Compression and Processing Problems in Tablets

Defects related to the tableting process:

1. Capping: It is partial or complete separation of the top or bottom of the tablet due to air-entrapment in the granular material.

2. Lamination: It is the separation of the tablet into two or more layers due to air-entrapment in the granular material.

3. Cracking: It is due to the rapid expansion of tablets when deep concave punches are used.

Defects related to excipient:

1. Chipping: It is due to very dry granules.

2. Sticking: It is the adhesion of granulation material to the die wall

3. Picking: It is the removal of material from the surface of the tablet and its adherence to the face of punch.

4. Binding: These problems (v, vi, vii) is due to more amount of binder in the granules or wet granules.

Defect related to more than one factor:

1. Mottling: It is either due to any one or more of these factors: Due to a colored drug, which has a different color than the rest of the granular material (Excipient- related); improper mixing of granular material (Process-related); dirt in the granular material or on punch faces; oil spots by using oily lubricant.

Defect related to the machine:

1. Double Impression: It is due to the free rotation of the punches, which have some engraving on the punch faces. Further, in this section, each problem is described along with its causes and remedies which may be related to either formulation (granulation) or of the machine (dies, punches, and entire tablet press).

Compression and Processing Problems in Tablets

Capping

Capping is the term used, when the upper or lower segment of the tablet separates horizontally, either partially or completely from the main body of a tablet and comes off like a cap, during ejection from the tablet press, or during subsequent handling.

Reason: Capping is usually due to the air–entrapment in a compact during compression and subsequent expansion of tablet on ejection of a tablet from a die.

Causes and Remedies of Capping related to Formulation (Granulation):

Causes:

• A large number of fines in the granulation.
• Too dry or very low moisture content (leading to loss of proper binding action).
• Not thoroughly dried granules.
• Insufficient amount of binder or improper binder.
• Insufficient or improper lubricant.
• Granular mass too cold.

Remedies:

• Remove some or all fines through 100 to 200 mesh screens.
• Moisten the granules suitably. Add hygroscopic substances e.g. sorbitol, methylcellulose, or PEG-4000.
• Dry the granules properly.
• Increasing the amount of binder.
• Adding dry binders such as pre-gelatinized starch, gum acacia, powdered sorbitol, PVP, hydrophilic silica, or powdered sugar.
• Increase the amount of lubricant or change the type of lubricant. • Compress at room temperature.

Causes and Remedies of Capping related to Machine (Dies, Punches and Tablet Press):

Causes:

• Poorly finished dies.
• Deep concave punches or beveled-edge faces of punches.
• Lower punch remains below the face of the die during ejection.
• Incorrect adjustment of sweep-off blade.
• High turret speed.

Remedies:

• Polish dies properly. Investigate other steels or other materials.
• Use flat punches.
• Make the proper setting of lower punch during ejection.
• Adjust sweep-off blade correctly to facilitate proper ejection.
• Reduce the speed of the turret (Increase dwell time).

Lamination

Lamination is the separation of a tablet into two or more distinct horizontal layers.

Reason: Air–entrapment during compression and subsequent release on ejection. The condition is exaggerated by the higher speed of the turret.

Causes and Remedies of Lamination related to Formulation (Granulation):

Causes:

• Oily or waxy materials in granules.
• Too much hydrophobic lubricant.
• Magnesium-stearate.

Remedies:

• Modify the mixing process. Add adsorbent or absorbent.
• Use a less amount of lubricant or change the type of lubricant.

Causes and Remedies of Lamination related to Machine (Dies, Punches & Tablet Press):

Causes:

• Rapid relaxation of the peripheral regions of a tablet, on ejection from a die.
• Rapid decompression.

Remedies:

• Use tapered dies, i.e. the upper part of the die bore has an outward taper of 3° to 5°.
• Use pre-compression step.
• Reduce turret speed and reduce the final compression pressure.

Chipping

Chipping is defined as the breaking of tablet edges, while the tablet leaves the press or during subsequent handling and coating operations.

Reason: Incorrect machine settings, specially misset ejection take-off.

Causes and Remedies of Chipping related to Formulation (Granulation):

Causes:

• Sticking on punch faces.
• Too dry granules.
• Too much binding causes chipping at the bottom.

Remedies:

• Dry the granules properly or increase lubrication.
• Moisten the granules to plasticize.
• Add hygroscopic substances.
• Optimize binding, or use dry binders.

Causes and Remedies of Chipping related to Machine (Dies, Punches and Tablet Press):

Causes:

• The groove of the die is worn at the compression point.
• Barreled die (center of the die wider than ends).
• Edge of punch face turned inside/inward.
• Concavity too deep to compress properly.

Remedies:

• Polish to open-end, reverse or replace the die.
• Polish the die to make it cylindrical.
• Polish the punch edges.
• Reduce concavity of punch faces.
• Use flat punches.

Cracking

Small, fine cracks observed on the upper and lower central surface of tablets, or very rarely on the sidewall are referred to as cracks.

Reason: It is observed as a result of the rapid expansion of tablets, especially when deep concave punches are used.

Causes and Remedies of Cracking related to Formulation (Granulation):

Causes:

• The large size of granules.
• Too dry granules.
• Tablets expand.
• Granulation is too cold.

Remedies:

• Reduce granule size.
• Add fines.
• Moisten the granules properly and add the proper amount of binder.
• Improve granulation.
• Add dry binders.
• Compress at room temperature.

Causes and Remedies of Cracking related to Machine (Dies, Punches and Tablet Press):

Causes:

• Tablet expands on ejection due to air entrapment.
• Deep concavities cause cracking while removing tablets.

Remedies:

• Use tapered die.
• Use special take-off.

