DESCRIPTION

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 62/018,728, filed June 30, 2014, which is assigned to the assignee hereof and hereby expressly incorporated by reference in its entirety.

FIELD OF THE INVENTION

[0002] The invention relates to improved aqueous pigment suspensions.

BACKGROUND OF THE INVENTION

[0003] Pigments give color to paints and other surface coatings and are generally insoluble in their vehicle. Pigments are often distinguished from dyes, which have traditionally been regarded as colorants that are soluble in their vehicle. Pigments may be organic or inorganic, and natural or synthetic. Water- insoluble pigments usually provide better light and heat stability, water and rubbing resistance compared to typical water-soluble and partially soluble dyes.

[0004] Naturally occurring pigments such as ochre have been used as colorants for thousands of years. The industrial revolution resulted in a huge expansion in the range of synthetic pigments, which are usually manufactured or refined from natural raw materials. Synthetic pigments are generally less expensive, more uniform in color, and easier to blend. However in some application natural pigments may be required or more desirable. For example, in the United States there are some food coloring additives are exempt from certification. Of these, the majority are based on natural pigments. Generally, synthetic pigments must be certified as color additives and approved for use by the Food and Drug Administration. There is also a strong and growing demand among customers for all natural products thereby increasing the demand for natural pigments and pigment systems that are compatible with natural pigments.

[0005] Aqueous suspensions of pigments are generally composed of water, pigments, and compounds that are meant to suspend the pigment particles, prevent or retard particle sedimentation, and control the flow properties. Pigment suspensions with high concentration of pigments, hence high color strength, are generally desirable because they decrease the required use level, which results in a reduced amount of water and other compounds in the dispersing medium that are applied to the end product.

[0006] Currently, commercial aqueous suspensions of water-insoluble pigments often include carriers such as sugar compounds and their derivatives to aid the suspension of the pigments. However, these types of carriers often need to be used at high concentration, which can result in a high overall product cost, and the presence of carriers in high concentration may not be desirable in the end application. Furthermore, even in high concentration, common carriers often fail to prevent settling of the suspended pigments.

[0007] There is a demand for pigment suspension systems that are compatible with natural and synthetic pigments, resistant to sedimentation and syneresis when stored without temperature control, and able to sufficiently recover an elastic gel form after exposure to multiple shear stress cycles while still being easily pourable and dispersible. The present invention fulfills this need.

SUMMARY OF THE INVENTION

[0008] The present invention provides an aqueous pigment suspension including a water- insoluble pigment, an iota-carrageenan hydrocolloid, at least one divalent cation, and water; wherein the iota-carrageenan hydrocolloid is soluble in water, one or more divalent cations interact with the iota-carrageenan hydrocolloid to form a stabilizing thixotropic gel network, the amount of divalent cation modifies the rheological properties of the stabilizing thixotropic gel network, the stabilizing thixotropic gel network suspends the water-insoluble pigment, the aqueous pigment suspension is resistant to sedimentation and syneresis at a storage temperature for a storage duration, and the aqueous pigment suspension is able to sufficiently recover an elastic gel form after exposure to multiple shear stress cycles.

