JP2007047635A - Backlight unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct type backlight unit having a polarization separation layer that can improve use efficiency of light emitting from a light source and has a simple structure. <P>SOLUTION: The backlight unit has a polarization separation layer 7 that transmits P-polarized light more than S-polarized light in the light emitting from a light source 5, wherein the polarization separation layer 7 comprises three layers of folded films 11 to 13 having peaks and valleys alternately formed, and air layers 14, 15 inserted between the folded film layers 11 to 13. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a direct-type backlight unit used in, for example, a liquid crystal display device.

In general, as a display method in a liquid crystal display device, a liquid crystal panel having a liquid crystal layer, a pair of glass substrates sandwiching the liquid crystal layer, and a polarizing plate provided on each of the pair of glass substrates is used to electrically change the alignment state of the liquid crystals. There is a method of controlling and visually recognizing transmitted light transmitted through the liquid crystal panel by a backlight unit that irradiates the liquid crystal panel with illumination light from the back side.
In the backlight unit used in such a liquid crystal display device, the other linearly polarized light component orthogonal to one of the linearly polarized light components transmitted through the polarizing plate is absorbed by the polarizing plate on the back side of the liquid crystal panel. Therefore, the light use efficiency is reduced. Therefore, by providing a polarization separation element that transmits the light emitted from the light source more in one linearly polarized light component than in the other linearly polarized light component, the proportion of light absorbed by the polarizing plate is reduced and the light use efficiency is improved. The structure to improve is proposed (for example, refer patent documents 1-3). These are used in so-called edge light type backlight units in which light emitted from a light source is introduced into a light guide plate and then the optical path is changed toward a liquid crystal panel.
By the way, in order to obtain a clearer display by irradiation of the backlight unit, a direct type backlight unit capable of irradiating a large amount of illumination light to the liquid crystal panel is used. As a polarization separation element applicable to such a direct type backlight unit, a plurality of birefringent material layers are laminated to transmit one linearly polarized light and reflect the other linearly polarized light, or on a substrate. There has been provided a polarization separation element in which cholesteric liquid crystals are stacked to transmit one circularly polarized light and to reflect reverse circularly polarized light (for example, see Non-Patent Documents 1 and 2).
Japanese Patent No. 2879555 Japanese Patent No. 3129444 Japanese Patent No. 3219943 “Nitto Technical Report”, May 2001, Vol. 39, No. 1, p. 33-36 “Practical Collection of the 82nd Lecture Meeting of the Japan Society for Plastic Processing”, p. 46-49

  However, the following problems remain in the polarization separation element applicable to the conventional backlight unit. That is, in the former polarization separation element, it is necessary to laminate a large number of films having a wavelength of about ¼ wavelength, and in the latter polarization separation element, a plurality of cholesteric liquid crystals are laminated in order to have a polarization separation function in the visible light region. Both of them are complex in structure and difficult to manufacture. Therefore, there is a problem that when the area is increased, it is difficult to make the polarization separation function uniform in the plane.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a direct type backlight unit having a polarization separation layer with an easy structure while improving the utilization efficiency of light irradiated by a light source. To do.

  The present invention employs the following configuration in order to solve the above problems. That is, the backlight unit of the present invention is a direct type including a polarization separation layer that transmits more of the first linearly polarized light than the second linearly polarized light whose polarization direction is orthogonal to the first linearly polarized light among the light irradiated from the light source. In the backlight unit, the polarization separation layer has a plurality of folded film layers in which peaks and valleys are alternately formed, and an air layer interposed between the folded film layers. It is characterized by.

According to this invention, since the polarization separation layer is formed by laminating a plurality of folded film layers with an air layer interposed therebetween, the polarization separation function is increased as compared with the case where the folded film layer is a single layer. And the utilization efficiency of the light irradiated by the light source can be improved. Further, since the structure is easy, the manufacturing cost can be reduced, and the polarization separation function can be made uniform in the plane of the polarization separation layer when the area of the polarization separation layer is increased.
Here, when the bending angle of the peak and the valley is the Brewster angle of light incident on the bent film layer, θ _B (deg), 180 ° −2θ _B or more, 180 ° −2 (θ _B + 15 °) or less. As a result, one first linearly polarized light of the light incident in the thickness direction of the polarization separating layer is transmitted through the bent film layer almost without reflection, so that the first linearly polarized light is transmitted more than the second linearly polarized light to be polarized. The separation function can be further enhanced.

