JP2000191836A - Flame retardant rubber composition and flame retardant rubber molded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition which emits reduced smoking and is free from irritant odors, suppresses occurrence of dripping and exhibits excellent flame retardancy while maintaining mechanical characteristics inherent in the rubber by admixing a hydrated metal oxide and a 1- hydroxyethylidene-1,1'-diphosphonic acid melamine salt with a rubber component. SOLUTION: To 100 pts.wt. of a rubber component such as natural rubbers, styrene-butadiene rubbers, butyl rubbers, polybutadiene rubbers and the like are incorporated 30-100 pts.wt. of one or more hydrated metal oxides such as calcium hydroxide, magnesium hydroxide, basic magnesium carbonate, aluminum hydroxide and the like and 3-20 pts.wt., in terms of phosphorus, of a 1- hydroxyethylidene-1,1'-diphosphonic acid melamine salt represented by the formula (wherein M is melamine; and n is 1-4) to give a flame retardant rubber composition. Further, 0.1-2.0 pts.wt., based on 100 pts.wt. of the rubber, of red phosphorus, preferably one with its surface modified with an organic matter and/or an inorganic matter, can be admixed with this flame retardant rubber composition to improve its flame retardant effect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flame-retardant rubber composition using a non-halogen flame retardant and a flame-retardant rubber molded article obtained by molding the same. The present invention relates to a rubber composition having excellent flame retardancy while suppressing the occurrence of dripping (melt dripping phenomenon) and maintaining the original mechanical properties of rubber, and a flame-retardant rubber molded article obtained by molding the same. Things.

[0002]

2. Description of the Related Art Conventionally, rubber is used for electric wires, electric parts, automobile parts, sealing materials for buildings, etc. because of its excellent electrical insulation, heat resistance, weather resistance and chemical resistance.

[0003] Since a dripping phenomenon called dripping occurs during burning of rubber, attempts have been made in such fields to impart rubber with flame retardancy in order to further ensure safety.

For example, pneumatic tires are used as wheels for monorails, subways and the like. Instead of flammable tires, flame-retardant tires that do not spread in the event of a fire are desired. Tires, wires, gaskets,
There is also a strong demand for various flame-retardant materials for electrical components and building seal materials.

[0005] One method of imparting flame retardancy to rubber is to add a known halogen-based flame retardant, or to add a large amount of a hydrated metal compound such as aluminum hydroxide or magnesium hydroxide. Has flame retardancy.

However, since such a flame retardant is compounded in a large amount in the rubber, the physical properties of the obtained rubber are deteriorated, so that it is difficult to practically use the flame retardant. The possibility of producing toxic dioxins in the human body has been pointed out, and there is an increasing demand for non-halogen flame retardants.

Using such non-halogen flame retardants,
Examples of a method for maintaining good physical properties of rubber include a method of containing red phosphorus and a method of containing aluminum hydroxide, red phosphorus and an acrylonitrile group-containing polymer in a rubber component (JP-A-6-192484). Containing a zinc acrylate compound (JP-A-6-1078)
No. 70) and a method of containing ammonium polyphosphate, melamine and pentaerythritol
-25379) and the like have been proposed.

[0008] Silicone rubber is also superior in heat resistance to other rubbers, but continues to burn once ignited, so that certain flame retardants are used depending on the application. For example, a method of compounding a platinum compound with silicone rubber (JP-A-48-92452 and JP-A-48-20839), a method of adding a platinum compound and a metal oxide in combination (JP-A-48-96650) JP-A-57-105455), a method of adding a platinum compound and carbon black in combination (JP-A-53-130).
No. 753) has been proposed.

However, when red phosphorus is added in a large amount, it has no reinforcing property to the rubber, so that physical properties such as durability and strength tend to be lowered. It becomes colored and coloring becomes impossible, and its use is limited. In addition, the working environment is deteriorated due to the generation of phosphine gas during processing, and red phosphorus is coated with a coating agent in order to suppress this. However, generation of phosphine gas cannot be completely suppressed. Can not.
In addition, the method of using a platinum compound in the silicone rubber,
Platinum compounds are expensive and have limited resources,
It is also known that when a large amount of a platinum compound is blended with silicone rubber, the flame retardancy is rather reduced.

