阅读说明：本技术 光学膜的制造方法 (Method for manufacturing optical film ) 是由 穗北祐树 于 2019-04-03 设计创作，主要内容包括：一种光学膜的制造方法,通过溶液流延成膜法制造光学膜。该制造方法包括：料浆移送工序,其使作为溶解度参数的SP值为10.5(MPa)~(1/2)以下的树脂在溶解釜中溶解于溶剂从而制作料浆,并将上述料浆经由中间釜向流延模移送；流延工序,其将上述料浆从流延模向支承体上流延。在料浆移送工序中,满足如下的条件式(1)～(3)。即,(1)T1＞T2＞T3,(2)T1－T3≤25℃,(3)5℃＜T2－T3＜15℃,其中,T1：刚离开溶解釜的料浆的温度(℃),T2：刚离开中间釜的料浆的温度(℃),T3：即将进入流延模的料浆的温度(℃)。(A method for manufacturing an optical film by a solution casting film forming method. The manufacturing method comprises the following steps: a slurry transfer step of adjusting the SP value as a solubility parameter to 10.5(MPa) 1/2 Dissolving the following resin in a solvent in a dissolving kettle to prepare slurry, and transferring the slurry to a casting die through an intermediate kettle; and a casting step of casting the slurry from a casting die onto a support. In the slurry transfer step, the following conditional expressions (1) to (3) are satisfied. That is, (1) T1 >T2 is more than T3, (2) T1-T3 is less than or equal to 25 ℃, (3) T2-T3 is more than 5 ℃ < 15 ℃, wherein, T1: temperature (° c) of slurry just exiting the dissolution tank, T2: temperature (. degree. C.) of slurry just after leaving the intermediate tank, T3: the temperature (. degree. C.) of the slurry to be fed into the casting die.)

1. A method for producing an optical film by a solution casting film-forming method, comprising:

a slurry transfer step of adjusting the SP value as a solubility parameter to 10.5(MPa)^1/2Dissolving the following resin in a solvent in a dissolving kettle to prepare slurry, and transferring the slurry to a casting die through an intermediate kettle;

a casting step of casting the slurry from the casting die onto a support;

in the slurry transfer step, the following conditional expressions (1) to (3) are satisfied:

(1)T1＞T2＞T3，

(2)T1－T3≤25℃，

(3)5℃＜T2－T3＜15℃，

wherein the content of the first and second substances,

t1: the temperature (° c) of the slurry just after leaving the dissolution tank,

t2: the temperature (° c) of the slurry just after exiting the intermediate tank,

t3: the temperature (DEG C) of the slurry immediately before entering the casting die.

2. The method of manufacturing an optical film according to claim 1,

in the slurry transfer step, the following conditional formula (4) is further satisfied:

(4)5℃＜Tmax－Tmin＜30℃，

wherein the content of the first and second substances,

tmax: the maximum temperature (DEG C) of the slurry between the intermediate tank and the casting die,

tmin: a minimum temperature (DEG C) of the slurry between the intermediate tank and the casting die.

3. The method of manufacturing an optical film according to claim 2,

the resin is a cycloolefin resin,

in the slurry transfer step, the following conditional expression (4a) is further satisfied:

(4a)10℃≤Tmax－Tmin≤15℃。

Technical Field

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

Background

When a gel-like substance is contained in a slurry used in a solution casting film formation method, the presence of the gel-like substance in a film becomes a cause of deterioration in the product quality of the film when film formation is performed by the solution casting film formation method (hereinafter also referred to as solution film formation) using the slurry. In view of the fact that the generation of gel-like substances from the slurry has a very close relationship with the slurry temperature or the temperature history of the slurry, for example, in patent document 1, the slurry temperature is kept as constant as possible when the slurry containing cellulose acetate and a solvent is transferred to the casting die, thereby suppressing the generation of gel-like substances.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 4753553 (see claims 1, 2, 0004, paragraphs 0010 to 0012, FIG. 1, FIG. 2, etc.)

Disclosure of Invention

Technical problem to be solved by the invention

In recent years, an optical film used in a display device is required to be a thin film and to have water repellency (low water permeability). Conventional optical films containing cellulose acetate have not satisfied the required conditions because they have high water permeability.

