JP6597020B2 - Polypropylene fiber manufacturing method and high-strength polypropylene fiber - Google Patents

Description

  The present invention relates to a method for producing polypropylene fibers used for industrial materials, interiors such as buildings and automobiles, medical / hygiene, and clothing, and high-strength polypropylene fibers.

  Polypropylene fiber has characteristics such as excellent water repellency and non-absorbability, low specific gravity, light weight, and excellent chemical resistance, so it can be used for industrial materials, buildings, automobiles, etc. Widely used for interior, medical / hygiene, clothing, etc. Especially for industrial materials, it is widely used for ropes, curing nets, horizontal nets, etc., taking advantage of lightness and strength.

  It is known that the strength of polypropylene fibers is greatly dependent on the drawing conditions. In particular, when the draw ratio is increased, the strength of the polypropylene fiber is greatly improved. However, when trying to draw at a high magnification at a normal drawing speed, fluff and yarn breakage occur frequently, making it difficult to produce stably. Therefore, attempts have been made to increase the strength by stretching at a high magnification as much as possible by slowing the stretching speed.

  For example, in Japanese Patent No. 5607817 (Patent Document 1), a spinning process in which polypropylene is melt-extruded and rapidly cooled to a temperature not lower than the glass transition temperature of the polypropylene and not higher than the glass transition temperature + 15 ° C., a cold-retaining process in which the temperature is kept at that temperature, and stretching A method for producing a polypropylene fiber including a process has been proposed. In this method, it is described that the strength becomes 1.6 GPa or more, but the stretching is performed at a very low speed with a hand-drawing stretcher, and it is industrially difficult to keep at 0 ° C. for several days. it is conceivable that.

  Further, in Japanese Patent Application Laid-Open No. 2003-293216 (Patent Document 2), a polypropylene fiber for concrete reinforcement having a streaky rough surface structure formed along a curved surface of a fiber surface and having a single fiber strength of 9 cN / dtex is disclosed. Proposed. However, this is also inferior in productivity because the stretching speed is about 50 m / min.

  Further, for example, in Japanese Patent Application Laid-Open No. 2002-180347 (Patent Document 3), a drawing tank in which pressurized saturated water vapor of about 0.3 to 0.5 MPa is filled as a drawing medium in a container sealed at both ends with pressurized water. Describes a method of stretching a crystalline polymer material using a slag. This technique makes it possible to produce high-strength polypropylene fibers of 9.7 cN / dtex or higher. However, this method requires a special and expensive pressurized saturated steam stretching apparatus as compared with normal hot plate stretching, and further, there is a problem that the input amount of fiber is limited in the pressurized saturated steam stretching. Therefore, it is not suitable for mass production.

  Furthermore, in JP 2009-007727 A (Patent Document 4), an undrawn yarn obtained by melt spinning polypropylene having an isotactic pentad ratio of 94% or more is drawn at a temperature of 120 ° C. to 150 ° C. at a draw ratio of 3 After pre-stretching at 10 to 10 times, the fiber strength is 7 cN / h by post-stretching at a temperature of 170 ° C. to 190 ° C. and a deformation rate of 1.5 to 15 times / min and a draw ratio of 1.2 to 3.0 times. A method for producing a polypropylene fiber having a concavo-convex structure with a dtex or more is described. In this technique, since the deformation rate in post-drawing is extremely slow, it is difficult to produce high-strength polypropylene fibers with high production.

Japanese Patent No. 5,607,827 JP 2003-293216 A JP 2002-180347 A JP 2009-007727 A

  An object of the present invention is to provide a high-strength polypropylene fiber and a method for producing the fiber with less fluff and bundle breakage by controlling the yarn in the drawing process to have a uniform structure.

  The method for producing a polypropylene fiber of the present invention is a method for producing a polypropylene fiber including a drawing step in which a polypropylene undrawn yarn is drawn in two or more stages, and the process yarn at the end of the first stage drawing is measured by small angle X scattering measurement. This is a method for producing a polypropylene fiber in which the meridian direction strength ratio to the equator direction strength is in the range of 1.01 to 1.60, and then the second and subsequent steps are stretched.

  In the method for producing a polypropylene fiber of the present invention, the area ratio of the melting peak of 160 ° C. or more and 166 ° C. or less with respect to the melting peak of 168 ° C. or more and 174 ° C. or less of the process yarn at the end of the first stage drawing is measured. A range of 50% or more and 57.5% or less is preferable.

  In the method for producing a polypropylene fiber of the present invention, the draw ratio of the first stage is preferably 5 times or more and 15 times or less.

