JP5601317B2 - Manufacturing method of optical film - Google Patents

Description

  The present invention is an optical that can be used for various functional films such as a polarizing plate protective film, a retardation film, a viewing angle widening film, a plasma display, an organic EL display, etc. used in a liquid crystal display device. The present invention relates to a method for producing a film, particularly a method for continuously producing an optical film having a stretching step.

With the recent increase in the screen size of display devices, it is required to widen the optical film. As a method for producing a wide optical film, a stretching process is generally performed in the width direction of the polymer film. When a tenter is used in the stretching process, both ends of the polymer film are gripped by clips, so that it is unlikely to shrink in the direction perpendicular to the stretching direction compared to the central portion in the width direction, and the film width direction There was a problem that uneven physical properties occurred. For example, the retardation of the film was not uniform in the width direction. Therefore, it was necessary to cut both ends of the film with a relatively large width by slitting, and it was difficult to produce a wide optical film. Furthermore, a tear occurred with the jagged end surface during cutting. When tearing occurs, tearing is transmitted to the center of the film during line conveyance, and in the worst case, the line may stop.
The stretching process generally has a preheating stage, a stretching stage, and a thermal relaxation stage.

In order to improve physical property unevenness in the width direction of the film, a technique for locally heating both ends of the film is known.
For example, Patent Document 1 discloses a technique in which, after the stretching stage, in the thermal relaxation stage, heat treatment is performed by providing a temperature gradient in the width direction of the film, and the retardation distribution in the film plane is suppressed to 2 nm or less. However, if a temperature gradient is provided only in the thermal relaxation stage after the stretching stage, the temperature balance in the tenter is lost, so that it is difficult to adjust the orientation angle (Boeing). Boeing is an index indicating the degree of uniformity of polymer chain orientation in the film width direction, and the smaller the value, the better. If the bowing is large, display unevenness occurs when the polarizing plate is processed, which is not preferable.

  Further, for example, in Patent Document 2, a thermoplastic resin film having a thickness gradient of 0.1 to 1.0% in the width direction is set to a temperature of 0.1 to 2 ° C. in the width direction so that the larger thickness side becomes a high temperature. A technique is disclosed in which after preheating with a gradient, the film is stretched to make the retardation value uniform over the entire surface of the film. However, even when a temperature gradient is provided in the preheating stage, the temperature balance in the tenter is lost, so it is still difficult to adjust the orientation angle (Boeing).

JP-A-11-77822 JP 11-258420 A

  An object of the present invention is to provide a method for producing an optical film in which unevenness in physical properties such as retardation in the width direction of the film and bowing are sufficiently reduced.

The present invention provides a method for producing an optical film having a stretching step of stretching the polymer film in the width direction, immediately after completing the start of stretching before and stretching, the temperature of the polymer film opposite end portions higher than the temperature of the polymer film central portion The average temperature T1sa at both ends of the polymer film immediately before the start of stretching and the average temperature T2sa at both ends of the polymer film immediately after the completion of stretching are represented by the following formula (3):
0.9 ≦ T1sa / T2sa ≦ 1.0 Formula (3)
It is related with the manufacturing method of the optical film characterized by satisfy | filling these relationships .

  According to the present invention, it is possible to manufacture an optical film in which uneven physical properties such as retardation in the in-plane direction and thickness direction in the film width direction and bowing are sufficiently reduced.

The schematic diagram when a polymer film is seen from the upper surface within the tenter which performs an extending | stretching process is shown. It is a disassembled perspective view which shows the outline of a structure of a liquid crystal display device.

(Stretching process)
The method for producing an optical film according to the present invention includes a stretching step of stretching the polymer film in the width direction. The temperature at both ends of the polymer film is set at the center of the polymer film immediately before the start of stretching and immediately after the stretching is completed. It is characterized by being higher than the temperature. Specifically, as shown in FIG. 1, the stretching process 1 usually has a preheating stage 11, a stretching stage 12, and a thermal relaxation stage 13, and the width direction (TD) of the polymer film 2 immediately before and immediately after the stretching stage 12. Direction) The temperature at both ends is made higher than the temperature at the center of the polymer film 2. FIG. 1 is a schematic view of a polymer film 2 as viewed from above in a tenter that performs the stretching step 1.

