JP4956472B2 - Reinforcing short fibers for cement-based moldings - Google Patents

Description

  The present invention relates to a synthetic resin reinforced short fiber for cement-based molded bodies, and more specifically, cement-based molded bodies for civil engineering and construction work, in particular, prevention of cracking of concrete, and accompanying concrete lump. The present invention relates to a reinforcing short fiber for cement-based molded article suitable for preventing peeling.

  Conventionally, steel fibers, vinylon fibers, polypropylene fibers, etc. are known as reinforcing fibers for cement-based molded bodies such as mortar and concrete, and are used for the purpose of improving the bending strength and imparting bending toughness of hardened cement-based bodies. ing. Recently, a higher level of safety is required for hardened cement bodies. Aggregates from each production area (crushed stone / crushed sand, mountain gravel / mountain sand, land gravel / land sand, river gravel / river sand, sea sand, etc.), types of cement There is a concern that the design, strength design of each construction work, and slump design specifications, etc. (ordinary Portland cement, blast furnace cement, etc.), in particular, have a negative impact on the bending toughness of the cemented hardened body. Also from this point, a reinforcing fiber capable of achieving higher bending toughness is demanded.

As reinforcing fibers, polypropylene fibers are attracting attention because they do not rust, have excellent alkali resistance to cement, and have the lowest specific gravity among fiber materials and the lowest mass ratio in the cement molded product. As a result, it is increasingly used for tunnel lining concrete.
However, the reinforcing fiber made of polyolefin resin such as polypropylene has a problem that its adhesiveness with cement is weak and it is difficult to obtain a sufficient reinforcing effect in the conventional fiber form.
In order to overcome this problem, a technique has been proposed to improve the fixing power to cement hardened bodies and provide resistance during drawing by giving mechanical irregularities to the fiber surface following the provision of necessary strength by stretching. (For example, Patent Document 1).
However, the technique described in Patent Document 1 can be machined continuously using a gear or a press-molding roll, is simple in terms of the fiber manufacturing process, can be manufactured at low cost, and is advantageous. However, the fixability to cement is still not sufficient.

On the other hand, the present applicants, as a reinforcing fiber that can improve the fixability to the cement cured body, for the purpose of increasing the contact area with the cement, the cross-sectional shape is a substantially polygon having 3 to 6 protrusions, And the polyolefin short fiber which shape | molded the recessed part or the convex part at the front-end | tip of this protrusion part with a pair of parallel uneven | corrugated stamping rollers etc. along the longitudinal direction of this fiber is proposed (refer patent document 2).
However, by using this fiber, it is possible to improve the fixing property with cement. However, in such a fiber having a concave portion or a convex portion at the tip of the protruding portion, at the time of loading as a cement molded body, first, The tensile stress is applied to the tip of the fiber protrusion on the maximum diameter side, and then applied sequentially toward the center. For this reason, it is not preferable to give a convex part, such as a concave part or a convex part, to the protruding part of the fiber cross section where tensile stress tends to concentrate.

In addition, in order to supply reinforcing fibers to various cement-based molded products such as flesh concrete, it is necessary to open the fibers in a short time and to supply them uniformly in consideration of the cement hardening time.
However, in the fiber having such a protruding portion tip, not only the fiber breaks easily as described above, but the fibers are caught by the unevenness of the surface at the time of charging into the cement-based fresh and kneading, and, There is a risk that the opening will be insufficient, and as a result, a problem may occur in the uniform dispersion in the cement-based molded body.
As described above, the conventional polypropylene fiber has advantages in alkali resistance, light weight, etc., but a reinforced short fiber for cement-based molded article that is practically satisfactory has not yet been obtained.

JP-A-11-116297 Japanese Patent Laid-Open No. 2005-220498

  The present invention has been made in order to solve the above-mentioned problems, and does not cause problems in the workability and dispersibility of fibers, the workability of concrete construction, and the like, and the bending toughness of the hardened cement-based molded body. It is an object to provide a reinforcing fiber for a cement-based molded body that can be improved.

The present inventors pay attention to the contact area between the reinforcing fiber and the cement, and have concave portions formed at predetermined intervals along the longitudinal direction of the fiber on two opposing surfaces having a substantially square cross-sectional shape. By providing the protrusions with fibers having recesses shaped at predetermined intervals along the longitudinal direction of the fibers, it is possible to open and disperse into cement fresh, dispersibility, strong fixability with cement, and to reinforce. And found that the necessary tensile strength of the fiber can be achieved.
That is, the present invention
(1) A drawn fiber having a polypropylene resin as a main component, and the cross-sectional shape of the fiber is a substantially rectangular shape having four protrusions, and the two opposing surfaces of the substantially rectangular shape are along the longitudinal direction of the fiber. And a concave portion shaped at a predetermined interval along the longitudinal direction of the fiber. Reinforced short fibers,
(2) The fineness is 3,000 to 3,500 dtex, the depth of the concave portion of the side portion is 0.1 to 0.2 mm, the length is 0.8 to 1.2 mm, and the concave portion is arranged in the fiber longitudinal direction. The interval is 2.5 to 3.5 mm, the depth of the concave portion of the protrusion is 0.1 to 0.2 mm, the length is 0.5 to 0.7 mm, and the arrangement interval of the concave portion in the fiber longitudinal direction is The reinforcing short fiber for cement-based molded article according to claim 1, which is 2.0 to 3.0 mm, and (3) the cement-shaped molded article according to claim 1 or 2, wherein the substantially square cross section is X-shaped. Reinforcing short fiber,
Is to provide.

The reinforcing short fiber for cement-based molded body of the present invention has been devised in such a manner that the fiber surface is not intertwined with each other while increasing the contact area with the cement. The fiber can be easily opened, and the fiber can be uniformly dispersed in the cement-based fresh.
In addition, the reinforcing short fiber of the present invention has concave portions formed at a predetermined depth and a predetermined interval at the side portion of the substantially square shape having four protrusions and the tip of the protrusion portion, respectively. The concave portion has a high resistance to pulling out from the cement while suppressing a decrease in the tensile properties of the fiber due to shaping. As a result, a high bending toughness coefficient can be obtained in the concrete molded product after hardening of the cement, and an extremely excellent reinforcing effect can be exhibited.
Moreover, since the specific gravity is small with the fiber made from a polypropylene resin, the reinforcing short fiber excellent in workability | operativity (workability) in carrying | working, the injection | pouring operation | work at the time of mix | blending with concrete, and concrete placement can be provided.

