WO2007118122A2

WO2007118122A2 - Anti-snooping sheet and display device comprising the same

Info

Publication number: WO2007118122A2
Application number: PCT/US2007/065965
Authority: WO
Inventors: Koji Hishitani; Hiroshi Ooshima; Tokutaro Hara; Norikazu Maeda
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2006-04-07
Filing date: 2007-04-04
Publication date: 2007-10-18
Anticipated expiration: 2008-10-07
Also published as: WO2007118122A3; JP2007279424A

Abstract

In one embodiment, the present invention provides an anti-snooping sheet comprising a first louver layer, a second louver layer and a prism layer capable of directing incident light. The first louver layer and the second louver layer each comprises a plurality of louvers extending in parallel to each other at predetermined intervals. The extending direction of the louver of the first louver layer intersects with the extending direction of the louver of the second louver layer. The prism layer comprises a plurality of prism elements extending in parallel to each other and causes the light incident in the direction perpendicular to the sheet to exit at a tilt of 15° to 25°.

Description

ANTI-SNOOPING SHEET AND DISPLAY DEVICE COMPRISING THE SAME

Background The present invention relates to an anti-snooping sheet and a display device comprising the same. More specifically, the present invention relates to an anti-snooping sheet and a display device, ensuring that an image can be restrictively viewed only by a user with high brightness.

A personal computer (PC), a portable terminal, an unmanned customer service device (e.g., automated teller machine (ATM) of bank, ticket- vending machine at station) and the like need to display an image to provide a user with information. This image is usually displayed by using a display device. Such a display device usually comprises, as the essential constituent element, a composite unit comprising a display and a light- transmitting panel disposed to cover the light-outgoing surface (display screen) of the display, that is, a display unit. The light-transmitting panel comprises a back surface facing the light-outgoing surface of the display and a front surface opposite the back surface, which an operator (user) can touch. The operator can view a displayed image through the light-transmitting panel.

As for the light-transmitting panel, a transparent protective panel used for protecting the display screen or a touch panel having a contact switch function is used. In the case where the light-transmitting panel is a touch panel, the display unit itself can be designed to have a function that switching is effected upon touching by a user directly with a finger or the like or indirectly by the use of a touch pen or the like (that is, an ON- OFF function). The display is, for example, a liquid crystal display (sometimes also called a liquid crystal display device). The liquid crystal display usually comprises a liquid crystal display panel (hereinafter, sometimes referred to as a "liquid crystal panel") and a light source (that is, a backlight) for illuminating the liquid crystal panel from its back surface (a surface opposite the display surface). The liquid crystal panel comprises a pair of first and second polarizing plates and a liquid crystal layer interposed therebetween. These two polarizing plates are disposed such that the polarization axis of the first polarizing plate (first polarization axis) and the polarization axis of the second polarizing plate (second polarization axis) make a certain angle with each other, for example, make an orthogonal arrangement. The backlight is, for example, a so-called edgelight-type backlight comprising a light-guide plate and a light source which supplies light into the light-guide plate from the lateral face of the light-guide plate. Such a backlight illuminates the back surface of the liquid crystal panel to spread the illuminating light over a relatively wide angle range, and the light transmitted through the liquid crystal panel exits also in the direction (side direction) remote from the front direction of the display surface. For example, when the light outgoing from the surface of an automobile-loaded display device such as car navigation system exits in the front window direction (longitudinal direction) and the side window direction (transverse direction), this comes to hinder the eyesight of a driver. Accordingly, it is demanded to control such light outgoing at a wide angle. Patent Document 1 (Japanese Unexamined Patent Publication (Kokai) No. 2004-109615) discloses a louver film comprising a first louver layer and a second louver layer, which are bonded to each other, wherein the first louver layer and the second louver layer each comprises a plurality of louvers extending in parallel to each other at predetermined intervals and the extending direction of the louver of the first louver layer intersects with the extending direction of the louver of the second louver layer. Such a film limits the angle of the outgoing light in a display device so that the light can exit at a narrow angle. However, this louver film limits the light outgoing direction over almost all directions (directions of all outgoing angles), and the display screen is obscured from the oblique direction, though good observation may be ensured from the direction perpendicular to the screen of the display device. For example, in a display device where the display screen is disposed at an angle relatively close to the horizontal direction, such as unmanned customer service device (e.g., automated teller machine (ATM) of bank, ticket-vending machine at station), the louver film may exert a certain effect of preventing a furtive glance from the lateral or rear direction but may obscure the screen also from the operator.

