JP2011093758A - Carbonaceous material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbonaceous material having high strength using carbon fibers which may be largely produced as recycled articles and mill ends from now on. <P>SOLUTION: The carbonaceous material is composed of carbon fibers with the average fiber length of ≤1 mm and a carbonaceous matrix, and has porosity of 15 to 30%. When the porosity of the carbonaceous material becomes less than 15%, owing to the short carbon fibers, large cracks are easy to be generated upon firing, and a carbonaceous material having low strength is made easy to be produced. When the porosity is ≥30%, adhesion between the carbon fibers is made weak, and the strength of the carbonaceous material is made low. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a carbonaceous material used in a high temperature environment such as solar cell manufacturing, nuclear power, nuclear fusion device, aerospace related, single crystal manufacturing device, semiconductor manufacturing device such as epitaxial growth, optical glass, optical fiber manufacturing device, metallurgy, casting, etc. Regarding materials.

For carbon fiber,
1) Light (specific gravity is 1/4 that of iron)
2) High strength (specific strength is 10 times that of iron)
3) High elasticity (specific modulus is 7 times that of iron)
4) Excellent chemical stability (no rust or deterioration)
There are advantages such as. For this reason, it has been used for relatively small consumer products such as golf clubs and fishing rods, and has accumulated results. It has come to be used in large quantities over a wide range.
In such applications, fabrics can be made by winding “strands” that bundle multiple fibers so that the fibers are not cut as much as possible so that the strength of the fibers can be fully demonstrated. CFRP (Carbon Fiber Reinforced Plastics), which is a composite material with resin by a method such as cross winding, is used.
In recent years, various studies have been conducted on how to use a large amount of carbon fiber fibers and fabric waste and discarded CFRP due to the problem of waste disposal.
Carbon fiber can be obtained by firing and carbonizing acrylic fiber or fiber originating from pitch at 1000 to 3000 ° C., but it needs to be treated at high temperature, so it has great energy at the manufacturing stage. Is used.
Recycling carbon fibers has been attempted for such waste disposal problems and energy reduction in the manufacturing stage (for example, Patent Document 1 and Non-Patent Document 1). Such recycled carbon fibers have a short fiber length and cannot be used in filament winding or cross winding applications that require the above-mentioned fiber length, but in CFRP applications, they can be used as reinforcing materials. It has become possible to obtain relatively high strength CFRP by uniformly dispersing in resin and molding.
In particular, milled fibers pulverized to shorten the fiber length can be easily obtained as long as they are pulverized regardless of the original form of carbon fiber, such as woven fabric or filament winding. Is easy.

JP-A-2005-307121

Sadayuki Sugawara, “Proposals from the Material Industry to Low Environmental Impact Society” [on line], June 19, 2008, Ministry of the Environment HP, [October 30, 2009 search], Internet <URL: http : //www.env.go.jp/council/06earth/y069-04/mat03.pdf>

However, until now, recycled carbon fibers have been limited to CFRP. Since it is difficult to form woven fabrics and strands with recycled carbon fiber, it is difficult to form composite materials using filament winding and cross winding methods. It can be used only in the form of chopped fibers cut to a length of 1 mm or milled fibers pulverized to a length of 1 mm or less. With CFRP, a relatively high strength CFRP could be obtained simply by molding a resin and a short cut carbon fiber. However, when used as a carbonaceous material that can be used at high temperatures, the fiber length of the carbon fiber is short. Therefore, the fiber and the carbonaceous matrix are not sufficiently entangled, and the firing shrinkage behavior of the fiber and the carbonaceous matrix is different, so that sufficient adhesive strength cannot be obtained. Also, as the carbonaceous matrix, those obtained by firing a phenol resin with a high carbonization yield or a high melting point pitch, etc. are used, but when formed into a predetermined shape with a high density, the pressure of the gas generated during the firing process As a result, the strength is greatly reduced by swelling, many microcracks, and voids. In particular, milled fibers having a short fiber length (1 mm or less) have been difficult to use as heat resistant carbon materials. For this reason, it has been difficult to use chopped fibers and milled fibers as carbon fiber reinforced carbon composites.
An object of the present invention is to provide a high-strength carbonaceous material using carbon fibers that can be generated in large quantities in the future as recycled products or mill ends.

