Los productos de poliimida son principalmente películas, recubrimientos, fibras, plásticos de ingeniería, materiales compuestos, adhesivos, espumas, películas de separación, agentes de alineación de cristal líquido, fotorresistentes, etc., que se pueden aplicar a la industria aeroespacial, aislamiento eléctrico, pantallas de cristal líquido, automoción médica energía atómica, satélite, submarino nuclear, microelectrónica, envasado de maquinaria de precisión, etc.

Proceso de producción de película de poliimida CPI

La producción de película de poliimida cpi es básicamente un método de dos pasos, el primer paso: síntesis de ácido polámico, el segundo paso: imidización formadora de película. Los métodos de formación de película incluyen principalmente el método de inmersión (o método de encolado de papel de aluminio), el método de fundición y el método de estiramiento salivante (método de estiramiento orientado biaxialmente). La película de PI producida por el método de salivación se puede utilizar actualmente en una pequeña cantidad en la producción de FCCL de grado relativamente bajo. La película producida por el método de estiramiento (método de orientación biaxial) tiene un rendimiento significativamente mejorado, pero el proceso es complicado y las condiciones de producción son duras, la inversión es grande, el precio del producto es alto y productos de película de alta calidad con alta estabilidad dimensional y se puede obtener una baja absorción de humedad.

1. Salivation

In the early days, the polyimide cpi film developed by DuPont was of the homobenzene type. This type of film is produced by the polycondensation reaction of pyromellitic dianhydride (PMDA) and aromatic diamine in a polar solvent to produce an intermediate polyamic acid, which is then cast, removed of the solvent, and dehydrated and closed-looped (imidization). Conversion from polyamic acid to polyimide.

The process of producing PI film by the salivation method is: uniformly spreading the polyamic acid (PAA) solution onto a continuously running metal belt, and following the movement of the metal belt through a drying box to evaporate a part of the solvent, and partially dried PAA film It can be peeled off from the metal belt, dried by the heating roller, and then quenched and coiled to obtain a continuous length of film. Such a process is called salivation. During the salivation molding process, because the solvent has to be evaporated, and the price of the solvent is relatively high, it is necessary to increase the solvent recovery system to reduce the cost. The process of making PI film by solution salivation is shown in the figure below.

The main equipment, preparation steps and product detection of PI film production by salivation are as follows.

(1) Main equipment: stainless steel resin solution storage tank, drooling nozzle, drooling machine, imidization furnace, winder and hot air system, etc.

(2) Preparation steps:

After defoaming, the polyamic acid (PAA) solution is pressed into the drool nozzle storage tank on the front handpiece from the stainless steel solution storage tank through the pipeline. 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 drooling nozzle to form a liquid film with a uniform thickness, and then enters the drying tunnel to dry.

The clean and dry air is sent into the heater by the blower and preheated to a certain temperature, and then enters the upper and lower drying channels. The direction of hot air flow is opposite to the running direction of the steel belt, so that the temperature of the liquid film gradually increases during drying, and the solvent gradually volatilizes, increasing the drying effect.

The polyamic acid film runs with it for one week on the steel belt, the solvent evaporates into a solid film, and the film peeled from the steel belt is guided to the imidization furnace through a guide roller.

The imidization furnace is generally in the form of multiple rollers, and the guide roller synchronized with the speed of the salivator guides the polyamic acid film into the imidization furnace. After imidization at high temperature, the polyimide film is taken up by the winder from cryogenic －269 ℃ to high temperature + 400 ℃ can still show excellent physical, mechanical and electrical properties.

(3) Product testing

After the product is manufactured, its tensile strength, elongation at break, power frequency electrical strength, surface resistivity, volume resistivity, etc. should be tested.

The PI film is produced by the salivation method, the length is not limited, the peeling is convenient, the flatness is good, and the thickness is uniform. However, the precision of the equipment is higher; and the viscosity of the PAA solution is larger, the defoaming and filtering are more difficult, and the production speed is slower. Therefore, the salivation method is mainly used for plastic products with high melting temperature and high melt viscosity, which are not suitable for extrusion or calendering, or plastic products whose decomposition temperature is very close to the melting temperature.

