JP2006114380A - Light guide plate and backlight unit - Google Patents

Abstract

A light guide plate made of a high-definition diffraction grating and a backlight unit using the light guide plate are designed, developed and manufactured in a short period of time.
The light guide plate 5 of the present invention guides light from a plurality of light sources 1 (# 1 to # 3), and guides light guides 7 (corresponding to the respective light sources 1 (# 1 to # 3)). # 1 to # 3), and each light guide path 7 (# 1 to # 3) diffracts the guided light to emit it outside the light guide path 7 (# 1 to # 3). It has. The backlight unit of the present invention includes the light guide plate 5 and a plurality of light sources 1 (# 1 to # 3).
[Selection] Figure 1

Description

  The present invention relates to a light guide plate using a diffraction grating as light emitting means, and a backlight unit using the light guide plate.

  In recent years, backlight units of liquid crystal display devices have been improved with higher brightness and thinner thickness. At present, the light guide plate by the white dot printing is disappearing, and instead, the light guide plate in which V-shaped grooves of about several tens of μm are arranged has become mainstream.

  However, there is still a strong demand for high brightness and thinning. Especially in small liquid crystal display devices (cell phones, PDAs, etc.), the light guide plate itself has a wedge shape and a prism sheet is stacked on the light guide plate. A light guide plate having a thickness of 0.5 mm has been developed by increasing the brightness and improving the injection molding technology.

  In addition, as a new technique, the technique disclosed in Patent Document 1 uses a diffraction grating as light emitting means in a light guide plate. As shown in FIG. 7, the light guide plate 5 using the diffraction grating 3 guides the light 4 introduced from the light source 1 along the average light guide direction F. The average light guide direction F is an average direction guided by the light guide plate 5.

  In this type of light guide plate 5, since the light emission angle from the light guide plate 5 can be controlled more freely than the emission means using V-shaped grooves or dot patterns, the conventionally used prism sheet can be omitted, and the back The entire light can be made thinner. Furthermore, since the light extraction efficiency can be freely adjusted by the diffraction grating 3, the luminance of the backlight is increased and the luminance unevenness is reduced.

  The diffraction grating 3 is produced by a method of directly drawing a diffraction grating on the surface of an EB resist substrate using a two-beam interference method using a photosensitive material or an electron beam (electron beam = EB), a metal For example, there is a method of machine cutting directly.

  A general backlight configuration includes a light source 1, a light guide plate 5, a scattering plate, and a prism sheet. Here, the role of the prism sheet is used to deflect light emitted from the light guide plate with an inclination of about 60 to 70 degrees in the front direction of the liquid crystal panel.

However, instead of the geometric optical method, as shown in FIG. 7, in the light guide plate 5 provided with the diffraction grating 3 using the diffraction phenomenon, the spatial frequency of the diffraction grating pattern is set to 2000 to 3000 lines / mm. Thus, the direction of the light 2 emitted from the light guide plate 5 can be set to the front direction of the liquid crystal panel, so that a prism sheet is not necessary. At this time, the pitch of the diffraction grating 3 is 1 μm or less, the grating depth is 0.5 μm or less, and the resolution is 1/10 or less than the geometrically optically designed light guide plate pattern.
Japanese Patent Laid-Open No. 7-248496

  Many of the diffraction gratings 3 used for the emission pattern of the light guide plate 5 are very fine (both size and height are 1 μm or less). Therefore, at present, it is essential to produce a diffraction grating pattern by EB drawing. However, since EB drawing is high definition, the production speed is very slow. For example, drawing a light guide plate pattern of a blazed diffraction grating having a size of 2.5 inches takes two months and requires a long time for new product development.

  In recent mobile phones, new models appeared in about three months, and the dimensions and specifications of the backlight have changed every time. The product development cycle is very fast, and product development using an EB drawing device has started. It is a difficult situation.

  In addition, it is difficult to keep the EB drawing apparatus continuously operated for 2 months, and the EB resist plate also changes over time after 2 months, the drawing conditions at the beginning and the drawing conditions at the end are substantially different, and the designed shape is I can't get it.

