Note: Descriptions are shown in the official language in which they were submitted.
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SILICONE POLYMER-COATED, HYDROPHOBIZED METAL OXIDES
Related Applications
This application is related to United States Serial Number 08/629,931, filed
April 12,
1996, now United States Patent 5,565,591, which is related to United States
Serial Number,
filed January 23, 1996, now United States Patent 5,562,897, which is related
to United States
Serial Number 549,873, filed October 30, 1995, now United States Patent
5,536,492, which is
related to United States Serial Number 490,494 filed June 14, 1995, now U.S.
Patent
5,486,631.
This invention relates to metal oxide particles made hydrophobic by a process
of
coating the metal oxide with a silicone polymer. They hydrophobized metal
oxide is
prepared by the reaction of a specific type of reactive silicone which is
applied to the metal
oxide, followed by heating the coated metal oxide to 40 to 100°C for
between 1 and 10 hours
for the reaction to occur. The resulting silicone coated metal oxide particles
are hydrophobic,
non-reactive, and not affected by water. The coated, hydrophobized metal
oxides or particles
also have a significantly decreased photoreactivity which makes them more
resistant to
degradation and more chemically inert than non-coated metal oxides.
Hydrophobized metal
oxides, such as zinc oxide, titanium dioxide and iron oxide, are particularly
useful in
compositions that are applied to the skin for protection from ultraviolet
radiation. Such
compositions made according to the invention are effective as delivery systems
which
produce a uniform hydrophobic film which is not interrupted by extraneous
oils, water and
other additives which may be in the final formulated product.
DESCRIPTION OF THE ART
Metal oxides, such as zinc oxide, titanium dioxide and iron oxide, are well
known
compounds that are useful in a variety of application. For example, titanium
dioxide, is used
as a pigment in paint, as an additive in cosmetic products, cements, glass,
rubber, glue,
matches, inks and semiconductors. The use of titanium dioxide in so many
application areas
is a direct result of the many differing and useful properties of the pigment.
It is very desirable to produce a metal oxide, such as titanium dioxide, which
has the
pigment properties but lacks the ability to react with other compounds or
materials which
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contact the metal oxide as found in various applications, compositions, or
formulations. One
area in which metal oxides have been used is in sunscreen products. Metal
oxides, such as
zinc oxide, titanium dioxide, iron oxide and cesium oxide, can protect the
skin from the
harmful effects of exposure to the sun. The traditional materials used for
protecting the skin
from the harmful effect of the sun are the organic sunscreen agents. These
include para-
amino benzoic acid (PABA) and other materials which absorb ultraviolet light.
Recently,
studies have indicated that ultraviolet light is a major factor in the aging
of skin. This has
resulted in the incorporation of sunscreens in products, such as cosmetics,
that are not aimed
specifically for use as sunscreen compositions. Additionally, there has been
an increased
interest in providing higher levels of protection to the skin. The so called
skin protection
factor (SPF) system has been developed to evaluate various materials for their
effectiveness
in protecting the skin from the damaging effects of the sun. The quest for
higher and higher
SPF values has resulted in the use of greater levels of organic sunscreens.
These materials
have a tendency to be irritating at high concentrations and have the effect of
increasing the
available organic material for bacteria. This in turn results in the need for
more preservative
to protect the higher level of organic sunscreen agent from bacterial
degradation. The higher
levels of preservative result in higher irritation levels which can be
addressed by
incorporation of irritation mitigants which, themselves, are degraded by
bacteria.
The use of inorganic sunscreen agents like titanium dioxide is a good way
around the
use of organic sunscreens since they are not attacked by bacteria. However,
their use does
have some other inherent problems. Specifically, these materials are not
easily formulated
into stable products due to the reactivity issues raised above. For example,
titanium dioxide
tends to agglomerate in many finished formulations, losing its effectiveness
in the
formulation and resulting in unacceptable aesthetic results, most commonly
whitening and
viscosity changes. In addition, untreated titanium dioxide reacts with vitamin
C in aqueous
solution, resulting in a pronounced yellowing of the solution. This is highly
undesirable in
many cosmetic applications. One approach has been to pre-disperse the titanium
dioxide in
an organic oil like Siltech's patented tri-(octyldodecyl)-citrate. While the
dispersion is fairly
stable, the coating is not permanent since there is no reaction between the
oil and the titanium
dioxide. The oil also disrupts the uniformity of the titanium dioxide on the
skin.
