JP2017057538A - Composite fiber and manufacturing method therefor, composite material and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite fiber by effectively composing a resin fiber and an inorganic material by making good use of their respective advantages, the composite fiber having mechanical physical properties suitable as a reinforced fiber and others.SOLUTION: There is provided a composite fiber having a coating layer containing: at least one hydrophilic polymer having a hydrophilic group having a coordination ability to a calcium ion; and a calcium carbonate crystal containing a calcite crystal and a vaterite crystal as main crystals and having the size of crystallite of 0.01 to 0.1 μm, each of which is formed on at least a part of a surface of a polar fiber mainly containing at least one vinyl alcohol resin, wherein an average thickness of the coating layer is 0.01 to 20 μm and a surface coating percentage of the polar fiber by the coating layer is 80 to 100%.SELECTED DRAWING: None

Description

  The present invention relates to a composite fiber and a manufacturing method thereof, and a composite material and a manufacturing method thereof.

In general, resins are easy to mold and lightweight, but tend to be inferior in mechanical properties such as tensile strength and elastic modulus. Therefore, in general, the resin alone is not suitable for applications requiring mechanical strength, such as aircraft members, automobile members, home appliance members, and building materials.
Therefore, in the above applications, a fiber reinforced resin (FRP) in which a reinforced fiber having a high tensile strength and a high elastic modulus is combined with a matrix resin is preferably used.

As reinforcing fiber,
Inorganic fibers such as glass fibers and carbon fibers;
And
Examples thereof include resin fibers such as PVA fibers.

In the present specification, “VA” is an abbreviation for vinyl alcohol.
In this specification, “VA resin” is an abbreviation for vinyl alcohol resin, and includes polyvinyl alcohol as a fully saponified product, and a copolymer containing vinyl alcohol units and vinyl acetate units as partially saponified products. It is.
In this specification, “PVA fiber” is a fiber mainly composed of one or more VA resins.

In general, resin fibers are less expensive than inorganic fibers.
In addition, since the PVA fiber has hydrophilicity derived from a hydroxy group, it is preferably used for a reinforcing fiber composited with a hydrophilic matrix resin or a matrix resin reactive with a hydroxy group.
The reinforcing fiber may be combined with a matrix material other than resin.

In general, the mechanical properties of a composite material containing reinforcing fibers are correlated with the mechanical properties of the reinforcing fibers to be combined. By using reinforcing fibers having excellent mechanical properties such as tensile strength and flexural modulus, a composite material having excellent mechanical properties can be obtained.
However, resin fibers are superior in mechanical properties such as tensile strength as compared with inorganic fibers, but tend to be inferior in mechanical properties such as flexural modulus.

  As a method of improving the bending elastic modulus of a composite material using reinforcing fibers having inferior bending elastic modulus, a method of laminating a plurality of composite materials in the bending direction, and increasing the proportion of reinforcing fibers in the composite material There are methods.

  However, the method of laminating a plurality of composite materials has problems such as an increase in overall thickness and mass, deterioration in thermoformability, a decrease in mechanical strength due to delamination, and an increase in cost.

The method for increasing the proportion of reinforcing fibers in the composite material has the following problems.
As a method for producing a composite material including a matrix resin and reinforcing fibers,
A method of solidifying the liquid raw material after impregnating the reinforcing fiber with the liquid raw material to be a matrix resin;
and,
There is a method of solidifying the liquid raw material after mixing the reinforcing fiber and the liquid raw material to be the matrix resin.
However, when increasing the proportion of reinforcing fibers in the composite material, it is difficult for the former production method to impregnate the reinforcing fibers with a liquid raw material serving as a matrix resin.
In the latter manufacturing method, the fluidity of the mixture of the matrix resin and the reinforcing fibers is reduced, and voids are formed at the interface between the matrix resin and the reinforcing fibers, which may reduce the mechanical strength of the composite material. In addition, uneven distribution of the reinforcing fibers in the matrix resin may cause variations in mechanical strength within one composite material or between a plurality of composite materials.

As a method for improving the mechanical strength of a composite material using resin fibers as reinforcing fibers, there is a method of further adding an inorganic substance to the matrix resin and the reinforcing fibers.
However, when an inorganic substance is added, the fluidity of the entire material is lowered, and voids are formed at the interface between the matrix resin and the reinforcing fiber or at the interface between the matrix resin and the inorganic substance, which may reduce the mechanical strength of the composite material. There is. In addition, depending on the particle size of the inorganic substance, the inorganic substance is unevenly distributed in the matrix resin, so that there is a possibility that the mechanical strength varies within one composite material or between a plurality of composite materials.

  Reinforcing fibers with excellent mechanical properties such as tensile strength and flexural modulus, and composite materials with excellent mechanical properties using the composite fibers obtained by combining inorganic fibers with excellent elastic modulus with resin fibers It is thought that it can be provided.

Patent Document 1 discloses a cement reinforcing fiber containing 2 to 20% by mass of calcium carbonate particles having an average diameter of less than 1 μm with respect to the mass of the PVA fiber (claim 1).
In Patent Document 1, a VA-based resin (saponification degree 99 mol%) is dissolved in water, and then added with boric acid and calcium carbonate particles to obtain a spinning stock solution. Spinning is performed using this spinning stock solution, and a composite fiber is obtained. (Example 1 etc.).
In patent document 1, the improvement effect of the bending strength of a cement product is reported (paragraph 0026 etc.).

However, in the method described in Patent Document 1, calcium carbonate particles are added before spinning of the PVA fibers.
In this method, the spinning of the VA resin may be hindered by the presence of calcium carbonate particles in the spinning dope. Therefore, there is a possibility that fiber characteristics such as crystallinity of the obtained PVA-based fiber are deteriorated. Moreover, there exists a possibility that a fiber shape may deteriorate because a calcium carbonate particle bites into the surface of a PVA type fiber. These may cause a decrease in tensile strength.

Prior to this application, the inventors have
In Patent Document 2,
A composite material comprising a hydrophilic polymer such as polyacrylic acid (PAA), polyglutamic acid, polyvinylpyrrolidone, PVA, and polyethylene glycol and amorphous calcium carbonate is disclosed (paragraphs 0035, 0040, and FIG. 1 and the like).
Patent Document 2 also discloses a method for producing a composite material having an amorphous structure by mixing a first solution containing a hydrophilic polymer and calcium ions and a second solution containing carbonate ions (claim). Item 10, claim 12, etc.).
For example, an amorphous calcium carbonate / polyacrylic acid composite material is manufactured by the following method (Claim 10, Claim 12, Paragraph 0037, FIG. 3, etc.).
A first aqueous solution containing PAA and calcium ions and a second aqueous solution containing carbonate ions are prepared separately. These aqueous solutions are mixed and allowed to stand for several hours. The resulting precipitated product is collected and dried.
In Patent Document 2, a first solution containing a hydrophilic polymer and calcium ions and a second solution containing carbonate ions are mixed to form a colloidal dispersion, and this colloidal dispersion is applied onto a substrate. Thus, a method of forming a thin film having a composite material having an amorphous structure is disclosed (claim 16 and paragraph 0074).

However, Patent Document 2 does not disclose application of the above technique to reinforcing fibers such as PVA fibers. Therefore, a suitable method for producing reinforcing fibers to which the above technique is applied is unknown, and the mechanical properties of the resulting reinforcing fibers are also unknown.
Moreover, the calcium carbonate in the composite material disclosed in Patent Document 2 has an amorphous structure.

JP 1994-192912 (Patent No. 2835812) Japanese Unexamined Patent Publication No. 2009-062445 (Japanese Patent No. 5299883)

  The present invention has been made in view of the above circumstances, a resin fiber and an inorganic material are effectively combined utilizing their respective advantages, a composite fiber having mechanical properties suitable as a reinforcing fiber, a method for producing the same, and An object of the present invention is to provide a composite material using the same and a manufacturing method thereof.

The conjugate fiber of the present invention is
On the surface of at least a part of the polar fiber mainly composed of at least one vinyl alcohol resin represented by the following general formula [I],
Calcium carbonate having at least one hydrophilic polymer having a hydrophilic group capable of coordinating with calcium ions, a main crystal being a calcite crystal and a vaterite crystal, and a crystallite size of 0.01 to 0.1 μm A coating layer containing crystals is formed,
The coating layer has an average thickness of 0.01 to 20 μm,
The surface coverage of the polar fiber by the coating layer is 80 to 100%.
It is a composite fiber.

(In formula [I], m is an integer of 100 or more, and n is an integer of 0 or more.)

