WO1999024020A1 - A process for making a free-flowing, dust-free, cold water dispersible, edible, film-coating composition - Google Patents

Abstract

Improved edible film-coating compositions are prepared by mixing a film-forming polymer with a plasticizer and water to obtain an extrudable polymer blend containing from 20 to 60 percent water, extruding the blend into strands, drying and milling the strands. The compositions are free-flowing, dust-free and readily dispersible in cold water, and are useful in pharmaceutical, confectionery and food applications.

Description

A PROCESS FOR MAKING A FREE-FLOWING, DUST-FREE, COLD WATER DISPERSIBLE, EDIBLE, FILM-COATING COMPOSITION

The present invention concerns an improved edible film-coating composition and its method of manufacture. The improved compositions are free-flowing, dust-free and cold water dispersible. Such compositions are useful in pharmaceutical, confectionery and food applications.

The use of dry, edible, film-coating compositions in applications such as coating pharmaceutical tablets is well known in the art. By mixing a dry polymer powder with pigment particles and by grinding the mixture to obtain a dry polymer-pigment composition as a fine powder, the problem of shipping pigment dispersions containing aqueous or non- aqueous solvents is reduced, although not eliminated. However, when this fine polymer pigment mixture is stirred into water and dispersed, the polymer makes lumps and "fish eyes" because it agglomerates, resulting in a non-uniform dispersion. Unless the dispersion is left to solvate for a considerable period of time, for example, overnight, the coating is lumpy and not uniform.

To improve the uniformity of the dispersion, U.S. Patent 4,543,370 discloses a method of making a dry-powder, edible, film-coating composition by mixing a powder of a film-forming polymer and powdered pigment particles in a blender to form a polymer-pigment mix, adding a plasticizer to the blender containing the polymer-pigment mix, and mixing until the combined mix is thoroughly blended. Optionally, surfactants can be added with the plasticizer. Such compositions disperse in water at room temperature and form usable dispersions an hour after mixing. However, such dry powders are still dusty and not easily transferred. In addition, the various components, such as the pigments, are susceptible to segregation.

In order to provide a composition which dissolves more quickly in cold water, flows more freely, and avoids the dust hazards associated with powders, U.S. Patent 4,816,298 discloses a method of making a granular, edible, fiim-coating composition by extruding a thermally moldable polymer and plasticizer at elevated temperatures, that is,

>70°C, cooling to solidify the extrudate and comminuting the extruded material to form a granulated product. Optionally, pigments and surfactants may be added to the granules or to the blend before extrusion. Unfortunately, the diameter of the strands produced by this extrusion process are of necessity relatively large, for example, 1/8 inch (3.175 millimeters), and the pellets produced are quite friable.

It would be highly desirable to formulate an edible film-coating composition which readily disperses in cold water and which eliminates the segregation of the components while remaining dust-free and free-flowing.

By mixing all of the ingredients of the film-coating composition together with an appropriate amount of water to form an aqueous polymer blend, extruding the polymer blend, drying the extrudate and cutting the strands of extruded polymer blend, an improved granular film-coating composition is prepared. The film-coating composition is readily dispersible in water, is dust-free and is free-flowing. Furthermore, the blended ingredients are relatively immune to segregation from the dry formulation.

One aspect of the present invention concerns a process for making an improved, granular, cold-water dispersible, edible film-coating composition for use in pharmaceuticals, confectionery and food which comprises (a) mixing a film-forming polymer with water and a plasticizer to obtain an extrudable polymer blend having a content of from 20 to 60 weight percent water, (b) extruding the polymer blend to obtain wet strands of polymer blend, (c) drying the strands of polymer blend to remove most of the water and (d) cutting the strands of dried polymer blend into pellets.

In another aspect, the present invention concerns the improved, granular, cold water dispersible, edible film-coating composition obtainable from the process of the present invention.

In still another aspect, the present invention concerns a method of making a coating dispersion for use in pharmaceutical, confectionery and food applications which comprises dispersing the granular, cold water dispersible, edible film coating composition obtainable from the process of the present invention into water without agglomeration to form a coating dispersion adapted for use as a film coating for tablets.

The present invention is a process for making an improved granular, cold water dispersible, edible film-coating composition. The process involves the steps of (a) mixing a film-forming polymer with water and a plasticizer to obtain an extrudable polymer blend, (b) extruding the polymer blend into wet strands and (c) drying the wet strands to remove most of the water and (d) cutting the strands of polymer blend into pellets. In addition to the film-forming polymer, plasticizer and water, various other ingredients such as pigments and colorants, surfactants and wetting agents, excipients and diluents, and detackifiers can be incorporated into the polymer blend.

