JP2620606B2 - High purity flexible expanded graphite sheet and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-purity flexible expanded graphite sheet and a method for producing the same, and more particularly, to a high-purity flexible expanded graphite having a very low content of all impurities, especially S. The present invention relates to a sheet and a method for manufacturing the sheet.

[Prior art] A flexible expanded graphite sheet itself is well known in the art, and this graphite sheet is usually obtained by anodizing natural scaly graphite or quiche graphite or adding acid such as nitric acid to sulfuric acid such as agricultural sulfuric acid. Immersed in a mixed acid, subjected to oxidation treatment, washed with water, dried and then subjected to a heat expansion treatment to form expanded graphite,
The expanded graphite obtained here is manufactured by compression molding with a press or a roll. This expanded graphite sheet is not only excellent in chemical resistance, heat resistance, heat and electric conductivity, but also excellent in flexibility and compression restorability, and has large anisotropy, which are characteristics of graphite. It is widely used as various packing materials and high-temperature insulation materials.

However, since the starting material of this expanded graphite sheet is natural flaky graphite or quiche graphite, it contains Si, other Fe,
It contains a large amount of impurities such as Al. In addition, since it is manufactured through an immersion treatment of a mixed acid based on agricultural sulfuric acid, there is a major drawback that a large amount of sulfur compounds remain, and particularly the S content is large. Therefore, when this expanded graphite sheet is used under conditions such as heating, decompression, or gas replacement, there is a disadvantage that the atmosphere is contaminated by these impurities. In particular, when the S content is high as an impurity, this disadvantage tends to be exhibited particularly remarkably.

[Problem to be Solved by the Invention] The problem to be solved by the present invention is to solve the above-mentioned drawbacks of this kind of expanded graphite sheet. In other words, the expanded graphite sheet having an extremely low impurity content. In particular, it is an object of the present invention to develop a flexible expanded graphite sheet of this kind which has particularly low S content and total impurities other than S.

[Means for Solving the Problems] This problem is solved by providing a highly pure and flexible expanded graphite sheet having an S content of 15 ppm or less and a total amount of impurities other than S of 20 ppm or less.

[Operation and Structure of the Invention] The first feature of the present invention is that the composition has flexibility with an extremely low S content of 15 ppm or less and the total amount of impurities other than S of 20 ppm or less. Such low-content expanded graphite sheets have not been developed at all. This feature is extremely clear from, for example, Example 1, Comparative Example 1, and Reference Example 1 described later.

If the S content exceeds 15 ppm, it may cause the product to have a poor purity in applications such as those shown in FIGS. Further, when impurities other than S exceed 20 ppm, the product is similarly adversely affected.

When manufacturing such a high-purity expanded graphite sheet, it can be manufactured by heat-treating a conventional expanded graphite sheet under the following conditions. That is, an expanded graphite sheet having a bulk density of 0.7 to 1.3 g / cm ³ , preferably 0.8 to 1.0 g / cm ³ (hereinafter abbreviated as “carbon sheet”) is placed in a container.
It is usually kept at 800 to 1000 ° C for 1 to 10 hours. When the temperature is lower than 800 ° C., the vapor pressure of the halogenated impurities does not reach, and sufficient evaporation and volatilization cannot be performed. Preferably, after maintaining for 3 to 5 hours, the temperature is gradually increased, and the temperature is adjusted to 2450 to 2500 ° C. while maintaining the temperature.
Hold for 24 hours. If the holding time is less than 5 hours,
The halogenated organic material does not sufficiently penetrate into the graphite sheet, and S or impurities other than S present in the sheet cannot be evaporated and volatilized by increasing the vapor pressure as a halide. Further, even if the holding time is longer than 24 hours, the evaporation and volatilization of impurities other than S and S are in a steady state, and the effect obtained is small. Preferably, it is maintained for 7 to 15 hours.

If the bulk density is less than 0.7 g / cm ³ , the strength is insufficient, and 1.3 g / c
It requires re-roll cliff like exceeds m ^3, and the cost becomes high.

