CA1285104C

CA1285104C - Red phosphorus flame retardant and nonflammable resinous composition containing the same

Info

Publication number: CA1285104C
Application number: CA000535782A
Authority: CA
Inventors: Ichiro Sakon; Masao Sekiguchi; Atsushi Kanayama
Original assignee: RINKAGUKU KOGYO CO., LTD.
Current assignee: RINKAGUKU KOGYO CO Ltd
Priority date: 1986-06-19
Filing date: 1987-04-28
Publication date: 1991-06-25
Anticipated expiration: 2008-06-25
Also published as: US4879067A; DE249723T1; DE3780088T2; US5026757A; DE3780088D1; EP0249723B1; EP0249723A2; EP0249723A3

Abstract

RED PHOSPHORUS FLAME RETARDANT AND NONFLAMMABLE
RESINOUS COMPOSITION CONTAINING THE SAME

ABSTRACT OF THE DISCLOSURE

A flame retardant comprising of spherical red phosphorus free of pulverized face which is directly produced in the form of fine powder by conversion of yellow phosphorus, without pulverizing process. The red phosphorus characterized by its surface state and shape entirely different from any prior pulverized red phosphorus has not only a high flame retarding ability, but also a superior combination of chemical and physical properties, particularly with regard to corrosion reistance, moisture resistance, mechanical strength and dielectric properties which make it highly valuable and useful as a flame retardant for various nonflammable resinous compositions used in electric articles including electronic parts, machines, automobiles and buildings. The flame retardant is desirably coated with thermosetting rein and/or hydroxide of aluminum and/or zinc, thereby greatly improved in its stability.

Description

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RED PHOSPHORUS FLAME E~ETARDANT AND NONFLAMMABLE
RESINOUS COMPOSITION CONTAINING THE SAME
, BACKGROUND OF rrHE INVENTION

[Field of the Invention]

: The present invention relates to a red phosphorusflame xetardant and a nonflammable resinous composition containIng the same. In particular, the present :~: invention ls d~rected to a red phosphorus having a ~: special surface configuration which has been produced by a special process and a nonflammable resincus composltion containing the red phosphoruswhich ca~sition is greatly imp~oved in its molsture-resistance, corrosion-resistance and heat resistance. Further, the present invention is directed to the provision of a : nonflammable resinous composition which can be easily and safely handled and is highly stable.

[Description of the Prior Art]

Since red phosphorus is useful as a ~lame :
~`: : retardant for synthetic rasins, it has been heretofore : used 1~ ther~osetting~rasins and thermoplastic resins - ~ , , ~

~2-to provide various nonflammable reslnous compositions which have been extensively utilized in a variety of applications, such as electronic components or parts, electric articles, machines, automobiles, buildings, etc.
However, when red phosphorus is used as it is, the following problems have been encountered because of its lability and sensitivity to heat, friction and shock.
Namely, red phosphorus presents a danger in handling, storing and mixing with resins;
formation of poisonous phosphine gas and oxidation products is caused due to the reaction of red phosphorus with moisture in the air, thereby polluting ~he working environment and impairing the physical and ~ electrical properties of resinous compositlons; and `~ there are difficulties in preparing a nonflammable composition due to the lack of compatibility with synthetic resins.
For these reasans, various ways of stabilizing the red phosphorus flame retardant with various organic or inorganic substances have been tried in order to overcome the foregoing problems but they have not been entirely successful. Accordingly, the use of the red phosphorus flame retardant is restricted to certain fields and it has been difficult to satisfy the ~ requirements for high qualities.
; Presently, the red phosphorus flame retardant has been extensively used as a flame retardant for thermosetting resin, particularly epoxy resin, and has been mainly used in insulating cast resinous compositions for use in electronic components for high voltage applications.
However, in recent years, with an increasing '',, :' :

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1~85~0 ) trend toward miniaturi~ation and hi~h-voltage application in electric or electronic articles, increasing demand is being directed to ~lectrically insulating materials with a high performance. For such a demand, the requirements for the physical properties of the red phosphorus flame retardant have become more critical and, thus, red phosphorus flame retardants - hereto~ore available can not fully meet the requirements. In other words, the electronic parts or components using, as an insulator, the non~lammable resinous composition aontaining the conventional red phosphorus ~lame ret~rdants are subjected to degradation of insulation and corrosion at metallic portions due to deterioration of the used re~in with the pas~ing of time, and thereby their properties are impaired. In such circumstances, it has been pointed out that the known nonflammable articles lack durability and lability. Such a lack is considered to be caused ~ mainly due to deterioration of the red phosphorus flame ; 20 retardant and, thus, improvement for this has been required. The deterioration of the red phosphorus flame retardant has been considered to be due to the formation of phosphine and corrosi~e oxidation products ~ resultlng from the reaction of the red phosphorus with a `~ 25 small amount of moisture and, as a method of stabilizing the known red phosphorus flame retardants, their powders are coated with various substances so as to be screened from the contact with moistureO
Howe~er, actually, such a kno~n method itself has limitations and, thus, can not meet the requirements for resinous materials intended to use in high performance electronic components in which an extremely ~ high resistance to moisture and corrosion is required.
`~ As an alternative method to render the insulating .~ .
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~L~85~L04 .~ cast resln nonflammable or the high voltage applications, organic halide flame retardants have been practically used either singly or in comblnation with antimony trioxide in some cases, becau~e they have good ~ 5 moisture resistance and corrosion resistance as ii compared to the foregoing red phosphorus. However, ,:
,~ these known halide flame retardants/ in addition to the inherent dlsadvantage that they evolve a large quantlty of poisonous gases when firing, cause serlous deterioration of the electrlcal propertlea of the :- resins because o~ the use~of them i9 required in large amounts. Further, since the halide flame retardant~
~ are expensive, the production cost is increased.
.~. In contrast to thi~, red phosphorus is considered ~ lS as a hopeful flame retardant material meeting the i~ : requirements, such as ~a~ety and minimization o~
: environmental pollution, because evolution of poisonous :. gases and smoking when burning are slight as compared ~ with the organic halides. Further, ~ince it exhiblts a .. ~` 20 very high flame-retarding ability in a small amount,the use of it not only reduce~ detrimental effects on ; the physical properties of the resins, but also is advantageous from the point of cost. Under such circumstances, there ~s a growing demand ~or 25 improvements in tha heat resistance and moisture re~istance.
o~ flame retardants of red phosphorus and more stabilized red phosphorus flame retardants are awaited.
Thermoplastic resins have been extensively used : in variou~ fields, ~uch a~ electric articles, machine3, ~:; 30 automobiles and buildings, because of their superior phy.cical and chemical properties. Generally, ther~oplastic resins are ~ub~ected to mix~ng and molding operations at relati~ely high temperatures ln comparl~on with thermo~t~ing resins and, thus, red .

