KR20080009490A - Light controlling structure and the surface lightning device using the same - Google Patents

Abstract

A light controlling structure and a surface lighting device using the same are provided to control high brightness and a specific sight angle by controlling the path of a light emitted through a waveguide using a medium with specific optical characteristics. A waveguide plate(20) has more than one incident plane(21) receives a lighting beam from an external light source, a light emission plane(22) emitting the lighting beam and a reflection plane to reflect the lighting beam. At least one prism sheet(30) corrects directivity of the emitted light from the light emission plane. A light transmitting material(40) is intervened between the waveguide plate and the prism sheet.

Description

LIGHT CONTROLLING STRUCTURE AND THE SURFACE LIGHTNING DEVICE USING THE SAME}

1 is a schematic cross-sectional structural view of a surface light source device including a light control structure according to the present invention.

FIG. 2 is a schematic diagram of a geometrical movement path of light on a prism inclined plane of the light guide plate. FIG.

3A to 3C are graphs showing reflection coefficients and reflectances according to incident angles when the light guide plate is made of PMMA material and the space between the light guide plate and the prism sheet is a different medium.

4 is a schematic diagram showing a path of transmission of transmitted light according to a change in the refractive index of the space portion between the light guide plate and the prism sheet.

5 is a graph showing changes in density and luminance of a micro disk pattern for the light control structure according to the embodiment of the present invention.

** Explanation of symbols for main parts of drawings **

10: light source 20: light guide plate

21: entrance face 22: exit face

23: reflective surface 24: distal face

25: prism 30: prism sheet

31: prism 40: light transmitting medium

50: optical film layer 60: reflector

70: reflective sheet

The present invention relates to a light control structure constituting a surface light source device such as a backlight unit used in a liquid crystal display device, and to a light control structure capable of high luminance and viewing angle control, and a surface light source device using the same.

A light guide plate is generally applied to a liquid crystal display device and used as a means for applying light to an LCD module which is a passive display device. That is, the light emitted from a light source such as a light emitting diode or a cold cathode fluorescent lamp disposed on at least one side or the bottom of the light guide plate is guided and diffused to apply light to the LCD module installed on the surface side. The light guide plate forms a backlight assembly (BLU) by stacking a diffusion sheet, a vertical / horizontal prism sheet, a protective sheet, and the like on an emission surface side from which light is emitted.

In the conventional backlight unit, the light emitted from the light guide plate is severely refracted by the air layer (refractive index 1), and controls the propagation direction of the light by the prism sheet. In this process, since the light proceeds in an undesired direction, a large amount of light is lost, which causes a problem of low luminance, and additional condensing means such as a plurality of prism sheets must be provided to control the front viewing angle. It was common to do.

However, since an optical film or sheet used in the backlight unit is expensive and causes thinning of the backlight unit, efforts have been made to reduce the number of parts of the backlight unit.

In addition, a predetermined prism pattern may be formed on the surface of the light emitting plate to guide the light to the outside, and the prism pattern is damaged during assembly of the backlight unit, causing product defects.

An object of the present invention devised to solve the above problems of the prior art has a high brightness and a specific viewing angle by controlling the path of light emitted to the light guide plate by using a medium having a specific optical characteristics, the defect rate is significantly remarked when assembling the product It is to provide a reduced light control structure and a surface light source device using the same.

The present inventors have increased the relative refractive index of the light guide plate when inserting a transparent transparent material having a larger refractive index in place of the air layer filling the space between the light guide plate and the prism sheet in the conventional surface light source device configuration. By reducing the reflectance of the outgoing light on the exit surface side of the light guide plate, that is, by reducing the amount of lost light, the light efficiency is improved. In anticipation of the present invention. The gist of the present invention for achieving the above object is as follows.

(1) a light guide plate having one or more incidence surfaces into which illumination light is introduced from an external light source, an emission surface for emitting the illumination light, and a reflection surface for reflecting the illumination light to the emission surface; At least one prism sheet for correcting directivity of the emitted light from the exit surface; And a light transmissive material interposed between the light guide plate and the prism sheet.

(2) The light control structure according to the above (1), wherein the light transmissive material has a visible light transmittance of 90% or more.

(3) The light control structure according to (1), wherein the light transmissive material has a relative refractive index (n) of the light guide plate of 0.87 to 1.16.

(4) The light control structure according to item (1), wherein the light transmissive material has a refractive index of 1.3 to 1.7 when the material of the light guide plate is made of PMMA.

(5) A prism column for correcting the directivity of the illumination light is formed perpendicularly to the incidence plane on either one of the emission surface and the reflection surface of the light guide plate, so that the directivity of the emission light is in front of the emission surface in a plane parallel to the entrance surface. The optical control structure as described in said (1) characterized by correcting in the direction.

(6) The prism of the prism sheet is formed on a surface opposite to the emitting surface of the light guide plate or the opposite surface, and corrects the directivity of the emitted light toward the front of the emitting surface in a plane perpendicular to the incident surface. The light control structure according to (5).

(7) The light control structure according to (6), wherein the vertex angle of the prism formed on the light guide plate and the prism sheet is 60 ° to 110 °.

(8) The light control structure according to item (6), wherein the prism of the light guide plate and the prism sheet has a symmetrical or asymmetrical structure.

(9) the light control structure according to any one of (1) to (8) above; A light source for irradiating illumination light onto the incident surface of the light guide plate; At least one selected from among a diffusion sheet, a polarizing sheet, and a lens lens for condensing, the surface light source device comprising a optical film layer disposed on the prism sheet.

(10) The surface light source device according to item (9), further comprising a reflection sheet disposed below the reflection surface of the light guide plate.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in the following embodiments, the same or similar parts will be denoted by the same or similar reference numerals.

1 is a cross-sectional structural view of a surface light source device including a light control structure according to an embodiment of the present invention. The light control structure 100 is composed of a light guide plate 20 for guiding light L emitted from a light source 10 located on the side, a prism sheet 30, and a light transmissive material 40 interposed therebetween.

At least one optical film layer 50 selected from a diffusion sheet, a polarizing film, and a protective sheet is disposed on the prism sheet 30 of the light control structure 100, and the reflective sheet 70 is disposed below the light guide plate 20. Is arranged to constitute the backlight unit of the liquid crystal panel. In the reflective sheet 70, the illumination light L leaking through the reflecting surface 23 of the light guide plate 20 is returned to the inside of the light guide plate by using a specular reflection member on which silver (Ag) having high reflectance with respect to the illumination light is deposited. The loss of the illumination light L is prevented. In order to increase the light efficiency, the reflector 60 is installed to surround the light source 10 to collect light scattered out of the light guide plate 20 toward the incident surface 21 of the light guide plate 20.

As shown in FIG. 1, the light L that is collected by the reflector 60 and introduced through the incident surface 21 of the light guide plate has an upper emission surface 22 and a lower scattering pattern (not shown). Between these imparted reflective surfaces 23, it propagates to the distal end surface 24 on the opposite side through repeated internal total reflection processes. In the illumination light L, the incident angle with respect to the exit surface 22 gradually decreases every time the reflection is repeated on the reflection surface 23. The decrease in the incident angle increases the component of the light L which is equal to or less than the critical angle with respect to the emission surface 22, promotes the emission from the emission surface 22, and thus the emission light in the region far from the light source 10. Lack is prevented.

The output light L1 from the exit surface 22 of the light guide plate 20 has the property of scattered light, but its main exit direction is from the front direction (normal direction of the exit surface 22) to the end surface 24, That is, it has directivity in the direction away from the light source 10. The directivity of the exit light is corrected in the front direction of the exit surface 22 by the prism sheet 30 provided at least one above the exit surface 22 of the light guide plate 20.

