxyamines or aromatic aminocarboxylic acids to the extent that the effects of the present invention are not impaired. For example, preferred structural units include those shown in Table 1.

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

More preferred structural units include structural units described in Examples (1) to (18) shown in Tables 2, 3 and 4 below. In addition, when the structural unit in the formula is a structural unit capable of exhibiting multiple structures, two or more of such structural units may be combined and used as the structural unit constituting the polymer.

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

Moreover, as Z, the substituent represented by the following formula is mentioned.

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

Further, the total amount of the structural units (A) and the structural units (B) may be, for example, 65 mol% or more, more preferably 70 mol% or more, and still more preferably 80 mol% of all structural units. % or more. Liquid crystalline polyesters containing 4 to 45 mol % of the constituent units of (B) in the polymer are particularly preferred.

In addition, thermoplastic polymers such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyether ether ketone, and fluororesin are added to the liquid crystalline polyester within a range that does not impair the effects of the present invention. good too. In addition, various additives such as inorganic substances such as titanium oxide, kaolin, silica, and barium oxide, carbon black, colorants such as dyes and pigments, antioxidants, ultraviolet absorbers, and light stabilizers may be included.

The liquid crystalline polyester fiber in the present invention is not limited in the method of fiberization as long as the above liquid crystalline polyester has the property that a part of the fiber surface can be melted by heating, but usually by melt spinning. The resulting fibers can be used. Melt spinning can be performed by a known or commonly used method. For example, after melting a fiber-forming resin for obtaining a liquid crystalline polyester fiber in an extruder, it is discharged from a nozzle at a predetermined spinning temperature and wound at a predetermined speed. You can get it by picking it up.

The fibers obtained by melt spinning are then preferably solid state polymerized. Here, the solid phase polymerization is to heat-treat the melt-spun liquid crystalline polyester fiber in order to improve the strength of the fiber. A known method can be used for solid phase polymerization, and examples thereof include atmospheric heating and contact heating. Either air or an inert gas (for example, nitrogen or argon) may be used as the atmosphere. The method of the heat treatment may be either batch method or roll-to-roll method as long as the effects of the present invention are not impaired. Further, regarding the heat treatment temperature for solid phase polymerization, when the melting point of the liquid crystalline polyester fiber before solid phase polymerization is Mp ₀ , the temperature is from Mp ₀ −80° C. to Mp ₀ . Since the melting point of the fiber increases as the solid-phase polymerization progresses, it is preferable from the viewpoint of production efficiency to treat with a temperature pattern in which the heat treatment temperature in the solid-phase polymerization is gradually increased.

Here, the melting point is measured by a differential scanning calorimeter (DSC; "DSC-60A" manufactured by Shimadzu Corporation) in accordance with JIS K 7121 test method, and is the main absorption peak temperature observed. . Specifically, 1 to 10 mg of a sample is placed in the DSC apparatus, sealed in an aluminum pan, and nitrogen is flowed as a carrier gas at 100 cc/min, and the endothermic peak is measured when the temperature is raised at 20° C./min. Depending on the type of polymer, if a clear peak does not appear in the 1st run in the DSC measurement, heat up to a temperature 50 ° C higher than the expected flow temperature at a heating rate of 50 ° C./min and hold for 3 minutes at that temperature. After the melt is completely melted, the temperature is lowered to 50° C. at a rate of 80° C./min, and then the endothermic peak is measured at a rate of temperature increase of 20° C./min.

Specifically, the temperature of the solid phase polymerization treatment may be, for example, 180 to 380°C, preferably 200 to 350°C, more preferably 250 to 350°C.

The heating time for the solid phase polymerization treatment is not particularly limited, and may be, for example, 1 hour or longer, preferably 5 hours or longer, and more preferably 8 hours or longer. Although the upper limit of the heating time is not particularly limited, it may be 100 hours or less, more preferably 50 hours or less.

