JP3553208B2 - Liquid crystal display - Google Patents

Description

但し ｎ₁ ：導光板４の屈折率
ａ：導光板４における、入光端面４Ａの板厚
ｂ：導光板４における、入光端面４Ａとは反対側端面４Ｄの板厚
ｃ：導光板４における、入光端面４Ａからその反対側端面４Ｄまでの長さ
【００１３】
上記（１）式で、 sin^-1（１／ｎ₁ ）は臨界角で、この角よりも出光時入射角θ₁ が大であると、光は外部に出射できない。
又、（ sin^-1（１／ｎ₁ ）−２× tan^-1（（ａ−ｂ）／ｃ））よりも出光時入射角θ₁ が小さくないと、手前側入射角θ₄ が臨界角よりも小となり、上記出射点よりも入光端面４Ａに近い箇所で、光が発光面４Ｂから外部に出射される。
この外部に出射された光と発光面４Ｂのなす角を、出光角θ₅ とすると、出光角θ₅ は、下記式により設定される。
【数４】

【００１４】
尚、上記（２）式は、導光板４の反射面４Ｃが鏡面に近いことが条件であるため、光反射板７として、銀フィルム等の反射性の良いフィルムを使用することは有効である。
ところで、今、導光板４をアクリル樹脂板とすると、ｎ₁ ＝１．４９５となる。又、上記ａ＝３ｍｍ、ｂ＝１ｍｍ、ｃ＝１６０ｍｍとすると、 tan^-1（（ａ−ｂ）／ｃ）で定義される、導光板４の楔角は０．７２°となる。従って、出光時入射角θ₁ は、４３．５３５°〜４０．６７１°の範囲となり、出光角θ₅ は、約０．４°〜１９．４°の範囲となる。
【００１５】
上記のように、導光板４を楔形とすることにより、導光板４の裏面に、特別な拡散手段（乱反射手段）を備えずとも、導光板４の発光面４Ｂから光が出射される。
しかし、出光角θ_５ が、例えば、約０．４°〜１９．４°の範囲のように、非常に小さいため、導光板４を、面光源として、正面から見ると、殆ど発光していないように見える。
そこで、本発明では、図２及び図３に示すように、液晶表示素子２の下側基板１０にプリズム部１３を並設し、導光板４から出射された光を、プリズム部１３の入光端面４Ａ側の側面から入射させて、屈折させた後、プリズム部１３における、入光端面４Ａ側とは反対側の側面で全反射させて、光の進行方向を液晶表示装置の略正面方向に変えるようにしている。
これにより、従来のように、導光板装置１と液晶表示素子２間に、プリズムシートを、別途、介装する必要がなく、それ故、液晶表示装置全体を薄くできる共に、その製造費も安価にできる。
【００１６】
外部に出射される光を、より正確に正面方向に向けるためには、プリズム部１３の頂角θ₂ が、下記の（３）式を満たすことが必要となる。
【数５】
θ₂ ＝（２／３）（９０＋ sin^-1（（ sinθ₃ ）／ｎ₂ ）） ……（３）
但し θ₃ ＝θ ₂ ／２＋
sin^-1（ｎ₁ × sin（θ₁ −２× tan^-1（（ａ−ｂ）／ｃ）））−９０
sin^-1（１／ｎ₁ ）＞θ₁ ＞
sin^-1（１／ｎ₁ ）−２× tan^-1（（ａ−ｂ）／ｃ）
ｎ₂ ：下側基板１０の屈折率

