JPH0752271A - Optical film or sheet - Google Patents

Abstract

PURPOSE:To obtain a film improved in film forming properties by using a polycarbonate copolymer containing 1-30mol% of a repeating unit shown by formula I and 99-70mol% of a repeating unit shown by formula II. CONSTITUTION:An optical film or sheet is made of a polycarbonate copolymer containing 1-30mol% of a repeating unit shown by formula I and 99-70mol% of a repeating unit shown by formula II. In the formulas, R1, R2, R3, and R4 are hydrogen atom or methyl group and the same or different, and X is 5-10C cycloalkylene group, 7-15C aralkylene group, or 1-5C haloalkylene group.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention is useful as an optical film or sheet made of a polycarbonate copolymer having an improved film-forming property, an alignment film for a retardation plate used in a liquid crystal display, a substrate for a liquid crystal display, etc. Optical film or sheet.

[0002]

2. Description of the Related Art In recent years, the progress of liquid crystal displays has been remarkable.
Among them, the progress of STN type liquid crystal displays is particularly remarkable. In this display element, a retardation film is laminated between the liquid crystal layer and the polarizing plate in order to improve the visibility of the image. This retardation film plays a role of converting elliptically polarized light transmitted through the liquid crystal layer into linearly polarized light. A uniaxially stretched film of polycarbonate mainly composed of bisphenol-A is used as the material and has been put into practical use. The reason is that the properties required for the retardation plate such as (1) high transparency, (2) high refractive index anisotropy, and (3) high heat resistance are satisfied. Generally, this polycarbonate film is cast from dichloromethane, but since the film for retardation film or liquid crystal substrate is a thick film, it is necessary to cast it from a high concentration dope from the viewpoint of economy and film-forming property. However, this polymer dissolves in dichloromethane at most about 20% by weight, and the solubility cannot be said to be sufficient. Moreover, the high-concentration dope is not stable, and clouding or gelation occurs due to crystallization. Also, crystallization (white turbidity) during the film formation process
Occurs. At the same time, when casting a thick film, it is difficult to obtain a smooth surface property if the dope viscosity is low. When high-molecular-weight polycarbonate is used to solve this problem, restrictions on solubility and dope stability become more and more severe.

In recent years, the use of chlorine-containing solvents including dichloromethane has been restricted from the viewpoint of global environment.
Moreover, since dichloromethane has a low boiling point (39 to 40 ° C.), it is easily volatilized during film formation, which poses a problem from the working environment. Therefore, there is an increasing demand for a technique for forming a film from a pollution-free solvent instead of dichloromethane. However, with solvents other than dichloromethane, the polycarbonate obtained from bisphenol-A is no longer able to cope with various problems such as solubility, dope stability, and smoothness of the coating film surface.

On the other hand, in addition to polycarbonate obtained from bisphenol-A, for example, JP-A-56-1307
No. 03, No. 63-189804, JP-A-1-
No. 4,160,084 and No. 4-84106 disclose 4,
Polycarbonates or copolymers derived from 4'-dioxydiarylalkanes have been proposed. further,
JP-A-2-12205 and JP-A-2-59702 propose a polycarbonate obtained from 4,4'-dihydroxydiphenylalkane or a halogen-substituted product thereof. Although some of the polycarbonates obtained from these 4,4'-dioxydiarylalkanes or 4,4'-dihydroxydiphenylalkanes are superior in solubility and amorphousness to the polycarbonates obtained from bisphenol-A, Since it has a low glass transition temperature (hereinafter abbreviated as Tg), it cannot be said that it is superior to bisphenol-A as a whole. Such high heat resistance is also required for a substrate film or sheet used for a liquid crystal display. The reason is that a conductive thin film for a transparent electrode must be provided on the substrate by vapor deposition or sputtering, and a liquid crystal alignment film usually made of polyimide must be formed.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical film or sheet having excellent heat resistance, transparency and optical properties.

