JPH09230316A - Optical film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to produce an optical film having excellent optical characteriatics with good productivity by a casting film forming method of polycarbonate. SOLUTION: The solvent-contg. film of the polycarbonate is peeled from a casting base and, thereafter, the film is transported for 2 to 4 minutes by applying tension at 3 to 7kg per 1 square cm on the film in its transporting direction at 15 to 40 deg.C atmosphere temp. in a first stage. In a second stage, the film is fed into a pin tenter. The atmosphere temp. is set at Tg-45 to Tg-5 deg.C (Tg: the glass transition temp. of the polycarbonate). The rail width of the pin tenter is made smaller by 2.5 to 7.5% than the film width and while both edges in the transverse direction of the film are clamped by pin clips, the film is transported for 2 to 6 minutes in the state that the section in the transverse direction draws a catenary. In a third stage, the film is fed into a roll suspension type drier. The film is transported for 30 to 90 minutes by applying tension of 0.4 to 1.5kg per 1 square cm on the film at Tg-10 to Tg deg.C atmosphere temp. The film is cooled down to room temp. in a fourth stage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical film used for a liquid crystal display device and the like and a method for manufacturing the same.

[0002]

2. Description of the Related Art Optical films are used in plastic liquid crystal cell substrates and retardation compensating film.
By producing such an optical film by a casting film-forming method, it is possible to obtain a film having a small amount of foreign matter and a small thickness unevenness.

When a film is produced by the casting film forming method, the film peeled from the casting support contains about 20% by weight of the solvent. Therefore, this solvent-containing film is subjected to a drying process in a subsequent step until it does not cause a problem in practical use. Because the residual solvent lowers the glass transition temperature due to its plasticizing effect,
It causes problems such that the heat resistance inherent in the polymer is not sufficiently exhibited, and the evaporation solvent has an adverse effect in the film processing step.

By the way, the film just peeled from the surface of the cast support is optically non-uniform when viewed optically (when viewed in-plane, there are large variations in the values of retardation and slow axis). ). Therefore, in order to produce an isotropic film (a film with the smallest possible retardation) from such a film, for example, the polymer chains are heat-relaxed at the same time as the solvent is removed by heating and drying sufficiently without tension. It is necessary to let

When the behavior of the solvent-containing film peeled from the support is dried by heating, the residual solvent is rapidly lost in the initial stage of heating, and the width, length and thickness of the film are first observed. The dimension in the direction shrinks by a few percent. That is, the dimensional shrinkage due to the evaporation of the solvent from the film and the orientation mildness of the molecular chains occur at the same time. The film thus heat-treated under free length exhibits an optically isotropic property due to sufficient drying and thermal relaxation.

However, if the above-mentioned drying and orientation warming are carried out in a continuous process, various problems occur. The current situation is that film formation cannot be carried out with good productivity.

As a technique for producing an optical film, a method of casting using a cast support having a low surface energy is described in JP-A-2-241709. This technique covers the surface of the support with a substance having a low surface energy, facilitates the peeling of the film from the support, reduces the peeling tension, and controls the orientation of the polymer chains in this step to control the low birefringence polymer. This is a method for producing a film. A film having low birefringence can be produced by this technique. However, it is difficult to manufacture a film in which the refractive index in the longitudinal, lateral, and thickness directions and the size of the slow axis are controlled.

Further, Japanese Patent Laid-Open No. 59-211006 and Japanese Patent Publication No. 21580/1992 disclose a method for producing a non-optical rotatory film. Then, there is treated while holding the end portion of the untreated film, thereby holding a stretchable woven or knitted fabric or the like between the holding portion of the processing device and the film. Is proposed. This method is suitable as a method for producing a sheet-shaped product. However, in continuous production, the process is rough and it is difficult to control the refractive index in the longitudinal, lateral, and thickness directions and the size of the slow axis.

