Tablet coating method

A method for coating pharmaceutical tablets is disclosed in which polymeric coating ingredients are combined with saccharides in a melt spinning operation to form composite particulates. The particulates are then dispersed in water to form an aqueous polymer coating solution, followed by application to pharmaceutical tablets by such methods as spray coating. The particulates dissolve extremely rapidly in water to form a dispersion of the polymer coating ingredients. Such rapid dissolution allows for increased processing rates and avoids disadvantages of the prior art such as the requirement of high shear rate mixing for long times.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to coated pharmaceutical dosage units such as 
tablets and the like. In particular, the invention relates to an improved 
method for coating pharmaceutical tablets with an aqueous polymer 
solution. 
2. Brief Description of the Prior Art 
Numerous methods for coating pharmaceutical tablets are known. They include 
sugar coating, solvent film coating, aqueous film coating, delayed release 
coating and granule coating techniques. 
Pharmaceutical tablets have been coated for a variety of reasons, including 
masking objectionable flavors or odors, protecting unstable tablet 
compositions, improving the ease with which the tablets are swallowed, 
providing protection of the tablets through the stomach with enteric 
coatings and improving the appearance of the tablets. For example, aspirin 
tablets and other tablets that are powdery and friable have been treated 
with a variety of coatings to keep them from dissolving too soon. 
In the past, sugar coating was the most commonly used coating technique. 
However, disadvantages of sugar coating such as relatively high cost, long 
coating time and high bulk have led to the use of other coating materials. 
Some of the most commonly used coatings today are polymeric film coating 
agents. Advantages of polymeric coatings include the ability to produce a 
tablet having a coating that comprises less than 3% of its weight, better 
resistance to chipping and increased tablet strength. Polymers have been 
applied to pharmaceutical tablets using both aqueous and non-aqueous 
solvents. 
Various methods for coating tablets with polymeric solutions are known, 
including rotating pan, fluid bed, spouted bed, coascervation tank and 
pressing methods. In most coating methods, the coating solutions are 
sprayed onto the tablets as the tablets are being agitated in a pan, fluid 
bed, etc. As the solution is being sprayed, a thin film is formed that 
adheres directly to each tablet. The coating may be formed by a single 
application or may be built up in layers through the use of multiple 
spraying cycles. 
Rotating coating pans are often used in the pharmaceutical industry. 
Uncoated tablets are placed in the pan, which is typically tilted at an 
angle from the horizontal, and the liquid coating solution is introduced 
into the pan while the tablets are tumbling. The liquid portion of the 
coating solution is then evaporated by passing air over the surface of the 
tumbling tablets. In contrast, a fluid bed coater operates by passing air 
through a bed of tablets at a velocity sufficient to support and separate 
the tablets as individual units. Once separated, the tablets are sprayed 
with the coating composition. 
Typical spray coating solutions include polymers, plasticizers, dyes and 
other ingredients dissolved or dispersed in an aqueous or non-aqueous 
medium. Aqueous systems are preferred due to lower costs and environmental 
compatability. However, a major disadvantage of conventional aqueous 
polymer coating methods is that they require relatively long mixing times 
at high shear rates in order to disperse the polymeric ingredients in 
water. Such long mixing times are detrimental because they result in 
significant reductions in processing rates. Furthermore, the high shear 
rates required for mixing the polymers, and the long times required for 
such mixing, cause excessive foaming of the solutions, resulting in 
further time delays while the foam dissipates. Antifoaming agents can be 
used to reduce foaming problems, but they increase costs. 
U.S. Pat. No. 4,302,440 issued Nov. 24, 1981 to John et al. discloses a 
method for aqueous spray coating hydroxypropyl methylcellulose onto the 
exterior surface of aspirin tablets. The aqueous solution comprises 2-15 
weight % hydroxypropyl methylcellulose and 15-25 weight % plasticizer 
based on the hydroxypropyl methylcellulose. The solution is sprayed onto 
uncoated aspirin tablets as they rotate in a baffled pan. This patent and 
all other patents cited herein are hereby incorporated by reference. 
U.S. Pat. No. 4,970,081 issued Nov. 13, 1990 to Frisbee discloses aqueous 
coating solutions containing an acrylate/methacrylate copolymer, 
hydroxypropyl methylcellulose, sodium chloride and talc. The solution is 
coated on aspirin granules to provide controlled release. 
