JP2001033829A - Liquid crystal display element having guest-host liquid crystal layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve light resistance of a liquid crystal display element without decreasing display quality, and to obtain the liquid crystal display element having a guest-host liquid crystal layer having a long life on which a waveform of AC driving voltage is controlled to the waveform of n-line inversion driving voltage. SOLUTION: The liquid crystal display element having a guest-host liquid crystal layer consists of a back light 1, back polarizing plate 2, back electrode substrate 3, guest-host liquid crystal layer 4 consisting of a liquid crystal material with addition of dye molecules, front electrode substrate 5, and front polarizing plate 6 arranged and joined in this order. A wavelength cut filter 8 having a wavelength region of light as the absorption wavelength region of light different from the wavelength region of light emitted by the back light 1 is attached to a front face of the liquid crystal display element. The liquid crystal display element has the guest-host liquid crystal layer on which the waveform of the driving voltage for the guest-host liquid crystal layer 4 is controlled to the waveform of n-line inversion driving voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having a guest-host type liquid crystal layer, and more particularly, to a wavelength cut filter having an absorption light wavelength region different from a light wavelength region emitted by a backlight. The present invention relates to a liquid crystal display device having a guest-host type liquid crystal layer which is mounted on a front surface and employs a configuration in which a guest-host type liquid crystal layer is driven by an n-line inversion drive voltage waveform.

[0002]

2. Description of the Related Art Super twisted nematic liquid crystal as a host
On the other hand, the absorption of visible light differs between the major axis and the minor axis of the molecule.
A dichroic dye, which is an anisotropic dye, is added as a guest.
Using guest-host type liquid crystal layer composed of liquid crystal
The guest-host type liquid crystal display device is commonly used. This
Guest-host type liquid crystal display devices are
It is also used as a control panel. See Figure 4 for this
As described below, the guest-host type liquid crystal display element 7 is
When a transmission type liquid crystal is used as the strost type liquid crystal,
Backlight 1, back polarizing plate 2, back electrode substrate 3,
Guest-host type liquid crystal layer 4, front electrode substrate 5, Freon
The polarizers 6 are arranged and joined in this order. here
FIG. 5 is a diagram for explaining electrodes of a passive liquid crystal display element.
Referring to this, the back electrode substrate 3 is aligned in the column direction.
Many are divided into slits and arranged in the row direction
Signal electrode X₁Or X₆Is formed on the substrate surface
Consisting of The front electrode substrate 5 has a slit in the row direction.
A large number of scanning electrodes Y
₁Or Y₆Are formed on the back surface of the substrate. Ba
Between the front surface of the back electrode substrate 3 and the back surface of the front electrode substrate 5
, A guest-host type liquid crystal layer 4 is joined and sandwiched. Faith
No. electrode X₁Or X₆And scanning electrode Y₁Or Y ₆Intersection of
The opposing areas constitute display dots.

Here, the guest-host type liquid crystal will be described as a transmission type liquid crystal in which a dichroic dye as a guest is a blue dye molecule and the backlight 1 is red light. In this case, if no voltage is applied to the opposing region between the back electrode substrate 3 and the front electrode substrate 5, the red light emitted from the backlight 1 passes through the back polarizer 2 and the back electrode substrate 3 to the guest-host type liquid crystal layer. 4, passes through the guest-host type liquid crystal layer 4, and is radiated from the front surface of the guest-host type liquid crystal display element 7 through the front electrode substrate 5 and the front polarizing plate 6. The light emitted from the front surface of the guest-host type liquid crystal display element 7 is light in which red light emitted from the backlight 1 has passed through blue dye molecules contained in the guest-host type liquid crystal layer 4, which is red and blue. It becomes black light which is a complementary color. On the other hand, when a voltage is applied to the facing region between the back electrode substrate 3 and the front electrode substrate 5, the molecules constituting the guest-host type liquid crystal layer 4 are aligned in the voltage application direction, and the red light emitted by the backlight 1 is emitted. The light does not pass through the blue dye molecules contained in the guest-host type liquid crystal layer 4 but passes through the guest-host type liquid crystal layer 4 almost as it is and is radiated from the front surface of the liquid crystal display element 7 corresponding to the electrode facing region to which the voltage is applied. You.
The color of the transmitted light in this case is the red light itself emitted from the backlight 1. This guest-host type liquid crystal display element 7
Is used as an instrument panel of an automobile, by applying a voltage between the back electrode substrate 3 and the front electrode substrate 5, the background color of the instrument panel is changed to red. can do.

