JPH0517593A - Heat-conductive molded article - Google Patents

Abstract

PURPOSE:To provide a heat-conductive molded article having excellent moldability and heat-conductivity and high mechanical strength and useful for heat-exchanger, etc. CONSTITUTION:A molding material for the subject article is produced by impregnating a thermosetting resin (e.g. epoxy resin) containing graphite powder having a purity of 75% and an average particle diameter of <=40mum (preferably <=10mum) in paralleled carbon fibers. The amount of the thermosetting resin is 20-80wt.% (preferably 30-70wt.%) and that of the sum of the carbon fiber and graphite powder is 20-80wt.%. The weight ratio of the carbon fiber to the graphite powder is 25:75 to 95:5, preferably 30:70 to 90:10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat conductive molded article. More specifically, the present invention relates to a molded product such as a heat transfer tube for a heat exchanger, which is excellent in moldability, thermal conductivity and mechanical strength.

[0002]

2. Description of the Related Art Conventionally, stainless steel, titanium alloy or the like has been generally used as a heat transfer tube for a corrosion resistant heat exchanger for heating a fluid such as hydrochloric acid or sulfuric acid. However, these materials are difficult to process and have poor smoothness on the finished surface. Therefore, pressure loss of the fluid is large, scale adhesion and heat transfer film are likely to occur, and heat exchange efficiency is disadvantageous.

Therefore, recently, attempts have been made to mold a heat transfer tube by injection molding or compression molding using a thermoplastic resin and a thermosetting resin having good corrosion resistance as raw materials. Generally, in order to improve the heat exchange efficiency of the heat exchanger, the smoothness is increased and the heat transfer area is made as large as possible, the film thickness of the heat transfer section is made thin, and the heat conductivity of the heat exchange section is increased to further improve the heat transfer efficiency. It is necessary to prevent the replacement part from getting dirty with scales.

The use of the resin material as described above has good smoothness and thus has an advantage of high fluid flow efficiency. However, since the thermal conductivity is small, a large heat transfer area is required.
In order to improve this, there is disclosed a technique in which a graphite powder or a carbon fiber having a good thermal conductivity and a short cut one are mixed with a resin to enhance the thermal conductivity. However, in the case of graphite powder, the mechanical strength is significantly impaired as the amount of the graphite powder mixed in the resin is increased. This seems to be because the graphite powder has no reinforcing effect due to the particle morphology.

Therefore, the amount of graphite powder added must be limited to a low level, and the thermal conductivity could not be sufficiently increased. Moreover, a molded product having a thin film thickness could not be used because of the risk of breakage during use. On the other hand, an attempt to increase the thermal conductivity by cutting the carbon fibers into short pieces and mixing them with a resin is not enough if the dispersion of the carbon fibers in the molded product becomes uneven and the mechanical strength is reduced. Therefore, the thermal conductivity could not be sufficiently increased.

Attempts have also been made to increase the thermal conductivity by mixing graphite powder and short cut carbon with a resin (Japanese Patent Laid-Open Nos. 63-194195 and 2-16313).
No. 7), the fluidity during molding is poor, it is difficult to mold a uniform thin film, and the mechanical strength cannot be sufficiently increased. That is, in the above method, it is difficult to effectively increase the thermal conductivity while maintaining the mechanical strength,
In addition, the flowability of the fluid cannot be increased due to the deterioration of the moldability when using graphite powder or carbon fiber and the decrease of the mechanical strength even if the thermal conductivity is increased, and the dirt components are deposited and the heat exchange rate is decreased. Met.

Recently, a carbon fiber-reinforced resin molded product obtained by impregnating unidirectionally aligned carbon fibers with a thermosetting resin to form a prepreg, and then laminating and molding the same in multiple layers is used for sports leisure such as fishing rods and golf shafts. It is being used as a member for aircrafts in terms of mechanical strength, elastic modulus and excellent formability. However, the heat conductivity was not sufficient as a heat conductive molded product such as a heat transfer tube for a heat exchanger.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat conductive molded product which has excellent moldability and simultaneously satisfies both thermal conductivity and mechanical strength.

[0009]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that carbon fibers aligned in one direction are impregnated with a thermosetting resin containing graphite powder. The present invention has been achieved by forming a molded article made of the above-mentioned molding material. That is, the present invention is a heat conductive molded article, which is made of a molding material in which carbon fibers aligned in one direction are impregnated with a thermosetting resin containing graphite powder.

The heat conductive molded article of the present invention is obtained by impregnating carbon fibers aligned in one direction with a compounded resin in which a thermosetting resin and graphite powder are uniformly mixed, or a strand prepreg or a tape shape. It can be obtained by molding as a heat transfer tube or the like by filament winding molding, roll molding, compression molding, pultrusion molding, etc. via a molding material such as a prepreg, a sheet-shaped prepreg, or a woven or knitted material prepreg, and heat curing.

