WO2020012732A1

WO2020012732A1 - Method for manufacturing optical film

Info

Publication number: WO2020012732A1
Application number: PCT/JP2019/014767
Authority: WO
Inventors: 祐樹穂北
Original assignee: コニカミノルタ株式会社
Priority date: 2018-07-11
Filing date: 2019-04-03
Publication date: 2020-01-16
Also published as: JPWO2020012732A1; KR102356401B1; CN112423959A; KR20210016611A; CN112423959B

Abstract

This method for manufacturing an optical film is for manufacturing an optical film by a solution casting film-forming method, the method including: a dope transport step in which a resin with an SP value as a solubility parameter of 10.5 (MPa)^1/2 or less is dissolved in a solvent in a dissolution vessel to prepare a dope, and the dope is transported to a casting die via an intermediate vessel; and a casting step, in which the dope is cast onto a support body from the casting die. In the dope transport step, the following conditional formulas (1)–(3) are satisfied. (1) T1 > T2 > T3, (2) T1 − T3 ≤ 25°C, and (3) 5°C < T2 − T3 < 15°C, where T1 is the temperature (°C) of the dope immediately after leaving the dissolution vessel, T2 is the temperature (°C) of the dope immediately after leaving the intermediate vessel, and T3 is the temperature (°C) of the dope immediately before entering the casting die.

Description

Optical film manufacturing method

The present invention relates to a method for producing an optical film by a solution casting method.

When a gel material is contained in the dope used in the solution casting film forming method, when a film is formed by the solution casting film forming method (hereinafter, also referred to as a solution film forming) using the dope, the gel is formed. Substances are present in the film and cause the product quality of the film to deteriorate. Therefore, for example, in Patent Document 1, in view of the fact that the generation of a gel-like substance from a dope and the dope temperature or the temperature history of the dope are very closely related, the dope containing cellulose acylate and a solvent is flown. When transferring to a rolling die, the temperature of the dope is kept as constant as possible to suppress the generation of a gel-like substance.

Japanese Patent No. 4753553 (refer to

claims

1 and 2, paragraphs [0004], [0010] to [0012], and FIGS. 1 and 2)

In recent years, optical films used for display devices have been demanded to be thin and water-blocking (low water permeability). Conventional optical films containing cellulose acylate do not satisfy required requirements because of their high water permeability.

Therefore, solution casting using a resin having low water permeability (for example, a resin having a low SP value as a solubility parameter) has become necessary. However, it was found that in a solution film formation using a resin having a low SP value, when the dope was transferred while keeping the temperature of the dope constant as in Patent Document 1, it was not possible to produce a film having smooth and good characteristics. Was. Specifically, in the manufactured optical film, a film thickness deviation occurs in which the film thickness is irregular and non-uniform in the width direction or the longitudinal direction, and a phase difference in which the phase difference expression due to stretching becomes non-uniform. It was found that a deviation occurred. The inventor of the present application speculates this reason as follows. In other words, a resin having a low SP value has a weaker interaction between molecules than cellulose acylate, so that the viscosity of the dope containing such a resin is low. Then, in the solution casting using the dope, when the dope is cast and transported on the support, the dope is formed on the support under the influence of the surrounding wind (wind pressure, wind speed) and temperature. The surface of the casting film is easily deformed (surface irregularities are easily generated). As a result, the thickness of the formed film becomes uneven. In addition, the surface deformation of the casting film causes uneven orientation of molecules during stretching, which appears as a phase difference deviation.

Thus, in a solution casting using a resin having a low SP value, it is desired to reduce the film thickness deviation and the phase difference deviation, but such a solution casting has not yet been realized.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical film capable of reducing a film thickness deviation and a phase difference deviation in a solution casting using a resin having a low SP value. It is to provide a method for producing a film.

The above object of the present invention is achieved by the following manufacturing method.

The method for producing an optical film according to one aspect of the present invention is a method for producing an optical film by producing an optical film by a solution casting method,
A dope is prepared by dissolving a resin having an SP value of 10.5 (MPa) ^1/2 or less as a solubility parameter in a solvent in a dissolving pot to prepare a dope, and transferring the dope to a casting die via an intermediate pot. A transfer process;
A casting step of casting the dope from the casting die onto a support,
A method for producing an optical film, wherein the dope transfer step satisfies the following conditional expressions (1) to (3);
(1) T1>T2> T3
(2) T1-T3 ≦ 25 ° C.
(3) 5 ° C <T2-T3 <15 ° C
However,
T1: Temperature (° C.) of the dope immediately after leaving the melting pot
T2: temperature of the dope immediately after leaving the intermediate pot (° C.)
T3: temperature of the dope immediately before entering the casting die (° C.)
It is.