  In the method for producing a polypropylene fiber of the present invention, it is preferable that the yarn temperature to be drawn in the first stage is drawn at 110 ° C. to 160 ° C.

In the method for producing polypropylene fiber of the present invention, the proportion of the crystal structure of the undrawn yarn is 40% by mass or less, and the birefringence value is 0.1 × 10 ⁻³ or more and 2.5 × 10 ⁻³ or less. Is preferred.

In the method for producing a polypropylene fiber of the present invention, the polypropylene undrawn yarn melts a polypropylene resin having a melt flow rate of 12 g / min to 28 g / min, and the melting point of the polypropylene resin is 80 ° C. to 150 ° C. The undrawn yarn is preferably an undrawn yarn that is discharged from a discharge hole of a spinning nozzle, then cooled and solidified, and taken up at 200 m / min to 500 m / min.

The polypropylene fiber of the present invention has a tensile strength of 6.5 cN / dtex to 10 cN / dtex, a tensile modulus of 85 cN / dtex to 170 cN / dtex , and a single fiber fineness of 3.5 dtex to 20 dtex.

  According to the present invention, a polypropylene fiber having high strength and high elastic modulus as described above with less fluff and bundle breakage is obtained by controlling the yarn in the middle of stretching under a uniform structure under the various conditions described above. be able to.

Hereinafter, the present invention will be described in detail.
● Undrawn yarn structure and drawability In the polypropylene fiber manufacturing process, which includes a drawing process in which drawing is performed in two or more stages after spinning, it is important that the process yarn at the end of the first stage of drawing be close to a homogeneous structure. . In general, in the second and subsequent stages, the stretching process is performed at a higher temperature than in the first stage. The inhomogeneous structure other than the stretched chain formed before the first stage stretching is efficient because the molecular chain rotational movement and the amorphous chain stretching occur in the second and subsequent stages, which are high-temperature stretching. It is difficult to form an extended chain. Further, if the process yarn at the end of the first stage of stretching is inhomogeneous, the tension distribution to the molecular chain becomes non-uniform in the second and subsequent stages of stretching, and thus fluff and thread breakage occur frequently.

  In this invention, it is a manufacturing method of the polypropylene fiber including the extending | stretching process of extending | stretching a polypropylene undrawn thread | yarn in 2 steps | paragraphs, Comprising: The process thread | yarn at the time of completion | finish of the 1st step | stretching is strength of the equator direction by a small angle X scattering measurement It is necessary that the intensity ratio in the meridian direction with respect to is 1.01 to 1.60. In a polypropylene process yarn with a laminated lamella structure, a peak is observed in the meridian direction in small-angle X-ray scattering measurement. That is, the process yarn obtained at the end of the first stage obtained in the present invention has a structure with a small ratio of the lamellar structure. If the strength ratio is 1.60 or less, the ratio of the lamellar structure of the process yarn is small, fluff and yarn breakage can be reduced in the second and subsequent stretches, stable stretching is possible, and stretched chains are formed. It becomes easy to obtain a high-strength polypropylene. In the process yarn at the end of the first stage of stretching, the meridian direction intensity ratio with respect to the equatorial intensity in the small angle X scattering measurement is more preferably 1.02 or more and 1.40 or less, and 1.03 or more and 1 More preferred is .25 or less.

  The process yarn at the end of the first stage of drawing preferably has an area ratio of a melting peak of 160 ° C. or higher and 166 ° C. or lower to a melting peak of 168 ° C. or higher and 174 ° C. or lower in DSC measurement of 57.5% or lower. It is considered that the melting peak at 168 ° C. or more and 174 ° C. or less is caused by melting of the extended chain, and the melting peak at 160 ° C. or more and 166 ° C. or less is caused by melting of the lamellar structure or the structure that could not be transferred to the extended chain. That is, it can be said that the smaller the area ratio of the melting peak at 160 ° C. or higher and 166 ° C. or lower with respect to the melting peak at 168 ° C. or higher and 174 ° C. or lower, the more uniform the structure. In DSC measurement, if the area ratio of the melting peak at 160 ° C. or higher and 166 ° C. or lower with respect to the melting peak at 168 ° C. or higher and 174 ° C. or lower is 57.5% or lower, the ratio of the heterogeneous structure is low. Fluffing and yarn breakage can be reduced during stretching. Since the stretched chain can be easily formed by the second and subsequent stretching, the strength of the final polypropylene fiber is improved. In the DSC measurement, the area ratio of the melting peak of 160 ° C. to 166 ° C. with respect to the melting peak of 168 ° C. to 174 ° C. is more preferably 57% or less, and further preferably 56.5% or less.

