JP2690982B2 - Thermally expandable graphite and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to thermally expandable graphite. Since the pH of the heat-expandable graphite of the present invention is controlled by the alkali metal, it has high stability over time and is advantageously used in various applications.

[Prior Art] Heat-expandable graphite instantly expands to several tens to several hundred times its original volume when heated to a high temperature, and the expanded graphite is pressed to be flexible without using a binder. It is well known as an industrially important material because an excellent graphite sheet can be obtained.

This thermally expandable graphite is usually natural graphite, pyrolytic graphite,
It is obtained by treating graphite such as quiche graphite with a mixture of concentrated sulfuric acid and a strong oxidizing agent, washing with water, and drying.
Since it contains free sulfuric acid other than sulfuric acid existing between graphite layers, it is acidic.

It is considered that this acidity can be theoretically neutralized by repeating the washing step to remove free sulfuric acid, but adding such a treatment is entirely practical in terms of economic efficiency. In general, the pH of an aqueous dispersion containing 1% by weight of thermally expandable graphite is not observed.
However, the thing of about 2.5-3.5 is used. In addition to being used for the graphite sheet as described above, the heat-expandable graphite is, for example, as described in US Pat. No. 3,574,644, a polymer compound such as grease, tar, asphalt, polyester, polystyrene, or for forming a film. Used as a flame retardant for latex or emulsion.

However, since the heat-expandable graphite obtained by the conventional method has a strong acidity, when it is added to an aqueous emulsion product or an aqueous latex product, the stability of these substances is impaired or it is added to a plastic product. However, there is a problem in that the machine parts for molding are corroded when processed at high temperature.

As a method for solving this problem, US Pat.
No. 4,644 describes a method in which ammonia is added to the latex before adding the heat-expandable graphite or the heat-expandable graphite is brought into contact with ammonia in advance and added to the latex.
However, this method is not always sufficient for preventing destabilization of emulsions and latexes and for preventing rusting, and the heat-expandable graphite treated with ammonia does not change with time when left in air. Its acidity tended to increase.

The reason for this is that ammonium sulfate, which is considered to be produced by neutralization with ammonia, is caused to decompose under the temperature conditions during plastic processing or to reduce the effect of neutralization by releasing ammonium in the air. It is thought to be done.

[Problems to be Solved by the Invention] The present invention has a low content of the above-mentioned free sulfuric acid, and its acidity does not change over time, and their stability when added to an aqueous emulsion product or an aqueous latex product. The present invention aims to provide a thermally expandable graphite that does not impair the properties.

[Means for Solving the Problem] The present invention is to control the amounts of free sulfuric acid and alkali metal contained in the thermally expandable graphite by causing an alkali metal compound to act on the free sulfuric acid in the thermally expandable graphite. Therefore, the above problems are to be solved. That is, according to the present invention, (1) the thermally expandable graphite contains an alkali metal, and the molar ratio of the alkali metal to the sulfate radicals other than sulfuric acid forming the intercalation compound contained in the thermally expandable graphite is 1 The above is the thermally expansive graphite characterized by the above.

(2) The thermally expansive graphite according to the item (1), wherein the alkali metal is Na or K.

(3) After treating the graphite with a mixture of concentrated sulfuric acid and an oxidizing agent, the reacted graphite is washed with water and then dried until the amount of free sulfuric acid with respect to the solid content of the substance to be washed is 1 mol / kg or less. After that, a method for producing heat-expandable graphite is characterized in that it is neutralized with an aqueous solution of an alkali metal compound so that the molar ratio of alkali metal to free sulfuric acid is 2 or more, and then dried.

(4) The method for producing thermally expandable graphite according to the above item (3), wherein the alkali metal is Na or K.

(5) The above (3) or (4), wherein the alkali metal compound is one or more selected from hydroxides, oxides, carbonates and organic acid salts. The gist of the invention is a method for producing thermally expandable graphite.

[Specific Structure of the Invention] The heat-expandable graphite can be produced by various methods in a broad sense and various compositions can be mentioned. In the present invention, natural graphite, pyrolytic graphite, and quiche are used. After treating graphite, such as graphite, with a mixture of concentrated sulfuric acid and a strong oxidant,
Heat-expandable graphite is manufactured by washing with water and drying.

This thermally expandable graphite has the property of expanding several tens to several hundred times in the C-axis direction when it is rapidly heated to about 500 ° C. or higher.

