JPH0340910A - Improved thermally expandable graphite - Google Patents

Abstract

PURPOSE:To reduce the loss of the weight of thermally expandable graphite even at a high temp. of >=220 deg.C and to make the graphite useful as a flame retardant for thermoplastic resins by coating the graphite with a compd. of an alkaline earth metal and a film forming resin. CONSTITUTION:Thermally expandable graphite of 20-150 mesh, preferably 30-100 mesh grain size is coated with a compd. of an alkaline earth metal such as CaCO3 or a metal hydroxide such as Al(OH)3 and a film forming resinous substance such as an acrylonitrile-butadiene copolymer having 15-50wt.% acrylonitrile content to obtain thermally expandable graphite hardly causing the loss of the weight even at a high temp. of about >=220 deg.C. The amt. of the metal compd. used is 0.1-50wt.% and that of the resinous substance is 0.01-5wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to thermally expandable graphite. For details, please refer to approximately 22
The present invention relates to thermally expandable graphite that has a low weight ff1M even at high temperatures of 0°C or higher.

[Conventional technology]

Thermally expandable graphite has the property of instantly expanding to several tens to hundreds of times its original volume when heated to high temperatures.At this time, the expanded graphite forms a flame-resistant layer, so this property can be used to As an industrially important material, it can be used as a flame retardant for combustible materials, or by pressing graphite expanded by heat to produce graphite sheets with excellent flexibility without using a binder. well known.

Such thermally expandable graphite is produced by acid-treating graphite with a mixture of concentrated sulfuric acid and a strong oxidizing agent. 54-25913), potassium permanganate (Japanese Patent Publication No. 5595609), perhalogenate (Japanese Patent Publication No. 51-96793), or anodization by electrolytic reaction (Japanese Patent Publication No. 56-1
Various methods are known, such as 8532).

Further, US Pat. No. 3,574,644 discloses adding this thermally expandable graphite to polyethylene, polyurethane, and other natural or synthetic resins to improve flame retardance.

[Problem to be solved by the invention]

When thermally expandable graphite is added to a thermoplastic polymer such as polyethylene, it is usually kneaded at a temperature of approximately 150° C. or higher using a kneading device prior to molding.

According to experiments conducted by the present inventors, sulfuric acid gas is generated during kneading, especially when kneading is attempted at high temperatures, and there is a high possibility of corroding the kneading equipment. It has become clear that the problem is that as a result of the vaporization of the components, the flame retardancy of the resin composition as expected may not be achieved.

On the other hand, when the thermal behavior of thermally expandable graphite was examined by differential thermal analysis, it was found that at approximately 240°C, a part of the volatile matter that exists between the eyebrows is released.
When we measure the weight loss when heated for 0 minutes, it is approximately 2
It has become clear that the weight decrease is extremely significant at high temperatures above 20°C.

[Means to solve the problem]

In order to solve the above problems, the present inventors have attempted to produce thermally expandable graphite that exhibits less weight loss and releases less sulfuric acid under the molding conditions of thermoplastic resins, particularly polyolefins such as polyethylene. As a result of extensive research aimed at this purpose, it was discovered that thermally expandable graphite coated with a specific substance shows little weight loss even when heated in a temperature range higher than 220°C, and the present invention was completed.

That is, the present invention is coated with (A) an alkaline earth metal compound or metal hydroxide and (B) a film-forming resinous substance, and the content of (A) is 0.1 to 50% by weight, ( B
The gist of the invention is thermally expandable graphite characterized by a content of o, oi to 5% by weight. The present invention will be explained in detail below.

The raw material graphite for the thermally expandable graphite of the present invention is not particularly limited.
Natural graphite, pyrolytic graphite, Quiche graphite, and other materials used in the production of normal thermally expandable graphite can be used. To produce the thermally expandable graphite of the present invention, the raw material graphite is, for example,
45°C in a mixture of 98% concentrated sulfuric acid and 60% hydrogen peroxide.
After contacting for 10 to 30 minutes, the acid-treated graphite is then washed with water, furnaced, dried, and then coated with an alkaline earth metal compound or metal hydroxide and a film-forming resinous substance.

The thermally expandable graphite used in the present invention desirably has a degree of expansion of 50 to 250 mJ2/g when rapidly heated at 1000°C for 10 seconds from the viewpoint of exhibiting a flame retardant effect.

In the present invention, "degree of expansion j" refers to 150 m
Take out the quartz bead of j2 outside the furnace, immediately put 0.5 g of thermally expandable graphite into it, quickly put it into the same furnace maintained at <1000°C, hold it there for 10 seconds, then take it out of the furnace, This is the capacity/weight ratio (unit: me/g) of expanded graphite after natural cooling.

