JP2009109969A - Prism sheet, optical member and planar light source device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a prism sheet that can improve luminance, an optical member, and a planar light source device using the same. <P>SOLUTION: The up-facing prism sheet has a substantially smooth light-incident surface, wherein prisms each having a substantially triangle-shaped cross-section are consecutively formed on a surface facing the light-incident surface. Assuming that an angular component formed between an incident light and a normal line of the light-incident surface and projected in a direction orthogonal to the prism is θi; a refractive index of the sheet is n; an angle formed between a front surface of the prism and the light-incident surface is α; and an angle formed between a rear surface of the prism and the light-incident surface is β; the shape of the prism satisfies all the expressions: (1) tan(β)=sin(θi)/ä-1+√[n2-sin2(θi)]}; (2) α>90-sin-1[(1/n)sin(θi)]; and (3)α<90-β+sin-1än*sin(sin-1(1/n)sinθi-β)}. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a prism sheet, an optical member, and a planar light source device using the prism sheet for improving the luminance of specific polarized light in a direction perpendicular to a light emitting surface.

  A liquid crystal display is used in a display unit of a mobile phone in addition to a display unit of a computer and a display panel of a home appliance, and further reduction in power consumption, weight reduction, and thinning are required. Since a liquid crystal display is not a self-luminous device, it is necessary to use an external light source or ambient ambient light. A typical example of the external light source is a backlight system in which a surface light source is installed on the back surface of the liquid crystal panel. In the case of the backlight system, it is necessary to emit light emitted from the surface light source in the front direction of the observer.

  A typical configuration of such a backlight system is shown in FIG. Light incident on the light guide plate 91 from the light source 90 and emitted obliquely is bent in the vertical direction by the condensing film 93 and diffused by the diffusion plate 97 so that the color dispersion becomes small, and the polarizing plate 94, the phase difference plate 95, etc. After that, a polarization state suitable for the liquid crystal panel characteristics is obtained, and the liquid crystal panel 96 for displaying an image is irradiated. In FIG. 1, as an example of the condensing film, a downward prism sheet in which a prism is formed on the lower surface is shown. This backlight type liquid crystal display is designed to optimize the shape of the light guide plate and the shape of the downward prism sheet 93 provided between the light guide plate and the liquid crystal to increase the front luminance.

  The incident angle θi of the light emitted from the light guide plate and incident on the light collecting film such as a downward prism sheet with respect to the light collecting film depends on the design of the light guide plate. As shown in FIG. 2, θi is often about 50 ° to 70 °, and the front luminance of the surface light source device is extremely small as it is. Therefore, the light condensing film 93 needs to bend the light efficiently in a direction where θo is 0 °, that is, in a direction perpendicular to the sheet. For this purpose, it is necessary to reduce the Fresnel reflection, which is the interface reflection between the air layer and the prism sheet, and to make as much light as possible travel in the direction of θo = 0 °. Further, when the emitted light has an angular distribution, the light bending angle is constant by providing a light bending characteristic that does not reduce the luminance in the vertical direction even if the incident angle θi varies slightly. Can also increase the brightness in the front direction. Furthermore, since the light source is white light, it is necessary to reduce the dependence of the bending angle on the wavelength to suppress the spectrum as much as possible. Spectroscopy degrades the display quality, for example, it degrades the color reproducibility of the color display of the liquid crystal.

  For example, a conventional downward prism sheet as described in Patent Document 1 mainly bends outgoing light using total reflection. In total reflection, the angle change of the incident light and the angle change of the outgoing light are equal. Therefore, the conventional downward prism sheet does not exhibit the light condensing property of “emitting incident light in a wide angle range into a narrow angle range”. Patent Document 2 discloses a downward prism sheet in which a prism surface is curved in order to impart light collecting properties. In either case, the downward prism sheet does not have a polarization separation function, and the utilization efficiency of specific polarized light cannot be improved. In order to solve this, it may be used in combination with a polarized light separating film as described below.

  As the polarization separation film, a film in which a number of different resin films are laminated (Patent Document 3), a multilayer film having birefringence (Patent Document 4), a film using cholesteric liquid crystal (Patent Document 5), A laminate in which a phase difference plate and an optically active layer are laminated (Patent Document 6), and a diffraction grating having a period equal to or shorter than the wavelength of visible light (Patent Document 7) are known. All of these have a function of transmitting a specific polarization component with respect to light incident substantially perpendicular to the film.