  The present invention has been made in view of such circumstances, and its purpose is to design, develop, and manufacture a light guide plate made of a high-definition diffraction grating and a backlight unit using the light guide plate in a short period of time. There is to do.

  In order to achieve the above object, the present invention takes the following measures.

  That is, the invention of claim 1 is provided with a light guide path corresponding to each light source that guides light from a plurality of light sources, and each light guide path is arranged outside the light guide path by diffracting the guided light. It is a light guide plate provided with a diffraction grating to be emitted.

  According to a second aspect of the present invention, in the light guide plate according to the first aspect, the diffraction grating is a blazed diffraction grating formed of an ultraviolet curable resin.

  A third aspect of the invention is a backlight unit comprising a plurality of light sources and the light guide plate of the first aspect of the invention.

  The invention of claim 4 is the backlight unit according to claim 3, wherein the diffraction grating is a blazed diffraction grating formed of an ultraviolet curable resin.

  According to the present invention, it is possible to design, develop, and manufacture a light guide plate made of a high-definition diffraction grating and a backlight unit using the light guide plate in a short period of time.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  In addition, the code | symbol in the figure used for description of the following embodiment attaches | subjects and shows the same code | symbol about the same part as FIG.

  A backlight unit including a light guide plate according to an embodiment of the present invention will be described with reference to the drawings.

  That is, the backlight unit according to the embodiment includes a plurality of light sources 1 and a light guide plate 5 as shown in FIG. FIG. 1 shows an example in which three light sources 1 (# 1 to # 3) are provided. The light guide plate 5 includes light guide paths 7 (# 1 to # 3) respectively corresponding to the light sources 1 (# 1 to # 3). And each light guide path 7 (# 1- # 3) will guide this light toward the average light guide direction F, if the light from each corresponding light source 1 (# 1- # 3) is each introduced from the end surface 6. Light guide. Each of the light guide paths 7 (# 1 to # 3) includes the diffraction grating 3 on the back surface 8b. By diffracting the guided light by the diffraction grating 3, the light guide path 7 is directed outward from the front surface 8a or the back surface 8b. , Emit as illumination light. The diffraction grating 3 is a blazed diffraction grating formed of, for example, an ultraviolet curable resin.

  Next, a specific example of the light guide plate configured as described above will be described.

Example 1
Here, a case where a blazed diffraction grating is produced as the diffraction grating 3 on a light guide plate having dimensions of 36 mm × 55 mm × 0.6 mm will be described as an example.

  First, a diffractive grating pattern having a size of 13 mm × 55 mm, in which the blazed diffraction grating is arranged while changing gradation from 10% density on the end face 6 on the light source 1 side to 90% density on the end face 9 farthest from the light source 1. Was made. The spatial frequency of the blazed diffraction grating was 3000 lines / mm, and the diffraction grating pattern was produced on an EB resist using an EB drawing apparatus for about two weeks.

  Subsequently, after developing, a thin film of nickel was formed on the EB resist by sputtering, and then a nickel stamper having a thickness of 100 μm was formed by nickel electroforming.

  Next, a 100 μm thick acrylic UV curable resin is applied to a 500 μm thick polycarbonate sheet, and the stamper is pressed on the polycarbonate sheet, and a mask that allows light to pass through the polycarbonate sheet side by a size of 10 mm × 55 mm is attached. Irradiation was about 1 J / cm ^ 2 with a mercury lamp.

  Subsequently, the polycarbonate sheet was peeled off from the stamper, moved to the right of the transferred pattern, an ultraviolet curable resin was applied, the stamper was bonded so that the transferred pattern and the stamper pattern overlap each other by 1 mm, and UV irradiation was performed again using a mask. Similar transfer, movement, and peeling steps were repeated to obtain a sheet on which a 37 mm × 55 mm size pattern was formed.

  Subsequently, using a punching die having a size of 36 mm × 55 mm, a light guide plate 5 having a size of 36 mm × 55 mm × 0.6 mm provided with three light guide paths 7 (# 1 to # 3) as shown in FIG. Obtained.

