JP2010140035A - Light controlling sheet and surface illuminant unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light controlling sheet that makes it possible to illuminate a display screen so that brightness of the screen is uniform without unevenness regardless of a position from which the screen is viewed, particularly, a light-controlling sheet that causes gradual luminance variation even at large exit angles, and a surface illuminant unit. <P>SOLUTION: The light-control sheet 24 is arranged on a direct surface illuminant unit and makes light emitted from light sources uniform and/or converges the light. The light-control sheet 24 includes a large number of unit lenses 241 arranged in parallel, with a lens surface of each unit lens protruding to the light-exiting side. The cross section of the lens surface of each unit lens 241 taken perpendicularly to the sheet surface is asymmetrical. The unit lens 241 is equipped with three kinds of curved surfaces comprising an apex surface WT forming an apex, an upper side surface WU that becomes an upper side from the apex surface WT in use, and a lower side surface WD that becomes a lower side from the apex surface WT in use. The apex surface WT, the upper side surface WU and the lower side surface WD are all different in the radius of curvature of the surface. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light control sheet used for illumination of a liquid crystal display device or the like, and a surface light source device.

Various surface light source devices have been proposed and put to practical use as surface light sources for illuminating a transmissive liquid crystal display or the like from the back. Surface light source devices are mainly classified into edge light type and direct type according to a method of converting a light source that is not a surface light source into a surface light source.
For example, in the direct type, light is introduced using a parallel cold cathode tube from the back side, and a distance between the cold cathode tube and a transmissive display unit such as an LCD panel is appropriately spaced, and a diffusion plate therebetween. In addition, a plurality of sheets for converging light were used.
However, in such a conventional method, the convergence characteristic is insufficient for the large number of optical sheets required, and the LCD panel is improved to compensate for the incident light from an oblique direction. Also, the structure did not degrade the image quality.

However, this method has a problem in that the light use efficiency is reduced and the configuration of the LCD panel is complicated, resulting in an increase in cost.
In particular, in the direct type, the light depends on whether it is a part close to the cold cathode tube (a position close to the cold cathode tube or a position close to a gap part of the cold cathode tubes arranged in parallel). Unevenness is likely to occur in intensity (luminance). In order to suppress this, if the gap between the cold cathode fluorescent lamp and the LCD panel is made large, there is a problem that the thickness of the display increases. In addition, when the diffusion is increased or the transmission amount is limited in order to suppress unevenness, there is a problem that the amount of light used is reduced.

For example, in the surface light source devices described in Patent Documents 1 and 2, uniformity is maintained by providing a light-shielding portion (lighting curtain, light-shielding dot layer). In this method, the amount of light used is as described above. Decreased.
Further, a method using a sheet provided with lenticular lenses on both sides has also been reported in, for example, Patent Document 3, but this is a configuration for performing diffusion control in two directions and has no function of converging light. . Accordingly, there is a problem that unevenness of brightness (luminance unevenness) occurs depending on the position of observing the screen because the optical axis varies depending on the position of the LCD panel depending on the positional relationship with the cold cathode tube.

  Furthermore, Patent Document 4 discloses a film that converges light by arranging a large number of triangular prisms. However, in the film having the triangular prism described in Patent Document 4, in addition to the luminance peak near the emission angle of 0 degrees, the second luminance peak exists in the direction of the large emission angle of about 60 to 80 degrees, During black display, there is a problem that the amount of light leakage increases and the contrast deteriorates. Further, the film having a triangular prism described in Patent Document 4 has a problem that a sharp change in viewing angle characteristics occurs in both the vertical viewing angle and the horizontal viewing angle, and the brightness changes drastically.

JP 05-119703 A JP 11-242219 A Japanese Patent Laid-Open No. 06-347613 JP-A-63-318003

  An object of the present invention is to provide a light control sheet and a surface light source device capable of performing uniform illumination without unevenness regardless of the position where the screen is observed, and having a gradual change in luminance even in a large emission angle direction. Is to provide.

