TW201730278A - Production method of optical film which is to cast the dope of material solution of the optical film on the support body in the solution casting film-making method and to form a blank sheet (a casted film) on the support body - Google Patents

Abstract

The present invention relates to a production method of optical film, which is a method that casts the dope of material solution of the optical film on a support body in the solution casting film-making method, forms a blank sheet (a casted film) on the support body, peels off the blank sheet from the aforementioned support body to produce the optical film. The method is characterized in that when the aforementioned dope is casted from the casting mold nozzle to the support body, the casting-draw ratio represented by the following formula 1 is 3~6. Formula (1): the casting draw ratio = the speed of the support body/effluent flowing rate.

Description

Optical film manufacturing method

The present invention relates to a method of producing an optical film used in a liquid crystal display device or the like.

Various optical films (for example, transparent protective films for protecting polarizing elements of the polarizing plates) are disposed in the image display area of the liquid crystal display device.

As such an optical film, for example, a resin film excellent in transparency of a cellulose ester film is used. Such an optical film is often produced as a long resin film by, for example, a solution casting (film formation) method.

The solution casting method is specifically a resin solution (dope) in which a transparent resin of a raw material resin is dissolved in a solvent, and is cast on a support which is being carried out, and dried to a peelable degree. The sheet (also referred to as a concentrated liquid film or a cast film) is peeled off from the support, and the peeled green sheet is conveyed by a conveyance roller, and dried or stretched, and the like is used as a method of growing a strip-shaped resin film.

Further, these optical films have recently increased the demand for films due to the thinning of liquid crystal display devices. If the film is thinned, the film properties are lowered. In the above solution casting method, the risk of cracking and cracking due to the jig for stretching in the conveyance, particularly the stretching step, also increases.

On the other hand, the optical properties required for the film are fixed regardless of the film thickness. However, since the optical properties are not easily exhibited as the film thickness becomes thin, it is necessary to further increase the elongation in order to achieve the goal. Therefore, the risk of film breakage in the stretching step is further increased, so the current situation requires improvement.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing a high-quality film without causing breakage in an extension step of a solution casting method or the like.

The inventors of the present invention have found that by adjusting the casting draw ratio to be large, the alignment of the stretched resin is promoted in the initial stage, and as a result, the elongation required in the stretching step can be lowered.

However, as a technique similar to the prior art, a technique for improving the planarity of a film by adjusting the casting draw ratio (support speed/discharge flow rate) in the solution casting method to 1 to 3 has been reported (Patent Document 1) ). Further, a technique for suppressing the horizontal section failure by adjusting the ratio of the tenter speed/the moving speed of the cooling drum is also reported (Patent Document 2).

However, the technical object described in the above Patent Document 1 is not based on a film, but is further considered to be a technique for improving the planarity, and is not based on the viewpoint of promoting alignment. Further, the technical object described in Patent Document 2 is also a technique for improving the film thickness at the time of peeling to prevent breakage, and is not intended to promote the resin alignment at an initial stage and to reduce the stretching ratio of the subsequent stretching step.

[Previous Technical Literature] [Patent Document]

[Patent Document 1] Japanese Patent No. 3674284

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2008-119866

As a result of the positive review by the inventors of the present invention, it has been found that the above problems can be solved by the method for producing an optical film having the following constitution, and the present invention is further reviewed based on the above findings.

In the method for producing an optical film according to the present invention, in a solution casting film forming method, a dope of a raw material solution of an optical film is cast on a support, and a green sheet is formed on the support (cast film) A method for producing an optical film by peeling a green sheet from the support, characterized in that the casting ratio shown by the following formula (1) when the dope is cast from the casting die to the support is 3~ 6.

Formula (1) Cast draw ratio = support speed / discharge flow rate.

According to the present invention, high-quality thin film optical films can be produced without causing breakage in the manufacturing steps.

1‧‧‧Solution kettle

2‧‧‧ pump

3‧‧‧casting nozzle

4‧‧‧Decompression chamber

5‧‧‧ Rolling drum before and after

6‧‧‧Rolling ring belt (support)

8‧‧‧ peeling roller

9‧‧ ‧ Blanks

10‧‧‧ tenter

11‧‧‧Rolling conveyor drying device

12‧‧‧Warm wind (dry wind)

13‧‧‧Winding machine

F‧‧‧film

Figure 1 is an optical thin showing the solution casting method using an endless belt support. A schematic view of the basic configuration of a film manufacturing apparatus.

