JP3431256B2 - Retardation film - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a retardation film. More specifically, it relates to a retardation film useful as a component of a liquid crystal display device, a composite polarizing plate using the same, and a liquid crystal display device.

[0002]

2. Description of the Related Art STN or TFT type liquid crystal display devices are generally used for large-sized liquid crystal display panels, and such display devices use a retardation film made of a polymer uniaxially stretched film or an optically isotropic film. It is laminated on one side or both sides of the liquid crystal cell. However, such a display device cannot sufficiently compensate the phase difference caused by the STN cell over all the wavelengths of light depending on the laminated films, and thus the problem that coloring occurs and the contrast ratio becomes low is not enough. I couldn't solve it. In addition, this problem is an obstacle when performing color display by covering the display device with a color filter. In order to solve this problem, it is considered to stack an equivalent liquid crystal cell as an optical compensation plate or to substitute an optical film having the same birefringence, and a uniaxially stretched or biaxially stretched film having various retardation values. Is being considered.

[0003]

DISCLOSURE OF THE INVENTION The present invention provides a solution cast film easily, has sufficient hue compensation, and has a color shift.
It is an object of the present invention to provide an aromatic polycarbonate resin retardation film that does not cause the inconvenience such as bleeding and solves the problem of poor color accuracy of conventional color display.

Aromatic polycarbonate resins made from 2,2-bis (4-hydroxyphenyl) propane (commonly called bisphenol A), which is a typical aromatic polycarbonate resin, have excellent transparency and appropriate rigidity.
An attempt was made to produce a retardation film with this aromatic polycarbonate resin. However, when a film is produced from this aromatic polycarbonate resin by a solution casting method, the desired film cannot be obtained due to poor solubility in a non-halogen solvent, and gelation occurs even in a halogen solvent, or The cast film obtained is easily whitened, and the retardation film produced from the obtained cast film has a large fluctuation range of retardation, and when the color display is performed, the hue compensation is insufficient, and color misregistration and bleeding easily occur. The problem arose.

The present inventor has solved the problems of the aromatic polycarbonate resin derived from bisphenol A, and conducted extensive studies as a means to achieve the above object. As a result, a part of bisphenol A was replaced with a specific dihydric phenol. The obtained aromatic polycarbonate resin having a specific viscosity can be easily formed into a film by a solution casting method, and if a retardation film obtained by stretching the obtained cast film is used, the above-mentioned problems are surprisingly solved. Based on this finding, they have completed the present invention.

[0006]

The present invention is directed to 50-99 mol% bisphenol A and 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,1-bis (4
-Hydroxyphenyl) cyclohexane, 1,1-bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane, 4,4'-dihydroxytetraphenylmethane, 1,3-bis (4-hydroxyphenyl)-
At least 1 mol% of 5,7-dimethyladamantane
The specific viscosity obtained by reacting the carbonate precursor with the dihydric phenol consisting of at least 50 mol% is 0.36.
The present invention relates to a retardation film obtained by orienting a film made of four or more aromatic polycarbonate resins in at least a uniaxial direction.

The divalent phenol used for synthesizing the aromatic polycarbonate resin constituting the retardation film of the present invention is mainly bisphenol A, and 1 mol% to 5% thereof.
Less than 0 mol% is 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,1-bis (4-hydroxyphenyl) cyclohexane, 1,1-bis (4-hydroxyphenyl) -3,3 , 5-Trimethylcyclohexane, 4,4'-dihydroxytetraphenylmethane, 1,3-bis (4-hydroxyphenyl) -5,7
A mixture of two or more divalent phenols substituted with at least one of dimethyl adamantane. The amount of the above divalent phenol other than bisphenol A is 1 mol%
If less, it is difficult to obtain a good film from the obtained aromatic polycarbonate resin by the solution casting method,
Further, the retardation film obtained by stretching the obtained cast film has a large fluctuation range of the retardation, and the hue compensation is insufficient at the time of displaying in color, so that problems such as color shift and bleeding easily occur. Also, if it is more than 50 mol%, the resulting polymer will suffer from other excellent properties of the aromatic polycarbonate resin from bisphenol A.
Incidentally, a small amount of trifunctional or higher functional compound can be used at the same time for branching.

