JPH1090697A - Production of liquid crystal element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve injection property and dispensability of a liquid crystal and to uniformly obtain a voltage-transmittance curve with high linearity all over the plane by injecting a liquid crystal between a pair of substrates, cooling the liquid crystal to the temp. to show a chiral smectic C phase and then increasing the temp. to show a chiral nematic phase. SOLUTION: A liquid crystal is injected between a pair of substrates at the temp. at which the liquid crystal shows N* (chiral nematic phase) (an arrow I), cooled to the temp. at which the liquid crystal shows SmC* (chiral smectic C phase) (an arrow II) after injection, and then further heated to the temp. at which the liquid crystal shows N* (chiral nematic phase) (an arrow III). Therefore, by injecting the liquid crystal while viscosity of the liquid crystal is maintained to a certain degree, dispersibility of a component such as fine particles in the liquid crystal is increased. By heating the liquid crystal to N* after cooling to SmC*, reorientation of the liquid crystal can be effectively performed and uniform orientation can be obtd. for the whole plane. Thus, characteristics with good linearity and easy controlling of gradation can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device (for example, a liquid crystal display) in which liquid crystal is disposed between a pair of substrates and regions having different threshold voltages for switching the liquid crystal are finely distributed. Element or a liquid crystal display).

[0002]

2. Description of the Related Art A liquid crystal display (LCD) using a liquid crystal as a display has features of low power consumption, thinness and light weight, and taking advantage of this, from a clock and a calculator to a computer display and a television receiver. (T
Application to V) is progressing.

Conventionally, a nematic liquid crystal has been used as a liquid crystal in such an LCD. However, as a limit of the nematic liquid crystal, the response speed is slow, and the twisted nematic liquid crystal (TN)
With 100 lines, super twisted nematic liquid crystal (S
TN) also has a limit of 240 lines, and in active matrix driving, the thin film transistor (TF) used
Considering the high price by T), there is a problem that it is difficult to enlarge the screen.

On the other hand, ferroelectric liquid crystal (FLC: ferroelect
R & D to apply ric liquid crystal to display devices has been actively pursued. Regarding FLC, a ferroelectric liquid crystal was first synthesized by Meyer in 1975, and a surface-stabilized ferroelectric liquid crystal capable of domain inversion by an electric field was invented in 1980 by Clark and Lagaard. FLC has a permanent dipole moment in the molecule itself, perpendicular to the long axis of the molecule,
A liquid crystal having spontaneous polarization and switchable by an electric field. An FLC display using the liquid crystal is an excellent one having mainly the following features (1) to (3).

(1) The switching speed is on the order of microseconds, the response is 1000 times faster than that of the TN liquid crystal display, and the high-speed response is excellent. (2) There is basically no twist structure in the molecular arrangement, and there is little viewing angle dependence. (3) Even if the power is turned off, the image is retained, the image has memory properties, and simple matrix driving is possible even for 1000 or more scanning lines that can support high definition.

Accordingly, the FLC display has a high definition,
It is a display that can pursue the performance of low cost and large screen.

Such an FLC display (ferroelectric liquid crystal display element) has a structure as schematically shown in FIGS. 9 and 10, for example. First, a transparent electrode (100 Ω / □ ITO: Indium tin oxide) is formed on a transparent glass substrate (Corning 7059, 0.7 mm thick) 1a, 1b.
2a and 2b are provided. These transparent electrodes are patterned into stripes by etching, and the data electrodes 2a and the scan electrodes 2 which intersect each other in a matrix form.
b.

On the transparent electrodes 2a, 2b, obliquely deposited SiO films 3a, 3b are formed as liquid crystal alignment films. In forming an obliquely deposited SiO film, a substrate is disposed vertically from a SiO deposition source in a vacuum deposition apparatus, and an angle between a vertical line and a substrate normal is set to 85 degrees. Si
After vacuum deposition of O at a substrate temperature of 170 ° C., baking is performed at 300 ° C. for 1 hour.

In the pair of substrates 1a and 1b provided with the alignment film thus manufactured, the alignment directions of the data electrode 2a and the scanning electrode 2b are antiparallel on opposite surfaces, and the data electrode 2a and the scanning electrode 2b are opposite to each other. 2b are arranged so that the electrode arrangement is orthogonal. As the spacer, glass beads (straightening sphere: 0.8 to 3.0 μm in diameter (manufactured by Catalyst Chemical Industry Co., Ltd.)) 4 corresponding to the target gap length are used. here,
Although the orientation processing directions are set antiparallel, they may be set parallel.

According to the size of the transparent substrates 1a and 1b, the spacer 4 is provided in a sealing material (UV-curable adhesive (Photorec: manufactured by Sekisui Chemical Co., Ltd.)) 6 which adheres to the periphery when the area is small. By dispersing about 0.3 wt%, the gap between the substrates is controlled. When the substrate area is large, the above-mentioned straightening spheres have an average density of 100 pieces / ball on the substrate.
After spraying mm ² , a gap was formed, a liquid crystal injection hole was secured, and the periphery of the cell was bonded with a sealant 6.

