JP2008248416A - Water repellent carbon fiber, and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon fiber rich in water repellency and having a good stability of the surface of its chemically modified carbon fiber. <P>SOLUTION: This water repellent carbon fiber is provided by bonding a triorganosilyl group (wherein, organo groups are each independently H, an alkyl or an alkoxy) with hydroxyl groups on the surface of the carbon fiber through oxygen atom, and showing a Si/C silicon concentration on the surface of the carbon fiber of ≥0.100, measured by an X-ray photoelectron spectrometry. It is preferable that on the surface of the carbon fiber, grooves continuing in parallel direction to fiber axis are formed. Further, it is preferable to have a contact angle to water of ≥90°, and more preferably 100-120°. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a water-repellent carbon fiber and a method for producing the same, and more particularly to a surface-modified carbon fiber having excellent water repellency and a method for producing the same.

  Carbon fiber has excellent specific strength and specific modulus compared to other fibers, and is widely used as a reinforcing fiber for compounding with resin by utilizing its light weight and excellent mechanical properties. Has been. In recent years, the industrial application of composite materials using carbon fibers has been spreading to various purposes.In particular, in industrial applications, sports / leisure fields, and aerospace fields, higher performance (high strength, high elasticity, and The demand for (high elongation) is increasing. In order to improve the performance of composite materials, it is essential to improve the properties of the carbon fiber itself, in addition to improving the physical properties of the resin.

  In the expansion of the application field of such carbon fibers, there are a wide variety of matrix resins such as epoxy resins, unsaturated polyester resins, vinyl ester resins, and phenol resins that are used when the carbon fibers are used as composite materials. Among them, epoxy resins are most frequently used, and their uses are expanding.

  Conventionally, when a carbon fiber and a resin are combined, the material characteristics of the composite have been improved by improving the interface characteristics. For the purpose of improving the interfacial characteristics between the carbon fiber and the resin, the most frequently used technique is to improve the adhesion and wettability with the resin by oxidizing the carbon fiber surface. That is, generally, a technique of chemically or electrochemically oxidizing a carbon fiber surface in a gas phase or a liquid phase and introducing many surface functional groups on the carbon fiber surface is widely used. By performing such surface oxidation treatment, the surface oxygen concentration O / C on the surface of the carbon fiber is increased, and many surface functional groups are formed. The surface functional groups are mainly OH groups and COOH groups that are hydrophilic. The formed surface functional group improves the wettability with the resin on the surface of the carbon fiber and improves the interface characteristics. In order to form an interface suitable for compounding with an epoxy resin or the like by improving the surface characteristics of the carbon fiber, carbon fibers having a hydrophilic OH group or COOH group formed on the surface have been manufactured for a long time. (See, for example, Patent Document 1).

  Patent Document 1 discloses a method for improving adhesiveness with a matrix resin by setting a hydrophilic functional group on the surface of a carbon fiber.

  As described above, hydrophilic carbon fibers have been widely studied. On the other hand, water-repellent carbon fibers are not manufactured or sold.

  In general, water repellency indicates difficulty in getting wet with water, and the water repellency phenomenon can be said to be a three-phase phenomenon of solid-liquid on the solid surface. Water repellency has been attracting attention in the industrial fields such as construction materials, cosmetics, fiber processing, and electronic components other than carbon fibers.

  On the other hand, in recent years, carbon fibers are being applied to electrode material applications, and water-repellent carbon fibers that have not been conventionally required for the above-mentioned industrial field applications, etc. have come to the spotlight and the need has arisen. (For example, refer to Patent Document 2).

  Patent Document 2 discloses a fuel cell including a battery cell in which a membrane electrode assembly is sandwiched between a gas diffusion layer that supplies a fuel gas and a gas diffusion layer that supplies an oxidizing gas. In this fuel cell, each gas diffusion layer includes a water repellent layer provided on the membrane electrode assembly side and a gas flow path inside the main body formed by the porous body. It has a structure in which a permeating gas channel layer is laminated.

However, the water repellent material is paper-made together with carbon fibers and binder fibers as particles. Therefore, it does not impart water repellency to the carbon fiber itself.
JP-A-11-93078 (Claims) JP 2006-339089 A (claim, paragraph number [0029])

  The present inventor has been diligently studying the above-mentioned problems. A silyl group having a predetermined structure is converted from a hydroxyl group to a silyl group on a raw material carbon fiber surface having a surface oxygen concentration O / C and a hydroxyl group concentration COH / C within a predetermined range. The carbon fiber surface is chemically modified with a silyl derivative having a predetermined structure and bonded with a functional group substitution rate within a predetermined range to a carbon fiber having water-repellent properties can be stably obtained. The present invention has been completed.

  Accordingly, an object of the present invention is to provide a water-repellent carbon fiber and a method for producing the same, which have solved the above problems.

