Polytetrafluoroethylene fiber and manufacturing method thereof

Abstract

To provide a polytetrafluoroethylene fiber that generates little fallen debris caused by abrasion with a guide in woven knitted fabric processing, and can be processed into a high quality woven knitted fabric, and a manufacturing method thereof.SOLUTION: The polytetrafluoroethylene fiber has yarn surface fine fluff of 3 pieces / 10 mm2 or less. A viscose with a viscosity / cellulose concentration ratio of 0.5 to 7.0 Pa s / % or higher is used as a matrix. In the manufacturing method of the polytetrafluoroethylene fiber, a mixture of the viscose and an aqueous dispersion of polytetrafluoroethylene is discharged into a coagulation bath controlled to have a sulfuric acid concentration of 7 to 13% and a sodium sulfate concentration of 7 to 15%, and subjected to spinning and refining. Then, a semi-baking process at 250 to 320°C is carried out using a baking roller while relaxing at 1 to 5%, after which baking is carried out at 320 to 380°C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to polytetrafluoroethylene fibers that are excellent in weaving and knitting processing, and to a method for producing the same. [Background technology]

[0002] Fluororesin fibers, such as polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), are widely used in industrial materials due to their excellent heat resistance, chemical resistance, and low coefficient of friction, making them excellent for sliding. Taking advantage of their low coefficient of friction in particular, they are widely used as sliding components in the form of woven or nonwoven fabrics in automobile components, office equipment components such as copy machines, and seismic isolation components for buildings. Among fluororesin fibers, PTFE fiber is known to have the best heat resistance, chemical resistance, and sliding properties. However, due to these characteristics, it is difficult to produce fibers using conventional melt spinning or wet spinning. Known manufacturing methods include matrix spinning, which uses a matrix substance and then undergoes a baking process, split peeling, and paste extrusion. Among these, PTFE fiber obtained by matrix spinning is characterized by a uniform fiber cross section and small variation in fineness, making it an excellent PTFE fiber for woven and knitted fabric processing.

[0003] However, in the PTFE fiber produced by this manufacturing method, depending on the remaining state of the baked carbide, which is a matrix component, the PTFE debris containing the baked carbide accumulates on the process guide during the weaving and knitting process, adheres to the yarn, and is carried over to the subsequent process, causing deterioration in operability and deterioration in the quality of the woven and knitted fabrics. Patent Document 1 proposes a fluororesin fiber that is less likely to tangle during weaving and knitting and has less thread shedding by controlling the dynamic friction coefficient within a certain range through the application of an oil agent containing a polyoxyethylene compound, but does not disclose how to control fallen debris. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-189993 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a PTFE fiber which is less likely to produce sludge when rubbed against a process guide and is excellent for processing into woven or knitted fabrics, and a method for producing the same. [Means for solving the problem]

[0006] As a result of extensive research, the inventors have discovered that the remaining state of the baked carbonized matrix component causes fine fuzz to form on the fiber surface, and that if a large number of these fine fuzzes are present, they will fall off due to friction with the process guide during the weaving and knitting process, accumulate on the process guide as fallen debris, and adhere to the yarn, which will be carried over to subsequent processes, causing deterioration in operability and deterioration in the quality of the woven and knitted products, and have arrived at this invention.

[0007] In order to solve the above problems, the present invention is configured as follows. [1] The fine fluff on the surface of the yarn is 3 pieces / 10 mm. 2 Polytetrafluoroethylene fiber, which is: [2] Polytetrafluoroethylene fiber having a total fineness of 40 to 1,000 dtex, a single fiber fineness of 1 to 20 dtex, a strength of 0.8 to 3.0 cN / dtex, and an elongation of 10 to 50%. [3] A method for producing the polytetrafluoroethylene fiber, characterized in that a mixture of viscose as a matrix having a viscosity / cellulose concentration ratio of 0.5 to 7.0 Pa s / % and an aqueous dispersion of polytetrafluoroethylene is extruded into a coagulation bath controlled at a sulfuric acid concentration of 7 to 13% and a sodium sulfate concentration of 7 to 15%, and the mixture is spun and refined, followed by a semi-baking step at 250 to 320°C using a baking roller while providing 1 to 5% relaxation, followed by baking at a temperature of 320 to 380°C. [Effects of the Invention]

[0008] According to the present invention, polytetrafluoroethylene fibers can be obtained which are less likely to produce sludge when rubbed against a process guide and which are excellent in woven and knitted fabric processing. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an example of a surface photograph (500x) of the polytetrafluoroethylene fiber of the present invention taken by a scanning electron microscope. DETAILED DESCRIPTION OF THE INVENTION

[0010] The polytetrafluoroethylene fiber of the present invention and its production method will be described in detail below.

