JPH10253807A - Prism array film and edge light type surface light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a luminance value in the normal direction of a light conductive plate light output surface of the emitting light by arranging a ridgeline of a unit prism composed of a triangle pole light transmissive substance so as to cross a main lobe of the incident light on an incident surface, and specifying an angle of two base angles running along a light input surface in its triangular cross section. SOLUTION: In a prism array film 10, a unit prism 12 composed of a triangle pole light transmissive substance is integrally arranged with this on a light transmissive film 18 in an incident surface 14 in a condition where a ridgeline 12A crosses a main lobe of the incident light on the incident surface 14 so that ridgelines 12A become parallel to each other by forming the incident surface 14 with one side of the triangular cross section. The main cutting surface of the unit prism 12 is formed in a scalene triangle shape different in incident surface 14 side base angles β1 and β2 . Here, of the base angles β1 and β2 , the main lobe directional base end side base angle β1 of the incident light is substantially set to 45 deg., and the opposite side base angle β2 is substantially set larger than 55 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge light type surface light source used for a backlight of a liquid crystal display device and the like, and a prism array film suitable for use in the edge light type surface light source.

[0002]

2. Description of the Related Art A conventional edge light type surface light source used for a liquid crystal display device or the like is made of a light-transmitting material, and a light guide plate having one surface as a light reflection surface and the other surface as a light emission surface, and this light guide plate And a light source that is arranged along one side end surface and that allows light to enter the light guide plate from the one side end surface.

As such an edge light type surface light source,
A light guide plate provided with a prism film provided on the liquid crystal panel side with a prism surface in which a number of convex portions are arranged in a waveform on the light exit surface side is disclosed in, for example, Japanese Utility Model Laid-Open No. 4-107201. I have.

The convex portion of the prism film is generally a triangular prism having an isosceles triangular cross section, and light from the light guide plate is strongly directed to the user at the triangular prism portion. , Thereby improving the luminance on the screen of the liquid crystal panel.

However, as described above, the edge light type surface light source described above has a main lobe (deflection angle by a luminance meter) when the light source is a one-sided light guide type provided only on one end face side of the light guide plate. The main peak at the time of measurement is inclined in the direction opposite to the light source as a whole, and the directivity of the liquid crystal display device toward the user is weakened.

On the other hand, for example, Japanese Patent Application Laid-Open No. 8-6242
As disclosed in Japanese Patent Laid-Open Publication No. 8 (1999) -1996, there is a prism film in which the triangular prisms in the prism film are left-right asymmetric (unequal-sided triangle).

[0007]

The above-mentioned Japanese Patent Application Laid-Open No. Hei 8-624.
The prism film disclosed in Japanese Patent Publication No. 28 has the advantage that the inclination of the main lobe can be corrected in the normal direction set on the light exit surface of the light guide plate, but the specific prism shape,
Particularly, the angle of the triangular prism was unclear. Further, there is a problem that the luminance value of the emitted light in the direction of the normal to the light exit surface of the light guide plate is not always improved as compared with the conventional left-right symmetric prism.

On the other hand, it is conceivable to adopt a double-sided light guide type in which light sources are provided at both ends of the light guide plate. However, in this case, there is a new problem that the number of parts, weight and power consumption increase. Occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and is intended to reduce the luminance of emitted light in the direction normal to the light exit surface of a light guide plate without increasing the number of parts, weight, and power consumption. It is an object of the present invention to provide a prism array film and an edge light type surface light source whose values are further improved.

[0010]

According to the present invention, a unit prism made of a triangular prism-shaped light-transmitting material is formed by forming one side of a triangle in a cross-sectional shape of the unit prism into an incident surface, and the ridge lines are parallel to each other. In the prism-arranged film, the ridge lines are arranged so as to intersect with the main lobe of the light incident on the incident surface, and the unit prism is divided into three.
The square cross-sectional shape is 2 along the light incident surface in the cross section.
Two base angles are different unequal triangles, and
In order to achieve the above object, one of the base angles is such that the base angle on the base end side in the main lobe direction of the incident light is substantially 45 ° and the other base angle is substantially 55 ° or more. is there.