According to the method for producing an optical film described above, the film thickness deviation and the phase difference deviation can be reduced in a solution casting using a resin having a low SP value.

It is an explanatory view showing the schematic structure of the manufacturing device of the optical film concerning an embodiment of the invention. It is a flowchart which shows the flow of the manufacturing process of the said optical film. It is explanatory drawing which shows the temperature history of the dope which flows between an intermediate pot and a casting die of the said manufacturing apparatus.

An embodiment of the present invention will be described below with reference to the drawings. In this specification, when the numerical range is described as AB, the numerical range includes the lower limit A and the upper limit B. In addition, this invention is not necessarily limited to the following content.

(Production method of optical film)
FIG. 1 is an explanatory diagram illustrating a schematic configuration of an optical film manufacturing apparatus 50 according to the present embodiment. FIG. 2 is a flowchart showing a flow of a manufacturing process of the optical film. The method for producing an optical film according to the present embodiment is a method for producing an optical film by a solution casting method, and as shown in FIG. 2, a dope transfer step (S1), a casting step (S2), and a peeling step. (S3), a first drying step (S4), a stretching step (S5), a second drying step (S6), a cutting step (S7), an embossing step (S8), and a winding step (S9). Hereinafter, each step will be described with reference to FIGS.

(S1: dope transfer step)
In the dope transferring step, a dope to be cast on the support 3 is prepared (prepared) in the dope transferring section 1 and transferred to the casting die 2. The details of the dope transfer step will be described later.

(S2: casting process)
In the casting step, the dope fed to the casting die 2 by the dope transfer unit 1 is transferred from the casting die 2 to a casting position on a support 3 made of a rotary drive stainless steel endless belt for infinitely transferring the dope. Extend. The support 3 transports the cast dope (cast dope) while supporting it. Thus, a casting film (web) 5 is formed on the support 3.

The support 3 is held by a pair of

rolls

3a and 3b and a plurality of rolls (not shown) located between them. One or both of the

rolls

3a and 3b are provided with a driving device (not shown) for applying tension to the support 3, whereby the support 3 is used under tension.

In the casting step, the web 5 formed by the dope cast on the support 3 is heated on the support 3 and the solvent is evaporated from the support 3 until the web 5 can be peeled off by the peeling roll 4. Let it. To evaporate the solvent, there are a method of blowing air from the web side, a method of transferring heat from the back surface of the support 3 by liquid, a method of transferring heat from the front and back by radiant heat, and the like, which is used alone or in combination as appropriate. Just fine.

(S3: peeling step)
In the above casting step, after the web 5 is dried and solidified or cooled and solidified on the support 3 until the web 5 has a releasable film strength, in the stripping step, the web 5 is left with a self-supporting property. Peeling is performed from the support 3 by the peeling roll 4.

The residual solvent amount of the web 5 on the support 3 at the time of peeling is desirably in the range of 25 to 120% by mass depending on the strength of the drying conditions, the length of the support 3, and the like. When the web 5 is peeled off at a point where the residual solvent amount is larger, if the web 5 is too soft, the flatness at the time of peeling is impaired, and wrinkles and vertical stripes are easily generated due to the peeling tension. The amount of solvent is determined. The residual solvent amount is defined by the following equation.

Residual solvent amount (mass%) = (mass before heat treatment of web−mass after heat treatment of web) / (mass after heat treatment of web) × 100
Here, the heat treatment at the time of measuring the amount of residual solvent means that heat treatment is performed at 115 ° C. for one hour.

(S4; first drying step)
The web 5 peeled from the support 3 by the peeling roll 4 is dried by the drying device 6. In the drying device 6, the web 5 is transported by a plurality of transport rolls, during which the web 5 is dried. The drying method in the drying device 6 is not particularly limited, and the web 5 is generally dried using hot air, infrared rays, a heating roll, a microwave, or the like. From the viewpoint of simplicity, a method of drying the web 5 with hot air is preferred. Note that the first drying step may be performed as needed.

(S5 stretching step)
In the stretching step, the web 5 dried by the drying device 6 is stretched by the tenter 7. The stretching direction at this time is either a film transport direction (MD direction; Machine Direction), a width direction perpendicular to the transport direction in the film plane (TD direction; Transverse Direction), or both of these directions. In the stretching step, a tenter method in which both side edges of the web 5 are fixed with clips or the like and stretched is preferable in order to improve the flatness and dimensional stability of the film. In the tenter 7, drying may be performed in addition to stretching.

