WO2020203531A1

WO2020203531A1 - Method for producing flame-proof fiber bundle, and method for producing carbon fiber bundle

Info

Publication number: WO2020203531A1
Application number: PCT/JP2020/013261
Authority: WO
Inventors: 岡村一真; 伊藤隆弘; 齋藤大祐
Original assignee: 東レ株式会社
Priority date: 2019-04-03
Filing date: 2020-03-25
Publication date: 2020-10-08
Also published as: JPWO2020203531A1; TW202104694A; JP7468343B2

Abstract

The present invention enables the production of a polyacrylonitrile-based carbon fiber bundle that is stable in terms of quality by suppressing adhesion of fine particles to a flame-proof fiber bundle. For the purpose of achieving the above objective, the present invention provides a method for producing a flame-proof fiber bundle, wherein: a polyacrylonitrile-based fiber bundle is subjected to a flame-proofing treatment at a temperature of 200-300°C in an oxidizing atmosphere where the concentration of fine particles having a particle diameter of 0.3 μm or more is 300 particles/liter or more; and if the specific gravity of the fiber bundle is from 1.15 to 1.25 and/or the specific gravity of the fiber bundle is from 1.30 to 1.45, the surface potential of the fiber bundle is set to a value from -1 kV to +1 kV.

Description

Method for manufacturing flame-resistant fiber bundle and method for manufacturing carbon fiber bundle

The present invention relates to a method for producing a flame-resistant fiber bundle and a method for producing a carbon fiber bundle. More specifically, the present invention relates to a method for producing a flame-resistant fiber bundle used for a carbon fiber bundle and a method for producing a carbon fiber bundle having high tensile strength obtained by using such a flame-resistant fiber bundle.

Since carbon fiber bundles have excellent specific strength and specific elastic modulus, they are used in a wide range of fields such as aerospace industry, sports applications such as fishing rods and tennis rackets, and general industrial applications such as wind power blades and automobiles. There is. In recent years, the demand for carbon fiber bundles has been increasing year by year not only for aircraft but also for automobiles. Customers demand improvements in the quality of carbon fiber bundles, especially in tensile strength (hereinafter abbreviated as "strength").

Since the strength of the carbon fiber bundle is affected by the type of the precursor fiber bundle that is the raw material of the carbon fiber bundle, the polyacrylonitrile-based precursor fiber bundle is preferably used rather than the pitch type because the strength is easily developed. .. Further, as one of the factors affecting the strength, minute defects existing in the carbon fiber bundle are known. The cause of the minute defects is that in the carbon fiber bundle manufacturing process, contact or adhesion with foreign matter such as dust or metal may cause scratches or voids in the single fibers constituting the carbon fiber bundle. Examples include scratches on the surface layer of single fibers due to adhesion between fibers, and scratches on the carbon fiber bundle itself caused by scratching with rollers and slits. Regardless of whether such defects occur on the surface layer or inside of the single fiber of the carbon fiber bundle, the strength of the carbon fiber bundle decreases as the size and number of the defects increase.

Polyacrylonitrile-based carbon fiber bundles are generally obtained by heating a polyacrylonitrile-based precursor fiber bundle at 200 to 300 ° C. in an oxidizing gas atmosphere to obtain a flame-resistant fiber bundle, and then 1200 in an inert atmosphere. Obtained by heating above ° C. The step of heat-treating the precursor fiber bundle to obtain a flame-resistant fiber bundle is called a flame-resistant step. Here, the “oxidizing gas atmosphere” is an atmosphere containing a gas that promotes an oxidizing action in order to perform an oxidizing treatment on the object to be treated. Air containing oxygen is contained in the oxidizing gas.

The polyacrylonitrile-based precursor fiber bundle usually consists of 1000 to 60,000 single fibers. In the flame resistance step, a method of applying a silicone-based oil agent to a polyacrylonitrile-based precursor fiber bundle is widely known in order to prevent fusion of single fibers to each other. Silicone-based oils have excellent heat resistance and are effective in preventing the fusion of single fibers, but silicone-based oils are oxidatively decomposed when heated and tend to generate fine particles. Then, the generated fine particles may adhere to the fiber bundle while floating in the flame-resistant furnace and staying in the furnace, damaging the fiber bundle and lowering the strength of the final product, the carbon fiber bundle.

In a flameproof furnace, the oxidizing gas (typically air) that circulates in the circulation flow path by a fan is controlled so that the temperature inside the furnace becomes constant by a heater provided in the circulation duct and its control mechanism. , The polyacrylonitrile fiber bundle is heat-treated at a predetermined temperature while being folded back in the furnace by a multi-stage roller.

In the flame-resistant treatment process for polyacrylonitrile fiber bundles, it is known that as the hot air circulation is repeated, foreign substances such as fluff and powder derived from the strands accumulate in the hot air and contaminate the flame-resistant fiber bundles. (Patent Document 1).

In response to this problem, Patent Document 1 discloses a method of removing fine particles by collecting fine particles in a flame-resistant furnace with a porous plate and stabilizing the strength of carbon fibers. Further, in Patent Document 2, in order to prevent fine particles such as dust contained in the oxidizing gas circulating in the flame-resistant furnace from adhering to the flame-resistant fiber bundle, the concentration of the fine particles in the oxidizing gas atmosphere and the flame-resistant fiber A method for producing a flame-resistant fiber bundle is disclosed, in which the width of the bundle, the wind velocity of the circulating hot air of the flame-resistant furnace, the length of the flame-resistant furnace, and the passing speed of the flame-resistant fiber bundle in the furnace are within a predetermined range.

In Patent Document 3, static electricity is generated in the fiber bundles after the precursor fiber bundles subjected to the flameproofing step, which are carbon fiber intermediate fiber bundles, and before being subjected to the preliminary carbonization step, that is, the fiber bundles in the flameproofing step. Disclosed is a method of suppressing the generation of static electricity by installing conductive fibers in response to operational problems such as wrapping around rollers and mixing with adjacent fiber bundles due to a decrease in the convergence of fiber bundles. There is.