On the other hand, Patent Document 2 (National Publication of Translated Version (Kohyo) No. 2003-513306) discloses a display device comprising a light modulation layer, a polarizer and a light-directing film comprising a prism structure. By the use of this display device, an optimal observation angle can be offset from the glare angle in a display. When this display device is applied to an unmanned customer service device, the visibility from the operator may be enhanced but a furtive glance cannot be prevented. In recent years, there arises a case that a video camera is disposed on an unmanned customer service device to spy out the personal identification number (PIN) of a customer, and a security apparatus installable in a display device is demanded. Summary of the Invention

In another embodiment, the present invention provides a display device comprising a backlight, the above-described anti-snooping sheet, a liquid crystal display (LCD) and a touch panel.

Brief Description of The Drawings

Fig. 1 is a schematic view showing the viewing range of image information from a display device where the anti-snooping sheet of the present invention is not disposed.

Fig. 2 is a schematic view showing the viewing range in the case of disposing an optical sheet comprising two louver layers, in which the extending direction of the louver of the first louver layer is intersecting with the extending direction of the louver of the second louver layer.

Fig. 3 is a schematic view showing the viewing range in the case of disposing the anti-snooping sheet of the present invention.

Fig. 4 is a schematic view showing an unmanned customer service device where a spy camera is disposed.

Fig. 5 is a cross-sectional view showing one embodiment of the anti-snooping sheet of the present invention.

Fig. 6 is a cross-sectional view showing one embodiment of the louver layer.

Fig. 7 is a top view of a stacked body where the first louver layer intersects with the second louver layer.

Fig. 8 is an enlarged cross-sectional view showing one embodiment of the prism layer.

Figs. 9a-9b are perspective views showing the anti-snooping sheet of the present invention. Figs. 1Oa-IOb are perspective views showing the anti-snooping sheet of the present invention. Figs. 1 Ia-I Ib are perspective views showing the anti-snooping sheet of the present invention.

Fig. 12 is a schematic view showing the extending directions of louvers and prism elements. Fig. 13 is a graph showing the relationship between the observation angle with respect to the screen of the display device and the brightness in Examples.

Figs. 14a-14c are graphs showing the relationship between the observation angle with respect to the screen of the display device and the brightness in Examples.

Detailed Description

An object of the present invention is to provide an anti-snooping sheet enhanced in the visual field restriction and visibility as compared with conventional techniques, and a display device comprising the same.

When the anti-snooping sheet of the present invention is used, the visual field angle of a display device is narrowed, so that a furtive glance by other than the operator can be prevented. Furthermore, the brightness in the operator direction increases, so that the visibility from the operator can be enhanced.

The present invention is described below based on its preferred embodiments. First, the outline of the present invention is described by referring to the drawings. Fig. 1 is a schematic view showing the viewing range of image information from a display device where the anti-snooping sheet of the present invention is not disposed. This display device (customer service device) 1 has a wide visual field range and allows for a furtive glance from all of the lateral, forward and backward directions of the operator 2 standing at the display device 1. Fig. 2 is a schematic view showing the viewing range in the case of disposing an optical sheet comprising two louver layers, in which the extending direction of the louver of the first louver layer is intersecting with the extending direction of the louver of the second louver layer. The visual field angle is narrowed and a certain effect of preventing a furtive glance can be obtained, but the viewing range spreads also ahead of the display device and a video camera can spy when disposed in the device upright part or the forward wall surface part. Fig. 3 is a schematic view showing the viewing range in the case of disposing the anti-snooping sheet of the present invention. The viewing range is limited to the operator 2 standing at the display device 1 and a furtive glance from the forward direction can be prevented. In turn, as shown in Fig. 4, the action of spying out the input information by disposing a video camera 3 on the front surface of the display device 1 or on the forward wall surface can be prevented. The anti-snooping sheet of the present invention is an anti-snooping sheet comprising a first louver layer, a second louver layer and a prism layer capable of directing incident light, in which the first louver layer and the second louver layer each comprises a plurality of louvers extending in parallel to each other at predetermined intervals, and the extending direction of the louver of the first louver layer intersects with the extending direction of the louver of the second louver layer. Fig. 5 is a cross-sectional view showing one embodiment of the anti-snooping sheet of the present invention. The anti-snooping sheet 1 comprises a prism layer 11, a first louver layer 12 and a second louver layer 13, and the first louver layer 12 and the second louver layer 13 are bonded by a highly transparent adhesive layer 14. The prism layer 11 comprises a sawtooth part 16 as a prism element formed on a base 15. The plurality of prism elements extend in parallel to each other and are present each by forming a triangular prism in the direction perpendicular to the paper surface of Fig. 5. The prism layer 11 is joined with the first louver 12 along the edge part of the prism layer 11 through an adhesive layer 17 and except for that portion, forms a void 18 between the sawtooth part 16 and the first louver layer 12.

The elements constituting the anti-snooping sheet of the present invention each is described below.

Louver Layer

The anti-snooping sheet of the present invention comprises a first louver layer and a second louver layer. The louver layer itself is known. The louver layer has in its inside a plurality of fine louvers (also sometimes called louver-like elements or louver members) extending in parallel to each other at predetermined intervals along the in-plane direction parallel to the louver layer surface. The plurality of louvers built-in inside the louver layer can exert an effect of controlling the travelling direction of light transmitted through the louver layer to fall in a specific outgoing angle range (direction-control effect). That is, the light output in the direction across the louver extending direction is absorbed or reflected by the louver, and the quantity of light outgoing in that direction can be controlled to be low, so that the light can be effectively prevented from outgoing in the lateral direction.

The construction, production method and usage of the louver layer are disclosed in several prior publications. For example, as described in U.S. Patent RE27,617, the louver layer may be formed by alternatingly providing a plastic layer having a relatively low optical density (transparent) and a plastic layer having a relatively high optical density

(colored), and skiving the resulting billet. After the billet is skived, the colored layer gives a louver-like element. The louver-like element is extending in a specific direction on the plane of the louver layer. The louver-like element may also be designed to extend at right angles to the louver layer surface or incline with respect to the louver layer surface. The louver layer absorbs or reflects light outgoing in the direction nearly perpendicular to the extending direction of the louver-like element, whereby the outgoing angle is restrained. On the other hand, the louver-like element does not exert such a restraining effect for the light output in the direction nearly parallel to the extending direction of the louver-like element.

The light-transmitting part of the louver layer is preferably formed of a polymer having high transparency. As for the polymer, a thermoplastic resin, a thermosetting resin, a photocurable resin and the like can be used. Examples thereof include a cellulose-based resin such as cellulose acetate butyrate and triacetylcellulose, a polyolefin resin such as polyethylene and polypropylene, a polyester resin such as polyethylene terephthalate, a polystyrene, a polyurethane, a polyvinyl chloride, an acrylic resin, and a polycarbonate resin.

On the other hand, the louver-like element is formed of a light-shielding material capable of absorbing or reflecting light. Examples of the light-shielding material include (1) a dark pigment or dye of black, gray or the like, (2) a metal such as aluminum and silver, (3) a white inorganic oxide such as titanium dioxide, and (4) a dark metal oxide. The louver-like element may also be formed of a material obtained by incorporating a substance of these (1) to (4) into the above-described polymer having high transparency.

The louver layer may be produced as follows. First, a layer containing a light- shielding material is fixed to one main surface of a polymer film used as the light- transmitting part to form a louver-like element, thereby obtaining a paired laminate film consisting of a polymer film and a light-shielding material layer. A plurality of such paired laminate films are prepared and stacked to form a louver film precursor in which the polymer film and the light-shielding material layer are alternately arranged and fixed to each other. This louver film precursor is sliced to a predetermined thickness along the direction (stacking direction) orthogonal to the main surface (stacked surface) of the precursor, whereby a louver layer can be obtained. The louver layer may comprise a polymer layer (a layer not containing a louver inside) covering either one or both of the front surface and the back surface.

