JPH08190806A - Lens sheet and backlight - Google Patents

Abstract

PURPOSE: To make front face brightness the highest and moderate the decrease of the brightness with the increase of a visibility angle by arranging a number of shape units which are formed through combining two convex column faces, whose generatrices are in parallel, right and left so that a contact face angle is less than 180 degrees. CONSTITUTION: Two convex column faces 10, 10', whose generatrices are mutually in parallel, are combined so as to be symmetrical right and left, and a shape unit 8 is formed so that contact faces at a combination portion 11 cross with an angle of less than 180 degrees. A number of shape units 8 are arranged in parallel in a vertical direction to the generatrix of at least one side face so as to constitute a lens sheet 9. It is desirable to form such a shape that reflected rays at the face 10 out of incident rays into the sheet 9 are totally reflected in an incident direction at the other side face 10', and no outgoing rays from the face 10' in a wide angle rays are not allowed to participate in the increase of front face brightness. The shape is formed according to a predetermined formula. Since the slant face shape of the sheet 9 is formed into curved face-like, the brightness decreases gradually with the increase of a visibility angle so that directional characteristics are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens sheet and a backlight used for a liquid crystal display device, and more particularly, a lens sheet capable of improving the front brightness of the backlight by optical means. And a backlight using such a lens sheet.

[0002]

2. Description of the Related Art In recent years, in battery-powered products such as portable notebook personal computers equipped with color liquid crystal display devices, portable liquid crystal TVs using color liquid crystal panels or video integrated liquid crystal TVs, the power consumption of the liquid crystal display device is a battery. It is an obstacle for extending the driving time. Above all,
The proportion of power consumption of the backlight used in liquid crystal display devices is large, and keeping this power consumption as low as possible is an important issue for extending the battery drive time and increasing the practical value of the above products. .

However, if the brightness of the backlight is lowered by suppressing the power consumption of the backlight, it is not preferable because the liquid crystal display is difficult to see. Therefore, it is desired to improve the optical efficiency of the backlight in order to suppress the power consumption without sacrificing the brightness of the backlight. As a means for achieving this, as shown in FIG. 8, a prism sheet 1 having prism rows 2 formed on one surface thereof is used.
There is proposed a backlight 3 in which is mounted on the exit surface side of the light guide body 7. The increase in frontal brightness due to the prism sheet 1 is caused by the following mechanism.

In such a backlight 3, the light guide 7
The light emitted from is incident on the prism sheet 1, part of the incident light is refracted and transmitted by the prism sheet 1, and the rest is reflected and returned to the light guide 7. For example, the edge-light type backlight 3 as shown in FIG. 8 generally has a directional characteristic that the front brightness is relatively low and the brightness when viewed in an oblique direction is high. By refracting, the directional characteristics are improved so that the brightness on the front side increases. In addition, the reflected light from the prism sheet 1 is diffused and reflected by the diffusion sheet 4 placed on the emission surface of the light guide 7, and the brightness of the emission surface can be increased.
Along with this, the front brightness is also increased.

[0005]

FIG. 9 shows a cross section of the prism array 2 of the prism sheet 1 as described above.
The light ray incident on the prism sheet 1 is a component a which directly passes through the prism slope and is emitted depending on the incident angle, or a component which is once reflected on one prism slope and then reflected again on the other prism slope to return to the incident side. b, a component c which is once reflected by one prism slope and then transmitted through the other prism slope to be emitted. In this case, depending on the selection of the apex angle of the prism, there is a component that undergoes multiple reflection, but the proportion thereof is usually small. Of these, the component a is a light beam that is emitted in the front direction, that is, the observation direction and is actually used. The component b is the light guide 7
Is an effective light beam that is diffusely reflected by the diffusion sheet 4 on the emission surface and increases the brightness of the emission surface. On the other hand, the component c
Is a light ray that is emitted at a wide angle outside the effective viewing angle of the liquid crystal display device, and is a light ray that is not involved in increasing the front brightness.

As a result, the light emitted from the prism sheet 1 has a viewing angle (vertical angle of 90 ° to 100 °, refractive index of 1.5 to 1) of about ± 40 ° from the front in the direction perpendicular to the ridgeline of the prism array 2. It is distributed in the range of about .59). When the viewing angle becomes larger than this, the brightness sharply decreases, and once it becomes almost zero, the brightness again increases at a larger viewing angle. Therefore, as a result, the emission range of the emitted light is narrowed to increase the brightness.

