1. Thinning of film
The thinnest PET films currently used are about 0.5μm thick, which is much thinner than other films, for example, bi-oriented PP films are 3μm thick, polycarbonate (PC) films are 2μm thick, and PE films are 8μm thick. Processes suitable for the production of thinner films are bidirectional drawing processes or solution casting processes. The former is suitable for PET and PP films, and the latter is suitable for PC films. Generally, the blowing process of blow molded film and the T-cast die head process are not suitable for the production of very thin films. In general, it is quite difficult to produce a film with a thickness of 10μm through the die gap. Some literature has suggested that the plasma polymerization method is a good method for producing extremely thin films, and the process is characterized by glow discharge in a monomer gas. However, the production of thinner films by this process is still a practical product at present.
2. Thinning technology
PET film minimum production size such as handkerchief size of extremely thin thickness trend film is very easy. Even about 30 years ago, limited sizes of 1μm thick PET films were produced. Of course, such a limited size cannot be used in industry, and the film must be wound around the core in a reasonable width and length (usually several thousand meters to tens of thousands of meters long). This rolled film is called - "roll". Therefore, the development of thinning technology can be expressed as "the development of the film from the size of a handkerchief to a roll."
(1) The stretching process
Drawing is the main factor in the production of thin films. A number of patents have been published on tensile methods and conditions.
(2) Accuracy of the machine
The film machine is composed of many rollers and other mechanical components, and it should have a high mechanical accuracy.
(3) Sliding performance
Good slippability of thin films is very important for proper machining and disposal of thin films. In order to get good slippability, some additives, such as inorganic or organic fillers, are usually added to the film. However, these additives sometimes cause the film to crack, losing electrical properties and insulation. It is often necessary to choose some sensible compromise to overcome these difficulties.
(4) Remove impurities
Impurities such as dust, carbonized polymers, and condensed particles often cause rupture, small holes, and degradation of physical properties. Therefore, a pure polymer, a clean working environment and a good filtration system are required. Thickness / μm
(5) hardness of the film
Because the hardness of the film is related to the cube of the thickness, it is very easy to wrinkle and sag in the production of thin films. Therefore, it is desirable to use polymers with high modulus when producing thin films. PET has a relatively high modulus, which provides advantages for the manufacture of thin films. The reduction of hardness is also easy to cause static electricity. Therefore, it is very important to prevent the accumulation of electrostatic charges and remove the static electricity.
(6) Thickness measurement
The Pm147 is usually used as a beta ray generator for measuring the thickness of extremely thin films. However, the accuracy of the measuring instrument is limited to the range of 0.1μm, and it cannot meet the measurement of thin films with thickness less than 1μm. More accurate measurement techniques are now required.
3. Thinning limits
The thinning of PET films is determined by factors such as polymer molecular structure, surface roughness, mechanical properties (ease of handling), dust and impurities, and the final application. By summarizing these factors, the actual lower limit of PET film thickness is expected to reach 0.3~0.5μm in the near future, and 0.025~0.05μm in the further future [58]. Efforts to obtain thinner films will continue, especially for capacitors. Recently at an electronics exhibition, a capacitor manufacturer demonstrated ultra-small film capacitors composed of 0.65μmPET films produced by Toray, which are expected to compete with tantalum electrolytic capacitors and ceramic capacitors in size.
