CN102667600A - Tn liquid crystal element, and method for producing same - Google Patents

Abstract

The invention provides a TN-type liquid crystal element and a manufacturing method thereof. The TN-type liquid crystal has a stable state and realizes a high-speed drop response speed. The above-mentioned TN-type liquid crystal element includes: a group of substrates, the group of substrates is arranged approximately in parallel and at least one of them is transparent; a group of alignment films, the group of alignment films is arranged on the opposite surface of the group of substrates, And the surface has been oriented so that the liquid crystal molecules in the liquid crystal material point to the same direction; and the liquid crystal layer, the liquid crystal layer is arranged between the set of alignment films, and includes a liquid crystal material and a chiral agent, wherein the A formed angle α of an alignment treatment direction of the group of alignment films is 70 degrees to 110 degrees, and the alignment treatment direction is a direction in which a uniform twisted structure is formed when the liquid crystal layer is twisted by the formed angle α, The stable STN liquid crystal with a twist angle of α+180 degrees in the state of no electric field realizes the stabilization of the polymer and becomes a TN type liquid crystal with a twist angle of α degrees.

Description

TN type liquid crystal element and its manufacturing method

technical field

The invention relates to a TN type liquid crystal element and a manufacturing method thereof.

Background technique

In recent years, the market for liquid crystal elements has gradually expanded from small-sized products used in mobile phones to large-sized products used in liquid crystal televisions.

This liquid crystal element has been developed centering on the so-called TN (Twisted Nematic: Twisted Nematic) type liquid crystal element with a structure in which the alignment treatment direction of the upper and lower substrates is twisted by 90 degrees. Vertical Aligned: multi-region vertical arrangement), IPS (In Plane Switching: coplanar switch) and other methods have gradually become mainstream. However, the TN method has advantages such as less change in transmittance (gap deviation) with respect to changes in cell thickness than other methods, and can be used in applications such as personal computers that do not have a particularly strict requirement for viewing angles. .

And in recent years, the combination of TN-type liquid crystal elements and optical films called wide view films (wideview film) that can expand the viewing angle of TN-type liquid crystals has gradually been able to be used for TVs below 26 inches, and the size below 26 inches TN-type liquid crystals already account for 80% of current LCD TVs.

In general, high-speed responsiveness is particularly required for liquid crystal elements used in television applications. The response speed of the TN type liquid crystal is expressed by the following formulas (1) and (2).

[mathematical formula 1]

${\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; on</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;\&epsiv;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; the\; th</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; off</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; K</span>}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Here, τ _on represents the rising (response from the state of no voltage applied to the state of applied voltage) response time, and τ _off represents the response time of falling (response from the state of voltage applied to the state of no voltage applied).

In addition, _γ1 represents the rotational viscosity of the liquid crystal material, _ε0 represents the vacuum permittivity, Δε represents the dielectric anisotropy, d represents the thickness of the liquid crystal layer, V represents the applied voltage, _Vth represents the threshold voltage, and K represents the elasticity of the liquid crystal material modulus. In TN-type liquid crystal, K=K ₁₁ -0.5K ₂₂ +0.25K ₃₃ , K ₁₁ , K ₂₂ , and K ₃₃ represent elastic modes for spray, twist, and bend deformations, respectively. quantity.

As can be seen from the above formula (1), since the rising response speed depends on the applied voltage, it is possible to increase the speed by applying the applied voltage. Conversely, since the falling response speed does not depend on the applied voltage, it cannot be increased by the signal voltage. For this reason, in the liquid crystal element, it is required to increase the speed of the falling response speed rather than the rising response speed.

In order to achieve a high-speed response to the drop, from the above formula (2), it can be considered to reduce γ ₁ (rotational viscosity), increase K (elastic modulus) and other material improvements, and reduce d (thickness of the liquid crystal layer) and other equipment. improvements. Regarding the thickness of the liquid crystal layer, it is known that TN-type liquid crystal must satisfy Δn·d≥0.50 (μm) (Δn is the refractive index anisotropy of the liquid crystal material). If this condition is not satisfied, the transmittance of the liquid crystal element decreases. Since Δn=0.25 is regarded as the limit in existing liquid crystal materials, it can be considered that d=2 (μm) is the limit. With regard to liquid crystal materials, there are limits to the improvement of their rotational viscosity and modulus of elasticity. For this reason, from the relationship of the above formula (2), it is difficult to greatly improve the drop response speed of the TN-type liquid crystal.

As a method not expressed in the above formulas (1) and (2), it is known, for example, to reduce the chiral pitch of the liquid crystal material by adding an optically active substance called a chiral agent to the liquid crystal material The ratio (p/d) of p to the thickness d of the liquid crystal layer, and the method of improving the response speed of the drop. Regarding this method, the following reports have been made so far.

Patent Documents 1 and 2 disclose techniques for speeding up liquid crystal elements by setting the thickness of the liquid crystal layer to 0.5 μm to 3 μm and the p/d value to less than 15.

Patent Document 3 discloses a technology for realizing high-speed TN-type liquid crystal within the range of 0.25<d/p<1 (ie, 1<p/d<4). This Patent Document 3 describes simulated values of the drop response speed from d/p=0.04 (p/d=25) to d/p=1 (p/d=1). In addition, the data of d/p=0.51 (p/d=2.0) are described as actual experimental data.

