JPH07278546A - Display device - Google Patents

Abstract

PURPOSE:To obtain a display device reduced in drive voltage, excellent in saving of electric power and useful for an information display device, etc., by using a chiral nematic liquid crystal containing a specified aromatic fluorine- containing compound as one component and controlling the chiral pitch so as to reflect visible light. CONSTITUTION:This is a display device containing a chiral nematic liquid crystal and having a chiral pitch controlled so as to reflect visible light. This display device reduced in drive voltage enough to be driven by a liquid crystal driver IC, excellent in saving of electric power and useful for, e.g. a computer, a television, a clock machinery, a notice board or a panel for control of a machine contains at least a specified compound represented by formula I [A is phenylene, cyclohexanylene, biphenylene or a group of formula II to V; R is an alkyl or an alkoxy; X is CN, H, F or Cl; (n) is an integer of >=1] as one component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display element used in an information display device such as a computer, a television, a timepiece device, an advertising board, and a device operation panel.

[0002]

2. Description of the Related Art In recent years, information devices have become smaller and more portable, and power consumption of display devices mounted on them has also been required. Therefore, recently, a bright reflective display device that does not use a polarizing plate is being developed.

SID 92 DIGEST, p. 759
According to the report, a cholesteric structure stabilized by a polymer is reported by adding a small amount of a polymer precursor to a cholesteric liquid crystal (chiral nematic liquid crystal) and polymerizing it with ultraviolet rays. This is a reflective display element having a property (memory function) of retaining the state at the time of writing even after the voltage is applied and writing is performed even when the electric field is cut off.

Further, Proceedings of t
he 13th IDRC (EURODISPLAY
'93), P. 157, a method has also been developed in which the electro-optical hysteresis when the applied voltage is increased and when it is decreased is used as a memory function.

Since these methods do not require repeated scanning, they are suitable for a display having a relatively large display capacity, and the power consumption can be suppressed low.

By mixing a nematic liquid crystal compound or a non-liquid crystal compound with a difluorobenzonitrile derivative, a liquid crystal composition having a low threshold voltage can be obtained (JP-A-4-159258).

[0007]

However, when a cholesteric (chiral nematic) liquid crystal as described above or a cholesteric structure stabilized by a polymer is used as a display device and driven by applying a voltage pulse of 40 msec, the device is driven. The voltage becomes 40 V or more. Therefore, there is a problem that power consumption increases. Further, the withstand voltage of the liquid crystal driver IC currently available is limited to around 40 V, and in order to drive the above display element using the liquid crystal driver IC, a voltage amplification device is indispensable between the display element and the liquid crystal driver IC. Is. Therefore, there is a problem that it goes against the reduction in size and weight of the display device.

Therefore, the present invention is to solve such a problem, and an object of the present invention is to provide a liquid crystal driver I.
An object is to provide a power-saving display element whose driving voltage is low enough to be sufficiently driven by C.

[0009]

The display device of the present invention is a display device in which a chiral nematic liquid crystal is used and a chiral pitch is adjusted so as to reflect visible light.

[0010]

[Chemical 3]

(R is an alkyl group or an alkoxy group, X
Is a compound containing at least one specific compound represented by CN or H, F, Cl, and n is an integer of 1 or more).

Further, in the display device in which the chiral nematic liquid crystal and the polymer are dispersed with each other and the chiral pitch is adjusted so as to reflect visible light, the compound group I

[0013]

[Chemical 4]

(R is an alkyl group or an alkoxy group, X
Is a compound containing at least one specific compound represented by CN or H, F, Cl, and n is an integer of 1 or more).

[0015]

【Example】

Example 1 In this example, compound B, which is one of the above compound group I, is added as an additive component.

[0016]

[Chemical 5]

An example in which BL008 (manufactured by Merck) is used as the base liquid crystal and a mixture of CB15 (manufactured by Merck) and R1011 (manufactured by Merck) as the chiral component is used. First, the material composition sealed between the substrates will be described. The additive component (the above compound B) was added to the base liquid crystal (BL008) so that the ratio by weight was 9: 1. This and chiral component (weight ratio CB1
5: R1011 = 85: 15 mixture), and the chiral pitch was adjusted so as to selectively reflect green visible light to obtain a material composition.