  The present invention for achieving the above object is as follows.

  [1] The hydroxyl group on the carbon fiber surface is represented by the following formula (1) via an oxygen atom.

A water-repellent carbon fiber comprising a triorganosilyl group and having a silicon fiber surface silicon concentration Si / C measured by X-ray photoelectron spectroscopy of 0.100 or more.

  [2] The water-repellent carbon fiber according to [1], wherein a groove continuous in a direction parallel to the fiber axis is formed on the surface of the carbon fiber.

  [3] The water-repellent carbon fiber according to [1], which has a contact angle with water of 90 to 120 degrees.

[4] Hydroxyl group concentration obtained by dividing the C _1s spectrum measured by X-ray photoelectron spectroscopy with a surface oxygen concentration O / C measured by X-ray photoelectron spectroscopy of 0.10 to 0.30. In 60% or more of the hydroxyl group of the carbon fiber having a carbon fiber surface with COH / C of 0.05 to 0.25, the following formula (1) is shown.

The triorganosilyl group is introduced, and the triorganosilyl group is bonded to the hydroxyl group on the carbon fiber surface through an oxygen atom, and the silicon concentration Si / C on the carbon fiber surface measured by X-ray photoelectron spectroscopy is A method for producing a water-repellent carbon fiber having a contact angle with respect to water of 90 to 120 degrees of 0.100 or more.

  In the carbon fiber of the present invention, a silyl group having a predetermined structure is substituted on the surface of a raw material carbon fiber having a predetermined range of surface oxygen concentration O / C and a hydroxyl group concentration COH / C. Since it is bonded at a rate, it is rich in water repellency. Since this silyl group is introduced into the carbon fiber surface by a chemical bond, the bond stability is good.

  According to the carbon fiber production method of the present invention, a raw carbon fiber having a surface oxygen concentration O / C and a hydroxyl group concentration COH / C within a predetermined range is immersed in a reaction solution containing a predetermined amount of a silyl derivative having a predetermined structure. By the operation, it is possible to produce a carbon fiber that is rich in water repellency and has good stability on the surface of the chemically modified carbon fiber.

  The carbon fiber of the present invention has three organic groups (alkyl group or alkoxy group) or a silyl group (triorganosilyl group) bonded with a hydrogen atom represented by the following formula (1) bonded to the surface of the carbon fiber. The carbon fiber surface silicon concentration Si / C measured by X-ray photoelectron spectroscopy is a water-repellent surface chemically modified carbon fiber of 0.100 or more.

  When the carbon fiber surface silicon concentration Si / C is less than 0.100, the water repellency of the carbon fiber surface is insufficient. The higher the contact angle with water, the better the water repellency, and 90 degrees or more is necessary. However, in order to obtain water-repellent carbon fibers having a contact angle with water exceeding 120 degrees, it is necessary to further increase the amount of triorganosilyl groups introduced on the carbon fiber surface of the raw material, that is, the surface silicon concentration Si / C.

  For this purpose, it is necessary to further increase the surface treatment amount of the raw material carbon fiber, that is, the surface oxygen concentration O / C and the hydroxyl group concentration COH / C, before introducing the triorganosilyl group. However, if the surface treatment amount of the raw material carbon fiber is further increased, surface oxidation proceeds more than necessary, new surface cracks are likely to occur, and carbon fiber properties are likely to deteriorate and vary. If the angle exceeds 120 degrees, it may not be suitable as a water-repellent carbon fiber.

The water-repellent carbon fiber of the present invention has a surface oxygen concentration O / C measured by X-ray photoelectron spectroscopy of 0.10 to 0.30, 0.12 to 0 on the carbon fiber surface to which a triorganosilyl group is bonded. .28, more preferably 0.15 to 0.25, and the hydroxyl group concentration COH / C determined by peak splitting of the C _1s spectrum measured by X-ray photoelectron spectroscopy is 0.05 to 0. .25, preferably 0.10 to 0.21.

  In the water-repellent carbon fiber of the present invention, the hydroxyl group (OH group) on the surface of the carbon fiber is substituted and bonded with a triorganosilyl group, and the functional group substitution rate is 60% or more, preferably 63 to 100%. Triorganosilyl groups bonded to the fiber surface are stable in air. If the functional group substitution rate is less than 60%, the water repellency decreases.

  Here, the functional group substitution means that the OH group on the surface of the carbon fiber reacts with a compound having a silyl group in which three organic groups (alkyl group or alkoxy group) or hydrogen atoms are bonded (triorganosilyl derivative). The hydrogen of the OH group on the carbon fiber surface is replaced with the triorganosilyl group. Therefore, the functional group substitution rate is expressed as a percentage of the triorganosilyl group concentration after the treatment with the triorganosilyl derivative on the carbon fiber surface.

  The water repellent carbon fiber of the present invention preferably has a contact angle with water of 90 ° or more, more preferably 100 to 120 °.