Therefore, it is necessary to form a film from a solution using a resin having low water permeability (for example, a resin having a low SP value, which is a solubility parameter). However, in the film formation using a solution of a resin having a low SP value, when the slurry is transferred while maintaining the temperature of the slurry constant as in patent document 1, a smooth film having good characteristics cannot be produced. Specifically, in the manufactured optical film, film thickness irregularities and uneven film thickness variations occur in the width direction or the longitudinal direction, or retardation variations occur in which the retardation is uneven due to stretching. For this reason, the inventors of the present application presume as follows. That is, since a resin having a low SP value has a weaker intermolecular interaction than cellulose acetate, the viscosity of a slurry containing the resin is low. In the solution film formation using the slurry, when the slurry is cast onto the support and transported, the surface of the cast film formed on the support is easily deformed (irregularities are easily generated on the surface) by the influence of ambient wind (wind pressure, wind speed) and temperature. As a result, the film thickness of the film after film formation is not uniform. In addition, the surface deformation of the cast film causes molecular orientation unevenness at the time of stretching, which is expressed as a phase difference deviation.

Therefore, in the solution film formation using a resin having a low SP value, it is desired to reduce the film thickness variation and the phase difference variation, but such solution film formation has not been achieved.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for manufacturing an optical film, which can reduce variations in film thickness and variations in retardation in film formation using a solution of a resin having a low SP value.

Technical solution for solving technical problem

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

A method for manufacturing an optical film according to an aspect of the present invention is a method for manufacturing an optical film by a solution casting film-forming method, including:

a slurry transfer step of adjusting the SP value as a solubility parameter to 10.5(MPa)^1/2Dissolving the following resin in a solvent in a dissolving kettle to prepare slurry, and transferring the slurry to a casting die through an intermediate kettle;

a casting step of casting the slurry from the casting die onto a support;

in the slurry transfer step, the following conditional expressions (1) to (3) are satisfied:

(1)T1＞T2＞T3，

(2)T1－T3≤25℃，

(3)5℃＜T2－T3＜15℃，

wherein the content of the first and second substances,

t1: the temperature (° c) of the slurry just after leaving the dissolution tank,

t2: the temperature (° c) of the slurry just after exiting the intermediate tank,

t3: the temperature (DEG C) of the slurry immediately before entering the casting die.

ADVANTAGEOUS EFFECTS OF INVENTION

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

Drawings

Fig. 1 is an explanatory view showing a schematic configuration of an optical film manufacturing apparatus according to an embodiment of the present invention.

Fig. 2 is a flowchart showing the flow of the above-described optical film manufacturing process.

FIG. 3 is an explanatory view showing the temperature history of the slurry flowing between the intermediate tank and the casting die of the above-mentioned manufacturing apparatus.

Detailed Description

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. In the present specification, when a numerical range is expressed as a to B, the numerical range includes values having a lower limit of a and an upper limit of B. The present invention is not limited to the following.

[ method for producing optical film ]

Fig. 1 is an explanatory diagram showing a schematic configuration of an optical film manufacturing apparatus 50 according to the present embodiment. Fig. 2 is a flowchart showing a flow of the manufacturing process of the optical film. As shown in fig. 2, the method for manufacturing an optical film according to the present embodiment is a method for manufacturing an optical film by a solution casting film forming method, and includes a slurry transfer step (S1), a casting step (S2), 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 fig. 1 and 2.

(S1: slurry transfer step)

In the slurry transfer step, a slurry to be cast on the support 3 is prepared (prepared) in the slurry transfer portion 1 and transferred to the casting die 2. The slurry transfer step will be described in detail later.

(S2: casting Process)

In the casting step, the slurry fed from the slurry feed section 1 to the casting die 2 is cast from the casting die 2 to a casting position on the support 3 formed of an endless belt of rotationally driven stainless steel which is endlessly fed. Then, the support 3 supports and conveys the slurry (casting slurry) being cast. Thereby, the casting film (band-like body) 5 is formed on the support 3.

The support body 3 is held by a pair of rollers 3a,3b and a plurality of rollers (not shown) located therebetween. A driving device (not shown) for applying tension to the support body 3 is provided to one or both of the rollers 3a and 3b, and thereby the support body 3 is used in a state in which it is stretched by applying tension thereto.

In the casting step, the strip 5 formed of the slurry cast on the support 3 is heated on the support 3 to evaporate the solvent until the strip 5 can be peeled from the support 3 by the peeling roller 4. The method of evaporating the solvent includes a method of blowing air from the side of the strip, a method of conducting heat from the back surface of the support 3 by a liquid, a method of conducting heat from the front and back surfaces by radiant heat, and the like, and can be used alone or in combination as appropriate.

(S3: peeling step)

After the strip-shaped body 5 is dried and solidified or cooled and solidified on the support 3 by the above-described casting process to a peelable film strength, the strip-shaped body 5 is peeled from the support 3 by the peeling roller 4 while maintaining the self-supporting property of the strip-shaped body 5 in the peeling process.

