JPS5949942B2 - Flame retardant thermosetting resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flame-retardant thermosetting resin composition comprising a thermosetting resin containing red phosphorus coated with a metal oxide.

Thermosetting resins generally have excellent physical, chemical, and electrical properties and are therefore used in many fields as molded products, cast products, surface coatings, or laminates.

However, their use always involves the risk of combustion, and the demand for flame retardancy in these thermosetting resins is increasing and is now the biggest challenge for the plastics industry, and research is progressing in many fields. is the current situation. Conventionally, substances that impart flame retardancy to thermosetting resins include organic halogen compounds, organic phosphorus compounds, mixtures of antimony compounds and halogen compounds, mixtures of phosphorus compounds and halogen compounds, boron compounds, aluminum compounds, etc. Inorganic compounds have been proposed.

However, when these flame retardants are added to thermosetting resins, it depends not only on the flame retardant effect but also on compatibility with the thermosetting resin, stability of the flame retardant, weather resistance, and purpose of use. It is required that the mechanical or electrical properties of the flame retardant thermosetting resin, the price and amount of flame retardant added, the operability during flame retardation, etc., be satisfied, but each has its advantages and disadvantages. However, there are many difficult problems in imparting flame retardancy to thermosetting resins, and there is no one that is completely satisfactory.

Furthermore, it is also known to add elemental red phosphorus as a flame retardant to resins to make them flame retardant. For example, adding 2 to 25 parts by weight of fine red phosphorus per 100 parts by weight of polyepoxide (Japanese Patent Publication No. 45-28510).
, adding 5 to 25 parts by weight of red phosphorus and 50 to 400 parts by weight of inorganic filler per 100 parts by weight of thermosetting resin (British Patent No. 1231814), 100 parts by weight of epoxy resin
Adding 0.2 to 5 parts by weight of red phosphorus and 0.1 to 20 parts by weight of an organic halogen compound per part by weight (U.S. Patent No. 3)
373135), foaming is carried out in the presence of 0.05 to 20 parts by weight of red phosphorus when producing foamed polyurethane (Japanese Patent Publication No. 41-113154). However, the use of commercially available red phosphorus as a flame retardant for thermosetting resins has various drawbacks as follows.

In other words, it is unstable in the resin compound composition before curing and the composition of the resin composition changes, and in the case of products that require a curing catalyst such as epoxy resins and unsaturated polyesters, red phosphorus consumes the catalyst. In many cases, curing does not proceed substantially and the desired product cannot be obtained, and even if it is cured, the curing is insufficient, resulting in deterioration of physical properties such as mechanical and electrical properties, and there are also defects in the product. It is stable, has poor weather resistance, and changes significantly over time.Furthermore, if the resin is exposed to heat or light, it may accelerate the change over time or cause deterioration of the resin itself.

These phenomena become more pronounced the longer red phosphorus is used after its production. The main cause of these drawbacks is that commercially available red phosphorus is stabilized with trace amounts of alumina and magnesia oxides, but the alumina used,
The amount of metal oxide in magnesia is 1% by weight relative to red phosphorus.
Because of the following, it has poor oxidation stability or hydrolysis stability, and is susceptible to oxidation or hydrolysis to produce acidic substances such as phosphoric acid and phosphorous acid, which is often caused by these acidic substances. be. Furthermore, when red phosphorus is dispersed in a resin and subjected to catalytic curing and heat curing, the red phosphorus that has generated or is likely to generate acidic substances will cause the resin to deteriorate as an acid. properties, especially electrical properties and strength, will be significantly reduced. Various proposals have been made to improve these drawbacks of red phosphorus, such as coating it with paraffin or wax, coating it with metal stearate, or resin.

However, using organic compounds as a coating method is dangerous because red phosphorus is easily flammable, and there are problems in the work process.Furthermore, when an object coated with an organic compound is heated, the organic compound There were drawbacks such as the need to take into account the reaction with red phosphorus. The present inventors have conducted various studies to overcome these drawbacks when using red phosphorus as a flame retardant for thermosetting resins, and as a result, they have found that red phosphorus coated with a specific amount of metal oxide is stable against oxidation. The present invention was completed based on the discovery that the properties and stability against hydrolysis are extremely excellent.