延伸 Note that the stretching step of S5 may be performed as needed, and can be omitted. For example, when stretching is performed after winding the optical film, the stretching step before winding can be omitted.

(S6: second drying step)
The web 5 stretched by the tenter 7 as required is dried by the drying device 8. In the drying device 8, the web 5 is transported by a plurality of transport rolls, during which the web 5 is dried. The drying method in the drying device 8 is not particularly limited, and the web 5 is generally dried using hot air, infrared rays, a heating roll, a microwave, or the like. From the viewpoint of simplicity, a method of drying the web 5 with hot air is preferred. Before entering the drying device 8, a step of roughly cutting both width end portions of the web 5 may be performed.

After the web 5 is dried by the drying device 8, the web 5 is conveyed as an optical film F toward the winding device 11.

(S7: cutting step, S8: embossing step)
The cutting unit 9 and the embossing unit 10 are arranged between the drying device 8 and the winding device 11 in this order. In the cutting section 9, a cutting step of cutting both ends in the width direction by a slitter while transporting the formed optical film F is performed. In the optical film F, the portions remaining after the cutting at both ends constitute a product part to be a film product. On the other hand, the portion cut from the optical film F is collected by a shooter and reused again as a part of raw materials for forming a film.

の後 After the cutting step, embossing (knurling) is performed by the embossed portion 10 on both ends in the width direction of the optical film F. The embossing is performed by pressing a heated emboss roller against both ends of the optical film F. Fine irregularities are formed on the surface of the embossing roller. By pressing the embossing roller against both ends of the optical film F, the irregularities are formed on the both ends. By such embossing, winding deviation and blocking (sticking between films) in the next winding step can be suppressed as much as possible.

(S9: winding step)
Finally, the optical film F on which the embossing has been completed is wound up by the winding device 11 to obtain the original roll (film roll) of the optical film F. That is, in the winding step, a film roll is manufactured by winding the optical film F around a core while transporting the same. The winding method of the optical film F may use a commonly used winder, and there is a method of controlling tension such as a constant torque method, a constant tension method, a taper tension method, and a program tension control method for constant internal stress. You can use them properly. The winding length of the optical film F is preferably from 1,000 to 15,000 m. In this case, the width is desirably 1000 to 3200 mm, and the film thickness is desirably 10 to 60 μm.

[Details of the dope transfer process]
Next, details of the above-described dope transfer step will be described. In the dope transferring step, a resin having an SP value as a solubility parameter (Solubility Parameter) of 10.5 (MPa) ^1/2 or less is dissolved in a solvent in a dissolving vessel 21 to prepare a dope, and the dope is transferred to an intermediate vessel. It is transferred to the casting die 2 via 22. In the intermediate pot 22, the dope is temporarily held, whereby air and bubbles in the dope are removed. The dope in the melting pot 21 is transferred to the intermediate pot 22 through the conduit 23, and the dope in the intermediate pot 22 is transferred to the casting die 2 through the conduit 24. At least one heat exchanger 25 is provided between the intermediate pot 22 and the casting die 2. In the heat exchanger 25, the conduit 24 is heated or cooled by a heating medium or a cooling medium, so that the dope passing through the conduit 24, that is, the dope flowing from the intermediate tank 22 toward the casting die 2 is heated or cooled. Is done. When a plurality of heat exchangers 25 are provided between the intermediate pot 22 and the casting die 2, it is possible to heat the dope once and then cool it, or to cool it once and then heat it.

Here, the above SP value will be described. The SP value is a value represented by the square root of the molecular cohesion energy, which is described in Polymer Hand Book (Second Edition), Chapter IV, Solubility Parameter Values, and is used. However, in the present application, the unit is (MPa) ^1/2 and shows a value at 25 ° C. In addition, about what has no description of data, R. F. It can be calculated by the method described in Fedors, Polymer Engineering Science, 14, p147 (1974). That is, it can be basically calculated according to the following equation.
Solubility parameter value (SP value) = (△ E / V) ^1/2
Here, ΔE represents the cohesive energy density. V represents molecular volume (molar volume).

は The above solubility parameter value (SP value) F. Based on the concept of Fedors, Scigres @ Explorer @ Ver. 2.4 (manufactured by Fujitsu Limited).

