KR102378884B1 - Liquid Crystal Display Device - Google Patents

Abstract

The present invention provides a first substrate and a second substrate facing each other; and a liquid crystal layer provided between the first and second substrates, wherein the liquid crystal layer includes first and second liquid crystal molecules different from each other, and among the first liquid crystal molecules and the second liquid crystal molecules One of the liquid crystal display devices has a better bend arrangement than a splay arrangement, and the other one of the first liquid crystal molecules and the second liquid crystal molecules has a better splay arrangement than the bend arrangement. to provide.

Description

Liquid Crystal Display Device

The present invention relates to a liquid crystal display, and more particularly, to a liquid crystal display capable of reducing flicker.

Recently, as we enter the information age, the field of display that visually expresses electrical information signals has developed rapidly, and in response to this, various display devices with excellent performance such as thinness, weight reduction, and low power consumption have been developed. is being developed

Specific examples of such a display device include a liquid crystal display device (LCD), a plasma display panel device (PDP), a field emission display device (FED), an organic light emitting display device ( Organic Light Emitting Display Device (OLED), etc. are mentioned.

The liquid crystal display device includes an upper substrate, a lower substrate, and a liquid crystal layer formed between the two substrates, and the arrangement of the liquid crystal layer is adjusted depending on whether or not an electric field is applied, and the transmittance of light is adjusted accordingly to display an image. am.

In the case of such a liquid crystal display, image quality defects may be caused by various causes, and image quality defects may also be expressed in various forms. Among various image quality defects, there is a problem in that a flicker phenomenon, which is a flickering phenomenon, occurs when an image is implemented. The flicker problem has been disclosed in Korean Patent Laid-Open No. 10-2003-0058076 (Title: Liquid crystal display device for improving flicker and driving method using the same).

An object to be solved according to an embodiment of the present invention is to provide a liquid crystal display capable of solving a flicker problem.

The problem to be solved according to the embodiment of the present invention is not limited to the above-mentioned problem, and another problem not mentioned will be clearly understood by those skilled in the art from the following description.

The liquid crystal layer of the liquid crystal display includes liquid crystal molecules made of an elastic dielectric. The liquid crystal molecules have a splay arrangement, a bend arrangement, or a twist arrangement. Among the arrangement of the liquid crystal molecules, in the case of a splay arrangement or a bend arrangement, fine electric polarization occurs in the liquid crystal molecules, thereby generating an additional electric field. As such, when an additional electric field is generated in the liquid crystal molecules, an unwanted behavior of the liquid crystal molecules is generated, which may be referred to as a flexoelectric effect.

The inventors of the present invention have confirmed that a flicker problem, which is a flickering phenomenon of the screen, may occur due to the behavior of liquid crystal molecules due to the transformation effect. Accordingly, the inventors of the present invention studied to find a way to suppress the transformation effect causing the flicker problem, and as a result, when a bent core liquid crystal is added to the liquid crystal layer, the transformation effect is suppressed to solve the flicker problem. The present invention was completed by confirming that it can be solved.

The present invention provides a first substrate and a second substrate facing each other; and a liquid crystal layer provided between the first and second substrates, wherein the liquid crystal layer includes first and second liquid crystal molecules different from each other, and among the first liquid crystal molecules and the second liquid crystal molecules One of the liquid crystal display devices has a better bend arrangement than a splay arrangement, and the other one of the first liquid crystal molecules and the second liquid crystal molecules has a better splay arrangement than the bend arrangement. to provide.

The present invention provides a first substrate and a second substrate facing each other; and a liquid crystal layer provided between the first and second substrates, wherein the liquid crystal layer includes first and second liquid crystal molecules different from each other, wherein the first liquid crystal molecules are positively driven and negatively driven. Provided is a liquid crystal display that causes a transformation effect due to polarization between time and the second liquid crystal molecules suppress the transformation effect between the positive driving and the negative driving.

The second liquid crystal molecule may include a bent core liquid crystal.

The bent core liquid crystal may have a bending angle α of 120 degrees or more and 170 degrees or less, in this case, the second liquid crystal molecules have a better bend arrangement than a splay arrangement, and the first liquid crystal molecules A splay arrangement may be superior to a bend arrangement.

The bent core liquid crystal may have a bending angle α of 40 degrees or more and less than 120 degrees, in this case, the second liquid crystal molecules have a better splay arrangement than a bend arrangement, and the first liquid crystal molecules A bend arrangement may be superior to a splay arrangement.

The bent core liquid crystal may be included in an amount of 5 wt % or less with respect to the entire liquid crystal layer.