  In the water-repellent carbon fiber of the present invention, it is preferable that a groove continuous in parallel to the fiber axis direction is formed on the surface of the carbon fiber to which the triorganosilyl group is bonded.

[Method for producing water-repellent carbon fiber]
The water-repellent carbon fiber of the present invention is not particularly limited as long as its physical properties are within the above range. For example, the water-repellent carbon fiber is not limited to a reaction solution composed of a triorganosilyl derivative. In a reaction solution in which the concentration of the silyl derivative is 12% by mass or more, preferably 15% by mass or more, the surface oxygen concentration O / C is 0.10 to 0.30, preferably 0.12 to 0.28, more preferably A raw carbon fiber having a fiber surface of 0.15 to 0.25 and a hydroxyl group concentration COH / C of 0.05 to 0.25, preferably 0.10 to 0.21, is obtained at a temperature of 10 to 30. It can be produced by immersing at 5 ° C. for 5 seconds or longer, preferably 5 to 20 seconds.

  Hereinafter, the manufacturing method of the water-repellent carbon fiber of this invention is demonstrated in detail along each process.

[Carbon fiber precursor fiber]
The precursor fiber for producing the raw carbon fiber (carbon fiber precursor fiber) into which the triorganosilyl group is introduced can be polyacrylonitrile (PAN) as long as the carbon fiber having a specific surface described later can be obtained. It is possible to apply precursor fibers such as those of rayon and rayon.

  Of these precursor fibers, a PAN-based precursor fiber that is excellent in handleability and from which high-strength carbon long fibers can be easily obtained is preferable. Here, in the case of a PAN-based precursor fiber, a copolymer containing acrylonitrile structural unit as a main component and containing vinyl monomer units such as itaconic acid, acrylic acid, and acrylic ester within 10 mol% is a conventional method. Thus, a carbon fiber precursor fiber can be obtained.

  The carbon fiber precursor fiber is preferably a long fiber having a fineness of 1.00 to 1.35 dtex.

[Flame resistance treatment]
The carbon fiber precursor fibers are bundled into 6000 to 24000 strands to form strands, and the precursor fiber strands are subjected to a flame resistance treatment in air at 240 to 280 ° C., thereby causing a cyclization reaction of the precursor fibers and oxygen bonding. Increasing the amount makes it infusible and flame retardant to obtain a flame resistant fiber.

[Carbonization treatment]
Next, initial carbonization is performed in a nitrogen atmosphere, followed by carbonization.

[Surface oxidation treatment]
Then, it can surface-treat, wash with water, and can dry in the air, and can obtain raw material carbon fiber.

  As a method for surface treatment of a fiber bundle subjected to carbonization treatment, there is a method in which a carbon fiber surface is chemically or electrochemically oxidized in a gas phase or a liquid phase, and a large number of surface functional groups are introduced to the carbon fiber surface. It is common. By performing such surface oxidation treatment, the surface oxygen concentration O / C on the surface of the carbon fiber is increased, and many surface functional groups are formed. The surface functional groups are mainly OH groups and COOH groups that are hydrophilic.

The raw material carbon fiber used in the production method of the present invention has a surface oxygen concentration O _1s / C _1s measured by X-ray photoelectron spectroscopy of 0.10 to 0.30, preferably 0.12 to 0.00 on the surface. 28, more preferably 0.15 to 0.25, and the surface hydroxyl group concentration COH / C is 0.05 to 0.25, preferably 0.10 to 0.21.

  When the surface hydroxyl group concentration COH / C is less than 0.05, a uniform coating state cannot be obtained on the raw carbon fiber, and the water repellency is lowered, so that it is not suitable for the chemically modified carbon fiber of the present invention.

  On the other hand, if the surface hydroxyl group concentration COH / C exceeds 0.25, surface oxidation of the raw material carbon fiber proceeds, new surface cracks are likely to occur, and variations in the physical properties of the carbon fiber are likely to occur. Not suitable for raw carbon fiber.

The surface hydroxyl group concentration COH / C is obtained by dividing the C _1s spectrum measured by X-ray photoelectron spectroscopy into peaks.

That is, in order to perform charge correction of the spectrum obtained by normal C _1s spectrum measurement, the maximum peak is 284.6 eV indicating the C—C bond energy, the peak position of hydroxyl group (COH) is 286.2 eV, carbonyl The peak position of the group (C = O) is 287.5 eV, the peak position of the carboxyl group (COOH) is 288.8 eV, the peak position of the carbonate (OCOO) is 290.6 eV, and the peak area of COH is C It is obtained by dividing by the area C of the entire peak of the _1s spectrum.

