NON-AQUEOUS ORAL CARE COMPOSITIONS

Field of the Invention
The present invention is concerned with non-aqueous oral care compositions.
Background of the Invention
Oral care compositions such as dentifrices typically contain dentally acceptable
abrasive, humectant, water, and water-soluble polymer which serves as a
thickener and binder for the ingredients. A variety of other ingredients such as
flavours, sweeteners, preservatives and fluoride are also utilized at low levels.
However there are many materials which are physically or chemically
incompatible with the aqueous environments found in typical dentifrice
formulations.
Non-aqueous formulations have been suggested as a way of improving the
stability of these materials. For example, WO96/031 08 describes a non-aqueous
dentifrice composition comprising a carboxyvinyl polymer, a humectant, a
polyethylene glycol and a dentally acceptable abrasive. The carboxyvinyl polymer
is stated to thicken the humectant materials and provide the necessary rheology in
order to suspend any required abrasive material. A polyethylene glycol selected
from PEG 300 and PEG 400 is stated to reduce stickiness from the formulation
and give a smooth textured product.
A problem with non-aqueous formulations such as those disclosed in
WO96/031 08 is that they do not behave Theologically like a typical aqueous
dentifrice. This problem is observed both during manufacture and during use by
the consumer. It has led to manufacturing difficulties and reduced acceptance
amongst consumers. Viscosity profile and flow characteristics are key factors
governing ease of processing, product performance and consumer perception of a
dentifrice.
The present inventors have found that this problem can be solved by the
incorporation of a particular combination of polyethylene glycols.
Summary of the Invention
The present invention provides a non-aqueous oral care composition with a liquid
continuous phase comprising a thickening agent, a humectant, and one or more
liquid polyethylene glycols having a melting point below 25°C, in which the liquid
continuous phase is structured with crystals of one or more solid polyethylene
glycols having a melting point of 25°C or above.
The rheological behaviour of the composition of the invention corresponds well
with the characteristic rheological behaviour of typical aqueous dentifrice
formulations. This correspondence is observed across a wide range of conditions
of temperature and shear. Compared to previous non-aqueous dentifrice
formulations, the composition of the invention has improved microstructure, ease
of processing and excellent sensory properties.
A particular advantage of the composition of the invention is its thermal storage
stability across an extended range of temperature. Contrary to what has been
observed in previous anhydrous dentifrice formulations, the composition of the
invention remains fully stable and functional at temperatures as low as 5°C and as
high as 50°C.
Detailed Description of the Invention
The composition of the invention is non-aqueous. By "non-aqueous" it is generally
meant that water is not deliberately added to the composition in any significant
quantity. However, the term "non-aqueous" does not mean that small amounts of
water cannot be present, for example as a consequence of its association with
hygroscopic raw materials. Accordingly, for the purposes of this invention, the
term "non-aqueous" generally means that water is present in an amount no
greater than about 5%, more preferably no greater than about 3% by weight
based on the total weight of the composition.
Thickening Agent
The liquid continuous phase of the composition of the invention comprises a
thickening agent. The thickening agent helps to impart a desirable viscosity profile
and desirable flow characteristics to the composition.
Suitable thickening agents for use in the invention are those which are operable in
non-aqueous systems. Examples of such materials include organic
macromolecules which do not necessarily require hydration with water in order to
build viscosity, but can also build viscosity by alternative mechanisms such as by
hydrogen bonding in the presence of hydroxyl donors such as polyols.
Carboxyvinyl polymers have been found to be useful in this context. Preferred
carboxyvinyl polymers for use in the invention have a molecular weight of at least
about 750,000, more preferably at least about 1,250,000, most preferably at least
about 3,000,000 g/mol. A suitable chemical class of such carboxyvinyl polymers
for use in the invention includes crosslinked polymers having a polymer backbone
derived from acrylic acid, substituted acrylic acid, or salts or esters thereof, in
which the crosslinking agent contains two or more carbon-carbon double bonds
and is derived from a polyhydric alcohol. Specific examples of such materials are
homopolymers of acrylic acid cross-linked with allyl ethers of sucrose or
pentaerythritol and homopolymers of acrylic acid cross-linked with divinyl glycol.