[0009] In certain other non- limiting embodiments of the present invention, the iota- carrageenan hydrocolloid is a Na-iota-carrageenan hydrocolloid and the divalent cation is calcium. In certain other non-limiting embodiments of the present invention, the suspension has a viscosity in the range of about 10 to about 10,000 Pa-s and more preferably about 100 to about 1,000 Pa-s when measured at 25°C and a shear rate of 1 reciprocal second. In certain other non-limiting embodiments of the present invention, the storage temperature is about 20°C to about 40°C. In certain other non-limiting embodiments of the present invention, the storage duration is about three days or more. In certain other non-limiting embodiments of the present invention, the storage temperature is about 20°C and the storage duration is about three weeks or more. In certain other non- limiting embodiments of the present invention, the water-insoluble pigment has a concentration of from about 1 to about 60 weight percent of the suspension. In certain other non- limiting embodiments of the present invention, the iota- carrageenan hydrocolloid has a concentration of from about 0.005 to about 5 weight percent, preferably from about 0.2 to about 5 weight percent, and more preferably from about 0.4 to about 5 weight percent of the suspension. In certain other non-limiting embodiments of the present invention, the divalent cation or cations have a concentration of from about 0.005 to about 5 weight percent, and preferably from about 0.01 to about 5 weight percent of the suspension. In certain other non-limiting embodiments of the present invention, the average particle size of the pigment is from about 0.01 to about 50 microns. In certain other non- limiting embodiments of the present invention, water accounts for at least about 20 weight percent and no more than about 95 weight percent of the suspension. In certain other non- limiting embodiments of the present invention, the water-insoluble pigment includes vegetable carbon, titanium dioxide, iron oxide, zinc oxide, lithopone, carotenoids, ultramarine, chromium (III) oxide, sienna, carmine lakes, chlorophyllin, and curcumin. In certain other non-limiting embodiments of the present invention, the water-insoluble iron oxide pigment is iron (III) oxide (Fe ₂ C>3), hydrated iron (III) oxide (FeO(OH) Ή ₂ 0), or iron (II, III) oxide (FeO-Fe ₂ C>3). In certain other non-limiting embodiments of the present invention, the aqueous pigment suspension further includes a water-soluble or miscible ingredient. In certain other non-limiting embodiments of the present invention, the water- soluble or miscible ingredient is selected from the group consisting of sugars, sugar alcohols, glycols, and their derivatives, and combinations thereof. In certain other non- limiting embodiments of the present invention, the aqueous pigment suspension further includes a preservative. In certain other non-limiting embodiments of the present invention, the preservative is selected from the group consisting of sorbic acid and salts thereof, benzoic acid and salts thereof, propionic acid and salts thereof, and parabens. In certain other non- limiting embodiments of the present invention, the aqueous pigment suspension further includes a sequestering agent selected from the group consisting of a salt of carboxylic acid and a salt of a phosphoric acid. In certain other non-limiting embodiments of the present invention, the aqueous pigment suspension further includes a surface active substance. In certain other non-limiting embodiments of the present invention, the aqueous pigment suspension additionally comprises one or more additional pigments that are either water- insoluble or water soluble. In certain other non-limiting embodiments of the present invention, the additional water soluble pigment in the aqueous pigment suspension is carminic acid, chlorophyllin, anthocyanin, carmine lakes, or curcumin. In certain other non- limiting embodiments of the present invention, the aqueous pigment suspension additionally includes a second hydrocolloid selected from the group consisting of non-iota-carrageenan, gellan gum, microcrystalline cellulose, modified carboxymethyl cellulose, gum arabic, furcellaran, cassia gum, guar gum, locust bean gum, tara gum, xanthan gum, konjac mannan, tragacanth, alginate, propylene glycol alginate, agar, agarose, gelatin, starch, a starch derivative, a cellulose derivative, a glucomannan, pectin, pullulan, a synthetic hydrocolloid, a protein, and combinations thereof. For embodiments including an additional hydrocolloid, the amounts of the other components may need to be adjusted using standard methods known in the art.

[0010] The present invention also provides a method of making the aqueous pigment suspension disclosed above, including the step of mixing the water-insoluble pigment, the iota-carrageenan hydrocolloid, and water.

[0011] The present invention also provides aqueous pigment suspensions disclosed above, that are useful as coloring agents for pharmaceutical, food, personal care, or household products.

DETAILED DESCRIPTION OF THE INVENTION

[0012] The invention relates to novel aqueous pigment compositions and methods of making and using the same. The inventors found that certain pigments can be dispersed at a high concentration in an aqueous medium in presence of certain hydrocolloids, preferably in combination with certain salts. The hydrocolloids form a thixo tropic gel network which immobilizes the dispersed pigment particles in the aqueous medium. Once set, this system is stable against sedimentation and syneresis when stored for a period of time depending on the storage temperature. For example, at 20°C the suspension is stable for at least about 3 weeks and at 40°C at least about 3 days. At the same time, the thixotropic property of the system facilitates the rapid, yet reversible, conversion of the elastic gel into a less viscous and thus easily pourable liquid when the gel is subjected to shear stress (e.g. , shaking, pumping, stirring, or the like). After exposure to shear stress, if the system is allowed to rest it is able to return to the stable elastic gel form of the thixotropic gel network. The system is able to sufficiently reform the stable elastic gel form even after exposures to multiple shear stress cycles.