In the present invention, it is important to perform heat treatment in which the liquid crystalline polyester fiber is brought into direct contact with a heating body. This heat treatment by contact heating is preferably carried out after the solid-phase polymerization described above. By performing heat treatment by contact heating, the fluff on the surface of the liquid crystal polyester fiber is pressed by the heating body and thermally fused to the surface of the liquid crystal polyester fiber, so the number of fluff on the surface of the liquid crystal polyester fiber can be reduced. can. Therefore, friction due to rubbing originating from the fluff is reduced, and as a result, abrasion resistance is improved. The heat treatment by contact heating, in which the liquid crystalline polyester fiber whose strength has been increased to 18 cN/dtex or more by solid phase polymerization (first heat treatment) is brought into direct contact with a heating body, is preferably used as the second heat treatment.

The type of the heating element is not particularly limited, and known plate heaters, heating guides, heat rollers and the like can be used. In addition, by using a heat roller and rotating the heat roller at the same speed as the yarn conveying speed, or by conveying the yarn using the rotation of the heat roller as a driving force, dynamic friction between the yarn and the heating body is eliminated. , which is preferable because deterioration of the yarn during heat treatment by contact heating can be avoided. Further, by using a plurality of heating bodies and setting different temperatures for each, contact heating may be performed while changing the heat treatment temperature in multiple steps.

Regarding the temperature of the heat treatment by contact heating (the temperature of the heating body during heat treatment), heating the surface of the liquid crystalline polyester fiber at a temperature moderately lower than the melting point of the liquid crystalline polyester fiber after solid phase polymerization can It is important to reduce the number of fluffs without increasing the fusing at the edge. Regarding the temperature of the heating element, the lower limit must be Mp-50°C or higher, preferably Mp-30, where Mp [°C] is the melting point of the liquid crystal polyester fiber after solid phase polymerization. °C or higher, more preferably Mp-10°C or higher. Moreover, the upper limit must be less than Mp, preferably Mp-5° C. or less.

If the heat treatment is performed at a temperature lower than the above lower limit, heat fusion of the fluff is insufficient, and an effect of improving wear resistance cannot be obtained. In addition, if the heat treatment is performed at a temperature higher than the above upper limit, not only is the fuzz on the surface of the single fiber melted to form a fusion point, but also the fusion between different single fibers is strengthened, resulting in multifilament. The filament becomes rigid, and the unfavorable effect of degrading quality such as process passability also appears. In the present invention, since the heat treatment temperature is lower than Mp, the number of fluffs on the single fiber surface can be reduced without increasing the fusion between the single fibers.

When the liquid crystalline polyester fiber is a monofilament, the product is composed of only a single single fiber, so the degree of fusion between different single fibers is irrelevant. When the temperature is higher than Mp, the fiber tends to be broken due to melting. Therefore, the preferred temperature of the heater is Mp-50° C. or higher and lower than Mp, which is the same as that of the multifilament.

Further, the time required for the heat treatment by contact heating is not particularly limited from the viewpoint of the present invention, and may be performed so as to obtain the liquid crystalline polyester fiber with the required physical properties. However, if the heat treatment time (contact time with the heating body) is too long, the yarn quality such as strength and wear resistance will decrease due to bending fatigue under heating, so it is preferable to set it to 10 seconds or less. 5 seconds or less is more preferable.

The liquid crystalline polyester fiber of the present invention has a smooth fiber surface shape and is characterized by improved wear resistance and improved processability. It is preferable to use As the finishing oil, a finishing oil commonly used for polyester fibers can be preferably applied.

The single fiber fineness of the liquid crystalline polyester fiber obtained by the present invention is preferably 0.5 dtex or more and 50 dtex or less. Since neither the solid phase polymerization nor the heat treatment by contact heating in the present invention greatly changes the fineness, the preferred ranges of the single fiber fineness before solid phase polymerization and the single fiber fineness before contact heating are the same as those described above. It is the same.

If the single fiber fineness is less than the above lower limit, the mechanical strength of the single fiber is low, so fluff and single fiber breakage often occur. Further, if the single fiber fineness exceeds the above upper limit, the heat is difficult to conduct to the inside of the single fiber, and solid phase polymerization may take a long time or the strength may be low. The lower limit of the single fiber fineness is more preferably 1 dtex or more, more preferably 1.5 dtex or more. The upper limit of the single fiber fineness is more preferably 15 dtex or less, and even more preferably 10 dtex or less.