  The proportion of the crystal structure of the undrawn yarn at the end of spinning in the present invention is preferably 40% by mass or less. The proportion of the crystal structure of the undrawn yarn can be confirmed using wide-angle X-ray diffraction (Ultrag 18 manufactured by Rigaku Corporation, wavelength λ = 1.54 mm). It is known that the structure of polypropylene includes a mesostructure which is an intermediate structure between crystal and amorphous, in addition to α, β and γ crystals which are crystal structures and an amorphous structure. In the α crystal according to the present invention, four sharp peaks are observed at diffraction angles = 14.1, 16.9, 18.6, and 21.6, and the diffraction angle is broad at 16 degrees in the amorphous structure. In the mesostructure, slightly broad peaks are observed at diffraction angles = 15 degrees and 21 degrees (Non-patent Documents Macromolecules 2005, 38, 8749-8754), and the proportion of each structure is calculated by waveform separation. can do. Specifically, for wide-angle X-ray diffraction patterns of undrawn yarns, diffraction angles = 14.1 degrees, 16.9 degrees, 18.6 degrees, 21.6 degrees (crystalline component), 16 degrees (amorphous component) ), 15 degrees and 21 degrees (mesostructured component), respectively, by separating the waveforms and separating the waveforms, and dividing the sum of the peak integrated intensities of the crystalline components by all the peak integrated intensities, the ratio of the crystalline components Can be calculated.

  The proportion of the crystal structure of the undrawn yarn is preferably 40% by mass or less, and more preferably 20% by mass or less from the viewpoint of drawability. In general, the α crystal, which is a crystal structure, has a folded structure. Although this folded structure is converted into an elongated chain in a later stretching step, it is energetically disadvantageous to convert the folded structure once formed into an elongated chain, compared to a mesostructure or an amorphous structure. is there. As a result, in the case of the α crystal, the stretchability is lowered as compared with the mesostructure and the amorphous structure.

The birefringence value of the undrawn yarn of the present invention is preferably 0.1 × 10 ⁻³ or more and 2.5 × 10 ⁻³ or less. The birefringence value is a quantification of the orientation state of polypropylene molecules, and the smaller the birefringence value, the lower the molecular orientation. If the molecular orientation of the undrawn yarn is small, it can be drawn at a high magnification in a subsequent drawing step, and a high-strength polypropylene fiber can be obtained. If the birefringence value is 2.5 × 10 ⁻³ or less, it can be stretched at a high magnification in the stretching step, and the strength of the resulting polypropylene fiber is likely to be improved. Further, if the birefringence value is 0.1 × 10 ⁻³ or more, it can be obtained industrially. From the above viewpoint, the birefringence value of the undrawn yarn is more preferably 0.3 × 10 ⁻³ or more and 2.2 × 10 ⁻³ or less, and 0.5 × 10 ⁻³ or more and 2.0 × 10 ⁻³ or less. More preferably, it is as follows.

● About raw material The melt flow rate (hereinafter referred to as MFR) of the polypropylene resin which is the raw material of the polypropylene fiber of the present invention (measured in accordance with JIS K 7201 at a temperature of 230 ° C., a load of 2.16 kg, and a time of 10 minutes) is 12 g. It is preferably at least 28 g / min. If the MFR is 12 g / min or more, the melt viscosity does not increase so much and the tension on the spinning line does not increase, and orientation crystallization is suppressed. Therefore, the undrawn yarn obtained does not have a high crystal structure ratio, and the birefringence value can be reduced.

  On the other hand, if the MFR is 28 g / min or less, the melt viscosity does not decrease and the spinning line tension does not decrease. However, since a polypropylene resin having a high MFR generally has a low molecular weight, the crystallization speed of the polypropylene resin is increased, and the resulting undrawn yarn has a higher crystal structure ratio. Therefore, the MFR of the polypropylene resin is preferably 14 g / min or more and 25 g / min or less, and more preferably 16 g / min or more and 22 g / min or less.

  The isotactic pentad ratio of the polypropylene resin used in the present invention is preferably 94% or more and 99% or less. If it is 94% or more, the polypropylene fiber can easily form a uniform crystal structure, while if it is 99% or less, polypropylene can be industrially obtained.

  The molecular weight distribution of the polypropylene resin is preferably 5 or less. If the molecular weight distribution is 5 or less, the polypropylene fiber is likely to have a uniform crystal structure, and the fiber strength is improved. From the above viewpoint, the molecular weight distribution is more preferably 4 or less.

  In the polypropylene resin used in the present invention, an antioxidant, a light stabilizer, an ultraviolet absorber, a neutralizer, a nucleating agent, an epoxy stabilizer, a lubricant, an antibacterial agent, as long as the effects of the present invention are not hindered. Additives such as flame retardants, antistatic agents, pigments, plasticizers and the like may be added as necessary.