Traditionally, dispersing aids have been added to formulations to minimize the
disruptive
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effect upon the film. These include phosphate esters and lecithin. These too
suffer from the
labile nature of the surface treatment and dissociation between the particle
and the oil. This is
especially evident when titanium dioxide is exposed to extreme mechanical or
thermal stress
as in the production of plastics or stick cosmetics.
~ 5 The present invention overcomes the shortfalls of titanium dioxide and
other metal
oxides by reacting a specific silicone compound under controlled conditions to
produce a
stable, surface treated metal oxide which maintains its state of dispersion
and does not
contribute significantly to chemical instability in the formulation.
SUMMARY OF THE INVENTION
The present invention provides processes for making the surface of metal
oxides
hydrophobic using a specific type of reactive silicone compound, the resulting
hydrophobized
metal oxides prepared from such processes, and methods for protecting skin
from ultraviolet
radiation using the hydrophobized metal oxides.
Thus, it is one aspect of this invention to provide a process for
hydrophobizing metal
oxides comprising contacting the metal oxide with an effective hydrophobizing
amount of a
silicone compound having the formula:
Me
R-Si- [-(-O-Si-)a-OR']3
Me
where Me is methyl,
R is alkyl having one to ten carbon atoms,
R' is methyl or ethyl,
a is an integer ranging from 4 to 12,
and heating the mixture of silicone compound and metal oxide to a temperature
of
~ 40°C to 100°C, for two to ten hours. The effective
hydrophobizing amount of silicone
compound is defined as that amount of silicone compound which is used to
produce a coated,
hydrophobized metal oxide particle containing a desired percent, preferably
ranging from 0.1
to 25%, by weight of the silicone compound. In one embodiment of the
hydrophobizing
process, the entire effective hydrophobizing amount of the silicone compound
is contacted
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with the metal oxide at one time and then heated. The metal oxides so produced
are referred
to as singly-coated metal oxides.
In a more preferred embodiment of the hydrophobizing process of this
invention, a
portion or increment of the effective hydrophobizing amount of the silicone
compound is
contacted with the metal oxide followed by heating, and these steps repeated
until the entire
effective hydrophobizing amount of the silicone compound has been reacted with
the metal
oxide. As used herein, "portion" refers to a fraction of the total amount
which would be
applied in a single coating step, and may include, for example, 1 /4, 1 /2,
3/4, etc., where the
fraction used in all of the coating steps equals 1. More preferably, the
hydrophobizing
process is carried out in two successive cycles of mixing one-half of the
effective
hydrophobizing amount of silicone compound with the metal oxide followed by
heating.
Metal oxides so produced are referred to as doubly coated metal oxides.
Compared to singly
coated metal oxides, doubly coated metal oxides have both an advantageously
lower
photoreactivity, giving the metal oxide an increased stability, and also an
enhanced skin
protection factor (SPF).
Preferably, applying the effective hydrophobizing amount of silicone compound
in
the processes of this invention results in a metal oxide having a percent
silicone compound
ranging from 0.1 to 25% by weight, more preferably 0.5 to 20% by weight, and
most
preferably 1.0 to 10% by weight.
In another preferred embodiment of this invention, the integer "a" of the
structure of
the silicone compound used to hydrophobize metal oxides ranges from 6 to 12
and, more
preferably, ranges from 4 to 8. In still another preferred embodiment, the R
group of the
silicone compound used to hydrophobize metal oxides is methyl, butyl, or
octyl.
Any of a variety of metal oxides may be hydrophobized by the processes of this
invention including zinc oxide, titanium dioxide, iron oxide, cesium oxide,
zirconium oxide,
silicon dioxide and antimony oxide. In a preferred embodiment, the metal
oxides
hydrophobized by the processes of this invention are those which have the
ability to absorb
ultraviolet radiation and, thus, are useful as sunscreen agents. Such metal
oxides include, but
are not limited to, zinc oxide, titanium dioxide, iron oxide, cesium oxide,
zirconium oxide,
and silicon dioxide.
The coated, hydrophobized metal oxides of this invention may be used in
various
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formulations and compositions that are applied to the skin for protection from
ultraviolet rays
of the sun. Such formulations include sunscreen compositions and cosmetics.
