HK1115450A - A backlight unit and a liquid crystal display - Google Patents

Description

Backlight unit and liquid crystal display device

Technical Field

The present invention relates to a backlight unit and a liquid crystal display device, and more particularly, to a backlight unit including a microlens array substrate and a light guide unit, and a liquid crystal display device including the backlight unit.

Background

In liquid crystal display devices, a technique using a microlens array for achieving high luminance and high field angle has been proposed. According to this technique, by disposing the microlens array substrate on the rear surface side of the liquid crystal display panel, it is possible to condense backlight (back light) light so as to avoid a TFT element or a black matrix (black matrix) formed on a transparent substrate of the liquid crystal display panel, thereby improving the utilization rate of light and realizing high luminance.

Patent document 1 (japanese patent application laid-open No. 8-166502) discloses a method of forming a microlens array made of glass on a glass substrate. In the method described in patent document 1, a film of photosensitive glass paste made of glass powder and a photosensitive resin is formed on a substrate, and then exposure, development, and heat treatment are performed to form a microlens array.

Patent document 2 (japanese patent application laid-open No. 10-333144) discloses a technique in which a microlens array is disposed between a liquid crystal display panel and a backlight.

Patent document 3 (japanese patent application laid-open No. 2006-114239) and patent document 4 (japanese patent application laid-open No. 2004-227956) disclose light guides that reflect light entering and propagating from a side surface side to a front surface side by prism-shaped reflection grooves and then emit the light through a plurality of lenses. However, the lenses described in patent documents 3 and 4 do not converge the backlight to avoid the TFT elements or the black matrix formed on the transparent substrate of the liquid crystal display panel

In order to improve the luminance of the liquid crystal display panel by the microlenses provided on the light guide, it is necessary to make incident light having high directivity enter the microlenses and condense the light so as to avoid the TFT elements or the black matrix with high accuracy. However, since the prism-shaped reflection groove provided on the bottom surface of the light guide must uniformly emit the incident light from the side surface over the entire region of the front surface of the light guide, the incident light does not first exit from the front surface of the light guide entirely on the reflection groove that has been reflected, but must be repeatedly reflected between the front surface-side interface of the light guide and the reflection groove a plurality of times before being guided to the vicinity of the side surface opposite to the surface on the incident side of the light guide. Therefore, it is impossible to emit light having high directivity from the front surface of the light guide and to enter the microlens by the reflection groove provided on the bottom surface of the light guide, and it is difficult to improve the luminance of the liquid crystal display panel.

Disclosure of Invention

The present invention has been made to solve the above problems, and an object of the present invention is to provide a backlight unit capable of further improving the luminance of a liquid crystal display panel, and a liquid crystal display device using the backlight unit.

A backlight unit according to the present invention is a backlight unit including a microlens provided on a rear surface side of a liquid crystal display panel to condense light in each pixel transmission region of the liquid crystal display panel, and includes: a light source; a light guide member that emits parallel light from a side surface opposite to a side surface on which the first prism portion is provided, by reflecting the light from the light source incident from an end portion on the first prism portion provided on the side surface; and a microlens array substrate on which parallel light emitted from the light guide member is incident from a side surface, reflected by a second prism portion provided on a bottom surface, and emitted to the liquid crystal display panel through the microlens provided on a front surface; the microlens array substrate includes: a microlens array composed of a plurality of microlenses; a transparent substrate on which a second prism portion is formed, the second prism portion being formed of a reflection groove extending in a direction perpendicular to a propagation direction of parallel light incident from the side surface; and a low refractive index layer formed between the microlens array and the transparent substrate and having a refractive index lower than that of the transparent substrate. With this configuration, light with high directivity can be incident on the microlens, and the backlight can be made to pass through the transmissive region of the pixel of the liquid crystal display panel with high accuracy, so that the luminance of the liquid crystal display panel can be improved.

Preferably, the light source includes a first light source provided at one end of the light guide and a second light source provided at the other end. In this way, by adopting a configuration in which light is incident from both ends of the light guide, it is not necessary to guide light from the light source to the vicinity of the opposite end, and therefore light with high directivity can be easily generated.

In addition, it is preferable that the light guide has a curved surface structure in which a central portion of a side surface on which the first prism portion is provided protrudes. With this configuration, light with high directivity can be easily generated.

Another backlight unit according to the present invention is a backlight unit including microlenses provided on a rear surface side of a liquid crystal display panel and configured to condense light in each pixel transmission region of the liquid crystal display panel, the backlight unit including: a light guide member emitting parallel light; and a microlens array substrate on which parallel light emitted from the light guide member is incident from a side surface, reflected by a second prism portion provided on a bottom surface, and emitted to the liquid crystal display panel through the microlens provided on a front surface; the microlens array substrate includes: a microlens array composed of a plurality of microlenses; a transparent substrate on which a second prism portion is formed, the second prism portion being formed of a reflection groove extending in a direction perpendicular to a propagation direction of parallel light incident from the side surface; and a low refractive index layer formed between the microlens array and the transparent substrate and having a refractive index lower than that of the transparent substrate. With this configuration, light with high directivity can be incident on the microlens, and the backlight can be made to pass through the transmissive region of the pixel of the liquid crystal display panel with high accuracy, so that the luminance of the liquid crystal display panel can be improved.

Here, the microlens is preferably a cylindrical lens extending in a direction perpendicular to the reflection groove of the second prism portion. More preferably, the optical film further includes a polarizer or a polarizing layer provided between the low refractive index layer and the microlens array.

The liquid crystal display device of the present invention comprises a liquid crystal cell having electrodes formed on the inner surface thereof

A liquid crystal display device comprising a liquid crystal display panel formed by opposing element substrates and a backlight unit provided on the back surface side of the liquid crystal display panel, the backlight unit comprising: the disclosed device is provided with: a light source; a light guide member that emits parallel light from a side surface opposite to a side surface on which the first prism portion is provided, by reflecting the light from the light source incident from an end portion on the first prism portion provided on the side surface; and a microlens array substrate on which parallel light emitted from the light guide member is incident from a side surface, reflected by a second prism portion provided on a bottom surface, and emitted to the liquid crystal display panel through the microlens provided on a front surface; the microlens array substrate includes: a microlens array composed of a plurality of microlenses; a transparent substrate on which a second prism portion is formed, the second prism portion being formed of a reflection groove extending in a direction perpendicular to a propagation direction of parallel light incident from the side surface; and a low refractive index layer formed between the microlens array and the transparent substrate and having a refractive index lower than that of the transparent substrate. With this configuration, light with high directivity can be incident on the microlens, and the backlight can be made to pass through the transmissive region of the pixel of the liquid crystal display panel with high accuracy, so that the luminance of the liquid crystal display panel can be improved.

