Coating processes – Particles – flakes – or granules coated or encapsulated – Inorganic base
Reexamination Certificate
1995-01-19
2001-06-12
Beck, Shrive (Department: 1762)
Coating processes
Particles, flakes, or granules coated or encapsulated
Inorganic base
C427S242000, C427S384000, C427S416000
Reexamination Certificate
active
06245384
ABSTRACT:
INTRODUCTION TO THE INVENTION
The present invention relates to the coating of tabletted, pelletized or other particulate materials, and more particularly to providing a polished wax coating on such materials.
The usual wax coating processes for tablets or other particles intended for human consumption involve treating the particles with solutions of wax in volatile organic solvents, evaporating the solvents and tumbling the coated particles in a fabric-lined drum or pan to polish the wax. With many localities being quite sensitive to the potential for air pollution formed by reactions of hydrocarbons, halogenated hydrocarbons or other volatile solvents in the atmosphere, it has become unacceptable to discharge such vapors from an industrial facility. Many recovery systems for organic vapors are commercially available, but they are universally expensive to purchase, install and operate; of course, none of the systems operate with total efficiency, resulting in some emissions to the atmosphere and some degree of indoor pollution hazards to industrial workers.
The process further suffers from inefficiencies, in that it is necessary to apply the wax solution in one piece of equipment, such as a rotating pan, remove the particles for drying, then transfer the particles to the polishing equipment. Special facilities, such as an explosion-proof room, are frequently necessary for worker and equipment protection.
Another coating procedure involves tumbling particles in a pan having a fabric liner which is impregnated with a wax, or using a fabric-lined pan and tumbling with pieces of solid wax. In general, the resulting wax coatings are not sufficiently uniform, the coating process requires very long residence times and particles are subjected to undesirable impact forces (causing excessive particle breakage) from the prolonged tumbling. Sometimes, powdered wax is sprinkled over particles, then melted using heated air to consolidate the coating; this procedure also suffers from a lack of coating uniformity.
It would be highly desirable to apply the waxes in a fluid form which will not involve large amounts of volatile organic compounds, such as in an aqueous medium. It would further be desirable to avoid transferring particles to various pieces of equipment for the coating processing steps, while providing an attractive polished tablet or particle. Also, a process is desired which rapidly gives the desired wax coating.
U.S. Pat. No. 3,438,797 to Biddle teaches applying a sugar solution containing a small amount of a wax emulsion to pharmaceutical tablets which are sticky from the recent application of a sugar syrup coating. Upon drying, an unpolished coating is obtained, which can be imprinted with ink. It is stated that the ink will not adhere to polished wax coated tablets. A further application of a protective transparent wax coating and polishing are done after the imprinting, presumably using the above-described solvent-based process.
U.S. Pat. No. 4,021,262 to Guerrero et al. pertains to a transparent coating for fruits and vegetables which permits gas exchange but is a barrier to moisture. This coating is produced by applying an emulsion formed from Candelilla wax, an unstable soap and xylene or toluene. It does not appear that this produces a polished coating, and the emulsion does not totally avoid volatile organic solvents.
U.S. Pat. No. 5,023,108 to Bagaria et al. describes a coating process for pharmaceutical solids, involving the preparation of an emulsion from a wax/lipid, an emulsifying agent and water, spray drying the emulsion to form a powder, dispersing the powder in water, and coating the dispersion onto the surface of medicaments.
SUMMARY OF THE INVENTION
The present invention provides polished wax coated tablets or other particles by a method comprising spraying the particles with an aqueous-continuous emulsion containing a wax in a discontinuous phase, dusting the tablets or particles with a powdered wax and tumbling to polish. This method has been found useful for particles having a sugary or other surface having an affinity for water. When sugar-coated particles are to be provided with a polished coating, the method can be conducted in the same pans or other equipment used for applying the sugar coating, immediately following the sugar coating operation.
DETAILED DESCRIPTION OF THE INVENTION
In this discussion and the examples, all percentages are stated as percent by weight, unless otherwise specified.
Suitable particles for coating in the present invention include, without limitation, medicinal and other tablets, pills, granules, beads, caplets and pellets, as well as chewing gums, candies and the like. In general, the particles will have a large proportion of contained sugar or will have a sugar-based coating; methods for sugar coating are well known in the art and typically involve distributing a small amount of a concentrated aqueous solution (syrup) of sucrose onto particles contained in an inclined rotating pan, and blowing warm air onto the particles to hasten drying. Being manual and highly operator-dependent, many variations of sugar coating processes are known and the selection of a particular variation is not a matter of concern in the present invention. It is expected that those having skill in the art will experiment with their sugar coating processes to optimize the subsequent wax coating.
An example of the present method for applying a polished wax coating to particles includes the steps of:
(a) spraying a wax-containing emulsion of the oil-in-water type onto particles in a rotating pan;
(b) dusting a powdered wax over the particles; and
(c) tumbling the coated particles in the pan to polish the wax.
Oil-in-water emulsions, also referred to in the art as “invert” emulsions, are characterized by a continuous aqueous phase having droplets of insoluble organic liquids dispersed throughout. While the emulsions of this invention may well comprise solid particles of wax dispersed in an aqueous medium upon cooling from the elevated temperatures at which the emulsions are formed, and thus are no longer true emulsions, they will be considered as being emulsions for purposes of the invention.
The emulsions are formed by mixing, under conditions of high shear, molten wax with water or an aqueous solution. To impart stability to the emulsion, one or more surface active agents also will be present at mixing; depending upon the nature of the surface active agents used, they can be dissolved or dispersed in either the aqueous material or the wax component, or can be separately introduced at the time of mixing. As is known in the art, various types of mixing are appropriate for emulsion formation, including forcing the two components together through a pump or vigorously agitating a mixture of the components in a vessel, under conditions of high shear. The method of emulsion formation is a matter of choice and is not critical to the invention.
Suitable waxes for use in the emulsions of the invention have melting points below about 100° C., so that they can be combined in liquid form with aqueous materials to form emulsions, without causing water to boil. The waxes can be of animal, plant or mineral origin, representative waxes including beeswax, candelilla wax, carnauba wax, rice wax, ceresin wax, montan wax, petroleum wax and the like.
Melting point is not a consideration for the powdered wax used as a final coating in certain embodiments of the invention, so the useful materials for this step can include any of the above waxes, plus synthetic hydrocarbon waxes. Mixtures of waxes can be used both for forming emulsions and in the final coating step.
In general, the formation of aqueous-continuous emulsions is facilitated by surface-active agents having hydrophilic-lipophilic balance values above about 9. This can be achieved with a single agent or a blend of agents having higher and lower values than the actual desired overall value for a given system. For example, Glyceryl monostearate (HLB about 11), Polysorbate 65 (a mixture of stearate esters of sorbitol a
Beck Shrive
Chen Bret B.
Franks Robert A.
Schering-Plough Healthcare Products Inc.
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