Sticking and picking are two common problems which may occur during the tablet compression operation. Most of the operators and pharmacists are confused with the term sticking and picking and they use the common term sticking for all cases. But there is a big difference between sticking and picking.
What is Tablet Sticking?
Tablet sticking is defined asÂ
The defect in which powder or granules adhere to the surface of the punch tip or walls of the die.
What is tablet picking?
Tablet picking is defined as
The defect in which powder or granules adhere to the letters or logo embossed or debossed on the surface of the punch tip.
Reasons for Sticking and picking
There are many reasons which may result in sticking and picking during the tablet compression operation. Some main reasons for sticking and picking are as follow,
- Formulation Related
- Machine Related
- Environment RelatedÂ
Formulation Related
- Moisture content
- Case hardening
- The ratio of fine powder
- Hygroscopic materials
- Lubricant
-
- Quantity of lubricant
- Blending of lubricant
- Sieving of lubricant
-
Compression Machine Related
- Condition of punches
- Condition of dies
Environment Related
- Relative Humidity(RH)
- Temperature
Formulation Related
Formulation of tablets plays an important role in manufacturing.
A good formulation helps to avoid many problems like sticking and picking.
Following are some main formulation related problems which may result in sticking and picking.
Moisture content
The moisture content of the product is the major reason for sticking and picking.
Majority of products in pharmaceutical industries are manufactured by wet granulation method in which solvent is added to form granules and the process of drying is used to remove the excessive moisture content. If granules are not properly dried during the drying process high moisture level is retained in the granules.
When these granules are compressed they stick to the punch surface, die walls or are picked by the punch-tip logo because of high moisture level.
Solution
- Granules should be dried properly during the drying stage.
- The high moisture level should not be present in granules.
- To prevent sticking and picking the optimum level of moisture should be present in granules which is determined by validation.
Important Note
If powder or granules stick to the inner side of the die bore then more pressure is exerted by the punches to clear the inside of the die bore. This increases the machine load. Sound of the machine is changed due to overloading and machine accident may occur resulting in tooling damage.
If powder or granules stick to the neck of the punch tip it takes more load to enter into the die bore and it may also result in a machine accident.
Read More
Reasons for compression machine accidents.
Case hardening
Case hardening is a defect which may occur during wet granulation method and may lead towards sticking and picking during compression.
During wet granulation, binder solution is added in powders and powder particles adhere with each other to form granules.
Sometime during local over-wetting, some large lumps are formed which are broken down by wet mills of the granulator.
Wet mill reduces the lump size but some large size granules may be left behind in which more binder is present.
During drying, the solvent is evaporated and forms a cover around the entrapped binder and prevents heat penetration inside the large granule so granules are dried from outside but binder inside is still wet it is called case hardening and during tablet compression, it results in sticking and picking. Case hardening may also occur if rapid drying is carried out.
Solution
Binder solution should be sprinkled at a uniform rate during wet granulation.
Try to avoid direct or manual addition of binder solution and ensure proper working of the chopper and wet mill.
During drying fan motor speed should be optimized for proper fluidization. Product trolley with a rotating rod should be used in FBD. Rotation of the rod after a specified time interval breaks large lumps. If required, break down large lumps manually during drying to ensure proper drying. Do not perform rapid drying because it may result in case hardening.
The ratio of fine powder
If a higher amount of fine powder is present in the formulation it may adhere to the punch surface or the logo of the punch and may result in sticking and picking.
Solution
Sieve the granules properly to generate less fine powder.
Machine pressure is increased which forces the powders to adhere to the tablet surface instead of adhering to the punch surface or logo.
Hygroscopic materials
During direct mixing or granulation of hygroscopic products, they may take up moisture from the environment and result in sticking and picking.
Solution
Temperature and humidity of the area should be properly maintained.
Lubricant
Lubricants are the excipients which are added in the formulation to prevent sticking and picking.
How lubricants work
Lubricants form a layer around the powders and granules, this layer reduces the friction between the product and machine toolings like punch tip and product and between die wall and product. After the addition of lubricant, machine load is reduced and tooling life is increased.
Lubricants are added in the final stage of blending so that the layer covers all the granules and fine powders and prevent sticking and picking.
Commonly used lubricants
Following are commonly used lubricants
- Mg Streate
- Sodium stearyl fumarate
Reason
Sticking and picking is related to
- Quantity of lubricant
- Blending of lubricant
- Sieving of lubricant
Quantity of lubricant
Lower quantities of lubricant in formulation does not form a proper layer of lubrication around particles so sticking and picking may occur.
Solution
The optimum concentration of lubricants should be added in the formulation to prevent sticking and picking.
Lubricants e.g Mg Stearate are added in the formulation as 0.25-5% concentration.
Blending stage of lubricant
Lubricant blending stage plays an important role to prevent sticking and picking.
If lubricants are added in the wetting stage they will lose their lubricant effect.
If lubricants are added in final blending before glidants, diluents or disintegrants they will not work properly and result in sticking and picking.
Solution
Always add lubricants at the last stage of final blending and no excipients should be added after lubricant blending.
Sieving of lubricant
- It is commonly observed that the sieving of lubricant increases its effect to prevent sticking and picking.
- Sieving increases the surface area of lubricant.
- Do not sieve lubricant by mixing it with other excipients.
Compression Machine Related
Compression machine and compression machine tooling may also result in sticking and picking of tablets during the compression operation. Machine related problems are as follow,
- Condition of punches
- Condition of dies
Condition of punches
Punches are used to determine the size and shape of the tablet during the compression operation. Most important part of the punch is the surface of the punch tip which is in direct contact with the product.
Two types of punch tip pattern are used
- Plain tip surface
- Tip surface with embossing
Plain tip surface
The surface of the punch tip has a chrome polishing layer which prevents sticking of the product to the punch tip. If this polishing layer is damaged, the product sticks with the punch surface during compression.
If the surface of the punch tip becomes rough it also results in sticking.
Solution
- Polish the punch tip with polishing material.
Tip surface with embossing
In some cases, the surface of the punch tip is embossed or debossed with letters or have some logo.
The embossing or logo may result in picking.
Solution
Deep or close letters should not be used in embossing.
Condition of dies
With passage of time inside of the die bore becomes rough and it results in sticking.
Solution
Replace the dies after regular time intervals.
Environment Related
The environmental conditions of the manufacturing area may also result in sticking and picking defects. Following are two major environmental factors,
- Relative Humidity(RH)
- Temperature
Relative Humidity ( RH)
If relative humidity ( RH) is high in the compression area, the hygroscopic materials may take the moisture when they are exposed to a high humidity level. Due to moisture uptake sticking and picking occur in such cases.
Solution
Humidity level of the compression area should be controlled by using a dehumidification system of HVAC.
Silica desiccants should be placed in the containers of the final blended product.
Temperature
The temperature of the compression area may also result in sticking and picking.
In the compression room, heat is also generated by the friction of machine parts. Some formulations containing ingredients like macrogol or Mg stea
rate start to melt at high temperature and result in sticking and picking.
Solution
The temperature of the compression room should be maintained properly by the HVAC system.
Important topics