In the passive liquid crystal display element 7 described above, the back electrode substrate 3 and the front electrode substrate 5 are generally driven in a time-division manner by a driving line pressure by a voltage averaging method. As an example of this voltage averaging method, all the scanning electrodes Y are set to 1
The polarity of the drive voltage is inverted within two frame times twice as long as one frame time for one scan, and the drive voltage is converted to AC to drive.
The frame AC driving method is adopted. Hereinafter, the outline of the two-frame AC driving method will be described with reference to FIGS.

FIG. 6 is a diagram for explaining a two-frame AC drive voltage waveform applied to the scanning electrodes of a passive liquid crystal display device. The liquid crystal alternating signal F based on the display clock CL
R and a synchronization signal SYNC are generated. The liquid crystal AC conversion signal FR is a signal for generating a two-frame AC drive voltage waveform for a liquid crystal drive voltage generation circuit (not shown). The synchronization signal SYNC is a clock pulse with a duty ratio of 50% synchronized with the frame period. In the example of FIG. 6, 32 display clocks CL are shown, but these form one frame. 3 of display clock CL
Two is a number corresponding to the fact that 32 scanning electrodes Y are formed. Here, the two-frame AC drive voltage waveform means that one cycle of the AC drive voltage waveform is a two-frame cycle. That is, the first one frame period is driven by the negative polarity of the AC drive voltage waveform as shown in FIG. 6, and the next one frame period is inverted and driven by the positive polarity of the AC drive voltage waveform. Hereinafter, in the same manner, the scan electrodes Y are AC-driven by reversing the polarity in one frame cycle. In addition, 2
For details on the frame AC drive method, see "Nikkei Electronics,
August 16, 1980, pages 150-174.

[0006]

The liquid crystal display element 7 described above
When used with being attached to an instrument panel of an automobile, the quality of the guest-host type liquid crystal layer 4 will be deteriorated when exposed to direct sunlight for a long time. When the quality of the guest-host type liquid crystal layer 4 is deteriorated, display unevenness occurs in the liquid crystal display element 7, and eventually the display quality of the liquid crystal display element 7 is reduced. Here, conventionally, light resistance is improved by mounting a wavelength cut filter on the front surface of the guest-host type liquid crystal display element 4. In this case, the wavelength cut filter absorbs and blocks only the light in the ultraviolet region where the energy is particularly large in the direct sunlight from the viewpoint of preventing the quality from being deteriorated by the direct sunlight incident on the guest-host type liquid crystal display element 4. An ultraviolet cut filter is used.

The light in the ultraviolet region is applied to the guest-host type liquid crystal layer 4.
Although it is certain that this is the largest cause of deterioration of the quality of the liquid crystal display device, the light that deteriorates the quality of the guest-host type liquid crystal layer 4 is not limited to light in the ultraviolet region. The liquid crystal display element 7 used by being attached to the instrument panel of the automobile has a high probability of being exposed to direct sunlight for a long time, and has a low ability to deteriorate the quality of light in the visible light wavelength region. As a result of studying the usage of the liquid crystal display element 7 for an instrument panel, it has been recognized that it greatly affects the shortening of the life of the guest-host type liquid crystal layer 4 of the liquid crystal display element 7.

When a wavelength cut filter is mounted on the front surface of the liquid crystal display element 7, a decrease in display characteristics of the liquid crystal display element cannot be avoided. The contrast due to the attachment of the wavelength cut filter decreases, and the amount of transmitted light of the backlight decreases. In addition, the display characteristics as a liquid crystal display element deteriorate. By the way, in a passive liquid crystal display element in which a dye is added to the above-described liquid crystal material to uniformly color the background portion of the display, the two-frame driving voltage waveform is changed to the scanning electrode Y.
, The liquid crystal layer 4 is driven, and if a specific pattern is displayed, if it is exposed to a high temperature for a long time, display unevenness also occurs. In a high-temperature test at 80 ° C. performed with a specific pattern displayed, when the liquid crystal layer 4 was driven with a two-frame AC drive voltage waveform, display unevenness occurred after about four hours had passed. When investigating the cause, it was found that this was caused by dot collapse.