The inside of the vessel is kept at 1 to 100 Torr, preferably about 10 to 40 Torr from the time of starting the heating, so that it is convenient for discharging the degassed gas which slightly evaporates at this stage. Pressure
If it exceeds 100 Torr, the effect of reducing the pressure will be small, and it will take time to achieve high purification, and the cost will increase. On the other hand, if it is less than 1 Torr, the amount of halogen is small, and the purification becomes insufficient.

At a stage where the graphitization has progressed to some extent, a halogenated organic gas, for example, a halogen gas such as dichlorodifluoromethane is supplied from the gas distribution pipe in a reduced pressure state (the flow rate is increased or decreased depending on the amount of the carbon material to be heated filled in the container, For example, 1-7
Supply about 3-8 hours (at about NPT / kg).

The halogenated organic gas used for the purification is required to increase the vapor pressure of impurities contained in the carbon sheet, particularly metal impurities, as halogen salts, and to evaporate and volatilize the same to increase the purity of the base carbon sheet. However, as the halogenated organic substance, any of those conventionally used for graphite materials can be used.For example, not only chlorine and chlorine compounds but also fluorine and fluorine compounds can be used. Gases may be used together.
Further, a compound containing fluorine and chlorine in the same molecule, for example, monochlorotrifluoromethane, trichloromonofluoromethane, cyclodifluoroethane, trichloromonofluoroethane and the like can also be used.

Since H ₂ has a high refining effect with respect to the kind of impurities, for example, sulfur content, if the supply of the halogenated organic substance is stopped and the H ₂ gas is subsequently supplied, the sulfur can be more completely removed. If the temperature is lower than 800 ° C., the reactivity between sulfur and hydrogen gas is not good, which is not preferable. On the other hand, if the pressure is higher than 100 Torr, the depressurizing effect is reduced, and if the pressure is lower than 1 Torr, the absolute amount of the supplied hydrogen gas is reduced, and it is not possible to sufficiently remove sulfur by the hydrogen gas.

When the purification operation is completed, the temperature in the furnace is preferably further increased, and the temperature is maintained at 3000 ° C. for about 10 to 30 hours to complete the process.

During the process of cooling the furnace, the pressure in the vessel was strongly reduced to about 10 ⁻² to 10 ⁻⁴ Torr at about 2000 ° C., and by cooling,
A high-purity carbon sheet with little outgas and S can be obtained. In addition, since the thickness of the sheet of Comparative Example 1 and Example 1 described later is increased, it is understood that the gas such as the halogenated organic gas and the outgas can enter and exit from the side of the sheet.

Stop energization, return to normal pressure and room temperature while filling and replacing the container with N ₂ gas. Next, compression molding is performed by ordinary compression molding means, for example, by rolling with a press or a roll.

In the process of removing impurities, i.e., in the purification step, a vacuum high-frequency heating furnace can be used in the present invention, which is extremely convenient. That is, when the carbon sheet to be heated is brought into contact with the halogenated organic substance under vacuum or reduced pressure conditions, the advantage is that the consumption amount is very small. Under vacuum or reduced pressure conditions, the halogenated organic gas is expanded and used, so that the utilization efficiency is high, and the contact with the carbon sheet is also good. Therefore, the test results conducted by the present inventor have shown that in the case of a current-bed type furnace (10 NPT / kg) compared to (3NP
T / kg) and dichlorodifluoromethane consumption have been reduced by a third.

The second advantage is that impurities in the halogenated or / and hydrogenated carbon sheet are likely to volatilize and desorb to the outside because the atmosphere is under reduced pressure, so that a small amount of halogenated organic gas can be used. In spite of this, a quicker and higher purity graphite material can be obtained.

