Flowpack is often used in the packaging of relatively smaller products. Especially with consumer products, the numbers could be extremely high. The products are then processed at high speed and the importance of dependability increases.
The problem free process ability of the materials is therefore essential. The print ability and screening properties of the foil are also extremely important.
Choosing the correct material is teamwork between the machine manufacturer, the marketing department and the raw materials supplier. To decide on the machine, the process ability is extremely important. Here are several points of interest that play a role here:
The material can be joined by either a hot or cold seal.
The hot seal process consists of three steps:
1. The heating of the two foil layers whereby the inner layers are brought into contact with each other under pressure.
2. The cooling of the materials
3. The consolidation of the seal between the two foil layers
In this process it is important that the temperature is adjusted to the melting point of the inner foil layer. This temperature must be well controlled. The pressure excerted on this, must be enough to get the outer layers to make good contact with one another and for the heat transfer to be able to take place between the layers, however this must not be too large so that the foil structure does not get damaged. The time during which the inner layer can stay warm and liquid is determined by the speed with which the foil is processed. The greater the required capacity, the shorter the available processing time and the higher the requirements will be for heat exchange between the sealer and the material.
A cold seal is applied when a hot seal is not possible because of the product properties, or when extremely high capabilities are necessary (processing speed higher than 80 meter per minute). In case of a cold seal, a layer is applied only there where the seal is made which attaches to the other foil layer under pressure during the processing at room temperature.
With regard to the surface, one should keep three important properties in mind with flow pack materials:
1. The smoothness of the film should be consistent.
2. The material should be able to release itself from the seal stamp.
3. The development of static electricity that originates with friction between machine and foil material should be prevented.
Apart from the seal and surface properties, there are obviously also more parameters of importance, of which we have listed the most important ones:
1. Rigidity: This is relevant because of the possibility that folds may develop in the seam. The rigidity depends on the production process with which the foil was made.
2. Tensile strength and point load resistance: the tensile strength and point load resistance are deciding factors for the break and tear risk.
3. Thermal stability: The material is subject to distortion, especially during the welding process.
The Flowpack material comprises mostly of multiple layers. Every layer has its own characteristics. By combining the various layers, a foil originates with the perfect qualities. A short summary of the most important available material types follow below.
Widely used as a base layer. PP is however not suitable for sealing in blown form. An extra layer is necessary for this. In blown form, it is thermally (to 150 deg. Celsius) extremely stable, clear and printed and therefore often used as outer layer. In cast form, PP is suitable for sealing. A combination of both is often used where the blown version is used for the outer layer and the cast version for the inner layer.
This is seldom used, most often in pharmaceutical applications. It must always be combined with an extra layer for the seam.
Its use is declining because it is usually replaced by a metalized polypropylene foil. It is however still used in the pharmaceutical industry. It has excellent properties, in regards to temperature resistance, clarity, hygiene and mold ability (keeping shape of folds and creases).
It must always be combined with an extra layer for the seam. It can be used at temperatures varying from -70 to +180 °C. It is therefore ideal for the packaging of products that must be frozen or sterilized. It is a clear material that does not allow any gas through.
Easily processable material which is often used as an inner layer because of its affordability and excellent sealing properties.