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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
method for producing a carbonaceous fiber sheet, and more particularly to a method for
producing a sheet obtained by binding carbonaceous fibers by a vapor phase method.
(Conventional art) Carbon fiber is a material which is rapidly expanding in recent years as
various composite materials due to its excellent mechanical properties. Conventional carbon
fibers have been produced by methods such as carbonizing organic fibers, but recently, attempts
have been made to produce carbon fibers by a gas phase method in which carbon fibers are
produced by thermal decomposition and catalytic reaction of hydrocarbons. □ As carbon fibers
used in conventional fiber composite materials, it is generally known that the smaller the
diameter is, the larger the contact surface precision of the resin or binder is, so that the
reinforcing effect or the binding property is excellent. In particular, carbon fibers having a
diameter as small as possible are desired because their wettability with resins is not good.
However, carbon fibers obtained by preparing conventional acrylic fibers or suspending a pinch
are only about 6 to 10 μm in diameter because spinning of precursor fibers is difficult. On the
other hand, it is known that carbon fibers can be obtained by thermal decomposition of
hydrocarbons in the presence of metals or metal compounds (for example, industrial materials,
July, 1995, p. 109, Endo, Koyama), In this method, fine particles of transition metal are dispersed
in advance on a substrate, and the substrate is placed in a reaction tube of an electric furnace,
and after setting the furnace temperature to a predetermined temperature, the hydrocarbon is
subjected to a flow of mixed gas containing hydrogen gas. The reaction is to produce fibers on
the substrate. In the fibers obtained by this method, the metal fine particles on the substrate
become growth nuclei, or the size of the metal particles varies, or the uniform dispersion thereof
is difficult, so the obtained fiber diameter is also 4 to 4 The variation was as large as 15 μm. In
addition, even if fine fibers were obtained, they were extremely difficult to be collected because
the fiber length is short and there is no tS shrinkage. Furthermore, according to JP-A-58-180615,
ultra-fine powders of refractory metals, for example, metals that do not vaporize at 950-1300 °
C. or oxides or nitrides thereof and salts thereof are suspended in the pyrolysis zone of
hydrocarbons. It is shown that carbon fiber is produced and grown by the presence of carbon
dioxide, but in this method, if the ultrafine powder adheres to it, the carbon fiber grows from
there and the branched portion Only a large number of fibers and a small fiber length / diameter
were obtained. When a sheet-like product is produced using the conventional carbon fibers as
described above, the diameter of the carbon fibers is large, the L / D is small, and the fibers are
less entangled because there is no crimp, and the sheet-like It is difficult to form a product, and
the adhesion to a resin and a binder is not sufficient, so the conductivity is also poor.
(Problems to be Solved by the Invention) The object of the present invention is that the diameter
of the fiber is extremely thin and has sufficient L / D, and when it is formed into a sheet, the
degree of entanglement between the fibers is large, and the electrical characteristics And
providing a process for producing a carbonaceous fibrous sheet having excellent mechanical
properties. (Means for Solving the Problems) In the present invention, the diameter of the fiber is
0.05 to 4 μm 1 fiber length / fiber diameter is 20 to 100 (the number of 1 line is 1 or more, the
crimp degree is 0.5 to 50% And, if necessary, a carbonaceous fiber formed by arranging a layer
of carbon which is easily converted to graphite or graphite parallel to the longitudinal axis in an
annual ring shape, and then mixing or not mixing with other fibers It is characterized in that it is
formed into a sheet form below, and the above-mentioned carbonaceous fibers are bound by selffusion of a binder or the above-mentioned other fibers. The carbonaceous fiber used in the
present invention has a fiber diameter of 05 to 4 .mu.m, preferably 0.1 to 3 .mu.m,
most preferably 0.2 to 2 pm, L / D of the fiber is 20 to 1000, preferably ioo to 700, number of
crimps is 1 or more, I-wire degree is 0.5 to 50%, preferably 5 to 50%, graphite, or a layer of
carbon which is easily converted to graphite, in an annual ring shape parallel to the longitudinal
axis It is formed by arranging. The number of crimps refers to the total number of peaks and
valleys of bending within a fiber length of 40 μm, and the crimp degree is 40 μm of aSb
between two points of fibers in a linear distance, and the actual fiber length between them ab
was measured with a pla-meter and calculated according to the following formula (randomly the
average of 5 measurements). When the fiber diameter is more than 4 μm, the surface area per
unit weight decreases, the wettability of the fiber is deteriorated, and the crimp becomes
insufficient, which is the same as the conventional carbon fiber. Also, if it does not reach 0,05
μm, substantial production of fibers becomes difficult. If L / D of fiber is less than 20,
intermingling between fibers is reduced when it is used as a filler, sufficient conductivity can not
be obtained, and if it exceeds 1000, substantial production is difficult. Furthermore, when the
number of crimped fibers is less than 1 and the degree of linearity does not reach 0.5%,
entanglement between fibers is reduced when used as a sheet, and it is difficult to obtain
sufficient conductivity. The above-mentioned carbonaceous fiber is produced by introducing
hydrocarbons and a specific organometallic compound into a heating zone together with a
carrier medium (carrier gas) as required, and pyrolyzing and catalyzing the hydrocarbons. .
