JP2902693B2 - Phase difference plate, method of manufacturing the same, and liquid crystal display device using the same - Google Patents

Description

The present invention relates to a method for manufacturing a retardation plate having an optical retardation, and a liquid crystal display device using the retardation plate.

(Prior Art) Generally, a retardation plate is a method of stretching a thermoplastic resin such as polyester, polycarbonate, polyacetate or polyethylene in a known stretching method, for example, in a uniaxial direction between two or more pairs of heating rolls having different peripheral speeds. Alternatively, it can be obtained by a method of biaxially stretching the uniaxially stretched product in a direction perpendicular to the uniaxial direction.

That is, a difference is generated in the refractive index between the stretching direction and the direction perpendicular to the stretching direction, and there is an optical phase difference. Such a retardation plate is used for a liquid crystal display element in which the background color is achromatic, as described in EP-0246842, for example.

Further, as described in Japanese Patent Application Laid-Open No. 60-256121, a birefringence control type liquid crystal display element which performs almost vertical alignment when no voltage is applied and controls birefringence by applying a voltage to perform display is obliquely oriented. A phase difference plate is used for the purpose of improving the contrast when observed from a distance.

FIG. 5 shows a liquid crystal display device using such a conventional optical retardation plate.

In FIG. 5, the liquid crystal display element includes a first polarizing plate 1,
The liquid crystal cell 2, the phase difference plate 3, and the second polarizing plate 4 are sequentially stacked as viewed from the light incident direction (arrow in the drawing).

The liquid crystal cell 2 has a liquid crystal composition sandwiched between substrates on which transparent electrodes are formed, and the periphery thereof is sealed and fixed with a sealant (not shown).

The twist angle φ of the liquid crystal composition is 240 degrees counterclockwise from the substrate 2a toward the substrate 2b, and the distance between the two substrates is 6.0 μm.

Note that ra and rb are the alignment directions of the respective alignment processes formed on the substrates 2a and 2b, and ra and rb are -30 ° C and + 30 ° C from a reference direction c parallel to one side of the liquid crystal cell 2.

A retardation plate 3 is disposed on one surface of the liquid crystal cell 2 such that the stretching direction has an angle A of 45 ° with respect to the reference direction c.

In addition, on the surface of the liquid crystal cell 2 on which the retardation plate is not provided and on the retardation plate 3, the angle P1 of the polarizer is 135 ° and the angle P2 is 90 ° with respect to the reference direction c. Are provided with polarizing plates 1 and 4, respectively.

At this time, the retardation set value of the retarder is 0.49
9 μm.

(Problems to be Solved by the Invention) Incidentally, the above-mentioned conventional retardation plate has a problem that a change in a retardation value (hereinafter, referred to as a retardation) becomes extremely large when left at high temperature.

FIG. 6 is a diagram showing a change in retardation when a retardation plate made of polypropylene is left in a high-temperature environment.

FIG. 7 is a diagram showing the relationship between the amount of deviation from the retardation set value of a liquid crystal display element using a phase difference plate and the change in contrast.

From FIG. 7, it can be seen that the amount of deviation of the retardation of the retardation plate from the set value has a great effect on the contrast of the liquid crystal display element.

For example, if the deviation from the retardation setting is 40
At nm or more, the contrast is reduced to about 1/5 of the retardation set value, and adversely affects display performance.

Such a deviation from the set value of the retardation of the retardation plate occurs because the durability of the retardation plate is insufficient, and is a serious problem in practical use.

As shown in FIG. 8, a liquid crystal display device using a retardation plate having a large change in retardation has a problem that the contrast is significantly reduced when used for a long time.

Therefore, in order to improve the reliability of the product, it is necessary to prevent the retardation change of the retardation plate regardless of the environmental conditions, and to keep the contrast of the liquid crystal display element higher and more stable.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a phase difference plate having excellent durability, a method for manufacturing the same, and a liquid crystal display device using the same.

