Organic compounds -- part of the class 532-570 series – Organic compounds – Four or more ring nitrogens in the bicyclo ring system
Reexamination Certificate
2002-01-25
2003-11-25
Raymond, Richard L. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Four or more ring nitrogens in the bicyclo ring system
C524S100000
Reexamination Certificate
active
06653474
ABSTRACT:
The invention relates to a polyphosphate salt of a 1,3,5-triazine compound, a process for its preparation, and use of the resulting salt as flame retardant in polymer compositions.
The polyphosphate of a 1,3,5-triazine compound can be represented by the general formula:
where M represents a 1,3,5-triazine compound and n is an integer greater than 3 that represents a measure of the number average degree of condensation. For high values of n, the polyphosphate of a 1,3,5-triazine compound can best be represented by the formula (MHPO
3
)
n
. Theoretically, the structure is substantially linear if the M/P (triazine/phosphorus) ratio is almost exactly 1.0. Similarly, if the M/P ratio is less than 1, it indicates that the product includes some crosslinking and, if the M/P ratio is less than 0.4, it indicates that the degree of crosslinking is sufficient for the product to form a network structure.
Melamine polyphosphate and a process for preparing melamine polyphosphate are described, inter alia, in WO 97/44377. According to this reference, melamine polyphosphate having a solubility of 0.01 to 0.10 g per 100 ml water at 25° C., a pH between 2.5 and 4.5, and a melamine/phosphorus molar ratio of between 1.0 and 1.1, may be obtained as a 10 wt % aqueous slurry at 25° C. WO 97/44377 also describes a two-step process for preparing the disclosed melamine polyphosphate slurry. In the first step melamine, urea, and an aqueous orthophosphoric acid solution (containing at least 40 wt % orthophosphoric acid), are mixed to produce a reaction mixture having a melamine/orthophophoric acid molar ratio between 1.0 and 1.5 moles and a urea/orthophophoric acid molar ratio between 0.1 and 1.5 at a temperature between 0 and 140° C. The resulting reaction mixture is then is stirred at a temperature between 0 and 140° C. and dehydrated to produce a powdery product comprising a double salt of orthophosphoric acid with melamine and urea. This powdery product is then heated to between 240 and 340° C. and maintained in this temperature range for between 0.1 and 30 hours while preventing agglomeration to obtain melamine polyphosphate.
One disadvantage of melamine polyphosphates having a melamine/phosphorus molar ratio between 1.0 and 1.1 such as those prepared according to WO 97/44377 is their general unsuitability for use as a flame retardant in polymers. This is particularly the case for polymers such as nylons and polyesters that are typically processed at elevated temperatures, temperatures at which the salts do not exhibit sufficient thermal stability. Moreover, the pH of such salts are relatively low, a property that tends to adversely affect the polymer's mechanical properties such as impact strength, tensile strength, and breaking strength.
It has been found, however, that salts of 1,3,5-triazine compounds with polyphosphoric acid having n values greater than 20, and preferably greater than 40, and M/P ratios of at least 1.1, and preferably at least 1.2, do not exhibit these disadvantages when combined with polymers. Further, according to the present invention, the n value of such salts should generally be between 20 and 200, preferably between 40 and 150, and the M/P ratio should be between 1.1 and 2.0, preferably between 1.2 and 1.8. Further, the pH of a 10 wt % aqueous slurry of salts prepared according to the present invention will generally be greater than 4.5 and preferably at least 5.0. The referenced pH value is determined by introducing 25 g of the salt and 225 g of pure, 25° C. water into a 300-ml beaker, stirring the resulting aqueous slurry for 30 minutes, and then measuring the pH.
The referenced n value, the number average degree of condensation, may be determined by means of 31p solid NMR. From J. R. van Wazer, C. F. Callis, J. Shoolery and R. Jones, J. Am. Chem. Soc., 78, 5715, 1956, the number of neighboring phosphate groups is known to give a unique ‘chemical shift’, which makes it possible to clearly distinguish between orthophosphates, pyrophosphates and polyphosphates.