(1) A carbonaceous material comprising a carbon fiber having an average fiber length of 1 mm or less and a carbonaceous matrix, and having a porosity of 15 to 30%.
(2) The carbonaceous material according to (1), which has a porosity of 15 to 25%.
(3) The carbonaceous material according to (1) or (2), wherein the carbon fiber volume fraction is 30% or more.

  According to the present invention, a high-strength carbonaceous material can be obtained even with fibers having an average fiber length of 1 mm or less, which is difficult to use as a heat-resistant carbonaceous material.

The reference figure which calculates the porosity and fiber volume ratio of the carbonaceous material of this invention. (A) The reference figure which calculates the porosity and fiber volume ratio of the carbonaceous material of Table 1. FIG. (B) Reference diagram for calculating the porosity and fiber volume ratio of the carbonaceous material in Table 2. The figure which shows the relationship between the carbon fiber volume fraction-porosity of an Example, and bending strength.

The carbonaceous material of the present invention is composed of carbon fibers and a carbonaceous matrix, and has a specific porosity. In the present invention, the carbon fiber volume fraction means a value obtained by dividing the volume occupied by carbon fibers by the total volume. Further, the carbonaceous matrix is obtained by dividing the volume occupied by the carbon matrix by the entire volume, and the porosity is obtained by dividing the volume occupied by the pores by the entire volume.
The carbonaceous matrix is a filler made of a carbonaceous material having a function of bonding carbon fibers.

  The carbon fiber contained in the carbonaceous material of the present invention is premised on an average fiber length of 1 mm or less. If the average fiber length is 1 mm or more, the fibers can be sufficiently entangled, and even if the adhesion between the carbonaceous matrix and the carbon fibers is insufficient, the carbonaceous material of the present invention can be easily secured. Even if it is not used, a sufficiently strong carbonaceous material can be obtained. However, fibers having an average fiber length of 1 mm or less can be easily obtained by pulverizing from recycled products or mill ends, but almost no entanglement between carbon fibers can be expected, and it has been difficult to obtain a carbonaceous material until now. However, a high-strength carbonaceous material can be obtained by using the present invention.

The average fiber length <L> of the carbon fibers in the present application may be measured by any method. In the raw material stage, it can be obtained by directly measuring the dispersed carbon fiber powder with a scanning electron microscope or the like. The calculation method of the average fiber length of carbon fibers can be obtained by measuring all the lengths Li of carbon fibers existing in an arbitrary region and dividing by the number n of measured carbon fibers, as shown in the following formula. it can. (Thickness and density of carbon fiber do not contribute to average fiber length)
<L> = ΣL _i / n
Moreover, you may measure the average fiber length of the carbon fiber in the state contained in a carbonaceous material by what kind of method. Although it is not easy to extract the carbon fiber alone, it can be measured by using a method such as a focused ion / electron beam processing observation apparatus (FIB-SEM). Specifically, the three-dimensional arrangement of fibers can be confirmed by SEM while processing a carbonaceous material little by little using a focused ion / electron beam or the like from the surface, and individual fiber lengths can be obtained. Furthermore, the fiber volume fraction, the carbonaceous matrix volume fraction, and the porosity can be calculated by calculating each time the area occupied by the carbon fiber portion, the carbonaceous matrix portion, and the pore portion is processed.

  In addition to directly analyzing the carbonaceous material, from the mass of the carbonaceous material, the apparent density, the mass and true density of the carbon fibers used in the production stage, the true density of the carbonaceous matrix after firing (product stage), Carbon fiber volume fraction and carbonaceous matrix volume fraction can also be calculated. These calculations are shown in Table 1 below.

  Below, the calculation method of a carbon fiber volume fraction and a porosity in case a carbonaceous material consists of carbon fiber and one type of carbonaceous matrix is demonstrated. FIG. 1 is a reference diagram for calculating the porosity and fiber volume fraction of the carbonaceous material of the present invention, and (a) is a reference diagram for calculating the porosity and fiber volume fraction of the carbonaceous material in Table 1. Such a carbonaceous material 1 is a case where the carbonaceous matrix 3 consists of one type of carbon precursor. For example, the carbonaceous material 1 obtained by mixing and carbonizing only the carbon fiber 2 and one kind of resin, or the carbonaceous material obtained by impregnating the carbon fiber 2 with only one kind of pitch.

