JP5838778B2 - Manufacturing method of optical film - Google Patents

Description

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

  In recent years, liquid crystal display devices such as notebook computers, televisions, and large monitors have been developed to reduce the thickness and weight, increase the screen size, and increase the definition. Accordingly, the protective film for the liquid crystal polarizing plate is increasingly required to be thinner, wider and higher quality. Furthermore, as the cost of optical films is reduced, a technique for increasing the film forming speed is required.

  For example, when a cellulose ester film is produced by a solution casting film forming method, generally, a resin solution (dope) of a cellulose ester is cast from a casting die onto a support that runs endlessly. A cellulose ester film is produced by peeling the web (casting film) at the peeling point where the support has made a full turn, drying it with a drying device while winding the roll group, and winding it.

  Since the solution casting film forming method has a low film forming speed, various techniques for increasing the film forming speed have been proposed. For example, when forming a web by casting a dope on a support, in order to enable stable high-speed casting, the pressure is reduced from the upstream side of the casting so that the web is formed in close contact with the support. Providing a vacuum chamber as a means to do this has been implemented. Thereby, the entrained air generated by the running of the support is removed, and the entrainment of bubbles due to the accompanying air is prevented.

  However, if the vacuum in the vacuum chamber is increased in order to cope with higher speed, the air flow is disturbed by the accompanying air and the suction air, and the casting liquid film (casting ribbon) from the casting die vibrates, resulting in uneven film thickness. This causes a problem of degrading optical quality.

  Therefore, in Patent Document 1, a dope containing a polymer and a solvent is cast from a die while forming a bead on a support to form a casting film, and a support on the support surface side of the bead is formed using a vacuum chamber. When the pressure in the region extending in the width direction is set lower than the pressure in the region extending in the width direction of the bead opposite to the support side, and when the casting film is peeled off from the support, an air supply unit is provided. The air flow in the decompression chamber is controlled by supplying air into the decompression chamber.

JP 2007-90866 A

  However, Patent Document 1 only controls the air flow in the decompression chamber, and does not directly suppress the entrained air generated by the travel of the support. There is not much effect to prevent vibration of the film, and the film thickness unevenness is not completely eliminated.

  An object of this invention is to provide the manufacturing method of the optical film which does not degrade optical quality by suppressing entrained air directly in the solution casting film forming method.

  In order to achieve the above object, the present invention provides an optical film manufacturing method in which a dope, which is a raw material solution for an optical film, is cast from a casting die onto a support to produce an optical film. The air is blown to the support surface on the upstream side of the die, and the angle at which the blower blows air to the support surface is in a range from vertical to parallel to the external direction.

  In the optical film manufacturing method described above, it is preferable that the upstream side of the casting die is decompressed by a decompression unit, and the air outlet of the blower unit is provided upstream of the suction port of the decompression unit.

  Further, in the above optical film manufacturing method, the upstream side of the casting die may be decompressed by the decompression unit, and the air outlet of the air blowing unit may be provided downstream of the suction port of the decompression unit. .

  Moreover, in the manufacturing method of said optical film, it is preferable that the wind speed of the said ventilation is 20-50 m / s.

  According to the present invention, deterioration of optical quality can be suppressed by directly suppressing entrained air by blowing air to the upstream support surface of the casting die by the blowing means.

It is a schematic diagram which shows an example of the manufacturing apparatus of the optical film used by this invention. It is a schematic diagram which shows another example of the manufacturing apparatus of the optical film used by this invention. It is sectional drawing of the casting die and chamber periphery of the apparatus of FIG. FIG. 2 is a bottom view of the casting die and chamber of the apparatus of FIG. 1. It is a perspective view of the casting die and chamber periphery of the apparatus of FIG. It is a figure which shows the film forming conditions of Examples 1-6 and Comparative Examples 1-5, and the evaluation result of horizontal unevenness.

  In this specification, the front refers to the film transport direction, and the left and right refer to the front.

