Patent Application
20090124746
This invention relates to a new thermoplastic elastomeric composition. Particularly, this invention relates to a thermoplastic elastomeric composition which has an excellent compression set and which can show an excellent conductivity even after receiving deformation stresses repeatedly.
Recently, with respect to the so-called entertainment electrical appliances such as television, personal computer, digital camera, portable music player, and cellular phone, high performance and multifunction as well as downsizing have been desired. Further, in the course of realizing such appliances, the development of a flexible sheet which shows electrical conductivity or electrical controllability have been expected.
Since thermoplastic elastomer does not need a vulcanization process and it can be molded by a usual molding machine for thermoplastic resin, it has been utilized in various fields involving typically automobile parts and household electrical product parts. If such a thermoplastic elastomer is provided with a desired electrical conductivity or electrical controllability, it will be possible to contribute to the achievement of the above mentioned appliances greatly.
It has been proposed to blend a filler having a high electrical conductivity into the thermoplastic elastomer in order to give the electrical conductivity or electrical controllability to the thermoplastic elastomer.
As the conductive filler, metallic fibers and metal powder, carbon black, carbon fibers and other similar materials are used in general. When metallic fibers or metal powder are used as the electroconductive filler, however, disadvantages such as inferior corrosion resistance and worse mechanical strength will arise.
On the other hand, when carbon fibers are used as the conductive filler, although a predetermined strength and elastic modulus may be obtained by adding relatively large amounts of generic reinforcing carbon fibers, electrical conductivity generally cannot be greatly enhanced by this approach. If one attempts to attain a predetermined conductivity by adding a large amount of the fibers, one would invariably degrade the intrinsic properties of the original polymer material.
Incidentally, with respect to a carbon fiber, it is expected that the conductivity-imparting effect increases as its diameter becomes smaller at an equivalent additive amount, because the contact area between the fiber and the matrix polymer increases.
Moreover, in recent years, fine carbon fibers such as carbon nano structures, which are represented by the carbon nanotube (hereinafter, referred to also as “CNT”.) have been developed, and an attempt of adding the fine carbon fibers to the thermoplastic elastomer has been also performed (See, for instance, Patent Literature 1)
The graphite layers which compose the carbon nano structure are materials each of which takes a six membered ring's regular array normally, and which can bring specific electrical properties, as well as chemically, mechanically, and thermally stable properties. Therefore, as long as such fine carbon fiber can make use of such properties upon blending and dispersing to the solid material involving various resins, ceramics, and metals, etc., or to the liquid material involving fuels, lubricant agents, etc., its usefulness as the additive can be expected.
On the other hand, however, such fine carbon fibers unfortunately show an aggregate state even just after their synthesis. When the aggregate is used as-is, it would arrive at a conclusion that the dispersion of the fine carbon fibers does not progress very far, and thus the product obtained can not enjoy ample properties. Accordingly, giving a desired property such as electric conductivity to a matrix such as resin, it is necessitated that the fibers are added as a relatively larger amount.
Further, the products or parts made of the thermoplastic elastomer may receive deforming stresses such as tensile force, bending stress, etc., repeatedly, owing to its characteristics. Because each fine carbon fiber dispersed in the elastomer is of fibrous, simple structure, it easily migrates in the matrix when the deforming stress is applied. Thus, it is impossible to improve the compression set of the elastomer. Further, a fear that the electrical properties after repetitive use are greatly different from the initial electrical properties will arise. Thus, an improvement has been sought in the art.
Therefore, this invention aims to provide a thermoplastic elastomeric composition which can demonstrate an improved compression set and excellent electrical properties even after receiving deforming stresses repeatedly.
As a result of our diligent study for solving the above problems, we, the inventors, have found that, in order to give adequate electrical, mechanical, and thermal properties even in a small adding amount to the matrix, the effective things are to adapt carbon fibers having a diameter as small as possible; to make an areolar structure of the carbon fibers where the fibers are mutually combined tightly so that the fibers do not behave individually and which sustains their areolar state in the resin matrix; and to adapt as the carbon fibers per se ones which are designed to have a minimum amount of defects. We have also found that when the carbon fibers are formed in such a three dimensional structure as mentioned above, the structure can exhibit a kind of spike or anchor effect in the matrix of the elastomer, and thus the structure does not migrate in the matrix at the occasion of receiving deforming stress, but it can deform elastically so as to follow the deformation of the matrix, and thus, the electrical properties after repetitive use do not change from the initial electrical properties and the compression set of the matrix is also able to be improved. Finally, we have accomplished the present invention.
The present invention to solve the above mentioned problems is, therefore, a thermoplastic elastomeric composition which includes 0.1-30 parts by weight of carbon fibrous structures per 100 parts by weight of a thermoplastic elastomer, wherein the carbon fibrous structure comprises a three dimensional network of carbon fibers each having an outside diameter of 15-100 nm, wherein the carbon fibrous structure further comprises a granular part with which the carbon fibers are tied together in the state that the concerned carbon fibers are externally elongated therefrom, and wherein the granular part is produced in a growth process of the carbon fibers.
Further, the present invention to solve the above mentioned problems is a thermoplastic elastomeric composition which includes 0-100 parts by weight of a rubber component at least a part of which are cross linked per 100 parts by weight of a thermoplastic elastomer, and 0.1-30 parts by weight of carbon fibrous structures per 100 parts by weight of total amount of the thermoplastic elastomer and the rubber component, wherein the carbon fibrous structure comprises a three dimensional network of carbon fibers each having an outside diameter of 15-100 nm, wherein the carbon fibrous structure further comprises a granular part with which the carbon fibers are tied together in the state that the concerned carbon fibers are externally elongated therefrom, and wherein the granular part is produced in a growth process of the carbon fibers.
In the present invention, it is preferable that the carbon fibrous structures have ID/IG ratio determined by Raman spectroscopy of not more than 0.2.
The present invention also provides the above mentioned thermoplastic elastomeric composition, wherein the carbon fibrous structures are produced using as carbon sources at least two carbon compounds which have mutually different decomposition temperatures.
The present invention further discloses a conductive sheet which is formed using the above mentioned thermoplastic elastomeric composition.
According to the present invention, since the carbon fibrous structure is one comprising carbon fibers of a ultrathin diameter which are configured three dimensionally, and are bound tightly together by a granular part produced in a growth process of the carbon fibers so that the concerned carbon fibers are externally elongated from the granular part, the carbon fibrous structures can disperse promptly into the thermoplastic elastomer on adding, while they maintain such a bulky structure. Thus, even when they added at a small amount to the matrix, the fine carbon fibers can be distributed uniformly over the matrix. Therefore, with respect to the electrical conductivity, it is possible to obtain good electric conductive paths throughout the matrix, and thus to improve the electrical conductivity adequately. Because, the fine carbon fibers are distributed evenly throughout the thermoplastic elastomeric composition only with a small dosage. With respect to the mechanical and thermal properties, improvements can be expected in analogous fashions, since the fine carbon fibers as fillers are distributed evenly over the matrix. Further, as mentioned above, since the carbon fibrous structure can exhibit a kind of spike or anchor effect in the matrix so as to present stably in the matrix, the electrical properties after repetitive use do not change from the initial electrical properties and the compression set of the matrix is also able to be improved.
Now, the present invention will be described in detail with reference to some preferable embodiments.
The thermoplastic elastomeric composition according to this invention is characterized in that carbon fibrous structures each having a specific structure like a three dimensional network as mentioned later are contained in a thermoplastic elastomer, or a thermoplastic elastomer which includes rubber component at least a part of which is cross linked.
Each carbon fibrous structure to be used in the present invention is, as shown in SEM photo of
The reason for restricting the outside diameter of the carbon fibers which constitutes the carbon fibrous structure to a range of 15 nm to 100 nm is because when the outside diameter is less than 15 nm, the cross-sections of the carbon fibers do not have polygonal figures as described later. According to physical properties of the carbon fiber, the smaller the diameter of a fiber, the greater the number of carbon fibers will be for the same weight and/or the longer the length in the axial direction of the carbon fiber. This property would be followed by an enhanced electric conductivity. Thus, carbon fibrous structures having an outside diameter exceeding 100 nm are not preferred for use as modifiers or additives for a matrix such as a resin, etc. Particularly, it is more desirable for the outside diameter of the carbon fibers to be in the range of 20-70 nm. Carbon fibers that have a diameter within the preferable range and whose tubular graphene sheets are layered one by one in the direction that is orthogonal to the fiber axis, i.e., being of a multilayer type, can enjoy a high flexural rigidity and ample elasticity. In other words, such fibers would have a property of being easy to restore their original shape after undergoing any deformation. Therefore, even if the carbon fibrous structures have been compressed prior to being mixed into the matrix material, they tend to take a sparse structure in the matrix.