Patent Document 4 describes the fact that the drop response speed is increased by shortening the chiral pitch of the liquid crystal material. It is also described that by increasing the pretilt angle of the alignment film, even if a short-pitch liquid crystal material is used, the 90-degree twisted state can be stabilized. Specifically, by setting the pretilt angle to 13.6 degrees, even a liquid crystal material that originally forms a 210-degree twisted state in a liquid crystal cell can maintain a 90-degree twisted state. A twisted state of 210 degrees corresponds to p/d=1.7.

Non-Patent Document 1 describes that in a liquid crystal layer with a thickness of 12 μm, by shortening the chiral pitch of the liquid crystal material from 70 μm (p/d=5) to 25 μm (p/d=2.1), the drop response speed is reduced by 400ms is improved to 200ms.

prior art literature

patent documents

Patent Document 1: JP-A-2007-193362

Patent Document 2: JP-A-2008-176343

Patent Document 3: JP-A-2003-161962

Patent Document 4: JP-A-2000-199901

non-patent literature

Non-Patent Document 1: S.Aftergut and H.S.Cole Jr., J.Appl.Phys.Lett., 30(8), P.363, (1977)

Non-Patent Document 2: Kanzaki, Ichimura, Funada, Ishii, Matsuura, Sharp Technical Report, 39(35), (1988)

Contents of the invention

The technical problem to be solved by the invention

As described above, by reducing the p/d value, it is possible to speed up the drop response speed. However, it is known that when the twist angle of the liquid crystal layer is α (degree), if the pitch is shortened, the twist angle is changed to α+180 (degree) (see Non-Patent Document 2). Therefore, in the case of a TN type liquid crystal with a twist angle of 90 degrees, if the pitch is shortened, an STN (Super Twited Nematic: Super Twisted Nematic) type liquid crystal with a twist angle of 270 degrees is formed. In addition, in Non-Patent Document 2, p/d=2 is the lower limit.

The aforementioned Patent Document 3 describes the simulation results of liquid crystal elements in the range of 1<p/d<4, but this is only the result of simulation calculation rather than the result of actual measurement. As an actual measured value, the minimum value is p/d=2.0.

Here, as described in the aforementioned Patent Document 4, by increasing the pretilt angle of the alignment film, the 90-degree twist state can be stabilized even if a short-pitch liquid crystal material is used. However, even if the pretilt angle is increased, there is a limit to the p/d value that can be realized, and even Patent Document 4 discloses only p/d=1.7. In addition, TN-type liquid crystals in this state are expected to be unstable liquid crystals, and it is considered that even if they are formed, they will transition to STN-type liquid crystals due to changes in temperature, application of stress, vibration, and the like.

In view of the above-mentioned technical problems, the object of the present invention is to provide a TN-type liquid crystal element and its manufacturing method, the state of the TN-type liquid crystal is stable, and the speed-up of the falling response speed is realized.

means of solving technical problems

In order to solve the above technical problems, the inventors of the present application conducted in-depth research. As a result, it was found that even if the p/d value is reduced, the STN liquid crystal with a twist angle of α+180 (degree) is more stable than the TN type liquid crystal with a twist angle of α (degree), and the STN type liquid crystal forms a splay Under the conditions of the structure, if a voltage is applied, the splayed structure is eliminated, and the state of the twist angle α (degrees) is temporarily maintained. And found that by adding a photocurable monomer to the liquid crystal material, and curing the photocurable monomer in a state where the twist angle is α (degree) temporarily, it is possible to realize the high molecular weight of the liquid crystal layer at the twist angle α (degree). stabilization. The present invention has been accomplished based on the above knowledge, and more specific contents are described below.

(1) A TN-type liquid crystal display element, characterized in that it includes: a group of substrates, the group of substrates is arranged approximately in parallel and at least one of them is transparent; a group of alignment films, the group of alignment films is set On the opposite side of the group of substrates, and the surface has been oriented so that the liquid crystal molecules in the liquid crystal material point in the same direction; and a liquid crystal layer, the liquid crystal layer is arranged between the group of alignment films, and includes Liquid crystal material and chiral agent, the angle α formed by the orientation treatment direction of the group of alignment films is 70 degrees to 110 degrees, and the orientation treatment direction is when the liquid crystal layer twists the formed angle α In the direction of forming a uniform twisted structure, the STN-type liquid crystal polymer with a stable twist angle of α+180 degrees in the state of no electric field is stabilized into a TN-type liquid crystal with a twist angle of α degrees.

(2) The TN-type liquid crystal display element according to (1) above, wherein in the same liquid crystal display element, the free energy of the STN-type liquid crystal with a twist angle of α+180 degrees is higher than that of the TN-type liquid crystal with a twist angle of α degrees in the same liquid crystal display element. The free energy is low, and the liquid crystal layer achieves polymer stabilization at the twist angle α degree.

(3) The TN-type liquid crystal display element according to the above (1) or (2), wherein when the thickness of the liquid crystal layer is d and the chiral pitch of the liquid crystal material is p, 0.5 ≤p/d≤1.6.

(4) The TN-type liquid crystal display element according to any one of (1) to (3) above, wherein the pretilt angle of the alignment film is 5 degrees or less.

(5) A method for manufacturing a TN-type liquid crystal display element, comprising: a step of forming an alignment film on a respective surface of a group of substrates at least one of which is transparent; The process of aligning the surface so that the liquid crystal molecules in the liquid crystal material point in the same direction; the process of arranging the set of substrates in such a way that the set of alignment films face each other; filling the gap between the set of alignment films containing chiral a liquid crystal material of an agent and a photocurable monomer to form a liquid crystal layer; a step of applying a voltage between the set of substrates; and a step of photocuring the photocurable monomer after stopping or reducing the applied voltage, A formed angle α of an alignment treatment direction of the group of alignment films is 70 to 110 degrees, and the alignment treatment direction is a direction in which a uniform twisted structure is formed when the liquid crystal layer is twisted by the formed angle α , in the process of applying voltage, after the liquid crystal layer is in a vertical alignment state by applying voltage, the applied voltage is stopped or reduced, so that the liquid crystal layer is temporarily transformed from an STN type liquid crystal with a twist angle of α+180 degrees to a twist angle It is a TN-type liquid crystal transition of α degree. In the photo-curing step, the photocurable monomer is photo-cured, so that the liquid crystal layer realizes polymer stabilization at a twist angle of α degree.

