Hydraulic composition and cured product

Abstract

The present invention relates to a hydraulic composition for additive manufacturing, said hydraulic composition comprising hydrophilic fibers which have a single filament linear density of not more than 50 dtex or a single filament fiber diameter of not more than 70 μm, and which have an equilibrium moisture content of not less than 1.5%.

Description

Hydraulic composition and cured product

[0001] The present invention relates to a hydraulic composition for additive manufacturing and a cured product of the hydraulic composition.

[0002] One known additive manufacturing technique, also known as 3D printing, is a material extrusion technique in which a fluid material is extruded through a nozzle to form layers. In material extrusion additive manufacturing, materials such as thermoplastic resins and hydraulic compositions such as cement and mortar are used.

[0003] Additive manufacturing techniques using hydraulic compositions as materials have attracted attention for their advantages, such as the simplification of the manufacturing process for hardened hydraulic compositions and the ability to mold them into any shape without using a formwork, since they do not require a formwork that is typically required when molding and hardening a hydraulic composition into a desired shape. Patent Document 1, for example, discloses a fiber-reinforced mortar used for extrusion lamination by an additive manufacturing device as a hydraulic composition used in additive manufacturing techniques. Patent Document 2 also discloses a hydraulic composition with added fibers as a conventional hydraulic composition not for additive manufacturing.

[0004] JP 2022-124859 A International Publication No. 2020 / 137466

[0005] It is known that resin fibers such as modified polyvinyl alcohol are added to conventional hydraulic compositions not intended for additive manufacturing in order to increase the strength of the resulting cured product, but conventional hydraulic compositions cannot be used as they are for additive manufacturing. In particular, it has been difficult to apply conventional hydraulic compositions directly to additive manufacturing because the material needs to be extruded from a nozzle or the like and the cured product often has a complex and large shape.

[0006] Additive manufacturing technology has the advantage of eliminating the manufacturing process because it does not require a mold, and of being able to create any shape without a mold, but because there is no mold, moisture tends to evaporate from the surface, which can lead to insufficient hydraulic reactions, especially near the surface where the moisture content is low. Also, while it has the advantage of being able to create complex shapes, the complex shape increases the surface area that comes into contact with air, which can easily lead to variations in the moisture content within the molded body, causing variations in the progress of the hydraulic reaction, which can result in insufficient strength in the hardened product, or the occurrence of cracks due to variations in strength.

[0007] Therefore, an object of the present invention is to provide a hydraulic composition that can easily suppress variations in the water content in the formed hydraulic composition during hardening, and that can sufficiently promote the hydraulic reaction, particularly on the surface where water is likely to be insufficient.

[0008] The present inventors conducted extensive research to solve the above-mentioned problems and have now completed the present invention. That is, the present invention encompasses the following preferred embodiments. [1] A hydraulic composition for additive manufacturing, comprising a hydrophilic fiber having a single filament fineness of 50 dtex or less or a single filament fiber diameter of 70 μm or less, and an equilibrium moisture regain of 1.5% or more. [2] The hydraulic composition according to [1], wherein the single filament fineness of the hydrophilic fiber is 15 dtex or less. [3] The hydraulic composition according to [1] or [2], wherein the water absorption of the hydrophilic fiber is 6.0% or more. [4] The hydraulic composition according to any one of [1] to [3], wherein the aspect ratio of the hydrophilic fiber is 50 to 400. [5] The hydraulic composition according to any one of [1] to [4], wherein the fiber length of the hydrophilic fiber is 10 mm or less. [6] The hydraulic composition according to any one of [1] to [5], wherein the volume ratio of the hydrophilic fiber is 0.1 to 10% when the volume of the matrix of the hydraulic composition is taken as 100. [7] The hydraulic composition according to any one of [1] to [6], wherein the single filament fineness of the hydrophilic fiber is 0.1 dtex or more. [8] The hydraulic composition according to any one of [1] to [7], wherein the fiber length of the hydrophilic fiber is 0.5 mm or more. [9] The hydraulic composition according to any one of [1] to [8], wherein the dispersion degree of the hydrophilic fiber in the hydraulic composition is 60% or more.

[10] The hydraulic composition according to any one of [1] to [9], wherein the ratio (W / B) of the mass of water (W) to the total mass of binder (B) in the hydraulic composition is 0.1 to 0.40.

[11] A cured product of the hydraulic composition according to any one of [1] to

[10] .

[12] A hydrophilic fiber used in additive manufacturing of a hydraulic composition molded body, the hydrophilic fiber having an equilibrium moisture regain of 1.5% or more and / or a water absorption rate of 6.0% or more, a single filament fineness of 50 dtex or less and / or a single filament fiber diameter of 70 μm or less.

[13] A converging yarn used in additive manufacturing of a hydraulic composition molded body, the converging yarn having an equilibrium moisture regain of 1.5% or more and / or a water absorption rate of 6.0% or more, a single filament fineness of 50 dtex or less and / or a single filament fiber diameter of 70 μm or less.

[14] A hydraulic composition for additive manufacturing, the hydraulic composition comprising a hydrophilic fiber having a single filament fiber diameter of 70 μm or less and a water absorption rate of 6.0% or more.

[15] The hydraulic composition according to

[14] , wherein the fiber length of the hydrophilic fibers in the hydraulic composition is 16 mm or less.

[16] The hydraulic composition according to

[14] or

[15] , wherein the aspect ratio of the hydrophilic fibers is 50 to 400.

[17] The hydraulic composition according to any one of

[14] to

[16] , wherein the fiber length of the hydrophilic fibers is 10 mm or less.

[18] The hydraulic composition according to any one of

[14] to

[17] , wherein the volume ratio of the hydrophilic fibers is 0.1 to 10% when the volume of the matrix of the hydraulic composition is taken as 100.

[19] The hydraulic composition according to any one of

[14] to

[18] , wherein the single filament fineness of the hydrophilic fibers is 0.1 dtex or more.

[20] The hydraulic composition according to any one of

[14] to

[19] , wherein the fiber length of the hydrophilic fibers is 0.5 mm or more.

[21] The hydraulic composition according to any one of

[14] to

[20] , wherein the dispersion degree of the hydrophilic fibers in the hydraulic composition is 60% or more.

[22] The hydraulic composition according to any one of

[14] to

[21] , wherein the ratio (W / B) of the mass of water (W) to the total mass of binders (B) in the hydraulic composition is 0.1 to 0.40.

[23] A cured product of the hydraulic composition according to any one of

[14] to

[22] .

[0009] According to the present invention, it is possible to provide a hydraulic composition that can easily suppress variations in the water content in the hydraulic composition during hardening after molding, and that can sufficiently promote the hydraulic reaction, particularly on the surface where water is likely to be insufficient.

[0010] Hereinafter, embodiments of the present invention will be described in detail, but it is not intended that the present invention be limited to the following embodiments.

[0011] (Fiber) The hydraulic composition of the present invention is a hydraulic composition for additive manufacturing, and contains fibers having a single filament fineness of 50 dtex or less or a single filament fiber diameter of 70 μm or less and an equilibrium moisture regain of 1.5% or more.