The heat-expandable graphite of the present invention, the raw material graphite, the acid treatment method is not particularly limited, as its characteristics, 1000 ° C. for 10 seconds, the expansion degree when rapidly heated is 50 ~ 250 m1 / gr. Is desirable.

Such heat-expandable graphite is, for example, 98% concentrated sulfuric acid and 60%.
Produced by contacting graphite crushed to about 20-100 mesh with a mixture of 10% hydrogen peroxide solution at 45 ° C or less for 10-30 minutes, then washing the reaction product with water, filtering and drying. However, in the heat-expandable graphite thus obtained, there are sulfuric acid taken inside the graphite layer as a graphite intercalation compound and a small amount of free sulfuric acid adhering to the solid surface. It is considered that this small amount of free sulfuric acid exhibits acidity and causes the above problems.

The "free sulfuric acid" in the present invention is attached sulfuric acid other than sulfuric acid forming an intercalation compound, and this free sulfuric acid is a state in which the heat-expandable graphite is dispersed in water and is held for about 10 minutes. Measured by alkali titration. At the time of alkali titration, adjusting the concentration to about 1 to 5% facilitates the titration operation.

The heat-expandable graphite of the present invention has a molar ratio of the alkali metal to 1 or more with respect to sulfate radicals other than sulfuric acid (hereinafter simply referred to as sulfate radicals) forming the intercalation compound contained therein. It is necessary, and the method for measuring the amount of sulfate radical and the amount of alkali metal is performed as follows.

That is, 1gr of thermally expansive graphite was placed in a 100m1 volumetric flask.
After adding 50 ml of deionized water and shaking for 10 minutes, make up to 100 ml with deionized water and filter with filter paper. A part of the filtrate is taken, an aqueous solution of barium chloride is added to produce barium sulfate, and turbidimetric analysis is performed with an absorptiometer to measure the amount of sulfate radicals. On the other hand, hydrochloric acid is added to a part of the filtrate, and the amount of alkali metal is measured by atomic absorption spectrometry according to a conventional method.

Thermally expandable graphite of the present invention, when washing the reaction product of raw material graphite and sulfuric acid containing an oxidizing agent, after washing until the amount of free acid relative to the solid content of the object to be washed is 1 mol / kg or less,
The solid content is separated by filtration, brought into contact with an aqueous solution of an alkali metal compound, and then the excess water is removed, followed by drying, or washing is performed until the amount of free sulfuric acid becomes 1 mol / kg or less based on the solid content of the object to be washed. After that, the cake in a wet state obtained by filtration is mixed with an aqueous solution of an alkali metal compound, filtered again, and then dried.

It is preferable to use an air flow dryer for the drying, and it is preferable to perform the drying until the water content is about 1% because it can be easily applied to various uses.

When the washing is brought into contact with an aqueous solution of an alkali metal compound without washing until the amount of free acid becomes 1 mol / kg or less relative to the solid content to be washed, various elements contained in the raw material graphite are treated with the acid of the graphite. By elution in the acid treatment liquid, and a reaction such as a hydroxide occurs by contact with an aqueous solution of an alkali metal compound, and by being contained in the heat-expandable graphite as an impurity that is difficult to remove, Not only the characteristics are deteriorated, but also the produced hydroxide causes clogging of the filter material in the filtration step, resulting in extremely poor filterability, which is not preferable.

The amount of free acid of the solid content to be washed is measured by collecting a cake in a wet state from a water washing step or a filtration step and dehydrating it by suction filtration, and then keeping 5 gr of the same in a hot air circulation dryer at 105 ° C. for 2 hours. After drying, it is measured by cooling in a desiccator and titrating with an aqueous solution of N / 2 to N / 10.

The alkali metal compound used in the present invention is a combination of one or more selected from Na, K hydroxides, oxides, carbonates and organic acid salts.

The heat-expandable graphite of the present invention contains a salt formed by the reaction of free sulfuric acid contained in the heat-expandable graphite and an alkali metal compound, but a part of the excess hydroxide used for neutralization. Alternatively, it may contain an alkali metal in the form of a carbonate or the like. If the molar ratio of the alkali metal to the sulfate radicals other than sulfuric acid forming the intercalation compound is less than 1, the acidity of the heat-expandable graphite is not sufficiently improved due to the free sulfuric acid remaining in the graphite. The stability of the emulsion when added cannot be maintained. That is, in the heat-expandable graphite of the present invention, the pH of the 1% by weight concentration of the heat-expandable graphite in the aqueous dispersion is preferably 4.5 or more. For example, when treating free sulfuric acid with an aqueous solution of an alkali metal salt and the molar ratio of the alkali metal to the free sulfuric acid is 2, the pH of the liquid in the reaction system is approximately pH 7, but the pH of the thermally expandable graphite after drying is 1
The pH of the aqueous dispersion having a concentration of wt% is about 4.5. When the pH of the heat-expandable graphite is lower than 4.5, when added to an aqueous emulsion product or an aqueous latex product, the effect of improving the stability inhibition of these is low, and the desired effect cannot be expected sufficiently.

