Compositions – Fire retarding – For solid synthetic polymer and reactants thereof
Reexamination Certificate
1999-06-11
2001-11-20
Anthony, Joseph D. (Department: 1714)
Compositions
Fire retarding
For solid synthetic polymer and reactants thereof
C558S162000, C558S092000, C558S110000, C524S127000, C524S145000, C524S141000, C524S143000
Reexamination Certificate
active
06319432
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a novel liquid flame retardant having a high bisphenol-A bis(diphenyl phosphate) content.
Bisphenol-A bis(diphenyl phosphate) is a well known flame retardant for use in normally flammable resins and is especially useful in flame retarding polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) compositions. It also finds use as a flame retardant in polyphenylene oxide/styrene compositions.
The art is replete with processes and process improvements for the production of bisphenol-A bis(diphenyl phosphate). See, for example, U.S. Pat. No. 2,520,090; U.S. Pat. No. 5,281,741; U.S. Pat. No. 5,750,756; GB 734,767; and WO 98/35970.
Despite past efforts, there is still a need for a liquid bisphenol-A bis(diphenyl phosphate)-based flame retardant which is resistant to crystallization at room temperature but which has a high phosphate content and a very low impurity content. It is an object of this invention to address such need. It is also an object of this invention to provide an improved bisphenol-A bis(diphenyl phosphate)-based flame retardant. It is a further object of this invention to provide a resin formulation containing the bisphenol-A bis(diphenyl diphosphate)s of the invention.
THE INVENTION
In its broadest sense, this invention provides a bisphenol-A bis(diphenyl phosphate) monomer-based flame retardant which is a liquid at room temperature, i.e., 20 to 25° C., and which is resistant to the fonnation of crystals over time. In a preferred form, this invention provides a flame retardant comprising bisphenol-A bis(diphenyl phosphate) and its dimer, the former having from about 78 to about 87 HPLC area % and from about 85 to less than 90 normalized area %, the normalized area % being based on the total HPLC area % of the bisphenol-A bis(diphenyl phosphate) and the dimer.
Additionally, this invention provides a bisphenol-A bis(diphenyl phosphate)-based flame retardant having a low isopropenylphenyl diphenyl phosphate content.
Further, this invention provides a bisphenol-A bis(diphenyl phosphate)-based flame retardant having a low triphenyl phosphate content.
Still further, this invention provides a bisphenol-A bis(diphenyl phosphate)-based flame retardant which is a liquid and is resistant to the formation of crystals and which has a high phosphorus content, a low isopropenylphenyl diphenylphosphate content and a low triphenyl phosphate content.
These and other features of the flame retardants of this invention are more fully discussed below.
DETAILED DESCRIPTION OF THE BIOPHENOL-A BIS(DIPHENYL PHOSPHATE) BASED FLAME RETARDANTS OF THE INVENTION
It has been discovered that it is possible to design a high phosphorus bisphenol-A bis(diphenyl phosphate)-based flame retardant so that, at room temperature, it is a liquid and is resistant to crystallization by specifying that the flame retardant contain certain levels of the dimer of bisphenol-A bis(diphenylphosphate). This discovery is based on work which shows that if the bisphenol-A bis(diphenylphosphate) content of the flame retardant is high, say 90+area % by HLPC, the flame retardant can be a solid at room temperature or if not a solid, a liquid which is very viscous and which has a tendency to form crystals in storage. (Unless otherwise indicated, all area %'s are determined by HPLC.) Thus, it was reasoned that if the bisphenol-A bis(diphenyl phosphate), i.e., the monomer, purity could be reduced by the presence of a specific amount of an impurity, the formation of the solid form or the tendency for crystallization to occur in the liquid form could be avoided. The impurity could not be one which would adversely affect the flame retardant's qualities or its performance in use. In addition, the impurity had to act as a solvent or a melting point depressant for the monomer to hold it in the liquid phase. An ideal impurity, it was discovered, is the dimer of bisphenol-A bis(diphenyl phosphate). The dimer not only attenuates the formation of a solid flame retardant or crystallization in the liquid form, it is also a contributor to the total phosphorus content of the flame retardant. (It is pointed out that the trimer of bisphenol-A bis(diphenyl phosphate) is also an impurity which contributes to the same functions as the dimer. However, the amount of trimer present is usually quite small and thus, focus is kept on the dimer in defining the flame retardants of this invention.) The dimer is easily obtained in situ as it is a product of the process for producing the bisphenol-A bis(diphenyl phosphate) from the reaction of POCl
3
and bisphenol-A followed by the reaction of phenol with the first reaction product. Not any amount of dimer, however, is suitable for these purposes.
The amount of dimer needed is tied to the amount of bisphenol-A bis(diphenyl phosphate) in the flame retardant. For the flame retardants of this invention, the amount of bisphenol-A bis(diphenyl phosphate) lies within the range of from about 78 to 87 area %, preferably 80 to 85 area %, amd most preferably 82 to 85 area %. The amount of dimer needed is that amount which will give a normalized area % for the bisphenol-A bis(diphenyl phosphate) which is within the range of from about 83 to less than about 90%, preferably from about 85 to about 89%, and most preferably from about 85 to about 88%. Again, the normalized area % is based on the total of the area %'s for the bisphenol-A bis(diphenyl phosphate) and its dimer. If less dimer than recited above is used, its useful effects are diminished, if more dimer is used, then the character of the flame retardant and its use in a resin formulation is affected. For each bisphenol-A molecule used to produce bisphenol-A bis(diphenyl phosphate), there are two phosphorus substituents, whereas for each molecule of bisphenol-A used to produce the dimer, there are only one and one-half phosphorus substituents. The structural formulas of the two make that clear. The bisphenol-A bis(diplhenyl phosphate) molecule, which can be referred to as a monomer, has the structure:
which has two phosphorus substituents per bisphenol-A constituent.
The dimer has the structure:
which has three phosphorus substituents for the two bisphenol-A constituents.
The amount of dimer in the flame retardants of this invention is within the range of from about 10 to about 13 area %, preferably from about 11 to about 13 area %, and most preferably from about 12 to about 13 area %.
The flame retardants of this invention will also have a trimer content, the trimer having the structure:
The role that the dimer content (or the trimer content) plays in determining that a bisphenol-A bis(diphenyl phosphate)-based flame retardant is liquid at room temperature and is resistant to crystallization during storage is not reported in the prior art. In addition, there is no known prior art method for specifically obtaining the required dimer contents of this invention. The method for producing the flame retardants of this invention is disclosed below.
The flame retardants of this invention also feature a very low isopropenylphenyl diphenyl phosphate content. This compound is considered by some in the resin formulation industry as a deleterious impurity whose presence must be minimized. The flame retardants of this invention preferably contain no more than 0.01 area % of this impurity. The structure for this impurity is:
It has been found that the isopropenylphenyl diphenyl phosphate content is not reduced by simply washing the crude product precursor to the final flame retardants of this invention. It is believed that the content of this impurity in the final flame retardant is determined early on in the manufacturing sequence. More discussion on this aspect is found below.
A widely recognized and particularly troublesome impurity found in bisphenol-A bis(diphenyl phosphate)-based flame retardants is triphenylphosphate. This impurity tends to “juice” in the resin formulation and adversely affect the formulation's physical characteristics. The flame retardants of this invention are advantage
Harrod William B.
Klobucar W. Dirk
Albemarle Corporation
Anthony Joseph D.
Spielman, Jr. E. E.
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