JPH07287118A - Phase film - Google Patents

Abstract

PURPOSE:To obtain wavelength dispersion of a large phase difference without coloring the image of a liquid crystal display device by constituting the phase film of polycarbonate having a repeating unit expressed by specified formula so that the film shows phase difference of specified conditions. CONSTITUTION:This film consists of polycarbonate containing >1mol% repeating unit expressed by formula. The ratio of phase difference Re(450)/Re(550) is specified to >1.080, wherein Re(450) is the phase difference at 450nm wavelength and Re(550) is the phase difference at 550nm wavelength. In formula, R1-R4 are independently hydrogen atoms or alkyl groups having l-5 carbon number. This polycarbonate contains the repeating unit expressed by formula by 1-100mol% of the total amt. If the amt. is <1mol%, the ratio Re(450)/Re(550) is smaller than 1.080, which is not preferable because enough compensation for phase difference is impossible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a display device such as a liquid crystal,
The present invention relates to a retardation film useful for optical applications such as an optical element such as a wave plate.

[0002]

2. Description of the Related Art In recent years, display devices such as liquid crystals, which have been put into practical use, have been attracting attention because of their low power consumption and excellent image quality. In this liquid crystal display device, various polymer films according to the purpose are polarizing plates,
It is used as a protective layer, retardation plate or electrode substrate.

A retardation film constituting a retardation plate is used for improving the visibility of an image in a liquid crystal display device, and converts elliptically polarized light transmitted through a liquid crystal layer into linearly polarized light, that is, a retardation film. Is responsible for compensation.

For example, in the STN type liquid crystal display device,
A retardation film having a retardation of 400 to 650 nm in the film plane is used. As the polymer material of this retardation film, each film such as uniaxially stretched polycarbonate or polyvinyl alcohol is mainly used. In particular, a polycarbonate represented by a polycarbonate obtained from bisphenol A and phosgene (hereinafter abbreviated as PC-A) is a colorless polymer having well-balanced heat resistance and various mechanical properties. It has excellent mechanical properties, and has extremely good moldability, transparency, and optical characteristics. Further, a film having high surface homogeneity without streaks and defects can be produced by the solution casting method, and it is relatively easy to obtain a film having a desired retardation by stretching.

Further, in the TN type liquid crystal display device, an in-plane retardation is 30 nm or less, preferably 10 nm or less, and a retardation film having a different in-plane refractive index and film thickness direction refractive index is used. ing. PC-A is also used as the polymer material of such a retardation film for the reasons described above.

By the way, recently, studies for increasing the response speed of the liquid crystal display element have been actively conducted, and a liquid crystal material having a larger birefringence than that of the conventional one has been used for the liquid crystal display element. However, since the wavelength dispersion of the retardation of the liquid crystal layer is larger than that of the conventional one, it becomes impossible to compensate the retardation in the entire visible light region with the conventionally used polycarbonate film, and as a result, the image of the display device is colored. I started to do it. Therefore, in order to realize black-and-white display, a retardation film having a wavelength dispersion with a large retardation that matches the liquid crystal layer is required.

For example, it is known that an aromatic polyether sulfone film has a large wavelength dispersion of retardation, and its application to the retardation film is being actively investigated. However, aromatic polyether sulfones are generally formed by a melt extrusion method, particularly the T-die method, and sufficient surface homogeneity is not obtained due to the generation of die lines or fish eyes, which is a problem peculiar to the T-die method. It has not been put to practical use. Also, if a film showing wavelength dispersion with a large retardation cannot be obtained with a single material,
It is also known that it can be realized by laminating a plurality of films with the same optical axis. However, using two or more films leads to an increase in cost, and it is technically very difficult to stack them while controlling the optical axis.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a polycarbonate retardation film having a large retardation wavelength dispersion in which an image on a liquid crystal display device is not colored.

[0009]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that (1) a retardation wavelength dispersion of a film made of a polycarbonate having a diphenyl sulfide derivative in the main chain skeleton is large. thing,
(2) A smooth film in which the polycarbonate is dissolved in a solvent at a high concentration, the solution composition (dope) thereof has excellent stability, is transparent and is optically homogeneous without causing cloudiness from the dope. The present invention has been accomplished by finding that the above can be manufactured.

That is, the present invention comprises a polycarbonate containing at least 1 mol% of a repeating unit represented by the following general formula (I), and has a retardation Re (450) at a wavelength of 450 nm and a retardation Re (550 at 550 nm. Ratio (Re (450) / Re (550)) is 1.080 or more.

