JP5942527B2 - Method for designing light diffusing film, method for producing light diffusing film, and method for evaluating diffusion characteristics of light diffusing film - Google Patents

Description

  The present invention relates to a method for designing a light diffusion film, a method for producing a light diffusion film, and a method for evaluating the diffusion characteristics of the light diffusion film.

  Light diffusion films for diffusing transmitted light are used in various fields. As an example, a light diffusion film may be laminated on the light output side (observer side) of a liquid crystal display panel (image forming apparatus) of a liquid crystal display device. In the liquid crystal display panel, an image is formed by controlling the light transmittance for each pixel. However, in a liquid crystal display panel, light traveling in an oblique direction cannot be accurately controlled because of its principle. For this reason, the light that is transmitted through the liquid crystal display panel and further the light from the backlight that illuminates the liquid crystal display panel from the back is designed so as to proceed mainly in the front direction, and is disposed on the light output side of the liquid crystal display panel. A method has been proposed in which light is diffused by a diffusion film to expand the viewing angle of an image displayed by a display device. Further, the present invention is not limited to application to an image forming apparatus comprising a liquid crystal display panel, and a light diffusing film is required to exhibit desired diffusion characteristics in various applications.

  Examples of the light diffusing film actually used include a light diffusing film in which a light diffusing agent is dispersed and a light diffusing film using a hologram (for example, Patent Document 1).

  With respect to the light diffusion film in which the light diffusing agent is dispersed, it is possible to adjust the intensity of the diffusivity to some extent, but adjustment such as imparting anisotropy to the diffusion characteristics is not easy. On the other hand, according to the light diffusion film using a hologram, by using the technique of a computer-generated hologram (for example, Patent Document 2), depending on the characteristics of incident light, the finally desired luminance distribution, etc., the diffusion characteristics Can be freely adjusted.

International Publication No. 2005-078483 JP 2001-356673 A

  Incidentally, it may be necessary to confirm and evaluate the diffusion characteristics of a computer-generated hologram once designed by simulation. When calculating the angular distribution of the light intensity for the emitted light beam that has passed through the light diffusion film using a computer-generated hologram, the hologram interference fringes are irregular and have no periodicity. The pattern of interference fringes is modeled by dividing into large areas. When the hologram is thin (three-dimensional structure can be ignored), consider the hologram as a light modulation surface with no thickness, and use Kirchhoff diffraction or Fresnel diffraction, or use a Fourier transform with a periodic structure of the hologram pattern Can do. If the hologram is thick (three-dimensional structure is not negligible), it is calculated by wave optics or electromagnetic field analysis optics in consideration of the three-dimensional structure of the hologram, and then calculated by Fuchrich Hoff diffraction, Fresnel diffraction, or Fourier transform. To do.

  As described above, the angular distribution relating to the intensity of the light beam emitted from the hologram can be obtained. However, compared to an element called a diffraction grating, when obtaining the angular distribution of the intensity of the light beam emitted from the hologram, the pattern of interference fringes with a very large area consisting of several to several hundreds of interference fringes Is also subject to calculation, and the amount of calculation becomes enormous. Moreover, the diffraction efficiency and the diffraction direction cannot be calculated separately, and the design / evaluation prospect is poor. Therefore, the calculation of the diffusion characteristics of the light diffusion film using the computer-generated hologram is extremely complicated and takes a long time.

  In addition, replacing the hologram interference fringe pattern with a model having a certain area results in a finite calculation of an infinitely widening interference fringe pattern. Therefore, the calculation result necessarily includes an error. Furthermore, when the interference fringe pattern is calculated with a finite number, it is necessary to appropriately treat the edges of the pattern, which causes further errors.

  Also, when designing a computer-generated hologram, an enormous calculation time is spent as in the case of evaluating a computer-generated hologram, and as a result, it is extremely difficult to reach a solution suitable for the design.

  On the other hand, the inventors of the present invention made extensive changes in their ideas to solve the conventional problems as described above, and conducted earnest research as follows. First, the present inventors have found that the evaluation of the diffusion characteristics of a light diffusion film using a diffraction grating element rather than an aperiodic and irregular hologram interference fringe can be greatly facilitated. Furthermore, the present inventors can easily design and manufacture a light diffusing film having desired light diffusing characteristics by utilizing a greatly facilitated evaluation method of diffusing characteristics. I found. The present invention is based on such knowledge of the inventors.

  That is, an object of the present invention is to easily design a light diffusing film having desired diffusion characteristics, a method for easily manufacturing a light diffusing film having desired diffusion characteristics, and the diffusion characteristics of the light diffusing film. It is to provide a method for easily evaluating the above.

The light diffusing film design method according to the present invention includes:
A method of designing a light diffusing film including a plurality of diffraction grating elements formed with different grating patterns,
For each of the plurality of diffraction grating elements included in the light diffusion film, a model setting step of selecting a diffraction grating element model given a specific configuration;
A first calculation step of calculating diffraction efficiency for each of the selected plurality of diffraction grating element models;
Considering the angular distribution of the intensity of incident light, the diffraction direction in each diffraction grating element model, the diffraction efficiency calculated for each diffraction grating element model, and the area ratio of each diffraction grating element model in the light diffusion film, A second calculation step of calculating the angular distribution of the intensity of the emitted light;
And a confirmation step for evaluating the calculated angular distribution of the intensity of the emitted light.

In the design method of the light diffusion film according to the present invention, based on the calculated angular distribution of the intensity of the emitted light, whether or not a preset condition is satisfied,
When it is confirmed that the preset conditions are not satisfied in the confirmation step, the process returns to the model setting step, and a specific configuration is provided for each of the plurality of diffraction grating elements included in the light diffusion film. Reselect the given diffraction grating element model, and perform the first calculation step, the second calculation step, and the confirmation step again,
When it is confirmed in the confirmation step that a preset condition is satisfied, the configuration of the diffraction grating element model that has been calculated is determined as the configuration of the corresponding diffraction grating element, and light diffusion is performed. The film design is complete.

  In the light diffusing film designing method according to the present invention, when it is confirmed that the preset condition is not satisfied in the confirmation step, the diffraction grating element model is selected when reselecting the plurality of diffraction grating element models. Only the area ratio may be changed.

In the method of designing a light diffusion film according to the present invention,
Each diffraction grating element model set in the model setting step is modeled as an uneven surface,
Among the plurality of selected diffraction grating element models, the pitch of the concavo-convex surface, the ratio of the width of the convex portion forming the concavo-convex surface to the pitch of the concavo-convex surface, the arrangement direction of the convex portions forming the concavo-convex surface, the concavo-convex One or more of the height of the convex portion forming the surface, the cross-sectional shape of the uneven surface, the area ratio with respect to another diffraction grating element model, and the refractive index difference on both sides of the uneven surface may be different.

In the method of designing a light diffusion film according to the present invention,
In the model setting step, a plurality of light diffusion film models having different configurations from each other, a plurality of light diffusion film models each including the plurality of diffraction grating element models are set,
The first calculation step, the second calculation step and the confirmation step are performed for each light diffusion film model,
In light of preset conditions, the most appropriate light diffusion film model is selected, and the configuration of the diffraction grating element model included in the selected light diffusion film model is determined as the configuration of the corresponding diffraction grating element. The design of the light diffusing film may be completed.

  In the first calculation step of the light diffusing film design method according to the present invention, each diffraction grating element model is calculated using Rigorous Coupled Wave Analysis or FDTD Finite Difference Time Domain method. The diffraction efficiency of each order may be calculated.

In the second calculation step of the light diffusing film design method according to the present invention, the angular distribution of the intensity of the emitted light may be calculated using the following equation.

  In the confirmation step of the light diffusion film design method according to the present invention, the half-value angle of the angular distribution of the intensity of the emitted light in a plane along a specific direction is evaluated as a preset condition. Also good.

  In the confirmation step of the light diffusing film designing method according to the present invention, the intensity of the emitted light traveling in the normal direction to the film surface of the light diffusing film may be evaluated as a preset condition.

  In the first calculation step and the second calculation step of the light diffusion film design method according to the present invention, calculation is performed for light of a plurality of wavelengths, and in the confirmation step, the emission light calculated for light of each wavelength is calculated. The angular distribution of intensity may be evaluated.

  In the confirmation step of the light diffusion film design method according to the present invention, the maximum value, the minimum value, and the average value regarding the intensity of the emitted light of each wavelength along the normal direction to the film surface of the light diffusion film are specified, and A value of a ratio of the difference between the maximum value and the minimum value to the average value may be evaluated as a preset condition.

The method for producing a light diffusion film according to the present invention comprises:
A method of manufacturing a light diffusion film including a plurality of diffraction grating elements formed with different grating patterns,
Designing the light diffusing film according to any of the light diffusing film design methods according to the invention described above;
Producing the designed light diffusion film.

The method for evaluating the diffusion characteristics of the light diffusion film according to the present invention is as follows.
A method for evaluating the diffusion characteristics of a light diffusing film including a plurality of diffraction grating elements formed with different grating patterns,
For each of the plurality of diffraction grating elements included in the light diffusion film, a model setting step for setting a diffraction grating element model having a corresponding configuration;
A first calculation step of calculating diffraction efficiency for each of the selected plurality of diffraction grating element models;
Considering the angular distribution of the intensity of incident light, the diffraction direction in each diffraction grating element model, the diffraction efficiency calculated for each diffraction grating element model, and the area ratio of each diffraction grating element model in the light diffusion film, A second calculation step of calculating an angular distribution of the intensity of the emitted light.

  In the first calculation step of the method for evaluating the diffusion characteristics of the light diffusing film according to the present invention, each diffractive grating is formed using Rigorous Coupled Wave Analysis or FDTD Finite Difference Time Domain method. For the element model, the diffraction efficiency of each order may be calculated.

In the second calculation step of the method for evaluating the diffusion characteristics of the light diffusion film according to the present invention, the angular distribution of the intensity of the emitted light may be calculated using the following equation.

  According to the present invention, a light diffusion film having desired diffusion characteristics can be easily designed and manufactured. Moreover, according to this invention, the diffusion characteristic of a light-diffusion film can be evaluated easily.

