NTA Level 6 • Semester 1 • PST06103

Compression

Pharmaceutical Production • Source Session/Topic 18

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Session 18: Compression

Total Session Time: 120 minutes

Pre-requisites

• None

Learning Tasks

By the end of this session students are expected to be able to:

• Define compression

• Explain the importance of pre-compression mixing

• List equipments used for tablet pressing

• Explain the events during compression

• Explain problems encountered in tablet production

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board and chalk/whiteboard markers

• LCD projector and computer

SESSION OVERVIEW

SESSION CONTENTS

STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)

READ or ASK students to read the learning tasks and clarify

ASK students if they have any questions before continuing

STEP 2: Compression and Pre-Compression Mixing (20 minutes)

• Compression is a unit process in pharmaceutical production in which

granules (obtained from granulation) or powder mix are compressed to form

tablets

• Compression is done after preparation of granules or mixing of

ingredients (in case of direct compression)

o The granules or powder mix are compressed to form tablets

• Compression is accomplished by using equipment called tablet machine or

tablet pres

• Materials to be compressed into tablets must have good flow properties

and compressibility

• During compression, the proximity of particles surface causes bond

formation between particles which provide coherence to the powder i.e.

compact formation

• Powder compression causes compaction and consolidation i.e. the increase

in mechanical strength of material from particle-particle interactions

• Before the granules or powder mix are compressed, pre-compression mixing

is done

o Excipients such as lubricants, glidants, antiadherents and

disintegrants are added in the required proportion onto the surface of

granules or powder particles in the powder mix

o The reason for pre-compression mixing is to improve tablet

manufacturing process e.g. by reducing friction and promoting flow of

materials into the compression machine and improve the pharmaceutical

quality of the tablets e.g. disintegration

• The unit processes in manufacture of tablets are;

o Dispensing (weighing)

o Granulation (wet or dry)

o Drying and sizing

o Lubrication

o Compression

o In-process checking

o Packing

o Final product analysis and release

• In some instances, powder mix is compressed into tablet without passing

through granulation process i.e. direct compression

• The unit processes in the manufacture of tablets are shown in figure 21.1

below;

Figure 21.1: Unit process in tablet manufacturing

[pic]

STEP 3: Equipment Used for Compression (35 minutes)

• After mixing the ingredients, the powder mix or the granules (after pre-

compression mixing) are compressed into tablets by using a machine called

Tablet Press

• There are two types of tablet presses;

o Single punch (single station) tablet press

▪ This is for small scale production of tablets

o Multi-station (rotary) tablet press

▪ This is for large scale production of tablets

• Tablet press

o A tablet press is a high speed machine that squeezes (compresses) the

ingredients (granules or powder mix) into required tablet shape and

size

o Tablet presses can also press the name of the manufacturer, of the

product or other markings into the top of the tablet

o A typical single punch tablet press consists of the following parts;

▪ A hopper shoe

• This is for holding and delivering powder mix or granules into

the compression chamber in the die

▪ A die

• A disc shaped piece of hardened steel with a hole cut up of

through its centre

• The hole in the die is known as a compression chamber

• The functions of the compression chamber;

• To receive materials for compression

• It is where compression takes place

• Provides shape and size to the tablets

▪ A punch (A set of two punches for each die)

• It is a rod-shaped hardened steel that fits into top or bottom

of the die

• For each die, there are two punches (a lower punch –which fits

into the bottom of the die and an upper punch –which fits into

the top of the die)

• The punches press name of the manufacturer, name of the product

or other markings into the top of the tablet during compression

• The function of the upper punch

• To compress the materials in the die chamber (by downward

movement) to form a tablet

• Functions of the lower punch

• Lower punch controls the size of the tablet

• Eject the tablet from the die chamber after it is formed

▪ Ejection regulating screw

• It controls the movement of the lower punch during ejection of

the tablet

▪ Capacity regulating screw

• Adjust lower punch movement to control volume of materials into

the die chamber

• This determines thickness of the tablet

o A typical multi-station or rotary tablet press consists of the

following sections and parts;

▪ Upper cam section

• Consists of the upper compression roller and all adjustment to

the position of upper compression rollers

• The primary components of the upper cam section are;

o Upper punch removal/dwell cam

o Upper punch lowering cam

o Upper pre-compression and main compression rollers section

depth adjustment

o Upper punch pull up-cam

o Cam material of construction

▪ Compression section

• Contains all the components that are exposed to the materials to

be compressed

• It is made up of the following parts

o Material hopper

o Feed frame

o Excess material stripper

o Tablet stripper

o Material recirculation

▪ Lower cam section

• This section is completely sealed from the compression section

• It houses the lower compression rollers, the entire lower cam

track that guide lower punch as the turret rotates

• Parts of the lower cam section includes;

o Fill cam

o Weight regulation cam

o Pre-compression and compression rail

o Ejection rail

▪ Lower mechanical section

• This section houses the main drive motor and the gearbox, the

hydraulic pump, the lubrication pump and signal wire

distribution

• Proper ventilation and cooling of the lower mechanical section

is essential to prevent machine damage and minimize heat

generation

• This section is equipped with cooling system for product that

are sensitive to heat generation e.g. contain low melting point

ingredients that are prone to picking and sticking

STEP 4: The Compression Cycle (25 minutes)