[Constitution of the Invention] (Means for Solving the Problems) The present inventor has conducted various experiments on a retardation plate having an optical retardation made of a thermoplastic resin, by performing a heat treatment under a specific temperature condition, It has been found that a retardation plate having a small rate of change of can be obtained, and the present invention has been completed.

That is, the retardation plate of the present invention is a film-like material obtained by stretching a thermoplastic resin at a first temperature, and this film-like material is subjected to a heat treatment at a second temperature lower than the first temperature. When the second temperature is T (° C.) and the glass transition point of the thermoplastic resin is Tg (° C.), the second temperature T is represented by a general formula: Tg + 65 ≦ T ≦ Tg + 110 (I) is satisfied and the temperature is lower than 100 ° C.

Further, in the method for producing a retardation plate of the present invention, the thermoplastic resin is stretched at a first temperature to form a film, and the film is formed at a second temperature lower than the first temperature. In performing the heat treatment, general formula: Tg + 65 ≦ T ≦ Tg + 110 (I) (where Tg represents the glass transition point (° C.) of the thermoplastic resin, and T represents the second temperature (° C.) indicating the heat treatment temperature. .), And at a second temperature T less than 100 ° C.,
The heat treatment is performed on the film-like material.

Furthermore, the liquid crystal display element of the present invention includes a liquid crystal cell in which a liquid crystal composition is sandwiched between a pair of substrates having electrode surfaces, a polarizing plate provided on one surface of the liquid crystal cell, and the other of the liquid crystal cell. And a retardation film disposed on the surface of the liquid crystal display element, wherein the retardation film is formed by forming a film of a thermoplastic resin stretched at a first temperature by a general formula: Tg + 65 ≦ T ≦ Tg + 110. ... (I) (where Tg is the glass transition point (° C) of the thermoplastic resin, T is the second temperature lower than the first temperature and represents the heat treatment temperature (° C)), and The heat treatment is performed at a second temperature T lower than 100 ° C.

The stretched film of the thermoplastic resin in the present invention is not particularly limited, and generally a film of a thermoplastic resin such as polyethylene or polypropylene is stretched by a known stretching method, for example, by heating two or more pairs having different peripheral speeds. It can be obtained by a method of stretching uniaxially between rolls, or a method of biaxially stretching the uniaxially stretched product in a direction perpendicular to the uniaxial direction.

In the present invention, in the case of a liquid crystal display device using a retardation plate, the rate of change of retardation under high-temperature conditions (70 ° C.) is 5% or less in order to prevent a decrease in contrast which is a practical problem when used for a long time. Preferably it is 3% or less.

In the heat treatment of the stretched film of the thermoplastic resin in the present invention, the temperature (T) is Tg + 65 ≦ T ≦
The range of Tg + 110 is preferable, and further, Tg + 70 ≦ T ≦ Tg + 1
The range of 00 is more preferable.

When the heat treatment temperature is lower than Tg + 65 ° C., the molecular orientation of the stretched film is less relaxed, the environment changes, and the retardation of the retardation plate changes greatly when used for a long time, so that the object of the present invention cannot be achieved.

On the other hand, if the heat treatment temperature exceeds Tg + 110 ° C., the film itself deforms due to heat change and heat shrinkage, and the surface state changes and deteriorates, which is not practical.

The heat treatment time may be long when the heat treatment temperature is low, and short when the heat treatment temperature is high. However, the heat treatment for at least 30 minutes can provide the intended retardation plate.

Further, as an effective method for reducing the rate of change of the retardation of the present invention, it is a preferred embodiment that the above-mentioned film is subjected to a heat treatment at its free end or under a limited shrinkage of 5.0% or more.

(Operation) The retardation plate of the present invention is manufactured by heat treatment in a specific temperature range.

This heat treatment thermally stabilizes the orientation state of the molecules forming the phase difference plate, so that the change in the environment and the change in the retardation of the phase difference plate during long-term use can be suppressed.

