KR20230084691A - Method for Alignment of Liquid Crystal on Atmospheric Pressure Plasma Treated Polyimide Layer - Google Patents

Abstract

A liquid crystal alignment method combining atmospheric pressure plasma and rubbing is presented. The method for aligning liquid crystals by combining atmospheric plasma and rubbing proposed in the present invention performs an atmospheric pressure plasma process by irradiating a plasma beam at a predetermined irradiation angle for a predetermined time in an oxygen atmosphere to align a liquid crystal (LC) and after performing the atmospheric pressure plasma process, rubbing the film-coated substrate along an alignment path using a rotating roller equipped with a rubbing cloth.

Description

Liquid crystal alignment method combining atmospheric pressure plasma and rubbing {Method for Alignment of Liquid Crystal on Atmospheric Pressure Plasma Treated Polyimide Layer}

The present invention relates to a liquid crystal alignment method combining atmospheric pressure plasma and rubbing.

Research on liquid crystal (LC) displays and organic light-emitting diode (OLED) displays continues, but liquid crystal displays (LCDs) have many advantages (eg, price competitiveness, high reliability and long operating time), it has a large share of the market.

In addition, next-generation displays such as mini-LED and quantum LED (Quantum LED; QLED) displays are increasing the demand for LCDs [1-4]. In the LCD manufacturing process, the LC alignment process plays an important role in determining the performance of the display. This has a great influence on the electro-optical properties, and the LC must be oriented in one direction to obtain good performance [5-7].

The rubbing process, which is a contact orientation method of LC, uses a rotating roller equipped with a rubbing cloth to sweep the film-coated substrate along an orientation path. Although this method has the advantage of being simple and inexpensive, dust particles and static electricity accumulate during this process, which negatively affects the alignment film, such as streaks. Additional cleaning and baking processes can eliminate these defects, but the efficiency of the rubbing process is reduced by increasing cost and production time. Nanomaterials can be added to the LC media to compensate for the negative effects of the rubbing process, but this is costly because additional processes involving nanomaterials must be introduced [8–11].

There are technologies that can compensate for the negative effects of non-contact alignment methods, such as ultraviolet UV alignment, ion-beam irradiation, nanoimprint lithography, and oblique deposition. However, this approach is difficult to commercialize because of the high cost of surface treatment and the need for additional expensive vacuum equipment [12–16].

In contrast, the atmospheric plasma process can produce displays continuously, and has advantages of relatively low production cost and short process time. In the case of the vacuum plasma process, additional equipment such as a chamber is required, and additional work is also required to enable vacuum, so there are equipment, time, cost, and space problems. On the other hand, atmospheric plasma processes enable the production of LC cells without the problems associated with vacuum plasma processes [17, 18].

The technical problem to be achieved by the present invention is to propose various methods for manufacturing an LC cell by combining an atmospheric pressure plasma process and a rubbing process and to provide a method for improving LC alignment characteristics.

In one aspect, the liquid crystal alignment method combining atmospheric pressure plasma and rubbing proposed in the present invention irradiates a plasma beam at a predetermined irradiation angle for a predetermined time in an oxygen atmosphere in order to align liquid crystal (LC), and atmospheric pressure plasma After performing the process and performing the atmospheric pressure plasma process, a step of rubbing the film-coated substrate along an alignment path using a rotating roller equipped with a rubbing cloth.

In another aspect, a liquid crystal alignment method combining atmospheric plasma and rubbing proposed in the present invention includes the steps of rubbing a film-coated substrate along an alignment path using a rotating roller equipped with a rubbing cloth to align liquid crystals, and the rubbing After performing the process, performing an atmospheric pressure plasma process by irradiating a plasma beam at a predetermined irradiation angle for a predetermined time in an oxygen atmosphere.