A liquid crystal composition in which, for example, a ferroelectric liquid crystal (CS-1014 manufactured by Chisso Corporation) 5 is uniformly dispersed at an isotropic phase temperature using an ultrasonic homogenizer is injected between the pair of substrates 1a-1b. Have been. This ferroelectric liquid crystal composition is injected under reduced pressure in a state showing fluidity such as an isotropic phase temperature or a chiral nematic phase temperature. After liquid crystal injection,
After slowly cooling and removing the liquid crystal on the glass substrate around the injection hole, the liquid crystal is sealed with an epoxy-based adhesive, and the FLC display 11 is manufactured.

As a driving method of the FLC display 11, an XY matrix method is used. 1H (one horizontal scanning time or one line selection time) is 63.5 μs, and since the voltage is applied in a bipolar manner, each selection pulse has a width of 63.5 / 2 μs. From the ROW side (electrode 2b), a select pulse which is a threshold is applied, and COLUM
A data pulse is applied from the N side (electrode 2a).

However, although the FLC display has the above-mentioned excellent features, it has been pointed out that it is difficult to display gradations. That is, the conventional ferroelectric liquid crystal display using the bistable mode is stable only in two states, and thus has been considered to be unsuitable for gradation display of video or the like. This is particularly remarkable in a so-called surface-stabilized ferroelectric liquid crystal in which the helical structure has been broken by the interaction with the alignment film. Only two states have a stable state, and only black and white binary display is performed. .

That is, a conventional ferroelectric liquid crystal element (for example, a surface-stabilized ferroelectric liquid crystal element) has an externally applied electric field E (Ps
(Spontaneous polarization), the orientation direction of the molecule M switches between two states, State 1 and State 2, as shown in FIG. This change in molecular orientation appears as a change in transmittance when the liquid crystal element is placed between orthogonal polarizing plates. As shown in FIG.
It changes sharply from 0% to 100% at _th . The voltage width at which the transmittance changes is generally 1 V or less. Furthermore, V
_th changes due to a small change in the cell gap. Therefore, in a conventional FLC liquid crystal element, it is difficult to provide a stable voltage range in a curve of transmittance-applied voltage, and it is difficult or impossible to perform gradation display by voltage control.

Therefore, a method of performing gradation by providing sub-pixels and adjusting the pixel area (area gradation method)
Further, a method such as a method of performing gray scale by repeating switching during one field by utilizing a high-speed switching property of ferroelectric liquid crystal (time sequential or time integration gray scale method) has been proposed. However, these methods have a problem that gradation display is still insufficient.

In the area gradation method, by dividing one pixel (pixel), the area of one pixel is controlled and halftone is displayed. However,
In order to display 64 gray scales or 256 gray scales required for a TV or the like by this method, one pixel is set to 6 pixels.
It is necessary to divide the pixel into eight and eight.

Therefore, when the pixel division of the six divisions and the eight divisions is actually performed, the number of wirings increases accordingly, and the mounting and the driving circuit are complicated (six times, eight times if the six divisions).
If it is divided, the number of external connections increases eight times). For this reason, the area required for one pixel is limited, which is not suitable for high-definition display. When the number of divisions increases, periodicity occurs in the image, and the image quality deteriorates.

In the case of the time-sequential gradation method, by utilizing the high-speed response of the ferroelectric liquid crystal, by switching black and white n times during one field, 2 ⁿ -level gradation display can be performed. However, when driving with a passive matrix (simple matrix), the time allocated to one line is limited,
For example, when performing video display with an NTSC signal,
Since interlacing is performed, the number of scanning lines is 25
If it is 6, 1H assigned to one line
Is 63 μs. If bipolar pulses are used to avoid electrolysis, the pulse width is 30 μs.

Therefore, in order to perform the time sequential operation, the switching must be performed n times during this 30 μsec. However, when the temperature decreases, the viscosity increases, and the response speed tends to decrease. Therefore, in order to realize, for example, six or more switching operations in a wide temperature range, the response speed of 5 μsec or less is set to a wide temperature range. It must be realized over a range. This is obviously very difficult.

Therefore, as a method of performing analog gray scale display for each pixel, a local distance is changed by changing a distance between opposing electrodes in one pixel or changing a thickness of a dielectric layer formed between opposing electrodes. How to create an electric field strength gradient in
It has been proposed to provide a voltage gradient by changing the material of the counter electrode.

However, the production of a liquid crystal display device having a practical level of analog gradation display characteristics is complicated in terms of steps, the control of the production conditions becomes very difficult, and the production cost is high. was there.

In order to solve the above-mentioned problem, in a liquid crystal display element in which an electrode layer is formed on the opposing surfaces of a pair of substrates, the effective electric field applied to the liquid crystal in one pixel has a distribution. It has been found that analog gray scale display can be achieved by widening the threshold voltage width for switching between liquid crystal bistable states in one pixel, and Japanese Patent Application No. 5-262951 by the present applicant. (This is hereinafter referred to as the prior invention).

According to the invention of the prior application, a method of adding and dispersing ultra-fine particles such as titanium oxide in a ferroelectric liquid crystal is used to increase the threshold voltage range.
By the addition of the ultrafine particles, fine regions (micro domains) having different threshold voltages (V _th ) are developed in one pixel, and the transmittance of the micro domains changes according to the magnitude of the applied voltage. Therefore, the transmittance does not change steeply, but shows a relatively gradual change, and analog gray scale display becomes possible. In one domain, if the liquid crystal molecules are bistable, they have a memory function, and one pixel is formed from a domain on the order of μm having a different threshold voltage, so that continuous gradation display is possible. Become.