[0013] The present invention provides an aqueous pigment suspension including a water- insoluble pigment, an iota-carrageenan hydrocolloid, at least one divalent cation, and water; wherein the iota-carrageenan hydrocolloid is soluble in water, one or more divalent cations interact with the iota-carrageenan hydrocolloid to form a stabilizing thixotropic gel network, the amount of divalent cation modifies the rheological properties of the stabilizing thixotropic gel network, the stabilizing thixotropic gel network suspends the water-insoluble pigment, once set the aqueous pigment suspension is resistant to sedimentation and syneresis, and the aqueous pigment suspension is able to sufficiently recover an elastic gel form after exposure to multiple shear stress cycles.

[0014] As used herein, the term soluble in water means the ingredient dissolves in water at or above about 1°C. As used herein, the term water- insoluble pigment refers to a pigment that is water-insoluble or sparingly soluble in water.

[0015] As used herein, the term water-insoluble pigment includes any iron oxide pigment (including pigments having different shades, e.g. , red, yellow, brown, black, and their blends), any pigment that is derived from iron oxide, vegetable carbon, titanium dioxide, or carotenoids. Non-limiting examples of iron oxides within the scope of the present invention include iron (III) oxide (Fe ₂ C>3) ; hydrated iron (III) oxide (FeO(OH) H ₂ 0); and iron (II, III) oxide (FeO-Fe ₂ C>3). Non-limiting examples of water-insoluble carotenoids include β- carotene, lycopene, bixin, and lutein. Moreover the term water-insoluble pigment includes certain pigments that are water-insoluble at a certain pH range. Examples include, but are not limited to, carmine lakes, chlorophyllin, or curcumin. These pigments are commercially available from a variety of sources that are generally known in the art.

[0016] As used herein, the term vegetable carbon refers to a black colored pigment in the form of a finely divided carbon produced from raw materials of vegetable origin. Methods for producing vegetable carbon are known in the art and include charring raw materials of vegetable origin at high temperatures. The resulting black pigment powder is also known as vegetable carbon black, vegetable black, activated vegetable carbon, carbo medicinalis vegetabilis, activated carbon, and carbon black. [0017] As used herein, the term hydrocolloid refers to a hydrophilic polymer that can be dispersed in water. Non-limiting examples of hydrocolloids within the scope of the present invention include carrageenan, including but not limited to iota-carrageenan, non-iota- carrageenan, kappa-carrageenan, kappa-2-carrageenan and lambda-carrageenan, gellan gum, microcrystalline cellulose, modified carboxymethyl cellulose, gum arabic, furcellaran, cassia gum, guar gum, locust bean gum, tara gum, xanthan gum, konjac mannan, tragacanth, alginate, propylene glycol alginate, agar, agarose, gelatin, starch, a starch derivative, a cellulose derivative, a glucomannan, pectin, pullulan, a protein, and combinations thereof. These polymers are commercially available from a variety of sources that are generally known in the art.

[0018] Carrageenan is a commercially significant galactan polysaccharide found in red seaweed. All carrageenans contain repeating galactose units that are joined by alternating ocl→3 and β1→4 glycosidic linkages and that are sulfated to varying degrees. The commercially most important types of carrageenan are iota-carrageenan, kappa-carrageenan, kappa-2-carrageenan, and lambda-carrageenan. The primary differences between these different types of carrageenan are the number and position of the ester sulfate groups on the repeating galactose units and the seaweed from which the carrageenan is obtained. Higher levels of ester sulfate tend to lower the temperature at which the carrageenan is soluble and tend to result in lower strength carrageenan gels. See Kirk-Othmer's Encyclopedia of Chemical Technology, 4 ^th Edition, Vol. 4, p. 942, which is incorporated herein by reference in its entirety.

[0019] Iota-carrageenan is characterized by a repeating unit of D-galactose-4-sulfate-3,6- anhydro-D-galactose-2-sulfate. Iota-carrageenan can be obtained, for example, from

