Stretch Film

Stretch film, also known as stretch film and heat shrink film, has undergone significant advancements in China over the years. Initially produced using PVC as the base material and DOA as the plasticizer and self-adhesive function, the industry faced challenges such as environmental concerns, high costs, poor stretchability, and limited unit packaging area compared to PE.

As a result, the production of PE stretch film emerged around 1994-1995, gradually replacing PVC. PE stretch film initially utilized EVA as the self-adhesive material but faced issues related to cost and odor. Subsequently, the industry saw the development of self-adhesive materials such as PIB and VLDPE, with the base material shifting towards LLDPE, including variations like C6, C8, and metallocene PE (MPE). The evolution of LLDPE stretch films transitioned from blown films to the casting method for better uniformity, high transparency, and suitability for pre-stretching requirements.

The three-layer co-extrusion structure became more favorable due to wider material selection, lower formula costs, and increased efficiency. Essential characteristics of stretch films include high transparency, longitudinal elongation, yield point, tear strength, and puncture performance, with classifications like PE stretch film, stretch stretch film, PE slit stretch film, and more. The primary principle behind stretch film is to utilize its winding force and retractability to securely bundle products, ensuring unitization, primary protection, compression fixation, and cost savings while enhancing packaging efficiency and reducing labor intensity.

The production process conditions involve controlling melt temperature, cooling roller temperature, and winding tension to optimize film quality and create firm packaging. The achievement of viscosity, through methods like adding PIB or VLDPE, plays a crucial role in ensuring the proper adherence of film layers, while storage conditions and temperature considerations impact the film's effectiveness post-stretching. Overall, the continuous innovations in stretch film production in China have not only addressed environmental concerns and cost efficiency but also enhanced packaging performance and versatility across various industries.

sPolyethylene (PE) encompasses various generations of industrialized polyethylene developed over the years, beginning in 1939 with high-pressure polyethylene (low-density polyethylene) and progressing to low-pressure polyethylene (high-density polyethylene) in 1953, linear low-density polyethylene (LLDPE) in 1977, ultra-low density polyethylene (VLDPE) in 1984, ultra-high molecular weight polyethylene (UHMWPE) in 1958, and metallocene polyethylene (MPE) in the 1990s.

These variations of PE involve the addition of small amounts of 4- or 8-carbon alpha olefin as comonomers during production, which helps retain many of PE's characteristics. Low density polyethylene (LDPE) is a translucent crystalline polymer known for its density of 0.91-0.925g/cm³, non-toxic nature, excellent transparency, heat sealability, and moisture resistance, making it ideal for low-temperature frozen packaging and moisture-resistant packaging.

However, LDPE's gas barrier is weak, limiting its utility with various gases, and while it offers some resistance to grease and organic solvents, it falls short compared to polypropylene. LDPE is flammable and needs careful handling to prevent static electricity issues during processing. On the other hand, medium density polyethylene (MDPE) shares LDPE's properties but with a higher density (0.926-0.94g/cm³) and increased crystallinity (70%-80%), resulting in higher melting temperature and product strength.

Transitioning to high-density polyethylene (HDPE) with a density of 0.94-0.965g/cm³ introduces superior rigidity, toughness, mechanical strength, solvent resistance, and stress crack resistance compared to LDPE, making it suitable for applications like garbage bags due to its high strength. As these different types of polyethylene each offer unique characteristics and applications, careful selection based on specific requirements is crucial for optimal performance in various industries.