In the present invention, by achieving the predetermined temperature gradient both immediately before the start of stretching and immediately after the completion of stretching, physical property unevenness such as retardation in the in-plane direction and thickness direction in the film width direction and bowing can be sufficiently reduced. Although the details of the mechanism for obtaining such an effect are not clear, it is considered to be based on the following mechanism.
When stretched, the film shrinks in a direction perpendicular to the stretching direction. However, this contraction is not uniform in the width direction, and the amount of contraction is particularly small at both ends in the width direction where the clip is held. This non-uniform shrinkage amount causes retardation unevenness. By heating both ends of the film in the width direction, the shrinkage of the both ends is promoted and the amount of shrinkage in the width direction is made uniform. As a result, it is considered that retardation unevenness can be reduced.
On the other hand, the film is deformed by this shrinkage, and the deformation is determined by the film hardness before and after stretching. For example, when the film hardness before stretching is smaller than the film hardness after stretching, the film is deformed in a convex shape with respect to the film conveying direction. By providing a predetermined temperature gradient before and after stretching, the deformation can be made relatively equal in the width direction, so that it is considered that the orientation angle unevenness can be sufficiently reduced.
If a predetermined temperature gradient is achieved only at one of the start of stretching and the end of stretching, the bowing cannot be reduced sufficiently. If the predetermined temperature gradient is not achieved both immediately before the start of stretching and immediately after the completion of stretching, physical property unevenness occurs, and slitting causes tearing of the end face.

  In the present invention, as shown in FIG. 1, the polymer film 2 (hereinafter sometimes simply referred to as a film) is held at both ends by clips 3 and conveyed in the conveying direction (MD direction), while being preheated step 11, Through the stretching step 12 and the thermal relaxation step 13, stretching in the width direction (TD direction) and, if desired, stretching in the MD direction is achieved.

The predetermined temperature gradient achieved just before the start of stretching and immediately after the completion of stretching may be achieved by any heating means, usually from hot air or inert gas blowing means, infrared irradiation means, heating wires and heating rolls. This is achieved by heating both ends of the polymer film by the end local heating means 4 selected from the group consisting of: You may employ | adopt combining 2 or more types of edge part local heating means.
Hereinafter, each stage and temperature gradient will be described in detail.

  In the preliminary stage 11, the film temperature is controlled by appropriately adjusting the atmospheric temperature and the set temperature of the edge local heating means 4, and as a result, the temperature at both ends of the film immediately before the start of stretching is made higher than the temperature at the center of the film.

  Immediately before the start of stretching means immediately before entering the stretching stage, and when indicated by the position in FIG. 1, it corresponds to a position upstream by x1 from where stretching is started in the MD direction. At this time, x1 may be within a range of 20 mm or less.

The end of the film immediately before the start of stretching is a position at a distance y1 from the film end surface in the TD direction, and y1 may be within a range of 20 mm or less.
The central portion of the film immediately before the start of stretching is a position equidistant from both ends of the film immediately before the start of stretching.

When the temperature at the edge of the film immediately before the start of stretching is T1s and the temperature at the center of the film immediately before the start of stretching is T1c, the temperature T1s at both ends is usually 5 ° C. or more, particularly 5 to 50 from the temperature T1c at the center. Increase by ℃. From the viewpoint of further reducing retardation unevenness and bowing, T1s at both ends is preferably set to be 8 to 16 ° C. higher than T1c at the center.
T1s at both ends is usually controlled to be isothermal, and a difference of 1 ° C. or less may occur.