The carbon fiber having the characteristics of the surface hydroxyl group concentration COH / C of 0.05 to 0.25 obtained by peak-splitting the C _1s spectrum measured by X-ray photoelectron spectroscopy is the surface in the gas phase or liquid phase. It can be obtained by oxidizing and increasing the number of surface functional groups. In the present invention, it is preferable to perform electrolytic surface treatment in the liquid phase using the fiber as an anode from the viewpoints of productivity, uniformity of treatment, stability, and the like.

  The surface-treated carbon fiber has a strand strength of preferably 3000 MPa or more, more preferably 4000 MPa or more, still more preferably 4500 MPa or more, and its strand elastic modulus is preferably 200 GPa or more before the coating treatment. More preferably, it is 220 GPa or more.

  A composite material manufactured using carbon fibers having such strength and elastic modulus can exhibit excellent characteristics. Here, the strand strength and strand elastic modulus of carbon fiber refer to the strength and elastic modulus measured according to the resin impregnated strand test method of JIS-R-7601. The upper limit of the strand strength and elastic modulus is preferably as high as possible, but is currently about 7000 MPa and 800 GPa, respectively.

  In order to impart more water-repellent properties, carbon fibers having grooves in the direction parallel to the fiber axis on the carbon fiber surface are preferable. There are two main factors that give water repellency: the solid surface free energy and the surface microstructure. By introducing the triorganosilyl group to the carbon fiber surface, the surface free energy of the solid is increased and the water-repellent carbon fiber can be obtained.

  Moreover, the water repellency can be further increased by using carbon fibers having grooves on the surface of the carbon fibers. This is presumably because the presence of grooves on the carbon fiber surface causes air to exist in the recesses on the surface of the grooves, thereby increasing water repellency (air has a contact angle of 180 degrees). The depth and interval of the grooves are preferably 10 to 35 μm and 50 to 200 μm, respectively.

  As a method for providing grooves on the carbon fiber surface, it can be obtained by performing wet spinning at the time of spinning the carbon fiber precursor fiber.

  In addition, even if it is a commercially available carbon fiber, if it satisfies the said conditions, it can be used as raw material carbon fiber of this invention.

[Chemical modification of carbon fiber surface]
In the chemical modification treatment of the carbon fiber surface, the carbon fiber surface functional group contributes to the reaction, and a triorganosilyl group is introduced to the carbon fiber surface. It reacts on the surface of carbon fiber previously dried. Specifically, a target water-repellent chemically modified carbon fiber can be obtained by dissolving a reactant in a solvent in a reaction solution tank and immersing the dried raw material carbon fiber to react on the surface. .

  The triorganosilyl derivative used as a chemical modification treatment agent (surface treatment agent) on the carbon fiber surface reacts with the OH group on the carbon fiber surface to give a triorganosilyl group. For example, silazane. Among them, those having high reactivity are hexamethyldisilazane and trimethylchlorosilane whose methyl group is an organo group, and the carbon fiber obtained using this triorganosilyl derivative has the best water repellency. Moreover, even if the organo group is a methoxy group or an ethyl group, water repellency can be obtained.

  On the other hand, even if dichlorodimethylsilane or the like having two reactive functional groups is reacted to introduce a chlorodimethylsilyl group, a certain degree of water repellency can be obtained. However, since there is a reactive site other than the reaction with the OH group on the surface of the carbon fiber, the stability in air is worse than the case where the triorganosilyl group is introduced. For example, the period in which data can be temporarily stored is limited until the next process is combined.

  The concentration of the reaction solution in which the chemical modification treatment agent is dissolved is 12% by mass or more, preferably 15% by mass or more with respect to the solvent. When triorganochlorosilane such as trimethylchlorosilane is used as the chemical modification treatment agent, the reaction can be carried out as it is without using a solvent. However, if there is no solvent or the concentration in the solution is too high, it may be difficult to keep the reaction solution stable in the air. In this case, it is difficult to industrially stably produce water-repellent carbon fibers. On the other hand, if the concentration is too low, the reactivity decreases, and as a result, the water repellency of the resulting chemically modified carbon fiber also decreases.

  Thereafter, washing with water is performed in a plurality of steps for the purpose of removing by-products and unreacted substances generated by the reaction. When washing with water, there is no problem if well water containing a calcium component, a sodium component, and a magnesium component is used, but it is desirable to use ion-exchanged water. When well water is used, it is desirable to replace it with ion-exchanged water in the final washing step. After such washing with water, a desired water-repellent chemically modified carbon fiber can be obtained by drying in air. The drying treatment is preferably performed using a dryer heated to 100 to 150 ° C. The moisture content of the chemically modified carbon fiber after drying is preferably less than 0.1% by mass.

  The carbon fiber obtained by the production method of the present invention may be attached with a sizing agent for improved handling. The water-repellent carbon fiber obtained by chemical modification has poor convergence in a dry state, and handling properties are improved when a sizing agent is used as the convergence agent. As the sizing agent, those generally used for carbon fibers can be used.