Further, by using this retardation plate for a liquid crystal display element, a stable contrast can be obtained, and the reliability can be improved.

(Example) Next, an example of the phase difference plate and the liquid crystal display element according to the present invention will be described with reference to the drawings.

Example 1 Polypropylene (MI = 1.7 g / 10 min, Tg = −18 ° C.)
It was extruded at 280 ° C. by an extruder equipped with a soybean, and was brought into contact with a cooling roll at 30 ° C. to obtain an unstretched film having a thickness of 1.1 mm.

This unstretched film is uniaxially stretched 4.5 times at 145 ° C. with two pairs of heating rolls having different rotation speeds, and tenter stretched 8.0 times at 152 ° C. in a direction perpendicular to the uniaxial stretching direction to a thickness of 30 μm.
Was formed.

Next, a normal process for stabilizing the film quality was performed, in which the retardation plate was left at a temperature of 34 ° C. for 78 hours. The retardation value of the retardation plate obtained at this time is 0.456 μ
m.

The obtained retardation plate is cut into 500 × 500 mm, and Tg + 65 ≦ T
≤ 50 to 90 ° C, corresponding to the range ≤ Tg + 110,
Heat treatment was performed at free ends for 3 hours at a temperature of 60 ° C, 60 ° C, 70 ° C, 80 ° C and 90 ° C.

These retardation plates were subjected to a high-temperature standing test (leaving at a high temperature of 70 ° C. for 500 hours), and the rate of change of the retardation thereafter was examined. This result is shown as a circle in FIG.

Further, as a comparative example, a retardation plate was prepared which was subjected to a heat treatment at a free end for 3 hours at a temperature lower than Tg + 65 ° C. and at a temperature higher than Tg + 110 ° C.

Perform the above high-temperature storage test on these retardation plates,
Similarly, the rate of change of the retardation after the test was examined. The results are shown as crosses in FIG. 1 together with the results of the examples.

From Fig. 1, the rate of change of the retardation after the high-temperature storage test is very large at a heat treatment temperature of 42 ° C (Tg + 60) or lower, whereas the retardation after the high-temperature storage test is about 64 ° C (Tg + 82 ° C) or higher. Is very small.

That is, 30 to 40 ° C. which is usually performed in order to stabilize the film quality of a film obtained by a method of stretching in a uniaxial direction, or a method of biaxially stretching the uniaxially stretched product in a direction perpendicular to the uniaxial direction. The treatment method in which the retardation plate is left at a moderate temperature for 72 to 100 hours is not sufficient for stabilizing the retardation of the retardation plate, and by performing a heat treatment at a temperature of Tg + 65 ° C. or more as in the present invention, the retardation can be completely stabilized. It was possible to achieve this.

On the other hand, when the heat treatment was performed at 100 ° C. (Tg + 118 ° C.), it was confirmed that the film was deformed and fine irregularities were formed on the film surface.

Example 2 Using a propylene-ethylene copolymer (MI = 2.3 g / 10 min, ethylene content 0.3% by weight, Tg = −25 ° C.), a 1.2 mm-thick unstretched film was obtained in the same manner as in Example 1. A product was obtained.

This unstretched film-like material was obtained by the same method as in Example 1
The film was uniaxially stretched 5.2 times at 0 ° C., and tenter-stretched 8.0 times at 148 ° C. in a direction perpendicular to the uniaxial stretching direction to form a 30 μm thick retardation plate.

Next, a normal film quality stabilization treatment was performed at 40 ° C. for 100 hours. The retardation value of the obtained retardation plate was 0.310 μm.

The obtained retardation plate is cut into 500 × 500 mm, and Tg + 65 ≦ T
≤ Tg + 110
Heat treatment was performed for 3 hours at free ends at temperatures of 50 ° C, 50 ° C, 60 ° C, 70 ° C and 80 ° C.