Further, a process has been found for the preparation of the desired polyphosphate salt of a 1,3,5-triazine compound having an n value of at least 20, and preferably at least 40, and a M/P ratio of at least 1.1. This process involves the conversion of a 1,3,5-triazine compound with orthophosphoric acid into its orthophosphate salt, followed by dehydration and thermal treatment to convert the orthophosphate salt into a polyphosphate of the 1,3,5-triazine compound. This thermal treatment is preferably performed at a temperature of at least 300° C., and preferably at least 310° C. In addition to orthophosphates of 1,3,5-triazine compounds, other 1,3,5-triazine phosphates may also be used, including, for example, a mixture of orthophosphates and pyrophosphates.
The orthophosphate of the 1,3,5-triazine compound may be prepared in a variety of processes. The preferred process involves adding the 1,3,5-triazine compound to an aqueous solution of orthophosphoric acid. An alternative process involves adding orthophosphoric acid to an aqueous slurry of the 1,3,5-triazine compound.
The process according to the present invention can also be carried out in the presence of a catalyst. As a result, the end product has better electrical properties as indicated by the Comparative Tracking Index (CTI) known from literature, measured according to the IEC 695-2-1 standard. Although any hydroxide may be utilized as a catalyst, alkali metal hydroxides and alkaline earth metal hydroxides are preferred. Salts of boric acid, for example zinc borate, may also be utilized as a catalyst. If used, the amount of catalyst used will generally be between 0.1 wt % and 10 wt %.
The reaction time required for satisfactory production of the desired polyphosphate of the 1,3,5-triazine compound is generally at least two minutes, and more generally at least five minutes, and generally less than 24 hours.
A polyphosphate of the 1,3,5-triazine derivative according to the present invention should contain less than 1 wt % of water-soluble material, and preferably less than 0.1 wt %. This low water-soluble material content indicates that the product consists primarily of the desired polyphosphate.
It has also been found that polyphosphate salts of 1,3,5-triazine compounds according to the present invention are particularly suitable as flame retardants in polymer compositions. When used in this manner, the amount of flame retardant used in a polymer composition generally ranges from 15 to 45 wt %, and more generally from 20 to 40 wt %. It is believed that the suitability of these particular 1,3,5-triazine polyphosphate salts of compounds results from the increased thermal stability and increased pH achieved by compounds according to the present invention when compared with other flame retardants, such as halogen compounds, melamine, etc.
The flame retardant polymer compositions according to the present invention preferably comprise the following components:
35-55 wt %
of polymer
15-45 wt %
of polyphosphate salt of a 1,3,5-triazine
compound with a number average
degree of condensation n higher than 20
0-50 wt %
of reinforcing fiber
0-20 wt %
of carbon-forming compound
0-10 wt %
of a catalyst promoting carbon formation
Suitable 1,3,5-triazine compounds include 2,4,6-triamine-1,3,5-triazine (melamine), melam, melem, melon, ammeline, ammelide, 2-ureidomelamine, acetoguanamine, benzoguanamine, diamine phenyltriazine or mixtures hereof. Melamine, melam, melem, melon or mixtures thereof, are preferred, and melamine in particular is preferred.
Polymers and polymer compositions to which polyphosphate salts of 1,3,5-triazine compounds prepared according to the present invention may be added to improve flame retardant properties include the following:
1. Polymers of mono- and diolefins, for example polypropylene (PP), polyisobutylene, polybutylene-1, polymethylpentene-1, polyisoprene or polybutadiene; polyethylenes (optionally crosslinked) including, for example, high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density
Kersjes Johanna G.
Kierkels Renier H. M.
Balasubramanian Venkataraman
Ciba Specialty Chemicals Corporation
Crichton David R.
Raymond Richard L.
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