In this specification, the temperature T1s at the end of the film immediately before the start of stretching is a value obtained by measuring the temperature at position P1s at x1 = 10 mm and y1 = 10 mm in FIG. 1 with a non-contact thermometer (ITOR-540N manufactured by HORIBA). Is used.
The temperature T1c at the center of the film immediately before the start of stretching is the value obtained by measuring the temperature at the position P1c at x1 = 10 mm at the same distance from both ends in the TD direction in FIG.
Although the temperature T1s at both ends of the film and the temperature T1c at the center of the film use values measured on the same surface of the film, they may be measured on different surfaces.

From the standpoint of further reducing retardation unevenness and bowing, and also effectively reducing the width direction hazyness, the temperature T1s at the film end is the temperature T1c at the center of the film at both ends, and the following formula:
Tg−25 ≦ T1c + 5 ≦ T1s ≦ Tg + 20 Formula (1)
In particular,
Tg-15 ≦ T1c + 8 ≦ T1s ≦ Tg + 15 Formula (1 ′)
It is preferable to satisfy the relationship (Tg is the glass transition temperature of the polymer film).

  In FIG. 1, the end local heating means 4 in the preheating stage 11 is arranged on the front side of the film 2 and locally heats the film end, but is not particularly limited as long as a predetermined temperature gradient is achieved, For example, it may be disposed on the back side of the film, or may be disposed above and below the film in the drawing. From the viewpoint of controlling the temperature gradient, the end local heating means 4 is preferably arranged from the front side or / and the back side of the film toward the film.

  The atmospheric temperature in the preheating stage 11 is not particularly limited as long as a predetermined temperature gradient is achieved, and it is usually only required to be maintained at a temperature comparable to the temperature T1c at the center of the film.

  In the stretching step 12, stretching in the TD direction is achieved, and further stretching in the MD direction is achieved as desired. The draw ratio in the TD direction is not particularly limited, and is usually 1.05 to 2.0 times, preferably 1.2 to 1.6 times. The draw ratio in the MD direction is usually 2.0 times or less, preferably 1.01 to 1.5 times.

  At this stage, it is not necessary to control the temperature in particular, and the atmospheric temperature at this stage may be maintained at the same level as the temperature T1c at the center of the film.

  In the thermal relaxation stage 13, the film temperature is controlled by appropriately adjusting the ambient temperature and the set temperature of the edge local heating means 4, and as a result, the temperature at both ends of the film immediately after the completion of stretching is more than the temperature at the center of the film. Make it high.

  Immediately after completion of stretching means immediately after exiting the stretching stage, and when indicated by the position in FIG. 1, it corresponds to a position downstream by x2 from the point where stretching has been completed in the MD direction. At this time, x2 may be within a range of 20 mm or less.

The end of the film immediately after completion of stretching is a position at a distance y2 from the film end surface in the TD direction, and y2 may be in a range of 20 mm or less.
The central portion of the film immediately after completion of stretching is a position equidistant from both ends of the film immediately after completion of stretching.

When the temperature at the end of the film immediately after completion of stretching is T2s and the temperature at the center of the film immediately after completion of stretching is T2c, the temperature T2s at both ends is usually 5 ° C. or more, particularly 5 to 50 from the temperature T2c at the center. Increase by ℃. From the viewpoint of further reducing retardation unevenness and bowing, T2s at both ends is preferably higher by 8 to 21 ° C. than T2c at the center.
T2s at both ends is normally controlled to be isothermal, and a difference of 1 ° C. or less may occur.

In this specification, the temperature T2s at the end of the film immediately after completion of stretching is a value obtained by measuring the temperature at the position P2s at x2 = 10 mm and y2 = 10 mm in FIG. 1 with the non-contact thermometer.
The temperature T2c at the center of the film immediately after the completion of stretching is the value obtained by measuring the temperature at the position P2c at x2 = 10 mm at the same distance from both ends in the TD direction in FIG. 1 with the non-contact thermometer.
The temperature T2s at both ends of the film and the temperature T2c at the center of the film are values measured on the same surface of the film together with the temperatures T1s and T1c, but may be measured on different surfaces.

