JP5931524B2 - Antireflection film - Google Patents

Description

The present invention relates to an antireflection film. The present invention relates to an antireflection film for use in, for example, a display device to prevent reflection of sunlight, room lighting , ambient light, and the like, thereby improving the visibility of the screen so that the screen can be clearly seen.

(Function of antireflection film)
Various devices such as a mobile phone, a mobile computer, and a personal computer include a display device that can display fine images. However, when external light such as sunlight or indoor illumination light is incident on the screen, the display device is partially reflected on the screen, thereby reducing the contrast of the image and causing the screen to become whitish.

  Such a phenomenon in which external light is reflected occurs as shown in FIG. 1A, for example. FIG. 1A shows a display device 11 in which a cover panel 13 is superimposed on the front surface of a liquid crystal display panel 12 via an air gap (space). When external light is incident on the display device 11, 4% of the incident external light is reflected by the front surface of the cover panel 13, and 3.8% of the incident external light is 3.8% of the cover panel 13. Reflected on the back surface, 3.7% of the incident external light is reflected on the front surface of the liquid crystal display panel 12. As a result, when 100% of the external light is incident on the display device 11, a total of 11.5% of the incident external light is reflected toward the front side. Therefore, the reflected light (white light) is superimposed on the image displayed on the liquid crystal display panel 12, and the contrast of the image is lowered, and the display quality is lowered.

  In order to prevent such a phenomenon, an antireflection film (ARS) is used. Examples of the antireflection film include those disclosed in Patent Document 1 and Patent Document 3. This antireflection film is formed by densely arranging fine optical protrusions having a refractive index equal to that of a film substrate on the surface of a transparent film substrate. The optical protrusion has a shape such as a cone shape, a truncated cone shape, or a quadrangular pyramid shape.

  FIG. 1B shows a case where an antireflection film 14 is pasted on the back surface of the cover panel 13. In this case, 4% of the incident external light is reflected by the front surface of the cover panel 13, and 0.34% of the incident external light is reflected by the back surface of the cover panel 13 and is incident. 3.8% of the external light is reflected by the front surface of the liquid crystal display panel 12. As a result, reflection on the back surface of the cover panel 13 to which the antireflection film 14 is pasted is greatly suppressed, and in total only 8.17% of the incident external light is reflected toward the front side. Therefore, by applying one antireflection film 14, the amount of reflected light is about 2/3 times that when the antireflection film 14 is not applied.

  FIG. 1C shows a case where an antireflection film 14 is pasted on the back surface of the cover panel 13 and the front surface of the liquid crystal display panel 12. In this case, 4% of the incident external light is reflected by the front surface of the cover panel 13, and 0.34% of the incident external light is reflected by the back surface of the cover panel 13 and is incident. Of the outside light, 0.33% of the light is reflected by the front surface of the liquid crystal display panel 12. As a result, reflection on the back surface of the cover panel 13 with the antireflection film 14 and the front surface of the liquid crystal display panel 12 is suppressed, and in total, only 4.67% of the incident external light is reflected toward the front side. Therefore, by attaching two antireflection films 14, the amount of reflected light becomes about 1/3 times that when the antireflection film 14 is not attached.

  Therefore, if an antireflection film is attached to the display device, reflection of external light can be reduced, and the contrast of the image can be increased to display the image vividly. In the above description, the reflectance on the surface where the antireflection film is not applied is 4%, and the reflectance on the surface where the antireflection film is attached is 0.35%, but these are typical values. The reflectance value may be slightly different depending on the type of the antireflection film and the material of the cover panel.

(Weak points of antireflection film)
A display device used for a mobile phone, a mobile computer or the like is likely to be contaminated with dirt or sebum. Therefore, the surface of the display device is frequently rubbed with a soft cloth or a cleaner to wipe off dirt and sebum. Since the cover panel is pressed with a finger when wiping dirt, sebum, etc. on the surface, if an antireflection film is applied as shown in FIG. 1B or 1C, the fine optical protrusions of the antireflection film are pressed against the opposing surface. It becomes easy to be crushed. Moreover, in the display apparatus provided with the touch panel on the surface, since the touch panel is pressed with a finger or a touch pen, if the antireflection film is stuck, the optical protrusions of the antireflection film are also pressed against the opposing surface and are easily crushed. If the optical protrusions are crushed in this way, the antireflection function of the antireflection film is lowered or impaired.