Figure 2 is a schematic view showing the non-casting range on the support.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited thereto.

[Method of Manufacturing Optical Film]

Fig. 1 is an explanatory view showing a schematic configuration of an apparatus for manufacturing an optical film used in the embodiment. The method for producing an optical film according to the present embodiment is a solution casting method in which a dope containing a polymer and a solvent is cast from a casting die to a supporting member which is traveling, and then peeled off as a film.

Further, each symbol in the drawing is expressed as follows. 1: Dissolving kettle, 2: pump, 3: casting die, 4: decompression chamber, 5: front and rear winding drum, 6: casting endless belt (support), 7: non-casting range, 8 : peeling roll, 9: blank, 10: tenter, 11: roll conveying and drying device, 12: warm air (dry wind), 13: coiler, F: film.

An outline of the solution casting method will be described using FIG. First, in the dissolution vessel 1, a resin such as cellulose ester is dissolved in a mixed solvent of a good solvent and a weak solvent, and an additive such as a plasticizer or an ultraviolet absorber is added thereto to prepare a resin solution (dope). Further, good solvents and weak solvents will be described later.

Next, the concentrated liquid prepared in the dissolution tank 1 is passed through the pressurized type quantitative gear pump 2, and the liquid is fed to the casting die 3 through the conduit, and is moved by infinity. The casting position on the support body 6 by rotating the stainless steel endless belt is fed, and the dope is cast from the casting die 3, whereby the green sheet 9 as a casting film is formed on the support 6. At this time, in the casting die 3, a decompression chamber (decompression chamber) 4 may be disposed on the upstream side in the moving direction of the supporting body 6 during traveling, and the casting die 3 may be formed by the decompression chamber 4. On the upstream side (especially from the upstream side of the casting die 3 to the upstream side of the casting rib of the support 6), the dope is cast from the casting die 3 to the support body 6.

a method of using a squeegee method in which a thickness of a green sheet of a casting die is adjusted by a squeegee, and a reverse roll coater for adjusting a thickness of a cast film by a counter-rotating roller, A method of using a pressurized die, or the like. Among them, the method of using a pressurizing die is preferable because the shape of the slit of the metal lid portion can be adjusted, and the film thickness is uniform. The pressurizing die mouth has a hanger type die mouth or a T die mouth, and the like, and any of them can be preferably used.

The support body 6 is held by a pair of front and rear rollers 5, 5 and a plurality of intermediate rollers (not shown). A driving device (not shown) for applying tension to the support body 6 is provided in one or both of the rollers 5, 5, whereby the support body 6 is used in a state of being stretched by applying tension.

Preferably, the width of the support body 6 is 1000 to 3000 mm, and the width of the film after winding is 1000 to 2500 mm. Thereby, an optical film for a liquid crystal display device having a wide width can be manufactured by a metal support.

When the annular strip is used as the support 6, the strip temperature is in the range of 0 ° C to the boiling point of the solvent in the general temperature range, but it is preferably the temperature of the boiling point of the solvent which does not reach the lowest boiling point in the mixed solvent. Further preferably, it is in the range of 5 ° C to the boiling point of the solvent - 5 ° C. At this point, it is necessary to surround The ambient humidity is controlled above the dew point. Further, the moving speed of the support 6 at the time of production conditions is preferably from 80 m/min to 200 m/min.

The dope thus spread on the support 6 can also increase the strength (film strength) of the gel film by promoting drying before stripping.

On the support 6, the green sheet 9 is dried and solidified until the film strength which can be peeled off from the support 6 by the peeling roller 8 is obtained.

The temperature of the green sheet when the green sheet 9 is peeled off from the support 6 is preferably from 0 to 30 °C. Further, since the green sheet 9 is peeled off from the support 6, the temperature is temporarily lowered rapidly due to evaporation of the solvent from the side of the support surface of the support 6, and it is easy to condense volatile components such as water vapor or solvent vapor in the environment. The temperature of the green sheet at the time of peeling is preferably 5 to 30 °C.

The green sheet 9 formed by the dope cast on the support 6 is heated on the support 6 to evaporate the solvent so that the green sheet can be peeled off from the support 6 by the peeling roller 8.

When the solvent is evaporated, there is a method of blowing air from the side of the green sheet, a method of transferring heat from the back surface of the support 6 by liquid, a method of transferring heat from the front side by radiant heat, or the like, and may be used singly or in combination.