[0012] The fibers contained in the hydraulic composition of the present invention have a single filament fineness of 50 dtex or less or a single filament diameter of 70 μm or less. If neither of the above conditions is met, i.e., if the single filament fineness exceeds 50 dtex and the single filament diameter exceeds 70 μm, the variation in the hydraulic reaction in a molded product of the hydraulic composition cannot be sufficiently suppressed. While the reason for this is unclear, it is understood that the fibers having a certain degree of fineness can increase the total surface area of ​​the fibers capable of retaining moisture, and the fibers retaining moisture on their surfaces form a dense network in the hydraulic composition. This is thought to suppress variation in the moisture content in the hydraulic composition during molding and hardening, suppress variation in the progress of the hydraulic reaction, and ultimately produce a hardened product with excellent mechanical properties. If the single filament fineness exceeds 50 dtex and the single filament diameter exceeds 70 μm, the fibers are thick and long, making it difficult to form a dense network of fibers capable of retaining moisture. Furthermore, it is believed that by adding a fibrous hydrophilic substance, the network formed makes it easier to reduce variations in hydraulic reaction compared to when, for example, a particulate hydrophilic substance is added.

[0013] From the viewpoint of suppressing variations in the water content in the molded hydraulic composition during hardening and from the viewpoint of fiber dispersibility, the single fiber fineness is preferably 50 dtex or less, more preferably 20 dtex or less, even more preferably 15 dtex or less, still more preferably 12 dtex or less, and may be 9 dtex or less. From the viewpoint of suppressing variations in the water content in the molded hydraulic composition during hardening, the single fiber fineness is preferably 0.1 dtex or more, more preferably 0.3 dtex or more, and even more preferably 0.5 dtex or more. The fiber fineness represents the weight per 10,000 m of fiber and is measured in accordance with JIS L1015 "Test Method for Chemical Fiber Staple (8.5.1)."

[0014] From the viewpoint of water retention, the single fiber diameter of the hydrophilic fiber is preferably 70 μm or less, more preferably 5 to 70 μm, even more preferably 5 to 39 μm, even more preferably 5 to 38.5 μm, particularly preferably 6 to 35 μm, especially preferably 6 to 30 μm, and particularly preferably 7 to 27 μm. The single fiber diameter of the hydrophilic fiber is the average fiber diameter, and is measured by the method described above for calculating the aspect ratio. The cross-sectional shape of the fiber is selected according to the purpose, such as circular, elliptical, or irregular cross-section. From the viewpoint of increasing the surface area of ​​the fiber and improving the water retention effect of the fiber, irregular cross-sections are preferred, while circular or elliptical cross-sections are preferred from the viewpoint of improving fluidity. In measuring the single fiber diameter, if the cross-sectional shape is circular, the diameter is measured, and if the cross-sectional shape is irregular, the cross-sectional area is measured, and the diameter of a circle having the same area as the obtained cross-sectional area is calculated, and this is used as the converted diameter.

[0015] The fiber has an equilibrium moisture content of 1.5% or more. If the equilibrium moisture content is less than 1.5%, the formed hydraulic composition cannot retain moisture during hardening, and moisture content variations cannot be sufficiently suppressed. As a result, the hardening reaction, particularly near the surface, becomes insufficient or varies. While the reason for this is unclear, it is believed that if the fiber has an equilibrium moisture content of less than 1.5%, the fiber is unable to retain moisture, and therefore is unable to distribute moisture to the surface even when the moisture content near the surface decreases due to drying. From the viewpoint of moisture retention, the fiber's equilibrium moisture content is preferably 1.8% or more, more preferably 2.0% or more, and even more preferably 2.2% or more. Furthermore, from the viewpoint of preventing poor hardening at the fiber interface due to excess retained water, the fiber's equilibrium moisture content is preferably 10.0% or less, more preferably 8.0% or less, and even more preferably 6.0% or less. The equilibrium moisture regain of a fiber refers to the moisture regain measured after bone drying at a temperature of 20°C and a relative humidity of 65% RH for 72 hours, in accordance with JIS L1015 "Testing Methods for Chemical Fiber Staples." An equilibrium moisture regain of 1.5% or more indicates that the fiber is a hydrophilic fiber, and in this specification, fibers with an equilibrium moisture regain of 1.5% or more are also referred to as hydrophilic fibers. In one embodiment of the present invention, the equilibrium moisture regain of the fiber is preferably 1.5 to 10.0%, more preferably 1.8 to 8.0%, even more preferably 2.0 to 6.0%, and even more preferably 2.2 to 6.0%.

[0016] The water absorption of the fiber is preferably 6.0% or more. When the water absorption of the fiber is 6.0% or more, it is possible to improve the water retention in the molded hydraulic composition during hardening and also to sufficiently suppress the variation in the water content. Therefore, it is preferable from the viewpoint of enhancing the curing reaction, particularly near the surface, and suppressing the variation in the curing reaction. Although the reason for this is not clear, it is thought that when the water absorption of the fiber is 6.0% or more, the water retention ability of the fiber is high, so that even if the water content near the surface decreases due to drying, it is possible to distribute water to the surface portion. From the viewpoint of water retention, the water absorption of the fiber is preferably 6.0% or more, more preferably 7.0% or more, even more preferably 8.0% or more, and even more preferably 9.0% or more. In addition, from the viewpoint of preventing poor curing at the fiber interface due to excessive retained water, the water absorption of the fiber is preferably 100.0% or less, more preferably 50.0% or less, even more preferably 30.0% or less, still more preferably 20.0% or less, and may be 15.0% or less, or may be 10.0% or less. In one embodiment of the present invention, the water absorption of the fiber is preferably 6.0 to 100.0%, more preferably 7.0% to 50.0%, even more preferably 8.0% to 30.0%, still more preferably 9.0% to 20.0%, and particularly preferably 9.0% to 10.0%. The water absorption rate is a value calculated by the following formula, where A is the mass of the fiber after stirring the fiber in a 0.1 mol / L NaOH aqueous solution (pH 13) at 30°C for 4 minutes and then spinning it in a centrifugal spin dryer at 3000 rpm for 5 minutes three times, and B is the mass of the fiber after spin drying in a dryer at 100°C for 16 hours. Formula: Water absorption rate = 100 x (A - B) / B (%)

[0017] From the viewpoint of suppressing variations in the hydraulic reaction, the aspect ratio of the hydrophilic fiber is preferably 50 to 400, more preferably 60 to 350, even more preferably 10 to 300, still more preferably 70 to 300, even more preferably 100 to 300, particularly preferably 150 to 300, and may be 200 to 250. Specifically, the aspect ratio can be 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, etc. When the hydrophilic fiber has an aspect ratio within the above range, it is considered that a network for distributing moisture to areas in the hydraulic composition where moisture is insufficient is easily formed. The aspect ratio refers to the ratio (L / D) of fiber length (L) to fiber diameter (D). The aspect ratio is calculated by calculating the average fiber length in accordance with JIS L1015 "Testing Method for Chemical Fiber Staples (8.5.1)" and then calculating the ratio to the average fiber diameter. The average fiber diameter is obtained by randomly selecting 20 fibers and measuring the fiber diameter at the center of each fiber in the longitudinal direction using an optical microscope.

[0018] From the viewpoint of suppressing variations in the hydraulic reaction, the fiber length of the hydrophilic fiber is preferably 10 mm or less, more preferably less than 10 mm, even more preferably 0.5 mm or more and 10 mm or less, even more preferably 0.5 mm or more and less than 10 mm, and particularly preferably 0.5 mm to 9 mm, or 0.5 mm to 8 mm. From the same viewpoint, the fiber length of the hydrophilic fiber may be preferably 0.5 mm or more and less than 8 mm, 1.0 to 6.0 mm, or 1.5 to 5.0 mm. When the fiber length is 10 mm or less, the network of the fibers that retain moisture becomes denser, and variations in the moisture content in the hydraulic composition are more easily suppressed. The fiber length of the hydrophilic fiber is the average fiber length, and is measured by the method described above for calculating the aspect ratio.