In Patent Document 4, the acrylic fiber bundle, which is a carbon fiber precursor, is a non-conductive material, and is peel-charged when passing through a roll in the process or triboelectrically charged by rubbing against various guides. Due to the charge of static electricity, surrounding dust easily adheres to the surface of the acrylic fiber bundle, which may cause quality deterioration, and also easily wraps around the roll of the process, causing process troubles. Therefore, the charged static electricity is eliminated. However, a method for producing an acrylic fiber bundle is disclosed.

Patent Documents 5 and 6 disclose a method of removing static electricity by contacting a fiber to which conductivity has been imparted by metal plating with an electrostatically charged object to be treated. Patent Document 7 discloses a static elimination brush in which a tip portion of a conductive fiber made of a metal fiber, a carbon fiber, or the like is attached to a holding member made of a conductive material such as stainless steel or aluminum.

Japanese Unexamined Patent Publication No. 2006-57222 Japanese Unexamined Patent Publication No. 2014-25167 Japanese Patent Application Laid-Open No. 8-246248 Japanese Unexamined Patent Publication No. 2010-13777 JP-A-48-95791 Jitsukaisho 49-9176 Japanese Patent Application Laid-Open No. 3-121009

However, although the invention described in Patent Document 1 describes that foreign matter in a flameproof furnace is removed by a porous plate such as a wire mesh or a punching plate which is a means for removing foreign matter, fine particles having a small particle size, tar, etc. It is difficult to completely remove the fine particles containing the volatile adhesive component of the above.

The invention described in Patent Document 2 describes that the concentration of fine particles in the flame-resistant step is controlled to be constant, but the fiber bundle or the flame-resistant fiber bundle during the flame-resistant heat treatment adheres when charged by static electricity. Even fine particles cannot be removed.

In the invention described in Patent Document 3, in a manufacturing apparatus for continuously producing carbon fibers, the pre-carbonized fiber which is a fiber bundle after the precursor fiber bundle subjected to the flame resistance or infusibilization step and before being supplied to the pre-carbonization step. It is stated that the static electricity generated when the carbon fiber intermediate fiber bundle, which is the fiber bundle up to the bundle, separates from the roller is reduced by removing the static electricity by installing the conductive fiber bundle such as the carbon fiber bundle in close proximity. is there. However, there is no description about the effect of fine particles such as dust present in the flame-resistant process on the running fiber bundle and the effect on the strength of the polyacrylonitrile-based carbon fiber bundle, and static electricity is generated to a level where the fine particles do not adhere to the flame-resistant fiber bundle. The effect of electrostatic static electricity elimination on the strength of carbon fiber bundles is unknown.

The invention described in Patent Document 4 includes a description of static electricity elimination of the polyacrylonitrile-based precursor fiber bundle which is a raw material of the carbon fiber bundle, but does not describe static electricity elimination in the firing process for producing the carbon fiber bundle. Since the fiber bundle is always exposed to the gas containing fine particles generated in the flame resistance step, even if the polyacrylonitrile-based precursor fiber bundle produced by static elimination is used, the fine particles adhere to the surface of the fiber bundle in the flame resistance step. It was not possible to solve the decrease in strength caused by this.

In the inventions described in Patent Documents 5 and 6, metal-plated fibers are used as conductive fibers for static electricity elimination, but there is no description regarding the influence of static electricity on carbon fiber bundles, and fine particles are flame-resistant fiber bundles. Sufficient studies have been made to reduce static electricity to a level that does not adhere to, and the effect of static electricity elimination on carbon fiber bundle strength is unknown.

The invention described in Patent Document 7 relates to a static elimination brush using conductive fibers such as carbon fiber, and the object to be statically eliminated is paper or a film for OHP, which is an output medium in equipment such as a printer, a copier, and a facsimile. There is no description about the effect of static electricity on the carbon fiber bundles, and the effect of static elimination on the carbon fiber bundle strength is unknown.

While the inventors are studying a method for suppressing the adhesion of fine particles floating in the flame-resistant furnace to the flame-resistant fiber bundle, the fiber bundle that passes through the flame-resistant process and the flame-resistant treatment are completed due to static electricity charging. It was found that suspended fine particles adhered to the flame-resistant fiber bundles to reduce the strength. That is, the fine particles floating in the flame-resistant furnace are charged and adhere to the flame-resistant fiber bundle by electrostatic interaction. In the production of polyacrylonitrile-based carbon fiber bundles, fine particles such as silica generated when the silicone-based oil agent is heated and oxidatively decomposed, dust flowing into the flame-resistant furnace from the outside air, and dust derived from tar solidification are flame-resistant furnace. It is easy to be generated in the inside, and the concentration of fine particles increases with the passage of time, and the fine particles tend to adhere to the fiber bundle running in the flame resistance process. Furthermore, it has been found that the fine particles adhering to the flame-resistant carbon fiber bundle are difficult to be removed even in the downstream carbonization step, and the strength of the carbon fiber bundle is lowered.

The problem to be solved by the present invention is the initial stage in the production of polyacrylonitrile-based carbon fiber bundles when flame-resistant heat treatment is performed in an oxidizing atmosphere in which the concentration of fine particles having a particle size of 0.3 μm or more is 300 particles / liter or more. By performing flame-resistant heat treatment while keeping the surface potential of the fiber bundle traveling in the stage and / or final stage low, it is possible to suppress the adhesion of fine particles to the flame-resistant fiber bundle and to produce a high-strength carbon fiber bundle. There is.

In order to solve the above problems, the present invention has the following configuration.

In a method for producing a flame-resistant fiber bundle in which a polyacrylonitrile-based fiber bundle is flame-resistant at a temperature of 200 to 300 ° C. in an oxidizing atmosphere in which the concentration of fine particles having a particle size of 0.3 μm or more is 300 pieces / liter or more. Flame resistant fibers having a fiber bundle surface potential of -1 kV to + 1 kV when the specific gravity of the bundle is 1.15 to 1.25 and / or when the specific gravity of the fiber bundle is 1.30 to 1.45. It is a method of manufacturing a bundle.

Further, as a method of statically eliminating the fiber bundle, a method of contacting or bringing a conductive fiber bundle having a specific resistance of 20 × 10 ^-4 Ω · cm or less into contact with or close to each other is provided. Provided is a method for producing a flame-resistant fiber bundle using a carbon fiber bundle as a conductive fiber bundle.