FIG. 1 is a perspective view illustrating a polarizing plate, an image forming apparatus, and a display device in which a light diffusion film is incorporated, for explaining an embodiment of the present invention. FIG. 2 is a perspective view corresponding to FIG. 1 and showing a modification of the display device. FIG. 3 is a diagram illustrating an example of the light diffusion film, and is a diagram illustrating a cross section along the normal direction to the film surface of the light diffusion film. FIG. 4 is a plan view showing another example of the light diffusing film, and is a diagram for explaining a grating pattern of a plurality of diffraction grating elements. FIG. 5 is a plan view showing still another example of the light diffusing film, and is a view for explaining a grating pattern of a plurality of diffraction grating elements. FIG. 6 is a plan view showing still another example of the light diffusing film, and is a diagram for explaining a grating pattern of a plurality of diffraction grating elements. FIG. 7 is a plan view showing still another example of the light diffusing film, and is a view for explaining a grating pattern of a plurality of diffraction grating elements. FIG. 8 is a plan view showing still another example of the light diffusing film, and is a diagram for explaining a grating pattern of a plurality of diffraction grating elements. FIG. 9 is a view showing still another example of the light diffusing film in the same cross section as that of FIG. 3, and is a view for explaining the cross-sectional shapes of a plurality of diffraction grating elements. FIG. 10 is a view showing still another example of the light diffusing film in the same cross section as that of FIG. 3, and is a view for explaining the cross-sectional shapes of a plurality of diffraction grating elements. FIG. 11 is a plan view showing still another example of the diffraction grating element included in the light diffusion film. FIG. 12 is a plan view showing still another example of the diffraction grating element included in the light diffusion film. FIG. 13 is a plan view showing still another example of the diffraction grating element included in the light diffusion film. FIG. 14 is a plan view showing still another example of the light diffusing film, for explaining the arrangement of the light diffusing elements. FIG. 15 is a flowchart for explaining a method for evaluating the diffusion characteristics of a light diffusion film. FIG. 16 is a plan view showing an example of a diffraction grating element model to be evaluated for diffusion characteristics. FIG. 17 is a graph showing an example of the angular distribution of the intensity of the incident light beam. FIG. 18 is a graph showing a calculation result of the angular distribution of the intensity of the emitted light beam when the incident light beam having the orientation shown in FIG. 17 is incident on the diffraction grating element model shown in FIG. FIG. 19 is a diagram showing the calculation result of the angular distribution of the emitted light intensity for Sample 1 corresponding to the light diffusion film of FIG. FIG. 20 is a diagram showing the calculation result of the angular distribution of the emitted light intensity for sample 2 corresponding to the light diffusion film of FIG. FIG. 21 is a diagram showing the calculation result of the angular distribution of the emitted light intensity for the sample 3 corresponding to the light diffusion film of FIG. FIG. 22 is a diagram illustrating the calculation result of the angular distribution of the emitted light intensity for the sample 4 corresponding to the light diffusion film of FIG. FIG. 23 is a graph showing the calculation result of the angular distribution of the emitted light intensity in the plane along both the front direction and the first direction for Sample 1 corresponding to the light diffusion film of FIG. FIG. 24 is a graph showing the calculation result of the angular distribution of the emitted light intensity in the plane along both the front direction and the first direction for Sample 2 corresponding to the light diffusion film of FIG. FIG. 25 is a graph showing the calculation result of the angular distribution of the emitted light intensity in the plane along both the front direction and the first direction for the sample 3 corresponding to the light diffusion film of FIG. FIG. 26 is a graph showing the calculation result of the angular distribution of the emitted light intensity in the plane along both the front direction and the first direction for the sample 4 corresponding to the light diffusion film of FIG. FIG. 27 is a flowchart showing a method for designing a light diffusion film. FIG. 28 is a diagram for explaining an example of a method for producing a light diffusion film.

  FIG. 1 to FIG. 28 are diagrams for explaining an embodiment and its modification according to the present invention. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings attached to the present specification, for the sake of illustration and ease of understanding, the scale, the vertical / horizontal dimension ratio, and the like are appropriately changed and exaggerated from those of the actual product.

  In the following, first, the light diffusing film to be evaluated, designed and manufactured will be described together with the application applied to the display device 10, and then the diffusion property evaluation method for the light diffusing film, A design method and a method for producing a light diffusion film will be described.

<< light diffusion film >>
Here, an example in which the light diffusing film 30 that diffuses transmitted light is applied to the image forming apparatus 15 configured as the liquid crystal display panel 16 and the display device 10 including the liquid crystal display device is configured will be described. However, the present invention is not limited to the following examples, and the light diffusing film 30 is applied to, for example, an image display device configured as a cathode ray tube (CRT, cathode ray tube) or a plasma display panel (PDP), or the like, The present invention can be widely applied to various uses other than application to a display device as a member for diffusing transmitted light. First, the overall configuration of the display device 10 to which the light diffusion film 30 can be applied will be described.

  First, the overall configuration of the display device 10 and the image display device 15 including the light diffusion film 30 will be described with reference mainly to FIGS. 1 and 2. The display device 10 shown in FIG. 1 includes a liquid crystal display panel 16 as an image forming device 15 and a backlight 20 that illuminates the liquid crystal display panel 16 from the back side.

  The liquid crystal display panel 15 includes a pair of polarizing plates 11 and 12 and a liquid crystal cell 13 disposed between the pair of polarizing plates 11 and 12. A surface functional sheet 14 is provided on the light output side of the polarizing plate 12 disposed on the light output side. The surface functional sheet 14 is a layer expected to exhibit a specific function, and forms the most light-emitting side of the image forming apparatus 15, that is, the display surface of the display device 10. For example, the surface functional sheet 14 includes an antireflection layer (AR layer) having an antireflection function, an antiglare layer (AG layer) having an antiglare function, and a hard coat layer (HC layer) having scratch resistance. Further, it may be configured to include one or more of an antistatic layer (AS layer) having an antistatic function.

  The polarizing plates 11 and 12 have a function of decomposing incident light into two orthogonal polarization components, transmitting the polarization component in one direction, and absorbing the polarization component in the other direction orthogonal to the one direction. It has a polarizer. In the illustrated example, the polarizing plate 12 disposed on the light output side includes a polarizer 18 and a light diffusion film 30 provided on the light output side of the polarizer 18. The light diffusion film 30 has a function of diffusing transmitted light. The light diffusion film 30 also functions as a protective sheet for protecting the polarizer 18 in this example in which the polarizer 18 is formed by being bonded to the polarizer 18. However, a separate protective sheet may be provided on the polarizer 18, and the light diffusion film 30 may no longer be provided as a separate member from the polarizing plate 12. The light diffusion film 30 will be described in detail later.

  In the following, in order to distinguish a pair of polarizing plates included in the liquid crystal display panel 16, the light incident side polarizing plate 11 is referred to as a lower polarizing plate regardless of the arrangement state of the display device 10, and the light emitting side polarized light. The plate 12 is called an upper polarizing plate.

  The liquid crystal cell 13 has a pair of support plates and a liquid crystal disposed between the pair of support plates. In the liquid crystal cell 13, an electric field can be applied to each region where one pixel is formed. Then, the orientation of the liquid crystal in the liquid crystal cell 13 to which an electric field is applied changes. As an example, the polarization component of a specific direction (direction parallel to the transmission axis) transmitted through the lower polarizing plate 11 disposed on the light incident side has a polarization direction of 90 when passing through the liquid crystal cell 13 to which an electric field is applied. Rotate and maintain the polarization direction when passing through the liquid crystal cell 13 to which no electric field is applied. For this reason, depending on whether or not an electric field is applied to the liquid crystal cell 13, the polarized light component in a specific direction transmitted through the lower polarizing plate 11 further passes through the upper polarizing plate 12 disposed on the light output side of the lower polarizing plate 11, or It is possible to control whether the light is absorbed and blocked by the upper polarizing plate 12.

  By the way, the liquid crystal cell 13 can accurately control transmission or blocking of incident light (light source light) traveling in the front direction fd. On the other hand, for light traveling in a direction greatly inclined from the front direction fd, a phase shift occurs, so that transmission or blocking cannot be accurately controlled. For this reason, a retardation film may be provided for the purpose of compensating for a phase shift with respect to light traveling in a direction greatly inclined from the front direction. However, in this case, the use efficiency of light from the backlight 20 is lowered by providing the retardation film.

  For this reason, the backlight 20 disposed on the back side of the image forming apparatus 15 causes the liquid crystal display panel 16 to be placed on the back side by light condensed in a traveling direction within a narrow angle range centered on the front direction. It is configured so that it can be illuminated from. Note that when the image forming apparatus 15 is illuminated by the light condensed in the front direction fd, the light that forms the image also travels only within a narrow angle range centered on the front direction fd. In the illustrated form, the light diffusing film 30 is arranged on the light output side with respect to the polarizer 18 of the upper polarizing plate 12, and diffuses the light that forms the image to increase the viewing angle of the image displayed on the display device 10. It has come to expand. The light diffusion film 30 will be described in detail later.

  The backlight 20 shown in FIG. 1 is configured as an edge light type (side light type) surface light source device, and illuminates the liquid crystal display panel 16 from the back side. The backlight 20 includes a light guide plate 21 and a light source 23 including a light emitting portion 23 a provided on the side of the light guide plate 21. A light collecting sheet 25 is provided on the light output side of the light guide plate 21 which is the liquid crystal display panel side. In addition, a reflection sheet 29 is provided on the light guide plate 21 on the side opposite to the light collecting sheet 25 side.

  The light emitter 23a of the light source 23 can be constituted by, for example, a fluorescent lamp such as a linear cold cathode tube, an incandescent lamp, or a point-like LED (light emitting diode) as in the illustrated example. The light emitter 23a is disposed to face the side surface forming the light incident surface of the light guide plate 21, and the light emitted from the light emitter 23a enters the light guide plate 21 through the side surface. The light guide plate 21 guides light from the light emitter 23a in a direction (light guide direction) orthogonal to the incident surface. However, the light guide plate 21 has a light extraction element made of a white diffusing portion or an internally added diffusing agent provided on the back surface thereof. For this reason, the light traveling in the light guide plate 21 is emitted from each position of the light guide plate 21 along the light guide direction so that the light amount distribution along the light guide direction becomes substantially uniform. The light emitted to the back side of the light guide plate 21 is reflected by the reflection sheet 29 and the optical path is converted to the light output side.

  In the illustrated example, a large number of first unit prisms 21 a extending linearly are provided on the light output side of the light guide plate 21. The first unit prisms 21a are arranged in the light guide direction and extend in a direction orthogonal to the arrangement direction. And the component orthogonal to the light guide direction of the light radiate | emitted from the light-guide plate 21 to the light emission side is condensed by this 1st unit prism 21a in the front direction fd.

  The light emitted from the light guide plate 21 enters the light collecting sheet 25b. The condensing sheet 25 has a large number of second unit prisms 25a protruding to the light incident side. The second unit prisms 25a are arranged in a direction orthogonal to the arrangement direction of the first unit prisms 21a (that is, the light guide direction of the light guide plate 21), and extend in the direction orthogonal to the arrangement direction. And the component along the light guide direction of the light which injects into the condensing sheet 25 will be condensed by this 2nd unit prism 25a in the front direction fd.

  The light transmitted through the light collecting sheet 25 illuminates the liquid crystal display panel 16 as illumination light from the backlight 20. The illumination light from the backlight 20 is condensed in two orthogonal directions by the first unit prism 21a of the light guide plate 21 and the second unit prism 25a of the light collecting sheet 25. Therefore, the liquid crystal display panel 16 illuminated by the backlight 20 can form an image using light traveling in a direction within a narrow angle range centered on the front direction fd with high utilization efficiency.

  In addition, since the light which forms an image is diffused by the light-diffusion film 30, the observer of the display apparatus 10 can observe an image from various directions. In particular, as will be described later, since the light diffusion film 30 described here can exhibit various diffusion characteristics, it is possible to impart a desired viewing angle characteristic to the display device 10.

  The horizontal viewing angle characteristics and the vertical viewing angle characteristics required for the display device 10 are usually different. For example, a display device as a home television receiver is required to have a wide horizontal viewing angle, but there is usually no need to widen the vertical viewing angle. Conversely, display devices incorporated in mobile devices are required to narrow the horizontal viewing angle (horizontal viewing angle) from the viewpoint of peeping prevention, while the vertical viewing angle (vertical viewing angle) is reduced. It is required to set wider than the horizontal viewing angle. Such a demand for the viewing angle characteristics of the display device can be realized by the light diffusion film 30 exhibiting anisotropic diffusion characteristics.

  In the display device 10 shown in FIG. 1, the illumination light from the backlight 20 tends to have anisotropy, specifically, the component along the light guide direction is more than the component orthogonal to the light guide direction. Although the light tends to be strongly condensed, the viewing angle characteristic of the display device 10 can be made isotropic by the light diffusion film 30 exhibiting anisotropic diffusion characteristics. As an example, such a display device 10 can be suitably used for a display device for a tablet terminal that is assumed to be observed by changing the gripping direction.