U.S. Pat. No. 4,816,264 issued Mar. 28, 1989 to Phillips et al. discloses 
aqueous coating solutions containing multiple polymers such as 
hydroxypropyl cellulose and acrylic resin. The solution may also contain 
other ingredients such as antifoam agents, plasticizers and flavoring 
agents. The coating solution is used in a rotating pan to coat several 
different types of drug tablets. 
U.S. Pat. No. 5,047,258 issued Sep. 10, 1991 to Belanger et al. discloses a 
process for spray coating tablets that utilizes an acrylate enteric 
polymer and plasticizer in water. The spray coating solution requires no 
anti-adherent such as talc. The spray coating operation is carried out 
with conventional rotating perforated pans. 
U.S. Pat. No. 5,098,715 issued Mar. 24, 1992 to McCabe et al. discloses a 
method for aqueous spray coating tablets using solutions containing 
polymer, plasticizer, flavoring and sweetening ingredients. Titanium 
dioxide or other opacifying agents or colorants may optionally be used in 
the coating solutions. 
U.S. Pat. No. 3,935,326 issued Jan. 27, 1976 to Groppenbacher et al. 
discloses a process for coating tablets using a synthetic resin dispersed 
in water. 
U.S. Pat. No. 4,572,833 issued Feb. 25, 1986 to Pedersen et al. discloses a 
method for coating pharmaceutical tablets using organic or aqueous 
solutions. When an aqueous solution is used, the solution includes a 
hydrophobic substance such as wax and is applied at a temperature above 
the melting temperature of the hydrophobic material. A fluidized bed or 
rotating pan may be used to coat the tablets. 
U.S. Pat. No. 4,606,909 issued Aug. 19, 1986 to Bechgaard et al. discloses 
the use of organic solvents or aqueous solutions for coating 
pharmaceutical units. The aqueous solutions include acrylic polymers and 
produce coatings that are insoluble below a pH of 7. 
U.S. Pat. No. 4,800,087 issued Jan. 24, 1989 to Mehta discloses a method 
for microencapsulating pharmaceutical cores using an aqueous polymer 
coating. In addition to polymers, the coating solution may contain 
diluents, fillers, bulking agents, plasticizers, pigments and opacifiers. 
U.S. Pat. No. 4,556,552 issued Dec. 3, 1985 to Porter et al. discloses a 
method of spray coating pharmaceutical tablets using a dry powder that is 
mixed with water to form a coating suspension. The powder comprises 
polymer, plasticizer, pigment and anticaking ingredients. After the powder 
is mixed with water, an ammonia solution is added to the suspension, 
followed by spraying of the suspension onto the pharmaceutical tablets. 
U.S. Pat. No. 4,511,553 issued Apr. 16, 1985 to Boesig et al. discloses a 
coating process using an aqueous solution of saccharose and at least one 
additional sugar such as lactose. Additional flavors, fragrances, and 
coloring ingredients may be added to the aqueous solution. The solution 
may be used to coat pharmaceutical tablets, chocolate centers and hazel 
nuts. 
U.S. Pat. No. 4,704,295 issued Nov. 3, 1987 to Porter et al. discloses a 
method for coating pharmaceutical tablets utilizing a dry powder that is 
added to water and then sprayed onto the tablets. 
U.S. Pat. Nos. 4,855,326, 4,873,085, 4,997,856, 5,011,532, 5,028,632, 
5,034,421 and 5,096,492 issued to Fuisz disclose methods of producing 
filaments comprising various ingredients combined with a sugar carrier. 
The filaments are produced by a spinning technique similar to that used 
for making cotton candy. The ingredients, such as medicaments or 
cosmetics, are combined with the sugar carrier, and the mixture is then 
spun to form high aspect ratio fibers. 
The present invention has been developed in view of the foregoing and to 
overcome the deficiencies of the prior art. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a novel method for coating 
pharmaceutical tablets. 
Another object of the present invention is to provide a method for coating 
pharmaceutical tablets comprising the steps of melt spinning a mixture of 
saccharide and polymer coating ingredients to form particulates, mixing 
the particulates with water to form a coating solution, spray coating 
pharmaceutical tablets with the solution and drying the coated tablets. 
A further object of the present invention is to provide a coated 
pharmaceutical tablet made by the method of melt spinning a mixture of 
saccharide and polymer coating ingredients to form particulates, mixing 
the particulates with water to form a coating solution, applying the 
aqueous solution to pharmaceutical tablets and drying the coated tablets. 