Eucheuma denticulatum (also referred to as "Spinosum"). Kappa-carrageenan is

characterized by a repeating unit of D-galactose-4-sulfate-3,6-anhydro-D-galactose and can be obtained, for example, from Kappaphycus alvarezii (also known as "Eucheuma cottonii"). Kappa-2-carrageenan is reported by R. Falshaw, H. J. Bixler and K. Johndro, Structure and Performance of Commercial Kappa-2 Carrageenan Extracts, Food Hydrocolloids 15 (2001) 441-452, and by H. Bixler, K Johndro and R Falshaw, Kappa-2 carrageenan: structure and performance of commercial extracts II, Food Hydrocolloids 15 (2001) 619-630, to be characterized by copolymers containing a certain amount of kappa repeating units (3:6- anhydrogalactose (3:6- AG)) and iota repeating units (3:6-anhydrogalactose-2-sulfate (3:6- AG-2-S)) covalently bound in the copolymer backbone, and to be obtainable from certain Gigartinaceae algae. The foregoing references state that such kappa-2-carrageenans have distinctly different properties by comparison to simple mixtures of kappa- and iota- carrageenan. Kappa-2-carrageenan extracted from Gigartina atropurpurea is reported by R. Falshaw, H Bixler and K Johndro, Structure and Performance of Commercial Kappa-2 Carrageenan extracts III, Food Hydrocolloids 17 (2003) 129-139. While there has been considerable confusion historically about the physical nature of kappa-2-carrageenan, recent studies, such as those mentioned above, have confirmed that kappa-2-carrageenan is a copolymer containing kappa and iota repeating units covalently bound (in certain ratios of kappa to iota moieties) in the copolymer backbone in clear distinction to physical mixtures of kappa and iota polymers. See U.S. Patent No. 7,807,194, which is incorporated herein by reference in its entirety. By contrast to the aforesaid carrageenans, lambda-carrageenan carries three sulfate-groups per disaccharide unit.

[0020] Carrageenan is used in a wide variety of food as well as non-food applications. Carrageenan is commonly used as gelling agent, viscosity builder, and as a stabilizing and emulsifying agent. See Kirk-Othmer's Encyclopedia of Chemical Technology, 4 ^th Edition, Vol. 11, p. 827, which is incorporated herein by reference in its entirety. See also Kirk- Othmer's Encyclopedia of Chemical Technology, 4 ^th Edition, Vol. 12, pp. 847-850, which is incorporated herein by reference in its entirety. The four main types of carrageenan are widely known in the art and can be obtained from a variety of known commercial sources, including FMC Corporation, Philadelphia, PA.

[0021] According to the present invention, the aqueous pigment suspension includes a stabilizing thixotropic gel network that is able to suspend water-insoluble compounds in such a manner as to be resistant to sedimentation and syneresis. As used herein, the term thixotropic refers to the property exhibited by certain polymer dispersions of losing viscosity in a time-dependent response to shear, hence becoming easily pourable when stirred or shaken, and of returning to the more viscous gel state upon standing. Thixotropic dispersions of hydrocolloids are useful because they can prevent the settling of water-insoluble compounds embedded in the gel network (for example pigments), while making the dispersion pourable once it has been stirred or shaken. As used herein, the term syneresis refers to the extraction or expulsion, i.e., separation, of a liquid from a gel. Methods for determining the rheological properties of thixotropic gels are known in the art. See Kirk- Othmer's Encyclopedia of Chemical Technology, 4 Edition, Vol. 21, pp. 351-355, which is incorporated herein by reference in its entirety.

[0022] Resistance to sedimentation and syneresis, as well as thixotropy, are concepts known in the art, and the skilled artisan would know how to determine whether an aqueous pigment suspension is resistant to sedimentation and syneresis over prolonged period of time and whether it shows thixotropic properties. Phase separation is undesirable because, for example, it can lead to microbial instability and re-dispersion of the pigment may be difficult or incomplete. A non- limiting example of determining a pigment suspension's resistance to sedimentation and syneresis within the scope of the present invention is visual inspection of the suspension after it has been prepared and then left undisturbed for a prolonged period of time. Similarly, a non- limiting example of determining the thixotropic flow properties of an aqueous pigment suspension within the scope of the present invention includes visual inspection or instrumental analysis of the suspension before and after it has been subjected to shear such as stirring or shaking, and after it has been left standing for a period of time.

[0023] Commercial grades of carrageenans exist as counter ion salt forms, the most common counter ions being calcium, sodium, and potassium. Many commercial

carrageenans exist as mixed salt forms while others are predominantly of a specific counter ion salt form. The identity of the counter ion composition may influence several properties of the carrageenan including solubility, gelation characteristics, and application properties.

