JP5849679B2 - Manufacturing method of optical film - Google Patents

Description

  The present invention is, for example, a liquid crystal display device (LCD), in particular, a protective film for polarizing plates used for small and medium-sized LCDs such as touch panel applications, a retardation film, a viewing angle widening film, an antireflection film used for plasma displays, etc. The present invention relates to a method for producing an optical film that can be used as various functional films.

  Conventionally, a cellulose ester film has been adopted as a member of a liquid crystal display device such as a retardation film or a protective film for a polarizing plate. There are mainly a melt film-forming method and a solution film-forming method as a method for producing the cellulose ester film. In any method, a plasticizer is often added to the film raw material from the viewpoint of improving production suitability. For example, as plasticizers for cellulose ester films, phthalate esters and phosphate ester triphenyl phosphates are conventionally known.

  In recent years, along with the diversification of the usage environment of liquid crystal display devices, there has been a demand for optical films that have small dimensional variations and high durability under various wet and heat environments. In contrast, in general, a cellulose ester film in which an ester compound obtained by polymerizing a diol and a dicarboxylic acid in a film raw material is added has excellent dimensional stability under high temperature and high humidity. Reference 1 shows an ester compound that exhibits little variation in properties even when subjected to a durability test under high temperature and high humidity.

  When a cellulose ester film is produced by a solution casting method (solution casting casting method), a cellulose ester resin solution (dope) is generally run endlessly from a casting die. A cellulose ester film is produced by peeling the web (casting film) at the peeling point where the support has made one round, drying it with a drying device while winding the roll group, and winding it. .

  In this solution casting film forming method, a method for controlling the temperature of the support has been proposed in order to suppress unevenness in film thickness and to provide optical anisotropy in the thickness direction. For example, in Patent Document 2, in order to suppress unevenness of the thickness of the cast film, a single dope is cast toward the support, and a cast film made of the dope is formed on the surface of the support. A film forming step for heating, a film heating step for heating the casting film from the back side by heating the support, and an inner layer made of the liquid dope by applying cold air to the surface of the casting film being heated And a gelled layer forming step for obtaining the cast film provided with the surface layer comprising the gelated dope, and a drying step performed after the film heating step and the gelled layer forming step for impression of the cast film And a solution casting method comprising a peeling step of peeling off the dried cast film from the support.

  In Patent Document 3, the temperature of the support is adjusted to a range of 10 ° C. to 40 ° C. in order to suppress the thickness unevenness of the cast film, and the running speed of the support is set to 10 m / min to 150 m / min. A peeling roller for supporting the film immediately after being peeled off from the support, using the peeling roller and the film of the peeling roller. The distance L with respect to the contact position is in the range of 0.1 mm to 100 mm, the temperature of the film when peeling off the film is in the range of 10 ° C. to 50 ° C., and the film thickness is 60 μm or less. A film containing residual volatile matter (dry weight reference weight%) of 5 wt% or more (reference value −5) wt% or less, with the value at which the peeling load of the film is maximized as a reference value. Stripped, the reference value is 15 wt% to 35 wt% Solution casting method, characterized in that within the scope of the following is disclosed.

  Further, Patent Document 4 discloses a film forming process for forming a film by casting a thermoplastic resin solution containing a thermoplastic resin and a solvent onto a casting drum with a die in order to impart optical anisotropy in the thickness direction. Stretching the unstretched thermoplastic resin film formed in the film-forming step, and in the stretching step, one surface side and the other surface side of the unstretched thermoplastic resin film, And the manufacturing method of the optical film characterized by providing different temperature is disclosed.

JP 2010-53254 A Japanese Patent No. 4769612 Japanese Patent No. 4173395 JP 2011-47983 A

  By the way, in recent years, the number of small and medium-sized liquid crystal display devices such as touch panel applications has increased, and the use environment has been diversified. Therefore, it is demanded that there is no failure in endurance tests that are harsher than conventional ones. For example, there is a demand for no problem even if exposed to ultraviolet rays for a long time under high temperature and high humidity.

