JP5463807B2 - Agglomerates of finely divided fine carbon fibers - Google Patents

Description

  The present invention relates to a diatom-like aggregate of fine carbon fibers excellent in conductivity and a method for efficiently producing the diatom-like aggregate of fine carbon fibers. Specifically, agglomerated aggregates of fine carbon fibers are produced by a vapor phase growth method using a catalyst, and then the aggregates are crushed by applying an impact force to make fine particles without changing the bulk density. The present invention relates to a diatomaceous agglomerate of fine carbon fibers and a method for producing the same.

  Fine carbon fibers represented by a cylindrical tube shape, a fish bone shape (fishbone, cup-laminated type), a trump shape (platelet), and the like are expected to have various applications due to their shape and form. In particular, cylindrical carbon-like fine carbon fibers (carbon nanotubes) are attracting attention as next-generation conductive materials because they are superior in strength, conductivity, and the like compared to conventional carbon materials.

  Multi-walled carbon nanotubes (multi-layer concentric cylindrical shape) (non-fishbone-like) are described in, for example, Japanese Patent Publication No. 3-64606, Japanese Patent Publication No. 3-77288, Japanese Patent Publication No. 9-502487, Japanese Patent Application Laid-Open No. 2004-299986, and the like. The carbon nanotubes of this structure are composed of SP2-bonded carbon cylinders concentrically as a whole, but the actual form of carbon nanotubes exists as aggregates of several tens of μm to several mm in which these fibers are entangled To do.

  In the carbon nanotube, the graphite network surface is parallel to the fiber axis, and electrons flow along this, so that the conductivity in the major axis direction of a single fiber is good. However, regarding conductivity between adjacent fibers, a jumping effect (tunnel effect) due to the jumping out of π electrons cannot be expected because the side peripheral surface is constituted by a graphite network surface closed in a cylindrical shape. Therefore, in a composite with a polymer using carbon nanotubes as a conductive filler, there is a problem that the conductivity is not exhibited well unless sufficient contact between the fibers is ensured. Furthermore, the problem that the conductivity and the reinforcing effect are not satisfactorily exhibited is largely attributable to the fact that it is difficult to satisfactorily disperse the carbon nanotubes in the composite.

  Conventionally, arc discharge methods, vapor phase growth methods, laser methods, mold methods, and the like are known as methods for producing fine carbon fibers typified by carbon nanotubes. Among them, the vapor phase growth method using catalyst particles is attracting attention as an inexpensive synthesis method, but a mass production method has not been established. In addition, since the carbon nanotubes to be produced are heterogeneous fibers with low crystallinity, graphitization is required when high conductivity is required.

  For example, in Japanese Patent Laid-Open No. 9-502487 (Patent Document 1), as a conventional technique, a carbon fibril raw material (cylindrical tube shape) produced by the method described in Japanese Patent Laid-Open No. 2-503334 or Japanese Patent Laid-Open No. 62-500993 is disclosed. The graphite interplanar spacing (d002) in the XRD (X-ray diffraction) measurement is 0.354 nm, indicating that the crystallinity is not sufficient and the conductivity is low as it is. Further, it is described that by treating this fibril raw material at 2450 ° C., a fibril material having an improved crystallinity with a graphite interplanar spacing (d002) of 0.340 nm can be obtained.

  Fishbone carbon fibers (cup laminated carbon fibers) are disclosed in, for example, USP 4,855,091, M.C. Endo and Y.M. A. Kim et al. [Appl. Phys. Lett. , Vol80 (2002) 1267 ~], JP2003-073928, JP2004-360099, and the like. This structure has a shape in which cups having no bottom are laminated. As described in JP-A-2004-241300, the carbon fiber having this structure has a structure in which a cone-shaped carbon base bottom having an inclination in the fiber axis direction is laminated, and thus the conductivity in the fiber axis direction is extremely low. It cannot be said that it is suitable as a conductive material.

  Furthermore, platelet-type carbon nanofibers (trump-like) are disclosed in, for example, H.P. Murayama and T.A. Maeda [Nature, vol 345 [No. 28] (1990) 791-793], Japanese Patent Application Laid-Open No. 2004-300631, and the like. This structure is also basically a structure in which carbon base disks are stacked perpendicular to the fiber axis in the same manner as fishbone type carbon fiber (cup laminated type carbon fiber). In addition, it is not suitable as a conductive material for the same reason as in the case of fishbone-type carbon fiber.

  Fishbone-like and trump-like fine fibers expose the open end of the graphite mesh surface on the side peripheral surface, so that the conductivity between adjacent fibers is improved compared to carbon nanotubes. However, since the C-axis of the graphite network surface is laminated or inclined in parallel to the fiber axis direction, the conductivity in the fiber axis major axis direction of a single fiber is lowered.

  In addition to the above typical structure, Japanese Patent Application Laid-Open No. 2006-103996 (Patent Document 2) discloses a multilayer material containing nitrogen atoms chemically bonded to carbon atoms forming the core of the crystal lattice and having one end opened and the other end closed. Is a unit structure unit, and a fiber structure in a form in which a closed end of one unit is inserted into an open end of another unit, and a manufacturing method thereof are disclosed. However, since this fiber contains nitrogen atoms chemically bonded to carbon atoms on the graphite network surface, there is a problem that structural distortion occurs in the graphite network surface, resulting in low crystallinity, that is, low conductivity.

  Also, Applied Physics A 2001 (73) 259-264 (Ren Z. F. et al.) (Non-patent Document 1) is similar to Patent Document 2 (Japanese Patent Laid-Open No. 2006-103996), which is referred to as “bamboo-structure”. Fiber structure has been reported. The structure is synthesized by a vapor phase growth method at 750 ° C. using a catalyst in which iron is supported on silica and using a mixed gas of acetylene 20 vol% / ammonia 80 vol%. In this report, the chemical composition analysis of the fiber structure is not described at all. However, since the concentration of non-inert nitrogen contained in the raw material is very high (59 wt%), the fiber structure is also chemically analyzed. Contains nitrogen atoms bonded to carbon atoms, which is thought to cause structural disturbances. In addition, since the ratio of the product weight to the catalyst weight is as low as about 6, the fiber growth is not sufficient and the aspect ratio is small.