Examples of the resin having an SP value of 10.5 (MPa) ^1/2 or less include a cycloolefin resin (SP value: 9.6 (MPa) ^1/2 ) and a polycarbonate resin (SP value: 10.2 ( MPa) ^1/2 ) and an acrylic resin (SP value: 9.5 (MPa) ^1/2 ). Note that the resin having a low SP value is not limited to the above-mentioned resins, and any resin other than TAC (SP value; 10.9 (MPa) ^1/2 ) can be used.

混合 As the solvent, a mixed solvent of a good solvent and a poor solvent can be used. Note that a good solvent refers to an organic solvent having a property of dissolving a resin (solubility), such as 1,3-dioxolan, THF (tetrahydrofuran), methyl ethyl ketone, acetone, methyl acetate, methylene chloride (dichloromethane, methylene chloride), Toluene and the like correspond to this. On the other hand, a poor solvent refers to a solvent that does not have the property of dissolving a resin by itself, such as methanol or ethanol.

In the present embodiment, in the step of transferring the dope from the melting pot 21 to the casting die 2 via the intermediate pot 22, the following conditional expressions (1) to (3) are satisfied. That is,
(1) T1>T2> T3
(2) T1-T3 ≦ 25 ° C.
(3) 5 ° C <T2-T3 <15 ° C
However,
T1: Temperature of the dope immediately after coming out of the melting pot 21 (° C.)
T2: Dope temperature (° C.) immediately after leaving the intermediate pot 22
T3: Temperature of dope just before entering casting die 2 (° C)
It is.

Conditional expression (1) defines the magnitude relationship between the temperatures of the respective dopes immediately after leaving the melting vessel 21, immediately after leaving the intermediate vessel 22, and immediately before entering the casting die 2. Conditional expression (2) defines an appropriate range of the temperature difference between the dope immediately after leaving the melting vessel 21 and the dope immediately before entering the casting die 2. Conditional expression (3) defines an appropriate range of the temperature difference between the dope immediately after leaving the intermediate pot 22 and the dope immediately before entering the casting die 2. By satisfying conditional expressions (1) to (3), it is possible to reduce the thickness deviation and the phase difference deviation of the optical film F in the solution film formation using a low SP value. The present inventor considers the reason as follows.

By satisfying conditional expression (1), the dope immediately before entering the casting die 2 is cooled more than the dope immediately after leaving the melting pot 21 and the dope immediately after leaving the intermediate pot 22. . As described above, the low-viscosity dope containing the resin having a low SP value is cooled in the process of being transferred from the melting vessel 21 to the casting die 2, thereby generating a high-viscosity region in a part of the dope. it can. Moreover, by further satisfying the conditional expression (2), the degree of cooling of the dope is limited (because the dope is not cooled too much), so that it is possible to suppress the generation of a region having a high viscosity in the dope. it can.

Further, as the value of T2-T3 (temperature difference) is smaller, the generation of a high-viscosity region due to cooling of the dope is suppressed, and as the value of T2-T3 is larger, the generation of a high-viscosity region due to cooling of the dope is promoted. However, as long as the value of T2−T3 satisfies the conditional expression (3), a high-viscosity region and a low-viscosity region coexist in the dope. Thereby, it is possible to reduce the occurrence of the film thickness deviation and the phase difference deviation due to the interaction between the regions.

That is, a low-viscosity dope containing a resin having a low SP value is easily affected by the surrounding wind and temperature during casting from the casting die 2 and transporting on the support 3. As described above, the surface of No. 5 is easily deformed and the thickness deviation and the phase difference deviation are likely to occur. By generating a high-viscosity region in the dope as in the present embodiment, it is possible to prevent the surface of the web 5 from being deformed by the influence of wind or the like at the time of casting and transporting the dope onto the support 3. Can be. Thereby, it is possible to reduce the occurrence of the film thickness deviation and the phase difference deviation due to the influence of the wind at the time of the casting.

と If the dope is excessively cooled and a region having a high viscosity is generated in the dope, a gel-like substance is easily generated in the dope. Further, the surface of the dope is likely to have irregularities immediately after being discharged from the casting die 2 on the support 3, and the surface of the dope is less likely to be leveled (flattened) by the influence of stress due to uneven drying. In this case, the surface deformation of the dope remains as the surface deformation of the web 5 after drying. For this reason, due to the surface deformation of the web 5, a thickness deviation and a phase difference deviation occur in the optical film F finally obtained.

