Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-06-23
2001-02-13
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C427S214000, C427S215000, C428S404000, C428S405000
Reexamination Certificate
active
06187438
ABSTRACT:
The present invention relates to novel anatase titanium dioxides particles exhibiting anti-UV properties which can be used in particular in cosmetic formulations, varnishes and transparent coverings.
It is known to use titanium dioxide as anti-UV agent in numerous applications, in particular in cosmetics, paint, plastics, and the like.
In these applications, the titanium dioxide is generally provided in the form of particles with a size of less than 100 nm as a dispersion in an aqueous or organic phase.
The problem resulting from the use of these dispersions of titanium dioxide particles arises from the fact that the latter are often unstable. To control their stability, it is known to add dispersing agents to them, generally organic polymers.
However, the addition of these dispersing agents is not a solution which is without its disadvantages. This is because, when the titanium dioxide dispersion is mixed with other products in order to prepare a cosmetic, paint or plastic formulation, this agent can exhibit behaviour incompatible with the application (stability, agglomeration, toxicity, and the like) or be incompatible with the other components of the formula.
In these applications, the need is thus felt to be able to have available dispersions of titanium dioxide particles which are stable without the addition of dispersing agent.
One aim of the present invention is thus to provide dispersions of titanium dioxide particles which are stable and which do not contain dispersing agent.
With this aim, the invention relates to titanium dioxide particles at least partially covered:
with a first layer of at least one cerium and/or iron compound, and
with a second layer of at least one metal oxide, hydroxide or hydroxide oxide, the said particles exhibiting a BET specific surface of at least 70 m
2
/g and a relative density of the order of 2.5.
With this aim, the invention also relates to the process for the preparation of these particles in which the following stages are employed:
at least one cerium and/or iron compound is precipitated at the surface of anatase titanium dioxide particles with a size of at most 100 nm exhibiting a BET specific surface of at least 200 m
2
/g and a relative density of the order of 2.5, then
at least one metal oxide, hydroxide or hydroxide oxide is precipitated at the surface of particles obtained.
Finally, the invention also relates to the use of these particles as anti-UV agent in cosmetic, paint, varnish or transparent covering formulations and in plastics; and more particularly to an anti-UV cosmetic composition and to an anti-UV transparent covering composition.
The dispersions of particles according to the invention in addition exhibit the advantage of being stable over a wide pH range without addition of dispersing agent.
They can also exhibited high solids contents, while remaining stable and exhibiting a low viscosity, in particular of less than 1000 mPa·s.
Moreover, it is observed that these dispersions retain the same dispersion index even when they have been mixed with the components of a formulation, for example a cosmetic formulation.
Other characteristics, details and advantages of the invention will become more clearly apparent on reading the description and examples which will follow.
The invention first of all relates to titanium dioxide particles at least partially covered:
with a first layer of at least one cerium and/or iron compound, and
with a second layer of at least one metal oxide, hydroxide or hydroxide oxide, the said particles exhibiting a BET specific surface of at least 70 m
2
/g and a relative density of the order of 2.5.
The particles according to the invention are based on titanium dioxide with a largely anatase crystalline structure. “Largely” means that the level of anatase in the titanium dioxide particles of the coating is greater than 50% by mass. Preferably, the particles of the coating exhibit a level of anatase of greater than 80%. The degree of crystallization and the nature of the crystalline phase are measured by X-ray diffraction.
The mean diameter of these particles is at most 100 nm, preferably at least 25 nm, more preferably still between 50 and 70 nm. This diameter is measured by transmission electron microscopy (TEM).
The particles according to the invention exhibit a BET specific surface of at least 70 m
2
/g, preferably of at least 100 m
2
/g.
BET specific surface is understood to mean the specific surface determined by nitrogen adsorption in accordance with the ASTM standard D 3663-78 drawn up from the Brunauer-Emmett-Teller method described in the periodical “The Journal of the American [lacuna] Society”, 60, 309 (1938). In order to measure the specific surface of the particles according to the invention, when they are provided in the form of a dispersion, it is essential to follow the measuring protocol, which consists in removing the liquid phase from the dispersion and then in drying the particles under vacuum at a temperature of 150° C. for at least 4 hours.
The particles according to the invention also exhibit a relative density of the order of 2.5. “Of the order” is understood to mean that the relative density is 2.5+/−0.2. Such a relative density value is low with respect to the conventional relative density of anatase titanium dioxide, which is 3.8. This relative density is measured by picnometry.
The particles according to the invention are at least partially covered with a first inorganic layer based on at least one cerium and/or iron compound. These compounds are precursors of cerium or iron oxide, that is to say that they can be thermally decomposed to cerium or iron oxide. They can generally be cerium or iron salts.
According to the invention, particles covered with a cerium compound are preferred. The best results as regards dispersion properties were obtained for the particles where the ratio by weight of the cerium compound or compounds to the titanium dioxide is at most 6% by weight, expressed as CeO
2
.
This ratio can be optimized as a function of the size of the particles. Thus, it was observed that, for particles with a diameter of 25 nm, the optimum cerium content was 5.5% by weight, expressed as CeO
2
, with respect to the titanium dioxide, likewise, for particles with a diameter of 45 nm, this content is 4.5%, for particles with a diameter of 60 nm, this content is 3% and, for particles with a diameter of 80 nm, this content is 2%.
These particles are also at least partially covered with a second layer based on at least one metal oxide, hydroxide or hydroxide oxide. The oxide is generally SiO
2
, with regard to the metal hydroxide or hydroxide oxide, it can be chosen in particular from aluminium, zinc, titanium or tin hydroxides or hydroxide oxides, in the simple or mixed form. Mixed is understood to mean a metal compound based on at least two of the abovementioned elements (silicoaluminates, and the like).
In general, the ratio by weight of the metal oxide(s), hydroxide(s) or hydroxide oxide(s) to the titanium dioxide is at most 60% by weight. This ratio depends on the application for which the particles are intended. Preferably, when the particles are used in a cosmetic application, this ratio is at most 25%, more preferably still at most 20%.
These amounts of metal compounds, oxides, hydroxides or hydroxide oxides are measured on the dispersed particles by X-ray fluorescence.
According to the preferred form of the invention, the particles are at least partially covered with a first layer of a cerium compound and with a second layer based on silica and/or on an aluminium hydroxide or hydroxide oxide, in the simple or mixed form.
According to a preferred first alternative form, the particles are covered with a second layer based on silica and on aluminium hydroxide or hydroxide oxide in contents by weight of 15% of SiO
2
and 5% of Al
2
O
3
with respect to the titanium dioxide.
According to a second, even more preferred, alternative form, the particles are covered with a second layer based solely on silica in a content by weight of 30% of SiO
2
.
Acco
Chopin Thierry
Dupuis Dominique
Pacaud Bernard
Burns Doane Swecker & Mathis L.L.P.
Le H. Thi
Rhodia Chimie
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