[0019] The fibers are not particularly limited as long as they satisfy the above-mentioned single fiber fineness and equilibrium moisture regain, and examples thereof include synthetic polymer fibers such as polyvinyl alcohol (hereinafter sometimes referred to as PVA) fibers, polyamide fibers (including aramid fibers), acrylic fibers, and rayon fibers (polynosic fibers, solvent-spun cellulose fibers, etc.).Fibers made of hydrophobic resins whose fiber surfaces have been made hydrophilic by surface treatment or coating can also be used.

[0020] The PVA-based fiber is a fiber containing a vinyl alcohol-based polymer. From the viewpoints of mechanical performance, adhesion to hydraulic materials, and alkali resistance, the fiber preferably contains 30% by mass or more of the vinyl alcohol-based polymer, more preferably 60% by mass or more, and even more preferably 80% by mass or more. The fiber is preferably a PVA-based fiber from the viewpoints of retaining moisture in the formed hydraulic composition during hardening and allowing the hydraulic reaction to proceed sufficiently and uniformly, thereby increasing the strength of the resulting molded body. When the fiber is a PVA-based fiber, the denseness after hardening is not lost, and the strength of the molded body is less likely to decrease. Furthermore, when the fiber is a PVA-based fiber, due to its molecular structure, it is highly hydrophilic, and the interaction between the hydroxyl groups of the fiber and the calcium in the cement improves the affinity between the fiber and cement, making it easier to increase chemical adhesion and suppress cracking in the final hardened product.

[0021] The vinyl alcohol polymer constituting the PVA fiber may be a homopolymer of vinyl alcohol, or may be a copolymer of vinyl alcohol and other monomers, or may be modified, as long as the effects of the present invention are not impaired. From the viewpoint of easily improving the mechanical strength, alkali resistance, hot water resistance, etc. of the fiber, when the amount of all monomer units constituting the vinyl alcohol polymer is taken as 100 mol%, the total amount of structural units derived from optionally contained modified polyvinyl alcohol monomers and the amount of optionally contained monomers other than vinyl alcohol is preferably 30 mol% or less, more preferably 10 mol% or less.

[0022] The viscosity-average degree of polymerization of the vinyl alcohol polymer constituting the PVA fiber is preferably 1,000 or more, more preferably 1,500 or more, from the viewpoint of easily improving the mechanical strength, alkali resistance, and hot water resistance of the fiber. From the viewpoint of easily reducing the production cost of the vinyl alcohol polymer, the viscosity-average degree of polymerization is preferably 10,000 or less, more preferably 5,000 or less, and even more preferably 3,000 or less. The viscosity-average degree of polymerization is as described below for modified polyvinyl alcohol.

[0023] The degree of saponification of the vinyl alcohol polymer constituting the PVA fiber is preferably 99 mol% or more, more preferably 99.5 mol% or more, and even more preferably 99.8 mol% or more, from the viewpoints of heat resistance, durability, and dimensional stability of the fiber. The upper limit of the degree of saponification is 100 mol% or less. The method for measuring the degree of saponification is as described below for modified polyvinyl alcohol.

[0024] The fibers contained in the hydraulic composition of the present invention may be fibers made of one type of polymer, or may be composite fibers made of two or more types of polymers. Examples of the shape of the composite fibers include an islands-in-the-sea type, a core-sheath type, and a side-by-side type.

[0025] The method for producing the fibers contained in the hydraulic composition of the present invention is not particularly limited, and general melt spinning, solution spinning, dry spinning, etc. can be used. The fibers contained in the hydraulic composition of the present invention can be produced, for example, by the following method. For example, when the fibers are PVA-based fibers, a vinyl alcohol-based polymer is formed into aqueous chips with a concentration of 40 to 60% by mass, which are then heated, dissolved, and degassed in an extruder. A crosslinking agent is then added to this aqueous vinyl alcohol-based polymer solution. Examples of crosslinking agents include ammonium sulfate, sulfuric acid, ammonium phosphate, phosphoric acid, hydrochloric acid, nitric acid, acetic acid, and oxalic acid. However, ammonium sulfate is preferred because it does not corrode pipes, does not emit a foul odor, and does not foam the fibers. The amount of crosslinking agent added is preferably 0.5 to 10% by mass relative to the mass of the vinyl alcohol-based polymer. The temperature of the spinning dope is preferably 90 to 140°C. The spinning dope containing such a crosslinking agent is pressurized and discharged into the air through a nozzle hole, followed by dry spinning. The nozzle hole may be circular or may have a shape other than circular, such as a flat, cross, T-shape, Y-shape, L-shape, triangle, square, star shape, etc. The spinning method may be any of a wet method, a dry-wet method, and a dry method.

[0026] Next, the spun fibers are dried. The drying temperature is usually 100° C. or lower, and once drying has been completed to a certain extent, it is preferable to dry the fibers completely at a temperature of 100° C. or higher.

[0027] After drying, the fiber is stretched. The stretching is usually carried out at a stretching temperature of 200 to 250°C, preferably 220 to 240°C. The stretching ratio is usually 5 times or more, preferably 6 times or more. The stretching is carried out in a hot air stretching oven for about 20 seconds to 3 minutes. The stretched fiber is optionally heat-treated to achieve a fixed length or shrinkage. The fiber thus obtained may be crimped or coated with an oil agent as necessary. When the fiber is a polyvinyl alcohol-based fiber, a crosslinking agent added to the spinning dope reacts with the OH groups of the polyvinyl alcohol during stretching to form crosslinks.

[0028] (Hydraulic composition) The hydraulic composition of the present invention is a hydraulic composition for additive manufacturing, and is a composition containing fibers having a single fiber fineness of 15 dtex or less and an equilibrium moisture regain of 1.5% or more. In addition to the above-mentioned fibers, the hydraulic composition may contain binders, aggregates, other components, and water.

[0029] Binders are substances that undergo hydration in the presence of water to form solid hydrates or hydrated phases. Examples of binders include cement components. Examples of cement components include Portland cements such as ordinary Portland cement, high-early-strength Portland cement, extra-high-early-strength Portland cement, and moderate-heat Portland cement, alumina cement, blast-furnace cement, silica cement, and fly ash cement. Examples of binders other than cement components include slag, fly ash, silica fume, pozzolana, hydraulic lime, and the like. These binders may be used alone or in combination.

[0030] As the aggregate, various aggregates can be used as needed. Examples of such aggregates include fine aggregate, lightweight aggregate, and coarse aggregate. These aggregates may be used alone or in combination of two or more.

[0031] The fine aggregate may be one having a particle size of 5 mm or less, such as sands having a particle size of 5 mm or less; fine aggregates obtained by powdering or granulating inorganic materials such as silica stone, fly ash, blast furnace slag, volcanic ash-based shirasu, various sludges, and rock minerals. These fine aggregates may be used alone or in combination of two or more. Examples of sands include river sand, mountain sand, sea sand, crushed sand, silica sand, slag, glass sand, iron sand, ash sand, calcium carbonate, and artificial sand. These fine aggregates may be used alone or in combination of two or more.