Incidentally, when annealing at a temperature of not less than 2400° C., the spacing between the layered graphene sheets becomes lesser and the true density of the carbon fiber is increased from 1.89 g/cm3 to 2.1 g/cm3, and the cross sections of the carbon fiber perpendicular to the axis of carbon fiber come to show polygonal figures. As a result, the carbon fibers having such constitution become denser and have fewer defects in both the stacking direction and the surface direction of the graphene sheets that make up the carbon fiber, and thus their flexural rigidity (EI) can be enhanced.
Additionally, it is preferable that the outside diameter of the fine carbon fiber undergoes a change along the axial direction of the fiber. In the case that the outside diameter of the carbon fiber is not constant, but changed along the axial direction of the fiber, it would be expected that some anchor effect may be provided to the carton fiber in the matrix of the elastomer, and thus the migration of the carbon fiber in the matrix can be restrained, leading to improved dispersion stability.
Then, in the carbon fibrous structure used in the present invention, fine carbon fibers having a predetermined outside diameter and being configured three dimensionally are bound together by a granular part produced in a growth process of the carbon fibers so that the carbon fibers are elongated outwardly from the granular part. Since multiple carbon fibers are not only entangled each other, but tightly bound together at the granular part, the carbon fibers will not disperse as single fibers, but will be dispersed as intact bulky carbon fibrous structures when added to the matrix of elastomer. Since the fine carbon fibers are bound together by a granular part produced in the growth process of the carbon fibers in the carbon fibrous structure to be used in the present invention, the carbon fibrous structure itself can enjoy superior properties such as electric property. For instance, when determining electrical resistance under a certain pressed density, the carbon fibrous structure to be used in the present invention shows an extremely low resistivity, as compared with that of a simple aggregate of the fine carbon fibers and that of the carbon fibrous structures in which the fine carbon fibers are fixed at the contacting points with a carbonaceous material or carbonized substance therefrom after the synthesis of the carbon fibers. Thus, when the carbon fibrous structures added and distributed in a matrix, they can form good conductive paths within the matrix.
Since the granular part is produced in the growth process of the carbon fibers as mentioned above, the carbon-carbon bonds at the granular part are well developed. Further, the granular part appears to include mixed state of sp2- and sp3-bonds, although it is not clear accurately. After the synthesis process (in the “intermediate” or “first intermediate” defined hereinafter), the granular part and the fibrous parts are continuous mutually because of a structure comprising patch-like sheets of carbon atoms laminated together. Further, after the high temperature treatment, at least a part of graphene layers constituting the granular part is continued on graphene layers constituting the fine carbon fibers elongated outwardly from the granular part, as shown in
With respect to the carbon fibers, the condition of being “extended outwardly” from the granular part used herein means principally that the carbon fibers and granular part are linked together by carbon crystalline structural bonds as mentioned above, but does not means that they are apparently combined together by any additional binding agent (involving carbonaceous ones).
As traces of the fact that the granular part is produced in the growth process of the carbon fibers as mentioned above, the granular part has at least one catalyst particle or void therein, the void being formed due to the volatilization and elimination of the catalyst particle during the heating process after the generation process. The void (or catalyst particle) is essentially independent from hollow parts which are formed in individual fine carbon fibers which are extended outwardly from the granular part (although, a few voids which happened to be associated with the hollow part may be observed).
Although the number of the catalyst particles or voids is not particularly limited, it may be about 1-1000 a granular particle, more preferably, about 3-500 a granular particle. When the granular part is formed under the presence of catalyst particles the number of which is within the range mentioned above, the granular part formed can have a desirable size as mentioned later.
The per-unit size of the catalyst particle or void existing in the granular particle may be, for example, 1-100 nm, preferably, 2-40 nm, and more preferably, 3-15 nm.
Furthermore, it is preferable that the diameter of the granular part is larger than the outside diameter of the carbon fibers as shown in
Although the concrete value for the particle diameter of the granular part will be depended on the size of the carbon fibrous structure and the outer diameters of the fine carbon fibers in the carbon fibrous structure, for example, it may be 20-5000 nm, more preferably, 25-2000 nm, and most preferably, 30-500 nm, on average.
Furthermore, the granular part may be roughly globular in shape because the part is produced in the growth process of the carbon fibers as mentioned above. On average, the degree of roundness thereof may lay in the range of from 0.2 to <1, preferably, 0.5 to 0.99, and more preferably, 0.7 to 0.98.
Additionally, the binding of the carbon fibers at the granular part is very tight as compared with, for example, that in the structure in which mutual contacting points among the carbon fibers are fixed with carbonaceous material or carbonized substance therefrom. It is also because the granular part is produced in the growth process of the carbon fibers as mentioned above. Even under such a condition as to bring about breakages in the carbon fibers of the carbon fibrous structure, the granular part (the binding site) is maintained stably. Specifically, for example, when the carbon fibrous structures are dispersed in a liquid medium and then subjected to ultrasonic treatment with a selected wavelength and a constant power under a load condition by which the average length of the carbon fibers is reduced to about half of its initial value as shown in the Examples described later, the changing rate in the mean diameter of the granular parts is not more than 10%, preferably, not more than 5%, thus, the granular parts, i.e., the binding sites of fibers are maintained stably.
In carbon fibrous structures to be used in the present invention, it is preferable that the carbon fibrous structure has an area-based circle-equivalent mean diameter of 50-100 μm, and more preferably, 60-90 μm. The “area-based circle-equivalent mean diameter” used herein is the value which is determined by taking a picture of the outside shapes of the carbon fibrous structures with a suitable electron microscope, etc., tracing the contours of the respective carbon fibrous structures in the obtained picture using a suitable image analysis software, e.g., WinRoof™ (Mitani Corp.), and measuring the area within each individual contour, calculating the circle-equivalent mean diameter of each individual carbon fibrous structure, and then, averaging the calculated data.
Although it is not to be applied in all cases because the circle-equivalent mean diameter may be influenced by the kind of matrix material such as a resin to be complexed, the circle-equivalent mean diameter may become a factor by which the maximum length of a carbon fibrous structure upon combining with a matrix such as a resin is determined. In general, when the circle-equivalent mean diameter is not more than 50 μm, the electrical conductivity of the obtained composite may not be expected to reach a sufficient level, while when it exceeds 100 μm, an undesirable increase in viscosity may be expected to happen upon kneading of the carbon fibrous structures in the matrix. The increase in viscosity may be followed by failure of dispersion of the carbon fibrous structures into the matrix.
As mentioned above, the carbon fibrous structure according to the present invention has the configuration where the fine carbon fibers existing in three dimensional network state are bound together by the granular part (s) so that the carbon fibers are externally elongated from the granular part(s). When two or more granular parts are present in a carbon fibrous structure, wherein each granular part binds the fibers so as to form the three dimensional network, the mean distance between adjacent granular parts may be, for example, 0.5-300 μm, preferably, 0.5-100 μm, and more preferably, 1-50 μm. The distance between adjacent granular parts used herein is determined by measuring distance from the center of a granular part to the center of another granular part which is adjacent the former granular part. When the mean distance between the granular parts is less than 0.5 μm, a configuration where the carbon fibers form an inadequately developed three dimensional network may be obtained. Therefore, it may become difficult to form good electrically conductive paths when the carbon fiber structures each having such an inadequately developed three dimensional network are added and dispersed to a matrix such as a resin. Meanwhile, when the mean distance exceeds 300 μm, an undesirable increase in viscosity may be expected to happen upon adding and dispersing the carbon fibrous structures in the matrix. The increase in viscosity may result in an inferior dispersibility of the carbon fibrous structures to the matrix.
Furthermore, the carbon fibrous structure to be used in the present invention may exhibit a bulky, loose form in which the carbon fibers are sparsely dispersed, because the carbon fibrous structure is comprised of carbon fibers that are configured as a three dimensional network and are bound together by a granular part so that the carbon fibers are elongated outwardly from the granular part as mentioned above. It is desirable that the bulk density thereof is in the range of 0.0001-0.05 g/cm3, more preferably, 0.001-0.02 g/cm3. When the bulk density exceeds 0.05 g/cm3, it would become difficult to improve the physical properties of the matrix such as resin with a small dosage.
