Patent Application
20230128331
The present invention relates to a system and method which can prevent displaying using polarized light from being peeked at by a stranger from the outside, and a window piece for use therewith.
Display devices that use polarized light to perform displaying, such as liquid crystal display devices, are widely used. Large-sized display devices are often installed in conference rooms as monitors for presentation or video conferencing purposes, for example.
On the other hand, the use of open conference rooms that provide a sense of spatial openness is becoming more widespread. For example, the wall (or partition) of a conference room facing a walkway may be made of a glass panel (or an acrylic panel) to provide a sense of openness because of its transparency. While transparency of the wall provides a sense of openness, it can be a problem if an outside stranger peeks at the information that is being displayed on a display device in the conference room. To cope with this situation, for example, a frosted glass or colored panel are used to make the transparent wall opaque at eye level. However, when the transparent wall is partly made opaque in this way, the sense of openness will be compromised.
Patent Document 1 discloses a system where a polarizing filter is placed close to a transparent window, such that the polarizing filter transmits polarized light in a second direction being orthogonal to polarized light in a first direction which is emitted from a display device, thereby preventing the information that is displayed on the display device by using polarized light in the first direction from being seen, while still allowing the inside of the room to be seen through the transparent window.
However, in the system described in Patent Document 1, a display plane is disposed so as to be parallel and directly opposite to the transparent window, such that information displayed by using polarized light can be prevented from being seen when being viewed in a direction perpendicular to a polarizing filter that is disposed close to the transparent window, but that information displayed by using polarized light can still be seen when being viewed in an oblique direction (from above or below or from right or left) with respect to the polarizing filter (i.e., the window). This issue of peeking from oblique directions, as will be described later in detail, arises from the fact that, when displaying is viewed obliquely with respect to the polarizing filter, the relationship between the direction of the polarized light used for displaying used for displaying and the absorption axis of the polarizing filter (orthogonal to the second direction) is shifted from being parallel.
The present invention has been made in view of the above problems, and an objective thereof is to provide a peeking prevention system, a method of peeking prevention, and a window piece for use therewith that can prevent peeking from oblique directions.
According to embodiments of the present invention, means for solution as recited in the following Items are provided.
A peeking prevention system comprising:
a display device including a first polarizing layer on a front side of a display plane, the first polarizing layer having a first absorption axis that is parallel to a first direction; and
a partition to delimit from surroundings a space in which displaying is to be provided by the display device, the partition having a light-transmitting portion through which the inside of the space is viewable,
the light-transmitting portion including a transparent substrate and a second polarizing layer being disposed on a side of the transparent substrate facing the space and having a second absorption axis that is parallel to a second direction, wherein,
the system further comprises a phase film disposed on a front side of the first polarizing layer or a side of the second polarizing layer facing the space;
the phase film has a slow axis that is orthogonal to the first direction or parallel to a third direction, the third direction being parallel to the second direction; and
the display plane has an azimuth angle of 45°, and reduces a transmittance of a case where the display plane is viewed through the light-transmitting portion from an oblique direction with an elevation angle of 45°.
The peeking prevention system of Item 1, wherein,
in a plan view that is orthogonal to the oblique direction, when a smaller angle and a larger angle emerge as a result of the first absorption axis intersecting the second absorption axis, a direction bisecting the smaller angle defines a horizontal polarization axis and a direction bisecting the larger angle defines a vertical polarization axis,
Stokes parameters S1 and S3, defining a polarization state of linearly polarized light having been emitted from the display plane and transmitted through the phase film but before being incident on the second polarizing layer, satisfy the relationships:
0.25<S1<0.9; and
−0.4<S3<0.4.
The peeking prevention system of Item 1 or 2, wherein a frontal retardation Re that is defined by a product between a thickness and (nx−ny) of the phase film is not less than 200 nm and not more than 300 nm, and an Nz factor defined by (nx−nz)/(nx−ny) of the phase film is not less than −1.0 and not more than 2.0.
The peeking prevention system of Item 1 or 2, wherein the phase film includes a plurality of phase layers.
The peeking prevention system of any of Items 1 to 4, wherein one of the first direction and the second direction is the horizontal direction, and the other is the vertical direction.