In the embodiment of FIG. 1, the output plane 22 has a triangular prism 25 cross section having a ridge line perpendicular to the entrance plane 21, that is, substantially parallel to the overall traveling path of the light in the light guide plate. ) And corrects the path of the light L1 emitted in the plane parallel to the incident surface 21 in the front direction of the emission surface 22. Optionally, a column of prisms 25 for controlling the optical path on the light guide plate 20 may be formed on the reflective surface 23 side. The portion 25a shown in hidden line in FIG. 1 represents the valley of the prism 25 row.

In addition to the prism 25 formed on the light guide plate 20, the emission surface 22 of the light guide plate 20 is corrected to correct the directing of the exit light L1 irradiated onto the liquid crystal display panel in a direction away from the light source 10. The prism sheet 30 is arrange | positioned above. The lower surface of the prism sheet 30 is provided with a row of prisms 31 having a triangular cross-section having a ridgeline substantially parallel to the incident surface 21, and emits light L1 in a plane perpendicular to the incident surface 21. ) Is corrected in the front direction of the light guide plate 20, the exit surface 22.

The prism 31 rows of the prism sheet 30 are formed on the lower surface of the sheet 30 opposite to the exit surface 22 of the light guide plate 20 as in the embodiment of FIG. 1, or the upper surface opposite thereto. Can be formed on. Furthermore, in the case where there is no column of prisms 25 for correcting the directivity of the outgoing light in the plane parallel to the incidence plane 21 described above, the outflow plane 22 or the reflection plane 23 of the light guide plate 20 is It is also possible to laminate the sheet having the prism 31 rows on only one surface so as to have a multi-layered structure so that the rows of the prism 31 are oriented perpendicular to each other, or to replace the double-sided prism sheets having the prism 31 rows formed perpendicular to each other on both sides. .

On the other hand, the direction of the light irradiated from the backlight unit varies depending on the type and use of the liquid crystal display panel to be used, the direction of the light exiting through the light guide plate 20 and the prism sheet 30 is the emission surface 22 It is preferred to be perpendicular to. To this end, the vertex angle of the prism formed in the light guide plate 20 and the prism sheet 30 is preferably in the range of 60 ° ~ 110 °.

In addition, the prism 25 and 31 formed on the light guide plate 20 and the prism sheet 30 may be formed in a symmetrical or asymmetrical structure.

According to a feature of the invention, instead of an air layer of refractive index 1 filling the space between the conventional light guide plate 20 and the prism sheet 30 to control the amount of light exiting through the prism 25 of the light guide plate 20 and the viewing angle path. Is filled with a light transmissive material 40 having a predetermined visible light transmittance value.

The light transmissive material 40 is a material that forms a passage for the movement of light between the light guide plate 20 and the prism sheet 30, and thus has a high transmittance to visible light because absorption of the medium must be minimal to achieve high brightness. Preferably the ratio of the amount of transmitted light to the amount of illumination light is at least 90% or more.

As such a light transmitting material, a transparent resin layer such as, for example, a fluorinated acrylic resin is preferable, and the refractive index should be 1.3 to 1.7.

In the present invention, in terms of performance of the light control structure related to luminance, when the light transmissive material 40 is filled, the relative refractive index of the light transmissive material 40 which is the second medium to the light guide plate 20 which is the first medium ( n = n ₂ / n ₁ ) is increased to reduce the reflectance of the emitted light at the emission surface 22 side of the light guide plate 20 forming the interface of the medium, thereby maximizing the amount of light transmitted relatively to improve the light efficiency.

FIG. 2 is a schematic diagram of a geometrical movement path of light on the prism inclined surface 25 of the light guide plate 20. Fresnel reflection phenomenon occurs in which some of the incident light is reflected at the interface of the different media, such as the light guide plate 20 and the light transmissive material 40. That is, some of the illumination light i reaching the inclined surface 25 is refracted by the refracted light or the transmitted light t and proceeds into the light-transmitting material 40, and the other part is reflected by the reflected light r to reflect the light guide plate 20. Will return to. Such Fresnel reflections should be suppressed as much as possible because they reduce the amount of light emitted from the light guide plate 20, thereby reducing the overall brightness of the backlight unit.

