JP2012181377A - Optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film having properties that linear transmissivity of incident light is different depending on an incident angle, and circular light incident from a central axis is projected in an elliptic shape.SOLUTION: The optical film has a fine structure comprised of high and low levels of refractive index in the inside, and the scattering property of light incident from a central axis of scattering satisfies a relation of 1.5<Fx/Fy<4.5 between a peak width Fx in the value of 1/10 from the maximum value of diffuse transmittance Tx at an emission angle in the plane which an X-axis on the optical film plane parallel to the long axis direction of the elliptic shape, and the central axis of scattering form, and a peak width Fy in the value of 1/10 from the maximum value of diffuse transmittance Ty at an emission angle in a plane which a Y-axis on the optical film plane perpendicular to the X-axis, and the central axis of scattering form.

Description

  The present invention relates to an anisotropic diffusive optical film in which the diffusibility of transmitted light changes according to an incident angle.

  The light diffusing member has not been used for lighting fixtures and building materials for a long time, but is also widely used in recent displays, particularly LCDs. The light diffusion mechanism of these light diffusing members includes scattering due to irregularities formed on the surface (surface scattering), scattering due to the difference in refractive index between the matrix resin and the filler dispersed therein (internal scattering), and surface scattering. And internal scattering. However, these light diffusing members generally have isotropic diffusion performance, and even if the incident angle is slightly changed, the diffusion characteristics of the transmitted light are not greatly different.

(Type A with a plate-like structure)
A light control plate is known that allows incident light in a certain angle region to diffuse strongly and transmits incident light at other angles (commercially available from Sumitomo Chemical under the trade name “Lumisty”. For example, Patent Document 1). This light control plate is cured by irradiating parallel light from above the sheet-like photosensitive composition layer using a linear light source. Then, in the sheet-like substrate, as shown in FIG. 15, a plate shape having a refractive index different from that of the peripheral region coincides with the length direction of the linear light source 51 disposed above the optical film 50 when the optical film 50 is manufactured. It is considered that the structures 40 are formed in parallel to each other (hereinafter referred to as type A for convenience). As shown in FIG. 16, a sample is arranged between a light source (not shown) and the light receiver 3, and the sample passes straight through the sample surface while changing the angle about the straight line L of the sample surface, and enters the light receiver 3. The rate can be measured.

  FIG. 17 shows the incident angle dependence of the scattering characteristics of the optical film 50 of type A shown in FIG. 15 measured using the method shown in FIG. The vertical axis indicates the linear transmittance (an amount of parallel light emitted in the same direction as the incident direction when a predetermined amount of parallel light is incident), which is an index indicating the degree of scattering, and the horizontal axis indicates the incident angle. Indicates. A solid line and a broken line in FIG. 17 indicate cases where the optical film 50 is rotated around the AA axis (through the plate-like structure) and the BB axis (parallel to the plate-like structure) in FIG. . The sign of the incident angle indicates that the direction in which the optical film 50 is rotated is opposite. The solid line in FIG. 17 shows that the linear transmittance remains small both in the front direction and in the oblique direction. This is because the optical film 50 is scattered regardless of the incident angle when rotated about the AA axis. It means a state. In addition, the broken line in FIG. 17 shows that the linear transmittance is small in the direction near 0 °, but this is also true when the optical film is rotated with respect to the light in the front direction when rotated about the BB axis. Means that it is in a scattering state. Furthermore, the linear transmittance increases in the direction where the incident angle is large. This is because when the optical film is rotated around the BB axis, the optical film is in a transmission state with respect to light in an oblique direction. Means. Thanks to this structure, for example, although the transmissivity varies depending on the incident angle in the horizontal direction, the transmissivity does not change even if the incident angle is changed in the vertical direction. Here, the curve indicating the incident angle dependence of the scattering characteristic as shown in FIG. 17 is hereinafter referred to as an “optical profile”. The optical profile does not directly represent the scattering characteristics, but if it is interpreted that the diffuse transmittance is increased due to the decrease of the linear transmittance, the diffusion profile is generally indicated. I can say that.

(Type B with columnar structure)
On the other hand, although the light diffusivity has an incident angle dependency, as shown in FIG. 18, an optical film 60 having a columnar structure 62 extending in the film thickness direction (the normal direction P of the film) (hereinafter referred to as convenience). Type B) is also proposed (for example, Patent Document 2). This columnar structure is formed in the photosensitive composition layer in parallel with the traveling direction of the light by irradiating UV light parallel to the photosensitive composition layer. FIG. 19 shows an optical profile showing the change in linear transmittance when the incident angle is changed in this type B optical film. When AA is the rotation center axis, BB is the rotation center axis, and the linear transmittance is measured by changing the incident angle, the same optical profile is obtained in any case. It is done. That is, the optical film of FIG. 18 shows substantially the same linear transmittance even when the rotation center axis is changed, and is ± 5 to 10 ° compared to the transmittance when incident in the normal direction (0 °). The linear transmittance once reaches a minimum value at the incident angle, and the linear transmittance increases as the incident angle increases. The linear transmittance reaches the maximum value at an incident angle of ± 45 to 60 °.

  If these types A and B are described in more detail, in the case of an optical film in which a fine structure having a refractive index is present inside and the linear transmittance of incident light that is transmitted differs depending on the incident angle, the optical film Properties are defined by the type of internal structure and the inclination of the structure. For example, in the case of an optical film in which a fine structure having a different refractive index is formed in a plate-like structure as in the type A, the optical characteristics are defined by the inclination of the plate-like structure with respect to the film normal. On the other hand, in the case of an optical film having a columnar structure extending in the thickness (normal) direction of the film as in the type B, the optical characteristics are defined by the inclination of the columnar structure with respect to the film normal. In the case of a type A optical film, incident light from a direction substantially parallel to the plate-like structure is strongly diffused, and incident light passing through the plate-like structure is transmitted without being diffused. It can be said to be a light scattering surface. On the other hand, in the case of the type B optical film, the columnar structure is formed in parallel to the light traveling direction when the photosensitive composition layer is irradiated with parallel UV light. When the layer is irradiated with parallel UV light from its normal direction, the columnar structure extends in the normal direction. In such a case, (irradiation direction of UV light = extending direction of the columnar structure = normal direction), and as shown in FIG. 19, the relationship between the incident angle of light and the linear transmittance in any incident plane. Is symmetric about the normal, so this normal can be called the scattering central axis. Hereinafter, the scattering center axis will be described in more detail with reference to the drawings.

