JPWO2013089175A1 - Cement reinforcing fiber, method for producing the same, and hardened cement - Google Patents

Abstract

The method for producing a cement reinforcing fiber of the present invention is a method for producing a cement reinforcing fiber made of polypropylene fiber, wherein the Z average molecular weight Mz is 1 million or more, and the weight average molecular weight Mw / number average molecular weight Mn exceeds 5. Is melt-spun at a temperature of 300 to 400 ° C. and stretched to obtain polypropylene fibers having Mz of less than 1 million and Mw / Mn of more than 4 and 5 or less. The cement reinforcing fiber of the present invention is a cement reinforcing fiber obtained by the above production method, and has a Mz of less than 1,000,000 and an Mw / Mn of more than 4 and less than 5. The hardened cement body of the present invention includes a cement reinforcing fiber obtained by the above production method. The present invention provides a fiber for cement reinforcement, a method for producing the same, and a hardened cement body, which are low in cost and can obtain a highly crystalline polypropylene fiber without using a highly crystalline polypropylene.

Description

  The present invention relates to a cement reinforcing fiber made of polypropylene, a method for producing the same, and a hardened cement body.

  Polypropylene fibers are widely used for industrial applications because they are strong and lightweight. In order to reinforce the impact strength and bending strength of hydraulic hardened bodies such as concrete and mortar, short fibers made of polypropylene, vinylon or the like are used as reinforcing fibers. As the reinforcing fiber, a fiber excellent in fiber strength and fiber elongation is used. In order to obtain a fiber having excellent strength and elongation, a polymer has been selected.

  For example, Patent Document 1 proposes a highly crystalline polypropylene fiber having a specific range of Q value, boiling n-heptane insoluble content, isotactic pentad fraction, and the like. This proposal has the advantage that by using polypropylene with a narrow molecular weight distribution and a uniform molecular weight, the yarn can be easily taken up during spinning, the draw ratio can be increased, and a high-strength fiber can be obtained. Technology. Patent Document 2 proposes a polypropylene fiber having a specific range of isotactic pentad fraction, endothermic peak shape, and amount of change in melting enthalpy.

  However, the conventionally proposed highly crystalline polypropylene fiber has a problem of high cost because it employs a special catalyst and polymerization conditions for adjusting the molecular weight.

JP 05-170497 A JP 2008-266871 A

  In order to solve the above-described conventional problems, the present invention provides a cement reinforcing fiber that is low in cost and capable of obtaining a highly crystalline polypropylene fiber without using a highly crystalline polypropylene, a method for producing the same, and a cement cured body I will provide a.

  The method for producing a cement reinforcing fiber of the present invention is a method for producing a cement reinforcing fiber made of polypropylene fiber, wherein the Z average molecular weight Mz is 1 million or more, and the weight average molecular weight Mw / number average molecular weight Mn exceeds 5. To obtain a polypropylene fiber having a Z-average molecular weight Mz of less than 1 million and a weight-average molecular weight Mw / number-average molecular weight Mn of more than 4 and 5 or less. Features.

  The fiber for cement reinforcement of the present invention is a fiber for cement reinforcement obtained by the above production method, wherein the Z average molecular weight Mz is less than 1,000,000, and the weight average molecular weight Mw / number average molecular weight Mn exceeds 4 and is 5 or less. A range of polypropylene fibers.

  The hardened cement body of the present invention is characterized by including a cement reinforcing fiber obtained by the above production method.

  If the production method of the present invention is used, a low-cost polypropylene with a low crystallinity or a polypropylene with a wide molecular weight distribution can be used in the same degree as when a highly crystalline polypropylene or a polypropylene with a narrow molecular weight distribution is used. A cement reinforcing polypropylene fiber having fiber strength and single fiber elongation can be obtained.

