PROCESS FOR THE PREPARATION OF CONDENSED PHOSPHORIC ESTERS

Abstract: A condensed phosphoric ester having a very low content of isopropenyl phenyl diphenyl phosphate, which reduces heat resistance and causes the contamination of molds during the molding when the condensed phosphoric ester is used as an additive for a resin, is provided by a process including a first step of reacting a phosphorus oxytrihalide with a bisphenol A derivative at a specific ratio to prepare a phosphorohalidate; a second step of removing unreacted phosphorus oxytrihalide; a third step of reacting the reaction product obtained in the second step with a monophenol-based compound at a temperature equal to or lower than 120°C; and a fourth step of reacting the phosphorohalidate with the monophenol-based compound at a temperature equal to or higher than 120°C.

Description: TECHNICAL FIELD The present invention relates to a process for preparing a condensed phosphoric ester. More specifically, the present invention relates to a process for preparing a condensed phosphoric ester having a low content of volatile components, which is excellent as a flame retardant for resins. BACKGROUND ART Conventionally, various types of flame retardants are used for flame retardation of inflammable plastic materials, for example, halogen compounds such as decabromobiphenylether and tetrabromobisphenol A, and low molecular weight phosphorus compounds such as cresyl diphenyl phosphate and triphenyl phosphate. Today, resin compositions are required to be non-halogenic from an environmental point of view, for example, due to the hazardous effects of dioxin. Flame retardants containing heavy metals cause problems due to their toxicity. Under these circumstances, phosphorus-based flame retardants have now become a target of attention. Among the phosphorus-based flame retardants, aromatic phosphoric ester-based flame retardants are a target of attention for their effectiveness especially in the applications of engineering plastics such as PC/ABS alloys and modified PPE since they have little adverse influence on the environment as well as superb physical properties. Actually, the industrial demand for phosphorus-based flame retardants, especially aromatic phosphoric ester-based flame retardants, is good and continues to increase at a high rate. However, engineering plastics are molded at a very high temperature and therefore the following problems have occurred. When a low molecular weight monomer-type phosphoric ester such as triphenyl phosphate (TPP) or tricresyl phosphate (TCP) is used, the monomer-type phosphoric ester is thermally decomposed, bleeds out or volatizes during the molding process, which causes defective molding, contamination of the molds or the like. It is known that use of a high molecular weight condensed phosphoric ester as a flame retardant is effective for avoiding these problems. WO97/47631 discloses a process for preparing an aryldiphosphate ester by initially reacting aphosphoryl oxyhalide with a dihydric aromatic compound in the presence of an insoluble catalyst to form an intermediate. The intermediate is then reacted with a monohydric aromatic compound in the presence of an insoluble catalyst to form the aryldiphosphate ester, after which the catalyst is filtered from the product. In a first Example, bisphenol A tetrachlorodiphosphate is formed as an intermediate by reacting 4,4'-isopropylidenediphenol with 3.6 mol times the amount of phosphorus oxychloride in the presence of calcium chloride as catalyst. The intermediate is reacted with phenol also in the presence of calcium chloride at 180°C, after which the temperature is raised to 240°C and additional phenol was added. The product was a viscous light yellow liquid containing bisphenol A tetraphenyl diphosphate (81%) and triphenyl phosphate (3.6%). In the second and third examples, the contents of triphenyl phosphate in the product were 7% and 4%. Japanese Laid-Open Publication No. 63-227632 discloses a process for preparing a condensed phosphoric ester. According to this process, a condensed phosphoric ester is prepared by reacting a dihydroxy compound such as resorcin, hydroquinone, bisphenol A or the like with phosphorus oxychloride, thereafter removing unreacted phosphorus oxychloride, and then reacting the resultant product with phenol, cresol, xylenol or the like. This process can reduce, to some extent, monomer-type phosphoric ester which is generated by the reaction between phosphorus oxychloride and a monophenol-based compound contained in the condensed phosphoric ester. However, this process has the following problem. In the case where a condensed phosphoric ester is produced using a bisphenol A derivative as a starting material, especially on an industrial scale, the bisphenol A derivative is decomposed during the reaction and thus an isopropenyl aryl group-containing phosphate (hereinafter, referred also to as an "IPP") such as, for example, isopropenyl phenyl diphenyl phosphate is likely to be produced. This is likely to result in reduction in heat resistance, coloring-related