JP2009127159A - Sheet=type fiber construct made from polypropylene fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide sheet-type fiber construct that mainly consists of polypropylene fiber excellent in strength, heat tolerance and water-absorbing property heat resistance and strength and mainly includes a polypropylene fiber. <P>SOLUTION: The sheet-type fiber construct is formed by using a PP fiber having a fiber strength of 7 cN/dtex or more and exhibiting either or both of the following characteristics: (i) peaks-and-valleys characteristics having a single filament fineness of 0.1 to 3 dtex wherein peaks with a large diameter and non-peaks with a small diameter are alternately located along the fiber axis on the surface and the average interval of the peaks and valleys is from 6.5 to 20 μm and the average height thereof is from 0.35 to 1 μm, and (ii) a single shape exhibiting a maximum heat absorption peak shape having a half-value width of 10°C or lower and DSC characteristics exhibiting a melting enthalpy change (▵H) of 125 J/g. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a sheet-like fiber structure formed using polypropylene fibers.
More specifically, the present invention relates to a sheet-like fiber structure made of polypropylene fiber having high water retention, excellent heat resistance and mechanical properties.

Polypropylene fiber is superior in chemical resistance and light weight, can be easily melted, is excellent in recyclability, and does not generate harmful gases such as halogen gas even when incinerated. It is used for various applications such as non-woven fabric, synthetic paper, and net-like material.
For example, synthetic paper and nonwoven fabric made of polypropylene fiber are excellent in chemical resistance, and thus are used in various industrial material applications such as filters and separators. However, the hydrophobicity of polypropylene fibers is a problem in many applications. For example, synthetic paper and non-woven fabrics used as water-based filtration filters, alkaline secondary battery separators, etc. often require high hydrophilicity to the main fibers, but synthetic paper or non-woven fabric made of polypropylene fibers is hydrophilic. Therefore, it is difficult to use as it is for applications such as liquid filters and battery separators that require hydrophilicity.

  From the above points, techniques related to the improvement of hydrophilicity or water retention of polypropylene fibers have been proposed. For example, a method of producing water-absorbing polypropylene fibers by performing melt spinning using polypropylene in which a particulate water-absorbing resin is added and dispersed using polyethylene wax is known (Patent Document 1). However, when this method is used, the particulate water-absorbing resin added to the polypropylene may cause yarn breakage or non-uniform stretching at the time of spinning or stretching, thereby avoiding an influence on spinnability and stretchability. I can't. Moreover, since the polypropylene fiber obtained by this method has insufficient strength, sufficient strength cannot be obtained when it is formed into a sheet-like fiber structure such as woven or knitted fabric, nonwoven fabric, synthetic paper, or net-like material.

  In addition, as a method for improving the water retention rate of a sheet-like fiber structure (woven / knitted fabric, nonwoven fabric, synthetic paper, net-like material, etc.) made of polypropylene fiber, the polypropylene fiber having a roughened surface or an uneven surface. It is conceivable that a sheet-like fiber structure is produced using the above and water is retained in the recesses formed on the surface of the polypropylene fiber constituting the sheet-like fiber structure. However, in the conventionally known polypropylene fiber having irregularities formed on the surface and the polypropylene fiber having a roughened surface, the irregularities (roughening) are insufficient or there are restrictions on the formation of irregularities. Even if a sheet-like fiber structure is produced using polypropylene fibers, a sheet-like fiber structure having high water retention cannot be obtained.

For example, a reinforcing fiber for a hydraulic material in which irregularities are formed on the surface by irradiating ionizing radiation to polypropylene fibers (see Patent Document 2), and the melt-spun polypropylene fibers are embossed and stretched on the surface. Polypropylene fibers for cement blending with irregularities formed (see Patent Document 3), irregularities on the surface produced by applying a stretching treatment after changing the take-up speed of the polypropylene fiber melt-extruded by an extruder and then applying a stretching treatment Polypropylene fibers for cement blending (see cited document 4) and the like are known. Sheets such as knitted and knitted fabrics, nonwoven fabrics, synthetic papers and nets using these polypropylene fibers for blending hydraulic substances (cement) are known. Even if a fibrous fiber structure is produced, a sheet-like fibrous structure having a high water retention rate and excellent strength cannot be obtained.
Specifically, in the case of polypropylene fibers (particularly, fine fiber polypropylene fibers having a single fiber fineness of 10 dtex or less) obtained by the method for forming concavities and convexities described in Patent Documents 2 to 4 and among them, Patent Document 2 is markedly damaged. Therefore, even if a sheet-like fiber structure is formed using the polypropylene fiber, a sheet-like fiber structure having excellent strength cannot be obtained.

Furthermore, a polypropylene undrawn yarn is produced by drawing at 125 to 155 ° C. in a hot air tank, has a single yarn strength of 9 cN / dtex or more, and has a streaky rough surface structure along the curved surface of the fiber surface. A concrete reinforcing polypropylene fiber is known (Patent Document 5). However, in this polypropylene fiber, since the interval and height of the streaky rough surface structure existing on the fiber surface are both small, a sheet-like fiber structure excellent in water retention cannot be obtained.
Further, a polypropylene undrawn yarn is drawn in one step with pressurized saturated steam of 3.0 to 5.0 kg / cm ² (temperature 133 to 151 ° C.) to produce a drawn yarn having an optically bright part and a dark part. A method has been proposed (Patent Document 6). However, the drawn polypropylene yarn (polypropylene fiber) obtained by this method has insufficient formation of unevenness on the fiber surface, and the interval and height of the unevenness are small, so that a sheet-like fiber structure excellent in water retention is obtained. Absent.

For example, as a sheet excellent in recyclability and strength, a fiber-reinforced polyolefin sheet in which a polypropylene fiber fabric is laminated on a polyolefin sheet base material is known. In the production of the fiber-reinforced polyolefin sheet, the polyolefin sheet is melted at as high a temperature as possible to improve the productivity and the adhesion between the polypropylene fiber fabric and the polyolefin sheet substrate. It is necessary to bond a polypropylene fiber fabric. However, since the heat resistance of the polypropylene fiber fabric is insufficient and the polyolefin sheet base material cannot be melted at a high temperature during the production of the fiber reinforced sheet, the production rate cannot be sufficiently increased. Adhesion between the fabric and the polyolefin substrate becomes insufficient, resulting in a decrease in productivity and insufficient strength of the fiber-reinforced polyolefin sheet obtained.
In addition, a filter made of a synthetic fiber made of polypropylene fiber or a nonwoven fabric is sometimes used in a high-temperature environment, and therefore, heat resistance is required to be improved.

  As a conventional technique for improving the heat resistance of polypropylene fiber, the isotactic pentad fraction is 96% or more and less than 98.5%, and the melt flow rate (230 ° C., 2.16 kg load) is 0.1. A polypropylene fiber having a heat shrinkage rate of 10% or less at 170 ° C. for 10 minutes and a melting peak temperature of 178 ° C. or higher obtained by stretching a homopolypropylene resin of ˜30 g / 10 minutes after melt molding is known. (See Patent Document 7). However, since the endothermic peak shape of this polypropylene fiber is a broad double shape or a single shape and the crystals are not uniform, it cannot be said that the heat resistance is still sufficiently high.

  As another conventional technique, a polypropylene fiber having two DSC endothermic peaks at 155 to 170 ° C. obtained by melt spinning or melt spinning a polypropylene homopolymer having an isotactic index of 90 to 99%. Is known (see Patent Document 8). However, in this polypropylene fiber, the endothermic peak on the low temperature side of the two DSC endothermic peaks is an indicator of the heat resistance of the polypropylene fiber, and the endothermic peak shape is broad and the crystals are not uniform. Sex is not enough.

JP-A-4-41710 Japanese Examined Patent Publication No. 61-26510 JP-A-56-9268 Japanese Patent Publication No.61-301 JP 2003-293216 A Japanese Patent No. 3130288 JP 2002-302825 A JP 2001-20132 A “Macromolecules”, Vol. 6, 1973, p925 "Macromolecules", Vol. 8, 1975, p687

An object of the present invention is to provide a sheet-like fiber structure such as a nonwoven fabric made of polypropylene fiber, a synthetic paper, a woven or knitted fabric, and a net-like product, which has excellent water retention and excellent strength.
Moreover, the objective of this invention is providing the sheet-like fiber structure made from a polypropylene fiber which is excellent in intensity | strength and is excellent also in heat resistance.
Furthermore, the objective of this invention is providing the sheet-like fiber structure made from a polypropylene fiber excellent in water retention, intensity | strength, and heat resistance.

The inventor has intensively studied in order to achieve the above-described object. Then, using polypropylene having an isotactic pentad fraction (IPF) of a specific value or more, a predetermined diameter formed by alternately having large diameter raised portions and small diameter non-lifted portions along the fiber axis on the fiber surface. Thus, it was possible to obtain unprecedented polypropylene fibers with high water retention, having a single fiber fineness with excellent average spacing and average height, and excellent strength.
In addition, the present inventor uses polypropylene having a specific or higher isotactic pentad fraction (IPF) and exhibits specific endothermic / melting characteristics in scanning differential calorimetry (DSC) and has a uniform crystal structure. In addition, an unprecedented polypropylene fiber having excellent heat resistance and strength was obtained.
Furthermore, the present inventor uses polypropylene having an isotactic pentad fraction (IPF) of a specific value or more, and a large-diameter raised portion and a small-diameter non-raised portion alternately on the fiber surface along the fiber axis. Strength, water retention and heat resistance, having irregularities with a predetermined average interval and average height, and having specific endothermic / melting characteristics in scanning differential calorimetry (DSC), and having a uniform crystal structure It was possible to obtain a polypropylene fiber having excellent resistance.
And when this inventor manufactured sheet-like fiber structures, such as a knitted fabric, a nonwoven fabric, a synthetic paper, and a net-like material, using the polypropylene fiber obtained above, the said sheet-like fiber structure has high water retention. The present invention was completed by finding that it has a good ratio and excellent water retention, as well as excellent strength and heat resistance.