【００１７】
尚、出光時入射角θ_２ は、実際には、一定範囲の角度である。そのため、上記▲３▼式で設定される頂角θ_３ も一定範囲の角度となると共に、プリズム部１３で方向を変えられた光の進行方向も、全て、正面方向とならず、正面方向を中心とする一定範囲の方向となる。
従って、本発明は、上記のように、出光角θ_５ が狭い範囲の角度である場合には、効果的であるが、これとは逆に、導光板４の裏面に、特別な拡散手段（乱反射手段）を備えた場合のように、出光角θ_５ が広い範囲の角度である場合には、プリズム部１３で方向を変えられた光の進行方向も、正面方向を中心とする広い範囲の方向となるため、飛び抜けて、効果的であるとは言えない。
【００１８】
【発明の効果】
以上詳述したように、本発明によれば、液晶表示装置全体を薄くできる共に、その製造費も安価にできる。
【図面の簡単な説明】
【図１】本発明の一実施例を示す断面説明図である。
【図２】図１の要部の拡大図である。
【図３】図２の要部の拡大図である。
【図４】説明図である。
【図５】従来一例を示す断面説明図である。
【符号の説明】
１ 導光板装置
２ 液晶表示素子
４ 導光板
４Ａ 入光端面
４Ｂ 発光面
４Ｃ 反射面
４Ｄ 反対側端面
５ 光源
９，１０ 基板
１１ 液晶
１３ プリズム部[0001]
[Industrial applications]
The present invention relates to a liquid crystal display device.
[0002]
[Prior art]
As shown in FIG. 5, the liquid crystal display device includes a light guide plate device 21 for a backlight and a liquid crystal display element 22 disposed thereon. The light guide plate device 21 includes a light guide plate 23 made of a transparent acrylic resin plate or the like, a light source 24, and the like. One end surface of the light guide plate 23 is a light incident end surface 23A where light from the light source is incident, and the surface is The light-emitting surface 23B is used, and the back surface is used as a reflection surface 23C. In recent years, the light guide plate 23 has a so-called “wedge shape” in which the plate thickness gradually decreases as the distance from the light incident end surface 23A increases, in order to reduce the weight and improve the luminous efficiency.
[0003]
Meanwhile, in the light guide plate 23, the light that has entered the inside from the light incident end face 23A travels inside while repeating total reflection on the light emitting surface 23B and the reflecting surface 23C, and is emitted outside from the light emitting surface 23B. .
However, since the angle (light emission angle) between the light emitting surface 23B and the light emitted to the outside is small, the light guide plate device 21 includes, for example, a prism sheet 26 located above the light guide plate 23. The prism sheet 26 is provided with a number of juxtaposed prisms 27 each having an isosceles triangular cross-section, and the traveling direction of the light emitted to the outside by each prism 27 is substantially in the front direction. be changed.
[0004]
[Problems to be solved by the invention]
In the prior art, there is a problem that the prism sheet 26 increases the thickness of the entire liquid crystal display device, and the prism sheet 26 increases the manufacturing cost of the liquid crystal display device.
An object of the present invention is to provide a liquid crystal display device that can solve the above problem.
[0005]
[Means for Solving the Problems]
To achieve the above object, it is an feature of the present invention includes a light guide plate unit comprising a light guide plate, a liquid crystal display element disposed on the light guide plate, at least one end face of the light guide plate, The light incident end face where light is incident, the thickness of the light guide plate becomes smaller as the distance from the light incident end face decreases, and the liquid crystal display element has a pair of upper and lower substrates and a liquid crystal having liquid crystal filled between the two substrates. In the display device, on the lower surface of the lower substrate, a prism portion integrally formed with the lower substrate and having a cross section formed as an inverted isosceles triangular ridge goes from the light incident end surface side of the light guide plate to the opposite side. A plurality of prisms are arranged side by side in the direction, and the vertex angle θ ₂ of the prism portion is at a point set by the following equation.
(Equation 2)
θ ₂ = (2/3) (90 + sin ⁻¹ ((sin θ ₃ ) / n ₂ ))
However θ ₃ = θ _2/2 +
sin ⁻¹ (n ₁ × sin (θ ₁ −2 × tan ⁻¹ ((ab) / c))) − 90
sin ^-1 (1 / n ₁ )> θ ₁ >
sin ^-1 (1 / n ₁ ) -2 × tan ^-1 ((ab) / c)
θ ₁ : Incident angle at the time of light emission n _{1 on} the upper surface of the light guide plate: Refractive index n _{2 of the} light guide plate: Refractive index of the lower substrate a: Thickness of the light incident end face of the light guide plate b: Light incident end face of the light guide plate Is the thickness c of the opposite end face: the length from the light incident end face to the opposite end face of the light guide plate.
[Action]
Light from the light source enters the inside of the light guide plate from the light incident end surface. The incident light travels while repeating total reflection in which the incident angle and the reflection angle are equal due to the difference in optical density between the light-emitting surface and the reflection surface, which is the interface between the light guide plate and air. It goes to the end face opposite to the light incident end face.