Next, a substrate for enclosing the material composition will be described. FIG. 1 shows a cross-sectional view of the display device of this example. On the substrate 1 made of soda glass, ITO was formed by sputtering and then patterned to form the electrode 2. Next, polyimide was formed as the alignment film 3 and subjected to rubbing treatment. After the same treatment was applied to the substrate 7 made of soda glass, the substrates were fixed so that the orientation directions of the upper and lower substrates were substantially parallel to each other with a gap of about 5 μm between them.

The material composition described above was enclosed in the empty panel thus produced, and the light absorbing material 8 was placed on the back surface of the substrate 7.

Next, the measuring method will be described. The manufactured display element is arranged in the optical system as shown in FIG. 2, and a voltage pulse is applied to make it a bright state as an initial state. Then, pulses are sequentially applied from 0 V to 50 V, and 0. 1
The response after seconds is shown by the solid line in FIG. Next, similarly, after making a dark state, a pulse is applied and the response 0.1 second after each pulse is shown by the broken line in FIG. Here, the horizontal axis represents the peak value of the applied pulse, and the vertical axis represents the reflectance of the element when the reflectance is 100% when white paper is placed instead of the element. The larger the value, the brighter The smaller, the darker.
Each pulse is an AC rectangular wave and the application time is 40 ms.
And If the pulse application time is shorter than this, the drive voltage rises and the contrast decreases, and if it is longer than this, flicker is noticeable. The pulse crest value (Vr) determined by the above method was used as the voltage for transferring to the bright state, and the pulse crest value (Vs) was used as the voltage for transferring to the dark state.

The liquid crystal composition was prepared by the above method, the display device was prepared, and the measurement was carried out. As a result, the voltage (Vr) for transition to the bright state was 31 V, and the voltage (Vs) for transition to the dark state.
Became 21V.

In this embodiment, the voltage (V
r) and the voltage (Vs) for transition to the dark state showed smaller values than those of Comparative Example 1. Therefore, a display element having a driving voltage lower than that of Comparative Example 1 was obtained.

The R of the compound group I is not limited to those shown here, but may be determined so as to have an optimum liquid crystal temperature range depending on the application.

A and X of the compound group I are not limited to those shown here, but can be determined in consideration of the electro-optical characteristics required from the application. For example, the tolan group shown in claim 1 is used as A in order to reduce unnecessary fluorescence.

The types and mixing ratios of the base liquid crystal and the compound group I are not limited to those shown here, and can be determined in consideration of the operating temperature range and electro-optical characteristics required from the application.

The compound group I used here has various variations depending on the substitution position of fluorine, and only a part thereof is shown here. For example, fluorine may be substituted on all ring moieties.

The chiral components that can be used in this embodiment are not limited to those shown here. It is also possible to mix several chiral components and use them as a multi-component chiral component.

As the base liquid crystal that can be used in this embodiment, a liquid crystal containing a cyano group, a liquid crystal containing chlorine, a liquid crystal containing a tolan skeleton, a liquid crystal containing fluorine, or the like can also be used.

Comparative Example 1 In this comparative example, B was used as the liquid crystal.
L008 (Merck), CB15 as chiral component
An example in which a mixture of (made by Merck) and R1011 (made by Merck) is used and the above compound group I is not added will be shown.

A material composition containing no compound group I was prepared, a display device was prepared, and measurements were carried out in exactly the same manner as in Example 1. As a result, the voltage (Vr) for transition to the bright state was 39 V, and the dark state. The voltage (Vs) to be transferred to was 28V.

Example 2 In this example, compound B, which is one of the above compound group I, was added as an additive component.

[0032]

[Chemical 6]

Using BL008 as a base liquid crystal (manufactured by Merck), a mixture of CB15 (manufactured by Merck) and R1011 (manufactured by Merck) as a chiral component, M220 (manufactured by Toagosei Chemical Industry Co., Ltd.) as a polymer precursor. An example using is shown.

First, the material composition sealed between the substrates will be described. The additive component (the above compound B) was added to the base liquid crystal (BL008) so that the ratio by weight was 9: 1. This and chiral component (weight ratio CB
15: R1011 = 85: 15 mixture), and the chiral pitch was adjusted to selectively reflect green visible light to obtain a chiral nematic liquid crystal. The polymer precursor was mixed in an amount of 2% by weight with respect to 98% by weight of this chiral nematic liquid crystal, and benzophenone was added to this as a photopolymerization initiator in an amount of 1/2% of that of the polymer precursor.

