Organic compounds -- part of the class 532-570 series – Organic compounds – Phosphorus esters
Reexamination Certificate
2002-04-15
2003-09-02
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Phosphorus esters
C568S700000
Reexamination Certificate
active
06613928
ABSTRACT:
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.
For example, 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 compo
Fujisawa Taku
Nakamura Shin
Noguchi Kazuo
Ohkawa Takafumi
Daihachi Chemical Industry Co. Ltd.
McKane Joseph K.
Shiao Robert
Snell & Wilmer LLP
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