U.S. patent application number 14/726679 was filed with the patent office on 2017-08-10 for method of formulating zinc oxide powder blends for balanced uva/uvb attenuation.
The applicant listed for this patent is David Schlossman, Yun Shao. Invention is credited to David Schlossman, Yun Shao.
Application Number | 20170224594 14/726679 |
Document ID | / |
Family ID | 57396968 |
Filed Date | 2017-08-10 |
United States Patent
Application |
20170224594 |
Kind Code |
A9 |
Schlossman; David ; et
al. |
August 10, 2017 |
METHOD OF FORMULATING ZINC OXIDE POWDER BLENDS FOR BALANCED UVA/UVB
ATTENUATION
Abstract
Disclosed is a composition that comprises an effective
proportion of a first metal oxide powder having a primary particle
size and a secondary particle size selected for the first metal
oxide powder to attenuate UV A and an effective proportion of a
second metal oxide powder having a secondary particle size selected
for the second metal oxide powder to attenuate UVB. The mean
secondary particle size of the first metal oxide powder is greater
than the mean secondary particle size of the second metal oxide
powder. In one embodiment, the first and the second metal oxide
powders are both zinc oxide.
Inventors: |
Schlossman; David; (Short
Hills, NJ) ; Shao; Yun; (Belle Mead, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Schlossman; David
Shao; Yun |
Short Hills
Belle Mead |
NJ
NJ |
US
US |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20160346176 A1 |
December 1, 2016 |
|
|
Family ID: |
57396968 |
Appl. No.: |
14/726679 |
Filed: |
June 1, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12328631 |
Dec 4, 2008 |
9072918 |
|
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14726679 |
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60992711 |
Dec 5, 2007 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61K 8/27 20130101; A61K
2800/413 20130101; A61K 8/29 20130101; A61Q 17/04 20130101 |
International
Class: |
A61K 8/27 20060101
A61K008/27; A61Q 17/04 20060101 A61Q017/04; A61K 8/29 20060101
A61K008/29 |
Claims
1. A method of formulating a composition containing a Zinc oxide
powder comprising: mixing a first Zinc oxide powder and a second
Zinc oxide powder in an aqueous or non-aqueous medium to prepare a
dispersion of the first and the second Zinc oxide powders; wherein
the first Zinc oxide powder and the second Zinc oxide powder both
form aggregates in the dispersion and a mean secondary particle
size of the first Zinc oxide powder is greater than a mean
secondary particle size of the Zinc metal oxide powder wherein the
mean secondary particle size for the first Zinc oxide is about 150
nm to about 260 nm and the mean secondary particle size for the
second Zinc oxide is about 130 nm or smaller.
2. The method of claim 1 wherein the primary particle size of the
first Zinc oxide is about 100 nm or smaller and a primary particle
size of the second Zinc oxide is about 10 nm to about 30 nm.
3. The method of claim 2 wherein the primary particle size of the
first Zinc oxide is in the range of about 20 nm to about 60 nm and
a primary particle size of the second Zinc oxide is about 20
mm.
4. The method of claim 1 wherein the first Zinc oxide powder is
mixed with the aqueous or non-aqueous medium before the second Zinc
oxide powder is added.
5. The method of claim 4 wherein the first and second Zinc oxide
powders are separately formulated into a dispersion that are
thereafter blended together.
6. The method of claim 1 wherein the first and the second Zinc
oxide powders are separately mixed with separate volumes of the
aqueous or non-aqueous medium and are thereafter mixed
together.
7. The method of claim 1 further comprising milling the
dispersion.
8. The method of claim 1 wherein the aqueous or non-aqueous medium
is selected from the group consisting of an oil, a hydrocarbon, a
silicone, and water.
9. The method of claim 1 further comprising mixing the dispersion
with a biocompatible excipient.
10. The method of claim 1 wherein the Zinc oxide is about 5% to
about 90% by weight of the dispersion.
11. The method of claim 10 wherein the primary particle size of the
first Zinc oxide is about 30 nm or smaller and a primary particle
size of the second Zinc oxide is about 30 nm to about 260 nm.
12. A method to make a sunscreen composition comprising: mixing a
first Zinc oxide powder and a second Zinc oxide powder in an
aqueous or non-aqueous medium to prepare a dispersion of the first
and the second Zinc oxide powders; wherein the first Zinc oxide
powder and the second Zinc oxide powder both form aggregates in the
dispersion and a mean secondary particle size of the first Zinc
oxide powder is greater than a mean secondary particle size of the
second Zinc oxide powder, powder wherein the mean secondary
particle size for the first Zinc oxide is about 150 nm to about 260
nm and the mean secondary particle size for the second Zinc oxide
is about 130 nm or smaller.
13. The method of claim 12 wherein the sunscreen composition has an
SPF of at least about 25.
14. The method of claim 13 wherein the SPF is about 30.
15. The method of claim 13 wherein the sunscreen composition has a
PFA of at least about 8.
16. The method of claim 13 wherein the sunscreen composition has an
SPF:PFA ratio of about 3.5:1 or less.
17. A method to make a cosmetic composition comprising: mixing a
first Zinc oxide powder and a second Zinc oxide powder in an
aqueous or non-aqueous medium to prepare a dispersion of the first
and the second Zinc oxide powders; wherein the first Zinc oxide
powder and the second Zinc oxide powder both form aggregates in the
dispersion and a mean secondary particle size of the first Zinc
oxide powder is greater than a mean secondary particle size of the
second Zinc oxide powder wherein the mean secondary particle size
for the first Zinc oxide is about 150 nm to about 260 nm and the
mean secondary particle size for the second Zinc oxide is about 130
nm or smaller.
18. The method of claim 17 wherein the primary particle sizes of
the composition are both around 20 nm.
19. The method of claim 17 wherein the mean secondary particle size
of the first metal oxide is about 166 nm and the mean secondary
particle size of the second metal oxide is about 130 nm or less
20. The method according to claim 1, wherein the composition
further comprises TiO.sub.2.
21. The method according to claim 1, wherein the composition
further comprises comprising organic UV absorbers, sunscreen agents
or UV protective agents.
Description
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 60/992,711, filed on Dec. 5, 2007.
BACKGROUND
[0002] The present invention relates to novel zinc oxide powder
blends, their production and use and particularly, although not
exclusively their use in cosmetics compositions. The invention
includes methods of producing the novel zinc oxide powder blends,
the zinc oxide powder blends produced, and end product formulations
incorporating the zinc oxide powder blends. Without limitation the
invention furthermore includes cosmetic, pharmaceutical and
sunscreen formulations, as well as cosmetic and sunscreen
formulations all having UV-protective properties attributable to
the incorporated zinc oxide blends. The ultraviolet ("UV" herein)
region of the electromagnetic spectrum comprises three wavebands,
designated UV A from 320 to 400 nm, UVB from 290 to 320 nm and UVC
from 200 to 290 nm. The UV A bank can be further divided into UV AI
from 320 to 340 nm and UV All from 340 to 400 nm. The visible
portion of the spectrum is generally from about 400 to about 700
nm. Natural sunlight is a potent source of UV radiation. UV
radiation may compose about 10 percent of the solar radiation
reaching the earth's surface and is well recognized as the cause of
serious biological damage to humans and other animals.
[0003] Awareness of the risks and prevalence of UV-induced skin
cancer and consciousness of the damaging cosmetic effects of
ultraviolet radiation have fostered recognition in recent years of
the desirability of avoiding or controlling the physiological
damage wrought by harmful ultraviolet radiation, especially solar
ultraviolet. UVC radiation is generally not problematic as little
if any penetrates the atmosphere, but may be hazardous if
artificial sources such as germicidal lamps or high or low pressure
mercury arc lamps are employed.
[0004] In contrast to the UVC waveband which is filtered out, both
UV A and UVB radiation reach the earth's surface from the sun and
may be harmful. Longer wavelength ultraviolet rays in the UV A
region, adjacent the visible spectrum, which reportedly constitute
99% of the UV energy reaching the earth's surface, are considered
to be the primary cause of tanning but to cause little burning
However, in the longer term UVA rays are also believed responsible
for skin aging, causing blotching, freckling, wrinkling and
comparable problems. Ultraviolet radiation in the shorter
wavelength UVB region of from 290 to 320 nm, though comprising only
about 1% of the UV energy is considered more significant in causing
burning Accordingly, protection against UVB radiation has
traditionally been a primary target of sunscreen formulation. More
recently, there has been a recognition of the desirability of also
protecting against UV A radiation to reduce long term skin
deterioration.
[0005] More seriously, both the UVA and UVB wavebands may be
implicated in skin cancers including dangerous melanomas. Skin
cancer is by far the most prevalent of all cancers and the
incidence in the US is increasing rapidly. For these and other
reasons, consistent use of a topical sunscreen is now strongly
recommended and is widespread. In light of this need, the art
contains many proposals for sunscreen agents and compositions
intended to provide protection from damaging ultraviolet
radiation.
[0006] Many and diverse UV-protective agents suitable for topical
application in creams, sprays, lotions and the like is known and
has been used in sunscreens. However, most such agents are organic
chemicals that are prone to photo degradation and may cross-react
with other components of desirable topical formulations.
Furthermore, being absorbable into the skin, organic sunscreens may
irritate the skin or cause other dermatological or allergenic
problems. The art also contains proposals for broad spectrum UV
protection.
[0007] For example, Deckner U.S. Pat. No. 5,783,174 describes
sunscreen compositions intended to provide broad protection in both
the UV A and UVB regions which compositions combine a UV
A-absorbing dibenzoylmethane sunscreen with a UVB-absorbing
benzylidene camphor sunscreen. This composition is intended to
avoid problems of photochemical instability attributable, according
to Deckner, to photoinduced interaction between dibenzoylmethane
and the widely used UVB absorber octylmethoxy cinnamate.
[0008] A more recent demand for both higher SPF ("sun protection
factor") values and for broad-spectrum protection, has led
manufacturers to combine several different organic chemical
ingredients, aggravating potential problems of photo-induced cross
reactivity. To overcome this problem, Lapidot, et al. describe in
U.S. Pat. No. 6,436,375 a method for microencapsulating at least
one of two or more active sunscreen ingredients which are
photo-unstable when formulated together. The active ingredients can
be selected for UVA and UVB activity and can be encapsulated in
separate sol-gel microcapsules. A drawback of Lapidot et al.'s
proposal is that even if problems of cross-reactivity and photo
degradation can be overcome, which may or may not be the case,
Lapidot et al. 's method still requires use of active organic
sunscreen agents which may be harmful or irritating when absorbed.
Furthermore, use of sol-gel microcapsules adds complexity and
expense and may be undesirable in some topical formulations. Such
microcapsules may also raise issues of dispersibility and
compatibility with other ingredients of end product
formulations.
[0009] There is accordingly a need for a UV-protective agent having
broad spectrum activity against harmful solar radiation and which
does not depend upon organic chemicals. In light of the problems
with organic materials, the suitability of inorganic materials may
be considered. Several commercially useful inorganic UV-protective
agents are known, notably titanium dioxide, zinc oxide and iron
oxide. Iron oxides, however are usually colored or black and
therefore have rather limited use in sunscreen applications. Also,
they may not be approved for use as sunscreens by regulatory
authorities such as the US FDA.
[0010] Thus, considerable difficulties face a formulator or other
worker seeking broad spectrum UV-protective agents that will be
satisfactory for widespread commercial use in a full range of
topical commercial products.
[0011] Elsom et al. (WO 90/11067) provide single-species metal
oxide sunscreen compositions. Specifically provided are sunscreen
compositions containing blends of titanium dioxide powders having a
particle size of 1-100 nm.
[0012] Likewise, Cowie et al. U.S. Pat. No. 4,927,464 also provides
single-species titanium dioxide compositions for absorbing UV
radiation. Cowie et al. use acicular titanium dioxide wherein the
length of the longest dimension is 10-150 nm and the particles are
coated with a mixture of alumina and silica.
[0013] Iwaya U.S. Pat. No. 5,032,090 suggests use of a combination
of titanium dioxide and zinc oxide in anti-suntan cosmetic
compositions to block ultraviolet rays in both the UVB and UV A
regions. One drawback of this approach is that titanium dioxide may
undesirably whiten or blue the skin in some formulations. Also the
use of multiple metal oxides having significant reactivity in many
sunscreen systems may complicate the issues a formulator of
compositions for human topical application must address.
Furthermore, although titanium dioxide is approved by regulatory
agencies for many UV-protective applications, it is not approved
for use in combination with avobenzone, a popular organic sunscreen
agent. In addition, titanium is not naturally present in human and
other organisms, and may therefore be an undesired ingredient for
some prospective users.
[0014] Iwaya U.S. Pat. No. 5,032,090 suggests use of a combination
of titanium dioxide and zinc oxide with a primary particle size
great than 70 nm to 300 run in anti-suntan cosmetic compositions to
block ultraviolet rays in both the UVB and UV A regions. The
primary particle size of the zinc oxide claimed is too large to be
effective in UVB.
[0015] Other formulations of the prior art use single-species zinc
oxide compositions for UV absorption. For example, Kobayashi Kose
Co. JP 60-231607 provides anti-suntan cosmetics containing 10-30%
zinc oxide having a particle diameter of <100 nm.
[0016] Mitchell et al. U.S. Pat. No. 5,587,148 discloses sunscreen
products intended to absorb both UV A and UVB radiation while
providing a clear appearance on the skin One embodiment of Mitchell
et al.'s disclosure employs micronized particles of zinc oxide
having a size up to about 0.2 .mu.m and having what are purportedly
reduced levels of toxic heavy metals, which are formulated with a
liquid carrier into a colorless emulsion. According to Mitchell et
al., this formulation "is capable of absorbing a substantial
quantity, if not all, of the UV radiation to which the user is
exposed." (Column 7, lines 15-17.) However, the Mitchell et al.
specification provides little, if any, support for this conclusion.
Other distinct embodiments proposed by Mitchell et al. include: use
of large crystals of zinc oxide, measuring between about 1-100
microns in diameter; and use of transparent plastic spheres
measuring between about 0.01-100 microns in diameter which
incorporate a UV-absorbing additive.