  FIG. 20 is a schematic cross-sectional view of the microstructure of a type B optical film. A fine columnar structure extends in the normal direction of the sheet. Here, the halftone dot region and the white region indicate high and low refractive indexes. The light diffusibility of this optical film can be easily examined by the method shown in FIG. That is, when an optical film is fixed in parallel above a white paper at a certain interval, and a strong parallel beam such as a laser pointer is incident from above with a specific area of the optical film as an incident point, the diffusion state of transmitted light Is projected on white paper. Here, incident light from the normal direction is projected as a circular diffused light on white paper, while incident light from an oblique direction is projected in a crescent shape at a position away from the previous circular diffused light. Appears as light. FIG. 22 shows the shape of the diffused light projected on the white paper when the incident light is tilted and its orientation is changed. When the incident light is tilted little by little from the normal direction, the tilt angle becomes deeper. It can be seen that when the crescent shape becomes thin and the incident direction is changed at the same tilt angle, the crescent moon direction changes continuously even if the shape is the same. When the projected light shows a circular shape on white paper, the straight line connecting the center of the circle and the incident point on the optical film is the scattering center axis. In this case, this is the normal line. Will be.

  On the other hand, when the extending direction of the columnar structure of type B is inclined from the normal direction, the scattering center axis does not coincide with the normal direction. Such a tilted columnar structure is formed by irradiating the photosensitive composition layer with UV light obliquely. The incident direction of the UV light and the UV light passing through the photosensitive composition layer are formed. The extension direction of the columnar structure formed in parallel with the direction does not necessarily coincide with Snell's law. Further, depending on the temperature condition of the photosensitive composition layer during UV light irradiation, disturbance may occur in the extending direction of the columnar structure. In such a case, the scattering center axis is the method shown in FIG. Can be obtained. For example, when a diffusion pattern as shown in FIG. 23 is obtained, the straight line connecting the center of the substantially circular projection light and the incident point on the optical film at that time is the scattering center axis. In addition, when the region where the circular light is formed cannot be discriminated, when the light incident at an angle away from the scattering central axis diffuses in a crescent shape, a straight line that bisects the crescent shape as shown in FIG. Since there is a scattering center axis on the extended line, the position of the scattering center axis can be obtained from two crescents apart from each other. That is, the straight line connecting the intersection of two straight lines in FIG. 24 and the incident point on the optical film at that time becomes the scattering central axis.

When a type A plate-shaped optical film is similarly measured by the method of FIG. 21, it is as shown in FIG. 25 or FIG. FIG. 25 shows a case where the plate-like structure is formed in a direction including the normal line of the film. Here, the diffused light has an elliptical shape elongated in the X-axis direction on the Y-axis, and has a point-like shape that hardly spreads at other incident angles. Here, the plate-like structure stands perpendicular to the X axis and extends in the Y axis direction. FIG. 26 shows a case where the plate-like structure is formed tilted from the normal direction of the film. Although visible elongated spreading oval Again, the oval appear along the Y ₁ axis inclined to the X-axis direction from the normal direction is changed to extend the ellipse the angles of the Y ₁ is changed . In this case, the plate-like structure extends along the direction connecting the Y ₁ axis and the incident point of the optical film.

  The type A optical film having a plate-like structure has a track record as, for example, a construction material for preventing peeping, and is sometimes used for the purpose of widening the viewing angle and improving the visibility in a liquid crystal panel. On the other hand, a type B optical film having a columnar structure can also be used for a liquid crystal panel, and has been proposed for application to a projector screen. When an anisotropic diffusion film is used for a liquid crystal panel, a type suitable for a target viewing angle is selected depending on the application. However, in actuality, in type A, the viewing angle is expanded only in a certain azimuth angle direction, and the viewing angle is hardly expanded in the azimuth angle direction orthogonal thereto.

Japanese Patent No. 2547417 Japanese Patent Laid-Open No. 2007-114756

  In the case of Type A, the change in diffusibility when the incident angle of light is changed is very steep, so when this is applied to a panel, it appears as a rapid change in visibility, giving an unnatural feeling. There was a thing. On the other hand, with Type B, although the viewing angle expands almost equally in all directions, it does not meet the demand for further expanding the viewing angle in a certain direction (for example, the horizontal direction). Will drop. In order to improve these problems, it has been proposed to use in combination with other diffusion films, but due to cost requirements and simplification of the manufacturing process, the optical properties between these optical films are one. There was a need to have Therefore, an object of the present invention is to provide an optical film having both the properties of the type A and the type B based on the above prior art.

The present invention (1) is an optical film in which a fine structure having a high and low refractive index exists inside, and the linear transmittance of incident light passing therethrough varies depending on the incident angle,
Circular light incident from the scattering center axis has the property of being projected in an elliptical shape with respect to a plane parallel to the optical film,
The scattering characteristics of light incident from the scattering center axis are
The relationship Tx between the exit angle in the plane formed by the X axis on the optical film plane that is parallel to the major axis direction of the ellipse and the scattering center axis and the diffuse transmittance at the exit angle; and
The relationship Ty between the exit angle in the plane formed by the Y axis on the optical film plane perpendicular to the X axis and the scattering center axis and the diffuse transmittance at the exit angle is:
The peak width F _{max1 / 10} x at a value one-tenth from the maximum value of the diffuse transmittance peak in the relationship Tx, and the value one-tenth from the maximum value of the diffuse transmittance peak in the relationship Ty. And the peak width F _{max1 / 10} y satisfies the relationship of the following formula (1).
1.5 <F _{max 1/10} x / F _{max 1/10} y <4.5 (1)

In the present invention (2), the relationship between the incident angle of light and the linear transmittance in the plane formed by the X axis and the scattering central axis is
The maximum value F _A (%) of the linear transmittance and the angle A (°) that takes the maximum value, and the minimum value F _B (%) of the linear transmittance and the angle B (°) that takes the minimum value are as follows: It is an optical film of the said invention (1) characterized by satisfy | filling the relationship of (2) Formula.
_{0.70 <(F A -F B)} / | A-B | <2.0 ··· (2)

  In the present invention (3), the fine film has a fine cross section parallel to a plane formed by the X axis and the scattering center axis of the optical film and a cross section parallel to a plane formed by the Y axis and the scattering center axis of the optical film. The optical film according to the invention (1) or (2), wherein a structure appears.

  In the present invention (4), the density of the fine structure in the cross section parallel to the X axis-scattering central axis plane of the optical film is greater than the density of the fine structure in the cross section parallel to the Y axis-scattering central axis plane. The optical film according to the invention (3) is characterized by being high.