These retardation plates were subjected to a high-temperature standing test (leaving at a high temperature of 70 ° C. for 500 hours), and the rate of change of the retardation thereafter was examined. This result is shown as a circle in FIG.

Further, as a comparative example, a retardation plate was prepared which was subjected to a heat treatment at a free end for 3 hours at a temperature lower than Tg + 65 ° C. and at a temperature higher than Tg + 110 ° C.

Perform the above high-temperature storage test on these retardation plates,
Similarly, the rate of change of the retardation after the test was examined. The results are shown as crosses in FIG. 2 together with the results of the examples.

From FIG. 2, it can be seen that the rate of change of the retardation after the high temperature storage test is very large at a heat treatment temperature of 40 ° C. (Tg + 65 ° C.) or lower, whereas the change of the retardation after the high temperature storage test is high at a heat treatment temperature of 50 ° C. It can be seen that the rate of change is very small.

On the other hand, when heat treatment was performed at 90 ° C. (Tg + 115 ° C.), deformation of the film and deterioration of the surface state were observed.

Example 3 A 30 μm thick retardation plate was formed using the material used in Example 1.

At this time, this retardation plate was not subjected to the usual process for stabilizing the film quality (leaving at 34 ° C. for 78 hours).

The retardation value of the retardation plate obtained here is 0.43
It was 9 μm.

The obtained retardation plate is cut into 500 × 500 mm, and Tg + 65 ≦ T
≤ 50 to 90 ° C, corresponding to the range ≤ Tg + 110,
Heat treatment was performed at free ends for 3 hours at a temperature of 60 ° C, 60 ° C, 70 ° C, 80 ° C and 90 ° C.

These retardation plates were subjected to a high-temperature standing test (leaving at a high temperature of 70 ° C. for 500 hours), and the rate of change of the retardation thereafter was examined. This result is shown as a circle in FIG.

Further, as a comparative example, a retardation plate was prepared which was subjected to a heat treatment at a free end for 3 hours at a temperature lower than Tg + 65 ° C. and at a temperature higher than Tg + 110 ° C.

Perform the above high-temperature storage test on these retardation plates,
Similarly, the rate of change of the retardation after the test was examined. The results are shown as crosses in FIG. 3 together with the results of the examples.

As is clear from the comparison of the results shown in FIG. 3 with the results shown in FIG. 1, a normal treatment for stabilizing the film quality (78 ° C. at 34 ° C.) was carried out.
Even if the heat treatment according to the present invention is not performed, the retardation change rate can be reduced to the same degree as in Example 1.

Embodiment 4 Next, an embodiment of a liquid crystal display device using the above-mentioned retardation plate will be described.

A liquid crystal display element having the same configuration as the liquid crystal display element of FIG. 5 described above was manufactured by using, as the phase difference plate, a heat treatment at Tg + 88 ° C. among the retardation films made of polypropylene described in Example 1.

Therefore, this embodiment will be described with reference to FIG.

In FIG. 5, the liquid crystal display element includes a first polarizing plate 1,
The liquid crystal cell 2, the phase difference plate 3, and the second polarizing plate 4 are sequentially stacked as viewed from the light incident direction (arrow in the drawing).

The liquid crystal cell 2 has a liquid crystal composition sandwiched between substrates on which transparent electrodes are formed, and the periphery thereof is sealed and fixed with a sealant made of an epoxy adhesive (not shown).

As a liquid crystal composition, ZLI1132 (manufactured by E. Merck) was used by adding S-811 (manufactured by E. Merck) as a counterclockwise chiral agent, and the distance between the substrates was controlled to 6.0 μm. The substrates 2a and 2b were subjected to the alignment treatment in the directions of ra and rb so that the liquid crystal molecules had a twist angle ψ of 240 degrees counterclockwise between the substrates.

Note that ra and rb are respectively -30 ° and + from the reference direction c.
30 mm.

