Polyimide Film

Production Market
600+ customers annually. Products are exported to Vietnam, Singapore, India, the United States, Germany and so on.

R&D Capability
7 invention patents, 3 high-tech product certification certificates, 8 utility model patents, national high-tech enterprise, Suzhou Engineering Research Center.

Production Equipment
18 production coating lines / 9 rewinding machines
2 sample coating lines / 18 slitting machines / 11 cutting machines

Our Factory
Founded in 2008 TAILUN is one of the largest coating manufacturers in China, and is committed to the technical research and development and production of adhesive materials in consumer electronics, automotive, electrical and other industries Main products include protective film, adhesive tape, release film and PI products, etc.

Polyimide is a polymer composed of imide monomers. Polyimide is used as the insulating material in many digital isolators for a number of reasons, including excellent breakdown strength, thermal and mechanical stability, chemical resistance, ESD performance, and relatively low permittivity. Besides good high voltage performance, polyimide has excellent ESD performance that is capable of handling EOS and ESD events exceeding 15 kV. During energy limited ESD events, the polyimide polymer absorbs some of the charge to form stable radicals that interrupt the avalanche process and bleeds away some of the charge. Other dielectric materials such as oxide typically do not have this ESD tolerant characteristic and may go into avalanche once the ESD level exceeds the dielectric strength, even if the ESD energy is low. The polyimide also has high thermal stability, with a weight loss temperature over 500°C and a glass transition temperature of about 260°C. The polyimide also has high mechanical stability with a tensile strength over 120 MPa and a high elastic elongation over 30%. In spite of its high elongation, polyimide does not deform easily because the Young’s modulus is about 3.3 GPa.

The polyimide has excellent chemical resistance, which is one reason it has been widely used for insulation coatings for high voltage cables. Polyimide films can be coated on the semiconductor wafer substrates and high chemical resistance also helps to facilitate IC processing on top of polyimide layers, such as the Au plating used to create iCoupler transformer coils. Lastly, the thick polyimide films, with a dielectric constant of 3.3, work well with the small diameter Au transformer coils to minimize capacitance across the isolation barrier. Most iCoupler products exhibit less than 2.5 pF capacitance between input and output. Because of these characteristics, polyimide is increasingly used in microelectronics applications, and it is an excellent choice as insulating material for the iCoupler high voltage digital isolators.

The production of polyimide film is basically two-step method, the first step: Synthesis of polyamide acid, the second step: Film-forming imidization. Film forming methods mainly include impregnation method (or aluminum foil glue method), casting method and salivation stretching method (biaxial directional stretching method). The polyimide membrane produced by salivation method can be used in a small amount of fccl. The film produced by stretching method (biaxial orientation method) has significantly improved its properties, but the complex production conditions, large investment and high product price can obtain high quality film products such as high dimensional stability, low moisture absorption and so on.

The main equipment, preparation steps, and product testing of Polyimide Film produced by the salivation method are as follows.

Main Equipment

Stainless steel resin solution storage tank, salivation nozzle, salivation machine, imidization furnace, winder and hot air system, etc.

Preparation Steps
The defoamed polyamic acid (PAA) solution is pressed from the stainless steel solution storage tank through the pipeline into the salivation nozzle storage tank on the front head. The steel belt runs at a uniform speed in the direction shown in the figure, and the solution in the storage tank is taken away by the scraper in front of the saliva nozzle to form a liquid film with uniform thickness, and then enter the drying tunnel to dry.

The clean and dry air is sent to the heater by the blower to be preheated to a certain temperature and then enters the upper and lower drying channels. The flow direction of the hot air is opposite to the running direction of the steel strip, so that the temperature of the liquid film will gradually rise during drying, and the solvent will gradually volatilize to increase the drying effect.
The polyamic acid film runs on the steel belt for a week, and the solvent evaporates to become a solid film, and the film peeled from the steel belt is guided to the imidization furnace by a guide roller.
The imidization furnace is generally in the form of a multi-roller, and the guide roller at the synchronous speed of the casting machine guides the polyamic acid film into the imidization furnace. After the high temperature imidization, the polyimide film is rewinded by the winding machine from deep cooling. 269℃ to high temperature +400℃, it can still show excellent physical, mechanical and electrical properties.

Product Testing
After the product is manufactured, it must be tested for its tensile strength, elongation at break, power frequency electrical strength, surface resistivity, volume resistivity, etc.
The Polyimide Film produced by the salivation method has unlimited length, easy peeling, good flatness and uniform thickness. However, the precision of the equipment is relatively high; And the viscosity of PAA solution is relatively large, defoaming filtration is more difficult, and the production speed is slow. Therefore, the salivation method is mainly used for plastics that are not suitable for extrusion or calendering, such as high melting temperature and high melt viscosity, or plastics whose decomposition temperature is very close to the melting temperature.

Two, Salivation-two-way Stretching Method
Under heating conditions, the film is stretched along one (uniaxial) or two (biaxial) directions in the plane coordinates, so that the macromolecular chains are stretched and arranged along the stretching direction to change certain properties of the Polyimide film. This process is called PolyimideStretch orientation of the film. Generally speaking, stretching is suitable for improving the mechanical properties of thermoplastic materials. The stretching method for preparing Polyimide film can be divided into uniaxial stretching and biaxial (biaxial) stretching.

The uniaxial stretching equipment is relatively simple. However, although it strengthens the mechanical properties of the material in the stretching direction, it also makes the mechanical properties of the material in the vertical direction even worse than the unstretched one. Therefore, people are increasingly interested in biaxial stretching. Biaxial (biaxial) stretching can make the molecular chain oriented along the plane, so that the material has good planar properties. Two-way (biaxial) can be divided into secondary stretching and primary stretching. The so-called secondary stretching is to use a set of rollers with different drilling speeds to first stretch to a certain multiple parallel to the axial direction (longitudinal stretching), and then use the gradually enlarged opening angle on the fixture guide rail to stretch a certain amount perpendicular to the axial direction. Multiple (transverse stretch).

The biaxial stretching method generally adds a stretching orienting device after the salivation method. The film is heated to a specified temperature and stretched to a large extent, so that the molecular chains are arranged neatly along the stretching direction to a large extent, and one direction is unidirectional. Horizontal and vertical are two-way stretching. After stretching, the strength is 3-5 times better, the heat and cold resistance are improved, and the physical properties are significantly improved. High-quality membranes use this method. FCCL, which has high requirements in terms of performance (dimensional stability, etc.), all use Polyimide films produced by the biaxial orientation method.