However, in recent years, the directivity of the liquid crystal panel has been improved, and ± 40 even in the direction where the directivity is narrow.
A backlight having a practically useful contrast even at a viewing angle of more than 40 ° has been developed, and a backlight 3 having a directional characteristic such that the brightness sharply decreases in a range of more than ± 40 ° is not preferable. There is a demand for a backlight that has a moderate decrease in luminance with an increase in viewing angle and exhibits a wide range of directional characteristics. The present invention has a directional characteristic such that the luminance in the front direction is the highest, and has a luminance distribution that gradually decreases with an increase in the angle of view over a predetermined viewing angle, and the front luminance as described above. It is an object of the present invention to provide a lens sheet and a backlight that suppress the occurrence of the component c that is not involved in the increase of light emission and have a highly efficient brightness increasing effect.

[0008]

The inventors of the present invention have arrived at the present invention as a result of earnest studies on the lens shape of the lens sheet in view of such a situation. That is, the lens sheet of the present invention, on at least one surface,
A plurality of shape units in which two convex curved cylindrical surfaces whose busbars are parallel to each other are symmetrically coupled are formed side by side in a direction perpendicular to the generatrices, and both of the two convex curved cylindrical surfaces in the coupling portion are formed. It is characterized in that the contact surfaces intersect at an angle smaller than 180 °. In addition, the backlight of the present invention,
On the exit surface side of the light guide body, a shape unit in which two convex curved columnar surfaces whose busbars are parallel to each other are symmetrically coupled to each other via a diffusion layer having a diffuse reflection function is provided on at least one of the busbars. And a lens sheet formed by arranging a plurality of them in a direction perpendicular to each other, and in which the contact surfaces of both of the two convex curved column surfaces of the joint portion intersect at an angle of less than 180 °. is there.

As shown in FIG. 3, the lens sheet of the present invention has two convex curved cylindrical surfaces 10 whose generatrices are parallel to each other.
A large number of lens units having a shape in which 10 'are symmetrically coupled are formed side by side in a direction perpendicular to the generatrix, and each convex shape in the coupling portion 11 of the two convex curved columnar surfaces 10 and 10'. It has a shape in which the tangent surfaces to the curved column surface are combined so as to intersect at an angle of less than 180 °. In the lens sheet 9 having the lens unit having such a shape, one of the convex curved column surfaces 10 of the light rays incident on the lens sheet 9 is
Most of the light rays reflected by the other convex curved cylindrical surface 1
It is possible to reduce light rays that are totally reflected at 0 ′, return to the incident surface side, are reflected by one of the slopes, and then are emitted from the other slope at a wide angle and do not contribute to the increase in front luminance.

Further, in the lens sheet 9 of the present invention, the two convex curved columnar surfaces 10 and 1 constituting the lens unit are formed.
The shape of 0'is such that the light rays reflected by one convex curved column surface 10 of the light rays incident on the lens sheet 9 are totally reflected in the incident direction by the other convex curved column surface 10 '. This is preferable because there are only light rays that are directly transmitted light and light rays that are reflected and returned, and there are no light rays that are reflected by one slope and then exit from the other slope at a wide angle. The light rays that are totally reflected by the other convex curved cylindrical surface 10 'and returned to the incident surface side are diffused and reflected by the diffusing surface provided on the emitting surface of the light guide body, which effectively increases the brightness of the emitting surface. It becomes a light ray. Further, in the present invention, by making the slope shape of the lens sheet 9 a curved surface, the brightness does not sharply decrease at a specific viewing angle or more as in the conventional prism sheet, which is typical. In the example, the brightness is 30 ° to 35
The temperature gradually decreases from 0 ° to zero, and becomes a gentle decrease from 70 ° to 80 °.

Next, a preferred embodiment of the present invention will be specifically described with reference to FIGS. FIG.
FIG. 6 is an xz cross-sectional view of the lens sheet 9 in a preferred embodiment of the present invention, showing optical path tracing in the most characteristic case of φ = θc and p = T in the expressions (1) to (3). In order to prevent the generation of a light beam emitted at a wide angle that does not contribute to the increase in frontal luminance as described above, one convex curved surface 1
When the ray reflected at 0 reaches the other convex curved cylindrical surface 10 ', the convex curved cylindrical surface 10' is always kept at an incident angle larger than the total reflection angle.
The light may be incident on. That is, when the refractive index of the lens portion is n, the light ray reflected by one convex curved cylindrical surface 10 is represented by θc = sin ⁻¹ (1 / n), and the total reflection angle θ
If the convex curved cylindrical surface 10 'is incident at an angle of c or more, BD
As in the light beam shown in, the light is totally reflected by the convex curved columnar surface 10 ′ and returns to the incident surface side.

