JP3262938B2 - Retardation film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 crystal which have been put into practical use have attracted 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 composed of a polarizing plate,
It is used for a protective layer, a retardation plate or an 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. Has a role to compensate.

For example, in an 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 the retardation film, films such as polycarbonate and polyvinyl alcohol which are mainly uniaxially stretched are used. In particular, polycarbonate represented by polycarbonate (hereinafter abbreviated as PC-A) obtained from bisphenol A and phosgene is a colorless polymer with good balance of heat resistance and various mechanical properties. It has excellent mechanical properties and extremely good moldability, transparency and optical properties. Further, a film having a high surface uniformity without any streaks or defects can be produced by the solution casting method, and it is relatively easy to obtain a film having a desired retardation by stretching.

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

[0006] By the way, studies to increase the response speed of the liquid crystal display device have been actively conducted recently, and a liquid crystal material having a larger birefringence than in the past has been used for the liquid crystal display device. However, since the wavelength dispersion of the retardation of such a liquid crystal layer is larger than that of the conventional one, it is impossible to compensate for 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'm starting to do it. Therefore, in order to realize a monochrome display, a retardation film having a wavelength dispersion of a large retardation matching the liquid crystal layer is required.

For example, it is known that an aromatic polyethersulfone film has a large wavelength dispersion of retardation, and application to a retardation film is actively studied. However, aromatic polyether sulfones are generally formed by a melt extrusion method, particularly a T-die method, and sufficient surface homogeneity has not been obtained due to the generation of die lines or fish eyes, which is a problem inherent to the T-die method. It has not been put to practical use. In addition, when a film showing wavelength dispersion of a large retardation with a single material cannot be obtained,
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 laminate 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, which does not cause an image on a liquid crystal display device to be colored.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, (1) a film made of a polycarbonate having a diphenyl sulfide derivative in a main chain skeleton has a large retardation wavelength dispersion. thing,
(2) A smooth film in which the polycarbonate is dissolved in a solvent at a high concentration, the stability of the solution composition (dope) is excellent, and the dope is transparent and optically uniform without causing white turbidity. And found that the present invention can be produced.

That is, the present invention comprises 1 to 100 mol% of a repeating unit represented by the following general formula (I), and 99 to 0 mol% of a repeating unit represented by the following general formula (II).
Polycarbonate containing, wavelength 450n
ratio of the phase difference Re (450) at m to the phase difference Re (550) at 550 nm, Re (450) / R
e (550) is 1.080 or more, which is a retardation film.

Embedded image (In the formula (I), R ₁ and R ₂ are hydrogen atoms, and R ₃ and R ₄ are
Is a methyl group )

Embedded image (In Formula (II), X is an aliphatic hydrocarbon group selected from a methylene group, a 1,1-ethylene group, a 2,2-propylene group, and a 4-methyl-2,2-pentylene group, and has 1 to 1 carbon atoms.
15 divalent alicyclic hydrocarbon groups, or 1 to 15 carbon atoms
R ₅ , R ₆ , R ₇ , R ₈
Are each independently a hydrogen atom, a bromine atom or a carbon atom
To 4 hydrocarbon groups. )

Hereinafter, the present invention will be described in detail. In the retardation film of the present invention, 1 to 100 mol% of the repeating unit represented by the following general formula (I) and the repeating unit represented by the following general formula (II) are used based on the total amount of the repeating units constituting the polycarbonate. It is formed from a polycarbonate containing 0 to 99 mol% of units.