That is, the present invention
(1) An uplift with a large diameter on the surface, made of polypropylene having an isotactic pentad fraction (IPF) of 94% or more, a fiber strength of 7 cN / dtex or more and a single fiber fineness of 0.1 to 3 dtex 50% by mass or more of polypropylene fibers having irregularities with an average interval of 6.5 to 20 μm and an average height of 0.35 to 1 μm, in which portions and small-diameter non-raised portions are alternately present along the fiber axis A sheet-like fiber structure characterized by comprising:
(2) Half of the polypropylene having an isotactic pentad fraction (IPF) of 94% or more, a fiber strength of 7 cN / dtex or more, and an endothermic peak shape by scanning differential calorimetry (DSC) of 10 ° C. or less. A sheet-like fiber structure comprising a polypropylene fiber having a single shape having a width and a melting enthalpy variation (ΔH) of 125 J / g or more in a proportion of 50% by mass or more;
(3) Scanning differential calorimetry (DSC) made of polypropylene having an isotactic pentad fraction (IPF) of 94% or more, a fiber strength of 7 cN / dtex or more, and a single fiber fineness of 0.1 to 3 dtex. The endothermic peak shape by the single shape has a half width of 10 ° C. or less, the amount of change in melting enthalpy (ΔH) is 125 J / g or more, and a large-diameter raised portion and a small-diameter non-raised portion on the surface are fiber axes. A sheet-like fiber comprising polypropylene fibers having irregularities with an average interval of 6.5 to 20 μm and an average height of 0.35 to 1 μm alternately present along the length of 50% by mass or more A structure; and
(4) The sheet-like fiber structure according to any one of (1) to (3), having a water retention rate of 10% by mass or more;
It is.

  The sheet-like fiber structure of the present invention is made of polypropylene having an isotactic pentad fraction (IPF) of 94% or more, has a high fiber strength of 7 cN / dtex or more, and is on the surface of the fiber. A polypropylene fiber having specific irregularities having an average interval of 6.5 to 20 μm and an average height of 0.35 to 1 μm, in which large-diameter raised portions and small-diameter non-raised portions are alternately positioned along the fiber axis, By having the above-mentioned specific irregularities on the fiber surface, it has a high water retention rate and is excellent in strength. Therefore, the sheet-like fiber structure of the present invention formed by using the polypropylene fiber has a high water retention rate (generally a water retention rate of 10% by mass or more), is excellent in water retention, and is excellent in strength. .

  The sheet-like fiber structure of the present invention is made of polypropylene with an isotactic pentad fraction (IPF) of 94% or more, has a high fiber strength of 7 cN / dtex or more, and has a scanning differential. When the endothermic peak shape in calorimetry (DSC) is a single shape having a half width of 10 ° C. or less, and the amount of change in melting enthalpy (ΔH) is 125 J / g or more, the polypropylene fiber has the specific DSC characteristics described above. It has high crystallinity, uniform crystal structure, extremely excellent heat resistance, and maintains good fiber shape and fiber strength without melting easily even when exposed to high temperatures. can do. Therefore, the sheet-like fiber structure of the present invention formed using the polypropylene fiber has high strength and excellent heat resistance, and exhibits mechanical properties such as strength over a long period of time even when exposed to high temperatures. It can be maintained and has excellent durability.

In particular, the single fiber fineness is 0.1 to 3 dtex, the fiber strength is 7 cN / dtex or more, the surface has the above-described specific uneven structure, and the endothermic peak shape by scanning differential calorimetry (DSC) is 10 ° C. or less. The sheet-like fiber structure of the present invention formed by using a polypropylene fiber having a single shape having a half width and a melting enthalpy variation (ΔH) of 125 J / g or more has water retention, heat resistance and strength. In any of the above, the sheet-like fiber structure of the present invention formed by using the polypropylene fiber is extremely excellent in water retention, heat resistance, strength and durability.
The sheet-like fiber structure (woven fabric, non-woven fabric, synthetic paper, net-like material, etc.) of the present invention makes use of the above-mentioned properties for various uses such as filters, separators, reinforcing materials, clothing, wipers, makeup removers, etc. It can be used effectively for applications.

The present invention is described in detail below.
The sheet-like fiber structure of the present invention is formed using a specific polypropylene fiber defined in the present invention.
Here, the “sheet-like fiber structure” of the present invention uses a specific polypropylene fiber defined in the present invention and / or a fiber structure having a sheet shape produced using a yarn made of the polypropylene fiber. It is a general term for the body. The sheet-like fiber structure of the present invention includes a woven / knitted fabric, a nonwoven fabric, a synthetic paper, a net-like material, and a fiber structure formed by laminating two or more of them.

The polypropylene fiber forming the sheet-like fiber structure of the present invention is a polypropylene fiber made of polypropylene having an isotactic pentad fraction (IPF) (hereinafter sometimes simply referred to as “IPF”) of 94% or more. The IPF is preferably made of 95 to 99% polypropylene, and the IPF is more preferably made of 96 to 99% polypropylene.
When the IPF of polypropylene is less than 94%, it becomes difficult to form a uniform crystal structure on the polypropylene fiber, and the polypropylene fiber used in the sheet-like fiber structure of the present invention having sufficient strength and heat resistance cannot be obtained. . On the other hand, polypropylene having an IPF of over 99% is difficult to industrially mass-produce, and therefore has low practicality in terms of cost.

The polypropylene fiber forming the sheet-like fiber structure of the present invention may be formed from one type of propylene homopolymer or polypropylene as long as the IPF satisfies the above-described values as polypropylene. And a propylene copolymer composed of other copolymerizable monomers. Alternatively, if the IPF of the entire mixture satisfies the above-mentioned values, a mixture of two or more propylene homopolymers, one or two or more propylene homopolymers and one or two or more propylene copolymers. You may form from the mixture of a polymer, or the mixture of two or more types of propylene copolymers.
In addition, the polypropylene fiber forming the sheet-like fiber structure of the present invention may be composed of two or more types of propylene alone as long as the IPF in the entire propylene polymer constituting the polypropylene fiber satisfies the above-described value. It may be a composite spun fiber or a mixed spun fiber having a composite form or mixed form such as a core-sheath type, a sea-island type, a side-by-side type, etc., formed using a combined and / or propylene copolymer.

IPF in polypropylene is an index representing the stereoregularity, and affects the crystallinity when polypropylene is made into a fiber. In general, the higher the IPF, the higher the stereoregularity. The IPF in polypropylene can be determined from ¹³ C-NMR signals, and the IPF value of polypropylene in this specification refers to the value determined by the method described in the following examples.

  The sheet-like fiber structure of the present invention can be obtained from the point that the melt spinnability, stretchability, etc. when producing the polypropylene fiber are improved and the polypropylene fiber having the above-mentioned specific properties used in the present invention can be obtained smoothly. The formed polypropylene fiber has a melt flow rate (MFR) of 5 to 70 g, more preferably 10 to 50 g, especially 15 when measured under the conditions of a temperature of 230 ° C., a load of 2.16 kg and a time of 10 minutes in accordance with JIS K 7210. It is preferably formed from ˜40 g of polypropylene.

The polypropylene fiber forming the sheet-like fiber structure of the present invention has a fiber strength of 7 cN / dtex or more, and preferably has a fiber strength of 9 to 13 cN / dtex.
Here, the fiber strength (single fiber fineness strength) of the polypropylene fiber in this specification refers to the fiber strength measured by the method described in the following examples.
The sheet-like fiber structure of the present invention has high strength by being formed using the polypropylene fiber having the above-described fiber strength. When a sheet-like fiber structure is formed using polypropylene fibers having a fiber strength smaller than the above, the strength of the sheet-like fiber structure may be insufficient. On the other hand, a polypropylene fiber having a fiber strength exceeding 13 cN / dtex is difficult in practical use because it is necessary to adopt conditions with low mass productivity in the production.

The fineness (single fiber fineness) of the polypropylene fibers forming the sheet-like fiber structure of the present invention is not particularly limited, but the ease of production (especially ease of stretching) when producing polypropylene fibers, the sheet shape From the viewpoints of processability when producing a fiber structure, strength and durability of the sheet-like fiber structure, the fineness (single fiber fineness) of the polypropylene fiber is generally preferably 0.01 to 500 dtex. 0.05 to 50 dtex is more preferable, and 0.1 to 5 dtex is still more preferable.
If the fineness (single fiber fineness) of the polypropylene fiber is too small, the polypropylene fiber breakage may occur after forming the sheet-like fiber structure when the sheet-like fiber structure is formed. In some cases, the strength may decrease. On the other hand, if the strength is too large, the stretched physical properties for obtaining polypropylene fibers may decrease, and high strength and highly crystallized polypropylene fibers may not be obtained.

  Among the polypropylene fibers forming the sheet-like fiber structure of the present invention, together with the above-described fiber strength of 7 cN / dtex or more, “a single fiber fineness is 0.1 to 3 dtex, a large-diameter raised portion and a small diameter on the surface The polypropylene fibers having the characteristics that the non-protruding portions of the non-protruding portions have irregularities with an average interval of 6.5 to 20 μm and an average height of 0.35 to 1 μm, which are alternately present along the fiber axis, Is along the fiber axis, it has a high water retention rate (generally a water retention rate of 10% by mass or more) and is excellent in water retention. Therefore, the sheet-like fiber structure of the present invention formed by using the polypropylene fiber has a high water retention rate (generally a water retention rate of 10% by mass or more) and is excellent in water retention.

Here, in the present specification, “the polypropylene fiber has irregularities in which a large-diameter raised portion and a small-diameter non-raised portion are alternately positioned along the fiber axis on the surface” is a schematic diagram of FIG. As shown in FIG. 1, the polypropylene fiber does not have a uniform diameter along the length direction, and has a large bulge (convex portion) (A1, A2, A3, A4,... In FIG. 1). And non-protruding portions (concave portions) having a smaller diameter (B1, B2, B3, B4,... In FIG. 1) are alternately formed along the fiber axis (fiber length direction). It means that the fiber surface is uneven.
In the present specification, the “average interval” refers to an interval between two adjacent ridges (projections) among a large number of projections and depressions (bumps and non-bumps) formed along the fiber axis. It means the average value of (distance) (the length of A1-A2, A2-A3, A3-A4,... In FIG. 1).
The “average height” is an imaginary straight line that connects the minimum diameter portions of two adjacent non-protruding portions (concave portions) among a large number of irregularities (protruding portions and non-protruding portions) formed along the fiber axis. (A straight line connecting B1 and B2 in FIG. 1, a straight line connecting B2 and B3, a straight line connecting B3 and B4,...) Between the two adjacent non-protruding parts (concave parts) ( It means the average value of the lengths of the vertical lines (h1, h2, h3, h4,... In FIG. 1) from the apex of the convex portion.
The average interval and the average height of the irregularities formed along the fiber axis of the polypropylene fiber can be determined from a photograph of the polypropylene fiber taken using a scanning electron microscope or the like, and the average of the irregularities in the present specification The interval and the average height are values obtained by the method described in the following examples.