  In the reinforcing single fiber for cement-based molded article of the present invention (hereinafter, simply referred to as “reinforcing short fiber” or “fiber”), the fiber resin may be cement alkali resistance, fiber physical properties, low cost, and reinforcement. In view of efficiency and the like, a material mainly composed of polypropylene resin is preferably used. As the polypropylene resin, a propylene homopolymer, a block or random copolymer of an α-olefin such as ethylene and propylene, or a mixture thereof can be used. Further, the melt flow rate (MFR) of the polypropylene resin is preferably 0.1 to 20 g / 10 minutes, more preferably 0.3 to 10/10 minutes from the viewpoint of spinnability and fiber properties.

  Furthermore, the polypropylene resin as a fiber resin has other synthetic resins and modified resins, antioxidants, light stabilizers, nucleating agents, antibacterial agents, flame retardants, antistatics, as long as the effects of the present invention are not hindered. Agents, pigments, plasticizers, and other inorganic / organic fillers can be added as appropriate.

In the reinforced short fiber of the present invention, the substantially square cross-sectional shape means that the shape constituted by the lines connecting the vertices of each side of the fiber cross-section is a substantially square shape, and is an X shape, a cross shape, a square shape, a trapezoid shape. Etc.
In addition, since the apparent fiber thickness increases when the substantially square cross section is closer to the square as compared with a fiber having a conventional round cross section or flat round cross section, the cross-sectional secondary moment of the fiber is improved. For this reason, even short fibers with a relatively small tensile Young's modulus are prevented from bending due to collision with coarse aggregates, fine aggregates, etc. during cement mixing, and are dispersed in a form effective for reinforcement. A fiber reinforcing effect can be exhibited, and a high concrete property improving effect can be exhibited.
From the viewpoint of the contact area with the cement and the above-mentioned moment of inertia of the section, the X-section is particularly preferable. Further, when the fiber cross section is X-shaped, the number of grooves on the side is 4, and the recesses can be formed in the two grooves facing each other by a pair of rollers, so that stable production is easy.

The fiber of the present invention has a concave portion formed along the longitudinal direction of the fiber on the two opposing faces having a substantially square cross section, and a concave portion formed along the longitudinal direction of the fiber on the tip side of the substantially quadrangular protrusion. It has.
The cross section of the fiber is most preferably a substantially quadrangular shape having four protrusions from the viewpoint of the surface processing of the fiber forming the recess, and the side groove bottom formed continuously to the protrusion and the tip end side of the protrusion. It is necessary that recesses shaped at predetermined intervals are continuously formed along the longitudinal direction of the fiber. Preferably, it is formed on the groove bottoms on the two surfaces and on the tip end sides of the four protrusions connected to the groove bottoms. Moreover, the positional relationship with respect to the longitudinal direction of the fiber between the concave shape of the side portion and the concave shape of the protruding portion may partially overlap or may be shifted. From the viewpoint of the fixing effect with cement, it is more preferable that the positions of all the concave shapes are shifted.
In the present invention, the two planes are planes including respective sides facing each other in the fiber cross section, and the sides or sides are ridge lines (real lines) connecting adjacent protrusions (corners, vertices) in the fiber cross section. ) Means that the ridge line (real line) connecting adjacent protrusions (vertices) is curved toward the center of the fiber cross section from the straight line (virtual line) connecting adjacent protrusions (virtual line). For example, in the X-shaped cross-section, it means a V-shaped or arc-shaped groove-like portion that is continuously formed in the longitudinal direction of the fiber. In addition, a side part also has the meaning including the surface (surface) in which a side is included.

  The reinforcing short fibers of the present invention will be described more specifically. FIGS. 2 (C1) and 2 (C2) schematically show the Z-shaped reinforcing short fibers 1 having a substantially square cross section. It is a cross-sectional view taken along the arrow and has four protrusions (corner portions) 2 and four sides S, and rhombus-shaped recesses 4 and 4 'are formed on the upper and lower sides S, and the recesses are formed. In this example, wedge-shaped (substantially triangular prism-shaped) recesses 5 and 5 ′ that are perpendicular to the longitudinal direction of the fiber axis are continuously formed at predetermined pitches on the opposing protrusions on the side portions.

  The shape of the recess formed at the side and the tip of the protrusion is deeper, larger and sharper in terms of reinforcing performance with hardened concrete, and the larger the number, the better. However, these may cause deterioration in construction workability due to a decrease in fiber tensile properties, input spreadability in cement-based freshness, a decrease in dispersibility, a decrease in fluidity, and an increase in the amount of air entrained during kneading. Must be determined in consideration of

  First, in order to minimize the adverse effects on the physical properties of the fiber and to prevent the fibers from being caught during opening, a recess is formed on the groove bottom of the side, not on the outer diameter side of the fiber. Yes. Forming a recess on the fiber surface will reduce the fiber strength, but forming it on the groove bottom, not on the tip surface where the stress is concentrated, will minimize this. Can do. Also, the position of the groove bottom is a spatially indented place, the frequency of contact between fibers is low, and because it is shaped as a concave (part) instead of a convex (part), it almost has an adverse effect on the fiber opening properties. Does not affect.

In the present invention, in order to further improve the physical fixing property with the cement, a concave portion formed on the front end side of the protruding portion of the fiber is also provided. The tip of the protrusion is concentrated at the time of tension, and the portion between the fibers is in direct contact with each other. Therefore, the shaping (molding) form must be appropriate.
That is, it is necessary to increase the number of concave portions by forming a concave shape rather than a convex shape as in the above-described groove bottom, and having a relatively small shape with respect to the dimension of the fiber thickness.
Overall, by taking into account the balance of the shape of the groove at the side and the tip of the protrusion, the fiber opening properties, dispersibility in cement-based freshness, and fiber properties are maintained well. In addition, it is possible to improve the fixing property with the cement-based cured body.
For this purpose, the depth of the recesses on the side is 0.1 to 0.2 mm, the length is 0.8 to 1.2 mm, and the arrangement interval of the recesses in the longitudinal direction is 2.5 to 3 mm. 0.5 mm, the depth of the recess at the tip of the protrusion is 0.1 to 0.2 mm, the length is 0.5 to 0.7 mm, and the interval between the recesses in the longitudinal direction is 2. It is desirable that it is 0-3.0 mm.

