Analysis of Calendering Method for Manufacturing PVC Film

Calendering refers to a method of forming a thermoplastic into a film or sheet by passing it through a series of heated rolls (calenders). It is used to produce high quality bulk products, with soft and hard PVC accounting for approximately 80% of all calendering lines. The film production is carried out on a complete set of equipment based on a calender, which consists of a metering device, a high-speed mixer, a masticating equipment, a feeding device, a calendering machine and a post-calendering device. Mixing and feeding have different routes depending on the specified calendering operation.

The calender is a relatively complex heavy-duty high-precision machine that is divided into different types depending on the number of rolls and the arrangement of the rolls. For soft PVC, the most common calender is a 4-roll inverted L-type or F-type. This arrangement facilitates the plasticizer to saturate the vapor into the suction hood and then filter it into the atmosphere. For the production of hard PVC, the 4~7 roll L type calender is preferred. The main choice is 4 rolls or 5 rolls. For high quality hard and Soft Pvc Film, the patented universal 5-roll L-type calender provides specific thermal stability and excellent film appearance control. According to the patented calender, there are still four available roll gaps, but the roll/film hold roll length is reduced from 2.5π to 1.5π, which reduces the dwell time by 40%, reducing heat loss, shrinkage and hug. Roller. The post-calendering treatment device includes multi-roller separation, embossing, cooling, thickness measurement, and coiling. In addition, in order to improve the quality of the PVC film, high temperature processing and single and bidirectional orientation devices can also be provided.

1. Soft PVC film

There are many process routes for producing thin films, and the following process flow is taken as an example to illustrate the main points.

High-speed mixing: metering according to the formula, in the high-speed mixer low-speed operation, adding resin, plasticizer and other additives in turn, and then running at high speed, the temperature is raised to about 100 °C, the material is loose.

Mixing: The above mixture is put into the internal mixer, and it is mixed for 3~5min under the vapor pressure of 0.4~0.5MPa, and the material is discharged when the temperature reaches 160~165°C.

Two-roll mastic: The hardened material is masticated on a double roll machine (temperature 155-165 ° C, roll distance 2~3 cm), and refining, eliminating bubbles and compacting and homogenizing.

Extrusion feeding: The temperature of the single screw feeder is set to 150 ° C / 160 ° C / 165 ~ 175 ° C (die), the screw temperature is slightly lower than the barrel, the filter screen in front of the perforated plate is 8 mesh / 16 mesh / 32 mesh / 90 mesh (or 120 mesh) screen composed of to remove impurities in the melt.

Calendering: The temperature of the inverted L-type four-roll calender is set to 160 ° C for the offset roller, 160 to 165 ° C for the upper roller, 160 to 165 ° C for the middle roller, and 165 to 170 ° C for the lower roller. In addition, the speed of the roller should be controlled. Ratio, residual material between rolls, etc.

Cooling: The chill roll should have a speed gradient and stepwise cooling to avoid internal stress.

2. Semi-hard and hard PVC film

For the semi-rigid PVC film, the decorative process is taken as an example to illustrate the process flow and operation points. The discharge temperatures of the high speed mixer and the cooling mixer are 120 ° C and 40 to 60 ° C, respectively.

The planetary screw extruder has a barrel temperature of 175 to 180 ° C and a main screw temperature of 170 to 175 ° C.

The temperature of the twin roll machine is slightly below 180 °C.