problems of products, and reduction in moldability caused by the contamination of molds. The process described in Japanese Laid-Open Publication No. 63-227632 also has the problem that a significant amount, specifically about 4 to 7% by weight of monomer-type phosphoric ester is contained as an impurity, especially when the production is performed on an industrial scale. Therefore, the monomer-type phosphoric ester still volatizes or bleeds out, which causes defective molding, the contamination of the molds or the like. As such, it is difficult to obtain a satisfactory molding efficiency. Accordingly, production of a condensed phosphoric ester, especially on an industrial scale, requires that many conditions including the ratio of materials, reaction temperature, and reaction time should be carefully selected in order to reduce the content of the IPP and the monomer-type phosphoric ester as impurities. Until today, details of such conditions have not been studied, and thus the relationship between the conditions and the amount of impurity in the resultant product has not been clarified at all. Especially regarding the ratio of materials, the use of ratios that are obtained by theoretical calculations based on stoichiometry or slightly greater ratios has been considered to be the most efficient way to reduce the impurity. Therefore, the ratios obtained by stoichiometric calculations have been loyally adopted. For the reaction temperature, a relatively high temperature has been adopted for the purpose of raising the reaction speed. (Problems to be Solved by the Invention) An objective of the present invention is to solve the above-described problems by providing a process for preparing a condensed phosphoric ester formed from a bisphenol A derivative as a starting material, having a low content of IPP and monomer-type phosphoric ester as impurities. Another objective of the present invention is to enhance the quality of resin-molded products by using the condensed phosphoric ester produced by a process according to the present invention as a flame retardant, so as to make a contribution to the society. DISCLOSURE OF THE INVENTION (Means for Solving the Problems) As a result of active studies, the present inventors found that the above-described problems can be solved by a process for preparing a condensed phosphoric ester, including a first step of reacting a bisphenol A derivative with a phosphorus oxytrihalide in an amount equal to or greater than 4.5 mol times the amount of the bisphenol A derivative to prepare a phosphorohalidate; a second step of removing unreacted phosphorus oxytrihalide; a third step of reacting the reaction product obtained in the second step with a monophenol-based compound at a temperature equal to or lower than 120°C; and a fourth step of reacting the phosphorohalidate with the monophenol-based compound at a temperature equal to or higher than 120°C. Thus, the present inventors completed the present invention. The present invention provides the following processes. 1. A process for preparing a condensed phosphoric ester, comprising: a first step of reacting a bisphenol A derivative with a phosphorus oxytrihalide in an amount equal to or greater than 4.5 mol times the amount of the bisphenol A derivative to prepare a phosphorohalidate; a second step of removing unreacted phosphorus oxytrihalide after the first step; a third step of reacting the reaction product obtained in the second step with a monophenol-based compound at a temperature equal to or lower than 120°C; and a fourth step of reacting the phosphorohalidate with the monophenol-based compound at a temperature equal to or higher than 120°C. 2. A process according to above-described item 1, wherein the total amount of the monophenol-based compound used in the third step and the fourth step is greater, by equal to or less than 2 mol%, than the theoretically necessary amount for turning the entire amount of the phosphorohalidate into the condensed phosphoric ester. 3. A process according to above-described item 1 or 2, wherein the condensed phosphoric ester is 2,2-bis{4-[bis(phenoxy)phosphoryl]oxyphenyl}propane. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be specifically described. (First step) In the first step, a phosphorus oxytrihalide and a bisphenol A derivative are reacted, thereby preparing a phosphorohalidate. Examples of the phosphorus oxytrihalide include phosphorus oxychloride and phosphorus oxybromide. The bisphenol A derivative refers to bisphenol A or a derivative thereof, which is represented by the following formula (A): (where R 5 and R 6 are the same as or different from each other and represent an alkyl group containing 1 to 3 carbon atoms; and n1 and n2 each represent an integer from 0 to 4). In the present invention, a phosphorohalidate refers to a compound represented by the following formula (I): (where X represents a halogen atom; n represents an integer from 1 to 10; and R 5 , R 6 , n1 and n2 each refer to the same as above.) According to conventional, general technical knowledge, it is considered to be