Japanese Patent No. 2739730 JP 2003-187617 A Japanese Patent No. 3187821 Japanese Patent No. 3704364 JP-A-8-271837 JP 2006-106592 A JP 2007-178793 A "Applied Optics I" (Applied Physics Selection 1), Ikuo Tsuruta, Bafukan, 1990

The problem to be solved by the present invention is to provide a polarization separation type condensing film that condenses white light incident from an oblique direction by bending it in the vertical direction and preferentially emits linearly polarized light in a specific direction. And providing a simple surface light source device that uses the polarized light with high efficiency. Since the conventional prism sheet does not have a polarization separation function, it needs to be combined with a polarization separation film in order to increase the polarization utilization efficiency. On the other hand, the conventional polarization separation film cannot bend light incident obliquely. For this reason, the surface light source device with high polarization utilization efficiency must be used in combination, and there is a problem that the number of members, cost, and assembly man-hour increase.
It is an object of the present invention to provide a prism sheet, an optical member, and a planar light source device using the prism sheet that improve the luminance of specific polarized light in the direction perpendicular to the light exit surface.

  The present invention bends white light incident from an oblique direction in the vertical direction and preferentially emits linearly polarized light in a specific direction, thereby improving the brightness of the specific polarized light in the vertical direction of the light exit surface. And a planar light source device using the same.

In order to solve the above problems, an upward prism sheet according to the present invention has a substantially flat light incident surface, and a prism having a substantially triangular cross section is continuously formed on a surface facing the light incident surface. An upward prism sheet, the angle component projected in the direction perpendicular to the prism at the angle formed by the incident light and the normal of the incident surface is θi, the refractive index of the sheet is n, the incident light and the prism surface The angle between the prism surface with a larger normal line, that is, the angle between the prism front surface and the light incident surface is α, and the angle between the incident light and the prism surface normal line with a smaller angle, that is, the prism rear surface with the light incident surface is β. In this case, the prism shape satisfies all of the following expressions (1), (2), and (3).
tan (β) = sin (θi) / {− 1 + √ [n2−sin2 (θi)]} (1)
α> 90−sin−1 [(1 / n) sin (θi)] (2)
α <90−β + sin−1 {n * sin (sin−1 [(1 / n) sinθi] −β)} (3)

  The upward prism sheet according to the present invention preferably has a prism pitch of 4 μm or more and 30 μm or less.

  The planar light source device according to the present invention preferably uses the upward prism sheet.

In order to solve the above problems, an optical member according to the present invention has an approximately flat light incident surface, and a prism having a substantially triangular cross section formed continuously on a surface facing the light incident surface. An optical member in which a plurality of prism sheets are arranged so that the directions of the prisms are substantially parallel and the light incident surface of the adjacent upward prism sheet and the prism forming surface are in contact with each other. J0, and the j-th upward prism sheet counted from the upward prism sheet on which light is first incident, the direction perpendicular to the prism at the angle formed by the normal of the incident light and the incident surface of the sheet Θi (j) is the angle component projected onto the sheet, and θo (j) is the angle component projected in the direction perpendicular to the prism at the angle formed by the outgoing light and the normal of the incident surface of the sheet. Refractive index is n (j), incident light and prism Α (j) is the angle between the prism surface having a larger surface normal, that is, the prism front surface and the light incident surface, and the prism surface having the smaller angle between the incident light and the prism surface normal is the light incident surface. When the angle formed is β (j), the shape of the prism satisfies the following expressions (4), (5), (6), (7), and (8).
θo (j) = β (j) −sin−1 {√ [n (j) 2−sin2θi (j)] sinβ (j) −cosβ (j) sinθi (j)} (4)
θi (j) = θo (j−1) (5)
α (j)> 90−sin−1 [(1 / n) sinθi (j)] (6)
α (j) <90−β (j) + sin−1 {n * sin (sin−1 [(1 / n) sinθi (j)] − β (j))} (7)
θo (j0) = 0 (8)

  The optical member according to the present invention preferably has a prism pitch of 4 μm or more and 30 μm or less.

  The planar light source device according to the present invention preferably uses the optical member.

  According to the present invention, it is possible to provide a prism sheet, an optical member, and a planar light source device using the prism sheet that improve the luminance of specific polarized light in the direction perpendicular to the light exit surface.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. This embodiment is an upward prism sheet in which prisms having a substantially triangular cross section are continuously formed on a surface facing a light incident surface. In particular, the prism sheet of the embodiment uses a transparent optical film in which a prism having a substantially triangular cross section is formed on the exit surface of the film, and can improve the brightness of a specific deflection in the vertical direction of the light exit surface.