  Further, the backlight unit of the present invention is a direct type provided with a polarization separation layer that transmits more of the first linearly polarized light than the second linearly polarized light whose polarization direction is orthogonal to the first linearly polarized light among the light irradiated from the light source. In the backlight unit, the polarization separation layer is formed on a folded film layer in which peaks and valleys are alternately formed, and is formed on at least one surface of the folded film layer. And a high refractive index layer having a high refractive index.

According to this invention, the polarization separation layer forms a high refractive index layer on at least one surface of the folded film layer, and the refractive index of the folded film layer and the entire high refractive index layer is increased. Compared with the case where the second linearly polarized light is not provided, the polarization separation function can be increased by increasing the reflectance of the second linearly polarized light, and the utilization efficiency of the light irradiated by the light source can be improved. Further, since the structure is easy, the manufacturing cost can be reduced, and the polarization separation function can be made uniform in the plane of the polarization separation layer when the area of the polarization separation layer is increased.
Here, similarly to the above, it is desirable that the bending angle of the peak portion and the valley portion is 180 ° −2θ _B or more and 180 ° −2 (θ _B + 15 °) or less.

  According to the direct type backlight unit of the present invention, the light use efficiency of the light source can be improved and the structure of the polarization separation layer can be facilitated. Therefore, it is possible to reduce the manufacturing cost and to make the polarization separation function uniform in the plane when the polarization separation layer is enlarged.

Hereinafter, a first embodiment of a direct backlight unit according to the present invention will be described with reference to the drawings.
The direct type backlight unit in the present embodiment is used as illumination means of a liquid crystal display device 1 as shown in FIG. The liquid crystal display device 1 includes a backlight unit 2 and a liquid crystal panel 3.

The backlight unit 2 includes a light source 5, a diffusion plate 6, a polarization separation layer 7, and a housing 8 that stores these.
The light source 5 is composed of, for example, a cold cathode fluorescent lamp, and emits non-polarized light. The light source 5 is provided with a drive circuit (not shown) for driving and controlling the cold cathode fluorescent lamp, an inverter (not shown), and the like.
The diffusion plate 6 diffuses the light emitted from the light source 5 and makes the traveling direction of the illumination light from the light source 5 toward the polarization separation layer 7 uniform.

The polarized light separating layer 7 is composed of folded film layers 11 to 13 laminated in three layers, and air layers 14 and 15 interposed between the folded film layers 11 to 13.
The folded film layers 11 to 13 are made of, for example, a 50 μm thick resin film made of PMMA (polymethyl methacrylate) having a refractive index of 1.493. In addition, the bent film layers 11 to 13 are formed by alternately repeating a plurality of crests and troughs at the same bending angle at a constant interval, and the bending angle θ _P1 is, for example, 40 °. The interval between the vertices is 1 mm, for example.

Here, the bending angle θ _P1 of the bent film layers 11 to 13 will be described. First, the Brewster angle θ _B of light traveling from the medium A having a refractive index of n ₁ toward the interface with the medium B having a refractive index of n ₂ is
θ _B = tan ⁻¹ (n ₂ / n ₁ )
It becomes. Then, the incident angle to the interface between medium A and the medium B by a Brewster angle theta _B, P-polarized light, which is one of the linearly polarized light is transmitted through the non-reflective, S-polarized light surface is the other of the linearly polarized light Reflect on. In the present embodiment, since the refractive index n ₁ of the air that is the medium A is 1, and the refractive index n ₂ of the bent film layers 11 to 13 that are the medium B is 1.493, in the bent film layers 11 to 13 The Brewster angle θ _B is 56.19 °.
Maximum also generally, the polarization splitting function, which is the ratio of the P polarized light transmittance of incident on the interface between the medium A and the medium B and the transmittance of S polarization in incident angle slightly greater than the Brewster angle theta _B next, the polarization splitting function is maximized at large incidence angles of about 15 ° than the Brewster angle theta _B in this embodiment. From the above, a preferable range as the incident angle to the bent film layers 11 to 13 is 56.19 ° to 71.19 °.
Thus, the bending angle θ _P1 of the bent film layers 11 to 13 proceeds in the stacking direction of the bent film layers 11 to 13 with respect to the polarization separation layer 7, that is, the arrow X direction shown in FIGS. It is preferable that it is 37.62 ° -67.62 ° so that the incident angle of light is 56.19 ° -71.19 °.