Preferably, the light source includes a first light source provided at one end of the light guide and a second light source provided at the other end. In this way, by adopting a configuration in which light is incident from both ends of the light guide, it is not necessary to guide light from the light source to the vicinity of the opposite end, and therefore light with high directivity can be easily generated.

In addition, it is preferable that the light guide has a curved surface structure in which a central portion of a side surface on which the first prism portion is provided protrudes. With this configuration, light with high directivity can be easily generated.

The liquid crystal display device of the present invention comprises a liquid crystal layer formed on an inner surface thereof

A liquid crystal display device comprising a liquid crystal display panel formed between a pair of element substrates of electrodes and a backlight unit provided on the back surface side of the liquid crystal display panel, the liquid crystal display device comprising: a light guide member emitting parallel light; and a microlens array substrate on which parallel light emitted from the light guide member is incident from a side surface, reflected by a second prism portion provided on a bottom surface, and emitted to the liquid crystal display panel through the microlens provided on a front surface; the microlens array substrate includes: a microlens array composed of a plurality of microlenses; a transparent substrate on which a second prism portion is formed, the second prism portion being formed of a reflection groove extending in a direction perpendicular to a propagation direction of parallel light incident from the side surface; and a low refractive index layer formed between the microlens array and the transparent substrate and having a refractive index lower than that of the transparent substrate. With this configuration, light with high directivity can be incident on the microlens, and the backlight can be made to pass through the transmissive region of the pixel of the liquid crystal display panel with high accuracy, so that the luminance of the liquid crystal display panel can be improved.

Here, the microlens is preferably a cylindrical lens extending in a direction perpendicular to the reflection groove of the second prism portion. More preferably, the optical film further includes a polarizer or a polarizing layer provided between the low refractive index layer and the microlens array.

Further, it is preferable that the liquid crystal display panel has a plurality of pixels each having a rectangular shape, and has a pixel structure in which the pixels are arranged adjacent to each other with their longitudinal directions oriented in the same direction; the longitudinal direction of the micro-lenses of the backlight unit is arranged parallel to the width direction of the pixels. With this configuration, the light condensing degree is improved in the longitudinal direction of the pixel having a low aperture ratio, so that the transmittance of the liquid crystal display panel can be improved and the luminance thereof can be improved.

In addition, when the liquid crystal display device is a semi-transmissive liquid crystal display device, the present invention is more effective.

The present invention has an effect that it is possible to provide a backlight unit capable of further improving the luminance of a liquid crystal display panel and a liquid crystal display device using the backlight unit.

Drawings

Fig. 1 is a cross-sectional view schematically showing the structure of a liquid crystal display device according to embodiment 1 of the present invention.

Fig. 2 is a schematic diagram showing the structure of a backlight unit according to embodiment 1 of the present invention, fig. 2(a) is a schematic front view, fig. 2(b) is a schematic cross-sectional view taken along a P-P section line of fig. 2(a), and fig. 2(c) is a schematic cross-sectional view taken along a Q-Q section line of fig. 2 (a).

Fig. 3 is a schematic diagram showing the structure of a backlight unit according to embodiment 1 of the present invention, fig. 3(a) is a schematic rear view, fig. 3(b) is a schematic cross-sectional view taken along section line R-R of fig. 3(a), and fig. 3(c) is a schematic cross-sectional view taken along section line S-S of fig. 3 (a).

Fig. 4 is a diagram showing an example of the prism portion and the reflection portion.

Fig. 5 is a diagram showing an example of the prism portion and the reflection portion.

FIG. 6 is an enlarged schematic view of an LED and a light guide.

Fig. 7 is an enlarged schematic view of the light source side of the microlens array substrate.

Fig. 8 is a graph showing the relationship between the material of the low refractive index layer and various optical characteristics.

Fig. 9 is a perspective view of the backlight unit.

Fig. 10 is an explanatory diagram showing a positional relationship between the microlens and the pixel.

Fig. 11 is a view showing a method for manufacturing a microlens array substrate according to embodiment 1 of the present invention.

Fig. 12 is a cross-sectional view schematically showing the structure of a liquid crystal display device according to embodiment 2 of the present invention.

Fig. 13 is a schematic diagram showing a structure of a backlight unit according to embodiment 2 of the present invention, fig. 13(a) is a schematic front view, fig. 13(b) is a schematic cross-sectional view taken along a section line T-T of fig. 13(a), and fig. 13(c) is a schematic cross-sectional view taken along a section line U-U of fig. 13 (a).

Fig. 14 is a schematic diagram showing the structure of a backlight unit according to embodiment 2 of the present invention, fig. 14(a) is a schematic rear view, fig. 14(b) is a schematic cross-sectional view taken along a V-V section line of fig. 14(a), and fig. 14(c) is a schematic cross-sectional view taken along a W-W section line of fig. 14 (a).

Fig. 15 is a graph showing a luminance simulation of a liquid crystal display device using the backlight unit of the present invention.

In the figure: 100. 100 a-liquid crystal display panel, 101, 102-transparent substrate, 103-liquid crystal layer, 104-color filter layer, 105-black matrix, 106-transparent electrode, 107-orientation film, 108-TFT element, 109a, 109 b-polarizer, 110-spacer, 111-sealing material, 112a, 112b- λ/4 sheet, 200 a-microlens array substrate, 201-transparent substrate for forming microlens array, 202-microlens array, 202 a-microlens, 203-flange, 204-low refractive index layer, 205-prism portion, 205 a-groove, 206-reflector, 300-light source, 301a, 301 b-Light Emitting Diode (LED), 302-light guide.

Detailed Description

Embodiment 1 of the present invention is explained below.

A liquid crystal display device according to embodiment 1 of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view schematically showing the structure of a liquid crystal display device according to embodiment 1 of the present invention.