" This invention also provides methods of protecting the skin from ultraviolet
rays of
the sun which comprise contacting the skin with an effective protecting
concentration of a
S hydrophobized metal oxide prepared according to processes described in this
invention. An
effective protecting concentration of a hydrophobized metal oxide is the
amount necessary to
achieve a desired SPF.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a bar graph that compares the relative photoreactivity of non-
hydrophobized metal oxide particles (uncoated particles); singly-coated,
hydrophobized metal
oxide particles (coated x 1 with 5%); and doubly-coated, hydrophobized metal
oxide particles
(coated x 2 with 2.5% each time) prepared as described in Example 23. Zinc
oxide particles
(shaded bars), titanium dioxide particles (open bars).
DETAILED DESCRIPTION OF THE INVENTION
It has been found that a highly effective system for hydrophobizing metal
oxides, such
as zinc oxide and titanium dioxide, makes use of a silicone compound
conforming to the
following structure:
Me
R-Si- [-(-O- Si-)a-OR']3
where Me is methyl;
Me
R is alkyl having one to ten carbon atoms;
R' is methyl or ethyl;
a is an integer ranging from 4 to 12.
We have surprisingly learned that the value of the integer "a" in the
structure is critical
in developing a product which gives the desired hydrophobicity. The critical
range is from 4
to 12. The value of a metal oxide, such as titanium dioxide, as a pigment is
based upon its
ability to remain dispersed and unreacted. For example, untreated titanium
dioxide, placed
into water, loses its effectiveness and good aesthetic qualities due to
agglomeration. If the
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value of "a" is too low, the treated titanium dioxide is not sufficiently
hydrophobic and its
value as a pigment is destroyed. Making metal oxides, such as titanium
dioxide,
permanently hydrophobic by treatment with the correct silicone compound is
highly desirable
and heretofore has been very difficult to attain.
The silicone-coated, hydrophobized metal oxides of this invention are
especially
useful in many applications including as a sunscreen agent to prevent harmful
effects of
ultraviolet radiation from the sun. The compounds of the present invention are
hydrophobic
metal oxides which are prepared by the reaction of a silicone compound
conforming to the
following structure:
Me
R-Si-[-(-O-Si-)a-OR']3
Me
where Me is methyl,
R is alkyl having one to ten carbon atoms,
R' is methyl or ethyl,
a is an integer ranging from 4 to 12,
with a metal oxide.
The process for hydrophobizing a metal oxide comprises contacting the metal
oxide
with an effective hydrophobizing amount of a silicone compound having the
formula:
Me
R- Si- [- (- O- Si-)a- OR']3
Me
where Me is methyl,
R is alkyl having one to ten carbon atoms,
R' is methyl or ethyl,
a is an integer ranging from 4 to 12,
and heating the mixture of silicone compound and metal oxide to a temperature
ranging from
40°C to 100°C, for two to ten hours. The effective
hydrophobizing amount is the amount
necessary to result in particles of metal oxide which are coated with a
desired percent by
weight of the silicone compound. Preferably, the hydrophobized metal oxides of
this
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invention are 0.1 to 25% by weight silicone compound. More preferably, the
hydrophobized
metal oxides are 0.5 to 25% by weight silicone compound and most preferably,
the metal
oxides are 1.0 to 10% by weight silicone compound.
In one embodiment of a process of this invention, the entire effective
hydrophobizing
amount of the silicone compound is contacted with the metal oxide at one time
followed by
heating. The metal oxides so produced are referred to as singly coated metal
oxide and
exhibit advantageously decreased photoreactivity and increased SPF compared to
non-coated
metal oxide.
The desirable characteristics of coating metal oxides with the silicone
compound
according to this invention can be further enhanced if the effective
hydrophobizing amount of
silicone compound is applied to the metal oxide by successive cycles of
contacting a portion
of the effective hydrophobizing amount of the silicone compound with the metal
oxide
followed by heating, and repeating such cycles of reacting the silicone
compound with the
metal oxide until the entire effective amount of silicone compound has been
applied. For
example, if the goal is to produce hydrophobized metal oxide particles
containing a final
percent by weight of silicone compound of 10%, a portion of the total
effective
hydrophobizing amount of silicone compound (e.g., 1/2) is contacted with the
metal oxide
and heated to first produce a coated metal oxide particle containing 5%
silicone compound,
followed by reacting the 5% silicone coated metal oxide particle with another
portion (e.g.,
1/4) of the effective hydrophobizing amount of silicone compound to form a
particle
containing 7.5% silicone compound which, in turn, is reacted with the rest of
the effective
hydrophobizing amount of silicone compound (e.g., 1/4) to produce a coated,
hydrophobized
metal oxide particle containing the desired 10% by weight silicone compound.