The depth of the concave portion is preferably a sharp shape and a deep form, but if the depth exceeds 0.2 mm, the openability is deteriorated, and the loss (decrease) in fiber strength is large. If the depth is less than 0.1 mm, sufficient fixability cannot be expected. The length in the longitudinal direction (fiber axis direction) of the concave portion needs to be larger than the size of the aggregated cement particles in the cured body. However, especially in the shape of the tip of the protrusion, if the size exceeds the above range, the spreadability deteriorates and the dispersibility deteriorates due to secondary aggregation of the fibers due to dynamic stimulation during rotary kneading in the cement-based fresh. Concerned. The number of shaping points, that is, the shaping interval x is preferably in the range of 2.5 to 3.5 mm, and if it is 2.5 mm or more, the fiber strength may be reduced to less than necessary physical properties by shaping. In addition, if the shaping interval is 3.5 mm or less, the required pulling resistance in the cement-based cured body does not decrease, and a high fixing force can be obtained.
However, with respect to the shaping interval y at the tip of the protrusion, the shaping length l ₂ can be set shorter than the dimension of the fiber thickness (width w and thickness t) in order to maintain good fiber opening. In response to this, the fixing strength of the cemented hardened body can be maintained high by making it shorter than the shaping interval x to the groove bottom (that is, by increasing the number).
The shaping interval y at the tip of the protrusion is preferably in the range of 2.0 to 3.0 mm, and if it is 2.0 mm or more, the fiber strength may be reduced to less than necessary physical properties by shaping. In addition, if the shaping interval is 3.0 mm or less, the necessary pulling resistance in the cemented cured body does not decrease, and a high fixing force can be obtained.

In addition, the said shaping range of a groove bottom part and the front-end | tip part of protrusion is suitable for about 3,300 dtex (about 1 side length of a substantially square is about 0.74 mm) suitable for the fiber thickness of the fiber compounding concrete for tunnel lining. The depth of the recess may be adjusted as appropriate, for example, if the thickness is narrower than this, the depth of the recess is shallow, and if the thickness is thicker, the depth is increased.
The shape of the concave portion formed in the groove portion is not particularly limited, but a shape having a length l ₁ somewhat longer than the fiber width w is desirable from the viewpoint of fixing power.

  FIG. 1A is a perspective view schematically showing a reinforcing short fiber having a substantially square cross section, which has four protruding portions (corner portions) 2 and four side portions S, and has two upper and lower portions. Shown is a case where the rhombic recesses 4 are formed on the side S, and the rectangular recesses 5 and 5 'are continuously formed at a predetermined pitch including the corners on the side where the rhombus recesses 4 are formed. Yes.

In addition, the reinforcing short fiber of the present invention is easy to form with a pair of gear rollers and embossing rollers, and the resulting reinforcing fiber is also symmetrically shaped, so that the deviation from the fiber axis, etc. Is preferable.
When the recesses formed by the embossing roller or the gear roller are too deep and the number thereof is too large, the fixing property with the cement paste is improved, but on the other hand, the tensile strength of the fiber is lowered, and sufficient reinforcement becomes difficult. On the other hand, when it is too shallow and when the number is small, the decrease in the tensile strength of the fiber is small, but the fixing property with the cement paste is lowered and the reinforcement becomes difficult. As the fiber tensile strength, according to the Japan Road Authority tunnel construction management guidelines (fiber reinforced concrete lining, September 2003), the fiber strength required for cement concrete reinforcement for tunnels is 450 N / mm ² or more. It is defined and needs to be satisfied, and the depth and the arrangement interval of the recesses are determined in consideration of these.

  A pair of upper and lower file (rhombus) embossing rollers can be used for shaping the concave portion at the groove bottom of the side portion. Moreover, a pair of upper and lower gear spur gear rollers can be used for shaping the recess on the tip side of the protrusion. Each roller has an appropriate clearance (gap) and pressure according to the thickness (fineness) of the fiber, and shaping is performed by inserting the fiber between these rollers. It is efficient and economical to form these recesses continuously following the stretching because the recesses can be shaped while the fiber is heated by the heat applied during stretching.

A pair of upper and lower gear mesh spur gear rollers can be used for shaping the recess on the tip side of the protrusion, but by adjusting the relative positions of the upper and lower gear mesh spur gear rollers, The concave and convex positions in the fiber longitudinal direction on the upper and lower sides (front and back) can be shifted and shaped, and in this way, the fiber strength reduction rate can be achieved by shaping the concave portions at the same location on the upper and lower sides of the fiber (front and back) Is preferable because it can avoid the inconvenience of being improved.
The gear-shaped spur gear roller used for shaping the concave portion on the tip end side of the projection of the present invention is a spur gear, having a tooth profile of parallel teeth, a module of 0.75, a pressure angle of 20 °, and a number of teeth of 132. The tooth tip length is 0.5 mm, the roller diameter is 100.5 mm, the roller width is 160 mm, and the gear pitch in the circumferential direction is about 2.4 mm.

On the other hand, as a method of suppressing the decrease in the strength of the fiber even if the concave portions having the depths and the intervals as described above are formed in the concave portions to the groove portions, embossing is performed for each groove in embossing of the opposing grooves. It is desirable that the position is not shifted to the same position in the fiber length direction, but is shifted and shaped.
This is possible by shifting the shaping positions of the pair of embossing rollers.
The surface shape of the embossing roller having such a concave shape in the side groove portion is engraved with multiple rows of convex portions arranged linearly along the circumferential direction in the case of a fiber having a nominal thickness of 3,300 dtex. An embossing roller, the distance between the convex parts in the circumferential direction is 1 mm to 5 mm, the distance between the multi-row convex parts in the roller width direction is 0.7 mm to 0.8 mm, and the height of the engraved convex parts is 0.5 mm. By using an embossing roller in which the tip of the convex part is processed flat into a circular shape or a polygonal shape with an emboss of about 1 mm, and the convex ends of multiple rows are arranged in a staggered pattern, a large number of drawn strands The (fiber) can be continuously processed into a recess only in the groove.
That is, since the convex part of the embossing roller is linearly arranged in the circumferential direction, each strand of the strand is coupled with the groove part of the fiber cross section and the convex part of the embossing roller. Only the bottom of the cross-sectional groove can be formed with a recess.