[0012]

Embedded image

[0013]

Embedded image

(In the formula (I), R ₁ , R ₂ , R ₃ and R ₄ are a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.
In I), X is a methylene group, 1,1-ethylene group, 2,2
-Propylene group and 4-methyl-2,2-pentylene group
An aliphatic hydrocarbon group selected from the group consisting of divalent groups having 1 to 15 carbon atoms
An alicyclic hydrocarbon group or a divalent a
R ₅ , R ₆ , R ₇ , and R ₈ are each a laalkylene group.
Independently, a hydrogen atom, a bromine atom or a carbon atom having 1 to 4 carbon atoms
It is a hydrogen group. )

[0015] Here, Te formula (I) odor, R _1, R ₃ is a hydrogen atom, R _2, R ₄ is Ru der methyl group. In the formula (II), X is an aliphatic hydrocarbon group selected from a methylene group, a 1,1-ethylene group, a 2,2-propylene group and a 4-methyl-2,2-pentylene group; It is selected from a divalent alicyclic hydrocarbon group and a divalent aralkylene group having 1 to 15 carbon atoms. Specifically, methylene group, 1,1-ethylene group, 2,2-propylene group and 4-methyl-2,
An aliphatic hydrocarbon group selected from 2-pentylene groups,
1-cyclohexylene group, 3,3,5-trimethyl-
An alicyclic hydrocarbon group such as a 1,1-cyclohexylene group,
Aralkylene groups such as 1-phenyl-1,1-ethylene group, diphenylmethylene group, and 1,1-fluorenylene group are exemplified. Particularly preferred are a 2,2-propylene group and a 1,1-cyclohexylene group.

R ₅ , R ₆ , R ₇ , R ₈ are each independently a hydrogen atom, a bromine atom or a hydrocarbon group having 1 to 4 carbon atoms, preferably all of them are hydrogen atoms, or All are methyl groups.

The repeating unit represented by the above 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 (45
0), the ratio Re (450) / Re (550) to the phase difference Re (550) at 550 nm becomes smaller than 1.080 and approaches the conventional polycarbonate (PC-A), and the phase difference is sufficiently compensated. It is not preferable because it cannot be performed. The content of such a repeating unit can be appropriately adjusted according to the desired magnitude of wavelength dispersion of retardation. For example, when it is desired to slightly increase the wavelength difference of the retardation of PC-A which is a general polycarbonate, it is sufficient to set it to 1 to 50 mol%, and when it is desired to considerably increase it, it is set to 50 to 100 mol%. Good. If heat resistance of about 100 ° C is required, 8
0 mol% or less, about 120 ° C., 65 mol% or less, about 130 ° C., 50 mol% or less, 150 ° C.
In this case, it is preferably at most 35 mol%. When the demands on the optical properties such as the color tone of the film are extremely strict, it is 1 to 50 mol%, preferably 1 to 20 mol%. The upper limit of Re (450) / Re (550) is
In practice, it is 1.130 or less, preferably 1.120 or less, although it depends on the magnitude of the wavelength dispersion of the desired phase difference.

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

The molecular weight of the above polycarbonate is GPC
In terms of polystyrene-equivalent number average molecular weight (Mn) of 10,
If it is 000 or more and 400,000 or less, it is preferably used. If the Mn is 10,000 or less, the mechanical strength of the obtained film may be insufficient, and
If it is 0 or more, the viscosity of the solution composition (dope) used for forming a film by the solution casting method becomes too high, which may not only be difficult to handle but also 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 the stability of the solution composition (dope) is high. A film having good uniformity can be formed.