In addition, beads formed of a translucent material are arranged as spacers (gap forming members) 17 between the bent film layers 11 to 13. In addition, the spacer 17 should just be arrange | positioned by the space | interval of the grade which can ensure the air layers 14 and 15 between each bending film layers 11-13.
For example, the folded film layers 11 to 13 in this embodiment sandwich a resin film using a pair of molds in which a plurality of crests and troughs having an apex angle of 40 ° are alternately arranged at intervals of 1 mm. The resin film is formed by applying hot pressure to the resin film. Moreover, the edge part of each bending film layer 11-13 is integrated by adhesion | attachment or the other method. Thereby, handling of the bent film layers 11-13 becomes easy.
An inner reflection layer 18 is provided on the inner wall of the housing 8 to reflect the light that is reflected by the diffusion plate 6 and the polarization separation layer 7 and is directed toward the inner wall of the housing 8.

The liquid crystal panel 3 includes a liquid crystal layer 21, a pair of glass substrates 22 and 23 disposed on both surfaces of the liquid crystal layer 21, and polarizing plates 24 and 25 disposed on the outer surfaces of the glass substrates 22 and 23, respectively. Yes.
Transparent electrodes (not shown) made of ITO (Indium Tin Oxide) for applying a voltage to the liquid crystal layer 21 are provided on the inner surfaces of the pair of glass substrates 22 and 23 facing each other. .

  Illumination light emitted from the light source 5 and diffused by the diffusion plate 6 enters the polarization separation layer 7 and is separated into a P-polarized component which is one linearly polarized component and an S-polarized component which is the other linearly polarized component. , The P-polarized component is transmitted through the polarization separation layer 7 more than the S-polarized component. Thereafter, the light enters the liquid crystal panel 3. Here, a polarization separation method by the polarization separation layer 7 will be described.

As shown in FIG. 2, the P-polarized light incident on the polarization separation layer 7 in the direction of the arrow X is incident on the interface with the bent film layer 11 when the bent angle θ _P1 is 40 ° as in this embodiment. Since it is incident at 70 ° (= 90 ° −40 ° / 2), most of the incident light is transmitted through the bent film layer 11.
Then, the P-polarized light transmitted through the bent film layer 11 passes through the bent film layers 12 and 13 in the same manner as the bent film layer 11.

Further, since the S-polarized light incident on the polarization separation layer 7 in the X direction is incident on the bent film layer 11 at an incident angle of 70 °, a part thereof is reflected by the incident side surface 11a of the bent film layer 11 and the remainder Passes through the bent film layer 11.
A part of the S-polarized light transmitted through the bent film layer 11 is partially reflected by the bent film layers 12 and 13 and the remaining part is transmitted through the bent film layers 12 and 13 in the same manner as the bent film layer 11. However, by sequentially repeating reflection and transmission in the bent film layers 11 to 13, the S-polarized light transmitted through the bent film layer 13 which is the final layer of the bent film layers 11 to 13 is reduced.
On the other hand, the S-polarized light reflected by the bent film layer 11 is incident on the bent film layer 11 again at another position away from the reflection position, and the incident angle at that time is 30 °. The portion may pass through the bent film layer 11. However, since the reflection is complicatedly repeated by the folded film layers 11 to 13 having the three-layer structure, the S-polarized light transmitted through the folded film layer 13 which is the final layer is extremely reduced.
As described above, the polarization separation layer 7 separates P-polarized light and S-polarized light.