Further, Japanese Patent Application Laid-Open No. 60-159016 discloses a method for producing a plastic film having improved optical properties. There, reorientation of the molecules occurs in a layer close to the optically uniaxial birefringent plastic surface (corresponding to 10 to 30% of the total film thickness, preferably 15 to 20%), and It has been proposed to start the relaxation step, which keeps the formed structure after cooling or drying of the film, by heating or by immersion in a solvent or swelling agent. This method is also vertical, horizontal,
Also, it is difficult to control the refractive index in the thickness direction and the size of the slow axis.

As described above, a technique for reducing the retardation has been published as a conventional technique, but a technique for controlling the refractive index and the slow axis has not been clarified. Also,
The fact is that the technology for performing the control of these structures in a continuous process has not been clarified.

[0011]

The optical film is required to be isotropic not only in the film plane but also in the direction perpendicular to the film plane. In particular, it is desired that an optical film used for a liquid crystal cell substrate or an optical compensation film substrate having an optical layer such as a polymer liquid crystal formed thereon has no optical influence on the optical layer. That is, it is necessary that the anisotropy is small (the retardation is small) and the transparency is excellent.

Further, for example, when an optical axis in an optical layer such as a polymer liquid crystal is aligned with a slow axis of a film for an optical compensation substrate at an appropriate angle, a higher optical property is exhibited, or 2 When using more than one film in one liquid crystal display device, the direction of the slow axis of the optical film used as the substrate for the optical compensation film is a very important characteristic. When the optical compensation films using two optical compensation film substrates are laminated so that the slow axes are parallel to each other, the retardation value is the sum of the retardations of the respective substrates and the slow axes are made orthogonal to each other. If you make a difference Even if they have the same in-plane retardation, the retardation will be different depending on the bonding angle with other optical elements in this way, so if the slow axis is locally different in the plane,
The optical characteristics cannot be made uniform in the plane.

Usually, the substrate for the optical compensation film is used after being cut into an appropriate size according to the application. In order to minimize the loss during cutting, it is necessary that the slow axis angles are aligned within a certain range.

The optical film is stretched and oriented to have a retardation of an appropriate size to form a retardation compensating plate,
It is used as a substrate for an optical compensation film by forming an optical layer such as a polymer liquid crystal. However, when the slow axis distribution of the film before stretch orientation is small, both the slow axis distribution and the retardation distribution after stretching tend to be small. This tendency generally tends to occur when the draw ratio is increased, but such a film retains its effect even at a low draw ratio (and thus low retardation).

Heat resistance is one of the required characteristics of the substrate for the optical compensation film. When used in a liquid crystal display device or the like, it is required to have environmental resistance and heat resistance to withstand high temperature treatment in a manufacturing process in which an optical compensation layer such as a polymer liquid crystal is formed on the substrate. The present inventors have achieved the present invention as a result of earnest studies as a subject of an efficient production method of an optically isotropic film having excellent heat resistance of polycarbonate.

[0016]

The optical film of the present invention is a film or sheet made of polycarbonate, wherein the main refractive index in the film plane and the main refractive index in the thickness direction are nx, ny and nz, respectively. When d is set, 3 nm ≦ (nx−ny) × d <10 nm, −5
° ≤ slow axis angle ≤ + 5 °, [(nx + ny) / 2-n
z] × d ≦ 70 nm.

More preferably, the polycarbonate is an aromatic polycarbonate composed of bisphenol A and has an average molecular weight of 30,000 or more.

Alternatively, preferably, the polycarbonate has a bisphenol component having a perhydroisophorone skeleton and a bisphenol A copolymerization ratio of 5 to 30 mo.
It is an aromatic polycarbonate composed of a copolymer of bisphenol A copolymerized with 1%, and has an average molecular weight of 30,000 or more.

Alternatively or preferably, the polycarbonate is an aromatic polycarbonate composed of a copolymer of bisphenol A in which a bisphenol component composed of a fluorene skeleton is copolymerized with bisphenol A at a copolymerization ratio of 5 to 30 mol%, and Average molecular weight is 30,000
That is all.