From the standpoint of further reducing retardation unevenness and bowing, and also effectively reducing the transverse haze, the temperature T2s at the film end is, at both ends, the temperature T2c at the center of the film, and the following formula:
Tg−25 ≦ T2c + 5 ≦ T2s ≦ Tg + 30 Formula (2)
In particular,
Tg-10 ≦ T2c + 8 ≦ T2s ≦ Tg + 20 Formula (2 ′)
It is preferable to satisfy the relationship (Tg is the glass transition temperature of the polymer film).

From the viewpoint of more effectively reducing bowing, the average temperature T1sa at both ends of the polymer film immediately before the start of stretching and the average temperature T2sa at both ends of the polymer film immediately after completion of stretching are expressed by the following formulas:
0.9 ≦ T1sa / T2sa ≦ 1.0 Formula (3)
In particular,
0.95 ≦ T1sa / T2sa ≦ 0.99 Formula (3 ′)
It is preferable to satisfy the relationship.

  In FIG. 1, the edge local heating means 4 in the thermal relaxation stage 13 is disposed on the front side of the film 2 and locally heats the film edge, but is not particularly limited as long as a predetermined temperature gradient is achieved. For example, in the figure, you may arrange | position in the back | inner side of a film, or may arrange | position in the figure above and below a film. From the viewpoint of controlling the temperature gradient, the end local heating means 4 is preferably arranged from the front side or / and the back side of the film toward the film.

  The ambient temperature in the thermal relaxation stage 13 is not particularly limited as long as a predetermined temperature gradient is achieved, and it is usually only required to be maintained at a temperature comparable to the temperature T1c at the center of the film.

  The film conveying speed is not particularly limited as long as the object of the present invention is achieved, and is usually 40 to 120 m / min, particularly preferably 60 to 100 m / min.

(Slitting process)
After carrying out the stretching process, a slitting process is usually performed.
In the slitting process, the both ends of the film are cut and removed. In the present invention, in order to effectively reduce physical property unevenness and bowing in the width direction, the cut widths at both ends in the width direction may be relatively small. As a result, a wider film can be effectively produced.

For example, the film width W1 immediately before the slitting process and the film width W2 immediately after the slitting process are usually represented by the following formulas:
0.85 ≦ W2 / W1 ≦ 0.95 Formula (4)
In particular,
0.90 ≦ W2 / W1 ≦ 0.95 Formula (4 ′)
Satisfy the relationship.

  In the present invention, even if the film width W2 is 1900 to 3000 mm, particularly 2100 to 2800 mm, the effects of the present invention can be obtained effectively.

  The thickness d of the film obtained in the present invention is not particularly limited, and is usually 20 to 100 μm, preferably 30 to 80 μm.

(Polymer film)
The polymer film used in the method of the present invention may comprise a polymer known in the field of optical films. Examples of such polymers include cellulose ester resins, cycloolefin resins, polycarbonate resins, and the like. More preferably, a film made of a cellulose ester resin is used.

  In the case of using a cellulose ester resin, the cellulose as a raw material for the cellulose ester resin is not particularly limited, and examples thereof include cotton linter, wood pulp (derived from coniferous tree, derived from broadleaf tree), kenaf and the like. Moreover, the cellulose ester-type resin obtained from them can be mixed and used in arbitrary ratios, respectively. When the acylating agent is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride), these cellulose ester resins use an organic acid such as acetic acid or an organic solvent such as methylene chloride, It can obtain by making it react with a cellulose raw material using such a protic catalyst.

