JP4774944B2 - Surface light source device - Google Patents

Description

The present invention relates to a surface light source device that is used to illuminate the liquid crystal display device.

Various surface light source devices have been proposed and put into practical use as surface light sources for illuminating a transmissive liquid crystal display or the like from the back. The surface light source device mainly includes an edge light type and a direct type by 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 is made large, there is a problem that the thickness of the display becomes thick. 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. . Therefore, 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 location of the LCD depending on the positional relationship with the cold cathode tube.

Furthermore, the conventional surface light source device has an emission characteristic having a peak in the normal direction on the emission surface of the surface light source, and has a field of view for applications such as televisions often observed from the front to the top. There is a problem that the angular characteristics are not optimal and the light use efficiency is poor.
JP 05-119703 A JP 11-242219 A Japanese Patent Laid-Open No. 06-347613

An object of the present invention, the screen can be made uniform illumination without unevenness regardless of the position to observe, also provides a surface light source device that have a viewing angle characteristic that is suitable for observation from a specific direction That is.

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 .
Invention 請 Motomeko 1 is a direct type surface light source device for illuminating a transmission-type display unit from the rear, the light source unit formed by arranging a plurality of light sources in parallel with the (12, 13), light emitted from the light source A light control sheet (14) for uniformizing and / or converging the light, and the light control sheet includes a plurality of unit lenses (141) arranged side by side so as to protrude toward the emission side, and the unit lens (141). ) Is formed by combining a plurality of types of portions (141U, 141D) formed by a part of an elliptic cylinder whose long axis is orthogonal to the sheet surface and is continuous , and the arrangement of the unit lenses is orthogonal to the sheet surface. The first shape (141U) on one side in the arrangement direction of the unit lenses and the second shape (141D) on the other side are different from each other in terms of the cross-sectional shape in a cross section parallel to the direction. non-exist in the form Has a universal shape, towards the first shape, the second thickness is greater in the arrangement direction of the unit lens than shape, a surface light source device according to claim.
According to a second aspect of the invention, in the surface light source device according to claim 1, wherein the first shape (141U) and said second shape (141D) is formed by a portion of each elliptic cylinder, said first shape A part of the elliptical cylinder to be formed is a surface light source device characterized in that the ratio a / b between the major radius a and the minor radius b is smaller than that of the elliptical cylinder forming the second shape. is there.
According to a third aspect of the present invention, in the surface light source device according to the first or second aspect, the unit lenses (141) are arranged at a predetermined interval in the arrangement direction. It is a surface light source device.
According to a fourth aspect of the present invention, in the surface light source device according to any one of the first to third aspects, the light control sheet (14) is of the same or different type as the light control sheet on the observation side. The surface light source device is characterized in that at least one optical sheet (15) is further arranged.
According to a fifth aspect of the present invention, in the surface light source device according to the fourth aspect, one of the optical sheets provided closer to the observation side than the light control sheet (14) is a polarization separation sheet (15). There is a surface light source device characterized by being.

According to the present invention, the following effects can be obtained.
(1) Since the cross-sectional shape orthogonal to the sheet surface has an asymmetric shape and includes a plurality of unit lenses that are arranged side by side so as to protrude toward the emission side, the emission direction of the illumination light can be deflected.
(2) The unit lens has an asymmetric shape by combining a plurality of types of portions formed by a part of an elliptic cylinder whose major axis is continuous perpendicular to the sheet surface. In addition to the action, luminance unevenness can be prevented, and uniform illumination without unevenness can be performed regardless of the position where the screen is observed.
(3) Since the unit lens has an upper shape that is the upper side and a lower shape that is the lower side in the use state with respect to the apex thereof, the emission characteristics in the vertical direction can be controlled.
(4) Since the upper shape is thicker in the vertical direction in use than the lower shape, it is possible to increase the illumination light emitted from the front side to the upper side.

  The purpose is to provide uniform illumination with no unevenness regardless of the position where the screen is observed, and to provide viewing angle characteristics suitable for observation from a specific direction. It was realized by a light control sheet having a unit shape and having unit lenses that are arranged side by side so as to protrude toward the emission side.

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 linear light source that forms a light source unit of a backlight. 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 obtained by combining two partial shapes of continuous elliptic cylinders, 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 upper shape 141U is a partial shape of an elliptic cylinder having a major radius of 3.6 mm and a minor radius of 0.36 mm in the cross section shown in FIG. 3, and the major axis thereof is on the sheet surface of the light control sheet 14. They are orthogonal to each other.
On the other hand, the lower shape 141D is a partial shape of an elliptic cylinder having a major radius of 0.29 mm and a minor radius of 0.025 mm in the cross section shown in FIG. It is orthogonal to the sheet surface.
The outer shapes of the upper shape 141U and the lower shape 141D are in smooth contact with each other at the apex T, and the protruding amount is 0.074 mm. The thickness of the light control sheet 14 is 0.45 mm, and the unit lenses 141 are arranged so that the arrangement pitch thereof is 0.093 mm.

FIG. 4 is a diagram illustrating how the light incident on the light control sheet 14 travels. Note that FIG. 4 shows the same arrangement as in the case where the use state is cut, as in FIG.
In the shape of the unit lens 141 described above, the vertical thickness tU in the usage state of the upper shape 141U is thicker than the vertical thickness tD in the usage state of the lower shape 141D. Therefore, most of the light incident on the light control sheet 14 can be directed from the front to the top.

FIG. 5 is a diagram showing the distribution of illumination light immediately after passing through the light control sheet according to the present invention.
Illumination light emitted from the arc tube 13 passes through the light control sheet 14 so that the luminance peak position moves upward in the screen, and the front to upper direction has a higher luminance than the front to lower direction. Is getting wider.