Spinning After the above polypropylene raw material is put into an extruder and kneaded and melted, it is quantitatively discharged from the discharge hole of the spinning nozzle by a gear pump. The spinning temperature is preferably 60 ° C. to 150 ° C. higher than the melting point of the polypropylene raw material. If the spinning temperature is 60 ° C. or higher from the melting point of the polypropylene raw material, the melt viscosity on the spinning line is difficult to increase, and orientation crystallization is suppressed. The increase and the increase of the birefringence value can be suppressed. Therefore, stretchability is improved and fiber strength is improved. On the other hand, if the spinning temperature is 150 ° C. or higher than the melting point of the polypropylene raw material, the raw material itself hardly decomposes and the strength is not easily lowered. The spinning temperature is more preferably from 80 ° C. to 120 ° C. higher than the melting point.

  The amount of polymer discharged from the nozzle is preferably 0.3 g / min or more and 3 g / min or less per hole. If the discharge amount is 0.3 g / min or more, the yarn sway does not become noticeable due to the cold air in the quench cylinder, so that fusion between filaments and contact with the guide hardly occur, and an undrawn yarn is stably obtained. be able to. On the other hand, if the discharge amount is 3 g / min or less, it becomes difficult to be affected by the cold air in the quench cylinder, and the resin can be cooled, so that fusion between filaments hardly occurs at the time of take-up. The desired undrawn yarn can be obtained stably. The discharge rate is preferably 0.5 g / min to 2.5 g / min, and more preferably 1.0 g / min to 2.0 g / min.

  The fiber extruded from the nozzle is quenched by applying a cold air of 10 ° C. or more and 40 ° C. or less in a quench cylinder. From the viewpoint that the cooling of the fiber progresses and the fiber does not melt due to the yarn sway, the blowing speed of the cold air into the quench cylinder is preferably in the range of 0.5 m / second to 5 m / second. Thereafter, an oil agent is appropriately applied to the cooled and solidified fiber using an oiling device.

  The spinning draft is preferably 5 to 150 times. Here, the spinning draft is a value obtained by dividing the take-up speed (m / min) by the discharge linear speed (m / min). If the spinning draft is 5 times or more, the tension on the spinning line is applied, so that an undrawn yarn can be stably obtained. On the other hand, if the spinning draft is 150 times or less, the tension on the spinning line will not be too high, orientation crystallization will be suppressed, and the resulting undrawn yarn will have low crystallinity and low orientation, improving drawability. To do.

  The take-up speed is preferably 200 m / min or more and 500 m / min or less. If it is 200 m / min or more, sufficient productivity can be secured. On the other hand, if the winding speed is 500 m / min or less, the tension on the spinning line does not increase, and the desired unstretched structure can be obtained. The take-up speed is more preferably 250 m / min or more and 450 m / min or less.

● Drawing The undrawn yarn may be drawn off-line after the unwinded yarn is wound once, or may be continuously continued without being wound once from the spinning process. The stretching can be performed by a known method such as hot plate stretching, hot roll stretching, hot stove stretching, or the like. From the viewpoint of lowering the deformation rate, it is preferable to stretch with a hot plate or a hot air furnace. Here, the deformation speed can be calculated by dividing the value obtained by subtracting the speed of the supply roll from the speed of the winding roll by the length of the hot plate or the hot stove. Although it is difficult to actually determine the deformation speed when using a hot roll, since the film is stretched at the moment it is separated from the hot roll, the deformation speed is higher than that of hot plate or hot-blast furnace stretching. Stretching can be performed in one stage or divided into two or more stages. From the viewpoint of lowering the deformation rate, it is preferable to divide and stretch in two or more stages, and from the viewpoint of simplifying the process, it is more preferable to perform the stretching in two stages.

  When stretching in two stages, the first stage stretching temperature is preferably 110 ° C. or higher and 160 ° C. or lower. The drawing temperature is the temperature of the drawn fiber. If the first stage stretching temperature is 110 ° C. or higher, the stretchability is improved because the temperature is higher than the crystal dispersion temperature of polypropylene. When the drawing temperature is 160 ° C. or lower, the melting point of the polypropylene undrawn yarn is less than the melting point, so that melt fracture hardly occurs and the drawability is stabilized. The stretching temperature is more preferably 120 ° C. or higher and 155 ° C. or lower, and further preferably 130 ° C. or higher and 150 ° C. or lower.