Incidentally, the difference between JP-A-58-84181 and this method will be described briefly. In the known invention of the above-mentioned application, as is clear from the specification, chlorination (using HCl) is carried out at normal pressure (No. One step), the halogenated impurities are vacuumed (second step), and then H _{2 is} passed to remove other impurities (third step, pressure unknown). It is characterized in that it is performed at normal pressure, and that the chlorination step and the chlorinated impurity removal step are performed separately, and that a high-frequency heating furnace is not used.

On the other hand, the above-mentioned method adopted in the present invention performs the impurity removing step while flowing the halogenated organic substance and / or H ₂ .
There is a great difference in that both the halogenation reaction and the halide elimination reaction are carried out under reduced pressure or vacuum conditions and at the same time.

It is necessary to maintain the pressure in the vessel at the time of carrying out high purification according to the present invention in the range of 100 to 1 Torr. The pressure in the vessel is measured by a pressure gauge as the sum (total pressure) of the vapor pressures (partial pressures) of various compounds such as halides, chlorinated and / or fluorinated impurities, or residual N ₂ gas at the time of replacement. However, when the pressure is higher than 100 Torr, the depressurizing effect is reduced, so that the time required for high purification becomes longer, and the quality is the same as the conventional normal pressure method. The absolute supply is reduced,
It is not advisable that the purification of the deep part of the carbon sheet becomes insufficient or that a large amount of pump power is required to remove generated gas.

The inventors obtained various optimum values using the actual device.
It was confirmed that the best product was obtained at 〜100 Torr, particularly preferably 5-50 Torr.

As the expanded graphite sheet used in the present invention, any of the conventional expanded graphite sheets can be applied in a wide range. Usually, a bulk density of about 0.7 to 1.3 g / cm ³ is preferably used. Further, the manufacturing method itself is not limited at all, and may be manufactured by any method. As the heat treatment, not only normal heat treatment but also high-frequency heating as described above may be performed.

Since the high-purity flexible expanded graphite sheet of the present invention has a very low S content and the total amount of impurities other than S and has flexibility, various fields which have not been used in the prior art due to the presence of S, for example, FIG. It is very suitably used in the fields of internal heat insulating materials for high-temperature and high-pressure containers and spacers for semiconductor manufacturing equipment as shown in (1). Of course, in the field in which this type of conventional expanded graphite sheet has been used, it is of course preferably used particularly preferably under severe temperature conditions or under conditions requiring a high-purity atmosphere.

Hereinafter, typical examples of uses of the sheet of the present invention will be described with reference to the drawings.

FIG. 1 shows an example in which a single crystal pulling apparatus is used as a spacer and a heat insulating material. In FIG. 1, (1) is a spacer made of the sheet of the present invention, and (2) is a heat insulating material using the sheet of the present invention. In FIG. 1, (3) is a graphite heater, (4) is a graphite crucible, (5) is a quartz crucible,
(6) shows a graphite gantry, (7) shows silicon, (8) shows a single crystal, and (9) shows a pulling device. Spacer (1)
The quartz crucible (5) is placed directly on the quartz crucible (5), and the molten silicon (7) is present in the quartz crucible (5). Therefore, if impurities are precipitated from the spacer, it immediately affects the quality of the silicon single crystal, and contaminates and damages the quartz crucible. However, such a problem does not occur in the case of a high-purity sheet as in the present invention. Also, since the heat insulating material (2) is installed on the inner surface of the single crystal pulling apparatus, impurities from the heat insulating material contaminate the atmosphere in the apparatus and not only adversely affect the silicon single crystal, but also have an adverse effect on the silicon single crystal. Contamination corrosion may occur, but such a concern hardly occurs because the sheet of the present invention is of high purity.

FIG. 2 shows an apparatus for impregnating a metal under high pressure, particularly an apparatus for impregnating a carbon material with metal. Is shown. In FIG. 2, (15) is a carbon material to be impregnated with a metal, (16) is a porous basket, (17) is a molten metal, (1)
8) shows a resistance heating element, (19) shows an exhaust pipe, and (20) shows a crucible. Even if it is placed in this device, the purity of the heat insulating material installed on the inner surface of the device has a great effect, and the sheet of the present invention is highly suitable because of its high purity.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Reference Examples and Examples, which are production examples of expanded graphite sheets.