  According to the present invention (1), since the optical film of the present invention has a fine structure having a high and low refractive index inside, the linear transmittance of incident light that is transmitted can be made different depending on the incident angle. Further, the circular light incident from the scattering center axis is projected in an elliptical shape with respect to a plane parallel to the optical film. Light is diffused strongly in the major axis direction of the ellipse, and light is diffused weakly in the minor axis direction orthogonal to the major axis. Furthermore, it has the characteristics of both the type A plate-like structure and the type B columnar structure, and gives characteristics that could not be achieved by using two or more different anisotropic conversion films. Specifically, the light use efficiency can be substantially increased by preferentially diffusing light in a necessary direction.

  According to the present invention (2), the change in diffusivity when the incident angle of light is changed is gentle compared to the type A known so far, so that when this is applied to a panel, the visibility changes drastically. This makes it possible to give the observer a more natural impression.

  According to the present invention (3), the circular light incident from the scattering center axis is elliptical with respect to a plane parallel to the optical film, and the plane formed by the X axis and the scattering center axis, and the Y axis and the scattering center axis. Since a fine structure is formed on the plane formed by, scattering in the X-axis direction and scattering in the Y-axis direction can be performed simultaneously and the degree of diffusion in the X-axis direction and the Y-axis direction It is possible to have different properties in terms of the degree of diffusion.

  According to the present invention (4), since the density of the fine structure varies depending on the X-axis direction and the Y-axis direction, the diffusion of light can be made different depending on the direction in which the light is applied.

The conceptual diagram of the optical profile which the optical film of this invention has is represented. The conceptual diagram of the optical profile which the optical film of this invention has is represented. The conceptual diagram of the property which the optical film of this invention has is represented. This represents how to determine the scattering center axis of the optical film of the present invention. This represents how to determine the scattering center axis of the optical film of the present invention. A schematic diagram of a gonio-offset measurement experiment is shown. It represents the anisotropic diffusibility of the optical film of the present invention. The cross-sectional photograph of the optical film of this invention manufactured by irradiating UV light to the normal line direction of a film surface is represented. The cross-sectional photograph of the optical film of this invention manufactured by irradiating UV light from the direction inclined 10 degrees from the normal line direction of the film surface is represented. The cross-sectional photograph of the optical film of this invention manufactured by irradiating UV light from the direction inclined 45 degrees from the normal line direction of the film surface is represented. The schematic diagram of the one aspect | mode of manufacture of the optical film of this invention is represented. The schematic diagram of the one aspect | mode of manufacture of the optical film of this invention is represented. The measurement result of the optical profile (linear transmittance | permeability) regarding the optical film of the Example of this invention and a comparative example is represented. The measurement result of the anisotropic diffusivity (diffuse transmittance | permeability) regarding the optical film of the Example of this invention and a comparative example is represented. The schematic diagram of the optical film (having a plate-like structure) of type A of the prior art is represented. The measurement method of an optical profile is shown. 1 represents an optical profile of a prior art type A optical film. The schematic diagram of the optical film (having a columnar structure) of type B of the prior art is represented. 1 represents the optical profile of a prior art type B optical film. The schematic diagram of the cross section of the optical film of the type B of a prior art is represented. 1 represents a method for detecting a scattering center axis. The state of diffusion of a conventional type B optical film is shown (when UV irradiation is performed from the normal direction). The state of diffusion of a conventional type B optical film is shown (when UV irradiation is performed from an oblique direction). 1 represents a method for detecting a scattering center axis. The state of diffusion of a conventional type A optical film is shown (when UV irradiation is performed from the normal direction). The state of diffusion of a conventional type A optical film is shown (when UV irradiation is performed from an oblique direction).

  Here, the definitions of each term in the claims and the specification will be described.

  “A fine structure composed of high and low refractive indices” means a structure formed by a local difference in refractive index of the material constituting the optical film. For example, FIG. 8 shows an optical film according to Example 3. As shown in FIG. 8, the fine structure is a structure having a pattern that is optically observed in a cross section. These structures are formed when the material forming the optical film is cured. For example, it is presumed that the structures are formed by making a difference in density.

  The “scattering central axis” means a direction in which the scattering characteristic coincides with the incident angle of light having substantially objectivity with the incident angle as a boundary when the incident angle is changed. Here, the reason why it has a substantially target property is that, when the scattering center axis has an inclination with respect to the normal direction of the film surface, optical properties and the like to be described later do not have the target property strictly. . As will be described later, the scattering center axis can be found by observing the projection shape of circular light through the optical film while changing the incident angle. Hereinafter, the scattering center axis will be described. The spatial positioning of the scattering center axis has been described above with reference to FIGS. 21 to 26. If the azimuth direction of the inclination of the scattering center axis obtained by this is known, a plane formed by this and the normal line is formed. If the optical profile is measured, the accurate inclination angle of the scattering center axis can be obtained. In this optical profile, the scattering center axis can be expressed by an incident angle having a maximum value sandwiched between two minimum values. 1 and 2 are diagrams conceptually showing various optical profiles and scattering central axes. First, FIG. 1 shows an optical film (W type) which is an optical film produced by irradiating UV light in the normal direction of the film, and whose overall shape is substantially symmetrical. A thick vertical line that coincides with 0 degree is an incident angle that coincides with the scattering central axis in this case. FIG. 2 shows an optical film (W-type) that is an optical film produced by irradiating UV light from a direction different from the normal direction of the film, and whose overall shape is not a right and left object. Again, the thick vertical line passing through the maximum value Fc sandwiched between the two minimum values is the incident angle coincident with the scattering center axis in this case. As described above, in any case, the scattering central axis is determined by specifying the center of the valley region after first paying attention to a large valley region that is substantially symmetrical. Here, in the case of FIG.1 and FIG.2, the said trough area | region contains a minimum value on either side, and includes a maximum value between these minimum values. The position of this maximum value becomes the scattering center axis. When the optical profile is not a W type having a maximum value sandwiched between two minimum values but a U type in which a maximum is not seen in a large valley region, it is approximately equidistant from the inclined surfaces of the valleys on both sides. Thus, the vicinity of the center of the flat part of the valley bottom can be defined as the scattering center axis. Further, when the optical profile is V-shaped, the deepest portion at the center of the valley can be defined as the scattering center axis.

The linear transmittance relates to the linear transmittance of light incident on the optical film, and is the ratio between the amount of transmitted light in the linear direction and the amount of incident light when incident from a certain incident angle. Is done.
Linear transmittance (%) = (Linear transmitted light amount / incident light amount) × 100

  The present invention is an optical film in which a fine structure having a high and low refractive index exists inside, and the linear transmittance of incident light that is transmitted differs depending on the incident angle. That is, it is an optical film having anisotropic diffusibility. The optical film of the present invention provides properties that are intermediate between those provided by the type A plate-like structure and the type B columnar structure. Hereinafter, the content of this invention is demonstrated using a 1st form and a 2nd form.