  The principle will be described in detail below. First, the light condensing property of the upward prism sheet will be described. FIG. 3 is a view showing a part of a cross section of the upward prism sheet. The upward prism sheet 1 has a substantially flat prism sheet bottom surface 10 as the inner side of the light incident surface. A prism having a substantially triangular cross section with the prism front surface 11 and the prism rear surface 12 as two sides is formed on the surface facing the prism sheet bottom surface 10.

  In the upward prism sheet 1 having the structure as shown in FIG. 3, consider a case where the incident light 20 is incident obliquely at an angle θi with respect to the normal line of the prism sheet bottom surface 10. Incident light 20 is refracted in the prism sheet 1 and emitted from the prism rear surface 12.

  The following parameters θi, θo, φ1, φ2, and φ3 are defined as shown in FIG. Similarly, the definitions of the parameters α and β follow the description of FIG. That is, the angle formed by the normal of the incident surface and the incident light 20 is θi. Further, an angle formed between the normal line of the incident surface to the output surface side and the output light 24 is defined as θo. In addition, the refraction angle at the bottom surface of the prism, which is the inside of the incident surface of the prism, is φ1. Further, the incident angle of the incident light 20 with respect to the prism rear surface 12 is φ2. The incident angle of the outgoing light 24 with respect to the prism rear surface 12 is φ3. Further, an angle between the prism front surface 11 and the light incident surface (prism sheet bottom surface) is α. In addition, an angle between the prism rear surface 12 and the light incident surface is β.

The refraction angle φ1 at the bottom of the prism is Snell's law (see Non-Patent Document 1), where n is the refractive index of the material constituting the prism sheet,
n * sin (φ1) = sin (θi) (9)
Satisfied.

Similarly, upon refraction at the prism rear surface 12, the incident angle φ2 and the output angle φ3 with respect to the prism rear surface 12 are used,
n * sin (φ2) = sin (φ3) (10)
Holds.

Since the inclination angle (rear surface bottom angle) of the prism rear surface 12 with respect to the prism bottom surface 10 is β as described above,
φ2 = β−φ1 (11)
φ3 = β−θo (12)
Therefore, n * sin (β−φ1) = sin (β−θo) (13) by substituting Equations (11) and (12) into Equation (10).
It becomes. Based on the above, for each arbitrary incident angle θi with respect to the incident surface (prism sheet bottom surface 10) of the incident light 20, each value forming the optimum shape of the upward prism made of a material having a refractive index n is calculated.

First, an optimum value of the rear base angle β, which is an angle of the prism rear surface 12 with respect to the prism sheet bottom surface 10, is obtained. When the outgoing light 24 of the upward prism sheet 1 is directed in the normal direction (front direction) of the sheet bottom 10, θo = 0. Substituting θo = 0 and modifying equation (13),
-N * [sin (φ1) cos (β) −cos (θo) sin (β)] = sin (β) (14)
It becomes.

From equation (9)
sin (φ1) = (1 / n) sin (θi) (15)
n * cos (φ1) = √ [n2−sin2 (θi)] (16)
Therefore, substituting these into equation (14) and organizing them,
tan (β) = sin (θi) / {− 1 + √ [n2−sin2 (θi)]} (17)
Thus, the optimum value of the rear base angle β is obtained. However, θi and n must satisfy the relationship of the following equation.
−1 + √ [n2−sin2 (θi)]> 0 (18)

  When Expression (18) is not satisfied, the outgoing light 24 cannot be directed in the front direction no matter how the shape of the upward prism 1 is set. Therefore, when the incident angle θi to the upward prism sheet 1 is large, it is necessary to use a material having a higher refractive index n.

Next, the range of a desirable value of the front base angle α which is an angle of the prism front surface with respect to the prism sheet bottom surface 10 is obtained. FIG. 4 is a diagram showing stray light due to incidence on the prism front surface 11 in the upward prism sheet 1. As shown in FIG. 4, when the front base angle α is small, the light refracted at the prism sheet bottom surface 10 enters the prism front surface 11 and is totally reflected or refracted to generate stray light 21. In order not to cause stray light 21 due to reflection on the front surface of the prism,
α> 90−φ1 = 90−sin−1 [(1 / n) sin (θi)] (19)
It is necessary to become.

Next, stray light due to re-incident on the front surface of the prism will be described. FIG. 5 is a diagram showing the cause of stray light generated by re-incident on the prism front surface in the upward prism sheet 1. As shown in FIG. 5, when the front base angle α is large, part of the light emitted from the prism rear surface 12 reenters the prism front surface 11 to generate stray light.
α <90−θo (20)
If so, part of the light emitted from the prism rear surface 12 does not re-enter the prism front surface 11. If θo is obtained from Equation (13) and substituted,
α <90−β + sin−1 (n * sin (φ1−β)) (21)
Is obtained.