When the acylating agent is acid chloride (CH ₃ COCl, C ₂ H ₅ COCl, C ₃ H ₇ COCl), the reaction is carried out using a basic compound such as an amine as a catalyst. Specifically, it can be synthesized with reference to the method described in JP-A-10-45804. In addition, the cellulose ester resin used in the present invention is obtained by mixing and reacting the acylating agent according to the degree of substitution, and the acylating agent reacts with the hydroxyl group of the cellulose molecule. Cellulose molecules are composed of many glucose units linked together, and the glucose unit has three hydroxyl groups. The number of acyl groups derived from these three hydroxyl groups is called the degree of substitution (mol%). For example, cellulose triacetate has acetyl groups bonded to all three hydroxyl groups of the glucose unit (actually 2.6 to 3.0).

  Cellulose ester resin is a mixed fatty acid ester of cellulose in which propionate group or butyrate group is bonded in addition to acetyl group such as cellulose acetate propionate resin, cellulose acetate butyrate resin, or cellulose acetate propionate butyrate resin. There may be. In addition, the cellulose acetate propionate resin containing a propionate group as a substituent is excellent in water resistance and is useful as a film for a liquid crystal image display device.

  The number average molecular weight of the cellulose ester-based resin is preferably 40000 to 200000, and has a high mechanical strength when molded, and an appropriate dope viscosity in the case of the solution casting method, and more preferably 50000 to 150,000. . The weight average molecular weight (Mw) / number average molecular weight (Mn) is preferably in the range of 1.4 to 4.5.

  In the present specification, the average molecular weight and the molecular weight distribution can be measured by a known method using high performance liquid chromatography. Using this, the number average molecular weight and the weight average molecular weight can be calculated, and the ratio (Mw / Mn) can be calculated.

The measurement conditions are as follows.
Solvent: Methylene chloride column: Shodex K806, K805, K803G (used by connecting 3 products manufactured by Showa Denko KK)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 100000-500 calibration curves with 13 samples were used. The 13 samples are preferably used at approximately equal intervals.

The Tg of the polymer film is not particularly limited as long as the object of the present invention is achieved. For example, the Tg of the polymer film may be 50 to 200 ° C., particularly 70 to 180 ° C. The temperature is preferably 120 to 170 ° C. from the viewpoint of enabling the alignment state to be fixed.
In this specification, Tg uses the value measured by TMA8310 (made by RIGAKU) using the film after an extending process.

  The thickness of the polymer film used in the method of the present invention is not particularly limited, and is usually 20 to 100 μm, preferably 30 to 80 μm.

  The polymer film may contain additives such as ultraviolet absorbers, plasticizers, matting agents, antioxidants, conductive materials, antistatic agents, flame retardants, and lubricants.

  The polymer film used in the present invention may be in the course of production in a conventionally known optical film production method such as a so-called solution casting method or melt casting method, or a conventionally known optical film. The film may be a final product in the manufacturing method.

  For example, when a film in production in the solution casting method or a film as a final product of the solution casting method is used, a film having a residual solvent amount of 0.001 to 10% by weight, particularly 3 to 8% by weight is used. It is preferred that

When the polymer film is in the middle of production in a solution casting method including a so-called casting process, drying process, and peeling process, the stretching process implemented in the present invention and the slitting process implemented as desired are as follows: In the order of:
Order (S1); casting process-drying process-peeling process-stretching process-slitting process;
Order (S2); casting process-drying process-peeling process-drying process-stretching process-slitting process;
Order (S3); casting process-drying process-peeling process-stretching process-drying process-slitting process;
Order (S4); casting process-drying process-peeling process-drying process-stretching process-drying process-slitting process.
In the above case, the winding process may be performed at any time.

  For example, when a film in the middle of production in the melt casting method or a film as a final product of the melt casting method is used, it is preferable to use a film having a film thickness of 30 to 160 μm, particularly 40 to 100 μm.