Further, in the method for producing a carbon fiber bundle of the present invention, after obtaining a flame-resistant fiber bundle by the method for producing a flame-resistant fiber bundle, the flame-resistant fiber bundle is carbonized at a temperature of 1000 to 2500 ° C. in an inert atmosphere. It is characterized in that it is processed.

In the present invention, when the polyacrylonitrile fiber bundle is flame-resistant, the amount of fine particles adhering to the fiber bundle can be suppressed to a certain amount or less by setting the surface potential of the traveling fiber bundle to -1 kV to + 1 kV. As a result, it becomes possible to carbonize the polyacrylonitrile-based fiber bundle in which fine particles adhere to a certain amount or less, and the effect of increasing the strength of the obtained carbon fiber bundle can be obtained.

The polyacrylonitrile-based precursor fiber bundle used as a raw material for the carbon fiber bundle in the present invention is, for example, a homopolymer or copolymer of acrylonitrile as an acrylic polymer, and is spun using an organic or inorganic solvent. Can be obtained at. The acrylic polymer is a polymer composed of 90% by mass or more of acrylonitrile, and if necessary, a comonomer copolymerizable with acrylonitrile can be used in an amount of 10% by mass or less. The comonomer includes acrylic acid, methacrylic acid, itaconic acid and their methyl esters, propyl esters, butyl esters, alkali metal salts, ammonium salts, allyl sulfonic acids, metharyl sulfonic acids, styrene sulfonic acids and alkali metal salts thereof. At least one selected from the group consisting of the above can be used.

The method for producing the polyacrylonitrile-based precursor fiber bundle which is the raw material of the polyacrylonitrile-based carbon fiber bundle of the present invention is not particularly limited, but as the acrylic polymer, a homopolymer or copolymer of acrylonitrile is organically or It can be obtained by spinning with an inorganic solvent. As the solvent, a known solvent such as an organic solvent such as dimethylacetamide, dimethyl sulfoxide and dimethylformamide, and an aqueous solution containing an inorganic compound such as nitric acid, zinc chloride and sodium thiocyanate can be appropriately selected and used. The spinning method may be either wet spinning, which spins in a solvent in a coagulation bath, or dry-wet spinning, in which the undiluted spinning solution is once spun in the air and then coagulated in the bath. After spinning, a polyacrylonitrile-based precursor fiber bundle can be obtained through steps such as stretching, washing with water, oiling, drying and densification, and post-stretching if necessary. When producing a polyacrylonitrile-based precursor fiber bundle, a silicone-based oil agent may be applied as an oil agent, but the silicone-based oil agent added to the polyacrylonitrile-based precursor fiber bundle is amino-modified to at least a part thereof. It preferably contains silicone. Surfactants, heat stabilizers and the like may be added to these silicone-based oils. Further, the silicone-based oil agent is often used as an emulsion, and it is preferable that an emulsifier is used in combination at this time. The emulsifier is a compound having a surface activity that promotes the formation of an emulsion and stabilizes the emulsion, and as a specific example, polyethylene glycol alkyl ether is preferably used.

The single yarn fineness of the polyacrylonitrile-based fiber bundle to which the oil agent is applied is preferably 0.4 to 1.7 dtex. Further, the number of single yarns per fiber bundle is more preferably 1000 to 60,000.

The polyacrylonitrile fiber bundle thus obtained is heat-treated at a temperature of 200 to 300 ° C. to perform a flameproof treatment. In the method for producing a flame-resistant fiber bundle of the present invention, the polyacrylonitrile-based fiber bundle is subjected to a flame-resistant treatment in an oxidizing atmosphere to obtain a flame-resistant fiber bundle. As the gas used for the oxidizing atmosphere, air is preferable from the viewpoint of cost. When the polyacrylonitrile-based fiber bundle to which the silicone-based oil is applied is heat-treated in the flame-resistant step, when the silicone-based oil applied to the surface of the fiber bundle is heated to oxidize or volatilize, silicon is always added in the flame-resistant furnace. Since the contained fine particles called silica are formed, the amount of silicon-containing fine particles such as silica that is applied over time increases and is suspended in the flameproof furnace. That is, when the silicone-based oil is thermally decomposed in the flame-resistant furnace to form silica, which contaminates the flame-resistant furnace as fine particles together with dust and the like, and remains as foreign matter in the traveling fiber bundle, the carbon finally obtained is obtained. Reduces the strength of the fiber bundle. The amount of fine particles adhering to the flame-resistant fiber bundle running in the flame-resistant furnace increases with time, and the strength of the carbon fiber bundle tends to decrease with time. The present invention is particularly effective in suppressing the decrease in strength of carbon fibers over time, that is, maintaining the strength of carbon fiber bundles at a constant level over time.

When a silicone-based oil agent is used in the process of obtaining a polyacrylonitrile-based precursor fiber bundle, silicon derived from the silicone-based oil agent during the carbide treatment is carbon vaporized from the high-temperature furnace structural material or carbon derived from the carbon fiber itself. Alternatively, it is known that various silicon compounds such as silicon carbide or silicon nitride are produced by combining with nitrogen or the like used as an inert gas. When these silicon compounds adhere to the fiber bundles, they become defects in the high-temperature furnace, and when a large amount of silicon compounds are deposited in the high-temperature furnace, they rub against the running carbon fiber bundles and generate fluff. Reduces the strength of the bundle. For this reason, it is important to suppress the adhesion of fine particles such as silica to the fiber bundle running during the flame-resistant heat treatment so as not to reduce the strength of the carbon fiber bundle.

As the flameproofing furnace, a horizontal flameproofing furnace in which fiber bundles run horizontally in a heat treatment chamber in which hot air circulates is preferably used, but a vertical flameproofing furnace in which fiber bundles run in the vertical direction is also preferably used. Good. Rollers for folding fiber bundles are installed in multiple stages on both inner and outer ends of the flame-resistant furnace, and the fiber bundles that have passed through the flame-resistant furnace along the rollers reverse the direction of travel by the folding rollers. Instead, the polyacrylonitrile-based fiber bundle is treated to be flame-resistant by repeatedly passing through the flame-resistant furnace and circulating hot air in the direction perpendicular to or horizontal to the traveling direction of the fiber bundle to heat it. Horizontally crossed fiber bundles are for folding because of the productivity that can be removed from the fiber bundles wrapped around the folding roller without stopping and the ease of handling the fiber bundles such as threading and splitting of the fiber bundles. A horizontal flame-resistant furnace in which the traveling direction is reversed by a roller is preferable.