  In addition, a hard coat film in which a hard coat layer is applied to a cellulose ester film is often used in a liquid crystal display device to prevent scratches, but a liquid crystal display device having a hard coat film is exposed to ultraviolet rays for a long time under high temperature and high humidity. In the exposure test, it was found that black irregularities appear on the LCD screen with a certain probability.

  As a result of investigating each part of the liquid crystal display device in detail, when applying a hard coat layer to a cellulose ester film, it may be determined whether a black uneven pattern is generated depending on which side of the film is applied. all right. Therefore, if the surface on which the hard coat layer is applied can be selected, failure of the black uneven pattern can be prevented, but it is necessary to select the application surface at any time, and there is a film in which the hard coat layer is applied on both sides of the polarizing plate. Obviously, the cost of equipment increases to meet these requirements.

  As a result of further intensive studies, it was found that whether or not a black uneven pattern is generated is related to the amount of plasticizer on the surface of the film on which the hard coat layer is applied.

  Accordingly, the present invention provides a method for producing an optical film in which the ratio of the plasticizer is made uniform on both sides of the optical film in order to prevent the occurrence of a black uneven pattern even if a hard coat layer is provided on either side of the optical film. The purpose is to provide.

  To achieve the above object, the present invention provides an optical film for producing an optical film by casting a dope containing a cellulose ester, a solvent and a plasticizer from a casting die onto a support to form a web. In the method, the temperature at a position separated from the surface of the support by the film thickness of the web immediately after casting is 5 ° C. or more and 30 ° C. or less from the surface temperature of the support in a state where it is not cast on the support. In this range, the film is controlled to be low, and the film is formed under such conditions.

  In the method for producing an optical film described above, it is preferable that the temperature of the support is adjusted from the back side by the first temperature adjusting means, and the air is blown at a predetermined temperature to the surface side of the support by the second temperature adjusting means.

  In the method for producing an optical film, the temperature at a position separated from the support surface by the thickness of the web immediately after casting is preferably −5 ° C. or more and 55 ° C. or less.

  Moreover, in the manufacturing method of said optical film, it is preferable that the surface temperature of the said support body is 5 to 65 degreeC.

  Moreover, in the manufacturing method of said optical film, it is preferable that the residual solvent amount of the web at the time of conveying to the said conditions is 250 weight% or more.

  In the method for producing an optical film, it is preferable that a residual solvent amount of the web when the web is peeled off from the support is 150% by weight or less.

  In the method for producing an optical film, the additive is preferably an ester compound.

  According to the present invention, the ratio of the plasticizer on both sides of the optical film becomes uniform by controlling the temperature on the front side of the web on the support to be lower than the temperature on the back side in the range of 5 ° C to 30 ° C. Even if the hard coat layer is provided on either side of the optical film, the failure of the black uneven pattern is suppressed. Therefore, deterioration of optical quality can be suppressed.

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 a figure which shows the film forming conditions of Examples 1-27 and Comparative Examples 1-8, the amount of plasticizers, and the evaluation result of a black nonuniformity pattern.

  In this specification, the front refers to the film transport direction, and the left and right refer to the front. Further, upstream and downstream refer to the operation direction of the manufacturing apparatus (film transport direction).

  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.

  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.

  A decompression chamber 4 is provided on the upstream side of the casting die 3. The decompression force of the decompression chamber 4 can be set to, for example, −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 bubbles due to the entrained air is suppressed, so that the web 9 can easily adhere to the support 6. Become.

  Between the drums 5 and 5, two first temperature adjusting means 14 and 14 for adjusting the temperature of the support 6 from the back side are provided along the back side (inside) of the support 6. As the first temperature adjusting means 14, a heating device or a cooling device may be used according to the set temperature. As a method for heating or cooling the support 6, for example, a method of blowing a wind at a predetermined temperature to the support 6, a method of transferring heat by a liquid of a predetermined temperature, a method of transferring heat by radiant heat, and the like can be used. It may be used alone or in combination as appropriate. The surface temperature of the support 6 is preferably maintained at a first predetermined temperature of 5 ° C. or higher and 65 ° C. or lower, and more preferably maintained at a first predetermined temperature of 15 ° C. or higher and 55 ° C. or lower. Note that it is not always necessary to keep the entire support 6 at the first predetermined temperature, and a part of the support 6 may be kept at the first predetermined temperature. For example, only the first temperature adjusting means 14 described above may be provided. Further, the first predetermined temperature may be a plurality of different temperatures. In this case, the first predetermined temperature is different depending on the position of the support 6.

  From the position adjacent to the downstream side of the casting die 3 to the front side of the peeling roll 8 in the downstream direction, the second temperature adjustment is performed along the surface side (outside) of the support 6 while maintaining a predetermined distance from the surface of the support 6. Means 15 are provided. The second temperature adjusting means 15 is a device that blows air to the surface side of the support 6 at a predetermined temperature, and a heating device or a cooling device may be used according to the set temperature. As a method for heating or cooling the support 6, for example, a method of blowing a wind at a predetermined temperature to the support 6, a method of transferring heat by a liquid of a predetermined temperature, a method of transferring heat by radiant heat, and the like can be used. It may be used alone or in combination as appropriate.

  And in the state where dope is not cast on the support, the temperature at a position separated from the support surface by the film thickness of the web 9 immediately after casting is set to a second predetermined temperature of −5 ° C. or more and 55 ° C. or less. It is preferable to maintain, and it is more preferable to maintain the second predetermined temperature of 5 ° C. or higher and 45 ° C. or lower. Note that the second temperature adjusting unit 15 maintains the second predetermined temperature in a range opposite to the range in which the support 6 is maintained at the first predetermined temperature by the first temperature adjusting unit 14. The second predetermined temperature may be a plurality of different temperatures, and in that case, the second predetermined temperature is different depending on the position on the support.

  By the way, as a cause of the problem of the present invention, we have made the following estimation. On the support, the solvent is volatilized and dried from the surface side of the web 9, but when a mixed solvent having a different boiling point is used, the solvent composition tends to evaporate from the solvent that easily volatilizes. Change. At this time, the additive in the dope moves to the more compatible solvent side, and the ratio of the additive differs between the front side and the back side (support side) of the web 9. When the optical film is produced in such a state, the amount of the plasticizer contained in the additive is different on both sides of the film, and when the hard coat layer is applied, the adhesion of the hard coat layer is poor on at least one side. Become. When such a hard coat film is used in a liquid crystal display device, if it is used in an environment where ultraviolet rays are irradiated under high temperature and high humidity, a black uneven pattern, which is thought to be due to peeling of the hard coat layer, occurs on the liquid crystal screen. There are things to do.

  Therefore, the second predetermined temperature is controlled to be lower than the first predetermined temperature in the range of 5 ° C. to 30 ° C., more preferably in the range of 10 ° C. to 25 ° C., and the film is formed under the conditions. Although the surface side of the web 9 is cooled by the heat of vaporization, in addition to that, by making the second predetermined temperature lower than the first predetermined temperature, heat transfer from the back side to the front side becomes active in the web 9. This promotes convection of the dope. As a result, the additive is also convected, so that the additive is uniformly distributed in the web 9, and the optical film produced in such a state has a uniform plasticizer ratio on the front and back surfaces. Therefore, it is considered that the adhesion as designed can be obtained when the hard coat layer is applied.

  When the difference obtained by subtracting the second predetermined temperature from the first predetermined temperature is less than 5 ° C., the above-described convection hardly occurs and a desired effect cannot be obtained. On the other hand, when the difference obtained by subtracting the second predetermined temperature from the first predetermined temperature is larger than 30 ° C., the desired effect cannot be obtained. The cause of this is probably due to the fact that the surface state of the film changes at a fine level because the convection of the dope is large.

  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 having a surface subjected to hard chrome plating is used as a casting support. In addition, the first and second temperature adjusting means 14 and 15 are different from the apparatus of FIG. 1 in accordance with the shape of the rotary driving drum 7, and the first temperature adjusting means 14 is a circle provided in the rotary driving drum 7. The second temperature adjusting means 15 has a columnar form, and is a form in which a cylindrical part provided at a predetermined distance along the outer periphery of the rotary drive drum 7 is cut off. Since other configurations are the same as those in FIG. 1, the same reference numerals are given to the same configurations.

  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.

  Moreover, it is preferable that the residual solvent amount of the web 9 is 250% by weight or more at the time when the web 9 is transported on the support under conditions adjusted to the first and second predetermined temperatures. If the residual solvent amount is less than 250% by weight, the convection in the web 9 is weak and the effect is small.

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 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.

  Then, the web 9 is dried on the support at the first and second predetermined temperatures described above. 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 20 to 40 or 60 to 120% by weight. Especially preferably, it is 20-30 or 70-115 weight%. Although it depends on the film thickness of the web 9, if the amount of residual solvent at the time of peeling is too large, peeling is difficult, or conversely if the amount of residual solvent is too small, part of the residual solvent is peeled up to the peeling point.

  As a method for increasing the film forming speed, there is a gel casting method (gel casting) that can be peeled even if the amount of residual solvent is large. This includes adding a poor solvent for the cellulose ester in the dope, gelling the dope after casting, a method of gelling by lowering the temperature of the support, a method of adding a metal salt in the dope, etc. In any case, it is possible to peel even if the residual solvent amount is large by gelling on the support and strengthening the film. When peeling with a large amount of residual solvent, if the web is too soft, the flatness will be lost, and creases and vertical stripes are likely to occur due to the peeling tension, so the amount of residual solvent is in balance between economic speed and quality. Need to design.

  As for web temperature when peeling the web 9 from the support bodies 6 and 7, 0-30 degreeC is preferable. 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, as for the web temperature at the time of peeling, 5-30 degreeC is further more preferable.

  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 the exhaust air is discharged from the outlet of the rear portion of the ceiling of the drying device 11. It is dried by. 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.

  The cellulose ester film of the present invention can contain a plasticizer as necessary to obtain the effects of the present invention. The plasticizer is not particularly limited, but is preferably a polycarboxylic acid ester plasticizer, a phthalate ester plasticizer, a fatty acid ester plasticizer and a polyhydric alcohol ester plasticizer, a polyester plasticizer, or a glycolate plasticizer. Agent, acrylic plasticizer and the like. Among them, when two or more kinds of plasticizers are used, at least one kind is a polycarboxylic acid ester plasticizer, a phthalate ester plasticizer, a fatty acid ester plasticizer, a polyhydric alcohol ester plasticizer, or a polyester plasticizer. An ester plasticizer such as

  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 In addition to esters such as methyl, ethyl formate, methyl acetate, ethyl acetate, amyl acetate, and 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, citrate plasticizers, fatty acid ester plasticizers, carboxylic acid ester plasticizers, polyester plasticizers, acrylic plasticizers and the like can be preferably used, but ester plasticizers can be used. desirable.

  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 (1).

Formula (1) 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, 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 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.

  Examples of the polyester plasticizer include compounds represented by the following general formula (2) or (3).

General formula (2) B1- (GA-) mG-B1
Formula (3) 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 laccelic 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 general formula (2) or (3) 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.

  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.

  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.

  Further, as a commercially available ultraviolet absorber, TINUVIN 109, TINUVIN 171, TINUVIN 326, and TINUVIN 928 (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 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)
Methylene chloride 340 parts by weight Ethanol 64 parts by weight Cellulose triacetate (acetyl substitution degree 2.9) 100 parts by weight obtained by esterification of plasticizer (adipic acid: phthalic acid = 70: 30) and 1,2-ethanediol Ester compound (terminal group acetyl group) 10 parts by weight fine particle additive solution (see below) 10 parts by weight Tinuvin 928 2.5 parts by weight

(Particulate additive solution)
Methylene chloride 90 parts by weight Cellulose triacetate (acetyl substitution degree 2.9) 5 parts by weight Fine particle dispersion (see below) 5 parts by weight

(Fine particle dispersion)
R972V 16 parts by weight Ethanol 80 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 the endless belt support 6 at the first predetermined temperature (different in each example) by the casting die 3 made of a coat hanger die.

  In this way, the web 9 formed on the support 6 was dried with a drying air having a second predetermined temperature (different in each example) while being conveyed on the support 6. The amount of residual solvent in the web 9 at the start of drying differs in each example. Thereafter, the film is peeled off from the support 6 with the peeling roll 8 in a state where the residual solvent amount is 110%, and stretched to a stretching ratio of 32% in the width direction in an atmosphere of 140 ° C. by the tenter 10, and then the width retention is released to stretch. Relaxed at 140 for 60 seconds so that the rate was 30%. And drying was completed with 120-150 degreeC drying apparatus 11 carrying roll conveyance, and it wound up at 100 N / m with the winding apparatus 13. FIG.

  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.

  Then, a hard coat layer was applied to a cellulose triacetate film to produce a hard coat film, and a liquid crystal cell and a backlight were assembled using this hard coat film to produce a touch panel monitor.

  In each of the examples and comparative examples, the remaining of the web 9 at the time when the first and second predetermined temperatures are transferred to the first and second predetermined temperatures on the support (at the start of drying). The film was formed by changing the amount of solvent, the amount of residual solvent of the web 9 at the time of peeling from the support 6 (at the time of peeling), and the surface on which the hard coat layer was applied.

  And the quantity of the plasticizer mentioned later was quantified about the cellulose triacetate film produced as an Example and a comparative example, and the failure of the black nonuniformity pattern mentioned later about a touch panel monitor was evaluated.

  FIG. 3 shows the film forming conditions, the amount of the plasticizer, and the evaluation results of the black uneven pattern in Examples 1 to 27 and Comparative Examples 1 to 8. In Example 1, a film was formed at a first predetermined temperature of 25 ° C., a second predetermined temperature of 20 ° C., a residual solvent amount of 300% by weight at the start of drying, and a residual solvent amount of 110% by weight at the time of peeling. Examples 2 to 17 and Comparative Examples 1 to 8 differ from Example 1 in the same amount of residual solvent as Example 1 (residual solvent amount of 300% by weight at the start of drying and residual solvent amount of 110% by weight at the time of peeling). Films were formed at the first and second predetermined temperatures. Examples 18 to 27 are the same first and second predetermined temperatures (25 ° C. and 20 ° C.) as in Example 1, and different residual solvent amounts from Example 1 (residual solvent amount at the start of drying and residual solvent at the time of peeling) Film). The residual solvent amount at the start of drying was adjusted by changing the positions of the first and second temperature adjusting means 14 and 15. The amount of residual solvent during peeling was adjusted by changing the conveyance speed of the web 9.

  The amount of the plasticizer was determined by TOF-SIMS (Time of Flight-Secondary Ion Mass Spectrometry) for the cellulose triacetate film before the hard coat layer was provided. The measurement of TOF-SIMS can be observed by, for example, using TRIFTII type TOF-SIMS manufactured by Phi Evans and detecting fragments caused by the plasticizer present on the film surface layer. The TOF-SIMS method is described in detail in “Surface Analysis Technology Selection, Secondary Ion Mass Spectrometry” Maruzen Co., Ltd. (1999), edited by the Surface Science Society of Japan. For example, for a film using a polyester-based additive, the amount of the polyester-based additive is derived from the diol terminal of the polyester-based additive detected from the surface layer of the film having 10 parts by weight and the film having 0 parts by weight. A calibration curve is created from the intensity of the secondary ions, and the additive content of the surface layer is calculated.

  The black uneven pattern failure was evaluated as follows. For a touch panel monitor assembled with a cellulose triacetate film (hard coat film) provided with a hard coat layer, Xe was irradiated for 48 hours at 40 ° C. and 90% relative humidity using a Super Xenon Meter SX75 manufactured by Suga Test Instruments Co., Ltd. . Thereafter, the touch pan monitor was conditioned for 2 hours or more in a room at 25 ° C. and a relative humidity of 60%, the touch panel monitor was activated, and the presence or absence of a black uneven pattern on the display portion was examined visually under a dark room. When the hard coat layer was provided on either side of the cellulose triacetate film, the black pattern was not observed ◎, and when the hard coat layer was provided on either side, the black pattern was almost always seen. Although it was not possible, the case where a slight black unevenness pattern was rarely observed was evaluated as ◯, and the case where a black unevenness pattern was observed when a hard coat layer was provided on either surface was evaluated as ×. 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 black uneven pattern failure was evaluated as either ◎ or ◯ in Examples 1 to 27 and × in Comparative Examples 1 to 8. From this result, in Comparative Examples 1 and 5, there is no temperature difference between the first predetermined temperature and the second predetermined temperature, so that sufficient convection does not occur. In Comparative Examples 2 and 6, the second predetermined temperature is higher than the first predetermined temperature. Sufficient convection does not occur because it is high, and in Comparative Examples 3, 4, 7, and 8, the temperature difference between the first predetermined temperature and the second predetermined temperature is too large, so that the surface shape of the film at a fine level changes. In Comparative Example 5, it is presumed that sufficient convection did not occur because the temperature difference between the first predetermined temperature and the second predetermined temperature was too small. Therefore, in Comparative Examples 1-8, the difference in the amount of plasticizer between the front and back of the film was increased, and the adhesion of the hard coat layer was deteriorated. Therefore, it is presumed that a black uneven pattern failure occurred.

  Therefore, considering that the conditions of Comparative Examples 1 to 8 are inappropriate and the conditions of Examples 1 to 27 are appropriate, the second predetermined temperature is in the range of 5 ° C. to 30 ° C. from the first predetermined temperature. It can be said that a low control condition is suitable for manufacturing.

  Next, consideration will be given to the fact that the evaluation of failures with black uneven patterns in Examples 1 to 27 is divided into ◎ and ○. The evaluation of the failure of the black uneven pattern is ◯ in Examples 11, 14, 16, 17, 21, 22, 26, and 27. Here, in Example 11, the second predetermined temperature is slightly high as 60 ° C., and in Example 14, the second predetermined temperature is slightly low as −10 ° C. Therefore, it can be said that the second predetermined temperature is more preferably −5 ° C. or more and 55 ° C. or less.

  In Example 16, the first predetermined temperature is slightly high at 70 ° C., and in Example 17, the first predetermined temperature is slightly low at 0 ° C. Therefore, it can be said that the first predetermined temperature is more preferably 5 ° C. or more and 65 ° C. or less.

  In Examples 21 and 22, the residual solvent amounts at the start of drying are slightly low at 230 and 210% by weight, respectively. Therefore, it can be said that the residual solvent amount at the start of drying is more preferably 250% by weight or more. Further, in Examples 26 and 27, the residual solvent amounts at the time of peeling were slightly high at 160 and 170% by weight, respectively. Therefore, it can be said that the residual solvent amount at the time of peeling is more preferably 150% by weight or less.

3 Casting Die 6, 7 Support 9 Web 14 First Temperature Control Unit 15 Second Temperature Control Unit

Claims (6)

In the method for producing an optical film, an optical film is produced by casting a dope containing a cellulose ester, a solvent and a plasticizer from a casting die onto a support to form a web.
In a state where it is not cast on the support, the temperature at a position separated from the support surface by the film thickness of the web immediately after casting is in the range of 5 ° C. to 30 ° C. from the surface temperature of the support. Low control, film formation under the conditions ,
The surface temperature of the support is 5 ° C. or more and 65 ° C. or less,
The residual solvent amount of the web when the web is peeled from the support is 60 to 120% by weight,
The absolute value of the difference between the plasticizer content (% by weight) on the front side of the web and the plasticizer content (% by weight) on the back side of the web is 2.0 or less, A method for producing an optical film. The temperature of the support is adjusted from the back side by first temperature adjusting means,
The method for producing an optical film according to claim 1, wherein the second temperature adjusting means blows air at a predetermined temperature toward the surface of the support. The method for producing an optical film according to claim 1 or 2, wherein the solid content concentration of the dope is 15 to 30% by weight.   The surface temperature of the said support body is 5 to 65 degreeC, The manufacturing method of the optical film in any one of Claims 1-3 characterized by the above-mentioned.   The method for producing an optical film according to any one of claims 1 to 4, wherein a residual solvent amount of the web at the time when the web is conveyed under the condition is 250% by weight or more. The method for producing an optical film according to any one of claims 1 to 5, wherein the plasticizer is an ester compound.

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