JPH0694917A - Phase-difference film - Google Patents

Abstract

(57) [Summary] [Structure] The repeating unit is represented by the general formula:-(Ph-X ₁ -Ph-X ₂ -────Ph-
X _i ) _n − (wherein X _{1 to} X _i are a bonding group or a direct bond connecting aromatic rings, and at least one is an SO ₂ group). And retardation film. [Effect] The wavelength dispersion characteristic of birefringence is large, and it is excellent in heat resistance, moist heat resistance and the like.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a retardation film used in a liquid crystal display.

[0002]

2. Description of the Related Art STN (Super Twisted Nematic) used as a display device for various OA equipment
Since the liquid crystal display utilizes the birefringence of liquid crystal molecules, the intensity of light passing through the liquid crystal cell varies depending on the wavelength,
Therefore, there is a problem that the display is colored. In order to solve this problem, there is known a method of compensating with a retardation film having a specific retardation to solve the above coloring problem.

One of the important optical characteristics of the retardation film is the wavelength dispersion characteristic of birefringence. In order to improve the contrast and hue characteristics of liquid crystal displays, especially STN type liquid crystal displays, it is necessary to match the wavelength dispersion characteristics of liquid crystals (liquid crystal cells) used for STN.
That is, the incident light passes through the polarizing plate on the back surface to become linearly polarized light, then enters the liquid crystal layer and changes to elliptically polarized light. Since the degree of elliptically polarized light varies depending on the wavelength, the intensity of transmitted light differs, and the display is colored. Therefore, in order to prevent coloring, it is necessary to perform phase compensation for returning elliptically polarized light to linearly polarized light again.

In the STN type liquid crystal display, a liquid crystal material having a large wavelength dispersion characteristic of birefringence tends to be used for the purpose of high-speed response and high definition, and development of a retardation film having a large wavelength dispersion characteristic is required. Has been.

Conventionally, as retardation films, polyvinyl alcohol (JP-A-2-244006), vinyl chloride resin (JP-B-45-34477, JP-A-56-125702), polyarylate (JP-A-1-244006). 201607, JP-A-3-155502), methacrylic resin (JP-A-3-23404), polycarbonate (JP-B-41-12190, JP-A-56-130703, JP-A-1-20)
1608, JP-A-2-89006, JP-A-3-235902), acrylonitrile resin (JP-A-56-125702), styrene resin (JP-A-56-125703), vinylidene fluoride resin Mixture of methyl methacrylate (JP-A-2-186302,
JP-A-3-15005), high molecular weight acrylic polymer (JP-A-3-194503), polyolefin resin (JP-A-60-2)
No. 4502, JP-A No. 63-167304), and those using a propylene-α-olefin copolymer (JP-A No. 3-21902) have been proposed.

[0006] These retardation films have practical problems due to insufficient heat resistance, heat and moisture resistance, etc. Also, since the above-mentioned birefringence wavelength dispersion characteristics are not large, STN type liquid crystal is used. There is a problem that it cannot match the wavelength dispersion characteristics of the display.

[0007]

An object of the present invention is to obtain a retardation film which has a large wavelength dispersion characteristic of birefringence and is excellent in heat resistance, wet heat resistance and the like.

[0008]

In the present invention, the repeating unit is represented by the general formula:-(Ph-X ₁ -Ph-X ₂ ------- Ph-
X _i ) _n- (wherein X _{1 to} X _i are a bonding group or a direct bond connecting aromatic rings, at least one is a SO ₂ group, and Ph represents an aromatic ring) The present invention relates to a retardation film comprising a resin.

At least one SO ₂ group is present in the repeating unit of the aromatic polysulfone resin in the present invention. Other than the SO ₂ group, those linking the aromatic ring include an aliphatic group, a bonding group such as O, S, CO, COO, CONH, or a direct bond of the aromatic ring. In particular,
What is used for the retardation film of the present invention is S
A direct bond such as O ₂ , O or an aromatic ring is preferable. Specific examples of the aromatic polysulfone-based resin of the present invention include those having the following repeating units, but the present invention is not limited thereto.

-(Ph-SO ₂ -Ph-O-Ph-C (Me) ₂ -P
_{h-O) n - - (} Ph-SO 2 -Ph-O) n - - (Ph-SO 2 -Ph-O-Ph-O) n - - (Ph-SO 2 -Ph-O-Ph-Ph _{-O) n - - (Ph-} SO 2 -Ph-Ph-SO 2 -Ph-O-P
h-O) _n-

The aromatic polysulfone resin of the present invention is generally prepared in the presence of an alkali metal compound in an organic polar solvent.
It can be produced by a polycondensation reaction between a dihalogenodiphenylsulfone compound and a dihydric phenol compound, or a polycondensation reaction between an alkali metal di-salt of a dihydric phenol previously synthesized and a dihalogenodiphenylsulfone compound.