According to the present invention, by mounting a wavelength cut filter on the front surface of a liquid crystal display device having a guest-host type liquid crystal layer, the light resistance can be improved without deteriorating the display quality of the liquid crystal display device, and the AC driving voltage waveform can be improved. The present invention provides a liquid crystal display element having a guest-host type liquid crystal layer which has a longer life by solving the above problem with an n-line inversion drive voltage waveform.

[0010]

A backlight 1, a back polarizer 2, a back electrode substrate 3, a guest-host type liquid crystal layer 4 formed by adding dye molecules to a liquid crystal material, a front electrode substrate 5, In a liquid crystal display device having a guest-host type liquid crystal layer in which front polarizers 6 are arranged and joined in this order, a wavelength cut filter 8 having a light wavelength region different from the light wavelength region radiated by the backlight 1 as an absorption light wavelength region is used as a liquid crystal display device. A liquid crystal display element having a guest-host type liquid crystal layer mounted on the front surface of the display element and having a driving voltage waveform of the guest-host type liquid crystal layer 4 as an n-line inversion driving voltage waveform was formed.

A liquid crystal display device having a guest-host type liquid crystal layer according to claim 2:
A liquid crystal display device having a guest-host type liquid crystal layer in which the wavelength region of the absorption light of the wavelength cut filter 8 is a visible light wavelength region including the ultraviolet light wavelength region was formed. Claim 3: In the liquid crystal display device having the guest-host type liquid crystal layer according to claim 1, the guest-host type liquid crystal layer is made of transmissive liquid crystal using a dichroic dye as a guest as a blue dye molecule,
The backlight 1 is a red light source and the wavelength cut filter 8
A liquid crystal display device having a guest-host type liquid crystal layer as a short light wavelength cut filter that absorbs and blocks light in a light wavelength region other than the red light wavelength region including the ultraviolet region was constructed.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the embodiment shown in FIG. In FIG. 1, members common to those in FIG. 4 are denoted by common reference numerals. The backlight 1 of this embodiment comprises a light source that emits red light. The guest-host type liquid crystal layer 4 is formed of a transmission-type liquid crystal formed by adding a blue dye molecule as a guest to a host of a guest-host type liquid crystal that exhibits anisotropy of visible light absorption in the major axis direction and the minor axis direction of the molecule. This forms the background color of the liquid crystal display element.

Reference numeral 8 denotes a short light wavelength cut filter of the present invention mounted on the front surface of the front polarizing plate 6. As the short light wavelength cut filter 8 of this embodiment, the backlight 1
From the viewpoint of reducing the adverse effect of light in the light wavelength region other than the red light wavelength region radiated by the light on the guest-host type liquid crystal layer 4 of the liquid crystal display element 7, light in the light wavelength region including the ultraviolet region and other than the red light wavelength region. A short-wavelength cut filter that absorbs and blocks light is employed. That is, the light wavelength region other than the red light wavelength region includes the ultraviolet region and the wavelength range of 380 nm to 58 nm.
A visible light wavelength range of 0 nm is included.

Here, as a short light wavelength cut filter 8 for absorbing and blocking light in a light wavelength region other than the red light wavelength region, a filter number S manufactured by Fuji Film Co., Ltd. shown in FIG. 2 is used.
Using a C-52 optical filter, the light resistance test of the examples of the guest-host type liquid crystal display device was performed using light emitted from a xenon lamp. In this test, the voltage waveform applied to the scan electrode to drive the guest-host type liquid crystal layer 4 is an n-line inversion drive voltage waveform described later. The cutoff characteristic of the optical filter of this filter number SC-52 is as shown in FIG. 2, and the light transmittance in the visible light wavelength region of 580 nm or more is 90% or more, and 500 n
The light transmittance in the visible light wavelength region of m or less is 0%. By mounting the optical filter with the filter number SC-52 on the front surface of the liquid crystal display element 7, short-wavelength light including a visible light wavelength region of 500 nm or less is cut off.
Will not be incident. The light in the ultraviolet region is naturally included in the short-wavelength light, and the light in the ultraviolet region does not enter the liquid crystal display element 7. That is, the above short light wavelength cut filter 8 is a short light wavelength cut filter in a light transmission region in which a light transmittance of 580 nm or more has a light transmittance of 90% or more while a light cutoff region of 580 nm or less is a light cutoff region. Excitation radiation wavelength of 580 nm to 700 nm
When the backlight 1 that emits light in the red light wavelength region is used in combination, the red light wavelength region emitted from the backlight 1 is common to the light transmission region of the filter 8, so that the light of the backlight 1 is short. The light is emitted from the liquid crystal display element 7 without being blocked by the light wavelength cut filter 8. The short light wavelength region of 580 nm or less, which has a significant adverse effect on the guest-host type liquid crystal layer 4 of the liquid crystal display element 7, is shared with the light cutoff area of the filter 8, so that it is cut off, and the light enters the liquid crystal display element 7 from the outside. I can't. According to this test, the liquid crystal display element of the present invention was 500
Even after a lapse of time, the drive voltage hardly changes,
It was confirmed that no degradation in display quality caused by an increase in drive voltage occurred.

