PURPOSE: To prevent the optical performance of a plastic lens from being deteriorated even if it is used for the long period of time by using refrigerant in which diethylene glycol, glycerine and ethylene glycol are specified by weight.
CONSTITUTION: Refrigerant for cooling a cathode ray tube is used, which is composed of 20 to 40% diethylene glycol by weight, 20 to 40% glycerine by weight and 20 to 60% ethylene glycol by weight. In mixed solution of 3 constituents, that is, diethylene glycol, glycerine and ethylene glycol, when the amount of diethylene glycol is less than 20% by weight, a plastic lens is whitened because of moisture absorption, and when diethylene glycol is equal to or more than 40% by weight, the lens is apt to be whitened because of an increase in affinity of refrigerant with the plastic lens. When diethylene glycol is used in a range between 20% and 40% by weight, hygroscopic property is balanced with affinity, excellent optical performance can thereby be maintained even if it is used for the long period of time.
KANEGA FUMIAKI
MURANAKA MASAYUKI
YOSHIZAKI ISAO
HITACHI LTD