  In general, cement reinforcing fibers using polypropylene with a wide molecular weight distribution have different ease of deformation between the polymer chain part and the low molecular chain part, so tension is concentrated on a part of the molten polymer and necking occurs. There is a case. Furthermore, in the stretching step, the temperature at which stretch deformation is possible differs between the polymer chain portion and the low molecular chain portion, making it difficult to orient the entire fiber uniformly, and as a result, the maximum draw ratio is lowered. However, the fibers produced by the production method of the present invention are relatively uniform in molecular weight because molecular chains having a large molecular weight (for example, 1 million or more) are easily pyrolyzed due to a high spinning temperature. Thus, the problems of spinnability and stretchability are solved.

FIG. 1 is a graph showing molecular weight distributions of an example of the present invention and a comparative example.

  The present invention relates to a reinforcing fiber for improving the strength of a water-cured body such as concrete or mortar, which is a polypropylene fiber mixed with cement. This fiber is produced by melt spinning. The polypropylene supplied to melt spinning has a Z average molecular weight Mz of 1 million or more and a weight average molecular weight Mw / number average molecular weight Mn of more than 5. From the viewpoint of easy availability, the polypropylene supplied to melt spinning preferably has a weight average molecular weight Mw / number average molecular weight Mn of 5.1 or more. This polypropylene is melt-spun at a temperature of 300 to 400 ° C. and stretched. A temperature higher than the ordinary melt spinning temperature of less than 300 ° C. is employed, and a polymer having a relatively uniform molecular weight is obtained by utilizing thermal decomposition of a high molecular weight polymer, thereby improving spinnability and stretchability. In this way, polypropylene fibers having a Z average molecular weight Mz of less than 1 million and a weight average molecular weight Mw / number average molecular weight Mn of more than 4 and 5 or less are obtained.

  In the above, the value of weight average molecular weight Mw / number average molecular weight Mn indicates the polydispersity of the polymer, and the smaller the value, the narrower the molecular weight distribution.

  The temperature of melt spinning is preferably in the range of 330 to 380 ° C, more preferably in the range of 340 to 370 ° C. If the temperature of melt spinning is in the above range, the control of adjusting the molecular weight of the high molecular weight polymer by thermal decomposition is further stabilized. In addition, the polymer chain is not excessively thermally decomposed to reduce the fiber strength and the like. Although thermal decomposition is also affected by the residence time of the molten polymer, it is difficult to change the residence time in practical production, and a normal residence time (about 5 to 15 minutes) is adopted.

  In the above, the spinning (melt spinning) temperature refers to the temperature in the highest temperature range among the temperatures added while the raw material polymer is made into fibers, for example, the temperature inside the polymer kneading machine, the temperature inside the extruder, the spinneret temperature. Any of these may be used.

  In the production method of the present invention, the temperature in the polymer kneader and / or the extruder is preferably 300 to 400 ° C, more preferably 325 to 365 ° C. By setting the temperature in the polymer kneader and / or the extruder to 300 ° C. or higher, the thermal decomposition of the high molecular weight polymer is promoted. Further, by setting the temperature in the polymer kneader and / or the extruder to 400 ° C. or less, excessive thermal decomposition is hardly caused, and the molecular weight is extremely reduced to suppress the fiber strength and the like from being lowered.

  In the production method of the present invention, the temperature of the spinneret is preferably 10 ° C. or more, more preferably 30 ° C. or more, lower than the temperature in the polymer kneader and / or the extruder. With such a configuration, even when the spinning temperature is 300 ° C. or higher, the spinning filaments are not fused or little during filament take-up. Specifically, the temperature of the spinneret is preferably 255 to 295 ° C.

The melting enthalpy ΔH _P1 of polypropylene (polypropylene pellets) supplied to melt spinning is preferably less than 80 J / g, more preferably 50 J / g or more and less than 80 J / g, and even more preferably 50 to 79 J / g. Melting enthalpy delta _P1 indicates a higher that crystallinity is good. When the melting enthalpy ΔH _P1 of the polypropylene pellets is less than 80 J / g, thermal decomposition tends to occur, and the effects of the present invention are particularly easily obtained.