The above embodiment is directed to a super-twisted nematic liquid crystal display device in which a backlight 1, a back polarizer 2, a back electrode substrate 3, a super-twisted nematic liquid crystal layer 4, a front electrode substrate 5, and a front polarizer 6 are arranged and joined in this order. In the above, the light wavelength region emitted from the backlight 1 is a red light wavelength region, and the wavelength cut filter 8 is a short light wavelength cut filter that absorbs and blocks light in a light wavelength region other than the red light wavelength region.

According to the present invention, the wavelength cut filter 8 can be generally implemented as a wavelength cut filter 8 in which a light wavelength region different from the light wavelength region radiated by the backlight 1 is used as an absorption light wavelength region. For example, when the light wavelength region emitted by the backlight 1 is an orange light wavelength region,
In a case where the wavelength cut filter 8 is a wavelength cut filter that absorbs and blocks light in a light wavelength region other than the orange light wavelength region, a liquid crystal display element in which a pigment is added to a liquid crystal material to uniformly color the background portion of the display. When the liquid crystal layer 4 is driven by applying a two-frame drive voltage waveform to the scan electrode Y,
As described above, when a specific pattern is displayed, exposure to high temperature for a long time causes display unevenness.
The present invention reduces the occurrence of display unevenness due to dot collapse by adopting a configuration in which the drive voltage waveform is an n-line inversion drive voltage waveform and the guest-host type liquid crystal layer 4 is driven by the inversion drive voltage waveform. Realized that it can be.

Referring to FIG. 3, in the n-line inversion driving method, n scanning electrodes Y are driven by one polarity of the driving voltage, and the next n scanning electrodes Y are driven by the other of the driving voltages. The polarity is inverted every time n scan electrodes Y are driven, and the next n scan electrodes Y are driven by an AC voltage. In the example of FIG. 3, n =
5, the drive voltage waveform generated corresponding to the inverted waveform of the liquid crystal alternating signal FR is a 5-line inverted drive voltage waveform.
The number of inversions of the liquid crystal alternating signal FR is increased as compared with the case of two-frame AC driving.

However, from the viewpoint of eliminating display unevenness caused by crosstalk caused by the lowering of the threshold voltage of the liquid crystal display element at a low frequency, it is not possible to drive the liquid crystal display element with an n-line inversion drive voltage waveform. And JP-A-62-31825. However, as described above, the present invention employs an n-line inversion driving voltage waveform as a voltage waveform for driving a super-twisted nematic liquid crystal display element having a super-twisted nematic liquid crystal layer 4 formed by adding dye molecules to a liquid crystal material. Thus, by increasing the number of inversions of the inversion drive voltage waveform, it is possible to prevent the occurrence of display unevenness due to dot collapse. That is, in the liquid crystal display element of the present invention, in a high-temperature test at 80 ° C. performed while displaying a specific pattern, display unevenness caused by dot collapse did not occur even after 500 hours.

[0019]

As described above, according to the present invention, the display quality of the liquid crystal display device is not deteriorated by mounting the wavelength cut filter on the front surface of the liquid crystal display device having the guest-host type liquid crystal layer. A liquid crystal display device having a guest-host type liquid crystal layer having a long life can be provided by improving the light fastness and simultaneously changing the AC drive voltage waveform to an n-line inversion drive voltage waveform.

