Plastic film thickness uniformity is one of the most important indicators in product quality standards. Generally, the thickness of biaxially stretched plastic film changes little along the longitudinal direction, but the thickness changes along the transverse direction

 

The change value is also large, which has an important influence on the uniformity of the film. There are two key factors that can improve thickness uniformity:(1) basic film thickness uniformity control.

 

(2) thickness uniformity control during transverse stretching. In the process of drawing PTFE film, various factors have an impact on the uniformity of the film, such as resin.

 

Molecular weight, extrusion agent type, content, extrusion process, calendering process and stretching process, the most important of which is the stretching process conditions.

 

At present, there are few studies on the uniformity of PTFE film preparation, but there are a large number of literatures on the uniformity of other films formed by two-way stretching.

 

It has important reference significance for the study of the uniformity of PTFE film.

 

In the production of biaxially oriented films, transverse stretching is an important and complex process, and the whole process is carried out in a continuous thermal environment. Single-oriented thin after longitudinal stretching

 

In the process of transverse stretching after the end of the film, there is a complex thermodynamic coupling deformation, so the process is often called a black box that is difficult to analyze. In order to fully understand, understand, palm

 

In order to improve the uniformity of the film, the researchers studied the deformation mechanism of the film in the process of transverse stretching.

 

Some studies have shown that for biaxially stretched BOPP films, with the increase of the transverse stretch ratio, the transverse tensile strength of the film increases, the transverse elongation at break decreases, and the transverse elongation at break decreases.

 

The thickness deviation is also greatly reduced, and the performance indicators of the product are developing in a good direction. Using the elastic-sticky plastic rate-related and rate-unrelated constitutive equations, the horizontal of BOPP.

 

The stretching process is numerically simulated, and the stress concentration phenomenon at the center of the film and at the exit of the film is obtained, resulting in the inhomogeneity of the film, which is consistent with the experimental observation. There are also studies

 

The temperature field is considered to be the most important factor affecting the transverse stretching.

 

The transverse stretching process of PA66 plastic film was simulated by computer, and the three process parameters of material physical parameters and transverse stretching ratio, transverse stretching speed and stretching temperature were revealed.

 

The influence of the number on the relative crystallinity uniformity of the plastic film is obtained, and the distribution of the relative crystallinity is the main factor of the film thickness uniformity.

 

The relative crystallinity of the film is not uniform, which inevitably brings about the uneven thickness of the film. Another study summarizes the main factors affecting the uniformity of film thickness in the production of BOPET film.

 

There are two aspects of automatic control system and process, in which the process (such as temperature, stretch ratio, electrostatic state, oven state, etc.) has a greater impact on the thickness of the film.

 

Different stretching ratio, stretching temperature and casting conditions have a great influence on the thickness deviation, and the thickness uniformity of the film can be improved by selecting the appropriate process.

 

At present, although there is a large number of literature to study the various properties of two-way or one-way stretch film, but in the sample preparation is simple, the literature more use of vertical horizontal stretch method at the same time, or.

 

The step-by-step uniform transverse stretching method is quite different from the transverse stretching method of guide rail clips used in industrial practice, and the conclusions obtained are indirect in guiding the industry. Through research hair

 

Now, in the process of polytetrafluoroethylene film production, due to the inherent defects of transverse stretching, resulting in the non-uniform transverse stretching phenomenon in the tenter processing stage.

 

The stretching will lead to the non-uniformity of the structure and performance of the PTFE film, which will seriously affect the quality of the film. And about the non-uniform transverse caused by the tenter mechanic stage.

 

Studies on the phenomenon of stretching are rarely reported.

 

At present, there are two main methods for the preparation of PTFE polytetrafluoroethylene microporous film. One is to add the pore agent NaCl to PTFE, then make PTFE into a thin film, and then

 

NaCl is removed by heating and washing, and the vacancies left by NaCl form pores. The minimum pore size of the microporous membrane made by this method is 0.1 μm. The second is the mechanical stretching method, the side

 

The microporous membrane prepared by the method has a special micro-fiber connection island "knot" structure, which is the main method of preparing PTFE microporous membrane.