When the anti-snooping sheet of the present invention comprises two or more these louver layers, the light outgoing direction can be more restricted. That is, the first louver layer and the second louver layer are arranged such that the extending direction of the louver of the first louver layer intersects with the extending direction of the louver of the second louver layer. Therefore, the light outgoing in the direction nearly parallel to the extending direction of the louver of the first louver layer is suppressed from its outgoing by the louver of the second louver layer and the light as a whole can be controlled to exit at a narrow angle. Fig. 6 is a cross-sectional view showing one embodiment of the louver layer. The louver layer 12 or 13 comprises a plurality of louvers (louver- like elements) 19 and, as shown in the Figure, limits the outgoing angle to the visible angle α. In the Figure, the louver angle β of the louver layer 12 or 13 is 90°, but the louver may be slightly inclined. As seen from the Figure, the visible angle α is determined by the louver thickness of the louver layer and the pitch of louvers. In the case of a louver layer where the louver extends in the longitudinal direction of a display device, the visible angle is usually from 40 to 75°, preferably from 40 to 56°. Also, in the case of a louver layer where the louver extends in the transverse direction of a display device, the visible angle is usually from 40 to 75°, preferably from 40 to 56°. If the visible angle is excessively large, a sufficiently high effect of preventing a furtive glance cannot be brought out, whereas if it is too small, the edge part of the display screen is obscured also from the operator. The louver thickness of the louver layer is usually from 40 to 500 μm, and the width of the louver 19 is usually from 3 to 50 μm. In this case, in order to obtaine a visible angle in the above- described range, the distance between louvers 19 is from 9 to 229 μm. Preferably, the thickness of the louver layer is from 150 to 300 μm and the width of the louver 19 is from 5 to 15 μm. In this case, in order to obtain a visible angle in the above-described range, the distance between louvers 19 is from 36 to 137 μm. In the case of a louver layer having louvers extending in the longitudinal direction of a display device, the louver angle β is usually from 82 to 108°, preferably 90°. If the louver angle is too small or too large, a furtive glance from the right/left direction or obliquely backward direction is easily cast or the display screen is obscured due to low brightness. On the other hand, in the case of a louver layer having louvers extending in the transverse direction of a display device, the louver angle is usually from 84 to 114°, preferably from 90 to 100°. If the louver angle is too small, the image information may be easily spied out by a hidden camera disposed on the back surface side. Incidentally, in the case of a louver layer having louvers extending in the transverse direction of a display device, the louver angle β denoted is an angle when the right side of Fig. 6 is arranged as the top side of the display screen. Fig. 7 shows a top view of a stacked body where the first louver layer intersects with the second louver layer. The crossing angle γ between the first louver and the louver of the second louver layer is usually 90°±30°, preferably 90°±10°, and most preferably 90°. If this angle is less than 60°, the image information may be easily spied out by a hidden camera disposed on the back surface side, whereas if it exceeds an angle of 120°, a furtive glance from the right/left direction or obliquely backward direction may be easily cast. Incidentally, as shown in the Figure, the crossing angle γ denoted is an angle opened toward the top side of a display device.

The louver layer has a structure containing the louver in the vertical direction (or, depending on the case, the louver may be slightly inclined from the vertical direction) and therefore, tends to warp or curl. In order to avoid this, a transparent plastic layer is preferably disposed on at least one surface of the louver layer. The transparent plastic layer is bonded to the louver layer through an adhesive layer and exerts a function of protecting the louver layer from damages. As for the transparent plastic layer, a polyester (e.g., polyethylene terephthalate (PET), polyethylene naphthalate (PEN)), an acrylic polymer, a vinyl chloride-based polymer, a polyurethane and the like may be used. The thickness of the transparent plastic layer is not limited but is usually from 25 to 200 μm. A commercially available louver film may be used for the louver layer, and examples thereof include "Light Control Film (trademark)" produced by 3M.

Prism Layer

The prism layer directs the light from a display device to the operator so that the operator can view a high-brightness image and furthermore, a furtive glance from the forward direction of the operator can be more efficiently prevented.

The prism layer is not particularly limited as long as the directivity to the optimal observation angle can be achieved. Fig. 8 is an enlarged cross-sectional view showing one embodiment of the prism layer. The prism layer 11 comprises a base part 15 and a sawtooth part 16, and the sawtooth part 16 is extending to form a triangular prism in the direction perpendicular to the paper surface. The outgoing angle θ has a relationship with the incident angle of light on the prism layer 11 (usually in the direction perpendicular to the sheet) and the angles (a, b and c) of the prism. The outgoing angle θ is preferably on the order of 15 to 25° and most preferably 20°. With such an angle, highest operator visibility and highest privacy guarding function can be imparted.

The repeating distance of the sawtooth part 16 is preferably sufficiently small so that the sawtooth part cannot be perceived with a human eye from a typical observation distance. However, the sawtooth part must be large enough to ensure its formation. If the sawtooth part 16 is small, the procedure for the production of the prism layer becomes more difficult. In one embodiment, the repeating distance is from about 5 to about 200 μm, more preferably from 30 to about 80 μm, and most preferably about 50 μm.

The base part 15 has a function of supporting the sawtooth part 16. The base part

15 is sufficient if it has a thickness large enough to ensure the mechanical strength, and the thickness is usually 10 μm or more, preferably from 50 to 200 μm.

The prism layer may comprise a curable resin, an embossable thermoplastic material or other materials capable of forming the sawtooth part and having a desired optical property. The prism layer is preferably formed from a curable resin such as crosslinked epoxy acrylate. The prism layer is preferably free from a pinhole. The composition for the prism layer preferably has high transparency to visible light and high abrasion resistance and less releases a gas. The resin preferably maintains the sawtooth shape without causing shrinkage at the time of curing and exposure to heat and humidity. The crosslinked epoxy acrylate which is preferably used for the prism layer is, for example, a UV-curable composition containing the following components each in a certain range of wt%, that is, a bisphenol-A epoxy diacrylate (from 55 to 80%), a methylstyrene (from 5 to 25%), acrylated epoxy (from 1 to 10%), a photoinitiator (from 0.25 to 5%) (for example, Lucirin TPO) and a fluorosurfactant (from 0.1 to 0.3%). Furthermore, the composition may or may not contain a second photoinitiator such as Irgacure 184 in a wt% of maximum of 5%. The sawtooth part 16 can be formed by a large number of different methods known in the related technique, such as a method of inserting a curable resin between a base part

16 and a tool having a sawtooth part 16, polymerizing the composition under ultraviolet irradiation, and separating the sheet from the tool.

As described above, the anti-snooping sheet of the present invention comprises a first louver layer, a second louver layer and a prism layer, and the first louver layer and the second louver layer each preferably has a protective layer on one surface or both surfaces thereof. These layers may be joined by an adhesive layer. The adhesive layer may be formed from a normal adhesive such as pressure-sensitive adhesive, heat-sensitive adhesive and curable adhesive. The thickness of the adhesive layer is sufficient if it is large enough to join the layers, and the adhesive layer usually has a thickness of 10 to 100 μm.