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., , -5-; phosphorus flame retardant has not so o~ten been u~ed in the resins because of the lack of thermal stability. As other known flame retardarlts, organic halides, organic phosphorus compounds, antimony trioxide, etc., have been used practically eil:her singly or combinations `~ thereof in thermoplastic resins. However, these known f]ame retardants have, for example, the disadvantages that they present problems in safety and ~tabillty or cause serious deteriorat:Lon of -the physical properties of the resins. Recently, with an increasing ~emand ~or i~ much higher quality in all industrial fields, the requirements for thermoplastic resins have also become more strict. For example, with respect to nonflammability contemplated by the present invention, with increasing public demand for safety, a further higher technique has been required not only for obtaining a higher burning resistance but also for securing safety in working and burning and stability.
However, most of these retardant5 can not meet su~h a requirement. For example, thermoplastic resins are sub;ected to forming operations at relatively high temperatures and, during such a high temperature operation, the organic halide flame retardant yields corrosive thermal decomposition products or hydrolysis products, thereby damaging the metal mold. Further, ¦~ after molding, bleed-out occurs at the surfaces of the resulting molded articles and the surface appearance and the electrical proparties of the articles are ;~ ~ impaired. Further, the organic halide flame ratardant should be added in large amounts to impart an enough burning resistance to the resulting products but such a j ~ large amount of addition not only adver~ely affects the ~; mechanical properties, ~uch as tensile strength, folding endurance or impact resistance, but also results !~ ~
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in increased production cost. In recent years, as the most serlous problems associated with the use of , organic halide flame retardants in thermoplastic resins, particular attention has been given to the problems caused by a large amount of smoke or toxic gas generated when burning. Wlth an increasing demand for safety from burning in the u~e o~ synthetic resins, the-additives like organic halides, which may aause evolution of a large quantity o~ gas pollutants when burning, have been gradually limited from the viewpoints of personal saEety and maintenance o~
equipments or tools. Antimony trioxlde has been usually employed as a ~lame-retarding assistant or the organic halide flame retardants, but it not only lS exhibits detrimental effects on the physical properties of the used resins, particularly with regard to the reduction of tensile strength and impact resistance, but al~o presents problems or trouble3 in ensuring the safety of working environments because of its toxicity.
Further, it has known that most organic phosphorus compounds themselves act as a plasticizer and, . ,~ !
therefore, cause an unfavorable reduc~ion in the heat-resistance and mechanical properties of re~ins. Also, the organic phosphorus compounds increase the water absorbing property of the nonflammable resinous article, thereby leading to an unfavorable deformation of the article.
In contrast to this, red phosphorus exhibits a very high flame-retarding ability in a small amount and evolution of poisonous gases and smokin~ are slight as ;~ compared to the halide type flame retardant~
Therefore, red phosphorus is considered as a hopeful ~;~ flame retardant material which is safe from burning minimi~es environmental pollution problems. Under such :: ~
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circumstances, the foregoing mekhods o~ stabillzing red phosphorus powder by coating have been trled to improve the heat reæistance of the red phosphorus flame retard~nt used in thermoplastic resins, but they have not been successful. Therefore, there is a growing demand for a red phosphorus flame retardant which is stable and safe in working and burning.
`~ In response to such a demand, the present inventors have made many studies on the foreyoing problems, such as moisture resistance, corrosion resistance and heat resistance of red phosphorus as a flame retardant, and consider that there are limitations in the conventional method for surface treating red phosphorus powder. ~n the base o~ such ~ 15 consideration, the inventors have carefully studied the 6,l properties in question from a different angle and, as a result, fou~d that the red phosphorus powder obtained from a novel process di~feren~ from any prior art have a special configuration and are entirely different in their surface states and physical properties from those obtained from the prior art. The novel red phosphorus has a very high stability and may be employed as a flame retardant as it is. However, such a novel type of red phosphorus has been found to be ~ 25 considerably stabiliæed by a surface modifying }';~ treatment and, thereby, be very useful as a flame ! - retardant for resin compositions. The present inventions have been arrived based on the above findings wherein the above problems with respect to moisture resistance, corrosion resistance and heat resistance can be overcome.
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~ SUMMARY OF THE INVENTION

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Therefore, an object of the present invention ls to provide a flame retardant of red phosphorus and a nonflammable resinous composition containing the ~ame in which the flame retardant is provided in a ~pecial surface configuration and thereby it~ properties, ~arti~arly with respect to moisture resistance, corrosion resi~tan~e and thermal stability are greatly improved~
Another ob~ect of th~P present invention i9 to make it pos~ible to work or handle with ease and in safety.
A further ob~ect of the pre~ent invention to provide red phosphorus coated with re~in and/or hydroxide, ~uch as aluminum hydroxide andtor æinc hydrox~de.
. 15 Accor~ing to the present invention, there is : directly provided a flame retardant material of red .~ phosphorus powder in the form of spherical fine particle~ free of pulverlzed angular face and ~: aggregate thereof by a conversion proce~ o yellow phosphorus without requiring pul~erlzing process.
~ In a ~urther feature of the present invention, the ~ red phosphorus may be coated w~th thermo~etting re~in :; and/or hydroxide, ~uch as aluminum hydroxide and/or zinc hydroxide.
In a still further feature, a non lammable ; resinou~ compo~ition el~minating the foregolng troubles or problems heretofore experienced can be obtalned by . ~ adding the red phosphorus a~ a flame retardant to ;~: synthetic resin~, i.e~0 thermosetting re~in or thermoplastic res~n~ A~ the thermosetting ~: resin, epoxy reslns can be used and the thermopla3tic ~: resin may be at least one ~elected from the gxoup ~: con~i~ting of polyamlde, polye~ter, polyether, polyc~xbonate, polv~yrene, polyurethane and . ~