[0006]

DISCLOSURE OF THE INVENTION As a result of intensive studies made by the present inventors to solve the above-mentioned drawbacks of the prior art, when a small amount of a specific component is copolymerized, not only the solubility is remarkably improved. They have found that the crystallinity is remarkably suppressed and have reached the present invention. It was also found that copolymerization of such components does not impair the heat resistance of the polycarbonate obtained from bisphenol-A, but rather improves it.

That is, the present invention has the following general formula [I]

[0008]

[Chemical 3]

[Wherein R ₁ , R ₂ , R ₃ and R ₄ are the same or different and are a hydrogen atom or a methyl group, X is a cycloalkylene group having 5 to 10 carbon atoms, an araalkylene group having 7 to 15 carbon atoms, It is a haloalkylene group having 1 to 5 carbon atoms. ] Containing 1 to 30 mol% of a repeating unit represented by,
The following formula

[0010]

[Chemical 4]

An optical film or sheet comprising a polycarbonate copolymer containing 99 to 70 mol% of the repeating unit represented by

The polycarbonate copolymer used in the present invention comprises a repeating unit represented by the above formula [I] and a repeating component [II] containing bisphenol-A as a bisphenol component. In the above formula [I], R _{1 to} R ₄
Is a hydrogen atom or a methyl group. The methyl group has the effect of increasing the solubility without lowering the Tg. X is a cycloalkylene group, an araalkylene group, or a haloalkylene group.

Polycarbonates obtained from 4,4'-dioxydiarylalkanes and 4,4'-dihydroxydiphenylalkanes which have hitherto been proposed are polycarbonates obtained from bisphenol-A as shown in specific examples. Lower than Tg (149 ° C). For example, bis (4-oxyphenyl) methane (147
° C), 1,1-bis (4-oxyphenyl) ethane (1
Tg of polycarbonate obtained from 30 ° C.), 1,1-bis (4-oxyphenyl) butane (123 ° C.) and 2,2-bis (4-oxyphenyl) butane (134 ° C.)
It is also clear from (numerical values in parentheses). On the other hand,
The polycarbonate obtained from bisphenol having a cycloalkylene group used in the present invention has the effect of increasing Tg due to the rigidity derived from the ring structure. Moreover, the asymmetry due to the cycloalkane structure has the effect of increasing the solubility and the amorphousness. Therefore, it is understood that even a slight copolymerization of such a component significantly improves the solubility.

Specific examples of X used in the present invention include 1,1-cyclopentylene as a cycloalkylene group,
1,1-cyclohexylene, 1,1- (3,3,5-trimethyl) cyclohexylene, norbornane-2,2-
Diyl, tricyclo [5.2.1.0 ^2,6 ] decane-
8,8'-diyl, especially 1,1 because of easy availability of raw materials
-Cyclohexylene and 1,1- (3,3,5-trimethyl) cyclohexylene are preferably used. The araalkylene group includes phenylmethylene, diphenylmethylene, 1,1- (1-phenyl) ethylene, 9,9.
-For example, fluorenylene. Further, as the haloalkylene group, 2,2-hexafluoropropylene, 2,2
-(1,1,3,3-Tetrafluoro-1,3-dichloro) propylene and the like are preferably used. These may be one kind or two or more kinds.

In the present invention, the structural unit [I] contains 1 to 30 mol%, preferably 3 to 20 mol% of the structural unit [I] in the total repeating units of the polycarbonate.
I] is 99 to 70 mol%, preferably 97 to 80 mol%
included. The copolymerization ratio may be selected in consideration of the film physical properties (Tg) and the film forming property, but if the ratio of the structural unit [I] is less than this, the improvement results of the film physical properties and the film forming property are not remarkable, which is not preferable. . Further, if it exceeds it, it is not preferable from the viewpoint of economy including raw material cost.

