JP4539191B2 - Preparation method of diffusion film - Google Patents

Description

The present invention relates to a method for producing a diffusion film that has different diffusibility depending on the incident direction of light, that is, has an incident angle selectivity and can improve the visibility of a display image of a liquid crystal display device, and in particular, such a diffusion film. The present invention relates to a method for efficiently producing a seamless long shape.
In addition, the present invention relates to a diffusion film and a polarizing element that can be produced with a desired size without waste.

  The transmissive liquid crystal display element is one of the typical display elements of flat panel displays. It is light, thin, and has low power consumption, so it can be used in a wide range of applications such as LCD TVs, car navigation systems, personal computer monitors, notebook PCs, and FA. Has been used. Among these, it is important that the in-vehicle TV, the car navigation, and the like look good from an oblique direction because of the positional relationship with the driver's viewpoint. In addition, since a personal computer using a pen input device looks in from various directions, it is necessary to see a good image from an oblique direction. However, a major problem with liquid crystal display elements is that the viewing angle dependence is large. The viewing angle dependence means that what is supposed to be displayed in black when viewed from an oblique direction more than a certain angle looks whitish or the gradation is reversed, resulting in display contents that cannot be read accurately by the observer. It is. Accordingly, there has been a demand for a transmissive liquid crystal display element in which black display does not become whitish when viewed from any direction and gradation is not lost.

  Since the liquid crystal used in the liquid crystal display element has refractive index anisotropy, when the viewing angle is increased, the gradation is inverted and the contrast ratio is lowered, and the display quality is remarkably lowered. For example, in a general TN-oriented liquid crystal display element, gradation inversion occurs when the downward direction exceeds 5 degrees, and the contrast ratio decreases to 10 or less when the upward direction exceeds 30 degrees and the downward direction exceeds 50 degrees. Here, the gradation inversion means that the order of the original gradation recognized in the front is reversed when viewed from a certain oblique direction, and the contrast ratio is white display brightness / black display brightness.

  Accordingly, various proposals have been made to improve the viewing angle dependency of this type of liquid crystal display element. A viewing angle improving liquid crystal display element using an optical anisotropic element (see Patent Document 1) has a configuration using two optical anisotropic element films (hereinafter referred to as a first viewing angle expansion technique). The liquid crystal cell is sandwiched between optical anisotropic elements and further sandwiched between them by polarizing plates. The main refractive indexes nx, ny, and nz of the refractive index ellipsoid described here have a relationship of nx> ny> nz, where nx is inclined in the film plane, and ny and nz are inclined with the direction of nx as the rotation axis. With these configurations, a reduction in contrast due to birefringence of the liquid crystal itself is suppressed. However, even if the reduction in contrast is suppressed, the gradation inversion may not be suppressed, and when used in a TN liquid crystal display element, coloring in an oblique direction occurs.

  In addition, a viewing angle improving liquid crystal display element (see Patent Document 2) using a retardation compensation film having negative refractive index anisotropy has been proposed (hereinafter referred to as a second viewing angle expansion technique). The optically anisotropic element used here has an optically negative uniaxial property. When the triaxial refractive index is set to nα, nβ, nγ in ascending order, nα <nβ = nγ. There is. Therefore, it has the characteristic that the refractive index in the optical axis direction is the smallest. Similar to the first viewing angle expansion technique, the second viewing angle expansion technique may not be able to suppress gradation inversion, and coloration may occur.

  Also, a viewing angle improving liquid crystal display element using a diffusion film (see Patent Document 3) has been proposed (hereinafter referred to as a third viewing angle expanding technique). The light transmitted through the liquid crystal cell and the polarizing plate is diffused by the diffusion plate, the contrast is averaged, and the contrast ratio for a large viewing angle is improved. The diffusion plate used here has a layer including a diffusion material or a surface roughened.

  In such a diffusion film, a resin sheet whose surface is processed into a mat shape, a resin sheet including a diffusion material inside, or the like is used. Although it is possible to control the emission range / direction of diffused light (hereinafter referred to as “diffusion directivity”) by controlling the mat surface (such as uneven shape), a film whose diffusivity changes depending on the incident angle of light Is difficult in principle.

