U.S. patent application number 11/208607 was filed with the patent office on 2006-03-02 for glass reflector for projector and manufacturing method for the same.
This patent application is currently assigned to ASAHI TECHNO GLASS CORPORATION. Invention is credited to Naomi Hirano, Hiroshi Momoi, Hiroyasu Nishio, Nobuhisa Takada.
Application Number | 20060044810 11/208607 |
Document ID | / |
Family ID | 33535258 |
Filed Date | 2006-03-02 |
United States Patent
Application |
20060044810 |
Kind Code |
A1 |
Hirano; Naomi ; et
al. |
March 2, 2006 |
Glass reflector for projector and manufacturing method for the
same
Abstract
For example, the reflector according to the present invention is
a reflector made of glass for a projector which is composed of
amorphous glass whose thermal expansion coefficient is 30 to
45.times.10.sup.-7/.degree. C. and includes a reflective surface
for reflecting light emitted from a light source and an opening for
inserting a light source bulb or a conductor to the light source
bulb, in which the opening is smoothed by heat-treating the surface
thereof after opening-drilling, thus mechanical damage is removed
from the processed part.
Inventors: |
Hirano; Naomi; (Tokyo,
JP) ; Momoi; Hiroshi; (Chiba, JP) ; Nishio;
Hiroyasu; (Chiba, JP) ; Takada; Nobuhisa;
(Osaka, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
ASAHI TECHNO GLASS
CORPORATION
Funabashi-shi
JP
|
Family ID: |
33535258 |
Appl. No.: |
11/208607 |
Filed: |
August 23, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10722412 |
Nov 28, 2003 |
6957900 |
|
|
11208607 |
Aug 23, 2005 |
|
|
|
Current U.S.
Class: |
362/341 |
Current CPC
Class: |
F21V 7/24 20180201; F21V
7/10 20130101; C03B 11/10 20130101; C03B 23/26 20130101; C03B 23/20
20130101; F21V 7/28 20180201 |
Class at
Publication: |
362/341 |
International
Class: |
F21V 7/00 20060101
F21V007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 26, 2003 |
JP |
2003-182340 |
Claims
1-9. (canceled)
10. A manufacturing method for a reflector made of glass for a
projector having a reflective surface for reflecting light emitted
from a light source and an opening for inserting a light source
bulb or a conductor to said light source bulb, comprising: the
press-molding step of press-molding molten glass in a predetermined
reflector shape by a mold having a bottom mold and a plunger, the
opening forming step of forming said opening by removing glass at
the part touching said opening of said reflector formed at said
press-molding step, and the surface smoothing step of heat-treating
said opening formed at said opening forming step to smooth the
surface thereof, thereby removing mechanical damage from the
processed part.
11. A manufacturing method for a reflector made of glass for a
projector according to claim 10, wherein said opening forming step
heats said part touching said opening and then forms said opening
by punching from the side of said reflective surface.
12. A manufacturing method for a reflector made of glass for a
projector according to claim 10, wherein said opening forming step
forms said opening by a drill from the side of said reflective
surface.
13. A manufacturing method for a reflector made of glass for a
projector according to claim 10, wherein said opening forming step
forms said opening by cutting said part touching said opening.
14. A manufacturing method for a reflector made of glass for a
projector according to claim 10, wherein said surface smoothing
step smoothes said surface by applying a flame to said opening so
that the mean roughness of said surface becomes 0.03 .mu.m or
less.
15. A manufacturing method for a reflector made of glass for a
projector according to claim 10, wherein said surface smoothing
step smoothes said surface by radiating a laser beam to said
opening.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2003-182340, filed on Jun. 26, 2003, the entire contents of which
are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] (1) Field of The Invention
[0003] The present invention relates to a glass reflector used
together with the light source for a high-voltage mercury discharge
lamp and a manufacturing method therefor and more particularly to a
glass reflector suitable for the light source for a projector such
as a liquid crystal projector or a DLP projector and a
manufacturing method therefor.