If the fineness of the polypropylene fiber is less than 0.1 dtex in the above-described polypropylene fiber having the unevenness characteristics, spinning is performed using a die having an extremely large number of spinning holes in order to maintain mass productivity, and accordingly, the die In order to ensure sufficient space between the spinning holes at the center, it is necessary to make significant improvements to the equipment, such as increasing the scale of the spinning device, and because the fineness is small, yarn drawing troubles and fluff are likely to occur during the drawing process. Become. On the other hand, when the fineness of the polypropylene fiber exceeds 3 dtex, it becomes difficult to express the above-mentioned specific unevenness on the outer periphery of the fiber, and since the specific surface area of the fiber becomes small, it becomes impossible to secure sufficient water retention, and further the drawability is lowered. Thus, it becomes difficult to obtain sufficient fiber strength.
In the polypropylene fiber having the specific unevenness characteristics described above, the fineness (single fiber fineness) is preferably 0.2 to 2.5 dtex, and more preferably 0.3 to 2.4 dtex.

In the polypropylene fiber having irregularities on the surface, if the average interval of the irregularities is less than 6.5 μm and / or if the average height is less than 0.35 μm, the irregularities on the fiber surface become too fine, Water retention decreases. On the other hand, polypropylene fibers with an average irregularity interval of more than 20 μm and / or an average height of more than 1 μm cannot be produced unless the production speed of the polypropylene fiber is significantly reduced, and polypropylene with an IPF close to 100% is used. Because it is necessary to do so, it is not practical.
In the case where the sheet-like fiber structure of the present invention is formed from polypropylene fibers having the unevenness on the fiber surface, the average interval of the unevenness formed along the fiber axis direction is 6.6 to 20 μm in the polypropylene fiber. In particular, the average height is preferably 6.8 to 20 μm, and the average height is preferably 0.40 to 1 μm, and particularly preferably 0.45 to 1 μm.

When the polypropylene fiber having the above-described unevenness characteristics is used as the polypropylene fiber, the unevenness having an average interval of 6.5 to 20 μm and an average height of 0.35 to 1 μm is formed on the surface of the polypropylene fiber. The sheet-like fiber structure having a high water retention rate (generally a sheet-like fiber structure having a water retention rate of 10% by mass or more) in which water is retained in the concave and convex portions on the fiber surface. Obtainable.
When the sheet-like fiber structure of the present invention is used for an application where a high water retention rate is required, the water retention rate of the sheet-like fiber structure is preferably 10% by mass or more, and is 11 to 50% by mass. It is more preferable. In order to obtain a sheet-like fiber structure made of polypropylene fiber having a water retention rate exceeding 50%, the irregularities on the surface of the polypropylene fiber must be extremely large, and in reality, it is difficult to produce with high productivity. is there.
In addition, the water retention rate of the polypropylene fiber and the water retention rate of the sheet-like fiber structure in the present specification refer to the water retention rate measured by the method described in the examples below.

Among the polypropylene fibers forming the sheet-like fiber structure of the present invention, together with the above-described fiber strength of 7 cN / dtex or more, “by scanning differential calorimetry (DSC) (hereinafter sometimes simply referred to as“ DSC measurement ”) Polypropylene fiber having a specific DSC characteristic that the endothermic peak shape is a single shape having a half width of 10 ° C. or less and the amount of change in melting enthalpy (ΔH) is 125 J / g or more ”has such characteristics. Therefore, it is excellent in heat resistance.
Using a polypropylene fiber having a narrow (sharp) single shape with a half-value width of 10 ° C. or less as measured by DSC and having a melting enthalpy change (ΔH) of 125 J / g or more. When the sheet-like fiber structure of the present invention is formed, the polypropylene fiber is excellent in heat resistance, so that a sheet-like fiber structure that is resistant to fusing and deterioration in physical properties even when exposed to high temperatures is durable and excellent in durability. can get.
Here, the above-mentioned “endothermic peak shape” and “melting enthalpy change amount (ΔH)” by DSC measurement in the present invention are the endothermic peak shape and melting enthalpy change by DSC measurement performed by the method described in the following examples. The amount (ΔH).

In DSC measurement of isotactic polypropylene fiber, the endothermic peak observed at 160 ° C. or higher is generally derived from melting of α-crystal. Polypropylene fibers having an endothermic peak temperature of 160 ° C. or higher, and in some cases 175 ° C. or higher are known in the art (see Patent Document 7, etc.), but such conventional polypropylene fibers are still sufficiently crystallized. Therefore, the shape of the endothermic peak is a double peak shape or a wide (broad) single peak shape, and the crystal structure is not uniform as a whole.
On the other hand, “the endothermic peak shape by DSC measurement is a single shape having a half width of 10 ° C. or less, and the amount of change in melting enthalpy (ΔH) is 125 J / g forming the sheet-like fiber structure of the present invention. Polypropylene fiber having a DSC characteristic of “is the above” has an endothermic peak shape by DSC measurement having a narrow (sharp) single shape having a half-value width of 10 ° C. or less, and an amount of change in melting enthalpy When (ΔH) is 125 J / g or more, the crystallinity is high, a uniform crystal structure is formed, and the heat resistance is excellent.

Here, “endothermic peak shape by DSC measurement” and “half-value width” in this specification will be described.
First, FIG. 2 is a diagram schematically showing an endothermic peak shape by DSC measurement in polypropylene fiber.
In FIG. 2, (a) has a single endothermic peak (single peak), the single peak is sharp and has a large peak, and has a large change in melting enthalpy (ΔH). The typical example of the endothermic peak curve of the polypropylene fiber of the invention is shown.
On the other hand, in FIG. 2, (b) is an example of an endothermic peak curve of a conventional polypropylene fiber, which has two endothermic peaks (double peak), a large peak width (half-value width), and a change in melting enthalpy. The amount (ΔH) is small.
In FIG. 2, (c) is another example of the endothermic peak curve of the conventional polypropylene fiber. Although there is one endothermic peak (single peak), the amount of change in melting enthalpy (ΔH) is small.
Next, FIG. 3 is a diagram showing how to find the half width at the endothermic peak by DSC measurement of the polypropylene fiber used in the present invention, taking as an example the case where the peak shape is a single peak in the DSC curve.
In FIG. 3, when the intersection of the perpendicular line drawn from the vertex X of the endothermic peak (single peak) to the temperature axis and the base line of the endothermic peak is Y, the point at which the line segment XY is divided into two equal parts M And the length (temperature width) of the line segment N1-N2 is “half-value width (in this specification) where N1 and N2 are the intersection points of the straight line passing through M and parallel to the temperature axis and the endothermic curve, respectively. ° C) ”.

When the endothermic peak curve of the polypropylene fiber is a double peak having two endothermic peaks as shown in FIG. 2B, or when it has three or more endothermic peaks, the peak of the highest endothermic peak is X. , Y is the intersection of the perpendicular from the vertex X to the temperature axis and the baseline of the endothermic peak, M is the point that bisects the line segment XY, and a straight line passing through M and parallel to the temperature axis When the intersection having the lowest temperature is N1 and the intersection having the highest temperature is N2, the length (temperature width) of the line segment N1-N2 is referred to as “half” in this specification. It corresponds to “value width (° C.)”. In this case, the half width (° C.) is generally wide.
In the endothermic peak curve, the base line of the endothermic peak (see FIG. 3) and the area of the portion surrounded by the endothermic peak curve above the baseline are represented by the “melting enthalpy change amount (Δ H) ".

If the crystal formation in the polypropylene fiber is insufficient, an endothermic peak or an exothermic peak may newly appear due to the rearrangement of the crystal at the time of DSC measurement, resulting in a complicated DSC curve. Furthermore, if the crystal formation in the polypropylene fiber is insufficient, the endothermic peak curve changes due to the occurrence or disappearance of the endothermic peak or the exothermic peak even in the same sample due to the difference in the heating rate during DSC measurement. Sometimes.
On the other hand, among the polypropylene fibers used for forming the sheet-like fiber structure of the present invention, “the endothermic peak shape by DSC measurement is a single shape having a half width of 10 ° C. or less, and the amount of change in melting enthalpy (ΔH) Polypropylene fiber having a DSC characteristic of “Is 125 J / g or more” has the DSC characteristic, so that the temperature rising rate is within the range of 1-50 ° C./min when the DSC measurement is performed. Even if different, the endothermic peak curve has a sharp and large single peak shape with only one endothermic peak, and has a high amount of melting enthalpy change (ΔH). That is, among the polypropylene fibers used for forming the sheet-like fiber structure of the present invention, the polypropylene fibers having the DSC characteristics described above have uniform and high crystallinity, and as a result, have high heat resistance. That it is.

The higher the amount of change in melting enthalpy (ΔH) of the polypropylene fiber, the higher the heat resistance. However, polypropylene fibers exceeding 165 J / g are difficult to produce unless the production rate is significantly reduced, and the IPF is 100%. Therefore, it is industrially ineffective.
From this point, the polypropylene fiber forming the sheet-like fiber structure of the present invention preferably has a melting enthalpy change (ΔH) of 125 to 165 J / g, and preferably 130 to 165 J / g. More preferably, it is 135-165 J / g, still more preferably 140-165 J / g.

When the amount of change in melting enthalpy (ΔH) of the polypropylene fiber is less than 125 J / g, the heat resistance may be insufficient.
However, it is a polypropylene fiber that does not have the requirement that “the endothermic peak shape by DSC measurement is a single shape having a half width of 10 ° C. or less and the amount of change in melting enthalpy (ΔH) is 125 J / g or more”. "It is made of polypropylene having an IPF of 94% or more, the single fiber fineness is 0.1 to 3 dtex, the fiber strength is 7 cN / dtex or more, and a large-diameter raised portion and a small-diameter non-raised portion are along the fiber axis on the surface. In the case where a sheet-like fiber structure is formed using polypropylene fibers having the characteristics of having an unevenness with an average interval of 6.5 to 20 μm and an average height of 0.35 to 1 μm alternately present The polypropylene fiber has the above-described specific irregularities on the fiber surface, so that the entanglement between the polypropylene fibers constituting the sheet-like fiber structure is strengthened, It is possible to obtain a sheet-like fiber structure that is excellent in stickiness, shape retention, and the like and excellent in water retention.