The amount of the residual solvent of the strip-like body 5 on the support 3 at the time of peeling is preferably in the range of 25 to 120 mass% depending on the strength of the drying condition, the length of the support 3, and the like. When peeling is performed with a larger amount of residual solvent, the band-like body 5 is too soft, which affects flatness during peeling, and wrinkles and vertical streaks are likely to occur due to peeling tension, and therefore the amount of residual solvent during peeling is determined while achieving both economical speed and quality. The residual solvent amount is defined by the following formula.

The residual solvent amount (% by mass) is (mass before heat treatment of the strip-mass after heat treatment of the strip)/(mass after heat treatment of the strip) × 100

Here, the heat treatment in measuring the amount of the residual solvent means that the heat treatment is performed at 115 ℃ for one hour.

(S4: first drying step)

The strip-like body 5 peeled from the support body 3 by the peeling roller 4 is dried by the drying device 6. In the drying device 6, the strip-shaped bodies 5 are conveyed by a plurality of conveying rollers, and the strip-shaped bodies 5 are dried therebetween. The drying method in the drying device 6 is not particularly limited, and the strip-shaped body 5 is generally dried by using hot air, infrared rays, a heating roller, microwaves, or the like. From the viewpoint of simplicity, a method of drying the strip-shaped body 5 with hot air is preferable. The first drying step may be performed as needed.

(S5: drawing step)

In the stretching step, the band 5 dried in the drying device 6 is stretched by the tenter 7. The stretching Direction in this case may be a film transport Direction (MD Direction), a width Direction (TD Direction) perpendicular to the transport Direction within the film surface, or any of the two directions. In the stretching step, in order to improve the flatness and dimensional stability of the film, a tenter system is preferred in which both side edge portions of the strip-shaped body 5 are fixed by clips or the like and stretched. In addition to stretching, drying may be performed in the tenter 7.

The stretching step of S5 may be performed as needed, or may be omitted. For example, when the optical film is wound and then stretched, the stretching step before winding may be omitted.

(S6: second drying step)

The strip 5 stretched by the tenter 7 is dried by the drying device 8 as necessary. In the drying device 8, the strip-shaped bodies 5 are conveyed by a plurality of conveying rollers, and the strip-shaped bodies 5 are dried therebetween. The drying method in the drying device 8 is not particularly limited, and the strip-shaped body 5 is generally dried using hot air, infrared rays, a heating roller, microwaves, or the like. From the viewpoint of simplicity, a method of drying the strip-shaped body 5 with hot air is preferable. Before entering the drying device 8, a step of roughly cutting both width end portions of the strip-shaped body 5 may be performed.

After the strip-shaped body 5 is dried by the drying device 8, the strip-shaped body 5 is conveyed to the winding device 11 as the optical film F.

(S7: cutting step, S8: embossing step)

Between the drying device 8 and the winding device 11, a cutter 9 and an embossing unit 10 are disposed in this order. The cutting unit 9 performs a cutting step of cutting both ends in the width direction of the optical film F by a slitter while conveying the film. In the optical film F, the remaining portions after both end portions are cut constitute a product portion as a film product. On the other hand, the portion cut out from the optical film F is collected by the gas transport tube and reused as a part of the raw material for film formation.

After the dicing step, both ends of the optical film F in the width direction are subjected to embossing (knurling) by the embossing unit 10. The embossing is performed by pressing heated embossing rollers against both ends of the optical film F. Fine irregularities are formed on the surface of the embossing roller, and the embossing roller is pressed against both ends of the optical film F to form irregularities on the both ends. By the embossing, winding displacement and blocking (adhesion of films) in the next winding step can be suppressed as much as possible.

(S9: winding Process)

Finally, the embossed optical film F is wound by the winding device 11 to obtain a raw roll (film roll) of the optical film F. That is, in the winding step, the optical film F is wound while being conveyed to manufacture a film roll. The method of winding the optical film F may be a winding machine generally used, and a method of controlling tension such as a constant torque method, a constant tension method, an oblique tension method, a programmed tension control method in which internal stress is constant may be used flexibly. The roll length of the optical film F is preferably 1000m to 15000 m. In this case, the width is preferably 1000mm to 3200mm, and the film thickness is preferably 10 μm to 60 μm.