  The light diffusion film 30 described below is not limited to the display device 10, the image forming device 15, the liquid crystal display panel 16, and the backlight (surface light source device) 20 having the above-described configuration, and is a known device. Can be applied to. For example, for the backlight 20, a direct type surface light source device as shown in FIG. 2 can be used.

  The direct-type backlight 20 shown in FIG. 2 includes a light source 23 having a light emitter 23 a, a reflection sheet 29 disposed on the back side of the light source 23, and a diffusion plate disposed to face the light source 23. 22, and first and second light collecting sheets 26 and 27 arranged on the light output side of the diffusion plate 22. The first and second light collecting sheets 26 and 27 have first and second unit prisms 26a and 27a, respectively, projecting to the light output side. The first and second unit prisms 26a and 27a are arranged in a direction orthogonal to each other and extend in a direction orthogonal to each arrangement direction. Each unit prism 26a, 27a condenses the light component orthogonal to the arrangement direction, so that the light from the backlight 20 shown in FIG. 2 is directed in a direction within a narrow angle range centering on the front direction. Then, the liquid crystal display panel 16 is illuminated.

  In the example shown in FIG. 2, the same reference numerals are given to the parts that can be configured in the same manner as the form shown in FIG. 1.

  For details on other known display devices, image forming devices, liquid crystal display panels, and backlights, various known documents (for example, “Flat Panel Display Dictionary” (supervised by Tatsuo Uchida and Hiraki Uchiike), 2001 Industrial Survey The detailed description is omitted here.

  In the present specification, terms such as “film”, “sheet”, and “plate” are not distinguished from each other only based on the difference in names. Therefore, for example, the “light diffusion film” is a concept including a member that can also be called a light diffusion sheet or a light diffusion plate.

  Further, in this specification, the “film surface (sheet surface, plate surface)” corresponds to the plane direction of the target film-like member when the target film-like member is viewed as a whole and globally. Refers to the surface. And in this Embodiment, the film surface of the light-diffusion film 30, the plate surface of the upper polarizing plate 12, the panel surface of the liquid crystal display panel 16, and the display surface of the display apparatus 10 are mutually parallel. Further, in this specification, the “front direction” is a normal direction to the film surface of the light diffusion film 30, and in this embodiment, a normal direction to the plate surface of the upper polarizing plate 12, a liquid crystal display This also coincides with the normal direction to the panel surface of the panel 16, the normal direction to the display surface of the display device 10, and the like.

  Further, in this specification, the “light-emitting side” means the downstream side of the target member in the optical path planned for the observer (the upper side of the paper surface in FIGS. 1 and 2), that is, the observer side. The “light incident side” is the upstream side in the planned optical path. Further, the “back side” is the side opposite to the “light emission side” in the front direction fd.

  Furthermore, in this specification, the “unit prism” means an element (optical element) having a shape that can exert various optical actions (for example, reflection and refraction) on incident light. As optical elements, unit optical elements, unit shape elements, unit lenses and the like are not distinguished from each other only based on the difference in names.

  Furthermore, the terms used in this specification for specifying shapes and geometric conditions, for example, terms such as “parallel” and “orthogonal” are not limited to strict meaning, and expect similar optical functions. Interpretation will be made including possible errors.

  Next, the light diffusion film 30 will be described with reference mainly to FIGS.

  The light diffusing film 30 diffracts light having a specific wavelength traveling in at least the normal direction (that is, the front direction) fd to the film surface of the light diffusing film, thereby diffusing the light traveling in the front direction fd. 40 is included. The diffraction grating element 40 included in the light diffusion film 30 is an optical element including a grating pattern 41 having a periodic structure or a grating pattern 41 that changes continuously. The diffraction grating element 40 causes a diffraction phenomenon with respect to the transmitted light due to the grating pattern 41.

  The diffraction grating element 40 may be configured as an amplitude modulation type diffraction grating that generates amplitude modulation with respect to transmitted light in a pattern corresponding to the grating pattern 41, or is transmitted in a pattern corresponding to the grating pattern 41. You may comprise as a phase modulation type diffraction grating which produces phase modulation with respect to light. Furthermore, the diffraction grating element 40 may be configured as a complex amplitude type diffraction grating that generates both amplitude modulation and phase modulation.

  The diffraction grating element 40 that causes a diffraction phenomenon has at least a first modulation region 42a and a second modulation region 42b, and a grating pattern 41 is defined by the first modulation region 42a and the second modulation region 42b. In the amplitude modulation type diffraction grating, the transmittance of light to be diffused may be different between the first modulation region 42a and the second modulation region 42b. As a typical example, when visible light is used as light to be diffused, the first modulation region 42a may be configured to be transparent, and the second modulation region 42b may be configured as a black region using a pigment or the like.

  The phase modulation type diffraction grating element 40 may include a refractive index interface composed of the concave and convex surface 35 formed in a pattern corresponding to the grating pattern 41. The refractive index interface that defines the lattice pattern 41 may be an interface with the air layer, that is, a surface as an uneven surface. Alternatively, as shown in FIG. 3, the refractive index interface is composed of a concavo-convex surface 35 formed between two layers 31 and 32 having different refractive indexes, and the light diffusion film 30 has a pair of substantially parallel surfaces. It may be formed as a film material having a main surface, that is, having a constant thickness. According to such a light diffusing film 30, as shown in FIGS. 1 and 2, on both sides of the light diffusing film 30, for example, via an adhesive (a concept including an adhesive in this specification), Even if other sheet-like members are laminated, the uneven surface 35 is not filled by this adhesion, and the light diffusion film 30 can continue to exhibit the expected diffusion function.

  In addition, it is preferable that the refractive index difference between the two layers 31 and 32 is 0.1 or more from the viewpoint that the light diffusion film 30 can effectively exhibit the diffraction function. Further, the second layer 32 positioned on the light output side with respect to the uneven surface 35 forming the refractive index interface may include a diffusion component that diffuses light. When the second layer 32 has a light diffusion function, wavelength dispersion (color dispersion) that can be caused by the uneven surface 35 can be made inconspicuous.

  FIG. 3 shows an example of a cross section of the light diffusion film 30 along the front direction fd. In the example shown in FIG. 3, the light diffusion film 30 includes a first layer 31 having an uneven surface 35 and a second layer 32 laminated on the uneven surface 35 of the first layer 31 along the uneven surface 35. And have. The first layer 31 and the second layer 32 are made of materials having different refractive indexes. As a result, the first modulation region 42a corresponding to the convex portion (the convex portion of the concave and convex surface with reference to the first layer 31 and the concave portion of the concave and convex surface with reference to the second layer 32) forming the concave and convex surface 35. The phase modulation amount exerted from the light diffusing film 30 on the light passing through and the concave portion forming the concave-convex surface 35 (the concave portion of the concave-convex surface with respect to the first layer 31, with the second layer 32 as the reference) The amount of phase modulation exerted from the light diffusion film 30 on the light transmitted through the second modulation region 42b corresponding to the convex portion of the uneven surface becomes different, and as a result, the light transmitted through the light diffusion film 30 Will diffract.

  When the light diffusing film 30 in which the light diffusing function is expressed by the diffraction grating element 40 is applied to the display device 10, it has occurred in the conventional light diffusing film using a light diffusing agent that is widely used. Backscattering of outside light can be effectively prevented. As a result, it is possible to effectively prevent a decrease in contrast of the display image due to backscattering, and it is also possible to effectively avoid an image blur that reduces the sharpness of the image.

  In particular, the light diffusing film 30 described here includes a plurality of diffraction grating elements 40 formed of different grating patterns 41. A plurality of diffraction grating elements 40 formed with different grating patterns 41 are arranged while being shifted along the film surface of the light diffusion film 30. Therefore, by combining a plurality of diffraction grating elements 40 having different grating patterns 41, desired diffusion characteristics can be realized, and desired viewing angle characteristics can be imparted to the display device 10.

  4 to 10 show a plurality of diffraction grating elements 40, 40a, 40b, 40c, 40d, 40e, 40f, 40g, 40h, 40i, 40j that can be included in the light diffusion film 30. , 41c, 41d, 41e, 41f, 41g, 41h, 41i, and 41j. In the example shown in FIGS. 4 to 10, each diffraction grating element 40, 40 a to 40 j is composed of two types of modulation areas including a first modulation area 42 a and a second modulation area 42 b, and forms a refractive index interface. An example in which the lattice patterns 41 and 41a to 41j are defined by the uneven surface 35 is shown. As shown in FIGS. 4 to 10, the pitch p of the concavo-convex surface 35 and the pitch of the concavo-convex surface 35 between the two or more diffraction grating elements 40, 40 a to 40 j included in one light diffusion film 30. The ratio (w / p) of the width w of the convex portion 36 forming the concave / convex surface 35 to p, the arrangement direction of the convex portion 36 forming the concave / convex surface 35, the height h of the convex portion 36 forming the concave / convex surface 35, and the concave / convex surface One or more of the 35 cross-sectional shapes are different.

  First, the light diffusion film 30 shown in FIGS. 4 to 8 has two or more of the first to sixth diffraction grating elements 40a, 40b, 40c, 40d, 40e, and 40f. 4 to 8 show only the differences between the grating patterns 41a to 41f of the first to sixth diffraction grating elements 40a to 40f, and the areas of the diffraction grating elements 40a to 40f are shown to be the same. Yes. However, in the examples shown in FIGS. 4 to 8, the area ratio of the first to sixth diffraction grating elements 40 a to 40 f may be appropriately changed.

  In the example shown in FIG. 4, the light diffusion film 30 is arranged in the first direction (lateral direction in the drawing) d1 and extends in the direction intersecting the first direction d1 and the second modulation region 42a and the second modulation region. The first diffraction grating element 40a having the first grating pattern 41a defined by 42b is arranged in a second direction (vertical direction in the drawing) d2 intersecting the first direction d1 and intersects the second direction d2. And a second diffraction grating element 40b having a second grating pattern 41b defined by a first modulation area 42a and a second modulation area 42b extending in the direction.

  According to the light diffusion film 30 shown in FIG. 4, light can be effectively diffused in the first direction d1 by the first diffraction grating element 40a, and light can be diffused in the second direction d2 by the second diffraction grating element 40b. Can be effectively diffused. In the illustrated example, the first direction d1 and the second direction d2 are orthogonal to each other. The first modulation area 42a and the second modulation area 42b forming the first grating pattern 41a extend linearly in the second direction d2, and the first modulation area 42a and the second modulation area 42b forming the second grating pattern 41b. Extends linearly in the first direction d1.

  The light diffusing film 30 shown in FIG. 5 is arranged in the first direction (lateral direction in the drawing) d1 in addition to the first diffraction grating element 40a and the second diffraction grating element 40b described above and the first direction d1. A third diffraction grating element 40c having a third grating pattern 41c defined by the first modulation area 42a and the second modulation area 42b extending in the intersecting direction is further included. In the illustrated example, the first modulation region 42a and the second modulation region 42b forming the third grating pattern 41c of the third diffraction grating element 40c extend linearly in the second direction d2. The third grating pattern 41c of the third diffraction grating element 40c is equal to the pitch p of the first modulation area 42a and the second modulation area 42b along the first direction d1 with the first grating pattern 41a of the first diffraction grating element 40a. And the width w is different.