As shown in fig. 1, the liquid crystal display device includes a liquid crystal display panel 100, a microlens array substrate 200, and a light source unit 300. The liquid crystal display device according to the embodiment of the present invention is mounted on a display of a mobile phone, a mobile terminal, a mobile game machine, a car navigation system, or the like. The present invention can be applied to any of semi-transmissive and transmissive liquid crystal display devices. The present invention is particularly effective in a semi-transmissive liquid crystal display device. The transflective liquid crystal display device has a function of reflecting external light since it reflects and utilizes the external light at a place where the external light is strong. Therefore, the transmittance of the backlight is reduced compared to the transmissive type. The invention can focus the backlight by the micro lens in the transmission area, thereby preventing the light utilization rate from decreasing. This makes it possible to enlarge the reflection area and also to improve visibility when external light is used outdoors.

In addition, the microlens array substrate 200 and the light source unit 300 constitute a backlight unit. The liquid crystal display panel 100 has the structure: two transparent substrates 101 and 102 having transparent electrodes 106 and the like formed on the inner surfaces thereof are arranged so that the inner surfaces thereof face each other, and a liquid crystal layer 103 is interposed between the two transparent substrates 101 and 102.

First, the structure of the liquid crystal display panel 100 is explained in detail based on the drawings. As shown in fig. 1, spacers 100 for controlling the height (cell gap) of the liquid crystal layer 103 are dispersedly disposed between the transparent substrates 101, 102. The transparent substrates 101, 102 are attached with a sealing material 111 applied along the outer peripheral edges of the transparent substrates 101, 102. Polarizers 109a, 109b are mounted on the outer surfaces of the transparent substrates 101, 102, respectively.

The transparent substrate 101 is formed of a rectangular thin plate. As a material of the transparent substrate 101, glass, polycarbonate, or acrylate resin (acrylate resin) or the like is used. A color filter layer (color filter)104, a transparent electrode 106, and an alignment film 107 are sequentially stacked on the inner surface of the transparent substrate 101. Further, a black matrix 105 as a light-shielding film is formed between the pixels of the color filter layer 104. Each pixel has a transmissive region through which backlight light passes, in a region excluding a non-transmissive region such as the black matrix 105, the TFT element, and various wirings. The color filter layer 104, the transparent electrode 106, the alignment film 107, and the like are formed on the transparent substrate 101 to form an element substrate.

The transparent substrate 102 is formed of a rectangular thin plate. As a material of the transparent substrate 102, glass, polycarbonate, acrylic resin, or the like is used. On the inner surface of the transparent substrate 102, a TFT element 108, a transparent electrode 106, and an alignment film 107 are sequentially stacked. The TFT elements 108, the transparent electrode 106, the alignment film 107, and the like are formed on the transparent substrate 102 to form an element substrate. For example, Indium Tin Oxide (ITO-Indium Tin Oxide) is used as a material of the transparent electrode 106. For example, polyimide is used as a material of the alignment film 107.

Next, the structure of the microlens array substrate 200 and the light source 300 will be described in detail based on the drawings. As shown in fig. 1, the microlens array substrate 200 is disposed on the back surface side of the liquid crystal display panel 100. In addition, a light source unit 300 is disposed on one side of the microlens array substrate 200.

Fig. 2 is a schematic diagram showing the structure of a backlight unit according to embodiment 1 of the present invention, fig. 2(a) is a schematic front view, fig. 2(b) is a schematic cross-sectional view taken along a P-P section line of fig. 2(a), and fig. 2(c) is a schematic cross-sectional view taken along a Q-Q section line of fig. 2 (a).

Fig. 3 is a schematic diagram showing the structure of a backlight unit according to embodiment 1 of the present invention, fig. 3(a) is a schematic rear view, fig. 3(b) is a schematic cross-sectional view taken along section line R-R of fig. 3(a), and fig. 3(c) is a schematic cross-sectional view taken along section line S-S of fig. 3 (a). For convenience, in fig. 2(a) and 3(a), vertices of the transparent substrate 201 for forming a microlens array are referred to as a to D.

As shown in fig. 2 and 3, the extending direction (longitudinal direction) of the microlens 202a of the microlens array 202 and the extending direction (longitudinal direction) of the groove 205a of the prism portion 205 are substantially orthogonal to each other.

As shown in fig. 1, 2, and 3, the microlens array substrate 200 includes a transparent substrate 201 for forming a microlens array, a microlens array 202 including a plurality of microlenses 202a, a rim (rim)203, a low refractive index layer 204, a prism portion 205 having a plurality of grooves 205a, and a reflection portion 206.

The transparent substrate 201 for forming a microlens array is formed of a rectangular thin plate. In addition, glass is used as a material of the transparent substrate 201 for forming the microlens array.

In order to prevent the deviation of the liquid crystal pixels and the microlens array caused by the ambient temperature, the microlens array forming transparent substrate 201 is preferably a substrate having a thermal expansion coefficient close to that of a glass substrate used for the liquid crystal display panel, and is preferably a substrate having a thermal expansion coefficient of 10 × 10^-7100X 10 above (/. degree. C.)^-7(v. degree. C.) or less.

As shown in fig. 1, 2 and 3, a microlens array 202 and a convex side 203 are formed on the front surface of a transparent substrate 201 for forming a microlens array. Also, as shown in fig. 1, the microlens array substrate 200 is mounted on the back surface of the liquid crystal display panel 100 through the convex edge 203. As described later, a photosensitive resin (resist) is formed on the transparent substrate 201 for forming a microlens array, and then exposed and developed to form the microlens array 202 and the raised edge 203.

The microlens array 202 has a plurality of cylindrical microlenses 202 a. The microlens 202a is a cylindrical lens having a cylindrical lens shape and mainly has curvature in only one direction. However, the cylindrical lens described in the present invention means that the curvature in one direction is dominant, and does not mean that the curvature in the other direction is completely absent. As shown in fig. 2 and 3, a plurality of elongated microlenses 202a are formed on a transparent substrate 201 for forming a microlens array, the elongated microlenses being arranged in parallel with one another and being aligned in a direction substantially perpendicular to a side BC on which a light source unit 300 is disposed. Here, the width of the microlens 202a is set to be several mm or less corresponding to the pixel of the liquid crystal display panel 100.

As shown in fig. 2 and 3, a flange 203 as an outer frame portion is formed in a frame shape protruding along the outer peripheral edge of the microlens array 202. As shown in fig. 1, 2, and 3, a convex side 203 is formed to coincide with or be higher than the convex apex of the microlens array 202. The flange 203 is provided for mounting the microlens array substrate 200 on the rear surface of the liquid crystal display panel 100.

A prism portion 205 having a plurality of grooves 205a is provided on the back surface of the transparent substrate 201 for microlens array formation. A plurality of grooves 205a are formed in the transparent substrate 201 for microlens array formation so as to be arranged in parallel with each other in a direction substantially parallel to the side BC on which the light source unit 300 is arranged. That is, the extending direction (longitudinal direction) of the plurality of grooves 205a is substantially orthogonal to the extending direction (longitudinal direction) of the plurality of microlenses 202 a.

The prism portion 205 is formed by, for example, transferring a transparent photocurable resin having a prism-like shape in which the grooves 205a are formed in advance on a transparent substrate such as Polyethylene terephthalate (hereinafter, referred to as PET) by rolling, curing the transferred resin, and then attaching the cured resin to the transparent substrate 201, or by directly applying a photoreactive resin to the transparent substrate 201 and then forming the grooves 205a by photolithography using a gray mask or the like. Thus, the prism portion 205 can be easily manufactured.

The prism portion 205 may be formed by nanoimprinting (nanoimprinting) on a transparent base material such as polycarbonate using a stamp (stamp). The prism portion 205 may be formed on the back surface of the transparent substrate 201 for microlens array by a direct 2P method. The refractive index of the prism portion 205 is set to be equal to or higher than the refractive index of the microlens array forming substrate 201.

As shown in fig. 1, 2, and 3, the reflection portion 206 is formed along a plurality of grooves 205a on the surface of the prism portion 205. The reflection portion 206 is formed by vapor deposition or the like using a material such as gold, silver, aluminum, or an aluminum alloy. The sheet-like reflecting portion 206 may be formed of gold, silver, aluminum, or an aluminum alloy, and may be disposed so as to face the surface of the groove 205a in which the prism portion 205 is formed. That is, the reflection plate may be provided separately from the microlens array substrate 200 without forming a reflection film on the reflection portion 206.

Here, specific examples of the prism portion 205 and the reflection portion 206 are given. Fig. 4 and 5 show an example of the prism portion and the reflection portion. As shown in fig. 4 and 5, the prism portion 205 includes a PET sheet 2051, a photocurable resin 2052 applied to the PET sheet 2051, and a plurality of grooves 205a formed in the photocurable resin 2052. The PET sheet 2051 and the light-curable resin 2052 are made of materials having a refractive index of about 1.6.

In fig. 4, the plurality of grooves 205a are formed in an acute angle shape. In fig. 5, a plurality of grooves 205a are formed between cylindrical convex portions. As shown in fig. 4 and 5, the reflection portion 206 is formed along the groove 205a on the surface of the prism portion 205. The material of the reflection portion 206 is a thin film of gold, silver, aluminum, an aluminum alloy, or the like. At this time, as shown in fig. 4 and 5, since the reflection portion 206 is formed along the plurality of grooves 205a on the surface of the prism portion 205, light is reflected and scattered at the edge portion of each groove 205a, and the light emitted from the prism portion 205 is substantially uniform. As a result, emitted light with high uniformity and a large angle of view can be obtained. A hard coat layer (not shown) is formed on the reflection portion 206. As a material of the hard coating layer, a photocurable resin or the like is used. The hard coat layer is provided in order to protect the reflection portion 206 and prevent oxidation thereof. The prism 205 is not necessarily continuous but may be formed intermittently in parallel with the side BC.

As shown in fig. 2 and 3, the light source unit 300 includes, for example, light emitting diodes (hereinafter, referred to as LEDs) 301a and 301b as light sources, and a light guide 302. The light source unit 300 is provided on the side surface side of the side BC of the microlens array forming substrate 201. The light source unit 300 and the microlens array substrate 200 are disposed only a certain distance apart. Between which either air or a low refractive index layer having a lower refractive index than the microlens array substrate 200 is filled. The LEDs 301a, 301b are point light sources arranged at both ends (end side surfaces on the short side) of the light guide 302.

The light guide 302 is made of a transparent resin such as polycarbonate, polyolefin, or acrylic resin. On the light guide 302, a prism-shaped reflection groove is formed on a side surface 3022 opposite to the side surface 3021 on the microlens array substrate 200 side. Further, a reflective film may be formed on the side surface 3022. The reflection grooves formed in the side surface 301 are basically configured to irradiate light from the LEDs 301a, 301b or light emitted from the LEDs 301a, 301b and reflected by the side surface 3021 toward the microlens-forming substrate 201 side. That is, the reflection groove does not function to guide light from the incident side to the back side by repeating reflection between the side surface 3021 and the side surface 3022 a plurality of times. Therefore, the prism-shaped reflection grooves formed in the side surface 3022 of the light guide 302 are different from the prism-shaped reflection grooves formed in the bottom surface of the microlens substrate 200 and configured to reflect light toward the front side, and it is easy to improve the directivity of the reflected light.

Further, the side surface 3022 of the light guide 302 is formed into a curved surface having a curvature in the longitudinal direction (the direction of the side BC of the microlens array forming substrate 201). More specifically, side surface 3022 of light guide 302 has a curved surface shape in which the central portion protrudes in a convex shape toward the side opposite to the light exit direction of light guide 302. By having such a curved surface shape, directivity can be further improved, and light incident from both end portions can be incident on the end face of the microlens array substrate on the side face 3021 side.

Here, in the curved surface of the light guide 302, the curvature of the central portion is smaller than the curvatures of both end portions. Thus, the directivity of the light emitted from the central portion of the light guide 302 can be made higher than the directivity of the light emitted from the both end portions. In this example, as shown in fig. 6, the light emitted from the center portion has directivity with a half-width angle of about ± 2 degrees, and the light emitted from the vicinities of both end portions has directivity with a half-width angle of about ± 8 degrees.

Light guide 302 configured in this manner can emit light entering from both ends from side surface 3021 as an emission surface with significantly improved directivity. That is, the light emitted from side surface 3021 of light guide 302 is parallel light having a large component emitted from side surface 3021 perpendicularly to the longitudinal direction of light guide 302. The half-width angle of the light emitted from the light guide 302 in the preferred embodiment is ± 15 degrees or less, and more preferably ± 10 degrees or less. In the present specification, the term "parallel light" means that an angle having an emission intensity halved with respect to the peak intensity of light emitted from the light guide end surface 3021 is defined as a half-width angle, and light having a directivity of ± 15 degrees or less of the half-width angle is referred to as "parallel light".

As shown in fig. 1, 2 and 3, the low refractive index layer 204 as an intermediate layer is formed on the front surface of the transparent microlens array forming substrate 201 between the microlens array 202 and the transparent microlens array forming substrate 201. Here, the refractive index of the transparent substrate 201 for forming a microlens array is set to be larger than the refractive index of the low refractive index layer 204. The low refractive index layer 204 is formed by applying a fluorine-containing resin material, a material in which hollow nano silica (nanosilica) beads are dispersed in a transparent resin such as acrylate, or the like, on the front surface of the transparent substrate 201 for forming a microlens array. Here, the hollow nano silica beads mean silica spheres of about 40nm and have a hollow interior. By dispersing such hollow nano silica beads in a transparent resin, the refractive index of the transparent resin can be effectively reduced.

With this configuration, as will be described later using fig. 7, the critical angle θ max of total reflection at the interface between the microlens array forming substrate 201 and the refractive index retarder 204 can be reduced, so that light having a large incident angle to the microlenses 202a is reflected by the low refractive index retarder 204, and light having a large incident angle to the microlenses 202a can be prevented from transmitting through the interface between the microlens array forming substrate 201 and the low refractive index retarder 204. As a result, the light from the light source unit 300 disposed on the side surface of the microlens array substrate 200 can be efficiently introduced into the microlens array substrate 200 and efficiently emitted to the front surface side. As a result, the luminance in the pixels of the liquid crystal display panel 100 can be improved, and the angle of view can be increased.

If the low refractive index layer 204 is not formed, since the microlenses 202a having a cylindrical lens shape are formed on the emission surface of the microlens array substrate 200, the light emitted from the light guide 302 is reflected in various directions by the lenses of the microlenses 202a, and the directivity is lowered. In contrast, in the embodiment of the present invention, since the incident parallel light is totally reflected by the flat low refractive index layer 204 and guided to the entire region, the parallel light can propagate while maintaining the parallel light state, and the decrease in directivity can be suppressed. In this case, while the incident light is reflected by the prism-shaped reflection grooves provided on the bottom surface of the microlens array substrate 200 during propagation, the reflection grooves extend in a direction perpendicular to the propagation direction of the incident light, and thus the state of the parallel light is not disturbed by reflection.

Here, the critical angle θ max of total reflection at the interface between the transparent substrate 201 for microlens array formation and the low refractive index layer 204 is specifically calculated by trial. Fig. 7 is an enlarged schematic view of the light source side of the microlens array substrate. θ represents an incident angle when the light of the light source unit 300 enters the low refractive layer 204, and Φ represents a refractive angle when the light of the light source unit 300 enters the microlens array forming substrate 201 from the air layer. In addition, a line JK with an arrow and a line KL with an arrow shown in fig. 7 indicate optical path lengths when light of the light source unit 300 is totally reflected on the interface between the transparent substrate 201 for microlens array formation and the low refractive index layer 204.

Fig. 8 is a graph showing the relationship between the material of the low refractive index layer and various optical characteristics. As shown in fig. 7, three types of fluorine-containing transparent resin, transparent resin containing hollow nano silica beads, and silica are selected as the material of the low refractive index 204. If the total reflection condition is analyzed according to snell's law, the smaller the refractive index of the low refractive index layer 204, the smaller the critical angle θ max of total reflection at the interface between the transparent substrate for microlens array formation and the low refractive index layer.

As shown in fig. 8, when the fluorine-containing transparent resin having the smallest refractive index is selected, the critical angle θ max of total reflection can be reduced to about 63.5 °. At this time, the refraction angle Φ at which the light of the light source unit 300 is incident from the air layer to the microlens array formation substrate 201 is about 26.5 °. When the total reflection condition is analyzed according to snell's law, the refractive index of the transparent substrate 201 for forming a microlens array is 1.52.

Here, as the refraction angle Φ increases, light having a large incident angle on the microlens 202a is reflected more efficiently by the low refractive index layer 204, and light having a large incident angle on the microlens 202a can be effectively prevented from passing through the interface between the microlens array forming substrate 201 and the low refractive index layer 204 as it is. As a result, the incident angle of light actually incident on the microlens 202a can be effectively reduced, and light from the light source unit 300 disposed on the side surface side of the microlens array substrate 200 can be efficiently emitted toward the front surface side of the microlens array substrate 200.

As described above, a liquid crystal display device in which the microlens array substrate 200 is provided with a function of a light guide plate as a backlight can be obtained. Further, the light guide plate and the plurality of optical sheets used in the conventional liquid crystal display device can be eliminated, and the backlight unit can be thinned, and the thickness of the entire liquid crystal display device can be reduced. Further, by removing the light guide plate and the plurality of optical sheets, the component cost and the manufacturing cost can be reduced.

For example, when the thickness of a conventional liquid crystal display panel including a polarizer is 0.6mm, the thickness of a microlens array substrate is about 0.3mm, the thickness of a light guide plate is about 0.4mm, and the total thickness of a plurality of optical sheets is about 0.25mm, the thickness of the entire conventional liquid crystal display device is about 1.55 mm. Accordingly, in the liquid crystal display device according to embodiment 1 of the present invention, when the thickness of the liquid crystal display panel including the polarizer is 0.6mm and the thickness of the microlens array substrate is about 0.4mm, the thickness of the entire liquid crystal display device is about 1.0 mm. Thus, the thickness of the whole liquid crystal display device can be reduced by about 0.55 mm.

In addition, in recent years, as the liquid crystal display panel is made thinner, the rigidity of the liquid crystal display panel is lowered, and the liquid crystal display panel is easily broken. As in the above embodiment, by disposing the microlens array substrate 200 on the rear surface side of the liquid crystal display panel 100, the rigidity of the entire liquid crystal display device can be improved. In addition, since the microlens array substrate 200 is attached to the back surface of the liquid crystal display panel 100 via the convex edge 203, the rigidity of the entire liquid crystal display device can be further improved.

Fig. 9 is a perspective view of the backlight unit of embodiment 1 of the present invention. Referring to the figure, the behavior of light emitted from the LED301a until it exits from the exit surface of the microlens array substrate 200 is explained.

First, light emitted from the LED301a enters from the end of the light guide 302. On the light guide 302, the incident light is reflected on the side 3022 having the prism-like reflection grooves directly or after being reflected on the side 3021, and then exits from the side 3021 on the microlens array substrate 200 side. The outgoing light is parallel light having high directivity in a direction perpendicular to the longitudinal direction of the side surface 3021 as the outgoing surface.

The parallel light incident from the side of the microlens array substrate 200 is reflected between the low refractive index layer 204 and the prism portion 205 and then incident on the microlenses 202a, or immediately after being incident, is reflected on the prism portion 205 and then immediately incident on the microlenses 202 a. In this case, since the reflection grooves of the prism portion 205 extend in the direction perpendicular to the propagation direction of the parallel light, even if the parallel light is reflected by the reflection grooves, the state of the parallel light is not disturbed, and high directivity can be maintained. Further, since the low refractive index layer 204 also has a flat interface, even if it is reflected, the state of parallel light is not disturbed, and high directivity can be maintained.

Since light incident on the microlens 202a in a parallel light state is converged along a parallel plane of the parallel light in a direction perpendicular to the longitudinal direction of the microlens 202a, which is a cylindrical lens, it is possible to converge in a direction perpendicular to the longitudinal direction of the microlens 202a with high accuracy in accordance with the lens surface shape of the microlens 202 a.

Fig. 15 is a graph showing a luminance simulation (simulation) of a liquid crystal display device using the backlight unit of the present invention. From this, it is understood that the smaller the light source exit angle (almost parallel light), the higher the luminance.

Here, as shown in fig. 10, the pixels on the liquid crystal display panel are rectangular, and the long sides of the rectangles are normally arranged so as to be in contact with each other. For example, the QVGA pixel has a long side of 150 μm and a short side of 50 μm, and the VGA pixel has a long side of 75 μm and a short side of 25 μm. Further, since the aperture ratio of the openings in the pixels is lower in the longitudinal direction than in the short-side direction, incident light is more efficiently transmitted through the openings by converging the incident light in the longitudinal direction with high accuracy than by converging the incident light in the short-side direction with high accuracy, thereby improving luminance. Therefore, as shown in fig. 10, the longitudinal direction of the pixel is arranged in a direction perpendicular to the longitudinal direction of the microlens 202a, which can converge with high accuracy. Since the incident light is converged and diffused in the transmissive region of the pixel, the angle of view in the longitudinal direction of the pixel is large.

On the other hand, although the directivity in the longitudinal direction of the microlens 202a is not high, the directivity is aligned with the short-side direction having a high aperture ratio, and therefore the luminance drop is less affected. In this example, the directivity is reduced to secure the angle of view in the short-side direction.

In this way, since the light incident from the LED301a is emitted through the microlens 202a and incident on each pixel, the light can be avoided with high accuracy from the TFT element or the black matrix provided on the liquid crystal display panel, and the luminance of the liquid crystal display panel can be improved.

Next, a method for manufacturing a microlens array substrate according to embodiment 1 of the present invention will be described. Fig. 11 is a view showing a method for manufacturing a microlens array substrate according to embodiment 1 of the present invention.

First, as shown in fig. 11(a), a transparent substrate 201 made of glass for forming a microlens array is prepared, and a low refractive index layer 204 is formed by applying, for example, a fluorine-containing transparent resin on the front surface of the transparent substrate 201 for forming a microlens array. Here, as the transparent substrate 201 for microlens array, for example, a 400 μm thick glass substrate is used.

Next, as shown in fig. 11(b), in the transparent substrate 201 for forming a microlens array, a photosensitive resin (negative type transparent resist) is applied to the entire region of the surface on which the low refractive index layer 204 is formed, and the lens forming layer 20 is formed using a gray scale mask. As a coating method, spin coating (spin coat) or slot coating is available.

The photosensitive resin is preferably an ultraviolet curable resin. The photosensitive resin is preferably a resin that can be developed with any one of an organic solvent, an alkaline solution, and water. The ultraviolet curable resin is preferably a resin containing a photoreactive compound and a propylene copolymer having at least a carboxyl group and an ethylenically unsaturated group in a side chain. The propylene copolymer having a carboxyl group and an ethylenically unsaturated group in a side chain is a polymerization binder component, and can be produced by adding an ethylenically unsaturated group to a side chain in a propylene copolymer obtained by copolymerizing an unsaturated carboxylic acid and an ethylenically unsaturated compound.

The unsaturated carboxylic acid is, for example, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, anhydrides thereof, and the like. Examples of the ethylenically unsaturated compound include methyl acrylate, methyl methacrylate and ethyl acrylate. Examples of the side chain ethylenically unsaturated group include vinyl, allyl and propenyl groups.

Examples of the ethylenically unsaturated compound having a glycidyl (glycidyl) group include glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether. The photosensitive resin may be a photosensitive polymer or a non-photosensitive polymer other than the propylene copolymer as a polymerization binder component.

As the photosensitive polymer, there are a light-insoluble polymer and a light-soluble polymer; examples of the light-insoluble polymer include a mixture of a functional monomer or oligomer having one or more unsaturated groups in one molecule and a suitable polymer binder, a mixture of a photosensitive compound such as an aromatic diazo compound, an aromatic azide compound, or an organic halide and a suitable polymer binder, a photosensitive polymer obtained by adding a photosensitive group to an existing polymer as a pendant group or a modified product thereof, and a so-called diazo resin such as a diazo amine or a formaldehyde condensate. Examples of the light-soluble polymer include inorganic salts of diazo compounds, complexes with organic acids (complex), quinonediazides (quino-di-azides), and the like, mixed with an appropriate polymer binder, and naphthoquinone-1, 2-diazide-5-sulfonate esters of phenol and novolak resins, which are obtained by binding quinonediazides to an appropriate polymer binder.

Examples of the non-photosensitive polymer include polyvinyl alcohol, polyvinyl butyral, a methacrylate polymer, an acrylate-methacrylate copolymer, and an α -methylstyrene polymer.

As the photoreactive compound, a monomer or an oligomer containing a known photoreactive carbon-carbon unsaturated bond can be used. Examples of the photoreactive compound include allyl acrylate, benzyl acrylate, butoxyethyl acrylate, butoxytriglycol acrylate, and the like. Further, as typical examples of the oligomer, polyester acrylate, urethane acrylate, epoxy acrylate, and the like can be cited.

Examples of the photopolymerization initiator used for the ultraviolet curable resin include combinations of reducing agents such as benzophenone, methyl o-benzoylbenzoate, 4 bis (dimethylamine) benzophenone, 4 bis (diethylamino) benzophenone, and 4, 4 dichlorobenzophenone.

Next, as shown in fig. 11(c), the gradation mask 30 is disposed on the side opposite to the side on which the lens forming layer 20 is formed, and the lens forming layer 20 is exposed. Here, the gray mask 30 is formed corresponding to the shapes of the microlens array 202 and the raised edge 203 shown in fig. 2 and 3. In the formation region of the microlens array 202, intensity modulation can be applied to exposure light irradiated from the side of the gray-scale mask 30 by the gray-scale mask 30.

In detail, the intensity modulation is performed as follows: in the formation region of each microlens 202a, the exposure intensity is maximized at the central portion of each microlens 202a, and is reduced at both end portions. Depending on the lens forming region of the tone mask 30, the lens forming layer 20 can be cured into a cylindrical lens shape by the exposure light to which the intensity modulation is applied.

Further, by using the gray scale mask 30, exposure is also performed in the region where the flange 203 is formed, and the flange is cured into a flange shape. In this way, by simultaneously forming the plurality of microlenses 202a and the raised edge 203 using the same gray scale mask 30, the microlens array 202 and the raised edge 203 can be efficiently formed on the transparent substrate 201 for microlens array formation.

Next, as shown in fig. 11(d), after the exposure of the lens forming layer 20 is completed, the uncured portion is removed by developing the lens forming layer 20. In this case, since the exposure and development processes are not performed in the region other than the region where the microlens array 202 and the raised edge 203 are formed, the lens-forming layer 20 can be completely removed in this region. Thus, the microlens array 202 and the convex side 203 are formed on the transparent substrate 201 for forming a microlens array. At this time, the height of the microlens array 202 formed in a cylindrical shape, for example, is about 15 μm, and the height of the bank 203 is about 20 μm.

Next, as shown in fig. 11(e), in the microlens-forming substrate 201, a prism portion 205 and a reflection portion 206 are formed on the surface opposite to the surface on which the microlens array 202 is formed. Specifically, a prism portion 205 having a reflection portion 206 formed on the surface thereof is prepared, and is bonded to the surface of the microlens array forming substrate 201 on the side opposite to the surface on which the microlens array 202 is formed. Further, a hard coat layer (not shown) is formed on the reflection portion 206. The hard coat layer is made of a photocurable resin or the like. The hard coat layer is provided to protect the reflective portion 206 and prevent oxidation thereof.

Further, the prism portion 205 is formed as follows: for example, a transparent base material such as PET is subjected to roll transfer of a transparent photocurable resin having a prism-like shape in which the plurality of grooves 205a are formed in advance, and cured, and then is bonded to the transparent base sheet 201. The reflection portion 206 is formed by depositing gold, silver, aluminum alloy, or the like on the surface of the prism portion 205.

As above, the microlens array substrate 200 is fabricated.

Embodiment 2 of the present invention will be described below.

A liquid crystal display device according to embodiment 2 of the present invention will be described with reference to the drawings. Fig. 12 is a cross-sectional view schematically showing the structure of a liquid crystal display device according to embodiment 2 of the present invention. Fig. 13 is a schematic diagram showing a structure of a backlight unit according to embodiment 2 of the present invention, fig. 13(a) is a schematic front view, fig. 13(b) is a schematic cross-sectional view taken along a section line T-T of fig. 13(a), and fig. 13(c) is a schematic cross-sectional view taken along a section line U-U of fig. 13 (a).

Fig. 14 is a schematic diagram showing the structure of a backlight unit according to embodiment 2 of the present invention, fig. 14(a) is a schematic rear view, fig. 14(b) is a schematic cross-sectional view taken along a V-V section line of fig. 14(a), and fig. 14(c) is a schematic cross-sectional view taken along a W-W section line of fig. 14 (a).

In the liquid crystal display device according to embodiment 1 of the present invention, as shown in fig. 1, 2, and 3, polarizers 109a and 109b are respectively attached to the outer surfaces of the transparent substrates 101 and 102 of the liquid crystal display panel 100, and accordingly, as shown in fig. 12, 13, and 14, the liquid crystal display device according to embodiment 2 of the present invention is different in that: the polarizer 109b is disposed between the low refractive index layer 204 of the microlens array substrate 200a and the microlens array 202. At this time, the λ/4 plate 112b is disposed between the microlens array 202 and the polarizer 109 b. In addition, the λ/4 plate 112a is also disposed between the polarizer 109a and the transparent substrate 101 of the liquid crystal display panel 100 a.

Thus, the distance between the microlens array 202 and the inner surface of the transparent substrate 102 of the liquid crystal display panel 100a can be shortened, and the focal length of the microlenses 202a can be shortened. As a result, the angle of view of the liquid crystal display panel 100a can be further increased. For example, when the sheet thickness of the transparent substrate 102 is 0.2mm, the angle of view can be increased to about ± 40 °.

A method for manufacturing the microlens array substrate 200a of embodiment 2 of the present invention will now be described. First, a low refractive index layer 204, a polarizer 109b, and a λ/4 sheet 112b are sequentially laminated on a microlens array forming substrate 201, and then a lens layer 20 is formed on the λ/4 sheet. Then, the microlens array 202, the rim 203, and the like are formed in accordance with the manufacturing method shown in fig. 8.

The above description is of the embodiments of the present invention, but the present invention is not limited to the above embodiments. Further, the elements in the above embodiments can be easily changed, added, or changed by those skilled in the art within the scope of the present invention.

Although the low refractive index layer 204 is formed between the transparent microlens array forming substrate 201 and the microlens array 202 in the above embodiment, the low refractive index layer 204 does not need to be provided as long as the refractive index of the transparent microlens array forming substrate 201 itself can be made larger than that of the microlens array 202.

In the above embodiment, although the negative type photoresist is used, a positive type photoresist that decomposes a photosensitive portion and has good solubility in a solvent may be used.

In the above-described embodiments, the microlens array and the rim are formed using the same material, but the microlens array and the rim may be formed using different materials.

In the above embodiment, the microlens array and the bank are formed using the same gray scale mask, but different gray scale masks may be used. In the above embodiment, the convex edge is formed on the transparent substrate for forming a microlens array, but the convex edge may be formed separately. In the above embodiment, the microlens array substrate 200 is used for a liquid crystal display panel, but the present invention is not limited thereto, and the microlens array substrate may be used for other purposes.

In the above embodiment, the LEDs 301 are disposed at both ends of the light guide member, but may be disposed at either end.

Claims (14)

1. A backlight unit includes: a microlens provided on the back surface side of the liquid crystal display panel to condense light in each pixel transmission region of the liquid crystal display panel,

the disclosed device is provided with: a light source; a light guide member that emits parallel light from a side surface opposite to a side surface on which the first prism portion is provided, by reflecting the light from the light source incident from an end portion on the first prism portion provided on the side surface; and a microlens array substrate on which parallel light emitted from the light guide member is incident from a side surface, reflected by a second prism portion provided on a bottom surface, and emitted toward the liquid crystal display panel through the microlenses provided on a front surface,

the microlens array substrate includes: a microlens array composed of a plurality of microlenses; a transparent substrate on which a second prism portion is formed, the second prism portion being formed of a reflection groove extending in a direction perpendicular to a propagation direction of parallel light incident from the side surface; and a low refractive index layer formed between the microlens array and the transparent substrate and having a refractive index lower than that of the transparent substrate.

2. The backlight unit of claim 1,

the light source includes a first light source provided at one end of the light guide member and a second light source provided at the other end.

3. The backlight unit according to claim 1 or 2,

the side surface of the light guide member on which the first prism portion is provided has a curved surface structure in which a central portion protrudes.

4. A backlight unit includes: a microlens provided on the back surface side of the liquid crystal display panel to condense light in each pixel transmission region of the liquid crystal display panel,

the disclosed device is provided with: a light guide member emitting parallel light; and a microlens array substrate on which parallel light emitted from the light guide member is incident from a side surface, reflected by a second prism portion provided on a bottom surface, and emitted toward the liquid crystal display panel through the microlenses provided on a front surface,

the microlens array substrate includes: a microlens array composed of a plurality of microlenses; a transparent substrate on which a second prism portion is formed, the second prism portion being formed of a reflection groove extending in a direction perpendicular to a propagation direction of parallel light incident from the side surface; and a low refractive index layer formed between the microlens array and the transparent substrate and having a refractive index lower than that of the transparent substrate.

5. The backlight unit according to any one of claims 1 to 4,

the microlens is a cylindrical lens extending in a direction perpendicular to the reflection groove of the second prism portion.

6. The backlight unit according to any one of claims 1 to 5,

and a polarizer or polarizing layer provided between the low refractive index layer and the microlens array.

7. A liquid crystal display device includes: a liquid crystal display panel in which a liquid crystal is sandwiched between a pair of element substrates each having an electrode formed on an inner surface thereof, and a backlight unit provided on a back surface side of the liquid crystal display panel,

the backlight unit includes: the disclosed device is provided with: a light source; a light guide member that emits parallel light from a side surface opposite to a side surface on which the first prism portion is provided, by reflecting the light from the light source incident from an end portion on the first prism portion provided on the side surface; and a microlens array substrate on which parallel light emitted from the light guide member is incident from a side surface, reflected by a second prism portion provided on a bottom surface, and emitted toward the liquid crystal display panel through the microlenses provided on a front surface,

the microlens array substrate includes: a microlens array composed of a plurality of microlenses; a transparent substrate on which a second prism portion is formed, the second prism portion being formed of a reflection groove extending in a direction perpendicular to a propagation direction of parallel light incident from the side surface; and a low refractive index layer formed between the microlens array and the transparent substrate and having a refractive index lower than that of the transparent substrate.

8. The liquid crystal display device according to claim 7,

the light source includes a first light source provided at one end of the light guide member and a second light source provided at the other end.

9. The backlight unit according to claim 7 or 8,

the side surface of the light guide member on which the first prism portion is provided has a curved surface structure in which a central portion protrudes.

10. A liquid crystal display device includes: a liquid crystal display panel in which a liquid crystal is sandwiched between a pair of element substrates each having an electrode formed on an inner surface thereof, and a backlight unit provided on a back surface side of the liquid crystal display panel,

the disclosed device is provided with: a light guide member emitting parallel light; and a microlens array substrate on which parallel light emitted from the light guide member is incident from a side surface, reflected by a second prism portion provided on a bottom surface, and emitted toward the liquid crystal display panel through the microlenses provided on a front surface,

the microlens array substrate includes: a microlens array composed of a plurality of microlenses; a transparent substrate on which a second prism portion is formed, the second prism portion being formed of a reflection groove extending in a direction perpendicular to a propagation direction of parallel light incident from the side surface; and a low refractive index layer formed between the microlens array and the transparent substrate and having a refractive index lower than that of the transparent substrate.

11. The liquid crystal display device according to any one of claims 7 to 10,

the microlens is a cylindrical lens extending in a direction perpendicular to the reflection groove of the second prism portion.

12. The liquid crystal display device according to any one of claims 7 to 11,

and a polarizer or polarizing layer provided between the low refractive index layer and the microlens array.

13. The liquid crystal display device according to any one of claims 7 to 12,

the liquid crystal display panel has a plurality of pixels each having a rectangular shape, and has a pixel structure in which the pixels are arranged adjacent to each other with their longitudinal directions oriented in the same direction,

the longitudinal direction of the micro-lenses of the backlight unit is arranged parallel to the width direction of the pixels.

14. The liquid crystal display device according to any one of claims 7 to 13,

the liquid crystal display device is a semi-transmissive liquid crystal display device.