JP4053729B2 - Composite material and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a composite material technology having a metal as a matrix and vapor-grown carbon fibers as a filler.
[0002]
[Prior art]
Aluminum or aluminum alloy is excellent in thermal conductivity, so it is used for a heat sink or the like, and is used for local cooling or heat dissipation of a CPU or the like.
[0003]
However, as notebook-type devices and handheld devices that cannot use heat dissipation fans are being developed in recent years, extremely light-weight devices such as notebook devices and handheld devices are being developed one after another. The amount of heat generated is increasing.
In order to satisfy these contradictory requirements, a material that is lightweight and excellent in thermal conductivity is required.
[0004]
As such, aluminum or aluminum alloy to which carbon fiber is added as a filler is known, and the present inventors have already made a metal system using vapor-grown carbon fiber as a filler as a material having particularly high thermal conductivity. Composite materials have been proposed.
[0005]
However, such a vapor-grown carbon fiber-aluminum composite material has poor adhesion between the metal and the carbon fiber, and even if measures such as pressure reduction are taken during molding, a small gap (hereinafter referred to as “void”) is formed at the interface. In many cases, the excellent thermal conductivity that should be originally obtained cannot actually be obtained.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a composite material that improves the problems, that is, is lightweight and sufficiently exhibits its original high thermal conductivity.
[0007]
[Means for Solving the Problems]
Since the composite material of the present invention is to solve the above problems, a composite material as, for the composite material comprising a vapor grown carbon fiber and metal filler formed by the addition according to claim 1, wherein the metal is aluminum Alternatively, the composite material is an aluminum alloy and the filler is aluminum borate .
[0008]
The method of producing a composite material of the present invention, as described in claim 4, the vapor-grown carbon fiber and aluminum borate transferred to a vessel after dispersing in a solvent, then the solvent was removed vapor-grown carbon fibers Then, the fiber layer, filter, and metal are placed in the pressure vessel, and then the inside of the pressure vessel is evacuated and the metal is heated and melted, and the molten metal is pressure impregnated into the fiber layer. A method for producing a composite material, wherein the metal is aluminum or an aluminum alloy .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Since the composite material of the present invention uses vapor-grown carbon fiber (hereinafter also referred to as “VGCF”) having extremely good thermal conductivity, excellent thermal conductivity can be obtained when a composite material is used.
[0010]
Vapor-grown carbon fibers used in the composite material of the present invention are known in the form of needle crystals called whiskers, but these are one-dimensional in shape and are used for three-dimensional applications such as heat dissipation. Although it is necessary to control the orientation direction when molding a material, it is generally difficult to control the orientation direction.
[0011]
Similarly, carbon fibers of long fibers such as polyacrylonitrile-based carbon fibers and pitch-based carbon fibers, which are also known as one-dimensional shape carbon fibers, are chopped or milled (even if they are milled by ordinary methods, they are completely Those that do not become powdery and retain their shape as fibers) have similar geometrical defects, but they also have several lower thermal conductivities than vapor-grown carbon fibers (vapor-phase growth). Since the thermal conductivity of carbon fiber is about 1500 w / mK, these PAN-based and pitch-based carbon fibers are about 1-600 w / mK), so it is a composite with aluminum (the thermal conductivity is 200-270 w / mK). Even if the material is formed, the improvement in thermal conductivity is small.
[0012]
Moreover, in the composite material (refer FIG. 7) which has the textile fabric which consists of the carbon fiber of a conventional long fiber (a pitch type carbon fiber and a polyacrylonitrile type carbon fiber are known) inside, the direction of a fiber is two-dimensional. The thermal conductivity is also directional and good in one or two dimensions, but satisfactory thermal conductivity cannot be obtained by three-dimensional evaluation. Furthermore, although a so-called 3D woven fabric (three-dimensional woven fabric) can be used, it is difficult to obtain a packing density that can provide a sufficient effect, and such a woven fabric is extremely expensive and impractical.
[0013]
For this reason, it is desirable that the vapor-grown carbon fiber used in the composite material of the present invention is a vapor-grown carbon fiber that is a feather-like fiber body. Here, the vapor-grown carbon fiber that is a feather-like fiber body has a specific gravity of around 2.0 (a specific gravity of aluminum is 2.7), has a branch (branch), has a bend depending on the place, and in some cases. There is a constriction, and it is entangled with itself or with each other to form an indefinitely shaped fiber mass of 0.03 mm to 1 mm as a whole.
[0014]
Vapor-grown carbon fiber, which is a feather-like fiber body, is branched, and heat is conducted through its three-dimensional network. Therefore, when this fiber is used as a filler, it is a composite with extremely good three-dimensional thermal conductivity. A material is obtained. FIGS. 1 and 2 are scanning electron micrographs of vapor-grown carbon fibers that have such a bend and are constricted in some cases and are feather-like fibrous bodies that are entangled with each other. 3 shows a transmission electron micrograph.