The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to the Example of this invention is attached | subjected and demonstrated, it is not limited to this.
The invention according to claim 1 is a light control sheet that is provided in a direct type surface light source device and uniformizes and / or converges the light emitted from the light source, and the cross-sectional shape orthogonal to the sheet surface is asymmetric. The unit lens (241) includes a plurality of unit lenses (241) arranged in a protruding manner on the emission side. The unit lens (241) includes a vertex surface (241T) that forms a vertex, and an upper side of the vertex surface in use. The upper side surface (241U) and the lower side surface (241D) which is lower than the vertex surface in use, and the vertex surface, the upper side surface and the lower side surface are: Both are light control sheets (24) characterized in that the curvature radii of the surfaces are different.
According to a second aspect of the present invention, in the light control sheet of the first aspect, the radius of curvature of the three types of curved surfaces is the smallest in the radius of curvature of the apex surface (241T) and the radius of curvature of the lower surface (241D). Is the light control sheet (24) characterized by the largest.
The invention according to claim 3 is the light control sheet according to claim 1 or 2, wherein the radius of curvature of the lower surface is infinite, and the lower surface is a plane. It is a sheet.
According to a fourth aspect of the present invention, in the light control sheet according to any one of the first to third aspects, the radius of curvature of the apex surface (241T) is 0.02 mm to 0.08 mm. The light control sheet (24) characterized by the above.
According to a fifth aspect of the present invention, in the light control sheet according to any one of the first to fourth aspects, the pitch at which the unit lenses (241) are arranged is P, and the cross section is orthogonal to the sheet surface. When the width of the vertex surface (241T) is WT, the relationship 0.05mm <P <0.5mm is satisfied and the relationship 0.025 <WT / P <0.25 is satisfied. The light control sheet (24) to be used.
The invention according to claim 6 is the light control sheet according to any one of claims 1 to 5, wherein the light control sheet is formed of one kind of thermoplastic resin. ).
The invention according to claim 7 is a surface light source device for illuminating the transmissive display portion (11) from the back, and a light source portion (12, 13) in which a plurality of light sources are arranged, and from claim 1 to claim 6, It is a surface light source device provided with the light control sheet | seat (24) of any one of Claims.

According to the present invention, the following effects can be obtained.
(1) Since the cross-sectional shape orthogonal to the sheet surface is asymmetrical and includes unit lenses arranged in a large number so as to protrude to the exit side, uniform illumination without unevenness is performed regardless of the position where the screen is observed. Can do.

(2) Since the unit lens has a flat surface formed by a flat surface and a curved surface formed by a curved surface, the effect of increasing the luminance in the front direction and the effect of gradual luminance change can be obtained. .

(3) Since the ratio of the flat surface side to the curved surface side in the unit lens is in the range of 1: 1 to 1: 1.5 in the direction parallel to the sheet surface, the luminance near the exit angle of 0 degree. Without drastically reducing the luminance, it is possible to moderate the luminance change and suppress unnecessary luminance peaks.

(4) Since the ratio between the projecting dimension of the unit lens and the pitch of the unit lens is in the range of 1: 2 to 1: 2.5, the luminance change without greatly reducing the luminance near the emission angle of 0 degree. It is possible to moderate unnecessary luminance peaks.

(5) Since the curved surface side is provided so as to be on the upper side in the usage state, the viewing angle characteristic on the upper side can be changed gradually. In addition, the plane side is the lower side in use, and the change in the viewing angle characteristics below is large. However, the display device is hardly seen from below, and the output angle of 0 ° is obtained by the action of the plane side provided below. It is possible to prevent the brightness in the vicinity from greatly decreasing.

(6) Since the vertex of the unit lens is formed by a curved surface that smoothly connects each surface formed asymmetrically across the vertex, the luminance change can be made smoother, and other points that are overlapped with the light control sheet It is possible to prevent the sheet or the like from being damaged.

(7) The vertex surface, the upper side surface, and the lower side surface all have different curvature radii, so that uniform illumination without unevenness can be performed.