According to an embodiment of the present invention, the step of generating an antiparallel (AP) liquid crystal cell for evaluating the optical properties of a polyimide (PI) alignment layer and a twisted nematic (TN) liquid crystal cell for evaluating the electro-optical properties contains more

Through the liquid crystal alignment method combining the atmospheric pressure plasma process and the rubbing process, the liquid crystal cell has a more uniform alignment layer when performing only the atmospheric pressure plasma process or only the rubbing process, and the image quality in terms of light transmittance and color expression is improved. can be improved

The result of analyzing the pretilt angle of the liquid crystal cell measured by the crystal rotation method through the liquid crystal alignment method combining the atmospheric pressure plasma process and the rubbing process is more related to the alignment of the liquid crystal cell than when only the atmospheric pressure plasma process or the rubbing process is performed. The error rate that determines uniformity can be reduced.

The result of measuring the voltage-transmittance among the electro-optical properties through the liquid crystal alignment method combining the atmospheric pressure plasma process and the rubbing process is the critical voltage at the point where the transmittance is 90% compared to the case of performing only the atmospheric pressure plasma process or the case of performing only the rubbing process. and an effective switching voltage that is a difference between the saturation voltage and the saturation voltage.

Through the liquid crystal alignment method combining the atmospheric pressure plasma process and the rubbing process, the total response time, which is the sum of the rise time and the fall time, can be reduced compared to the case of performing only the atmospheric pressure plasma process or the case of performing only the rubbing process.

Residual Direct Current (RDC), which represents a brightness change according to a voltage change between ON/OFF states, compared to the case of performing only the atmospheric pressure plasma process or the case of performing only the rubbing process through the liquid crystal alignment method combining the atmospheric pressure plasma process and the rubbing process. can reduce

Through the liquid crystal alignment method combining the atmospheric pressure plasma process and the rubbing process, thermal stability of the liquid crystal cell can be improved compared to the case of performing only the atmospheric pressure plasma process or the case of performing only the rubbing process.

According to embodiments of the present invention, various methods of manufacturing an LC cell by combining an atmospheric pressure plasma process and a rubbing process may be proposed to improve LC alignment characteristics. Improvement of the disadvantages of the rubbing process, in which dust particles and static electricity accumulate during the rubbing process and have negative effects such as streaks on the alignment film, and combine the atmospheric pressure plasma process with the advantages of low production cost and short process time to improve LC alignment characteristics can improve

1 is a flowchart for explaining a liquid crystal alignment method combining atmospheric pressure plasma and rubbing according to a first embodiment of the present invention.
Figure 2 is a flow chart for explaining a liquid crystal alignment method combining atmospheric pressure plasma and rubbing according to a second embodiment of the present invention.
3 is a photomicrograph of a surface-modified PI layer of a TN LC cell of various LC alignment techniques according to an embodiment of the present invention.
4 is a diagram showing transmittance of various LC alignment techniques according to an embodiment of the present invention.
5 is a diagram showing voltage according to transmittance of a TN LC cell including a surface-modified PI layer according to an embodiment of the present invention.
6 is a diagram showing the response time of a TN LC cell including a surface-modified PI layer according to an embodiment of the present invention.
7 is a diagram showing residual DC characteristics of a TN LC cell including a surface-modified PI layer according to an embodiment of the present invention.
8 is a photomicrograph of an LC cell heat-treated at a temperature in the range of 90 ° C to 210 ° C to observe the thermal stability of the surface-modified PI layer according to an embodiment of the present invention.

In the present invention, a method of combining a rubbing process and an atmospheric pressure plasma process for liquid crystal alignment of a polyimide layer is proposed. When the two processes were used together, the pretilt angles of 2.150° and 2.601° were superior to those of the rubbing process alone. Regarding the electro-optical characteristics, the low-power driving voltage was less than 2.5V and the effective switching voltage was more than 20% lower than when only the conventional rubbing process was performed. In addition, the thermal stability and orientation characteristics after treatment at 150 °C were superior to those obtained using only the atmospheric pressure plasma process. The present invention proposes an LC display manufacturing route with better performance and efficiency than is achievable with current LC orientation methods. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flowchart for explaining a liquid crystal alignment method combining atmospheric pressure plasma and rubbing according to a first embodiment of the present invention.

A liquid crystal alignment method combining atmospheric plasma and rubbing according to a first embodiment of the present invention is an atmospheric pressure plasma process by irradiating a plasma beam at a predetermined irradiation angle for a predetermined time in an oxygen atmosphere to align liquid crystals (LC) After performing the atmospheric pressure plasma process (110) and performing the atmospheric pressure plasma process, it may include a step (120) of rubbing the film-coated substrate along an alignment path using a rotating roller equipped with a rubbing cloth.

의 시트 저항의 33 × 22 × 1.1 mm³ 전극으로서, 아세톤, 이소프로필 알코올 및 탈이온수로 초음파 세척한 후 건조 캐비닛에서 6시간 동안 건조시켰다. 그런 다음 실온에서 700rpm에서 5초 동안, 3,000rpm에서 30초 동안 스핀 코팅을 하여 충분한 PI를 ITO 코팅 유리 기판에 코팅했다. 코팅 직후 80℃의 뜨거운 판에서 10분 동안 가열하여 소프트 베이킹(soft baking) 공정을 수행했다. 이후, PI 배향 층은 230℃에서 1시간 동안 오븐에서 하드 베이킹(hard baking) 공정을 통해 형성되었다.In an embodiment of the present invention, homogeneous polyimide (PI; SE-7492; Nissan Chemical Engineering) was used as the LC orientation layer. Indium-Tin Oxide (ITO) coated Corning 1737 glass substrate with 10

As a 33 × 22 × 1.1 mm ³ electrode with a sheet resistance of , it was ultrasonically cleaned with acetone, isopropyl alcohol and deionized water and then dried in a drying cabinet for 6 hours. Then, enough PI was coated on the ITO-coated glass substrate by spin coating at 700 rpm for 5 seconds and 3,000 rpm for 30 seconds at room temperature. Immediately after coating, a soft baking process was performed by heating on a hot plate at 80° C. for 10 minutes. Thereafter, the PI alignment layer was formed through a hard baking process in an oven at 230° C. for 1 hour.

In the liquid crystal alignment method combining atmospheric pressure plasma and rubbing according to the first embodiment of the present invention, first, in order to align the liquid crystal in step 110, a plasma beam is irradiated at a predetermined irradiation angle for a predetermined time in an oxygen atmosphere to atmospheric pressure plasma. do the process In the atmospheric plasma process, the cell was irradiated at a plasma beam irradiation angle of 45° for 30 seconds in an oxygen atmosphere.

After performing the atmospheric pressure plasma process, in step 120, the film-coated substrate is rubbed along an alignment path using a rotating roller equipped with the rubbing cloth. In the rubbing process, nylon cloth was applied to a rubbing machine (SRMS-50-M; Sciencetown) as a rubbing cloth.

According to the first embodiments of the present invention, the LC alignment characteristics may be improved by performing a rubbing process after performing the atmospheric pressure plasma process. More specifically, it improves the problem of negative effects such as stripes on the alignment film due to accumulation of dust particles and static electricity during the rubbing process, which is a disadvantage of the rubbing process, and combines the atmospheric pressure plasma process with the advantages of low production cost and short process time. Thus, the LC orientation characteristics can be improved.

Figure 2 is a flow chart for explaining a liquid crystal alignment method combining atmospheric pressure plasma and rubbing according to a second embodiment of the present invention.

A liquid crystal alignment method combining atmospheric plasma and rubbing according to a second embodiment of the present invention uses a rotating roller equipped with a rubbing cloth to align a liquid crystal (LC), and a film-coated substrate is aligned along an alignment path. It may include a step 210 of rubbing along and, after performing the rubbing process, a step 220 of performing an atmospheric pressure plasma process by irradiating a plasma beam at a predetermined irradiation angle for a predetermined time in an oxygen atmosphere.

의 시트 저항의 33 × 22 × 1.1 mm³ 전극으로서, 아세톤, 이소프로필 알코올 및 탈이온수로 초음파 세척한 후 건조 캐비닛에서 6시간 동안 건조시켰다. 그런 다음 실온에서 700rpm에서 5초 동안, 3,000rpm에서 30초 동안 스핀 코팅을 하여 충분한 PI를 ITO 코팅 유리 기판에 코팅했다. 코팅 직후 80℃의 뜨거운 판에서 10분 동안 가열하여 소프트 베이킹(soft baking) 공정을 수행했다. 이후, PI 배향 층은 230℃에서 1시간 동안 오븐에서 하드 베이킹(hard baking) 공정을 통해 형성되었다. In an embodiment of the present invention, homogeneous polyimide (PI; SE-7492; Nissan Chemical Engineering) was used as the LC orientation layer. Indium-Tin Oxide (ITO) coated Corning 1737 glass substrate with 10

