Film calendering is to use calender to make rubber material into smooth film with specified section thickness and width, such as inner and outer rubber and intermediate film of rubber hose and tape, tire buffer film, isolation film and oil skin film, etc. When the section thickness of the calendered film is large and it is difficult to ensure the quality at one time, it can be calendered into more than two thin films respectively, and then pasted into films with specified thickness requirements, or the films of two different rubber materials can be pasted together to make films that meet the requirements, and the rubber material can also be made into a certain section thickness and width with certain patterns on the surface, That is, the film with a certain geometric section. Therefore, the calendering of film includes lamination, film lamination and molding.

（1） Tablet pressing

The film with a section thickness of less than 3mm can be calendered at one time by calender, which is called lamination.

The quality requirement of calendered film is that the surface of the film is smooth without drawing shrinkage; The interior is dense without holes, bubbles or sponges; break

The surface thickness is uniform and accurate, and the shrinkage deformation rate of each part is uniform.

According to different equipment, the tablet pressing process is divided into two main methods: three roll calender and four roll calender. Two roll calender and open rubber mixer can also be used for film pressing, but the precision of film thickness is too low.

The tablet pressing process is shown in figure 13-9. (a) and (b) in the figure are three roll machine tablet pressing, and (c) is four roll machine tablet pressing. The three roll calender can be divided into two methods, in which a is the calendering method without glue accumulation between the middle and lower rolls, and B is the calendering method with glue accumulation between the middle and lower rolls. An appropriate amount of accumulated glue can make the film surface smooth, reduce internal bubbles and improve the internal compactness of the film, but it will increase the calendering effect. This method is applicable to styrene rubber. If too much glue is accumulated, bubbles will be brought in. Contrary to the rule of no glue accumulation, it applies to natural rubber.

When the four roll calender is used to press the film, the shrinkage of the film is smaller than that of the three roll calender, and the section thickness precision is higher, but the calendering effect is larger, which should be paid attention to in the process. When the film section thickness is required to be very precise, it is best to press the film with a four roller machine, and the film thickness range can reach 0. 04—1。 00mm。 If the film thickness is 2-3mm, it is also ideal to use a three roll calender.

The main factors affecting the tablet pressing process and quality are roll temperature, roll speed, raw rubber type, rubber plasticity and rubber content.

High roll temperature, low viscosity of rubber, good calendering fluidity, low shrinkage of semi-finished products and smooth surface; However, if it is too high, it is easy to produce bubbles and scorch; Too low roll temperature will reduce the fluidity of rubber, rough the surface of semi-finished products and increase the shrinkage. Therefore, the roll temperature should be determined according to the type of raw rubber, plasticity and glue content of the formula. Generally, the calendering roll temperature should be appropriately higher if the formula has high glue content, low plasticity or high elasticity of rubber; The opposite is true. In addition, in order to make the film transfer smoothly in the predetermined direction between the rollers, an appropriate temperature difference must be maintained between the rollers. For example, natural rubber is easy to stick to the hot roller. When the film is transferred from one roller to the rear roller, the roller temperature of the latter should be appropriately increased, while synthetic rubber is just the opposite. The temperature difference between rolls is generally 5 ~ 10 ℃.