The molecular weight of the polycarbonate copolymer used in the present invention is not particularly limited, but in general, the average molecular weight determined from the viscosity measurement at 20 ° C. in a dichloromethane solution having a concentration of 0.5 g / dl is 8,000 or more. 100,
000 or less, preferably 10,000 or more and 70,000
The following ranges are used. If it is less than that, the mechanical strength is not sufficient, which is not preferable. On the other hand, if it exceeds the range, the viscosity becomes too high and the film forming property is significantly impaired, which is not preferable.

The method for producing the polycarbonate copolymer used in the present invention is not particularly limited, but a commonly used interfacial polymerization method between phosgene and the corresponding bisphenol and a melt polymerization method between diphenyl carbonate and bisphenol are preferable. Used.

The obtained polycarbonate is generally formed into a film or a sheet by a solution casting method or a melt extrusion method. However, since optical applications require a high degree of homogeneity, the casting method from a solution is preferably used. The solvent used is not particularly limited, but may be dichloromethane, chloroform, 1,2-
Haloalkanes such as dichloroethane; cyclic ethers such as tetrahydrofuran, 1,3-dioxolane and 1,4-dioxane; ketones such as methylethylketone, methylisobutylketone and cyclohexanone; aromatic solvents such as chlorobenzene are used. Of these, dichloromethane, 1,2-dichloroethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexane, chlorobenzene and the like are particularly preferable from the viewpoint of solubility and dope stability. These may be one kind or a mixed solvent of two or more kinds. The concentration is also not particularly limited, but the retardation film or the film for liquid crystal display intended by the present invention has a high concentration of 15% by weight or more, preferably 20% by weight or more in order to form a thick film.

As the casting method, generally, a casting method of extruding a solution from a die, a doctor knife method and the like are preferably used. On the other hand, for forming a film or sheet by the melting method, a general melt extrusion molding method may be used.

The film thickness may be selected according to the application, but it is generally 50 to 500 μm, preferably 80 to 300 μm.
The range of is used. If it is less than that, sufficient retardation (product of birefringence Δn and film thickness d) based on refractive index anisotropy cannot be obtained in the case of a retardation film, and it is sufficiently flexible (rigidity) in a liquid crystal display substrate. I can't get the film. On the other hand, if it exceeds it, film formation becomes difficult, which is not preferable. At the same time, in the case of a film for a retardation film, the retardation exceeds the destination even with a slight stretching when the film thickness is reached, which is not preferable because the stretching precision cannot keep up.

The film or sheet of the present invention has a Tg of 1
It is 50 ° C or higher. When Tg is lower than 150 ° C,
Due to the heating during the orientation treatment or the like, thermal deformation and thermal contraction are large, and problems such as peeling, image distortion, and deterioration of durability may occur.

The liquid crystal display substrate of the present invention is used as it is unstretched because optical isotropy is required. However, biaxial stretching may be performed as long as optical isotropy is satisfied. On the other hand, since the retardation film utilizes the refractive index anisotropy, a uniaxially stretched film is used.

In the present invention, as the uniaxial stretching method, a longitudinal uniaxial stretching method, a tenter transverse uniaxial stretching method, a roll stretching method and the like are used. The stretching temperature depends on the Tg of the film used and is generally Tg-50 ° C or higher and Tg + 20 ° C or lower, preferably Tg-30 ° C or higher and Tg + 10 ° C or lower. If it is less than that, uniform orientation becomes difficult because the motion of polymer molecules is frozen, which is not preferable. Moreover, since the molecular motion of the polymer becomes strong when it exceeds that,
The orientation is relaxed by stretching, and it is not preferable because the expected degree of orientation cannot be obtained and it becomes difficult to suppress the orientation. Further, the stretching ratio may be appropriately selected according to the size of the retardation of the target film. This value also depends on the stretching temperature and the film thickness. Generally, for thick films, the draw ratio may be small, and for example, 5 to 50% is preferable. It should be large for thin films. The retardation value of the retardation plate used for STN type liquid crystal display is
Generally, the range of 400 to 650 nm is used.