non-preferable that the amount of the phosphorus oxytrihalide is greater than a stoichiometrical reaction amount which is calculated from the amount of the bisphenol-based compound, i.e., 2 mol times the amount of the bisphenol-based compound. The reason is that the amount of remaining unreacted phosphorus oxytrihalide necessarily increases, which complicates the operation for recovering the unreacted phosphorus oxytrihalide. According to the present invention, however, the amount of the phosphorus oxytrihalide is equal to or greater than 4.5 mol times, more preferably equal to or greater than 5 mol times, and still more preferably equal to or greater than 5.4 mol times the amount of the bisphenol A derivative. By using such excessive amounts of phosphorus oxytrihalide, an unexpected advantage that the decomposition of the bisphenol A derivative is suppressed is obtained, which is quite surprising. Here, "mol times" refers to the ratio based on the mol value. When the relative amount of the phosphorus oxytrihalide to the amount of bisphenol A derivative is insufficient, the amount of the IPP, which is produced by decomposition of the bisphenol A derivative by a hydrogen halide produced as a by-product of the reaction of the phosphorus oxytrihalide and the bisphenol A derivative, increases. The upper limit of the amount of the phosphorus oxytrihalide cannot be determined. When the amount of the phosphorus oxytrihalide is excessive, an unnecessarily large amount of phosphorus oxytrihalide needs to be removed in the second step described below, and decreases the operation efficiency in the reactor and also the productivity. The phosphorus oxytrihalide is usually used in an amount equal to or less than 8 mol times, and more preferably equal to or less than 6 mol times the amount of the bisphenol-based compound. Still more preferably, the amount of the phosphorus oxytrihalide and the bisphenol A derivative are adjusted within the above-mentioned ranges so that the concentration of the hydrogen halide in the reaction solution is equal to or less than 5%. According to the present invention, a catalyst can be used. Usable catalysts include, for example, Lewis acid-based catalysts such as aluminum chloride, magnesium chloride and titanium tetrachloride. The other conditions, for example, the reaction temperature, reaction time and reduction in pressure can be appropriately selected in accordance with the type of the intended condensed phosphoric ester, condensation degree, and type and scale of the apparatus used. The temperature is preferably 80 to 130°C, and more preferably 80 to 120°C. It is acceptable to start with a temperature lower than 80°C and then raise the temperature to 80 to 130°C. For example, it is acceptable to start with room temperature and then raise the temperature to 80 to 130°C. The reaction time is preferably 3 to 20 hours. Hydrogen halide gas generated by the reaction is preferably captured by water. An organic solvent can be used when necessary although it is not usually necessary. For example, aromatic group-based organic solvents including toluene, xylene, and dichlorobenzene and aliphatic group-based organic solvents including hexane and heptane are usable. When it is necessary to prevent the resultant product from being colored, a phosphorus-based compound such as, for example, triphenyl phosphite or tri(2,6-di-t-butyl) phosphite; a hindered phenol-based compound such as, for example, 2,6-di-t-butyl-p-cresol (BHT) or 2-methyl-6-t-butyl-p-cresol; or the like can be added as a coloring prevention agent. In the first step, a small amount of IPP is usually produced as a by-product. After the first step, operations only for removing the residual IPP, for example, purification by chromatography, can be performed. However, the process according to the present invention allows the second step to be performed without conducting any specific operation only for removing the IPP. (Second step) In the second step, the phosphorus oxytrihalide remaining unreacted after the first step is removed. The removal of the phosphorus oxytrihalide can be performed using any known method. The removal of the unreacted phosphorus oxytrihalide is usually performed at normal pressure or under reduced pressure. Performing the third step described below in the state where the phosphorus oxytrihalide is not sufficiently removed, i.e., in the state where phosphorus oxytrihalide remains, causes generation of a monomer-type phosphoric ester. Therefore, it is preferable to remove and recover the maximum possible amount of the phosphorus oxytrihalide. Preferable conditions for removing and recovering the phosphorus oxytrihalide are, for example, as follows. The pressure is reduced to equal to or less than 200 mmHg, more preferably equal to or less than 100 mmHg, and still more preferably equal to or less than 50 mmHg, by a vacuum pump. The recovery temperature is preferably 100 to 200°C, more preferably 100 to 170°C, and still more preferably 100 to 150°C. In the reaction product after the second step, usually, a part of the IPP produced as