In manufacturing such a ferroelectric liquid crystal element containing fine particles, a liquid crystal cell (empty cell) is constituted by arranging a pair of substrates provided with a transparent electrode and an alignment film in this order, with a predetermined gap therebetween. There is a method in which a ferroelectric liquid crystal containing fine particles is injected at a temperature at which the liquid crystal exhibits an isotropic phase (Iso).

According to this injection method, as shown in FIG. 13, the ferroelectric liquid crystal containing fine particles is converted into an isotropic phase (Is
o) Inject into the liquid crystal cell at the temperature shown (arrow V) and cool to the chiral smectic C phase which is the target state (arrow)
VI).

However, when the ferroelectric liquid crystal containing fine particles is injected into the liquid crystal cell at a temperature showing the isotropic phase (Iso) as in this injection method, the viscosity of the liquid crystal becomes low at the temperature showing the isotropic phase (Iso). In many cases, since the specific gravities of the liquid crystal and the fine particles are different from each other, precipitation and aggregation of the fine particles are likely to occur, and the dispersibility of the fine particles may be deteriorated at the time of injection.

As shown in FIG. 13, a ferroelectric liquid crystal containing fine particles is injected into a liquid crystal cell at a temperature at which the liquid crystal exhibits a chiral nematic phase (arrow VII), and an isotropic phase (Iso) is obtained for reorientation. ) (Arrow VIII),
There is also a method of cooling to the chiral smectic C phase which is the target state (arrow IX).

In this injection method, when the liquid crystal is injected in a chiral nematic phase, the liquid crystal molecules tend to flow (become aligned along the flow direction) and may not coincide with the alignment direction of the alignment film. After the injection, the temperature is raised to a temperature indicating an isotropic phase (Iso) for reorientation. This temperature increase causes a twist (twist) in the gray level (gradation display level) of the voltage-transmittance curve. A domain with a structure may occur. For this, the voltage-
The linearity of the transmittance curve may be lost, and the color purity may be reduced. In addition, since the temperature is raised to a temperature showing an isotropic phase after the injection, the dispersibility of the fine particles is likely to be deteriorated for the above-described reason.

In either of the two injection methods described above, the dispersibility of the fine particles is deteriorated because the temperature is raised to the isotropic phase, and at the same time, the isotropic phase is converted into the chiral smectic phase through the chiral nematic phase. If there is a portion with insufficient orientation due to the phase transition process, this remains as a defect as it is, and the threshold voltage of the domain itself becomes unstable, which tends to cause variation. These causes the linearity of the voltage-transmittance curve to be impaired.

[0030]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal device in which liquid crystal is disposed between a pair of substrates and regions having different threshold voltages for switching the liquid crystal are finely distributed. It is an object of the present invention to provide a method for manufacturing a liquid crystal element capable of improving the injectability and dispersibility of liquid crystal and obtaining a highly uniform voltage-transmittance curve over the entire surface.

[0031]

That is, according to the present invention, there is provided a liquid crystal device in which liquid crystal is disposed between a pair of substrates, and regions having different threshold voltages for switching the liquid crystal are finely distributed. In producing, after injecting the liquid crystal between the pair of substrates at a temperature indicating a chiral nematic phase, cooled to a temperature indicating a chiral smectic C phase,
The present invention further relates to a method for producing a liquid crystal element (hereinafter, referred to as a production method of the present invention) in which the temperature is raised to a temperature at which a chiral nematic phase is exhibited.

According to the manufacturing method of the present invention, as shown in FIG. 1, a liquid crystal is injected between a pair of substrates at a temperature at which the liquid crystal shows N ^* (chiral nematic phase) (arrow I), and the injection is completed. Thereafter, the liquid crystal is cooled to a temperature showing SmC ^* (chiral smectic C phase) (arrow II) and further heated to a temperature showing N ^* (chiral nematic phase) (arrow III), so that the viscosity of the liquid crystal is maintained to some extent. The dispersibility of components such as fine particles in the liquid crystal can be improved by injecting the liquid crystal in the liquid crystal, and since the temperature is raised to N ^* after cooling to SmC ^* , the liquid crystal can be effectively realigned. , Because it does not pass through the isotropic phase, uniform orientation can be realized over the entire surface,
It is possible to suppress the occurrence of the twist structure at the gradation display level, and obtain characteristics with good linearity and easy gradation control.

In the production method of the present invention, the cooling rate at the time of cooling to a temperature showing a chiral smectic C phase after the completion of the liquid crystal injection is preferably 0.1 to 10 ° C./min. The rate of temperature rise from the chiral smectic C phase to the chiral nematic phase is 0.
It is desirable to be 5 to 100 ° C./min. Further, after the temperature is stabilized, it is preferable to cool down again to a chiral smectic C phase (ferroelectric phase) at a rate of 0.1 to 10 ° C./min.

FIG. 1 shows the phase transition series of a ferroelectric liquid crystal (chiral smectic C liquid crystal) usable in the present invention in the order of temperature: Iso (isotropic phase) -N ^* (chiral nematic phase) -SmA. (Smectic A phase) -SmC ^* (Chiral smectic C phase) -Cry (crystal phase).

