JP5163222B2 - Manufacturing method of optical film - Google Patents

Description

The present invention can be used for various functional films such as a protective film for a polarizing plate used for a liquid crystal display (LCD), a retardation film, a viewing angle widening film, and an antireflection film used for a plasma display. The present invention relates to a film manufacturing method .

  In recent years, liquid crystal display devices have come to be used in televisions and large monitors due to improvements in image quality and high definition technology. In particular, these liquid crystal display devices are costly due to their large size and efficient production. The demand for down and the like has become stronger in materials for liquid crystal display devices, and a wider optical film is required.

  In recent years, the demand for optical films has been increasing rapidly in response to the rapid growth of liquid crystal TVs, and there is a strong demand for improved productivity. For optical films produced by the solution casting method, the production rate can be increased because a thin film requires less solvent to be dried.

  Various optical films are used for liquid crystal displays and plasma displays. In the liquid crystal display, functional films such as a polarizing plate (film), a retardation film, and a viewing angle widening film are used, and these films are mainly produced by coating or bonding. Among them, the polarizing plate has a configuration in which a polarizing plate protective film made of cellulose ester is laminated on both sides of a polarizer made of polyvinyl alcohol film or the like in which iodine or dye is adsorbed and oriented.

  By the way, a polarizing plate can be produced by a general method. Alkali saponification treatment using a completely saponified polyvinyl alcohol aqueous solution on both sides of a polarizing film prepared by subjecting an optical film such as cellulose ester film to alkali saponification treatment and dipping and stretching the polyvinyl alcohol film in iodine solution A method of bonding a cellulose ester film is known.

  Here, the alkali saponification treatment refers to a treatment of immersing the cellulose ester film in a high-temperature strong alkaline solution in order to improve the wetness of the water-based adhesive and improve the adhesiveness. However, the process of saponifying with a strong alkali has problems such as maintenance, safety, and environment related to waste liquid.

  On the other hand, vacuum glow discharge treatment, flame treatment, and the like have been proposed as techniques that can promote the adhesion of the constituent layers to the substrate. However, flame treatment has many problems due to damage to the substrate, non-uniformity of the treatment surface due to fluctuation of the flame, difficulty in controlling the intensity of treatment, danger, and the like. The vacuum glow discharge treatment is not a preferable method in terms of productivity and cost because the facility itself to be treated is evacuated and thus the capacity is naturally limited.

Patent Documents 1 and 2 below disclose a film in which the surface of a protective film for polarizing plate that is in contact with a polarizer is hydrophilized by plasma treatment at normal pressure to improve adhesion.
JP 2000-356714 A JP 2002-82223 A

 However, in the methods described in Patent Documents 1 and 2 above, the film is indeed activated immediately after the treatment by the atmospheric pressure plasma treatment, and the adhesiveness is high. If it is stored in a humid place for a long time, the activation degree of the activated surface is reduced and it often returns to the surface state before the treatment, and the surface activation degree immediately after the treatment cannot be maintained. there were.

The object of the present invention is to solve the above-mentioned problems of the prior art, and with respect to a method for producing an optical film by a solution casting film forming method , it is possible to eliminate deterioration with time of the surface-modified layer and to have excellent adhesiveness. An object of the present invention is to provide a method for producing an optical film used for a protective film for a polarizing plate.

To achieve the above object, the invention of claim 1 is a method for producing an optical film that by the solution casting film forming method, cast resin solution (dope) on a casting support, While the cast film (web) moves on the support, the processing strength of 0.1 to 36 W / cm ² and the processing conditions of 0.001 to 0.6 seconds are applied to the surface of the web by the atmospheric pressure plasma apparatus. Or high-energy treatment by excimer UV irradiation with an excimer UV irradiation device under a light amount of 1 to 3000 mJ / cm ² and a treatment condition of 0.001 to 0.6 seconds. more, the surface energy is characterized that you produce an optical film which is 60~100mN / m.

The invention according to claim 2 is the method for producing an optical film according to claim 1, wherein the resin solution contains cellulose acylate .

The invention of claim 1 is a method of manufacturing an optical film that by the solution casting film forming method, a resin solution (dope) was cast onto a casting support, casting film (web) the support During the transition, the surface of the web is subjected to high energy treatment by plasma irradiation with a treatment pressure of 0.1 to 36 W / cm ² and a treatment condition of 0.001 to 0.6 seconds by a normal pressure plasma apparatus. or also by an excimer UV irradiation apparatus, the processing conditions of 1～3000MJ / amount of cm ² and 0.001 to 0.6 seconds, more applying high energy treatment by excimer UV irradiation, the surface energy 60~100mN / a is to said that you produce an optical film m, according to the first aspect of the invention, it is possible to modify the surface of the web during film formation, yet in a state of containing the solvent treatment To do Accordingly, since the active processing layer film from the formed is gradually solidified on the surface, it can be formed without degradation with time stable modified layer. As a secondary effect, in the method for producing an optical film of the present invention, since the radical-containing gas is blown onto the liquid film web, the surface of the casting film evaporates and hardens, and is blown by subsequent conveyance. There is no disturbance of the surface due to the applied dry wind, and the film has an excellent flatness.

Invention of Claim 2 is a manufacturing method of the optical film of Claim 1, Comprising: Cellulose acylate is contained in the resin solution, According to invention of Claim 2, it is contained in a film. When at least one of the resins is cellulose acylate, the ultraviolet absorbing ability and the infrared absorbing ability are maintained for a long time while keeping the transparency of the film, and the optical film has an effect of being excellent in durability .

  Next, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

Method for producing an optical film according to the present invention is a method for producing an optical film that by the solution casting film forming method, cast resin solution (dope) on a casting support, casting film (web) Is transferred to the support by a normal pressure plasma apparatus, and the high energy by plasma irradiation at a treatment strength of 0.1 to 36 W / cm ² and a treatment condition of 0.001 to 0.6 seconds. processing performed, or alternatively by an excimer UV irradiation apparatus, the processing conditions of 1～3000MJ / amount of cm ² and 0.001 to 0.6 seconds, more applying high energy treatment by excimer UV irradiation, the surface energy to produce an optical film which is 60~100mN / m is characterized in Rukoto.

  That is, in the method for producing an optical film according to the present invention, an atmospheric pressure plasma is formed in an arbitrary section while a cast film in which a dope is cast on a metal support is transported on the metal support, so-called on-line. The surface of the cast film is modified by applying high-energy surface treatment with an apparatus or an excimer UV apparatus.

The method for producing an optical film according to the present invention greatly improves the adhesion by performing such a high energy surface treatment on the cast film surface in an arbitrary section while being conveyed on the metal support . It was possible to eliminate deterioration over time.

  Furthermore, since the radical-containing gas is blown onto the liquid film, the surface of the cast film is solidified by evaporation of the solvent, and the surface is not disturbed by the dry air blown by the subsequent transport, and is excellent in flatness.

  About the high energy surface treatment by such an atmospheric pressure plasma apparatus and excimer UV apparatus, since the mechanism is not fully elucidated at present, it is speculated. A functional group containing oxygen is formed on the surface, and adhesion is improved. However, this functional group reverses over time and sinks into the base material, so that the adhesiveness returns to the same level as before the treatment.

However, as in the present invention, in any section while being transported on the metal support , high energy treatment is performed on the treatment surface by the resin containing the solvent, that is, in the soft liquid film state. Since the film hardens after the layers and functional groups are formed, the treatment layer is stabilized, adhesion is greatly improved compared to the case where the film is processed as in the past, and deterioration with time is further reduced. Can be considered.

As described above, according to the method for producing an optical film of the present invention, it is possible to provide a protective film for a polarizing plate having high processability, a polarizing plate using the same, and a liquid crystal display by eliminating the deterioration of adhesiveness over time. Is.

  Hereafter, the manufacturing method of the optical film by this invention is described in detail. The film can be produced by a solution casting method.

FIG. 1 is a flow sheet showing a specific example of an apparatus for carrying out the method for producing an optical film of the present invention by a solution casting film forming method. Note that the implementation of the present invention is not limited to the process of the drawings shown below.

  In the figure, first, in a dissolving pot (1), for example, a cellulose ester resin is dissolved in a mixed solvent of a good solvent and a poor solvent, and an additive such as a plasticizer or an ultraviolet absorber is added to the resin solution. (Dope) is prepared.

  Next, the dope adjusted in the melting pot (1) is fed to the casting die (3) by a conduit through, for example, a pressurized metering gear pump (2) and transferred infinitely, for example, from a rotationally driven stainless steel endless belt The dope is cast from the casting die (3) to the casting position on the metal support (6).

  Here, the metal support (6) for casting the dope is made of, for example, stainless steel (SUS316 or SUS304), and the surface has a three-dimensional surface roughness (Ra) measured by a scanning atomic force microscope (AFM). An endless belt (6) polished to a super mirror surface with an average of 1.0 nm is used.

  In order to cast the dope by the casting die (3), there is a doctor blade method in which the film thickness of the cast dope film (web) is adjusted with a blade, or a reverse roll coater method in which the film is adjusted with a reverse rotating roll. However, a pressure die that can adjust the slit shape of the die portion and can easily make the film thickness uniform is preferable. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used.

  In addition, as a casting die (3), the pressure die which can adjust the slit shape of a nozzle | cap | die part and is easy to make a film thickness uniform is preferable. The casting die (3) is usually provided with a decompression chamber (4).

  Here, it is preferable that the solid content concentration of the cellulose ester solution (dope) is 15 to 30% by weight. If the solid content concentration of the cellulose ester solution (dope) is less than 15% by weight, sufficient drying cannot be performed on the metal support (6), and a part of the dope film is on the metal support (6) during peeling. This leads to belt contamination and is not preferable. If the solid concentration exceeds 30% by weight, the dope viscosity increases, filter clogging is accelerated in the dope adjustment process, and pressure increases when cast onto the metal support (6), making it impossible to extrude. It is not preferable.

  In the illustrated film forming apparatus having a rotationally driven endless belt as the metal support (6), the belt metal support (6) includes a pair of front and rear winding drums (5) and (5) and a plurality of intermediate rolls. (Not shown).