[0015]
The vapor grown carbon fiber which is such a feather-like fibrous body can be obtained by a method almost the same as a general needle-like vapor grown carbon fiber. That is, vapor growth is performed using hydrocarbons such as benzene as a carbon supply source and iron as a nucleus in the presence of hydrogen. At this time, by changing the conditions such as temperature, atmospheric pressure, feed amount of hydrocarbons, etc., it has branching (branching), has bending depending on the place, sometimes constricted, and entangles itself or with each other A vapor-grown carbon fiber that is a feather-like fiber body can be obtained. At this time, the plurality of feather-like fiber bodies are entangled with each other to form a fiber mass. Conventionally, when producing vapor-grown carbon fibers, these conditions have been set so that they can be used for ordinary applications such as obtaining mechanical strength, and those that do not have branching or bending can be obtained. It was.
[0016]
The metal used as a matrix in the composite material of the present invention is preferably a metal having a high thermal conductivity and a low specific gravity for the purpose of the present invention. That is, aluminum, various aluminum alloys, magnesium, a magnesium alloy, etc. are mentioned.
[0017]
In the composite material of the present invention, in addition to the vapor-grown carbon fiber as the filler and the metal as the matrix, the vapor-grown carbon fiber and the metal having good wettability are added as the second filler. The wettability at the interface with the matrix metal is also specifically improved. As a result, thermal conductivity as a composite material is improved, and various mechanical performances are remarkably improved.
[0018]
When the metal which is a matrix is aluminum or an aluminum alloy, it is desirable to use aluminum borate as a filler having good wettability with these. Further, when the aluminum borate is a whisker, uniform dispersion is easy, and the effects of the present invention can be obtained uniformly throughout the composite material of the product.
Such an aluminum borate whisker can be obtained from Shikoku Chemicals.
[0019]
The composite material of the present invention can be obtained, for example, as follows.
Vapor-grown carbon fiber, which is a feather-like fibrous body, is delicate and brittle, and easily collapses when stress is applied, so that a three-dimensional network is easily lost. Therefore, it is dispersed in water or an organic solvent such as alcohols and ketones (a mixed solvent may be used) (these are collectively referred to as “solvent”). At this time, a filler having good wettability with a metal is added, and a chemical that improves dispersibility such as a surfactant is added as necessary, and a porous material (filter paper) having a liquid permeability at the bottom as a slurry. Or a porous ceramic or the like) (see FIG. 4 (a)), and then the solvent is removed, as shown in FIG. 4 (b), a metal in which a matrix metal and a filler having good wettability are dispersed. A filler layer having good wettability forms a fiber layer made of vapor-grown carbon fibers that are feather-like fiber bodies.
[0020]
This fiber layer is transferred to a container (pressure container) capable of pressure increase / decrease provided with a heater as shown in FIG. The bottom of the pressure vessel (“base material” in the figure) is removable as will be described later.
[0021]
A filter made of a heat-resistant porous material (here, porous ceramic) is laminated on such a fiber layer, and a metal (solid) is laminated on the filter.
After placing the fiber layer, the filter and the metal in the pressure vessel in this way, the inside of the pressure vessel is evacuated and the metal is heated and melted by the heater attached to the vessel, and the molten metal that has passed through the filter is in the vessel. After being introduced into the container, the inside of the container is pressurized using a gas that is inert to the molten metal and carbon that forms the matrix, argon gas, etc. (in this example, pressurized with argon gas), and the molten metal is applied to the fiber layer in the matrix. Impregnation under pressure as a component.
[0022]
Thereafter, heating by the heater of the container is stopped, the system is cooled to solidify the metal, and after standing to cool, the base material at the bottom of the container is removed, and from the vapor grown carbon fiber and the metal that is the obtained feather-like fiber body Take out the composite material.
[0023]
Thus, by impregnating the molten metal under an inert gas pressure, a good composite material can be obtained while using a molten metal that is easily oxidized. In addition to the matrix metal and the vapor-grown carbon fiber, this composition contains a filler that has good wettability with the matrix metal, so the wettability of the vapor-grown carbon fiber with the matrix metal is dramatically improved. In addition, a good composite material having no voids at the interface between the two can be obtained.
[0024]
The above-mentioned filter can move up and down in the pressure vessel, and in order to keep the space below it optimally, the resulting composite material does not needlessly increase the matrix components, and it is a feather-like fiber body. Since almost no destruction of a certain vapor-grown carbon fiber occurs, the effect of improving thermal conductivity and the effect of reducing the weight by the vapor-grown carbon fiber that is the feather-like fiber body can be sufficiently exhibited.
[0025]
In addition, by changing the shape of the base material and the porous ceramic in the above, it is possible to obtain a conformal shape, for example, a shape suitable as a heat sink, and the post-processing for adjusting the shape is unnecessary or after such Processing can be facilitated.
