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10
Automation of coating processes
Graham C.Cole
SUMMARY
Current Good Manufacturing Practice (cGMP) and the demands of the regulatory authorities world-
wide requires greater care in the design of manufacturing facilities, the selection of materials used in
their construction, their layout, the equipment used in the preparation of tablets to be coated and the
coating operation. It is claimed that robotic systems will eventually take over all processing tasks!
(Kanig & Rudic, 1986). This chapter will discuss automation concepts and suggestions based on cGMP
(DHSS, 1983) in two areas:
An examination of Fig. 7.1
(Chapter 7) shows the general requirement, and this chapter will describe
how automation of this process can be achieved.
10.1 INTRODUCTION
Since 1970 the explosion in the development of the microprocessor, the programmable controller and
personal computers has provided tools to make substantial productivity improvements in manufacturing
systems. Many of the major pharmaceutical products in the oral solid dosage field are now produced
using automated plants. Merck’s ALDOMET manufacturing facility is well known and a well-
documented example (Lumsden, 1982; Fig 10.1
). This process uses fluidized bed coating columns. Figs
10.2
and
10.3
show schemes that uses both side
-
vented and conventional pans.
•

the design and layout of the building
•


poor material
-
handling facilities
•

the high cost of quality control
•

inefficient use of manufacturing equipment
•

short runs and a variable product mix.
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10.2 SYSTEMS
For the application of computer control to the coating process, some of the possible alternatives
available are highlighted here. There are three main possibilities:
Each system is briefly described with points to consider when evaluating each of them and finally
suggestions and conclusions on the final choice. It is not an exhaustive list but more a discussion to
assist in making the basic decisions.
10.2.1 Data acquisition system
Fig. 10.4 shows the layout of a data acquisition system. These are normally small devices for low levels
of inputs only, but some have limited computing power. They can also be used to provide printouts of
the information gathered, similar to that described in Chapter 6
. They do not provide any plant control
and have only limited processing of information capacity. Some can be linked to high-powered
computers which would store data or manipulate it, depending on the degree of automation required.
The field inputs have to be cabled back to a control location such as a control room and the system
interface requires safety protection.
Advantages:


Long lengths of field cabling required.
•

No local operator interface.
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Each hardware item performs a specific task and information is passed between the various hardware
items using a dual data highway. This dual highway provides good security for communications.
The field devices, such as the input, output and control devices, must be protected by suitable housing
and safety equipment for use in a hazardous area, particularly if flammable solvents are used in the
coating process.
Computer type functions are distributed throughout the process area using smaller microprocessor
devices. It can support local operator control devices located in the plant area providing these are
adequately protected.
This system can provide process control for continuous variables such as atomizing air pressure and
tablet-bed temperature and batch or sequence control. It can be linked to other devices such as an
existing in-house computer.
Advantages:
Disadvantages:
10.2.3 Centralized control system
Fig. 10.6 shows the layout of a centralized computer control system. This is very similar to the
distributed control system. It can perform all the same functions, but they are centralized within a
computer system. The computer would normally be the process control manufacturer’s standard.
Advantages:
Disadvantages:
•

Batch, sequence operations and continuous control is available.
•


•

Same as distributed system.
•

System size tends to be intermediate between the systems illustrated in Figs
10.4
and
10.5
.
•

Long lengths of field cabling required.
• System operation dependent on one device (the computer) thus a redundancy of a back-up
computer may be required to increase reliability.
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Fig. 10.6 Centralized computer system.
Ideally the type of system required for a coating plant should have the following capability:
•

Data logging and process control of various parameters, temperature; spray rates.
•

Batch control is required with various recipes and sequences.
•

Optimization of batch control parameters.
•

Flexibility to change the process, size of batches, product, etc.