  One or both of the winding drums (5) and (5) at both ends of the rotary drive endless belt metal support (6) are provided with a drive device for applying tension to the belt metal support (6). Thus, the belt metal support (7) is used in a tensioned state.

  The width of the metal support (6) is preferably 1700 to 2500 mm, the casting width of the cellulose ester solution is 1600 to 2400 mm, and the width of the film after winding is preferably 1400 to 2400 mm. Thereby, the wide optical film for liquid crystal display devices can be manufactured by a metal support body system.

  Moreover, it is preferable that the peripheral speed of a metal support body (6) is 40-200 m / min.

  When an endless belt is used as the metal support (6), the belt temperature during film formation is a general temperature range of 0 ° C. to a temperature lower than the boiling point of the solvent, and less than the boiling point of the solvent having the lowest boiling point in the mixed solvent. The range of 5 ° C. to (solvent boiling point−5 ° C.) is more preferable. At this time, it is necessary to control the ambient atmospheric humidity above the dew point.

  The dope cast on the surface of the metal support (6) as described above also increases the strength (film strength) of the gel film by promoting drying until stripping.

  In the system using an endless belt as the metal support (6), the film strength on which the web (9) can be peeled from the metal support (6) by the peeling roll (8) on the metal support (6). In order to dry and solidify until it becomes, it is preferable to dry to 150 weight% or less of the residual solvent amount in a web (9), and 80 to 120 weight% is more preferable. Moreover, as for the web temperature when peeling a web (9) from a metal support body (6), 0-30 degreeC is preferable. Further, immediately after the web (9) is peeled off from the metal support (6), the temperature rapidly decreases once due to the solvent evaporation from the metal support (6) contact surface side, and water vapor or solvent vapor in the atmosphere. For example, the web temperature at the time of peeling is more preferably 5 to 30 ° C. because volatile components are easily condensed.

  Here, the residual solvent amount can be expressed by the following equation.

Residual solvent amount (% by weight) = {(M−N) / N} × 100
In the formula, M is the weight of the web at an arbitrary time point, and N is the weight when a weight M is dried at a temperature of 110 ° C. for 3 hours.

  The amount of residual solvent in the cast film during high energy treatment is preferably 300 to 100% by weight. More preferably, the treatment is performed at 200 to 150% by weight. Here, if the residual solvent amount is 300% by weight or more, the treatment layer and the functional group immediately sink into the casting film, which is not preferable. In addition, if the amount of residual solvent is 100% by weight or less, a stable treatment layer is not formed, and the surface state before treatment is restored over time, which is not preferable.

  The dope film (web) (9) formed by the dope cast on the endless belt metal support (6) is heated on the metal support (6), and then from the metal support (6). The solvent is evaporated until the web is peelable by the peeling roll (8).

  In order to evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back surface of the metal support (6) by a liquid, a method of transferring heat from the front and back by radiant heat, and the like.

In the system using an endless belt for the metal support (6), the peeling tension when peeling the metal support (6) and the web (9) with the peeling roll (8) is usually 50 N / m to 200 N. / M, but in the method for producing an optical film according to the present invention, which is thinner than the conventional method , the amount of residual solvent of the web (9) is large at the time of peeling, and it tends to extend in the transport direction. The film tends to shrink in the width direction, and when drying and shrinkage overlap, the end curls and folds, so that wrinkles are likely to occur. Therefore, it is preferable to peel at a minimum tension that can be peeled off to 170 N / m, more preferably. Is to peel at a minimum tension of ~ 140 N / m.

  In the present invention, the web (9) is dried and solidified on the metal support (6) until the web (9) has a peelable film strength, and then the web (9) is peeled off by the peeling roll (8). In the process tenter (11), the web (9) is stretched.

FIG. 2 is a flow sheet showing another specific example of an apparatus for carrying out the method for producing an optical film of the present invention by a solution casting film forming method. A metal support (7) for casting a dope is, for example, The surface of a stainless steel drum is subjected to hard chrome plating, and the surface has a three-dimensional surface roughness (Ra) measured by a scanning atomic force microscope (AFM) on an ultra-mirror surface with an average of 1.0 nm. A polished drum (7) is used.

  The other points of the optical film manufacturing apparatus in FIG. 2 are the same as those of the optical film manufacturing apparatus in FIG.

The present invention is a manufacturing method of an optical film that by the solution casting film forming method, cast on the resin solution (dope) of the casting support (6) (7), the cast film (web) While (9) moves on the supports (6) and (7), the surface of the web (9) is treated with a treatment pressure of 0.1 to 36 W / cm ² and 0.001 to 0 by a normal pressure plasma apparatus. .High energy treatment by plasma irradiation under treatment conditions for 6 seconds, or by excimer UV irradiation with an excimer UV irradiation apparatus with a light amount of 1 to 3000 mJ / cm ² and treatment conditions of 0.001 to 0.6 seconds. By performing a high energy treatment, the surface of the web (9) is modified to produce an optical film having a surface energy of 60 to 100 mN / m.
Here, the treatment intensity (W / cm ² ) of the atmospheric pressure plasma apparatus is the electric power supplied between the counter electrodes of the reactor, and the applied area (/ cm ² ) of the electrode is an area in a range where discharge occurs. Point to.

In the present invention, the place where the high energy surface treatment is performed, in other words, the place where the high energy surface treatment apparatus (20) comprising the atmospheric pressure plasma apparatus or the excimer UV irradiation apparatus is installed is the solution flow shown in FIGS. In the optical film manufacturing apparatus using the film-forming method, each section is indicated by a symbol “A”. In other words, the place where the high-energy surface treatment apparatus (20) is installed is that the web (film) (9) is peeled off immediately after the dope is cast on the metal support (6) (7). Limited to section (A).

If the treatment strength is less than 0.1 W / m ² under the treatment conditions for high energy treatment using the atmospheric plasma apparatus, the effect of surface modification is weak and sufficient adhesion cannot be obtained, which is not preferable. Moreover, since the film surface will deteriorate when process intensity | strength exceeds 36 W / cm < ² >, it is unpreferable. Moreover, if the time of plasma irradiation is less than 0.001 second, the effect of surface modification is weak and it returns to the surface state before processing in a short time, which is not preferable. When the plasma irradiation time exceeds 0.6 seconds, a so-called weak boundary layer (Weak Boundary Layer: WBL) is formed and, on the contrary, the adhesion is lowered, which is not preferable.

On the other hand, if the amount of light is less than 1 mJ / cm ² under high energy processing conditions using an excimer UV irradiation apparatus, the effect of surface modification is weak and sufficient adhesion cannot be obtained, which is not preferable. Moreover, since a film surface will deteriorate when a light quantity exceeds 3000 mJ / cm < ² >, it is unpreferable. Further, if the excimer UV irradiation time is less than 0.001 seconds, the effect of surface modification is weak, and the surface state before treatment is restored in a short time, which is not preferable. If the excimer UV irradiation time exceeds 0.6 seconds, a weak boundary layer (WBL) is formed and, on the contrary, the adhesion is lowered, which is not preferable.

The method for producing an optical film according to the present invention is not preferable if the surface energy of the film subjected to high energy treatment is less than 60 mN / m because sufficient adhesiveness is not obtained. Moreover, when the surface energy of the film subjected to high energy treatment exceeds 100 mN / m, the adhesion is too high and a failure such as sticking occurs, which is not preferable.

Next, the atmospheric pressure plasma apparatus used in the method for producing an optical film according to the present invention will be described in detail.

  In the atmospheric pressure plasma apparatus in the present embodiment, a reactive gas is brought into a plasma state by applying a high-frequency voltage between opposing electrodes to discharge, and the casting film surface is exposed to the reactive gas in the plasma state. Thus, the surface of the cast film is modified.

  In the atmospheric pressure plasma apparatus, a high frequency voltage is applied to a reactive gas by applying a high frequency power between electrodes arranged opposite to each other so as to sandwich a substrate to be processed, and a method called a direct method or a planar method in which a supply gas is converted into plasma. There are methods called remote method and downstream method, which are introduced between the added electrodes and converted into plasma, and any method can be used in the present invention. However, in the method of manufacturing an optical film of this embodiment, casting is performed. For forming the surface treatment film on the film surface, it is preferable to use the latter method called remote method or downstream method.

  FIG. 3 is an explanatory diagram for explaining the principle of the atmospheric plasma apparatus.

  3, (a) and (b) are counter electrodes of the atmospheric pressure plasma apparatus, (g) is a reactive gas, and (s) is a cast film.

  As a simple structure of the atmospheric pressure plasma apparatus in FIG. 3, a reactive gas (g) is introduced between the counter electrodes (a) and (b) to which a high-frequency voltage has been applied, and is converted into plasma to form a cast film ( s) A surface treatment film is formed by spraying on the surface.

  In the present embodiment, it is necessary to employ an electrode capable of applying such a high power voltage and maintaining a uniform glow discharge state in the atmospheric pressure plasma apparatus.

  Such an electrode is preferably a metal base material coated with a dielectric. It is preferable to coat a dielectric on at least one side of the opposed application electrode and the ground electrode, and more preferably coat both of the opposed application electrode and the ground electrode with a dielectric. The dielectric is preferably an inorganic substance having a relative dielectric constant of 6 to 45. Examples of such a dielectric include ceramics such as alumina and silicon nitride, silicate glass, borate glass, and the like. Glass lining material and the like.

  In addition, when a cellulose ester film, which is a transparent film base material, is placed between electrodes or transported between electrodes and exposed to plasma, the transparent film base material has a roll electrode specification that can be transported in contact with one electrode. Furthermore, the dielectric surface and the gap between the electrodes can be kept constant by polishing the dielectric surface and setting the electrode surface roughness Rmax (JIS B 0601) to 10 μm or less. It is preferable that the discharge state can be stabilized, and further, the distortion and cracking due to the difference in thermal shrinkage and residual stress can be eliminated and the non-porous, highly accurate inorganic dielectric can be coated to greatly improve the durability. .