[0010] On the other hand, in other methods of making a rubber flame-retardant, it is difficult to impart the flame-retardancy while maintaining the mechanical properties inherent in the rubber, and there is a problem in the smoke-generating property during combustion.

[0011]

SUMMARY OF THE INVENTION Organophosphorus flame retardants are:
It is particularly noted as a halogen-free flame retardant.
The flame-retardant mechanism has a high volatility, and the phosphorus compound vaporized by heating is used as an inhibitor of combustion in the gas phase.
Plastic combustion is suppressed by the effect of dilution of oxygen gas, the effect of cooling the combustion system by volatilization, and the effect of suppressing the chemical reaction of combustion. On the other hand, those with low volatility decompose thermally to generate phosphoric acid, which becomes metaphosphoric acid and polymetaphosphoric acid, and forms a non-volatile phosphate polymer on the solid phase or molten layer surface of the plastic to be fired. I do. Also, the plastic is carbonized by the dehydration reaction of phosphoric acid,
A carbonized layer is formed, thereby blocking the ingress of air and cutting off the supply of heat energy from the outside to suppress combustion.

At present, various types of organophosphorus flame retardants have been proposed, such as phosphate esters and phosphites. However, most of these compounds have low hydrolysis resistance and low affinity for rubber. Since the P content is low, a large amount of P must be contained in the resin in order to enhance the flame retardant effect, and mechanical properties are impaired.

The present inventors have first focused on 1-hydroxyethylidene-1,1'-diphosphonic acid having a high P content, and have used a melamine salt of the compound and a hydrated metal oxide as a flame retardant. A composition and a flame-retardant resin composition were invented (Japanese Patent Application No. 10-251781). The present inventors have further studied and found that the flame retardant composition can impart excellent flame retardancy to various rubbers without impairing the mechanical properties inherent in the rubber. Thus, the present invention has been completed.

[0014] That is, the present invention provides a rubber composition having excellent flame retardancy and a rubber molded article having flame retardancy while maintaining the mechanical properties inherent in rubber, having low smoke emission and no irritating odor. The purpose is to:

[0015]

Means for Solving the Problems The flame-retardant rubber composition to be provided by the present invention has the following general formula (1):

[0016]

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(Wherein, M represents melamine, and n represents 1-4)
Represents an integer. 1) -hydroxyethylidene-1,1'-diphosphonic acid melamine salt represented by the formula (1). Further, it is preferable that the flame retardant rubber composition further contains red phosphorus.

Further, a flame-retardant rubber molded article to be provided by the present invention is characterized in that it is formed by molding the above-mentioned flame-retardant rubber composition.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The flame-retardant rubber composition of the present invention contains a rubber, a hydrated metal oxide, and a melamine 1-hydroxyethylidene-1,1′-diphosphonic acid represented by the following general formula (1) as active ingredients. It is characterized by.

[0020]

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Examples of the hydrated metal oxide include one or more of calcium hydroxide, magnesium hydroxide, basic magnesium carbonate, and aluminum hydroxide. These hydrated metal oxides may be surface-treated.

The mixing ratio of the hydrated metal oxide is 100
The amount is usually 30 to 100 parts by weight, preferably 40 to 80 parts by weight based on parts by weight.

In the formula (1), M is melamine, and n is an integer of 1 to 4.

Specific examples of the 1-hydroxyethylidene-1,1'-diphosphonic acid melamine salt represented by the general formula (1) include 1-hydroxyethylidene-1,1'-diphosphonic acid.
Melamine 1-hydroxyethylidene-1,1'-diphosphonic acid
2 melamine 1-hydroxyethylidene-1,1'-diphosphonic acid
3 melamine 1-hydroxyethylidene-1,1'-diphosphonic acid
4 melamine, and these compounds are used alone or in combination of two or more.

The method for producing the 1-hydroxyethylidene-1,1'-diphosphonic acid melamine salt represented by the general formula (1) according to the present invention is not particularly limited, and a known method can be used. For example, the following general formula (2)

[0026]

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1-hydroxyethylidene-
1,1'-diphosphonic acid and melamine may be reacted in an aqueous solvent such as water, a mixed solvent of water-acetone, or water-alcohol.

