From tablet design to tool material specification
Efficiency in solid dose manufacturing can be improved at the earliest stages of the tablet design process by utilising precise tooling specifications.
Design and material selection can have a major influence on the final product. With the help of a quality tooling manufacturer to identify specific requirements, the elimination of downstream tableting problems can be achieved.
It is important to implement an effective tooling specification for a number of reasons, including reducing the time to market, by addressing specific product challenges and preventing non-conforming product that will ultimately reduce costs through Quality by Design (QbD) and result in a faultless end product.
To introduce effective tooling specification, it is key to initiate discussions with your tablet tooling supplier. By providing detailed information, the most productive solutions can be found for specific tableting requirements. Details including tablet product and press and tooling information will all help to specify the most appropriate requirements for the job (Figure 1).
Figure 1: Effective tooling specification
Tablet tooling manufacturers can optimize the design and material selection to allow the best possible productivity for the tablet tooling in the press. This is done by obtaining clear basic information on the product. It is important, first of all, to look at the formulation being used, as this can have a significant influence on tablet design, tool material selection and coating.
Some formulations can cause adverse effects on the punch tips during compression, causing abrasion, pitting or corrosion. Although tools are manufactured from hardened and tempered tool steel, the demanding processes involved can lead to deterioration if the tool material is not optimised to suit the formulation being compressed. Some granules are extremely hard and abrasive and can scratch, wear and impregnate the steel surface (Figure 2). Other granules can contain corrosive elements that react with the steel.
Figure 2: Issues you might encounter (sticking, pitting, corrosion, wear)
These effects can be reduced by understanding the nature of the formulation to be compressed and carefully selecting a tool steel and/or tool coating to resist this at the earliest stage of the tool specification process. A competent tooling supplier will have a range of steels and coatings to fulfil a mix of properties. The optimum being those that combine the very best combination of properties to suit your specific product.
Dwell time is the time that the punch head remains in contact with the compression roller and is another important factor to be considered when initiating good tooling set-up. Many tablet formulations are dwell-sensitive and require more time under compression to guarantee they come off the press without any faults.
Some granules are extremely difficult to compress effectively and require extended time under peak compression to obtain the required tablet hardness and prevent any problems. Slowing the tablet press down to achieve an increase in dwell time can eradicate these issues; but, this leads to a reduction in tablet production. With the help of a tablet tooling expert who has innovative tooling solutions, it is possible to increase the dwell time without slowing the press speed.
The correct tablet shape and profile is key to finding a successful tooling specification (Figure 3). When specifying tablet tooling, a very important element to start with is the design of the tablet. The choice of shape and profile is critical as different tablet shapes and profiles can present different challenges.
Figure 3: Tablet profile
There are two basic tablet shapes, round and non-round; however, the complexity of non-round shapes is extremely varied and many complex designs may require specialized tool manufacturing capability. Once the shape has been decided, the next thing to consider is the tablet profile. The type of profile required is influenced by several factors: the granule, embossing requirements, coating process, packaging and the company’s branding.
If the design is to be heavily embossed with a lot of characters, it is important to avoid tablet profiles with a deep cup, such as a ball or pill. Deep cup profiles can cause a softer core in the tablet, which can, in turn, lead to sticking.
It will also reduce the available space for the embossing itself. The use of a profile that is shallower with a reduced cup depth will allow for a larger embossing area. These are all details that any quality tooling provider will be aware of and can be incorporated easily into the design.
When considering the visual appearance of the tablet, it is crucial to think about the type of font and logo (Figure 4). Typefaces and designs must take into account the practicality of tablet manufacture. Tablet designers need to consider how the identification will scale-up and down, according to the size of the tablets being produced.
Figure 4: Logos and embossing
The correct font style should also be taken into account to avoid tableting problems such as sticking and picking (Figure 5). Sticking occurs when tablet particles adhere to the punch face.
Figure 5: Sticking versus picking
It has a negative effect on the appearance of the tablet and can become so serious that production can be interrupted. In extreme cases, the punches may have to be removed to be cleaned. This is disruptive, labour intensive, reduces yields and increases production costs.
Picking is another problem directly linked to tablet design. Picking is compressed granule that has adhered to the detail on the punch face, resulting in ‘picking out’ of parts from the tablet face.
To reduce picking, the best practice is to design font styles that have large open counters and no sharp corners, which could act as a trap for granules. Selecting the right font style can also help to avoid coating problems, tooling failures and lack of distinction. Failure to consult with an expert tablet design team could result in a product that looks good on paper … but is not practical to produce.
Successful coating is dependent on the tablet’s profile and its ability to roll to ensure even coverage. Coated tablets present challenges for the tablet designer. Many of the variables are within the manufacturer’s control, but expert tablet design can help to eliminate potential problems.
Coating can also be a major factor in the choice of the cup profile being used. Applying a double radius profile can help if the product is to be coated, as it allows the tablet to roll better in the coating pan to ensure even coverage. If a flat bevel profile, for example, was applied, the tablet would just skid in the pan and not roll over, leading to a number of problems (including twinning [Figure 6], when tablets stick together). This is normally caused by the flat surfaces of the tablets coming into contact and adhering to each other. To avoid this, a slightly curved surface can be applied, which reduces the contact area and eliminates the problem.
The process of defining the best shape and profile for the coating process can be addressed easily if an effective tooling specification is implemented. Problems such as twinning will have a major effect on tablet waste; however, it can be avoided with the expert knowledge of the tooling supplier.
With counterfeiters becoming more technologically advanced, basic tablet designs are easily reproduced. The purpose of an anticounterfeiting feature is usually to enable the authentication of an item, and also to act as a deterrent to anyone considering counterfeiting a product. An expert tablet designer can employ techniques to make this more difficult.
If counterfeiting is a threat to your product and brand, it is important that your marketing or R&D departments work in partnership with a specialist tablet design team so that any anticounterfeiting measures can be incorporated into the design from the outset. If left unchecked, counterfeiters my take a share of your market and, indeed, your profits.