JP2009103763A - Lens sheet used for backlight, backlight using the same and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens sheet which exhibits high front brightness by the use of one sheet and attains a wide viewing angle. <P>SOLUTION: The lens sheet 17 used for backlight includes a base film 21, a lenticular lens layer 22, a prism layer 23 and a filler layer 24. The lenticular lens layer 22 is formed on the surface 211 of the base film 21 and includes a plurality of cylindrical lenses 220. The prism layer 23 is formed on the surface 212 of the base film 21, includes a plurality of prisms 230 juxtaposed in the same direction as the juxtaposed direction of the cylindrical lenses 220 and has a refractive index lower than that of the base film 21. The filler layer 24 is filled onto the surface on which the prisms 230 are juxtaposed and has a refractive index higher than that of the prism layer 23. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lens sheet, a backlight using the lens sheet, and a liquid crystal display device. More specifically, the present invention relates to a lens sheet that has a function of improving front luminance and is used for a backlight, a backlight using the lens sheet, and a liquid crystal display device.

  A liquid crystal display device represented by a display is required to improve front luminance. Therefore, a lens sheet that collects light from the surface light source in the front and improves the front brightness is laid on the backlight used for the display. As such a lens sheet, a prism sheet as disclosed in Japanese Patent No. 3262230 is generally used.

  Referring to FIGS. 21 and 22, a conventional prism sheet 100 includes a plurality of columnar prisms PL arranged in parallel with each other on the surface. The refractive index of the prism sheet 100 is about 1.5 to 1.6. The diffused light R100 from the surface light source is refracted on the surface of the prism PL, deflected to the front, and emitted. Thus, the prism sheet 100 improves the front luminance of the display by condensing the diffused light in the front.

  As described above, although the prism sheet 100 improves the front luminance, it also increases the luminance in the front oblique direction. FIG. 23 shows a prism sheet on a backlight having a plurality of fluorescent lamps arranged in the vertical direction of the display screen of the liquid crystal display device so that the method of arranging the prisms is the same as the direction of arranging the fluorescent lamps. It is a graph which shows the viewing angle dependence of the brightness | luminance at the time of laying. The broken line in the figure shows the viewing angle dependence of the luminance in the vertical direction of the display screen, and the solid line in the figure shows the viewing angle dependence of the luminance in the horizontal direction. In the figure, the horizontal axis represents the viewing angle, and the vertical axis represents the relative luminance based on the front luminance of the liquid crystal display device in which no prism sheet is laid.

  Referring to FIG. 23, in both the vertical direction and the horizontal direction, the luminance is substantially constant up to a predetermined viewing angle (about ± 30 deg in the vertical direction and about ± 50 deg in the horizontal direction) centering on the viewing angle 0 deg. However, when a predetermined viewing angle is exceeded, the brightness rapidly decreases in both the vertical direction and the horizontal direction. Further, in the vertical direction, when the viewing angle exceeds ± 50 deg, the luminance increases again, and so-called side lobes appear. Such a sudden decrease in luminance and side lobe gives the user a discomfort when viewing the display screen of the liquid crystal display device. Therefore, it is preferable that the luminance has a natural orientation distribution that gradually decreases with a widening of the viewing angle with a viewing angle of 0 deg (that is, the normal direction of the display screen) as a peak.

  In order to eliminate such an unnatural luminance viewing angle characteristic, recently, a liquid crystal display device using a backlight in which two diffusion sheets are laminated has appeared. In this case, the viewing angle dependency of the luminance is a natural orientation distribution in which the luminance gradually decreases with the widening of the viewing angle with the viewing angle of 0 deg as the luminance peak. Further, since two diffusion sheets are used, high front luminance can be obtained.

  However, the distribution width of the viewing angle dependency of luminance is narrowed. A user who uses a liquid crystal display device has more opportunities to view a display screen from a diagonal direction than a diagonal direction. Therefore, it is particularly preferable that the left and right direction has a wide viewing angle. Specifically, in the viewing angle dependency of the luminance in the left-right direction of a liquid crystal display device including an IPS liquid crystal panel, a luminance viewing angle range (hereinafter referred to as a １ ／ viewing angle) that is 1/3 or more of the front luminance. ) Is preferably 120 deg or more.

  In addition, two diffusion sheets must be stacked on the surface light source, which complicates the manufacturing process.

Furthermore, when the backlight includes a plurality of line light sources arranged in parallel with each other, luminance unevenness may occur. The luminance unevenness gives the user viewing the display screen a feeling of strangeness. Therefore, it is preferable to suppress the occurrence of luminance unevenness.
Japanese Patent No. 3262230 Japanese Patent Application No. 2006-126839 (unpublished prior application of the same applicant)

  An object of the present invention is to provide a lens sheet that has high front luminance and can realize a wide viewing angle.

  Another object of the present invention is to provide a lens sheet that can suppress luminance unevenness.

Means for Solving the Problems and Effects of the Invention

  The lens sheet according to the present invention is used for a backlight. The lens sheet includes a base film, a lenticular lens layer, a prism layer, and a filling layer. The lenticular lens layer includes a plurality of cylindrical lenses formed on one surface of the base film and arranged in parallel with each other. The prism layer includes a plurality of first prisms formed on the other surface of the base film and arranged in the same direction as the parallel arrangement direction of the plurality of cylindrical lenses, and has a lower refractive index than the base film. . The filling layer is filled on the surface on which the first prisms of the prism layer are arranged side by side, and has a refractive index higher than that of the prism layer. Here, the base film may be a film shape, a sheet shape, or a plate shape.

  In the lens sheet according to the present invention, incident light rays are condensed stepwise. Since the refractive index of the filling layer is higher than the refractive index of the prism layer, the diffused light incident on the filling layer is refracted on the prism surface and collected on the front surface. Next, since the refractive index of the base film is higher than the refractive index of the prism layer, the light beam incident on the base film from the prism layer is refracted on the surface of the base film and condensed more on the front. Furthermore, the light beam emitted from the base film enters the lenticular lens layer, is refracted on the convex surface of the cylindrical lens, and is condensed and emitted to the front. As described above, the lens sheet of the present invention includes the prism and the cylindrical lens, and reduces the refractive index of the prism layer to be smaller than the refractive indexes of the base film and the filling layer, thereby allowing the incident light beam to enter the lens sheet. The light can be condensed step by step. Therefore, high front luminance can be obtained with a single sheet.