[0004] (2) Description of The Related Art
[0005] As a light source for a liquid crystal projector and a DLP
projector (hereinafter, these are all referred to as a projector),
in the early stage, a combination of a halogen lamp and a reflector
made of heat-resisting glass such as borosilicate glass is used.
However, in recent years, an HID lamp (a discharge lamp) excellent
in the respects of the brightness of a projected image, a light
color closer to white, and a life span of the lamp has been
substituted for it. To this substitution, the progress in
miniaturization and high output of a discharge lamp
contributes.
[0006] Projectors, in correspondence with the spread of video
instruments such as a personal computer and a DVD, are widely used
from business presentation to household. Therefore, simultaneously
with progress of miniaturization of a projector itself, there are
increasing requests for preventing the brightness from impairment,
that is, preventing a lamp from reduction in the output thereof. An
increase in the output of a lamp causes an increase in the amount
of heat from the lamp, and the temperature of the light source
extremely rises also due to the effect of miniaturization of the
projector frame, and the neck of the reflector may be at more than
600.degree. C.
[0007] In a conventional projector, the highest temperature of the
glass face is about 400 to 450.degree. C. However, in a recent
projector, the highest temperature of the glass face rises to 450
to 550.degree. C. Therefore, as a projector, instead of a
conventional reflector made of heat-resisting glass such as
borosilicate glass, a reflector made of glass-ceramic glass of low
thermal expansion excellent in heat resistance is widely used (for
example, refer to Japanese Patent Publication 7-37334).
[0008] The reason is that there is a possibility that the rise
temperature of a reflector may exceed the transformation point of
borosilicate glass conventionally used and it is believed that at
550.degree. C., a conventional reflector made of borosilicate glass
has a high probability of cracking.
[0009] On the other hand, a reflector made of glass is manufactured
by press-molding molten glass using a mold manufactured on the
basis of a desired optical design.
[0010] Meanwhile, a reflector for a light source is required to be
provided with an opening for inserting and fixing a light source
lamp at the top of the reflective surface. The opening is formed by
forming a neck on the rear side of the reflective surface along the
optical axis of the reflector during press-molding, cutting it, and
making an opening. It is well known that a reflector for a halogen
lamp is punched to make an opening and then the neighborhood of the
opening is rounded by a flame of a burner (refer to Japanese
Utility Model Patent 2568541).
[0011] However, it is related to a reflector for a halogen lamp and
not related to a reflector for a projector and the temperature of
the glass surface is not increased so high.
BRIEF SUMMARY OF THE INVENTION
[0012] An object of the present invention is to provide a glass
reflector for a projector which is inexpensive and heat resisting
even when the temperature of the glass surface thereof rises very
high and has a reflective surface excellent in accuracy and a
manufacturing method therefor.
[0013] The present invention provides a reflector made of glass for
a projector which is composed of amorphous glass whose thermal
expansion coefficient is 30 to 45.times.10.sup.-7/.degree. C. and
includes a reflective surface for reflecting light emitted from a
light source and an opening for inserting a light source bulb or a
conductor to the light source bulb, in which the opening is
smoothed by heat-treating the surface thereof after
opening-drilling, thus mechanical damage is removed from the
processed part.
[0014] The present invention provides a manufacturing method for a
reflector made of glass for a projector including a reflective
surface for reflecting light emitted from a light source and an
opening for inserting a light source bulb or a conductor to the
light source bulb, comprising the press-molding step of
press-molding molten glass in a predetermined reflector shape by a
mold having a bottom mold and a plunger, the opening forming step
of forming the opening by removing the glass at the part touching
the opening of the reflector formed by the press-molding step, and
the surface smoothing step of heat-treating the opening formed by
the opening forming step to smooth the surface thereof, thereby
removing mechanical damage from the processed part.