At this time, in order to exhibit sufficient strength when the carbon fiber bundle is manufactured, the single yarn fineness of the flame-resistant fiber bundle is preferably 0.4 to 1.7 dtex. The specific gravity of the fiber bundle is 1.15 to 1.25 and / or the specific gravity of the fiber bundle is 1.30 to 1.45. The specific gravity of the polyacrylic nitrile fiber bundle increases as the heat treatment in the flame resistance step progresses. That is, when the specific gravity of the fiber bundle is 1.15 to 1.25, it corresponds to the initial stage of the flame resistance step in an oxidizing atmosphere, and the specific gravity of the fiber bundle is 1.30 to 1.45. In some cases, it corresponds to the final stage of the flameproofing process and the stage where the heat treatment in the flameproofing process through the flameproofing furnace is completed. That is, the polyacrylonitrile-based fiber bundle, which is a fiber bundle to be statically eliminated, is a fiber bundle in the middle of the flame-resistant heat treatment in the initial stage or the final stage in the flame-resistant process, or a flame-resistant furnace after the flame-resistant heat treatment is completed. It is a flame-resistant fiber bundle after passing through a furnace.

In general, when objects are rubbed against each other, positive and negative static electricity is generated at the same time. That is, static electricity is generated when atoms on the surface come into contact with each other due to friction between substances. An object in which electrons move and receive an electron is negatively charged, and an object that has lost an electron is positively charged. Static electricity is electricity generated by repeating friction and peeling of two objects, and there is a charging column that indicates whether positive or negative static electricity is likely to be charged. It is known that acrylic fibers containing polyacrylonitrile-based precursor fiber bundles tend to be charged with negative electrostatic charges as compared with other natural fibers and synthetic fibers in the charged train of fibers. The present invention makes use of the characteristic of static electricity that the voltage becomes zero in an instant due to electric discharge, and is a fiber charged with static electricity generated by repeated friction and peeling of a fiber bundle traveling in a flame resistance process with a folding roller. It is characterized in that the conductive fibers are brought close to or in contact with the bundle to eliminate static electricity efficiently and at no cost.

In the flame-resistant furnace, fine particles such as silica and dust generated by heating and oxidizing silicone-based oil, and outside air sucked into the flame-resistant furnace from around the flame-resistant furnace and fine particles and dust containing metal elements from the equipment. In addition to the fine particles, fine particles derived from silicone-based oils and tar components generated from the polyacrylonitrile-based fiber bundle itself are likely to accumulate in the flame-resistant furnace due to the continuous production of carbon fiber bundles, and these are strong. It causes a decrease. It is better that the hot air circulating in the flame-resistant furnace contains less fine particles such as the above-mentioned dust present in the oxidizing gas such as air, but such fine particles are constantly generated and accumulated in the oxidizing gas, so that the fine particle concentration is reduced to zero. It is extremely difficult to do industrially. Typical metal elements of fine particles containing metal elements include sodium, magnesium, aluminum, manganese, iron, cobalt, nickel and zinc. These fine particles and dust adhere to the traveling fiber bundle and form defects on the surface and inside of the single yarn constituting the carbon fiber bundle, which causes a decrease in the strength of the carbon fiber bundle. The fine particles having a particle size of 0.3 μm or more specified in the present invention are fine particles composed of such silica, dust such as dust, tar, and metal fine particles containing metal elements as a single substance, or particles in which a plurality of these substances are combined. Includes all particles.

On the other hand, when the outside air supplied to the flame-resistant furnace is taken in, it is filtered with a high-performance filter, etc., the metal part used for the flame-resistant furnace is made of a rust-resistant material such as stainless steel, and silicone-based oils are used. The strength level of the obtained carbon fiber bundle can be maintained at a high level by keeping the amount used low within the range in which the desired physical properties are exhibited. As the lower limit of the industrial fine particle concentration, the concentration of fine particles of 0.3 μm or more is generally 300 pieces / liter or more. And the present invention exerts an even more remarkable effect at such a fine particle concentration. In the present invention, when the fiber bundle travels in the presence of fine particles such as dust in the flameproof furnace, the surface potential of the fiber bundle is changed from -1 kV to + 1 kV so that the fine particles do not adhere to the fiber bundle due to static electricity. Therefore, even if fine particles are present, adhesion of fine particles due to static electricity can be suppressed. Therefore, even if a small amount of fine particles are present in the flameproof furnace, the carbon fiber bundles run in a state where they do not easily adhere to the fiber bundles, so that the strength of the carbon fiber bundles is higher than that in the case where the surface potential is not controlled. Express. However, if too many fine particles are present in the flameproof furnace, the fine particles are not charged by static electricity, that is, the fine particles naturally adhere to the fiber bundle even in the state of static electricity removal, which causes a decrease in strength. Therefore, the particle size is 0. The upper limit of the concentration of fine particles of .3 μm or more is not particularly limited, but is preferably 10,000 particles / liter or less.

According to the present invention, when a polyacrylonitrile fiber bundle is flame-resistant at a temperature of 200 to 300 ° C. in an oxidizing atmosphere, the surface potential, which is a basic characteristic of static electricity of the traveling fiber bundle, is set to -1 kV to + 1 kV. It is a method of chemical processing. In particular, when the specific gravity of the traveling fiber bundle is 1.15 to 1.25 and / or when the specific gravity of the fiber bundle is 1.30 to 1.45, that is, during the flame resistance treatment or the flame resistance treatment. It is necessary to control the surface potential of the polyacrylonitrile-based fiber bundle, which is the flame-resistant fiber bundle for which the above is completed, to -1 kV to + 1 kV. When there is a lot of static electricity, that is, when the surface potential is high, the force of static electricity acts to attract the traveling fiber bundles to the rollers, causing wrapping and fluffing, which not only deteriorates both quality and process passability. Since the fiber bundle itself is damaged, the toughness of the fiber bundle itself is reduced. Further, dust and fine particles around the fiber bundle traveling in a state of being charged by static electricity adhere to the fiber bundle, and scratches are generated on the single yarn due to scratching due to contact with the roller. Further, defects due to fine particles attached during high temperature treatment in the pre-carbonization step or the carbonization step may be formed.