a by-product in the first step remains. After the first step, operations only for removing the residual IPP, for example, purification by chromatography can be performed. However, the process according to the present invention allows the second step to be performed without conducting any specific operation only for removing the IPP. (Third step) In the third step, a monophenol-based compound is acted on the product obtained after the second step, at a relatively low reaction temperature. In the present invention, the condensed phosphoric ester refers to a compound represented by the following formula (II): (where R 1 , R 2 , R 3 and R 4 represent an identical or different aryl group containing 6 to 15 carbon atoms; and R 5 , R 6 , n1, n2 and n represent the same as above.) Examples of the aryl group containing 6 to 15 carbon atoms include phenyl, (o-, m-, p-)methylphenyl, (o-, m-, p-)ethylphenyl, (o-, m-, p-)n-propylphenyl, (o-, m-, p-)isopropylphenyl, (o-, m-, p-)n-butylphenyl, (o-, m-, p-)sec-butylphenyl, (o-, m-, p-)tert-butylphenyl, (2,3-2.4-, 2,5-, 2,6-, 3,4-, 3,5-)dimethylphenyl, (2,3- 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)diethylphenyl, 2-methyl-3-ethylphenyl. 2-methyl-4-ethylphenyl, 2-methyl-5-ethylphenyl. 2-methyl-6-ethylphenyl, 3-methyl-4-ethylphenyl, 3-methyl-5-ethylphenyl, 2-ethyl-3-methylphenyl, 2-ethyl-4-methylphenyl, 2-ethyl-5-methylphenyl, 3-ethyl-4-methylphenyl, (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)di-n-propylphenyl, (2,3-, 2,4-, 2,5-, 2,6-, 3,4-,3,5-)diisopropylphenyl, (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)di-n-butylphenyl, (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)di-sec-butylphenyl, (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)di-tert-butylphenyl, (2,3,6-, 2,3,5-, 2,3.4-, 2,4,5-, 2,4,6-, 3,4,5-)trimethylphenyl, (2,3,6-, 2,3,5-, 2,3,4-, 2,4,5-, 2,4,6-, 3,4,5-)triethylphenyl, (2,3,6-, 2,3,5-, 2,3,4-, 2,4,5-, 2,4,6-, 3,4,5-)tripropylphenyl, and naphtyl. Here, "(o-, m-, p-)" indicates that substituents independently exist in either positions of o- (ortho), m-(meta) or p- (para) on a benzene ring. "(2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)" indicates that substituents independently exist in positions 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, or 3,5- on a benzene ring. "(2,3,6-, 2,3,5-, 2,3,4-, 2,4,5-, 2,4,6-, 3,4,5-)" indicates that substituents independently exist in positions 2,3,6-, 2,3,5-, 2,3,4-, 2,4,5-, 2,4,6-, or 3,4,5- on a benzene ring. Specific examples of the condensed phosphoric ester represented by formula (II) include 2,2-bis{4-[bis(phenoxy)phosphoryl]oxyphenyl}propane, 2,2-bis{4-[bis(methylphenoxy)phosphoryl]oxyphenyl}propane, 2,2-bis{4-[bis(dimethylphenoxy)phosphoryl]oxyphenyl}, and 2,2-bis{4-[bis(methylethylphenoxy) phosphoryl]oxyphenyl}propane which are made from a bisphenol A derivative. A monophenol-based compound refers to phenol or a substituted phenol containing one phenolic hydroxyl group. Examples of the monophenol-based compound include phenol, (o-, m-, p-)methylphenol, (o-, m-, p-)ethylphenol, (o-, m-, p-)n-propylphenol, (o-, m-, p-)isopropylphenol, (o-, m-, p-)n-butylphenol, (o-, m-, p-)sec-butylphenol, (o-, m-, p-)tert-butylphenol, methylphenol, (2,3- 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)dimethylphenol, (2,3- 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)diethylphenol, 2-methyl-3-ethylphenol, 2-methyl-4-ethylphenol, 2-methyl-5-ethylphenol, 2-methyl-6-ethylphenol, 3-methyl-4-ethylphenol, 3-methyl-5-ethylphenol, 2-ethyl-3-methylphenol, 2-ethyl-4-methylphenol, 2-ethyl-5-methylphenol, 3-ethyl-4-methylphenol, (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)di-n-propylphenol, (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)diisopropylphenol, (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)di-n-butylphenol, (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)di-sec-butylphenol, (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)di-tert-butylphenol. (2,3,6-, 2,3,5-, 2,3,4-,2,4,5-, 2,4,6-, 3,4,5-)trimethylphenol, (2,3,6-, 2,3,5-, 2,3,4-, 2,4,5-, 2,4,6-, 3,4,5-)triethylphenol, (2,3,6-, 2,3,5-, 2,3,4-, 2,4,5-, 2,4,6-, 3,4,5-)tripropylphenol, and naphtol. Phenol is especially preferable. One monophenol-based compound or a combination of two or more monophenol-based compounds can be used. In the present invention, a monomer-type phosphoric ester refers to a triester produced by the reaction of a phosphorus oxytrihalide and a monophenol-based compound. Specific examples of the monomer-type phosphoric ester include triphenyl phosphate when the monophenol-based compound is, for example, phenol; tricresyl phosphate [(o-, m-, p-)methylphenyl phosphate] when the monophenol-based compound is cresol [(o-, m-, p-)methylphenol]; and trixylyl phosphate [(2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)dimethylphenyl phosphate] when the monophenol-based compound is xylenol [(2,3-, 2,4, 2,5-, 2,6-, 3,4-, 3,5- )dimethylphenol] In the third step, the reaction temperature needs to be equal to or lower than 120°C, preferably equal to or lower than 