The reaction with the carbonate precursor for synthesizing the aromatic polycarbonate resin using the above dihydric phenol is the reaction used when synthesizing the usual aromatic polycarbonate resin from bisphenol A, such as dihydric phenol and phosgene. Or a transesterification reaction between a dihydric phenol and a bisaryl carbonate is preferably used. Examples of the carbonate precursor include phosgene, bischloroformates of the above dihydric phenols, diphenyl carbonate, di-p-tolyl carbonate, phenyl-p-tolyl carbonate and di-p-.
Examples thereof include chlorophenyl carbonate and dinaphthyl carbonate, and of these, phosgene and diphenyl carbonate are preferable.

The reaction between the dihydric phenol and phosgene is usually carried out in the presence of an acid binder and a solvent. As the acid binder, for example, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, pyridine or the like is used. As the solvent, for example, a halogenated hydrocarbon such as methylene chloride or chlorobenzene is used. Further, for the purpose of accelerating the reaction, for example, a tertiary amine, a catalyst such as a quaternary ammonium salt can be used, and as a molecular weight regulator, for example, phenol,
It is desirable to use an end-capping agent such as p-tert-butylphenol. The reaction temperature is usually 0 to 40 ° C., the reaction time is several minutes to 5 hours, and the pH during the reaction is usually preferably kept at 10 or higher.

In the transesterification reaction, the dihydric phenol and the bisaryl carbonate are mixed in the presence of an inert gas, and the reaction is usually carried out at 120 to 350 ° C. under reduced pressure. The degree of reduced pressure is changed stepwise, and finally, the phenols produced at 1 mmHg or less are distilled out of the system. The reaction time is usually about 1 to 4 hours. Moreover, you may add a molecular weight regulator and antioxidant as needed.

The molecular weight of the aromatic polycarbonate resin is
0.7 g of the polymer was dissolved in 100 ml of methylene chloride and 2
The specific viscosity measured at 0 ° C. needs to be 0.364 or more. If the specific viscosity does not reach 0.364, the strength of the film becomes insufficient and the stretching process becomes difficult, which is not suitable. An aromatic polycarbonate resin having a specific viscosity of 0.418 to 4.89 is particularly preferable. Further, in such an aromatic polycarbonate resin, various additives such as a stabilizer, a lubricant, a release agent, a flame retardant, within a range not impairing the gist of the present invention,
An antistatic agent, a weather resistance agent, etc. may be added, and other polymers may be added. These additives can be mixed by any method such as a tumbler, a super mixer and a Nauta mixer.

As a method for producing a film from the above aromatic polycarbonate resin, for example, a solution casting method,
A melt extrusion method, a calender method and the like can be mentioned, but a method which is excellent in thickness uniformity and which does not cause optical defects such as gel, spots, fish eyes and scratches is preferable.

The film produced by such a method is
The retardation film is stretched and oriented as it is or in at least a uniaxial direction so as to have optimum birefringence properties. As the uniaxial stretching method, any method such as a horizontal uniaxial stretching by a tenter method, a longitudinal uniaxial stretching between rolls, or a roll-to-roll rolling method can be used. The stretching conditions are not particularly limited, but the stretching temperature is preferably 10 to 60 ° C. higher than the glass transition temperature of the resin used, and the stretching ratio is preferably about 1.1 to 4 times. After stretching, it is preferable to perform heat treatment in order to improve dimensional stability, uniformity of retardation, and stability. The thickness of the film is preferably in the range of 5 to 300 μm.

When the retardation film thus obtained has a too low retardation value, the function as a retardation film becomes insufficient, and when it is too high, the film must be extremely thick. If it is too thick, the optical uniformity tends to be impaired, and the hue compensation effect tends to decrease, so the range of 60 to 1200 nm is preferable, and the range of 200 to 1000 nm is particularly preferable. Further, if the fluctuation range of the retardation becomes too large, a deviation in hue compensation occurs, causing color spots. Therefore, the fluctuation rate is preferably 10% or less, particularly preferably 5% or less,
2% or less is more preferable.

The retardation film of the present invention is preferably laminated on a polarizing plate and used as a composite polarizing plate. This composite polarizing plate can be formed by laminating the optical axis of a normal polarizing plate and the optical axis of a retardation film within a range of 40 to 50 degrees in a single layer or multiple layers. This composite polarizing plate has excellent features such as excellent heat resistance and durability, and little change in retardation with time.