Furthermore, a carbon fibrous structure to be used in the present invention can enjoy good electric properties in itself, since the carbon fibers configured as a three dimensional network in the structure are bound together by a granular part produced in the growth process of the carbon fibers as mentioned above. For instance, it is desirable that a carbon fibrous structure to be used in the present invention has a powder electric resistance determined under a certain pressed density, 0.8 g/cm3, of not more than 0.02Ω·cm, more preferably, 0.001 to 0.010Ω·cm. If the particle's resistance exceeds 0.02Ω·cm, it may become difficult to form good electrically conductive paths when the structures are added to a matrix such as a resin.
In order to enhance the strength and electric conductivity of the carbon fibrous structure used in the present invention, it is desirable that the graphene sheets that make up the carbon fibers have a small number of defects, and more specifically, for example, the ID/IG ratio of the carbon fiber determined by Raman spectroscopy is not more than 0.2, more preferably, not more than 0.1. Incidentally, in Raman spectroscopic analysis, with respect to a large single crystal graphite, only the peak (G band) at 1580 cm−1 appears. When the crystals are of finite ultrafine sizes or have any lattice defects, the peak (D band) at 1360 cm−1 can appear. Therefore, when the intensity ratio (R=I1360/I1580=ID/IG) of the D band and the G band is below the selected range as mentioned above, it is possible to say that there is little defect in graphene sheets.
Furthermore, it is desirable that the carbon fibrous structure to be used in the present invention has a combustion initiation temperature in air of not less than 750° C., preferably, 800° C.-900° C. Such a high thermal stability would be brought about by the above mentioned facts that it has little defects and that the carbon fibers have a predetermined outside diameter.
A carbon fibrous structure having the above described, desirable configuration may be prepared as follows, although it is not limited thereto.
Basically, an organic compound such as a hydrocarbon is chemical thermally decomposed through the CVD process in the presence of ultrafine particles of a transition metal as a catalyst in order to obtain a fibrous structure (hereinafter referred to as an “intermediate”), and then the intermediate thus obtained undergoes a high temperature heating treatment.
As a raw material organic compound, hydrocarbons such as benzene, toluene, xylene; carbon monoxide (CO); and alcohols such as ethanol may be used. It is preferable, but not limited, to use as carbon sources at least two carbon compounds which have different decomposition temperatures. Incidentally, the words “at least two carbon compounds” used herein not only include two or more kinds of raw materials, but also include one kind of raw material that can undergo a reaction, such as hydrodealkylation of toluene or xylene, during the course of synthesis of the fibrous structure such that in the subsequent thermal decomposition procedure it can function as at least two kinds of carbon compounds having different decomposition temperatures.
When as the carbon sources at least two kinds of carbon compounds are provided in the thermal decomposition reaction system, the decomposition temperatures of individual carbon compounds may be varied not only by the kinds of the carbon compounds, but also by the gas partial pressures of individual carbon compounds, or molar ratio between the compounds. Therefore, as the carbon compounds, a relatively large number of combinations can be used by adjusting the composition ratio of two or more carbon compounds in the raw gas.
For example, the carbon fibrous structure to be used in the present invention can be prepared by using two or more carbon compounds in combination, while adjusting the gas partial pressures of the carbon compounds so that each compound performs mutually different decomposition temperature within a selected thermal decomposition reaction temperature range, and/or adjusting the residence time for the carbon compounds in the selected temperature region, wherein the carbon compounds to be selected are selected from the group consisting of alkanes or cycloalkanes such as methane, ethane, propanes, butanes, pentanes, hexanes, heptane, cyclopropane, cyclohexane, particularly, alkanes having 1-7 carbon atoms; alkenes or cycloolefin such as ethylene, propylene, butylenes, pentenes, heptenes, cyclopentene, particularly, alkenes having 1-7 carbon atoms; alkynes such as acetylene, propyne, particularly, alkynes having 1-7 carbon atoms; aromatic or heteroaromatic hydrocarbons such as benzene, toluene, styrene, xylene, naphthalene, methyl naphtalene, indene, phenanthrene, particularly, aromatic or heteroaromatic hydrocarbons having 6-18 carbon atoms; alcohols such as methanol, ethanol, particularly, alcohols having 1-7 carbon atoms; and other carbon compounds involving such as carbon monoxide, ketones, ethers. Further, to optimize the mixing ratio can contribute to the efficiency of the preparation.
When a combination of methane and benzene is utilized among such combinations of two or more carbon compounds, it is desirable that the molar ratio of methane/benzene is >1-600, preferably, 1.1-200, and more preferably 3-100. The ratio is for the gas composition ratio at the inlet of the reaction furnace. For instance, when as one of carbon sources toluene is used, in consideration of the matter that 100% of the toluene decomposes into methane and benzene in proportions of 1:1 in the reaction furnace, only a deficiency of methane may be supplied separately. For example, in the case of adjusting the methane/benzene molar ratio to 3, 2 mol methane may be added to 1 mol toluene. As the methane to be added to the toluene, it is possible to use the methane which is contained as an unreacted form in the exhaust gas discharged from the reaction furnace, as well as a fresh methane specially supplied.
Using the composition ratio within such a range, it is possible to obtain the carbon fibrous structure in which both the carbon fiber parts and granular parts are efficiently developed.
Inert gases such as argon, helium, xenon; and hydrogen may be used as an atmosphere gas.
A mixture of transition metal such as iron, cobalt, molybdenum, or transition metal compounds such as ferrocene, metal acetate; and sulfur or a sulfur compound such as thiophene, ferric sulfide; may be used as a catalyst.
The intermediate may be synthesized using a CVD process with hydrocarbon or etc., which has been conventionally used in the art. The steps may comprise gasifying a mixture of hydrocarbon and a catalyst as a raw material, supplying the gasified mixture into a reaction furnace along with a carrier gas such as hydrogen gas, etc., and undergoing thermal decomposition at a temperature in the range of 800° C.-1300° C. By following such synthesis procedures, the product obtained is an aggregate, which is of several to several tens of centimeters in size and which is composed of plural carbon fibrous structures (intermediates), each of which has a three dimensional configuration where fibers having 15-100 nm in outside diameter are bound together by a granular part that has grown around the catalyst particle as the nucleus.
The thermal decomposition reaction of the hydrocarbon raw material mainly occurs on the surface of the catalyst particles or on growing surface of granular parts that have grown around the catalyst particles as the nucleus, and the fibrous growth of carbon may be achieved when the recrystallization of the carbons generated by the decomposition progresses in a constant direction. When obtaining carbon fibrous structures according to the present invention, however, the balance between the thermal decomposition rate and the carbon fiber growth rate is intentionally varied. Namely, for instance, as mentioned above, to use as carbon sources at least two kinds of carbon compounds having different decomposition temperatures may allow the carbonaceous material to grow three dimensionally around the granular part as a centre, rather than in one dimensional direction. The three dimensional growth of the carbon fibers depends not only on the balance between the thermal decomposition rate and the growing rate, but also on the selectivity of the crystal face of the catalyst particle, residence time in the reaction furnace, temperature distribution in the furnace, etc. The balance between the decomposition rate and the growing rate is affected not only by the kinds of carbon sources mentioned above, but also by reaction temperatures, and gas temperatures, etc. Generally, when the growing rate is faster than the decomposition rate, the carbon material tends to grow into fibers, whereas when the thermal decomposition rate is faster than the growing rate, the carbon material tends to grow in peripheral directions of the catalyst particle. Accordingly, by changing the balance between the thermal decomposition rate and the growing rate intentionally, it is possible to control the growth of carbon material to occur in multi-direction rather than in single direction, and to produce three dimensional structures that are related to the present invention. In order to form the above mentioned three-dimensional configuration, where the fibers are bound together by a granular part, with ease, it is desirable to optimize the compositions such as the catalyst used, the residence time in the reaction furnace, the reaction temperature and the gas temperature.
With respect to the method for preparing the carbon fibrous structure to be used in the present invention with efficiency, as another approach to the aforementioned one that two or more carbon compounds which have mutually different decomposition temperature are used in an appropriate mixing ratio, there is an approach that the raw material gas supplied into the reaction furnace from a supply port is forced to form a turbulent flow in proximity to the supply port. The “turbulent flow” used herein means a furiously irregular flow, such as flow with vortexes.