[0032] Examples of lightweight aggregates include natural lightweight aggregates such as volcanic gravel, expanded slag, and charcoal husk, as well as perlites such as expanded perlite and expanded black rock, mesalites such as expanded shale, vermiculite, shirasu balloons, and fly ash microballoons. These lightweight aggregates may be used alone or in combination.

[0033] The coarse aggregate is an aggregate containing 85% by mass or more of particles with a particle size of 5 mm or more. The coarse aggregate may be composed of particles with a particle size of more than 5 mm. Examples of coarse aggregate include various types of gravel, artificial aggregate (such as blast furnace slag), and recycled aggregate (such as recycled aggregate from construction waste). These coarse aggregates may be used alone or in combination of two or more types.

[0034] The hydraulic composition may contain a functional aggregate in addition to the aggregate described above. Examples of functional aggregates include colored aggregates, hard aggregates, elastic aggregates, and aggregates having specific shapes. Specific examples include layered silicates (e.g., mica, talc, and kaolin), alumina, and silica. The ratio of the functional aggregate to the aggregate can be appropriately set depending on the type of aggregate. For example, the mass ratio of the aggregate to the functional aggregate (aggregate / functional aggregate) may be 99 / 1 to 70 / 30, preferably 98 / 2 to 75 / 25, and more preferably 97 / 3 to 80 / 20. These functional aggregates may be used alone or in combination of two or more types.

[0035] The mass ratio of the total amount of aggregate (S) to the total mass of binder (B) (aggregate (S) / binder (B)) may be preferably 1 / 10 to 5 / 1, more preferably 1 / 8 to 4 / 1, and even more preferably 1 / 6 to 3 / 1.

[0036] The hydraulic composition may contain various admixtures as needed. Examples of admixtures include air-entraining agents, superplasticizers, water-reducing agents, high-performance water-reducing agents, air-entraining water-reducing agents, high-performance air-entraining water-reducing agents, thickeners, water-retention agents, water-repellents, expanding agents, hardening accelerators, setting retarders, and polymer emulsions (acrylic emulsions, ethylene-vinyl acetate emulsions, and SBR (styrene butadiene rubber) emulsions). The admixtures may be contained alone or in combination. The polymer emulsion not only strengthens the final molded body, but also enhances the adhesive strength between components in the molded body. Furthermore, the combination of a polymer emulsion not only improves the water-resistance of the molded body, but also suppresses excessive drying.

[0037] In a preferred embodiment, the hydraulic composition contains an admixture, preferably an air-entraining water-reducing admixture. In this case, the mass ratio of the total mass of the binders (B) contained in the hydraulic composition to the admixture (SP) (binder (B) / admixture (SP)) may be preferably 1 / 0.001 to 1 / 0.05, more preferably 1 / 0.002 to 1 / 0.03, and even more preferably 1 / 0.005 to 1 / 0.02.

[0038] The hydraulic composition may contain a water-soluble polymeric substance as needed. The water-soluble polymeric substance in this embodiment excludes hydrophilic fibers having a single fiber fineness of 15 dtex or less and an equilibrium moisture regain of 1.5% or more. Examples of water-soluble polymeric substances include cellulose ethers such as methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and hydroxypropyl methyl cellulose, polyvinyl alcohol, polyacrylic acid, and lignin sulfonates. These water-soluble polymeric substances may be used alone or in combination.

[0039] The amount (weight) of the hydrophilic fibers contained in the hydraulic composition can be appropriately set depending on the type, fiber length, aspect ratio, etc. of the hydrophilic fibers. For example, it is preferably 1 to 70 kg / m based on the volume of the finally obtained molded product (cured product). ３, more preferably 2 to 40 kg / m ３ , more preferably 2 to 30 kg / m ３ When the amount of hydrophilic fibers added is within the above range, the water retention and distribution effects of the hydrophilic fibers are easily enhanced, and entanglement of fibers due to an excessive fiber content is easily suppressed, so that the above effects of the hydrophilic fibers are easily improved.

[0040] Furthermore, the volume ratio of the hydrophilic fibers contained in the hydraulic composition, when the volume of the hydraulic composition matrix is ​​taken as 100, is preferably 0.1 to 10%, more preferably 0.3 to 8%, even more preferably 0.5 to 6%, and particularly preferably 1.0 to 5%. Here, the volume of the hydraulic composition matrix is ​​the sum of the volumes calculated from the weights and densities of the materials constituting the hydraulic composition. When the volume ratio of the hydrophilic fibers is within the above range, the water retention and distribution effects of the hydrophilic fibers can be improved, and the above effects can also be improved by suppressing entanglement of fibers due to the presence of an excess of fibers.

[0041] The degree of dispersion of the hydrophilic fibers in the hydraulic composition is preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and even more preferably 90% or more, from the viewpoint of the water retention and distribution effect of the hydrophilic fibers. The degree of dispersion can be measured by the method described in the Examples, specifically, by the method described in the Examples.

[0042] The number of fiber balls contained in the final molded product is preferably 0 to 5, more preferably 0 to 1. A number of fiber balls in the mortar concrete within the above range is preferable in that it sufficiently enhances the water retention and distribution effect of the hydrophilic fibers, sufficiently promotes the hydraulic reaction, and improves the mechanical strength of the molded product. Fiber balls are formed by poor mixing of the fibers and cement components in the hydraulic composition, and are formed by the fibers becoming entangled, resulting in a ball-like shape. The number of fiber balls can be measured by the method described in the Examples.

[0043] The slump loss of the molded product is preferably 6 cm or less, more preferably 4 cm or less, and even more preferably 2 cm or less. When the slump loss is below the above upper limit, the miscibility of the fibers and the cement component is high, thereby improving workability. The lower limit of the slump loss is not particularly limited, but is usually 1 cm or more. The slump loss can be measured by conducting a slump test in accordance with the concrete slump test method according to JIS A1101:2020.

[0044] The hydraulic composition of the present invention can be produced by mixing the above-mentioned hydrophilic fibers having a single fiber fineness of 50 dtex or less and an equilibrium moisture regain of 1.5% or more with water, cement components, aggregate, and, if necessary, other components such as various admixtures within a range that does not impair the effects of the present invention.The hydraulic composition can then be hardened to produce a molded product (hardened product) such as mortar concrete.

[0045] The hydraulic composition is kneaded by a known or commonly used kneading means such as a mixer. The kneading order of the constituent materials is not particularly limited, but is appropriately adjusted depending on the constitution of the hydraulic composition, the water / binder ratio (W / B), etc., in order to minimize the physical impact on the fibers.

[0046] In the hydraulic composition, the ratio (W / B) of the mass of water (W) to the total mass of binders (B) is preferably 0.1 to 0.40, more preferably 0.15 to 0.38, and even more preferably 0.20 to 0.36, from the viewpoint of achieving both fluidity and shape retention. Here, the total mass of binders refers to the total mass of substances exhibiting hydraulic properties contained in the hydraulic composition.

[0047] The method for supplying the hydrophilic fibers to the hydraulic composition is not particularly limited. For example, various constant-volume feeders (e.g., vibration feeders, screw feeders, belt feeders, etc.) can be used as a device for supplying the fibers while controlling the input amount and / or input speed.

[0048] The state of the fibers when they are supplied to the hydraulic composition is not particularly limited, and they may be added as they are or as a bundling thread. The bundling thread is a fiber in which a plurality of fibers having a single filament fineness of 15 dtex or less and an equilibrium moisture regain of 1.5% or more are bound together by a bundling agent, and when the fiber is added to the hydraulic composition, the bundling agent dissolves, separating and dispersing the plurality of fibers.

