JP2013186414A - Reflection type display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection type display device which has a wide view angle and is excellent in display quality.SOLUTION: A reflection type display device comprises a light reflection part and a light diffusion film 5. The light reflection part scatters and reflects light that is incident. The diffusion film 5 faces the light reflection part and has forward scattering characteristics.

Description

  Embodiments described herein relate generally to a reflective display device.

  In general, a reflection type display device is known as a display device. Examples of the reflective display device include a reflective liquid crystal display device and a reflective display device such as an electrophoretic method, an electronic powder fluid method, an interference modulation method, an electrowetting method, and an electrochromic method. Among them, typical methods of the reflective liquid crystal display devices which are currently mainstream include a diffuse reflector method, a back scattering liquid crystal method, and a forward scattering film method.

JP 2003-270630 A JP 2000-147481 A JP-A-6-175126 JP-A-5-323292 Japanese Patent Laid-Open No. 8-201802

By the way, in general, a reflection type display device having a completely diffusive reflecting surface has a low reflectance, and is not particularly suitable for color display. Therefore, a display device using specular reflection is effective for obtaining a high reflectance. However, the diffuse reflection plate method has a strong reflected light directivity and it is difficult to widen the viewing angle. In the forward scattering film method, the viewing angle can be widened by increasing the haze of the forward scattering film. However, when the haze is increased, the viewing angle is widened, but the backscattering of the forward scattering film becomes strong, and the display quality is lowered. For example, the contrast is lowered, the image is blurred, and the front luminance level is lowered.
The present invention has been made in view of the above points, and an object thereof is to provide a reflective display device having a wide viewing angle and excellent display quality.

A reflective display device according to an embodiment includes:
A light reflecting portion that scatters and reflects incident light; and
And a light diffusing film having a forward scattering characteristic facing the light reflecting portion.

FIG. 1 is a perspective view showing a reflective liquid crystal display device according to the first embodiment. FIG. 2 is a plan view schematically showing a wiring structure of the reflective liquid crystal display device. FIG. 3 is a cross-sectional view showing the reflective liquid crystal display device taken along line AA in FIG. FIG. 4 is an enlarged cross-sectional view of the forward scattering film shown in FIG. FIG. 5 is a cross-sectional view showing a part of the reflective liquid crystal display device according to the second embodiment.

Hereinafter, the reflective liquid crystal display device according to the first embodiment will be described in detail with reference to the drawings.
As shown in FIGS. 1 to 3, the reflective liquid crystal display device includes an array substrate 1, a counter substrate 2 disposed opposite to the array substrate with a predetermined gap, and sandwiched between the array substrate and the counter substrate. The liquid crystal layer 3, the color filter 4, a light diffusion film 5 having forward scattering characteristics (hereinafter referred to as a forward scattering film), a polarizing plate 6, and a retardation plate 7 are provided. The liquid crystal display panel has a rectangular display area.

  The array substrate 1 has a rectangular glass substrate 10. The counter substrate 2 has a rectangular glass substrate 20. The first substrate and the second substrate are not limited to glass substrates, but may be any transparent insulating substrate. In the display region, the liquid crystal display device includes a plurality of pixels PX provided in a matrix between the glass substrate 10 and the glass substrate 20. The pixels PX are arranged in a first direction d1 and a second direction d2 that are orthogonal to each other.

  In the array substrate 1, a plurality of signal lines 11 extending on the glass substrate 10 in the first direction d1 and arranged at intervals in the second direction d2, and intersecting the plurality of signal lines in the second direction A plurality of scanning lines 12 extending and arranged at intervals in the first direction are arranged in a grid pattern. Each pixel PX is provided so as to overlap an area surrounded by two adjacent signal lines 11 and two adjacent scanning lines 12.

  For example, a plurality of TFTs (thin film transistors) 13 are provided as a plurality of switching elements near the intersection of the signal line 11 and the scanning line 12 on the glass substrate 10. The TFT 13 includes a gate electrode 13a extending a part of the scanning line 12, a gate insulating film (not shown) provided on the gate electrode, a semiconductor layer 13c facing the gate electrode through the gate insulating film, and one of the semiconductor layers. A source electrode 13d connected to the region and a drain electrode 13e connected to the other region of the semiconductor layer are provided.

  The source electrode 13d is connected to the signal line 11, and the drain electrode 13e is connected to a pixel electrode 15 described later. The TFT 13 is formed of a common gate insulating film. One TFT 13 is provided for each pixel PX, and constitutes a pixel.