Alternatively,
a metal oxide particle containing 10% by weight silicone compound may be
produced by
reacting the silicone compound with the metal oxide in a different series of
successive cycles
of reacting portions of the effective hydrophobizing amount of silicone
compound with metal
oxide. For example, the coating may be applied in fractions of 1/10, 3/10,
3/10, 3/10.
Successive cycles of reaction yielding first a 1 % silicone compound metal
oxide, then a 4%
silicone compound metal oxide, then a 7% silicone compound metal oxide and,
finally, the
desired 10% silicone compund metal oxide is one of many possible permutations
of this
aspect of the invention.
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As another illustration, if the goal is to produce a hydrophobized metal oxide
containing 20% by weight silicone compound, the coating may be applied in
portions of 1/5,
1/5, 2/5, and 1/5. The successive cycles of reaction yielding a metal oxide
containing 4% by
weight silicone compound, then a metalo oxide containing 8% silicone compound,
then a
S metal oxide, containing 16% silicone compound, and finally a metal oxide
containing the
desired 20% by weight silicone compound. In one alternative procedure, the 20%
by weight
silicone compound metal oxide particles are produced using two successive
steps of reacting
one-half of the effective hydrophobizing amount of silicone compound with
metal oxide
which first produces a 10% silicone compound metal oxide and then, in the
second cycle, the
desired 20% silicone compound metal oxide.
Thus, it should be understood by the above examples that the exact number of
successive cycles used to produce a particular silicone coated, hydrobphobized
metal oxide of
this invention is determined by the skilled practitioner's judgment for
allocating time and
resources to produce a particular amount of a metal oxide containing a desired
percent by
weight silicone compound. Preferrred successive coatings are in the range of
two to ten
successive coatings. In a preferred embodiment of this invention, the silicone
compound is
applied to the metal oxide in two successive cycles of contacting one-half of
the effective
hydrophobizing amount of silicone compound with the metal oxide followed by
heating.
Metal oxides coated with the silicone compound in this manner are referred to
as doubly
coated metal oxides.
While not wishing to be limited to a specific theory of why only specific
silicone
compounds of the present invention are effective, we believe that the
placement of the
reactive groups on the molecule have a dramatic effect upon the efficiency of
hydrophobization.
The reaction by which hydrophobization occurs has been studied in detail using
titanium dioxide as a representative metal oxide. The reaction by which
hydrophobization
occurs is one in which active sites on the metal oxide, in this case, titanium
dioxide, react
with the silicone to result in a covalent bond between silicone and titanium
dioxide, and the
formation of R'OH. The reaction is summarized as follows:
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Me Si
R-Si-[-(-O-Si-)a-OR']3 + TiOz -~ Ti02 + R'OH.
Me
It should be clear from the above that the presence of three R' groups on the
silicone
compound can result in the formation of multiple bonds between silicone and
the titanium
dioxide crystals. Since no water is present in this process, the metal oxide
crystals remain
intact and "frozen" in shape by the silicone which acts like a matrix for the
titanium dioxide
crystals. The silicone preserves the structure of the titanium dioxide
crystals, eliminates the
reactivity in water, and makes them hydrophobic. This allows for the exposure
of the
hydrophobic titanium dioxide to water without deleterious effect to the
titanium dioxide
caused by the reactivity of the titanium dioxide in aqueous products. All
these improvements
are a direct unexpected result of modifying the surface of the titanium
dioxide with a specific
silicone compound, freezing the structure of the titanium oxide,
hydrophobizing it, and
removing the undesired reactivity.
When drawn out in its full structure, it becomes clear that the position of
the R' groups
can be varied by variation in "a". That is, as integer "a" increases, the
distance between the R'
groups increase and the three dimensional structure changes.
Me
(O- Si- )a- OR'
~ Me
Me
R- Si-(-O-Si-)a-OR'
Me
Me
(O-Si-)a-OR'
Me
We have learned that the value of "a" is critical to the functionality of the
hydrophobizing
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process. Specifically, if "a" is zero, the treated titanium dioxide does not
maintain its
structure when exposed to water. There is little effect upon the effectiveness
of the
hydrophobization until a value of about 4 is reached. The best performance is
attained as "a"
approaches 8. As "a" is increased further, the silicone molecule becomes more
hydrophobic
5 and higher in molecular weight; this limits its effectiveness in coating the
titanium dioxide.