[ details of the slurry transfer step ]

Next, the slurry transfer step will be described in detail. In the slurry transfer step, the SP value as a Solubility Parameter (Solubility Parameter) was set to 10.5(MPa)^1/2The following resins are dissolved in a solvent in a dissolving tank 21 to prepare a slurry, and the slurry is transferred to a casting die 2 through an intermediate tank 22. In the intermediate tank 22, the slurry is temporarily held, whereby air and bubbles in the slurry are discharged. The slurry in the dissolution tank 21 is transferred to the intermediate tank 22 through the conduit 23, and the slurry in the intermediate tank 22 is transferred to the casting die 2 through the conduit 24. At least one heat exchanger 25 is provided between the intermediate tank 22 and the casting die 2. In this heat exchanger 25, the conduit 24 is heated or cooled by a heating medium or a cooling medium, whereby the slurry passing through the conduit 24, that is, the slurry flowing from the intermediate tank 22 to the casting die 2 is heated or cooled. In the case where a plurality of heat exchangers 25 are provided between the intermediate tank 22 and the casting die 2, the slurry may be heated and then cooled or cooled and then reheated.

Here, the SP value will be described. The SP value is a value represented by the square root of the molecular cohesive energy, and is described in Polymer Hand Book (Polymer Edition) in chapter IV Solubility Parameter Values, and used. However, in the present application, the expression unit is (MPa)^1/2And at 25 ℃. Note that, for portions not described in the data, calculation can be performed by a method described in r.f. fedors, Polymer Engineering Science, 14, p147 (1974). That is, the calculation can be basically performed as follows.

Solubility parameter value (SP value) ═ Delta E/V)^1/2

Here, Δ E represents cohesive energy density. V represents a molecular volume (molar volume).

The solubility parameter value (SP value) can be calculated based on the idea of r.f. fedors using Scigress Explorer ver.2.4 (product of fujiton, japan).

The SP value was 10.5(MPa)^1/2As the following resin, for example, a cycloolefin resin (SP value: 9.6(MPa) can be used^1/2) Polycarbonate resin (SP value: 10.2(MPa)^1/2) Acrylic resin (SP value: 9.5(MPa)^1/2). The resin having a low SP value is not limited to the above-mentioned resin, as long as TAC (SP value: 10.9 (MPa))^1/2) Other resins can be used basically.

As the solvent, a mixed solvent of a good solvent and a poor solvent can be used. The good solvent is an organic solvent having a property of dissolving a resin (solubility), and corresponds to 1, 3-dioxolane, THF (tetrahydrofuran), methyl ethyl ketone, acetone, methyl acetate, Methylene chloride (Dichloromethane, Methylene chloride), toluene, or the like. On the other hand, the poor solvent is a solvent having no property of dissolving the resin alone, and corresponds to methanol, ethanol, or the like.

In the present embodiment, the following conditional expressions (1) to (3) are satisfied in the step of transferring the slurry from the dissolution tank 21 to the casting die 2 through the intermediate tank 22. That is to say that the first and second electrodes,

(1)T1＞T2＞T3，

(2)T1－T3≤25℃，

(3)5℃＜T2－T3＜15℃，

wherein the content of the first and second substances,

t1: the temperature (. degree. C.) of the slurry just after leaving the dissolution tank 21,

t2: the temperature (. degree. C.) of the slurry just after leaving the intermediate tank 22,

t3: the temperature (. degree. C.) of the slurry to be fed into the casting die 2.

The conditional expression (1) specifies the magnitude relation of the temperature of each slurry just after leaving the dissolution tank 21, just after leaving the intermediate tank 22, and just before entering the casting die 2. The conditional expression (2) specifies an appropriate range of the temperature difference between the slurry just after leaving the dissolution tank 21 and the slurry just before entering the casting die 2. The conditional expression (3) specifies an appropriate range of the temperature difference between the slurry just leaving from the intermediate tank 22 and the slurry just before entering the casting die 2. By satisfying the conditional expressions (1) to (3), it is possible to reduce the film thickness variation and the phase difference variation of the optical film F in film formation using a solution having a low SP value. The inventors of the present application consider the reason as follows.

By satisfying the conditional expression (1), the slurry just about to enter the casting die 2 is cooled more sufficiently than the slurry just exiting from the dissolving tank 21 and the slurry just exiting from the intermediate tank 22. Thus, the low-viscosity slurry containing the resin having a low SP value is cooled while being transferred from the dissolution tank 21 to the casting die 2, and a high-viscosity region can be formed in a part of the slurry. Further, by satisfying the conditional expression (2), the degree of cooling of the slurry is limited (the slurry is not excessively cooled), and thus the excessive occurrence of a high viscosity region in the slurry can be suppressed.