  A diffusing film including a diffusing material is not suitable for applications in which only light in a specific direction is scattered because light incident from any direction has similar diffusibility. In addition, attempts have been made to control the refractive index, size, shape, etc. of the diffusing material in order to control the diffusivity, but it is technically difficult and cannot be said to be practically sufficient. Currently.

  In particular, a diffusion film including the above diffusing material has no diffusion anisotropy or off-axis light diffusing characteristics and low light diffusion directivity, so that the contrast of the front surface is reduced or a diffusion plate is provided on the upper surface of the polarizing plate. Some things look whitish due to diffuse reflection. The reason why the front contrast is lowered is that light leaked in the diagonal direction of black display is diffused in the front direction. Therefore, even when applied to a display element, there are problems such as a decrease in display brightness and contrast in the front direction.

  As a thing corresponding to such a use, the diffusion film (refer patent document 6) from which a diffusivity changes with incident directions (refer patent document 6), and the visual field expansion technique (refer patent document 7) using such a diffused film are well-known. (Hereinafter, this is referred to as a fourth viewing angle expansion technique). However, such a film diffuses a wide range of light in the downward direction, and the diffusion spread cannot be sufficiently obtained, and a sufficient anti-inversion effect cannot be obtained.

  Further, when the diffusion pattern is recorded on the film by the method of Patent Document 7, the pattern of the diffusion plate must be recorded intermittently, so that the mass productivity cannot be improved and the joint can be formed on the diffusion pattern recorded on the film. There are disadvantages such as poor extraction efficiency.

  It is also known that the diffusivity is maximized with respect to light incident from two or more different angles by causing two light beams to interfere with each other and irradiating the photosensitive material with the two light beams.

  Although such a film can control diffusion anisotropy and diffusion directivity, it is accompanied by spectroscopy (wavelength dispersion), so the color of the display light changes as the viewpoint to be observed changes. There is a problem that it is visible.

  Further, a method using an in-line hologram method is known as a method for irradiating a diffusion plate with visible light or the like to record a diffusion pattern on a photosensitive material. This is a method of recording a hologram by interference between light that is not scattered by the diffuser and scattered light. However, in this method, since light is scattered only in the incident direction when recording a hologram, a diffusion plate having two or more directions in which the diffusion is maximized cannot be obtained.

  Moreover, as an optical production method of such a diffusion film, a method of producing a diffusion film with a speckle pattern produced by applying coherent light to a diffusion plate is known (see Patent Document 8). However, the diffusion plate manufactured in this way can control the scattering distribution of the emitted light, but the diffusivity does not differ depending on the incident direction. Therefore, even if such a diffusion plate is used, the contrast at the front is lowered.

  The speckle pattern is a bright and dark spot pattern that occurs when light with good coherence is scattered or reflected or transmitted by a rough surface. Light scattered by minute irregularities on the rough surface interferes with an irregular phase relationship. It happens.

Also, a method for producing a film having different scattering properties depending on the incident angle is known. (See Patent Document 9). In such a method, since only diffused light can be produced only in one direction, when combined with a liquid crystal display, the image becomes unnatural such as a double image. Moreover, the film produced by such a production method cannot control the diffusion, and cannot efficiently spread light to an angle that cannot be compensated by the retardation compensation film. In addition, the spread of the diffused light cannot be controlled and sufficient optimization cannot be performed.
JP-A-7-120619 JP-A-7-159614 JP-A-60-202464 Japanese Patent Laid-Open No. 9-152602 JP-A-10-104611 JP 2000-171619 A JP 2003-295167 A Japanese Patent Laid-Open No. 55-88002 Japanese Patent Laid-Open No. 2-67501 JP 2000-297110 A

  In the conventional method of optically recording holograms and speckle patterns when creating a diffusion film that compensates for the downward viewing angle of the liquid crystal display element and obtains a liquid crystal display element with a wide viewing zone, When recording on a film or the like using a glass plate, the diffusion pattern is recorded in a certain area according to the size of the glass plate at once. The part was made, and it was a factor that raised the cost. In addition, the conventional method of continuously recording a diffusion pattern cannot obtain a diffusion film having excellent characteristics.