  Further, the gap between the blow-out slit for performing plasma supply and the surface of the cast film (s) is preferably 0.5 to 6 mm, and more preferably 1 to 4 mm. If it is too close, there is a risk of contacting or damaging the surface of the cast film (s). If it is too far, the effect of modifying the surface is weakened.

  Various reactive gases (g) such as nitrogen, oxygen, argon, and helium can be used. Nitrogen is preferable from the viewpoints of environment, exhaust aftertreatment, and running cost. It is preferable to mix a small amount of oxygen. The mixing ratio of oxygen is preferably 2% by volume or less with respect to the volume of the source gas.

  Further, the air volume of the source gas of atmospheric pressure plasma is desirably 20 to 5000 L / min per 1 m of the effective width of plasma irradiation. Furthermore, 40-2500 L / min is more preferable.

 However, since this plasma treatment has the effect of deteriorating the film surface at the same time, when the plasma treatment intensity exceeds a certain upper limit, a so-called weak boundary layer (Weak Boundary Layer: WBL) is formed, and conversely the adhesion Decreases.

  Further, in the atmospheric pressure plasma apparatus, since there is a concern about damage such as roughening of the cast film surface due to induced current or discharge, it is desirable to use an apparatus having a shield mechanism.

Next, an excimer UV apparatus used in the method for producing an optical film according to the present invention will be described.

  FIG. 4 is an explanatory diagram for explaining the principle of the excimer UV apparatus.

  In the figure, (u) is an excimer UV lamp, (r) is a reflector, (p) is a purge gas, and (s) is a casting film.

In the present invention, the excimer UV lamp (u) shown in FIG. 4 is used to irradiate the cast film (s) mainly with ultraviolet light having a wavelength of 172 nm with a light quantity of 1 to 3,000 mJ / cm ^2. . When such ultraviolet rays are irradiated onto the surface of the polymer film, hydrophilic groups such as hydroxyl groups, carboxyl groups, and carbonyl groups can be generated on the surface to improve the adhesion.

  In addition, if the gap between the excimer UV lamp (u) and the casting film (s) is too close, there is a risk of contact and damage to the surface of the casting film. Is absorbed, and the effect of modifying the surface of the cast film is weakened, so 0.5 to 4 mm is preferable, and 1 to 3 mm is more preferable.

  When these high-energy surface treatment apparatuses are brought into a film production line for optical applications, measures for maintaining cleanliness become a problem. In particular, it is important to take measures to maintain cleanliness in a normal pressure plasma apparatus having a structure in which dust generated is discharged into the line.

In the method for producing an optical film according to the present invention, a resin solution (dope) is cast on a casting support (6) (7) by a solution casting film forming method, and the casting film (web) (9) is formed. While moving on the support (6) (7), the surface of the web (9) is treated with a treatment pressure of 0.1 to 36 W / cm ^{2 and} a treatment of 0.001 to 0.6 seconds by a normal pressure plasma apparatus. High energy treatment by plasma irradiation is performed under conditions, or high energy treatment by excimer UV irradiation is performed by an excimer UV irradiation apparatus with a light amount of 1 to 3000 mJ / cm ² and a processing condition of 0.001 to 0.6 seconds. Thus, the surface of the cast film (9) is modified.

  As described above, the place where the high-energy surface treatment is performed is indicated by the symbol “A” in FIGS. 1 and 2 when the dope is cast on the metal support (6) and (7) during film formation. It is a section. That is, it is limited to the section (A) during which the web (film) (9) is peeled off immediately after the dope is cast onto the metal support (6) (7).

  According to the present invention, by modifying the casting film surface by high energy treatment, the adhesion can be greatly improved, the deterioration with time can be eliminated, the casting film surface can be hardened, and the flatness can be improved. As a result, it is possible to meet the recent demands for thinning, widening, and improving the quality of protective films for polarizing plates.

  Next, in the present invention, a resin solution (dope) for producing an optical film contains a resin such as cellulose ester resin as a main material, and includes a plasticizer, a retardation adjusting agent, an ultraviolet absorber, fine particles, and It contains at least one or more kinds of low molecular weight substances and a solvent.

  Hereinafter, these will be described.

  In the method for producing the optical film of the present invention, various resins can be used as the film material, and cellulose ester is particularly preferable.

  A cellulose ester is a cellulose ester in which a hydroxyl group derived from cellulose is substituted with an acyl group or the like. Examples thereof include cellulose acylates such as cellulose acetate, cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate propionate butyrate, and cellulose acetate having an aliphatic polyester graft side chain. Among these, cellulose acetate, cellulose acetate propionate, and cellulose acetate having an aliphatic polyester graft side chain are preferable. Other substituents may be included as long as the effects of the present invention are not impaired.

  As an example of cellulose triacetate, the substitution degree of acetyl groups is preferably 2.0 or more and 3.0 or less. By setting the degree of substitution within this range, good moldability can be obtained, and desired in-plane direction retardation (Ro) and thickness direction retardation (Rt) can be obtained. If the substitution degree of the acetyl group is lower than this range, the heat resistance as a retardation film, particularly the dimensional stability under wet heat may be inferior, and if the substitution degree is too large, the necessary retardation characteristics will not be exhibited. There is a case.

Although there is no limitation in particular as a cellulose of the raw material of the cellulose ester used for the manufacturing method of the optical film of this invention, Cotton linter, wood pulp, kenaf etc. can be mentioned. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

  In the present invention, the number average molecular weight of the cellulose ester is preferably in the range of 60000 to 300000, since the mechanical strength of the resulting film is strong. Furthermore, 70000-200000 are preferable.

  In the present invention, various additives can be added to the cellulose ester.

  In the method for producing an optical film according to the present invention, it is preferable to use a dope composition containing a cellulose ester and an additive for reducing the thickness direction retardation (Rt).

  In the present invention, reducing the thickness direction retardation (Rt) of the cellulose ester film is important in terms of increasing the viewing angle of the liquid crystal display device operating in the IPS mode. In the present invention, such thickness direction retardation is used. The following are mentioned as an additive which reduces (Rt).

  In general, retardation of a cellulose ester film appears as the sum of retardation derived from a cellulose ester and retardation derived from an additive. Therefore, an additive for reducing the retardation of the cellulose ester is an additive that disturbs the orientation of the cellulose ester and is difficult to orient itself and / or has a small polarizability anisotropy. It is a compound that effectively reduces it. Therefore, as an additive for disturbing the orientation of the cellulose ester, an aliphatic compound is preferable to an aromatic compound.

  Here, as a specific retardation reducing agent, for example, a polyester represented by the following general formula (1) or (2) may be mentioned.

B1- (GA-) mG-B1 (1)
B2- (GA-) nG-B2 (2)
In the above formula, B1 represents a monocarboxylic acid component, B2 represents a monoalcohol component, G represents a divalent alcohol component, A represents a dibasic acid component, and these are synthesized. B1, B2, G, and A are all characterized by not containing an aromatic ring. m and n represent the number of repetitions.

  There is no restriction | limiting in particular as a monocarboxylic acid component represented by B1, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, etc. can be used.

  Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-12. When acetic acid is contained, the compatibility with the cellulose ester is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

  Preferred monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, tridecylic acid , Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laxeric acid, undecinic acid, Examples thereof include unsaturated fatty acids such as oleic acid, sorbic acid, linoleic acid, linolenic acid and arachidonic acid.

  The monoalcohol component represented by B2 is not particularly limited, and known alcohols can be used. For example, an aliphatic saturated alcohol or aliphatic unsaturated alcohol having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-12.

  Examples of the divalent alcohol component represented by G include the following, but the present invention is not limited thereto. For example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,6- Hexanediol, 1,5-pentylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and the like can be mentioned. Among these, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexanediol, diethylene glycol, and triethylene glycol are preferred, and 1,3-propylene glycol, 1,4-butylene glycol Lumpur, 1,6-hexanediol, diethylene glycol is preferably used.

  The dibasic acid (dicarboxylic acid) component represented by A is preferably an aliphatic dibasic acid or an alicyclic dibasic acid. Examples of the aliphatic dibasic acid include malonic acid, succinic acid, glutaric acid, and adipic acid. , Pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid and the like, in particular, aliphatic carboxylic acid having 4 to 12 carbon atoms, at least one selected from these To do. That is, two or more dibasic acids may be used in combination.

  The number of repetitions m and n in the above general formula (1) or (2) is preferably 1 or more and 170 or less.

  The weight average molecular weight of the polyester is preferably 20000 or less, and more preferably 10,000 or less. In particular, polyesters having a weight average molecular weight of 500 to 10,000 have good compatibility with cellulose esters, and neither evaporation nor volatilization occurs during film formation.

  Polycondensation of polyester is carried out by a conventional method. For example, a direct reaction of the dibasic acid and glycol, a hot melt condensation method by the polyesterification reaction or transesterification reaction of the dibasic acid or alkyl esters thereof, for example, a methyl ester of dibasic acid and glycols, or Although it can be easily synthesized by any method of dehydrohalogenation reaction between acid chloride of these acids and glycol, it is preferable that polyester having a weight average molecular weight not so large is by direct reaction. Polyester having a high distribution on the low molecular weight side has a very good compatibility with the cellulose ester, and after forming the film, a moisture permeability is small, and a cellulose ester film rich in transparency can be obtained.

  The method for adjusting the molecular weight is not particularly limited, and a conventional method can be used. For example, although depending on the polymerization conditions, the amount of these monovalent compounds can be controlled by a method of blocking the molecular ends with a monovalent acid or monovalent alcohol. In this case, a monovalent acid is preferable from the viewpoint of polymer stability. For example, acetic acid, propionic acid, butyric acid, etc. can be mentioned, but during the polycondensation reaction, it is not distilled out of the system, but is stopped and such monovalent acid is removed from the reaction system. The one that is easy to accumulate is selected. These may be used in combination. In the case of direct reaction, the weight average molecular weight can also be adjusted by measuring the timing of stopping the reaction by the amount of water distilled off during the reaction. In addition, it can be adjusted by biasing the number of moles of glycol or dibasic acid to be charged, or can be adjusted by controlling the reaction temperature.