The retardation plate composed of the uniaxially stretched film or sheet thus obtained can be put to practical use by laminating it with a polarizing plate. Then, a protective film is laminated on the polarizing plate side via an adhesive layer, and a release film is laminated on the retardation plate side via an adhesive layer to obtain a product form in which the retardation plate and the polarizing plate are integrated. Further, since polycarbonate is a resin having a positive intrinsic birefringence, the uniaxially stretched film or sheet and a resin having a negative intrinsic birefringence, for example, polystyrene, uniaxially stretched film or sheet made of polymethylmethacrylate or the like are laminated. It is possible to increase the viewing angle dependency. The unstretched film or sheet is used as a substrate for liquid crystal display. At that time, a transparent electrode layer of tin oxide / indium or the like is laminated thereon, and the transparent electrode layer is coated with, for example, a polyimide liquid crystal alignment thin film for use. The liquid crystal element is completed by rubbing this alignment film and sandwiching the liquid crystal layer between the two laminated substrates with the alignment film inside.

[0025]

INDUSTRIAL APPLICABILITY According to the present invention, there is provided an optical film or sheet such as a retardation plate having high heat resistance and a substrate for liquid crystal display, which is free from turbidity due to crystallization or the like.

[0026]

EXAMPLES The present invention will be described in detail below with reference to examples. However, the present invention is not limited to this.

The physical properties measured in the examples were measured by the following methods. 1) Mechanical property of film: It was performed according to JIS K7113. 2) Viscosity average molecular weight: Substituting the intrinsic viscosity measured with a methylene chloride solution into the Mark-Houwink-Sakurada formula,
It was calculated. 3) Birefringence: Automatic birefringence meter (KOBRA- manufactured by Kanzaki Paper Co., Ltd.)
21AD) was used to measure the birefringence value in visible light of 590 nm. 4) Tg: manufactured by DuPont (Differential Scannin
g Carorimeter 910) using a heating rate of 20 ℃ / min
It was measured at. 5) Light transmittance: Shimadzu Corporation spectrophotometer (UV-24
0) was used.

[0028]

Example 1 1,1-Cyclohexylene bis (4-phenol) and bisphenol-A (molar ratio = 10/9)
A transparent viscous solution was obtained by adding 23 parts by weight of a polycarbonate resin (viscosity average molecular weight 38,000) containing 0) as a bisphenol component to 77 parts by weight of dichloromethane and stirring at room temperature for 10 hours. The dope viscosity of this solution was 1.8 × 10 ⁴ cps at 30 ° C., showing a high solution viscosity. This solution did not change even when left at room temperature in a sealed state for 3 days, and neither white turbidity nor gelation was observed.

The obtained solution was cast on a stainless steel substrate using a doctor knife and dried in a dryer having a wind speed of 2 m / sec at 30 ° C. for 10 minutes, 50 ° C. for 30 minutes, and 130 ° C. for 30 minutes.
The film was heated for a minute to obtain a transparent unstretched film having a film thickness of 102 μm. The transmittance of the obtained film was 89% in the visible region of 500 nm, which was extremely high in transparency.
Also, the retardation (R
e) was 10 nm or less, and the optical isotropy was extremely high. The Tg of this film determined by DSC was 152 ° C., indicating high heat resistance. The obtained film had a breaking strength of 6.3 kg / mm ² , an elongation of 105%, and an initial modulus of 130 kg / mm ² , which was extremely strong.

The unstretched film thus obtained was stretched 10% at 140 ° C. by a tenter method to obtain an oriented film. The Re of this stretched film was 510 nm, and a film having desired birefringence was obtained.

When the solution was extruded from a die having a slit width of 300 μm onto a stainless substrate running at 1 m / min, the solution was uniformly extruded in a so-called curtain shape. The resulting film is transparent and has a film thickness of 8
The thickness unevenness was 1 μm or less with respect to 5 μm.