In effect, the reactive silicone is acting more like an oil than like a
hydrophobizing agent,
resulting in a titanium dioxide which is not covalently bonded to silicone. A
noncovalent
bond is easily removed by contact with water, resulting in agglomeration of
the titanium
dioxide, due to reactive groups present in the titanium dioxide, and silicone
oil floating on the
10 top of the aqueous formulation.
The production of R'OH as a byproduct in a dry process, as opposed to a slurry
process, is very desirable. Another approach is the use of silicone compounds
containing
silanic hydrogen compounds of the structure Si-H, which results in the
evolution of copious
amounts of flammable hydrogen gas. In addition, the use of these kinds of
compounds do not
give the desired properties.
The hydrophobizing processes of this invention may also be used to coat metal
oxides
other than zinc oxide and titanium dioxide, including, but not limited to,
iron oxide, cesium
oxide, zirconium oxide, silicon dioxide, and antimony oxide, or combinations
thereof.
Particularly useful are metal oxides that are sunscreen agents, owing to their
ability to absorb
ultraviolet radiation. Such metal oxides having utility as sunscreen agents
include, zinc
oxide, titanium dioxide, iron oxide, cesium oxide, zirconium oxide, and
silicon dioxide.
The coated, hydrophobized metal oxides of this invention may also be used in
various
combinations with other coated or uncoated metal oxides, for example, coated
zinc oxide
with coated or uncoated titanium dioxide particles. Such combinations may be
provided in
any selected ratio of coated/coated or coated/uncoated metal oxide, such as,
1:1, 1:3, 5:1,
10:1.
In a preferred embodiment the concentration of silicone compound in a silicone
polymer coated hydrophobized metal oxide particle prepared according to this
invention
ranges from 0.1 to 30 % by weight.
In another preferred embodiment the concentration of silicone compound in a
silicone
polymer coated hydrophobized metal oxide particle prepared according to this
invention
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Ranges from 0.5 to 20% by weight.
In another preferred embodiment the concentration of silicone compound in a
silicone
polymer coated hydrophobized metal oxide particle prepared according to this
invention
ranges from 1.0 to 10.0%.
In a preferred embodiment "a" is an integer ranging from 6 to 12.
In another preferred embodiment "a" is an integer ranging from 4 to 8.
In a preferred embodiment R is methyl.
In another preferred embodiment R is octyl.
In another preferred embodiment R is butyl.
In another preferred embodiment R is ethyl.
In a preferred embodiment, the process of the present invention is conducted
at a
temperature of between 80 and 100°C.
In another preferred embodiment, the process of the present invention is
conducted at
a temperature of between 90 and 100°C.
TESTING FOR SUN PROTECTION FACTOR (SPF)
It may be desirable to test a composition of the invention for its ability to
protect the
surface to which it is applied from ultraviolet radiation. Testing is
particularly important for
a composition which is useful for application to human skin, e.g., as a
sunscreen or cosmetic
composition. Sunscreens may be tested as described in the Federal Drug
Administration
guidelines entitled "Sunscreen Drug Products for Over-the counter Humaal Use,
Part II", 43
Fed. Reg. 166, 38259-38262 (August 25, 1978) (published by the U.S. Office of
the Federal
Register of the U.S. National Archives and Records Administration in
Washington D.C.).
The testing procedure is as follows.
Sunscreen testing may be performed on human male or female volunteers. For
inclusion in the test, the following criteria should be met. The subjects
should be free of any
dermatological or systemic disorder which would interfere with the results,
e.g., no known
abnormal response to sunlight, heat rash, chronic skin allergies, suntan or
sunburn, etc. The
subjects should not be under a doctor's care, or taking medication which may
mask or
interfere with the results. These determinations may be made by trained
dermatological
medical staff. The subjects should read, understand, and sign an informed
consent document,
as required by 21 C.F.R. 20. The panel of subject volunteers should be
classified as a skin
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type I, II, or III defined according to 43 Fed. Reg. 38260 (1978) and as
follows.
Type I--Always burns easily; never tans (sensitive)
Type II --Always burns easily; tans minimally (sensitive)
Types III--Burns moderately; tans gradually (light brown--normal).
The light source employed in the test is a 150 watt Xenon Arc Solar Simulator
(Berger, D. S.: Specification and design of solar ultraviolet simulators. J.
Invest. Dermatol.