Further, in Carbon 2003 (41) 2949-2959 (Gadelle P. et al.) (Non-Patent Document 2), the graphite mesh surface constituting the fiber is in a cone shape, and the open end thereof is at an appropriate interval on the fiber side peripheral surface. Exposed structures have been reported. In this document, 0.2 g of a mixture of cobalt salt and magnesium salt co-precipitated with citric acid is activated with H ₂ and then reacted with a raw material gas composed of CO and H ₂ (H ₂ concentration: 26 vol%). This gives 4.185 g of product. However, in the fiber structure obtained by this method, the angle formed by the cone-shaped side peripheral surface and the fiber axis is approximately 22 °, which is greatly inclined with respect to the fiber axis. For this reason, there exists a problem similar to the said fishbone-like carbon fiber about the electroconductivity of a single fiber major axis direction. In addition, since the fiber growth is insufficient and the aspect ratio is small, it is difficult to impart conductivity and reinforcement to the composite with the polymer. Further, since the product weight with respect to the catalyst weight is as small as 21 times, not only is the production method not efficient, but the use is limited due to the increased impurity content.

  As described above, fine carbon fibers having various structures and methods for producing the same have been proposed. Since such fine carbon fibers are obtained by a vapor phase growth method based on catalyst particles, the fine carbon fibers can be obtained from several tens of μm. It is produced as a large aggregate of massive particles intricately entangled with several mm. For this reason, the opening of the aggregates does not progress during mixing and combining with the resin, and the aggregates remain as large lump particles of 50 μm or more in the composite, so that there is a problem with the molding device (discharge unit filter clogging, heat shrinkage nonuniformity) Etc.) and the appearance of the conductivity of the molded product, surface appearance, and mechanical properties cannot be obtained.

  For this reason, optimization of resin molecular weight (Patent Document 3: Japanese Patent Laid-Open No. 2001-310994), blending of modified resin, elastomer, and compatibilizer (Patent Document 4: Japanese Patent Laid-Open No. 2007-231219, Patent Document 5: Japanese Patent Laid-Open No. 2004-230926) , Patent Document 6: JP 2007-169561, Patent Document 7: JP 2004-231745), Surface modification treatment of carbon nanotubes (Patent Document 8: JP 2004-323738), etc. Therefore, special surface modification treatment is required, and the type and composition of the resin are restricted. Further, Patent Document 9 (Japanese Patent Application Laid-Open No. 2005-239531) proposes a method of crushing and granulating carbon nanotubes by a high-speed air current impact method. According to this method, it has been reported that a substantially spherical granulated product can be obtained by crushing carbon nanotubes in a high-speed air stream and then granulating them. However, this method requires a long processing time of 3 to 30 minutes while using impact force in a high-speed air stream for crushing, and also requires two steps of crushing and granulation as described above. Become. Also, Patent Document 10 (Japanese Patent Laid-Open No. 2006-143532) proposes a method of crushing and granulating carbon nanotubes by a high-speed air current impact method. According to this method, by applying a large impact force to the carbon nanotube aggregate, the density of the aggregate can be adjusted to the solvent, and as a result, the carbon nanotube aggregate is difficult to settle in the solvent, and it is easy to disperse. Has been. For example, when the solvent is water, the bulk density of the carbon nanotube aggregate is 1 g / ml, which is the same density as water. However, it is very difficult to actually set the bulk density of the carbon nanotube aggregate to 1 g / ml.

JP 9-502487 JP 2006-103996 A JP 2001-310994 A JP 2007-231219 A JP 2004-230926 A JP 2007-169561 A JP 2004-231745 A JP 2004-323738 A Japanese Patent Laid-Open No. 2005-239531 JP 2006-143532 A

Applied Physics A 2001 (73) 259-264 (Ren Z. F. et al.) Carbon 2003 (41) 2949-2959 (Gadelle P. et al.)

  The present invention provides a special surface treatment of fine carbon fibers and a special kneading / mixing method or compounding recipe, for example, without using a rubber component, a surfactant, a compatibilizing agent, etc. An object of the present invention is to provide a diatom-like aggregate of fine carbon fibers with improved kneadability and dispersibility in compositing. Furthermore, a fine carbon fiber diatomaceous agglomerate excellent in composite workability, and excellent in functions such as conductivity, thermal conductivity, slidability, reinforcement and flame retardancy of the composite, and an efficient production method thereof The purpose is to provide.

  The present invention relates to the following matters. In the present specification, the “fine carbon fiber” refers to a connected carbon fiber schematically shown in FIG. 2 obtained by a vapor phase growth method described later. Further, the “fine aggregate of fine carbon fibers” refers to particles obtained by agglomerating fine carbon fibers immediately after being produced by a vapor phase growth method. “Fine carbon fiber diatomaceous agglomerates” refers to fine carbon fiber aggregates obtained by pulverizing fine carbon fiber aggregates according to the method described later, and are nearly spherical. The term is used to distinguish it from agglomerates because of its shape.

1. It is obtained by crushing agglomerates of fine carbon fibers produced by a vapor phase growth method,
The diameter is 1-150 μm, the bulk density is 0.05-0.15 g / ml,
The fine carbon fiber has at least one structure in which structural unit aggregates constituting the carbon fiber are bonded to each other via a graphite base surface.

2. In the fine carbon fiber, the graphite net surface forms a structural unit having a closed top portion and a trunk portion having an open lower portion, and the structural unit is formed in a layered form with 2 to 30 layers sharing a central axis. 2. The fine structure according to 1 above, wherein the structural unit aggregates are stacked to form a structural unit aggregate, and the structural unit aggregates are continuously bonded in a Head-to-Tail manner through each graphite base surface. Aggregates of carbon fibers.

