Acrylic chemical named poly methyl methacrylate (PMMA). Because PMMA surface hardness is not high, easy to wipe hair, low impact resistance, molding flow performance and other shortcomings, PMMA modification has appeared. Such as methyl methacrylate and styrene, butadiene copolymerization, PMMA and PC blend, etc.

The flow generation ratio of PMMA is lower than PS and ABS, and the melt viscosity is sensitive to the change of temperature. In the molding process, the melt viscosity is mainly changed from the injection temperature. PMMA is an amorphous polymer with melting temperature over 160℃ and decomposition temperature up to 270℃.

1. Treatment of plastics

PMMA has a certain water absorption, its water absorption rate of 0.3-0.4%, and injection molding must be in the humidity below 0.1%, usually 0.04%. The existence of water makes the melt appear bubbles, air lines, transparency and so on. So it has to be dried. Drying temperature 80-90℃, time for more than 3 hours. Recycled material can be used 100% in some cases, the actual amount depends on the quality requirements, usually more than 30%, recycled material should avoid contamination which will affect the transparency and the nature of the finished product.

2. Selection of injection molding machine

PMMA has no special requirements for injection molding machines. Because of its high melt viscosity, it needs a deeper spiral groove and a larger diameter nozzle hole. If the strength of the product is higher, it is necessary to use a larger ratio of length to diameter of the screw to carry out low temperature plasticizing. In addition, PMMA must be stored in a dry hopper.

3. Mold and gate design

Mold temperature can be 60℃-80℃, the diameter of the main channel should match the internal taper, the best Angle is 5° to 7°, if 4mm or more products to injection, the Angle should be 7°, the diameter of the main channel is 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 shall be 6-8mm

For products with wall thickness greater than 4mm, the runner diameter shall be 8-12mm and the depth of the side, fan and vertical sprue shall be 0.7 to 0.9t(t is the wall thickness of the product), and the diameter of the needle sprue shall be 0.8 to 2mm; Use smaller sizes for low viscosity.

The common vent has a depth of less than 0.05 and a width of 6mm, and the demoldingdraft angle is between 30 '-1° and 35' -1° for the cavity part.

4. Melt temperature

It can be measured by air injection method: ranging from 210℃ to 270℃, depending on the information provided by the supplier.

Exit the backseat so that the injection molding machine nozzle away from the main passage bushing, and then manually plasticize injection molding, this is air injection molding.

5. Injection temperature

Rapid injection can be used, but to avoid high internal stress, multi-level injection should be used, such as slow - fast - slow, etc., when injection thick parts, slow speed is used.

6. Retention time

If the temperature is 260 ° C, the maximum retention time cannot exceed 10 minutes; if the temperature is 270 ° C, the maximum retention time cannot exceed 8 minutes.