As a 33 × 22 × 1.1 mm ³ electrode with a sheet resistance of , it was ultrasonically cleaned with acetone, isopropyl alcohol and deionized water and then dried in a drying cabinet for 6 hours. Then, enough PI was coated on the ITO-coated glass substrate by spin coating at 700 rpm for 5 seconds and 3,000 rpm for 30 seconds at room temperature. Immediately after coating, a soft baking process was performed by heating on a hot plate at 80° C. for 10 minutes. Thereafter, the PI alignment layer was formed through a hard baking process in an oven at 230° C. for 1 hour.

In the liquid crystal alignment method combining atmospheric plasma and rubbing according to the second embodiment of the present invention, first, in step 210, a film-coated substrate is aligned using a rotating roller equipped with a rubbing cloth to align the liquid crystal. Rub along the path. In the rubbing process, nylon cloth was applied to a rubbing machine (SRMS-50-M; Sciencetown) as a rubbing cloth.

After performing the rubbing process, in step 120, an atmospheric pressure plasma process is performed by irradiating a plasma beam at a predetermined irradiation angle for a predetermined time in an oxygen atmosphere. In the atmospheric plasma process, the cell was irradiated at a plasma beam irradiation angle of 45° for 30 seconds in an oxygen atmosphere.

According to the second embodiments of the present invention, after performing the rubbing process, an atmospheric pressure plasma process may be performed to improve LC alignment characteristics. More specifically, it improves the problem of negative effects such as stripes on the alignment film due to accumulation of dust particles and static electricity during the rubbing process, which is a disadvantage of the rubbing process, and combines the atmospheric pressure plasma process with the advantages of low production cost and short process time. Thus, the LC orientation characteristics can be improved.

3 is a photomicrograph of a surface-modified PI layer of a TN LC cell of various LC alignment techniques according to an embodiment of the present invention.

The LC alignment characteristics were measured by applying four individual alignment conditions to the cells manufactured according to the examples of the present invention. In the rubbing process according to embodiments of the present invention, nylon cloth was applied to a rubbing machine (SRMS-50-M; Sciencetown) as a rubbing cloth. In the atmospheric plasma process, the cell was irradiated at a plasma beam irradiation angle of 45° for 30 seconds in an oxygen atmosphere.

The cell in the first alignment condition performed only the rubbing process.

In the cell under the second alignment condition (ie, the first embodiment of the present invention), an atmospheric pressure plasma process was performed after performing the rubbing process.

The cell under the third alignment condition (that is, the second embodiment of the present invention) was subjected to the atmospheric pressure plasma process and then to the rubbing process.

The fourth cell performed only the atmospheric pressure plasma process.

Cells made under each condition were AP (Antiparallel) LC cells with a 60 μm cell gap to evaluate the optical properties of the PI alignment layer and TN (Twisted Nematic) LC cells with a 5 μm cell gap to evaluate the electro-optical properties. It became.

= 4.1,

= 0.110)이었다. 편광 광학 현미경(BX53M; 올림푸스)이 다양한 배향 방법을 사용하여 제조된 LC 셀에 대한 PI 배향 층의 LC 배향을 관찰하기 위해 사용되었다. 각 LC 셀의 배향 상태는 결정 회전 방법에 의해 LC의 선경사각(TBA 107; Autronic)을 분석하여 결정되었다. 표면 접촉각(UNI-CAM/A; GITSoftTech)은 각 LC 셀에 사용되는 PI 방향 공정에 따라 표면 특성을 특성화하기 위해 측정되었다. TN LC 셀의 전자 광학적 특성을 평가하기 위해 LCD 평가 시스템(LCMS-200; 세심 광학 기술)을 사용하여 전압-투과율, 응답 시간 및 잔류 직류(Residual Direct Current; RDC) 전압 측정을 수행했다. 마지막으로, LC 셀의 열 안정성은 90℃에서 210℃까지 30℃간격으로 오븐에서 가열하여 평가되었다. 그리고 LC 셀의 내부는 편광 현미경을 사용하여 관찰하였다. The LC used in the manufacturing process according to the embodiment of the present invention is homogeneous (ZSM-50087XX; JNC;