  An interlayer insulating film (not shown) is formed on the glass substrate 10, the signal line 11, the scanning line 12, and the TFT 13. In the display region, a plurality of pixel electrodes 15 are provided in a matrix on the interlayer insulating film. The pixel electrode 15 is formed of a layer containing a conductive material having light reflectivity such as aluminum or silver. Each pixel electrode 15 is electrically connected to the drain electrode 13e of the corresponding TFT 13 through a contact hole formed in the interlayer insulating film. The pixel electrode 15 has a one-to-one correspondence with the pixel PX, and constitutes a pixel.

  The pixel electrode 15 is overlaid on the TFT 13. The peripheral edge of the pixel electrode 15 overlaps the signal line 11 and the scanning line 12. Therefore, the pixel electrode 15 is partially raised.

  The pitch P of the pixels PX is 150 μm or less, and the pixel electrodes 15 are arranged at a pitch P of 150 μm or less. In this embodiment, the pitch P is 100 μm. As described above, when the pitch P is 150 μm or less, the pixel electrode 15 can increase the ratio of the protrusion, and thus can scatter and reflect incident light. Here, the pitch P is a pitch in the direction along the short axis of the pixel electrode 15. The plurality of pixel electrodes 15 form a light reflecting portion.

  A plurality of columnar spacers (not shown) are formed on the pixel electrode 15 as a plurality of spacers. The spacer is not limited to the columnar spacer, and may be another spacer such as a spherical spacer. An alignment film 17 is formed on the glass substrate 10 on which the pixel electrodes 15 and the columnar spacers are formed.

  In the counter substrate 2, a grid-shaped first light-shielding portion and a rectangular frame-shaped second light-shielding portion (not shown) and a color filter 4 are disposed on the glass substrate 20. The first light shielding portion is formed surrounding the pixel PX. The second light shielding portion is formed surrounding the display area. The first light shielding part and the second light shielding part function as a black matrix.

The color filter 4 has a plurality of colored layers. In this embodiment, the color filter 4 has red, green, and blue colored layers. The colored layers of red, green, and blue are formed in a stripe shape, extend in the first direction d1, and are alternately arranged in the second direction d2. Each colored layer is disposed with its peripheral edge overlapping the first light shielding portion.
A common electrode 23 made of a transparent conductive material such as ITO is formed on the color filter 4. An alignment film 25 is formed on the common electrode 23.

The array substrate 1 and the counter substrate 2 are arranged to face each other with a predetermined gap by columnar spacers. The array substrate 1 and the counter substrate 2 are joined to each other by a sealing material 31 disposed on the peripheral edge of both substrates.
The liquid crystal layer 3 is sandwiched between the array substrate 1 and the counter substrate 2. The liquid crystal layer 3 is located between the pixel electrode 15 and the forward scattering film 5. The liquid crystal layer 3 functions as a switching unit that switches between the first state and the second state. The first state is a state in which incidence of incident light from the front scattering film 5 to the pixel electrode 15 and emission of reflected light from the pixel electrode 15 to the front scattering film 5 are permitted. The second state is a state in which at least one of incidence of incident light from the front scattering film 5 to the pixel electrode 15 and emission of reflected light from the pixel electrode 15 to the front scattering film 5 are prohibited. A liquid crystal injection port 32 is formed in a part of the sealing material 31, and the liquid crystal injection port is sealed with a sealing material 33.

  A phase difference plate 7, a polarizing plate 6 as a polarizer, and a forward scattering film 5 are sequentially provided on the outer surface of the glass substrate 20 (counter substrate 2). In this embodiment, circularly polarized light is generated by using the polarizing plate 6 and the phase difference plate 7. The front scattering film 5 has a display surface S. The front scattering film 5, the polarizing plate 6, and the retardation film 7 are overlapped at least in the display area.

  The front scattering film 5 faces the plurality of pixel electrodes 15 and the like. The front scattering film 5 transmits incident light (external light) from the display surface S side to the pixel electrode 15 side, and scatters and emits the light reflected by the pixel electrode 15.

  Here, in the forward scattering film 5, light scattered in the direction of incident light is referred to as forward scattered light, and light scattered in a direction opposite to the direction of incident light is referred to as backscattered light. Then, in the forward scattering film 5, the intensity of the backscattered light is weaker than the intensity of the forward scattered light.

