Introduction VFFS & HFFS Material Requirement for VFFS & HFFS Liquid Products Sealing Part of Auto Machine Trouble Shooting
Material requirements for VFFS & HFFS
Packagers continually endeavor to increase the speed of their machines in order to augment production without being impelled to buy more machines. Consequently, makers of packaging films and resins are under constant pressure to create better-quality products that will accommodate an increase in the speed at which machines work. The film-related prerequisites explained below for VFFS machines are also applicable to other kinds of packaging machines, although in varying degrees.
The attributes that largely determine the efficacy with which a film will run on VFFS as well as other packaging machines include the following:
- Coefficient of friction (COF)
- Tensile strength and flexibility
- Sealing properties.
Coefficient of Friction
It is possible to lower COF by applying additives or coatings to films that are without sound slip properties – or by selecting resin-based films that possess good slip characteristics. To illustrate, OPP film, which possesses an ideal combination of strength and clarity, has a relatively high COF of 0.4, which can be reduced by 50% using the application of acrylic coatings or slip additives including stearates.
Tensile Strength and Flexibility
These properties assume significance because the film gets pulled at very acute angles around the forming horn on a VFFS machine. At this stage, any reduction in either flexibility or strength can lead to frequent film breaks.
When it comes to VFFS machines, hot tack is arguably the most important rate-constraining film factor. “Hot tack” refers to the degree of resistance towards peeling apart and can be developed by a sealant layer while it remains hot immediately after being released by sealing bars. It is notable that the hot tack of packaging films that are used extensively, such as LDPE, is relatively poor.
In comparison, the hot tack of cost-effective ethyne copolymer films like EVA is better, although of all plastic films that are used in packaging, ionomer films have the highest hot tack. In fact, several packagers do not mind paying more money to incorporate these resins into their film structures as the dollar savings achieved through these structures (which offer higher machine speeds) more than compensates for the higher cost of the film. With an increase in the weight of the contents of a package this aspect becomes increasingly significant.
In case product filling is done in-line, the importance of hot tack reduces as compared to a VFFS & HFFS machine, although it still remains important. Jaw release and COF assume as much significance as they do on VFFS & HFFS machines.
On the other hand, if pouches are created to fill products offline, it becomes necessary for them to be easily opened using a modified form of the air jet device. In turn, this puts a premium on the film’s supposed ‘anti-block’ properties. In this context, the term “blocking” signifies a film’s disposition to stick to itself. A viable option is to use a coating to reduce blocking for plastics affected by this disadvantage.