  Furthermore, a plurality of embossing rollers can be arranged in multiple stages within a range that does not adversely affect the physical properties of the reinforcing short fiber of the present invention, and the same groove or other grooves can be provided with a recess. In this case, the convex shape of each pair of embossing rollers is different from that of the previous stage, and different concave portions are formed in one groove or between the grooves to adjust the fixing property to the cement paste. You can also.

  In addition, when the thickness of the reinforcing fiber is changed, the multi-row convex spacing in the horizontal direction and the height of the convex portions of the embossing roller are adjusted appropriately. For example, in the case of a thick fiber, the multi-row convex portion in the horizontal direction is adjusted. It is necessary to make adjustments while taking into consideration the balance between the suppression of fiber physical properties deterioration and the fixing property with cement paste by increasing the spacing and the height of the convex portion. It is important to form continuously at predetermined intervals in the longitudinal direction of the fiber.

  In addition, the reinforced short fiber of this invention can use not only a single layer fiber but the composite fiber which uses a high melting component as a core layer, and uses a low melting component as a sheath layer. The manufacturing method of such a composite fiber is well-known.

The method for producing the reinforcing short fiber itself of the present invention is not particularly limited, and various methods can be employed. Usually, first, a resin having polypropylene as a main component is melt-spun from a nozzle having a shape corresponding to a desired substantially square cross section, and after cooling and stretching, a rectangular or fin-like shape that is continuous in the longitudinal direction of the fiber. A monolayer fiber or a composite fiber having a substantially square cross section having a protrusion is manufactured. Next, as described above, a groove corresponding to the front end width of the gear is formed on the front end side of the projection, while contacting with the gear-shaped spur gear roller on the front end side of the protrusion, and a groove portion existing between the protrusions. Next, an embossing roller having a convex part corresponding to the concave part shape is contacted, a concave part is formed in a groove on a predetermined side part, and a surface-active agent is attached, and finally cut to a desired length. Can be manufactured.
It should be noted that the order of the shape with the concave portion on the tip end side of the protrusion and the shape with the concave portion of the groove on the side portion is not particularly limited, and either may be first.

The method for spinning a substantially square single fiber having four protrusions is not particularly limited, and the cross section provided with the protrusions is, for example, an X-shaped, cross-shaped, substantially rectangular nozzle, Polypropylene resin is melt-extruded from a die and solidified by cooling, and first, continuous unstretched fibers can be obtained.
Next, the unstretched fiber obtained as described above is subjected to heat stretching and, if necessary, heat relaxation treatment. By this heat treatment, the rigidity of the fiber can be increased, and a fiber suitable for cement reinforcement having a small elongation can be obtained. The hot stretching is performed at a temperature below the melting point of the polypropylene resin and above the softening point.
As the thermal stretching method, a heating method such as a hot roll method, a hot plate method, an infrared irradiation method, a hot air oven method, a hot water method, a water vapor method and the like can be adopted. The stretching operation may be one-stage stretching, two-stage stretching, or multi-stage stretching.

Further, in the reinforced short fiber of the present invention, the single yarn fineness is preferably 3,000 to 3,500 dtex from the viewpoints of the reinforcing effect, mixing workability, dispersibility, shapeability of the concave portion in the groove portion, and the like.
If it is 3,000 dtex or more, it is possible to form a recess at the bottom of the groove with an embossing roller, and if it is less than 3,500, the number of fibers in the cement mixture will be reduced. The reinforcing effect can be effectively exhibited without a reduction in the reinforcing effect.

The reinforcing short fibers can be subjected to various treatments before or after cutting to make short fibers. For example, the surface of the fiber may be treated with a surfactant, a dispersant, a coupling agent, etc., or in the case of a polyolefin resin fiber or surface activated or crosslinked by corona discharge treatment, ultraviolet irradiation, electron beam irradiation, etc. You may perform the process of. In particular, from the viewpoint of enhancing the dispersibility when blended in a cement-based molded body, it is advantageous and preferable in terms of cost to perform surface hydrophilization treatment with a surfactant or the like.
As the surfactant, a hydrophilic surfactant is preferably used in order to improve the affinity between the hydrophobic polypropylene fiber and the cement paste. Dispersibility is improved by imparting hydrophilicity to the polypropylene fiber, and fiber reinforcing effect is improved by uniformly mixing the fiber and the cement paste.
Any hydrophilic surfactant can be used without particular limitation as long as it does not adversely affect the cement hydration reaction. Among them, a polyethylene glycol alkyl ester-based nonionic surfactant, an alkyl phosphate-based anionic surfactant, and the like. Agents, polyhydric alcohol type amide nonionic surfactants and the like can be preferably used.

As the polyethylene glycol alkyl ester, those in which the long-chain aliphatic alkyl group constituting the polyethylene glycol alkyl ester has 6 to 18, preferably 8 to 16 carbon atoms are preferable from the viewpoint of the stability of the aqueous dispersion and the fiber adhesion. Specific examples of preferable polyethylene glycol alkyl esters include polyethylene glycol laurate, polyethylene glycol oleate, and polyethylene glycol stearate.
The alkyl phosphate is a phosphate having an average carbon number of 18 or less, preferably 6 to 16, more preferably 8 to 14 alkyl groups in one molecule, preferably 1 and an alkali metal salt as a salt. , Alkaline earth metal salts, ammonium salts, and amine salts. Specific examples of preferred alkyl phosphates include salts of higher alcohol phosphates such as octyl phosphate, lauryl phosphate, stearyl phosphate, such as sodium, potassium, magnesium, calcium, and amine salts. The neutralization is preferably 50% or more of the free hydroxyl group, particularly a completely neutralized product.
As the polyhydric alcohol type amido nonion, an addition reaction product of an alkylamine having 4 to 18 carbon atoms and polyglycerin having 3 to 13 hydroxyl groups is used, preferably an alkylamine having 11 to 17 carbon atoms and 3 Addition reactants with polyglycerin having ˜6 hydroxyl groups are used.