  The polyester represented by the general formula (1) or (2) is preferably contained in an amount of 1 to 40% by weight based on the cellulose ester. It is particularly preferable to contain 5 to 15% by weight.

  In the present invention, examples of the additive for reducing the thickness direction retardation (Rt) include the following.

The dope used in the method for producing an optical film of the present invention is mainly a cellulose ester, a polymer as an additive for reducing retardation (Rt) (a polymer obtained by polymerizing an ethylenically unsaturated monomer, an acrylic polymer). And an organic solvent.

  In the present invention, in order to synthesize a polymer as an additive for reducing the thickness direction retardation (Rt), it is difficult to control the molecular weight in normal polymerization, and a method that can make the molecular weight as uniform as possible by a method that does not increase the molecular weight too much. It is desirable to use it. Such polymerization methods include a method using a peroxide polymerization initiator such as cumene peroxide and t-butyl hydroperoxide, a method using a polymerization initiator in a larger amount than normal polymerization, and a mercapto compound in addition to the polymerization initiator. And a method using a chain transfer agent such as carbon tetrachloride, a method using a polymerization terminator such as benzoquinone and dinitrobenzene in addition to the polymerization initiator, and JP-A No. 2000-128911 or JP-A No. 2000-344823. Examples include a compound having a single thiol group and a secondary hydroxyl group as described in the publication, or a bulk polymerization method using a polymerization catalyst in which the compound and an organometallic compound are used in combination. In particular, the method described in the publication is preferred.

  In the present invention, monomers as monomer units constituting a polymer as an additive for reducing useful thickness direction retardation (Rt) are listed below, but are not limited thereto.

  As the ethylenically unsaturated monomer unit constituting the polymer as an additive for reducing the thickness direction retardation (Rt) obtained by polymerizing an ethylenically unsaturated monomer, first, as a vinyl ester, for example, vinyl acetate, propionic acid, etc. Vinyl, vinyl butyrate, vinyl valerate, vinyl pivalate, vinyl caproate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl octylate, vinyl methacrylate, Examples include vinyl crotonate, vinyl sorbate, vinyl benzoate, and vinyl cinnamate.

  Next, as acrylate ester, for example, methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n-, i-, s-, t-), pentyl acrylate ( n-, i-, s-), hexyl acrylate (n-, i-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-), nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), cyclohexyl acrylate, acrylic acid (2-ethylhexyl), benzyl acrylate, phenethyl acrylate, acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl) ), Acrylic acid (2-hydroxypropyl), acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2- Dorokishibuchiru) acrylate-p-hydroxymethylphenyl,-p-acrylic acid (2-hydroxyethyl) phenyl and the like; as methacrylic acid ester, the acrylic acid ester include those changed to methacrylic acid esters.

  Furthermore, examples of the unsaturated acid include acrylic acid, methacrylic acid, maleic anhydride, crotonic acid, itaconic acid, and the like.

  The polymer composed of the above monomers may be a copolymer or a homopolymer, and is preferably a vinyl ester homopolymer, a vinyl ester copolymer, or a copolymer of vinyl ester and acrylic acid or methacrylic acid ester.

  In the present invention, an acrylic polymer (simply referred to as an acrylic polymer) refers to a homopolymer or copolymer of acrylic acid or alkyl methacrylate having no monomer unit having an aromatic ring or a cyclohexyl group.

  Examples of the acrylate monomer having no aromatic ring and cyclohexyl group include, for example, methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n-, i-, s-, t-), pentyl acrylate (n-, i-, s-), hexyl acrylate (n-, i-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-) , Nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), acrylic acid (2-ethylhexyl), acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid 2-methoxy-ethyl), acrylic acid (2-ethoxyethyl), or the acrylic acid ester may include those obtained by changing the methacrylic acid ester.

  The acrylic polymer is a homopolymer or copolymer of the above-mentioned monomers, but it is preferable that the acrylic acid methyl ester monomer unit has 30% by weight or more, and the methacrylic acid methyl ester monomer unit has 40% by weight or more. It is preferable. In particular, a homopolymer of methyl acrylate or methyl methacrylate is preferred.

  Polymers obtained by polymerizing the above ethylenically unsaturated monomers and acrylic polymers are both highly compatible with cellulose ester, excellent in productivity without evaporation and volatilization, and retainability as a protective film for polarizing plates The moisture permeability is small, and the dimensional stability is excellent.

  In the present invention, an acrylic acid or methacrylic acid ester monomer having a hydroxyl group is not a homopolymer but a constituent unit of a copolymer. In this case, the acrylic acid or methacrylic acid ester monomer unit having a hydroxyl group is preferably contained in the acrylic polymer in an amount of 2 to 20% by weight.

  In the method for producing the optical film of the present invention, the dope composition contains a cellulose ester and an acrylic polymer having a weight average molecular weight of 500 or more and 3000 or less as an additive for reducing the thickness direction retardation (Rt). Is preferred.

  Moreover, in the method for producing the optical film of the present invention, the dope composition contains a cellulose ester and an acrylic polymer having a weight average molecular weight of 5,000 to 30,000 as an additive for reducing the thickness direction retardation (Rt). It is preferable.

  In the present invention, if the weight average molecular weight of the polymer as an additive for reducing the thickness direction retardation (Rt) is 500 or more and 3000 or less, or if the polymer has a weight average molecular weight of 5000 or more and 30000 or less, Compatibility is good and neither evaporation nor volatilization occurs during film formation. Moreover, the transparency of the cellulose ester film after film formation is excellent, the moisture permeability is extremely low, and it exhibits excellent performance as a protective film for polarizing plates.

 In the present invention, a polymer having a hydroxyl group in the side chain can also be preferably used as an additive for reducing the thickness direction retardation (Rt). The monomer unit having a hydroxyl group is the same as the monomer described above, but acrylic acid or methacrylic acid ester is preferable. For example, acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3 -Hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid-p-hydroxymethylphenyl, acrylic acid-p- (2-hydroxyethyl) phenyl, or these acrylic acids. The thing replaced with methacrylic acid can be mentioned, Preferably, it is 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate. The acrylic acid ester or methacrylic acid ester monomer unit having a hydroxyl group in the polymer is preferably contained in the polymer in an amount of 2 to 20% by weight, more preferably 2 to 10% by weight.

  The polymer as described above containing 2 to 20% by weight of the monomer unit having the above hydroxyl group, of course, is excellent in compatibility with cellulose ester, retention, dimensional stability, and low moisture permeability. It is particularly excellent in adhesion with a polarizer as a protective film for a polarizing plate, and has an effect of improving the durability of the polarizing plate.

  In the present invention, it is preferable that at least one terminal of the main chain of the polymer has a hydroxyl group. The method of having a hydroxyl group at the end of the main chain is not particularly limited as long as it has a hydroxyl group at the end of the main chain, but radical polymerization having a hydroxyl group such as azobis (2-hydroxyethylbutyrate). A method of using an initiator, a method of using a chain transfer agent having a hydroxyl group such as 2-mercaptoethanol, a method of using a polymerization terminator having a hydroxyl group, a method of having a hydroxyl group at the terminal by living ion polymerization, Using a polymerization catalyst in which a compound having one thiol group and a secondary hydroxyl group as disclosed in JP-A No. 2000-128911 or JP-A No. 2000-344823, or a combination of the compound and an organometallic compound is used. It can be obtained by a polymerization method or the like, and the method described in the publication is particularly preferable. The polymer produced by the method related to the description in this publication is commercially available as Act Flow Series manufactured by Soken Chemical Co., Ltd., and can be preferably used.

  In the present invention, the polymer having a hydroxyl group at the terminal and / or the polymer having a hydroxyl group in the side chain has an effect of significantly improving the compatibility and transparency of the polymer with respect to the cellulose ester.

  In the present invention, useful additives for reducing the thickness direction retardation (Rt) include, in addition to the above, for example, an ester compound of diglycerin polyhydric alcohol and fatty acid described in JP-A No. 2000-63560, An ester or ether compound of a hexose sugar alcohol described in JP-A-2001-247717, a trialiphatic alcohol phosphate compound described in JP-A-2004-315613, and a general formula (1) described in JP-A-2005-41911 A phosphoric acid ester compound described in JP-A No. 2004-315605, a styrene oligomer described in JP-A No. 2005-105139, and a polymer of a styrene monomer described in JP-A No. 2005-105140. .

  In the present invention, an additive for reducing the thickness direction retardation (Rt) can also be found by the following method.

  A dope formulation in which cellulose ester is dissolved in a mixed organic solvent composed of methyl acetate and acetone is formed on a glass plate and dried at 120 ° C./15 min to produce a cellulose ester film having a thickness of 80 μm. The retardation in the thickness direction of the cellulose ester film is measured, and this is defined as Rt1.

  Next, 10% by weight of the polymer additive is added to the cellulose ester and dissolved in a mixed organic solvent composed of methyl acetate and acetone to prepare a dope formulation. A cellulose ester film with a film thickness of 80 μm is prepared in the same manner as above with this dope formulation. The retardation in the thickness direction of the cellulose ester film is measured, and this is defined as Rt2.

And the relationship of retardation in the thickness direction of the above two cellulose ester films
Rt2 <Rt1
Then, it can be said that the polymer additive added to the cellulose ester is an additive for reducing the thickness direction retardation (Rt).

  In the present invention, the thickness direction retardation (Rt) of the cellulose ester is −10 nm to +10 nm, preferably −5 nm to +5 nm. Here, in either case where the thickness direction retardation (Rt) of the cellulose ester is smaller than −10 nm or larger than +10 nm, the viewing angle becomes narrow and the effect of the present invention does not appear.

  In the present invention, the in-plane retardation (Ro) of the cellulose ester is 0 nm to +5 nm, preferably 0 nm to +2 nm, more preferably 0 nm to +1 nm, and particularly preferably about 0 nm. Here, in either case where the in-plane retardation (Ro) is smaller than 0 nm or larger than +5 nm, the viewing angle becomes narrow and the effect of the present invention does not appear.

  The content of the additive for reducing the thickness direction retardation (Rt) described above is preferably 5 to 25% by weight based on the cellulose ester resin. If the content of the additive for reducing the thickness direction retardation (Rt) is less than 5% by weight, the effect of reducing the thickness direction retardation (Rt) of the film is not exhibited. On the other hand, if the content of the additive for reducing the thickness direction retardation (Rt) exceeds 25% by weight, so-called bleed-out occurs and the stability in the film decreases, which is not preferable.

  In the present invention, the retardation value of the film is determined by measuring the three-dimensional refractive index at a wavelength of 590 nm using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.). It can be calculated from Ny and Nz.

Ro = (Nx−Ny) × d
Rt = ((Nx + Ny) / 2−Nz) × d
In the formula, Nx, Ny, and Nz represent the refractive indexes in the principal axes x, y, and z directions of the refractive index ellipsoid, respectively, Nx, Ny represent the refractive index in the film in-plane direction, and Nz represents the film thickness direction. Refractive index. Further, Nx ≧ Ny, and d represents the thickness (nm) of the film.

  In the present invention, the cellulose ester film has an angle θ (radian) formed between the slow axis direction and the film forming direction and the retardation value (Ro) in the in-plane direction as shown below. It is preferably used as a cellulose ester film.

P ≦ 1-sin ² (2θ) sin ² (πRo / λ)
Here, P is 0.9999 or less.

  θ is the angle (° radians) formed between the slow axis direction in the film plane and the film forming direction (straight direction of the film), and λ is the three-dimensional refractive index measurement for obtaining the above Nx, Ny, Nz, and θ. The wavelength of light is 590 nm, and π is the circumference.

  In the method for producing an optical film according to the present invention, an organic solvent having good solubility with respect to the cellulose derivative is referred to as a good solvent, and has a main effect on dissolution, and an organic solvent used in a large amount among them is mainly used. It is called (organic) solvent or main (organic) solvent.

  Examples of good solvents include ketones such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, ethers such as tetrahydrofuran (THF), 1,4-dioxane, 1,3-dioxolane, 1,2-dimethoxyethane, formic acid Esters such as methyl, ethyl formate, methyl acetate, ethyl acetate, amyl acetate, γ-butyrolactone, methyl cellosolve, dimethylimidazolinone, dimethylformamide, dimethylacetamide, acetonitrile, dimethyl sulfoxide, sulfolane, nitroethane, methylene chloride And 1,3-dioxolane, THF, methyl ethyl ketone, acetone, methyl acetate and methylene chloride are preferable.

  In addition to the organic solvent, the dope preferably contains 1 to 40% by weight of an alcohol having 1 to 4 carbon atoms. After casting the dope on the metal support, the solvent starts to evaporate and the alcohol ratio increases, so the web (name of the dope film after casting the cellulose derivative dope on the metal support) Is used as a gelling solvent that makes the web strong and makes it easy to peel off from the metal support, or when these ratios are small, cellulose derivatives of non-chlorine organic solvents There is also a role to promote the dissolution of.

  Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol, and propylene glycol monomethyl ether. Of these, ethanol is preferred because it has excellent dope stability, has a relatively low boiling point, good drying properties, and no toxicity. These organic solvents alone are not soluble in cellulose derivatives and are called poor solvents.

  The most preferable solvent for dissolving a cellulose derivative, which is a preferable polymer compound satisfying such conditions, at a high concentration is a mixed solvent having a ratio of methylene chloride: ethyl alcohol of 95: 5 to 80:20. Alternatively, a mixed solvent of methyl acetate: ethyl alcohol 60:40 to 95: 5 is also preferably used.

In the method for producing an optical film in the present invention, a plasticizer that imparts processability, flexibility, and moisture resistance to the film, fine particles that impart slipperiness to the film (mat agent), an ultraviolet absorber that imparts an ultraviolet absorption function, You may contain the antioxidant etc. which prevent deterioration of a film.

  The plasticizer used in the present invention is not particularly limited. However, a cellulose derivative or a reactive metal compound capable of hydrolytic polycondensation can be used so as not to cause haze, bleed out or volatilize from the film. It preferably has a functional group capable of interacting with the condensate by hydrogen bonding or the like.

  Examples of such functional groups include hydroxyl groups, ether groups, carbonyl groups, ester groups, carboxylic acid residues, amino groups, imino groups, amide groups, imide groups, cyano groups, nitro groups, sulfonyl groups, sulfonic acid residues, Examples thereof include a phosphonyl group and a phosphonic acid residue, and a carbonyl group, an ester group and a phosphonyl group are preferred.

  Examples of such plasticizers include phosphate ester plasticizers, phthalate ester plasticizers, trimellitic acid ester plasticizers, pyromellitic acid plasticizers, polyhydric alcohol ester plasticizers, glycolate plasticizers. Agents, citric acid ester plasticizers, fatty acid ester plasticizers, carboxylic acid ester plasticizers, polyester plasticizers, etc. can be preferably used, but polyhydric alcohol ester plasticizers, glycolate plasticizers are particularly preferred. And non-phosphate ester plasticizers such as polycarboxylic acid ester plasticizers.

  The polyhydric alcohol ester is composed of an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule.

  The polyhydric alcohol used in the present invention is represented by the following general formula (3).

R ^1- (OH) n (3)
In the formula, R ¹ represents an n-valent organic group, and n represents a positive integer of 2 or more.

  Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these.

  Examples of preferred polyhydric alcohols include adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1, 2-butanediol, 1,3-butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, gallium Examples include lactitol, mannitol, 3-methylpentane-1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, and xylitol. In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

  In the present invention, the monocarboxylic acid used in the polyhydric alcohol ester is not particularly limited, and known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid and the like can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred in terms of improving moisture permeability and retention.

  Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. When acetic acid is contained, the compatibility with the cellulose derivative is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

  Examples of preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, Tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, mellicic acid, laccellic acid, etc., undecylen Examples thereof include unsaturated fatty acids such as acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenylcarboxylic acid, naphthalenecarboxylic acid, and tetralincarboxylic acid. Examples thereof include aromatic monocarboxylic acids and derivatives thereof, and benzoic acid is particularly preferable.

  The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose derivatives.

  The carboxylic acid used for the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the OH groups in the polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are.

  The glycolate plasticizer is not particularly limited, but a glycolate plasticizer having an aromatic ring or a cycloalkyl ring in the molecule can be preferably used. As preferred glycolate plasticizers, for example, butyl phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate and the like can be used.

  For phosphate ester plasticizers, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc. For phthalate ester plasticizers, diethyl phthalate, dimethoxy Ethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dicyclohexyl phthalate, and the like can be used, but in the present invention, it is preferable that a phosphate ester plasticizer is not substantially contained.

  Here, “substantially does not contain” means that the content of the phosphoric ester plasticizer is less than 1% by weight, preferably 0.1% by weight, and particularly preferably not added.

  These plasticizers can be used alone or in combination of two or more.

  The amount of the plasticizer used is preferably 1 to 20% by weight. 6 to 16% by weight is further preferable, and 8 to 13% by weight is particularly preferable. If the amount of the plasticizer used is less than 1% by weight relative to the cellulose derivative, the effect of reducing the moisture permeability of the film is small, so this is not preferred. If it exceeds 20% by weight, the plasticizer bleeds out from the film, and the film Since the physical properties of the material deteriorate, it is not preferable.

  In the present invention, it is preferable to add fine particles such as a matting agent to the cellulose derivative in order to impart slipperiness. Examples of the fine particles include fine particles of an inorganic compound or fine particles of an organic compound.

  Examples of the fine particles of the inorganic compound include fine particles of silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, tin oxide and the like. Of these, fine particles of a compound containing a silicon atom are preferred, and fine silicon dioxide particles are particularly preferred. Examples of the silicon dioxide fine particles include Aerosil 200, 200V, 300, R972, R972V, R974, R202, R812, R805, OX50, and TT600 manufactured by Aerosil Co., Ltd.

  Examples of the organic compound fine particles include fine particles such as acrylic resin, silicone resin, fluorine compound resin, and urethane resin.

  The primary particle size of the fine particles is not particularly limited, but the average particle size in the film is preferably about 0.05 to 5.0 μm. More preferably, it is 0.1-1.0 micrometer.

  When the cellulose ester film is observed with an electron microscope or an optical microscope, the average particle diameter of the fine particles indicates an average value of the lengths in the major axis direction of the particles at the observation position of the film. As long as the particles are observed in the film, they may be primary particles or secondary particles in which the primary particles are aggregated, but most of the particles that are usually observed are secondary particles.

As an example of the measurement method, 10 vertical cross-sectional photographs are taken at random for each film, and the number of particles in 100 μm ² whose major axis length is in the range of 0.05 to 5 μm for each cross-sectional photograph. Count. The average value of the major axis lengths of the particles counted at this time is obtained, and a value obtained by averaging the average values of 10 locations is defined as the average particle size.

  In the case of fine particles, the primary particle size, the particle size after being dispersed in a solvent, and the particle size after being added to the film often change, and what is important is that the fine particles are finally combined with the cellulose ester in the film. And controlling the particle size formed by aggregation.

  Here, if the average particle size of the fine particles exceeds 5 μm, haze deterioration or the like may be observed, or it may cause a failure in a wound state as a foreign matter. Moreover, when the average particle diameter of fine particles is less than 0.05 μm, it becomes difficult to impart slipperiness to the film.

  The fine particles are used by adding 0.04 to 0.5% by weight to the cellulose ester. Preferably, 0.05 to 0.3% by weight, more preferably 0.05 to 0.25% by weight is added. When the amount of fine particles added is 0.04% by weight or less, the film surface roughness becomes too smooth and blocking occurs due to an increase in the friction coefficient. If the amount of fine particles added exceeds 0.5% by weight, the coefficient of friction on the film surface will be too low, causing winding misalignment during winding, and the transparency of the film will be low and haze will be high. The above range is essential because it has no value as a film.

  For the dispersion of the fine particles, it is preferable to treat the composition in which the fine particles and the solvent are mixed with a high-pressure dispersion apparatus. The high-pressure dispersion apparatus used in the present invention is an apparatus that creates special conditions such as high shear and high pressure by passing a composition in which fine particles and a solvent are mixed at high speed through a narrow tube.