Fibers of the present invention, the melting enthalpy [Delta] H _F after fiberization, is preferably 100 J / g or more, and more preferably 110J / g or more. When the melting enthalpy [Delta] H _F after fiberization is 100 J / g or more, it tends to give a fiber excellent in single fiber strength. A preferable upper limit of the [Delta] H _F is 140 J / g.

Fibers of the present invention, the melting enthalpy [Delta] H _P2 measured by the following method is preferably a 80~100J / g. ΔH _P2 is the melting enthalpy of the polymer when it is once melted after fiberization and re-solidified, and indicates the crystallinity of the polymer in a state where the fiber orientation is released. Further, [Delta] H _P2 indicates a high natural orientation of the larger the value polymer.

(Measuring method of ΔH _P2 )
The fiber is heated from 20 ° C. to 200 ° C. at a rate of 10 ° C./min, then lowered from 200 ° C. to 20 ° C. at a rate of 10 ° C./min, and again from 20 ° C. to 200 ° C. at 10 ° C. / endothermic energy when it was elevated at a rate and enthalpy of fusion [Delta] H _P2.

Fibers of the present invention is preferably [Delta] H _F - [Delta] H _P2 is 25 J / g or more. ΔH _F −ΔH _P2 is a value obtained by removing the natural orientation of the polymer from the orientation of the fiber, and is an index indicating the degree of crystal orientation of the molecular chain in the fiber state. When ΔH _F −ΔH _P2 is 25 J / g or more, the proportion of regularly aligned molecular chains is high, and even when a polymer with low crystallinity is used, the single fiber strength and fiber elongation are improved. Excellent fibers can be obtained. Further, such a fiber is expected to have a low dry heat shrinkage and a small phenomenon (stretching return) that the fiber shrinks after the stretching step.

  In the present invention, it is preferable that the Z average molecular weight Mz / weight average molecular weight Mw of the polypropylene supplied to melt spinning exceeds 3, and the Z average molecular weight Mz / weight average molecular weight Mw of the polypropylene fiber exceeds 2.55 and less than 3. . More preferably, the Z average molecular weight Mz / weight average molecular weight Mw of polypropylene supplied to melt spinning is 3.1 or more, and the Z average molecular weight Mz / weight average molecular weight Mw of polypropylene fiber is 2.60 to 2.95. . Z average molecular weight Mz / weight average molecular weight Mw also indicates the polydispersity of the polymer, which means that polypropylene pellets have a relatively wide molecular weight distribution, but polypropylene fibers have a relatively narrow molecular weight distribution. Such polypropylene pellets are available at a relatively low cost.

  The cement reinforcing fiber of the present invention is a polypropylene fiber having a Z average molecular weight Mz of less than 1,000,000 and a weight average molecular weight Mw / number average molecular weight Mn of more than 4 and 5 or less. Preferably, the fiber for cement reinforcement is a polypropylene fiber having a weight average molecular weight Mw / number average molecular weight Mn of 4.1 to 5. Moreover, it is preferable that Z average molecular weight Mz / weight average molecular weight Mw of the said polypropylene fiber is more than 2.55 and less than 3, More preferably, it is 2.6-2.95. Such polypropylene fibers have a relatively narrow molecular weight distribution.

In the present invention, the ratio of the number average molecular weight Mn _F of the polypropylene fiber after spinning to the number average molecular weight Mn _P of polypropylene supplied to melt spinning is preferably 0.9 to 1.1, and preferably 0.95 to 1 .05 is more preferable. Mn _F / Mn _P indicates the amount of change in the number average molecular weight before and after fiberization, and the closer the value is to 1, the smaller the number average molecular weight before and after fiberization. When Mn _F / Mn _P is in the range of 0.9 to 1.1, the number of molecules whose molecular weight has been changed due to thermal decomposition is small, and the fiber strength is suppressed from becoming extremely low.