[0011]

[Chemical 2]

(In the formula (I), R 1, R 2, R 3 and R 4 are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms)

The present invention is described in detail below. The retardation film of the present invention has a repeating unit represented by the following general formula (I) of 1 to 100 mol% and a repeating unit represented by the following general formula (II) with respect to the total amount of repeating units constituting the polycarbonate. It is formed from a polycarbonate containing 0 to 99 mol% of units.

[0014]

[Chemical 3]

[0015]

[Chemical 4]

(In the formula (I), R 1, R 2, R 3 and R 4 are hydrogen atoms or alkyl groups having 1 to 5 carbon atoms. Formula (II)
Wherein X is a divalent hydrocarbon group having 1 to 15 carbon atoms, R
5, R6, R7 and R8 are each independently a hydrogen atom, a bromine atom or a hydrocarbon group having 1 to 4 carbon atoms. )

In the formula (I), R1, R2, R
It is preferable that 3, R4 are all hydrogen atoms, or R1 and R3 are hydrogen atoms and R2 and R4 are methyl groups.
In the formula (II), X is a divalent hydrocarbon group having 1 to 15 carbon atoms and is selected from a divalent aliphatic hydrocarbon group having 1 to 15 carbon atoms, an alicyclic hydrocarbon group and an alkylene group. . Specifically, methylene group, 1,1-ethylene group, 2,2-propylene group, aliphatic hydrocarbon group such as 4-methyl-2,2-pentylene group, 1,1-cyclohexylene group, 3,3,5 Alicyclic hydrocarbon group such as -trimethyl-1,1-cyclohexylene group, 1
-Phenyl-1,1-ethylene group, diphenylmethylene group, 1,
Examples thereof include aralkylene groups such as 1-fluorenylene group. Particularly preferred are 2,2-propylene group and 1,1-cyclohexylene group.

R5, R6, R7 and R8 are each independently a hydrogen atom, a bromine atom or a hydrocarbon group having 1 to 4 carbon atoms, preferably all hydrogen atoms or all methyl groups. Is.

The repeating unit represented by the general formula (I) is contained in an amount of 1 to 100 mol% based on the total amount. If it is less than 1 mol%, the phase difference Re (450) at a wavelength of 450 nm
Of phase difference Re (550) at 550 nm, R
Since e (450) / Re (550) becomes smaller than 1.080, it approaches that of conventional polycarbonate (PC-A), and the phase difference cannot be sufficiently compensated, which is not preferable.
The content of such repeating units can be appropriately adjusted according to the desired wavelength dispersion of retardation. For example, when it is desired to increase the phase difference of the retardation of PC-A, which is a general polycarbonate, by a little, it may be 1 to 50 mol%, and when it is considerably large, it may be 50 to 100 mol%. Good. When heat resistance of about 100 ° C is required, 80 mol% or less, 120
It is preferably 65 mol% or less in the case of about 130C, 50 mol% or less in the case of about 130C, and 35 mol% or less in the case of about 150C. When the demand for optical properties such as color tone of the film is extremely strict, it is 1 to 50 mol%, preferably 1 to 20 mol%. Re (450) / R
The upper limit of e (550) depends on the size of the wavelength dispersion of the desired retardation, but is practically 1.130 or less, preferably 1.1.
It is 20 or less.

The polycarbonate of the retardation film of the present invention is synthesized by a known method such as an interfacial polycondensation method using phosgene or a melt polycondensation method. Legal is preferred.

The molecular weight of the above polycarbonate is GPC.
By polystyrene equivalent number average molecular weight (Mn) 10,000
It is preferably used if it is not less than 400,000 and not more than 400,000. Mn is 10,
If it is 000 or less, the mechanical strength of the obtained film may be insufficient, and if it is 400,000 or more, the viscosity of the solution composition (dope) used when forming a film by the solution casting method becomes too high in handling. Not only difficult, but sometimes difficult to dissolve. Particularly preferably, it is 20,000 to 120,000.

The polycarbonate used in the present invention is soluble in various solvents, and its solution composition (dope) has a high stability. A film with good uniformity can be formed.