  In this embodiment, when there is only one folded film layer, the transmittance for P-polarized light is 95.72%, the reflectance is 4.28%, the transmittance for S-polarized light is 70.33%, and the reflectance is The polarization separation layer 7 has a configuration in which three folded film layers 11 to 13 are laminated so that the transmittance of P-polarized light is 74.6% and the reflectance is 20. The transmittance of S-polarized light was 25.9%, and the reflectance was 68.8%.

According to the backlight unit 2 configured as described above, the polarization separation layer 7 has a configuration in which the bent film layers 11 to 13 formed by bending the resin film are stacked, and one bent film layer is formed. Compared with the case, the polarization separation function can be enhanced to improve the light use efficiency of the light source. Further, the structure of the polarization separation layer 7 becomes easy. Accordingly, the manufacturing cost can be reduced and the polarization separation function can be made uniform in the plane.
Here, since the spacer 17 is arrange | positioned between each bending film layers 11-13, the air layers 14 and 15 can be ensured reliably.

  In addition, in this embodiment, although the spacer 17 is interposed between each bending film layers 11-13, at least any one of the incident side of each bending film layers 11-13, and the surface of an output side. The surface may be a mat surface on which fine irregularities are formed. Even if it does in this way, it can prevent easily that each bending film layer 11-13 adheres.

  Next, a second embodiment will be described with reference to FIG. The embodiment described here has the same basic configuration as the first embodiment described above, and is obtained by adding another element to the first embodiment described above. Therefore, in FIG. 3, the same components as those in FIG.

The difference between the second embodiment and the first embodiment is that the backlight unit has one folded film layer 31 and a high refractive index layer 32 on both the incident side and the exit side of the folded film layer 31. And a polarization separation layer 34 provided with 33.
Similar to the bent film layer 11 in the first embodiment, the bent film layer 31 is made of a resin film of PMMA, the bent angle θ _P2 is 40 °, and the distance between the apexes of the peaks is 1 mm. ing.
The high refractive index layers 32 and 33 are made of, for example, titanium oxide having a refractive index of 2.28, and are formed on both surfaces of the bent film layer 31 by vapor deposition. The thicknesses of the high-refractive index layers 32 and 33 are, for example, 60.3 nm (= 550 nm) so that the wavelength is ¼ wavelength in the light having a typical wavelength of 550 nm from the wavelength of 380 nm to 780 nm that is the visible light region. /(2.28×4)). Therefore, the high refractive index layer 32 is a so-called increased reflection film due to the thin film interference phenomenon of light.

Therefore, most of the P-polarized light incident on the polarization separation layer 34 is transmitted through the high refractive index layer 32, the folded film layer 31, and the high refractive index layer 33 formed on the incident side surface of the folded film layer 31. .
On the other hand, the S-polarized light is partially reflected on the incident-side surface of the high refractive index layer 32 and transmitted through the remaining portion. However, since the high refractive index layers 32 and 33 are provided to increase the reflectance, the polarization separation layer is provided. At 34, most of the S-polarized light is reflected.
In the present embodiment, the polarization separation layer 34 is provided with high refractive index layers 32 and 33 on both the incident side and the exit side of the bent film layer 31, and the transmittance of P-polarized light is 80.9% and the reflectance is high. The transmittance of S-polarized light was 31.7%, and the reflectance was 68.3%.

  The backlight unit configured as described above has a higher refractive index by the high refractive index layers 32 and 33, and as a result, has a smaller transmittance of S-polarized light. The utilization efficiency can be improved. Further, the structure of the polarization separation layer 34 is easy, and it is possible to reduce the manufacturing cost and make the polarization separation function in-plane uniform.

  Next, a third embodiment will be described with reference to FIGS. The embodiment described here has the same basic configuration as the second embodiment described above, and is obtained by adding another element to the second embodiment described above. Therefore, in FIG.4 and FIG.5, the same code | symbol is attached | subjected to the same component as FIG. 3, and the description is abbreviate | omitted.