  FIG. 1 is a schematic view showing an example of an apparatus for producing an optical film used in the present invention. This apparatus is a solution casting film forming apparatus using a solution casting film forming method. In FIG. 1, first, a resin such as cellulose ester is dissolved in a mixed solvent of a good solvent and a poor solvent in a dissolving pot 1, and an additive such as a plasticizer or an ultraviolet absorber is added thereto to prepare a dope. .

  Next, the dope adjusted in the melting pot 1 is fed to the casting die 3 through a pressure-type metering gear pump 2 by a conduit and transferred to an endless belt on an endless belt support 6 made of a rotationally driven stainless steel endless belt. The dope is cast from the casting die 3 at the casting position, and the cast film (web) 9 formed thereby is brought into contact with the endless belt support 6. The endless belt support 6 is held by a pair of front and rear drums 5 and 5 and a plurality of intermediate rolls (not shown), and is attached to one or both of the drums 5 and 5 at both ends of the endless belt support 6. A driving device (not shown) for applying tension to the endless belt support 6 is provided, and the endless belt support 6 is used in a tensioned state.

  Moreover, the thing of another form may be used for a support body. FIG. 2 is a schematic view showing another example of an apparatus for producing an optical film used in the present invention. This solution casting film forming apparatus is different from the apparatus shown in FIG. 1 in that a rotating drive drum 7 made of stainless steel whose surface is hard chrome plated is used as a casting support. Since other configurations are the same as those in FIG. 1, the same reference numerals are given to the same configurations.

  The dope is cast by the casting die 3 using a doctor blade method in which the film thickness of the cast web is adjusted by a blade, a method by a reverse roll coater in which the film thickness is adjusted by a reverse rotating roll, There is a method using a pressure die. Among them, a method using a pressure die is preferable because the slit shape of the base portion can be adjusted and the film thickness can be easily made uniform. The pressure die includes a coat hanger die and a T die, and any of them can be preferably used.

  As shown in detail in FIGS. 3 to 5, a chamber 4 as a decompression (suction) means and a blowing means is provided on the upstream side of the casting die 3. The chamber 4 is divided into a decompression chamber 20 and front and rear blowing chambers 30 and 40. The chamber 4 has a top wall 24 and an inclined wall 45 at the front end.

  The decompression chamber 20 has a rectangular suction port 28 provided substantially at the center below the chamber 4, and has a width substantially the same as the width of the casting die 3. The decompression chamber 20 includes left and right side walls 21 and 22, a rear wall 23, and a front inclined wall 25. A duct opening 27 of a suction duct 26 is provided on the top wall 24 of the decompression chamber 20, and the pressure is reduced by sucking air from the duct opening 27. The decompression force of the decompression chamber 20 is preferably −1000 to −100 Pa.

  By reducing the pressure on the upstream side of the casting die 3, the entrained air generated by the travel of the support 6 is removed to some extent, and the entrainment of the bubbles due to the entrained air is prevented to some extent. Become.

  A plurality of decompression chambers may be provided. For example, the decompression chamber may be provided upstream of the rear air blowing chamber 30 or downstream of the front air blowing chamber 40.

  The rear air blowing chamber 30 has a rear wall 33 at a predetermined interval along the outer side of the rear wall 23 of the decompression chamber 20, and the left and right side walls 21 and 22 of the decompression chamber 20 are extended rearward. The left and right side walls 31 and 32 are provided, and a blower outlet 38 is provided below. In FIG. 3, the air outlet 38 is inclined in the external direction (upstream side), but the angle θ for blowing air with respect to the surface of the support 6 is changed from vertical (90 °) to parallel (0 °) to the external direction. (0 ° <θ ≦ 90 °). Further, a duct opening 37 of a blower duct 36 is provided on the top wall 24 of the blower chamber 30, and air is blown by sending air from here.