  The present invention has been made to solve the above-described problems of the prior art, and the object of the present invention is to provide a diffusion film whose diffusibility changes depending on the incident direction of light and whose diffusion angle can be controlled. It is an object to provide a method for producing a diffusion film capable of efficiently producing a film. Another object of the present invention is to provide a diffusion film produced by an efficient production method. In addition, the present invention provides a polarizing element having a diffusion layer that is not wasted when carrying out squeezing.

  A film in which a photosensitive material layer is disposed on a transparent support and a master diffusion film are overlaid, and at least a part of the overlapped portion is irradiated with ultraviolet rays, visible rays, ultraviolet rays, or visible rays. Provided is a method for producing a diffusion film, in which a diffusion pattern is formed in a layer and the diffusivity changes depending on the incident direction of light.

  Also provided is a method for producing a diffusion film in which at least one of the film on which the photosensitive material layer is arranged and the master diffusion film is unwound and supplied from a state in which a long film is wound. This makes it possible to produce a diffusion film with no seams at all or with a long seam between seams and a substantially seamless seam. As a diffusion film for use, it is possible to obtain a film that is not wasted when carrying out a nuisance process.

  Further, at that time, there is provided a method for producing a diffusion film in which at least a part thereof is irradiated with ultraviolet rays, visible rays, ultraviolet rays, or visible rays while conveying a film on which a photosensitive material layer is disposed and a master diffusion film. Thereby, it can produce continuously more efficiently. Moreover, the manufacturing method of the diffusion film which conveys the film in which the photosensitive material layer is arrange | positioned, and a master diffusion film at the same speed is provided. Thereby, since the speckle pattern formed by the diffusion film does not change while being conveyed, a more preferable diffusion pattern can be recorded.

  Moreover, the manufacturing method of the diffusion film which integrates and conveys the film in which the photosensitive material layer is arrange | positioned, and the said master diffusion film is provided. At this time, by preliminarily laminating both films to form an integrated wound body, pattern displacement is unlikely to occur and handling becomes easier.

  Further, the present invention provides a method for producing a diffusion film in which ultraviolet rays and visible rays are irradiated obliquely with respect to the normal direction of the film when the film surface on which the photosensitive material layer is disposed is irradiated. Thereby, a diffusion film suitable for a portion that cannot be compensated by the retardation compensation film can be produced. At that time, it is more preferable to irradiate the irradiation light as parallel light because the directions of the diffusion patterns can be aligned with higher accuracy.

  Also provided is a method for producing a diffusion film using laser light as ultraviolet light and visible light. By using coherent light, the diffusion pattern can be formed better. Furthermore, when the laser beam is used while scanning, the light utilization efficiency is good. At this time, the laser light may be in the form of a beam or light spread in one direction.

  Provided is a method for producing a diffusion film using the master diffusion film in which a diffusion pattern is formed on an unstretched film. By using an unstretched film with low birefringence, a speckle pattern can be satisfactorily formed.

  Moreover, the diffusion film from which the diffusivity differs with the incident direction produced by one of the said production methods is provided. As a result, there is no seam, and a diffusion film can be obtained without waste when carrying out squeezing.

  Moreover, the polarizing element by which the layer which has negative refractive index anisotropy, a polarizing layer, and the diffusion film of this invention are arrange | positioned is provided. Thereby, a polarizing element having a diffusion layer can be easily obtained.

By recording a speckle pattern on the photosensitive material by irradiating coherent light onto the master diffusion film, it is possible to easily produce a diffusion film whose diffusivity differs depending on the incident direction and whose spreading can be controlled. Can do. At this time, in particular, a seamless film-like long master diffusion film is overlapped with a film provided with a long photosensitive material layer, and is recorded while moving at the same speed, so that the seamless pattern has a seamless length. A long diffusion film can be produced. Moreover, it is such a seamless diffusion film, and a diffusion film that can reduce waste during cutting or the like can be obtained. A seamless polarizing element can be obtained by laminating such a seamless diffusion film with a layer having a negative refractive index anisotropy and a polarizing layer.

  FIG. 5 shows the principle diagram of the method for producing the diffusion film of the present invention. It comprises a master diffusion film 53, a photosensitive material layer 51, and a transparent support 55 that supports it. In this configuration, when coherent parallel light 50 is incident from the master diffusion film side, the light is diffused by the diffusion film, and a speckle pattern 54 is formed behind the light. Thereafter, the photosensitive material layer 52 on which the speckle pattern is formed by the fixing process is obtained.