When the fiber bundle traveling in this way is charged with static electricity, the strength of the carbon fiber bundle is reduced in both the fiber bundle and the single yarn constituting the fiber bundle, and the surface potential of the fiber bundle is minimized. It is extremely important to achieve high strength of the carbon fiber bundle. It is best when the surface potential is zero, that is, when it is not charged, but since the traveling fiber bundle is in a state where it is in contact with the roller and scraped to generate static electricity at all times, it is industrially in the range of -1 kV to + 1 kV. It is preferable to be in.

In the present invention, as a method of setting the surface potential of the fiber bundle to -1 kV to + 1 kV, that is, a method of removing static electricity from the fiber bundle, there are a contact type using a conductive fiber bundle and a non-contact type, but the method is limited to either one. It's not a thing. As a contact type static elimination method, there is a method of directly contacting the conductive fiber bundle with the traveling fiber bundle. As a non-contact static elimination method, there is a method of installing a conductive fiber bundle in the immediate vicinity of the traveling fiber bundle.

As a general static eliminator method, there are a method of using a voltage application type static eliminator and a method of utilizing the self-discharge of charged static electricity by a conductor. When using a static eliminator, installation costs are incurred, which is disadvantageous in terms of cost. When the charged static electricity is self-discharged by the conductor, it is considered that the larger the surface area of the conductor, the larger the discharge amount, and in the case of the fiber bundle, the larger the surface area, the more static electricity is discharged. The effect of electric discharge may occur on the fiber bundle. In addition, there is a method of promoting discharge by applying water to the running fiber bundles and rollers, but surrounding dust and fine particles are adsorbed on the sprayed water, and such water adheres to the fiber bundles. As a result, there may be a problem that the strength of the carbon fiber bundle is lowered due to the dust and fine particles contained in the water.

The method of static electricity-removing an electrostatically charged fiber bundle with a conductive fiber bundle can efficiently eliminate static electricity because the single yarns constituting the fiber bundle are in close proximity to each other or in contact with each other. In order to arrange the conductive fiber bundle, for example, it can be easily arranged by a method such as arranging it on a grounded metal roller stand via a metal fastener. If the conductive fiber bundle is damaged, it can be removed and easily replaced with a new conductive fiber bundle. As described above, the static elimination method using the conductive fiber bundle of the present invention is superior to the conventional static elimination method in terms of cost and handleability.

The conductive fiber bundle used to eliminate static electricity may be a metal fiber, but if it is rubbed in contact with it, it may cause thread breakage or fluffing, and a part of the metal component adheres to the fiber bundle to reduce its strength. By using carbon fiber bundles as conductive fiber bundles, the defects that cause the above are formed, and if they are mixed into the furnace of a high temperature furnace such as a carbonization furnace, they become impurities and cause a decrease in strength. It is also more preferable in that no contamination occurs. Further, the same type of material is preferable because the charged rows are close to each other and the generation of new static electricity can be suppressed even when static electricity is removed while in contact with each other. The charged train is an index indicating whether positive or negative charging is likely to occur when two substances are brought into contact with each other.

The conductive fiber bundle may have an appropriate size, and the lower limit of the total number of single yarns of the conductive fiber bundle is about 6000. Either a carbon fiber bundle in which a plurality of carbon fiber bundles having a small number of filaments are bundled or a carbon fiber bundle having a large number of filaments may be used. There is virtually no upper limit to the number of filaments in the conductive fiber bundle, but 60,000 may be sufficient. When a carbon fiber bundle is used as the conductive fiber bundle, it suffices if the static electricity of the traveling fiber bundle can be eliminated, and in addition to the fiber bundle, ropes, brushes, strings, knits, and woven fabrics can be mentioned, and the present invention is not particularly limited. Absent.

The conductive fiber bundles may be installed at one place or at a plurality of places at intervals as long as the static electricity of the traveling fiber bundle is eliminated. In particular, the static electricity elimination effect is high when the fiber bundle, which tends to generate static electricity due to peeling or friction generated between the fiber bundle and the roller or guide, is installed at a position away from the roller. At this time, the position where the conductive fiber bundle is installed is such that the distance in the traveling direction of the fiber bundle from the point where the fiber bundle is separated from the roller is 0 to 30 cm, preferably 0 to 10 cm. Further, with respect to the direction perpendicular to the traveling direction of the fiber bundle, the closer the distance between the traveling fiber bundle and the tip of the conductive fiber bundle is, the easier it is for the fiber bundle to be statically eliminated and the surface potential can be reduced. The distance from the tip of the conductive fiber bundle is 0 to 50 mm, preferably 0 to 25 mm. In the present invention, the proximity of the conductive fiber bundle to the fiber bundle means a state in which the distance between the fiber bundle and the tip of the conductive fiber bundle is preferably 0 to 50 mm, more preferably 0 to 25 mm.

In the present invention, it is preferable to use a conductive fiber bundle as a means for removing static electricity from the traveling fiber bundle. The conductive fiber bundle is a fiber bundle having conductivity, and is effective for adhesion of dust and discharge of static electricity. Conductive fiber bundles include those in which conductive substances such as metal, carbon, and graphite are uniformly dispersed in synthetic fibers or generated by chemical changes, such as stainless steel, copper, aluminum, iron, nickel, and titanium. There are metal fibers made of metal into fibers, those in which the surface of the fibers is coated with metal, those in which the surface of the fibers is coated with a resin containing a conductive substance, carbon fibers, and metal-coated carbon fibers.

The advantage of using a conductive fiber bundle as a means of eliminating static electricity is that unlike metal wires such as wires and wires, the single yarn constituting the conductive fiber bundle always contacts the traveling fiber bundle at a plurality of points. , The effect of eliminating static electricity is high. Further, even if some of the single yarns constituting the conductive fiber bundle are broken, the remaining single yarns that are not broken can continue the static electricity elimination effect, and the shape of the traveling fiber bundle charged with static electricity. It is also an advantage that the shape can be constantly changed so that the conductive fiber bundles can come into contact with each other.