The difference between the third embodiment and the second embodiment is that the backlight unit includes a bent film layer 31 having high refractive index layers 32 and 33 formed on the surface, and a birefringent material layer 41. This is a point having a separation layer 42.
The birefringent material layer 41 is formed by stretching a resin film having a high photoelastic coefficient, such as polycarbonate (PC), in the direction of arrow A shown in FIG. 5, and is orthogonal to the refractive index n ₁ in the stretching direction. The refractive index n _{2 in the} direction is different. The birefringent material layer 41 changes the polarization direction according to the retardation amount, which is the product of the refractive index difference Δ for each polarization direction and the optical path length passing through the inside. The birefringent material layer 41 is set so that the retardation amount Δd for P-polarized light is ½ wavelength when the thickness is d. In FIG. 5, the bent film layer 31 and the birefringent material layer 41 are illustrated in a shifted manner for explanation.

Therefore, most of the P-polarized light incident on the high refractive index layer 32 passes through the bent film layer 31 and enters the birefringent material layer 41. Here, since the birefringent material layer 41 functions as a half-wave plate with respect to the P-polarized light, the P-polarized light incident on the birefringent material layer 41 is rotated by 90 ° to be converted into S-polarized light and emitted.
On the other hand, a part of the S-polarized light is reflected by the bent film layer 31, and the S-polarized light reflected by the bent film layer 31 is incident on the bent film layer 31 again. At this time, since the S-polarized light is incident on the folded film layer 31 at an incident angle of 30 °, a part of the S-polarized light that is re-incident passes through the folded film layer 31. Then, the S-polarized light transmitted through the bent film layer 31 enters the birefringent material layer 41 at an incident angle of 40 °. Here, the amount of retardation of the S-polarized light incident on the birefringent material layer 41 is
Δd / cos (40 °) = 1.3 Δd
It becomes. As a result, the S-polarized light incident on the birefringent material layer 41 rotates by 0.3Δd more than the P-polarized light, so that when it is emitted from the birefringent material layer 41, it becomes an elliptically polarized light having a P-polarized component. To do.

The backlight unit configured in this way also has the same operations and effects as those of the second embodiment described above. However, by providing the birefringent material layer 41 on the exit side of the bent film layer 31, birefringence is achieved. S-polarized light incident on the material layer 41 is converted into elliptically polarized light, and the polarization separation function can be improved.
In the present embodiment, the birefringent material layer 41 is set to convert P-polarized light incident at an incident angle of 0 ° into S-polarized light and emit S-polarized light incident at an incident angle of 40 ° as S-polarized light. May be. Thereby, the polarization separation function can be further improved.
Further, the birefringent material layer 41 may be set so that P-polarized light incident at an incident angle of 0 ° is emitted as P-polarized light. Here, the birefringent material layer 41 is set so that P-polarized light incident at an incident angle of 0 ° is emitted as P-polarized light, and S-polarized light incident at an incident angle of 40 ° is converted into P-polarized light and emitted. Also good.

  Next, a fourth embodiment will be described with reference to FIG. The embodiment described here has the same basic configuration as the first embodiment described above, and is obtained by adding another element to the first embodiment described above. Therefore, in FIG. 6, the same components as those in FIG.

The difference between the fourth embodiment and the first embodiment is that the backlight unit has a polarization separation layer 56 in which the folded film layers 51 to 53 are laminated with the air layers 54 and 55 interposed therebetween, Among the bent film layers 51 to 53, two adjacent bending angles in the stacking direction are different from each other.
As in the first embodiment described above, the folded film layers 51 and 53 have a folding angle θ _P3 of 40 °, for example, and a vertex interval of 1 mm.
Further, the bent film layer 52 has a bending angle θ _P4 of 60 °, for example, and the interval between the apexes is 1 mm like the bent film layers 51 and 53.