(Protective pillar for antireflection film)
Therefore, in the antireflection film disclosed in Patent Document 2, protective columns of micron order higher than the height of the optical protrusions are scattered on the antireflection film formed by densely arranging nano-order optical protrusions on the surface. . And the optical protrusion is protected by the protective pillar, and even if the surface of the display device is pressed, the optical protrusion is not easily crushed.

  Patent Document 2 describes a conical protection column such as a cone, a quadrangular pyramid, and a triangular pyramid and a columnar protection column such as a quadrangular column, a cylinder, and an elliptical column. However, in the case of the conical protection pillar, the tip is easily crushed when the protection pillar is pressed against the opposing surface. Therefore, it is necessary for the protection column to be able to withstand the load with the tip surface as a flat surface. Moreover, in order to withstand the load, it is preferable that the tip surface of the protective column has as large an area as possible. However, since the antireflection structure cannot be provided on the protective column, the optical performance of the antireflection film deteriorates when the area of the front end surface of the protective column is increased. In addition, when the side surface of the protective column is inclined, the area of the base end surface of the protective column increases, and the area of the antireflection film without the antireflection structure increases accordingly. On the other hand, in the case of a column-shaped protective column having a uniform cross section, the releasability at the time of molding the antireflection film is poor and the protective column is difficult to peel off from the mold, making it difficult to raise the protective column Become. Therefore, those skilled in the art want to reduce the useless area of the protective column by making the side surface of the protective column as close as possible to the vertical as much as possible without affecting the formability. A protective column having a truncated cone shape that is inclined and close to a cylinder is used.

  However, when the protective column of the antireflection film is formed into a truncated cone (the angle between the side surface and the central axis is about 20 °), external light is applied to the surface (front surface) provided with the optical protrusion 16 and the protective column 15 as shown in FIG. 2A. Compared to the case where light is incident (hereinafter referred to as front-surface incidence), as shown in FIG. The antireflection effect of incident is worsened. FIG. 2B is a photomicrograph of the antireflection film surface when external light is incident on the surface, and FIG. 2D is a photomicrograph of the antireflection film backside when external light is incident on the back surface. As can be seen from these photomicrographs, in the case of back-side incidence, the portions of the respective protection pillars shine considerably brighter than in the case of front-side incidence. In particular, since the side surface of the protection pillar shines strongly, it shines in an annular shape. In terms of numerical values, in the case of backside incidence, the reflectance of the antireflection film is increased by 0.49% compared to the case of frontside incidence.

  The reason is as follows. As shown in FIG. 3, when the light L1 is incident on the frustoconical protection column 15 on the back surface, the incident light L1 is retroreflected by being totally reflected a plurality of times on the side surface and the tip surface of the protection column 15. As a result, in the case of backside incidence, the reflectance of the antireflection film 14 is increased.

  Thus, in the conventional antireflection film provided with the protective column, the optical characteristics are greatly different between the case where the back surface incidence is performed and the case where the front surface incidence is performed. For this reason, for example, the reflectance differs greatly between the case where it is attached to the front surface of a liquid crystal display panel (when incident on the front surface) and the case where it is attached to the rear surface of the cover panel (when incident on the rear surface). It was inconvenient for use and difficult to use.

JP 2002-122702 A JP 2004-70164 A Japanese Patent No. 4539759

  This invention is made | formed in view of the above technical subjects, and the place made into the objective is to prevent the retroreflection by a protection pillar in the antireflection film provided with the protection pillar.