(6) The method for manufacturing a TN-type liquid crystal display element according to the above-mentioned (5), wherein when d is the thickness of the liquid crystal layer and p is the chiral pitch of the liquid crystal material, 0.5≤ p/d≤1.6.

Invention effect

According to the present invention, it is possible to provide a TN-mode liquid crystal display element in which the state of the TN-mode liquid crystal is stable and which achieves a high-speed drop response speed, and a method for manufacturing the same.

Description of drawings

FIG. 1 is a diagram illustrating an example of a method of manufacturing a TN-mode liquid crystal element according to the present invention.

FIG. 2 is a diagram schematically showing an alignment treatment direction and a rising direction of liquid crystal molecules.

FIG. 3 is a diagram schematically showing how liquid crystal molecules are arranged with a left twist.

FIG. 4 is a diagram schematically showing how liquid crystal molecules are arranged in a right-hand twist.

FIG. 5 is a graph showing simulation results of the drop response time τ _off when the chiral pitch of the liquid crystal material is changed.

FIG. 6 is a diagram showing directions of alignment treatment of upper and lower alignment films in Example 1. FIG.

7 is a graph showing changes in the liquid crystal layer observed when a voltage was applied to the liquid crystal cell prepared in Example 1. FIG.

8 is a box plot showing the measurement results of the response time τ _off when the voltage is turned off in the state where the V10 voltage is applied at 25° C. for the five TN-type liquid crystal elements (elements 1 to 5 ) prepared in Example 1.

Fig. 9 is a graph showing the transparency of the five TN-type liquid crystal elements (elements 1 to 5) prepared in Example 1, when they are in the state of applying a voltage of V50 at a time of 20 ms and in a state of no voltage being applied at a time of 520 ms. A graph of the rate of change over time.

FIG. 10 is an enlarged view from the time of 510 ms to the time of 570 ms in FIG. 9 .

11 is a box plot showing the measurement results of the response time τ _off when the voltage is turned off with the V10 voltage applied at -20° C. for the five TN-type liquid crystal elements (elements 1 to 5) prepared in Example 1.

Detailed ways

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.

The liquid crystal material constituting the liquid crystal layer will first be described below, followed by a method for manufacturing the TN-mode liquid crystal element according to the present invention, and finally, the TN-mode liquid crystal element according to the present invention will be described.

[Liquid crystal material]

The liquid crystal material constituting the liquid crystal layer in the present invention includes a chiral agent and a photocurable monomer.

A nematic liquid crystal is used as the liquid crystal material. The type is not particularly limited, but in consideration of the aforementioned formula (2) regarding the drop response speed, a liquid crystal material with a low rotational viscosity and a large modulus of elasticity is preferable.

The chiral agent is not particularly limited, and conventionally known chiral agents can be used. S-811, R811, CB-15, MLC6247, MLC6248, R1011, S1011 (all are manufactured by Merck) etc. are mentioned as an example. By adjusting the content of the above-mentioned chiral agent, the chiral pitch of the liquid crystal material can be adjusted.

It does not specifically limit as a photocurable monomer. Examples include: ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, isooctyl methacrylate, lauryl methacrylate, octadecyl methacrylate , isomyristyl methacrylate, isostearylmethacrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, methyl methacrylate Methyl carbitol methacrylate, ethyl carbitol methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, 2-hydroxyethyl methacrylate, Phenoxy methacrylate, methoxy dipropylene glycol methacrylate, trifluoroethyl methacrylate, dimethylamino methacrylate, methyl [2-(4-Morpholinyl)ethyl] acrylate, Perfluoroalkyl methacrylate, Polyethylene glycol dimethacrylate, Polypropylene glycol dimethacrylate, Polybutylene glycol dimethyl Acrylate (polybutylene glycol dimethacrylate), aliphatic dimethacrylate, epichlorohydrin modified 1,6-hexanediol dimethacrylate, dicyclopentenyl dimethacrylate (dicyclopentenyl dimethacrylate), Bisphenol A dimethacrylate, epichlorohydrin modified bisphenol A dimethacrylate, ethylene oxide modified bisphenol A dimethacrylate, propylene oxide modified bisphenol A dimethyl Acrylate, butylene oxide modified bisphenol A dimethacrylate, 3,3-dimethylol pentane dimethacrylate (3,3-dimethylol pentane dimethacrylate), 3,3-dimethacrylate Dimethylol heptane (3,3-dimethylol heptane dimethacrylate), caprolactone modified dipentaerythritol hexamethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, dipentaerythritol tetramethacrylate , dipentaerythritol hexamethacrylate, methacrylate urethane, N,N-dimethylacrylamide, N,N-dimethylaminopropylacrylamide, etc.

Moreover, as a photocurable monomer, what exhibits liquid crystallinity is preferable. The photocurable monomers exhibiting liquid crystallinity are described in, for example, JP-A-8-3111, JP-A-2000-178233, JP-A-2000-119222, JP-A-2000-327632, JP-A-2002-220421 Publication No. 2003-55661, Japanese Patent Application Publication No. 2003-12762, etc.

