Title:  Method for encapsulating reactive dental agents

United States Patent:  6,258,343

Assignee:  Colgate-Palmolive Company (New York, NY)

Filed:  August 15, 2000

A method for encapsulating a water soluble reactive agent in an alkyl cellulosic polymer to provide an encapsulated product from which leaching of the reactive agent into an aqueous dentifrice containing another compound reactive with the agent is prevented or controlled, said method comprising the steps of (a) uniformly dispersing the reactive agent in the alkyl cellulose and a solvent for the polymer to form a paste; (b) casting the paste onto a sheet forming substrate; (c) grinding and subdividing the sheet having the reactive agent encased therein into particles of a predetermined size; (d) washing the particles with water to remove any encased agent exposed by the grinding; and, (e) drying the particles of encapsulated reactive agent.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present invention, encapsulated water soluble reactive agents such as soluble calcium and fluoride salts, such as calcium chloride, calcium acetate, sodium fluoride, sodium monofluorophosphate or other compounds such as peroxide compounds including calcium peroxide, urea peroxide and hydrogen peroxide, potassium salts including chloride, stannate, and nitrate, manganese, copper, iron and zinc salts including chloride, gluconate, citrate, acetate which release reactive ions are isolated from the surrounding aqueous dentifrice environment by a water impermeable alkyl cellulosic polymer coating which subsequently releases the reactive agent, that is, ruptures, in response to forces exerted during toothbrushing.

In the practice of the present invention, the reactive agent comprises about 40 to about 80% by weight of the particles and the encapsulating alkyl cellulosic polymer comprises about 20 to about 60% by weight of the particles and preferably about 50 to about 70% by weight of the reactive agent and about 30 to about 50% by weight of the cellulosic polymer.

The encapsulation material used to prepare the water impermeable particles of the present invention is a substantially water-insoluble film forming alkyl cellulosic polymer material. The term "alkyl cellulosic polymer" includes within its meaning methyl cellulose, ethyl cellulose, hydroxyethylcellulose, and hydropropyl methyl cellulose.

It is a feature of the present invention that substantially water impermeable, pressure rupturable encasement of reactive agent ingredients is accomplished with an alkyl cellulosic polymer material which does not require modification by a plasticizer.

In the method of the present invention a solution of alkyl cellulosic polymer is mixed with a solvent for the alkyl cellulosic polymer preferably a monohydric alcohol such as ethanol, in a conventional mixing apparatus such as a Ross mixer with the water soluble reactive agent to form a viscous paste. The paste is then delivered to a sheet formed therefrom on a heated sheet forming carrier substrate.

The carrier substrate is heated to a temperature between about 100^o to 120^o C. Sufficient solvent is removed from the sheet within about a minute and dispelled to a recovery unit whereby the dried sheet is rendered somewhat brittle. The sheet is then physically broken into small particles by grinding, using equipment such as a mixed media grinder (Sweco.TM. grinder). The particles are then subject to one or more water washing steps at 18^o to 65^oC. to remove any encased reactive agent which has been subsequently exposed by the grinding operation.

In the preferred method of the present invention, ethyl cellulose is used as an encapsulating material and an organic solvent for ethyl cellulose such as ethanol is placed in a mixing apparatus. A reactive agent such as calcium acetate and the ethyl cellulose are added to the ethanol in the mixer. Mixing is a batch operation carried out with agitation provided by a high shear mixer (Ross.TM.). The preferred composition of ingredients charged to the mixer is about 35% by weight of a reactive agent such as calcium acetate, about 15% ethyl cellulose and about 50% by weight ethanol. After the ingredients have been added to the solvent, the mixer is closed and sealed to prevent loss of solvent. When ethyl alcohol is used as the solvent, the mixing is performed at ambient (22^oC.) temperature. Preferably, mixing continues until the viscosity of the mixture assumes a paste form.

Thereafter, the mixture is pumped by suitable means to a casting surface. The casting surface, or substrate, can be a casting drum or endless belt of highly polished stainless steel, copper or silicone rubber. In a preferred embodiment, the casting surface is a double drum dryer or single drum dryer with an applicator roll which rotates at a speed of about 1.5 ft./min. providing a moving casting surface in a casting chamber provided with a solvent vapor recovery system which is closed to the environment.