3. The outer diameter D of the end of the aggregate body is 5 to 40 nm, the inner diameter d is 3 to 30 nm, and the aspect ratio (L / D) of the aggregate is 2 to 150. 2. A fine carbon fiber aggregate according to 2.

4). 4. The fine carbon fiber aggregate according to any one of 1 to 3 above, wherein the ash content is 4% by weight or less.

5. The fine half-width W (unit: degree) of the 002 plane of fine carbon fiber measured by an X-ray diffraction method is 2 to 4, and the fine carbon fiber according to any one of 1 to 4 above Aggregates of carbon fibers.

6). 6. The fine carbon fiber aggregation according to any one of 1 to 5 above, wherein the fine carbon fiber has a graphite plane spacing (d002) of 0.341 to 0.350 nm as measured by an X-ray diffraction method. Aggregation.

7). Use of the fine carbon fiber aggregate according to any one of the above 1 to 6, which is used as a conductive material, a conductive additive, a heat conductive material, a sliding material, a reinforcing material, a flame retardant, and an abrasive. .

8). Crushing treatment is performed by applying impact force to fine carbon fibers grown by supplying a mixed gas containing CO and H ₂ on a catalyst containing cobalt spinel oxide in which magnesium is substituted and dissolved. A method for producing an aggregate of fine carbon fibers characterized by comprising:

9. Said spinel-type _oxide, when expressed in _{Mg x Co 3-x O y} , the value of x indicating a solid solution range of magnesium, according to the above 8, which is a 0.5 to 1.5 Of producing fine carbon fiber aggregates.

10. 10. Production of fine carbon fiber aggregates according to 8 or 9 above, wherein a hammer mill, an ultracentrifugal mill, a pin mill, a turbo mill, or a jet mill that generates an impact action during the crushing treatment is used. Method.

11. 11. The method for producing an aggregate of fine carbon fibers according to any one of 8 to 10 above, wherein the crushing treatment with the impact force is performed in a dry manner without using an additive.

  According to the present invention, when pulverizing the aggregates of fine carbon fibers immediately after being produced by the vapor phase growth method, the structural features of the fine carbon fibers can suppress the damage of the fibers and make the particles fine. The micronized carbon fiber diatomaceous agglomerates of the present invention are easy to flow and disperse, so that they are less likely to contaminate the working environment when handled as powders, and are miscible with resins, Excellent spreadability and dispersibility. As a result, the physical properties of the resulting composite material are also excellent. Furthermore, the crushing process in the manufacturing process of the fine carbon fiber diatomaceous agglomerates of the present invention can be carried out more easily and in a shorter time than before, and is efficient.

(A) It is a figure which shows typically the minimum structural unit (structural unit) which comprises fine carbon fiber. (B) It is a figure which shows typically the aggregate | assembly in which 2-30 structural units were piled up. (A) It is a figure which shows typically a mode that an aggregate | assembly connects with a space | interval and comprises a fiber. (B) It is a figure which shows typically a mode that it bent and connected, when an aggregate | assembly connects with a space | interval. 2 is a TEM photographic image of fine carbon fibers produced in Example 1. FIG. It is explanatory drawing by which an impact force is converted into a tensile stress at an intermediate point when the impact force is applied to the fine carbon fiber from the lateral direction. It is a SEM photograph of the aggregate of the fine carbon fiber immediately after manufactured by the vapor phase growth method. It is a SEM photograph of the diatom-like aggregate of the fine carbon fiber which pulverized the aggregate of the fine carbon fiber immediately after manufactured by the vapor phase growth method with a hammer mill.

<Structure of fine carbon fiber>
The fine carbon fiber constituting the diatomaceous agglomerate of the present invention has a structure as shown in FIG. 1A as a minimum structural unit. The temple bell is found in Japanese temples, has a relatively cylindrical body, and is different in shape from a conical Christmas bell. As shown in FIG. 1A, the structural unit 11 has a top 12 and a body 13 having an open end, and has a rotating body shape that is rotated about the central axis. The structural unit 11 is formed of a graphite network surface made of only carbon atoms, and the circumferential portion of the body portion open end is the open end of the graphite network surface. In FIG. 1A, the central axis and the body portion 13 are shown as straight lines for convenience, but they are not necessarily straight lines and may be curved as shown in FIG.

  The trunk portion 13 gradually spreads toward the open end, and as a result, the generatrix of the trunk portion 13 is slightly inclined with respect to the central axis of the structural unit, and the angle θ formed by both is smaller than 15 °. Preferably, 1 ° <θ <15 °, more preferably 2 ° <θ <10 °. If θ is too large, fine fibers composed of the structural unit exhibit a fishbone-like carbon fiber-like structure, and the conductivity in the fiber axis direction is impaired. On the other hand, when θ is small, the structure is close to a cylindrical tube shape, and the frequency at which the open end of the graphite mesh surface constituting the body of the structural unit is exposed to the outer peripheral surface of the fiber becomes low, so the conductivity between adjacent fibers deteriorates. .

  The fine carbon fiber has defects and irregular turbulence. However, when such an irregularity is eliminated and the shape of the whole is captured, the body portion 13 is gently expanded toward the open end. It can be said that it has. Fine carbon fiber does not mean that θ indicates the above range in all parts, but when the structural unit 11 is captured as a whole while excluding defective parts and irregular parts, Overall, it means that θ satisfies the above range. Therefore, in the measurement of θ, it is preferable to exclude the vicinity of the crown 12 where the thickness of the trunk may be irregularly changed. More specifically, for example, when the length of the structural unit aggregate 21 (see below) is L as shown in FIG. 1B, (1/4) L, (1/2) L from the top of the head. Further, θ is measured at three points of (3/4) L to obtain an average, and the value may be used as the overall θ for the structural unit 11. In addition, it is ideal to measure L with a straight line. However, since the body part 13 is often a curved line in practice, it may be closer to the actual value when measured along the curve of the body part 13. .