Sticking

Sticking refers to the tablet material adhering to the die wall. Filming is a slow form of sticking and is largely due to excess moisture in the granulation.

Reason: Improperly dried or improperly lubricated granules.

Causes and Remedies of Sticking related to Formulation (Granulation):

Causes:

• Granules not dried properly.
• Too little or improper lubrication.
• Too much binder.
• Hygroscopic granular material.
• Oily or way materials.
• Too soft or weak granules.

Remedies:

• Dry the granules properly. Make moisture analysis to determine limits.
• Increase or change lubricant.
• Reduce the amount of binder or use a different type of binder.
• Modify granulation and compress under controlled humidity.
• Modify the mixing process. Add an absorbent.
• Optimize the amount of binder and granulation technique.

Causes and Remedies of Sticking related to Machine (Dies, Punches and Tablet Press):

Causes:

• Concavity is too deep for granulation.
• Too little pressure.
• Compressing too fast.

Remedies:

• Reduce concavity to the optimum.
• Increase pressure.
• Reduce speed.

Picking

Picking is the term used when a small amount of material from a tablet is sticking to and being removed off from the tablet surface by a punch face.

The problem is more prevalent on the upper punch faces than on the lower ones. The problem worsens if tablets are repeatedly manufactured in this station of tooling because more and more material getting added to the already stuck material on the punch face.

Reason: Picking is of particular concern when punch tips have engraving or embossing letters, as well as the granular material is improperly dried.

Causes and Remedies of Picking related to Formulation (Granulation):

Causes:

• Excessive moisture in granules.
• Too little or improper lubrication.
• Low melting point substances, may soften from the heat of compression and lead to picking.
• Low melting point medicament in high concentration.
• Too warm granules when compressing.
• Too much amount of binder.

Remedies:

• Dry properly the granules, determine the optimum limit.
• Increase lubrication; use colloidal silica as a polishing agent, so that material does not cling to punch faces.
• Add high melting-point materials. Use high melting point lubricants.
• Refrigerate granules and the entire tablet press.
• Compress at room temperature. Cool sufficiently before compression.
• Reduce the amount of binder, change the type or use dry binders.

Causes and Remedies of Picking related to Machine (Dies, Punches and Tablet Press):

Causes:

• Rough or scratched punch faces.
• Bevels or dividing lines too deep.
• The pressure applied is not enough; too soft tablets.

Remedies:

• Polish faces to a high luster.
• Design lettering as large as possible.
• Plate the punch faces with chromium to produce a smooth and non-adherent face.
• Reduce depths and sharpness.
• Increase pressure to the optimum.

Binding

Binding in the die is the term used when the tablets adhere, seize or tear in the die. A film is formed in the die and ejection of the tablet is hindered. With excessive binding, the tablet sides are cracked and it may crumble apart.

Reason: Binding is usually due to an excessive amount of moisture in granules, lack of lubrication, and/or use of worn dies.

Causes and Remedies of Binding related to Formulation (Granulation):

Causes:

• Too moist granules and extrudes around the lower punch.
• Insufficient or improper lubricant.
• Too coarse granules.
• Too hard granules for the lubricant to be effective.
• Granular material is very abrasive and cutting into dies.
• Granular material is too warm.
• Sticks to the die.

Remedies:

• Dry the granules properly.
• Increase the amount of lubricant or use a more effective lubricant.
• Reduce granular size, add more fines, and increase the quantity of lubricant.
• Modify granulation. Reduce granular size.
• If coarse granules, reduce their size.
• Use wear-resistant dies.
• Reduce temperature.
• Increase clearance if it is extruding.

Causes and Remedies of Binding related to Machine (Dies, Punches and Tablet Press):

Causes:

• Poorly finished dies.
• Rough dies due to abrasion, corrosion.
• Undersized dies. Too little clearance.
• Too much pressure in the tablet press.

Remedies:

• Polish the dies properly.
• Investigate other steels or other materials or modify granulation.
• Rework to the proper size. Increase clearance.
• Reduce pressure, or Modify granulation.

Mottling

Mottling is the term used to describe an unequal distribution of color on a tablet, with light or dark spots standing out on an otherwise uniform surface. Reason: One cause of mottling may be a colored drug, whose color differs from the color of excipients used for the granulation of a tablet.

Causes and Remedies of Mottling:

Causes:

• A colored drug is used along with colorless or white-colored excipients.
• A dye migrates to the surface of granulation while drying.
• Improperly mixed dye, especially during Direct Compression.
• Improper mixing of a colored binder solution.

Remedies:

• Use appropriate colorants.
• Change the solvent system, Change the binder, Reduce drying temperature and use a smaller particle size.
• Mix properly and reduce the size of it is larger to prevent segregation.
• Incorporate dry color additive during powder blending step, then add finely powdered adhesives such as acacia and tragacanth and mix well and finally add granulating liquid.

Double Impression

Double impression involves only those punches, which have a monogram or other engraving on them.

Reason: At the moment of compression, the tablet receives the imprint of the punch. Now, on some machines, the lower punch freely drops and travels uncontrolled for a short distance before riding up the ejection cam to push the tablet out of the die, now during this free travel, the punch rotates, and at this point, the punch may make a new impression on the bottom of the tablet, resulting in ‘Double Impression‘.

Causes and Remedies of Double Impression:

Causes:

• Free rotation of either upper punch or lower punch during ejection of a tablet.

Remedies:

• Use keying in tooling, i.e. inset a key alongside the punch, so that it fits the punch and prevents punch rotation.
• Newer presses have anti-turning devices, which prevent punch rotation.

Make sure you also check our other amazing Article on : Excipients Used in Tablet Formulation