The composite material of the present invention is
It includes a matrix material and the above-described composite fiber of the present invention.

The method for producing the conjugate fiber of the present invention includes:
At least one hydrophilic polymer having at least one calcium ion source represented by the following general formula [II] at 20 mM or more and having a hydrophilic group capable of coordinating with calcium ions is 10 to 80 mM in terms of monomer. A first aqueous solution containing the calcium carbonate aqueous solution containing amorphous calcium carbonate and the hydrophilic polymer by reacting the second aqueous solution containing 20 mM or more of at least one carbonate ion source represented by the following general formula [III]. Obtaining
A polar fiber mainly composed of at least one vinyl alcohol resin represented by the following general formula [I] is immersed in the calcium carbonate aqueous solution, and the calcium carbonate is formed on at least a part of the surface of the polar fiber. And a step of attaching the crystal and the hydrophilic polymer.

(In formula [I], m is an integer of 100 or more, and n is an integer of 0 or more.)

CaX ₂ · nH ₂ O ... [II]
(In the formula [II], X represents a halogen atom, and n represents a real number of 0 or more.)

M _a (CO ₃ ) _b · nH ₂ O ... [III]
(In formula [III], each symbol has the following meaning.
M represents at least one metal atom, ammonium, or hydrogen atom.
a and b are integers of 1 or more, and n represents a real number of 0 or more. )

The first method for producing a composite material of the present invention includes:
The above-mentioned composite fiber obtained by the above-described composite fiber manufacturing method of the present invention is impregnated with a liquid raw material to be a matrix material, and then the liquid raw material is solidified.

The method for producing the second composite material of the present invention comprises:
The composite fiber obtained by the above-described method for manufacturing a composite fiber of the present invention is mixed with a liquid raw material to be a matrix material, and then the liquid raw material is solidified.

"Main component"
In the present specification, unless otherwise specified, the “main component” is defined as a component of 50% by mass or more.

"Fiber diameter of PVA fiber"
In the present specification, unless otherwise specified, the “fiber diameter of the PVA fiber” is measured by observation with an optical microscope or a scanning electron microscope (SEM).
Note that “VE-9800” manufactured by KEYENCE Corporation is used as the SEM.

"Crystallinity, crystal orientation, crystallite size of PVA fibers"
In this specification, unless otherwise specified, “the degree of crystallinity, the degree of crystal orientation, and the size of crystallites of PVA fibers” are calculated by wide-angle X-ray diffraction (WAXD) measurement.
As a measuring device, “D8 Discover with GADDS” manufactured by Bruker is used. As a detector, “PSPC / HI-Star” is used.

The degree of crystallinity is based on the following formula from the area intensity obtained by converting the equator data of the WAXD profile and fitting the diffraction peak appearing at 2θ = 5 to 38 ° using the peak separation method. calculate.
Crystallinity (%) = (total area of crystal peak) ÷ (total peak area) × 100

The degree of crystal orientation is calculated from the meridian data of the WAXD profile, using the diffraction peak appearing at 2θ = 73 to 107 ° as the use data range, and based on the following formula from the half-value width of the appearing diffraction peak.
Crystal orientation (−) = (180−half width) ÷ 180

As crystallite size, D (100) and D (002) are measured.
D (100) is calculated by converting the equator line data and using the Scherrer equation from the half width of the diffraction peak at 2θ = 5 to 20 °.
D (002) is calculated from the meridian data and calculated from the half width of the diffraction peak at 2θ = 65 to 85 ° using the Scherrer equation.
The Scherrer constant K is 0.94.

“Weight average molecular weight of resin (Mw)”
In the present specification, unless otherwise specified, “resin weight average molecular weight (Mw)” is a value obtained by converting a chromatogram measured by gel permeation chromatography (GPC) into a molecular weight of standard polystyrene.

"Average degree of polymerization of resin"
In the present specification, unless otherwise specified, the average degree of polymerization of the VA-based resin is a value indicated by the viscosity average degree of polymerization derived from the intrinsic viscosity according to JIS K 6726.

"Crystal structure of calcium carbonate"
In this specification, unless otherwise specified, “the crystal structure of calcium carbonate attached to polar fibers” is “BL03XU” of the large synchrotron radiation facility SPring-8, and MICRO-WAXD (Wide-Angle X-Ray Diffraction) is used. It shall be evaluated by analysis.
(X-ray measurement conditions)
The X-ray wavelength is 0.13051 nm. X-rays are irradiated to the sample in a helium atmosphere without being attenuated by an attenuator, a chopper, or the like.
The brightness of the X-ray is approximately 6 × 10 ⁹ photon / sec with respect to the irradiation area.
The exposure time is 5 seconds. In addition, it has been confirmed in advance that there is no damage to the calcium carbonate crystal and the calcium carbonate crystal does not melt by irradiation for 5 seconds.
The camera distance of the MICRO-WAXD measurement from the sample is approximately 44 mm.
An FPD detector is used as the detector.
(Measuring method)
Measurement is performed on the measurement sample fiber while scanning X-rays by 1 μm in the fiber radial direction (perpendicular to the fiber axis direction) from the outside of the fiber. Thereby, in the cross section of the measurement sample fiber, WAXD data is obtained at intervals of 1 μm from one end to the other end in the radial direction.
(analysis method)
After performing the above measurement, a circular average is obtained in the omnidirectional WAXD data for each measurement position to obtain a one-dimensional WAXD pattern.
Other measurement conditions are as described in the “Examples” section below.
When a diffraction peak is detected in the above analysis, the crystal structure can be identified by comparing the detected diffraction peak with the diffraction peak data of the standard sample crystal.
In the above analysis, when a clear diffraction peak is not detected, it is determined as “amorphous”.
Generally, the types of calcium carbonate crystals include aragonite crystals, calcite crystals, and vaterite crystals.
In the present specification, one type or two or more types of crystals exhibiting a diffraction peak clearly detected by the above analysis are defined as “main crystals”.
The deposit may contain a trace amount of crystals other than the main crystal in an amount below the detection limit of the apparatus.
The deposits may contain amorphous calcium carbonate in addition to calcium carbonate crystals.

"Calcium crystallite size"
In this specification, unless otherwise specified, the “crystallite size of calcium carbonate crystal” is calculated using the Scherrer equation by obtaining the half width of the diffraction peak detected in the above analysis. The Scherrer constant K is 0.94.

"Surface coverage of polar fibers by coating layer and average thickness of coating layer"
In the present specification, unless otherwise specified, the “surface coverage of polar fibers by the coating layer and the average thickness of the coating layer” are evaluated by the following methods.
Using SEM (Scanning Electron Microscope) or TEM (Transmission Electron Microscope), cross-sectional observation of the composite fiber is performed, and the surface coverage of the polar fiber by the coating layer on the obtained image or photograph, and the coating layer Measure overall average thickness.

"Interfacial adhesion of adhered matter (coating layer) to polar fibers"
In this specification, unless otherwise specified, “adhesiveness of an adherent (coating layer) to polar fibers” is evaluated by the following method.
The interfacial adhesion is the interfacial shear stress (IFSS) calculated from the shear stress in the interface direction between the adherent (coating layer) and the polar fiber with respect to the area of the adherent (coating layer) and the polar fiber. Is used as an index.
The interfacial shear stress (IFSS) is measured by a microdroplet method using a composite material interface property evaluation apparatus.
The specific measurement method is as described in the section of [Example] below.

  According to the present invention, a resin fiber and an inorganic substance are effectively combined utilizing each advantage, a composite fiber having mechanical properties suitable as a reinforcing fiber, a method for producing the same, and a composite material using the same A manufacturing method thereof can be provided.