[0017] Cole et al. U.S. Pat. No. 5,340,567 provides sunscreen
products intended for UV absorbance. Cole et al. provide mixed
metal oxide compositions containing titanium dioxide having a
particle size of less than about 35 nm and zinc oxide having a
particle size of less than about 50 nm. The metal oxide particles
used by Cole et al. are each of a single substantially uniform
size.
[0018] A disclosure by inventors herein Yun Shao and David
Schlossman, "Effect of Particle Size on Performance of Physical
Sunscreen formulas" PCIA conference, Shanghai, China R. P. (1999)
("Shao et al. 1999" hereinafter) and available, at the date of this
application, describes some of the effects of size, surface
treatment, dispersion vehicle, dispersant and other factors on the
UV-protective performance of inorganic sunscreens, notably titanium
dioxide and zinc oxide. Shao et al. 1999 emphasize the importance
of studying size reduction and the relationship between particle
size and performance.
[0019] Shao et al. 1999 describe use of dispersions, or
"pre-dispersions" of titanium dioxide and zinc oxide, intended for
formulation with other ingredients to provide useful end product.
Shao et al. 1999 concluded at that time that a high loading of
solids in the dispersion were important to size reduction and that
other factors should also be considered, including pigment
selection, surface treatment, vehicle and dispersant. Titanium
dioxide is described as providing excellent protection against UVB
along with effective UV A protection at a larger size where
scattering may contribute significantly. However, such larger sizes
may sacrifice some degree of SPF and transparency.
[0020] The protection afforded by zinc oxide is considered by Shao
et al. 1999 to vary inversely with particle size. Also, zinc oxide
is described as providing efficient UVA protection, often with a
low SPF. One difficulty these findings present to the worker
seeking to provide a broad-spectrum inorganic UV-protective agent
suitable for topical application, is that desired sizes of titanium
dioxide particles may cause whitening on the skin, as may be
understood from FIG. 5 of Shao 1999. (Nor does Shao et al. 1999
describe an adequate zinc oxide formulation.
[0021] Another disclosure of inventors, Yun Shao and David
Schlossman herein, namely Discovering an Optimum Micropigment for
High UV Shielding and Low Skin Whitening, 23rd IFSCC Congress
Orlando 2004 ("Shao et al. 2004" hereinafter) describes studies on
the UV attenuation of dispersions of titanium dioxide having a
primary particle size ("PPS") as small as 15 nm and of zinc oxide
as small as 20 nm which studies include studies of their in vivo
SPF efficacy. Shao et al. 2004 conclude that size reduction of
titanium dioxide and zinc oxide can remarkably improve the
appearance of a sunscreen lotion and can improve the SPF in many
cases. However, according to Shao et al. 2004, if the size of the
titanium dioxide particles is too small, the energy absorption may
shift to UVC wavelengths, weakening the attenuation in the UV A and
UVB wavebands. Shao et al. 2004 conclude that zinc oxide could
provide an effective SPF at (secondary) particle sizes under 130
nm, but "at the cost of UV A protection".
[0022] In this specification, "primary particle size" may be
understood to reference an average or mean particle size of the
metal oxide as dry powder while "particle size" sometimes
referenced herein as "secondary particle size" for greater clarity,
can be understood to reference the average mean particle size as it
is determined in a dispersion of the metal oxide powder in a
liquid.
[0023] As may be understood from Shao et al. 2004, secondary
particle size may often be more important for ultraviolet
protection than is the primary particle size, but the primary
particle size of the dry powder is often, but not always, a
principal factor in determining the secondary particle size in a
liquid dispersion. Some of the data described in Shao et al. 2004
shows that secondary size does not always correlate with primary
size. The secondary particle size will usually be substantially
greater than the primary particle size, possibly as much as five
times greater or even more.
[0024] In vivo studies reported in boxes 7-9 of Shao et al. 2004
describe several properties of sunscreens employing the described
titanium dioxide and zinc oxide dispersions, including the SPF, the
SPF per % of active ingredient and, in box 8, the PFA. "PFA" is a
measure of the protection afforded against UVA. Desirable values
for PFA may be in the range of from about 4 to about 8. Referring
to box 8, which addresses the UV protection of zinc oxide
dispersions, no PF As are reported for the first three test
samples, reading down Table 7, which are all described as having
relatively smaller (secondary) particles sizes, "PS(nm)", of 110 nm
or 130 nm. The last three samples are described as having larger
(secondary) particles sizes of 228 nm, or greater, and yield PFAs
which are in the target range.
[0025] Elsom et al. (WO 90/11067) provide sunscreen compositions
which comprise a blend of different particle sizes of titanium
dioxide. Preferred compositions comprise 10 to 70% of titanium
dioxide having a mean primary particle size of about 15 nm and at
least one further grade of titanium dioxide having a mean primary
particle size of between about 30 nm and about 50 nm. One drawback
of this approach is that titanium dioxide may undesirably whiten or
blue the skin in some formulations. The compositions are described
as substantially transparent, however, because the refractive index
of titanium dioxide is 2.6 they are likely to be too whitening when
the objective is to obtain an SPF 25 with a UV balance of 4:1.
[0026] "Shao et al. 2004" is here described for the sake of
completeness in elucidating the background of the present
invention. However, it is to be understood that no admission is
made regarding the availability of Shao et al. 2004 as a reference
in the United States or any other state or region against the
claims of the present application.
[0027] Thus notwithstanding the foregoing and other proposals in
the art, there is a need for improved UV-protective compositions
having properties satisfying the various cosmetic and prophylactic
needs of the end user as well as the requirements of a cosmetic
formulator who must provide appealing, functional products which
can be provided to consumers in a satisfactory and aesthetic
condition.
[0028] In an earlier filed P.C.T. Patent Application No.
PCT/US2006/041417, filed Oct. 23, 2006, we describe a composition
which provides an inorganic UV-protective composition which can
provide broad-spectrum UV protection, while also being capable of
being formulated into end products which have good transparency to
visible light on the skin
[0029] Generally, in accordance with the present invention,
sunscreen ingredients for cosmetics, sun tanning lotion, or the
like in both powder and in liquid dispersion form are made from two
different sunscreen materials. Each of these two different
sunscreen materials is selected for its characteristic of
addressing either the UV A or the UVB component of sunlight. In
connection with this, it is noted that both of these components
will attenuate UVA and UVB, but are, in the context of the
multi-mode formulations of the present invention, more effective in
addressing either the UV A or the UVB component.
[0030] A desirable additional object of the invention is to provide
an inorganic UV-protective composition capable of being formulated
into dispersions which are non-whitening or induce little whitening
at high solids loadings. A still further useful object is to
provide dispersions containing the inorganic UV-protective
composition that avoid or induce little bluing on pigmented
skin.
[0031] These and other objects can be achieved by one or more
embodiments of the invention described herein.
[0032] In one aspect, the invention provides a zinc oxide powder
composition for UV-protective use comprising a blend of:
[0033] a) an effective proportion of a first zinc oxide powder
component having a first particle size selected for the first zinc
oxide powder component to attenuate UVA; and
[0034] b) an effective proportion of a second zinc oxide powder
component having a second particle size selected for the second
zinc oxide powder component to attenuate UVB;
[0035] wherein the mean particle size of the first zinc oxide
component is greater than the mean particle size of the second zinc
oxide component.