  When manufactured as a fine carbon fiber, the shape of the top of the head is smoothly continuous with the trunk and has a curved surface convex upward (in the drawing). The length of the top of the head is typically about D (FIG. 1B) or less and about d (FIG. 1B) or less about the structural unit aggregate.

  Furthermore, since active nitrogen is not used as a raw material as will be described later, other atoms such as nitrogen are not included in the graphite network surface of the structural unit. For this reason, the crystallinity of the fiber is good.

  In the fine carbon fiber, as shown in FIG. 1B, 2 to 30 of such structural units share the central axis to form a structural unit aggregate 21. That is, adjacent structural units form a joint portion with the base surface of the graphite crystal, and the structural unit assembly 21 has at least one special coupling portion. The number of stacked layers is preferably 2 to 25, and more preferably 2 to 15.

  The outer diameter D of the body part of the structural unit assembly 21 is 5 to 40 nm, preferably 5 to 30 nm, and more preferably 5 to 20 nm. When D is increased, the diameter of the fine fibers formed is increased, so that a large amount of addition is required in order to impart functions such as conductive performance in the composite with the polymer. On the other hand, when D becomes small, the diameter of the fine fibers formed becomes thin and the aggregation of the fibers becomes strong. For example, in the preparation of a composite with a polymer, it becomes difficult to disperse. The measurement of the trunk outer diameter D is preferably performed by measuring at three points (1/4) L, (1/2) L, and (3/4) L from the top of the aggregate. In addition, although the trunk | drum outer diameter D is shown for convenience in FIG.1 (b), the value of actual D has the preferable average value of the said 3 points | pieces.

  The inner diameter d of the aggregate body is 3 to 30 nm, preferably 3 to 20 nm, more preferably 3 to 10 nm. The measurement of the trunk inner diameter d is also preferably measured and averaged at three points (1/4) L, (1/2) L, and (3/4) L from the top of the structural unit assembly. . In addition, although the trunk | drum internal diameter d is shown in FIG.1 (b) for convenience, the actual value of d has the preferable average value of the said 3 points | pieces.

  The aspect ratio (L / D) calculated from the length L of the structural unit aggregate 21 and the body outer diameter D is 2 to 150, preferably 2 to 50, more preferably 2 to 30, and still more preferably 2 to 2. 20. When the aspect ratio is large, the structure of the formed fiber approaches a cylindrical tube shape, and the conductivity in the fiber axis direction of one fiber is improved. However, the open end of the graphite network surface constituting the structural unit body is a fiber. Since the frequency of exposure to the outer peripheral surface is reduced, the conductivity between adjacent fibers is deteriorated. On the other hand, when the aspect ratio is small, the open end of the graphite mesh surface constituting the structural unit body portion is more frequently exposed to the outer peripheral surface of the fiber, so that the conductivity between adjacent fibers is improved. Since many short graphite mesh surfaces are connected in the axial direction, conductivity in the fiber axial direction of one fiber is impaired.

  As shown in FIG. 2A, the fine carbon fiber is formed by further connecting the aggregates in a head-to-tail manner. The head-to-tail style is a structure of fine carbon fibers in which the joining portions of the adjacent aggregates are the top (Head) of one aggregate and the lower end (Tail) of the other aggregate. ) In combination. Specifically, the form of the joining portion is the top of the structural unit of the outermost layer of the unit assembly 21b through the graphite crystal basal plane of the structural unit of the innermost layer at the lower end opening of the first structural unit assembly 21a. A graphite basal plane is formed, and adjacent structural units are joined to each other via the graphite basal plane. Furthermore, the top of the third structural unit assembly 21c is inserted into the lower end opening of the second structural unit assembly 21b, and this further continues to form a fiber.

  Each joint part forming one fine fiber of fine carbon fibers does not have structural regularity, for example, the fiber axis direction of the joint part of the first aggregate and the second aggregate The length of is not necessarily the same as the length of the junction of the second assembly and the third assembly. In addition, as shown in FIG. 2 (a), the two structural unit assemblies to be joined may be connected linearly sharing the central axis, but the structural unit assemblies 21b and 21c in FIG. 2 (b). As described above, the central axis may be joined without being shared, resulting in a bent structure at the joint. The length L of the structural unit aggregate is generally constant for each fiber. However, in the vapor phase growth method, since raw material and by-product gas components and catalyst and product solid components coexist, in the exothermic carbon deposition reaction, a heterogeneous reaction consisting of the gas and solid is performed. A temperature distribution is generated in the reactor, such as a locally high temperature is formed depending on the flow state of the mixture, and as a result, some variation in the length L may occur.

  In XRD of fine carbon fiber, the peak half-value width W (unit: degree) of the 002 plane measured is in the range of 2-4. When W exceeds 4, the graphite crystallinity is low and the conductivity is low. On the other hand, when W is less than 2, the graphite crystallinity is good, but at the same time, the fiber diameter becomes large, and a large amount of addition is required to impart functions such as conductivity to the resin.

  The graphite plane distance d002 obtained by XRD measurement of fine carbon fibers constituting the fine carbon fibers is 0.350 nm or less, preferably 0.341 to 0.348 nm. If d002 exceeds 0.350 nm, the graphite crystallinity is lowered and the conductivity is lowered. On the other hand, the fiber of less than 0.341 nm has a low yield in production.

  The ash content contained in the fine carbon fiber is 4% by weight or less, and refining is not required for normal use. Usually, it is 0.3 wt% or more and 1.5 wt% or less, more preferably 0.3 wt% or more and 1 wt% or less. The ash content is determined from the weight of oxide remaining after burning 1 g or more of fiber.