Further, the generation of the high viscosity region due to the cooling of the slurry can be suppressed as the value (temperature difference) of T2 to T3 is smaller, and the generation of the high viscosity region due to the cooling of the slurry can be promoted as the value of T2 to T3 is larger, but the high viscosity region and the low viscosity region coexist in the slurry in a range where the value of T2 to T3 satisfies the conditional expression (3). Thus, the occurrence of film thickness variation and phase difference variation can be reduced by the interaction of the respective regions.

That is, as described above, the low viscosity slurry containing the resin having a low SP value is easily affected by the surrounding wind and temperature during the casting from the casting die 2 and the transportation on the support 3, and the surface of the strip 5 on the support 3 is deformed to easily cause the film thickness variation and the phase difference variation. As in the present embodiment, by generating a high viscosity region in the slurry, it is possible to suppress deformation of the surface of the strip-like body 5 due to the influence of wind or the like when the slurry is being fed onto the support body 3. This can reduce film thickness variation and phase difference variation caused by the influence of wind or the like due to the above-described delay.

Further, if the slurry is cooled too much and a high viscosity region is excessively generated in the slurry, a gel-like substance is easily generated in the slurry. In addition, unevenness is likely to occur on the surface of the slurry after the support 3 is discharged from the casting die 2, and the surface of the slurry is difficult to level (flatten) under the influence of stress caused by uneven drying. In this case, the surface deformation of the slurry remains as surface deformation of the strip 5 after drying. Therefore, the surface of the strip-shaped body 5 is deformed, and the finally obtained optical film F has film thickness variation and phase difference variation.

However, in the present embodiment, since the slurry can be made to coexist with the high viscosity region and the low viscosity region while suppressing the increase of the high viscosity region due to excessive cooling, even if unevenness occurs on the surface of the slurry due to the presence of the high viscosity region after casting on the support 3, the stress due to the flow of the slurry to the low viscosity region and the drying unevenness is transmitted to the periphery by the low viscosity region, and the surface of the entire slurry is leveled. This can suppress surface deformation of the strip-shaped body 5, and thus can reduce film thickness variation and phase difference variation that occur in the optical film F finally obtained due to the surface deformation. Further, since the slurry has a low viscosity region, the generation of gel-like substances can be suppressed.

As described above, by satisfying the conditional expressions (1) to (3), the low viscosity region remains in the slurry to maintain the fluidity, and the high viscosity region serving as the core is generated (not excessively generated), whereby the influence of local wind during the casting and the stress due to uneven drying are reduced, and the entire surface of the slurry (the belt-like body 5) can be leveled by the movement of the low viscosity region having high fluidity. As a result, the occurrence of gel-like substances can be reduced, and the occurrence of variations in film thickness and variations in phase difference can be reduced.

In the slurry transfer step of S1, it is preferable that the following conditional expression (4) is further satisfied. That is to say that the first and second electrodes,

(4)5℃＜Tmax－Tmin＜30℃，

wherein the content of the first and second substances,

tmax: maximum temperature (. degree. C.) of slurry between the intermediate pot 22 and the casting die 2

Tmin: the minimum temperature (. degree. C.) of the slurry between the intermediate tank 22 and the casting die 2.

Note that the temperature change of the slurry satisfying the conditional expression (4) can be achieved by heating or cooling the slurry flowing in the conduit 24 by at least one heat exchanger 25 as described above.

Fig. 3 shows the temperature history (temperature of passing position of each slurry) of the slurry flowing between the intermediate tank 22 and the casting die 2. The position of the horizontal axis passing through point 0 corresponds to the position of the intermediate pot 22, and the position of the horizontal axis passing through point 6 corresponds to the position of the casting die 2. By satisfying the conditional expression (4), various temperature histories can be realized between the intermediate pot 22 and the casting die 2. For example, even when the temperature of the slurry leaving the intermediate pot 22 is constant (same) and the temperature of the slurry entering the casting die 2 is constant (same), as the temperature history of the slurry, it is possible to realize a case where the temperature of the slurry is increased and then decreased (refer to a solid line a), a case where the temperature of the slurry is decreased and then increased (refer to a broken line B), a case where the temperature of the slurry is decreased and then increased and then decreased again (refer to a dashed-dotted line C), and the like, as the slurry moves from the intermediate pot 22 to the casting die 2. In the figure, Ta, Tb, and Tc correspond to the difference between the maximum temperature Tmax and the minimum temperature Tmin of the slurry in each case (temperature history).