In the reaction furnace, immediately after the raw material gas is supplied into the reaction furnace from the supply port, metal catalyst fine particles are produced by the decomposition of the transition metal compound as the catalyst involved in the raw material gas. The production of the fine particles is carried out through the following steps. Namely, at first, the transition metal compound is decomposed to make metal atoms, then, plural number of, for example, about one hundred of metal atoms come into collisions with each other to create a cluster. At the created cluster state, it can not function as a catalyst for the fine carbon fiber. Then, the clusters further are aggregated by collisions with each other to grow into a metal crystalline particle of about 3-10 nm in size, and which particle comes into use as the metal catalyst fine particle for producing the fine carbon fiber.
During the catalyst formation process as mentioned above, if the vortex flows belonging to the furiously turbulent flow are present, it is possible that the collisions of metal atoms or collisions of clusters become more vigorously as compared with the collisions only due to the Brownian movement of atoms or collisions, and thus the collision frequency per unit time is enhanced so that the metal catalyst fine particles axe produced within a shorter time and with higher efficiency. Further, since concentration, temperature, etc. are homogenized by the force of vortex flow, the obtained metal catalyst fine particles become uniform in size. Additionally, during the process of producing metal catalyst fine particles, a metal catalyst particles' aggregate in which numerous metal crystalline particles was aggregated by vigorous collisions with the force of vortex flows can be also formed. Since the metal catalyst particles are rapidly produced as mentioned above, the decomposition of carbon compound can be accelerated so that an ample amount of carbonaceous material can be provided. Whereby, the fine carbon fibers grow up in a radial pattern by taking individual metal catalyst particles in the aggregate as nuclei. When the thermal decomposition rate of a part of carbon compounds is faster than the growing rate of the carbon material as previously described, the carbon material may also grow in the circumferential direction so as to form the granular part around the aggregate, and thus the carbon fiber structure of the desired three dimensional configuration may be obtained with efficiency. Incidentally, it may be also considered that there is a possibility that some of the metal catalyst fine particles in the aggregate are ones that have a lower activity than the other particles or ones that are deactivated on the reaction. If non-fibrous or very short fibrous carbon material layers grown by such catalyst fine particles before or after the catalyst fine particles aggregate are present at the circumferential area of the aggregate, the granular part of the carbon fiber structure to be used in the present invention may be formed.
The concrete means for creating the turbulence to the raw material gas flow near the supply port for the raw material gas is not particularly limited. For example, it is adaptable to provide some type of collision member at a position where the raw material gas flow introduced from the supply port can be interfered by the collision section. The shape of the collision section is not particularly limited, as far as an adequate turbulent flow can be formed in the reaction furnace by the vortex flow which is created at the collision section as the starting point. For example, embodiments where various shapes of baffles, paddles, tapered tubes, umbrella shaped elements, etc., are used singly or in varying combinations and located at one or more positions may be adaptable.
The intermediate, obtained by heating the mixture of the catalyst and hydrocarbon at a constant temperature in the range of 800° C.-1300° C., has a structure that resembles sheets of carbon atoms laminated together, (and being still in a half-raw, or incomplete condition). When analyzed with Raman spectroscopy, the D band of the intermediate is very large and many defects are observed. Further, the obtained intermediate is associated with unreacted raw materials, nonfibrous carbon, tar moiety, and catalyst metal.
Therefore, the intermediate is subjected to a high temperature heat treatment at 2400-3000° C. using a proper method in order to remove such residues from the intermediate and to produce the intended carbon fibrous structure with few defects.
For instance, the intermediate may be heated at 800-1200° C. to remove the unreacted raw material and volatile flux such as the tar moiety, and thereafter annealed at a high temperature of 2400-3000° C. to produce the intended structure and, concurrently, to vaporize the catalyst metal, which is included in the fibers, to remove it from the fibers. In this process, it is possible to add a small amount of a reducing gas and carbon monoxide into the inert gas atmosphere to protect the carbon structures.
By annealing the intermediate at a temperature of 2400-3000° C., the patch-like sheets of carbon atoms are rearranged to associate mutually and then form multiple graphene sheet-like layers.
After or before such a high temperature heat treatment, the aggregates may be subjected to crushing in order to obtain carbon fibrous structures, each having an area-based circle-equivalent mean diameter of several centimeters. Then, the obtained carbon fibrous structures may be subjected to pulverization in order to obtain the carbon fibrous structures having an area-based circle-equivalent mean diameter of 50-100 μm. It is also possible to perform the pulverization directly without crushing. On the other hand, the initial aggregates involving plural carbon fibrous structures to be used in the present invention may also be granulated for adjusting shape, size, or bulk density to one's suitable for using a particular application. More preferably, in order to utilize effectively the above structure formed from the reaction, the annealing would be performed in a state such that the bulk density is low (the state that the fibers are extended as much as they can and the voidage is sufficiently large). Such a state may contribute to improved electric conductivity of a resin matrix.
The carbon fibrous structures used in the present invention may have the following properties:
A) a low bulk density;
B) a good dispersibility in a matrix such as resin;
C) a high electrical conductivity;
D) a high heat conductivity;
E) a good slidability;
F) a good chemical stability;
G) a high thermal stability; and etc.
The thermoplastic elastomeric composition according to this invention is prepared by adding the carbon fibrous structures as mentioned above into a thermoplastic elastomer, or a thermoplastic elastomer which includes rubber component at least a part of which is cross linked. With respect to the thermoplastic elastomer used in the present invention, there is no particular limitation and various known thermoplastic elastomers may be usable.
Concretely, for instance, polyester type thermoplastic elastomer resins such as polybutylene terephthalate (PBT)-polytetramethylene glycol (PTMG) copolymer, PBT-polylactone copolymer, PBT-polyolefin copolymer, etc.; polyamide type thermoplastic elastomer resins such as nylon 6 (N6)-PTMG copolymer, nylon 12 (N12)-PTMG copolymer, etc; polyurethane type thermoplastic elastomer resins such as tolylene diisocyanate (TDI)-PTMG copolymer, diphenyl methane diisocyanate (MDI)-polypropylene glycol (PPG) copolymer, TDI-PPG copolymer, etc.; silicone type thermoplastic elastomer resins; olefin type thermoplastic elastomer resins such as ethylene content enriched ethylene-propylene copolymer, metal carboxylate-polyethylene, ethylene-vinyl acetate copolymer, chlorinated polyethylene, etc.; styrene type thermoplastic elastomer resins including styrene type elastomers such as styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, etc., and hydrogenated forms of these stylene type elastomer; polybutadiene type thermoplastic elastomer resins such as 1,2-polybutadiene resin, trans-1,4-polybutadiene, etc.; and other types including polyvinyl chloride type thermoplastic elastomer resins and fluorine containing type thermoplastic elastomers are enumerated. These can be used singly or in a combination of two or more species.
Further, as the thermoplastic elastomer, elastomers of which crystallinity are about 15-55% are preferable, although that depends upon the kind of the thermoplastic elastomer. When the crystallinity is less than 15%, there is a fear that the compression set of the obtained composition becomes high. When the crystallinity exceeds 50%, there is a fear that the workability of the composition becomes low.
With respect to the thermoplastic elastomeric composition of the present invention, if necessary, a rubber component at least a part of which is cross linked can be added to the thermoplastic elastomer as mentioned above in the proportions of 0-100 parts, preferably, 30-60 parts the rubber to 100 parts the elastomer.
By adding the rubber component, the compression set of the thermoplastic elastomer can be improved.
As rubber which constitutes the rubber component, for instance, diene type rubbers, olefin type rubbers, halogen containing type rubbers, sulfur containing type rubbers, rubbers which are modified with some additional component having highly reactive functional group, etc., are enumerated.
Concretely, as the diene type rubbers, for instance, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), 1,2-butadiene rubber (1,2-BR), styrene-butadiene copolymerized rubber (SBR), acrylonitrile-butadiene copolymerized rubber (NBR, NIR, NBIR), chloroprene rubber (CR), and partially hydrogenated NBR or SBR, etc., are enumerated.
As the olefin type rubbers, for instance, butyl rubber (IIR), ethylene-propylene copolymerized rubber (EPM), ethylene-propylene-diene copolymerized rubber (EPDM), copolymer of isobutylene and aromatic vinyl monomer or diene type monomer, acrylic rubber (ACM), etc., are enumerated.