A high concentration dope is required to obtain a film having a thickness of 50 to 200 μm by the solution casting method. Examples of the solvent that dissolves the above polycarbonate used in the present invention in a high concentration include polar solvents such as dimethylacetamide, dimethylformamide, pyridine and N-methylpyrrolidone, dichloromethane, chloroform, 1,1,2,2-tetrachloroethane, Examples thereof include halogen-based solvents such as 1,1,2-trichloroethane and cyclic ether-based solvents such as 1,3-dioxolane, 1,4-dioxane and tetrahydrofuran. Of these, halogen-based and cyclic ether-based solvents are preferably used, and cyclic ether-based solvents are more preferable. Since the polar solvent has a high boiling point, the residual solvent in the film-forming film cannot be easily lowered and it is not practical as a film-forming solvent. Although a halogen-based solvent such as dichloromethane is suitable as a solvent for film formation, its influence on environmental pollution is regarded as a problem, and it is necessary to consider solvent recovery and the like. Among the cyclic ether solvents, 1,3-dioxolane is particularly excellent in terms of high-concentration solubility, dope stability, boiling point (76 ° C.), and film-forming property. Tetrahydrofuran has a low boiling point (6
Although it is advantageous for drying at 5 ° C), 1,3-dioxolane is superior from the viewpoint of solubility and solution stability. In addition, 1,4-dioxane has high solubility like 1,3-dioxolane,
Since it has a high boiling point (100 ° C), 1,3-
Dioxolane is superior. A mixed solvent containing 60% by weight or more of a halogen-based or cyclic ether-based solvent may be used. The other solvent used is not particularly limited and may be used in consideration of the effect. The effects referred to here are, for example, by mixing a solvent in a range that does not sacrifice solubility or stability, for example, improving the surface property of a film formed by a solution casting method (leveling effect), evaporation rate or system Viscosity control, crystal suppression effect, etc. The kind and addition amount of the solvent to be mixed may be determined depending on the degree of these effects, and one or two or more kinds may be used as the solvent to be mixed. As the solvent preferably used, a hydrocarbon solvent such as toluene and xylene, a ketone solvent such as acetone, methyl ethyl ketone and cyclohexanone, an ester solvent such as ethyl acetate and butyl acetate, an ether solvent such as ethylene glycol dimethyl ether and methoxy ethyl acetate. Can be given.

The concentration of the dope is 15 to 100 parts by weight, preferably 20 to 90 parts by weight, based on 10 parts by weight of the polycarbonate. If the amount of solvent is more than this, the stability of the solution will not be a problem, but it is not preferable because the working concentration is low, and when the film is formed by the solution casting method using this solution composition, the solution viscosity is low and external disturbance is caused. Is likely to occur, and it is difficult to obtain surface smoothness, which is not preferable. Conversely, if the amount of solvent is less than this, it is difficult to obtain a stable solution. These concentrations are determined mainly in consideration of the stability of the solution and the viscosity of the solution.

If impurities or insoluble matters such as undissolved matters or suspended matters are contained in the obtained dope, or if haze is observed in the dope, they must be removed by a treatment such as filtration. This is because if such treatment is not carried out, not only the optical characteristics of the formed film are deteriorated but also the storage stability of the prepared dope is lowered.

The retardation film of the present invention is preferably obtained by casting the above dope on a supporting substrate and then heating it to evaporate the solvent. The industrial continuous film-forming process generally comprises three steps of casting process, drying process and heat treatment process. The casting step is a step of smoothly casting the dope, the drying step is a step of evaporating and removing most of the solvent from the cast dope, and the heat treatment step is a step of removing the remaining solvent.

In the casting process, a doctor blade method, a reverse roll coater method, a die extrusion method, or the like is used. Industrially, the most common method is to continuously extrude a dope from a die onto a belt-shaped or drum-shaped supporting substrate. The supporting substrate used is not particularly limited, but a glass substrate, a metal substrate such as stainless steel or a ferro type, a plastic film such as polyethylene terephthalate, or the like is used. However, a metal substrate having a mirror-finished surface is most commonly used in order to industrially obtain a homogeneous film having a high degree of optical isotropy, which is the main object of the present invention.

The viscosity of the dope is an extremely important factor in producing the retardation film of the present invention. The viscosity depends on the concentration of polycarbonate, the molecular weight and the type of solvent, but a preferable viscosity is 300 to 50,000 cps.
Is. If it exceeds this range, the fluidity of the solution may decrease, and a smooth film may not be obtained. On the other hand, if it is less than that, the fluidity is too high, and the surface is disturbed due to external disturbance, so that a uniform and smooth film may not be obtained. A more preferable viscosity is 400 to 30,000 cps.

