PVC, PET, and PP are prevalent plastic types utilized in plastic thermoforming machine processing. Their disparities in chemical structure and physical properties lead to variations in the entire thermoforming process, ranging from parameter setting to the performance of the final molded products. The detailed differences are as follows:
1. Variations in Processing Temperature Requirements
PVC (polyvinyl chloride) is categorized into rigid and flexible types. Rigid PVC exhibits poor thermal stability and operates within a narrow processing temperature range, typically between 160 and 190°C. When the temperature is too low, the plastic fails to plasticize adequately, resulting in rough surfaces and visible textures on the products. Conversely, if the temperature exceeds the optimal range, PVC decomposes, releasing hydrogen chloride gas, which causes discoloration and degrades product performance.
PET (polyethylene terephthalate) has a relatively high melting point, with processing temperatures usually falling between 250 and 290°C. Within this temperature interval, PET melts and flows smoothly, forming a homogeneous melt. Temperatures below this range impede complete melting, leading to molding difficulties and internal stress in the products. Excessive temperatures, on the other hand, trigger degradation of PET, negatively impacting the strength and transparency of the final products.
PP (polypropylene) requires a lower processing temperature, generally ranging from 160 to 230°C. Its excellent melt fluidity makes it highly sensitive to temperature fluctuations. While it can be rapidly molded at appropriate temperatures, significant temperature variations cause dimensional instability in the products.
2. Divergences in Molding Process Adaptability
In the blister molding process, PVC's remarkable flexibility and plasticity enable it to conform swiftly to the mold surface, facilitating the production of intricately shaped items such as toy casings and packaging boxes. PET, renowned for its high transparency and luster, yields aesthetically pleasing products post - blister molding, making it a preferred choice for manufacturing food packaging boxes, cosmetic packages, and other products with stringent appearance requirements. Owing to its low hygroscopicity and minimal molding shrinkage, PP is well - suited for fabricating blister products that demand high - precision dimensions, like trays for electronic components.
During compression molding, PVC's chemical stability and corrosion resistance make it ideal for producing plates and sheet products that require resistance to chemical corrosion. PET, with its high rigidity and strength, results in compression - molded products with excellent mechanical properties, suitable for manufacturing parts with strict structural strength demands. The high crystallinity and rapid crystallization rate of PP during compression molding enhance production efficiency, rendering it a common choice for manufacturing items such as turnover boxes and bottle caps.
Regarding blow molding, PVC's high melt strength makes it suitable for producing small, thin - walled containers, such as plastic bottles. PET's superior transparency and barrier properties position it as an optimal material for manufacturing beverage bottles and edible oil containers. PP, characterized by its good impact resistance, ensures that blow - molded large - scale containers, such as chemical barrels and water tanks, possess excellent drop - resistance capabilities.
3. Disparities in Product Performance
PVC products offer good electrical insulation and chemical stability. However, plasticizers added to flexible PVC may leach out, compromising the product's environmental friendliness. Moreover, PVC emits toxic gases when burned. PET products feature outstanding mechanical properties, high transparency, and glossiness, along with excellent gas barrier properties, effectively extending the shelf life of food products. Nevertheless, their poor weather resistance makes them susceptible to aging when exposed to outdoor environments for extended periods. PP products are lightweight due to their low density and exhibit good chemical corrosion resistance and heat resistance, allowing for sterilization at temperatures above 100°C. However, their impact resistance deteriorates at low temperatures, making them prone to brittleness.
4. Distinctions in Processing Precautions
When processing PVC, due to its thermal instability, heat stabilizers must be incorporated into the formulation, and strict control over processing temperature and duration is essential to prevent decomposition. Additionally, exhaust gases generated during PVC processing require proper treatment to avoid environmental contamination. For PET processing, raw material drying is crucial because PET readily absorbs moisture, which can lead to defects such as bubbles and silver streaks in the products. After molding, PET products often develop internal stress, necessitating post - processing to relieve it. In the case of PP processing, close attention should be paid to its molding shrinkage rate, and mold dimensions should be carefully designed to ensure product dimensional accuracy. Since PP is prone to oxidation at high temperatures, antioxidants can be added to enhance its thermal stability.