Therefore, in the molded article of the present invention, it is essential that the unidirectionally aligned carbon fibers and graphite powder are used together. It is difficult to unambiguously determine the usage ratio of both, because it depends on the particle size of the graphite powder used, the required characteristics of the molded product, and the like. However, generally, the ratio of carbon fiber to graphite powder is 25:75 to 95: 5 (weight ratio), and preferably selected in the range of 30:70 to 90:10 (weight ratio).

The carbon fibers used in the present invention include graphite fibers, specifically, polyacrylonitrile (PAN).
Carbon fiber, pitch-based (petroleum-based, coal-based), rayon-based carbon fiber, and the like. In order to increase the thermal conductivity of the molded product, carbon fiber having a high fiber elastic modulus is preferable, but when the fiber elastic modulus becomes high, Since it is accompanied by a decrease in mechanical strength, it can be used depending on the desired thermal conductivity and mechanical strength.

The graphite powder used in the present invention is natural graphite,
Artificial graphite with a purity of 75% or more, and its particle size is 40 μm or less, preferably 10 μm in average particle diameter by electron microscopy.
m or less, and one or two or more selected from these may be used. Further, instead of graphite powder, inorganic powder such as silica, alumina, magnesium oxide, boron nitride, beryllium oxide, etc. can be used under specific conditions.

As the thermosetting resin (hereinafter referred to as resin base material) used in the present invention, any thermosetting resin can be used as long as carbon fibers can be impregnated and graphite powder can be mixed. For example, a phenol resin, a urea resin, an unsaturated polyester resin, a vinyl ester resin, a silicone resin, a urethane resin, an epoxy resin, a bismaleimide resin, a polyamide resin, a polyimide resin, or the like can be used and can be used depending on the purpose. it can.

Of these resin base materials, those based on an epoxy resin which is excellent in mechanical properties, chemical resistance, heat resistance, moldability and has a good balance of the above properties are most preferable.
As the epoxy resin, bisphenol A type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, bisphenol F type epoxy resin, glycidyl amine type epoxy resin or thermoplastic resin may be mixed and used. It is not limited to. From the point of heat resistance, bisphenol A
It is preferable to use a phenol novolac resin or a glycidyl amine type resin mixed with the type epoxy resin.

Generally, any curing agent for epoxy resin may be used, such as acid anhydride, dicyandiamide, aromatic diamine, phenol resin, etc., but the acid anhydride is preferable for acid resistant use. .
These curing agents are generally used in combination with a curing accelerator, and examples thereof include imidazole derivatives, urea derivatives, boron fluoride complex salts, tertiary amines, etc., but are not limited thereto.

The compounding ratio of the resin base material in the molded article of the present invention is 20 to 80% by weight, preferably 30 to 70% by weight.
Is. If the resin base material is less than 20% by weight, the fluidity at the time of molding becomes insufficient, resulting in a low-quality molded product and low mechanical strength. On the other hand, when it exceeds 80% by weight, the thermal conductivity is lowered and sufficient mechanical strength cannot be obtained.

In the present invention, various additives can be added within a range that does not impair the characteristics of the molded product. For example, thermoplastic resins, flow control agents, plasticizers, stabilizers, lubricants, inorganic fillers containing metals, etc. may be mentioned. In the production of the molded product of the present invention, the resin base material, the graphite powder and various additives are kneaded with a planetary mixer, a kneader, a roll kneader or the like. Further, if necessary, the viscosity is adjusted using one or more solvents selected from solvents such as methylene chloride, methyl ethyl ketone, methyl cellosolve, acetone, methanol, etc. to prepare a compounded resin.

The molding step is carried out by the above-mentioned method, etc.
When a solvent is used as the compounded resin, it is removed after the carbon fiber is impregnated with the compounded resin. Since the heat conductive molded article of the present invention can adopt the above-described molding method, the carbon fiber and the graphite powder can be uniformly dispersed, and 1 m
Thin films of m or less are now possible.

Further, due to the structure in which the unidirectionally aligned carbon fibers are arranged in an arbitrary direction, the mechanical strength characteristics of the carbon fibers can be fully utilized and excellent mechanical strength can be obtained. Furthermore, the molded article of the present invention greatly improves the thermal conductivity by shortening the interlayer distance with graphite particles or by tying with graphite particles between the layers of carbon fibers having excellent thermal conductivity. It has become possible.