(Comparison evaluation)
A surface light source device obtained by removing the reflective polarizing sheet (DBEF) 15 and the LCD panel 11 from the transmissive display device 10 of this example was compared with a conventional surface light source device and a comparative example.
In the surface light source device of this example, the luminance can be improved by 10% as compared with the conventional surface light source device using the non-directional milky white plate, the matte film, and the brightness enhancement film BEF (manufactured by Sumitomo 3M Limited). Uneven brightness can be avoided, and the number of sheets can be reduced. Furthermore, the half-value angle in the upward direction was enlarged by 10 °.
On the other hand, in the comparative example using the brightness enhancement film BEF having a vertex angle of 90 ° on the light emission side instead of the light control sheet 14, the half-value angle is about 40 ° and the luminance is unnatural at the portion where the emission angle is 60 ° or more. There was a rise.

As described above, in this embodiment, the illumination light is made uniform, the light use efficiency is improved, and the front luminance is improved, so that a low-cost and highly efficient surface light source device is obtained.
Further, in this embodiment, the emission direction of the illumination light is controlled, and the luminance distribution can be biased in one direction. When this light control sheet 14 is used for the vertical control and the viewing angle characteristics are controlled individually in the upward and downward directions, there is almost no opportunity to observe in front or above, particularly for television applications. In addition, a more suitable viewing angle can be realized.

FIG. 6 is a sectional view showing Example 2 of the light control sheet according to the present invention. FIG. 6 shows a cross section similar to that of FIG. The transmissive display apparatus of Example 2 is the same as Example 1 except that the shape of the unit lens 241 of the light control sheet 24 is different from that of the light control sheet 14 of Example 1. Therefore, parts having the same functions as those of the first embodiment described above are denoted by the same reference numerals, and redundant descriptions are omitted as appropriate.
In the cross section shown in FIG. 6, the upper shape 241U is a partial shape of an elliptic cylinder having a major radius of 0.22 mm and a minor radius of 0.07 mm, and its major axis is on the sheet surface of the light control sheet 24. They are orthogonal to each other.
On the other hand, the lower shape 241D is a partial shape of an elliptic cylinder having a major radius of 0.2 mm and a minor radius of 0.037 mm in the cross section shown in FIG. It is orthogonal to the sheet surface.
The outer shapes of the upper shape 241U and the lower shape 241D are in smooth contact with each other at the apex T, and the protruding amount is 0.065 mm. The thickness of the light control sheet 24 is 0.45 mm, and the unit lenses 241 are arranged so that the arrangement pitch thereof is 0.077 mm.

FIG. 5 shown above also shows the distribution of illumination light immediately after passing through the light control sheet 24 of the second embodiment.
As shown in FIG. 5, the illumination light emitted from the arc tube 13 passes through the light control sheet 24, whereby the luminance peak position moves upward in the screen, and the front-upward direction is the front- The range with higher brightness than below is wider. And compared with Example 1, the peak brightness | luminance is high.

(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 sheet has shown an example in which many unit lens shapes having the same cross-sectional shape extending in one direction are arranged. However, the present invention is not limited to this. It may be a lens array (so-called eyelet lens) sheet arranged in the above. In that case, a plurality of unit lens shapes formed by a part of a spheroid whose different major axes are orthogonal to the sheet surface may be combined.

(2) In each embodiment, the light control sheet has shown an example in which one type of unit lens is arranged on the exit side. However, the present invention is not limited to this. For example, a combination of a plurality of types of unit lenses can be used on the exit side. You may arrange.

(3) In each embodiment, an example in which one light control sheet is arranged so as to be able to perform control in the vertical direction has been shown. However, the present invention is not limited thereto, and for example, control in the horizontal direction can be performed. One more light control sheet may be arranged. In this case, it is preferable to use a light control sheet that has symmetrical light control characteristics in the left-right direction.

It is a figure which shows the Example 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 a figure explaining how the light which injects into the light control sheet | seat 14 advances. It is a figure which shows distribution of the illumination light immediately after passing through the light control sheet | seat by this invention. It is sectional drawing which shows Example 2 of the light control sheet | seat by this invention.

Explanation of symbols

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 15 Reflective polarizing sheet 16 Milky white plate

Claims (5)

A direct-type surface light source device that illuminates a transmissive display unit from the back,
A light source unit in which a plurality of light sources are arranged in parallel;
A light control sheet for uniformizing and / or converging light emitted from the light source;
With
The light control sheet includes unit lenses that are arranged side by side so as to protrude to the emission side,
The unit lens is
A long axis is formed by combining a plurality of types of parts formed by a part of an elliptic cylinder that is continuous perpendicular to the sheet surface ,
A cross-sectional shape in a cross section orthogonal to the sheet surface and parallel to the arrangement direction of the unit lenses is a first shape that is one side in the arrangement direction of the unit lenses and a second shape that is the other side with respect to the apex. Are asymmetrical shapes that are different from each other ,
The first shape is thicker in the arrangement direction of the unit lenses than the second shape;
A surface light source device. The surface light source device according to claim 1 ,
The first shape and the second shape are each formed by a part of an elliptic cylinder,
A portion of the elliptic cylinder that forms the first shape has a smaller ratio a / b between the major radius a and the minor radius b than a portion of the elliptic cylinder that forms the second shape,
A surface light source device. In the surface light source device according to claim 1 or 2 ,
The unit lenses are arranged at predetermined intervals in the arrangement direction;
A surface light source device. In the surface light source device according to any one of claims 1 to 3 ,
That at least one optical sheet of the same or different type from the light control sheet is further arranged on the observation side of the light control sheet;
A surface light source device. The surface light source device according to claim 4 ,
One of the optical sheets provided on the observation side of the light control sheet is a polarization separation sheet,
A surface light source device.

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