In the reaction for obtaining the melamine salt of 1-hydroxyethylidene-1,1'-diphosphonic acid as the target product of the above reaction, the starting material, 1-hydroxyethylidene-1,1'-diphosphonic acid represented by the general formula (2), is used. The mixing ratio of the acid and the melamine is usually in the range of 1 to 4 mol of melamine per 1 mol of the phosphonic acid of the general formula (2), and within that range, the amount of melamine introduced into the target substance, for example, 1 to 4 The amount of melamine used may be appropriately adjusted depending on the amount of the four melamines.

The compounding ratio of the melamine 1-hydroxyethylidene-1,1'-diphosphonic acid represented by the general formula (1) is 3 as P with respect to 100 parts by weight of rubber.
To 20 parts by weight, preferably 5 to 15 parts by weight. The reason is that if the blending ratio is less than 3 parts by weight, it is difficult to obtain a sufficient flame retardant effect, while if it is more than 20 parts by weight, the flame retardant effect increases but the mechanical properties of the molded article tend to deteriorate. It is not preferable because there is.

The flame retardant effect can be enhanced by further adding red phosphorus to the flame retardant rubber composition of the present invention.

In this case, it is preferable that the surface of the red phosphorus is modified with an organic substance and / or an inorganic substance, for example, phenol resin, epoxy resin, ethylene-vinyl acetate copolymer, melamine-formaldehyde polycondensate, Mg, C
a, Ti, Al, Co and Zr hydroxides and those surface-treated with one or more selected from these oxides, but are not limited thereto.

The compounding ratio of red phosphorus is generally 0.1 to 2.0 parts by weight, preferably 0.5 to 2.0 parts by weight, per 100 parts by weight of rubber.
1.0 part by weight.

The rubber raw material applicable in the present invention is not particularly limited. For example, natural rubber, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR), polybutadiene rubber (BR) , Ethylene-propylene rubber (EPD
M), chlorobutylene rubber (CR), polyisobutylene rubber, allyl rubber, hydrogenated acrylonitrile-butadiene rubber, polysulfide rubber, urethane rubber, cririsulfonated rubber, silicone rubber, and modified products thereof. Or a blend of two or more rubbers.

As other components, a filler, a vulcanizing agent, a vulcanization accelerator, a vulcanization aid, a softening agent, an antioxidant, a foaming agent, a plasticizer and the like which are usually added to rubber are used. Can be.

As the filler, white carbon, carbon black, zeolite, calcium carbonate, clay,
One or more of inorganic fillers such as barium sulfate and magnesium carbonate, and organic fillers such as high styrene resin, lignin and phenol resin are exemplified.

A vulcanizing agent is a substance that forms a three-dimensional network structure by crosslinking and mixing raw rubber molecules. In many cases, sulfur, sulfur chloride, sulfur dichloride, morpholine disulfide, alkylphenol disulfide, tetramethylthiuram disulfide is used. And selenium compounds such as selenium dithiocarbamate. As other compounds, for example, dicumyl peroxide, 2,5-dimethyl-2,5-di (t-
Butylperoxy) hexane, 2,5-dimethyl-2,
5-di (benzoylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne, di-t-butyl peroxide, di-t-butylperoxy-3,3,5-trimethylcyclohexane, t Organic peroxides such as -butyl hydroperoxide, quinone dioxime, mercaptoimidazine, modified phenolic resins, lead monoxide, lead trioxide, tin chloride, zinc white, and the like.

Examples of the vulcanization aid include sulfur, quinone dioxime compounds such as p-quinone dioxime, acrylic compounds such as ethylene glycol dimethacrylate and trimethylolpropane trimethacrylate, diallyl phthalate and triallyl isocyanurate. Such as allyl compounds, other maleimide compounds, divinylbenzene, zinc white,
Zinc compounds such as basic zinc carbonate, zinc hydroxide and zinc stearate can be mentioned.