It is a SEM surface photograph of the composite fiber obtained in Example 1-9. It is a SEM surface photograph of the composite fiber obtained in Example 1-9. It is a SEM cross-sectional photograph of the composite fiber obtained in Example 1-9. It is a SEM cross-sectional photograph of the composite fiber obtained in Example 1-9. It is a WAXD pattern of the composite fiber obtained in Example 1-9. It is a WAXD pattern of the composite fiber obtained in Example 1-9. It is a model perspective view of the conjugate fiber obtained in Example 1-9. It is a SEM surface photograph of the composite fiber obtained in Example 8-9. It is a SEM surface photograph of the composite fiber obtained in Example 8-9. It is a SEM cross-sectional photograph of the composite fiber obtained in Example 8-9. It is a SEM cross-sectional photograph of the composite fiber obtained in Example 8-9. It is a WAXD pattern of the composite fiber obtained in Example 8-9. It is a WAXD pattern of the composite fiber obtained in Example 8-9. It is a model perspective view of the composite fiber obtained in Example 8-9. It is a graph which shows the measurement result of the interface shear strength (IFSS) of the original PVA type fiber (fiber sample 1) and the composite fiber obtained in Example 1-9. It is a graph which shows the measurement result of the tensile strength of the original PVA type fiber (fiber sample 1) and the composite fiber obtained in Examples 1-7 to 1-9. It is a graph which shows the measurement result of DYM of the composite fiber obtained by the original PVA type fiber (fiber sample 1) and Examples 1-7 to 1-9. It is a graph which shows the measurement result of the tensile strength of the composite fiber obtained by the original PVA type fiber (fiber sample 8) and Examples 8-7 to 8-9. It is a graph which shows the measurement result of DYM of the composite fiber obtained by the original PVA type fiber (fiber sample 8) and Examples 8-7 to 8-9.

  Hereinafter, the present invention will be described in detail.

"Composite fiber"
The conjugate fiber of the present invention is such that an adherent containing a hydrophilic polymer and calcium carbonate (CaCO ₃ ) crystals is formed on at least a part of the surface of a polar fiber.
In the present invention, the deposit can form a coating layer covering at least a part of the surface of the polar fiber.
The conjugate fiber of the present invention can be produced by the production method of the present invention described later.

(Polar fiber)
In the conjugate fiber of the present invention, as the polar fiber, a PVA fiber mainly composed of at least one vinyl alcohol (VA) resin represented by the following general formula [I] is used.
One type or two or more types of PVA fibers can be used.

(In formula [I], m is an integer of 100 or more, and n is an integer of 0 or more.)

The VA resin is a crystalline polymer.
The VA-based resin is not particularly limited by its production method, and is produced, for example, by saponifying polyvinyl acetate with an alkali or an acid. The partially saponified product of polyvinyl acetate is a copolymer containing vinyl alcohol units and vinyl acetate units.
The “VA resin” includes polyvinyl alcohol which is a completely saponified product, and a copolymer containing vinyl alcohol units and vinyl acetate units which are partially saponified products.
Generally, VA-based resins have hydrophilicity because they have hydroxyl groups.
In general, as the saponification degree becomes higher, the VA-based resin has higher crystallinity and tends to improve hydrophilicity.
In this specification, “PVA fiber” is a fiber mainly composed of one or more VA resins.

The PVA fiber may contain one or more other optional components in accordance with the VA resin that is the main component resin.
The amount of the main component resin in the PVA fiber is preferably large.
The amount of the main component resin in the PVA fiber is 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more.

In the method for producing a composite fiber of the present invention described later, calcium carbonate is crystal-grown on the surface of the PVA fiber.
It is considered that the calcium carbonate easily grows along the crystal orientation of the PVA fiber because the PVA fiber has good crystallinity.
Accordingly, in the present invention, it is preferable to use a PVA fiber having good crystallinity.
The crystallinity of the PVA-based fiber can use “crystallinity” and “crystal orientation” as indices.

The PVA fiber can be produced by a known method.
PVA fibers are generally produced by spinning a fiber raw material, drying it if necessary, heat-treating it if necessary, drawing it if necessary, and cutting it if necessary.
In the present invention, the fiber raw material contains one or more VA-based resins as a main component, and may contain an optional component as necessary.

By subjecting the spun PVA fibers to heat treatment and further stretching treatment, the crystallinity of the PVA fibers can be effectively improved and the tension can be improved.
Therefore, in this invention, the PVA type fiber in which the extending | stretching process was performed is used preferably.
The crystallinity of the PVA fiber can be adjusted by the draw ratio.
As the draw ratio increases, the crystallinity of the PVA fiber tends to increase.

In the present invention, the degree of crystallinity of the PVA fiber is not particularly limited and is preferably higher.
The crystallinity of the PVA fiber is preferably 50% or more, more preferably 70% or more. In the present invention, the degree of crystal orientation of the PVA fiber is not particularly limited and is preferably higher.
The degree of crystal orientation of the PVA fiber is preferably 0.8 or more, more preferably 0.9 or more.
In addition, as described above, the crystallinity of the PVA fiber can be adjusted by the saponification degree and the draw ratio of polyvinyl acetate.

Since the hydrophilicity and crystallinity of the PVA fiber are high and more calcium carbonate crystals can be grown on the surface of the PVA fiber, it is preferable that the molar ratio of vinyl alcohol units in the VA resin is high.
In addition, there exists a tendency for the molar ratio of the vinyl alcohol unit in VA-type resin to increase, so that saponification degree becomes high.
From the viewpoint of excellent hydrophilicity and crystallinity, the molar ratio of the vinyl alcohol unit in the VA resin is preferably 50 to 100 mol%, more preferably 70 to 100 mol%, and particularly preferably 90 to 100 mol%. .

The average degree of polymerization of the VA resin is not particularly limited.
Considering fiberization or the like, the average degree of polymerization is preferably 300 or more, more preferably 1500 or more.
Considering fiberization or the like, the average degree of polymerization is preferably 10,000 or less, more preferably 2400 or less.

(Hydrophilic polymer)
The hydrophilic polymer used in the present invention is a polymer having a hydrophilic group having a coordination ability for calcium ions.
Hereinafter, unless otherwise specified, the “hydrophilic group” means a hydrophilic group having a coordination ability for calcium ions.
The hydrophilic polymer can contain one or more of the above hydrophilic groups.
One or two or more hydrophilic polymers can be used.

Examples of the hydrophilic group include a carboxy group, an amino group, a hydroxyl group, and an amide group.
Examples of the hydrophilic polymer having such a hydrophilic group include polyacrylic acid (PAA), ethylene / acrylic acid copolymer, polyallylamine, polyglutamic acid, polyvinylpyrrolidone (PVP), vinyl alcohol (VA) resin, and polyethylene glycol. (PEG) and the like.
The vinyl alcohol (VA) resin used as the hydrophilic polymer is a copolymer (partially saponified product) containing a vinyl alcohol unit and a vinyl acetate unit because it exhibits good hydrophilicity and water solubility. Is preferred.

  In the production method of the present invention, it is presumed that the surface energy of calcium ions can be reduced by the presence of the hydrophilic polymer around the calcium ions. As a result, it is surmised that the calcium carbonate crystals can be prevented from excessively precipitating in the solution before the calcium carbonate crystal growth on the surface of the PVA fiber proceeds well. Thus, it is presumed that calcium carbonate can be preferentially grown on the surface of the PVA fiber.

Among the hydrophilic groups, a carboxy group and / or an amino group are more preferable because they have a good coordination ability for calcium ions and can effectively reduce the surface energy of calcium ions.
Examples of the hydrophilic polymer having a carboxy group and / or an amino group include polyacrylic acid (PAA), ethylene / acrylic acid copolymer, polyallylamine, and polyglutamic acid.

The weight average molecular weight (Mw) of the hydrophilic polymer is not particularly limited, and a commercially available hydrophilic polymer having an arbitrary weight average molecular weight (Mw) can be used.
Depending on the application or the like, there may be various suitable physical properties (such as mechanical properties and thermophysical properties) in the deposit (coating layer) formed on the surface of the PVA fiber and containing the hydrophilic polymer and calcium carbonate crystals. In this case, a hydrophilic polymer having a suitable range of Mw can be selected according to the desired physical properties of the deposit (coating layer).

(Calcium carbonate crystal)
In the production method of the present invention, calcium carbonate is crystal-grown on the surface of the PVA fiber.
Generally, the types of calcium carbonate crystals include aragonite crystals, calcite crystals, and vaterite crystals.

In the production method of the present invention, a calcium carbonate crystal whose main crystals are calcite crystals and vaterite crystals and whose crystallite size is 0.01 to 0.1 μm can be grown on the surface of the PVA fiber. .
In addition, an aragonite crystal having an amount below the detection limit may grow.

The form of the calcium carbonate crystal in the deposit (coating layer) is not particularly limited.
In the production method of the present invention, calcium carbonate crystals can be formed on the surface of the PVA fiber in the form of a plate or particles (see the SEM photograph in the section of “Examples” below). .
The diameter (average diameter) of calcium carbonate such as plate or particles is not particularly limited.
Depending on applications, the composite fiber of the present invention or the composite material of the present invention may have various suitable physical properties (such as mechanical properties and thermophysical properties). In this case, plate-like or particulate calcium carbonate having a suitable range of diameters can be grown according to the desired physical properties.
In the manufacturing method of this invention, the diameter (average diameter) of calcium carbonate, such as plate shape or particle shape, can be adjusted by adjusting manufacturing conditions.