Further, the total fineness of the multifilament of the liquid crystalline polyester fiber obtained by the present invention is preferably 10 dtex or more and 50000 dtex or less. Since neither the solid phase polymerization nor the heat treatment by contact heating in the present invention greatly changes the fineness, the preferred range of the total fineness before solid phase polymerization and before contact heating is the same as above. Moreover, the preferable range of the total fineness of the liquid crystal polyester monofilament is structurally consistent with the preferable range of the single fiber fineness.

If the total fineness is less than the above lower limit, yarn breakage trouble may easily occur during heat treatment by contact heating, which will be described later. If the total fineness exceeds the above upper limit, it is difficult for heat to be conducted to the fibers in the inner layer of the multifilament, resulting in longer solid phase polymerization, lower strength, and greater variation in the quality of the obtained fibers. sometimes. The lower limit of the total fineness is more preferably 15 dtex or more, more preferably 25 dtex or more. The upper limit of the total fineness is more preferably 30000 dtex or less, and even more preferably 10000 dtex or less.

The liquid crystalline polyester fibers obtained by the present invention may be aligned and used as a tow. The tow thickness is preferably 0.1 mm or more and 10 mm or less. The lower limit of the tow thickness is more preferably 0.2 mm or more, and even more preferably 0.3 mm or more. The upper limit of the tow thickness is more preferably 5 mm or less, and even more preferably 3 mm or less. Since neither the solid phase polymerization nor the heat treatment by contact heating in the present invention greatly changes the fineness, the preferable ranges of the thickness of the tow before solid phase polymerization and before contact heating are the same as above.

The liquid crystalline polyester fiber obtained by the present invention preferably has high strength. "High strength" in the present invention means that the tensile strength is 18 cN/dtex or more. The tensile strength is more preferably 20 cN/dtex or more, still more preferably 23 cN/dtex or more. Although the upper limit of the tensile strength is not particularly limited, it is about 30 cN/dtex as a value that can be achieved by the present invention. In addition, the tensile strength is calculated by the measuring method described in Examples described later.

The fusion bonding strength of the liquid crystalline polyester multifilament fiber obtained by the present invention is preferably A to C in the grade (four-grade evaluation from A to D) defined by the measurement method described in the examples described later. . If the fusion bond is stronger than the above range, the obtained fiber becomes hard and difficult to bend, so that buckling defects are likely to occur, and workability in higher processing steps may deteriorate. The fusion grade range is more preferably AB.

The heat treatment by contact heating in the present invention is characterized in that the wear resistance can be improved without impairing the high strength of the liquid crystal polyester fiber, so the strength retention rate before and after the heat treatment by contact heating is preferably 80% or more, and more. It is preferably 85% or more, more preferably 90% or more.

The strength retention rate before and after heat treatment by contact heating as used herein refers to the value obtained by dividing the tensile strength of the liquid crystalline polyester fiber after heat treatment by contact heating by the tensile strength of the liquid crystalline polyester fiber before heat treatment by contact heating. .

The fiber of the present invention has a smooth fiber surface and is excellent in abrasion resistance and strength, so that it is excellent in post-processability and physical properties after processing. Therefore, for example, tension members (electrical wires, optical fibers, heater wire core threads, cords for various electrical products such as earphone cords, etc.), sail cloths, ropes, ropes, land nets, lifelines, fishing lines, fishing nets, longlines, etc. It can be suitably used as a fiber used in products and the like.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. Various characteristics of the present invention were evaluated by the following methods.

<Total fineness>
In accordance with JIS L 1013: 2010 8.3.1 A method, a 100 m skein of liquid crystal polyester fiber is taken using a measuring instrument manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd., and the weight (g) is multiplied by 100 to 1 level. Measurement was performed twice per measurement, and the average value was taken as the total fineness (dtex) of the obtained liquid crystal polyester fiber.

<Single fiber fineness>
A single fiber fineness (dtex) was obtained by dividing the total fineness by the number of filaments.

