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What are the main considerations when selecting blisterpacking materials?
The choice of forming and sealing materials used depends on the degree to which the product needs to be protected from light, heat and moisture. Each material has different resistance to each of these elements and will affect the shelf life and storage conditions of the packaged drugs. Tests are usually carried out during a drug's development (stability studies) to identify which materials are most suitable, bearing in mind the differing cost implications.
The plastic forming films such as polyvinyl chloride (PVC), polypropylene (PP) and polyester (PET) are thermoformed, and are usually colorless and transparent. However for child-proof packs, or if the drug must be protected from light, forming films can also be opaque.
The forming film is the packaging component that receives the product in deep drawn pockets. Plastic forming films such as polypropylene (PP), polyvinyl chloride (PVC) can be thermoformed, but support materials containing aluminum are cold formed. The forming film and lidding material are an integrated package and must match one another precisely.
The forming film is usually colorless and transparent. However if the manufacturer wishes to make a childproof package, or if the drug must be protected from light, then forming films can also be opaque.
PVC (polyvinyl chloride)
(Contributed by : Helmuth Leitner, Solvay SolVin, Sept 2004)
PVC used as a forming film is called rigid PVC because it is almost free of softening agents. Currently it is the most widely used forming film and displays ideal forming characteristics. Its water-vapor permeability is very low. However, PVC was widely criticized because its combustion results in hydrochloride emissions, and if combustion takes place under certain conditions it can produce dioxins. New studies* have shown that in today's incineration plants PVC doesn't create any problem and energy recovery of plastics including PVC is a sustainable operation.
1. Wikstrøm, E., 1999. The Role of Chlorine during Waste Combustion. Thesis - Umeå University ; Wikstrøm, E., 2000. Final Report
2. Umeå-study. Doctoral thesis by E. Wikstrøm, University of Umeå, Sweden The role of Chlorine during Waste Combustion (Wikstrøm, 1999).
3. Doris Menke, Hiltrud Fiedler und Dr.-Ing. Heiner Zwahr; Mull und abfall 6-02, June 2002, page 322-332, ISSN 0027-2957.
4. PVC and municipal solid waste combustion : burden or benefit ? by LPM Rijpkema TNO report R 99/462 . Institute of Environmental Sciences, Energy Research and Process Innovation. TNO-MEP P.O. Box 342 7300 AH Apeldoorn, The Netherlands. Phone : 31 55 549 34 93 fx : 31 55 541 98 37
PVDC (polyvinylidene chloride)
PVDC-coated PVC has characteristics similar to those of uncoated PVC except that the water vapor permeability of films coated in this way is reduced by a factor of 5-10. The coating is applied on one side and usually faces the product and the lidding material.
PVC and ACLAR (CTFE)
PVC-CTFE films made from PVC and ACLAR (CTFE) have the lowest water-vapor permeability of all the films used for blisterpackaging. The environmental concerns raised about PVC also apply to PVC-CTFE film.
There is an increasing trend towards the use of PP as a support material for blister packages. The water-vapor permeability of uncoated PP is lower than that of PVC and is comparable to the water vapor permeability of PVDC coated PVC. One problem posed by PP processing is thermoforming. The temperature required for thermoforming PP and the temperature of the subsequent cooling process must be precisely controlled.
Another problem is warping of package - often resulting in the requirement for PP formed packages to be straightened before cartoning.
New high barrier thermoforming film
There is a new high barrier thermoforming film based on a new type of plastic granules called COC (cyclo-olefine copolymer). It is suitable for pharmaceutical and cosmetic packaging applications, where excellent moisture barrier properties, outstanding transparency and good rigidity are required.
There are different structures available of which the common ones are:
|30 my PP / 190 my COC / 30 my PP - AMPARIS 190|
|30 my PP / 300 my COC / 30 my PP - AMPARIS 300|
The COC films are solvent-free laminated to both sides with 30 micron PP films, consequently the laminate is free from solvents. The packaging system in combination with PP-sealable aluminum push-thru lidding foils guarantees a high seal integrity. Peel and peel-push laminates are also available.
The AMPARIS films can be thermoformed on existing blister lines for PVC, PVC/PVDC and ACLAR.
These new films are sold by Algroup Wheaton under the trade name Amparis.
PS is perfectly suitable for thermoforming but its high water-vapor permeability does not permit its use as a blister material for pharmaceutical purposes.
Coldform film (biaxally orientated polyamide (OPA), aluminum and PVC)
OPA-ALU-PVC (nylon-ALU-PVC), makes it possible to almost entirely eliminate water-vapor permeability. Also because of the high share of aluminum in this laminate, recycling of this material has become feasible, particularly because most lidding materials also consist of aluminum. Enormous efforts are being made to replace PVC with PP in such laminates in order to comply with environmental standards. Like other laminates containing aluminum, the OPA-aluminum-PVC laminate is cold formed instead of being thermoformed. The cost/m2 of this is equivalent to PVDC-coated PVC. Cold forming, however, requires more packaging material than thermoformed plastic film for packaging the same number and the same size of tablet or capsules.