  The front blowing chamber 40 is adjacent to the casting ribbon cast from the casting die 3, and has an inclined wall 45 at a predetermined interval along the outer side of the inclined wall 25 of the decompression chamber 20, Furthermore, the left and right side walls 21 and 22 of the decompression chamber 20 have left and right side walls 41 and 42 formed to extend forward, and have a blowout port 48 below. In FIG. 3, the air outlet 48 is inclined in the external direction (upstream side), but the angle θ for blowing air with respect to the surface of the support 6 is changed from vertical (90 °) to parallel (0 °) to the external direction. (0 ° <θ ≦ 90 °). Further, a duct opening 47 of a blower duct 46 is provided on the top wall 24 of the blower chamber 40, and air is blown by sending air from here.

  Here, the wind speed blown from the blower chamber 40 is preferably 20 to 50 m / s. If it is this range, the entrained air which arises by the driving | running | working of the support body 6 can be removed, the disturbance of the airflow in the casting die 3 vicinity is lose | eliminated, and the vibration of a casting liquid film is suppressed. When the wind speed is less than 20 m / s, the above effect is not obtained so much. On the other hand, when the wind speed exceeds 50 m / s, the air flow inside the chamber 4 may be disturbed and the casting liquid film may vibrate. is there. Further, it is preferable to reduce the flow rate of the air so as not to hinder the effect of decompression.

  In this way, by blowing air to the upstream support 6 surface of the casting die 3 by the front and rear blowing chambers 30 and 40, the stability of the casting liquid film is improved even in the high-speed film forming region, and the casting liquid is increased. It is possible to reduce film thickness unevenness in the film conveyance direction due to vibration of the film, and it is possible to produce a film with good smoothness, that is, a film with good optical quality.

  Even if the decompression chamber 20 and the blower chamber 30 or 40 are omitted, that is, even if only the blower chamber 30 or 40 is provided as a chamber, the entrained air can be removed. Unevenness in thickness can be reduced.

  In addition, even if the one blower chamber 30 or 40 is omitted, that is, the decompression chamber 20 and the blower chamber 30 or 40 are provided as chambers, entrained air can be removed, so that the vibration of the casting liquid film is suppressed. Unevenness in film thickness can be reduced.

  Next, the solution casting film forming method will be described in more detail.

  In the solution casting film forming method, the solid content concentration of a dope such as cellulose ester cast from the casting die 3 onto the support comprising the rotary drive endless belt 6 shown in FIG. 1 or the rotary drive drum 7 shown in FIG. It is preferably 15 to 30% by weight. If the solid content concentration of the dope is less than 15% by weight, sufficient drying cannot be performed on the supports 6 and 7, and part of the web remains on the supports 6 and 7 at the time of peeling, leading to belt contamination. It is not preferable. Further, if the solid content concentration exceeds 30%, the dope viscosity is increased, filter clogging is accelerated in the dope adjustment process, or pressure is increased during casting on the supports 6 and 7, which is not preferable. Absent.

  The widths of the supports 6 and 7 are preferably 1700 to 2500 mm, the dope casting width is 1600 to 2400 mm, and the film width 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.

  When endless belts are used as the supports 6 and 7, the belt temperature during film formation is 0 ° C. to less than the boiling point of the solvent in a general temperature range, and less than the boiling point of the lowest boiling solvent in the mixed solvent. The film can be cast at a temperature, and more preferably in the range of 5 ° C to the boiling point of the solvent-5 ° C. At this time, it is necessary to control the ambient atmospheric humidity above the dew point. In addition, it is preferable that the peripheral speed of the support bodies 6 and 7 is 40-200 m / min.

  The dope cast on the surfaces of the supports 6 and 7 in this way also increases the strength of the gel film (film strength) by promoting drying until stripping.

  Since the web 9 is dried and solidified on the supports 6 and 7 made of a rotary drive endless belt or a rotary drive drum until the web 9 has a film strength that can be peeled off from the supports 6 and 7 by the peeling roll 8, the residual solvent in the web 9 The amount is preferably dried to 150% by weight or less, more preferably 80 to 120% by weight. Moreover, 0-30 degreeC is preferable for the web temperature when peeling the web 9 from the support bodies 6 and 7. FIG. Further, immediately after the web 9 is peeled off from the supports 6 and 7, the temperature once drops rapidly due to solvent evaporation from the contact surface side of the supports 6 and 7, and volatile components such as water vapor and solvent vapor in the atmosphere are condensed. Since it is easy to do, the web temperature at the time of peeling has more preferable 5-30 degreeC.