That is, the present invention uses 100 parts by weight of a thermosetting resin and 3 to 2 parts of red phosphorus coated with a metal oxide of 3 to 40% by weight based on red phosphorus.
5 parts by weight, the thermosetting resin is a phenolic resin,
One or more resins selected from epoxy resin, unsaturated polyester resin, urethane resin, melamine resin, aniline resin, furan resin, alkyd resin, and xylene resin, and the metal oxide coating is Si, Al, Mg. , Ti
, Fe, and Zr oxides.

Resins applicable to the present invention include various thermosetting resins in general.

Examples include phenol resin, epoxy resin, unsaturated polyester resin, urethane resin, melamine resin, aniline resin, furan resin, alkyd resin, and xylene resin.
Epoxy resins include glycidyl ethers of polyhydric phenols such as bisphenol A, linear aliphatic and cycloaliphatic epoxy resins, and even if they have substituents such as halogen atoms, hydroxyl groups and ether groups. Often various types of epoxy resins can be used.

Specific commercially available products include Epicoat manufactured by Siel Kagaku, Araldite manufactured by Ciba Kirkey, and Tauepoxy resin manufactured by Tau Chemical International. As curing agents for epoxy resins, amines such as aliphatic amines such as diethylenetriamine, triethylenetetramine, ethylenediamine, diethylaminopropylamine, n-hydroxyethyldiethylenetriamine, diaminodiphenylmethane, tris(diethylaminomethyl), etc.
Aromatic amines such as phenol, diaminodiphenylsulfone, metaphenylenediamine, bis(3-methyl-4
Cycloaliphatic amines such as monoaminophenyl)methane, bis(4-aminocyclohexyl)methane, and other heterocyclic amines are used, and the amount added is generally at least one amino hydrogen atom per epoxy equivalent of polyepoxy. Use an amount that gives . At this time, curing is accelerated by adding an accelerator such as salicylic acid or lactic acid. Further, carboxylic anhydride-based curing catalysts such as phthalic anhydride, maleic anhydride, dodecylsuccinic anhydride, methylnadic anhydride, pyromellitic anhydride, benzophenonetetracarboxylic anhydride, succinic anhydride, etc. can also be used. The amount added is generally 0.8 to 2.3 acid equivalents per epoxy equivalent. At this time, accelerators such as tertiary amines, sulfides, and organic phosphines can also be added. Unsaturated polyester resin is an ester product of an unsaturated carboxylic acid such as maleic anhydride or phthalic acid, a saturated polybasic acid represented by phthalic anhydride, and a polyhydric alcohol such as propylene glycol or ethylene glycol as a styrene monomer. General liquid resins diluted with polymerizable monomers such as the following can be used.

Specific commercially available products include Dainippon Ink Co., Ltd.'s Polylite, Takeda Pharmaceutical Co., Ltd.'s Polycol, and Hitachi Chemical Co., Ltd.
Polyset etc. can be mentioned. As curing agents for unsaturated polyester resins, organic peroxides such as benzoyl peroxide, methyl ethyl ketone peroxide, lauroyl peroxide, ketone peroxides such as t-butyl perpenzoate, acyl peroxides, and hydroperoxides are used. The amount added is about 0.02 to 5% by weight based on the unsaturated polyester. Curing of unsaturated polyesters requires a curing accelerator. As the curing accelerator, cobalt-based, vanadium-based, manganese-based, amine-based, quaternary ammonium salts, and mercaptans such as cobalt naphthenate, manganese naphthenate, vanadyl octoenoate, and dimethylaniline are used. The present invention can also be applied to other general thermosetting resins such as phenol resins, urethane resins, melamine resins, furan resins, alkyd resins, and xylene resins using ordinary curing methods.

Next, the red phosphorus used as the flame retardant of the present invention is a stable red phosphorus having excellent oxidation stability and hydrolysis stability, the particle surface of which is coated with a metal oxide.