  Furthermore, even if the lens sheet according to the present invention includes a plurality of prisms, the occurrence of side lobes can be suppressed. The following can be considered as reasons for suppressing the occurrence of side lobes. The side lobe in the prism sheet is formed by light emitted at a wide angle with respect to the normal of the prism sheet (hereinafter referred to as side lobe light). In such sidelobe light, a light beam totally reflected on one of the surfaces (two side surfaces) of the prism is transmitted and emitted on the other side surface. In the lens sheet of the present invention, the filling layer is filled between the plurality of prisms of the prism layer. That is, a plurality of prisms are also formed on the surface of the filling layer. Although the refractive index of the prism layer is smaller than that of the filling layer, it is larger than that of air. Therefore, the critical angle is larger on the prism surface on the packed layer than on the conventional prism sheet. Therefore, the ratio of total reflection of light rays on the side surfaces of the prism on the filling resin layer is reduced, and the occurrence of side lobes is suppressed.

  In addition, in the cylindrical lens formed on the surface of the lens sheet of the present invention, light that is totally reflected on one side like a prism is rarely transmitted on the other side, and light that has been totally reflected once is rarely transmitted. When it is incident on the convex surface of the lens again, it is often totally reflected again. Therefore, sidelobe light emitted at a wide angle with respect to the lens sheet normal can be suppressed.

  Furthermore, in the lens sheet of the present invention, the parallel arrangement direction of the cylindrical lenses and the parallel arrangement direction of the first prism are substantially the same. Therefore, the viewing angle dependence of the luminance in the longitudinal direction of the cylindrical lens and the first prism shows a wide distribution and a wide viewing angle. Moreover, since the parallel arrangement direction of the cylindrical lenses and the parallel arrangement direction of the first prism are substantially the same, the occurrence of uneven brightness can be suppressed.

  Here, the parallel arrangement direction of the cylindrical lenses and the parallel arrangement direction of the first prisms do not have to be exactly the same, and may be almost the same. Specifically, it may be the same as long as the effect of the present invention is achieved.

  Preferably, the filling layer includes a plurality of second prisms each filled between adjacent first prisms, and the ridge line of the second prism meanders in the width direction of the second prism. Yes.

  In this case, the occurrence of moire caused by the arrangement of the cylindrical lenses and the arrangement of the second prism can be suppressed.

  Preferably, the pitches of the plurality of first prisms and / or the plurality of cylindrical lenses are non-uniform.

  When the pitch of the first prism is constant and the pitch of the cylindrical lens is constant, that is, when the first prism and the cylindrical lens are regularly arranged, the pitch of the first prism and the cylindrical Moire occurs when the pitch of the lens synchronizes at a constant period. If the arrangement pitch of the first prism and / or the cylindrical lens is not uniform, the pitch of the cylindrical lens 220 and the pitch of the prism 240 are difficult to synchronize with each other at a constant period, so that the generation of moire can be suppressed.

  Preferably, the filling layer includes a resin and a plurality of particles. The plurality of particles are dispersed in the resin and have a refractive index different from that of the resin.

  In this case, the light incident on the filling layer diffuses in the filling layer and enters the prism layer. Therefore, the generation of moire can be suppressed.

  The backlight according to the present invention includes the lens sheet described above. A display device according to the present invention includes the backlight. A liquid crystal display device according to the present invention includes the above-described backlight and a liquid crystal panel laid on the backlight.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is incorporated.
[overall structure]
With reference to FIGS. 1 and 2, the liquid crystal display device 1 includes a backlight 10 and a liquid crystal panel 20 laid in front of the backlight 10. The backlight 10 includes a surface light source 16 that emits diffused light, and a lens sheet 17 laid on the surface light source 16.
[Surface light source]
The surface light source 16 includes a housing 11, a plurality of fluorescent tubes 12 that are line light sources, and a light diffusion plate 13. The housing 11 is a housing having an opening 110 on the front surface, and houses the fluorescent tube 12 therein. The inner surface of the housing 11 is covered with a reflective film 111. The reflection film 111 diffuses and reflects the light emitted from the fluorescent tube 12 and guides it to the opening 110. The reflective film 111 is, for example, Toray Lumirror (registered trademark) E60L or E60V, and preferably has a diffuse reflectance of 95% or more.

  The plurality of fluorescent tubes 12 are juxtaposed in the vertical direction (y direction in FIG. 1) in front of the rear surface of the housing 11. The fluorescent tube 12 is a linear light source extending in the left-right direction (x direction in FIG. 1), and is, for example, a cold cathode tube or an EEFL (External Electrode Fluorescent Lamp). A plurality of point light sources such as LEDs (Light Emitting Device) may be housed in the housing 11 together with the fluorescent tube 12. Moreover, a pseudo line light source may be formed by arranging a plurality of housed LEDs in a line.

  The light diffusing plate 13 is fitted into the opening 110 and is disposed in parallel with the back surface of the housing 11. The interior of the housing 11 is sealed by fitting the light diffusing plate 13 into the opening 110. Therefore, it is possible to prevent light from the fluorescent tube 12 from leaking out of the housing 11 from locations other than the light diffusion plate 13, and the light utilization efficiency is improved.

The light diffusion plate 13 diffuses the light from the fluorescent tube 12 and the light reflected by the reflection film 111 and emits the light to the front. The light diffusion plate 13 is composed of a transparent base material and a plurality of particles dispersed in the base material. Since the particles dispersed in the base material have a refractive index different from that of the base material for light having a wavelength in the visible light region, the light incident on the light diffusion plate 13 is diffusely transmitted. The base material of the light diffusing plate 13 is, for example, glass, polyester resin, polycarbonate resin, polyacrylate resin, alicyclic polyolefin resin, polystyrene resin, polyvinyl chloride resin, polyvinyl acetate resin. Resins such as resins, polyether sulfonic acid resins, and triacetyl cellulose resins. The light diffusion plate 13 also functions as a support for the lens sheet 17.
[Lens sheet]
3 and 4, the lens sheet 17 is formed on the base film 21, the lenticular lens layer 22 formed on one surface 211 of the base film 21, and the other surface 212 of the base film 21. The collimated layer 25 is provided. These are integrally formed.