[0049] The present invention also provides a hydrophilic fiber used in the additive manufacturing of hydraulic composition molded articles, the hydrophilic fiber having an equilibrium moisture regain of 1.5% or more and / or a water absorption rate of 6.0% or more and a single filament fineness of 50 dtex or less, and a bundling yarn used in the additive manufacturing of hydraulic composition molded articles, the bundling yarn having an equilibrium moisture regain of 1.5% or more and / or a water absorption rate of 6.0% or more and a single filament fineness of 50 dtex or less.

[0050] The bundle yarn of the present invention includes a plurality of fibers and the specific sizing agent, and the plurality of fibers are integrated by the sizing agent. The plurality of fibers being integrated by the sizing agent means that the plurality of fibers are bonded to each other and bundled by the sizing agent.

[0051] When fibers are added as the bundle thread, it is preferable to use a water-soluble resin as the bundle agent. In this specification, the water-soluble resin is preferably a resin having a solubility of 16 g / L or more in alkaline water of pH 12 at room temperature (20°C). From the viewpoint of easily improving the defibration property of the bundle thread and easily improving the toughness of the molded body, the solubility of the water-soluble resin is preferably 18 g / L or more, more preferably 20 g / L or more. From the viewpoint of easily improving the convergence property of the fiber and easily preventing the occurrence of buckling, etc., the solubility is preferably 50 g / L or less, more preferably 45 g / L or less, and even more preferably 40 g / L or less. Furthermore, from the viewpoint of easily improving the defibration property of the bundle thread and easily improving the toughness of the molded body, the water-soluble resin is a resin having a solubility of preferably 18 g / L or more, more preferably 20 g / L or more, and even more preferably 22 g / L or more in water of pH 12 at room temperature. The solubility in alkaline water of pH 12 at room temperature (20°C) is, for example, the amount of water-soluble resin that dissolves without leaving any residue when a film-like water-soluble resin is added to alkaline water adjusted to pH 12 with sodium hydroxide and stirred at room temperature (20°C).

[0052] The water-soluble resin is not particularly limited as long as it is a resin having such solubility that it dissolves when added to the hydraulic composition, and examples thereof include polyvinyl alcohol-based resins (resins containing structural units derived from vinyl alcohol), ethyleneimine-based resins (resins containing structural units derived from ethyleneimine), acrylic resins, urethane resins, and epoxy resins.

[0053] From the viewpoint of solubility in the cement composite, the water-soluble resin is preferably a resin selected from the group consisting of polyvinyl alcohol-based resins, ethyleneimine-based resins, acrylic-based resins, and epoxy resins, and more preferably a resin selected from the group consisting of polyvinyl alcohol-based resins, ethyleneimine-based resins, and acrylic-based resins.

[0054] The water-soluble resin is preferably a vinyl alcohol resin containing structural units derived from vinyl alcohol, and more preferably a modified polyvinyl alcohol.

[0055] For example, the water-soluble resin may be modified polyvinyl alcohol. The modified polyvinyl alcohol preferably has at least a plurality of structural units derived from vinyl ester monomers as monomers and a structural unit (X) derived from an unsaturated carboxylic acid or a derivative thereof. In this case, the amount of the structural unit (X) is preferably 0.1 to 10 mol % when the amount of all monomer units in the modified polyvinyl alcohol is taken as 100 mol %.

[0056] The amount of the structural unit (X) is more preferably 0.5 to 10 mol %, even more preferably 1 to 9.5 mol %, and even more preferably 2 to 9 mol %, from the viewpoint of easily increasing the fiber defibration degree, easily decreasing the fiber aggregation degree, and easily enhancing the effect of water retention and distribution by the hydrophilic fiber. Note that the amount of the structural unit (X) derived from an unsaturated carboxylic acid or a derivative thereof contained in the modified polyvinyl alcohol is determined by the amount of the structural unit (X) in the modified polyvinyl alcohol. １ It may be determined from the H-NMR peak or from the monomer charge ratio when producing the modified polyvinyl alcohol.

[0057] The saponification degree of the modified polyvinyl alcohol is preferably 85 mol% or more, more preferably 88 mol% or more, even more preferably 90 mol% or more, still more preferably 95 mol% or more, and particularly preferably 98 mol% or more, from the viewpoint of easily sufficiently increasing the solubility of the modified polyvinyl alcohol in water. The upper limit of the saponification degree is 100 mol% or less, and from the viewpoint of improving the solubility in water by reducing the crystallinity of the modified polyvinyl alcohol, it is preferably 99.9 mol% or less, more preferably 99.8 mol% or less. The saponification degree can be measured by the method described in JIS K 6726 (1994).

[0058] The viscosity-average degree of polymerization of the modified polyvinyl alcohol is preferably 100 to 5,000, more preferably 100 to 4,000, and even more preferably 300 to 3,500. When the viscosity-average degree of polymerization is equal to or greater than the lower limit, the fiber sizing ability as a sizing agent is easily improved. When the viscosity-average degree of polymerization is equal to or less than the upper limit, the solubility of the modified polyvinyl alcohol in water can be improved, and rapid and sufficient defibration of the fibers is easily achieved. The viscosity-average degree of polymerization can be measured by the method described in JIS K 6726 (1994). Specifically, when the saponification degree is less than 99.5 mol%, the viscosity-average degree of polymerization (P) can be calculated by the following formula using the intrinsic viscosity [η] (liters / g) of PVA saponified to a saponification degree of 99.5 mol% or more, measured in water at 30°C: P = ([η] x 10 ４ / 8.29) （１／０．６２）

[0059] Examples of unsaturated carboxylic acids that provide the structural unit (X) contained in the modified polyvinyl alcohol include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, phthalic acid, maleic acid, and itaconic acid. Derivatives of these include alkyl esters and metal salts of the above-mentioned ethylenically unsaturated carboxylic acids. The modified polyvinyl alcohol used as a sizing agent may have one type of structural unit, two or more types of structural units, or additional structural units as the structural unit (X) derived from the unsaturated carboxylic acid or a derivative thereof.

[0060] The unsaturated carboxylic acid or its derivative is preferably at least one selected from the group consisting of (meth)acrylic acid, (meth)acrylic acid alkyl esters, and (meth)acrylic acid metal salts, from the viewpoint of easily increasing the degree of fiber defibration when the bundle yarn is kneaded with a hydraulic material and easily reducing the degree of cohesion of the defibrated fibers. Note that the term "(meth)acrylic" used in this specification means "acrylic and / or methacrylic."

[0061] Examples of (meth)acrylic acid alkyl esters include esters of (meth)acrylic acid with linear or branched alcohols having 1 to 5 carbon atoms, and specific examples include (meth)acrylic acid methyl ester, (meth)acrylic acid ethyl ester, (meth)acrylic acid propyl ester, (meth)acrylic acid butyl ester, and (meth)acrylic acid pentyl ester. Examples of metal salts of (meth)acrylic acid include alkali metal salts of (meth)acrylic acid. Examples of alkali metal elements include lithium, sodium, and potassium.