There is no particular upper limit to the pH, but in the case where the pH exceeds 12, for example, an excessive amount of alkali metal is contained, so that the pH value is usually 4.5 to 11 as a preferable range.

PH of 1% by weight aqueous dispersion of thermally expandable graphite of the present invention
Is measured with a pH electrode after pouring 1 gr of the thermally expansive graphite to be measured into 99 gr of deionized water and stirring for 10 minutes.
The pH of the deionized water used in this measurement must be in the range of 5.5 to 7.0.

Needless to say, the thermally expandable graphite of the present invention is used as a conventionally known industrial material after being thermally expanded.
It is also useful as a flame retardant, and particularly when added to a synthetic resin emulsion such as polyacrylic acid or polyvinyl chloride, it does not impair the stability of the emulsion.

Further, it has an advantage that corrosion of equipment and the like is unlikely to occur.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples and the like.
The present invention is not limited to the following examples unless it exceeds the gist.

 The "part" in the examples is an important part.

Examples 1 to 4 <Production of thermally expandable graphite> 400 parts of natural scaly graphite (particle size; 36 mesh to 80 mesh) produced in Canada with fixed carbon content of 90% and ash content of 8% is 98%.
In addition to 1500 parts of sulfuric acid, 20 parts of 60% hydrogen peroxide water,
The reaction was carried out at 30 to 35 degrees for 15 minutes. Then 1500 parts of reactant
After diluting with 30% sulfuric acid, filter the glass fiber (GA10
0) was used to suction-filter with a Nutsche and the residue was taken out.
50 parts of this filtration residue was divided into 4 portions, each of which was put into water of the amount shown in Table 1 below, and after stirring and washing for 30 seconds, the residue was again separated by suction filtration. From each of the four types of residue, 5 gr was taken, dried at 105 ° C. for 2 hours with a hot air circulation dryer, and alkali titrated to measure the content of each free sulfuric acid.

Further, the remaining 40 parts of each of the four types of filtration residue obtained by suction filtration after washing with water were not subjected to a drying treatment, and based on 100 parts of water and the amount of free sulfuric acid in the solid content of the heat-expandable graphite,
Calculate the amount of free sulfuric acid in the undried heat-expandable graphite, add an aqueous solution of alkali N / 5 hydroxide so that the molar ratio of alkali metal to the free sulfuric acid is 2 or more, and stir for 10 minutes. Suction filtration was performed using Nuttsu using filter paper (GA100), and the taken out filter residue was dried in a hot air circulation dryer at 105 ° C. for about 90 minutes to obtain four types of thermally expandable graphite.

Further, for the heat-expandable graphite obtained in this way, separately, 1gr was taken into a 100m1 volumetric flask, 50m1
Deionized water was added, and after shaking for 10 minutes, the volume was increased to 100 m1 with deionized water and filtered with No. 131 filter paper.
A part of the filtrate was taken, barium chloride aqueous solution was added to produce barium sulfate, and nephelometry was performed by an absorptiometer to measure the amount of sulfate radical. Hydrochloric acid was added to another part of the filtrate, and the amount of alkali metal was measured by atomic absorption spectrometry according to a conventional method.

Amount of water and alkali hydroxide aqueous solution, measured value of free sulfuric acid, type of alkali metal hydroxide used for neutralization, molar ratio of free sulfuric acid and alkali metal at the time of neutralization, filterability after neutralization,
The sulfate group content, alkali metal content and the molar ratio of the obtained heat-expandable graphite are collectively shown in Table 1.

In addition, a 1 wt% aqueous dispersion of the thermally expandable graphite obtained here
pH and thermal expansion graphite 50gr obtained here is 20 cm in diameter, 4 c in depth
Table 1 also shows the measured pH values after the cells were placed in a petri dish of m and stored at room temperature under open condition for 1 week.