<Tensile strength>
In accordance with JIS L 1013: 2010 8.5.1, using Shimadzu Corporation's Autograph "AGS-100B", yarn length 10 cm, tension speed 10 cm / min. Measurement was performed 6 times, and the average value was defined as strength (cN/dtex).

<Strength retention rate>
The strength of the sample before heat treatment by contact heating was α (cN/dtex), and the strength of the sample after heat treatment by contact heating was β (cN/dtex), which were measured under the same measurement conditions and calculation method as the tensile strength described above. In this case, the quotient obtained by dividing the strength β of the sample after heat treatment by the strength α of the sample before heat treatment and multiplying the result by 100 was taken as the strength retention rate (%).

[Number 1]
Strength retention rate (%) = 100 x (β/α) (1)

<Melting point>
It was measured with a differential scanning calorimeter (DSC; "DSC-60A" manufactured by Shimadzu Corporation) in accordance with JIS K7121 test method, and the observed main absorption peak temperature was taken as the melting point. Specifically, 1 to 10 mg of a sample was taken in the DSC device and sealed in an aluminum pan, then nitrogen was flowed as a carrier gas at 100 cc/min, and the endothermic peak was measured when the temperature was raised at 20 ° C./min. .

<Method for measuring fluff count>
A fiber sample was placed on a scanning electron microscope (SEM) observation stage, two ends of the sample outside the observation area were fixed with cellophane tape so that the sample would not slack, and gold deposition was performed. The sample was oriented horizontally with respect to the observation direction so that the side surface of the fiber could be observed. For each sample, SEM observation was performed at multiple points at random, and the number of fluffs of the two samples before and after heat treatment by contact heating was counted.

Here, "fluff" refers to a structure present on the side surface of a single fiber, in which the resin is partially split in the fiber axis direction, and one end is peeled off and protruded.

In addition, from the viewpoint of balancing accuracy and observation time, a range in which 10 to 100 fluff counts can be confirmed in the sample before heat treatment by contact heating was confirmed in advance, and this range was observed. In addition, before and after the heat treatment by contact heating, the magnification and the range of the field of view during observation were the same. For example, 25 observation fields for each multifilament and 50 observation fields for each monofilament in Reference Examples, Examples, and Comparative Examples of the present invention were photographed, and the number of fluffs was counted.

<Abrasion resistance>
Abrasion resistance was evaluated using the following two methods depending on the total fineness of the liquid crystal polyester fiber.

<Abrasion resistance evaluation method for fibers having a total fineness of 100 dtex or more>
The liquid crystal polyester fiber is Z-twisted at 80 T/m, and Z-twisted 3 times with a cord durability tester (manufactured by Yasuda Kiko Co., Ltd.), and a test weight is applied with a constant load. The fiber was suspended at a temperature of 20 times/min, and the twisted portion was abraded, and the number of times until the fiber was cut was measured. Then, each sample was measured eight times, and the average value was evaluated as wear resistance. The weight of the load was appropriately determined so that the number of times until cutting fell within the range of 1,000 to 100,000 from the viewpoint of achieving a balance between accuracy and observation time. For example, the multifilaments in Reference Example 1, Examples 1 to 7, and Comparative Examples 1 to 4 of the present invention were all evaluated under a load of 5 kg.

<Abrasion resistance evaluation method for fibers having a total fineness of less than 100 dtex>
A fiber with a load of 0.98 cN / dtex is hung vertically, and a ceramic rod guide (manufactured by Yuasa Itodo Kogyo Co., Ltd., material YM-99C) with a diameter of 4 mm is perpendicular to the fiber. Press at 3°, rub the guide in the fiber axis direction with a stroke length of 20 mm and a stroke speed of 600 times/min. The time until the wear resistance was reached was measured, and the average value of 10 measurements was taken as the wear resistance. If no white powder or fibrils were observed even after 500 seconds of rubbing, the time was set to 500 seconds. At this time, wear resistance was rated A when 300 seconds or more, B when 200 seconds or more and less than 300 seconds, C when 50 seconds or more and less than 200 seconds, and D when less than 50 seconds.