The bent core liquid crystal has the following formula:

can be made with In the above formula, A is an aromatic compound or an aromatic compound in which at least one hydrogen atom is substituted with a polar molecule, wherein X, X', Y, and Y' are each independently -COO-, -N=CH -, -C = C-, -COS-, -C≡C-, and -N = consisting of a functional group selected from the group consisting of N-, wherein Z and Z' are each independently -O-, -S- and -COO- consisting of or omitted from a functional group selected from the group consisting of, wherein R and R' are each independently composed of R1 _a R2 _b O _c , wherein R1 consists of C or Si, and R2 is H or made of a halogen element, a, b, and c are each an integer, and the bending angle α may be 40 degrees or more and 170 degrees or less.

,

,

,

,

,

,

, 및

로 이루어진 군에서 선택될 수 있다. The aromatic compound constituting A is

,

,

,

,

,

,

, and

It can be selected from the group consisting of.

A horizontal electric field and a vertical electric field are generated together between the first substrate and the second substrate, and the first liquid crystal molecules exhibit a transformation effect due to polarization between positive driving and negative driving in the region where the vertical electric field is generated. It may contain positive liquid crystals that cause

Details of other embodiments are included in the detailed description and drawings.

According to this embodiment of the present invention, one liquid crystal molecule having a better splay arrangement than a bend arrangement in the liquid crystal layer and another liquid crystal molecule having a better bend arrangement than a splay arrangement By including, a flexoelectric effect due to the polarization of the entire liquid crystal layer is prevented, thereby preventing a flicker problem.

In addition, according to an embodiment of the present invention, since the liquid crystal layer includes a second liquid crystal molecule made of a bent core liquid crystal, a flicker problem due to a difference in luminance between positive (+) driving and negative (-) driving is solved. can be prevented

In addition, according to an embodiment of the present invention, by adjusting the bending angle α of the bent core liquid crystal, it is possible to prevent a flicker problem due to a difference in luminance between positive (+) driving and negative (-) driving. there is.

The effects of the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

Since the content of the invention described in the problem to be solved above, the means for solving the problem, and the effect do not specify the essential characteristics of the claim, the scope of the claim is not limited by the matters described in the content of the invention.

1 is a view showing a splay arrangement, a bend arrangement, and a twist arrangement state, which are arrangement states of liquid crystal molecules.
FIG. 2 is a diagram illustrating electrical polarization occurring when liquid crystal molecules are in a splay arrangement or a bend arrangement state.
3A illustrates an arrangement state of liquid crystal molecules during positive (+) driving when a fringe field is formed between the common electrode and the pixel electrode.
3B illustrates an arrangement state of liquid crystal molecules during negative (-) driving when a fringe field is formed between the common electrode and the pixel electrode.
FIG. 3C is a graph showing a difference between light transmittance during positive (+) driving according to FIG. 3A and light transmittance during negative (−) driving according to FIG. 3B .
4 is a schematic cross-sectional view of a liquid crystal display according to an exemplary embodiment.
5 is a graph showing the amount of change in DC offset (V) according to the type and content of the bent core liquid crystal.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different forms, and only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the technical field to which the present invention belongs It is provided to fully inform the possessor of the scope of the invention, and the present invention is only defined by the scope of the claims.

The shapes, sizes, proportions, angles, numbers, etc. disclosed in the drawings for explaining the embodiments of the present invention are illustrative and the present invention is not limited to the illustrated matters. Like reference numerals refer to like elements throughout. In addition, in describing the present invention, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. When 'including', 'having', 'consisting', etc. mentioned in this specification are used, other parts may be added unless 'only' is used. When a component is expressed in the singular, cases including the plural are included unless otherwise explicitly stated.

In interpreting the components, it is construed as including an error range even if there is no separate explicit description.

In the case of a description of the positional relationship, for example, when the positional relationship of two parts is described as 'on', 'on', 'on', 'beside', etc., 'right' Alternatively, one or more other parts may be positioned between two parts unless 'directly' is used.

In the case of a description of a temporal relationship, for example, 'immediately' or 'directly' when a temporal relationship is described with 'after', 'following', 'after', 'before', etc. It may include cases that are not continuous unless this is used.

Although the first, second, etc. are used to describe various elements, these elements are not limited by these terms. These terms are only used to distinguish one component from another. Accordingly, the first component mentioned below may be the second component within the spirit of the present invention.

Each feature of the various embodiments of the present invention can be partially or wholly combined or combined with each other, technically various interlocking and driving are possible, and each of the embodiments may be independently implemented with respect to each other or implemented together in a related relationship. may be

Hereinafter, with reference to the drawings, it will be described that a flicker problem may occur due to a transformation effect, and an embodiment of the present invention for solving such a flicker problem will be described in detail.