The peeling tension when the support body 6 and the green sheet 9 are peeled off by the peeling roller 8 is larger than the peeling force measured by the peeling force as in JIS Z 0237, because the peeling tension is compared with JIS at the time of high speed film formation. When the peeling force obtained by the measurement method is equal, the peeling position proceeds to the downstream side, and therefore, it is performed to be stable in order to stabilize. Further, it has been confirmed that even if the film is formed at the same peeling tension in the step, if the peeling force is lowered by the JIS measuring method, the variation in the cross-sectional nibble transmittance (CNT) of the film is greatly reduced. low.

The peeling tension value in the step is usually 20 to 400 N/m. However, the optical film produced by thinning is more likely to be stretched in the conveying direction due to the large amount of residual solvent in the film 9 at the time of peeling, so the width direction is The film is easily contracted, and if the drying and shrinkage overlap, the end portion is curled and folded, and wrinkles are easily generated. Therefore, the peeling tension is preferably a minimum tension of peelable ~300 N/m, more preferably a minimum tension of ~200 N/m.

In addition, although the belt-shaped support body is illustrated as a support body in FIG. 1, the support body of this embodiment is not limited to a belt shape, For example, the roll-shaped support body can also be used.

After the green sheet 9 is dried and solidified on the support 6 to a peelable film strength, the green sheet 9 is peeled off by the peeling roller 8, and then the green sheet 9 is stretched by the tenter 10 in the extending step.

In the stretching step, as a film for a liquid crystal display device, it is preferable to use a tenter method in which both side edges of the green sheet 9 are fixed and extended by a jig or the like to improve the planarity or dimensional stability of the film.

The amount of residual solvent of the green sheet 9 before entering the tenter 10 in the stretching step is preferably from 5 to 50% by mass, more preferably from 10 to 35% by mass. The elongation of the green sheet in the tenter 10 of the extending step is 3 to 100%, preferably 5 to 80%, and more preferably 5 to 60%.

Further, the temperature of the tenter 10 which is blown by the warm air and blown out from the slit mouth is desirably 70 to 200 ° C, preferably 110 to 190 ° C, and more preferably 115 to 185 ° C.

After extending the tenter 10 of the step, it is better to set the drying device 11. In the drying device 11, the green sheet 9 is serpented by a plurality of conveying rollers arranged in a zigzag shape from the side, and the green sheet 9 is dried therebetween. Further, the film transport tension of the drying device 11 is affected by the physical properties of the liquid, the amount of residual solvent during the peeling and the film transporting step, the drying temperature, etc., but the film transport tension during drying is 10 to 400 N/m, preferably 20~. 300N/m.

Further, the means for drying the green sheet 9 is not particularly limited, and is generally carried out by hot air, infrared rays, heating rolls, microwaves or the like. From the viewpoint of simplicity, it is preferred to dry with hot air. For example, the dry air 12 is blown from the warm air inlet of the drying device 11, and the exhaust air is discharged from the outlet of the drying device 11 to dry the green sheet 9, thereby forming the optical film F. The temperature of the dry wind 12 is preferably from 40 to 160 ° C, and is preferably from 50 to 160 ° C because of good planarity and dimensional stability.

These steps from self-casting to transport drying can be carried out in an air atmosphere or in an inert gas atmosphere such as nitrogen. In this case, of course, the drying environment is carried out in consideration of the explosive limit concentration of the solvent.

It is preferable that the optical film F which has finished the transport drying step has a majority in the end portion of the optical film F in order to prevent roll-off or adhesion of the winding step (attachment of the films to each other) before introduction to the winding step. The embossed portion of the bump.

Next, the film which has finished the formation of the embossed portion is taken up by the winding device 13, and a green roll of the optical film F is obtained. When the amount of the residual solvent of the film at the end of the drying is 0.5% by mass or less, preferably 0.1% by mass or less, a film having good dimensional stability can be obtained.

The winding method of the film may be a winding machine that is generally used, and a method of controlling the tension such as a fixed moment method, a fixed tension method, a gradual tension method, or a program tension control method in which internal stress is fixed, and the case may be used as the case may be. can. The joining of the film to the take-up core (core) may be by double-sided tape or by one of the single-sided tapes. The film width of the optical film F after winding is preferably from 1000 to 2500 mm.

Hereinafter, the features of the manufacturing method of the present embodiment will be described in more detail.

In the method for producing an optical film according to the present embodiment, in the solution casting film forming method described above, a dope of a raw material solution of an optical film is cast on a support, and a green sheet (cast film) is formed on the support. The method for producing an optical film by peeling the green sheet from the support, one of the great features is that the casting solution has a casting stretch ratio of 3 in the following formula (1) when the dope is cast from the casting die to the support. ~6.

