Film critics choose the clearer alternatives

In the second part of an investigation into the blister packaging sector, Andrew Smith looks at the properties and types of materials used in their production

Choosing a blister pack material revolves around a number of variables. Looking at practical considerations, compatibility with the product, level of barrier required, 'processability' and degree of clarity required are the most obvious criteria. Of the non-performance related variables, cost and the ability of the supplier to provide consistent quality film are most important.

Currently, despite indifferent barrier properties and concerns over their environmental impact, PVC films and PVC combinations remain among the most commonly used in the industry, especially for low margin and generic products. The much heralded and environmentally-friendlier PP monoblister has not gained the general acceptance expected as many converters have been unwilling to make the required machine modifications.

Much improved barrier performance can be achieved by PVDC, but it is too brittle and uneconomic to use as a monofilm and is therefore copolymerised with acrylic to make it more supple and cost-effective. However, blending affects its barrier properties and it is therefore commonly combined with a layer of PVC and sometimes also a layer of PE to make a triple 'sandwich'.

Multiple sandwich films may, however, be problematical, especially if clarity is important and the film industry's response has been to use proprietary products.

The demand for improved film performance — in terms of 'processability', clarity and resistance to moisture, oxygen, light and temperature — has been the drivery of blister material development and the new films have found particular favour with higher margin products, or those with specific barrier requirements.

Moreover, in the past few years, recommendations for more stringent and accelerated stability testing from the International Conference on Harmonisation have led to an increase in the use of films with high barrier properties.

This is especially the case when time to market is important and companies may launch a product in a high barrier film to ensure approval, then subsequently run tests to determine if there is a suitable lower cost alternative.

popular proprietary products

One of the most popular proprietary products on the market is Aclar, a PCTFE film originally developed by AlliedSignal, which is now integrated into Honeywell. Unlike PVDC, it is applied through lamination rather than coating and has excellent barrier properties, especially against moisture.

Indeed, in its 'raw' state it provides excessive protection — as well as being too expensive — and so it is laminated with either PVC or PVC/PE film to give it the required barrier at an affordable cost. Different versions are available with prices falling in-line with the level of barrier protection provided.

Apart from improved clarity, Aclar also has less tendency to curl than multiple sandwich films with an equivalent barrier performance, and there are processing benefits in that it has the ability to be formed at a range of temperatures. The required sealing temperature is also relatively low.

The most recent family of resins to reach the market are Cycloolefin copolymers (COC). These offer excellent optical clarity and temperature resistance and, most importantly, very high moisture barriers while having excellent thermoforming properties and yield.

COC-based films again provide barrier levels which at the very least match that of highly coated PVDC, but without the halogens which will be important to companies keen to avoid the health and environmental issues surrounding packaging containing chlorine and fluorine. They are commonly laminated with non-halogenated polymers such as PP.

Moreover, although like-for-like, COC based products are more expensive than polymers, they have a low specific gravity and can, therefore, be applied in thinner layers without suffering undue loss of barrier protection. This improves the yield from each batch reducing the amount of film required, while also enhancing clarity.

Rexam Medical Packaging, which recently introduced Pharm C, a COC resin with outer layers of PP to provide flexibility and grease resistance, also argues that benefits can also be realised from the capability of COC products to be directly co-extruded from pellet to finished product in one process. It says that because the product is co-extruded rather than adhesive laminated, the manufacturing process is simplified, cleaner and offers greater cost efficiencies.

Kloeckner Pentaplast has also introduced a new line of Pentapharm COC films which are available with either a vinyl or PP layer, while Celanese group company, Ticona, has shown faith in this new resin by investing €60m (US$54m) in the world's largest COC plant which will turn out 30,000 tpa of its Topas film.

Where very high levels of barrier protection are required, cold-formed aluminium remains the material of choice. Usually, as monolayer alu can be prone to cracking, it is laminated in a sandwich of PVC or PP and biaxially oriented nylon or oriented polyamide (OPA).

ultimate barrier for drug stability

However, for the ultimate barrier and drug stability, particularly for products with a hygroscopic nature or for use in tropical climates, Teich Flexibles says it has now solved the cracking problem and can offer a total alu/alu pack.

The pack is made from foil coated with a heat seal lacquer on both lid and base. The base web is cold formed, then filled and the hard temper peelable lidding sealed on. Teich says the lidding can either be standard soft foil or a paper-film-foil laminate depending on requirement. Other claimed added benefits are that there is no potential for delamination, total and easy recycling is facilitated and it has the potential for high quality print on both sides.

One problem with alu/alu based blisters is that traditionally they have been significantly larger than comparable plastic products as the forming properties of aluminium do not allow it to be subjected to the same stresses as polymer without pinholing. The answer has been to form the pockets with angled walls to avoid sharp corners at the base, but this obviously takes more material and results in an oversize pack.