1 is a view showing a splay arrangement, a bend arrangement, and a twist arrangement state, which are arrangement states of liquid crystal molecules. Each arrangement is as shown in FIG. 1 . In FIG. 1 , n represents the direction of the liquid crystal director, and ▽ is a vector operator representing the divergence and curl of the liquid crystal director.

Liquid crystal molecules may have a splay arrangement, a bend arrangement, and a twist arrangement as described above due to the intrinsic properties of the liquid crystal molecules, among which the splay arrangement and the bend arrangement In this case, electric polarization occurs in the liquid crystal molecules.

FIG. 2 is a diagram illustrating electrical polarization occurring when liquid crystal molecules are in a splay arrangement or a bend arrangement state. In FIG. 2, arrows indicate the direction of polarization within the liquid crystal molecules.

As can be seen from FIG. 2 , in the initial arrangement state of the liquid crystal molecules, the polarization direction in the liquid crystal molecules becomes a random state, so that electrical polarization (P) does not occur, but the liquid crystal molecules have a splay arrangement or a bend arrangement state. Then, the polarization direction in the liquid crystal molecules becomes constant, and electrical polarization (P) occurs. As such, when the electrical polarization P occurs, the arrangement state of the liquid crystal molecules may be changed due to a coupling effect with an electric field applied to the liquid crystal molecules.

In particular, according to the experiment, in the case of a low frequency of 60 Hz or less, during polarity inversion driving, which is positive (+)/negative (-) switching driving, liquid crystal molecules cause electrical polarization while splay arrangement and bend arrangement to form an undesired arrangement. confirmed that. That is, since the above-described flexoelectric effect occurs, a deviation between the luminance in the positive frame upon positive (+) driving and the luminance at the negative frame upon negative (−) driving may occur, resulting in a flicker problem. Here, the polarity inversion includes column inversion and row inversion, and the polarities of adjacent columns and adjacent rows are different, and the polarity is also changed when the frame is changed.

Even when driving at high frequencies, the liquid crystal molecules splay and bend during positive (+)/negative (-) switching driving to cause electrical polarization, but at high frequencies, the frame changes quickly, so electrical polarization is recognized can't do it Accordingly, the flicker problem due to the transformation effect may be a problem in the case of a low frequency of 60 Hz or less, but is not necessarily limited thereto.

3A illustrates an arrangement state of liquid crystal molecules in a positive frame upon positive (+) driving when a fringe field is formed between the common electrode and the pixel electrode, and FIG. 3B is a diagram illustrating the arrangement between the common electrode and the pixel electrode. When a fringe field is formed, the arrangement state of liquid crystal molecules in a negative frame when viewed with a negative (-) drive is shown. It is a graph showing a difference in light transmittance in a negative frame for viewing negative driving according to FIG. 3B .

3A and 3B, reference numeral 10 denotes a common electrode, reference numeral 20 denotes a pixel electrode, and reference numeral 30 denotes an insulating layer. In addition, the solid line indicates the electric field between the common electrode and the pixel electrode, and the arrow indicates the polarization direction in the liquid crystal molecules.

3A and 3B , a positive frame is shown when a (+) voltage is applied to the pixel electrode 20 during positive (+) driving, and (-) is applied to the pixel electrode 20 ( The negative frame is shown when a voltage of -) is applied.

As can be seen from FIGS. 3A and 3B , a near-vertical electric field is formed at a position above the pixel electrode 20 and a position above the middle region of the neighboring pixel electrodes 20 , and in a region where a near-vertical electric field is formed It can be seen that a bend arrangement and a spray arrangement are made.

Specifically, as shown in FIG. 3A , during positive (+) driving, nematic liquid crystal molecules above the pixel electrode 20 bend, and the nematic liquid crystal molecules above the middle region of the neighboring pixel electrodes 20 . It can be seen that the liquid crystal molecules are arranged in a splay state. In addition, as can be seen from FIG. 3B , during negative (-) driving, nematic liquid crystal molecules above the pixel electrode 20 form a splay arrangement, and nematic liquid crystal molecules above the middle region of the neighboring pixel electrodes 20 bend. It can be seen that the array of states is done.

That is, as can be seen from FIGS. 3A and 3B , during positive (+) and negative (-) driving, the nematic liquid crystal molecules positioned in the region where an electric field close to vertical is formed have a bend arrangement and a spray arrangement. In particular, it can be seen that the arrangement state at the time of positive (+) driving and the arrangement state at the time of negative (-) driving are different from each other.