  The base film 21 is transparent with respect to wavelengths in the visible light region. The base film 21 is, for example, glass, polyester resin, polycarbonate resin, polyacrylate resin, alicyclic polyolefin resin, polystyrene resin, polyvinyl chloride resin, polyvinyl acetate resin, polyether. It is composed of a resin such as a sulfonic acid resin or a triacetyl cellulose resin. Both the surfaces 211 and 212 of the base film 21 are flat. Further, the base film 21 may be a film shape, a sheet shape, or a plate shape.

  The lenticular lens layer 22 is formed on the surface 211. The lenticular lens layer 22 includes a plurality of cylindrical lenses 220 arranged side by side. The cylindrical lens 220 is arranged in parallel in the vertical direction of the screen of the liquid crystal display device 1 (y direction in FIG. 1). In other words, the cylindrical lens 220 is juxtaposed in the same direction as the juxtaposition direction of the plurality of fluorescent tubes 12 in the housing 11.

  The transverse shape of the convex surface 221 of the cylindrical lens 220 shown in FIGS. 3 and 4 is a circular arc, but it may be an elliptical arc as shown in FIG. 5A, or the vicinity of the edge of the cylindrical lens is a straight line as shown in FIG. 5B. It may be an arcuate shape.

  The collimating layer 25 includes a filling layer 24 and a prism layer 23. The prism layer 23 includes a plurality of prisms 230 formed on the surface 212 of the base film 21 and arranged in parallel with each other.

  The filling layer 24 is filled on the surface of the prism layer 23 on which the prisms 230 are arranged. A portion of the filling layer 24 filled between the plurality of prisms 230 constitutes a prism 240. Since the prisms 230 are arranged side by side, the plurality of prisms 240 are also arranged side by side. The surface 243 opposite to the surface on which the prisms 240 are arranged is flat. The surface 243 faces the surface light source 16.

  The prisms 230 and 240 are arranged in parallel in the vertical direction of the screen of the liquid crystal display device 1 (y direction in FIG. 1). That is, the parallel direction of the cylindrical lenses 220 is the same as the parallel direction of the prisms 230 and 240. Since the lenticular lens layer 22 is formed on the collimating layer 25 composed of the prisms 230 and 240, no side lobe appears in the luminance viewing angle characteristics, and the luminance increases as the viewing angle increases with the front as a peak. Forms a natural light distribution that decreases. In addition, since the cylindrical lens 220 and the prisms 230 and 240 are arranged side by side in the same vertical direction, the width of the luminance angle distribution in the horizontal direction is widened, and the occurrence of luminance unevenness can be suppressed.

The lenticular lens layer 22, the prism layer 23, and the filling layer 24 are made of resin. More specifically, the lenticular lens layer 22 and the prism layer 23 are made of an ionizing radiation curable resin. The ionizing radiation curable resin is a resin that is cured by ionizing radiation such as ultraviolet rays and electron beams. For example, a polyester acrylate resin, a urethane acrylate resin, a polyether acrylate resin, an epoxy acrylate resin, a polyester methacrylate resin, A urethane methacrylate resin, a polyether methacrylate resin, and an epoxy methacrylate resin. The filling layer 24 may be made of an ionizing radiation curable resin, or may be made of another resin such as polycarbonate or polystyrene.
[Refractive index of each layer in the lens sheet]
The refractive index n23 of the prism layer 23 has the relationship of the following formula (1) with the refractive index n24 of the filling layer 24, and has the relationship of the following formula (2) with the refractive index n21 of the base film 21.

n23 <n24 (1)
n23 <n21 (2)
In short, the refractive index n23 is smaller than the refractive index n24 and the refractive index n21. Since the prism layer 23 is made of resin as described above, its refractive index n23 is larger than the refractive index na of air = 1.0.

  Since the refractive index n24 of the filling layer 24 is larger than the refractive index n23 of the prism layer 23, the collimating layer 25 collimates the light incident on the filling layer 24 to the front and emits it to the base film 21. If the refractive index n24 is increased, the light refraction angle at the lower surface 243 of the filling layer 24 is increased. The light beam collimated by the lower surface 243 reaches the surface of the prism 240 and is collimated further to the front surface. Therefore, the front luminance is further improved when the refractive index n24 is larger. A preferable refractive index n24 of the filling layer 24 is 1.5 <n24 ≦ 1.8. However, even if the refractive index n24 is 1.5 or less, the effect of the present invention can be achieved to some extent as long as it is larger than the refractive index n23.

  The refractive index of the prism layer 23 is smaller than the refractive index of the filling layer 24, but is larger than the refractive index na of air = 1.0. For this reason, the critical angle of light incident on the surface of the prism 240 in the collimating layer 25 is increased. If the critical angle is increased, the ratio of the total reflection of the light incident on the filling layer 24 is reduced, so that the emission of sidelobe light can be suppressed. This point will be described later. A preferable refractive index n23 of the prism layer 23 is 1.3 ≦ n23 ≦ 1.5. However, even if the refractive index n23 is outside the above range, the effects of the present invention can be achieved to some extent if the refractive index n23 satisfies the expressions (1) and (2).

  The refractive index n21 of the base film 21 is larger than the refractive index n23. Therefore, when the light condensed on the front surface by the collimating layer 25 is incident on the surface 212 of the base film 21, it is further collimated on the front surface. Therefore, the base film 21 contributes to the improvement of the front luminance.

The lens sheet 17 having the above configuration suppresses the occurrence of side lobes and has a wide viewing angle in the left-right direction. Moreover, it has the same high front luminance as when two diffusion sheets are laminated. Further, luminance unevenness is suppressed. Hereinafter, these effects will be described in detail.
[Suppression of side lobe]
The lens sheet 17 suppresses the occurrence of side lobes in the vertical viewing angle by the collimating layer 25 and the lenticular lens layer 22.

  The reason why the collimating layer 25 suppresses the side lobes is not necessarily clear, but it is assumed that the following matters are mainly caused.

  First, a side lobe generation mechanism in a conventional prism sheet will be described. In FIG. 6A, among the light beams incident on the prism PL on the conventional prism sheet 100, the light beam R2 is totally reflected by one side surface BP1 of the prism PL, then transmitted through the other side surface BP2 and emitted to the outside. The light ray R2 forms a side lobe.