(Physical properties of the deposit (coating layer))
In the composite fiber of the present invention, at least a part of the surface of the polar fiber is covered with an attachment containing at least one hydrophilic polymer and calcium carbonate crystals.
In the production method of the present invention, the deposit can form a coating layer covering at least a part of the surface of the polar fiber.
In the production method of the present invention, the coating layer can be formed on the surface of the polar fiber with a high surface coverage.
Specifically, the surface coverage of the polar fiber by the coating layer is 80 to 100%, preferably 90 to 100%.
In the conjugate fiber of the present invention, the coating layer has an average thickness of 0.01 to 20 μm.
In the present invention, since the coating layer can be formed on the surface of the polar fiber at a high surface coverage, a larger amount of calcium carbonate crystals can be combined with the polar fiber.

In the present invention, since the calcium carbonate can be grown on the surface of the polar fiber along the crystal orientation of the polar fiber, compared with the case of simply attaching amorphous calcium carbonate on the surface of the polar fiber. The adhesion of calcium carbonate to polar fibers becomes strong.
The adhesion of the deposit (coating layer) containing the calcium carbonate crystal is, for example, between the deposit (coating layer) and the polar fiber with respect to the area of the adhesion interface between the deposit (coating layer) containing the calcium carbonate crystal and the polar fiber. It can be estimated by the interface shear stress (IFSS) calculated from the shear stress in the interface direction.
The interfacial shear stress (IFSS) is preferably 5 MPa or more, more preferably 15 MPa or more, and particularly preferably 25 MPa or more.
In this invention, the composite fiber which was excellent in the adhesiveness of the deposit (coating layer) containing a calcium carbonate crystal | crystallization which has this interface shear stress, and polar fiber can be provided.

In the manufacturing method of this invention, the calcium carbonate crystal | crystallization which is an inorganic substance can be favorably compounded on the surface of the polar fiber (PVA type fiber) which is a resin fiber.
Therefore, according to the present invention, it is possible to provide a composite fiber in which the resin fiber and the inorganic substance are effectively combined utilizing their respective merits and have mechanical properties suitable as a reinforcing fiber or the like.

Resin fibers are easy to mold and have excellent mechanical properties such as tensile strength, but tend to be inferior in mechanical properties such as flexural modulus.
Conversely, inorganic materials have excellent mechanical properties such as flexural modulus but tend to be inferior in mechanical properties such as tensile strength.
In the present invention, even if an inorganic substance is combined on the surface of the resin fiber, the good tensile strength inherent to the resin fiber is not impaired, for example, a composite fiber having a tensile strength equal to or higher than that of the original polar fiber is used. Can be provided. Furthermore, in this invention, a bending elastic modulus can be improved by compounding an inorganic substance on the surface of a resin fiber.
Therefore, according to the present invention, it is possible to provide a composite fiber that has both the good tensile strength inherently possessed by the resin fiber and the good flexural modulus inherent in the inorganic substance.

Furthermore, the present invention can form a coating layer with a high surface coverage on the surface of the polar fiber, so that a larger amount of calcium carbonate crystals can be combined with the polar fiber.
In addition, since calcium carbonate can be grown on the surface of the polar fiber along the crystal orientation of the polar fiber, the polar fiber is simply compared to the case of attaching amorphous calcium carbonate on the surface of the polar fiber. Adhesiveness of calcium carbonate to the water becomes strong.
Combined with these effects, according to the present invention, the flexural modulus can be more effectively improved.

"Production method of composite fiber"
The conjugate fiber of the present invention can be produced by the following production method.

(Preparation of polar fiber)
First, PVA fibers are prepared as polar fibers.
Commercially available PVA fibers may be used, or they may be produced by known methods.
PVA fibers are generally produced by spinning a fiber raw material, drying it if necessary, heat-treating it if necessary, drawing it if necessary, and cutting it if necessary.

The spinning method is not particularly limited, and examples thereof include a melt spinning method, a dry spinning method, and a wet spinning method.
The melt spinning method is a method in which a heated and melted polymer is cooled while being extruded into a fiber form from a nozzle to be fiberized.
The dry spinning method is a method in which a spinning stock solution in which a polymer is dissolved in a volatile solvent is prepared, and the solvent is vaporized by heating while extruding the polymer from a nozzle into a fiber shape, and fiberized.
The wet spinning method is a method in which a dissolved spinning stock solution in which a polymer is dissolved in a low-volatile solvent is prepared, extruded into a fiber form from a nozzle, and then solidified in a coagulating liquid to be fiberized. .

Among the above, the wet spinning method and the like are preferable.
In the wet spinning method, since the spinning stock solution may have a low viscosity, a polymer with a high degree of polymerization can be spun and high-tensile fibers can be obtained.

Hereinafter, the production of polar fibers by a wet spinning method will be described as an example.
One or two or more VA-based resins, which are polar fiber raw materials, are dissolved in a low-volatile solvent to obtain a spinning dope.
The solvent is not particularly limited, and examples thereof include dimethyl sulfoxide (DMSO), water, methanol, glycerin, and N-methylpyrrolidone (NMP).
The dissolution method is not particularly limited.
For example, the VA resin can be dissolved by adding the VA resin to the solvent and stirring the solvent while stirring the solvent.
The concentration and dissolution temperature of the VA resin in the spinning dope are adjusted as appropriate within a range suitable for stable spinning.
For example, when a VA resin having an average degree of polymerization of about 1700 is used, the concentration of the VA resin in the spinning dope is preferably 13 to 20% by mass, and the dissolution temperature is preferably about 70 to 120 ° C.

The obtained spinning dope is extruded into a fiber form from a nozzle and then solidified in a coagulating liquid.
The coagulation liquid is a liquid that does not dissolve the polymer but has good compatibility with the solvent of the spinning dope.
In the case of PVA fibers, for example, methanol, toluene, acetone, ethanol and the like are suitably used as the coagulating liquid.
If necessary, a substance that improves the coagulation property, such as water or ketones, can be added to the coagulation liquid.
From the viewpoint of spinnability and economy, the temperature of the coagulation liquid is preferably 0 to 20 ° C.

As another embodiment, there is a method in which an alcohol group in a VA resin in a spinning dope is chemically reacted with a reactive substance in a coagulation liquid. In this case, the heat resistance and water resistance of the fiber can be improved.
As the reactive substance, formaldehyde and benzaldehyde are preferably used.

Next, the PVA fiber taken out from the coagulation liquid is dried to remove liquid components remaining in the fiber (spinning solution solvent, coagulation liquid, and reactive substances).
From the viewpoint of improving crystallization, heat drying is preferred as the drying method.
The drying temperature is preferably 80 to 200 ° C.

Next, the PVA fiber after drying can be further heat-treated as necessary.
By performing the heat treatment, the crystallinity of the PVA fiber can be improved and the tension can be improved.
From the viewpoint of improving fiber crystallization, the heat treatment temperature is preferably 200 to 260 ° C.
Long-time heat treatment usually does not contribute to improving the crystallinity of the VA-based resin.
For example, about 2 seconds is sufficient as the heat treatment time.

If necessary, the PVA fiber can be further stretched.
By performing the stretching treatment, the crystallinity of the PVA fiber can be effectively improved and the tension can be further improved.
From the viewpoint of improving the crystallization of the fiber, the stretching method is preferably a dry heat stretching method.
In the dry heat stretching method, for example, primary stretching can be performed at a stretching ratio of 1.3 to 3 times at 80 to 230 ° C. Furthermore, secondary stretching can be performed so that the total stretching ratio is 3 to 24 times at 160 to 230 ° C.
In the present invention, PVA fibers having a total draw ratio of 3 to 24 times are preferably used.
As described above, the PVA fiber is manufactured.

The produced PVA-based fiber can be processed into an arbitrary form as necessary.
The PVA fiber may be subjected to processing such as mechanical crimping or check-out, and spinning or nonwoven fabric processing may be performed.
A plurality of PVA fibers may be aligned in one direction to obtain a yarn, and further processed into an anisotropic two-dimensional structure in which a plurality of yarns are arranged in parallel in a direction perpendicular to the fiber direction.
Using a loom, the PVA fibers may be made into a plain or twill fabric. Further, a three-dimensional structure may be formed by a braiding process.

As the polar fiber, one type or two or more types of PVA fibers can be used.
As the polar fiber, a mixed yarn of PVA fiber and other resin fiber may be used.