[0036] The relative proportions of the first and second zinc oxide
components can be adjusted, or selected, to provide a desired
balance of UV A versus UVB protection. For example, the proportion
by weight of the first component to the second component may be
selected to be in the range of from about 1:2 to about 2: 1. Some
useful embodiments of the invention employ a proportion by weight
of the first component to the second component in the range of from
about 1:1.4 to about 1:1.
[0037] In another aspect, the invention provides a UV-protective
composition comprising an effective amount of a first zinc oxide
particulate component having a mean primary particle size in the
range of from about 30 to about 200 nm and an effective amount of a
second zinc oxide particulate component having a mean primary
particle size in the range of from about 10 to about 30 nm. As
indicated above, "primary particle size" references the size of the
dry, untreated powder.
[0038] In a further aspect, the invention provides an UV-protective
composition comprising a dispersion in a liquid vehicle of an
effective amount of a first zinc oxide particulate component having
a mean secondary particle size greater than about 180 nm and an
effective amount of a second zinc oxide particulate component
having a mean secondary particle size less than about 150 nm. As
indicated above, the secondary particle size references the size of
the particles in the dispersion. Particle sizes referenced herein
are as determined by light scattering analysis, as described
hereinafter unless otherwise indicated explicitly or by the
context.
[0039] Suitable dispersions may employ hydrocarbon or other fluids
or oils or silicone fluids as liquid vehicles, although aqueous
vehicles may also be used. The dispersions are preferably
solids-rich. Usefully, the solids-rich zinc oxide dispersions may
employ effective, usually small, proportions of chemical dispersing
agents, or dispersants, as is known to those skilled in the art.
Also the zinc oxide particles may be coated to enhance their
dispersibility, as is also known in the art.
[0040] Alternatively, the formulator may incorporate the zinc oxide
powder blend, in powder form, with other suitable ingredients to
prepare a final product. As a further alternative the zinc oxide
powder components, rather than being pre-blended may be separately
added.
[0041] The two zinc oxide components can be supplied for
incorporation into the UV-protective product as a particulate or
powder blend or may be separately added to one or more other
ingredients to provide the UV-protective composition. Some process
embodiments of the invention include steps of blending the two or
more dry zinc oxide powder ingredients together and adding the
blend to other ingredients. Pursuant to the invention it is
believed that, in end product formulations, the first and larger
zinc oxide component can provide useful UVA protection and the
second and smaller zinc oxide component can provide useful UVB
protection.
[0042] The first zinc oxide powder component can have a mean
primary particle size in the range of from about 50 to about 200 nm
to provide UV A protection. In one embodiment of the invention the
primary particle size of the first zinc oxide component is in the
range of from about 60 to about 100 nm.
[0043] The second zinc oxide powder component can have a mean
primary particle size in the range of from about 10 to about 30 nm
to provide UVB protection. In another embodiment of the invention
the primary particle size of the second zinc oxide component is
about 20 nm.
[0044] Our earlier composition contemplated embodiments employing
combinations of the mean particle sizes of the first and second
components, for example one tranche of zinc oxide particles having
a mean size in the range of about 50 to about 200 nm with another
tranche of zinc oxide particles having a mean size in the range of
about 10 to about 30 nm, for particles of size of from about 60 to
about 100 nm of the first component may be combined with particles
of size of about 20 nm of the second component.
SUMMARY
[0045] In accordance with the present invention, it has been
discovered that when it is desired to fabricate blends of zinc
oxide intended to provide protection against both UV A and UVB
radiation, effectively secondary particle size is of particular
importance in achieving the desired attenuation in the UV A range,
while primary particle size is relatively unimportant. Conversely,
while secondary particle size is determinative in the case of
attenuating UVB radiation, primary particle size is desirably kept
within certain ranges. Moreover, in accordance with the present
invention, the distribution of particle sizes, and more
particularly the content of oversize particles (for example, those
greater than 280 nm) may be particularly important in preventing
whitening.
DETAILED DESCRIPTION
[0046] Some embodiments of the invention, and of making and using
the invention, as well as the best mode contemplated of carrying
out the invention, are described in detail below. The following
more detailed description of the invention is intended to be read
as a whole with the preceding summary and background descriptions
which may also include pertinent description of the invention, the
scope of application of the invention or of elements of the
invention, as will be apparent to those skilled in the art, in
light of this specification when read as a whole.
[0047] The present invention provides novel inorganic compositions
of particulate, i.e. powdered, UV-protective ingredients that have
broad spectrum activity and provide useful absorption and/or
scattering in both the UV A and UVB wavebands of the solar energy
received at the earth's surface.
[0048] In one embodiment, the inventive compositions comprise first
and second zinc oxide powder components having particle sizes, or
size distributions chosen to selectively attenuate, by absorption,
scattering or both absorption and scattering, the UV A and UVB
wavebands respectively. For example, the one component may have
relatively larger particles to selectively absorb UV A and the
other component may have relatively smaller particles to
selectively absorb UVB. Desirably, the two zinc oxide powder
components can be formulated into compositions, such as
dispersions, which are transparent when topically applied, for
which purpose relatively small, submicron sized particles may be
employed.
[0049] UV-protective agents are agents which help or are intended
to help protect organisms, especially humans and other susceptible
animals, from the harmful effects of UV radiation, notably, without
being so limited, solar radiation at the earth's surface.
Typically, although not exclusively, such protection is obtained by
topical application to the skin and other surfaces of compositions
formulated with suitable, protective proportions of one or more
UV-protective agents. It will be understood that compositions,
including compositions described herein, which effectively protect
human skin, may have other useful protective functions e.g. in
industrial coatings, plastics or other products.
[0050] "UVA" as used herein references the electromagnetic waveband
from about 320 nm to about 400 nm and "UVB" references the waveband
from about 290 nm to about 320 nm. The first zinc oxide component
can be selected to provide an attenuation peak in the UV A
waveband, by absorption and/or scattering of the radiation which
attenuation peak is useful in preventing the harmful effects of UV
A radiation. Comparably, the second zinc oxide component can be
selected to provide an attenuation peak in the UVB waveband, by
absorption and/or scattering of the radiation which is useful in
preventing the harmful effects of UVB radiation. Such a combination
of components can provide effective broad-spectrum protection
against the UV components of atmospherically filtered solar
radiation.
[0051] The inventive zinc oxide powder blends are to be understood
to include not only dry physical admixtures of the two defined zinc
oxide powder components but also other combination these two zinc
oxide powder components, for example dispersions of the two
components in a liquid vehicle, which dispersions are formed by
separate addition of the individual zinc oxide powder components to
the liquid vehicle. End products, or intermediate products, which
are themselves powder blends, or largely comprise powder blends,
can also comprise the individually added or blended zinc oxide
components.