  As a master diffusion film used at this time, a haze of 40 or more is appropriate, and 50 to 90 is preferable. Desirably, a speckle pattern is formed by interference of light using coherent light, and therefore, an unstretched film having low birefringence is preferably used as the base film used for the diffusion film. Examples of such an unstretched film include PC, PP, and TAC films. In particular, when a photosensitive material is coated on a transparent support and a film on which a diffusion pattern is recorded is laminated, and the diffusion pattern is transferred to the photosensitive material by ultraviolet rays or the like, there is no seam, or the seam and seam. A substantially seamless diffusion film having a distance of 5 m or more can be produced, for example, in the form of a roll. By using such a seamless diffusion film, the film is cut by post-processing. When applied to a liquid crystal panel, it can be applied to panels of various sizes, and waste can be reduced.

  At this time, if the diffusion degree of the diffusion film as a master is increased, the diffusion pattern recorded in the diffusion pattern becomes finer.

  Further, if an isotropic film is used as the master diffusion film, it is embossed with a film coated with general transparent beads, etc., or with a roll roughened by sandblasting as exemplified in FIG. In addition, a film having a matte surface may be used. Further, if the side of the master diffusion film that contacts the photosensitive material is made into a weak antiglare shape, an antiglare film can be obtained. Moreover, if it makes it a glare shape, it can be set as a glare-like film.

  An example of a method for actually producing a diffusion film using such a film is shown in FIG. Here, first, a photosensitive material is applied to a long transparent film 13 to provide a photosensitive material layer 12, and a long master diffusion film 11 is laminated thereon. In general, an uncured photosensitive material is difficult to handle because of its tackiness. However, in such a form, the photosensitive material is sandwiched between films, which makes it easy to handle. Next, when the photosensitive material is sandwiched and irradiated with coherent light 10, speckles are formed by the master diffusion film 11, and the diffusion pattern can be recorded on the photosensitive material layer 12.

  In an ordinary light-sensitive material, heating is performed as a subsequent process to promote diffusion movement, and then the monomer is completely cured by ultraviolet rays or the like to perform fixing processing. In this process, a post-process can be performed with the master diffusion film laminated, and the film can be used as it is as a protective film during winding.

  As shown in FIGS. 2 and 3, a photosensitive material is applied to a transparent film 13 to provide a photosensitive material layer 12, and a separate film 14 is laminated on the photosensitive material layer 12. Alternatively, the master diffusion film 11 may be brought into close contact to record a diffusion pattern. Further, after the diffusion pattern is recorded by the above method, post-processing such as heating or ultraviolet irradiation may be performed.

  As a light source irradiated at this time, a high-pressure mercury lamp, an ultra-high pressure mercury lamp, a metallohalide lamp, a krypton laser, an argon laser, a solid UV laser, or the like, which is a short arc lamp, can be used. Light from these light sources can be made into substantially parallel light by a concave mirror or convex lens, and can be irradiated to the photosensitive material. These light sources have a sufficiently high output so that a high line speed can be obtained during replication. At this time, the distribution of the amount of light may be made uniform using a fly-eye lens, a diffusion plate, or the like, so that a highly uniform diffusion film can be obtained. When laser light is used, more efficient irradiation can be achieved by irradiating while scanning.

  When the irradiation direction of the coherent light is irradiated from a direction inclined from the normal direction of the film surface, a pattern 60 composed of inclined regions having different refractive indexes as shown in FIG. 6 is formed in the photosensitive material layer. When light is incident in a direction substantially parallel to the boundary surface of the layered regions having different refractive indexes of such a film, the light is scattered by the boundary. On the other hand, light incident at an angle close to the perpendicular to the boundary surface of the layered regions having different refractive indexes is transmitted as it is because there is no scattering at the boundary.

  In this way, in a diffusion film formed by alternately inclining a specific direction with a region having a different refractive index, an angle is formed in a direction that cannot be compensated by the retardation compensation film, and the diffusibility is maximized. Is applied to the liquid crystal using the retardation compensation film, the angle at which the contrast inversion cannot be compensated by the retardation compensation film of the liquid crystal display device and the contrast is not inverted (first angle). Since (second angle) light can be brought in, contrast inversion can be effectively suppressed. Next, in a direction where the contrast is sufficient, such as the front direction, light is transmitted as it is without being scattered so much. Thereby, it acts selectively only on the angle at which contrast inversion occurs without reducing the front contrast much. As a result, both front contrast and prevention of inversion can be achieved.