Metal oxide coatings include Si, Al, Mg, Ti, Fe.
, Zr, Sb, and Zn. Examples of metal oxides coated with red phosphorus include those that have been neutralized from metal salts and precipitated in colloidal form. , generally takes the form of metal oxides, metal hydroxides, and condensates formed by bonds between metal hydroxides.
Both are amorphous. By heating each of these metal oxides to a predetermined temperature, each becomes a regular metal oxide. However, the metal oxide coating used in the present invention may be a general metal oxide, a hydroxide, or an amorphous coating. Therefore, the metal oxides used in the present invention do not mean only metal oxides in a strict sense, but also include metal hydroxides, condensates of metal hydroxides, etc. Alternatively, it also includes a mixture thereof. Regarding the amount of metal oxide coating, it may be coated with one or more oxides of the above-mentioned metals, and in any case, the total amount must be at least 3% by weight based on the red phosphorus. . In other words, if it is less than 3% by weight, red phosphorus cannot be sufficiently stabilized, and the object of the present invention cannot be achieved.There is no upper limit, but it is important to consider economic efficiency and the resin according to the present invention. This is naturally limited by the amount of phosphorus in the composition, and a coating of about 40% by weight is sufficient, preferably from 5 to 20% by weight. In addition, the red phosphorus used to produce the metal oxide-coated red phosphorus according to the present invention may not only be untreated after production, but also non-yellow phosphorus such as red phosphorus or black phosphorus stabilized by adding magnesium oxide. A mixture of phosphorus allotropes may be used, but it is preferable that it be in the form of a fine powder and that 95% or more of it can pass through a 200-mesh sieve.

To produce the metal oxide-coated red phosphorus used in the present invention, fine red phosphorus is suspended in an aqueous alkaline medium, the pH is adjusted appropriately, and the colloids or hydroxides precipitated from the metal salt are removed. It can be easily obtained by forming a metal oxide coating by depositing it on the surface of phosphorus particles and then generally by drying.

That is, for each metal, to produce silica-coated red phosphorus, fine red phosphorus is suspended in an aqueous alkaline medium, and then the pH is adjusted to 9.0 or higher, and the pH is adjusted to at least 70.
It can be easily obtained by introducing activated silica obtained by a reaction between an alkali silicate and a mineral acid into this slurry at a temperature above °C, depositing the silica on the surface of the red phosphorus particles, and forming a coating of amorphous silica. I can do it. Alumina-coated red phosphorus is produced by using an aqueous solution of mineral acid aluminum salts such as aluminum chloride, aluminum sulfate, and aluminum nitrate, and adding alkaline water dropwise while coexisting with red phosphorus to maintain a constant pH.
It can be produced by attaching a gel to the surface of red phosphorus by applying temperatures such as It can also be manufactured by Generally, magnesia-coated red phosphorus is produced by dissolving magnesium chloride, magnesium sulfate, or magnesium nitrate in water and adding alkaline water such as sodium hydroxide or sodium bicarbonate dropwise while coexisting with red phosphorus.
It can be produced by depositing a gel-like deposit on the surface of red phosphorus by stirring while maintaining a constant pH and temperature, and then filtering and drying it.

This magnesia coating is normal magnesia or a magnesia coating having hydroxyl groups. Zirconia-coated red phosphorus can be produced by using zirconyl sulfate and zirconyl nitrate in the presence of red phosphorus and adding alkaline water dropwise. In addition, iron oxide-coated red phosphorus can be produced by using iron chloride, iron sulfate, and iron nitrate to coexist with red phosphorus and dropping alkaline water, and titanium oxide-coated red phosphorus can also be produced by can be obtained by dropping alkaline water using titanium chloride, titanium sulfate, and basic hydroxytitanium in the presence of red phosphorus. Antimony and zinc-coated red phosphorus can similarly be obtained from their respective raw materials. When obtaining the thermosetting resin composition of the present invention using the above-described metal oxide-coated red phosphorus and thermosetting resin, the ratio of the metal oxide-coated red phosphorus to the thermosetting resin should be determined depending on the purpose of use of the resin and Although it varies depending on the type and filler described below, it is approximately 100% thermosetting resin.
1 to 25 parts by weight is sufficient. Particularly 3-1
5 parts by weight is preferred. If it is less than 1 part by weight, a sufficient flame retardant effect cannot be obtained, and if it is more than 25 parts by weight, a flame retardant effect can be obtained, but the phenomenon of residual red phosphorus itself after extinguishing the flame is observed, which is not preferable.