  Specifically, the light ray R0 emitted in the direction of the angle θ0 from the normal line n0 (front surface of the backlight) of the emission surface of the surface light source 16 reaches the side surface BP1 of the prism PL. When the incident angle θi1 of the light ray R0 is larger than the critical angle θc1, the light ray R0 is totally reflected and propagates in the prism PL as the light ray R1. If the incident angle θi2 is smaller than the critical angle θc1 when the light ray R1 reaches the side surface BP2, the light ray R1 is emitted to the outside as sidelobe light R2 having a wide angle with respect to the normal line n0 (front). .

  In contrast, the collimating layer 25 suppresses the generation of sidelobe light. Referring to FIG. 6B, the collimating layer 25 includes a prism layer 23 and a filling layer 24 that satisfy the relationship of formula (1), and a prism 240 is filled between the plurality of prisms 230.

  Here, it is assumed that the refractive index n24 of the filling layer 24 is the same as the refractive index n100 of the prism sheet 100. In this case, the relative refractive index when the light beam enters the prism layer 23 from the filling layer 24 is smaller than the relative refractive index when the light beam enters the air from the prism sheet 100. This is because the refractive index n23 of the prism layer 23 made of resin is larger than the refractive index of air (= 1.0).

  Since the relative refractive index is small, the critical angle θc0 on the surfaces 241 and 242 of the prism 240 in the collimating layer 25 is larger than the critical angle θc1 on the surfaces BP1 and BP2 of the prism PL of the prism sheet 100. As a result, on the surface of the prism 240, it is considered that the ratio of the light ray R0 that is totally reflected is reduced, and the emission of the sidelobe light R2 can be suppressed.

  The reason why the lenticular lens layer 22 in the lens sheet 17 can suppress the emission of sidelobe light is not necessarily clear, but is presumably mainly due to the following reason. Referring to FIG. 6C, the light ray R0 incident at the same angle θ0 as in FIG. 6A reaches the boundary surface BP3 on the convex surface 221 of the cylindrical lens 220. When the incident angle θi1 of the light ray R0 is larger than the critical angle θc2, the light ray R0 is totally reflected and reaches the boundary surface BP4 on the convex surface. At this time, the incident angle θi2 of the light ray R0 is often larger than the critical angle θc2. Therefore, the light ray R0 is totally reflected again and returns to the surface light source 16. In short, in the cylindrical lens 220, the light beam that has been totally reflected once is more likely to be totally reflected again and return to the surface light source than to be transmitted and emitted to the outside. Therefore, emission of the side lobe light R2 can be suppressed, and generation of side lobes in the luminance angle distribution can be suppressed.

For the above estimated reason, the lens sheet 17 suppresses the occurrence of side lobes at the vertical viewing angle. As a result, it is possible to obtain the viewing angle dependency of the luminance, which shows a natural orientation distribution in which the luminance gradually decreases with the widening of the viewing angle with a viewing angle of 0 deg as a peak.
[Realization of wide viewing angle]
The cylindrical lens 220, the prism 230, and the prism 240 of the lens sheet 17 are all arranged in the same direction as the arrangement direction of the fluorescent tubes 12. Therefore, light in the left-right direction (x direction in the figure) is less likely to be condensed than in the up-down direction (y direction in the figure). As a result, a wide viewing angle can be realized in the luminance angle characteristic in the left-right direction.

  FIG. 7 shows an example of the luminance angle dependency of the lens sheet 17. The horizontal axis in FIG. 7 is the viewing angle. With respect to the viewing angle, the normal direction (front) of the display screen is defined as the 0 deg axis, the tilt angle from the 0 deg axis in the vertical direction is defined as the vertical viewing angle, and the tilt angle from the 0 deg axis in the horizontal direction is defined as the left and right viewing angle. Of the left and right viewing angles, the tilt angle (viewing angle) from the normal to the right is indicated by plus (+), and the tilt angle (viewing angle) from the normal to the left is indicated by minus (−). Similarly, of the vertical viewing angles, the inclination angle (viewing angle) from the normal to the upward direction is indicated by plus (+), and the inclination angle (viewing angle) from the normal to the downward direction is indicated by minus (−). . The vertical axis in FIG. 13 indicates the relative luminance (au), which is the ratio of the luminance at each viewing angle with respect to the front luminance of the surface light source as a reference (1.0). The solid line in FIG. 7 indicates the viewing angle dependency of the luminance in the left-right direction, and the broken line indicates the viewing angle dependency of the luminance in the vertical direction.

  Referring to FIG. 7, the luminance angle dependency of the lens sheet 17 shows a natural orientation distribution in which the viewing angle is 0 deg in both the vertical direction and the horizontal direction, and the luminance gradually decreases as the viewing angle widens.

Furthermore, the luminance angle dependency in the left-right direction is wider than that in the up-down direction. More specifically, when used in a liquid crystal display device including an ISP liquid crystal panel, the viewing angle range in which the luminance is 1/3 or more of the front luminance is 120 deg (−60 deg to +60 deg) or more. The user of the liquid crystal display device has more opportunities to view the display screen from the left and right diagonal directions than the opportunity to view the display screen from the upper and lower diagonal directions. In the present embodiment, the luminance angle dependency in the left-right direction is a wide viewing angle. Therefore, even if the user looks at the display screen from an oblique direction, it is difficult for the user to feel an extreme change in luminance, and the display screen can be viewed without a sense of incongruity.
[Improve front brightness]
In the lens sheet 17, the light incident from the lower surface is condensed on the front by each of the collimating layer 25, the base film 21, and the lenticular lens layer 22. Therefore, the front luminance can be further improved with one sheet.

  The refractive index n24 of the filling layer 24 in the collimating layer 25 is larger than the refractive index n23 of the prism layer 23. Therefore, the collimating layer 25 condenses the diffused light from the surface light source in the front and emits it to the base film 21.

  The refractive index n21 of the base film 21 is larger than the refractive index n23 of the prism layer 23. Therefore, the light beam incident on the base film 21 from the collimating layer 25 is refracted on the lower surface of the base film 21, further condensed on the front surface, and emitted to the lenticular lens layer 22.

  Due to the shape of the convex surface 221, the lenticular lens layer 22 condenses incident light further on the front and emits it to the outside.