  Here, as a master diffusion film, a PET film, a TAC film, a polycarbonate film, a polyethylene film, a polypropylene film, an acrylic film, or the like on which a polymer layer containing beads is formed is embossed on these transparent supports. What recorded the diffusion pattern by the process etc. can be used. In particular, it is more preferable to use an unstretched film as the transparent support because ultraviolet rays enter the photosensitive material without disturbing the polarization.

  Moreover, a diffusion film can also be produced by irradiating ultraviolet rays, visible rays, ultraviolet rays, or visible rays while conveying the film. Thereby, a film can be produced, always flowing a film. Thereby, the film conveying apparatus for production can be simplified and the production speed can be increased.

  Furthermore, if the diffusion film and the photosensitive material are conveyed at the same speed during conveyance, the speckle pattern formed by the diffusion film does not change during the conveyance on the photosensitive material. preferable.

  FIG. 7 shows a schematic diagram of a method of creating while conveying. The master diffusion film 70 wound in a roll and the film 71 provided with the photosensitive material layer are superposed while being conveyed in the direction of the arrow, and the light source 72 irradiates ultraviolet rays, visible rays, ultraviolet rays, or visible rays, and then winds them up. Like. A fixing unit 74 including an ultraviolet light source for fixing the formed pattern may be provided. Further, the master diffusion film may be used repeatedly in the form of an endless loop as in 73. In the figure, the master diffusion film and the film provided with the photosensitive material layer are formed as separate rolls. However, as described above, both of them can be laminated in advance to form a roll, which can be irradiated while being conveyed. It is.

  With such a seamless diffusion film, waste during cutting or the like can be reduced. Moreover, such a diffusion film is directly formed on a film having low birefringence such as a TAC film, a ZEONOR film, an ARTON film, a polycarbonate film, etc., and this diffusion form and another transparent support are used to form polyvinyl alcohol and iodine. A polarizing plate having a diffusing layer can be easily produced by sandwiching a polarizing layer composed of, for example.

  Unlike the diffusion film as described in Patent Document 9, the film thus produced has a feature that diffused light diffuses not only in one direction but also in both vertical and horizontal directions. When they are put together, an unnatural thing such as a double image is not seen. Also, horizontal and vertical diffusion can be optimized. Furthermore, since a pattern finer than 1 μm can be recorded, a pattern having a wide diffusion range can be obtained.

  Then, the structure of the diffusion film of this invention is demonstrated in detail. As described above with respect to the production method of the present invention, a portion with different refractive index is distributed in an irregular shape / thickness inside the diffusion film of the present invention, thereby forming a light and shade pattern having a high and low refractive index. ing.

  If the difference in refractive index is too small, the scattering property is deteriorated. On the other hand, if the difference is too large, light scattering occurs regardless of the angle at which light is incident. It becomes difficult to make it. Therefore, light scattering does not occur only by the difference in refractive index on the surface, and it is necessary that the refractive index difference is optimal so as to have sufficient scattering properties due to the thickness of the film.

  In the present invention, the refractive index difference is appropriately selected in the range of 0.001 to 0.2 so as to meet the above conditions, and the film thickness is appropriately selected in the range of 1000 μm to 1 μm according to the refractive index difference. it can.

  Since the refractive index difference that can be recorded is limited by the film production method and the recording material, the present invention can be achieved by thinning the film if it has a large refractive index difference and increasing the film if it has a small refractive index difference. It is possible to realize a diffusion film.

  For example, in a film having an average refractive index of 1.52 and a thickness of 20 μm, a portion having a refractive index of 1.56 (refractive index difference of 0.04) is distributed to form a shading pattern. A diffusion film having sufficient diffusivity and incident angle selectivity can be obtained.

  In such a case, it is very preferable to use a photosensitive material having a wide latitude so that the diffusivity does not change any more when a certain amount of exposure is applied.