  According to the light diffusion film 30 shown in FIG. 5, light can be effectively diffused in the first direction d1 not only by the first diffraction grating element 40a but also by the third diffraction grating element 40c. However, the diffusion characteristics in the first direction d1 are different between the first diffraction grating element 40a and the third diffraction grating element 40c. Therefore, according to the light diffusion film 30 shown in FIG. 5, compared with the light diffusion film 30 shown in FIG. 4, light can be diffused more uniformly along the first direction d <b> 1. The angular distribution of the emitted light intensity in the plane along the one direction d1 can be changed more gently. Further, as described in the description of the light diffusion film 30 shown in FIG. 8, according to the first lattice pattern 41a and the third lattice pattern 41c arranged at different pitches p in the same direction d1, the first direction d1. The color dispersion can be made inconspicuous effectively.

  In addition to the first diffraction grating element 40a and the second diffraction grating element 40b described above, the light diffusion film 30 shown in FIG. 6 has a third direction (in the drawing, which intersects both the first direction d1 and the second direction d2). A fourth diffraction grating having a fourth grating pattern 41d defined by a first modulation area 42a and a second modulation area 42b arranged in a direction d3 and extending in a direction crossing the third direction d3. First modulation that is arranged in a fourth direction d4 (a direction extending obliquely downward to the right in the drawing) d4 intersecting the element 40d and any of the first direction d1 to the third direction d3 and extending in a direction intersecting the fourth direction d4 And a fifth diffraction grating element 40e having a fifth grating pattern 41e defined by the region 42a and the second modulation region 42b. In the illustrated example, the third direction d3 is inclined by 45 ° from both the first direction d1 and the second direction, and is orthogonal to the fourth direction d4. The first modulation area 42a and the second modulation area 42b that form the fourth grating pattern 41d extend linearly in the fourth direction d4, and the first modulation area 42a and the second modulation area 42b that form the fifth grating pattern 41e. Extends linearly in the third direction d3.

  According to the light diffusion film 30 shown in FIG. 6, the light can be effectively diffused in the third direction d3 by the fourth diffraction grating element 40d, and the light in the fourth direction d4 can be diffused by the fifth diffraction grating element 40e. Can be effectively diffused. Therefore, according to the light diffusion film 30 shown in FIG. 6, the angular distribution of the emitted light intensity in an arbitrary plane along the front direction fd can be adjusted.

  The light diffusion film 30 shown in FIG. 7 has the first to fifth diffraction grating elements 40a, 40b, 40c, 40d, and 40e described above. Therefore, according to the light diffusion film 30 shown in FIG. 7, the angular distribution of the emitted light intensity in an arbitrary plane along the front direction fd can be adjusted, and in particular, along the first direction d1. It becomes possible to change the angular distribution of the emitted light intensity in the plane more smoothly. Further, as described in the description of the light diffusing film 30 shown in FIG. 8, the first lattice pattern 41a and the third lattice pattern 41c arranged in the same direction d1 at different pitches p can be used in the first direction d1. Color dispersion can be effectively made inconspicuous.

  The light diffusion film 30 shown in FIG. 8 is arranged in the first direction (lateral direction in the drawing) d1 in addition to the first diffraction grating element 40a and the third diffraction grating element 40c described above, and the first direction d1. A sixth diffraction grating element 40f having a sixth grating pattern 41f defined by the first modulation area 42a and the second modulation area 42b extending in the intersecting direction is further included. In the illustrated example, the first modulation region 42a and the second modulation region 42b forming the sixth grating pattern 41f of the sixth diffraction grating element 40f extend linearly in the second direction d2. The pitch p and the width w in the first direction d1 of the first modulation region 42a and the second modulation region 42b that define the sixth grating pattern 41f of the sixth diffraction grating element 40f are the first and second pitches of the first diffraction grating element 40a. The first modulation area 42a and the second modulation area 42b that define the grating pattern 41a are larger than the pitch p and the width w in the first direction d1, and define the third grating pattern 41c of the third diffraction grating element 40c. The first modulation region 42a and the second modulation region 42b are smaller than the pitch p and the width w in the first direction d1. According to the light diffusion film 30 shown in FIG. 8, the angular distribution of the emitted light intensity in the plane along the first direction d1 can be changed very gently.

  Incidentally, the diffraction grating element 40 generally does not have wavelength selectivity. Therefore, when the incident light to the diffraction grating element 40 is white light, the diffracted light of the same order is color-dispersed in rainbow colors. On the other hand, when the light diffusing film 30 including the diffraction grating element 40 is applied to the display device 10, if the wavelength dispersion phenomenon occurs due to the diffraction grating element 40, the color of the displayed image changes, and the image quality is remarkably improved. It will deteriorate.

  On the other hand, the light diffusion film 30 shown in FIG. 8 includes three types of diffraction grating elements 40a, 40c, and 40f having different pitches p along the first direction d1 of the grating pattern 40. Therefore, the diffraction directions of the light in the respective wavelength ranges can be overlapped with each other, thereby making chromatic dispersion inconspicuous. In particular, the three types of diffraction grating elements 40a, 40c, and 40f can diffract light in the red wavelength region, light in the green wavelength region, and light in the blue wavelength region that are incident from the same direction, respectively, in the same direction. If so, chromatic dispersion can be made very inconspicuous.

  Note that the function of making the chromatic dispersion inconspicuous when observed from various directions in the plane along the first direction d1 is that the pitches p of the lattice patterns 41a and 41c along the first direction d1 are different from each other. The light diffusion film 30 shown in FIGS. 5 and 7 including the first diffraction grating element 40a and the third diffraction grating element 40c is also used. Further, in order to make the chromatic dispersion in a plane along a desired direction inconspicuous without being limited to the first direction d1, two or more diffraction grating elements having different pitches p of the grating pattern 41 along the direction. 40 may be incorporated into the light diffusion film 30.

  As described above, in the light diffusion film 30 shown in FIGS. 4 to 8, the pitch p of the uneven surface 35 and the uneven surface 35 are set between the plurality of diffraction grating elements 40 included in the light diffusion film 30. The arrangement direction of the convex portions 36 is changed. In addition to these examples, in adjusting the diffusion characteristics of the light diffusing film 30, the ratio (w / p) of the width w of the convex portion 36 forming the concave and convex surface 35 to the pitch p of the concave and convex surface 35, and the concave and convex surface 35 are formed. It is also effective to change the height h of the convex portion 36, the cross-sectional shape of the concave and convex surface 35, and the like.

  In the light diffusion film 30 shown in FIG. 9, an example is shown in which the ratio (w / p) of the width w of the convex portion 36 forming the concave-convex surface 35 to the pitch p of the concave-convex surface 35, that is, the duty ratio is changed. Yes. Specifically, the light diffusion film 30 shown in FIG. 9 includes a seventh diffraction grating element 40g and an eighth diffraction grating element 40h, and the duty ratio of the seventh grating pattern 41g of the seventh diffraction grating element 40g. Is larger than the duty ratio of the eighth grating pattern 41h of the eighth diffraction grating element 40h. As a result of extensive research conducted by the present inventors, it has been found that the diffraction efficiency can be improved by adjusting the duty ratio according to the pitch p, the height h, the width w, and the like. Therefore, according to the light diffusion film 30 shown in FIG. 9, it is also possible to adjust the diffusion characteristics by changing the diffraction efficiency of each diffraction grating element 40.

  FIG. 10 shows an example in which the cross-sectional shape is changed between the plurality of diffraction grating elements 40i and 40j. The light diffusion film 30 shown in FIG. 10 has a ninth diffraction grating element 40i and a tenth diffraction grating element 40j, and the ninth diffraction pattern element 41i and the tenth diffraction grating element 40j of the ninth diffraction grating element 40i. The shape of the convex portion 36 of the concave / convex surface 35 forming each diffraction grating element 40 is different from the tenth grating pattern 41j. More specifically, the shape of the convex portion 36 of the concavo-convex surface 35 forming each diffraction grating element 40 is complementary between the ninth grating pattern 41 i and the tenth grating pattern 41 j. That is, the contour of the cross-sectional shape of the convex portion 36 of the ninth lattice pattern 41i is the same as the contour of the cross-sectional shape of the concave portion formed between the convex portions 36 of the tenth lattice pattern 41j. The contour of the cross-sectional shape of the convex portion 36 of the lattice pattern 41j is the same as the contour of the cross-sectional shape of the concave portion formed between the convex portions 36 of the ninth lattice pattern 41i.

  As in the example described later, the diffraction grating element 40 can be manufactured by curing the resin using a mold. At this time, the diffraction grating element 40 can be produced by producing a second mold using the first mold produced first, and curing the resin using the second mold. Further, the diffraction grating element 40 can be manufactured by manufacturing a third mold using the second mold and curing the resin using the third mold. Furthermore, the diffraction grating element 40 can be manufactured by curing the resin using the n-th mold that is manufactured in the n-th (n: natural number) in this way.

  However, the pitch p, the height h, the width w, and the like are substantially the same among the finally obtained diffraction grating elements 40, but actually, the convex portions 36 forming the concave and convex surface 35 are different. It has a cross-sectional shape (different contour). Then, depending on the accuracy in manufacturing the first mold, the convex portion 36 of the concave-convex surface 35 that forms the grating pattern 41 of the diffraction grating element 40 manufactured with the second k-1 (k: natural number) mold, and The convex portion 36 of the concave-convex surface 35 forming the grating pattern 41 of the diffraction grating element 40 manufactured in the 2k (k: natural number) mold has a complementary shape. That is, the light diffusion film 30 shown in FIG. 10 was manufactured with the ninth diffraction grating element 40i manufactured with the 2k-1 (k: natural number) type and with the 2k (k: natural number) type. And a tenth diffraction grating element 40j. Further, when the diffraction grating element 40 is manufactured using the n-th (n: natural number) mold, when the number n increases, the convex portion 36 of the uneven surface 35 that forms the grating pattern 41 of the manufactured diffraction grating element 40. The degree of who is generated in the shape of the film becomes increasingly prominent.

  Then, as a result of extensive research conducted by the present inventors, even if the planned pitch p, height h, width w, and the like are the same, the uneven surface 35 that forms the lattice pattern 41 due to manufacturing conditions and the like. It has been found that the diffraction efficiency changes if the cross-sectional shapes of the films differ. Therefore, according to the light diffusing film 30 having a plurality of diffraction grating elements 40 having different cross-sectional shapes of the concavo-convex surface 35 forming the grating pattern 41 as in the light diffusing film 30 shown in FIG. It is possible to adjust the diffusion characteristics by changing the diffraction efficiency.

  Further, in the illustrated example, the plurality of diffraction grating elements 40 included in the light diffusion film 30 have the same area, but the area ratio of the plurality of diffraction grating elements 40 included in the light diffusion film 30 is changed. May be. Even if the combination of the plurality of diffraction grating elements 40 is the same, the diffusion characteristics of the light diffusion film 30 can be adjusted by changing the area ratio of the plurality of diffraction grating elements 40.

  In each of the examples of the diffraction grating element 40 described above, an example in which the first modulation region 42a and the second modulation region 42b forming the grating pattern 41 extend linearly in a direction orthogonal to the arrangement direction, in other words, a stripe shape. An example of arrangement is shown in However, the first modulation region 42a and the second modulation region 42b forming the grating pattern 41 of the diffraction grating element 40 included in the light diffusion film 30 may be configured in a curved shape as shown in FIGS. Good. In the diffraction grating element 40 shown in FIG. 11, the first modulation region 42a and the second modulation region 42b are formed in stripes extending in an arc shape. In the diffraction grating element 40 shown in FIG. 12, the first modulation region 42a and the second modulation region 42b are formed in stripes extending in an elliptical arc shape.

