There are many factors that affect the thermoforming of plastic films. Among them, some properties and physical parameters of the film itself have a great influence on the thermoforming properties and processes.
(A) film thickness
For the thermoformed plastic film, the allowable thickness of the film deviation of not more than 4 ~ 8%, if the greater the thickness deviation, the longer the heating time. In addition, if the thickness of the film used for molding is changed, it is necessary to consider extending or shortening the heating time of the thermoforming accordingly. Only to ensure uniform heating and temperature in order to get a good product. If the thickness of the film is too large, it is possible to break the thinnest.
(B) the viscosity or melt index of the resin used for the film
If the viscosity of the raw materials used in each batch of plastic film is very different, it is easy to have problems in thermoforming, especially for polyolefin plastics, this problem is more prominent. The temperature of the thermoforming is also changed accordingly due to the change in melt viscosity (or melt index). High melt viscosity of plastic (low melt index) is relatively high thermal strength, the need for higher thermoforming temperature.
(C) the density of the film
The density of the film material increases, the corresponding shrinkage, tensile strength, hardness and toughness are also increased, then the thermoforming conditions have to change.
(D) the orientation of the film
In general, both extruded and calendered films have a certain degree of orientation. The longitudinal orientation of the unextended extruded film is about 12 to 15% and the transverse direction is about 2 to 5%. There is a certain orientation, you can get more consistent tolerance of the product, because its strain can be long to remain constant.
(5) the temperature of the film
Plastic thermoforming has a wide temperature range. To shorten the molding cycle, the temperature of the film can be taken in the temperature range near the lower limit, because it can shorten the time required to heat the film.