Optical: systems and elements – Projection screen – Rear projection screen
Reexamination Certificate
2000-07-27
2002-06-25
Adams, Russell (Department: 2851)
Optical: systems and elements
Projection screen
Rear projection screen
C359S443000, C359S453000
Reexamination Certificate
active
06411436
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transmission type projection screen which can be used with a projector.
2. Description of the Related Art
In a transmission type projection screen (also called a “rear type screen”), a picture projected from a projector from behind the screen is focused on the rear surface thereof (i.e., the surface opposite to the front surface facing the audience), so that the picture can be seen through the screen from the front side (audience side) thereof.
FIG. 5
shows an explanatory view of such a conventional transmission type projection screen, showing the laminated structure thereof. This conventional screen is a laminate screen which is composed of a transparent layer
1
as a base layer of the screen and an optical diffusion layer (hereinafter simply called “diffusion layer”)
2
which is laminated to the transparent layer
1
on one side thereof.
The transparent layer
1
is a base layer of the screen and can be made of, for example, a hard (non-deformable) transparent plastic plate which ensures a required strength of the whole screen while maintaining the shape thereof. Alternatively, the transparent layer
1
can be made of a soft transparent plastic sheet which is bendable and/or able to be rolled up into a tube.
The diffusion layer
2
is a translucent layer (a milk-white layer) whose base material (binder) is, e.g., a translucent synthetic resin (a milk-white layer) such as acrylic resin or vinyl chloride. A light diffusing material such as mica powder, silicon compound powder, a magnesium oxide or a titanium oxide is mixed into the base material to form the translucent diffusion layer
2
.
The diffusion layer
2
faces the front (the audience side) while the transparent layer
1
faces the rear (the projector side). Projection light L emitted by a projector (not shown) towards the screen from behind passes through the transparent layer
1
to reach the diffusion layer
2
so that the projection light L is focused on the diffusion layer
2
. Consequently, the picture formed by the projection light can be seen through the screen from the front thereof.
In a conventional transmission type projection screen as shown in
FIG. 5
, among the diffused light (radially diffused light rays surrounded by a dotted circle line shown in
FIG. 5
) of the light L in the diffusion layer
2
, the light which is diffused by the diffusion layer
2
rearwardly to be totally reflected by the rear surface (the right surface as viewed in
FIG. 5
on the projector side) of the transparent layer
1
to thus proceed back to the diffusion layer
2
, i.e., reflected light La shown in
FIG. 5
is a problem.
Regarding the light which is diffused by the diffusion layer
2
to be reflected by the rear surface (the right surface as viewed in
FIG. 5
on the projector side) of the transparent layer
1
, the diffused light is totally reflected by the rear surface of the transparent layer
1
if the angle of incidence of the diffused light (the angle “&agr;” shown in
FIG. 5
) on the rear surface of the transparent layer
1
is equal to or greater than 42 degrees on condition that the refractive index of the transparent layer
1
is 1.494. If the gain of the screen is approximately 1.0 while the absorbance of the screen is small, the amount of light which is diffused by the diffusion layer
2
to proceed rearwardly towards the transparent layer
1
is large, and therefore the amount of the reflected light La becomes large. Consequently, this reflected light La is incident on the diffusion layer
2
. The image of the reflected light La which is formed on the diffusion layer
2
is a blurry image (out-of-focus image) and has an adverse influence on a proper image focused on the diffusion layer
2
in the form of noise (halation). This decreases the contrast and resolution of the proper image focused on the diffusion layer
2
.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a transmission type projection screen which makes it possible to prevent the contrast and resolution of the proper image focused on the diffusion layer from deteriorating due to the aforementioned reflected light La.
To achieve the object mentioned above, according to an aspect of the present invention, a transmission type projection screen is provided, including a diffusion layer on which projection light is focused, and a neutral gray layer positioned behind the diffusion layer on a rear side of the diffusion layer at which the projection light enters. The optical density of the neutral gray layer is in the range of 0.05 to 0.7.
Preferably, the neutral gray layer includes at least a coloring matter and/or a carbon black pigment, and the diffusion layer includes a neutral gray coloring matter. The projection screen can be either non-deformable, bendable, or able to be rolled up.
According to another aspect of the present invention, a transmission type projection screen is provided, including a diffusion layer, a transparent layer, and a neutral gray layer. The optical density of the neutral gray layer is in the range of 0.05 to 0.7.
In an embodiment, the diffusion layer, the transparent layer and the neutral gray layer are arranged in this order from an audience side to a projector side.
In another embodiment, the diffusion layer, the neutral gray layer and the transparent layer are arranged in this order from an audience side to a projector side.
Preferably, the neutral gray layer includes at least a coloring matter and/or a carbon black pigment, and the diffusion layer includes a neutral gray coloring matter. The projection screen can be either non-deformable, bendable, or able to be rolled up.
The transparent member can made from either a non-deformable transparent plastic plate, a bendable transparent plastic sheet, or a transparent plastic sheet which is able to be rolled up.
According to another aspect of the present invention, a transmission type projection screen is provided, including a diffusion layer, a first neutral gray layer, a transparent layer, and a second neutral gray layer. The diffusion layer, the first neutral gray layer, the transparent layer and the second neutral gray layer are arranged in this order from an audience side to a projector side; and the total optical density of the first neutral gray layer and the second neutral gray layer is in the range of 0.05 to 0.7.
Preferably, the neutral gray layer includes at least a coloring matter and/or a carbon black pigment, and the diffusion layer includes a neutral gray coloring matter. The projection screen can be either non-deformable, bendable, or able to be rolled up.
The transparent member can made from either a non-deformable transparent plastic plate, a bendable transparent plastic sheet, or a transparent plastic sheet which is able to be rolled up.
According to another aspect of the present invention, a transmission type projection screen is provided, including a diffusion layer, and a neutral gray layer positioned behind the diffusion layer on a rear side of the diffusion layer at which the projection light enters. The diffusion layer is made of a bendable plastic sheet, and the optical density of the neutral gray layer is in the range of 0.05 to 0.7.
Preferably, the neutral gray layer includes at least a coloring matter and/or a carbon black pigment.
According to the transmission type projection screen to which the present invention is applied, since the screen is provided behind the diffusion layer with a neutral gray layer whose optical density is in the range of 0.05 to 0.7, the quantity of the light (reflected light) which is diffused by the diffusion layer to be subsequently reflected by the rear surface of the transparent layer to thus proceed back to the diffusion layer can be largely reduced, which makes it possible to prevent the contrast and resolution of the proper image focused on the diffusion layer from deteriorating due to the reflected light.
The present disclosure relates to subject matter contained in Japanese Patent Applications No
Adams Russell
Cruz Magda
Kikuchi Science Laboratory Inc.
McCormick Paulding & Huber LLP
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