  Further, in each example of the diffraction grating element 40 described above, an example in which the grating pattern 41 is configured as a periodic pattern, for example, the first modulation region 42a and the second modulation region 42b forming the grating pattern 41 are constant. An example in which the width w and the constant pitch p are arranged is shown. However, as shown in FIG. 13, the lattice pattern 41 may be configured as a pattern that changes continuously. In the diffraction grating element 40 shown in FIG. 13, the width w and the pitch p of the first modulation region 42a and the second modulation region 42b gradually increase (or decrease) along the arrangement direction. It is changing continuously.

  For example, the minimum width and the minimum pitch of the first modulation region 42a and the second modulation region 42b of the diffraction grating element 40 shown in FIG. 13 are the same as those of the first diffraction grating element 40a of the light diffusion film 30 shown in FIG. The maximum width and the maximum pitch of the first modulation region 42a and the second modulation region 42b of the diffraction grating element 40 shown in FIG. 13 are the same as the width w and the pitch p of the first modulation region 42a and the second modulation region 42b. However, the width w and the pitch p of the first modulation region 42a and the second modulation region 42b of the third diffraction grating element 40c of the light diffusion film 30 shown in FIG. 8 may be the same. In this case, according to the diffraction grating element 40 shown in FIG. 13, the light diffusion film 30 including the first, third, and sixth diffraction grating elements 40a, 40c, and 40f shown in FIG. Instead, the angular distribution of the emitted light intensity in the plane along the arrangement direction of the lattice pattern 41 can be changed more gently.

  Further, in each of the examples of the diffraction grating element 40 described above, an example in which the grating pattern 41 of the diffraction grating element 40 is defined by only two modulation areas including the first modulation area 42a and the second modulation area 42b. Indicated. However, the present invention is not limited to this, and the grating pattern 41 of the diffraction grating element 40 may be defined by three or more modulation regions. For example, when the grating pattern 41 of the diffraction grating element 40 is constituted by the uneven surface 35 forming the refractive index interface as shown in FIG. 3, a plurality of types of convex portions having different heights are formed. It may be. That is, the concavo-convex surface 35 may be configured not as a two-step concavo-convex surface but as a three-step concavo-convex surface.

  Incidentally, as described above, the light diffusion film 30 includes a plurality of diffraction grating elements 40 having different grating patterns 41. And when it is better to change the diffusion characteristic of the light diffusion film 30 at each position along the film surface of the light diffusion film 30, the diffusion of each diffraction grating element 40 included in the light diffusion film 30 The arrangement and area ratio of each diffraction grating element 40 may be determined in consideration of the characteristics.

  On the other hand, in each position along the film surface of the light diffusing film 30, the lattice pattern 41 is different as shown in FIG. The plurality of diffraction grating elements 40 may constitute the unit diffusing element 45, and the light diffusing film 30 may have two or more unit diffusing elements 45 arranged along the film surface of the light diffusing film 30. For example, the unit diffusion element 45 can be formed by a combination of a plurality of diffraction grating elements 40 shown in FIGS.

  That is, the pitch p of the concavo-convex surface 35, the ratio of the width w of the concavo-convex surface 35 to the pitch p of the concavo-convex surface 35, and the concavo-convex between the plurality of diffraction grating elements 40 included in one unit diffusion element 45 One or more of the arrangement direction of the protrusions 36 forming the surface 35, the height of the protrusions 36 forming the uneven surface 35, and the cross-sectional shape of the uneven surface 35 may be different (for example, FIG. 4 to 10). Further, the pitch p of the grating pattern 41 may be different between two or more of the plurality of diffraction grating elements 40 included in one unit diffusion element 45 (see, for example, FIG. 8). ). Furthermore, the area may be different between two or more diffraction grating elements 40 among the plurality of diffraction grating elements 40 included in one unit diffusion element 45, or included in one unit diffusion element 45. A plurality of diffraction grating elements 40 may have the same area. Further, at least one diffraction grating element 40 among the plurality of diffraction grating elements 40 included in one unit diffusion element 45 changes the pitch p (the pitch p is not constant), and the pitch p is continuously increased. You may have the lattice pattern 41 which changes (for example, refer FIG. 13).

  Assuming that two or more unit diffusing elements 45 include a plurality of diffraction grating elements 40 in the same combination, when light of the same orientation is incident on each unit diffusing element 45, the output from each unit diffusing element 45 is The angular distribution of the intensity of incident light is the same. Thereby, the diffusion characteristic in each position along the film surface of the light-diffusion film 30 containing the multiple types of diffraction grating elements 40 can be equalized. In particular, each unit diffusing element 45 includes a plurality of diffraction grating elements 40 having different grating patterns 41. Therefore, by adjusting the diffraction characteristics of each diffraction grating element 40, while ensuring a high degree of freedom in design. Desired diffusion characteristics can be imparted to the unit diffusion element 45.

  Further, by evaluating the diffusion characteristics of the small-area unit diffusion element 45, the diffusion characteristics of the large-area light diffusion film 30 can be evaluated. Therefore, as will be described later, when evaluating the diffusion characteristics of the light diffusion film 30 by simulation or the like, compared with a light diffusion film composed of a hologram optical element including irregular interference fringes, the calculation time in the computer is reduced. It is possible to greatly shorten the time and greatly improve the accuracy of the simulation.

  In the light diffusing film 30 shown in FIG. 14, the unit diffusing elements 45 are arranged side by side with no gap along each of two orthogonal directions extending on the film surface of the light diffusing film 30. However, the unit diffusion elements 45 may be arranged with a gap. Further, unlike the square arrangement shown in FIG. 14, the unit diffusion elements 45 may be arranged in a staggered arrangement in which the unit diffusion elements 45 in adjacent rows are arranged with a half-pitch or one-pitch shift. Further, unlike the example shown in FIG. 14, the planar shape of the unit diffusing element 45 may be a quadrangular shape other than a square, a polygonal shape other than a square shape, or a polygonal shape. Other than the shape, it may be a circle or an ellipse.

<< Diffusion characteristics evaluation method >>
Next, a method for evaluating the diffusion characteristics of the light diffusion film 30 including a plurality of diffraction grating elements 40 formed with different grating patterns 41 will be described.

  When the light diffusing film 30 is designed and manufactured, the diffusion characteristics of the obtained light diffusing film 30 are usually evaluated before actually applying to various devices and the like. In particular, conventional light diffusing films containing a light diffusing agent are easy to manufacture, so if the actual product actually produced is incorporated into the object to be applied, the diffusion characteristics can be evaluated. Good. On the other hand, a conventional light diffusing film 30 including a plurality of diffraction grating elements 40 described above, or a conventional computer-generated hologram as disclosed in Patent Document 1 (WO2005-0708383) and Patent Document 2 (JP2001-356673A). In order to manufacture a light diffusion film, it is generally necessary to manufacture a mold having an ultra-precision structure. For this reason, in a conventional light diffusion film using a computer-generated hologram, the diffusion characteristics are often evaluated by simulation before preparing an expensive mold.

  However, when calculating the angular distribution of the light intensity for the outgoing light flux that has passed through the conventional light diffusion film using a computer-generated hologram, the light interference film has irregularities and no periodicity, so the light diffusion film The interference fringe pattern is modeled by dividing the pattern into a relatively large area. When the hologram is thin (three-dimensional structure can be ignored), consider the hologram as a light modulation surface with no thickness, and use Kirchhoff diffraction or Fresnel diffraction, or use a Fourier transform with a periodic structure of the hologram pattern Can do. However, when the hologram is thick (three-dimensional structure cannot be ignored), the calculation is performed by wave optics or electromagnetic field analysis optics in consideration of the three-dimensional structure of the hologram, and then by Kirchhoff diffraction, Fresnel diffraction, or Fourier transform. Will be calculated.

  In this way, the angular distribution related to the intensity of the emitted light beam from the computer-generated hologram can be obtained, but an interference fringe pattern having a very large area consisting of several to several hundred interference fringes is also subject to calculation. As a result, the calculation amount becomes enormous. Moreover, the diffraction efficiency and the diffraction direction cannot be calculated separately, and the design / evaluation prospect is poor. Therefore, the calculation of the diffusion characteristics of the light diffusion film using the computer-generated hologram is extremely complicated and takes a long time.

  In addition, replacing the hologram interference fringe pattern with a model having a certain area results in a finite calculation of an infinitely widening interference fringe pattern. Therefore, the calculation result necessarily includes an error. Furthermore, when the interference fringe pattern is calculated with a finite number, it is necessary to appropriately treat the edges of the pattern, which causes further errors.

  On the other hand, unlike the computer-generated hologram having irregular interference fringes, the light diffusion film 30 described above exhibits a light diffusion function using the diffraction grating element 40 that forms the grating pattern 41. ing. For this reason, the diffusion characteristic of each diffraction grating element 40 can be calculated with high accuracy in a short time as compared with the diffusion characteristic of the computer-generated hologram. In addition, in the evaluation method described below, by using the area ratio of the plurality of diffraction grating elements 40, the diffusion characteristics of the light diffusion film 30 including the plurality of diffraction grating elements 40 having different grating patterns 41 are reduced for a short time. Can be calculated with high accuracy. Hereinafter, a method for evaluating the diffusion characteristics of the light diffusion film 30 will be described with reference to FIGS. 15 to 26.

As shown in FIG. 15, the evaluation method of the diffusion characteristics of the light diffusion film 30 described here is:
A model setting step of setting a diffraction grating element model having a corresponding configuration for each of the diffraction grating elements 40 included in the light diffusion film 30;
A first calculation step of calculating diffraction efficiency for each of a plurality of selected diffraction grating element models;
Considering the angular distribution of incident light intensity, the diffraction direction in each diffraction grating element model, the diffraction efficiency calculated for each diffraction grating element model, and the area ratio of each diffraction grating element model in the light diffusion film 30 Calculating the angular distribution of the intensity of the emitted light,
Is included.

  In the model setting step, a plurality of diffraction grating elements 40 included in the light diffusion film 30 to be evaluated are specified as a diffraction grating element model. As in the example shown in FIG. 3, when the grating pattern 41 of the diffraction grating element 40 of the target light diffusion film 30 is defined by the concavo-convex surface 35 forming the refractive index interface, as described above. Among the plurality of selected diffraction grating element models, the pitch p of the concavo-convex surface 35, the ratio (w / p) of the width w of the concavo-convex surface 35 to the pitch p of the concavo-convex surface 35, and the concavo-convex surface 35 Of the convex portions 36 forming the concave and convex surfaces 35, the height h of the convex portions 36 forming the concave and convex surfaces 35, the cross-sectional shape of the concave and convex surfaces 35, the area ratio with respect to other diffraction grating element models, and the refractive index difference on both sides of the concave and convex surfaces 36. , So that one or more of them are different.

  When the light diffusing film 30 is composed of a large number of unit diffusing elements 45 configured in the same manner, attention should be paid only to the plurality of diffraction grating elements 40 included in one unit diffusing element 45. At this time, by evaluating the diffusion characteristics of the small-area unit diffusion element 45, the diffusion characteristics of the large-area light diffusion film 30 can be evaluated. Therefore, as compared with a light diffusion film made of a hologram optical element including irregular interference fringes, it is possible to greatly reduce the calculation time in the computer and greatly improve the accuracy of evaluation.

