JP2014141760A - Carbon fiber bundle and production method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon fiber bundle that is controlled in a specified range cross-connection form and is excellent in high-order processability; a production method of the same.SOLUTION: A carbon fiber bundle is that the largest value Gmax(N) of a tensile force difference between an outlet side of a pin body and an inlet side of the pin body that is measured by using an apparatus that includes: guidance means in which a carbon fiber bundle is made to travel in a prescribed route; collection means in which the carbon fiber bundle is collected at an end edge part of the route; pin body taking out and putting in means that is disposed in the route and performs taking out and putting in of the pin body to the carbon fiber bundle; and tensile force detecting means disposed at the inlet side of the pin body and the outlet side of the pin body and detecting tensile forces acting to the carbon fiber bundle, and a thickness a (mm) of the carbon fiber bundle have the following relation (formula 1), and a circularity of a carbon fiber single yarn is in a range of 0.80-0.99, and a surface area ratio is in a range of 1.00-1.10, and a production method of the same is provided. 8≤Gmax/a≤50 (formula 1)

Description

  The present invention relates to a carbon fiber bundle that is controlled in a certain range of entanglement form and excellent in high-order workability, and a method for producing the same.

  Carbon fiber is a material having high strength and high elastic modulus, and is used for aircraft use, sports use, and general industrial use. When using carbon fiber for such an application, for example, a prepreg formed by combining a carbon fiber bundle and a thermosetting resin is used as an intermediate substrate.

  If the carbon fiber bundle used has a lot of fluff, the carbon fiber composite material produced using the fluff also has many disadvantages. Therefore, a high-quality carbon fiber bundle with few fluff is required.

  In recent years, a prepreg with a thinner thickness has been required for further weight reduction. When producing such a prepreg, if the bundle of carbon fiber bundles used is poor, single fibers are easily cut and fluff is generated. On the other hand, carbon fiber bundles with high bundling properties have poor spreadability, making it difficult to produce thinner prepregs.

  Thus, there is a contradictory relationship between improving the convergence and trying to suppress the fluff of the carbon fiber bundle, and improving the spreadability to obtain a thinner prepreg. A technique for controlling the entanglement form of the carbon fiber bundle within a certain range is required.

  These are not limited to processing into a prepreg as a unidirectional material, but when processing into a prepreg via a woven fabric, or by preparing a preform such as a woven fabric and impregnating and curing it with a liquid resin. In various processing methods such as a molding method, a filament wind method, a pultrusion method, and a pull wind method, it is necessary to achieve both suppression of fuzz and good spreadability.

  In order to realize both of these, for example, Patent Document 1 discloses a fiber entanglement value (hereinafter referred to as a CF value) in a carbon fiber hook drop method depending on a shape of a die for spinning an acrylonitrile-based polymer and a pressure of a high-speed fluid. ) In the range of 10 to 100 and the CF value of the polyacrylonitrile-based fiber in the range of 10 to 40, it is said that a carbon fiber excellent in bundling property and resin impregnation property is obtained. In Patent Literature 2, the CF value of the acrylic fiber yarn for carbon fiber production is 10 to 80 and the CV value (standard deviation / average value) indicating the uniformity of the CF value is 10% or less by fluid entanglement treatment. It is said that a carbon fiber bundle excellent in openability can be obtained by controlling.

  The CF value is an index determined by the hook drop method of JIS-L1013 (2010), that is, the hook drop length. That is, the entanglement form of the fibers during the fall of the hook has not been grasped, and the entanglement state of the carbon fiber bundle has not been defined in more detail. Therefore, even if the CF value and the CV value thereof are defined, the entanglement form of the carbon fiber bundle cannot be strictly controlled, and there is a problem that unevenness occurs in the opening property at the time of high-order processing.

JP-A-10-195718 JP 2002-294517 A

  The subject of this invention is providing the carbon fiber bundle excellent in high-order workability, and its manufacturing method by controlling the single yarn to comprise to the entanglement form of a fixed range.

The present invention has the following configuration in order to solve the above problems. That is,
(1) Guide means for causing the carbon fiber bundle to travel along a predetermined path, collection means for recovering the carbon fiber bundle at the end of the path, and inserting and removing a pin body into the traveling carbon fiber bundle disposed on the path Pin body insertion / removal means, and a device having tension detection means for detecting the tension acting on the carbon fiber bundle on the entry side of the pin body and the exit side of the pin body. The maximum value Gmax (N) of the difference in tension between the side and the entry side of the pin body and the thickness a (mm) of the carbon fiber bundle have the following relationship (Equation 1) and A carbon fiber bundle having a circularity in the range of 0.80 to 0.99 and a surface area ratio in the range of 1.00 to 1.10.
8 ≦ Gmax / a ≦ 50 (Formula 1).

