Compositions – Vaporization – or expansion – refrigeration or heat or energy...
Reexamination Certificate
2000-05-26
2003-01-14
Einsmann, Margaret (Department: 1751)
Compositions
Vaporization, or expansion, refrigeration or heat or energy...
C165S104110, C348S749000, C348S776000, C348S805000, C348S748000
Reexamination Certificate
active
06506317
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a novel cooling medium and a cooling device using the same that is used mainly for the purpose of cooling the projector-type cathode-ray tube in a projector television.
2. Description of the Prior Art
The optical equipment utilizing electron beams generally accompanied by heat generation and the performance of optical equipment is often adversely influenced by the generated heat. The heat generation in the projector-type cathode-ray tube of projector television is very serious, so that its influences must be brought under deliberation.
That is, in the projector-type cathode-ray tube of projector television, highly bright optical images can be obtained by intensifying the energy of electron beams applied to a fluorescent substance. The high energy electron beams inevitably produce Joule heat simultaneously with the conversion into light. The thermal conductivity of front glass panel that is coated with a fluorescent substance, is low. Because the release of heat is not so large in the middle part of panel, the temperature rise in that part is especially serious. Therefore, the phenomenon called thermal extinction is caused to occur to reducing the luminous intensity of fluorescent substance. To avoid this, cooling operation using a cooling medium is often carried out.
The cooling medium for a projector-type cathode-ray tube of projector television is sealed into the space between glass-made cathode-ray tube and a plate or a lens made of glass or plastic. This cooling medium is generally circulated by natural convection.
Accordingly, in order to allow this natural convection to proceed smoothly within a fluid-tight space, it is important that the cooling medium is low in viscosity.
Furthermore, in order to project clearly the image formed on a fluorescent surface of a cathode-ray tube to a screen without the loss of picture quality, it is also important that cathode-ray tube, cooling medium and lens do not absorb visible light rays (wave length: 400 to 700 nm) that pass through them and that refractive indexes of all the three materials are close to one another. If the difference in refractive indexes is large, multiple reflection is caused by the difference of refractive indexes at the boundary surface, which causes the deterioration of projected images.
Therefore, in order to obtain satisfactory images, the refractive index of cooling medium is required to be in the range between the refractive index of glass and that of plastic materials.
As the plastic materials, the following ones are preferably used. Polymeric materials of PMMA (polymethyl methacrylate), PC (polycarbonate), PS (polystyrene), CR-39 (diethylene glycol bisallylcarbonate), AS (acrylonitrile-styrene copolymer), MS (methyl methacrylate-styrene copolymer) and TPX (poly(4-methylpentene-1)) are generally used.
Among them, the most preferable material is PMMA, especially the copolymer of methyl methacrylate with a comonomer such as &agr;-methylstyrene, maleic anhydride or its imide, or an alicyclic methacrylic ester is desirable because it is excellent in thermal stability and is most suitable for making projection lenses. The refractive index of this thermal-resistant PMMA is 1.51.
Meanwhile, concerning optical glass materials, various materials having refractive indexes of 1.47 to 1.95 are used for various parts. Among them, borosilicate crown grass having them, borosilicate crown glass having the highest transmittance is used typically for lenses, which has a refractive index of 1.52.
For the above reasons, the refractive index of a cooling a medium used for projector-type cathode-ray tube of projector television is desirably in the range of 1.51 to 1.52.
Among the compounds used as the cooling medium, the refractive indexes of aliphatic hydrocarbons are considerably lower than the refractive index of 1.51 to 1.52 that is required of the cooling medium.
For raising the value of refractive index of aliphatic hydrocarbon, it is considered to introduce a cyclic moiety of alicyclic structure or aromatic structure or double bond into the compound. However, the mere introduction of a cyclic structure is insufficient in order to raise the refractive index. In addition, it causes the increase in the number of carbon atoms and increased viscosity of the cooling medium, which lowers the cooling effect under natural convection. Accordingly, the cooling medium treated with such a measure is not suitable. Meanwhile, if a double bond or an aromatic structure is introduced into a compound, the solvent power of the compound is increased and it becomes liable to dissolve plastic materials, so that the reaction product is not suitable either as a cooling medium.
In the conventional art, as the cooling oil used for a cooling device of projector-type cathode-ray tube, a compound having at least two carbon rings and a degree of aromaticity of 30% or less is proposed in Japanese Laid-Open Patent Publication No. Hei 9-176624. There is also proposed that the degree of aromaticity is lowered in order to reduce solvent power in Japanese Laid-Open Patent Publication No. Hei 9-286977. However, as described above, the compound having an aromatic ring is high in solvent power, so that problems are caused in that it dissolves or swells plastic lenses and other parts. Furthermore, in order to lower the degree of aromaticity, the introduction of an alicyclic structure is generally required. However, the lowering of refractive index is caused and the difference in refractive indexes between the cooling medium and glass or plastic material becomes large, so that the quality of the image is impaired.
Furthermore, as described in the foregoing passages, the projection-type cathode-ray tube is designed to produce optical images of high luminance by enhancing the energy of electron beams. In the case that it is not cooled in practical operation, the glass-made front panel that is coated with a fluorescent substance is heated to temperatures as high as 120° C. Therefore, in view of safety, the cooling medium must be high in boiling points, with a flash point of 120° C. or above, and is preferably fire retardant.
As described above, the problem to be solved by this invention is to propose a cooling medium and a cooling device for optical equipment using the same. The cooling medium must have a suitable refractive index, be free from the problem of dissolving or swelling plastic lens and other machine parts, have a flash point of 120° C. or above, and be preferably fire retardant.
BRIEF SUMMARY OF THE INVENTION
The present inventors have carried out extensive investigation in order to develop a cooling medium that can meet the required criteria, that is, it has a refractive index that is quite close to those of glass and plastic lenses, it neither dissolves nor swells plastic lenses, and the cooling effect thereof is high due to its low viscosity. As a result, they have found out that hydrocarbons having specific structures can attain the above objects, thereby accomplishing the present invention.
It is, therefore, the primary aspect of the present invention to provide a cooling medium for an optical equipment having a flash point of 120° C. or above and a melting point of −20° C. or below, which cooling medium comprises a cyclic aliphatic hydrocarbon having at least one cross linkage.
A second aspect of the present invention relates to a cooling medium for optical equipment as mentioned in the primary aspect, which is characterized in that the cyclic aliphatic hydrocarbon having at least one cross linkage is at least one member selected from the group consisting of compounds having 13 to 18 carbon atoms as represented by the following general formulae (I) to (IV).
in which each of R
1
to R
3
denotes a hydrogen atom or a methyl group, and R
4
denotes an alkyl group having 2 or 3 carbon atoms.
A third aspect of the present invention relates to a cooling device for optical equipment, in which the space between a pair of transparent optical elements is filled with a c
Hoshino Hiroyuki
Kiyota Takashi
Einsmann Margaret
Hollander Law Firm, P.L.C.
Nippon Petrochemicals Company Limited
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