Hydrocarbons used as a raw material are not particularly limited, and are solid hydrocarbons at
room temperature including anthracene, naphthalene and the like, carbon hydrogen hydrogen at
room temperature liquid including benzene, toluene, hexane, isooctane and the like, Or any of
gaseous hydrocarbons including methane, propane, ethylene, acetylene and the like may be used.
Further, as the organic metal compound, Group 1 Va (especially T s% Z r), Group Va (especially
v), Group a (especially Cr, Mo) of the periodic table. W), compounds of metals belonging to Group
a (especially Mn), Group 1 (especially Fe% Go, Ni, Ru, Rh, Pd, Os, Ir% Pt), especially
cyclopentajenyl-based metals Compounds, carbonyl metal compounds, benzene-metal
compounds, alkyl, allyl or alkynyl metal compounds, β-diketone metal complexes, keto acid ester
metal complexes, metal carboxylates, their substituted products, derivatives and the like are
preferably used. Among these, iron, such as bis (cyclopentajenyl) iron, cyclopentajenyl
compounds, such as nickel or cobalt, iron carbonyl, nickel carbonyl, cobalt carbonyl,
cyclopentajenylcarbonyl iron, such as iron, nickel or cobalt Iron, nickel or cobalt complexes such
as iron complexes of carbonyl compounds such as di or dolypsacetylacetone, irons such as iron
fumarate, iron naphthenate, fumaric acid such as nickel or cobalt, and carboxylic acids of higher
hydrocarbons Salts, (and their derivatives give good results. As a method of supplying the
organometallic compounds, these may be directly heated and supplied in a gaseous state, or the
organometallic compounds may be melted in a liquid of hydrocarbon and then be supplied by
heating or spouted. And other methods are used. The feed amount of the organometallic
compound (feed weight by weight of each spectrum) is at least 0.01% by weight, preferably at
least 0.05, particularly preferably at least 0.2% by weight, based on the mixture with the
hydrocarbon. When the amount of the organic metal compound is too low, fibrous materials tend
to be formed <<. The temperature range for introduction of hydrocarbons and organometallic
compounds is suitably 1500 ° C. or less, preferably 1300 ° C. or less, particularly preferably
100 to 500 ° C. When the temperature at the introduction position is too low, it is difficult for
the raw material to maintain the gas phase state, and it is also not preferable for activation of the
organic metal compound. If the temperature is higher than 1500 ° C., carbonization tends to
increase the formation of particulates, causing clogging and decreasing the yield of fibers. The
reaction heating temperature zone is 500 to 1800 ° C., preferably 800 to 1500 ° C.,
particularly preferably 900 to 1500 ° C. When the temperature of the reaction part is less than
900 ° C., particulate matter is easily generated. In general, the higher the temperature, and the
more disturbed the hydrocarbon (or carrier medium) flow path, the higher the number of crimps
and the crimped fibers are obtained.
The carbonaceous fiber thus obtained is formed into a sheet by a known method after
graphitizing as it is or by heat treatment at 2000 ° C. or higher. As a method of forming the
sheet-like material, either a dry method or a wet method can be applied. For example, the
obtained carbonaceous fiber is crushed by a mill or the like if necessary, and then deposited or
pressed to form a sheet, and then the formed product is impregnated with a binder, or dipped
and dried to solidify, It is manufactured by binding carbonaceous fibers. In order to form a
carbonaceous fiber in the form of a deposit or sheet, the carbonaceous fiber is dispersed in water
together with a dispersant, filtered through a filter to form a paper-made sheet, and a binder is
attached thereto to bind the fibers together. Or, after mixing fibers made of thermoplastic resin
with other carbonaceous fibers to form a deposit of the mixed fibers, the mixture is heated to a
temperature higher than the melting point of the other fibers to cause self-fusion. Or a method of
compressing the aggregate of carbonaceous fibers with a roll or the like. As the binder, known
ones can be used, and for example, thermoplastic or thermosetting resins of phenol type, vinyl
alcohol type, polyester type, polyamide type, and rubber such as butyl rubber are dissolved in a
suitable solvent to be liquid. Those used are preferably used. In order to attach the binder to the
carbonaceous fiber, the liquid may be impregnated, spread or sprayed onto the carbonaceous
fiber. (Effects of the Invention) The carbonaceous fiber sheet obtained by the present invention is
a sheet having excellent contact with a large number of contact points and having excellent
conductivity because the constituent fibers are extremely thin and has a stir. It can be a thing. In
addition, since a carbonaceous fiber produced by a vapor phase method is used, a sheet having
excellent mechanical properties such as strength and Young's modulus can be obtained, and can
be effectively used as a material for a filter or the like. Due to the above properties, the sheet of
the present invention is effectively used as, for example, a battery electrode agent having a small
current loss, a filter having a large surface area and capable of filtering small diameter particles,
and various acoustic equipment diaphragms etc. can do. Hereinafter, examples of the present
invention will be described. Example 1 A mixed solution of 1.5% by weight of iron carbonyl
mixed in benzene is introduced into a furnace whose center is heated to 1200 ° C., as a carrier
gas, hydrogen and argon together with a 1: 1 mixed gas, The carbonaceous fiber obtained by
pyrolyzing a carbonaceous fiber is 0 ° 5, crm, L / D is 300 to 1000, crimp number 1 to 3, crimp
degree 15%, electron It was found from analysis by a microscope that the carbon layers were
arranged in an annual ring shape in the cross section and almost parallel to the longitudinal axis
The carbonaceous fiber was graphitized by heat treatment under argon atmosphere at 2700 °
C. for 30 minutes. The obtained carbonaceous fiber was subjected to X-ray analysis (the 002
plane spacing do02 was 36 people, and the crystal size LC in the C-axis direction was 262
people. The carbonaceous fiber was crushed by a small mill, and the L / D of the fiber was
adjusted to 300 to 600. In this way, 100 parts by weight of the pulverized polyvinyl alcohol fiber
40 parts by weight to 1 to 3 m, 50 parts by weight of a polymeric anionic surfactant Polyster OM
(trade name of Nippon Oil and Fats Co., Ltd.) as a dispersant, It was mixed in water 21 with 110
parts by weight of acrylamide as a thickener and stirred with a mixer. The mixed solution was
supplied to a papermaking machine equipped with a No. 180 filter, to make a papermaking
sheet, dried with a hot air drier at 80 ° C., and at the same time, the polyvinyl alcohol fiber was
fused. The basis weight of the obtained carbonaceous fiber sheet was 36 g / rrr, and when the
electrical resistance of the surface was measured, it was about 8 to 15 Ω in the vertical and
horizontal directions and 1 to 6 Ω in the thickness direction. Further, when the obtained sheet
was passed through water in which silicon powder having an average particle diameter of about
1 μm was suspended as a filter, most of the silicon powder was removed by the sheet.
Comparative Example 1 A carbonaceous fiber produced by sintering an acrylic fiber was heattreated in the same manner as in Example 1, and then subjected to 1 to 3 fi. . The basis weight of
the obtained sheet was 29 g / rrr. The electric resistance of the surface was measured to be 100
to 200 Ω in the longitudinal and lateral directions, and 10 to 15 Ω in the thickness direction.