53: 192 - 199 (1969), Solar Light Co., Philadelphia, Pa., Model 12S, Model 14S
or Model
600) having a continuous emission spectrum in the ultraviolet B (UV-B) range
from 290 to
320 nm. Xenon arc was selected on the basis of its black body radiation
temperatures to
6000 ° K which produces continuous UV spectra (all wavelengths)
substantially equivalent to
that of natural sunlight. This devise is equipped with a dichroic mirror
(which reflects all
radiation below 400 nm) and works in conjunction with a 1 mm thick Schott WG-
320 filter
(which absorbs all radiation below 290 nm) to produce simulation of the solar
ultraviolet A
(UVA) - ultraviolet B (UVB) spectrum. A 1 mm thick UG 5 or UG 11 filter (black
lens) is
added to remove reflected (infra-red, greater than 700 nm) heat and remaining
visible
radiation.
UVB radiation may be monitored continuously during exposure using a Model DCS-
1
Sunburn UV Meter/Dose Controller System (Solar Light Co.), formerly known as
the
Robertson-Berger Sunburn meter (R-B meter). Measurements are taken at a
position within 8
mm from the surface of the skin. The field of irradiation is 1 cm in diameter.
Realignment of
the Light Sources and calibration of the sunburn meters should be conducted at
list semi-
annually.
The SPF testing procedure is based on that described in the 43 Fed. Reg. 38264
38267 (1978). One test site area served to determine each subject's Minimal
Erythema Dose
(MED). This is executed by exposing the back to a series of timed incremental
UV exposures
at 25% intervals. The subject's smallest exposure or the least amount of
energy required to
produce erythema (MED) is the shortest time of exposure that produces
minimally
perceptible erythema at 20 to 24 hours post-irradiation. The test area is
described as the
infrascapular area of the back to the right and left of the midline. An 8%
homosalate standard
is delivered to the test site through a plastic volumetric syringe. This
standard will give a
uniform SPF of approximately 4 - 5.
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The material is then evenly applied to a rectangular area measuring 5 cm x 10
cm (50
cm2) for a final concentration of 2.0 mg/cm2. Fifteen (15.0) minutes after
application, a series
' of UV light exposures in 25% increments, calculated from previously
determined MEDs,
bracketing the intended SPF is administered from the solar simulator to
subsites within the
treated area. On the actual day of testing, another series of exposures
similar to the one given
on the pervious day is administered to an adjacent untreated, unprotected area
of the skin to
re-determine the MED. Another adjacent test site is then selected to perform
an SPF
determination on the test substance.
Responses are evaluated as follows. Twenty to twenty-four hours post-exposure,
the
volunteers are evaluated for delayed erythemic response. The smallest exposure
or the least
amount of energy required to produce erythema (MED) in the treated site is
recorded. The
SPF is then calculated according to the following equations:
SPF = MED Protected Skin/MED Unprotected Skin. Results are rejected if the
responses on the treated test site are randomly absent or out of sequence.
This is an
indication that the products are not spread uniformly. Results also are
rejected if an MED
could not be obtained due to elicited response at all exposure sites. If the
exposure series
failed to elicit an MED response on either the untreated or the applied skin
areas, the test is
then considered a technical failure and the subject's data is discarded.
The SPF of sunscreen formulations according to this invention will be in the
range of
2 to 60, preferably 5 to 50, more preferably 10 to 30, and most preferably 15
to 20.
TESTING FOR PHOTOCATALYTIC ACTIVITY (PHOTOREACTIVITY)
Photocatalytic activity, also called photoreactivity, refers to the ability of
a compound
to undergo degradation by exposure to light, such as UVA radiation. A standard
assay to test
specimens of the silicone coated, hydrophobized metal oxides of this invention
for this
photocatalytic activity is described below.
Each specimen is subjected to dispersion in analytical grade propan-2-of (750
mg/1)
sparged with pure oxygen for 10 minutes, and then exposed to a focused beam of
UVA
radiation for one hour with continuous stirring.
At the termination of the period of irradiation, approximately 10 ml of the
reaction
liquor are removed by syringe and the particular material separated by
expelling the liquor
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through a MILLIPORE filter. The clarified liquor is then injected into a gas
chromatograph
fitted with a POROPAK Q column, and the propanone peak area obtained therefrom
is
compared to that of a pre-prepared standard solution of propanone in propan-2-
ol. '
It is known that the photoreaction is of zero order and, hence, the rate of
production of
propanone can be calculated to an accuracy of approximately 1 %.