The casting surface is provided with a heating zone and a cooling. Generally, the sheet is heated in the casting surface at 800 to 120^oC. which causes the solvent to vaporize, removing the solvent from the paste deposited on casting belt to form the sheet.

The dried sheet is cooled and then stripped from the casting surface, passed into a mixed media grinder and pulverized into particles which are screened to pass through a 30 mesh screen but retained on a 100 mesh screen to a particle size referred to as -30+100 mesh. Thereafter the particles are washed with water and then dried in an air stream at 150^o to 200^oC. whereby any reactive agent which has been exposed by the grinding action is removed.

The dentifrice composition in which the encapsulated reactive agent particles are incorporated is prepared in the form of a semi-solid product of desired consistency which is extrudable from a pump or collapsible tube. In general, the liquids that form the dentifrice vehicle will comprise water, in an amount ranging from about 5 to about 30% by weight and preferably about 5 to about 20% by weight and a humectant such as glycerin, sorbitol polyethylene glycol or a mixture thereof in an amount greater than about 35% by weight and preferably about 50 to about 70% by weight.

In the preparation of dentifrices which are to be used for the fluoridation of teeth, agents which interact with fluoride ions which are included in the dentifrice composition of the present invention are maintained physically isolated from the fluoride ingredient by their encapsulation in a coating of the alkyl cellulosic polymer. To obtain freshly precipitated calcium fluoride upon brushing teeth with the dentifrice composition, there is included in the dentifrice composition a water soluble calcium salt such as calcium chloride, calcium acetate, calcium butylate, calcium citrate, calcium lactate, calcium salicylate, and other non-toxic salts of calcium and inorganic or organic acids which are soluble in an aqueous media and are present in the dentifrice at a level required for substantial interaction with the fluoride compound to deposit CaF₂ during the time the dentifrice is applied to the teeth and brushed.

Particles of the encapsulated calcium ion releasable salt are incorporated in the dentifrice composition of the present invention at a concentration of about 0.1% to about 5% by weight and preferably at about 0.15 to about 1.5% by weight.

Suitable fluoride salts useful as fluoridation agents include alkali metal fluoride salts such as sodium fluoride, sodium monofluorophosphate and tin salts such as stannous fluoride. The fluoride salt is incorporated in the dentifrice composition at a concentration of about 0.1 to about 1% by weight, and preferably at about 0.25 to about 0.5% by weight. At these preferred concentrations, about 500 ppm to about 2200 ppm, fluoride ion will be available to teeth when the dentifrice composition is applied to the teeth.

Surfactants are used in the compositions of the present invention to achieve increased prophylactic action and render the dentifrice compositions more cosmetically acceptable. The surfactant is preferably a detersive material which imparts to the composition detersive and foaming properties. Suitable examples of surfactants are water-soluble salts of higher fatty acid monoglyceride monosulfates, such as the sodium salt of the monosulfated monoglyceride of hydrogenated coconut oil fatty acids, higher alkyl sulfates such as sodium lauryl sulfate, alkyl aryl sulfonates such as sodium dodecyl benzene sulfonate, higher alkyl sulfoacetates, sodium lauryl sulfoacetate and higher fatty acid esters of 1,2-dihydroxy propane sulfonate. The surfactant is typically present in the dentifrice compositions of the present invention in an amount of about 0.3 to about 5% by weight, preferably about 0.5 to about 2% by weight.

Thickening agents commonly used as dentifrice thickening agents such as guar gum, carboxymethyl cellulose and polyoxyethylene polyoxypropylene glycol block copolymers and xanthan gum are used at a concentration of about 0.5 to about 2% in the preparation of the dentifrice composition of the present invention which amount is sufficient to form of a semi-solid, extrudable, shape retaining product.

An abrasive is generally included in the dentifrice composition of the present invention at a concentration of about 10 to about 60% by weight and preferably at a concentration of about 15 to about 55% by weight. Soluble abrasives include precipitated amorphous hydrated silica, such as Sorbosil AC-35 marketed by Crosfield Chemicals, or Zeodent 115 from J.M. Huber Company, sodium metaphosphate, potassium metaphosphate, tricalcium phosphate, calcium phosphate dihydrate, anhydrous dicalcium phosphate, calcium pyrophosphate, sodium bicarbonate, calcium carbonate and calcined alumina.