(2) The roundness of the single yarn constituting is in the range of 0.90 to 0.99, the surface area ratio is in the range of 1.00 to 1.05, the tensile strength is 6.0 GPa or more, and the elastic modulus is 300 GPa or more. The maximum value Gmax (N) of the difference in tension between the exit side of the pin body and the entry side of the pin body, and the thickness a (mm) of the carbon fiber bundle are as follows (Formula 2): The carbon fiber bundle according to claim 1, wherein
10 ≦ Gmax / a ≦ 40 (Formula 2).

  (3) After a spinning solution in which a polyacrylonitrile-based polymer is dissolved in a solvent is discharged from a die to a coagulation bath by a wet spinning method or a dry-wet spinning method, and then washed and stretched in a water bath to give an oil agent The carbon of (1) above, wherein the carbon fiber precursor fiber bundle obtained by dry heat treatment and steam drawing is flame-resistant in an oxidizing atmosphere and then carbonized in an inert atmosphere at a maximum temperature of 1200 to 1700 ° C. A method of manufacturing a fiber bundle, wherein the carbon fiber precursor fiber bundle has a roundness of a single yarn constituting a range of 0.80 to 0.99 and a surface area ratio of 1.00 to 1.10. The fiber bundle is obtained by subjecting the fiber bundle to a tangling treatment with a fluid from the vertical direction in a state where the fiber bundle is supported under tension and tension in the range of 0.3 to 1.2 cN / dtex between the rolls. A method for producing a carbon fiber bundle.

  (4) A spinning solution in which a polyacrylonitrile-based polymer is dissolved in a solvent is discharged from a die to a coagulation bath by a dry and wet spinning method, then washed and stretched in a water bath, and after applying an oil agent, a drying heat treatment is performed. The carbon fiber bundle according to (2) above, wherein the carbon fiber precursor fiber bundle obtained by steam drawing is flame-resistant in an oxidizing atmosphere and then carbonized in an inert atmosphere at a maximum temperature of 1300 to 1700 ° C. The carbon fiber precursor fiber bundle is a surface area of the carbon fiber precursor fiber bundle having a fineness of 0.4 to 1.2 dtex and a roundness of 0.90 to 0.99. A fiber bundle having a ratio in the range of 1.00 to 1.05 is supported from the vertical direction of the fiber bundle in a state where the fiber bundle is supported under tension and tension in the range of 0.3 to 1.2 cN / dtex between the rolls. Carbon fiber obtained by entanglement treatment with Manufacturing method of the bundle.

  (5) The method for producing a carbon fiber bundle according to (3) or (4), wherein the entanglement treatment with the fluid is performed under a pressure in the range of 0.1 to 0.4 MPa.

  According to the present invention, by controlling the constituting single yarn to a certain range of entanglement form, it is possible to achieve both convergence and spreadability, and carbon excellent in workability at the time of high-order processing including prepreg. A fiber bundle and a manufacturing method thereof can be provided.

It is the schematic of the apparatus which measures the tension difference G (N) prescribed | regulated by this invention. It is an example (Example 1) of the measurement result of the tension | tensile_difference difference G (N) prescribed | regulated by this invention.

  The carbon fiber bundle of the present invention is characterized in that the entanglement form defined by the tension when the pin body is inserted and the carbon fiber bundle is run is in a specific range. Measured in FIG. 1 is a schematic view of an apparatus for measuring the tension difference G (N) defined in the present invention.

  The measuring device in the form of entanglement used for measuring the tension difference G (N) defined in the present invention includes a guide means 2 for causing a carbon fiber bundle to travel along a predetermined path, and a carbon fiber bundle at the end of the path. A recovery means 4 for recovering the carbon fiber, a pin body insertion / removal means 5 for inserting / removing the pin body 6 into / from a running carbon fiber bundle disposed in the path, and an input side of the pin body and an outlet side of the pin body There is tension detecting means 3 for detecting the tension acting on the fiber bundle.

  The carbon fiber bundle is pulled out from the wound bobbin 1, travels along a predetermined route according to the guide means 2 disposed at an appropriate place, passes through the tension detection means 3, and is then disposed at the end of the route. It is recovered by the recovery means 4.

  The tension (initial tension) acting on the traveling carbon fiber bundle before inserting the pin body, defined in the present invention, is preferably set in the range of 2 to 10N, and the variation is preferably in the range of ± 1N. However, in this invention, it is good to measure at 5N ± 1N. Although not shown, the initial tension is controlled through a known bobbin rotational torque or a dancer.

  The guide means defined in the present invention comprises a drive roller, a motor for rotating the drive roller, etc., and there is no problem if the speed is in the range of 0.1 to 10 m / min. It is better to measure at a rate of ± 0.5 m / min.

  The pin body is inserted into the carbon fiber bundle traveling by the pin body insertion / extraction means, and the tension acting on the input side of the pin body and the exit side of the pin body is detected by the tension detection means.