Using the uniaxially stretched film as a retardation plate,
The liquid crystal panel was applied to one side of a TN liquid crystal cell (FIG. 1) to prepare a black and white display liquid crystal panel. The contrast ratio of the obtained liquid crystal panel in the driven state and the non-driven state was 11.5:
It was 1.

[0033]

Comparative Example 1 25 parts by weight of a polycarbonate resin (molecular weight 38,000) obtained from bisphenol-A was added to 75 parts.
It tried to dissolve in the weight part, but the insoluble part remained. Therefore, the concentration was reduced from 20 parts by weight to 70 parts by weight to prepare a uniform solution. This dope has a viscosity of 4.8 × 10 ³ cps
Met. A film was cast from the solution according to Example 1 to obtain a transparent unstretched film. The Tg of this film was 148 ° C., which was lower than that of the film obtained in Example 1.

Further, as in the first embodiment, the slit width 300
The solution was extruded from a μm die, but the solution was extruded in a non-uniform manner, with a somewhat blind shape. In addition, some turbidity was observed during the drying process. The film thickness unevenness of the obtained film having a film thickness of 78 μm was 5 μm, and the film thickness unevenness was remarkable.

[0035]

Example 2 23 parts by weight of a polycarbonate resin (viscosity average molecular weight 43,000) containing 1,1-cyclohexylene bis (4-phenol) / bisphenol-A (molar ratio = 5/95) as a bisphenol component was added to dichloromethane 77. A transparent viscous solution was obtained by adding 5 parts by weight and stirring at room temperature for 5 hours. This solution did not change even when left at room temperature in a sealed state for 3 days, and neither white turbidity nor gelation was observed. The obtained solution was cast on a stainless steel substrate using a doctor knife and heated at 30 ° C. for 10 minutes, 50 ° C. for 30 minutes and 130 ° C. for 30 minutes in a dryer with a wind speed of 2 m / sec to obtain a film thickness of 95 μm. To obtain a transparent unstretched film. The transmittance of the obtained film was 90% in the visible region of 500 nm, which was extremely high in transparency.
Also, the retardation (R
e) was 10 nm or less, and the optical isotropy was extremely high. The Tg of this film determined by DSC was 150 ° C., which showed higher heat resistance than the polycarbonate film obtained from bisphenol-A. The unstretched film thus obtained was stretched by 10% at 140 ° C. by a tenter method to obtain an oriented film. The Re of this stretched film was 520 nm, and a film having desired birefringence was obtained.

[0036]

Example 3 23 parts by weight of the resin of Example 1 was added to 77 parts by weight of dioxane and heated and stirred at 50 ° C. for 5 hours to obtain a transparent viscous liquid. The dope did not cloud or gel even when left at room temperature for 3 days. The film was cast from this viscous solution using a doctor knife and dried at 40 ° C for 15 minutes at 60 ° C in a dryer with a wind speed of 2 m / sec.
After heating for 30 minutes at 130 ° C. for 30 minutes, a transparent unstretched film having a film thickness of 100 μm was obtained. And the obtained Tg is 15
The temperature was 1 ° C., which was almost the same as the Tg of the unstretched film obtained in Example 1. The retardation of the film obtained by stretching the film at 140 ° C. by 10% was Re = 505 nm, which was almost the same as that of the stretched film of Example 1.

[0037]

Comparative Example 2 Using the resin of Comparative Example 1, an attempt was made to obtain a 23 wt% dioxane solution in the same manner as in Example 3, but the resin did not dissolve. To that end, it was diluted to make a 20% by weight solution. When this solution was allowed to stand at that temperature for one day, white turbidity occurred and it could not withstand film formation. Casting was performed under the conditions of Example 3 using a transparent solution immediately after dissolution, but whitening due to crystallization was observed, and yuzu-skin-like wrinkles were observed on the surface.