(First form)
In the first embodiment, the content of the present invention will be described by taking the case where the scattering center axis is parallel to the normal direction of the optical film as an example. FIG. 3 is a conceptual diagram for explaining optical characteristics of the optical film according to the present invention. In FIG. 3, 1 is the optical film of the present invention, and 2 is a plane parallel to the optical film. As shown in FIG. 3, the optical film according to the present invention has the property that circular light incident on the position P from the scattering center axis is projected in an elliptical shape on a plane 2 parallel to the optical film. . Here, the circular light means light whose vertical cross section has a circular shape. Although it does not specifically limit as circular light, For example, lasers, such as a laser pointer, are mentioned.

  The elliptical light projected on the parallel plane 2 has a major axis A-A 'and a minor axis B-B'. The elliptical shape spreads in the major axis AA ′ direction when circular light is diffused and transmitted in the X-axis direction, and spreads in the minor axis BB ′ direction when circular light is diffused in the Y-axis direction. The projected shape. That is, being projected in an elliptical shape means that the degree of diffusion in the X-axis direction and the Y-axis direction of the optical film is different. As described above, not only has the difference in diffusibility depending on the direction, but also in the present invention, constant light diffusion can be observed in the direction of the short axis B-B '.

  FIG. 4 shows the scattering characteristics when the scattering center axis is in the normal direction as in the optical film of this embodiment. That is, FIG. 4 is a diagram showing the shape of the light that is transmitted through the point P in FIG. 3 and projected onto the plane 2 when the incident angle is changed. Since the optical film of the present invention aims at an optical characteristic intermediate between the plate-like structure and the rod-like structure, it has the scattering center axis described in the rod-like structure. As shown in FIG. 4, the central diffusion shape is elliptical. Thus, the incident angle forming the central diffusion shape coincides with the scattering central axis. However, it is rounder than the ellipse shown in FIG. 25, and the diffused shape of the oblique incident light is also an intermediate shape between the crescent shape of FIG. 22 and the ellipse shape of FIG. As described above, the scattering center axis of the optical film can be found only by using a simple device such as a laser pointer even if the irradiation direction of the UV light in manufacturing is not known. If it is difficult to find the scattering center axis, the method shown in FIG. 24 is applied, and the scattering center axis is on the extension of the straight line that bisects the crescent moon shape. The position can be determined.

In the present invention, a particularly remarkable feature appears in the scattering characteristics of light incident from the scattering center axis.
The relationship between the peak widths of the relationship Tx indicating the scattering characteristics in the X-axis direction and the relationship Ty indicating the scattering characteristics in the Y-axis direction satisfies a predetermined relationship. That is, the peak width F _{max1 / 10} x at a value one-tenth from the maximum value of the diffuse transmittance peak in the relationship Tx, and one-tenth from the maximum value of the linear transmittance peak in the relationship Ty. And the peak width F _{max1 / 10} y satisfy the relationship of the following formula (1).
1.5 <F _{max 1/10} x / F _{max 1/10} y <4.5 (1)

The peak width F _{max1 / 10} reflects the scattering characteristics of the optical film. When the ratio of the peak widths falls within such a range, the difference in scattering characteristics between the X-axis direction and the Y-axis direction is appropriately adjusted.

Here, the relationship Tx is a relationship between the emission angle in the plane formed by the X axis on the optical film plane and the scattering center axis, and the diffuse transmittance at the emission angle.
On the other hand, the relationship Ty is a relationship between the exit angle in the plane formed by the Y axis on the optical film plane and the scattering center axis, and the diffuse transmittance at the exit angle.

In the present invention, it is more preferable to satisfy the following characteristics.
2.0 <F _{max 1/10} x / F _{max 1/10} y <3.0

  The scattering characteristics of the optical film of the present invention are evaluated by the method shown in FIG. 6 using a goniophotometer. The optical film of the present invention is irradiated with light, and the transmittance of light emitted from the film is measured. The measurement is performed by rotating the light receiver around the light source in the X direction (up and down direction on the paper surface) and in the Y direction (front to back of the paper surface).

FIG. 7 shows the scattering characteristics of the optical film of Example 2 described later. In FIG. 7, the horizontal axis represents the angle of the detector with respect to the optical film, and the vertical axis represents the transmittance defined below.
Diffuse transmittance = (detected light amount of detector / detected light amount when a detector is disposed in front of the light source without an optical film) × 100

In FIG. 7, the outgoing angle in the plane formed by the X axis and the scattering central axis, the diffuse transmittance at the outgoing angle, and the relationship T _x are indicated by broken lines (X axis direction), and the Y axis and the scattering central axis are formed. the relationship T _Y and diffuse transmittance at the emission angle and the emission angle in a plane shown by the solid line (Y-axis direction). F _{max1 / 10} x is a peak width at a value (X axis max1 / 10) of 1/10 from the maximum value (X axis max) of the diffuse transmittance peak of the relationship Tx. On the other hand, F _{max1 / 10} Y is a peak width at a value (Y axis max1 / 10) of 1/10 from the maximum value (Y axis max) of the diffuse transmittance peak of the relationship Ty.

Furthermore, in the optical film of the present invention, the relationship between the incident angle of light and the linear transmittance (%) in the plane formed by the X axis and the scattering center axis is the maximum value of linear transmittance F _A (% ) And the angle A (°) that takes the maximum value, the minimum value F _B (%) of the linear transmittance, and the angle B (°) that takes the minimum value satisfy the relationship of the following formula (2): Is preferred.
_{0.70 <(F A -F B)} / | A-B | <2.0 ··· (2)

  By satisfying such characteristics, the angle dependency of the linear transmittance becomes moderate. For example, when used in a display, the problem that the image quality changes suddenly depending on the angle can be solved.

In the present invention, it is more preferable to satisfy the following characteristics.
0.90 <(F _A -F _B ) / | A-B | <1.7

Here, the angles A and B mean angles with respect to the normal line of the optical film. With respect to this relationship, returning to FIG. 1, the relationship (optical profile) between the incident angle of light and the linear transmittance in the optical film of the present invention will be described in detail. The optical profile of the optical film of the present invention forms a substantially symmetrical curve about the scattering center axis. The curve has three maximum values and two minimum values. That is, when the linearly transmitted light is measured while changing the incident angle, there are local minimum values F _B1 and F _{B2 at} two locations (note that the incident angle at which the minimum value F _B1 is reached is B ₁ and the incident value at which the minimum value F _B2 is at minimum) the angle and _{B 2.).} A relatively small maximum value Fc exists at a position between the minimum values. The incident angle at the maximum corresponds to the scattering center axis. The local maximum value F _A1 and the local maximum value F _A2 exist on both sides of the local maximum value Fc with the local minimum values F _B1 and F _B2 being sandwiched between them (the incident angle at which the local maximum value F _A1 is reached is A ₁ and the local maximum value F _A2 is obtained). the incident angle and _{a 2.).}

The relationship in equation (2) is that two types of local maximum values (F _A1 and F _A2 ) and local minimum values (F _B1 and F _B2 ) are: _{Let A} and A, F _B and B.
(A) (F _A1 -F _B1 ) / | A ₁ -B ₁ |
(B) (F _A2 -F _B2 ) / | A ₂ -B ₂ |
That is, in the optical profile, the side where the gradient from the minimum value to the maximum value is large is used. Under this condition, the optical film of the present invention satisfies the relationship of the above formula (2). The optical profile measurement method is as described in the background art and FIG.