  Immediately after the production by the vapor phase growth method described later, fine carbon fibers having the above characteristics form an aggregate intricately intertwined into a mass of several tens μm to several mm. In the present invention, an agglomerate can be obtained by applying an impact force to the massive agglomerate by a method described later and crushing it. Fine carbon fibers with fine cracks that are divided and made into fine particles while being cut by the crushing process, the bulk density does not change, and the cohesive force between the fine carbon fibers is weakened Diatomaceous agglomerates. Fine carbon fiber diatomaceous agglomerates are generally spherical bodies that are easy to flow and disperse, and therefore facilitate the opening and dispersion of the agglomerates in a kneading composite with a polymer.

  When impact force is applied to the aggregates of fine carbon fibers, the joints of the structural unit aggregates are joined at the graphite bases adjacent to each other. Sliding easily occurs between them, and the structural unit aggregate is cut so as to be pulled out from each other and shortened. At this time, since the structural unit aggregate has a structure joined by van der Waals force, the joined portion can be separated with small energy, and the obtained fine carbon fiber is not damaged at all. In addition, fine carbon fibers cut by crushing are derived, but the fibers gather together in diatomaceous agglomerates that are atomized by van der Waals forces between the fibers, and each fine carbon fiber is independent. And never exist.

  FIG. 4 shows a state in which the impact force is applied to the fine carbon fiber. In this case, the force applied to the points A, B, and C acts as a compressive force perpendicular to the fiber axis direction and a tension parallel to the fiber axis direction with the B ′ point as a fulcrum. This tension acts at the joint of the structural unit assembly, which has the lowest tensile strength of the fiber of the present invention, in other words, easily slips between the graphite AB planes (between the graphite base surfaces), and the fibers are separated and cut at this portion. Is done.

  On the other hand, fine carbon fibers having no defects, which are called normal carbon nanotubes, are made of carbon SP2 bonds, so that not only a great deal of energy is required to cut these bonds, but they are also cut. The outer wall of the fiber is severely damaged.

  The graphite network surface of the portion of the structural unit assembly joint cut out is exposed on the outer peripheral surface of the fiber, and the end surface of the graphite layer exists as a more active site. As a result, the conductivity between adjacent fibers by the jumping effect (tunnel effect) due to the jumping out of the π electrons is less than the fine carbon fiber before pulverization without impairing the conductivity in the fiber axis direction of one fiber. Is expected to be further improved and the affinity with the polymer is also improved.

  The fine carbon fiber diatomaceous agglomerates obtained by such partial fiber shortening have several structural unit aggregates (ie, 2 to 9) to several tens (ie, 100 or less, 80 (Up to about 70, preferably up to about 70), preferably about 10 to 50 fine carbon fibers connected to each other are secondary structures intertwined with each other. The aspect ratio of one fine carbon fiber forming the diatom-like aggregate of fine carbon fibers is about 5 to 200. A more preferred aspect ratio is 10 to 50. Even if an impact force is applied, the fiber straight body portion composed of the carbon SP2 bond of the structural unit assembly does not cause the fiber to be cut and is smaller than the structural unit assembly.

Here, the diatomaceous agglomerates of fine carbon fibers have a generally spherical shape, and generally have a rounded shape, such as an elliptical sphere or egg shape, from a nearly spherical shape. Specifically, for example, it means that the ratio (r ₁ / r ₂ ) between the longest axis r ₁ and the shortest axis r ₂ when the aggregate is viewed from one direction is in the range of 1 to 2. .

  The particle diameter of the fine carbon fiber diatom aggregates subjected to the crushing treatment is preferably 1 to 150 μm, and more preferably 2 to 120 μm.

  The bulk density of the diatomaceous agglomerates of fine carbon fibers is preferably 0.05 to 0.15 g / ml, more preferably 0.08 to 0.11 g / ml. As shown in Examples 1 and 2, the bulk density hardly changes before and after the crushing treatment by impact force.

  Next, the manufacturing method of the diatomaceous aggregate of the fine carbon fiber of this invention is demonstrated.

<Method for producing agglomerates of fine carbon fibers>
First, the manufacturing method of the aggregate of the fine carbon fiber which is the raw material of the diatomaceous aggregate of the fine carbon fiber of the present invention is as follows. Using a catalyst in which magnesium is replaced by a solid solution with an oxide having a spinel crystal structure of cobalt, a mixed gas containing CO and H ₂ is supplied to the catalyst particles, and the fine carbon fibers in a lump are formed by vapor phase growth. Produce an assembly.

The spinel type crystal structure of cobalt in which Mg is substituted and dissolved is represented by Mg _x Co _3-x O _y . Here, x is a number indicating the replacement of Co by Mg, and formally 0 <x <3. In addition, y is a number selected so that the entire expression is neutral in terms of charge, and formally represents a number of 4 or less. That is, in the spinel oxide Co ₃ O ₄ of cobalt, there are divalent and trivalent Co ions, where the divalent and trivalent cobalt ions are represented by Co ^II and Co ^III , respectively. A cobalt oxide having a spinel crystal structure is represented by Co ^II Co ^III ₂ O ₄ . Mg displaces both Co ^II and Co ^III sites and forms a solid solution. When Mg substitutes Co ^III for solid solution, the value of y becomes smaller than 4 in order to maintain charge neutrality. However, both x and y take values in a range where the spinel crystal structure can be maintained.

  As a preferable range that can be used as a catalyst, the solid solution range of Mg has a value x of 0.5 to 1.5, and more preferably 0.7 to 1.5. When the value of x is less than 0.5, the catalyst activity is low and the amount of fine carbon fibers produced is small. When the value of x exceeds 1.5, it is difficult to prepare a spinel crystal structure.

  The spinel oxide crystal structure of the catalyst can be confirmed by XRD measurement, and the crystal lattice constant a (cubic system) is in the range of 0.811 to 0.818 nm, more preferably 0.812. ~ 0.818 nm. If “a” is small, the solid solution substitution of Mg is insufficient and the catalytic activity is low. Also, the spinel oxide crystal having a lattice constant exceeding 0.818 nm is difficult to prepare.