(First step)
First, the following first aqueous solution and second aqueous solution are prepared.

  The first aqueous solution is an aqueous solution containing at least one calcium ion source represented by the following general formula [II] and at least one hydrophilic polymer having a hydrophilic group having a coordination ability for calcium ions. .

CaX ₂ · nH ₂ O ... [II]
(In the formula [II], X represents a halogen atom, and n represents a real number of 0 or more.)

  Examples of the calcium ion source represented by the general formula [II] include calcium chloride, calcium acetate, calcium bromide, calcium iodide, and hydrates thereof.

Examples of the hydrophilic group having coordinating ability for calcium ions include a carboxy group, an amino group, a hydroxyl group, and an amide group.
Examples of the hydrophilic polymer having such a hydrophilic group include polyacrylic acid (PAA), ethylene / acrylic acid copolymer, polyallylamine, polyglutamic acid, polyvinylpyrrolidone (PVP), vinyl alcohol (VA) resin, and polyethylene. A glycol (PEG) etc. are mentioned.
The vinyl alcohol (VA) resin used as the hydrophilic polymer is a copolymer (partially saponified product) containing a vinyl alcohol unit and a vinyl acetate unit because it exhibits good hydrophilicity and water solubility. Is preferred.

Among the hydrophilic groups, a carboxy group and / or an amino group are more preferable because they have a good coordination ability for calcium ions and can effectively reduce the surface energy of calcium ions.
Examples of the hydrophilic polymer having a carboxy group and / or an amino group include polyacrylic acid (PAA), ethylene / acrylic acid copolymer, polyallylamine, and polyglutamic acid.

The concentration of the calcium ion source in the first aqueous solution is 10 mM or more, preferably 15 mM or more, more preferably 20 mM or more.
The upper limit of the concentration of the calcium ion source in the first aqueous solution is not particularly limited, and the concentration of the calcium ion source in the first aqueous solution is preferably 100 mM or less, more preferably 50 mM or less.

  The density | concentration of the hydrophilic polymer in 1st aqueous solution is 10-100 mM in monomer conversion, Preferably it is 10-50 mM, More preferably, it is 13-17 mM.

For example, when the hydrophilic polymer is polyacrylic acid (PAA), the monomer is acrylic acid (AA).
The concentration of polyacrylic acid (PAA) in the first aqueous solution is obtained by converting into the amount of PAA raw material monomer (acrylic acid (AA)) based on the weight average molecular weight.
The concentration of vinyl alcohol (VA) resin, etc., in which no monomer is used in the actual polymer production method, is converted to the amount of raw material monomer by regarding each structural unit as being derived from the raw material monomer based on the average degree of polymerization. , To seek.

The reason why the concentration of the hydrophilic polymer is converted into a monomer is that the relationship between the amount of calcium ions and the amount of hydrophilic groups having coordination ability with respect to calcium ions is important.
By defining the concentration of the calcium ion source and the concentration of the hydrophilic polymer in the first aqueous solution as described above, a hydrophilic group having a coordination ability with respect to calcium ions is coordinated with respect to calcium ions in a suitable range. Can be made.

  In the production method of the present invention, it is presumed that the surface energy of calcium ions can be reduced by the presence of the hydrophilic polymer around the calcium ions. As a result, it is surmised that the calcium carbonate crystals can be prevented from excessively precipitating in the solution before the calcium carbonate crystal growth on the surface of the PVA fiber proceeds well. Thus, it is presumed that calcium carbonate can be preferentially grown on the surface of the PVA fiber.

In addition, if the amount of the hydrophilic group having the coordination ability to the calcium ion is too small relative to the calcium ion, the effect of reducing the surface energy of the calcium ion becomes insufficient, and the calcium carbonate crystal is excessively precipitated in the solution. End up.
On the other hand, if the amount of the hydrophilic group having the coordination ability to the calcium ion is excessive with respect to the calcium ion, the effect of reducing the surface energy of the calcium ion becomes excessive, and the crystal growth rate of calcium carbonate on the surface of the PVA fiber is increased. Will drop significantly.
By defining the concentration of the calcium ion source and the concentration of the hydrophilic polymer in the first aqueous solution as described above, while suppressing excessive crystal precipitation of calcium carbonate in the solution, carbonic acid is formed on the surface of the PVA fiber. Calcium can be grown satisfactorily.

(Second step)
A second aqueous solution containing at least one carbonate ion source represented by the following general formula [III] is prepared.

M _a (CO ₃ ) _b · nH ₂ O ... [III]
(In formula [III], each symbol has the following meaning.
M represents at least one metal atom, ammonium, or hydrogen atom.
a and b are integers of 1 or more, and n represents a real number of 0 or more. )

  Examples of the carbonate ion source represented by the above formula include carbonic acid, sodium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, potassium carbonate, and hydrates thereof.

The concentration of the carbonate ion source in the second aqueous solution is 10 mM or more, preferably 15 mM or more, more preferably 20 mM or more.
The upper limit of the concentration of the carbonate ion source in the second aqueous solution is not particularly limited, and the concentration of the carbonate ion source in the second aqueous solution is preferably 100 mM or less, more preferably 50 mM or less.

(Third step)
In this step, the first aqueous solution obtained in the first step and the second aqueous solution obtained in the second step are mixed and reacted. Thereby, a calcium carbonate aqueous solution containing amorphous calcium carbonate and a hydrophilic polymer is obtained.

In consideration of the yield of calcium carbonate in the mixed aqueous solution, the calcium ion and carbonate ion in the mixed aqueous solution are preferably equimolar or close to each other, and more preferably equimolar. preferable.
For example, it is preferable that the calcium ions in the first aqueous solution and the carbonate ions in the second aqueous solution have an equimolar or close relationship, and the first aqueous solution and the second aqueous solution are mixed in an equal volume or a close relationship. .
However, the calcium ions and carbonate ions in the mixed aqueous solution may deviate from an equimolar or close relationship within a range in which calcium carbonate is favorably generated in the mixed aqueous solution.

(4th process)
In this step, the polar fiber (which may be obtained by processing a polar fiber) is immersed in an aqueous calcium carbonate solution containing amorphous calcium carbonate and a hydrophilic polymer obtained in the second step.
As a result, a composite fiber in which calcium carbonate crystals and a hydrophilic polymer are adhered to at least a part of the surface of the polar fiber is manufactured.

The deposition time of the deposit containing the calcium carbonate crystals and the hydrophilic polymer on at least a part of the surface of the polar fiber is not particularly limited, and a sufficient amount of calcium carbonate is formed on the surface of at least a part of the polar fiber. The time for crystal growth can be set.
As the deposition time becomes longer, the amount of adhesion tends to increase, but the effect is saturated even if a certain amount of deposition time is exceeded.
The deposition time is preferably about 24 hours to 3 weeks, more preferably about 24 hours to 1 week.
For example, in Examples 1-7 to 1-9 and 8-7 to 8-9, which will be described later, within the range of 1 to 3 weeks, even if immersed for 2 weeks or more, the adhesion amount with respect to the immersion for 1 week No significant increase was observed, and about one week was sufficient.
However, it is considered that a suitable precipitation time varies depending on the concentrations of the first aqueous solution and the second aqueous solution used.
After the immersion treatment, the composite fiber obtained from the calcium carbonate aqueous solution is taken out.

The first to fourth steps described above can be performed at any temperature within a temperature range higher than the freezing point of water and lower than the boiling point of water, for example, within a range of 10 to 90 ° C.
However, in the fourth step, the reaction proceeds excessively at 60 ° C. or higher, and the calcium carbonate crystals may become a relatively large lump and adhere to the polar fiber.
The first step to the fourth step are preferably carried out within a range of 10 to 50 ° C, more preferably carried out within a range of 10 to 40 ° C, and carried out within a range of 10 to 30 ° C. Particularly preferred.
The 1st process-the 4th process can be carried out under normal room temperature (for example, 20-30 ° C).
The first to fourth steps can also be performed under normal atmospheric pressure.

(5th process)
The composite fiber taken out from the calcium carbonate aqueous solution can be washed as necessary.
For example, when calcium chloride is used as the calcium ion source and sodium carbonate is used as the carbonate ion source, sodium chloride is by-produced. In order to remove such a by-product, the polar fiber taken out from the calcium carbonate aqueous solution can be washed with water or the like.

(Sixth step)
Finally, the obtained composite fiber is dried. Thereby, water adhering to the composite fiber can be removed.
The drying method is not particularly limited, and a known method can be applied.
The composite fiber of this invention is manufactured as mentioned above.