The most preferred carboxyvinyl polymer for use in the compositions of the
present invention is a homopolymer of acrylic acid crosslinked with allyl ethers of
pentaerythritol, which is slightly pre-neutralised ( 1 to 3%) by potassium salt. This
pre-neutralisation is done in order to precipitate polyacrylic acid in the presence of
the polymerisation solvent. Such a material is commercially available, for
example, as CARBOPOL® 974P NF Polymer, ex Lubrizol Advanced Materials,
Inc. Mixtures of any of the above described materials may also be used.
The level of thickening agent will depend on the particular type chosen, but
generally ranges from 0.05 to 10% by total weight thickener based on the total
weight of the composition. When the thickening agent is a carboxyvinyl polymer
(as described above), the amount of carboxyvinyl polymer in compositions of the
invention suitably ranges from 0.05 to 5%, preferably from 0.1 to 2%, more
preferably from 0.2 to 0.5% by total weight carboxyvinyl polymer based on the
total weight of the composition.
Humectant
The liquid continuous phase of the composition of the invention comprises a
humectant. The humectant helps to keep the composition from hardening or
crystallizing upon exposure to air. It also helps to give the composition a moist feel
to the mouth, and may in some cases impart a desirable sweetness.
Preferred humectants for use in the invention include organic polyols having 3 or
more hydroxyl groups in the molecule (hereinafter termed "organic polyols").
Examples of such materials include glycerol, sorbitol, xylitol, mannitol, lactitol,
maltitol, erythritol, and hydrogenated partially hydrolyzed polysaccharides. The
most preferred organic polyol is glycerol. Mixtures of any of the above described
materials may also be used.
The level of humectant will depend on the particular type chosen, but generally
ranges from about 20 to 90% by weight based on the total weight of the
composition. When the humectant is one or more organic polyols (as described
above), the amount of organic polyol suitably ranges from 35 to 75%, more
preferably from 45 to 70% by total weight organic polyol based on the total weight
of the composition. Most preferably the composition of the invention is organic
polyol-based. In the context of the present invention, the term "organic polyolbased"
means that the composition is not oil-based or water-based, but instead,
organic polyols (as defined above) are a principal component in the composition.
By "principal component" is meant that the organic polyols (as defined above)
when taken together, make up a higher portion of the composition's weight than
any other compound. Ideally the composition of the invention is glycerol-based
(i.e glycerol makes up a higher portion of the composition's weight than any other
compound) and contains from 45 to 70% by weight glycerol based on the total
weight of the composition.
Solid Polyethylene Glycol
The liquid continuous phase of the composition of the invention is structured with
crystals of one or more solid polyethylene glycols having a melting point of 25°C
or above. Preferably the melting point ranges from 35 to 65°C, more preferably
from 55 to 60° C.
The crystals of the solid polyethylene glycol(s) help to provide an optimised
microstructure for the composition.
Polyethylene glycols have the general formula H(OCH2CH2 ) n OH, where n is the
number of repeating oxyethylene units. Commercially available polyethylene
glycols are usually not uniform chemical compounds, but instead consist of a
distribution of similar polymer members of the homologous polyethylene glycol
series, defined by average values of n and molecular weight. The melting point
generally increases with increasing average values of n and molecular weight.
Suitable solid polyethylene glycols have an average value of n in the above
general formula ranging from about 20 to 220, preferably from about 40 to 150,
more preferably from about 32 to 90, most preferably from about 60 to 75. The
average molecular weight suitably ranges from about 950 to 11,250, preferably
from about 1800 to 6600, more preferably from about 1400 to 4400, most
preferably from about 2700 to 3700 g/mol. Suitable commercially available
materials include for example Polyglykol® 3000 (ex Clariant). Mixtures of any of
the above described materials may also be used.