According to a second aspect of the present invention, there is provided a light guide plate comprising a light-transmitting material, one surface of which is a light reflecting surface and the other surface of which is a light emitting surface.
A light source arranged along one side end surface of the light guide plate to enter light into the light guide plate from the one side end surface; and a substantially triangular prism-shaped translucent material arranged on the light exit surface side of the light guide plate. A plurality of unit prisms are formed from one end face on the light source side to an end face on the opposite side such that one side of the triangle is parallel to and parallel to the light emitting surface, and the ridge lines are parallel to each other. An edge light type surface light source comprising an adjacently arranged prism array film, and an incident angle of main lobe light from the light guide plate to the unit prism of 40 ° or more, and the unit prism The cross-sectional shape of the triangle is such that the two base angles along the light emitting surface in the cross section are different unequal sides and the base angle on the light source side of the two base angles is substantially the same. 45 ° and the other base angle is substantially 55 ° or more In the so that, it is to achieve the above object.

In the edge light type surface light source, an incident angle of light from the light guide plate to the unit prism may be approximately 80 °.

[0013] The invention of claim 4 is made of a translucent material,
A light guide plate having one surface as a light reflection surface and the other surface as a light exit surface, a light source arranged along one end surface of the light guide plate, and light incident on the light guide plate from the one end surface; and the light guide plate The unit prism, which is disposed on the light exit surface side and is made of a substantially triangular prism-shaped light-transmitting material, is arranged such that one side of the triangle is parallel to the light exit surface and the ridge lines are parallel to each other. A plurality of prism-arranged films arranged adjacent to each other from one end surface on the light source side to the opposite end surface, wherein the unit prism is formed in a triangular cross section. The shape is a trapezoidal triangle having two different base angles along the light exit surface in the cross section, and the base angle on the light source side is substantially 45 out of the two base angles.
The above object is achieved by setting the other base angle to be 46 ° or more and 78.1 ° or less.

In the edge light type surface light source, a light diffusion sheet may be interposed between the light emitting surface of the light guide plate and the prism array film.

In the present invention, it is most preferable that the triangle of the triangular prism be an unequal triangle, and that the base angle of the base side of the main lobe direction of the incident light be 45 ° among the two base angles of the triangle. It was confirmed by experiments that the luminance value of the emitted light in the normal direction was improved, and further, the optimum value of the base angle on the opposite side was obtained by calculation, so that the luminance value in the normal direction was maximized. is there.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings.

The prism array film 10 according to the present invention
As shown schematically in FIG. 1, a unit prism 12 made of a triangular prism-shaped light-transmitting material is formed such that one side of a triangle in a cross-sectional shape forms an incident surface 14 and a ridge line. In the state where the ridge line 12A crosses the main lobe of the incident light 16 on the incident surface 14 so that the ridge lines 12A are parallel to each other, the incident surface 14 is integrally formed on the light-transmitting film 18 on the incident surface 14. It is provided in a special way.

As shown in FIG. 2, the unit prism 12 has a main cutting plane (a plane cut so that each angle of the prism is minimized, and is generally a plane orthogonal to the ridge line 12A). The base angles β1 and β2 on the incident surface 14 side are different unequal triangles.

Here, among the base angles β1 and β2, the base angle β1 of the base end side (left side in FIGS. 1 and 2) of the incident light 16 in the main lobe direction is substantially 45 °, and the base angles on the opposite sides. β2 is set substantially larger than 45 °.

When the unit prism 12 is an inequilateral triangular shape having two different base angles on the main cutting plane and the base angle β1 is substantially 45 °, as a result of an experiment by the present inventor, the unit prism 12 The light transmitting film 1 in the outgoing light of
A phenomenon in which the luminance in the normal direction set to 8 was further improved was confirmed.

The reason is that the light rays other than the main lobe, which are incident on the prism array film 10, can be most efficiently directed in the normal direction, and the base angle β1 should be within 45 ° ± 3 °. For example, it was possible to obtain the above-described brightness enhancement phenomenon in the normal direction.

The base angle β2 on the front side of the main lobe is determined as follows.