The present invention also provides a method for producing such an optical film of the present invention by a casting film forming method of polycarbonate, in which the solvent-containing film of polycarbonate is peeled off from the casting support, and then the following four steps are carried out. When the film is cooled to room temperature continuously through the following, in the first step, the tension in the film conveying direction is 3 to 3 per 1 cm <2> under the ambient temperature of 15 to 40 [deg.] C.
It is conveyed for 2 to 4 minutes while applying 7 kg, and in the second step, the film is fed into the pin tenter, and the ambient temperature is Tg-in comparison with Tg which is the glass transition temperature of polycarbonate.
Under 45 to Tg-5 ° C, with the rail width of the pin tenter reduced by 2.5 to 7.5% from the film width,
While holding both edges of the film width direction by the pin clip, while the cross section of the film width direction draws a catenary line, 2
It is conveyed for ~ 6 minutes, and in the third step, the film is sent to a roll-suspended dryer, and a tension of 0.4 to 1.5 kg per 1 cm 2 is applied while the atmospheric temperature is Tg-10 to Tg ° C. , 30 to 90 minutes, and in the fourth step, the film is cooled to room temperature.

More preferably, between the second step and the third step, the film is fed into an air floating type dryer, and the ambient temperature is from Tg-30 to Tg ° C., and the film is 0.2 per square cm. The intermediate treatment of the film is performed between the second step and the third step by feeding the film for 1 to 5 minutes while applying a tension of 4 to 3 kg.

Specifically, the film peeled from the support is
1) Apply tension in the first step to align the molecular chains of the polymer, 2) Then, dry without applying tension in the lateral (or width) direction as much as possible, and in the direction of the film flow generated in the previous stage. The step of transporting and drying while maintaining the orientation of the polymer chains of 3) and the step of heating and drying while applying a relatively weak tension in the flow direction in the next step to relax the molecular chains and reduce the orientation The present invention has been found to enable efficient production of a film having the characteristics of the present invention in a continuous process by passing through the above steps.

Specifically, a polycarbonate made of bisphenol A, a bisphenol component having a perhydroisophorone skeleton as the polycarbonate is bisphenol A.
And an average molecular weight of bisphenol A copolymerized at a copolymerization ratio of 5 to 30 mol% is 3000.
An aromatic polycarbonate having a molecular weight of 0 or more and a bisphenol component in which the polycarbonate has a fluorene skeleton and a bisphenol A copolymer having an average molecular weight of 30
000 or more aromatic polycarbonate is dissolved in a solvent and cast on a support such as a casting drum or casting belt. This is peeled off from the support when the content of the solvent is about 15 to 20% by weight. The film peeled from the support is treated as follows in successive steps.

The solvent-containing film is subjected to a tension of 3 to 7 kg per 1 cm 2 in the flow direction of the film at an ambient temperature of 15 to 40 ° C. At this time, some evaporation of the solvent and alignment of the polycarbonate molecular chains occur. As a method of applying tension, a method of passing a film between two pairs of nip rolls or a method in which a plurality of free-rotating rolls and a tension control device are arranged between the peeling roll of the casting film and the film guide roll of the pin tenter inlet The method etc. which it implements can be taken.

Next, the film is fed into a pin tenter, and both ends are held and fixed by pin sheets and conveyed while being heated. The heating temperature at this time is (Tg-5 ° C) to (Tg-45).
° C). (Here, Tg is the glass transition temperature of the polycarbonate.) In this pintenter heating and conveying step, the film shrinks due to the rapid evaporation of the solvent. In order to eliminate the adverse effects of this shrinkage stress (retardation, increase in slow axis angle), the rail width of the pin tenter is reduced so that the film does not pass through the tensioned state in all the steps of the pin tenter.

At this time, the rail width is reduced by 2.5 to 7.5% with respect to the film width. Here, the film does not pass through the tension state in all the steps of the pin tenter described above means that the film in the pin tenter is not in a taut state wherever the film is seen and the cross section in the width direction draws a so-called catenary line. means.