<Additional test for water-based paint> 40% of the thermally expansive graphite obtained in Examples 1 to 4 was added to the solid content of a commercially available water-based alkaline paint, and high-speed stirring was performed at room temperature using a homomixer to homogeneity. A solid slurry was obtained.
The compounding recipe is shown in Table 2.

 This was left to stand at room temperature and examined for changes over time.

It was left at room temperature for 3 days, and the state at that time was expressed in the following two stages.

1) Viscosity and dispersibility when the slurry is manually agitated with a glass rod are almost the same as those at the start of the test ... Stable 2) Slurry is gel-like ... Gelation.

For those that gelled, the approximate time to gelation was shown.

 The test results are shown in Table 2.

As shown in Table 2, it is recognized that the thermally expansive graphite of the present invention does not impair the stability when added to the acrylic paint.

<Corrosion test for metal surface> Using the thermally expansive graphite obtained in Examples 1 to 4, 100 ° C, 7
A corrosion test was conducted using a mild steel test piece for 2 hours.

 The test method is as follows.

3gr of each of the heat-expandable graphite obtained in Examples 1 to 4 and 0.5gr of water were well stirred and placed in an 18-8 stainless steel cup having a diameter of 70mm and a volume of 100m1, and a support stand made of stainless steel wire mesh was erected above the cup. Width x length x thickness = 25mm x 50mm on the support
A test piece of × 1.5 mm was placed on the test piece, and the upper end of the stainless steel cup was covered with a commercially available household wrap film and kept in an oven kept at 100 ° C. for 72 hours. The gap between the thermally expandable graphite and the support was about 15 mm, the gap between the upper surface of the test piece and the wrap film was 20 mm, and the thermally expandable graphite and the test piece were not in direct contact with each other.

The lower surface of the test piece after 72 hours (the surface facing the heat-expandable graphite) was visually observed, and the test results are shown in four stages of ++, +, ±, and −, and shown in Table 3. The evaluation criteria are as follows. The test was repeated 3 times.

The metal surface is almost the same as before the test ...- Several point-like corrosion and rust can be seen on the metal surface. Corrosion is recognized on about 5 to 20% of the metal surface. Corrosion and rust are observed ... ++ Comparative Examples 1 to 3 <Production of Thermally Expandable Graphite> An example in which graphite is not treated to neutralize in the same manner as in Examples 1 to 4 (Comparative Example 1), alkali An example of neutralization using ammonia instead of metal (Comparative Example 2) and the amount of free acid
The results are summarized in Table 1 for the case of exceeding 1 mol / kg (Comparative Example 3).

<Addition test for water-based paint> Using the heat-expandable graphite obtained in Comparative Examples 1 and 2, Example 1 was used.
The test was carried out in the same manner as ~ 4. In addition, as a blank test, the test was conducted without adding the thermally expansive graphite. The results are summarized in Table 2.

<Corrosion Test for Metal Surface> Using the heat-expandable graphite obtained in Comparative Examples 1 and 2, Example 1 was used.
The test was carried out in the same manner as ~ 4. A blank test was conducted without adding thermally expansive graphite. The results are summarized in Table 3.

[Effects of the Invention] As described above, since the pH of the thermally expandable graphite obtained by the present invention is controlled to about 4.5 or more by the alkali metal, its change with time is small, and it is stable by an acidic substance such as an aqueous paint. Has the effect that it can be added directly to products that are easily damaged.

Further, it can be advantageously used because it is unlikely to cause corrosion of processing equipment during molding of polyolefin or the like.

Claims (5)

(57) [Claims] 1. The heat-expandable graphite contains an alkali metal, and the molar ratio of the alkali metal to the sulfate radicals other than sulfuric acid forming the intercalation compound contained in the heat-expandable graphite is 1 or more. Thermally expandable graphite characterized by the above. 2. The heat-expandable graphite according to claim 1, wherein the alkali metal is Na or K. 3. When the graphite is treated with a mixture of concentrated sulfuric acid and an oxidizing agent, and the reacted graphite is washed with water and then dried,
After washing until the amount of free sulfuric acid with respect to the solid content of the object to be washed is 1 mol / kg or less, neutralize with an aqueous solution of alkali metal compound so that the molar ratio of alkali metal to free sulfuric acid is 2 or more, and then dry. A method for producing thermally expansive graphite, comprising: 4. The method for producing thermally expandable graphite according to claim 3, wherein the alkali metal is Na or K. 5. The alkali metal compound is a hydroxide, an oxide,
The method for producing heat-expandable graphite according to claim (3) or (4) above, which is one or more selected from carbonates and organic acid salts.