  The reason why such a catalyst is suitable is that, as a result of the substitutional dissolution of magnesium in the spinel structure oxide of cobalt, the present inventors formed a crystal structure in which cobalt is dispersedly arranged in a magnesium matrix. Thus, it is presumed that the aggregation of cobalt is suppressed under the reaction conditions.

  The particle size of the catalyst can be selected as appropriate. For example, the median diameter is 0.1 to 100 μm, preferably 0.1 to 10 μm.

  The catalyst particles are generally used by being applied to a suitable support such as a substrate or a catalyst bed by a method such as spraying. The catalyst particles may be sprayed directly onto the substrate or the catalyst bed, but the catalyst particles may be sprayed directly, but a desired amount may be sprayed by suspending in a solvent such as ethanol and drying.

The catalyst particles are preferably activated before reacting with the raw material gas. Activation is usually performed by heating in a gas atmosphere containing H ₂ or CO. These activation operations can be performed by diluting with an inert gas such as He or N ₂ as necessary. The temperature at which the activation is performed is preferably 400 to 600 ° C, more preferably 450 to 550 ° C.

  There is no particular limitation on the reactor for the vapor phase growth method, and the reaction can be performed by a reactor such as a fixed bed reactor or a fluidized bed reactor.

A mixed gas containing CO and H ₂ is used as a source gas that becomes a carbon source for vapor phase growth.

The added concentration of H ₂ gas {H ₂ / (H ₂ + CO)} is preferably 0.1 to 30 vol%, more preferably 2 to 20 vol%. If the addition concentration is too low, a cylindrical graphitic network surface forms a carbon nanotube-like structure parallel to the fiber axis. On the other hand, when it exceeds 30 vol%, the inclination angle with respect to the fiber axis of the carbon side peripheral surface of the structure becomes large, and it exhibits a fishbone shape, leading to a decrease in conductivity in the fiber direction.

Further, the raw material gas may contain an inert gas. Examples of the inert gas include CO ₂ , N ₂ , He, Ar, and the like. The content of the inert gas is preferably such that the reaction rate is not significantly reduced, for example, 80 vol% or less, preferably 50 vol% or less. Further, the synthesis gas containing H ₂ and CO or the waste gas discharged from the converter can be appropriately treated as necessary.

  The reaction temperature for carrying out the vapor phase growth is preferably 400 to 650 ° C, more preferably 500 to 600 ° C. If the reaction temperature is too low, fiber growth does not proceed. On the other hand, if the reaction temperature is too high, the yield decreases. Although reaction time is not specifically limited, For example, it is 2 hours or more, and is about 12 hours or less.

  The reaction pressure for carrying out the vapor phase growth is preferably normal pressure from the viewpoint of simplifying the reaction apparatus and operation, but it is carried out under pressure or reduced pressure as long as Boudard equilibrium carbon deposition proceeds. It doesn't matter.

  According to this method for producing fine carbon fibers, it was shown that the amount of fine carbon fibers produced per unit weight of the catalyst is much larger than conventional production methods, for example, the method described in Non-Patent Document 2. . The amount of fine carbon fibers produced by this fine carbon fiber production method is 40 times or more per unit weight of the catalyst, for example, 40 to 200 times. As a result, it is possible to produce fine carbon fibers with less impurities and ash as described above.

  Although the formation process of the joints unique to the fine carbon fibers produced by this fine carbon fiber production method is not clear, the catalyst has a balance between the exothermic Boudouard equilibrium and the heat removal by the flow of the raw material gas. Since the temperature in the vicinity of the cobalt fine particles formed from oscillates up and down, it is considered that carbon deposition is formed by intermittent progress. That is, [1] formation of the top of the structure body, [2] growth of the trunk of the structure, [3] growth stop due to temperature rise due to heat generation in the above [1] and [2] processes, [4] cooling by flowing gas These four processes are repeated on the catalyst fine particles, so that it is estimated that a fine carbon fiber structure-specific joint is formed.

<Method for producing diatomaceous agglomerates of fine carbon fibers>
Next, the manufacturing method of the diatomaceous aggregate of the fine carbon fiber of this invention is demonstrated. The diatomaceous agglomerates of fine carbon fibers of the present invention are produced by applying an impact force to the fine aggregates of fine carbon fibers produced by the above method and crushing them. As a specific crushing method, a hammer mill, an ultracentrifugal mill, a pin mill, a turbo mill, or a jet mill is suitable.

  A hammer mill, an ultracentrifugal mill, a pin mill, and a turbo mill strike a lump aggregate with a swinging hammer or fixed pins, blades, and edges, and separate and cut a part of fine carbon fibers. The impact force is determined by the speed of the collision body, and is 80 m / second or less, preferably 10 m / second to 70 m / second, at the outer peripheral speed of the pulverizer. By crushing in this range, the aggregates of fine carbon fibers are opened and made into smaller particles, and a part of the fine carbon fibers are shortened (partially cut), and simultaneously pulverized. The assembled aggregates are almost spherical, that is, diatom-like aggregates. Also, the jet mill and the turbo mill may cause the shock wave generated when the compressed air flow is released from pressure to act on the aggregates, or the air streams containing the aggregates collide, and the aggregates collide, Breaks up agglomerates into diatom-like, generally spherical agglomerates by causing an air stream containing agglomerates to collide with the impact plate.

  The time for pulverizing the aggregated mass by the impact method is as short as several seconds (that is, within 5 seconds, preferably within 3 seconds, more preferably within 1 second).

  The crushing treatment of the fine aggregates of fine carbon fibers can be performed either dry or wet, but is more preferably performed dry. When the dry process is performed, not only a process for removing the solvent is required, but there is no fear that fine carbon fibers are re-agglomerated during drying to form large aggregate particles. Further, residual solvent and additives remain in the product, and when this product is used as a composite filler, there is no influence such as suppression of polymerization and suppression of physical properties. The atmosphere in the dry crushing treatment can be selected from an inert atmosphere and an oxidizing atmosphere depending on the purpose.