In the present invention, PVA fibers mainly composed of at least one vinyl alcohol (VA) resin are used as polar fibers.
Although calcium carbonate in the calcium carbonate aqueous solution is amorphous, in the present invention, the PVA fiber has good crystallinity, so that the calcium carbonate is formed on the surface of the fiber along the crystal orientation of the PVA fiber. It is considered that the crystal can be grown satisfactorily.

In the present invention, the degree of crystallinity of the PVA fiber is not particularly limited and is preferably higher.
The crystallinity of the PVA fiber is preferably 50% or more, more preferably 70% or more.
In the present invention, the degree of crystal orientation of the PVA fiber is not particularly limited and is preferably higher.
The degree of crystal orientation of the PVA fiber is preferably 0.8 or more, more preferably 0.9 or more.
The crystallinity of the PVA fiber can be adjusted by the saponification degree and the draw ratio of polyvinyl acetate.

The shape of the calcium carbonate crystal attached on the surface of the fiber is not particularly limited, and is, for example, a plate shape or a particle shape.
In addition, it is thought that the hydrophilic polymer containing the hydrophilic group which has the coordinating ability with respect to a calcium ion with a calcium carbonate crystal | crystallization adheres on the surface of a PVA type fiber simultaneously.
The distribution of calcium carbonate crystals and hydrophilic polymer in the deposit is not particularly limited.
As the form of the deposit, a plate-like or particle-like form in which a hydrophilic polymer is attached around a calcium carbonate crystal and a plate-like or particle-like substance containing calcium carbonate crystal and a hydrophilic polymer are generated. And the like.

  In the production method of the present invention, a calcium carbonate crystal whose main crystals are calcite crystals and vaterite crystals and whose crystallite size is 0.01 to 0.1 μm can be grown on the surface of the PVA fiber. .

In the present invention, in the second step, a relatively large amount of calcium carbonate can be generated in the calcium carbonate aqueous solution. Therefore, a relatively large amount of the calcium carbonate crystal can be grown on the surface of the PVA fiber.
As a result, in the present invention, it is possible to form a coating layer that covers at least a part of the surface of the polar fiber by the deposit containing calcium carbonate crystals and the hydrophilic polymer.

In the present invention, a coating layer having an average thickness of 0.01 to 20 μm can be formed.
In the present invention, it is also possible to form a coating layer in which the surface coverage of the PVA fiber is 80 to 100%.
The surface coverage of the polar fiber by the coating layer is preferably 90 to 100%.

  In the present invention, since the coating layer can be formed on the surface of the polar fiber at a high surface coverage, a larger amount of calcium carbonate crystals can be combined with the polar fiber.

  In addition, in the manufacturing method of this invention, it is guessed that the surface energy of a calcium ion can be reduced because a hydrophilic polymer exists around a calcium ion. As a result, it is surmised that the calcium carbonate crystals can be prevented from excessively precipitating in the solution before the calcium carbonate crystal growth on the surface of the PVA fiber proceeds well. Thus, it is presumed that calcium carbonate can be preferentially grown on the surface of the PVA fiber.

  In the present invention, since the calcium carbonate can be grown on the surface of the polar fiber along the crystal orientation of the polar fiber, compared with the case of simply attaching amorphous calcium carbonate on the surface of the polar fiber. The adhesion of calcium carbonate to polar fibers becomes strong.

In the manufacturing method of this invention, the calcium carbonate crystal | crystallization which is an inorganic substance can be favorably compounded on the surface of the polar fiber which is a resin fiber.
Therefore, according to the present invention, it is possible to provide a composite fiber in which the resin fiber and the inorganic substance are effectively combined utilizing their respective merits and have mechanical properties suitable as a reinforcing fiber or the like.

Resin fibers have excellent mechanical properties such as tensile strength, but tend to be inferior in mechanical properties such as flexural modulus.
Conversely, inorganic materials have excellent mechanical properties such as flexural modulus but tend to be inferior in mechanical properties such as tensile strength.
In the present invention, even if an inorganic substance is combined on the surface of the resin fiber, the good tensile strength inherent to the resin fiber is not impaired, for example, a composite fiber having a tensile strength equal to or higher than that of the original polar fiber is used. Can be provided. Furthermore, in this invention, a bending elastic modulus can be improved by compounding an inorganic substance on the surface of a resin fiber.
Therefore, according to the present invention, it is possible to provide a composite fiber that has both the good tensile strength inherently possessed by the resin fiber and the good flexural modulus inherent in the inorganic substance.

Furthermore, the present invention can form a coating layer with a high surface coverage on the surface of the polar fiber, so that a larger amount of calcium carbonate crystals can be combined with the polar fiber.
In addition, since calcium carbonate can be grown on the surface of the polar fiber along the crystal orientation of the polar fiber, the polar fiber is simply compared to the case of attaching amorphous calcium carbonate on the surface of the polar fiber. Adhesiveness of calcium carbonate to the water becomes strong.
Combined with these effects, according to the present invention, the flexural modulus can be more effectively improved.

"Composite"
The composite material of the present invention includes a matrix material and the above-described composite fiber of the present invention.

The first method for producing a composite material of the present invention is a method in which a liquid material is solidified after impregnating a composite fiber with a liquid material to be a matrix material.
The manufacturing method of the 1st composite material of this invention is a method of solidifying a liquid raw material, after mixing a composite fiber and the liquid raw material used as a matrix material.

As a composite fiber, the thing of arbitrary forms, such as an aggregate of a plurality of composite fibers, and various fiber processed products, can be used.
For example, a fiber assembly in which a plurality of fibers are aggregated with voids inside is preferably used.

The matrix material is not particularly limited, and a matrix material (matrix resin) made of at least one resin is preferable from the viewpoint of moldability and the like.
A matrix material (matrix resin) made of at least one resin and a composite material including the composite fiber of the present invention can be suitably used as a so-called fiber reinforced resin (FRP).

Resin used as a matrix material is not particularly limited,
Thermosetting resins such as unsaturated polyesters, epoxy resins, amide resins, and phenol resins;
and,
Examples thereof include thermoplastic resins such as (meth) acrylic resins.

  A well-known technique can be applied to the liquid raw material used as the matrix material and the solidifying method thereof.

When a thermosetting resin is used as the matrix material, the liquid raw material that becomes the matrix material is a thermosetting liquid raw material that becomes the matrix material by thermosetting.
As the thermosetting liquid raw material, known materials can be used, which can include a monomer of a thermosetting resin, a dimer, or a precursor polymer of a relatively low molecular thermosetting resin.
The thermosetting liquid raw material can be solidified by thermosetting.

When a thermoplastic resin is used as the matrix material, the liquid raw material used as the matrix material includes a thermoplastic resin heated melt, a solution obtained by dissolving the thermoplastic resin in a solvent, and the thermoplastic resin dispersed in a dispersion medium. Dispersions and the like.
The heated melt of the thermoplastic resin can be solidified by cooling.
The solution or dispersion of the thermoplastic resin can be solidified by removing the solvent or dispersion medium by drying.

  As described above, according to the present invention, a resin fiber and an inorganic substance are effectively combined utilizing their respective strengths, and a composite fiber having suitable mechanical properties as a reinforcing fiber, a manufacturing method thereof, and the It is possible to provide a composite material using the same and a method for producing the same.

  According to the present invention, for example, a composite fiber capable of improving the flexural modulus while maintaining the inherent tensile strength of the resin fiber, a method for producing the same, and a composite material using the composite fiber and a method for producing the same are disclosed. Can be provided.

The use of the composite fiber and composite material of the present invention is not particularly limited.
The composite fiber of the present invention is suitable as a reinforcing fiber, and the composite fiber of the present invention and the composite material using the composite fiber can be suitably used for applications such as aircraft members, automobile members, home appliance members, and building materials.

Examples of the present invention and comparative examples will be described below.
[Polar fiber production example 1]
As a resin material for polar fibers, “Kuraray Poval PVA-117” manufactured by Kuraray Co., Ltd., which is polyvinyl alcohol (completely saponified product) consisting only of vinyl alcohol units (average polymerization degree of about 1700, vinyl alcohol unit amount of 100 mol%, A polyvinyl alcohol concentration of 94% or more in the product) was prepared.

  The resin raw material was dissolved in dimethyl sulfoxide (DMSO) at 100 ° C. to obtain a 20% by mass spinning dope.

  The spinning stock solution obtained above was extruded into a fiber form from a nozzle using a known wet spinning apparatus, solidified in a methanol coagulating liquid, and stretched 3 times in a solidifying bath.