Another object of the present invention is to provide composite 
particulates for use in coating pharmaceutical tablets. The particulates 
comprise saccharide and polymer coating ingredients, and are capable of 
dissolving extremely rapidly in water. 
As used herein, the term "saccharide" is broadly defined to include 
monosaccharides, disaccharides, polysaccharides and sugars. 
These and other objects of the invention will become more readily apparent 
from the following description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention relates to a method for coating pharmaceutical 
tablets in which a melt spinning technique is used to form particulates 
comprising saccharide and polymer coating ingredients. These particulates 
are then mixed with water to form a coating solution or suspension. The 
coating solution is applied to pharmaceutical tablets and the solution is 
dried to form a solid polymeric coating. 
In the melt spinning step, at least one saccharide selected from 
monosaccharides, disaccharides, polysaccharides and sugars is combined 
with polymer coating ingredients to form a mixture that is then subjected 
to the melt spinning process. The process yields composite particulates 
comprising a combination of the saccharide and polymer coating 
ingredients. These particulates are then added to water to form a coating 
solution in which the polymer coating ingredients are substantially 
uniformally dispersed. In accordance with the present invention, the use 
of saccharide-containing composite particulates has been found to 
significantly accelerate the dispersion of the polymer coating ingredients 
in water. The use of high shear rate mixing for long periods of time is 
therefore avoided. Once the polymer coating ingredients are dispersed in 
water, the resulting solution is used to coat pharmaceutical tablets by 
methods such as spray coating. 
The particulates typically comprise from about 20 to about 99 weight % 
saccharide and from about 1 to about 80 weight % polymer coating 
ingredients. Preferably, the saccharide comprises from about 40 to about 
90 weight % of the particulates, and more preferably from about 60 to 
about 80 weight %. 
Suitable saccharides include sucrose, lactose, maltose, polydextrose, 
dextrans, corn syrup, corn syrup solids, sorbitol, xylitol and 
combinations thereof. Preferred saccharides include sugars such as 
sucrose, lactose and maltose, and polydextrose and dextrans. Alcohol 
sugars are particularly preferred. Since the saccharides are melted during 
the melt spinning process, they should have a melting point that is below 
the temperature at which adverse reactions of the polymer coating 
ingredients occur. 
The polymer coating ingredients comprise at least one coating polymer and 
may include plasticizers, colorants, opacifiers, glidants, flavoring 
agents, diluents, fillers, bulking agents and other ingredients suitable 
for use in polymeric coatings. Suitable polymers include cellulose ethers, 
vinyls, glycols and acrylics. Of the cellulose ethers, hydroxypropyl 
methylcellulose, hydroxypropyl cellulose, methylcellulose and 
ethylcellulose are suitable. Polyvinylpyrrolidone, polyethylene glycols, 
methacrylic amino ester copolymers, sodium alginate, povidone and gelatin 
are also suitable coating polymers. A particularly preferred coating 
polymer is hydroxypropyl methylcellulose (HPMC). Many other polymers are 
suitable for use in accordance with the present invention, as long as they 
possess satisfactory solubility, permeability and mechanical 
characteristics in the final coating form. The polymers must be 
sufficiently soluble in the gastrointestinal tract, must be sufficiently 
impermeable to moisture and must possess satisfactory tensile strength, 
elastic modulus and film adhesion characteristics. In general, polymers 
having increased molecular weight tend to possess increased tensile 
strength and elastic modulus but decreased film adhesion characteristics. 
Multiple polymers may be combined to form the coating polymer. 
The polymer coating ingredients of the present invention preferably include 
a plasticizer. The use of a plasticizer promotes softening and ease of 
deformation of the polymer, and may also reduce the glass transition 
temperature of the polymer. External plasticizers are preferred and 
typically comprise a low molecular weight liquid. Such plasticizers 
typically comprise from about 1 to about 40 weight % of the polymer 
coating ingredients based on the weight of the polymer. Typical 
plasticizers include glycerin, propylene glycol, low molecular weight 
polyethylene glycols, triacetin, sorbitol, acetylated monoglycerides, 
citrate esters, phthalate esters, mineral oil and vegetable oils. A 
preferred plasticizer is polyethylene glycol MW 4000. 
