Polyester resins with particular carbon black as a reheat additive in the production of stretch blow molded bottles and containers

A method of improving the reheat and color value L* of a preform and forming a clear bottle, the method comprising:

• mixing a lamp black carbon black with a first co-polyester resin in molten form to form a lamp black carbon black composition,
• mixing the lamp black carbon black composition and a second co-polyester resin to form a molding composition, wherein the second co-polyester resin does not contain a reheat additive, a colorant or a pigment other than the lamp black carbon black,
• injection molding the molding composition into a mold to form the preform, wherein the preform has a CIE L* of at least 70 and a haze of no more than 7%,
• heating the preform with infra-red heat, then
• stretch-blow molding the infra-red heated preform to form the clear bottle,
• wherein the lamp black carbon black has an average primary particle size of from 106 to 130 nm,
• wherein the lamp black carbon black is present in the clear bottle at a concentration of from 3 ppm to 11 ppm by weight of the first and second resin compositions,
• wherein the temperature of the heated preform during the injection molding is at least 8° C. higher than the temperature of an equivalently heated preform in the absence of the lamp black carbon black, and
• wherein the first and second co-polyester resins comprise 70-95 mol % of reacted units of terephthalic acid and 5-30 mol % of reacted units of isophthalic acid, wherein mol % is based on the total number of mols of dicarboxylic acid units in the second co-polyester resin, and reacted units of polyethylene glycol.