Method:

The rheological property of PET in molten state is good, and the influence of pressure on viscosity is greater than that of temperature. Therefore, the fluidity of melt is mainly changed from pressure. The common shower gel bottle shampoo bottle, also known as PET bottle, is made of PET. PET, the scientific name of which is polyethylene terephthalate, is a kind of thermoplastic (thermoplastic means that plastic can melt when heated and harden when cold), which is commonly used in daily plastic bottle packaging. This characteristic makes the PET material reversible, that is, it can be repeatedly heated, remolded and repeatedly cooled.

1, plastic processing

Because PET macromolecules contain fatty groups and have certain hydrophilicity, pellets are sensitive to water at high temperature. When the water content exceeds the limit, the molecular weight of PET decreases during processing, and the products become colored and brittle. Therefore, the materials must be dried before processing, and the drying temperature is 150℃ for more than 4 hours, generally 170℃ for 3-4 hours. You can check whether the material is completely dry by aerial shooting.

2. Selection of injection molding machine

Because the stable time of PET after melting point is short and the melting point is high, it is necessary to choose an injection system with more temperature control sections and less self-friction heat generation during plasticization, and the actual weight of the product should not be less than 2/3 of the machine injection quantity. Based on these requirements, Ramada has developed a small and medium-sized series of special plasticizing systems for PET in recent years. The clamping force should be more than 6300t/m2.

3, mold and gate design

Generally, PET bottle blank is formed by hot runner mold, and it is best to have a heat insulation board between the mold and the template of injection molding machine, with a thickness of about 12mm, and the heat insulation board can certainly withstand high pressure. Exhaust must be sufficient to avoid local overheating or fragmentation, but the depth of the exhaust port should generally not exceed 0.03mm, otherwise it is easy to produce flash.

4. Melting temperature

It can be measured by aerial shooting. 270-295℃, and the enhanced grade GF-PET can be set to 290-315℃.

5. Injection speed

Generally, the injection speed should be fast to prevent premature solidification during injection. But too fast and high shear rate make the material fragile. Shooting is usually completed within 4 seconds.

6. Back pressure

The lower the better, so as to avoid wear and tear. Generally not more than 100bar. Usually do not need to use.

7. Retention time

Do not use too long residence time to prevent the molecular weight from decreasing. Try to avoid temperatures above 300℃. If the downtime is less than 15 minutes. Only aerial shooting is needed; If it exceeds 15 minutes, clean it with viscosity PE, and reduce the barrel temperature to PE temperature until it is restarted.

8. Matters needing attention

If the mold temperature is not well controlled or the material temperature is not properly controlled, it is easy to produce "white fog" and is opaque. The mold temperature is low and uniform, the cooling speed is fast, and the product is transparent with less crystallization.

Advantages:

① It has good mechanical properties, the impact strength is 3~5 times that of other films, and the folding resistance is good. ② Oil resistance, fat resistance, dilute acid resistance, dilute alkali resistance, and resistance to most solvents. (3) It has excellent high and low temperature resistance, and can be used in the temperature range of 120℃ for a long time, 150℃ and -70℃ for a short time, with little influence on its mechanical properties. ④ The permeability of gas and water vapor is low, and it has excellent gas, water, oil and odor resistance. ⑤ High transparency, blocking ultraviolet rays and good gloss. ⑥ Non-toxic, tasteless, good hygiene and safety, and can be directly used for food packaging.