JP2003059324A - Backlight device and light reflection film for backlight - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To increase the amount of light of a backlight device without increasing power consumption of a light source. A light reflection film, a light guide plate provided on the light reflection film, diffusion layers provided on the light guide plate, and a side surface of the light guide plate. Light sources 12 and 14 for introducing light. The light reflection film 2 has a film substrate 2B and a white layer 2A formed on the lower surface thereof, and the white layer 2A contains titanium oxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device used for liquid crystal displays and the like, and a light reflecting film for the backlight.

[0002]

2. Description of the Related Art As a backlight device for illuminating a liquid crystal display, a side light type device having a light source on its side surface is widely used. The sidelight type backlight device includes a transparent plastic light guide plate and a light reflection film arranged below the light guide plate,
It has a diffusion sheet provided above the light guide plate and a light source such as a cold cathode tube provided on the side surface of the light guide plate, and diffuses light from the light source in the light guide plate. The light escaping downward from the light guide plate is returned upward by the light reflection film, passes through the light guide plate again, and is further diffused by the diffusion sheet. This allows
A thin backlight device that emits light uniformly over the entire surface can be realized.

As a light reflecting film, a film to which a white pigment such as titanium oxide is added has been used because a high light reflectance is required, but this kind of pigment added film has a limit in improving the reflectance. However, the brightness of the screen was not sufficient.

Therefore, in Japanese Patent Laid-Open No. 4-239540, it is proposed to use a polyester film whitened by containing fine air bubbles therein as a light reflecting film. According to such a foamed polyester film, the light amount can be increased to some extent as compared with the pigment-added film.

[0005]

However, there is still a strong demand for higher light intensity and lower power consumption of the backlight device, and there is a limit to the improvement of reflectance by the foamed polyester film.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a backlight device and a light-reflecting film for a backlight which can increase the light amount of the backlight device without increasing the power consumption of the light source. It is an issue.

[0007]

In order to solve the above problems, a backlight device according to the present invention is provided with a light reflecting film, a light guide plate provided on the light reflecting film, and a light guide plate provided on the light guide plate. And a light source for introducing light from the side surface of the light guide plate, and the light reflection film,
It has a film base material and a white layer formed on the lower surface of the film base material, and the white layer contains titanium oxide.

The light reflecting film for a backlight according to the present invention has a film substrate and a white layer formed on the lower surface of the film substrate, and the white layer contains titanium oxide. The white layer may have a thickness of 0.5 to 20 μm, and the white layer has an average particle size of 0.05 to 3 μm.
5 to 70% by weight of titanium oxide particles of m may be added. The film substrate may be a plastic film whitened by containing air bubbles inside.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a backlight device according to the first embodiment of the present invention. In this backlight device, a light reflecting film 2, a light guide plate 4, a lower light diffusing film 6, a prism sheet 8, and an upper light diffusing film 10 are sequentially laminated on a support 1. The planar shape of the backlight device is generally rectangular, but is not necessarily limited thereto. A cold cathode tube 14 is arranged so as to face the side surface 4B of the light guide plate 4, and a reflecting mirror 12 for guiding light from the cold cathode tube 14 to the side surface 4B of the light guide plate 4 is arranged around the cold cathode tube 14. It is arranged. In this specification, the light emitting surface of the backlight device is described as the upper side, but this vertical relationship does not limit the usage mode of the backlight device, and the light emitting surface may be directed in a direction other than the above. You can use it.

This backlight device is arranged, for example, in parallel with the back surface of the liquid crystal display, and is used for illuminating the back surface of the liquid crystal display and transmitting light to the liquid crystal display so that the displayed contents can be easily viewed. However, the backlight device of the present invention is not limited to the illumination of the liquid crystal display as described above, and can be used in various other applications as a surface emitting device.

The support 1 is for supporting the above-mentioned constitutions 2 to 10 from the lower side to increase the flatness, and the material and shape are not limited. For example, it may be formed of any material such as plastic, metal, and ceramics. The support 1 may be a housing that houses the backlight device.