Examples of the vulcanization accelerator include N-cyclohexyl-2-benzothiazolesulfenamide, N-
Oxydiethylene-2-benzothiazolesulfenamide, N, N'-diisopropyl-2-benzothiazolesulfenamide, 2-mercaptobenzothiazole, 2- (2,4-dinitrophenyl) mercaptobenzothiazole, 2- (2 Thiazole compounds such as benzothiazole and dibenzothiazyl-disulfide, guanidine compounds such as diphenylguanidine, triphenylguanidine and diorthotolylguanidine, acetaldehyde-aniline condensate, butyraldehyde -Aldehyde amine compounds such as aniline condensates, imidazoline compounds such as 2-mercaptoimidazoline, thiourea compounds such as diethylthiourea and dibutylthiourea, and tetramethylthiuram monosulfide , Rauramu compounds such as tetramethylthiuram disulfide, zinc dimethyl dithiocarbamate, zinc diethyl dithiocarbamate, dithio acid salt-based compound tellurium diethyl carbamic acid, xanthate-based compounds such as dibutyltin xanthate zinc, zinc white and the like.

As the softener, for example, process oil,
Lubricating oil, paraffin, liquid paraffin, petroleum asphalt, petroleum-based substances such as petrolatum, coal tar, coal tar such as coal tar pitch, castor oil, rapeseed oil,
Fatty oils such as soybean oil and coconut oil, tall oil, beeswax, carnauba wax, waxes such as lanolin, ricinoleic acid, palmitic acid, stearic acid, barium stearate, fatty acids such as calcium stearate or metal salts thereof, naphthenic acid or Such as metal soaps, pine oil, rosin or derivatives thereof, terpene resins, petroleum resins, cumarone indene resins, atactic polypropylene, dioctyl phthalate, dioctyl adipate, ester plasticizers such as dioctyl sebacates, diisododecyl carbonate, etc. Carbonate ester plasticizers, other microcrystalline waxes, sub (factice), liquid polybutadiene, liquid thiocol, hydrocarbon synthetic lubricating oils, and the like.

Examples of the anti-aging agent include aromatic secondary amine-based stabilizers such as phenylbutylamine and N, N'-di-2-naphthyl-p-phenylenediamine, dibutylhydroxytoluene, tetrakis [methylene (3,5) -Di-t-butyl-4-hydroxy) hydrocinnamate]
Phenolic stabilizers such as methane, bis [2-methyl-4
-(3-n-alkylthiopropionyloxy) -5-
thioether stabilizers such as [t-butylphenyl] sulfide; chlorine dithiocarbamate stabilizers such as nickel dibutyldithiocarbamate;

As foaming agents, sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonium carbonate,
Inorganic blowing agents such as ammonium nitrite, nitroso compounds such as N, N'-dinitrosoterephthalamide, N, N'-dinitrosopentamethylenetetramine, azodicarbonamide, azobisisobutyronitrile, azocyclohexylnitrile, azo Azo compounds such as diaminobenzene and barium azodicarboxylate, benzenesulfonyl hydrazide, toluenesulfonyl hydrazide,
Sulfonyl hydrazide compounds such as p, p-oxybis (benzenesulfonyl hydrazide) diphenylsulfone-3,3-disulfonyl hydrazide; and azide compounds such as calcium azide, 4,4-diphenyldisulfonyl azide, and paratoluenemalonyl azide. .

Examples of the plasticizer include phthalic acid esters, aliphatic dibasic acid esters, phosphoric acid esters, fatty acid esters, and epoxidized soybean oil.

In addition, processing of higher fatty acids or salts thereof such as white sub, black sub, ricinoleic acid, stearic acid, palmitic acid, lauric acid, barium stearate, calcium stearate, zinc stearate, and esters of higher fatty acids. Auxiliaries, foaming aids such as salicylic acid, phthalic acid, stearic acid, oxalic acid, urea and derivatives thereof, binders, pigments, antibacterial agents, flame retardants such as platinum-based compounds, conductive fillers, etc. as required Can be used.

Using the flame-retardant rubber composition according to the present invention,
In order to obtain a rubber molded article, for example, a rubber component, 1-hydroxyethylidene-1,1′-diphosphonic acid melamine salt,
In addition to hydrated metal oxides and red phosphorus, if necessary, fillers, vulcanizing agents, vulcanization accelerators, vulcanization aids, softeners, antioxidants, foaming agents, plasticizers usually added to rubber Rolls, by using a conventional kneading machine such as Banbury, to obtain a vulcanizable rubber composition, and then extruder, calender roll, press, injection molding machine, transfer molding machine, etc. Molded into a shape, usually 120
C. or higher, preferably about 1-3 at a temperature of 150-270 ° C.
By vulcanizing for 0 minutes, a rubber molded body can be obtained. In addition, any of press vulcanization, steam vulcanization, hot air vulcanization, etc. can be applied for vulcanization.