The antireflection film according to the present invention includes a film substrate, an antireflection structure including a plurality of fine optical protrusions formed on the surface of the film substrate, and the optical protrusions formed on the surface of the film substrate. In the antireflection film having a plurality of convex portions having a large height, the convex portion has a cross-sectional area that is gradually reduced in cross section parallel to the surface of the film substrate from the base end side toward the tip end side. And a frustoconical shape in which the area of the distal end surface is smaller than the area of the proximal end surface, the diameter at the proximal end of the convex portion is D, the height of the convex portion is H, and the central axis of the convex portion When the angle between the side surface of the convex portion and the central axis of the convex portion in the cross section passing through is θ,
D> 2H × tan (2θ) (Condition 1)
It has the relationship of these.

In the antireflection film of the present invention, since the convex portion has a truncated cone shape and satisfies the above condition 1, the light incident on the back surface of the convex portion does not recurse toward the original direction, and is not reflected in the film substrate . Led. Therefore, even when the antireflection film is used in the form of back-surface incidence, the convex portion is less likely to shine, and the effect of the antireflection film becomes better. As a result, the difference in reflectance between the case where the light is incident on the back surface of the antireflection film and the case where the light is incident on the front surface is small. It is not necessarily required that all the convex portions satisfy the condition 1. Even if at least some of the convex portions only satisfy the condition 1, there is an effect of reducing the reflected light at the time of incident on the back surface.

In an embodiment of the antireflection film according to the present invention, when the refractive index of the convex portion is n, at least one convex portion among the plurality of convex portions is
θ> 0.5 × arcsin (1 / n) (Condition 2)
Meet the relationship. Condition 2 is a case where the regression reflection is satisfied in the conventional example. Therefore, when the condition 2 is satisfied, the present invention can be applied to reduce the reflected light when incident on the back surface.

Another embodiment of the antireflection film according to the present invention is characterized in that, when used in an overlapping manner with a liquid crystal panel, the arrangement direction of the convex portions is inclined with respect to the arrangement direction of the pixels of the liquid crystal panel. According to such an embodiment, moire fringes are less likely to occur even when the arrangement pitch of the protrusions in the antireflection film is substantially equal to the pixel pitch of the liquid crystal panel.

  Yet another embodiment of the antireflection film according to the present invention is characterized in that a height H of the convex portion is 2 μm or more. According to this embodiment, it is possible to prevent interference fringes from occurring between a member facing the antireflection film, such as the surface of the liquid crystal panel.

  Yet another embodiment of the antireflection film according to the present invention is characterized in that the density per unit area of the convex portions is 1% or more. The convex portion for protecting the antireflection structure must be able to withstand a certain load and support the antireflection film. For that purpose, it is necessary to occupy at least about 1% of the area of the antireflection film. Also, if the density of the protrusions decreases, the area between the protrusions may bend and come into contact with the opposing member, so it is necessary not to widen the distance between the protrusions too much. A density of 1% or more is required.

  The means for solving the above-described problems in the present invention has a feature in which the above-described constituent elements are appropriately combined, and the present invention enables many variations by combining such constituent elements. .

FIG. 1A is a schematic cross-sectional view of a display device without an antireflection film. FIG. 1B is a schematic cross-sectional view of a display device using a single antireflection film. FIG. 1C is a schematic cross-sectional view of a display device using two antireflection films. FIG. 2A is a diagram illustrating light incident on the antireflection film. FIG. 2B is a photomicrograph showing the state of the surface side of the antireflection film on which light is incident. FIG. 2C is a diagram illustrating light incident on the back surface of the antireflection film. FIG. 2D is a photomicrograph showing the state of the back surface side of the antireflection film on which light is incident on the back surface. FIG. 3 is a schematic diagram showing a state in which regression reflection is caused by a protective column in a conventional antireflection film. FIG. 4 is an enlarged perspective view showing a part of the antireflection film according to the present invention. FIG. 5 is a schematic view showing a cross section passing through the central axis of one protective pillar. FIG. 6 is a diagram showing the relationship between the diameter of the protective column and the strength of the retroreflection by the protective column. FIG. 7 is a diagram for explaining the case of a protective column having a curved cross-sectional shape. 8A, 8B and 8C are schematic diagrams for explaining how to use the antireflection film . FIG. 9A is a diagram illustrating a state in which the antireflection film facing the liquid crystal panel is bent. FIG. 9B is a diagram showing a case of a reflective film having a protective column having a height of 2 μm or more. FIG. 10A is a diagram illustrating interference fringes (Newton rings) generated in an antireflection film without a protective column. FIG. 10B is a diagram showing an antireflection film having a protective column having a height of 3 μm. FIG. 11 is a diagram for explaining the arrangement of the antireflection film and the image display panel.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments, and various design changes can be made without departing from the gist of the present invention.

(Structure of antireflection film)
FIG. 4 is an enlarged perspective view showing a part of the antireflection film 21 according to the present invention. FIG. 5 is a cross-sectional view showing a cross section passing through the convex portion, that is, the central axis of the protective column 24. The antireflection film 21 is formed by densely forming transparent optical protrusions 23 having a refractive index equal to that of the film substrate 22 on a smooth surface of the transparent film substrate 22. In addition, on the surface of the film substrate 22, frustoconical transparent protective columns 24 (protrusions for preventing adhesion) having the same or substantially the same refractive index as the film substrate 22 are arranged at a constant pitch.

  The film substrate 22 is formed into a plate shape using a transparent resin having a high refractive index, such as polycarbonate resin or acrylic resin. The film substrate 22 may be a hard resin substrate or a thin flexible film substrate, and the thickness is not particularly limited.

  The optical protrusion 23 is a nano-sized minute protrusion and has a conical shape, a truncated cone shape, a quadrangular pyramid shape, or the like. Moreover, the shape of the optical protrusion 23 may be a part of the spheroid.

The protection column 24 has a truncated cone shape in which the area of the tip surface is smaller than the area of the bottom surface, and has a height higher than that of the optical protrusion 23. The protective column 24 has a side surface 24 a and a front end surface 24 b, and the front end surface 24 b is parallel to the surface of the film substrate 22. When the light L2 is incident on the back surface of the antireflection film 21 perpendicularly, the light L2 impinging on the side surface 24a is totally reflected on the side surface 24a and further incident on the front end surface 24b as shown by a solid arrow in FIG. After the total reflection at the front end surface 24b , the light enters the film substrate 22 without re-entering the side surface 24a and is guided in the lateral direction in the film substrate 22. Therefore, even if light is incident on the back surface of the antireflection film 21, the light is retroreflected by the protective column 24 and does not return to the original direction. As a result, in the case where the surface of incidence and a back illuminated, the effect of cutting the reflected light in the same way can be obtained.

Next, the conditions for the back incident light to behave as shown in FIG. 5 will be clarified. The light that is most likely to be retroreflected is the light that has entered the end of the protection column 24 (point a in FIG. 5). If this light can no longer be retroreflected, any light reflected by the side surface 24a will not be retroreflected. . If the refractive index of the protective column 24 is n and the angle formed by the side surface 24a with respect to the central axis in the cross section passing through the central axis of the protective column 24 is θ, the light L3 incident on the point a at the end of the protective column 24 is reflected on the side surface 24a. The condition of total reflection at
0 ° <θ <arccos (1 / n) (Condition 3)
It becomes. The light L3 totally reflected at the point a is incident on the tip surface 24b. The condition for the light L3 to be totally reflected by the tip surface 24b is as follows.
θ> 0.5 × arcsin (1 / n) (Condition 4)
It becomes. Further, the condition for the point b to be on the distal end surface 24b instead of on the side surface 24a is that the diameter of the base end surface of the protective column 24 is D and the height of the protective column 24 is H.
H × tan (2θ) <D−H × tan (θ) (Condition 5)
It becomes. Further, in order to prevent the light L3 incident on the back surface from being retroreflected, the light totally reflected by the front end surface 24b only needs to pass through the left side of the point c at the end of the side surface 24a. for that purpose,
D> 2H × tan (2θ) (Condition 6)
Should be satisfied.