  In the case of the upward prism sheet 1, a curved surface or a flat portion can be formed at the tip of the prism without impairing the light collecting performance. FIG. 6 is a diagram showing a blind region generated on the prism front surface 11 side of the upward prism sheet 1. As shown in FIG. 6, when α is larger than 90−φ1, the shaded portion at the tip of the prism is behind the prism valley, and no light is incident. Therefore, for example, as shown in FIG. 7, even if a curved portion that falls within the hatched area shown in FIG. 6 is provided, the optical characteristics of the upward prism sheet are not affected. When the prism sheet is used, the prism tip is often worn, deformed or missing, but the upward prism sheet 1 has the advantage of high tolerance to such damage. Further, by providing a curved portion at the prism tip in advance, it is possible to prevent the optical member adjacent to the prism tip from being damaged.

  It will be shown below that the upward prism sheet 1 designed in accordance with the above has a light collecting property. 8 and 9, the correlation between the incident angle θi and the outgoing angle θo obtained from the equations (9) and (13) is plotted. The slanted line in the figure has an inclination when the change amount of the incident angle is equal to the change amount of the exit angle. In the region where the incident angle is larger than the arrow in the figure, the change amount of the emission angle is smaller than the change amount of the incident angle. That is, the upward prism sheet 1 exhibits a light collecting property with respect to incident light having an incident angle in this range.

  FIG. 8 shows the incident angle-output angle correlation when the rear base angle β is 60 degrees and the refractive index of the constituent material of the upward prism sheet is changed from 1.45 to 1.65. As the refractive index is higher, the direction of the emitted light is closer to the front direction, but the lower limit of the incident angle range showing the light condensing property is increased. FIG. 9 shows an incident angle-output angle correlation when the refractive index is 1.5 and the rear base angle β is changed from 50 degrees to 75 degrees. As the rear base angle β is larger, the direction of the emitted light is closer to the front direction, but the lower limit of the angle range showing the light condensing property is increased. Therefore, in order to utilize the light condensing property of the upward prism sheet, it is preferable to combine with a light guide plate having a characteristic of emitting light at a high angle as shown in FIG.

Second, the polarization separation characteristics of the upward prism sheet 1 will be described. Consider a case where non-polarized light as shown in FIG. 10 is incident on the upward prism sheet 1 obliquely. When incident on the prism sheet bottom surface 10 and the prism rear surface 12, incident light is Fresnel-reflected at a constant rate determined by the incident angle and the refractive index of the prism material. According to Non-Patent Document 1, the transmittance T (S1) of s-polarized light at the prism bottom surface 10 is
T1 (s) = sin (2 * θi) sin (2 * φ1) / sin2 (θi + φ1) (22)
The transmittance T (S2) of s-polarized light at the rear surface of the prism is
T2 (s) = sin [2 * (β−φ1)] sin (2 * β) / sin2 (4 * β-2 * φ1) (23)
It is expressed. On the other hand, the transmittances T1 (p) and T2 (p) on each surface of p-polarized light are
T1 (p) = sin (2 * θi) sin (2 * φ1) / sin2 (θi + φ1) cos2 (θi−φ1) (24)
T2 (p) = sin [2 * (β-φ1)] sin (2 * φ1) / sin2 (4 * β-2 * φ1) sin2 (2 * φ1) (25)
It becomes. The s-polarized light transmittance of the entire upward prism sheet is represented as T2 (s) T1 (s), and the p-polarized light transmittance is represented as T2 (p) T1 (p).

  Table 1 shows the results of calculating the exit angle and the output light intensity using the above formulas for the upward prism sheet 1 having a refractive index (n =) of 1.73 and a rear base angle (β =) of 60 degrees. When the incident angle to the rear surface of the prism exceeds the critical angle and the light is totally reflected and becomes stray light, it is described as “total reflection”. In particular, when the incident angle is around 60 degrees, all incident light of p-polarized light is transmitted without causing any Fresnel reflection. The transmittance ratio of p-polarized light and s-polarized light is about 2 or more, and it can be seen that the prism sheet has a polarization separation function. In addition, the angle range through which incident light is transmitted is 35.0 degrees from an incident angle of 50 degrees to an incident angle of 85 degrees, whereas the amount of change in the exit angle is 17.2 degrees. It can be seen that the condensing characteristic of emitting incident light 20 having a certain angular spread to a narrower angular range is shown.