As the halogen containing type rubbers, for instance, brominated butyl rubber (Br-IIR), chlorinated butyl rubber (Cl-IIR), bromide of isobutylene-p-methyl styrene copolymer (Br-IPMS), chloroprene rubber (CR), hydrin rubber (CHR, CHC), chlorosulfonated polyethylene (CSM), chlorinated polyethylene (CM), etc., are enumerated.
As the rubbers which are modified with some additional component having highly reactive functional group, for instance, rubbers which are modified with an additional component having highly reactive functional group such as epoxy group, maleic acid group, maleic anhydride group, etc., are enumerated. More concretely, epoxidated natural rubber, maleic acid modified ethylene-propylene copolymerized rubber (M-EPM), maleic acid modified ethylene-propylene-diene copolymerized rubber (M-EPDM), maleic acid modified chlorinated polyethylene (M-CM), etc., are enumerated.
Among them, diene type rubbers and the rubbers which are modified with some additional component having highly reactive functional group are particularly preferable. Because, such preferable rubbers can improve the density of cross-linkage, and thus, it is possible to allow the elastomeric composition of the present invention to be more firmly cross linked, and possible to reduce the permanent set.
As cross linking agents for the above mentioned rubbers, generic cross linking agents such as sulfur type, organic peroxide type, metallic oxide type, phenolic resin type, quinonedioxime, etc., may be usable.
Although the content of the cross linking agent is not particularly limited as far as the content is within the range generally used, it is desirable to be in the range of 0.1-10 parts by weight, more preferably, 0.3-5 parts by weight per 100 parts by weight of rubber.
Moreover, the above mentioned rubber component may contain a vulcanization accelerator, a vulcanization aid, a vulcanization retarder, and a compounding agent, if necessary, besides the above mentioned ingredients.
As the vulcanization accelerator, aldehyde-ammonia type, guanidine type, thiourea type, thiazole type, sulfenamide type, thiuram type, dithiocarbamate type vulcanization accelerators, etc., are enumerated.
As the vulcanization aid, generic aids for rubber may be used. For instance, zinc oxide, stearic acid, oleic acid, Zn salts of these acids, etc., are enumerated.
It is desirable that the content of vulcanization accelerator and the vulcanization aid is in the range of 0.1-10 parts by weight, more preferably, 0.5-5 parts by weight per 100 parts by weight of rubber which composes the above mentioned rubber component.
As the vulcanization retarder, concretely, for instance, organic acids such as phthalic anhydride, benzoic acid, salicylic acid, acetyl salicylic acid, etc.; nitroso compounds such as N-nitroso-diphenyl amine, N-nitroso-β-naphthyl amine, polymer of N-nitroso-trimethyl-dihydroquinoline, etc.; halides such as trichloro melamine; 2-mercapto benzimidazole; Santoguard PVI; etc., are enumerated.
It is desirable that the content of vulcanization retarder is in the range of 0.1-0.3 parts by weight, more preferably, 0.1-0.2 parts by weight per 100 parts by weight of rubber which composes the abovementioned rubber component.
As the compounding agent, it is possible to use various generic compounding agents. For instance, plasticizers, bulking agents, thixotropy giving agent, pigments, dyes, age resistors, antioxidants, antistatic agent, flame retardants, tacking giving agents, dispersing agents, dehydrating agents, ultraviolet rays absorbents, solvents, etc., are enumerated.
The thermoplastic elastomeric composition according to this invention contains an effective amount of the minute carbon fibrous structures as mentioned above into a thermoplastic elastomer, or a thermoplastic elastomer which includes rubber component at least a part of which is cross linked.
Although the amount may be varied depending upon the usage of the thermoplastic elastomeric composition, the kinds of the thermoplastic elastomer and the rubber component which constitute the matrix, etc., it may be about 0.1-30% based on 100 parts by weight of the thermoplastic elastomer, or at least based on 100 parts by weight of total amount of the thermoplastic elastomer and the rubber component.
When it is less than 0.1%, there is fear that improvements of electrical conductivity, mechanical strength, heat stability, etc., in the thermoplastic elastomeric composition can not be amply attained. Furthermore, it is likely that the compression set can not be improved enough.
On the other hand, when it exceeds 30%, there is fear that mechanical strength, elasticity, etc., of the thermoplastic elastomer decrease more than necessary.
With respect to the thermoplastic elastomeric composition according to the present invention, fine carbon fibers of the carbon fibrous structures can distribute themselves uniformly throughout the matrix even when the carbon fibrous structures are added at a relative small amount. Thus, the thermoplastic elastomeric composition which has an excellent electrical conductivity and an improved compression set can be prepared as mentioned above.
The elastomeric composition of this invention may contain the above mentioned cross linking agent (vulcanizing agent), the vulcanization accelerator, the vulcanization aid, the vulcanization retarder, and the compounding agent, as well as a compatibilizer, if necessary, besides the above mentioned thermoplastic resin, the rubber component, and the carbon fiber structures.
The compatibilizer may be generally designed as a copolymer which owns both of or each one of the thermoplastic resin structure and the rubber component structure, or as a copolymer which is equip with a reactive group capable of reacting with the thermoplastic resin component or the rubber component, such as epoxy group, carboxyl group, carbonyl group, halogen atom, amino group, oxazoline group, hydroxide group, etc., and thus it is selected depending upon the kinds of the thermoplastic resin component and the rubber component to be kneaded.
As usually used compatibilizer, styrene-ethylene-butylene-styrene type block copolymer (SEBS) and maleic acid modified body thereof; EPDM, EPM and maleic acid modified bodies thereof; EPDM-styrene or EPDM-acrylonitrile graft copolymer and maleic acid modified body thereof; styrene-maleic acid copolymer; maleic acid- or epoxy-modified ethylene-vinyl chloride copolymer; reactive phenoxin; etc., are enumerated.
The rubber compound can be dispersed more finely and more uniformly in the thermoplastic resin by adding such a compatibilizer.
It is preferable that the additive amount of the compatibilizer optionally added is in the range of 0.5-20 parts by weight per 100 parts by weight of total amount of the thermoplastic resin and the rubber component.
When the additive amount of the compatibilizer lies in the above range, the interfacial tension between the thermoplastic resin and the rubber component is decreased. As a result, the size of the rubber component particles which constructs dispersion phases become smaller, and the breaking strength of the obtained elastomeric composition can be improved. Thus, it is preferable.
The thermoplastic elastomeric composition according to the present invention can be prepared by using some known kneading machine such as uniaxial extruder, biaxial extruder, kneader, Banbury mixer, Plastomill, rollers, etc., so as to disperse the carbon fibrous structures into the thermoplastic elastomer.
Incidentally, in the case that the thermoplastic elastomeric composition contains the rubber component, it is possible that kneading of thermoplastic elastomer and the rubber component in melted state is carried out so as to distribute the rubber component as disperse phases in the thermoplastic elastomer which forms a continuous phase in advance, and thereafter the carbon fibrous structures are added and dispersed to the mixture. Alternatively, it is also possible that the rubber component and the carbon fibrous structures are almost coincidentally added and dispersed in the thermoplastic elastomer; otherwise, after the carbon fibrous structures are added and dispersed in the thermoplastic elastomer, the rubber component is added and dispersed in the mixture.
The cross linking of the rubber component may be performed by dynamic vulcanization, that is, by adding a cross linking agent (a vulcanization accelerator, a vulcanization aid, etc., being included if necessary) under kneading.
Incidentally, although the addition of cross linking agent, compatibilizer, etc., to the thermoplastic elastomer or the rubber component may be carried out under the kneading, it is preferable to add them in advance of the kneading because of less influence to the thermoplastic elastomer and because of successful progress of the cross linking of the rubber component.
Condition of kneading in melted state, condition of vulcanization, kind and amount of the cross linking agent to be used, etc., may be determined properly according to the kind and amount of the thermoplastic resin or rubber component used, and thus, there is no particular limitation about these conditions. For instance, although the kneading temperature is not particularly limited as long as the temperature is not less than the temperature at which the thermoplastic elastomer melts and not more than the temperature at which decomposition of thermoplastic elastomer does not occur, it is preferable to be in the range of 150-300° C., more desirably, 180-250° C.
When it is desired that the thermoplastic elastomeric composition according to the present invention is molded into a molded article of an expected shape, a known method such as melted extrusion, press molding, etc., are applicable.