As shown in FIG. 2, the unit prism 1
The incident angle of the incident light 16 incident on the second incident surface 14 is θ1,
The outgoing angle of the outgoing light beam emitted from the inclined surface 12B of the unit prism 12 is θ4, the refraction angle at the incident surface 14 is θ2,
Assuming that the angle of incidence of the refracted light on the inclined surface 12B is θ3 and the refractive index of the material of the unit prism 12 is n, the following formula (1) is established by the known Snell's formula. In addition,
The refractive index of the surrounding air is set to 1.

N sin θ 2 = sin θ 1, n sin θ 3 = sin θ 4 (1)

The following equation (2) holds geometrically between the base angle β2 and θ1 and θ2.

Β2 = θ1 + θ2 (2)

The outgoing light 20 from the inclined surface 12B of the unit prism 12 is emitted in a direction perpendicular to the incident surface 14 using the above formulas (1) and (2) and the formula of a known trigonometric function. By solving θ1 with respect to β2 so as to have a relationship, the following equation (3) is obtained.

Β 2 = tan ⁻¹ [sin θ 1 / {(n ² −sin ² θ 1) −1}] (3)

Here, when the refractive index n of the unit prism 12 is 1.57, for example, the relationship between θ1 and β2 is as shown in Table 1 below.

[0030]

[Table 1]

On the other hand, when the base angle β 2 is smaller than the other base angle β 1, the emitted light 20 is deflected in the normal direction of the incident surface 14, but the normal direction set on the incident surface 14. Is suppressed. Therefore, the base angle β2 must be larger than β1 so as not to reduce the overall effect of improving the luminance in the normal direction. The base angle β2 is greater than the incident angle θ1
Will be determined according to

This is consistent with the fact that the incident angle θ in a one-sided light guide type backlight source is large, which is convenient.

Even when the incident angle θ1 of the incident light 16 is small, it is desirable that the base angle β2 is larger than 45 ° for the following reasons.

Using the formulas (1) and (2) and the known trigonometric function formula, the outgoing light 16
When the base angle β2 is solved for the incident angle θ1 under the condition perpendicular to the following, the following equation (4) is obtained.

Θ ¹ = sin ⁻¹ [−sin β ² ｛cos β ² ± {(n ² −sin β ² )}] (4)

In the equation (4), for example, n = 1.5
7, when β2 = 45 °, θ1 = 29.4 °. Therefore, under this condition, the incident angle of the main lobe of the incident light 16 does not follow Table 1 from 0 ° to 29.4 °, and β2
Is set to an angle greater than 45 °, more preferably 46 °.

The apex angle α of the triangle in the unit prism 12 is given by α = 180 ° − (β
1 + β2).

Here, the prism array film 10
Can be obtained by molding the unit prism 12 directly or separately on the translucent film 18.

As a method of forming the prism shape, a known hot pressing method (see Japanese Patent Application Laid-Open No. 56-157310), an ultraviolet curable thermoplastic resin film is embossed with a roll embossing plate, and then irradiated with ultraviolet rays. To cure the film (JP-A-61-15)
No. 6273).

Translucent film 18 and unit prism 12
The material of the polymethyl methacrylate, acrylate or methacrylate alone or copolymer such as polymethyl acrylate, polyethylene terephthalate, polyester such as polyethylene terephthalate,
It is composed of a sheet-shaped or plate-shaped member made of a transparent material such as a transparent resin such as polycarbonate or polyethylene, transparent glass, or transparent ceramics.

The translucent film 18 preferably has a thickness of about 20 to 1000 μm when used for a backlight source in a liquid crystal display device, for example.

The pitch of the unit prism 12 is 1 to 10
00 μm, more preferably 10 μm.

Next, an edge light type surface light source using the prism array film 10 will be described with reference to FIG.

The edge light type surface light source 30 is made of a translucent material, one surface of which is a light reflecting surface 32A and the other surface of which is a light emitting surface 3A.
2B, a light source 34 such as a fluorescent lamp or the like, which is disposed along one end face 32C of the light guide plate 32 and allows light to enter the light guide plate 32 from the one end face 32C; And the prism array film 10 disposed on the light exit surface 32B side of the light plate 32.

The reference numeral 36 in FIG.
A light diffusion sheet 38 disposed between B and the prism array film 10 indicates a light diffusion material coated on the light reflection surface 32A side of the light guide plate 32, respectively.