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 web 9 formed by the dope cast on the supports 6 and 7 is heated on the supports 6 and 7, and the solvent is evaporated until the web can be peeled from the supports 6 and 7 by the peeling roll 8. Let

  For evaporating the solvent, there are a method in which air is blown from the web side, a method in which heat is transferred from the back surfaces of the supports 6 and 7 by liquid, a method in which heat is transferred from the front and back by radiant heat, and the like. Can be used.

  The peeling tension at the time of peeling the supports 6 and 7 and the web 9 with the peeling roll 8 is peeled off with a tension larger than the peeling force obtained by the peeling force measurement like JIS Z 0237. If the peel tension is made equal to the peel force obtained by the JIS measurement method, the peel position may be taken downstream, so this is done at a higher level for stabilization. However, even if the film is formed with the same peeling tension in the process, it is confirmed that the variation in the crossed Nicols transmittance (CNT) of the film is greatly reduced when the peeling force by the JIS measuring method is lowered.

  As the peeling tension value in the process, peeling is usually performed at 50 to 250 N / m. However, in the case of the optical film produced by the method of the present invention which is made thinner than the conventional, Since the amount of residual solvent is large and easily stretches in the transport direction, the film tends to shrink in the width direction, and when drying and shrinkage overlap, the edge curls and folds, making it easy to wrinkle, so it can be peeled off. Peeling at a tension of 170 N / m is preferable, and peeling at a minimum tension of 140 N / m is more preferable.

  After drying and solidifying until the web 9 has a peelable film strength on the supports 6 and 7, the web 9 is peeled off by the peeling roll 8, and then the web 9 is stretched in the tenter 10 in the stretching process.

  In the stretching step, a tenter system in which both side edges of the web 9 are fixed with clips or the like and stretched is preferable as the liquid crystal display device film in order to improve the flatness and dimensional stability of the film.

  The residual solvent amount of the web 9 immediately before entering the tenter 10 in the stretching process is preferably 10 to 35% by weight. Moreover, the stretch ratio of the web in the tenter 10 in the stretching process is 3 to 100%, preferably 5 to 80%, and more preferably 5 to 60%.

  Moreover, the temperature of the warm air blown from the warm air blowing slit port in the tenter 10 is 100 to 200 ° C, preferably 110 to 190 ° C, and more preferably 115 to 185 ° C.

  It is preferable to provide the drying apparatus 11 after the tenter 10 in the stretching step. In the drying device 11, 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 in the meantime. The film transport tension in the drying apparatus 11 is affected by the physical properties of the dope, the amount of residual solvent in the peeling and film transport process, the drying temperature, etc., but the film transport tension during drying is 10 to 300 N / m. The width is more preferably 20 to 270 N / 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 hot air inlet of the drying device 11 and dried by exhausting the exhaust air from the outlet of the drying device 11. 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.

  It is preferable to form an embossed part having a large number of irregularities at the end of the optical film F before introducing it into the winding process for the optical film F that has finished the transport drying process.

  Next, the film in which the embossed portion has been formed is wound up by the 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. The optical film F preferably has a width of 1400 to 2400 mm after winding.

  The film thickness after drying of a resin film such as cellulose ester is preferably in the range of 20 to 150 μm as a finished film from the viewpoint of thinning the 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 optical film after winding is too thin, the intensity | strength required as a protective film for polarizing plates may not be acquired, for example. On the other hand, if the film thickness is too thick, the advantage of thinning the film over conventional resin films such as cellulose ester is lost. For adjusting the film thickness, the dope concentration, the pumping amount, the slit gap of the die of the casting die 3, the extrusion pressure of the casting die 3, the speed of the supports 6 and 7 are adjusted so as to obtain a desired thickness. It is good to control etc. 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, or may be performed in an inert gas atmosphere such as nitrogen gas or carbon dioxide gas. Of course, the danger of the explosion limit of the evaporating solvent in the dry atmosphere must always be taken into account.

