How to Choose Materials for a Stand-up Spout Pouch

A stand-up spout pouch is a flexible pouch with a horizontal supporting structure at its base and a spout fitted at the top or on the side. That self-standing base keeps it upright without any external support. How much strength, barrier performance and heat-seal quality the finished pouch achieves depends largely on how the materials for each layer are chosen.

Flexible laminates are normally selected layer by layer: the outer layer carries printing and external strength, the middle layer provides barrier, and the inner layer handles heat sealing. The three have to match one another, and the form of the contents - dry solid or liquid - usually decides the direction taken for each layer.

The outer layer is the printing substrate. Besides ordinary OPP, the substrates commonly used for stand-up pouches include high-strength, high-barrier materials such as PET and PA, which can be selected according to need. For dry goods such as dried fruit, ordinary materials such as BOPP and matte BOPP will do; for liquid products, PET or PA is generally chosen.

The middle layer is usually a high-strength, high-barrier material such as PET, PA, VMPET or aluminium foil. It must have surface tension that meets the lamination requirement and good affinity with the adhesive, otherwise the bond strength of the laminate suffers.

The inner layer is the heat-seal layer, generally PE, CPE or CPP - materials with strong low-temperature sealing performance. Its lamination face must meet the surface-tension requirement, while the surface tension of the sealing face must be below 34mN/m, and it needs good anti-contamination performance, antistatic behaviour and sealing properties.

Three things must be balanced when setting the sealing temperature: the characteristics of the sealing material, the film thickness, and both the number of sealing passes and the size of the sealing area. Where the same spot is sealed several times, the temperature can usually be set a little lower. Proper pressure is needed to bring the sealing faces together, but excessive pressure squeezes out molten material, spoiling the flatness of the pouch and harming the seal, which reduces seal strength. Sealing time depends not only on temperature and pressure but also on the properties of the sealing material and the heating method, and the setting has to be adjusted on trial runs with the specific equipment and material. When pouches are made, the heating method of the sealing bar falls into two types - single-side heating and two-side heating - and two-side heating is the more efficient and more practical of the two.