JP2002040417A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device which enhances luminance and achieves a high display grade by stably lighting an illumination device (backlight) of an edge light system under broad environments from a high temperature to a low temperature and enhancing the reliability thereof. SOLUTION: The liquid crystal display device 10 is provided with CFLs 11 and 12 changed in luminance characteristics for the temperature environments on the end faces of a light transmission plate 2 and is disposed with a light reflective reflector 4 so as to cover these CFLs 11 and 12. The captioned number 6 denotes a light diffusion plate. A liquid crystal display 8 is disposed above this backlight unit 13. The backlight unit 13 and the liquid crystal display 8 are supported and fixed by a casing 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a liquid crystal display device having an edge light type illumination device (backlight).

[0002]

2. Description of the Related Art A liquid crystal display device is frequently used as a display device of a word processor, a personal computer, or the like, and a backlight is provided in a lighting device for that purpose.

As the backlight, an edge light system has been proposed. A conventional liquid crystal display device 1 will be described with reference to FIG.

[0004] Reference numeral 2 denotes a light guide plate made of a transparent material, 3 denotes a cold cathode discharge tube (hereinafter abbreviated as CFL) disposed on an end face of the light guide plate 4, and 4 denotes a light-reflective reflector attached so as to cover the CFL 3. Reference numeral 5 denotes a light reflecting plate, and reference numeral 6 denotes a light diffusing plate for diffusing the emitted light when the light entering the light guide plate 2 is emitted while being reflected by the light reflecting plate 5. Further, a lens sheet for condensing outgoing light passing through the light diffusion plate 6 may be provided.

A liquid crystal display 8 is disposed on such a backlight unit 7 and the backlight unit 7 is provided.
The liquid crystal display 8 is supported and fixed by the housing 9.

[0006] In recent years, such liquid crystal display devices 1 have been applied to a variety of applications, and accordingly the use environment has become more severe.

[0007] For example, as a representative example, products that are compatible with various use environments are required.

In general, the use environment of liquid crystal has been
Although it is designed on the assumption of about 50 ° C., if it is out of the range, there are various problems.

As an example, when the backlight is used on a low temperature side, there has been a problem that the luminance is extremely reduced and the life is significantly reduced at the same time.

That is, when the temperature is lowered, the mercury vapor pressure is reduced, and the ultraviolet light hitting the phosphor is reduced, whereby the brightness tends to be reduced.

In order to solve this problem, a heater is wrapped around the CFL 3, the ambient temperature is detected by a thermistor, and the CFL 3 itself is heated at a low temperature, thereby improving the brightness and lighting performance at a low temperature. The following technique has been proposed (see Japanese Patent Application Laid-Open No. 10-133177).

On the other hand, the CFL 3 has a double structure of an outer tube and an inner tube, and the space between the inner tube and the outer tube is in a state close to a vacuum. A technique for remarkably improving the rising characteristic and the saturation luminance has been proposed (see Japanese Patent Application Laid-Open No. 10-172512).

[0013]

However, among the above proposals, the technique disclosed in Japanese Patent Application Laid-Open No. Hei 10-133177 has a structure in which a heater is attached to the CFL, so that an additional work step is required, and the ambient temperature is further reduced. Control circuits associated with the detection system were required, which increased the manufacturing cost.

In the technology disclosed in Japanese Patent Application Laid-Open No. Hei 10-172512, the rising characteristics of luminance and the saturation luminance are improved on the low temperature side, but on the other hand, the heat insulation becomes excessive on the high temperature side and the luminance is quickly saturated. Therefore, there is a problem that the luminance is reduced. In addition, the use of such an excessively adiabatic state causes the movement of molecules and ions of the internal gas to be intense, and thus violently collides with the electrodes, thereby promoting the consumption of the electrodes of the CFL and shortening the service life. I was

Accordingly, it is an object of the present invention to stably light an edge-light type illuminating device (backlight) in a wide environment from a high temperature to a low temperature, and to enhance the reliability of the illuminating device (backlight) so as to increase the brightness and obtain a high display. An object of the present invention is to provide a liquid crystal display device that has achieved quality.

It is another object of the present invention to provide a high quality and low cost liquid crystal display device by reducing the manufacturing cost and extending the life of the lighting device.

[0017]

According to the present invention, there is provided a liquid crystal display device comprising a light guide plate having a tubular light source disposed on an end face, a light reflecting member provided on one main surface and a light scattering member provided on the other main surface. A liquid crystal display panel is mounted on the light scattering member, and the tubular light source comprises a plurality of cold cathode tubes, each of which has a different luminance characteristic with respect to a temperature environment.