  As a specific example, the first diffraction grating element 40a and the second diffraction grating element 40b included in the light diffusion film 30 shown in FIG. 4 are replaced with the first diffraction grating element model 55a and the second diffraction grating element 55a shown in FIG. Evaluation was made as a lattice element model 55b. In this evaluation, for the convenience of understanding, the first diffraction grating element model 55a and the second diffraction grating element model 55b were set as follows. The first diffraction grating element model 55a and the second diffraction grating element model 55b are composed of a first layer 31 on the light incident side and a second layer 32 on the light emission side as in the light diffusion film 30 shown in FIG. The uneven surface 35 forming the refractive index interface is formed between the first layer 31 and the second layer 32. The refractive index of the material forming the first layer 31 was 1.588, and the refractive index forming the second layer 32 was 1.410. The first diffraction grating element model 55a and the second diffraction grating element model 55b are different in that the arrangement directions of the grating patterns are different, and the configuration of the other uneven surface 35 is the same. In other words, the first diffraction grating element model 55a is specified to be the same as the second diffraction grating element model 55b when turned 90 °. The area ratio of the first diffraction grating element model 55a and the second diffraction grating element model 55b was set to 1: 1.

  Next, in the first calculation step, the diffraction efficiency is calculated for each of the plurality of selected diffraction grating element models. For each diffraction grating element model, calculation is performed for zero-order diffraction efficiency, first-order diffraction efficiency, and, if necessary, second-order or higher diffraction efficiency. For example, the diffraction efficiency of each order can be calculated for each diffraction grating element model using Rigorous Coupled Wave Analysis or FDTD Finite Difference Time Domain method. When using the strict coupled wave theory or the time domain difference method, specify the incident angle of incident light, the wavelength of incident light, the configuration of the diffraction grating element model (cross-sectional shape and refractive index difference on the uneven surface 35), The diffraction efficiency of each order can be calculated. Therefore, when it is assumed that light in a plurality of wavelength regions is incident on the light diffusion film 30 to be evaluated, each of the light in the plurality of wavelength regions in the first calculation step and the second calculation step described below. What is necessary is just to calculate about. In addition, when it is assumed that light enters the light diffusion film 30 to be evaluated with an angular width, diffraction efficiency is calculated for a plurality of incident angles.

Here, regarding the first diffraction grating element model 55a and the second diffraction grating element model 55b shown in FIG. 16, the pitch of the uneven surface 35 is 0.9 μm, and the height h of the convex portion 36 forming the uneven surface 35 is 1. Table 1 shows the result of calculating the diffraction efficiency of each order with setting to 3 μm. In addition, the diffraction efficiency of Table 1 is a calculation result when incident light is incident on the first diffraction grating element model 55a and the second diffraction grating element model 55b from the front direction fd.

となっている。ｍ番目の回折格子のｎ次の回折光分布を示すD_m,n(X, Y, x, y, λ)の式では、デルタ関数δを用いており、デルタ関数中の(d_x, d_y)は格子ベクトルである。したがって、D_m,n(X, Y, x, y, λ)の式は、入射光が回折格子素子モデルにより回折されて伝播方向が変わることを表している。また、O(X, Y, λ)は、基本的に光線追跡法で求められる。すなわち、まず、入射光束を多数の光線で表し、一本ごとの光線の回折格子素子モデルでの回折現象を計算する。その後、回折された光を集め、出射光束の強度の角度分布を得ている。計算機合成ホログラムを用いた従来の光拡散フィルムでは、このような方法により、O(X, Y, λ)を求めることは不可能である。 Finally, in the second calculation step, the angle distribution of the intensity of incident light, the diffraction direction in each diffraction grating element model, the diffraction efficiency calculated for each diffraction grating element model, and each diffraction grating in the light diffusion film 30 The angle distribution of the intensity of the emitted light is calculated in consideration of the area ratio of the element model. The angular distribution of the intensity of the emitted light can be calculated using the following formula.

It has become. In the expression of D _{m, n} (X, Y, x, y, λ) indicating the nth-order diffracted light distribution of the mth diffraction grating, the delta function δ is used, and (d _x , d _y ) is a lattice vector. Therefore, the expression D _{m, n} (X, Y, x, y, λ) represents that the incident light is diffracted by the diffraction grating element model to change the propagation direction. O (X, Y, λ) is basically obtained by the ray tracing method. That is, first, the incident light beam is represented by a number of light beams, and the diffraction phenomenon of each light beam in the diffraction grating element model is calculated. Thereafter, the diffracted light is collected to obtain an angular distribution of the intensity of the emitted light beam. In a conventional light diffusion film using a computer-generated hologram, it is impossible to obtain O (X, Y, λ) by such a method.

  FIG. 17 shows a graph showing an example of the angular distribution of the intensity of the incident light beam. In the graph of FIG. 17, the solid line indicates the angular distribution of the intensity of the incident light beam in the plane along both the front direction fd and the first direction d1, and the broken line indicates the front direction fd and the second direction d2. The angular distribution of the intensity of the incident light beam in the plane along both is shown. When the incident light beam having the orientation shown in FIG. 17 is incident on the first diffraction grating element model 55a and the second diffraction grating element model 55b shown in FIG. 16, the first diffraction grating element model 55a and the second diffraction grating element model 55a. The angular distribution of the intensity of the emitted light beam that has passed through the diffraction grating element model 55b is shown as a graph in FIG. Note that the incident light beam shown in FIG. 17 is assumed to be light from the edge light type backlight 20 shown in FIG. 1, and the light guide direction at the light guide plate 21 is parallel to the first direction d1. Assuming that

  In the graph of FIG. 18, the angular distribution of the intensity of the emitted light beam in the plane along both the front direction fd and the first direction d1 is shown. In this evaluation of the angular distribution of the intensity, that is, in the evaluation in which the result of FIG. 18 is obtained, 400 nm light, 500 nm light, 600 nm light, and 700 nm light are included in the incident light flux with the same light amount. The conditions were adopted. Further, in the evaluation in which the result of FIG. 18 was obtained, the pitch of the uneven surface 35 of the first diffraction grating element model 55a and the second diffraction grating element model 55b shown in FIG. The height h of the convex portion 36 was set to 1.3 μm, and the width w of the convex portion 36 forming the uneven surface 35 was set to 0.45 μm. Further, the incident light beam is linearly polarized light that vibrates along the first direction d1.

  Further, the pitch p of the uneven surface 35 of the first diffraction grating element model 55a and the second diffraction grating element model 55b, and the convex portion 36 forming the uneven surface 35 of the first diffraction grating element model 55a and the second diffraction grating element model 55b. The height h was set to various values, and the diffusion characteristics of the first diffraction grating element model 55a and the second diffraction grating element model 55b were evaluated and calculated. The pitch p of the uneven surface 35 was changed by 0.2 μm from 0.9 μm to 2.1 μm. About the height h of the convex part 36 which makes the uneven | corrugated surface 35, it set to 1.3 micrometers, 1.5 micrometers, and 1.7 micrometers.

Table 2 shows the ratio of the luminance in the front direction, the half-value angle in the angular distribution of the emitted light intensity in the plane along both the front direction fd and the first direction d1, and the chromatic dispersion coefficient obtained for each condition, respectively. It shows in Table 3 and Table 4. The chromatic dispersion coefficient is a maximum value, a minimum value, and an average value related to the intensity of the emitted light of each wavelength along the normal direction fd to the film surface of the light diffusion film 30. Is the value (x / y) of the ratio x (see FIG. 18) to the average value y. The greater the value of the chromatic dispersion coefficient, the more dispersed the color. As shown in Tables 2 to 4, it was confirmed that the diffusion characteristics of the light diffusion film 30 can be greatly changed by changing the pitch p of the uneven surface 35 and the height h of the convex portion 36 forming the uneven surface 35. It was.

In addition, the inventors of the present invention evaluated the diffusion characteristics of the light diffusion films 30 shown in FIGS. 4 to 7 as samples 1 to 4, respectively. The conditions for the incident light were the same as those used in the evaluation whose results are shown in FIG. As described above, the light diffusion film 30 shown in FIGS. 4 to 7 includes two or more of the first diffraction grating element 40a to the fifth diffraction grating element 40e. The area ratio of the first diffraction grating element 40a to the fifth diffraction grating element 40e included in each light diffusion film 30 was as shown in Table 5. It was assumed that the grating pattern 41 forming each of the first diffraction grating element 40a to the fifth diffraction grating element 40e was defined by an uneven surface 35 forming a refractive index interface as in the example shown in FIG. In each of the first diffraction grating element 40a to the fifth diffraction grating element 40e, the pitch p of the uneven surface 35 was set as shown in Table 5. In each of the first diffraction grating element 40a to the fifth diffraction grating element 40e, the height h of the convex portion 36 forming the concave and convex surface 35 was 1.5 μm.

  19 to 22 show the angular distribution of the intensity of the emitted light beam. In FIG. 19 to FIG. 22, an angle region in which an intensity of 80% or more with respect to the reference intensity is secured is represented as a first angle area Za, and an intensity of less than 80% and 60% or more with respect to the reference intensity. Is represented as the second angle region Zb, and the angle region in which the strength of less than 60% and 40% or more is secured with respect to the reference strength is represented as the third angle region Zc. On the other hand, an angle region in which an intensity of less than 40% and 20% or more is ensured is expressed as a fourth angle region Zd, and an angle region in which an intensity of less than 20% is secured with respect to a reference strength is defined as a fifth angle region Zd. Represents. In addition, the intensity | strength used as a reference is common in FIGS. In addition, the graphs of FIGS. 23 to 26 show the angular distribution of the intensity of the emitted light beam in the plane along both the front direction fd and the first direction d1 for the samples 1 to 4, respectively. The vertical axis | shaft of the graph of FIGS. 23-26 is shown as an intensity | strength ratio with respect to the reference | standard common among samples 1-4.

  In sample 2 including two types of diffraction grating elements 40 having different pitches p in the first direction, the chromatic dispersion coefficient could be significantly reduced as compared with sample 1. In the samples 3 and 4 including not only the diffraction grating elements 40 arranged in the first direction d1 and the second direction d2, but also the diffraction grating elements 40 arranged in an oblique direction (the third direction d3 and the fourth direction d4). The viewing angle characteristics were corrected isotropically.

  According to the method for evaluating the diffusion characteristics of the light diffusion film 30 as described above, the diffraction grating element 40 included in the light diffusion film 30 has the periodic grating pattern 41 and two or more having different grating patterns 41. Since the area ratio of the diffraction grating element 40 is used, it is not necessary to consider the shape of the end of the pattern as in the conventional light diffusion film using a computer-generated hologram, and the calculation area of the pattern is considered. There is no need to do. Thereby, there are few errors, the accuracy of the evaluation result is greatly improved, and the calculation time is shortened. In particular, in the light diffusing film 30 composed of a large number of unit diffusing elements 45 having the same configuration, only a small portion of the light diffusing film 30 needs to be calculated, and a conventional computer-synthesized hologram that needs to calculate a large area is used. Compared with the light diffusion film, the calculation time can be greatly shortened.

  In the above description, an example in which the incident light is a specific polarization component has been shown. However, the evaluation method described above can also be used when the incident light includes two types of polarization components. In this example, first, in the first calculation step, diffraction efficiency is calculated for two types of polarization components TM (for example, a polarization component oscillating in the first direction d1) and TE (for example, a polarization component oscillating in the second direction d2). Calculate each. Next, in the second calculation step, the angle distribution of the emitted light intensity is calculated for each polarization component in consideration of the diffraction efficiency calculated in the first calculation step for the polarization component. .

<< Design method >>
Next, a method for designing the light diffusion film 30 will be described.