  Specifically, the number average molecular weight Mn of polypropylene pellets supplied to melt spinning is preferably 50,000 to 100,000, and more preferably 5.5 to 80,000. Moreover, the number average molecular weight Mn of the polypropylene fiber after spinning is preferably 50,000 to 100,000, more preferably 5.5 to 80,000.

In the present invention, the ratio of the weight average molecular weight Mw _F of the polypropylene fiber after spinning to the weight average molecular weight Mw _P of polypropylene supplied to melt spinning is preferably 0.6 to 0.9, and preferably 0.7 to 0. .8 is more preferable. Mw _F / Mw _P indicates the amount of change in the weight average molecular weight before and after fiberization, and the smaller the value, the lower the high molecular weight polymer after fiberization. When Mw _F / Mw _P is in the range of 0.6 to 0.9, a part of the high molecular weight polymer is moderately decomposed, resulting in a narrow molecular weight distribution and a fiber that is easily oriented. can get.

Specifically, the weight average molecular weight Mw _P of polypropylene supplied to melt spinning is preferably from 30 to 450,000, and more preferably from 35 to 400,000. Moreover, it is preferable that it is 20-350,000, and, as for the weight average molecular weight Mw _F of the polypropylene fiber after spinning, it is more preferable that it is 25-300,000.

In the present invention, the ratio of the Z average molecular weight Mz _F of the polypropylene fiber after spinning to the Z average molecular weight Mz _P of the polypropylene supplied to melt spinning is preferably 0.5 to 0.8, and 0.6 to 0 .7 is more preferable. Mz _F / Mz _P indicates the amount of change in the Z average molecular weight before and after fiberization, and the smaller the value, the lower the high molecular weight polymer after fiberization. When Mz _F / Mz _P is within the range of 0.5 to 0.8, a part of the high molecular weight polymer is moderately decomposed, resulting in a narrow molecular weight distribution and a fiber that is easily oriented. can get.

Specifically, Z average molecular weight Mz _P polypropylene supplied to the melt spinning is 1,000,000 or more, the upper limit is not particularly limited, for example, the upper limit may be 200 to 250,000. Moreover, the Z average molecular weight Mz _F of the polypropylene fiber after spinning is less than 1,000,000, preferably 60 to 950,000, and more preferably 700 to 800,000.

  In the present invention, the isotactic pentad fraction (hereinafter also referred to as IPF) of polypropylene supplied to melt spinning is preferably 90% or more, and more preferably 93% or more. Thermal decomposition tends to occur when the IPF is 90% or more. This is presumably because the thermal decomposition of polypropylene tends to occur at isotactic sites, that is, structures where the asymmetric carbon has the same absolute configuration.

  In the present invention, any method of polymerizing polypropylene may be used. For example, it may be polymerized with a metallocene catalyst or polymerized with a Ziegler-Natta catalyst. The polypropylene may be a homopolymer of propylene or a copolymer of propylene and another α-olefin having about 2 to 20 carbon atoms.

  Inorganic fibers may be dispersed in the cement reinforcing fiber of the present invention. When inorganic particles are dispersed in polypropylene fibers, the affinity with a hydraulic material such as cement is further increased, and the strength of a hydraulic cured body such as a cement cured body is also increased. In addition, the fiber is less likely to float during dispersion due to the increase in the apparent specific gravity of the fiber. The content of the inorganic particles is preferably in the range of 0.1 to 20% by mass and more preferably in the range of 1 to 10% by mass with respect to 100% by mass of the polypropylene fiber.

  When the cement reinforcing fiber of the present invention contains inorganic particles, it is preferable to obtain a polypropylene fiber as a core-sheath composite fiber and include inorganic particles in the sheath component. When inorganic particles are included in the sheath component, convex portions are formed on the fiber surface, and the fibers are difficult to be removed from the cement cured body, so that the bending strength of the cement cured body is improved. In this case, the content of the inorganic particles is preferably in the range of 0.1 to 40% by mass, more preferably in the range of 1 to 20% by mass with respect to 100% by mass of the sheath component of the polypropylene fiber. In addition, the core component may contain the inorganic particle and does not need to contain it.