110°C, more preferably equal to or lower than 105°C, and especially preferably equal to or lower than 100°C. By adopting such a relatively low temperature, a portion of the monophenol-based compound reacts with the IPP contained in the reaction mixture generated after the second step. As a result, the IPP is removed. When the reaction temperature is too high, the monophenol-based compound reacts with the phosphorohalidate with priority, and therefore the reaction of the monophenol-based compound and the IPP is unlikely to sufficiently proceed. Therefore, the amount of the IPP is unlikely to be sufficiently reduced. The lower limit of the reaction temperature is not specifically determined. Notably, a temperature at which the IPP and the monophenol-based compound can contact each other efficiently without a dehydrohalogenation reaction being caused is preferable. The lower limit of the reaction temperature is appropriately determined based on the combination of the type and amount of the monophenol-based compound, the speed at which the monophenol-based compound is added, the reaction scale, and other reaction conditions (e.g., reaction time, reduction in pressure, whether a solvent is used or not). The lower limit of the reaction temperature is preferably, for example, equal to or higher than 40°C, more preferably equal to or higher than 60°C, and still more preferably equal to or higher than 80°C. The time period for the third step is preferably 30 minutes to 8 hours, and more preferably 1 to 6 hours. (Fourth step) According to the present invention, the fourth step is performed for further reaction after the third step. The fourth step is performed at an elevated temperature equal to or higher than 120°C. The temperature for the fourth step is preferably 120 to 170°C and more preferably 140 to 160°C. The time for the fourth step is preferably 10 minutes to 5 hours, more preferably 30 minutes to 5 hours, still more preferably 30 minutes to 4 hours, and especially preferably 1 to 3 hours. Preferably, the reaction temperature in the third step is increased to the reaction temperature in the fourth step, over 30 minutes to 8 hours and more preferably 1 to 6 hours. The total amount of the materials used in the third step and the fourth step is preferably added before the third step is started. When necessary, a portion of the materials can be added during the third step, between the third step and the fourth step, or during the fourth step. The "amount of the reactive materials" used in the third step and the fourth step described in this specification refers to the total amount of the materials added before the completion of the fourth step. In a preferred embodiment, the amount of the monophenol-based compound is greater by an excess ratio of equal to or less than 2 mol% than the amount which is theoretically necessary for turning the entire amount of the phosphorohalidate contained in the reaction mixture after the second step into a condensed phosphoric ester. In this embodiment, the production of a monomer-type phosphoric ester as a by-product which is caused by interesterification of the condensed phosphoric ester produced and the monophenol-based compound can be suppressed without reducing yield or quality. Considering that interesterification of the condensed phosphoric ester and the monophenol-based compound is likely to occur especially in industrial, large scale production due to the long reaction time, the process of the present invention which can suppress the production of a monomer-type phosphoric ester as a by-product is very advantageous. Here, the term "industrial scale" indicates that the total amount of the monophenol-based compound and the phosphorohalidate which are reacted with each other is an amount used in usual industrial production. Specifically, industrial scale is preferably equal to or greater than 5 liters, more preferably equal to or greater than 30 liters, still more preferably equal to or greater than 100 liters, and especially preferably equal to or greater than 300 liters. The total amount of the monophenol-based compound and the phosphorohalidate which are reacted with each other is specifically preferably equal to or less than 20000 liters, and more preferably equal to or less than 10000 liters due to restrictions caused by, for example, the reaction apparatus. When the amount of the monophenol-based compound is smaller than the theoretical amount stoichiometrically calculated, unreacted phosphorohalidate will inevitably remain, which is likely to cause problems which complicate the purification and post-processing steps. When the amount of the monophenol-based compound is the theoretical amount stoichiometrically calculated, the reaction is likely to be incomplete. As a result, unreacted phosphorohalidate remains, which is likely to cause the problems of, for example, the phosphorohalidate remaining in the product as an impurity or complicating the purification and post-processing steps. An excess amount of the monophenol-based compound is not preferable since the amount of the