As described above, of the light guided to the light emitting surface of the light guide plate, the light guided at a critical angle or less is emitted to the outside from the light emitting surface.
The traveling direction of the light emitted to the outside can be changed substantially in the front direction by the prism unit.
[0007]
【Example】
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a liquid crystal display device having an edge type light guide plate device 1 for a backlight and a liquid crystal display element 2.
As shown in FIGS. 2 to 4, the light guide plate device 1 includes a light guide plate 4, a light source 5 disposed on one side of the light guide plate 4, a light-shielding cover 6, and a rear surface of the light guide plate 4. It has the arranged light reflection plate 7 and the like.
The light guide plate 4 has a rectangular plate shape, and is made of a transparent resin plate such as acrylic, polystyrene, polycarbonate, vinyl chloride, methacrylic resin, or a transparent glass plate.
[0008]
The end face of the light guide plate 4 on the side of the light source 5 is a light incident end face 4A on which light is incident, and the cross section of the light guide plate 4 is wedge-shaped. The light guide plate 4 is formed so that its thickness becomes gradually smaller, so that the light guide plate 4 is reduced in weight and luminous efficiency is improved. The surface of the light guide plate 4 is a horizontal light emitting surface 4B, and the back surface is an inclined reflecting surface 4C.
Light-shielding tape 8 (edge tape, reflective tape) is attached to the three end faces of the light guide plate 4 except for the light incident end face to prevent light leakage from the three end faces. As the light shielding tape 8, a white film, a silver vapor-deposited film, a silver film, or the like is used. Note that, instead of the light-shielding tape 8, a white paint may be used.
[0009]
A linear light source such as a fluorescent lamp or a cold cathode tube is used as the light source 5, but a point light source such as a lamp or an LED may be used side by side.
The light-shielding cover 6 is formed, for example, by attaching a silver vapor-deposited film to the inner surface of a polyethylene film, and covers the outer periphery of the light source 5 so that the light of the light source 5 does not leak outside.
The light reflection plate 7 is in contact with (or close to) the reflection surface 4C of the light guide plate 4, and is made of a film obtained by depositing aluminum on a white film such as a silver film or polyethylene terephthalate (PET).
[0010]
The liquid crystal display element 2 is disposed on the light guide plate 4 and includes a pair of upper and lower substrates 9 and 10, a liquid crystal 11 filled between the substrates 9, 10, an electrode, and the like. The substrates 9 and 10 are made of glass or various transparent plastics (synthetic resins). The lower substrate 10 is formed by integrally forming an upper plate-shaped main body portion 12 and a plurality of lower prism portions 13 with a plate thickness of, for example, about 1.1 mm. A large number of prism portions 13 are provided on the lower surface of the lower substrate 10 in the direction from the light incident end surface side of the light guide plate 4 toward the opposite side, and the cross section is formed as an inverted isosceles triangular ridge. It is protruding. In addition, in order to reduce the thickness of the lower substrate 10, the pitch of the prism portions 13 is reduced to about 10 to 150 μ, preferably about 35 to 100 μ.
[0011]
By the way, as shown in FIG. 4, in the light guide plate device 1, light from the light source 5 is incident (light enters) from the light incident end face 4 </ b> A of the light guide plate 4. The incident light travels on the light emitting surface 4B and the reflecting surface 4C, which are the interface between the light guide plate 4 and the air, while repeating total reflection at the same incident angle and the same reflection angle due to the difference in optical density, thereby guiding the light. It goes to the end face 4D of the light plate 4 opposite to the light incident end face 4A.
As described above, of the light guided to the light emitting surface 4B of the light guide plate 4, the light guided at a critical angle or less is emitted (emitted, emitted) from the light emitting surface 4B to the outside.
[0012]
By the way, in the light emitted to the outside, the incident angle with respect to the light emitting surface 4B at the emission point, the incident angle at the time of light emission θ ₁ , the incident angle at the time of incidence on the light emitting surface 4B immediately before the emission point, When the front side incident angle theta _4, Idemitsu when the incident angle theta ₁ is set by the following equation.
(Equation 3)