  The front scattering film 5 has a haze in the range of 70% to 95%. In this embodiment, the forward scattering film 5 has a haze in the range of 80% to 95%. When the parallel light is vertically incident on the forward scattering film 5, the forward scattering film 5 has a diffusion half-value angle of light that is diffused and emitted from the light transmitted through the film within a range of 10 ° to 35 °. It is configured as follows. Here, the diffusion half-value angle is a luminance value that is half the peak luminance value in the distribution of transmitted diffused light when light (parallel light) in a direction perpendicular to the forward scattering film 5 is incident on the forward scattering film 5. It is an angle indicating the distribution range of transmitted light indicating.

  As shown in FIG. 4, the forward scattering film 5 includes a transparent resin film 51 as a transparent film, a transparent resin layer 52 as a transparent layer, an adhesive layer 53, and a plurality of fine particles 54.

  The transparent resin film 51 becomes a base film. The transparent resin film 51 has a flat surface. In this embodiment, the transparent resin film 51 is flat on both sides. The transparent resin layer 52 is located between the transparent resin film 51 and the counter substrate 2 (pixel electrode 15). The transparent resin layer 52 may be an adhesive transparent resin layer.

  The adhesive layer 53 is located between the transparent resin layer 52 and the counter substrate 2 (pixel electrode 15). The front scattering film 5 is attached to the polarizing plate 6 by the adhesive layer 53. The plurality of fine particles 54 exhibit translucency and are dispersed in at least one of the transparent resin layer 52 and the adhesive layer 53. In this embodiment, the plurality of fine particles 54 are dispersed in the transparent resin layer 52. The average particle diameter of the plurality of fine particles 54 is in the range of 1 μm to 10 μm. The transparent resin layer 52 in which the plurality of fine particles 54 are dispersed forms a light diffusion layer.

  The relative refractive index difference of the constituent material of the front scattering film 5 is in the range of 0.01 to 0.1. In this embodiment, the relative refractive index difference among the transparent resin film 51, the transparent resin layer 52, the adhesive layer 53, and the plurality of fine particles 54 is in the range of 0.01 to 0.1.

  According to the reflective liquid crystal display device according to the first embodiment configured as described above, the reflective liquid crystal display device includes a plurality of pixel electrodes 15 that scatter and reflect incident light, and a forward scattering film. And 5. In the forward scattering film 5, the intensity of the back scattered light is weaker than the intensity of the forward scattered light. Since the intensity of the backscattered light can be suppressed, it is possible to reduce a decrease in contrast, blurring of an image, a decrease in front luminance, and the like.

  The forward scattering film 5 desirably has a haze in the range of 80% to 95%. By designing the haze of the front scattering film 5 so as not to cause problems such as bleeding, backscattering, and reduction in contrast, the reflected light as a whole (the entire device) should have strong scattering characteristics without impairing display characteristics. As a result, high contrast can be obtained over a wide viewing angle.

  When the haze is less than 80%, scattering of reflected light is insufficient and a metallic display is obtained. When the haze is 80% or more, a display close to paper white can be obtained. However, when the haze exceeds 95%, light scattering occurs more than necessary, leading to a reduction in front luminance.

  Further, in order to set the haze in the range of 80% to 95%, it is necessary to increase the density of the fine particles 54 in the transparent resin layer 52 and to increase the thickness of the transparent resin layer 52. For this reason, there exists a possibility that the malfunction that the flatness of the front scattering film 5 (transparent resin film 51) may be lost due to the high density of the fine particles 54 may occur. Further, the thickening of the transparent resin layer 52 causes the forward scattering film 5 to be bent due to stress, the display image to blur, the manufacturing cost to increase, and the desired scattering characteristics cannot be obtained due to the aggregation of the fine particles 54. There is a risk of malfunction. In this case, the above problem can be solved by taking measures to disperse the fine particles 54 in the adhesive layer 53.

The surface of the transparent resin film 51 is flat. For this reason, the backscattering by the surface of the transparent resin film 51 can be reduced.
The relative refractive index difference among the transparent resin film 51, the transparent resin layer 52, the adhesive layer 53, and the plurality of fine particles 54 is in the range of 0.01 to 0.1. Back scattering can be reduced by reducing the refractive index difference at any interface. From the above, it is possible to give the reflected light the necessary scattering characteristics while keeping the backscattering very low, and as a result, the viewing angle can be widened, and a bright and high-contrast image display can be realized. Can do.

  The film used as the light diffusion plate can be broadly divided into a surface diffusion method in which irregularities are formed on the surface of the resin film by embossing or chemical surface treatment on the surface, and an internal diffusion method in which translucent fine particles are dispersed inside the resin. Can be divided into Of these, the internal diffusion method is desirable to control the intensity of the backscattered light.