Colorants, opacifiers and glidants may also be included with the polymer 
coating ingredients in order to improve the appearance and other 
characteristics of the coating. Suitable colorants and opacifiers include 
water soluble dyes, water insoluble pigments and natural colorants. 
Examples of suitable colorants include D&C and FD&C Blue, Red and Yellow 
lakes and dyes. A preferred natural colorant is carmel. The amount of 
colorant used depends upon the appearance desired and can be adjusted 
accordingly. Pigments including titanium dioxide, calcium carbonate, 
calcium sulfate, magnesium oxide, magnesium carbonate, aluminum silicate, 
aluminum hydroxide, talc and iron oxide may be used due to their 
uniformity, stability and hiding power. Metal oxides are preferred 
opacifiers, with titanium dioxide being a particularly preferred 
opacifier. Opacifiers can be advantageously used to increase hiding power 
while reducing the amount of colorant necessary. Thus, the use of a 
relatively inexpensive, inorganic opacifier such as titanium dioxide can 
minimize the use of relatively expensive colorants. Examples of glidants 
for improved processing and to reduce coating tackiness are talc, metal 
stearates, inorganic clays, silicas, natural and synthetic waxes and oils. 
In accordance with the present invention, the polymer coating ingredients 
are combined with the saccharide to form a mixture that is subjected to a 
melt spinning process. In the melt spinning process, the mixture is 
heated, typically above the melting point of the saccharide, in a spinning 
head having appartures in the sides thereof. Once the mixture is heated to 
the appropriate temperature, the head is rotated and the mixture is 
ejected from the appartures by centrifugal force. A suitable spinning 
machine is the Econofloss Model 3017 manufactured by Gold Medal Products 
Company. The rotation speed and temperature of the mixture during spinning 
may be adjusted to achieve the desired particulate morphology. Rotation 
speeds of from 3000 to 5000 rpm are preferred, with 4000 rpm being a 
particularly preferred speed. The aperature size or slit width of the 
spinning head can be adjusted to produce the desired size of particulates. 
In accordance with the present invention, the spun material is in the form 
of composite particulates which comprise a combination of the polymer 
coating ingredients and saccharide. The particulates preferably have an 
average size of from about 0.1 to about 8 mm. The particulates are 
advantageously formed in the shape of equiaxed particles, flakes, rods and 
the like, having relatively low aspect ratios. It is preferred that the 
particulates possess an average aspect ratio of less than 20:1 and more 
preferably less than 10:1. Such a low aspect ratio morphology results in 
durable particulates having minimal friability. The low aspect ratio 
particulates are easily handled in the subsequent coating process, 
substantially reducing dust problems associated with conventional polymer 
coating powders. 
The composite particulates of the present invention, comprising polymer 
coating ingredients in combination with saccharides, have been found to 
significantly improve the dispersion of the polymer coating ingredients 
once the particulates are added to water. In conventional aqueous spray 
coating processes, the coating ingredients such as polymers, plasticizers 
and colorants are added to water in loose powder form. These powders do 
not readily mix with water. Instead, the powders are non-wetted and tend 
to agglomerate. As a result, high shear rate mixing for long periods of 
time is required for preparing conventional aqueous polymer coating 
solutions. In addition to non-wetting and aglomeration problems, 
conventional polymer coating powders suffer from handling problems. Large 
amounts of dust are often produced during the preparation of conventional 
aqueous coating solutions because the coating ingredients are provided in 
loose powder form that readily becomes airborne. The particulates of the 
present invention substantially eliminate such problems because the 
polymer coating ingredients are combined together with saccharide in a 
particulate form that avoids the use of fine powders and promotes 
dispersion of the coating ingredients in water. When the particulates of 
the present invention are added to water, they typically dissolve within a 
few seconds with only minimal stirring. In contrast, prior art polymeric 
powders can take hours or even days to dissolve. Even with the use of high 
shear rate mixing techniques, conventional polymeric powders require 
excessively long times for satisfactory dispersion. Such high sheer rate 
mixing techniques are costly due to the relatively complex machinery 
involved and the requirement of additional ingredients such as antifoaming 
agents. The particulates of the present invention produce surprisingly 
superior results in comparison to prior art powder coating ingredients as 
illustrated in the following Example 1. The examples provided herein are 
for illustrative purposes only and are not intended to limit the scope of 
the present invention. 
