Achieving The Perfect Temperature Requirements for Blister Packaging

By Dr. Egon Huefner, Bürkert Fluid Control Systems

When tablets are packaged in blisters, the plastic film must be the right temperature at the right moment: which is no easy task at an output of up to 1,300 blisters per minute. A customer-specific combination for proportional valve, temperature sensor and controller master is using the regulation of cooling water flow. If needed, machine developers can implement 13 parallel-working temperature control circuits.

Blister packs have replaced plastic bottles as the most-sold type of medication packaging worldwide. Advantages such as acceptance of medication by patients, higher flexibility in logistics, sterility through individual packaging, child safety, and marketing attractiveness will expand their distribution as packaging for pharmaceutical products. However, the manufacturing of blister packs represents a critical process for companies that package medications, as these packs have a relatively complex structure consisting of two or more components. A constant and repeatable blister size is also necessary. Temperature regulation plays a decisive roll affecting blister size and shrinking properties, as well as ensuring that the cover is reliably sealed. In a collective effort with Uhlmann Pac-Systems, a German manufacturer for medication packaging systems, Bürkert has developed an individual system for regulating temperature. This system not only fulfils general criteria for blister packaging, but also meets specific customer requirements such as packaging speed.

Blister creation at the highest Speed

During the blister pack manufacturing process, a special plastic film is heated to a maximum of 240 °C in a continuous process. Afterwards, the blister material is formed into the heated film, performed by the forming tool adapted to the product. The film is then cooled and tablets are placed into it. Then the filled film is heat-sealed to the cover and cooled off again. The control unit of the cooling water flow of Bürkert is used in both film cooling processes. Constant blister size and packing flatness help the tablets to be placed exactly in the formed material and ensure that the tablet blister can be processed further and packaged automatically. This requires precise adjustment and monitoring of temperature, all at extremely high processing speeds of up to 1,300 blisters per minute with low, permissible temperature fluctuations. Uhlmann Pac-Systems, working for Bayer Schering Pharma, turned to Bürkert with these demanding requirements. A project team was assembled to develop a complete system in only three months based on these specifications. This short development time frame could be met by the project team because they could make use of the many standard components for the system from the Bürkert product portfolio, such as proportional valves, temperature sensors, and temperature regulators. The temperature regulator was developed based on a standard product as a customer-specific, individual solution. The first machine equipped with this unique system has been operating since 2006 at Bayer Schering Pharma.

Valve and control technology, ideal for cooling systems

The new development of solenoid proportional valves has enabled the realization of up to 13 parallel-operating temperature regulation circuits. The special property of the proportional valve is the friction-free support of the solenoid core using specially designed formed springs. Stick-slip effects cannot occur using this valve. This is shown in excellent function data, such as very good responsiveness (0.1 percent of the end value), a short transition time, as well as excellent regulation quality. The measurement range was improved from 1:25 to 1:100 compared to previous proportional valves. These properties made it possible to control the smallest fluctuations in temperature using very precise valve lift corrections.

Customer-specific tasks require a broad product range in addition to basic understanding of the problem. There are three essential parts of a control circuit: actuating system, sensor, and controller. The controller plays a major role in this chain. It must be capable of processing different sensor signals such as temperature, pressure, flow, and analysis (pH, conductivity). It must also be capable of activating different actuation systems (pneumatic or electric). The newly developed universal controller eControl has all of these properties, and was especially developed for all kinds of cooling system applications. Essential features of the universal controller eControl:

• Temperature regulation
• Pressure regulation
• Flow regulation
• Activation of open/close solenoid valves, solenoid proportional valves, process control valves, and electromotor control valves
• Recording of typical sensor signals (standard signal 4-20mA, frequency, PT100).

All components of a control system have been tested over many years, with coordinated function, and delivered preset