The amount of solid polyethylene glycol (as defined above) in compositions of the
invention suitably ranges from 0.1 to 5%, preferably from 0.5 to 3%, more
preferably from 1 to 2.5% by total weight solid polyethylene glycol (as defined
above) based on the total weight of the composition.
Liquid Polyethylene Glycol
The liquid continuous phase of the composition of the invention one or more liquid
polyethylene glycols having a melting point below 25°C. Preferably the melting
point ranges from -50 to 22°C, more preferably from - 15 to 8° C, most preferably
from 4 to 8°C.
The liquid polyethylene glycol(s) helps to make processing of the composition
easier, especially at high shear, by reducing the overall viscosity of the liquid
continuous phase.
Preferred liquid polyethylene glycols have an average value of n in the general
formula (2 2)(as described above) ranging from about 4 to 12, more
preferably about 6 to 8, most preferably about 8 . The average molecular weight
suitably ranges from about 190 to 630, more preferably from about 285 to 420,
most preferably from about 380 to 420 g/mol. Suitable commercially available
materials include for example PEG 400 (ex BDH Chemicals). Mixtures of any of
the above described materials may also be used.
The amount of liquid polyethylene glycol (as defined above) in compositions of the
invention suitably ranges from 1 to 20%, preferably from 5 to 15%, more
preferably from 8 to 12% by total weight liquid polyethylene glycol (as defined
above) based on the total weight of the composition.
Product Form and Optional Ingredients
The composition of the invention is typically in the form of a dentifrice. The term
"dentifrice" denotes a formulation which are used to clean the surfaces of the oral
cavity. The dentifrice is an oral composition that is not intentionally swallowed for
purposes of systemic administration of therapeutic agents, but is retained in the
oral cavity for a sufficient time to contact substantially all of the dental surfaces
and/or mucosal tissues for purposes of oral activity. Preferably the dentifrice is
suitable for application with a toothbrush and is rinsed off after use. Preferably the
dentifrice is in the form of an extrudable semi-solid such as a cream, paste or gel
(or mixture thereof).
A dentifrice composition according to the invention will generally contain further
ingredients to enhance performance and/or consumer acceptability such as
abrasive cleaning agent and surfactant.
For example, a dentifrice will usually comprise an abrasive cleaning agent in an
amount of from 3 to 75% by weight based on the total weight of the dentifrice.
Suitable abrasive cleaning agents include particulate abrasive materials such as
abrasive silicas, aluminas, calcium carbonates, zirconium silicate,
polymethylmethacrylate, dicalcium phosphates, calcium pyrophosphates,
hydroxyapatites, trimetaphosphates, insoluble hexametaphosphates and
agglomerates and/or mixtures thereof.
Furthermore, a dentifrice will usually contain a surfactant in an amount of from 0.2
to 5% by weight based on the total weight of the dentifrice. Suitable surfactants
include anionic surfactants, such as the sodium, magnesium, ammonium or
ethanolamine salts of Cs to Cis alkyl sulphates (for example sodium lauryl
sulphate), Cs to Cis alkyl sulphosuccinates (for example dioctyl sodium
sulphosuccinate), Csto Cis alkyl sulphoacetates (such as sodium lauryl
sulphoacetate), Cs to Cis alkyl sarcosinates (such as sodium lauryl sarcosinate),
Cs to Cis alkyl phosphates (which can optionally comprise up to 10 ethylene oxide
and/or propylene oxide units) and sulphated monoglycerides. Other suitable
surfactants include nonionic surfactants, such as optionally polyethoxylated fatty
acid sorbitan esters, ethoxylated fatty acids, esters of polyethylene glycol,
ethoxylates of fatty acid monoglycerides and diglycerides, and ethylene
oxide/propylene oxide block polymers. Other suitable surfactants include
amphoteric surfactants, such as betaines or sulphobetaines. Mixtures of any of
the above described materials may also be used.
Being non-aqueous, the composition of the invention is particularly suitable as a
vehicle for oral care actives which may be physically or chemically incompatible
with water, or which may function less efficiently in an aqueous environment.