Formula (1) Cast draw ratio = support speed / discharge flow rate.

According to these configurations, it is considered that the high-quality thin film optical film can be stably obtained without any trouble of breakage or unevenness in display at the time of production.

As a result of active investigation by the inventors of the present invention, it is considered that, in particular, when the film is formed into a film, by setting the stretching ratio in a specific range as described above, it is possible to increase the billet by aligning the green sheet immediately after stretching in the conveying direction. Sheet properties and film quality. Therefore, it is considered that in the production of the film, the stretching ratio of the stretching step can be lowered, the film breakage in the stretching step or the like can be prevented, and the optical properties of the film can be achieved.

In the present embodiment, the dope is a resin solution of a film raw material, and after being cast on a support, it is gelled and has a hardness as a film, and is called a green sheet (cast film). That is, the film in the drying process before the completed optical film is referred to as a green sheet. However, the boundary between the dome film formed by the dope and the green sheet and the film is not strictly defined in advance. Further, as described above, the casting stretch ratio is a ratio of the support body speed to the discharge flow rate, that is, (support speed/discharge flow rate), but the discharge flow rate is passed through the die slit (hereinafter referred to as a die slit). The speed of the concentrated liquid inside, the speed at which the support body speed travels in a ring shape.

Further, in the present embodiment, immediately after the stretching, the green sheet is discharged from the nozzle, and by adjusting the casting ratio as described above, it is considered that the sheet can be stretched and extended before being in contact with the support.

The casting casting ratio is preferably in the range of 3 to 5. Thereby, it is considered that the above effects can be obtained more surely.

In a preferred embodiment, when the dope is cast on the support, it is desirable to further carry out molecular alignment by cooling the green sheet.

As means for cooling the green sheet on the support, for example, a cooling device may be used, but the support may be made in a state in which the concentrated liquid is cast on the support so as to be continuous with respect to the entire length of the support 1 The ratio of the non-casting range of the green sheet (cast film) is 3 to 50%, and the casting start position and the green sheet peeling position are adjusted.

More specifically, FIG. 2 shows an outline of the steps of enlarging the solution from the dope to the exfoliation blank 9 and transporting it to the tenter 10. The portion indicated by 7 in the figure indicates a non-casting range, and the non-casting region 7 is as described above. Within the range, the green sheets can be aligned before the stretching step, whereby the stretching ratio which should be achieved in the stretching step can be suppressed. Further, it is considered that the risk of film breakage can be further reduced.

More preferably, the aforementioned non-casting range is expected to be 30 to 45%.

The non-casting range in the present embodiment can be controlled, for example, by adjusting the position of the casting die 3.

The film thickness (final film thickness) after drying of the optical film of the present embodiment is preferably in the range of 5 to 40 μm as a finished film, from the viewpoint of thinning of the liquid crystal display device. Here, the film thickness after drying refers to a film in a state in which the amount of residual solvent in the film is 0.5% by mass or less.

According to the production method of the present embodiment, the above-described effects can be further exhibited in the production of the film, and a high-quality optical film can be provided.

In the method for producing an optical film by the solution casting film forming method of the present embodiment, the resin solution (dope) which is a resin containing a cellulose ester or the like as a main material preferably contains a plasticizer, a retardation adjuster, and an ultraviolet ray. At least one or more of an absorbent, a fine particle (atomizing agent), and a low molecular weight substance, and a solvent. The materials are described below.

In the present embodiment, the resin used as the film material is not particularly limited, and a resin used in a general solution casting method can be used. The resin material for producing an optical film is exemplified by, for example, good adhesion to a polarizer, optical transparency, and the like. It can be said that the transmittance of visible light is 60% or more, preferably 80% or more, and particularly preferably 90% or more.

The resin which can form an optical film having the above properties can be used without particular limitation, and can be exemplified by, for example, a cellulose diacetate tree. a cellulose ester resin such as a fat, a cellulose triacetate resin, a cellulose acetate butyrate resin or a cellulose acetate propionate resin; a polyester resin, a polycarbonate resin, and a polyaryl Polyester resin such as ester resin, polyfluorene (including polyether oxime) resin, polyethylene terephthalate resin or polyethylene naphthalate resin; polyethylene resin, polypropylene resin, celluloid Fen, polyvinylidene chloride resin, polyvinyl alcohol resin, ethylene-vinyl alcohol resin, syndiotactic polystyrene resin, polycarbonate resin, cycloolefin resin, polymethylpentene resin, polyether ketone resin, poly An ether ketone oxime imide resin, a polyamide resin, a fluororesin, a nylon resin, a polymethyl methacrylate resin, an acrylic resin, or the like. Among them, a cellulose ester resin, a cycloolefin resin, a polycarbonate resin, and a polyfluorene (including a polyether oxime) resin are preferable. In the present invention, in particular, a cellulose ester resin is based on a production cost and a cost. From the viewpoints of transparency, adhesion, and the like, it can be preferably used.

