U.S. patent application number 11/387299 was filed with the patent office on 2007-09-27 for high-cleaning, low abrasion, high brightness silica materials for dentrifices.
Invention is credited to Patrick D. McGill.
Application Number | 20070224132 11/387299 |
Document ID | / |
Family ID | 38481742 |
Filed Date | 2007-09-27 |
United States Patent
Application |
20070224132 |
Kind Code |
A1 |
McGill; Patrick D. |
September 27, 2007 |
HIGH-CLEANING, LOW ABRASION, HIGH BRIGHTNESS SILICA MATERIALS FOR
DENTRIFICES
Abstract
Unique abrasive materials that are in situ generated
compositions of precipitated silicas and silica gels are provided.
Such compositions exhibit different beneficial, particularly
simultaneously high pellicle film cleaning properties and moderate
dentin abrasion levels. Such a result thus accords the user a
dentifrice that effectively cleans tooth surfaces without
detrimentally abrading such surfaces. Furthermore, the produced
abrasive materials also exhibit very high and desirable brightness
properties that permit easy incorporation and utilization within
dentifrices for aesthetic purposes. Encompassed within this
invention is a unique method for making such gel/precipitated
silica composite materials for such a purpose, particularly under
high shear conditions, as well as the different materials within
the structure ranges described above and dentifrices comprising
such.
Inventors: |
McGill; Patrick D.;
(Darlington, MD) |
Correspondence
Address: |
William S. Parks, Esq.;J.M. Huber Corporation
333 Thomall Street
Edison
NJ
08837
US
|
Family ID: |
38481742 |
Appl. No.: |
11/387299 |
Filed: |
March 23, 2006 |
Current U.S.
Class: |
424/49 |
Current CPC
Class: |
A61K 8/25 20130101; A61Q
11/00 20130101 |
Class at
Publication: |
424/049 |
International
Class: |
A61K 8/25 20060101
A61K008/25 |
Claims
1. A gel/precipitate silica combination, wherein said combination
exhibits a technidyne brightness of at least 95.5, and, when
incorporated into a dentifrice composition in an amount of 20% by
weight, said dentifrice exhibits a RDA (Radioactive Dentin
Abrasion) of at most 120, and a PCR (Pellicle Cleaning Ratio):RDA
ratio of from 0.7 to 1.0.
2. A dentifrice comprising the gel/precipitate combination of claim
1.
3. The gel/precipitate silica combination of claim 1 wherein said
dentifrice exhibits a PCR:RDA ratio of from 0.8 to 1.0.
4. A dentifrice comprising the gel/precipitate combination of claim
3.
5. The gel/precipitate silica combination of claim 3 wherein said
dentifrice exhibits a PCR:RDA ratio of from 0.85 to 1.0.
6. A dentifrice comprising the gel/precipitate combination of claim
5.
7. The gel/precipitate silica combination of claim 5 wherein said
dentifrice exhibits a PCR:RDA ratio of from 0.9 to 1.0.
8. A dentifrice comprising the gel/precipitate combination of claim
7.
9. The gel/precipitate silica combination of claim 7 wherein said
dentifrice exhibits a PCR:RDA ratio of from 0.95 to 1.0.
10. A dentifrice comprising the gel/precipitate combination of
claim 9.
Description
FIELD OF THE INVENTION
[0001] This invention relates to unique abrasive materials that are
in situ generated compositions of precipitated silicas and silica
gels. Such compositions exhibit different beneficial, particularly
simultaneously high pellicle film cleaning properties and moderate
dentin abrasion levels. Such a result thus accords the user a
dentifrice that effectively cleans tooth surfaces while controlling
the amount of abrasion applied to the surfaces of the subject
teeth. Furthermore, the produced abrasive materials also exhibit
very high and desirable brightness properties that permit easy
incorporation and utilization within dentifrices for aesthetic
purposes. Encompassed within this invention is a unique method for
making such gel/precipitated silica composite materials for such a
purpose, particularly under high shear conditions, as well as the
different materials within the structure ranges described above and
dentifrices comprising such.
BACKGROUND OF THE PRIOR ART
[0002] An abrasive substance has been included in conventional
dentifrice compositions in order to remove various deposits,
including pellicle film, from the surface of teeth. Pellicle film
is tightly adherent and often contains brown or yellow pigments
which impart an unsightly appearance to the teeth. While cleaning
is important, the abrasive should not be so aggressive so as to
damage the teeth. Ideally, an effective dentifrice abrasive
material maximizes pellicle film removal while causing minimal
abrasion and damage to the hard tooth tissues. Consequently, among
other things, the performance of the dentifrice is highly sensitive
to the extent of abrasion caused by the abrasive ingredient.
Conventionally, the abrasive cleaning material has been introduced
in flowable dry powder form to dentifrice compositions, or via
redispersions of flowable dry powder forms of the polishing agent
prepared before or at the time of formulating the dentifrice. Also,
and more recently, slurry forms of such abrasives have been
provided to facilitate storage, transport, and introduction within
target dentifrice formulations.
[0003] Synthetic low-structure silicas have been utilized for such
a purpose due to the effectiveness such materials provide as
abrasives, as well as low toxicity characteristics and
compatibility with other dentifrice components, such as sodium
fluoride, as one example. When preparing synthetic silicas, the
objective is to obtain silicas which provide maximal cleaning with
minimal impact to the hard tooth surfaces. Dental researchers are
continually concerned with identifying abrasive materials that meet
such objectives.
[0004] Synthetic silicas (of higher structure) have also been
utilized as thickening agents for dentifrices and other like paste
materials in order to supplement and modify the rheological
properties for improved control, such as viscosity build, stand up,
brush sag, and the like. For toothpaste formulations, for example,
there is a need to provide a stable paste that can meet a number of
consumer requirements, including, and without limitation, the
ability to be transferred out of a container (such as a tube) via
pressure (i.e., squeezing of the tube) as a dimensionally stable
paste and to return to its previous state upon removal of such
pressure, the ability to be transferred in such a manner to a
brushhead easily and without flow out of the tube during and after
such transference, the propensity to remain dimensionally stable on
the brush prior to use and when applied to target teeth prior to
brushing, and the exhibiting of proper mouthfeel for aesthetic
purposes, at least, for the benefit of the user.