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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Red phosphorus has been usually produced by heat treating yellow phosphonls over a peri~d of several days in a reactor and the red phosphorus resulting such a known process has been obtained as a solldly coagulated cake-like lump of high density. When red phosphorus is used as a flame retardant in synthetlc resins, it should be in a ~ine powder ~orm and, thu~, a pulverizing step is indispensable for the conventlonal red phosphorus obtained as a lump.
In contrast to this, according to the present invention, there is directly obtained red phosphorus in a fine powder form by a novel conversion process, without requiring a pulverization step and the thus obtained red phosphorus is a light amorphous powder having a small bulk density, in comparison with the conventional pulverized powder of red phosphorus.
Although such light, amorphous red phosphorus itself is highly stable, a very high stability can be obtained by coating a ~hermosetting resin and/or hydroxide~ such as aluminum hydroxide and/or zinc hydroxide, and the reactlvity of the coated red phosphorus to moisture i9 ~ almost negligibly small in compar~on with the ; 25 reactivity of known pulverized red phvsphorus similarly coated. When the coated pho~phorus of the present invention i9 incorporated as a flame retardant into synthetic resin, the resulting nonflammable resinous composit~on is outstandingly lmpro~ed in moisture ~;~ 30 resistance and corro~ion resistance as compared to any - known nonflammable compound and, with respect to these properl:ies, i9 w~ll comparable with a reslnous .
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- 1 o -composition not contalning a flame retardant.
Further, slnce the coated red phosphorus of the present invention has a high ignition point, it can be sa~ely incorporated into thermoplastic resin without accompanying evolution of phosphine gas.
i It is considered that the unusual stability of theflame retardant of the present invention is ascribable to the surface state of the red phosphorus which i~
quite different ~rom the surface state of the pulveri2ed red phosphorus in the prior art. More specifically, pulverized powder obtained by pulverizing a strongly coagulated lump, as in the prior art, is made up o~ particles having a complicated polyhedral configuration consisting of acute ridge lines and sharp-edged angular facets. In contrast to thls, since the particles of the present invention are not sub~ected to pulverization, such ridge lines and facets are rarely found. It has been confirmed by means of an electron microscope that the invention red ~; 20 phosphorus powder is made up of fine spherical particles having a naturally occurring continuous surface ~daggregate thereof. In the speci~ication, the red phosphorus of the present invention is re~erred to as "spherical red pho5phorus" in the sense o~ a red phosphorus having a spherical surface~
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In the known pulveri2ed red phosphorus, since the pulverizlng step produces many active sites on the surface of particle and maXes it labile, moisture and ; oxygen tend to adhere onto the sites and thereby phosphine and oxidation products result from dlsproportionation and ~urning occurs. On the o~her hand, such active sites are rarely found in tha spherical red phosphorus ~icles which have not been subjected to ~ pulverization process and their surface state is ,: ~

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' - 1 1 -very stable. Therefore, it can be consldered that adsorption of oxygen and moisture and disproportlonation do not occur in the spherical red phosphorus and the red phosphoru~ itself is considerably stabilized. Further, with respect to coating of red phosphorus powder with thermosetting resin or aluminum hydroxide, etc., it is difficult to coat unlformly the pulverized powder due to its surace state and some portions of the unstable facec~ tend ko be left uncoated. In contrclst to this, the spherical red phosphoruq can be unlformly and wholly coated and, it is considered that 9uch a difference in uni~ormity o~
the coating leads to a definitive difference in stability over known pulverized powder.
Since the spherical red phosphorus ltself has such ;~ a very highly stable surface, lt exhibits abllities which are by no means inferior to any conventional coated flame retardant obtained from the pulverized red phosphorus, even when it ls employed as a flame retardant without any coating treatment, in applications in which the required levels for moisture resistance and corrosion resistance are not so high, or the operation temperatures, ~or example, in mixing with resin or molding, are relatively low. However, or applications such as electronic parts, in which high levels of moisture-resistance and corrosion resistance are required, or fox use in resins with a high molding -~ temperature, lt is desired to coat the spherical red phosphorus with a thermosetting resin or hydroxide, such as aluminum hydroxide, and thereby most of the possible problems which may be caused by the addition of the red phosphorus flame retardant will be eliminated.
; This coating not only provides almost pexfect red , ~

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phosphorus in moisture resistance and corroslon resistance properties, but also ~avorably increases the compatibillty with resins used in the preparation of a nonflammable composition, thereby facilitating processing operations.
~ As a further advantage of the aoated red ;~ phosphorus of the present invention, it has no ~etrimental effect on the inherent properties of the used resin.
It has been known ~hat when the conventional pulverized red phosphorus is added as a flame retardant to a reslnou~
composition, the tensile strength, flexural strength and electrical properties of the resin are adversely affected. However, such deterious effects on those . physical properties are hardly detected on addition of lS the spherical red phosphorus o the present invention to the resinous composition. The deterioration of the ~; physical properties of the resin associated with the ~- addition of the pulverized red ph~sphorus is considered to be caused by the surface state of the particles having angular pulverized faces and the degradation ~, .
s~ products. In contrast to thls, the spherical red phosphorus powder is not only chemically stable, but also has an advantageous shape causing no deterioration of the physical properties of the resln.
As set forth above, the nonflammable resinous composition according to the present invention can be safely handled and is highly stabilized by using the spherical red phosphorus as a ~lame retardant, without ;~ losing the advantages of the red phosphorus flame i ~ 30 retardant.
The spherical red phosphorus according to the present invention can be produced by the following methodO
In a sealed container filled with an inert gas, :
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yellow phosphorus is heated to a temperature near its ; ' boiling temperature to initiate tha conversion reaction ~-~ to red phosphorus, and when the resulting nuclei of red phosphorus are grown to t:he desired particle size, the conversion reaction ls discontinued. After removing unconverted yellow phosphorus, the spherical xed phosphorus is obtained in a fine powder form having a small bulk density, without requiring any pulverizing process. ~he conversion ratio and the particle size o~
the red phosphorus can be arbitrarily adjusted by controlling the time and temperature of the conversion .~, process. As preferable ~onditions of the production of the red phosphorus contemplated by the present ~ invention, the reaction temperature is in the range of 3 15 250 to 600 C and the conversion ls 70 % or less. When the reaction temperature is less than 250 C, the conversion rate is slow and is impractical. On the other hand, since a temperature exceedlng 600 C makes '~ it difficult to control of the conversion, the resulting i 20 products are not uniform in their properties and can not satisfy the requirements for the surface shape purposed by the present inventionO When the conversion ~- is more than 70 ~, the resulting red phosphorus becomes a lump and needs a pulverizing step for use as a flame retardant. ~his pulverizing step makes it impossible to achieve the ob;ects of the present invention.
Usually, the longer the reaction time and the higher ~; the reaction temperature, the greater the conversion j and the larger the particle size become. For example, ~; 30 conversion at 280 C for four hours provides a ~ conver~ion of 40 % and an average particle size of 50 ; Ipm. The particle size distribution of the red phosphorus thus obtained is ln a very narrow range and extremely uniform as compared to the oxdinary . ~:
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1 ?~85104 pulveri~ed powder. Therefore, even in case where the invention xed phosphorus has the same average particle size as that of the pulverized one, it has a hlgher poroslty, and, thereby, it can be obtained as a light ~ 5 powder having a small bulk density. In the '~ nonfla~mable composition of the pre~ent invention, the particle size of the red phosphorus may be 200j~m or ,~ less, and, more pre~erably, it is 100 ~m or less in view of lnfluence on the physical properties o~ the resulting resinou~ composition and the appearance quality of the molded article~.
In the present inventton, when the foregoing spherical red phosphorus i~ desired to be coated with , hydroxide, an aqueous solution of water-soluble salts lS of aluminum or zinc, for example, aluminum sulfatel aluminum chloride, zinc sulfate or zinc chloride, is added to an aqueous suspenslon of the red phosphorus `l powder and is allowed to be adsorbed onto the powder i~ in the form of aluminum hydroxide or zinc hydroxide resulted from neutralization by sodium hydroxide or double decomposition by addition of ammonium blcarbonate. In this coating, if necessary, the foregoing water soluble salts may be used in combination thereof to form aluminum hydroxide and zinc hydroxide on the red phosphorus powder.
In practicing this coating processr it is - preferred that the amount of the xed phosphorus in the aqueous suspension be in the range of 10 to 100 parts by weight with respect to 100 parts by weight of water and the concentration of the water soluble salt of aluminum or zinc in the a~ueous solution be in the range of 5 to 30 ~ by weight. The coating amount of the hydroxide is preferably from 0.3 to 30 parts by weight ~rith respect to 100 parts by weight of the red .~ ' ,~,, `~