monomer-type phosphoric ester produced as a by-product is increased. Therefore, the monophenol-based compound is preferably greater than the stoichiometrically theoretical amount by equal to or less than 2.0 mol%, more preferably equal to or less than 1.8 mol%, still more preferably equal to or less than 1.6 mol%, and especially preferably equal to or less than 1.5 mol%. The stoichiometrically theoretical amount necessary for turning the entire amount of the phosphorohalidate into a condensed phosphoric ester refers to the amount which is necessary for substituting all the halogen atoms contained in the phosphorohalidate with arylester groups. For example, in the case where n=1 in formula (I) above, such an amount of the monophenol-based compound is 4 mol with respect to 1 mol of the phosphorohalidate. In the case where n=2, such an amount of the monophenol-based compound is 5 mol with respect to 1 mol of the phosphorohalidate. In the case where n=3, such an amount of the monophenol-based compound is 6 mol with respect to 1 mol of the phosphorohalidate. Here, the excess ratio is a value obtained by subtracting the stoichiometrically theoretical mol value from the used mol value of the monophenol-based compound, dividing the resultant value by the stoichiometrically theoretical mol value to obtain a ratio, and then multiplying the ratio by 100 so as to be represented by a percentage. The lower limit of the amount of the monophenol-based compound cannot be exactly determined since it varies in accordance with, for example, the type of the condensed phosphoric ester and the reaction conditions. The lower limit is preferably equal to or greater than 0.2 mol%, more preferably equal to or greater than 0.3 mol%, especially preferably equal to or greater than 0.4 mol%, and still more preferably equal to or greater than 0.5 mol%. The other reaction conditions (e.g., the reduction in pressure and the time to add the monophenol-based compound) are appropriately selected as desired. The hydrogen halide generated during the reaction and remaining after the reaction is preferably recovered at normal pressure or low pressure. The hydrogen halide can be, for example, captured by water to be recovered. A condensed phosphoric ester prepared in this manner usually contains a great amount of impurities including partially reacted components, unreacted components, and remaining catalysts. Therefore, the impurities are removed from the crude condensed phosphoric ester by known purification methods such as neutralization, water rinsing, steam distillation or the like. When, for example, a method using an epoxy compound is adopted for purification, the epoxy compound is added to an -OH group of a partially reacted component and then selective hydrolysis is performed. Thus, the partially reacted product can be converted into phosphoric acid. By washing the phosphoric acid with hot water, the phosphoric acid components can be removed so as to reduce the acid value of the product. A product obtained in this manner is a high quality condensed phosphoric ester having a very low content of IPP and monomer-type phosphoric ester. Such a high quality condensed phosphoric ester can be used for various types of resins as a flame retardant. Specifically, the high quality condensed phosphoric ester can be used for, for example, the following resins: thermoplastic resins such as polyethylene-based resins, polypropylene-based resins, polybutadiene-based resins, polystyrene-based resins, polyphenylene ether-based resins, polycarbonate-based resins, ABS (acrylonitrile-butadiene-styrene)-based resins, high impact styrene-based resins, SAN (styrene-acrylonitrile)-based resins, polyamide-based resins, polyester-based resins, polyphenylene sulfide-based resins, polyacrylic resins, polymethacrylic resins, and the like; and thermosetting resins such as epoxy-based resins, polyurethane-based resins, polyimide-based resins, phenol-based resins, novolac-based resins, polyetherimide-based resins, melamine-based resins, urea-based resins and the like. A condensed phosphoric ester obtained by a process of the present invention can be especially advantageously used for a resin having a high molding temperature, for example, a resin moldable at a temperature of equal to or higher than 160°C in one embodiment, a resin moldable at a temperature of equal to or higher than 180°C in a more preferable embodiment, and a resin moldable at a temperature of equal to or higher than 200°C in an especially preferable embodiment. When a condensed phosphoric ester obtained by a process of the present invention is added to any of the above-listed resins as a flame retardant, a high quality molded product having excellent resistance against heat and resistance against coloring can be obtained without generating gas despite the high process temperature during the molding process of the resin using a molding apparatus. A condensed phosphoric ester obtained by a process of the present invention is added to a resin and molded. As result, any desired flame retardant molded product is provided. For adding