(8) As for the curvature radii of the three types of curved surfaces, since the curvature radius of the apex surface is the smallest and the curvature radius of the lower surface is the largest, it is possible to smooth the upper luminance change frequently observed while maintaining a high front luminance. . In addition, it is possible to prevent the stacked sheets from being damaged, and to prevent the apex surface from being damaged.

(9) Since the curvature radius of the lower surface is infinite and the lower surface is a flat surface, the front luminance can be increased.

(10) Since the radius of curvature of the vertex surface is 0.02 mm or more and 0.08 mm or less, unnecessary peaks emitted in the direction of a large emission angle of 50 ° or more are reduced, and the strength of the vertex surface is reduced. It can be secured to prevent the loss of the apex surface.

(11) Since the relationship of 0.05 mm <P <0.5 mm is satisfied and the relationship of 0.025 <WT / P <0.25 is satisfied, there is no need to emit in a large emission angle direction with an emission angle of 50 ° or more. Major peaks can be reduced. In addition, generation of moire can be suppressed.

(12) Since it is formed of one kind of thermoplastic resin, the environmental resistance can be improved. Moreover, light resistance can be improved.

It is a figure which shows Example 1 of the transmissive display apparatus by this invention. FIG. 6 is a perspective view showing a light control sheet 14. It is sectional drawing which cut | disconnected the light control sheet | seat 14 by the S1-S2 cross section shown by the arrow in FIG. It is the figure which showed the luminance distribution of the perpendicular direction of the light control sheet | seat 14 of Example 1 compared with the luminance distribution of the comparative example. It is the figure which showed the luminance distribution of the horizontal direction of the light control sheet | seat 14 of Example 1 compared with the luminance distribution of the comparative example. It is the figure which showed the luminance distribution of the perpendicular direction of the light control sheet 14-2 compared with the luminance distribution of the comparative example. FIG. 4 is a cross-sectional view of the light control sheet 24 of Example 2 cut in the same manner as in FIG. 3. It is the figure which showed the luminance distribution of the perpendicular direction of the light control sheet | seat 24 of Example 2 compared with the luminance distribution of the comparative example and the light control sheet | seat 14-2 of Example 1. FIG. Difference in brightness distribution in the vertical direction of the light control sheet when the ratio WD: WU of the width in the direction parallel to the sheet surface and the ratio H: P of the projection dimension of the unit lens and the pitch of the unit lens are changed. FIG.

  Uniform illumination with no irregularity regardless of the position where the screen is observed And a light control sheet having unit lenses arranged in a large number so as to protrude toward the emission side, and in particular, a light control sheet having unit lenses formed by combining a plane and a curved surface.

FIG. 1 is a diagram showing Example 1 of a transmissive display device according to the present invention.
In addition, each figure shown below including FIG. 1 is the figure shown typically, and the magnitude | size and shape of each part are exaggerated suitably for easy understanding.
The transmissive display device 10 in this embodiment includes an LCD panel 11, a reflecting plate 12, an arc tube 13, a light control sheet 14, a reflective polarizing sheet 15, a milky plate 16, and the like, and an image formed on the LCD panel 11. It is a transmissive liquid crystal display device that displays information by illuminating it from the back. As the surface light source device for illuminating the LCD panel 11 from the back, the reflecting plate 12, the arc tube 13, the light control sheet 14, the reflective polarizing sheet 15, and the milky white plate 16 are applicable.