In Fresnel reflection, the reflectance (ratio of the intensity of the reflected light to the intensity of the illumination light) R is calculated from the following equation (1).

Where r _s and r _p represent the reflection coefficients of the s-polarized light and the p-polarized light (the ratio of reflected light to amplitude of illumination light), and θ _i and θ _t represent the incident angle and the transmission angle (refractive angle), and R _s and R _p represents the reflectance of s-polarized light and p-polarized light. From equation (1), the reflectance is expressed as the square of the reflection coefficient, and given the angle of incidence (θ _i ), the angle of refraction (θ _t ) is determined so that these reflection coefficients are a function of the angle of incidence for a particular relative refractive index (n) It can represent a graph.

3A to 3C are graphs showing reflection coefficients and reflectances according to incident angles when the light guide plate is made of a PMMA material having a refractive index of 1.49 and is used in different media between the light guide plate 20 and the prism sheet 30. . That is, FIG. 3A illustrates the case where the medium of the space part is a conventional air layer having an absolute refractive index of 1, that is, when the relative refractive index is n = 0.67, and FIGS. 3B and 3C show a predetermined visible light transmittance of the medium of the space part according to the present invention. In the case where the light-transmitting material 40 having the layer is formed, that is, the relative refractive index n is set to 0.87 to 1.16.

3A and 3B illustrate a case where the refractive index of the space medium is smaller than the light guide plate 20, and FIG. 3C illustrates a case where the refractive index of the space medium is larger than the light guide plate 20.

As can be seen in FIGS. 3A to 3C, the larger the angle θ _i of the illumination light incident on the prism inclined surface 25 of the light guide plate 20, the greater the reflection coefficient and reflectance. In particular, in the illumination light incident in a range where the incident angle θ _i is small, that is, incident in a direction substantially perpendicular to the prism inclined plane 25 of the light guide plate 20, the larger the relative refractive index n, the higher the reflection coefficient and reflectance are. It becomes smaller, and the ratio of the transmitted light that is relatively refracted becomes large, which is advantageous for high brightness.

That is, in the present invention, when the light transmissive material 40 is filled, the relative refractive index (n = n ₂ / n ₁ ) of the light transmissive material 40 as the second medium with respect to the light guide plate 20 as the first medium is determined. In order to reduce the reflectance of the outgoing light at the emission surface 22 side of the light guide plate 20 forming the interface of the medium, the light transmittance is maximized to improve the light efficiency.

On the other hand, according to another aspect of the present invention, by inserting the light transmitting material 40 to concentrate the refracted light in the front direction. 4 is a schematic diagram showing a path of the transmitted light according to the change in the refractive index of the space portion between the light guide plate 20 and the prism sheet. The illumination light i incident on the prism inclined surface 25 of the light guide plate 20 is refracted at a predetermined angle according to Equation (2) below regarding Snell reflection law and proceeds into the medium 40.

Here, n ₁ represents the refractive index of the light guide plate 20, n ₂ represents the refractive index of the medium 40 occupying the space portion, θ _i represents the angle of incidence and θ _t represents the refractive angle, respectively.

From equation (2), the refractive angle θ _t of the transmitted light is assumed that the incident angle θ _i and the refractive index n ₁ of the light guide plate 20 are constant, so that the refractive index n ₂ of the space medium 40 is larger. It becomes small. That is, the angle of the refracted light t forming the normal line v of the prism inclined surface 25 is made small so that the intensity of the refracted light component directed upward of the light guide plate 20 is relatively concentrated. By reducing the light loss component directed in the parallel direction, it is possible to improve the brightness of the entire backlight and at the same time improve the front viewing angle.

As the front viewing angle is improved, an extra vertical prism sheet for guiding the light emitted from the light guide plate 20 upwards becomes unnecessary, so that it is possible to simplify the configuration by reducing the number of parts of the entire backlight unit.

