Casting process of acrylic sheet

Acrylic sheet (plexiglass, PMMA) can be divided into two types according to the production process: casting sheet and extrusion sheet. Next, let's take a closer look at the casting process of acrylic sheet.

Cast Acrylic Sheet process: Pour liquid MMA (methyl methacrylate) monomer into the mold and cure it by heating or ultraviolet light.

1. Specific steps:

(1) Raw material preparation

MMA monomer: high-purity methyl methacrylate (a small amount of plasticizer, UV stabilizer or dye may be added).

Initiator: Such as benzoyl peroxide (BPO) or azobisisobutyronitrile (AIBN), used to trigger the polymerization reaction.

Mold: Usually a glass or metal flat plate with a highly polished surface to ensure the transparency of the sheet.

(2) Mixing and degassing

Mix the MMA monomer with the initiator and additives evenly, and remove bubbles by vacuum degassing to avoid defects in the finished product.

(3) Mold filling

The mixed liquid is injected into two parallel molds, and the molds are sealed with rubber pads around to control the thickness (adjusted by gaskets).

(4) Polymerization reaction

Water bath heating method:

The mold is immersed in a water bath and the temperature is gradually raised to 40~60℃ to initiate prepolymerization (partial polymerization to form a viscous slurry), and then the temperature is raised to 80~100℃ to complete complete polymerization. (Note: Low temperature and slow polymerization can reduce internal stress and improve sheet performance)

UV curing method:

Applicable to thin sheets, and polymerization is accelerated by ultraviolet irradiation.

(5) Cooling and demoulding

Cool slowly to room temperature to avoid cracking or stress concentration caused by sudden cooling.

After demolding, remove the edge burrs to obtain the original casting plate.

(6) Post-treatment

Heat treatment: Annealing to eliminate internal stress (such as constant temperature treatment at 60℃ for several hours).

Surface treatment: Polishing, cutting or CNC machining to required size. 

2. Casting process characteristics

(1) High optical performance: light transmittance ≥ 92%, comparable to glass, and no crystal points or impurities. It has a wide range of applications in optics, lighting and other fields.

(2) Flexible thickness: Ultra-thick plates ranging from 1 mm to 300 mm can be produced (extrusion process is usually limited to less than 10 mm).

(3) Excellent weather resistance: high molecular weight, UV resistance, yellowing resistance, suitable for outdoor use (such as billboards, swimming pool windows).

(4) Processing friendliness: The edge still maintains high transparency after cutting, engraving and polishing, which is suitable for fine craftsmanship.

(5) High stiffness and strength: the casting process can make acrylic sheets have a higher molecular weight, thereby improving their stiffness and strength, so that they can withstand greater external forces without deformation or cracking.

(6) Complete specifications: Acrylic sheets of various thicknesses, sizes and shapes can be produced according to different needs and mold designs to meet the usage requirements of different fields and industries.

(7) Flexible color and surface texture: During the casting process, acrylic sheets of various colors can be produced by adding different pigments and masterbatches; at the same time, through the design and production of molds, acrylic sheets can be given various surface textures and patterns, such as frosted, embossed, pearlescent and other effects.