the flame retardant to the resin and for molding the resin supplied with the flame retardant, any known method is usable. For example, the components (e.g., the resin, flame retardant, plasticizer, flame-retarding adjuvant, releasing agent, ultraviolet absorbing agent, anti-oxidant, light-shielding agent, weather resistance improving agent, and inorganic filler) can be melted and kneaded using a multi-purpose kneading apparatus such as a single-screw extruder, a twin-screw extruder, a Banbury mixer, a kneader, a mixer, a roll or the like and mixed with each other. Alternatively, a molding apparatus such as an extruding molding apparatus can be used to produce a plate-like, sheet-like, or film-like molded product. Thus, a desired molded product is obtained. (Examples) Hereinafter, preferable examples of the present invention will be described, but the present invention is not limited to these examples. In the examples, the content of the monomer-type phosphoric ester in each product was measured by high-performance liquid chromatography (device: LC10AD, column: SilicaODS-80TM, oven: CTO-10A, eluant: methanol:water = 8:2 (v/v), flow rate: 0.8 ml/min., detector: SPD10A, UV frequency of the detector: 254 nm). In the examples, "%" represents "% by weight" unless otherwise specified. (Example 1) An 8000 L reaction device including a stirrer, a thermometer, a dripper, a hydrochloric acid recovery device and a condenser (30°C) was filled with 6631 kgs (43.2 kmol) of phosphorus oxychloride, 1827 kgs (8 kmol) of bisphenol A and 18.4 kgs of magnesium chloride. These materials were heated to 105°C over 6 hours while being stirred, and then reacted for another 3 hours. Hydrochloric acid generated was recovered by the hydrochloric acid recovery device (amount recovered: 556 kgs). Then, treatment was performed at a temperature of 130°C and a pressure of 50 mmHg for 5 hours in a nitrogen atmosphere. As a result, unreacted phosphorus oxychloride (4195 kgs) was recovered. The concentration of chlorine in the resultant reaction mixture was 30.4%. 2994 kgs (excess ratio: 1%) of phenol was added to 3683 kgs of the resultant reaction mixture over 6 hours at 100°C and normal pressure, then the temperature was raised to 150°C over 4 hours, and the reaction was continued for another 1 hour for aging. Hydrochloric acid generated was recovered by the hydrochloric acid recovery device (amount recovered: 1125 kgs). Then, the hydrochloric acid remaining in the system was completely removed at 150°C and 10 mmHg over 1 hour. Thus, 5564 kgs of crude condensed phosphoric ester was obtained. The crude condensed phosphoric ester was diluted with toluene and then washed with an aqueous solution of diluted hydrochloric acid. Then, the organic phase containing the crude condensed phosphoric ester was treated with propylene oxide. After the resultant substance was repetitively rinsed with water, toluene was recovered by distillation under reduced pressure. Then, unreacted phenol was removed by steam distillation. As a result, 5385 kgs of condensed phosphoric ester (2,2-bis{4-[bis(phenoxy)phosphoryl]oxyphenyl}propane) was obtained. The content of the IPP in the resultant product was 0.035%, the content of the monomer-type phosphoric ester (TPP) in the resultant product was 1.6%, and the acid value ( KOH/mg ) thereof was 0.035. (Comparative example 1) A condensed phosphoric ester was prepared in a similar process to that of the example except that the amount of the phosphorus oxychloride was 4421 kgs (28.8 kmol), the amount of the phenol was 3083 kgs (excess ratio: 4%) and the phenol was added at 150°C. The content of the IPP in the resultant product was 2.5%, the content of the monomer-type phosphoric ester (TPP) in the resultant product was 4.5%, and the acid value (KOH/mg) thereof was 0.04. (Comparative example 2) A condensed phosphoric ester was prepared in a similar process to that of the example except that the phenol was added at 150°C. The content of the IPP in the resultant product was 1.3%, the content of the monomer-type phosphoric ester (TPP) in the resultant product was 2.2%, and the acid value (KOH/mg) thereof was 0.04. INDUSTRIAL APPLICABILITY According to a process for preparing a condensed phosphoric ester of the present invention, the content of the monomer-type phosphoric ester can be reduced to equal to or less than about 3% without reducing the yield of the products. Accordingly, a condensed phosphoric ester prepared by the process of the present invention is excellent in heat resistance, volatility and coloring resistance. When used as a plasticizer or a flame retardant for a resin, the condensed phosphoric ester prepared by the process of the present invention has the advantages of preventing generation of hazardous gas and the contamination of the molds during the molding, and reduction in the heat resistance of the molded product. Among these advantages, improved prevention of the contamination of the molds is industrially especially advantageous since it increases the number of continuous shots and thus reduces the production costs.

