Acrylic referred to as PMMA, is a kind of plastic raw materials commonly used in decorations, which has crystal clear and great transmittance, above 92%. Acrylic sheet colored with dye has great color effect. In addition, acrylic material is stable and is easy to be colored and processed. It is usually applied into products like acrylic light boxes, advertising signs, artificial marble and other products with great varieties and wide application ranges. A good injection molding product is a key process because it is directly related to the appearance quality of products. So, what should be considered in acrylic material injection molding, and what are the specific technological processes. Let’s have a look.

1.Handling of plastics
PMMA has a capacity to absorb water, with a water absorption rate from 0.3%-0.4%, while the humidity for injection molding must be lower than 0.1%, usually is 0.04%. The content of water will cause bubbles, gas marks, low transparency on the melt. Thus, the drying temperature must be 80-90℃ for more than 3 hrs. The recycled material can be 100% used. The real volume is determined by the quality, usually can be higher than 30%. It should be avoided the pollution of recycled material as the transparency and quality may be affected.

2. Selection of injection molding machine
PMMA does not have specific requirements for injection molding machines. Due to the high viscosity, it requires deep threaded grooves and larger diameter nozzle holes. If the products have higher requirements for the strength, a larger low-temperature plasticizing of screw with length-diameter ratio is needed. Besides, PMMA must be fed with dried hopper.

3. Mold and gate design
The temperature of mold is 60℃-80℃. The diameter of main runners should fit for the internal taper. The angle of is 5°~7°. If the injection molded products is higher than 4mm, the angel should be 7°. The diameter of main runners is 8-10mm. The overall length of gate should not exceed 50mm. For products of which the wall thickness is lower than 4mm the diameter of runners should be 6-8mm. For products of which the wall thickness is higher than 4mm, the diameter of runner should be 8-12mm. The depth of sector and tab gate is 0.7-0.9t (“t” means wall thickness). The diameter of pin gate is 0.8-2mm. smaller sizes should be selected for the ones with low viscosity.

The common vent holes are within 0.05mm deep and 6mm wide, and the demolding slope is between 30'-1° and 35'-1°30° for the cavity part.

4. temperature of melt
The air injection method can use to measure, from 210℃~270℃, which is determined specifically information provided by suppliers. Pull out the back seat so that the injection molding machine nozzle leaves the sprue bushing, then start injection molding and plasticizing manually. This is air injection molding.

5. temperature of injection molding
High speed injection molding is recommended with multi-stage injection to prevent the generation of high internal stress, such as slow-fast-slow, etc. When it is thick parts, then slow injection is recommended.

6. Residence time
If the temperature is 260℃, the time for residence is no more than 10 minutes. If the temperature is 270℃, the time should not be higher than 8mins.

In addition to the unrivaled high brightness, acrylic also has other advantages, such as good toughness, not easy to damage, strong repairing capacity. Besides, it is easy to clean with the soft foam toothpaste. Its texture is soft, so there is no chilly feeling in winter. The bright colors can meet the individual pursuit of different tastes.