The content of the photocurable monomer varies depending on the type of the photocurable monomer and the pretilt angle of the alignment film, and is preferably 0.1% by mass to 15% by mass relative to the liquid crystal material, more preferably 0.5% by mass to 10% by mass %. By setting the content to 0.1% by mass or more, the polymer stabilization effect described later can be sufficiently obtained. Moreover, by making content into 15 mass % or less, the increase of the drive voltage of a liquid crystal element and the fall of contrast can be suppressed.

[Manufacturing method of TN type liquid crystal element]

The method for manufacturing a liquid crystal element according to the present invention is characterized in that it includes: a step of forming an alignment film on each surface of a group of substrates at least one of which is transparent; performing an alignment treatment on the surface of the group of alignment films The process of making the liquid crystal molecules in the liquid crystal material point in the same direction; the process of arranging the group of substrates in such a way that the group of alignment films face each other; filling the group of alignment films with a chiral agent and photocuring The process of forming a liquid crystal layer by using a liquid crystal material of a curable monomer; the process of applying a voltage between the set of substrates; and the process of photocuring the photocurable monomer after stopping or reducing the applied voltage, wherein the A formed angle α of an alignment treatment direction of a group of alignment films is 70 degrees to 110 degrees, and the alignment treatment direction is a direction in which a uniform twisted structure is formed when the liquid crystal layer is twisted by the formed angle α, so In the step of applying a voltage, after the liquid crystal layer is in a vertical alignment state by applying a voltage, the applied voltage is stopped or reduced, so that the liquid crystal layer is temporarily transformed from an STN type liquid crystal with a twist angle of α+180 degrees to an STN type liquid crystal with a twist angle of α In the photo-curing step, the photo-curable monomer is photo-cured, so that the liquid crystal layer realizes polymer stabilization at a twist angle α degree.

Hereinafter, an example of the manufacturing method of the TN mode liquid crystal element which concerns on this invention is demonstrated in detail, referring FIG. 1 suitably. FIG. 1 is a diagram showing a manufacturing process of a TN-type liquid crystal element broken down into individual steps.

Firstly, the surfaces of a group of substrates, at least one of which is transparent, are cleaned and dried (steps S10, S11). Next, an alignment film (polyimide film) is formed by applying polyimide to one surface of each of the aforementioned set of substrates, followed by drying and firing (steps S12 and S13 ). Then, a rubbing treatment (orientation treatment) is performed on the surface of each alignment film so that the liquid crystal molecules in the liquid crystal material are aligned in the same direction (step S14 ).

FIG. 2 schematically shows the orientation treatment direction and the rising direction of liquid crystal molecules. After the alignment treatment is carried out on the surface of the alignment film 100, the liquid crystal molecules 101 on the surface of the alignment film stand up obliquely relative to the alignment treatment direction in a plane including the alignment treatment direction shown by the arrow in the figure and the direction perpendicular to the alignment film 100. angle theta. This angle θ is called a pretilt angle.

In the present invention, the pretilt angle of the alignment film is preferably 5 degrees or less. By setting the pretilt angle to 5 degrees or less, it is possible to speed up the response speed of the descent.

Next, after cleaning and drying the rubbed substrate (step S15 ), spacers are spread (step S16 ). Then, a sealant is applied and dried on the periphery of the substrate (step S17 ). At this time, an injection port and an exhaust port for injecting the liquid crystal material are reserved and formed during sealing.

Next, after assembling the aforementioned set of substrates (step S18 ), the sealing agent is heated to be cured, and the outer periphery of the liquid crystal element is sealed (step S19 ). When assembling, the above-mentioned set of substrates is arranged such that a set of the above-mentioned alignment films faces each other. Wherein, the angle α formed by the orientation treatment directions of the two alignment films is 70° to 110°. If the formed angle α is smaller than 70 degrees or larger than 110 degrees, light leakage will occur during black display and the contrast will be lowered. In addition, when displaying in black, light leakage (light 抜け) increases depending on the viewing direction. In addition, the contrast/viewing angle dependence is further improved by setting the formed angle α to be 80 degrees to 100 degrees.

In addition, the direction of the alignment treatment of the two alignment films is the direction in which a uniform twisted structure is formed when the liquid crystal layer is twisted by the angle α formed above.

Here, a case where a liquid crystal material is filled between a group of alignment films whose angle α formed in the alignment treatment direction is 90 degrees is considered. In FIG. 3 , the liquid crystal molecules 112 stand obliquely from the upper alignment film 110 and the lower alignment film 111 at a pretilt angle θ. Then, in a state where the pretilt angle θ is maintained between the upper and lower alignment films, the liquid crystal molecules are arranged twisted 90 degrees to the right (clockwise) from the upper alignment film 110 to the lower alignment film 111 .

On the other hand, in FIG. 4 , the liquid crystal molecules 122 stand obliquely from the upper alignment film 120 and the lower alignment film 121 by a pretilt angle θ. Then the polar angle of the liquid crystal molecules between the upper and lower alignment films (the angle formed between the liquid crystal molecules and the alignment film) starts to change continuously from the pre-tilt angle, and the upper alignment film is θ, and becomes 0 degrees in the central part (parallel to the substrate ), and θ in the lower alignment film. Accompanied by this twist in the direction perpendicular to the substrate, the orientation film 111 is twisted to the left (counterclockwise) by 90 degrees from the upper alignment film 110 to the lower alignment film 111 . The structure shown in Figure 4 is called a splay structure.