Subsequently, application examples of the diffusion film of the present invention will be further described.
<Application to TN liquid crystal>
By disposing the diffusing film of the present invention with respect to the TN-oriented liquid crystal, the downward light, which cannot be compensated for viewing angle depending on the combination with the discotic liquid crystal, mainly brings the light near 15 degrees to around 45 degrees. Thus, compensation is made around 45 degrees in the downward direction where contrast inversion is most likely to occur. At the same time, by scattering light in the downward direction and widely scattering light, it is possible to obtain appropriate characteristics in a wide range without causing a sudden deterioration in characteristics.

In addition, in order to increase the surface hardness of the outermost surface of the diffusion film of the present invention, there is one in which a hard coat layer is used and the pencil hardness at a load of 500 g is about 2H to 4H. Further, a low reflection layer having a reflectance of about 1% may be provided thereon. Further, an antistatic layer, an antifouling layer, or the like may be added to or separately from this layer.
<Liquid crystal display device>
A configuration example in which the diffusion film of the present invention is applied to a liquid crystal display device will be described.

  The retardation compensation film is a special discotic liquid crystal film made of a polymer liquid crystal whose molecular shape is a disk shape, and the disk-shaped molecules are substantially horizontally directed from one surface of the film to the other surface. They are oriented sequentially so as to rise almost vertically from the lying state. The direction along the central axis of the change in orientation of these discotic molecules (the direction parallel to the film surface in the diameter direction of the discotic molecules) is the slow axis, and the direction perpendicular thereto is the fast axis.

  For example, in a twist type liquid crystal in which the liquid crystal cell has a twist angle of about 90 degrees, one discotic liquid crystal film has a slow axis substantially parallel to the alignment direction of the liquid crystal molecules in the vicinity of one substrate of the liquid crystal display element. It is preferable that the orientation direction of the other discotic liquid crystal is provided substantially parallel to the orientation direction of the liquid crystal molecules in the vicinity of the other liquid crystal.

  Therefore, in the twist type liquid crystal display device, the two discotic liquid crystal films are turned to face each other with the same alignment state of the disk-like molecules, and the respective slow axes are made substantially perpendicular to each other, It is desirable to arrange on both sides of the liquid crystal display element.

  In the two discotic liquid crystal films, the product Δn ′ · d ′ of the refractive index anisotropy Δn ′ of each liquid crystal and the film thickness d ′ has a total value of the refractive index anisotropy of the liquid crystal of the liquid crystal cell. It is desirable that the value is substantially the same as the product Δn · d of Δn and the film thickness d. In this case, the birefringence of the discotic liquid crystal film does not adversely affect the display.

  According to the liquid crystal display device having such a configuration, when only the twist type liquid crystal display device and the discotic liquid crystal are used, the contrast is lowered at about 45 degrees and the image is very difficult to see. By using the diffusion film, a reduction in contrast can be suppressed even at 60 degrees or more, and a liquid crystal display device having a wide viewing area can be realized.

  At this time, if the scattering property (haze) of the film is increased, a more effective film can be obtained. However, increasing the haze decreases the contrast on the front.

  As a result of various experiments, when a light diffusion film having a haze of 70 or more is used, a practically sufficient contrast cannot be obtained even with a liquid crystal having a high contrast at the front, and blurring is observed when an image is observed from the front. Since it was not acceptable, satisfactory image quality could not be obtained. For this reason, it is desirable to increase the effect of lowering the haze and expanding the viewing area. However, in view of the image quality in the front, it has been experimentally obtained that it is appropriate to set the haze to 70 or less. .

In addition, in applications that are not expected to be observed in a downward direction, such as a personal liquid crystal display, if the application does not place importance on the image quality observed from the bottom with the highest priority on the image quality on the front, A light diffusion film having a low haze can also be used. When such a light diffusion film was used, the image quality from the lower direction was not good, but the front image quality was better. With respect to what was supposed to be used in this way, a product having a haze of 60 or less was obtained.
<Explanation of diffuser>
FIG. 6 is a diagram showing a cross-section of an example of a diffusion film created by the production method of the present invention. As shown in the figure, portions having different refractive indexes are distributed inside the diffusion film, and the refractive index A light and shade of high and low (expressed in white-black in the figure) is formed.

  In addition, in order to suppress coloring due to light diffraction, a portion having a different refractive index is aperiodic within a minute region (about 0.1 to 1 mm), but its size is regular, and its spatial frequency is Any place is almost constant.