The cellulose ester is a cellulose ester in which a hydroxyl group derived from cellulose is substituted with a mercapto group. For example, cellulose acetate, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate propionate butyrate, etc. Or cellulose acetate having an aliphatic polyester grafted side chain or the like. Among them, cellulose triacetate, cellulose acetate propionate, and cellulose acetate having an aliphatic polyester graft side chain are preferred. The cellulose esters used in the process of the invention may also contain other substituents.

As an example of the cellulose triacetate, the degree of substitution of the ethyl ketone group is preferably 2.0 or more and 3.0 or less. By setting the degree of substitution to this range, good formability can be obtained, and a desired in-plane retardation (Ro) and thickness direction retardation (Rt) can be obtained. When the degree of substitution of the thiol group is lower than the range, there is a phase The heat resistance of the poor film, especially in the case of poor dimensional stability under moist heat, may not exhibit the necessary retardation characteristics when the degree of substitution is too large.

The cellulose which is a raw material of the cellulose ester used in the present embodiment is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Further, the cellulose esters obtained by the above may be used in combination at any ratio.

When the number average molecular weight of the cellulose ester is in the range of 20,000 to 300,000, the mechanical strength of the obtained film is strong and preferable. Further preferably, it is 40,000 to 200,000. Various additives can be formulated in the cellulose ester.

Further, the dope used in the present embodiment may contain fine particles as an atomizing agent in addition to the cellulose ester-based resin described above.

In this case, the fine particles used are appropriately selected depending on the purpose of use, but are preferably fine particles which can be scattered by visible light by being contained in a transparent resin. The fine particles may be inorganic fine particles such as cerium oxide or organic fine particles such as acrylic resin.

Further, when the fine particles represented by cerium oxide are surface-treated with an organic substance, it is preferable from the viewpoint of reducing the haze of the produced optical film. Preferred organic substances in the surface treatment are exemplified by, for example, halodecanes, alkoxydecanes, decazanes, decanes, and the like. The larger the average particle diameter of the fine particles, the larger the atomization effect, and the smaller the average particle diameter, the more excellent the transparency. Therefore, the average particle diameter of the primary particles of the preferred fine particles is from 5 nm to 50 nm, more preferably from 7 nm to 14 nm.

As the fine particles of cerium oxide, for example, AEROSIL AEROSIL 200, 200V, 300, R972, R972V, R974, R202, R812, OX50, TT600, etc., preferably AEROSIL 200, 200V, R972, R972V, R974, R202, R812, and the like.

The solvent used in the present embodiment may contain a solvent which is a good solvent for the transparent resin, and may contain a weak solvent insofar as the transparent resin is not precipitated. The good solvent for the cellulose ester-based resin is, for example, an organic halogen compound such as dichloromethane. Further, examples of the weak solvent of the cellulose ester-based resin include alcohols having 1 to 8 carbon atoms such as methanol.

The dope used in the present embodiment may contain other components (additives) other than the transparent resin, the fine particles, and the solvent, within a range not inhibiting the effects of the present invention. Examples of the additives include, for example, a plasticizer, an antioxidant, an ultraviolet absorber, a heat stabilizer, a conductive material, a flame retardant, a slip agent, and an atomizing agent.

The plasticizer which can be used in the embodiment is not particularly limited, but a phosphate ester plasticizer, a phthalate plasticizer, a trimellitate plasticizer, and pyromellitic acid can be preferably used. It is a plasticizer, a glycolate plasticizer, a citric acid ester plasticizer, a polyester plasticizer, and the like.

As the phosphate ester, for example, triphenyl phosphate, tricresyl phosphate, tolyldiphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, and tributyl phosphate can be preferably used. Ester, etc., as a phthalate type, for example, diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, orthophthalic acid can be preferably used. Dioctyl acid ester, dibutyl phthalate, di-2-ethylhexyl phthalate, benzyl phthalate, etc., can be preferably used as a trimellitic acid plasticizer, for example. Tributyl trimellitate, triphenyl trimellitate, triethyl trimellitate, etc., as a pyromellitic ester plasticizer, preferably used, for example, tetrabutyl pyromelliate, Tetraphenyl pyromelliate, tetraethyl pyromelliate, etc., as a glycolate plasticizer, for example, triacetin, tributyrin, ethyl acetophenate Ester, methyl phthalic acid ethyl methacrylate, butyl phthalic acid butyl phthalate, etc., as a citric acid ester plasticizer, for example, triethyl citrate and citric acid can be preferably used. Butyl ester, ethoxylated triethyl citrate, ethionyl tri-n-butyl citrate, acetyl citrate tri-n-(2-ethylhexyl ester) and the like.

Further, as the polyester-based plasticizer, for example, a copolymerized polymer of a dibasic acid such as an aliphatic dibasic acid, an alicyclic dibasic acid or an aromatic dibasic acid and a diol can be used as the aliphatic dibasic acid. It is not particularly limited, and for example, adipic acid, sebacic acid, phthalic acid, terephthalic acid, 1,4-cyclohexyl dicarboxylic acid or the like can be used.

Further, as the diol, for example, ethylene glycol, diethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,4-butanediol, 1,3-butanediol, 1,2-butyl can be used. Glycol and the like. These dibasic acids and diols may be used singly or in combination of two or more. When the molecular weight of the polyester is in the range of from 500 to 2,000 by weight average molecular weight, it is preferred from the viewpoint of compatibility with the cellulose resin.

Further, the cellulose ester film of the present embodiment is protected In the liquid crystal material or the like, an ultraviolet absorber is preferably used, and as the ultraviolet absorber, it is preferable to use an ultraviolet absorbing energy having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of the liquid crystal, and it is preferable to use a wavelength of 400 nm from the viewpoint of good liquid crystal display properties. The above absorption of visible light is as small as possible.

In the cellulose ester film having a thickness of from 20 μm to 200 μm, the transmittance of the wavelength of 370 nm is 10% or less, and the durability of the polarizing plate is not deteriorated, so that a preferable polarizing plate can be provided. The transmittance at a wavelength of 370 nm is more preferably 5% or less, and particularly preferably 2% or less.

Further, a solution of the cellulose ester resin was obtained by mixing the above respective components. Further, the solution of the obtained cellulose ester-based resin is preferably filtered using a suitable filter material such as filter paper.

The optical film produced by the manufacturing method of the present embodiment is used for various displays such as liquid crystal displays, plasma displays, and organic EL displays, and particularly, functional films for liquid crystal displays, including a polarizing plate protective film, a retardation film, and an antireflection film. An optical compensation film such as a brightness enhancement film or an enlarged viewing angle.

By using the protective film for a polarizing plate made of the optical film of the present embodiment, it is possible to provide a polarizing plate which is thinned and excellent in durability, dimensional stability, and optical isotropic properties.

Further, by using the polarizing plate having the optical film of the embodiment, a liquid crystal display device of high image quality or the like can be realized. In particular, since the optical film of the present embodiment is a film, it can be preferably used for applications such as smart phones and tablet computers.

Although the present specification discloses various techniques as described above, the main techniques are summarized as follows.

In the method for producing an optical film according to the present invention, in the solution casting film forming method, a dope of a raw material solution of an optical film is cast on a support, and a green sheet (cast film) is formed on the support. The method for producing an optical film by peeling the green sheet from the support is characterized in that the casting ratio of the following formula (1) when the dope is cast from the casting die to the support is 3 to 6.

Formula (1) Cast draw ratio = support speed / discharge flow rate.

According to this configuration, it is possible to promote the alignment by stretching the green sheet immediately after the casting, and it is considered that the occurrence of breakage or unevenness in the stretching step at the time of production is not caused, and the production can be efficiently and stably performed. Quality thin film optical film.

Further, in the above production method, the final film thickness of the obtained optical film is preferably 5 to 40 μm. The production method of the present invention can further exert effects in the production of such films.

Further, in the above production method, it is preferred that the dope is cast on the support so that the non-casting of the green sheet (cast film) does not exist on the support body with respect to the entire length of the support body 1 The ratio of the range is 3 to 50%, and the starting position of the casting and the peeling position of the green sheet are adjusted. Thereby, the green sheet can be further aligned before the stretching step as compared with the conventional method, and accordingly, the stretching ratio which should be achieved in the stretching step can be suppressed. Further, it is considered that the risk of film breakage can be further reduced.