  High refractive materials having a refractive index n exceeding 1.7 as described above include optical glasses such as heavy flint glass, lanthanum flint glass, and lanthanum crown glass, resin materials containing heteroatoms such as sulfur and bromine, and fine particle oxidation. A composite material in which a metal oxide such as titanium is dispersed in a resin as fine particles having a particle diameter equal to or smaller than the wavelength of visible light is known. Optical glass is easily broken and difficult to handle because it requires high temperature for molding. In addition, many resin materials containing heteroatoms have low environmental resistance and are likely to be colored, and there is concern about the environmental impact during disposal. The composite material has a problem that the stability of the dispersed state, the transparency, and the mold followability at the time of molding are inferior, and the wear of the mold increases.

  In addition, when the rear base angle β of the prism is small, stray light is easily generated due to total reflection on the rear surface of the prism. In addition, in mass production, there is a problem that it is difficult to manufacture a mold and transfer from the mold.

  Therefore, it is preferable to use a general transparent resin material such as acrylic and to realize light condensing property and polarization separation property with the upward prism sheet 1 having a rear base angle β of 70 degrees or less. For this purpose, a method in which a plurality of upward prism sheets 1 are used in an overlapping manner is conceivable. In this case, since the light bending effect of each sheet is superimposed, the light bending angle of each upward prism sheet 1 may be small, and the desired effect can be obtained even with a small refractive index n and a rear base angle β. realizable.

When a plurality of upward prism sheets are used, the total number of prism sheets is j0, and the refractive index, incident angle, exit angle, front base angle, and rear base angle of the j-th prism sheet are n (j) and θi, respectively. Assuming (j), θo (j), α (j), and β (j), α (j) and β (j) must satisfy the following Expression 26-30. However, the lowermost prism sheet is the first and the uppermost prism sheet is the J0th. FIG. 11 illustrates a configuration in the case where four prism sheets are used.
θo (j) = β (j) −sin−1 {√ [n (j) 2−sin2θi (j)] sinβ (j) −cosβ (j) sinθi (j)} (26)
θi (j) = θo (j−1) (27)
α (j)> 90−sin−1 [(1 / n) sinθi (j)] (28)
α (j) <90−β (j) + sin−1 {n * sin (sin−1 [(1 / n) sinθi (j)] − β (j))} (29)
θo (j0) = 0 (30)

  As an example, Table 2 shows the calculated values of the incident angle, the outgoing angle, and the outgoing light intensity when two upward prism sheets are used. The lower upward prism sheet had a rear base angle β = 60 degrees, the upper prism sheet had a rear base angle β = 50 degrees, and the refractive index n was 1.50. The light condensing property of emitting light in the range of about −12 degrees to 2.5 degrees with respect to the light having an incident angle of 60 degrees to 85 degrees can be seen. Further, in the angle range where the light is not totally reflected, the p-polarized light and the s-polarized light are polarized and separated at an intensity ratio of 3: 2 to 2: 1. For example, when light having an angular distribution as shown in FIG. 2 is used as incident light, good polarization separation ability and light condensing performance can be realized.

  In FIG. 12, the lower upward prism sheet has a front base angle α = 60 °, a rear base angle β = 30 °, and a pitch d = 30 μm, and the upper upward prism sheet has a front base angle α = 75 °. This is an outgoing light distribution measured when light having an angular distribution as shown in FIG. 2 is incident when the rear base angle β is 55 ° and the pitch d is 30 μm. Separation of s-polarized light and p-polarized light components can be confirmed. Further, the peak of the incident light is 24 °, whereas the half width of the emitted light is 18 °, and it has been demonstrated that the above-mentioned light condensing property is obtained.

  Next, the problem of coloring the upward prism sheet will be described. When the light is bent by refraction, the angle at which the light is bent differs because the refractive index is different for each wavelength. For this reason, for example, in a lens optical system, chromatic aberration in which the focal length changes depending on the wavelength occurs (see Non-Patent Document 1). Similarly, since the upward prism sheet also bends light by refraction, coloring occurs.

  FIG. 13 is a CIE chromaticity coordinate distribution of light emitted from the same upward prism sheet as FIG. As the material of the prism, an acrylic photo-curing resin with nd = 1.50 is used. The chromaticity coordinates are distributed over a wide range of x from 0.29 to 0.40 and y from 0.31 to 0.42, and it can be seen that a remarkable spectral effect occurs.

  In the case of a lens system, chromatic aberration is eliminated by fabricating a plurality of lenses using a material having a refractive index different from the wavelength change amount of the refractive index and bonding them together. However, application to an optical film or a planar light source is not preferable because the film thickness increases and the structure becomes complicated.