Claims: A process for preparing a condensed phosphoric ester, comprising: a first step of reacting a bisphenol A derivative with a phosphorus oxytrihalide in an amount equal to or greater than 4.5 mol times the amount of the bisphenol A derivative to prepare a phosphorohalidate; a second step of removing unreacted phosphorus oxytrihalide after the first step; a third step of reacting the phosphorohalidate obtained in the second step with a monophenol-based compound at a temperature equal to or lower than 120°C; and a fourth step of reacting the phosphorohalidate with the monophenol-based compound at a temperature equal to or higher than 120°C. The process of claim 1, wherein the amount of phosphorus oxytrihalide is 5-8 mol times, preferably 5.4-6 mol. times, the amount of the bisphenol A derivative. The process of claim 1 or 2, wherein the first step is carried out in the presence of a catalyst which is aluminium chloride, magnesium chloride, titanium tetrachloride or another Lewis acid. The process of any preceding claim, wherein the third step of reacting the phosphorohalidate with the monophenol-based compound is at a temperature of 60-110°C, preferably 80-100°C. The process of any preceding claim, wherein the total amount of the monophenol-based compound used in the third step and the fourth step is greater, by equal to or less than 2 mol%, than the theoretically necessary amount for turning the entire amount of the phosphorohalidate into the condensed phosphoric ester. The process of any preceding claim, wherein the temperature for the fourth step is 120-170°C, preferably 140-160°C. The process of any preceding claim, wherein the bisphenol A or derivative thereof is represented by the formula: wherein R 5 and R 6 which may be the same or different each represent an alkyl group containing 1-3 carbon atoms and n 1 and n 2 each represent an integer from 0 to 4. The process of any preceding claim, wherein the condensed phosphoric ester is a compound represented by the formula: wherein R 5 , R 6, n 1 and n 2 have the meanings given in claim 16, n is an integer from 1 to 10 and R 1 , R 2 , R 3 and R 4 which may be the same or different each represent an aryl group containing 6-15 carbon atoms. The process of claim 8, wherein R 1 , R 2 , R 3 and R 4 each represent phenyl, (o-, m-, p-)methylphenyl, (o-, m-, p-)ethylphenyl, (o-, m-, p-)n-propylphenyl, (o-, m-, p-)isopropylphenyl, (o-, m-, p-)n-butylphenyl, (o-, m-, p-)sec-butylphenyl, (o-, m-, p-)tert-butylphenyl, (2,3-2,4-, 2,5-, 2,6-, 3,4-, 3,5-)dimethylphenyl, (2,3- 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)diethylphenyl, 2-methyl-3-ethylphenyl, 2-methyl-4-ethylphenyl, 2-methyl-5-ethylphenyl, 2-methyl-6-ethylphenyl, 3-methyl-4-ethylphenyl, 3-methyl-5-ethylphenyl, 2-ethyl-3-methylphenyl, 2-ethyl-4-methylphenyl, 2-ethyl-5-methylphenyl, 3-ethyl-4-methylphenyl, (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)di-n-propylphenyl, (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)diisopropylphenyl, (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)di-n-butylphenyl, (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)di-sec-butylphenyl, (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-)di-tert-butylphenyl, (2,3,6-, 2,3,5-, 2,3,4-, 2,4,5-, 2,4,6-, 3,4,5-)trimethylphenyl, (2,3,6-, 2,3,5-, 2,3,4-, 2,4,5-, 2,4,6-, 3,4,5-)triethylphenyl, (2,3,6-, 2,3,5-, 2,3,4-, 2,4,5-, 2,4,6-, 3,4,5-)tripropylphenyl, or naphtyl. The process of any of claims 1-6, wherein the condensed phosphoric ester is 2,2-bis{4-[bis(phenoxy)phosphoryl]oxyphenyl}propane.

Inventors: FUJISAWA TAKU, NAKAMURA SHIN, NOGUCHI KAZUO, OHKAWA TAKAFUMI, FUJISAWA, TAKU, NAKAMURA, SHIN, NOGUCHI, KAZUO, OHKAWA, TAKAFUMI
Applicants: DAIHACHI CHEM IND, DAIHACHI CHEMICAL INDUSTRY CO., LTD.
Application year: 1999
Main classification: C07F9
IPC codes: C07F9