= 4.1;

= 0.110). A polarized optical microscope (BX53M; Olympus) was used to observe the LC orientation of the PI orientation layer for LC cells fabricated using various orientation methods. The orientation state of each LC cell was determined by analyzing the pretilt angle of the LC (TBA 107; Autronic) by the crystal rotation method. The surface contact angle (UNI-CAM/A; GITSoftTech) was measured to characterize the surface properties according to the PI orientation process used for each LC cell. To evaluate the electro-optical characteristics of the TN LC cell, voltage-transmittance, response time, and residual direct current (RDC) voltage measurements were performed using an LCD evaluation system (LCMS-200; Sesim Optical Technology). Finally, the thermal stability of the LC cell was evaluated by heating in an oven from 90 °C to 210 °C at 30 °C intervals. And the inside of the LC cell was observed using a polarizing microscope.

The alignment state of LCs in LCDs is a useful indicator of image quality. In the prior art, it has been shown that uniform LC alignment, regular linear angles, and specific electro-optical properties are required for high-quality images [19].

Figure 3 shows photomicrographs obtained when the direction of polarization crosses the LC cells produced under the four orientation conditions. FIG. 3(a) is a case where only the rubbing process is performed, FIG. 3(b) is a case where the atmospheric pressure plasma process is performed after the rubbing process is performed, and FIG. 3(c) is a case where the rubbing process is performed after the atmospheric pressure plasma process is performed. 3(d) is a photomicrograph of the surface-modified PI layer of the TN LC cell when only the atmospheric plasma process was performed. Here "A" stands for "analyzer" and "P" stands for "polarizer".

The LC cell in the case of performing only the atmospheric plasma process tended to have LC molecules oriented in one direction, but the LC cell as a whole was not uniform. On the other hand, the LC array was well oriented and uniformly oriented in the LC cell as it was subjected to the rubbing process (as evidenced by the completely black surface in Fig. 3). Uniform orientation improves image quality in terms of light transmittance and color expression.

4 is a diagram showing transmittance of various LC alignment techniques according to an embodiment of the present invention.

Figure 4 shows the linear squares measured using the crystal rotation method to evaluate the LC orientation of AP LC cells fabricated under different LC orientation conditions.

FIG. 4(a) shows a case in which only a rubbing process is performed, FIG. 4(b) shows a case in which an atmospheric pressure plasma process is performed after performing a rubbing process, and FIG. 4(c) shows a case in which a rubbing process is performed after performing an atmospheric pressure plasma process. 4(d) shows the transmittance as a function of the incident angle of LC molecules to the PI layer when only the atmospheric pressure plasma process is performed.

A linear quadrangle representing the tilt angle of the LC molecule can prevent defects such as reverse tilt. The blue line in FIG. 4 represents the ideal theoretical value and the red line corresponds to the measured value. Coincidence of the two lines indicates a uniform LC orientation. The linear square can be estimated with high reliability using the crystal rotation technique. Conversely, a difference between the two lines indicates that the oriented layer is not composed of fully oriented LC molecules, meaning that it is unstable. The criterion for determining uniformity is the error rate, which must be less than 0.01 [20]. Fig. 4(d) shows that the error rate is 0.023 when only the atmospheric plasma process is performed, that is, when the LC molecules are randomly oriented on the atmospheric plasma treated PI surface. On the other hand, when only the rubbing process was performed, the error rate was 0.006 (Fig. 4(a)). The case of performing the atmospheric pressure plasma process after performing the rubbing process showed an error rate of 0.003 (FIG. 4(b)), whereas the case of performing the rubbing process after performing the atmospheric pressure plasma process showed an error rate of 0.004 (FIG. 4(c)). The theoretical and measured curves are almost identical, indicating a uniform LC direction and high reliability. Table 1 summarizes the average linear square and standard deviation determined by measurements at three locations.

