JPH03181906A - Optical delay plate and liquid crystal display element by using the same - Google Patents

Abstract

PURPOSE:To lessen the change in retardation values with lapse of time by forming the optical delay plate in such a manner that the retardation values of a 1st optically anisotropic layer and 2nd optically anisotropic layer having the optical axes intersecting orthogonally with each other vary from each other and the characteristics of the change therein with lapse of time exhibit a similar tendency. CONSTITUTION:This optical delay plate has the two-layer structures adjacent to each other. The optical axes of the 1st optically anisotropic layer 1 and the 2nd optically anisotropic layer 2 intersect approximately orthogonally with each other and the retardation values of the 1st optically anisotropic layer 1 and the 2nd optically anisotropic layer vary from each other. The characteristics of the change therein with lapse of time indicate the similar tendency. The optically anisotropic layer 1 and the optically anisotropic layer 2 which have the similar tendency of the change in the retardation values thereof with lapse of time are, therefore, selected by which the optical delay plate 3 obtd. by intersecting these layers orthogonally with each other is offset in the change in the respective retardation values thereof with lapse of time. The change in the retardation values with lapse of time is lessened in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an optical delay plate and a liquid crystal display element using the same.

(Prior Art) In the past, optical delay plates having an optical phase difference were made of mica, quartz, etc., and were used in optical elements. In recent years, with the advancement of polymer technology, optical retardation plates made of various materials have been manufactured and the field of application is expanding.

Polyvinyl alcohol, polyester, polycarbonate, polyethylene, and the like are known as polymeric materials used as optical retardation plates.

The application of such an optical retardation plate to a liquid crystal display element is, for example, as described in EP-0246842, using a super-twisted nematic type or a super-twisted birefringence effect (S B E) type. It is used in liquid crystal displays to make the background color achromatic.

(Problems to be Solved by the Invention) Generally, the retardation value of an optical retardation plate made of a polymeric material changes with time. For this reason, liquid crystal display elements using optical delay plates have problems with the durability of display characteristics. For example, in the case of an achromatic liquid crystal display element using an optical delay plate, even if an achromatic, high-contrast display is initially obtained, the background becomes slightly colored and the contrast decreases as the retardation value changes over time. There was a problem.

As a solution to this problem, by aging the optical retardation plate in advance, the change in the crystallinity of the optical retardation plate that causes the change in retardation value can proceed to a certain extent, and the change in retardation value during practical use can be prevented. There is a way to make it smaller. In this case, in order to obtain a stable retardation value, aging must be performed for a long time, and even if aging is performed, it may not converge to a constant value.

As described above, in the conventional optical retardation plate, it is difficult to suppress the change in retardation value over time, and there is a problem in the durability of the liquid crystal display element using the same. The present invention solves this problem by providing an optical retardation plate in which the change in retardation value of the optical retardation plate is suppressed over time, and by using this optical retardation plate, a highly durable liquid crystal display element is provided. It is something to do.

[Structure of the Invention (Means for Solving the Problem) The invention according to claim 1 has a two-layer structure in which a first optically anisotropic layer and a second optically anisotropic layer are adjacent to each other, and the first optically anisotropic layer and the second optically anisotropic layer are adjacent to each other. The optical axes of the optically anisotropic layer and the second optically anisotropic layer are substantially perpendicular to each other, and the retardation values of the first optically anisotropic layer and the second optically anisotropic layer are different from each other. The present invention is an optical retardation plate characterized in that the characteristics of change exhibit similar trends.

The invention according to claim 2 provides first and second substrates, each having electrodes formed on opposing surfaces and placed opposite each other;
A liquid crystal display element comprising a liquid crystal cell made of a liquid crystal composition sandwiched between a second substrate and a second substrate, and two polarizing plates disposed on both sides of the liquid crystal cell. A liquid crystal display element comprising at least one optical retardation plate according to claim 1 between the polarizing plate on one side.

(Function) As shown in Figure 1, two optically anisotropic layers 1. 2 are superimposed so that their optical axes are substantially perpendicular to each other to form one optical retardation plate, the retardation values of the optically anisotropic layers are offset.

For this reason, the optically anisotropic layer 1. If the retardation values of 2 are R1 and R2 (R1>R2), respectively, then the retardation value of the manufactured optical delay plate 3 is R-R1-R2.

Figure 4 shows the retardation value R1(t) (initial value R1)
An example of changes over time in the retardation values of the optically anisotropic layer 1 and the optically anisotropic layer 2 with a retardation value R2(t) (initial value R2) is shown (R1>R2). The retardation value R(t) of the optical retardation plate obtained by orthogonally intersecting these optically anisotropic layers 1.2 is expressed as the difference between these retardation values, R(t) = R2(t )−R1(
t). Here, if the changes over time in the retardation values of optically anisotropic layer 1 and optically anisotropic layer 2 are the same, the changes over time in the retardation values of each optically anisotropic layer cancel each other out, so that the obtained optical retardation plate There is no change in retardation value over time, and an optical retardation plate having a retardation value of R-R1-R2 can be obtained.

Therefore, if the optically anisotropic layer 1 and the optically anisotropic layer 2 are selected such that their retardation values tend to change over time in a similar manner, the optical retardation plate obtained by orthogonally crossing them will have the respective retardation values. The changes over time cancel each other out, making it possible to obtain an optical retardation plate whose retardation value changes less over time than an optical retardation plate consisting of a single optically anisotropic layer. Note that, as a material having a similar tendency in the change in retardation value over time, for example, a material in which the optically anisotropic layer 1 and the optically anisotropic layer 2 are formed of the same material can be used.

A liquid crystal display element using such an optical delay plate has excellent durability and can maintain stable display quality.

