JPH01162134A - Pretilt angle measurement for liquid crystal cell - Google Patents

Abstract

PURPOSE:To obtain a pretilt angle of a liquid crystal cell even when the pretilt angle is large, by determining the pretilt angle from a value of an angle giving a maximum of 1 or 0 in a permeability curve. CONSTITUTION:Linear polarizing plates 1 and 3 parallel with each other are arranged before and after a liquid crystal cell 2 respectively. Light with a specified wavelength is incident into the polarizing plates and the cell 2 is turned to measure a permeability characteristic with respect to an angle of the incident light. Angle giving maximum or minimum in a permeability curve as represented by theta, the thickness of a liquid crystal layer of the liquid crystal cell (d), normal refractive index of liquid crystal n0, abnormal reflective index of liquid crystal ne and wavelength of incident light lambda are substituted into a formula with k=2pi/lambda, N=n0<2>cos<2>alpha0+ne<2>, sin<2>alpha2 and DELTAn=n-n0 to determine a pretilt angle alpha0, wherein P is a specified natural number. Thus, several angles giving maximum of 1 or 0 are sure to appear even when the pretilt angle alpha0 is larger thereby enabling the determination of a pretilt angle alpha0 of the cell 2.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a method for measuring a pretilt angle between a liquid crystal panel substrate and the long axis of liquid crystal molecules aligned in a certain direction, and has the purpose of expanding the measurable range of the pretilt angle. Then, linear polarizing plates parallel to each other are arranged before and after the liquid crystal cell, light of a specific wavelength is incident on these, and the liquid crystal cell is rotated to measure the transmittance characteristics with respect to the angle of the incident light, and the transmittance curve is The angle that gives the maximum or minimum value is θ, the thickness of the liquid crystal layer of the liquid crystal cell is d, the ordinary refractive index of the liquid crystal is no, the extraordinary refractive index of the liquid crystal is n, the wavelength of the incident light is λ, k-2π/λ , N=n, “cos”αo+na”s in”αo
Substituting 1Δn=n·-nils into the following formula (where p is a specific natural number), the pretilt angle α is determined. including determining and configuring.

[Industrial application field]

The present invention relates to a method for measuring a pretilt angle between a liquid crystal panel substrate and the long axis of liquid crystal molecules aligned in a certain direction.

In liquid crystal, the pretilt angle is an important factor that determines the display characteristics of the liquid crystal panel. Therefore, measuring the pretilt angle is important in optimizing the liquid crystal display.

[Conventional technology]

There are three methods for measuring the pretilt angle: the crystal rotation method, the magnetic field capacitance zero method, and the capacitance-voltage method.Among them, the crystal rotation method requires a small measuring device and requires a short measurement time. Mainly used.

To explain this crystal rotation method, linear polarizing plates are placed in parallel to each other before and after the liquid crystal cell, and by injecting light of a specific wavelength and further rotating the liquid crystal cell, the transmittance of the liquid crystal cell depending on the angle of incidence of light is Measure properties. Figure 4 shows an example of the transmittance curve.
, (C) have pretilt angles of 0°, 10°, and 30°, respectively.
It is a transmittance curve of a liquid crystal cell of m. In this way, a transmittance curve generally has multiple extreme values of O or 1 and one minimum value that is not O. Conventionally, the pretilt angle was determined by focusing on the angle that gives this only one minimum value that is not 0. was. The angle that gives this extreme value other than O is φ. , the thickness of the liquid crystal layer of the liquid crystal cell is d, the ordinary refractive index of the liquid crystal is n0, the extraordinary refractive index of the liquid crystal is no, the wavelength of the incident light is λ, k-2π/λ, N-no"cos"α6+n@" s i n”αo1Δ
Using n=n・-nos, substitute into the following equation to obtain the pretilt angle α. had decided.

Or α. is α. When ≦20°, use the following approximate formula instead of the above formula to calculate the pretilt angle α. was looking for.

[Problem that the invention seeks to solve]

The majority of current liquid crystal devices use liquid crystal molecules twisted by 90 degrees, but this does not allow for the production of large screens. It needs to be twisted, ideally 270. ”
Preferably twisted.

To twist the liquid crystal molecules by more than 180°, set the pretilt angle to 5
If it is not larger than °, it will not twist stably.

However, when measuring the transmittance characteristics with respect to the incident angle of light, when the pretilt angle is 15° or more, (C) in Figure 4.
As seen in φ. will no longer appear.

Therefore, with the conventional method, it is impossible to measure the pretilt angle of a liquid crystal cell whose pretilt angle exceeds 15°.

Therefore, an object of the present invention is to expand the measurable range of pretilt angles.