When the polymer film is in the middle of production in a melt casting method including a so-called casting process, cooling process, and peeling process, the stretching process implemented in the present invention and the slitting process implemented as desired are as follows: In the order of: Order (M1); casting process-cooling process-peeling process-stretching process-slitting process;
Order (M2); casting process-cooling process-peeling process-cooling process-stretching process-slitting process;
Order (M3); casting process-cooling process-peeling process-stretching process-cooling process-slitting process;
Order (M4); casting process-cooling process-peeling process-cooling process-stretching process-cooling process-slitting process.
In the above case, the winding process may be performed at any time.

(Use)
The optical film manufactured by the above method is useful as a functional film used in various display devices such as a liquid crystal display device, a plasma display device, and an organic EL display device, particularly a liquid crystal display device. Among these, it is particularly suitable as a polarizing plate protective film, a retardation film, an antireflection film, a brightness enhancement film, an optical compensation film for expanding a viewing angle, and the like.

  When using the optical film of this invention as a functional film of a liquid crystal display device, the liquid crystal display device of a structure as shown in FIG. 2 can be manufactured, for example.

  In FIG. 2, 21a and 21b are protective films, 22a and 22b are retardation films, 25a and 25b are polarizers, 23a and 23b are slow axis directions of the film, 24a and 24b are transmission axis directions of the polarizer, and 27 is A liquid crystal cell 29 is a liquid crystal display device. Reference numerals 26a and 26b denote polarizing plates, which include a protective film, a retardation film, and a polarizer.

  In such a liquid crystal display device, the optical film of the present invention may be used as the protective films 21a and 21b and / or may be used as the retardation films 22a and 22b.

  The optical film of the present invention is preferably used for a liquid crystal display device having a diagonal length of a display screen of 32 inches or more, particularly 32 to 107 inches.

<Example 1>
[Preparation of dope]
Cellulose triacetate propionate 100 parts by weight (acetyl group substitution degree 1.95, propionyl group substitution degree 0.7, Mn = 100000, Mw / Mn = 1.90)
Triphenyl phosphate 10 parts by weight Ethylphthalyl ethyl glycolate 2 parts by weight Tinuvin 326 (manufactured by Ciba Specialty Chemicals) 1 part by weight AEROSIL 972V (manufactured by Nippon Aerosil Co., Ltd.) 0.1 part by weight Methylene chloride 300 parts by weight Ethanol 40 parts by weight Part The above materials were mixed in an airtight container, heated to 80 ° C., and then stirred for 3 hours to be completely dissolved. Thereafter, stirring was stopped, the liquid temperature was lowered to 43 ° C., and filtration was performed using a filter paper having a filtration accuracy of 0.005 mm. By allowing this to stand overnight, the bubbles in the dope were degassed.

[Production of cellulose ester film]
The dope was adjusted to a dope temperature of 35 ° C. and a support temperature of 25 ° C., and cast from a casting die onto a mirror-treated support belt made of stainless steel. The film (web) was peeled from the support at a peeling residual solvent amount of 80% by weight, and the transport tension was 100N. Subsequently, after the film was dried by a drying air at 120 ° C. in a roll conveyance drying process in which the films were arranged in a staggered manner to obtain a residual solvent amount of 8% by weight, the stretching process and slitting process described below were performed.

(Stretching process)
The film was stretched in the width direction while holding both ends of the film with a clip with a tenter. At this time, as shown in FIG. 1, both ends of the film 2 were heated by the edge local heating means 4 immediately before the start of stretching and immediately after completion of stretching. An infrared irradiation means was used as the end local heating means 4. The temperature T1s at the end of the film immediately before the start of stretching was 155 ° C., and was common to both ends. The temperature T1c at the center of the film immediately before the start of stretching and the temperature T2c at the center of the film immediately after completion of stretching were 140 ° C. in common. The temperature T2s at the end of the film immediately after completion of stretching was 160 ° C., and was common to both ends. The draw ratio in the width direction was 30%, and the draw ratio in the transport direction was 1%. The glass transition temperature of the film was 158 ° C.