In the splayed structure shown in FIG. 4 , since the liquid crystal molecules are also twisted in the vertical direction, the free energy is high. Thus in case the liquid crystal material does not contain a chiral agent and has no inherent twist, the liquid crystal material spontaneously twists to the right by 90 degrees. Also, when a chiral agent that induces a right twist is added to the liquid crystal material, the right twist is also twisted by 90 degrees as shown in FIG. 3 .

That is, in the orientation treatment direction as shown in FIG. 3 , when the liquid crystal material is twisted by the formed angle α, a uniform twisted structure is formed instead of a splayed structure. On the other hand, when the same liquid crystal material as above is used in the case where the orientation treatment direction of one of the upper and lower alignment films is opposite, a splay structure is formed. In addition, if it is the orientation treatment direction as shown in FIG. 3 , when a chiral agent that induces left twist is added to the liquid crystal material, a splayed structure is also formed.

In addition, in the orientation treatment direction shown in FIG. 3 , if the twist angle of the liquid crystal material is changed to 270 degrees by, for example, adding a chiral agent that induces a right twist, a splayed structure is formed.

Next, a liquid crystal material containing the chiral agent and a photocurable monomer is injected between a group of alignment films to form a liquid crystal layer (step S20 ), and then the injection port and the exhaust port are sealed (step S21 ). As mentioned above, the chiral pitch of the liquid crystal material can be adjusted by adjusting the content of the chiral agent. In the present invention, in order to achieve a high-speed drop response, it is preferable to set the ratio (p/d) of the chiral pitch p of the liquid crystal material to the thickness d of the liquid crystal layer to be 0.5≤p/d≤1.6, more preferably set to 1.0 ≤p/d≤1.6.

Here, in the present invention, the STN-type liquid crystal having a twist angle of α+180 (degrees) is stable in an electric field-free state. That is, in the same liquid crystal display element, the free energy of the STN liquid crystal having a twist angle of α+180 (degrees) is lower than the free energy of the TN type liquid crystal having a twist angle of α (degrees).

The "same liquid crystal display element" refers to an element in which all elements affecting the performance of the liquid crystal element such as the liquid crystal material and its chiral pitch, the thickness of the liquid crystal layer, or the material of the alignment film, the rubbing direction, and the rubbing intensity are the same.

In addition, "the free energy of the STN liquid crystal with a twist angle of α + 180 (degrees) is lower than that of the TN type liquid crystal with a twist angle of α (degrees)" means that although there are TN-type liquid crystals with a twist angle of α (degrees), Liquid crystals can also form STN-type liquid crystals with a twist angle of α+180 (degrees), but the free energy of STN-type liquid crystals with a twist angle of α+180 (degrees) is relatively lower. Among them, since the free energy in the strict sense is difficult to calculate, "the free energy of the STN type liquid crystal is relatively lower" means: specifically, by placing it at room temperature, after a period of time (several seconds to several hours), it changes from TN type liquid crystal to The transition from liquid crystal to STN type liquid crystal.

As described above, when the p/d value is set in the range of 0.5≦p/d≦1.6, the TN-type liquid crystal transitions to the STN-type liquid crystal after a period of time (refer to Non-Patent Document 2 if necessary). This is because the free energy of the STN type liquid crystal is lower than that of the TN type liquid crystal. That is, the range of 0.5≤p/d≤1.6 is the state that "the free energy of the STN liquid crystal with a twist angle of α + 180 (degree) is lower than the free energy of the TN type liquid crystal with a twist angle of α (degree) in the same liquid crystal display element" .

Next, a voltage is applied between the substrates (step S22 ). Specifically, after the voltage is applied to make the liquid crystal layer into a vertical alignment state, the liquid crystal layer is temporarily changed from an STN type liquid crystal with a twist angle of α+180 (degrees) to a TN type liquid crystal with a twist angle of α (degrees) by stopping or reducing the applied voltage. LCD transition. In addition, the degree of reduction when the voltage is reduced may be low enough to change the liquid crystal layer from a vertically aligned state to a twisted state with a twist angle of α (degree).

As mentioned above, in the present invention, since the free energy of the STN type liquid crystal with a twist angle of α+180 (degree) in the same liquid crystal display element is in a state lower than that of the TN type liquid crystal with a twist angle of α (degree), a period of After a period of time, it changes from TN type liquid crystal to STN type liquid crystal. However, by applying a voltage sufficiently higher than the saturation voltage, it is possible to temporarily switch from STN-type liquid crystal to TN-type liquid crystal. This is considered to be because the liquid crystal layer forms a splayed structure in the STN liquid crystal state, but the splayed structure is eliminated by applying a voltage sufficiently higher than the saturation voltage to form a uniform twisted structure.

The applied voltage varies depending on the type of liquid crystal material and the like, but is preferably 1.5 to 5 times the saturation voltage. And the application time is preferably several tens of seconds to several minutes.

Next, by irradiating ultraviolet light to the photocurable monomer in the liquid crystal material to perform photocuring, polymer stabilization of the liquid crystal layer at the twist angle α (degrees) is achieved (step S23 ). Due to such polymer stabilization, even when the p/d value is set within the range of 0.5≦p/d≦1.6 as described above, the transition from TN type liquid crystal to STN type liquid crystal can be suppressed.

In addition, the time for which the liquid crystal layer maintains the twisted state with a twist angle of α (degrees) differs depending on the type of liquid crystal material and the pretilt angle of the alignment film. Since the TN-type liquid crystal having a twist angle of α (degree) becomes more stable as the pretilt angle increases, the time for maintaining the twisted state of the twist angle of α (degree) is prolonged.