  Before inserting the pin body, the tension acting on the input side of the pin body and the exit side of the pin body is the same. By inserting the pin body, the tension detected by the tension detecting means on the exit side of the pin body gradually increases the resistance acting on the pin body as the pin body approaches the vicinity of the entangled portion of the carbon fiber bundle, The tension acting on the carbon fiber bundle on the exit side of the pin body is detected high. On the other hand, the tension detected by the tension detecting means on the entry side of the pin body is the tension that has acted on the carbon fiber bundle on the entry side of the pin body before the pin body is inserted. Is detected equal to That is, the tension acting by the entanglement of the carbon fiber bundle is detected by measuring the difference in tension G (N) between the exit side of the pin body and the entrance side of the pin body.

  The stronger the entanglement of the carbon fiber bundle, the more entangled portions that run in the vicinity of the pin body when the pin body is inserted into the carbon fiber bundle, so that the tension on the exit side of the pin body is detected higher.

  The tension defined in the present invention is preferably 2 mm in diameter of the pin body used, and is obtained by measuring the tension when the pin body is inserted into a carbon fiber bundle and run at a predetermined speed. . The material of the pin body is not particularly problematic as long as it does not break or bend even when inserted into the traveling carbon fiber bundle. In the present invention, it is preferable to use an inexpensive iron having a smooth surface and a sharp tip.

  In the measurement of the tension defined in the present invention, the greater the thickness of the carbon fiber bundle, the higher the tension detected on the outlet side of the pin body. Therefore, it is necessary to control the value obtained by measuring the thickness of the carbon fiber bundle and dividing the tension difference G defined in the present invention by the thickness of the carbon fiber bundle.

  Then, after the pin body is inserted by the pin body inserting / removing means, the carbon fiber bundle is run for 500 mm, the guide means is stopped, and the pin body is removed from the carbon fiber bundle by the pin body inserting / removing means. Run a little yarn. Thereafter, a plurality of measurements can be performed by repeating the above operation.

  By measuring while the carbon fiber bundle is run 500 mm after inserting the pin body, unevenness in the longitudinal direction of the yarn can be eliminated, and the measurement length becomes excessive, and the carbon fiber bundle It is possible to eliminate the influence of breaking the single yarn constituting the pin body. The maximum value of the tension difference after 10 measurements is taken as Gmax (N) defined in the present invention.

  FIG. 2 shows an example of a single measurement result of the tension difference G defined in the present invention. Gmax in this example is 0.82 N, and a value 16 divided by the thickness 0.05 mm of the carbon fiber bundle separately measured is Gmax / a (N / mm) defined in the present invention.

  Gmax / a obtained by this measurement can measure the degree of entanglement of the entire bundle as compared with the entanglement expressed by the CF value. Therefore, it can be said that a more appropriate value can be defined for evaluating the workability at the time of high-order machining including prepreg.

And as for this invention, as a result of measuring by this method, the maximum value Gmax (N) of the tension | tensile_difference difference of the exit side of the said pin body and the entrance side of the said pin body, and the thickness a (mm) of a carbon fiber bundle are the following. It is necessary to satisfy the relationship of (Formula 1) 8 ≦ Gmax / a ≦ 50 (Formula 1).

  Carbon fiber bundles with a Gmax / a (N / mm) of 8 or more can suppress the generation of fluff during the production of carbon fiber bundles, and can impart appropriate convergence to the carbon fiber bundle, producing prepregs. It is possible to suppress the breakage of the single fiber during the process. Further, in the carbon fiber bundle having Gmax / a (N / mm) of 50 or less, the convergence property of the carbon fiber bundle can be moderately suppressed, the operability at the time of manufacturing the carbon fiber bundle is good, and a thin prepreg is used. The expansibility at the time of manufacture can be made into a favorable level. From this viewpoint, a better range is 10 ≦ Gmax / a ≦ 40 (Formula 2).

  In the carbon fiber bundle of the present invention, the roundness of the single yarn constituting the carbon fiber bundle is in the range of 0.80 to 0.99, and the surface area ratio is in the range of 1.00 to 1.10. The roundness and surface area ratio controlled by the carbon fiber precursor are maintained at substantially the same values even when the carbon fiber is formed. From such a viewpoint, the carbon fiber precursor fiber bundle used for the production of the carbon fiber bundle of the present invention preferably has a cross-sectional shape of the single yarn constituting a shape close to a perfect circle and a smaller surface irregularity. Although the reason is mentioned later, it is more preferable that the roundness of the single yarn constituted from this viewpoint is in the range of 0.90 to 0.99, and the surface area ratio is in the range of 1.00 to 1.05.

  The carbon fiber bundle of the present invention is a spinning solution in which a polyacrylonitrile-based polymer is dissolved in a solvent. After discharging the spinning solution from a die to a coagulation bath by a wet spinning method or a dry-wet spinning method, washing and stretching in a water bath, A method for producing a carbon fiber bundle in which a carbon fiber precursor fiber bundle obtained by drying and heat-treating after applying an oil agent and steam drawing is flame-resistant in an oxidizing atmosphere and then carbonized in an inert atmosphere, The carbon fiber precursor fiber bundle comprises a fiber bundle having a roundness of a single yarn constituting 0.80 to 0.99 and a surface area ratio of 1.00 to 1.10. It is preferably obtained by entanglement treatment with a fluid from the vertical direction of the fiber bundle in a state where the fiber bundle is supported under a tension of 0.3 to 1.2 cN / dtex.