The fiber may be preheated before stretching. For preheating before stretching, a heating roll, a hot plate, a hot stove, or the like can be used. The temperature of the preheated fiber is preferably 50 ° C. or higher and 120 ° C. or lower, and more preferably 60 ° C. or higher and 110 ° C. or lower.
The first stage draw ratio is preferably 5 to 15 times. If the draw ratio is 5 times or more, highly oriented polypropylene fibers can be easily obtained, and high strength polypropylene fibers can be easily obtained. If the draw ratio is 15 times or less, fluff and bundle breakage are reduced, and high-strength polypropylene fibers can be stably obtained. The draw ratio is preferably 5.5 to 12 times, more preferably 6 to 10 times.

The first stage and the second stage of stretching may be performed once after the first stage of stretching is completed and wound up once, or may be performed continuously. From the viewpoint of productivity, it is preferable to continuously perform the first and second stage stretching.
The second stage draw ratio is preferably 1.01 to 2.00 times. If the draw ratio is 1.01 times or more, the effect of drawing is expressed, and if it is 2.00 times or less, yarn breakage or bundle breakage hardly occurs and stable drawing can be performed. The draw ratio of the final stage is more preferably from 1.05 times to 1.6 times, and even more preferably from 1.1 times to 1.4 times.

  The stretching temperature in the second stage is preferably 140 ° C. or higher and 180 ° C. or lower. If the stretching temperature is 140 ° C. or higher, the crystal structure formed up to the previous stage can be further deformed by the final stage stretching. Therefore, a polypropylene fiber having a highly oriented crystal chain and amorphous chain can be obtained. When the stretching temperature is 180 ° C. or lower, molecular relaxation is unlikely to occur, and crystal chains and amorphous chains are sufficiently oriented. The stretching temperature is more preferably 145 ° C. or higher and 175 ° C. or lower, and further preferably 150 ° C. or higher and 168 ° C. or lower.

  The fiber may be preheated before the second stage drawing. For the preheating before stretching, a heating roll, a hot plate, a hot stove, or the like can be used. The temperature of the preheated fiber is preferably 100 ° C. or higher and 140 ° C. or lower, and more preferably 110 ° C. or higher and 130 ° C. or lower.

  The deformation speed of the second stage is preferably 1 (1 / second) or more and 10 (1 / second) or less. When the deformation rate is 1 (1 / second) or more, molecular relaxation hardly occurs during stretching, and highly oriented crystal chains and amorphous chains can be obtained. When the deformation speed is 10 (1 / second) or less, the molecular chain is not forcibly stretched, and breakage of the yarn and bundle breakage hardly occur. The deformation speed is more preferably 1.5 (1 / second) to 8 (1 / second), and further preferably 2 (1 / second) to 7 (1 / second).

  The stretching speed in the second stage is preferably 100 m / min or more and 1000 m / min or less. Here, the stretching speed is the take-up roll speed when stretching. If the stretching speed is 100 m / min or more, sufficient productivity can be secured. On the other hand, if the drawing speed is 1000 m / min or less, the deformation speed does not become too fast, and therefore yarn breakage can be reduced. The stretching speed of the second stage is preferably 150 m / min or more and 800 m / min or less, and more preferably 200 m / min or more and 600 m / min or less.

-Physical property of final yarn The polypropylene fiber obtained by the present invention has few fluffs, and a high strength polypropylene fiber having a breaking strength of 6.5 cN / dtex to 13 cN / dtex can be obtained. If the breaking strength is 6.5 cN / dtex or more, the strength is sufficient when used for ropes, curing nets, horizontal nets, etc., so that it is not necessary to use a large amount of polypropylene fiber, and the weight can be reduced. On the other hand, if it is 13 cN / dtex or less, this strength polypropylene fiber can be industrially obtained. From the above viewpoint, the strength of the polypropylene fiber is more preferably 7 cN / dtex or more and 13 cN / dtex or less, and further preferably 8 cN / dtex or more and 13 cN / dtex or less.

  The initial elastic modulus of the polypropylene fiber of the present invention is a high elastic modulus of 85 cN / dtex or more and 200 cN / dtex or less. If the initial elastic modulus is 85 cN / dtex or more, when used for a rope, a curing net, a horizontal net, etc., it is not necessary to use a large amount of polypropylene fiber, and the weight can be reduced. On the other hand, if it is 200 cN / dtex or less, it is possible to industrially obtain a polypropylene fiber having this initial elastic modulus. The initial elastic modulus is more preferably 110 cN / dtex or more and 200 cN / dtex or less, and further preferably 120 cN / dtex or more and 200 cN / dtex or less.

  The breaking elongation of the polypropylene fiber of the present invention is preferably 10% or more and 30% or less. When the breaking elongation is 10% or more, the process passability is good when the polypropylene fiber is processed. On the other hand, if the breaking elongation is 30% or less, the shape stability of the obtained processed product is good. The breaking elongation of the polypropylene fiber of the present invention is preferably 11% or more and 25% or less, and 13% or more and 20% or less.