[0015] FIG. 1A-1E are drawings for explaining the steps of
manufacturing a reflector by Embodiment 1 of the present
invention.
[0016] FIG. 2A-2D are drawings for explaining the steps of
manufacturing a reflector by Embodiment 2 of the present invention.
FIG. 3A-3D are drawings for explaining the steps of manufacturing a
reflector by Embodiment 3 of the present invention.
[0017] FIG. 4 is a drawing showing the structure of a mold used for
press molding of the reflectors of the embodiments of the present
invention.
[0018] FIG. 5 is a drawing showing the measured results of the
properties of the embodiments of the present invention and
comparison examples.
[0019] FIG. 6 is a drawing showing the measured results of the
three-dimensional shape of the reflective surface of the reflecting
substrate of Embodiment 1(A) of the present invention.
[0020] FIG. 7 is a drawing showing the measured results of the
three-dimensional shape of the reflective surface of the reflecting
substrate of Comparison Example 3.
[0021] FIG. 8 is a drawing showing the constitution when the
section is heat-treated by a laser beam in other embodiments of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment
[0022] The first embodiment of the present invention will be
explained hereunder by referring to the accompanying drawings. As
glass of the reflectors of the embodiment and comparison example,
two kinds of glass (A) and (B) having the components indicated
below are used. % indicates a weight percentage.
[0023] (A) SiO.sub.2: 80.9%, Al.sub.2O.sub.3: 2.3%, Na.sub.2O: 4%,
B.sub.2O.sub.3: 12.7%, thermal expansion coefficient (at 0 to
300.degree. C.): 32.5.times.10.sup.-7/.degree. C.
[0024] (B) SiO.sub.2: 78%, Al.sub.2O.sub.3: 2.1%, Na.sub.2O: 5.2%,
B.sub.2O.sub.3: 14.5%, thermal expansion coefficient (at 0 to
300.degree. C.): 38.times.10.sup.-7/.degree. C.
[0025] Further, the samples of the embodiment and comparison
example are deformed reflectors having an external size of 50 mm
(length) by 50 mm (width) viewed in the direction of the optical
axis and a rotational elliptical surface at a focal distance F of 6
mm. The neck length is 5 mm from the boundary line with the
reflective surface, and the thickness in the neighborhood of the
focus is 4.5 mm, and the inside diameter of the neck (the opening
face diameter) is 10 mm, and the opening diameter is 9 mm.
Embodiment 1
[0026] In Embodiment 1, the raw materials are mixed so as to obtain
the above glass composition and melted at about 1600.degree. C. and
a glass gob in a predetermined weight is dropped into a bottom mold
41 shown in FIG. 4, compressed by a plunger 42 from above, and
pressed to a reflector shape having the above dimensions. (Further,
the same may be said with Embodiment 2 and Comparison Example 1
which will be described later.)
[0027] At the time of pressing, when the glass gob is compressed
until the glass temperature lowers under about 800.degree. C.,
there is an advantage that the transfer accuracy of the plunger
shape which is a reflective surface is good and the accuracy of the
reflective surface can be made good.
[0028] The reflector pressed as mentioned above is shown in FIG.
1A. In Embodiment 1, for pressing, a thickness d1 of an opening
scheduled part 11 is preferably 1.5 mm or less. Therefore, the gap
between the molds is designed so as to make the thickness d1 equal
to or less than 1.5 mm and for example, the thickness is set to 1.2
mm.
[0029] Further, when the thickness of the opening part is more than
1.5 mm, heating during punching takes a lot of time, and the
opening is burred, and the punch life is shortened, so that it is
not preferable. Further, in this kind of glass, when molten glass
is to be pressed, as glass becomes thinner due to contact with the
mold, the glass is solidified because heat is quickly taken, so
that actually, a thickness of about 1 mm is generally a limit of
molding.