In order to satisfy the conditional expression (4), the temperature of the slurry is increased or decreased between the intermediate pot 22 and the casting die 2, whereby the low viscosity region and the high viscosity region are mixed in the slurry in a balanced manner. This can improve the effect of leveling the entire surface of the slurry (the belt-like body 5) by moving the low viscosity region having high fluidity, and can further reduce at least the variation in film thickness.

In particular, when a slurry in which a cycloolefin resin is dissolved in a solvent is used, it is preferable that the following conditional formula (4a) is satisfied. That is to say that the first and second electrodes,

(4a)10℃≤Tmax－Tmin≤15℃。

in the solution film formation using the cycloolefin resin, by further satisfying the conditional expression (4a), both the film thickness variation and the retardation variation can be reliably reduced by utilizing the leveling effect of the surface of the belt body due to the low viscosity region.

[ examples ]

Hereinafter, examples of specific examples of the method for producing an optical film according to the present embodiment will be described with reference to comparative examples. The present invention is not limited to the following examples.

< first embodiment >

An optical film 1 formed of a cycloolefin resin film (COP film) was produced by the following production method (solution casting film forming method).

(preparation of silica Dispersion dilution)

A silica dispersion was prepared by stirring and mixing 10 parts by mass of fumed silica R812 and 80 parts by mass of ethanol in a dissolver for 30 minutes, and then dispersing in a homogenizer. 80 parts by mass of methylene chloride was added to the prepared silica dispersion with stirring, and after stirring and mixing for 30 minutes in a dissolver, the mixture was filtered through a fine particle dispersion diluent filter (TOYOBO ADVANTEC, Japan, polypropylene drum filter TCW-PPS-1N) to prepare a silica dispersion diluent.

(preparation of slurry)

Thermoplastic resin: cycloolefin resins

The above-mentioned materials were put into a closed vessel, heated and stirred to be completely dissolved, and filtered by using an Amyda filter paper No.24 manufactured by Japan (Japan) to prepare a slurry.

Next, the prepared slurry was transferred from the dissolution tank to a casting die through an intermediate tank by using a tape casting film forming apparatus. Here, when the temperature of the slurry immediately after the dissolution vessel was T1 (c), the temperature of the slurry immediately after the intermediate vessel was T2 (c), and the temperature of the slurry immediately before the casting die was T3 (c), the temperatures of T1, T2, and T3 were adjusted to the temperatures 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 ℃) of the solvent (here, methylene chloride). When the maximum temperature and the minimum temperature of the slurry between the intermediate pot and the casting die were set to Tmax (. degree. C.) and Tmin (. degree. C.), respectively, at least one heat exchanger was provided between the intermediate pot and the casting die, and the Tmax and Tmin were adjusted to the values shown in Table 1.

The temperature of T1, T2, and T3 was adjusted as follows. For T1, temperature adjustment was performed by passing warm or cold water through a water jacket provided on the outside of the dissolution tank. For T2, temperature adjustment was performed by passing warm or cold water through a water jacket provided on the outer side of the intermediate tank. In T3, the temperature was adjusted by a heat exchanger between the dissolution tank and the intermediate tank (by passing a heating medium or a cooling medium through the outside of the pipe).

The respective temperatures of T1, T2, T3, Tmax and Tmin were measured by using a thermometer (Model No. rbn, a temperature measuring resistor manufactured by okazaki corporation, japan) as follows. T1 was measured by placing the thermometer in the dissolution tank and measuring the temperature of the slurry with the thermometer completely immersed in the slurry, and the result was T1. In regard to T2, the result of estimating the slurry temperature by providing the above thermometer in the pipe through which the slurry separated from the intermediate tank passes, the pipe being located one meter away from the joint between the outlet of the intermediate tank and the pipe in the slurry traveling direction was T2. T3 was measured by providing the thermometer in the pipe just before entering the casting die at a position one meter away from the joint of the pipe and the casting die in the direction opposite to the slurry traveling direction, and the slurry temperature was T3. Tmax and Tmin, in the piping between the intermediate tank and the casting die, thermometers were installed at intervals of 50cm between the thermometer for measuring T2 and the thermometer for measuring T3 to measure the slurry temperature, and the maximum temperature among the temperatures at the plurality of measurement sites was Tmax, and the minimum temperature was Tmin.