<Strength of fusion>
First, a sample cut to a length of 20 mm was dispersed by applying ultrasonic waves in water for 20 minutes using "Brensonic 220" manufactured by Yamato Scientific Co., Ltd., and the total number (n) of single yarns dispersed in water was calculated. The fusion degree (f) was calculated from the number of single yarns (N) before the solid phase polymerization treatment and the following formula (2). This value is the average value of 10 measurements of randomly collected samples.

[Number 2]
f=N/n (2)

Next, according to the numerical value of f, the welding strength was classified into the following four classes. As is clear from the formula (2), A has the least fusion and D has the most fusion.
A: f<5
B: 5≤f<10
C: 10≤f<50
D: 50≦f

[Reference example 1]
A liquid crystalline polyester (resin melting point: 281° C.) in which the structural units (A) and (B) are (A)/(B)=73/27 (molar ratio) was used. This was melt-extruded by an extruder, and the polymer was supplied to the spinning head while being weighed by a gear pump. The spinning head was equipped with a spinneret having 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 168 g/min and wound on a bobbin at a winding speed of 1000 m/min. The fiber obtained here is wound around an aluminum bobbin so as to have a winding density of 0.6 g/cm ³ , and heat-treated (solid phase polymerization) in a closed oven at 250 to 280° C. for 16 hours in a nitrogen atmosphere. Thus, a liquid crystal polyester multifilament with a total fineness of 1670 dtex and 300 filaments was obtained. In order to confirm that no oil agent adhered to this sample, the washing weight loss of this sample was calculated according to the method described in JIS L 1013:2010 8.28. A sufficiently small value was obtained compared to the fiber. This sample was used in Examples 1 to 7 and Comparative Examples 1 to 4 as a sample to be subjected to heat treatment by contact heating. Table 5 shows the analysis results of this sample. The wear resistance was measured after applying the same finishing oil as used in Examples and Comparative Examples described later in the same manner.

[Example 1]
While the sample of Reference Example 1 is unwound from the bobbin, it is passed through a roller equipped with a heating device (hereinafter referred to as "heat treatment heat roller"), and heat treatment is performed by contact heating in which the sample is brought into direct contact with the heat treatment heat roller. After that, the sample after the heat treatment was wound on another bobbin with a winder. Next, while unwinding this sample from the bobbin, an aqueous dispersion of finishing oil was applied using an oiling guide so that 1% by weight of finishing oil adhered to the liquid crystal polyester multifilament, and the temperature was set to 80°C. The film was passed through a heated roller for drying to remove moisture, and wound on another bobbin with a winder. The temperature of the heat roller for heat treatment was 290° C., and the contact time was 4.8 seconds. Also, the aqueous dispersion of the finishing oil used was a water emulsion of 5% by weight of lauric acid and 5% by weight of polyoxyethylene lauryl ether. Table 5 shows the analysis results of this sample.

In addition, the state of fluff in the sample before and after the heat treatment was observed with a scanning electron microscope (SEM). A scanning electron microscope (SEM) photograph of the sample before heat treatment is shown in FIG. 1, and a scanning electron microscope (SEM) photograph of the sample after heat treatment is shown in FIG.

As shown in FIGS. 1 and 2, by performing heat treatment by contact heating, the fluff on the surface of the sample (the portion protruding outward from the surface of the sample) is pressed by the heating body, and the entire fluff is removed. It can be seen that the protruding portion has disappeared as a result of thermal fusion bonding to the sample surface.

[Example 2]
The procedure was the same as in Example 1, except that the contact time of the heat roller for heat treatment was set to 1.7 seconds. Table 5 shows the analysis results of this sample.

[Example 3]
The procedure was the same as in Example 1 except that the temperature of the heat roller for heat treatment was set at 310°C. Table 5 shows the analysis results of this sample.

[Example 4]
The same procedure as in Example 1 was carried out except that the temperature of the heat roller for heat treatment was changed to 310° C. and the contact time was changed to 1.7 seconds. Table 5 shows the analysis results of this sample.

[Example 5]
Example 1 was repeated except that the temperature of the heat roller for heat treatment was changed to 310° C. and the contact time was changed to 1.1 seconds. Table 5 shows the analysis results of this sample.

