Tablet presses are used to press granular or powdered materials into tablets, and are a key piece of equipment in industries such as pharmaceuticals and nutraceuticals to improve the productivity of tablet products. However, many manufacturers encounter a variety of problems with tablet presses that not only affect productivity, but also product quality and increase maintenance costs. Let’s explore the common problems in the tableting process and their corresponding solutions.
Tablet Weight Out of Tolerance Phenomenon
When there is a significant difference in particle size, the flow rate of granules during compression varies, leading to uneven filling of the die cavity with coarse and fine particles. This results in increased tablet weight variation. For example, an excess of coarse particles produces lighter tablets, while an excess of fine particles produces heavier tablets. This issue can be mitigated by thoroughly mixing the granules or sieving out excessive fine particles to reduce particle size variation.
Fine powder tends to adhere to the punches, causing punch sticking. This phenomenon restricts the smooth rotation of the lower punch, further exacerbating weight variation. Regular inspection and cleaning of the lower punch and die cavity are necessary to address this issue.
Poor granule flowability leads to inconsistent filling of the die cavity, causing excessive tablet weight variation. Solutions include re-granulation or the addition of glidants (e.g., colloidal silicon dioxide) to enhance granule flowability.
Loose Tablet Formation
Reportedly, insufficient drug particle fineness, excessive fibrous, elastic, or oily ingredients, or inadequate mixing can lead to loose granules. Solutions include grinding the drug through a 100-mesh sieve, selecting binders with higher viscosity, appropriately increasing compression pressure, and thoroughly mixing oily ingredients with absorbents.
Insufficient or inappropriate use of binders or wetting agents may result in loose granule texture or uneven particle size distribution, causing segregation of coarse and fine particles. This can be resolved by selecting suitable binders, increasing binder dosage, optimizing granulation processes, thoroughly mixing soft materials, and ensuring uniform granule blending.
Excessively dry granules (low moisture content) exhibit higher elasticity. For drugs containing crystalline water, excessive loss of crystalline water during drying can make granules brittle and prone to crumbling. Therefore, granule moisture should be controlled based on specific formulations. If granules are too dry, spraying a diluted ethanol solution (50%–60%) and mixing evenly before compression can help.
Industry experts suggest that loose tablets may also stem from inherent drug properties. For example, compact tablets may have adequate hardness but poor resistance to impact, or poor granule flowability may lead to uneven filling of die cavities. Additionally, blockages caused by large aggregates or foreign particles in the scraper blade or feeding port can disrupt granule flow and filling consistency.
Furthermore, tablet press operation parameters can affect tablet quality. Issues such as insufficient compression pressure, uneven punch lengths, excessive speed, or inconsistent granule levels in the hopper may contribute to loose tablets. Adjusting compression pressure, inspecting punch and die integrity, optimizing machine speed, and maintaining consistent granule levels in the hopper can address these challenges.
Cracked Tablets
When the tablet is vibrated or placed, the cracks starting from the waist are called waist cracks; the cracks starting from the top are called top cracks. Waist cracks and top cracks are collectively called flaky cracks.
When the drug itself is more elastic, fibrous drugs or oily ingredients are more, sugar powder can be added to reduce the elasticity of the fiber, enhance adhesion or increase the absorbency of the oily drug, and the tablets are fully mixed before tableting.
Excessive use of lubricants or insufficient use of adhesives will lead to insufficient adhesion of particles during tableting, resulting in flaky cracks. The amount of lubricant should be appropriately reduced, or the appropriate type of lubricant, such as magnesium stearate, should be selected to balance the lubrication effect and the mechanical strength of the tablets.
If the particles are too dry or the drug containing crystal water loses too much water, the particles will not have enough adhesion, resulting in flaky cracks. At this time, the particle size can be reduced and fine powder can be added; ensure that the particles are fully dried and use a suitable adhesive.
It is reported that the tablet press has too high pressure and large rebound force, which can cause tablets to break; too fast speed or the die does not meet the requirements, the punch is too long or too short, the die hole is worn, the middle part of the die is larger than the upper and lower parts, or the punch curls inward, which can cause tablets to break when ejected. You can adjust the pressure and speed, improve the matching of the die, and check and replace them in time.
Mottling and Spotting
Mottling and Spotting are common appearance quality issues in tablet production, primarily manifested as unevenly colored spots on the tablet surface, which compromise visual quality.
Oil spots caused by grease contamination from the upper punch falling into granules during compression require cleaning of the grease and installing rubber rings on the upper punch to prevent oil leakage.
Spotting may result from excessive binder dosage, overly hard granules, melted sugar in sugar-containing formulations, uneven coloring of colored tablets, inconsistent moisture content, uneven density, or insufficient mixing of lubricants. Solutions include improving granulation processes to produce looser granules, adopting appropriate coloring methods for uniform color distribution before granulation, ensuring uniform particle size and density, and passing lubricants through a fine sieve followed by thorough mixing with granules as required.
In compound tablets, mottling caused by uneven color of APIs/excipients (due to insufficient grinding or mixing) can be addressed by finely grinding raw materials before granulation and ensuring thorough mixing of granules prior to compression. Tablets exhibiting mottling during compression should be reprocessed.
Summary
In short, the above phenomena are common problems in the tableting process. Preventing these problems requires comprehensive consideration of the formulation and machine settings. It is crucial to ensure that the raw materials are fully prepared, well mixed and properly pressed. In addition, adjusting machine parameters such as tableting pressure, speed and mold usage can ensure the consistency of tablet quality. Regular monitoring of environmental conditions is also an important part of ensuring tablet quality.