[0062] Here, taking into consideration that the structural unit (X) derived from an unsaturated carboxylic acid or a derivative thereof contained in the modified polyvinyl alcohol preferably accounts for 0.1 to 10 mol % when the amount of all monomer units in the modified polyvinyl alcohol is taken as 100 mol %, it is considered that the majority of the structural unit (X) is present adjacent to a structural unit derived from a vinyl ester monomer. In this case, the structural unit (X) and the structural unit derived from the vinyl ester monomer may be present as separate structural units (monomer units), or at least a portion of the multiple structural units (X) may be present as ring-closed structural units with a hydroxyl group contained in an adjacent structural unit derived from a vinyl ester monomer.

[0063] In addition, a structural unit formed by ring closure between, for example, a carboxyl group contained in a structural unit (X) derived from an unsaturated carboxylic acid or a derivative thereof and a hydroxyl group contained in a structural unit derived from vinyl alcohol is also a structural unit containing the structural unit (X) and is a structural unit derived from an unsaturated carboxylic acid or a derivative thereof. Herein, when calculating the amount of all monomer units of a modified polyvinyl alcohol, the ring-closed structural unit is not considered to be one structural unit, but the structural unit (X) before ring closure and the structural unit derived from vinyl alcohol, which are structural units corresponding to the monomer, are considered to be separate monomer units.

[0064] When modified polyvinyl alcohol is used as a sizing agent, the modified polyvinyl alcohol has a structural unit (X) derived from an unsaturated carboxylic acid or its derivative, and / or a structural unit in which the structural unit (X) is ring-closed with a structural unit derived from an adjacent vinyl ester monomer. When polyvinyl alcohol is modified with a structural unit (X) derived from an unsaturated carboxylic acid or its derivative, the modified polyvinyl alcohol exhibits excellent sizing agent performance, particularly fiber sizing, when not dissolved in water. This facilitates preventing fiber damage when dry-mixing the sizing yarn with a hydraulic material. Polyvinyl alcohol modified with the structural unit (X) has high solubility in water due to carboxyl groups, etc., and a sizing yarn containing such a modified polyvinyl alcohol as a sizing agent is characterized by the rapid dissolution of the sizing agent when mixed with water, resulting in rapid and sufficient fiber defibration. Regarding the required speed of defibration, the required speed may vary depending on the amount of sizing yarn used, the application of the hydraulic material, etc., but the examples in this specification evaluate defibration performance when kneaded for a very short time, for example, on the order of several tens of seconds.

[0065] In particular, when the modified polyvinyl alcohol has a structural unit (X) derived from an unsaturated carboxylic acid or a derivative thereof, and / or a structural unit formed by ring-closing the structural unit (X) with a structural unit derived from an adjacent vinyl ester monomer, the solubility of the modified polyvinyl alcohol in water is very low in the ring-closed state, and therefore the performance as a sizing agent is excellent and fiber damage during dry mixing is easily suppressed. Such a closed-ring structure has a very high ring-opening property when dissolved in water, especially in an alkaline environment, and the modified polyvinyl alcohol having the structural unit (X) after ring-opening has high solubility in water. Therefore, a sizing yarn containing such a modified polyvinyl alcohol as a sizing agent is characterized in that the sizing agent dissolves rapidly when mixed with water, making it easy to achieve rapid and sufficient fiber defibration.

[0066] In terms of easily increasing the fiber defibration degree of the bundle yarn and easily suppressing fiber aggregation, the modified polyvinyl alcohol preferably has a structural unit (X) derived from an unsaturated carboxylic acid or a derivative thereof represented by the formula (X1): [in formula (X1), X is a hydrogen atom or a methyl group] and / or a structural unit represented by formula (X2): In formula (X2), X is a hydrogen atom or a methyl group, and Y is a hydrogen atom, an alkali metal atom, or an alkyl group having 1 to 5 carbon atoms.

[0067] The structural unit represented by formula (X2) is a structural unit derived from at least one selected from the group consisting of (meth)acrylic acid, (meth)acrylic acid alkyl esters, and metal salts of (meth)acrylic acid, and when the structural unit (X2) undergoes ring closure with a structural unit derived from an adjacent vinyl ester-based monomer, it becomes the structural unit (X1). When the modified polyvinyl alcohol contains the structural unit represented by formula (X1) and / or the structural unit represented by formula (X2) as the structural unit (X), when the convergence yarn is kneaded with a hydraulic material such as cement and water, it is easy to achieve rapid defibration of the fibers, it is easy to improve the degree of defibration of the fibers, and it is easy to prevent aggregation of the defibrated fibers.

[0068] The modified polyvinyl alcohol may contain one type of structural unit represented by formula (X1) or two types of structural units represented by formula (X1). The modified polyvinyl alcohol may contain one type of structural unit represented by formula (X2) or two or more types of structural units represented by formula (X2).

[0069] When the modified polyvinyl alcohol contains a structural unit represented by formula (X1) and / or a structural unit represented by formula (X2), the ratio of the molar amount of the structural unit represented by formula (X1) to the total molar amount of the structural unit represented by formula (X1) and the structural unit represented by formula (X2) (X1 / (X1+X2)) is preferably 0.65 or more and 1.0 or less, more preferably 0.70 or more and 0.99 or less, even more preferably 0.85 or more and 0.99 or less, and particularly preferably 0.90 or more and 0.99 or less. When the content ratio of the structural unit represented by formula (X1) is equal to or more than the above lower limit, the performance as a sizing agent is easily improved, and, for example, damage to fibers when the sizing yarn and a hydraulic material are dry-mixed is easily suppressed. Note that the contents (molar amounts) of the structural unit (X1) and the structural unit (X2) contained in the modified polyvinyl alcohol are determined by the molar amount of the modified polyvinyl alcohol. １ It may be determined from the H-NMR peak or from the monomer charge ratio when producing the modified polyvinyl alcohol.

[0070] The modified polyvinyl alcohol preferably contains at least a structural unit represented by formula (X1). In this case, the amount of the structural unit represented by formula (X1) is preferably 0.1 to 10 mol%, more preferably 0.5 to 10 mol%, more preferably 1 to 9.5 mol%, and particularly preferably 2 to 9 mol%, based on 100 mol% of the total amount of monomer units in the modified polyvinyl alcohol. When the amount of the structural unit represented by formula (X1) is within the above range, the performance as a sizing agent (e.g., fiber adhesion) is easily improved, and fiber damage during dry mixing of the sizing yarn with a hydraulic material is easily suppressed. Furthermore, rapid and sufficient fiber defibration is easily achieved when the sizing yarn is mixed with water. As a result, the degree of fiber defibration of the sizing yarn is easily increased, fiber aggregation is easily suppressed, and the mechanical strength of the molded product is easily increased.

[0071] The method for dispersing the fibers after adding them is not particularly limited, as long as the fibers can be dispersed in a state where they are not substantially present as fiber aggregates. For example, when a mixer or kneader with high stirring performance is used, examples of the mixer or kneader with high stirring performance include a double-arm kneader, a pressure kneader, an Eirich mixer, a super mixer, a planetary mixer, a Banbury mixer, a continuous mixer, or a continuous kneader. In this way, a hydraulic composition containing a specific hydrophilic fiber can be produced.

