Leaking of fill from Softgels is often encountered in manufacturing, storage and worst even in the final package. Both product and in market losses can be very costly due to leakers. Most leakers are caused by sealing failures. Corrective Action Plans for in process leakers are created to solve the problem in an easiest to fix most likely cause basis.
Other non-seal leakers are causes by cracking of capsules due to over-drying of the shell; Over drying in the process or moisture/ plasticizer moving from the shell to the fill. To investigate and remedy the cause of softgel seal leaking one must separate the sealing process into its two main components: Creating the sealing surface contact area and developing sealing surface adhesion. Seal surface contact area is development is controlled by ribbon thickness, die land alignment, and ribbon distortions during the filling/sealing process.
Pressing the ribbon together and cutting creates the seal contact area. Sealing surface creation efficiency is monitored by % sealing efficiency (seal width/ ribbon thickness *100). A good sealing efficiency (>70%) is generally targeted. This monitors contact area and not seal adhesion. Seal contact area can be decreased by fill pressure pulling and stretching the ribbon and the pull of the mangle roller on the web.
Misalignment of die lands also creates a step seal which decreases seal contact area. Increasing ribbon thickness theoretically increases seal contact area but can add increased filling pressure unless the ribbon plasticity is adjusted. Seal contact area should be corrected to a defined thickness first before looking into issues of poor adhesion. Often for a product that is running fine then develops leakers the issue is lack of proper adhesion.
Adhesion of the seal area is more chemically related than mechanical. Adjusting ribbon adhesion/tackiness is done by adjusting wedge temperature. Too low a wedge temperature the ribbon is too stiff and non-tacky. Too high the ribbon to plastic and deformable creating a thicker seal area but tackiness is lost. Checking adhesion at line of formed caps is done by cutting fresh made caps in half with a wire cutter to test resealing of the cut.
The cut seal should be firm enough to with stand finger pressure; Thus, creating a tight seal for the cut half-cap. If hand cut caps reseal and seal efficiency is acceptable the next step is to check pump timing. Pump timing is checked by observing the timing marks vs pump pulse start in the timing window.
Photographing of the timing window at pump pulse can aide in the timing check process. Normally side port fills are ~50% from the lead seal and end port fills are ~33% off the lead seal. Late or early timing can put fill in the sealing area causing either lead or trialing seal leakers. Often timing is adjusted to accommodate the slot needed in the wedge tip to accommodate the larger fill quantities and fill rates needed for larger caps running at faster RPMs.
A non-clean cut can cause leakers especially in the trailing seal. Check netting for lack of clean cutting and tags. Check ribbon lube pool at wedge die roll junction. Is it pooling? Adequate lube is needed for both lubrication and heat transfer.
Check the logbook. An earlier leaking distributor gaskets and/or leaking of a slide valve slots can put fill into the thermal wells. This can cause variation in left side to right side wedge temperature.
Wedge thermal probe indicates the wedge is the right temperature but temperature is correct in area of probe but higher or colder on the other side of the wedge. Isobars inserts can distribute temperature down the wedge but not from one side to the other.
Changing the temperature of the casting drum to change ribbon plasticity is done but usually as a last resort and for running at higher RPMs as the change in casting drum temperatures are very slow. If ribbon temperature off the casting drum change is to be investigated, changing spreaderbox temperature is faster in response.
Casting drum temperature is usually set as low as it can go and yet maintain a stable temperature. The temperature of the spreaderbox is the adjustment, if used, to change the ribbon temperature off of the casting drum.
Change in ribbon temperature changes plasticity of the ribbon being drawn over the alignment rollers and to the wedge. The ribbon temperature off the casting drum must be cold enough to peel off the drum. From that temperature and lower we can modify the plasticity of the ribbon to allow the ribbon stretch for filling and the adhesive quality requirement is adjusted by a wedge temperature change.
Leakers in the drying process as well as after the drying in storage is the costliest. The shell in drying is shrinking and pulling on the seal which can cause the seal to separate and leak. Having sufficient shell plasticity to allow shrinkage without excessive seal pull is a balance between rate of water removal in drying and the formulation of the fill as well as the shell.