FIG. 2 schematically shows the phase transition series of FIG. 1. T ₁ is the phase transition temperature between the isotropic phase and the chiral nematic phase, and T ₂ is the chiral nematic phase and the smectic A. Phase transition temperature with phase, T ₃ is smectic A
Phase and a phase transition temperature of the chiral smectic C phase, T ₄ denotes a phase transition temperature of the chiral smectic C phase and a crystalline phase.

Here, for example, at the phase transition temperature T ₁ , the isotropic phase and the chiral nematic phase are in a mixed state. When the temperature is increased, the ratio of the isotropic phase is increased. indicates that a state, the temperature becomes the increases the ratio of the chiral nematic phase low, even lower, indicating that a state of a chiral nematic phase only in a temperature range of T _1.

That is, in FIGS. 1 and 2, t ₁ is a temperature range showing only the chiral nematic phase, t ₂ is a temperature range showing only the smectic A phase, and t ₃ is a temperature range showing only the chiral smectic C phase. It is.

In the manufacturing method of the present invention, as shown in FIGS. 1 and 2, a liquid crystal is injected (arrow I) in a temperature range (t ₁ ) showing substantially only a chiral nematic phase, and a chiral smectic C phase is injected. After cooling to a temperature range (t ₃ ) showing (C) (arrow II), it is preferable to raise the temperature to a temperature range (t ₁ ) showing substantially only a chiral nematic phase (arrow III). Thereafter, the mixture is cooled to a temperature range (t ₃ ) showing a chiral smectic C phase (arrow IV).

As described above, by injecting the liquid crystal within the temperature range (t ₁ ) showing substantially only the chiral nematic C phase and raising the temperature to the same temperature range, the orientation of the liquid crystal becomes uniform. That is, if a chiral nematic phase and a smectic A phase or an isotropic phase are mixed, the latter phase causes a disorder in the orientation as a defect portion, so that the threshold of the obtained ferroelectric phase fluctuates, It is easy to become unstable.

Here, the ferroelectric liquid crystal usable in the present invention is a group of smectic liquid crystal materials exhibiting spontaneous polarization typified by chiral smectic C (SmC ^* ) liquid crystal. Some ferroelectric liquid crystals have no phase. For this reason, the manufacturing method of the present invention can be applied even when there is no smectic A phase in FIGS.

The ferroelectric liquid crystal in the present invention is actually a mixture of a chiral smectic C (SmC ^* ) liquid crystal and a non-chiral smectic C (SmC) liquid crystal. Or a mixture of a plurality of types.

Here, chiral smectic C (SmC
^* ) As liquid crystal (ferroelectric liquid crystal), pyrimidine-based CS-1017: Iso 68, N ^* 64, SmA 55, SmC ^* -20, Cry CS-1015: Iso 78, N ^* 68, SmA 57, SmC ^* -17, Cry CS-1014: Iso 81, N ^* 69, SmA 54, SmC ^* -21, Cry CS-3000: Iso 80, N ^* 71, SmA 60, SmC ^* -37, Cry, etc. . However, in the phase transition series of these ferroelectric liquid crystals (all manufactured by Chisso Corporation), the numerical values indicate the phase transition temperature of the liquid crystal.

In addition to the above, known chiral smectic C (SmC ^* ) liquid crystals can be used. For example, biphenyl type, phenyl benzoate type, etc. (However, these ferroelectric liquid crystals may show a chiral nematic phase, a smectic phase, etc., depending on a change in temperature.)
Is a chiral smectic C liquid crystal (ferroelectric liquid crystal).

Usable non-chiral liquid crystals include non-chiral nematic (N) liquid crystals such as ZLI-2008-000 manufactured by Merck (melting point -6 ° C., nematic phase temperature range -20 to 64 ° C.). Is mentioned. In addition to this liquid crystal, a known non-chiral smectic liquid crystal can be used. For example, biphenyl, terphenyl, 3
Ring cyclohexyl, cyclohexylphenyl, biphenylcyclohexane, cyclohexylethane, ester, pyrimidine, pyridazine, ethane, dioxane and the like.

According to the present invention, similarly to the display shown in FIGS. 9 and 10, a pair of substrates provided with a transparent electrode and an alignment film in this order are opposed to each other with a predetermined gap therebetween, and a ferroelectric is provided in the gap. The present invention can be applied to a liquid crystal element into which a liquid crystal is injected.

In the manufacturing method of the present invention, the above-mentioned “the regions having different threshold voltages are finely distributed” means that the transmittance is due to the inversion domain (for example, black domain in white or vice versa). Is 25%, a domain (microdomain) having a size of 2 μmφ or more is 1 mm ²
300 or more (preferably 600 or more) in the field of view
It means that it exists and has a threshold voltage width in its domain of 1 V or more, preferably 2 V or more in a range of transmittance of 10 to 90%.

Therefore, as illustrated in FIG. 4, in the liquid crystal element obtained by the present invention, the transmittance is changed by the applied voltage as shown in FIG.
It shows a relatively gradual change instead of a steep change as shown in FIG. This is because, as described above, in particular, in one pixel, micro-domains having different threshold voltages (V _th ) are developed, and the transmittance of the micro-domains is changed according to the magnitude of the applied voltage. Is changed. Then, in one domain, when the liquid crystal molecules are bistable, they have a memory function, and one pixel is formed from μm-order domains having different threshold voltages, so that continuous gradation display is possible. .