The peeking prevention system of Item 5, wherein the first direction is the horizontal direction and the phase film is disposed on the front side of the first polarizing layer.
The peeking prevention system of Item 5, wherein the second direction is the horizontal direction, and the phase film is disposed on the side of the second polarizing layer facing the space.
The peeking prevention system of any of Items 1 to 7, wherein,
the display plane and the light-transmitting portion are parallel to the vertical direction; and
an angle made by the display plane and the light-transmitting portion is not less than 30° and not more than 150°.
The peeking prevention system any of Items 1 to 8, wherein the transmittance is 6% or less.
The peeking prevention system any of Items 1 to 9, wherein the transmittance is 3% or less.
A window piece to be provided on a wall of a room, the window piece comprising:
a transparent substrate;
a polarizing layer being disposed on a side of the transparent substrate facing the room, the polarizing layer having an absorption axis that is parallel to the vertical direction or the horizontal direction; and
a phase film disposed on a side of the polarizing layer facing the room, wherein,
in a plan view of an imaginary plane located inside the room as viewed along a line-of-sight direction from outside of the room, when linearly polarized light having a polarization axis that is orthogonal to a horizontal line segment (or a vertical line segment) on the imaginary plane propagates in a direction with an angle θ greater than 0° emerging between the polarization axis and the absorption axis, the phase film has a birefringence to convert a polarization state of the linearly polarized light so that the polarization axis rotates beyond the absorption axis.
The window piece of Item 11, wherein an angle by which the phase film rotates the polarization axis of the linearly polarized light beyond the absorption axis is 3 times as large or more and 10 times as large or less than the angle θ.
The window piece of Item 11 or 12, wherein,
the line-of-sight direction has an incident angle of 45° with respect to the imaginary plane, with a plane of incidence intersecting the horizontal plane at an angle of 45°,
in a plan view that is orthogonal to the line-of-sight direction, when a smaller angle and a larger angle emerge as a result of the absorption axis intersecting the horizontal line segment, a direction bisecting the smaller angle defines a horizontal polarization axis and a direction bisecting the larger angle defines a vertical polarization axis,
Stokes parameters S1 and S3, defining a polarization state of the linearly polarized light having been transmitted through the phase film but before being incident on the polarizing layer, satisfy the relationships:
0.25<S1<0.9; and
−0.4<S3<0.4.
A method of peeking prevention comprising:
disposing a display device including a first polarizing layer on a front side of a display plane, the first polarizing layer having a first absorption axis that is parallel to a first direction;
disposing a partition to delimit from surroundings a space in which displaying is to be provided by the display device, the partition having a light-transmitting portion through which the inside of the space is viewable, the light-transmitting portion including a transparent substrate and a second polarizing layer being disposed on a side of the transparent substrate facing the space and having a second absorption axis that is parallel to a second direction; and
disposing a phase film at a front side of the first polarizing layer or a side of the second polarizing layer facing the space, the phase film having a slow axis that is orthogonal to the first direction or parallel to a third direction that is parallel to the second direction, thereby reducing a transmittance of a case where the display plane is viewed through the light-transmitting portion from an oblique direction with an elevation angle of 45° when the display plane has an azimuth angle of 45°.
According to embodiments of the present invention, a peeking prevention system, a method of peeking prevention, and a window piece for use therewith that can prevent peeking from oblique directions are provided.
Hereinafter, with reference to the drawings, a peeking prevention system, a method of peeking prevention, and a window piece for use therewith according to embodiments of the present invention will be described. Peeking prevention systems, methods of peeking prevention, and window pieces according to embodiments of the present invention are not limited to what will be illustrated hereinbelow.
In the following description of the present specification, a polarizing layer means a layer that absorbs linearly polarized light, the layer not having any phase difference (retardation); usually, it is composed of a polyvinyl alcohol layer containing iodine, exclusive of any triacetyl cellulose (TAC) layer or the like to protect the polarizing layer. On the other hand, a phase film may include a plurality of phase layers and adhesion layers. As will be described later by way of Examples, a phase film is inclusive of those having two or more phase layers, being respectively represented by different refractive index ellipsoids, that are stacked with an optical adhesive or an optical tackiness agent.