[0005] Generally, dentifrices comprise a majority of a humectant
(such as sorbitol, glycerin, polyethylene glycol, and the like) in
order to permit proper contact with target dental subjects, an
abrasive (such as precipitated silica) for proper cleaning and
abrading of the subject teeth, water, and other active components
(such as fluoride-based compounds for anticaries benefits). The
ability to impart proper rheological benefits to such a dentifrice
is accorded through the proper selection and utilization of
thickening agents (such as hydrated silicas, hydrocolloids, gums,
and the like) to form a proper network of support to properly
contain such important humectant, abrasive, and anticaries
ingredients. It is thus evident that formulating proper dentifrice
compositions can be rather complex, both from a compounding
standpoint as well as the number, amount, and type of components
present within such formulations. As a result, although it is not a
high priority within the dentifrice industry, the ability to reduce
the number of such components, or attempt to provide certain
components that meet at least two of these needed properties could
potentially reduce formulation complexity, not to mention
potentially reducing the overall manufacturing costs.
[0006] A number of water-insoluble, abrasive polishing agents have
been used or described for dentifrice compositions. These abrasive
polishing agents include natural and synthetic abrasive particulate
materials. The generally known synthetic abrasive polishing agents
include amorphous precipitated silicas and silica gels and
precipitated calcium carbonate (PCC). Other abrasive polishing
agents for dentifrices have included chalk, magnesium carbonate,
dicalcium phosphate and its dihydrate forms, calcium pyrophosphate,
zirconium silicate, potassium metaphosphate, magnesium
orthophosphate, tricalcium phosphate, perlite, and the like.
[0007] Synthetically-produced precipitated low-structure silicas,
in particular, have been used as abrasive components in dentifrice
formulations due to their cleaning ability, relative safeness, and
compatibility with typical dentifrice ingredients, such as
humectants, thickening agents, flavoring agents, anticaries agents,
and so forth. As known, synthetic precipitated silicas generally
are produced by the destabilization and precipitation of amorphous
silica from soluble alkaline silicate by the addition of a mineral
acid and/or acid gases under conditions in which primary particles
initially formed tend to associate with each other to form a
plurality of aggregates (i.e., discrete clusters of primary
particles), but without agglomeration into a three-dimensional gel
structure. The resulting precipitate is separated from the aqueous
fraction of the reaction mixture by filtering, washing, and drying
procedures, and then the dried product is mechanically comminuted
in order to provide a suitable particle size and size
distribution.
[0008] The silica drying procedures are conventionally accomplished
using spray drying, nozzle drying (e.g., tower or fountain), wheel
drying, flash drying, rotary wheel drying, oven/fluid bed drying,
and the like.
[0009] As it is, such conventional abrasive materials suffer to a
certain extent from limitations associated with maximizing cleaning
and minimizing dentin abrasion. The ability to optimize such
characteristics in the past has been limited generally to
controlling the structures of the individual components utilized
for such purposes. Examples of modifications in precipitated silica
structures for such dentifrice purposes are described in the art
within such publications as U.S. Pat. Nos. 3,967,563, 3,988,162,
4,420,312, and 4,122,161 to Wason, U.S. Pat. Nos. 4,992,251 and
5,035,879 to Aldcroft et al., U.S. Pat. No. 5,098,695 to Newton et
al., and U.S. Pat. Nos. 5,891,421 and 5,419,888 to McGill et al.
Modifications in silica gels have also been described within such
publications as U.S. Pat. Nos. 5,647,903 to McGill et al., U.S.
Pat. No. 4,303,641, to DeWolf, II et al., U.S. Pat. No. 4,153,680,
to Seybert, and U.S. Pat. No. 3,538,230, to Pader et al. Such
disclosures teach improvement in such silica materials in order to
impart increased pellicle film cleaning capacity and reductions in
dentin abrasion levels for dentifrice benefits. However, these
typical improvements lack the ability to deliver preferred property
levels that accord a dentifrice producer the ability incorporate
such an individual material in different amounts with other like
components in order to effectuate different resultant levels of
such cleaning and abrasion characteristics. To compensate for such
limitations, attempts have been undertaken to provide various
combinations of silicas to permit targeting of different levels.
Such silica combinations involving compositions of differing
particle sizes and specific surface areas are disclosed in U.S.
Pat. No. 3,577,521. to Karlheinz Scheller et al., U.S. Pat. No.
4,618,488 to Macyarea et al., U.S. Pat. No. 5,124,143 to Muhlemann,
and U.S. Pat. No. 4,632,826 to Ploger et al. Such resultant
dentifrices, however, fail to provide desired levels of abrasion
and high pellicle cleaning simultaneously.
[0010] Another attempt has been made to provide physical mixtures
of precipitated silicas of certain structures with silica gels,
notably within U.S. Pat. 5,658,553 to Rice. It is generally
accepted that silica gels exhibit edges, and thus theoretically
exhibit the ability to abrade surfaces to a greater degree, than
precipitated silicas, even low structured types. Thus, the blend of
such materials together within this patent provided, at that time,
an improvement in terms of controlled but higher levels of
abrasiveness coupled with greater pellicle film cleaning ability
than precipitated silicas alone. In such a disclosure, it is shown
that separately produced and co-incorporated silica gels and
precipitated silicas can permit increased PCR and RDA levels but
with apparently greater control for lower abrasive characteristics
than for previously provided silicas exhibiting very high PCR
results. Unfortunately, although these results are certainly a step
in the right direction, there is still a largely unfulfilled need
to provide a silica-based dental abrasive that exhibits
sufficiently high pellicle film cleaning properties with
simultaneously lower radioactive dentin abrasive characteristics
such that film removal can be accomplished without deleterious
dentin destruction. In effect, the need is for a safer abrasive
that exhibits a significantly higher PCR level versus RDA level
than has previously been provided within the dental silica
industry. Again, the Rice patent is merely a start toward desirable
abrasive characteristics. Furthermore, the requirement to produce
these separate gel and precipitate materials and meter them out for
proper target levels of such characteristics adds costs and process
steps to the manufacturing procedure. A manner of providing the
benefits of such combinations, but to a very high level of pellicle
film cleaning and at a relatively low to moderate degree of dentin
abrasion, with simultaneous facilitation of incorporation within
dentifrice formulation are thus unavailable to the industry at this
time.