The diatomaceous agglomerates of fine carbon fibers according to the present invention are effective in conducting various resins or inorganic materials and assisting in conducting them. In particular, non-conductive or low-conductivity organic polymers, semi-metals, oxides, fluorides, nitrides, carbides, borides, sulfides, regardless of the shape, such as spherical, whisker, flat, or nanoparticles It is effective for conducting and assisting the conduction of inorganic compounds such as hydrides and hydrides, especially solid materials used as battery materials.
Further, the diatomaceous agglomerates of fine carbon fibers according to the present invention are made conductive and conductive by taking advantage of the high thermal conductivity and slidability characteristic of carbon having a graphite structure, as well as high tensile strength and elastic modulus. In addition to the use as an auxiliary, it is useful as a filler for a heat conductive material, a sliding material, a flame retardant and a reinforcing material by compounding with a resin or an inorganic material, or as an abrasive.

  Examples of the present invention will be described below together with comparative examples.

<Example 1>
In 500 mL of ion exchange water, 115 g (0.40 mol) of cobalt nitrate [Co (NO ₃ ) ₂ .6H ₂ O: molecular weight 291.03], magnesium nitrate [Mg (NO ₃ ) ₂ .6H ₂ O: molecular weight 256.41 102 g (0.40 mol) was dissolved to prepare a raw material solution (1). Further, 220 g (2.78 mol) of ammonium bicarbonate [(NH ₄ ) HCO ₃ : molecular weight 79.06] powder was dissolved in 1100 mL of ion-exchanged water to prepare a raw material solution (2). Next, the raw material solutions (1) and (2) were mixed at a reaction temperature of 40 ° C., and then stirred and mixed for 4 hours. The produced precipitate was filtered, washed and dried.

  After baking this, it grind | pulverized in the mortar and 43g of catalysts were acquired. The crystal lattice constant a (cubic system) of the spinel structure in the present catalyst was 0.8162 nm, and the ratio of metal elements in the spinel structure by substitutional solid solution was Mg: Co = 1.4: 1.6.

A quartz reaction tube (inner diameter: 75 mmφ, height: 650 mm) was installed upright, a support made of quartz wool was provided at the center, and 0.9 g of catalyst was sprayed thereon. After heating the furnace temperature to 550 ° C. in a He atmosphere, a mixed gas composed of CO and H ₂ (volume ratio: CO / H ₂ = 95.1 / 4.9) was used as a raw material gas from the bottom of the reaction tube. Flowing at a flow rate of 28 L / min for 7 hours, fine carbon fibers were synthesized.

  The yield was 53.1 g, and the ash content was 1.5% by weight. The peak half-value width W (degree) observed by XRD analysis of the product was 3.156, and d002 was 0.3437 nm. The TEM image of the fine carbon fiber obtained in Example 1 is shown in FIG. From the TEM image, the structural unit constituting the obtained fine carbon fiber and the parameters relating to the size of the aggregate are D = 12 nm, d = 7 nm, L = 114 nm, L / D = 9.5, and θ is 0. It was 7 ° and averaged about 3 °. Further, the number of stacked structural units forming the aggregate was 4 to 10. D, d, and θ were measured at three points (1/4) L, (1/2) L, and (3/4) L from the top of the aggregate.

  Using a swing hammer type impact crusher (sample mill) manufactured by Fuji Paudal Co., Ltd., 200 g of a lump of approximately 10 cm in length, 3 cm in width and 2 cm in thickness prepared by the above method was pulverized using Nutsche, and from 50 μm After forming 2 mm, an average particle size of 700 μm, and bulk particles having a bulk density of 0.10 g / ml, the residence time of the bulk particles in the sample mill was within 1 second. The crushing treatment was performed at a screen mesh diameter of 0.2 mm (200 μm), a hammer rotation speed of 12,000 rotations / second: an outer peripheral speed of 78.5 m / second. A diatom-like aggregate of fine carbon fibers was obtained. The obtained diatomaceous agglomerates were observed with SEM, and the particle size distribution and the shape factor were measured by image analysis of the SEM photograph. Moreover, about 85 ml of diatomaceous agglomerates were inserted without giving vibration to a 100 ml graduated cylinder, and the value obtained by dividing the weight of the diatomaceous agglomerates by volume was taken as the bulk density. As a result, the minimum particle size of the same particle is 2 μm, the maximum particle size is 80 μm, the average particle size is 25 μm, and the sphericity of the particles (the average value of the maximum length / minimum length of each particle) is 1.32. Was presenting. The bulk density was 0.11 g / ml.

<Example 2>
100 g of agglomerated fine carbon fiber agglomerates prepared by the above method using a Lecce ultracentrifugal mill (agglomerate particle size is 50 μm to 2 mm, average particle size 700 μm, bulk density 0.10 g / ml) 6000 revolutions / second: Crushing was performed at an outer peripheral speed of 31 m / second. The residence time of the massive aggregate in the centrifugal mill was within 1 second.
The obtained diatomaceous agglomerates of fine carbon fibers were made into fine particles, and the particle size, particle shape and bulk density were measured in the same manner as in Example 1. As a result, the minimum particle size of the particles is 6 μm, the maximum particle size is 120 μm, the average particle size is 40 μm, and the sphericity of the particles (the average value of the maximum length / minimum length of each particle) is 1.25, which is almost spherical. Was presenting. The bulk density was 0.09 g / ml.