Specific examples of the dihydric phenol compound include:
For example, hydroquinone, catechol, resorcin,
In addition to 4,4′-biphenol, at least one hydrogen atom of bis (hydroxyphenyl) alkanes, dihydroxydiphenylsulfones, dihydroxydiphenylethers, or their benzene ring is a suitable substituent (eg, methyl group, ethyl group). Group, a lower alkyl group such as a propyl group, or a substituent such as a lower alkoxy group such as a methoxy group and an ethoxy group). It is also possible to use a mixture of two or more of the above dihydric phenol compounds.

In the present invention, it is preferable to use hydroquinone and 4,4'-biphenol as the dihydric phenol compound in a specific charging ratio in order to improve the heat resistance and mechanical properties of the aromatic polysulfone resin.

That is, repeating unit (I) of the following formula formed by condensation of hydroquinone and dihalogenodiphenyl sulfone compound,

[Chemical 1] And a repeating unit (II) of the following formula formed by the condensation of 4,4'-biphenol and a dihalogenodiphenyl sulfone compound

[Chemical 2] The ratio of 0 to 70:30 to 100 (mol%), especially 10 to 6
An aromatic polysulfone-based resin having a ratio of 0:40 to 90 (mol%) is preferable.

The dihydric phenol compound is preferably used in a substantially equimolar amount with the dihalogenodiphenyl sulfone compound. In order to control the molecular weight of the aromatic polysulfone-based resin produced, the dihydric phenol compound may be used in an equimolar amount to a slight excess amount or an excessive amount amount. For this purpose, small amounts of monohalogenodiphenyl compounds or monohydric phenol compounds can be added to the polymerization solution.

Examples of the dihalogenodiphenyl sulfone compound include 4,4'-dichlorodiphenyl sulfone and 4,4'-difluorodiphenyl sulfone. As the alkali metal compound, an alkali metal carbonate, an alkali metal hydroxide, an alkali metal hydride, or
Examples thereof include alkali metal alkoxides.
Particularly, sodium carbonate and potassium carbonate are preferable.

The organic polar solvent is not particularly limited as long as it dissolves the produced polymer at the polycondensation temperature. For example, dimethyl sulfoxide, sulfoxide solvent such as diethyl sulfoxide, N, N-dimethylformamide, amide solvent such as N, N-dimethylacetamide, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone and other pyrrolidone -Based solvents, piperidone-based solvents such as N-methyl-2-piperidone, 1,3-dimethyl-2-imidazolinone, 1,3-diethyl-
Examples thereof include 2-imidazolinone-based solvents such as 2-imidazolinone, hexamethylene sulfoxide, γ-butyrolactone, sulfolane, and diphenyl compounds such as diphenyl ether and diphenyl sulfone. Particularly, N-methyl-2-pyrrolidone and N, N-dimethylacetamide are preferably used.

The polycondensation temperature is usually 140 to 340 ° C.
Water produced as a by-product during the reaction is accompanied by an inert gas flow outside the system,
Alternatively, it is preferable to distill off with an azeotropic dehydrating agent in order to produce a high molecular weight polyaryl ether. Examples of azeotropic dehydrating agents include benzene, toluene, xylene, and aromatic halogen compounds. At the end of the polycondensation, a methylating agent such as chloromethane may be added to the reaction solution as a polymer terminal stopper at 90 to 150 ° C.

The inorganic solid such as the alkali metal compound or the alkali metal halide remaining in the reaction solution can be separated by filtering or centrifuging the reaction solution. After separating the inorganic solid contained in the reaction solution by filtration or centrifugation, or without separating the inorganic solid, adding a poor solvent to the reaction solution to separate the aromatic polysulfone resin as a precipitated solid. You can

Examples of the poor solvent for the aromatic polysulfone resin include alcohols such as methanol, ethanol, isopropanol and butanol, nitriles such as acetonitrile, water and the like.
Further, two or more kinds of the above compounds can be mixed and used. Further, the poor solvent may contain a good solvent for the polymer such as the above-mentioned polymerization reaction solvent, within the range where the polymer can be precipitated.

The precipitated solid is washed with a poor solvent and dried to obtain an aromatic polysulfone resin powder.

The molecular weight of the aromatic polysulfone-based resin of the present invention is not particularly limited, but the reduced viscosity (ηsp / c) measured at 30 ° C. for a solution of N-methyl-2-pyrrolidone at a concentration of 0.5 g / 100 ml. However, 0.2 to 2 is preferable,
Those of 0.4 to 1.5 are particularly preferably used. When the molecular weight is smaller than the above range, the physical properties of the film are lowered, and when it is larger than the above range, the film forming property of the film is deteriorated, which is not preferable.