[0011] The ability to provide low dentin abrasive properties with
simultaneously high pellicle film cleaning capabilities,
particularly when the ratio of such characteristics is 1 or lower,
has heretofore been unattained within the dental industry.
OBJECTS AND SUMMARY OF THE INVENTION
[0012] It has now been found that modifications in the processes
for producing precipitated silicas can result in the in situ
simultaneous production of targeted amounts of silica gels therein,
particularly those in which the final structure of the in situ
generated composite can be controlled. Such a novel method thus
permits the production of in situ generated gel/precipitate silica
materials that provide excellent dentin abrasion and pellicle film
cleaning capabilities within dentifrices or, in the alternative,
such formulations that exhibit excellent thickening properties as
well as desirable abrasive and cleaning properties through the
introduction of such a singularly produced, stored, and introduced
additive. Importantly, as well, is the need to incorporate a high
shear treatment step after the initial gel production process has
been accomplished. Such an extra procedure provides previously
unattained PCR and RDA results, as well as increased brightness of
the materials, as described herein.
[0013] In particular, the specific in situ formed composites
exhibit very high levels pellicle film cleaning properties compared
with lower radioactive dentin abrasion results such that the
resultant materials can be added with other abrasive materials
(such as lower structure precipitated silicas, calcium carbonates,
and the like) for the dentifrice producer to target certain high
levels of cleaning with lower abrasiveness thus providing the
optimization of cleaning while providing a larger margin of
abrasion protection to the ultimate user. It is also believed,
without intending to be bound to any specific scientific theory,
that the increased amount of silica gel within the final composite
materials aids in providing narrower particle size ranges in order
to contribute a controlled result of high cleaning and reduced
dentin abrasion levels. As will be discussed in greater detail
below, the physically mixed combination of such materials (i.e.,
not simultaneously produced within the same reaction) has been
found to impart limited levels of such properties, namely the need
to provide materials (particularly a precipitated silica component)
that exhibits an extremely high, potentially deleterious dentin
abrasion level in order to impart, at the same time, an acceptable
high pellicle film cleaning level. The novel in situ generated
precipitated/gel combination silicas unexpectedly provide a higher
degree of pellicle film cleaning with a significantly lower dentin
abrasion value, thus according the dentifrice industry not only a
potentially more desirable lower abrasive material for better
dental protection. It has been realized that the presence of varied
amounts of such a silica gel component permits the benefit of the
sharp edges exhibited by the gel agglomerates for abrasiveness,
with the coexistence of variable levels of silica precipitates of
different structures to accord an overall composite exhibiting high
cleaning properties. When produced in situ, such a resultant
gel/precipitate material provides unexpectedly improved properties
as compared with dry blends of such separately produced components,
particularly when the production method incorporates high shear
flow subsequent to the initial gel production step. Such high shear
conditions appear to provide ultimate beneficial results in terms
of the composite materials abrasive properties and brightness
characteristics. In such a manner, it has been found that although
the pellicle film cleaning level is quite high, in fact the
resultant dentin abrasion level is limited, thereby imparting an
excellent cleaning material without also imparting too high an
abrasion level to the target dental substrate.
[0014] All parts, percentages and ratios used herein are expressed
by weight unless otherwise specified. All documents cited herein
are incorporated by reference.
[0015] Accordingly, it is one object of the present invention to
provide a precipitated silica and gel silica composite material
providing improved pellicle film cleaning without an unacceptably
high corresponding increase in dentin or enamel abrasion. Another
object of the present invention is to provide a new method for the
production of such effective precipitated/gel silica combinations
wherein such materials are produced simultaneously and in situ,
thereby permitting the proper ratios of such materials to be made
during production of the materials, rather than during dentifrice
production. Also an object of this invention is to provide an in
situ generated precipitated/gel silica composite material wherein
the brightness of the high PCR, low RDA product silica materials
are very high as well.
[0016] Accordingly, this invention encompasses a method for
producing simultaneously silica gels and precipitated silicas, said
method comprising the sequential steps of
[0017] a) admixing a sufficient amount of an alkali silicate and an
acidulating agent together to form a silica gel composition;
[0018] b) subsequent to silica gel composition formation, treating
the resultant composition under high shear conditions;
[0019] c) simultaneously introducing to said silica gel composition
of step "b" a sufficient amount of an alkali silicate and an
acidulating agent to form a precipitated silica, thereby producing
a precipitate/gel silica combination. Encompassed as well within
this invention is the product of such a process wherein the silica
gel amount present therein is from 5 to 80% by volume of the total
precipitated/gel silica resultant simultaneously produced
combination. Further encompassed within this invention are the
composite materials made therefrom and dentifrice formulations
comprising such materials as well as the product of the inventive
process noted above.
[0020] Generally, synthetic precipitated silicas are prepared by
admixing dilute alkali silicate solutions with strong aqueous
mineral acids under conditions where aggregation to the sol and gel
cannot occur, stirring and then filtering out the precipitated
silica. The resulting precipitate is next washed, dried and
comminuted to desired size.
[0021] Generally, as well, silica gels include silica hydrogels,
hydrous gels, aerogels, and xerogels. Silica gels are also formed
by reacting alkali silicate solutions with strong acids or
vice-versa, to form a hydrosol and aging the newly formed hydrosol
to form the hydrogel. The hydrogel is then washed, dried and
comminuted to form the desired materials.
[0022] As noted above, the separate production of such materials
has historically required manufacture of these separate materials,
and proper metering of the two together during the incorporation
within a dentifrice formulation in such a way as to provide the
desired cleaning/abrasion levels thereof.
[0023] To the contrary, the inventive method for simultaneous
production of such materials permits the producer to target a range
of amounts of silica gel and precipitated silica components as well
as structures of precipitated components to impart the desired
level of cleaning/abrasion through controlled parameters during
production, a significant difference from previous physicals
mixtures (i.e., dry blends) of such materials through separate
incorporation. Basically, the novel method entails targeting the
amount of silica gel desired and specifically selecting certain
reaction conditions in order to generate such a desired level
during amorphous precipitated silica production.