  The inorganic particles are not particularly limited, and known inorganic particles can be used. As the inorganic particles, for example, particles such as magnesium carbonate, silicon oxide, aluminum oxide, barium sulfate, calcium carbonate, and talc can be used.

  The inorganic particles preferably have an average particle size of 0.1 to 10 μm. More preferably, it is 0.2-5 micrometers, More preferably, it is 0.3-2 micrometers. When the average particle diameter of the inorganic particles is 0.1 μm or more, a convex portion is formed on the fiber surface, and the effect that the fibers are difficult to be removed from the hardened cement body can be obtained more remarkably. When the average particle diameter of the inorganic particles is 10 μm or less, it is possible to suppress the occurrence of yarn breakage in the fiber spinning process, and in the obtained fiber, the inorganic particles are less likely to fall off the fiber surface. The average particle diameter of the inorganic particles is measured with a particle size distribution measuring device (manufactured by Shimadzu Corporation, trade name “SALD-2000”).

  The cement reinforcing fiber of the present invention is a stretched fiber. By stretching an unstretched filament obtained by spinning, a molecular chain is aligned in the stretching direction, and a fiber excellent in single fiber strength and fiber elongation can be obtained. The stretching treatment is preferably performed by dry stretching. For example, the stretching temperature may be 145 to 165 ° C. Further, from the viewpoint of increasing the single fiber strength and decreasing the fiber elongation and obtaining fibers excellent for cement reinforcement, the draw ratio is preferably 2 to 10 times, and 2.5 to 5 times. More preferably.

  In the cement reinforcing fiber of the present invention, it is preferable to attach a fiber treatment agent (also referred to as a fiber oil agent) to the surface of the drawn polypropylene fiber. The fiber treatment agent is not particularly limited as long as it is used for the purpose of improving the hydrophilicity of the fiber. The fiber treatment agent may be applied by any of dipping, spraying, and coating methods.

  The cement reinforcing fiber preferably has a fiber treatment agent attached to at least one hydrophilic treatment selected from fluorine gas treatment, plasma discharge treatment and corona discharge treatment. With such a configuration, the affinity with cement is further improved. In addition, the hardened cement body including the cement reinforcing fiber having such a configuration has better bending fracture strength.

When carrying out the corona discharge treatment, it is not particularly limited, but the discharge amount per time in the corona discharge treatment is preferably 50 W / m ² / min or more, and the total discharge amount is 100 to 5000 W / m ² / min. It is preferable that A more preferable total discharge amount is 250 to 5000 W / m ² / min. The plasma treatment is not particularly limited, but is preferably atmospheric pressure plasma treatment, and may be performed at a voltage of 50 to 250 kV and a frequency of 500 to 3000 pps. The atmospheric pressure plasma treatment is convenient because it can be treated at a low voltage, and there is little deterioration of the fiber. The fluorine gas treatment is not particularly limited, and can be performed using, for example, a mixed gas containing fluorine gas and oxygen gas or a mixed gas containing fluorine gas and sulfurous acid gas.

  The preferred single fiber fineness of the cement reinforcing fiber of the present invention is 0.1 to 50 dtex, more preferably 0.2 to 5 dtex, and particularly preferably 0.3 to 3 dtex. A preferable fiber length is about 1 to 20 mm.

  The cement reinforcing fiber of the present invention preferably has a single fiber strength of 5 cN / dtex or more, and more preferably 7 cN / dtex or more. In addition, the preferable upper limit of single fiber strength is 20 cN / dtex.

  The fiber for cement reinforcement of the present invention preferably has a fiber elongation of 15 to 45%, more preferably 20 to 40%.