The light reflecting film 2 has a film base material 2B having a constant thickness and a white coating layer 2A formed on the lower surface of the film base material 2B. White layer 2A on the lower surface of the film substrate 2B for further increasing the reflectance
Is a main feature of the present invention.

As the film substrate 2B, preferably,
A whitened plastic film substrate is used by containing fine air bubbles inside and scattering light by the air bubbles. Film base material 2B whitened by foaming
Besides, a film base material to which a white pigment is added can be used, but a foamed film is preferable from the viewpoint of increasing the reflectance. This is because the light absorption by the bubbles is less than the light absorption by the white pigment. More preferably, the film substrate 2B does not contain a white pigment.

The material of the film substrate 2B having fine air bubbles contained therein is not limited, but polyester is preferable. The polyester referred to in the present invention is a polymer obtained by polycondensation of a diol and a dicarboxylic acid. Examples of the diol include ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol and the like. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, adipic acid and sebacic acid. Examples of polyesters include polyethylene terephthalate, polyethylene naphthalate, polymethylene terephthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-
1,4-cyclohexylene dimethylene terephthalate,
Examples thereof include polyethylene-2,6-naphthalenedicarboxylate. In the present invention, polyethylene terephthalate and polyethylene naphthalate are preferable in terms of light reflectance, durability and cost.

The polyester may be a homopolyester or a copolyester, and examples of the copolymerization component include diol components such as diethylene glycol, neopentyl glycol and polyalkylene glycol, adipic acid, sebacic acid and phthalic acid. Examples of the dicarboxylic acid component include isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 5-sodium sulfoisophthalic acid. Further, various additives such as an antioxidant and an antistatic agent may be added to the polyester forming the film substrate 2B.

In order to form fine bubbles in the film base material 2B, high-melting-point incompatible polymer particles may be dispersed in the film base material and the base material may be biaxially stretched. This creates bubbles around the incompatible polymer particles,
A light scattering effect is obtained. The immiscible polymer means polyolefin, polymethylpentene, poly-4-methylpentene-1, poly-3-methylphthalene-1, polyvinyl-t.
-Butane, 1,4-trans-poly-2,3-dimethylbutadiene, polyvinylcyclohexane, polystyrene, polymethylstyrene, polydimethylstyrene, polyfluorostyrene, poly-2-methyl-4-fluorostyrene, polyvinyl-t- Polymers having a melting point of 200 ° C. or higher selected from butyl ether, cellulose triacetate, cellulose tripropionate, polyvinyl fluoride, polychlorotrifluoroethylene and the like can be preferably used. Among them, polyolefin and polymethylpentene which are highly incompatible with the polyester base material are particularly preferable.

When the incompatible polymer is added to the film substrate 2B, the addition amount is preferably 2 to 25% by weight. If it is less than this, the degree of whitening is insufficient, and it becomes difficult to obtain high reflectance. On the other hand, if it is higher than the above range, the strength of the film substrate 2B may be insufficient.

It is necessary that the incompatible polymer and the bubbles are uniformly dispersed in the film substrate 2B. By uniformly dispersing, the reflectance of the light reflecting film 2 can be made uniform. In the present invention, in order to make the brightness of the light emitting surface of the backlight device uniform, it is preferable that the value of the maximum reflectance-the minimum reflectance in the wavelength range of 400 to 700 nm is 10% or less. The porosity of the film substrate 2B is preferably such that the apparent specific gravity of the film substrate 2B is 0.5 or more and 1.2 or less.

The white layer 2A is a layer formed by applying a coating agent containing titanium oxide powder to the film substrate 2B, and has a structure in which titanium oxide particles are uniformly dispersed in the resin layer. ing. The thickness of the white layer 2A is not limited, but is preferably 0.5 to 20 μm. If it is thinner than this range, it is difficult to obtain a sufficient reflectance as the light reflecting film 2 as a whole, and if it is thicker than this range, it is difficult to further improve the reflectance. The thickness of the white layer 2A is more preferably 1 to 10 μm.