[0052] The invention provides compositions comprising relatively
simple ingredient mixtures that are attractive to a cosmetics
formulator to use in preparing formulations for topical
application. Such formulations may include, without limitation,
sunscreen oils, creams, lotions and the like, and other cosmetic,
dermatologic, pharmaceutical or medicament compositions for topical
or other use. One object fulfilled by the invention is to provide
beneficial UV-protective compositions which avoid presenting new
challenges or concerns to a cosmetics formulator. Another is to
provide the formulator easy-to-use UV-protective compositions which
can readily be incorporated not only in topical sunscreen products
to provide protection against acute exposure, but also in other
cosmetic products including, without limitation, products such as
lipsticks and lip balms, makeups, nail polishes, hair treatments,
and so on, to provide everyday protection.
[0053] With these objectives in mind, the formulator may be faced
with the daunting challenge of assessing not only the individual
safety and efficacy of a long list of ingredients under various
conditions, but also that of determining whether adverse
cross-reactivity or other interactions may occur. For these
understandable reasons, the formulator may be reluctant to employ
unfamiliar or untried ingredients or combinations of ingredients
that do not have a long history of safe and effective use. The
compositions of the present invention avoid these problems by
providing novel UV-protective compositions which employ active
ingredients that are known to be safe and effective and have a long
history of satisfactory use in a wide variety of cosmetic and other
formulations.
Proportion of Zinc Oxide in Solids Dispersions
[0054] The dual component zinc oxide materials of the invention can
be dispersed into a suitable lipid, silicone or aqueous liquid
vehicle in any desired proportion that will provide a smooth,
homogenous dispersion and an effective proportion of zinc oxide for
the intended purpose. For example, a proportion of from about 5 to
about 90 percent by weight the zinc oxide material, based on the
weight of the dispersion, can be employed.
[0055] Some useful embodiments of the invention employ a zinc-oxide
solids loading, or proportion of at least about 20 percent,
desirably at least about 30 percent, by weight, for example a
proportion in a range of from about 20 to about 80 percent by
weight. Lower proportions containing, for example, up to about 40
percent zinc oxide material, can be useful for direct topical
application or other purposes. Higher proportions containing, for
example, from about 50 to about 80 percent zinc oxide material, can
provide useful "premix" solids-rich dispersions suitable for use by
cosmetic, pharmaceutical or other formulators for combining with
other ingredients to provide useful consumer or other products, as
described herein.
[0056] For higher SPF values in the end product, and for other
purposes, it may be desirable to use a high proportion of zinc
oxide solids in the dispersion, consistent with providing a stable,
homogenous, dispersion that has enough fluidity for processing. In
other words, a high loading of solids is generally desirable for
product efficacy, but a loading which is too high may cause
processing difficulties or yield a poor quality product. Some
useful embodiments of the invention employ more-or-less the highest
loading of zinc oxide which can be obtained in a smooth dispersion
that has sufficient fluidity for processing. Such products may have
a solids content in the range of from about 40 to about 75 percent
by weight of the dispersion.
[0057] A high proportion of solids in the liquid dispersion medium
can be beneficial to the objectives of the invention, as is
described herein. For example, during milling of the dispersion,
when milling is employed, a high proportion of solid particles can
enhance attrition, causing more collisions between particles and
converting more of the input energy to size reduction. In addition,
a high proportion of solids provides the resultant dispersion with
a high viscosity which may be advantageous, for example helping to
control re-agglomeration.
Proportions of Zinc Oxide in End Products
[0058] Any proportion of zinc oxide powder or powder blend, may be
employed in end product formulations that is effective for one or
more of the purposes described herein may be employed.
[0059] For example a desirable proportion of the two-component zinc
oxide material of the invention may comprise from about 0.1 percent
to about 50 percent by weight of the end product. Desirably, the
proportion is from about 1 to about 40 percent by weight. Higher
proportions in either of these ranges, for example from about 2 to
about 30 percent can be useful in a variety of preparations that
function primarily as sunscreens and lower proportions, for example
from about 0.1 to about 5 percent by weight can be useful in
preparations having other utilities where a lower level of UV
protection is considered useful, e.g. everyday cosmetics.
[0060] The invention includes embodiments of sunscreen or
UV-protective compositions intended for topical application to
skin, nail or hair comprising from about 2 to about 25 percent by
weight zinc oxide material. One such embodiment, or group of
embodiments, has a proportion of zinc oxide material of from about
5 to about 10 percent by weight of the end product. Another employs
from about 10 to about 15 percent by weight of zinc oxide
material.
Preparation of Dispersions and Formulation into End Products
[0061] Various methods can be employed to prepare the zinc oxide
materials of the invention for delivery in a useful form to a
cosmetics, pharmaceutical or other formulator, for formulation into
UV-protective products useful to consumers or other end users.
[0062] For example, a specialist vendor, or other supplier may
prepare a solids rich dispersion of the zinc oxide powder blend in
a liquid vehicle for use by a formulator, or possibly for direct
topical application. The liquid vehicle in such solids-rich
dispersions may comprise a suitable oil, a hydrocarbon, a silicone
fluid, an aqueous medium or other useful and suitable liquid
medium.
[0063] The solids-rich zinc oxide dispersions in oil can for
example be prepared by first mixing two or more dry powdered
commercially available zinc oxide powder components of desired size
with the liquid vehicle, in a homogenizer or blender to break up
agglomerates. Suitable zinc oxide materials are available inter
alia from Tayca Corp. and Advanced Nanotechnology Ltd., (Welshpool,
Western Australia). Suitable oils include, for example, isononyl
isononanoate, octyl dodecyl neopentanoate and many other oils as
are known in the cosmetics, pharmaceutical and other relevant arts.
Other suitable liquids include aqueous vehicles and silicone
fluids.
[0064] The product of mixing, using a high sheer mixer or
homogenizer, may be satisfactory, without milling.
[0065] However, if desired the dispersion product of the
homogenizing or blending process can then be processed in a ball
mill or the like to reduce agglomerates and aggregates into smaller
particles, continuing milling until a smooth, homogenous dispersion
is obtained. The zinc oxide powder components can be added as a
powder blend or may be added separately to the liquid vehicle,
while mixing, and/or agitating.
Surface Treatments or Coatings
[0066] Usefully, the zinc oxide powder materials may be surface
treated to enhance the quality of the dispersion, increase the
proportion of solids that can be successfully loaded into the
liquid vehicle and thus help provide the end product with a small
particle size. If desired, the surface treatment can be selected
according to the nature of the intended end product, some options
for which are described below.
[0067] One or more surface treatment materials, for example a
coating agent, is or are blended together with the zinc oxide
powder, employing a small quantity of solvent or dispersion
vehicle, if needed for workability. This mixture is then heated,
while blending or agitating, to a suitable temperature, e.g. from
about 110 to about 130 OC and for an appropriate time e.g. from
about 2 to about 4 hours or other suitable time period in the range
of from about 30 minutes to 24 hours to effect the surface
treatment and any associated chemical reaction such as surface
bonding, polymerization or cross-reaction. The treated zinc oxide
material is mixed into a suitable cosmetic or other liquid vehicle
and milled to a fine particle size, for example to the finest size
routinely obtainable.