In order to prevent the return reflection at the time of incidence on the back surface as described above, the above conditions 2 to 6 should be satisfied. Here, when the angle θ formed with the central axis of the side surface 24a approaches 45 °, the diameter D of the protective column 24 has to be very large. Therefore, in practice, θ must be smaller than 45 degrees. Therefore, the condition 3 is naturally satisfied if the value is a general refractive index n. If condition 6 is satisfied, condition 5 is also satisfied. Therefore, it can be understood that the conditions 4 and 6 should be satisfied. However, if all the protective pillars 24 do not satisfy the condition 4 , the light passes through the tip surface 24b and does not return and is not a problem. Accordingly, the present invention is useful when at least a part of the protective pillars 24 satisfy the condition 4 . Eventually, it can be seen that if the condition 6 is satisfied, the protective column 24 can be prevented from shining by regressive reflection.

  In addition, although it is preferable that all the protection pillars 24 satisfy the condition 6, it is not necessarily required until all the protection pillars 24 satisfy the condition 6. If at least a part of the protective pillars 24 satisfies the condition 6, the effect can be obtained within that limit.

  In consideration of the ease of removing the protective column 24 from the mold and the difficulty of occurrence of chipping when the antireflection film 21 is molded, the angle θ of the side surface 24a is preferably 30 ° or more and 40 ° or less, particularly 30 ° or more. 35 degrees or less is desirable. Therefore, as an example of the protective pillar 24 that satisfies the condition 6, for example, the height H may be about 3 μm and the diameter D may be about 20 μm.

  FIG. 6 is a photomicrograph of each when light is incident on the back side of the protective pillars having different diameters D. FIG. In the horizontal axis direction, the diameters of the protective pillars are arranged from small to large, and the vertical axis is arranged from small to large reflected light. Under the measurement conditions, the height H of the protective column was 3 μm, and the angle θ of the side surface 24a was 30 °. In this numerical example, the minimum value of the diameter D obtained from Condition 6 is about 10 μm. The two diameters D from the left are 3 μm and 5 μm in the conventional example, and the one having a diameter of 10 μm is at the boundary. Further, the right three having a diameter D of 21 μm, 41 μm and 61 μm are examples of the present invention. When the diameter D is 3 μm or 5 μm, the reflection is recursively reflected. When the diameter is 10 μm, the retroreflected light remains due to surface accuracy and the like. When the diameter is 21 μm, the retroreflected light is almost unknown.

(Extension to a protective column with a curved section)
Application of Condition 6 when the cross section of the protective column 24 is curved will be described. FIG. 7 shows a protective column 24 having an elliptical cross section as an example of such a protective column. First, when the height of the apex P measured from the bottom surface of the protective column 24 is H, points N1 and N2 on the surface of the protective column 24 at a height ½ of the height H are considered. That is, the height measured from the bottom surface of the horizontal plane T passing through the apex P and parallel to the bottom surface is H, and the points on the surface of the protective column 24 at the height H / 2 from the bottom surface are N1 and N2. Next, in the cross section passing through the central axis of the protection column 24, tangent lines S1 and S2 that contact the surface of the protection column at points N1 and N2 are obtained, and intersection points between the tangent lines S1 and S2 and the bottom surface are B1, B2, and Let the intersections with T be C1 and C2. The frustum shape defined by the trapezoidal shape B1-N1-C1-P-C2-N2-B2 composed of the tangents S1, S2 and the horizontal plane T defined in each cross section in this way is for applying the condition 6. It becomes a shape. That is, when the condition 6 is applied to the protection column 24 having such a shape, the distance between B1 and B2 may be the diameter D, and the angle between the tangents S1 and S2 and the central axis may be θ.

(Configuration of display device)
8A-8C show some forms of the display device to which the antireflection film 21 according to the present invention is attached. The display device 31 shown in FIG. 8A is obtained by overlapping a cover panel 33 on the front surface of an image display panel 32 such as a liquid crystal display panel (LCD) or an organic EL (OLED) with an air gap (space). The antireflection film 21 is pasted on the back surface of the panel 33 and the front surface of the image display panel 32. 8B has the antireflection film 21 pasted on the front and back surfaces of the cover panel 33 and the front surface of the image display panel 32. If the antireflection film 21 is also applied to the front surface of the cover panel 33 as shown in FIG. 8B, the antireflection effect is enhanced. However, since the antireflection film 21 on the front surface of the cover panel 33 is touched by the user, it is damaged or dirty. There is a risk of In the display device 35 shown in FIG. 8C, the antireflection film 21 is stuck only on one of the back surface of the cover panel 33 and the front surface of the image display panel 32. In the form shown in FIG 8C, the effect of preventing the reflection is low, the cost is reduced, it is effective in some applications. The image display panel 32 may be for monochrome display or for color display. The cover panel 33 is a protective sheet having a uniform thickness made of a transparent resin.