6 is a view angle measurement data of the light control structure according to the embodiment of the present invention. As can be seen in Figure 6, by forming a vertical prism on the upper surface of the light guide plate and a medium having a specific refractive index between the transverse prism can be controlled to the viewing angle of 90 degrees.

On the other hand, in the present invention by bonding the light-transmitting material between the light guide plate 20 and the prism sheet 30 of the light control structure 100 via a medium, the conventional prism sheet 30 is simply mounted on the light guide plate 20. After the reliability test, etc., the mechanically fragile pieces of the prism are separated and the problem of deterioration of the display quality as the material acts as a foreign material between the light guide plate 20 and the prism sheet 30 is improved.

As described above, the preferred embodiments of the present invention have been described, but the scope of the present invention is not limited to the above embodiments, and the present invention can be applied to various modifications without departing from the essential features and essential features of the present invention. Of course.

For example, in the present invention, the light guide plate may have a plate shape in which the emission surface and the reflection surface are parallel to each other in addition to the wedge shape of FIGS. 1 and 2, and the light source may be a point light source or a linear light source in one of the side cross-sections of the light guide plate. It can be installed at or on the sides of the two side sections facing each other.

In addition, the light guide plate 20 may use a transparent light guide plate or a scattering light guide plate (a type in which a plurality of fine particles are dispersed in a transparent matrix), and in the case of using a scattering light guide plate, a diffusion sheet of the optical film layer may be omitted.

In addition, the prism heat and the scattering pattern of the light guide plate 20 may be selectively formed on an emission surface or a rear surface (reflection surface) of the light guide plate.

In addition, the prism formed on the prism sheet 30 may have a single-sided prism sheet in which a prism row is formed on only one surface thereof, or a double-sided prism sheet may be used alone. The face is opposite to the exit face of the light guide plate or can be shaved on the opposite side.

Accordingly, the embodiments described above are merely illustrative and do not have a limiting meaning, and the scope of the present invention should be understood to include the matters described in the appended claims and all modifications that may be understood therefrom. .

According to the present invention, it is possible to reduce the number of parts of the backlight unit, simplify the configuration, control the high brightness and the viewing angle, and effectively reduce the defect rate that occurs during the manufacturing process.

Claims (10)

A light guide plate having at least one incidence surface into which illumination light is introduced from an external light source, an emission surface for emitting the illumination light, and a reflection surface for reflecting the illumination light to the emission surface; At least one prism sheet for correcting directivity of the emitted light from the exit surface; And a light transmissive material interposed between the light guide plate and the prism sheet. The structure of claim 1, wherein the light transmissive material has a visible light transmittance of 90% or more. The structure of claim 1, wherein the light transmissive material has a relative refractive index (n) of 0.87 to 1.16 of the light guide plate. The structure of claim 1, wherein the light transmissive material has a refractive index of 1.3 to 1.7 when the material of the light guide plate is made of PMMA. The method according to claim 1, wherein a prism column for correcting the directivity of the illumination light is formed perpendicular to the incidence plane on any one of the emission surface and the reflective surface of the light guide plate, the directivity of the exit light in the plane parallel to the incident surface Light control structure, characterized in that for correcting in the front direction of the. The prism of claim 5, wherein the prism of the prism sheet is formed on a surface opposite to the light emitting surface of the light guide plate or on the opposite surface of the prism sheet, thereby correcting the directivity of the light emitted in the front direction of the light emitting surface in a plane perpendicular to the light incident surface. Light control structure. The light control structure of claim 6, wherein a vertex angle of the prism formed on the light guide plate and the prism sheet is 60 ° to 110 °. The structure of claim 6, wherein the prism of the light guide plate and the prism sheet has a symmetrical or asymmetrical structure. A light control structure according to any one of claims 1 to 8; A light source for irradiating illumination light onto the incident surface of the light guide plate; At least one selected from among a diffusion sheet, a polarizing sheet, and a lens lens for condensing, the surface light source device comprising a optical film layer disposed on the prism sheet. The method according to claim 9, And a reflective sheet disposed below the reflective surface of the light guide plate.

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