The titanium oxide particles of the white layer 2A preferably have an average particle size of 0.05 to 3 μm. If the average particle size is smaller or larger than this range, the effect of increasing the reflectance of the light reflecting film 2 is reduced. The average particle size of the titanium oxide particles is more preferably 0.1 to 1 μm.

Although the content of titanium oxide particles in the white layer 2A is not limited, it is preferably 5 to 70% by weight based on the total weight of the white layer 2A. If it is less than this range, the effect of increasing the reflectance as the light reflecting film 2 is reduced,
Even if it is more than the above range, the reflectance does not rise above the upper limit value and only the cost is increased. The content of titanium oxide particles is more preferably 10 to 40% by weight.

The material of the resin layer of the white layer 2A is not limited, but preferably, acrylic resin, amino resin, cellulose resin, polyester resin, butyral resin, epoxy resin, urethane resin, urea-melamine resin, phenol resin, chloride. Vinyl resin, polyacetal resin, polycarbonate resin, silicon resin, vinyl acetate resin, fluororesin, styrene resin, and 2 selected from these
Mixtures of the above resins are used. Of these, acrylic resins, amino resins, and polyester resins are particularly preferable, and these have good adhesion to the substrate when cured.

A silane coupling agent may be added as an auxiliary agent to the resin layer of the white layer 2A. The silane coupling agent is an organosilicon compound having a functional group capable of chemically bonding to both an inorganic material and an organic material which are not well compatible with each other, and has a general formula of RSiX ₃ . The addition of the silane coupling agent improves the bondability between the resin layer and the titanium oxide particles, and facilitates the formation of the white layer 2A. R is not limited, but may be an organic functional group such as a vinyl group, a glycidoxy group, a methacryl group, an amino group, and a mercapto group. Among these, those having R = glycidoxy group, those having R = amino group, or a mixture thereof are particularly preferable. According to such a silane coupling agent, the reactive groups (hydroxyl group, amino group,
(Isocyanate group) and dienes are bonded to the silane coupling agent to accelerate the curing of the resin, so that a denser resin film is formed and the adhesion to the substrate is enhanced. The addition amount of the silane coupling agent is not limited in the present invention, but is preferably 0.05 to 2% by weight with respect to the entire white layer 2A.

To form the white layer 2A, a coating agent obtained by mixing the resin forming the resin layer, a solvent, a necessary auxiliary agent, and titanium oxide powder is applied to the film substrate 2B to form a solvent. Should be volatilized. The amount of the solvent to be contained in the coating agent may be about 30 to 95% by weight of the resin. It is more preferably 60 to 95% by weight.
The type of solvent is not limited, for example, toluene, ethyl acetate, cyclohexane, xylene, butyl acetate, ethylene glycol monoethyl ether, methyl ethyl ketone, methyl isobutyl ketone, cellosolve acetate,
Also, a mixture of two or more of these can be used.

The light guide plate 4 has a thin plate shape made of a highly transparent resin, and has a rectangular shape in this embodiment. The light guide plate 4 is thick on the side surface 4B facing the cold cathode tube 14 and faces the opposite side surface. It has a cross-sectional shape in which the thickness decreases linearly. Thereby, the light from the cold cathode tubes 14 can be efficiently introduced into the light guide plate 4, and the introduced light can be diffused and reflected to the upper surface side, and the light can be uniformly emitted from the entire upper surface. The thickness of the light guide plate 4 is not limited, but in the case of this type of inclined light guide plate, the width of the side surface 4B is 25 to 188 μm,
The width of the side surface 4B is preferably about 1.1 to 10 times the width of the other side surface 4C. Within this range, the introduction of light and the diffused reflection become good. As a material for the light guide plate 4, acrylic resin or the like having a high transparency and a relatively high refractive index is suitable.

On the lower surface of the light guide plate 4, halftone dot printing is performed over the entire surface to form a halftone dot printing portion 4A. Each dot printing section 4A may be a small circular film of pigmented ink or a metal thin film, or may be a recess or a projection formed on the surface of the light guide plate 4. The density of the halftone dot printing section 4A is set so as to gradually change from the side closer to the cold cathode tube 14 to the side farther from it. Since the density of the halftone dots is inclined in this way, the cold cathode fluorescent lamp 14
A certain amount of light can be emitted regardless of the distance from.

