POF Film Production Process Control


POF heat shrink film is a biaxially oriented heat shrinkable polyolefin packaging film. The product requires high force equipment, and the process is the main factor affecting product performance. In the POF film production process, the optical and heat sealing performance indicators of the product are mainly adjusted by controlling the temperature field and force field during the processing.

POF film production is a low temperature cold drawing biaxial stretching process, which requires low temperature stretching, so the equipment should not be too large. If the equipment range is too large, the foam stability is poor, the temperature control is high, the stretching speed is also slow, and the product quality will drop significantly. Use small equipment to increase extrusion output, increase the pulling speed of the rear section, good foam stability, low temperature control, fast stretching speed, and double the product quality. Using this equipment for production, the equipment is properly selected.

In the case of good process control, the output is not lower than that of large-scale equipment, and the product quality and performance are good. The control principles of various parameters in POF film production are as follows:

Temperature Control During POF Shrink Film Production

Temperature control of extrusion unit

Middle extruder temperature control:

The middle layer raw material mainly adopts LLDPE, which has high viscosity and higher crystallinity than LDPE, and the viscosity decreases slightly with the increase of temperature. Generally, the method of increasing the processing temperature is not used to increase the extrusion volume, but the method of adding LDPE or processing aids is used. method to solve this problem.

Therefore, the temperature setting of the extruder generally adopts a gradual heating method, that is, the processing temperature of the feeding section is low, and the processing temperature of the plasticizing section and the mixing section is high. Oxidative degradation, the lower the temperature the better.

Middle extruder temperature control:

The inner and outer layers are mainly made of ternary copolymer polypropylene, which has high crystallinity, high melting point, large melt index and good fluidity. Therefore, the temperature setting of the inner and outer extruders is based on the principle of sufficient plasticization. Under the condition of ensuring sufficient plasticization, the lower the temperature control, the more conducive to the product performance of the finished product.

In order to prevent bridging at the feed inlet, the inner and outer layer extruder generally adopts a gradual heating method, that is, the temperature of the feed inlet is lower, and the temperature of the plasticizing section and the mixing section is higher.

Temperature control of extruder unit and die head connector:

The main function of this section is to rely on pressure to feed raw materials into the co-extrusion die head. The raw materials in this section have been fully plasticized, so the temperature control is generally slightly lower than the temperature of the plasticizing section and mixing section of the extruder in the previous section. The specific temperature refers to the temperature in the previous section. set up.


The extrusion unit is the first step in production and processing, which has a great influence on product performance. If the temperature is too low, the plasticization of raw materials is insufficient, and the original crystal phase cannot be fully melted, which will lead to high crystallinity of the tube blank, affecting the transparency and gloss of the film.

If the temperature is too high, the raw materials will be overheated, easy to thermal oxidative degradation, and affect the mechanical properties of the product. The temperature setting of the extruder is greatly affected by the raw material and the machine, and the specific temperature should be flexibly controlled according to the extrusion volume, thermal conductivity of the equipment, raw materials and other factors.


Die head temperature control for pof film production

POF film production uses a tube-sleeved 3-layer or 5-layer co-extrusion die head. The defect of this type of die head is that the two raw material layers penetrate each other and are heated together by the external heating device of the die head. Therefore, the single layer cannot be accurately processed.

The temperature setting of the die head is generally based on the transparency and gloss of the vesicles. The temperature of the die head when the transparency and gloss of the vesicles are high is the best temperature. The higher the temperature of the die head, the higher the strength of the three-layer composite, but the mechanical properties will be adversely affected.


Furnace temperature setting for pof shrink film manufacturing

The POF film production process requires the tube blank to be stretched at a temperature range higher than the softening point and lower than the melting point. The lower the stretching temperature, the better the molecular orientation and the better the mechanical properties of the film. In order to ensure the synchronization of vertical and horizontal drawing of the tube blank, the process requires that the temperature of the tube blank should be 10-20°C lower than the softening point of the tube blank at the bottom of the preheating section, and the temperature of the tube blank can be non-contact at the bottom of the preheating section of the furnace Infrared temperature sensor detection.

After the tube blank is reheated through the extension section, the temperature rises above the softening point of the tube blank, and after the center ring stabilizes, it begins to stretch vertically and horizontally. The lower the furnace temperature is when normal production is guaranteed, the better the mechanical properties of the product will be. As the temperature decreases, the product performance will increase exponentially. In the normal production process, the furnace temperature control should be considered comprehensively according to the equipment condition, production speed and other factors.


Force Field Control

In the production process, the speed of each traction, the speed ratio, and the blowing ratio of each foam are all in the category of force field. The following takes 19µm as an example for a brief description:

Extrusion speed:

Output per minute ÷ cross-sectional area of die opening ÷ melt density = 1.502m/min

Normal winding speed 40m/min

The first traction speed 7.5m/min

According to this production process, the transverse blowing magnification of the first section of the tube blank is 1.2 times, and the drawing magnification is 5 times.

The increase of the bubble ratio will effectively improve the molecular stretching orientation and improve the mechanical properties and thermal shrinkage ability of the film, but it will reduce the sealing performance of the film.

Masterbatch

The smooth opening masterbatch is an indispensable functional additive in the heat shrinking process of POF. After adding this masterbatch, it can prevent the film from sticking during the winding process, and make the film roll more smooth when unwinding and slitting , and make the film have good opening performance during use. The open masterbatch is suitable for adding to the inner and outer layers of the film, and the smooth masterbatch is added to the middle layer of the film, with low consumption, reflecting the characteristics of small body and high energy.