Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Patent
1999-02-05
2000-07-11
Group, Karl
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
106245, 106419, 106420, 106425, 106430, 106436, 106441, C09C 104, C09C 124, C09C 136
Patent
active
060866675
DESCRIPTION:
BRIEF SUMMARY
The invention relates to pigments coated with an UV-absorbing agent, to a method for their preparation and to paints containing them.
A variety of techniques, in particular passive thermal control, are used for the thermal control of space vehicles.
Passive thermal control is based on the thermo-optical properties of the coatings applied to the space vehicles, that is to say: ##EQU1##
This solar absorption coefficient is integrated over the solar spectrum between 0.2 and 2.8 .mu.m. nature of the coatings.
By way of explanation, it is known that all bodies emit radiation proportional to the fourth power of their absolute temperature, to their surface area, to time and to the emissivity e.
The following equation therefore follows: surroundings, ##EQU2##
Passive thermal control coatings can be divided into a variety of categories, among which particular distinction is made between the following, depending on the ratio a.sub.s /e: films, quartz mirrors, etc.) metals, etc.).
White paints consist of a binder, at least one white pigment and a solvent.
The most commonly used white pigments are: titanium dioxide (TiO.sub.2), zinc oxide (ZnO), zinc orthotitanate (Zn.sub.2 TiO.sub.4), zinc orthostannate (Zn.sub.2 SnO.sub.4), tin orthotitanate (Sn TiO.sub.4), etc. as well as mixtures of these pigments.
When white paints are exposed to a space environment, they suffer degradation, especially in their thermo-optical properties (increase in the solar absorption coefficient: a.sub.s), under the combined action of the various factors involved in this space environment, principally by the effect of ultraviolet solar radiation and additionally by the effect of particle radiation (electrons, protons).
This solar radiation is distributed between 180 and 2800 nm, and short ultra-violet radiation (180 to 250 nm) is responsible for almost all the degradation.
One hypothesis which may be put forward to explain this degradation is as follows:
Under the action of UV radiation, the white pigments, essentially metal oxides MO.sub.x, will lose oxygen to give a product MO.sub.x-y whose thermo-optical properties (a.sub.s) are degraded.
The increase in the solar absorption coefficient a.sub.s is detrimental to passive thermal control and may be the origin of heating which can have serious consequences for the components of the space vehicle and/or the on-board equipment.
There is therefore a need for white pigments whose degradation, in particular under the effect of UV solar radiation, is reduced or eliminated.
Furthermore, coloured pigments consist of a binder, at least one colour pigment and a solvent.
The coloured pigments may be oxides of iron, lead, chromium, etc. or organic pigments, for example diazo compounds etc.
When coloured paint films are exposed to UV radiation, this leads to decolouration, especially for organic pigments.
There is therefore also a need for coloured pigments whose degradation, in particular under the effect of UV solar radiation, is reduced.
The object of the present invention is to meet these requirements, as well as others which will become apparent on reading the following description.
More particularly, the invention relates to pigments in the form of fine particles having enhanced stability with respect to solar ultraviolet radiation and particle radiation (electrons, protons), characterized in that the pigment particles are coated with a UV filter which absorbs ultraviolet radiation with a wavelength below 300 nm, but is transparent between the near infrared and the near ultraviolet (that is to say substantially between 2500 nm and 300 nm) and is selected from
The amount of UV filter applied to the pigment particles is not of critical importance. It will usually represent from 1 to 15% of the weight of the pigment.
The invention also relates to a method for improving the stability of pigments with respect to ultraviolet or particle radiation, characterized in that it consists in coating particles of a pigment with an aqueous solution, or a solution in a polar solvent, of at least one UV filter then in
REFERENCES:
patent: 3607338 (1971-09-01), Webb et al.
patent: 4460665 (1984-07-01), Jacobson
patent: 5296285 (1994-03-01), Babel et al.
Chemical Abstracts, vol. 114, No. 4, Jan. 28, 1991, No. 26686a.
Guillaumon Jean-Claude
Nabarra Pascale Veronique
Centre National d'Etudes Spatiales
DiVerdi Michael J.
Group Karl
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