  The cement cured body of the present invention preferably contains 0.1 to 5% by mass of the above-mentioned cement reinforcing fiber with respect to the cement. When the content of the cement reinforcing fiber is 0.1% by mass or more, a hardened cement body excellent in impact strength and bending strength can be obtained. Further, when the content of the cement reinforcing fiber is 5% by mass or less, fiber balls (dama) are hardly formed during stirring.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited to the following Example.

<Measurement method>
1. Molecular weight distribution measurement Using the GPC method, the average molecular weight and molecular weight distribution were measured under the following measurement conditions.
10 mg of a sample was added to 5 mL of 1,2,4-trichlorobenzene, heated and stirred at 170 ° C. for 30 minutes, and dissolved to obtain a sample solution for measurement. Next, 0.2 mL of the measurement sample solution was injected into a gel permeation chromatograph GPC (gel permeation chromatography, “PL-220” manufactured by Polymer Laboratories), and the number average molecular weight Mn, the weight average molecular weight Mw, and the Z average molecular weight Mz were calculated. It was measured. In the above measurement, a differential refractive index detector (manufactured by Polymer Laboratories) is used as a detector, a column is used as Shodex HT806M (φ7.8 mm × 30 cm, Showa Denko), and a standard sample is used as a monodisperse polystyrene. And the column temperature was measured at 145 ° C.
2. Melting enthalpy measurement Melting enthalpy measurement was performed by a differential scanning calorimetry (DSC) method using a differential scanning calorimeter. More specifically, a differential scanning calorimeter (manufactured by Seiko Instruments Inc., trade name “EXSTAR6000 / DSC6200”) is used, the sample amount is 3 mg, and the heating rate is from 20 ° C. to 10 ° C./min. in a heated sample melted to 200 ° C., to obtain a heat of fusion curve a, from the resulting heat of fusion curve a, to determine the enthalpy of fusion [Delta] H _P1 and [Delta] H _F.
Then, according to the above procedure, the sample heated up to 200 ° C. and melted is cooled to 20 ° C. at a temperature lowering rate of 10 ° C./min, and after reaching 20 ° C., again at a temperature rising rate of 10 ° C./min. The sample was melted to obtain a heat of fusion curve B. From the heat of fusion curve B obtained, the enthalpy of fusion _ΔHP2 was determined.

<Polymer used>
The following polypropylene pellets were used.
PP1: Z average molecular weight Mz is 114,000, melting enthalpy ΔH _P1 is 76.8 J / g
PP2: manufactured by Nippon Polypro Co., Ltd., trade name “SA01A”, Z average molecular weight Mz is 811000, melting enthalpy ΔH _P1 is 87.9 J / g
PP3: manufactured by Prime Polymer Co., Ltd., trade name “S135L”, melting enthalpy ΔH _P1 is 95.8 J / g
PP4: Z average molecular weight Mz is 116,000, melting enthalpy ΔH _P1 is 79.2 J / g

Example 1
Using PP1 as a raw material polymer, melt extrusion from a spinning nozzle (pore diameter 0.6 mm) at a spinning temperature of 354 ° C., cooling the vicinity of the spinning nozzle, setting the take-up magnification (spinning draft) to 625 times, and a fineness of 4.0 dtex A spinning filament was obtained. More specifically, the cooling was performed by applying cooling air having a wind pressure of 40 mmAq (392 Pa) and a temperature of 25 ° C. to the filament-shaped resin discharged from the spinning nozzle. Next, the obtained spinning filament was dry-drawn at a drawing temperature of 155 ° C. and a draw ratio of 4.0 times to obtain a drawn filament having a fineness of 0.9 dtex. A fiber treating agent was applied to the obtained drawn filament, and then cut into a fiber length of 6 mm to obtain a polypropylene fiber of Example 1. The evaluation results are summarized in Tables 1 and 2.

(Example 2)
A polypropylene fiber composed of drawn filaments having a fineness of 1.3 dtex was obtained in accordance with the procedure of Example 1 except that the take-up magnification was 585 times, a spun filament having a fineness of 4.4 dtex was obtained, and the draw ratio was 3.4 times. It was. The evaluation results are summarized in Tables 1 and 2.