Specific examples of oral care actives which may be included in the compositions
of the invention include:
fluoride sources such as sodium fluoride, stannous fluoride, sodium
monofluorophosphate, zinc ammonium fluoride, tin ammonium fluoride, calcium
fluoride, cobalt ammonium fluoride and mixtures thereof;
plant-derivable antioxidants such as flavonoid, catechin, polyphenol, and tannin
compounds and mixtures thereof;
antioxidant vitamins such as tocopherols and/or derivatives thereof, ascorbic acid
and/or derivatives thereof and mixtures thereof.
Preferred examples of oral care actives for inclusion in the compositions of the
invention include agents for the remineralisation of teeth. The term
"remineralisation" in the context of the present invention means the in situ
generation of hydroxyapatite on teeth.
A specific example of a suitable agent for the remineralisation of teeth is a mixture
of a calcium source and a phosphate source which, when delivered to the teeth
results in the in situ generation of hydroxyapatite on teeth.
Illustrative examples of the types of calcium source that may be used in this
context (hereinafter termed "remineralising calcium sources") include, for
example, calcium phosphate, calcium gluconate, calcium oxide, calcium lactate,
calcium glycerophosphate, calcium carbonate, calcium hydroxide, calcium
sulphate, calcium carboxymethyl cellulose, calcium alginate, calcium salts of citric
acid, calcium silicate and mixtures thereof. Preferably the remineralising calcium
source is calcium silicate.
The amount of remineralising calcium source(s) (e.g. calcium silicate) in the
composition of the invention typically ranges from 1 to 30%, preferably from 5 to
20% by total weight remineralising calcium source based on the total weight of the
oral care composition.
Illustrative examples of the types of phosphate source that may be used in this
context (hereinafter termed "remineralising phosphate sources") include, for
example, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium
pyrophosphate, tetrasodium pyrophosphate, sodium tripolyphosphate, sodium
hexametaphosphate, potassium dihydrogenphosphate, trisodium phosphate,
tripotassium phosphate and mixtures thereof. Preferably the remineralising
phosphate source is a mixture of trisodium phosphate and sodium dihydrogen
phosphate.
The amount of remineralising phosphate source(s) (e.g. trisodium phosphate and
sodium dihydrogen phosphate) in the composition of this invention typically
ranges from 2 to 15%, preferably from 4 to 10% by total weight remineralising
phosphate source based on the total weight of the oral care composition.
Mixtures of any of the above described materials may also be used.
Compositions of the present invention may also contain further optional
ingredients customary in the art such as anticaries agents, anticalculus agents,
buffers, flavouring agents, sweetening agents, colouring agents, opacifying
agents, preservatives, antisensitivity agents, antimicrobial agents and the like.
Process
The invention also provides a process of preparing a non-aqueous oral care
composition as defined above, comprising the steps of forming a mixture
comprising the thickening agent, the humectant, the liquid polyethylene glycol(s)
and the solid polyethylene glycol(s), heating the mixture to a temperature above
the melting point of the solid polyethylene glycol(s), and cooling the mixture to
form crystals of the solid polyethylene glycol(s).
A preferred process according of the invention comprises the following steps:
(i) heating a mixture of the humectant and the liquid polyethylene glycol(s) to
a temperature above the melting point of the solid polyethylene glycol(s) and
dispersing the solid polyethylene glycol(s) into the mixture;
(ii) adding powdered ingredients (such as abrasive cleaning agent and/or
surfactant) to the mixture so obtained;
(iii) adding the thickening agent to the mixture so obtained, and
(iv) cooling the mixture to form crystals of the solid polyethylene glycol(s).
Further optional ingredients (such as the fluoride sources and/or the agents for the
remineralisation of teeth, as described above) may suitably be added between
steps (i) and (ii).
The invention is further illustrated with reference to the following, non-limiting
Example.
EXAMPLE
The following formulation represents a dentifrice composition according to the
invention.