When the mass of the carbonaceous material 1 is M _c and the density is ρ _c , the volume of the entire carbonaceous material is V _c (= M _c / ρ _c ). When the mass of the carbon fiber 2 used for manufacturing the carbonaceous material is M _f and the density is ρ _f , the volume of the carbon fiber 2 in the carbonaceous material is V _f (= M _f / ρ _f ). The carbon fiber volume fraction is k _f (= V _f / V _c ). Since the mass M _m of the carbonaceous matrix 3 is the balance, it becomes (= M _c1 −M _f ). When the density of the carbonaceous matrix 3 measured separately is ρ _m , the volume of the carbonaceous matrix 3 is V _m ( = M _m / ρ _m ). Accordingly, the volume V _{p of the} pore portion is obtained by removing the volume V _f of the carbon fiber 2 and the volume M _{m of the} carbonaceous matrix (= V _c −V _f −V _m ) from the total volume V _c . The volume fraction k _p (= V _p1 / V _c ) of the pore portion obtained by dividing this by the total volume V _c of the carbonaceous material corresponds to the porosity of the pore 4. (Fig. 1 (a))

  Next, the calculation method of the carbon fiber volume fraction and the porosity will be described in the case where the carbonaceous material is composed of carbon fibers and two types of carbonaceous matrices. FIG. 1B is a reference diagram for calculating the porosity and fiber volume ratio of the carbonaceous material shown in Table 2. Such a carbonaceous material 1 is a case where a carbonaceous matrix consists of two types of carbon precursors. For example, a carbonaceous material obtained by impregnating a carbonaceous material obtained by mixing and carbonizing only carbon fiber and one type of resin and further impregnating another carbon precursor such as pitch.

When the mass of the carbon fiber 2 used for manufacturing the carbonaceous material 1 is M _f and the density is ρ _f , the volume of the carbon fiber 2 in the carbonaceous material is V _f (= M _f / ρ _f ). . Since the mass before impregnation of the carbonaceous material (first carbonaceous material) is M _c1 and the mass M _m1 of the first carbonaceous matrix 3A is the balance, it becomes (= M _c1 −M _f ) and is measured separately. Assuming that the density of the first carbonaceous matrix 3A is ρ _m1 , the volume of the first carbonaceous matrix 3A is V _m1 (= M _m1 / ρ _m1 ). The volume V _p1 of the first pores is the total volume V _c1 excluding the volume V _f of the carbon fibers 2 and the volume V _m1 of the first carbonaceous matrix (= V _c1 −V _f −V _m ). . The carbon fiber volume ratio is k _f (= V _f / V _c1 ), and the first porosity is k _p1 (= V _p1 / V _c1 ).

  The case where the carbonaceous material thus obtained is further impregnated with a second carbon precursor to obtain a carbonaceous material composed of two types of carbonaceous matrices will be further described.

Subtracting the weight of the first carbon material _{M c1} mass _M m @ 2 of the second carbonaceous matrix 3B ₍₌ M c2 _{-M c1)} is calculated from the mass of the second carbonaceous material _{M c2.} When the density of the second carbonaceous matrix 3B measured separately is ρ _m2 , the volume of the second carbonaceous matrix 3B is V _m2 (= M _m2 / ρ _m2 ). When the masses of the first and second carbonaceous matrices are divided by the density and added together, the combined volume of the first and second carbonaceous matrices is calculated. V _m1 + V _m2 (= M _m1 / ρ _m1 + M _m2 / ρ _m2 ). Further, the volume ratio of the carbonaceous matrix can be obtained by dividing by the total volume V _{c2 of} the second carbonaceous material (= V _c1 : the carbon material of the present invention is dense and hardly changes in volume due to impregnation).