[0024] The inventive abrasive compositions are ready-to-use
additives in the preparation of oral cleaning compositions, such as
dentifrices, toothpastes, and the like, particularly suited as a
raw material in a toothpaste making process. Furthermore, such
silica products can be utilized in applications wherein sharp edges
and lower abrasiveness may be desired, such as, without limitation,
foam inhibitors within certain formulations, such as, without
limitation, automatic dishwashing detergents. Additional potential
uses of such materials include food carriers, rubber additives and
carriers, cosmetic additives, personal care additives, plastic
antiblocking additives, and pharmaceutical additives, without
limitation.
DETAILED DESCRIPTION OF THE INVENTION
[0025] The abrasive and/or thickening combinations used in the
present invention are in situ formed materials that can be readily
formulated on demand with other ingredients to prepare oral
cleaning compositions having a high cleaning efficacy without
causing undue abrasion on tooth surfaces. The essential as well as
optional components of the abrasive and/or thickening compositions
and related methods of making same of the present invention are
described in more detail below.
General Production Method
[0026] The silica compositions of the present invention are
prepared according to the following two-stage process with a silica
gel being formed in the first stage and precipitated silica formed
in the second stage. In this process, an aqueous solution of an
alkali silicate, such as sodium silicate, is charged into a reactor
equipped with mixing means adequate to ensure a homogeneous
mixture, and the aqueous solution of an alkali silicate in the
reactor preheated to a temperature of between about 40.degree. C.
and about 90.degree. C. Preferably, the aqueous alkali silicate
solution has an alkali silicate concentration of approximately 3.0
to 35 wt %, preferably from about 3.0 to about 25 wt %, and more
preferably from about 3.0 to about 15 wt %. Preferably the alkali
silicate is a sodium silicate with a SiO.sub.2:Na.sub.2O ratio of
from about 1 to about 4.5, more particularly from about 1.5 to
about 3.4. The quantity of alkali silicate charged into the reactor
is about 10 wt % to 80 wt % of the total silicate used in the
batch. Optionally, an electrolyte, such as sodium sulfate solution,
may be added to the reaction medium (silicate solution or water).
Next, an aqueous acidulating agent or acid, such as sulfuric acid,
hydrochloric acid, nitric acid, phosphoric acid, and so forth
(preferably sulfuric acid), added as a dilute solution thereof
(e.g., at a concentration of between about 4 to 35 wt %, more
typically about 9.0 to 15.0 wt %) is added to the silicate to form
a gel. Once the silica gel is produced and the pH adjusted to the
desired level, such as between about 3 and 10, the acid addition is
stopped and the gel is heated to the batch reaction temperature,
preferably between about 65.degree. C. to about 100.degree. C. It
is important to note that after this first stage is completed, the
produced silica gel is subjected to high shear conditions to modify
the gel from its initial produced form. Such high shearing may be
performed in any known manner, such as by increased flow rate of
liquids added thereto, physical mixing in a blending setting, and
the like. The requirement of high shear conditioning is met simply
by the modification of the gel component after initial production.
Such modification is measurable by a reduction in the average
particle size of the gel material after such high shear treatment
is undertaken. Preferably, the modification via high shear
conditioning is attained once the average particle size of the gel
component is reduced at least 5 microns. The resultant gel is
otherwise not washed, purified, or cleaned, in any other manner
prior to commencement of the second stage.
[0027] Next, the second stage begins after the gel reaction
temperature is increased, with the simultaneous addition to the
reactor of, all while the shear rate remains at the substantially
the same level throughout: (1) an aqueous solution of the same
acidulating agent previously used and (2) additional amounts of an
aqueous solution containing the same species of alkali silicate as
is in the reactor, the aqueous solution being preheated to a
temperature of about 65.degree. C. to about 100.degree. C. The rate
of acidulating agent and silicate additions can be adjusted to
control the simultaneous addition pH during the second stage
reaction. This pH control can be used to control product physical
properties, generally with higher average batch pH providing lower
structure silica products and relatively lower average batch pH
providing higher structure silica products. In addition to the high
shear conditions present already, high shear recirculation may be
utilized, and the acid solution addition continues until the
reactor batch pH drops to between about 4 to about 9. For purposes
of this inventive method, the term "average batch pH" is intended
to mean the average pH obtained by measuring the pH level every 5
minutes during the precipitate formation stage and averaging the
total aggregate over total time elapsed.
[0028] After the inflows of the acidulating agent and the alkali
silicate are stopped, the reactor batch allowed to age or "digest"
for between 5 minutes to 30 minutes, with the reactor contents
being maintained at a constant pH. After the completion of
digestion, the high shear mixing, etc., is curtailed, and the
resultant reaction batch is filtered and washed with water to
remove excess by-product inorganic salts until the wash water from
the silica filter cake results in at most 5% salt byproduct content
as measured by conductivity.
[0029] The silica filter cake is slurried in water, and then dried
by any conventional drying techniques, such as spray drying, to
produce an amorphous silica containing from about 3 wt % to about
50 wt % of moisture. The silica may then be milled to obtain the
desired median particle size of between about 3 .mu.m to 25 .mu.m,
preferably between about 3 .mu.m to about 20 .mu.m. Classification
of even narrower median particle size ranges may aid in providing
increased cleaning benefits as well.
[0030] In addition to the above-described production process
methodologies of precipitating the synthetic amorphous silicas, the
preparation of the silica products is not necessarily limited
thereto and it also can be generally accomplished in accordance
with the methodologies described, for example, in prior U.S. Pat.
Nos. 3,893,840, 3,988,162, 4,067,746, 4,340,583, and 5,891,421, all
of which are incorporated herein by reference, as long as such
methods are appropriately modified to incorporate recirculation and
high shear treatments. As will be appreciated by one skilled in the
art, reaction parameters which affect the characteristics of the
resultant precipitated silica include: the rate and timing at which
the various reactants are added; the levels of concentration of the
various reactants; the reaction pH; the reaction temperature; the
agitation of the reactants during production; and/or the rate at
which any electrolytes are added.
[0031] Alternative methods of production for this inventive
material include in slurry form such as, without limitation,
procedures taught within U.S. Pat. No. 6,419,174, to McGill et al.,
as well as filter press slurry processes as described within and
throughout U.S. Published Pat. Appl. No. 20030019162 to Huang.