  When 36 mm × 55 mm is drawn at the stage of EB drawing, the conventional technique requires a period of about 2 months to manufacture the light guide plate 5, but can be manufactured in about 3 weeks by manufacturing as described above. Thus, it is possible to produce an inexpensive light guide plate 5 with a significantly shortened delivery time.

  In other words, when a plurality of light guide paths 7 are provided as in the present embodiment, only one diffraction grating pattern needs to be produced. Therefore, when producing a diffraction grating pattern over the entire light guide plate. Compared to this, the production period can be shortened.

  Note that the diffraction grating patterns need not all be the same for each light guide path 7 (# 1 to # 3). For example, different diffraction grating patterns may be used for the central light guide path 7 (# 2) and the light guide paths 7 (# 1) and 7 (# 3) at both ends, and at least two light guide paths 7 are used. If the same diffraction grating pattern can be used, the production period can be shortened.

(Example 2)
Here, the light guide plate 5 having dimensions of 39 mm × 50 mm × 0.5 mm is manufactured, and the backlight unit 11 is installed on the end face 6 side of the light guide plate 5 using four white LEDs as the light sources 1 (# 1 to # 4). A case will be described as an example.

  First, a diffractive grating pattern having a size of 10 mm × 50 mm, in which the blazed diffraction grating is arranged with gradation changed from 10% density on the end face 6 on the light source 1 side to 90% density on the end face 9 farthest from the light source 1. Was made. The spatial frequency of the blazed diffraction grating was 3000 lines / mm, and the diffraction grating pattern was produced on an EB resist using an EB drawing apparatus for about two weeks.

  Subsequently, after developing, a thin film of nickel was formed on the EB resist by sputtering, and then a nickel stamper having a thickness of 100 μm was formed by nickel electroforming.

  Subsequently, an acrylic UV curable resin is applied to the surface of a 250 μm thick easy-adhesive PET film (Toyobo A4300) with a thickness of 125 μm, the stamper is bonded, and a high pressure mercury lamp is irradiated with UV light at about 1 J / cm ^ 2. After curing, it was peeled off to obtain a pattern transfer sheet.

  Similarly, after 4 faces were attached, a lenticular sheet was bonded to the back surface of the transfer sheet to form a 0.5 mm thick sheet. Punching was performed with a size of 9 mm × 50 mm each, and four light guides 7 (# 1 to # 4) were obtained.

  Next, as shown in FIG. 2, the light guides 7 (# 1 to # 4) are arranged on the backlight package 10 in parallel with a space of 1 mm between the light guides 7 (# 1 to # 4). The backlight unit 11 is configured by arranging four white LEDs as corresponding light sources (# 1 to # 4) on the end face 6 side of 4).

  Here, the interval at which the light guides 7 are arranged is 1 mm, but even when the light guides 7 are arranged with an interval of 1 mm, a substantially uniform light amount distribution can be obtained by overlapping a diffusion plate (not shown) or the like thereon. Illumination light can be obtained. This will be described with reference to FIG.

  FIG. 3 shows the distribution of relative light intensity over the position along the line AA in FIG. 3 (# 1 to # 4) shown in FIG. 3 is a light intensity distribution by the emitted light obtained from the single light guide 7 (# 1 to # 4), and 13 shown in FIG. It is a light intensity distribution obtained by combining # 1 to # 4), that is, obtained by the backlight unit 11.

  Further, as shown in FIG. 4, light 19 incident from a direction orthogonal to the diffraction grating array 24 is diffracted in the designed direction 21, but light 20 incident from a direction parallel to the diffraction grating array 24. In this case, the diffraction direction changes greatly as in 22 and 23, and the designed direction 21 is not diffracted.

  Furthermore, in the case of a blazed diffraction grating, the light 19 from the design front direction is diffracted very strongly, but sufficient diffraction efficiency cannot be obtained with the light 20 from other directions.

  Here, although a plurality of light sources 1 (# 1 to # 4) are provided as shown in FIG. 5, a plurality of light sources 1 (# 1 to # 1) are provided at point P of the light guide plate formed of a single light guide path 7. Since the various lights 14 emitted from 4) enter the emission pattern (diffraction grating), it is difficult to design the grating and to realize a light-guide plate with high brightness.

  On the other hand, as shown in FIG. 6, in the light guide plate including the light guides 7 (# 1 to # 4) divided corresponding to the respective light sources 1 (# 1 to # 4), the respective side surfaces ( It is also possible to dispose a diffusion pattern for improving the uniformity of the exit surface and a reflecting material for enhancing the reflectivity of the side surface on the light source 1 (#) at the point P, for example. Since only the light 14 from 3) enters, the design of the grating becomes easy and it is easy to realize a light guide plate with a bright and uniform exit surface.

  In addition, in injection molding, which is a general manufacturing method for submicron-size patterns, transfer is incomplete, the structure is rounded, and the structure is generally shallow. However, if an ultraviolet curable resin that is liquid at room temperature is used, high-precision transferability is possible even with a high-definition diffraction grating pattern.

  When a diffraction grating pattern is formed on one side of a transparent film, color change may occur in the spectrum of diffracted light, and a diffusion pattern that matches the diffraction grating pattern is always required on the other side. The In order to further improve the light emission efficiency of the light guide plate 5, it is desirable that the diffraction grating 3 is a blazed diffraction grating having the best diffraction efficiency.

  In this example, an easy-adhesion PET film and a polycarbonate sheet were used, but as a usable transparent resin sheet, sheets and films of polyethylene, polypropylene, polystyrene, acrylic, polyester, polycarbonate, cycloolefin, and the like can be used. In consideration of high transparency and adhesion to an ultraviolet curable resin, polyester and polycarbonate are preferable.

  Furthermore, a base material suitable for efficient production by roll-to-roll needs to have sufficient flexibility and punching suitability, and its film thickness is 500 μm or less. Moreover, in order to use as a light guide plate, it is necessary to consider the light taking in from a light source to a light guide plate, and the film base material of 250-500 micrometers thickness is the most suitable.

  The best mode for carrying out the present invention has been described above with reference to the accompanying drawings, but the present invention is not limited to such a configuration. Within the scope of the invented technical idea of the scope of claims, a person skilled in the art can conceive of various changes and modifications. The technical scope of the present invention is also applicable to these changes and modifications. It is understood that it belongs to.

  For example, arranging a plurality of independent light guides having light guide paths 7 corresponding to the light source 1 to form a single light guide plate does not depart from the gist of the present invention and is included in the light guide plate of the present invention. It is. Moreover, the backlight provided with such a light-guide plate is also contained in the backlight of this invention.

The perspective view which shows the structural example of the backlight unit provided with the light-guide plate which concerns on embodiment of this invention. The top view which shows another structural example of the backlight unit provided with the light-guide plate which concerns on embodiment of this invention. The relative light intensity distribution by the backlight unit shown in FIG. The figure explaining the imprinted resin plate. The figure for demonstrating the light guide state of the light in the light-guide plate provided with the single light guide with respect to the several light source. The figure for demonstrating the light guide state of the light in the light-guide plate which concerns on embodiment of this invention. The perspective view which shows the structural example of the backlight unit provided with the light-guide plate by a prior art.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Light source, 2, 4, 14, 19, 20 ... Light, 3 ... Diffraction grating, 5 ... Light guide plate, 6 ... End surface, 7 ... Light guide path, 8a ... Front surface, 8b ... Back surface, 9 ... End surface, 10 ... Back Light package, 11 ... backlight unit, 21 ... designed direction, 24 ... diffraction grating array

Claims (4)

A light guide path corresponding to each light source that guides light from a plurality of light sources,
Each of the light guides is a light guide plate provided with a diffraction grating that diffracts the guided light and emits the light to the outside of the light guide. The light guide plate according to claim 1,
A light guide plate in which the diffraction grating is a blazed diffraction grating formed of an ultraviolet curable resin. Multiple light sources;
A light guide path corresponding to each light source that guides light from each of the plurality of light sources is provided, and each light guide path is emitted as illumination light to the outside of the light guide path by diffracting the guided light. A backlight unit comprising a light guide plate provided with a diffraction grating. The backlight unit according to claim 3,
A backlight unit in which the diffraction grating is a blazed diffraction grating formed of an ultraviolet curable resin.

Images