Knowledge of PMMA injection molding process

- Jul 21, 2017-

Polymethyl methacrylate, acrylic acid and its ester polymerization of the polymer referred to as acrylic resin, the corresponding plastic collectively referred to as polyacrylic plastic, of which the most widely used polymethyl methacrylate. Poly methyl methacrylate abbreviation for the PMMA, commonly known as plexiglass, is so far synthesized transparent material in the texture of the most excellent, the price is more appropriate varieties.

Application:

PMMA is soluble in organic solvents, such as phenol, anisole and so on, through the spin coating can form a good film, with good dielectric properties, can be used as organic FET (OFET), also known as organic thin film transistor (OTFT) dielectric layer The

PMMA resin is non-toxic and environmentally friendly materials, can be used for the production of tableware, sanitary ware, etc., with good chemical stability, and weatherability.

PMMA resin in the broken is not easy to produce sharp debris, the United States, Japan and other countries and regions have made mandatory in the law, primary and secondary schools and kindergarten building glass must use PMMA resin. Across the country to speed up the pace of urban construction, street signs, advertising light boxes and telephone booths, such as a large number of materials used in which a considerable part of the PMMA resin. Beijing Olympic project outdoor color building materials also use a large number of green PMMA resin.

As the surface hardness of PMMA is not high, easy to wipe, low impact resistance, poor flow forming performance and other shortcomings, PMMA modification have emerged. Such as methyl methacrylate and styrene, butadiene copolymerization, PMMA and PC blends. 372 plexiglass is methyl methacrylate and styrene copolymerization derived.

If you add 372 plexiglass in a small amount of nitrile rubber (about 50%) to 373 plexiglass. PMMA flow than the PS, ABS difference, the melt viscosity of the temperature changes are more sensitive, in the molding process, mainly from the injection temperature to change the melt viscosity. PMMA is an amorphous polymer with a melting temperature greater than 160 ° C and a decomposition temperature of 270 ° C.

1, plastic processing

PMMA has a certain water absorption, the water absorption of 0.3-0.4%, while the injection must be below 0.1% of the temperature, usually 0.04%. The presence of moisture causes the bubbles to appear, such as bubbles, wrinkles, and transparency. So it is necessary to carry out drying treatment. Drying temperature 80-90 ℃, the time is 3 hours or more.

Recycled material in some cases can be 100% of the use of the actual weight depends on quality requirements, usually over 30%, recycling materials to avoid pollution or will affect the transparency and the nature of the finished product.

2, injection molding machine selection

PMMA has no special requirements for injection molding machines. Because of its melt viscosity, the need for deeper groove and larger diameter nozzle hole. If the strength of the product requirements are higher, then use a larger aspect ratio of the implementation of low temperature plastic screw. In addition PMMA must use a dry hopper storage.

3, mold and gate design

Mold the temperature can be 60 ℃ -80 ℃, the diameter of the main channel should be combined with the inner taper, the best angle is 5 to 7, to injection 4mm or more products, the angle should be 7, the main channel diameter of 8 to 10mm, The overall length of the gate should not exceed 50mm.

For products with a wall thickness less than 4mm, the diameter of the runner shall be 6-8mm. For products with a wall thickness greater than 4mm, the diameter of the runner shall be 8-12mm in diameter, and the depth of the fan and the plate shall be 0.7 to 0.9t (T is the thickness of the product wall), the diameter of the needle gate should be 0.8 to 2mm; low viscosity should be used in smaller size.

Common vent holes are 0.05 to 0.07 mm deep, with a 6 mm wide stripping angle between 30'-1 cavity sections 35'-130.

4, melt temperature

Available for empty injection measurement: from 210 ℃ -270 ℃ range, depending on the information provided by the supplier may be.

5, injection temperature

Can be used for rapid injection, but to avoid a high degree of internal stress, it is appropriate to use multi-stage injection, such as slow - fast - slow, injection thick pieces, the use of slow.

6, retention time

If the temperature is 260 ℃, the residence time is not more than 10 minutes, if the temperature is 270 ℃, the residence time can not exceed 8 minutes.

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