[0032] The inventive in situ generated composites (also referred to
as "combinations") of silica gel and precipitate are useful as
high-cleaning, dental abrasives with correlative lower abrasiveness
(with low RDA measurements of at most about 110, for instance, and
as low as about 70). The in situ process of this invention has thus
surprisingly yielded, with degrees of selectivity followed in terms
of reaction pH, reactant concentrations, amount of gel component,
high shear production conditions, and, as a result, overall
structure of the resultant gel/precipitate silica composite
materials made therefrom, a method for producing a mid-range
product (relatively high, cleaning levels with lower abrasion
levels) composites as. Thus, selection of differing concentrations,
pH levels, ultimate gel proportions, among other things, can
produce gel/precipitate silica composite materials of overall
medium structures in order to accord relatively high pellicle film
cleaning results, with lower abrasive properties as compared with
the high cleaning materials described above.
[0033] For this cleaning material, the gel component is present in
an amount between 10 and 60% by weight of the ultimately formed
gel/precipitate silica composite material (and thus the
precipitated silica component is present in an amount of from 90 to
40% by weight as a result). The overall amount of gel to be
produced is preferably relatively low (from up to 40%, for
instance). Such percentages of gel component actually represent the
volume amount of silicate present during the production phases for
each different silica material, as described above for the high
cleaning material.
[0034] Generally, it has been determined that such specific
mid-range cleaning abrasives may be produced through a method of
admixing a suitable acid and a suitable silicate starting material
(wherein the acid concentration, in aqueous solution, is from 5 to
25%, preferably from 10 to 20%, and more preferably from 10 to 12%,
and the concentration of the silicate starting material is from 4
to 35%, also within an aqueous solution), to initially form a
silica gel. Subsequent to gel formation, sufficient silicate and
acid are added (without any washing, or other type of purification,
or physical modification of the gel) to the formed gel for further
production of appropriately structured precipitated silica
component desired for a mid-range cleaning composite material to be
formed. The pH of the overall reaction may be controlled anywhere
within the range of 3 to 10. Depending on the amount of gel
initially formed, the amount and structure of precipitated silica
component may be targeted in much the same way as for the high
cleaning material. It has been realized that in order to provide a
mid-range cleaning, low abrasive material through this process, the
amount of gel is preferably higher (as noted above, from 10 to 60%
by volume of the composite, preferably from 20 to 33%) and the
amount of low structure precipitated silica is preferably lower
(from 90 to 40% by volume of the composite, preferably from 80 to
67%).
[0035] Broadly, the inventive mid-range cleaning gel/precipitated
silica combination generally have the following properties: 10%
Brass Einlehner hardness values in the range between 2.5 and 12.0,
and, within a test dentifrice formulation (as presented below
within the examples) RDA (Radioactive Dentin Abrasion) values
between about 80 to about 120, and (within the same test dentifrice
formulation) PCR (Pellicle Cleaning Ratio) values of 80 to 120,
with a ratio of PCR to RDA within the range of 0.7 to 1.0.
Dentifrice Uses of the Inventive Materials
[0036] The inventive in situ generated gel/precipitate silica
composite materials described herein may be utilized alone as the
cleaning agent component provided in the dentifrice compositions of
this invention, or as an additive with other abrasive materials
therein. A combination of the inventive composite materials with
other abrasives physically blended therewith within a suitable
dentifrice formulation is potentially preferred in this regard in
order to accord targeted dental cleaning and abrasion results at a
desired protective level. Thus, any number of other conventional
types of abrasive additives may be present within inventive
dentifrices in accordance with this invention. Other such abrasive
particles include, for example, and without limitation,
precipitated calcium carbonate (PCC), ground calcium carbonate
(GCC), dicalcium phosphate or its dihydrate forms, silica gel (by
itself, and of any structure), amorphous precipitated silica (by
itself, and of any structure as well), perlite, titanium dioxide,
calcium pyrophosphate, hydrated alumina, calcined alumina,
insoluble sodium metaphosphate, insoluble potassium metaphosphate,
insoluble magnesium carbonate, zirconium silicate, aluminum
silicate, and so forth, can be introduced within the desired
abrasive compositions to tailor the polishing characteristics of
the target formulation (dentifrices, for example, etc.), if
desired, as well.
[0037] The precipitate/gel silica combination described above, when
incorporated into dentifrice compositions, is present at a level of
from about 5% to about 50% by weight, more preferably from about
10% to about 35% by weight, particularly when the dentifrice is a
toothpaste. Overall dentifrice or oral cleaning formulations
incorporating the abrasive compositions of this invention
conveniently can comprise the following possible ingredients and
relative amounts thereof (all amounts in wt %):
[0038] Dentifrice Formulation TABLE-US-00001 Ingredient Amount
Liquid Vehicle: humectant(s) (total) 5-70 deionized water 5-70
binder(s) 0.5-2.0 anticaries agent 0.1-2.0 chelating agent(s)
0.4-10 silica thickener* 3-15 surfactant(s) 0.5-2.5 abrasive 10-50
sweetening agent <1.0 coloring agents <1.0 flavoring agent
<5.0 preservative <0.5
[0039] In addition, as noted above, the inventive abrasive could be
used in conjunction with other abrasive materials, such as
precipitated silica, silica gel, dicalcium phosphate, dicalcium
phosphate dihydrate, calcium metasilicate, calcium pyrophosphate,
alumina, calcined alumina, aluminum silicate, precipitated and
ground calcium carbonate, chalk, bentonite, particulate
thermosetting resins and other suitable abrasive materials known to
a person of ordinary skill in the art.
[0040] In addition to the abrasive component, the dentifrice may
also contain one or more organoleptic enhancing agents.
Organoleptic enhancing agents include humectants, sweeteners,
surfactants, flavorants, colorants and thickening agents, (also
sometimes known as binders, gums, or stabilizing agents),
[0041] Humectants serve to add body or "mouth texture" to a
dentifrice as well as preventing the dentifrice from drying out.
