JP6610027B2 - Manufacturing method of optical film - Google Patents

Description

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

  Various optical films (for example, a transparent protective film for protecting the polarizing element of the polarizing plate) are disposed in the image display region of the liquid crystal display device.

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

  Specifically, the solution casting method is obtained by casting a resin solution (dope) obtained by dissolving a transparent resin, which is a raw material resin, in a solvent, onto a traveling support and drying it to a peelable extent. In a method in which the obtained web (also referred to as a dope film or a casting film) is peeled from the support, and the peeled web is dried or stretched while being transported by a transport roller to form a long resin film. is there.

  In the above solution casting method, it is known that in the web peeling from the support, the peeling load varies depending on the web residual solvent ratio (%) at the time of peeling, and a low residual solvent (Z = 0 to 40% residual). It has been reported that there is a peak (peeling peak) where the peeling load increases between the solvent ratio; Z is as described later) and a high residual solvent (Z = 65 to 120% residual solvent ratio) (Patent) Reference 1). Therefore, it is said that it is preferable to manufacture at a residual solvent ratio of Z = 0 to 40% and a residual solvent ratio of Z = 65 to 120% so that the residual solvent ratio of the web at the time of peeling is avoided. In general, from the viewpoint of production efficiency, it is more preferable to produce by web peeling at a residual solvent ratio of Z = 65 to 120%, which can shorten the drying time. In this case, peeling conditions with a residual solvent ratio of Z = 0 to 40% are taken at the initial stage of startup when the support running speed is slow, but Z = 65 to 120 at the final production conditions (steady operation) thereafter. The peeling residual solvent rate is shifted at the time of start-up so that the peeling condition with a residual solvent rate of% is achieved.

JP 2004-291448 A

  However, if the conventional film has a certain thickness, there was no problem with the above method. However, when producing a thin film having a film thickness of 30 μm or less, as in the past, with an increase in production speed (support speed). It has been found that when the final flow rate is reached, since the film thickness is thin, it is easy to dry and peeling under production conditions is performed with a residual solvent ratio with a large peeling load.

  If a thin film is produced for a long time in this state, the peeled state is not stable, and a foreign matter failure due to the remaining peeled or in the worst case breakage.

  In order to avoid such problems, there is a method of keeping the residual solvent ratio high at the time of peeling by increasing the production speed and shortening the drying time compared with the conventional product, but this is because the web flutters because the thin film is conveyed at high speed. Easily scratches and wrinkles. Also, in casting, if the production speed (support speed) is increased, the accompanying wind (wind that winds along with the movement of the support) increases, so that there is a problem that the web is swayed and the lip is soiled and dice are easily generated.

  Therefore, an attempt was made to produce a product by paying attention to exfoliation with a low residual solvent ratio of Z = 0 to 40% in Patent Document 1 instead of the conventional exfoliation of high residual solvent of Z = 65 to 120%. However, from the start-up at a residual solvent ratio of Z = 0 to 40%, the residual solvent remains as such (without reaching the residual solvent ratio of Z = 65 to 120%) to the production conditions (steady operation). When a film was produced, breakage sometimes occurred during startup.

  This invention is made | formed in view of this situation, Comprising: It aims at providing the manufacturing method which obtains a high quality thin film efficiently by a solution casting method.

  As a result of intensive studies, the present inventor has found that the above problems can be solved by a method for producing an optical film having the following configuration, and has further completed the present invention based on such findings.

In the method for producing an optical film according to one aspect of the present invention, in a solution casting film forming method, a dope that is a raw material solution of an optical film is cast on a support, and a web (casting film) is formed on the support. A method of manufacturing and forming an optical film by peeling a web from the support, wherein when the dope is cast, the casting die travels at the start-up from the start of film manufacture to the steady operation Each time the web film thickness (Hw) represented by the following formula is reduced by 20 to 50 μm, the reduced pressure value is reduced by −40 to −100 Pa in the decompression chamber provided on the upstream side in the direction and the support side is open. It is characterized by that.
Web film thickness (Hw) (μm) =
Dope flow rate (m ³ / min) ÷ web width (m) ÷ support travel speed (m / min) × 10 ⁶

  According to such a configuration, a high-quality optical film can be obtained efficiently and stably without causing unevenness that causes failure or breakage.

Moreover, in the said manufacturing method, the residual solvent rate Z of the web represented by the following formula at the time of peeling a web from a support body in all the steps at the time of the start-up is a Z = 0 to 40% range. It is preferable to keep the solvent ratio.
Residual solvent ratio Z (%) = {(W−V) / V} × 100
(W is the weight of the web containing the solvent, and V is the weight when W is dried at 120 ° C. for 2 hours)

  Thereby, from the start of film production to steady operation, the transition can be made most efficiently and in a short time without passing through the residual solvent ratio region (peeling peak) having a high peeling load.

  Moreover, in the said manufacturing method, it is preferable that the final film thickness of the optical film obtained is 5-30 micrometers. The production method of the present invention is more effective in producing such a thin film.

  According to the present invention, it is possible to efficiently and stably manufacture a high-quality optical film without causing unevenness that causes failure or breakage.

FIG. 1 is a schematic view showing a basic configuration of an optical film manufacturing apparatus by a solution casting method using an endless belt support.

  At the time of film production start-up, if the thin film web is peeled at a low residual solvent ratio (Z = 0 to 40%) at the time of peeling, the casting flow rate is lowered than before in order to promote drying without reducing the production rate. There is a need. When this is performed, the film thickness of the web containing the solvent immediately after casting becomes thin.

  However, while adjusting to the production conditions for steady operation immediately after start-up, the pressure reduction value in the pressure reduction chamber (reference numeral 4 in FIG. 1) is changed, the support speed is changed, and the dope flow rate is changed. There are various condition changes such as changing the pressure of air conditioning, and these are factors that have a physical influence on the web immediately after casting.

  As a result of repeated research by the present inventors, when the flow rate at the time of start-up was greatly reduced in order to enable peeling with a low residual solvent as described above, the web film thickness at the time of start-up became thinner than before and the strength decreased. As a result, it was found that the web sways at the timing of changing the conditions during startup, particularly at the time of changing the reduced pressure, causing stepped unevenness, causing wrinkles and causing breakage during conveyance.

  In the technique disclosed in Patent Document 1, a film having a thickness of 60 μm or less is manufactured in peeling with a residual solvent ratio of Z = 0 to 40%. However, strictly speaking, a thickness of 30 μm or less is insufficient for the above reason. It is thought.

  Therefore, the present inventor has further researched, and at the time of start-up, by adjusting the reduced pressure value slightly according to the web film thickness, the sudden web fluctuation at the time of changing the reduced pressure condition is suppressed, and step unevenness is generated. It was found that a film can be stably produced.

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

[Method for producing optical film]
FIG. 1 is an explanatory diagram showing a schematic configuration of an optical film manufacturing apparatus used in the present embodiment. The optical film manufacturing method of the present embodiment uses a solution casting method in which a dope containing a polymer and a solvent is cast from a casting die on a traveling support and then peeled off as a film. Hereinafter, the manufacturing method of this embodiment will be described in more detail.

  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 to the resin solution ( Dope) is prepared. The good solvent and the poor solvent will be described later.

  Next, the dope adjusted in the melting pot 1 is fed to the casting die 3 by a conduit through a pressurized metering gear pump 2, and cast on a support 6 made of a rotationally driven stainless steel endless belt that is infinitely transported. The dope is cast from the casting die 3 at a position, thereby forming a web 9 as a casting film on the support 6. At this time, a decompression chamber (decompression chamber) 4 is disposed upstream of the casting die 3 in the moving direction of the traveling support 6, and the upstream side of the casting die 3 (particularly, by the decompression chamber 4). The dope is cast from the casting die 3 onto the support 6 while reducing the space on the upstream side of the casting ribbon from the casting die 3 to the support 6.

  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.

  The support 6 is held by a pair of front and rear drums 5 and 5 and a plurality of intermediate rolls (not shown). One or both of the drums 5 and 5 are provided with a driving device (not shown) for applying tension to the support body 6, whereby the support body 6 is used in a tensioned state.

  The width of the support 6 is preferably 1000 to 3000 mm, and the width of the film after winding is preferably 1000 to 2500 mm. Thereby, the wide optical film for liquid crystal display devices can be manufactured by a metal support body system.

  In the case of using an endless belt as the support 6, the belt temperature during film formation is 0 ° C. to less than the boiling point of the solvent in a general temperature range, but the mixed solvent is less than the boiling point of the lowest boiling solvent. In particular, the range of 5 ° C. to the boiling point of the solvent −5 ° C. is more preferable. At this time, it is necessary to control the ambient atmospheric humidity above the dew point. In addition, it is preferable that the moving speed of the support body 6 under production conditions is 80 m / min to 200 m / min.

  The dope cast on the support 6 in this manner also increases the strength of the gel film (film strength) by promoting drying until stripping.

  On the support 6, the web 9 is dried and solidified until the film strength is such that the support 6 can be peeled off by the peeling roll 8.

In the method for producing an optical film according to the present embodiment, in the solution casting film forming method as described above, when casting the dope to a support, at the start-up from the start of film production to the steady operation, Each time the web film thickness (Hw) represented by the following formula is reduced by 20 to 50 μm in a decompression chamber provided on the upstream side of the casting die in the traveling direction and the support side is open − It is characterized by being lowered by 40 to -100 Pa.
Web film thickness (Hw) (μm) =
Dope flow rate (m ³ / min) ÷ web width (m) ÷ support travel speed (m / min) × 10 ⁶

  According to such a configuration, a high-quality optical film can be obtained efficiently and stably without causing unevenness that causes failure or breakage.

  In the present embodiment, “step unevenness” refers to stepped thickness unevenness that occurs in the film (or web) conveyance direction.

  In the present embodiment, the time of starting production refers to the timing at which casting starts with a product type dope that is a product. And the steady operation means that the flow rate of the dope, the running speed of the support belt for casting the dope and the reduced pressure value of the decompression chamber become constant, and the film thickness of the film obtained is a desired thickness (for example, If it is a thin film, it will be referred to as steady operation after the point of time such as 25 μm. Therefore, the time of start-up refers to the period from the production start timing to the start of steady operation.

Moreover, in the decompression adjustment in the decompression chamber, every time the web film thickness (Hw) is reduced by 20 to 50 μm, the decompression value is reduced by −40 to −100 Pa. Under each condition, the dope flow rate, the web width, and the support travel speed are reduced. The web film thickness (Hw) is calculated by recording, and the dope flow rate (m ³ / min) ÷ web width (m) ÷ support running speed (m / min) × 10 ⁶ , and the film thickness is reduced by 30 μm, for example. At that time, the reduced pressure value in the decompression chamber is reduced within the above range . Name your, web width is also affected, such as the so-called neck-in and contraction, but may be calculated using a simple doped discharge width of the casting die.

  Rather than suddenly lowering the reduced pressure value at such a start-up, step unevenness is not generated by gradually adjusting the reduced pressure value within a predetermined range according to the web film thickness as in this embodiment. It is thought that it can be suppressed.

  If the reduced pressure value to be reduced at a time exceeds -100 Pa at the time of start-up, the cast film becomes unstable due to a sudden change in pressure, causing unevenness of the film, resulting in film failure. On the other hand, if the reduced pressure value to be reduced at a time is less than −40 Pa, it is necessary to change the conditions many times during start-up, and there is a problem that the production efficiency is inferior because it takes time.

  Moreover, if the timing of pressure reduction at the time of start-up is performed for each thickness exceeding the web film thickness (Hw) 50 μm, the pressure reduction value required for production conditions (steady operation) may not be reached even after start-up is completed. (The reduction rate of the reduced pressure value is too low for the reduction of the web film thickness, so the start-up condition is not satisfied). On the other hand, even when the reduced pressure is changed every time the web film thickness (Hw) is less than 20 μm, it is necessary to change the conditions many times during start-up, and there is a problem that the production efficiency is inferior because it takes time.

  More preferably, every time the web film thickness (Hw) is reduced by 30 to 50 μm, it is desirable to reduce the reduced pressure value by −50 to −80 Pa. Film production can be performed more reliably.

Moreover, in this embodiment, the residual solvent rate Z of the web represented by the following formula when the web is peeled from the support in all the steps at the time of start-up is a residual Z in the range of 0 to 40%. It is preferable to keep the solvent ratio.
Residual solvent ratio Z (%) = {(W−V) / V} × 100
(W is the weight of the web containing the solvent, and V is the weight when W is dried at 120 ° C. for 2 hours)

  As a result, from the start of film production to steady operation, the transition can be made most efficiently and in a short time without passing through a residual solvent ratio region (peeling peak) with a high peeling load.

  As described above, the means for holding the web at the time of peeling at a low residual solvent ratio (Z = 0 to 40%) throughout the start-up period is not particularly limited.

  Specifically, for example, a method of adjusting by the dope flow rate, a method of adjusting by the drying temperature of the web, a method of adjusting by the running speed of the support, and the like can be mentioned.

  In the method of adjusting according to the running speed of the support, the productivity may be lowered when the running speed of the support is lowered. Therefore, the method of adjusting by the dope flow rate or the method of adjusting by the web drying temperature is preferable. Among these, from the viewpoint of obtaining a higher quality film, a method of adjusting by the dope flow rate is preferable.

  Specifically, the method of adjusting by the dope flow rate is, for example, by increasing the dope flow rate (L / hour) cast along with the support speed (production speed) at the time of start-up, and adjusting the final production condition (steady state). The method of shifting to (operation) is mentioned. The change in flow rate at this time varies depending on the final product film thickness, product width, solid content ratio of the dope, etc., for example, when the residual solvent ratio at the start-up is shifted to 40% or less, 100 L / hour Increase from ˜700 L / hour to 800 liter / hour to 1700 liter / hour depending on the support speed. Further, in the method of adjusting according to the drying temperature of the web, drying can be accelerated by increasing the temperature without finely adjusting the dope flow rate, and the peeling residual solvent ratio can be reduced even at the same flow rate. However, if the web temperature is raised too much, foaming may occur due to the boiling point of the solvent or more, and the unevenness of the drying temperature also increases.

  In the method of adjusting according to the running speed of the support, drying can be accelerated and the peeling residual solvent ratio can be reduced by increasing the drying time by reducing the speed, but the support speed directly affects the production speed and production efficiency. Therefore, it is necessary to take this into consideration.

  The web temperature when the web 9 is peeled from the support 6 is preferably 0 to 30 ° C. Further, immediately after the web 9 is peeled off from the support 6, the temperature once drops rapidly due to solvent evaporation from the contact surface side with the support 6, and volatile components such as water vapor and solvent vapor in the atmosphere tend to condense. Therefore, the web temperature during peeling is more preferably 5 to 30 ° C.

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

  In order to evaporate 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 surface of the support 6 by liquid, a method in which heat is transferred from the front and back by radiant heat, and the like. That's fine.

  The peeling tension when peeling the support 6 and the web 9 by the peeling roll 8 is larger than the peeling force obtained by measuring the peeling force as in JIS Z 0237. If it is equivalent to the peel force obtained by the measurement method, the peel position may be taken downstream, so it is increased for stabilization. In addition, even if it forms into a film with the same peeling tension in a process, if the peeling force by a JIS measuring method falls, it has also been confirmed that the variation in the cross nicols permeability (CNT) of a film reduces significantly.

  The peeling tension value in the process is usually 20 to 400 N / m. However, in the optical film produced by making the film thinner than before, the residual solvent amount of the web 9 is large at the time of peeling, and it is easy to extend in the conveying direction. For this reason, the film tends to shrink in the width direction, and when drying and shrinkage overlap, the end curls and folds, so that wrinkles are likely to occur. For this reason, it is preferable that peeling tension is the minimum tension which can peel -300N / m, More preferably, it is minimum tension-200N / m.

  In FIG. 1, a belt-like support is illustrated as the support, but the support of the present embodiment is not limited to a belt-like support. For example, a drum-like support may be used. .

  After drying and solidifying until the web 9 has a peelable film strength on the support 6, 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 step.

  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 step is preferably 5 to 50% by weight, and more 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 70 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. Further, the film transport tension in the drying device 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 400 N / m. The width is more preferably 20 to 300 N / m.

  The means for drying the web 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 point of simplicity. For example, the web 9 can be dried by blowing the drying air 12 from the hot air inlet of the drying device 11 and exhausting the exhaust air from the outlet of the drying device 11, so that the optical film F can be obtained. The temperature of the drying air 12 is preferably 40 to 160 ° C, and more preferably 50 to 160 ° C, in order to improve flatness and dimensional stability.

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

  For the optical film F that has finished the transport drying process, before introducing it into the winding process, in order to prevent winding slippage and blocking (sticking between films) in the winding process, at the end of the optical film F It is preferable to form an embossed portion having a large number of irregularities.

  Next, the film in which the embossed portion has been formed is taken up by the take-up device 13 to obtain the original roll of the optical film F. By setting the residual solvent amount of the film at the end of drying to 0.5% by weight or less, preferably 0.1% by weight or less, a film having good dimensional stability can be obtained.

  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 bonded 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 1000 to 2500 mm after winding.

  The film thickness after drying of the optical film of the present embodiment is preferably in the range of 5 to 30 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.

  According to the manufacturing method of the present embodiment, a high-quality optical film can be provided even in manufacturing such a thin film.

  In the method for producing an optical film by the solution casting film forming method of the present embodiment, a resin solution (dope) containing a resin such as cellulose ester as a main material, a plasticizer, a retardation adjusting agent, an ultraviolet absorber, fine particles, and It is preferable that at least one kind of low molecular weight substances and a solvent are contained. Hereinafter, these materials will be described.

  In the present embodiment, 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 method of 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 used as a raw material for the cellulose ester used in the present embodiment 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 20,000 to 300,000 because the mechanical strength of the resulting film is strong. Furthermore, 40000-200000 are preferable. Various additives can be blended in the cellulose ester.

  In the method for producing an optical film according to the present embodiment, 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.

Formula (1) B1- (GA-) mG-B1
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 the following, but the present invention is not limited thereto.

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

  Preferred monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, tridecylic acid , Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and 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 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 in the production of the optical film of the present embodiment 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- Dorokishibuchiru) acrylate-p-hydroxymethylphenyl,-p-acrylic acid (2-hydroxyethyl) phenyl and the like; as methacrylic acid ester, the acrylic acid ester include those changed to methacrylic acid esters.

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

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

  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 ester, excellent in productivity without evaporation and volatilization, and retainability as a protective film for polarizing plates The moisture permeability is small, and the dimensional stability is excellent.

  In the 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 of the present embodiment, the dope composition contains a cellulose ester and an acrylic polymer having a weight average molecular weight of 500 or more and 3000 or less as an additive for reducing the thickness direction retardation (Rt). It is preferable.

  In the present embodiment, the dope composition preferably contains a cellulose ester and an acrylic polymer having a weight average molecular weight of 5000 or more and 30000 or less as an additive for reducing the thickness direction retardation (Rt).

  If the weight average molecular weight of the polymer as an additive for reducing the thickness direction retardation (Rt) is 500 or more and 3000 or less, or if the weight average molecular weight of the polymer is 5000 or more and 30000 or less, it is compatible with the cellulose ester. And no evaporation or 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 acrylic acid or methacrylic acid ester is preferable. For example, acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3 -Hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid-p-hydroxymethylphenyl, acrylic acid-p- (2-hydroxyethyl) phenyl, or these acrylic acids. The thing replaced 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.

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

  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 produced by the method related to the description in this publication is commercially available as Act Flow Series manufactured by Soken Chemical Co., Ltd., and can be preferably used.

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

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

  In addition to the organic solvent, the dope preferably contains 1 to 40% by weight of an alcohol having 1 to 4 carbon atoms. 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.

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

  The plasticizer used in the 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 this embodiment 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 the following, but the present invention is not limited to these.

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

  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 preferable in terms of improving moisture permeability and retention.

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

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

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

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

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

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

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

  The glycolate plasticizer is not particularly limited, but a glycolate plasticizer having an aromatic ring or a cycloalkyl ring in the molecule can be preferably used. As preferred glycolate plasticizers, for example, butylphthalylbutyl glycolate, ethylphthalylethyl glycolate, methylphthalylethyl glycolate, or 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 present embodiment, 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 one film, and the number of particles in 100 μm 2 whose major axis length is in the range of 0.05 to 5 μm is taken 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, if the average particle size of the fine particles exceeds 5 μm, haze deterioration or the like may be observed, or it may cause a failure in a wound state as a foreign matter. Moreover, when the average particle diameter of fine particles is less than 0.05 μm, it becomes difficult to impart slipperiness to the film.

  The fine particles are used by adding 0.04 to 0.8% by weight to the cellulose ester. Preferably, 0.05 to 0.5% by weight, more preferably 0.05 to 0.35% 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 25 to 100% by weight, more preferably 50 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 928, TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by Ciba Specialty Chemicals) can be preferably used.

  Further, specific examples of the benzophenone-based compound that is an ultraviolet absorber that can be used in the present embodiment include 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, and 2-hydroxy-4-methoxy-5. -Sulfobenzophenone, bis (2-methoxy-4-hydroxy-5-benzoylphenylmethane) and the like can be mentioned, but are not limited thereto.

  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.

  Further, as the ultraviolet absorber that can be used in the optical film of the present embodiment, the polymer ultraviolet absorber (or ultraviolet absorbing polymer) described in JP-A-6-148430 and JP-A-2002-47357 is preferably used. Can be 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 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 polarizing plates made of the optical film of the present embodiment, it is possible to provide a polarizing plate that is excellent in durability, dimensional stability, and optical isotropy as well as being made thinner.

  Further, by using a polarizing plate provided with the optical film of this embodiment, a high-quality liquid crystal display device or the like can be realized. In particular, since the optical film of the present embodiment is a thin film, it is preferably used for applications such as smart phones and tablets.

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

[Example 1]
An optical film was produced by the following method.

(Preparation of dope)
Cellulose triacetate (acetyl substitution degree 2.88) 100 parts by weight Triphenyl phosphate 8 parts by weight Ethylphthalyl ethyl glycolate 2 parts by weight UV absorber (Tinuvin 326) 1 part by weight AEROSIL 200V 0.1 part by weight Methylene chloride 418 parts by weight 23 parts by weight of ethanol The above materials were put into a sealed container, heated, completely dissolved with stirring, and filtered to prepare a dope.

(Manufacture of optical films)
A cellulose acetate film was produced by the solution casting film forming apparatus shown in FIG. 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 filtered dope was uniformly cast on a SUS316 endless belt support (6) made of SUS316 at a dope temperature of 35 ° C. by a casting die (3) made of a coat hanger die. The distance between the support and the tip of the die was set to 1 mm. When the web (9) is formed on the support (6), the web (9) is opened downward as a means for depressurizing from the upstream side of the casting so that the web (9) is formed in close contact with the support (6). The pressure reduction value under production conditions including the pressure reduction chamber (4) was -300 Pa.

Moreover, about the pressure reduction change at the time of starting until it reaches | attains production conditions (steady operation), every time the web film thickness (Hw) decreased by 20 micrometers, the pressure reduction value was reduced by -40Pa .

  Thus, after the web (9) formed on the support (6) is dried by a drying air constant at a temperature of 30 ° C. while being conveyed on the support (6), the temperature is kept constant at a temperature of 30 ° C. After drying with the dry air, the film is peeled off from the support (6) by the peeling roll (8). Thereafter, the tenter (10) is 1.06 in the width direction in an atmosphere of 100 ° C. when the residual solvent amount is 10%. After double-stretching, the width was released, the drying was completed with a drying device (11) at 125 ° C. while being conveyed by a roll, and the film was wound with a winding device (13).

  In addition, the dope amount from the casting die was adjusted so that the residual solvent ratio at the time of peeling of the web from the start of startup was always 40% or less.

  The obtained cellulose triacetate film (F) had a film thickness of 25 μm, a film width of 2000 mm, and a film winding length of 3000 m.

[Examples 2 to 9 and Comparative Examples 1 to 10]
A cellulose triacetate film was obtained in the same manner as in Example 1 except that the reduced pressure value adjustment in the reduced pressure chamber was changed as shown in Table 1 at the time of startup. In the table, for example, “−20 μm / −40 Pa” means that the reduced pressure value in the decompression chamber is lowered by 40 Pa every time the web film thickness (Hw) decreases by 20 μm.

(Evaluation)
About the optical film (Examples 1-9 and Comparative Examples 1-10) produced as mentioned above, the state at the time of start-up or the state of the obtained film was comprehensively evaluated according to the following criteria.
1: There was no failure due to step unevenness and a good film was obtained. 2: Although step unevenness did not occur, it took too much time and was inefficient because the number of times the reduced pressure value was changed during startup.
3: The reduced pressure value of the production condition was not reached (the reduction efficiency of the reduced pressure value was too low with respect to the decrease in the web film thickness, and the production condition from the start-up state could not be reached). The flatness (unevenness) of the film was confirmed.
4: The decrease in the reduced pressure value at one time was large, and the cast film became unstable because of a sudden change in the reduced pressure.

[Discussion]
As can be seen from Table 1, in the optical films of the examples obtained by the production method of the present invention, the occurrence of failure due to unevenness was suppressed, and a high-quality film was stably obtained.

  Further, among Examples 1 to 9, particularly in Example 8, the condition change time (efficiency) and the ribbon stability at the start-up were more preferable results.

  On the other hand, in the case of the comparative example, there is a problem that a step unevenness failure occurs due to a sudden change in the pressure reduction value, the production efficiency is greatly reduced, or the production conditions are not reached even after the start-up period is over. Each occurred.

(Example 10)
Except for adjusting the dope flow rate so that the residual solvent rate during peeling of the web during startup is 15% to 80%, and the residual solvent rate during peeling in steady operation (final production conditions) is 30%. A cellulose triacetate film was obtained in the same manner as in Example 1. As a result, when compared with the film obtained in Example 1, a film having good flatness was obtained, but the start-up time was lengthened and the production efficiency was lowered.

1: Melting pot 2: Pump 3: Casting die 4: Decompression chamber 5: Front and rear winding drum 6: Stainless steel endless belt for casting (support)
7: Rotary drive stainless steel drum for casting (support)
8: Peeling roll 9: Web 10: Tenter 11: Roll conveying and drying device 12: Hot air (dry air)
13: Winder F: Film 21: Undercoating device 22: Undercoating coater 23: Undercoating dryer 26: Roll (roll group)

Claims (3)

In the solution casting method, an optical film is prepared by casting a dope that is a raw material solution of an optical film on a support, forming a web (casting film) on the support, and peeling the web from the support. In the method of manufacturing
When casting the dope, in the decompression chamber provided on the upstream side in the running direction of the casting die at the start-up from the start of film production to the steady operation, the decompression chamber is open and the decompression is performed. The value is lowered by −40 to −100 Pa every time the web film thickness (Hw) represented by the following formula decreases by 20 to 50 μm.
Web film thickness (Hw) (μm) =
Dope flow rate (m ³ / min) ÷ web width (m) ÷ support travel speed (m / min) × 10 ⁶ In all the steps at the time of start-up, the residual solvent ratio Z of the web represented by the following formula when peeling the web from the support is kept at a low residual solvent ratio in the range of Z = 0 to 40%. The method for producing an optical film according to claim 1, wherein the method is characterized in that:
Residual solvent ratio Z (%) = {(W−V) / V} × 100
(W is the weight of the web containing the solvent, and V is the weight when W is dried at 120 ° C. for 2 hours)   The manufacturing method of the optical film of Claim 1 or 2 whose final film thickness of the optical film obtained is 5-30 micrometers.

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