It is preferable that the maximum pressure condition inside the apparatus is 980 N / cm ² or more in a thin tube having a tube diameter of 1 to 2000 μm, for example, by processing with a high-pressure dispersion apparatus. More preferably, the maximum pressure condition inside the apparatus is 1960 N / cm ² or more. Further, at that time, those having a maximum reaching speed of 100 m / sec or more and those having a heat transfer speed of 100 kcal / hr or more are preferable.

  Examples of the high-pressure dispersing device as described above include an ultra-high pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation or a nanomizer manufactured by Nanomizer, and other manton gorin type high-pressure dispersing devices such as those manufactured by Izumi Food Machinery. A homogenizer etc. are mentioned.

  In the present invention, the fine particles are dispersed in a solvent containing 25 to 100% by weight of a lower alcohol, and then mixed with a dope in which a cellulose ester (cellulose derivative) is dissolved in a solvent, and the mixed solution is placed on a metal support. A cellulose ester film is obtained which is cast and dried to form a film.

  Here, the content ratio of the lower alcohol is preferably 50 to 100% by weight, more preferably 75 to 100% by weight.

  Examples of lower alcohols preferably include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol and the like.

  Although it does not specifically limit as solvents other than a lower alcohol, It is preferable to use the solvent used at the time of film formation of a cellulose ester.

  The fine particles are dispersed in the solvent at a concentration of 1 to 30% by weight. Dispersing at a concentration higher than this is not preferable because the viscosity increases rapidly. The concentration of the fine particles in the dispersion is preferably 5 to 25% by weight, more preferably 10 to 20% by weight.

  The ultraviolet absorbing function of the film is preferably imparted to various optical films such as a polarizing plate protective film, a retardation film, and an optical compensation film from the viewpoint of preventing deterioration of the liquid crystal. For such an ultraviolet absorbing function, a material that absorbs ultraviolet rays may be included in the cellulose derivative, and a layer having an ultraviolet absorbing function may be provided on a film made of the cellulose derivative.

  Examples of ultraviolet absorbers that can be used in the present invention include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. A benzotriazole-based compound with little coloring is preferable. In addition, ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574 and polymer ultraviolet absorbers described in JP-A-6-148430 are also preferably used.

  As the ultraviolet absorber, those having excellent absorption ability of ultraviolet rays having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of a polarizer or liquid crystal and those having little absorption of visible light having a wavelength of 400 nm or more from the viewpoint of liquid crystal display properties. preferable.

  Specific examples of useful UV absorbers in the present invention include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-). Butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) ) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 '-(3 ", 4", 5 ", 6" -tetrahydrophthalimidomethyl) -5'-methylphenyl) benzotriazole, 2,2- Methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol, 2- (2'-hydroxy) 3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol, octyl -3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy-5 A mixture of-(5-chloro-2H-benzotriazol-2-yl) phenyl] propionate can be mentioned, but is not limited thereto.

  Further, as commercially available products of ultraviolet absorbers, TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by Ciba Specialty Chemicals) can be preferably used.

  Specific examples of the benzophenone compounds that are ultraviolet absorbers that can be used in the present invention include 2,4-dihydroxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5- Examples thereof include, but are not limited to, sulfobenzophenone and bis (2-methoxy-4-hydroxy-5-benzoylphenylmethane).

  In this invention, the compounding quantity of these ultraviolet absorbers has the preferable range of 0.01 to 10 weight% with respect to a cellulose ester (cellulose derivative), and also 0.1 to 5 weight% is preferable. If the amount of the ultraviolet absorber used is too small, the ultraviolet absorbing effect may be insufficient. If the amount of the ultraviolet absorber is too large, the transparency of the film may be deteriorated. The ultraviolet absorber is preferably one having high heat stability.

Further, the ultraviolet absorber that can be used in the method for producing an optical film of the present invention is a polymer ultraviolet absorber (or ultraviolet absorbing polymer) described in JP-A-6-148430 and JP-A-2002-47357. Can be preferably used. In particular, it is represented by the general formula (1) described in JP-A-6-148430, the general formula (2), or the general formulas (3), (6), and (7) described in JP-A-2002-47357. A polymer ultraviolet absorber is preferably used.

  In general, the antioxidant is also referred to as a deterioration inhibitor, but is preferably contained in a cellulose ester film as an optical film. That is, when a liquid crystal image display device or the like is placed in a high humidity and high temperature state, the cellulose ester film as an optical film may be deteriorated. The antioxidant has a role of delaying or preventing the film from being decomposed by, for example, halogen in the residual solvent in the film or phosphoric acid of the phosphoric acid plasticizer, so that it is preferably contained in the film. .

  As such an antioxidant, a hindered phenol compound is preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di- -T-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octa Sil-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxy Benzyl) -isocyanurate and the like. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3 -(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination.

  The amount of these compounds added is preferably 1 ppm to 1.0% by weight, more preferably 10 to 1000 ppm by weight with respect to the cellulose derivative.

In the specific example of the apparatus for carrying out the method for producing the optical film of the present invention shown in FIGS. 1 and 2, the stretching step is performed on both side edges of the web (or film) (9) as a film for a liquid crystal display device. A tenter method in which the film is fixed with a clip or the like and stretched is preferable in order to improve the flatness and dimensional stability of the film.

  The residual solvent amount of the web (film) (9) immediately before entering the tenter (11) in the stretching step is preferably 10 to 35% by weight.

  In this Embodiment, the extending | stretching ratio of the web in the tenter (11) of an extending process is 3 to 100%, It is preferable that it is 5 to 80%, and it is further desirable that it is 5 to 60%. Moreover, the temperature of the warm air blown from the warm air blowing slit port in the tenter (11) is 100 to 200 ° C, preferably 110 to 190 ° C, and more preferably 115 to 185 ° C.

  As shown in FIGS. 1 and 2, it is preferable to provide a drying device (10) on the rear side of the tenter (11) in the stretching step. In addition, although illustration was abbreviate | omitted, drying apparatus (10) may be provided in the front and back both sides of the tenter (11) of an extending process.

  In the drying device (10), the web (9) is meandered by a plurality of conveying rolls arranged in a staggered manner as viewed from the side, and the web (9) is dried during that time. Moreover, although the film conveyance tension | tensile_strength in a drying apparatus (10) is influenced by the physical property of dope, the amount of residual solvents at the time of peeling and a film conveyance process, drying temperature, etc., the film conveyance tension | tensile_strength at the time of drying is 30-300N. / Width m, more preferably 40 to 270 N / width m.

  The means for drying the web (film) (9) is not particularly limited, and is generally performed by hot air, infrared rays, a heating roll, microwaves, or the like. It is preferable to dry with hot air from the viewpoint of simplicity, for example, it is dried by the drying air (12) blown from the warm air inlet at the front portion of the bottom of the drying device (10), and is dried on the ceiling of the drying device (10). It is dried by exhaust air being discharged from the outlet of the rear portion. The temperature of the drying air (12) is preferably 40 to 160 ° C, and more preferably 50 to 160 ° C in order to improve the flatness and dimensional stability.

  These steps from casting to post-drying may be performed in an air atmosphere or in an inert gas atmosphere such as nitrogen gas. In this case, it goes without saying that the dry atmosphere is carried out in consideration of the explosion limit concentration of the solvent.

  For example, a cellulose ester film that has finished the transport drying process is generally processed to form an emboss on the film by an embossing apparatus before the introduction to the winding process.

  Here, the height h (μm) of the emboss is set in the range of 0.05 to 0.3 times the film thickness T, and the width W is set in the range of 0.005 to 0.02 times the film width L. . Embossing may be formed on both sides of the film. In this case, the height h1 + h2 (μm) of the emboss is set in the range of 0.05 to 0.3 times the film thickness T, and the width W is set in the range of 0.005 to 0.02 times the film width L. For example, when the film thickness is 40 μm, the emboss height h1 + h2 (μm) is set to 2 to 12 μm. The emboss width is set to 5 to 30 mm.

  The film after drying is wound up by a winding device (13) to obtain the original roll of the optical film. A film having good dimensional stability can be obtained by setting the residual solvent amount of the film to be dried to 0.5% by weight or less, preferably 0.1% by weight or less.

  The winding method of the film may be a generally used winder, and there are methods for controlling the tension such as a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, etc. Use it properly.

  The film may be joined to the winding core (winding core) by either a double-sided adhesive tape or a single-sided adhesive tape.

In the method for producing an optical film according to the present invention, the width of the film after winding is preferably 1200 to 2500 mm.

  In this invention, the film thickness after drying of a cellulose-ester film has the preferable range of 20-150 micrometers as a finished film from a viewpoint of thickness reduction of a liquid crystal display device. Here, the film thickness after drying refers to a film in which the amount of residual solvent in the film is 0.5% by weight or less.

  Here, when the film thickness of the cellulose ester film after winding is too thin, for example, the required strength as a protective film for a polarizing plate may not be obtained. If the film thickness is too thick, the advantage of thinning the film becomes less than the conventional cellulose ester film. In order to adjust the film thickness, the dope concentration, the pumping amount, the slit gap in the die of the casting die, the extrusion pressure of the casting die, the speed of the metal support, etc. are controlled so as to obtain the desired thickness. It is good. Further, as a means for making the film thickness uniform, it is preferable to use a film thickness detection means to feed back and adjust the programmed feedback information to each of the above devices.

  In the process from immediately after casting through the solution casting film-forming method to drying, the atmosphere in the drying apparatus may be air, but may be performed in an inert gas atmosphere such as nitrogen gas or carbon dioxide gas. . However, of course, the danger of the explosion limit of the evaporating solvent in the dry atmosphere must always be considered.

  In the present invention, the cellulose ester film preferably has a moisture content of 0.1 to 5%, more preferably 0.3 to 4%, and even more preferably 0.5 to 2%.

  In the present invention, the cellulose ester film desirably has a transmittance of 90% or more, more preferably 92% or more, and further preferably 93% or more.