  Therefore, most of the P-polarized light incident on the polarization separation layer 56 is transmitted through each of the folded film layers 51 to 53 as in the first embodiment described above. On the other hand, most of the S-polarized light is reflected on the incident-side surface of the bent film layer 51 as described above.

The backlight unit configured in this way also has the same operations and effects as those of the first embodiment described above, but the polarization separation layer 56 is adjacent to the folded film layers 51 to 53 in the stacking direction. The bent film layers have different bending angles, and other surfaces except the apex on the incident side and the emission side of the bent film layers 51 to 53 can be easily prevented from sticking to each other.
In addition, in this embodiment, the bending angle of the folding film layers 51-53 should just differ from the bending angle of the two bending film layers adjacent in a lamination direction, and the incident angle mentioned above. If it is a bending angle within the range of 37.62 ° to 67.62 °, the angle may be appropriately changed so as to be 19 ° to 71.19 °.

  Next, a fifth embodiment will be described with reference to FIG. The embodiment described here has the same basic configuration as that of the first embodiment described above, and is obtained by adding another element to the above-described fourth embodiment. Therefore, in FIG. 7, the same components as those in FIG. 6 are denoted by the same reference numerals, and the description thereof is omitted.

The difference between the fifth embodiment and the first embodiment is that the backlight unit has two layers of folded film layers 61 and 62 having a non-uniform thickness with the air layer 63 interposed therebetween. This is a point having the layer 64.
Each of the bent film layers 61 and 62 has an incident side surface bending angle θ _P5 of, for example, 60 °, an output side surface bending angle θ _P6 of, for example, 40 °, and a vertex interval of 1 mm. The part is formed of a resin film that is thicker than the valley.

Therefore, most of the P-polarized light incident on the polarization separation layer 64 is transmitted through the folded film layers 61 and 62 and emitted as in the first embodiment described above. Here, since each of the folded film layers 61 and 62 has a smaller bending angle on the exit-side surface than that on the incident-side surface, the P-polarized light is reflected from the folded film layers 61 and 62 at the peak of the peak portion. Condensed to the side and emitted.
On the other hand, most of the S-polarized light is reflected by the incident-side surface of the folded film layer 61 as described above.

The backlight unit configured in this way also has the same operations and effects as the fourth embodiment described above, but the bending angle of the exit-side surface is incident on each of the bent film layers 61 and 62. By making it smaller than the bending angle of the side surface, it is possible to collect the light transmitted through each of the bent film layers 61 and 62.
In the present embodiment, the bending angles of the bent film layers 61 and 62 only have to be smaller than the bending angle of the incident side surface and the bending angle of the incident side surface. The angle may be appropriately changed within the range of 37.62 ° to 67.62 °.

In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.
For example, although the resin film comprised by PMMA is used as a bending film layer in the said embodiment, other resin films, such as an acryl, PS (polystyrene), PC (polycarbonate), COP (cycloolefin polymer), are used. May be.
Moreover, you may change suitably the thickness, bending angle, space | interval, etc. of a bending film layer according to design.
Further, the thickness of each air layer may be appropriately changed according to the design.
Moreover, although the diffusion sheet is arrange | positioned between the polarization separation layer and the light source, it is good also as a structure which does not arrange | position a diffusion sheet. Moreover, it is good also as a structure which has arrange | positioned the diffusion sheet and the prism sheet between the polarization splitting layer and the liquid crystal panel.