[0068] Some suitable surface treatments are described in Shao et
al. 1999 and include: use of metal soaps, titanates such as
isopropyl titanium triisostearate or lecithin or the like to
provide the treated zinc oxide particles with lipophilic
properties; use of various silicone materials such as methicone,
dimethicone and multifunctional reactive silanes, e.g. triethoxy
caprylylsilane to provide hydrophobic properties; and use of
reactive fluorinated compounds such as fluoroalcohol phosphate to
provide both lipophobic and hydrophobic properties.
[0069] Other materials can be used for surface coating as known to
those skilled in the art, or as becomes known as the art develops.
Some such useful coatings, coated zinc oxide materials and
formulations embodying same are disclosed in U.S. Patent
Publications Nos.: 2005/0037041 "Duplex coated color lake and other
powders, their preparation and cosmetic and other uses"; U.S.
2004/0234613 "Hybrid coated cosmetic powders and methods of making
and using same"; and U.S. 2003/0161805 "Organosilicon treated
cosmetic powders, their production and use"; each of which patent
publications has at least one inventor in common with the present
application and are commonly owned with the present application at
the date hereof. The disclosure of each of said patent publications
is hereby incorporated herein by this specific reference
thereto.
Dispersing Agent
[0070] With advantage a dispersing agent or dispersant can be
employed in the dispersion to improve dispersion quality, for
example PEG 10 dimethicone or acrylates/ethylhexyl
acrylate/dimethicone methylacrylate copolymer, or any other
suitable dispersing agent as is known or becomes known in the art,
some examples of which include polymeric acid amines formed by
condensation of a polymeric acid with an amine, for example as
described in U.S. Pat. No. 4,349,389 at col. 5, 11.5-35, the
disclosure of which is hereby incorporated herein by reference
thereto. The polymeric acid can be a polyester derived from a
suitable hydroxy organic acid, for example hydroxystearic acid. The
amine employed can be a lower alkylamine, di-or tri-lower
alkylamine, or a polyamine for example methylamine, diethylamine,
triethylamine, dimethylaminopropylamine, ethylenediame,
triethylenetetramine, guanidine or a derivative thereof. Useful
dispersing agents include SOLSPERSE (trademark), SOLSPERSE 9000,
SOLSPERSE 3000 dispersing agents available from ICI Americas Inc.,
Wilmington, Del. and the dispersing agents disclosed in U.S. Pat.
Nos. 4,349,389, 3,778,287 and 4,157,266. Many other suitable
dispersing agents will be known to those skilled in the art, or
will become known as the art evolves.
[0071] For example, one useful embodiment of the invention employs
a polyhydroxystearic acid as a dispersant for an oil, ester or
hydrocarbon vehicle. Another embodiment employs castor oil
phosphate as a dispersant for such vehicles. For silicone-based
dispersions, in silicone fluids, a further embodiment of the
invention employs a silicone polyether, for example PEG-IO
dimethicone as a dispersant.
Dispersion Analysis
[0072] With advantage, the viscosity and particle size of the
resultant dispersion are then determined. Viscosity can be measured
using a Brookfield RVT viscometer, or other suitable instrument,
after incubating samples at 25.degree. c for 24 hours. Particle
size can be measured by any suitable method. One useful particle
size measurement employs a light scattering analyzer, for example a
NICOMP 370 photo-correlation particle analyzer. Secondary particle
sizes described herein are to be understood to be as determined by
such an instrument. Primary particle sizes are as determined and
specified by a product supplier. If desired, the primary particle
size can be determined or verified by such light scattering
analytic methods. As is known in the art, primary particle size can
be measured from a SEM (scanning electron micrograph) picture or
calculated from the specific surface area.
[0073] The formulator, or other party can mix the solids-rich zinc
oxide dispersion, produced by the above or other suitable methods,
with other ingredients to provide a desired cosmetic,
pharmaceutical or other product for topical application. Other
suitable ingredients include cosmetic or pharmaceutical vehicles,
pharmaceutically or cosmetically active ingredients, excipients,
additives, colorants, pigments, perfumes, water and the like, as is
known, or becomes known, or apparent in the respective art.
Blending, grinding, milling, mixing, heating, agitation,
homogenization and other techniques may be employed, as will be
understood by these skilled in the art, to combine and process the
various ingredients into useful end products.
[0074] If desired, and with advantage, in vivo tests can be
performed on the sunscreen compositions produced, to determine in
vivo values of SPF, optionally using a US FDA, or other suitable
protocol. Such in vivo tests can also be used to determine
appearance, spreadability, aroma, and other aesthetic qualities, if
desired.
[0075] In another embodiment of this aspect of the invention, the
zinc oxide powder blend, or the components thereof is, or are,
admixed with other powder ingredients, for example pigments,
fillers and so on, to provide a powdered end product, for example
make up.
Supplemental Organic Sunscreen Agent
[0076] The invention also provides a UV-protective composition
comprising the dual-component zinc oxide material of the invention
in combination with an organic sunscreen agent or agents. Usefully,
the organic sunscreen agent can be selected to provide protection
against UVB radiation, supplementing that provided by the inventive
zinc oxide material. Any desired organic UV-protective agent may be
employed, as known, or that becomes known, to those skilled in the
art, provided it is compatible with zinc oxide and other
ingredients employed in the end product.
[0077] One example of a suitable organic UV-protective agent that
may be employed is octylmethoxy cinnamate (or 2-ethylhexyl
p-methoxycinnamate), commonly abbreviated as "OMC". Others include
p-aminobenzoic acid, various benzophenones, oxybenzone, avobenzone,
salicylates, various other cinnamates and such organic sunscreen or
UV-protective agents as are described in Gildenberg U.S. Pat. No.
6,217,852 and in the patents and other publications referenced in
Gildenberg. The disclosure of each one of said patents and other
publications is hereby incorporated herein by this specific
reference thereto.
[0078] Some examples of other organic UV-protective agents that can
be employed include octyl salicylate, octocrylene, oxybenzone,
2-ethylhexyl NsNdimethylaminobenzoate, p-aminobenzoic acid,
2-phenyl-benzamidazole-5-sulfonic acid, homomenthyl salicylate,
avobenzone (e.g., Parsol 1789), DEA pmethoxycirmamate, octylmethoxy
cinnamate, 4/4'-methoxy-tbutyldibenzoylmethane,
4-isopropyldibenzoylmethane, 3-(4-methylbenzylidene) camphor,
3-benzylidene camphor, 4-N,N-dimethylaminobenzoic acid ester with
2,4-dihydroxybenzophenone, 4-NsN-dimethylaminobenzoic acid ester
with 2-hydroxy-4-(2-hydroxyethoxy)benzophenone,
4-N,N-dimethylaminobenzoic acid ester with
4-hydroxydibenzoyl-methane, 4-NsN-dimethylaminobenzoic acid ester
with 4-(2-hydroxyethoxy)dibenzoylmethane,
4-NsN-di(2-ethylhexyl)aminobenzoic acid ester with
2,4-dihydroxybenzophenone, 4-N,N-di(2-ethylhexyl)aminobenzoic acid
ester with 4-hydroxydibenzoylmethane,
4-N,Ndi(2-ethylhexyl)aminobenzoic acid ester with
4-(2-hydroxyethoxy)dibenzoylmethane,
4-NsN-(2-ethylhexyl)methylaminobenzoic acid ester with
2,4-dihydroxybenzophenone, 4-NsN-(2-hydroxyethoxy)benzophenone,
4-N,N-(2-ethylhexyl)methylaminobenzoic acid ester with
4-hydroxydibenzoylmethane, 4-N,N-(2-ethylhexyl)methylaminobenzoic
acid ester with 4-(2-hydroxyethoxy)dibenzoylmethane and mixtures of
any two or more of the foregoing organic UV-protective agents.