  The present invention is “with a fiber strength of 7 cN / dtex or more, a single fiber fineness of 0.1 to 3 dtex, and a DSC characteristic as defined in the present invention [an endothermic peak shape by DSC measurement is a half-value width of 10 ° C. or less. With a single shape having a melting enthalpy change amount (ΔH) of 125 J / g or more] and the above-mentioned specific unevenness characteristics (a large-diameter raised portion and a small-diameter non-raised portion on the surface along the fiber axis) And a sheet-like fiber structure formed by using a polypropylene fiber having an unevenness with an average interval of 6.5 to 20 μm and an average height of 0.35 to 1 μm. . The sheet-like fiber structure of the present invention formed using such polypropylene fibers is further excellent in properties such as water retention, heat resistance and strength.

  The shape (transverse cross-sectional shape) of the above-described polypropylene fiber forming the sheet-like fiber structure of the present invention is not particularly limited, and may be a solid circular cross-sectional shape, or other irregular cross-sectional shape. Either may be sufficient. Specific examples of the case where the cross section of the fiber has an irregular cross section include a flat shape, a cross shape, a Y shape, a T shape, a V shape, a star shape, a multi-leaf shape, an array shape, and a hollow shape. .

As long as the object of the present invention is not hindered, the polypropylene fibers forming the sheet-like fiber structure of the present invention are, for example, heat stabilizers, ultraviolet absorbers, antioxidants, colorants, fillers, antistatic agents and the like. You may contain 1 type, or 2 or more types.
The polypropylene fiber forming the sheet-like fiber structure of the present invention may not be subjected to surface treatment depending on the use of the sheet-like fiber structure, or may have improved affinity with various substances, charging For the purpose of prevention and stabilization of the treatment agent, the surface treatment may be performed with any surface treatment agent.
When using surface-treated polypropylene fibers, specific examples of the surface treatment agent that can be used include polyoxyethylene softanol, fatty acid potassium soap, alkyl phosphate potassium salt, and dialkylthiodipropionate. , Di-2-ethylhexylsulfosuccinate sodium salt, polyethylene glycol fatty acid ester, polyoxyethylene decyl ether phosphate potassium salt, polyoxyethylene castor oil ether, alkansulfonate sodium salt, isooctyl palmitate, isooctyl stearate, Isocetyl phosphate potassium salt, coconut fatty acid amide, oleyl alcohol, polyoxyethylene alkyl ether, dioctyl flufosuccinate sodium salt, polyoxye Ren decyl ether phosphate amine salts, and the like polyethylene glycol coconut fatty acid ester.

The production method of the polypropylene fiber forming the sheet-like fiber structure of the present invention is not particularly limited, the fiber strength is 7 cN / dtex or more, and the above-mentioned single fiber fineness and unevenness characteristics (single fiber fineness is 0.1 to 3 dtex and The characteristic is that the surface has irregularities with an average interval of 6.5 to 20 μm and an average height of 0.35 to 1 μm. Polypropylene fiber having a fiber strength of 7 cN / dtex or more and the above-mentioned DSC characteristics [a single shape having an endothermic peak shape of 10 ° C. or less by DSC measurement and a melting enthalpy change amount (ΔH) of 125 J / G or more], or a polypropylene fiber having the above-mentioned fiber strength, unevenness characteristics and DSC characteristics Any method can be used as long as it can be used.
Among them, the polypropylene fiber forming the sheet-like fiber structure of the present invention is produced by melt spinning a polypropylene having an IPF of 94% or more to produce a polypropylene unstretched fiber (unstretched yarn), and cooling and solidifying it. The cooled and solidified unstretched polypropylene fiber can be smoothly produced by the method described below for pre-stretching and post-stretching under specific conditions.

First, in producing polypropylene unstretched fibers by melt spinning polypropylene, a method of cooling and solidifying a polypropylene having an IPF of 94% or more at a spinning speed of 200 to 3500 m / min, particularly 300 to 2000 m / min. Is preferably employed.
The melt spinning of polypropylene and the cooling and solidification of the melt-spun polypropylene fiber can be performed by a usual method. Generally, after polypropylene is melt-kneaded at 200 to 300 ° C., it is melted from a spinneret at 220 to 280 ° C. A method of cooling and solidifying by blowing a cooling gas (air or the like) at 5 to 50 ° C. is used.
The single fiber fineness of the unstretched polypropylene fiber is not particularly limited and can be determined according to the draw ratio in the stretching step, the use of the finally obtained polypropylene fiber, etc., but generally 0.3 to 90 dtex, In particular, it is preferably 1 to 60 dtex from the viewpoint of easiness of stretching and strength.

In the production of the polypropylene fiber forming the sheet-like fiber structure of the present invention, when melt spinning is performed at a low spinning speed (generally when the spinning speed is about 200 to 1000 m / min), cooling is performed after melt spinning. Polypropylene unstretched fiber (unstretched yarn) obtained by solidification is stretched at a high magnification in the next stretching step (generally, a total stretching ratio of 5 to 20 times), thereby having high strength and high heat resistance, In particular, a polypropylene fiber having a fiber strength of 7 cN / dtex or more, a single shape having an endothermic peak shape of 10 ° C. or less by DSC measurement, and a melting enthalpy change (ΔH) of 125 J / g or more is smooth. Can be manufactured.
On the other hand, when melt spinning is performed at a high spinning speed (generally when the spinning speed is about 1000 to 3500 m / min), polypropylene unstretched fibers (unstretched yarn) obtained by cooling and solidifying after melt spinning are stretched. Even when the draw ratio at that time is low (generally, the total draw ratio is 3.9 to 7 times), the orientation at the stage of cooling and solidifying the melt-spun fiber is high, and as a result, the fiber strength is 7 cN / dtex or more and As a result, it is possible to smoothly produce a polypropylene fiber having the same DS characteristics and excellent strength and heat resistance.

In the production of polypropylene fiber, the cooled and solidified polypropylene unstretched fiber (unstretched yarn) may be subjected to a stretching process without being wound, or may be subjected to a subsequent stretching process while being unwound and then unwound. Among them, it is preferable to perform the next stretching treatment while winding after winding once, because it is easy to control and manage the stretching conditions.
The polypropylene fiber forming the sheet-like fiber structure of the present invention is a polypropylene solid unstretched fiber (unstretched yarn) that has been cooled and solidified, and has a total stretch ratio (total stretch ratio of pre-stretch and post-stretch) of 3.9 to 20 times. After pre-stretching at a temperature of 120 to 150 ° C. and a stretching ratio of 3 to 10 times, at a temperature of 170 to 190 ° C., a deformation rate of 1.5 to 15 times and a stretching tension of 1.0 to 2.5 cN / It can be smoothly produced by post-drawing at a draw ratio of 1.2 to 3.0 times under dtex conditions.

The above-described pre-stretching and post-stretching are preferably performed using a hot air furnace or a hot plate from the viewpoint that the stretching process is performed smoothly. Both pre-stretching and post-stretching may be performed using a hot air furnace, both pre-stretching and post-stretching may be performed using a hot plate, or pre-stretching is performed using a hot air furnace, and post-stretching. A hot plate may be performed, or pre-stretching may be performed using a hot plate, and post-stretching may be performed using a hot air furnace.
When pre-stretching and / or post-stretching is performed using a hot air furnace, the above temperature at the time of pre-stretching and the above temperature at the time of post-stretching refer to the atmospheric temperature of the hot air furnace, and the pre-stretching and / or post-stretching is performed on a hot plate. When performing using, the said temperature at the time of pre-stretching and the said temperature at the time of back stretching say the temperature of a hot plate.

Pre-stretching of the polypropylene unstretched fiber (unstretched yarn) formed by cooling and solidification may be performed in one stage or in multiple stages, and is generally preferably performed in one to three stages. .
In addition, the post-drawing of the drawn polypropylene fiber (drawn yarn) that has been pre-drawn may be performed in one stage or may be performed in multiple stages, and is generally preferably performed in one to five stages.
In performing the stretching treatment, a method may be employed in which a polypropylene stretched fiber (stretched yarn) obtained by pre-stretching is continuously wound without being wound, or after-stretching, or a polypropylene stretched fiber obtained by pre-stretching. A method may be employed in which the (drawn yarn) is cooled (generally at about room temperature) and wound up and then unwound again and then drawn. Among them, the latter method in which a polypropylene drawn fiber (drawn yarn) obtained by pre-drawing is once wound, rewound and then drawn is smoother than the polypropylene fiber having the above-described characteristics used in the composite material of the present invention. It is preferable from the point which can be obtained.

In the pre-drawing, polypropylene undrawn fiber (undrawn yarn) formed by cooling and solidification is introduced into a hot air oven having a temperature (atmospheric temperature) of 120 to 150 ° C, particularly 125 to 140 ° C, or a temperature of 120 to 150. It is preferably carried out in contact with a heat plate at 125 [deg.] C., particularly 125-140 [deg.] C., in a single stage or multiple stages at a stretching ratio of 3 to 10 times, particularly 3 to 5 times.
In addition, the post-stretching is a polypropylene stretched fiber (drawn yarn) obtained by pre-stretching under the above-described conditions, and the temperature (atmosphere temperature) is 170 to 190 ° C, more preferably 170 to 185 ° C, particularly 170 to 180 ° C. It is introduced into a hot stove or brought into contact with a hot plate having a temperature of 170 to 190 ° C., further 170 to 185 ° C., particularly 170 to 180 ° C., and a draw ratio of 1.2 to 3.0 times in one or more stages. In particular, it is preferably performed at 1.3 to 2.5 times.
When post-stretching is performed using a hot air furnace or a stretching plate, the atmospheric temperature of the hot air furnace or the stretching plate temperature is set to a temperature higher than the endothermic start temperature + 10 ° C. in the DSC curve of the polypropylene fiber immediately before the post-stretching treatment. It is preferable to perform post-stretching.
The total draw ratio of pre-stretching and post-stretching is preferably 3.9 to 20 times, more preferably 4.5 to 11 times, and still more preferably 4.7 to 10.5 times.
Further, the melt spinning speed for producing polypropylene unstretched fibers (unstretched yarn) was A (m / min), and the total stretch ratio after the above-described pre-stretching and post-stretching was defined as B (times). Sometimes, the value of A × B is in the range of 3000 to 17000 (m · times / min), especially 3500 to 15000 (m · times / min), and the polypropylene is melt-spun and the above-mentioned pre-stretching and When the post-drawing is performed, the target polypropylene fiber can be produced smoothly.