  The single fiber fineness of the polypropylene fiber of the present invention is preferably 1 dtex or more and 20 dtex or less. If the single fiber fineness is 1 dtex or more, the process passability during processing is good, and the workability of the processed product is also good. When the single fiber fineness is 20 dtex or less, the structural homogeneity within the fiber is hardly deteriorated, and a polypropylene fiber having high strength and high elastic modulus is easily obtained. The single fiber fineness is more preferably 3 dtex or more and 15 dtex or less, and further preferably 3.5 dtex or more and 10 dtex or less.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely, referring Examples 1-7 and Comparative Examples 1-4, this invention is not limited to a following example at all. In Examples, the melting point of polypropylene resin, wide-angle X-ray diffraction of undrawn yarn, birefringence value, small-angle X-ray scattering measurement of process yarn at the end of the first stage, DSC measurement, fiber strength of final fiber, single fiber fineness are Measured by the method described below.

(Melting point of polypropylene)
The melting point of the polypropylene resin was calculated using a DSC apparatus (DSC220 manufactured by SII Nano Technology). The polypropylene resin pellet was finely cut and 10 mg was put into a sample pan. The measurement was performed from room temperature to 240 ° C. at a temperature rising rate of 10 ° C./min in a nitrogen atmosphere. The peak top temperature of the obtained DSC curve was taken as the melting point.

(Wide-angle X-ray diffraction of undrawn yarn)
The structural analysis of the undrawn yarn was performed using a wide-angle X-ray diffractometer (Ultrag 18 manufactured by Rigaku Corporation, wavelength λ = 1.54 mm). The undrawn yarn was cut to about 5 cm to prepare 30 mg. The fibers were aligned in one axial direction and attached to the sample holder. The tube voltage was 40 kV, the tube current was 200 mA, and the irradiation time was 30 minutes.
From the obtained two-dimensional diffraction image, a one-dimensional profile was cut out in all directions, and then the background was subtracted to obtain a final one-dimensional profile. About the ratio of the crystal component, it implemented by the method mentioned above. The fitting peak function was a pseudo-Forked function, which is a superposition of a Gaussian function and a Lorentz function, and the ratio of the Gauss function to the Lorentz function was fixed at 1: 1.

(Birefringence value of undrawn yarn)
The birefringence value of the undrawn yarn was calculated using a polarizing microscope (ECLIPSE E600 manufactured by Nikon Corporation). An interference filter was inserted so that the wavelength was 546 nm, and retardation measurement was performed. The birefringence value was calculated by dividing the obtained retardation by the fiber diameter. The fiber diameter was calculated from the fineness and density (0.91 g / cm ³ ) of the undrawn yarn. Five measurements were taken and the average value was used.

(Intensity ratio by small angle X-ray scattering)
The structural analysis of the process yarn at the end of the first stage uses a small-angle X-ray scattering measurement device (Rigaku Ultra18, wavelength λ = 1.54 mm) and a DSC measurement device (SII Nanotechnology DSC220). went. In small-angle X-ray scattering measurement, the undrawn yarn was cut to about 5 cm and prepared to 50 mg. The fibers were aligned in one axial direction and attached to the sample holder. The tube voltage was 40 kV, the tube current was 200 mA, and the irradiation time was 30 minutes. For the obtained two-dimensional diffraction image, a one-dimensional profile was obtained in the range of β = 70 degrees to 110 degrees in the equator direction and in the range of 2θ = 0.2 degrees to 2 degrees. In the meridian direction, a one-dimensional profile was obtained for β = 160 ° to 200 ° and for 2θ = 0.2 ° to 2 °. For each 2θ, the maximum value obtained by dividing the one-dimensional profile in the meridian direction by the one-dimensional profile in the equator direction was used as the intensity ratio in the meridian direction to the intensity in the equator direction (intensity ratio by small-angle X-ray scattering).

(DSC peak ratio)
The DSC measurement of the process yarn at the end of the first stage was performed by finely cutting the polypropylene process yarn and adding 10 mg to the sample pan. The measurement was performed from room temperature to 240 ° C. at a temperature rising rate of 10 ° C./min in a nitrogen atmosphere. The obtained DSC profile was subjected to waveform separation with peaks placed between 168 ° C. and 174 ° C. and between 160 ° C. and 166 ° C., and the area ratio was calculated. The function used for waveform separation was a pseudo-Forked function, which is a superposition of a Gaussian function and a Lorentz function, and the ratio of the Gaussian function to the Lorentz function was fixed at 1: 1.
The DSC peak ratio was a value obtained by dividing the area of the melting peak at 160 ° C. to 166 ° C. by the area of the melting peak at 168 ° C. to 174 ° C.