Here, the retardation plate 3 was heat-treated at Tg + 88 ° C., and the stretching direction (optical axis) was at an angle A with respect to the reference direction c.
It is arranged to be 45 ゜.

In addition, on the surface of the liquid crystal cell 2 on which the retardation plate is not provided and on the retardation plate 3, the angle P1 of the polarizer is 135 ° and the angle P2 is 90 ° with respect to the reference direction c. Polarizing plates 1 and 4 (LLC2-81-18: manufactured by Sanritsu Electric Co., Ltd.) are installed respectively.

At this time, the set value of the retardation of the retarder 3 is 0.
499 μm.

When such a liquid crystal display device was multiplex-driven at a duty of 1/200 and examined the contrast ratio,
It was 14 in black and white display.

The contrast after leaving the liquid crystal display device at a high temperature of 70 ° C. for 500 hours still maintained a high contrast of 12.

On the other hand, in the case of a liquid crystal display element using a conventional retardation plate that has not been subjected to the heat treatment as described above, the temperature is reduced to 70 ° C.
The contrast ratio dropped to less than half after only 20 hours of standing.

As described above, by performing the heat treatment on the retardation plate 3 in a specific temperature range, a retardation plate having a small change in retardation value can be obtained. Further, by using such a retardation plate for a liquid crystal display element, It was possible to obtain a highly reliable liquid crystal display element in which the contrast was maintained well even when used for a long period of time or when left under severe conditions.

Example 5 Among the retardation plates composed of the propylene-ethylene copolymer described in Example 2, those which were heat-treated at Tg + 95 ° C. were used.
A liquid crystal display device as shown in FIG. 4 was produced.

In FIG. 4, the liquid crystal display element has a first polarizing plate 11,
Liquid crystal cell 12, first retardation plate 13 and second retardation plate 1
4, and the second polarizer 15 are sequentially stacked as viewed from the light incident direction (arrow in the figure). The liquid crystal cell 12 used was the same as the liquid crystal cell 2 of the fourth embodiment.

Here, the phase difference plates 13 and 14 are heat-treated at Tg + 95 ° C., and the first phase difference plate 13 is arranged such that the stretching direction (optical axis) has an angle A1 of 60 ° with respect to the reference direction c. It is.

Then, on this first retardation plate 13, as the second retardation plate 14, the stretching direction has an angle A2 of 20 with respect to the reference direction c.
It is arranged to be ゜.

The retardation values of the first and second retardation films 13 and 14 were both 0.355 μm.

Further, on the surface of the liquid crystal cell 12 on which the retardation plate is not provided and on the second retardation plate 14, the angle P1 of the polarizer with respect to the reference direction c is 76 ° and the angle P2 is 115 °. The polarizing plates 11 and 15 (LLC2-92-18: manufactured by Sanritsu Electric Co., Ltd.) are installed respectively so that

The contrast ratio when such a liquid crystal display element is driven in a multiplex of 1/200 datum is a black and white display.
It was 25.

The contrast after the liquid crystal display device was left at a high temperature of 70 ° C. for 500 hours was still 20 at a high contrast.

On the other hand, in the case of a liquid crystal display element using a conventional retardation plate that has not been subjected to the heat treatment as described above, the temperature is reduced to 70 ° C.
The contrast ratio dropped to less than half after only 20 hours of standing.

Thus, by performing the heat treatment on the retardation plates 13 and 14 in a specific temperature range, a retardation plate with a small change in retardation value can be obtained, and such a retardation plate can be used for a liquid crystal display device. With long use,
In addition, a highly reliable liquid crystal display element in which the co-trust is favorably maintained even under severe conditions was obtained.

Note that, in the above-described embodiment, an example in which a polypropylene-based retardation plate is used has been described. However, even when a retardation plate other than a polypropylene-based retardation plate is used, the same effect can be obtained by performing the heat treatment according to the present invention. Of course.