In the present invention, instead of the light guide plate 4,
It is also possible to use a light guide plate having a uniform thickness with no lower surface being inclined.

The lower light diffusing film 6 and the upper light diffusing film 10 are both films made of transparent resin and having a uniform thickness, and their materials and thickness are not limited. Typical thickness is 100-125 μm,
Suitable materials are polyester, polycarbonate, acrylic and the like.

As shown in the enlarged cross section of FIG. 2, the prism sheet 8 has a sheet lower layer 8A, a sheet upper layer 8B formed on the sheet lower layer 8A, and prism portions 8C formed on the sheet upper layer 8B side by side without any gap. . The sheet lower layer 8A, the sheet upper layer 8B, and the prism portion 8C are all made of transparent resin. The prism portion 8C has a quadrangular pyramid shape, and the apex angle thereof is set to be substantially right. This prism part 8
Since the Cs are arranged without a gap, the light incident on the prism sheet 8 is further refracted by the prism portion 8C,
The amount of light can be made uniform. In a preferred example, the sheet lower layer 8A and the sheet upper layer 8B are formed of a polyester resin, and the prism portion 8C is formed of an acrylic resin that is easy to process and has a high optical refractive index.

The thickness of the lower sheet layer 8A and the upper sheet layer 8B is not limited, but is set to, for example, about 50 to 80 μm so as to obtain sufficient strength to support the prism portion 8C. Although the height of the prism portion 8C is not limited, it is preferably 20 to 50 μm in order to obtain a sufficient scattering effect.

The above constitutions 1, 2, 4, 6, 8 and 10 are
Although they may not be adhered to each other, they may be adhered to each other via an adhesive. The adhesive in this case is not limited, but preferably polyvinyl acetate, nitrile rubber,
Urethane, epoxy, acrylic, etc. can be used,
The preferable thickness is about 0.1 to 20 μm.

The cold cathode tube 14 is arranged in parallel with the side surface 4B so as to face the side surface 4B of the light guide plate 4. Cold cathode tube 1
The length of 4 is substantially the same as the length of the side surface 4B. The light source used in the present invention is not limited to the cold cathode tube 14, and any light source having a structure capable of efficiently entering light from the side surface 4B can be used.

The reflecting mirror 12 is a reflecting mirror having an elliptic arc shape in section, which is arranged over substantially the entire length of the light emitting portion of the cold cathode tube 14.
The curved surface shape is set so that all the light from the cold cathode tubes 14 can be emitted toward the side surface 4B.

According to the backlight device having the above structure, since the light reflecting film 2 including the film base material 2B and the white layer 2A is formed on the lower surface of the light guide plate 4,
The light escaping downward from between the halftone dot printing portions 4A is first scattered in the film base material 2B, and a certain proportion of the scattered light enters the light guide plate 4 through the gaps in the halftone dot printing portions 4A, and goes up. Is released to. On the other hand, of the light scattered in the film base material 2B, the light escaping further downward is diffusely reflected by the titanium oxide particles contained in the white layer 2A, and the film base material 2
After passing through the gap between B and the halftone dot printing unit 4A, the light enters the light guide plate 4 and is emitted upward. By such a two-step reflection action of the light reflection film 2, the ratio of the amount of light emitted from the backlight device to the amount of light emitted by the cold cathode fluorescent lamp 14 can be increased, and the backlight can be increased without increasing power consumption. The light quantity of the device can be increased. Further, due to the interaction between the white layer 2A and the film base material 2B, light scattering in the light reflection film 2 is good, and while the reflectance of the light reflection film 2 is increased, the light amount over the entire surface of the backlight device is increased. Does not impede the uniformity of

Further, with the light reflecting film 2 for a backlight according to the present invention, it becomes possible to manufacture a backlight device having excellent light characteristics as described above.