  For this reason, in this embodiment, the forward scattering film 5 employs an internal diffusion method. By setting the average particle diameter of the fine particles 54 within the range of 1 μm to 10 μm, the backscattering in the forward scattering film 5 can be reduced. Next, the reason why the backscattering is reduced will be described.

  A particle size parameter related to the wavelength of light incident on the forward scattering film 5 and the size of the fine particles 54 is defined as α. When the circumference ratio is π, the diameter of the fine particles 54 is D, and the wavelength of light incident on the forward scattering film 5 is λ, the particle size parameter α can be expressed by the following equation.

α = πD / λ
When α << 1, Rayleigh scattering is dominant, and the forward scattered light and the back scattered light have the same intensity.
When α≈1, Mie scattering is dominant, and the forward scattering characteristic (intensity) increases as the particle size of the fine particles 54 increases.
In the case of α >> 1, diffraction and reflection characteristics handled by geometric optics are shown.
From the above, in the forward scattering film 5 adopting the internal diffusion method, the average particle diameter of the fine particles 54 is set in the range of 1 μm to 10 μm, controlled by Mie theory.

  The diffusion half-value angle of the front scattering film 5 is desirably in the range of 10 ° to 35 °. If the diffusion half-value angle is less than 10 °, the transmitted light of the front scattering film 5 is not sufficiently scattered, and thus there is a possibility that a wide viewing angle cannot be achieved. Further, if the diffusion half-value angle exceeds 35 °, the scattering range of the transmitted light of the front scattering film 5 becomes unnecessarily wide, so that a wide viewing angle can be achieved, but the front luminance is lowered. There is a fear. The diffusion half-value angle is more preferably in the range of 15 ° to 30 °.

  The pixel electrode 15 is a thin film, but the peripheral edge is raised to overlap the wiring. Further, the pixel electrodes 15 are arranged at a pitch P of 150 μm or less. By achieving high definition (miniaturization of the pixel PX pitch), the diffraction phenomenon at the end of the pixel electrode 15 can be used effectively as light scattering, so that the pixel electrode 15 efficiently exhibits light scattering characteristics. Can be obtained.

  By shortening the distance from the surface of the front scattering film 5 to the pixel electrode 15, bleeding of the display image can be reduced. For this reason, the thickness of the forward scattering film 5 is desirably 100 μm or less. In addition, it is also desirable to make the counter substrate 2 (color filter substrate), which is the thickest member, normally thin. In this case as well, bleeding of the display image can be reduced and display quality can be improved.

  The front scattering film 5 desirably has high transparency and low birefringence. For example, the front scattering film 5 can use a light diffusion film using TAC (triacetyl cellulose) as the material of the transparent resin film 51.

  From the above, a reflective liquid crystal display device having a wide viewing angle and excellent display quality can be obtained.

Next, the reflective liquid crystal display device according to the second embodiment will be described in detail.
As shown in FIG. 5, the pitch P of the pixels PX exceeds 150 μm, and the pixel electrodes 15 are arranged at a pitch P exceeding 150 μm. In this embodiment, the pitch P is 300 μm.

The pixel electrode 15 has an uneven surface on the side facing the forward scattering film 5. Thereby, the degree of scattering of the reflected light from the pixel electrode 15 can be increased. For this reason, in this embodiment, the forward scattering film 5 has a haze in the range of 70% to 95%.
In the second embodiment, other configurations are the same as those of the first embodiment described above, and the same portions are denoted by the same reference numerals and detailed description thereof is omitted.

  According to the reflective liquid crystal display device according to the second embodiment configured as described above, the reflective liquid crystal display device includes a plurality of pixel electrodes 15 that scatter and reflect incident light, and a forward scattering film. And 5. In the forward scattering film 5, the intensity of the back scattered light is weaker than the intensity of the forward scattered light. For this reason, the effect similar to 1st Embodiment mentioned above can be acquired.

The forward scattering film 5 desirably has a haze in the range of 70% to 95%. When the haze is less than 70%, scattering of reflected light is insufficient and a metallic display is obtained. When the haze is 70% or more, a display close to paper white can be obtained. However, when the haze exceeds 95%, light scattering occurs more than necessary, leading to a reduction in front luminance.
The fine particles 54 may be dispersed in the adhesive layer 53.