  FIG. 8 is a cross-sectional photograph of the optical film of the present invention. 8A is a cross-sectional photograph in a direction parallel to the X axis-scattering central axis plane, and FIG. 8B is a cross-sectional photograph in a direction parallel to the Y axis-scattering central axis plane. As shown in FIG. 8, in the X-axis direction cross section, a fine structure having a high and low refractive index in μm units appears in a vertically long striped pattern. On the other hand, what appears to be a fine structure appears in the cross section in the Y-axis direction perpendicular thereto, but the structure may not be confirmed. As is clear from this photograph, the density of the fine structure in the cross section parallel to the X axis-scattering central axis plane of the optical film of the present invention and the fine structure in the cross section parallel to the Y axis-scattering central axis plane are shown. When compared with the density, the former is higher than the latter. That is, the optical film of the present invention diffuses light strongly because a fine structure is densely present in one direction, while the fine structure is sparsely diffused in a direction perpendicular to it, and diffuses light weakly. I think that.

(Second form)
The second embodiment according to the present invention is an optical film having an inclination in which the scattering center axis does not coincide with the normal direction of the optical film. FIG. 5 shows the scattering characteristics when the scattering central axis is inclined in the Y-axis direction. FIG. 5 shows light that passes through the point P in FIG. 3 and changes the plane when the incident angle is changed. It is the figure which showed the shape of the light projected on 2. FIG. This also shows an intermediate property between FIG. 22 and FIG. In any case, the diffusion shape when the incident angle is changed and the light is incident is a circular to elliptical shape with a high symmetry, and the incident angle that becomes the scattered light having the central elliptical shape is It coincides with the scattering center axis.

  Even in the second embodiment, although the scattering center axis is different from the normal direction of the optical film, the same scattering characteristics and optical profile as in the first embodiment are shown.

  FIG. 9 is a cross-sectional photograph of an optical film produced by irradiating with UV light inclined by 10 ° from the normal direction of the film surface. In this case as well, a fine structure having a high and low refractive index in the stripe pattern is formed in the X-axis direction (FIG. 9A), but in the Y-axis direction (FIG. 9B) perpendicular thereto. Almost no microstructure is confirmed.

  FIG. 10 is a cross-sectional photograph of an optical film produced by irradiating UV light inclined at 45 ° from the normal direction of the film surface. Also in this case, a fine structure consisting of high and low refractive index of the stripe pattern is formed in the X-axis direction (FIG. 10B), but in the Y-axis direction (FIG. 10A) orthogonal thereto. Although a fine structure can be confirmed, it becomes a thin stripe pattern as compared with the X-axis direction.

Method for Producing Optical Film The optical film of the present invention can be produced by subjecting a specific photocurable resin layer to UV irradiation under special conditions. Hereinafter, the raw material of the optical film will be described first, and then the manufacturing process will be described.

Raw material for optical film (photo-curable compound)
The photocurable compound, which is a material for forming the optical film of the present invention, is composed of a photopolymerizable compound selected from polymers, oligomers, and monomers having a radical polymerizable or cationic polymerizable functional group and a photoinitiator. It is a material that polymerizes and solidifies when irradiated with ultraviolet rays and / or visible rays.

  The radically polymerizable compound mainly contains one or more unsaturated double bonds in the molecule, and specifically includes epoxy acrylate, urethane acrylate, polyester acrylate, polyether acrylate, polybutadiene acrylate, silicone acrylate, and the like. An acrylic oligomer called by name, 2-ethylhexyl acrylate, isoamyl acrylate, butoxyethyl acrylate, ethoxydiethylene glycol acrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, isonorbornyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-acryloyloxyphthalic acid, dicyclopentenyl acrylate, triethylene glycol diacrylate, Opentyl glycol diacrylate, 1,6-hexanediol diacrylate, EO adduct diacrylate of bisphenol A, trimethylolpropane triacrylate, EO modified trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, ditrimethylol Examples thereof include acrylate monomers such as propanetetraacrylate and dipentaerythritol hexaacrylate. In addition, these compounds may be used alone or in combination. Similarly, although methacrylate can be used, acrylate is generally preferable to methacrylate because it has a higher photopolymerization rate.

  As the cationically polymerizable compound, a compound having at least one epoxy group, vinyl ether group or oxetane group in the molecule can be used. The compounds having an epoxy group include 2-ethylhexyl diglycol glycidyl ether, glycidyl ether of biphenyl, bisphenol A, hydrogenated bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetrachloro Diglycidyl ethers of bisphenols such as bisphenol A and tetrabromobisphenol A, polyglycidyl ethers of novolac resins such as phenol novolak, cresol novolak, brominated phenol novolak, orthocresol novolak, ethylene glycol, polyethylene glycol, polypropylene glycol, Butanediol, 1,6-hexanediol, neopentyl glycol, trimethyl Diglycidyl ethers of alkylene glycols such as propane adduct of 1,4-cyclohexanedimethanol, bisphenol A, PO adduct of bisphenol A, glycidyl ester of hexahydrophthalic acid, diglycidyl ester of dimer acid, etc. Examples thereof include glycidyl esters.

  Further, 3,4-epoxycyclohexylmethyl-3 ′, 4′-epoxycyclohexanecarboxylate, 2- (3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy) cyclohexane-meta-dioxane, di (3,4-epoxycyclohexylmethyl) adipate, di (3,4-epoxy-6-methylcyclohexylmethyl) adipate, 3,4-epoxy-6-methylcyclohexyl-3 ′, 4′-epoxy-6′-methyl Cyclohexanecarboxylate, methylenebis (3,4-epoxycyclohexane), dicyclopentadiene diepoxide, di (3,4-epoxycyclohexylmethyl) ether of ethylene glycol, ethylenebis (3,4-epoxycyclohexanecarboxylate), lactone modification 3, -Epoxycyclohexylmethyl-3 ', 4'-epoxycyclohexanecarboxylate, tetra (3,4-epoxycyclohexylmethyl) butanetetracarboxylate, di (3,4-epoxycyclohexylmethyl) -4,5-epoxytetrahydrophthalate, etc. Although the alicyclic epoxy compound of these is also mentioned, it is not limited to these.