At this time, depending on the purpose of use, it may be used in combination with other general flame retardants, such as organic or inorganic halogen compounds, organic phosphorus compounds, inorganic compounds such as antimony oxide or boron compounds, or other resin additives. In particular, when used in combination with halogenated compounds, the synergistic effect is large and effective. Furthermore, if necessary, the resin composition of the present invention may contain fillers or reinforcing materials such as glass fiber, cotton, rayon, asbestos, paper, synthetic fiber materials, or silica sand, alumina, silica, borate, glass powder, etc. is possible, and the amount added varies depending on the purpose of use, but it is 0 to 9 of the total resin composition.
It can be contained over a wide range of 5% by weight.
Various methods can be used to add metal oxide-coated red phosphorus to thermosetting resins, but any method is particularly limited as long as it can be mixed uniformly before the resin gels and within its pot life. The molding process can be carried out by a conventional method, and a conventional molding method can be adopted depending on the type of resin.

For example, metal oxide-coated red phosphorus may be directly added as a fine powder to the resin compounding components, or the required amount may be added and mixed with one of the resin compounding components as a so-called masterbatch that has been processed in advance to form a suspension or paste. Examples include a method in which the curing agent, curing accelerator, or other resin additive is blended in advance and added to the resin. The thermosetting resin composition of the present invention obtained by adding metal oxide-coated red phosphorus to the thermosetting resin is made flame retardant and has excellent self-extinguishing properties.

In addition, red phosphorus used as a flame retardant is extremely stable against oxidation and hydrolysis, so it is stable in the resin composition before curing and does not change its composition, and is a good curing catalyst for epoxy resins, unsaturated polyester resins, etc. For products that require curing, curing can be completed without consuming it, and physical property deterioration due to incomplete curing will not occur. It has good thermal stability and oxidation resistance even during high temperature molding, and is not affected by heat changes. In the final product, it is stable as an immobile body, and the physical properties such as mechanical strength and electrical properties of the final product do not change, resulting in advantages such as product stability, good weather resistance, and no change over time. The present invention is applicable to various uses requiring flame retardancy, such as molded products or castings; flame retardant coatings used to form flame retardant coatings on various flammable surfaces by brushing, spraying, dipping, etc. Or fire-retardant paints or foams; laminates or fiber-reinforced resins obtained by impregnating or mixing them with fiber materials such as glass fiber, cotton, rayon, synthetic fibers, and paper; flame-retardant adhesives; It can be used in applications such as resin concrete in combination with inorganic aggregate.

Specifically, these include paints, building materials, decorative laminates, adhesives, electrical parts, mechanical parts, vehicle parts, decorations, structural materials, tanks, etc. Next, the present invention will be specifically explained with reference to reference examples and examples. Incidentally, the flame retardancy test was based on the method of JISK-6911-1970. Reference Example 1 400ml of water and 50ml of commercially available red phosphorus were placed in 11 reaction vessels equipped with a stirrer, thermometer, reflux condenser, and 2 dropping loads.
Add 0g and stir to uniformly disperse.

The pH of this red phosphorus slurry was adjusted to 9.5 to 10.0 with about 25 g of a 3% by weight aqueous sodium hydroxide solution. Separately, prepare the following liquids A and B and add them during the above dropwise loading.

Solution A: No. 3 sodium silicate (SiO2/Na2O molar ratio 3.1-3.3, SiO2 content 27-30% by weight)
) 35.79 (equivalent to 10.01 as SiO2) and make the total volume 175ml with water.

B solution: Take 5.089 ml of concentrated sulfuric acid and make the total volume 175 m with water.
Set to 1.

The aqueous slurry of red phosphorus is heated to 90 to 95° C. while stirring, and equal amounts of liquid A and liquid B are simultaneously added dropwise uniformly over about 90 minutes.

During this time, the temperature of the aqueous slurry was kept at 90 to 95°C, and the pH value was adjusted to 9.5 to 9.5 by occasionally adding a 2% by weight aqueous sodium hydroxide solution.
Maintain within 10.0 range. After the completion of dropwise addition of liquids A and B, the mixture is further stirred at 9.0 to 95°C for 30 minutes. After the reaction is complete, the product is filtered and washed until the alkali is removed.
60.degree. C. under reduced pressure and dried for 5 hours to obtain red phosphorus coated with about 20% by weight of amorphous silica based on the weight of red phosphorus.
99 is obtained. Reference Example 2 A 1.51-sized 40 flask was equipped with a stirring bar, a thermometer, a reflux condenser, and 2 drip loads.

A flask was charged with 400 g of water and 50 I of red phosphorus, which had not been stabilized with any metal oxide, and was stirred to be uniformly dispersed.