<Table 1>

The data is graphically represented in Figure 4(e). Using only the rubbing process, the average angle was 5.125° and the standard deviation was 0.251°. When the rubbing and atmospheric plasma processes were performed together, the average angles were 2.150° (rubbing-plasma) and 2.601° (plasma-rubbing), and the standard deviations were 0.158° and 0.060°, respectively. Using only the atmospheric plasma process, the average angle was 0.109° and the standard deviation was 0.130°. Due to atmospheric pressure plasma irradiation, anisotropic deformation of the substrate occurred [21], so the linear dead angle was reduced during the process. A small standard deviation indicates that the direction is uniform.

5 is a diagram showing voltage according to transmittance of a TN LC cell including a surface-modified PI layer according to an embodiment of the present invention.

Among electro-optical properties, voltage-transmittance was measured for a TN LC cell under each LC orientation condition. Polarizers were alternately attached to the two substrates of the LC cell, and measurements were made in the normally white (NW) state. The transmittance change according to the increase in the voltage applied to the TN LC cell (0 to 7V, increment by 0.2V) is shown.

5(a) shows the case in which only the rubbing process according to the increase in the 0 to 7V voltage applied to the TN LC cell is performed (511), the case in which the atmospheric pressure plasma process is performed after the rubbing process (512), and the atmospheric pressure plasma process followed by rubbing Transmittance change in the case of performing the process (513) and the case of performing only the atmospheric pressure plasma process (514), and FIG. ), when the atmospheric pressure plasma process is performed after performing the rubbing process (522), when the rubbing process is performed after performing the atmospheric pressure plasma process (523), and when only the atmospheric pressure plasma process is performed (524).

Table 2 shows the threshold voltage (Vth) and saturation voltage (Vsat) measured at the point where the transmittance became 90%.

<Table 2>

The effective switching voltage is the difference between Vth and Vsat. When the rubbing and atmospheric plasma processes were used together, the Vth of the TN LC cell changed more smoothly at low power and the effective switching voltage was more than 20% lower than that of the conventional rubbing process alone. On the other hand, the Vsat of the cell exposed only to the atmospheric plasma process was abnormally high (7.53V) and the effective switching voltage reached 4.912V. These high voltages make atmospheric plasma treatment cells unsuitable for industrial use.

6 is a diagram showing the response time of a TN LC cell including a surface-modified PI layer according to an embodiment of the present invention.

6 shows a case in which only a rubbing process is performed (611), a case in which an atmospheric pressure plasma process is performed after performing a rubbing process (612), a case in which a rubbing process is performed after performing an atmospheric pressure plasma process (613), and a case in which only an atmospheric pressure plasma process is performed Response time of a TN LC cell comprising a surface-modified PI layer of (614).

Rise time is the time it takes for the voltage to change instantaneously from 0V to 5V. The transmittance decreased when the LC of the TN LC cell was in the NW state and the light did not pass through the polarizer. Conversely, fall time is the time it takes to respond to a momentary drop in voltage from 5V to 0V, i.e. back to the initial NW state. In this process, the transmittance gradually increases. The sum of the rise and fall times is defined as the total response time. The total measurement time was 200 ms. The response time varied greatly depending on the orientation method (Table 2). Using only the atmospheric plasma process, the rise time was 47.748 ms and the fall time was 76.208 ms, resulting in a total response time of 123.956 ms. These features will make the cell difficult to use industrially. In the case of the TN LC cell, the rise times of 4.926, 5.460, and 8.966 ms and 16.493, 9.488, and 10.082 ms respectively in the case of performing the rubbing process, the case of performing the rubbing-atmospheric pressure plasma process, and the case of performing the atmospheric pressure plasma-rubbing process, respectively. Indicates the corresponding fall time. Therefore, the total response times are 21.419, 14.948, and 19.048 ms, respectively. The total response time is less than 30 ms, except when only the atmospheric plasma process is performed, so it can be used as an LCD in an industrial environment.

7 is a diagram showing residual DC characteristics of a TN LC cell including a surface-modified PI layer according to an embodiment of the present invention.

