How to go about making polyimide film
Release Time：
2023-06-06
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How to go about making polyimide film
Polyimide film is used almost exclusively in the electrical industry, with a small amount used for non-electrical applications in aviation, aerospace, nuclear industry and bioengineering. It is a film material with high temperature resistance (Class C or higher), deep cold resistance, high strength, high chemical resistance, non-flammable, non-softening (thermosetting), radiation resistance and superior performance. There has been a rapid development in recent years.
It can work at -269～+250℃ for a long time, and can also be used at higher temperatures for a short time (such as 1 hour at 400℃).
Polymers with imine structure in the main chain are collectively called polyimide PI, but we are only talking about polyimide films synthesized from homophthalic dianhydride and 4,4′-diaminodiphenyl ether, which are widely used.
The raw materials are mainly: homophthalic dianhydride (PMDA) or biphenyl tetracarboxylic dianhydride (BPDA): (most of them are the former, the latter in small quantities, the domestic production has not been reported.)and 4,4′-diaminodiphenyl ether (also known as diphenyl ether diamine, or ODA).
The two raw materials (commonly known as the two monomers) are synthesized in a solvent as polyamido acid resin. At present, the majority of polar solvent dimethyl acetamide (DMAC) is used as the solvent. The resin is defoamed, filtered and pressurized under vacuum before entering the film making process.
PI film compared with BOPP, BOPET film production, the characteristics of the worthy of note in the patent are:
First, PI resin is a solution, not a melt like BOPP and BOPET.
Second, the resin is not ****** polymer polyimide PI, but an intermediate product polyamide acid. This leads to another important feature - in addition to the general physical processing, the film making process is accompanied by chemical reactions from the beginning to the end, i.e. "imidation" reactions. In addition to good film making technology, the film making process also requires a strict "synchronization" of the two, so that no one can be ahead or behind.
Thirdly, the resin becomes film not in the way of rapid cold casting, but in the way of evaporating the solvent on the steel belt under the hot air environment to become film.
Polyimide film production method
This is a production method with much lower efficiency than BOPP or BOPET rate (the general production line is 100-500 tons/year), the reason is because PI has no softening point (thermosetting), and it can only be processed before PI is formed. At present, the domestic and foreign levels can only use the above process.
Here it is necessary to mention in particular the process of "imidation" method. There are three ways of imidation, three different ways of imidation production line cost, production efficiency is completely different, the PI film performance, use is also completely different:
1. Chemical imination, domestic is still in the research and development, here omitted.
2. Air-roller heating, imidizing under small longitudinal tension. The film obtained in this way is commonly known as "salivating PI film". It has the characteristics of low cost and easy to grasp, and is produced in large quantities and used widely in China, mainly for general insulation.
3. Imidizing under the mechanical condition of biaxial stretching is called "biaxial stretching PI film". Bi-directional stretch PI film is costly and technically difficult, and the process and equipment have higher requirements, and the overall performance of the product is also better than that of the "flow saliva film". At present, it is mainly used as a substrate for flexible printed circuit boards.
It is worth mentioning here that the author believes that the "biaxial stretch" state is only an important way of imidization. It is not exactly the same as the process of molecular aggregation (longitudinal or crystalline) during biaxial stretching of BOPP or BOPET, but has its own molecular microscopic behavior, and the stretching is accompanied by chemical reactions until the winding. Moreover, the film obtained is not the same as the biaxially oriented BO-(Biaxially Oriented-), so it is not inappropriate to call it "biaxially oriented film", but the product is called "BOPI", which is at least theoretically very debatable. The term "BOPI" is at least theoretically debatable.
PI film production is the same as other films in that the quality of the film depends on the comprehensive guarantee of raw materials, technology, operation technology, process conditions, process equipment (production line) and production environment, but differs in that it has different production and post-processing methods, and at present, resin synthesis must be carried out simultaneously with film production, and film production must deal with the synchronous relationship between physical processing and chemical reaction matching.
In the steel belt salivation machine, the production technology elements are:
--resin molecular weight and composition, guaranteed by the previous process.
--Resin flow viscosity.
--The support of the strip, the geometry of the drum and the speed of operation.
--Hot air control (solvent vapor content, temperature, air speed, uniformity, stability, etc.).
--Design and manufacturing level of salivation nozzle, adjustability, installation method and precision, etc..
-- Strict control of remaining solvent content (or strict control and regulation of volatilization amount).
--Surface of the steel strip and the way of de-filming.
The main elements of the subamination process are:
--level of equipment, accuracy of force field .
--The mastery of temperature and time ******.
--Better balance between theoretical endpoint and actual production endpoint, which is crucial for product quality impact.
Related Information
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2023-06-06
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