  In the carbon fiber precursor fiber bundle used for the production of the carbon fiber bundle of the present invention, it is preferable that the cross-sectional shape of the single yarn constituting it is close to a perfect circle and the surface irregularities are small. Specifically, the roundness is preferably in the range of 0.80 to 0.99, and more preferably in the range of 0.90 to 0.99. The surface area ratio is preferably in the range of 1.00 to 1.10, and more preferably in the range of 1.00 to 1.05. By setting the roundness to 0.80 or more, it is possible to suppress the occurrence of sagging between single yarns constituting the carbon fiber precursor fiber bundle when imparting entanglement, and to prevent the occurrence of fluff. In addition, fluff during high-order processing can be prevented, and spreadability can be secured. The surface area ratio is preferably smaller for the same reason. Such roundness and surface area ratio can be measured by the method described later, and can be controlled by spinning conditions. For example, a spinning solution kept at a temperature higher than that of the coagulation bath is once discharged from the die into the air and introduced into a coagulation bath kept at a relatively low temperature, and the polymer concentration, the solvent concentration of the coagulation bath, and the temperature are set. It is possible to produce a carbon fiber precursor fiber bundle having a specific roundness and a surface area ratio by subjecting the solidified yarn to drawing, washing with water, oil treatment, steam drawing, and the like, and making it flame resistant and carbonized. From this viewpoint, the preferable temperature of the coagulation bath is preferably in the range of 0 to 20 ° C, more preferably in the range of 5 to 15 ° C. The roundness and surface area ratio controlled by the carbon fiber precursor are maintained at substantially the same values even when the carbon fiber is formed. That is, the carbon fiber bundle produced by such a method has a roundness and a surface area ratio of the carbon fiber single yarn constituting 0.80 to 0.99 and 1.00 to 1.10, preferably 0, respectively. .90 to 0.99 and 1.00 to 1.05.

  The carbon fiber precursor fiber bundle used for the production of the carbon fiber bundle of the present invention is supported by a fluid from the vertical direction of the fiber bundle in a state where the carbon fiber precursor fiber bundle is supported under a tension of 0.3 to 1.2 cN / dtex. It is preferable that it is obtained by entanglement treatment, and more preferably in the range of 0.5 to 1.0 cN / dtex. The value described here is a value obtained by dividing the tension by the total fineness before performing the entanglement process. In addition, although it is the entanglement process by the fluid from the perpendicular | vertical direction, it may incline in the range with the objective of this invention (for example, it may be an angle of about 80-100 degree with respect to a fiber bundle). By setting the tension at the time of performing the entanglement treatment to 0.3 cN / dtex or more, excessive entanglement can be prevented, so that the fiber opening property is in a good range. In addition, by setting the tension at the time of performing the entanglement treatment to 1.2 cN / dtex or less, moderate entanglement can be imparted, and fluffing at the time of carbonization and high-order processing is prevented, and good processability is ensured.

  The entanglement treatment with the fluid defined in the present invention is preferably performed under a pressure in the range of 0.1 to 0.4 MPa, and more preferably performed under a pressure in the range of 0.1 to 0.3 MPa. By setting the fluid pressure at the time of performing the entanglement treatment to 0.1 MPa or more, the spreadability is good when the fluid is applied, and the entanglement is easily applied. Moreover, it can suppress that the single yarn which comprises a carbon fiber precursor fiber bundle is damaged, and a fluff generate | occur | produces by making the fluid pressure at the time of performing an entangling process into 0.4 Mpa or less.

  The step of performing the entanglement treatment is preferably a step in which stretching has been substantially completed, and any step may be used as long as it is between them, but water and oil adhering to the carbon fiber precursor fiber bundle are not dropped off. From the point of view, the drying heat treatment step and after are preferable.

  The entanglement fluid may be either liquid or gas, but gas is preferable because the liquid is likely to drop off the oil when sprayed. Furthermore, cheap air is preferable for the gas.

  The shape of the entanglement nozzle used in the entanglement process and the spraying direction on the vertical surface of the carbon fiber precursor fiber bundle are not particularly limited, but in order to give uniform entanglement to the carbon fiber precursor fiber bundle, from the 360 degree direction, that is, It is preferable to spray evenly from all directions. Preferred examples of the blowing nozzle include those having a blowing portion on the slit and those that blow from a hole shape, and those that blow gas from nozzles in which 3 to 6 holes are arranged at an equal angle are preferable. Further, a plurality of the entanglement nozzles may be provided, but it is desirable to spray the yarn so as to maintain a non-twisted state because uniform entanglement is not provided when the yarn is twisted.