[0026]
According to the method for producing a composite material, it is possible to easily obtain FRM (fiber reinforced metal) in which the specific gravity of the matrix, which has heretofore been difficult to produce, is larger than the specific gravity of the reinforcing material. It is an excellent composite material with excellent dispersibility of phase-grown carbon fibers, variation in various performances (heat transfer characteristics, conductivity, strength, elasticity, etc.), less directivity, and fewer voids. The above-described method for producing a composite material according to the present invention can be similarly applied to the production of a composite material using a normal vapor-grown carbon fiber as a filler in addition to the vapor-grown carbon fiber that is a feather-like fiber body.
[0027]
【Example】
Here, by the method described above, 6% by weight of vapor grown carbon fiber which is a feather-like fiber body, 88% by weight of aluminum as a matrix metal, and 6% of aluminum borate whisker as a filler having good wettability with aluminum. %, And vapor-grown carbon fibers and aluminum borate whiskers, which are feather-like fibrous bodies, are dispersed into a slurry by using ethyl alcohol as a solvent at the time of dispersion, and the bottom has liquid permeability. After transferring to a container made of a porous material, the remaining alcohol was heated and evaporated, and then a composite material A of an example according to the present invention was produced in an argon atmosphere.
Similarly, a composite material B of Comparative Example was prepared without adding aluminum borate having good wettability with aluminum.
The cross sections of these composite materials A and B were observed with an electron microscope. The results at that time are shown in FIGS. 5 (a) and 6 (a), respectively.
[0028]
In these FIG. 5A and FIG. 6A, the highlight portion (however, the portion excluding the photographing data below these drawings) is a void generated at the interface between the fiber and the matrix.
[0029]
Here, the same image processing is applied to FIGS. 5 (a) and 6 (a), respectively, and the distribution of the highlight portion in FIGS. 5 (a) and 6 (a) is indicated by black dots. 5 (b) and FIG. 6 (b).
From these figures, it can be understood that the composite material A according to the present invention has very few voids between the fibers and the matrix as compared with the composite material B according to the prior art.
[0030]
【The invention's effect】
The composite material of the present invention is lightweight and has good thermal conductivity without directionality, and has vapor grown carbon fiber as a filler, and can fully exhibit its excellent thermal conductivity. Composite material with excellent mechanical strength.
[0031]
In addition, the method for producing a composite material of the present invention has an excellent composite material that has a smaller specific gravity than the matrix component and is excellent in dispersion of the filler, has various performance variations, and has little directionality even when a brittle and delicate filler is used. (Fiber reinforced metal) can be obtained without voids.
[Brief description of the drawings]
FIG. 1 is a scanning electron micrograph of vapor grown carbon fiber which is a feather-like fiber body.
FIG. 2 is another scanning electron micrograph of vapor-grown carbon fiber that is a feather-like fiber body.
FIG. 3 is a transmission electron micrograph of vapor grown carbon fiber which is a feather-like fiber body.
FIG. 4 is a diagram showing an example of a method for producing a composite material of the present invention.
(A) It is a figure (model figure) which shows the state which pours into a container the slurry which disperse | distributed the vapor growth carbon fiber which is a feather-like fiber body to the solvent.
(B) It is a figure (model figure) which shows that the fiber layer which consists of a vapor growth carbon fiber which is a feather-like fiber body was formed in the container of (a).
(C) It is a model sectional view showing the state where the above-mentioned fiber layer is impregnated with molten metal.
(D) It is a figure (model figure) which shows the composite material (composite material which consists of the vapor growth carbon fiber which is a feather-like fiber body, and a metal) based on this invention.
5A is an electron micrograph of a cross section of a composite material A according to the present invention. FIG.
(B) It is the figure which showed distribution of the highlight part (a void other than a photography data part) of (a).
FIG. 6A is an electron micrograph of a cross section of a composite material B according to the prior art.
(B) It is the figure which showed distribution of the highlight part (a void other than a photography data part) of (a).
FIG. 7 is a diagram (model diagram) showing a composite material having a woven fabric made of long-fiber carbon fibers as a filler.

Claims (4)

A composite material in which a filler is added to a composite material composed of vapor-grown carbon fiber and metal ,
A composite material, wherein the metal is aluminum or an aluminum alloy, and the filler is aluminum borate . The composite material according to claim 1, wherein the aluminum borate is an aluminum borate whisker . The composite material according to claim 1 , wherein the vapor-grown carbon fiber is a feather-like fiber body . Vapor-grown carbon fiber and aluminum borate are dispersed in a solvent and then transferred to a container, and then the solvent is removed to form a fiber layer made of vapor-grown carbon fiber. It is a method for producing a composite material that is placed and then evacuated and the metal is heated and melted, and the fiber layer is pressure-impregnated with the molten metal,
A method for producing a composite material, wherein the metal is aluminum or an aluminum alloy.

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