  Examples of the compound having a vinyl ether group include diethylene glycol divinyl ether, triethylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, hydroxybutyl vinyl ether, ethyl vinyl ether, dodecyl vinyl ether, and trimethylolpropane trivinyl ether. , Propenyl ether propylene carbonate and the like, but are not limited thereto. Vinyl ether compounds are generally cationically polymerizable, but radical polymerization is also possible by combining with acrylates.

  As the compound having an oxetane group, 1,4-bis [(3-ethyl-3-oxetanylmethoxy) methyl] benzene, 3-ethyl-3- (hydroxymethyl) -oxetane and the like can be used.

The above cationic polymerizable compounds may be used alone or in combination. The photopolymerizable compound is not limited to the above. In order to cause a sufficient difference in refractive index, fluorine atoms (F) may be introduced into the photopolymerizable compound in order to reduce the refractive index, and in order to increase the refractive index, Sulfur atoms (S), bromine atoms (Br), and various metal atoms may be introduced. Further, as disclosed in JP 2005-514487, on the surface of ultrafine particles made of a metal oxide having a high refractive index such as titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), tin oxide (SnOx), It is also effective to add functional ultrafine particles into which a photopolymerizable functional group such as an acryl group, a methacryl group, or an epoxy group is introduced to the above-described photopolymerizable compound.

Raw material for optical film (photoinitiator)
Photoinitiators that can polymerize radically polymerizable compounds include benzophenone, benzyl, Michler's ketone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2- Diethoxyacetophenone, benzyldimethyl ketal, 2,2-dimethoxy-1,2-diphenylethane-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2 -Methyl-1- [4- (methylthio) phenyl] -2-morpholinopropanone-1, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propane-1 -One, bis (cyclo Ntadienyl) -bis (2,6-difluoro-3- (pyr-1-yl) titanium, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1,2,4,6 -Trimethyl benzoyl diphenyl phosphine oxide etc. Moreover, these compounds may be used individually or may be used in mixture of two or more.

The photoinitiator of a cationic polymerizable compound is a compound that generates an acid by light irradiation and can polymerize the above-mentioned cationic polymerizable compound with the generated acid. Generally, an onium salt or a metallocene complex is used. Preferably used. As the onium salt, a diazonium salt, a sulfonium salt, an iodonium salt, a phosphonium salt, a selenium salt, or the like is used, and these counter ions include anions such as BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ^{− and the} like. Used. Specific examples include 4-chlorobenzenediazonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium hexafluorophosphate, (4-phenylthiophenyl) diphenylsulfonium hexafluoroantimonate, (4-phenylthiophenyl) diphenyl. Sulfonium hexafluorophosphate, bis [4- (diphenylsulfonio) phenyl] sulfide-bis-hexafluoroantimonate, bis [4- (diphenylsulfonio) phenyl] sulfide-bis-hexafluorophosphate, (4-methoxyphenyl) Diphenylsulfonium hexafluoroantimonate, (4-methoxyphenyl) phenyliodonium hexafluoroantimonate Bis (4-t-butylphenyl) iodonium hexafluorophosphate, benzyltriphenylphosphonium hexafluoroantimonate, triphenyl selenium hexafluorophosphate, (η5-isopropylbenzene) (η5-cyclopentadienyl) iron (II) hexa Although fluorophosphate etc. are mentioned, it is not limited to these. In addition, these compounds may be used alone or in combination.

Optical film raw materials (mixing amount, other optional components)
In this invention, the said photoinitiator is 0.01-10 weight part with respect to 100 weight part of photopolymerizable compounds, Preferably it is 0.1-7 weight part, More preferably, it is about 0.1-5 weight part. Blended. This is because when less than 0.01 parts by weight, the photo-curing property is lowered, and when blending more than 10 parts by weight, only the surface is cured and the internal curability is lowered, coloring, columnar structure This is because it inhibits the formation of. These photoinitiators are usually used by directly dissolving powder in a photopolymerizable compound, but if the solubility is poor, a photoinitiator dissolved beforehand in a very small amount of solvent at a high concentration is used. It can also be used. Such a solvent is more preferably photopolymerizable, and specific examples thereof include propylene carbonate and γ-butyrolactone. It is also possible to add various known dyes and sensitizers in order to improve the photopolymerizability. Further, a thermosetting initiator capable of curing the photopolymerizable compound by heating can be used in combination with the photoinitiator. In this case, by heating after photocuring, it can be expected to further accelerate the polymerization and curing of the photopolymerizable compound to complete it.

  In the present invention, the anisotropic diffusion layer can be formed by curing the above-described photo-curable compound alone or by mixing a plurality of the mixed compositions. The anisotropic diffusion layer of the present invention can also be formed by curing a mixture of a photocurable compound and a polymer resin that does not have photocurability. Polymer resins that can be used here include acrylic resin, styrene resin, styrene-acrylic copolymer, polyurethane resin, polyester resin, epoxy resin, cellulose resin, vinyl acetate resin, vinyl chloride-vinyl acetate copolymer, polyvinyl Examples include butyral resin. These polymer resins and photo-curable compounds must have sufficient compatibility before photo-curing, but various organic solvents, plasticizers, etc. are used to ensure this compatibility. It is also possible. In addition, when using an acrylate as a photocurable compound, it is preferable from a compatible point to select as a polymer resin from an acrylic resin.

[process]
Next, the manufacturing method (process) of the optical film of this invention is demonstrated. The above-mentioned photocurable composition is applied onto a suitable substrate such as a transparent PET film to provide a coating film (photocurable resin layer). Although it dries as needed and a solvent is volatilized, the dry film thickness is 10-200 micrometers, More preferably, it is 20-100 micrometers, More preferably, it is 25-50 micrometers. When the dry film thickness is less than 10 μm, the light diffusibility obtained through the UV irradiation process described later is poor, which is not preferable. On the other hand, when the dry film thickness exceeds 200 μm, the overall diffusibility is too strong and it becomes difficult to obtain the characteristic anisotropy of the present invention, and it is not preferable because it is not suitable for thinning applications. . Further, a release film and a mask to be described later are laminated on this coating film to form a photosensitive laminate.