[0048] In Figure 4, of the threshold voltage at which the transmittance is changed, the transmittance of 10% when the V _th1, if the time of transmission of 90% was V _th2, the threshold voltage variation ( △ V
_th = V _th2 −V _th1 ) is 1 V or more.

As for the micro domain, FIG.
As shown in the figure, when the transmittance is 25%, domains MD having a size of 2 μmφ or more are present at a rate of 300 or more / mm ² . Such a fine light-transmitting portion of the microdomain can realize a halftone screen (transmittance) as a whole, but since the structure of such a microdomain has a so-called starry sky,
Hereinafter, it is referred to as “starlight texture”.

According to the starlight texture, the light transmitting portion MD of the micro domain is expanded (increased in transmittance) or reduced as shown by a dashed line in FIG. 5A according to the magnitude of the applied voltage. (Decrease in transmittance), and the transmittance can be arbitrarily changed by the applied voltage. In contrast, in the elements of FIGS. 9 and 10,
As shown in FIG. 5B, since the threshold voltage width is extremely small, the light transmission portion D due to the applied voltage increases or disappears only abruptly, and it is extremely difficult to perform gradation display. It is.

In the method of manufacturing a liquid crystal element of the present invention, as means for forming the above-mentioned microdomain, fine particles (or ultrafine particles) can be dispersed in the liquid crystal 5 in a liquid crystal cell.

Here, the change of the threshold voltage due to the ultrafine particles will be described in principle with reference to FIG. When the particle diameter of the ultrafine particles 10 is d ₂ , the dielectric constant is ε ₂ , the thickness of the liquid crystal 5 excluding the ultrafine particles 10 is d ₁ , and the dielectric constant is ε ₁ , the electric field Eeff applied to the ultrafine particles is expressed by the following equation (1). ). Eeff = (ε ₂ / (ε ₁ d ₂ + ε ₂ d ₁ )) × Vgap (1)

Therefore, when ultrafine particles having a dielectric constant smaller than that of the liquid crystal are added (ε ₂ <ε ₁ ), the total thickness dga of the liquid crystal layer is increased.
By introducing fine particles (d ₂ ) smaller than p (= d ₁ + d ₂ ), Eeff <Egap, and a smaller electric field Eeff acts on the liquid crystal as compared with the case where no fine particles are inserted (Egap). Conversely, by adding fine particles having a dielectric constant larger than that of the liquid crystal (ε ₂ > ε ₁ ), Eeff> Egap, and the electric field Eeff is larger than in the case where no fine particles are added to the liquid crystal (Egap). Works.

The above is summarized as follows. When ε ₁ > ε ₂ → Eeff <(Vgap / d ₁ + d ₂ )
_{= Vgap / dgap = Egap ε 1} = ε 2 when → Eeff = Egap ε ₁ <when ε ₂ → Eeff> Egap

In any case, the addition of the ultrafine particles changes the effective electric field Eeff applied to the liquid crystal itself, and the effective electric field applied to the liquid crystal differs between the region where the ultrafine particles exist and the region where the ultrafine particles do not exist. . As a result, even when the same electric field Egap is applied, there is a region where an inversion domain is generated and a region where no inversion domain is generated between these regions.
The starlight texture structure as shown in (A) can be expressed.

From this, the starlight texture structure is suitable for realizing continuous gradation, and the applied voltage (magnitude, pulse width, etc.) is controlled with the addition of ultrafine particles (ie, two or more types). , A variety of transmittances (that is, two or more types of gradation levels) can be obtained. Contrary to this, only the presence of fine particles gives only the one shown in FIG. 5 (B). In particular, even if fine particles of 0.3 to 2 μm are present in a minute gap (about 2 μm), It is apparent that the display performance cannot be obtained, and even if the gap is not very small, color unevenness occurs due to the fine particle portion. In the present invention, desired performance can be obtained without such a phenomenon.

In the liquid crystal device of the invention described above, the fine particles to be added to the liquid crystal include the effective electric field intensity applied to the liquid crystal 5 existing between the opposed transparent electrode layers 2a and 2b shown in FIGS. Any fine particles can be used as long as they can have a distribution. For example, fine particles of a plurality of materials having different dielectric constants can be mixed and used. The presence of the fine particles having different dielectric constants as described above forms a distribution of the dielectric constant in each pixel.

As a result, as described above, even when an external electric field is uniformly applied between the transparent electrode layers 2a and 2b of the pixel, the effective electric field applied to the liquid crystal in the pixel has a distribution, and The distribution width of the threshold voltage for switching between bistable states (especially ferroelectric liquid crystal) can be widened, and analog gray scale display can be performed within one pixel.

When fine particles having the same dielectric constant are used as the fine particles to be used, the size may be distributed. As described above, the presence of fine particles having different dielectric constants but different sizes allows distribution of the thickness of the liquid crystal layer. As a result, even when an external electric field is applied uniformly between the transparent electrode layers 2a and 2b of one pixel, the effective electric field intensity applied to the liquid crystal in that pixel is distributed, and analog gradation display is performed in one pixel. Becomes possible. Regarding the distribution of the size of the fine particles, it is preferable that the spread of the distribution be large to some extent because excellent analog gradation display can be performed.

In the liquid crystal device of the present invention, it is desirable that the fine particles added to the liquid crystal have a surface having a pH of 2.0 or more. This is because it is easily deteriorated.

The amount of the fine particles is not particularly limited and can be appropriately determined in consideration of the desired analog gradation, etc., but is not more than 50% by weight and not less than 0.1% by weight. Desirably, it is added to the liquid crystal. If the added amount is too large, it is difficult to develop a starlite texture structure due to aggregation, and it is difficult to inject liquid crystal.

The usable fine particles may be composed of carbon black and / or titanium oxide. The carbon black is preferably carbon black produced by a furnace method, and the titanium oxide is preferably amorphous titanium oxide. Pyrolytic carbon black produced by the furnace method has a relatively wide particle size distribution of fine particles, and amorphous titanium oxide has good surface properties and excellent durability.

The usable fine particles, in the form of non-aggregated primary fine particles, preferably have a size of not more than half (0.4 μm or less, particularly 0.1 μm or less) of the liquid crystal cell gap.
Although the gradation display characteristics can be controlled by the particle size distribution, it is desirable that the standard deviation of the particle size distribution be 9.0 nm or more in that the change in transmittance (transmittance) can be moderated. The specific gravity of the fine particles is 0.1 to 1 of the liquid crystal.
A ratio of 0 is desirable from the viewpoint of preventing sedimentation when dispersed in the liquid crystal, and it is preferable that the fine particles are surface-treated with a silane coupling agent or the like so as to exhibit good dispersibility.

As described above, since the size of the fine particles is extremely small, the fine particles may be referred to as ultrafine particles.

In the present invention, the fine particles are desirably present in the liquid crystal between the opposing electrodes. In addition, they may be present in the liquid crystal alignment film or on the liquid crystal alignment film. The configuration other than the presence of the fine particles between the opposing electrodes can be the same as that of the liquid crystal display device (particularly, the ferroelectric liquid crystal display device) shown in FIGS.

For example, a transparent glass plate is used as a substrate, ITO (indium tin oxide) or the like is used as an electrode layer, and a rubbed polyimide film or SiO 2 is used as a liquid crystal alignment film.
An obliquely deposited film can be used. The driving method may be the same as that described above. However, since the gray level of the micro domain starlight texture is obtained by changing the voltage of the data pulse, the data pulse is always applied to one entire frame.

The above-mentioned fine particles play an important role in expressing microdomains in the starlight texture and performing gradation display. However, according to the manufacturing method of the present invention, the fine particles cause aggregation during the injection of the ferroelectric liquid crystal. Without waking up
Since the particles can be uniformly dispersed, the effect of adding fine particles can be sufficiently obtained.

The injection of the ferroelectric liquid crystal can be performed by a liquid crystal injection device as illustrated in FIG.

First, a liquid crystal reservoir 21 containing a ferroelectric liquid crystal composition 5 in which an empty cell 20 composed of a pair of substrates 1a and 1b and ultrafine particles such as titanium oxide are added and mixed is placed inside a bell jar 24. With the arrangement, the inside of the empty cell 20 is vacuum degassed from the exhaust hole 22 and the liquid crystal reservoir 21 is also vacuum degassed.

Next, the empty cell 20 is immersed in the liquid crystal 5 arranged in the liquid crystal reservoir 21, the evacuation operation is stopped, and the liquid crystal 5 is quietly discharged from the injection port 23 by utilizing the capillary action of the empty cell. Inject into When the liquid crystal 5 is filled in a part of the empty cell, the injection of the liquid crystal is continued while introducing a dry inert gas into the bell jar 24 and returning the pressure to normal pressure.

In this case, it is preferable that the atmosphere before and / or during the injection of the liquid crystal 5 be a gas having a high thermal conductivity (eg, helium). By using a gas having a high thermal conductivity as the atmosphere, when the liquid crystal injection device as illustrated in FIG. 3 is heated by the surrounding heater 25, the temperature in the device becomes uniform quickly, so that the injection time is shortened. In addition, since the uniformity of the temperature of the empty cells 20 is improved, a liquid crystal element having a uniform alignment can be manufactured.

As described above, the liquid crystal is injected in a temperature range showing substantially only the chiral nematic phase, and after cooling, the temperature is raised to a temperature range showing substantially only the chiral nematic phase for reorientation. Since it is preferable to use the gas having high thermal conductivity as the atmosphere at that time, even when the temperature range is narrow, the target temperature can be set quickly and uniformly, which is effective. .

Helium is preferably used as the gas having high thermal conductivity.

[0074]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples.

In the ferroelectric liquid crystal (FLC) display according to the present embodiment, a CS manufactured by Chisso Corporation was used as FLC.
-1014 was used. This CS-1014 is one of pyrimidine-based chiral smectic C liquid crystals. As the ultrafine particles for forming the starlight texture structure, 1% by weight of amorphous titanium oxide (IT-OA manufactured by Idemitsu Kosan Co., Ltd.) having an average particle diameter of 17 nm (0.017 μm).
Added to FLC, 12 isotropic temperature range
The mixture was warmed to 0 ° C. and sufficiently dispersed with an ultrasonic homogenizer.
Then, it was gradually cooled.

On the other hand, an ITO electrode (100Ω) was placed on each of a pair of glass substrates having a thickness of 3 mm and a size of 25 × 60 mm.
/ □) and patterned in stripes to form data electrodes and select electrodes. On top of this, SiO
Was vacuum-deposited at an incident angle of 85 ° by a resistance heating method. The film thickness was controlled at 60 nm. The substrate was made antiparallel, and around the periphery, a mixture of 1.6 μm silica spacers (straight spheres) mixed with an ultraviolet curable resin (Photorec: manufactured by Sekisui Chemical Co., Ltd.) was screen-printed.
The cell gap was set to 1.6 μm.

In order to inject the above-mentioned FLC containing ultrafine particles into the cell, the above-mentioned FLC is brought into contact with the injection port of the empty cell as shown in FIG. 3, and as shown in FIG. The cell (empty cell) was heated to 75 ° C., the FLC was raised to a temperature (75 ° C.) showing a chiral nematic phase, and the FLC was injected into the gap between the pair of substrates while maintaining a certain degree of viscosity.

After completion of the injection, the mixture is cooled at a cooling rate of 3 ° C./min to a temperature (45 ° C.) showing a chiral smectic C phase, and further raised to a temperature showing a chiral nematic phase for reorientation. For orientation, the sample was gradually cooled to a temperature (25 ° C.) showing a chiral smectic C phase.

Here, the above-mentioned temperature at which the chiral nematic phase is exhibited is defined as a temperature range t at which only the chiral nematic phase is exhibited.
The temperature in ₁ . Helium was used as an atmosphere to be introduced before and after injecting FLC containing ultrafine particles into a liquid crystal cell (empty cell).

The change in transmittance (relative value) of the thus produced FLC display panel according to the applied voltage (V / μm) is shown in FIGS. 7 and 8 together with Comparative Examples 1, 2 and 3 described later.

In FIG. 7, solid line: FLC containing ultrafine particles was injected into an empty cell at a temperature (75 ° C.) showing a chiral nematic phase, cooled to a temperature (45 ° C.) showing a chiral smectic phase, and further cooled to a chiral nematic phase. 5 shows a voltage-transmittance curve of an FLC panel produced by raising the temperature to the temperature shown in FIG. 1 and then cooling to a chiral smectic C phase (Example 1).

Dashed line: temperature (90) indicating Iso (isotropic phase)
C)), a voltage-transmittance curve of an FLC panel produced with the same composition as in Example 1 except that the ultra-fine particle-containing FLC was injected into an empty cell and cooled to a temperature (25 ° C) showing a chiral smectic C phase. (Comparative Example 1).

One-dot chain line: Voltage-transmittance curve of an FLC panel produced in the same manner as in Example 1 except that no ultrafine particles are contained (Comparative Example 2).

In FIG. 8, solid line: voltage-transmittance curve of the FLC panel of Example 1.

Dashed line: Same as in Example 1 except that the ultrafine particle-containing FLC was injected into the empty cell at a temperature (75 ° C.) showing a chiral nematic phase, and then heated to a temperature (90 ° C.) showing an isotropic phase. Voltage of FLC panel made with the following composition:
Transmittance curve (Comparative Example 3).

After injecting the ultrafine particle-containing FLC into an empty cell at a temperature (75 ° C.) showing a chiral nematic phase, it is cooled to a temperature (45 ° C.) showing a chiral smectic C phase, and iso (Isotropic phase) is cooled. An FLC panel was produced with the same composition as in Example 1 except that the temperature was raised to the indicated temperature (90 ° C.) (Comparative Example 4).

One-dot chain line: Voltage-transmittance curve of the FLC panel of Comparative Example 2.

As can be seen from FIGS. 7 and 8, in the FLC panel of the conventional method (Comparative Examples 1 and 3), the dispersibility of the fine particles at the time of injecting the liquid crystal is poor, and the alignment defect is caused by the transition through Iso → N ^*. Tend to occur, and the gray level (gray scale display portion) of the voltage-transmittance curve is twisted.
A domain having a structure is generated, and linearity in a voltage-transmittance curve is impaired. This has the same tendency in Comparative Example 4. Also, the FLC panel containing no ultrafine particles (Comparative Example 2) is not suitable for gradation display because the transmittance changes sharply from 0% to 100% at the threshold voltage _Vth with respect to the applied electric field. is there.

On the other hand, in the FLC panel of Example 1, the fine particles were sufficiently dispersed, and the alignment was performed because of the reorientation by annealing to N ^* and the transition without going through Iso → N ^*. Is also good, the voltage with high linearity −
A transmittance curve is obtained, which is suitable for gradation display.

Further, helium having high thermal conductivity is used as an atmosphere before and after injecting FLC containing ultrafine particles into a liquid crystal cell (empty cell).
Compared with the case where nitrogen or air is used as the atmosphere, an FLC panel with uniform quality as a whole can be obtained in a short time. Of course, nitrogen or air can be used.

Although the embodiments of the present invention have been described above, the above embodiments can be further modified based on the technical idea of the present invention.

For example, the types and combinations of the above-mentioned liquid crystals,
Conditions that affect the object of the present invention, such as the material and physical properties of the fine particles, may be variously changed as long as the object can be realized.

The above-mentioned transparent electrode includes the above-mentioned I
In addition to TO, known transparent electrodes such as tin oxide and indium oxide can be used, and conventionally known materials for the liquid crystal element such as a transparent substrate, a spacer, and a sealing material can also be used.

Further, the material of the alignment film and the alignment method can be variously changed. This alignment film and the ITO electrode,
It is possible to perform alignment processing in various combinations such as magnetic field alignment and electric field alignment, and alignment film and electric field alignment.

Further, as for the driving method, in addition to the simple matrix method, various driving methods such as an active matrix method can be used.

Further, a polarizing plate, a polarizer and the like may be provided in the device of the above embodiment. In addition to the above display, this element can be used for an optical shutter, an optical switch, an optical blind, and the like. Further, when combined with an electro-optical element or the like, a liquid crystal prism, a liquid crystal lens, an optical path switch,
It can also be used for optical modulators, phase diffraction gratings, A / D converters, optical logic circuits and the like.

[0097]

As described above, the present invention provides a liquid crystal device in which a liquid crystal is disposed between a pair of substrates, and regions having different threshold voltages for switching the liquid crystal are finely distributed. Upon manufacturing, after injecting the liquid crystal between the pair of substrates at a temperature indicating a chiral nematic phase,
Since the liquid crystal is cooled to a temperature showing a chiral smectic C phase and further raised to a temperature showing a chiral nematic phase, by injecting the liquid crystal in a state where the viscosity of the liquid crystal is maintained to some extent, components such as fine particles in the liquid crystal are reduced. Dispersibility can be improved, and since the temperature is raised to the chiral nematic phase after cooling to the chiral smectic C phase, the liquid crystal can be effectively re-oriented, and the liquid crystal may not pass through the isotropic phase. In addition, uniform orientation can be realized over the entire surface, and the occurrence of a twist structure at a gradation display level can be suppressed, and characteristics with good linearity and easy gradation control can be obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a method for manufacturing a liquid crystal element of the present invention together with a phase transition series of a liquid crystal.

FIG. 2 is a schematic diagram illustrating a phase transition state of a liquid crystal.

FIG. 3 is a schematic sectional view of the same liquid crystal injection device.

FIG. 4 is a voltage-transmittance characteristic diagram showing a threshold voltage characteristic of the ferroelectric liquid crystal element.

FIGS. 5A and 5B are a schematic diagram for explaining a change in transmittance at the time of switching of a liquid crystal element, and a similar schematic diagram when there is no gradation.

FIG. 6 is a schematic diagram for explaining an effective electric field in the liquid crystal of the liquid crystal element.

FIG. 7 is a diagram showing voltage-transmittance characteristics of an example of the present invention and a comparative example.

FIG. 8 is a voltage-transmittance characteristic diagram of the example and the comparative example of the present invention.

FIG. 9 is a schematic plan view of a conventionally used liquid crystal element viewed from a select electrode side.

FIG. 10 is a sectional view taken along line XX of FIG. 9;

FIG. 11 is a model diagram of a ferroelectric liquid crystal.

FIG. 12 is a voltage-transmittance characteristic diagram showing a threshold voltage characteristic of a conventionally used liquid crystal element.

FIG. 13 is a flowchart showing a conventional method for manufacturing a liquid crystal element together with a phase transition series of a liquid crystal.

[Explanation of symbols]

1a, 1b: substrate, 2a, 2b: transparent electrode layer, 3a, 3
b: SiO oblique deposition layer, 5: liquid crystal (FLC), 10: fine particles, 11: FLC element, 24: bell jar, 22: exhaust (degassing) port, 21: liquid crystal reservoir, 25: heater, 20 ...
Empty cell, 23 ... Injection port, Iso ... Isophase, N ^* ... Chiral nematic phase, SmA ... Smectic A phase, SmC ^*
... Chiral smectic C phase, Cry ... Crystal phase, MD ...
Micro domain

 ──────────────────────────────────────────────────の Continuation of the front page (72) Inventor Akio Yasuda 6-7-35 Kita Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation

Claims (8)

[Claims] When manufacturing a liquid crystal element in which liquid crystal is arranged between a pair of substrates and regions having different threshold voltages for switching the liquid crystal are finely distributed,
A method for producing a liquid crystal device, comprising: injecting the liquid crystal between the pair of substrates at a temperature indicating a chiral nematic phase, cooling the liquid crystal to a temperature indicating a chiral smectic C phase, and further raising the temperature to a temperature indicating a chiral nematic phase. 2. Injecting a liquid crystal in a temperature range showing substantially only a chiral nematic phase, cooling to a temperature range showing a chiral smectic C phase, and then raising the temperature to a temperature range showing substantially only a chiral nematic phase. The manufacturing method according to claim 1. 3. The method according to claim 1, wherein fine particles are added to the liquid crystal in order to form fine regions having different threshold voltages. 4. The fine particles have a surface having a pH of 2 or more,
The method according to claim 3. 5. The method according to claim 3, wherein the fine particles are added to the liquid crystal at a ratio of 50% by weight or less. 6. The method according to claim 3, wherein the fine particles are made of carbon black and / or titanium oxide. 7. A pair of substrates provided with a transparent electrode and an alignment film in this order are opposed to each other with a predetermined gap therebetween, and a ferroelectric liquid crystal is injected into the gap to manufacture a liquid crystal element.
When the transmittance by the inversion domain is 25% or more,
300 or more domains having a size of ² μmφ or more exist in a visual field of 1 mm ² , and a threshold voltage width in the domain is 1 volt or more in a range of a transmittance of 10 to 90%. The method according to claim 1, wherein the liquid crystal element is configured so as to be able to perform gradation display. 8. The method according to claim 1, wherein the atmosphere before and / or during the injection of the liquid crystal is a gas having high thermal conductivity.