JP2621130B2 - Liquid crystal element - Google Patents

Description

Description: TECHNICAL FIELD [0001] The present invention relates to a liquid crystal element suitable for two-frequency driving.

[Technical background of the invention]

In recent years, liquid crystal elements have been applied to image display on television receivers, computer displays, and the like, and optical writing of optical writing printers used as computer terminals or office equipment.

The liquid crystal element used for image display, optical writing, etc.
Micro shutter parts for controlling light transmission are arranged at close intervals, and the shutter parts have transparent electrodes formed on a pair of transparent substrates facing each other with a liquid crystal layer interposed therebetween. It is constituted by.

The liquid crystal element used for the image display or the like is generally driven by selectively applying a voltage equal to or higher than a threshold voltage of the electro-optical effect and a voltage lower than the threshold voltage to the shutter section.

However, in such a driving method, for example, in the case of a liquid crystal element using a liquid crystal composition having positive dielectric anisotropy, liquid crystal molecules are vertically aligned with respect to the substrate by applying a voltage higher than the threshold. Sometimes, the applied voltage causes the liquid crystal molecules to behave immediately.However, when the liquid crystal molecules are oriented in parallel to the substrate by applying a voltage lower than the threshold voltage, the liquid crystal molecules may be moved between the liquid crystal composition and the alignment film of the substrate. Since the liquid crystal molecules behave slowly because they are aligned only by the alignment regulating force acting therebetween, there is a problem that the shutter unit cannot be driven to open and close at high speed.

For this reason, when it is necessary to drive a large number of shutter sections at a high speed and a high contrast is obtained, a two-frequency driving method utilizing the dielectric dispersion phenomenon of liquid crystal is adopted.

The two-frequency driving method is such that when a high-frequency electric field is applied to the liquid crystal, the liquid crystal molecules try to be oriented so as to be orthogonal to the electric field, and when a low-frequency electric field is applied, the liquid crystal molecules are parallel to the electric field. In this driving method, an electric field is applied to the liquid crystal composition both when the liquid crystal molecules are aligned parallel to the substrate and when the liquid crystal molecules are aligned vertically. Can respond at high speed.

With this driving method, a positive display TN type (twisted nematic type) liquid crystal element in which the polarization axes of polarizing plates are orthogonal to each other is opened, the shutter part is opened (light transmission) when a high frequency is applied, and when a low frequency is applied. Shutter closed (opaque)
In the case of a GH-type (guest-host) liquid crystal element, the shutter is closed (impermeable, colored) by applying a high frequency,
When a low frequency is applied, the shutter is opened (light transmission: no color).

[Problems of background technology]

However, when driving the liquid crystal element at two frequencies,
A high frequency (100 KHz or more) and a low frequency are applied to the liquid crystal. However, if the application time of the high frequency is long, there is a problem that the response of the liquid crystal to the next application of the low frequency is deteriorated.

This is due to the hysteresis effect of the liquid crystal. Since the hysteresis effect of the liquid crystal occurs particularly at high frequencies, the influence of the high frequency remains strong when the application time of the high frequency is long, and even when the low frequency is applied next. This is because the liquid crystal stops responding immediately.

That is, when the liquid crystal element is driven at two frequencies, the liquid crystal behaves by applying high and low frequencies so that the liquid crystal molecules are aligned parallel and perpendicular to the substrate. Instead of being oriented completely parallel and perpendicular to it, it behaves over a range of angles. However, when the application time of the high frequency is long, the applied electric field is accumulated and acts on the liquid crystal, so that the liquid crystal molecules are strongly aligned parallel to the substrate. Can not stand up.

The magnitude of the hysteresis effect due to the high frequency depends on the strength of the electric field applied to the liquid crystal. When the electric field applied to the liquid crystal is strong, the hysteresis effect due to the high frequency appears strongly.

For this reason, when the conventional liquid crystal element is driven at two frequencies, in the case of a TN type liquid crystal element for positive display, the operation when the shutter unit switches from the open state to the closed state becomes slow, and the GH type liquid crystal element In the case of, the operation when the shutter section switches from the closed state to the open state becomes slow. Therefore, when the conventional liquid crystal element is driven at two frequencies at a high speed, the conventional liquid crystal element is closed with the open shutter section. There is a problem that the contrast with the shutter unit is deteriorated.

[Object of the invention]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and an object of the present invention is to provide a shutter in which even when a high frequency is applied for a comparatively long time, liquid crystal molecules are immediately activated by applying a low frequency. It is an object of the present invention to provide a liquid crystal element which can open and close the unit with high responsiveness at high speed, is suitable for high-speed two-frequency driving, and has good contrast.

