Drug – bio-affecting and body treating compositions – Topical sun or radiation screening – or tanning preparations
Reexamination Certificate
2002-06-17
2004-05-25
Page, Thurman K. (Department: 1616)
Drug, bio-affecting and body treating compositions
Topical sun or radiation screening, or tanning preparations
C106S436000, C106S442000, C423S610000, C424S401000, C424S489000, C424S490000, C502S350000
Reexamination Certificate
active
06740312
ABSTRACT:
The present invention relates to novel anatase titanium dioxide particles exhibiting anti-UV properties which can be used in particular in cosmetic formulations.
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 anatase titanium dioxide particles with a size of at most 100 nm, the said particles being at least partially covered with a layer of at least one metal oxide, hydroxide or hydroxide oxide and exhibiting a BET specific surface of at least 70 m
2
/g and a relative density of the order of 2.2.
With this aim, the invention also relates to the process for the preparation of these particles in which at least one metal oxide, hydroxide or hydroxide oxide 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.
Finally, the invention also relates to the use of these particles as anti-UV agent in cosmetic, paint or varnish formulations and in plastics; and more particularly to an anti-UV cosmetic composition comprising particles according to the invention in an amount such that the content of titanium dioxide in the said composition is at least 1% and preferably at most 25% by weight.
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 exhibit 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 anatase titanium dioxide particles with a size of at most 100 nm, the said particles being at least partially covered with a layer of at least one metal oxide, hydroxide or hydroxide oxide and exhibiting a BET specific surface of at least 70 m
2
/g and a relative density of the order of 2.2.
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 Chemical Society”, 60, 309 (1938). In order to measure the is 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 2.2. “Of the order” is understood to mean that the relative density is 2.2+/−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 an inorganic layer based on at least one metal oxide, hydroxide or hydroxide oxide. These metal oxides, hydroxides or hydroxide oxides can be chosen in particular from SiO
2
, ZrO
2
or aluminium, zinc, titanium or tin oxides, 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%.
This amount of metal oxide, hydroxide or hydroxide oxide is 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 layer of silica and/or of an aluminium oxide, hydroxide or hydroxide oxide, in the simple or mixed form.
According to a preferred alternative form, the particles are covered with a layer of silica and of aluminium hydroxide or hydroxide oxide in contents by weight of 30% of SiO
2
and 15% of Al
2
O
3
with respect to the titanium dioxide.
According to an even more preferred alternative form, the particles covered with a layer of silica and of 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 are particularly advantageous.
According to the preferred form of the invention, the particles are provided in the form of a dispersion.
This dispersion generally exhibits a conductivity of at most 3 msiemens.
This dispersion can exhibit a proportion of suspended solid (solids content) of between 10 and 60% by weight, preferably of at least 35%, more preferably still of at least 40%.
The dispersions of particles according to the invention exhibiting a solids content of at least 35% have the advantage of being only very slightly viscous; thus, their viscosity is generally at most 1000 mPa·s.
This dispersion generally exhibits a dispersion index of the particles in the liquid phase of at most 0.5.
The dispersion index is determined by the formula:
I
=
∅
84
-
∅
16
2
∅
50
in which:
ø
84
is the diameter of the particles for which 84% of the particles have a diameter of less than ø
84
,
ø
16
is the diameter of the particles for which 16% of the particles have a diameter of less than ø
16
,
ø
50
is the mean diameter of the particles.
The diameters of use in the determination of the dispersion index are measured by centrifugal sedimentation of the particles of the dispersi
Chopin Thierry
Dupuis Dominique
Willemin Claudie
Burns Doane Swecker & Mathis L.L.P.
Lamm Marina
Page Thurman K.
Rhodia Chimie
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