[0030] Further, the opening scheduled part 11 is desirably
installed in a position dented from the reflective surface. This
part is heated during punching and is applied with a flame by
subsequent fire polish, so that a step part is provided between the
opening part and the reflective surface, thus the effect of heating
on the accuracy of the reflective surface can be reduced.
[0031] Next, as shown in FIG. 1B, the interval between a side 13 of
a neck 12 which is not the reflective surface and the opening
scheduled part 11 is applied with a flame by a burner 14 to soften
the glass. Thereafter, as shown in FIG. 1C, the reflector is loaded
on a die 15, and the opening scheduled part 11 is punched by a
punch 16 in the direction of the reflective surface of the
reflector as shown by an arrow 17, and an opening 18 is formed
(direct punching). The temperature of the glass of the opening
during punching is equal to or higher than the softening point and
the viscosity is about 300 to 500 Pa.s (3000 to 5000 P).
[0032] Thereafter, as shown in FIG. 1D, the interval between the
side 13 of the neck 12 which is not the reflective surface and an
opening 18 is fire-polished. Namely, the interval is uniformly
applied with a flame by the burner 14 to melt the glass surface
again and make it round and smooth. The time required for applying
a flame is about 3 to 5 seconds per each. Each fire-polished
reflector is eliminated thereafter by an annealing kiln to obtain a
sample substrate (FIG. 1E).
Embodiment 2
[0033] In Embodiment 2, each sample substrate is drilled an
opening, for example, by a diamond core drill 26. Namely, it is
pressed as shown in FIG. 4 to obtain a press-molded reflector as
shown in FIG. 2A. At the time of pressing, a thickness d2 of an
opening scheduled part 21 of the reflector is thicker than the
thickness d1 of the opening scheduled part 11 in Example 1.
[0034] The reflector is loaded on a die 25, applied with the core
drill 26 from the reflective surface side, and rotated in the
direction of an arrow 27, thus an opening is drilled in the opening
scheduled part 21 to form an opening 28 (FIG. 2B).
[0035] Next, as shown in FIG. 2C, the opening 28 is applied with a
flame of a burner 29 to melt the glass surface into a round and
smooth state and then slowly cooled by the annealing kiln (FIG.
2D).
Embodiment 3
[0036] In Embodiment 3, using a mold having a neck slightly longer
than those of Embodiments 1 and 2, a reflector with the rear end of
the neck blocked is manufactured by pressing (FIG. 3A). Next, the
reflector is eliminated and then the rear end of a neck 31 is cut
and removed on the face perpendicular to the optical axis by a
cutter 33 where the residual neck length is in the same position as
that in Embodiments 1 and 2 (FIG. 3B).
[0037] Next, a section 34, as shown in FIG. 3C, is applied with a
flame by a burner 35 to be fire-polished and eliminated by the
annealing kiln to obtain a sample substrate (FIG. 3D).
COMPARISON EXAMPLE 1
[0038] In Comparison Example 1, a reflector is manufactured by
pressing borosilicate glass and eliminated, and then drilled with a
core drill in the same way as with Embodiment 2 to form an opening,
though it is not fire-polished thereafter.
COMPARISON EXAMPLE 2
[0039] In Comparison Example 2, a reflector using borosilicate
glass with the rear end of the neck put into the blocked state is
manufactured by pressing and eliminated in the same way as with
Embodiment 3, and then drilled by cutting the rear end of the neck,
though the processed surface is not fire-polished thereafter.
COMPARISON EXAMPLE 3
[0040] Comparison Example 3 is an example using glass-ceramic
glass, which is made of glass-ceramic glass equivalent to that of
Embodiment (1) of Japanese Patent Publication 7-37334 and in the
same way as with Embodiment 3, a reflector is molded and then the
rear end of the neck is cut and removed on the face perpendicular
to the optical axis, though the section is not fire-polished
thereafter.
