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2025
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From Parameters to Finished Products—The 3 Essential Raw Material Knowledge Areas Every Sheet-Machine Operator Must Master
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Just starting out in the plastic packaging industry—haven't you found yourself still a bit unsure about processing different plastic materials? Even though they’re all used to make sheets, the temperature and screw speed settings required for PP, PS, PET, and PE are vastly different, and the resulting product characteristics vary dramatically as well.
Today, we’ll walk you through, in one stop, the four most commonly used sheet materials in the plastic packaging industry—from temperature control and parameter tips during processing, to the hardness and transparency of the finished products, all the way to the everyday disposable items we encounter every day—covered thoroughly! Newcomers, save this article—it’ll help you avoid unnecessary detours during processing and adjustment!
I. Polypropylene (PP): The “Takeout Marvel” with Temperature Resistance and Durability
What should I pay attention to when processing?
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Temperature control is crucial: The melting temperature of PP is 160–170℃. The barrel should be divided into three temperature-controlled zones (180–190℃ / 200–210℃ / 210–220℃), and the die head should be maintained at 190–200℃. If the temperature is too high, yellowing is likely to occur; if it’s too low, surface blemishes may appear. Precise control is essential.
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No need to worry about the raw materials: They have an extremely low water absorption rate—just bake them at 80–90℃ for 1–2 hours if they get damp, making them easy to handle even for beginners.
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The parameters must match: screw rotation speed of 30–60 r/min, traction speed synchronized with the rotation speed, and die gap of 0.8–2.0 mm to ensure uniform sheet thickness.
Does the finished sheet look like this? It’s relatively hard yet highly resilient and doesn’t easily crack even after repeated bending. Common thickness ranges from 0.2 to 1.5 mm. Its natural color is semi-transparent with a matte finish; adding additives can make it fully transparent.
Everyday applications you can encounter The square, compartmentalized lunch boxes for takeout, the sturdy soup bowls designed for packing hot soups, and the rigid straws that don’t easily bend—these are all made from PP sheets! They have excellent temperature resistance and can even be microwaved, making them truly “essential tools for takeout.”
II. Polystyrene (PS): The “beauty icon” that’s transparent and fragile
What should I pay attention to when processing?
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Don't set the temperature too high: The melting temperature of PS is 100–120℃, while the barrel temperature should be maintained at 140–150℃ / 160–170℃ / 170–180℃, and the die temperature at 160–170℃. If the temperature exceeds 200℃, the material will decompose, emit an unpleasant odor, and develop scorch marks.
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Dry promptly: Although the water absorption rate is low, in humid environments, bake at 70–80℃ for 2–3 hours to prevent defects in the sheets.
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The rotational speed should be slowed down: a screw speed of 20–40 r/min is sufficient. If the speed is too high, excessive shear heat can easily cause degradation. Only a stable drawing speed can prevent cracking.
Does the finished sheet look like this? It has extremely high hardness but is highly brittle—breaks easily upon impact. Commonly used thickness ranges from 0.1 to 0.8 mm, primarily in thin sheets, with a transparency exceeding 90%, as smooth and clear as glass.
Everyday applications you can encounter ： The transparent cake-cutting trays from bakeries, the small tasting cups used for supermarket promotions, and the clear packaging boxes for sliced fresh fruit—all are the work of PS. They’re visually appealing and low-cost, but they’re a bit “delicate” and easily damaged by collisions.
3. Polyethylene terephthalate (PET): The high-end, impact-resistant “drink favorite”
What should I pay attention to when processing?
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The temperature must be high enough: The melting temperature of PET is 250–260℃, with the barrel set at 230–240℃ / 250–260℃ / 260–270℃, and the die at 250–260℃. If the temperature is too low, the melt will not be uniformly distributed and may stratify; if it’s too high, the material is prone to yellowing and degradation.
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Drying is crucial: If the water absorption rate is high, you must bake at 120–140℃ for 4–6 hours; otherwise, the sheets will be riddled with bubbles and completely unusable.
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Proper setting is essential: Screw rotation speed, 25–50 r/min; hot setting at a draw roller temperature of 80–100℃; die gap precisely adjusted to 0.5–1.2 mm—ensuring the sheet is both smooth and stable.
Does the finished sheet look like this? High hardness and excellent toughness, more shatter-resistant than PS; commonly used thickness ranges from 0.15 to 1.0 mm, with medium-thin sheets being the most prevalent. Its transparency is second only to PS, and it boasts exceptionally high surface gloss.
Everyday applications you can encounter ： The transparent plastic cups used in milk tea shops, the high-end takeout boxes from sushi restaurants, and the blister packs for strawberries in supermarkets—all are made from PET sheets. They not only showcase the food’s visual appeal but also offer excellent impact resistance and are shatterproof, making them the ideal choice for premium packaging.
The above three ingredients cover most scenarios involving single-use plastic packaging. You can adjust the parameters accordingly based on your actual processing needs. If you encounter any specific issues, feel free to leave a comment in the discussion section—we’re happy to exchange ideas and keep improving together!
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