As can be seen from FIG. 3C , it can be seen that the light transmittance during the positive (+) driving is higher than the light transmittance during the negative (−) driving. As such, when a difference ΔL occurs between light transmittance during positive (+) driving and light transmittance during negative (-) driving, the luminance between positive (+) driving and negative (-) driving The car causes flicker on the screen.

Therefore, as described with reference to FIGS. 3A to 3C , the arrangement state of liquid crystal molecules during positive (+) driving and the arrangement state of liquid crystal molecules during negative (−) driving are different from each other, and the difference in light transmittance between each case It can be seen that the luminance difference due to (ΔL) is caused.

The flicker phenomenon due to the difference in luminance between the positive (+) driving and the negative (-) driving is fringe field switching in which a fringe field is formed between the common electrode and the pixel electrode; FFS) mode liquid crystal display may be a problem.

This will be described with reference to FIGS. 3A and 3B , and as can be seen from FIGS. 3A and 3B , the liquid crystal display in the fringe field switching mode is formed between the pixel electrode 20 and the common electrode 10 formed on the same substrate. A fringe field is formed in the upper portion of the pixel electrode 20 and the upper portion of the intermediate region between the pixel electrodes due to the structural reason that the pixel electrode 20 and the common electrode 10 overlap each other in the upper and lower portions of the vertical electric field. ) is formed, and a horizontal or parallel electric field is formed above the other regions.

As described above, in the liquid crystal display of the fringe field switching (FFS) mode, both the pixel electrode 20 and the common electrode 10 are formed on the same substrate to have a horizontal electric field, but for structural reasons of the pixel electrode or the common electrode. Since it additionally has a region in which a vertical electric field is formed, a splay arrangement and a bend arrangement are performed in the region in which the vertical electric field is formed.

In this case, the area above the pixel electrode 20 in the area where the vertical electric field is formed is affected by the electrical polarity of the pixel electrode 20 , but the area above the middle area of the neighboring pixel electrodes 20 in the area where the vertical electric field is formed is It is affected by the electrical polarity of the common electrode 10 . That is, electrical polarities are different between the upper region of the pixel electrode 20 and the upper region of the middle region of the neighboring pixel electrodes 20 so that when one region performs a splay arrangement, the other region performs a bend arrangement.

Accordingly, the splay arrangement and the bend arrangement are performed between positive (+) driving in which a (+) voltage is applied to the pixel electrode 20 and negative (-) driving in which a (-) voltage is applied to the pixel electrode 20 . , and in addition, a difference in polarization characteristics of liquid crystal molecules occurs between positive (+) driving and negative (-) driving, resulting in a flicker phenomenon due to a luminance difference.

In particular, the liquid crystal molecules constituting the liquid crystal layer can be divided into a positive liquid crystal and a negative liquid crystal. When a positive liquid crystal is used as the liquid crystal layer, the flicker phenomenon further occurs.

The positive liquid crystal is a liquid crystal having a positive (+) dielectric anisotropy (Δε=ε|| - ε⊥). That is, the positive liquid crystal is a liquid crystal having a horizontal dielectric constant (ε ) greater than a vertical dielectric constant (ε ⊥). Therefore, when the positive liquid crystal is used in a liquid crystal display of a fringe field switching (FFS) mode, the above-described bend arrangement and spray arrangement are easily performed while the direction of the positive liquid crystal is perpendicular in the vertical electric field. Accordingly, a flicker problem may occur.

On the other hand, the negative liquid crystal is a liquid crystal having a negative (-) dielectric anisotropy (Δε=ε|| - ε⊥). That is, the negative liquid crystal is a liquid crystal whose horizontal dielectric constant (ε ) is smaller than the vertical dielectric constant (ε ⊥). When used in a liquid crystal display of a fringe field switching (FFS) mode, in the vertical electric field, the direction of the negative liquid crystal is not perpendicular to the above-described bend arrangement and spray arrangement, and thus flicker The problem doesn't happen much.

Hereinafter, a liquid crystal display device according to an embodiment of the present invention capable of preventing the above-described flicker problem will be described.

4 is a schematic cross-sectional view of a liquid crystal display according to an exemplary embodiment.

As can be seen from FIG. 4 , the liquid crystal display according to an exemplary embodiment includes a first substrate 100 , a second substrate 200 , and a liquid crystal layer 300 .

A thin film transistor (TFT), a passivation layer 120 , a first planarization layer 130 , a common electrode 140 , a second planarization layer 150 , and a pixel electrode 160 are formed on the first substrate 100 . has been

The thin film transistor TFT includes a gate electrode 110 , a gate insulating layer 112 , a semiconductor layer 114 , a source electrode 116 , and a drain electrode 118 . The gate electrode 110 is formed on the first substrate 100 . The gate insulating layer 112 is formed on the gate electrode 110 to insulate the gate electrode 110 from the semiconductor layer 114 . The semiconductor layer 114 is formed on the gate insulating layer 112 . The semiconductor layer 114 is made of various semiconductor materials known in the art, such as a silicon-based semiconductor material or an oxide-based semiconductor material. The source electrode 116 and the drain electrode 118 face each other while being spaced apart from each other on the semiconductor layer 114 . The source electrode 116 extends in the direction of one end of the semiconductor layer 114 , and the drain electrode 118 extends in the direction of the other end of the semiconductor layer 114 .

Such a thin film transistor (TFT) may be modified with various structures and materials known in the art. For example, although the drawing shows a bottom gate structure in which the gate electrode 110 is positioned under the semiconductor layer 114 , the gate electrode 110 is the semiconductor layer 114 . It may have a top gate structure positioned above it.

The passivation layer 120 is formed on the thin film transistor TFT to protect the thin film transistor TFT. The passivation layer 120 may be formed of an inorganic insulating material such as silicon oxide (SiOx) or silicon nitride (SiNx), but is not limited thereto.

The first planarization layer 130 is formed on the passivation layer 120 to planarize the substrate surface. The first planarization layer 130 may be made of an organic insulating material such as an acrylic polymer, but is not limited thereto.

The common electrode 140 is formed on the first planarization layer 130 .

The second planarization layer 150 is formed on the common electrode 140 to insulate the common electrode 140 from the pixel electrode 160 and planarize the substrate surface. The second planarization layer 150 may be made of an organic insulating material such as an acrylic polymer, but is not limited thereto.

The pixel electrode 160 is formed on the second planarization layer 150 . The pixel electrode 160 is connected to the drain electrode of the thin film transistor TFT through the contact hole CH provided in the passivation layer 120 , the first planarization layer 130 , and the second planarization layer 150 . 118) is connected.

The pixel electrode 160 is patterned to include slits 161 . Accordingly, a fringe field is generated between the pixel electrode 160 and the common electrode 140 through the slit 161 to control the arrangement of the liquid crystal layer 300 . The pixel electrode 160 may have a straight shape or a zig-zag shape having at least one bending portion. In addition, an alignment layer is formed on the pixel electrode 160 to control the arrangement of the liquid crystal layer 300 .

A light blocking layer 210 , a color filter layer 220 , and an overcoat layer 230 are formed on the second substrate 200 .

The light blocking layer 210 blocks light leakage to areas other than the pixel area, and is formed in a matrix structure.

The color filter layer 220 is formed in a region between the light blocking layers 210 of the matrix structure. The color filter layer 220 includes a red color filter, a green color filter, and a blue color filter.

The overcoat layer 230 is formed on the color filter layer 220 to planarize the substrate surface. In addition, an alignment layer is formed on the overcoat layer 230 to control the arrangement of the liquid crystal layer 300 .

The liquid crystal layer 300 is formed between the first substrate 100 and the second substrate 200 . The liquid crystal layer 300 includes first liquid crystal molecules 310 and second liquid crystal molecules 320 .

The first liquid crystal molecules 310 may be formed of a nematic liquid crystal. In particular, the first liquid crystal molecules 310 may be formed of a positive liquid crystal. As described above, the positive liquid crystal is a liquid crystal having a positive dielectric anisotropy (Δε=ε|| - ε⊥), and a director of the liquid crystal is arranged in an electric field direction. Accordingly, the director of the positive liquid crystal is arranged in a direction parallel to a fringe field generated between the pixel electrode 160 and the common electrode 140, thereby causing the above-described flicker problem. can do. As the positive liquid crystal, various liquid crystal molecules known in the art may be used. In particular, the first liquid crystal molecules 310 may be formed of a combination of a plurality of different positive liquid crystal molecules.

However, the first liquid crystal molecules 310 according to the present invention are not necessarily made of only positive liquid crystals, but may be made of negative liquid crystals or a combination of positive liquid crystals and negative liquid crystals.

The second liquid crystal molecules 320 are formed of bent core liquid crystals. In addition, the second liquid crystal molecules 320 may be formed of a combination of a plurality of bent core liquid crystals different from each other.

As described above, according to the embodiment of the present invention, since the liquid crystal layer 300 includes the second liquid crystal molecules 320 made of a bent core liquid crystal, a difference between positive (+) driving and negative (-) driving is performed. A flicker problem caused by a difference in luminance can be prevented.

