TABLETING
Picking is affected by the font style and letter spacing
Increased compression force and dwell time are helpful to reduce sticking and picking
PRE-PICKING AND TAPERED ENGRAVING CUTS Pre-picking decreases the height of the resulting island or pad, which can reduce or eliminate picking inside islands. Do not exceed more than 30% pre-pick on coated tablets.
TAPERING Characters that do not have fully enclosed areas are also prone to picking. Tapering peninsulas starts at the internal corner and ramps up to the tablet surface.
LOGO/IDENTIFIER PLACEMENT The size and spacing of the characters can be modified to reduce picking. Best practice for spacing between characters is a minimum of one stroke width apart with 1.5 times the stroke width as optimum. Moving the placement of the characters off centre on a curved face tablet can also be helpful.
EXPLORING TOOLING MATERIAL If sticking has been observed, specialty grade steel types or coatings may be considered to help eliminate these issues.
It is widely accepted that high
chromium punch steels, such as M340, are beneficial for sticky products because the high chrome content yields improved product-release characteristics. In some cases, a coating may be
advantageous to address sticking/ picking. The most common are Hard Chrome & Chromium Nitride. A sticking assessment with an FT4 rheometer is recommended to compare the propensity of sticking between a specific formulation and different steels or coatings.
FORMULATION Other factors can affect sticking, including moisture content, lubricant %, particle size distribution (PSD), and fragmentability. Generally, excessive moisture can increase sticking or picking. While increasing the amount of lubricant can improve product release, too much or over-blending the lubricant will impair tablet bonding. Fines (particles below 76 microns) should be minimised. Using particles that can fragment during compaction improves bonding.
PROCESS RELATED Increasing compression force and
dwell time are often helpful in reducing sticking and picking. Extended head flats can increase
dwell time improving bonding for strain rate sensitive (SRS) formulations. Both increased compression forces and extended dwell times can help to reduce sticking. An overlooked cause of sticking is
using a deeper than necessary fill cam or running the feeder too fast. Excessive recirculation or paddle speed can cause segregation and generate fines in the feeder impairing formulation performance. It is best practice to use the shallowest fill cam and slowest feeder paddle speed that can still achieve consistent target tablet weight.
A PROACTIVE APPROACH Consulting with a qualified tooling vendor and discussing sticking issues early in the development process will help reduce production issues.
AUTHOR: Todd Martin, senior technical service engineer Natoli
For more information visit:
www.natoli.com
www.scientistlive.com 43
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