EXAMPLE 1 
A polymer coating composition is prepared by mixing 88 weight % 
hydroxypropyl methylcellulose (HPMC) polymer, 2 weight % total titanium 
dioxide opacifier and FD&C blue colorant, and 10 weight % polyethylene 
glycol plasticizer. The mixture is divided in half and one sample weighing 
57 grams is mixed with 170 grams of saccharide in the form of corn syrup 
solids. This mixture is subjected to a melt spinning process using an 
Econofloss model 3017 at a temperature of 150.degree. C. and a head 
rotation speed of about 4000 rpm to form particulates comprising about 25 
weight % polymer coating ingredients in combination with about 75 weight % 
saccharide. The particulate sample and the powder sample are each added to 
148 milliliters of water at room temperature with gentle stirring. The 
particulate sample completely dissolves within 3 minutes, forming a 
uniform dispersion. The powder sample agglomerates upon addition to the 
water and does not disperse after 3 hours of stirring. 
The particulates of the present invention may be added to water in amounts 
of from about 5 to about 80 weight % and preferably from about 30 to about 
60 weight %. When mixed, the saccharide readily dissolves in the water and 
the polymeric coating ingredients are also dissolved or dispersed in the 
water to form an aqueous coating solution. Dissolution typically takes 
less than about 3 minutes and usually less than about 20 seconds. The term 
"solution" is defined broadly in accordance with the present invention to 
include true solutions of the polymeric coating ingredients in water and 
also dispersions of the polymer coating ingredients in water. Once 
dissolved, the aqueous coating solutions preferably contain concentrations 
of the coating polymer of from about 1 to about 30%, and more preferably 
from about 3 to about 15%. 
When the particulates are added to water, it is preferred to use low sheer 
rate mixing. "Low sheer rate mixing" is defined in accordance with the 
present invention as that amount of mixing or agitation in which 
substantially no vortex or aeration of the solution occurs. 
Once the aqueous coating solution is formed by the method of the present 
invention, the solution is applied to pharmaceutical tablets in any 
suitable manner. It is preferred to spray coat the pharmaceutical tablets 
using a rotating pan or other device. However, other coating methods may 
also be satisfactory. The term "pharmaceutical tablet" is defined broadly 
in accordance with the present invention to include a wide variety of 
pharmaceutical units such as tablets, capsules, granules, crystals and 
powders. While the coating of pharmaceutical tablets is the primary object 
of the present invention, it is also recognized that other tablets may be 
coated by the present methods. For example, other edible items such as 
confections can be coated by the methods of the present invention. 
As stated above, the coating solutions prepared in accordance with the 
present invention can be applied to pharmaceutical tablets by various 
coating techniques, with the use of spray coating being the most 
preferred. In the spray coating process, the pharmaceutical tablets are 
placed in a rotating pan or other suitable vessel and the coating solution 
is sprayed onto the tablets as the tablets are agitated. Vessels such as 
rotating pans are commercially available for tablet coating purposes. The 
equipment necessary for spraying the coating solution includes a pumping 
system and at least one spray gun, which are also commercially available. 
Both air spray and airless spray coating techniques are suitable. Spraying 
parameters such as flow rate and spray time are controlled in a manner 
known in the art in order to produce the desired coating. The spraying 
operation can be carried out in a single step or in multiple steps in 
which layers of coating material are built-up on the tablets. 
During the coating process, the coatings are dried in order to remove the 
water and to obtain a solid coating. It is particularly preferred to use 
forced air convection drying wherein the inlet air temperature, inlet air 
humidity and exhaust air volume are controlled in order to optimize drying 
rates. In the preferred rotating pan spray coating method, spraying and 
drying typically occur simultaneously during the coating process. It is 
thus necessary to adjust the drying parameters to take into account such 
factors as the surface area of the tablets, pan dimensions, degree of 
atomization of the spray, spray gun placement, pan speed and spray rate. 
Such parameters can be adjusted to achieve high quality coatings at 
optimum coating rates. 
The following examples illustrate various aspects of the present invention. 
EXAMPLE 2 
Composite particulates having compositions indicated as 2A, 2B and 2C in 
the Table below are prepared as follows. The indicated amounts of 
ingredients are mixed in dry powder form and added to the preheated 
spinning head of an Econofloss Model 3017 spinning machine, at a rotation 
speed of about 4000 rpm. The temperature is maintained at 150.degree. C. 
for composition 2A, 130.degree. C. for composition 2B and 115.degree. C. 
for composition 2C. The resultant spun particulates are in the form of 
composite flakes having the compositions indicated in the Table below. 