[0024] In certain embodiments of the present invention, the counter ion salt form of the iota-carrageenan and divalent cation are selected in such a way that the interaction between the iota-carrageenan and the divalent cation forms a thixotropic gel with desirable rheological properties. Non-limiting examples of divalent cations that may be used within the scope of the present invention include Ca ²⁺ , and Mg ²⁺ ions. In preferred embodiments of the present invention, the divalent cation is Ca ²⁺ . Calcium ions or other divalent cations may be provided to the pigment suspension using any suitable ingredient. Non- limiting examples include calcium salts, such as, but not limited to, calcium chloride, calcium gluconate, calcium lactate, calcium sulphate, tricalcium citrate, and dicalcium phosphate.

[0025] In certain cases, divalent cations will be naturally present in some of the other components used to make the suspension, for example the water. To further control the amount and form of divalent cation present, demineralized water may be used for the preparation of the inventive aqueous pigment suspension. In certain other embodiments of the present invention, one or more surface active substance is used to control dispersion of one or more insoluble substance in the thixotropic gel network. In certain embodiments of the present invention, a sequestering or chelating agent is used. In certain other embodiments of the present invention, the sequestering or chelating agent is used to aid the solubilization of the hydrocolloid. Non- limiting examples of such sequestering or chelating agents within the scope of the present invention include a salt of carboxylic acid and a salt of phosphoric acid. Such sequestering or chelating agents are generally known and widely used in the art. The amount of available divalent cation is dependent upon the level and type of the calcium source added, the presence of chelating agents that can bind the divalent cations, and the pH of the suspension. The relationships between the pH of the suspension and rheological properties are known to the person of ordinary skill in the art. The pH of the suspension may also be adjusted using methods known and used within the art.

[0026] In certain embodiments of the present invention, the water-insoluble pigment has a concentration of from about 1 to about 70, from about 5 to about 50, from about 5 to about 35, from about 5 to about 30, from about 10 to about 30, from about 1 to about 10, from about 10 to about 20, from about 20 to about 30, from about 30 to about 40, from about 40 to about 50, from about 50 to about 60, or from about 60 to about 70 weight percent of the suspension.

[0027] In certain embodiments of the present invention, the iota-carrageenan

hydrocolloid has a concentration of from about 0.005 to about 5, from about 0.01 to about 4, from about 0.05 to about 3, from about 0.1 to about 2, from about 0.1 to about 1, from about 0.15 to about 0.75, or from about 0.2 to about 0.5 weight percent of the suspension.

[0028] In certain embodiments of the current invention, the iota-carrageenan hydrocolloid is predominantly in the sodium salt form, hereafter called Na-iota-carrageenan. In these embodiments, Na-iota-carrageenan accounts for from about 50% to 100% of the total iota- carrageenan content by weight. The Na-iota-carrageenan was found to be particularly advantageous as it is essentially soluble in cold solutions, from about 1°C to about 30 °C, such that heating is not required in the production process. Furthermore because Na-iota- carrageenan contains little or no divalent cations, therefore Na-iota-carrageenan does not form a strong gel unless a divalent cation, such as calcium, is added. This is particularly advantageous because the desired level of gelation can be controlled in a reproducible manner by adjusting the level of Na-iota-carrageenan and the amount and type of calcium source added. Control of the crosslinking reaction of divalent cations and Na-iota- carrageenan results in the formation of a thixotropic gel that provides good suspension and phase stabilization properties at low shear, for example during storage in a container. When shear is applied, the viscosity of the suspension decreases allowing for ease of processing. This change in viscosity is reversible such that when allowed to remain at rest, gel formation is recovered and stability is achieved. Suitable suspensions are those that have viscosities in the range of 10 to 10,000 Pa s, more preferably 100 to 1,000 Pa s, when measured at 25° C and a shear rate of 1 reciprocal second.

[0029] In certain embodiments of the present invention, the divalent cations have a concentration of from about 0.005 to about 0.2, from about 0.01 to about 0.15, from about 0.05 to about 0.1, from about 0.005 to about 0.02, from about 0.02 to about 0.08, or from 0.08 to about 0.2 weight percent of the suspension. In certain other embodiments of the present invention, the divalent cations have a concentration of from about 0.005 to about 5 weight percent of the suspension.

[0030] In certain embodiments of the present invention, the iron oxide of the aqueous pigment suspension includes iron (III) oxide. Iron (III) oxide is also commonly called hematite and commercially available from a variety of sources that are generally known in the art and therefore not specifically mentioned here. In certain other embodiments of the present invention, all the iron oxide in the pigment suspension is iron (III) oxide.