[0079] Any suitable proportion of the organic sunscreen agent can
be employed. For example, the quantity, by weight may be somewhat
less than the quantity of the inventive zinc oxide material
employed, for example, from about 0.1 to about 2 parts organic
agent, or agents, per part of zinc oxide material referring to the
combined weight of organic agents if more than one is employed.
Some useful embodiments of the invention employ from about 0.5 to
about 1.2 parts organic agent, or agents, per part of zinc oxide
material, one embodiment of which employs about 0.8 parts organic
agent, or agents, per part of zinc oxide material.
Benefits
[0080] The novel dual-component zinc oxide powder materials of the
present invention, compositions formulated from the dual zinc oxide
powders and the related methods described herein, provide a
flexible, biocompatible solution to many ultraviolet protection
problems. Cosmetic, dermatological, pharmaceutical, veterinary and
other formulators are provided with a novel means of affording both
UV A and UVB protection with good transparency, biocompatibility
and stability, in sunscreens and other products.
[0081] The invention provides a simple inorganic composition, or
ingredients therefor, useful embodiments of which have good
broad-spectrum ultraviolet efficacy, good SPF (sun protection
factor) and PFA (protection factor UVA) which is easy to use,
attractive to a cosmetics formulator who must consider physical and
chemical properties and interactions of a multiplicity of
ingredients. Useful embodiments of the invention also provide good
transparency enabling end products that provide good protection
against sunlight, are non-allergenic and suitable for extended
daily wear and which are attractive to a wide range of users by
virtue of their freedom from whitening or bluing.
[0082] The provision, by means of the invention, of broad spectrum
UV protection using zinc oxide alone, is chemically and
biochemically advantageous. The properties of zinc oxide are well
understood. The complications of using multiple, chemically diverse
components can be avoided. If it is desired to employ an organic
sunscreen agent for supplemental UV A protection, the use of a
single chemical entity for primary broad spectrum protection limits
potential interactivity problems.
[0083] The various proportions of ingredients described herein are
to be understood to be by weight based on the weight of the
relevant composition comprising the ingredient in question, unless
the context indicates otherwise.
[0084] Products were prepared utilizing zinc oxide of various size,
which were treated, by methods known to one of skill in the art,
with isopropyl titanium triisostearate or triethoxycaprylylsilane
crosspolymer for easy dispersion. The treated zinc oxide was
dispersed in isononyl isononanoate using a convention media mill,
such as that made by Premier or Netzsch. Alternately, C12-C15 alkyl
benzoate may be used as an effective substitute for isononyl
isononanoate. The mixture was then milled to the desired size in a
manner known to one of skill in the art.
[0085] The resultant zinc oxide dispersions were used to make a
water in oil sunscreen lotion, as more fully appears below. SPF
(protection against UVB) and PFA (protection against UVA) were
tested in-vivo on three panelists. To determine PFA, the PPD
(persistent pigment darkening) method was used. Particle size in
the dispersion was measured using a NICOMp C370 photo correlation
size analyzer, Mean size of intensity weighted distribution is
given below. Primary particle size of zinc oxide is calculated from
their BET specific surface area.
[0086] It is noted that the component referred to as providing UV A
protection also provides some UVB protection and vice versa, and
that such reference is to the primary function.
[0087] Water in oil sunscreen formulas were prepared to investigate
the effect of particle size on PF A, which, as noted above,
measures effectiveness in protecting against UVA. Table 1
illustrates the composition, by weight percent, of Formula 1,
results for which are reported in Table 2.
TABLE-US-00001 TABLE 1 Phase W/W % INCI NAME 1 3.00 Cetyl
Dimethicone 7.50 Cyclomethicone 6.00 Isononyl Isononanoate 0.50
Methyl Glucose Sesquistearate 2.00 Dioctyl Malate 5.00
Polyglyceryl-4 Isostearate (and) Cetyl Dimethicone Copolyol (and)
Hexyl Laurate (ABIL.RTM.WEO9 available from DeGussa) 2 21.33 Zinc
Oxide dispersion in Isononyl Isononanoate 3 51.07 Water 0.50 Sodium
Chloride 2.50 PEG150/Decyl Alcohol/Smdi Copolymer (Aculyn 44
available from Rohm & Haas) 0.60 Phenoxyethanol (and) parabens
(Phenonip.RTM. available from Nipa) 100
[0088] Formula 1 was prepared by mixing the Phase 1 ingredients,
namely cetyl dimethicone, cyclomethicone, isononyl isononanoate,
methyl glucose sesquistearate, dioctyl malate, and polyglyceryl-4
isostearate, cetyl dimethicone and hexyl laurate, using a propeller
mixer. Mixing is done until the mixture exhibits uniformity. Mixing
may be carried out at room temperature or, optionally, heated to a
temperature of 70-80.degree. C. The zinc oxide dispersion of Phase
2 is then added to the contents of the propeller mixer to complete
the "oil" phase.
[0089] The dispersion is made using a conventional method.
[0090] In a separate propeller mixer, the Phase 3 ingredients,
water, sodium chloride, peg-150/decyl alcohol/smdi copolymer,
Phenonip.RTM., are mixed at a temperature between 70.degree. C. and
80.degree. C., until the mixture is uniform, thus forming the water
phase. Phase 3 is then slowly poured into the mixture of Phase 1
and Phase 2, and mixing is continued until uniformity is achieved.
Overmixing is not a problem and mixing may thus be continued until
uniformity stabilizes. The resulting mixture is then homogenized at
3000 rpm in a conventional homogenizer for 10 minutes at
70-80.degree. C. The finished mixture is then allowed to cool to
room temperature.
TABLE-US-00002 TABLE 2 Formula 1 2 3 4 5 PPS (nm) -100 15-35 60 20
20 PS in disp. 263 228 163 166 130 (nm) Active (%) 16 14.97 14.97
14.97 13.80 SPF 12.6 14 20.4 17.4 25.4 SPF/Active % 0.79 0.93 1.36
1.16 1.84 PFA 5.83 7.50 7.58 8.17 4.75 PFA/Active % 0.46 0.50 0.51
0.54 0.34 SPF/PFA 2.2/1 1.9/1 2.7/1 2.1/1 5.4/1
[0091] In Table 2, the size of primary particles in manometers is
reported as "PPS". "PS" refers to secondary particle size, or the
particle size of aggregates in the dispersion. "Active (%)" refers
to the percentage by weight of the active ingredient, namely the
zinc oxide. "PF A" refers to UV A protection.
[0092] Formulae 2-5 were prepared in the same manner as a Formula
1, except for the use of zinc oxide having the primary particle
size and the secondary particle size indicated in Table 2, and
except for the adjustment of the amount of isononyl isononanoate.