Here, the above-mentioned draw ratio in the pre-drawing is obtained by dividing the length of the fiber (yarn) immediately after being discharged from the pre-drawing step by the length of the undrawn fiber (undrawn yarn) introduced in the pre-drawing step. The drawing ratio in the post-drawing is the value obtained by dividing the length of the fiber (yarn) immediately after being discharged from the post-drawing step by the length of the fiber (yarn) introduced in the post-drawing step. Say.
The total draw ratio of the above-mentioned pre-drawing and post-drawing is the length of the undrawn fiber (undrawn yarn) introduced into the pre-drawing step by the length of the fiber (yarn) immediately after being discharged from the post-drawing step. The value divided by the above.

The post-stretching employs the above-described temperature (170 to 190 ° C.) and stretch ratio (1.2 to 3.0 times), a deformation rate of 1.5 to 15 times / min, and a stretching tension of 1.0 to 2. Adopting the condition of 5 cN / dtex. By adopting such post-drawing conditions, it is possible to obtain a polypropylene fiber having the above-described characteristics used in the present invention.
The deformation rate at the time of post-drawing is preferably 1.6 to 12 times / min, and more preferably 1.7 to 10 times / min.
The stretching tension during post-stretching is preferably 1.1 to 2.5 cN / dtex, more preferably 1.3 to 2.5 cN / dtex.

Here, the above-described deformation rate in post-stretching is the time (minutes) required for post-stretching the draw ratio (times) in post-stretching [in the case of post-stretching in a hot air furnace, the fiber (yarn) is in the hot air path. When the film was post-stretched with the stretching plate for the existing time, the value divided by the time when the fiber (yarn) was in contact with the stretching plate], and when post-stretching was performed in multiple stages, the final post-stretching A value obtained by dividing the stretching ratio (total stretching ratio) by the total stretching time required for post-stretching.
The drawing tension in the post-drawing is measured by using a tensiometer for the yarn tension immediately after the final drawing in the post-drawing.

  Moreover, after extending | stretching a polypropylene fiber on the above-mentioned conditions, you may give a heat setting or a shrinking process. The treatment temperature and shrinkage rate at that time are not particularly limited as long as the properties of the polypropylene fiber used in the present invention are not impaired.

  The above-described method for producing a polypropylene fiber by pre-stretching a polypropylene unstretched fiber obtained by melt-spinning polypropylene having an IPF of 94% or more and then solidifying by cooling, under the above-described conditions, and then post-stretching under the above-described conditions. The polypropylene fiber excellent in heat resistance and strength, in particular, the endothermic peak shape by DSC measurement is a single shape having a half width of 10 ° C. or less, the amount of change in melting enthalpy (ΔH) is 125 J / g or more, and A polypropylene fiber having a fiber strength of 7 cN / dtex or more and excellent in heat resistance and strength can be produced smoothly.

  Furthermore, when polypropylene polypropylene having an IPF of 94% or more is melt-spun and then cooled and solidified, the polypropylene unstretched fiber is pre-stretched under the above-described conditions and then further stretched under the above-described conditions to produce a polypropylene fiber. In addition, by adjusting the single fiber fineness of the polypropylene unstretched fiber to be supplied to the pre-drawing step, the draw ratio in the pre-drawing and / or post-drawing, etc., the single fiber fineness is finally 3 dtex or less, particularly 0.1-3 dtex. The above-mentioned fiber strength of 7 cN / dtex or more and the above-mentioned specific DSC characteristics [the endothermic peak shape by DSC is a single shape having a half width of 10 ° C. or less, and the melting enthalpy Characteristic that the amount of change (ΔH) is 125 J / g or more] and a large-diameter raised portion on the surface A polypropylene fiber having a specific concavo-convex structure, “small bulges having small diameters are alternately present along the fiber axis, and have an average interval of 6.5 to 20 μm and an average height of 0.35 to 1 μm”. Obtainable. Since this polypropylene fiber is excellent in heat resistance and strength and has high water retention by having the above-mentioned specific irregularities on the surface, by forming a sheet-like fiber structure using this polypropylene fiber, A sheet-like fiber structure excellent in water retention, mechanical properties and heat resistance is obtained.

The sheet-like fiber structure of the present invention contains the above-described polypropylene fiber in a proportion of 50% by mass or more based on the mass of the sheet-like fiber structure, and preferably contains 60% by mass or more. More preferably, it is contained in a proportion of 65% by mass or more.
When the content ratio of the above-described polypropylene fiber in the sheet-like fiber structure is too small, excellent performance such as high water retention performance, heat resistance, strength and the like of the polypropylene fiber cannot be imparted to the sheet-like fiber structure.

The type and form of the sheet-like fiber structure of the present invention are not particularly limited, and may be any sheet-like fiber structure containing the above-described polypropylene fiber at a ratio of 50% by mass or more, for example, woven / knitted fabric, nonwoven fabric, Examples thereof include synthetic paper, a net-like material, and a laminated fiber structure obtained by laminating two or more of them.
When the sheet-like fiber structure of the present invention is a woven fabric, for example, a plain woven fabric, an oblique woven fabric, a satin woven fabric, a suede woven fabric manufactured using a jet loom, a sulzer loom, a lapia loom, a dobby loom, a jacquard loom, etc. It may be any of a woven fabric, a multiaxial fabric, a multilayer fabric, and the like.
Moreover, when the sheet-like fiber structure of the present invention is a knitted fabric, it can be various knitted fabrics obtained by using a circular knitting machine, a warp knitting machine, a weft knitting machine, a tricot machine or the like.
When the sheet-like fiber structure of the present invention is a nonwoven fabric, it may be any of a wet papermaking nonwoven fabric, a needle punched nonwoven fabric, a thermal bond nonwoven fabric, an airlaid nonwoven fabric, a spunlace nonwoven fabric, and the like.

  In the case where the sheet-like fiber structure of the present invention contains other fibers together with the above-described polypropylene fibers, the types of other fibers are not particularly limited. For example, natural fibers such as cotton, silk, wool, hemp, and polyester fibers , Nylon fibers, acrylic fibers, polyvinyl alcohol fibers, polypropylene fibers other than the polypropylene fibers described above, polyolefin fibers such as polyethylene fibers, synthetic fibers such as polyvinylidene chloride fibers, aramid fibers, polyarylate fibers, and half of viscose, rayon, etc. One or two or more of inorganic fibers such as synthetic fibers, glass fibers, and carbon fibers can be used in a proportion of 50% by mass or less, preferably 40% by mass or less, more preferably 35% by mass or less.

  When other fibers are used in combination with the above-described polypropylene fibers, the combined form is not particularly limited, and can be appropriately selected according to the type, form, use, etc. of the sheet-like fiber structure. The sheet-like fiber structure of the present invention may be, for example, a woven or knitted fabric or a net-like material produced using a yarn made of the above-described polypropylene fiber and a yarn made of another fiber. It may be a woven or knitted fabric or a net-like material produced using yarns obtained by blending fibers, a nonwoven fabric produced by blending the above-mentioned polypropylene fibers and other fibers, or synthetic paper, It may be a laminate of the woven or knitted fabric or nonwoven fabric made of the polypropylene fibers described above and the woven or knitted fabric or nonwoven fabric made of other fibers.

  Although not limited in any way, examples of the sheet-like fiber structure of the present invention include woven fabrics, knitted fabrics, nets, and the above-described polypropylene fibers and other fabrics produced by using the above-mentioned polypropylene fibers alone. Textiles, knitted fabrics, nets, yarns composed of the above-mentioned polypropylene fibers and yarns composed of other synthetic fibers and / or produced using blended yarns obtained by blending synthetic fibers, natural fibers and / or semi-synthetic fibers Examples thereof include woven fabrics, knitted fabrics, and nets manufactured by combining yarns made of natural fibers. For example, when a knitted fabric (knit) is produced by using a yarn obtained by mixing the above-mentioned polypropylene fiber and cotton, or a combination of the above-described yarn made of polypropylene fiber and a cotton spun yarn, it has excellent heat resistance and is a floor of a gymnasium. Even if it rubs, it does not melt, and it can obtain a knitted fabric (knit) suitable for sports clothing that is lightweight, has high water retention and is excellent in sweat absorption.

  In addition, when the sheet-like fiber structure of the present invention is a nonwoven fabric or synthetic paper, for example, a felt-like fiber manufactured by crimping, cutting, and needle punching after carding the above-described polypropylene fiber. Non-woven fabric, binder fiber having at least a surface portion that melts at a lower temperature than the polypropylene fiber when crimping, cutting, and carding the above-described polypropylene fiber (for example, the core portion is made of polypropylene and the sheath portion is made of polyethylene) A dry nonwoven fabric made by mixing and heat-treating polypropylene fibers with binder fibers, and making a water-dispersed slurry by mixing binder fibers with the short fibers made of the above-mentioned polypropylene fibers. And wet nonwoven fabric (synthetic paper) obtained by drying It is possible. The nonwoven fabric of the present invention formed using the above-described polypropylene fiber has high heat resistance, and the nonwoven fabric can be subjected to treatment processes such as an adhesion treatment process and a drying treatment process at a high temperature. Can be manufactured at a high production rate.

  The sheet-like fiber structure of the present invention formed by using the above-described polypropylene fiber has a high water retention rate and excellent water retention, and is excellent in heat resistance, mechanical properties, chemical resistance, and the like. Can be used effectively for various applications such as industrial filters, alkaline secondary battery separators, polypropylene fiber reinforced polyolefin sheets, clothing fabrics (woven fabrics, non-woven fabrics, etc.), sanitary goods, and daily goods. .

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. In the following examples, etc., the isotactic pentad fraction (IPF) of polypropylene, the stretching tension at the time of stretching, the DSC characteristics of the polypropylene fiber, the single fiber fineness, the fiber strength, the average spacing and the average height of the irregularities on the fiber surface The water retention of polypropylene fiber, the water retention of the sheet-like fiber structure (polypropylene fiber nonwoven fabric), and the processability of the cylinder drying treatment were measured, calculated or evaluated by the methods described below.

(1) Isotactic pentad fraction (IPF) of polypropylene:
Using a superconducting nuclear magnetic resonance apparatus (“Lambda500” manufactured by JEOL Ltd.), the IPF of polypropylene was determined according to “ ¹³ C-NMR spectrum method” described in Non-Patent Document 1. Specifically, the content ratio (fraction) of propylene units (isotactic pentad units) in which five propylene monomer units are continuously isotactically bonded in a ¹³ C-NMR spectrum in polypropylene (%) ) To obtain IPF. At that time, the peak assignment in the ¹³ C-NMR spectrum was determined according to the method described in Non-Patent Document 2.