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phosphorus and, thereby, a superior red phosphorus flame retardant can be obtained. However, this invention is not limited only to those.
i In the present invention, when the spherical red S phosphorus i9 required to be coated with thermosetting resin, any raw material of the resiniand i~s initial condensate may be used as long as they can readily cause polymerlzation in the red phosphorus aqueous suspension or the initial condensate can be emulsified in the suspension, and are allowed to uniformly deposit onto the surface of the red ;; phosphorus powder, thereby ~orming a coating of the thexmosetting resin. Usually~ the coating material is selected from various types of materials, ~uch as j~ 15 p~enol ~drma~d~hy~e~yste~ urea-formaldehyde system, melamine-formaldehyde system, furfuryl alcohol-formaldehyde sy9~em, ; aniline-formaldehyde system and polyhydric alcohol-,' polybasic acid system and, among them, for example, the materials of furfuryl alcohol-formaldehyde system, aniline-formaldehyde system and polyhydric alcohol-polybasic acid ystem are desirably added to the aqueous red phosphorus suspension after preparing their initial condensation products, because the polymerization of these materials is difflcult in the presenae of a large quantity of water.
Although the conditions o~ coating the red phosphorus with the resin are varied somewhat depending the kind of the used resin, the resin-forming raw material or the lnitial condensate thereof is added in 30' an amount of 1 to 35 parts by weight with respect to 100 parts by weight of the red phosphorus to an aqueous suspension containing the red phosphorus in an amount ~-~ of 10 to 100 parts by weight with respect to 100 parts by weight of water. In the case of u~lng the resin-' k~,,' :

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formlng raw material, the material i8 stirred at `~ temperatures of 40 to 100 C for a period of time of one to three hours, and, in the case of uslng the inltial condensate previously prepared, the condensate is stirred at temperatures o 60 to 100 ~C for a period of time of one to two hours. In this step, a polymerization catalyst and a ~iller, such as aluminum - hydroxide, magnesium hydroxide or titanium hydroxide, may be coexistent in the mixture. Addition o~ the filler increases the mechlanlcal ~trength o~ the resin coating and, at the same time, ha~ an ef~ect oE
covering the purple color characteristic of red phosphorus, thereby making contribution to a further ~ expanded use o~ the red phosphorus of the present 1 15 invention. The filler is preferably added in amounts of 1 to 35 parts by weight with respect to 100 parts by weight of the red phosphorus. The intended reaction product is removed, washed w~th water and is dried at tamperature~ of 130 to 140 C to complete the polymerization reaction. After such procedures, there ` ~ can be obtained the invention red phosphorus flame retardant having a very high level of stabllity ~; combined with a very high resistance to moisture and corrosion.
-~ 25 As a further method, when aluminum hydroxide and/or zinc hydroxide i~ adsorbed onto the red :
phosphorus powder prior to coating with the ~ thermosetting resin, the red phosphorus is ~urther -~ improved in its moisture resistance, corrosion -~ 30 resistance and stability and the resinous composition ; which is~rendered nonflammable by the red phosphorus thus coated is not affected by the addition of the red phosphoxus over a long period of time. The pretreatment with aluminum hydroxide and æinc hydroxide ,, . ~ .

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, ~ 2~S~L04 ls performed in an aqueous suspension containing 100 parts by weight of water and 5 to 100 parts by weight of the red phosphorus by forming aluminum hydrvxide or zinc hydroxide by the neutrallzation of a water solubl~
compound, such as sulfate or chloride of aluminum or zinc, with caustic alkali or double decomposition with ammonium bicarbonate and then causing adsorption of the thus formed hydroxide onto the red phosphorus powder.
The aluminum salt or zina salt is added in amount~
; lO required to ~ield 0.1 to 30 parts by weight oE the hydoxide with respect to 100 parts by weight of the red phosphorus.
As shown in Examples below, the red phosphorus ~lame retardant of the present invention exhibits an extremel~ high resistance to moisture and corrosion and is extremely highly stable. Further~ this flame retardant has a high ignition temperature and hardly causes the problems of phosphine and corrosive oxidation products, which are considered to be produced due to adsorption o oxygen and moisture. As a result, the red phosphoru~ may be safely incorporated into resins to ~e cast at high temperatures and resinous compositions containing it ~an be stored stably over a long period in ~ the presence of moisture or at high temperatures, ; ; 25 without deterioration. 5uch advantageous properties make the red phosphorus highly valuable and use~ul in nonflammable resinous compositions.
For example, since the red phosphorus flame retardant according to the present invention is free from the deterioration problems of resinous compositions due to the deterioration of r~d phosphorus ~ flame retardant, it is desirable a3 a flame retardant ; for thermosetting reslns used in high vo~tage electronic parts in which a high degree of ~sta~i~ity .:
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Therefore, one feature of the present invention resides in the provision of a nonflammable thermosetting resln compositlon containing the highly stable red phosphorus set forth above, the resinou~ composition comprising 100 parts by~weight of epoxy resin as a thermosetting resin, S to 40 parts by weight of the red phosphorus flame retardant, 5 to 150 parts by weight of aluminum hydroxlde as a Piller or a ~lame-retarding assistant, 20 to 90 parts by weight of acid anhydride hardener and an appropriate amount o~ a hardening promoter. In the present inventian, the term "epoxy resin" i9 i~tended to mean epoxide of aromatic-, alicyclic- or aliphatic-type havinq one or more epoxy group~ in their molecules and, epoxy resin which is liquid at room temperature i9 particularly preferable !:, for insulating cast resin compositions for electronic parts. For example, bisphenol A dlglycidyl ether, bisphenol F diglycidyl ether, and polyglycidyl ester of polycarboxylic acid (e~g. phthalic acid or terephthalic ' acid), are suitable for practical use.
An excess use of aluminum hydroxide lead~ to an unfavorable increase in the viscosity of the resinous composition and thereby will present difficulties in the casting operation. On the other hand! an insufficient use of aluminum hydroxide can not provide - a sufficient effect as a flame retarding assistant.
Therefore, aluminum hydroxide is preferably employed in the range of 5 to 150 parts by we~qht with respect to 100 parts by weight of epoxy resin.
The amount of the red phosphorus flame retardant is preferably in the range of 5 to 40 parts by weight with respect to 100 parts by weight of epoxy resin, ~ taking into account the flame retarding effect and the ,. -'`':`
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As the hardener, an acid anhydride is most preferable and known anhydrides, such as phthalic anhydride, tetrahydrophthalic anhydride, succinic anhydride, etc., 5 are widely useful. As the hardening promoter, J imidazole derivatives of 2-phenylimidazole, 2-ethyl-4-methylimidazole, etc., are preferable from the view-point of ease of operation~.
The red phosphorus of the present invention may be 10 also used with thermopla~tic resin and is particularly useful in the so-called engineering plastic ~ compositions ~or structural materials and functional part~ of electric articles or machines which are used ¦- under relatively severe conditions and the present15 invention is directed to a resinous composition for such applications.
¦~ The thermoplastic resin to be rendered nonflammable by the present invention may be selected - from the group consisting o~ polyamide, polyester, 5~ 20 polyether, polycarbonate, polystyrene, polyurethane and ~ ~ polyacrylate. In addition to the red phosphorus flame 5 ~ retardant, appropriate additives known in the art, such as filler, stabilizer, plastiaizer, colorant, glass ~;~ fiber or lubrlcant may be added, if necessary. The red 25 phosphorus flame retardant is preferably added in an amount of 0.1 to 30 parts by weight with respect to 100 parts by weight of the thermoplas~ic resin. When the amount ls less than 0.1 part by weight, a sufficient ~lame retarding ~fect can not be expected. However, 30 an excess use exceeding 30 parts by weight adversely affects the physical properties of the resin component.
ID the nonflammable compositions of the present invention~ known ~lame retardant~ may be employed in combination of the flame retardant of th~ present > .
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The present invention will now be described in detail with reference to the following Examples.
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, Example 1 ! 5 ~Preparation of Spherlcal Red Phosphorus) . .
, 500 g of yellow phosphorus was pla~ed in the stainle~s vessel fllled with nitrogen gas, sealed and ,~ heated at 270 C for fOUI' hours to convert it to red phosphorus. Unconverted yellow phosphorufs was removed and there was obtained 211 g of ~pherical red phosphorus in ~lowable spherical powder having an , average particle size of 50 ~m and a bulk densit~ of 0.86 ~/cm3. The spherical red phosphorus thus , ~ obtained was employed in the following Examples.