The flame-retardant rubber molded article of the present invention thus obtained has a low smoke emission property, no irritating odor, no dripping (melt dripping phenomenon) during combustion, and impairs the original mechanical properties of rubber. It has excellent flame retardancy without
It is useful for materials such as tires, electric wires, gaskets, electrical components, and building sealing materials that require flame retardancy.

[0046]

The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

<1-hydroxyethylidene-1,1'-
Preparation of melamine diphosphonic acid salt> Sample A; 1-hydroxyethylidene-1,1'-diphosphonic acid / 2 melamine salt 15 L of tap water and 1-hydroxyethylidene-1,1'-diphosphonic acid (hereinafter referred to as 18 L stainless steel container) , HED
Abbreviated as P. ) (60% aqueous solution) 1030.0 g
(2.99 mol) was added and stirred. After the temperature was raised to 80 ° C., 756.0 g (5.99 mol) of melamine was gradually added and stirred. After completion of the melamine addition, stirring is continued at 80 ° C. until the pH of the reaction solution becomes constant (about 1.3). Thereafter, centrifugal filtration was performed to obtain white crystals. The crystals were dried at 100 ° C. for 24 hours and pulverized with a mixer to obtain 1456.3 g of the desired product. Yield 10
6.2% (yield based on HEDP). Next, as a result of measuring C, H, and N by elemental analysis, C: 19.9%,
H: 4.2%, N: 34.8%.

Sample B; 1-hydroxyethylidene-
1,1'-diphosphonic acid / 4 melamine salt In a 18 L stainless steel container, 15 L of tap water and HEDP (6
833.3 g (2.42 mol) of a 0% aqueous solution was added and stirred. After the temperature was raised to 80 ° C., melamine 122
3.2 g (9.69 mol) was gradually added and stirred. After completion of melamine addition, the pH of the reaction solution is constant (about 5.2)
Stirring was continued at 80 ° C. until. Thereafter, centrifugal filtration was performed to obtain white crystals. The crystals are treated at 100 ° C. for 24 hours.
After drying for a period of time and crushing with a mixer,
09.7 g were obtained. Yield 99.4% (yield based on HEDP). Next, as a result of measuring C, H and N by elemental analysis, C: 22.5%, H: 4.2%, N: 44.8%
Met.

Examples 1 and 2 and Comparative Examples 1 to 4 EPDM rubber (manufactured by Nippon Synthetic Rubber Co., Ltd .; trade name: EP2)
1) To 100 parts by weight, the mixing ratio shown in Table 1 (parts by weight)
After adding various additives and kneading with a pressure kneader, 4 parts by weight of dicumyl peroxide was added to prepare a compound. Then, this was added to 200 kg / cm ² , 16
The sheet was heated under pressure at 0 ° C. for 15 minutes to prepare a sheet having a thickness of 3 mm, and further, a test piece having a length of 125 mm and a width of 13 mm was prepared. Note that red phosphorus whose surface was coated with a phenol resin was used.

<Flame Retardancy Test> The flame retardancy test was conducted by subjecting the rubber prepared as described above to a length of 125 mm × a width of 13 mm × a thickness of 3 mm to a UL94 classified material in a vertical combustion test (9).
4V-O, 94V-1, 94V-2). The results are shown in Table 1. The conditions for UL94 are as shown in Table 2.

<Evaluation of Drip> The evaluation of the presence or absence of drip was performed based on Test 4 of the UL94 vertical combustion test (in Table 2).

<Molding Processability> The molding processability is determined according to JIS K
6301 according to JIS-A. In Table 1, “○”, “△”, and “×” in the column of moldability indicate the following. ；: Good moldability. Δ: Mold flowability is slightly poor. ×: Poor mold flowability.