(2) Stretch tension during stretching:
Using a load tension measuring instrument ("DTMX-5B" manufactured by Nidec Simpo Co., Ltd.), measure the tension of the yarn immediately after coming out of the drawing furnace (hot air furnace) or just after leaving the drawing plate. It was set as the stretching tension (cN / dtex).

(3) Fineness of polypropylene fiber (single fiber fineness):
The polypropylene fiber was left to stand for 5 days in an atmosphere at a temperature of 20 ° C. and a relative humidity of 65%, and then the humidity was adjusted. Then, a fixed length (900 mm) of the conditioned polypropylene fiber (monofilament) was taken and its mass was measured. The fineness was calculated. About the same humidity control polypropylene fiber, the same measurement operation as the above was performed 10 times, and the average value was taken as the fineness (single fiber fineness) of the polypropylene fiber. In addition, when the fineness was not able to be measured by mass measurement of a fixed length because the fiber was thin, the fineness was measured using the fineness measuring device (“VIBROMAT M” manufactured by Texttechno) for the same humidity control fiber.

(4) Fiber strength of polypropylene fiber:
The polypropylene fiber is left to stand for 5 days in an atmosphere of a temperature of 20 ° C. and a relative humidity of 65%, and then the humidity is adjusted. Then, the polypropylene fiber (single fiber) is cut to a length of 60 mm to obtain a sample. A single fiber is gripped at both ends (gripping from both ends to 10 mm), and using a fiber strength measuring device (“FAFEGRAPH M” manufactured by Texttechno) under an environment of a temperature of 20 ° C. and a relative humidity of 65%, a tensile speed of 60 mm The tensile strength at the time of cutting was measured, and the fiber strength (cN / dtex) was determined by dividing the value by the fineness of the polypropylene single fiber. In addition, the same operation was performed 10 times about the same polypropylene fiber, fiber strength was calculated | required, the average value was taken, and it was set as the fiber strength of polypropylene fiber (polypropylene single fiber).

(5) Average spacing and average height of irregularities on the fiber surface of polypropylene fiber:
Using a scanning electron microscope ("S-510" manufactured by HITACHI), polypropylene fibers (single fibers) were photographed at a magnification of 1000 times from the direction perpendicular to the fiber axis. According to the method described above based on 1, the average interval and the average height of the irregularities on the fiber surface were obtained. In calculating the average interval and the average height, for ten polypropylene fibers (single fibers), five locations (interval of 10 cm between each measurement location) were selected for each fiber, and the uneven spacing at each location and The height was measured (total of 50 locations), and the average value thereof was taken as the average interval (μm) and the average height (μm).

(6) DSC measurement of polypropylene fiber:
Polypropylene fibers were allowed to stand for 5 days in an atmosphere at a temperature of 20 ° C. and a relative humidity of 65%, and then the humidity was adjusted. Then, the polypropylene fibers were cut to a length of 1 mm, and 5 mg was weighed to obtain an aluminum pan (capacity 100 μL) No. 51119872), sealed using an aluminum pan cover (Meteller Toledo "No. 51119871"), and in a nitrogen atmosphere using a scanning differential calorimeter (TA Instruments "DSC2010"). From the 1st run DSC curve measured at a heating rate of 10 ° C./min, the half-value width (° C.) of the endothermic peak and the amount of change in melting enthalpy (ΔH) (J / g) are shown in FIG. 2 and FIG. In particular, it was determined by the method described above with reference to FIG.

(7) Water retention rate of polypropylene fiber and sheet-like fiber structure (nonwoven fabric made of polypropylene fiber):
1 g of polypropylene fiber or sheet-like fiber structure (nonwoven fabric made of polypropylene fiber) was sampled and dried at 105 ° C. for 5 hours, and its mass (M1) was measured. The dried sample was immersed in 30 ml of ion-exchanged water, allowed to stand at 20 ° C. for 10 minutes, then taken out and left in an exposed state (without wrapping with other materials), a tabletop centrifuge (“H” manufactured by KOKUSAN -27F "), centrifuged at a rotational speed of 3000 rpm for 5 minutes at a temperature of 20 ° C, measured the mass (M2) at that time, and determined the water retention rate (mass%) from the following formula (1). )

Water retention (mass%) = {(M2-M1) / M1} × 100 (1)

(8) Processability of cylinder drying process:
The processability of the cylinder drying process was evaluated according to the following evaluation criteria.
[Evaluation criteria for processability of cylinder drying]
-Good : There is no adhesion of the polypropylene fiber sheet to the cylinder, it passes well, the texture after the drying treatment is good, and the water retention rate is not reduced.
-Poor : The polypropylene fiber sheet is stuck on the cylinder, and the permeability is poor, and the water retention rate decreases after the drying process.

<< Production Example 1 >> [Production of Polypropylene Fiber (a-1)]
(1) Polypropylene [“Y2000GV” manufactured by Prime Polymer Co., Ltd., IPF = 97%, MFR = 18 g / 10 min (230 ° C., load 2.16 kg)] is put into an extruder of a melt spinning apparatus and melt kneaded at 240 ° C. Then, from a spinneret attached to the spinning head at a temperature of 245 ° C. [24 holes (circular holes), hole diameter 0.2 mm], 22.3 g / min is discharged and polypropylene is unstretched at a take-up speed of 800 m / min. A yarn was produced, wound on a bobbin, and stored at room temperature (total fineness of polypropylene undrawn yarn = 288 dtex / 24 filament).
(2) The polypropylene undrawn yarn obtained in the above (1) is unwound from a bobbin, introduced into a hot air oven at a temperature of 128 ° C., and pre-drawn 4.6 times in two stages to obtain a polypropylene pre-drawn yarn. It was manufactured, wound on a bobbin and stored at room temperature (total fineness of polypropylene predrawn yarn = 63 dtex / 24 filament, endothermic onset temperature = 153.5 ° C.).
(3) The polypropylene pre-drawn yarn obtained in (2) above was unwound from a bobbin and introduced into a hot air oven at a temperature of 172 ° C., and the deformation rate was 1.7 times / minute and the draw tension was 1.18 cN / dtex. Under the conditions, polypropylene stretch yarn (total fineness = 48 dtex / 24 filament) [polypropylene fiber (a-1)] having a total draw ratio of 6.0 times was produced by post-drawing in 1.3 stages in three stages. .
(4) About the polypropylene drawn yarn [polypropylene fiber (a-1)] obtained in the above (3), DSC measurement [measurement of endothermic peak shape, half width, amount of change in melting enthalpy (ΔH)] and fiber Measurement of strength, surface unevenness dimensions (average interval and average height of unevenness) and water retention rate were carried out by the methods described above, and the results were as shown in Table 1 below.
Moreover, when the polypropylene drawn yarn [polypropylene fiber (a-1)] obtained in the above (3) was photographed using a scanning electron microscope (“S-510” manufactured by HITACHI) (magnification 1000 times). As shown in FIG.

<< Production Example 2 >> [Production of polypropylene fiber (a-2)]
(1) A polypropylene undrawn yarn was produced in the same manner as in (1) of Production Example 1 except that the undrawn yarn take-up speed was changed to 3000 m / min in Production Example 1 (1), and a bobbin was produced. And wound at room temperature (total fineness of polypropylene undrawn yarn = 214 dtex / 24 filament).
(2) The polypropylene undrawn yarn obtained in (1) above is unwound from a bobbin, introduced into a hot air oven at a temperature of 128 ° C., pre-drawn 3.1 times in two steps, and a polypropylene pre-drawn yarn Was wound around a bobbin and stored at room temperature (total fineness of polypropylene predrawn yarn = 69 dtex / 24 filament, endothermic onset temperature = 155.3 ° C.).
(3) The polypropylene pre-drawn yarn obtained in (2) above was unwound from a bobbin and introduced into a hot air oven at a temperature of 172 ° C., and the deformation rate was 1.8 times / min and the draw tension was 1.34 cN / dtex. Under the conditions, a polypropylene drawn yarn (total fineness = 46 dtex / 24 filament) [polypropylene fiber (a-2)] having a total draw ratio of 4.7 times was produced by post-drawing in three stages to 1.5 times. .
(4) For the polypropylene drawn yarn [polypropylene fiber (a-2)] obtained in (3) above, DSC measurement [measurement of endothermic peak shape, half width, amount of change in melting enthalpy (ΔH)], and fiber Measurements of strength, surface unevenness dimensions (average interval and average height of unevenness) and water retention were carried out by the methods described above. The results were as shown in Table 1 below.

<< Production Example 3 >> [Production of Polypropylene Fiber (a-3)]
(1) The same polypropylene used in (1) of Production Example 1 was put into an extruder of a melt spinning apparatus, melted and kneaded at 240 ° C., and a spinneret with a temperature of 245 ° C. attached to the spinning head [number of holes 48 Each piece (cross-shaped hole) was discharged at a rate of 20.2 g / min from a hole diameter of 0.2 mm], and undrawn polypropylene yarn was produced at a take-up speed of 800 m / min, wound on a bobbin and stored at room temperature (polypropylene). Total fineness of undrawn yarn = 436 dtex / 48 filament).
(2) The polypropylene undrawn yarn obtained in (1) above is unwound from a bobbin, introduced into a hot air oven at a temperature of 138 ° C., pre-drawn 3.9 times in two stages, and a polypropylene pre-drawn yarn Was wound around a bobbin and stored at room temperature (total fineness of polypropylene pre-drawn yarn = 112 dtex / 48 filament, endothermic temperature = 155.2 ° C.).
(3) The polypropylene pre-drawn yarn obtained in (2) above was unwound from a bobbin and introduced into a hot air oven at a temperature of 172 ° C., and the deformation rate was 2.1 times / minute and the draw tension was 1.12 cN / dtex. Under the conditions, a polypropylene drawn yarn (total fineness = 86 dtex / 48 filament) [polypropylene fiber (a-3)] having a total draw ratio of 5.1 times was produced by post-drawing 1.3 times in one stage. .
(4) About the polypropylene drawn yarn [polypropylene fiber (a-3)] obtained in the above (3), DSC measurement [measurement of endothermic peak shape, half width, amount of change in melting enthalpy (ΔH)] and fiber Measurements of strength, surface unevenness dimensions (average interval and average height of unevenness) and water retention were carried out by the methods described above. The results were as shown in Table 1 below.