  When performing the entanglement treatment, the number of single yarns constituting the carbon fiber precursor fiber bundle is preferably 24,000 or less, more preferably 12000 or less. By setting the number of single yarns constituting the carbon fiber precursor fiber bundle to 24,000 or less, formation of a portion where no entanglement is performed in the fiber bundle can be prevented, and entanglement formation can be made uniform. After performing the entanglement treatment, carbon fiber precursor fiber bundles of two or more yarns can be combined and adjusted to the number of filaments necessary for the final product. Preferably, the carbon fiber precursor fiber bundle constituting the carbon fiber precursor fiber bundle is entangled with a fiber bundle having a number of single strands of 6000 or less so that the carbon fiber precursor fiber bundle having 12000 or more, more preferably 24000 or more is not twisted. It is preferable that the yarns are integrated with each other and subjected to a flameproofing treatment, and it is preferable that the yarns are combined between the post-drawing and winding to be wound up as a carbon fiber precursor fiber bundle.

  Next, a polyacrylonitrile-based copolymer that can be suitably used in the present invention will be described. In the present invention, a polyacrylonitrile-based polymer obtained by polymerizing 90% by weight or more of acrylonitrile as a monomer is preferable. In addition, if it is a ratio of less than 10 weight%, it is preferable that another monomer is copolymerized. As the copolymerizable monomer, acrylic acid, methacrylic acid, itaconic acid and their methyl ester, propyl ester, butyl ester, alkali metal salt, ammonium salt, or allyl sulfonic acid, Ryl sulfonic acid, styrene sulfonic acid, and alkali metal salts thereof can be used.

  In order to obtain the polyacrylonitrile-based polymer, emulsion polymerization, bulk polymerization, solution polymerization and the like can be used. For the purpose of uniformly polymerizing acrylonitrile and the copolymer component, it is preferable to use solution polymerization.

  The obtained polyacrylonitrile-based polymer can be made into a spinning solution obtained by dissolving in a solvent such as dimethyl sulfoxide, dimethylacetamide, dimethylformamide, nitric acid, zinc chloride aqueous solution, and rhodium soda aqueous solution. Among these, dimethyl sulfoxide is preferably used from the viewpoint of solubility of the acrylonitrile polymer. The polymer concentration in the spinning solution is preferably in the range of 10 to 30% by weight, and more preferably in the range of 15 to 25% by weight.

  The obtained spinning solution can be discharged from a die into a coagulation bath by a wet spinning method or a dry and wet spinning method. The composition of the coagulation bath includes a solvent such as dimethyl sulfoxide, dimethylacetamide, dimethylformamide, nitric acid, zinc chloride aqueous solution, and rhodium soda aqueous solution used as a solvent in the spinning solution, and an acrylic resin such as water, methanol, ethanol, and acetone. It is preferable to use a mixture of coagulation promoting components that do not dissolve the coalesced and is compatible with the polymer solvent.

  The carbon fiber precursor fiber bundle discharged to the coagulation bath can be washed and stretched in a water bath. Stretching may be performed prior to washing, or stretching may be performed after removing the solvent by washing. Stretching is preferably performed in a single or a plurality of stretching baths that are usually temperature-controlled at a temperature in the range of 30 to 98 ° C. The draw ratio at that time is preferably in the range of 1 to 3 times.

  It is preferable to apply an oil agent to the carbon fiber precursor fiber bundle subjected to the washing / stretching process for the purpose of preventing adhesion between the constituting single yarns. As the oil agent, it is preferable to apply an oil agent made of silicone or the like. It is preferable to use a silicone oil that contains a modified silicone such as an amino-modified silicone with high heat resistance. In addition, an epoxy-modified silicone, an alkylene oxide-modified silicone, other surfactants, additives, and the like are included. It is also more preferable.

  The carbon fiber precursor fiber bundle to which the oil agent is applied is preferably subjected to a dry heat treatment in the range of 70 to 200 ° C. and then subjected to steam stretching. The steam stretch ratio is preferably in the range of 2 to 10 times. The fineness of the single yarn constituting the carbon fiber precursor fiber bundle thus obtained is preferably in the range of 0.4 to 1.2 dtex, more preferably in the range of 0.5 to 1.1 dtex. is there. By setting the fineness of the single yarn constituting the carbon fiber precursor fiber bundle to 0.4 dtex or more, generation of fluff of the carbon fiber precursor fiber bundle and a decrease in productivity can be prevented, and 1.2 dtex or less. Keeps the difference in the inner and outer structures of the single yarns that make up the fiber bundle after flame resistance uniform, and prevents deterioration in processability in the subsequent carbonization process and reduction in tensile strength and tensile modulus of the resulting carbon fiber bundle. It becomes possible.

  The carbon fiber precursor fiber bundle obtained by the above heat treatment and steam drawing is flame-resistant in an oxidizing atmosphere, and then the maximum temperature is in the range of 1200 to 1700 ° C. in an inert atmosphere, more preferably 1300 to 1700. By carbonizing in the range of ° C., a carbon fiber bundle defined in the present invention and controlled in an entangled form is obtained. The carbon fiber bundle obtained in this manner is excellent in high-order workability, but preferably exhibits high mechanical properties such as a tensile strength of 6.0 GPa or more and an elastic modulus of 300 GPa or more. In addition, a sizing treatment can be performed to impart convergence to the carbon fiber bundle. As the sizing agent, a sizing agent having good compatibility with the matrix resin can be appropriately selected according to the type of the matrix resin used in the composite material.