• Compression cycle is a series of events which eventually results in

formation of a tablet

• The events of a compression cycle for a single punch tablet press are;

o Opening of the die (chamber)

▪ To allow the die chamber to be filled

▪ The lower punch moves down in at this phase and upper punch stays

▪ The hopper moves in to fill the die chamber (in multi-station

press the die table moves the die chamber under the hopper)

o Filling of the die with powder mix or granules

▪ This is by gravitational flow of powder mix or granules into the

die chamber

o Compression

▪ The upper punch descents and enter the die and the materials are

compressed until a tablet is formed

▪ During compression (as the upper punch moves downward) the lower

punch remain stationary or moves upward in the die (to a pre-set

level)

▪ After maximum applied force, the upper punch leaves the

compressed mix/granules i.e. the decompression phase

o Ejection

▪ During this phase, the lower punch rises until its tip reaches

the level of the top of the die

▪ The tablet is subsequently removed from the die by the hoper as

it moves in to fill the die chamber (for multi-station presses the

tablet is removed from the die table by a pushing device)

• The working of a multi-station tablet press is based on the compression

of materials between a pair of moving punches within a stationary die

• The events of a compression cycle in a multi-station (rotary) tablet

press are;

o Die filling

o Volume control

o Compression

o Tablet ejection

STEP 5: Problems Occurring in Compression (25 minutes)

• Proper understanding of material compression characteristics and

knowledge of tablet compression equipment (the press) is essential for

efficient troubleshooting of production problem

|Activity: Small Group Discussion (10 minutes) |

| |

|DIVIDE students into small manageable groups |

| |

|ASK students to discuss on the following question |

|List common problems that occur during compression |

| |

|ALLOW students to discuss for 15 minutes |

| |

|ALLOW few groups to present and the rest to add points not mentioned |

| |

|CLARIFY and SUMMARIZE by using the contents below |

• Various tablets problems occur during production;

o Tablet weight variation

▪ Caused by various factors including poor flow, increasing machine

speed

▪ Excessive weight variation should call for examination of the

following;

▪ Condition of the lower punch pull-down cam

▪ Condition and position of excess material stripper

▪ Feeder paddle speed cam

▪ Minimum amount of material recirculation is necessary

o Low hardness

▪ May be due to capping or non-compressibility

▪ In this case the following should be done;

▪ Pre-compression and compression with large diameter roller

▪ Press speed is reduced in order to increase total compression

time

o Punch variation

o Hardness variation

o Poor flow of powder mix or granules

o Tablet jam and chipping

o Picking and sticking

▪ The following should be done to minimize picking and sticking;

▪ Heat of compression

▪ Press speed

▪ Pre-compression force

▪ Tool condition (tooling set comprises of a die and a pair of

punches)

▪ Tablet stripper

o Capping and lamination

STEP 6: Key Points (5 minutes)

• Compression is a unit process in pharmaceutical production in which

granules (obtained from granulation) or powder mix are compressed to form

tablets

• During compression, the proximity of particles surface causes bond

formation between particles which provide coherence

• Tablets may be produced by direct compression that does not involve

formation of granules

• Tablets are produce by compression by an equipment called tablet press

• For small scale production of tablets, a single punch tablet press is

used while multi-station or rotary tablet press is used for industrial

scale production of tablets

• During compression, four events take place namely die opening, die

filling, compression and ejection

• A number of problems may occur during compression and knowledge of the

characteristics of powder mix and granules as well as the knowledge of

tablet press is useful in troubleshooting these problems when they occur

STEP 7: Evaluation (5 minutes)

• What is compression?

• What is consolidation?

• What are the parts of multi-station (rotary) tablet press?

• What are the events occurring in a compression cycle?

References

Aulton M.E & Kevin M.G,( Eds): (2013) Pharmaceutics: The design and

manufacture of medicines, (4th ed.) Churchill Livingstone

Hugo and Russell (2011), Pharmaceutical Microbiology (8th ed.), Willey-

Blackwel publications

Gennaro, R. A. , et.al (Eds) (1995) Remington: The Science and Practice of

Pharmacy, Volume I & II, (19th ed.): Mack Publishing Company, Easton,

Pennsylvania 18042

Liebsch, B et al (1988): Tanzania Pharmaceutical Handbook, Dar es Salaam

University Press.

Lund, W. Editor (1994). The Pharmaceutical Codex, Principles and Practice

of Pharmaceutics (12th ed.): The Pharmaceutical Press, London

Polderman, J. (1990) Introduction to Pharmaceutical Production: Novib, The

Hague

Rawlins E.A, Editor: (1977) Bentley’s Textbook of Pharmaceutics, 8th Ed.

Baillie're Tindall. London Kamm, G. and Kohler, B. Editors: (1995)

Manual for Decentralized Infusion Production, Infusion Unit Project

Tanzania

Schmidt, O. (ed) (2000) Pharmaceutical Quality systems, Interpharm Press,

Colorado.

Shayne C et al. (2008), Pharmaceutical Manufacturing Handbook: Production

and processes, John Wiley & Sons

Watson, D. G (1999) Pharmaceutical Analysis: A Textbook for Pharmacy

Students and Pharmaceutical Chemists: Churchill Livingstone,

Edinburgh.

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