Each of the particulate compositions dissolves completely within 3 minutes 
after adding to water, with only mild stirring in which no vortex is 
formed and no aeration occurs. 
TABLE 
______________________________________ 
Wt. % 
______________________________________ 
Composition 2A 
Polydextrose 50.0 
Hydroxypropyl cellulose 5.0 
Hydroxylpropyl methylcellulose 
22.0 
Magnesium sterate 5.0 
Titanium dioxide (fine grind) 
3.0 
FD&C yellow No. 6 aluminum lake (fine grind) 
5.0 
D&C yellow No. 10 aluminum lake fine grind) 
5.0 
Polyethylene glycol 3350 5.0 
Composition 2B 
Corn syrup solids 60.0 
Hydroxymethyl cellulose 12.0 
Talc 7.0 
FD&C blue #1 aluminum lake 5.0 
D&C red #7 calcium lake 2.0 
Triacetin 7.0 
Sorbitol 7.0 
Composition 2C 
Sorbitol 38.8 
Polydextrose 25.0 
Hydroxypropyl cellulose 12.0 
Hydroxymethyl cellulose 12.0 
Propylene Glycol 2.0 
Titanium dioxide 5.0 
Talc 5.0 
Colloidal silica 0.2 
______________________________________ 
EXAMPLE 3 
The following powder ingredients are formed as a dry mixture: Corn syrup 
solids 30.0 weight %; Polydextrose 40.0 weight %; Hydroxypropyl cellulose 
8.0 weight %; Hydroxypropyl methylcellulose 12.0 weight %; FD&C red No. 28 
aluminum lake 5.0 weight %; and Polyethylene glycol 3350 5.0 weight %. 
This dry mixture is charged into the preheated head of a melt spinning 
device as in Example 2, and is spun at 150.degree. C. to form particulate 
flakes. The particulate material is then dissolved in water by adding 400 
grams of the particulate to 600 grams of deionized water in a stainless 
steel vessel while stirring with a conventional lab top mixer. A uniform 
dispersion is achieved in less than 3 minutes, thereby forming a tablet 
coating solution suitable for introduction into the pump reservoir of a 
conventional tablet coater. 
EXAMPLE 4 
A tablet coating solution is formed by adding 750 grams of particulate 
material having a composition as in Example 3 to 2,250 grams of purified 
water in a 5 liter stainless steel vessel while using a Tekmar lab top 
stirrer with a 5 cm, 4-prong blade. The coating solution is stirred for 1 
minute. An 8.5 kg charge of uncoated tablets is placed in a 24 inch 
Accela-Cota tablet coater, manufactured by Thomas Engineering, Inc. The 
tablets are preheated until the bed temperature reaches 42.degree. C. The 
pan rotation is then set to 12 rpm and the tablets are coated with the 
solution using a Binks Model 460 spray gun operating at 55 psi. The 
coating solution is pumped at a rate of between approximately 30-60 cc per 
minute using a peristalic pump. The tablet bed temperature is maintained 
between 42.degree.-50.degree. C. during the spray coating operation. After 
drying, the coating possesses a good appearance and favorable mechanical 
properties. 
EXAMPLE 5 
A coating solution is formed by adding 200 grams of particulates of 
composition 2A in Example 2 to 300 grams of deionized water in a 2 liter 
stainless steel vessel, while mixing using a spatula for 2 minutes. The 
resultant uniformly dispersed coating solution is added to the coating pan 
pump reservoir of a Vector LDCS tablet coater, manufactured by Vector 
Corp. A 1 kg charge of uncoated tablets is placed into the pan of the 
coater. The tablets are then preheated until the outlet air temperature of 
the coating pan reaches 4.degree. C. The pan is then rotated at 20 rpm and 
the atomization air pressure is set to between 14-16 psi. The coating 
solution is sprayed at a rate of between approximately 5-8 cc per minute 
until the desired coating thickness is achieved. The coating possesses a 
good appearance and favorable mechanical properties. 
It is understood that the above description of the present invention is 
susceptible to various modifications, changes and adaptations by those 
skilled in the art, and that such modifications, changes and adaptations 
are to be considered to be within the spirit and scope of the invention as 
set forth by the following claims.