JPH0486812A - Method for refining liquid crystal - Google Patents

Abstract

PURPOSE:To remove impurities from a liquid crystal by bringing the liquid crystal to be refined into contact with oriented layers and impressing the AC electric field above the threshold thereto. CONSTITUTION:The liquid crystal to be refined is supplied from an injection port 12 and a clock 14 is held closed at this time. A voltage is applied between electrodes 3 and 4 by an AC power source 15 to form the AC electric field above the threshold of the liquid crystal in a space 10. The liquid crystal impressed with such electric field makes molecular motion and the metallic ions which are the impurities contained in the liquid crystal move downward by the effect of such molecular motion and gravity. The impurities are gathered in the lower part 16 of the space 10 and the impurity concn. in the liquid crystal is increased. The impurity concn. in the remaining part of the space 10 is correspondingly decreased and the liquid crystal is refined.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for purifying liquid crystal.

Prior art For example, liquid crystals commonly used in pure matrix type liquid crystal display devices preferably have a specific resistance of about 10 Ωcm-' or more. If the liquid crystal contains a large amount of impurities, such as metal ions such as Na, the resistivity will decrease to 101
Therefore, due to the Kerr-Helfrich effect, when an electric field above a certain value is applied, a dynamic scattering phenomenon is observed, which adversely affects display characteristics, causing flicker and threshold voltage Vth.
Fluctuations in the display quality may cause display unevenness, resulting in a deterioration in display quality. Is it necessary to remove impurities from liquid crystal?

Prior art involves distillation of liquid crystals and also column chroma)
-Uses krahui and moshikura thief.

Invention or Problem to be Solved None of these prior art techniques is simple and has the problem that the price of the liquid crystal material increases significantly when introduced into the manufacturing process.

An object of the present invention is to provide a method for purifying liquid crystal that allows impurities to be removed from liquid crystal using a simple method.

Means for Solving the Problems The present invention is a method for purifying liquid crystal, which is characterized in that the liquid crystal to be purified is brought into contact with an alignment layer and an alternating current electric field of a threshold value or higher is applied.

Function According to the present invention, the liquid crystal to be purified is brought into contact with an alignment layer,
An alternating current electric field of a threshold value or higher is applied to this liquid crystal, thereby causing the liquid crystal molecules to change their slope at the frequency of the alternating current of the electric field due to a fitteric transition. In the vicinity of the alignment layer, the center of rotation of the liquid crystal molecules is shifted from the center of gravity of the liquid crystal molecules, and furthermore, the electric field causes the liquid crystal molecules to rise at an angle with respect to the alignment layer, and after the electric field becomes zero, The response speed of the relaxation to return to the alignment direction of the alignment layer is different, and the response speed of the rising time is larger than the response speed of the relaxation time, so liquid crystal molecules whose tilt changes repeatedly due to the alternating electric field are included in the liquid crystal. Impurities such as metal ions are pushed in one direction and moved. On the LCD screen,
A region with a high impurity concentration is formed, and by removing the liquid crystal with a high impurity concentration, a liquid crystal with a low impurity concentration can be obtained.

Embodiment 1 Section 1 is a perspective view of an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along section line A-B-C-D of FIG. 1. A pair of glass substrates 1 and 2 have electrodes 3 and 4 made of ITO (indium oxide with soot added) formed thereon, and Si for protection of the electrodes 3.4. An insulating film 5.6 is formed, and an alignment layer 7.8 of polyimide is further formed thereon. The alignment layers 7 and 8 have alignment directions that are lahed in directions 7a and 8a parallel to the vertical direction in FIGS. 1 and 2.

An electrically insulating synthetic resin heather 9 is interposed between the alignment layers 7, 8, and the liquid crystal to be purified is supplied to the space 10 thereof. Acrylic sealing material 11 is placed on the outer periphery of the substrates 1 and 2.
The space 10 is made airtight. Substrate 1.2
A supply port 12 for supplying the liquid crystal to be purified is formed in the sealing material 11 at the upper part of the sealing material 11 . A discharge pipe 13 is connected to the sealing material 11 at the bottom of the substrates 1 and 2, and a cock 14 serving as an on-off valve is provided.

An AC power source 15 is connected to the electrodes 3 and 4. This AC power supply 15 generates, for example, a sine wave with an amplitude of 3 mm and a frequency of 30 Hz, thereby providing an electric field above a threshold value at which the liquid crystal in the space 0 is caused to tilt in the direction perpendicular to the electric field by the Fredericks transition. It becomes possible.