The peeking prevention system 100 includes: a display device 10D including a first polarizing layer 10 on a front side of a display plane, the first polarizing layer 10 having a first absorption axis AX1 that is parallel to a first direction; and a partition to delimit from the surroundings a space (inside of the room) PSS in which displaying is to be provided by the display device 10D, the partition having a light-transmitting portion 20W through which the inside of the space PBS is viewable. The light-transmitting portion 20W includes: a transparent substrate; and a second polarizing layer 20 being disposed on a side of the transparent substrate facing the space PBS and having a second absorption axis AX2 that is parallel to a second direction. Hereinafter, the display plane may be denoted by the same reference numeral 10D as the display device.
Note that the first direction and the second direction may be reversed, i.e., the first direction may be the vertical direction and the second direction may be the horizontal direction. In either case, they may be offset respectively by about 5° from the horizontal direction or the vertical direction; even if the first direction and the second direction are offset by about 10° from an orthogonal relationship, the effect of peeking prevention as described below will be obtained. While a configuration for obtaining an effect of peeking prevention in the case where the first direction and the second direction are of an orthogonal relationship will be described herein, configurations for obtaining an effect of peeking prevention in the case where the first direction and the second direction are offset from an orthogonal relationship will be apparent to those skilled in the art based on the disclosure of the present specification. Although a liquid crystal display device having an absorption axis along the horizontal direction will be illustrated as an example, this being widely used for large-sized liquid crystal display devices, this is not a limitation.
The partition in
The peeking prevention system 100 further includes a phase film 30 disposed on the front side of the first polarizing layer 10. When the direction of the slow axis of the phase film 30 is termed a third direction, this third direction is orthogonal to the first direction, or parallel to the second direction. As will be described later, the phase film 30 may be disposed on a side of the second polarizing layer 20 facing the space PSS.
The phase film 30 has an azimuth angle ϕ of 45°, for example, and acts to reduce the transmittance of the case where the display plane 10D is viewed through the light-transmitting portion 20W from an oblique direction with an elevation angle θE of 45°. When the display plane 10D is regarded as a clock face, the azimuth angle ϕ is 0° at 3 o'clock and reads positive counterclockwise. The elevation angle θE is referenced against a horizontal plane that is perpendicular to the display plane 10D (0°). With such a phase film 30, when the display plane 10D is viewed from an oblique direction (from above or below (elevation angle θE≠0°) or from right or left (azimuth angle ϕ≠0°) relative to the first polarizing layer 10, via the second polarizing layer 20 making 30° to 150° with the display plane 10D, the information displayed thereon can be made difficult to be seen.
In the present specification, the following physical properties or parameters are used to characterize the optical anisotropy of a phase film. Principal refractive indices for three orthogonal axes x, y and z are denoted as nx, ny and nz, where nx≥ny. The thickness of the phase film is denoted as d; a product (nx−ny)·d between (nx−ny) and d is referred to as a frontal retardation Re; and a product (nx−nz)·d between (nx−nz) and d is referred to as a thickness-direction retardation Rth. Rth/Re is referred to as an Nz factor. Moreover, nx>ny=nz defines a positive A plate; nx=ny>nz defines a negative C plate; nz=nx>ny defines negative A plate; and nz>nx=ny defines a positive C plate. A positive C plate may be denoted as +C, whereas a negative C plate may be denoted as −C.