  As described above, the diffusion characteristics of the light diffusion film 30 including a plurality of diffraction grating elements 40 formed with different grating patterns 41 are compared with those of a conventional light diffusion film using a computer-generated hologram. Thus, it can be evaluated with high accuracy in a short time. Then, the present inventors have found that by utilizing this point, the light diffusion film 30 capable of exhibiting a desired diffusion function can be designed with high accuracy in a short time using a computer. Hereinafter, a method for designing the light diffusion film 30 based on the findings of the present inventors will be described.

As shown in FIG. 27, the design method of the light diffusion film 30 described here is:
A model setting step of selecting a diffraction grating element model provided with a specific configuration for each of the plurality of diffraction grating elements 40 included in the light diffusion film 30;
A first calculation step of calculating diffraction efficiency for each of a plurality of selected diffraction grating element models;
Considering the angular distribution of incident light intensity, the diffraction direction in each diffraction grating element model, the diffraction efficiency calculated for each diffraction grating element model, and the area ratio of each diffraction grating element model in the light diffusion film A second calculation step for calculating an angular distribution of the intensity of the emitted light;
Confirming whether or not a preset condition is satisfied based on the calculated angular distribution of the intensity of the emitted light, and a confirmation step;
Is included.

  First, in the model design process, a plurality of diffraction grating element models having different grating patterns are selected. As an example, when each diffraction grating element model set in the model setting step is modeled as an uneven surface, the pitch p of the uneven surface 35 and the pitch p of the uneven surface 35 between the plurality of diffraction grating element models. The ratio (w / p) of the width w of the convex portion 36 forming the concave / convex surface 35 to the height, the arrangement direction of the convex portion 36 forming the concave / convex surface 35, the height h of the convex portion 36 forming the concave / convex surface 35, and the cross section of the concave / convex surface 35. A plurality of diffraction grating element models may be selected so that one or more of the shape, the area ratio with respect to other diffraction grating element models, and the refractive index difference on both sides of the uneven surface 35 are different.

  In the model setting step, it is preferable that a plurality of diffraction grating element models are selected in consideration that a preset condition is satisfied. At this time, based on the results obtained in advance, for example, information in Tables 2 to 4 is investigated and acquired in advance, and this information is compared with the desired outgoing light orientation, It is preferable to select a diffraction grating element model.

  The first calculation step and the second calculation step performed next are performed in the same manner as the first calculation step and the second calculation step in the method for evaluating the diffusion characteristics of the light diffusion film 30 described above. By passing through the second calculation step, information on the diffusion characteristics of the temporarily designed light diffusion film 30, for example, information as shown in FIGS. 18 to 26 is obtained.

  In the confirmation process, the light diffusion film 30 provisionally designed in the model setting process based on the information on the obtained diffusion characteristics exhibits an effective light diffusion function with respect to the incident light flux of the assumed orientation. It is examined whether or not a predetermined condition regarding the angular distribution of the intensity of the emitted light beam is satisfied. The predetermined condition confirmed here is a condition determined according to the intended use of the light diffusion film 30 to be designed.

  As an example, in the confirmation step, whether the half-value angle of the angular distribution of the intensity of emitted light in a plane along a specific direction is equal to or greater than a preset angle (or exceeds a preset angle) ) Whether or not the intensity of the emitted light traveling in the normal direction fd to the film surface of the light diffusion film 30 is equal to or higher than a preset value (or exceeds a preset value). Or whether the intensity of the emitted light traveling in the normal direction fd to the film surface of the light diffusion film 30 is less than a preset value (or less than a preset value), etc. Can be determined.

  In the first calculation step and the second calculation step, when calculation is performed for light of a plurality of wavelengths, the confirmation step sets in advance based on the angular distribution of the intensity of the emitted light calculated for the light of each wavelength. It may be confirmed whether or not the conditions are satisfied. For example, it may be determined whether or not the calculated angular distribution of the intensity for light of all wavelengths satisfies a predetermined condition. Further, in the confirmation step, the chromaticity angle change may be confirmed as a predetermined condition. As a specific example, the maximum value, the minimum value, and the average value regarding the intensity of the emitted light of each wavelength along the normal direction fd to the film surface of the light diffusion film 30 are specified, and between the maximum value and the minimum value It is determined in the confirmation step whether the ratio of the difference to the average value, that is, whether the above-described chromatic dispersion coefficient is equal to or less than a preset value (or less than a preset value). Also good.

  As shown in FIG. 27, when it is confirmed that a preset condition is satisfied in the confirmation process, the configuration of the diffraction grating element model that is the object of calculation is the configuration of the corresponding diffraction grating element. And the design of the light diffusing film is completed. On the other hand, when it is confirmed that the preset condition is not satisfied in the confirmation process, the process returns to the model setting process, and a specific configuration for each of the plurality of diffraction grating elements 40 included in the light diffusion film 30 Are selected again, and the first calculation step, the second calculation step, and the confirmation step are performed again. At this time, if it is confirmed that a preset condition is satisfied in the second confirmation step, the configuration of the diffraction grating element model that is the second calculation target is determined as the configuration of the diffraction grating element. This completes the design of the light diffusion film. Conversely, when it is confirmed that the preset condition is not satisfied in the second confirmation process, it is confirmed that the preset condition is satisfied in the confirmation process performed thereafter. Until it is done, the first calculation step, the second calculation step, and the confirmation step are repeated.

  As an example, when it is confirmed that a preset condition is not satisfied in the confirmation process, the area of the diffraction grating element model is selected when a plurality of diffraction grating element models are selected again in the subsequent model process. Only the ratio may be changed, that is, the configuration other than the area ratio of each diffraction grating element model may be maintained. When such a method is used, in the first model setting step, the directions of the grating patterns 41 are different between two or more diffraction grating element models among a plurality of selected diffraction grating element models. It is preferable. According to such a method, when the second calculation process is performed again, it is possible to use a part of the calculation result obtained in the first second calculation process. By using the calculation result obtained in the calculation process as it is, it is not necessary to actually perform the first calculation process again.

  When it is confirmed that the preset condition is not satisfied in the confirmation process, it is necessary to reselect a plurality of diffraction grating element models in the model setting process that is subsequently performed. The next model condition value is determined by changing the model condition value so that the evaluation value (a value indicating the degree to which the condition is satisfied) is improved, and changing the model condition value. If the value improves, a method of adopting the change and proceeding can be exemplified. Examples of the former include a damped least-squares method (DLM), and examples of the latter include a genetic algorithm (GA) and simulated annealing (SA).

  As described above, it is possible to design the light diffusion film 30 that can exhibit the effective light diffusion characteristics with respect to the assumed incident light and can control the orientation of the emitted light.

  In the embodiment described above, in the confirmation step, it is confirmed whether or not a preset condition is satisfied based on the calculated angular distribution of the intensity of the emitted light, and the condition preset in the confirmation step is confirmed. If it is confirmed that the above is not satisfied, the process returns to the model setting step, and the diffraction grating element model to which a specific configuration is assigned for each of the plurality of diffraction grating elements included in the light diffusion film is selected again. The example which performs a 1st calculation process, a 2nd calculation process, and a confirmation process again was shown. However, it is not limited to this.

  The light diffusing film design method includes the above-described model setting step, first calculation step, and second calculation step, and in the subsequent confirmation step, the angular distribution of the intensity of the emitted light calculated in the second calculation step is evaluated. You may make it do. For example, once the model is set, the diffraction efficiency is calculated, and the angle distribution of the emitted light intensity is calculated. And the configuration of the corrected diffraction grating element model may be determined as the configuration of the corresponding diffraction grating element. According to this example, the first calculation process is performed again and the second calculation is performed again by correcting the configuration of the diffraction grating element model in consideration of accumulated data, empirical rules, and restrictions due to manufacturing. While omitting the steps, it is possible to design a light diffusion film exhibiting desired diffusion characteristics with a certain degree of accuracy. Therefore, it is possible to further simplify the design of the light diffusion film 30 that can exhibit the effective light diffusion characteristics with respect to the assumed incident light and can control the orientation of the emitted light.

  Further, as another light diffusion film design method, in the model setting step, a plurality of light diffusion film models having different configurations from each other, each of which includes a plurality of diffraction grating element models May be set, and the first calculation step, the second calculation step, and the confirmation step may be performed on each light diffusion film model. That is, in the model setting step, a range that can be a model of the light diffusion film to be investigated for the angular distribution of the emitted light intensity is determined in advance, and all or some of the models of the light diffusion film within the determined range are determined. On the other hand, a 1st calculation process, a 2nd calculation process, and a confirmation process are implemented.

  Then, in light of preset conditions, a light diffusion film model showing the most suitable angle distribution of the emitted light intensity is selected, and the configuration of the diffraction grating element model included in the selected light diffusion film model is The configuration of the corresponding diffraction grating element may be determined, and the design of the light diffusion film may be completed. That is, the angle distribution of the emitted light intensity obtained for each light diffusion film model is compared, and the diffraction grating of the light diffusion film model exhibiting the optimum angle distribution of the emitted light intensity in light of preset conditions. The configuration of the element model can be the configuration of the corresponding diffraction grating element of the light diffusion film.

  Here, the preset condition may be the same as the above-described condition. For example, if the preset condition is the half-value angle of the angular distribution of the intensity of the emitted light in a plane along a specific direction, the model exhibiting the largest half-value angle is selected as the angle of the optimum emitted light intensity. It can be set as the light-diffusion film model which exhibited distribution. Further, at this time, the second condition is set to the chromatic dispersion coefficient, and the model exhibiting the largest half-value angle among the models exhibiting the predetermined chromatic dispersion coefficient exhibits the angular distribution of the optimum emission light intensity. It can be a light diffusion film model. The preset condition may be a plurality of types of conditions.

  By the way, when designing a conventional light diffusion film using a computer-generated hologram, interference fringes (patterns) that can exhibit a predetermined diffraction characteristic in consideration of a desired outgoing light distribution and an assumed incident light distribution. ) Is calculated. However, due to restrictions on the amount of calculation in the computer, in general, in the design of interference fringes in a computer-generated hologram, the calculation is performed assuming that the incident light is a parallel light beam from a specific incident angle and is monochromatic light. It has been broken. For this reason, when the assumed incident light is non-parallel light or light in a plurality of wavelength ranges, the diffraction direction and diffraction efficiency change according to the incident angle and wavelength. I will have to. Further, even if the assumed incident light is actually a monochromatic parallel light, the diffraction efficiency depends on the structure of the interference fringes, so some additional calculation is required. In particular, when the interference fringes have a three-dimensional structure, it is necessary to use a non-analytic method for calculating the diffraction efficiency. For this reason, designing a conventional light diffusion film using a computer-generated hologram requires enormous calculation time, and as a result, it is difficult to reach a solution suitable for the design.

  On the other hand, according to the design method of the light diffusion film described here, the problems in the design of the conventional light diffusion film using the computer-generated hologram can be solved and it can be performed in a relatively short time. Based on this calculation, the light diffusion film 30 exhibiting desired diffusion characteristics can be designed with high accuracy.

<< Manufacturing method >>
Next, the manufacturing method of the light-diffusion film containing the several diffraction grating element 40 formed with the mutually different grating pattern 41 is demonstrated. The manufacturing method of the light-diffusion film demonstrated here includes the process of designing the light-diffusion film 30, and the process of producing the designed light-diffusion film 30. FIG. The process of designing the light diffusion film is as described above. On the other hand, the designed light diffusion film 30 is generally produced by curing a resin using a mold. Therefore, first, an example of a method for producing a mold for producing a desired light diffusion film 30 will be described.