(Single fiber fineness)
The single fiber fineness was calculated by dividing the total fineness of the polypropylene fiber bundle by the number of filaments. As the total fineness of the polypropylene fiber bundle, a value obtained by sampling 100 m and multiplying its mass by 100 was used.

(Fiber strength, initial elastic modulus, elongation)
Fiber strength, initial elastic modulus, and elongation were measured according to JIS L 1013. Using a tensile tester (Shimadzu AG-IS), the strain-stress curve was measured under the conditions of a sample length of 200 mm and a tensile speed of 100% / min under the conditions of an ambient temperature of 20 ° C. and a relative humidity of 65%. The elongation was determined from the value of, and the strength was determined from the stress at the breaking point. The initial elastic modulus was calculated from the slope of the strain-stress curve. Five measurements were taken and the average value was used.

Tables 1 and 2 show all the measurement data of Examples 1 to 7 and Comparative Examples 1 to 4 and their evaluations.
Example 1
A polypropylene resin (Y2000GV manufactured by Prime Polymer Co., Ltd., melting point of resin = 169.8 ° C., MFR = 18 g / min (230 ° C., load 2.16 kg, 10 min)) was charged into the extruder of the melt spinning apparatus at 280 ° C. After melt-kneading, a resin at 280 ° C. was discharged from a spinning nozzle having a discharge hole diameter of 0.5 mmφ and a discharge hole number of 36 holes at a discharge rate of 45.3 g / min (1.26 g / min per hole). After cooling and solidifying by applying cold air of 20 ° C. to the fiber, an oil agent was adhered and wound on a bobbin at a take-up speed of 300 m / min to obtain an undrawn yarn. The ratio of the crystal structure of the undrawn yarn is 0%, the ratio of the meso structure is 53.0%, the ratio of the amorphous structure is 47.0%, and the birefringence value is 0.88 × 10 ⁻³ . Low crystallinity and low orientation. The obtained undrawn yarn was preheated with a hot roll so that the yarn temperature was 85 ° C., and the first stage of drawing was hot plate drawn at a yarn temperature of 145 ° C. and a draw ratio of 6.0 times. . When structural analysis of the process yarn at the end of the first stage of drawing was performed, as shown in Table 1, the intensity ratio in the meridian direction to the intensity in the equator direction by small angle X scattering measurement was 1.45, and by DSC measurement. The area ratio of the melting peak at 160 ° C. to 166 ° C. with respect to the melting peak at 168 ° C. to 174 ° C. was 54.6%, and the ratio of the heterogeneous structure was small. Continuously, preheating is performed with a hot roll so that the yarn temperature becomes 120 ° C., and the second stage of drawing is performed at a yarn temperature of 165 ° C., a draw ratio of 1.2 times, and a deformation rate of 2.78 (1 / Second). The drawing speed was 300 m / min to obtain polypropylene fibers. The strength of the obtained fiber was 6.7 cN / dtex, the initial elastic modulus was 86.1 cN / dtex, both strength and elastic modulus were high, and there were few fluffs. The elongation was 21.8% and the single fiber fineness was 5.8 dtex. These results are shown in Tables 1 and 2.

(Example 2)
The single fiber fineness is 4.2 dtex in the same manner as in Example 1 except that the second stage drawing is performed at a yarn temperature of 165 ° C., a draw ratio of 1.66 times, and a deformation rate of 6.63 (1 / second). Polypropylene fibers were obtained. The results are shown in Tables 1 and 2. The obtained polypropylene fiber had few fuzz.

(Example 3)
A polypropylene fiber having a single fiber fineness of 4.4 dtex was obtained in the same manner as in Example 1 except that the first stage drawing was performed at a yarn temperature of 145 ° C. and a draw ratio of 8.0 times. The results are shown in Tables 1 and 2. The obtained polypropylene fiber had few fuzz.

Example 4
The single fiber fineness is 4.7 dtex in the same manner as in Example 1 except that the second stage of drawing was performed at a yarn temperature of 165 ° C., a draw ratio of 1.5 times, and a deformation rate of 5.56 (1 / second). Polypropylene fibers were obtained. The results are shown in Tables 1 and 2. The resulting polypropylene fibers had few fuzz.

(Example 5)
Single fiber as in Example 1 except that the yarn temperature for the first stage drawing was 135 ° C., the draw ratio for the second stage drawing was 1.5 times, and the deformation rate was 5.56 (1 / second). A polypropylene fiber having a fineness of 4.6 dtex was obtained. The results are shown in Tables 1 and 2. The obtained polypropylene fiber had few fuzz.

