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Polyvinyl chloride and polyvinylidene chloride are two blister packaging materials commonly used in the pharmaceutical industry – but they can be environmentally polluting and harmful to humans. So pharmaceutical companies are looking for new alternatives. Polypropylene is a strong candidate, but its processing presents some difficulties. In this regard, this article conducts a brief analysis and shares some coping strategies.
Polyvinyl chloride (Polyvinyl chloride, hereinafter referred to as “PVC”) sheet is a pharmaceutical blister packaging material, which is easy to form and seal, low in price, and can provide sufficient support for glass packaging such as ampoules, vials, and syringes And protection, so it is widely used by pharmaceutical companies in production. However, PVC has poor thermal stability, especially poor moisture barrier performance and oxygen barrier performance. Some PVC packaged products often fail to pass the stability test of packaging materials due to moisture absorption or oxidation, and even cause medication risks.
Therefore, in subtropical or tropical regions with high humidity, pharmaceutical companies usually use coated polyvinylidene chloride (PVDC) for packaging products that are prone to moisture absorption or are unstable after moisture absorption. Its different coating thickness can also achieve different barrier properties, so PVDC hard sheet has become one of the commonly used packaging materials in the pharmaceutical industry due to its good moisture resistance and excellent easy forming and sealing properties.
However, PVC or PVDC also has many disadvantages. The combustion of PVC will produce hydrochloride, and in the case of incomplete combustion, it will also produce highly toxic dioxins, so Germany and Switzerland even legislate to prohibit their incineration; and PVDC films will produce chlorine and hydrogen chloride after heating, which is harmful to the environment. Metal machinery, molds and special protective coatings on heating plates corrode, affecting the health of operators. So pharmaceutical companies have been looking for alternatives to them. In this case, polypropylene (Polypropylene, hereinafter referred to as “PP”) membrane has entered the field of vision of pharmaceutical companies as a substitute with good performance.
PP is a partially crystalline plastic with high transparency. As a blister packaging material, it can overcome some shortcomings of PVC and PVDC. For example, PP molecules are not polar, so they do not bond to metal production equipment like PVDC does. Therefore, its adding performance far surpasses that of PVC and PVDC.
Compared with PVC, PP sheet has a lower density, so PP film with the same area and thickness as PVC film is lighter. This means that with the same weight, PP sheets can wrap more medicines.
In addition, PP sheet has good barrier properties. Experiments have shown that the water vapor transmission rate of uncoated PP is lower than that of uncoated PVC, which is basically the same as that of PVC with PVDC coating. If the sealing layer is made of PP, its performance is also comparable to that of aluminum foil: it is suitable for all printing processes and can be easily opened to take out medicines like ordinary aluminum foil, and has a sealing performance comparable to that of aluminum foil.
Another important advantage of PP is environmental protection: it is easy to recycle and does not release toxins when incinerated. Recipharm once conducted a study, which showed that PP blister packaging has an 86% lower impact on global warming than traditional aluminum-plastic blister packaging. This is mainly because the production process of the former material consumes less energy than aluminum and PVC.
Despite having so many advantages, there are still fewer blister packs made of PP single material than other aluminum-plastic blister packs in the market today. This is because the processability of PP single-material blister packaging is not as good as PVC. The problems mainly focus on the following aspects: first, the thermal expansion and cold contraction of PP are more obvious; second, PP can only be molded in a very narrow temperature range; It can be used; the fourth is that the molding temperature of PP is higher, which has higher requirements for heat; the fifth is that the cooling capacity required by PP in the cooling process after sealing is also higher; the sixth is that the speed of heat absorption of PP film is relatively slow , and the rate of releasing heat when cooling is also slow.
So is there a way to solve the problem of PP processing and molding? The processing performance of thermoforming film on blister packaging machine mainly depends on the size of the thermoelastic range of the film. The wider the range, the easier it is to process, and vice versa. The difficulty in achieving a good thermoelastic range is: first, the film must be heated to the required temperature within the corresponding process time; second, the preheating plate of the blister packaging machine should be longer, or the heating power should be considered in the design of the equipment go in.
Next, this article will take the design of Körber blister packaging machine as an example to explain how to optimize the blister packaging of PP film through temperature, molding process control and equipment improvement. Process stability and repeatability can be achieved by controlling the temperature of the PP film. The main method is to maximize the time of the crystalline film and reduce the shrinkage of the PP film.
The first is temperature control. Forming film heating requires at least 3 strokes, and the temperature heating of each area can be adjusted. When designing, the omentum can be fixed correctly before the feeding area to avoid the omentum from shrinking perpendicular to the traction direction. After molding, the temperature of the film must be controlled and kept within the set range. Controlling the temperature in the feeding area at 50°C to 60°C can keep the PP film in a crystalline state, and it is also helpful to reduce the internal tension of the film. Precise control of the sealing roll temperature ensures process stability. After sealing, precise control of the cooling roll temperature is also required to reduce the tension inside the material.
The second is to adjust the molding process. The interplay of omentum traction, vacuum, mechanically assisted forming, compressed air and dwell time are all very important influencing parameters. The ability to find the best process parameters depends largely on the experience of the technician. Each PP material responds differently. Theoretically, a long residence time of the omentum is desirable, so that the crystallization time of the material can be extended as much as possible.
Finally, when it comes to blister packaging equipment it can be upgraded to optimize PP film handling. Some specific upgrade methods include:
(1) The length of the preheating station is designed to be more than 3 times of traction, and the heating temperature can be individually controlled to make the temperature rise of the film more gentle and ensure the uniformity of the temperature inside and outside the film, so as to increase the stability of the molding process.
(2) The forming mold is directly water-cooled, and the film and the bubble can be basically shaped when forming. Compared with the traditional method of separate cooling after forming, it can reduce the shrinkage of the PP film. The specific method is as follows: Heating the auxiliary molding tool and controlling the temperature – on the one hand, the application of the auxiliary molding tool can make the processing and molding of the PP film easier, and at the same time increase the uniformity of the cell wall thickness; on the other hand, the control of the auxiliary molding temperature can be reduced Eliminate uncontrollable factors and increase the stability of the process.
(3) The sealing lid film can be preheated to make all components of the blister controllable.
(4) Direct water cooling of the sealing station is similar to direct cooling during molding, but reduces the shrinkage of the PP film after heating.
(5) Before punching, the position of omentum and blister can be controlled automatically to ensure accurate punching to meet the quality requirements of the product.
(6) The anti-drug board curling device is arranged as far back as possible in the process to ensure that the medicine board is flat before entering the box and meets the requirements of the medicine board entering the box.
Although PVC and PVDC are still irreplaceable in the short term, with the breakthrough of blister packaging technology, PP film, which was unprocessable in the past, will gradually become a better alternative. Due to its more environmentally friendly and economical characteristics, its usage is gradually increasing, which has injected new impetus into the development of blister packaging.