When viewed from the respective points on the convex curved columnar surface 10 on the right slope in FIG. 3, the convex curved columnar surface 1 on the left slope at the smallest incident angle.
The ray incident on 0'is the reflected light from point P, so P
If the angle between the straight line connecting each point of the convex curved cylindrical surface 10 'and the normal of the tangent surface at each point of the convex curved cylindrical surface 10' is selected to be equal to the total reflection angle θc, the convex The light reflected from other points on the curved columnar surface 10 is totally reflected by the convex curved columnar surface 10 '. That is, O that corresponds to the valley of the convex curved pillar surface 10 '
If the point is the origin (0,0), the coordinates of point P are (T, 0)
Therefore, the convex curved cylindrical surface 10 ′ satisfies the condition of the following formula (4) when x = 0 and satisfies the condition of the following formula (5) when 0 <x <T / 2. For example, all the reflected light from the convex curved columnar surface 10 is totally reflected by the convex curved columnar surface 10 '.

[0013]

[Equation 4] z = 0 (x = 0) (4)

[0014]

[Formula 5] dz / dx = {ztanθc + (xT)} / {(xT) tanθc-z} (0 <x <T / 2) (5) Regarding the convex curved cylindrical surface 10 on the right slope Similarly, x =
When T, the condition of the following expression (6) is satisfied, and T / 2 <x <
If the following expression (7) is satisfied at T, the convex curved cylindrical surface 1
All the reflected light from 0'will be totally reflected by the convex curved cylindrical surface 10.

[0015]

[Equation 6] z = 0 (x = T) (6)

[0016]

[Formula 7] -dz / dx = {ztan θc-x} / {-xtan θc-z} (T / 2 <x <T) (7) The case where φ = θc and p = T has been described above. But,
The directional characteristics of the lens sheet 9 can be changed by adjusting the values of φ and p. For example, φ>
When θc or p <T, the slope of the slope of the lens unit becomes uniformly gentle, and the effective viewing angle can be widened, which is particularly effective when a wide viewing angle is required. In this case, no light ray is emitted at a wide angle, but the increase rate of the front luminance is φ = θ by increasing the viewing angle.
It tends to be lower than in the case of c and p = T. If the increase rate of the front brightness is too low, the merit of using the lens sheet 9 is diminished.
It is preferable that the angle is up to about θc and p is up to about 0.8T.

On the other hand, in the case of φ <θc or p> T, the viewing angle becomes narrower, but the rate of increase of the front luminance can be further increased, and high front luminance is required even if the viewing angle is sacrificed to some extent. Is effective when In this case, some light rays are emitted at a wide angle. However, φ
If p is slightly decreased or p is slightly increased, practically no light beam emitted at a wide angle is generated, and there is no particular problem. That is, FIG. 4 shows optical path tracing when p is slightly larger than T. However, after being reflected by one convex curved column surface 10, a wide angle is obtained from the other convex curved column surface 10 ′. The emitted light ray C reaches the adjacent lens unit and returns to the lens sheet 9 again, and as a result, a light ray emitted at a wide angle is hardly generated. When p is further increased, light rays that are emitted at a substantially wide angle are generated, but if the ratio is small, this does not pose a serious problem in practice. The same applies to φ, and even if φ is reduced to such an extent that the proportion of light rays emitted at a wide angle is small, it does not pose a serious problem in practice. However, if p is made too large or φ is made too small, the proportion of light rays emitted at a wide angle increases, leading to a decrease in front luminance, which is not preferable. Therefore, it is preferable that φ is at most about 0.8θc and p is at most about 1.5T.

Therefore, in the lens sheet 9 of the present invention, the shape of the convex curved upper cylinder surface forming the lens unit is x = 0.
Alternatively, when x = T, the condition of the following formula (1) is satisfied,
When 0 <x <T / 2, the condition of the following expression (2) is satisfied,
When T / 2 <x <T, it is preferable that the shape satisfies the condition of the following expression (3). In this case, φ is 0.
The range is 8θc to 1.2θc, and p is 0.8T to 1.5T.