The LCD panel 11 is formed of a transmissive liquid crystal display element, and can display a 30-inch size and 800 × 600 dots. The direction along the longitudinal direction of the arc tube 13 is used as the horizontal direction, and the direction in which the arc tubes 13 are arranged is used as the vertical direction.
The arc tube 13 is a cold cathode tube of a line light source that forms a light source part of the surface light source device. In this embodiment, six are arranged in parallel at regular intervals of about 75 mm. A reflection plate 12 is provided on the back surface of the arc tube 13.
The reflection plate 12 is provided over the entire surface of the arc tube 13 on the side opposite to the light control sheet 14 (back side), and diffusely reflects the illumination light traveling toward the back side toward the light control sheet 14 (outgoing direction). It works to make the incident light illuminance uniform.
The reflective polarizing sheet 15 is a polarization separation sheet that is disposed between the LCD panel 11 and the light control sheet 14 and increases the luminance without narrowing the viewing angle. In this embodiment, DBEF (manufactured by Sumitomo 3M Limited) is used.
The milky white plate 16 is a diffusion plate having non-directional light diffusion characteristics, and is disposed on the light source side of the light control sheet 14.

FIG. 2 is a perspective view showing the light control sheet 14.
The light control sheet 14 is a lens sheet that reduces and equalizes the luminance unevenness of the light emitted from the arc tube 13, and a unit lens 141 that converges and emits the light is formed on the emission side. The unit lens 141 has a shape combining a flat surface and a curved surface, and a large number of the unit lenses 141 are arranged in parallel on the emission side surface of the light control sheet 14. The direction in which the unit lenses 141 are aligned is the same as the direction in which the arc tubes 13 are aligned (see FIG. 1).
The light control sheet 14 of this example is formed by extrusion molding using transparent PMMA (acrylic resin) having a refractive index of 1.49. The light control sheet 14 is not limited to PMMA, and may be used by appropriately selecting another thermoplastic resin having light permeability, or may be manufactured by a method called ultraviolet molding using an ultraviolet curable resin. Also good.

3 is a cross-sectional view of the light control sheet 14 taken along the S1-S2 cross section indicated by the arrow in FIG. Note that FIG. 3 shows an arrangement similar to that when the usage state is cut, and the vertical direction in the figure is the vertical (up and down) direction, and the left side in the figure is the emission side.
The shape of the unit lens 141 will be described separately on the upper upper shape 141U and the lower lower shape 141D on the basis of the vertex T.
The lower shape 141D is a plane (plane side) having a width in the direction parallel to the sheet surface from the position A to the apex T of 0.09 mm, that is, a vertical width WD = 0.09 mm in the cross section shown in FIG. Yes, it is formed with an angle of 46 degrees with respect to the sheet surface.
Here, the sheet surface indicates a surface defined as a planar direction of the light control sheet 14 when viewed as the light control sheet 14 as a whole, and in this embodiment, the surface on the incident side of the light control sheet 14. And are used as the same definition in the following description and in the claims. In the following description, the emission angle is an angle formed by the outgoing light with the normal of the sheet surface.
In the cross section shown in FIG. 3, the upper shape 141U has a cylindrical surface (having a radius of 0.195 mm passing through the position B and the apex T) at a position B which is 0.189 mm upward in parallel with the sheet surface from the position A. Curved surface side). Therefore, the width WU in the vertical direction of the upper shape 141U is 0.099 mm, and the ratio of the plane side to the curved surface side in the unit lens 141 is the ratio of the width in the direction parallel to the sheet surface WD: WU = 1. : 1.1.

Here, in the light control sheet 14 of the present embodiment, a comparative example having a triangular prism is prepared in order to confirm the effect of providing a cylindrical surface as the upper shape 141U and a plane as the lower shape 141D. Each was used for a surface light source device to measure the luminance distribution. The luminance distribution was measured with the LCD panel 11 and the reflective polarizing sheet 15 removed.
FIG. 4 is a diagram showing the luminance distribution in the vertical direction of the light control sheet 14 of Example 1 in comparison with the luminance distribution of the comparative example. In FIG. 4, the luminance is shown with the maximum luminance value in the comparative example as a reference value (luminance 1), and the emission angle minus side is the upper side in use and the emission angle plus side is the lower side.