A more complete appreciation of this invention and the advantages thereof can
be
obtained from the following non-limiting examples.
EXAMPLES
Silicone Compounds
The silicone compounds useful for the preparation of the compounds of the
present
invention were provided by Siltech Inc. and conform to the following
structures:
Me
R- Si- [-(- O- Si- )a- OR']3
Me
where Me is methyl;
R is alkyl having one to ten carbon atoms;
R' is methyl or ethyl;
a is an integer ranging from 4 to 12.
Silicone Compounds Useful for the Present Invention.
The following are examples of materials which are compounds useful in treating
the
titanium dioxide according to our invention;
Silicone
E~cample ~ R' a
1 CH3 CH3 4
2 CH3 CH?CH3 8
3 CH3 CH3 12
4 C4H9 CH3 4
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C4H9 CHZCH3 12
6 CBH,~ CH3 4
7 CBH,~ CHZCH3 8
5 Silicone
Compounds
Not Useful
for the
Present
Invention
(For comparison)
Silicone
E~~ R _ R' ~-
8 CH3 CH3 0
9 CH3 CHZCH3 2
10 C4H9 CH3 0
11 C4H9 CH~CH3 2
Titanium Dioxide
Titanium dioxide used in the preparation of the compounds of the present
invention
are commercially available from, SunSmart Inc.
The titanium dioxide used in the preparation of the products in the examples
is
SunSmart's T-Cote.
Process
The compounds of the present invention are prepared by contacting titanium
dioxide
with an effective hydrophobizing amount (preferably an amount to produce metal
oxides
containing silicone polymer ranging from 0.1 % and 25 % by weight) of a
silicone which
conforms to the following structure:
Me
R- Si- j- (-O- Si-)a-OR']3
Me
where Me is methyl;
R is alkyl having one to ten carbon atoms;
R' is methyl or ethyl;
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a is an integer ranging from 4 to 12;
then heating the intermediate to a temperature of between 40 C and 100 C, for
between 2 hr
and 10 hr. During this time alcohol is removed. The reaction is considered
complete when '
97% of the theoretical alcohol is removed. The quantity of alcohol removed is
considered
more important than the time at which the material is held at temperature.
When R' is CH3, the alcohol removed is methanol. When R' is CH2CH3 the alcohol
removed is ethanol.
The titanium dioxide is coated dry. The silicone can be applied by simply
mixing it
with the titanium dioxide, or in a preferred method using traditional methods
for applying
liquids to solids like a "V" blender.
Example 12
To 90.0 grams of titanium dioxide is added an effective hydrophobizing amount
of
10.0 grams of silicone Example # 1. The powder is then mixed well. The powder
is then
placed in an oven and heated to 80 C, for 6 hr. During this time alcohol is
removed. The
reaction is considered complete when 97 % of the theoretical alcohol is
removed. The amount
of alcohol removed is determined by weighing the contained.
Examples 13-22
Example 12 is repeated only this time the specified effective hydrophobizing
amount
of the specified silicone is added in place of the 10 grams of silicone
Example 1 and the
specified number of grams of titanium dioxide are used.
Compounds of the Present Invention
Silicone Compound Titanium dioxide
xa a Example / Grams Grams
13 2 25.0 75.0
14 3 1.0 99.0
15 4 5.0 95.0
16 5 10.0 90.0
17 6 0.1 99.1
1 g 7 10.0 90.0
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19 8 25.0 75.0
20 9 1.0 99.0
21 10 5.0 95.0
22 11 10.0 90.0
Applications Results
(a) Viscosity in Formulations
The viscosity of a dispersion of titanium dioxide in octyl palmitate is also
an
indication of the effectiveness of the treatment of titanium dioxide.
Particles which are
effectively treated do not swell in oil. The more the titanium dioxide swells
the higher the
viscosity of a dispersion.
The following test formula was evaluated:
ei t Material
33.0 titanium dioxide
67.0 Octyl Palmitate
100.0
The dispersions were made using a sonic probe 100 watts at 50% power. The
viscosity was
measured using a Brookfield Viscometer. Again the higher the viscosity, the
greater the oil
swell and the less efficient the coating.
Test Material Visco~stv in formulation
Example 19 440 cps
Example 22 410 cps
Example 21 S00 cps
Untreated Ti02 960 cps
'The lower the viscosity, the more effective the surface treatment.