[Means for solving problems]

The above problem can be solved by placing linear polarizing plates parallel to each other in front and behind the liquid crystal cell, injecting light of a specific wavelength into the liquid crystal cell, and measuring the transmittance characteristics with respect to the angle of the incident light by rotating the liquid crystal cell. The angle that gives the maximum or minimum value of the rate curve is θ
, the thickness of the liquid crystal layer of the liquid crystal cell is d, and the ordinary refractive index of the liquid crystal is n'
, the extraordinary refractive index of the liquid crystal is no, the wavelength of the incident light is λ, k=2π/λ, N=no"cos"αo+n*"s in"αo
Assuming 5ΔQ=n and j16°, substitute it into the following formula (where P is a specific natural number) to obtain the pretilt angle α. This problem is solved by a method of measuring the pretilt angle of a liquid crystal cell, which is characterized by determining the .

Also, α. is α. When ≦20°, the pretilt angle α0 can be determined with an accuracy of 90% or more even if the following approximate formula, a...(1), is used instead of the above formula.

[For production]

The method for measuring the pretilt angle of a liquid crystal cell according to the present invention determines an angle that gives a plurality of extreme values of 1 or 0 in a transmittance curve with respect to the incident angle of light. This angle always appears even when the pretilt angle becomes large. Therefore, even if the pretilt angle is large, it is possible to determine the pretilt angle of the liquid crystal cell from these angles.

〔Example〕

The pretilt angle measurement method of the present invention is performed on an evaluation cell. The prepared cell was a polyimide alignment film formed by rubbing, and had a cell thickness of d-20 μm, an ordinary refractive index of n=1.50, and an extraordinary refractive index of n=1.635.

FIG. 1 is a layout diagram of an apparatus for measuring the transmittance of a liquid crystal cell. In the same figure, ■ and 3 are linear deflection plates, 2
is an evaluation cell. As shown in the figure, evaluation cell 2
Linear polarizing plates 1 and 3 are arranged in parallel to each other before and after. The polarization directions of linear polarizers 1 and 3 are both 45° with respect to the horizontal axis.

Light with a wavelength of λ-632.8 nm is incident horizontally on this,
Rotate the evaluation cell around the vertical axis to create evaluation cell 2.
Examine the transmittance characteristics with respect to the angle.

Next, the evaluation cell 2 is turned over and its transmittance characteristics are examined again.

Figure 2 is a graph of this. In the same figure, T1 (φ) is the transmittance curve of the -th measurement, T2 (φ)
is the second transmittance curve measured with the front and back sides changed. 0
Angle φ that gives a local minimum value that is not. , and φ. Let the midpoint of 2 be the true 0°, and take the arithmetic average of T1 (φ) and T2 (-φ),
This is taken as the average transmittance. This is shown in FIG. From the figure, the angles θ that give the maximum and minimum values are -5°, 19°,
It can be read as 42.5@, 62°. At this time, the values of p are selected as 8, 7, and 6.5, respectively, as shown in the figure.

Also, φ at this time. The value is -41#. By substituting these data into equations (1) and (2), the pretilt angle α can be calculated. Calculate. φ in Figure 3.

Table 1 shows pretilt angle α. It is better to calculate and average the conventional single φ. α from the value of . The accuracy is higher than that obtained by calculating .

〔Effect of the invention〕

According to the liquid crystal pretilt angle measurement method of the present invention, the transmittance characteristics of the liquid crystal cell with respect to the incident angle of light are investigated, and the transmittance curve obtained at this time always has a plurality of angles that give an extreme value of 1 or 0. Since the pretilt angle is determined from the value of this angle, it is possible to determine the pretilt angle of the liquid crystal cell even if the pretilt angle is large.

Also, a plurality of pretilt angles α obtained from the value of the angle θ that gives an extreme value of 1 or O. Since the pretilt angle is determined by taking the average of φ, the only conventional data is φ. Pretilt angle α from the value of . The accuracy is improved compared to calculating .

[Brief explanation of the drawing]

Figure 1 is a layout diagram of an apparatus for measuring the transmittance of a liquid crystal cell, Figure 2 is a transmittance curve diagram, Figure 3 is an average transmittance curve diagram, and Figure 4 explains a conventional example. FIG. (Explanation of symbols) 1.3...Linear polarizing plate, 2...Evaluation cell.

Claims (2)

[Claims] (1) Arrange linear polarizing plates parallel to each other before and after the liquid crystal cell, enter light of a specific wavelength into these, rotate the liquid crystal cell, measure the transmittance characteristics with respect to the angle of the incident light, and calculate the transmittance curve. θ is the angle that gives the maximum or minimum value of λ, N=n_0^2cos^2α_0+n_■^2sin^
2α_0, Δn=n_■-n_0, the following formula, (n_■^2-n_0^2)/2N^2sin2α_■
sinθ=n_■n_0/N^2N^2-sin^2θ
-n_■^2-sin^2θ-pπ/kd, (here p
is a specific natural number. ) to determine the pretilt angle α_0. (2) When α_0 is α_0≦20°, the following approximate formula is used instead of the above formula, α_0≒n_0/(2+Δn/n_0) sinθ・{√
[1-(sinθ/n_■)^2]-pπ/Δnkd}
A method for measuring a pretilt angle of a liquid crystal cell according to claim 1, using the method.