  Since the water-repellent carbon fiber obtained by applying a sizing agent and chemically modifying the water-repellent carbon fiber as it is does not exhibit an effect, it is preferable to perform a de-sizing treatment after processing. The desize treatment can be performed using an organic solvent described in JIS-R-7601. Generally, acetone, methyl ethyl ketone, etc. are mentioned.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, evaluation of operation conditions and measurement of each physical property were based on the following methods.

[Surface oxygen and silicon concentrations O / C, Si / C on carbon fiber surface]
Surface oxygen and silicon concentrations O / C and Si / C on the carbon fiber surface were determined by XPS (ESCA) according to the following procedure.

After cutting the carbon fibers and arranging them on a stainless steel sample support table, the photoelectron escape angle was set to 90 degrees, MgKα was used as the X-ray source, and the inside of the sample chamber was vacuumed at 1 × 10 ⁻⁶ Pa. Keep it up. As a correction of the peak accompanying charging during measurement, first, the binding energy value B. of the main peak of C _1s . E. Is adjusted to 284.6 eV. The Si _1s peak area is obtained by drawing a straight base line in the range of 92 to 116 eV, the O _1s peak area is obtained by drawing a straight base line in the range of 528 to 540 eV, and the C _1s peak area is It was determined by drawing a straight baseline in the range of 282 to 296 eV. The surface oxygen concentration O / C on the surface of the carbon fiber was determined by calculating the ratio of the O _1s peak area to the C _1s peak area. The surface silicon concentration Si / C on the surface of the carbon fiber was calculated and calculated by the ratio of the Si _1s peak area to the C _1s peak area.

  In addition, the peak of Si binding energy measured by X-ray photoelectron spectroscopy was expanded, and the position of the maximum point was obtained. The ratio of the generated photoelectrons varies depending on each element, and the conversion factor including the device constant in the case of the X-ray photoelectron spectrometer ESCA JPS-9000MX manufactured by JEOL Ltd. is 2.69.

[How to obtain COH / C of surface functional groups]
The surface hydroxyl group concentration COH / C was determined by dividing the C _1s spectrum measured by X-ray photoelectron spectroscopy into peaks.

That is, in order to perform charge correction of the spectrum obtained by normal C _1s spectrum measurement, the maximum peak is 284.6 eV indicating the C—C bond energy, the peak position of hydroxyl group (COH) is 286.2 eV, carbonyl The peak position of the group (C = O) is 287.5 eV, the peak position of the carboxyl group (COOH) is 288.8 eV, the peak position of the carbonate (OCOO) is 290.6 eV, and the peak area of COH is C It was determined by dividing by the area C of the entire peak of the _1s spectrum.

  Although the specific description of the method of calculating | requiring hydroxyl group density | concentration COH / C is shown below, it is not limited to this example.

After cutting carbon fiber strands as raw materials and spreading them on a stainless steel sample support table, they were placed in a measurement chamber depressurized to 10 ⁻⁶ Pa, and X-ray photoelectron spectrometer ESCA JP-9000MX manufactured by JEOL Ltd. Then, the photoelectron spectrum generated from carbon atoms was measured when X-rays generated under the conditions of an electron beam acceleration voltage of 10 kV and a current of 10 mA were applied with Mg as a counter electrode and the escape angle of photoelectrons was 90 °. Subsequently, the obtained spectrum is converted into the VAMAS format by the analysis software attached to the apparatus, and the above-mentioned peak correction and division are performed by the analysis software Compro6 distributed by the Surface Analysis Science Society. Asked.

Although the specific description of the method of _{calculating |} requiring the surface oxygen concentration _O1s / _C1s of a carbon fiber is shown below, it is not limited to this example.

After cutting carbon fiber strands as raw materials and spreading them on a stainless steel sample support table, they were placed in a measurement chamber depressurized to 10 ⁻⁶ Pa, and X-ray photoelectron spectrometer ESCA JP-9000MX manufactured by JEOL Ltd. Measure the photoelectron spectrum generated from carbon atoms and oxygen atoms when the X-rays generated under conditions of an electron beam acceleration voltage of 10 kV and a current of 10 mA are applied with Mg as the counter electrode and the escape angle of photoelectrons is 90 °. The area ratio was calculated.

  The ratio of the generated photoelectrons varies depending on each element, and the conversion factor including the device constant in the case of the X-ray photoelectron spectrometer ESCA JPS-9000MX manufactured by JEOL Ltd. is 2.69.

[Measurement of functional group substitution rate]
By X-ray photoelectron spectroscopy, measure the surface of the raw carbon fiber and the chemically modified carbon fiber,
Si / C of raw material carbon fiber: Si / C1
Si / C after reaction: Si / C2
It calculated | required by calculation as COH / C of raw material carbon fiber: COH / C1.
Specifically, the ratio defined by the following formula [(Si / C2) − (Si / C1)] / (COH / C1)
The functional group substitution rate can be calculated by

[Carbon fiber strand strength, elastic modulus]
It was measured by the method defined in JIS R7601.