The pH value of the red rinsing slurry is adjusted to 9.5 to 10.0 with about 20 grams of 3% by weight sodium hydroxide.

Separately, prepare the following solutions A and B.

Solution A: No. 3 sodium silicate (SiO2/Na2O=3
．． 1-3.3, SiO2 content 27-30% by weight) 17
．． 99 (equivalent to SiO25.O9) and make the total volume 100 with water.

Solution B: Take 2.549 ml of concentrated sulfuric acid and dilute the total volume to 100 m with water.
Set to 1.

heating an aqueous slurry of red phosphorus to 85°C or higher while stirring;
Equal amounts of liquid A and liquid B are simultaneously and uniformly added dropwise over 70 minutes.

During this time, the temperature was maintained at 85 to 95°C, and the pH was adjusted to 9.5 to 10 by adding 2% by weight of sodium hydroxide as necessary.
．． Maintain at 0. After the dropwise addition is completed, the mixture is heated and stirred for 30 minutes. Next, sodium aluminate 0.8039 (Al
2O3O. 59 equivalent) was dissolved in about 20 grams of water, added, stirred for 30 minutes, and then adjusted to pH with about 30 grams of 3% sulfuric acid.
was adjusted to 6.0 to 6.5.

Next, add 0.259 g of benzalkonium chloride to about 3 g of water.
Dissolve in 0ml and continue stirring for a while. When the product is separated by filtration, washed until no sulfate groups are removed, and dried, SlO forms a dense amorphous coating on the surface of the red phosphorus particles.
55.2 g of red phosphorus containing about 10% by weight of Al2O3 and about 1.5% by weight of Al2O3 can be obtained.

Reference Example 3 Add 100 g of water to 150 g of unstabilized red phosphorus to make a slurry, and make a 0.5% by weight ZrO2 aqueous solution of zirconyl sulfate (HZrOOHSO4.2H20) 52
Zirconium treatment is performed by adding 0 mi and further adding an aqueous sodium hydroxide solution to adjust the pH of the slurry to about 6.0.

Thereafter, red phosphorus coated with zirconium is obtained by washing with water and drying in a conventional manner. This red phosphorus is ZrO2
It contains 1.7% by weight. 50g of red phosphorus coated with zirconium was taken and coated with silica according to Reference Example 1 to obtain 52.61 pieces of red phosphorus coated with 5% by weight of silica.

This product contains 1.7% by weight of ZrO2 based on red phosphorus.
It is coated with 5% by weight of SiO2. Reference Example 4 100 g of titanium tetrachloride is placed in a mixture of 300 g of ice and 100 g of water to obtain a solution of partially hydrolyzed titanium tetrachloride.

This solution contained 8.4% by weight of TiO2. Add 29.81 g of the partially hydrolyzed titanium tetrachloride aqueous solution into a stirring tank containing 50 g of unstabilized red phosphorus and 400 g of water while stirring.

Further, while heating the stirred material to 70°C, add 3% by weight of sodium hydroxide to maintain the pH at 3 to 4, stir for an additional 3 hours, and separate the product by filtration until the pH reaches 6 to 7. Wash and dry thoroughly. The obtained product has a dense amorphous coating of titanium oxide and titanium hydroxide formed on the surface of red phosphorus, and 52.99% of red phosphorus containing about 5% by weight of TiO2 can be obtained.

Reference example 5 Unstabilized red phosphorus 509 was added to 400a of water and while stirring, 35% of a 20% by weight aqueous magnesium chloride solution was added.
．． 59, and while heating to 70° C., add a 3% by weight aqueous sodium hydroxide solution, and stir for 3 hours while maintaining the pH at 9.5 to 10.5.

Thereafter, the product is separated by filtration, thoroughly washed and dried until the pH becomes 6 to 7. The obtained product has a dense amorphous coating of fine magnesium hydroxide formed on the surface of red phosphorus, and 53.59% of red phosphorus containing 6% by weight of M9O can be obtained. Reference Example 6 Add 400a of water to unstabilized red phosphorus 509, add 40.79a of 10% by weight ferric chloride aqueous solution while stirring, and add 3% by weight aqueous sodium hydroxide solution while heating to 70°C. Maintain pH between 9.5 and 10.5 and stir for 3 hours.

Thereafter, the product is separated by filtration, thoroughly washed and dried until the pH reaches 6.