In order to eliminate static electricity from a traveling fiber bundle, the conductivity of the conductive fiber should be sufficient, and a specific resistance, which is an electrical resistivity, is a typical index of conductivity. Specifically, the specific resistance of the conductive fiber bundle is preferably 20 × 10 ^-4 Ω · cm or less. If the conductive fiber bundle has a specific resistance to be applied, the static electricity of the fiber bundle that runs suitably can be eliminated. There is no particular limitation on the lower limit of the resistivity.

Since the flameproofing step is an environment containing a large amount of the above-mentioned fine particles, it is preferable to install these conductive fiber bundles as the static elimination means in the entire flameproofing step, but more preferably, poly. The acrylonitrile fiber bundle is installed at a position where the specific gravity of the fiber bundle running in the flameproof furnace is 1.15 to 1.25 and / or at a position where the specific gravity of the fiber bundle is 1.30 to 1.45. .. Since the fiber bundle that runs during the flameproof heat treatment is repeatedly rubbed and peeled off from the rollers, static electricity is generated in the entire flameproofing process, but as described below at the initial stage or the final stage of flameproofing. Since the generation of static electricity is remarkable, the effect of the present invention is particularly large.

This is because the polyacrylonitrile-based precursor fiber bundle, which is the raw material of the carbon fiber bundle, is a non-conductive material and is easily charged with static electricity, and the fiber bundle at the initial stage of the flame-resistant heat treatment has a large thermal shrinkage. This is because static electricity is likely to be generated. Therefore, if the conductive fiber bundle is installed in contact with or close to the fiber bundle having a specific gravity of 1.15 to 1.25 corresponding to the initial stage of the flame resistance step, the static elimination effect is large. In addition, in the fiber bundle at the end of flame resistance or after passing through the flame resistance furnace, the fiber bundle itself becomes fragile and the tension of the fiber bundle increases due to the accumulation of mechanical loss due to the folding roller in the flame resistance process. Static electricity is likely to be generated when rubbing with the rollers, and the conductive fiber bundle is in contact with or close to the fiber bundle having a specific gravity of 1.30 to 1.45, which is the final stage of the flame resistance process or the stage after the flame resistance is passed through the furnace. Even if it is installed, the static electricity elimination effect is large.

The flame-resistant fiber bundle thus obtained is pre-carbonized in an inert atmosphere such as nitrogen at a temperature of 300 to 1000 ° C., and then carbonized in an inert atmosphere such as nitrogen at a temperature of 1000 to 2500 ° C. The carbon fiber bundle can be obtained by the treatment.

After the carbonization treatment, an oxidized surface treatment is performed for the purpose of generating functional groups on the surface of the carbon fiber bundle and enhancing the adhesiveness with the matrix resin. Oxidized surface treatment methods include liquid phase oxidation using a chemical solution, electrolytic surface treatment in which carbon fibers are surface-treated in an electrolytic solution, and vapor-phase oxidized surface treatment by plasma treatment, etc., but they are relatively easy to handle. , An electrolytic surface treatment method which is advantageous in terms of manufacturing cost is preferably used. As the electrolytic solution used in the electrolytic surface treatment, either an acidic aqueous solution or an alkaline aqueous solution can be used, but the acidic aqueous solution is preferably sulfuric acid or nitrate showing strong acidity, and the alkaline aqueous solution is ammonium carbonate, ammonium hydrogencarbonate or heavy. An aqueous solution of an inorganic alkali such as ammonium carbonate is preferably used. If necessary, the carbon fiber bundle subjected to the electrolytic surface treatment is subjected to a water washing step, and then the water content is evaporated in a dryer, and then a sizing agent is applied. The type of sizing agent referred to here is not particularly limited, but the sizing agent may be appropriately selected from bisphenol A type epoxy resin and polyurethane resin whose main component is epoxy resin, depending on the matrix resin used in higher-order processing. it can.

When a carbon fiber bundle is produced using the flame-resistant fiber bundle thus obtained, a carbon fiber bundle having high strength can be obtained.

Examples and comparative examples of the present invention will be described in more detail below. The evaluation method and measurement method for each characteristic were as described below.

<Measurement of fine particle concentration>
The concentration of fine particles having a particle size of 0.3 μm or more was measured using a light scattering particle counter (for example, KC-01E manufactured by RION). Sample air, which is an oxidizing gas, is sucked from the flameproof furnace at 0.5 liter / minute for 34 seconds, and the number of particles of 0.3 μm or more contained in 0.283 liter is measured and per liter. The value converted into the number of fine particles in the above was taken as the fine particle concentration (pieces / liter).

<Specific gravity of fiber bundle>
The specific gravity of the fiber bundle conformed to the method described in JIS R7601 (2006). The measurement was performed using a fiber bundle for measuring the surface potential. Ethanol (special grade manufactured by Wako Pure Chemical Industries, Ltd.) was used as the reagent without purification. A bundle of fibers of 1.0 to 1.5 g was collected and dried at 120 ° C. for 2 hours. After measuring the absolute dry mass (A), it was impregnated with ethanol having a known specific gravity (specific gravity ρ), and the fiber bundle mass (B) in the ethanol was measured. The specific gravity was calculated according to the following formula.
Specific gravity = (A × ρ) / (AB).

<Surface potential of fiber bundle>
The surface potential of the fiber bundle is measured at a position 10 cm away from the point where the fiber bundle is separated from the folding roller in the flame resistance step in the traveling direction of the fiber bundle, and 2 from the fiber bundle in the direction perpendicular to the fiber bundle. A non-contact static electricity measuring device FMX-003 manufactured by Simco Japan Co., Ltd. was installed at a distance of .5 cm, and the surface potential, which is the static electricity of the fiber bundle, was measured.

<Strength of carbon fiber bundle>
It was determined according to the following procedure in accordance with the carbon fiber tensile property test method of JIS R7608 (2007). As the resin formulation, "Ceroxide (registered trademark)" 2021P (manufactured by Daicel Chemical Industry Co., Ltd.) / Borone monoethylamine trifluoride (manufactured by Tokyo Chemical Industry Co., Ltd.) / Acetone = 100/3/4 (part by mass) The curing conditions used were normal pressure for pressure, 125 ° C. for temperature, and 30 minutes for time. Five carbon fiber bundles were measured, and the average value was taken as the strength of the carbon fiber bundles.