In order to solve this, the chromatic aberration may be eliminated by using the diffraction effect. Since the transparent material used for optical applications has a higher refractive index as the wavelength is shorter, it bends more as the wavelength is shorter. On the other hand, when using a diffraction grating, m is the diffraction order, λ is the wavelength of the incident light,
θo = sin−1 [sin (θi) −mλ / d] (31)
It is expressed. That is, the smaller the λ, the smaller the change in angle due to diffraction and the opposite behavior to chromatic aberration due to refraction. Therefore, the chromatic aberration can be eliminated by adjusting the pitch d to an appropriate size.

  As the photocurable resin for forming the upward prism sheet 1, an acrylic resin-based ultraviolet curable resin, for example, urethane acrylate or epoxy acrylate is used.

  Next, the manufacturing apparatus and manufacturing method of the upward prism sheet 1 will be described. FIG. 14 is a view showing a specific example of an apparatus for manufacturing the upward prism sheet 1. As shown in FIG. 14, in the manufacturing apparatus 88 of the upward prism sheet 1, a supply head 68 for supplying the photocurable resin 70 is disposed opposite to the mold roll 82. A metering roll 78, a nip roll 80, an ultraviolet irradiation device 86, and a mold release roll 84 are provided in this order on the downstream side of the mold roll 82 in the rotational direction.

  A diffraction grating groove is formed on the peripheral surface of the mold roll 82, and the diffraction grating groove is transferred to the surface of the photocurable resin 70. In forming the diffraction grating grooves, a diamond cutting tool was manufactured, and the surface of the mold roll 82 was grooved with a diamond cutting tool and a precision processing machine. The die roll 82 was made of a brass material, and after grooving with a diamond tool, chrome electroless plating was performed promptly to protect the surface for oxidation, gloss, and mechanical strength.

  At the time of manufacture, the photocurable resin 70 is supplied from the resin tank 64 to the mold roll 82 via the pressure control device 66 and the supply head 68. At the time of supply, the pressure applied to the mold roll 82 is adjusted by controlling the supply pressure of the photocurable resin 70 with the pressure controller 66 while detecting the pressure with the pressure sensor. The photocurable resin 70 applied to the mold roll 82 is adjusted to have a constant film thickness by a metering roll 78. The metering roller 78 is provided with a doctor blade 72, which scrapes off the resin adhering to the metering roller 78 and determines the uniformity of the resin applied to the mold roller 82. Stabilized.

  A transparent base film (translucent film) 74 is supplied between the nip roll 80 and the mold roll 82 downstream of the metering roll 78. Is sandwiched between the nip roll 80 and the mold roll 82, and the transparent base film 74 is adhered to the photocurable resin 70. When reaching the ultraviolet irradiation device 86 with the transparent base film 74 in close contact with the photocurable resin 70, the photocurable resin 70 is cured by the ultraviolet rays emitted from the ultraviolet irradiation device 86 and the transparent base film 74. Then, the integrated film sheet 76 is peeled off from the mold roll 82 by the release roller 84. Thereby, the long film sheet 76 can be obtained continuously.

  The film sheet 76 thus manufactured is cut into a predetermined size to obtain an upward prism sheet 1. The upward prism sheet 1 can also be produced by injection molding or a hot press method. In that case, an acrylic thermoplastic resin such as polymethyl methacrylate, or a thermoplastic resin such as polycarbonate or polycycloolefin can be used.

  The transparent base film 74 used in this embodiment is polyethylene terephthalate (PET). However, the present invention is not limited thereto, and polycarbonate, acrylic resin, thermoplastic urethane, or the like may be used. it can. Also, as the photocurable resin 70, other materials such as acrylic-modified epoxy and acrylic-modified urethane can be selected. The light source of the ultraviolet irradiation device 86 was a metal halide lamp (maximum 8 Kw), and the film sheet 76 was manufactured at a feed rate of 3 m / min. The feed speed varies depending on the curing characteristics of the photocurable resin 70 and the light absorption characteristics of the transparent base film 74, but the feed speed can be increased by using a metal halide lamp having a higher W (wattage). It is.

  As one of the methods for producing an upward prism sheet, it contains at least one monomer such as pentaerythritol acrylate that can be polymerized as shown in Japanese Patent Application Laid-Open No. 2004-37518 or FIG. Irradiating the photosensitive negative resin composition layer with actinic rays and forming a latent image of four or more gradations of exposure amount of actinic rays on the photosensitive negative resin composition layer, without performing an etching operation There is a method using surface unevenness obtained by the heating step. In the figure, a prism shape approximating a step shape of N = 4 is obtained by exposing the photosensitive resin three times. In the figure, a base film 111, a photosensitive negative resin composition layer 112, a photomask 113, a light shielding portion 114, and an opening 115 are shown.