[Summary of the Invention]

That is, the present invention eliminates the influence of the high-frequency hysteresis effect, makes the liquid crystal respond sufficiently fast even to low frequencies, and obtains a good contrast. Is set to a predetermined value.
According to the present invention, the driving voltage V applied to the electrode is reduced so as to reduce the high frequency hysteresis effect of the liquid crystal due to the application of the high frequency electric field.
The constant α = V / G determined by (V) and the thickness G (μm) of the liquid crystal layer between the electrodes is set in the range of 3.85 ≦ α ≦ 5.09.

(Example of the invention)

An embodiment of the present invention will be described below with reference to the drawings, taking a liquid crystal element used for optical writing of an optical writing printer as an example.

First, the configuration of the optical writing type printer will be described. In FIG. 2, 1 is a photoconductive photosensitive drum, 2 is a charger for uniformly charging the surface of the photosensitive drum 1, and 3 is a charged surface of the photosensitive drum 1. The optical recording unit 3 is driven by a recording control unit 4 that controls timing and the like based on recording information such as an image.
Optical writing is performed by irradiating the surface of the photosensitive drum 1 with light and erasing the charge of the light-irradiated portion of the photosensitive drum surface.

The electrostatic latent image on the surface of the photosensitive drum formed by the optical writing of the optical recording unit 3 is developed by the developing unit 5 with toner.

The recording paper 6 is fed by a paper feed roll 7, temporarily stopped by a standby roll 8, and then sent to a transfer unit 9 in synchronization with the toner image on the surface of the photosensitive drum. The toner image on the drum surface is transferred to the paper 6 in the transfer unit 9. This paper 6
At 10, the toner image is separated from the photosensitive drum 1, the toner image is fixed by a fixing device 11, and is sent out by a paper discharge roller 12.

The photosensitive drum 1 on which the toner image has been transferred onto the paper 6 is
After the toner charge is neutralized by the static eliminator 13, the cleaner 14
Thus, the remaining toner is cleaned, and the surface charge is neutralized by the eraser 15.

The optical recording unit 3 includes, as shown in FIG.
It comprises a liquid crystal element 20 for optical writing and an imaging lens 17, and irradiates light from the light source 16 to the surface of the photosensitive drum via the liquid crystal element 20 and the imaging lens 17.

The liquid crystal element 20 is horizontally long along the axial direction of the photosensitive drum 1. The liquid crystal element 20 has a large number of minute shutters for controlling light transmission at close intervals along the length direction. It is formed.

That is, FIGS. 1 and 4 to 8 show the liquid crystal element 20 described above, and here show a GH type liquid crystal element.

The structure of the liquid crystal element 20 will be described. In the figure, reference numerals 21 and 22 denote a pair of upper and lower transparent substrates made of a glass plate having a thickness of about 0.7 mm. A laterally long frame-shaped outer sealing material 23a as shown in the figure, and a pair of mutually parallel inner sealing materials formed inside the outer sealing material 23a at an interval d of about 2 mm with respect to both side portions thereof.
23b, 23b.

The distance e between the pair of inner seal members 23b, 23b is about 1 mm, and the length of the narrow gap between the inner seal members 23b, 23b is, for example, for a printer for recording on a maximum B4 size sheet. It is 249 mm in the case of a liquid crystal element. Further, both ends of the inner seal members 23b, 23b are connected to both side portions of the outer seal member 23a, respectively, and the inner seal members 2 between the substrates 21, 22 are formed.
Spaces 30, 30 are defined by portions surrounded by 3b, 23b and both side portions of the outer sealing material 23a. In FIG. 5, reference numerals 31 and 31 denote substrates 2 when the pair of substrates 21 and 22 are superposed and bonded.
This is an air hole for allowing the air between 1 and 22 to escape to the outside, and the air holes 31 and 31 are sealed with sealing materials 32 and 32 applied after bonding the substrates 21 and 22. . Therefore, the space 30,
The space 30 is filled with air (clean air) left when the substrates 21 and 22 are bonded.

Also, both ends of the narrow gap between the inner seal members 23b, 23b are communicated with the wide gaps at both ends surrounded by the outer seal material 23a, and the narrow gap and the wide gap between the substrates 21, 22 are provided. The gap is filled with a liquid crystal composition 24 to which a dichroic dye is added. Reference numeral 33 denotes a liquid crystal injection hole provided at one end of the outer sealing material 23a.
Is also used as an air hole for releasing air between the substrates 21 and 21 to the outside when the pair of substrates 21 and 22 are superimposed and bonded,
The liquid crystal injection hole 33 is sealed by applying a sealing material 34 after injecting the liquid crystal composition 24 (injecting by a vacuum injection method).