[0038]

Examples 4 to 10 Table 1 shows various properties of a film obtained by casting a polycarbonate containing bisphenol A and a predetermined amount of various repeating units shown in Table 1 in the same manner as in Example 1. All of them were dissolved in high concentration and a stable solution was obtained.
Further, all of the cast unstretched films were tough, had high transparency, and had small optical anisotropy (<10 nm). Any of them can be stretched, and a stretched film having a desired optical anisotropy was obtained by controlling the stretching temperature and the stretching ratio.

[0039]

[Table 1]

Correspondence between the abbreviations in Table 1 and the structure of repeating unit [I] is as follows. Z: In the formula [I], R _{1 to} R ₄ are hydrogen atoms, and X is 1,1-
Repeating unit which is cyclohexylene AP: R _{1 to} R ₄ in the formula [I] are hydrogen atoms, and X is 1,1.
Repeating unit which is — (1-phenyl) ethylene FL: R _{1 to} R ₄ in the formula [I] are hydrogen atoms, and X is 9,9.
-Repeating unit which is fluorenylene IP: R _{1 to} R ₄ in the formula [I] are hydrogen atoms, and X is 1,1.
-(3,3,5-Trimethyl) cyclohexylene is a repeating unit BP: R _{1 to} R ₄ in the formula [I] are hydrogen atoms, and X is 1,1.
-Repeating unit which is diphenylphenylene FA: In the formula [I], R _{1 to} R ₄ are hydrogen atoms, and X is 2,2.
- repeating units hexafluoropropylene M _v: viscosity average molecular weight (× 10 ^-4) T: light transmittance (500 nm,%)

[0041]

Example 11 1,1-Cyclohexylene bis (3,5
-Dimethyl-4-phenol) / bisphenol-A
A transparent viscous solution was obtained by adding 25 parts by weight of a polycarbonate resin (viscosity average molecular weight 23,000) containing (15/85) as a bisphenol component to 75 parts by weight of dichloromethane and stirring at room temperature for 5 hours. This solution did not change even when left at room temperature in a sealed state for 3 days, and neither white turbidity nor gelation was observed. The obtained solution was cast and dried by heating at 30 ° C. for 10 minutes, 50 ° C. for 30 minutes, and 130 ° C. for 30 minutes to obtain a transparent unstretched film having a film thickness of 105 μm. The transmittance of this film was 89%, and the retardation was 10 nm or less. And that Tg
Was 154 ° C. The retardation of the oriented film obtained by stretching 10% at 140 ° C. was 480 nm.

[Brief description of drawings]

FIG. 1 shows a sectional view of a liquid crystal panel.

[Explanation of symbols]

 1, 7: polarizing plate 2: retardation plate 3, 6: substrate 4: sealing material 5: liquid crystal layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location // B29K 69:00 (72) Inventor Masanori Abe 4-3-2 Asahigaoka, Hino-shi, Tokyo Teijin Tokyo Research Center Co., Ltd.

Claims (4)

[Claims] 1. The following general formula [I]: [In the formula, R ₁ , R ₂ , R ₃ and R ₄ are the same or different and each is a hydrogen atom or a methyl group, X is a cycloalkylene group having 5 to 10 carbon atoms, an araalkylene group having 7 to 15 carbon atoms, and a carbon number. 1 to 5 haloalkylene groups. Containing 1 to 30 mol% of a repeating unit represented by the following formula [II] An optical film or sheet comprising a polycarbonate copolymer containing 99 to 70 mol% of the repeating unit represented by 2. The optical film or sheet according to claim 1, which has a glass transition temperature of 150 ° C. or higher. 3. A retardation film or sheet comprising an oriented film obtained by uniaxially stretching the optical film according to claim 1. 4. A liquid crystal display substrate comprising the optical film or sheet according to claim 1.