~ 15 Example 2 f',.;~ ~ 500 g of the spherical red pho phorus was suspended in 800 ml of water and then 300 ml of a 10%
aqueous solution of alumlnum sulfate was added. After 100 ml of a 5~ aqueous solution of sodium hydroxide was added dropwlse while fully stirring, the suspension was heated to 50 C and was kept at the temperature for 30 minutes. The resultant suspension was filtered, washed l~ with water and dried at 120 C. The yield of the ,~ resultant coated red phosphorus was 516 g.
,~' Example 3 ~; 500 g of the spherical red phosphoru~ was suspe~ded in 800 ml of water and then 200 ml of a 20%

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ammonium bicarbonate was added dropwise while thoroughly ,~ stirring and the suspension was heated to 50 C ancl , 5 allowed to stand at 50 C for 30 minutes. After ~ cooling in the air, the suspensiorl was filtered, washed - with water and dried at 120 C. The yield o~ the ; coated red phosphorus thus obtained was 536 g.
,.s:
~? Example 4 ., 500 g of the spherical red phosphorus was suspended in 800 g of water and 300 ml of a 20~ aqueous solution of zinc chloride was added. 400 ml of a 10~
sodium hydroxide aqueou~ solution was added dropwise to the suspension under stirring and the suspension was heated to 50 C and then allowed to stand at this s~ temperature for 30 minutes. After cooling in the air, sS ~ the resultant suspension was filtered, washed with s;- water and dried at 120 C. The yield of the coated red :,,;
~ phosphorus thus obtained was 540 g.
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~s~ 20 Example 5 :, ~, 500 g of the spherical red phosphorus was ~ suspended in 1,000 ml of water and then 15 g of phenol ?' ~ and 27 g of 37~ formalin was added. After heating this suspension to 80 C, 10 g of 85% phosphoric acid was ~j~ 25 added while stirring, and heated at this temperature for `s a period of one hour under stirring. ~hen the s:~
suspension was cooled in the air, filtered and washed --wi~h water. The filtered product was dried at 140 C
I over a period of three hours. The coated red !': ~ 30 phosphorus thus obtained was 523 g.
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i Example 6 500 g of the spherical red phosphorus was suspended in 750 ml of water and 10 g of urea and 20 g of 37% formalin wexe added to the suspension. The suspenslon was heated to 90 C under agitation and, after adding 10 g of 85% phosphoric acid, heated at this kemperatllre for a period of two hours under stirring. A~ter allowing t:he suspension to stand over a whole day and night, the suspension was Eiltered, washed with water and dried at 140 C for three hours.
The coatad red phosphorus thus obtained was 514 g.
; , Example 7 ., A viscous initlal condensate which was obtained by reacting a mixture consisting of 27 g of furfuryl alcohol, 3 ml of water and 0.5 g of 85~ phosphoric acid on a boiled water bath for ~ive hours and 10 g of 37%
formalin were added to a suspension conslsting o~ 500 g of the spherical red phsphorus and 800 ml of water under strong agitation and then was heated to 90 ~C.
After heating at the same temperature for one hour under stirring, the suspension was filtered, washed with water and dried at 130 ~C for a period of three ~ hours. The coated red phosphorus thus obtained was 525 .~ g., ,:
Example 8 6 g of melamine, 28 g of 37% formalin and 10 g of sodium carbonate were added to a suspension consisting of 500 g of the spherical red phosphorus, 50 g of ,~:

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magneslum hydroxide and 750 ml of water and then allowed to react at 90 C for two hours under stirring.
After the resulting mixture was cooled ln the air over a whole day and night~ it was filtered, washed with water and dried at 135 C over a period of khree houxs~
The coated red phosphoruc3 thus obtained was 555 g.
j Example 9 4.3 g of 98% glycerine, 2.5 g of phthalic anhydride and 15 g of fatty acid o~ linseed oil wexe mixed and heated to a temperature of 200 to 230 C
while passing carbonic acid gas. To the resulting mixture was added 3.3 g of phthalic anhydride and then the mixture was heated to 245 C. When the acid value ,:
of the mixture became 12 to 15, the mixture was cooled, -~ 15 then 2 ml of emulsifying dispersant (e.g., nonionic ;::
surfactant)was added, and the resulting mixture was dispersed in 100 ml of water. The resulting emulsion was mixed with a suspension consisting of 750 ml of water, 500 g of the spherical red phosphorus and 50 g of aluminum hydroxide and then stirred at 90 C for one hour. The resulting mixture was cooled, filtered, washed with water and dried at 140 C for four hours.
The coated red phosphorus thus obtained was 573 g.
":
Example 10 '. ' 250 g of the spherical red phosphorus was suspended in 500 ml of water, then 40 ml of a 8~
aqueous solution of aluminum sulfate was added to the suspenslon and stirred thoroughly. Thereafter, 18 ml of a ~ a~ueous solution of sodium hydroxide was added ~ 3~ dropwise to tbe suspension and the suspension was ':' '~
A~

~. ?~351~9 heated to 50 C and held at this temperature ~or 10 minutes. To the suspension, 8 g of phenol and 15 g of 37% formaline were added and the suspension was heated at 80 C for one hour under agitation. The suspension was cooled in the air, flltered, washed with water and dried at 140 C for three hours. The yield of the coated red phosphorus was 270 g.

