The blown film unit needs to be able to adapt to various plastic materials, such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), etc. Because different raw materials have different physical and chemical properties, for example, PE has better flexibility, PP has higher hardness and transparency, and PVC has better toughness and chemical resistance. A good blown film unit should be able to make appropriate process adjustments based on different raw materials to produce high-quality films.

During the blown film process, temperature is a critical parameter. Different plastic raw materials have different melting temperature ranges, and the temperature requirements vary in different areas of the extruder. For example, in the production of polypropylene film, the feed section temperature of the extruder can be set at 180-200 ℃, the plasticizing section temperature at 200-220 ℃, and the die head temperature at 220-240 ℃. Accurate temperature control can ensure that plastic raw materials are fully melted and evenly extruded, thereby producing high-quality films.

How to choose the suitable mold for Dalian blown film unit?

Consider the types and applications of thin films

Packaging film

If producing films for food packaging, such as regular snack packaging bags, there are certain requirements for the transparency, flexibility, and barrier properties of the films. For this situation, a spiral core rod die is more suitable. Because it can evenly distribute plastic melt and produce thin films with uniform thickness, which helps to improve transparency. Moreover, the film produced by this mold also performs well in terms of flexibility, which can meet the requirements of food packaging for the tactile sensation of the film.

If producing heavy-duty packaging films for industrial products, higher strength and thicker thickness are required. The hanger style die is a good choice, as its width adjustment range is wide and can flexibly adjust the film width according to the packaging size of large industrial products. At the same time, when producing thicker films, it can effectively ensure the reasonable flow of the melt in the mold head, making the performance of the film uniform and the strength meet the requirements.

Agricultural film

For agricultural greenhouse film, the anti-aging property, thermal insulation property and width of the film need to be considered. Due to its flexible width adjustment, the hanger type mold head is suitable for producing wide width greenhouse films. In addition, by selecting appropriate plastic materials to match with the die head, anti-aging agents and other additives can be added to the film, so that the film can better resist the erosion of ultraviolet rays and the natural environment and extend its service life.

The production of plastic film places more emphasis on the strength and toughness of the film to prevent cracking during laying and use. The spiral core rod mold head can ensure uniform thickness of the plastic film, thereby ensuring consistent strength distribution of the film and saving raw material costs while ensuring quality.

Special film

The production of optical films, such as polarizer protective films for liquid crystal displays, requires high precision in film thickness and optical performance. The spiral core rod type die is a choice, which can accurately control the distribution of the melt, achieve micrometer level uniformity in film thickness, and ensure the consistency of optical properties such as transparency and refractive index of the optical film.

For special films with barrier properties, such as high barrier films used for drug packaging, the lotus petal die has advantages. It can better bond multiple layers of different plastic melts, produce composite films with tight adhesion between each layer, improve the barrier effect of the film, and ensure the quality and shelf life of drugs.

Select based on the characteristics of plastic raw materials

Thermosensitive plastic

For heat sensitive plastics such as polyvinyl chloride (PVC), hanger style molds are a better choice. Because the residence time of the melt in this mold is relatively short, it can reduce the risk of plastic degradation or performance changes due to prolonged heating. For example, in the production of PVC cling film, using a hanger type die can improve production efficiency while ensuring the quality of the film.

High viscosity plastic

It is relatively difficult for high viscosity plastic melt to flow inside the mold head, and a good flowability design is required for the mold head. The spiral channel inside the spiral core rod die can guide high viscosity melt to flow uniformly in the circumferential direction. For example, in the production of some high filling plastic films (such as PE films containing a large amount of calcium carbonate fillers), the spiral core rod die can better handle high viscosity melt, making the quality of the film more stable.

Multi layer co extrusion raw material combination

When conducting multi-layer co extrusion blown film, it is necessary to consider the compatibility and flow characteristics between different raw material layers. The lotus petal shaped die performs well in this situation, as it can be designed with reasonable flow channels based on the characteristics of different raw material layers, allowing the molten layers to be uniformly combined at the die outlet. For example, in the production of a three-layer composite film with an outer layer of wear-resistant PP, a middle layer of barrier ethylene vinyl alcohol copolymer (EVOH), and an inner layer of soft PE, the lotus petal mold head can ensure a tight fit between each layer and leverage their respective performance advantages.

Consider the cost and maintenance difficulty of the mold

Cost factors

Generally speaking, spiral core rod die heads are relatively expensive due to their complex structure and high precision requirements. But if high-quality, high value-added films are produced, such as optical films or high-end food packaging films, the quality improvement they bring can offset the higher costs. The hanger style die is reasonably priced and suitable for the production of various conventional films, with good cost-effectiveness. The lotus petal die head is also relatively expensive, especially when used in special processes such as multi-layer co extrusion. However, it has unique advantages in producing special films and improving the quality of composite films. When considering cost, it is necessary to comprehensively evaluate its impact on product quality and added value.

Maintenance difficulty

The internal structure of the spiral core rod die is complex, and cleaning and maintenance are relatively difficult. If there is melt blockage or wear, the repair time may be longer and professional technicians are required. The maintenance of the hanger type die is relatively simple, the flow channel is more intuitive, and it is easier to clean blockages or replace worn parts. The maintenance difficulty of the lotus petal mold is between the two, and attention should be paid to its special structure during maintenance to ensure the normal function of each lotus petal structure and the smooth flow of each layer of channels.

The blown film unit is a commonly used plastic processing equipment, widely used in the plastic packaging industry. The main function of the blown film unit is to blow and expand plastic particles into thin films through heating, extrusion, and cooling processes, and then produce various plastic film products through rewinding, cutting, and other steps, such as bagged film, rolled film, etc.

The multi-layer co extrusion blown film technology is receiving increasing attention. By co extruding multiple layers of plastic materials with different properties in the same blown film unit, composite films with multiple functions can be produced. For example, combining materials with barrier properties with soft packaging materials to produce food packaging films that not only have good oxygen and water vapor barrier functions, but also have flexibility and toughness. This technology can flexibly adjust the raw materials and thickness of each layer according to different application requirements, improving the performance of the film.