  As shown in FIG. 16, the upward prism sheet repeats the process of etching after irradiating the photosensitive negative resin composition layer with actinic rays and forming a latent image on the photosensitive negative resin composition layer. There is a method using surface irregularities obtained by In the figure, a prism shape approximating a stepped shape with N = 4 is obtained by exposing the photosensitive resin twice. In the figure, a base film 100, a photosensitive negative resin composition layer 101, a photomask 102, a light shielding portion 104, an opening portion 103, and a resin photosensitive portion 105 are shown.

  In order to efficiently mass-produce an upward prism sheet with a deep groove and a large area used here, it is suitable to transfer it from a mold. The transferred resin is cured by heat or UV light. As a method for producing a mold having a deep groove used in the present invention, an electron beam resist is applied on a substrate, and after drawing an electron beam, a method of digging by RIE, a method of exposing / developing with X-ray radiation, a gray scale, and the like. -A method of exposing and developing the pattern of the mask, and a method of producing by a machining method using a tool. The material to be transferred is preferably an acrylic photo-curing resin with good light transmission according to the use conditions.

  FIGS. 17, 18, and 19 are simulation results of the chromaticity coordinate distribution when the pitch d is 8, 6, and 4 μm, respectively. For the simulation, GSover version 4.20 (manufactured by Grafting Solver Development) was used. When d = 8 μm, the chromaticity coordinate distribution is smaller than when d = 30 μm, and when d = 6 μm, the distribution range of chromaticity coordinates is narrower. When d = 4 μm, the diffraction effect becomes dominant, and the chromaticity coordinate distribution is expanded again.

  20, FIG. 21, and FIG. 22 show the results of simulating the emission angle distribution of p-polarized light and s-polarized light in the same manner as described above when the pitch d is 8, 6, and 4 μm, respectively. When the pitch d of the diffraction grating approaches the wavelength of the incident light, it is expected that the light collection characteristic is deteriorated due to the spectral effect. However, when the pitch is 6 μm or more, the light collection characteristic is hardly deteriorated. When the pitch is 4 μm, the full width at half maximum of the peak is large, and the light condensing property is deteriorated.

  As described above, for example, an acrylic resin is used and the lower upward prism sheet has a front base angle α = 60 °, a rear base angle β = 30 °, and a pitch d = 6 μm, and the upper upward prism sheet is a front surface. When the base angle α = 75 °, the rear base angle β = 55 °, and the pitch d = 6 μm, good light collecting properties and polarization separation characteristics can be obtained.

It is a figure which shows the example of a liquid crystal display device. It is a figure which shows angle distribution of the light which injects into an upward prism sheet. It is a figure which shows the optical bending characteristic and shape parameter of an upward prism sheet. It is a figure which shows the generation | occurrence | production factor of the stray light by the incident on the prism front surface in an upward prism sheet. It is a figure which shows the generation | occurrence | production factor of the stray light by the re-incident on the prism front surface in an upward prism sheet. It is a figure which shows the blind region produced on the prism front side of an upward prism sheet. It is a figure which shows the example of the prism sheet which remove | excluded the sharp part, without affecting an optical characteristic. It is a figure which shows the refractive index dependence of the condensing characteristic of an upward prism sheet. It is a figure which shows the back surface bottom angle dependence of the condensing characteristic of an upward prism sheet. It is a figure which shows the relationship between an upward prism sheet and a polarization component. It is a figure which shows the example of the planar light source device using a plurality of upward prism sheet. It is a figure which shows the measurement result of the polarization separation characteristic of an upward prism sheet. It is a figure which shows the measurement result of chromaticity coordinate distribution of an upward prism sheet. It is a figure which shows the example of the continuous production apparatus of the upward prism sheet using a roll metal mold | die and photocuring resin. It is a figure which shows the example of a manufacturing method of the upward prism sheet by gradation exposure. It is a figure which shows the example of a manufacturing method of the upward prism sheet by gradation exposure and an etching. It is a figure which shows the simulation result of chromaticity coordinate distribution of the upward prism sheet | seat with a pitch of 8 micrometers. It is a figure which shows the simulation result of chromaticity coordinate distribution of the upward prism sheet | seat with a pitch of 6 micrometers. It is a figure which shows the simulation result of chromaticity coordinate distribution of the upward prism sheet | seat with a pitch of 4 micrometers. It is a figure which shows the simulation result of the polarization splitting characteristic of an upward prism sheet with a pitch of 8 μm. It is a figure which shows the simulation result of the polarization splitting characteristic of an upward prism sheet | seat with a pitch of 6 micrometers. It is a figure which shows the simulation result of the polarization separation characteristic of the upward prism sheet | seat with a pitch of 4 micrometers.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Upward prism sheet 10 Prism sheet bottom face 11 Prism front face 12 Prism rear face 20 Incident light 21 Stray light 22 by reflection on prism front face Stray light 23 generated by re-entering and refracting outgoing light on the prism front face Stray light 24 that is generated by re-incidence and reflection 25 outgoing light 25 Fresnel reflected light 26 on the bottom surface of the prism sheet 26 Fresnel reflected light 30 on the rear surface of the prism 30 electric field vector 31 of p-polarized component of incident light 31 s-polarized component of incident light Electric field vector 32 Electric field vector 33 of p-polarized component of outgoing light Electric field vector 64 of s-light component of outgoing light Resin tank 66 Pressure control device 68 Photo-curing resin supply head 70 Photo-curing resin 72 Doctor blade 74 Transparent base Film 76 Film sheet 78 Metering roll 80 Nip roll 82 Mold roll 84 Release roller 86 UV irradiation device 88 Upward prism sheet manufacturing device 90 Light source 91 Light guide plate 92 Reflector plate 93 Downward prism sheet (light collecting film)
94 Polarizing plate 95 Phase difference plate 96 Liquid crystal panel 97 Diffusion plate 100, 111 Base film 101, 112 Photosensitive resin 102, 113 Photomask 103, 115 Photomask opening 104, 114 Photomask shading part 105 Photosensitivity Exposed part of resin

