Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-09-21
2003-11-11
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C252S609000
Reexamination Certificate
active
06646030
ABSTRACT:
The invention relates to a flame-retarding composition and a process for the preparation thereof.
A flame-retarding composition and a process for the preparation thereof are for example described in the Japanese patent publication JP 59-45352, in which the melamine condensation products melem and melon are prepared and used as flame retardants in polyamide compositions. In this publication melem is prepared by heating melamine at a temperature of 400-500° C. for several hours. Melon is prepared by heating melamine at 500-550° C. until no more ammonia is released. JP 59-45352 mentions that the decomposition temperature of melem lies above 500° C. and that of melon above 600° C. This means that melem and melon have a particularly good thermal stability. According to JP 59-45352, the nitrogen contents of both compounds lie above 60%, as a result of which the substances are non-combustible. JP 59-45352 also mentions that other known flame retardants can also be used in combination with melem or melon, for example melamine, cyanuric acid, melamine cyanurate or melam. JP 59-45352 does not mention the composition of the product obtained.
Melamine and its condensation products all have a characteristic thermal degradation curve. This means that melamine and its condensation products decompose to form nitrogen-containing products at a certain temperature. These nitrogen-containing products that are released in the thermal degradation play an important part in the flame-retardant behaviour. To obtain good flame-retardant behaviour in polymers it may be favourable to combine flame-retarding components, such as melam, melem and the higher condensation products of melamine and/or melem, having different degradation characteristics, in a single composition. The advantage of this is that, irrespective of the temperature prevailing in a fire, there will almost always be a component present that degrades at the prevailing temperature and produces sufficient nitrogen-containing components having a flame-retarding effect. However, if the flame-retarding composition contains volatile components, such as urea and/or water, this will have a negative effect on the processing properties when the composition is used in polymers with a high melting temperature, for example in polyesters such as polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) or in polyamides. Such a negative effect could be foaming during extrusion or the formation of deposits on the mould in injection-moulding. If the flame-retarding composition contains too high a concentration of higher condensation products of melamine and/or melem, the composition will be yellow, which is undesirable in the case of processing in (uncoloured) polymer compositions. The use of pure melamine condensation products such as pure melam or melem or melon as a flame retardant in polymers is unfavourable because it will usually be difficult, and hence expensive, to prepare pure compounds and because pure components have only one mode of degradation and will hence work optimally only in a limited temperature range.
The applicant has discovered that excellent processing properties and excellent flame-retarding properties and colour properties can be obtained in polymer compositions by using a flame-retarding composition containing:
10-90 wt. % melem,
0.01-30 wt. % melam,
0.01-15 wt. % melamine,
0.1-65 wt. % higher condensation products of melamine and/or melem, the concentration of volatile components being lower than 3 wt. % and the sum of the individual components amounting to 100 wt. %.
The concentration of volatile components is here defined as the decrease in weight that occurs in heating the flame-retarding composition from room temperature to 300° C. in a TGA measurement (TGA=thermogravimetric analysis) at a heating rate of 200° C. per minute.
The applicant has also found a process for preparing a flame-retarding composition comprising 10-90 wt. % melem, 0.01-30 wt. % melam, 0.01-15 wt. % melamine, 0.1-65 wt. % higher condensation products of melamine and/or melem, the concentration of volatile components being lower than 3 wt. % and the sum of the individual components amounting to 100 wt. %, by heating a starting product containing melamine, for example by passing it through a heating zone, for longer than 0.1 sec., preferably 1 sec. to 400 minutes, in particular 2 sec. to 300 minutes, at a temperature of 350-800° C., preferably between 375 and 600° C. and at a pressure between 1 KPa and 50 MPa, preferably between atmospheric pressure and 30 MPa, more in particular between atmospheric pressure and 15 Mpa.
Examples of heating zones are heating zones of the kind that are to be found in extruders, such as single- and twin-screw extruders; autoclaves; turbo mixers; plough blade mixers; tumble mixers; turbulence mixers; ribbon-blade mixers; mixtruders; continuous and discontinuous kneading machines; rotating drum ovens, etc.
A mixture of melamine, melem, melam and higher condensation products of melamine and/or melem can optionally be obtained by treating the product of the heating further, to obtain a flame-retarding composition comprising 10-90 wt. % melem, 0.01-30 wt. % melam, 0.01-10 wt. % melamine, 0.1-65 wt. % higher condensation products of melamine and/or melem, the concentration of volatile components being lower than 1 wt. % and the sum of the individual components amounting to 100 wt. %. This further treatment is preferably washing with water to dissolve and remove from the flame-retarding composition a portion of the melamine and/or other water-soluble components.
As the starting material for the present process, use can be made of virtually pure melamine, as for example obtained from a continuously operating gas-phase melamine plant where the melamine is purified by means of crystallisation. A method for the preparation of melamine via a gas-phase process is for example known from U.S. Pat. No. 3,210,352. This high degree of purity is however not necessary. Melamine contaminated with melam and/or melem and/or higher condensation products of melamine and/or melem can optionally be used as the starting material, for example the product that is formed during start-up of a melamine plant or melamine of the kind that is prepared in a gas-phase melamine plant before purification by means of crystallisation has taken place or melamine contaminated with melam and/or melem and/or higher condensation products of melamine and/or melem formed in some other way. It is also possible to use melamine obtained in a liquid-phase process as the starting material. A known process for the preparation of melamine via a liquid-phase process is described in U.S. Pat. No. 4,565,867, of which it is known that the degree of purity is less than that of the product of a gas-phase process; in particular, its melam content is higher. Contaminants like residual catalyst, ureidomelamine and/or guanidine carbonate may also be present without any objection. Oxygen-containing triazine compounds such as ammeline, ammelide and/or cyanuric acid may also be present up to 5 wt. % without any objection. Remains of the starting materials used for the preparation of melamine, such as urea and/or dicyanodiamide, may also be present; dicyanodiamide may be present up to 10 wt. % without any objection, while the melamine may contain up to 30 wt. % urea. The starting material for the present process may also contain contaminants containing mixtures of urea, oxygen-containing triazine compounds, dicyanodiamide, guanidine carbonate, ureidomelamine and residual catalyst.
In a preferred embodiment of the invention the flame-retarding composition is prepared by heating the melamine-containing starting product in an autoclave or in an extruder. Preferably at a pressure between atmospheric pressure and 20 Mpa, at a temperature of 350-625° C. and with a residence time of between 0.1 sec. and 360 minutes. More in particular the heating of the melamine-containing starting product is carried out in an extruder with a residence time in the extruder of between 0.1 sec. and 60
Heinen Wouter
Kierkels Renier H. M.
Ciba Specialty Chemicals Corporation
Crichton David R.
Sanders Kriellion A.
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