Compositions: coating or plastic – Coating or plastic compositions – Contains fireproofing or biocidal agent
Patent
1993-06-04
1994-02-15
Bell, Mark L.
Compositions: coating or plastic
Coating or plastic compositions
Contains fireproofing or biocidal agent
106 1811, 106461, 252601, 252609, 423161, 423164, 423331, 423583, C09D 516, C09D 518
Patent
active
052862852
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a finely powdery magnesium hydroxide suitable especially as flame-retardant filler for plastic compounds, the particles thereof being provided optionally with a thin coating of a surfactant.
Frequently, finely powdery magnesium hydroxide is used as flame-retardant filler for plastic compounds, especially those on basis of thermoplastic materials. In such a use relatively high amounts of magnesium hydroxide are added to the plastics, the weight of the magnesium hydroxide frequently amounting to the half up to the double weight of the plastic. Kinds of finely powdery magnesium hydroxide often have properties which exert a negative influence on the mechanical properties of plastic compounds to which such a magnesium hydroxide has been added as filler. Often e.g. a tendency of such plastic compounds and articles produced from such plastic compounds respectively to take up relatively high amounts of water, to a decrease of the tensile strength and to an increased ageing may be observed.
Frequently, the flowability and formability of such plastic compounds and the appearance of the surface of articles formed from such plastic compounds is adversely influenced by the properties of certain kinds of finely powdery magnesium hydroxide, e.g. by the grain structure and the contents of water thereof.
DE-C3-2 624 065 describes a magnesium hydroxide having the special structure of particles which should eliminate in use of said magnesium hydroxide in plastic compounds disadvantages as mentioned above. The particles should have a deformation in the <101>-direction of not more than 3.times.10.sup.-3, a crystallite size in the <101>-direction of more than 800 .ANG. and a specific surface, determined according to BET, of less than 20 m.sup.2 /g. According to DE-C3-2 659 933 in addition to that structure of the particles of the magnesium hydroxide said particles are covered with anionic surfactants so as to eliminate the above mentioned disadvantages.
Now it has been found that the above mentioned structural parameters are not suitable for the characterization of a magnesium hydroxide to be used for the above mentioned purpose, by which the above mentioned disadvantages can be eliminated reliably. Despite of such a structure in the practice, the mentioned disadvantages may occur.
It is an object of the present invention to provide a finely powdery magnesium hydroxide as defined above, which in use as flame-retardant filler in plastic compounds eliminates reliably the mentioned disadvantages and which, also after a longer period of time, does not induce both any impairment of the chemical-physical properties, especially of the electrical insulating property and of the chemical resistance, and any impairment of the mechanical properties and of the dimensional stability and does not favor disadvantageous changes of the plastic compounds under the influence of moisture and other environmental influences. The finely powdery magnesium hydroxide to be prepared should allow also a simple processing of plastic compounds, in which it serves as flame-retardant filler, and should allow to obtain good strength properties of articles prepared from such plastic compounds as well as a uniformly closed surface of said articles, which does not show any trouble by surface faults.
The finely powdery magnesium hydroxide of the present invention is characterized by a grain size, measured by laser diffraction, of below 10 .mu.m, the median value of the grain size being greater than 0.8 .mu.m and 3 .mu.m at the utmost and further characterized in, that the magnesium hydroxide contains water-soluble ionic impurities, viz. Ca.sup.++, Na.sup.+, K.sup.+, SO.sub.4.sup.--, Cl.sup.-, in amounts below the following limits (in parts by weight): the following limits (in parts by weight):
Magnesium hydroxide having such features allows to achieve well the above mentioned objects.
In experiments carried out during the development of subject matter of this invention is was found that by keeping the values of water-sol
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Grill Michael
Meier Andreas
Bell Mark L.
Marcheschi Michael
Veitscher Magnesitwerke-Actien-Gesellschaft
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