The degree of expansion of thermally expandable graphite generally depends on the particle size of the thermally expandable graphite, and when the particle size is finer than approximately 80 mesh, the degree of expansion tends to be small, and when it is finer than 150 mesh, the degree of expansion is extremely low. As a result, the flame retardant effect is significantly reduced. Therefore, the particle size of the thermally expandable graphite used in the present invention is preferably 20-150 mesh, and most preferably classified into about 30-100 mesh.

The particle size of thermally expandable graphite usually depends on the particle size of the raw material graphite used to manufacture it, so the particle size may be adjusted using the raw material graphite.Also, the expanded graphite may be crushed and classified. You may go.

The thermally expandable graphite of the present invention is produced by treating raw graphite with an acid as described above, and then treating the raw graphite with one or more basic compounds selected from ammonia, aliphatic lower amines, alkali metal compounds, and alkaline earth metal compounds. The released sulfuric acid may be neutralized. Neutralization treatment is carried out by subjecting raw graphite to acid treatment, and mixing and contacting with ammonia water, caustic soda aqueous solution, etc. after or during the water washing process.

As for the degree of neutralization, it is preferable that the pH of the 1% by weight aqueous dispersion of thermally expandable graphite is about 4.5 to 10.

The alkaline earth metal compounds and metal hydroxides used to coat the thermally expandable graphite are provided, for example, for plasti, ivy, and rubber, and those with fine particle diameters are advantageous. Examples of alkaline earth metal compounds include hydroxides, oxides, and carbonates of calcium, magnesium, and barium; specific examples include calcium carbonate, calcium oxide,
Examples include calcium hydroxide, magnesium carbonate, magnesium oxide, magnesium hydroxide, barium carbonate, barium oxide, barium hydroxide, and among them, calcium carbonate, calcium hydroxide, magnesium carbonate, and magnesium oxide are preferred. Further, as the metal hydroxide, argonium hydroxide is preferable.

Film-forming resinous substances include synthetic polymeric substances, such as acrylonitrile-butadiene copolymers, styrene-butadiene copolymers, etc.
butadiene copolymer, ethylene-vinyl acetate copolymer,
Examples include polyvinyl acetate resin, polyvinyl chloride resin, polyacrylate resin, and mixtures thereof.These include chemically modified monomers, or copolymerized second and third components. or additives such as plasticizers may be added. Among these, acrylonitrile-butadiene copolymer with an acrylonitrile content of 15 to 50% by weight, and a styrene content of 20 to 30% by weight.
Preferred are styrene-butadiene copolymers with a weight percent content and ethylene-vinyl acetate copolymers with a vinyl acetate content of 20 to aomt percent. These polymeric substances are used as emulsified dispersions that are emulsified with anionic or nonionic surfactants, and those having a solid content concentration of 1 to 50% are suitable.

Further examples of film-forming resinous substances include synthetic water-soluble polymeric substances or natural water-soluble polymeric substances, such as polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid Na salt, carboxymethyl cellulose Na salt, carboxymethyl starch Na salt, and alkyne fil N. a Salt, hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose.

In addition to ethyl cellulose, water-soluble derivatives of natural products such as milk casein protein, glue, gelatin, mannan, gum arabic, guar gum, and chitin may be used, and these may be used alone or as a mixture. These water-soluble polymer substances are usually used as an aqueous solution of about 0.1 to 10% depending on their solubility, but they may be alkaline or acidic for the purpose of improving solubility.

The content ratio of thermally expandable graphite, alkaline earth metal compound or metal hydroxide, and film-forming resinous substance in the improved thermally expandable graphite of the present invention must be within the following range.

That is, the content of the alkaline earth metal compound or metal hydroxide is 0.1 to 50% by weight, and if it is less than 0.1% by weight, the effect of suppressing the release of acidic gas at high temperatures cannot be obtained; Even if the weight exceeds the weight, there is no corresponding improvement in the effect of suppressing the release of acidic gases, and when added to synthetic resins, the properties of the resin may be impaired.

Further, the content of the film-forming resinous substance is 0.01 to 5% by weight, and if it is less than 0.01% by weight, the thermally expandable graphite and the alkaline earth metal compound or metal hydroxide may be sufficiently bonded. Therefore, adding more than 5% does not increase the effect as a binder.

To coat thermally expandable graphite, the film-forming resin material described above is made into an emulsified dispersion or an aqueous solution, a predetermined amount of an alkaline earth metal compound or metal hydroxide is dispersed therein, and the mixture is sprayed onto the thermally expandable graphite. Addition by methods such as
Then, drying is performed, or thermally expandable graphite is added to an emulsified dispersion of a film-forming resinous substance or an aqueous solution in which a predetermined amount of an alkaline earth metal compound or metal hydroxide is dispersed, and then separated and recovered. However, it also depends on the method of drying.