The film-forming polymers that may be used in this invention are soluble either in water or in the plasticizer and are acceptable for human consumption. Such film- forming polymers include cellulosics, vinyl polymers such as polyvinyl pyrrolidone, acrylics such as dimethylaminoethyl methacrylate-methacrylic acid ester copolymer, and carbohydrate polymers such as maltodextrins or polydextroses. Preferred film-forming polymers are cellulose ethers that are water soluble. Some typical examples of cellulose ethers that are water-soluble and are particularly useful in the invention are methylcellulose, methylethyl cellulose, hydroxypropyl methylcellulose, hydroxypropyl cellulose, and hydroxyethyl methylcellulose. Mixtures of these cellulose ethers can also be used. Most preferred cellulose ethers are methylcellulose and hydroxypropyl methylcellulose.

The viscosity and the substitution of the cellulose ethers preferred in the invention are not critical as long as the cellulose ether is water-soluble. For example, methylcellulose with a 2 percent aqueous viscosity of 3 to 200,000 mPa-s (millipascal- seconds) can be used. The methoxy substitution of the methylcellulose can vary from 10 percent to 50 percent by weight. The hydroxypropyl substitution can vary from 0 percent to 40 percent by weight. The hydroxyethyl substitution can vary from 0 percent to 45 percent by weight.

Exemplary of the polymer plasticizer for use in the film-coating compositions of the invention are polyethylene glycol, for example, polyethylene glycol having a molecular weight of 200 to 8000, glycerin, propylene glycol, glycerin triacetate, acetylated monoglyceride, diethyl phthalate and mineral oil.

The polymer plasticizer, which softens the polymer and makes it less brittle, may be a liquid or a solid plasticizer; a preferred plasticizer is a liquid such as polyethylene glycol 400.

Pigment dispersions typically used in pharmaceutical formulations, such as aluminum-lake pigments, and colorants, such as dyes, may be added to the blend. Likewise, excipients or detackifiers such as sugars or starches may be added to the blend.

Surfactants, such as dioctylsodium sulfosuccinates or sodium lauryl sulphate, may optionally be added before or after the extrusion or milling to reduce surface tension of water in contact with the granules and increase the wetting of the particles.

Typically, the polymer blend to be extruded is from 40 to 70 weight percent film-forming polymer, 20 to 60 weight percent water and 1 to 20 weight percent plasticizer. The addition of pigments, surfactants and other additives is optional. Typically, the polymer blend comprises from 0 to 0.3 weight percent surfactant, 0 to 30 weight percent pigment or colorant, and 0 to 40 weight percent other additives such as excipients, diluents, detackifiers, surfactants and wetting agents.

In a typical extrusion of a polymer or polymer blend, the polymer is wetted, forced through a die and cooled to solidify the extruded strands prior to milling. In the present invention, the polymer blend contains water so that it will flow under pressure. The water content of the polymer blend is only important in that it should neither be so low that excessive pressure is required to extrude it nor so high that the extruded strands fail to maintain their shape after extrusion. Generally, this calls for a water content of from 20 to 60 weight percent of the polymer blend.

By conventional means, the plasticizer, film-forming polymer and water are mixed to form a homogeneous blend. This can be done at the inlet of an extruder or in an external mixing device. Preferably, the blend is premixed and is slowly added to the extruder.

In general, the shape and size of the orifices fix the cross-sectional shape and size of the extrudate. Although any shape of orifice will suffice, that is, circle, triangle, square, or rectangle, it is preferred that the extrusion of the polymer blend be through equiaxial orifices. Equiaxial orifices are orifices that have approximately equal dimensions in all directions.

The size of the orifices, that is, cross-sectional area, should be small enough so that the final product particle size is not so large that excessive time is required for dissolution. On the other hand, the cross-sectional area of the orifice should not be so small that an excessive amount of energy must be exerted to press the polymer blend through the orifices. Generally, the orifices are of 4.5x10^"9 m² to 4.5x10^"5 m². Preferably, the orifices have a cross-sectional area of 9.9x10^"8 m² to 2.0x10^"5 m². Most preferably, the orifices have a cross-sectional area of 5x10^"8 m² to 2x10^"7 m². The polymer blend to be extruded is temperature sensitive in that at elevated temperatures it expels water and solidifies. When the blend solidifies, it no longer flows under pressure and cannot be extruded. For this reason, the temperature of the polymer blend during extrusion is maintained so that the polymer blend remains hydrated. While temperatures of up to 65°C or 70°C give acceptable results, typically the temperature is maintained below 40°C. Similarly, at low temperatures the water freezes and the polymer blend solidifies. While temperatures of down to 10°C are acceptable, typically the temperature is maintained above 20°C. Ambient temperature is preferred.