Abrasives such as calcium carbonate and dicalcium phosphate (anhydrous and/or dihydrate) may be encapsulated in accordance with the method of the present invention for although substantially water insoluble, will nonetheless release amounts of water soluble calcium ion in sufficient amounts to interact and thereby inactivate reactive agents such as fluoride ion present in the dentifrice.

In addition to abrasive materials being incompatible with fluoride salts, it has been further determined that water soluble pyrophosphate salts, normally included in dentifrice compositions as antitartar agents, have also been determined to inactivate fluoride ion so it is desirable that these salts be encapsulated in accordance with the practice of the present invention. Exemplary antitartar pyrophosphate salts include dialkali or tetraalkali metal pyrophosphate salts such as Na₄ P₂ O₇, K₄ P₂₀₇, Na₄ K₂ P₂ O₇, Na₄ H₂ P₂ O₇ and K₂ H₂ P₂ O₇ long chain polyphosphates such as sodium hexametaphosphate, sodium tripolyphosphate and cyclic phosphates such as sodium trimetaphosphate. These salts are included in the dentifrice composition of the present invention at a concentration of about 1 to about 7% by weight.

Synthetic anionic polycarboxylates may also be used in the dentifrice compositions of the present invention to enhance the efficacy of other active agents present in the dentifrice such as antibacterial agents and the antitartar pyrophosphate salts. Such anionic polycarboxylates are generally employed in the form of their free acids or preferably partially or more preferably fully neutralized water soluble alkali metal, e.g., potassium and preferably sodium or ammonium salts. Preferred polycarboxylate compounds are 1:4 to 4:1 copolymers of maleic anhydride or acid with another polymerizable ethylenically unsaturated monomer, preferably methyl vinyl ether/maleic anhydride having a molecular weight (M.W.) of about 30,000 to about 1,000,000 most preferably about 30,000 to about 500,000. These copolymers are commercially available, for example, under the trade designation, as Gantrez, e.g. AN 139 (M.W. 500,000), AN 119 (M.W. 250,000); and preferably S-97 Pharmaceutical Grade (M.W. 70,000). The synthetic anionic carboxylates may be included in the dentifrice composition of the present invention at a concentration of about 0.5 to about 5% by weight.

The dentifrice composition of the present invention may also contain a flavoring agent. The flavoring agent is incorporated in the dentifrice composition at a concentration of about 0.1 to about 5% by weight and preferably about 0.5 to about 1.5% by weight. Flavoring agents which are used in the practice of the present invention include essential oils as well as various flavoring aldehydes, esters, alcohols, and similar materials. Examples of the essential oils include oils of spearmint, peppermint, wintergreen, sassafras clove, sage, eucalyptus, marjoram, cinnamon, lemon, lime, grapefruit, and orange. Of these, the most commonly employed are the oils of peppermint and spearmint.

Various other materials may be incorporated in the dentifrice compositions of this invention, including antibacterial agents such as Triclosan, chlorhexidine, desensitizers such as potassium nitrate, and potassium citrate, whitening agents such as hydrogen peroxide, calcium peroxide and urea peroxide, preservatives, silicones, and chlorophyll compounds. These adjuvants, when present, may also be encapsulated when they are incorporated in the dentifrice composition in amounts which are reactive with other dentifrice ingredients such as fluoride salts.

The preparation of dentifrice compositions is well known in the art. U.S. Pat. Nos. 3,996,863, 3,980,767, 4,328,205 and 4,358,437, which are incorporated herein by reference, describe toothpastes and methods of production thereof which may be utilized for production of the dentifrices of the present invention.

Claim 1 of 6 Claims

What is claimed is:

1. A method for encapsulating a water soluble reactive agent in an alkyl cellulosic polymer matrix to provide an encapsulated product from which leaching of the reactive agent into an aqueous dentifrice containing a compound reactive with the encapsulated agent is substantially prevented, the method comprising the steps of

(a) uniformly dispersing the reactive agent in an alkyl cellulosic polymer and a solvent for the polymer to form a paste;

(b) casting the paste onto a sheet forming substrate to form a sheet of reactive agent encased in the alkyl cellulose polymer;

(c) grinding and subdividing the sheet having the reactive agent encased therein into particles of a predetermined size;

(d) washing the particles with water to remove any encased agent exposed by the grinding; and

(e) drying the particles of encapsulated reactive agent.

____________________________________________
If you want to learn more about this patent, please go directly to the U.S. Patent and Trademark Office Web site to access the full patent.