Where n ₁ : refractive index of the light guide plate 4 a: plate thickness of the light incident end face 4A of the light guide plate 4 b: plate thickness of the light guide plate 4 on the end face 4D opposite to the light incident end face 4A c: light guide plate 4 And the length from the light incident end face 4A to the opposite end face 4D.
In the above equation (1) , sin ⁻¹ (1 / n ₁ ) is a critical angle, and if the incident angle θ ₁ at the time of light emission is larger than this angle, light cannot be emitted to the outside.
If the incident angle θ ₁ at the time of light emission is not smaller than (sin ⁻¹ (1 / n ₁ ) −2 × tan ⁻¹ ((ab) / c)), the front-side incident angle θ ₄ becomes the critical angle. small becomes than at a point closer to the light incident face 4A than the exit point, the light is emitted to the outside from the light emitting surface 4B.
The angle formed between the light emitted to the external light emission face 4B, when the light exit angle theta _5, Idemitsu angle theta ₅ is set by the following equation.
(Equation 4)

[0014]
Since the above expression (2) requires that the reflection surface 4C of the light guide plate 4 be close to a mirror surface, it is effective to use a film having good reflectivity such as a silver film as the light reflection plate 7. .
However, now, the light guide plate 4 when the acrylic resin plate, and n ₁ = 1.495. If a = 3 mm, b = 1 mm, and c = 160 mm, the wedge angle of the light guide plate 4 defined by tan ^-1 ((ab) / c) is 0.72 °. Therefore, Idemitsu when the incident angle theta ₁ becomes in the range of 43.535 ° ~40.671 °, Idemitsu angle theta ₅ is a range of about 0.4 ° ~19.4 °.
[0015]
As described above, by forming the light guide plate 4 in a wedge shape, light is emitted from the light emitting surface 4B of the light guide plate 4 without providing a special diffusion means (diffuse reflection means) on the back surface of the light guide plate 4.
However, Idemitsu angle theta ₅ is, for example, as in the range of about 0.4 ° ~19.4 °, very small, the light guide plate 4, as a surface light source, as viewed from the front, hardly emission looks like.
Therefore, in the present invention, as shown in FIGS. 2 and 3, the prism portions 13 are provided side by side on the lower substrate 10 of the liquid crystal display element 2, and light emitted from the light guide plate 4 is incident on the prism portions 13. After being incident from the side surface on the end surface 4A side and refracted, the light is totally reflected on the side surface of the prism portion 13 opposite to the light incident end surface 4A side, so that the traveling direction of light is substantially in the front direction of the liquid crystal display device. I try to change it.
This eliminates the need to separately interpose a prism sheet between the light guide plate device 1 and the liquid crystal display element 2 as in the related art. Therefore, the entire liquid crystal display device can be made thinner, and its manufacturing cost is low. Can be.
[0016]
In order to more accurately direct the light emitted to the outside in the front direction, the vertex angle θ ₂ of the prism portion 13 needs to satisfy the following expression (3) .
(Equation 5)
θ ₂ = (2/3) (90 + sin ⁻¹ ((sin θ ₃ ) / n ₂ )) (3)
However θ ₃ = θ _2/2 +
sin ⁻¹ (n ₁ × sin (θ ₁ −2 × tan ⁻¹ ((ab) / c))) − 90
sin ^-1 (1 / n ₁ )> θ ₁ >
sin ^-1 (1 / n ₁ ) -2 × tan ^-1 ((ab) / c)
n ₂ : refractive index of lower substrate 10

[0017]
Incidentally, Idemitsu when the incident angle theta ₂ is actually an angle within a predetermined range. Therefore, the apex angle θ ₃ set by the above equation ( ₃₎ also becomes an angle within a certain range, and the traveling directions of the light whose directions have been changed by the prism unit 13 are not all in the front direction, but are set in the front direction. The direction is a certain range around the center.
Accordingly, the present invention is, as described above, when the light exit angle theta ₅ is a narrow range of angles is effective, on the contrary, on the rear surface of the light guide plate 4, a special diffuser ( as in the case with the irregular reflection means), when the light exit angle theta ₅ is a wide range of angles is also the traveling direction of the light redirected by the prism portion 13, a wide range around the front direction Because it is a direction, it jumps out and is not effective.
[0018]
【The invention's effect】
As described in detail above, according to the present invention, the entire liquid crystal display device can be made thinner, and the manufacturing cost can be reduced.
[Brief description of the drawings]
FIG. 1 is an explanatory sectional view showing one embodiment of the present invention.
FIG. 2 is an enlarged view of a main part of FIG.
FIG. 3 is an enlarged view of a main part of FIG. 2;
FIG. 4 is an explanatory diagram.
FIG. 5 is an explanatory sectional view showing an example of the related art.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 light guide plate device 2 liquid crystal display element 4 light guide plate 4A light incident end surface 4B light emitting surface 4C reflecting surface 4D opposite end surface 5 light source 9,10 substrate 11 liquid crystal 13 prism section

Claims (1)

A light guide plate device including a light guide plate, and a liquid crystal display element disposed on the light guide plate,
At least one end surface of the light guide plate is a light incident end surface on which light is incident,
The thickness of the light guide plate becomes smaller as it goes away from the light incident end face,
In a liquid crystal display device in which a liquid crystal display element has a pair of upper and lower substrates and liquid crystal filled between the two substrates,
On the lower surface of the lower substrate,
・ A prism section integrally formed on the lower substrate and having a cross section formed as an inverted isosceles triangular ridge,
In the direction from the light incident end face side of the light guide plate to the opposite side, many are arranged side by side,
The vertex angle θ _{2 of the} prism part is
(Equation 1)
θ ₂ = (2/3) (90 + sin ⁻¹ ((sin θ ₃ ) / n ₂ ))
However θ ₃ = θ _2/2 +
sin ⁻¹ (n ₁ × sin (θ ₁ −2 × tan ⁻¹ ((ab) / c))) − 90
sin ^-1 (1 / n ₁ )> θ ₁ >
sin ^-1 (1 / n ₁ ) -2 × tan ^-1 ((ab) / c)
θ ₁ : Incident angle at the time of light emission n _{1 on} the upper surface of the light guide plate: Refractive index n _{2 of the} light guide plate: Refractive index of the lower substrate a: Thickness of the light incident end face of the light guide plate b: Light incident end face of the light guide plate Is a plate thickness of the opposite end face c: a liquid crystal display device characterized by being set in accordance with an expression of a length from the light incident end face to the opposite end face of the light guide plate.

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