When the apparent density (second apparent density) of the second carbonaceous material is ρ _c2 , the total volume V _c2 of the carbonaceous material is M _c2 / ρ _c2 . Further, since the volume V _p2 of the second pore portion is V _c2 −V _f − (V _m1 + V _m2 ), when divided by the total volume V _c2 of the second carbonaceous material, the volume of the second pore portion The rate k _p2 can be obtained. The volume ratio k _p2 of the second pore portion corresponds to the actual porosity of the pores 4 of the carbonaceous material 1. (Fig. 1 (b))

  Furthermore, when impregnating / firing a matrix with a different true density, the matrix volume can be determined by measuring the mass of the carbonaceous material after firing, the apparent density, and the true density of the newly impregnated matrix component each time. The rate can be calculated.

  The true density of the carbonaceous matrix and carbon fiber may be measured by any method. (A carbonaceous matrix is measured after heat treatment at a firing temperature in advance.) For example, measurement with a specific gravity bottle of JIS K2151 “Cokes-Test Method”, or measurement with an auto-true denser manufactured by Seishin Corporation. I can do it.

  The porosity of the carbonaceous material of the present invention is 15-30%. If it is less than 15%, the carbon fibers are short, so that large cracks are likely to occur during firing, and a low-strength carbonaceous material can be easily produced. If it is 30% or more, the adhesion between the carbon fibers is weakened and the strength of the carbonaceous material is lowered. A desirable range of porosity is 15-25%.

  A desirable range of the carbon fiber volume fraction of the carbonaceous material of the present invention is 30% or more. If it is 30% or more, a bending strength of 100 MPa or more can be obtained. A more desirable range of the carbon fiber volume fraction is 30 to 45%.

The density (bulk density) of the carbonaceous material of the present invention is preferably 1.2 g / cm ³ or more from the viewpoint of securing the connection between the carbon fibers.

Any carbon fiber may be used in the present invention. It may be a polyacrylonitrile (PAN) type carbon fiber, a pitch type carbon fiber, or a mixture of both. Moreover, the thickness of carbon fiber is not specifically limited.
The average fiber length of the carbon fibers is 1 mm or less, preferably 0.2 to 1 mm. This is because if it is less than 0.1 mm, it acts as carbon fiber or powder, and the function as a fiber cannot be fully exhibited.
The aspect ratio of the carbon fiber is preferably 10 or more. This is because if it is 10 or less, the carbon fiber acts as a powder and the function as a fiber cannot be sufficiently exhibited. The aspect ratio is the length / diameter of the carbon fiber.

The carbonaceous matrix in the carbonaceous material of the present invention can be obtained by baking and carbonizing a binder. The binder may be any material as long as it is fired and carbonized. For example, a thermosetting resin, pitch, or the like can be used effectively, and a phenol resin, an imide resin, a furan resin, a vinylidene chloride resin, a COPNA resin, or the like can be preferably used as the thermosetting resin. The pitch can be suitably used as long as it has a high carbonization yield regardless of whether it is petroleum or coal-based. Moreover, it can utilize also with the PVC pitch obtained by heat-processing a vinyl chloride resin. Among these, high molecular weight phenol resin powder can be suitably used. For example, “Bellepearl” (registered trademark) manufactured by Air Water Co., Ltd. and “Unibex” (registered trademark) manufactured by Unitika Co., Ltd. are particularly desirable. Since these high molecular weight phenol powders have a high carbonization yield of around 70% and a fine particle size of 1 to 20 μm, they can form a uniform structure.
It is preferable that the compounding quantity of a binder shall be 100-200 mass parts with respect to 100 mass parts of carbon fibers.

The manufacturing method of the carbonaceous material of this invention can be performed as follows.
1) Carbon fiber adjustment process 2) Preform formation process 3) Press process 4) Curing process 5) First degreasing process 6) (Impregnation process)
7) (Second degreasing step)
8) Firing step It is possible to increase the density by adding the impregnation step and the second degreasing step as described above.

The role of each process will be described below.
1) Carbon fiber adjustment step When carbon fiber for CFRP is reused, the activator is attached to the fiber surface and is removed to facilitate dispersion in water. Any removal method may be used, but since it is an organic substance, it can be easily removed by heat treatment in a reducing atmosphere. Next, it is dispersed in water and pulverized with a pulverizer. The pulverizer may be a mixer that rotates blades at high speed, and “Henschel Mixer” (registered trademark) manufactured by Mitsui Mining Co., Ltd. can be used effectively. In this carbon fiber adjustment step, the average fiber length is adjusted to 1 mm or less. The reason for setting the average fiber length to 1 mm or less is that the original fiber lengths are uneven because carbon fibers are reused. If it is 1 mm or less, even if it is the end material of carbon fiber cloth, for example, even if it is powdery carbon fiber powder generated at the time of cutting, carbon fiber powder having the same fiber length can be always supplied. .