  Other preferable surfactants include polyoxyalkylene alkylphenyl ether phosphate esters and polyoxyalkylene fatty acid esters. Specific examples of the polyoxyalkylene alkyl phenyl ether phosphate ester include polyoxyethylene nonyl phenyl ether phosphate ester, polyoxyethylene dodecyl phenyl ether phosphate ester, and specific examples of the polyoxyalkylene fatty acid ester include Examples thereof include polyoxyethylene oleate and polyoxyethylene stearate. These surfactants can be used singly or in combination of two or more.

  The amount of the surfactant attached to the fiber is not particularly limited, but it is usually used in the range of 0.05 to 2% by mass with respect to the total fiber from the viewpoint of suppressing the generation of bubbles when blending cement. If the adhesion amount to the fiber is less than 0.05% by mass with respect to the total fiber, the polyolefin fiber may not be sufficiently hydrophilic, and if it exceeds 2% by mass, the hydrophilicity will reach its peak, and the fiber kneading will be performed. It is not preferable because air bubbles are generated in various cement-based molded products represented by the time-fresh concrete, and the physical properties such as compressive strength and bending strength of the cement-based molded products may be lowered. Adhesion of 0.5% or more affects the fresh properties (air content) of the cement system, so it is necessary to adjust with a known air conditioner when blending the fibers.

  The method for attaching the surface treatment agent to the polyolefin fiber is not particularly limited, and any of a dipping method, a spray method, and a coating method can be employed. After the surface treatment agent is applied to the fiber, it can be penetrated into the fiber assembly using a squeeze roll or the like, if necessary.

The reinforcing synthetic fiber thus obtained is cut to a predetermined length and used as a cement reinforcing short fiber. From the viewpoint of improving the cracking resistance (toughness) of the cement-based molded body, the short fiber has a smaller thickness (fiber diameter D) and a longer length (fiber length L), that is, an aspect of the short fiber. The higher the ratio (L / D), the better. However, the reinforcing short fiber of the present invention has a shorter fiber length as long as the short fiber diameter is the same, even if the aspect ratio is smaller than that of the conventional product. Is also characterized by a large reinforcing effect.
The short fiber for reinforcement of the present invention has a short fiber length (apparent length) of 10 to 80 mm, preferably 15 to 70 mm, and more preferably 20 to 60 mm. If the fiber length is 10 mm or more, it is difficult for the cement to come off from the cement, and if it is within 80 mm, the dispersibility does not become poor.

  Next, the reinforcing short fiber of the present invention is used as a reinforcing fiber material in cement, fine aggregate, coarse aggregate, water and an appropriate amount of concrete admixture, or cement, fine aggregate, water and an appropriate amount of mortar admixture. It is compounded and used, and it can be set as cement-type molded objects, such as concrete and mortar. Here, as the cement, it is possible to use ordinary portland cement, blast furnace cement, silica cement, fly ash cement, hydraulic cement such as white portland cement, alumina cement, or cement such as plaster, air-cement cement such as lime. it can. Fine aggregates include river sand, sea sand, mountain sand, quartz sand, glass sand, iron sand, ash sand, and other artificial sand. Coarse aggregates include gravel, gravel, crushed stone, slag, Various artificial lightweight aggregates can be mentioned. As the admixture, an air entraining agent (AE agent), a fluidizing agent, a water reducing agent, a thickening agent, a water retention agent, a water repellent, a swelling agent and the like can be mixed and used.

  The blending amount of the reinforcing short fibers with respect to the cement is usually 0.05 to 2% by volume with respect to the volume of the cement-based molded body. From the viewpoints of uniform dispersibility of fibers at the time of cement blending, fluidity of blended cement, workability, and improvement in physical properties of cement-based molded products, the blending amount of reinforcing short fibers is preferably 0.1 to 1.5 volumes. %, More preferably in the range of 0.3 to 1% by volume.

When the short fiber for reinforcement of the present invention is used for the production of a cement-based molded body, the reinforcing short fiber is dispersed in a cement-based powder, a cement-based flash or a slurry to form a cement-based mixture, and this is a wet papermaking molding method, After molding into a predetermined shape by extrusion molding or cast molding, various cement-based molded bodies can be produced by natural curing, steam curing, autoclave curing, or the like.
More specifically, it is preferable to use a concrete mixture made of cement, fine aggregate, coarse aggregate, water or the like as base concrete, and after kneading the base concrete, the reinforcing short fibers are subsequently added and kneaded. Although the kneading time varies depending on the amount of mixing per one time, generally, the range of 45 to 90 seconds is appropriate for the mixing of the base concrete, and the range of 45 to 90 seconds is appropriate for the kneading after the reinforcing short fibers are added.

The cement-based molded body thus obtained is particularly suitable as a concrete molded body for civil engineering and construction work. For example, in the concrete road pavement field, it is possible to reduce the amount of reinforcing bars to improve the bending strength by fiber reinforcement, and to reduce the thickness of the concrete plate, which is effective for shortening the construction period and saving raw materials. In addition, when used in the tunnel inner wall spraying method, the fibers are flexible and elastic, hydrophilic and light, so there is little flaking of aggregates and fibers during spraying, less falling of concrete, and yield safety. It is effective in terms.
As a concrete product, it can also be used for sheet piles formed by molding, concrete pulp, piles, poles, etc. of hollow cylindrical products. As road concrete, it can be used for sidewalk concrete flat plates, reinforced concrete U-shaped, concrete guardrails and the like. In addition, it can also be used for plastering mortars, exterior materials and roofing materials as building-related members, and wall materials, reliefs, flooring materials, ceiling materials as interior materials.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.