[0019]

[Equation 8] z = 0 (x = 0, x = T) (1)

[0020]

[Equation 9] dz / dx = {ztanφ + (x-p)} / {(x-p) tanφ-z} (0 <x <T / 2) (2)

[0021]

[Formula 10] -dz / dx = {ztanφ + (Txp)} / {(Txp) tanφ-z} (T / 2 <x <0) (3) The lens sheet 9 of the present invention is shown in FIG. As shown in FIG. 5, a plurality of lens units 8 having the above-described shape are formed in parallel on at least one surface. Usually, the thickness of the lens sheet 9 is about 0.1 mm to 3 mm, and the lens unit 8
It is preferable that the pitch T is about 30 μm to 0.5 mm. Such a lens sheet 9 is placed on the emission surface side of the light guide 7 in place of the prism sheet 1 shown in FIG. 8 to form the backlight 3 of the present invention. Further, as shown in FIG. 2, by using the lens sheet 9 of the present invention by stacking a plurality of the lens units 8 orthogonally to each other,
The effect of increasing the front luminance of the backlight 3 can be further improved.

In the backlight of the present invention, the exit surface of the light guide is used as a diffusion surface, or a diffusion sheet is placed on the exit surface and a lens sheet is placed on the diffusion sheet. This is because by providing a diffusing surface having a diffusive reflection function on the incident surface side of the lens sheet, the light is reflected by one convex upper curved surface that constitutes the lens unit of the lens sheet and then by the other convex curved surface. This is because the light ray that has been totally reflected and returned to the incident surface side is diffused and reflected by the diffusing surface or the diffusing sheet and becomes an effective light ray that again enters the lens sheet and increases the brightness of the emitting surface. In addition, on the surface opposite to the exit surface of the light guide,
Usually, a reflective layer is formed by a reflective sheet or the like,
With such a reflective layer, among the light rays that are reflected by one of the convex curved cylindrical surfaces that form the lens unit of the lens sheet and then are totally reflected by the other convex curved cylindrical surface and returned to the incident surface side, A light ray that has passed through the surface or the diffusion sheet and is incident on the light guide is an effective light ray that is reflected by the reflection layer and is incident on the lens sheet again to increase the brightness of the exit surface.

[0023]

The present invention will be described below in detail with reference to examples.

Example 1 For each lens sheet made of polycarbonate having a refractive index of 1.59 and polymethylmethacrylate having a refractive index of 1.49, φ = θ based on equations (4) to (6).
The shape of each lens when c and p = T was determined, and the cross-sectional shapes thereof are shown by a solid line and a dotted line in FIG. 5, respectively. Based on this cross-sectional shape, a pitch T for each lens unit was set to 50 μm, and a mold having a lens pattern similar to the cross-sectional shape shown in FIG. Using this mold, a lens pattern was transferred to a polycarbonate plate having a thickness of 0.5 mm (refractive index = 1.59) by hot pressing to obtain a lens sheet.
Then, a diffusion sheet was placed on the exit surface of the edge light type light guide, and the obtained lens sheet was placed to form a backlight. For this backlight, the angular distribution of luminance was measured, and the result is shown by the solid line in FIG. The increase rate of the front luminance at this time was 1.4 times.
The angular distribution of luminance shown by the dotted line in FIG. 6 is measured for a backlight that does not use a lens sheet.

Comparative Example 1 A mold having a lens pattern formed by arranging prisms having an apex angle of 90 ° at a pitch of 50 μm was manufactured. Using this mold, a polycarbonate plate having a thickness of 0.5 mm (refractive index 1.
59), the lens pattern was transferred by hot pressing to obtain a prism sheet. The prism sheet thus obtained was mounted with the diffusion sheet on the exit surface of the edge light type light guide, and the lens sheet obtained was then mounted to form a backlight. For this backlight, the angular distribution of luminance was measured, and the result is shown by the solid line in FIG. The increase rate of the front luminance at this time was 1.55 times. Note that FIG.
The angular distribution of the luminance indicated by the dotted line is measured for a backlight that does not use a lens sheet.

As is clear from the comparison between FIG. 6 and FIG.
The front surface luminance of the lens sheet of the present invention is slightly lower than that of the conventional prism sheet, but the viewing angle does not decrease sharply as the viewing angle increases like the conventional prism sheet. Shows a directional characteristic in which the brightness gradually decreases with increasing. As a result, the full width at half maximum is expanded by about 20 °, and the directional characteristics are maintained without impairing the performance of the liquid crystal panel with a wide viewing angle. Further, unlike the conventional prism sheet shown in FIG. 7, there is no increase in brightness in a wide angle region of 50 ° or more, and generation of a light beam emitted at a wide angle that does not contribute to increase in front brightness is suppressed. It is a thing.