  As shown in FIG. 6, in the film cross section, portions having different refractive indices are substantially columnar and distributed in a uniform direction. The angle of the columnar structure is set as appropriate depending on the angle desired to be observed.

  According to the description (p266-p268) of “Optical Measurement Handbook Asakura Shoten, Toshiharu Tadashi et al., Published on November 25, 1994”, the speckle pattern in which the concentration and phase show random values depending on the position, The average size of the pattern is determined in inverse proportion to the angle at which the diffusion plate is viewed from the photosensitive material. Therefore, when the size of the diffusion plate is made larger in the vertical direction than in the horizontal direction, the pattern recorded on the photosensitive material is finer in the vertical direction than in the horizontal direction.

  In the speckle pattern produced by the manufacturing method in the optical system, the wavelength of the laser beam used, the size D of the ground glass, and the distance F between the ground glass and the photosensitive material determine the average size d of the recorded speckle pattern. In general, d is expressed by the following equation.

d = 1.2λF / D
The average length t of this speckle pattern in the depth direction is
t = 4.0λ (F / D) ²
It is represented by

  As described above, a light scattering film having a desired three-dimensional refractive index distribution can be obtained by optimizing the F / D value so as to have an optimum scattering property.

  As an example, when λ = 0.355 μm and F / D = 1, d = 0.43 μm, t = 1.42 μm, and the shading pattern on the film surface is distributed with an average of 0.43 μm, and the thickness direction of the film Will be distributed with an average size of 1.42 μm in the direction according to the inclination angle.

  Further, when λ = 0.355 μm and F / D = 2, d = 0.85 μm, t = 5.68 μm, and the shading pattern on the film surface is distributed with an average of 0.85 μm, in the thickness direction of the film. Are distributed in an average size of 5.68 μm in the direction according to the inclination angle.

  However, these sizes are only average sizes, and actually, these sizes are various in size, centering on these sizes. The same is true when the diffusion film is irradiated with coherent light. By recording this speckle pattern on the photosensitive material, regions having different refractive indexes are folded in a specific direction as shown in FIG. It becomes a diffusion film.

In the above description, the diffusion film is obtained by separating ground glass with a certain size to produce a speckle pattern, but it can be similarly produced by using a film that scatters light within a specific range.
<Distribution of scattering>
Light in the direction along the tilt direction of a minute region with a different refractive index is scattered if the shape of the film surface of the portion with a different refractive index is horizontally long (longitudinal), and incident light is scattered and emitted. It has a diffusion characteristic that makes it vertically long (horizontally long) centering on the light that is transmitted as it is. For example, if the shape is horizontally long, the scattered outgoing light from the diffusion film has a distribution that becomes a vertically long ellipse.

  Furthermore, when the shape on the film surface of the part having a different refractive index is isotropic, for example, circular, when the light incident on the part is scattered and emitted, the light scattering characteristics of the emitted light from each part are Isotropic scattering distribution. In order to control the scattering characteristics in the vertical and horizontal directions, the vertical / horizontal length ratio is selected between about 30: 1 to 1:30, and the size is preferably in the range of 0.5 μm to 100 μm, particularly preferably 0. In the range of 5 μm to 15 μm, the desired scattering property and scattering angle are selected. The shape on the surface of such a portion having a different refractive index can be controlled by the light spreading method of the diffusion film serving as a master. For this reason, the scattering property in the diffusion film can be controlled within a certain range.

  In addition, for light incident from a direction deviated from the tilt direction of a minute region having a different refractive index, the portion having a different refractive index is vertically long, horizontally long, or circular, depending on the shape on the film surface. The spread method is not symmetric about the light that is transmitted without being scattered, and in general, it is an asymmetric spread in which the scattering is strong in the direction of the tilt direction of the regions having different refractive indexes. It becomes a person. Further, the spread of the vertically and horizontally scattered light can be inclined with respect to the long side of the film, and can be designed to be suitable for use in a final display.