[Evaluation of contact angle]
The interfacial characteristics of the carbon fiber can be examined by measuring the contact angle between water and the surface of the chemically modified carbon fiber. The contact angle measurement was performed by a droplet method at a temperature of 20 ° C. using a DM700 type fully automatic contact angle meter manufactured by Kyowa Interface Science Co., Ltd.

  The droplets are sprayed with distilled water in a spray bottle, and the droplets are attached to the surface of the chemically modified carbon fiber. Arbitrary droplets on the surface of the chemically modified carbon fiber were observed from the eyepiece of the apparatus, and the contact angle was measured. Subsequently, the contact angle of 20 arbitrary droplets attached to the carbon fiber surface was measured, and the average value was used as the contact angle value.

  The higher the contact angle, the better the water repellency and may be considered as an index showing water repellency.

  Carbon fibers are usually coated with a sizing agent for the purpose of improving handling properties, and generally uncured epoxy resins are used. The contact angle with water of a general carbon fiber sized with an uncured epoxy resin is 81 degrees. For example, the contact angle of Toray T700 24000-50C (sizing agent is unsaturated polyester resin, etc.) is 80.5 degrees. On the other hand, the chemically modified carbon fiber into which the triorganosilyl group of the present invention is introduced has a considerably high contact angle with water of 90 to 120 degrees, and the water repellency is dramatically improved. Further, as described above, the water repellency can be further improved by using carbon fibers in which grooves continuous in a direction parallel to the fiber axis are formed on the carbon fiber surface.

  In order to impart more water-repellent properties, carbon fibers having grooves in the direction parallel to the fiber axis on the carbon fiber surface are preferable. There are two main factors that give water repellency: the solid surface free energy and the surface microstructure. By introducing the triorganosilyl group to the carbon fiber surface, the surface free energy of the solid is increased and the water-repellent carbon fiber can be obtained.

  Moreover, the water repellency can be further increased by using carbon fibers having grooves on the surface of the carbon fibers. This is presumably because the presence of grooves on the carbon fiber surface causes air to exist in the recesses on the surface of the grooves, thereby increasing water repellency (air has a contact angle of 180 degrees). The depth and interval of the grooves are preferably 10 to 35 μm and 50 to 200 μm, respectively.

[Stability of chemically modified carbon fiber surface]
After chemical modification, the contact angle between water and the chemically modified carbon fiber surface is measured. Let the measured contact angle be α degrees. Thereafter, when two weeks have passed after being left at room temperature in the air, the contact angle between water and the surface of the chemically modified carbon fiber is measured again. The measured contact angle is β degrees. Then, using the measured values (α degree and β degree), the following formula is obtained: Stability (%) = β / α × 100
Thus, the stability of the surface of the chemically modified carbon fiber was evaluated.

[Interlaminar shear strength of composite materials (ILSS)]
A curing agent and an accelerator were added to an epoxy resin (trade name: Epicoat manufactured by Yuka Shell Epoxy Co., Ltd.) to prepare an epoxy resin composition for carbon fiber impregnation.

This resin composition was applied onto release paper with a film coater to obtain a resin film. After aligning carbon fibers on this resin film at equal intervals and heating, carbon fiber is impregnated by heating to produce a carbon fiber reinforced epoxy resin composition having a basis weight of 350 g / m ² and a resin impregnation rate of 35% by mass. did.

The carbon fiber reinforced epoxy resin composition produced by the above method is laminated so that the thickness after molding becomes 2.8 mm, put into a mold, and placed at 130 ° C. for 1.5 hours, 0.49 MPa-Gauge (5 0.0 kgf / cm ² -Gauge) to form a carbon fiber reinforced molded plate (CFRP plate: composite) in which fibers are arranged in one direction. The ILSS of this CFRP plate was measured at 23 ° C. according to ASTM-D-2344.

[Observation of groove on raw carbon fiber surface]
A carbon fiber having a continuous groove formed on the surface in a direction parallel to the fiber axis was used as a raw material carbon fiber. The fiber surface can be observed with a scanning electron microscope (SEM).

  Further, the depth and interval of the groove on the fiber surface can be measured by observation with a scanning probe microscope (SPM).

  The raw material carbon fiber was fixed on a stainless steel plate for SPM measurement with a double-sided tape, and measured with a tapping mode using a probe with a cantilever length of 125 μm.

  Furthermore, the measurement was performed with respect to a 0.5 μm square of the surface of a certain arbitrary fiber so that the axial direction of the fiber would be the scanning direction.

  For the depth of the groove, a line perpendicular to the fiber axis was drawn from the measured value at 0.5 μm square, and the height difference of the uneven portion was calculated. The groove interval was calculated as the interval between the protrusions. This observation was performed 20 times at an arbitrary position on the fiber surface, and the depth and interval of the grooves were determined.