In order to obtain a film having a thickness of 50 to 200 μm by the solution casting method, a high concentration of dope is required. Examples of the solvent for dissolving the polycarbonate at a high concentration used in the present invention include polar solvents such as dimethylacetamide, dimethylformamide, pyridine and N-methylpyrrolidone, dichloromethane, chloroform, 1,1,2,2.
Halogen solvents such as 2-tetrachloroethane and 1,1,2-trichloroethane, 1,3-dioxolan, 1,4
And cyclic ether solvents such as dioxane and tetrahydrofuran. Of these, halogen and cyclic ether solvents are preferably used, and cyclic ether solvents are more preferable. Since the polar solvent has a high boiling point, the residual solvent in the film-forming film cannot be easily reduced, and is not practical as a film-forming solvent. Halogen solvents such as dichloromethane are suitable as solvents for film formation, but their influence on environmental pollution is regarded as a problem, and consideration must be given to solvent recovery and the like. Of the cyclic ether solvents, 1,
3-Dioxolane is particularly excellent from the viewpoint of high concentration solubility, dope stability, boiling point (76 ° C.), and film forming property. Tetrahydrofuran has a low boiling point (65 ° C.) and works advantageously for drying, but 1,3-dioxolan is superior from the viewpoint of solubility and solution stability. Also, 1,4-dioxane is
Like 1,3-dioxolane, it has high solubility, but 1,3-dioxolane is superior in terms of residual solvent due to its high boiling point (100 ° C.). Further, 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 herein include, for example, the improvement of the surface properties of a film formed by a solution casting method (leveling effect), the evaporation rate, and the These include viscosity control and crystallization suppression effects. The type and amount of the solvent to be mixed may be determined according to the degree of these effects, and one or more solvents may be used as the mixed solvent. Suitable solvents include hydrocarbon solvents such as toluene and xylene, ketone solvents such as acetone, methyl ethyl ketone and cyclohexanone, ester solvents such as ethyl acetate and butyl acetate, and ether solvents such as ethylene glycol dimethyl ether and methoxyethyl acetate. Is raised.

The concentration of the dope is such that the amount of the solvent 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 the solvent is more than this, there is no problem in the stability of the solution, but it is not preferable because the running concentration is low. This is not preferable because surface smoothness cannot easily be obtained. Conversely, if the amount of the solvent is less than this, it is difficult to obtain a stable solution. These concentrations are determined mainly in consideration of solution stability and solution viscosity.

If the obtained dope contains insoluble matters or suspended matters such as impurities or undissolved matters, or if haze is observed in the dope, it must be removed by a treatment such as filtration. Not performing such treatment not only deteriorates the optical characteristics of the formed film, but also decreases the storage stability of the adjusted dope.

The retardation film of the present invention is preferably obtained by casting the above-mentioned dope on a supporting substrate and then heating it to evaporate the solvent. The industrial continuous film forming process generally includes three steps: a casting process, a drying process, and a 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 step, a method using a doctor blade, a method using a reverse roll coater, a method extruding from a die, and the like are used. Industrially, the most common method is to continuously extrude a dope from a die onto a belt-shaped or drum-shaped support substrate. The support substrate to be used is not particularly limited, but a glass substrate, a metal substrate of stainless steel or ferro type, a plastic film of polyethylene terephthalate or the like is used. However, a metal substrate having a mirror-finished surface is most commonly used to industrially obtain a homogeneous film having excellent optical isotropy, which is the main feature of the present invention.

In producing the retardation film of the present invention, the viscosity of the dope is a very important factor. The viscosity depends on the concentration of the polycarbonate, the molecular weight and the type of the solvent, but the preferred viscosity is 300 to 50,
000 cps. If it exceeds this, a smooth film may not be obtained because the fluidity of the solution decreases. On the other hand, if it is less than this, the fluidity is so high that the surface is disturbed due to external disturbance, and a uniform and smooth film may not be obtained. More preferred viscosity is 400 to 30,000 cps
It is.

In the drying step, it is necessary to evaporate and remove most of the solvent from the dope cast on the supporting substrate in as short a time as possible. However, drying conditions should be carefully selected, since rapid evaporation will cause deformation by foaming. In the present invention, the reaction is carried out within the range of the minimum boiling point used, preferably the boiling point of -10 ° C. Usually, in the initial stage, a method of sequentially or continuously raising the temperature from a temperature lower than the boiling point of the solvent used, for example, 30 ° C., is employed. Moreover, you may send a wind as needed. Generally, the wind speed is in the range of 1 to 20 m / sec. If it is less than this, the effect is not sufficient, and if it exceeds this, it is not preferable because a smooth surface cannot be obtained due to wind disturbance. The preferred 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 that time, if the amount of the residual solvent is large, the film is soft and the polymer flows and deforms in the film, and if the amount of the residual solvent is small, the adhesiveness to the substrate is high and stress distortion occurs. Therefore, the amount of the residual solvent is an important factor, and the amount of the residual solvent is preferably selected in the range of 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 to reduce the residual solvent amount to 3% by weight or less.
It is necessary to be preferably 1% by weight or less, more preferably 0.5% by weight or less. If the amount of the residual solvent is large, deformation occurs with time, or dimensional change occurs when heat is applied in a post-processing step. In particular, it is important for a liquid crystal display device because an optically uniform film is required. Industrially, a method of drying while transporting a film by a pin tender method or a roll hanging method is used. The drying temperature must be selected from a range that does not cause deformation of the film. 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 is less likely to occur as residual solvent decreases. Therefore, it is preferable to adopt a method in which the temperature is raised at a low temperature in the initial stage and then sequentially or continuously. Further, air may be sent in the same manner as in the drying step.