Residual Direct Current (RDC) represents a brightness change according to a voltage change between ON/OFF states. 7 shows a case in which only a rubbing process is performed (711), a case in which an atmospheric pressure plasma process is performed after performing a rubbing process (712), a case in which a rubbing process is performed after performing an atmospheric pressure plasma process (713), and a case in which only an atmospheric pressure plasma process is performed The RDC for the TN LC cell of (714) is the measurement result.

When an LC cell is driven, an afterimage remains when impurity ions are adsorbed on the internal PI surface. RDC measurements can thus indicate the presence of defects. The smaller the difference between the initial transmittance and the final transmittance, the more constant luminous intensity can be obtained at a given voltage. The voltage at the point where transmittance becomes 50% at (+) and (-) voltages is defined as (+) RDC and (-) RDC, respectively. The smaller the difference between the (+) RDC voltage and the (-) RDC voltage, the smaller the residual afterimage. For the measurement, the voltage was increased from 0V to 5V, from 5V to -5V, and from -5V to 0V by 0.2V, and the sequence was performed twice. The measurement is performed when only the rubbing process is performed (711), when the atmospheric pressure plasma process is performed after the rubbing process (712), when the rubbing process is performed after the atmospheric pressure plasma process is performed (713), when only the atmospheric pressure plasma process is performed ( 714) were 0.069, 0.014, 0.021, and 0.477V, respectively, and the corresponding (-) RDC values were 0.071, 0.032, 0.015, and 0.538V, respectively. Only the LC cell with the atmospheric plasma process displayed significantly different RDC curves during the DC sweep. That is, the method in the other direction showed excellent RDC performance.

8 is a photomicrograph of an LC cell heat-treated at a temperature in the range of 90 ° C to 210 ° C to observe the thermal stability of the surface-modified PI layer according to an embodiment of the present invention.

When only the rubbing process was performed (Rubbing), when the atmospheric pressure plasma process was performed after the rubbing process (Rubbing-Plasma), when the rubbing process was performed after the atmospheric pressure plasma process (Plasma-Rubbing), when only the atmospheric pressure plasma process was performed Photomicrographs showing the relationship between stability and ability to maintain LC direction under various thermal conditions of plasma [22].

To measure the thermal stability of the LC cell, the temperature was increased by 30 °C from 90 °C to 210 °C at each observation step. These molecules were observed after annealing in an oven at the target temperature for 10 minutes and stabilization at room temperature for 1 hour. When the annealing temperature was less than 150 °C, all LC cells showed a clear LC orientation except for the cell that performed only the atmospheric plasma process. The LC direction started to change at 180 °C for the cells subjected to only the rubbing process, but became evident at this temperature when the rubbing and atmospheric plasma processes were performed together. In the case of performing only the atmospheric pressure plasma process, a non-uniform LC direction was observed at 90 ° C or higher, indicating that the thermal stability was very poor. In the other orientation method, no orientation change of up to 150 ° C was observed, confirming the thermal stability suitable for LCD use.

As described above, although the embodiments have been described with limited examples and drawings, those skilled in the art can make various modifications and variations from the above description. For example, the described techniques may be performed in an order different from the method described, and/or components of the described system, structure, device, circuit, etc. may be combined or combined in a different form than the method described, or other components may be used. Or even if it is replaced or substituted by equivalents, appropriate results can be achieved.

Therefore, other implementations, other embodiments, and equivalents of the claims are within the scope of the following claims.

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Claims (16)