(Method of providing a composition containing a photocurable compound in a sheet form on a substrate)
Here, as a method of providing a composition containing a photocurable compound in a sheet form on a substrate, a normal coating method or printing method is applied. Specifically, air doctor coating, bar coating, blade coating, knife coating, reverse coating, transfer roll coating, gravure roll coating, kiss coating, cast coating, spray coating, slot orifice coating, calendar coating, dam coating, dip coating Coating such as die coating, intaglio printing such as gravure printing, printing such as stencil printing such as screen printing, and the like can be used. When the composition has a low viscosity, a weir having a certain height can be provided around the substrate, and the composition can be cast in the area surrounded by the weir.

(Stacking of masks)
In order to efficiently form the fine structure that is a feature of the optical film of the present invention, it is also possible to stack a mask that closely contacts the light irradiation side of the photocurable composition layer and locally changes the light irradiation intensity. It is. As a mask material, a light-absorbing filler such as carbon is dispersed in a polymer matrix, and a part of incident light is absorbed by carbon, but the opening has a structure that allows light to pass sufficiently. Those are preferred. Also, simply laminating a normal transparent film on the photocurable composition layer is effective in preventing oxygen damage and promoting the formation of columnar bodies.

(light source)
As a light source for irradiating a composition containing a photocurable compound, a short arc ultraviolet light source is usually used, and specifically, a high pressure mercury lamp, a low pressure mercury lamp, a metahalide lamp, a xenon lamp or the like is used. Is possible. The light beam applied to the composition containing the photocurable compound needs to include a wavelength capable of curing the photocurable compound, and light of a wavelength centering around 365 nm of a mercury lamp is usually used.

  In order to make the parallel light beam 12 from the light from the UV light of the short arc described above, for example, a reflecting mirror is arranged behind the light source so that the light is emitted as a point light source in a predetermined direction, and the light is further emitted. Parallel light can be obtained by the Fresnel lens. A Fresnel lens is a lens in which a normal lens is divided into concentric regions to reduce the thickness, and has a saw-like cross section. When the light beam emitted from the point light source passes through the Fresnel lens, the directions of the light beams having different directions are unified in one direction to become parallel light beams. However, in order to obtain the parallel UV emission light necessary for producing the optical film of the present invention, a Fresnel lens is not necessarily required, and various methods including a laser can be used.

(1) Irradiation of UV rays along the normal line In order to produce the optical film of the present invention, the above-mentioned photosensitive laminate is irradiated with UV rays from the release film or mask side from the normal direction. However, it is important to simultaneously irradiate not only the above-described parallel rays but also diffuse rays diffused in one direction together with the parallel rays. In order to irradiate such a light beam, for example, a lenticular lens can be used. When the UV parallel light beam passes through the lenticular, the light beam (diffused light beam diffused in one direction with the parallel light beam) can be formed. The lenticular in this case may be a light beam of only a diffuse light source diffused in one direction (parallel light beams may be mixed somewhat). An exposure mask can be combined with the lenticular lens. The lenticular lens is a lens having a convex surface in which a plurality of semicylindrical or arc-shaped elongated convex portions are arranged in parallel, and the opposite side of the convex surface is a flat surface (hereinafter referred to as `` lenticular lens ''). For convenience, the above-mentioned “semi-cylindrical or arcuate elongated protrusions” are referred to as “kamaboko”).

  Here, in the example using the lenticular lens, the meaning of “simultaneously irradiating both the parallel light beam and the diffused light beam diffused in one direction” is a fan-like shape that requires a convex portion of the lenticular lined up in parallel. It is understood that the light rays spread in the horizontal direction (diffused in a plane fan shape) are arranged in parallel in the vertical direction (parallel as the diffusion plane).

  FIG. 11 shows an embodiment of the method for producing an optical film of the present invention. A photosensitive laminate 10 (a release PET or mask 18, a photocurable resin layer 20 and a transparent PET 22 from the side close to the lens) is placed in parallel with a lenticular lens 14 in which a horizontally long substantially semi-cylindrical convex portion 14a is vertically aligned, A UV parallel light beam 12 is irradiated from the normal direction of the lenticular lens 14 toward the lenticular lens 14 and photocured. When the UV light passes through the lenticular lens 14, the light 16 is diffused in the Y direction by the convex portion 14 a of the lenticular, and is irradiated on the photosensitive laminate 10. Through the lenticular lens, there is a wide spread in one direction (Y direction in FIG. 11, depth direction of the paper surface), and only a narrow spread in the direction perpendicular to it (X direction, vertical direction of the paper surface in FIG. 11). Anisotropic light 16 is formed. When the photosensitive laminate 10 is irradiated, it is photocured and becomes a cured resin layer having an internal structure in the photocurable resin layer.

(2) Irradiation of UV rays that are not in the normal direction As another aspect, the photosensitive laminate may be irradiated with parallel rays inclined from a direction different from the normal direction. An example of this aspect is shown in FIG. A parallel light beam 12 (having an angle of 60 ° from the lenticular lens) inclined by 30 ° from the normal direction of the lenticular lens 14 is irradiated from a direction opposite to the convex surface (kamaboko-shaped surface) 14a of the lenticular lens. In that case, the diffused light 16 is irradiated in an oblique direction from the convex surface 14a of the lenticular lens. As a result, as shown in the figure, the diffused light 16 spreads in a flat fan shape around the direction inclined by 30 ° with respect to the X axis from the normal line of the photosensitive laminate, and is irradiated from the oblique direction of the photosensitive laminate 10. Then, photocuring is performed in the photocured layer 20.

  In addition, the above-mentioned UV irradiation method using a lenticular lens is one method for producing the optical film of the present invention, and the present invention is not limited to this. In short, in order to form a specific internal structure in the photocurable composition layer, it is important to irradiate the photosensitive laminate with UV light that spreads in a flat fan shape.

  That is, a fine structure composed of high and low refractive indexes according to the present invention is formed by the step of irradiating the light-curing resin layer with light having a flat fan shape. In addition, the light to irradiate has a wavelength which can harden the said photosensitive composition. In the irradiation step, it is preferable to use light obtained by diffusing parallel rays into a flat fan shape.

When producing the optical film of the present invention, the illuminance of the UV light irradiated to the photosensitive laminate through the lenticular lens or the like is preferably in the range of 0.01 to 100 mW / cm ² , More preferably, it is the range of 0.1-20 mW / cm < ² >. If the illuminance is 0.01 mW / cm ² or less, it takes a long time to cure, resulting in poor production efficiency. If the illuminance is 100 mW / cm ² or more, the photo-curing compound is cured too quickly to form a structure, This is because the desired anisotropic diffusion characteristic cannot be expressed.

  Although the irradiation time of UV is not particularly limited, it is 10 to 180 seconds, more preferably 30 to 120 seconds. Then, the anisotropic diffusion optical film of this invention can be obtained by peeling a release film.