[0072] In another embodiment of the present invention, the present invention also provides a hydraulic composition for additive manufacturing, which is a hydraulic composition of another embodiment that can easily suppress variations in the water content in a molded hydraulic composition during hardening and can sufficiently promote the hydraulic reaction, particularly on surfaces that are prone to moisture shortage. The hydraulic composition of this embodiment includes hydrophilic fibers having a single fiber diameter of 70 μm or less and a water absorption of 6.0% or more. The hydraulic composition of this embodiment has a high water retention capacity, similar to the previously described hydraulic composition containing hydrophilic fibers having an equilibrium moisture regain of 1.5% or more, in that the water absorption of the contained hydrophilic fibers is 6.0% or more. This makes it easy to suppress variations in the water content in a molded hydraulic composition during hardening and can sufficiently promote the hydraulic reaction, particularly on surfaces that are prone to moisture shortage. The above-mentioned explanations, preferred features, etc. regarding the hydraulic composition of the present invention also apply to the hydraulic composition of this embodiment.

[0073] <Hydraulic Composition for Additive Manufacturing and Cured Product> The hydraulic composition of the present invention is a hydraulic composition for additive manufacturing. An additive manufacturing device (3D printer) typically extrudes a photocurable resin or hydraulic composition from a nozzle, layers the uncured composition in a desired shape, and cures it to ultimately form a pre-designed three-dimensional shape. When additive manufacturing is performed using a hydraulic composition, a mold typically used in the manufacture of hydraulic compositions is not used, which means that moisture is likely to evaporate from the surface in contact with air. Furthermore, the three-dimensional shape to be molded is often complex or large, making curing, for example, by covering it with a sheet impossible. However, the hydraulic composition of the present invention allows for uniform moisture distribution in the molded hydraulic composition during curing, internally curing the hydraulic composition, and allowing the hydraulic reaction to proceed sufficiently and uniformly.

[0074] A method for manufacturing a three-dimensional shape using an additive manufacturing apparatus includes supplying the hydraulic composition of the present invention to the additive manufacturing apparatus and extruding it from the nozzle of the additive manufacturing apparatus to form a three-dimensional shape. For example, the hydraulic composition is first ejected or extruded from the nozzle to form a two-dimensional layered body so as to ultimately obtain a pre-designed three-dimensional shape loaded into a control computer or the like of the additive manufacturing apparatus. Next, a hydraulic composition is ejected or extruded from the nozzle on top of the layered body to form a second layered body. This operation is repeated to finally form a cured product of the hydraulic composition having the designed three-dimensional shape. The present invention also provides a cured product of the hydraulic composition of the present invention.

[0075] The hydraulic reaction proceeds in the formed three-dimensional shape, resulting in a final set of hydraulic composition. Here, the hydraulic reaction is a reaction in which cement and other components in the hydraulic composition react with water to hydrate and harden. To ensure that the hydraulic reaction proceeds uniformly and sufficiently, it is considered necessary for water to be retained and distributed in the formed three-dimensional shape during hardening. If the hydraulic reaction is insufficient, the strength of the final set product may not be high. Furthermore, if the hydraulic reaction does not proceed uniformly, cracks or fractures may occur in the final set product. According to the hydraulic composition of the present invention, the hydrophilic fibers retain moisture on the fiber surfaces and form a dense network within the hydraulic composition, thereby ensuring uniform moisture distribution in the molded hydraulic composition during hardening, and allowing the hydraulic reaction to proceed sufficiently and uniformly even on the surface of the molded product, which is prone to moisture loss.

[0076] By using the hydraulic composition of the present invention, various civil engineering and construction structures, such as buried formwork for bridge piers and abutments, exterior walls of buildings, and precast concrete structures of complex shapes can be produced.

[0077] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In the examples, percentages refer to mass unless otherwise specified. First, the measurement and evaluation methods are described below.

[0078] <Mortar Mix> A mortar mix was prepared with the following mix ratios, with reference to Marchment, T. et al.: Method of enhancing interlayer bond strength in construction scale 3D printing with mortar by effective bond area amplification, Materials and Design, Vol. 169, pp. 1-9, 2019. Binder: Ordinary Portland cement (AS3972-22) Aggregate: Fine aggregate (average particle size 500 μm and 800 μm) Other: High-performance air-entraining water-reducing agent (polycarboxylic acid compound) Water / binder ratio = 0.36 / 1 (W / B) Aggregate / binder = 1.5 / 1 (S / B) Water-reducing agent / binder = 0.02 / 1

[0079] <Fibers> (Examples 1-2, 5, 7-8 and Comparative Example 2) PVA fibers were used having the physical properties shown in Table 1. (Example 3) Rayon fibers were used having the physical properties shown in Table 1. (Examples 4, 6, 9, and Comparative Example 1) Sizing agent Sizing agent 1: A modified polyvinyl alcohol having a viscosity average degree of polymerization of 1,500, a degree of saponification of 99.5 mol%, a content of the structural unit (X) derived from acrylic acid of 5 mol%, a content of the structural unit (X1) of 4.8 mol%, a content of the structural unit (X2) of 0.2 mol%, a ratio of (X1) to the total amount of the structural units (X1) and (X2) of 0.96, and in which the functional groups X and Y in the structural units (X1) and (X2) are both hydrogen atoms. Sizing yarn Sizing yarn 1: To each fiber having the single yarn fineness, equilibrium moisture regain, and water absorption rate set forth in Examples 4, 6, 9, and Comparative Examples 1 and 5 in Table 1, an aqueous solution containing sizing agent 1 in an amount of 80 g / L was added by roller touch in an amount of 5.5 mass% relative to the mass of the fiber, and the added solution was then dried to adhere sizing agent 1 to the fiber. Thereafter, bundle yarns were obtained by cutting the fibers to an average fiber length of 6 mm in Example 4, 8 mm in Example 6, 16 mm in Example 9, 12 mm in Comparative Example 1, and 15 mm in Comparative Example 5. (Comparative Example 3) PP fibers having the physical properties shown in Table 1 were used.

[0080] <Evaluation Method> The single yarn fineness of the fiber was measured in accordance with JIS L1015:2021 "Test method for chemical fiber staple (8.5.1)".

[0081] [Fiber length, fiber diameter, aspect ratio] The aspect ratio refers to the ratio (L / D) of fiber length (L) to fiber diameter (D). In the present invention, the average fiber length was calculated in accordance with JIS L1015:2021 "Test method for chemical fiber staples (8.4.1)," and the aspect ratio of the fiber was calculated from the ratio to the average fiber diameter. Regarding the average fiber diameter, 20 fibers were randomly selected, and the fiber diameter (single fiber diameter) at the center of each fiber in the length direction was measured using an optical microscope.

[0082] [Equilibrium moisture regain] Using the above fibers as measurement samples, the equilibrium moisture regain was measured by the following method. Referring to JIS L1015:2021 "Testing methods for synthetic fiber staples (8.3)," the sample was dried in a dryer at 105°C, and then conditioned at a temperature of 20°C and a relative humidity of 65%RH for 72 hours. The moisture regain contained in the sample relative to the sample's mass in the bone-dry state was calculated and expressed as a percentage (%). Fibers with an equilibrium moisture regain of 1.5% or more in the above measurement were considered hydrophilic fibers.

[0083] [Water Absorption] Using the above fiber as a measurement sample, the water absorption was measured by the following method. The water absorption is a value calculated by the following formula, where the mass of the fiber after stirring the fiber in a 0.1 mol / L NaOH aqueous solution (pH 13) at 30°C for 4 minutes and then spinning it in a centrifugal spin dryer at 3000 rpm for 5 minutes three times is mass A, and the mass of the fiber after spinning it in a dryer at 100°C for 16 hours is mass B. Formula: Water absorption = 100 x (A - B) / B (%)

[0084] Example 1 A hydraulic composition was prepared by mixing the mortar mixture prepared as described above with PVA fibers having the physical properties shown in Table 1 so that the volume ratio of the hydrophilic fibers in the hydraulic composition was 2%. The hydraulic composition was then poured into a formwork having internal dimensions of a rectangular parallelepiped (W 240 mm x D 60 mm x H 10 mm) and cured for 28 days at 20°C and 40% RH with the top surface open, to obtain a hardened product.