[0031] In certain embodiments of the present invention, the pigments of the aqueous suspension have an average particle size of from about 0.01 to about 50, from about 0.1 to about 10, from about 1 to about 2, from about to 0.01 to about 0.1, from about 0.1 to about 1, from about 1 to about 10, or from about 10 to about 50 microns. Decreasing the average particle size of a pigment increases the coloring power of the aqueous pigment suspension containing the pigment. Methods for decreasing average particle size are known in the art and include wet milling. Wet milling pigment particles can also increase the coloring properties of the aqueous pigment suspension by facilitating the breakdown of agglomerated particles and increasing pigment dispersion. The average particle size of pigments may be determined by any of the methodologies generally known in the art. A non- limiting example of methods that may be used within the scope of the present invention is laser diffraction. [0032] In certain embodiments of the present invention, the aqueous pigment suspension further includes a water-soluble or miscible ingredient. Non-limiting examples of water- soluble or miscible ingredients within the scope of the present invention include one or more sugars, sugar alcohols, glycols, their derivatives, and combinations thereof.

[0033] In certain embodiments of the present invention, the aqueous pigment suspension further includes one or more preservatives. Non-limiting examples of preservatives within the scope of the present invention include sorbic acid and salts thereof, benzoic acid and salts thereof, propionic acid and salts thereof, parabens, and mixtures thereof. All of these preservatives are commercially available from a variety of sources that are generally known in the art and therefore not specifically mentioned here.

[0034] In certain embodiments of the present invention, the aqueous pigment suspension further includes one or more additional pigments. The additional pigments may be water- insoluble or water soluble pigments. Non-limiting examples of water-insoluble pigments within the scope of the present invention include metal oxides such as, but not limited to, titanium dioxide and other insoluble pigments such as, but not limited to, vegetable carbon, and mixtures thereof. Non-limiting examples of water soluble pigments within the scope of the present invention include carminic acid, extract of safflower (Carthamus tinctorius L.), and anthocyanin. Moreover it includes certain pigments that are water-soluble at a certain pH range. Examples include carmine lakes, cholorphyllin, or curcumin. These pigments are commercially available from a variety of sources that are generally known in the art, including, for example, FMC Corporation, Philadelphia, PA.

[0035] In certain embodiments of the present invention, the aqueous pigment suspension further includes one or more additional hydrocolloids. Non-limiting examples of such additional hydrocolloids within the scope of the present invention include non-iota- carrageenan, gellan gum, microcrystalline cellulose, modified carboxymethyl cellulose, gum arabic, furcellaran, cassia gum, guar gum, locust bean gum, tara gum, xanthan gum, konjac mannan, tragacanth, alginate, propylene glycol alginate, agar, agarose, gelatin, starch, a starch derivative, a cellulose derivative, a glucomannan, pectin, pullulan, a synthetic hydrocolloid, a protein and combinations thereof. These additional hydrocolloids are commercially available from a variety of sources that are generally known in the art. [0036] The present invention also provides a method of making the inventive aqueous pigment suspension. The order in which the different components of the suspension are added to each other and the manner in which these components are mixed are not critical. It is preferred, however, to disperse the hydrocolloid and the pigment first, before adding a gel inducing agent to the mixture. The present invention also contemplates preparing separate batches of pigment/water and hydrocolloid/water, which are then mixed with each other after the pigment is dispersed well and the hydrocolloid is fully dissolved.

[0037] Preferably, the gel inducing agent (e.g., a divalent cation from any desired source) is added to and mixed with the hydrocolloid/pigment dispersion at a temperature above the gel setting temperature to avoid gelation before the gel inducing agent is homogenously mixed with the hydrocolloid/pigment dispersion. The resulting dispersion may cool down during or after the mixing step.

[0038] Numerous methods of making the inventive aqueous pigment suspension and of controlling the gel setting and other final properties are known to those skilled in the art, and are therefore not specifically mentioned here.

[0039] The inventive aqueous pigment suspension can also be dried using the methods known in the prior art.