Performing an atmospheric pressure plasma process by irradiating a plasma beam at a predetermined irradiation angle for a predetermined time in an oxygen atmosphere to align liquid crystal (LC); and
After performing the atmospheric pressure plasma process, rubbing the film-coated substrate along an orientation path using a rotating roller equipped with a rubbing cloth.
A liquid crystal alignment method comprising a. According to claim 1,
Generating an antiparallel (AP) liquid crystal cell for evaluating the optical properties of a polyimide (PI) alignment layer and a twisted nematic (TN) liquid crystal cell for evaluating the electro-optical properties
A liquid crystal alignment method further comprising a. According to claim 2,
By performing the rubbing process after performing the atmospheric pressure plasma process,
The liquid crystal cell has a more uniform alignment layer when only the atmospheric pressure plasma process or the rubbing process is performed, and the image quality in terms of light transmittance and color expression is improved.
Liquid crystal alignment method. According to claim 2,
By performing the rubbing process after performing the atmospheric pressure plasma process,
The pretilt angle analysis result of the liquid crystal cell measured by the crystal rotation method reduces the error rate for determining the uniformity of the alignment of the liquid crystal cell compared to the case of performing only the atmospheric pressure plasma process or the case of performing only the rubbing process.
Liquid crystal alignment method. According to claim 2,
By performing the rubbing process after performing the atmospheric pressure plasma process,
Among the electro-optical characteristics, the result of measuring the voltage-transmittance is that the effective switching voltage, which is the difference between the threshold voltage and the saturation voltage, is reduced at the point where the transmittance becomes 90% compared to the case of performing only the atmospheric pressure plasma process or the case of performing only the rubbing process.
Liquid crystal alignment method. According to claim 2,
By performing the rubbing process after performing the atmospheric pressure plasma process,
The total response time, which is the sum of the rise time and fall time, is reduced compared to the case of performing only the atmospheric pressure plasma process or the case of performing only the rubbing process.
Liquid crystal alignment method. According to claim 2,
By performing the rubbing process after performing the atmospheric pressure plasma process,
Residual Direct Current (RDC), which represents a change in brightness due to a voltage change between ON/OFF states, is reduced compared to the case of performing only the atmospheric pressure plasma process or the case of performing only the rubbing process.
Liquid crystal alignment method. According to claim 2,
By performing the rubbing process after performing the atmospheric pressure plasma process,
Improving the thermal stability of the liquid crystal cell compared to the case of performing only the atmospheric pressure plasma process or the case of performing only the rubbing process
Liquid crystal alignment method. rubbing the film-coated substrate along an orientation path using a rotating roller equipped with a rubbing cloth to align liquid crystal (LC); and
After performing the rubbing process, performing an atmospheric pressure plasma process by irradiating a plasma beam at a predetermined irradiation angle for a predetermined time in an oxygen atmosphere.
A liquid crystal alignment method comprising a. According to claim 9,
Generating an antiparallel (AP) liquid crystal cell for evaluating the optical properties of a polyimide (PI) alignment layer and a twisted nematic (TN) liquid crystal cell for evaluating the electro-optical properties
A liquid crystal alignment method further comprising a. According to claim 9,
By performing the atmospheric pressure plasma process after performing the rubbing process,
The liquid crystal cell has a more uniform alignment layer when only the atmospheric pressure plasma process or the rubbing process is performed, and the image quality in terms of light transmittance and color expression is improved.
Liquid crystal alignment method. According to claim 10,
By performing the atmospheric pressure plasma process after performing the rubbing process,
The pretilt angle analysis result of the liquid crystal cell measured by the crystal rotation method reduces the error rate for determining the uniformity of the alignment of the liquid crystal cell compared to the case of performing only the atmospheric pressure plasma process or the case of performing only the rubbing process.
Liquid crystal alignment method. According to claim 10,
By performing the atmospheric pressure plasma process after performing the rubbing process,
Among the electro-optical characteristics, the result of measuring the voltage-transmittance is that the effective switching voltage, which is the difference between the threshold voltage and the saturation voltage, is reduced at the point where the transmittance becomes 90% compared to the case of performing only the atmospheric pressure plasma process or the case of performing only the rubbing process.
Liquid crystal alignment method. According to claim 10,
By performing the atmospheric pressure plasma process after performing the rubbing process,
The total response time, which is the sum of the rise time and fall time, is reduced compared to the case of performing only the atmospheric pressure plasma process or the case of performing only the rubbing process.
Liquid crystal alignment method. According to claim 10,
By performing the atmospheric pressure plasma process after performing the rubbing process,
Residual Direct Current (RDC), which represents a change in brightness due to a voltage change between ON/OFF states, is reduced compared to the case of performing only the atmospheric pressure plasma process or the case of performing only the rubbing process.
Liquid crystal alignment method. According to claim 10,
By performing the atmospheric pressure plasma process after performing the rubbing process,
Improving the thermal stability of the liquid crystal cell compared to the case of performing only the atmospheric pressure plasma process or the case of performing only the rubbing process
Liquid crystal alignment method.

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