～Mystery near 80℃～
Polyester (PET) film required for transparent touch panels is a commonly used film in screen printing.
Many electronic parts such as computer keyboards and IC cards are made by printing electric circuits on this film with conductive ink. This PET film has a strange property against heat. When the ink is printed and dried, the temperature below 60℃ will not change the film. However, if the ink is dried at 80°C or higher, the PET film will shrink.
Also, when embossing (making unevenness on the film) with a mold, if the film is processed at 60°C or less and left in an atmosphere with a higher temperature, the embossed unevenness will return to its original state.
However, when embossed at a high temperature of 130°C or higher, the embossed unevenness does not change even if it is left in an atmosphere of 80°C.
Many electronic parts such as computer keyboards and IC cards are made by printing electric circuits on this film with conductive ink. This PET film has a strange property against heat. When the ink is printed and dried, the temperature below 60℃ will not change the film. However, if the ink is dried at 80°C or higher, the PET film will shrink.
Also, when embossing (making unevenness on the film) with a mold, if the film is processed at 60°C or less and left in an atmosphere with a higher temperature, the embossed unevenness will return to its original state.
However, when embossed at a high temperature of 130°C or higher, the embossed unevenness does not change even if it is left in an atmosphere of 80°C.
Why is this happening? This is due to the thermal properties of PET film. Plastics have a glass transition point. As the plastic heats up, the molecules begin to vibrate due to the heat. Further heating causes the molecules to move and the plastic to melt. The temperature at which this molecule begins to move is called the glass transition point.
In the case of PET film, the glass transition point is roughly between 60°C and 80°C. The physical properties change at this point.
Therefore, the things shown at the beginning occur at this temperature.
PET film can be used as it is without any treatment if it is used at a temperature well below the glass transition point.
However, when using at a temperature higher than this, it is necessary to heat treat at a temperature higher than the operating temperature to remove internal stress.
This also applies to plastic films other than PET films. When printing on plastic film by screen printing, the glass transition point is the point.
If you are thinking of printing on plastic film, please check the glass transition point.If the material changes after screen printing and drying, it may be related to the glass transition temperature.