(Slitting process)
Next, after drying with 120 degreeC dry air and winding up with the winder, the film both ends with the tenter clip trace were cut and removed. The film width W1 immediately before the slitting process was 2400 m, and the film width W2 immediately after the slitting process was 2100 m. The final film thickness of the film was 40 μm.

<Examples 2-7 / Comparative Examples 1-3>
Changing the edge local heating means in the drawing process to the one described in the table, controlling the temperatures T1s, T1c, T2c, and T2s to predetermined values, and adjusting the widths W1 and W2 in the slitting process Except for the above, a film was produced in the same manner as in Example 1.
T1s and T2s were controlled by adjusting the temperature or output of the edge local heating means.
T1c and T2c were controlled by adjusting the atmospheric temperature in the tenter.
In Comparative Example 1, the edge local heating means was not used immediately before the start of stretching and immediately after the completion of stretching.
In Comparative Example 2, the edge local heating means was not used immediately after the completion of stretching.
In Comparative Example 3, the edge local heating means was not used immediately before the start of stretching.

<Evaluation>
The manufactured film was evaluated for the following items.
[Evaluation of retardation]
Using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments), the refractive indexes Nx and Ny at a wavelength of 590 nm at a pitch of 10 mm in the width direction of the film in an environment of a temperature of 23 ° C. and a humidity of 55% RH. Nz was determined. According to the following formula, retardation (Ro) in the in-plane direction of the film and retardation (Rth) in the thickness direction were calculated.

Ro = (Nx−Ny) × d
Rth = ((Nx + Ny) / 2−Nz) × d
Nx is the refractive index in the slow axis direction in the plane of the film, Ny is the refractive index in the fast axis direction in the film plane, and Nz is the refractive index in the thickness direction of the film.
d represents the thickness (nm) of the film.

  The retardation unevenness of the film was evaluated according to the following criteria. The unevenness was evaluated by the difference between the maximum value and the minimum value of the measured values.

(Ro unevenness)
A: In-plane retardation (Ro) unevenness ≦ 2.0 nm;
○: 2.0 nm <in-plane retardation (Ro) unevenness ≦ 3.0 nm;
Δ: 3.0 nm <in-plane retardation (Ro) unevenness ≦ 3.5 nm;
X: 3.5 nm <in-plane retardation (Ro) unevenness.

(Rth unevenness)
A: Thickness direction retardation (Rth) unevenness ≦ 4.5 nm;
○: 4.5 nm <thickness direction retardation (Rth) unevenness ≦ 6.0 nm;
Δ: 6.0 nm <thickness direction retardation (Rth) unevenness ≦ 7.0 nm;
X: 7.0 nm <thickness direction retardation (Rth) nonuniformity.

[Evaluation of Boeing]
In the film production process described above, a straight line is drawn in the width direction with oil-based magic ink on the film before the stretching process, and stretching is performed. After the stretching step, bowing was evaluated by measuring the maximum convex amount or concave amount of a concave or convex arcuate line (Boeing line) deformed into a concave shape or a convex shape in the film conveyance direction.

Evaluation was performed according to the following criteria.
A: The maximum convex amount or concave amount of the bowing line is within ± 2 mm;
○: The maximum convex amount or concave amount of the Boeing line is within ± 4 mm;
Δ: The maximum convex amount or concave amount of the Boeing line is within ± 6 mm;
X: The maximum convex amount or concave amount of the Boeing line is outside ± 6 mm.

[Measurement of haze]
The haze value (three-sheet value) of the film was measured using TURBIDITYMETERT-2600DA manufactured by Tokyo Denshoku Co., Ltd. The film was measured at a pitch of 10 mm in the width direction of the film, and in Table 1, the maximum haze value (three-sheet value) in the width direction of the film was evaluated according to the following criteria.
A: Maximum haze value ≦ 0.35%;
○: 0.35% <maximum haze value ≦ 0.45%;
Δ: 0.45 <maximum haze value ≦ 0.60%;
X: 0.60 <maximum haze value.