The thickness of the retardation film of the present invention is from 10 to
A range of 300 μm is preferred. 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 uneven thickness. A more preferred film thickness is 50 to 200 μm.

The retardation film of the present invention may be stretched to obtain a desired retardation according to the intended use. The stretching method is not particularly limited, but may be a longitudinal stretching method using two pairs of rolls having different peripheral speeds, or a transverse stretching method using a tenter. The stretching temperature and the stretching ratio are appropriately set in order to obtain a desired retardation. However, the stretching temperature is a temperature higher than the glass transition point of the retardation film, and the stretching ratio is 1.01 to 1.01.
What is necessary is just to carry out in the range of 3.00 times.

[0031]

According to the present invention, it is possible to obtain a retardation film exhibiting a larger wavelength dispersion of retardation than PC-A and having good surface uniformity. The film is made of a display element such as an STN type liquid crystal or a TN type liquid crystal, a λλ plate, a λλ
It is suitable for a retardation film useful for optical applications such as an optical element such as a plate.

[0032]

The present invention will be described below in detail 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 type manufactured by Tokyo Keiki Co., Ltd. is used.
Measured at 30 ° C. Total light transmittance and haze value in visible light region: Automatic digital haze meter UDH-20D manufactured by Nippon Denshoku Industries Co., Ltd.
use. Phase difference wavelength dispersion: M-150 ellipsometer manufactured by JASCO Corporation was used. Film thickness: Measured by a stylus type film thickness meter manufactured by Anritsu Corporation.

Reference Examples 1 to 4 The following formula (I) was obtained by an ordinary interfacial polymerization method using phosgene.
II) Three types of polycarbonates (hereinafter abbreviated as PC-MeS / Z) composed of repeating units represented by the following formula (IV), and polycarbonates (hereinafter PC-SSA) composed of the repeating units represented by the following formula (IV) Abbreviated) was synthesized. The number average molecular weight (M
n) and the glass transition point are shown in Table 1.

[0035]

Embedded image

[0036]

Embedded image

[0037]

[Table 1]

Examples 1-4 The polycarbonates (PC-Me) obtained in Reference Examples 1-4 above were used.
S / Z (8/2), (5/5), (2/8), PC-S
SA) in dichloromethane, each containing 11.1%,
13.5%, 13.5%, 10.0% viscous dope was prepared. These dopes are sealed at room temperature in a closed state.
No change was observed even after standing for a week, and no clouding or gelling phenomenon was observed.

After casting the dope on a glass substrate using a doctor blade, the dope was dried at 30 ° C. for 20 minutes, at 50 ° C. for 20 minutes, and at 80 ° C. for 20 minutes using a dryer having a wind speed of 1.5 m. Was peeled off. At this point, the amount of residual solvent in each film was almost 15% by weight.
Met. Each film was further treated at 100 ° C. for 60 minutes, 13
Dry at 0 ° C. for 120 minutes. In addition, PC-MeS / Z (8 /
2) and PC-SSA were not dried at 130 ° C. Thus, a retardation film in which the amount of the residual solvent 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 retardation Re (450) of the retardation Re (450) at a wavelength of 450 nm at 550 nm were obtained.
Table 2 shows the results of measurement of the ratio Re (450) / Re (550) to the ratio 50).

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, yuzu skin and waving phenomenon.

Further, the retardation film was stretched at a temperature near the glass transition point in the in-plane direction of the film at a stretching ratio of 1.02. Table 2 also shows the results of measuring the retardation Re (550) at a wavelength of 550 nm in each of the obtained films. The ratio of the phase difference Re (450) at a wavelength of 450 nm to the phase difference Re (550) at a wavelength of 550 nm, Re (450) / Re (5)
50) was the same as that before stretching.

Comparative Example 1 A film was produced in the same manner as in Example 1 using polycarbonate “C-1400” manufactured by Teijin Chemicals Ltd. Table 2 shows the obtained results.

[0044]

[Table 2]

Example 5 The polycarbonate (PC-MeS / Z (5
/ 5)) was dissolved in 1,3-dioxolane to prepare a 13.5% dope. 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 dryer having a wind speed of 1.2 m, and then the film was peeled off. The residual solvent amount at this point was approximately 15% by weight. 120 minutes at 100 ° C,
After drying at 130 ° C for 240 minutes, the residual solvent amount is 0.8% by weight.
Was obtained. This retardation film had good transparency, and the surface was uniform without foaming, yuzu skin and waving phenomenon.

The retardation film is further heated at 140 ° C.
The film was stretched 1.10 times in the in-plane direction of the film. The obtained film has a phase difference of 510 at a wavelength of 550 nm.
nm, and the wavelength dispersion value Re (450) / Re (550) was 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 (P) having different compositions obtained in Reference Examples
C-MeS / Z (8/2), (5/5), (2/8))
Was dissolved in 1,3-dioxolane, 1,4-dioxane, and tetrahydrofuran to prepare a 13.5% dope. Table 3 shows the viscosities of these dopes. All of them were transparent and did not change even when left for 1 week in a closed state at room temperature, and no clouding or gelation was observed.

[0049]

[Table 3]

[Examples 6 to 14] Each of the nine kinds of dopes obtained in Reference Examples 5 to 7 was cast on a glass substrate using a doctor blade.
20 minutes at 30 ° C, 30 minutes at 50 ° C using a 2 m dryer,
After drying at 80 ° C. for 60 minutes, the film was peeled off. The residual solvent amount at this time was almost 15% by weight.
Further drying was performed at 100 ° C. for 120 minutes and at 130 ° C. for 240 minutes. In addition, it is 130 about PC-MeS / Z (8/2).
No drying at 0 ° C was 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 foaming, yuzu skin and waving phenomenon, and transparency was good. Further, similarly to Examples 1 to 4, the retardation Re (550) at a wavelength of 550 nm and Re (450) / Re (550) were evaluated. Table 4 shows the results. As can be seen from Table 4, Re
The value of (450) / Re (550) is 1.080 to 1.1.
It is in between 00.

[0052]

[Table 4]

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 5/30

Claims (2)

(57) [Claims] 1. A polycarbonate comprising 1 to 100 mol% of a repeating unit represented by the following general formula (I) and 99 to 0 mol% of a repeating unit represented by the following general formula (II). Of the phase difference Re (450) at a wavelength of 450 nm and the phase difference Re (5) at a wavelength of 550 nm.
50) The retardation film, wherein the ratio Re (450) / Re (550) to 1.0) is 1.080 or more. Embedded image (In the formula (I), R ₁ and R ₃ are hydrogen atoms, and R ₂ and R ₄ are
( It is a methyl group having 1 to 5 carbon atoms. ) (In Formula (II), X is an aliphatic hydrocarbon group selected from a methylene group, a 1,1-ethylene group, a 2,2-propylene group, and a 4-methyl-2,2-pentylene group, and has 1 to 1 carbon atoms.
15 divalent alicyclic hydrocarbon groups, or 1 to 15 carbon atoms
R ₅ , R ₆ , R ₇ , R ₈
Are each independently a hydrogen atom, a bromine atom or a carbon atom
To 4 hydrocarbon groups. ) 2. The repeating unit represented by the above formula (I)
The retardation film according to claim 1, which contains 1 to 80 mol%.
M