  In the comparative example, there is a sharp decrease in luminance near the emission angle of 40 degrees, and there is a second luminance peak in the large emission angle direction of about 60 to 80 degrees in addition to the luminance peak near the emission angle of 0 degrees. Yes. When observed, the amount of light leakage increased during black display, and the contrast deteriorated. On the other hand, in the case of the light control sheet 14 of the present example, although the luminance near the emission angle of 0 degree was slightly lowered, the skirt portion in the vicinity of the light control sheet 14 was widened, and the way in which the luminance decreased gradually. Further, the unnecessary luminance peak on the emission angle minus side (upper side) disappeared, and the value of the unnecessary luminance peak on the emission angle plus side (lower side) also decreased.

FIG. 5 is a diagram showing the luminance distribution in the horizontal direction of the light control sheet 14 of Example 1 in comparison with the luminance distribution of the comparative example.
In the horizontal direction, although there is no unnecessary luminance peak in both the comparative example and the light control sheet 14, the luminance change that suddenly decreases in the comparative example near the emission angle of 60 degrees is reduced by using the light control sheet 14. The change became smooth.
As described above, when the light control sheet 14 of the present embodiment is used, the change in viewing angle characteristics becomes gentle in both the horizontal and vertical directions. In addition, unnecessary luminance peaks can be eliminated or suppressed in the vertical direction.
Hereinafter, this reason will be described. The sudden change in luminance in the comparative example naturally occurs because a triangular prism having a flat surface is used. It was found that a unit lens made of a curved surface should be used in order to suppress this sudden change and make it a gradual change and eliminate unnecessary peaks. However, on the other hand, it has been found that it is effective to use a plane to increase the luminance near the exit angle of 0 degrees.

Here, when viewing a display device as shown in this embodiment, human eyes may be arranged in the horizontal direction, and the viewing angle characteristics in the horizontal direction are required to be symmetrical. However, the viewing angle characteristics need not be symmetric with respect to the vertical direction. Since the viewing angle characteristic in the vertical direction is rarely seen from below, the viewing angle is narrowed with a steep viewing angle characteristic to improve the front (outgoing angle 0 degree direction) luminance. It is to let you. On the other hand, with respect to the upper characteristic, a gradual change in viewing angle is desirable, and it is necessary to suppress unnecessary luminance peaks. Furthermore, as for the horizontal characteristics, it is desirable to change the viewing angle as wide and gradual as possible.
Therefore, in the present embodiment, as the asymmetric unit lens 141 having the upper shape 141U as a cylindrical surface and the lower shape 141D as a plane, the luminance change in the upper direction is moderated without greatly reducing the luminance near the emission angle of 0 degrees. In this way, unnecessary upper luminance peaks are suppressed.

In the light control sheet 14 of this embodiment, the viewing angle characteristics can be changed by changing the composition ratio between the cylindrical surface of the upper shape 141U and the plane of the lower shape 141D.
As an example in which the composition ratio of the cylindrical surface of the upper shape 141U and the plane of the lower shape 141D is changed, the width WU in the vertical direction of the upper shape 141U is 0.09 mm, and the plane side and the curved surface side occupied in the unit lens 141 A light control sheet 14-2 (not shown) was prepared in which the ratio of the width in the direction parallel to the sheet surface was WD: WU = 1: 1.
FIG. 6 is a diagram showing the luminance distribution in the vertical direction of the light control sheet 14-2 in comparison with the luminance distribution of the comparative example.
Although the light control sheet 14-2 is less effective than the light control sheet 14 shown above, the luminance change is moderate as compared with the comparative example.