The material composition described above was enclosed in an empty panel prepared in exactly the same manner as in Example 1 and irradiated with ultraviolet rays (300 nm to 400 nm, 3.8 mW / cm 2, 15).
The polymer precursor was photopolymerized at 20 ° C. for 10 minutes. Then, the light absorbing material 8 was arranged on the back surface of the substrate 7.

In the same manner as in Example 1, the response after one second of pulse was applied (the display element as used in this Example has a memory function capable of holding the display state without applying an electric field, but pulse application Only the response after 1 second is shown in this example.) As a result, the voltage (Vr) for transferring to the bright state is 34V, and the voltage (Vs) for transferring to the dark state is 2V.
It became 4V.

In this embodiment, the voltage (V
r) and the voltage (Vs) for transition to the dark state showed smaller values than those of Comparative Example 2. Therefore, a display element having a driving voltage lower than that of Comparative Example 2 was obtained.

The R of the compound group I is not limited to those shown here, but may be determined so as to have an optimum liquid crystal temperature range depending on the application.

A and X of the compound group I are not limited to those shown here, and can be determined in consideration of the electro-optical characteristics required from the application.

The types and mixing ratios of the base liquid crystal and the compound group I are not limited to those shown here, and can be determined in consideration of the operating temperature range and electro-optical characteristics required from the application.

The compound group I used here has various variations depending on the substitution position of fluorine, and only a part thereof is shown here. For example, fluorine may be substituted on all ring moieties.

As for the chiral component and the base liquid crystal that can be used in this embodiment, those shown in Embodiment 1 can be similarly used.

In addition to the above, the polymer precursor can use acrylate, vinyl, epoxy, etc. in the polymerized portion, and alkyl, alkyl ether, biphenyl, terphenyl, quarterphenyl, tolan, etc. can be used as the non-polymerized portion. , May be partially substituted with halogen such as fluorine.

(Comparative Example 2) In this comparative example, B was used as the liquid crystal.
L008 (Merck), CB15 as chiral component
An example is shown in which a mixture of (made by Merck) and R1011 (made by Merck), M220 (made by Toagosei Chemical Industry Co., Ltd.) as a polymer precursor, and the above compound group I are not added.

A material composition containing no compound group I was prepared, a display device was prepared, and measurements were carried out in exactly the same manner as in Example 2. As a result, the voltage (Vr) for transition to the bright state was 42 V, and the dark state. The voltage (Vs) transferred to was 31 V.

[0046]

As described above, according to the present invention, a display element in which a chiral nematic liquid crystal is used and a chiral pitch is adjusted to reflect visible light, or a chiral nematic liquid crystal and a polymer are dispersed into each other to reflect visible light. In such a display element having a controlled chiral pitch, by containing at least one specific compound group as described above as a component, a display element having a low driving voltage that can be sufficiently driven by a liquid crystal driver IC, and a power saving display element Is now available.

[Brief description of drawings]

FIG. 1 is a diagram simply showing a partial cross section of a display element in Examples 1 and 2 of the present invention.

FIG. 2 is a diagram showing an optical system when measuring electro-optical characteristics of display elements in Examples 1 and 2 of the present invention.

FIG. 3 is a diagram showing electro-optical characteristics of display elements according to Examples 1 and 2 of the present invention.

[Explanation of symbols]

 1 Substrate 2 Electrode 3 Alignment Film 4 Material Composition 5 Alignment Film 6 Electrode 7 Substrate 8 Light Absorbing Material 9 Display Element 10 Convex Lens 11 Detector 12 Light Source

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C09K 19/10 9279-4H 19/14 9279-4H 19/18 9279-4H 19/20 9279-4H G02F 1/1333 1/137 (72) Masayuki Yazaki, Masayuki Yazaki, 3-3-5 Yamato, Suwa, Nagano Seiko Epson Corporation (72) Hidehito Iizaka, 3-5, Yamato, Suwa, Nagano Prefecture Seiko Epson Within the corporation

Claims (2)

[Claims] 1. A display device in which a chiral nematic liquid crystal is used and a chiral pitch is adjusted so as to reflect visible light. (R is an alkyl group or an alkoxy group, X is CN or H, F, Cl, and n is an integer of 1 or more) A display device containing a specific compound as at least one component. 2. A display device in which a chiral nematic liquid crystal and a polymer are dispersed in each other and the chiral pitch is adjusted so as to reflect visible light. (R is an alkyl group or an alkoxy group, X is CN or H, F, Cl, and n is an integer of 1 or more) A display device containing a specific compound as at least one component.