[TN type liquid crystal element]

The TN-type liquid crystal element involved in the present invention is characterized in that it includes: a group of substrates, the group of substrates is arranged approximately in parallel and at least one of them is transparent; a group of alignment films, the group of alignment films is arranged on the The opposite surfaces of the group of substrates, and the surfaces have been oriented so that the liquid crystal molecules in the liquid crystal material point in the same direction; and a liquid crystal layer, the liquid crystal layer is arranged between the group of alignment films and contains the liquid crystal material and a chiral agent, wherein the formed angle α of the alignment treatment direction of the group of alignment films is 70 degrees to 110 degrees, and the alignment treatment direction is when the liquid crystal layer twists the formed angle α In the direction of forming a uniform twisted structure, the STN-type liquid crystal with a stable twist angle of α+180 degrees in the state of no electric field realizes polymer stabilization and becomes a TN-type liquid crystal with a twist angle of α degrees.

Since this TN-type liquid crystal element is manufactured by the above-mentioned TN-type liquid crystal element manufacturing method, its detailed description is omitted.

Since the p/d value of such a TN type liquid crystal element can be set within the range of 0.5≤p/d≤1.6, it is possible to achieve a faster fall response speed than a normal TN type liquid crystal element.

Here, the simulation results using the liquid crystal molecular alignment simulator LCD Master (manufactured by Shintec Corporation) are shown in FIG. 5 . Figure 5 shows the parameters of the liquid crystal material ZL1-4792 (manufactured by Merck). The pretilt angle of the alignment film is set to 20 degrees, and the distance between the alignment films (that is, the thickness of the liquid crystal layer) is set to 5 μm, so that the hand of the liquid crystal material The graph of the change of the fall response time τ _off when the pitch is changed. The above τ _off means that the voltage is cut off from the state of applied voltage to 0V when the transmittance reaches 50% of the transmittance when no voltage is applied, and the transmittance when no voltage is applied is set to 100, and 50% When the transmittance is set to 0, the time required for the transmittance to change from 10 to 90. As is known from FIG. 5 , the smaller the chiral pitch of the liquid crystal material is, the shorter the off-response time τ _off is. It can be understood from this that by setting the p/d value in the range of 0.5≤p/d≤1.6, which was difficult to achieve in the prior art, the drop response speed of the liquid crystal element can be accelerated compared with the prior art, and the animation characteristics can be improved. .

Example

Hereinafter, examples of the present invention will be described, but the scope of the present invention is not limited by these examples.

[Example 1, Comparative Example 1]

A 1 cm x 1 cm transparent electrode and an electrode portion for leading the electrode to the outside were formed on a glass substrate of 2 cm x 2 cm x 1.1 cm in size. On the glass substrate prepared in this way, a mixture of polyimide PIA-x768-01x and PIA-x359-01x for liquid crystal alignment films manufactured by Chisso Petrochemical Co., Ltd. in a ratio of 45:55 was applied to a thickness of about 1 μm. Thus, an alignment film is formed. This alignment film was rubbed using a kapok velvet cloth. The rubbing treatment direction (orientation treatment direction) follows the direction shown in FIG. 6 . In addition, the pretilt angle of the alignment film was 21 degrees.

Next, spread a silicon dioxide spacer (HIPRESICA (ハイプシカ) UF 5 microns, manufactured by Ube Nitto Chemical Co., Ltd.) with a diameter of 5 μm on one of the alignment films, and then apply an epoxy-based sealant on the periphery, and heat at 150°C. Heat for 1 hour to cure. When sealing, two holes are made as an injection port for injecting liquid crystal material and an exhaust port.

Next, a liquid crystal material is injected into the space sealed with the epoxy-based sealant. The liquid crystal material preparation process is as follows: After adding 27 mg of photocurable monomer UCL-003 (DIC company) to 475 mg of ZLI-4792US123 (manufactured by Merck) whose chiral pitch is adjusted to 7.5 μm by adding a chiral agent , made by heating on a hot plate at 100°C for 3 minutes. The liquid crystal material has a left-handed pitch length of 7.5 μm. That is, p/d=1.5. The liquid crystal material is brought into contact with the injection port, and the liquid crystal material is injected into the entire liquid crystal element by capillary phenomenon.

After the liquid crystal material was injected, it was slowly cooled and the alignment state of the liquid crystal was observed with a polarizing microscope, and it was observed that the alignment of the liquid crystals was all the same. When two polarizers are assembled into a so-called crossed polarizer (crossed Nichol) whose absorption axes are perpendicular to each other, and the liquid crystal element is placed between the two polarizers so that the transmission axis of the polarizer is parallel to the rubbing direction and observed , the overall coloration is observed to be blue. When the liquid crystal layer is twisted by 90 degrees between the substrates, no coloring should occur and a white state should be formed in this observation. This state can therefore be considered to be a state in which the liquid crystal layer is twisted by 270 degrees between the substrates.

Next, a rectangular wave of 20 V was applied to the electrodes of the liquid crystal cell to bring the liquid crystal layer into a homeotropic alignment state and maintain this state for 5 minutes. When the change during this period was observed with a polarizing microscope, it was observed that the liquid crystal arrangement gradually changed from a uniform state ( FIG. 7( a )) to a point-like liquid crystal arrangement ( FIG. 7( b )). Then, this liquid crystal alignment gradually expands ((c) and (d) of FIG. 7 ), and finally forms a newly generated liquid crystal alignment that is all the same ((e) of FIG. 7 ). This change is considered to be the result of the appearance of a TN liquid crystal state with a twist angle of 90 degrees in an STN liquid crystal state with a twist angle of 270 degrees.