  Hereinafter, the present invention will be described by way of examples. The characteristics used in the present invention are specifically measured as follows.

<Roundness>
The carbon fiber bundle was cut with a razor perpendicular to the fiber axis, and the cross-sectional shape of the single fiber was observed using an optical microscope. The measurement magnification was 200 to 400 times so that the thinnest single fiber was observed at about 1 mm. By analyzing the obtained image, the cross-sectional area and circumference of the single yarn constituting the carbon fiber bundle are obtained, and the cross-sectional diameter (fiber diameter) of the single yarn when assuming a perfect circle from the cross-sectional area is 0. Calculated in units of 1 μm, and the roundness of the single yarn constituting the carbon fiber bundle was determined using the following formula. As the roundness, an average value of 10 single yarns selected at random was used.
Roundness = 4πS / L ² (wherein S represents the cross-sectional area of the single yarn constituting the carbon fiber bundle, and L represents the circumference of the single yarn).

<Surface area ratio>
An atomic force microscope (SPI3800N / SPA-400, manufactured by Seiko Instruments Inc.) was prepared by placing several single yarns constituting a carbon fiber bundle on a sample stage and fixing both ends with an adhesive liquid (for example, a stationery correction liquid). ) To obtain an image of a three-dimensional surface shape under the following conditions.
Probe: Silicon cantilever (Seiko Instruments, DF-20)
Measurement mode: Dynamic force mode (DFM)
・ Scanning speed: 1.5Hz
・ Scanning range: 3μm × 3μm
・ Resolution: 256 pixels x 256 pixels The obtained measurement image is fitted with a first-order plane obtained from the entire data of the image by the least square method using the attached software in consideration of the curvature of the fiber cross section. After performing the first-order inclination correction to correct the inclination, and then the second-order inclination correction to similarly correct the quadratic curve, the surface roughness analysis is performed by the attached software, and the surface area ratio to the surface assumed to be smooth Was calculated. The measurement was performed by sampling five different single yarns at random, and performing each measurement once for each single yarn for a total of 5 times, and taking the average value as a value.

<Tensile strength and elastic modulus of carbon fiber>
The tensile strength and elastic modulus of the carbon fiber bundle were determined according to JIS R7601 (2006). Carbon fiber bundles were impregnated with 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexane-carboxylate (100 parts by mass) / 3 boron fluoride monoethylamine (3 parts by mass) / acetone (4 parts by mass), It was prepared by curing at 130 ° C. for 35 minutes. The number of measurement was set to five, and the arithmetic average value of each measurement result was taken as the tensile strength and elastic modulus of the carbon fiber bundle.

<Confounding state>
The tension difference G was measured under the following conditions using a measuring apparatus showing a schematic diagram of FIG.
・ Pin body diameter: 2mm
・ Thread speed: 5m / min ± 0.5m / min ・ Measurement length: 500mm
・ Initial tension: 5N ± 1N
Gmax / a was determined by dividing the maximum value of Gmax by 10 times during the measurement and dividing by the thickness of the carbon fiber bundle.
FIG. 2 shows a typical measurement result example.

  The thickness a (mm) of the carbon fiber bundle was measured in 0.01 mm units with a screw micrometer, and obtained as an average value of 10 times.

<Fiber entanglement value (CF value) in hook drop method>
It measured according to the entanglement degree measuring method of JIS-L1013 (2010) "Chemical fiber filament yarn test method". A load of 100 g was hung at a position below the carbon fiber bundle sample, a hook with a load of 10 g was inserted, the descent distance was measured 50 times, and the following formula was obtained from the arithmetic average value.
CF value = 1000/50 arithmetic average values of hook descent distance (mm).

<Number of fuzz>
The carbon fiber bundle with the sizing agent attached is sequentially passed through the first to fourth stainless steel chrome-plated mirror surface guides (diameter: 9.5 mm) so that the contact angles are 57 ± 3 degrees, respectively. The guide surface was rubbed at a speed of 3 m / min under (23 ° C.). At this time, the tension of the carbon fiber bundle guided to the first guide was adjusted to be 5N. And the number of fluff of the carbon fiber bundle derived from the 4th guide was measured using Toray Engineering Co., Ltd. fluff counter DT-105 (S special). If the number of fluff is 3 or less, good high-order processability can be provided.

<Spreadability>
The spreadability of the carbon fiber bundle was measured as follows. A metal cylinder having a diameter of 50 mm and a surface roughness Rmax of 3 μm and having a chromium plating applied is heated to a surface temperature of 80 ° C., and 5 carbon fibers are in contact with the metal cylinder at a distance of 150 mm and a total of 540 ° contacts. It arranges alternately in the up-down direction so that it may pass while contacting at the corner. Then, the carbon fiber bundles are sequentially passed over the metal cylinder and passed at a speed of 6 m / min under a tension of 1.2 N, and the width of the carbon fiber bundle on the metal cylinder at the final stage is measured in units of 0.5 mm by a ruler. 30 points are measured, and the simple average value is defined as spreadability.

<Prepreg processability>
Using the obtained carbon fiber bundles, the prepreg processability when a prepreg process with an area of 50 m ² was performed by a hot melt type prepreg apparatus (product width: 1 m) was evaluated. The resin used for the evaluation was a 130 ° C. cure type epoxy resin, the resin basis weight was adjusted to 32% according to the corresponding fiber basis weight, and the resin film was supplied from above and below at a speed of 10 m / min. Pre-preg. At that time, the fiber basis weight is changed in units of 20 g / m ² , the temperature and pressure are adjusted within a range in which defects such as fluff do not occur, and the product has a length of 250 mm or more and a width of 1 mm or more in the direction of assembling the carbon fiber bundle. The fluff quality was evaluated by the minimum basis weight at which no yarn breakage occurred and the sensory test at that time. A fluff having a major axis of 10 mm or more was regarded as a fuzz defect, and 2 or less per 50 m ² was marked with ◯, 3 to 4 were marked with Δ, and 5 or more were marked with ×.

[Example 1]
A polyacrylonitrile polymer composition obtained by copolymerizing 95 parts by weight of acrylonitrile, 4 parts by weight of methyl acrylate, and 1 part by weight of itaconic acid is dissolved in dimethyl sulfoxide so that the polymer concentration becomes 20% by weight. The spinning solution was once run through a 5 mm air gap from the die by a dry and wet spinning method, discharged into a 20 ° C. coagulation bath made of 35% by weight dimethyl sulfoxide aqueous solution, then washed in a water bath and doubled in a 65 ° C. water bath. Then, after applying a mixed oil mainly composed of an amino-modified silicone-based oil, it was subjected to a dry heat treatment using a roller heated to a temperature of 180 ° C., and subjected to 5 times steam stretching in 0.5 MPa pressurized steam. The carbon fiber precursor fiber bundle having a fineness of the single yarn constituting 0.7 dtex was supported under a tension of 1.0 cN / dtex between the rolls. In state, under a pressure of 0.3 MPa, the single yarns 12000 constituting the carbon fiber precursor fiber bundle, through six small holes in the vertical direction of the fiber bundle was subjected to entangling treatment by air.

  The carbon fiber precursor fiber bundle was made flame resistant in an oxidizing atmosphere and then carbonized in an inert atmosphere at 1500 ° C. to obtain a carbon fiber bundle. The roundness of the single yarn constituting the obtained carbon fiber bundle was 0.91, the surface area ratio was 1.03, and the CF value of the obtained carbon fiber bundle was 15. The obtained carbon fiber bundle was excellent in both the number of fluff and spreadability. Moreover, the tensile strength of the obtained carbon fiber bundle was 6.1 GPa, and the elastic modulus was 320 GPa.

[Example 2]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the pressure during the entanglement treatment was changed to 0.4 MPa. The obtained carbon fiber bundle was excellent in both the number of fluffs and spreadability, and the prepreg processability was also good.

[Example 3]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the tension during the entanglement treatment was changed to 0.5 cN / dtex. The obtained carbon fiber bundle was excellent in both the number of fluffs and spreadability, and the prepreg processability was also good.

[Example 4]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the aqueous dimethylsulfoxide solution in the coagulation bath was changed to 70% by weight. The single yarn constituting the obtained carbon fiber bundle had a roundness of 0.85 and a surface area ratio of 1.04. The obtained carbon fiber bundle resulted in the number of fluffs being worse than that in Example 1, but the prepreg processability was at a practically acceptable level. Moreover, the tensile strength of the obtained carbon fiber bundle was 6.0 GPa, and the elastic modulus was 310 GPa.

[Example 5]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the aqueous dimethylsulfoxide solution in the coagulation bath was changed to 79% by weight. The single yarn constituting the obtained carbon fiber bundle had a roundness of 0.90 and a surface area ratio of 1.07. The obtained carbon fiber bundle resulted in the number of fluffs being worse than that in Example 1, but the prepreg processability was at a practically acceptable level. Moreover, the tensile strength of the obtained carbon fiber bundle was 6.2 GPa, and the elastic modulus was 310 GPa.

[Example 6]
A carbon fiber bundle was obtained in the same manner as in Example 5 except that the tension during the entanglement treatment was changed to 0.5 cN / dtex. Although the obtained carbon fiber bundle resulted in deterioration of the spreadability as compared with Example 3 and Example 5, it was a practically acceptable level.

[Comparative Example 1]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the wet spinning method was changed and the dimethyl sulfoxide aqueous solution in the coagulation bath was changed to 60% by weight. The roundness of the single yarn constituting the obtained carbon fiber bundle was 0.78, and the surface area ratio was 1.14. The obtained carbon fiber bundle had a result that the number of fluff and spreadability were significantly deteriorated as compared with Example 1. Moreover, the tensile strength of the obtained carbon fiber bundle was 5.9 GPa, and the elastic modulus was 315 GPa.