In addition, the thermoplastic elastomeric composition of the present invention may include various known additives such as bulking agents, reinforcing agents, various stabilizers, antioxidants, ultraviolet rays absorbents, flame retardants, lubricants, plasticizers, solvents, etc., within the range where the primary objective of the present invention is not obstructed.
Especially, when it is desired to manufacture an electrical conductivity resin molded article in the present invention, any other conductive fillers such as metallic powder, carbon powder, etc., may be added to the composition.
Incidentally, in the case that the thermoplastic elastomeric composition according to the present invention contains the other conductive filler such as metal powder, carbon powder, etc., in addition to the abovementioned carbon fibrous structures, the high conductivity which has been never attained in the art unless quite large amount of the conductive filler is added to the composition can be attained when a relatively small amount of the carbon fibrous structures are added to the composition instead of the addition of a relatively large amount of the conductive filler. Thus, the problems due to the increment of the additive amount of the conductive filler such as degression of cured film strength, easy exfoliating tendency, etc., can be solved, and simultaneously, an advantage in costs owing to the reduction in the using amount of expensive metal can be obtained.
Although the accurate functions and mechanisms for exhibiting such a high conductivity is not yet elucidated, it can be presumed that the relatively small carbon fibrous structures would be in contact with the relatively large conductive filler such as metal or carbon powder in the resin matrix, and which contributes to the high conductivity.
In details, it can be presumed that the high conductivity would be obtained by formation of electrical chains which are constituted by allowing the carbon fibrous structures to enter into and place in gaps caused when the conductive filler comes into contact mutually.
As the metal powder, for instance, metals such as silver, platinum, palladium, copper, nickel, etc., can be used singly or in various mixtures thereof, although it is not particularly limited thereto.
The particle shape of the metal powder is not particularly limited as far as the powder in the shape can be used for the conductive filler, such as flake, spherical, dendritic, acinous, indefinite, etc.
Although the particle size of the metal powder is not particularly limited, for instance, it is desirable to be in the range of 0.5-15 μm.
When mean particle size is less than 0.5 μm, the surface area of the metal powder becomes larger, and therefore, the metal powder becomes easy to be oxidized, and the desired adequate conductivity is no longer obtained.
Contrary, when mean particle size is more than 0.5 μm, there is a fear that numeral gaps are formed when the particles come into contact mutually, and the desired adequate conductivity is no longer obtained.
As the carbon powder which constitutes the conductive filler, it is desirable to use carbon black in general, although it is not particularly limited thereto.
As the carbon black, although any known carbon black obtained by various methods can be used, for instance, furnace black, channel black, thermal black, Ketjen black, etc., are enumerated as preferable examples. In addition, gas black, oil black, acetylene black, etc., which are classified by the difference of raw material, are also enumerated as preferable examples. Among them, acetylene black and Ketjen black are particularly preferable.
In the case that the conductive filler such as the metal powder and carbon powder is added to the thermoplastic elastomeric composition, for instance, with respect to the filler being of the metal powder, it is preferable that the additive amount of the filler is in the range of 100-500 parts by weight per 100 parts by weight of the thermoplastic elastomer. When it is less than 100 parts by weight, there is a fear that a sufficient conductivity may not be obtained because the contacting points between the metal particles will become lesser. On the other hand, when it is more than 500 parts by weight, there is a fear that the tendency of bearing some malfunction, such as easy exfoliation of the conductive path made by this conductive resin composition, is increased, because the relative content of the resin component in the composition decreases.
With respect to the filler being of the carbon black, it is preferable that the additive amount of the carbon black is in the range of 5-50 parts by weight per 100 parts by weight of the thermoplastic elastomer. When it is less than 5 parts by weight, there is a fear that a sufficient conductivity may not be obtained. On the other hand, when it is more than 50 parts by weight, there is a fear that a sufficient conductivity may not be obtained, because both of the relative content of the resin component and that of the carbon fibrous structures in the composition decrease, or a fear that the tendency of bearing some malfunction, such as easy exfoliation of the conductive path made by this conductive resin composition, is increased.
Incidentally, when the conductive filler is added to the elastomeric composition, the reasonable additive amount of the carbon nanostructures is in the range of 0.3-30 parts by weight per 100 parts by weight of thermoplastic elastomer.
Molded article made of the thermoplastic elastomeric composition according to the present invention can possess, typically, a surface resistivity of not more than 1013Ω/cm2, particularly, of 104-1012Ω/cm2, and an improvement in compression set of 3-70%, the compression set being determined under the condition in accordance with the measuring method defined in JIS K 6301. These properties of the molded articles are, however, not limited thereto.
Hereinafter, this invention will be illustrated in detail by practical examples. However, it is to be understood that the invention is not limited to the described examples.
Incidentally, the respective physical properties described in later are measured by the following protocols.
First, a photograph of pulverized product was taken with SEM. On the taken SEM photo, only carbon fibrous structures with a clear contour were taken as objects to be measured, and broken ones with unclear contours were omitted. Using all carbon fibrous structures that can be taken as objects in one single field of view (approximately, 60-80 pieces), about 200 pieces in total were measured with three fields of views. Contours of the individual carbon fibrous structures were traced using the image analysis software, WinRoof™ (trade name, marketed by Mitani Corp.), and area within each individual contour was measured, circle-equivalent mean diameter of each individual carbon fibrous structure was calculated, and then, the calculated data were averaged to determine the area based circle-equivalent mean diameter.
1 g of powder was placed into a 70 mm caliber transparent cylinder equipped with a distribution plate, then air supply at 0.1 Mpa of pressure, and 1.3 liter in capacity was applied from the lower side of the distribution plate in order to blow off the powder and thereafter allowed the powder to settle naturally. After the fifth air blowing, the height of the settled powder layer was measured. Any 6 points were adopted as the measuring points, and the average of the 6 points was calculated in order to determine the bulk density.
The Raman spectroscopic analysis was performed with the equipment LabRam 800 manufactured by HORIBA JOBIN YVON, S.A.S., and using 514 mm the argon laser.
Combustion behavior was determined using TG-DTA manufactured by MAC SCIENCE CO. LTD., at air flow rate of 0.1 liter/minute and heating rate of 10° C./minute. When burning, TG indicates a quantity reduction and DTA indicates an exothermic peak. Thus, the top position of the exothermic peak was defined as the combustion initiation temperature.
Using the powder X ray diffraction equipment (JDX3532, manufactured by JEOL Ltd.), carbon fibrous structures after annealing processing were examined. κα ray which was generated with Cu tube at 40 kV, 30 mA was used, and the measurement of the spacing was performed in accordance with the method defined by The Japan Society for the Promotion of Science (JSPS), described in “Latest Experimental Technique For Carbon Materials (Analysis Part)”, Edited by Carbon Society of Japan, 2001), and as the internal standard silicon powder was used.
1 g of CNT powder was scaled, and then press-loaded into a resinous die (inner dimensions: 40 L, 10 W, 80H (mm)), and the displacement and load were read out. A constant current was applied to the powder by the four-terminal method, and in this condition the voltage was measured. After measuring the voltage until the density come to 0.9 g/cm3, the applied pressure was released and the density after decompression was measured. Measurements taken when the powder was compressed to 0.5, 0.8 or 0.9 g/cm3 were adopted as the particle's resistance.
First, a photograph of the carbon fibrous structures was taken with SEM in an analogous fashion as in the measurement of area based circle-equivalent mean diameter. On the taken SEM photo, only carbon fibrous structures with a clear contour were taken as objects to be measured, and broken ones with unclear contours were omitted. Using all carbon fibrous structures that can be taken as objects in one single field of view (approximately, 60-80 pieces), about 200 pieces in total were measured with three fields of views.
On the carbon fibrous structures to be measured, assuming each individual granular part which is the binding point of carbon fibers to be a particle, contours of the individual granular parts were traced using the image analysis software, WinRoof™ (trade name, marketed by Mitani Corp.), and area within each individual contour was measured, circle-equivalent mean diameter of each individual granular part was calculated, and then, the calculated data were averaged to determine the area based circle-equivalent mean diameter. Roundness (R) was determined by inputting value of the area (A) within each individual contour computed by the above and a measured value of each individual contour's length (L) to the following equation to calculate the roundness of each individual granular part, and then, averaging the calculated data.