In addition, one of the substrates 21 and 22
As shown in FIG. 5 and FIG. 7, the inner surface of the segment substrate (hereinafter referred to as a segment substrate) has a length of about one side over the entire length thereof in the narrow gap between the inner seal members 23b. 180μm, almost square segment electrodes S1, S1,
.., S2, S2,...
As shown in FIG. 6, two strip-shaped common electrodes C1 and C2 each having a width of 3 mm are provided on the inner surface of the common substrate 2 (hereinafter referred to as a common substrate) as shown in FIG.
They are formed in parallel with a minute interval of about 30 μm.

The segment electrodes S1, S1,..., S2, S2,.
1 and C2 are transparent electrodes, and a shutter section a for controlling light transmission at a portion where the segment electrodes S1, S1,..., S2, S2,. , a,... are formed.

.., S2, S2,... Of one of the two rows of segment electrodes S1, S1,. .. Are arranged in two rows with a shift of 1/2 pitch.

The reason why the shutter units a, a,... Are arranged in two rows while being shifted by 1/2 pitch is that the shutter units a, a,.
Between the rows of irradiation points on the surface of the photosensitive drum irradiated with light passing through the shutter section a, a,. This is for forming a latent image. The shutter sections a, a,... Are a liquid crystal element for a printer that records on a maximum B4 size sheet, and are arranged 587 per row, and the shutter sections a, a,. (The distance between the centers of the shutter sections a, a) P1 and P2 are about 200 μm, respectively, and the pitch between the shutter sections a, a,... In one row and the shutter sections a, a,. The distance D between the centers is about 260 μm.

Also, the segment electrodes S1, S1,... Of one row and the segment electrodes S2, S2,... Of the other row are adjacent to each other with a shift of 1/2 pitch. Are connected by the electrodes 25, 25,..., And the drive circuit connection leads 26, 26,... Of the segment electrodes are alternately led out from one of the commonly connected segment electrodes S1, S2. The reason why the segment electrodes S1, S1,... Of one row are commonly connected to the segment electrodes S2, S2,.
If the drive circuit connection leads are individually derived from 2, S2, ..., the number of drive circuit connection leads becomes so large that it is difficult to route the leads. Therefore, in this liquid crystal element, Segment electrode S1, S in one row
Are connected in common with the segment electrodes S2, S2,... Of the other row, and the common electrodes C1, C2 are opposed to the respective segment electrode rows to drive the liquid crystal element in a time-division manner.

, S2, S2,..., Common connection electrodes 25, 25, and drive circuit connection leads 26, 26,.
Is integrally formed of a transparent conductive material such as indium oxide.

In FIGS. 1 and 7, 27, 27,... Are the common connection electrodes 25, 25,.
Are low-resistance metal films made of chromium or gold or the like, which are deposited on the common connection electrodes 2.
5, 25,... And the drive circuit connection leads 26, 26,. The drive circuit connection leads 26, 26,...
The metal films 27, 27,... that cover the drive circuit connection leads 26, 26,. , Except for the drive circuit connection terminal portions 26a, 26a,.

In FIGS. 1 and 6, low-resistance metal films 28, 28 are applied on the common electrodes C1, C2 except for the shutter portions a, a,. 28 is to reduce the electric resistance of the common electrodes C15 and C2,
are provided to regulate the light transmission area of a, a,.
28a, 28a,... Indicate light transmitting portions (portions where the transparent common electrodes C1, C2 are exposed) regulated by the metal films 28, 28. The light transmitting portions 28a, 28a,. Length l1, l
2 (see FIG. 7) each have a square shape of about 90 μm.

, S2, S2,... And the common electrodes C1, C2 have a thickness of 200 to 300 mm, and the metal films 27, 27,.
And the thickness of 28,28 is about 1700mm.

Reference numerals 29, 29 denote liquid crystal alignment films formed on the inner surfaces of both substrates 21, 22, and the thickness of the alignment films 29, 29 is 200 to 400 °.

In this embodiment, inner sealing members 23b, 23b are provided on both sides of an array portion of the segment electrodes S1, S1,..., S2, S2,. The reason why the liquid crystal filling area is made smaller is that when the liquid crystal filling area is made wider, the liquid crystal composition is also obtained from the leads 26, 26, ... of the segment electrodes S1, S1, ..., S2, S2, ... when a high frequency signal is applied. This is because a high-frequency current flows through the common electrodes C1 and C2 through 24 to promote heat generation of the common electrodes C1 and C2.
The heat generated by the common electrodes C1 and C2 can be reduced by avoiding the liquid crystal composition as much as possible at the portions where the leads 26, 26,... Of S2, S2,. Can be. In this embodiment, the segment electrodes S1, S
On both sides of the liquid crystal filling part where 1,…, S2, S2,… are arranged,
Because of the double wall structure including the inner seal member 23b and the outer seal member 23a, it is possible to completely prevent fine dust and moisture from entering the liquid crystal layer from the outside.