[Example 6]
The same procedure as in Example 1 was carried out except that the temperature of the heat roller for heat treatment was changed to 310° C. and the contact time was changed to 0.6 seconds. Table 5 shows the analysis results of this sample.

[Example 7]
As in Example 1, the temperature of the heat roller for heat treatment was changed to 310° C. and the contact time was set to 7.2 seconds. Table 5 shows the analysis results of this sample.

[Comparative Example 1]
The procedure was the same as in Example 1 except that the temperature of the heat roller for heat treatment was changed to 260°C. Table 5 shows the analysis results of this sample.

[Comparative Example 2]
The procedure was the same as in Example 1 except that the temperature of the heat roller for heat treatment was changed to 80°C. Table 5 shows the analysis results of this sample.

[Comparative Example 3]
The procedure was the same as in Example 1 except that the temperature of the heat roller for heat treatment was changed to 350°C. Table 5 shows the analysis results of this sample.

[Comparative Example 4]
The same procedure as in Example 1 was carried out, except that the temperature of the heat roller for heat treatment was changed to 350° C. and the contact time was changed to 1.7 seconds. Table 5 shows the analysis results of this sample.

[Reference example 2]
A liquid crystalline polyester (resin melting point: 281° C.) in which the structural units (A) and (B) are (A)/(B)=73/27 (molar ratio) was used. This was melt-extruded by an extruder, and the polymer was supplied to the spinning head while being weighed by a gear pump. The spinning head was equipped with a spinneret having a hole diameter of 0.125 mmφ, a land length of 0.175 mm and 20 holes, and the polymer was discharged at a discharge rate of 11.2 g/min. Nineteen of the discharged polymers were removed by suction with an air mover, and the remaining one was wound on a bobbin at a winding speed of 1000 m/min. One fiber obtained here is wound around an aluminum bobbin so as to have a winding density of 0.6 g/cm ³ , and heat-treated at 250 to 280° C. for 16 hours in a nitrogen atmosphere using a closed oven (solid phase polymerization) to obtain a liquid crystal polyester monofilament with a total fineness of 10 dtex and a single filament. When the washing weight loss of this sample was calculated in the same manner as in Reference Example 1, it was less than 0.01%, which is sufficiently small compared to known fibers. This sample was used in Examples 8-14 and Comparative Examples 5-7 as a sample subjected to heat treatment by contact heating. Table 6 shows the analysis results of this sample. The wear resistance was measured after applying the same finishing oil as used in Examples and Comparative Examples described later in the same manner.

[Example 8]
While the sample of Reference Example 2 is unwound from the bobbin, it is passed through the heat roller for heat treatment described above, heat treatment is performed by contact heating in which the sample is brought into direct contact with the heat roller for heat treatment, and then the sample after heat treatment is wound by a winder. was wound on another bobbin. Next, while unwinding this sample from the bobbin, an aqueous dispersion of finishing oil was applied using an oiling guide so that 1% by weight of finishing oil adhered to the liquid crystal polyester multifilament, and the temperature was set to 80°C. The film was passed through a heated roller for drying to remove moisture, and wound on another bobbin with a winder. The temperature of the heat roller for heat treatment was 280° C., and the contact time was 4.8 seconds. Also, the aqueous dispersion of the finishing oil used was a water emulsion of 5% by weight of lauric acid and 5% by weight of polyoxyethylene lauryl ether. Table 6 shows the analysis results of this sample.

[Example 9]
The procedure of Example 8 was repeated except that the contact time of the heat roller for heat treatment was set to 1.7 seconds. Table 6 shows the analysis results of this sample.

[Example 10]
The procedure was the same as in Example 8 except that the temperature of the heat roller for heat treatment was set to 300°C. Table 6 shows the analysis results of this sample.

[Example 11]
Example 8 was repeated except that the temperature of the heat roller for heat treatment was changed to 300° C. and the contact time was changed to 1.7 seconds. Table 6 shows the analysis results of this sample.