However, in the present embodiment, the high-viscosity region and the low-viscosity region can coexist in the dope while suppressing the increase in the high-viscosity region due to excessive cooling. Immediately after rolling, even if the surface of the dope has irregularities due to the presence of the high-viscosity region, the low-viscosity region of the dope flows, and the stress due to uneven drying is transmitted to the periphery by the low-viscosity region. Is leveled. Thereby, since the surface deformation of the web 5 can be suppressed, it is possible to reduce the occurrence of the thickness deviation and the phase difference deviation in the optical film F finally obtained due to the surface deformation. Further, the presence of a low-viscosity region in the dope also suppresses the generation of a gel-like substance.

As described above, by satisfying conditional expressions (1) to (3), while maintaining the fluidity while leaving a low viscosity region in the dope, a high viscosity region serving as a core is formed so as not to be excessive. ) To reduce the influence of local wind during casting and the stress due to drying unevenness, and then level the entire surface of the dope (web 5) by moving a region with high fluidity and low viscosity. be able to. As a result, it is possible to reduce the occurrence of the gel-like substance, the thickness deviation, and the phase difference deviation.

In the above-described doping transfer step of S1, it is desirable that the following conditional expression (4) is further satisfied. That is,
(4) 5 ° C <Tmax-Tmin <30 ° C
However,
Tmax: the maximum temperature of the dope between the intermediate pot 22 and the casting die 2 (° C.)
Tmin: minimum temperature (° C.) of dope between the intermediate pot 22 and the casting die 2
It is. In addition, the temperature change of the dope that satisfies the conditional expression (4) can be realized by heating or cooling the dope flowing in the conduit 24 by at least one heat exchanger 25 as described above.

FIG. 3 shows the temperature history of the dope flowing between the intermediate pot 22 and the casting die 2 (temperature at each dope passage position). The position of the passing point 0 on the horizontal axis corresponds to the position of the intermediate shuttle 22, and the position of the passing point 6 corresponds to the position of the casting die 2. By satisfying conditional expression (4), various temperature histories can be realized between the intermediate pot 22 and the casting die 2. For example, even if the temperature of the dope coming out of the intermediate kettle 22 is constant (same) and the temperature of the dope entering the casting die 2 is constant (same), the temperature of the dope is cast from the intermediate kettle 22 as the temperature history of the dope. The case where the temperature of the dope rises and falls once as the dope moves toward the die 2 (see the solid line A), the case where the temperature of the dope falls and rises once (see the broken line B), and the temperature of the dope falls once It is possible to realize a case of rising and falling again (see the dashed line C). Ta, Tb, and Tc in the figure correspond to the difference between the maximum temperature Tmax and the minimum temperature Tmin of the dope in each case (temperature history).

By raising or lowering the dope temperature between the intermediate pot 22 and the casting die 2 so as to satisfy the conditional expression (4), the low-viscosity region and the high-viscosity region in the dope are well-balanced. Mix. Thereby, the effect of leveling the entire surface of the dope (web 5) by movement of the region with high fluidity and low viscosity can be enhanced, and at least the film thickness deviation can be further reduced.

In particular, when a dope in which a cycloolefin-based resin is dissolved in a solvent is used, it is preferable that the following conditional expression (4a) is satisfied. That is,
(4a) 10 ° C. ≦ Tmax−Tmin ≦ 15 ° C.
It is. In the solution casting using a cycloolefin-based resin, by further satisfying the conditional expression (4a), both the film thickness deviation and the phase difference deviation are surely reduced by the leveling effect of the web surface by the low viscosity region. It becomes possible.

〔Example〕
Hereinafter, specific examples of the method for manufacturing an optical film of the present embodiment will be described with reference to comparative examples. Note that the present invention is not limited to the following embodiments.

<Example 1>
An optical film 1 made of a cycloolefin-based resin film (COP film) was produced by the following production method (solution casting method).

(Preparation of silicon dioxide dispersion diluent)
10 parts by mass of Aerosil R812 and 80 parts by mass of ethanol were stirred and mixed with a dissolver for 30 minutes, and then dispersed with Manton-Gaulin to prepare a silicon dioxide dispersion. 80 parts by mass of dichloromethane was added to the prepared silicon dioxide dispersion with stirring, and the mixture was stirred and mixed with a dissolver for 30 minutes. 1N) to prepare a silicon dioxide dispersion diluent.

(Preparation of dope)
Thermoplastic resin: Cycloolefin resin (G7810, manufactured by JSR Corporation) 145 parts by mass Fine particles: Silicon dioxide dispersion diluent 25 parts by mass Dichloromethane 360 parts by mass Ethanol 12 parts by mass The above is charged into a closed container, heated and stirred. While completely dissolved, and Azumi Filter Paper No. The resulting solution was filtered using No. 24 to prepare a dope.

