JPH05178605A - Production of thermally expansible graphite - Google Patents

Abstract

PURPOSE:To obtain thermally expansible graphite excelling in thermal stability by acid-treating graphite with a mixture of sulfuric acid and an oxidizing agent and giving it water washing and filter separation before drying it so that the ratio of the whole volatile component after drying to that before drying may be the prescribed one. CONSTITUTION:After graphite is crushed and acid-treated with a mixture of sulfuric acid and a oxidizing agent, it is washed with water and separated by filtration to obtain wet cake. Next, the wet cake is dried so that the ratio of the whole volatile component after drying to that before drying may be 60-95wt.% to get thermally expandable graphite. Here, the whole volatile component before drying is calculated by the formula, (A1-A2)/A1, where A1 grams represents the weight of a dried substance which is obtained by drying the wet cake after water washing and filter separation at 105 deg.C for 2hr and A2 grams represents the weight of the substance after heating at 1000 deg.C for 10sec. The whose volatile component after drying is calculated by the formula, (B1-B2)/B1, where B1g represents the weight of the dried sample and B2g represents the weight of the heated substance after heating at 1000 deg.C for 10sec.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing thermally expandable graphite. More specifically, it relates to a method for producing thermally expandable graphite having excellent thermal stability.

[0002]

2. Description of the Related Art Thermally expandable graphite expands to several tens to several hundreds of its original volume when heated to a high temperature, and when it is pressed, a highly flexible graphite sheet can be obtained, or a polyurethane foam. It is known as an industrially important material because it can be added to the above to impart flame retardancy.

The heat-expandable graphite is usually obtained by treating natural graphite, pyrolytic graphite, quiche graphite or the like with a mixture of concentrated sulfuric acid and a strong oxidant (hereinafter this treatment is referred to as acid treatment), washing with water and drying. It is obtained by doing. As the acid treatment method, a method using nitric acid and its salt in concentrated sulfuric acid (Japanese Patent Publication No.
4-25913), a method using potassium permanganate (JP-A-55-95609) and a perhalogenate (JP-A-51-96793) as an oxidizing agent, or an anode of graphite by an electrolytic reaction. A method of performing oxidation (Japanese Patent Publication No. 56-18352) is known.

[0004]

The heat-expandable graphite produced by the usual method is the graphite produced by the acid treatment.
The intercalation compound of sulfuric acid becomes a residual compound by washing with water and becomes thermally expansive. However, about 200 ℃ or more,
In particular, when it is heated to about 250 ° C. or more, a remarkable loss on heating is observed, and it has a characteristic of extremely poor thermal stability. Therefore, there is a problem that the temperature to be applied is limited when the thermally expandable graphite is blended with the thermoplastic resin or the like.

[0005]

The present invention provides a method for producing thermally expandable graphite by subjecting graphite to acid treatment with a mixture of sulfuric acid and an oxidizing agent, washing with water, filtering and drying. Provided is a method for producing thermally expandable graphite, wherein the wet cake after filtration is carried out such that the total volatile content after drying is 60 to 95% by weight with respect to the total volatile content before drying. The total volatile component of the wet cake was washed with water and filtered to remove the wet cake at 105 ° C.
After drying for an hour, the dried product (A ₁ g) is dried at 1000 ° C. for 10
It is a value calculated by the following formula (1) (A ₁ -A ₂ ) / A ₁ (1) from the weight (A ₂ g) of the object to be heated after heating for a second, and the total volatile content after drying. Is the weight (B ₂ g) of the object to be heated after heating the dried sample (B ₁ g) at 1000 ° C. for 10 seconds and the following formula (2) (B ₁ −B ₂ ) / B ₁ It is the value calculated by (2). ).

The inventors of the present invention have made extensive studies as to thermally expansive graphite which has a small heating loss at 250 ° C. and does not impair the expansion performance, and as a result, found that the above-mentioned problems can be solved by a specific treatment. The present invention has been completed. In the present invention, the heat-expandable graphite means natural graphite, pyrolytic graphite, graphite obtained by acid treatment of graphite such as Kish graphite with a mixture of concentrated sulfuric acid and a strong oxidizing agent, followed by washing with water and drying. To do. That is, it means industrially thermally expandable graphite used for producing a graphite sheet or the like.

The thermally expandable graphite is, for example, 98% sulfuric acid and 6%.
Graphite crushed to about 20 to 100 mesh in a mixture of 0% hydrogen peroxide water is contacted at 45 ° C. or lower for 10 to 30 minutes for acid treatment, then washed with water and dried.