The obtained PVA fiber was dried by heating to remove the liquid component remaining in the fiber to obtain a spinning yarn.
The drying temperature was 95 ° C. and the drying time was 5 minutes.
The PVA fiber at this time was designated as “fiber sample 8” and used for the production of composite fibers of Examples and Comparative Examples described later.

  Further, the obtained spinning yarn was stretched 4 times at 230 ° C. (total 12 times stretching). This was designated as “fiber sample 1” and used for the production of composite fibers of Examples and Comparative Examples described later.

With respect to the obtained fiber sample 1 and fiber sample 8, the fiber diameter, crystallinity, crystal orientation, and crystallite size were measured in accordance with the method defined in [Means for Solving the Problems]. The evaluation results are shown in Table 1.
The fiber sample 1 was a sample having a relatively high crystallinity, and the crystallinity was 70.1%.
The fiber sample 8 was a sample having a relatively low crystallinity, and the crystallinity was 57.6%.

[material]
The following raw materials were prepared.
(Calcium ion source)
As a calcium ion source, calcium chloride (WAKO, Calcium Chloride, Anhydrous, purity 95%) was prepared.
(Carbonate source)
As a carbonate ion source, sodium carbonate (manufactured by KANTO CHEMICAL CO., INC., Sodium Carbonate, purity 99.8%, anhydrous) was prepared.
(Hydrophilic polymer)
Polyacrylic acid (PAA) (manufactured by ALDRICH, Poly (acrylic acid), powder, purity 90%, average polymerization degree 25, weight as a hydrophilic polymer having a hydrophilic group having a coordinating ability for calcium ions in the side chain An average molecular weight of 1800) was prepared.

[Examples 1-7 to 1-9, Examples 8-7 to 8-9]
First, 20 mM calcium chloride and 1.1 × 10 ⁻¹ mass% polyacrylic acid (PAA) were dissolved in water to obtain a first aqueous solution.
The amount of PAA in the first aqueous solution was 15M in terms of monomer.

  Separately, 20 mM sodium carbonate was dissolved in water to obtain a second aqueous solution.

Next, said 1st aqueous solution and said 2nd aqueous solution were mixed by equal volume. Thereby, an aqueous calcium carbonate solution containing amorphous calcium carbonate and polyacrylic acid (PAA) was obtained.
As a result of visual observation, no precipitate of calcium carbonate was found in the aqueous calcium carbonate solution.

  In addition, it was confirmed by a well-known XRD analysis that the calcium carbonate in this calcium carbonate aqueous solution was amorphous.

  Next, 0.01 g of polar fibers were immersed in 100 mL of the obtained aqueous calcium carbonate solution.

In Examples 1-7 to 1-9, the above fiber sample 1 (a sample having a relatively high crystallinity, a crystallinity of 70.1%) was used as the polar fiber, and the immersion time (deposition time of deposit) Was as follows.
Example 1-7: 1 week,
Example 1-8: 2 weeks,
Example 1-9: 3 weeks.

In Examples 8-7 to 8-9, the above fiber sample 8 (sample with relatively low crystallinity, crystallinity of 57.6%) was used as the polar fiber, and the immersion time (deposition time of deposit) Was as follows.
Example 8-7: 1 week,
Example 8-8: 2 weeks,
Example 8-9: 3 weeks.

  All of the above series of experimental operations were performed at normal room temperature (20 to 30 ° C.) and atmospheric pressure.

In each example, after the immersion, the composite fiber obtained from the aqueous calcium carbonate solution was taken out, washed with water to remove sodium chloride, and then heated and dried at 60 ° C. for 30 minutes.
A composite fiber was produced as described above.

  Table 2 shows the main production conditions and implementation conditions of Examples 1-7 to 1-9 and Examples 8-7 to 8-9.

[Comparative Example 1-1]
A composite fiber was obtained in the same manner as in Example 1-7, except that polyacrylic acid (PAA) was not added to the first aqueous solution.
In Comparative Example 1-1 in which polyacrylic acid (PAA) was not added to the first aqueous solution, the first aqueous solution and the second aqueous solution were mixed, and then immediately after visual observation, amorphous calcium carbonate was found in the aqueous solution. A large solid was observed to precipitate and precipitate.
Although the fiber sample 1 was immersed as a polar fiber in the calcium carbonate aqueous solution containing this calcium carbonate precipitate, before the calcium carbonate crystal grew on the surface of the fiber by visual observation, the amorphous fiber carbonate was added to the polar fiber. A large number of large lumps were attached.

[Evaluation items and methods]

(SEM observation)
About the composite fiber obtained in each example of Examples 1-7 to 1-9, Examples 8-7 to 8-9, and Comparative Example 1-1, using SEM (scanning electron microscope), composite Fiber surface observation and cross-sectional observation were performed.
As the SEM, “VE-9800” manufactured by KEYENCE Corporation was used.

(MICRO-WAXD (Wide-Angle X-Ray Diffraction) analysis)
The composite fibers obtained in Examples 1-9 and 8-9 were subjected to MICRO-WAXD (Wide-Angle X-Ray Diffraction) analysis.
As a measuring device, “BL03XU” of the large synchrotron radiation facility SPring-8 was used.
Measurement was performed on the measurement sample fiber while scanning X-rays by 1 μm in the fiber radial direction (perpendicular to the fiber axis direction) from the outside of the fiber.
Thereby, in the cross section of the measurement sample fiber, WAXD data was obtained at intervals of 1 μm from one end to the other end in the radial direction.
The above measurement was performed for all directions, and the ring average of the WAXD data was obtained for each radial position to obtain a WAXD pattern.
The measurement conditions were as follows.
X-ray wavelength: 0.13051 nm,
X-ray diameter: Full width at half maximum when approximating the intensity distribution with a Gaussian function is about 1 μm,
Exposure time: 5 seconds
Attenuator and chopper: not used,
Position resolution: 1 μm.

The analyzed diffraction peaks are as follows.
Aragonite crystal: (111),
Calcite crystal: (104),
Vaterite crystals: (112).

Of the diffraction peaks of the aragonite crystal, the calcite crystal, and the vaterite crystal, the strongest diffraction peak was fitted with a Gaussian function to determine the integrated intensity and the peak width.
The integrated intensity is an index of the amount of deposits including calcium carbonate crystals.
Further, the half width was obtained from the peak width, and the crystallite size was obtained using Scherrer's equation. Scherrer's constant K was set to 0.94.

(Measurement of interfacial shear strength (IFSS))
The following evaluation was implemented about the composite fiber obtained in Example 1-9.
The original PVA system before adhering calcium carbonate crystals by the microdroplet method using a composite material interface property evaluation device as an evaluation of the interfacial adhesion of the deposit (coating layer) containing calcium carbonate crystals to PVA fibers The interfacial shear strength (IFSS) of the fiber and the resulting composite fiber was measured.
As a measuring device, “HM410” manufactured by Toei Sangyo Co., Ltd. was used.
An epoxy curing solution containing a monomer of a thermosetting epoxy resin was dropped on the measurement sample fiber. This operation was repeated, and droplets of the epoxy curable liquid were adhered to a plurality of locations of the measurement sample fiber at intervals. Thereafter, the adhered epoxy-based curable liquid was heated and cured at 80 ° C. for 3 hours in an air atmosphere to form a plurality of microdroplets.
Next, the obtained sample was set on the pedestal of the composite material interface property evaluation apparatus, and fixed by sandwiching the plurality of microdroplets with a pair of blades.
Next, the pedestal was moved to conduct a pull-out test, and the pull-out load was detected with a load cell.
Interfacial shear strength (IFSS) is calculated from the drawing load data based on the following equation.
τ = F / π · d · L
(In the above formula, each symbol has the following meaning.
τ: interfacial shear strength,
F: Pull-out load,
d: fiber diameter,
L: Droplet length. )

(Tensile test)
The following tensile tests were carried out on the original PVA fibers and the resulting composite fibers before the calcium carbonate crystals were attached.
“Fafegraph” manufactured by Texttechno was used as a measuring device.
The measurement items were as follows.
Fineness [dtex]: fiber mass per unit length,
Tensile elongation [%]: Elongation at break of fiber in tensile test,
Tensile strength [cN]: Fiber breaking strength in tensile test,
DYM [cN]: Tensile strength against a constant strain in the initial elastic region,
Tensile strength [cN / dtex]: Tensile strength / fineness value
Tensile Young's modulus [cN / dtex]: DYM / fineness value.