[0040] The inventive aqueous pigment suspension can be used as a coloring agent in the manufacture of pharmaceutical, food, personal care, or household products using the methods known in the prior art. Coloring of such products with pigment suspensions is routinely done in the art. For example, food products including baked goods and confections are routinely colored using pigment suspensions. Pigment suspensions can be applied to baked goods by adding the pigment suspension to a frosting, fondant, glaze, syrups, filling, wet batter, dry mix, or other component of the baked good. Confections such as but not limited to hard candy, gummy candy, jelly candy, rock candy, gum, marshmallow candy, and chocolate can be either internally colored or coated. See U.S. Patent No. 4,636,261. Pigment suspensions can also be used to color processed meat products such as but not limited to ham, sausage, and other deli meats. Further examples of meat products that are colored using pigments can be found in U.S. Patent No. 5,443,852. For example, the aqueous nature of the dispersing medium and pourability of the invention makes it particularly suitable for use in

pharmaceutical coating formulations. Such formulations may be prepared for applications including sugar coating and film coating, and therefore the formulation may include a sugar such as sucrose, a plasticizer such as a polyol, a stabilizer, and a film forming resin. For example, in accordance with the descriptions by Kurt H. Bauer et ah , Coated pharmaceutical dosage forms - fundamentals, manufacturing techniques, biopharmaceutical aspects, test methods and raw materials, CRC Press/Medpharm, Boca Raton/Stuttgart, 1998, which is incorporated herein by reference in its entirety. Pigment suspensions are also used in personal care products such as cosmetics, shampoos, lotions, and soaps. See U.S. Patent No. 7,351,406.

EXAMPLES

[0041] The following examples are provided to illustrate the invention in accordance with the principles of this invention, but are not to be construed as limiting the invention in any way except as indicated in the appended claims.

EXAMPLE 1

[0042] An aqueous pigment suspension was prepared with 30 weight percent of synthetic red iron (III) oxide pigment (particle size range: 0.1 to 0.3μιη), 0.60 weight percent of SeaSpen IN® (FMC BioPolymer, Philadelphia, PA). SeaSpen IN is the calcium counter ion salt form of iota-carrageenan and is known to also contain a calcium salt and a calcium sequestering phosphate. In this example, additional cation salt was not added to modify the rheological properties of the suspension. The resulting pigment suspension was pourable (upon shaking); however supernatant has been observed after three weeks of storage at about 20 °C.

EXAMPLE 2

[0043] An aqueous pigment suspension was prepared with 30 weight percent of synthetic red iron (III) oxide pigment (particle size range: 0.1 to 0.3μιη), 0.35 weight percent of Na- iota-carrageenan (Viscarin® SD 389, FMC BioPolymer, Philadelphia, PA), and 0.10 weight percent of Ca( 0 ₃ 1150 ₃ )2· 5H ₂ 0. The resulting pigment suspension was pourable (upon shaking), did not settle, and did not show syneresis after three weeks of storage at about 20 °C. This is in contrast to Example I where cation levels were not adjusted and sedimentation was observed. The same results were observed in replicate samples which were subjected to a series of disruption cycles. In each cycle, the gel was exposed to shear stress by shaking then allowed to rest to observe whether the disrupted gel would recover its elastic gel form. A total of four disruptions cycles were performed during three weeks of storage. The aqueous suspension was able to recover an elastic gel structure after exposure to four disruption cycles.

EXAMPLE 3

[0044] An aqueous pigment suspension was prepared with 30 weight percent of synthetic red iron (III) oxide pigment (particle size: 0.1 to 0.3μιη), 0.40 weight percent of Na-iota- carrageenan (Viscarin® SD 389, FMC BioPolymer, Philadelphia, PA), and 0.16 weight percent of Ca^HsC^r 5H ₂ 0. The resulting pigment suspension was pourable (upon shaking), did not settle, and did not show syneresis after three months of storage at about 20 °C. The recovery performance to gel state following disruptions by shaking was more complete than the composition tested in Example 2 which has suggested an improved stability of the tested composition. Moreover the elastic gel structure has been retained for about three days at about 40 °C storage conditions where the suspension did not settle, and did not show syneresis during the storage.

EXAMPLE 4

[0045] An aqueous pigment suspension was prepared with 30 weight percent of synthetic red iron (III) oxide pigment (particle size: 0.1 to 0.3μιη), 0.40 weight percent of Na-iota- carrageenan (Viscarin® SD 389, FMC BioPolymer, Philadelphia, PA), 0.16 weight percent of Ca(C ₃ H ₅ 0 ₃ ) ₂ - 5H ₂ 0, 0.11 weight percent of potassium sorbate. The acidity of the composition was adjusted to about pH 4.3. The resulting pigment suspension was pourable (upon shaking), did not settle, and did not show syneresis after three months of storage at about 20 °C. This result suggests use of a preservative for controlling microbial activity in the aqueous pigment suspension.