In addition, the optical film manufactured by the method of the present invention has a haze of 0.3 to 2.0 when three sheets are stacked. According to the method of manufacturing an optical film of the present invention, the haze of the film Is very low, and has optical properties excellent in transparency and flatness.

  Here, the haze of the optical film may be measured using, for example, a haze meter (1001DP type, manufactured by Nippon Denshoku Industries Co., Ltd.) according to the method defined in JIS K6714.

Further, the tensile modulus in the machine direction (MD direction) of the cellulose ester film as the optical film produced by the method of the present invention is 1500 MPa to 3500 MPa, and the tensile modulus in the direction perpendicular to the machine direction (TD direction) is It is preferably 3000 MPa to 4500 MPa, and the ratio of the elastic modulus in the TD direction / the elastic modulus in the MD direction of the film is preferably 1.40 to 1.90.

  Here, if the ratio of the elastic modulus in the TD direction / the elastic modulus in the MD direction of the optical film is less than 1.40, the sag of the central portion becomes large in winding a film having a width exceeding 1650 mm, and Since sticking increases, it is not preferable. Further, if the ratio of the elastic modulus in the TD direction / the elastic modulus in the MD direction exceeds 1.90, warpage after overheating on the deflecting plate occurs, or the backlight is heated by the heat of the backlight when incorporated in the liquid crystal panel. Since the dimensional change behavior of the polarizing plate on the side and the surface side is greatly different, unevenness occurs at the corner, which is not preferable.

  As a specific method for measuring the tensile modulus of elasticity in the MD direction and TD direction of the film, for example, the method of JIS K7217 can be mentioned.

  That is, using a tensile tester (TG-2KN, manufactured by Minebea Co., Ltd.), a sample was set at a chucking pressure: 0.25 MPa, a distance between marked lines: 100 ± 10 mm, and a pulling speed: 100 ± 10 mm / min. Pull on. As a result, from the obtained tensile stress-strain curve, the elastic modulus calculation start point is 10N, the end point is 30N, and the tangent line drawn between them is extrapolated to calculate the elastic modulus.

In the optical film manufactured by the method of the present invention, the in-plane retardation (Ro) defined by the following formula is 30 to 300 nm under the conditions of a temperature of 23 ° C. and a humidity of 55% RH, and the thickness direction retardation (Rt) is It is preferably 70 to 400 nm under the conditions of a temperature of 23 ° C. and a humidity of 55% RH.

Ro = (nx−ny) × d
Rt = {(nx + ny) / 2−nz} × d
In the formula, Ro is the retardation value in the film plane, Rt is the retardation value in the film thickness direction, nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, and nz is the film. The refractive index in the thickness direction (refractive index measured at a wavelength of 590 nm), d represents the thickness (nm) of the film.

  The retardation values Ro and Rt can be measured using an automatic birefringence meter. For example, using KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.), the wavelength can be obtained at 590 nm in an environment of a temperature of 23 ° C. and a humidity of 55% RH.

The optical film produced by the method of the present invention is preferably used for a liquid crystal display member, specifically a protective film for a polarizing plate. In particular, in a protective film for a polarizing plate that has strict requirements for both moisture permeability and dimensional stability, the optical film produced by the method of the present invention is preferably used.

By using the protective film for polarizing plates made of the optical film produced by the method of the present invention, it is possible to provide a polarizing plate excellent in durability, dimensional stability, and optical isotropy as well as thinning.

The aforementioned polarizing plate, to an optical film produced by the method of the present invention may be prepared by bonding the retardation film and an optical film produced by the method of the present invention the retardation film and the protective film Alternatively, it may be produced by directly bonding to a polarizing film. The method of bonding is not particularly limited, but can be performed with an adhesive composed of an aqueous solution of a water-soluble polymer. The water-soluble polymer adhesive is preferably a completely saponified polyvinyl alcohol aqueous solution. Furthermore, a long polarizing plate can be obtained by laminating a long polarizing film stretched in the longitudinal direction and treated with a dichroic dye and a long retardation film according to the present invention. A polarizing plate is a sticking type in which a peelable sheet is laminated on one or both sides thereof via a pressure sensitive adhesive layer (for example, an acrylic pressure sensitive adhesive layer). Or the like can be easily attached).

  The polarizing plate thus obtained can be used for various display devices. In particular, a liquid crystal display device using a VA mode liquid crystal molecule in which liquid crystal molecules are substantially vertically aligned when no voltage is applied, or a TN mode liquid crystal cell in which liquid crystal molecules are substantially horizontal and twisted when no voltage is applied. Is preferred.

The optical film produced by the method of the present invention includes a hard coat layer, an antiglare layer, an antireflection layer, an antifouling layer, an antistatic layer, a conductive layer, an optical anisotropic layer, a liquid crystal layer, an alignment layer, an adhesive layer, Various functional layers such as an adhesive layer and an undercoat layer can be provided. These functional layers can be provided by a method such as coating or vapor deposition, sputtering, plasma CVD, or atmospheric pressure plasma treatment.

  Thus, the obtained polarizing plate is provided in the one or both surfaces of a liquid crystal cell, and a liquid crystal display device is obtained using this.

A liquid crystal display device includes a liquid crystal cell in which rod-like liquid crystal molecules are sandwiched between a pair of glass substrates, a polarizing film disposed so as to sandwich the liquid crystal cell, and two polarizing plates each including a transparent protective layer disposed on both sides thereof. It is what you have.

By using the protective film for polarizing plates made of the optical film produced by the method of the present invention , it is possible to provide a polarizing plate excellent in durability, dimensional stability, and optical isotropy as well as thinning. Furthermore, a liquid crystal display device using this polarizing plate or retardation film can maintain stable display performance over a long period of time.

The optical film produced by the method of the present invention can also be used as a base material for an antireflection film or an optical compensation film.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Examples 1-9
(Preparation of dope)
The following materials were put into a sealed container, heated, stirred and completely dissolved, and filtered to prepare a dope. Silicon dioxide fine particles (Aerosil R972V) were added after being dispersed in ethanol.

(Dope composition)
Cellulose triacetate (acetyl substitution degree 2.88) 100 parts by weight Triphenyl phosphate 8 parts by weight Biphenyl diphenyl phosphate (liquid plasticizer) 4 parts by weight 5-chloro-2- (3,5-di-sec-butyl-2- Hydroxyphenyl)
-2H-benzotriazole (liquid UV absorber) 1 part by weight Methylene chloride 418 parts by weight Ethanol 23 parts by weight Silicon dioxide fine particles (Aerosil R972V) 0.1 part by weight Next, the solution casting film forming apparatus shown in FIG. A cellulose triacetate film was produced. That is, the metal support (6) for casting the dope was polished to a super mirror surface with an average of 1.0 nm of three-dimensional surface roughness (Ra) measured by a scanning atomic force microscope (AFM) manufactured by SUS316. An endless belt was used.

  The dope filtered as described above was uniformly cast on a SUS316 endless belt support (6) made of SUS316 at a dope temperature of 35 ° C. by a casting die (3) made of a coat hanger die. The temperature of the drying air was constant at 30 ° C.

In the method for producing an optical film according to the present invention, a resin solution (dope) is cast on a casting support (6) by a solution casting method, and the casting film (web) (9) is on the support. During the transition of (6), the surface of the cast film (9) was modified by subjecting the surface of the web (9) to high energy treatment by plasma irradiation using a normal pressure plasma apparatus.

  Here, the place where the high-energy surface treatment is performed, in other words, the place where the high-energy surface treatment apparatus (20) comprising the atmospheric pressure plasma apparatus is installed is cast on the support (6) in this embodiment. This was carried out at a point where the amount of residual solvent during conveyance was 180%.

  Next, the web (film) peeled from the endless belt support (6) is then dried while being rolled in an atmosphere at a temperature of 90 ° C., and the tenter (11) is 100 ° C. when the residual solvent amount is 10%. After stretching 1.06 times in the width direction in the atmosphere, release the width holding, finish drying in a 125 ° C drying zone while carrying the roll, and apply a knurling process with a width of 10mm and a height of 8μm on both ends of the film. Thus, a cellulose ester film having a thickness of 40 μm was produced. The film width was 2000 mm and the winding length was 1500 m.

(Normal pressure plasma treatment)
Using the atmospheric pressure plasma irradiation apparatus shown in FIG. 3, the transport speed of the casting film (web) (s) is set under the condition that the gap from the plasma injection slit to the surface of the casting film (web) (s) is 3 mm. As shown in Table 1 below, the treatment intensity and the irradiation time were variously changed, and the normal pressure plasma irradiation treatment was performed.

  The composition of the mixed gas (reactive gas) used for the atmospheric pressure plasma treatment is shown below. The atmospheric pressure was 1.0 atmospheric pressure.

Nitrogen 99.98% by volume
Oxygen 0.02% by volume
Mixed gas flow rate 2m ³ / min
The surface energy of the cellulose triacetate film produced in this way, the adhesiveness immediately after production and after 1 week of production were measured as follows.

(Measurement of surface energy)
The surface free energy of the cellulose triacetate film is determined by measuring the contact angles of the film with respect to three kinds of liquids of known pure water, ethylene glycol, and dipropylene glycol, as shown below. The surface free energy values γ _L ^d , γ _L ^p , γ _L ^h , and γ _L of ethylene glycol and dipropylene glycol are calculated using the following formulas (A), (B), and (C), respectively. The surface free energy (dispersion force, polar force, hydrogen bond component) is calculated.

γ _s = γ _SL + γ _L cos θ (Young-Dupre's equation)
_{γ SL = γ s + γ L} -2 (γ S d γ L d) 1 / 2-2 (γ S p γ L p) 1/2
^{_{-2 (γ S h γ L h}} ) 1/2 ... ( b)
γ _L = γ _L ^d + γ _L ^p + γ _L ^h (C)
In the formula, θ is the contact angle, γ is the surface free energy, γ ^d is the dispersion force component of the surface free energy, γ ^p is the polar force component of the surface free energy, and γ ^h is the hydrogen bond component of the surface free energy. The subscript indicates L for liquid, S for solid, and SL for solid-liquid interface.

