1. Field of the Invention
The present invention relates to a reflection mirror of a projection television and a fabrication method thereof, and more particularly, to a reflection mirror of a projection television and a fabrication method thereof in which a frame for supporting a reflection film placed on an optical path of the projection television is improved to realize a more definitive picture quality.
2. Description of the Related Art
A projection television is provided, between a projection light source and a screen, with a reflection mirror so as to reduce the overall volume. Images projected from the projection light source are reflected by the reflection mirror and displayed on the screen in a size that is greater than the original image size.
In particular, the reflection mirrors can be classified into a glass type reflection mirror formed of glass and a film type reflection mirror formed from a film obtained by fixing a soft reflection film with a predetermined flatness to the frame.
Although the glass type reflection mirror shows outstanding flatness and endurance characteristics, it is not used any more due to its disadvantages such as heavy weight, danger of fracture and high costs. Recently, the film type reflection mirror is being widely used.
FIG. 1 is a sectional view of a conventional projection television.
Referring to FIG. 1, a projection television 1 includes a projector serving as a light source for projecting a projection light, a reflection mirror 20 for reflecting the projected light, and a screen 45 on which the projected light is incident to form a picture.
FIG. 2 is a perspective view of a conventional reflection mirror.
Referring to FIG. 2, a conventional reflection mirror 20 includes a trapeziform frame 22 in which the upper side is shorter than the lower side, and a reflection film 21 formed on the frame in a state that a tight tension is maintained on the upper surface of the frame.
The reflection film 21 generally includes a thin metal film with an outstanding reflection performance, and a resin layer having a superior transparency performance and for maintaining the flatness of the thin metal film and completely reflecting an incident light.
The frame 22 is shaped to have a strength enough to maintain the tension of the reflection film and to satisfy a minimum weight condition.
In the meanwhile, considering the characteristic of the reflection surface of the reflection mirror 20, it is most important to maintain the flatness of the reflection film 21. In case the flatness of the reflection mirror 20 is not perfect, the image displayed on the screen seems curved or distorted abnormally.
Then, the conventional reflection mirror 20 does not have an enough strength for the frame 22. Hence, in case the conventional reflection mirror 20 is continuously used, a dull curved face or a wrinkle is formed at the conventional reflection mirror 20, so that images formed on the screen are frequently distorted.
In particular, in case the temperature variation of a place where the projection television is positioned is serious, a wrinkle is generated at the reflection film 21 due to a difference in the thermal expansion coefficient between the frame 22 made of metallic aluminum (Al) and the reflection film 21 made of resin. For instance, when a surrounding temperature is low, a contraction amount of the reflection film 21 is larger than that of the frame 22, so that the tension of the reflection film 21 is not maintained at the same level as the tension of when it was fabricated.
FIGS. 3 and 4 illustrate occurrence of wrinkle in a conventional reflection mirror structure.
Referring to FIG. 3, if the tension for allowing the reflection film 21 to be maintained in a tight state is continuously applied to and exceeds the endurance limit of the frame 22, the frame 22 is deformed as shown in the drawing.
FIG. 4 is a sectional view taken along the line B-B′ of FIG. 3, and shows that upper side edges of the frame 22 are inwardly pushed due to the tension of the reflection film 21 occurring at the upper side edges of the frame 22. In FIG. 4, the dotted lines show that the frame 22 is deformed.
As aforementioned, when a larger tension is applied to the reflection film 21 in order to prevent wrinkle from being generated due to the variation in temperature, the deformation of the frame is further accelerated while high and low temperatures are repeatedly applied, so that permanent wrinkles may be formed.