<Example 3>
A suitable amount of the fine carbon fiber diatom aggregates of Example 1 and a low density polyethylene resin (LF441H manufactured by Nippon Polychem Co., Ltd.) were blended, and heated and melted and mixed uniformly at 160 ° C. with a two-roll mill. The fibers were spread and dispersed in the resin. The obtained molten composition was pelletized to obtain a conductive resin composition. From SEM observation of the conductive resin composition, fine carbon fiber aggregates of 10 μm or more were not observed. This pellet was melt-molded into a film having a thickness of 100 μm by a film molding machine. The volume resistivity (Ω · cm) of the obtained film (applied voltage: 10 V) is the same as that of the resin composition. The low resistivity meter Loresta GP (MCP-T610) and the high resistivity meter Hiresta UP (MCP- (HT450) (manufactured by Dia Instruments Co., Ltd.). The measurement results are shown in Table 1 together with the composition.

<Comparative Example 1>
Table 1 shows the results of mixing and melt-molding the bulk fine carbon fiber aggregate base material in the same manner as in Example 3 and measuring the volume resistance value of the film.

<Example 4>
An appropriate amount of the fine carbon fiber diatom aggregates of Example 2 and a polycarbonate resin (Iupilon S-3000 manufactured by Mitsubishi Engineering Plastics Co., Ltd.) were premixed with a Henschel mixer, and then the compound was mixed with a twin-screw extrusion kneader. Was melt-mixed at 250 ° C., and the molten mixture was pelletized to obtain a conductive resin composition. This pellet was hot press molded at 285 ° C. to prepare a sheet having a thickness of 100 μm. The volume resistance value (applied voltage 10 V) of the obtained film was measured. The results are shown in Table 2.

<Comparative example 2>
Mixed in the same manner as conformal Example 4 mass-like fine fine carbon fiber aggregates, and melt-molding, Table 2 shows the results of measuring the volume resistivity of the film.

<Example 5>
An appropriate amount of the diatomaceous agglomerate of carbon fibers of Example 1 and nylon 12 (3012U manufactured by Ube Industries) were premixed with a Henschel mixer, and the blend was melted at 230 ° C. with a twin-screw extruder kneader. After mixing, the molten mixture was pelletized to obtain a conductive resin composition. This pellet was hot press molded at 250 ° C. to prepare a sheet having a thickness of 100 μm. The volume resistance value (applied voltage 10 V) of the obtained film was measured. The results are shown in Table 3.

<Comparative Example 3>
Table 3 shows the results of mixing and melt-molding the bulk fine carbon fiber aggregate base material in the same manner as in Example 5 and measuring the volume resistance value of the film.

  The conductive resin composition containing the fine carbon fiber diatom aggregates of the present invention exhibits high conductivity while maintaining the original physical properties of the resin. Therefore, as an electromagnetic shielding member, an antistatic component, an electrostatic coating member in the electric and electronic fields and the automobile field, and further, trays, packaging materials, building materials for clean rooms, dust-free clothing, It is useful for applications such as electronic device conductive members (belts, sheaths, rolls, connectors, gears, tubes, etc.).

DESCRIPTION OF SYMBOLS 11 Structural unit 12 Head top part 13 Traction part 21, 21a, 21b, 21c Assembly

Claims (11)

It is obtained by crushing agglomerates of fine carbon fibers produced by a vapor phase growth method,
The diameter is 1-150 μm, the bulk density is 0.05-0.15 g / ml,
The fine carbon fibers, at least one have the structure structural unit aggregate constituting the carbon fiber is bonded via the graphite basal plane with each other,
The structural unit constituting the structural unit aggregate has a top portion and a trunk portion having an open end, and has a rotating body shape rotated about a central axis. , Fine carbon fiber aggregates.   In the fine carbon fiber, the graphite net surface forms a structural unit having a closed top portion and a trunk portion having an open lower portion, and the structural unit is formed in a layered form with 2 to 30 layers sharing a central axis. The fine structure according to claim 1, wherein the structural unit aggregates are stacked to form a structural unit aggregate, and the structural unit aggregates are continuously bonded in a head-to-tail manner via each graphite base surface. Carbon fiber aggregates.   The outer diameter D of the end of the aggregate body is 5 to 40 nm, the inner diameter d is 3 to 30 nm, and the aspect ratio (L / D) of the aggregate is 2 to 150. Or an aggregate of fine carbon fibers according to 2;   The fine carbon fiber aggregate according to any one of claims 1 to 3, wherein the ash content is 4% by weight or less.   The peak half-value width W (unit: degree) of the 002 plane of fine carbon fibers measured by X-ray diffraction method is 2-4. Agglomerates of fine carbon fibers.   The fine carbon fiber according to any one of claims 1 to 5, wherein a fine carbon fiber has a graphite plane interval (d002) of 0.341 to 0.350 nm as measured by an X-ray diffraction method. Fiber agglomerates.   It is used as a conductive material, a conductive auxiliary material, a heat conductive material, a sliding material, a reinforcing material, a flame retardant material and an abrasive material, and the fine carbon fiber aggregation according to any one of claims 1 to 6, Use of collectives. Crushing treatment is performed by applying impact force to fine carbon fibers grown by supplying a mixed gas containing CO and H ₂ on a catalyst containing cobalt spinel oxide in which magnesium is substituted and dissolved. A method for producing an aggregate of fine carbon fibers, characterized in that:
The fine carbon fiber has at least one structure in which structural unit aggregates constituting the carbon fiber are bonded to each other via a graphite base surface;
A fine carbon fiber characterized in that the structural unit constituting the aggregate of structural units has a top shape and a body portion having an open end, and has a shape of a rotating body rotated about a central axis. A method for producing an aggregate . Said spinel-type _oxide, when expressed in _{Mg x Co 3-x O y} , the value of x indicating a solid solution range of magnesium, to claim 8, characterized in that 0.5 to 1.5 The manufacturing method of the aggregate of the fine carbon fiber of description.   The fine carbon fiber aggregate according to claim 8 or 9, wherein a hammer mill, an ultracentrifugal mill, a pin mill, a turbo mill, or a jet mill that generates an impact action during the crushing treatment is used. Production method.   The method for producing a fine carbon fiber aggregate according to any one of claims 8 to 10, wherein the crushing treatment with the impact force is performed in a dry manner without using an additive.