PURPOSE: To prevent the whitening of a plastic lens and the deterioration in optical function due to coloring and the like of a cooling liquid even when used for a long time by using a cooling liquid comprising ethylene glycol, triethylene glycol as well as glycerine.
CONSTITUTION: A cooling liquid comprising ethylene glycol, triethylene glycol, and glycerine, is used. Since the viscosity of ethylene glycol is low, while hygroscopicity thereof is large, bad effect such as whitening of lens is expected when it is used individually. The hygroscopicity of triethylene glycor is low for polyor, however, when it is used individually, a plastic lens is whitened, since it has affinity with plastic. Since glycerine is high in the refractive index, it is useful because the reflection loss at the boundary surface between the lens that is in contact with a cooling liquid and the glass of a cathode-ray tube becomes small, however, viscosity is extremely high. When these three materials are mixed with each other into a ternary mixed liquid, the balance between hygroscopicity and affinity becomes good, and excellent low hygroscopicity is obtained, and the whitening of plastic lens or the deterioration in optical function due to the coloring and the like of the cooling liquid is thus prevented.
KANEGA FUMIAKI
MURANAKA MASAYUKI
YOSHIZAKI ISAO
HITACHI LTD