By this pin tenter treatment, a dry heat treatment is carried out until the residual solvent amount in the film becomes 1 to 4% by weight. The edge of the film held by the pin is cut off, and the film is passed through a roll-suspended processing machine at temperature Tg.
(Tg-10) ° C., and the take-up tension is 0.4 to 1.5 kg per 1 cm 2 for dry heat treatment. Finally, it is cooled to room temperature and wound into a roll to obtain a product.

The roll-suspending type processing machine referred to here is an apparatus in which a large number of rolls are installed in parallel in the air oven in an alternating manner and the rolls are conveyed while heating the film. is there. The film is dry heat treated by hot air circulating in the oven.

As a process after the pin tenter treatment, air-floating drying and then roll-suspended heat treatment can be employed. This process makes the control of the optical properties relatively easy. At the end of the pin tenter process, the film edge part gripped by the pin is cut off, and the product part is sent to an air-floating dryer for dry heat treatment. The processing temperature at this time is T
g- (Tg-30) [deg.] C., the take-up tension is 0.4-3 kg per 1 cm <2>. The air-floating dryer here is a device that has a structure in which air is blown out from nozzles provided above and below the film in an oven, and the film is passed between the upper and lower nozzles to perform non-contact dry heat treatment. .

Further, this film is passed through a roll-suspending type processor and subjected to a dry heat treatment at a temperature of Tg to (Tg-10) ° C. and a take-up tension of 0.4 to 1.5 kg per 1 cm 2. Finally, it is cooled to room temperature and wound into a roll to obtain a product.

The polycarbonate used in the present invention is a general term for aromatic polycarbonates in which bisphenol is mainly bonded to a carbonate bond, and the production method is not particularly limited, but it is generally produced by the phosgene method or the diphenyl carbonate method. Bisphenol A is typical as the bisphenol used. Further, the copolymerization ratio of bisphenol A is 5 to 30.
Polycarbonate obtained by copolymerizing a bisphenol component having a perhydroisophorone skeleton at a mol%. further,
It is an aromatic polycarbonate obtained by copolymerizing a bisphenol component having a fluorene skeleton with a copolymerization ratio of 5 to 30 mol% with respect to bisphenol A.

The average molecular weight of these polycarbonates is 30,000 or more. If it is less than 30,000, the mechanical strength of the film is weak, which is not preferable. The upper limit of the molecular weight is about 100,000. If it is higher than this, the solution becomes too viscous and the film-forming property is significantly impaired, which is not preferable.

In the polycarbonate resin of the present invention, if necessary, for example, triphenyl phosphite, tris (nonylphenyl) phosphite, distearyl pentaerythritol diphosphite, diphenyl hydrogen phosphite, Irganox 1076 [stearyl-β- Stabilizers such as (3,5-di-tert-butyl-4-hydroxyphenyl) propionate],
For example, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole 2- (2'-hydroxy-
3 ', 5'-di-tert-amylphenyl) benzotriazole, 2- (2'-hydroxy-4'-octoxyphenyl) benzotriazole, 2-hydroxy-4
-Additives such as a weathering agent such as octoxybenzophenone, a colorant, an antistatic agent, a release agent and a lubricant may be added within a range not impairing the transparency of the film.

Further, in the present invention, the solvent used for the polycarbonate solution may be any solvent which dissolves the polycarbonate and has a low boiling point. For example, halogen-based solvents such as methylene chloride, 1,2-dichloroethane, 1,1,2-trichloroethane, chlorobenzene, 1,3-dioxolane,
Cyclic ether solvents such as 1,4-dioxane and tetrahydrofuran, aromatic ether solvents such as anisole, and ketone solvents such as cyclohexanone can be used. Of these, methylene chloride, 1,3-dioxolane, and 1,4 from the viewpoints of solubility, solution stability, and film-forming property.
-Dioxane is particularly preferred.

The solution concentration depends on the molecular weight of the polycarbonate, but is 10 to 35% by weight, preferably 1
A range of 2-30% by weight is used. If the concentration exceeds this upper limit, the stability of the solution is lowered, or the solution viscosity becomes too high, which makes uniform film formation difficult, which is not preferable. On the other hand, if it is less than the lower limit, it is unfavorably affected by external disturbance in the casting process, and the surface uniformity is lowered.

The thickness of the polycarbonate film of the present invention is preferably 50 to 150 μm in consideration of the handling property and the retardation value in the process of manufacturing the optical compensation film and the step of laminating with another retardation plate or a liquid crystal cell.

The film characteristics were measured and evaluated as follows.

1) Retardation measurement and slow axis direction measurement (nx-ny) × d, [(nx + ny) / 2-nz] ×
The measurement of d and the angle of the slow axis can be easily determined by a commonly used birefringence measuring device. For example, trade name "KOBRA-21" manufactured by Shin Oji Paper Co., Ltd.
ADH "and the product name" M-150 "by JASCO Corporation can measure. Since the measurement of the three-dimensional refractive index can be determined by the attached software, [(nx + ny) / 2-n
The value of z] × d can be determined from the measured value and the film thickness.

Here, (nx-ny) × d = R, [(nx
The measurement method of the three-dimensional refractive index necessary for determining + ny) / 2−nz] × d will be described. Although the three-dimensional refractive index can be measured by an Abbe refractometer or the like, it is preferably determined by the birefringence measuring device described in the specification from the viewpoint of measurement accuracy. Assuming that the polymer film is a three-dimensional index ellipsoid, it can be calculated from the incident angle dependence of the R value. That is, the above refractive indices nx, n
Using y and nz, the following relational expression holds.

[0040]

[Equation 1]

[0041]

[Equation 2]

Therefore, the average refractive index n = of the polymer film is
After determining (nx + ny + nz) / 3, the R (θ) value, which is the retardation at the incident angle θ, was measured by changing the incident angle θ, and the refractive indices nx, ny, and n were calculated from the formula-1 and the formula-2.
Determine z. Note that Δn (θ) is the birefringence at the incident angle θ, and d is the film thickness. Also, it is possible to use literature values for n.

In the present invention, a birefringence measuring device (trade name "KOBRA-21ADH", manufactured by Shin Oji Paper Co., Ltd.) was used to measure at a wavelength of 590 nm. The direction of the slow axis was based on the film flow direction. The measurement was performed by sampling at 40 mm intervals.

2) Measurement of molecular weight of polycarbonate The viscosity average molecular weight was obtained by measuring viscosity at 20 ° C. in a dichloromethane solution having a concentration of 0.5 g / dl.

3) Measurement of Flatness of Polycarbonate Film A film cut into a width of 1000 mm and a length of 2000 mm was spread on a flatness measuring table, and air was pushed out so that no air pool was formed between the measuring table and the film. I left it for more than a minute. Then, the length of the natural bulging portion of the film was measured, the sum of the respective lengths was obtained, and this was divided by the measurement area to express the flatness in mm per square meter.

4) Measurement of Tg A predetermined amount of sample was heated to 300 ° C. and cooled to room temperature. Further, DSC is performed at a heating rate of 10 ° C / min
I drew a curve and calculated from the inflection point.

[0047]

Example 1 Polycarbonate having a molecular weight of 38,000 obtained by condensation of phosgene and bisphenol A was dissolved in methylene chloride to prepare a 20% solution. This was cast on a steel belt, dried and stripped continuously.
At this time, the concentration of methylene chloride in the film is 17
%Met. The thickness of the film was about 110 μm.

When the Re value of this film was measured, it varied within the range of 2 to 10 nm in the width direction of the film. Also, the size of the slow axis was not constant and was randomly oriented.

The film just after being stripped was passed between rolls at 20 ° C. to apply a tension of 6 kg per 1 cm 2 to the film. After that, both sides in the film width direction were gripped and conveyed by a pin tenter. At this time, the temperature of the pin tenter was 140 ° C. In addition, in transporting the film, the width direction is always slack when the film is in the pin tenter oven in order to suppress the contraction due to the rapid evaporation of methylene chloride and to suppress the increase of the molecular orientation and the slow axis direction due to the contraction stress. The rail width was adjusted so as to draw a so-called catenary line. The reduction ratio of the rail width was 3.5%.

The residence time of the film in the pin tenter oven was 6 minutes. At the exit of the pin tenter, the film of the pin grip part is cut off by edge trim, and then the product part is continuously passed through the dancer roll and the tension is 1 sq.
It was collected at room temperature at 1.5 kg per m. Further, this film was fed into a suspension type heat treatment machine and the exit tension of the film was adjusted to 0.4 to 1.0 kg per 1 cm 2 and the oven air temperature was set to 155 ° C. for dry heat treatment. The residence time of the film was about 1.5 hours. The film had a thickness of 100 μm and a width of 1100 mm.

The characteristic values of the film thus obtained are as follows. (1) Widthwise distribution of retardation values: Min to MAX 6 to 9 nm. (2) Width direction distribution of slow axis angles: Min to MAX -3 ° to 3 °. (3)
[(Nx + ny) / 2-nz] × d widthwise distribution: Mi
n-MAX 55-60 nm. (4) Tg: 158 ° C.
(5) Film flatness: 450m per square meter
m.

[0052]

Comparative Example 1 A film having a thickness of 100 μm was prepared in the same manner as in Example 1 except that the tension was applied in the vertical direction of the vertical direction tension applying device by 2.5 kg per 1 cm 2. The characteristic values of the obtained film were as follows.

(1) Widthwise distribution of retardation values:
Min-MAX 5-13 nm. (2) Width-direction distribution of slow axis angles: Min to MAX-6 ° to 6 °. (3) [(n
x + ny) / 2−nz] × d widthwise distribution: Min to M
AX 50-60 nm. (4) Tg: 158 ° C. (5)
Film flatness: 480 mm per square meter.

[0054]

COMPARATIVE EXAMPLE 2 A film having a thickness of 100 μm was prepared in the same manner as in Example 1 except that the rail width of the pin tenter was reduced by 1% from the film width during the film heat treatment and the film was allowed to pass through. The characteristic values of the obtained film were as follows. (1) Widthwise distribution of retardation values: Min to MAX 6 to 20 nm. (2) Width-direction distribution of slow axis angles: Min to MAX-20 ° to 20 °.
(3) Width direction distribution of [(nx + ny) / 2-nz] * d: Min-MAX 60-90 nm. (4) Tg: 1
58 ° C. (5) Film flatness: 470 mm per square meter.

[0055]

[Comparative Example 3] Heat treatment conditions by a roll-suspended heat treatment machine were a temperature of 130 ° C and a tension of 2.0 to 2.3 per square cm.
Other conditions were the same as in Example 1 except that the amount was 10 kg.
A film having a thickness of 0 μm was prepared. The characteristic values of the obtained film were as follows.

(1) Widthwise distribution of retardation values:
Min-MAX 15-25 nm. (2) Width direction distribution of slow axis angles: Min to MAX-3 ° to 3 °. (3)
[(Nx + ny) / 2-nz] × d widthwise distribution: Mi
n-MAX 70-80 nm. (4) Tg: 158 ° C.
(5) Film flatness: 470m per square meter
m.

[0057]

Example 2 Bisphenol A and bisphenol having a perhydroisophorone skeleton were copolymerized by the phosgene method to obtain an aromatic polycarbonate resin having an average molecular weight of 35,000. The copolymerization ratio was 15 mol% of bisphenol having a perhydroisophorone skeleton with respect to the bisphenol A component, and the glass transition temperature was 172 ° C.

The polymer was dissolved in methylene chloride to prepare a 20% by weight solution. This was cast on a steel belt, dried and stripped continuously. At this time, the concentration of methylene chloride in the film was 17% and the thickness was about 11
It was 0 μm. The film immediately after being stripped was passed through a roll at room temperature and conveyed while applying a tension of 7 kg per 1 cm 2 to the film.

After that, both ends in the width direction of the film were gripped and conveyed by a pin tenter. At this time, the temperature of the air in the pin tenter was set to 155 ° C., and the reduction ratio of the rail width was set to 5%.
The residence time of the film in the pintenter oven was 6 minutes. The film of the pin grip portion was separated by an edge trim at the pin tenter outlet, and the product portion was continuously passed through a dancer roll and pulled off at room temperature with a tension of 1.5 kg per square cm. Further, this film was fed into a suspension type heat treatment machine, the exit tension of the film was set to 0.4 to 1.0 kg per 1 cm 2, and the air temperature of the oven was set to 170.
Film retention time after drying and heat treatment at approx.
It was time. The thickness of the obtained film was 100 μm. The characteristic values of the film thus obtained are as follows.

(1) Widthwise distribution of retardation values:
Min-MAX 7-10 nm. (2) Width direction distribution of slow axis angle: Min to MAX-4 ° to 4 °. (3)
[(Nx + ny) / 2-nz] × d widthwise distribution: Mi
n-MAX 55-60 nm. (4) Tg: 170 ° C.
(5) Flatness: 430 mm per square meter.

[0061]

Example 3 Bisphenol A and bisphenol having a fluorene skeleton were copolymerized by the phosgene method to obtain an aromatic polycarbonate resin having an average molecular weight of 36000. The copolymerization ratio was 16 mol% of bisphenol having a fluorene skeleton with respect to the bisphenol A component, and the glass transition temperature was 175 ° C.

20% by weight of the polymer was dissolved in methylene chloride, cast on a steel belt, dried and stripped. The solvent-containing film immediately after being stripped off was passed through a roll at 40 ° C. while being applied with a tension of 5.5 kg per 1 cm 2.

Subsequently, both ends in the width direction of the film were gripped by a pin tenter and conveyed. At this time, the temperature of the air in the pin tenter was 155 ° C., and the reduction ratio of the rail width was 5%. The residence time of the film in the pin tenter oven was 5 minutes.

At the outlet of the pin tenter, the film of the pin gripping portion is separated by edge trim, the product portion is continuously passed through an air floating type dryer at 160 ° C. for 5 minutes, and the tension is 1 cm 2.
It was collected at 0.4 to 1.0 kg. Further, this film was fed into a suspension type heat treatment machine, and the dry film heat treatment was carried out with the outlet tension of the film being 0.4 to 1.0 kg per 1 cm 2 and the air temperature of the oven being 170 ° C. The residence time of the film was 90 minutes. Thus, a 100 μm film was obtained. The characteristic values of the film thus obtained are as follows.

(1) Widthwise distribution of retardation values:
Min-MAX 5-8 nm. (2) Width direction distribution of slow axis angle: Min to MAX-3 ° to 4 °. (3)
[(Nx + ny) / 2-nz] × d widthwise distribution: Mi
n-MAX 45-50 nm. (4) Tg: 173 ° C.
(5) Flatness: 300 mm per square meter.

[0066]

Example 4 Bisphenol A and bisphenol having a fluorene skeleton were copolymerized by the phosgene method to obtain an aromatic polycarbonate resin having an average molecular weight of 36000. The copolymerization ratio was 16 mol% of bisphenol having a fluorene skeleton with respect to the bisphenol A component, and the glass transition temperature was 175 ° C.

The polymer was added to 1,3-dioxolane 20
It was melted by weight%, cast on a steel belt, dried and stripped. The solvent-containing film immediately after being stripped was passed through a roll at 40 ° C. while being applied with a tension of 3 kg per 1 cm 2. Subsequently, both ends in the width direction of the film were gripped and conveyed by a pin tenter. At this time, the air temperature of the pin tenter was set to 145 ° C, and the reduction ratio of the rail width was 3.5%.
And The residence time of the film in the pin tenter oven was 5 minutes.

At the exit of the pin tenter, the film of the pin gripping portion is separated by edge trim, the product portion is subsequently passed through an air floating dryer at 165 ° C. for 5 minutes, and a tension of 1 cm 2 is applied.
It was collected at 0.6 kg per unit. Further, this film was sent to a suspension type heat treatment machine, the exit tension of the film was set to 0.5 kg per 1 cm 2, and the air temperature in the oven was set to 170.
Drying heat treatment was performed at ℃. The residence time of the film was 90 minutes. Thus, a 50 μm film was obtained. The characteristic values of the film thus obtained are as follows.