Suitable humectants include polyethylene glycol (at a variety of
different molecular weights), propylene glycol, glycerin
(glycerol), erythritol, xylitol, sorbitol, mannitol, lactitol, and
hydrogenated starch hydrolyzates, as well as mixtures of these
compounds. Typical levels of humectants are from about 20 wt % to
about 30 wt % of a toothpaste composition.
[0042] Sweeteners may be added to the toothpaste composition to
impart a pleasing taste to the product. Suitable sweeteners include
saccharin (as sodium, potassium or calcium saccharin), cyclamate
(as a sodium, potassium or calcium salt), acesulfane-K, thaumatin,
neohisperidin dihydrochalcone, ammoniated glycyrrhizin, dextrose,
levulose, sucrose, mannose, and glucose.
[0043] Surfactants are used in the compositions of the present
invention to make the compositions more cosmetically acceptable.
The surfactant is preferably a detersive material which imparts to
the composition detersive and foaming properties. Suitable
surfactants are safe and effective amounts of anionic, cationic,
nonionic, zwitterionic, amphoteric and betaine surfactants such as
sodium lauryl sulfate, sodium dodecyl benzene sulfonate, alkali
metal or ammonium salts of lauroyl sarcosinate, myristoyl
sarcosinate, palmitoyl sarcosinate, stearoyl sarcosinate and oleoyl
sarcosinate, polyoxyethylene sorbitan monostearate, isostearate and
laurate, sodium lauryl sulfoacetate, N-lauroyl sarcosine, the
sodium, potassium, and ethanolamine salts of N-lauroyl,
N-myristoyl, or N-palmitoyl sarcosine, polyethylene oxide
condensates of alkyl phenols, cocoamidopropyl betaine,
lauramidopropyl betaine, palmityl betaine and the like. Sodium
lauryl sulfate is a preferred surfactant. The surfactant is
typically present in the oral care compositions of the present
invention in an amount of about 0.1 to about 15% by weight,
preferably about 0.3% to about 5% by weight, such as from about
0.3% to about 2%, by weight.
[0044] Flavoring agents optionally can be added to dentifrice
compositions. Suitable flavoring agents include, but are not
limited to, oil of wintergreen, oil of peppermint, oil of
spearmint, oil of sassafras, and oil of clove, cinnamon, anethole,
menthol, thymol, eugenol, eucalyptol, lemon, orange and other such
flavor compounds to add fruit notes, spice notes, etc. These
flavoring agents consist chemically of mixtures of aldehydes,
ketones, esters, phenols, acids, and aliphatic, aromatic and other
alcohols.
[0045] Colorants may be added to improve the aesthetic appearance
of the product. Suitable colorants are selected from colorants
approved by appropriate regulatory bodies such as the FDA and those
listed in the European Food and Pharmaceutical Directives and
include pigments, such as TiO.sub.2, and colors such as FD&C
and D&C dyes.
[0046] Thickening agents are useful in the dentifrice compositions
of the present invention to provide a gelatinous structure that
stabilizes the toothpaste against phase separation. Suitable
thickening agents include silica thickener; starch; glycerite of
starch; gums such as gum karaya (sterculia gum), gum tragacanth,
gum arabic, gum ghatti, gum acacia, xanthan gum, guar gum and
cellulose gum; magnesium aluminum silicate (Veegum); carrageenan;
sodium alginate; agar-agar; pectin; gelatin; cellulose compounds
such as cellulose, carboxymethyl cellulose, hydroxyethyl cellulose,
hydroxypropyl cellulose, hydroxymethyl cellulose, hydroxymethyl
carboxypropyl cellulose, methyl cellulose, ethyl cellulose, and
sulfated cellulose; natural and synthetic clays such as hectorite
clays; as well as mixtures of these compounds. Typical levels of
thickening agents or binders are from about 0 wt % to about 15 wt %
of a toothpaste composition.
[0047] Therapeutic agents are optionally used in the compositions
of the present invention to provide for the prevention and
treatment of dental caries, periodontal disease and temperature
sensitivity. Examples of therapeutic agents, without intending to
be limiting, are fluoride sources, such as sodium fluoride, sodium
monofluorophosphate, potassium monofluorophosphate, stannous
fluoride, potassium fluoride, sodium fluorosilicate, ammonium
fluorosilicate and the like; condensed phosphates such as
tetrasodium pyrophosphate, tetrapotassium pyrophosphate, disodium
dihydrogen pyrophosphate, trisodium monohydrogen pyrophosphate;
tripolyphosphates, hexametaphosphates, trimetaphosphates and
pyrophosphates, such as; antimicrobial agents such as triclosan,
bisguanides, such as alexidine, chlorhexidine and chlorhexidine
gluconate; enzymes such as papain, bromelain, glucoamylase,
amylase, dextranase, mutanase, lipases, pectinase, tannase, and
proteases; quartemary ammonium compounds, such as benzalkonium
chloride (BZK), benzethonium chloride (BZT), cetylpyridinium
chloride (CPC), and domiphen bromide; metal salts, such as zinc
citrate, zinc chloride, and stannous fluoride; sanguinaria extract
and sanguinarine; volatile oils, such as eucalyptol, menthol,
thymol, and methyl salicylate; amine fluorides; peroxides and the
like. Therapeutic agents may be used in dentifrice formulations
singly or in combination at a therapeutically safe and effective
level.
[0048] Preservatives may also be optionally added to the
compositions of the present invention to prevent bacterial growth.
Suitable preservatives approved for use in oral compositions such
as methylparaben, propylparaben and sodium benzoate may be added in
safe and effective amounts.
[0049] The dentifrices disclosed herein may also a variety of
additional ingredients such as desensitizing agents, healing
agents, other caries preventative agents, chelating/sequestering
agents, vitamins, amino acids, proteins, other
anti-plaque/anti-calculus agents, opacifiers, antibiotics,
anti-enzymes, enzymes, pH control agents, oxidizing agents,
antioxidants, and the like
[0050] Water provides the balance of the composition in addition to
the additives mentioned. The water is preferably deionized and free
of impurities. The dentifrice will usually comprise from about 20
wt % to about 35 wt % of water.
[0051] Useful silica thickeners for utilization within such a
toothpaste formulation include, as a non-limiting example, an
amorphous precipitated silica such as ZEODENT.RTM. 165 silica.