In addition, as long as the liquid crystal display element uses a retardation plate as an optical function, it can be combined with a liquid crystal panel in any operation mode to maintain good contrast and improve reliability. it can.

[Effects of the Invention] As described above, according to the present invention, a retardation plate having excellent durability can be obtained by an easy and inexpensive method, and by using this retardation plate, a stable and high contrast can be obtained. It is possible to obtain a liquid crystal display element that keeps.

That is, the present invention greatly contributes to quality improvement and reliability improvement.

[Brief description of the drawings]

FIGS. 1, 2 and 3 are diagrams showing the heat treatment temperature of the retardation plate according to one embodiment of the present invention and the retardation change rate of the retardation plate after the high-temperature storage test, and FIG. Schematic configuration diagram of a liquid crystal display element using a retardation plate according to one embodiment,
FIG. 5 is a schematic structural view of a liquid crystal display device using a retardation plate according to another embodiment of the present invention, and also a diagram for explaining a conventional retardation plate, and FIG. 6 is a retardation of the retardation plate. FIG. 7 is a diagram showing the relationship between the amount of retardation deviation of the retardation plate and the contrast ratio, and FIG. 8 is a diagram showing the change over time in the rate of change in the contrast ratio of the liquid crystal display element. 1, 11 first polarizing plate 2, 12 liquid crystal cell 3, 13, 14 retardation plate 4, 15 second polarizing plate

Continuation of the front page (72) Inventor Mitsuo Kamura 10-25-704, Chikkocho, Tokuyama-shi, Yamaguchi (72) Inventor Naoki 7-3, Hanabatake-cho, Tokuyama-shi, Yamaguchi (56) References JP-A-55-55 123426 (JP, A) JP-A-60-97323 (JP, A) JP-A-1-118805 (JP, A) JP-A-60-24502 (JP, A) JP-A-63-58302 (JP, A) JP-A-2-244006 (JP, A) JP-A-3-21902 (JP, A) JP-A-3-235902 (JP, A) JP-B-53-11228 (JP, B2) (58) (Int.Cl. ⁶ , DB name) G02B 5/30

Claims (4)

(57) [Claims] 1. A retardation film in which a thermoplastic resin is a film stretched at a first temperature, and the film is heat-treated at a second temperature lower than the first temperature. When the second temperature is T (° C.) and the glass transition point of the thermoplastic resin is Tg (° C.), the second temperature T is represented by the following general formula: Tg + 65 ≦ T ≦ Tg + 110 (I) A retardation plate that satisfies the above and is smaller than 100 ° C. 2. A method of stretching a thermoplastic resin at a first temperature to form a film, and subjecting the film to a heat treatment at a second temperature lower than the first temperature, a general formula: Tg + 65 ≦ T ≦ Tg + 110 (I) (where Tg represents the glass transition point (° C.) of the thermoplastic resin, and T represents the second temperature (° C.) indicating the heat treatment temperature), and 100 A method for manufacturing a retardation plate, wherein a heat treatment is performed on the film at a second temperature T lower than 0 ° C. 3. The method according to claim 2, wherein the heat treatment is performed on the film-like material at a free end or under a limited shrinkage of 5.0% or more. 4. A liquid crystal cell having a liquid crystal composition sandwiched between a pair of substrates having an electrode surface, a polarizing plate disposed on one surface of the liquid crystal cell, and disposed on the other surface of the liquid crystal cell. In the liquid crystal display device having a retardation plate, the retardation plate is formed by adding a thermoplastic resin film stretched at a first temperature to a film-like material having a general formula: Tg + 65 ≦ T ≦ Tg + 110 (I) However, Tg satisfies the glass transition point (° C.) of the thermoplastic resin, T is the second temperature lower than the first temperature and represents the heat treatment temperature (° C.), and is lower than 100 ° C. A liquid crystal display element which has been subjected to a heat treatment at a second temperature T.