The Advanced forming technique (AFT), devised by Lawson Mardon, now integrated into AlgroupWheaton, is a method of cold forming blisters from Formpack, an aluminium based laminate, which reduces the size of alu blisters by up to 20%.

For example, a typical PVC blister containing 10 tablets of 9.1mm diameter would measure 78x31mm, whereas a traditional aluminium blister holding the same tablets would be 99x40mm, an increase in overall area of 64%.

material savings

The AFT process overcomes this problem by using a two-stage process. In the first stage, a preliminary pocket is formed by stretching the material. This occurs primarily in the sealing area which subjects the bottom of the pocket to less strain. At the second forming station the base of the cavity is formed with a Teflon plug, resulting in pockets with steeper walls.

Apart from material savings, cutting the size of the pack also reduces carton size, and therefore cost. Larger cartons can also reduce machine output if fewer blisters can be formed per stroke. However, moving to this technology is best planned when new lines are being specified, as modified blister packers with two forming stations are required.

Factors outside commercial developments are also driving material and pack changes, not least the current debate over the child resistance of blisters and other non-reclosable packs.

The UK currently has standards for child-resistance for reclosable packs only, as opaque unit dose packaging had been deemed by the British National Poisons Unit to be as effective as CRCs on reclosable containers.

The USA and some European countries, notably Germany and the Netherlands, have standards in place. However, as in the UK, the general European position has been that there was no need for a standard test for non-reclosable packs.

This is about to change, as both the UK and the EC have draft standards in place. The proposed British Standard basically adopts the current German DIN 55559 and is due for release this autumn.

In Brussels, things are taking a little longer. A Working Party to establish a European standard was established several years ago, but has yet to report anything definitive. A draft has been issued, but the discussion is far from over, with, unsurprisingly, the question of testing methodology at the centre of the debate and the latest promise is that something will be in place by mid-2002.

The DIN testing protocol accepts 'type' testing whereby not every pack has to be tested by a panel of children aged 42 to 51 months, the age range deemed most at risk. Once a pack which has a particular method of inhibiting child access has been successfully tested, then all packs of this type are approved.

One reason cited for this is that the test panels would eventually run out of eligible children if every pack were tested, as they can only be volunteered once because part of the test involves monitoring successful entrance to the pack after being given a demonstration of how it works.

working party arguments

However, there are those on the European Working Party who argue that different materials and dose forms could produce different results from the same pack type and they are lobbying for testing of all packs unless they are similar, and hold a similar dose form, to an already approved blister pack.

Where they are going to find literally thousands of children — 200 are required for each full test — within the specified age range whose parents are willing to let them be trained to open a blister pack has yet to be answered.

A reliable method of mechanical testing which imitated manipulation by small hands would obviously resolve the problem and this is a route being considered.

Unfortunately, such a test has yet to be successfully devised and even if a methodology were to be invented tomorrow, it would face a lengthy period of testing before receiving approval from the appropriate authorities.

achieving a balance

Thankfully, one thing that all sides agree upon is that the packs should also be tested on adults to confirm practical usability. However, achieving the balance of being both child resistant and senior citizen friendly is no mean feat when it comes to flexible packaging.

In the US, those adults who wish for non-CRC packs request, and get them, without question. The penetration of blister packs in the north American medicines market is also much less than in Europe, so the problem is also inherently less of an issue. In Europe, things are different. Here blisters represent upwards of 30% of the primary packaging market for solid dose forms and, unlike in the US, we are not used to asking for alternative presentations of drugs.

The most common child resistant blisters revolve around the requirement to remove a laminate layer before gaining access to the final layer of lidding material, and, hence, then into the drugs. There are a number of film suppliers who have their own solutions based on this principle.

However, while this methodology can work extremely well in CR testing, it can also be problematical for those with elderly or arthritic fingers.

One of the latest products on the US market, and available in Europe through Brecon Pharmaceuticals, which addresses this problem is the 'Pick and Peel' system devised by Pennsylvania-based ProClinical. This is a patented blistercard which is said to provide high levels of child-resistance while maintaining ease of use for senior citizens.

sealing the back

The system works by sealing the back of each individual blister pocket with a peel away tab. Once this is removed, the dose form can then be pushed through from the reverse side as with a conventional blister pack. However, one of its key attributes is the ability to remove the child-resistant element without compromising the packaging should the medicines be intended for use by dexterity impaired adults.

The company says the blistercard, which is suitable for both commercial and clinical trial use, has undergone protocol testing stipulated in the USA's Poison Prevention Packaging Act for both child-resistant and senior-adult use effectiveness, and has been reviewed by the Consumer Product Safety Commission and certified for use.

Other attributes of the blister pack include its compactness — the package size is not affected by the added security — and the method's compatibility with all current films and foils.

The system can be incorporated into the pack before or after the blisters are filled and a variety of shapes and sizes are available for both tablets and capsules.