<< Production Example 4 >> [Production of Polypropylene Fiber (a-4)]
(1) The same melt spinning conditions as (1) of Production Example 1 using polypropylene [“ZS1337A” manufactured by Prime Polymer Co., Ltd., IPF = 96%, MFR = 20 g / 10 min (230 ° C., load 2.16 kg)] Was used to produce a polypropylene undrawn yarn and wound around a bobbin (total fineness of polypropylene undrawn yarn = 288 dtex / 24 filament).
(2) The polypropylene undrawn yarn obtained in the above (1) is unwound from a bobbin, introduced into a hot air oven at a temperature of 135 ° C., pre-drawn 4.8 times in two stages, and a polypropylene pre-drawn yarn Was wound around a bobbin and stored at room temperature (total fineness of polypropylene predrawn yarn = 60 dtex / 24 filament, endothermic onset temperature = 152.0 ° C.).
(3) The polypropylene pre-drawn yarn obtained in (2) above is unwound from a bobbin and introduced into a hot air oven at a temperature of 172 ° C., and the deformation rate is 1.6 times / minute and the drawing tension is 1.33 cN / dtex. Under the conditions, polypropylene stretch yarn (total fineness = 50 dtex / 24 filament) [polypropylene fiber (a-4)] having a total draw ratio of 8.6 times was produced by post-drawing in three stages to 1.8 times. .
(4) DSC measurement [measurement of endothermic peak shape, half width, amount of change in melting enthalpy (ΔH)] and fiber for the drawn polypropylene yarn [polypropylene fiber (a-4)] obtained in (3) above Measurements of strength, surface unevenness dimensions (average interval and average height of unevenness) and water retention were carried out by the methods described above. The results were as shown in Table 1 below.

<< Production Example 5 >> [Production of polypropylene fiber (a-5)]
(1) Using polypropylene [IPF = 98%, MFR = 16 g / 10 min (230 ° C., load 2.16 kg)], adopting the same melt spinning conditions as in (1) of Production Example 1 and unstretched polypropylene A yarn was produced and wound on a bobbin (total fineness of undrawn yarn = 293 dtex / 24 filament).
(2) The polypropylene undrawn yarn obtained in the above (1) is unwound from a bobbin, introduced into a hot air oven at a temperature of 128 ° C., and pre-drawn 4.6 times in two stages to obtain a polypropylene pre-drawn yarn. It was manufactured and wound on a bobbin and stored at room temperature (total fineness of polypropylene predrawn yarn = 64 dtex / 24 filament, endothermic onset temperature = 156.4 ° C.).
(3) The polypropylene pre-drawn yarn obtained in (2) above was unwound from a bobbin and introduced into a hot air oven at a temperature of 178 ° C., and the deformation rate was 2.8 times / min and the drawing tension was 1.54 cN / dtex. Under the conditions, polypropylene stretch yarn (total fineness = 29 dtex / 24 filament) [polypropylene fiber (a-5)] having a total draw ratio of 10.1 times was produced by post-drawing to 2.2 times in four stages. .
(4) DSC measurement [measurement of endothermic peak shape, half-value width, amount of change in melting enthalpy (ΔH)] and fiber for the drawn polypropylene yarn [polypropylene fiber (a-5)] obtained in the above (3) The measurement of strength, friction-fusibility, surface unevenness dimensions (average interval and average height of unevenness) and water retention rate were carried out by the methods described above. The results were as shown in Table 1 below.

<< Production Example 6 >> [Production of Polypropylene Fiber (a-6)]
(1) Polypropylene [IPF = 98%, MFR = 16 g / 10 min (230 ° C., load 2.16 kg)] and polypropylene [“Y3002G” manufactured by Prime Polymer, IPF = 93%, MFR = 30 g / 10 min (230 C., load 2.16 kg)] in a mass ratio of 1: 1 (IPF of the mixture = 95.5%), using the same melt spinning conditions as in Production Example 1 (1), A polypropylene undrawn yarn was produced and wound on a bobbin (total fineness of polypropylene undrawn yarn = 288 dtex / 24 filament).
(2) The polypropylene undrawn yarn obtained in the above (1) is unwound from a bobbin, introduced into a hot air oven at a temperature of 128 ° C., and pre-drawn 4.6 times in two stages, and the polypropylene pre-drawn yarn Was wound around a bobbin and stored at room temperature (total fineness of polypropylene predrawn yarn = 63 dtex / 24 filament, endothermic onset temperature = 152.5 ° C.).
(3) The polypropylene pre-drawn yarn obtained in (2) above was unwound from a bobbin and introduced into a hot air oven at a temperature of 171 ° C., and the deformation rate was 1.7 times / min and the draw tension was 1.18 cN / dtex. Under the conditions, polypropylene stretched yarn (total fineness = 48 dtex / 24 filament) [polypropylene fiber (a-6)] having a total draw ratio of 6.0 times was produced by post-drawing in 1.3 stages in three stages. .
(4) About the drawn polypropylene yarn [polypropylene fiber (a-6)] obtained in (3) above, DSC measurement [measurement of endothermic peak shape, half width, amount of change in melting enthalpy (ΔH)], and fiber Measurement of strength, surface unevenness dimensions (average interval and average height of unevenness) and water retention rate were carried out by the methods described above, and the results were as shown in Table 1 below.

<< Production Example 7 >> [Production of Polypropylene Fiber (a-7)]
(1) A spinneret [24 holes (circular holes), hole diameter 0.2 mm] for producing core-sheath composite fibers is attached to a spinning head of a melt spinning apparatus, and polypropylene ("Y3002G" manufactured by Prime Polymer Co., IPF = 93%) using a core component and polypropylene [IPF = 98%, MFR = 16 g / 10 min (230 ° C., load 2.16 kg)] as a sheath component, and a mass ratio of core component: sheath component = 1: 2. , Melt-kneaded at 240 ° C., discharged from the spinneret (die temperature: 245 ° C.) at an amount of 22.3 g / min, and wound on a bobbin at a take-up speed of 800 m / min to produce a core-sheath type polypropylene undrawn yarn And stored at room temperature (total fineness of polypropylene undrawn yarn = 287 dtex / 24 filament).
(2) The polypropylene undrawn yarn obtained in the above (1) is unwound from a bobbin, introduced into a hot air oven at a temperature of 128 ° C., and pre-drawn 4.6 times in two stages to obtain a polypropylene pre-drawn yarn. It was manufactured and wound on a bobbin and stored at room temperature (total fineness of polypropylene predrawn yarn = 62 dtex / 24 filament, endothermic onset temperature = 152.2 ° C.).
(3) The polypropylene pre-drawn yarn obtained in (2) above was unwound from a bobbin and introduced into a hot air oven at a temperature of 171 ° C., and the deformation rate was 1.8 times / minute and the draw tension was 1.18 cN / dtex. Under the conditions, polypropylene stretched yarn (total fineness = 48 dtex / 24 filament) [polypropylene fiber (a-7)] having a total draw ratio of 6.0 times was produced by post-drawing in 1.3 stages in three stages. .
(4) About the polypropylene drawn yarn [polypropylene fiber (a-7)] obtained in (3) above, DSC measurement [measurement of endothermic peak shape, half width, amount of change in melting enthalpy (ΔH)] and fiber Measurements of strength, surface unevenness dimensions (average interval and average height of unevenness) and water retention were carried out by the methods described above. The results were as shown in Table 1 below.

<< Production Example 8 >> [Production of Polypropylene Fiber (a-8)]
(1) Using the same polypropylene as used in (1) of Production Example 1 and employing the same conditions as in (1) of Production Example 1, a polypropylene unstretched yarn was produced and wound on a bobbin.
(2) The polypropylene undrawn yarn obtained in the above (1) is unwound from a bobbin, introduced into a hot air oven at a temperature of 128 ° C., pre-drawn 4.6 times in one stage, and a polypropylene pre-drawn yarn Was wound around a bobbin and stored at room temperature (total fineness of polypropylene pre-drawn yarn = 63 dtex / 24 filament).
(3) The polypropylene pre-drawn yarn obtained in (2) above is unwound from a bobbin and brought into contact with a hot plate at a temperature of 172 ° C., with a deformation rate of 13.8 times / min and a draw tension of 1.43 cN / dtex. Under the conditions, polypropylene stretch yarn (total fineness = 39 dtex / 24 filament) having a total draw ratio of 7.4 times after post-stretching 1.6 times in one stage (contact time to the heat plate = 15 seconds) [ Polypropylene fiber (a-8)] was produced.
(4) About the drawn polypropylene yarn [polypropylene fiber (a-8)] obtained in (3) above, DSC measurement [measurement of endothermic peak shape, half width, amount of change in melting enthalpy (ΔH)], and fiber Measurements of strength, surface unevenness dimensions (average interval and average height of unevenness) and water retention were carried out by the methods described above. The results were as shown in Table 1 below.

<< Production Example 9 >> [Production of Polypropylene Fiber (b-1)]
(1) Using polypropylene (“Y3002G” manufactured by Prime Polymer Co., Ltd., IPF = 93%), the same melt spinning conditions as in (1) of Production Example 1 were adopted to produce a polypropylene undrawn yarn and wound on a bobbin And stored at room temperature (total fineness of polypropylene undrawn yarn = 288 dtex / 24 filament).
(2) The polypropylene undrawn yarn obtained in the above (1) is unwound from a bobbin, introduced into a hot air oven at a temperature of 128 ° C., and pre-drawn 4.6 times in two stages, and the polypropylene pre-drawn yarn Was wound around a bobbin and stored at room temperature (total fineness of polypropylene predrawn yarn = 68 dtex / 24 filament, endothermic onset temperature = 151.8 ° C.).
(3) The polypropylene pre-drawn yarn obtained in (2) above was unwound from a bobbin and introduced into a hot air oven at a temperature of 171 ° C., and the deformation rate was 1.7 times / min and the draw tension was 0.96 cN / dtex. Under the conditions, polypropylene stretched yarn (total fineness = 48 dtex / 24 filament) [polypropylene fiber (b-1)] having a total draw ratio of 6.0 times was produced by post-drawing by 1.3 times in three stages. .
(4) About the polypropylene drawn yarn [polypropylene fiber (b-1)] obtained in (3) above, DSC measurement [measurement of endothermic peak shape, half-value width, change in melting enthalpy (ΔH)], and fiber When the strength and the water retention rate were measured by the methods described above, the results were as shown in Table 1 below. The polypropylene fiber obtained in Production Example 9 did not have irregularities on the surface.