The extrusion can be done with any device that applies sufficient pressure to push the polymer blend through the extrusion orifices at a temperature which keeps the polymer blend hydrated. For example, a positive displacement extruder, such as one employing a positive displacement piston or a gear pump, can be used. Positive displacement extruders are highly preferred in this invention because they are energy efficient and can extrude the polymer blend without unduly increasing its temperature. Another example of typical extrusion equipment is a screw-type extruder which advances the polymer blend by means of a screw rotating inside a cylinder. Screw-type extruders are not as energy efficient as positive displacement extruders and convert much of the energy to heat. This causes the temperature of the blend to increase and dehydration to occur. Thus, when a screw-type extruder is used, it is generally necessary to use a cooling device to keep the hydrated cellulose ether temperature below 40°C.

The elongated extrudate is the polymer blend that has been pressed through the extrusion orifices. Generally, the elongated extrudate is in the form of long narrow strands. The strands of extrudate have a uniform cross-sectional area that is approximately the same as the extrusion orifices described above.

Normally, the extrudate is cooled in order to provide a solidified or hardened product. In the present invention since cooling does not harden the polymers at these water levels, the extrudate is dried to remove most of the water and to give a hardened product. The drying of the elongated extrudate can be accomplished with standard drying equipment and methods known in the art. Typical dryers include belt dryers and steam tube dryers. Belt dryers are preferred because there is a large surface area upon which the polymer blend strands can be spread. Preferably, the extruded strands are dried to a moisture content such that the strands are sufficiently brittle to be cut. Generally, the polymer blend strands are dried to a moisture content of less than 10 percent.

In order to reduce the strands of polymer blend into smaller particles, it is necessary to cut the strands. The cutting can be accomplished by using standard equipment known in the art. Typical cutting devices are air-swept impact mills, ball mills, hammer mills, knife grinders, and disk mills. In most cases, the size of the extrusion orifice is selected to fix two of the dimensions of the polymer blend. Therefore, it is only necessary to cut the strands to shorten the length. Typically, the extrudate is cut to a length/diameter ratio of 0.5 to 10. Preferably, the extrudate is cut to a length/diameter ratio of 1 to 4. This is preferably done in an air-swept impact mill because the other mills, that is, ball mills, have a tendency to overmill the product into fine particles that are dusty. In-addition, an air-swept impact mill will dry the extrudate, if necessary, by blowing hot air across the mill. Thus, if a hot air mill is used, it may only be necessary to dry the extruded strands to a moisture content of 25 percent before feeding them to the hot air mill.

The granular film-coating composition that results can be added to cold water under agitation to form a coating solution. The solution can be used in a conventional coating operation, for example, spraying the solution directly onto a tablet bed in a coater. The composition may be used to coat pharmaceuticals, foods and food supplements to protect, color, harden, make more palatable, and mask the taste of solid dosage forms.

In a typical example of the process, the film-forming polymer is agitated in a high shear mixer/granulator. Plasticizer and optional ingredients such as pigment, colorant or surfactant are conveniently added to water and sprayed onto the film-forming polymer under agitation to form a wet polymer blend. Dry ingredients, such as some excipients and detackifiers can be dry blended with the film-forming polymer before spraying with the aqueous solution of plasticizer. The polymer blend is then extruded through a die face using a piston pump. The wet strands are dried and cut with an air swept impact mill to form a free-flowing, non-dusty composition.

The following examples illustrate the invention. Example 1 - Clear Coating Formulation

METHOCEL^* E5 Premium, a film-forming polymer consisting of an hydroxypropyl methylcellulose (having a 2 percent aqueous viscosity of 3.75-7.0 mPa-s at 20°C, a methoxy substitution of 28-30 percent and a hydroxypropyl substitution of 7-12 percent), (1260.8 grams (g)) was charged into a 10 liter (L) high speed mixer/granulator and agitated at a rate of 300 revolutions per minute (rpm) for the main impeller and 1500 rpm for the side chopper blades. While maintaining the agitation rate, a solution of 124.8 g of polyethylene glycol 400 in 1275 g of water was sprayed onto the film-forming polymer. The wetted polymer blend was extruded through circular die openings having a cross-sectional area of 1.46x10"⁷ m². The extruded strands were dried and then milled using an Alpine 100 UPZ mill equipped with a short track without screen.