Example 11 40 ml of a 8% aqueous solution of aluminum sulfate was added to a suspenslon con~isting of 250 g of the spherical red phosphorus and 500 ml of water and stirred. 45 ml of a 15% aqueous solution of ammonium bicarbonate was added dropwise to the suspension and then the suspension was allowed to stand at 50 C for 20 minutes. After adjusting the pH of the suspension to 10.0 with an aqueous ammonia, 100 g of 12.5~ of a resol type phenol resin prepolymer (phenol/~ormaldehyde molar ratio: 1/2) previously prepared and 25 g o~
ammo~ium chloride were added to the suspension and stirred at 50 C for 30 minutes. The resulting suspenslon was cooled ln the air, filtered, washed with ;~ water and dried at 120 C for one hour. The yield of the resulting coated red phosphorus was 264 g.
.
~ Example 12 , .
80 ml of a 8% aqueous solution of zinc sulfate was added to a suspension consisting of 500 g of the spherical red phosphorus and 900 ml of water and st~rred. Further~ 100 ml of a 15% aqueous solution of ammonium b~carbonate was added dropwise and heated at 60 C for 20 m~nutes. A reactlon mixture of acetone-': ~

' .
formaldehyde initial cordensate prepared ~rom khe reaction between 26 g of acetone and 42 g o~ 37% formalin was added the suspension and heated at 65 DC ~or 30 minutes under stirring. The resulting suspension was cooled in the air, filtered, washed with water and then dried at 130 C for one hour. The coated red phosphorus obtained was 572 g.

Example 13 65 ml o~ a 10% aluminum Rul~ate aqueous solution was added to a su~pension consisting o~ 500 g o~ the spheriaal red phosphorus and 750 ml o~ water and stirred. Then, 100 ml of a 15% aqueous solution of ammonlum bicarbonate was added dropwi~e to the suspension and heated at 60 C for 20 minutes. Then, a ; 15 suspension consisting of 30 g of titanium hydroxide and 30 ml of water, 6 g of melamine and 28 g of 37%
formalin were added to the suspension and ~he pH value of the resulting suspension was adjusted to 7.5 with an aqueous ammonia. After stirring the suspens~on such adjusted at 90 C for two hours and leaving over a whole day and night in the air, the suspension was filtered, washed with water and dried at 135 ~C for three houxs. The coated red phosphorus thus obtained was 518 g.
, In order to examine the chemical properties of the uncoated pherical red phosphorus (Example 1) and the coated spherical red phosphorus ~Examples 2 to 13), their ignitlon points, the amounts of evolved phosphine and the eluted P2~5 were measured and the results are given in ~able 1. For the purpose for comparison, the `~ followlng comparative flame retardants (Comparatlve -' , ~

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.' Examples 1 to 7) were examined in the same manner as ' set forth above.
'' Comparative Example 1: Red phosphorus commercially . available ~bulk density: 1.12 g/cm3) Comparative Example 2, 3, 4, 5, 6 and 7:
, Coated pulveriz~d red phosphorus obtained by .; I treating the pu:~verized one (Comparative Example 1) in the same way as in Examples 2, 5, 6l 10, 11 and 12, respectively.

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, 27-:, ' Table 1 , Red Phosphorus ~gnition Evolution of Elution of Point(C) PhoSphine (ppm) P2s (mg) ;~ Example No.
1 3450.1 31.5 :~ .
2 3480.0 5.3 ~ 3 3500.0 4.7 ;~ 4 3490.0 6.5 3550.0 5.6 6 3530.0 6.~
` 7 3500.0 5.8 -l ~ 8 3510.0 7.3 9 3520.0 7.9 3570.0 3.7 ;~ 11 3580.0 3.1 12 3550.0 2.8 if ~ 13 3520.0 4.2 '.'~.~-~.
Comparative Example No.
'~ 1 291225~3 213.1 3,'., ~ 2 29576.3 121.2 g'~ 3 3291.4 67.5 j ~ 4 3271.~ 66.~
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6 3350.3 4~.7 7 3310.2 40.8 ~- Measurement Method Bulk density:
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, 10 g of each sample was taken in a bulkdensitometer (Volume: 20 ml) and, after shaking 100 times, bulk densily was measured.

Ignition Point:
1 g of ~ach sample was placed in a 10 ml porcelain crucible, then put in an electric furnace and heated at a heating rate of 1 C/min to measure ~ Ignition point.
',I~'j Evolution of phosphine:
20 g of each sample was suspended in 40 ml of water contained in a 500 ml flask and was fully shaken.
Then, the sealed sample was allowed to stand for 24 hours and the amount o~ phosphine evolved in a space above the suspension was measured.

Elution of P2O5:
5 g of each sample was suspended in 100 ml o~
.~ water, was allowed to stand for 100 hours at 121 C at 2 atm. and filtered. The P2O5 content in the filtrate was measured.

In order to show the advantageous effect.s of the nonflammable epoxy resin compositions of the present invention, the various compositions (Examples 14 to 26) containing the spherical red phosphorus (Example 1) or .:
the spherical red phosphorus coated in Examples 2 to 13 were thoroughly mixed, hardened by heating at 60 C for four hours~and then at 105 ~C for se~en hours. The hardened compositions were tested for their~flame resistance,~moisture resistance, aorrosion resistance and electrlcal properties and were compared with comparatlve nonflammable epoxy resin compositions ." .
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~ ~51~)4 (comparative Examples No. 8 to 11) contalning the s pulverized red phosphorus flame retardants. The flame retardants used in Comparative Examples No. 8, 9, 10 ,~ and 1I were coated by treating the pulverized red - 5 phosphorus (Comparative Example 1) in the same ways as described in Example Nos. 2, 5, 7 and 11, respectively.
able 2 shows the composi.tions of the present invention and the comparative example~ and 'rable 3 shows the test re~ults.