[0011] <Polytetrafluoroethylene fiber> In addition to PTFE, fluororesins generally include copolymers of TFE and HFP, such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene olefin copolymer (ETFE), which are produced by melt spinning. However, in the present invention, PTFE resin, which has the best heat resistance and chemical resistance, is used. The PTFE of the present invention may be polytetrafluoroethylene, but is not particularly limited. Preferably, the number-average molecular weight of PTFE is 1,000,000 or more, and more preferably 2,000,000 or more but less than 12,000,000. A number-average molecular weight of PTFE of 2,000,000 or more provides good tensile strength and good processability in weaving and carding processes, resulting in high-quality woven fabrics, knitted fabrics, and webs. If the number-average molecular weight of PTFE is 12,000,000 or more, spinnability is significantly impaired, making industrial production difficult.

[0012] The polytetrafluoroethylene fiber of the present invention has a fine fluff density of 3 fluffs per 10 mm on the surface of the yarn. 2The following polytetrafluoroethylene fibers are used. The fine fluff on the yarn surface refers to the fine fluff (mainly on the order of microns) present on the surface of a single fiber (the fine fluff can be seen near the center of Figure 1), and in the present invention, the value is measured by the method described below. The fine fluff on the yarn surface is 3 fluffs / 10 mm. 2 If the value exceeds this, the amount of fluff that falls off due to friction with the process guide during woven / knitted fabric processing will increase, and the accumulated fluff residue will be carried over to subsequent processes, which will lead to an increase in the frequency of weaving / knitting machine stoppages and an increase in defects in the woven / knitted fabric, which is undesirable.

[0013] The polytetrafluoroethylene fiber of the present invention preferably has a total fineness of 40 to 1,000 dtex, more preferably 400 to 900 dtex. If the total fineness is 40 to 1,000 dtex, it can be processed into woven or knitted fabrics that are excellent in flexibility and mechanical strength.

[0014] The single fiber fineness of the fibers constituting the polytetrafluoroethylene fiber of the present invention is preferably 1 to 20 dtex, more preferably 3 to 15 dtex. If the single fiber fineness is 1 to 20 dtex, the fiber can be produced without problems by the matrix spinning method and has strength suitable for processing into woven or knitted fabrics.

[0015] The polytetrafluoroethylene fiber of the present invention preferably has a strength of 0.8 to 3 cN / dtex, more preferably 1 to 2 cN / dtex, and preferably has an elongation of 10 to 50%, more preferably 15 to 40%.

[0016] If the strength is 0.8 to 3 cN / dtex, there will be no problems with thread breakage or handling when processing the woven or knitted fabric, the woven or knitted fabric will not tear when used as a sliding material, and the fabric can be produced by a normal matrix spinning method.

[0017] If the elongation is 10 to 50%, there will be no problems with thread breakage or handling when processing the woven or knitted fabric, the woven or knitted fabric will not break when used as a sliding material, and it can be produced by a normal matrix spinning method. <Method of manufacturing polytetrafluoroethylene fiber> The polytetrafluoroethylene fiber of the present invention is made of PTFE resin, which is a type of fluororesin, and is preferably produced by a matrix spinning method in which a matrix substance is used for spinning, followed by a baking step.

[0018] The matrix material used in the present invention is preferably viscose with a viscosity / cellulose concentration ratio of 0.5 to 7.0 Pa·s / %. If the viscosity / cellulose concentration ratio is less than 0.5 Pa·s / %, cellulose carbonization tends to occur unevenly near the yarn surface, resulting in increased fine fuzz on the yarn surface due to carbonization during drawing, leading to poor operability and poor quality of textiles and knitted fabrics. On the other hand, if the viscosity / cellulose concentration ratio exceeds 7.0 Pa·s / %, continuous productivity is reduced due to poor degassing of the spinning dope and increased spinneret back pressure. It is preferable to use viscose with a viscosity of 4.5 to 45 Pa·s, a cellulose concentration of 5.0 to 11.0 wt%, an alkali concentration of 4.0 to 10.0 wt%, and carbon disulfide of 27.0 to 32.0 wt% (relative to cellulose).

[0019] Next, these spinning dope solutions are discharged from a spinneret immersed in a coagulation bath and coagulated in the coagulation bath.