In the drying step, it is necessary to evaporate and remove most of the solvent from the dope cast on the supporting substrate in the shortest possible time. However, the drying conditions should be chosen carefully because they undergo deformation due to foaming when rapid evaporation occurs. In the present invention, it is carried out within the range of the lowest boiling point used, preferably the boiling point of −10 ° C. as an upper limit. Usually, in the initial stage, a method of raising the temperature below the boiling point of the solvent to be used, for example, 30 ° C. sequentially or continuously is adopted. Moreover, you may blow air as needed. Generally, a wind speed in the range of 1 to 20 m / sec is used. If it is less than that, the effect is not sufficient, and conversely, if it exceeds it, a smooth surface cannot be obtained due to wind disturbance, which is not preferable. The preferable wind speed is 2 to 15 m / sec. The wind speed may be changed sequentially or continuously. On the other hand, at this stage the film is on the substrate and is peeled off from the substrate at the end of this step. At this time, if the amount of residual solvent is large, the film is soft and thus flow deformation of the polymer occurs in the film, and if the amount of residual solvent is small, stress adhesion occurs due to high adhesion to the substrate. Therefore, the residual solvent amount is an important factor, and the range of the residual solvent amount is preferably 5 to 30% by weight, more preferably 10 to 20% by weight.

In the heat treatment step, the film peeled from the substrate is further dried so that the residual solvent amount is 3% by weight or less,
It should be preferably 1% by weight or less, more preferably 0.5% by weight or less. If there is a large amount of residual solvent, deformation occurs over time, and if heat is applied in the post-processing step, dimensional change occurs. This is particularly important in liquid crystal display devices because an optically uniform film is required. Industrially, a method of drying while transporting the film by a pintender method or a roll suspension method is adopted. The drying temperature must be selected within a range that does not cause film deformation. That is, a range of (Tg-100 ° C) to Tg, preferably a range of (Tg-80 ° C) to (Tg-10 ° C) is selected. Thermal deformation becomes less likely to occur as the residual solvent decreases. Therefore, it is preferable to employ a method in which the temperature is initially low and then sequentially or continuously. Moreover, you may ventilate similarly to a drying process.

The thickness of the retardation film of the present invention is 10 to
The range of 300 μm is preferable. If it is thicker than 300 μm, it is difficult to remove the residual solvent, and if it is thinner than 10 μm, it is difficult to suppress the thickness unevenness. A more preferable film thickness is 50 to 200 μm.

The retardation film of the present invention may be stretched to obtain a desired retardation depending on the intended use. The stretching method is not particularly limited, but there is a longitudinal stretching method using two pairs of rolls having different peripheral speeds, or a horizontal stretching method using a tenter. The stretching temperature and the stretching ratio are appropriately set to obtain a desired retardation, but the stretching temperature is higher than the glass transition point of the retardation film, and the stretching ratio is 1.01 to 3.00.
It can be done in a double range.

[0033]

According to the present invention, it is possible to obtain a retardation film exhibiting a larger retardation wavelength dispersion than PC-A and having good surface homogeneity. The film is a display element such as STN type liquid crystal or TN type liquid crystal, 1 / 4λ plate, 1 / 2λ
It is suitable for retardation films useful for optical applications such as optical elements such as plates.

[0034]

EXAMPLES The present invention will be described in detail below with reference to examples. However, the present invention is not limited to this. The measurement items performed in the examples were measured by the following methods.

Solution viscosity: B-type viscometer BH manufactured by Tokyo Keiki Co., Ltd.
Use type. Measured at 30 ° C. Total light transmittance and haze value in the visible light region: using an automatic digital haze meter UDH-20D manufactured by Nippon Denshoku Industries Co., Ltd. Phase difference wavelength dispersion: M-150 ellipsometer manufactured by JASCO Corporation is used. Film thickness: Measured with a stylus type film thickness meter manufactured by Anritsu Corporation.

[Reference Examples 1 to 4] Three kinds of polycarbonates having different compositions, which are composed of repeating units represented by the following formula (III), are prepared by the usual interfacial polymerization method using phosgene (hereinafter referred to as PC-MeS / Z). Abbreviated) and a polycarbonate composed of a repeating unit represented by the following formula (IV) (hereinafter PC-SSA
Abbreviated) was synthesized. Table 1 shows the number average molecular weight (Mn) and glass transition point of each polymer obtained.

[0037]

[Chemical 5]

[0038]

[Chemical 6]

[0039]

[Table 1]

[Examples 1 to 4] The polycarbonates obtained in Reference Examples 1 to 4 (PC-MeS / Z (8/2), (5/5), (2/8), PC-SS)
A) is dissolved in dichloromethane and 11.1% and 13.5% respectively
%, 13.5% and 10.0% viscous dopes were prepared. These dopes did not change even after standing for 1 week in a sealed state at room temperature, and no clouding or gelation phenomenon was observed.