Other preferred (though non-limiting) silica thickeners are
ZEODENT.RTM. 163 and/or 167 and ZEOFREE.RTM.153, 177, and/or 265
silicas, all available from J. M. Huber Corporation, Havre de Grace
Md., U.S.A.
[0052] For purposes of this invention, a "dentifrice" has the
meaning defined in Oral Hygiene Products and Practice, Morton
Pader, Consumer Science and Technology Series, Vol. 6, Marcel
Dekker, NY 1988, p. 200, which is incorporated herein by reference.
Namely, a "dentifrice" is " . . . a substance used with a
toothbrush to clean the accessible surfaces of the teeth.
Dentifrices are primarily composed of water, detergent, humectant,
binder, flavoring agents, and a finely powdered abrasive as the
principal ingredient . . . a dentifrice is considered to be an
abrasive-containing dosage form for delivering anti-caries agents
to the teeth." Dentifrice formulations contain ingredients which
must be dissolved prior to incorporation into the dentifrice
formulation (e.g. anti-caries agents such as sodium fluoride,
sodium phosphates, flavoring agents such as saccharin).
[0053] The various silica and toothpaste (dentifrice) properties
described herein were measured as follows, unless indicated
otherwise.
[0054] The Brass Einlehner (BE) Abrasion test used to measure the
hardness of the precipitated silicas/silica gels reported in this
application is described in detail in U.S. Pat. No. 6,616,916,
incorporated herein by reference, involves an Einlehner AT-1000
Abrader generally used as follows: (1) a Fourdrinier brass wire
screen is weighed and exposed to the action of a 10% aqueous silica
suspension for a fixed length of time; (2) the amount of abrasion
is then determined as milligrams brass lost from the Fourdrinier
wire screen per 100,000 revolutions. The result, measured in units
of mg loss, can be characterized as the 10% brass Einlehner (BE)
abrasion value.
[0055] The oil absorption values are measured using the rubout
method. This method is based on a principle of mixing linseed oil
with a silica by rubbing with a spatula on a smooth surface until a
stiff putty-like paste is formed. By measuring the quantity of oil
required to have a paste mixture which will curl when spread out,
one can calculate the oil absorption value of the silica--the value
which represents the volume of oil required per unit weight of
silica to saturate the silica sorptive capacity. A higher oil
absorption level indicates a higher structure of precipitated
silica; similarly, a low value is indicative of what is considered
a low-structure precipitated silica. Calculation of the oil
absorption value was done as follows: Oil .times. .times.
absorption = ml .times. .times. oil .times. .times. absorbed weight
.times. .times. of .times. .times. silica , grams .times. 100 = ml
.times. .times. oil / 100 .times. .times. gram .times. .times.
silica ##EQU1##
[0056] Median particle size is determined using a Model LA-930 (or
LA-300 or an equivalent) laser light scattering instrument
available from Horiba Instruments, Boothwyn, Pa.
[0057] The % 325 mesh residue of the inventive silica is measured
utilizing a U.S. Standard Sieve No. 325, with 44 micron or 0.0017
inch openings (stainless steel wire cloth) by weighing a 10.0 gram
sample to the nearest 0.1 gram into the cup of the 1 quart Hamilton
mixer Model No. 30, adding approximately 170 ml of distilled or
deionized water and stirring the slurry for at least 7 min.
Transfer the mixture onto the 325 mesh screen; wash out the cup and
add washings onto the screen. Adjust water spray to 20 psi and
spray directly on screen for two minutes. (Spray head should be
held about four to six inches above the screen cloth. Wash the
residue to one side of the screen and transfer by washing into an
evaporating dish using distilled or deionized water from a washing
bottle. Let stand for two to three minutes and decant the clear
water. Dry (convection oven @ 150.degree. C. or under infrared oven
for approx. 15 min.) cool and weigh residue on analytical
balance.
[0058] Moisture or Loss on Drying (LOD) is the measured silica
sample weight loss at 105.degree. C. for 2 hours. Loss on ignition
(LOI) is the measured silica sample weight loss at 900.degree. C.
for 2 hours (sample previously predried for 2 hours at 105.degree.
C.).
[0059] The pH values of the reaction mixtures (5 weight % slurry)
encountered in the present invention can be monitored by any
conventional pH sensitive electrode.
[0060] To measure brightness, fine powder materials pressed into a
smooth surfaced pellet were evaluated using a Technidyne
Brightmeter S-5/BC. This instrument has a dual beam optical system
where the sample is illuminated at an angle of 45.degree., and the
reflected light viewed at 0.degree.. It conforms to TAPPI test
methods T452 and T646, and ASTM Standard D985. Powdered materials
are pressed to about a 1 cm pellet with enough pressure to give a
pellet surface that is smooth and without loose particles or
gloss.
[0061] The Radioactive Dentin Abrasion (RDA) values of dentifrices
containing the silica compositions used in this invention are
determined according to the method set forth by Hefferen, Journal
of Dental Res., July-August 1976, 55 (4), pp. 563-573, and
described in Wason U.S. Pat. Nos. 4,340,583, 4,420,312 and
4,421,527, which publications and patents are incorporated herein
by reference.
[0062] The cleaning property of dentifrice compositions is
typically expressed in terms of Pellicle Cleaning Ratio ("PCR")
value. The PCR test measures the ability of a dentifrice
composition to remove pellicle film from a tooth under fixed
brushing conditions. The PCR test is described in "In Vitro Removal
of Stain With Dentifrice" G. K. Stookey, et al., J. Dental Res.,
61, 1236-9, 1982. Both PCR and RDA results vary depending upon the
nature and concentration of the components of the dentifrice
composition. PCR and RDA values are unitless.
PREFERRED EMBODIMENTS OF THE INVENTION
[0063] The inventive materials were prepared by sequentially
forming (in situ) a first silica gel (or gel-like material) and
adding thereto sufficient amounts of reactants to form a
precipitated silica component present simultaneously with the
initially produced gel (or gel-like material). The amount of gel is
controlled by the quantity of reactants in the first stage while
the amount of precipitated silica is controlled by the quantity of
reactants in the second stage. The structure of the final product
is controlled by the amount of gel first produced as related to the
amount of precipitated silica, as well as reaction parameters, such
as temperature, rates, concentrations, pH, and so forth, as
discussed in greater detail above.