Figs. 9 to 11 are perspective views showing several embodiments of the anti- snooping sheet of the present invention. In Fig. 9(a), the extending direction of the louver of the first louver layer 12 and the extending direction of the louver of the second louver layer 13 are orthogonal to each other, and the extending direction of the prism element of the prism layer 11 is nearly parallel to the extending direction of the louver of the second louver layer 13. Also, the louver angle of each louver of the first louver layer 12 and the second louver layer 13 is 90°. Fig. 9(b) shows a sheet analogous to that of Fig. 9(a), but the extending direction of the prism element of the prism layer is nearly parallel to the extending direction of the louver of the first louver layer 12. Fig. 10(a) shows a sheet analogous to that of Fig. 9(a), but the louver angle of the second louver 13 exceeds 90° and therefore, the directivity of the display device to the operator side is more enhanced. Fig. 10(b) shows a sheet analogous to that of Fig. 9(b), but the louver angle of the first louver 12 exceeds 90° and therefore, the directivity of the display device to the operator side is more enhanced. Fig. 1 l(a) shows a sheet analogous to that of Fig. 10(a), but the prism layer 11 is disposed on the second louver layer side. Fig. 1 l(b) shows a sheet analogous to that of Fig. 10(b), but the prism layer 11 is disposed on the second louver layer side. In such a case, the prism layer 11 can be joined at its entire surface with the second louver layer 13 through an adhesive layer. A display device forms an image from a plurality of fine pixels. When a regular pattern is superposed on such a device, a periodic fringe pattern, so-called "moire fringes", may appear due to interference of pixels with each other. The anti-snooping sheet of the present invention has a structure that the louvers of the louver layers and the prism element of the prism layer each extends in a fixed direction, and therefore, readily causes the formation of moire fringes in an image on a display device. One method for solving this problem is to deviate each extending direction of the louver of the first louver layer and the louver of the second louver layer from the horizontal and vertical directions. The extending direction of the prism element is also preferably deviated from the horizontal and vertical directions. Fig. 12 is a schematic view showing the extending directions of louvers and prism elements. The extending directions of the louver 19 of the first louver layer, the louver 19' of the second louver layer and the prism element (sawtooth part 16) of the prism layer each is deviated from the horizontal and vertical directions of the display device (namely, from the horizontal and vertical directions of the sheet), whereby generation of moire fringes can be prevented. The angle (counterclockwise) x made by the extending direction of the sawtooth part 16 and the horizontal direction of the sheet (that is, when disposed on a display device, the horizontal direction of the display device) is preferably from 0 to 10° or from 170 to 180°. If this angle is from more than 10° to less than 170°, the light directivity of the sheet deviates to allow for easy glance reading from the obliquely backward side. The angle y made by the louver 19 (the louver extending nearly in the horizontal direction of the display screen of a display device) of the first louver layer and the horizontal direction of the sheet is preferably from 5 to 20° or from 160 to 175°. If this angle is more than 175° or less than 5°, moire fringes are readily formed, whereas if it is from more than 20° to less than 160°, this allows for easy glance reading from the obliquely backward side. The angle z made by the louver 19' (the louver extending nearly in the vertical direction of the display screen of a display device) of the second louver layer and the horizontal direction of the sheet is preferably from 70 to 85° or from 95 to 110°. If this angle is from more than 85° or less than 95°, moire fringes are readily formed, whereas if it is more than 110° or less than 70°, this allows for easy glance reading from the obliquely backward side. Another means for preventing moire fringes is to form non-flat shapes on the surface of the anti-snooping sheet. In order to prevent generation of moire, the non-flat shape is preferably such that the arithmetic mean roughness (Ra) is 0.5 μm or less and the average distance (RSm) between raised or depressed portions is 80 μm. Incidentally, the arithmetic mean roughness (Ra) and the average distance (RSm) between raised or depressed portions are values measured by a surface roughness meter according to JIS- B0601 : 1994. The non-flat shapes may be formed on the front surface or the back surface of the anti-snooping sheet. However, the non-flat shapes cause reduction in the light directivity and therefore, must be designed not to impair the effects of the anti-snooping sheet of the present invention, that is, operator visibility and visible angle restriction. The formation of non-flat shapes has an effect that the adhesion of the film to the opposing surface (for example, a liquid crystal panel or a touch panel) can be prevented.

Display Device

The anti-snooping sheet of the present invention may be incorporated into a display device. The display device having incorporated thereinto the anti-snooping sheet of the present invention includes an unmanned customer service device (e.g., ATM of bank, ticket- vending machine at station). The anti-snooping sheet of the present invention is disposed closer to the operator side than the light source (that is, on the upper side than the light source). The display device is typically a liquid crystal display (LCD) device, and a backlight/an LCD cell/the anti-snooping sheet of the present invention are disposed in this order. The display device may comprise a touch panel and in this case, the touch panel may be disposed above or beneath the anti-snooping sheet. In this way, these members may be disposed in the order of a backlight/an LCD cell/the anti-snooping sheet of the present invention/a touch panel, a backlight/an LCD cell/a touch panel/the anti- snooping sheet of the present invention, or a backlight/the anti-snooping sheet of the present invention/an LCD cell/a touch panel.