  As illustrated in FIG. 5, when coherent parallel light is incident from the diffusion film side of the master diffusion film, the photosensitive material layer, and the transparent support that supports the master diffusion film, the light is diffused by the diffusion film. Diffused and forms a speckle pattern behind it. The speckle pattern is recorded on the photosensitive material by hitting the photosensitive material whose refractive index changes depending on the intensity of irradiated light. As the photosensitive material used here, for example, a photosensitive material as disclosed in Patent Document 10 can be used. In such a photosensitive material, it is considered that a photoradical reaction occurs when exposed to light, and a reactive substance moves to the nucleus of the reaction, thereby causing a layer separation of the substance and forming a refractive index distribution. ing. For this reason, in a rough pattern (a pattern with a low spatial frequency), the substance does not move sufficiently, and thus there is a tendency that a difference in refractive index does not easily occur. Such a tendency is shown in the graph of FIG. On the other hand, a typical spatial frequency of the speckle pattern of the diffusion film is shown in FIG. When such a speckle pattern is recorded on a photosensitive material as shown in FIG. 10, a spatial frequency distribution as shown in FIG. 11 is exhibited.

  When light is incident on a diffusion film having such a spatial frequency, it is scattered most when the slope, spatial frequency, and incident angle of the regions having different refractive indexes are in the black condition. A diffusion film having such diffusibility can be obtained.

  In this specification, the term “scattering” is used to mean that the direction of light emission is bent in a direction different from the incident direction, similar to diffusion. In particular, the term “scattering” is often used conventionally. Is described as scattering, and is technically identical to the term diffusion.

In addition, the diffusion film of the present invention has been described in the present specification with the term film, but it may be a sheet formed on a hard substrate such as a glass substrate or a resin substrate.

The figure which shows an example of the preparation methods of the diffusion film of this invention The figure which shows an example of the preparation methods of the diffusion film of this invention The figure which shows an example of the preparation methods of the diffusion film of this invention The figure which shows an example of a master diffusion film Principle diagram of the manufacturing method of the present invention Sectional drawing of an example of the diffusion film created with the preparation method of this invention Schematic diagram showing an example of the manufacturing method of the present invention The figure which shows an example of the incident angle dependence of the light of the diffusion film of this invention The figure which shows an example of the spatial frequency distribution of the intensity of a speckle pattern The figure which shows an example of the spatial frequency distribution of the refractive index modulation degree of a photosensitive material The figure which shows an example of the spatial frequency distribution of the refractive index modulation degree when a speckle pattern is recorded on the photosensitive material

Explanation of symbols

10 .. Coherent light 11 .. Master diffusion film 12 .. Photosensitive material layer 13 .. Transparent film 14 .. Separate film 40 .. Master diffusion film 41 .. Matte surface 50 .. Coherent light 51 .. Photosensitive material layer 52 .. Photosensitive material layer 53 on which a speckle pattern is formed .. Master diffusion film 54 ..Speckle pattern 55 ..Transparent film

Claims (6)

A film in which a photosensitive material layer is disposed on a transparent support and a master diffusion film having a haze value of 50 to 90 in which a diffusion pattern is formed on an unstretched film are superimposed,
A film in which a photosensitive material layer is disposed on the transparent support and the master diffusion film are laminated and integrated,
At least part of the overlapped portion is scanned with either ultraviolet light or visible laser light, or both ultraviolet light and visible light, in the normal direction of the film surface on which the photosensitive material layer is disposed. By irradiating from an oblique direction,
A method for producing a diffusion film, wherein a diffusion pattern is formed on a photosensitive material layer, and the diffusivity changes depending on the incident direction of light. 2. The film according to claim 1, wherein at least one of a film having a photosensitive material layer disposed on the transparent support and the master diffusion film is unwound from a state in which a long film is wound and overlapped. A method for producing a diffusion film. 3. At least a part of the film on which the photosensitive material layer is disposed and the master diffusion film are conveyed, and at least part of the film is irradiated with ultraviolet rays, visible rays, ultraviolet rays, or visible rays. The manufacturing method of the diffusion film in any one. The method for producing a diffusion film according to any one of claims 1 to 3, wherein the film on which the photosensitive material layer is disposed and the master diffusion film are conveyed at the same speed. The method for producing a diffusion film according to claim 4, wherein the film on which the photosensitive material layer is disposed and the master diffusion film are integrally conveyed. 6. The method for producing a diffusion film according to claim 1, wherein both ultraviolet light, visible light, ultraviolet light, and visible light are parallel light.

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