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​Common Tablet Defects That Can Be Avoided Easily

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12 September 2016 No comments

A professional and experienced technician can turn any ordinary product into a high quality one whereas a novice or unexperienced one cannot and might even be afraid to adjust their machines in order to prevent or correct problems. The key is to understand the different areas of the equipment and have thorough knowledge of the process. This is why one must undergo proper training in order to be able to fix equipment and prevent any or minimize these problems. When the equipment is properly operated the tablet production will go smoothly.

Problems can cause the company not only money but also time and sales.

Common problems that afflict the industry include:

  • Weight variation
  • Friability
  • Hardness
  • Sticking
  • Picking
  • Capping
  • Laminating
  • Chipping
  • Mottling
  • Double press or impression

Although there are several defects that affect the process, capping/laminating, hardness and sticking/picking are the three most common ones.

The reason for defects can also come from the following reasons:

  • Problems with the unit upstream
  • Problems with the tablet press
  • Poor quality raw materials
  • Defects caused by the formulation
  • Failure of compression
  • Poor flow and compressibility of the powder
  • Product is too dry or too wet preventing proper ejection
  • Milling process causes too many fines that result to capping, hardness, lamination and black spots

As we discuss the different ways to prevent the problem from occurring, it is also important to be able to solve these problems and to check the procedure to determine the source or root of the problem. The focus of this article is to find ways to fix common problems at the start and identify the main problem in order to fix the issues before it reaches the presses. That said, if the

problems do occur during production, one must be able to fix the problem at the press as one cannot stop the entire production and have the design sent back to the drawing board.

Below are the three common defects that we would be discussing and how best to prevent them in order to lower the company’s expenditures.

Capping

Capping happens when the tablet is top fractured or separates itself from the body or the rest of the tablet piece. It is often caused by the trapped air during the compression stage. It is also defined as a failure of the press to compress the formulation due to the collection of fines.

During the compression stage, air is removed from the granules allowing each particle to stick with one another. The press is designed to allow the air to dissipate during the compression process. During this process, the air released also pushes the dry granule fines out. These particles generally do not stick together and when the particles are pushed to the line of air being released near the cup and the tablet band, the fines prevent the granules to be compressed resulting to the tablet fracturing.

As the air is evacuated in the upper punch die tip, capping only happens to the tablet’s top cap. If the break happens on the lower cap, then this is referred to as lamination, which will be tackled later.

The faster the press speed is, the more likely that capping will happen and slowing the press would often solve the issue. That said, there are other ways that one can fix this problem.

Poor formulation as well as bad processing practice can often cause capping. Dry blends can cause capping, as less moisture would prevent the particles from blending with one another. Another factor is when the formula has inadequate binder, which prevents the particles from blending, as the granules do not have the ability to bind themselves. Improper blending can add air to the formulation, break down the granules and even over blending can cause problems. On the other hand, under mixing can cause the powders to segregate resulting to the capping problem.

Capping is easy to fix and through proper diagnosis or analysis, the problem would easily be resolved eliminating the capping problem. One way to do so is to increase the dwell time allowing the particles to come together. If other problems exist, it is better to evaluate the process in order to identify and correct the issue.

Lamination

Lamination happens when the split happens anywhere in the tablet except in the upper cap. Laminating is the same with capping and can happen in any surface area of the tablet. However, capping occurs exclusively in the tablet’s top cap. It is important to diagnose the problem correctly to ensure that proper steps are conducted to solve the problem. Lamination often occurs due to the over compression of the tablet. Too much compression can lead to the granules flattening out and thus preventing them from locking together. This can also happen when light or fine particles do not combine, as these particles do not compress well. To prevent this, one needs to reduce the tablet’s thickness and/or increase the dwelling time to allow the fine particles to combine. To increase dwell time, one can add pre-compression or slow the machine’s speed. These suggested solutions would help fix the problem allowing the particles to bind together; another way is to add a taper to the die, which will prevent capping, and laminating problems.

Steps in Eliminating Capping

1.Punch Penetration. Check if the tablet press has an adjustable punch penetration. Adjusting the upper punch penetration depth in the die will allow better air exhaust,

which can often solve the issue readily. The pre-compression penetration does not have to have the same setting as the main compression but it should be deeper.

2.Pre-compression. New models have pre-compression, which is a tool that is made specifically for high-speed rotary tablet press. This is the same as that of a 4-wheel drive for cars although it is not always a prerequisite, the same with pre-compression.

2 Ways to use Pre-Compression:

a.Pre-compression is used if there are dry dust fines or particles; pre-compressioncan bind the particles using light force so they cannot migrate during final compression.

b.If the tablet needs more dwelling time, one can use the pre-compression twice with higher force to extend the dwelling time.

3.Slow the Press Down. In decreasing the speed of the press, it increases the dwell time or the time that the tablet is under pressure. By slowing the press and extending the dwell time, it allows air to evacuate, gives the particles time to bind themselves and ensures a controlled hardness once tablets are released. However, it is important to check and make sure that the tablets do not stay too long as it would result to dry particles resulting to laminating. To solve capping, extended dwelling time is seen as one way; however, too much dwelling time would result to laminating which will result to inferior tablet quality at the same time. It is therefore important that one check the time so that it can solve one problem without resulting in another arising.