Examples The anti-snooping sheet of the present invention is described in greater detail below by referring to Examples. Example 1:

Two sheets of films (lOOC 0UB48 (trade name) and IOOPA 0UB48 (trade name), produced by 3M) each having a plurality of louvers were prepared. These are a film where one sheet of polyethylene terephthalate film (PET) or pressure-sensitive adhesive is laminated on both surfaces of the louver film comprising a plurality of louvers arrayed in parallel, through a UV-curable adhesive (lOOC 0UB48: PET/UV-curable adhesive/louver/UV -curable adhesive/PET, IOOPA 0UB48: pressure-sensitive adhesive/UV-curable adhesive/louver/UV-curable adhesive/PET). The thicknesses of respective films are PET/UV-curable adhesive/louver/UV-curable adhesive/PET = 100 μm/25 μm/250 μm/25 μm/100 μm and pressure-sensitive adhesive/UV-curable adhesive/louver/UV-curable adhesive/PET = 50 μm/25 μm/250 μm/25 μm/100 μm. These films were stacked to form a stacked body comprising a first louver layer and a second louver layer. At this time, the louver layers were arranged such that the extending direction of the louver of the first louver layer and the extending direction of the louver of the second louver layer intersect at 90°. Furthermore, a prism film (IDFII20 (article number), produced by 3M) was laminated to surround the entire circumference at the edge part of the stacked body by a double-sided pressure-sensitive adhesive tape (49058 (article number), produced by 3M), thereby obtaining the anti-proofing sheet of the present invention shown in Fig. 12. The extending directions of the louvers and prism layer were, as expressed by the angles x, y and z in the Figure, x=175°, y=10° and z=100°. The prism film is a film in which a prism structure is formed on a 0.13 mm-thick PET film and the entire thickness is 0.15 mm and which causes the incident light from the normal direction to be bent at 20° on outgoing. The obtained anti-snooping sheet was disposed on a liquid crystal display device, and the relationship between the observation angle with respect to the screen of the display device and the brightness was measured by EZ CONTRAST manufactured by ELDIM. Figs. 13 and 14 show the results. Comparative Example 1:

The relationship between the observation angle with respect to the screen of the display device and the brightness was measured in the same manner as in Example 1 except for not disposing the anti-snooping sheet. Figs. 13 and 14 show the results.

Comparative Example 2:

A sheet was formed in the same manner as in Example 1 except for laminating a prism film. This sheet was disposed on a liquid crystal display device, and the relationship between the observation angle with respect to the screen of the display device and the brightness was measured. Figs. 13 and 14 show the results.

It is seen from these results that the anti-snooping sheet of the present invention can enhance the effect of preventing a furtive glance not only from the right, left and backward directions of the observer but also from the forward direction. In other words, as shown in Fig. 4, in the case where the display device is an unmanned customer service device, the secret data such as personal identification number can be prevented from being spied out through a camera placed by a criminal.

Claims

What is claimed is:

1. An anti-snooping sheet comprising a first louver layer, a second louver layer and a prism layer capable of directing incident light, wherein said first louver layer and said second louver layer each comprises a plurality of louvers extending in parallel to each other at predetermined intervals, the extending direction of the louver of the first louver layer intersects with the extending direction of the louver of the second louver layer, and said prism layer comprises a plurality of prism elements extending in parallel to each other and causes the light incident in the direction perpendicular to the sheet to exit at a tilt of 15° to 25°.

2. The anti-snooping sheet as claimed in claim 1, wherein the extending directions of the louver of said first louver layer and the louver of said second louver layer are deviated from the horizontal and vertical directions of the sheet.

3. The anti-snooping sheet as claimed in claims 1 or 2, wherein non-flat shapes are provided on the front or back surface of said anti-snooping sheet.

4. A display device comprising the anti-snooping sheet claimed in any one of claims 1 to 3.

5. A display device comprising the anti-snooping sheet of claim 1, a backlight, a liquid crystal display cell, and a touch panel.

6. The display device as claimed in claim 4, wherein the backlight, the liquid crystal display cell, the touch panel and the anti-snooping sheet are disposed in this order.

7. The display device as claimed in claim 4, wherein the backlight, the anti-snooping sheet, the liquid crystal display cell and the touch panel are disposed in this order.