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Introduction of PMMA Injection Molding Process

Introduction of PMMA Injection Molding Process

PMMA is commonly known as plexiglass, acrylic, etc. The chemical name is polymethylmethacrylate. Due to the PMMA's shortcomings such as low surface hardness, easy scratching, low impact resistance, poor molding fluidity, the modification of PMMA injection molding has appeared one after another.

For example, the copolymerization of methyl methacrylate with styrene and butadiene, the blending of PMMA and PC, etc. 372 plexiglass is obtained by copolymerizing methyl methacrylate and styrene. If a small amount of nitrile rubber (about 50%) is added to 372 plexiglass, it can become 373 plexiglass.

The flow of PMMA is worse than that of PS and ABS, and the melt viscosity is more sensitive to temperature changes. During the PMMA injection molding process, the melt viscosity is changed mainly from the injection temperature. PMMA is an amorphous polymer with a melting temperature greater than 160°C and a decomposition temperature up to 270°C.

1. Plastic processing

PMMA has a certain degree of water absorption, with a water absorption rate of 0.3-0.4%. However, the injection molding must be at a temperature below 0.1%, usually 0.04%. The presence of moisture causes bubbles, gas lines, and reduces transparency in the melt. So it needs to be dried. The drying temperature is 80-90℃, and the process of drying takes more than 3 hours.  Recycled materials can be used 100% in some cases. The actual amount depends on the quality requirements, which is usually beyond 30%. Recycled materials should be avoided from pollution, otherwise the transparency and the properties of the end products will be influenced.

2. The temperature of the melt

It can be measured by air injection method: 210℃-270℃, depending on the materials provided by the supplier.

3. Injection temperature

Fast injection is adopted, but you should avoid causing high internal stress during the process. Using multi-level injection, such as slow-fast-slow, is much better. When it comes to thick parts, please inject with a slow speed.

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