4.Tooling Design. It is important to consider the tooling design as it can aid with preventing capping or laminating problems. A dome head tool can extend dwelling time and changing the cup depth and radius can help make air release faster during compression stage. Additionally, adding a taper to the die can help evacuate trapped air during compression and reduce the tablets’ tendency to cap. Aside from this, tapering can also reduce the action force that contributes to the tablets’ tendency to laminate. Remember that proper care and maintenance can eliminate other problems such as j- hook, compression wear rings within the die and premature punch tip wear.

Sticking and Picking

The sticking defect occurs when the granules stick themselves to the press punch’s face. Picking, on the other hand, happens when the granules stick to the design of the punch such as in lettering or logos. Either of these results to the defects in the tablet. To ensure the quality of the batch, often a visual inspection is done; however, this is time-consuming and can decrease the yield production but many manufacturers have no option. As the batch reaches the compression stage, the operator must adjust the press to comply with the product’s characteristic designs. Even if the manufacturer develops the same product day in and day out, the product is always not the same. There are variables that affect the end production including the tablet press, setup, operation, tooling as well as maintenance. There are times when the granules are still wet and can affect the quality of the tablet. The wet granules will harden during the processing but the core remains wet inside causing the tablets to break open during production and stick to the design or the surface of the punch press. If this happens, it is important to check the drying process.

Steps to Improve and Eliminate Sticking:

1.Adjusting the compression force. The compression force can affect the product in that increasing the force would cause sticking for over granulated products and decreasing force would result to the particles to stick to the punch face than to each other.

2.Increase pressure. If picking is observed, one can increase the pressure so that the particles would stick with each other rather than to the punch design

3.Pre-compression. Use of extended dwelling time through pre-compression or slowing the press speed would make the granules stick together rather than on the punch face.

4.Polishing. Polishing the punch face would help with the sticking problem.

5.Proper lubricant mix. It is important to mix the lubricant properly as over mixing would result to the lubricant being ineffective in preventing sticking or picking.

Sticking can happen anytime during production; however, it most often happens during the initial setup of the press although it can happen anytime during a run. Although sometimes unpredictable, it can also be occurring quite frequently. With some products, sticking is a regular occurrence that often operators would consider it a successful production if they can do work in two hours’ time without encountering any sticking problems. To determine whether the product would stick, it pays if one knows the product properties including the moisture content, size distribution of the particles and other attributes. That said, knowing these specifications would not mean that the product would not stick or pick. In fact, one would not be able to determine if the product would compress successfully until it is in the tablet press.

To prevent sticking during pressing, one can increase the tablet’s hardness by making it thinner. Another solution is to increase the dwelling time to make sure that the wet granules would stick to the other granules instead of the punch face. When the blending is incomplete, sticking or picking may also occur. This happens when the lubrication in the formula is not blended well with the granules and as such exposing the latter to stick to the punch face. Improper blending usually results to the sticking problem and should be corrected to prevent this from happening further. If this does not solve the problem, polishing the cup surface can help prevent the problem from occurring. Other causes of the problem would be the product itself, the upstream process, operation of the press or the tooling. It can also be a combination of the problems mentioned.

Products that have high compressible forms tend to turn out high quality tablets; however, they are prone to sticking to the punch face. If this were the problem then more than likely, it would worsen over time. Powders that are sensitive to compression will still compact together as they go through the hopper and feeding frame; however if it reaches the die cavity before compacting, the bulk density would increase thus reducing one’s ability to control the weight of the tablet. This can be a problem, as fluctuations with the weight would cause the compression force to fluctuate as well. This variation would result to further tendency of the product to stick making it worse over time.

To solve this problem, some experienced operators would likely shock the press or increase the compression making several hard tablets in the process. By shocking the press, the compaction force increases causing the granules to stick to the tablet including the stuck granules away from the punch face. Although effective, frequent use of this process can cause the punch to overload causing it to break or be damaged.

For this reason, it pays to have experienced operators working with the tablet press. An experienced operator would pay attention to their equipment and know when a problem is present and how best to handle it.

Tablet Hardness

Another problem with tablet production is the variation on the hardness of the tablet. A soft tablet can cause a multitude of problems not only with the press but also with consistency, film coating process and packaging which can sometimes lead to product recall.

The first step in solving this problem is to check the press before going back upstream.

1.Weight Control. Maintaining the weight of the tablet is the key to controlling the hardness of the tablet. The fluctuation in the weight causes changes in the tablet’s hardness. When one is speaking about weight control, accuracy is crucial especially on the targeted weight. A tablet that is lighter in weight would result to a softer tablet whereas a heavier weighted tablet would produce a harder one. If there are variations in the bulk density, then the die filling will not be the same resulting to wider weight fluctuations.

2.Scraper blade and die fill. The scraper blade is often overlooked as a wear item and should be replaced regularly. If the product were abrasive then this would mean that the scraper blade should be changed on a daily basis. For other regular products, the blade can last for months or even longer. It is therefore dependent on the product type and how well the blade is maintained.