<Specific resistance of conductive fiber bundles>
The ratio of conductivity when the electrical resistivity per 1 m of the conductive fiber bundle is R (Ω / m), the grain which is the mass per 1 m is Y (g / m), and the density is D (g / cm ³ ). The resistance was calculated by the following formula.

Specific resistance (× 10 ^-4 Ω · cm) = R × Y ÷ D.

[Example 1]
After preparing a spinning stock solution from an acrylic polymer, the spinning stock solution was coagulated by a dry-wet spinning method. The obtained coagulated yarn was washed with water, stretched, oiled, dried, and steam-stretched to obtain a polyacrylonitrile-based precursor fiber bundle having a single fiber fineness of 1.1 dtex and a single yarn number of 12,000.

The silicone-based oil used was an amino-modified silicone, and an amino-modified silicone emulsion containing polyethylene glycol alkyl ether as an emulsifier was used.

Next, in a horizontal hot air circulation type flame-resistant furnace in which the concentration of fine particles having a particle size of 0.3 μm or more in the furnace at a furnace temperature of 220 to 270 ° C. is 2500 pieces / liter, in an oxidizing atmosphere composed of air. A carbon fiber bundle having a specific resistance of 15 × 10 ^-4 Ω · cm as a conductive fiber is placed on a fiber bundle having a specific gravity of 1.18, which has been heat-resistant and heat-treated, at a position 10 cm from the point where the fiber bundle separates from the roller. The surface potential of the fiber bundle was -0.2 kV (that is, the measurement result of the surface potential after static elimination) when the fiber bundle was brought into contact with the fiber bundle running in. For reference, the surface potential of the fiber bundle before static elimination was −5.0 kV.

Then, the flame-resistant fiber bundle obtained by the flame-resistant treatment was carbonized at a maximum single carbonization temperature of 1350 ° C. in an inert atmosphere, and a sizing agent was applied after the surface treatment to produce a carbon fiber bundle. The strength of the obtained carbon fiber bundle was 540 kgf / mm ² (5.3 GPa). The results are shown in Table 1.

[Example 2]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the carbon fiber bundle, which is a conductive fiber, was installed close to the running fiber bundle at a position 2 cm vertically away from the fiber bundle. The surface potential of the fiber bundle after static elimination was −1.0 kV, and the strength of the obtained carbon fiber bundle was 520 kgf / mm ² (5.1 GPa). The results are shown in Table 1.

[Example 3]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the specific gravity of the fiber bundle that had been heat-treated for flame resistance was 1.45. The surface potential of the fiber bundle after static elimination was +0.5 kV, and the strength of the obtained carbon fiber bundle was 520 kgf / mm ² (5.1 GPa). The results are shown in Table 1.

[Example 4]
When the specific gravity of the fiber bundle that has been heat-resistant and heat-treated is 1.18, and when the specific gravity of the fiber bundle is 1.45, the specific resistance of the fiber bundle is 15 × 10 ^-4 Ω as a conductive fiber. A carbon fiber bundle was obtained in the same manner as in Example 1 except that the cm carbon fiber bundle was brought into contact with each fiber bundle running at a position 10 cm from the point where the fiber bundle was separated from the roller. The surface potentials of the fiber bundles after static elimination were −0.2 kV and +0.2 kV, respectively, and the strength of the obtained carbon fiber bundles was 550 kgf / mm ² (5.4 GPa). The results are shown in Table 1.

[Example 5]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that a nickel-coated carbon fiber strand "Tenax (registered trademark)" HTS40 MC (trade name) manufactured by Teijin Limited was used as the conductive fiber. Since the nickel coating was applied, the specific resistance decreased to 0.75 × 10 ^-4 Ω · cm and the static elimination effect was enhanced. Therefore, the surface potential of the fiber bundle after static elimination was 0 kV. However, the nickel-coated carbon fibers are always in contact with the fiber bundles, and the fiber bundles are constantly rubbed against the nickel, causing single-thread damage, and at the same time, the nickel adhering to the fiber bundles form defects in the carbonization process. The strength of the obtained carbon fiber bundle was 520 kgf / mm ² (5.1 GPa). The results are shown in Table 1.

[Example 6]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the concentration of fine particles having a particle size of 0.3 μm or more in the flameproof furnace was set to 320 cells / liter. The surface potential of the fiber bundle after static elimination was −0.2 kV. The inside of the flame-resistant furnace was in a clean state in which dust and fine particles did not easily adhere to the fiber bundles, and the strength of the obtained carbon fiber bundles was 550 kgf / mm ² (5.4 GPa). The results are shown in Table 1.

[Example 7]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the concentration of fine particles having a particle size of 0.3 μm or more in the flameproof furnace was set to 5000 pieces / liter. The surface potential of the fiber bundle after static elimination was −0.2 kV. The strength of the obtained carbon fiber bundle was 520 kgf / mm ² (5.1 GPa). The results are shown in Table 1.

[Example 8]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the concentration of fine particles having a particle size of 0.3 μm or more in the flameproof furnace was set to 8000 pieces / liter. The surface potential of the fiber bundle after static elimination was −0.2 kV. The strength of the obtained carbon fiber bundle was 510 kgf / mm ² (5.0 GPa). The results are shown in Table 1.

[Example 9]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that a wire having a diameter of 3 mm and made of iron was used. Since the specific resistance of the wire decreased to 0.097 × 10 ^-4 Ω · cm and the static elimination effect was enhanced, the surface potential of the fiber bundle after static elimination was 0 kV. However, unlike the conductive fiber bundle, the wire is constantly rubbed in a state where the fiber bundle and the wire are in point contact, so that single yarn damage occurs and at the same time, the iron attached to the fiber bundle forms a defect in the carbonization process. The strength of the obtained carbon fiber bundle was 510 kgf / mm ² (5.0 GPa). The results are shown in Table 1.