(1) Widthwise distribution of retardation values:
Min-MAX 8-10 nm. (2) Width direction distribution of slow axis angle: Min to MAX-4 ° to 5 °. (3)
[(Nx + ny) / 2-nz] × d widthwise distribution: Mi
n-MAX 50-60 nm. (4) Tg: 174 ° C.
(5) Flatness: 350 mm per square meter

[0070]

The polycarbonate film of the present invention is advantageous in that the retardation and the slow axis optical anisotropy are controlled to desired values, and the thickness unevenness is extremely flat. It also has excellent transparency and heat resistance. Therefore, when it is used as various film substrates for liquid crystals, it exhibits particularly excellent effects.

Therefore, the optical film of the present invention comprises an optical compensation film substrate, an electrode substrate material for a touch panel, a polarizing plate material, and an optical filter material, which is used by forming an optical layer of a plastic liquid crystal cell, a polymer liquid crystal or the like on the optical film. , The retardation value when stretched using the optical film of the present invention and the distribution of the retardation axis angle are uniform, and it can be used as a goggle material, and a retardation plate material, an elliptical (or circular) polarizing plate. It is also an excellent material.

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Claims (6)

[Claims] 1. A film or sheet made of polycarbonate, wherein 3 nm.ltoreq. (Nx-ny), where nx and ny and nz are the main refractive indices in the film plane and the thickness direction, respectively, and the film thickness is d. ) × d <10
nm, −5 ° ≦ slow axis angle ≦ + 5 °, [(nx + n
y) / 2-nz] × d ≦ 70 nm, an optical film. 2. Polycarbonate is bisphenol A
Aromatic polycarbonate consisting of, and having an average molecular weight of 30,000 or more.
The optical film described. 3. A polycarbonate is an aromatic polycarbonate comprising a copolymer of bisphenol A obtained by copolymerizing a bisphenol component comprising a perhydroisophorone skeleton with bisphenol A at a copolymerization ratio of 5 to 30 mol%, and The optical film according to claim 1, having an average molecular weight of 30,000 or more. 4. An aromatic polycarbonate comprising a bisphenol A copolymer obtained by copolymerizing a bisphenol component comprising a fluorene skeleton with a bisphenol A at a copolymerization ratio of 5 to 30 mol%, and having an average molecular weight. Is 30000 or more, The optical film according to claim 1, wherein 5. A method for producing the optical film according to any one of claims 1 to 4 by a polycarbonate film-casting method, wherein after peeling the solvent-containing film of polycarbonate from the casting support, When the film is cooled to room temperature through the four steps continuously, in the first step, the tension is 3 to 1 cm <2> in the film conveying direction under the ambient temperature of 15 to 40 [deg.] C.
It is conveyed for 2 to 4 minutes while applying 7 kg, and in the second step, the film is fed into the pin tenter, and the ambient temperature is Tg-in comparison with Tg which is the glass transition temperature of polycarbonate.
Under 45 to Tg-5 ° C, with the rail width of the pin tenter reduced by 2.5 to 7.5% from the film width,
While holding both edges of the film width direction by the pin clip, while the cross section of the film width direction draws a catenary line, 2
It is conveyed for ~ 6 minutes, and in the third step, the film is sent to a roll-suspended dryer, and a tension of 0.4 to 1.5 kg per 1 cm 2 is applied while the atmospheric temperature is Tg-10 to Tg ° C. For 30 to 90 minutes, and in the fourth step, the film is cooled to room temperature. 6. Between the second step and the third step, the film is fed into an air floating dryer, and the ambient temperature is Tg-30 to Tg ° C. and 0.4 to 3 kg per 1 cm 2 The method for producing an optical film according to claim 5, wherein the intermediate treatment of the film is performed between the second step and the third step by feeding the film for 1 to 5 minutes while applying the tension.