Example 1 and Example 2
Using a single-screw melt extruder equipped with a nozzle having 22 holes and an X-shaped hole, isotactic polypropylene resin (WF464N; manufactured by Sumitomo Chemical Co., Ltd.) at MFR = 2 g / 10 min is used at 240 ° C. In the first drawing machine equipped with five parallel rollers while being cooled and solidified, the extruded resin is continuously taken out at a constant speed. It led to the hot water heating extending | stretching tank of 0 degreeC, and it extended 7.2 times with the 2nd extending | stretching roller. Furthermore, it led to the 129 degreeC steam heating extending | stretching tank continuously to this, and it extended | stretched 1.71 times with the 3rd extending | stretching roller, and performed the two-stage extending | stretching of 12.3 times in total.
Subsequently, the stretched strand is guided in the order of the following pair of upper and lower gear-shaped shaped rollers (first shaped roller) and the upper and lower pair of file-shaped shaped rollers (second shaped roller), Concave portions were continuously formed along the strand direction at the tip of the protrusion and the bottom of the side central groove of the X-shaped cross section.

In addition, the shape and shaping conditions of the shaping roller for shaping the recess to the protrusion are as follows.
・ First shaped roller: spur gear, tooth profile: parallel teeth, module 0.75, pressure angle 20 °, number of teeth 132, tooth tip length 0.5 mm, roller diameter 100.5 mm, roller width 160 mm, circumferential direction Gear pitch of 2.4 mm.
Using the above-mentioned first shaped roller, adjust the shortest tip clearance of the top and bottom gears to 0.46 mm, rotate the tip speed forward at the same speed as the strand speed, and dent in the top and bottom of the four protrusions on the X section A shape was added.

Moreover, the shape and shaping conditions of the 2nd shaping roller for shaping a recessed part to a side part are as follows.
・ Second shaped roller: Embossed roller, Tip shape: Rhombus shape with a short diagonal length of 0.35 mm × long diagonal length of 0.625 mm, with a convex spacing in the circumferential direction of 2.93 mm and a convex spacing in the roller width direction 1.33 mm, the height of the convex portion is 0.9 mm, the roller diameter is 101 mm, and the roller width is 160 mm.
Using the above-mentioned second shaped roller, the shortest tip clearance of the embossed convex part of the upper and lower rollers is adjusted to 0.16 mm, the surface speed is rotated forward at the same speed as the strand speed, A recess was formed in the center groove bottom.

  After shaping, the alkyl phosphate amine salt surfactant diluted with water (manufactured by Takemoto Yushi) is continuously attached to the strand so as to be about 0.07 to 0.13% by mass by spraying, What was cut into 40 mm with a fan type cutter (Example 1) and what was cut into a constant length of 48 mm (Example 2) were produced as polypropylene short fibers.

The short fiber made of polypropylene of Example 1 and Example 2 has an X-shaped cross-section, and is typically in the form shown in the perspective view of FIG. 4 and 4 ′ are provided with recesses 5 and 5 ′ at the four protrusion tips connected to the bottom of the central groove, and the recesses have a dimension such as a recess depth of 0 in FIG. .14 mm, the length l ₁ was 1.0 mm, and the distance x in the fiber length direction was 2.6 mm. On the other hand, the depth of the recess on the tip end side of the protrusion was 0.14 mm, the length l ₂ was 0.6 mm, and the distance y in the fiber length direction was 2.1 mm.
The physical properties were a fineness of 3,260 dtex and a tensile strength of 521 N / mm ² . (Fiber physical properties: see Table 1)

Comparative Example 1
Only the following pair of upper and lower gear shaped shaping rollers (first shaping roller) different from the examples are used as the shaping rollers for the drawn strand, and the following shaping conditions are as follows. A polypropylene short fiber was produced in the same manner as in Example 1 except that the thickness was only 40 mm.
First shaped roller: spur gear, tooth profile: parallel tooth, module 1.0, pressure angle 20 °, number of teeth 100, tooth tip length 0.9 mm, roller diameter 102 mm, roller width 160 mm, circumferential gear pitch 3.1 mm.
Using the first shaped roller, adjust the shortest tip clearance of the upper and lower teeth to 0.42 mm, rotate the tip speed forward at the same speed as the strand speed, and exist on the left and right connected to the opposite upper and lower sides of the X section A total of four projecting tips were formed with concave shapes.
The shape of this polypropylene short fiber is an X-shaped cross section, and concave portions are formed only at the four protrusion tip portions. Each concave portion is substantially triangular columnar, the maximum depth of the concave portion is 0.16 mm, and the length is The distance in the fiber length direction was 1.1 mm and 2.9 mm. The physical properties were a fineness of 3,300 dtex and a tensile strength of 482 N / mm ² . These results are summarized in Table 1. (Fiber physical properties: see Table 1)

Comparative Example 2 and Comparative Example 3
Polypropylene short fibers were produced in the same manner as in Example 1 except that only the pair of upper and lower file-shaped shaping rollers (second shaping roller) was used as the shaping roller for the drawn strand.
In the same manner as in Example 1 and Example 2, those cut to 40 mm with a fan-type cutter (Comparative Example 2) and those cut to 48 mm (Comparative Example 3) were produced as polypropylene short fibers.
This polypropylene short fiber has an X-shaped cross section, and the recess is formed only at the bottoms of the opposite center grooves, the recess depth of the side is 0.15 mm, the length is 1.0 mm, the fiber The distance in the length direction was 2.9 mm.
The physical properties were a fineness of 3,340 dtex and a tensile strength of 531 N / mm ² . These results are summarized in Table 1. (Fiber physical properties: see Table 1)

  The fiber physical property test method including the above fiber physical properties is described below.