R=A*4π/L2 [Numerical Formula 1]
Further, the outer diameter of the fine carbon fibers in the individual carbon fibrous structures to be measured were determined, and then, from the outer diameter determined and the circle-equivalent mean diameter of the granular part calculated as above, the ratio of circle-equivalent mean diameter to the outer diameter of the fine carbon fiber was calculated for each individual carbon fibrous structure, and then the data obtained are averaged
First, a photograph of the carbon fibrous structures was taken with SEM in an analogous fashion as in the measurement of area based circle-equivalent mean diameter. On the taken SEM photo, only carbon fibrous structures with a clear contour were taken as objects to be measured, and broken ones with unclear contours were omitted. Using all carbon fibrous structures that can be taken as objects in one single field of view (approximately, 60-80 pieces), about 200 pieces in total were measured with three fields of views.
On the carbon fibrous structures to be measured, all places where the granular parts were mutually linked with a fine carbon fiber were found out. Then, at the respective places, the distance between the adjacent granular parts which were mutually linked with the fine carbon fiber (the length of the fine carbon fiber including the center of a granular part at one end to the center of another granular part at another end) was measured, and then the data obtained were averaged.
To 100 ml of toluene in a lidded vial, the carbon fiber structures were added at a rate of 30 μg/ml in order to prepare the dispersion liquid sample of the carbon fibrous structure.
To the dispersion liquid sample of the carbon fibrous structure thus prepared, Ultrasound was applied using a ultrasonic cleaner (manufactured by SND Co., Ltd., Trade Name: USK-3) of which generated frequency was 38 kHz and power was 150 w, and the change of the carbon fibrous structure in the dispersion liquid was observed in the course of time aging.
First, 30 minutes after the application of ultrasound was started, a 2 ml constant volume aliquot of the dispersion sample was pipetted, and the photo of the carbon fibrous structures in the aliquot was taken with SEM. On the obtained SEM photo, 200 pieces of fine carbon fibers in the carbon fibrous structures (fine carbon fibers at least one end of which is linked to the granular part) were selected randomly, then the length of the each individual selected fine carbon fibers was measured, and mean length D50 was calculated. The mean length calculated is taken as the initial average fiber length.
Meanwhile, on the obtained SEM photo, 200 pieces of granular parts which each were the binding point of carbon fibers in the carbon fibrous structures were selected randomly. Assuming each individual selected granular part to be a particle, contours of the individual granular parts were traced using the image analysis software, WinRoof™ (trade name, marketed by Mitani Corp.), and area within each individual contour was measured, circle-equivalent mean diameter of each individual granular part was calculated, and then, D50 mean value thereof is calculated. The D50 mean value calculated was taken as the initial average diameter of the granular parts.
Thereafter, according to the same procedure, a 2 ml constant volume aliquot of the dispersion sample was pipetted every constant periods, and the photo of the carbon fibrous structures in the each individual aliquot was taken with SEM, and the mean length D50 of the fine carbon fibers in the carbon fibrous structure and the mean diameter D50 of the granular part in the carbon fibrous structure were calculated individually.
At the time when the mean length D50 of the fine carbon fibers comes to be about half the initial average fiber length (in the following Examples, 500 minutes after the application of ultrasound is stated.), the mean diameter D50 of the granular part was compared with the initial average diameter of the granular parts in order to obtain the rate of variability (%) thereof.
compression set was determined by a method in accordance with the method defined in JIS K 6301. That is, between two chrome plated metallic plates in parallel, a spacer corresponding to 25% compressibility and a sample of thermoplastic elastomer were put, and they were fixed by bolting. Thereafter, the sample was subjected to heat treatment at a prescribed temperature for a prescribed time as mentioned below. After the heat treatment, the sample piece was removed from the compression test assembly, and then left standing for 24 hours. After standing, the thickness of the sample was determined and the compression set was calculated from the following equation.
(Compression Set) (%)={(Thickness of sample before test)−(Thickness of sample after test)}×100/{(Thickness of sample before test)−(Thickness of spacer)}
In an obtained sheet sample, using 4-pin probe type low resistivity meter (LORESTA-GP, manufactured by Mitsubishi Chemical), the resistance (Ω) at nine points of coated film surface was measured, and then average was calculated.
By the CVD process, carbon fibrous structures were synthesized from toluene as the raw material.
The synthesis was carried out in the presence of a mixture of ferrocene and thiophene as the catalyst, and under the reducing atmosphere of hydrogen gas. Toluene and the catalyst were heated to 380° C. along with the hydrogen gas, and then they were supplied to the generation furnace, and underwent thermal decomposition at 1250° C. in order to obtain the carbon fibrous structures (first intermediate).
The generation furnace used for the carbon fibrous structures (first intermediate) is illustrated schematically in
The synthesized first intermediate was baked at 900° C. in nitrogen gas in order to remove hydrocarbons such as tar and to obtain a second intermediate. The R value of the second intermediate measured by the Raman spectroscopic analysis was found to be 0.98. Sample for electron microscopes was prepared by dispersing the first intermediate into toluene.
Further, the second intermediate underwent a high temperature heat treatment at 2600° C. The obtained aggregates of the carbon fibrous structures underwent pulverization using an air flow pulverizer in order to produce the carbon fibrous structures to be used in the present invention.
A sample for electron microscopes was prepared by dispersing ultrasonically the obtained carbon fibrous structures into toluene.
Further, X-ray diffraction analysis and Raman spectroscopic analysis were performed on the carbon fibrous structure before and after the high temperature heat treatment in order to examine changes in these analyses. The results are shown in
Additionally, it was found that the carbon fibrous structures had an area based circle-equivalent mean diameter of 72.8 μm, bulk density of 0.0032 g/cm3 Raman ID/IG ratio of 0.090, TG combustion temperature of 786° C., spacing of 3.383 Å, particle's resistance of 0.0083Ω·cm, and density after decompression of 0.25 g/cm3.
The mean diameter of the granular parts in the carbon fibrous structures was determined as 443 nm (SD 207 nm), that is 7.38 times larger than the outer diameter of the carbon fibers in the carbon fibrous structure. The mean roundness of the granular parts was 0.67 (SD 0.14).
Further, when the destruction test for carbon fibrous structure was performed according to the above mentioned procedure, the initial average fiber length (D50) determined 30 minutes after the application of ultrasound was started was found to be 12.8 μm, while the mean length D50 determined 500 minutes after the application of ultrasound was started was found to be 6.7 μm, which value was about half the initial value. This result showed that many breakages were given in the fine carbon fibers of the carbon fibrous structure. Whereas the variability (decreasing) rate for the diameter of granular part was only 4.8%, when the mean diameter (D50) of the granular part determined 500 minutes after the application of ultrasound was started was compared with the initial average diameter (D50) of the granular parts determined 30 minutes after the application of ultrasound was started. Considering measurement errors etc., it was found that the granular parts themselves were hardly destroyed even under the load condition that many breakages were given in the fine carbon fibers, and the granular parts still function as the binding site for the fibers mutually.
Table 2 provides a summary of the various physical properties as determined in Synthetic Example 1.
By the CVD process, carbon fibrous structures were synthesized using a part of the exhaust gas from the generation furnace as a recycling gas in order to use as the carbon source the carbon compounds such as methane, etc., included in the recycling gas, as well as a fresh toluene.
The synthesis was carried out in the presence of a mixture of ferrocene and thiophene as the catalyst, and under the reducing atmosphere of hydrogen gas. Toluene and the catalyst as a fresh raw material were heated to 380° C. along with the hydrogen gas in a preheat furnace, while a part of the exhaust gas taken out from the lower end of the generation furnace was used as a recycling gas. After it was adjusted to 380° C., it was mixed with the fresh raw material gas on the way of the supplying line for the fresh raw material to the generation furnace. The mixed gas was then supplied to the generation furnace.
The composition ratio in the recycling gas used were found to be CH4 7.5, C6H6 0.3%, C2H2 0.7%, C2H6 0.1%, CO 0.3%, N2 3.5%, and H2 87.6% by the volume based molar ratio. The mixing flow rate was adjusted so that the mixing molar ratio of methane and benzene in the raw material gas to be supplied to the generation furnace, CH4/C6H6 was set to 3.44 (wherein, it was considered that the toluene in the fresh raw material gas had been decomposed at 100% to CH4:C6H6=1:1 by the heating in the preheat furnace.