Normally the permeability of plastic forming films increases with rising temperature. This is not true for aluminum formed packaging. Forming plastic film also causes a noticeable reduction in the thickness of the material. However when comparing the water-vapor transmission rates of the base material with that of the finished package there is not always a direct relationship between the thickness of the film and the water-vapor barrier effect.
|Material||Water Vapour Transmission Rate*||Cost per square metre|
|PVC/PVDC 40 gsm||0.75||$1.44|
|Aclar (Suprex 900)||0.23||$8.80|
|Aclar (Ultrex 2000)||0.12||$12.00|
|OPA/ALU/PVC (cold form)||Zero Transmission||$5.00|
The lidding material consists of support material eg aluminum that has a printed primer on one side and a sealing agent eg a heat-sealing lacquer on the other side. The sealing agent side faces the product and the forming films
After the tablets or capsules have been properly fed to the preformed support materials the lidding material is sealed onto the support material. Temperatures for this can range from 140-300°C. There are two sealing techniques: intermittent sealing with sealing plates and continuous sealing with sealing rollers. Intermittent sealing machines are operated at lower sealing temperatures than are continuous sealing machines. Intermittent sealing machines also have a longer sealing time.
An essential component of lidding material is the sealing coating. The side of the lidding material that faces the product and the forming film must be provided with a coating material suitable for heat sealing. This is usually accomplished by means of a heat sealing lacquer which must comply with FDA standards and must precisely match the respective forming films. Precisely match means that with predetermined sealing parameter, a permanent sealing effect between the lidding material and the forming film must be guaranteed under any climatic conditions. An additional requirement is that the sealing strength must fall within a predetermined tolerance.
Hard Aluminum is the push through lidding material that is most widely used in Europe. The foil usually has a thickness of about 25 micron. However this may in time be reduced to 15 micron. The hardness of the aluminum facilitates push through opening. Usually only the print-primer side features a printed design, but occasionally the side with the heat-sealing lacquer can also be printed. A double coat of heat-sealing lacquer (a heat sealing primer and the actual heat-sealing lacquer) has become the standard for lidding materials.
The heat-sealing primer ensures optimum adhesion of the heat-sealing lacquer to the aluminum foil. Then the heat-sealing lacquer can be perfectly matched to the formed films. If the heat sealing primers are colored then the heat-sealing lacquer applied over the primer can protect the packaged product from coming into contact with the pigments. If additional printing is required on the side of the heat sealing lacquer, the only alternative is to apply two coats of the lacquer. This is necessary because the printing inks must be between the heat-sealing primer and the actual heat-sealing lacquer.
This is frequently used for child-proof push-thru foils. With the exception of the type of aluminum used, the structure of this lidding material corresponds to that of hard aluminum. The softness and thickness of this type of aluminum help prevent children from pushing tablets through it. The lidding material is also provided with a perforation along the sealed seams to prevent the lidding material from being peeled off the form film in one piece.
For a combination of paper and aluminum the weight of the paper amounts to 40-50g/m 2. In the USA the thickness of the aluminum is greater than in Europe. The reason for this is that in Europe this lidding material is used for childproof push-thru packages. Therefore the aluminum foil is relatively thin. In the USA, this type of material is used as a peel-off foil and for effective peeling the aluminum foil must be relatively thick. Printing can take place directly on to the paper surface.
Lidding material made of a paper-polyester-aluminum laminate is often called peel-off-push-thru foil. This kind of material is used predominantly in the USA and is virtually unknown in Europe. The concept is to first peel off the paper-PET laminate from the aluminum and then the tablet is pushed through the aluminum.
Requirements for Lidding Components
The print primer should meet the following requirements: It must withstand sealing temperatures as high as 300°C without showing discoloration or tackiness (blocking). It should offer sufficient resistance to abrasion and be a substrate to which printing inks can adhere strongly enough to withstand the peeling force of adhesive tapes. Finally the print primer must comply with FDA recommendations.
Similarly, printing inks must withstand sealing temperatures as high as 300°C without showing any discoloration or tackiness (blocking). The adhesion of the printing inks to the print primer must offer sufficient resistance to abrasion and to the peeling force of adhesive tapes and the inks must comply with FDA recommendations.
The basic lidding material must meet requirements for elasticity or inelasticity specific to the type of machine used. It must guarantee water-vapor transmission rate that is at least as low as that of the forming films and it must be suitable for the type of opening appropriate to the package eg. push-thru or peel-off.
The heat-sealing coat must be compatible with the plastic material of the form films and it must ensure constant sealing for any given sealing parameter. The sealing strength must be suitable for push-thru or peel-off opening and of course it must comply with FDA recommendations.
The eye marks must be carefully adjusted to the type of machine used. If the machine is controlled by a feed mechanism, the eye marks must have extremely close tolerances. The total deviation across a distance of 1000mm must not exceed +/- 0.4mm. If the machine is controlled by a straightening mechanism that carries a roller with the lidding material, the distances between the eye marks are deliberately printed in the negative range because the lidding material is stretched to correspond to the speed of the machine.