[Fiber physical property test method]
(1) Fineness and tensile strength: according to JIS L 1013.
(2) Depth measurement of shaped concave part i) Depth measurement of protrusion tip part: The concave part depth of the protrusion tip part is the adjacent unattached shape at the protrusion tip part of the upper and lower shaped surfaces of the short fiber. When a tangent line is drawn between the parts, it means a perpendicular length from the tangent line to the deepest position of the concave formed part existing between the tangent lines.
In other words, the measurement method is to take a photo from the lateral direction of the top and bottom surface of the fiber, use commercially available PC image distance measurement software, or enlarge the print photo, and measure the perpendicular length on the paper using the standard scale as the measurement standard. It was measured.
ii) Depth measurement at the bottom of the side groove: The depth of the recess at the bottom of the side groove is the distance from the upper end of the non-grooved part to the lower end of the shaped part. When a tangent line is drawn between adjacent unshaped parts adjacent to each other on the upper and lower shaped surfaces, the perpendicular length from the tangent line to the deepest position of the concave shaped part existing between them is said.
The measuring method used the surface roughness measuring device (Tokyo Seimitsu Co., Ltd. product: Surfcom E-MD-S138A type | mold), and measured the recessed part depth by scanning a fiber direction range 6 mm-8 mm for a detection needle.
In both (1) and (2), the recess depths of 100 or more of 50 cut fibers collected at random were measured, and the average value was defined as the recess depth.
(3) Measuring the length of the concave portion The length of the concave portion means the length of the concave portion stamped by the shaping roller in the fiber length direction.
The measurement was performed by taking a photograph of the fiber top / bottom shaped surface and using commercially available personal computer image distance measurement software, or by printing an enlarged photograph, and measuring the recess length on paper using the standard scale as a measurement standard.
(4) Measurement of distance between recesses The number of recesses per cut fiber length was counted and calculated as fiber length / number of recesses. This was measured in the same manner with 100 cut fibers, and the average value was defined as the recess interval.
(5) Fiber length The fiber length of 100 cut fibers was measured with calipers, and the average value was defined as the fiber length.

Next, using the fibers of Examples 1 and 2 and Comparative Examples 1 to 3, as a scale representing the fixability with cement, the embedded fiber pull-out test (pulling resistance measurement), and the fiber-mixed concrete compression test, bending Tests (bending strength and bending toughness coefficient measurement) were performed.
[Fiber pulling resistance]
After embedding approximately 15 mm of fiber in cement mortar and curing in air at room temperature for 7 days, pull the fiber from cement at a rate of 2 mm / min with Tensilon, and measure the maximum value of stress (pulling resistance) at that time did.
The cement mortar uses early-strength cement mortar (Toyo Materan Co., Ltd. product: early-strength Portland cement and silica sand pre-mixed product), and water content = water 214 (cc) / early-strength cement mortar 1 (kg) A kneaded mixture was used.
In comparing the drawing resistance value due to the difference in the shape of the concave portion of the fiber, the measured embedded length of each fiber measurement sample was measured, and this was proportionally converted to the embedded length per 15 mm to obtain the drawing resistance value. The results are shown in Table 1.

[Compression and bending property test of fiber blended concrete]
(1) Using the prepared 50L forced biaxial mixer concrete physical tests specimen, so that the total volume of 35L, cement 350 kg / m ^3, fine aggregates 873kg / m ^3, coarse aggregate 900 kg / m ^3, water The mixture was kneaded in advance for 90 seconds at a blending ratio of 175 kg / m ³ and a high-performance AE water reducing agent 2.8 kg / m ³ . Next, the fibers of Examples 1 and 2 and Comparative Examples 1 to 3 were added at a blending ratio of 2.73 kg / m ³ , respectively, and further kneaded for 45 seconds.
Using the obtained fresh concrete, specimens for compression and bending tests were prepared according to JSCE-F552-1983 (How to make specimens for strength and toughness test of steel fiber reinforced concrete).
The specimens were subjected to room temperature mold curing for 24 hours, then demolded, and then water-cured until the age of 28 days was used as specimens.
Materials used:
・ Cement: Normal portland cement (specific gravity: 3.16, made by Taiheiyo Cement)
・ Fine aggregate:
S1: Land sand (surface dry density: 2.60 g / cm ³ , coarse particle ratio: 2.40), Kamisu S2: Crushed sand (surface dry density: 2.70 g / cm ³ , coarse particle ratio: 3.10) S1 and S2 from Sano (Karasawa Mine) were mixed at a weight ratio of 7: 3.
・ Coarse aggregate: Crushed stone (surface dry density: 2.67 g / cm ³ , maximum particle size 25 mm), Ishioka (Someya, Ishioka city) ・ Water: municipal water ・ High-performance AE water reducing agent: Leo build SP8SV X2.5 (BASF Pozzolith) (Made by company)

[Observation of fiber condition on concrete fracture surface]
After carrying out the bending physical property test, the specimen was completely separated at the crack surface, and the pulled-out state and the cut state of the fiber on the fracture surface were visually observed. The number of fibers that can be visually confirmed on both fractured surfaces is classified into the number by pulling and the number by cutting, and the total number is counted, and the respective occupation ratio (drawing rate, cutting rate) is calculated in 100 minutes (%). did. The results are shown in Table 1.

[Concrete property test method]
-Bending strength and bending toughness test: According to JHS 730-2002 (bending toughness test method for fiber-reinforced lining concrete).
Compressive strength: According to JIS A 1108 (Method for testing compressive strength of concrete).
-Slump test: According to JIS A 1118 (concrete slump, air volume test).
-Air quantity test: Follow JIS A 1118 (concrete slump, air quantity test).

Loading workability and dispersibility (1) Fiber opening property test Fiber opening grid installed in the input hopper of the fiber input machine to the agitator car (outside dimensions: 490 mm x 700 mm; grid interval: 75 mm constant, grid Material: φ2.5SUS rod), and the time for a person to manually pass 3 kg of fiber was measured.
-Fiber of Example 1 (fiber length 40 mm): 40, 37, 42, 44, 35 seconds (average: 40 seconds)
-Fiber of Example 2 (fiber length 48 mm): 55, 65, 62, 54, 60 seconds (average: 59 seconds)
-Fiber of Comparative Example 1 (fiber length 40 mm): 57, 46, 51, 48, 51 seconds (average: 51 seconds)
-Fiber of Comparative Example 2 (fiber length 40 mm): 43, 37, 40, 38, 41 seconds (average: 40 seconds)
-Fiber of Comparative Example 3 (fiber length 48 mm): 65, 64, 59, 58, 60 seconds (average: 61 seconds)
Usually, when the fiber is shaped on the surface, the restraint between the fibers increases and the spreadability decreases, but the fibers of the examples of the present invention are compared with the fibers of the comparative examples in comparison with the same fiber length. The spreadability is not deteriorated, and good spreadability is maintained. Therefore, the fiber of the embodiment can easily open (break apart) the fiber mass, can suppress the cement fresh hardening due to the time required for the fiber input at the time of the implementation, and can reduce the cement fresh. The inside fiber dispersion can be maintained well. Therefore, it can contribute to the improvement of workability in concrete placing.

