Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2001-10-02
2003-04-29
Lester, Evelyn A (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S583000, C359S584000, C359S589000, C359S839000, C359S267000
Reexamination Certificate
active
06556350
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a half mirror which transmits light from the back of a mirror body and which is used as rearview mirrors provided at the interior and the exterior of a vehicle.
2. Description of the Related Art
Usually, rearview mirrors are provided at the interior and the exterior of a vehicle compartment. A mirror of this type includes a mirror body. The mirror body includes a plate-configured glass substrate, on which a metal reflecting film is formed. The glass substrate is secured to a mirror holder and is housed in a case, such as a visor.
The mirror holder is formed in a dish-shape, that opens at one end in the depth direction thereof. The mirror body is housed within the mirror holder such that the reflecting film on the glass substrate faces the opening end of the mirror holder. The case, such as a visor, is formed in a dish-shape or a bowl-shape. The mirror holder is housed within the case with the opening end thereof facing the opening end of the case. The mirror holder is fixed at a predetermined position of a vehicle via the casing.
Recently, these inner and outer rearview mirrors have been studied for use not only for providing a rearview of a vehicle but also as a kind of indicator, for example, as a direction indicator when the vehicle turns, or as a speed indicator.
When a mirror is also used as an indicator, a mirror known as a “half mirror,” which transmits light from the back of the reflecting film (i.e., from the glass substrate side thereof), is used as a mirror body. In such a mirror, indicating devices like a turn signal, a character display panel for indicating speed, or the like are disposed at the back of the glass substrate (i.e., on the side of the glass substrate opposite to the side where the reflecting film is formed). When the indicating device lights up, characters and marks are transmitted through the glass substrate and the reflecting film so as to enable an occupant of the vehicle or an occupant of another vehicle approaching from behind (i.e., one who observes the mirror from the opening side of the mirror holder) to observe these characters and marks.
The structure of a mirror body
122
used in an aforementioned half mirror
120
for a vehicle is schematically shown in a cross-sectional view in FIG.
8
. As shown in
FIG. 8
, a silicon (Si) thin film having a thickness T
4
of about 20 nm is usually used as a reflecting film
126
provided on a surface of a glass substrate
124
which is a component of a mirror body
122
. A protective film
128
is provided at the front of the reflecting film
126
. The protective film
128
consists of a silicon dioxide (SiO
2
) film
130
having the thickness T
5
of about 20 nm, which is formed on the reflecting film
126
, and a titanium dioxide (TiO
2
) film
132
having the thickness T
6
of about 15 nm, which is formed on the silicon dioxide film
130
. The protective film
128
prevents the reflecting film
126
from deterioration, damage that may otherwise be caused to the reflecting film
126
when the mirror body
122
is mounted on the mirror holder or when the above-described indicating device (not shown) is mounted at the back of the mirror body
122
, and the like.
Accordingly, three thin films, namely, the reflecting film
126
and the two protective films
128
, are provided on the glass substrate
124
of the aforementioned mirror body
122
.
In the above-described mirror body
122
, the overall reflectance of the mirror body
122
is significantly affected by even slight variations in the thickness of each thin film, namely, the reflecting film
126
, the silicon dioxide film
130
, and the titanium dioxide film
132
. Accordingly, to ensure the reflectance of a predetermined standard, the accuracy in providing a particular film thickness for the reflecting film
126
, the silicon dioxide film
130
, and the titanium dioxide film
132
respectively, must be strictly controlled. However, because such rigorous control of accuracy in film thickness is extremely difficult, it has become a major reason for increased manufacturing costs.
SUMMARY OF THE INVENTION
In view of the aforementioned facts, it is an object of the present invention to provide a half mirror which includes a protective film, for protecting a reflecting film and which has stable quality and does not require any strict quality (film thickness) control, thereby resulting in lower manufacturing costs.
A half mirror relating to a first aspect of the present invention comprises a substrate that at least transmits light having predetermined wavelengths; a reflecting film, comprising substantially silicon of a thickness of 20 to 45 nm and being integrally formed on a surface of the substrate, for reflecting light that is made incident upon the reflecting film from the substrate side thereof and transmitting, toward the substrate side of the reflecting film at a fixed ratio, light made incident upon the reflecting film from the side opposite to the substrate side; and a protective film, which is made of a translucent material that at least transmits light having particular wavelengths, formed on the surface of the reflecting film opposite to the surface on which the substrate is formed.
According to the thus structured half mirror, the light that is made incident upon the reflecting film from the side of the substrate opposite to the surface where the reflecting film is formed (hereinafter, referred to as the front of the substrate) is reflected by the reflecting film. On the other hand, the light that is made incident upon the reflecting film from the side of the protective film opposite to the surface where the reflecting film is formed (hereinafter, referred to as the back of the protective film) is transmitted through the reflecting film, and then passes through the substrate. Accordingly, the light that is made incident upon the reflecting film from the front of the substrate and is reflected at the reflecting film, and the light that is made incident upon the reflecting film from the back of the protective film, can both be observed from the substrate side of the mirror.
In the half mirror, the reflecting film is formed at the back of the substrate. Accordingly, by accommodating the substrate in, for example, a housing (casing) such as a mirror holder having a base, the reflecting film can be protected against any foreign substances which may otherwise contact or attach to the reflecting film. In addition, a protective layer made of a translucent material is formed on the reflecting film. This structure makes it impossible for any foreign substances to directly contact the reflecting film when, for example, the reflecting film is accommodated in aforementioned housing or the like. Accordingly, the reflecting film can be protected from deterioration or damages that may be caused thereto.
In the half mirror of the present invention, because the reflecting film is provided at the back of the substrate and the protective film is provided at the back of the reflecting film, light is made incident upon the reflecting film from the substrate side thereof is basically not affected by the protective film. Accordingly, so long as the thickness of the reflecting film is accurate, even if there is any inaccuracy with respect to the thickness of the protective film, the reflectance of the light, that is made incident upon the reflecting film from the substrate side thereof and is reflected by the reflecting film, is not affected. As a result, a predetermined reflectance can be ensured. As described above, the protective film can be produced with less rigorous thickness control, thereby reducing the manufacturing costs.
Note that, in the present invention, it suffices that the substrate and the protective film can at least transmit light having predetermined wavelengths. That is, the substrate and the protective film may be transparent and transmit light having any wavelengths, or, alternatively, they may transmit or restrict only the light having particular wavele
Ayabe Masao
Nakaho Jun-ichi
Takai Noriyuki
Yoshida Hiroshi
Cole Thomas W.
Dinh Jack
Lester Evelyn A
Nixon & Peabody LLP
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