When coating by spraying, coating components may be contained in a desired amount by repeating addition and drying to form a multilayer coating of thermally expandable graphite.

Alternatively, a predetermined amount of thermally expandable graphite and a powdered alkaline earth metal compound or metal hydroxide are mixed, a small amount of water is used as a binder if necessary, and a film-forming resin is added to the mixture. An emulsified dispersion or aqueous solution of the substance may be added by a method such as spraying, and then dried.

Drying is preferably carried out so that the loss on drying at 105°C is approximately 0.5 to 2%.

As drying progresses, the thermally expandable graphite is bound by the resin content, and the apparent particle size may increase, so in this case, it is ground to the desired particle size using a commonly used dry grinder.

It is preferable to use a flash dryer or the like for drying, and it is desirable to dry until the moisture content is around 1% because it is easy to apply to various uses.

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. In the Examples and Comparative Examples, "parts" indicate parts by weight, and "%" indicate "parts by weight."

Examples 1 to 6, Comparative Examples 1 and 2 <Manufacture of thermally expandable graphite> Natural flaky graphite produced in Canada with a fixed carbon content of 90% and an ash content of 8% (particle size: 36 mesh to 80 mesh) 400
1 part was added to a mixed solution of 1,500 parts of 98% sulfuric acid and 20 parts of 60% hydrogen peroxide solution, and the mixture was reacted at 30 to 35 degrees for 15 minutes. Next, 1,500 parts of 30% sulfuric acid was added to the reaction mixture to dilute it, and the residue was removed by suction using a nuncher using glass fiber paper (GAloo). 50% of this filtration residue
After pouring into 00 parts of water and stirring and washing for 30 seconds,
The residue was separated by suction again. After performing the same water washing process again, 0.5N caustic soda was added to the resulting residue.
After sprinkling calcium hydroxide or ammonia aqueous solution, suction filtration was performed, and the filtration residue was then dried for about 90 minutes using a hot air circulation drying method at 105°C to form three types (■, ■, ■).
thermally expandable graphite was obtained.

The swelling degree of these materials at 1000° C. for 10 seconds and the pH of the 1% by weight aqueous dispersion were as follows.

■: Particle size 36-80 mesh, neutralized with NaOH, swelling degree; 200 ml/g, pt (; 7.7■:
Particle size 36-80 mesh, neutralized with Ca(OH)z, swelling degree: 195 ml/g, pH: 1-2■2 particle size 36-80 mesh, neutralized with NH3, swelling degree: 205 ml/g , pH; 5.4 In a stainless steel bowl with a capacity of about 2000 mf, 50 parts of the above thermally expandable graphite and an alkaline earth metal compound or metal hydroxide of the type and amount shown in Table 1 (in the table, indicated as metal compound) were added. )
While stirring the contents with a spatula, a film-forming resin adjusted to the type and concentration shown in Table 1 was added using a sprayer. After the spraying was completed, the contents were transferred to a stainless steel hat and placed in a drying tool kept at 105°C for 2 hours.
The mixture was dried for about 1 hour while stirring at a rate of ◯ times every 0 minutes to obtain thermally expandable graphite of the present invention.

1.0g of the thermally expandable graphite obtained in this way was
The sample was placed in a mj2 platinum dish, heated for a predetermined time in an electric furnace maintained at 250°C, and then cooled, and the weight after heating was measured. The results are shown in Table 1 as weight loss rates.

Weight reduction rate (%) The types of metal compounds and film-forming resins used are shown below.

Metal compound CaCO2: “Sankyo Tan Cal A” Af manufactured by Sankyo Seifun Co., Ltd.
(OH) 3: Showa Denko Co., Ltd. %A “Hygilite H-31J” Mg(OH)2: Asahi Glass Co., Ltd. “High Purity Water Mug”
200-6゜ Film-forming resin NBR: NBR Latinx rNi manufactured by Nippon Zeon Co., Ltd.
ppol 1571J PVA: Manufactured by Hikigou Kagaku Kogyo Co., Ltd. “Gosenol”
NH-18S” aqueous solution CMC-Na: Daiichi Kogyo Seiyaku Co., Ltd. “Celogen
3HJ water? Liquid [Effects of the Invention] The thermally expandable graphite of the present invention has a small loss on heating at high temperatures of about 220° C. or higher and is highly stable, so it is advantageous when added to thermoplastic resins.

Claims (1)

[Claims] (1) coated with (A) an alkaline earth metal compound or metal hydroxide and (B) a film-forming resinous substance, with a content of (A) of 0.1 to 50% by weight; A thermally expandable graphite having a content of 0.01 to 5% by weight.