In order to confirm this idea, two polarizers were assembled into crossed polarized light, and when the liquid crystal element was arranged between the two polarizers in such a way that the transmission axis of the polarizer was parallel to the rubbing direction and observed, it was found that before the voltage was applied The overall coloring was blue, but no coloring was observed in the liquid crystal alignment due to voltage application. It was thus confirmed that the liquid crystal alignment before the voltage application corresponds to the STN type liquid crystal with a twist angle of 270 degrees, and the liquid crystal alignment due to the voltage application corresponds to the TN type liquid crystal with a twist angle of 90 degrees.

Immediately after stopping the voltage application, the photocurable monomer was photocured by irradiating ultraviolet rays with a wavelength of 365 nm for 5 minutes through a Longlife (registered trademark) filter (manufactured by SPECTROLINE). After being left as it is for 30 days after being irradiated with ultraviolet rays, the state of TN-type liquid crystal with a twist angle of 90 degrees was still maintained. In addition, although specific data are not shown, even if no ultraviolet rays are irradiated after the voltage application is stopped, the TN liquid crystal state with a twist angle of 90 degrees is maintained for several minutes to several hours.

Five TN-type liquid crystal elements of Example 1 were prepared according to the above method.

In addition, five TN-type liquid crystal elements of Comparative Example 1 were prepared in the same manner as in Example 1 except that no chiral agent and photocurable monomer were added to the liquid crystal material.

For each of the prepared five TN-type liquid crystal elements of Example 1 and Comparative Example 1, the fall response time at 25° C. was determined using a liquid crystal element photoelectric characteristic measuring device LCD5200 (manufactured by Otsuka Electronics Co., Ltd.). Specifically, when the light transmittance in the state of no voltage application is 100%, and the light transmittance of crossed polarizers is 0%, for the applied voltages V50 and V10 to obtain light transmittances of 50% and 10%, The response time (τ _off ) when the voltage was turned off from the applied voltage state of V50 and V10 was measured. This τ _off is the time required for the light transmittance to change from 10% to 90% when the light transmittance is 100% when no voltage is applied and the light transmittance is 0% when each voltage is applied. The average values of the measured values of each of the five TN-type liquid crystal elements and the 2σ value are shown in Table 1 below. In addition, the measured values when the voltage V10 was applied are shown in the box plot of FIG. 8 .

[Table 1]

As can be seen from Table 1 and Figure 8, the TN-mode liquid crystal element of Example 1 and Compared with the TN mode liquid crystal element of the comparative example 1 to which a chiral agent and a photocurable monomer were not added, the fall response speed was remarkably accelerated.

Regarding the five TN-type liquid crystal elements (elements 1 to 5) prepared in Example 1, when the time of 20 ms is the applied voltage state of V50 and the time of 520 ms is the state of no voltage applied, the transmittance at 25 ° C Time changes are shown in Figure 9. In addition, the falling portion (from the time of 510 ms to the time of 570 ms) in FIG. 9 is enlarged and shown in FIG. 10 .

As can be seen from Figs. 9 and 10, the rising and falling response characteristics are reproducible. Furthermore, it can be seen that the state of the TN type liquid crystal is fixed from the fact that the response speed is high.

In addition, about each of the five TN-type liquid crystal elements prepared in Example 1 and Comparative Example 1, the fall response time at -20° C. was determined using a liquid crystal element photoelectric characteristic measuring device LCD5200 (manufactured by Otsuka Electronics Co., Ltd.). Specifically, the response time (τ _off ) when the voltage was turned off from the voltage applied state of V10 was measured. The average values of the measured values of each of the five TN-type liquid crystal elements and the 2σ value are shown in Table 2 below. In addition, the measured values when the voltage V10 was applied are shown in the box plot of FIG. 11 .

[Table 2]

As can be seen from Table 2 and Figure 11, even at a low temperature of -20°C, by adding a chiral agent to make p/d = 1.5, the polymer is stabilized in a TN liquid crystal state with a twist angle of 90 degrees The TN-mode liquid crystal element of Example 1 also significantly increased the drop response speed compared to the TN-mode liquid crystal element of Comparative Example 1 to which no chiral agent and photocurable monomer were added.

[Example 2]

Except that the pretilt angle of the alignment film was set to 3 degrees, and the addition amount of the photocurable monomer UCLA-003 (manufactured by DIC Corporation) was set to 52.8 mg, the rest were prepared in the same manner as in Example 1 to produce five samples of Example 2. TN type liquid crystal element.

For these five TN-type liquid crystal elements, the fall response time at 25° C. was determined using a liquid crystal element photoelectric characteristic measuring device LCD5200 (manufactured by Otsuka Electronics Co., Ltd.). Specifically, the response time (τ _off ) when the voltage was turned off from the applied voltage state of V50 and V10 was measured. The average value of the measured values of the five TN type liquid crystal elements and the 2σ value are shown in Table 3 below. In addition, for reference, Table 3 also shows the measured values of the five TN-type liquid crystal elements related to Example 1 at the same time.

[table 3]

As can be seen from Table 3, the TN-type liquid crystal element of Example 2 having a pretilt angle of 3 degrees significantly increased the fall response speed compared to the TN-type liquid crystal element of Example 1 having a pretilt angle of 21 degrees.

[Example 3]

In addition to using a liquid crystal material in which 57 mg of a photocurable monomer UCL-003 (manufactured by DIC) was added to 475 mg of ZLI-4792US184 (manufactured by Merck) whose chiral pitch was adjusted to 5.0 μm by adding a chiral agent, For the rest, four TN-type liquid crystal elements (p/d=1.0) of Example 3 were prepared in the same manner as in Example 1.