[0020] As the coagulation bath, an aqueous solution of an inorganic mineral acid or an inorganic salt is used, but in the present invention, it is preferable to use a mixed aqueous solution containing sulfuric acid and sodium sulfate. In this case, the sulfuric acid concentration is preferably 7 to 13 wt%. If the sulfuric acid concentration is less than 7 wt%, the rate at which the yarn coagulates in the coagulation bath becomes very slow, which is undesirable as it reduces production capacity or requires a longer immersion line. On the other hand, if the sulfuric acid concentration exceeds 13 wt%, it becomes difficult to deoxidize the sulfuric acid attached to the fiber surface.

[0021] Furthermore, it is preferable to adjust the sodium sulfate concentration to 7 to 15 wt%. Sodium sulfate suppresses rapid coagulation of cellulose. If the sodium sulfate concentration is less than 7 wt%, the rate at which the yarn coagulates in the coagulation bath becomes very fast, making it difficult to control the fiber cross-section, which is undesirable. On the other hand, if the sodium sulfate concentration exceeds 15 wt%, the rate at which the yarn coagulates in the coagulation bath becomes very slow, making it difficult to control the fiber cross-section, which is undesirable. Using a mixed aqueous solution containing both sulfuric acid and sodium sulfate concentrations within the above-mentioned specific ranges as the coagulation bath is effective for producing uniform polytetrafluoroethylene fibers.

[0022] The coagulated fibers are then degummed, that is, deoxidized in hot water, washed in an alkaline washing step, and then semi-burned and burned.

[0023] For deoxidation treatment with hot water, washing with hot water in a tray-type bath is preferred. The temperature of the hot water is preferably 60°C or higher and 90°C or lower. If the temperature is lower than 60°C, the washing efficiency decreases. On the other hand, if the temperature is higher than 90°C, the bath liquid becomes more turbulent, which can cause interference with adjacent yarns or yarn breakage due to increased resistance to the counterflow.

[0024] The alkaline washing step preferably involves washing with an alkaline aqueous solution containing an alkali salt. Such an alkaline washing bath uses an aqueous solution of a compound selected from hydroxides, carbonates, and bicarbonates of alkali metals or alkaline earth metals. Generally, an aqueous solution of an alkali metal salt, particularly an aqueous solution of caustic soda, is used. The concentration of these alkali salts is preferably 0.08 wt% or more and 0.18 wt% or less. More preferably, it is 0.10 wt% or more and 0.16 wt% or less. A concentration of less than 0.08 wt% results in insufficient deoxidation, leading to poor sintering. On the other hand, a concentration of more than 0.18 wt% dissolves cellulose during alkaline washing, causing residue to easily accumulate in the alkaline bath and on the guides. Furthermore, this is undesirable because it reduces the strength of the undrawn yarn and increases the likelihood of process problems, such as winding during the process.

[0025] Furthermore, the temperature of the alkaline bath is preferably 20° C. or lower, and more preferably 15° C. or lower. An alkaline bath temperature above 20° C. is also undesirable because, similar to a case where the alkaline concentration is too high, cellulose dissolves during alkaline washing, causing residue to easily accumulate in the alkaline bath and on the guides, and also making process passing problems such as winding more likely to occur.

[0026] After scouring, semi-calcination is carried out. For semi-calcination, a contact type calcination roller or a non-contact type calcination heater can be used, but a contact type calcination roller is preferably used.

[0027] Undrawn yarns extracted from a scouring bath or alkaline bath can be passed through a contact-type semi-baking process maintained at a temperature of 250°C to 320°C while being relaxed between baking rollers by 1% to 5% or less, either directly or after being squeezed using nip rollers. The semi-baking process can be performed by passing the undrawn yarn through a contact-type semi-baking process maintained at a temperature of 250°C to 320°C. In a contact-type semi-baking process maintained at a temperature of 250°C to 320°C, the undrawn yarns introduced to the rollers rapidly shrink on the rollers, increasing their tension. If the relaxation rate is less than 1%, the tension becomes too high, making it difficult to maintain a uniform fiber cross-section, and yarn breakage due to shrinkage is likely to occur frequently. If the relaxation rate exceeds 5%, the yarn becomes loose, which can cause problems with process passability. However, the relaxation can be applied only once between the rollers immediately after entering the semi-baking process, or it can be applied between the rollers in the semi-baking process and between the rollers in the baking process. The semi-baking process is performed before entering the subsequent baking process. If the roller temperature in the semi-baking step is lower than 200°C, heat is applied to the fibers all at once in the subsequent baking step, causing deformation of the fiber cross section or fusion between the single yarns. On the other hand, if the temperature is higher than 320°C, heat is applied to the fibers all at once in the semi-baking step, causing deformation of the fiber cross section or fusion between the single yarns. Therefore, the roller temperature in the semi-baking step is preferably 250°C or higher and 320°C or lower. In this case, the temperature of each roller may be changed individually. Furthermore, the temperature of the baking rollers may be individually different within the above range.