If the ratio of the upper surface 141U to the cylindrical surface is increased, the characteristics can be made gentler. However, if the cylindrical surface is excessively increased, the front luminance is lowered.
As a result of producing and evaluating various light control sheets, the ratio of the plane side to the curved surface side in the unit lens is the ratio of the width in the direction parallel to the sheet surface WD: WU = 1: 1 to 1: 1. It was found that the range of 5 is desirable in order to moderate the luminance change and suppress the unnecessary luminance peak without greatly reducing the luminance near the emission angle of 0 degree.
The ratio H: P = 1: 2 to 1: 2.5 between the projection dimension H of the unit lens and the pitch P where the unit lenses are arranged does not greatly reduce the luminance near the exit angle of 0 degree. Further, it has been found that it is desirable to moderate the luminance change and suppress unnecessary luminance peaks. In the light control sheet 14 of the present embodiment, the projecting dimension H of the unit lens 141 is 0.093 mm, and the pitch P of the unit lenses 141 is 0.198 mm. Therefore, the projecting dimension of the unit lenses and the pitch of the unit lenses are arranged. Ratio H: P = 1: 2.13, which falls within the above range.
FIG. 9 shows the vertical direction of the light control sheet when the ratio WD: WU of the width in the direction parallel to the sheet surface and the ratio H: P of the protruding dimension of the unit lens and the pitch of the unit lenses are changed. It is a figure which shows the difference in luminance distribution. In FIG. 9, the luminance is shown using the maximum luminance value in the comparative example as a reference value (luminance 1), and the emission angle minus side is the upper side in the use state, and the emission angle plus side is the lower side.
In the light control sheet in which WD: WU is deviated from 1: 1 on the lower limit side to 1: 0.75, and H: P is deviated from the upper limit of 1: 2.5 to 1: 2.75, the emission angle is widened. The brightness in the front (exit angle 0 degree) direction is too low.
Further, in the light control sheet in which WD: WU deviates from 1: 5 on the upper limit side to 1: 1.75, and H: P deviates from the lower limit 1: 2 to 1: 1.7, the emission angle becomes too narrow. Cannot be used.
Thus, the range of WD: WU = 1: 1 to 1: 1.5 is desirable, and the range of H: P = 1: 2 to 1: 2.5 is desirable.

  According to the present embodiment, since the light control sheet has an asymmetric unit lens combining a plane and a curved surface, uniform illumination without unevenness can be performed regardless of the position where the screen is observed. Unnecessary luminance peaks generated in the emission angle direction can be suppressed, and the luminance change can be moderated.

Since the second embodiment is the same as the first embodiment except that the shape of the unit lens is changed, the same reference numerals are given to the portions that perform the same functions as the above-described first embodiment, and the description is repeated. Are omitted as appropriate.
7 is a cross-sectional view of the light control sheet 24 of Example 2 cut in the same manner as FIG. FIG. 7 shows an arrangement similar to that in the case where the use state is cut, as in FIG. 3, so that the vertical direction in the figure is the vertical (up and down) direction and the left side in the figure is the emission side. Show.
The light control sheet 24 of Example 2 is a lens sheet that reduces and equalizes the luminance unevenness of the light emitted from the arc tube 13, and a unit lens 241 that converges and emits light is formed on the emission side. . The unit lens 241 has a shape obtained by combining three types of curved surfaces, and a large number of the unit lenses 241 are arranged in parallel on the emission side surface of the light control sheet 24. The direction in which the unit lenses 241 are aligned is the same as the direction in which the arc tubes 13 are aligned.

The unit lens 241 has a shape obtained by combining three types of shapes, a vertex shape 241T, an upper shape 241U, and a lower shape 241D.
The apex shape 241T is an apex surface that forms the apex of the unit lens 241, has a radius of curvature of 0.02 mm, and has a vertical width WT = 0.011 mm in use.
The upper shape 241U is an upper surface formed above the vertex shape 241T in the use state, has a radius of curvature of 0.195 mm, and has a vertical width WU = 0.099 mm in the use state.
The lower shape 241D is a lower side surface formed below the vertex shape 241T in the use state, has a radius of curvature of 1 mm, and has a vertical width WU = 0.09 mm in the use state.
Therefore, the unit lenses 241 are arranged at a pitch P = 0.2 mm.

