Transparent polyester film with low visible light transmittance and high infrared-blocking rate and method for making the same

A method for making a transparent polyester film with low visible light transmittance and a high infrared-blocking rate as well as has a common film thickness ranged from 12 to 75 μm, comprising the steps of:

• a) preparing a nanoparticle-based thermal insulation slurry with a viscosity of 50-200 cps, wherein the thermal insulation slurry comprises the following ingredients a1)-a3) to add up to 100%:
• a1) 10-50 wt % of thermal insulation particles, based on the total weight of the thermal insulation slurry;
• and the thermal insulation particles having a chemical formula of CsXNYWO3-ZClC with an average particle size of 10-90 nm,
• wherein Cs is cesium;
• N is tin (Sn), antimony (Sb), or bismuth (Bi);
• W is tungsten;
• O is oxygen;
• and X, Y, Z, and C are positive numbers satisfying the following conditions:
• X≦1.0;
• Y≦1.0;
• Y/X≦1.0;
• Z≦0.6, and C≦0.1;
• a2) 30-70 wt % of ethylene glycol, based on the total weight of the thermal insulation slurry;
• and
• a3) 5-40 wt % of a dispersing aid, based on the total weight of the thermal insulation slurry;
• wherein the dispersing aid is one or more selected from the group consisting of an anionic dispersant, a non-ionic dispersant and a polymeric dispersant;
• b) preparing a nanoparticle-based black pigment slurry with a viscosity of 30-120 cps, wherein the pigment slurry comprises the following ingredients b1)-b3) to add up to 100%:
• b1) 5-25 wt % of carbon black particles with an average particle size of 20 -80 nm, based on the total weight of the pigment slurry;
• b2) 40-75 wt % of ethylene glycol, based on the total weight of the pigment slurry;
• and
• b3) 10-50 wt % of a dispersing aid, based on the total weight of the pigment slurry;
• wherein the dispersing aid is one or more selected from the group consisting of an anionic dispersant, a non-ionic dispersant and a polymeric dispersant;
• c) making polyester resins by steps of:
• c1) providing ethylene glycol monomers and terephthalic acid or dimethyl terephthalate as polymerization materials, and reacting 5-40 wt % of the prepared nanoparticle-based thermal insulation slurry of step a) and/or 0.005-0.1 wt % of the prepared nanoparticle-based black pigment slurry of step b) with the polymerization materials, by weight of the polymerization materials respectively;
• c2) performing esterification at 250-285° C. for 100-140 min, and effecting pressure reduction for 30-45 min after the esterification is completed;
• and
• c3) performing polycondensation at about 260° C. for 160-240 min in the presence of an antimony or titanium catalyst to produce a molten mass of polyester and a byproduct, removing the byproduct by refinery distillation, cooling the molten mass of polyester, and cutting the cooled molten mass of polyester into polyester resins;
• and
• d) extruding the polyester resins at 270-290° C. to form a transparent polyester film whose physical properties feature a low visible light transmittance of 5-50% according to the JIS K7705 testing standard, a high infrared-blocking rate of at least 90% according to the JIS R3106 testing standard, and a haze level lower than 1.5% according to the JIS K7705 testing standard..