2) Preform formation step In the preform formation step, an object is to obtain a molded body of a mixture of a binder having a desired shape and carbon fibers using a mold or the like.
Any method can be used for forming the preform. Sheet winding, mold molding, papermaking, etc. can be used.
In sheet winding, a felt-like sheet made of carbon fiber and a binder is formed in advance by a method such as pressing or papermaking, and is attached to a mold or wound. The next pressing step may be performed as it is, but for ease of handling, heat may be applied to the extent that the binder does not cure to adhere the felt-like sheet so that the desired shape can be maintained.
In mold filling, a mixture of carbon fiber and binder is put into a mold having a desired shape, heated to such an extent that the binder does not harden, the binder is melted, and the mold is cooled. When the mixture is taken out from the mold after cooling, a preform having a desired shape can be obtained.
In papermaking, carbon fiber and a binder are dispersed in water to produce a slurry. Next, a suction mold having a net on the surface is connected to a vacuum pump, and the slurry is sucked and adhered to the suction mold surface. The papermaking product thus obtained can be dried to obtain a preform.
Note that a flocculant may be added to the slurry so that the carbon fibers do not pass through the suction type net. The flocculant is not particularly limited as long as the carbon fiber dispersed in the slurry can be formed into an agglomerate having a diameter of 2 to 50, for example, so as not to pass through the suction type net, but anionic, nonionic, cationic System, amphoteric polymer flocculants and the like are preferably used. A thick papermaking product can be obtained in a short time by aggregating the carbon fibers in advance. Further, starch, pulp, latex or the like may be added in order to easily maintain the shape of the papermaking body.

3) Pressing process The pressing process aims to increase the density of a preform having a desired shape.
Although the pressing method is not particularly limited, for example, flat plate press, CIP molding (cold isostatic pressing), autoclave molding, etc. can be used, and when using thermosetting resin, spring back can be kept small by using heat together. Can do.

4) Curing process The curing process is required when a thermosetting resin is used. The shape is fixed so that the molded body obtained in the pressing step is not deformed in a subsequent step. The temperature and time vary depending on the type of thermosetting resin to be used. For example, in the case of Belpearl (registered trademark) S890 grade, the gelation time is 65 seconds / 180 ° C., and it is sufficient to add more temperature and time.

5) First degreasing step In the degreasing step, the binder component is carbonized in an inert atmosphere and changed to a carbonaceous matrix. In the degreasing step, peeling, cracking, foaming and the like are likely to occur due to the gas generated from the molded body, and thus it is desirable to heat at a temperature rising rate of 100 ° C./h or less. Further, the treatment temperature is preferably at least 500 ° C. or more although it depends on the kind of binder. This is because normal organic substances are carbonized at 500 ° C. or higher.

6) (Impregnation process)
In the impregnation step, the binder component is impregnated in order to increase the density of the carbonaceous material. The binder used in the impregnation step is liquid. A melt pitch, a liquid resin solution, a resin melt or the like can be used.
Place the fired compact in an autoclave and vacuum. After completion of evacuation, the binder to be impregnated is placed in an autoclave and pressurized. It is possible to impregnate the pores inside the molded body by applying pressure.

7) (Second degreasing step)
In the second degreasing step, the binder component is carbonized in an inert atmosphere as in the first degreasing step, and changed to a carbonaceous matrix. In the degreasing step, peeling, cracking, foaming and the like are likely to occur due to the gas generated from the molded body, and thus it is desirable to heat at a temperature rising rate of 100 ° C./h or less. Further, the treatment temperature is preferably at least 500 ° C. or more although it depends on the kind of binder. This is because normal organic substances are carbonized at 500 ° C. or higher.
The impregnation step and the second degreasing step are performed as necessary when the densification is insufficient. Moreover, when densification is inadequate, you may perform an impregnation process and a 2nd degreasing process repeatedly.