The distance d between the spaces 10 and the heaps 9 is, for example, 1 mm. No electrode 34 is formed in the lower part 16 of the second space 10, and the height h of the space 10 in which the electrode 56 of the lower part 16 is not formed is, for example, 1 cm. Discharge pipe 13
An analogy could be a crow.

The liquid crystal to be purified is supplied from the injection port 12 as described above,
At this time, the cock 14 is kept closed. A voltage is applied between the electrodes 3 and 4 by an AC power source 15 to form an AC electric field in the space 10 that is higher than the threshold of the liquid crystal. The liquid crystal to which such an electric field is applied undergoes molecular motion, and due to this molecular motion and the action of gravity, metal ions, which are impurities contained in the liquid crystal, move downward, and the lower part 16 of the space 10 moves downward. As a result, the impurities are collected and the impurity concentration in the liquid crystal becomes high, and the impurity concentration in the remaining part of the space 10 is reduced accordingly, thereby refining the liquid crystal.

The time period during which the AC electric field is applied by the AC power supply 15 is, for example, 3 hours. By opening the cock 14, the liquid crystal whose impurity concentration has increased in the lower part 16 of the space 10 is discharged downward through the discharge pipe 13. Thus space 10
The purified liquid crystal remains, and with such purified liquid crystal, the current flowing to the AC power supply 15 is significantly reduced.

The inventor of the present invention considers the reason for such a phenomenon in which liquid crystal is purified as follows. Figure 3 (1) shows the state of liquid crystal molecules that occurs when no voltage is applied between electrodes 3 and 4, and Figure 3 (2) shows the state when that voltage is applied. , FIG. 4 shows the state of the liquid crystal molecules in an enlarged and simplified manner. When no voltage is applied to the electrode 3.4, the liquid crystal molecules 1819 near the substrate 1.2 are in a so-called lying state, as shown by the solid lines in FIGS. 3(1) and 4. , the liquid crystal molecules 20 located in the center between the substrates 1 and 2 are as shown by the solid line 20 in FIG.
The image is tilted in a direction perpendicular to the plane of the paper.

When a voltage is applied between the electrodes 3 and 4, the liquid crystal molecules 1819 move as indicated by the arrow 2, as shown by the broken lines in FIGS. 3(2) and 4.
The liquid crystal molecules tilt in the directions of 1 and 22, so to speak, in a standing position.
5 is shown. Liquid crystal molecules 20 in the center of the substrate 12
The projected length on the paper surface changes as shown by the line 25 as a voltage is applied.

Although the liquid crystal molecules 20 located at the center between the substrates 1 and 2 perform a rotational motion about the center of gravity 20a of the molecules, no anisotropy of motion is observed.

On the other hand, the liquid crystal molecules 18 and 1 near the substrates 1 and 2 are
The centers 18a, 19a of the rotational movement, which have strong interaction with the molecules on the surface of the alignment films 7, 8 and rotate in the direction of the arrow 2122 by applying a voltage, are separated from the centers of gravity 18b, 19b of the liquid crystal molecules 18.19. It shifts toward the substrates 1 and 2, resulting in so-called anisotropy of motion.

The response speed of these liquid crystal molecules 18, 19, 20 between the rising state 23, 24, 25 when a voltage is applied and the relaxation state in which the liquid crystal molecules return to the alignment direction after the voltage is no longer applied is as follows. That is, the rising response speed Ton of the liquid crystal molecule 1519.20 and the relaxation response speed Toff of the liquid crystal molecule 18.19.2o are as follows: η is the viscosity of the liquid crystal, d is the liquid crystal layer thickness, and ε. is the vacuum permittivity, Δε is the dielectric anisotropy, X' is the voltage applied by the AC power source 15, and I is the elastic constant of the liquid crystal.

In reality, the rising response speed Ton of the liquid crystal is larger than the relaxation response speed Toff, and has a large amount of energy.

Ton>Toff-<3) Therefore, the liquid crystal 1819 near the substrates 1 and 2 is
Depending on the response speed Ton at the time of rising voltage,
Arrows 21 and 22 push metal ions, which are impurities contained in the liquid crystal, downward, and the metal ions descend under their own weight. By applying a voltage, the reference numerals 23 and 24 in FIG.
, 25, when the voltage is no longer applied, the liquid crystal molecules return to the opposite direction of arrows 21 and 22. Hateful.