[Evaluation results]
(Results of SEM observation and MICRO-WAXD analysis)
<Examples 1-7 to 1-9>
SEM observation revealed the following.
In each of Examples 1-7 to 1-9, a composite fiber in which a deposit mainly composed of calcium carbonate crystals was formed on the surface of the PVA fiber was obtained.
In Examples 1-7 to 1-9, the deposit formed a coating layer covering at least a part of the surface of the PVA-based fiber.
In addition, it is guessed that the deposit | attachment (covering layer) also contains polyacrylic acid (PAA).

As representative examples, FIGS. 1A to 1D show SEM photographs of the composite fibers obtained in Example 1-9.
1A and 1B are SEM surface photographs.
1C and 1D are SEM cross-sectional photographs.

As shown in these photographs, the composite fiber obtained in Example 1-9 had a structure in which the entire surface of the PVA fiber was completely covered with a coating layer. That is, the surface coverage was 100%.
In a cross-sectional view, on the entire surface of the PVA system, a layer in which a plurality of relatively wide crystals close to a rectangle are arranged side by side along the surface of the PVA fiber is formed with a thickness of about 1 μm. Was observed. For convenience, this layer is hereinafter referred to as a “plate layer”.
Furthermore, it was observed in a cross-sectional view that a large number of particulate crystals having a relatively small diameter adhered to the outside of the plate-like layer with a thickness of about 200 to 300 nm. For convenience, this layer is hereinafter referred to as a “particulate layer”. See also the SEM surface picture for the particulate layer.
The composite fibers obtained in Example 1-7 and Example 1-8 also had a similar structure.

As a result of the MICRO-WAXD analysis, the following became clear.
2A and 2B show the WAXD patterns of the composite fibers obtained in Example 1-9.
The composite fiber obtained in Example 1-9 had a structure in which a layer mainly composed of calcite crystal and vaterite crystal was present outside the PVA fiber.
The crystallite size was as follows.
Calcite crystallite size: 25 nm or more,
Crystallite size of the vaterite crystal: about 20 nm.
There was no crystal orientation and random orientation.

  A schematic perspective view of the conjugate fiber obtained in Example 1-9 is shown in FIG.

<Examples 8-7 to 8-9>
SEM observation revealed the following.
In each of Examples 8-7 to 8-9, a composite fiber in which a deposit mainly composed of calcium carbonate crystals was formed on the surface of the PVA fiber was obtained.
In Examples 8-7 to 8-9, the deposit formed a coating layer covering the surface of at least a part of the PVA fiber.
The deposit (covering layer) is presumed to contain polyacrylic acid (PAA).
As representative examples, FIGS. 4A to 4D show SEM photographs of the composite fibers obtained in Example 8-9.
4A and 4B are SEM surface photographs.
4C and 4D are SEM cross-sectional photographs.

As shown in these photographs, each of the conjugate fibers obtained in Examples 8-9 had a structure in which the entire surface of the polar fiber was completely covered with the coating layer. That is, the surface coverage was 100%.
In a cross-sectional view, on the entire surface of the PVA fiber, a layer in which a large number of relatively small crystals close to a rectangle extending in the thickness direction are arranged side by side along the surface of the PVA fiber has a thickness of about 1 μm. The formation was observed. For convenience, this layer is hereinafter referred to as a “plate layer”.
Furthermore, it was observed in a cross-sectional view that a layer in which amorphous relatively thick and large crystals were densely arranged outside the plate-like layer was formed with a thickness of about 2 μm. For convenience, this layer is hereinafter referred to as a “dense layer”.
Furthermore, it was observed that a large number of particulate crystals having a relatively small diameter adhered to the outside of the dense layer with a thickness of about 1 μm. For convenience, this layer is hereinafter referred to as a “particulate layer”. See also the SEM surface picture for the particulate layer.
The composite fibers obtained in Example 8-7 and Example 8-8 also had a similar structure.

As a result of the MICRO-WAXD analysis, the following became clear.
FIG. 5A and FIG. 5B show the WAXD patterns of the composite fibers obtained in Examples 8-9.
The composite fiber obtained in Example 8-9 had a structure in which a layer mainly composed of calcite crystal was present outside the PVA-based fiber and a layer mainly composed of vaterite crystal was present outside thereof. .
The crystallite size was as follows.
Calcite crystallite size: 20-50 nm,
Crystallite size of vaterite crystals: 10-20 nm.
There was no crystal orientation and random orientation.
FIG. 6 shows a schematic perspective view of the conjugate fiber obtained in Example 8-9.

(Measurement result of interfacial shear strength (IFSS))
In FIG. 7, the measurement result of the interface shear strength (IFSS) of the original PVA type fiber (fiber sample 1) and the composite fiber obtained in Example 1-9 is shown.
As shown in FIG. 7, the composite fiber to which the calcium carbonate crystal was adhered showed an effect of improving the interfacial shear strength (IFSS).
This shows that the interfacial adhesion of the deposit (coating layer) containing calcium carbonate crystals to the PVA fibers is good.

(Result of tensile test)
8A to 8D show measurement results of tensile strength and DYM.
FIG. 8A is a graph showing the measurement results of the tensile strength of the original PVA fibers (fiber sample 1) and the composite fibers obtained in Examples 1-7 to 1-9.
FIG. 8B is a graph showing the DYM measurement results of the original PVA fibers (fiber sample 1) and the composite fibers obtained in Examples 1-7 to 1-9.
FIG. 8C is a graph showing the measurement results of tensile strength of the original PVA-based fiber (fiber sample 8) and the composite fibers obtained in Examples 8-7 to 8-9.
FIG. 8D is a graph showing DYM measurement results of the original PVA-based fiber (fiber sample 1) and the composite fibers obtained in Examples 8-7 to 8-9.

  The composite fibers obtained in Examples 1-7 to 1-9 and Examples 8-7 to 8-9 all had the same tensile strength and DYM level as the original PVA fibers.

Claims (8)

On the surface of at least a part of the polar fiber mainly composed of at least one vinyl alcohol resin represented by the following general formula [I],
Calcium carbonate having at least one hydrophilic polymer having a hydrophilic group capable of coordinating with calcium ions, a main crystal being a calcite crystal and a vaterite crystal, and a crystallite size of 0.01 to 0.1 μm A coating layer containing crystals is formed,
The coating layer has an average thickness of 0.01 to 20 μm,
The surface coverage of the polar fiber by the coating layer is 80 to 100%.
Composite fiber.

(In formula [I], m is an integer of 100 or more, and n is an integer of 0 or more.) The hydrophilic group is at least one selected from the group consisting of a carboxy group, an amino group, a hydroxyl group, and an amide group.
The composite fiber according to claim 1. The hydrophilic polymer is at least one selected from the group consisting of polyacrylic acid, a copolymer of ethylene and acrylic acid, polyallylamine, and polyglutamic acid.
The composite fiber according to claim 1 or 2.   The composite material containing a matrix material and the composite fiber in any one of Claims 1-3.   The composite material according to claim 4, wherein the matrix material is made of at least one kind of resin. At least one hydrophilic polymer having at least one calcium ion source represented by the following general formula [II] at 20 mM or more and having a hydrophilic group capable of coordinating with calcium ions is 10 to 80 mM in terms of monomer. A first aqueous solution containing the calcium carbonate aqueous solution containing amorphous calcium carbonate and the hydrophilic polymer by reacting the second aqueous solution containing 20 mM or more of at least one carbonate ion source represented by the following general formula [III]. Obtaining
A polar fiber mainly composed of at least one vinyl alcohol resin represented by the following general formula [I] is immersed in the calcium carbonate aqueous solution, and the calcium carbonate is formed on at least a part of the surface of the polar fiber. Adhering crystals and the hydrophilic polymer.
A method for producing a composite fiber.

(In formula [I], m is an integer of 100 or more, and n is an integer of 0 or more.)
CaX ₂ · nH ₂ O ... [II]
(In the formula [II], X represents a halogen atom, and n represents a real number of 0 or more.)
M _a (CO ₃ ) _b · nH ₂ O ... [III]
(In formula [III], each symbol has the following meaning.
M represents at least one metal atom, ammonium, or hydrogen atom.
a and b are integers of 1 or more, and n represents a real number of 0 or more. ) The composite fiber obtained by the composite fiber manufacturing method according to claim 6 is impregnated with a liquid raw material to be a matrix material, and then the liquid raw material is solidified.
A method of manufacturing a composite material. After mixing the conjugate fiber obtained by the method for producing a conjugate fiber according to claim 6 and a liquid raw material to be a matrix material, the liquid raw material is solidified.
A method of manufacturing a composite material.