There are many different types of tablets that can be coated, ranging from a cosmetically coated tablet to
those that use the osmotic pump principle to release the drug. Examples were illustrated in Fig. 7.3
(Chapter 7).
In the development and implementation of any automated tablet-coating process there are a number
of objectives that must be addressed:
•

Printouts and logs required.
•

System size relatively small (150 loops approximately).
•

A dual processor computer to provide back
-
up security for control and data storage.
• Links to an in-house computer can be accommodated if a separate system is used. This data can
be passed to the in
-
house system for processing or display if required.
•

Inventory control could be added.
• In a potentially hazardous plant, it may be worth considering a separate emergency shutdown
system for increased safety.
•

It is smaller and cheaper.
•


conditions (protection from light and oxygen).
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Fig. 10.8 Schematic of an instrumented and computer-controlled coating pan.
of a facility, the refurbishment of an existing operation or in selection of new equipment for
development and production purposes.
10.5 PROCESS CONCEPT
To design the facility requires an understanding of the overall tablet-coating process. The building and
building services provide the envelope around the process and the process operation must be performed
in areas designed to conform to cGMP. It will also need a validation programme.
For any tablet-coating operation there are four essential requirements:
A flow diagram should be developed, as shown in Fig. 11.2
. (Chapter 11). All or some of these
operations take place whether in a laboratory or on a production scale. For efficient and accurate
operations the following stages must be assessed:
1.
a supply of tablet cores;
2.
a supply of coating materials;
3.
the process equipment;
4.
a building to house the equipment, raw materials and finished product.
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10.5.1 Warehousing
In all companies, the size of the inventory is critical to the efficient operation of any plant. More and
more companies are employing Just-in-Time (JIT) concepts to minimize stock levels and ensure that
First In First Out (FIFO) principles apply. A typical flow diagram is shown in Fig. 10.9
. In addition,
storage space must be available for raw materials and finished stock. The simplest way of handling all
these requirements is by installing a computer-controlled materials management system. This records

3.
process operations
4.
packaging.
Balance 1 0.010 kg (sensitivity 0.01 mg)
Balance 2 10.0 kg (sensitivity 500 mg)
Balance 3 50.0 kg (sensitivity 1.0 g)
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Fig. 10.9 Flow diagram for storage of materials.
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Fig. 10.10 Schematic diagram for an automated pharmaceutical dispensary.
materials to the production area for preparation of the powder mix ready for tablet core manufacture and
raw materials for the preparation of the coating.
The layout of the process area will depend on the material-handling concept. If pneumatic transfer is
used for an automatic transfer operation, then the IBC can be linked to the blender/granulator/dryer/mill
and the blender to the tablet machine or an intermediate bulk container (IBC; see Fig. 10.11
).
Figs 10.2
and 10.3 show an automated feed and receiving system for tablet-coating equipment. Units
are linked to a process monitoring and control system (PMCS). For an automated system, coated tablets
can be stored in an IBC until released to packaging; the IBC can be positioned above the packaging unit
and the coated tablets are then gravity fed into the blister packer or securitainer filling unit.
The objective in all these operations should be to minimize manual transfer and reduce exposure and
contact of the product to the operator and the environment.
10.5.4 Layout and design of facility
A typical layout is shown in Fig. 10.12. Process areas require high-quality finishes to maintain cGMP
standards. Traditionally pharmaceutical secondary manufacturing facilities have been designed on the
basis of single rooms or cubicles for each stage of the manufacturing process. Transfer of materials has
been accomplished using a large drum or mobile trolley. Today the industry is investing in more
automatic transfer systems for material handling in an attempt to reduce costs and improve yields. This

equipment. To a certain degree the system chosen will depend on the extent of damage that occurs and
this relates to the robustness of each part of the tablet. It will also depend on how much deterioration the
Quality Assurance Department can accept and write into the specifications. Older products can
withstand little mechanical shock, whereas modern formulations have been developed using current
materials which provide a greater degree of robust handling.
To transport tablets various systems have been tried, all with limited success. These are:
•

bucket conveyors;
•

fluidized bed transfer system;
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Fig. 10.16 Ground-floor layout for an automated facility.
Fig. 10.17 First-floor layout for an automated facility.
•

a mixture of perforated plates with a layer of fluidizing air;
•

pulse air systems;
•

vacuum systems;
•

spiral vibrating chutes.
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Fig. 10.18 Flow diagram for an automated facility.
REFERENCES