JPH04365002A - Phase difference compensating plate - Google Patents

Abstract

PURPOSE:To provide a phase difference compensating plate with wavelength dependency capable of compensating the phase difference of an STN liquid crystal in all wavelengths of visible light. CONSTITUTION:A film made of a condensation copolymer of 4,4'- dichlorodiphenylsulfone and sodium salt of bisphenol A is drawn in one-axis direction, the thickness (d) after it is drawn is set to 30-150mum, and the product of the thickness (d) and the difference n between the refraction factor nx in the drawing direction and the refraction factor ny in the perpendicular direction to the drawing direction in the plane of the film is set within the range 200-800nm.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to liquid crystal displays, etc.
The present invention relates to a retardation compensating plate suitable for compensating for retardation caused by birefringence of liquid crystal to improve display.

0002

[Prior Art] In recent years, the display capacity of liquid crystal display devices has increased.
STN (Super Twisted Nemat) can accommodate larger screens and achieve high contrast.
ic) Liquid crystals are being used in personal computers and word processors.

[0003] A display device using an STN liquid crystal uses elliptically polarized light due to the birefringence of the STN liquid crystal, and the display color is mainly blue or yellow. Therefore, it is being considered to change the display color to black and white by compensating for the phase difference due to birefringence of the STN liquid crystal and returning the elliptically polarized light to linearly polarized light.

Means for compensating the phase difference include the D-STN method, which uses a compensating liquid crystal cell with the same configuration as the liquid crystal display cell but with only the opposite phase, and the F-STN method, which uses a birefringent film.
There is also a TN method. Among these, the FTN method is D-STN.
This is a desirable display device because it is lighter and thinner than conventional display devices, and also has cost advantages.

[0005] In order to make the display colors of a liquid crystal display black and white using the FTN method, the birefringent film used as a retardation compensator has the ability to compensate for retardation at all wavelengths of visible light. It is necessary to have wavelength dependence of phase difference compensation.

[0006] As a retardation compensation plate used in the FTN system, polycarbonate or polyvinyl alcohol has been conventionally stretched to orient the molecules to achieve retardation compensation, and polyarylate is also used as described in Japanese Patent Laid-Open No. 1-2016
This is proposed in Publication No. 07 and the like. However, in both cases, the wavelength dependence is insufficient.

[0007] Furthermore, in order to compensate for phase differences at all wavelengths of visible light, Japanese Patent Laid-Open No. 2-120804 proposes stacking a plurality of phase difference compensating plates. However, in this case as well, there are problems such as a decrease in yield due to the difficulty of laminating the stretched axes of the stretched films, which are retardation compensation plates, in a desired state, and an increase in cost due to the use of two or more retardation compensation plates. A point occurs.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to obtain a retardation compensating plate having wavelength dependence capable of compensating for the retardation of STN liquid crystal at all wavelengths of visible light.

[0009]

[Means for Solving the Problems] Since the Abbe number, which is a value unique to a material, is related to the wavelength dependence of phase difference compensation, the present invention uses a new material discovered in consideration of the Abbe number, The above-mentioned problem has been overcome by using a phase difference compensating plate under the following conditions.

That is, the present invention provides weight average molecular weight (Mw
) is in the range of 5 x 104 to 2 x 105 in terms of styrene, and is formed by uniaxially stretching a film or sheet made of a co-condensation polymer of 4,4'-dichlorodiphenylsulfone and sodium salt of bisphenol A. A film or sheet with a thickness (d) of 3 after stretching.
from 0μ to 150μ, and the refractive index in the stretching direction (n
The product of the difference (Δn) in the refractive index (nY) in the plane of the film or sheet perpendicular to the stretching direction and the thickness is 2
The present invention provides a retardation compensating plate characterized in that the wavelength is in the range of 00 nm to 800 nm.

The cocondensation polymer constituting the film or sheet used in the present invention is a type of polysulfone obtained by cocondensation polymerization of 4,4'-dichlorodiphenylsulfone and sodium salt of bisphenol A. Weight average molecular weight in terms of 5 x 104 to 2 x 1
It is in the range of 0.05.

[0012] As a method for forming a film or sheet of the co-condensed polymer, a solution casting method is preferable, that is, a solution of the co-condensed polymer dissolved in a solvent such as methylene chloride is cast onto a belt or drum. The method is to obtain a film or sheet by casting (casting), drying, and then peeling off. In this case, if the molecular weight is less than 5 x 104, the solution becomes unstable due to gelation, and the toughness of the formed film is also impaired. On the other hand, if it exceeds 2×10 5 , the solution viscosity increases and the concentration decreases, making it impossible to form a film.

[0013] As a method for stretching the film or sheet obtained by the solution casting film forming method, both vertical uniaxial roll stretching and horizontal uniaxial tenter stretching are possible. It is important to ensure that the

[0014] As for the stretching conditions, the temperature of the film or sheet is 170°C to 220°C, preferably 190°C.
to 210°C, and the stretching ratio is preferably 1.1 to 2.0 times. The thickness after stretching is preferably 30μ to 150μ. The larger the stretching ratio is, the larger the retardation can be obtained, and the thicker the thickness, the larger the retardation can be obtained. If it is less than 30μ, the mechanical strength is low and it is not suitable for practical use, and if it exceeds 150μ, even at the lowest stretching ratio, the retardation will not be suitable for compensating for the retardation of STN liquid crystal. The retardation suitable for compensating the retardation of STN liquid crystal is the refractive index in the stretching direction (nX
) and the difference in refractive index (nY) in the plane of the film or sheet in the direction perpendicular to the stretching direction (Δn) and the thickness is 200
It is in the range of 800 nm to 800 nm.

[0015]

[Operation] A film or sheet of the co-condensed polymer is uniaxially stretched to a thickness of 30μ to 150μ,
The difference between the refractive index (nX) in the stretching direction and the refractive index (nY) in the direction perpendicular to the stretching direction within the plane of the film or sheet (
When the product of Δn) and thickness is in the range of 200 nm to 800 nm, the retardation of the STN liquid crystal and the retardation of this retardation compensator will be almost equal at any wavelength, improving the retardation compensation performance and producing more desirable black and white images. It can be displayed.

[0016]

[Examples] The present invention will be explained in more detail below using examples. Example 1 A resin having a weight average molecular weight of 7 x 104 in terms of styrene was dissolved in methylene chloride to prepare a 20% solution by cocondensation polymerization of 4,4'-dichlorodiphenylsulfone and the sodium salt of bisphenol A. This was cast onto a rotating chrome-plated steel belt, dried and peeled off to obtain a 75μ thick film. This film was stretched 1.7 times in the width direction using a horizontal uniaxial tenter stretching machine heated to 200°C.

The retardation of the obtained film was measured under a perpendicular Nicol condition, and the results were as shown in FIG. here,
As an evaluation measure of how well the retardation matches the retardation of STN liquid crystal, the ratio of the retardation at 450 nm to the retardation at 590 nm was defined as wavelength dependence, and is summarized in Table 1. At the same time, the thickness of the film, the difference (Δn) between the refractive index in the stretching direction (nX) and the refractive index in the direction perpendicular to the stretching direction within the plane of the film (nY) measured with an Abbe refractometer, and the thickness (d)
The product (Δn×d) is also shown in Table 1. Example 2 A resin having a weight average molecular weight of 1.2 x 105 in terms of styrene was dissolved in methylene chloride to make a 13% solution by cocondensation polymerization of 4,4'-dichlorodiphenylsulfone and sodium salt of bisphenol A. . This was cast onto a rotating chrome-plated steel belt, dried, and peeled off to obtain a film with a thickness of 115 μm. This film was stretched 1.4 times in the width direction under the same conditions as in Example 1.

The retardation of the obtained film was measured under a perpendicular Nicol condition, and the results were as shown in FIG. The thickness, Δn×d, and wavelength dependence after stretching were as shown in Table 1. Comparative Example Commercially available polycarbonate resin (weight average molecular weight in terms of styrene: 7 x 104) was dissolved in methylene chloride.
It was made into a 0% solution. This is cast onto a rotating chrome-plated steel belt, dried and peeled off to a thickness of 7.
A 5μ film was obtained. This film was stretched 1.4 times in the width direction using a horizontal uniaxial tenter stretching machine heated to 175°C.

The retardation of the obtained film was measured under a perpendicular Nicols condition, and the results were as shown in FIG. The thickness, Δn×d, and wavelength dependence after stretching were as shown in Table 1. Further, Table 1 shows the wavelength dependence of STN liquid crystal for comparison.

[0020]

[Table 1]

From FIG. 1, it can be seen that the film of the example has almost the same retardation as the STN liquid crystal in all wavelength ranges of visible light, and from Table 1, the wavelength dependence of the film of the example It can be seen that the value of stability is almost equal to the value of STN liquid crystal.

[0022]

Effects of the Invention The retardation compensator of the present invention has a STN of all wavelengths of visible light even if it is a single retardation compensator.
It has wavelength dependence that can compensate for the phase difference of the liquid crystal, has excellent phase difference compensation performance, and can provide desirable black and white display.

[Brief explanation of the drawing]

FIG. 1 is a graph of retardation versus visible wavelength of films of Examples and Comparative Examples according to the present invention, and STN liquid crystals.

Claims (2)

[Claims] Claim 1: 4,4 having a weight average molecular weight (Mw) in the range of 5 x 104 to 2 x 105 in terms of styrene.
'-dichlorodiphenylsulfone and bisphenol A
A film or sheet formed by uniaxially stretching a film or sheet consisting of a co-condensation polymer of a sodium salt of
μ, and the product of the difference (Δn) between the refractive index in the stretching direction (nX) and the refractive index (nY) in the in-plane direction of the film or sheet perpendicular to the stretching direction and the thickness is 200 nm to 8
A retardation compensating plate characterized in that the retardation compensation plate has a phase difference in the range of 00 nm. 2. The retardation compensating plate according to claim 1, wherein the film or sheet is uniaxially stretched at a stretching ratio of 1.1 to 2.0 times.