[0028] The semi-baked yarn is then baked at a temperature between 320°C and 380°C. At this stage, most of the cellulose is decomposed and vaporized, and the PTFE particles dispersed in the cellulose are thermally fused to form fibers, resulting in unstretched PTFE yarn. Baking temperatures below 320°C are undesirable, as the PTFE particles within the fibers are not sufficiently fused together, resulting in frequent yarn breakage during stretching after baking and reduced fiber strength. On the other hand, baking temperatures above 380°C result in deformation of the fiber cross-sectional shape, a non-uniform cross-sectional shape, and interfiber adhesion, which increases the likelihood of fabric defects during the weaving process and reduces productivity. Furthermore, PTFE decomposes thermally, resulting in frequent yarn breakage during stretching after baking and reduced fiber strength, which is undesirable. The temperature of each roller during baking may be changed independently. Furthermore, it can be set without any particular limitations as long as it is within the above range.

[0029] The PTFE unstretched yarn obtained by baking may be stretched after being wound up once, or may be stretched continuously without being wound up.

[0030] Hot stretching is preferably performed at a temperature of 300°C to 380°C, more preferably 310°C to 370°C. If the temperature is below 300°C, stretching breakage occurs frequently, leading to a decrease in yield due to process troubles. If the temperature exceeds 380°C, PTFE decomposes, leading to a decrease in fiber tensile strength.

[0031] The draw ratio is preferably 5 to 10 times, more preferably 6 to 8 times. The strength and elongation are greatly affected by the draw ratio, and if the draw ratio is less than 5 times, sufficient strength cannot be obtained. On the other hand, if the draw ratio exceeds 10 times, breakage due to drawing and single yarn breakage frequently occurs.

[0032] After drawing, an oil is applied to the fiber and it is wound up on a winder.

[0033] In this way, it is possible to obtain PTFE fibers that are less likely to fall off when rubbed against the process guide and that are excellent for processing into woven or knitted fabrics. [Example]

[0034] Next, the present invention will be specifically described based on examples. However, the present invention is not limited to these examples. Various modifications and alterations are possible within the scope of the present invention. The methods for measuring various properties used in the examples are as follows.

[0035] [Measurement and evaluation method] (1) Total fineness The fineness measurement method B (simple method) of JIS L1013:2010 "Testing methods for chemical fiber filament yarn" was applied.

[0036] (2) Single fiber fineness It was calculated by dividing the total fineness measured in (1) above by the number of filaments.

[0037] (3) Strength and elongation Measurements were made in accordance with the standard test of JIS L1013:2010 "Testing methods for chemical fiber filament yarns."

[0038] (4) Number of fine fluffs on the yarn surface Ten single fibers were randomly taken from the multifilament, and surface photographs (illustrated in Figure 1) were taken at 500x magnification over a fiber length of 10 cm using a scanning electron microscope (Keyence Corporation's "VHX-D500") to measure the number of fine fuzz on the surface of the single fiber, and the average value was calculated. The surface area of ​​the observation point (photographed from above perpendicular to the fiber surface, so half of the fiber surface area at a fiber length of 10 cm) was calculated from the single fiber fineness and specific gravity, and the number of fine fuzz on the yarn surface (number / 10 mm 2 ) was calculated as

[0039] (5) Amount of fallen debris The PTFE fiber with a total fineness of 440 dtex (single fiber fineness 7.4 dtex, number of filaments 60) wound on a bobbin was regulated with a guide and unwound for 10 minutes at a yarn speed of 150 m / min and a tension of 40 g. After that, the fallen debris adhering to the guide was collected and its mass was measured.

[0040] (6) Evaluation method for textile quality Using a rapier loom, a double weave was woven using PTFE fiber with a total fineness of 440 dtex (single fiber fineness 7.4 dtex, filament count 60) and polyphenylene sulfide (PPS) fiber with a total fineness of 220 dtex (single fiber fineness 4.4 dtex, filament count 50) for the warp and weft, with a warp density of 140 threads / 2.54 cm and a weft density of 120 threads / 2.54 cm, measuring 172 cm wide and 10 m long, and the fabric was inspected to evaluate the number of defects in the PTFE fiber. The criteria for evaluation were as follows: S: Less than 2 defects per 10m of fabric length A: 2 or more but less than 5 defects per 10m of fabric length B: 5 or more defects per 10m of fabric length.

