PP high transparency sheet extrusion line

PP high transparency sheet extrusion line is mainly used to produce polypropylene (PP) high transparency sheet. Due to its good transparency, chemical resistance, toughness and recyclability, it is widely used in food packaging, medical supplies packaging, electronic product protection, printing substrates and other fields.

The following is an overview of the basic components and workflow of the production line:

Raw material preparation

First, use dry PP resin particles as raw materials. These raw materials need to undergo strict drying treatment to remove moisture and avoid bubbles during processing, which will affect the transparency and quality of the sheet.

Extruder

The mixed materials are fed into a single-screw or twin-screw extruder through a feeding system. The extruder melts the granular materials into a uniform melt through heating and the shearing section, plasticizing section, and conveying section of the screw.

Filtration system

In order to ensure the transparency and purity of the sheet, the melt will pass through a precision filter after extrusion to remove possible impurities, such as unmelted resin particles or foreign matter.

Metering pump

The filtered melt enters the metering pump. By accurately controlling the flow rate of the melt and working in conjunction with the main machine, the molten material can be effectively and stably delivered to the sheet forming die, playing a key role in adjusting the thickness of the sheet.

Mold and die

After the molten PP material comes out of the extruder, it passes through a specially designed mold and die to form a sheet shape with the required thickness and flatness, and control the width of the product. For high-transparency sheets, the design of the mold and die is particularly critical, ensuring that the material flows evenly and no bubbles are generated to achieve high transparency requirements.

Cooling and shaping system

The hot melt sheet coming out of the die head passes through the mold or die and immediately enters the calender for rapid cooling and shaping to adjust the thickness and width of the extrusion sheet.  The calender controls the roller temperature to cool the water through the water tower (or chiller). Since PP has a relatively large shrinkage, it must be completely cooled before winding to eliminate internal stress, so that the product can reach the standard and will not shrink after being left for a period of time after winding.

Traction and trimming device

After cooling and shaping, the sheet passes through the trimming device and is cut according to the required size. The required width of the sheet is adjusted and the unqualified edges on both sides are cut off. The traction device and the calender are synchronously linked, which can effectively control the production of the sheet, control its speed and tension, and maintain the flatness and thickness uniformity of the sheet.

Winding system

Finally, the cut sheets are wound onto the reel. The reel is controlled by a servo motor with constant tension, which can ensure the neatness of the edges of the coils. The winding tension of the inner and outer coils is the same, so the coils will not be tight inside and loose outside, which is convenient for subsequent packaging, storage and transportation.

If you want to make slicing, folding, printing and packaging, you need to add a slicer at the back end. In the production process, you also need to add a laminating device to laminar the upper and lower sides of the sheet before slicing (the film can be torn off by hand) to protect the sheet during transportation without damaging the surface of the sheet.

Throughout the production process, temperature control, material ratio, cooling efficiency and mechanical precision are key factors affecting the quality of PP high-transparency sheets.  In addition, to meet different application requirements, the production line may also be integrated with an additive feeding system to add antistatic agents, lubricants or other modifiers to improve sheet performance.