(b) Stability in Aqueous Vitamin C
As noted above, untreated Ti02 will react with an aqueous solution of vitamin
C to
produce a yellow color. The more intense the color, the greater the reactivity
of the Ti02. This
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offers a good analytical test for effectiveness of the treatment method.
Method '
S.0 grams of the test TiOz is added to 5 grams of a 1 % weight /weight
solution of
vitamin C in water. 0.05 grams of dioctylsulfosuccinate is then added to speed
up the wetting
of the Ti02. The resultant slurry is mixed with a magnetic stirrer for 10
minutes. 5 grams of a
2% weight/weight solution of xanthan gum in water is added under agitation.
This results in a
thick slurry which can be drawn into a film on a glass plate. The slurry is
drawn down on
Form 3NT-3 ink test coat book paper from Leneta Co in Hohokus N.J., using a #
22 wire
wound dry down bar. The film is allowed to dry 1 hour. The color of the
resultant film is
measured using an X-rite model 418 reflectance densitometer on the white
yellow filter. Four
films are cast for each product evaluated.
Untreated
Tip- Ex19 x.22 Baclsg~round
Test 1 0.20 0.17 0.17 0.16
Test 2 0.19 0.16 0.17 0.15
Test 3 0.21 0.17 0.16 0.15
Test 4 0.19 0.16 0.17 0.15
Average 0.1975 0.165 0.17 0.1 S
The background is subtracted from the measurement for a yellowing measurement.
Untreated
Ti Ex1919 Ex22
Average 0.1975 0.165 0.17
Average-
Background 0.0475 0.015 0.02
The untreated is over 3 times more yellow than Example 19 and 2 times more
yellow than
Example 22. The reduction in reactivity is a demonstration of the
effectiveness of the
coating.
The hydrophobized titanium dioxide is used in a variety of applications and
formulations. These applications include personal care sun screen
applications.
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Metal Oxide Compositions
A particular species of coated metal oxide of this invention may be combined
with
other species of coated or non-coated metal oxides to form compositions that
exhibit the
qualities of the various metal oxide species. For example, a hydrophobized
titanium dioxide
of this invention may be combined with a hydrophobized iron oxide and/or a non-
coated zinc
oxide and used in a sunscreen or cosmetic formulation.
Coated metal oxides of the invention may also be provided in admixture with
(i.e.,
uniformly dispersed within) pharmaceutically acceptable biocompatible
ingredients which
may include water, inorganic pigments, organic pigments, emulsifiers, oil
soluble sunscreens,
water soluble sunscreens, alpha hydroxy acids, dispersants, oil soluble
vitamins, water
soluble vitamins, waxes, silicone, and combinations thereof.
Example 23.
In this example, titanium dioxide and zinc oxide were coated with the silicone
compound in a manner similar to that used to produce the hydrophobized, singly
coated metal
oxides of Examples 12 to 22, described above, except that the total amount of
silicone
compound that was to be applied to the metal oxide (the hydrophobizing amount)
was
divided into two equal portions and each portion applied in two successive
cycles of
contacting each portion of silicone compound to the metal oxide followed by
heating. Metal
oxide particles produced by two successive steps of silicone application are
referred to as
doubly coated metal oxides.
The bar graph in Figure 1 shows the relative photoreactivity of titanium
dioxide (open
bar) and zinc oxide (shaded bar) particles treated in various ways: not
hydrophobized
(uncoated particles); hydrophobized in one step (singly coated) to contain a
total of S% by
weight silicone compound (coated x 1 with 5%); and hydrophobized to contain a
total of 5%
by weight silicone compound in two successive steps (doubly coated) at 2.5 %
by weight per
step (coated x 2 with 2.5% each time). Singly coated titanium dioxide
exhibited a decreased
photoreactivity compared to untreated titanium dioxide, i.e., from a relative
measurement of
197 (untreated) to 109 (singly coated). Doubly coated titanium dioxide
exhibited an even
greater decrease in relative photoreactivity from 197 (untreated) to 84. A
similar
improvement was seen in the case of zinc oxide where the relative
photoreactivity was
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decreased from 16 for untreated particles to 3.5 for singly coated particles
and 1.5 for doubly
coated particles.
Other Embodiments
5 - While the invention has been described in detail and with reference to
specific
embodiments thereof, it will be apparent to one skilled in the art that
various changes and
modifications can be made therein without departing from the spirit and scope
thereof.
Other embodiments of the invention are found within the following claims.