[0085] <Examples 2 to 9 and Comparative Examples 1 to 3 and 5> Hydraulic compositions and cured products were obtained in the same manner as in Example 1, except that the PVA fiber was changed to a fiber having the physical properties shown in Table 1. In Examples 4, 6, and 9 and Comparative Examples 1 and 5, hydraulic compositions were prepared by mixing the compound with a bundle of fibers having the physical properties shown in Table 1.

[0086] Comparative Example 4 A hydraulic composition and a set product were obtained in the same manner as in Example 1, except that PVA granules having the physical properties shown in Table 1 were used instead of the PVA fibers.

[0087] Comparative Example 6 A hydraulic composition and a set product were obtained in the same manner as in Example 1, except that the PVA fibers were not added.

[0088] <Methods for evaluating hydraulic compositions and cured products> The fibers obtained as described above, the hydraulic compositions of the examples and comparative examples, and the cured products thereof were evaluated as follows. The results are shown in Table 1.

[0089] [Fluidity] The fluidity of the hydraulic compositions produced in the Examples and Comparative Examples was evaluated by JIS R5201:2015 "Physical Testing Methods for Cement", Section 12. Flow Test. The flow values ​​were evaluated according to the following criteria: ◯: 120 mm or more △: 100 mm or more and less than 120 mm ×: Less than 100 mm

[0090] [Degree of Dispersion] The degree of dispersion of fibers in the hydraulic composition was measured by the following procedure. 20 g of the hydraulic composition was sampled and applied to a 40-mesh wire netting in a uniform thickness, and immediately washed with water to remove the binder component. The fibers were removed from the components remaining on the wire netting, and the dispersed fibers and the undispersed fibers (undisintegrated or agglomerated fibers) were separately collected with tweezers and dried at 100°C for 24 hours, after which the mass of the dispersed fibers (W ｆ ) (unit: g), and the mass of the undispersed convergent yarn (W ｇ ) (unit: g) were measured. The degree of dispersion was calculated by the following formula: Degree of dispersion [%] = (W ｆ / (W ｆ +W ｇ)) x 100 The dispersion was evaluated according to the following criteria: ○: 80% or more △: 60% or more and less than 80% ×: Less than 60%

[0091] [Volume Ratio of Hydrophilic Fibers] The volume ratio of the fibers when the volume of the hydraulic composition is taken as 100 was calculated by calculating the total volume of the hydraulic composition, V, and the volume of the fibers, Vf, from the specific gravity and weight of the materials constituting the hydraulic composition, and using these values, according to the following formula: Volume ratio of fibers = Vf / V x 100 (%)

[0092] [W / B] The ratio of W to B (W / B) was calculated from the total mass (B) [g] of the binder (cement) in the hydraulic composition and the mass (W) [g] of water.

[0093] [Surface / internal reaction rate ratio (curing effect)] For the hardened products obtained in the examples and comparative examples, the reaction rate R of the cement on the upper surface, which corresponds to the surface, was Ａ and the reaction rate of the cement at the bottom, which corresponds to the inside, R Ｂ was measured by small angle scattering (SAXS) and the reaction rate ratio between the top and bottom surfaces (R Ａ / R Ｂ × 100) [%] was calculated, and the curing effect was evaluated according to the following criteria: ◯: 80% or more △: 70% or more but less than 80% ×: Less than 70%

[0094]

[0095] It was confirmed that the hydraulic compositions of the present invention exhibited a high surface / internal reaction ratio even when cured in a dry environment. Although the reason for this is unclear, it is believed that the dispersion of thin fibers with low single-fiber fineness or small single-fiber diameters in the hydraulic composition, which sufficiently increased the fiber surface area and formed a fiber network, resulted in excellent water retention and water diffusibility, resulting in a high surface / internal reaction ratio even when cured in a dry environment. Furthermore, the cured products produced in this manner exhibited high and consistent strength. In contrast, the hydraulic compositions of Comparative Examples 1, 2, and 5, which contained fibers with high single-fiber fineness, were unable to secure sufficient fiber surface area due to the thick fibers, thereby failing to enhance the curing effect of the fibers, resulting in a low surface reaction ratio. The hydraulic composition of Comparative Example 3, which contained fibers with a low equilibrium moisture content, also failed to enhance the curing effect of the fibers due to its weak water retention, resulting in a low surface reaction ratio. Furthermore, in Comparative Example 4, which used PVA granules, the lack of fibers prevented the formation of a network and the resulting lack of water diffusibility, likely contributing to the low surface reaction ratio. In the case of Comparative Example 6 in which no hydrophilic fibers were added, the amount of moisture during curing was insufficient, and the hardening reaction on the surface was insufficient.

Claims

1. A hydraulic composition for additive manufacturing, comprising hydrophilic fibers having a single filament fineness of 50 dtex or less or a single filament fiber diameter of 70 μm or less, and an equilibrium moisture regain of 1.5% or more.

2. The hydraulic composition according to claim 1, wherein the hydrophilic fiber has a single filament fineness of 15 dtex or less.

3. A hydraulic composition according to claim 1 or 2, wherein the water absorption rate of the hydrophilic fibers is 6.0% or more.

4. The hydraulic composition according to claim 1 or 2, wherein the aspect ratio of the hydrophilic fibers is 50 to 400.

5. A hydraulic composition according to claim 1 or 2, wherein the hydrophilic fibers have a fiber length of 10 mm or less.

6. The hydraulic composition according to claim 1 or 2, wherein the volume ratio of the hydrophilic fibers is 0.1 to 10% when the volume of the matrix of the hydraulic composition is taken as 100.

7. A hydraulic composition according to claim 1 or 2, wherein the hydrophilic fiber has a single filament fineness of 0.1 dtex or more.

8. A hydraulic composition according to claim 1 or 2, wherein the hydrophilic fibers have a fiber length of 0.5 mm or more.

9. The hydraulic composition according to claim 1 or 2, wherein the degree of dispersion of the hydrophilic fibers in the hydraulic composition is 60% or more.

10. The hydraulic composition according to claim 1 or 2, wherein the ratio (W / B) of the mass of water (W) to the total mass (B) of the binder in the hydraulic composition is 0.1 to 0.

40.

11. A hardened product of the hydraulic composition according to claim 1 or 2.

12. A hydrophilic fiber used in the additive manufacturing of hydraulic composition moldings, having an equilibrium moisture content of 1.5% or more and / or a water absorption rate of 6.0% or more, a single filament fineness of 50 dtex or less and / or a single filament fiber diameter of 70 μm or less.

13. A convergence yarn used in the additive manufacturing of hydraulic composition moldings, having an equilibrium moisture content of 1.5% or more and / or a water absorption rate of 6.0% or more, a single yarn fineness of 50 dtex or less and / or a single yarn fiber diameter of 70 μm or less.

14. A hydraulic composition for additive manufacturing, comprising a hydrophilic fiber having a single fiber diameter of 70 μm or less and a water absorption rate of 6.0% or more.

15. The hydraulic composition according to claim 14, wherein the hydrophilic fibers in the hydraulic composition have a fiber length of 16 mm or less.

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