EXAMPLE
[0064] The inventive example initially involved the provision of
8140 liters of 6.0% sodium silicate to which was added 11.4%
sulfuric acid at a rate of 191.3 liters/minute for 8 minutes at a
temperature of 50.degree. C. within a reactor. The resultant silica
gel-containing slurry was then heated up to 93.degree. C. for 53
minutes thereafter. Subsequently, 13 minutes into the heating step,
high shear flow of 3000 liters/minute of reactor slurry (gel) was
started and continued throughout the remainder of the example
production. After the 53 minutes completed, 30 kilograms of dry
weight of sulfuric acid (243.8 liters) was then added to the gel
slurry. Thereafter, simultaneous sulfuric acid and sodium silicate
addition was started with introduction of both to the reactor to
initiate the precipitation step. The sodium silicate of 16.21%
concentration (at a temperature of 85.degree. C.) was added at 339
liters/minute and dilute sulfuric acid (11.4% concentration) was
introduced at 191.3 liters/minute. The silicate was added for a
duration of 48 minutes. The acid was added until the pH of the
resultant slurry was dropped to 7.0. At that point, the acid flow
was reduced to 110 liters/minute until the pH was between 5.3 and
5.5, at which point acid addition was stopped. The resultant
composition was then allowed to digest for another 10 minutes at
93.degree. C. The resultant slurry was then recovered by
filtration, washed to a sodium sulfate concentration of less than
about 5% (preferably less than 4%, and most preferably below 2%) as
determined by monitoring the filtrate conductivity and then spray
dried to a level of about 5% moisture. The dried product was then
milled to uniform size.
COMPARATIVE EXAMPLE
[0065] The same basic method as above was followed, except that no
high shear conditions after gel formation were utilized.
[0066] Certain properties of the resultant materials from the
Example and Comparative Example were then measured. The following
table shows those results: TABLE-US-00002 TABLE 1 Material
Properties Example Ex. Comp. % moisture 3.4 4.1 % LOI 2.9 2.8 % 325
Mesh Residue 0 0 5% pH 7.0 7.21 Brightness (technidyne) 96 94.6
Average Particle Size, .mu.m Median Particle Size 9.64 9.35
(Horiba) Mean Particle Size (Horiba) 10.95 10.64 Einlehner Abrasion
(mg 3.53 6.17 loss/100,000 rev) Oil Absorption (cc/100 g) 105
99
[0067] A brightness of at least 95.5 is a significant improvement
over the comparative type and is thus the low end of the brightness
level of the inventive materials.
Dentifrice Formulations
[0068] Toothpaste formulations were prepared using the
above-described gel/precipitated silica example and comparative
example to demonstrate the ready-to-use on demand capabilities of
the inventive compositions without furthering metering of the two
components for optimum dental protection benefits.
[0069] To prepare the dentifrices, the glycerin, sodium
carboxymethyl cellulose, polyethylene glycol and sorbitol were
mixed together and stirred until the ingredients were dissolved to
form a first admixture. The deionized water, sodium fluoride,
tetrasodium pyrophosphate and sodium saccharin were also mixed
together and stirred until these ingredients are dissolved to form
a second admixture. These two admixtures were then combined with
stirring. Thereafter, the optional color was added with stirring to
obtain a "pre-mix". The pre-mix was placed in a Ross mixer (Model
130 LDM) and silica thickener, abrasive silica and titanium dioxide
were mixed in without vacuum. A 30-inch vacuum was drawn and the
resultant admixture was stirred for approximately 15 minutes.
Lastly, sodium lauryl sulfate and flavor were added and the
admixture was stirred for approximately 5 minutes at a reduced
mixing speed. The resultant dentifrice was transferred to plastic
laminate toothpaste tubes and stored for future testing. The
dentifrice formulations are given in Table 2 below. The dentifrice
formulation utilized was considered a suitable test dentifrice
formulation for the purposes of determining PCR and RDA
measurements for the inventive and comparative cleaning abrasives.
TABLE-US-00003 TABLE 2 Example Comparative Formulation Formulation
Glycerin 11 11 (99.5%), % Sorbitol (70%), % 40 40 Deionized 20 20
water, % CARBOWAX .RTM. 3 3 600.sup.1, % CEKOL .RTM. 500T 1.2 1.2
CMC.sup.2, % Tetrasodium 0.5 0.5 pyrophosphate Sodium 0.2 0.2
Saccharin, % Sodium 0.243 0.243 Fluoride, % Silica thickener 1.5
1.5 Zeodent .RTM. 165.sup.3, % Example 20 abrasive, % Comp. Example
20 abrasive, % TiO.sub.2, % 0.5 0.5 Sodium lauryl 1.2 1.2 sulfate,
% Flavor, % 0.65 0.65 .sup.1A polyethylene glycol available from
Dow Chemical Company, Midland, MI .sup.2A carboxymethylcellulose
available from CPKelco Oy, Arnhem, The Netherlands .sup.3An
amorphous, precipitated high structure silica thickening available
from J. M. Huber Corporation, Havre de Grace, MD
[0070] The dentifrice formulations prepared above were evaluated
for PCR and RDA properties, according to the methods described
above; the measurements, as well as the PCR:RDA ratios for each
dentifrice formulation are provided in Table 3 below.
TABLE-US-00004 TABLE 3 Example Comparative Formulation Formulation
PCR 85 87 RDA 88 113 PCR/ 0.97 0.77 RDA
[0071] The results show highly effective cleaning capabilities with
relatively low dentin abrasion properties for both examples, but
much pronounced improvement in the inventive example in terms of
lowered RDA with very low ratio of PCR/RDA. A ratio of as close to
1.0 is preferred; thus, above 0.8 is desired, with above 0.85 more
preferred, above 0.90 still more preferred, and above 0.95 most
preferred.
[0072] While the invention will be described and disclosed in
connection with certain preferred embodiments and practices, it is
in no way intended to limit the invention to those specific
embodiments, rather it is intended to cover equivalent structures
structural equivalents and all alternative embodiments and
modifications as may be defined by the scope of the appended claims
and equivalence thereto.
* * * * *