(Example 3)
A polypropylene fiber composed of drawn filaments having a fineness of 2.2 dtex was obtained in accordance with the procedure of Example 1 except that the take-up magnification was 353 times and a spun filament having a fineness of 7.8 dtex was obtained and the draw ratio was 3.5 times. It was. The evaluation results are summarized in Tables 1 and 2.

Example 4
Except that PP4 was used as the raw material polymer, the polypropylene fiber of Example 4 consisting of drawn filaments having a fineness of 1.3 dtex was obtained according to the procedure of Example 2. The evaluation results are summarized in Table 1.

(Comparative Example 1)
Except for using PP2 as the raw material polymer, a polypropylene fiber composed of a drawn filament having a fineness of 2.2 dtex was obtained according to the procedure of Example 3. The evaluation results are summarized in Tables 1 and 2.

(Reference Example 1)
Except for using PP3 as the raw material polymer, a polypropylene fiber composed of a drawn filament having a fineness of 1.3 dtex was obtained according to the procedure of Example 2. The evaluation results are summarized in Table 2.

(Reference Example 2)
Except for using PP3 as a raw material polymer, a polypropylene fiber composed of a drawn filament having a fineness of 2.2 dtex was obtained according to the procedure of Example 3. The evaluation results are summarized in Table 2.

  As is clear from Tables 1 and 2, the examples of the present invention have the same single fiber strength and unity as those obtained when polypropylene having a broad molecular weight distribution is used and using a highly crystalline polypropylene or a polypropylene having a narrow molecular weight distribution. It was confirmed that a polypropylene fiber for cement reinforcement having fiber elongation could be obtained. Further, from the molecular weight distribution curves of the raw material polymer (polypropylene pellet) and the obtained polypropylene fiber in FIG. 1, it was found that in the examples, the fiber had a narrower molecular weight distribution and less high molecular weight component.

(Example 5)
Using PP4 as the raw material polymer, melt extrusion from a spinning nozzle (pore diameter 0.6 mm) with a spinning temperature of 354 ° C., cooling the vicinity of the spinning nozzle, setting the take-up magnification (spinning draft) to 585 times, and a fineness of 4.4 dtex A spinning filament was obtained. More specifically, the cooling was performed by applying cooling air having a wind pressure of 40 mmAq (392 Pa) and a temperature of 25 ° C. to the filament-shaped resin discharged from the spinning nozzle. Subsequently, the obtained spinning filament was dry-drawn at a drawing temperature of 155 ° C. and a draw ratio of 3.4 times to obtain a drawn filament having a fineness of 1.3 dtex. The obtained drawn filament is passed through a corona discharge treatment machine to make it hydrophilic by corona discharge treatment with a discharge amount of 0.5 kW / m ² / min, and then a fiber treatment agent is applied and cut to a fiber length of 6 mm. Thus, a polypropylene fiber of Example 5 was obtained.

(Comparative Example 2)
A polypropylene fiber of Comparative Example 2 was obtained according to the procedure of Example 5 except that PP2 was used as the raw material polymer.

  The Charpy impact strength and bending strength of the cured cement containing the polypropylene fiber of Example 5 or Comparative Example 2 were measured as follows, and the results are shown in Table 3 below. In Table 3 below, the value calculated by dividing the bending fracture strength (MOR) by the density is shown as the ratio MOR. Table 3 below also shows the results of using a vinylon fiber (manufactured by Unitika Ltd., trade name “22A”, fineness 2.2 dtex, fiber length 6 mm) as Reference Example 3.

(Charpy impact strength test method)
Portland cement 400g, silica sand 100g, pulverized pulp 5g, fiber 1.5g and water 4500g are mixed thoroughly to prepare a cemented body of 25cm in length and 25cm in width, which is naturally cured at room temperature for 28 days. A natural cured cement cured body was obtained. Next, a measurement sample having a length of 1 cm and a width of 13 cm was prepared from the cured natural cement, and Charpy impact strength was measured according to JIS B 7722.