[Evaluation of tearing]
The cross section of the end face obtained by cutting in the slitting process was observed with an optical microscope (× 500 times). The film cross section was evaluated according to the following criteria.
A: The cross section is smooth;
○: A cross-section is present on the cross section;
X: The cross section is jagged.

  1: stretching step, 2: polymer film, 3: tenter clip, 4: end local heating means, 11: preheating stage, 12: stretching stage, 13: thermal relaxation stage, 21a: 21b: protective film, 22a: 22b: Retardation film, 23a: 23b: slow axis direction of film, 24a: 24b: transmission axis direction of polarizer, 25a: 25b: polarizer, 26a: 26b: polarizing plate, 27: liquid crystal cell, 29: liquid crystal display device .

Claims (9)

In the method for producing an optical film having a stretching step of stretching a polymer film in the width direction, the temperature at both ends of the polymer film is made higher than the temperature at the center of the polymer film immediately before the start of stretching and immediately after the stretching is completed, and immediately before the start of stretching. The average temperature T1sa at both ends of the polymer film and the average temperature T2sa at both ends of the polymer film immediately after completion of stretching are represented by the following formula (3):
0.9 ≦ T1sa / T2sa ≦ 1.0 Formula (3)
The manufacturing method of the optical film characterized by satisfy | filling the relationship of these .   The optical according to claim 1, wherein the temperature at both ends of the polymer film is made higher than the temperature at the center of the polymer film by heating both ends of the polymer film by the edge local heating means immediately before the start of stretching and immediately after the completion of stretching. A method for producing a film.   The temperature at both ends of the polymer film is made higher than the temperature at the center of the polymer film by local end heating means selected from the group consisting of high temperature air or inert gas blowing means, infrared irradiation means, heating wire and heating roll. The manufacturing method of the optical film of Claim 1 or 2. Immediately before the start of stretching, the temperature at both ends of the polymer film is made 5 ° C. higher than the temperature at the center of the polymer film
The method for producing an optical film according to any one of claims 1 to 3, wherein the temperature at both ends of the polymer film is set 5 ° C or more higher than the temperature at the center of the polymer film immediately after completion of stretching. The temperature T1s at the end of the polymer film immediately before the start of stretching is the temperature T1c at the center of the polymer film immediately before the start of stretching at both ends, and the following formula (1);
Tg−25 ≦ T1c + 5 ≦ T1s ≦ Tg + 20 Formula (1)
The manufacturing method of the optical film in any one of Claims 1-4 satisfy | filling the relationship (Tg is the glass transition temperature of a polymer film). The temperature T2s at the end of the polymer film immediately after completion of stretching is the temperature T2c at the center of the polymer film immediately after completion of stretching at both ends, and the following formula (2):
Tg−25 ≦ T2c + 5 ≦ T2s ≦ Tg + 30 Formula (2)
The manufacturing method of the optical film in any one of Claims 1-5 which satisfy | fill the relationship of (Tg is the glass transition temperature of a polymer film). The average temperature T1sa at both ends of the polymer film immediately before the start of stretching and the average temperature T2sa at both ends of the polymer film immediately after completion of stretching are represented by the following formula (3 ′) :
0.95 ≦ T1sa / T2sa ≦ 0.99 Formula (3 ′)
The manufacturing method of the optical film in any one of Claims 1-6 which satisfy | fills these relationships. It is a manufacturing method of the optical film in any one of Claims 1-7 which performs the slitting process which cuts the both ends of a polymer film after an extending process,
The polymer film width W1 immediately before the slitting treatment and the polymer film width W2 immediately after the slitting treatment are expressed by the following formula (4):
0.85 ≦ W2 / W1 ≦ 0.95 Formula (4)
The manufacturing method of the optical film which satisfy | fills these relationships.   The method for producing an optical film according to any one of claims 1 to 8, wherein the polymer film width W2 immediately after the slitting treatment is 1900 to 3000 mm.

Images