(Example 1) FIG. 1 shows an optical retardation plate of the present invention. Optically anisotropic layers 1 and 2
Each is made of polycarbonate and has a thickness of approximately 200 μm.
organic film was used. The first optically anisotropic layer 1 has an initial retardation value of 0.690 μm and a change over time of 0.6
Those that progress to 65 μm are heated in a nitrogen atmosphere at 60°C for 4
Aged for 8 hours and the retardation value was 0.875μ
m was used.

The second optically anisotropic layer 2 had an initial retardation value of 0.345 μm and a change over time that progressed to 0.335 μm, and was used without aging. Changes in retardation values of these optically anisotropic layers 1 and 2 over time show similar trends.

The first and second optically anisotropic layers 1.2 are stacked and placed and attached so that their respective stretching directions (optic axes) are orthogonal to the stretching direction of the optically anisotropic layers, and the retardation value is 0.33.
An optical retardation plate 3 with a thickness of 0 μm (=0.675-0.345) was produced.

In this example, a heat resistance test (70°C, dry atmosphere,
500 hours) and heat/humidity resistance test (60℃, humidity 70%,
As a result, the retardation value was 0.331 < -C1,H5-C1,335)μm.
There was almost no change.

(Example 2) FIG. 2 shows the structure of a liquid crystal display element of the present invention, and FIG. 3 shows a cross-sectional view thereof.

Transparent electrodes 8, 8' and alignment films 9, 9' made of polyimide
The substrates 4, 4' on which are formed are placed almost parallel to each other, a liquid crystal composition 10 is sealed between them, and the periphery thereof is sealed and fixed with a sealant 11 made of epoxy adhesive. It is an LCD selfie.

In this liquid crystal self, the liquid crystal molecules are aligned in the alignment direction r, which is obtained by rubbing the alignment film 9 on the substrate 4 side, and in the alignment direction r, which is obtained by rubbing the alignment film 9 on the substrate 4' side.
The orientation is twisted counterclockwise at a twist angle of -240° due to the orientation direction r' that is rubbed. Note that the orientation direction r
, r- were set at 130 degrees and +30 degrees from a reference direction C parallel to one side of the substrates 4, 4, respectively. Further, the tilt angle θ of the liquid crystal molecules is 2.0 degrees, and the cell thickness (substrate spacing) d is 6.0 degrees.
It is 7 μm. As a liquid crystal composition, Z L I 37
11 (E, manufactured by Merck & Co.) as a counterclockwise chiral agent.
-811 (E, manufactured by Merck & Co.) was used.

The organic film of Example 1 was used for the optical retardation plate 3, and the second
As shown in the figure, the first optically anisotropic layer 1 is arranged and pasted so that the stretching direction is Al-50 degrees with respect to the reference direction C of the liquid crystal self, and the second optically anisotropic layer is applied thereon. They were arranged and pasted so that the stretching direction of No. 2 was A2-140 degrees with respect to the reference direction C. Also, LLC is provided as first and second polarizing plates 5 and 6 on the outside of the liquid crystal self and the first and second optically anisotropic layers 1 and 2.
281-18 (manufactured by Royal Electric Co., Ltd.), each with PL = 65°
, P2 was installed and attached at a polarizing plate angle of -44°.

In this example, a voltage is applied to the first liquid crystal self, and 1
When the liquid crystal was turned on and off by multiplex driving with a duty ratio of /200, the contrast was as high as about 14:1, and a wide viewing angle was obtained.

Further, as a result of a heat resistance test (70 degrees Celsius, dry atmosphere, 500 hours) and a heat/humidity resistance test (60 degrees Celsius, humidity 70%, 500 hours), the contrast was about 14=1, which was almost unchanged.

(Comparative Example) In Example 2, instead of the optical retardation plate 3 having the first and second optically anisotropic layers, the initial retardation value was 0.
An optical retardation plate made of one polycarbonate film having a thickness of 330 μm is stretched at a length of 50' with respect to the reference direction C.
It was arranged and pasted so that

In this comparative example, the initial contrast value was about 14:1. However, the heat resistance and humidity resistance test (60 degrees, humidity 70%)
, 500 hours), the retardation value significantly decreased due to shrinkage of the optically anisotropic layer made of polycarbonate, and a significant decrease in contrast was observed.

Effects of the Invention According to the present invention, an optical retardation plate whose retardation value changes less over time, and a liquid crystal display element with high display quality and durability using the same can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an optical retardation plate of the present invention, FIG. 2 is a diagram illustrating the structure of a liquid crystal display element using an optical retardation plate of an embodiment of the present invention, and FIG. 3 is a diagram of an embodiment of the present invention. FIG. 4, a cross-sectional view of a liquid crystal display element using an optical retardation plate, is a diagram showing changes over time in retardation values of two types of optically anisotropic layers. 1... First optically anisotropic layer, 2... Second optically anisotropic layer

Claims (2)

[Claims] (1) It has a two-layer structure in which a first optically anisotropic layer and a second optically anisotropic layer are adjacent to each other, and the optical axes of the first optically anisotropic layer and the second optically anisotropic layer are substantially similar to each other. orthogonal to each other, and the first
An optical retardation plate characterized in that the retardation values of the optically anisotropic layer and the second optically anisotropic layer are different from each other, and the characteristics of their changes over time exhibit similar trends. (2) A liquid crystal cell comprising first and second substrates placed opposite each other and having electrodes formed on their opposing surfaces, and a liquid crystal composition sandwiched between the first substrate and the second substrate. ,
In a liquid crystal display element having two polarizing plates arranged on both sides of the liquid crystal cell, at least one optical retardation plate according to claim 1 is provided between the liquid crystal cell and at least one polarizing plate. A liquid crystal display element featuring: