Thermoplastic resin substrate for curved mirror and method for preparing the same

A thermoplastic resin substrate for a curved mirror, characterized in that:

• the substrate has a length of 300-400 mm, a width of 150-300 mm, and a thickness of 3-6 mm,
• the surface roughness of the substrate is ≤10 nm,
• wherein for the dimensional stability the following applies:
• a) the peak-to-valley (PV) value of the substrate is <25 μm (at 25° C.);
• b) after storage at 100° C. for 4 hours, the peak-to-valley (PV) value of the substrate is ≤25 μm.

A method for preparing a thermoplastic resin substrate for a curved mirror, comprising the following steps:

• A) heating up a mold of an injection molding machine to a temperature in a range of 130-190° C. and closing the mold,
• B) injecting a molten thermoplastic resin into the cavity of the mold, the holding pressure of the screw being in a range of 50-150 bar,
• C) applying a pressure of 300-700 bar to the cavity for a period of 5 to 50 seconds,
• D) stopping applying pressure to the cavity and cooling the mold to a temperature in a range of 60-100° C., wherein, when applying the pressure to the cavity is stopped, the gap between the parting surfaces of the mold cavity is no more than 0.1 mm,
• and
• E) opening the mold and taking out the molded thermoplastic resin substrate, wherein a gap of 0.3-1 mm is left between the parting surfaces of the cavity of the mold prior to applying the pressure to the cavity, and wherein the thermoplastic resin is a mineral-filled polycarbonate material or a mineral-filled polycarbonate-polyethylene terephthalate blend.