Washing with water is carried out by separating and removing a liquid phase portion such as sulfuric acid from the acid-treated slurry, adding the acid-treated graphite separated as a solid content to a large amount of water, and thoroughly stirring. Washing with water may be repeated if necessary. After washing with water, the acid-treated graphite from which the liquid phase has been separated and removed is recovered as a solid content. When it is necessary to neutralize the recovered acid-treated graphite with ammonia water, usually, the acid-treated graphite is added to the tank containing the ammonia water, and the mixture is thoroughly stirred and then separated and recovered. It is carried out by a method of directly sprinkling ammonia water on the recovered substance which is the residue in the filtration step of separating and removing and contacting it. The concentration of ammonia water is usually 3 to 4%. The acid-treated graphite obtained by washing with water and optionally with neutralization is subjected to volatile components (at 105 ° C. for 2 hours at a temperature of about 120 to 180 ° C.) by a method such as tray drying, air flow drying, and fluidized drying. Weight loss when heated) is 1%
It is dried to the front and back.

In the present invention, drying (hereinafter also referred to as heat treatment) means that after acid treatment of graphite with a mixture of sulfuric acid and an oxidizing agent, the wet cake filtered and washed with water is dried with respect to all volatile components before drying. Drying or heat treatment is performed so that the total volatile content afterward becomes 60 to 95%. The total volatile matter before drying means the weight of the heated object after the wet cake filtered after washing with water is dried at 105 ° C. for 2 hours and the dried product (A ₁ g) is heated at 1000 ° C. for 10 seconds. (A ₂ g) is a value calculated by the following equation (1) (A ₁ −A ₂ ) / A ₁ (1). The total volatile content after drying is calculated from the following formula (2) (B ₁ −) based on the weight (B ₂ g) of the object to be heated after heating the dried sample (B ₁ g) at 1000 ° C. for 10 seconds. It is a value calculated by B ₂ ) / B ₁ (2).

In the measurement of total volatile matter, about 5-10
When g is used as a sample, it is dried at 105 ° C. for about 1 hour until the volatile content becomes 1% or less, and then it becomes a constant value and shows a constant value.
The use of 10 to 10 g is preferred.

When the total volatile content after drying is less than 60% with respect to the total volatile content before drying, the thermal expansion property is lowered and a desired expanded product cannot be obtained. If it exceeds 95%, the thermal stability becomes insufficient.

The relationship between the drying temperature and the treatment time is appropriately selected according to the heating method and scale, but is preferably 23.
It is 0 ° C or higher. If the temperature is lower than 230 ° C, the heating time becomes long and it is not economical. At 400 ° C. or higher, the expansivity, which is a characteristic of the thermally expansive graphite, decreases except for the case of short-time treatment, and it is difficult to obtain a desired expanded product. The drying of the present invention may be carried out by using a tray dryer, a gas stream dryer, a fluidized dryer or the like which is usually used for drying the acid-treated graphite from which the liquid phase has been separated and removed after washing with water. Further, the drying of the present invention may be carried out after drying at 120 to 180 ° C. which is a usual drying condition.

When the obtained heat-expandable graphite is required to be neutral, the wet cake after washing with water is treated with ammonia water, and when the usual drying step is carried out, the drying step is carried out in the drying step.
Alternatively, it may be neutralized with ammonia gas after the drying of the present invention.

Hereinafter, the present invention will be described in more detail based on examples. The thermal stability and degree of expansion measured in each of the following examples were measured as follows. Thermal stability: 1 g of a sample was sampled in a crucible and held for 30 minutes in a thermostat held at 250 ° C., and the weight difference before and after holding was expressed as a percentage of the weight before holding. Expansion degree: A quartz beaker with a volume of 120 ml, which was kept in an electric furnace maintained at 1000 ° C. for 10 minutes or more, was taken out of the furnace, and 0.5 g of a sample was immediately added to the beaker immediately.
Place in an electric furnace maintained at 00 ° C. After holding as it is for 10 seconds, the sample is taken out of the furnace, naturally cooled, and then the volume of the sample after expansion is measured by a scale attached to a beaker. The degree of expansion was expressed as the ratio of the volume after expansion to the weight of the sample (unit: ml / g). In each of the following examples,% means% by weight unless otherwise specified.