Example 2 As shown in FIG. 2, two polycarbonate lens sheets obtained in Example 1 were used, and the lens units thereof were orthogonally overlapped with each other. Composed of lights. When the front luminance and the angular distribution of the luminance of this backlight were measured, the increase rate of the front luminance was 1.7 times, and the half width of the luminance (viewing angle) was ± 3.
It was 5 °.

[0028]

According to the lens sheet of the present invention, the shape of each lens unit has two convex curved cylindrical surfaces whose generatrix are parallel to each other and which are symmetrically coupled to each other, and which has two convex curved cylindrical surfaces in the coupling portion. By making the contact surfaces of both sides intersect at an angle smaller than 180 °, the directional characteristics of the lens sheet can be improved and it can be used for liquid crystal panels with a wide viewing angle without impairing the effect of improving the front brightness. It is possible to provide a backlight having various directivities.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of a lens sheet of the present invention.

FIG. 2 is a perspective view of an embodiment of a backlight using the lens sheet of the present invention.

FIG. 3 is a cross-sectional view illustrating the operation of the lens sheet of the present invention.

FIG. 4 is a cross-sectional view illustrating the operation of the lens sheet of the present invention.

FIG. 5 is a design example of a lens unit formed on one surface of the lens sheet of the present invention.

FIG. 6 is a diagram showing a change in the brightness angle of the backlight using the lens sheet of the example.

FIG. 7 is a diagram showing a change in the luminance of a backlight using a conventional prism sheet of a comparative example.

FIG. 8 is a perspective view showing a form in which a conventional prism sheet or a lens sheet of the present invention is used.

FIG. 9 is a cross-sectional view illustrating the operation of a conventional prism sheet.

[Explanation of symbols]

 1 ・ ・ ・ Prism sheet 2 ・ ・ ・ Prism row 3 ・ ・ ・ Backlight 4 ・ ・ ・ Diffusion film 5 ・ ・ ・ Cold cathode tube 6 ・ ・ ・ Reflective film 7 ・ ・ ・ Light guide 8 ・ ・ ・ Lens sheet Surface forming unit 9 ... Convex curved column surface of lens sheet 10, 10 '... According to one embodiment of the present invention 11 ... Coupling portion

Claims (4)

[Claims] 1. A plurality of shape units in which two convex curved columnar surfaces whose generating lines are parallel to each other are symmetrically connected to each other are formed on at least one surface side by side in a direction perpendicular to the generating lines. 2. A lens sheet, characterized in that the contact surfaces of both of the two convex curved cylindrical surfaces in 2) intersect at an angle smaller than 180 °. 2. A shape in which a convex curved column surface is such that a light ray reflected by one convex curved column surface of the light rays incident on the lens sheet is totally reflected in the incident direction by the other convex curved column surface. The lens sheet according to claim 1, wherein 3. The z axis is parallel to the normal line of the lens sheet, the y axis is parallel to the generatrix of the convex curved cylindrical surface, and the x axis is in the column direction of the shape unit.
The lens sheet according to claim 1, wherein the shape unit has a shape satisfying the following formulas (1) to (3) when the axis is taken. [Equation 1] z = 0 (x = 0, x = T) (1) [Equation 2] dz / dx = {ztanφ + (xp)} / {(xp) tanφ-z} (0 <x <T / 2) ・ ・ ・ (2) [Formula 3] -dz / dx = {ztanφ + (Txp)} / {(Txp) tanφ-z} (T / 2 <x <0) ・ ・ ・ (3 In the formulas (1) to (2), φ = 0.8θc to 1.2θc (where θc = sin ⁻¹ (1 / n), n represents the refractive index of the forming unit), and p = 0.8T to 1.5. T and T represent the width of the forming unit. 4. A shape unit in which two convex curved columnar surfaces whose generating lines are parallel to each other are symmetrically coupled to each other on the exit surface side of the light guide body through a diffusion layer having a diffuse reflection function. Are formed side by side in a direction perpendicular to the generatrix line, and the two tangential surfaces of the two convex curved column surfaces of the joint are 180
A backlight characterized by placing lens sheets that intersect at an angle smaller than °.