| 摘要 |
<p>PURPOSE:To make a refractive index of a boundary be small and to enlarge its contrast so that there is no danger of breaking a projection tube by using 1.3-butylene glycol as a liquid for cooling the projector. CONSTITUTION:As a cooling liquid A, 1.3-butylene glycol is used in a cooling chamber 2d. A liquid in which ethylene glycol of 50 wt% or less is mixed with 1.3-butylene glycol, or also a liquid in which glycerine of 30 wt% or less is mixed with 1.3-butylene glycol, is used for this cooling liquid A. Hence, a refractive index R1 of a boundary surface between a front of a projection tube 1 and the cooling liquid A becomes 0.110%. The refractive index R2 of a boundary surface between a plastic lens 11 and the cooling liquid A becomes 0.302%. Therefore, the whole refractive index becomes 0.142%, which is half or less of the conventional one, so that a contrast by the projection tube 1 can be much improved. When 1.3-butylene glycol is used, because of very small vapor pressure in itself, the vapor pressure in the cooling liquid A can be made small so that projection tube 1 and the lens 11 can be prevented from being broken due to its pressure.</p> |
