Crystal cosmetic bottle injection molding production line is very simple. Though the flow rate of acrylic is worse than PS and ABS, and the melt viscosity is more sensitive to temperature changes. During the Cosmetic Bottle injection molding process, we can adjust the injection temperature to find the best melt viscosity. PMMA is an amorphous polymer, which melting temperature is greater than 160°C and the decomposition temperature is up to 270°C.
1. Acrylic Material Processing Before Injection Molding
The acrylic has a certain degree of water absorption about 0.3-0.4%, but the injection molding process needs about 0.1% to 0.04%.
It will causes bubbles, gas lines, and reduced transparency in the melting if the moisture is high. So the acrylic must be dried before injection molding.
Normally, the drying temperature is set between 80 to 90℃, and the drying time is at less 3 hours.
Recycled materials can be used 100% in some cases. The actual percentage depends on the quality requirements, usually about 30%.
Recycled materials should avoid pollution, otherwise it will affect the transparency and the properties of the finished product.
2. How to Select a Right Injection Molding Machine
PMMA has no special requirements for injection molding machines. Because of its high melt viscosity,
It need a screw with deeper groove and a nozzle with larg diameter hole.
A screw with a larger L/D ratio should be used for low-temperature plasticization if the product needs higher strength.
In addition, a hopper dryer should be picked for acrylic cosmetic bottle injection molding.
3. Acrylic Injection Mold
The mold temperature should be set as 60℃- 80℃. The diameter of the main runner should match the inner taper. The best angle is 5° to 7°.
If you want to inject 4mm or more products, the angle should be 7°, and the diameter of the runner should reach 8 to 10mm, the overall length of the gate should not exceed 50mm. For products with wall thickness less than 4mm, the diameter of the runner should be 6-8mm.
For products with wall thickness greater than 4mm, the runner diameter should be 8-12mm. Diagonal, fan-shaped and tabular gate depth should be 0.7 to 0.9t (t is the thickness of the product wall), and the diameter of the needle gate should be 0.8 to 2mm; smaller size should be used for low viscosity.
The common vent hole has a depth of less than 0.05 and a width of 6mm, and the demolding slope is between 30′-1° and 35′-1°30° of the cavity part.
4. Melting temperature
It can be measured by the air injection method: ranging from 210°C to 270°C, depending on the information provided by the supplier.
Withdraw the back seat, make the nozzle of the injection molding machine leave the main runner bushing, and then manually carry out plasticization injection molding, which is air injection molding.
5. Injection temperature
Fast injection can be used, but to avoid high internal stress, it is advisable to use multi-level injection, such as slow-fast-slow, etc. When injecting thick parts, use slow speed.
6. Detention time
If the temperature is 260℃, the residence time should not exceed 10 minutes, if the temperature is 270℃, the residence time should not exceed 8 minutes.