(2) Concrete dispersibility test of fiber 12.3 kg (corresponding to 0.3 vol%) of the fiber of the example and the fiber of the comparative example in a mixer drum high-speed rotation state on an agitator vehicle loaded with 4.5 m ³ of fresh concrete ) For about 3 minutes (Example 1 with a fiber length of 40 mm and Comparative Example 2 fiber), about 3.5 minutes (Comparative Example 1 with a fiber length of 40 mm) Fiber) 4.4 minutes (fibers of Example 2 and Comparative Example 3 having a fiber length of 48 mm), and kneading was continued for 2 minutes. The fiber-mixed fresh concrete was discharged from the agitator wheel, and the mixed and dispersed state of the fibers was visually observed using a shovel at each of the start, middle and end of the concrete.
The fiber of the example and the fiber of the comparative example were not inferior and both dispersibility was good.
The above results are summarized in Table 1.

As is clear from Table 1, the reinforcing short fiber of Example 1 of the present invention has a drawing resistance value of about 1.2 to 1.7 times larger than that of Comparative Examples 1 and 2, and as a result, a concrete specimen. The bending toughness coefficient of the steel also increased.
In particular, the fibers on the specimen fracture surface using the fiber length of 48 mm in Example 2 were cut at a rate of 55%, and more than half were cut, and the fixability to cement was extremely excellent.
Also in the toughness curve in the bending toughness test, the stress behavior of the concrete specimen using the fiber of Example 2 repeats a small stress drop and recovery as the bending deflection increases, as shown in FIG. Therefore, it can be interpreted that a part of the fiber existing at the position in the direction of the load lower surface in a tension state is broken. The fibers of Comparative Examples 2 and 3 also exceeded the design standard bending strength (4.1 kN) and the managed bending toughness coefficient (1.40 N / mm ² ). As can be seen, in comparison with the examples, the fiber lengths were the same, and each example exceeded the load of the comparative example.
This result shows that the cement fixability due to the shaping applied to the fiber of Example 2 exceeded the tensile strength of the fiber present on the fracture surface, and is extremely excellent in the fixability with cement. Represents that.
In addition, the reinforcing short fibers of the examples of the present invention were excellent with no problems in terms of workability for feeding fibers into an agitator vehicle and dispersibility in concrete.
As is clear from Table 1, the reinforcing short fiber of Example 1 of the present invention has a higher tensile strength and a pulling resistance value of about 1.7 times that of the fiber of Comparative Example 1, and has a fixing property with cement paste. It was very good.
In addition, the reinforcing short fibers of Example 1 of the present invention were superior to the reinforcing short fibers of the comparative example in terms of workability for feeding fibers into an agitator vehicle and dispersibility in concrete.
And the concrete molding using the fiber of an Example had a larger bending toughness coefficient than the concrete using the fiber of a comparative example, and was excellent in the reinforcement effect.

  The reinforcing short fiber for cement-based molded body of the present invention is excellent in the charging work and workability when blended with concrete, and has a high fiber reinforcing effect. Therefore, various types of tunnel lining, road floor, viaduct, etc. It can be effectively used as a reinforcing short fiber for cement moldings in civil engineering and architectural applications.

It is a schematic perspective view of the reinforcing short fiber for cement-based molded article of the present invention having (A) a substantially square cross section and (B) a substantially X-shaped cross section. It is a schematic diagram of one embodiment (X-shaped cross section) of the reinforcing short fiber for cement-based molded article of the present invention. (A) Schematic plan view, (B1), (B2), (B3) YY arrow sectional view (form example), (C1) ZZ arrow side view (shaped part), (C2) Z '-Z' side view (unattached part) 2 is a plan photograph and a side photograph of a reinforcing short fiber for cement-based molded article of the present invention obtained in Example 1. FIG. It is a load-deflection curve of the bending toughness test of the concrete using the reinforced short fiber for cement-type molded objects of Example 1 (fiber length 40mm) of this invention. It is a load-deflection curve of the bending toughness test of the concrete using the reinforcing short fiber for cement-type molded objects of Example 2 (fiber length 48mm) of this invention. It is a load-deflection curve of the bending toughness test of the concrete using the reinforced short fiber for cement-type molded objects of the comparative example 2 (fiber length 40mm) of this invention. It is a load-deflection curve of the bending toughness test of the concrete using the reinforced short fiber for cement-type molded objects of the comparative example 3 (fiber length 48mm) of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reinforcing short fiber 2 Protrusion part S Side part 3 Groove part 4, 4 'Concave part formed in the side part 5, 5' Concave part formed in the front-end | tip of a projection part

Claims (3)

  A drawn fiber having a polypropylene resin as a main component, wherein the cross-sectional shape of the fiber is a substantially quadrangle having four protrusions, and a predetermined length along the longitudinal direction of the fiber on two opposing faces of the substantially quadrangle Reinforcing short fibers for a cement-based molded article, comprising: concave portions shaped at intervals; and concave portions shaped at predetermined intervals along the longitudinal direction of the fibers in the substantially square protrusions . The fineness is 3,000 to 3,500 dtex, the depth of the concave portion on the side is 0.1 to 0.2 mm, the length is 0.8 to 1.2 mm, and the arrangement interval of the concave portions in the fiber longitudinal direction is 2. 0.5 to 3.5 mm, the depth of the concave portion of the protrusion is 0.1 to 0.2 mm, the length is 0.5 to 0.7 mm, and the arrangement interval of the concave portion in the fiber longitudinal direction is 2.0. The reinforcing short fiber for cement-based molded article according to claim 1, which is ˜3.0 mm.   The reinforcing short fiber for cement-based molded body according to claim 1 or 2, wherein the substantially square cross section is an X shape.

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