The obtained product has a dense amorphous coating of iron hydroxide and iron oxide formed on the surface of red phosphorus, and is designated as Fe2O3.
52.39 of red phosphorus containing 0% by weight can be obtained. Example 1 Using commercially available red phosphorus and metal oxide-coated red phosphorus as a reference example as a flame retardant, and using pentapromotoluene as necessary, an unsaturated polyester resin (Polylite 8010 manufactured by Dainippon Ink Co., Ltd.) was used. ) and mix uniformly, then add the curing agent and curing accelerator and mix with stirring.
It was put into a mold and allowed to harden.

Table 1 shows the composition ratio, gelation time, and combustion test results. As a result, in Experiment No. 2 in which commercially available red phosphorus was used, curing did not proceed completely and the desired resin molding could not be obtained.

The curing time of the one using the metal oxide-coated red phosphorus obtained in the reference example was almost the same as that of the one without the addition of red phosphorus, and the curing time was about 5 minutes.

It can be seen that flame retardancy is affected by the amount of red phosphorus added. (
Phr (abbreviation for Perhundredresin) in parentheses represents parts by weight of red phosphorus relative to parts by weight of comb (1).

Example 2 Unsaturated polyester resin (Polylite TP-1140 manufactured by Dainippon Ink Co., Ltd.) 1001, curing agent methyl ethyl ketone peroxide 55% 1.61, cobalt naphthenate 6% 0.59, flame retardant: Shaped silica coated red phosphorus 9.61 (8 phr as red phosphorus),
Furthermore, as aggregate, silica sand No. 3 360y1 silica sand No. 5 2701)
A blended composition consisting of alumina (fine particles) 18011 calcium carbonate 90θ was mixed uniformly and hardened and molded to obtain polyester resin concrete.

When a flame retardant test was conducted according to JIS-K-6911-'70, self-extinguishing properties were exhibited with an afterflame time of 0.5 seconds and a combustion distance of about 12 mm.

The mechanical strength was compressive strength was 1350 kg/CWL) and tensile strength was 125 kg/CIIL. Polyester resin concrete was obtained under the same conditions as above except that commercially available red phosphorus was used instead of amorphous silica-coated red phosphorus. However, curing did not proceed completely and only weak mechanical strength was obtained, with a compressive strength of 160 K9/1 and a tensile strength of 55 kg/d.

In addition, the results of the flame retardant test did not show self-extinguishing properties. Example 3 Commercially available red phosphorus and reference example red phosphorus were added to an epoxy resin (Epicote 828, manufactured by Shell Chemical), mixed uniformly, and then a hardening agent (diethylenetriamine) was added and a test piece was molded in a mold.

The composition ratio and combustion test results at that time are shown in Table 2. When commercially available red phosphorus was added, curing was incomplete and the flame retardant effect was not very good.

The metal oxide coating with red phosphorus added completely cures as in the case without red phosphorus, and its flame retardancy is 5p red phosphorus.
It can be seen that when added for more than hr, it exhibits self-extinguishing properties with an afterflame time of around 1 second, which is preferable.

Example 4 Each component was quickly stirred and mixed using a well-known method for producing a foamed urethane material, and the mixture was poured into a mold to obtain a porous material.

Table 3 shows the composition ratio and combustion test results at that time.

Experiment number 1 melts and burns.

In Experiment No. 2, commercially available red phosphorus was added, and a complete molded product could not be obtained. Experiment No. 3 was self-extinguishing, but the amount of red phosphorus was small and the afterflame time was long. red phosphorus 6ph
It is preferable to add R or more because it becomes self-extinguishing with an afterflame time of 2 to 3 seconds. Experiments Nos. 8 and 9 show that hexabromobenzene completely burns when used alone, but when used in combination with silica-coated red phosphorus, flame retardation can be achieved due to the synergistic effect.

Claims (1)

[Claims] 1 100 parts by weight of thermosetting resin and 3 to 3 parts of red phosphorus
It consists of 3 to 25 parts by weight of red phosphorus coated with 40% by weight of metal oxide, and the thermosetting resin is phenolic resin, epoxy resin, unsaturated polyester resin, urethane resin, melamine resin, aniline resin, furan resin, alkyd resin. and xylene resin, and the metal oxide coating is one or two or more resins selected from oxides of Si, Al, Mg, Ti, Fe, and Zr. A flame-retardant thermosetting resin composition characterized by the following.