[0041] In Comparison Example 3, concretely, the raw materials are
mixed so as to obtain a composition of 60% of SiO.sub.2, 21% of
Al.sub.2O.sub.3, 5.5% of Li.sub.2O, 4% of TiO.sub.2+ZrO.sub.2, 5%
of P.sub.2O.sub.5, 2.5% of B.sub.2O.sub.3, 4% of ZnO+MgO, and 1.5%
of K.sub.2O+Na.sub.2O, melted at 1500.degree. C. to be vitrified,
and formed in a substrate shape of a reflector by pressing.
[0042] The glass molded part is held at 57.degree. C. for 1 hour,
then heated up to 770.degree. C. at a rise temperature of 3.degree.
C. per minute, held at this temperature for 1 hour, and then
cooled. The transparent molded part before heat treatment is
changed to milky-white and becomes a .beta.-spodumene solid
solution. The glass--ceramic glass has a thermal expansion
coefficient of 6.times.10.sup.-7/.degree. C.
[0043] Therefore, on the inner periphery of the neck of each of the
reflectors produced in Embodiments 1 and 2 and Comparison Example
1, a ring projection remains, while on the inner periphery of the
neck of each of the reflectors produced in Embodiment 3 and
Comparison Examples 2 and 3, there is no ring projection.
[0044] As mentioned above, on the reflective surface of each of the
reflector substrates produced in the embodiments and comparison
examples, reflective films are formed by alternately laminating a
TiO.sub.2 film and an SiO.sub.2 film up to 30 layers by vacuum
vapor deposition to produce a reflector sample.
EVALUATION RESULTS OF EMBODIMENTS AND COMPARISON EXAMPLES
[0045] The evaluation results of the embodiments and comparison
examples are shown in FIG. 5 indicating the mean value of each ten
samples. Further, the column of No. 51 shown in the table indicates
the ratio of the mean intensity of illumination of each projection
face of each embodiment and comparison example to the mean
intensity of illumination of each projection face of Comparison
Example 3.
(1) Existence of Mechanical Damage of Processed Parts
[0046] Firstly, burrs, cuts, and roughened surfaces of processed
parts are observed visually. The reflectors of the embodiments have
all round and smooth surfaces free of burrs and cuts. On the other
hand, the processed surfaces of the comparison examples have
roughened surfaces in a ground glass shape with machining traces
recognized and fine cuts are recognized at the edge of each
opening.
[0047] Next, a laser beam is radiated to each surface of the
processed parts and scattered light is observed. In the reflectors
of the embodiments, scattered light caused by cracking is not
recognized because mechanical damage has been minimized or removed
from the processed parts.
(2) Surface Toughness of Processed Parts
[0048] The surface roughness of the processed part of each sample
is measured using a feeler type surface roughness meter. In
Embodiments 1 and 2 and Comparison Example 1, each reflector is
divided into two parts along the optical axis, and the inner
peripheral surface of the neck is exposed, and the inner peripheral
surface of the opening is measured in an extent of 1 mm in the
direction of the optical axis, and in Comparison Examples 2 and 3,
the end face of each neck is measured along the section.
[0049] In each embodiment, the mean roughness Ra is 0.01 to 0.03
.mu.m, while each comparison example has a rough surface having
mean roughness Ra of about 1 .mu.m and irregularities of 17 to 18
.mu.m at maximum.
(3) Reflective Surface Accuracy
[0050] The reflective surface of each sample is measured in the
radial direction using a feeler type three-dimensional shape
measuring instrument and the accuracy for the designed value of the
reflective surface is .+-.10 to 15 .mu.m in Embodiments 1, 2, and 3
and Comparison Examples 1 and 2. On the other hand, in Comparison
Example 3, it is ascertained that there is a variation of about
.+-.70 .mu.m.
[0051] Generally, according to the present invention, the surface
accuracy in the neighborhood of the opening is preferably less than
.+-.20 .mu.m for an ideal curved surface. The neighborhood of the
opening in this case means a range up to about 20 mm from the end
of the opening in the radial direction.