On the other hand, in FIG. 5, S0 and S0 are the segment electrodes S
1, S1,..., S2, S2,... Are laterally elongated auxiliary segment electrodes formed at both ends of the array portion.
S0 and S0 face the common electrodes C1 and C2 of the common substrate 22 to form a margin erasing shutter unit. The margin erasing shutter section includes the two rows of shutter sections a, used for optical writing.
a,… irradiate light to both ends of the photosensitive drum (corresponding to the margins on both sides of the recording paper) that are not irradiated with the light passing therethrough to erase the charged charges on both ends of the photosensitive drum, The margin erasing shutter is driven to be always open (light transmitting). In FIG. 5, St and St are test segment electrodes formed outside the auxiliary segment electrodes S0 and S0. The test segment electrodes St and St are also connected to the common electrodes C1 and C2 of the common substrate 22. A test shutter section is formed facing the test shutter section. Reference numerals 23c, 23c denote spacers provided on both sides of the test segment electrodes St, St to maintain an interval between the substrates 21, 22.

The auxiliary segment electrodes S0, S0 and the test segment electrodes St, St are connected to the common electrodes C1, C2 of the common substrate 22.
The common electrodes C1 and C2 of the common substrate 22
The metal films 28, 28 deposited on the auxiliary segment electrodes S0, S0 of the common electrodes C1, C2 and the test segment electrodes St,
It is attached so as to expose portions 28b, 28b and 28c, 28c facing St (see FIG. 6).

 In FIG. 8, reference numeral 35 denotes a polarizing plate.

As shown in FIG. 4, the driving circuit 40 connected to the liquid crystal element 20 supplies the segment electrodes S1, S1,..., S2,
Apply drive signal between S2, ... and common electrode C1, C2
When the shutter portions a, a,... Are opened (light transmission), the segment electrodes S1, S1,.
When a drive voltage having a waveform as shown in FIG. 9A is applied between S2,... And the common electrodes C1, C2, and the shutter portions a, a,. The electrodes S1, S1,…, S2,
A drive voltage having a waveform as shown in FIG. 9B is applied between S2,... And the common electrodes C1, C2. In FIG. 9,
The waveform of one cycle T1 for controlling the shutter parts a, a,... Is shown, and the shutter part is opened and closed by a start signal (T2 time zone signal), and a holding signal (T3 time zone signal).
Is held open or closed.

By the way, when driving the liquid crystal element 20 at two frequencies,
As described above, when the application time of the high frequency becomes longer, the responsiveness of the liquid crystal at the time of the next application of the lower frequency becomes poor. However, the stronger the electric field applied to the liquid crystal, the stronger the hysteresis effect by the high frequency appears. The strength of the electric field applied to the liquid crystal is determined by the driving voltage and the thickness of the liquid crystal layer between the electrodes. Therefore, if the driving voltage and the thickness of the liquid crystal layer are appropriately selected, the effect of the high-frequency hysteresis effect is obtained. To make the liquid crystal respond sufficiently fast to a low frequency and obtain a good contrast.

Therefore, in order to reduce the influence of the high-frequency hysteresis effect and make the liquid crystal respond sufficiently fast to the low frequency, and to obtain a good contrast, in order to obtain the ratio between the driving voltage and the thickness of the liquid crystal layer, For each liquid crystal element with a different liquid crystal layer thickness G, drive voltage V _OP = 25 V (constant) T1 = 2 ms T2 = T3 = 1 ms Low frequency drive frequency = 5 KHz High frequency drive frequency = 320 KHz When the shutter characteristics of each liquid crystal element were examined, the following results were obtained. Here,
The layer thickness of the liquid crystal layer means the layer thickness G of the liquid crystal layer in the shutter portions a and a shown in FIG. 1 (the unit is μm between the alignment films 29 and 29 between the segment substrate 21 and the common substrate 22). pointing.

For the liquid crystal element having a liquid crystal layer thickness of 5.4 μm and the liquid crystal element having a liquid crystal layer thickness of 6.5 μm, the drive voltage V was selected to be 25 V or 27.5 V, and the shutter characteristics in each case were determined. Upon examination, the following results were obtained.