<< Production Example 10 >> [Production of Polypropylene Fiber (b-2)]
(1) The same operation as (1) and (2) of Production Example 1 was performed to produce a polypropylene pre-drawn yarn [polypropylene fiber (b-2)].
(2) About the polypropylene predrawn yarn [polypropylene fiber (b-2)] obtained in (1) above, DSC measurement [measurement of endothermic peak shape, half-value width, change in melting enthalpy (ΔH)], and When the fiber strength and the water retention rate were measured by the methods described above, the results were as shown in Table 1 below. In addition, the polypropylene fiber obtained by this manufacture example 10 did not have an unevenness | corrugation on the surface.

<< Production Example 11 >> [Production of Polypropylene Fiber (b-3)]
(1) Using the same polypropylene (“Y2000GV” manufactured by Prime Polymer Co., Ltd., IPF = 97%) as used in (1) of Production Example 1, the same melt spinning conditions as in (1) of Production Example 1 were adopted. A polypropylene undrawn yarn was produced and wound on a bobbin.
(2) The polypropylene undrawn yarn obtained in (1) above is unwound from a bobbin, introduced into a hot air oven at a temperature of 143 ° C., drawn 6.9 times in one stage, and drawn polypropylene yarn (total Fineness = 42 dtex / 24 filament) [polypropylene fiber (b-3)] was produced.
(3) About the polypropylene drawn yarn [polypropylene fiber (b-3)] obtained in (2) above, DSC measurement [measurement of endothermic peak shape, half-value width, amount of change in melting enthalpy (ΔH)], and fiber Measurements of strength, surface unevenness dimensions (average interval and average height of unevenness) and water retention were carried out by the methods described above. The results were as shown in Table 1 below.

<< Production Example 12 >> [Production of Polypropylene Fiber (b-4)]
(1) Polypropylene [“ZS1337A” manufactured by Prime Polymer Co., Ltd., IPF = 96%, MFR = 20 g / 10 min (230 ° C., load 2.16 kg)] is charged into an extruder of a melt spinning apparatus and melt kneaded at 300 ° C. Then, from the spinneret attached to the spinning head at a temperature of 320 ° C. [24 holes (circular holes), hole diameter 0.2 mm], 22.3 g / min is discharged and polypropylene is unstretched at a take-up speed of 600 m / min. A yarn was produced, wound on a bobbin, and stored at room temperature (“total fineness of polypropylene undrawn yarn = 304 dtex / 24 filament).
(2) The polypropylene unstretched yarn obtained in (1) above is unwound from the bobbin, pre-stretched 1.5 times in a single step with a heating roll at a temperature of 90 ° C., wound on the bobbin and stored at room temperature. (Total fineness of polypropylene pre-drawn yarn = 203 dtex / 24 filament, endothermic start temperature = 150.8 ° C.).
(3) The polypropylene pre-drawn yarn obtained in (2) above is unwound from a bobbin, introduced into a hot air oven at a temperature of 138 ° C., and post-drawn in a single step to 4.9 times, and the total draw ratio is A 7.4 times drawn polypropylene yarn (total fineness = 40.8 dtex / 24 filament) [polypropylene fiber (b-4)] was produced.
(4) About the polypropylene drawn yarn [polypropylene fiber (b-4)] obtained in the above (3), DSC measurement [measurement of endothermic peak shape, half-value width, amount of change in melting enthalpy (ΔH)], and fiber Measurements of strength, surface unevenness dimensions (average interval and average height of unevenness) and water retention were carried out by the methods described above. The results were as shown in Table 1 below.

<< Production Example 13 >> [Production of Polypropylene Fiber (b-5)]
(1) Melt spinning of the same polypropylene used in (1) of Production Example 1 [“Y2000Gv” manufactured by Prime Polymer Co., Ltd., IPF = 97%, MFR = 18 g / 10 min (230 ° C., load 2.16 kg)] The amount is 35.4 g / min from a spinneret (24 holes (circular holes), hole diameter 0.2 mm) having a temperature of 260 ° C. attached to the spinning head and charged into an extruder of the apparatus at 255 ° C. The polypropylene undrawn yarn was produced at a take-off speed of 600 m / min, wound on a bobbin and stored at room temperature (“total fineness of polypropylene undrawn yarn = 635 dtex / 24 filament).
(2) The polypropylene undrawn yarn obtained in the above (1) is unwound from a bobbin and drawn 11.5 times in a single stage by a steam tank at a temperature of 145 ° C. to obtain a polypropylene drawn yarn (total fineness = 55. 2 dtex / 24 filament) [polypropylene fiber (b-5)].
(3) About the polypropylene drawn yarn [polypropylene fiber (b-5)] obtained in (2) above, DSC measurement [measurement of endothermic peak shape, half width, amount of change in melting enthalpy (ΔH)] and fiber Measurements of strength, surface unevenness dimensions (average interval and average height of unevenness) and water retention were carried out by the methods described above. The results were as shown in Table 1 below.

<< Examples 1-8 >>
(1) Each of the polypropylene fibers (a-1) to (a-8) obtained in Production Examples 1 to 18 is cut into a fiber length of 51 mm to make a short fiber, carding, hydroentanglement treatment, calendar treatment (temperature) 140 ° C.) and cylinder drying treatment (temperature 170 ° C., transfer rate 50 cm / second) were sequentially performed to produce a sheet-like fiber structure (nonwoven fabric made of polypropylene fiber).
(2) When the water retention of the sheet-like fiber structure (polypropylene fiber nonwoven fabric) obtained in (1) above and the processability of the cylinder drying treatment were measured or evaluated by the methods described above, as shown in Table 2 below. Met.

<< Comparative Examples 1-5 >>
(1) Each of the polypropylene fibers (b-1) to (b-5) obtained in Production Examples 9 to 13 was cut into a fiber length of 51 mm to form short fibers, and under the same conditions as in Examples 1 to 8, Carding, hydroentanglement treatment, calendar treatment (temperature 140 ° C.) and cylinder drying treatment (temperature 170 ° C., transfer rate 50 cm / second) were sequentially performed to produce a sheet-like fiber structure (nonwoven fabric made of polypropylene fiber).
(2) When the water retention of the sheet-like fiber structure (polypropylene fiber nonwoven fabric) obtained in (1) above and the processability of the cylinder drying treatment were measured or evaluated by the methods described above, as shown in Table 2 below. Met.

As seen in Table 2 above, in Examples 1 to 8, the fiber strength is 7 cN / dtex or more, which is made of polypropylene having an IPF of 94% or more, and the single fiber fineness and the unevenness characteristics of the fiber surface are defined by the present invention. Polypropylene fiber satisfying the requirements, DSC characteristics satisfy the requirements defined in the present invention, or single fiber fineness, fiber surface unevenness characteristics and DSC characteristics satisfy the requirements defined in the present invention (a-1) The sheet-like fiber structure (polypropylene fiber nonwoven fabric) obtained in Examples 1 to 8 was produced by producing a sheet-like fiber structure (polypropylene fiber nonwoven fabric) using any one of (a-8). The water retention rate is as high as 10.2 to 25.0 mass%, the water retention is excellent, the heat resistance is further excellent, and the processability of the cylinder drying process is good.
On the other hand, in Comparative Examples 1 to 5, a sheet using any of polypropylene fibers (b-1) to (b-5) in which both the unevenness characteristics and the DSC characteristics on the fiber surface are out of the definition of the present invention. The sheet-like fiber structure (nonwoven fabric made of polypropylene fiber) obtained in Comparative Examples 1 to 5 has a water retention rate of 3.5 to 8.0% by mass by producing the fiber-like fiber structure. Compared to the sheet-like fiber structure (polypropylene fiber nonwoven fabric) obtained in 1 to 8, the water retention rate is significantly lower, the water retention is inferior, the processability of the cylinder drying process is poor, and the heat resistance However, it is greatly inferior to the sheet-like fiber structure (polypropylene fiber nonwoven fabric) obtained in Examples 1-8.

  The sheet-like fiber structure of the present invention is formed using polypropylene fibers having specific irregularities on the surface, high crystallinity, a uniform crystal structure, extremely excellent heat resistance, and higher fiber strength. Therefore, it is excellent in water retention, heat resistance, and strength, and can be effectively used for various applications such as filters, separators, reinforcing materials, clothing, wipers, and makeup removers.

It is the figure which showed how to obtain | require the average space | interval and average height of an unevenness | corrugation while showing typically the uneven | corrugated shape of the polypropylene fiber which forms the sheet-like fiber structure of this invention. It is the figure which showed typically the endothermic peak shape by DSC measurement in a polypropylene fiber. It is the figure which showed how to obtain | require the half value width in the endothermic peak by DSC measurement of a polypropylene fiber. 2 is a photograph taken with a scanning electron microscope of the polypropylene fiber obtained in Production Example 1. FIG.

Claims (4)

  It is made of polypropylene with an isotactic pentad fraction (IPF) of 94% or more, the fiber strength is 7 cN / dtex or more, the single fiber fineness is 0.1 to 3 dtex, the surface has a large diameter bulge and a small diameter Non-protruding portions of the fibers are alternately present along the fiber axis, and polypropylene fibers having irregularities with an average interval of 6.5 to 20 μm and an average height of 0.35 to 1 μm are included at a ratio of 50% by mass or more. A sheet-like fiber structure characterized by the above.   A half-value width consisting of polypropylene having an isotactic pentad fraction (IPF) of 94% or more, a fiber strength of 7 cN / dtex or more, and an endothermic peak shape by scanning differential calorimetry (DSC) of 10 ° C. or less. A sheet-like fiber structure comprising a polypropylene fiber having a single shape and a polypropylene fiber having a melting enthalpy change (ΔH) of 125 J / g or more at a ratio of 50% by mass or more.   An endothermic peak measured by scanning differential calorimetry (DSC) with polypropylene having an isotactic pentad fraction (IPF) of 94% or more, a fiber strength of 7 cN / dtex or more, and a single fiber fineness of 0.1 to 3 dtex. The shape is a single shape having a half width of 10 ° C. or less, the amount of change in melting enthalpy (ΔH) is 125 J / g or more, and a large-diameter raised portion and a small-diameter non-raised portion are along the fiber axis on the surface. A sheet-like fiber structure comprising polypropylene fibers having irregularities with an average interval of 6.5 to 20 μm and an average height of 0.35 to 1 μm alternately present at a ratio of 50% by mass or more.   The sheet-like fiber structure according to any one of claims 1 to 3, which has a water retention rate of 10% by mass or more.