The second liquid crystal molecules 320 made of the bent core liquid crystal may change a flexoelectric effect due to the polarization of the first liquid crystal molecules 310, and accordingly, during positive (+) driving and negative (-) ), the luminance difference between the positive (+) driving and the negative (-) driving can be prevented by making the arrangement of the liquid crystal layer 300 uniform during driving.

That is, in an upper region of the pixel electrode 160 where a large difference in luminance between positive (+) driving and negative (−) driving occurs, and an upper region of a middle region of the neighboring pixel electrodes 160 , the By suppressing a flexoelectric effect due to polarization in the liquid crystal layer 300 , it is possible to eventually prevent a flicker phenomenon due to a luminance difference.

Meanwhile, depending on the molecular structure of the bent core liquid crystal, a flexoelectric effect due to polarization in the liquid crystal layer 300 may be suppressed, but may be further increased. That is, depending on whether the first liquid crystal molecules 310 have a bend arrangement better than a splay arrangement or a splay arrangement better than a bend arrangement, the bent core liquid crystal Different types must be selected. This will be described below.

5 is a graph showing the amount of change in DC offset (V) according to the type and content of the bent core liquid crystal.

In FIG. 5 , the X-axis represents the content of the bent core liquid crystal, and the Y-axis represents a DC offset (V). The DC offset (V) is a value indicating whether liquid crystal molecules have a bend arrangement better than a splay arrangement or a splay arrangement better than a bend arrangement. Specifically, when the DC offset (V) is (+), the bend arrangement is superior to the splay arrangement, and when the DC offset (V) is (-), the bend arrangement is better than the bend arrangement. The splay arrangement is excellent.

In FIG. 5 , the first bent core liquid crystal is a bent core liquid crystal represented by Chemical Formula 1 below, the second bent core liquid crystal is a bent core liquid crystal represented by Chemical Formula 2 below, and the third bent core liquid crystal is represented by Chemical Formula 3 below. A bent core liquid crystal represented by is used.

Formula 1

Formula 2

Formula 3

In addition, FIG. 5 shows an experiment on a liquid crystal layer in which first to third bent core liquid crystals and positive liquid crystals are mixed, and the positive liquid crystal includes liquid crystals represented by Chemical Formulas 4 and 5 below.

Formula 4

Formula 5

(in Formula 5, n is an integer greater than or equal to 1)

As can be seen from FIG. 5 , when the bent core liquid crystal is not included, that is, when only positive liquid crystal is included, it can be seen that the DC offset (V) is (-). That is, it can be seen that the positive liquid crystal has a better splay arrangement than a bend arrangement.

As such, it can be seen that the change in the DC offset (V) is different when the first to third bent core liquid crystals are added to the positive liquid crystal having a better splay arrangement than a bend arrangement.

Specifically, when the second bent core liquid crystal and the third bent core liquid crystal are added, the value of the DC offset (V) changes from (-) to (+), but when the first bent core liquid crystal is added, the It can be seen that the value of DC offset (V) changes to a larger (-). That is, the second vent core liquid crystal and the third vent core liquid crystal can suppress a flexoelectric effect due to polarization by adjusting the value of the DC offset (V) to 0, but the first vent core liquid crystal is the Since the value of DC offset (V) is made further away from 0, the flexoelectric effect due to polarization is further increased.

Therefore, it is preferable to add the second bent core liquid crystal or the third bent core liquid crystal to the positive liquid crystal having a better splay arrangement than a bend arrangement. That is, the second bent core liquid crystal or the third bent core liquid crystal has a better bend arrangement than a splay arrangement, and thus a positive liquid crystal having an excellent splay arrangement than a bend arrangement, and When combined, the flexoelectric effect due to the polarization of the entire liquid crystal layer is prevented, thereby preventing the flicker problem.

In addition, as it can be seen that the value of the DC offset (V) gradually increases as the content of the second bent core liquid crystal or the third bent core liquid crystal increases, in particular, when the second bent core liquid crystal is added, While the value of the DC offset (V) continues to increase as the content of the second vent core liquid crystal increases, when the third vent core liquid crystal is added, the content of the third vent core liquid crystal increases up to 2% by weight. Although the value of the offset (V) continues to increase, it can be seen that the value of the DC offset (V) remains constant even when it exceeds 2 wt%.

Therefore, by appropriately selecting the content of the second bent core liquid crystal or the third bent core liquid crystal according to the characteristics of the positive liquid crystal, the DC offset (V) value of the entire liquid crystal layer can be adjusted to 0 or a value close to 0. can be known However, in terms of preventing the value of the DC offset (V) from continuously increasing, the content of the second bent core liquid crystal or the third bent core liquid crystal is preferably 5% by weight or less in the entire liquid crystal layer 300 . And, more preferably, it is added in an amount of 2% by weight or less.

