Thermoformed film packaging, also known as stretch forming packaging, thermoplastic plastic sheet heated and stretched after the formation of blisters, holes, cartridges, etc., and then fixed the product between the blister and the substrate, so that In the transport and sales process is not easy to damage, and stretch forming film packaging to the shape of complex, fragile fragile goods are effectively protected, so this packaging can protect the goods to extend the shelf life, but also play promotional products Expand the role of sales, has now been familiar with the most typical example is the supermarket inside the processing of meat products. Now most of the processed meat products have been used in such packaging.
The whole process is the main test of the film in both hot forming and heat sealing steps. In the thermoforming process, the film should be able to even stretch, to avoid tiger spots, but can not appear holes. Even so, the bottom corner portion after the stretch forming is the thinnest. In order to meet the barrier requirements, where the film (especially the barrier layer) need to maintain a certain thickness. And in the heat seal, you need to overcome the filling process on the thermal cover of pollution. If the anti-pollution heat sealing is not good, there may be insufficient heat sealing strength, or even leakage of the situation.
Formulation of thermoformed film
Because of the uniqueness of the thermoforming process, the structure and formulation of the thermoformed film is very different from the conventional film design. The design points are summarized as follows:
① In order to meet the requirements of the barrier, usually with EVOH 7 layer or 9 layer coextrusion structure. And some even reach 11 layers of co-squeeze.
② In order to avoid the hot film forming process in the hot surface of the mold, the outermost material needs to have a certain temperature resistance. Such as PA or PP.
A. Among them PA has a better tensile and low temperature performance as a surface structure.
B. The structure of PP as a surface layer has the advantage of lower cost, but because of poor performance, it is only used in the lower end of the application.
(3) In order to ensure that the interlayer fastness after stretching is sufficient, it is necessary to use a dedicated thermoformed binder resin or to design a formulation for the adhesive layer. (Adhesive resin can refer to our previous article: film production commonly used resin - adhesive resin)
④ In order to overcome the shortcomings of EVOH poor stretch, you can use PA wrapped EVOH structure. Use PA to assist EVOH stretching, to avoid the EVOH layer pull off the phenomenon.
⑤ In order to achieve good resistance to heat sealing, commonly used high proportion of metallocene or plastic material to do heat sealing layer.
⑥ In order to get a beautiful film appearance, the need to carefully design the thickness ratio of each layer, while attention to the flow of each layer match, it will not appear because of instability between the layers of orange peel or water ripples.
Based on the above considerations, the current structure on the market, including PA / tie / PE / tie / PA / EVOH / PA / tie / PE 9-layer structure, or PA / tie / PA / tie / EVOH / PA / tie / PE 7-layer structure. More excellent thermoformed film formulations and solutions can be linked to film pass.
Forming process of thermoformed film
The crystal size of the polymer has some effect on the effect of thermoforming. In general, the smaller the crystallinity, the better the stretch formability. So most of the thermoformed film is the use of cast or under the water-cooled process to produce. These two production processes have the ability to quickly quench, so the film produced by the smaller crystallization is conducive to hot forming stretch. In contrast, casting and blowing water cooling each have their own advantages and disadvantages. Cast the output of large, wide, uniform thickness distribution, but the investment is greater. Under the cooling of the water cooling faster, high transparency, the film is more soft, less investment, but the width is small, the output is small. So according to the end products and orders to determine the situation for their own production process.