The reason why the shape of the unit lens 241 is a combination of the three shapes of the vertex shape 241T, the upper shape 241U, and the lower shape 241D as described above will be described.
When the curvature radius of the upper shape 241U or the lower shape 241D is large, the luminance change becomes steep, but the front luminance can be increased.
Since the display device is rarely observed from below, the front luminance can be improved in a state in which the luminance change is difficult to be observed by setting the shape of the lower shape 241D to a large curvature radius (including infinity). .
On the other hand, the upper shape 241U has a smaller radius of curvature than the lower shape 241D for the purpose of moderating the luminance change.
It is desirable that the vertex shape 241T is sharp in order to increase the front luminance. However, there are problems that chipping occurs when it is sharp, and other sheets such as the reflective polarizing sheet 15 installed on the exit side of the present sheet are damaged. Therefore, in order to solve the above problem while maintaining the front luminance, it is desirable to use a small radius of curvature.

Here, in the light control sheet 24 of the present embodiment, in order to confirm the effect obtained by combining the three shapes of the vertex shape 241T, the upper shape 241U, and the lower shape 241D, FIG. 6 results were compared.
FIG. 8 is a diagram showing the luminance distribution in the vertical direction of the light control sheet 24 of Example 2 compared with the luminance distribution of the light control sheet 14-2 of Example 1 and Example 1. Note that the luminance distribution is measured in the same manner as in the first embodiment, and the expression method in FIG. 8 is the same as that in FIGS. 4 and 6 in the first embodiment.
In the light control sheet 24 of the present embodiment, an unnecessary luminance peak in the vicinity of the lower emission angle (exit angle plus side) of the emission angle of 70 to 90 ° is suppressed to be lower than that of the light control sheet 14-2. This is mainly due to the action of the lower shape 241D having a curved surface.
Further, in the light control sheet 24 of the present embodiment, an unnecessary luminance peak in the vicinity of the upper (emission angle minus side) emission angle of −70 to −90 ° is suppressed to be lower than that of the light control sheet 14-2, and the emission angle. The luminance in the vicinity of −30 to −50 ° is improved, and the luminance change in this range is also gradual. This is mainly due to the action of the vertex shape 241T having a curved surface.

The shape of the unit lens 241 preferably satisfies the following conditions.
(Condition 1) The radius of curvature of the vertex shape 241T is 0.02 mm or more and 0.08 mm or less to reduce unnecessary peaks emitted in a large emission angle direction with an emission angle of 50 ° or more, and overlapping. It is desirable to prevent damage to the reflective polarizing sheet 15 that is arranged in the above manner, to ensure the strength of the vertex shape 241T, and to prevent the vertex shape 241T from being lost.

(Condition 2) When the pitch at which the unit lenses 241 are arranged is P, and the width of the apex surface 241T in the cross section orthogonal to the sheet surface is WT,
0.05 mm <P <0.5 mm (1)
While satisfying the relationship
0.025 <WT / P <0.25 Formula (2)
It is desirable to satisfy the relationship.
By satisfying these expressions (1) and (2) (satisfying condition 2), it is possible to reduce unnecessary peaks that are emitted in a large emission angle direction with an emission angle of 50 ° or more. It should be noted that if the pitch P where the unit lenses 241 are arranged is too large, the effect of forming a curved surface on the vertex shape 241T is reduced and moire is generated, so it is desirable to satisfy the equation (1).

Here, the following test was performed in order to confirm how the shape of the unit lens 241 affects the front luminance, the damage to other stacked sheets, and the loss of the vertex shape 241T.
A sample in which the pitch P of the unit lens is fixed to 0.2 mm and the width WT of the vertex shape is changed is prepared, and the vertex shape width WT = 0, that is, a sheet having no vertex shape and having a sharp vertex is used as a reference. The reduction rate of the front luminance was measured.
In addition, a vibration test is performed in a state where the milky white plate 16, the light control sheet of the sample, and the reflective polarizing sheet 15 are disposed on the reflective plate 12 and the arc tube 13, and the loss of the light control sheet and the reflective polarized light are detected. The adhesive sheet 15 was examined for damage. The results are shown in Table 1 below.

  When the luminance reduction rate shown in Table 1 exceeds 10%, the front luminance is too low and the light collecting effect is reduced. From Table 1, it can be seen that WT / P is desirably greater than 0.0025 and desirably less than 0.25.