  First, a resist layer having dry etching resistance is formed in a thin film shape on a chromium thin film of a photomask blank plate in which a surface low-reflection chromium thin film is laminated on a substrate such as synthetic quartz. As an example of the resist for dry etching, ZEP7000 manufactured by Nippon Zeon Co., Ltd. can be used, and the lamination of the resist can be performed by spin coating using a spinner or the like. The resist layer is subjected to pattern exposure. The pattern exposure can be performed by a plate-like pattern, laser beam scanning with a laser drawing apparatus, or electron beam scanning with an electron beam drawing apparatus. This exposure forms a readily soluble part in which the resist resin is cured and an unexposed part. Therefore, the resist pattern is formed by removing the easily soluble part by solvent development by spray development performed by spraying a developer. Form.

  Using the formed resist pattern, the portion of the chromium thin film not covered with the resist is removed by dry etching, and the underlying quartz substrate is exposed in the removed portion. Next, dry etching is similarly performed on the exposed quartz substrate, and the quartz substrate is etched. The quartz substrate in which the concave portion generated by the progress of etching, the chromium thin film, and the resist thin film are sequentially coated from the bottom. A convex portion made of the original portion is formed. Thereafter, the resist thin film is removed by dissolution or the like, and a quartz substrate having a concave portion formed by etching the quartz substrate and a convex portion composed of a portion where a chromium thin film is laminated on the top is obtained.

  With only the above method, only the binary structure of the convex part and the concave part (high and low two steps, the depth is generated in addition to the surface of the original quartz substrate) is obtained. However, by repeating the photo-etching process consisting of resist formation → pattern exposure → resist development → dry etching of the chromium thin film → dry etching of the quartz substrate → resist removal for the above obtained Further, photo-etching can be further performed on the concave portions and the convex portions generated by the first photo-etching. By repeating this a plurality of times, it is possible to accurately obtain a plurality of irregularities having a height difference. In this way, after obtaining a predetermined number of steps, the chromium thin film is removed by wet etching, and a mold of the light diffusion film 30 in which irregularities having a predetermined number of steps are formed on the surface of the quartz substrate can be obtained.

  Next, a method for producing the light diffusion film 30 using the produced mold for the light diffusion film 30 will be described. First, the first layer 31 of the light diffusing film 30 is produced using the mold, and the first layer 31 is produced by, for example, a method of pressing the mold against a resin layer that is softened by heating, an injection method, or A casting method or the like can be used. As the resin used in these methods, both thermoplastic and thermosetting can be used.

  Industrially preferred is that an uncured resin composition containing an ultraviolet curable resin is brought into contact with the surface on which the unevenness of the mold is formed, and a film serving as the base layer of the first layer 31 is formed on the opposite side of the resin composition. Lamination is performed so that the resin composition is sandwiched between the mold and the plastic film (base film). From such a state, the resin composition is cured by irradiating ultraviolet rays or the like, and then the film and the ultraviolet curable resin composition layer formed with an uneven surface 35 that is cured and forms a lattice pattern 41 are formed. Are released from the mold, the first layer 31 is formed. That is, the 1st layer 31 is formed by laminating | stacking the resin layer which has the uneven surface 35 on one surface of the base material layer which has translucency.

  As a specific apparatus for forming the first layer 31, a molding apparatus 60 shown in FIG. 28 can be used. The apparatus 60 shown in FIG. 28 has a molding die 70 having a substantially cylindrical outer contour. A cylindrical mold surface (uneven surface) 72 is formed in a portion corresponding to the outer peripheral surface (side surface) of the column of the molding die 70. The molding die 70 having a cylindrical shape has a central axis CA that passes through the center of the outer peripheral surface of the cylinder, in other words, a central axis CA that passes through the center of the cross section of the cylinder. That is, the molding die 70 is configured as a roll die that molds the first layer 31 of the light diffusion film 30 as a molded product while rotating about the central axis CA as the rotation axis.

  As shown in FIG. 28, the molding device 60 includes a material supply device 64 that supplies a resin composition 53 having fluidity between a base film 50 that extends in a strip shape and a mold surface 72 of a molding die 70, And a curing device 66 that cures the resin composition 53 between the base film 50 and the uneven surface 72 of the molding die 70. The curing device 66 can be appropriately configured according to the curing characteristics of the resin composition 53 to be cured. Further, the molding device 60 has a pair of rollers 68 for holding the base film 50 coated with the resin composition 53 on the molding die 70. By using such a molding apparatus 60, the first layer 31 can be continuously manufactured.

  Next, the second layer 32 is stacked on the first layer 31. The second layer 32 is formed by applying a thermoplastic resin, a thermosetting resin, an ultraviolet curable resin, or the like before curing onto the first layer 31 using a squeegee, and then the resin corresponds to the resin. It can be formed by curing by a curing method. In addition, an adhesive (concept including an adhesive) can be used as the second layer 32. In this case, a method of applying an adhesive on the first layer 31 can be used.

DESCRIPTION OF SYMBOLS 10 Display apparatus 11 Polarizing plate, lower polarizing plate 12 Polarizing plate, upper polarizing plate 13 Liquid crystal cell 14 Surface functional sheet 15 Image forming device 16 Liquid crystal display panel 18 Polarizer 20 Backlight, surface light source device 21 Light guide plate 21a Unit prism, first prism 1 unit prism 22 light diffusing plate 23 light source 23a light emitter 25 condensing sheet 25a unit prism, second unit prism 26 first condensing sheet 26a unit prism, first unit prism 27 second condensing sheet 27a unit prism, second Unit prism 29 Reflective sheet 30 Light diffusion film 31 First layer 32 Second layer 35 Uneven surface 36 Convex part 40 Diffraction grating elements 40a to 40j Diffraction grating elements, 1st to 10th diffraction grating elements 41 Lattice patterns 41a to 41j Lattice patterns, First to ten lattice patterns 42a First modulation region 42b Second modulation region 45 Unit diffusion element 7 the second unit diffusing element 48 third unit diffusion element 49 fourth unit diffusion element 50 fifth unit diffusing element 55a first diffraction grating element model 55b second grating model

Claims (15)

A method of designing a light diffusing film including a plurality of diffraction grating elements formed with different grating patterns,
For each of the plurality of diffraction grating elements included in the light diffusion film, a model setting step of selecting a diffraction grating element model given a specific configuration;
A first calculation step of calculating diffraction efficiency for each of the selected plurality of diffraction grating element models;
Considering the angular distribution of the intensity of incident light, the diffraction direction in each diffraction grating element model, the diffraction efficiency calculated for each diffraction grating element model, and the area ratio of each diffraction grating element model in the light diffusion film, A second calculation step of calculating the angular distribution of the intensity of the emitted light;
A method for designing a light diffusing film, comprising: a confirmation step of evaluating an angular distribution of the calculated intensity of emitted light. In the confirmation step, based on the calculated angular distribution of the intensity of the emitted light, confirm whether or not a preset condition is satisfied,
When it is confirmed that the preset conditions are not satisfied in the confirmation step, the process returns to the model setting step, and a specific configuration is provided for each of the plurality of diffraction grating elements included in the light diffusion film. Reselect the given diffraction grating element model, and perform the first calculation step, the second calculation step, and the confirmation step again,
When it is confirmed in the confirmation step that a preset condition is satisfied, the configuration of the diffraction grating element model that has been calculated is determined as the configuration of the corresponding diffraction grating element, and light diffusion is performed. The method of designing a light diffusing film according to claim 1, wherein the design of the film is finished.   When it is confirmed that a preset condition is not satisfied in the confirmation step, only the area ratio of the diffraction grating element model is changed when reselecting the plurality of diffraction grating element models. 3. A method for designing a light diffusing film according to 2. Each diffraction grating element model set in the model setting step is modeled as an uneven surface,
Among the plurality of selected diffraction grating element models, the pitch of the concavo-convex surface, the ratio of the width of the convex portion forming the concavo-convex surface to the pitch of the concavo-convex surface, the arrangement direction of the convex portions forming the concavo-convex surface, the concavo-convex 2. One or more of a height of a convex portion forming a surface, a cross-sectional shape of the uneven surface, an area ratio with respect to another diffraction grating element model, and a refractive index difference on both sides of the uneven surface are different. The design method of the light-diffusion film as described in any one of -3. In the model setting step, a plurality of light diffusion film models having different configurations from each other, a plurality of light diffusion film models each including the plurality of diffraction grating element models are set,
The first calculation step, the second calculation step and the confirmation step are performed for each light diffusion film model,
In light of preset conditions, the most appropriate light diffusion film model is selected, and the configuration of the diffraction grating element model included in the selected light diffusion film model is determined as the configuration of the corresponding diffraction grating element. The method of designing a light diffusion film according to claim 1, wherein the design of the light diffusion film is completed.   In the first calculation step, the diffraction efficiency of each order is calculated for each diffraction grating element model using rigorous coupled wave analysis or FDTD Finite Difference Time Domain method. The design method of the light-diffusion film as described in any one of Claims 1-5. The light diffusion film design method according to any one of claims 1 to 6, wherein in the second calculation step, the angular distribution of the intensity of the emitted light is calculated using the following formula.

  The said confirmation process WHEREIN: The half value angle of the angle distribution of the intensity | strength of the emitted light in the plane along a specific direction is evaluated as a preset condition, The evaluation is any one of Claims 1-7. Design method of light diffusion film.   The light diffusion according to any one of claims 1 to 8, wherein, in the confirmation step, the intensity of the outgoing light traveling in the normal direction to the film surface of the light diffusion film is evaluated as a preset condition. How to design a film. In the first calculation step and the second calculation step, calculation is performed for light of a plurality of wavelengths,
The light diffusion film design method according to any one of claims 1 to 9, wherein in the confirmation step, an angular distribution of the intensity of the emitted light calculated for the light of each wavelength is evaluated.   In the confirmation step, the maximum value, the minimum value, and the average value regarding the intensity of the emitted light of each wavelength along the normal direction to the film surface of the light diffusing film are specified, and between the maximum value and the minimum value The light diffusion film design method according to claim 10, wherein a value of a ratio of the difference to the average value is evaluated as a preset condition. A method of manufacturing a light diffusion film including a plurality of diffraction grating elements formed with different grating patterns,
Designing a light diffusing film according to the design method described in any one of claims 1 to 11, and
And a step of producing the designed light diffusion film. A method for evaluating the diffusion characteristics of a light diffusing film including a plurality of diffraction grating elements formed with different grating patterns,
For each of the plurality of diffraction grating elements included in the light diffusion film, a model setting step for setting a diffraction grating element model having a corresponding configuration;
A first calculation step of calculating a diffraction efficiency for each of the plurality of set diffraction grating element models;
Considering the angular distribution of the intensity of incident light, the diffraction direction in each diffraction grating element model, the diffraction efficiency calculated for each diffraction grating element model, and the area ratio of each diffraction grating element model in the light diffusion film, A method for evaluating diffusion characteristics of a light diffusion film, comprising: a second calculation step of calculating an angular distribution of intensity of emitted light.   In the first calculation step, the diffraction efficiency of each order is calculated for each diffraction grating element model using rigorous coupled wave analysis or FDTD Finite Difference Time Domain method. The evaluation method of the diffusion characteristic of the light-diffusion film of Claim 13. The evaluation method of the diffusion characteristic of the light-diffusion film of Claim 13 or 14 which calculates the angle distribution of the intensity | strength of emitted light in the said 2nd calculation process using the following formula | equation.

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