Tablet Press - Analysis of Uneven Surface of Tablets

One sided unevenness is a common appearance quality problem in tablet production, which refers to the appearance of unevenness, spots, rough surface, uneven color or local defects on the surface of the tablet (one-sided). It not only affects the appearance of the tablet, but may also indirectly reflect problems with the production process or materials, and even affect the stability and uniformity of the drug. The following provides a detailed analysis of the main manifestations, causes, and solutions of one sidedness: Firstly, the main manifestation of one sidedness is pockmarks: many small pits or pockmarks appear on one sidedness, with a rough texture, commonly found in local areas of the tablet surface. Spot or uneven color: Spot that appears on one side that is different from the overall color (such as dark spots, white spots), or the same side has different shades of color. Uneven and uneven: A partial protrusion or depression on one side, which may be accompanied by irregular edges, and even "top protrusion" (central protrusion) or "edge depression". One sided defect caused by adhesive punching: The surface of the punch sticks to the material, causing some powder to be lifted up from the surface of the tablet, forming local defects or rough surfaces. Unilateral cracks: Minor cracks appear on one side (not fragments, only surface cracks), which may be accompanied by the detachment of fine powder. 2、 The common reasons for one-sided unevenness are that the material is unevenly distributed and subjected to uneven forces in the mold holes during the tablet pressing process, or there is abnormal interaction (such as adhesion) between the material and the equipment surface. The specific reasons can be analyzed from three dimensions: material properties, process operation, and equipment conditions: 1 Reasons related to material properties: poor particle flowability or unreasonable particle size distribution

Uneven particle size (excessive fine powder or inclusion of coarse particles) leads to uneven distribution when filling the mold hole: the concentrated area of fine powder is prone to local looseness (forming pits) after compression, while the concentrated area of coarse particles may form protrusions due to uneven stress. For example, in traditional Chinese medicine tablets, if the mixture of extract powder and medicinal powder is uneven and there is a large difference in particle size, uneven color and sesame surface are prone to occur during compression. Inappropriate moisture content of particles: Excessive moisture content: particles are prone to adhere to the surface of the punch or die hole (sticky punching), causing one side to be "lifted" and forming defects or rough surfaces (especially when there are scratches on the punch surface, the adhesion is more severe). Low moisture content: increased brittleness of particles, easy detachment of fine powder during compression, and easy appearance of small micropores on one side. Uneven mixing of materials, insufficient mixing of drugs and excipients (such as diluents and coloring agents), resulting in local component differences: for example, coloring agents (such as iron oxide red) are not evenly dispersed, and dark spots appear on one side; Particles containing hygroscopic components may locally aggregate and form protrusions due to hygroscopic expansion after compression. Uneven mixing of lubricants: When there is a local excess of lubricant (such as magnesium stearate), there is excessive lubrication between particles in that area, weak bonding, and a tendency to produce rough surfaces; Local deficiencies may lead to adhesive flushing. There is a significant difference in particle hardness

The hardness of the particles formed during the granulation process is inconsistent (some are too soft, some are too hard), and soft particles are easily compacted during compression, while hard particles are difficult to deform, resulting in uneven surfaces due to different degrees of particle compression. 2. Reasons related to process operation: Improper granulation process during wet granulation, insufficient amount of adhesive added or stirring time, loose and fragile particles, and excessive fine powder; During granulation, local overheating (such as high-speed stirring causing material temperature rise) can cause some materials to melt and re solidify, forming hard particles with a large difference in hardness compared to other particles. When using the dry granulation method, the rolling pressure is uneven, the particle density varies greatly, and the compression rate during compression is inconsistent, resulting in uneven surface. Unreasonable compression operation parameters and uneven filling amount: When the particle flowability is poor, the filling amount of the mold hole fluctuates. The area with less filling amount is prone to concave on the surface after compression, while the area with more filling amount may protrude. The compression speed is too fast: the particles cannot be fully filled and distributed in time, and the material in the mold hole is pushed out before being compacted, resulting in one-sided looseness and the appearance of a rough surface. Insufficient pressure or pressure fluctuations: When the pressure is too low, the overall binding force of the particles is weak, and one side is prone to fine powder detachment and formation of micropores; Unstable pressure (such as hydraulic system failure) can lead to different compression levels of different tablets or different areas of the same tablet, resulting in unevenness. Improper use of lubricants

Insufficient lubricant dosage or short mixing time prevents the formation of a uniform lubricating film on the surface of particles, resulting in particle adhesion to the punch (sticky punch) and the appearance of defects on one side; If the lubricant is a hydrophobic substance (such as magnesium stearate), local excess may also lead to the appearance of "white spots" on one side (because this area has strong hydrophobicity and is different from other areas in terms of reflection). 3. Equipment condition related reasons: abnormal punch or die hole surface. Punch surface wear, scratches, rust, or oil stains: materials are prone to adhere to defects and transfer to one side during pressing, forming a rough surface or defect; If the surface of the punch is uneven (such as burrs on the edges), the edge of one side is prone to indentation. The gap between the punch and the die hole is too large: particles are prone to leak out of the gap ("powder leakage"), resulting in insufficient material filling in the die hole and partial depression on one side. Improper equipment debugging and improper installation of the upper or lower punch of the tablet press: During tablet pressing, the punch is offset from the center of the mold hole, resulting in uneven pressure distribution and causing one side to protrude and one side to sink. Low punch position: Insufficient depth of filling in the mold hole, or failure to fix the punch after filling, resulting in uneven force on the material during compression, forming a one-sided unevenness. Incomplete cleaning of equipment

The materials from the previous batch of production remain in the punch or die hole, and are mixed with the current batch of materials for compression, forming heterochromatic spots; Or residual materials may dry and harden, and when compressed, they may be pressed into one side to form protrusions.