<Presence or absence of generation of pungent odor (phosphine gas)> The phosphine gas (PH ₃ ) at the time of molding was measured by a detector tube method. "None" and "Yes" in the column of presence or absence of phosphine gas in Table 1 indicate the following. None; Less than 0.15 ppm Available; 0.15 ppm or more

[0054]

[Table 1]

[0055]

[Table 2]

Examples 3 and 4 and Comparative Example 5 Ethylene / propylene / 5-ethylidene-2-norbornene copolymer rubber (ethylene / propylene molar ratio = 7
5:25) To 100 parts by weight, various additives were added at the mixing ratios (parts by weight) shown in Table 3 and kneaded and mixed at 130 ° C. for 3 minutes with a Banbury mixer.

Next, 316 parts by weight of the rubber composition shown in Table 3 was added to an organic peroxide (Nippon Oil & Fats Co .; Perhexa 3M-4).
0C) 7.5 parts by weight, a crosslinking aid (Sanshin Chemical Industry Co., Ltd .;
Sunceler AP) was added in an amount of 1.0 part by weight, and an unvulcanized sheet having a thickness of 5 mm was obtained using an open roll. The surface temperature of the open roll at this time was 50 ° C. before and 60 ° C. after.

The unvulcanized sheet was press-vulcanized at 160 ° C. for 15 minutes using a 150-ton press molding machine to obtain a 125 m long sheet.
A vulcanized sheet having a size of mx 13 mm in width x 3 mm in thickness (and 2 mm in thickness) was prepared.

<Flame Retardancy Test> In the flame retardancy test, the vulcanized sheet having a length of 125 mm, a width of 13 mm and a thickness of 3 mm prepared above was subjected to a vertical combustion test (94) of a material classified as UL94.
VO, 94V-1, 94V-2).
Table 3 shows the results.

<Mechanical Properties> Evaluation of the mechanical properties (tensile strength, elongation, 100% modulus, hardness) is based on the above-prepared test piece of 125 mm length × 13 mm width × 2 mm thickness according to JIS K-6301. It went according to.

[0061]

[Table 3]

Examples 5 and 6 and Comparative Example 6 Polydiorganosiloxane having an average degree of polymerization of 7,000, comprising 0.2 mol% of methylvinylsiloxane units and the remaining dimethylsiloxane units, the terminal groups of which are blocked by trimethylsiloxane units. To 100 parts by weight, various additives were added at the mixing ratio (parts by weight) shown in Table 4 and kneaded with a kneader.

Then, 2,5-dimethyl-2,5-di-tert-butylperoxyhexane was added to a mixture of two rolls.
5 parts by weight were kneaded to prepare a silicone rubber composition. <Flame retardancy test> Length 100 mm x width 10 mm x thickness 2 m
m, and the resulting silicone rubber composition was immediately poured into a mold having a cavity whose surface was coated with polytetrafluoroethylene, and heated in an oven at 150 ° C. for 2 hours. Obtained.

A vertical combustion test (94V-O, 94V-1, 94V-) of a material obtained by classifying the obtained test piece into UL94 was performed.
Tested according to 2). Table 4 shows the results.

[0065]

[Table 4]

[0066]

As described above, the flame-retardant rubber composition of the present invention and the flame-retardant rubber molded product obtained from the composition use a non-halogen flame retardant, have low smoke emission properties and have a pungent odor. In addition, the present invention provides a rubber composition and a flame-retardant rubber molded product that suppress generation of dripping (melt dripping phenomenon) and have excellent flame retardancy while maintaining the mechanical properties inherent in rubber.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Nishimura 9-11-1, Kameido, Koto-ku, Tokyo Nippon Kagaku Kogyo Co., Ltd. No. 1 F-term in R & D Division of Nippon Kagaku Kogyo Co., Ltd. 4H028 AA35 BA06 4J002 AC001 DA058 DE046 EW047 FD136 FD137 FD138 GQ01

Claims (3)

[Claims] 1. A hydrated metal oxide having the following general formula (1): (Wherein, M represents melamine and n represents an integer of 1 to 4) 1-hydroxyethylidene-1,1 ′
-A flame retardant rubber composition containing a melamine diphosphonic acid salt. 2. The flame-retardant rubber composition according to claim 1, further comprising red phosphorus. 3. A flame-retardant rubber molded article obtained by molding the flame-retardant rubber composition according to claim 1 or 2.