[0021]

The present invention will be described in more detail with reference to the following examples. The physical properties shown in the examples are based on the following measuring methods. Moreover, a part shows a weight part. (1) Thermal Conductivity Sampled from the flat plate (thickness: about 2 mm) of each example,
Using a thermal constant measuring device TC-2000 (manufactured by Vacuum Riko Co., Ltd.), the specific heat capacity Cp (Jouule / gK) and the thermal diffusivity α
(Cm ² / sec) was directly measured by the flash method, and from the density ρ (g / cm ³ ) separately measured, the thermal conductivity λ (W / W /
cmK) is calculated by λ = α · Cp · ρ and converted to Kcal /
m ² · hr · ° C). The thermal diffusivity was measured by TC-2000 by a non-contact method, and the specific heat was measured by a contact method. The density was measured by the density gradient tube method. (2) Tensile strength Based on JIS K7073, the tensile strength was measured after holding in an atmosphere of a constant temperature bath of 160 ° C for 15 minutes. (3) Compressive strength After holding a hollow pipe filled with silicone oil in a silicone oil tank at 160 ° C for 10 minutes, the silicone oil was pressurized to measure the compressive strength.

[0022]

Examples 1 to 8 and Comparative Examples 1 to 6 Bisphenol A type epoxy resin (AER331, manufactured by Asahi Chemical Industry Co., Ltd.) 10
0 parts, tetraglycidyl amine type epoxy resin (TET
RAD-X, Mitsubishi Gas Chemical Industry Co., Ltd. 100 parts, methyl nadic acid anhydride (methyl hymic acid anhydride, Hitachi Chemical Co., Ltd.) 220 parts, imidazole (1B2E)
2 parts of Z, manufactured by Shikoku Kasei Kogyo Co., Ltd. was kneaded with the resin base material with a heating kneader.

Next, the particle size is 0.4 μm, 2 μm, 10
Graphite powders of μm, 45 μm, and 60 μm were added at the compounding weight ratio shown in Table 1 and further kneaded. At this time, if necessary,
Methyl cellosolve or methylene chloride was added and kneaded. Further, the mixture was kneaded on a roll mill to obtain a uniform blended resin. Next, the compounded resin was coated on release paper to obtain a film. On this film, high-strength carbon fiber having an elastic modulus of 24 TON / mm ² (H
T) and high-elasticity carbon fibers (HM) having an elastic modulus of 40 TON / mm ² were aligned, and a release paper was placed thereon, followed by compression with a hot roll and impregnation to obtain a unidirectional prepreg.

The prepared prepreg is cut into 30 cm squares, laminated at ± 45 ° so as to be plane symmetrical, and cured in an autoclave at 80 ° C. for 1 hour, 150 ° C. for 2 hours, 180 ° C. for 3 hours to form a flat plate having a thickness of 2 mm. Obtained. Also, the outer diameter is 7 mm
Round prepregs on round steel with a sheet rolling molding machine ± 45
After laminating at 0 ° and taping with polyester tape, the same curing as in autoclave molding is performed and the outer diameter is 8.0 m.
A hollow pipe having an inner diameter of 7.0 mm and an inner diameter of 7.0 mm was formed.

The thermal conductivity and the tensile strength of the obtained flat plate were measured, and the pressure resistance of the hollow pipe was measured. The results are shown in Table 2.

[0026]

COMPARATIVE EXAMPLE 7 Compounded resins shown in Table 1 were prepared by the same resin base material and method as in Examples 1 to 8 and Comparative Examples 1 to 6. This compounded resin is vacuum degassed at 60 to 70 ° C and then poured into a metal mold having a chrome-plated 25 cm square and a thickness of 2 mm, 80 ° C for 1 hour, 150 ° C for 2 hours, 180 ° C.
Compression molding was carried out for 3 hours to obtain a flat plate.

The thermal conductivity and tensile strength of the flat plate thus obtained were measured. The hollow pipe could not be molded. The results of these measurements are shown in Table 2. The heat conductive molded article of the present invention includes a heat exchanger panel, fins, heat transfer tubes, heat radiating electric parts (heat radiating panel of refrigerator, cooling of speaker coil, etc.), sliding member, electron varnish substrate, radiator panel for vehicle, etc. It is useful for applications requiring thermal conductivity and mechanical strength.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

EFFECTS OF THE INVENTION The heat conductive molded product of the present invention has excellent moldability, high thermal conductivity and high heat resistance as compared with the conventional products. Further, since it has excellent smoothness and high mechanical strength, it is possible to increase the flow velocity in the pipe, which is useful for applications where it is necessary to suppress the deposition of scale and the like.

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Claims (2)

[Claims] 1. A thermally conductive molded article, which comprises a molding material in which unidirectionally aligned carbon fibers are impregnated with a thermosetting resin containing graphite powder. 2. The thermosetting resin is 20-80% by weight, the total amount of unidirectionally aligned carbon fibers and graphite powder having a particle size of 40 μm or less is 20-80% by weight, and the carbon fibers and the graphite powder. And the ratio is 25:75 to 95: 5 (weight ratio).