Here, as the liquid crystal filling the liquid crystal element 20,
As a dichroic dye, a liquid crystal composition obtained by mixing the liquid crystal compounds shown in the following table at the mixing ratios shown in the table, The above two dyes were mixed at 1.2% by weight each.

Note that the liquid crystal composition has a Δε at 200 Hz of +6.
4, Δε at 100KHz is -3.3, cross frequency fc is 19.0KH
z, viscosity at 25 ° C is 70.5 cP.

It can be seen from the above experimental results that the drive voltage is 25
In the case of V, if the layer thickness G of the liquid crystal layer is in the range of 4.5 ≦ G ≦ 6.5, satisfactory shutter characteristics can be obtained, but if the layer thickness G of the liquid crystal layer is made smaller than this, the liquid crystal layer will be applied to the liquid crystal accordingly. In addition to the increased electric field strength, the high-frequency hysteresis effect increases and the responsiveness deteriorates, and the apparent dye concentration in the liquid crystal decreases, making it impossible to absorb light enough to close the shutter. If the thickness G of the liquid crystal layer is made larger than this, the electric field intensity actually applied to the liquid crystal with respect to the driving voltage V becomes smaller, and the response of the liquid crystal becomes slower.

When the thickness G of the liquid crystal layer is 5.4 μm and 6.5 μm,
If the drive voltage is in the range of 25 V to 27.5 V, that is, the constant α is in the range of 3.85 ≦ α ≦ 5.09, the high frequency hysteresis effect does not increase even if the electric field intensity increases, and the electric field intensity is not too small and the response is small. There is no slowing down.

Therefore, if the constant α = V / G determined by the drive voltage V and the layer thickness G of the liquid crystal layer between the electrodes is set within the range of 3.85 ≦ α ≦ 5.09, the effect of the high frequency hysteresis effect is reduced, and However, the liquid crystal responds at a sufficiently high speed, and a good contrast can be obtained.

In the above embodiment, a liquid crystal element used for optical writing of an optical writing type printer has been described. However, the present invention is also applicable to a liquid crystal element used for image display such as a television receiver or a computer display. Of course, it can be applied not only to the GH type but also to a TN type liquid crystal element.

〔The invention's effect〕

The liquid crystal element of the present invention has a constant α = V / determined by the drive voltage V (V) and the thickness G (μm) of the liquid crystal layer between the electrodes.
Since G is set within the range of 3.85 ≦ α ≦ 5.09, the effect of the high frequency hysteresis effect is reduced, and even when a high frequency is applied for a relatively long time, the liquid crystal molecules are immediately applied by the next low frequency application. And the shutter can be opened and closed at a high speed with good responsiveness, and the contrast can be improved.

[Brief description of the drawings]

1 shows an embodiment of the present invention. FIG. 1 is an enlarged view of a shutter portion shown in FIG. 8, and FIGS. 2 and 3 show an optical writing type printer which performs optical writing using a liquid crystal element. FIG. 4 is a plan view of a liquid crystal element, FIGS. 5 and 6 are plan views of a segment substrate and a common substrate of the liquid crystal element, and FIG. 7 is a segment electrode of the segment substrate. FIG. 8 is an enlarged plan view of the formation portion, FIG. 8 is a cross-sectional view of the liquid crystal element along the line AA in FIG. 7, and FIG. 9 is a driving waveform diagram of the liquid crystal element. 21,22 …… Substrate, S1, S2 …… Segment electrode, C1, C2 ……
Common electrode, a: shutter part, G: layer thickness of liquid crystal layer.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenzo Endo 5 2951 Ishikawa-cho, Hachioji City Casio Computer Co., Ltd. Hachioji Plant (56) References JP-A-57-64722 (JP, A)

Claims (1)

(57) [Claims] 1. A semiconductor device having a positive dielectric anisotropy in a low-frequency electric field having a frequency lower than an intersection frequency at which the value of the dielectric anisotropy is 0 between a pair of substrates on which opposing electrodes are formed, A liquid crystal for two-frequency driving showing negative dielectric anisotropy is enclosed in a high-frequency electric field having a frequency higher than the frequency, and the low-frequency electric field and the high-frequency electric field are used to maintain the low-frequency electric field and the behavior state of liquid crystal molecules. In a liquid crystal element that controls light transmittance by selectively applying the high-frequency electric field and the high-frequency electric field and the superposed electric field to the liquid crystal, respectively. The drive voltage V applied to the electrodes is
(V) and a constant α = V / G determined by a layer thickness G (μm) of the liquid crystal layer between the electrodes is set in a range of 3.85 ≦ α ≦ 5.09.