Production Example [Production of Thermally Expandable Graphite] 200 g of natural scaly graphite (particle size: 36 to 80 mesh) produced in China with fixed carbon content of 98% and ash content of 2% is 98% sulfuric acid 600 g, 60% peroxidation. It was added to a mixed solution of hydrogen water 9.9 g and reacted at 30 to 35 ° C. for 15 minutes. After 1800 g of 58% sulfuric acid was added to the reaction product to dilute it, suction filtration was performed with a Nutsche using a glass fiber filter paper (GA100), and the residue was taken out. The filtration residue was put into 1600 g of water, washed with stirring for 30 seconds, and then suction-filtered to separate the residue as a wet cake.
Seven samples of 20 g each were separated from this wet cake, and the following operations were performed. In addition, 0.5 g of this wet cake was dried for 2 hours at 105 ° C. in a hot air circulation dryer.
Was precisely weighed and then held in an electric furnace kept at 1000 ° C. for 10 seconds, then taken out of the furnace, naturally cooled, and then weighed to determine the total volatile content.
It was 162.

Examples 1 to 2 About 2 samples of the wet cake obtained in the production example, about 10 g of each of them was heated at 250 ° C. for 70 minutes (Example 1), 300
C., 35 minutes (Example 2), heat treatment was performed in a hot-air circulation dryer, 0.5 g of each was kept in an electric furnace kept at 1000.degree. C. for 10 seconds, then taken out of the oven, and allowed to stand naturally. After cooling, the weight was measured to determine the total volatile content.

Examples 3 to 4 Two wet cake samples obtained in the production examples were added to 60 g of ammonia water having a concentration of 3.7%, stirred for 3 minutes, and then suction-filtered to separate them. About 10 g of each sample was heated at 230 ° C. for 45 minutes (Example 3), 350 ° C., 8
For 5 minutes (Example 4), heat treatment was performed in a hot air circulation dryer, and 0.5 g of each was held in an electric furnace held at 1000 ° C. for 10 seconds, and then taken out of the furnace.
After natural cooling, the weight was measured to determine the total volatile content.

Comparative Examples 1 to 2 About 2 samples of the wet cake obtained in the production example, about 10 g of each sample was 250 ° C. for 13 minutes (Comparative Example 1), 3
Heat treatment was performed in the same manner at 00 ° C. for 90 minutes (Comparative Example 2) to determine the total volatile content.

Comparative Example 3 One sample of the wet cake obtained in the production example was dried at 105 ° C. for 2 hours in a hot air circulation dryer. Table 1 shows the values of total volatile matter, thermal stability, and expansion coefficient before and after heat treatment obtained in each example.

Table 1 Example 1 2 3 4 Heat treatment temperature (° C.) 250 300 300 230 350 Heat treatment time (min) 70 35 45 8 Total volatile content after heat treatment 0.127 0.099 0.149 0.103 (X / Y ) × 100 78.4 61.1 88.3 63.6 Thermal stability (%) 0.06 0.00 0.00 0.80 0.00 Expansion coefficient (ml / g) 200 180 200 200 190

Table 1 (continued) Comparative Example 1 2 3 Heat treatment temperature (° C.) 250 300 Blank heat treatment time (min) 13 90 Total volatile content after heat treatment 0.159 0.080 (X / Y) × 100 98.1 49 .4 Thermal stability (%) 3.02 0.00 3.9 Expansion coefficient (ml / g) 210 80 210 Note: X: Total volatiles after heat treatment Y: Total volatiles before heat treatment Examples 1-4 The heat-expandable graphite obtained in 1. had excellent thermal stability as compared with Comparative Example 3 in which heat treatment was not performed, and the expansion degree was hardly reduced.

[0022]

EFFECTS OF THE INVENTION According to the present invention, there is provided a production method in which a heat loss is extremely small and a thermally expansive graphite excellent in thermal stability can be easily obtained.

Claims (1)

[Claims] 1. A method for producing heat-expandable graphite by subjecting graphite to acid treatment with a mixture of sulfuric acid and an oxidizing agent, washing with water, filtering and drying to dry the wet cake after filtering the drying. A method for producing heat-expandable graphite, wherein the total volatile content after drying is 60 to 95% by weight relative to the total volatile content before drying (wherein the total volatile content before drying is filtered after washing with water) The wet cake thus obtained was dried at 105 ° C. for 2 hours, and the dried product (A ₁ g) was heated at 1000 ° C. for 10 seconds to obtain the weight (A
₂ g) and the value calculated by the following formula (1) (A ₁ −A ₂ ) / A ₁ (1), and the total volatile content after drying is the dried sample (B ₁ g) Is the value calculated by the following equation (2) (B ₁ -B ₂ ) / B ₁ (2) from the weight (B ₂ g) of the object to be heated after heating at 1000 ° C. for 10 seconds. ).