  By the way, in the method for producing an optical film by the solution casting film forming method, a dope containing a resin such as cellulose ester as a main material, a plasticizer, a retardation adjusting agent, an ultraviolet absorber, fine particles, and a low molecular weight substance. At least one or more substances and solvents are included. Hereinafter, these will be described.

  In the method for producing an optical film by the solution casting film forming method, various resins can be used as the film material, and among them, cellulose ester is preferably used.

  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 triacetate, cellulose acetate propionate, and cellulose acetate having an aliphatic polyester graft side chain are preferable. The cellulose ester used in the present invention may contain other substituents.

  As an example of cellulose triacetate, the substitution degree of acetyl group 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 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.

  The cellulose as a raw material for the cellulose ester is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

  The number average molecular weight of the cellulose ester is preferably in the range of 60,000 to 300,000 because the mechanical strength of the resulting film is strong. Furthermore, 70000-200000 are preferable. Various additives can be blended in the cellulose ester.

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

  Reducing the thickness direction retardation (Rt) of the cellulose ester film is important in terms of widening the viewing angle of the liquid crystal display device operating in the IPS mode, but such an additive for reducing the thickness direction retardation (Rt). The following may be mentioned as:

  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.

General formula (1) B1- (GA-) mG-B1
General formula (2) B2- (GA-) nG-B2
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, but are not limited to, the following.

  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.

  Examples of the additive for reducing the thickness direction retardation (Rt) include the following.

  The dope used for the production of the 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 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 it is desirable to use a method that can align the molecular weight as much as possible without increasing the molecular weight. . 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 preferable.

  Although the monomer as a monomer unit which comprises the polymer as an additive which reduces useful thickness direction retardation (Rt) is mentioned below, it is not limited to this.

  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-hydroxy) Rokishibuchiru) 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 a homopolymer of vinyl ester, a copolymer of vinyl ester, or a copolymer of vinyl ester and acrylic acid or methacrylic acid ester is preferable.

  An acrylic polymer (simply called an acrylic polymer) refers to a homopolymer or copolymer of acrylic acid or methacrylic acid alkyl ester 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 esters, 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 case of an acrylic acid or methacrylic acid ester monomer having a hydroxyl group, it 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 an optical film by the solution casting film forming method, the dope composition has a weight average molecular weight of 500 or more and 3000 or less, or a weight average molecular weight as an additive for reducing the cellulose ester and thickness direction retardation (Rt). It is preferable to contain 5000 or more and 30000 or less acrylic polymer.

  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 the polymer has a weight average molecular weight of 5000 or more and 30000 or less, the compatibility with the cellulose ester is good. It 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.

As an additive for reducing the thickness direction retardation (Rt), a polymer having a hydroxyl group in the side chain can also be preferably used. The monomer unit having a hydroxyl group is the same as the monomer described above, but is preferably acrylic acid or methacrylic acid ester. 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 by 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.

  Such a polymer containing 2 to 20% by weight of the above-mentioned monomer unit having a hydroxyl group is, of course, excellent in compatibility with cellulose ester, retention property, dimensional stability, low moisture permeability, and polarized light. It is particularly excellent in adhesiveness with a polarizer as a protective film for plates, and has the effect of improving the durability of the polarizing plate.

  Moreover, it is preferable to have a hydroxyl group at least at one terminal of the main chain of the polymer. 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 having a hydroxyl group at the terminal and / or a polymer having a hydroxyl group in a side chain has an advantage of remarkably improving the compatibility and transparency of the polymer with respect to the cellulose ester.

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

  In the method of producing an optical film by the solution casting film forming method, an organic solvent having good solubility with respect to the above cellulose derivative is called a good solvent, and shows a main effect on dissolution, and an organic solvent to be used in a large amount among them. The solvent is referred to as the main (organic) solvent or the 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. These are gels that, after casting the dope onto the support, the solvent begins to evaporate and the proportion of alcohol increases, making the web gel, making the web strong and easy to peel off from the support When used as a solvating solvent, or when the proportion of these is small, it also has a role of promoting the dissolution of a cellulose derivative of a non-chlorine organic solvent.

  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 the 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.

  An optical film produced by a solution casting method is a plasticizer that imparts processability, flexibility, and moisture resistance to the film, fine particles that impart slipperiness to the film (matting agent), and an ultraviolet absorbing function. You may contain the ultraviolet absorber, the antioxidant which prevents deterioration of a film, etc.

  The plasticizer used in the solution casting film forming method is not particularly limited, but the cellulose derivative and reactivity capable of hydrolytic polycondensation so as not to cause haze, bleed out or volatilize from the film. It preferably has a functional group capable of interacting with a polycondensate of a metal compound 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 solution casting film forming method is represented by the following general formula (3).

Formula (3) R1- (OH) n
(However, R1 represents an n-valent organic group, and n represents a positive integer of 2 or more.)
Examples of preferred polyhydric alcohols include, but are not limited to, the following.

  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.

  There is no restriction | limiting in particular as monocarboxylic acid used for polyhydric alcohol ester, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. 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 are 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, melicic 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 plasticizers, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenylbiphenyl 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 it is preferable that substantially no phosphate ester plasticizer is 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 order to impart slipperiness to the cellulose derivative in the solution casting film forming method, it is preferable to add fine particles such as a matting agent. 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 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 to aggregate. And controlling the particle size formed.

  Here, when 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 solution casting film-forming method is an apparatus that creates special conditions such as high shear and high-pressure conditions 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 solution casting film forming method, 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 to support the mixed solution. A cellulose ester film obtained by casting on a body and drying to form a film is obtained.

  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 solution casting film forming method include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. However, 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 include 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) benzo Triazole, 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- (straight 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- (5-chloro) -2H-benzotriazol-2-yl) phenyl] propionate and the like, but not limited thereto.

  Moreover, as a commercial item of an ultraviolet absorber, TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by BASF Japan Ltd.) can be preferably used.

  Specific examples of the benzophenone compound that is an ultraviolet absorber that can be used in the solution casting film forming method include 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, and 2-hydroxy-4- Examples thereof include, but are not limited to, methoxy-5-sulfobenzophenone and bis (2-methoxy-4-hydroxy-5-benzoylphenylmethane).

  The blending amount of these ultraviolet absorbers is preferably in the range of 0.01 to 10% by weight, more preferably 0.1 to 5% by weight, based on the cellulose ester (cellulose derivative). If the amount of the UV absorber used is too small, the UV absorbing effect may be insufficient, and if the amount of the UV absorber used is too large, the transparency of the film may be deteriorated. The ultraviolet absorber is preferably one having high heat stability.

  Moreover, the ultraviolet absorber which can be used for the optical film of a solution casting film forming method 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.

  The optical film according to the present invention is manufactured by the above-described optical film manufacturing method, and the film thickness is preferably in the range of 20 to 150 μm as a finished film from the viewpoint of thinning the liquid crystal display device.

  The optical film targeted by the present invention is a functional film used for various displays such as a liquid crystal display, a plasma display, and an organic EL display, particularly a liquid crystal display. A polarizing plate protective film, a retardation film, an antireflection film, It includes an optical compensation film such as a brightness enhancement film and a viewing angle expansion.

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

  By the way, the polarizing film is a film that has been conventionally stretched by treating a film that can be stretched and oriented, such as a polyvinyl alcohol film, with a dichroic dye such as iodine. Since the polarizing film itself does not have sufficient strength and durability, a polarizing plate is generally obtained by adhering a cellulose ester film having no anisotropy as a protective film to both surfaces thereof.

  The polarizing plate may be prepared by laminating the optical film produced by the method of the present invention as a retardation film, and the optical film produced by the method of the present invention is a retardation film and a 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 that has been stretched in the longitudinal direction and treated with a dichroic dye and a long retardation film produced by the method of 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.

  By the way, a polarizing plate can be produced by a general method. For example, there is a method in which an optical film or a cellulose ester film is subjected to alkali saponification treatment, and a polyvinyl alcohol film is bonded to both surfaces of a polarizing film produced by immersing and stretching in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. is there. 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.

  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 irradiation 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.

  The liquid crystal display device here 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 transparent protective layers disposed on both sides thereof. It has a polarizing plate.

  In addition, since the polarizing plate here uses an optical film excellent in flatness on at least one side, when the polarizing plate is incorporated in a liquid crystal panel, the contrast of the liquid crystal panel is reduced and the density unevenness occurs. There is no, and it is excellent in visibility.

  In addition, since the display device here uses a polarizing plate having an optical film having excellent flatness, it does not cause a decrease in contrast or unevenness of density of the liquid crystal panel, and has excellent visibility. It is what.

  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.

  Next, examples of the present invention will be described together with comparative examples, but the present invention is not limited to these examples.

(Preparation of dope)
The following materials were put into a sealed container, heated, stirred and completely dissolved, and filtered to prepare a dope.

(Dope composition)
Cellulose triacetate (acetyl substitution degree 2.88) 100 parts by weight Triphenyl phosphate 8 parts by weight Ethylphthalylethyl glycolate 2 parts by weight Tinuvin 326 1 part by weight AEROSIL 200V 0.1 part by weight Methylene chloride 418 parts by weight Ethanol 23 parts by weight

  Next, the cellulose triacetate film was manufactured with the solution casting film forming apparatus shown in FIG. That is, as the support 6 for casting the dope, an endless belt made of SUS316 and 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). 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.

  In this way, the web 9 formed on the support 6 is dried on the support 6 with a drying air constant at a temperature of 30 ° C. while being transported on the support 6, and then peeled off from the support 6 by the peeling roll 8. 10 and when the residual solvent amount is 10%, the film is stretched 1.06 times in the width direction in an atmosphere of 100 ° C., then the width is released, and the drying is finished with the drying device 11 at 125 ° C. while being conveyed by rolls. It wound up with the winding device 13.

  The obtained cellulose triacetate film had a film thickness of 40 μm, a film width of 2000 mm, and a film winding length of 3000 m.

  In each of the examples and comparative examples, the film was formed by changing the form of the decompression chamber 20 and the air blowing chambers 30 and 40 and the angle θ at which air was blown from the air outlets 38 and 48 of the air blowing chambers 30 and 40 to the support surface.

  And about the cellulose triacetate film produced in the said Examples 1-6 and Comparative Examples 1-5, the horizontal unevenness used as the parameter | index of a film thickness nonuniformity was evaluated. A method for evaluating the horizontal unevenness will be described later.

  FIG. 6 shows the film forming conditions of Examples 1 to 6 and Comparative Examples 1 to 5 and the evaluation results of film thickness unevenness. Example 1 formed a film at θ = 90 ° using a chamber in which the front blower chamber 40 was omitted in FIGS. In Example 2, the film was formed at θ = 5 ° using a chamber in which the front air blowing chamber 40 was omitted in FIGS. In Example 3, the film was formed at θ = 45 ° using a chamber in which the front blowing chamber 40 in FIGS. 3 to 5 was omitted.

In Example 4, a film was formed at θ = 90 ° using a chamber in which the rear blowing chamber 30 in FIGS. 3 to 5 was omitted. Example 5 formed a film at θ = 5 ° using a chamber in which the rear blowing chamber 30 in FIGS. 3 to 5 was omitted. Example 6 formed a film at θ = 45 ° using a chamber in which the rear air blowing chamber 30 was omitted in FIGS. Examples 1 and 4 in which θ = 90 ° are merely reference examples of the present invention and do not belong to the present invention.

  In Comparative Example 1, a film was formed using a chamber in which the front and rear blowing chambers 30 and 40 in FIGS. Comparative Example 2 formed a film at θ = 95 ° using a chamber in which the front blowing chamber 40 in FIGS. 3 to 5 was omitted. Comparative Example 3 formed a film at θ = 0 ° using a chamber in which the front air blowing chamber 40 was omitted in FIGS. Comparative Example 4 formed a film at θ = 95 ° using a chamber in which the rear air blowing chamber 30 was omitted in FIGS. Comparative Example 5 formed a film at θ = 0 ° using a chamber in which the rear blowing chamber 30 in FIGS. 3 to 5 was omitted.

  Evaluation of horizontal unevenness was performed by measuring the thickness of the manufactured optical film with a film thickness meter (film thickness measuring device DH-150 manufactured by Tokyo Seimitsu Co., Ltd.). The difference between the maximum value and the minimum value / average film thickness) × 100 ”was determined and evaluated according to the following criteria. That is, the horizontal unevenness (%) is a value obtained by dividing the difference between the maximum value and the minimum value of the unevenness of the thickness unevenness of the optical film by the average film thickness of the optical film. The thickness of the optical film was continuously measured in the length direction, and the pitch of periodic thickness unevenness and the maximum value, minimum value, and average value (average film thickness) of thickness unevenness were read from the chart.

  And, when the horizontal unevenness is less than 0.4%, ◎, when 0.4% or more and less than 0.6%, ◯, when 0.6% or more and less than 0.8%, △, 0.8% The above case was set as x. In the case of x, it is a condition that is not suitable for manufacturing because there are many defects and the productivity is poor.

  As a result, the evaluation of the horizontal unevenness was any of ◎, ◯, and Δ in Examples 1 to 6, and × in Comparative Examples 1 to 5. From this result, if there is no blowing means as in Comparative Example 1, the horizontal unevenness is large, and if the blowing angle θ is directed inward from the vertical as in Comparative Examples 2 and 4, entrained air is increased. The horizontal unevenness is large, and it can be said that there is no effect of suppressing the entrained air unless the angle θ of the air blow is horizontal, that is, hits the support surface as in Comparative Examples 3 and 5.

  Moreover, since the evaluation result of horizontal unevenness is better in Example 2 than Example 5 and in Example 3 than Example 6, it is better to provide the air blowing chamber on the rear side than on the front side. You might also say that.

  From the above, considering that the conditions of Comparative Examples 1 to 5 are inappropriate and the conditions of Examples 1 to 6 are appropriate, when the blowing angle θ is in the range of 0 ° <θ ≦ 90 °, It can be said that the horizontal unevenness is small and suitable for manufacturing.

3 Casting die 4 Chamber (pressure reducing means and air blowing means)
6, 7 Support body 20 Decompression chamber (decompression means)
28, 38 Suction port 30 Rear air blowing chamber (air blowing means)
40 Front blower chamber (blower means)
38, 48 outlet

Claims (3)

In the method for producing an optical film in which an optical film is produced by casting a dope, which is a raw material solution of an optical film, onto a support from a casting die,
Providing a blowing means for sending air for removing the entrained air generated by the running of the support,
It was blown into the upstream side of the support surface of the casting die by the blowing means, and,
Depressurizing the upstream side of the casting die with a decompression means,
The air blowing means and the pressure reducing means are installed in contact with each other,
Further, the casting die and the air blowing means or the pressure reducing means are adjacent to each other,
The air blowing angle perpendicular to the support surface is 90 °, the direction perpendicular to the air blowing direction of 90 °, and the direction opposite to the traveling direction of the cast film cast on the support When the air blowing angle toward
The method of manufacturing an optical film, wherein an angle θ at which the blowing unit blows air with respect to the support surface is within a range of 0 ° <θ <90 ° . The method for producing an optical film according to claim 1, wherein the air outlet of the blower means is provided on the downstream side of the suction port of the pressure reducing means. The method for producing an optical film according to claim 1, wherein the wind speed of the blown air is 20 to 50 m / s.

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