In the above embodiment, the light reflection film 2 was directly attached to the inclined surface of the light guide plate 4, but FIG.
As shown in, the light guide plate 16 having the same inclined cross-sectional shape as the light guide plate 4 may be arranged on the lower surface of the light guide plate 4 so that the inclination is reversed. In this case, the same effect as that of the above embodiment can be obtained. Like the light guide plate 4, the light guide plate 16 is preferably formed of a transparent acrylic resin or the like. Further, in this case, as shown in FIG.
It is possible to illuminate from both sides by arranging 4 etc.

The present invention is not limited to the above embodiments, and for example, the lower light diffusing film 6, the prism sheet 8 and the upper light diffusing film 10 may be formed as one diffusing layer. In addition, the dot printing section 4 is provided on the light guide plate 4.
Instead of forming A, fine unevenness may be formed on the entire lower surface of the light guide plate 4, and light from the cold cathode tube 14 may be irregularly reflected by these unevennesses.

[0038]

According to the backlight device of the present invention, since the light reflecting film composed of the film base material and the white layer is formed on the lower surface of the light guide plate, the light escaping downward from the light guide plate is First, the light is scattered in the film substrate, and a certain proportion of the scattered light enters the light guide plate again and is emitted upward. On the other hand, of the light scattered in the film base material, the light escaping further downward is diffusely reflected by the titanium oxide particles contained in the white layer, passes through the film base material and the light guide plate, and is emitted upward. By such a two-step reflection effect of the light reflecting film, the ratio of the amount of light emitted from the backlight device to the amount of light emitted from the light source can be increased, and the amount of light of the backlight device can be increased without increasing power consumption. Can be increased. Furthermore, due to the interaction between the white layer and the film substrate, the light scattering in the light reflecting film is good, and while increasing the reflectance of the light reflecting film, the uniformity of the light amount over the entire surface of the backlight device is ensured. It does not interfere.

Furthermore, the light reflecting film for a backlight according to the present invention makes it possible to manufacture a backlight device having excellent light characteristics as described above.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view showing an embodiment of a backlight device according to the present invention.

FIG. 2 is an enlarged cross-sectional view showing a prism sheet of the backlight device.

FIG. 3 is an enlarged cross-sectional view showing another embodiment of the backlight device according to the present invention.

[Explanation of symbols]

1 support 2 Light reflection film 2A white layer 2B film base 4 Light guide plate 4A halftone printing section 6 Lower light diffusion film 8 prism sheet 8B sheet upper layer 8A sheet lower layer 8C prism part 10 Upper light diffusion film 12 Reflector 14 Cold cathode tube 16 Light guide plate

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) // F21Y 103: 00 F21Y 103: 00 F term (reference) 2H042 BA02 BA12 BA15 BA20 2H091 FA16Z FA31Z FA41Z FB08 FB12 LA17

Claims (5)

[Claims] 1. A light reflection film (2), a light guide plate (4) provided on the light reflection film (2), and a diffusion layer (6, 8,) provided on the light guide plate (4). 10) and a light source (12, 1) for introducing light from the side surface of the light guide plate (4).
And a white layer (2A) formed on the lower surface of the film substrate (2B), wherein the light reflection film (2) comprises a film substrate (2B).
And a white layer (2A) containing titanium oxide. 2. A film base (2B) and a white layer (2A) formed on the lower surface of the film base (2B), wherein the white layer (2A) contains titanium oxide. Characteristic light reflection film for backlight. 3. The white layer (2A) has a thickness of 0.5 to 2
0 .mu.m, and the white layer (2A) had an average particle size of 0.
The light-reflecting film for a backlight according to claim 2, wherein titanium oxide particles having a diameter of 05 to 3 μm are added in an amount of 5 to 70% by weight. 4. The light reflecting film for a backlight according to claim 2, wherein the film base material (2B) is a whitened plastic film by containing bubbles therein. 5. The light reflecting film for a backlight according to claim 2, wherein the white layer (2A) contains 0.05 to 2% by weight of a silane coupling agent.