Polyimide film (PI for short) This kind of polyimide film has excellent thermal stability, low thermal expansion modulus and excellent thermal resistance compared with other polyimide materials in the world Can, known as the "gold film.".
Because of this, it is widely used in electrical and electronic fields (FPC, self-adhesive tape, cable insulation materials, etc.), aerospace fields, solar photovoltaic fields, electronic products fields (mobile phones, computers, audio, etc.) , as well as bar code, radar, fire hood and other fields.
1. Production technology of polyimide PI film
The preparation of PI film can be divided into impregnation method, tape casting method and tape casting drawing method. Impregnation is one of the traditional methods. The polyamic acid solution is impregnated on the aluminum foil substrate, and the polyamic acid film is formed by baking and drying. The substrate and film were put into a high temperature baking oven for dehydration and imidization reaction, and then the polyimide PI film was prepared by peeling, trimming, winding, pickling, washing and drying.
Tape casting is a polyamide acid solution that flows through the casting nozzle to the lower part of the stainless steel strip. It is dried to form a self supporting gel film. The polyimide PI film was prepared by stripping the gel film from the rigid strip and implanting it at high temperature. The uniformity and mechanical properties of the film were improved significantly.
2. Thickness uniformity of PI film
Flexible printed circuit board (FPC) is one of the key application fields of polyimide PI film. The greater characteristic of FPC is that it can move, bend, fold and stretch freely in three-dimensional space. Therefore, the polyimide PI film is required to be light and thin with excellent tensile properties and insulation. GB 13555-92 "flexible copper clad polyimide PI films for printed circuits" and GB / T 13542.6-2006 "films for electrical insulation-Part 6: polyimide PI films for electrical insulation" also specify the thickness, tensile peeling property and electrical properties of polyimide PI films.
In GB / T 13542.6-2006, PI films are divided into nine categories according to the nominal thickness (μ m), namely, 7.5, 13, 20, 25, 40, 50, 75, 100 and 125, and the corresponding numerical requirements for tensile strength, elongation at break and AC electrical strength of various materials are proposed. It can be seen that the thickness is a basic and key index in many performance standards, which is of great significance to the stability of the physical properties of thin films and the operation of subsequent processes.
Firstly, the uniformity of film thickness affects its mechanical properties to a certain extent. When the thickness of PI film is less than 20 μ m, the transverse and longitudinal tensile strength and elongation at break show a positive correlation with the thickness. When the thickness is more than 20 μ m, the transverse and longitudinal tensile strength and elongation at break tend to be stable.
Second, the uniformity of film thickness is closely related to AC electrical strength. When the thickness of PI film is 20-25 μ m, the AC electrical strength reaches a higher value-200V / μ m and above. When the thickness of PI film is less than 20 μ m or more than 25 μ m, the AC electrical strength decreases. The overall trend of the relationship between the two is like a peak.
Third, the poor uniformity of film thickness will greatly reduce the quality and efficiency of later winding.
Fourth, the problem of film thickness uniformity will cause the abnormal increase of production cost, thus reducing the market competitiveness of products to a certain extent.
3. Thickness measurement of PI film
In view of the great significance of PI film thickness uniformity to application effect and production cost, monitoring and controlling PI film thickness uniformity has become an important and indispensable link in industrial production.
Among all the monitoring methods, "online real-time monitoring + offline sampling inspection" mode is a typical and effective thickness control scheme in current enterprises. Online real-time monitoring is convenient, fast and timely to obtain the thickness data of batch films. If the deviation from the specified value fluctuates greatly, the production line can be stopped in time to check the problem.
4. Improvement of PI film thickness uniformity
The variation of transverse thickness of polyimide PI film is the main reason for the decrease of the quality of the finished product. For this problem, the thin and thin part of the gel film before imidization can be selectively heated and adjusted, and the film will be dried during adjustment or adjustment. To measure the longitudinal thickness of polyimide PI film and heat the thinner part, this kind of heating is generally carried out in the gelatinous film drying process. Therefore, it is suggested to install a film longitudinal thickness deviation monitoring system connected with the drying channel heating system at the outlet of the drying channel. When the thickness deviation of one or several narrow channels is large, the thickness deviation monitoring system will send out a signal to indicate the corresponding position The heating system of the narrow channel is used to adjust the temperature, which is repeated until the appropriate thickness is obtained.
Of course, other factors in industrial production will also lead to the thickness uniformity deviation of polyimide PI film. The influence of each production process on the thickness uniformity of polyimide PI film can be monitored by establishing the whole thickness measurement and control system.
The thickness uniformity of polyimide PI film is the premise and foundation to ensure its various properties, and it is also one of the effective entry points for enterprise cost control. Through thickness monitoring and process improvement, better thickness parameters of film quality and cost can be obtained to ensure the better performance of the film.http://www.china-polyimide.com