As described above, in the lens sheet 17, each of the collimating layer 25, the base film 21, and the lenticular lens layer 22 collimates the incident light beam in the front. Therefore, the front luminance can be further improved with a single lens sheet 17.
[Preventing uneven brightness]
As described above, when the plurality of fluorescent tubes 12 are arranged in the vertical direction, luminance unevenness is likely to occur in the vertical direction. Specifically, the luminance is highest at the portion directly above the fluorescent tube 12, and the luminance is likely to be lowest at the intermediate portion between the adjacent fluorescent tubes 12.

However, in the lens sheet 17 according to the present embodiment, the direction in which the prism 230 and the prism 240 are arranged is the same as the direction in which the plurality of fluorescent tubes 12 in the surface light source 16 are arranged, and the cylindrical lens 220 is arranged in parallel. The direction is also the same as the direction in which the fluorescent tubes 12 are juxtaposed. Therefore, the lens sheet 17 collects more light in the vertical direction (y direction in FIG. 1) and emits it to the front. Therefore, the occurrence of uneven brightness can be suppressed.
[Prevention of moire]
When the prism 230, the prism 240, and the cylindrical lens 220 are arranged in the same direction, moire is likely to occur if the arrangement pitch of these lenses is constant.

  Therefore, preferably, the arrangement pitch of the prisms 230 and / or the arrangement pitch of the cylindrical lenses 220 are made non-uniform. For example, as shown in FIG. 8, a plurality of prisms 230 having the same apex angle are arranged so that the distances Pn and Pn + 1 (n = 1 to 6) between the ridge lines of adjacent prisms 230 are different from each other. Moiré is obtained when the pitch of the cylindrical lenses 220 and the pitch of the prisms 230 and 240 are synchronized with each other when the pitch of the cylindrical lenses 220 is constant and the arrangement pitch of the prisms 230 and 240 is constant. appear. Therefore, if the arrangement pitch of the prisms 230 and / or the cylindrical lenses 220 is not uniform, the pitch of the cylindrical lenses 220 and the pitch of the prisms 230 are difficult to synchronize with each other at a constant period, so that the occurrence of moire can be suppressed.

  9A and 9B, when the collimating layer 25 is viewed from above, adjacent prisms 240 have the same pitch, but the ridgelines of the prisms 240 are not straight but meander in the width direction of the prisms 240. You may do it. Also in this case, since the pitch of the cylindrical lens 220 and the pitch of the prism 240 are difficult to synchronize with each other at a constant period, the occurrence of moire can be suppressed. 9A and 9B, the height of the prism 240 may change in the axial direction.

  As shown in FIG. 10, the pitch of the prisms 230 is preferably smaller than the pitch of the cylindrical lenses 220. The prism 230 is made of a low refractive index resin, but the low refractive index resin is expensive to manufacture. Therefore, it is preferable that the prism layer 23 is formed with as little resin as possible. If the pitch of the prisms 230 in the prism layer 23 is made smaller than the pitch of the cylindrical lenses 220, the period in which the pitches of the cylindrical lenses 220 and the prisms 230 are synchronized becomes longer, so that the occurrence of moire can be suppressed to some extent.

  Furthermore, particles having a refractive index different from the refractive index of the resin constituting the filling layer 24 may be contained in the filling layer 24 that is the lowermost layer of the lens sheet 17. Referring to FIG. 11, the filling layer 24 includes a transparent resin 244 and a plurality of particles (fillers) 245 dispersed in the resin. The filler 245 has a refractive index different from that of the resin.

  The light incident on the inside of the filling layer 24 is diffused to some extent by the filler 245 and emitted to the prism layer 23. Therefore, the occurrence of luminance unevenness and moire can be suppressed.

The filler 245 may be made of an organic material or an inorganic material. The filler 245 is, for example, calcium carbonate, barium sulfate, titanium oxide, silicone fine particles, acrylic fine particles, styrene fine particles, MS fine particles, glass fine particles, or the like. These may be used alone or in combination. The particle size of the filler 245 is not particularly limited, but if it is excessively large, it is difficult to form the filling layer 24. On the other hand, if it is too small, the diffusion effect is small. A preferable particle size of the filler 245 is 0.5 μm to 10 μm. If the filler 245 is excessively contained, the front luminance of the lens sheet 17 is lowered. Therefore, the preferable filler 245 content is 0.1 to 30 parts by weight with respect to 100 parts by weight of the resin.
[Production method]
As an example of a manufacturing method of the lens sheet 17, a manufacturing method by a roll-to-roll method using a roll plate will be described.

  First, the collimating layer 25 is formed on the surface 212 of the base film 21. A cylindrical first roll having a film-like base film 21 wound on the surface, and a prism roll plate 50 (hereinafter simply referred to as roll) having a transfer groove 52 of the prism 230 on the surface as shown in FIGS. 12A and 12B. Plate 50). The cross sectional shape of the transfer groove 52 is the same as the cross shape of the prism 230, and the cross shape of the ridge 53 corresponding to the edge (flange portion) of the transfer groove 52 is the same as the cross shape of the prism 240. is there. The transfer groove 52 is juxtaposed in the roll axis direction. As shown in FIG. 9A, when the ridgeline of the prism 240 is meandered, the cross section of the transfer groove 52 is not constant in the height of the ridge 53 as shown in FIG. 12B. For example, as shown in FIG. Even if the pitch P0 of the transfer groove 52 is the same as that in FIG. 12B, a portion having a different depth of the transfer groove 52 is provided. That is, the angle (vertical angle) of the valley of the transfer groove 52 is constant, and the depth is changed in the longitudinal direction of the transfer groove 52. In this case, since the ridge line of the prism 240 corresponds to the top of the ridge 53 of the transfer groove 52, the ridge line of the formed prism 240 becomes a wavy curve meandering in the width direction of the prism 240.

  The first roll and the roll plate 50 are arranged so that the axial direction of the first roll is parallel to the axial direction of the roll plate 50. After the arrangement, the surface of the roll plate 50 is filled with an ionizing radiation curable resin having a refractive index n23 lower than the refractive index n21 of the base film 21. The charged ionizing radiation curable resin is transferred onto the base film 21 fed from the first roll while rotating the first roll and the roll plate 50. At this time, the transfer is performed while the base film 21 is sandwiched between the backup roll disposed opposite to the roll plate 50 with the base film 21 interposed therebetween and the roll plate 50. The transferred ionizing radiation curable resin is irradiated with ionizing radiation to cure the ionizing radiation curable resin, thereby forming the prism layer 23.