That is, by mounting a wavelength cut filter on the front surface of the liquid crystal display element having an absorption light wavelength region different from the light wavelength region emitted by the backlight, the light is radiated from the front surface of the liquid crystal display device. The transmission of the desired light is not hindered, and all harmful light wavelength regions including ultraviolet light other than this light are absorbed and blocked so that the light does not enter the liquid crystal display element, so that the deterioration of the guest-host type liquid crystal layer is reduced. The deterioration of the guest-host type liquid crystal layer due to the AC drive voltage waveform is also reduced by using the n-line inversion drive voltage waveform as the AC drive voltage waveform, and the liquid crystal display device having the guest-host type liquid crystal layer has a long life. Be transformed into

In particular, by setting the absorption light wavelength region of the wavelength cut filter to the visible light wavelength region including the ultraviolet light wavelength region, the light resistance of the guest-host type liquid crystal layer against direct sunlight is improved, and the liquid crystal display element is improved. Quality deterioration is greatly improved, and a decrease in display quality can be prevented. The guest-host type liquid crystal layer is formed of a transmission type liquid crystal having a dichroic dye as a guest as a blue dye molecule, a backlight 1 as a red light source, a wavelength cut filter including an ultraviolet region, and a light other than a red wavelength region. By using a short light wavelength cut filter that absorbs and blocks light in the wavelength region, the visible light wavelength region of harmful short light wavelengths including ultraviolet light is blocked. Since the light entering and exiting the liquid crystal display element is also light in the red light wavelength region having a relatively low ability to degrade the guest-host type liquid crystal layer, the quality deterioration of the liquid crystal display element is further reduced. Therefore, this guest-host type liquid crystal display device can be a liquid crystal display device suitable for use in a place where use conditions are severe, such as an instrument panel of an automobile, exposed to direct sunlight.

[Brief description of the drawings]

FIG. 1 illustrates an embodiment.

FIG. 2 is a diagram illustrating a short light wavelength cut filter.

FIG. 3 is a diagram illustrating n-line inversion driving.

FIG. 4 is a diagram illustrating a conventional example.

FIG. 5 illustrates electrodes of a passive liquid crystal display element.

FIG. 6 is a diagram illustrating a two-frame AC drive voltage waveform.

[Explanation of symbols]

 Reference Signs List 1 backlight 2 back polarizing plate 3 back electrode substrate 4 liquid crystal layer 5 front electrode substrate 6 front polarizing plate 7 liquid crystal display element 8 wavelength cut filter

Continued on the front page F term (reference) 2H088 EA23 GA02 HA06 HA11 HA18 HA28 JA05 JA06 JA13 MA01 2H091 FA01X FA08X FA08Z FA41Z GA11 HA07 HA08 HA10 LA16 2H093 NA32 NA33 ND01 ND47 NE06 NF05 NF06 NF13

Claims (3)

[Claims] 1. A guest-host type liquid crystal in which a backlight, a back polarizer, a back electrode substrate, a guest-host type liquid crystal layer formed by adding dye molecules to a liquid crystal material, a front electrode substrate, and a front polarizer are arranged and joined in this order. In a liquid crystal display device having a layer, a wavelength cut filter having an absorption light wavelength region different from the light wavelength region radiated by the backlight is mounted on the front surface of the liquid crystal display device, and the driving voltage of the guest-host type liquid crystal layer is provided. A liquid crystal display device having a guest-host type liquid crystal layer, wherein the waveform is an n-line inversion drive voltage waveform. 2. The liquid crystal display device having a guest-host type liquid crystal layer according to claim 1, wherein the wavelength region of the absorption light of the wavelength cut filter is a visible light wavelength region including an ultraviolet light wavelength region. A liquid crystal display device having a guest-host type liquid crystal layer. 3. The liquid crystal display device having a guest-host type liquid crystal layer according to claim 1, wherein the guest-host type liquid crystal layer is made of transmissive liquid crystal having a dichroic dye serving as a guest as a blue dye molecule. A liquid crystal display having a guest-host type liquid crystal layer, wherein the light is a red light source, and the wavelength cut filter is a short light wavelength cut filter that absorbs and blocks light in a light wavelength region other than the red light wavelength region including the ultraviolet light region. element.