The light guide plate 32 is formed of the same material as the prism array film 10, and has a light reflection surface 32A.
Is composed of, for example, a white PET (polyethylene terephthalate) film. Also, the light diffusion sheet 36
Is made of a material containing fine small spheres such as acrylic beads, and diffuses incident light from the light exit surface 32B.
Further, the light diffusing substance 38 is similarly formed by applying a paint containing fine acrylic spheres or the like.

As described above, the edge light type surface light source 30 emits the outgoing light 20 having a large component perpendicular to the incident surface 14 by the prism array film 10 as described above. When used as, the brightness of the screen can be greatly improved.

[0048]

The present invention is configured as described above.
There is an excellent effect that the luminance value in the normal direction of the light emitting surface can be improved without increasing the number of parts, weight, and power consumption.

[Brief description of the drawings]

FIG. 1 is an enlarged perspective view showing a main part of a prism array film according to the present invention.

FIG. 2 is an enlarged schematic view showing one unit prism in the prism array film.

FIG. 3 is a side view showing an edge light type surface light source using the prism array film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Prism arrangement film 12 ... Unit prism 12A ... Ridge line 12B ... Slope surface 14 ... Incident surface 16 ... Incident light 18 ... Translucent film 20 ... Outgoing light 30 ... Edge light type surface light source 32 ... Light guide plate 32A ... Light reflecting surface 32B: Light emitting surface 32C: One side end surface 34: Light source 36: Light diffusion sheet

Claims (5)

[Claims] 1. A prism array film in which unit prisms made of a triangular prism-shaped light-transmitting substance are arranged such that one side of a triangle in a cross-sectional shape forms an incident surface and ridge lines are parallel to each other. In the above, the ridge line is arranged so as to intersect with a main lobe of light incident on the incident surface, and the unit prism has a triangular cross-sectional shape, and two base angles along the light incident surface in the cross section. Different inequilateral triangles, and of the two base angles, the base angle on the base end side in the main lobe direction of the incident light is substantially 45 °, and the other base angle is substantially 55 ° or more. A prism array film characterized in that: 2. A light guide plate made of a light-transmitting material, one surface of which is a light reflection surface and the other surface of which is a light exit surface, and is disposed along one end surface of the light guide plate, and the light guide plate is arranged from the one end surface. A light source for entering light into the light guide plate;
A unit prism made of a prismatic translucent material is placed on the opposite side from the one side end surface of the light source side such that one side of the triangle is parallel to the light exit surface and parallel to the ridge line. An edge light type surface light source comprising: a plurality of prism-arranged films arranged adjacent to each other toward an end surface of the unit prism, wherein an incident angle of main lobe light from the light guide plate to the unit prism is 40 ° or more. And the unit prism,
The triangular cross-sectional shape is an inequilateral triangle with two different base angles along the light-emitting surface in the cross-section, and
Of the two base angles, the base angle on the light source side is substantially 4
An edge light type surface light source characterized in that the base angle is 5 ° and the other base angle is substantially 55 ° or more. 3. The edge light type surface light source according to claim 2, wherein an incident angle of light from said light guide plate to said unit prism is approximately 80 °. 4. A light guide plate made of a translucent material, one surface of which is a light reflection surface and the other surface of which is a light exit surface, and is disposed along one end surface of the light guide plate, and the light guide plate is arranged from the one end surface. A light source for entering light into the light guide plate;
A unit prism made of a prismatic translucent material is placed on the opposite side from the one side end surface of the light source side such that one side of the triangle is parallel to the light exit surface and parallel to the ridge line. An edge light type surface light source comprising: a plurality of prism-arranged films arranged adjacent to each other toward an end face of the unit prism, wherein the unit prism has a triangular cross-sectional shape along the light-emitting surface in the cross-section. The two base angles are different unequal triangles, and of the two base angles, the base angle on the light source side is substantially 45 °, and the other base angle is 46 ° or more,
An edge-light type surface light source characterized in that the angle is 78.1 ° or less. 5. The edge light type surface light source according to claim 2, wherein a light diffusion sheet is interposed between the light exit surface of the light guide plate and the prism array film.