More particularly, the adjustment of the amount of isononyl
isononanoate was made to compensate for the change in percent
actives. For example, in Formula 2, the amount of zinc oxide is
reduced by 1.03 parts. Accordingly, the amount of isononyl
isononanoate was increased by 1.03 parts to result in a product
having the reported percent of active material.
[0093] From the above, it can be concluded that the smaller the
reported size in dispersion, the more effective ZnO is in
protecting against UVB. At a size of 130 nm or smaller, ZnO can be
a very effective UVB sunscreen. It also appears that it is largely
the aggregate size, rather than the primary particle size, that has
a decisive influence on SPF score.
[0094] For UVA protection, there is an optimal size range of
secondary particle sizes, which was found to include 160-230 nm and
is believed to range between 150 nm and 250 nm. When size is
larger, the ZnO is not fully utilized for absorption, as particles
located on the outside of the large aggregate shield inside
particles from radiation. When the size is smaller, the effective
absorption range narrows.
[0095] It also appears from the above results that optimal sizes
for UVA and UVB attenuation for zinc oxide are different. In order
to formulate for a balanced UV protection, a combination of
different sizes appears desirable. Thus, a zinc oxide dispersion
with a secondary particle size of 130 nm will provide excellent UVB
protection. Zinc oxide dispersions with much larger size particles
were used to provide UV A protection, in a number of formulations
tested, as detailed in Table 3.
TABLE-US-00003 TABLE 3 Formula 6 7 8 ZnO for UVB PPS (nm) 20
Attenuation PS (nm) 130 % 12 10 10 ZnO for UVA PPS (nm) 60 15-35
Attenuation PS (nm) 250 193 220 -- 10 10 12 SPF 31.4 30 30.7 PFA
11.6 8.7 9.3 FDA rating High High High
[0096] The water in oil sunscreen formulations designated Formulae
6-8 were prepared using the method described above in connection
with the preparation of Formula 1. Again, to the extent that the
percentage of zinc oxide has been reduced from 16%, the amount of
isononyl isononanoate has been increased by the same weight. In
Formulae 6-8, the UVB attenuating zinc oxide with a primary
particle size of 20 nm was obtained from a dispersion sold by Kobo
under its catalog number TNP50ZSI. In Formula 6, the UV A
attenuating zinc oxide was obtained by using a dispersion sold by
Kobo under its catalog number TNC65SZ5. In Formula 7, the UV A
attenuating zinc oxide was obtained by using a dispersion sold by
Kobo under its catalog number TNP50FZS. In Formula 8, the UV A
attenuating zinc oxide was obtained by using a dispersion sold by
Kobo under its catalog number INH73MZ.
[0097] All of the above formulae have SPF of 30 or higher and an
excellent PA, indicating excellent broad-spectrum protection.
Formula 6 used sizes at two extremes, and the results met the
standard of 3/1 SPF/PFA ratio. Accordingly it is believed that high
balanced UV protection can be achieved with a blend of ZnO with
sizes at two extremes.
[0098] The UV attention of zinc oxide depends more on its aggregate
size than the primary size. At very small size, it can be an
effective SPF provider. When the particle size is in the range of
about 165-220 nm, it is very effective against UVA.
[0099] In accordance with the invention, it has been learned that
the component of zinc oxide useful for attenuating UVA radiation
may be fabricated with zinc oxide particles having a mean primary
particle size less than 120 nm. The dispersion is made to result in
a secondary mean particle size of 150 to 250 nm, preferably 160 to
240 nm. However, secondary mean particle sizes of 140 to 260 nm
will work well and functional results can be obtained with
secondary mean particle sizes of 120-280 nm.
[0100] It is noted that the above specifications apply to zinc
oxide particulates currently available on the market. Other
materials having different, for example, more narrow, particle size
distributions may enable equivalency outside these ranges.
[0101] Secondary particle sizes for particles intended to protect
against UV A radiation need only be less than 120 nm in size, as
such smaller particles may be aggregated during the dispersion
manufacturing process to be in the above specified ranges.
[0102] Dispersions incorporating mixtures of zinc oxide particles
meant to attenuate UV A radiation should be formulated to have 30%
or more of the above particles for an SPF of 30 and a ratio of SPF
to PFA of 3:1. For similar results finished products should have
secondary particle size zinc oxide concentrations as specified
above in the range of 8% by weight.
[0103] However, dispersions having 10% or greater UVA attenuating
zinc particles may be usefully employed. Likewise, finished
products having 2% or more UV A attenuating zinc oxide with
secondary particles sizes as specified above will also find useful
employment.
[0104] The component of zinc oxide useful for attenuating UVB
radiation may be fabricated with zinc oxide particles having a mean
primary particle size less than 55 nm, preferably less than 35 nm.
However primary particle sizes less than 75 nm will yield useful
results.
[0105] Secondary particle sizes are preferably less than 140 nm,
and more preferably less than 130 nm, although mean particle sizes
in the 50-150 nm range will provide functional results.
[0106] It is noted again that the above specifications apply to
zinc oxide particulates currently available on the market. Other
materials having different, for example, more narrow, particle size
distributions may enable equivalency outside these ranges.
[0107] Dispersions incorporating mixtures of zinc oxide particles
should be formulated to have 30% or more of the above particles
meant to attenuate UVB radiation for an SPF of 30 and a ratio of
SPF to PFA of 3:1. For similar results finished products should
have secondary particle size zinc oxide concentrations as specified
above in the range of 8% by weight.
[0108] However, dispersions having 10% or greater UVB attenuating
zinc particles may be usefully employed. Likewise, finished
products having 2% or more UVB attenuating zinc oxide with
secondary particles sizes as specified above will also find useful
employment.
[0109] As alluded to above, the mean secondary particle sizes are
determined by measuring using a photon correlation particle size
analyzer, also known as a dynamic light scattering particle size
analyzer, such as that made by Particle Size Systems of Santa
Barbara, Calif.
[0110] With respect to primary particle size measurements, the same
are specified using sizes determined using the BET surface area
calculation method.
[0111] Dispersions may be prepared by incorporating zinc oxide
particles into suitable carriers and milling using conventional
techniques of UV A attenuating zinc oxide has the desired secondary
particle size to make a first dispersion. The dispersions or
compositions incorporating such dispersions may also include at
least one biocompatible excipient (e.g., buffer (neutralizer or pH
adjusters), emulsifier, surfactant, diluent, adjuvant,
preservative, and/or electrolyte).
[0112] The UVB attenuation particles are then incorporated into a
carrier and milled until the desired secondary particle size is
obtained to make a second dispersion.
[0113] The first and second dispersions are then combined.
[0114] The entire disclosure of each and every United States patent
and patent application, each foreign and international patent
publication, of each other publication and of each unpublished
patent application that is referenced in this specification or
elsewhere in this patent application, is hereby incorporated
herein, in its entirety, by the respective specific reference that
has been made thereto.
[0115] While illustrative embodiments have been described above, it
is, of course, understood that various modifications will be
apparent to those of ordinary skill in the art. Many such
modifications are contemplated as being within the spirit or scope
of the appended claims.
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