  When the antireflection film 21 is used in combination with the image display panel 32 as described above, the arrangement pitch of the protective pillars 24 in the antireflection film 21 and the pixel pitch of the image display panel 32 may be substantially the same. . If the array pitch of the protection pillars 24 and the pixel pitch are substantially the same, moire fringes may occur on the screen of the display device.

When moire fringes are generated in this way, as shown in FIG. 11 , the direction in which the pitch of the antireflection film 21 is the same is rotated about 90 ° with respect to the image display panel 32, and the arrangement of the protective pillars 24 is further arranged. The direction may be slightly inclined with respect to the pixel arrangement direction. In the image display panel 32 of FIG. 11 , the red pixel, the green pixel, and the blue pixel constitute a single pixel.

  Further, when the cover panel 33 faces the image display panel 32 and the antireflection film is not attached to the cover panel 33, the cover panel 33 is pushed and the gap between the cover panel 33 and the image display panel 32 is reached. When the thickness becomes about 60 μm, interference fringes (Newton rings) are generated. FIG. 10A shows an interference fringe generated by pressing the cover panel 33 with a fingertip. On the other hand, when the antireflection film 21 is pasted on the inner surface of the cover panel 33, interference fringes are not generated unless the gap is about 2 μm.

  Therefore, as shown in FIG. 9B, if the protective column 24 having a height of 2 μm or more, preferably a protective column 24 having a height of about 3 μm is provided, the generation of interference fringes can be prevented. FIG. 10B shows an antireflection film 21 having a protective column 24 having a height of 3 μm, which is attached to the back surface of the cover panel 33. FIG. 10B is also a photograph when pressed with a finger as in FIG. 10A, but no interference fringes are generated. Therefore, in order to prevent interference fringes, it is effective to provide the anti-reflection film 21 with a protective column 24 having a height of 2 μm or more, preferably about 3 μm. Further, when the protective pillar 24 is provided, it is effective to provide the protective pillar 24 at a density of 1% or more per unit area. This is because if the density of the protection pillars 24 is small, the intermediate region between the protection pillars 24 and 24 may be in close contact with the image display panel 32.

DESCRIPTION OF SYMBOLS 21 Antireflection film 22 Film substrate 23 Optical protrusion 24 Protection pillar 24a Side surface 24b Front end surface 31, 34, 35 Display apparatus 32 Image display panel 33 Cover panel

Claims (5)

A film substrate; an antireflection structure comprising a plurality of fine optical projections formed on the surface of the film substrate; and a plurality of convex portions formed on the surface of the film substrate and having a height higher than the optical projections. In the antireflection film provided with
The convex portion is a cone whose sectional area in a cross section parallel to the surface of the film substrate is gradually reduced from the base end side toward the tip end side , and the tip end surface area is smaller than the base end face area. It has a trapezoidal shape
When the diameter at the base end of the convex portion is D, the height of the convex portion is H, and the angle between the side surface of the convex portion and the central axis of the convex portion in a cross section passing through the central axis of the convex portion is θ ,
D> 2H × tan (2θ)
An antireflection film having the following relationship: When the refractive index of the convex portion is n, at least one convex portion among the plurality of convex portions is
θ> 0.5 × arcsin (1 / n)
The antireflection film according to claim 1, wherein the relationship is satisfied. 2. The antireflection film according to claim 1, wherein in the case of using the liquid crystal panel so as to overlap with the liquid crystal panel, the arrangement direction of the convex portions is inclined with respect to the pixel arrangement direction of the liquid crystal panel.   The antireflection film according to claim 1, wherein a height H of the convex portion is 2 μm or more. Wherein the density per unit area of the convex portion is 1% or more, the antireflection film of claim 4.

Images