Then, the slurry was uniformly cast from the casting die onto a stainless steel belt support, the solvent was evaporated on the stainless steel belt support until the residual solvent amount was 80 mass% to form a strip-like body, and the strip-like body was peeled from the stainless steel belt support. The obtained ribbon was further evaporated while maintaining the temperature at 35 ℃, slit to a width of 1.15m, and dried at a drying temperature of 160 ℃. Then, the film was conveyed by a large number of rolls in a drying apparatus at 130 ℃ and dried for 15 minutes, and then slit to a width of 1.0m and wound on a winding core to obtain an optical film 1. The optical film 1 had a thickness of 40 μm and a roll length of 5000 m.

< second to sixteenth embodiments, first to sixth comparative examples >

The optical films 2 to 16 of the second to sixteenth examples and the optical films 21 to 26 of the first to sixth comparative examples were produced in the same manner as in the first example, 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 slurry transfer step were adjusted to the temperatures shown in table 1. In the ninth to fourteenth embodiments, heating and cooling of the slurry by the heat exchanger are repeated at least once between the intermediate tank and the casting die under the condition that Tmax is T2 and Tmin is T3. Also, in the sixteenth embodiment, the temperature is linearly changed from T2 to T3.

< evaluation >

(deviation of film thickness)

The thickness of the optical films 1 to 16 of the first to sixteenth examples and the optical films 21 to 26 of the first to sixth comparative examples was measured in the width direction by using a digital thickness gauge (manufactured by sanfeng, japan). The film thickness was measured at intervals of 100mm in the width direction from the left end to the right end of the obtained 1.0m wide film, and the thickness variation (difference between the maximum value and the minimum value of the film thickness in the width direction) was determined. Then, the measurement was performed three times at intervals of 50m in the longitudinal direction, and the average value was obtained. Then, the thickness unevenness (film thickness variation) was evaluated based on the following evaluation criteria. It is preferable that the thickness unevenness is small.

Reference to evaluation

5: the thickness unevenness was less than 1 μm (very good).

4: the thickness is not 1 μm or more but less than 2 μm (quite good).

3: the thickness is not less than 2 μm but less than 3 μm (good).

2: the thickness is not less than 3 μm but less than 5 μm (difference).

1: the thickness was not less than 5 μm (rather poor).

(deviation of phase difference)

The in-plane retardation (retardation) Ro was measured in the width direction of the optical films 1 to 16 of the first to sixteenth examples and the optical films 21 to 26 of the first to sixth comparative examples using an Ro measuring apparatus (AXOSCAN-AFM-2000 x500H manufactured by Axometrics). Ro was measured in the same manner as in the measurement of the thickness unevenness.

That is, Ro was measured at intervals of 100mm in the width direction from the left end to the right end of the obtained 1.0m wide film, and the variation in Ro (difference between the maximum value and the minimum value of Ro in the width direction) was determined. Then, the measurement was performed three times at intervals of 50m in the longitudinal direction, and the average value was obtained. Then, the unevenness of Ro (phase difference deviation) was evaluated based on the following evaluation criteria. It is preferable that the variation in Ro is small.

Reference to evaluation

5: ro unevenness was below 1nm (very good).

4: ro is not always 1nm or more but less than 2nm (quite good).

3: ro is not less than 2nm but less than 3nm (good).

2: ro unevenness is 3nm or more and less than 5nm (difference).

1: ro is not always 5nm or more (rather poor).

Table 1 shows the evaluation results of the optical films 1 to 16 of the first to sixteenth examples and the optical films 21 to 26 of the first to sixteenth comparative examples. In table 1, PC refers to a polycarbonate resin, Acryl refers to an acrylic resin, and TAC refers to cellulose triacetate.

[ Table 1]

According to table 1, in the first to sixth comparative examples, both the film thickness unevenness (film thickness variation) and the Ro unevenness (phase difference variation) were different. In the first comparative example, since T2 > T1 in the slurry transfer step, the solvent evaporates in the intermediate tank, and the concentration of the liquid, i.e., the slurry, changes. Therefore, since the film is formed by using a slurry different from the design, the variation in film thickness becomes large, and it is considered that the variation in film thickness and the variation in phase difference occur due to this. In the second comparative example, T3 > T2 in the slurry transfer step failed to sufficiently cool the slurry entering the casting die, and therefore a high viscosity region could not be sufficiently generated in the slurry, and as a result, it is considered that the reason for this was that the surface of the slurry was changed by the influence of ambient wind or the like after casting on the support. In the third comparative example, since the temperature difference between T2 and T3 was too small at 5 ℃ T2 to T3, and the slurry entering the casting die could not be sufficiently cooled, a high viscosity region could not be sufficiently generated in the slurry, similarly to the second comparative example, and it is considered that the reason for this was that the surface of the slurry was changed by the influence of ambient wind or the like after the slurry was cast on the support.