  After forming the prism layer 23, the filling layer 24 is formed on the prism layer 23. First, a roll plate having a smooth surface is prepared. Next, an ionizing radiation curable resin having a refractive index n24 higher than the refractive index n23 is applied to the roll plate. A roll plate having a surface coated with an ionizing radiation curable resin is pressed against the surface of the prism layer 23 on which the prism 230 is formed to transfer the ionizing radiation curable resin. Then, by irradiating with ionizing radiation, the transferred ionizing radiation curable resin is cured, and the filling layer 24 is formed.

  The filling layer 24 may be manufactured by the following method instead of the above method. First, a paint in which a resin having a refractive index n24 higher than the refractive index n23 of the prism layer 23 is dissolved in a solvent is prepared. Using the gravure coater or the like, the prepared paint is uniformly applied on the prism layer 23. The applied paint is dried to form the filling layer 24.

  Through the above steps, the collimating layer 25 is formed on the surface 212 of the base film 21. The base film 21 on which the collimating layer 25 is formed is arranged in parallel in the axial direction.

  Next, the lenticular lens layer 22 is formed on the surface 211 of the base film 21. A roll plate 60 for lenticular lenses (hereinafter, simply referred to as a roll plate 60) shown in FIGS. 13A and 13B is prepared and arranged so that the axial direction thereof is parallel to the axial direction of the second roll. As shown in FIGS. 13A and 13B, a transfer groove 62 of the cylindrical lens 220 arranged in the axial direction is formed on the surface of the roll plate 60.

  The transfer groove 62 of the roll plate 60 is filled with ionizing radiation curable resin. While the second roll and roll plate 60 are rotated, the charged ionizing radiation curable resin is transferred to the surface 211 of the base film 21 fed from the second roll. At this time, transfer is performed while the film is sandwiched between backup rolls. The transferred ionizing radiation curable resin is cured by irradiating with ionizing radiation to form a lenticular lens layer 22. The lens sheet 17 is formed by the above process.

  In the manufacturing method described above, the collimating layer 25 is formed first, and then the lenticular lens layer 22 is formed. However, the lenticular lens layer 22 may be formed first, and then the collimating layer 25 may be formed.

  As described above, the manufacturing method by the roll-to-roll method using the roll plate has been described as an example of the manufacturing method, but the lens sheet 17 can be manufactured by other manufacturing methods. The collimating layer 25 and the lenticular lens layer 22 may be formed using a plate-shaped plate instead of the roll-to-roll method. The lenticular lens layer 22 may be formed by an extrusion method, a hot press method, or an injection molding method.

  As described above, in the lens sheet 17 according to the present embodiment, the refractive index n23 of the prism layer 23, the refractive index n24 of the filling layer 24, and the refractive index n21 of the base film 21 satisfy the expressions (1) and (2). Thus, the front luminance can be improved and the occurrence of side lobes can be suppressed.

  Further, since the parallel arrangement direction of the cylindrical lens 220 and the parallel arrangement direction of the prism 230 are substantially the same, the luminance angle dependency in the left-right direction can be a wide viewing angle. Specifically, the 1/3 viewing angle when used in a liquid crystal display device including an ISP liquid crystal panel can be set to 120 deg or more. Here, the parallel arrangement direction of the cylindrical lens 220 and the parallel arrangement direction of the prism 230 do not have to be the same. For example, if the angle formed by the cylindrical lens 220 and the prism 230 is within 10 °, the wide field of view described above is used. You can get a corner. If the angle formed by the cylindrical lens 220 and the prism 230 is 3 ° or more, the occurrence of moire can be prevented.

  Since the plurality of prisms 240 in the collimating layer 25 are filled between the plurality of prisms 230 in the prism layer 23, the top portions thereof are not exposed on the surface. The top surface of the cylindrical lens 220 constituting the lenticular lens layer 22 is a curved surface. Therefore, unlike the top part of the conventional prism sheet, scratches are unlikely to occur during manufacture and transportation, and a protective sheet for protecting the top part is unnecessary.

  In the present embodiment, the backlight 10 is a direct type, but it may be an edge light type.

  3 and 4, each of the plurality of cylindrical lenses 220 is brought into contact with each other. However, a gap may be provided between adjacent cylindrical lenses 220. Similarly, a gap may be provided between adjacent prisms 240. Moreover, although the cross-sectional shape of the prisms 230 and 240 is a triangle, it may be a trapezoid. Further, the tops of the prisms 230 and 240 may be rounded.

試験番号１〜６は、図３及び図４に示す形状のレンズシートであった。これらのレンズシートを以下の方法で製造した。 Lens sheets of test numbers 1 to 8 having the shapes and refractive indexes shown in Table 1 were prepared.

Test numbers 1 to 6 were lens sheets having the shapes shown in FIGS. 3 and 4. These lens sheets were manufactured by the following method.

  A prism roll plate having a surface with a plurality of prism transfer grooves arranged in the axial direction was prepared. A polyethylene terephthalate (PET) film having a thickness of 188 μm and a refractive index (n21) = 1.6 was prepared as a base film. The roll plate was filled with an ultraviolet curable resin for the prism layer. And the ultraviolet curable resin was transcribe | transferred by pressing a roll plate on the surface of PET film. The ultraviolet curable resin transferred by irradiating with ultraviolet rays was cured to form a prism layer.

  Subsequently, a packed layer was produced. First, a roll plate having a smooth surface was prepared. An ultraviolet curable resin for a filling layer was applied to the roll plate, and the roll plate having the surface coated with the ultraviolet curable resin was pressed against the surface of the prism layer to transfer the ultraviolet curable resin. By irradiating ultraviolet rays, the transferred ultraviolet curable resin was cured to form a filling layer.