According to the liquid crystal display device of the present invention, in the illumination device (backlight) as described above, the tubular light source is composed of a plurality of cold cathode tubes, and each of the cold cathode tubes has a different luminance characteristic with respect to the temperature environment. That is, by combining the cold cathode tube with high brightness characteristics on the low temperature side and the cold cathode tube with high brightness characteristics on the high temperature side, and
By selecting a cold-cathode tube to be lit according to the environmental temperature by a thermistor or the like, high brightness and a sufficient life can be achieved in a wide temperature range.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to FIGS.
This will be described in detail below. FIG. 1 shows a liquid crystal display device 1 shown in (Example 1).
FIG. 3 is a cross-sectional view of the liquid crystal display device 14 shown in (Example 2), and FIG. 4 is a cross-sectional view of the liquid crystal display device 17 shown in (Example 3). FIG. 5 and FIG. 8 are data showing luminance characteristics. FIG. 9 shows the liquid crystal display devices 10, 14, 17
It is principal part sectional drawing of.

(Example 1) According to the liquid crystal display device 10 shown in FIG. 1, 2 is a light guide plate made of an acrylic resin having a thickness of 6 mm made of a transparent material, and 11 and 12 are CFLs disposed on the end faces of the light guide plate 2. And a certain distance is maintained between them by a rubber holder. Reference numeral 4 denotes a light-reflecting reflector which is formed by injection-molding polycarbonate of a high reflection material attached so as to cover the CFLs 11 and 12.

Reference numeral 5 denotes a light reflection plate which is provided with a reflection layer on the surface of a white sheet such as PET, and guides light incident on the light guide plate 2 to a light exit surface.

Reference numeral 6 denotes a light diffusing plate for diffusing the light entering the light guide plate 2 when the light is emitted while being reflected by the light reflecting plate 5. Fine irregularities (for example, embossing) are applied to one surface of a white sheet such as PC or PET.

Further, a lens sheet for condensing outgoing light passing through the light diffusion plate 6 may be provided. This lens sheet is composed of only one sheet or a laminated structure of a plurality of sheets. The CFL 1 between the light guide plate 2 and the light diffusion plate 6
Light-shielding dot patterns are provided near 1 and 12,
Alternatively, a black light-absorbing dot pattern may be formed between the light guide plate 2 and the light reflection plate 5.

A 7.2 inch diagonal VGA liquid crystal display 8 is disposed on the backlight unit 13, and the backlight unit 13 and the liquid crystal display 8 are supported and fixed by the housing 9. I do.

In the present invention, as described above, two C
FLs 11 and 12 are juxtaposed.

The CFL 11 is a general CFL, is a single tube having a diameter of 2.3 mm, and is made of Stanley.

On the other hand, the CFL 12 is a double-structure CFL having a heat insulating structure, and has a pipe diameter of 2.4 m made by Toshiba Lilac.
m is a double tube.

The temperature characteristics of the luminance of the CFL 11 are as shown in FIG. 5, and the temperature characteristics of the luminance of the CFL 12 are as shown in FIG.
As shown in FIG.

In these figures, the horizontal axis represents the ambient temperature (° C.), and the vertical axis represents the luminance.
Are measured.

As shown in FIG. 5, the temperature characteristic of the luminance of the CFL 11 becomes a characteristic curve a, and as shown in FIG.
The temperature characteristic of the luminance of 12 is a characteristic curve b.

As is clear from these figures, CFL1
In No. 1, an extreme decrease in luminance is observed on the low temperature side, and the maximum luminance is obtained on the high temperature side rather than on the low temperature side. On the other hand, the brightness on the low temperature side of CFL12 is C
It is much higher than FL11.

In FIG. 7, these CFL1s
Characteristic data when the surface luminance of the light guide plate 2 is measured by turning on 1 and 12 are shown.

As is apparent from FIG. 3, by performing lighting control at the temperature of the intersection C of the luminance curve, stable luminance can be obtained in a wide temperature range.

Thus, according to the liquid crystal display device 10 of the present invention, the CFs having different luminance characteristics depending on the ambient temperature are used.
By using L11 and L12, by selecting a CFL to be lit according to the environmental temperature by a thermistor or the like, high luminance and sufficient life can be achieved in a wide temperature range.

Incidentally, this thermistor utilizes the characteristic that the resistance value changes according to the environmental temperature.
Is connected to the power supply circuit of the CFL via an IC. For this connection, for example, two types of CFLs
For this purpose, an A inverter and a B inverter are prepared, and the A inverter and the B inverter are switched according to the voltage level, so that the temperature can be controlled.

(Example 2) In the liquid crystal display device 10 shown in (Example 1), a general single tube CFL 11 is
Instead, a CFL 12 having a heat insulating structure is used, but instead, in the backlight unit 13a of the liquid crystal display device 14 of the present embodiment, as shown in FIG. CFLs 15 and 16 are used. In FIG. 3, the same parts as those in FIG. 1 are denoted by the same reference numerals.