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Flame R sistance V-0 V-0 V-0 V-0 Moisture Resistance 8.11 4.82 4.88 3.24 ' (Water Absorption) %

Corrosion Resiskance 62 32 40 26 . . .
, . . .
`~ Dielectric Constant at 10 KH2 Before Corrosion Test 4.08 4.02 4.01 3.97 After Corrosion Test 6~02 5.40 5.64 4.70 ! ~ Dielectric Dissipation Factor at 10 KHz at 25 C
Before Corrosion Test 0.68 0.67 0.68 0.63 After Corrosion Test 9.21 _ 8.82 8~35 7.72 :.
;~ Testing Method ,. ~
Flame Resistance:
Measured in accordance to the testing method B for flame resistance specified in JIS K-6911 , ~ 5 Moisture Resistance (Water Absorption)~
In accordance to testing method of boiling water absorption speci~ied in JIS K-6911. (Measurement conditions: 121:C, 2 atm, 100 ~ RH and 100 hours) ''' ;' ' : ~ .
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Each resln composition in a given amount was applied onto a copper plate having a specified surface area, hardened, and then allowed to stand ln the air at 140 C, ~0% RH ~or 200 hours to form a resin layer. After peeling the resln layer ~rom the copper plate, a transparent section paper of 1 m~ square was placecl onto the copper plate and the number o 1 mm ~quare which changed in aolor wa~
counted in the area of 1 am~ (1 mm2 x 100) i Dielectxlc constant and dialectric dissipation factor:
Measured in acaordance to Measuring methods for dielectric constant and dielectric dissipation ~actor ~pecified JIS K-6911.
, .
lS It is clear from the test results that the ~ compositions containing the spherical red phosphorus -~ flame retardant according to the present ~nvention are ~ far superior in all of the te~ted items to the '~ comparative composition~ and the composition~ of the 2a present invention are hardly affected by the addition of the flame retardant. Therefore, when the ;~ nonflammable compositions of the present invention are ; employed in electronic parts, use~ul life and ~eliabllity can be conslderably improved.

2B Examples 27 - 3~

Nylon 60 polybutylene terephthalate, polyphenylene oxide~ polycarbonate, polystyrene, polyphenylene oxlde-polystyrene copolymer and thermopla~tic polyurethane resin were each molten in a ~; ~ 30 mixing extruder and then khe flame retardants of the . -...,, ''',: ~ , ' ' - ' ~ . .

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351.0'~a ; _3~¢sS_ spherical red phosphorus obtained in Examples 1, 2, 4, 5, 6 ands 10 were added to each resin melt. In ~xample 35, 5 parts by welght of glass ~iber was used as a filler. Test samples were made by extruding the resulting mixtures through a nozzle. Table 4 shows the compositions o~ the test samples thus obtained.
Comparakive Examples 12 t:o 20 ,, .
For the purpose of comparison, comparative test sample~
were prepared in the same manner described ln Examples 27 - 35 except that the uncoated or coated pulverized red phosphorus obtained in Comparative Examples 1 - 4 were employed as a ~lame retardant. The compositions of the samples are shown in parts by weight in Table 4.
., Table 4 Thermoplastic Resin Composition (parts by weight) ~ Example_No. Resin Red P_osphorus i3~ ~; 27 Polyamide (Nylon 6) : 90 Example 1: 10 ~¢~ 28 Polyamade (Nylon 6) : 90 Example 2: 10 $,~` 29 Polybutylene Example 4: 15 ~ terephthalate : 85 .3 30 Polyphenylene oxide: 95 Example 2: 5 ¢ ~ 31 Polycarbonate : 90 ~xample S: 10 32 Polystyrene : 80 Example 6: 20 33 Polyphenylene oxide: 65 Example 10: 10 , ~ Poly~tyrene : 25 34 Pol~urethane 85 Exam~le 2- 15 ? . ~ ' ~
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Table 4 ~continued) Thermoplastic Resin Composition (parts by weight) .. , .... ~ _ . _ ExamE~e No Resin ~ _ _ ~ Red Ph_~phorus Polybutylene Example 2: 10 terephthalate : 85 Comparative Example No.
12 Polyamide (Nylon 6): 90 Comparative Example 1: 10 13 Pol~amide (Nylon 6): 90 Comparative Example 2: 10 14 Polybutylene Comparative ~ terephthalate : 85 Example 3: 15 :~ 15 Polyphenylene oxide: 95 Comparative . Example 2: 5 16 Polycarbonate : 90 Comparative Example 3: 10 17 Polystyrene : 25 Comparative Example 4: 20 18 Polyphenylene oxide: 65 Comparatlve ~: Polystyrene : 25 Example 3: 10 19 Polyurethane : 85 Comparative Example 2: 15 Polybutylene Comparative ~ terephthalate o 85 Example 2: 10 .~
The samples obtained above were te~ted for the properties given in Table 5 and the test re~ults have proved that the re~inous compositions which were rendered nonflammable by the spherical red phosphorus ,. ~

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of the present invention are far superior to those using the conventional pulverized red phosphorus and are hardly affected by the addition of the spherical red phosphorus. From such results, the nonflammable composition of thermoplastic resin accordlng to the present invention are almost free ~rom the disadvantages associated with the conventional red phosphorus flame retardant while maintalning the aclvantages of the conventiorlal red,phosphorus and are very useful. Therefore, the nonflammable resinous composltion o~ the present invention can be extensively used in a varlety o~ applications, such as various molded articles, films and sheets.

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The test results were all obtained in accordance with ASTM. More specifically, burning resistance was measured in accordance with UL-94 Vertical Burning Test and tensile strength, dielectric strength and bending strength were measured in accordance with 638, 149 and 790, respectively, in which "measurement values after molding" are the values measured immediately after moldlng and "percentages of reduction" are the percentage o~ reduction resulted by leaving each samples at 121 C, 2 atm and 100~ RH ~or 100 hours to the values measured after moldlng~ The moisture resistance was calculated as ~ollows:
(Percentage of the weight of each test sample which has increased by leaving at 121 C, 2 atm and 100% RN to the weight before leaving) - (Percentage of the increase in weight measured under the same conditions for a reference sample having the same composition a~
each test sample except that a flame retardant is not contained.) ,. , ' ' ' , .

Claims

1. A flame retardant comprising spherical particles consisting of red phosphorus and aggregates of said spherical particles, said particles having been directly produced as red phosphorus powder in the form of spherical particles free of pulverized surfaces by conversion of yellow phosphorus, without a pulverizing treatment, said flame retardant having an ignition temperature of at least 345°C.

2. A flame retardant as claimed in claim 1 in which said spherical particles of red phosphorus are produced by heating yellow phosphorus at a temperature of 250°C to 600°C
in a reactor filled with an inert gas to cause the conversion of said yellow phosphorus to said spherical particles of red phosphorus in a conversion of 70% or less.

3. A flame retardant as claimed in claim 1 in which said spherical particles are in the form of powder having a particle size of 200 µm or less.

4. A flame retardant as claimed in claim 1 in which said spherical particles are coated with thermosetting resin.

5. A flame retardant as claimed in claim 1 in which said spherical particles are coated with aluminum hydroxide and/or zinc hydroxide.

6. A flame retardant as claimed in claim 1 in which said spherical particles are firstly coated with aluminum hydroxide and/or zinc hydroxide and further coated with thermosetting resin.

7. A flame retardant as claimed in claim 4 in which said thermosetting resin is coated in the presence of at least one compound selected from the group consisting of aluminum hydroxide, magnesium hydroxide and titanium hydroxide.

8. A flame retardant as claimed in claim 6 in which said thermosetting resin is coated in the presence of at least one compound selected from the group consisting of aluminum hydroxide, magnesium hydroxide and titanium hydroxide.