The direction of movement of impurities is determined by the directionality of the liquid crystal molecules 18 and 19 when they rise due to voltage application, as described in 2 above. Note that the liquid crystal molecules 20 located in the center between the substrates 1 and 2 are inclined with respect to the center of gravity, and have almost no function of moving metal ions downward.

The movement of impurities occurs due to the movement of liquid crystal molecules, and the degree of impurity movement varies greatly depending on the magnitude and frequency of the applied electric field.

The electric field applied to the liquid crystal, and therefore the voltage applied by the AC power supply 15, must be selected to be equal to or higher than the threshold value that causes the Fredericks transition. Further, the frequency needs to be lower than the breakover frequency that the liquid crystal can follow.

Referring to FIG. 5, in the electric field, polarization occurs within the liquid crystal molecule with charges +δ and -δ, and this causes the liquid crystal force against impurities such as charged metal ions. On the other hand, during relaxation by removing the electric field, polarization of the liquid crystal molecules 27 does not occur, and therefore the influence of the liquid crystal molecules 27 on impurities having an electric field becomes small.

Second, as described above, the impurities are moved downward by the change in the tilt of the liquid crystal molecules 27 due to the electric field.

The output of the AC power supply 15 may be a rectangular wave, or may be a sine wave or other waveform.

FIG. 6(1) shows the state immediately after an electric field is applied to the liquid crystal 28 containing impurities, and FIG. 6(2) shows the state after a certain amount of time has passed after the voltage application. The storage device 29.30 having a positive or negative polarity is moved by the application of an electric field and is relaxed by the substantial potential difference of the liquid crystal 28 with impurities or by the movement of the impurity, which is the substance 29.30; Liquid crystal molecules move. When a rectangular wave is applied to the electrodes 3 and 4 as in the above embodiment, the effective voltage applied to the impurity-containing liquid crystal 28 becomes smaller, and the movement of the liquid crystal molecules is observed as flicker.

Since the polarity of the voltage applied to the electrodes 3.4 by the AC power source 1 is alternately repeated, the states of FIG. 6(1) and FIG. 6(2) are repeated. The effect of the voltage relaxation phenomenon when such a rectangular wave is applied becomes smaller as the frequency becomes higher, so a frequency of about 20 to 50 Hz is effective, and preferably 30 Hz is selected as described above.

Impurities include metal ions as described above, as well as organic ions and highly polar organic substances.

In the present invention, an electric field may be applied to the liquid crystal by a structure other than the electrodes 3 and 4 described above.

As another embodiment of the present invention, the rubbing direction of the alignment layers 7 and 8 is set to θ1 with respect to the vertical line 31 in FIG. For example, θ1. θ
2 may be at 45°.

In other words, when viewed from the normal direction to the substrate surface of the substrate 1.2, the rubbing direction of the alignment layers 7 and 8 of the two substrates 1.2 is opposite to the movement direction of the impurity to be controlled. In each of the substrates 1.2 (180°245
゛).

As another embodiment of the present invention, the rubbing direction 7a8a may be a horizontal direction, in which case the impurities will move to the right or left.

The electrodes 3 and 4 may not be transparent electrodes, but may be electrodes made of other metals.

Effects of the Invention As described above, according to the present invention, by applying an alternating current electric field of a threshold value or higher while the liquid crystal to be purified is in contact with an alignment layer, impurities in the liquid crystal are moved and the liquid crystal is purified. A region with a high impurity concentration is generated, and by collecting and removing the liquid crystal in the region with a high impurity concentration, it is possible to obtain a liquid crystal with a low impurity concentration.Is this method easy to implement? Therefore, the quality of the liquid crystal display can be improved, and the price of the liquid crystal material will not increase.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of the present invention, FIG. 2 is a cross-sectional view taken from section line A-B-C-D in FIG. FIG. 4 is a diagram showing the orientation of liquid crystal molecules in a state where an applied voltage is applied. FIG. 4 is a simplified diagram for explaining the orientation of the liquid crystal molecules in an easy-to-understand manner. FIG. FIG. 6 is a diagram showing a state in which impurities in the liquid crystal 28 containing impurities move. 1.2 Substrate, 3.4・Electrode, 7,8 Orientation layer, 10・
... Space, 15... AC power supply agent Patent attorney Keibu Saikyo Part 1 Figure 1

Claims (1)

[Claims] A method for purifying liquid crystal, which comprises bringing the liquid crystal to be purified into contact with an alignment layer and applying an alternating current electric field of a threshold value or higher.