Further, in a liquid crystal display panel in which polarizing plates are arranged on one side or both sides of a liquid crystal cell, by disposing the retardation film between the polarizing plate on the viewing side and the liquid crystal cell, birefringence of liquid crystal It is possible to form a black and white liquid crystal display panel in which coloring due to the above is eliminated. Furthermore, by covering this black and white liquid crystal panel with a color mask, the three RGB colors are developed with a black and white gray density, and a full color liquid crystal display panel. Can be formed.

[0017]

EXAMPLES The present invention will be further described below with reference to examples. In the examples, parts and% are parts by weight and% by weight.

Synthesis Example 1 A reaction tank equipped with a stirrer, a thermometer and a reflux condenser was charged with 2738.4 parts of a 48.5% aqueous sodium hydroxide solution and 23800 parts of water, and nitrogen gas was bubbled for 30 minutes. Deoxygenated. 1,1-
Bis (4-hydroxyphenyl) -1-phenylethane (356.6 parts) and 2,2-bis (4-hydroxyphenyl) propane (2523.2 parts) were dissolved, and hydrosulfite (7.1 parts) was added. Add 16700 parts of methylene chloride deoxygenated by nitrogen gas bubbling and add 20 ° C.
Then, 1400 parts of phosgene was blown in over about 60 minutes. Then, 506.8 parts of a 48.5% aqueous sodium hydroxide solution and p-tert-butylphenol 3 which were deoxygenated in the same manner were used.
After 6.9 parts was added and emulsified, 11 parts triethylamine was added and stirred at 30 ° C. for about 2 hours to complete the reaction. After completion of the reaction, the organic phase is separated, washed with water, acidified with hydrochloric acid, and washed repeatedly with water. 0.6 part (yield 97%) was obtained. The specific viscosity of this polymer was 0.469.

Synthesis Example 2 4,4'-Dihydroxytetraphenylmethane 21 in place of 356.6 parts of 1,1-bis (4-hydroxyphenyl) -1-phenylethane
Polymer 3071.6 parts (yield 96%) in the same manner as in Synthesis Example 1 except that 6.4 parts was used and the amount of 2,2-bis (4-hydroxyphenyl) propane used was 2663.4 parts. Got The specific viscosity of this polymer was 0.473.

[Synthesis Example 3] A device similar to that of Synthesis Example 1 has four units.
Charge 569 parts of 8.5% aqueous sodium hydroxide solution and 3374 parts of ion-exchanged water, and add 82 parts of 1,1-bis (4-hydroxyphenyl) cyclohexane and 2,2-
After 280 parts of bis (4-hydroxyphenyl) propane was dissolved, 0.8 part of hydrosulfite was added, 1692 parts of methylene chloride was added, and phosgene 1 was added at about 23 ° C. with stirring.
95 copies were blown in for about 60 minutes. Next, 2.2 parts of p-tert-butylphenol was added to emulsify, 0.5 part of triethylamine was added, and the mixture was stirred at about 30 ° C. for 2 hours to complete the reaction. After completion of the reaction, the same treatment as in Synthesis Example 1 was carried out to obtain 394.7 parts of a polymer (yield 98%). The specific viscosity of this polymer was 0.915.

[Synthesis example 4]
Charge 464 parts of 8.5% sodium hydroxide aqueous solution and 2213 parts of ion-exchanged water, and add 19 parts of 1,1-bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane and 2,2-bis (4-). Hydroxyphenyl) propane (272 parts) was dissolved and hydrosulfite 0.4
After 1 part was added, 1380 parts of methylene chloride was added, and 149 parts of phoskene was blown in at 20 ° C. for about 60 minutes. Then p
After adding 5.7 parts of -tert-butylphenol and emulsifying the mixture, 0.4 part of triethylamine was added and stirred at about 30 ° C. for 2 hours to complete the reaction. After the completion of the reaction, the same treatment as in Synthesis Example 1 was carried out to obtain 314 parts of a polymer (yield 97%). The specific viscosity of this polymer was 0.443.

[Synthesis Example 5] The same apparatus as in Synthesis Example 1 was
264 parts of 8.5% sodium hydroxide aqueous solution and 2300 parts of ion-exchanged water were charged, and 1,3-bis (4-hydroxyphenyl) -5.7-dimethyladamantane 19 was added.
Part, 237 parts of 2,2-bis (4-hydroxyphenyl) propane and 0.7 part of hydrosulfite are dissolved,
Further, 1620 parts of methylene chloride was added, and 141 parts of phosgene was blown in at 20 ° C. for about 60 minutes. Then 48.5%
After 29 parts of an aqueous sodium hydroxide solution and 4.1 parts of p-tert-butylphenol were added for emulsification, 0.8 part of triethylamine was added and stirred at about 30 ° C. for 2 hours to complete the reaction. After the completion of the reaction, the same treatment as in Synthesis Example 1 was carried out to obtain 275.4 parts of a polymer (yield 97%). The specific viscosity of this polymer was 0.451.