In the final raw material gas, C2H2, C2H6, and CO which were involved in the recycling gas to be mixed were naturally included. However, since these ingredients were very small amount, they may substantially be ignored as the carbon source.
Then they were underwent thermal decomposition at 1250° C. in order to obtain the carbon fibrous structures (first intermediate) in an analogous fashion as Synthetic Example 1.
The constitution of the generation furnace used for the carbon fibrous structures (first intermediate) was the same as that shown in
The synthesized first intermediate was baked at 900° C. in argon gas in order to remove hydrocarbons such as tar and to obtain a second intermediate. The R value of the second intermediate measured by the Raman spectroscopic analysis was found to be 0.83. Sample for electron microscopes was prepared by dispersing the first intermediate into toluene. SEM photo and TEM photo obtained for the sample are in much the same with those of Synthetic Example 1 shown in
Further, the second intermediate underwent a high temperature heat treatment at 2600° C. in argon gas. The obtained aggregates of the carbon fibrous structures underwent pulverization using an air flow pulverizer in order to produce the carbon fibrous structures to be used in the present invention.
A sample for electron microscopes was prepared by dispersing ultrasonically the obtained carbon fibrous structures into toluene. SEM photo and TEM photos obtained for the sample are in much the same with those of Synthetic Example 1 shown in
Separately, the obtained carbon fibrous structures were mounted on a sample holder for electron microscope, and observed for the particle distribution. The obtained results are shown in Table 3.
Further, X-ray diffraction analysis and Raman spectroscopic analysis were performed on the carbon fibrous structure before and after the high temperature heat treatment in order to examine changes in these analyses. The results are in much the same with those of Synthetic Example 1 shown in
Additionally, it was found that the carbon fibrous structures had an area based circle-equivalent mean diameter of 75.8 μm, bulk density of 0.004 g/cm3, Raman ID/IG ratio of 0.086, TG combustion temperature of 807° C., spacing of 3.386 Å, particle's resistance of 0.0077Ω·cm, and density after decompression of 0.26 g/cm3.
The mean diameter of the granular parts in the carbon fibrous structures was determined as 349.5 nm (SD 180.1 nm), that is 5.8 times larger than the outer diameter of the carbon fibers in the carbon fibrous structure. The mean roundness of the granular parts was 0.69 (SD 0.15).
Further, when the destruction test for carbon fibrous structure was performed according to the above mentioned procedure, the initial average fiber length (D50) determined 30 minutes after the application of ultrasound was started was found to be 12.4 μm, while the mean length D50 determined 500 minutes after the application of ultrasound was started was found to be 6.3 μm, which value was about half the initial value. This result showed that many breakages were given in the fine carbon fibers of the carbon fibrous structure. Whereas the variability (decreasing) rate for the diameter of granular part was only 4.2%, when the mean diameter (D50) of the granular part determined 500 minutes after the application of ultrasound was started was compared with the initial average diameter (D50) of the granular parts determined 30 minutes after the application of ultrasound was started. Considering measurement error, etc., it was found that the granular parts themselves were hardly destroyed even under the load condition that many breakages were given in the fine carbon, and the granular parts still function as the binding site for the fibers mutually.
Table 4 provides a summary of the various physical properties as determined in Example 2.
0.1, 1, 5, 10, or 30 parts by weight of the carbon fibrous structures obtained in Synthetic Example 1 were added to 100 parts by weight of 1,2-polybutadiene type thermoplastic elastomer (JSR RB 830, manufactured by JSR), then the obtained mixture was kneaded using a kneader for 10 minutes at 140° C. Thereafter, the resultant composition were applied to rollers for sheeting, and then, using a press molder, sheets of 2 mm in thickness for measuring resistivity and cylindrical samples of 28.7 mm in diameter and 12.7 mm in thickness for measuring compression set were manufactured.
According to the above described methods, determination of the compression set and the electrical resistivity were performed to the obtained samples. The results obtained were shown in Table 5.
Incidentally, as described above, the compression set was determined by a method in accordance with the method defined in JIS K 6301. That is, between two chrome plated metallic plates in parallel, a spacer corresponding to 25% compressibility and a sample of thermoplastic elastomer were put, and they were fixed by bolting. Thereafter, the sample was subjected to heat treatment at 70° C. for 22 hours. After the heat treatment, the sample piece was removed from the compression test assembly, then left standing for 24 hours. After standing, the thickness of the sample was determined and the compression set was calculated from the equation indicated above.
Using the same 1,2-polybutadiene as in Examples 1-5 and omitting the addition of the carbon fibrous structures, samples were manufactured, and the obtained samples underwent the determination, in accordance with the same procedure and manners as in Examples 1-5. The results obtained were shown in Table 5.
0.1, 1, 5, 10, or 30 parts by weight of the carbon fibrous structures obtained in Synthetic Example 2 were added to 100 parts by weight of 1,2-polybutadiene type thermoplastic elastomer (JSR RB 830, manufactured by JSR), then the obtained mixture was kneaded using a kneader for 10 minutes at 140° C. Thereafter, the resultant composition were applied to rollers for sheeting, and then, using a press molder, sheets of 2 mm in thickness for measuring resistivity and cylindrical samples of 28.7 mm in diameter and 12.7 mm in thickness for measuring compression set were manufactured.
In accordance with the same manners as in Examples 1-5, determination of the compression set and the electrical resistivity were performed to the obtained samples. The results obtained were shown in Table 6, accompanied with the result of Control 1.
15 parts by weight of FEF carbon black, 2.5 parts by weight of ZnO, 0.5 part by weight of stearic acid, 0.2 part by weight of sulfur, 1.0 part by weight of vulcanization accelerator CZ, 1.0 part by weight of vulcanization accelerator TT, and 0.1, 1, 5, 10, or 30 parts by weight of the carbon fibrous structures obtained in Synthetic Example 2 were added to 50 parts by weight of 1,2-polybutadiene type thermoplastic elastomer (JSR RB 830, manufactured by JSR), and 50 parts by weight of NBR (middle-high NBR, Nipol 1042, manufactured by Zeon corporation), then the obtained mixture was kneaded using a kneader for 10 minutes. Thereafter, the resultant composition was applied to rollers for sheeting. Then, using a press molder, the composition underwent vulcanization molding at 150° C. for 30 minutes, and was formed into sheets of 2 mm in thickness for measuring resistivity and cylindrical samples of 28.7 mm in diameter and 12.7 mm in thickness for measuring compression set. According to the above described methods, determination of the compression set and the electrical resistivity were performed to the obtained samples. The results obtained were shown in Table 7.
Incidentally, the compression set was determined by the same manner as in Examples 1-10 except that the test conditions of the compression set were changed to 130° C. for 22 hours. Meanwhile, the electric conductivity was determined using the identical conditions which were used in Examples 1-10.
Using the same 1,2-polybutadiene type thermoplastic elastomer and NBR blended composition as in Examples 11-15 except that addition of the carbon fibrous structures was omitted, samples were manufactured, and the obtained samples underwent the determination, in accordance with the same procedure and manners as in Examples 11-15. The results obtained were shown in Table 7.
30 parts by weight of FEF carbon black, 5 parts by weight of ZnO, 1 part by weight of stearic acid, 0.4 part by weight of sulfur, 2.0 part by weight of vulcanization accelerator CZ, 2.0 part by weight of vulcanization accelerator TT, and 0.1, 1, 5, 10, or 30 parts by weight of the carbon fibrous structures obtained in Synthetic Example 2 were added to 100 parts by weight of NBR (middle-high NBR, Nipol 1042, manufactured by Zeon corporation), then the obtained mixture was kneaded using a kneader for 10 minutes. Thereafter, the resultant composition was applied to rollers for sheeting. Then, using a press molder, the composition underwent vulcanization molding at 150° C. for 30 minutes, and was formed into sheets of 2 mm in thickness for measuring resistivity and cylindrical samples of 28.7 mm in diameter and 12.7 mm in thickness for measuring compression set. In accordance with the same manners as in Examples 11-15, determination of the compression set and the electrical resistivity were performed to the obtained samples. The results obtained were shown in Table 8.
Using the same NBR blended composition as in Examples 16-20 except that addition of the carbon fibrous structures was omitted, samples were manufactured, and the obtained samples underwent the determination, in accordance with the same procedure and manners as in Examples 16-20. The results obtained were shown in Table 8.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-305070 | Oct 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/320729 | 10/18/2006 | WO | 00 | 4/18/2008 |