In the fourth and fifth comparative examples, T2-T3 were both 15 ℃ and, in addition, T1-T3 were 26 ℃ for the fifth comparative example, and the slurry entering the casting die was excessively cooled. Therefore, it is considered that the excessive generation of the high viscosity region in the slurry tends to generate unevenness on the surface of the slurry after the slurry is cast on the support, and the surface deformation of the slurry remains as surface deformation of the strip after drying, which causes the film thickness variation and the phase difference variation in the final film.

In the sixth comparative example, film formation was performed using TAC. In the case of using a high-viscosity resin such as TAC, it is preferable to keep the temperature as constant as possible during slurry transfer in order to suppress the generation of gel-like substances (see patent document 1), but in the sixth comparative example, since T2 to T3 are 20 ℃, the temperature greatly changes during transfer, and thus gel-like substances are generated, which is considered to be a cause of the generation of film thickness variation and phase difference variation.

In contrast, in the first to sixteenth embodiments, good results were obtained with respect to the film thickness variation and the phase difference variation. In the first to sixteenth embodiments, the following conditional expressions (1) to (3) are satisfied for T1, T2, and T3. That is to say that the first and second electrodes,

(1)T1＞T2＞T3，

(2)T1－T3≤25℃，

(3)5℃＜T2－T3＜15℃。

in this case, even when solution film formation is performed using a resin having a low SP value such as COP, since the high viscosity region and the low viscosity region can coexist in the slurry, the entire surface of the slurry can be leveled by moving the low viscosity region having high fluidity in the slurry while reducing the influence of local wind on the flow delay. This can reduce the occurrence of film thickness variation and phase difference variation.

In the first to fifteenth embodiments, the film thickness variation and the phase difference variation are further reduced as compared with the sixteenth embodiment. In the first to fifteenth embodiments, in order to satisfy the following conditional expression (4), that is,

(4)5℃＜Tmax－Tmin＜30℃，

since the slurry temperature is increased or decreased between the intermediate tank and the casting die, the low viscosity region and the high viscosity region are mixed in a balanced manner in the slurry, and it is considered that the leveling effect of the low viscosity region on the surface of the slurry (strip) can be improved.

Among them, in the ninth to eleventh embodiments, the effects of reducing the film thickness deviation and the phase difference deviation are the highest. In the ninth to eleventh embodiments, in the film formation from a solution using a cycloolefin resin, by further satisfying the following conditional formula (4a),

(4a)10℃≤Tmax－Tmin≤15℃，

it is believed that the low viscosity region further enhances the leveling effect on the surface of the belt.

[ others ]

The method for producing an optical film according to the present embodiment described above can be expressed as follows.

1. A method for producing an optical film by a solution casting film-forming method, comprising:

a slurry transfer step of adjusting the SP value as a solubility parameter to 10.5(MPa)^1/2Dissolving the following resin in a solvent in a dissolving kettle to prepare slurry, and transferring the slurry to a casting die through an intermediate kettle;

a casting step of casting the slurry from the casting die onto a support;

in the slurry transfer step, the following conditional expressions (1) to (3) are satisfied:

(1)T1＞T2＞T3，

(2)T1－T3≤25℃，

(3)5℃＜T2－T3＜15℃，

wherein the content of the first and second substances,

t1: the temperature (° c) of the slurry just after leaving the dissolution tank,

t2: the temperature (° c) of the slurry just after exiting the intermediate tank,

t3: the temperature (DEG C) of the slurry immediately before entering the casting die.

2. The method for producing an optical film according to claim 1, wherein the slurry transfer step further satisfies the following conditional expression (4):

(4)5℃＜Tmax－Tmin＜30℃

wherein the content of the first and second substances,

tmax: maximum temperature (DEG C) of the slurry between the intermediate pot and the casting die

Tmin: a minimum temperature (DEG C) of the slurry between the intermediate tank and the casting die.

3. The method for producing an optical film according to the above 2, wherein the resin is a cycloolefin resin,

in the slurry transfer step, the following conditional expression (4a) is further satisfied:

(4a)10℃≤Tmax－Tmin≤15℃。

the embodiments of the present invention have been described above, but the scope of the present invention is not limited to the above, and the present invention may be implemented as expanded or modified within the scope not departing from the gist of the present invention.

Industrial applicability

The method for producing an optical film of the present invention can be applied to the case of producing an optical film by a solution casting film-forming method using a resin having a low SP value.

Description of the reference numerals

2, casting a mould; 3a support; 21, a dissolving kettle; 22 intermediate kettle; and F, an optical film.