(5) Next, using a belt casting film forming apparatus, the dope prepared above was transferred from the melting pot to the casting die via the intermediate pot. Here, the temperature of the dope immediately after leaving the melting pot is T1 (° C.), the temperature of the dope immediately after leaving the intermediate pot is T2 (° C.), and the temperature of the dope immediately before entering the casting die is T3 ( ° C), each temperature of T1, T2, and T3 was adjusted to the temperature shown in Table 1, respectively. At this time, T1 was set to a temperature equal to or higher than the boiling point (about 39.5 ° C.) of the solvent (here, dichloromethane). When the maximum temperature and the minimum temperature of the dope between the intermediate pot and the casting die are Tmax (° C.) and Tmin (° C.), respectively, at least one dope is provided between the intermediate pot and the casting die. A heat exchanger was provided, and Tmax and Tmin were adjusted to have the values shown in Table 1.

調整 In addition, the adjustment of each temperature of T1, T2, and T3 was performed as follows. For T1, the temperature was adjusted by flowing hot or cold water through a jacket provided outside the melting pot. For T2, the temperature was adjusted by flowing hot or cold water through a jacket provided outside the intermediate pot. As for T3, the temperature was adjusted by a heat exchanger between the melting pot and the intermediate pot (by flowing a heating medium or a cooling medium outside the pipe).

Moreover, each temperature of T1, T2, T3, Tmax, and Tmin was measured as follows using a thermometer (RTD made by Okazaki Seisakusho; Model No. RBN). As for T1, the above-mentioned thermometer was set in the melting vessel, and the dope temperature was measured in a state where the thermometer was completely immersed in the dope. The obtained result was defined as T1. Regarding T2, in the pipe through which the dope that has exited the intermediate kettle passes, the above-mentioned thermometer is installed in the pipe from the joint between the outlet of the intermediate kettle and the pipe to a position 1 m in the dope advancing direction to adjust the dope temperature. The measurement was performed, and the obtained result was defined as T2. Regarding T3, the above-mentioned thermometer was installed in a pipe just before entering the casting die, in a pipe 1 m away from the joint between the pipe and the casting die in a direction opposite to the dope advancing direction. The temperature was measured, and the obtained result was defined as T3. Regarding Tmax and Tmin, dope by installing a thermometer every 50 cm between the thermometer for T2 measurement and the thermometer for T3 measurement in the pipe between the intermediate pot and the casting die. The temperature was measured, and the maximum temperature was measured as Tmax and the minimum temperature was measured as Tmin among the plurality of measured temperatures.

Subsequently, the dope is uniformly cast on the stainless steel band support from the casting die, and the web is formed on the stainless steel band support by evaporating the solvent until the residual solvent amount becomes 80% by mass. The web was peeled off from the body. The obtained web was kept at 35 ° C to further evaporate the solvent, slit to a width of 1.15 m, and dried at a drying temperature of 160 ° C. Thereafter, the film was dried for 15 minutes while being conveyed by a number of rollers in a drying apparatus at 130 ° C., slit to a width of 1.0 m, and wound around a core to obtain an optical film 1. The thickness of the optical film 1 was 40 μm, and the winding length was 5000 m.

<Examples 2 to 16, Comparative Examples 1 to 6>
Except that the resin dissolved in the solvent was changed to the resin shown in Table 1, and the temperatures of T1, T2, T3, Tmax, and Tmin in the dope transfer step were adjusted to the temperatures shown in Table 1. In the same manner as in Example 1, optical films 2 to 16 of Examples 2 to 16 and optical films 21 to 26 of Comparative Examples 1 to 6 were produced. In Examples 9 to 14, heating and cooling of the dope between the intermediate pot and the casting die was repeated at least once by a heat exchanger under the conditions of Tmax = T2 and Tmin = T3. In Example 16, the temperature was changed linearly from T2 to T3.