For these four TN-type liquid crystal elements, the fall response time at 25° C. was determined using a liquid crystal element photoelectric characteristic measuring device LCD5200 (manufactured by Otsuka Electronics Co., Ltd.). Specifically, the response time (τ _off ) when the voltage was turned off from the voltage applied state of V50 was measured. The average value of the measured values of the four TN type liquid crystal elements and the 2σ value are shown in Table 4 below. In addition, for reference, Table 4 also shows the measured values of the five TN-type liquid crystal elements related to Example 1 at the same time.

[Table 4]

As can be seen from Table 4, the TN-mode liquid crystal element of Example 3 having p/d=1.0 has a significantly faster fall response speed than the TN-mode liquid crystal element of Example 1 having p/d=1.5.

[Reference example 1, 2]

Five TN-type liquid crystal elements (p/d=1.5) of Reference Example 1 were prepared in the same manner as in Example 1 except that no photocurable monomer was added to the liquid crystal material. In addition, except that no photocurable monomer was added to the liquid crystal material and the amount of the chiral agent was changed so that the pitch length of the liquid crystal material was 10 μm, five TN-type liquid crystal elements of Reference Example 2 were prepared in the same manner as in Example 1 ( p/d=2.0). Then, the fall response time at 25° C. was determined in the same manner as in Example 1 until the transition from the TN-type liquid crystal having a twist angle of 90 degrees to the STN-type liquid crystal having a twist angle of 270 degrees. The average values of the measured values of each of the five TN-type liquid crystal elements and the 2σ value are shown in Table 5 below.

[table 5]

As can be seen from Reference Example 1 in Table 5, even when no photocurable monomer is added, as long as it is the period before the transition from TN type liquid crystal to STN type liquid crystal, the response speed is lower than that of Comparative Example 1, and the speed is also increased. . However, since the response speed is slower than that of Example 1, it can be seen that the decrease response speed can also be increased by stabilizing the polymer. Furthermore, it was confirmed from Reference Examples 1 and 2 that the fall response speed can be increased by making the pitch of the liquid crystal material shorter.

Symbol Description

100. Alignment film 101. Liquid crystal molecules

110. Upper orientation film 111. Lower orientation film

112. Liquid crystal molecules 120. Upper alignment film

121. Lower alignment film 122. Liquid crystal molecules

Claims (6)

1. a TN type liquid crystal display cells is characterized in that, comprising:

One group substrate, said group substrate almost parallel configuration and be transparent one of at least;

One group of alignment films, said one group of alignment films is arranged at the opposite face of a said group substrate,

And orientation process has been carried out on the surface, so that the liquid crystal molecule in the liquid crystal material points to equidirectional;

And

Liquid crystal layer, said liquid crystal layer are disposed between said one group of alignment films, and comprise liquid crystal material and chirality agent,

The formed angle α of the orientation process direction of said one group of alignment films be 70 degree to 110 degree, and said orientation process direction is when said liquid crystal layer twists said formed angle α, to form even twist structured direction,

To be that the STN type liquid crystal polymer of α+180 degree is stable turn to the TN type liquid crystal that twist angle is the α degree to stable twist angle under the no electric field status.

2. TN type liquid crystal display cells according to claim 1 is characterized in that,

Twist angle is that the free energy of the STN type liquid crystal of α+180 degree is that the free energy of TN type liquid crystal of α degree is low than twist angle in same liquid crystal display cells,

Said liquid crystal layer has been realized polymer-stabilized at twist angle α degree.

3. TN type liquid crystal display cells according to claim 1 and 2 is characterized in that,

When the thickness of establishing said liquid crystal layer is the chirality pitch of d, said liquid crystal material when being p, 0.5≤p/d≤1.6.

4. according to each described TN type liquid crystal display cells in the claim 1 to 3, it is characterized in that,

The tilt angle of said alignment films is below 5 degree.

5. the manufacturing approach of a TN type liquid crystal cell is characterized in that, comprising:

In that one of them is the operation that forms alignment films on the surface separately of a transparent group substrate at least;

Orientation process is carried out so that the liquid crystal molecule in the liquid crystal material points to the operation of equidirectional in the surface of one group of said alignment films;

Dispose the operation of a said group substrate with one group of relative mode of said alignment films;

Thereby between one group of said alignment films, fill the operation that the liquid crystal material that comprises chirality agent and photo-curable monomer forms liquid crystal layer;

Between a said group substrate, apply the operation of voltage; And

Stop or reducing applying the operation that makes said photo-curable monomer photocuring behind the voltage,

The formed angle α of the orientation process direction of one group of said alignment films be 70 degree to 110 degree, and said orientation process direction is when said liquid crystal layer twists said formed angle α, to form even twist structured direction,

Apply in the operation of voltage; Through after applying voltage and making said liquid crystal layer be in vertical orientated state; Stopping or reducing applying voltage, is that the STN type liquid crystal that α+180 are spent is the TN type liquid crystal transformation of α degree to twist angle by twist angle temporarily thereby make said liquid crystal layer

In the photocuring operation, through making said photo-curable monomer photocuring, thereby make said liquid crystal layer realize polymer-stabilized at twist angle α degree.

6. the manufacturing approach of TN type liquid crystal cell according to claim 5 is characterized in that,

When the thickness of establishing said liquid crystal layer is the chirality pitch of d, said liquid crystal material when being p, 0.5≤p/d≤1.6.

Images