^*a trademark of The Dow Chemical Company

Example 2 - Yellow Coating Formulation

The procedure of Example 1 was repeated using the following ingredients:

METHOCEL E5 Premium 1260.8 g polyethylene glycol 400 124.8 g

Yellow OPASPRAY^** Liquid Color Cone. 116.8 g water 969.9 g

The yellow colorant was added to the solution of the plasticizer and water before spraying onto the film-forming polymer. After extrusion, drying and milling, a dust- free, free-flowing granular composition was obtained from which the colorant would not segregate.

^**a trademark of Colorcon, Inc.

Example 3 - Blue Coating Formulation

The procedure of Example 2 was repeated using the following ingredients: METHOCEL E5 Premium 1260.8 g polyethylene glycol 400 124.8 g

Blue OPASPRAY Liquid Color Cone. 127.4 g water 1000.0 g

Example 4 - Red Coating Formulation

The procedure of Example 2 was repeated using the following ingredients:

METHOCEL E5 Premium 884.5 g

MALTODEXTRINE^*** 2774 402.0 g polyethylene glycol 400 124.8 g

Red OPASPRAY Liquid Color Cone. 105.1 g water 469.0 g

The MALTODEXTRIN 2774 was dry blended with the METHOCEL E5 Premium in the high shear granulator prior to spraying with the aqueous mixture of plasticizer and colorant. A CoMil model 197-S mill was used instead of the Alpine 100 UPZ mill.

^***a trademark of National Starch Company

Example 5 - Tablet-Coating Solution

A 10 percent tablet coating solution was prepared by quickly adding the formulations of Examples 1-4 into moderately agitated water at 23°C. The pellets quickly dispersed and went into solution within 20 to 30 minutes.

Claims

WHAT IS CLAIMED IS:

1 . A process for making an improved, granular, cold water-dispersible edible film-coating composition for use in pharmaceuticals, confectionery and food which comprises: (a) mixing a film-forming polymer with water and a plasticizer to obtain an extrudable polymer blend having a content of from 20 to 60 weight percent water;

(b) extruding the polymer blend to obtain wet strands of polymer blend;

(c) drying the wet strands of polymer blend to remove most of the water; and

(d) cutting the strands of dried polymer blend into pellets.

2. The process of Claim 1 in which the film-forming polymer is a cellulose ether.

3. The process of Claim 2 in which the cellulose ether is a methylcellulose or an hydroxypropyl methylcellulose.

4. The process of Claim 1 in which the polymer blend comprises:

(a) from 40 to 70 weight percent film-forming polymer,

(b) from 20 to 60 weight percent water,

(c) from 1 to 20 weight percent plasticizer, (d) from 0 to 30 weight percent pigment or colorant, and

(e) from 0 to 40 weight percent excipients, diluents, detackifiers, surfactants or wetting agents.

5. The process of Claim 1 in which the plasticizer is polyethylene glycol.

6. The process of Claim 1 in which the extrusion is conducted at a temperature between 10°C and 65°C.

7. The process of Claim 6 in which the extrusion is conducted at a temperature between 20°C and 40°C.

8. The film-coating composition prepared by the process of Claim 1 .

9. A process for making an improved, granular, cold water-dispersible, edible film-coating composition for use in pharmaceutical, confectionery and food which comprises:

(a) mixing: (i) from 40 to 70 weight percent cellulose ether polymer,

(ii) from 20 to 60 weight percent water,

(iii) from 1 to 20 weight percent plasticizer,

(iv) from 0 to 30 weight percent pigment or colorant, and

(v) from 0 to 40 weight percent excipients, diluents, detackifiers, surfactants or wetting agents to obtain an extrudable polymer blend;

(b) extruding the polymer blend to obtain wet strands of polymer blend;

(c) drying the wet strands of polymer blend to remove most of the water; and (d) cutting the strands of dried polymer blend into pellets.

10. The process of Claim 9 in which the cellulose ether is a methylcellulose or an hydroxypropyl methylcellulose.

11. The process of Claim 9 in which the plasticizer is polyethylene glycol.

12. The process of Claim 9 in which the extrusion is conducted at a temperature between 10°C and 65°C.

13. The process of Claim 12 in which the extrusion is conducted at a temperature between 20°C and 40°C.

14. The film-coating composition prepared by the process of Claim 9.