[0052] The three-dimensional measured results of Embodiment 1(A)
and Comparison Example 3 are shown in FIGS. 6 and 7. In the
drawings, the measured values displayed are enlarged in the normal
line direction at each measuring point for an ideal curved surface
(curved line). The curved line of the reflective surface (measured
values) is enlarged 50 times and displayed and the distances
between the center line and the upper and lower lines are
respectively 50 .mu.m.
(4) Lighting Evaluation
[0053] An extra-high voltage mercury lamp (UHP; Registered
Trademark) of 150 W is loaded in the reflector of each sample, and
a motor driven fan with a diameter of 1 cm is installed at a
distance of 10 cm from the neck of the reflector, and the
temperature of the neck of the reflector is measured by a
thermocouple, and simultaneously the air flow rate of the fan is
controlled so that the temperature after temperature rise is made
equal to a preset temperature (450.degree. C., 550.degree. C.), and
lighting evaluation of repeating to light the lamp continuously for
2.5 hours and switch the lamp off for 0.5 hours is executed. The
operation is performed for each 10 samples of each embodiment and
comparison example.
[0054] As a result, the results shown in the table in FIG. 5 are
obtained. In the lighting evaluation shown in FIG. 5, the numerator
of each fraction means the number of cracked samples among 10
samples.
[0055] In the embodiments using glass (A) and Comparison Example 3,
no reflectors are cracked after 2000 hours. On the other hand, in
Comparison Examples 1 and 2, there are some samples cracked after
1000 hours at 450.degree. C. and moreover, at 550.degree. C., half
of the 10 samples are cracked after 50 hours.
[0056] The reason is considered to be that in the embodiments of
the present invention, mechanical damage is removed from the
processed parts. In this case, removal of mechanical damage from
the processed parts means a state that burrs and cracks caused by
punching, cuts caused by mechanical processing, roughened surfaces,
and minute cracks with a diameter of several tens .mu.m or less on
the surfaces do not exist.
[0057] (5) Intensity of Illumination of Projection Faces
(1.times.)
[0058] On each reflector of Embodiments 1, 2, and 3 and Comparison
Example 3 free of cracking in the lighting evaluation, an
extra-high voltage mercury lamp (UHP) of 150 W is loaded, and they
are mounted in an actual liquid crystal projector, and no-image
light is projected onto the screen at a distance that the
projection screen size is 40 inches diagonally, and the intensity
of illumination is measured by an illumination photometer arranged
at the center of each section of the projection face divided into 9
sections of 3.times.3 rows, and the brightness is evaluated.
[0059] As compared with the average of the intensity of the 9
sections, the measured values of each embodiment are all higher
than the measured values of Comparison Example 3 by about 3 to 5%.
With respect to the reflectors of the embodiments, as compared with
the same optical system, the illumination difference between the
central section and the peripheral sections is smaller than that of
the reflector of Comparison Example 3 and comparatively uniform
intensity of illumination is obtained including the peripheral
part.
[0060] As a result, it can be judged that the reflectors of the
present invention using no glass-ceramic glass are superior in the
reflective surface accuracy.
[0061] Meanwhile, in the aforementioned embodiments, the surface
treatment after the opening-drilling process is carried out by fire
polishing. The use of fire polishing like this provides an
advantage that the surface treatment after the opening-drilling
process can be carried out easily.
Other Embodiments
[0062] However, the present invention is not limited to fire
polishing and in place of it, a laser beam may be radiated to the
concerned section to carry out heat treatment. In the other
embodiment of the present invention, even if microcracks are
generated on the opening-drilled surface, thereafter, a laser beam
is radiated onto the section for heat treatment, so that the
microcracks are eliminated. Therefore, in the subsequent processes
or in the state that this reflector for a projector is loaded, even
if the glass substrate is applied with mechanical or thermal
stress, the glass can be prevented from careless cracking starting
from the microcracks. Furthermore, the heat treatment is carried
out by laser radiation, so that unlike chamfering, there is an
advantage that the treating speed is fast.