[Comparative Example 2]
A carbon fiber bundle was obtained in the same manner as in Example 5 except that the tension during the entanglement treatment was changed to 0.1 cN / dtex. The obtained carbon fiber bundle resulted in deterioration in both the number of fluff and spreadability as compared with Example 5.

[Comparative Example 3]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the tension during the entanglement treatment was changed to 0.1 cN / dtex. The obtained carbon fiber bundle resulted in deterioration in both the number of fluff and spreadability as compared with Example 1.

[Comparative Example 4]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the tension during the entanglement treatment was changed to 1.6 cN / dtex. The obtained carbon fiber bundle had a result that the number of fluffs was significantly deteriorated as compared with Example 1.

[Comparative Example 5]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the pressure during the entanglement treatment was changed to 0.05 MPa. The obtained carbon fiber bundle had a result that the number of fluffs was significantly deteriorated as compared with Example 1.

[Comparative Example 6]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the direction of air when performing the entanglement treatment was changed to a direction inclined in the traveling direction by 30 degrees with respect to the vertical direction of the carbon fiber precursor fiber bundle. . The CF value of the obtained carbon fiber bundle was 17, which was the same value as in Example 1. However, the obtained carbon fiber bundle resulted in deterioration in both the number of fluff and spreadability as compared with Example 1.

DESCRIPTION OF SYMBOLS 1 Carbon fiber bundle 2 Guide means 3 Tension detection means 4 Recovery means 5 Pin body insertion / extraction means 6 Pin body

Claims (5)

Guide means for causing the carbon fiber bundle to travel along a predetermined path, collection means for recovering the carbon fiber bundle at the end portion of the path, and a pin body that is disposed in the path and inserts and removes the pin body into the traveling carbon fiber bundle Measured by using an apparatus having tension detecting means for detecting tension acting on a carbon fiber bundle on the entry side of the pin body and the exit side of the pin body, and the exit side of the pin body and the pin body The maximum value Gmax (N) of the difference in tension on the entry side of the pin body and the thickness a (mm) of the carbon fiber bundle are in the relationship of (Equation 1) below, and the roundness of the single yarn to be configured is A carbon fiber bundle having a range of 0.80 to 0.99 and a surface area ratio of 1.00 to 1.10.
8 ≦ Gmax / a ≦ 50 (Formula 1) A carbon fiber having a roundness of 0.90 to 0.99, a surface area ratio of 1.00 to 1.05, a tensile strength of 6.0 GPa or more, and an elastic modulus of 300 GPa or more. The maximum value Gmax (N) of the difference in tension between the exit side of the pin body and the entrance side of the pin body and the thickness a (mm) of the carbon fiber bundle are in the relationship of the following (formula 2): The carbon fiber bundle according to claim 1, wherein
10 ≦ Gmax / a ≦ 40 (Formula 2) A spinning solution in which a polyacrylonitrile-based polymer is dissolved in a solvent is discharged from the die to the coagulation bath by a wet spinning method or a dry-wet spinning method, then washed and stretched in a water bath, and after applying an oil agent, a drying heat treatment is performed. The carbon fiber bundle according to claim 1, wherein the carbon fiber precursor fiber bundle obtained by steam drawing is flame-resistant in an oxidizing atmosphere and then carbonized in an inert atmosphere at a maximum temperature of 1200 to 1700 ° C. The carbon fiber precursor fiber bundle has a roundness of a single yarn constituting a range of 0.80 to 0.99 and a surface area ratio of a range of 1.00 to 1.10. The fiber bundle is obtained by subjecting the fiber bundle to fluid entanglement treatment from the vertical direction in a state where the fiber bundle is supported under tension and tension in the range of 0.3 to 1.2 cN / dtex. A method for producing a carbon fiber bundle. A spinning solution in which a polyacrylonitrile-based polymer is dissolved in a solvent is discharged from the die to the coagulation bath by a dry and wet spinning method, then washed and stretched in a water bath, and after applying an oil agent, a dry heat treatment, and a steam stretch. The carbon fiber precursor fiber bundle obtained in this way is flame-resistant in an oxidizing atmosphere, and then carbonized in an inert atmosphere at a maximum temperature of 1300 to 1700 ° C. The carbon fiber precursor fiber bundle has a fineness of a single yarn constituting 0.4 to 1.2 dtex, a roundness of 0.90 to 0.99, and a surface area ratio of 1. In a state where the fiber bundle in the range of 00 to 1.05 is supported between the rolls under the tension of 0.3 to 1.2 cN / dtex, the fiber bundle is entangled with the fluid from the vertical direction. Made of carbon fiber bundles Method. The method for producing a carbon fiber bundle according to claim 3 or 4, wherein the entanglement treatment with the fluid is performed under a pressure in a range of 0.1 to 0.4 MPa.

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