<Evaluation>
(Thickness deviation)
With respect to the optical films 1 to 16 of Examples 1 to 16 and the optical films 21 to 26 of Comparative Examples 1 to 6, the film thickness in the width direction was measured using a digimatic thickness gauge (manufactured by Mitutoyo). The measurement of the film thickness was performed on the obtained film having a width of 1.0 m from the left end to the right end at intervals of 100 mm along the width direction, and the thickness was varied (the maximum value of the film thickness in the width direction). (Difference between the minimum value and the minimum value). This measurement was performed three times every 50 m in the longitudinal direction, and the average value was obtained. Then, the thickness variation (film thickness deviation) was evaluated based on the following evaluation criteria. The smaller the thickness variation, the better.
"Evaluation criteria"
5: Thickness variation is less than 1 μm (very good).
4: Thickness variation is 1 μm or more and less than 2 μm (very good).
3: The thickness variation is 2 μm or more and less than 3 μm (good).
2: The thickness variation is 3 μm or more and less than 5 μm (defective).
1: Thickness variation is 5 μm or more (very poor).

(Phase difference deviation)
For the optical films 1 to 16 of Examples 1 to 16 and the optical films 21 to 26 of Comparative Examples 1 to 6, in-plane retardation in the width direction using a Ro measurement device (AXOSCAN-AFM-2000x500H manufactured by Axometrics). (Retardation) Ro was measured. The Ro measurement was performed in the same manner as the measurement of the thickness variation described above.

That is, the measurement of Ro is performed on the obtained film having a width of 1.0 m from the left end to the right end at intervals of 100 mm along the width direction, and the variation of Ro (the maximum value of Ro in the width direction) is measured. (Difference between the minimum value and the minimum value). This measurement was performed three times every 50 m in the longitudinal direction, and the average value was obtained. Then, the variation (phase difference deviation) of Ro was evaluated based on the following evaluation criteria. It is preferable that the variation of Ro is smaller.
"Evaluation criteria"
5: The variation in Ro is less than 1 nm (very good).
4: The variation in Ro is 1 nm or more and less than 2 nm (very good).
3: Ro variation is 2 nm or more and less than 3 nm (good).
2: The variation in Ro is 3 nm or more and less than 5 nm (poor).
1: Ro variation is 5 nm or more (very bad).

Table 1 shows the evaluation results of the optical films 1 to 16 of Examples 1 to 16 and the optical films 21 to 26 of Comparative Examples 1 to 6. In Table 1, PC indicates a polycarbonate resin, Acryl indicates an acrylic resin, and TAC indicates triacetyl cellulose.

より Table 1 shows that Comparative Examples 1 to 6 all have poor film thickness variation (film thickness deviation) and Ro variation (phase difference deviation). In Comparative Example 1, since T2> T1 in the dope transfer step, the solvent evaporates in the intermediate vessel, and the concentration of the liquid dope fluctuates. Therefore, film formation is performed using a dope that is out of design, so that the film thickness varies greatly, which is considered to cause a film thickness deviation and a phase difference deviation. In Comparative Example 2, in the dope transfer step, T3> T2, and the dope entering the casting die could not be sufficiently cooled, so that a high-viscosity region could not be sufficiently generated in the dope. As a result, it is considered that the cause is that the surface of the dope fluctuates under the influence of the surrounding wind or the like immediately after casting on the support. In Comparative Example 3, T2−T3 = 5 ° C., and the temperature difference between T2 and T3 was too small to sufficiently cool the dope entering the casting die. It is considered that a high-viscosity region cannot be sufficiently generated therein, and the surface of the dope fluctuates immediately after casting on the support under the influence of the surrounding wind or the like.

In Comparative Examples 4 and 5, T2-T3 is 15 ° C, and in Comparative Example 5, T1-T3 is 26 ° C, and the dope entering the casting die is cooled too much. For this reason, a region of high viscosity is generated in the dope too much, and the surface of the dope is likely to have irregularities immediately after casting on the support, and the surface deformation of the dope remains as the surface deformation of the web after drying, and this is It is considered that a film thickness deviation and a phase difference deviation are caused in the final film.

In Comparative Example 6, a film was formed using TAC. When using a high-viscosity resin such as TAC, it is desirable to keep the temperature as constant as possible during the transfer of the dope in order to suppress the generation of a gel-like substance (see Patent Document 1). Since -T3 is set to 20 ° C. and the temperature is largely changed during the transfer, a gel-like substance is generated, which is considered to cause a film thickness deviation and a phase difference deviation.

On the other hand, in Examples 1 to 16, good results were obtained for the film thickness deviation and the phase difference deviation. In Examples 1 to 16, all of T1, T2, and T3 satisfy the following conditional expressions (1) to (3). That is,
(1) T1>T2> T3
(2) T1-T3 ≦ 25 ° C.
(3) 5 ° C <T2-T3 <15 ° C
It is. In this case, even when a solution casting is performed using a resin having a low SP value such as COP, a high-viscosity region and a low-viscosity region can coexist in the dope. While reducing the influence and the like, the entire surface of the dope can be leveled by the movement of the region having high fluidity and low viscosity in the dope. Thus, it is considered that the occurrence of the film thickness deviation and the phase difference deviation can be reduced.