From the result according to FIG. 5, in the case of a positive liquid crystal having a better bend arrangement than a splay arrangement having a DC offset (V) value of (+), the second bent core liquid crystal and the third bent core When liquid crystal is added, the value of DC offset (V) is further away from 0, and when the first bent core liquid crystal is added, the value of DC offset (V) is changed from (+) to (-) to DC It can be expected that the value of offset(V) can be adjusted to 0.

Therefore, it is preferable to add the first bent core liquid crystal to the positive liquid crystal having a better bend arrangement than a splay arrangement.

That is, the first bent core liquid crystal has a characteristic superior in a splay arrangement than a bend arrangement, and thus, when combined with a positive liquid crystal having an excellent bend arrangement than a splay arrangement, the entire liquid crystal layer A flexoelectric effect due to polarization can be prevented.

In addition, as it can be seen that the value of the DC offset (V) gradually decreases as the content of the first bent core liquid crystal increases, in particular, as the content of the first bent core liquid crystal increases, the DC offset (V) of It can be seen that the value continues to decrease.

Accordingly, it can be seen that by appropriately selecting the content of the first bent core liquid crystal according to the characteristics of the positive liquid crystal, the DC offset (V) value of the entire liquid crystal layer can be adjusted to zero or a value close to zero. However, in terms of preventing the value of the DC offset (V) from continuously decreasing, the content of the first bent core liquid crystal is preferably 5% by weight or less, and more preferably 2% by weight or less.

The bent core liquid crystal constituting the second liquid crystal molecule 320 will be described in more detail as follows.

The bent core liquid crystal according to an embodiment of the present invention may be formed of a compound represented by the following Chemical Formula 6;

Formula 6

,

,

,

,

,

,

, 및

로 이루어진 군에서 선택된 방향족 화합물로 이루어질 수 있지만, 반드시 그에 한정되는 것은 아니다. 또는 상기 A는 상기 방향족 화합물에서 적어도 하나의 수소원소가 극성 분자로 치환된 화합물로 이루어질 수 있다. 상기 극성 분자는 할로겐 원자로 이루어질 수 있다. In Formula 6 above, A consists of an aromatic compound. Specifically, A is

,

,

,

,

,

,

, and

It may consist of an aromatic compound selected from the group consisting of, but is not necessarily limited thereto. Alternatively, A may consist of a compound in which at least one hydrogen element is substituted with a polar molecule in the aromatic compound. The polar molecule may be formed of a halogen atom.

In Formula 6, X, X', Y, and Y' are each independently -COO-, -N=CH-, -C=C-, -COS-, -C≡C-, and -N=N It may consist of a functional group selected from the group consisting of -.

In Formula 6, Z and Z' may each independently consist of a functional group selected from the group consisting of -O-, -S-, and -COO-. In some cases, the Z and Z' may be omitted so that R and R' may be directly connected to the benzene ring.

In Formula 6, R and R' may each independently consist of R1 _a R2 _b O _c . Here, R1 consists of C or Si, R2 consists of H or a halogen element, and a, b, and c are each an integer.

According to the bending angle α in Formula 6, the arrangement characteristics of the bent core liquid crystal may be changed. Specifically, when the bending angle α is large, the bend arrangement of the bent core liquid crystal is superior to that of the splay arrangement. In particular, when the bending angle α is in the range of 120 degrees or more to 170 degrees or less, the bent core liquid crystal has a better bend arrangement than a splay arrangement. As such, the bending angle α of the bent core liquid crystal in the range of 120 degrees or more to 170 degrees or less is combined with a liquid crystal having a better splay arrangement than a bend arrangement of the liquid crystal layer 300 as a whole. A flexoelectric effect due to polarization is prevented, thereby preventing a flicker problem.

As a result, when the first liquid crystal molecules 310 are formed of a liquid crystal having a better splay arrangement than a bend arrangement, in particular, a positive liquid crystal, the second liquid crystal molecules 320 have a bending angle α. It is preferable that the bent core liquid crystal has a range of 120 degrees or more to 170 degrees or less.

Conversely, when the bending angle α is small, the bent core liquid crystal has a better splay arrangement than the bend arrangement. In particular, when the bending angle α is in the range of 40 degrees or more to less than 120 degrees, the bent core liquid crystal has a better splay arrangement than the bend arrangement. As such, the bending angle α of the bent core liquid crystal in the range of 40 degrees or more to less than 120 degrees is combined with a liquid crystal having a better bend arrangement than a splay arrangement of the liquid crystal layer 300 as a whole. A flexoelectric effect due to polarization is prevented, thereby preventing a flicker problem.