Hereinafter, the problem of being peeked at from an oblique direction will be described by contrasting it with the problem of leakage of light at oblique viewing angles in a liquid crystal display device. First, with reference to
As shown in
However, as shown in
With reference to
First,
On the other hand, when the liquid crystal display device LCD is viewed obliquely as shown in
In the optical compensation by the liquid crystal display device LCD, as shown in
Next, with reference to
Through a simulation, configurations for the phase film for preventing leakage of light in the peeking prevention system 100 were studied. For the simulation, LCD Master 1D Scription by SHINTECH Co., Ltd. was used, and visual transmittance was determined for visible light in a wavelength range from 380 nm to 780 nm. The first polarizing layer 10 and the second polarizing layer 20 both had a transmittance of 43.1% and a degree of polarization of 99.99%. The angle made by the first polarizing layer 10 and the second polarizing layer 20 was 90°, and the second polarizing layer 20 was supposed to be formed on a glass substrate having a refractive index of 1.5. The polarizing layer 20 had an ordinary light refractive index of 1.5, and the angle θb (see
Upon studying various configurations, it was found that, as is schematically shown in
Next, examples of specific configurations for a peeking prevention system according to an embodiment of the present invention will be described. The configuration of a peeking prevention system according to an embodiment of the present invention can be classified into five Types A to E, as characterized by: the azimuth angle ϕ (0° or 90°) of the absorption axis AX1 of the first polarizing layer 10 and the absorption axis AX2 of the second polarizing layer 20; the azimuth angle ϕ of the slow axis SX of the phase film; in the case where the phase film includes a first phase layer and a second phase layer (the first phase layer being disposed closer to the polarizing layer than is the second phase layer), the azimuth angles (ϕ1, ϕ2) of the respective slow axes SX1 and SX2; and the magnitudes of Re and Rth, the value of the Nz factor, and the wavelength dispersion (normal, anomalous, or flat) of each phase layer. Characteristic aspects of Types A to E are shown in Table 1. The preferable conditions for each type are based on the aforementioned simulation. Some of specific simulation results are exemplified in Table 2, and will be described below. Regarding wavelength dispersions of the phase layers in Table 1, those configurations which say anomalous dispersion or flat are meant to indicate that anomalous dispersion or flat is particularly preferable, although a phase layer with normal dispersion is still usable. Those configurations whose wavelength dispersion is left blank have no preferable wavelength dispersions associated therewith in particular.
Hereinafter, with reference to the drawings, characteristic aspects of the respective configurations of Types A to E will be described.
[Type A]
The peeking prevention system 100A1 of Type A shown in
The peeking prevention system 100A2 of Type A shown in
In the peeking prevention system 100A1, as shown in
The peeking prevention system 100B1 of Type B shown in
The peeking prevention system 100B2 of Type B shown in
In the peeking prevention system 100B1, as shown in
[Type C]
The peeking prevention system 1001C of Type C shown in
The peeking prevention system 100C2 of Type C shown in
The slow axes SX-B1 and SX-B2 of the first and second phase layers 30B1 and 30B2 are both parallel to the vertical direction, and orthogonal to the absorption axis AX2.
In the peeking prevention system 1001C, as shown in
[Type D]
The peeking prevention system 100D1 of Type D shown in
The peeking prevention system 100D2 of Type D shown in
In the peeking prevention system 100D1, as shown in
[Type E]
The peeking prevention system 100E1 of Type E shown in
The peeking prevention system 100E2 of Type E shown in
In the peeking prevention system 100E1, as shown in
Some of the results of simulations performed for the specific examples of a peeking prevention system according to an embodiment of the present invention are shown in Table 2. As Comparative Example 1, Table 2 also shows a result for the case of not performing compensation by a phase film. Also, shown as Example 0 is an example of employing the phase film which was used for preventing leakage of light in the liquid crystal display device described with reference to
Discussed next are results of prototyping a system corresponding to the peeking prevention system 1001C shown in
In Table 3, “Reference” corresponds to using no phase film. Experimental Example 1 used a first phase layer (Re: 65 nm, Nz factor: 3.8) and a second phase layer (Re: 85 nm, Nz factor: 1.0) (corresponding to Example 9 in Table 2). Experimental Example 2 used a first phase layer (Re: 52 nm, −Nz factor: 2.4) and a second phase layer (Re: 140 nm−Nz factor: 1.0) (corresponding to Example 8 in Table 2). As the phase layer, a phase film made of a cyclo olefin (ZeonorFilm (registered trademark) manufactured by Nippon ZEON Co., Ltd.) was used in every case. As the first polarizing layer 10 and the second polarizing layer 20, polarizing plates of an acrylic resin (manufactured by Nitto Denko Corporation) having a transmittance of 43.2% and a degree of polarization of 99.99% was used in every case. It will be appreciated that the phase layers and polarizing layers to be used for embodiments of the present invention are not limited to these, and known phase layers and polarizing layers can be used. A polarizing layer and a phase layer, or two phase layers, are to be attached together by using an optical adhesive or an optical tackiness agent. Alternatively, a polarizing layer and a phase layer may be directly stacked without using any adhesive/tackiness agent. Furthermore, as necessary, a protection layer (e.g., a TAC layer) may be provided. The retardation of a phase film is inclusive of the retardations of an adhesion layer and a protection layer.