(Bending strength test method)
In the same manner as in the Charpy impact strength test method, a naturally-cured cement-cured body is obtained, a measurement sample having a length of 5 cm and a width of 10.5 cm is prepared from the naturally-cured cement-cured body, and bent according to JIS A 1408. Elastic limit strength LOP and bending fracture strength MOR were measured.

(Ratio MOR)
The value calculated by dividing the bending fracture strength MOR by the density was taken as the ratio MOR (bending fracture strength MOR per density).

  The hardened cement body including the cement reinforcing fiber of Example 5 has higher values of bending elastic limit strength LOP, bending fracture strength MOR, and specific MOR than the hardened cement body including the cement reinforcing fiber of Comparative Example 2. It was. From this result, the hardened cement body including fibers using PP4 as the raw material polymer has superior bending elastic limit strength LOP, bending fracture strength MOR, and specific MOR than the hardened cement body including fibers using PP2 as the raw material polymer. It was confirmed that it was obtained.

  The cured cement containing the cement reinforcing fiber of Example 5 had larger values of Charpy impact strength, bending fracture strength MOR, and specific MOR than the cured cement containing the vinylon fiber of Reference Example 3. This result means that the cured cement containing the cement reinforcing fiber (polypropylene fiber) of Example 5 is superior to the cured cement containing the vinylon fiber of Reference Example 3 in each physical property. The cured cement containing general polypropylene fiber tends to have lower bending fracture strength MOR and specific MOR than the cured cement containing vinylon fiber. It was confirmed that the hardened cement body containing the cement hardened body containing vinylon fibers was superior in bending fracture strength MOR and specific MOR.

  The cement reinforcing fiber of the present invention is suitable for autoclave curing because of its high heat resistance. In addition, it can be applied to air curing, underwater curing, poultry curing, and the like. The molding method can be applied to casting molding, vibration molding, centrifugal molding, suction molding, extrusion molding, press molding, and the like. The molded product can be applied to an extruded cement board (ECP) or a precast concrete (PC) panel.

Claims (7)

A method for producing a cement reinforcing fiber made of polypropylene fiber,
By melt spinning and stretching a polypropylene having a Z average molecular weight Mz of 1 million or more and a weight average molecular weight Mw / number average molecular weight Mn exceeding 5 at a temperature of 300 to 400 ° C.,
A method for producing a cement reinforcing fiber, wherein a polypropylene fiber having a Z average molecular weight Mz of less than 1 million and a weight average molecular weight Mw / number average molecular weight Mn of more than 4 and 5 or less is obtained.   The method for producing a fiber for reinforcing a cement according to claim 1, wherein a temperature of the melt spinning is in a range of 330 to 380 ° C. The fusion enthalpy [Delta] H _P1 polypropylene supplied to the melt spinning method of producing a cement reinforcing fiber according to claim 1 or 2 is less than 80 J / g.   The Z average molecular weight Mz / weight average molecular weight Mw of the polypropylene supplied to the melt spinning is more than 3, and the Z average molecular weight Mz / weight average molecular weight Mw of the polypropylene fiber is more than 2.55 and less than 3. The manufacturing method of the fiber for cement reinforcement in any one. A cement reinforcing fiber obtained by the production method according to claim 1,
A cement reinforcing fiber characterized by being a polypropylene fiber having a Z average molecular weight Mz of less than 1 million and a weight average molecular weight Mw / number average molecular weight Mn of more than 4 and 5 or less.   6. The cement reinforcing fiber according to claim 5, wherein the cement reinforcing fiber has a Z average molecular weight Mz / weight average molecular weight Mw of more than 2.55 and less than 3. A hardened cement body comprising a cement reinforcing fiber obtained by the production method according to claim 1.

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