Ingredient (% w/w)
Glycerol (99.5% a.i.) 55.14
PEG 400 (ex BDH Chemicals) 10.5
Flavour 1.0
Trisodium phosphate 3.8
Calcium silicate 15.0
Sodium monofluorophosphate 1.1 1
Sodium saccharin 0.2
CARBOPOL® 974P NF Polymer, (ex Lubrizol 0.3
Advanced Materials, Inc.)
Monosodium dihydrogen phosphate 3.2
Polyglykol® 3000 (ex Clariant) 1.75
Sodium lauryl sulphate (powdered) 2.0
Abrasive silica (powdered) 6.0
The formulation was prepared as follows:
(i) Heat the glycerol and the PEG 400 to 60°C, and disperse the Polyglykol®
3000;
(ii) Add the trisodium phosphate, monosodium dihydrogen phosphate, sodium
monofluorophosphate and sodium saccharin and mix until lump free, keeping the
temperature at 60°C;
(iii) Add the mixture to a Fryma®DT1 0 mixer and mix for 5 minutes;
(iv) Draw the calcium silicate slowly into the mixture and mix for 10 minutes;
(v) Pre-mix the sodium lauryl sulphate and abrasive silica, draw in to the mixture
and mix for 10 minutes;
(vi) Add the CARBOPOL® 974P NF Polymer and mix for 5 minutes;
(vii) Cool the mixture to 30°C, add flavour and mix to disperse.
CLAIMS
1. A non-aqueous oral care composition with a liquid continuous phase
comprising a thickening agent, a humectant, and one or more liquid polyethylene
glycols having a melting point below 25°C, in which the liquid continuous phase is
structured with crystals of one or more solid polyethylene glycols having a melting
point of 25°C or above.
2 . A composition according to claim 1, in which the carboxyvinyl polymer has
a molecular weight of at least 750,000 g/mol.
3 . A composition according to claim 1 or claim 2, in which the carboxyvinyl
polymer is selected from homopolymers of acrylic acid cross-linked with allyl
ethers of sucrose or pentaerythritol; and homopolymers of acrylic acid crosslinked
with divinyl glycol.
4 . A composition according to any one of claims 1 to 3, in which the
humectant is one or more organic polyols having 3 or more hydroxyl groups in the
molecule.
5 . A composition according to any one of claims 1 to 4, in which the solid
polyethylene glycol has a melting point ranging from 35 to 65°C.
6 . A composition according to any one of claims 1 to 5, in which the solid
polyethylene glycol has the general formula (2 2)OH, where n is the
number of repeating oxyethylene units, and the average value of n ranges from 60
to 75.
7 . A composition according to any one of claims 1 to 6, in which the liquid
polyethylene glycol has a melting point ranging from - 15 to 8° C.
8 . A composition according to any one of claims 1 to 7, in which the liquid
polyethylene glycol has the general formula H(OCH2CH2)nOH, where n is the
number of repeating oxyethylene units, and the average value of n ranges from 4
to 12 .
9 . An oral care composition according to any one of claims 1 to 8, which is in
the form of a dentifrice comprising an abrasive cleaning agent in an amount of
from 3 to 75% by weight based on the total weight of the dentifrice, and a
surfactant in an amount of from 0.2 to 5% by weight based on the total weight of
the dentifrice.
10 . An oral care composition according to any one of claims 1 to 9, which
further comprises a mixture of a calcium source and a phosphate source which,
when delivered to the teeth results in the in situ generation of hydroxyapatite on
teeth.
11. An oral care composition according to claim 10, in which the calcium
source is calcium silicate and the phosphate source is a mixture of trisodium
phosphate and sodium dihydrogen phosphate.
12 . An oral care composition according to any one of claims 1 to 11, which
further comprises one or more oral care actives selected from fluoride sources,
plant-derivable antioxidants and antioxidant vitamins.
13 . A process of preparing a non-aqueous oral care composition according to any
one of claims 1 to 12, comprising the steps of forming a mixture comprising the
thickening agent, the humectant, the liquid polyethylene glycol(s) and the solid
polyethylene glycol(s), heating the mixture to a temperature above the melting
point of the solid polyethylene glycol(s), and cooling the mixture to form crystals
of the solid polyethylene glycol(s).