As can be seen from the results in Table 3, simulation results well match the actually measured values. It can also be seen that, a peeking prevention system according to an embodiment of the present invention can prevent peeking from oblique viewing angles highly accurately.
In the peeking prevention systems according to embodiments of the present invention described above, a display device including a first polarizing layer on a front side of a display plane, the first polarizing layer having a first absorption axis that is parallel to a first direction, was exemplified by: a liquid crystal display device that includes a polarizing layer having an absorption axis in the horizontal direction (or the vertical direction). However, this is not a limitation. For example, an LED display device (including a micro LED display device) or an organic EL display device performs displaying by using unpolarized light. Also, liquid crystal display devices are known in which a ¼ wavelength plate or a phase layer having a large retardation is disposed further outside of the polarizing layer on the front side, so that displaying will be seen even through polarizing sunglasses. In the case of using a display device such that the light which is emitted from the display device itself is unpolarized light or circularly polarized light, the first polarizing layer may be provided on the front side of the display device. The direction of the absorption axis of the first polarizing layer is preferably parallel to the horizontal direction or the vertical direction, and is particularly preferably parallel to the horizontal direction.
Furthermore, a phase layer having a frontal retardation of 4000 nm or more may further be disposed between the display plane and the first polarizing layer, in the case of using: a liquid crystal display device, such as a TN mode liquid crystal display device, in which the direction of the absorption axis of a polarizing layer that is disposed on the front side of the display plane is greatly offset from the horizontal direction or the vertical direction (in the case of a TN mode liquid crystal display device, the azimuth angle is 45° or 135°); or a display device in which a circular polarizing plate is disposed on the front side of the display plane in order to suppress a decrease in visual recognition due to external light (e.g., an organic EL display device), such that the absorption axis of the polarizing layer has an uncertain (i.e., unknown to the user) orientation. A phase layer having such an extremely large frontal retardation acts to depolarize light. For example, even if linearly polarized light with a degree of polarization of 99% or more is incident, after it passes through such a phase layer, its degree of polarization may become 1% or less. The light which has been depolarized (unpolarized light) is converted by the first polarizing layer into polarized light of a predetermined polarization direction. Therefore, this is usable as the aforementioned peeking prevention system.
As a phase layer having a frontal retardation of 4000 nm or more, for example, a phase film described in Japanese Patent No. 3105374 or Japanese Laid-Open Patent Publication No. 2011-107198 can be used. Although not particularly limited, the upper limit value of the frontal retardation may be e.g. 30000 nm. While exceeding this does not affect depolarization effect, it may reduce manufacturing yield. A configuration using such a phase layer is described in Japanese Patent Application No. 2020-064553, filed on the same day as the present application. The entire disclosure of Japanese Patent Application No. 2020-064553 is incorporated herein by reference.
As described above, according to an embodiment of the present invention, a peeking prevention system and a method of peeking prevention using the same that can prevent peeking from oblique directions are provided. In a peeking prevention system according to the present embodiment, the phase film 30 may be provided on the polarizing layer 10 (phase film 30A), or on the polarizing layer 20 (phase film 30B). In the case where the phase film 30B is provided on the polarizing layer 20, a window piece for use in a peeking prevention system is provided. The window piece includes: a polarizing layer 20 disposed on the room side of a transparent substrate (not shown), the polarizing layer 20 having an absorption axis that is parallel to the vertical direction or the horizontal direction; and a phase film 30 disposed on the room side of the polarizing layer 20. In a plan view of an imaginary plane (corresponding to the display plane 10D) located inside the room as viewed along a line-of-sight direction from outside of the room, when linearly polarized light having a polarization axis that is orthogonal to a horizontal line segment or a vertical line segment on the imaginary plane propagates in a direction with an angle θ (corresponding to the angle θa in
With a peeking prevention system, a method of peeking prevention, and a window piece for use therewith according to an embodiment of the present invention, oblique peeking can be prevented highly accurately.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-064604 | Mar 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/013051 | 3/26/2021 | WO |
