Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-11-20
2004-01-27
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S266000, C524S265000, C424S401000, C516S033000, C516S034000
Reexamination Certificate
active
06683130
ABSTRACT:
This invention relates to dispersions of metal oxides and in particular to dispersions of metal oxides in a silicone dispersing medium wherein certain polyalkylene oxide/siloxane copolymers are employed as dispersing agents.
Metal oxides such as titanium dioxide, zinc oxide and iron oxides have been employed as attenuators of ultraviolet light in applications such as sunscreens, plastics films and resins. Generally, metal oxides which are useful in these applications have an average primary particle size less than 200 nm. Dispersions of such metal oxides in certain oily media and in water are known and these dispersions have been used to formulate products such as sunscreening creams and lotions. The availability of the metal oxide in the form of a dispersion which is subsequently mixed with other conventional formulation ingredients to prepare a product has been shown to be advantageous in preparing the products.
The use of siloxane based oils in cosmetics has become popular because they can produce an improved skin feel. Hence, metal oxide dispersions in siloxane based dispersing media are desirable. Such dispersions have been difficult to produce.
It is an object of this invention to make available a stable dispersion of metal oxide in a siloxane dispersing medium and a method of producing sunscreening cosmetics based on siloxane fluids.
According to one aspect of the invention, a dispersion comprises at least 30 per cent by weight of particles of a metal oxide having an average primary particle size of less than 200 nm dispersed in a siloxane fluid dispersing medium and a dispersing agent wherein said metal oxide particles are hydrophobic, and said dispersing agent is a polyalkylene oxide/polyalkylsiloxane block copolymer comprising at least 30 per cent by weight of, the copolymer of polyalkylsiloxane.
The polyalkylene oxide/polyalkylsiloxane block copolymer preferably has the formula (1) below
in which Y
1
and Y
3
are oxyalkylene moieties, R
1
and R
2
are alkyl groups, X
1
and X
2
are alkylene groups, each R
3
is, independently, H or an alkyl group and p, q and r are integers chosen such that the proportion of polyalkysiloxane (—R
1
R
2
SiO—) moieties in the copolymer is at least 30 per cent by weight.
As mentioned above, the metal oxide particles used in the invention are hydrophobic. The metal oxide particles may be rendered hydrophobic, for example, by application of a hydrophobic coating on the surface of the metal oxide particles (core particles). The hydrophobic coating may be applied prior to formation of the dispersion, or alternatively in situ, ie during dispersion formation. In addition, as described hereinafter, the particles preferably carry an inorganic coating. Therefore, the term “particles of metal oxide”, as used herein is taken to mean the complete particles, i.e. the core particles plus any coating which has been applied.
Preferably the metal oxide used in the invention comprises an oxide of titanium, zinc or iron and most preferably the metal oxide is titanium dioxide in either the rutile or anatase crystal form.
The average primary particle size of the particles of metal oxide is less than 200 nm and where the particles are substantially spherical then this size will be taken to represent the diameter. However, the invention also encompasses particles of metal oxides which are non-spherical and in such cases the average primary particle size refers to the largest dimension. The average particle size which characterises the metal oxides used in the invention is the average size of primary particles, this average size typically being determined by electron microscopy. The size therefore relates to particles of metal oxide which are not aggregated. Frequently, the primary particles consist of single crystals but may also comprise several crystals fused together.
Preferably the average primary particle size of the particles is from 5 to 150 nm and more preferably from 10 to 100 nm when they are substantially spherical. For titanium dioxide particles having an acicular shape the average largest dimension of the primary particles is preferably less than 150 nm and more preferably from 20 to 100 nm.
When the metal oxide is titanium dioxide the particles are preferably acicular in shape and have a ratio of largest dimension to shortest dimension of from 10:1 to 2:1.
When the metal oxide is zinc oxide the particles preferably have an average primary particle size of 30 to 100 nm and very useful products have an average particle size of 30 to 70 nm.
The particles of metal oxide may comprise substantially pure metal oxide but preferably also carry an inorganic coating. For example, particles of titanium dioxide can be coated with oxides of other elements such as oxides of aluminium, zirconium or silicon and a form of acicular titanium dioxide, coated with alumina and silica, which is especially useful in the process of this invention is disclosed in UK Patent GB 2 205 088. Alternatively, particulate metal oxides which carry alumina as the only inorganic oxide coating have also been found to be useful in this invention. The preferred amount of inorganic coating is in the range 4 to 20 per cent by weight, calculated as inorganic oxide with respect to weight of metal oxide core particles. More preferably, the amount of inorganic coating is in the range 5 to 15 per cent by weight, calculated as inorganic oxide with respect to weight of metal oxide core particles. Suitable inorganic coatings can be applied using any appropriate technique and a person skilled in the art will readily be able to apply such a technique. A typical process comprises forming an aqueous dispersion of metal oxide core particles in the presence of a soluble salt of the inorganic element whose oxide will form the coating. This dispersion is usually acidic or basic, depending upon the nature of the salt chosen, and precipitation of the inorganic oxide is achieved by adjusting the pH of the dispersion by the addition of acid or alkali as appropriate.
The particles of metal oxide used to prepare the dispersions of the invention are hydrophobic. Generally, the particles have been treated with a water-repellent material in order to render them hydrophobic. Suitable water-repellent materials include fatty acids, preferably fatty acids containing 10 to 20 carbon atoms, such as lauric acid, stearic acid and isostearic acid, salts of the above fatty acids such as sodium salts and aluminium salts, fatty alcohols, such as stearyl alcohol, and silicones such as polydimethylsiloxane and substituted polydimethylsiloxanes and reactive silicones such as methylhydrosiloxane polymers and copolymers.
The hydrophobic treatment can be applied using any conventional process. Typically, metal oxide core particles (uncoated or with an inorganic coating) are dispersed in water and heated to a temperature in the range 50° C. to 80° C. A fatty acid is then deposited on the metal oxide particles by adding a salt of the fatty acid (e.g. sodium stearate) to the dispersion, followed by an acid. Alternatively, the metal oxide core particles or inorganically coated core particles can be mixed with a solution of the water-repellent material in an organic solvent, followed by evaporation of the solvent. In an alternative embodiment of the invention, the water-repellant material can be added directly to the dispersion of the present invention, during preparation thereof, such that the hydrophobic coating is formed in situ.
Generally, the particles are treated with up to 20 per cent by weight of the water-repellent material, calculated with respect to the coated or uncoated core particles, as appropriate, and preferably with from 6 to 16 per cent by weight of water-repellent material, calculated with respect to coated or uncoated core particles.
The dispersion preferably contains at least 40, more preferably at least 45, and particularly at least 50 per cent by weight of particles of metal oxide.
The metal oxide used in the dispersion of the invention is dispersed in a siloxane fluid dispersing medium. Any suitable siloxa
Imperial Chemical Industries PLC
Moore Margaret G.
Pillsbury & Winthrop LLP
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