[Example 10]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the specific gravity of the fiber bundle that had been heat-treated for flame resistance was 1.23. The surface potential of the fiber bundle after static elimination was −0.2 kV, and the strength of the obtained carbon fiber bundle was 530 kgf / mm ² (5.2 GPa). The results are shown in Table 1.

[Example 11]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the specific gravity of the fiber bundle that had been heat-treated for flame resistance was 1.33. The surface potential of the fiber bundle after static elimination was +0.4 kV, and the strength of the obtained carbon fiber bundle was 520 kgf / mm ² (5.1 GPa). The results are shown in Table 1.

[Comparative Example 1]
When the same procedure as in Example 1 was carried out except that the conductive fiber bundle was not used, the surface potential increased to −5.0 kV due to the generation of static electricity. The traveling fiber bundle is always attracted to the single yarn that constitutes the fiber bundle when it separates from the roller due to static electricity, and because there are many fine particles such as dust and silica in the flameproof furnace, the traveling fiber bundle becomes Due to the adhesion of fine particles of silica, it was observed that a large number of particulate white silica was attached to the flame-resistant fiber bundle after the flame-resistant furnace was passed. The strength of the obtained carbon fiber bundle was reduced to 480 kgf / mm ² (4.7 GPa). The results are shown in Table 1.

[Comparative Example 2]
When the same procedure as in Example 7 was carried out except that the conductive fiber bundle was not used, the surface potential increased to −5.0 kV due to the generation of static electricity. The traveling fiber bundle is always attracted to the roller when it separates from the roller due to static electricity, and the traveling fiber bundle has a large amount of fine particles such as dust and silica in the flameproof furnace. Due to the adhesion of fine particles of silica, it was observed that a large number of particulate white silica was attached to the flame-resistant fiber bundle after the flame-resistant furnace was passed. The strength of the obtained carbon fiber bundle was reduced to 470 kgf / mm ² (4.6 GPa). The results are shown in Table 1.

[Comparative Example 3]
When the same procedure as in Example 8 was carried out except that the conductive fiber bundle was not used, the surface potential increased to −5.0 kV due to the generation of static electricity. The traveling fiber bundle is always attracted to the roller when it separates from the roller due to static electricity, and the traveling fiber bundle has a large amount of fine particles such as dust and silica in the flameproof furnace. Due to the adhesion of fine particles of silica, it was observed that a large number of particulate white silica was attached to the flame-resistant fiber bundle after the flame-resistant furnace was passed. The strength of the obtained carbon fiber bundle was reduced to 460 kgf / mm ² (4.5 GPa). The results are shown in Table 1.

[Comparative Example 4]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the carbon fiber bundle, which is a conductive fiber bundle, was installed close to the running fiber bundle at a position 10 cm vertically away from the running fiber bundle. Since the static elimination effect of the conductive fiber bundle was reduced, the surface potential of the fiber bundle after static elimination was as high as −2.0 kV, and the static elimination was not sufficient. The strength of the obtained carbon fiber bundle was 490 kgf / mm ² (4.8 GPa). The results are shown in Table 1.

[Comparative Example 5]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the fiber bundle subjected to the flame-resistant heat treatment was placed close to the fiber bundle having a specific gravity of 1.45 at a position 10 cm vertically away from the fiber bundle. Since the static elimination effect of the conductive fiber bundle was reduced, the surface potential of the fiber bundle after static elimination was as high as +2.0 kV, and the static elimination was not sufficient. The strength of the obtained carbon fiber bundle was 490 kgf / mm ² (4.8 GPa). The results are shown in Table 1.

[Comparative Example 6]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the specific gravity of the fiber bundle in contact with the conductive fiber bundle was set to 1.50. As the specific gravity increased, the fiber bundle became brittle, and static electricity was likely to be charged due to friction with the rollers. The surface potential after static electricity elimination increased to +3.0 kV, and static electricity elimination was not sufficient. The strength of the obtained carbon fiber bundle was reduced to 480 kgf / mm ² (4.7 GPa). The results are shown in Table 1.

[Comparative Example 7]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the specific gravity of the fiber bundle in contact with the conductive fiber bundle was set to 1.28. Since the place where the fiber bundle having such a specific gravity travels is a place where static electricity is relatively unlikely to be charged in the flame resistance process, the static electricity elimination effect by the conductive fiber bundle is limited, and the surface potential after static electricity removal is high. It was + 1.2 kV. The strength of the obtained carbon fiber bundle was reduced to 490 kgf / mm ² (4.8 GPa). The results are shown in Table 1.

Claims

In a method for producing a flame-resistant fiber bundle in which a polyacrylonitrile-based fiber bundle is flame-resistant at a temperature of 200 to 300 ° C. in an oxidizing atmosphere, when the specific gravity of the fiber bundle is 1.15 to 1.25, and / Or, a method for producing a flame-resistant fiber bundle in which the surface potential of the fiber bundle is -1 kV to + 1 kV when the specific gravity of the fiber bundle is 1.30 to 1.45.
In a method for producing a flame-resistant fiber bundle, in which a polyacrylonitrile-based fiber bundle is flame-resistant at a temperature of 200 to 300 ° C. in an oxidizing atmosphere in which the concentration of fine particles having a particle size of 0.3 μm or more is 300 pieces / liter or more. Flame resistance with a surface potential of -1 kV to + 1 kV when the specific gravity of the fiber bundle is 1.15 to 1.25 and / or when the specific gravity of the fiber bundle is 1.30 to 1.45. A method for manufacturing a fiber bundle.
Claim 1 or 2 in which a conductive fiber bundle having a specific resistance of 20 × 10 -4 Ω · cm or less is brought into contact with or close to the polyacrylonitrile fiber bundle to set the surface potential of the fiber bundle to -1 kV to + 1 kV. The method for producing a flame-resistant fiber bundle according to.
The method for producing a flame-resistant fiber bundle according to claim 3, wherein the conductive fiber bundle is a carbon fiber bundle.
After obtaining a flame-resistant fiber bundle by the method for producing a flame-resistant fiber bundle according to any one of claims 1 to 4, carbon that carbonizes the flame-resistant fiber bundle in an inert atmosphere at a temperature of 1000 to 2500 ° C. Method for manufacturing fiber bundles.