[0041] [Example 1] 46% by mass of viscose (viscosity 45 Pa·s, cellulose concentration 7.0 wt%, alkali concentration 6.0 wt%) and 54% of a 60% aqueous PTFE dispersion were mixed and degassed under a reduced pressure of 10 Torr to obtain a spinning solution. This spinning solution was used to produce yarn by wet spinning in a spinning bath solution containing 9.0% sulfuric acid and 10.0% sodium sulfate at 15°C. After washing with warm water at 70°C, the yarn was introduced into an alkaline bath containing a 0.12% aqueous caustic soda solution for refinement and complete removal of the acid components. The unsintered yarn removed from the alkaline bath was then squeezed with nip rollers, semi-sintered at 250-300°C with 5% relaxation, and then sintered at 350-375°C. After being wound up, the yarn was hot-drawn 7 times at 355°C to obtain PTFE fiber. The obtained PTFE fiber had a single fiber fineness of 7.4 dtex (440 dtex - 60 filaments), a strength of 1.5 cN / dtex, and an elongation of 22%. The fine fluff on the surface of the PTFE fiber was measured, and the number of fluffs was 1 fluff / 10 mm. 2 The amount of sloughing generated from this PTFE fiber was measured and found to be 0.01 g. When the PTFE fiber was used to evaluate the quality of the fabric, the number of defects was 0 and the evaluation of the quality of the fabric was S. The results are shown in Table 1.

[0042] [Example 2] PTFE fibers were obtained in the same manner as in Example 1, except that the viscosity of the viscose was changed to 6 Pa·s, the cellulose concentration to 10.0 wt%, and the alkali concentration to 6.2 wt%. The obtained PTFE fibers had a single fiber fineness of 7.4 dtex (440 dtex - 60 filaments), a strength of 1.4 cN / dtex, and an elongation of 24%. The fine fluff on the yarn surface of this PTFE fiber was measured, and it was found to be 2 fluffs / 10 mm. 2 The amount of sludge generated from this PTFE fiber was measured and found to be 0.02 g. When the PTFE fiber was used to evaluate the quality of the fabric, the number of defects was 1 and the evaluation of the quality of the fabric was S. The results are shown in Table 1.

[0043] [Comparative Example 1] PTFE fibers were obtained in the same manner as in Example 1, except that the viscosity of the viscose was changed to 4 Pa·s, the cellulose concentration to 10.0 wt%, and the alkali concentration to 6.1 wt%. The obtained PTFE fibers had a single fiber fineness of 7.4 dtex (440 dtex - 60 filaments), a strength of 1.3 cN / dtex, and an elongation of 21%. Measurement of the fine fluff on the surface of the yarn showed 20 fluffs / 10 mm. 2 The amount of sloughing generated from this PTFE fiber was measured and found to be 0.8 g. When the PTFE fiber was used to evaluate the quality of the fabric, the number of defects was 9 and the evaluation of the quality of the fabric was B. The results are shown in Table 1.

[0044] Comparative Example 2 The same procedures as in Example 1 were used, except that the viscose viscosity was changed to 50 Pa s, the cellulose concentration was changed to 7.0 wt%, and the alkali concentration was changed to 6.1 wt%. However, spinning was impossible due to frequent winding in the process caused by poor degassing. The results are shown in Table 1.

[0045] [Table 1]

[0046] The polytetrafluoroethylene fiber of the present invention is excellent for use in woven and knitted fabrics, and is therefore expected to be used in sliding components such as automobile components, office automation equipment components, and seismic isolation components for buildings.

Claims

1. 3 fine fluffs per 10mm on the surface of the yarn ２ Polytetrafluoroethylene fiber, which is:

2. 2. The polytetrafluoroethylene fiber according to claim 1, having a total fineness of 40 to 1,000 dtex, a single fiber fineness of 1 to 20 dtex, a strength of 0.8 to 3.0 cN / dtex, and an elongation of 10 to 50%.

3. 3. A method for producing polytetrafluoroethylene fiber according to claim 1 or 2, characterized in that a mixture of viscose as a matrix having a viscosity / cellulose concentration ratio of 0.5 to 7.0 Pa s / % and an aqueous dispersion of polytetrafluoroethylene is extruded into a coagulation bath controlled at a sulfuric acid concentration of 7 to 13% and a sodium sulfate concentration of 7 to 15%, spun and refined, and then subjected to a semi-baking step at 250 to 320°C using a baking roller while providing 1 to 5% relaxation, followed by baking at a temperature of 320 to 380°C.

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