  When the pixel electrodes 15 are arranged at a pitch P exceeding 150 μm, reflection by the pixel electrodes 15 is close to specular reflection. For this reason, by providing the pixel electrode 15 with an uneven surface, it is possible to scatter and reflect incident light. A technique for providing the pixel electrode 15 with a concavo-convex surface is disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-9911 “Diffusion reflector, method for manufacturing the same, and reflective display device”.

When the pixel electrode 15 and the front scattering film 5 are used and a high reflectance is obtained in a wide viewing angle, the haze of the front scattering film 5 can be set high. In addition, when obtaining a higher reflectance in the front direction, the pixel electrode 15 has a certain degree of light condensing property, and the haze of the front scattering film 5 is set to be low so that the viewing angle is not reduced extremely. It is possible to design a highly reflective light profile.
From the above, a reflective liquid crystal display device having a wide viewing angle and excellent display quality can be obtained.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  For example, even if the pitch P of the pixels PX (pixel electrodes 15) is 150 μm or less, the pixel electrodes 15 may have an uneven surface on the side facing the forward scattering film 5. Thereby, arbitrary reflection characteristics can be imparted to the pixel electrode 15.

  The above-described embodiments can be applied to, for example, a polarizing liquid crystal display device of a polarizing plate type or a guest host type. Further, the above-described embodiment is not limited to the reflective liquid crystal display device, and can be applied to various reflective display devices. Examples of the reflective display device include a reflective display device having a specular reflection structure such as an electrophoretic method, an electronic powder fluid method, an interferometric modulation method, an electrowetting method, and an electrochromic method. The reflective display device includes a switching unit that switches between the first state and the second state instead of the liquid crystal layer 3.

  A front light device may be provided on the front surface of the reflective display device. The front light device is disposed opposite to the forward scattering film 5. Thereby, even in an environment where the brightness of outside light is not sufficient, it is possible to display an image having a luminance level equal to or higher than a certain value.

  DESCRIPTION OF SYMBOLS 1 ... Array substrate, 2 ... Opposite substrate, 3 ... Liquid crystal layer, 4 ... Color filter, 5 ... Forward scattering film, 11 ... Signal line, 12 ... Scanning line, 13 ... TFT, 15 ... Pixel electrode, 51 ... Transparent resin film 52 ... Transparent resin layer, 53 ... Adhesive layer, 54 ... Fine particles, P ... Pitch.

Claims (10)

A light reflecting portion that scatters and reflects incident light; and
A reflective display device comprising: a light diffusion film facing the light reflecting portion and having forward scattering characteristics.   The reflective display device according to claim 1, wherein the light diffusion film has a haze in a range of 70% to 95%. The light diffusion film is
A transparent film having a flat surface;
A transparent layer positioned between the transparent film and the light reflecting portion;
An adhesive layer located between the transparent layer and the light reflecting portion;
The average particle diameter is in a range of 1 μm to 10 μm, exhibits translucency, and includes a plurality of fine particles dispersed in at least one of the transparent layer and the adhesive layer. 2. A reflective display device according to 2.   The reflective display device according to claim 3, wherein a relative refractive index difference between the transparent film, the transparent layer, the adhesive layer, and the plurality of fine particles is within a range of 0.01 to 0.1.   5. The light diffusing film is configured such that a diffusion half-value angle of transmitted diffused light when parallel light is vertically incident is within a range of 10 [deg.] To 35 [deg.]. The reflective display device according to any one of the above.   A first state permitting incidence of incident light from the light diffusing film to the light reflecting portion and emission of reflected light from the light reflecting portion to the light diffusing film; and from the light diffusing film to the light reflecting portion. A switching unit that switches to one of a second state in which at least one of incidence of incident light on the light and emission of reflected light from the light reflecting unit to the light diffusion film is prohibited. The reflective display device according to claim 1, wherein the reflective display device is a reflective display device. An array substrate having a plurality of pixel electrodes;
A counter substrate having a common electrode facing the plurality of pixel electrodes;
A liquid crystal layer sandwiched between the array substrate and the counter substrate, and
The light reflecting portion is formed by the plurality of pixel electrodes,
The reflective display device according to claim 6, wherein the switching unit is formed of the liquid crystal layer.   The reflective display device according to claim 7, wherein the plurality of pixel electrodes are arranged at a pitch of 150 μm or less.   The reflective display device according to claim 1, wherein the light reflecting portion has an uneven surface on a side facing the light diffusing film.   The reflective display device according to claim 1, wherein the light reflecting portion is formed of a layer containing aluminum or silver.

Images