Further, in Examples 1 to 15, the film thickness deviation and the phase difference deviation are further reduced as compared with Example 16. In Examples 1 to 15, the following conditional expression (4):
(4) 5 ° C <Tmax-Tmin <30 ° C
In order to satisfy the above, the dope temperature is raised or lowered between the intermediate pot and the casting die, so that the low-viscosity region and the high-viscosity region are mixed in the dope in a well-balanced manner. It is considered that the leveling effect of the surface of the dope (web) by the region of the viscosity was enhanced.

Above all, in Examples 9 to 11, the effect of reducing the film thickness deviation and the phase difference deviation is the highest. In Examples 9 to 11, in solution casting using a cycloolefin-based resin, the following conditional expression (4a):
(4a) 10 ° C. ≦ Tmax−Tmin ≦ 15 ° C.
This is probably because the leveling effect of the web surface by the low-viscosity region is further improved by satisfying the following.

[Others]
The method for manufacturing an optical film of the present embodiment described above can be expressed as follows.

1. A method for producing an optical film by producing an optical film by a solution casting method,
A dope is prepared by dissolving a resin having an SP value of 10.5 (MPa) ^1/2 or less as a solubility parameter in a solvent in a dissolving vessel to prepare a dope, and transferring the dope to a casting die via an intermediate vessel. A transfer process;
A casting step of casting the dope from the casting die onto a support,
A method for producing an optical film, wherein the dope transfer step satisfies the following conditional expressions (1) to (3);
(1) T1>T2> T3
(2) T1-T3 ≦ 25 ° C.
(3) 5 ° C <T2-T3 <15 ° C
However,
T1: Temperature (° C.) of the dope immediately after leaving the melting pot
T2: temperature of the dope immediately after leaving the intermediate pot (° C.)
T3: temperature of the dope immediately before entering the casting die (° C.)
It is.

2. 2. The method for producing an optical film according to the above 1, wherein the dope transferring step further satisfies the following conditional expression (4);
(4) 5 ° C <Tmax-Tmin <30 ° C
However,
Tmax: maximum temperature of the dope between the intermediate pot and the casting die (° C.)
Tmin: minimum temperature (° C.) of the dope between the intermediate pot and the casting die
It is.

3. The resin is a cycloolefin resin,
3. The method for producing an optical film according to the above 2, wherein the dope transferring step further satisfies the following conditional expression (4a);
(4a) 10 ° C. ≦ Tmax−Tmin ≦ 15 ° C.
It is.

Although the embodiment of the present invention has been described above, the scope of the present invention is not limited to this, and can be extended or modified without departing from the gist of the invention.

光学 The method for producing an optical film of the present invention can be used when an optical film is produced by a solution casting method using a resin having a low SP value.

2 Casting die 3 Support 21 Melting pot 22 Intermediate pot F Optical film

Claims

A method for producing an optical film by producing an optical film by a solution casting method,
A dope is prepared by dissolving a resin having an SP value of 10.5 (MPa) 1/2 or less as a solubility parameter in a solvent in a dissolving pot to prepare a dope, and transferring the dope to a casting die via an intermediate pot. A transfer process;
A casting step of casting the dope from the casting die onto a support,
A method for producing an optical film, wherein the dope transferring step satisfies the following conditional expressions (1) to (3);
(1) T1>T2> T3
(2) T1-T3 ≦ 25 ° C.
(3) 5 ° C <T2-T3 <15 ° C
However,
T1: Temperature (° C.) of the dope immediately after leaving the melting pot
T2: temperature of the dope immediately after leaving the intermediate pot (° C.)
T3: temperature of the dope immediately before entering the casting die (° C.)
It is.
The method for producing an optical film according to claim 1, wherein the dope transfer step further satisfies the following conditional expression (4);
(4) 5 ° C <Tmax-Tmin <30 ° C
However,
Tmax: maximum temperature of the dope between the intermediate pot and the casting die (° C.)
Tmin: minimum temperature (° C.) of the dope between the intermediate pot and the casting die
It is.
The resin is a cycloolefin resin,
The method for producing an optical film according to claim 2, wherein the dope transfer step further satisfies the following conditional expression (4a);
(4a) 10 ° C. ≦ Tmax−Tmin ≦ 15 ° C.
It is.