  The unit lens 241 of the second embodiment satisfies the condition 1 because the radius of curvature is 0.02 mm, the pitch P = 0.2 mm, and the width WT = 0.011 mm of the vertex shape 241T, so WT / P = 0. .011 / 0.2 = 0.055, which satisfies the condition 2.

According to the present embodiment, an unnecessary luminance peak that occurs in a large emission angle direction can be further suppressed, and a luminance change in a necessary range can be moderated.
Furthermore, since the vicinity of the apex is a curved surface, the wear resistance can be improved.
Furthermore, since it is made of one kind of resin by extrusion molding, environmental resistance is improved.
In addition, light resistance can be improved by using a thermoplastic resin.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, and these are also within the equivalent scope of the present invention.
(1) In each embodiment, the light control sheets 14 and 24 are examples in which one type of unit lenses 141 and 241 are arranged on the emission side. However, the present invention is not limited to this example. These may be combined and placed on the exit side.

(2) In Example 1, the vertex T of the unit lens 141 has a sharp shape that simply connects the upper shape 141U and the lower shape 141D. However, the present invention is not limited to this. A curved surface that smoothly connects the upper shape 141U and the lower shape 141D formed asymmetrically with respect to each other may be formed at the apex portion of the unit lens 141. Thereby, a brightness | luminance change can be made smoother and it can prevent damaging the reflective polarizing sheet 15 grade | etc., With which the light control sheet 14 is piled up.

(3) In each embodiment, an example in which linear light sources are arranged in the light source unit has been described. However, the present invention is not limited thereto, and for example, a light source unit in which many point light sources are arranged may be used.

(4) In each embodiment, the upper shape 141U (curved surface side), the vertex shape 241T, the upper shape 241U, and the lower shape 241D are cylindrical surfaces. However, the present invention is not limited to this example. Or a curved surface formed by combining a plurality of types of curved surfaces.

DESCRIPTION OF SYMBOLS 10 Transmission type display apparatus 11 LCD panel 12 Reflector 13 Light emission tube 14,24 Light control sheet 141,241 Unit lens 141U, 241U Upper shape 141D, 241D Lower shape 241T Vertex shape 15 Reflective polarizing sheet 16 Milky plate

Claims (7)

A light control sheet that is provided in a direct-type surface light source device and uniformizes and / or converges light emitted from the light source,
A cross-sectional shape orthogonal to the sheet surface is an asymmetrical shape, and includes unit lenses arranged in a large number so as to protrude to the emission side,
The unit lens is
Vertex faces forming vertices;
An upper surface that is above the top surface in use, and
A lower surface that is lower than the top surface in use, and
There are three types of curved surfaces
The apex surface, the upper side surface, and the lower side surface are all different in curvature radius of the surface,
Light control sheet characterized by. The light control sheet according to claim 1,
The curvature radii of the three kinds of curved surfaces are such that the curvature radius of the vertex surface is the smallest and the curvature radius of the lower surface is the largest,
Light control sheet characterized by. In the light control sheet according to claim 1 or 2,
The radius of curvature of the lower surface is infinite, and the lower surface is a plane;
Light control sheet characterized by. In the light control sheet according to any one of claims 1 to 3,
The radius of curvature of the apex surface is 0.02 mm or more and 0.08 mm or less,
Light control sheet characterized by. In the light control sheet according to any one of claims 1 to 4,
When the pitch at which the unit lenses are arranged is P, and the width of the apex surface in the cross section orthogonal to the sheet surface is WT,
0.05mm <P <0.5mm
While satisfying the relationship
0.025 <WT / P <0.25
Satisfying the relationship
Light control sheet characterized by. In the light control sheet according to any one of claims 1 to 5,
Formed of one kind of thermoplastic resin,
Light control sheet characterized by. A surface light source device that illuminates a transmissive display unit from the back,
A light source section in which a plurality of light sources are arranged;
The light control sheet according to any one of claims 1 to 6,
A surface light source device comprising:

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