In the method for producing an optical film according to the present invention, the surface energy of the high energy treated film is 60 to 100 mN / m.

(Measurement of contact angle)
Using a contact angle meter (trade name PG-X, Matsubo Corporation, Inc.), when the liquid 3 mm ³ was dropped, was measured static contact angle. At an interval of 50 mm in the width direction and the longitudinal direction of the web, a range of 1 m ² on the web (9) was measured at each position and in the vicinity thereof at five points, and the average value was taken as the contact angle.

(Adhesive evaluation)
After laminating the polarizer and the protective film, the peelability was measured by hand, and ranked according to the degree of occurrence of material destruction, and was ranked into the following three stages and evaluated.

○: Material destruction occurs Δ: Partial material destruction occurs, but the area peeled off between the sample film and the PVA film is large ×: The material film is peeled off between the sample film and the PVA film In Table 1 below, Examples 1 to 9 The treatment strength (W / cm ² ), the irradiation time (seconds), the surface energy of the cellulose triacetate film (mN / m), and the adhesion results immediately after production and 1 week after production, Shown together.

Comparative Examples 1-9
For comparison, it is carried out in substantially the same way as in the case of Example 1, except that the surface treatment by the atmospheric pressure plasma apparatus is not performed, or the surface treatment by the atmospheric pressure plasma apparatus is different. At least one of the processing intensity of the processing and the irradiation time is set to be out of the scope of the present invention.

Next, for the cellulose triacetate films prepared in Comparative Examples 1 to 9, as in the case of Example 1 above, the surface energy and the adhesiveness immediately after preparation of atmospheric plasma and after one week of preparation were measured. The treatment intensity (W / cm ² ) of the atmospheric pressure plasma in the comparative example, the irradiation time (seconds), the surface energy of the cellulose triacetate film (mN / m), and the adhesion results immediately after production and 1 week after production, The results are shown in Table 1 below.

(Preparation of polarizing plate)
Next, using the optical films prepared in Examples 1 to 9 and Comparative Examples 1 to 9 as a protective film for polarizing plates, polarizing plates were prepared and evaluated according to the following methods.

(Preparation of polarizing film and polarizing plate)
First, a long polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times). This stretched film was immersed in an aqueous solution consisting of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and then a temperature of 68 ° C. consisting of a ratio of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. Soaked in an aqueous solution. This was washed with water and dried to obtain a long polarizing film.

  Subsequently, according to the following processes 1-5, the polarizing film and the optical film were bonded together and the polarizing plate was produced.

  Step 1: The long optical film produced in Example 1 was immersed in a 2 mol / L sodium hydroxide solution at 50 ° C. for 90 seconds, then washed with water and dried. A protective film (made of polyethylene terephthalate) that can be removed again was attached to the surface provided with the antireflection film in advance for protection.

  Similarly, a long cellulose ester film (used as a substrate for an optical film) was immersed in a 2 mol / L sodium hydroxide solution at 50 ° C. for 90 seconds, then washed with water and dried.

  Process 2: The above-mentioned long polarizing film was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by mass for 1 to 2 seconds.

  Step 3: Excess adhesive adhered to the polarizing film in Step 2 was lightly removed, and it was sandwiched between the optical film and the cellulose ester film that had been subjected to alkali treatment in Step 1, and then laminated.

Process 4: It bonded together at the speed | rate of about 2 m / min with the pressure of 20-30 N / cm < ² > with the two rotating rollers. At this time, care was taken to prevent bubbles from entering.

  Step 5: The sample produced in Step 4 was dried for 2 minutes in a dryer at 80 ° C. to produce the polarizing plate of Example 1 of the present embodiment.

  Similarly, using the long optical films prepared in Examples 2 to 9 and Comparative Examples 1 to 9, the polarizing plates of Examples 2 to 9 and Comparative Examples 1 to 9 of the present embodiment Produced.

(Production of liquid crystal display panel)
The polarizing plate on the outermost surface of a commercially available liquid crystal display panel (NEC color liquid crystal display, MultiSync, LCD 1525J, model name LA-1529HM) was carefully peeled off, and the polarizing plates of Examples 1 to 9 and Comparative Examples 1 to 9 described above were used. A polarizing plate was attached with the polarization direction aligned, to produce a liquid crystal display panel.

(Evaluation of polarizing plate)
Each liquid crystal display panel produced in this way was visually evaluated by a plurality of evaluators by visually observing unevenness that appeared whitish when viewed from the front and oblique directions.

  The criteria for visual evaluation of the occurrence of unevenness in the polarizing plate are as follows. The obtained results are shown in Table 1 below.

○ None of the evaluators can see any unevenness △ Some evaluators may see slight unevenness, but the level that can be used as a product × Many evaluators showed faint but unevenness

Examples 10-18
Although it is carried out in substantially the same way as in the case of Example 1, the difference from Example 1 is that an excimer UV treatment is performed using an excimer UV irradiation apparatus as a high-energy surface treatment.

(Excimer UV treatment)
Using an excimer UV irradiation apparatus shown in FIG. 4 and an apparatus including four excimer UV lamps with Xe ₂ wavelength of 172 nm, the flow from the glass outer surface of the lamp to the casting film surface was set to 3 mm. Excimer UV irradiation treatment was performed by changing the conveying speed of the cast film (web) (s) and passing it under the excimer UV irradiation apparatus, and changing the amount of light and the irradiation time as shown in Table 2 below. .

  The surface energy of the cellulose triacetate films of Examples 10 to 18 thus prepared, and the adhesion immediately after production and after 1 week of production were measured in the same manner as in Example 1 above.

Table 2 below shows the amount of light (mJ / cm ² ), irradiation time (seconds), surface energy of cellulose triacetate film (mN / m), immediately after production, and 1 week after production in each example. The results of the adhesion were summarized.

Comparative Examples 10-18
For comparison, it is carried out in substantially the same way as in the case of Example 10, except that the surface treatment by the excimer UV irradiation apparatus is not performed or the light amount of the excimer UV irradiation apparatus is different. At least one of the irradiation times is set so as to be out of the scope of the present invention.

  Next, for the cellulose triacetate films prepared in Comparative Examples 10 to 18, as in the case of Example 1, the surface energy and the adhesiveness immediately after the preparation and one week after the production were measured.

Table 2 below shows the amount of light (mJ / cm ² ), irradiation time (seconds), surface energy of the cellulose triacetate film (mN / m), immediately after production, and 1 week after production in each comparative example. The results of adhesion were also shown.

Next, polarizing plates and liquid crystal display panels using the optical films produced in Examples 10 to 18 and Comparative Examples 10 to 18 as protective films for polarizing plates are used in Examples 1 to 9 and Comparative Examples 1 to 9. The polarizing plate produced and obtained in the same manner as above was subjected to visual evaluation for occurrence of unevenness in the same manner as described above, and the obtained results are shown in Table 1 below.

As is clear from the results in Tables 1 and 2 above, as in Examples 1 to 9 and Examples 10 to 18 of the present invention, the cast film (web) (9) migrates on the support (6). In the meantime, the surface of the web (9) is subjected to high energy treatment by plasma irradiation using an atmospheric pressure plasma apparatus, or by high energy treatment using excimer UV irradiation using an excimer UV irradiation apparatus, thereby adhering the cellulose triacetate film. As a result, the processability was improved, the processability was excellent, the deterioration with time of the surface-modified layer could be eliminated, and the adhesion deterioration with time could also be prevented.

  On the other hand, as in Comparative Examples 1-9 and Comparative Examples 10-18, the surface treatment by the atmospheric plasma apparatus and the excimer UV irradiation apparatus is not performed, or the surface treatment by the atmospheric pressure plasma apparatus and the excimer UV irradiation apparatus is performed. When at least one of the processing intensity, light intensity, and irradiation time is set to be out of the scope of the present invention, even if the adhesion immediately after irradiation is good, the adhesive deterioration with time Could not prevent.

  Moreover, the liquid crystal display panel using the polarizing plate produced by the film of Comparative Examples 1-18 from the result of the visual evaluation of a polarizing plate using the polarizing plate produced by the film of Examples 1-18 was used. Compared with the panel, it was confirmed that there was no unevenness in reflected light and the display performance was excellent.

It is a flow sheet which shows the specific example of the apparatus which enforces the manufacturing method of the optical film of this invention. It is a flow sheet which shows another specific example of the same apparatus. It is explanatory drawing for demonstrating the principle of the atmospheric pressure plasma irradiation apparatus used in the apparatus which enforces the manufacturing method of the optical film of this invention. It is explanatory drawing for demonstrating the principle of the excimer UV irradiation apparatus used in the apparatus which enforces the manufacturing method of the optical film of this invention.

1: Melting pot 2: Pump 3: Casting die 4: Depressurization chamber 5: Front and rear winding drum 6: Endless belt for casting (metal support)
7: Rotary drive drum for casting (metal support)
8: Release roll 9: Web (cast film)
10: Roll conveying and drying device 11: Tenter 12: Hot air (dry air)
13: Winder 20: High energy surface treatment apparatus A: Section in which high energy surface treatment is performed a: Counter electrode of reactor of atmospheric pressure plasma apparatus b: Counter electrode of reactor of atmospheric pressure plasma apparatus g: Reaction gas u: Excimer Excimer UV lamp of UV apparatus r: reflector p: purge gas

Claims (2)

A method for manufacturing an optical film that by the solution casting film forming method, a resin solution (dope) was cast onto a casting support, while the casting film (web) to migrate on the support, The surface of the web is subjected to high energy treatment by plasma irradiation with a treatment pressure of 0.1 to 36 W / cm ² and a treatment condition of 0.001 to 0.6 seconds by an atmospheric plasma device, or an excimer UV irradiation device. Accordingly, in processing conditions 1～3000MJ / amount of cm ² and from 0.001 to 0.6 seconds, more applying high energy treatment by excimer UV irradiation, the surface energy of the optical film is 60~100mN / m characterized that you manufacturing method of the optical film. The method for producing an optical film according to claim 1, wherein the resin solution contains cellulose acylate.

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