Reference Example 1 Natural scaly graphite immersed in a mixed solution of 7 to 25 parts by weight of potassium permanganate in concentrated sulfuric acid with respect to 100 parts by weight of graphite was heated to 800 to 1000 ° C., and the volume was 140 to 160 cm ³ / g. The expanded graphite was press-molded to obtain an expanded graphite sheet having an apparent density of 1.0 g / cm ³ . The total ash content of this expanded graphite sheet,
The contents and the flexibility of S, Fe, Si, and Al were measured, and the results are shown in Table 1.

The total ash content was ashed by heating at 850 ° C. in the air for 15 hours and evaluated by the weight ratio of the remaining portion. S content is determined by ion chromatography,
Si was evaluated by an absorption method, and Fe and Al were evaluated by ICP. The flexibility was evaluated by inverting the sample on a 10φ glass rod each time and winding the sample until it was cut.

Comparative Example 1 The expanded graphite sheet produced in Reference Example 1 was heated in the presence of difluoromethane at a total pressure of 20 Toor and 900 ° C. for 10 hours to produce a high-purity expanded graphite sheet. The thickness increase rate at this time is 1.
7%. The total ash content of this high-purity expanded graphite sheet,
S, Fe, Si, Al and flexibility were measured, and the results are shown in Table 1.

Example 1 The expanded graphite obtained in Reference Example 1 was subjected to press molding to have an apparent bulk density of 1.
After producing an expanded graphite sheet of 0 g / cm ³ and heating in a gas atmosphere of difluoromethane at 10 Toor and 1000 ° C. for 20 hours, the supply of difluoromethane was stopped, and then the hydrogen gas was subjected to a total pressure of 10 Toor and 1000 ° C. For 3 hours to obtain a high-purity expanded graphite sheet. At this time, the thickness increase rate was 14%.

This was compression-molded with a press to obtain a high-purity expanded graphite sheet having an apparent bulk density of 1.3. The total ash, S, Fe, Si, Al and flexibility were measured, and the results are shown in Table 1.

Example 2 A heat-insulating material and an internal member inside a high-pressure impregnating device incorporating a resistance heating element shown in FIG. 2 were obtained by using the graphite sheet subjected to the high-purification treatment described in Example 1 and the unpurified sheet described in Reference Example 1 Used as

In the apparatus shown in FIG. 2, the heat insulating materials (12) and (13) used for the inner ceiling and the bottom are flat graphite sheets (thickness of 0.1 mm).
52m / m) was cut, laminated to a thickness of 3cm, and attached to the inner wall.

The heat insulating material (II) used for the surrounding wall is made by winding a long roll of graphite sheet (0.38 m / m thick) to a thickness of 5 cm.
It is fitted on the inner wall of the reaction vessel. Graphite sheet material is an extremely anisotropic material among carbon materials, and x,
It is suitable for transmitting heat well to the y-axis (plane direction) and for achieving a uniform temperature distribution inside the device, but has the property of shutting off heat on the z-axis (direction perpendicular to the plane). It is suitable as a material.

A graphite sheet material was also used as a cushioning material (14) between the crucible (isotropic graphite material) and the lower crucible mount (made of steel other than cast steel). This graphite sheet material is a material obtained by compacting expanded graphite with a roll, and has a small space inside so that it has flexibility and cushioning properties. Therefore, a spacer, a cushioning material, a gasket material, a sliding member Often used as In the case of this example, a low consolidation grade graphite sheet having a thickness of 0.8 m / m is laminated to a thickness of 10 cm, and the central portion is cut into this shape so that the crucible bottom can be fitted. A graphite sheet is used as a spacer having a buffering action so that the graphite crucible is not broken by contact with the gantry due to the weight of the metal inside.