(Example 6)
The first stage of draw ratio is 8.0 times hot plate, and the second stage of draw temperature is 165 ° C, draw ratio is 1.35 times, deformation rate is 4.32 (1 / second) A polypropylene fiber having a single fiber fineness of 3.9 dtex was obtained in the same manner as in Example 1 except that hot plate stretching was performed. The results are shown in Tables 1 and 2. The obtained polypropylene fiber had few fuzz.

(Example 7)
A polypropylene fiber having a single fiber fineness of 4.4 dtex was obtained in the same manner as in Example 1 except that the yarn temperature of the first stage drawing was 155 ° C. and the draw ratio was 8.0 times. The results are shown in Tables 1 and 2. The obtained polypropylene fiber had few fuzz.

(Comparative Example 1)
The same as in Example 1 except that the draw ratio of the first-stage drawing was 4.0 times, the draw ratio of the second-stage drawing was 1.8 times, and the deformation rate was 7.41 (1 / second). Thus, a polypropylene fiber having a single fiber fineness of 5.8 dtex was obtained. The results are shown in Tables 1 and 2. The obtained polypropylene fiber had a strength of 4.5 cN / dtex and an initial elastic modulus of 65.4 cN / dtex, both strength and elastic modulus being low, and having a lot of fluff.

(Comparative Example 2)
The same as Example 1 except that the draw ratio of the first-stage drawing was 4.0 times, the draw ratio of the second-stage drawing was 2.0 times, and the deformation rate was 8.33 (1 / second). Thus, a polypropylene fiber having a single fiber fineness of 5.1 dtex was obtained. The results are shown in Tables 1 and 2. The resulting polypropylene fiber had a strength of 5.8 cN / dtex, an initial elastic modulus of 81.6 cN / dtex, low strength and elastic modulus, and a lot of fluff.

(Comparative Example 3)
Polypropylene in the same manner as in Example 1 except that the draw ratio of the first-stage drawing was 4.0 times, the draw ratio of the second-stage drawing was 2.5 times, and the deformation rate was 10 (1 / second). An attempt was made to produce a fiber, but yarn breakage occurred and the final fiber could not be obtained.

(Comparative Example 4)
Polypropylene in the same manner as in Example 1 except that the yarn temperature for the first drawing was 155 ° C., the draw ratio for the second drawing was 1.5 times, and the deformation rate was 5.56 (1 / second). An attempt was made to produce a fiber, but yarn breakage occurred and the final fiber could not be obtained.

Claims (7)

  A method for producing a polypropylene fiber comprising a drawing step in which a polypropylene undrawn yarn is drawn in two or more stages, wherein the process yarn at the end of the first stage drawing has a strength in the meridian direction relative to the strength in the equator direction by small angle X scattering measurement. A method for producing a polypropylene fiber, wherein the ratio is in the range of 1.01 or more and 1.60 or less, and then the second and subsequent steps are drawn.   The process yarn at the end of the first stage of stretching is in a range where the area ratio of the melting peak at 160 ° C. or higher and 166 ° C. or lower with respect to the melting peak at 168 ° C. or higher and 174 ° C. or lower is 50% or higher and 57.5% or lower. The method for producing a polypropylene fiber according to claim 1.   The manufacturing method of the polypropylene fiber of Claim 1 or 2 which makes the draw ratio of the 1st step 5 times or more and 15 times or less.   The method for producing a polypropylene fiber according to any one of claims 1 to 3, wherein the yarn temperature of the first stage is set to 110 ° C or higher and 160 ° C or lower. 5. The undrawn yarn has a crystal structure ratio of 40% by mass or less and a birefringence value of 0.1 × 10 ⁻³ or more and 2.5 × 10 ⁻³ or less. The manufacturing method of the polypropylene fiber as described in any one of. The polypropylene undrawn yarn melts a polypropylene resin having a melt flow rate of 12 g / min or more and 28 g / min or less and discharges it from a discharge hole of a spinning nozzle at a temperature of 80 ° C. or more and 150 ° C. or less of the melting point of the polypropylene resin. The manufacturing method of the polypropylene fiber as described in any one of Claims 1-5 which is an undrawn thread | yarn which is solidified by cooling and taken up at 200 m / min or more and 500 m / min or less. A polypropylene fiber having a tensile strength of 6.5 cN / dtex or more and 10 cN / dtex or less, a tensile modulus of 85 cN / dtex or more and 170 cN / dtex or less , and a single fiber fineness of 3.5 dtex or more and 20 dtex or less.