  After the collimating layer was formed on the base film by the above steps, a lenticular lens layer was formed on the surface of the base film opposite to the surface on which the collimating layer was formed. A roll plate for a lenticular lens having a surface on which cylindrical lens transfer grooves are arranged in the axial direction was prepared. The UV curable resin for the lenticular lens layer was filled in the transfer groove of the roll plate for the lenticular lens and transferred onto the surface of the PET film. The transferred ultraviolet curable resin was cured by irradiating with ultraviolet rays to form a lenticular lens layer.

  The transverse shape of the prism of the prism layer of the test number 1 manufactured by the above manufacturing method was an isosceles triangle, the apex angle was 110 °, and the base was 50 μm. The distance between the apexes of the prisms adjacent to each other, that is, the pitch between the prisms was 50 μm. The height of each prism periodically changed in the longitudinal direction in the range of 10.5 μm to 17.5 μm. Furthermore, the height of each prism on the same cross section was different from each other. The ridge line of the prism of the packed bed was not a straight line but a curve that vibrated in the direction in which the prisms were juxtaposed.

  The cross-sectional shape of each cylindrical lens was an elliptical arc whose apex is the end point of the major axis, and the curvature radius at the apex was 13 μm, the major axis diameter was 138 μm, and the minor axis diameter was 60 μm. In addition, the height from the lens edge to the top of the convex surface is 22.3 μm, the angle formed by the convex surface and the surface including the lens edge (hereinafter referred to as contact angle) is 68 °, the distance between the tops of adjacent cylindrical lenses, The pitch between the cylindrical lenses was 48 μm. In addition, there was a flat gap between adjacent cylindrical lenses, and the gap width was 3.8 μm. The parallel direction of the cylindrical lenses was the same as the parallel direction of the prisms in the prism layer.

  The refractive index of the formed prism layer was 1.49, which was lower than the refractive index of the filling layer (= 1.56) and the refractive index of the lenticular lens layer (= 1.56).

  Unlike the test number 1, the prism of the prism layer of the test number 2 had a constant height (16 μm). The prism base was 23 μm and the pitch between prisms was 23 μm. For this reason, the pitch between prisms (= 23 μm) and the pitch between cylindrical lenses (= 48 μm) are in a prime relationship. Other configurations were the same as those in Test No. 1.

  The prism layer of test number 3 includes a plurality of first prisms having a height of 6.5 μm and a prism base of 13 μm, a plurality of second prisms having a height of 11.5 μm and a prism base of 23 μm, A plurality of third prisms having a height of 16.5 μm and a prism base of 33 μm were formed. These prisms are arranged side by side, but the arrangement order is irregular. All the prisms had an apex angle of 90 °. The other configuration was the same as that of test number 1.

  The filler of Test No. 4 contained 1 part by weight of filler with respect to 100 parts by weight of UV curable resin for the filler layer. The filler was made of titanium oxide, and the average particle size was 0.5 μm. Further, the apex angle of the prism of the prism layer was 90 °, and the prism height was constant at 25 μm. The other configuration was the same as that of test number 1.

  In the lens sheet of test number 5, the parallel arrangement direction of the cylindrical lenses and the parallel arrangement direction of the prisms intersected. Specifically, the angle formed by the parallel arrangement direction of the cylindrical lenses and the parallel arrangement direction of the prisms was 5 °. The height of the prism was constant at 17.5 μm. The other configuration was the same as that of test number 1.

  In the lens sheet of test number 6, as compared with test number 5, the parallel arrangement direction of the cylindrical lenses was the same as the parallel arrangement direction of the prisms. Other configurations were the same as those in Test No. 5.

  In test number 7, unlike the above test numbers 1 to 6, two diffusion sheets having 80% haze were laminated. In test number 8, a diffusion sheet was laid on the prism sheet. The refractive index of the prism sheet was 1.56, the apex angle was 110 °, the base was 50 μm, the pitch between prisms was 50 μm, and the height of each prism was 17.5 μm. Further, the haze of the diffusion sheet was 80%. In short, the test numbers 7 and 8 were obtained by combining two lens sheets.

[Investigation of viewing angle dependence of luminance and 1/3 viewing angle]
The viewing angle dependence of luminance was investigated using the lens sheets of test numbers 1 to 8.

  A plurality of surface light sources each including a housing housing 16 external electrode cathode tubes therein and a diffusion plate having a total light transmittance of 65% as shown in Table 1 were prepared.

  On each surface light source, lens sheets of test numbers 1 to 8 were respectively laid to manufacture backlights of test numbers 1 to 8. An IPS liquid crystal panel was laid on each of the backlights of test numbers 1 to 8 to manufacture liquid crystal display devices of test numbers 1 to 8.

  The viewing angle dependence of the liquid crystal display device in the vertical and horizontal directions when the manufactured liquid crystal display device displayed white was investigated. With respect to the viewing angle, the normal direction (front) of the display screen was defined as the 0 deg axis, the tilt angle from the 0 deg axis in the vertical direction was defined as the vertical viewing angle, and the tilt angle in the horizontal direction was defined as the left and right viewing angle. Of the left and right directions, the inclination angle from the normal to the right direction is indicated by plus (+), and the inclination angle to the left direction is minus (−). Similarly, of the vertical viewing angles, the inclination angle from the normal to the upper direction is indicated by plus, and the inclination angle from the lower direction is indicated by minus.

  Furthermore, about each test number, the 1/3 viewing angle of the up-down direction and the left-right direction was calculated | required with the following method. First, as shown in FIGS. 7 and 14 to 20, graphs of the viewing angle dependence of the luminance of each test number 1 to 8 were created. As shown in Table 1, FIG. 7 is a graph of the viewing angle dependency of the luminance of the test number 1, and FIGS. 14 to 20 are graphs of the viewing angle dependency of the test numbers 2 to 8, respectively. The horizontal axis of the graph indicates the viewing angle. The vertical axis represents the ratio of the luminance at each viewing angle to the front luminance obtained in test number 7 (hereinafter referred to as relative luminance). The solid line in the figure indicates the viewing angle dependency of the luminance in the left-right direction, and the broken line indicates the viewing angle dependency of the luminance in the vertical direction.

  Of the viewing angle dependency of the vertical and horizontal luminances shown in FIGS. 7 and 14 to 20, a viewing angle range in which the luminance is 1/3 or more of the front luminance is obtained, and the obtained viewing angle range is 1/3. The vertical viewing angle and 1/3 horizontal viewing angle were used.

[Investigation of uneven brightness and moire]
Luminance unevenness and moire were evaluated by the following methods. Using the liquid crystal display devices with the test numbers 1 to 8 described above, whether or not luminance unevenness and moire were generated on the display screen was visually evaluated.

[Investigation result]
The survey results are shown in Table 1. “None” in the “brightness unevenness” and “moire” items in Table 1 indicates that the brightness unevenness and moire could not be visually confirmed, and “present” indicates that it was visually confirmed.

  Referring to Table 1, the left and right viewing angles of test numbers 1 to 6 were all 120 deg or more. Moreover, in the test numbers 1-6, the brightness nonuniformity did not generate | occur | produce. Further, referring to FIGS. 7 and 14 to 18, generation of side lobes was also suppressed. Further, the front luminance was almost the same as that of test number 7 (two diffusion sheets laminated).

  Furthermore, in the test number 1, since the ridge line of the prism of the packed bed meandered, moire did not occur. In Test No. 2, the pitch of the prisms of the prism layer and the pitch of the cylindrical lenses were different and had a prime relationship with each other, so no moire was generated. In Test No. 3, since the arrangement pitch was not uniform in the prism of the prism layer, no moire was generated. In test number 4, since the packed bed contained filler, moire did not occur. In Test No. 5, since the cylindrical lens and the prism intersected, moire did not occur.

  On the other hand, in Test No. 6, moire was observed. In Test Nos. 7 and 8, the left and right viewing angles were less than 120 deg, and uneven brightness was observed.

  While the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

It is a perspective view of the display apparatus provided with the lens sheet by embodiment of this invention. It is sectional drawing in line segment II-II in FIG. 1 is a perspective view of a lens sheet according to an embodiment of the present invention. It is sectional drawing in line segment IV-IV in FIG. It is a cross-sectional view of another lenticular lens layer different from the lenticular lens layer in FIG. It is a cross-sectional view of another lenticular lens layer different from the lenticular lens layer of FIGS. 3 and 5A. It is a schematic diagram for demonstrating the locus | trajectory of the light ray which injected into the prism sheet. It is a schematic diagram for demonstrating the locus | trajectory of the light ray which injected into the collimating layer in FIG. It is a schematic diagram for demonstrating the locus | trajectory of the light which injected into the lenticular lens layer in FIG. It is a figure which shows an example of the viewing angle dependence of the brightness | luminance of the lens sheet shown in FIG. It is sectional drawing of the other lens sheet different from FIG. It is a top view of the collimating layer of the other lens sheet different from FIG.4 and FIG.8. It is sectional drawing in line segment IXB-IXB in FIG. It is sectional drawing of the other lens sheet different from FIG.4, FIG8 and FIG.9. It is sectional drawing of the other lens sheet different from FIG.4 and FIG.8-10. It is a perspective view of the roll plate for prisms for manufacturing the lens sheet shown in FIG. It is a figure which shows the example of a part of roll shown to FIG. 11A. It is a figure which shows the example of a part of roll different from FIG. 11B. FIG. 4 is a perspective view of a lenticular lens roll plate for manufacturing the lens sheet shown in FIG. 3. It is a figure which shows the example of a part of roll shown to FIG. 12A. It is a figure which shows the viewing angle dependence of the brightness | luminance of the lens sheet of the test number 2 in a present Example. It is a figure which shows the viewing angle dependence of the brightness | luminance of the lens sheet of the test number 3 in a present Example. It is a figure which shows the viewing angle dependence of the brightness | luminance of the lens sheet of the test number 4 in a present Example. It is a figure which shows the viewing angle dependence of the brightness | luminance of the lens sheet of the test number 5 in a present Example. It is a figure which shows the viewing angle dependence of the brightness | luminance of the lens sheet of the test number 6 in a present Example. It is a figure which shows the viewing angle dependence of the brightness | luminance of the lens sheet of the test number 7 in a present Example. It is a figure which shows the viewing angle dependence of the brightness | luminance of the lens sheet of the test number 8 in a present Example. It is a perspective view of the conventional prism sheet. It is sectional drawing in line segment XXII-XXII in FIG. FIG. 22 is a luminance angle distribution diagram of the prism sheet shown in FIG. 21.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 10 Backlight 11 Housing 12 Fluorescent tube 13 Light diffusing plate 16 Surface light source 17 Lens sheet 20 Liquid crystal panel 21 Base film 22 Lenticular lens layer 23 Prism layer 24 Filling layer 220 Cylindrical lenses 230 and 240 Prism

Claims (6)

A lens sheet used for a backlight,
A base film,
A lenticular lens layer including a plurality of cylindrical lenses formed on one surface of the base film and arranged side by side;
A prism formed on the other surface of the base film and including a plurality of first prisms arranged in substantially the same direction as the parallel arrangement direction of the plurality of cylindrical lenses, and having a refractive index lower than that of the base film. Layers,
A lens sheet comprising: a filling layer filled on a surface of the prism layer on which the first prisms are arranged side by side and having a refractive index higher than a refractive index of the prism layer. The lens sheet according to claim 1,
The filling layer includes a plurality of second prisms each filled between the adjacent first prisms,
The ridge line of the second prism meanders in the width direction of the second prism. The lens sheet according to claim 1,
The lens sheet according to claim 1, wherein pitches of the plurality of first prisms and / or the plurality of cylindrical lenses are not uniform. The lens sheet according to claim 1,
The packed bed is
Resin,
A lens sheet comprising: a plurality of particles dispersed in the resin and having a refractive index different from that of the resin. A housing having an opening on the front;
A plurality of linear light sources stored in the housing and arranged in parallel with each other;
A diffusion plate laid on the opening;
A lens sheet laid on the diffusion plate,
The lens sheet is
A base film,
A lenticular lens layer comprising a plurality of cylindrical lenses formed on one surface of the base film and arranged side by side;
A plurality of first prisms formed on the other surface of the base film and arranged in substantially the same direction as the parallel arrangement direction of the plurality of cylindrical lenses, and having a refractive index lower than the refractive index of the base film A prism layer having
A backlight comprising: a filling layer filled on a surface of the prism layer on which the first prisms are arranged side by side and having a refractive index higher than that of the prism layer. A backlight according to claim 5;
A liquid crystal display device comprising: a liquid crystal panel laid on the backlight.

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