[Example 1]
Polymerization was carried out in an aqueous zinc chloride solution using 95% by mass of acrylonitrile (AN), 4% by mass of methyl acrylate, and 1% by mass of itaconic acid to prepare a spinning dope (copolymer). Using this spinning dope, an acrylic fiber having a single fiber (filament) fineness of 1.30 dtex (1.18 denier) was obtained by a wet spinning method. This acrylic fiber forms a strand in which 12,000 filaments are bundled.

  The obtained acrylic fiber strand was heated in air at 240 to 280 ° C. at a draw ratio of 1.05 times to obtain flame resistant fibers. This flame-resistant fiber was initially carbonized at a temperature rising rate of 230 ° C./min in a temperature range of 300 to 700 ° C. in a nitrogen atmosphere, and further carbonized to 1350 ° C. while shrinking by 5.5%. Thereafter, an electrolytic surface treatment was carried out at 20 coulomb per 1 g of carbon fiber using a 10 mass% ammonium sulfate aqueous solution as an electrolytic solution. The carbon fiber subjected to the electrolytic surface treatment was subsequently washed with ion exchange water and dried in heated air at 160 ° C. to obtain a raw carbon fiber.

  The obtained raw carbon fiber had a basis weight of 0.800 g / m, a specific gravity of 1.77, a strand strength of 5100 MPa, a strand elastic modulus of 242 GPa, and an ILSS of 106 MPa. When surface analysis of the raw material carbon fiber was performed by X-ray photoelectron spectroscopy, the surface oxygen concentration O / C was 0.20, the hydroxyl group concentration COH / C was 0.14, and the surface silicon concentration Si / C was 0.107. Met.

  When the surface of the raw material carbon fiber was observed with an electron microscope (SEM), grooves were observed on the surface as shown in FIG. The depth and interval of the grooves were 20 to 30 nm and 50 to 200 nm, respectively.

  Subsequently, trimethylchlorosilane (J1.466D, boiling point 57 ° C.) having a trimethylsilyl group as a group that reacts with the functional group on the surface of carbon fiber is dissolved in carbon tetrachloride as a solvent to prepare a 20 mass% reaction solution. After imparting to the raw carbon fiber, it was washed with ion-exchanged water and further dried with a 120 ° C. dryer.

  As a result of measuring the functional group substitution rate of the obtained chemically modified carbon fiber using an X-ray photoelectron spectrometer, it was 70%. The chemically modified carbon fiber thus obtained was evaluated for water repellency with respect to water. The contact angle was 112 degrees, indicating water repellency.

[Example 2]
After firing the carbon fiber in the same manner as in Example 1, surface treatment was performed, and then hexamethyldisilazane having a trimethylsilyl group (J7.217F) as a group that reacts with the functional group on the surface of the carbon fiber was dissolved in pyridine as a solvent. A 40% by mass reaction solution was prepared and applied to the raw carbon fiber by the dipping method, and then treated in the same manner as in Example 1.

[Example 3]
After firing the carbon fiber in the same manner as in Example 1, surface treatment was performed, and subsequently, triethylchlorosilane (J47.877F) having a triethylsilyl group as a group that reacts with the functional group on the surface of the carbon fiber was dissolved in a solvent to obtain 20% by mass. A reaction solution was prepared and applied to the raw carbon fiber by a dipping method, and then treated in the same manner as in Example 1.

[Example 4]
After firing the carbon fiber in the same manner as in Example 1, surface treatment was performed, and subsequently, trimethoxychlorosilane (J968.020I) having a trimethoxysilyl group as a group that reacts with the functional group on the surface of the carbon fiber was dissolved in a solvent and 20 masses. % Reaction solution was prepared, applied to the raw carbon fiber by the dipping method, and then treated in the same manner as in Example 1.

[Example 5]
After firing the carbon fiber in the same manner as in Example 1, the surface treatment was performed, and subsequently, trimethylchlorosilane having a trimethylsilyl group and hexamethyldisilazane as a group reacting with the functional group on the surface of the carbon fiber were in a molar ratio of 1: 3. The reaction solution was prepared so as to be a 40% by mass pyridine solution, applied to the raw carbon fiber by the dipping method, and then treated in the same manner as in Example 1.

[Example 6]
After firing the carbon fiber in the same manner as in Example 1, surface treatment was performed, and trimethylchlorosilane having a trimethylsilyl group as a group that reacts with the functional group on the surface of the carbon fiber was applied to the raw carbon fiber by a dipping method without a solvent. Thereafter, the same treatment as in Example 1 was performed.

[Comparative Example 1]
After firing the carbon fiber in the same manner as in Example 1, surface treatment was performed, and as a group that reacts with the functional group on the surface of the carbon fiber, dimethyldichlorosilane was dissolved in a solvent to prepare a 20% by mass reaction solution. It applied to raw material carbon fiber, and it processed similarly to Example 1 after that.

[Comparative Example 2]
After firing the carbon fiber in the same manner as in Example 1, the amount of electricity at the surface treatment was electrolytic surface treatment at 5 coulombs per gram of carbon fiber. This raw carbon fiber had a surface oxygen concentration O / C of 0.08 and a hydroxyl group concentration COH / C of 0.06. As a group that reacts with the surface functional group of the raw carbon fiber, trimethylchlorosilane was dissolved in a solvent to prepare a 20% by mass reaction solution, which was applied to the raw carbon fiber by the dipping method, and then treated in the same manner as in Example 1. .

[Comparative Example 3]
After firing the carbon fiber in the same manner as in Example 1, surface treatment was performed, and subsequently, trimethylchlorosilane having a trimethylsilyl group as a group that reacts with the functional group on the surface of the carbon fiber was dissolved in a solvent to prepare a 10% by mass reaction solution. It applied to the raw material carbon fiber by the dipping method, and then processed in the same manner as in Example 1.

[Example 7]
In the production of carbon fiber precursor fiber, it was carried out in the same manner as in Example 1 except that the carbon fiber precursor fiber was solidified using a dry and wet spinning method (air gap 3 mm), and continuous on the surface of the carbon fiber in the direction parallel to the fiber axis. A raw material carbon fiber in which no groove was formed was obtained.

  The obtained raw material carbon fiber had a basis weight of 0.802 g / m, a specific gravity of 1.78, a strand strength of 5150 MPa, a strand elastic modulus of 243 GPa, and an ILSS of 107 MPa. When surface analysis of the raw material carbon fiber was performed by X-ray photoelectron spectroscopy, the surface oxygen concentration O / C was 0.21, the hydroxyl group concentration COH / C was 0.16, and the surface silicon concentration Si / C was 0.00. 125.

  When the surface of the raw carbon fiber was observed with an electron microscope (SEM), no groove was observed on the surface as shown in FIG. Using this raw material carbon fiber, the same treatment as in Example 1 was performed thereafter.

  As shown in Tables 1-2, in Examples 1-7, water-repellent carbon fibers having good physical properties were obtained. In addition, the carbon fiber obtained in Examples 1 to 6 has a groove formed on the surface thereof in a direction parallel to the fiber axis, and is even better than Example 7 in which no groove is formed. It was a water-repellent carbon fiber with excellent physical properties.

  In contrast to Examples 1-7, in Comparative Example 1, dimethyldichlorosilane was used as the surface treating agent, and thus the obtained carbon fiber had low stability on the surface of the chemically modified carbon fiber.

  In Comparative Example 2, since the surface oxygen concentration O / C of the raw carbon fiber is as low as 0.08, the obtained chemically modified carbon fiber has a low contact angle between water and the surface of the carbon fiber and lacks water repellency. Also, the stability of the surface of the chemically modified carbon fiber was low.

  In Comparative Example 3, since the concentration of the surface treatment agent in the reaction solution is low, the obtained carbon fiber sheet has a low contact angle between water and the carbon fiber surface, lacks water repellency, and does not have good physical properties. It was.

It is a drawing substitute electron microscope (SEM) photograph which shows an example of the surface of the raw material carbon fiber obtained by the manufacturing method of this invention. It is a drawing substitute electron microscope (SEM) photograph which shows the other example of the surface of the raw material carbon fiber obtained by the manufacturing method of this invention.

Claims (4)

The hydroxyl group on the surface of the carbon fiber is represented by the following formula (1) via an oxygen atom.
A water-repellent carbon fiber comprising a triorganosilyl group and having a silicon fiber surface silicon concentration Si / C measured by X-ray photoelectron spectroscopy of 0.100 or more. The water-repellent carbon fiber according to claim 1, wherein a groove continuous in a direction parallel to the fiber axis is formed on the surface of the carbon fiber. The water repellent carbon fiber according to claim 1, wherein the contact angle with water is 90 to 120 degrees. Surface oxygen concentration O / C measured by X-ray photoelectron spectroscopy is 0.10 to 0.30, and hydroxyl group concentration COH / C obtained by peak splitting of C _1s spectrum measured by X-ray photoelectron spectroscopy In the following formula (1), 60% or more of the hydroxyl groups of the carbon fiber having a carbon fiber surface of 0.05 to 0.25,
The triorganosilyl group is introduced, and the triorganosilyl group is bonded to the hydroxyl group on the carbon fiber surface through an oxygen atom, and the silicon concentration Si / C on the carbon fiber surface measured by X-ray photoelectron spectroscopy is A method for producing a water-repellent carbon fiber having a contact angle with respect to water of 90 to 120 degrees of 0.100 or more.