EXAMPLE 5

[0046] An aqueous pigment suspension was prepared with 20 weight percent of vegetable carbon (particle size range: 5 to ΙΟμιη), 0.45 weight percent of Na-iota-carrageenan

(Viscarin® SD 389, FMC BioPolymer, Philadelphia, PA), and 0.17 weight percent of Ca(C ₃ H ₅ 0 ₃ ) ₂ - 5H ₂ 0. The resulting pigment suspension was pourable (upon shaking), did not settle, and did not show syneresis after three months of storage at about 20 °C. The same results were observed in replicate samples which were subjected to a series of disruption cycles. In each cycle, the gel was exposed to shear stress by shaking then allowed to rest to observe whether the disrupted gel would recover its elastic gel structure. A total of four disruptions cycles were performed during three weeks of storage. The aqueous pigment suspension was able to sufficiently recover an elastic gel form after exposure to four disruption cycles. Suspensions with similar properties and increased coloring power have been identified in additional replicate samples. In these samples, the vegetable carbon pigment was subjected to a wet milling process in order to reduce the particle size of the pigment prior to suspension.

EXAMPLE 6

[0047] An aqueous pigment suspension was prepared with 30 weight percent of synthetic red iron (III) oxide pigment (particle size: 0.1 to 0.3μιη), 0.40 weight percent of Na-iota- carrageenan (Viscarin® SD 389, FMC BioPolymer, Philadelphia, PA), 0.07 weight percent of xanthan gum (XG 200, FMC Biopolymer, Philadelphia, PA), 0.14 weight percent of calcium sorbate. The acidity of the composition was adjusted to about pH 4.3. The resulting pigment suspension was pourable (upon shaking), did not settle, and did not show syneresis after five months of storage at about 20 °C. This composition provides an example on the use of additional hydrocolloid to impart properties of the suspension. In contrast to Example 4, it also demonstrates use of a single compound (i. e. calcium salt of sorbic acid) to meet the requirement for gel inducing and microbial preservative needs at the same time. This approach can be particularly advantageous where presence of additional monovalent cations is not desired.

EXAMPLE 7

[0048] A method for determining the viscosity of a shear-thinning suspension using a stress-controlled rheometer. An AR1500ex stress-controlled rheometer equipped with a pel tier- type temperature control system was set to 25 °C with a measurement geometry consisting of 40 mm diameter stainless steel flat plates set at a gap of 1000 micrometers. A sample was loaded onto the peltier plate surface and the geometry was lowered onto the sample. The sample was allowed to reach equilibrium over a 10 minute period. Shear stress was measured as a function of shear rate while increasing shear rate from 0.01 to 100 reciprocal second over 5 minutes. Viscosity was determined by dividing the shear stress by the shear rate at 1 reciprocal second. [0049] A comparison of the aqueous pigment suspension in Example 1 with the inventive aqueous pigment suspension of Example 2 illustrates the critically improved performance of the invention in its ability to resist sedimentation and syneresis when stored. Furthermore, the inventive aqueous pigment suspension was able to recover an elastic gel form that is resistant against sedimentation and syneresis even after being exposed to multiple disruption cycles. This allows for reduced waste in the use of the inventive aqueous pigment suspension. For example, prior to use the inventive aqueous pigment suspension must be exposed to shear (i.e. by shaking). If not all of the amount exposed to shear is used, rather than being discarded as waste, the unused portion may be stored in its original packaging and used at a later time because the unused portion is able to recover it stable elastic gel form. In Example 5, the inventive aqueous pigment suspension using a natural pigment showed similar results as observed in Example 2. As shown in Example 3, the inventive aqueous pigment suspension is also able to remain stable at elevated temperatures. This allows for transportation or storage under conditions that are not temperature controlled resulting in reduced energy consumption and greater logistical flexibility. As shown in Example 4, the inventive aqueous pigment suspension system is compatible with the use of preservatives. Given the prolonged stability of the inventive aqueous pigment suspension system even in conditions that are not temperature controlled, the ability to use preservatives in the system may be beneficial.