Claims (8)

An upward prism sheet having a substantially flat light incident surface and continuously forming prisms having a substantially triangular cross section on a surface facing the light incident surface,
The angle component projected in the direction perpendicular to the prism at the angle formed by the incident light and the normal to the incident surface is θi, the refractive index of the sheet is n, and the angle between the incident light and the prism surface normal is larger. When the angle between the prism surface, that is, the prism front surface, and the light incident surface is α, and the angle between the incident light and the prism surface normal is smaller, that is, the angle between the prism rear surface and the light incident surface is β, An upward prism sheet whose shape satisfies all of the following expressions (1), (2), and (3).
tan (β) = sin (θi) / {− 1 + √ [n2−sin2 (θi)]} (1)
α> 90−sin−1 [(1 / n) sin (θi)] (2)
α <90−β + sin−1 {n * sin (sin−1 [(1 / n) sinθi] −β)} (3)   2. The upward prism sheet according to claim 1, wherein the pitch of the prism is 4 μm or more and 30 μm or less.   The upward prism sheet according to claim 1, wherein a curved surface is formed at a tip portion of the prism.   A planar light source device using the upward prism sheet according to any one of claims 1 to 3. An upward prism sheet in which prisms having a substantially flat light incident surface and having a substantially triangular cross-section are continuously formed on a surface opposite to the light incident surface, the directions of the prisms are substantially parallel and adjacent to each other. A plurality of optical members arranged so that the light incident surface of the upward prism sheet and the prism forming surface are in contact with each other,
The total number of the optical sheets is j0, and the angle formed between the incident light and the normal of the incident surface of the sheet for the j-th upward prism sheet, counting from the upward prism sheet on which the light first enters. The angle component projected in the direction perpendicular to the prism is θi (j), and the angle component projected in the direction perpendicular to the prism at the angle formed by the normal line of the incident light and the incident surface of the sheet is θo (j ), The refractive index of the sheet is n (j), the prism surface having a larger angle between the incident light and the prism surface normal, that is, the angle between the prism front surface and the light incident surface is α (j), and the incident light and the prism. When the prism surface having a smaller angle formed by the surface normal, that is, the angle formed by the rear surface of the prism and the light incident surface is β (j), the shape of the prism is expressed by the following equations (4), (5), and ( 6) An optical member that satisfies all of the expressions (7) and (8).
θo (j) = β (j) −sin−1 {√ [n (j) 2−sin2θi (j)] sinβ (j) −cosβ (j) sinθi (j)} (4)
θi (j) = θo (j−1) (5)
α (j)> 90−sin−1 [(1 / n) sinθi (j)] (6)
α (j) <90−β (j) + sin−1 {n * sin (sin−1 [(1 / n) sinθi (j)] − β (j))} (7)
θo (j0) = 0 (8)   The optical member according to claim 5, wherein the prism pitch is 4 μm or more and 30 μm or less.   The optical member according to claim 5, wherein a curved surface is formed at a tip portion of the prism.   A planar light source device using the optical member according to claim 5.

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