In addition, it is preferable to adjust the casting start position and the green sheet peeling position so that the ratio of the non-casting range of the entire length of the support body is 30 to 45%, and it is considered that the above effect can be obtained more reliably. .

[Examples]

The invention is more specifically illustrated by the following examples, but the invention is not limited by the examples.

[Example 1]

An optical film was produced by the method shown below.

(modulation of dope)

Put the material of the above dope composition 1 into a closed container, while heating and stirring Mix well and dissolve completely and filter. The filtration was filtered through a pressure filter and passed through a metal sintered filter (capture particle size = 10 μm). Further, the cerium oxide microparticles (AEROSIL 972V) were added after being dispersed in ethanol.

(Manufacture of optical film)

A cellulose acetate propionate film was produced by the solution casting film forming apparatus shown in Fig. 1. Further, the support (6) for casting a dope was made of SUS316 and polished to a super-mirror ring having a three-dimensional surface roughness (Ra) of 1.0 nm observed by a scanning atomic force microscope (AFM). Belt.

The filtered dope is preferably at a temperature of 35 ° C at a dope temperature, and the casting die (3) formed by the coat hanger of the SUS316 ring-shaped belt support (6) at a temperature of 20 ° C is uniformly extended. The distance between the support and the tip end of the die was set to 1 mm. When the green sheet (9) is formed on the support (6), the green sheet (9) is formed to adhere to the support body (6) so as to be formed as a means for decompressing from the upstream side of the casting. Decompression chamber (4) (average pressure of decompression chamber - 400 Pa).

Further, in Example 1, the discharge flow rate from the nozzle was 23 m/min, the support speed was 80 m/min, and the casting draw ratio was 3.5. Furthermore, the ratio of the non-casting range is 2%.

In this manner, the green sheet (9) formed on the support body (6) is conveyed on the support body (6), dried by a fixed dry air at a temperature of 25 ° C, and then self-supported by a peeling roller (8). The body (6) is peeled off, and then, in a tenter (10), at a residual solvent amount of 10% in an environment of 100 ° C After extending 1.28 times (28%) in the width direction, the release width was maintained, and the drying was carried out at 125 ° C while the roll was being conveyed, and the winding was carried out by the winding device (13).

The resulting cellulose triacetate propionate film (F) had a final film thickness of 20 μm, a film width of 1300 mm, and a film winding length of 4000 m.

[Examples 2 to 5 and Comparative Examples 1 to 3]

Cellulose acetate propionate was obtained in the same manner as in Example 1 except that the discharge flow rate, the support speed, the casting stretch ratio, the non-casting range, the stretching ratio, and the final film thickness were adjusted as shown in Table 2. Moreover, the adjustment of the non-casting range is performed by changing the position of the nozzle.

(Evaluation)

The following evaluation tests were carried out on the optical films (Examples 1 to 5 and Comparative Examples 1 to 3) obtained as described above.

[step suitability]

For the steps, evaluate on the following basis:

○: The film can be produced without problems and can be wound up by a winding machine

×: cracked and ruptured when stretched

[display unevenness]

The prepared film sample is sandwiched between a polarizing plate set to a crossed nibble state and Between the polarizing plates, the crossed ridges are shifted from the transmitted light to the state where the light passes, and the gradation of the transmitted light is visually observed.

Further, as the polarizing plate, a polarizing plate produced as follows was used.

(production of polarizing film)

In order to produce a liquid crystal display device using the cellulose ester film produced in the above Examples and Comparative Examples, a polarizing film was first produced. That is, a polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched at a temperature of 110 ° C and a stretching ratio of 5 times. This was immersed in an aqueous solution of 0.075 g of iodine, 5 g of potassium iodide, and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C made of 6 g of potassium iodide, 7.5 g of boric acid, and 100 g of water. It was washed with water and dried to obtain a polarizing film.

(production of polarizing plate)

Next, according to the following steps 1 to 5, a KCICA MINOLTA KC4UY 40 μm cellulose triacetate film (polarizing plate protective film: T-1) and cellulose B produced in each example were bonded to the polarizing film. A polarizing plate was produced by using an acid ester propionate film (phase difference film: T-2).

Step 1: It was immersed in a 2 mol/L sodium hydroxide solution at 60 ° C for 90 seconds, followed by washing with water and drying to obtain a polarizing plate protective film and a retardation film which were saponified to the side to which the polarizing film was bonded.

Step 2: The polarizing film was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by mass for 1 second to 2 seconds.

Step 3: Excessive adhesion to the polarizing film in step 2 The agent is lightly wiped off, and the polarizing plate protective film and the retardation film processed in the step 1 are laminated on both sides of the polarizing film.

Step 4: The phase difference film, the polarizing film, and the back side polarizing plate protective film laminated in the step 3 were bonded at a pressure of 20 N/cm ² to 30 N/cm ² and a conveying speed of about 2 m/min.

Step 5: The sample obtained by bonding the polarizing film and the retardation film and the polarizing plate protective film prepared in the step 4 was dried in a dryer at 80 ° C for 5 minutes to prepare a polarizing plate.

A sample in which unevenness could not be confirmed was evaluated by a polarizing plate, and was confirmed by panel evaluation prepared as follows.

The polarizing plate on the viewing side of the pre-bonded side of the SONY 40-type display KLV-40J3000 of the VA mode liquid crystal display device is peeled off, and the polarizing plate produced above is bonded to the liquid crystal cell so that the absorption axes of the polarizing plates are aligned. A VA mode liquid crystal display device was fabricated on the glass surface. At this time, the retardation film T-2 is bonded so as to become the liquid crystal cell side. The evaluation criteria for unevenness are as follows.

◎: No unevenness was observed even by panel evaluation

○: No lightness through the light

△: I saw a little light through the light.

×: See the lightness of the light

The results are shown in Table 1.

[discussion]

As is understood from Table 1, in Examples 1 to 5 obtained by the production method of the present invention, since the phase difference can be obtained even if the stretching ratio is lowered, the step suitability is satisfied without the breakage or the like in the manufacturing step. Moreover, the optical films obtained in the examples have no display unevenness and are of high quality.

In particular, in Example 4, in which the proportion of the non-casting range was relatively large, a film of a very high quality was obtained. On the other hand, in Example 1, in which the ratio of the non-casting range was relatively small, or Example 5 in which the final film thickness was increased, the result of unevenness was slightly inferior.

With respect to Comparative Example 1 in which the casting stretch ratio did not satisfy the range of the present invention, a phase difference was obtained by increasing the stretching ratio, but the result was fracture when extended. When the casting stretch ratio was the same as in Comparative Example 1 and the stretching ratio was lowered (Comparative Example 2), a sufficient phase difference could not be obtained and display unevenness occurred. Further, in Comparative Example 3 in which the casting draw ratio was larger than the range of the present invention, it was judged that the flow delay caused the rib film to adhere to the impression mark.

This application is filed on December 14, 2015 in Japan. Patent Application No. 2015-242968 is hereby incorporated by reference.

In order to demonstrate the present invention, the present invention will be described in detail with reference to the drawings, and the embodiments of the present invention will be described in detail. Therefore, the modified form or the modified form of the present invention should be construed as being included in the scope of the claims as long as it does not depart from the scope of the claims.

[Industrial Applicability]

The present invention has wide industrial applicability in the technical field of optical films.

1‧‧‧Solution kettle

2‧‧‧ pump

3‧‧‧casting nozzle

4‧‧‧Decompression chamber

5‧‧‧ Rolling drum before and after

6‧‧‧Rolling ring belt (support)

8‧‧‧ peeling roller

9‧‧ ‧ Blanks

10‧‧‧ tenter

11‧‧‧Rolling conveyor drying device

12‧‧‧Warm wind (dry wind)

13‧‧‧Winding machine

F‧‧‧film

Claims (4)

A method for producing an optical film, which is a solution casting method in which a dope of a raw material solution of an optical film is cast on a support, and a green sheet (cast film) is formed on the support, from the foregoing A method for producing an optical film by peeling a green sheet from a support, characterized in that a casting ratio of the following formula (1) is 3 to 6 when the dope is cast from a casting die to a support. 1) Cast draw ratio = support speed / discharge flow rate. The method for producing an optical film according to claim 1, wherein the final film thickness of the obtained optical film is 5 to 40 μm. The method for producing an optical film according to claim 1 or 2, wherein in the state in which the dope is cast on the support, the green sheet (cast film) is not present on the support with respect to the entire length of the support 1 The ratio of the non-casting range is 3 to 50%, and the starting position of the casting and the peeling position of the green sheet are adjusted. The method for producing an optical film according to claim 3, wherein the casting start position and the green sheet peeling position are adjusted so that the ratio of the non-casting range is 30 to 45% with respect to the entire length of the support body 1 circumference. .