As a carbon material to be impregnated with metal, bulk density 1.601g / c
m ³ , electrical specific resistance 750 μΩcm, bending strength 78 kg / cm ² , compressive strength 115 kg / cm ² , elastic modulus 793 kg / cm ² , porosity 26.9%, viscous flow diffusion coefficient 2.5 × 10 ^-8 and thermal expansion coefficient 1.3 A carbon material having physical properties of × 10 ⁻⁶ / ° C. was used. Lead (melting point: 328 ° C.) was used as the metal (17) to be impregnated.

A carbon material (diameter 15 cm, length 24 cm) is placed in a heat-resistant special steel basket (16) held at the top of a pressure vessel (diameter 30 cm, length 60 cm) with a built-in heating element, and the above lead is added to the container. At the bottom. The container was evacuated to 5 mmHg,
Heat in minutes. Temperature is measured with a thermocouple inserted from the bottom of the pressure vessel. Raise the temperature to 500 ° C, hold at this temperature, then lower the heat-resistant special steel basket (16) held at the top of the container and immerse the carbon material (15) in the molten lead (17) I do. Next, the pressure reducing pump is stopped, nitrogen gas is injected under pressure so that the pressure in the container becomes 50 kg / cm ^2, and the temperature is maintained for about 1 hour. Then, the heat-resistant special steel basket (16) is pulled up, and the pressure in the container is returned to 1 atm.
After being taken out of the pressure vessel, it is allowed to cool naturally, and lead attached to the surface of the carbon material is scraped off. Thus, the carbon material of the present invention is obtained.

Prior to the completion of the high-purity flexible expanded graphite sheet material according to the present invention, the unpurified carbon material shown in Reference Example was used. The corrosion caused by the material caused a connection failure, and repair was required in about 2 months. However, when using the high-purity heat insulation and cushioning member according to the present invention, the repair interval was extended to about 6 months, and it was obvious that The effect was recognized.

In addition, carbon material impregnated with lead is cut and used as a sliding member for machinery, but when high-purity heat insulation and cushioning material are used, prevention of deterioration of lead by sulfur components is complete, and sleeves using this are used. (Rotating shaft sliding member) also improved the non-defective rate by mechanical strength measurement to 100%. Incidentally, when the conventional graphite sheet was used, the non-defective rate was 96% in comparison with the case where all other conditions were the same, and the effect was recognized also in terms of quality.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a single crystal pulling apparatus using the sheet of the present invention, and FIG. 2 is a sectional view of a high pressure impregnating apparatus. DESCRIPTION OF SYMBOLS 1 ... Spacer, 11-13 ... Insulation material 2 ... Insulation material, 14 ... Spacer 3 ... Graphite heater, 15 ... Carbon material 4 ... Graphite crucible, 16 ... Porous basket 5 ... Quartz crucible , 17 ... metal 6 ... graphite stand, 18 ... heating element 7 ... silicon, 19 ... exhaust pipe 8 ... single crystal, 20 ... crucible 9 ... pulling device

Claims (3)

(57) [Claims] (1) S content is 15 ppm or less and total impurities other than S are 2 ppm.
High purity flexible expanded graphite sheet having flexibility of 0 ppm or less. 2. An expanded graphite sheet having a bulk density of 0.7 to 1.3 g / cm ³ is heated at 800 ° C. or more for 5 to 24 hours under reduced pressure of 100 to 1 Torr in the presence of a halogenated organic substance, and then cooled.
The method for producing a high-purity flexible expanded graphite sheet according to claim 1, wherein the sheet is compression-molded. 3. The method for producing a high-purity flexible expanded graphite sheet according to claim 2, wherein after the heat treatment with the halogenated organic substance is performed, the supply of the halogenated organic substance is stopped, and then the substitution is continued. While supplying hydrogen gas to
The method for producing a high-purity flexible expanded graphite sheet according to claim 2, wherein the treatment is performed at a temperature of 800 ° C or more under a reduced pressure of 1 to 1 Torr.