In the liquid crystal display device 10 of this example, C
The FL 16 uses the same CFL 12 as described above, and the other CFL 15 uses this CFL 16 (CFL 1
Compared with 2), the degree of vacuum between the inner tube and the outer tube is reduced, thereby suppressing the heat insulating effect and obtaining different temperature characteristics.

Also in the liquid crystal display device 14 of the present invention, by using CFLs 15 and 16 having different luminance characteristics depending on the ambient temperature, a CFL to be lit according to the ambient temperature by a thermistor or the like is selected, so that a wide temperature range is obtained. , A high brightness and a sufficient life are achieved.

(Example 3) In the liquid crystal display device 10 shown in (Example 1), a common single tube CFL 11 is
Instead, the CFL 12 having a double structure having a heat insulating structure is used. Instead, in the backlight unit 13b of the liquid crystal display device 17 of the present embodiment, as shown in FIG. CFLs 18 and 19 are used. In FIG. 4, the same parts as those in FIG. 1 are denoted by the same reference numerals.

In the liquid crystal display device 17 of this example, C
The FL 18 uses the same CFL 11 as described above, and the other CFL 19 uses this CFL 18 (CFL 1
Set the gas pressure in the pipe higher than in 1),
It compensates for the amount of heat generated at the beginning of lighting and achieves high brightness.

That is, an inert gas is sealed in the tube, and when the gas pressure increases, the emission of electrons from the electrodes,
The amount of heat generated increases due to the movement of the mercury vapor and the inert gas, but this has the effect of increasing the luminous efficiency, resulting in high brightness.

Also in the liquid crystal display device 17 of the present invention, by using CFLs 18 and 19 having different luminance characteristics depending on the ambient temperature, a CFL to be lit according to the environmental temperature by a thermistor or the like is selected, so that a wide temperature range is obtained. , A high brightness and a sufficient life are achieved.

For reference, in FIG. 8, the vacuum degree is reduced in the order of vacuum degree A, vacuum degree B, and vacuum degree C, and ordinary tubes with further reduced vacuum degree are also prepared. This shows the relationship with luminance.

The horizontal axis represents tube current, and the vertical axis represents luminance.
As is clear from the figure, the luminance characteristics fluctuate by changing the degree of vacuum, and CFLs 18 and 19 having different luminance characteristics depending on the ambient temperature can be obtained by using and combining such various luminance characteristics.

(Regarding Liquid Crystal Display Devices 10, 14, 17) One example of the liquid crystal display devices 10, 14, 17 of the present invention will be described with reference to a transflective liquid crystal display device with reference to FIG. A retardation plate 21 made of polycarbonate or the like and an iodine-based polarizing plate 22 are sequentially stacked on the outer surface of a transparent substrate 20 of the liquid crystal panel, and a retardation plate 24 made of polycarbonate or the like and an iodine-based polarized light are placed on the outer surface of the transparent substrate 23. The plates 25 are sequentially stacked. These are attached using an adhesive made of an acrylic material.

Further, the backlight 13 on the polarizing plate 25,
13a and 13b are provided.

On a transparent substrate 20 such as a glass substrate, a signal electrode 26 and an alignment film (not shown) made of a polyimide resin rubbed in a certain direction are sequentially formed. Note that an insulating layer made of SiO ₂ or the like may be interposed between the signal electrode 26 and the alignment film.

A semi-transmissive film 27 is formed on the inner surface of a transparent substrate 23 made of a glass substrate or the like, and a color filter 28 is provided on the semi-transmissive film 27. Further color filter 2
A black matrix, which is a light-shielding film formed of a thin film made of a metal such as aluminum or chromium, or a photosensitive resist, may be formed between the layers.

Then, the SiO 2 is formed on the color filter 28.
₂ , an overcoat layer 29 made of a resin, a scan electrode 30 on the overcoat layer 29, and an alignment film (not shown) made of a polyimide resin rubbed in a certain direction.
Are sequentially formed. The scanning electrode 30 is orthogonal to the signal electrode 26. Note that an insulating layer made of SiO ₂ or the like may be provided between the scanning electrode 30 and the alignment film.

The semi-transmissive film 27 has both light transmissive and light reflective properties, and prevents a phase difference from occurring when sandwiched between two polarizing plates. In addition, the semi-transmissive film 27 may be specular or scattering.
In order to manufacture the semi-transmissive film 27 having a scattering property, the semi-transmissive film 27 may be formed in an uneven shape with a resin, and the semi-transmissive film may be formed thereon.

The color filter 28 is of a pigment dispersion type.
That is, a photosensitive resist prepared in advance with a pigment (red, green, blue, or the like) is applied on a substrate and formed by photolithography.

Each of the transparent substrates 20 and 23 thus formed is
Are bonded together with a sealing material 32 via a liquid crystal layer 31 made of, for example, a chiral nematic liquid crystal twisted at an angle of 200 to 270 °. Furthermore, both transparent substrates 2
A number of spacers 33 are arranged between 0 and 23 in order to keep the thickness of the liquid crystal layer 31 constant.

In the liquid crystal display devices 10, 14, and 17 having the semi-transmissive film 27 arranged as described above, when used as a reflection type (reflection mode), external devices such as sunlight and fluorescent lamps are used. The light emitted by the illumination is polarized by the polarizing plate 22 and the retarder 2
1 sequentially pass through the liquid crystal panel, but the light incident on the inside of the liquid crystal panel passes through the color filter 28, reaches the semi-transmissive film 27, is reflected by the semi-transmissive film 27, and passes through the liquid crystal panel. The light is emitted through the phase difference plate 21 and the polarizing plate 22.

On the other hand, when the liquid crystal display devices 10, 14, 17 are in the transmission mode, the backlights 13, 13a,
13b sequentially passes through the polarizing plate 25, the phase difference plate 24, and the transparent substrate 23 of the liquid crystal panel, and
7, the light passes through the color filter 28, passes through the liquid crystal panel, passes through the phase difference plate 21 and the polarizing plate 22, and is emitted.

Such a semi-transmissive film 27 is made of a metal thin film of, for example, aluminum, chromium, SUS, or Ag. As the film thickness increases, the light transmittance decreases and the light reflectivity increases. The thickness of such a metal thin film has a different light absorption coefficient depending on the type of metal, and is also determined by which of the applications, the reflection mode and the transmission mode, requires improved performance. , Usually 50-500 °, preferably 100-400 °
It is good to Further, the semi-transmissive film 27 may be formed by a dielectric half mirror. That is, a laminated structure in which low-refractive-index layers and high-refractive-index layers are alternately laminated sequentially may be used.

It should be noted that the present invention is not limited to the above embodiment, and various changes and improvements can be made without departing from the scope of the present invention. For example, in the above example, two sets of CFLs are prepared, but three or more CFLs may be prepared instead.

Further, the liquid crystal display devices 10 and 14 of the present invention
Although the example of 17 has been described using a transflective liquid crystal display device, a transmissive liquid crystal display device may be used instead.

[0057]

As described above, according to the liquid crystal display device of the present invention, the light guide plate having the tubular light source disposed on the end face is provided with a light reflecting member on one main surface and a light scattering member on the other main surface. A liquid crystal display panel is mounted on the light scattering member of the device, and the tubular light source is composed of a plurality of cold cathode tubes. The combination of a cold-cathode tube with high brightness characteristics and a cold-cathode tube with high brightness characteristics on the high-temperature side, and selecting a cold-cathode tube that is lit according to the ambient temperature with a thermistor, etc. High brightness and sufficient life are achieved in the range. As a result, in a wide range of environments from high to low temperatures, edge-light type lighting devices (backlights)
By stably turning on the LED and increasing the reliability thereof, a liquid crystal display device with high luminance and high display quality could be provided.

Further, according to the present invention, a high quality and low cost liquid crystal display device can be provided by reducing the manufacturing cost and extending the life of the lighting device.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a liquid crystal display device of the present invention.

FIG. 2 is a schematic sectional view of a conventional liquid crystal display device.

FIG. 3 is a schematic sectional view of another liquid crystal display device of the present invention.

FIG. 4 is a schematic sectional view of still another liquid crystal display device of the present invention.

FIG. 5 is a diagram showing the relationship between ambient temperature and luminance for a CFL used in a lighting device.

FIG. 6 is a diagram showing the relationship between ambient temperature and luminance for another CFL used in a lighting device.

FIG. 7 is a diagram showing the relationship between ambient temperature and luminance for two CFLs used in the lighting device.

FIG. 8 is a diagram showing a relationship between a degree of vacuum, a tube current, and luminance for a CFL used in a lighting device.

FIG. 9 is an enlarged sectional view of a main part of the liquid crystal display device of the present invention.

[Explanation of symbols]

1, 10, 14, 17: liquid crystal display device, 2: light guide plate, 3, 11, 12, 15, 16, 18, 19 ...
CFL, 5: light reflecting plate, 6: light diffusing plate, 7, 1
3, 13a, 13b ... backlight unit, 8.
..Liquid crystal display members, 9 ... Cases

Claims (1)

[Claims] 1. A liquid crystal display panel is mounted on a light-scattering member of a lighting device having a light-guiding plate provided on one end surface of a light guide plate having a tubular light source disposed on an end surface and a light-scattering member provided on the other main surface. A liquid crystal display device, wherein the tubular light source comprises a plurality of cold cathode tubes, and each of the cold cathode tubes has a different luminance characteristic with respect to a temperature environment.