2. Salivation-bidirectional stretching method

Under heating conditions, the film is stretched in one (uniaxial) or two (biaxial) directions in plane coordinates, so that the macromolecular chains are stretched along the stretching direction to change some properties of the film. The stretch orientation of the film. In general, stretching is suitable for improving the mechanical properties of thermoplastic materials. The stretching methods for preparing plastic films are divided into uniaxial stretching and bidirectional (biaxial) stretching methods.

Uniaxial stretching equipment is relatively simple, however, although it enhances 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 that of the unstretched. Therefore, people's interest in biaxial stretching is increasing. Bidirectional (biaxial) stretching can orient the molecular chains along a plane, thereby making the material have good planar properties. Bidirectional (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 stretch parallel to the axial direction to a certain multiple (longitudinal stretching), and then use the gradually expanding opening angle on the jig guide rail to stretch a certain amount perpendicular to the axial direction. Multiple (horizontal stretch).

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

El método de estiramiento utilizado en la película PI ahora se subdivide en dos tipos: método de estiramiento único y método de estiramiento babeante. En la actualidad, la industria es más respetada. La película de PI se prepara mediante el método de estiramiento de salivación. La película se forma al babear la solución de PAA y una parte del disolvente se evapora para formar una película. En la etapa de ácido poliamico, el estiramiento direccional se realiza para hacer que las cadenas moleculares tengan un cierto grado de disposición regular. Esto conduce a un rendimiento del producto equilibrado, estable y consistente.

El método de estiramiento y salivación de orientación biaxial incluye síntesis de resina, fundición, orientación biaxial, enrollado y otros procesos. El diagrama de flujo del proceso se muestra a continuación.

Diagrama de flujo de proceso del método de orientación de dos ejes

In the preparation of PI film by the biaxial stretching method, the main factors that affect the performance of the stretched film are:

(1) Stretched films of the same variety often differ greatly in their final structural properties due to differences in process parameters such as draw ratio, draw speed, and draw temperature. In general, it can be summarized into two points: First, under the specified drawing ratio and drawing temperature, the faster the drawing speed, the higher the degree of molecular orientation. Second, at a prescribed stretching speed and stretching temperature, the greater the stretching ratio, the higher the degree of molecular orientation.

(2) Does the polymer have a tendency to crystallize? The specific implementation process of stretching is different. For polymers that do not have a tendency to crystallize, stretching is relatively easy and can be directly stretched. When the molecular weight is relatively large, the degree of molecular chain orientation is low. The crystallization of the polymer has a significant effect on the stretching process. When the crystalline polymer is stretched, it is not easy to increase the degree of orientation. Therefore, the polymer should be as free of crystalline phase as possible before stretching. The method is to heat the polymer above the melting point to break the crystal, and then quench to maintain the amorphous state. Secondly, the stretching process makes macromolecules arranged regularly, and it is possible to form induced crystals. In addition, even if stretching is performed in a constant temperature chamber, if the thickness of the stretched film is uneven or the heat dissipation is poor, the entire process is actually not isothermal, and the quality of the resulting product is relatively poor. Therefore, it is preferable that the polymer having a tendency to crystallize is stretched under a temperature gradient.

(3) Influencia de las condiciones del tratamiento térmico. El propósito del tratamiento térmico de la película estirada es mantener la estabilidad dimensional de la película y evitar el encogimiento por calor. Para los polímeros sin tendencia a cristalizar, el tratamiento térmico relaja las moléculas de hebra corta y los segmentos moleculares que se han estirado y orientado, pero no afecta la orientación principal de la cadena macromolecular. Para los polímeros que tienen tendencia a cristalizar, el tratamiento térmico mantiene el polímero con suficiente cristalinidad para evitar la contracción. La técnica clave es captar la temperatura adecuada de tratamiento térmico.