As a method for forming a film from the aromatic polysulfone resin of the present invention, known methods such as a solution casting method and an extrusion molding method can be used.

It is important that the retardation film has excellent thickness uniformity, and the solution casting method is preferable.

In the solution casting method, a solution obtained by dissolving an aromatic polysulfone resin in a solvent such as methylene dichloride is cast on a rotating drum or belt and dried to obtain a film.

As a solution of the aromatic polysulfone resin,
The solution obtained by separating the inorganic solid such as the remaining alkali metal compound or alkali metal halide from the above polycondensation reaction solution may be used as it is without precipitating the polymer.

The above-mentioned film is further uniaxially or biaxially stretched to impart birefringence to give a retardation film.

As the stretching method, known methods such as longitudinal uniaxial stretching or transverse uniaxial stretching method can be used as the uniaxial stretching method. The stretching conditions are not particularly limited, but the film temperature is preferably 220 to 240 ° C. The stretching ratio is preferably 5 to 70%.

The retardation film needs to have a specific retardation capable of solving the coloring problem of the applied liquid crystal display by compensation. Retardation (R) is birefringence (Δn) and thickness (t)
(R = Δn · t), and by adjusting the birefringence and the thickness, a retardation film having a desired retardation can be obtained.

The thickness of the retardation film of the present invention is not particularly limited, and is preferably 20 μm to 200 μm in view of productivity and handleability.

[0031]

INDUSTRIAL APPLICABILITY The retardation film of the present invention has a large birefringence wavelength dispersion characteristic, is excellent in heat resistance, moist heat resistance and the like, and uses an S liquid crystal material having a large birefringence wavelength dispersion characteristic
It matches the TN liquid crystal display, and can improve the contrast and hue characteristics of the liquid crystal display.

[0032]

EXAMPLES In the present invention, birefringence and its wavelength dispersion characteristics were evaluated by the rotation analyzer method.

Example 1 (Production of Aromatic Polysulfone Resin) 4,4'-Dichlorodiphenylsulfone 73.3 g (0.255 mol), Hydroquinone 1
3.7g (0.124mol) and 4,4'-biphenol 23.2g (0.124mo)
l) was added to 30 ml of azeotropic dehydration toluene and 300 ml of N-methyl-2-pyrrolidone under a nitrogen atmosphere and dissolved, and then dissolved in nitrogen.
37.9 g of potassium carbonate which had been heat-treated at 70 ° C. for 30 minutes was stirred and reacted at 180 ° C. for 8 hours in a nitrogen atmosphere to obtain a polymerization solution. After completion of the reaction, in order to separate the inorganic substances from the polymerization solution, the polymerization solution was obtained by filtering at a nitrogen pressure of 1.5 kg / cm ² . 300 g of the polymerization solution was poured into 2000 ml of ethanol, the polymer was precipitated while stirring at 5000 rpm, filtered and separated to obtain a polymer. After washing 50 g of this polymer with 500 ml of ethanol, 90
The powder was dried at ° C to obtain a powder of aromatic polysulfone resin.

The reduced viscosity (ηsp / c) of the obtained aromatic polysulfone-based resin (N-methyl-2-pyrrolidone was used as a solvent.
(Measured at 30 ° C. for a 0.5 g / 100 ml solution) was 0.52. The ratio of repeating units (I) to repeating units (II) is 50:50.
(Mol%)

The aromatic polysulfone resin was dissolved in methylene chloride and formed into a film having a thickness of 100 μm by a solvent casting method.

This film is stretched at a temperature of 230 ° C. and a stretch ratio.
It was uniaxially stretched at 1.3 times to obtain a retardation film.

The retardation of this retardation film is
It was 540 nm. The wavelength dependence of birefringence is shown in FIG.

Comparative Examples 1 to 3 The wavelength dependence of the birefringence of the polycarbonate resin (Comparative Example 1), the polymethacrylate resin (Comparative Example 2) and the polyvinyl alcohol resin (Comparative Example 3) produced in the same manner as in the Examples was examined. It is shown in FIG.

[Brief description of drawings]

FIG. 1 shows wavelength dependence of birefringence of a retardation film.

Claims (1)

[Claims] 1. The repeating unit has the general formula:-(Ph-X ₁ -Ph-X ₂ ---------- Ph-
X _i ) _n- (wherein X _{1 to} X _i are a bonding group or a direct bond connecting aromatic rings, at least one is a SO ₂ group, and Ph represents an aromatic ring) A retardation film comprising a resin.