[0063] Even when the surface treatment is carried out by a laser
beam, at the previous steps, as shown in FIGS. 1 to 3, each sample
is drilled by a core drill by fire-polishing and direct punching or
an opening can be formed by a step of cutting by a cutter.
[0064] In the opening-drilling process as indicated in Embodiments
1 and 2, needless to say, a laser beam may be radiated only in one
direction. However, the radiated surface is located inside the
neck, so that at the time of radiation of a laser beam, when light
is radiated in the two directions such as from the rear end side of
the neck outside the reflector and the reflective surface side,
cuts at the end part and cracks can be preferably removed surely in
a short time.
[0065] In this case, as shown in FIG. 8, for example, a laser beam
emitted from a carbon dioxide laser 81 is led to laser emission
units 83a and 83b via a light leading system 82 and laser beams 84a
and 84b are radiated to the end of the opening part (ridgeline)
remaining in the drilled part in the two directions. At this time,
the radiation directions can be controlled to radiate the laser
beams along the opening shape. Further, when the opening shape is
circular, the radiation point is fixed, and the reflector is
rotated around the optical axis thereof, thus the heat treatment
can be easily carried out throughout the entire periphery of the
opening.
[0066] When the heat treatment is to be carried out by a laser
beam, the heating range becomes local more than that by fire
polishing, thus there is an advantage of reducing the effect on the
reflective surface.
[0067] Further, when the end of the neck is to be cut to make an
opening like Embodiment 3, a laser beam may be radiated to the
section from behind.
[0068] Further, amorphous glass used in the present invention may
have a thermal expansion coefficient of 30 to
45.times.10.sup.-7/.degree. C. When the thermal expansion
coefficient is lower than 30.times.10.sup.-7/.degree. C., the
molding capacity is decreased and in a reflector requiring an
accurate reflective surface, the yield rate is reduced. Further,
when the thermal expansion coefficient is higher than
45.times.10.sup.-7/.degree. C., the heat resistance is not
sufficient and the amorphous glass cannot be combined with a
high-output light source. Amorphous glass of the present invention
more preferably has a thermal expansion coefficient of 30 to
40.times.10.sup.-7/.degree. C. Concretely, in addition to
borosilicate glass used in the aforementioned embodiments,
aluminosilicate glass can be suitably used.
[0069] According to the present invention, since mechanical damage
due to the opening-drilling process is removed, although amorphous
glass is used, there is an effect that a highly heat-resisting
reflector free of cracking can be obtained.
[0070] Further, the reflector according to the present invention
uses amorphous glass, so that there are no deformation and
shrinkage due to the crystallization process which cannot be
avoided in glass-ceramic glass and the accuracy of the reflective
surface can be brought closer to that of an ideal surface.
Therefore, there is an effect that a reflector that the projection
intensity of illumination is high and the difference in intensity
of illumination between the central part and the peripheral part is
small, that is, a reflector suitable for a projector light source
can be obtained.
[0071] This kind of reflector is provided with a means for coating
a dielectric multi-layer for reflecting visible rays and
transmitting infrared rays on the reflective surface and preventing
a radiated article from heating by infrared rays. Therefore,
infrared rays emitted from the light source transmit the
multi-layer and pass through the substrate of the reflector.
However, in glass-ceramic glass, infrared rays are scattered on the
crystalline interface, so that in the frame of the projector, the
periphery of the reflector is apt to be filled with heat. On the
other hand, amorphous glass transparent to infrared rays transmits
infrared rays linearly without scattering them, so that there is an
advantage that an intensive heat dissipation measure can be easily
taken on the rear of the reflector.
[0072] According to the present invention, a glass reflector
suitable for a projector in which the heat resistance is high and
the reflection accuracy is superior and which is inexpensive and a
manufacturing method for it can be obtained.
* * * * *