Moreover, in the said 1st Embodiment, although the spacer is provided between each bending film layer, as long as it can fix with a frame etc. so that each bending film layer may not closely_contact | adhere, it is good also as a structure which does not provide a spacer. .
Moreover, in the said 1st, 4th, 5th embodiment, you may change suitably the lamination | stacking number of a bending film layer according to design.
Moreover, in the said 1st, 4th, 5th embodiment, you may provide a birefringent material layer in the output side of a bending film layer similarly to the said 3rd Embodiment. Thereby, since the S polarization | polarized-light which permeate | transmitted the bending film layer is converted into an elliptical polarization | polarized-light, a polarization separation function can be improved more.
Also in the first, fourth, and fifth embodiments, similarly to the second or third embodiment, a high refractive index layer is formed on the incident side surface and the exit side surface of the folded film layer. May be. Furthermore, the high refractive index layer should just be formed in at least one of the incident side and output side of a bending film layer.
In the second and third embodiments, titanium oxide is used as the high refractive index layer. However, from a resin film such as ITO, which has translucency in the visible light region and is used for the bent film layer. May be a material having a high refractive index. Further, the high refractive index layer is not limited to vapor deposition, and may be formed by other thin film forming methods such as sputtering. Furthermore, it is good also as a structure which laminates | stacks on the surface of a bending film layer what disperse | distributed the nanoparticle whose refractive index is higher than the resin film used for a bending film layer in resin.
In the second and third embodiments, the thickness of the high refractive index layer is (400 / (4 × n)) nm or more (700 /), where n is the refractive index of the high refractive index layer. If (4 × n)) nm or less, it may be appropriately changed.
In the third embodiment, a PC stretched in one direction is used as the birefringent material layer, but another film having a high photoelastic coefficient stretched in one direction may be used. Other uniaxial birefringent materials such as calcite and quartz may be used.
Also in the fourth and fifth embodiments, as in the first embodiment, a spacer may be provided between each folded film layer, and the incident side and the exit side of the folded film layer At least one of the surfaces may be a mat surface.

1 is a schematic diagram showing a liquid crystal display device according to a first embodiment of the present invention. It is sectional drawing which shows the polarization separation layer of FIG. It is sectional drawing which shows the polarization separation layer in the 2nd Embodiment of this invention. It is sectional drawing which shows the polarization separation layer in the 3rd Embodiment of this invention. It is a top view which shows the polarization separation layer of FIG. It is sectional drawing which shows the polarization separation layer in the 4th Embodiment of this invention. It is sectional drawing which shows the polarization separation layer in the 5th Embodiment of this invention.

Explanation of symbols

2 Backlight unit 5 Light source 7, 32, 42, 56, 64 Polarization separation layers 11-13, 31, 51-53, 61, 62 Bent film layers 14, 15, 54, 55, 63 Air layer 17 Spacer (gap Forming member)
41 Birefringent material layer

Claims (9)

In the direct-type backlight unit including a polarization separation layer that transmits more of the first linearly polarized light than the second linearly polarized light whose polarization direction is orthogonal to the first linearly polarized light among the light emitted from the light source,
The polarized light separating layer includes a plurality of folded film layers in which peaks and valleys are alternately formed, and an air layer interposed between the folded film layers. Light unit. In the direct-type backlight unit including a polarization separation layer that transmits more of the first linearly polarized light than the second linearly polarized light whose polarization direction is orthogonal to the first linearly polarized light among the light emitted from the light source,
The polarization separation layer is formed on a folded film layer in which peaks and valleys are alternately formed, and is formed on at least one surface of the folded film layer and has a higher refractive index than the folded film layer. A backlight unit comprising a refractive index layer.   The thickness of the high refractive index layer is (400 / (4 × n)) nm or more and (700 / (4 × n)) nm or less, where n is the refractive index of the high refractive index layer. The backlight unit according to claim 2.   4. The backlight unit according to claim 2, wherein the polarization separation layer includes a plurality of the folded film layers and an air layer interposed between the folded film layers. 5.   The backlight unit according to claim 1, wherein a spacer is interposed between the bent film layers.   6. The backlight according to claim 1, wherein unevenness finer than the ridges and valleys is formed on at least one surface of the bent film layer. unit.   7. The backlight according to claim 1, wherein bending angles of two bent film layers adjacent to each other in the stacking direction among the plurality of bent film layers are different from each other. unit.   The bent film layer has a thickness that increases toward the peak of the peak, and the bending angle of the peak on the exit side surface is smaller than the bending angle of the peak on the incident side. The backlight unit according to any one of claims 1 to 7. The backlight unit according to any one of claims 1 to 8, wherein the polarization separation layer includes a birefringent material layer disposed on an exit side of the bent film layer.

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