8) Firing step After the first degreasing step and the second degreasing step, heat treatment is performed at 1000 to 2500 ° C. In the firing step, a thermal history is added to the matrix component so that it is thermally stabilized and is not deformed during actual use. Further, since crystal growth of the matrix component is promoted, heat and electrical conductivity are improved. In addition, since most volatile components are volatilized in the degreasing process, there is almost no mass change in the firing process compared to the degreasing process. For this reason, _{Mc2 of the} said Table 2 can substitute with the mass after a 1st degreasing process, even if it does not pass through a baking process.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.
<Example>
(1) Carbon fiber adjustment process A PAN-based end material for CFRP was prepared. The average thickness was 7 μm. In order to improve the dispersibility in water, the activator applied to the fiber surface is baked and removed in a reducing atmosphere at 550 ° C., then dispersed in water, and pulverized with a mixer until the average fiber length becomes 150 μm. Dehydrated and dried.
(2) Preform formation step For 100 parts by mass of the carbon fiber powder obtained in the carbon fiber adjustment step, 5 parts by mass of latex for maintaining the shape of the papermaking product, and 0.3 parts by mass of a flocculant (Percoll 292) A phenol resin ("Belpearl" S890 manufactured by Airwater Co., Ltd. (addition amount is Table 3)) as a binder is once dispersed in water and left to stand for aggregation, and then from the inside with a cylindrical mold having a 1 mm wire mesh on the surface. Suction was performed to form a cylindrical preform. Although it was a wire mesh with an opening of 1 mm, the carbon fibers were agglomerated, so there was almost no carbon fiber passing through the mesh. It was left as it was for a while, and after moisture was removed by gravity, it was dried with a drier at about 60 ° C.
(3) Pressing step The preform obtained in the above step was inserted into a cylindrical metal mold, and the surface was further covered with a film. The surface was placed in an autoclave and pressurized while applying heat at 150 ° C. The pressurizing pressure is shown in Table 3.
(4) Curing step When pressing in an autoclave, it can be cured simultaneously. The maximum pressure was left for 2 hours. By this step, the binder (phenol resin) was cured.
(5) Degreasing process The metal mold | die of the molded object obtained at the said process was removed, and it baked with the reducing atmosphere furnace. Firing was performed at a maximum temperature of 550 ° C. at 70 ° C./h.
(6) (Impregnation step)
If the fiber volume ratio and porosity of the present invention are not obtained by the first degreasing step, further impregnation is performed.
In this example, the sample was placed in an autoclave heated to 200 ° C., and after evacuation, a pitch having a softening point of about 80 ° C. was flowed and pressurized at 4 MPa to impregnate the molded body with the pitch. (The presence or absence of impregnation is described in Table 1)
(7) (Second degreasing step)
The molded body that has undergone the impregnation step is degreased again. The conditions were the same as in the degreasing step (5).
(8) Firing step The impregnated and non-impregnated ones were finally fired. In a reducing atmosphere, heating was performed at a temperature rising rate of 150 ° C./H, and processing was performed up to 2000 ° C. By this firing step, the adhesive force between the matrix and the carbon fiber is increased, and the strength can be expressed.
Table 3 shows the bending strength, porosity, carbon fiber volume fraction, and bulk density of the completed carbonaceous material. (Porosity and carbon fiber volume fraction were calculated from the amount of carbon fiber used, bulk density, etc.)

<Comparative example>
A carbonaceous material was manufactured through the same steps as in the example. Table 3 shows the bending strength, porosity, carbon fiber volume fraction, and bulk density of the carbonaceous material. (Porosity and carbon fiber volume fraction were calculated from the amount of carbon fiber used, bulk density, etc.)

1 carbonaceous material 2 carbon fiber 3 carbonaceous matrix 3A first carbonaceous matrix 3B second carbonaceous matrix 4 pores

Claims (3)

  A carbonaceous material comprising a carbon fiber having an average fiber length of 1 mm or less and a carbonaceous matrix, and having a porosity of 15 to 30%.   The carbonaceous material according to claim 1, which has a porosity of 15 to 25%.   The carbonaceous material according to claim 1 or 2, wherein the carbon fiber volume fraction is 30% or more.

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