9. A flame retardant comprising: spherical particles consisting of red phosphorus and agglomerates of said spherical particles, said spherical particles having particle sizes of not greater than 200 µm and having continuous external surfaces which are substantially free of ridges and active sites formed by pulverizing which would be capable of adsorbing moisture and oxygen whereby the surfaces of said particles are stable and adsorption of oxygen and moisture and disproportionation do not occur on said surfaces.

10. A flame retardant as claimed in claim 9 in which said spherical particles of red phosphorus have been prepared by heating yellow phosphorus to a temperature in the range of 250°C to 600°C in a reactor filled with inert gas until not more than about 70 wt. % of said yellow phosphorus has been converted to spherical particles of red phosphorus having a size of not greater than 200 µm, then removing unconverted yellow phosphorus from said spherical particles, the spherical particles having been prepared without subjecting them to a size reduction step after the heating step.

11. A flame retardant as claimed in claim 9 in which said spherical particles are coated with thermosetting resin.

12. A flame retardant as claimed in claim 9 in which said spherical particles are coated with aluminum hydroxide and/or zinc hydroxide.

13. A flame retardant as claimed in claim 9 in which said spherical particles are firstly coated with aluminum hydroxide and/or zinc hydroxide and further coated with thermosetting resin.

14. A flame retardant as claimed in claim 11 in which said thermosetting resin is coated in the presence of at least one compound selected from the group consisting of aluminum hydroxide, magnesium hydroxide and titanium hydroxide.

15. A flame retardant as claimed in claim 13 in which said thermosetting resin is coated in the presence of at least one compound selected from the group consisting of aluminum hydroxide, magnesium hydroxide and titanium hydroxide.

16. A flame retardant as claimed in claim 1 in which said spherical particles of red phosphorus have been prepared by heating yellow phosphorus to a temperature in the range of 250°C to 600°C in a reactor filled with inert gas until not more than about 70 wt. % of said yellow phosphorus has been converted to spherical particles of red phosphorus having a size of not greater than 200 µm, then removing unconverted yellow phosphorus from said spherical particles, the spherical particles having been prepared without subjecting them to a size reduction step after the heating step.

17. A nonflammable resinous composition comprising a mixture of synthetic resin and a flame retardant comprised of spherical particles consisting of red phosphorus and aggregates of said spherical particles, said particles having been directly produced as red phosphorus powder in the form of spherical particles free of pulverized surfaces by conversion of yellow phosphorus, with-out a pulverizing treatment, said flame retardant having an ignition temperature of at least 345°C.

18. A nonflammable resinous composition as claimed in Claim 17 in which said spherical particles of red phosphorus are pro-duced by heating yellow phosphorus at a temperature of 250 to 600°C in a reactor filled with an inert gas to cause the conver-sion of said yellow phosphorus to said spherical particles of red phosphorus in a conversion of 70% or less.

19. A nonflammable resinous composition as claimed in Claim 17 in which said spherical particles of red phosphorus are in the form of powder having a particle size of 200 µm or less.

20. A nonflammable resinous composition as claimed in Claim 17 in which said spherical particles of red phosphorus are coated with thermosetting resin.

21. A nonflammable resinous composition as claimed in Claim 17 in which said spherical particles of red phosphorus are coated with aluminum hydroxide and/or zinc hydroxide.

22. A nonflammable resinous composition as claimed in Claim 17 in which said spherical particles of red phosphorus are firstly coated with aluminum hydroxide and/or zinc hydroxide and further coated with thermosetting resin.

23. A nonflammable resinous composition as claimed in Claim 20 in which said thermosetting resin is coated in the presence of at least one compound selected from the group consisting of aluminum hydroxide, magnesium hydroxide and titanium hydroxide.

24. A nonflammable resinous composition as claimed in Claim 22 in which said thermosetting resin is coated in the presence of at least one compound selected from the group consisting of aluminum hydroxide, magnesium hydroxide and titanium hydroxide.

25. A nonflammable resinous composition as claimed in Claim 17 in which said composition comprises 100 parts by weight of epoxy resin; 5 to 40 parts by weight of said flame retardant; 5 to 150 parts by weight of aluminum hydroxide; and harder and hardening promotor in amounts sufficient for hardening.

26. A nonflammable resinous composition as claimed in Claim 17 in which said synthetic resin is at least one thermoplastic resin selected from the group consisting of polyamide, polyester, polyether, polycarbonate, polystyrene, polyurethane and poly-acrylate and said flame retardant is contained in an amount in the range of from 0.1 to 30 parts by weight per 100 parts by weight of said thermoplastic resin.

27. A nonflammable resinous composition comprising a mixture of synthetic resin and a flame retardant comprising spherical particles consisting of red phosphorus and agglomerates of said spherical particles, said spherical particles having particle sizes of not greater than 200 µm and having continuous external surfaces which are substantially free of ridges and active sites formed by pulverizing which would be capable of adsorbing mois-ture and oxygen whereby the surfaces of said particles are stable and adsorption of oxygen and moisture and disproportionation do not occur on said surfaces.

28. A nonflammable resinous composition as claimed in Claim 27 in which said spherical particles of red phosphorus are pro-duced by heating yellow phosphorus at a temperature of 250 to 600°C in a reactor filled with an inert gas to cause the conver-sion of said yellow phosphorus to said spherical particles of red phosphorus in a conversion of 70% or less.

29. A nonflammable resinous composition as claimed in Claim 27 in which said spherical particles of red phosphorus are coated with thermosetting resin.

30. A nonflammable resinous composition as claimed in Claim 27 in which said spherical particles of red phosphorus are coated with aluminum hydroxide and/or zinc hydroxide.

31. A nonflammable resinous composition as claimed in Claim 27 in which said spherical particles of red phosphorus are firstly coated with aluminum hydroxide and/or zinc hydroxide and further coated with thermosetting resin.

32. A nonflammable resinous composition as claimed in Claim 27 in which said thermosetting resin is coated in the presence of at least one compound selected from the group consisting of aluminum hydroxide, magnesium hydroxide and titanium hydroxide.

33. A nonflammable resinous composition as claimed in Claim 31 in which said thermosetting resin is coated in the presence of at least one compound selected from the group consisting of aluminum hydroxide, magnesium hydroxide and titanium hydroxide.

34. A nonflammable resinous composition as claimed in Claim 28 in which said composition comprises 100 parts by weight of epoxy resin; 5 to 40 parts by weight of said flame retardant; 5 to 150 parts by weight of aluminum hydroxide; and harder and hardening promotor in amounts sufficient for hardening.

35. A nonflammable resinous composition as claimed in Claim 28 in which said synthetic resin is at least one thermoplastic resin selected from the group consisting of polyamide, polyester, polyether, polycarbonate, polystyrene, polyurethane and poly-acrylate, and said flame retardant is contained in an amount in the range of 0.1 to 30 parts by weight per 100 parts by weight of said thermoplastic resin.