Optical: systems and elements – Projection screen – Embedded particles
Reexamination Certificate
2001-12-07
2004-03-16
Adams, Russell (Department: 2851)
Optical: systems and elements
Projection screen
Embedded particles
C359S455000, C359S459000, C428S167000, C428S172000
Reexamination Certificate
active
06707606
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection screen, a lens sheet suitably used therein, and a method of manufacturing the lens sheet.
2. Description of the Related Art
A projection screen is constructed of sheets that include a lenticular lens sheet, a Fresnel lens sheet, etc. The Fresnel lens is for the purpose of making the light emitted and projected from an image source substantially parallel with rays that are directed toward a viewing person side and thereby making the brilliance of the screen uniform. On the other hand, the lenticular lens is for the purpose of diffusing the light so that an image may be viewed over a wide range on the viewing side. Accordingly, it is conventionally practiced in general to mix light diffusion fine particles into the lenticular lens sheet. In contrast to this, as the Fresnel lens sheet, conventionally, there has been used a transparent sheet having no light diffusion agent particles mixed thereinto. In recent years, however, in order to eliminate image obstructions due to the rise surfaces (the leading surfaces) of the Fresnel lens, it has become generally practiced to mix the light diffusion agent particles into the Fresnel lens sheet as well.
These lenticular lens sheet and Fresnel lens sheet have hitherto been manufactured with methods such as a thermal pressing molding, extrusion-molding, thermal polymerization molding, ionizing radiation curing molding, etc. Among these methods, the ionizing radiation curing molding method having a merit in that the mold configuration is excellent in reproducibility; and the molding process time length is short, especially a UV curing molding method that uses ultraviolet rays as ionizing radiation has now been generally practiced.
The ionizing radiation curing molding method, as illustrated in
FIGS. 4A
to
4
G, is constructed of the following processes. A temperature adjustment process (
FIG. 4A
) that adjusts a mold
12
for a lens sheet to a temperature suitable for molding the lens. The first resin coating process (
FIG. 4B
) that coats a liquid ionizing radiation curable resin over the entire surface of the temperature-adjusted mold
12
. A second resin coating process (
FIG. 4C
) that coats the liquid ionizing radiation curable resin onto the position on the pressurization starting side that is located on the mold
12
. A base material supply process (
FIG. 4D
) that covers the mold
12
with a base material sheet
14
transmitting ionizing radiation therethrough from over the ionizing radiation curable resin layer
13
. A leveling lamination process (
FIG. 4E
) that presses the base material sheet
14
and the mold
12
with pressurizing rolls
15
a
,
15
b
from the pressurization starting end side towards the pressurizing termination end side and thereby laminating the base material sheet
14
onto the ionizing radiation curable resin layer
13
while leveling the same (
13
). A resin curing process (
FIG. 4F
) that radiates ionizing radiation onto the ionizing radiation curable resin layer
13
from over the base sheet
14
and cures the same (
13
). An exfoliation process (
FIG. 4G
) that exfoliates the cured ionizing radiation curable resin
13
from the mold
12
jointly with the base sheet
14
.
In the leveling lamination process (
FIG. 4E
) of the ionizing radiation curing molding method, the light diffusion agent particles that have protruded from the surface of the base sheet repeatedly contact with the forward end portions of the mold
12
; and cause damages to the forward end of the mold. This shortens the service life of the expensive mold
12
. That method had these problems. They have recently become more and more prominent. The reason for this is that, as the thickness of the lens sheet becomes gradually smaller owing to a demand for the increase in the fineness of the images, etc., the same amount of light diffusion agent particles is mixed into a smaller thickness of sheet. In addition, there has been a demand for the improvement in the optical function of the light diffusion agent particles.
SUMMARY OF THE INVENTION
Thereupon, the present invention has an object to provide a lens sheet that without, when molding the resin, damaging the mold can enhance the optical function of the light diffusion agent particles, a projection screen, and a method of manufacturing the lens sheet.
Hereinafter, the present invention will be explained. It is to be noted that although in order to make easier the understanding of the present invention the reference symbols in the appended drawings will additionally be written by being bracketed this does not impose a limitation upon the present invention by the illustrated embodiments.
The lens sheet in the first aspect of the present invention is a lens sheet having a base material sheet (BS) that has a lens formed on at least one surface thereof using an ionizing radiation curable resin, wherein light diffusion agent particles (D) are mixed into the base material sheet and have amass average particle diameter of 3 to 25 &mgr;m. Here, the wording “mass average particle diameter” is calculated as follows,
&Sgr;
nd
4
/&Sgr;nd
3
where “n” represents the number of the particles; and “d” represents the particle diameter.
According to the lens sheet of this aspect, the mass average particle diameter of the light diffusion agent particles has been made small. Therefore, enlarging the interval between the troughs of the lens sheet and the surface of the base material sheet is not needed very much. The amount of ionizing radiation curable resin used can be reduced. In addition, the molding of it becomes also stable. Also, generally, to obtain the same light diffusion at half-maximum angle in case the differences between the light diffusion agent particles and the base material sheet in terms of the refractive index are the same, it is more preferable to use the light diffusion agent particles that is small in the mass average particle diameter than to use the light diffusion agent particles that is large in the mass average particle diameter. This is because it is possible to lessen the adding amount (the weight) of light diffusion agent particles. Therefore the sum of the cross-sectional areas of the light diffusion agent particles, which protrude from the surface of the base material sheet, becomes small. And also because the possibility of damaging the mold becomes small. Accordingly, it is preferable that the mass average particle diameter be 25 &mgr;m or less. Provided, however, that in case the mass average particle diameter of the light diffusion agent particles is smaller than 3 &mgr;m the scatter angle of the light has dependency upon the wavelength with the result that the lens sheet looks yellowish. Therefore, that range is not preferable.
The lens sheet in the second aspect of the present invention is a lens sheet having a base material sheet that has a lens formed on at least one surface thereof using an ionizing radiation curable resin, wherein light diffusion agent particles are mixed into the base material sheet; and, when d represents the mass average particle diameter of the light diffusion agent particles and h represents the interval between the trough (
9
) of the lens configuration of the lens and the surface on the lens-formation surface side of the base sheet material, there hold true the inequality:
h>d/
3
According to the lens sheet of this second aspect, the interval between the trough portion of the lens configuration corresponding to the crest portion of the mold and the surface of the base sheet material has been made large. Therefore, it is not possible that the unevenness of the diffusion material damage the crest portion of the mold. Resultantly, it is possible to prolong the service life of the mold.
The lens sheet in the third aspect of the present invention is a lens sheet having a base material sheet that has a lens formed on at least one surface thereof using an ionizing radiation curable resin, wherein light diffusion agent particles are mixed into the base
Hashimoto Ryuji
Kimura Makoto
Watanabe Hitomu
Adams Russell
Cruz Magda
Dai Nippon Printing Co. Ltd.
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