[Synthesis Example 6] 2,2-bis (4-hydroxyphenyl) propane 28 instead of 3,566 parts of 1,1-bis (4-hydroxyphenyl) -1-phenylethane 28
Polymer 3061 parts (98%) was obtained in the same manner as in Synthesis Example 1 except that 03.6 parts were used. The specific viscosity of this polymer was 0.540.

Examples 1 to 5 10% 1,3-dioxolane solutions of the polymers synthesized in Synthesis Examples 1 to 5 were prepared,
After casting on a glass plate using a doctor blade, it was dried, peeled from the glass, and dried until the residual solvent disappeared. A uniaxially stretched film was produced from this film using a tenter under the conditions shown in Table 1. The retardation of the obtained film and its variation (%) are shown in Table 1.
It was shown to. These films were adhered to one surface of the polarizing plate with an adhesive so that the optical axis was 45 ° to obtain a composite polarizing plate. Then, this product was pasted and used between the liquid crystal cell of the STN liquid crystal display device and the upper polarizing plate, and a black and white display with a white background and a black display with good contrast was obtained. In addition, a clear full-color display device could be obtained by attaching a backlight to this black and white liquid crystal display, covering the upper part with a color filter, and displaying RGB cells in black and white gray density.

Comparative Example 1 A casting film was prepared in the same manner as in Example 1 using the polycarbonate prepared from bisphenol A prepared in Synthesis Example 6, and a uniaxially stretched film was obtained under the conditions shown in Table 1. When this film was used by adhering it between the STN liquid crystal cell and the upper polarizing plate in the same manner as in Example 1, almost black and white display was obtained, but hue compensation was insufficient and color misregistration occurred, resulting in a slightly reddish color tone. Became. In addition, we tried to make a color display by making a liquid crystal display with a backlight with the hue of this black and white display insufficient and covering it with a color filter to make RGB cells emit light, but there was a color shift and bleeding, and a clear full color display. I couldn't.

[0026]

[Table 1]

[0027]

EFFECTS OF THE INVENTION The retardation film of the present invention is easy to solution cast, and a composite polarizing plate and a liquid crystal display device using the same have few optical spots, which enables clear black and white display and color display. Since it has excellent performance and durability as compared with the conventional liquid crystal display device, it can be applied to a wider range of applications such as in-vehicle use and heat-generating parts, and its effect is remarkable.

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Claims (8)

(57) [Claims] 1. 50-99 mol% of 2,2-bis (4-hydroxyphenyl) propane and 1,1-bis (4-)
Hydroxyphenyl) -1-phenylethane, 1,1-
Bis (4-hydroxyphenyl) cyclohexane, 1,
At least one of 1-bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane, 4,4'-dihydroxytetraphenylmethane and 1,3-bis (4-hydroxyphenyl) -5,7-dimethyladamantane
Retardation obtained by orienting at least uniaxially a film made of an aromatic polycarbonate resin having a specific viscosity of 0.364 or more obtained by reacting a carbonate precursor with a dihydric phenol consisting of 1 mol% or more and less than 50 mol% of species. Of 60 to 1200 nm and the retardation variation is 10% or less. 2. Hue compensation is sufficient when displaying in color,
The retardation film according to claim 1, wherein color shift and bleeding do not occur. 3. The retardation film according to claim 1, wherein the method for uniaxially orienting the film is lateral uniaxial stretching by the Denter method, longitudinal uniaxial stretching by rolls or rolling between rolls. 4. The uniaxial stretching temperature is Tg + of the resin used.
The retardation film according to claim 3, which has a temperature of 10 ° C to Tg + 60 ° C. 5. The retardation film according to claim 3, wherein the stretching ratio of uniaxial stretching is 1.1 to 4 times. 6. The retardation film according to claim 1, wherein the thickness of the film is 5 to 300 μm. 7. A composite polarizing plate obtained by laminating at least one layer of the retardation film according to claim 1 on a polarizing plate. 8. A liquid crystal display device comprising the composite polarizing plate according to claim 7 arranged in a liquid crystal cell.