As a result, when the first liquid crystal molecules 310 are formed of a liquid crystal having a better bend arrangement than a splay arrangement, in particular, a positive liquid crystal, the second liquid crystal molecules 320 have a bending angle α. It is preferable that the bent core liquid crystal has a range of 40 degrees or more to less than 120 degrees.

In the bent core liquid crystal of Chemical Formula 6, the bending angle α may be controlled by the bonding position between the aromatic compound of A and X and X'. That is, when the bonding position of the aromatic compound of A and X and the bonding position of the aromatic compound of A and X' are narrowed, the bending angle α may be reduced. In addition, when the bonding position of the aromatic compound of A and X and the bonding position of the aromatic compound of A and X' are widened, the bending angle α may be increased.

In addition, the bending angle (α) can be increased by substituting a polar molecule for a hydrogen atom in the aromatic compound of A. That is, when a hydrogen atom is substituted with a polar molecule in the aromatic compound of A, a repulsive force repels each other between the polar molecule and the X or X' to increase the bending angle α. In order to increase the repulsive force, the polar molecule is preferably substituted at a position closer to the X or X' than the central position. The polar molecule may be, for example, a halogen element or CN, NCS, NO2, etc., but is not limited thereto.

Although embodiments of the present invention have been described in more detail with reference to the accompanying drawings, the present invention is not necessarily limited to these embodiments, and various modifications may be made within the scope without departing from the technical spirit of the present invention. . Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. The protection scope of the present invention should be interpreted by the claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

100: first substrate 200: second substrate
300: liquid crystal layer 310: first liquid crystal molecules
320: second liquid crystal molecules

Claims (11)

a first substrate and a second substrate facing each other; and
a liquid crystal layer provided between the first substrate and the second substrate;
The liquid crystal layer includes first and second liquid crystal molecules different from each other,
the first liquid crystal molecules cause a transformation effect due to polarization between positive and negative driving, and the second liquid crystal molecules suppress the transformation effect between positive and negative driving,
The second liquid crystal molecule comprises a bent core liquid crystal,
The bent core liquid crystal has a bending angle (α) of 40 degrees or more to less than 120 degrees, the liquid crystal display device. a first substrate and a second substrate facing each other; and
a liquid crystal layer provided between the first substrate and the second substrate;
The liquid crystal layer includes first and second liquid crystal molecules different from each other,
the first liquid crystal molecules cause a transformation effect due to polarization between positive and negative driving, and the second liquid crystal molecules suppress the transformation effect between positive and negative driving,
The second liquid crystal molecule comprises a bent core liquid crystal,
The bent core liquid crystal has a bending angle α of 120 degrees or more and 170 degrees or less. delete delete 3. The method of claim 2,
The second liquid crystal molecules have a better bend arrangement than a splay arrangement, and the first liquid crystal molecules have a better splay arrangement than a bend arrangement. delete According to claim 1,
The second liquid crystal molecules have a better splay arrangement than a bend arrangement, and the first liquid crystal molecules have a better bend arrangement than a splay arrangement. 3. The method of claim 1 or 2,
The vent core liquid crystal is included in an amount of 5 wt% or less with respect to the entire liquid crystal layer. 3. The method of claim 1 or 2,
The bent core liquid crystal has the following formula:

(In the above formula, A consists of an aromatic compound or an aromatic compound in which at least one hydrogen atom is substituted with a polar molecule,
wherein X, X', Y, and Y' are each independently -COO-, -N=CH-, -C=C-, -COS-, -C≡C-, and -N=N- consisting of a functional group selected from
Wherein Z and Z' are each independently composed of or omitted from a functional group selected from the group consisting of -O-, -S-, and -COO-,
wherein R and R' are each independently composed of R1 _a R2 _b O _c , wherein R1 is composed of C or Si, R2 is composed of H or a halogen element, and a, b, and c are each an integer; And,
The bending angle (α) is greater than or equal to 40 degrees and less than or equal to 170 degrees)
A liquid crystal display comprising a compound consisting of 10. The method of claim 9,
The aromatic compound constituting A is

,

,

,

,

,

,

, and

A liquid crystal display device selected from the group consisting of. 3. The method of claim 1 or 2,
A horizontal electric field and a vertical electric field are generated together between the first substrate and the second substrate, and the first liquid crystal molecules exhibit a transformation effect due to polarization between positive driving and negative driving in the region where the vertical electric field is generated. A liquid crystal display comprising a positive liquid crystal that causes

Images