[Example 12]
The same procedure as in Example 8 was carried out except that the temperature of the heat roller for heat treatment was changed to 300° C. and the contact time was changed to 1.1 seconds. Table 6 shows the analysis results of this sample.

[Example 13]
Example 8 was repeated except that the temperature of the heat roller for heat treatment was changed to 300° C. and the contact time was changed to 0.6 seconds. Table 6 shows the analysis results of this sample.

[Example 14]
As in Example 8, the temperature of the heat roller for heat treatment was changed to 300° C. and the contact time was set to 7.2 seconds. Table 6 shows the analysis results of this sample.

[Comparative Example 5]
The procedure of Example 8 was repeated except that the temperature of the heat roller for heat treatment was changed to 250°C. Table 6 shows the analysis results of this sample.

[Comparative Example 6]
The procedure of Example 8 was repeated except that the temperature of the heat roller for heat treatment was changed to 80°C. Table 6 shows the analysis results of this sample.

[Comparative Example 7]
Example 8 was repeated except that the temperature of the heat treatment heat roller was changed to 320°C and the contact time was set to 1.7 seconds. quickly melted and broke, and no liquid crystalline polyester fiber was obtained.

As shown in Table 5, the liquid crystal polyester multifilament was directly contacted with a heat roller for heat treatment heated to a temperature of Mp-50 ° C. or more and less than Mp (that is, 266 ° C. or more and less than 316 ° C.). In Examples 1 to 7, compared to Reference Example 1 in which contact heating was not performed, the number of fluffs on the surface of the sample was significantly reduced, excellent abrasion resistance, excellent strength, and further It can be seen that fusion is suppressed to a certain level or less.

In addition, in Comparative Examples 1 and 2, heat treatment was performed at a temperature lower than Mp -50 ° C., so compared to Reference Example 1 in which contact heating was not performed, the number of fluffs was the same, and the wear resistance was also improved. I know not.

In addition, in Comparative Example 3, since the heat treatment was performed at a temperature higher than Mp, not only the fluff was reduced, but also the fusion between different single fibers occurred and the fibers became rigid, which compared with Reference Example 1. It can be seen that the wear resistance is rather lowered in comparison. Similarly, in Comparative Example 4, since the heat treatment was performed at a temperature higher than Mp, it can be seen that the wear resistance was not improved.

Further, as shown in Table 6, the liquid crystal polyester monofilament was directly contacted with a heat roller for heat treatment heated to a temperature of Mp -50 ° C. or more and less than Mp (that is, 258 ° C. or more and less than 308 ° C.). Contact heating was performed. In Examples 8 to 14, the number of fluffs on the surface of the sample is significantly reduced compared to Reference Example 2 in which contact heating was not performed, and it can be seen that the abrasion resistance is excellent and the strength is excellent. .

In addition, in Comparative Examples 5 and 6, heat treatment was performed at a temperature lower than Mp -50 ° C., so compared to Reference Example 2 in which contact heating was not performed, the number of fluffs was the same, and the wear resistance was also improved. I know not.

The liquid crystalline polyester fiber of the present invention does not use materials such as inorganic particles that may peel off and fall, and has a smooth fiber surface and excellent abrasion resistance and strength. It can be suitably used as a fiber for high-order processed products such as thread, cords for various electrical products such as earphone cords, etc.), sailcloth, rope, rope, land net, lifeline, fishing line, fishing net, longline.

Claims (4)

Including a heat treatment step by contact heating in which the liquid crystal polyester fiber is brought into direct contact with the heating body,
A method for producing a liquid crystal polyester fiber, wherein the temperature of the heater is Mp-50° C. or more and less than Mp, where Mp [° C.] is the melting point of the liquid crystal polyester fiber. 2. The method for producing a liquid crystalline polyester fiber according to claim 1, wherein the heat treatment step is performed on a liquid crystalline polyester fiber having a tensile strength of 18 cN/dtex or more. 3. The method for producing a liquid crystalline polyester fiber according to claim 1, wherein the heat treatment time of said heat treatment step is 10 seconds or less. The method for producing a liquid crystalline polyester fiber according to any one of claims 1 to 3, wherein the heating body is a heat roller.

Images