The optical film of the present invention is obtained by forming a specific internal structure in the photocurable composition layer by irradiating low-illuminance UV light for a relatively long time as described above. For this reason, unreacted monomer components remain by such UV irradiation alone, and stickiness may occur, which may cause problems in handling properties and durability. In such a case, the residual monomer can be polymerized by additional irradiation with UV light having a high illuminance of 1000 mW / cm ² or more. The UV irradiation at this time is preferably performed from the opposite side of the mask side.

According to the following method, the optical film of the present invention and the optical film of the comparative example were produced.
Example 1 On a transparent PET film with vertical irradiation of 100 μm, a photocurable composition having a formulation shown in Example 3 of Special Table 2005-514487 is applied, and a coating film with a dry film thickness of 50 μm is provided. Further, a 38 μm release PET film was laminated on this coating film so that the release surface was in contact with the coating film. From the direction of 0 ° with respect to the normal line from the release PET film side of this laminate, parallel UV rays (formed using a Fresnel lens) of 5 mW / cm ² are formed with a radius (r) = 0.5 mm and a pitch ( p): Irradiated for 90 seconds through a 0.5 mm lenticular lens (installed parallel to the laminate). By removing the release PET film from the cured laminate, the optical film (transparent PET / photocured resin layer) of the present invention was obtained (see FIG. 11). The UV light irradiated through the lenticular lens was almost unscattered in the X direction (longitudinal direction on the paper) but parallel, but was scattered in the Y direction (depth direction on the paper).

Example 2 The optical film of the present invention (transparent PET / photocuring resin) was used in the same manner as in Example 1 except that the lenticular lens used for vertical irradiation had a radius (r) = 0.5 mm and a pitch (p) = 0.7 mm. Layer).

Example 3 An exposure in which an optical density (OD) obtained by applying and drying a polyvinyl alcohol resin aqueous solution in which graphite particles having an average particle diameter of 3 μm are dispersed on a PET film is 0.50 instead of a vertical irradiation release PET film. An optical film (transparent PET / photocured resin layer) of the present invention was prepared in the same manner as in Example 1 except that a mask was used and the lenticular lens had a radius (r) = 0.05 mm and a pitch (p) = 0.1 mm. Obtained.

Example 4 The optical film (transparent PET / photocured resin layer) of the present invention is obtained in the same manner as in Example 2 except that the direction of oblique irradiation is inclined 30 ° from the normal direction of the laminate to the X-axis side. (See FIG. 12). In addition, the lenticular lens and the laminate were installed so as to be parallel, and the UV light irradiated through the lenticular lens was parallel to the X direction while being inclined by 30 °, and scattered in the Y direction.

Comparative Example 1
An optical film (transparent PET / photocured resin layer) for comparison was obtained in the same manner as in Example 1 except that a lenticular lens was not used. Since a lenticular lens was not used, a perfect parallel light beam was irradiated to obtain an optical film having a type B columnar fine structure.

Comparative Example 2
A commercially available Lumisty (registered trademark, Sumitomo Chemical) was used as an optical film having a fine structure of type A plate.

Evaluation 1 Comparison of optical profiles (linear transmittance)
Incidence angle dependency was evaluated by a method using a goniophotometer (Genesia GENESIA Gonio / Far Field Profiler) shown in FIG. It is obtained by placing a sample between a light source (not shown) and the light receiver 3 and measuring the linear transmittance entering the light receiver 3 through the sample while changing the angle around the straight line L of the sample surface. (The details of the measurement method are described in paragraph No. 0048 of JP-A-2005-265915). The results for Examples 1 to 3 and Comparative Examples 1 and 2 are shown in FIG. In addition, since the result of Example 2 was the same as Example 1, it has written together. According to this result, the optical films of Examples 1, 2 and 3 have a maximum value near 0 ° which is the normal direction, and a minimum value F _B is taken at an incident angle B of ± 5 to 10 °. further expanding the angle of incidence from, it takes a maximum value _{F a} at an incident angle a of around 40 to 50 °. (F _A −F _B ) / | A−B | was calculated from the optical profile obtained by the measurement, and is shown in Table 1.

Evaluation 2 The diffusion permeability and diffusion anisotropy when the light receiver was rotated were evaluated by the method shown in FIG. 6 using a goniophotometer. Using the optical films produced in the examples and comparative examples, light was irradiated and the transmittance of light emitted from the film was measured. In the measurement, in FIG. 6, the light receiver was rotated in the X direction (up and down direction on the paper surface) and the Y direction (front to back direction on the paper surface) around the emission point of the light from the optical film. The results are shown in FIG. F _{max1 / 10} x / F _{max1 / 10} y was calculated and shown in Table 1.

Claims (4)

A fine structure consisting of high and low refractive index is present inside, and the linear transmittance of incident light that is transmitted differs depending on the incident angle,
Circular light incident from the scattering center axis has the property of being projected in an elliptical shape with respect to a plane parallel to the optical film,
The scattering characteristics of light incident from the scattering center axis are
The relationship Tx between the exit angle in the plane formed by the X axis on the optical film plane that is parallel to the major axis direction of the ellipse and the scattering center axis and the diffuse transmittance at the exit angle; and
The relationship Ty between the exit angle in the plane formed by the Y axis on the optical film plane perpendicular to the X axis and the scattering center axis and the diffuse transmittance at the exit angle is:
The peak width F _{max1 / 10} x at a value one-tenth from the maximum value of the diffuse transmittance peak in the relationship Tx, and the value one-tenth from the maximum value of the diffuse transmittance peak in the relationship Ty. And the peak width F _{max1 / 10} y satisfy the relationship of the following formula (1).
1.5 <F _{max 1/10} x / F _{max 1/10} y <4.5 (1) In the plane formed by the X axis and the scattering central axis, the relationship between the incident angle of light and the linear transmittance is
The maximum value F _A (%) of the linear transmittance and the angle A (°) that takes the maximum value, and the minimum value F _B (%) of the linear transmittance and the angle B (°) that takes the minimum value are as follows: The optical film according to claim 1, wherein the relationship of formula (2):
_{0.70 <(F A -F B)} / | A-B | <2.0 ··· (2)   The fine structure appears in a cross section parallel to a plane formed by the X axis and the scattering center axis of the optical film and a cross section parallel to a plane formed by the Y axis and the scattering center axis of the optical film, The optical film according to claim 1 or 2. The density of the fine structure in a cross section parallel to the X axis-scattering central axis plane of the optical film is higher than the density of the fine structure in a cross section parallel to the Y axis-scattering central axis plane. The optical film according to claim 3.