 

In the 1960 s, PuPont company first made PTFE stretch membrane by uniaxial stretching method, but the size, porosity and strength of the membrane were not ideal. Mid -70 century

 

Gore Company of the United States successfully developed expanded PTFE microporous membrane using biaxial stretching technology, after which Japan has made great progress in this area, and applied for a number of special applications.

 

Leigh. China has been developing PTFE stretch film since the 1970 s, but it has been stuck in the unidirectional stretching process for a long time. Since the 1990 s, some units have developed and produced PTFE stretch film.

 

Out of the two-way stretch microfiltration membrane.

 

PTFE PTFE fine powder and additives are fully mixed into the extruder, the powder is pushed out of the strip PTFE, and then compressed into a diaphragm under the roller press. Heating addition

 

After adding the agent, the vertical and horizontal stretching can be carried out, and then the two-way stretching microfiltration membrane can be obtained by heat treatment, cutting and winding.

 

In general, polytetrafluoroethylene films can be prepared by different methods, and the materials used can be organic (polymer) or inorganic (ceramic, metal, glass). Using polymer materials

 

The preparation methods of PTFE film include: sintering, stretching, tracking, phase inversion and so on. According to different classification standards, the preparation methods of PTFE films are different.

 

Classification. It is reported in the literature that the preparation technology of PTFE film is divided into six categories according to the process: stretching highly filled plastic film technology, molecules that can form a microfiltration network aggregation state structure.

 

Membrane technology, phase separation into membrane technology, hollow fiber microfiltration membrane technology, chemical crosslinking foaming technology, physical mechanical perforation technology, etc. According to the micropore formation mechanism can be attributed to charge

 

3 mechanisms, such as filling mechanism, deformation mechanism and phase change mechanism. Of course, in many cases, multiple mechanisms work at the same time.

 

The production of plastic film by biaxial stretching process has been more than 80 years of history, the main production process including tube film method and plane biaxial stretching method. Planar Biaxial Stretch Film Varieties

 

More, many crystalline polymers and non-crystalline polymers can be stretched into a film. At present, the two-way stretch films that have been industrialized are: polypropylene BOPP, poly

 

Ethylene terephthalate BOPET, polyamide BOPA, polystyrene BOPS, polyethylene POPE, etc. For the good performance of the planar biaxially stretched film, the product application

 

At present, the development speed of this stretching method is far faster than that of tube film stretching method. In the planar two-way stretching process, it mainly includes two-step continuous stretching and synchronous two-way stretching.

 

Two processes, and two-step continuous stretching, that is, the first longitudinal stretching and then transverse stretching process for its strong controllability, stretching the film comprehensive performance is excellent and a large number of mining.

 

Use. At present, the synchronous two-way stretching equipment is still not domestic, imported equipment is expensive, mostly BOPET, BOPE and so on film used.

 

For PTFE film, the production process mainly includes: calendering, turning and stretching, among which only the stretched film has a good microporous structure. Preparation of polytetrafluoroethylene

 

The traditional process of ene film is to mix a certain proportion of PTFE PTFE powder and extrusion aid, after extrusion, calendering, drying, stretching, sintering, cooling and a series

 

process, and finally make a porous material. On the basis of the traditional process, countries around the world have developed improved methods for the preparation of PTFE films, such as multiple

 

The secondary stretching method, the stress-free sintering stretching method, etc.

 

Due to the strict blockade of foreign technology and the relative weakness of China's basic technology, at present, China's PTFE film production equipment is developed on the basis of raw material belt.

 

of. The raw material belt is mainly formed by longitudinal unidirectional stretching. On this process and basis, a transverse stretching process is added to process a biaxially stretched PTFE film.

 

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