The dope was cast on a glass substrate using a doctor blade, dried at 30 ° C. for 20 minutes, at 50 ° C. for 20 minutes, and at 80 ° C. for 20 minutes using a drier having a wind speed of 1.5 m. The film was peeled off. The amount of residual solvent in each film at this point was approximately 15% by weight.
Met. Each film is further heated at 100 ° C for 60 minutes, 13
It was dried at 0 ° C for 120 minutes. PC-MeS / Z (8/2) and PC-
SSA was not dried at 130 ° C. In this way, a retardation film in which the residual solvent amount in each film was 1% by weight or less was obtained.

For each of the retardation films, the film thickness, the total light transmittance, the haze, and the ratio of the retardation Re (450) at a wavelength of 450 nm to the retardation Re (550) at 550 nm, Re (450) / Re (550). Table 2 shows the result of measurement.

As can be seen from Table 2, each physical property of the obtained retardation film was good. Further, the film surface was uniform without foaming, citron skin, or waviness.

Further, each of the retardation films was stretched in the in-plane direction of the film at a stretching ratio of 1.02 at a temperature near the glass transition point. Table 2 also shows the results of measuring the retardation Re (550) at a wavelength of 550 nm in each of the obtained films. Further, when the ratio of the retardation Re (450) at the wavelength of 450 nm to the retardation Re (550) at 550 nm, Re (450) / Re (550), was obtained, it was not different from that before stretching.

[Comparative Example 1] A film was prepared in the same manner as in Example 1 using polycarbonate "C-1400" manufactured by Teijin Chemicals Ltd. The obtained results are shown in Table 2.

[0046]

[Table 2]

Example 5 The polycarbonate obtained in Reference Example (PC-MeS / Z (5/5)) was dissolved in 1,3-dioxolane to give 13.5.
% Dope was prepared. This was cast on a glass substrate using a doctor blade, dried at 30 ° C. for 20 minutes, at 50 ° C. for 30 minutes, and at 80 ° C. for 60 minutes using a drier having a wind speed of 1.2 m, and then the film was peeled off. The residual solvent amount at this point was about 15% by weight. 120 at 100 ° C
Min, and dried at 130 ° C. for 240 minutes to obtain a retardation film having a residual solvent amount of 0.8% by weight. This retardation film had good transparency, and the surface was uniform without foaming, rustling, or waviness.

The retardation film is further heated at 140 ° C.
Then, the film was stretched 1.10 times in the in-plane direction. The obtained film has a retardation of 510 at a wavelength of 550 nm.
nm and wavelength dispersion value Re (450) / Re (550) were 1.090.

When this film was incorporated into an STN type liquid crystal display, monochrome display without coloring was possible.

[Reference Examples 5 to 7] Three polycarbonates (PC-MeS / Z (8/2), (5/5), (2 /
8)) was dissolved in 1,3-dioxolane, 1,4-dioxane and tetrahydrofuran to prepare 13.5% dopes.
The viscosities of these dopes are shown in Table 3. All of them were transparent and did not change even after standing for 1 week in a sealed state at room temperature, and neither clouding nor gelation phenomenon was observed.

[0051]

[Table 3]

[Examples 6 to 14] Each of the nine types of dopes obtained in Reference Examples 5 to 7 was cast on a glass substrate using a doctor blade and then dried using a drier having a wind speed of 1.2 m.
After drying at 0 ° C. for 20 minutes, 50 ° C. for 30 minutes, and 80 ° C. for 60 minutes, the film was peeled off. The residual solvent amount at this point was all about 15% by weight. 12 at 100 ° C
It was dried for 0 minutes at 130 ° C. for 240 minutes. In addition, PC-MeS / Z (8 /
Regarding 2), drying at 130 ° C was not performed.

The retardation films thus obtained all had a residual solvent content of 1% by weight or less. The surface of this film was uniform without any foaming, citron skin, or waviness, and had good transparency. Further, as in Examples 1 to 4, the phase difference Re (550) and Re (4
50) / Re (550) was evaluated. The results are shown in Table 4. As can be seen from Table 4, the values of Re (450) / Re (550) are in the range of 1.080 to 1.100.

[0054]

[Table 4]

Claims (1)

[Claims] 1. A ratio of a retardation Re (450) at a wavelength of 450 nm to a retardation Re (550) at 550 nm, the polycarbonate comprising at least 1 mol% of a repeating unit represented by the following general formula (I). , Re
A retardation film having a (450) / Re (550) of 1.080 or more. [Chemical 1] (In the formula (I), R 1, R 2, R 3 and R 4 are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms)